Reaction Mechanisms and Kinetics of Xylo-Oligosaccharide Hydrolysis by Dicarboxylic Acids

Hydrothermal pretreatment of lignocellulosic materials generates a liquid stream rich in pentose sugar oligomers. Cost-effective hydrolysis and utilization of these soluble sugar oligomers is an integral process of biofuel production. We report integrated rate equations for hydrolysis of xylo-oligomers derived from pretreated hardwood by dicarboxylic maleic and oxalic acids. The highest xylose yield observed with dicarboxylic acids was 96%, and compared to sulfuric acid, was 5-15% higher with less xylose degradation. Dicarboxylic acids showed an inverse correlation between xylose degradation rates and acid loadings unlike sulfuric acid for which less acid results in less xylose degradation to aldehydes and humic substances. A combination of high acid and low-temperature leads to xylose yield improvement. Hydrolysis time course data at three different acid concentrations and three temperatures between 140 and 180 degrees C were used to develop a reaction model for the hydrolysis of xylo-oligosaccharides to xylose by dicarboxylic acids. (C) 2012 American Institute of Chemical Engineers AIChE J, 59: 188-199, 2013