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7690
INDUSTRIAL CROPS AND PRODUCTS An International Journal
Industrial Crops and Products 5 (1996) 301-305
Com fiber citrate: preparation and ion-exchange properties Robert E. Wing * Plant Polymer Research, National Center for Agricultural Utilization Research, USDA 1815 N. University St.• Peoria. lL 61604. USA
I,
Agricultural Research Service,
Received 7 May 1996; accepted 3 July 1996
Supplied by U.S. Dept. of Agriculture National Center for Agricultural Utilization Research, Peoria, nnnois
ELSEVIER
INDUSTRIAL CROPS AND PRODUCTS Editors-in-Chief For the Americas
Dr. ES. Nakayama, USDA-ARS, US Water Conservation Lab., 4331 East Broadway, Phoenix. AZ 85040. USA For the rest ofthe world
Dr. AH. Eenink, Agrotechnological Research Institute (ATO-DLO), P.O. Box 17, 6700 AA Wageningen. The Netherlands
Book Review Editor D.T. Ray, Department of Plant Science, University of Arizona, Tucson, AZ 85721, USA Editorial Advisory Board T.P. Abbott, NCAUR-ARS-USDA, Peoria, IL, USA P. Ahlgren, University of Karlstad, Karlstad, Sweden M.G. Blase, University of Missouri-Columbia, Columbia, MO, USA C. Botti, Universidad de Chile, Santiago, Chile D. Byrom, ZENECA LifeScience Molecules, Cleveland, UK P. Colonna, INRA, Nantes, France K. Cornish, USDA-ARS, Albany, CA, USA S.A Graham, Kent State University, Kent, OH, USA R.W Kessler, Fachhochschule Reutlingen, Reutlingen, Gennany
S.J. Knapp, Oregon State University, Corvallis. OR. USA B. Mattiasson, Dept. of Biotechnology. Lund, Sweden P.L. Milthorpe, Condobolin. NSW, Australia A Noguchi, JIRCAS, Tsukaba, Ibaraki. Japan Y. Popineau, INRA, Nantes, France G. R6bbelen, lnstitut fUr Pflanzenbau und Pflanzenziichtung, G6ttingen. Germany . S.E Thames, Dept. of Polymer Science. Hattiesburg. MS. USA H. Tournois, ATO-DLO. Wageningen, The Netherlands G. Wegener, Institute for Wood Research. Munich, Gennany
Aims and Scope publishes papers reporting the results of original research. short communications and critical reviews on all aspects of industrial crops and products. This covers a wide range of aspects of cultivation, crop improvement, crop compounds. processing and integrated chain control, all focusing on the exploitation of agricultural crops for industrial use. The scope of the journal covers a vast range of crops and research disciplines. Crops should contain significant renewable resources such as:
INDUSTRIAL CROPS AND PRODUCTS, AN INTERNATIONAL JOURNAL,
• • • • • • •
fibres and fibre compounds; carbohydrates; oils and fatty acids; waxes, resins, gums, rubber and other polymers; proteins; essential oils for i,nk, lubricants, plastics, cosmetics; biologically active compounds for pharmaceuticals, herbicides and insecticides, and preservatives.
Examples of new or potential crops are agave, cassava, crambe, cuphea, elephant grass, fibre hemp, flax, guar, guayule, jojoba, kenaf, lesquerella, maize, meadowfoam, oil palm, peas, plantago, potato, pyrethrum, rape seed, safflower, soybean, Stokes aster, sugar beet, sunflower veronia and wheat. Papers within the above indicated frame-work will be accepted if they cover or integrate research on: • • • • • • •
agronomic production and modelling; breeding, genetics and biotechnology; post-harvest treatment and storage; (bio)process technology; (bio)chemistry product testing, development and marketing; economics, and systems analysis and optimization.
