industrial chemical - National Open University of Nigeria [PDF]

NATIONAL OPEN UNIVERSITY OF NIGERIA

SCHOOL OF SCIENCE AND TECHNOLOGY

COURSE CODE: CHM 415

COURSE TITLE: INDUSTRIAL CHEMICAL TECHNOLOGIES II

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Course Guide INTRODUCTION Industrial Chemical Technology II was written with the assumption that you have had the background knowledge of Chemical Technology from Industrial Chemical Technology course I. The course is packaged in such a way that you will learn using a technique peculiar to the open learning system as recommended by the University. You will learn the content of this course at reasonable pace and in a systematic way by adopting the step by step approach in the study of this course. I wish you success and hope that you will find it both interesting and useful. What you will learn in this course This course is titled “Industrial Chemical Technology” Consequently; it deals with some of the scientific background of techniques used in the chemical industry in converting raw materials into desired products on an industrial scale, applying one or more chemical conversions. The course gives detailed information on some common raw materials, chemicals and products available for industrial application and ultimately human consumption. Such common products include soap and detergent, sugar, varnishes and plastics. Learning Outcomes – Aims and Objectives The broad aims of this course “Industrial Chemical Technology II” can be summarized below. That is, on completion of the course , you should be able to: i. Comprehend the day to day problem of chemical technology in industries ii. Lists the several raw materials available in chemical industries ii. Identify the relationship between raw materials and products iii. Discuss the production process of some basic material available in our environment, that is, product such as soap, plastics paper, varnishes, sugar. e.tc. iv. Understand the effects of industrial technology on our environment via pollutants from processing or manufacturing industries. iv. Mention the various unit operations obtainable in the industry 2

v. Identify chemical technology equipments Course Materials There are three different sets of course material that will help in the understanding of this course. i. A course guide which spells out the broad details of the industrial chemical technology course including aim and objectives. ii. The study units with detailed learning information. Each study unit has a set of performance objectives along with other relevant learner guide. Thus, the course is divided into nine broad units as prescribe by the course outlines given by the University, and each unit having subsections. iii. A set of recommended textbooks and relevant website are listed at the end of each study unit.

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Table of Contents

Course Outlines

Pages

Unit 1: Hydrogen and Carbon monoxide Synthesis gas, oxoprocess,water gas, sources of Hydrogen and its application……………………………………………..………………………….….1 1.0 Introduction…………………………………………………………………………………………… 1 1.1 Objectives………………………………………………………………………………………………1 1.2 Hydrogen……………………………………………………………………………………………….1 1.3 Production processes……………………………………………………………………………………2 1.3.1 Laboratory preparation……………………………………………………………………………….2. 1.3.2 Industrial preparation………………………………………………………………………………....2 1.3.2.1 Steam reformer process……………………………………………………………………………2 1.3.2.2 Hydrocarbon by partial oxidation………………………………………………………………….4 1.3.2.3. Water gas and Steam……………………………………………………………………………..4 1.3.2.4 Steam –Iron Process……………………………………………………………………………….5 1.3.2.5 Electrolysis of Water…………………………………………………………………………..….6 1.3.2.6 From Methanol and Steam………………………………………………………………………..6 1.3.2.7 Other Sources…………………………………………………………………………………….6 1.4 Application…………………………………………………………………………………………….6 1.4.4 Consumption………………………………………………………………………………………..6 1.4.2 Coolant…………………………………………………………………………………………..…7 1.4.3 Energy Carrier………………………………………………………………………………………7 1.4.4 Semiconductor Industry…………………………………………………………………………….8 1.5 Carbon monoxide……………………………………………………………………………………..8 4

1.5.1 Application………………………………………………………………………………………….9 1.6 Water Gas……………………………………………………………………………………………..9 1.7 Oxo- process…………………………………………………………………………………………..9 1.7.1 Chemistry of Oxo –Process………………………………………………………………………10 1.7.2 Leuna Operation………………………………………………………………………………….13 1.7.3 Catalyst Preparation………………………………………………………………………………15 1.8 Conclusion…………………………………………………………………………………………16 1.9 Summary……………………………………………………………………………………………16 1.10. Tutor- Marked Assignments………………………………………………………………………17 1.11. References…………………………………………………………………………………………17

Unit 2: Industrial Organic Materials, Raw materials, Technical and economic

principles of

Processed and product routes. Flow diagram……………………………………………………….18 2.0 Introduction…………………………………………………………….……………………………18 2.1 Objectives……………………………………………………………….…………………………..18 2.2 Raw Materials…………………………………………………………….…………………………18 2.2.1 Organic Raw Materials…………………………………………………………………………..18 2.2.2 Inorganic Raw Materials………………………………………………………………………….22 2.3 Conclusion………………………………………………………………………………………….22 2.4 Summary…………………………………………………………………………………………..23 2.5 Tutor- Marked Assignments……………………………………………………………………….23 2.6 References…………………………………………………………………………………………23

Unit 3: Selected oil and fats………………………………………………………………………….24 3.1 Introduction………………………………………………………………………………………..24 3.0 Objectives………………………………………………………………………………………….24 3.2 Fats and Oils……………………………………………………………………………………….24 3.2.1 Sources of fats and oils………………………………………………………………………..…26 5

3.2.2 Structure of Fatty Acids…………………………………………………………………………26 3.2.3 Hydrogenated Vegetable oils…………………………………………………………………….28 3.2.4 Phospholipids……………………………………………………………………………………..30 3.2.5 Steroids…………………………………………………………………………………………..31 3.2.6 Lipoproteins………………………………………………………………………………………31 3.2.7 Uses of Fats and oils……………………………………………………………………................32 3.3 Conclusion…………………………………………………………………………………………..32 3.4 Summary …………………………………………………………………….……………………..32 3.5 Tutor – Marked Assignment………………………………………………….……………………..33 3.6 References…………………………………………………………………..………………………33

Unit 4: Soaps and Detergents………………………………………………….……………………..34 4.0 Introduction…………………………………………………………………..……………………..34 4.1 Objectives……………………………………………………………………………………………34 4.2 Soaps………………………………………………………………………….……………………..34 4.2.1 The Chemistry of Soaps and Detergent Function…………………………………………………35 4.2.2 The Soap manufacturing process………………………………………….………………………38 4.2.2.2 Hot Processes…………………………………………………………………………………….39 4.2.2.3 Ancilliary Processes………………………………………………………..……………………40 4.2.2.4 Purification and Finishing………………………………………………………………………..41 4.2.2.5 Moulds……………………………………………………………………….…………………..42 4.3 The Detergents Manufacturing Process …………………………………………….……………….42 4.3.1 Preparation of a Detergent ……………………………………………………………..………….42 4.4 Environmental Implications…………………………………………………………………….…..43 4.4.1 Synthetic Detergent Biodegradability……………………………………………………………..43 4.4.2 Detergent Powder………………………………………………………………………………….44 4.5 Role of laboratory……………………………………………………………………………………44 4.6 Conclusion…………………………………………………………………………………...............44 6

4.7 Summary …………………………………………………………………………………………….45 4.8 Tutor-Marked Assignment…………………………………………………………………………..45 4.8 References…………………………………………………………………………………………..45

Unit 5: Sugar ………………………………………………………………………………………..46 5.0 Introduction………………………………………………………………………………………46 5.1 Objectives…………………………………………………………………………………………46 5.2 What is Sugar…………………………………………………………………………… ……….48 5.2.1 Categories of Sugar…………………………………………………………………………….48 5.2.2 Simple and Complex Sugar…………………………………………………………………….49 5.3 Popular …………………………………………………………………………………………..49 5.3 Chemical…………………………………………………………………………………………50 5.4 Purity Standard………………………………………………………………………………..….51 5.5 Natural Polymers of Sugar……………………………………………………………………….51 5.6 Types of Sugar………………………………………………………………………..………….52 5.7 Conclusion…………………………………………………………………………….…………52 5.8 Summary……………………………………………………………………………….…………53 5.9 Tutur –Marked Assignment ………………………………………………………………………53 5.10 References……………………………………………………………………..…………………53

Unit 6: Varnishes……………………………………………………………………….……………54 6.0 Introduction ……………………………………………………………………………………….54 6.1Objectives………………………………………………………………………………………..…54 6.2 Varnish……………………………………………………………………………………………..55 6.3 Component of Varnishes……………………………………………………………………………55 6.3.1 Film- Forming Materials………………………………………………………………………….55 6.3.2 Thinners or Solvent………………………………………………………………….……………56 7

6.3.3 Driers………………………………………………………………………………….………….56 6.3.4 Antiskinning agents………………………………………………………………………………56 6.4 Types of Varnishes…………………………………………………………………………………56 6.4.1 Spirit Varnishes……………………………………………………………………….………….56 6.4.2 Oleoresinous Varnishes……………………………………………………………..……………56 6.4.3 Examples of Varnishes………………………………………………………………………….57 6.5 Applicaton of Varnishes……………………………………………………………………………..61 6.6 Conclusion……………………………………………………………………………………………62 6.7 Summary……………………………………………………………………………………………..62 6.8 Tutor –Marked Assignments…………………………………………………………………………62 6.9 References……………………………………………………………………………………………62

Unit 7: Plastics…….……………………………………………………………………………………64 7.0 Introduction……………………………………………………………………………………….…64 7.1 Objectives……………………………………………………………………………………………64 7.2 Plastics……………………………………………………………………………………………….64 7.2.1 Classification ………………………………………………………………………………………65 7.2.2 Thermoplastic and Thermosetting Polymers……………………………………………………….65 7.2.3 Chemical Structure…………………………………………………………………………………66 7.3 History66 7.4 Fossil based Plastics………………………………………………………………………………….67 7.4.1 Bakelite……………………………………………………………………………………………..67 7.4.2 Polystyrene and Polyvinylchloride ………………………………………………………………..68 7.4.3 Nylon………………………………………………………………………………………………68 7.4.4 Rubber……………………………………………………………………………………………..70 7.4.5Synthetic rubber ……………………………………………………………………………………70 7.5Bioplastics……………………………………………………………………………………………70 7.5.1Cellulosed –Based Plastics…………………………………………………………………………70 8

7.5.2 Biodegradable ( Compostable) plastics……………………………………………………………71 7.5.3 Oxo-biodegradable……………………………………………………………

…………..........71

7.6 Processing Methods…………………………………………………………………………………71 7.6.1 Injection Moulding…………………………………………………………………………………71 7.6.2 Extrusion…………………………………………………………………………………………..72 7.6.3 Thermoforming……………………………………………………………………………………72 7.6.4 Calendering……………………………………………………………………………………….73 7.6.5 Casting…………………………………………………………………………………………….73 7.6.6 Transfer molding………………………………………………………………………………….73 7.6.7 Compression Molding…………………………………………………………………………….73 7.6.8 Hand (or Spray) Lay up……………………………………………………………………….….73 7.6.9 Laminating ………………………………………………………………………………………74 7.6.10 Filament Winding………………………………………………………………………………74 7.7.0 Common Plastics and Uses………………………………………………………………………74 7.7.1 Special purpose plastics………………………………………………………………………….75 7.8 Toxicity…………………………………………………………………………………………….75 7.8.1 Environmental Issues…………………………………………………………………………….76 7.9 Conclusion…………………………………………………………………………………………77 7.10 Summary………………………………………………………………………………………….78 7.11 Tutor –Marked Assignments……………………………………………………………………..78 7.12 References……………………..………………………………………………………………….78

Unit 8: Wood pulp and Paper…..……………………………………………………………………79 8.0 Introduction…………………………………………………………………………………………79 8.1 Objectives…………………………………………………………………………………………..79 8.2 Wood, pulp and paper……………………………………………………………………………….79 8.2.1 Making Paper…………………………………………………………………………..………….80 8.2.2 Beating…………………………………………………………………………………………….80 9

8.2.3 Pulp to Paper…………………………………………………………………………………..….80 8.2.4 Finishing…………………………………………………………………………………….……81 8.3 Manufacture of Wood Pulp…………………………………………………………………………81 8.3.1 Harvesting Trees………………………………………………………………………………….82 8.3.2 Preparation for Pulping…………………………………………………………….......................82 8.3.3 Mechanical Pulp………………………………………………………………………………….82 8.3.4 Thermomechanical Pulp……………………………………………………………………….…83 8.3.5 Chemithermomechanical Pulp…………………………………………………………………….83 8.3.6 Chemical Pulp………………………………………………………………………………….…83 8.3.7 Recycled Pulp……………………………………………………………………………………..83 8.3.8 Organosolv Pulping………………………………………………………………………………..84 8.3.9 Alternatives Pulping Methods……………………………………………………………………..84 8.4 Alternative to Wood pulp……………………………………………………………………………84 8.5 Market pulp………………………………………………………………………………………….85 8.5.1 Air dry pulp………………………………………………………………………………………..85 8.5.2 Roll Pulp…………………………………………………………………………………………...85 8.5.3 Flash dried pulp…………………………………………………………………………………....85 8.6 Environmental Concerns…………………………………………………………………………….85 8.6.1 Forest resources……………………………………………………………………………………86 8.6.2 Effluents from Pulp Mills………………………………………………………………………….86 8.6.3 Odour problems……………………………………………………………………………………86 8.6.4 Harmful Chemicals…………………………………………………………………………………86 8.7 Conclusion……………………………………………………………………………………………87 8.8 Summary………………………………………………………………………………………………87 8.9 Tutor –Marked Assignments………………………………………………………………………….87 8.10 References……………………………………………………………………………………………87

Unit 9: Environmental Pollutions …………………………………………………………………….. 88 10

9.0 Introduction……………………………………………………………………………………………88 9.1 Objectives……………………………………………………………………………………………..89 9.2 Pollution………………………………………………………………………………………………89 9.2.1 Types of Enviromental Pollution……………………………………………………………………89 9.2. Air Pollution…………………………………………………………………………………………..90 9.2.2 Water Pollution……………………………………………………………………………………..90 9.2.3 Land Pollution………………………………………………………………………………………90 9.2.4 Others form of Pollution……………………………………………………………………………90

9.3.0 Environmental Pollutants................………………………………………………………..91 9.3.1 Types of Pollutants………………………………………………………………………..91 9.3.2. Biodegradable Pollutants………………………………………………………………….91 9.3.3 Non- Biodegradable Pollutants……………………………………………………………91 9.4 Effects of Pollution…………………………………………………………………………..92 9.5 Pollution Control…………………………………………………………………………….92 9.6 Conclusion……………………………………………………………………………..........93 9.7 Summary……………………………………………………………………………………93 9.8. Tutor –Marked Assignments ………………………………………………………………93 9.9 References…………………………………………………………………………………..93

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Unit 1 HYDROGEN AND CARBON MONOXIDE SYNTHESIS, OXO-PROCESS, WATER GAS, SOURCES OF HYDROGEN AND ITS APPLICATION.

1.0

Introduction

Hydrogen and its associated gases are very important materials in petroleum and chemical industry. The importance of these gases cannot be over emphasized as they are required in large quantities for industrial purposes. The most important various sources of these required gases will be discussed in this unit. 1.1 Objectives By the end of this unit, you should be able to 

State the properties of hydrogen gas



Describe the various sources of hydrogen and carbon monoxide gases



Describe the production of hydrogen via steam reforming process.



Give a brief description of other methods of producing hydrogen



State several uses of hydrogen gas and carbon monoxide gas



Describe an oxo-process reaction



Write an equation of reaction of an oxo-process



Describe the process condition and operation of oxo-process.

1.2 HYDROGEN Hydrogen is the chemical element with the atomic number 1.It is represented by the symbol ‘H’. Hydrogen is known to be the lightest and most abundant chemical element constituting roughly 75% of the universe chemical elemental mass with atomic weight of 1.007944. It is widely distributed in combination with other elements e.g in water, natural gas, petroleum. This element is also a constituent of most other organic substances such as proteins, carbohydrates, and fats which are essential components of all living things. Hydrogen gas is known to be one of the industrial gases required in large quantities for industrial purposes. There are various processes for manufacturing hydrogen gas, in which most often produced in associated with carbon monoxide. 12

1.3 PRODUCTION PROCESSES Hydrogen can be prepared in the laboratory in a small quantity and also in a large quantity by several industrial processes. 1.3.1 Laboratory preparation of hydrogen Hydrogen can be prepared in the laboratory by any of these three methods i.

ii.

iii.

Action of zinc on dilute hydrochloric acid or tetraoxosulphate (vi) acid Zn

+ 2HCl

Zn

+ H2SO4

ZnCl2

+ H2

ZnSO4

+

H2

Action of Zinc or Aluminium on Sodium hydroxide Zn

+ 2NaOH

Na2ZnO2

+ H2

2Al

+ 2H2O

2NaAlO3

+ 3H2

Action of Iron on Steam 3Fe + 4H2O

Fe3O4

+ 4H2

1.3.2 Industrial Preparation of hydrogen When required in a commercial level, hydrogen can be prepared by a variety of methods of which the production from hydrocarbon- based sources is the most important. 1.3.2.1 From Hydrocarbon And Steam (Steam Reformer Process) The largest quantities of hydrogen are manufactured by catalytically reacting hydrocarbon and steam, to yield hydrogen and carbon monoxide (carbon II oxide), followed by water gas shift reaction. The most commonly used raw material is natural gas, although other natural and refinery hydrocarbon may also be used, for if propane is used, the following reaction will take place. CH3CH2CH3(g) + 3H2O(g) → 3CO(g) +

7H2(g)

3CO(g) + 3H2O(g) → 3CO(g) + 3H2(g) CH3CH2CH3(g) + 6H2O(g)

→ 3CO2 + 10H2(g)

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PROCESS DESCRIPTION The propane in form of vapor to be used is purified by passing it through a heater at a temperature of about 3700c. The hot gases then pass over bauxite or metallic oxide catalyst which converts the sulphur compounds (mercaptans, organic sulphides, and carbonyl sulphides) to hydrogen by sulphide .Thereafter, the gases are scrubbed with aqueous sodium hydroxide and water to remove the soluble sulphides. When natural gas is used as the process feed, sulphur is removed by passing the gas through drums containing activated carbon. The sulphur free propane vapor are mixed with steam and passed into the top of a reforming furnace containing nickel catalyst at temperature of about 7600c to 9800c and pressure of 600psi(4.21mpa). Although the steam hydrogen reaction is favored by low pressure, there are compensating economic advantage s in operating at high pressure. The reformed gases comprises mainly of hydrogen, carbon monoxide, and carbon dioxide are cooled to about 370oC by mixing with steam, and then passed into the into the first stage carbon monoxide converter containing an iron oxide catalyst promoted with chromium oxide. The exothermic conversion reaction (water-gas shift) takes place at a temperature of about 4250c and a space velocity of 100volumes of gas/volumes of catalyst per hour. Both these catalysts are rugged and have a normal life of 1 year or more. Thereafter, the gases from the converter containing a small amount of carbon monoxide are cooled to about 38oC and passed into a packed tower. Here aqueous monoethanolamine 15-20% is circulated down through the center current blowing gas (GIRBOTOL PROCESS). The amine solution absorbs the carbon dioxide and, after passing through heat exchangers, is run to the top of a reactivating tower. The carbon dioxide is desorbed by steam generated by heating the solution in a reboiler at the bottom of the tower. The carbon dioxide removed amounts to about 30volumes/100volumes of hydrogen and since it is recorvered at 8 purity of 99.8% it is available as a useful by product. The regenerated amine is then returned to the system. At atmospheric pressure and hydrogen gas containing 20% carbon dioxide may be purified to 0.1% carbon monoxide by scrubbing with the monoethanolamine absorbing 15 to 30m3 carbon dioxide/m3 carbon monoxide/m3 of solution circulated. Approximately 0.12kg steam/liter of solution is required for registration. The carbon dioxide free hydrogen coming from the absorber still contains about 1% carbon monoxide. This is removed by passing through two more stages of carbon monoxide conversion, followed by carbon dioxide removal. From the last absorber, the purified hydrogen analysis is better than 99.9% pure. The gas may be compressed to about 150psi [1mpa] and charge into storage tanks.

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1.3.2.2 From Hydrocarbons By Partial Oxidation Synthetic gas (mixture of hydrogen and carbon monoxide) may be made by partially burning hydrocarbon feed with oxygen. The carbon monoxide formed is then reacted with water vapor in a shift converter to form more hydrogen. CnH2n-2 + MO2

CO + H2O

→ xCO2 + n-XCO + n-yH2 + pH2O

→

CO2

+ H2

The reaction products are removed continuously from the reaction core. In addition to the major products, carbon monoxide and hydrogen burner effluents contain 5 mole% water, less than 2 mole % carbondioxide, less than 0.1 mole% oxygen and about 0.5 unreacted methane if natural gas is used as feed. The gases may be saturated, and then passed to a shift converter, where the carbon monoxide reacts with steam to produce carbon dioxide and hydrogen. The hydrogen can then be purified, compressed and stored. 1.3.2.3 From Water Gas And Steam Hydrogen can equally be produced along with carbon dioxide by catalytically reacting water gas (40% carbon monoxide and 50% hydrogen) with steam at elevated temperature. The carbon dioxide is removed by the gas, relatively pure hydrogen remains. The process is particularly adaptable to low purity hydrogen containing nitrogen and carbon monoxide for the synthesis of ammonia and methanol respectively. C(amorp) + H2O → CO + H2 (water gas) CO

+ H2O → CO2 + H2

PROCESS DESCRIPTION The water gas is produced by the reaction of steam on incandescent coke or coal at a temperature of 100oC or higher. The gas from the holder is run into a saturator, where it contracts hot water and is heated to 75-85%. The saturated water gas (1 volume) is then mixed with steam (3 volumes) and passed into a two stage steam converter, where carbon monoxide is reacted with water vapor. The first stage operates at a temperature of 425-4800C, and the second stage at 3704000C, with heat exchangers between the stages. Two stages are employed because of the exothermic character of the reaction and the decreased conversion at elevated temperature. By using this two stage procedure on the so called water gas shift reaction, the major part of the reaction takes place with a relatively small catalyst, whereas the balance is affected at a lower temperature conducive to high overall yield. 15

The catalyst commonly used is iron oxide promoted with chromium oxide. The exit gases containing about 64% hydrogen, 31% carbon dioxide, 4% nitrogen and methane, and 1% carbon monoxide are cooled in water towers and passed to purification units. This can be done using GIRBOTOL PROCESS as described under steam reformer process. 1.3.2.4 Steam-Iron Process This process produces hydrogen by the reaction of steam at high temperature on reduced iron oxide to yield hydrogen, and then reducing the iron oxide with a reducing gas such as water gas or producer gas in a cyclic operation.

Fig 1:- flow diagram showing the production of H2 via steam iron process.

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1.3.2.5 Electrolysis Of Water Direct current is passed between iron or nickel-plated iron electrode in a solution consisting of 10-26% caustic soda or potash. Only distilled water is added to the electrolyte, since the solute is not consumed. This process of producing hydrogen is attractive where low cost of electricity is available. Hydrogen is also obtained as a byproduct in other electrochemical processes, although it is not always economical to recover it. 1.3.2.6 From Methanol And Steam Hydrogen of higher than 98% purity may be manufactured by the catalytic reaction of methanol and steam at 2600C CH3OH(l)

+ H2O →

CO2(g)

+

H2O(g)

The ease and simplicity of fabricating the plants, handling raw material and purifying the hydrogen makes the process particularly practical for portable plants. 1.3.2.7 Other Sources Other sources where hydrogen can be manufactured on a large scale are: 

Thermal decomposition of hydrocarbon where it is obtained as a by-product in the manufacture of carbon black by the thermal decomposition of natural gas.



