Optimization of supercritical phase and combined supercritical/subcritical conversion of lignocellulose for hexose production by using a flow reaction system

A flow reaction system was utilized to investigate lignocellulose conversion using combined supercritical/subcritical conditions for hexose production. Initially, investigation of cellulose hydrolysis in supercritical water and optimization of reaction parameters were done. Oligosaccharide yields reached over 30% at cellulose concentrations of 3-5 g L-1 and reaction times of 6-10 s at 375 degrees C, and 2.5-4 g L-1 and 8-10 s at 380 degrees C. Temperatures above 380 degrees C were not appropriate for the supercritical phase in the combined process. Subsequently, conversion of lignocellulosic materials under combined supercritical/subcritical conditions was studied. Around 30% hexose was produced from corn stalks under the optimal parameters for supercritical (380 degrees C, 23-24 MPa, 9-10 s) and subcritical (240 degrees C, 8-9 MPa, 45-50 s) phases. Flow systems utilizing the combined supercritical/subcritical technology present a promising method for lignocellulosic conversion. The results of this study provide an important guide for the operational optimization and practical application of the proposed system. (C) 2012 Elsevier Ltd. All rights reserved.