Copyright © 1996, Elsevier Science B.V. All rights reserved
0926-6690/96/$15.00
7690
Supplied by U.S. IJept. of AgriculturE National Center for Agricultural Utilization Research, Peoria, IlIinoi~
INDUSTRIAL CROPS AND PRODUCTS AN INTERNATIONAL JOURNAL
ELSEVIER
Industrial Crops and Products 5 (1996) 301-305
Corn fiber citrate: preparation and ion-exchange properties Robert E. Wing * Plant Polymer Research, National Center for Agricultural Utilization Research, USDA 1815 N. University St., Peoria. 1L 61604. USA
I,
Agricultural Research Service.
Received 7 May 1996; accepted 3 July 1996
Abstract Com fiber (CF) was allowed to react thermochemically with citric acid (CA) to yield potentially biodegradable products possessing high ion-exchange capacity. The reaction variables studied were; citric acid level (0-100 g), reaction time (0-24 h), pH (1.5-8.3) and temperature (l10-140"C). Moisture content and pH were found to be controlling factors. Reaction efficiencies approaching 100% were achieved, while minimizing cross-linking and maximizing carboxyl content. Carboxyl content (0.5-3.6 mmol/g) was determined and copper-binding capacity (0.1-2.0 mmol/g) at pH 4.5 was evaluated for the various CF-CA products. Keywords:
Com fiber; Citric acid; Agricultural residue; Polysaccharide; Thermochemical reaction
1. Introduction Petrochemically derived ion-exchange resins have been used for decades to remove toxic heavy metal ions from industrial wastewaters. These resins are expensive ($3-25/kg), regenerative and nonbiodegradable. More stringent environmental regulations will create a 5.8% annual growth in ionexchange materials in the U.S. in the next few years. Presently more than 60 million kg of petrochemically based resins are currently in use. Over the last 20 years, several agriculturally produced materials have been derivatized to yield products possessing ion-exchange capability, that are inexpensive and • Tel. +1 (309) 681-6353; Fax: + 1 (309) 68 j -6691. I Names are necessary to report factually on available data; however the USDA neither guarantees nor warrants the standard of the product, and the use of the name by USDA implies no approval of the product to the exclusion of others that may also be suitable.
biodegradable. A compilation (Wing, 1996) of agriculturally derived ion-exchange materials included starch, cellulose, peanut skins, onion skins, wool, soybean hulls, sugar beet fiber, pectin, corn cobs, apple residues, wheat straw, and citrus peels. Only one product from this list, insoluble starch xanthate (Wing, 1983), has been commercialized ($5/kg). Agricultural waste in the U.S. exceeds 320 billion kg/year and is generally considered of little monetary value. In 1995, to implement the Clean Air Act of 1990, ethanol use as an oxygenated fuel additive reached 5 billion 1, leading to 1.4 billion kg of corn fiber as a potential non-animal food waste. Currently, corn fiber is combined with corn distillers as solubles, dried ($0.09/kg) and corn gluten animal feed sold at $O.13/kg. Other alternative uses (nonanimal feed) of corn fiber is necessary to take care of the large volume of waste material. Corn fiber is essentially all polymeric carbohydrate, containing 20-30% starch.
0926-6690/96/$15.00 Copyright © 1996 Elsevier Science B.Y. All rights reserved. PIl S0926- 6690(96 )0003 0-1
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R.E. Wingl/ndusrrial Crops and ProducEs 5 (1996) 301-305
A main objective at our Center is to expand the use of agricultural materials for industrial appli. cations with value-added products. Recently, Wing (1994) reported that the thermochemical oxidation of starch yielded products possessing novel properties. Research using thermochemical processing was expanded to evaluate the reaction of starch with citric acid (Wing, 1996). Results showed that the products were highly cross-linked and possessed high ionexchange potential. The products were economically prepared and could serve as one-time biodegradable ion-exchange materials ($1.70/kg). Reaction efficiency was 98% under controlled conditions. Other studies with citric acid and cellulosic fiber in cloth (Andrews et al., 1993) and citric acid with cellulosic wood fiber (Caulfield, 1994) yielded cross-linked products. Cellulose powder has been reacted with citric acid to yield products with ion-exchange properties (Touey and Kiefer, 1956). The purpose of the present study was to maximize the thermochemical reaction of com fiber and citric acid for producing products with high cationicexchange properties. Reaction conditions were controlled to minimize complete cross-linking and to maximize carboxyl content to attain this feature (product cost "'-'$1.50/kg). The products of this study could serve as putative biodegradable ion-exchange materials. 2. Materials and methods
2.1. Materials Com fiber (CF) was supplied by Pekin Energy, Pekin, II., at 40% solids. Average dry weight analysis was: starch (25%); cellulose (27%); hemicellulose (32%); protein (10%); lipid (2%); lignin (2%); ash (2%); 2-20 mesh. Citric acid (CA) was supplied by Archer Daniels Midland, Decatur, II.,. All other chemicals were reagent grade.