Catalytic reforming of petroleum stocks, and



Dissociation of ammonia i.e. cracking ammonia gas at pressure up to 20psi(350kpa) and temperature of about 900oC- 950oC in the presence of nickel oxide as catalyst.

Conclusively, the manufacturing process is essentially identical except that the gas mixture must be purified to produce pure (95-100%) hydrogen. Nevertheless the steam reforming process is by far the most important, next in importance is the hydrocarbon partial oxidation process where natural gas, liquefied petroleum gases and propane may all be used as feedstock according to availability and cost. 1.4 Application 1.4.1 Consumption in Processes The manufacturing of hydrogen is largely an integral part of the other chemical manufacturing process. Large quantities of hydrogen are needed in the petroleum and chemical industries. The largest application of H2 is for the processing ("upgrading") of fossil fuels, and in the production of ammonia. The key consumers of H2 in the petrochemical plant include hydrodealkylation, 17

hydrodesulfurization, and hydrocracking. H2 has several other important uses. H2 is used as a hydrogenating agent, particularly in increasing the level of saturation of unsaturated fats and oils (found in items such as margarine), and in the production of methanol. It is similarly the source of hydrogen in the manufacture of hydrochloric acid. H2 is also used as a reducing agent of metallic ores. Hydrogen is highly soluble in many rare earth and transition metals and is soluble in both nanocrystalline and amorphous metals. Hydrogen solubility in metals is influenced by local distortions or impurities in the lattice. These properties may be useful when hydrogen is purified by passage through hot palladium disks, but the gas's high solubility is a metallurgical problem, contributing to embrittle of many metals, complicating the design of pipelines and storage tanks. Apart from its use as a reactant, H2 has wide applications in physics and engineering. It is used as a shielding gas in welding methods such as atomic hydrogen welding.H2 is used as the rotor coolant in electrical generators at power stations, because it has the highest thermal conductivity of any gas. Liquid H2 is used in cryogenic research, including superconductivity studies. Because H2 is lighter than air, having a little more than 1⁄15 of the density of air, it was once widely used as a lifting gas in balloons and airships. In more recent applications, hydrogen is used pure or mixed with nitrogen (sometimes called forming gas) as a tracer gas for minute leak detection. Applications can be found in the automotive, chemical, power generation, aerospace, and telecommunications industries. Hydrogen is an authorized food additive (E 949) that allows food package leak testing among other anti-oxidizing properties. Hydrogen's rarer isotopes also each have specific applications. Deuterium (hydrogen-2) is used in nuclear fission applications as a moderator to slow neutrons, and in nuclear fusion reactions. Deuterium compounds have applications in chemistry and biology in studies of reaction isotope effects. Tritium (hydrogen-3), produced in nuclear reactors, is used in the production of hydrogen bombs, as an isotopic label in the biosciences, and as a radiation source in luminous paints. The triple point temperature of equilibrium hydrogen is a defining fixed point on the ITS-90 temperature scale at 13.8033 kelvins. 1.4.2 Coolant Hydrogen is commonly used in power stations, as a coolant in generators, due to its specific heat capacity being considerably higher than any other gas. 1.4.3 Energy Carrier Hydrogen is not an energy resource, except in the hypothetical context of commercial nuclear fusion power plants using deuterium or tritium, a technology presently far from development. The Sun's energy comes from nuclear fusion of hydrogen, but this process is difficult to achieve 18

controllably on Earth. Elemental hydrogen from solar, biological, or electrical sources require more energy to make it than is obtained by burning it, so in these cases hydrogen functions as an energy carrier, like a battery. Hydrogen may be obtained from fossil sources (such as methane), but these sources are unsustainable. The energy density per unit volume of both liquid hydrogen and compressed hydrogen gas at any practicable pressure is significantly less than that of traditional fuel sources, although the energy density per unit fuel mass is higher. Nevertheless, elemental hydrogen has been widely discussed in the context of energy, as a possible future carrier of energy on an economy-wide scale. For example, CO2 sequestration followed by carbon capture and storage could be conducted at the point of H2 production from fossil fuels. Hydrogen used in transportation would burn relatively cleanly, with some NOx emissions, but without carbon emissions. However, the infrastructure costs associated with full conversion to a hydrogen economy would be substantial. 1.4.4 Semiconductor Industry Hydrogen is employed to saturate broken ("dangling") bonds of amorphous silicon and amorphous carbon that helps stabilizing material properties. It is also a potential electron donor in various oxide materials, including ZnO, SnO2, CdO, MgO, ZrO2, HfO2, La2O3, Y2O3, TiO2, SrTiO3, LaAlO3, SiO2, Al2O3, ZrSiO4, HfSiO4, and SrZrO3. 1.4.5 Others Include (i) Hydrogenation of edible oils to produce shortenings and margarines, many of which are low cholesterol. (ii) Hydrogen is used in large electric generators to reduce windage losses and heat. (iii)Liquefied hydrogen is used as rocket fuel. 1.5 CARBON MONOXIDE Carbonmonoxide (CO) is a colourless, odourless, and tasteless gas which is slightly lighter than air. It is slightly toxic to humans and animals in higher quantities. The major sources of carbon monoxides individually are (i) REACTION OF STEAM WITH HYDROCARBON It can be obtained by catalytically reacting steam with hydrocarbon to produce hydrogen and carbon as explained in the production of hydrogen. This leads to the production of mixture of hydrogen and carbonmonoxide known as synthetic gas. (ii) COMBUSTION OF CARBON Another major industrial source of carbon monoxide is producer gas, a mixture containing mostly carbon monoxide and nitrogen formed by combustion of carbon in air at high temperature 19

when there is an excess carbon. In an oven, air is passed through a bed of coke. The initially produced CO2 equilibrates with the remaining hot carbon to give CO. (iii)Carbon monoxide is also a by-product of the reduction of metal oxide ore with carbon which can be shown in the simple equation below + C →M

MO

+ CO

MO is the oxide of the metal to be reduced. Since CO is a gas, the reduction process can be driven by heating, exploiting the positive entropy of reaction. 1.5.1 Applications Carbon monoxide is an industrial gas that has many applications in bulk chemical manufacturing, examples is in the production of aldehyde i.e. by the hydroformylation reaction of alkenes, carbon monoxide and hydrogen. It is used in the production acetic acid. CO is also useful in the field of medicine and also for preserving of the freshness meat product. 1.6 WATER GAS Water gas is a synthetic gas, containing carbon monoxide and hydrogen. It is a useful product but requires careful handling because of the risk of CO processing. The gas is made by passing steam over red hot hydrocarbon fuel such as coke. H2O

+

C

→

H2

+ CO ∆H = +131kj/mol

The reaction is endothermic so the fuel must be continually re-heated to keep the reaction going. This was usually done by alternating the steam with an air stream. Required heat is provided by burning carbon. O2

+

C

→

CO2 ∆H = -393.5KJ/mol

1.7 OXO PROCESS Oxo synthesis or Oxo process ,also known as Hydroformylation, is an important industrial process for the production of aldehydes from alkenes. This chemical reaction entails the addition of a formyl group (CHO) and a hydrogen atom to a carbon-carbon double bond. This process has undergone continuous growth since its invention in the 1930s: production capacity reached 6.6×106 tons in 1995. It is important because the resulting aldehydes are easily converted into 20

many secondary products. For example, the resulting aldehydes are hydrogenated to alcohols that are converted to detergents. Hydroformylation is also used in specialty chemicals, relevant to the organic synthesis of fragrances and natural products. The development of hydroformylation, which originated within the German coal-based industry, is considered one of the premier achievements of 20th century industrial chemistry. The process typically is accomplished by treatment of an alkene with high pressures (between 10 to 100 atmospheres) of carbon monoxide and hydrogen at temperatures between 40 and 200 °C. Transition metal catalysts are required The OXO Process consists of the reaction of olefins with water gas in the presence of Fischer Tropsch catalyst to give aldehydes according to the general equation.

The aldehydes are hydrogenated to alcohols in a subsequent step. The basic reaction was discovered by Ruhrchemie but the large-scale development of a continuous process resulted from a co-operative effort by Ruhrchemie and the I.G. The ChemoGesellschaft was a development organization formed by these two companies on a 50/50 participation basis. The process was later licensed to the operating company - the OXO Gesselschaft. Extensive research on the process was carried out at Leuna where a plant of 100 T/month design capacity operated for 1½-2 years. The actual production was, however,only 40/50 T/month because of shortage of the preferred raw material -Kogasin. Leuna processed a certain amount of “Gelböl”, an olefinic by-product of the higher alcohols process to supplement their Kogasin supplies but it was stated that it was an inferior raw material. The present report is limited to information obtained at Leuna. Details of Ruhrchemie work are given in other reports, notably that on the Ruhrbenzin A.G. Target No. 30/5.01. 1.7.1 Chemistry of the OXO Process: The first step in the process appears to consist of the addition of CO to the olefine according to the equation-

21

This intermediate product cannot be isolated because it is hydrogenated immediately to give aldehydes as follows:

dependent on the point at which hydrogen enters to molecule. Further hydrogenation, mainly carried out in a separate reaction stage, yields the corresponding primary alcohols. It will be seen that oven in the simplest case, the OXO Process gives a mixture of aldehydes or alcohols. This tendency towards a mixed product is further increased by isomerisation of the olefine under the OXO Process conditions, thus:

The reaction involving the least sterie hindrance predominates. Thus, using isobutylene as the olefine is obtained in greater quantity than

22

Similarly, when using trimethylpentenes obtained from polymerisation of iso-butylene, the main

OXO products are those derived from the isomer as distinct from the

isomer

as distinct from The mixed alcohols obtained from the OXO Process are mainly used after suphonation for detergent manufacture. For this purpose the mixed alcohols are said to be better raw materials than single compounds. Process Conditions: The first stage of the process is carried out at about 200 ats. pressure and 150°-160°C in the liquid phase. Finely divided Fischer Tropsch catalyst is suspended in the liquid feed in a concentration of 3-5% by weight. Most of the catalyst is recycled and the make up requirement is said to be very small. Normally, when using Kogasin as the olefinic feed, the reaction time required is of the order of 20 minutes is of the order of 20 minutes. Lower olefins reacted very readily. In the case of low molecular weight olefins, they have to be used in solution in a liquid medium. A number of side reactions occur in the OXO stage. Aldehydes polymerize to give “Dicköl” which comprises up to 20% of the crude product. About one third of the aldehydes initially formed are also hydrogenated to the corresponding alcohol. It is thus not practicable to isolate aldehydes from the crude product obtained in the first stage of the process. If these products are required, it is considered preferable to complete the hydrogenation in the second step, separate the alcohols and oxidize them to the corresponding aldehydes. This second step of hydrogenation in addition to converting the aldehydes in the alcohols, breaks down about 50% of the Dicköl to alcohols of the same composition as are derived from the corresponding aldehydes. The hydrogenation is hindered by the presence of CO. It is therefore necessary to let down to atmospheric pressure the crude product from the first OXO stage and to carry out the hydrogenation in a separate step. This stage is carried out at about 200 ats and at a temperature of 170-195° C. The same catalyst can be filtered out of the first stage crude and it can be replaced by the more readily available copper chromite. When Fischer Tropsch catalyst is employed, some carbon monoxide is formed in the hydrogenation reaction as a result of reduction of cobalt carbonyl. In order to keep down the concentration of carbon monoxide in the circulating hydrogen, the exit gas is treated over an iron catalyst to convert carbon monoxide to methane. The methane content of recycle gas can be as high as 10% without adverse effect on the reaction. This concentration is maintained by bleeding off the requisite amount of gas from the circulating system.

23

The first step of the OXO Process is not affected by the presence of sulphur compounds in the raw materials but these impurities do hinder the chromite catalyst. When dealing with sulphurcontaining olefine raw material, therefore, it is necessary to filter off the first-stage catalyst and to carry out the hydrogenation over fixed nickel tungsten sulphide catalyst. It is necessary to carry out a partial hydrogenation of the crude first-stage product prior to filtration in order to convert any cobalt carbonyl into cobalt. 1.7.2 Leuna Operation: The process, as originally worked out by Ruhrchemie, was a batch process and the pilot plant at Holten consisted of 18 units originally intended for batch operation. Work at Leuna showed that considerably higher through-puts were obtained from continuous operations. The following description of the latest method of operation of the Leuna plant was obtained by W.A. Horne from Dr. Gemassmer, who was the chemist directly in charge of these operations. The olefine or olefine-containing charge is mixed with 3-5% by weight of catalyst, most of which is recycled material. This suspension is pumped at the rate of 300-700 litres/hour and at a pressure of 220-240 ats. through a heater which raises its temperature to approximately 150°C. The preheated feed enters the bottom of the first reactor and passes upward concurrently with a steam of 60 M3/hour of carbon monoxide and hydrogen which has been separately preheated to 150-190° C (maximum: 200°C). This synthesis gas is partly recycle gas from the process (40-50 M3/hour) and partly make up gas which consists of equal molecular proportions of hydrogen and carbon monoxide. The first reactor, which is constructed of carbon steel, has an internal diameter of 200 mm. and a length of 8 M. It contains 6 vertical 21 mm. OD, 17 mm. ID, steel cooling tubes which are connected to a water jacket surrounding the reactor. Cooling by these tubes is used only when very reactive olefins are charged and the heat release is high. A thermocouple well extends the length of the reactor and the temperature of the exit products is normally controlled at 150°C. The temperature and feed rate depend on the concentration and molecular weight of the olefins in the charge stock. As previously stated, lower molecular weight olefins are more reactive. Low concentration of olefins in the feed necessitates the use of lower feed rates and higher temperatures in order to ensure that reaction proceeds to the required extent. Normally, roughly 70% of the olefins charged are converted in the first reactor. The exit products from the top of this first reactor pass to the bottom of the second reaction vessel where they come into contact with an additional 60 M3/hour of synthesis gas. The second reactor has the same dimensions as the first by is fitted with baffles to increase the efficiency of contact. No cooling tubes are required and the normal operating temperature is 170° C. Essentially all the remaining olefins are converted and some 20% of the aldehydes made are hydrogenated to alcohols. The exit products from the top of the second OXO reactor now flow through a water cooler to a separator from which synthesis gas is recycled to the preheater. The liquid product is let down to atmospheric pressure and the released dissolved gases are purged after scrubbing with crude second-stage product to prevent loss of liquid by entrainment. The first-stage product is now 24

pumped under a pressure of 200-250 ats. to the second-stage preheater from which it passes to the bottom of the first reactor of the hydrogenation stage. 60 M3/hour of a mixture of preheated fresh hydrogen and methanised recycle gas is also introduced at the bottom of the reactor. The reactor is identical with the first reactor of the OXO stage by operates at an exit temperature of this second reactor is roughly 200°C. The draw-off of liquid product from the bottom of this converter is regulated so as to keep the reactor full of liquid. The top of the second reactor serves as a high pressure separator vessel for hydrogen and liquid products. The hydrogen containing some carbon monoxide is water-cooled and passes to a catch-pot for separation of condensed liquid which is returned to the hydrogenation reactor. Before being recycled to the hydrogenation reactors, the gas is reacted at 250° C over an iron catalyst (similar to that used in the Synol Process) in order to convert carbon monoxide to methane. The liquid product is let down to a pressure of 10 ats. to a separator from which dissolved gases are vented. The liquid from this separator is charged under its own pressure to the filter system. The liquid, in batches of 700 litres, enters the filter vessel (which is pressured with nitrogen through Valve 1) and is filtered through the porous ceramic tubes situated at the bottom of the vessel. This operation requires about 10 minutes with a new filter but can take up to 30 minutes when the filters are old. When filtration is complete, fresh olefine charge is introduced through Valve 3 and passes in the reverse direction through the filter thereby washing off the catalyst material. The whole vessel is rotated at 60 revs/minute for 2-3 minutes. It is stopped in the inverted position and the olefine catalyst suspension is forced out through Valve 4 by nitrogen pressure, nitrogen being introduced through Valve 3. This suspension is then transferred to the feed mixer of the OXO Process. The cycle time for a complete operation of the filter is one hour per batch of 700 litres of crude product. The treatment of the filtrated crude product depends on the type of olefinic raw material used. If this raw material has initially a boiling range not exceeding 30°C, the alcohols can be separated from hydrocarbons by simple distillation. If, on the other hand, a raw material of wider boiling range is employed, alcohols have to be separated by the boric acid method. A number of variations of the above process had been tried out at Leuna. The effect of introduction of liquid feed at the top of one or both of the OXO reactors was tried, as was also the operation of the OXO Process with liquid and gas flowing counter-currently. The process was also operated with only one reactor in the OXO and hydrogenation stages. According to Dr. Gemassmer, however, the method described in detail above was found to be the most satisfactory. An essential of any scheme for operating the OXO process is that the synthesis gas rate in both the OXO and hydrogenation stage must be sufficiently high to ensure efficient stirring and complete suspension of the catalyst . A large excess of synthesis gas is not necessary for the purely chemical standpoint. Research carried out by the I.G. suggests that the OXO stage might be operated at 40-50 ats. pressure but under these conditions the throughput would be lower and the temperature somewhat higher. One of the difficulties sometimes encountered was that unless the conditions in the OXO stage are carefully controlled olefine polymerization takes place. The 25

polymers so formed, after hydrogenation in the second step, are difficult to separate from the higher boiling alcohol products. 1.7.3 Catalyst Preparation: The Fischer Tropsch catalyst used in the OXO Process was obtained from the catalyst plant of Ruhrchemie at Oberhausen-Holten. It was reported to have the following approximate composition: 30 2% 2% 66% Kieselguhr

% Thorium Magnesium

Cobalt oxide Oxide

Due to the scarcity of cobalt, the content of this component of the catalyst has latterly been decreased. The last shipment contained only about 25% of cobalt. This apparently had little effect on the process operation. The catalyst in powder form is reduced with pure sulphur-free hydrogen. the hydrogen flow is controlled at a rate high enough to prevent settling of the catalyst powder, i.e. the catalyst is fluidized by the hydrogen stream. The period of reduction is 2-4 hours. 1.7.4 OXO Processing of Cracked Middle Oil: In addition to Kogasin and Gelböl, Leuna had investigated the treatment of cracked petroleum oil by the OXO Process. Dr. Gemassmer provided the following date from a run, the conditions of which were not considered to be optimum. The olefinic feed material had the following properties: Density Pour Point Av. Molecular Wt. iodine No. (Hanus) Sulphur Content Boiling Range Volume % soluble Kattwinkel solution

0.848 -18° C 195 46-48 .24% by wt 230°-350° C 51.

The charge was mixed with 3 % by weight of catalyst and reacted with water gas at 240 ats. Total reaction time in the OXO stage was approximately 1 hour. The temperature at the inlet to the first reactor was 150 C and that at the exit of the second reactor 190 C. The hydrogenation of the crude product was carried out at 220 ats with hydrogen of 97% purity. The temperature was 195-200 C and the total reaction time approximately 1 hour. The product had the following properties: 26

Density Iodine No. (Hanus) OH No. CO No. Saponification No.

.862 19.6 36-40mgm KOH/gm 3.5 5 mgm KOH/gm.

The OH number is determined by acetylation with acetic anhydride followed by titration with KOH solution. The CO umber is a measure of the aldehyde and ketone content and is determined by forming the oximes of aldehydes and detones followed by titration with KOH solution. The crude product contains 16-17% alcohols which may be separated from the hydrocarbons by forming boric esters. It is not possible to separate the alcohols by simple distillation because of the wide boiling range of the charge stock. Only about 60% of the olefins were converted and of this, approximately 80% was recovered 1.8 Conclusion Hydrogen can be prepared in several ways, but economically the most important processes involved removal of hydrogen from hydrocarbons. Commercial bulk hydrogen is usually produced by the steam reforming of natural gas. At high temperatures (1000–1400 K, 700– 1100 °C or 1300–2000 °F), steam (water vapor) reacts with methane to yield carbon monoxide and H2. Hydrogen is sometimes produced and consumed in the same industrial process, without being separated. In the Haber process for the production of ammonia, hydrogen is generated from natural gas. Electrolysis of brine to yield chlorine also produces hydrogen as a co-product. The manufacturing of hydrogen and its associated gases is largely an integral part of the other chemical manufacturing process. 1.9 Summary You have learned in this unit the characteristics, methods of preparation and uses of hydrogen, carbon monoxide and water gas. That is, the industrial preparation of hydrogen from hydrocarbon via steam reforming process as the most important source was discussed. Other processes are partial oxidation of hydrocarbon, electrolysis of water, steam iron process, from water gas and steam, methanol and steam, thermal decomposition of hydrocarbon, and dissociation of ammonia. Also learned in this unit is the chemistry of oxo-process that leads to the production of aldehyde from alkene. Therefore, what you have learned in this unit concerns the production of valuable gases such as hydrogen, carbon monoxides, water gas and their uses in chemical manufacturing process. 27

1.10. Tutor – Marked Assignments 

Describe the industrial preparation of hydrogen gas via steam reforming process



Outlines the various industrial methods of producing hydrogen gas



Discuss the chemistry of oxo- process



Enumerate the uses of hydrogen and carbon monoxide gases

1.11 References 1.Uppal, M.M; Bhatia, S.C (2008). Engineering Chemistry (Chemical Technology). Khanna publishers.7th ed. Pg 460-465. 2.http://en.wikipedia.org/wiki/hydrogen 3.www.chiyode_corp.com

28

Unit 2 INDUSTRIAL ORGANIC MATERIALS

2.0 Introduction In the last unit, the production of hydrogen, synthesis and carbon monoxide was discussed. Also, the importance and application of these industrial gases as they served as raw material in chemical industry were equally highlighted. This may not be achieved without the required raw material needed for their production. Thus, the importance of raw material in production processes cannot be underestimated. Therefore, if there are no raw materials, there will be no production. In this unit, the major raw material available for industrial usage will be discussed. 2.1 Objectives At the end of this unit, you should be able to 

Lists the various organic raw materials



State why petroleum is preferred to coals as industrial organic material



Discuss how coal can serve as a base material for the chemical industry



Lists the various inorganic materials.



Sketch the flow diagram showing relationship between organic raw materials and products

2.2 Raw Materials 2.2.1 Organic Materials i. Petroleum Crude oil or Petroleum is a complex mixture of mainly hydrocarbon. Hetero compound are also found e.g hydrocarbon containing one or more sulphur, oxygen or nitrogen atoms which may be incorporated in the molecular structures in different ways. Distillation is by far the most important method of obtaining primary product from crude oil. For the chemical industries, cracking of naphtha and gas oil is an important operation to produce raw materials. The relationship between oil, air and several intermediate chemicals is as shown in figure 2 below.

29

Steam conversion Methane

or

Synthesis gas (CO, H2, CO2, possibly N2)

Partial oxidation

nitrogen air

Urea nitric acid nitrates hydrocyanic acid

NH3

oxygen

Thermal cracking of naphtha or gas oil

oil

Sulfur

propylene

SO2

NH3

Figure 2: The relationship between raw materials and intermediates

30

Ammonia Urea Methanol Formaldehyde Liquid HC

isoppropanol acetone tetramer glycerol allylic chloride epichlorohydrin acrylic acid butyraldehyde n-butanol acrylonitrile propylene oxide

sulfates sulfites sulfides

Petroleum (crude oil and natural gas ) serves as the most important raw material for the production of organic intermediates . This has not always been the case, before the Second World War, coal was the main source of industrial organic chemicals, especially in Europe. Benzene is now the only base chemical produced in significant volume from coal. The tonnage of inorganic chemical produced from petroleum is also very large. Main products are ammonia from natural gas, sulphur from natural gas and oil refineries and carbon black from aromatic oil fractions. The reasons for this development are as follows: 

Up to 1973 oil was cheaper than coal. In particular in Western Europe, where coal generally in zones which are difficult to exploit, the steep rise in the costs of wages made coal expensive. But even in the USA and South Africa where coal can be Open Cast mined, oil was cheaper.



