Reaction Kinetic Model of Dilute Acid-Catalyzed Hemicellulose Hydrolysis of Corn Stover under High-Solid Conditions

High-solid conditions are desirable in pretreatment of lignocellulosic biomass. An advanced dilute-acid pretreatment reactor has been developed at National Renewable Energy Laboratory (NREL). It is a continuous auger-driven reactor that can be operated with high-solid charge at high temperature and with short residence time resulting in high productivity and high sugar concentration. We investigated the kinetics of the reactions associated with dilute-acid pretreatment of corn stover, covering the reaction conditions of the NREL reactor operation: 155–185 °C, 1–2 wt % sulfuric acid concentration, and 1:2 solid:liquid ratio. The experimental data were fitted to a first-order biphasic model which assumes that xylan is composed of two different fragments: fast and slow reacting fractions. Because of the high solid loading conditions, a significant amount of xylose oligomers was observed during the pretreatment. The oligomers were included as an intermediate entity in the kinetic model. The effect of acid concentration was incorporated into the pre-exponential factor of the Arrhenius equation. The kinetic model with best-fit kinetic parameters has shown good agreement with experimental data. The kinetic parameter values of the proposed model were noticeably different from those previously reported. The activation energies of xylan hydrolysis are lower and the acid exponents are higher than the average of literature values. The proposed model can serve as a useful tool for design and operation of pretreatment systems pertaining to corn stover.