(452f) The Kinetics of Reversion Reactions During Acid Pretreatment of Biomass

Nimlos, M. R., National Renewable Energy Laboratory
Johnson, D. K., National Renewable Energy Laboratory

Reversion reactions of the sugars released during acid pretreatment have been studied using a microwave-heated robotic reactor system. These reactions represent a potential loss of sugars during biofuels processes and knowledge of the kinetics of these reactions is necessary to optimize pretreatment. Towards that end the rates of reactions of monomer sugars to form dimers have been studied. Though xylose dimerization is difficult to study due to the lack of standards, reversion reactions of glucose are tractable. The rates for glucose were measured and these have been used to predict rates for xylose, which is more prevalent during pretreatment. The mechanisms for forming disaccharides involve dehydration of one monomer, forming a carbo-cation at C1 and addition by the hydroxyl group of another sugar molecule. Thus, reversion reactions necessarily result in dimers link at the C1 position of one of the sugars. In addition, we have observed that at temperatures above 140 °C equilibrium is rapidly established between glucose and the resulting disaccharides. The kinetics of glucose reversion reactions are measured and modeled and are used to predict rates for xylose. The impact of these rates on optimal pretreatment conditions will be discussed.