All organic intermediates contain much more hydrogen than coal. Because oil also has a higher H/C ratio than coal it is economically more attractive. To produce such intermediates from coal would mean increasing the amount of hydrogen by gasification, but this means use of extra raw material and energy.



Oil has the advantage of being a liquid. Transportation and processing of fluids is always easier and cheaper. Another drawback of the use of solids is that a pretreatment is often required to achieve a proper particle size distribution. Hence, continuous automatic processing of oil is easier than coal.



The composition of oil is less variable than the composition of coal. Moreover, the different main components of oil are easier to separate, usually by distillation. Coal contains highly condensed structures which are difficult to separate and are insoluble in any liquid.

In the future it can be expected that the relative scarcity of oil will lead to a larger role for other raw material. Also, in several countries there is a trend toward lessening their dependency on oil producing countries. ii. Natural gas. Natural gas can be found together with petroleum or in separate field. In the former case, the gas not only contains methane but also higher alkane and if the oil contain sulphur, the gas contain hydrogen sulphide. To use natural gas, it is generally necessary to desulphurise and dry it. Higher alkane are condense. Apart from it use as energy source, natural gas is a raw material for the production of synthesis gas and chlorinated hydrocarbon.

31

iii. Coal. Coal has been formed from plant material under the influence of temperature and pressure by which carbohydrate and lignin were converted. The process known as carbonization converts the vegetable material in stages into peat, lignite ( or brown coal),bituminous (or soft) coal and finally, anthracite (hard ) coal which is about 95% carbon. In Nigeria, large amounts of coal are mined in Udi and Enugu hills of Anambra state, and in Jos Plateau. There are also large lignite deposits in Onitsha and Asaba. Coal consist mainly of aromatic ring structure which are peri condensed by C,O,S and N bridges. Heterocyclic structures also generally occur. Coal is converted on a large scale to produce coke for the steel industries. This mean pyrolysis ( with exclusion of air ) at high temperature e.g 1000oC. In this way the coal is cracked. The by-product gases contain aromatic (benzene, toluene ,xylene), hydrogen and tar. The nitrogen in the coal form NH3 and HCN, and sulphur is release as H2S. The pyrolysis takes about 24hours in chamber oven. Coal can serve as a base material for the chemical industry in several ways: 

Products made by coal pyrolysis can be use to produce a large number of predominantly aromatics chemical. Infact, coal pyrolysis products have formed the basis of the industry since it first began to develop in the second half of the 19th century.



Synthesis gas can be made from coal by gasification with steam and air or oxygen; further conversion into liquid or gaseous hydrocarbon is possible by catalytic conversion in the Fischer-Tropsch process. Similarly, synthesis gas can be converted into methanol, which is further processed into liquid hydrocarbon mixture high in aromatic content.



Hydrogenation of coal to liquid products is possible, these products can then serve as feedstock for chemical processes in a similar manner as petroleum oils.

iv. Other Organic Raw Materials Apart from the raw materials mentioned above, others are used, albeit on a smaller scale, such as vegetable materials like fatty oils, starch, sugar and molasses, wood and straw. With these materials less drastic conversions are applied in comparison with coal and oil, to make as much use of the chemical structures in the feed as possible. On the other hand, the products spectrum then is much narrower and production volumes are generally smaller, in other words the products are much less important as building blocks of the chemical industry as compared with ethene, propene,benzene. e.t.c.

32

2.2.2 Inorganic Raw Materials The inorganic industry is based on minerals as well as on air and water. Many of the minerals are processed for making the corresponding metal or metal compounds; there is , however, a group of raw materials from which a limited number of rather important inorganic intermediates is made that find widespread uses. These are: 

Air, the source of oxygen and nitrogen, can be separated via liquefaction and distillation. It is also possible to let the oxygen react, e.g. to CO2 and water, followed by the oxygencontaining reaction product. This is practiced in the production of ammonia and its derivatives.



Sulphur is another inorganic raw material gotten from sulphates, or sulphur deposits and is also recovered as a by-product from oil, coal or natural gas processing. The main product made from it is sulphuric acid , the most important inorganic intermediate in terms of production volume.



Sodium Chloride is another important material for making soda ash, caustic soda, chlorine and its derivatives.



Water which serves as feed, solvent or auxiliary material in very many chemical processes.



Bauxite, mainly Al2O3 forms the basis for alumina and aluminums and for a limited number of adsorbents and aluminum compounds, e.g the sulphate which is used in papermaking and water treatment.



Silica is another inorganic material which is used in making adsorbents as well as synthetic compounds containing Si such as silicones and



Calcium carbonate used in producing CaO and CO2 .

2.3 Conclusion A manufacturing process needs a chemical plant, and the establishment of such plant depends on the economics of the process. The economic feasibility of any chemical industry before it is sited depends on the availability of raw materials, energy requirement and transportation. Therefore, the importance of organic raw materials such as petroleum, coal and natural gas in the manufacturing processes cannot be overemphasized considering the volumes of products that can be gotten from these substances. Although, petroleum is preferred to coal because of the economic advantages, and array of products gotten from it.

33

2.4 Summary In this unit, you have learned about the various various organic raw materials such as petroleum, natural gas, and coal. Petroleum is therefore considered to be the most important organic raw material on which chemical industries depend on for their production. 2.5 Tutor- Marked Assignments 

Mention the basic organic raw material



Give reasons why petroleum is preferred to coal as industrial organic material.



Discuss the use of coal as base material for chemical industry.



Draw flow diagram showing relationship between petroleum and chemical industry.



Lists the main inorganic raw material available for production process.

2.6 References 1.Uppal, M.M; Bhatia, S.C (2008). Engineering Chemistry (Chemical Technology). Khanna publishers.7th ed. Pg 460-465. 2.Jong , W.A et al (1979). Introduction to Chemical Process Technolgy. press.2nd ed. Pg 15-17.

34

Delft University

Unit 3 FATS AND OILS

3.0 Introduction In unit 2, fats and oil was mentioned as one of the organic raw material available for chemical industry. Fats and oils play an important role in human nutrition because they are sources of energy and of the essential fatty acids in the diet. In addition, fat deposits in the body serve as insulation and provide protective cushions for the organs. Fats are the most concentrated form of energy in foods, yielding more than twice as much energy as equal portions of either carbohydrates or proteins. There are certain fatty acids which man needs for good health that the body cannot produce. These are the essential fatty acids, and include the following three acids: linoleic, linolenic, and arachidonic. Fats are known to protect the body in two ways. The deposits of fat under the skin act as nonconductors of heat, helping to insulate the body and prevent the rapid loss of heat. Furthermore, the viscera and certain organs of the body, such as the kidneys, are supported and cushioned by fat. In this unit, you will learn about the properties of fats and oils, sources, uses and several types of fat. 3.1 Objectives At the end of this unit, you should be able to: 

Differentiate between fats and oils



Name the element inherent in fats and oils



State the difference between CIS and TRANS fatty acid



Distinguish between saturated fat and unsaturated fat



State the uses of fats and oils.



Mention some of the natural sources of fats and oils.

3.2 Fats and Oils Fats and oils are naturally occurring alkanoates. They belong to a group of biological substances called lipids. Lipids are biological chemicals that do not dissolve in water,and serves a variety of functions in organisms, such as regulatory messengers (hormones), structural components of membranes, and as energy storehouses. Fats and oils generally function in the latter capacity. 35

Fats differ from oils only in that they are solid at room temperature, while oils are liquid. Fats and oils share a common molecular structure, which is represented by the formula below. This structural formula shows that fats and oils contain three ester functional groups. Fats and oils are esters of the tri-alcohol, glycerol (or glycerine). Therefore, fats and oils are commonly called triglycerides, although amore accurate name is triacylglycerols. One of the reactions of triglycerides is hydrolysis of the ester groups.This hydrolysis reaction produces glycerol and fatty acids, which are carboxylic acids derived from fats and oils.In the fatty acids, Ra, Rb, and Rc, represent groups of carbon and hydrogen atoms in which the carbon atoms are attached to each other in an unbranched chain. They are made from two kinds of molecules: glycerol (a type of alcohol with a hydroxyl group on each of its three carbons) and three fatty acids joined by dehydration synthesis. Since there are three fatty acids attached, these are known as triglycerides. Examples of these fatty acids are given in table 3.1 Table 3.1 shows some common fatty acid and their formula Common

Source

Formula

IUPAC

Name Palmitic

Nomenclature Oil palm

CH3(CH2)14COOH

acid Stearic acid

Oleic acid

Hexadecanoic acid

Tallow

CH3(CH2)16COOH

Octadecanoic

(animal fat)

acid

Olive

Octadeca-9-

or CH3(CH2)CH=CH(CH2)7COOH

Peanut Oil Linoleic

Vegetable

acid

oil

enoic acid CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH Octadeca-9,12dienoic acid

Fats and oils are composed of the elements carbon, hydrogen, and oxygen in the form of glycerides or compounds of fatty acids and glycerol. The properties of fats will differ according to the properties of the fatty acids of which they are composed. The ratio of carbon and hydrogen to oxygen in the fat molecule, however, is much greater than that in a carbohydrate. The main distinction between fats and oils is whether they’re solid or liquid at room 36

temperature, and this, as we’ll soon see, is based on differences in the structures of the fatty acids they contain. Fats are solid at room temperature, usually of animal origin while oils are liquid at room temperature mainly of plant origin. 3.2.1 Sources of fats and oils There are several sources of fats and oils which may be of plant origin or animal origin as shown in the table below. Table 3.2 shows some common fats and oils, and their natural sources Fats or Oils

Natural Source

1

Groundnut oil

Groundnut

2

Palm oil

Palm

3

Coconut oil

Coconut

4

Cotton seed oil

Cotton

5

Soya bean oil

Soya bean

6

Castor oil

Castor seed

7

Palm kernel oil

Palm kernel

8

Sunflower oil

Sunflower

9

Tallow fat

Sheep and Cow

10

Lard fat

Pigs

11

Coco butter

Cocoa

12

Wool grease

Sheep

3.2.2 Structure of Fatty Acids The “tail” of a fatty acid is a long hydrocarbon chain, making it hydrophobic. The “head” of the molecule is a carboxyl group which is hydrophilic. Fatty acids are the main component of soap, where their tails are soluble in oily dirt and their heads are soluble in water to emulsify and wash away the oily dirt. However, when the head end is attached to glycerol to form a fat, that whole molecule is hydrophobic. 37

The terms saturated, mono-unsaturated, and poly-unsaturated refer to the number of hydrogen’s attached to the hydrocarbon tails of the fatty acids as compared to the number of double bonds between carbon atoms in the tail. Fats, which are mostly from animal sources, have all single bonds between the carbons in their fatty acid tails, thus all the carbons are also bonded to the maximum number of hydrogen’s possible. Since the fatty acids in these triglycerides contain the maximum possible amount of hydrogen, these would be called saturated fats. The 38

hydrocarbon chains in these fatty acids are, thus, fairly straight and can pack closely together, making these fats solid at room temperature. Oils, mostly from plant sources, have some double bonds between some of the carbons in the hydrocarbon tail, causing bends or “kinks” in the shape of the molecules. Because some of the carbons share double bonds, they’re not bonded to as much hydrogen as they could if they weren’t double bonded to each other. Therefore these oils are called unsaturated fats. Because of the kinks in the hydrocarbon tails, unsaturated fats can’t pack as closely together, making them liquid at room temperature. Many people have heard that the unsaturated fats are “healthier” than the saturated ones. The addition of hydrogen to unsaturated fats, thus converting oils into solid fats, is known as hydrogenation. The fats so produced are neutral in flavor, have a high enough smoking temperature to make them useful for frying, and have good shortening power. Some hydrogenated fats have been undesirably hard when refrigerated, because they were too highly hydrogenated. Today, because of the market demand for unsaturated fat products, a processing method is used in which all the oil or fat undergoes partial hydrogenation. This process increases the firmness of the glyceride without producing saturated fatty acids (selective hydrogenation). In selective hydrogenation the polyunsaturated fatty acids are changed to monounsaturated rather than saturated fatty acids. 3.2.3 Hydrogenated vegetable oil Unsaturated vegetable fats and oils can be transformed through partial or complete "hydrogenation" into fats and oils of higher melting point. The hydrogenation process involves "sparging" the oil at high temperature and pressure with hydrogen in the presence of a catalyst, typically a powdered nickel compound. As each carbon-carbon double-bond is chemically reduced to a single bond, two hydrogen atoms each form single bonds with the two carbon atoms. The elimination of double bonds by adding hydrogen atoms is called saturation; as the degree of saturation increases, the oil progresses toward being fully hydrogenated. An oil may be hydrogenated to increase resistance to rancidity (oxidation) or to change its physical characteristics. As the degree of saturation increases, the oil's viscosity and melting point increase. The use of hydrogenated oils in foods has never been completely satisfactory. Because the center arm of the triglyceride is shielded somewhat by the end fatty acids, most of the hydrogenation occurs on the end fatty acids, thus making the resulting fat more brittle. A margarine made from naturally more saturated oils will be more plastic (more "spreadable") than a margarine made from hydrogenated soy oil. While full hydrogenation produces largely saturated fatty acids, partial hydrogenation results in the transformation of unsaturated cis fatty acids to trans fatty 39

acids in the oil mixture due to the heat used in hydrogenation. Since the 1970s, partially hydrogenated oils and their trans fats have increasingly been viewed as unhealthy. Hydrogenated vegetable oil (as in shortening and commercial peanut butters where a solid consistency is sought) started out as “good” unsaturated oil. However, this commercial product has had all the double bonds artificially broken and hydrogen artificially added (in a chemistry lab-type setting) to turn it into saturated fat that bears no resemblance to the original oil from which it came (so it will be solid at room temperature). In unsaturated fatty acids, there are two ways the pieces of the hydrocarbon tail can be arranged around a C=C double bond. In cis bonds, the two pieces of the carbon chain on either side of the double bond are either both “up” or both “down,” such that both are on the same side of the molecule. In trans bonds, the two pieces of the molecule are on opposite sides of the double bond, that is, one “up” and one “down” across from each other. Naturally-occurring unsaturated vegetable oils have almost all cis bonds, but using oil for frying causes some of the cis bonds to convert to trans bonds. If oil is used only once like when you fry an egg, only a few of the bonds do this so it’s not too bad. However, if oil is constantly reused, like in fast food French fry machines, more and more of the cis bonds are changed to trans until significant numbers of fatty acids with trans bonds build up. The reason this is of concern is that fatty acids with trans bonds are carcinogenic, or cancer-causing. The levels of trans fatty acids in highly-processed, lipidcontaining products such as margarine are quite high, and I have heard that the government is considering requiring that the amounts of trans fatty acids in such products be listed on the labels.

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We need fats in our bodies and in our diet. Animals in general use fat for energy storage because fat stores 9 KCal/g of energy. Plants, which don’t move around, can afford to store food for energy in a less compact but more easily accessible form, so they use starch (a carbohydrate, NOT A LIPID) for energy storage. Carbohydrates and proteins store only 4 KCal/g of energy, so fat stores over twice as much energy/gram as fat. By the way, this is also related to the idea behind some of the high-carbohydrate weight loss diets. The human body burns carbohydrates and fats for fuel in a given proportion to each other. The theory behind these diets is that if they supply carbohydrates but not fats, then it is hoped that the fat needed to balance with the sugar will be taken from the dieter’s body stores. Fat is also is used in our bodies to a) cushion vital organs like the kidneys and b) serve as insulation, especially just beneath the skin. Most fats and oils need protection from air, heat and light. Fats and oils in partially filled containers keep longer if they are transferred to smaller containers in which there is little or no air space 3.2.4 Phospholipids Phospholipids are made from glycerol, two fatty acids, and (in place of the third fatty acid) a phosphate group with some other molecule attached to its other end. The hydrocarbon tails of the fatty acids are still hydrophobic, but the phosphate group end of the molecule is hydrophilic because of the oxygens with all of their pairs of unshared electrons. This means that phospholipids are soluble in both water and oil. An emulsifying agent is a substance which is soluble in both oil and water, thus enabling the two to mix. A “famous” phospholipid is lecithin which is found in egg yolk and soybeans. Egg yolk is mostly water but has a lot of lipids, especially cholesterol, which are needed by the developing chick. Lecithin is used to emulsify the lipids and hold them in the water as an emulsion. Lecithin is the basis of the classic emulsion known as mayonnaise.

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Our cell membranes are made mostly of phospholipids arranged in a double layer with the tails from both layers “inside” (facing toward each other) and the heads facing “out” (toward the watery environment) on both surfaces.

3.2.5 Steroids The general structure of cholesterol consists of two six-membered rings side-by-side and sharing one side in common, a third six-membered ring off the top corner of the right ring, and a fivemembered ring attached to the right side of that. The central core of this molecule, consisting of four fused rings, is shared by all steroids, including estrogen (estradiol), progesterone, corticosteroids such as cortisol (cortisone), aldosterone, testosterone, and Vitamin D. In the various types of steroids, various other groups/molecules are attached around the edges. Know how to draw the four rings that make up the central structure.

Cholesterol is not a “bad guy!” Our bodies make about 2 g of cholesterol per day, and that makes up about 85% of blood cholesterol, while only about 15% comes from dietary sources. Cholesterol is the precursor to our sex hormones and Vitamin D. Vitamin D is formed by the action of UV light in sunlight on cholesterol molecules that have “risen” to near the surface of the skin. At least one source I read suggested that people not shower immediately after being in the sun, but wait at least ½ hour for the new Vitamin D to be absorbed deeper into the skin. Our cell membranes contain a lot of cholesterol (in between the phospholipids) to help keep them 42

3.2.6 Lipoproteins Lipoproteins are clusters of proteins and lipids all tangled up together. These act as a means of lipoproteins distinguished by how compact/dense they are. LDL or low density lipoprotein is the “bad guy,” being associated with deposition of “cholesterol” on the walls of someone’s arteries. HDL or high density lipoprotein is the “good guy,” being associated with carrying “cholesterol” out of the blood system, and is more dense/more compact than LDL. 3.2.7 Uses of Fats and Oils 

As foodstuffs: most fats are consumed as food , together with carbohydrates, they provides source of energy for animals.

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In making soaps: Fats and oils serve as basic raw material for the production of soaps and detergent. Some of the commonly used are tallow, palm kernel, coconut oil, bleached palm oil, soya bean oil and olive oil.

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In making glycerol: glycerol is obtained as a by-product in the manufacture of soaps. It is used in the manufacture of creams, medicine etc.

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In making paints: Linseed oil serves as useful material in the production of paint.

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In making margarine: This is made by hardening of oils.

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In making candles: Tallow (animal fats) can be hydrolyzed to give products used in making candles

3.3 Conclusion Knowledge of fats and oil is necessary as well as knowing how to use them in food preparation and cooking. As industrial raw material, oils and fats are used in the production of soaps, skin products, candles, perfumes and other personal care and cosmetic products. Some oils are particularly suitable as drying oils, and are used in making paints and other wood treatment products. Dammar oil (a mixture of linseed oil and dammar resin), for example, is used almost exclusively in treating the hulls of wooden boats. Vegetable oils are increasingly being used in the electrical industry as insulators as vegetable oils are not toxic to the environment, biodegradable if spilled and have high flash and fire points. However, vegetable oils are less stable chemically, so they are generally used in systems where they are not exposed to oxygen. Lastly ,they play an important role in human nutrition because they are sources of energy and of the essential fatty acids in the diet. In addition, fat deposits in the body serve as insulation and provide protective cushions for the organs. 43

3.4 Summary In this unit; you have learned about fats and oils as natural occurring alkanoates obtained from fatty acid and trihydric alkanols. Also, you have learned the various sources of fats and oils with their properties. In addition, several uses of fats and oils were also mentioned.

3.5 Tutor – Marked Assignment 

State the differences between fats and oils

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Write the formula for stearic acid

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Name the elements tha can be found in fats and oils

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State the uses of fats and oils.

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What are lipoprotein?

3.6 Reference 1. Uppal, M.M; Bhatia, S.C (2008). Engineering Chemistry (Chemical Technology). Khanna publishers.7th ed. Pg 460-465. 2. Sienko, Michell J. and Robert A. Plane. (1966). Chemistry: Principles and Properties. McGraw-Hill Book Co., NY. (and other chemistry texts and handbooks) 3. http://en.wikipedia.org/wiki/vegetable_fats_and_oils 4. http:// en.wikipedia.org/wiki/cooking_oil 5. scifun.chem.wisc.edu/chemweek

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Unit 4

SOAPS AND DETERGENTS 4.0 Introduction In the last unit, properties and various classes of fats and oils were discussed. In unit 2, it was equally mention that they are organic raw material available for the industry. Thus, fats and oils serve as the basic raw materials for the production of soap. Consequently, their importance in the production of cleaning products cannot be over emphasized. Cleaning products play an essential role in our daily lives. By safely and effectively removing soils, germs and other contaminants, they help us to stay healthy, care for our homes and possessions, and make our surroundings more pleasant. Soaps and detergents are widely used in our society today, and we find it hard to imagine a time when people were kept sweet-smelling by the action of perfume rather than soap. However, the current widespread use of soap is only a very recent occurrence, despite the fact that it has been made for more than 2500 years. The first recorded manufacture of soap was in 600BC, when Pliny the Elder described its manufacture by the Phonecians from goats tallow and ash, and it was known among the British Celts and throughout the Roman Empire. However, these people used their soap medicinally, and it was not until the second century AD that it was used for cleaning, and not until the nineteenth century that it began to be commonly used in the Western world. Early this century the first synthetic detergents were manufactured, and these have now taken the place of soap for many applications. In this unit, the industrial production of soap and detergent, chemistry and their functioning properties shall be discussed. 4.1 Objectives At the of this unit, you should be able to:  Mention the raw materials for soap and detergent production  Outline the basics step involved in the production of soaps  State the basic components of soaps and detergents  Write equation for the reaction for the production of soaps and detergents  Differentiate between soaps and detergents  Mention the various manufacturing processes  Describe briefly the process of manufacturing soaps and detergents  Explain briefly the functioning ability of soaps detergents in relation to dirts 45

4.2 Soaps In chemistry, soap is a salt of a fatty acid. Soaps are mainly used as surfactants for washing, bathing, and cleaning, but they are also used in textile spinning and are important components of lubricants. Soaps for cleansing are obtained by treating vegetable or animal oils and fats with a strongly alkaline solution. Fats and oils are composed of triglycerides: three molecules of fatty acids attached to a single molecule of glycerol. The alkaline solution, often called lye, brings about a chemical reaction known as saponification. In saponification, the fats are first hydrolyzed into free fatty acids, which then combine with the alkali to form crude soap. Glycerol, often called glycerine, is liberated and is either left in or washed out and recovered as a useful byproduct according to the process employed. Soaps are key components of most lubricating greases, which are usually emulsions of calcium soap or lithium soaps and mineral oil. These calcium- and lithium-based greases are widely used. Many other metallic soaps are also useful, including those of aluminium, sodium, and mixtures of them. Such soaps are also used as thickeners to increase the viscosity of oils. In ancient times, lubricating greases were made by the addition of lime to olive oil.

