Monday, April 30, 2012
Napoleon Ballroom C-D, 3rd fl (Sheraton New Orleans)
Dilute-acid pretreatment is one of the most advanced and widely accepted pretreatment technologies. NREL has developed a continuous auger-driven pretreatment reactor that can be operated with high-solid charge. It operates at high temperature and with short residence time resulting high productivity and sugar concentration above 10 wt%. We investigated the kinetics of the reactions occurring in dilute-acid pretreatment of corn stover, covering the reaction conditions similar to those of the NREL reactor. For this purpose, batch experiments were performed under high solid conditions and the data were put into a kinetic model. The conventional bi-phasic kinetic model was initially adopted: two different fragments of hemicellulose to oligomers, to xylose, and to decomposition products. In the model verification process, we observed consistent discrepancy that xylose and its oligomers are over-estimated during the latter phase of the reactions. It was then speculated that side reactions may occur, especially recombination of xylose and its oligomers with soluble lignin forming lignin-carbohydrate complex (LCC). In subsequent investigation, we have positively identified the presence of LCC in the reaction liquid by NMR and by FTIR of the solids. The kinetic model was therefore modified incorporating the side reactions. The revised model has shown close and consistent agreement with the experimental data. Although it is a simplified empirical model, the experimental data yielded reliable degree of confidence in the Arrhenius plots for all of the rate constants. This model can thus serve as a useful tool for optimal design and operation of dilute-acid pretreatment reactors.