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 °C, and 2.5–4 g L−1 and 8–10 s at 380 °C. Temperatures above 380 °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 °C, 23–24 MPa, 9–10 s) and subcritical (240 °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.

► Flow system was used in combined super/subcritical conversion of lignocellulose.
► Cellulose hydrolysis in supercritical water was optimized by using the flow system.
► Combined super/subcritical conversion of corn stalks was studied in the flow system.
► Around 30% of hexoses was produced from corn stalks under the optimal parameters.