Soaps are the product of the reaction between a fat and sodium hydroxide: fat + 3NaOH → glycerine + 3 soap Soaps are produced industrially in four basic steps. This article lists different steps because in the industrial processes described each of these is done over several process steps, but in principle it could be done in the four steps outlined here. Step 1 - Saponification A mixture of tallow (animal fat) and coconut oil is mixed with sodium hydroxide and heated. The soap produced is the salt of a long chain carboxylic acid. Step 2 - Glycerine removal Glycerine is more valuable than soap, so most of it is removed. Some is left in the soap to help make it soft and smooth. Soap is not very soluble in salt water, whereas glycerine is, so salt is added to the wet soap causing it to separate out into soap and glycerine in saltwater. Step 3 - Soap purification Any remaining sodium hydroxide is neutralized with a weak acid such as citric acid and two thirds of the remaining water removed. Step 4 - Finishing Additives such as preservatives, colour and perfume are added and mixed in with the soap and it is shaped into bars for sale. Detergents are similar in structure and function to soap, and for most uses they are more efficient than soap and so are more commonly used. In addition to the actual ’detergent’ molecule, detergents usually incorporate a variety of other ingredients that act as water softeners, freeflowing agents etc. 46

4.2.1 The Chemistry of Soap and Detergent Function All soaps and detergents contain a surfactant as their active ingredient. This is an ionic species consisting of a long, linear, non-polar ’tail’ with a cationic or anionic ’head’ and a counter ion. The tail is water insoluble and the head is water soluble - a difference in solubility which has two important implications. Firstly, this makes the surfactant molecule a wetting agent: the tails migrate to align themselves with the solid:water interface, lowering the surface tension at that point so that it penetrates the fabric better. Secondly, it allows the oily dirt particles to form an emulsion with the water: the tails of many surfactant molecules surround an oily dirt particle, forming a micelle with a drop of oil in the centre and the ionic heads of the surfactant molecules pointing outwards and hence keeping the micelle in the polar solution. Fats are isolated from plants and animals. The properties such as solubility relate to their chemical structures. Fats are heated with a strong base to convert them into soaps. The fat you use to make soap, reacts with potassium hydroxide to produce a potassium soap, the potassium salt of the fatty acid. One typical animal fat, stearol, reacts with KOH to form potassium stearate, a soap. Most naturally occuring fats produce a mixture of different salts of fatty acids when they are converted to soap.

The potassium soap formed from your fat is converted to a sodium soap by replacing the potassium ions with sodium ions. A large excess of sodium chloride supplies the sodium ion. You may also notice that the potassium soap is softer than the sodium soap. In addition there is a difference in the way the sodium and potassium soaps behave in water.

Both potassium and sodium soaps dissolve in water and are effective as cleaning agents. Each has a polar end to the molecule identified by the negative charge and an end that is primarily carbon and hydrogen. The polar end attracts polar water molecules. The other end, hydrocarbon 47

end, attracts oils and other water insoluble materials like fat or grease. Water is a polar solvent and dissolves polar and ionic molecules. Gasoline is nonpolar and dissolves nonpolar materials such as fat or oil. A way to remember this behavior is the simple axiom; "Like dissolves like."

The nonpolar ends of the molecule associate with the fat, grime or dirt which is also nonpolar, The polar or ionic end of the molecule attracts the water molecules. A spherical structure with the polar portions of the molecule on the surface and the nonpolar parts of the molecule in the center is attracted to the water and carries the non-water-soluble material away with it. This spherical shaped unit of soap and grime is a micelle. Magnesium and calcium salts of the same fatty acids that make up potassium and sodium soaps are not water soluble. When sodium or potassium soaps are put into water containing calcium and magnesium ions, the cloudyness, scum or curds consist of less soluble calcium and magnesium soaps. To achieve the same washing or cleaning action, more soap must be added.

There are other materials that also have cleaning capacity like soaps. The molecules of detergents also have polar and nonpolar ends. They clean like soaps except that their calcium and magnesium salts are generally more soluble in water than their soap counterparts. In recent years many different detergents have been introduced for use in cleaning. The conversion of one alkyl sulfate into a detergent is shown below. 48

4.2.2 The Soap Manufacturing Process These days, the industrial production of soap involves continuous processes, involving continuous addition of fat and removal of product. Smaller scale production involves the traditional batch processes. These have three variations: the cold process where the reaction takes place substantially at room temperature, the semi-boiled or hot process where the reaction takes place at near boiling point, and the fully boiled process where the reactants are boiled at least once and the glycerol recovered. The cold process and hot process (semi-boiled) are the simplest and typically used by small artisans and hobbyists producing hand made decorative soaps and similar. The glycerine remains in the soap and the reaction continues for many days after the soap is poured into moulds. In the hot process method also, the glycerine is left in but at the high temperature employed, the reaction is practically completed in the kettle, before the soap is poured into moulds. This process is simple and quick and is the one employed in small factories all over the world. Handmade soap from the cold process also differs from industrially made soap in that an excess of fat is used, beyond that which is used to consume the alkali (in a cold-pour process this excess fat called "superfatting"), and the glycerine left in acts as moisturizing agent. However it also makes the soap softer and less resistant to becoming "mushy" if left wet. Soap from the hot process also has left-over glycerine (as it is better to add too much oil and have left over fat, than to add too much lye and have left over lye) and the related pros and cons. Further addition of glycerine and processing of this soap produces glycerin soap. Superfatted soap, which contains excess fat, is more skin-friendly than one without extra fat, though, if too much fat is added, it can leave a "greasy" feel to their skin. Sometimes an emollient additive such as jojoba oil or shea butter is added "at trace" (in the cold process method, the point at which the saponification process is sufficiently advanced that the soap has begun to thicken) in the belief that nearly all the lye will be spent and it will escape saponification and remain intact, or in the case of hotprocess soap, after the initial oils have saponified, so that they remain unreacted in the finished soap. Superfatting can also be accomplished through a process known as "lye discount", whereby instead of adding extra fats, the soap maker uses less alkali than theoretically required. 4.2.2.1 Cold process Even in the cold soap making process some heat is usually required for the process. The temperature is usually raised sufficiently to ensure complete melting of the fat being used. The batch may be kept warm for some time after mixing to ensure that the alkali(hydroxide) is 49

completely used up. This soap is safe to use after approximately 12–48 hours, but is not at its peak quality for use for several weeks. Cold-process soapmaking requires exact measurements of lye and fat amounts and computing their ratio, using saponification charts to ensure that the finished product does not contain any excess hydroxide or too much free unreacted fat. Saponification charts should also be used in hot-processes, but are not necessary for the "fully boiled hot process" soaping. A cold-process soapmaker first looks up the saponification value of the fats being used on a saponification chart. This value is used to calculate the appropriate amount of lye. Excess unreacted lye in the soap will result in a very high pH and can burn or irritate skin. Not enough lye, a.nd the soap is greasy. Most soap makers formulate their recipes with a 4–10% deficit of lye so that all of the lye is converted and that excess fat is left for skin conditioning benefits. The lye is dissolved in water. Then oils are heated, or melted if they are solid at room temperature. Once the oils are liquified and the lye is fully dissolved in water they are combined. This lye-fat mixture is mixed until the two phases (oils and water) are fully emulsified. Emulsification is most easily identified visually when the soap exhibits some level of "trace", which is the thickening of the mixture. (Modern-day amateur soapmakers often use a stick blender to speed this process). There are varying levels of trace. Depending on how additives will affect trace, they may be added at light trace, medium trace or heavy trace. After much stirring, the mixture turns to the consistency of a thin pudding. "Trace" corresponds roughly to viscosity. Essential oils and fragrance oils can be added with the initial soaping oils, but solid additives such as botanicals, herbs, oatmeal, or other additives are most commonly added at light trace, just as the mixture starts to thicken. The batch is then poured into molds, kept warm with towels or blankets, and left to continue saponification for 12 to 48 hours. (Milk soaps or other soaps with sugars added are the exception. They typically do not require insulation as the presence of sugar increases the speed of the reaction and thus the production of heat.) During this time, it is normal for the soap to go through a "gel phase" where the opaque soap will turn somewhat transparent for several hours, before once again turning opaque. After the insulation period, the soap is firm enough to be removed from the mold and cut into bars. At this time, it is safe to use the soap, since saponification is essentially complete. However, cold-process soaps are typically cured and hardened on a drying rack for 2–6 weeks before use. During this cure period, trace amounts of residual lye is consumed by saponification and excess water evaporates. 4.2.2.2 Hot processes Hot processed soaps are created by encouraging the saponification reaction by adding heat to the reaction. This speeds the reaction. Unlike cold-processed soap, in hot process soaping the oils are completely saponified by the end of the handling period, whereas with cold pour soap the bulk of the saponification happens after the oils and lye solution emulsification is poured into molds. 50

In the hot-process, the hydroxide and the fat are heated and mixed together 80–100°C, a little below boiling point, until saponification is complete, which, before modern scientific equipment, the soapmaker determined by taste (the sharp, distinctive taste of the hydroxide disappears after it is saponified) or by eye; the experienced eye can tell when gel stage and full saponification has occurred. Beginners can find this information through research, and classes. It is highly recommended not to "taste" soap for readiness. Sodium and potassium hydroxides when not saponified, are a highly caustic materials. An advantage of the fully boiled hot process in soap making is that the exact amount of hydroxide required need not be known with great accuracy. They originated when the purity of the alkali hydroxides were unreliable, as these processes can use even naturally found alkalis such as wood ashes and potash deposits. In the fully boiled process, the mix is actually boiled (100C+) and after saponification has occurred, the "neat soap" is precipitated from the solution by adding common salt, and the excess liquid drained off. This excess liquid carries away with it much of the impurities and colour compounds in the fat, to leave a purer, whiter soap, and with practically all the glycerine removed. The hot, soft soap is then pumped into a mould. The spent hydroxide solution is processed for recovery of glycerine. 4.2.2.3 Ancilliary Processes Glycerine recovery As has already been stated, glycerine is more valuable than the soap itself, and so as much of it as possible is extracted from the soap. This is done in a three step process. Step 1 - Soap removal The spent lye contains a small quantity of dissolved soap which must be removed before the evaporation process. This is done by treating the spent lye with ferrous chloride. However, if any hydroxide ions remain the ferrous ions react with them instead, so these are first removed with hydrochloric acid: HCl + NaOH → NaCl + H2O The ferrous chloride is then added. This reacts with the soap to form an insoluble ferrous soap: FeCl2 + 2RCOONa → 2NaCl + (RCOO)2Fe This precipitate is filtered out and then any excess ferrous chloride removed with caustic: 2NaOH + FeCl2 → Fe(OH)2 (s) + 2NaCl This is filtered out, leaving a soap-free lye solution. Step 2 - Salt removal Water is removed from the lye in a vacuum evaporator, causing the salt to crystallise out as the solution becomes supersaturated. This is removed in a centrifuge, dissolved in hot water and stored for use as fresh lye. When the glycerine content of the solution reaches 80 - 85% it is pumped to the crude settling tank where more salt separates out. XI-Detergents-A-Soap-11

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Step 3 - Glycerine purification A small amount of caustic soda is added to the crude glycerine and the solution then distilled under vacuum in a heated still. Two fractions are taken off - one of pure glycerine and one of glycerine and water. The glycerine thus extracted is bleached with carbon black then transferred to drums for sale, while the water/glycerine fraction is mixed with the incoming spent lye and repeats the treatment cycle.

4.2.2.4 Purification and finishing In the fully boiled process on factory scale, the soap is further purified to remove any excess sodium hydroxide, glycerol, and other impurities, colour compounds etc. These components are removed by boiling the crude soap curds in water and then precipitating the soap with salt. At this stage the soap still contains too much water, which has to be removed. This was traditionally done on a chill rolls, which produced the soap flakes commonly used in the 1940s and 1950s. This process was superseded by spray dryers and then by vacuum dryers. The dry soap (approximately 6–12% moisture) is then compacted into small pellets or noodles. These pellets/noodles are now ready for soap finishing, the process of converting raw soap pellets into a saleable product, usually bars. Soap pellets are combined with fragrances and other materials and blended to homogeneity in an amalgamator (mixer). The mass is then discharged from the mixer into a refiner, which, by means of an auger, forces the soap through a fine wire screen. From the refiner, the soap passes over a roller mill (French milling or hard milling) in a manner similar to calendaring paper or plastic or to making chocolate liquor. The soap is then passed through one or more additional refiners to further plasticize the soap mass. Immediately before extrusion, the mass is passed through a vacuum chamber to remove any trapped air. It is then extruded into a long log or blank, cut to convenient lengths, passed through a metal detector, and then stamped into shape in refrigerated tools. The pressed bars are packaged in many ways. Sand or pumice may be added to produce a scouring soap. The scouring agents serve to remove dead skin cells from the surface being cleaned. This process is called exfoliation. Many newer materials that are effective but do not have the sharp edges and poor particle size distribution of pumice are used for exfoliating soaps. Nanoscopic metals are commonly added to certain soaps specifically for both coloration and anti-bacterial properties. Titanium powder is commonly used in extreme "white" soaps for these purposes; nickel, aluminium, and silver are less commonly used. These metals exhibit an electron-robbing behavior when in contact with bacteria, stripping electrons from the organism's surface and thereby disrupting their functioning and killing them. Because some of the metal is left behind on the skin and in the pores, the benefit can also extend beyond the actual time of 52

washing, helping reduce bacterial contamination and reducing potential odors from bacteria on the skin surface. 4.2.2.5 Moulds Many commercially available soap moulds are made of silicone or various types of plastic, although many soap making hobbyists may use cardboard boxes lined with a plastic film. Soaps can be made in long bars that are cut into individual portions, or cast into individual moulds.

4.3 THE DETERGENT MANUFACTURING PROCESS Detergents use a synthetic surfactant in place of the metal fatty acid salts used in soaps. They are made both in powder and liquid form, and sold as laundry powders, hard surface cleansers, dish washing liquids, fabric conditioners etc. Most detergents have soap in their mixture of ingredients, but it usually functions more as a foam depressant than as a surfactant.

4.3.1 Preparation Of A Detergent A synthetic detergent, a sodium alkyl sulfate called sodium dodecylsulfate, will be prepared by reacting dodecyl alcohol (dodecanol) with sulfuric acid.dodecanol sulfuric acid dodecylsulfate The resulting dodecylsulfate is converted to the sodium salt by a reaction with sodium hydroxide. dodecylsulfate sodium dodecylsulfate Materials Needed Dodecanol (dodecyl alcohol), C12H25OH Sulfuric acid, H2SO4, concentrated Sodium hydroxide, NaOH, 6M Phenolphthalein solution, 1% Sodium chloride, NaCl, technical grade Erlenmeyer flask, 125-mL Beakers, 400-mL, 150-mL, 100-mL Graduated cylinders, 10-mL, 25-mL, 125-mL Funnel, Spatula, Stirring rod, Cheesecloth, Watch glass and Scissors Procedure Place 5 ml of dodecanol into a 100-mL beaker. Measure 2 mL of concentrated sulfuric acid, H2SO4, in a 10-mL graduated cylinder. With stirring, slowly add the 2 mL of concentrated sulfuric acid to the dodecanol in the beaker. Continue to stir for 1 minute after addition of the sulfuric acid is complete. Let the mixture stand for 10 minutes. Fill a 250-mL beaker one-third full of ice, add about 10 g of sodium chloride, NaCl, and mix thoroughly. Add water to bring the total volume of the mixture to 75 ml. Mix 5 ml of 6 M sodium hydroxide with 10 mL of water in a small beaker. Mix well, then add 4 drops of phenolphthalein indicator. The pink color of the phenolphthalein may begin to fade in the strongly basic solution. Prepare a mixture of about 25 mL of ice water. 53

After the 10 minutes, carefully pour the sodium hydroxide solution into the dodecanol-sulfuric acid mixture. Stir until the pink color disappears. A large amount of solid detergent should form. Pour the detergent mixture into the ice-salt bath. Stir to break up large lumps of detergent. Filter the precipitated detergent mixture through 2-3 layers of cheesecloth in a funnel mounted on a ringstand. Wash the collected detergent twice with 10 ml portions of ice-cold water. Remove the cheesecloth from the funnel, squeeze excess water from the solid detergent, and save the detergent for use.

4.4 ENVIRONMENTAL IMPLICATIONS Soap is designed as a product to be used once then flushed down the drain, so as expected the environmental implications of its manufacture are not nearly so great as many other chemical processes. There are two main areas of concern: the safe transport and containment of the raw materials, and the minimisation of losses during manufacture. The three main components of soap by both cost and volume are oils, caustic and perfumes. Oils and perfume are immiscible in water and if spilled create havoc, although the oils do solidify at room temperature. Transport of these products is by trained carriers, and the systems for pumping from the truck to storage tanks are carefully designed. Perfumes are bought in lined steel drums which are quite robust, and flammable perfumes are not used in soaps. All storage tanks are surrounded by bunds to catch the contents of a tank should it rupture or a valve fail. When the storage system is designed, all the safety features (such as access to tank and valves) are designed in, as well as procedures to deal with the product should it end up in the bunded area. Within the plant, all the process areas are also bunded, and the trade waste from there piped to an interception tank before draining to the council’s trade waste system. The contents of the interception tank are continuously monitored for acidity or alkalinity, and are designed to settle out excess solids or light phase chemicals. If a spill is detected in the plant itself, apportion of the interception tank can be isolated off and the effects of the spill neutralized before the waste is dumped. In most cases, however, potential problems are identified and stopped before they happen. Often an off-spec product can be reprocessed and blended rather than dumped, and even washout water can be reprocessed to minimised the discharges from the plant.Finally, the manufacturing process itself is closely monitored to ensure any losses are kept to a minimum. Continuous measurements of key properties such as electrolyte levels and moisture both ensure that the final product is being made to spec, and ensures the manufacturing process is working as it was designed to. Hence the losses in the plant will indirectly be minimised because the process itself is being monitored. 4.4.1 Synthetic detergent biodegradability There has recently been a strong move away from the environmentally hazardous biologically stable detergents used in the past to biodegradable ones. The sulphonic acid and nonionic detergents used in New Zealand to produce both liquid and powder detergents are fully biodegradable and comply with the relevant Australian standard. The sulphonic acid is made from a highly linear alkylbenzene, mainly dodecylbenzene, and the nonionics are ethoxylated long chain alcohols. The sodium lauryl ether sulphates also used in liquid detergents and shampoos are highly biodegradable, being made from either natural or synthetic linear C12 - C15 alcohols. 54

4.4.2 Detergent powder Detergent powder manufacture has some specific environmental issues associated with it that are not present in other areas of the industry. These are dust control and volatile organic emissions. Dust present during delivery and transfer of bulk powdered detergent (and powdered raw materials) is a potential problem. Dry and wet cyclones are used to filter outmost of the dust, and all emissions are monitored. If the dust level in these does exceed acceptable limits, appropriate remedial action is taken. Dust levels in emissions must be kept below 50 mg m-3. The spray drying tower also releases volatile organics. These emissions are minimised by having tight specifications on what can be added as primary detergent active material. Any potentially hazardous material is added with the secondary actives after the tower so that it is not heated. Spot checks are done on the total hydrocarbon content of the exhaust gases using a flame ionisation detector. 4.5 Role Of The Laboratory The laboratory monitors the formulation and specification of products from raw material to finished goods. Many soaps are formulated locally, and the laboratory tests a range of formulations for stability and manufacturing practicality. The trial formulations are aged in a warm oven to simulate a couple of years of shelf life, then checked for perfume loss or alteration, base odour, colour stability and any general rancidity. Formulations are also constantly checked for cost effectiveness, and soaps are frequently reformulated for cost and supplier considerations. When a new formula has been agreed the laboratory will lay down the specifications that the finished soap and its intermediary stages must meet. These could be colour, odour, moisture or electrolyte concentrations, or the concentrations of impurities or additives. These specifications are also constantly being revised as the production equipment is improved, or consumer demands change. The laboratory lays down all the specifications for raw materials to be purchased against. These specifications become the basis for the supplier to quote against. The materials are constantly tested against these specifications, either on a shipment basis or supplier’s batch size. In some cases the manufacturing plant is inspected and approved, and if the supplier can validate their process then the need for many routine or expensive tests can be reduced or eliminated. In most cases quality testing is performed at the process, by the process operators. The laboratory hold samples of every batch of finished goods for twelve months, so that if there are any consumer complaints, an original sample can be tested against the defect sample to determine the cause of the complaint. 4.6 Conclusion Soaps and detergents are cleaning ingredients that are able to remove oil particles from surfaces because of their unique chemical properties. Soaps are created by the chemical reaction of a fatty acid with an alkali metal hydroxide. In a chemical sense, soap is a salt made up of a carboxylic acid and an alkali like sodium of potassium. Soaps are a specific type of the more general category of compounds called detergents. The cleaning action of soaps and detergents is a result of their ability to surround oil particles on a surface and disperse it in water. Bar soap has been used for centuries and continues to be an important product for bathing and cleaning. It is also a 55

mild antiseptic and ingestible antidote for certain poisons. Soap and cleanliness are inseparable, and cleansing, be it personal hygiene or laundering, is part of human history. Stringent guidelines with regard to the cleanliness of holy sites are a part of all the major religions, and the sanctification of the state of cleanliness as well as its signification of purity of body and soul are recurrent themes in their liturgies. 4.7 Summary You have learned in this unit the basic methods of making soaps and detergents. Also, you have learned that all soaps and detergents contain a surfactant as their active ingredient. This is an ionic species consisting of a long, linear, non-polar ’tail’ with a cationic or anionic ’head’ and a counter ion. The chemistry of soap and detergent in the removal of dirt’s and oily materials from textile were equally discussed. The difference between soap and detergents especially in their raw material and mode of preparation were discussed. Lastly, the environmental implication of the non biodegradable substance in detergent were mentioned. 4.8 Tutor –Marked Assignment       

What is soap? Differentiate between soap and detergent Write equation only to show the production of soap and detergent Lists the basic steps involved in the production of soap What is saponification? Lists the raw material needed for soap production Lists the raw material that is required in laboratory preparation of detergent.

