Optimization and estimated production cost of a citric acid-modified soybean hull ion exchanger

Soybean hulls modified with citric acid have enhanced capabilities for adso rbing metals from wastewater and have the potential to compete in the marke tplace as ion-exchange resins. The objective of this study was to determine the optimal conditions for citric acid modification of soybean hulls and t o estimate the cost of the modification process. Adsorption capacities for copper ion (Cu2+) were determined on unwashed, water-washed and 0.1 N NaOH- washed soybean hulls. All three samples had the same adsorption capacities. Therefore, unwashed hulls were selected as the feedstock for citric acid m odification. The citric acid-treated hulls required a drying step before mo dification could proceed. However, the drying and modification steps could be combined into a single process step when the wet hulls were heat-treated at 120 degreesC for 1.5 h. A process flow diagram was developed based on t hese results. From the process description and equipment needed to manufact ure the modified product, the capital and operating costs were determined. The product cost was estimated, based on a daily input of 10 000 kg of soyb ean hulls and a daily output of modified product of 7900 kg, with a yield o f 79%. An estimated production cost for the modified product was $1.17/kg v ersus typical retail costs of $4-40/kg for commercial, petroleum-based cati on-exchange resins when purchased in bulk quantities. Published by Elsevier Science B.V.