Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/9/2003
Publication Date: 6/25/2003
Citation: Marshall, W.E., Wartelle, L.H. 2003. Acid recycling to optimize citric acid-modified soybean hull production. Industrial Crops and Products. 18(2):177-182.
Interpretive Summary: A process has been developed to modify soybean hulls in order to enhance their capacity to bind metals and improve their value in the marketplace through citric acid modification. Soybean hulls modified with citric acid have been compared to commercially available materials used for removal of metals from water and costs for the scale-up of the process have been calculated. The most costly factor in the process was the citric acid which could be recycled in part and re-introduced into the process. One objective of this study was to develop a washing process that would maximize citric acid recovery. Another objective was to determine if unreacted citric acid could be combined with virgin citric acid to produce modified soybean hulls without a significant reduction in metals adsorption. Our results showed that two water wash cycles were sufficient to remove the maximum amount of unreacted citric acid from the modified hulls, and that the recycling of citric acid to modify soybean hulls caused only a slight reduction in copper ion binding.
Technical Abstract: The objectives of this study were 1) to develop a wash procedure to remove non-reacted or residual citric acid after soybean hull modification in order to maximize the amount of non- reacted acid removed but minimize the subsequent effect on the product's ability to adsorb copper ion (Cu2+) and 2) to determine whether using non-reacted acid in the modification process, along with virgin acid, produces a product with similar copper ion adsorption compared to the use of virgin acid only. In order to meet these objectives, an effective water washing procedure was developed to remove the residual citric acid associated with the modified soybean hulls. This washing procedure included removal of non-reacted acid, evaporation of excess water to the original volume of acid solution used, and addition of virgin citric acid to reconstitute the solution to its original molarity. Reconstituted citric acid solutions prepared in this manner were used through three cycles of soybean hull modification. The effectiveness of the reconstituted citric acid to modify soybean hulls after each cycle was measured by the modified hulls ability to bind copper ions in solution. After three reaction cycles, there was a 10% reduction in copper ion adsorption among the samples. Our results show that generally, two water wash cycles were necessary to remove sufficient non-reacted citric acid so that metal ion binding of the hulls was not affected, and that use of residual citric acid to modify soybean hulls can be successfully accomplished with only a small reduction in copper ion binding.