4.9 References 1. http://en.wikipedia.org/wiki/detergent 2. http://science.csustan.edu/hny/chem1002/soapexp.htm 3. http://www.citycollegiate.com/industry2.htm 4. http://www.detergentsandsoaps.com/soap_detergent.html

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Unit 5 SUGAR 5.0 Introduction Sugar is a term for a class of edible crystalline carbohydrates, mainly sucrose, lactose, and fructose, characterized by a sweet flavor. In food, sugar almost exclusively refers to sucrose, which primarily comes from sugar cane and sugar beet. Other sugars are used in industrial food preparation, but are usually known by more specific names—glucose, fructose or fruit sugar, high fructose corn syrup, etc. Sugar forms a major element in confectionery and desserts. Cooks use it for sweetening—its fructose component, which has almost double the sweetness of glucose, makes sucrose distinctively sweet in comparison to other carbohydrate foods.[7] It can also act as a food preservative when used in sufficient concentrations. Sucrose is important to the structure of many foods, including biscuits and cookies, cakes and pies, candy, and ice cream and sorbets. It is a common ingredient in many processed and so-called "junk foods." 5.1 Objectives By the end of this unit, you should be able to  Describe what sugar is  State the different types of sugar  Outline the production process Historically Sugar, because of its simpler chemical structure, was once assumed (without scientific research) to raise blood glucose levels more quickly than starch, but results from more than twenty studies demonstrate that sugar and starch cause blood glucose to rise at similar rates. This finding showed that controlling all carbohydrates is necessary for controlling blood glucose levels in diabetics, the idea behind carbohydrate counting. Some experts believe that eating excessive amounts of sugar does not increase the risk of diabetes, although the extra calories from consuming large amounts of sugar can lead to obesity, which may increase the risk of diabetes. However, a 2010 meta-analysis of eleven studies involving 310,819 participants and 15,043 cases of type 2 diabetes found that "SSBs [sugar-sweetened beverages] may increase the risk of [metabolic syndrome] and type 2 diabetes not only through obesity but also by increasing dietary glycemic load, leading to insulin resistance, β-cell dysfunction, and inflammation." In regard to contributions to tooth decay, the role of starches is disputed. Lower rates of tooth decay have been seen in individuals with hereditary fructose intolerance. Sugar has been produced in the Indian subcontinent since ancient times. It was not plentiful or cheap in early times—honey was more often used for sweetening in most parts of the world. 57

Originally, people chewed sugarcane raw to extract its sweetness. Sugarcane was a native of tropical South Asia and Southeast Asia. Different species likely originated in different locations with S. barberi originating in India and S. edule and S. officinarum coming from New Guinea. Sugar remained relatively unimportant until the Indians discovered methods of turning sugarcane juice into granulated crystals that were easier to store and to transport. Crystallized sugar was discovered by the time of the Imperial Guptas, around 5th century AD. Indian sailors, consumers of clarified butter and sugar, carried sugar by various trade routes. Traveling Buddhist monks brought sugar crystallization methods to China. During the reign of Harsha (r. 606–647) in North India, Indian envoys in Tang China taught sugarcane cultivation methods after Emperor Taizong of Tang (r. 626–649) made his interest in sugar known, and China soon established its first sugarcane cultivation in the seventh century. Chinese documents confirm at least two missions to India, initiated in 647 AD, for obtaining technology for sugar-refining. In South Asia, the Middle East and China, sugar became a staple of cooking and desserts. During the Muslim Agricultural Revolution, Arab entrepreneurs adopted sugar production techniques from India and then refined and transformed them into a large-scale industry. Arabs set up the first cane sugar mills, refineries, factories and plantations. The Arabs and Berbers spread the cultivation of sugar throughout the Arab Empire and across much of the Old World, including Western Europe after they conquered the Iberian Peninsula in the eighth century AD. Ponting traces the spread of the cultivation of sugarcane from its introduction into Mesopotamia, then the Levant and the islands of the eastern Mediterranean, especially Cyprus, by the 10th century. He also notes that it spread along the coast of East Africa to reach Zanzibar. Crusaders brought sugar home with them to Europe after their campaigns in the Holy Land, where they encountered caravans carrying "sweet salt". Early in the 12th century, Venice acquired some villages near Tyre and set up estates to produce sugar for export to Europe, where it supplemented honey as the only other available sweetener. Crusade chronicler William of Tyre, writing in the late 12th century, described sugar as "very necessary for the use and health of mankind". In August 1492 Christopher Columbus stopped at La Gomera in the Canary Islands, for wine and water, intending to stay only four days. He became romantically involved with the Governor of the island, Beatriz de Bobadilla Ossorio, and stayed a month. When he finally sailed she gave him cuttings of sugarcane, which became the first to reach the New World. In 1792, sugar rose to a high price in Great Britain. The East India Company was called upon to help lower the price of sugar. Lieutenant J. Paterson, of the Bengal establishment, reported that sugar-cane could be cultivated in British India with many advantages, and at less expense than in the West Indies. As a result, a number of sugar factories were established in Bihar in British India. More recently it is manufactured in very large quantities in many countries, largely from sugar cane and sugar beet. In processed foods it has increasingly been supplanted by corn syrup. 58

5.2 What is Sugar? Sugar is a carbohydrate. Sugar is a source of energy in the body and is a structural component of the cells. For example, d-ribose, a form of sugar is a building block of adenosine triphosphate (ATP), a nucleotide produced by the body for energy release. Most people recognize sugar as a white crystalline substance used as a sweetener in food and drink. However sugar is a 'loose term' and refers to a collection of different types of carbohydrates - not just white refined sugar so prevalent in the western diet. 5.2.1There are two main categories of sugar: simple and complex. i) Simple Sugars Simple sugars are a basic form of carbohydrate. 'Simple' refers to the sugar molecules structural formation. Simple sugars belong to one of two categories: monosaccharides and disaccharides. Saccharides are a group of carbohydrates which include starches and sugars. Examples of monosaccharides include:    

ribose glucose fructose galactose

Sources of simple sugars include:   

fruit milk hop - a plant and ingredient in beer

ii) Complex Sugars (Complex Carbohydrates) By contrast and by name, complex sugars are more 'complex' in their structure compared to simple sugars. Complex sugars contain three or more units of sugar. 59

As sugar is a carbohydrate, complex sugars are often referred to as complex carbohydrates, although this term encompasses other items including starches.. The are two types of complex carbohydrates: assimilable polysaccharides and non-assimilable polysaccharides. a) Assimilable Polysaccharides If a complex carbohydrate is assimilable it can be readily absorbed by the body and incorporated into body tissue. Examples of assimilable complex carbohydrates include starch and amylose. Sources of Complex Carbohydrates (Assimilable Polysaccharies) include:   

potatoes pasta rice

b) Non-assimilable Polysaccharides These complex carbohydrates are not readily absorbed by the body. Examples of non-assimilable polysaccharides include cellulose, gums and pectins. Sources of Complex Carbohydrates (Non-Assimilable Polysaccharies) include:   

seeds pulses green vegetables

5.2.2 Simple & Complex Sugar Sugars & The Glycemic Index The glycemic index is a measure of scale which ranks the effect a carbohydrate has on raising blood sugar levels after eating. In general, simple sugars have higher glycemic index (GI) values giving a more rapid rise in blood sugar levels. Complex carbohydrates tend to have lower GI values and raise blood sugar to a lower level

5.2 Popular The term sugar usually refers to sucrose, which is also called "table sugar" or "saccharose." Sucrose is a white crystalline disaccharide. It is often obtained from sugar cane or sugar beet. Sucrose is the most popular of the various sugars for flavoring, as well as properties (such as mouthfeel, preservation, and texture) of beverages and food. 60

(The saccharides is a large family with the general formula CnH2nOn. The simplest of the sugars is glucose, C6H12O6, although its physical chemistry is not that simple because it occurs in two distinct forms which affect some of its properties. Sucrose, C12H22O11, is a disaccharide, a condensation molecule made up of two glucose molecules [less a water molecule to make the chemistry work]. The process whereby plants make sugars is photosynthesis. The plant takes in carbon dioxide from the air though pores in its leaves and absorbs water through its roots. These are combined to make sugar using energy from the sun and with the help of a substance called chlorophyll. Chlorophyll is green which allows it to absorb the sun's energy more readily and which, of course, gives the plants' leaves their green colour. The reaction of photosynthesis can be written as the following chemical equation when sucrose is being made: 12 CO2 + 11 H2 O = C12 H22 O11 + 12 O2 carbon dioxide + water = sucrose + oxygen This shows that oxygen is given off during the process of photosynthesis. Historically, sugar was only produced from sugar cane and then only in relatively small quantities. This resulted in it being considered a great luxury, particularly in Europe where cane could not be grown. The history of man and sugar is a subject in its own right but suffice to say that, even today, it isn't easy to ship food quality sugar across the world so a high proportion of cane sugar is made in two stages. Raw sugar is made where the sugar cane grows and white sugar is made from the raw sugar in the country where it is needed. Beet sugar is easier to purify and most is grown where it is needed so white sugar is made in only one stage.) 5.3 Chemical "Sugar" can also be used to refer to water-soluble crystalline carbohydrates with varying sweetness. Sugars include monosaccharides (e.g., glucose, fructose, galactose), disaccharides (e.g., sucrose, lactose, maltose), trisaccharides, and oligosaccharides, in contrast to complex carbohydrates such as polysaccharides. Corn syrup, dextrose, crystalline fructose, and maltose, for example, are used in manufacturing and preparing food. Different culinary sugars have different densities due to differences in particle size and inclusion of moisture. Bulk density    

Dextrose sugar 0.62 g/mL Granulated sugar 0.70 g/mL Powdered sugar 0.56 g/mL Beet sugar 0.80 g/mL

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5.4 Purity standards The International Commission for Uniform Methods of Sugar Analysis sets standards for the measurement of the purity of refined sugar, known as ICUMSA numbers; lower numbers indicate a higher level of purity in the refined sugar. Chemistry

Sucrose: a disaccharide of glucose (left) and fructose (right), important molecules in the body. Scientifically, sugar loosely refers to a number of carbohydrates, such as monosaccharides, disaccharides, or oligosaccharides. Monosaccharides are also called "simple sugars," the most important being glucose. Almost all sugars have the formula CnH2nOn (n is between 3 and 7). Glucose has the molecular formula C6H12O6. The names of typical sugars end with "-ose," as in "glucose", "dextrose", and "fructose". Sometimes such words may also refer to any types of carbohydrates soluble in water. The acyclic mono- and disaccharides contain either aldehyde groups or ketone groups. These carbon-oxygen double bonds (C=O) are the reactive centers. All saccharides with more than one ring in their structure result from two or more monosaccharides joined by glycosidic bonds with the resultant loss of a molecule of water (H2O) per bond. Monosaccharides in a closed-chain form can form glycosidic bonds with other monosaccharides, creating disaccharides (such as sucrose) and polysaccharides (such as starch). Enzymes must hydrolyse or otherwise break these glycosidic bonds before such compounds become metabolised. After digestion and absorption. the principal monosaccharides present in the blood and internal tissues include glucose, fructose, and galactose. Many pentoses and hexoses can form ring structures. In these closed-chain forms, the aldehyde or ketone group remains unfree, so many of the reactions typical of these groups cannot occur. Glucose in solution exists mostly in the ring form at equilibrium, with less than 0.1% of the molecules in the open-chain form. 5.5 Natural polymers of sugars Biopolymers of sugars are common in nature. Through photosynthesis plants produce glucose, which has the formula C6H12O6, and convert it for storage as an energy reserve in the form of other carbohydrates such as starch, or (as in cane and beet) as sucrose (table sugar). Sucrose has the chemical formula C12H22O11. Starch, consisting of two different polymers of glucose, is a readily degradable chemical energy stored by cells, convertible to other types of energy. 62

Cellulose is a polymer of glucose used by plants as structural component. DNA and RNA are built up of the sugars ribose and deoxyribose. The sugar in DNA is deoxyribose, and has the formula C5H10O4.

5.6 Types of Sugar The process of extracting and purifying sugars from sugar cane and sugar beet allows for the production of a large variety of sugars. Sugars may differ in colour, flavour, sweetness and crystal size. Each of these characteristics allows sugar to perform a variety of functions in food products, in addition to providing a sweet taste. Some types of sugar are listed below. Brown sugar Burnt Sugar Caramelized Sugar Caster (Castor) Sugar Coarse Sugar Confectioner’s Sugar Demerara-style Sugar Fondant Sugar Fruit Sugar Golden Syrup Golden Yellow Sugar

Granulated Sugar Icing Sugar Liquid Invert Sugar Liquid Sugar Molasses Muscovado Sugar Organic Sugar Pearl Sugar Plantation ‘Raw’ Sugar Powdered Sugar

Raw Sugar Refined Sugar syrup Refiner’s Syrup Sanding Sugar Soft Sugar Sugar Superfine Sugar Table Sugar Turbinado – style Sugar White sugar

5.7 Conclusion Sugar is a class of edible crystalline carbohydrates, mainly sucrose, lactose, and fructose, characterized by a sweet flavor. Sucrose in its refined form primarily comes from sugar cane and sugar beet. It and the other sugars are present in natural and refined forms in many foods, and the refined forms are also added to many food preparations. In food, "sugars" refer to all monosaccharides and disaccharides present in food, but excludes polyols, while in its singular form, "sugar" normally refers to sucrose. The other sugars are usually known by more specific names — glucose, fructose or fruit sugar, high fructose corn syrup, etc.

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5.8 Summary You have learned in this unit that simple sugars are basic form of carbohydrate. 'Simple' refers to the sugar molecules structural formation. "Sugar" can also be used to refer to water-soluble crystalline carbohydrates with varying sweetness. It include monosaccharides (e.g., glucose, fructose, galactose), disaccharides (e.g., sucrose, lactose, maltose), trisaccharides, and oligosaccharides, in contrast to complex carbohydrates such as polysaccharides. Corn syrup, dextrose, crystalline fructose, and maltose, for example, are used in manufacturing and preparing food. Sugars may differ in colour, flavour, sweetness and crystal size. Each of these characteristics allows sugar to perform a variety of functions in food products, in addition to providing a sweet taste. 5.9 Tutor- Marked Assignments   

What is Sugar? Give examples of simple sugar and complex sugar Differentiate between assimilable polysaccharides and non-assimilable polysaccharides.

5.10. References 1. http://en.wikipedia.org/wiki/sugar 2. www.sugar.org 3. www.thedailygreen.com

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Unit 6 VARNISHES 6.0 Introduction Historically, early varnishes were developed by mixing resin, like pine sap, with a solvent and applying them with a brush to get the golden and hardened effect we see in today's varnishes. The ancient Egyptians were acquainted with the art of varnishing, but its origin appears to be far east of there in India, China and Japan, where the practice of lacquer work, a species of varnish application, was known at a very early date. It has been claimed that Japan was acquainted with the art of lacquering by 500 or 600 B.C.E., but the majority of authorities place its first usage there to the 3rd century of our era, as an art acquired from their neighbors the Koreans. The natives of China and India probably knew the art much earlier than the Japanese. Varnish and lacquer work are, however, generally treated in the arts as separate and distinct. Varnish is a transparent, hard, protective finish or film primarily used in wood finishing but also for other materials. After being applied, the film-forming substances in varnishes either harden directly, as soon as the solvent has fully evaporated, or harden after evaporation of the solvent through certain curing processes, primarily chemical reaction between oils and oxygen from the air (autoxidation) and chemical reactions between components of the varnish. Resin varnishes "dry" by evaporation of the solvent and harden almost immediately upon drying. Acrylic and waterborne varnishes "dry" upon evaporation of the water but experience an extended curing period. Oil, polyurethane, and epoxy varnishes remain liquid even after evaporation of the solvent but quickly begin to cure, undergoing successive stages from liquid or syrupy, to tacky or sticky, to dry gummy, to "dry to the touch", to hard. Environmental factors such as heat and humidity play a very large role in the drying and curing times of varnishes. In classic varnish the cure rate depends on the type of oil used and, to some extent, on the ratio of oil to resin. The drying and curing time of all varnishes may be sped up by exposure to an energy source such as sunlight, ultraviolet light, or heat. Many varnishes rely on organic solvents, or on organic oils or resins for their binder; these are highly flammable in their liquid state. All drying oils, certain alkyds, and many single-component polyurethanes produce heat during the curing process. Therefore, oil-soaked rags and paper can smolder or ignite hours after application if they are bunched or piled together, or, for example, placed in a container where the heat cannot dissipate.

6.1 Objectives At the end of this unit, you should be able to:    

Describe what varnishes are State the various components of a varnish with example State the two types of varnishes Give examples of natural and synthetic resins available for varnish production. 65

  

Differentiate varnish from paint Described the application process of varnish Give examples of varnishes

6.2 Varnish A varnish is a colloidal dispersion or solution of synthetic or natural resin in oil,or in thinner or in oil and thinner both. When it is applied on a surface, it gives a transparent tack –free film.The film dries up by evaporation, oxidation and polymerization of portions of its constituents. If only thinner is used for dissolving the resin, then the film dries up by evaporation only. However, if oil is also present, the film dries up due to the oxidation and polymerization of drying oil and evaporation of thinner. Varnish has little or no colour, is transparent, and has no added pigment, as opposed to paints or wood stains, which contain pigment and generally range from opaque to translucent. Varnishes are also applied over wood stains as a final step to achieve a film for gloss and protection. Some products are marketed as a combined stain and varnish. 6.3 Components of varnishes The following are the various raw materials used in the manufacture of varnish. 6.3.1 Film- Forming Materials: These are of two types, oil and resins. The purpose and function of film-forming materials is that they form a protective film. They also serve as binders for pigments when the solvents are evaporated and the varnish oil is dried.

(i) Drying oil: There are many different types of drying oil, including linseed oil, tung oil, and walnut oil. Other oils used are dehydrated castor oil , castor oil, castor oil, fish oil, soya oil, cotton seed oil, and coconut oil. These contain high levels of polyunsaturated fatty acids.

(ii) Resins: These may be natural or synthetics. Natural resins that are used in varnishes include shellac, amber, kauri gum, dammar, copal, rosin (pine resin), sandarac, balsam,manila,elemi etc. Synthetic resins are phenol aldehyde (oil soluble) alkyde resin, mannitol ester, limed rosin, coumarone,indene, melamine, and urea formaldehyde, chlolrinated rubber, diphenyl acrylates, vinyl resins etc. .In the 1900s in Canada, resins from local trees were used to finish pianos. As a result these now antique pianos are considered difficult to refinish. However, shellac can be used over the existing resins provided sufficient time is allowed for thin coats to cure. Thus the original finish can be returned to its original lustre while preserving the colour and age related crackle.

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6.3.2 Thinners or solvent Traditionally, natural (organic) turpentine was used as the thinner or solvent, but has been replaced by several mineral based turpentine substitutes such as white spirit or "paint thinner", also known as "mineral spirit". Other solvents used include kerosene, dipentene, naphthas ( aliphatic), naphthas (aromatic), xylol, toluol, alcohols. etc. Their function is to dissolve and control viscosity of film forming materials. 6 .3.3 Driers. They are added to increase the rate of drying or hardening of varnish film. Driers added are cobalt, manganese, lead, zinc naphthenates, rosinates, linoleates etc. 6.3.4 Antiskinning agents: Anti-skinning agents are equally added. An example is tertiary amyl phenol. 6.4 Types of varnishes There are two types of varnishes, spirit varnish and oleoresinous varnish 6.4.1 Spirit Varnishes: It is solution or dispersion of film –forming resin in a volatile solvent. Such a varnish dries up by evaporation of the solvent . The films formed by spirit varnishes are brittle and thus crack and peel off very soon. To avoid this some plasticisers are added.Such varnishes are made by simple mixing of resin and solvent in a barrel. Stirring is continued till the resin is completely dissolved. An example is resin shellac in alcohol. 6.4.2 Oleoresinous Varnishes: This type of varnish is a solution of natural or synthetic resin in drying oil to which has been added driers and thinners. The method of manufacture will vary according to the type of resin employed, that is, whether natural or synthetics resin. When the resin is natural ,the resin is heated and stirred at a temperature from 300oC to 350o C until the foaming ceases. By so doing depolymerisation ofresin takes place. This process is known as “Running” Running is necessitated by the insolubility of natural resin which are made soluble by heating and depolymerisation. Then preheated drying oil is added and heating is continued to get correct viscosity. The whole mixture is cooled and thinner and drier are added. When resin is synthetic, there is no need for preheating the resin or oil separately. Oil and resin are mixed and heated together to get a homogenous solution of desired viscosity. The mixture is cooled, and thinner and drier are added. Whatever be the procedure, the varnish formed is clarified by filteration or centrifuging. After this varnish is allowed to age in large tanks so that fine gel type particles may be precipitated.

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6.4.3 Examples Varnishes

a) Violin Violin varnishing is a multi-step process involving some or all of the following: primer, sealer, ground, color coats, and clear topcoat. Some systems use a drying oil varnish as described below, while others use spirit (or solvent) varnish. Touchup in repair or restoration is only done with spirit varnish. Drying oil such as walnut oil or linseed oil may be used in combination with amber, copal, rosin or other resins. The oil is prepared by cooking or exposing to air and sunlight. The refined resin is typically available as a translucent solid and is then "run" by cooking or literally melting it in a pot over heat without solvents. The thickened oil and prepared resin are then cooked together and thinned with turpentine (away from open flame) into a brushable solution. Some violin finishing systems use vernice bianca (egg white and gum arabic) as a sealer or ground.

b) Resin Most resin or "gum" varnishes consist of a natural, plant- or insect-derived substance dissolved in a solvent, called spirit varnish or solvent varnish. The solvent may be alcohol, turpentine, or petroleum-based. Some resins are soluble in both alcohol and turpentine. Generally, petroleum solvents, i.e. mineral spirits or paint thinner, can substitute for turpentine. The resins include amber, dammar, copal, rosin, sandarac, elemi, benzoin, mastic, balsam, shellac, and a multitude of lacquers. Synthetic resins such as phenolic resin may be employed as a secondary component in certain varnishes and paints. Over centuries, many recipes were developed which involved the combination of resins, oils, and other ingredients such as certain waxes. These were believed to impart special tonal qualities to musical instruments and thus were sometimes carefully guarded secrets. The interaction of different ingredients is difficult to predict or reproduce, so expert finishers were often prized professionals.

c) Shellac Shellac is a resin gathered from the lac insect. The best shellac is called "true orange shellac," and it is not dyed to look orange. Shellac is insoluble in turpentine, but is soluble in alcohol. Shellac is a very widely used single component resin varnish that is alcohol soluble. It is not used for outdoor surfaces or where it will come into repeated contact with water such as around a sink or bathtub. The source of shellac resin is a brittle or flaky secretion of the female lac insect, Kerria lacca, found in the forests of Assam and Thailand and harvested from the bark of the trees where she deposits it to provide a sticky hold on the trunk. Shellac is the basis of French polish, which for centuries has been the preferred finish for fine furniture. Specified "dewaxed" 68

shellac has been processed to remove the waxy substances from original shellac and can be used as a primer and sanding-sealer substrate for other finishes such as polyurethanes, alkyds, oils, and acrylics. Prepared shellac is typically available in "clear" and "amber" (or "orange") varieties, generally as "three pound cut" or three pounds dry shellac to one US gallon of alcohol. Other natural color shades such as ruby and yellow are available from specialty pigment or woodworker's supply outlets. Dry shellac is available as refined flakes, "sticklac," "button lac," or "seedlac." "White pigmented" shellac primer paint is widely available in retail outlets, billed as a fast-drying interior primer "problem solver", in that it adheres to a variety of surfaces and seals off odors and smoke stains. Shellac clean-up may be done either with pure alcohol or with ammonia cleansers. It dries to a hard, tough, flexible film when applied to something other than the surface of a painting. On paintings it tends to crack and to darken with age. It can be useful as a sizing or an isolating varnish between paint layers (especially egg tempera). It is also a good, cheap fixative for charcoal and other drawings. It dries in about thirty minutes.

d) Alkyd Typically, modern commercially produced varnishes employ some form of alkyd for producing a protective film. Alkyds are chemically modified vegetable oils which operate well in a wide range of conditions and can be engineered to speed up the cure rate and thus harden faster. Better (and more expensive) exterior varnishes employ alkyds made from high performance oils and contain UV-absorbers; this improves gloss-retention and extends the lifetime of the finish. Various resins may also be combined with alkyds as part of the formula for typical "oil" varnishes that are commercially available.