2.2. Reaction procedure CA (0-100 g) was dissolved in water (500 rnl), poured over CF (241 g) and thoroughly mixed. The mixtures were dehydrated at 60"C for 24 h in forced air ovens. At this point, all surface moisture was removed and CF particles were coated with CA.
The oven temperature was raised to the desired level (110-140°C) and the mixtures allowed to react. Reaction products were slurried in water (1200 ml) for 30 min, adjusted to pH 2. filtered and washed with water (2000 rnl). The product was air-dried overnight and ground to 40-60 mesh before analysis. The filtrate was evaporated to obtain a weight for unreacted CA. Reaction efficiency was calculated by: (CA added - CA recovered)/CA added. Washed, unreacted CF contained 3% solubles.
2.3. Carboxyl detennination A dry sample (1.000 g) was slurried in water (100 rnl) and 0.0975 N NaOH was added. After stirring for 24 h, the mixture was back-titrated with 0.116 N HCl to the phenolphthalein end point. Conversion factors were determined using oxalic and citric acid as standards. Untreated CF was oven-dried at 120°C and used as a control. The presence of protein and lipids yielded higher-than-expected carboxyl content. No corrections were made for de-esterification, since the pH was always maintained between 10 and 10.5 since in-house studies showed that there was complete product stability at pH 11.
2.4. Copper-binding capacity Samples (1.000 g) were slurried in water (100 ml) containing Cu+2 (200 mg). The pH was adjusted to 4.5 with 0.1 N NaOH and maintained for 24 h. The solid was filtered, stripped of copper with 50% nitric acid, refiltered and diluted to 1 1 for copper analysis using a Perkin-Elmer Plasma 400 Emission Spectrometer. 3. Results and discussion CA when heated will dehydrate to yield a reactive anhydride. When CF is present in the reaction mixture, the anhydride can react to form a CFcitrate adduct (Wing, 1996). Further heating can result in additional dehydration (anhydride formation) with the possibility of cross-linking (Fig. 1). The following data show that the reaction can be controlled to maximize reaction efficiency, minimize cross-linking and maximize carboxyl content. It is important that the CA is completely solubilized
R.E. Wing / Industrial Crops and Products 5 (19961301-305
ft
H2C-C-OCF
-
CF·OH
ft H2C-C-OCF
I
I I H2G-COOH
Ho-C-COOH
40
-
CF·OH
Ho-C-COOH
I
H2C-C-OCF
"
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at 60°C. The effect of grinding reaction mixtures after predehydration, but before high-temperature reaction. resulted in 3-25% reduction in carboxyl content and copper binding. One CF sample (Table 1. 6) was dried and ground before CA treatment. This pretreatment, while increasing product cost but reducing the particle size, did result in increased carboxyl content and copper binding. These CF-CA results show a 10-200% reduction in carboxyl content and a 25-425% reduction in copper binding compared to similar starch-CA reactions (Wing, 1996). However, the reaction efficiencies increased 5-25%.
o
Fig. I. Thermochemical reaction of corn fiber and citric acid.
Table I Effect of temperature on corn fiber (CF)-