Acid-treated soy hull carbon structure and adsorption performance

Abstract  The objective of this study was to evaluate the effect of 14 N phosphoric acid and 12 N hydrochloric acid treatments on soy hull carbon structure and adsorption performance. Scanning electron micrographs showed that acid treatments disrupted the carbon structure whereas X-ray diffraction data indicated that hydrochloric acid had a greater effect than phosphoric acid in creating a more amorphous carbon structure. Both acids significantly reduced carbon pH from 9.8, but hydrochloric acid reduced the pH to a much greater degree (pH 2.77) than phosphoric acid (pH 5.95). Both acids increased the carbon titratable surface charge. The greatest increase was in surface lactone and phenol groups, but increases were also seen in noncarboxylic carbonyls and the generation of carboxyls. Acidified carbon was most effective as a phospholipid adsorbent, and its lower affinity for other oil components may be due to competitive adsorption. Nonacidified carbon and hydrochloric acid-treated carbon adsorbed most free fatty acids, whereas the nonacidified control and commercial carbon control were most effective at adsorbing peroxides. However, vacuum adsorption conditions alone increased the contents of saturated carbonyls that were probably formed by peroxide cleavage.