e) Spar varnish Spar varnish (also called marine varnish) was originally intended for use on ship or boat spars, to protect the timber from the effects of sea and weather. Spars bend under the load of their sails. The primary requirements were water resistance and also elasticity, so as to remain adhering as the spars flexed. Elasticity was a pre-condition for weatherproofing too, as a finish that cracked would then allow water through, even if the remaining film was impermeable. Appearance and gloss was of relatively low value, in comparison. Modified tung oil and phenolic resins are often used. When first developed, no varnishes had good UV-resistance. Even after more modern synthetic resins did become resistant, a true spar varnish maintained its elasticity above other virtues, even if this required a compromise in its uv-resistance. Spar varnishes are thus not necessarily the best choice for outdoor woodwork which does not need to bend in service. Despite this, the widespread perception of "marine products" as "tough" led to domestic outdoor varnishes being branded as "Spar varnish" and sold on the virtue of their weather- and uvresistance. These claims may be more or less realistic, depending on individual products. Only 69

relatively recently have spar varnishes been available that can offer both effective elasticity and uv-resistance.

f) Drying Oils By definition, drying oils, such as linseed and tung oil, are not true varnishes though often in modern terms they accomplish the same thing. Drying oils cure through an exothermic reaction between the polyunsaturated portion of the oil and oxygen from the air. Originally, the term "varnish" referred to finishes that were made entirely of resin dissolved in suitable solvents, either ethanol (alcohol) or turpentine. The advantage to finishers in previous centuries was that resin varnishes had a very rapid cure rate compared to oils; in most cases they are cured practically as soon as the solvent has fully evaporated. By contrast, untreated or "raw" oils may take weeks or months to cure, depending on ambient temperature and other environmental factors. In modern terms, "boiled" or partially polymerized drying oils with added siccatives or dryers (chemical catalysts) have cure times of less than 24 hours. However, certain non-toxic byproducts of the curing process are emitted from the oil film even after it is dry to the touch and over a considerable period of time. It has long been a tradition to combine drying oils with resins to obtain favourable features of both substances.

g) Polyurethane Polyurethane varnishes are typically hard, abrasion-resistant, and durable coatings. They are popular for hardwood floors but are considered by some to be difficult or unsuitable for finishing furniture or other detailed pieces. Polyurethanes are comparable in hardness to certain alkyds but generally form a tougher film. Compared to simple oil or shellac varnishes, polyurethane varnish forms a harder, decidedly tougher and more waterproof film. However, a thick film of ordinary polyurethane may de-laminate if subjected to heat or shock, fracturing the film and leaving white patches. This tendency increases with long exposure to sunlight or when it is applied over soft woods like pine. This is also in part due to polyurethane's lesser penetration into the wood. Various priming techniques are employed to overcome this problem, including the use of certain oil varnishes, specified "dewaxed" shellac, clear penetrating epoxy sealer, or "oil-modified" polyurethane designed for the purpose. Polyurethane varnish may also lack the "hand-rubbed" lustre of drying oils such as linseed or tung oil; in contrast, however, it is capable of a much faster and higher "build" of film, accomplishing in two coats what may require multiple applications of oil. Polyurethane may also be applied over a straight oil finish, but because of the relatively slow curing time of oils, the emission of certain chemical byproducts, and the need for exposure to oxygen from the air, care must be taken that the oils are sufficiently cured to accept the polyurethane. Unlike drying oils and alkyds which cure, after evaporation of the solvent, upon reaction with oxygen from the air, true polyurethane coatings cure after evaporation of the solvent by a variety of reactions of chemicals within the original mix, or by reaction with moisture from the air. Certain polyurethane products are "hybrids" and combine different aspects of their parent components. "Oil-modified" polyurethanes, whether water-borne or solvent-borne, are currently the most widely used wood floor finishes. 70

Exterior use of polyurethane varnish may be problematic due to its heightened susceptibility to deterioration through ultra-violet light exposure. All clear or translucent varnishes, and indeed all film-polymer coatings (e.g. paint, stain, epoxy, synthetic plastic, etc.) are susceptible to this damage in varying degrees. Pigments in paints and stains protect against UV damage. UVabsorbers are added to polyurethane and other varnishes (e.g. spar varnish) to work against UV damage but are decreasingly effective over the course of 2–4 years, depending on the quantity and quality of UV-absorbers added as well as the severity and duration of sun exposure. Water exposure, humidity, temperature extremes, and other environmental factors affect all finishes. By contrast, wooden items retrieved from the Egyptian pyramids have a new and fresh appearance after 4000 years of storage. Even there, however, fungal colonies were present, and mildew and fungus are another category of entities which attack varnish. In other words, the only coat of varnish with near perfect durability is the one stored in a vacuum, in darkness, at a low and unvarying temperature. Otherwise, care and upkeep are required.

h) Lacquer The word lacquer refers to quick-drying, solvent-based varnishes or paints. Although their names may be similarly derived, lacquer is not the same as shellac and is not dissolved in alcohol. Lacquer is dissolved in lacquer thinner, which is a highly-flammable solvent typically containing butyl acetate and xylene or toluene. Lacquer is typically sprayed on, within a spray booth that evacuates overspray and minimizes the risk of combustion. Outside America, the rule of thumb is that a clear wood finish formulated to be sprayed is a lacquer but if it is formulated to be brushed on then it is a varnish. Thus the vast majority of wooden furniture is lacquered.

i)Acrylic Acrylic varnishes are typically water-borne varnishes with the lowest refractive index of all finishes and high transparency. They resist yellowing. Acrylics have the advantage of water clean-up and lack of solvent fumes, but typically do not penetrate into wood as well as oils. They sometimes lack the brushability and self-levelling qualities of solvent-based varnishes. Generally they have good UV-resistance. In the art world, varnishes offer dust-resistance and a harder surface than bare paint – they sometimes have the benefit of ultraviolet light resistors, which help protect artwork from fading in exposure to light. Acrylic varnish should be applied using an isolation coat (a permanent, protective barrier between the painting and the varnish, preferably a soft, glossy gel medium) to make varnish removal and overall conservation easier.

j)Two-Part Various epoxies have been formulated as varnishes or floor finishes whereby two components are mixed directly before application. Often, the two parts are of equal volume and are referred to as "part A" and "part B". True polyurethanes are two-part systems. All two-part epoxies have 71

a "pot-life" or "working time" during which the epoxy can be used. Usually the pot-life is a matter of a few hours but is also highly temperature dependent. Both water-borne and solvent based epoxies are used.

k) Conversion Used when a fast-curing, tough, hard finish is desired, such as for kitchen cabinets and office furniture. Comes in two parts - a resin and an acid catalyst. The first is a blend of an amino resin and an alkyd. The acid catalyst is added right before application in a set ratio determined by the manufacturer. Most produce minimal yellowing. There are, however, two downsides to this finish. The first is that as the finish cures, it gives off formaldehyde, which is toxic and carcinogenic. The second is that the finish can crack or craze if too many coats are applied. 6.5 Application of Varnishes When applying varnish, the first consideration is whether the painting is really dry. Although a painting may feel dry to the touch within days or weeks, the layers below the surface may not be thoroughly dry. A paint film dries by reacting with the oxygen in the air. If a painting is varnished before this reaction is completed in the paint layers below the surface, these paint layers are sealed off from their source of oxygen and cannot complete their drying process. The painting may remain soft and sticky for a considerable length of time and, with improper drying, the paint film may not bond properly to other film layers. Another problem caused by premature varnishing is that the solvent of the varnish may penetrate the paint layers that are not completely dry, thus softening them and affecting the appearance as well as the stability of the paint films. Most paintings of average thickness and painted with a lean medium will be ready for varnishing between six months and a year after completion. Unless driers were used throughout the painting, one year is usually the safest choice when in doubt. If the paint is thick, one year will not be long enough. Never heat or place a painting in the sun to accelerate the drying process. Because drying of oil paint is a chemical reaction with oxygen, rather than evaporation, rushing the process can cause wrinkling and other horrors. It is best to store the painting where there is light, ventilation, warmth, low humidity, and loving care. Paintings that must be displayed before they are thoroughly dry can be shown either unvarnished or coated with a retouch varnish, which will even the surface appearance and will provide some protection. It will also slow the ultimate drying time, but will not prevent proper oxidation. During the lengthy drying process, the surface of the painting may collect dust or dirt, which must be removed before varnishing. Any cleaning must not involve the use of water because the water can penetrate the paint layers, thus reaching the ground and causing it to swell. This will weaken the bond between the ground and the paint and can result in serious cracking. The best way to remove dust is first with a feather duster or a pigeon wing. Then take a loaf of fresh bread and pull out the center, squeeze it into a ball, and roll this over the surface of the painting. If there are slight grease stains, they may be removed by blotting with mineral spirits. If there are problems beyond those described here, professional advice is preferable to experimentation. 72

When the painting is dry, has a clean surface, and is in a dust-free, dry, warm environment, the varnish can be applied. The two basic methods of application are spraying and brushing. Spray varnishing can be successful when applied to a surface that has a minimum of texture, but a spray cannot cover textural irregularities as well as a brush. If a spray is held too close to the surface, the application will be too heavy and may run or pool. If the spray is too far from the surface, some of the particles of spray may partially dry en route to the surface and give it a frosted or powdered look. If you begin to spray off the surface and then move evenly onto the surface, pooling can be avoided on the surface because the areas where you start, stop, or change direction will be outside the painted area. Two thin coats are superior to one thick coat. For textured and irregular surfaces, brush application of varnish is best. The varnish can be worked into areas that are not easily accessible with a spray. For a heavily textured surface, a hog or bristle brush is necessary to force the varnish into difficult areas. Ox hair is excellent for smoother surfaces. After the application of the varnish, the painting should be laid flat to dry for one or two days. The surface should be protected from falling particles and dust. This may be accomplished by laying a board over some books or strips of wood placed on opposite sides of the painting. This will bridge the painting and will keep the protective covering a few inches off the surface. 6.6 Conclusion Varnish is a transparent, hard, protective finish or film primarily used in wood finishing but also for other materials. Varnish is traditionally a combination of a drying oil, a resin, and a thinner or solvent. Varnish finishes are usually glossy but may be designed to produce satin or semi-gloss sheens by the addition of "flatting" agents. Varnish has little or no colour, is transparent, and has no added pigment, as opposed to paints or wood stains, which contain pigment and generally range from opaque to translucent. Varnishes are also applied over wood stains as a final step to achieve a film for gloss and protection. Thus, they are modified form of paints. 6.7 Summary You have learned in this unit what a varnish is, the various component of varnishes such as filmforming agents, thinner or solvent, driers and anti-skinning agents. Also, the two types of varnishes were equally metioned. 6.8 Tutor- Marked Assignments 

What are varnishes?

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Mention the two types of varnish

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Gives the two types of film forming agents

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Differentiate between varnish and paint

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Describe how varnishes can be applied to substance such as wood. 73

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State the uses of varnishes

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Give three examples each of production.

natural and synthetic resins available for varnish

6.9 Reference 1.Uppal, M.M; Bhatia, S.C (2008). Engineering Chemistry (Chemical Technology). Khanna publishers.7th ed. Pg 796-797. 2. http:// en.wikipedia.org/wiki/varnish.

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Unit 7 PLASTICS 7.0 Introduction In unit 2, you learn that the most important organic raw materials are petroleum and natural gas, and that without the required raw material, production of products will be practically impossible. In this unit, we shall be discussing an important organic product known as ‘Plastics’. These material display properties that are unique when compared to other materials and have contributed greatly to quality of our everyday life. Plastics, properly applied, will perform functions at a cost that other materials cannot match. Many natural plastics exist, such as shellac, rubber, asphalt, and cellulose, however, it is man's ability to synthetically create a broad range of materials demonstrating various useful properties that have so enhanced our lives. Plastics are used in our clothing, housing, automobiles, aircraft, packaging, electronics, signs, recreation items, and medical implants to name but a few of their many applications. 7.1 Objectives At the end of this unit, you should be able to:        

Describe a plastic Mention the basic raw materials available for the production of plastics Lists some common plastics and their uses Classify plastics as thermoplastics and thermosets Differentiate between thermoplastics and thermosetting materials State the different types of plastics Gives brief history on plastics Describe the production process of plastics

7.2 Plastics The word plastic is derived from the Greek πλαστικός (plastikos) meaning capable of being shaped or molded, from πλαστός (plastos) meaning molded. It refers to their malleability, or plasticity during manufacture, that allows them to be cast, pressed, or extruded into a variety of shapes—such as films, fibers, plates, tubes, bottles, boxes, and much more. The common word plastic should not be confused with the technical adjective plastic, which is applied to any material which undergoes a permanent change of shape (plastic deformation) when strained beyond a certain point. Aluminum which is stamped or forged, for instance, exhibits plasticity in this sense, but is not plastic in the common sense; in contrast, in their finished forms, some plastics will break before deforming and therefore are not plastic in the technical sense. 75

Due to their relatively low cost, ease of manufacture, versatility, and imperviousness to water, plastics are used in an enormous and expanding range of products, from paper clips to spaceships. They have already displaced many traditional materials, such as wood; stone; horn and bone; leather; paper; metal; glass; and ceramic, in most of their former uses. The use of plastics is constrained chiefly by their organic chemistry, which seriously limits their properties, such as hardness, density,heat resistance, organic solvents, oxidation, and ionizing radiation. In particular, most plastics will melt or decompose when heated to a few hundred degrees celsius. While plastics can be made electrically conductive, with the conductivity of up to 80 kS/cm in stretch-oriented polyacetylene, they are still no match for most metals like copper which have conductivities of several hundreds kS/cm. Plastics are still too expensive to replace wood, concrete and ceramic in bulky items like ordinary buildings, bridges, dams, pavement, and railroad ties. 7.2.1 Classification Plastics are usually classified by their chemical structure of the polymer's backbone and side chains. Some important groups in these classifications are the acrylics, polyesters, silicones, polyurethanes, and halogenated plastics. Plastics can also be classified by the chemical process used in their synthesis, such as condensation, polyaddition, and cross-linking. Other classifications are based on qualities that are relevant for manufacturing or product design. Examples of such classes are the thermoplastic and thermoset, elastomer, structural, biodegradable, and electrically conductive. Plastics can also be classified by various physical properties, such as density, tensile strength, glass transition temperature, and resistance to various chemical products. 7.2.2 Thermoplastics and thermosetting polymers There are two types of plastics: thermoplastics and thermosetting polymers. Thermoplastics are the plastics that do not undergo chemical change in their composition when heated and can be moulded again and again. Examples include polyethylene, polypropylene, polystyrene, polyvinyl chloride, and polytetrafluoroethylene (PTFE). Common thermoplastics range from 20,000 to 500,000 amu, while thermosets are assumed to have infinite molecular weight. These chains are made up of many repeating molecular units, known as repeat units, derived from monomers; each polymer chain will have several thousand repeating units. Thermosets can melt and take shape once; after they have solidified, they stay solid. In the thermosetting process, a chemical reaction occurs that is irreversible. The vulcanization of rubber is a thermosetting process. Before heating with sulfur, the polyisoprene is a tacky, slighly runny material, but after vulcanization the product is rigid and non-tacky. The basic raw materials needed to make most plastics come from petroleum and natural gas.

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Table 7.1: Difference between thermoplastics and thermosets Thermoplastics i.They are heat soften,and thus can be reformed or process into a desire form. ii. They possesed linear chain iii.They are soluble in organic solvent iv.They are flexible v.Examples include polyethylene,polypropylene, Polyvinylchloride (PVC), nylon etc.

Thermosets i.They are not heat softened, once formed, it can not be reshaped. ii. They are formed by cross- linked bond iii.They are not soluble in organic solvent iv.They are not flexible Examples include urea resin, unsaturated polyester, melamin resin etc.

7.2.3 Chemical structure Common thermoplastics range from 20,000 to 500,000 amu, while thermosets are assumed to have infinite molecular weight. These chains are made up of many repeating molecular units, known as repeat units, derived from monomers; each polymer chain will have several thousand repeating units. The vast majority of plastics are composed of polymers of carbon and hydrogen alone or with oxygen, nitrogen, chlorine or sulfur in the backbone. (Some of commercial interests are silicon based.) The backbone is that part of the chain on the main "path" linking a large number of repeat units together. To customize the properties of a plastic, different molecular groups "hang" from the backbone (usually they are "hung" as part of the monomers before linking monomers together to form the polymer chain). This fine tuning of the properties of the polymer by repeating unit's molecular structure has allowed plastics to become an indispensable part of twenty first-century world. Some plastics are partially crystalline and partially amorphous in molecular structure, giving them both a melting point (the temperature at which the attractive intermolecular forces are overcome) and one or more glass transitions (temperatures above which the extent of localized molecular flexibility is substantially increased). The so-called semi-crystalline plastics include polyethylene, polypropylene, poly (vinyl chloride), polyamides (nylons), polyesters and some polyurethanes. Many plastics are completely amorphous, such as polystyrene and its copolymers, poly (methyl methacrylate), and all thermosets. 7.3 History The first human-made plastic, called parkesine, was patented by Alexander Parkes in 1856. It was unveiled at the 1862 Great International Exhibition in London. The development of plastics has come from the use of natural plastic materials (e.g., chewing gum, shellac) to the use of chemically modified natural materials (e.g., rubber, nitrocellulose, collagen, galalite) and finally to completely synthetic molecules (e.g., bakelite, epoxy, polyvinyl chloride, polyethylene).

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In 1866, Parkes formed the Parkesine Company to mass produce the material. The company, however, failed due to poor product quality as Parkes tried to reduce costs. Parkesine's successors were Xylonite, produced by Daniel Spill (an associate of Parkes), and Celluloid from John Wesley Hyatt. Parkesine was made from cellulose treated with nitric acid and a solvent. The generic name of Parkesine is pyroxylin, or Celluloid. Parkesine is often synthetic ivory. The Parkesine company ceased trading in 1868. Pictures of Parkesine are held by the Plastics Historical Society of London. There is a plaque on the wall of the site of the Parkesine Works. 7.4 Fossil-based plastics 7.4.1 Bakelite The first so called plastic based on a synthetic polymer was made from phenol and formaldehyde, with the first viable and cheap synthesis methods invented in 1907, by Leo Hendrik Baekeland, a Belgian-born American living in New York state. Baekeland was looking for an insulating shellac to coat wires in electric motors and generators. He found that mixtures of phenol (C6H5OH) and formaldehyde (HCOH) formed a sticky mass when mixed together and heated, and the mass became extremely hard if allowed to cool. He continued his investigations and found that the material could be mixed with wood flour, asbestos, or slate dust to create "composite" materials with different properties. Most of these compositions were strong and fire resistant. The only problem was that the material tended to foam during synthesis, and the resulting product was of unacceptable quality. Baekeland built pressure vessels to force out the bubbles and provide a smooth, uniform product. He publicly announced his discovery in 1912, naming it bakelite. It was originally used for electrical and mechanical parts, finally coming into widespread use in consumer goods in the 1920s. When the Bakelite patent expired in 1930, the Catalin Corporation acquired the patent and began manufacturing Catalin plastic using a different process that allowed a wider range of coloring. Bakelite was the first true plastic. It was a purely synthetic material, not based on any material or even molecule found in nature. It was also the first thermosetting plastic. Conventional thermoplastics can be molded and then melted again, but thermoset plastics form bonds between polymers strands when cured, creating a tangled matrix that cannot be undone without destroying the plastic. Thermoset plastics are tough and temperature resistant. Bakelite was cheap, strong, and durable. It was molded into thousands of forms, such as cases for radios, telephones and clocks, and billiard balls. Phenol-based ("Phenolic") plastics have been largely replaced by cheaper and less brittle plastics, but they are still used in applications requiring their insulating and heat-resistant properties. For example, some electronic circuit boards are made of sheets of paper or cloth impregnated with phenolic resin.

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7.4.2 Polystyrene and Polyvinyl Chloride Plastic piping and firestops being installed in Ontario. Certain plastic pipes can be used in some non-combustible buildings, provided they are firestopped properly and that the flame spread ratings comply with the local building code. After the First World War, improvements in chemical technology led to an explosion in new forms of plastics. Among the earliest examples in the wave of new plastics were polystyrene (PS) and polyvinyl chloride (PVC). Polystyrene is a rigid, brittle, inexpensive plastic that has been used to make plastic model kits and similar knick-knacks. It would also be the basis for one of the most popular "foamed" plastics, under the name styrene foam or Styrofoam. Foam plastics can be synthesized in an "open cell" form, in which the foam bubbles are interconnected, as in an absorbent sponge, and "closed cell", in which all the bubbles are distinct, like tiny balloons, as in gas-filled foam insulation and flotation devices. In the late 1950s, high impact styrene was introduced, which was not brittle. It finds much current use as the substance of toy figurines and novelties.

Polyvinyl Chloride (PVC, commonly called "vinyl") has side chains incorporating chlorine atoms, which form strong bonds. PVC in its normal form is stiff, strong, heat and weather resistant, and is now used for making plumbing, gutters, house siding, enclosures for computers and other electronics gear. PVC can also be softened with chemical processing, and in this form it is now used for shrink-wrap, food packaging, and rain gear.

All PVC polymers are degraded by heat and light. When this happens, hydrogen chloride is released into the atmosphere and oxidation of the compound occurs. Because hydrogen chloride readily combines with water vapor in the air to form hydrochloric acid, polyvinyl chloride is not recommended for long-term archival storage of silver, photographic film or paper (mylar is preferable). 7.4.3 Nylon

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The real star of the plastics industry in the 1930s was polyamide (PA), far better known by its trade name nylon. Nylon was the first purely synthetic fiber, introduced by DuPont Corporation at the 1939 World's Fair in New York City. In 1927, DuPont had begun a secret development project designated Fiber66, under the direction of Harvard chemist Wallace Carothers and chemistry department director Elmer Keiser Bolton. Carothers had been hired to perform pure research, and he worked to understand the new materials' molecular structure and physical properties. He took some of the first steps in the molecular design of the materials. His work led to the discovery of synthetic nylon fiber, which was very strong but also very flexible. The first application was for bristles for toothbrushes. However, Du Pont's real target was silk, particularly silk stockings. Carothers and his team synthesized a number of different polyamides including polyamide 6.6 and 4.6, as well as polyesters.

General condensation polymerization reaction for nylon It took DuPont twelve years and US$27 million to refine nylon, and to synthesize and develop the industrial processes for bulk manufacture. With such a major investment, it was no surprise that Du Pont spared little expense to promote nylon after its introduction, creating a public sensation, or "nylon mania". Nylon mania came to an abrupt stop at the end of 1941 when the USA entered World War II. The production capacity that had been built up to produce nylon stockings, or just nylons, for American women was taken over to manufacture vast numbers of parachutes for fliers and paratroopers. After the war ended, DuPont went back to selling nylon to the public, engaging in another promotional campaign in 1946 that resulted in an even bigger craze, triggering the so called nylon riots. Subsequently polyamides 6, 10, 11 and 12 have been developed based on monomers which are ring compounds; e.g. caprolactam. Nylon 66 is a material manufactured by condensation polymerization. Nylons still remain important plastics, and not just for use in fabrics. In its bulk form it is very wear resistant, particularly if oil-impregnated, and so is used to build gears, plain bearings, and because of good heat-resistance, increasingly for under-the-hood applications in cars, and other mechanical parts.

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7.4.4 Rubber Natural rubber is an elastomer (an elastic hydrocarbon polymer) that was originally derived from latex, a milky colloidal suspension found in the sap of some plants. It is useful directly in this form (indeed, the first appearance of rubber in Europe is cloth waterproofed with unvulcanized latex from Brazil) but, later, in 1839, Charles Goodyear invented vulcanized rubber; this a form of natural rubber heated with, mostly, sulfur forming cross-links between polymer chains (vulcanization), improving elasticity and durability. 7.4.5 Synthetic rubber The first fully synthetic rubber was synthesized by Sergei Lebedev in 1910. In World War II, supply blockades of natural rubber from South East Asia caused a boom in development of synthetic rubber, notably styrene-butadiene rubber. In 1941, annual production of synthetic rubber in the U.S. was only 231 tonnes which increased to 840,000 tonnes in 1945. In the space race and nuclear arms race, Caltech researchers experimented with using synthetic rubbers for solid fuel for rockets. Ultimately, all large military rockets and missiles would use synthetic rubber based solid fuels, and they would also play a significant part in the civilian space effort. 7.5 Bioplastics 7.5.1 Cellulose-based plastics Parkes developed a synthetic replacement for ivory which he marketed under the trade name Parkesine, and which won a bronze medal at the 1862 World's fair in London. Parkesine was made from cellulose (the major component of plant cell walls) treated with nitric acid as a solvent. The output of the process (commonly known as cellulose nitrate or pyroxilin) could be dissolved in alcohol and hardened into a transparent and elastic material that could be molded when heated.[19] By incorporating pigments into the product, it could be made to resemble ivory. Bois Durci is a plastic molding material based on cellulose. It was patented in Paris by Lepage in 1855. It is made from finely ground wood flour mixed with a binder, either egg or blood albumen, or gelatine. The wood is probably either ebony or rose wood, which gives a black or brown resin. The mixture is dried and ground into a fine powder. The powder is placed in a steel mold and compressed in a powerful hydraulic press while being heated by steam. The final product has a highly polished finish imparted by the surface of the steel mold. High oil prices have seen a resurgence in interest in bioplastics made from renewable cellulose and starch., including:  

Pea starch film with trigger biodegradation properties for agricultural applications (TRIGGER). Biopetroleum.

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Because of the fragmentation in the market and ambiguous definitions it is difficult to describe the total market size for bioplastics, but estimates put global production capacity at 327,000 tonnes. In contrast, global consumption of all flexible packaging is estimated at around 12.3 million tonnes. 7.5.2 Biodegradable (compostable) plastics Research has been done on biodegradable plastics that break down with exposure to sunlight (e.g., ultra-violet radiation), water or dampness, bacteria, enzymes, wind abrasion and some instances rodent pest or insect attack are also included as forms of biodegradation or environmental degradation. It is clear some of these modes of degradation will only work if the plastic is exposed at the surface, while other modes will only be effective if certain conditions exist in landfill or composting systems. Starch powder has been mixed with plastic as a filler to allow it to degrade more easily, but it still does not lead to complete breakdown of the plastic. Some researchers have actually genetically engineered bacteria that synthesize a completely biodegradable plastic, but this material, such as Biopol, is expensive at present. The German chemical company BASF makes Ecoflex, a fully biodegradable polyester for food packaging applications. 7.5.3 Oxo-biodegradable Oxo-biodegradable (OBD) plastic is polyolefin plastic to which has been added very small (catalytic) amounts of metal salts. As long as the plastic has access to oxygen (as in a littered state), these additives catalyze the natural degradation process to speed it up so that the OBD plastic will degrade when subject to environmental conditions. Once degraded to a small enough particle they can interact with biological processes to produce to water, carbon dioxide and biomass. The process is shortened from hundreds of years to months for degradation and thereafter biodegradation depends on the micro-organisms in the environment. Typically this process is not fast enough to meet ASTM D6400 standards for definition as compostable plastics. 7.6 Processing Methods

(a) Thermoplastic Plastics are changed into useful shapes by using many different processes. The processes that are used to mold or shape thermoplastics basically soften the plastic material so it can be injected into a mold, flowed through a die, formed in or over a mold, etc. The processes usually allow any scrap parts or material to be ground up and reused. Some of the more common processes are injection molding, extrusion, blow molding, rotational molding, calendering, thermoforming (which includes vacuum forming), and casting. 7.6.1 Injection Molding 82

"Injection Molding" is used to make three dimensional shapes with great detail. The material is placed in the hopper of an injection molding machine where it is fed into a chamber to be melted. The melting is achieved by conducting heat into the material in a "Plunger" machine, while the material is primarily heated by shearing or mechanically working the material in a "Screw" machine. Several shots of material are being heated and held in the injection unit. The maximum volume of material a machine can inject in a single shot determines its shot capacity. The capacity is given in ounces of a material. Once melted the material is forced, under pressure, into the mold where it conforms to the shape of the cavity. The mold is temperature controlled, usually by circulating temperature controlled water through it. Once the part is cooled, the mold is opened and the part removed. The mold is then closed and ready for the next shot. The mold is clamped shut while the material is being injected in to the cavity since the cavity pressure may be as much as 5,000 psi. The clamp is sized by the "Tonnage" it holds. Injection molding machines will be referred to by its shot size in ounces and its tons of clamping ability. An example would be a 6 oz, 80 Ton machine. The molds are most often made out of hardened steel and carefully finished. They may also be made out of prehard steel, aluminum, epoxy, etc. The type of mold material selected depends on the number of parts to be made and the plastic material to be used. Parts are often machined to test the shape and function of a part before a mold is built. 7.6.2 Extrusion "Extrusion" is like squeezing toothpaste out of its tube. The process produces continuous two dimensional shapes like sheet, pipe, film, tubing, gasketing, etc. The material is fed into the extruder where it is melted and pumped out of the extrusion die. The die and the take-off line shape the material as it cools and control the final dimensions of the cross-section of the shape. The equipment is designed and controlled to produce melted plastic at a very uniform temperature and pressure which control the size and quality of the extruded product. The extrusion process is also used with a system of molds and called "Blow Molding." This is how bottles, such as the gallon milk bottle, are produced. 7.6.3 Thermoforming An extruded or cast sheet can be heated, draped over a mold, and allowed to cool to produce a part. This process is called thermoforming. The material can be made to better conform to the shape of a mold by using a vacuum to pull the material down. A bubble or shape can also be blown up with air pressure. These are but two of the techniques that can be used to push the material into some desired shape. They basically require that the material be softened so a low force can be applied to shape the part. Signs, skylights, bubble packaging, boat and motorcycle windshields are some examples of parts made using this process.

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7.6.4 Calendering Calendering is a process that usually uses four heated rolls rotating at slightly different speeds. Again the material is fed into the rolls, heated and melted, and then shaped in sheet or film. PVC is the most commonly calendered material. 7.6.6 Casting Acrylic and nylons can also be cast. Just as the name implies, the material in a liquid form is poured into a mold and hardened. The process requires considerable process control to obtain high quality parts. Tubing, rods, sheets, and slabs are often made this way.

(b) Thermosets Thermosets must use a process that allows the material to flow to the desired shape and then become crosslinked and rigid. The material cannot be remelted or reused after crosslinking occurs. Some of the processes commonly used to process thermoset materials are injection molding, transfer molding, compression molding, hand (or spray) lay-up, lamination, and filament winding. The injection molding of thermosets is similar to the injection molding of thermoplastics except the material is kept cool until it is pushed into the heated mold where it is crosslinked. The mold is then opened and the hot, but rigid, part is removed. 7.6.7 Transfer Molding In transfer molding, only enough material for one shot is placed in a separate chamber or pot. The material is then pushed from the pot into the hot mold and crosslinked. All of the "cured" material is removed from the machine and another charge loaded for the next shot. 7.6.8 Compression Molding A single charge of material is placed directly into the cavity of the heated mold. The material flows and fills the cavity as the mold closes. The mold is kept closed until the material crosslinks. All of the cured material is removed from the mold prior to recharging the cavity. 7.6.9 Hand (Or Spray) Lay-Up Hand lay-up is used to produce products, such as fiberglass boats and camper shells. The plastic resin, usually a polyester, is rolled or sprayed with glass reinforcement into a mold. A catalyst is added to the material to cause the material to crosslink or harden at room temperature. This process lends itself to making large and strong parts. 84

7.6.10 Laminating Thermosets are also used in making laminates. The materials to be laminated are stacked in a press, clamped, and heated. Some examples of laminates using thermosets are plywood (the adhesive), electronic circuit boards, cloth reinforced phenolic sheet, and counter top laminates. 7.6.11 Filament Winding Filament winding is an automated version of the hand lay-up process. Reinforcing filaments are covered with a resin and then wound over a mandrel. The number of layers and orientation can be varied depending on the load that the part is to carry. A strong thin hollow part is left after the mandrel is removed. Storage tanks and street lighting poles are some examples of filament wound parts 7.7.0 Common Plastics and Uses A chair made with a polypropylene seat              

Polyester (PES) - Fibers, textiles. Polyethylene terephthalate (PET) - Carbonated drinks bottles, peanut butter jars, plastic film, microwavable packaging. Polyethylene (PE) - Wide range of inexpensive uses including supermarket bags, plastic bottles. High-density polyethylene - Detergent bottles and milk jugs. Polyvinyl chloride (PVC) - Plumbing pipes and guttering, shower curtains, window frames, flooring. Polyvinylidene chloride (PVDC) (Saran) - Food packaging. Low-density polyethylene (LDPE) - Outdoor furniture, siding, floor tiles, shower curtains, clamshell packaging. Polypropylene (PP) - Bottle caps, drinking straws, yogurt containers, appliances, car fenders (bumpers), plastic pressure pipe systems. Polystyrene (PS) - Packaging foam/"peanuts", food containers, plastic tableware, disposable cups, plates, cutlery, CD and cassette boxes. High impact polystyrene (HIPS) -: Refrigerator liners, food packaging, vending cups. Polyamides (PA) (Nylons) - Fibers, toothbrush bristles, fishing line, under-the-hood car engine moldings. Acrylonitrile butadiene styrene (ABS) - Electronic equipment cases (e.g., computer monitors, printers, keyboards), drainage pipe. Polycarbonate (PC) - Compact discs, eyeglasses, riot shields, security windows, traffic lights, lenses. Polycarbonate/Acrylonitrile Butadiene Styrene (PC/ABS) - A blend of PC and ABS that creates a stronger plastic. Used in car interior and exterior parts, and mobile phone bodies.

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Polyurethanes (PU) - Cushioning foams, thermal insulation foams, surface coatings, printing rollers (Currently 6th or 7th most commonly used plastic material, for instance the most commonly used plastic found in cars).

7.7.1 Special purpose plastics 

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Melamine formaldehyde (MF) - One of the aminoplasts, and used as a multi-colorable alternative to phenolics, for instance in moldings (e.g., break-resistance alternatives to ceramic cups, plates and bowls for children) and the decorated top surface layer of the paper laminates (e.g., Formica). Plastarch material - Biodegradable and heat resistant, thermoplastic composed of modified corn starch. Phenolics (PF) or (phenol formaldehydes) - High modulus, relatively heat resistant, and excellent fire resistant polymer. Used for insulating parts in electrical fixtures, paper laminated products (e.g., Formica), thermally insulation foams. It is a thermosetting plastic, with the familiar trade name Bakelite, that can be molded by heat and pressure when mixed with a filler-like wood flour or can be cast in its unfilled liquid form or cast as foam (e.g., Oasis). Problems include the probability of moldings naturally being dark colors (red, green, brown), and as thermoset it is difficult to recycle. Polyetheretherketone (PEEK) - Strong, chemical- and heat-resistant thermoplastic, biocompatibility allows for use in medical implant applications, aerospace moldings. One of the most expensive commercial polymers. Polyetherimide (PEI) (Ultem) - A high temperature, chemically stable polymer that does not crystallize. Polylactic acid (PLA) - A biodegradable, thermoplastic found converted into a variety of aliphatic polyesters derived from lactic acid which in turn can be made by fermentation of various agricultural products such as corn starch, once made from dairy products. Polymethyl methacrylate (PMMA) - Contact lenses, glazing (best known in this form by its various trade names around the world; e.g., Perspex, Oroglas, Plexiglas), aglets, fluorescent light diffusers, rear light covers for vehicles. It forms the basis of artistic and commercial acrylic paints when suspended in water with the use of other agents. Polytetrafluoroethylene (PTFE) - Heat-resistant, low-friction coatings, used in things like non-stick surfaces for frying pans, plumber's tape and water slides. It is more commonly known as Teflon. Urea-formaldehyde (UF) - One of the aminoplasts and used as a multi-colorable alternative to phenolics. Used as a wood adhesive (for plywood, chipboard, hardboard) and electrical switch housings.

7.8 Toxicity Due to their insolubility in water and relative chemical inertness, pure plastics generally have low toxicity in their finished state, and will pass through the digestive system with no ill effect (other than mechanical damage or obstruction). However, plastics often contain a variety of toxic additives. For example, plasticizers like adipates and phthalates are often added to brittle plastics like polyvinyl chloride (PVC) to make them pliable enough for use in food packaging, toys and 86

teethers, tubing, shower curtains and other items. Traces of these chemicals can leach out of the plastic when it comes into contact with food. Out of these concerns, the European Union has banned the use of DEHP (di-2-ethylhexyl phthalate), the most widely used plasticizer in PVC. Some compounds leaching from polystyrene food containers have been found to interfere with hormone functions and are suspected human carcinogens.[26] Moreover, while the finished plastic may be non-toxic, the monomers used in its manufacture may be toxic; and small amounts of those chemicals may remain trapped in the product. The World Health Organization's International Agency for Research on Cancer (IARC) has recognized the chemical used to make PVC, vinyl chloride, as a known human carcinogen. Some polymers may also decompose into the monomers or other toxic substances when heated. In 2011, it was reported that "almost all plastic products" sampled released chemicals with estrogenic activity, although the researchers identified plastics which did not leach chemicals with estrogenic activity. The primary building block of polycarbonates, bisphenol A (BPA), is an estrogen-like endocrine disruptor that may leach into food. Research in Environmental Health Perspectives finds that BPA leached from the lining of tin cans, dental sealants and polycarbonate bottles can increase body weight of lab animals' offspring. A more recent animal study suggests that even low-level exposure to BPA results in insulin resistance, which can lead to inflammation and heart disease. 7.8.1 Environmental Issues The biggest threat to the conventional plastics industry is most likely to be environmental concerns, including the release of toxic pollutants, greenhouse gas, litter, biodegradable and nonbiodegradable landfill impact as a result of the production and disposal of petroleum and petroleum-based plastics. Of particular concern has been the recent accumulation of enormous quantities of plastic trash in ocean gyres Plastics are durable and degrade very slowly; the molecular bonds that make plastic so durable make it equally resistant to natural processes of degradation. Since the 1950s, one billion tons of plastic have been discarded and may persist for hundreds or even thousands of years. In some cases, burning plastic can release toxic fumes. Burning the plastic polyvinyl chloride (PVC) may create dioxin. Also, the manufacturing of plastics often creates large quantities of chemical pollutants. Prior to the ban on the use of CFCs in extrusion of polystyrene (and general use, except in lifecritical fire suppression systems; see Montreal Protocol), the production of polystyrene contributed to the depletion of the ozone layer; however, non-CFCs are currently used in the extrusion process. By 1995, plastic recycling programs were common in the United States and elsewhere. Thermoplastics can be remelted and reused, and thermoset plastics can be ground up and used as filler, though the purity of the material tends to degrade with each reuse cycle. There are methods by which plastics can be broken back down to a feedstock state. 87

Plastic can be converted as a fuel. It is made from crude oil, so it can be broken down to liquid hydrocarbon. One kilogram of waste plastic produces a liter of hydrocarbon. Plastic wastes are used in cement plants as a fuel. To assist recycling of disposable items, the Plastic Bottle Institute of the Society of the Plastics Industry devised a now-familiar scheme to mark plastic bottles by plastic type. A plastic container using this scheme is marked with a triangle of three "chasing arrows", which encloses a number giving the plastic type: Plastics type marks: the resin identification code 1. 2. 3. 4. 5. 6.

PET (PETE), polyethylene terephthalate HDPE, high-density polyethylene PVC, polyvinyl chloride LDPE, low-density polyethylene, PP, polypropylene PS, polystyrene

Unfortunately, recycling of plastics has proven to be a difficult process. The biggest problem is that it is difficult to automate the sorting of plastic wastes, making it labor intensive. Typically, workers sort the plastic by looking at the resin identification code, although common containers like soda bottles can be sorted from memory. Typically, the caps for PETE bottles are made from a different kind of plastic which is not recyclable, which presents additional problems to the automated sorting process. Other recyclable materials such as metals are easier to process mechanically. However, new processes of mechanical sorting are being developed to increase capacity and efficiency of plastic recycling. While containers are usually made from a single type and color of plastic, making them relatively easy to be sorted, a consumer product like a cellular phone may have many small parts consisting of over a dozen different types and colors of plastics. In such cases, the resources it would take to separate the plastics far exceed their value and the item is discarded. However, developments are taking place in the field of active disassembly, which may result in more consumer product components being re-used or recycled. Recycling certain types of plastics can be unprofitable, as well. For example, polystyrene is rarely recycled because it is usually not cost effective. These unrecycled wastes are typically disposed of in landfills, incinerated or used to produce electricity at waste-to-energy plants.

7.9 Conclusion A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs. Monomers of plastic are either natural or synthetic organic compounds 88

The major two types of plastics are thermoplastics and thermosetting polymers. Thermoplastics are the plastics that do not undergo chemical change in their composition when heated and can be moulded again and again; While, thermosets can melt and take shape once; after they have solidified, can not be heat soften, they stay solid. 7.10 Summary You have learnt in this unit that plastics are typically polymer in which the basic raw materials are sourced from petroleum and natural gas. Also, the several types of plastics and their uses were discussed. You equally learned the several ways of processing plastic and lastly, the environmental implications of plastic product were mentioned. 7.11 Tutored-Marked Assignment      

What are plastics? Differentiate between thermoplastics and thermosets Briefly discuss the several processing methods of thermoplastics Mention five examples of special purpose plastics Give two examples each of thermoplastics and thermosets Lists the processing methods of thermosets plastics.

7.12 References 1. Stephen Fenichell, Plastic: The Making of a Synthetic Century, HarperBusiness, 1996, ISBN 0887307329 p. 17 2. http://en.wikipedia.org/wiki/plastics 3. www.nobel prize.org/educational/chemistry/plastics 4. http://en.wikipedia.org/wiki/ category/Thermsetting_polymer_plastics.

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Unit 8 WOOD PULP AND PAPER 8.0 Introduction Wood pulp and waste paper are both intermediate products and are used as raw materials in the manufacture of paper, paperboard, and other wood-fiber-based products. Wood pulp is the fibrous material that results when wood is separated into its constituent fibers by chemical or mechanical means. Waste paper is composed of previously discarded paper or paperboard products. Both contain cellulose fiber that can be subsequently combined with other inputs to manufacture paper, paperboard, or other wood-fiber-based products.

Pulp is a lignocellulosic fibrous material prepared by chemically or mechanically separating cellulose fibres from wood, fibre crops or waste paper. Wood pulp is the most common raw material in papermaking. 8.1 Objectives At the end of this unit, you should be able to:      

State the importance of paper in our society Lists the basic raw material used in making paper Describe the process of transforming wood to paper Outlines the major processes of changing wood to paper State the various types of pulping Discuss the environmental impact of producing wood pulp.

8.2 Wood, Pulp And Paper Historically, using wood to make paper is a fairly recent innovation. In the 1800s, fibre crops such as linen fibres were the primary material source, and paper was a relatively expensive commodity. The use of wood to make pulp for paper began with the development of mechanical pulping in Germany by F.G. Keller in the 1840s, and by the Canadian inventor Charles Fenerty in Nova Scotia. Chemical processes quickly followed, first with J. Roth's use of sulfurous acid to treat wood, followed by B. Tilghman's U.S. patent on the use of calcium bisulfite, Ca(HSO3)2, to pulp wood in 1867. Almost a decade later the first commercial sulfite pulp mill was built in Sweden. It used magnesium as the counter ion and was based on work by Carl Daniel Ekman. By 1900, sulfite pulping had become the dominant means of producing wood pulp, surpassing mechanical pulping methods. The competing chemical pulping process, the sulfate or kraft process was developed by Carl F. Dahl in 1879 and the first kraft mill started (in Sweden) in 1890. The invention of the recovery boiler by G. H. Tomlinson in the early 1930s allowed kraft mills to recycle almost all of their pulping chemicals. This, along with the ability of the kraft process to accept a wider variety of types of wood and produce stronger fibres made the kraft process the dominant pulping process starting in the 1940s. 90

Global production of wood pulp in 2006 was 160 million tonnes (175 million tons). In the previous year, 57 million tonnes (63 million tons) of market pulp (not made into paper in the same facility) was sold, with Canada being the largest source at 21% of the total, followed by the United States at 16%. Chemical pulp made up 93% of market pulp. The major processes in transforming wood to paper are as follow,

8.2.1 Making pulp Several processes are commonly used to convert logs to wood pulp. In the mechanical process, logs are first tumbled in drums to remove the bark. The logs are then sent to grinders, which break the wood down into pulp by pressing it between huge revolving slabs. The pulp is filtered to remove foreign objects. In the chemical process, wood chips from de-barked logs are cooked in a chemical solution. This is done in huge vats called digesters. The chips are fed into the digester, and then boiled at high pressure in a solution of sodium hydroxide and sodium sulfide. The chips dissolve into pulp in the solution. Next the pulp is sent through filters. Bleach may be added at this stage, or colorings. The pulp is sent to the paper plant.

8.2.2 Beating The pulp is next put through a pounding and squeezing process called, appropriately enough, beating. Inside a large tub, the pulp is subjected to the effect of machine beaters. At this point, various filler materials can be added such as chalks, clays, or chemicals such as titanium oxide. These additives will influence the opacity and other qualities of the final product. Sizings are also added at this point. Sizing affects the way the paper will react with various inks. Without any sizing at all, a paper will be too absorbent for most uses except as a desk blotter. A sizing such as starch makes the paper resistant to water-based ink (inks actually sit on top of a sheet of paper, rather than sinking in). A variety of sizings, generally rosins and gums, is available depending on the eventual use of the paper. Paper that will receive a printed design, such as gift wrapping, requires a particular formula of sizing that will make the paper accept the printing properly.

8.2.3 Pulp to paper In order to finally turn the pulp into paper, the pulp is fed or pumped into giant, automated machines. One common type is called the Fourdrinier machine, which was invented in England in 1807. Pulp is fed into the Fourdrinier machine on a moving belt of fine mesh screening. The pulp is squeezed through a series of rollers, while suction devices below the belt drain off water. If the paper is to receive a water-mark, a device called a dandy moves across the sheet of pulp and presses a design into it. The paper then moves onto the press section of the machine, where it is pressed between rollers of wool felt. The paper then passes over a series of steam-heated cylinders to remove the remaining water. A large machine may have from 40 to 70 drying cylinders. 91

8.2.4 Finishing Finally, the dried paper is wound onto large reels, where it will be further processed depending on its ultimate use. Paper is smoothed and compacted further by passing through metal rollers called calendars. A particular finish, whether soft and dull or hard and shiny, can be imparted by the calendars. The paper may be further finished by passing through a vat of sizing material. It may also receive a coating, which is either brushed on or rolled on. Coating adds chemicals or pigments to the paper's surface, supplementing the sizings and fillers from earlier in the process. Fine clay is often used as a coating. The paper may next be supercalendered, that is, run through extremely smooth calendar rollers, for a final time. Then the paper is cut to the desired size.

8.3 Manufacture of wood pulp The timber resources used to make wood pulp are referred to as pulpwood. Wood pulp comes from softwood trees such as spruce, pine, fir, larch and hemlock, and hardwoods such as eucalyptus, aspen and birch. A pulp mill is a manufacturing facility that converts wood chips or other plant fibre source into a thick fibre board which can be shipped to a paper mill for further processing. Pulp can be manufactured using mechanical, semi-chemical or fully chemical methods (kraft and sulfite processes). The finished product may be either bleached or non-bleached, depending on the customer requirements. Wood and other plant materials used to make pulp contain three main components (apart from water): cellulose fibres (desired for papermaking), lignin (a three-dimensional polymer that binds the cellulose fibres together) and hemicelluloses, (shorter branched carbohydrate polymers). The aim of pulping is to break down the bulk structure of the fibre source, be it chips, stems or other plant parts, into the constituent fibres. Chemical pulping achieves this by degrading the lignin and hemicellulose into small, watersoluble molecules which can be washed away from the cellulose fibers without depolymerizing the cellulose fibres (chemically depolymerizing the cellulose weakens the fibres). The various mechanical pulping methods, such as groundwood (GW) and refiner mechanical (RMP) pulping, physically tear the cellulose fibres one from another. Much of the lignin remains adhering to the fibres. Strength is impaired because the fibres may be cut. There are a number of related hybrid pulping methods that use a combination of chemical and thermal treatment to begin an abbreviated chemical pulping process, followed immediately by a mechanical treatment to separate the fibres. These hybrid methods include thermomechanical pulping, also known as TMP, and chemithermomechanical pulping, also known as CTMP. The chemical and thermal treatments reduce the amount of energy subsequently required by the mechanical treatment, and also reduce the amount of strength loss suffered by the fibres. 92

8.3.1 Harvesting trees All kinds of paper are made out of 100% wood with nothing else mixed into them (with some exceptions, like fancy resume paper, which may include cotton). This includes newspaper, magazines and even toilet paper. Most pulp mills use good forest management practices in harvesting trees to ensure that they have a sustainable source of raw materials. One of the major complaints about harvesting wood for pulp mills is that it reduces the biodiversity of the harvested forest. Trees raised specifically for pulp production account for 16 percent of world pulp production, old growth forests account for 9 percent, and second- and third- and more generation forests account for the rest. Reforestation is practiced in most areas, so trees are a renewable resource. The FSC (Forest Stewardship Council) certifies paper made from trees harvested according to guidelines meant to ensure good forestry practices. The number of trees consumed depends whether mechanical processes or chemical processes are used. It has been estimated that based on a mixture of softwoods and hardwoods 12 metres (40 ft) tall and 15-20 centimetres (6–8 in) in diameter, it would take an average of 24 trees to produce 0.9 tonne (1 ton) of printing and writing paper, using the kraft process (chemical pulping). Mechanical pulping is about twice as efficient in using trees since almost all of the wood is used to make fibre therefore it takes about 12 trees to make 0.9 tonne (1 ton) of mechanical pulp or newsprint. There are roughly 2 short tons in a cord of wood. 8.3.2 Preparation for pulping Woodchipping is the act and industry of chipping wood for pulp, but also for other processed wood products and mulch. Only the heartwood and sapwood are useful for making pulp. Bark contains relatively few useful fibres and is removed and used as fuel to provide steam for use in the pulp mill. Most pulping processes require that the wood be chipped and screened to provide uniform sized chips. Pulping There are a number of different processes which can be used to separate the wood fibres: 8.3.3 Mechanical pulp Manufactured grindstones with embedded silicon carbide or aluminum oxide can be used to grind small wood logs called "bolts" to make stone groundwood pulp (SGW). If the wood is steamed prior to grinding it is known as pressure groundwood pulp (PGW). Most modern mills use chips rather than logs and ridged metal discs called refiner plates instead of grindstones. If the chips are just ground up with the plates, the pulp is called refiner mechanical pulp (RMP) and if the chips are steamed while being refined the pulp is called thermomechanical pulp (TMP). Steam treatment significantly reduces the total energy needed to make the pulp and decreases the 93

damage (cutting) to fibres. Mechanical pulps are used for products that require less strength, such as newsprint and paperboards. 8.3.4 Thermomechanical pulp Thermomechanical pulp is pulp produced by processing wood chips using heat (thus thermo) and a mechanical refining movement (thus mechanical). It is a two stage process where the logs are first stripped of their bark and converted into small chips. These chips have a moisture content of around 25-30% and a mechanical force is applied to the wood chips in a crushing or grinding action which generates heat and water vapour and softens the lignin thus separating the individual fibres. The pulp is then screened and cleaned, any clumps of fibre are reprocessed. This process gives a high yield of fibre from the timber (around 95%) and as the lignin has not been removed, the fibres are hard and rigid.

8.3.5 Chemithermomechanical pulp Wood chips can be pretreated with sodium carbonate, sodium hydroxide, sodium sulfite and other chemicals prior to refining with equipment similar to a mechanical mill. The conditions of the chemical treatment are much less vigorous (lower temperature, shorter time, less extreme pH) than in a chemical pulping process since the goal is to make the fibres easier to refine, not to remove lignin as in a fully chemical process. Pulps made using these hybrid processes are known as chemithermomechanical pulps (CTMP).

8.3.6 Chemical pulp Chemical pulp is produced by combining wood chips and chemicals in large vessels known as digesters where heat and the chemicals break down the lignin, which binds the cellulose fibres together, without seriously degrading the cellulose fibres. Chemical pulp is used for materials that need to be stronger or combined with mechanical pulps to give a product different characteristics. The kraft process is the dominant chemical pulping method, with sulfite process being second. Historically soda pulping was the first successful chemical pulping method. 8.3.7 Recycled pulp Recycled pulp is also called deinked pulp (DIP). DIP is recycled paper which has been processed by chemicals, thus removing printing inks and other unwanted elements and freed the paper fibres. The process is called deinking. DIP is used as raw material in papermaking. Many newsprint, toilet paper and facial tissue grades commonly contain 100% deinked pulp and in many other grades, such as lightweight 94

coated for offset and printing and writing papers for office and home use, DIP makes up a substantial proportion of the furnish.

8.3.8 Organosolv pulping Organosolv pulping uses organic solvents at temperatures above 140 °C to break down lignin and hemicellulose into soluble fragments. The pulping liquor is easily recovered by distillation. 8.3.9 Alternative pulping methods Research is under way to develop biological pulping, similar to chemical pulping but using certain species of fungi that are able to break down the unwanted lignin, but not the cellulose fibres. This could have major environmental benefits in reducing the pollution associated with chemical pulping. The pulp is bleached using chlorine dioxide stage followed by neutralization and calcium hypochlorite.The oxidizing agent in either case oxidizes and destroys the dyes formed from the tannins of the wood and accentuated (reinforced) by sulfides present in it. Bleaching The pulp produced up to this point in the process can be bleached to produce a white paper product. The chemicals used to bleach pulp have been a source of environmental concern, and recently the pulp industry has been using alternatives to chlorine, such as chlorine dioxide, oxygen, ozone and hydrogen peroxide. 8.4 Alternatives to wood pulp Today, some people and groups advocate using field crop fibre or agricultural residues instead of wood fibre as being more sustainable. However, wood is also a renewable resource, with about 90% of pulp coming from plantations or reforested areas. Non-wood fibre sources account for about 5-10% of global pulp production, for a variety of reasons, including seasonal availability, problems with chemical recovery, brightness of the pulp etc. Non-wood pulp processing requires a high use of water and energy. Nonwovens are in some applications alternatives to paper made from wood pulp, like filter paper or tea bags. Comparison of typical feedstocks used in pulping Component Wood Nonwood Carbohydrates 65-80 % 50-80 % Cellulose 40-45 % 30-45 % Hemicellulose 23-35 % 20-35 % Lignin 20-30 % 10-25 % Extractives 2-5 % 5-15 % 95

Proteins Inorganics SiO2

< 0.5 % 0.1-1 % < 0.1 %

5-10 % 0.5-10 % 0.5-7 %

8.5 Market pulp Market pulp is any variety of pulp that is produced in one location, dried and shipped to another location for further processing. Important quality parameters for pulp not directly related to the fibres are brightness, dirt levels, viscosity and ash content. 8.5.1 Air dry pulp Air dry pulp is the most common form to sell pulp. This is pulp dried to about 10 % moisture content. It is normally delivered as sheeted bales of 250kg. The reason to leave 10 % moisture in the pulp is that this minimizes the fibre to fibre bonding and makes it easier to disperse the pulp in water for further processing to paper. 8.5.2 Roll pulp Roll pulp or reel pulp is the most common delivery form of pulp to non tradtitional pulp markets. Fluff pulp is normally shipped on rolls (reels). This pulp is dried to 5 - 6 % moisture content. At the customer this is going to a comminution process to prepare for further processing. 8.5.3 Flash dried pulp Some pulps are flash dried. This is done by pressing the pulp to about 50 % moisture content and then let it fall trough silos that are 15 -17 m high. Gas fired hot air is the normal heat source. The temperature is well above the char point of cellulose, but large amount of moisture in the fibre wall and lumen prevents the fibres from being incinerated. It is often not dried down to 10% moisture (air dry). The bales are not as densely packed as air dry pulp. 8.6 Environmental concerns The major environmental impacts of producing wood pulp come from its impact on forest sources and from its waste products. The number of trees and other vegetation cut down in order to make paper is enormous. Paper companies insist that they plant as many new trees as they cut down. Environmentalists contend that the new growth trees, so much younger and smaller than what was removed, cannot replace the value of older trees. Efforts to recycle used paper (especially newspapers) have been effective in at least partially mitigating the need for destruction of woodlands, and recycled paper is now an important ingredient in many types of paper production. 96

The chemicals used in paper manufacture, including dyes, inks, bleach, and sizing, can also be harmful to the environment when they are released into water supplies and nearby land after use. The industry has, sometimes with government prompting, cleared up a large amount of pollution, and federal requirements now demand pollution free paper production. The cost of such clean-up efforts is passed on to the consumer. 8.6.1 Forest resources The impact of logging to provide the raw material for wood pulp is an area of intense debate. Modern logging practices, using forest management seek to provide a reliable, renewable source of raw materials for pulp mills. The practice of clear cutting is a particularly sensitive issue since it is a very visible effect of logging. Reforestation, the planting of tree seedlings on logged areas, has also been criticized for decreasing biodiversity because reforested areas are monocultures. Logging of old growth forests accounts for less than 10% of wood pulp, but is one of the most controversial issues. 8.6.2 Effluents from pulp mills The process effluents are treated in a biological effluent treatment plant, which guarantees that the effluents are not toxic in the recipient. Mechanical pulp is not a major cause for environmental concern since most of the organic material is retained in the pulp, and the chemicals used (hydrogen peroxide and sodium dithionite) produce benign byproducts (water and sodium sulfate (finally), respectively). Chemical pulp mills, especially kraft mills, are energy self-sufficient and very nearly closed cycle with respect to inorganic chemicals. Bleaching with chlorine produces large amounts of organochlorine compounds, including dioxins. 8.6.3 Odor problems The kraft pulping reaction in particular releases foul-smelling compounds. The hydrogen sulfide reagent that degrades lignin structure also causes some demethylation to produce methanethiol, dimethyl sulfide and dimethyl disulfide. These compounds have extremely low odor thresholds and disagreeable smells. The same compounds are released in microbial decay, or into e.g. Camembert cheese, although the kraft process is a chemical one and does not involve any microbial degradation. 8.6.4 Harmful Chemicals The chemicals used in paper manufacture, including dyes, inks, bleach, and sizing, can also be harmful to the environment when they are released into water supplies and nearby land after use. The industry has, sometimes with government prompting, cleared up a large amount of pollution, 97

and federal requirements now demand pollution free paper production. The cost of such clean-up efforts is passed on to the consumer. 8.7 Conclusion The major components of wood are cellulose (70-80 percent) and lignin (20-30 percent). Lignin is the material that bonds cellulose fibers together. Wood pulp results when wood is separated into its constituent fibers by either chemical or mechanical means. Chemical pulping begins once pulpwood is debarked and chipped. The chips are cooked in solutions of various chemicals, screened to remove any uncooked chips, and washed to remove the cooking “liquor.” If necessary, the pulp is bleached to increase its purity, brightness, and whiteness. Chemical pulping actually separates useable cellulose fibers from the lignin. As a result, chemical pulping yields higher quality (strength and permanence) pulps albeit of lower yields (45-55 percent) than mechanical pulps.

8.8 Summary You have learned in this unit that paper manufactured depends solely on wood pulp, and waste paper as both contain cellulose fiber that can be subsequently combined with other inputs to manufacture paper, paperboard or other wood-fiber based product. Also, learned is the process of converting logs to woodpulp, the several pulping process were equally discussed. Lastly, the impact of wood pulping as it affects the environment in terms of chemical used in the manufacturing process such as dyes, inks, bleach, and sizing, can also be harmful to the environment when they are released into water supplies and nearby land after use. The number of trees and vegetation cut down in order to make paper is enormous, and thus, affect the ecosystem. 8.9 Tutor- Marked Assignment     

What is pulp? Explain briefly the process of converting log in wood pulp, Lists the various pulping process. Discuss briefly on the effect of wood pulping process in the making of paper to the environment. Is there any alternative to pulping process? if yes give reason.

8.10. References 1. http://en.wikipedia.org/wiki/Pulp_paper 2. www.usitc.gov/publications/332/pub3490pdf 3. http://en.wikipedia.org/wiki/Bleaching_of_wood_pulp 98

Unit 9 ENVIROMENTAL POLLUTION

9.0 Introduction Environmental pollution is “the contamination of the physical and biological components of the earth/atmosphere system to such an extent that normal environmental processes are adversely affected”. Although pollution had been known to exist for a very long time (at least since people started using fire thousands of years ago), it had seen the growth of truly global proportions only since the onset of the industrial revolution during the 19th century. It was the industrial revolution that gave birth to environmental pollution as we know it today. The emergence of great factories and consumption of immense quantities of coal and other fossil fuels gave rise to unprecedented air pollution and the large volume of industrial chemical discharges added to the growing load of untreated human waste. The industrial revolution brought with it technological progress such as discovery of oil and its virtually universal use throughout different industries. Technological progress facilitated by super efficiency of capitalist business practices (division of labour – cheaper production costs – overproduction – overconsumption – overpollution) had probably become one of the main causes of serious deterioration of natural resources. At the same time, of course, development of natural sciences led to the better understanding of negative effects produced by pollution on the environment. Environmental pollution is a problem both in developed and developing countries. Factors such as population growth and urbanization invariably place greater demands on the planet and stretch the use of natural resources to the maximum. In modern industrialized societies, fossil fuels (oil, gas, coal) transcended virtually all imaginable barriers and firmly established themselves in our everyday lives. Not only do we use fossil fuels for our obvious everyday needs (such as filling a car), as well as in the power-generating industry, they (specifically oil) are also present in such products as all sorts of plastics, solvents, detergents, asphalt, lubricating oils, a wide range of chemicals for industrial use, etc. Combustion of fossil fuels produces extremely high levels of air pollution and is widely recognized as one of the most important “target” areas for reduction and control of environmental pollution. 99

Fossil fuels also contribute to soil contamination and water pollution. For example, when oil is transported from the point of its production to further destinations by pipelines, an oil leak from the pipeline may occur and pollute soil and subsequently groundwater. When oil is transported by tankers by ocean, an oil spill may occur and pollute ocean water. Of course, there are other natural resources whose exploitation is a cause of serious pollution; for example, the use of uranium for nuclear power generation produces extremely dangerous waste that would take thousands of years to neutralize. But there is no reasonable doubt that fossil fuels are among the most serious sources of environmental pollution. 9.1 Objectives At the end of this unit, you should able to: 

Define pollution

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Show the intre- relation between chemistry of industrial technology and environmental pollution.

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State the various types of pollution

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Mention sources of air pollution

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State some possible pollution control measure

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Mention types of pollutants

9.2 Pollution Pollution is the introduction of contaminants into a natural environment that causes instability, disorder, harm or discomfort to the ecosystem i.e. physical systems or living organisms. Pollution can take the form of chemical substances or energy, such as noise, heat or light. Pollutants, the components of pollution, can be either foreign substances/energies or naturally occurring contaminants. Pollution is often classed as point source or nonpoint source pollution. 9.20 Types of Environmental Pollution Generally speaking, there are many types of pollution but the most important ones are: 

Air pollution

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Water pollution 100

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Soil pollution (contamination)

9.21 Air pollution:- The release of chemicals and particulates into the atmosphere. Some of the most notable air pollutants are sulfur dioxide, carbon monoxide, ozone, volatile organic compounds (VOCs) and airborne particles, with radioactive pollutants probably among the most destructive ones (specifically when produced by nuclear explosions),chlorofluorocarbons (CFCs) and nitrogen oxides produced by industries and motor vehicles. Photochemical ozone and smog are created as nitrogen oxides and hydrocarbons react with sunlight. Air pollution comes from both natural and man made sources. Though globally man made pollutants from combustion, construction, mining, agriculture and warfare are increasingly significant in the air pollution equation. Motor vehicle emissions are one of the leading causes of air pollution. Principal stationary pollution sources include chemical plants, coal-fired power plants, oil refineries, petrochemical plants, nuclear waste disposal activity, incinerators, large livestock farms (dairy cows, pigs, poultry, etc.), PVC factories, metals production factories, plastics factories, and other heavy industry. Agricultural air pollution comes from contemporary practices which include clear felling and burning of natural vegetation as well as spraying of pesticides and herbicides. About 400 million metric tons of hazardous wastes are generated each year. The United States alone produces about 250 million metric tons. Americans constitute less than 5% of the world's population, but produce roughly 25% of the world’s CO2, and generate approximately 30% of world’s waste. In 2007, China has overtaken the United States as the world's biggest producer of CO2, while still far behind based on per capita pollution - ranked 78th among the world's nations. 9.22 Water pollution: Human activity and especially those arising from the chemical processes releases pollutant that can affects living organism adversely into water body. For example, the discharge of wastewater from commercial and industrial waste (intentionally or through spills) into surface waters; discharges of untreated domestic sewage, and chemical contaminants, such as chlorine, from treated sewage; release of waste and contaminants into surface runoff flowing to surface waters (including urban runoff and agricultural runoff, which may contain chemical fertilizers and pesticides); waste disposal and leaching into groundwater; eutrophication and littering , all these causes water pollution. Water pollutants include insecticides and herbicides, food processing waste, pollutants from livestock operations, volatile organic compounds (VOCs), heavy metals, chemical waste and others. 9.23 Land pollution: Soil contamination occurs when chemicals are released by spill or underground leakage. Among the most significant soil contaminants are hydrocarbons, heavy metals, MTBE, herbicides, pesticides and chlorinated hydrocarbons. Some soil pollutants are: hydrocarbons, solvents and heavy metals. Other forms of pollution include Noise pollution:- which encompasses roadway noise, aircraft noise, industrial noise as high-intensity sonar. 101

well as

Visual pollution:- which can refer to the presence of overhead power lines, motorway billboards, scarred landforms (as from strip mining), open storage of trash, municipal solid waste or space debris. Light pollution:- includes light trespass, over-illumination and astronomical interference. Thermal pollution:- which is a temperature change in natural water bodies caused by human influence, such as use of water as coolant in a power plant. 9.30 Environmental Pollutants A pollutant is a waste material that pollutes air, water or soil. Three factors determine the severity of a pollutant: its chemical nature, the concentration and the persistence. Pollutants are constituent parts of the pollution process. They are the actual “executing agents” of environmental pollution. They come in gaseous, solid or liquid form. 9.31Types of pollutants The two known types of pollutants are biodegradable and non – biodegradable. 9.32 Biodegradable Pollutants Biodegradable pollutants are the ones that can be broken down and processed by living organisms, including organic waste products, phosphates, and inorganic salts. For example, if a pollutant is organic, it can be used by a living organism to obtain energy and other material from carbohydrates, proteins etc. Therefore, biodegradable pollutants are only “temporary nuisances” that can be neutralised and converted into harmless compounds. However, it is important to remember that they can become serious pollutants if released in large amounts in small areas, thus exceeding the natural capacity of the environment to “assimilate” them. 9.32 Non-Biodegradable Pollutants Non-biodegradable pollutants are the ones that cannot be decomposed by living organisms and therefore persist in the ecosphere for extremely long periods of time. They include plastics, metal, glass, some pesticides and herbicides, and radioactive isotopes. In addition to that, fat soluble (but not water soluble) non-biodegradable pollutants, ex. mercury and some hydrocarbons, are not excreted with urine but are accumulated in the fat of living organisms and cannot be metabolised. 102

9.4 Effects of Pollution There is no doubt that pollution posed serious danger to the ecosystem. For example, adverse air quality can kill many organisms including humans. Ozone pollution can cause respiratory disease, cardiovascular disease, throat inflammation, chest pain, and congestion. Water pollution causes approximately 14,000 deaths per day, mostly due to contamination of drinking water by untreated sewage in developing countries. An estimated 700 million Indians have no access to a proper toilet, and 1,000 Indian children die of diarrhoeal sickness every day. Nearly 500 million Chinese lack access to safe drinking water. 656,000 people die prematurely each year in China because of air pollution. In India, air pollution is believed to cause 527,700 fatalities a year. Studies have estimated that the number of people killed annually in the US could be over 50,000. Air pollution is believed to cause 527,700 fatalities a year. Oil spills can cause skin irritations and rashes. Noise pollution induces hearing loss, high blood pressure, stress, and sleep disturbance. Mercury has been linked to developmental deficits in children and neurologic symptoms. Older people are majorly exposed to diseases induced by air pollution. Those with heart or lung disorders are under additional risk. Children and infants are also at serious risk. Lead and other heavy metals have been shown to cause neurological problems. Chemical and radioactive substances can cause cancer and as well as birth defects. Lead poison has led to several death in Zamfara state and oil spillage had been sources of several severe adverse effect to lives in Niger Delta in Nigeria. To protect the environment from the adverse effects of pollution, many nations worldwide have enacted legislation to regulate various types of pollution as well as to mitigate the adverse effects of pollution. In Nigeria, agencies like FEPA have been legislated to control and monitor the level of discharged into the air, land and water bodies. 9.50 Pollution control Pollution control is a term used in environmental management. It means the control of emissions and effluents into air, water or soil. Without pollution control, the waste products from consumption, heating, agriculture, mining, manufacturing, transportation and other human activities, whether they accumulate or disperse, will degrade the environment. In the hierarchy of controls, pollution prevention and waste minimization are more desirable than pollution control. In the field of land development, low impact development is a similar technique for the prevention of urban runoff. Pollution control can be carried out by employing practices or devices that can help in reducing the effects in our environment. Some of these practices include; recycling, reusing, reducing, mitigating and preventing while some pollution control devices that can be employed include; dust collection system such as baghouses, cyclones, electrostatics preciptator; scrubber such as baffle spray,spray scrubber,wet scrubber and sewage treatment such as sendimentation, aerated lagoon, activated sludge biotreaters e.t.c

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9.6 Conclusion In this unit, you have learned a number of important issues that relate to the activity of man in terms of technological advancement and its effects on the ecosystem. The various types of pollution and pollutants were equally learned in this unit. 9.7 Summary Environmental pollution had been a fact of life for many centuries but it became a real problem since the start of the industrial revolution. Man in his quest for technological advancement in transforming the world via chemical technology releases pollutants into its environment thereby leading to the different types of pollution such water, air and land pollution.

9.8 Tutor- Marked Assignments (a) Define pollution and state the different types of pollution. (b) What are the main pollutants in air, water and land? (c) Write short note on biodegradable and non –biodegradable pollutants (d) State some pollution control practices 9.9 References www.en.wikipedia.org/wiki/pollution. www.tropical-rainforest- com www.library.thinkquest.org www.unep.org/enviroment

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