Hydrolysis of microcrystalline cellulose for fermentable hexose in supercritical water

Ethanol extracted from cellulose has attracted considerable attention and previous studies have shown that hydrolysis is a key process for extraction of hexose from cellulose. This study describes the effects of solid-liquid ratio of cellulose/water on production of fermentable hexose by hydrolyzing microcrystalline cellulose in supercritical water (400°C) at different reaction times (6, 7, and 8 min). Thermal property of microcrystalline cellulose was characterized by thermogravimetric (TG) analysis. The concentration of fermentable hexose (glucose and fructose) was determined by using high-performance liquid chromatography (HPLC). Scanning electron microscopy (SEM) was carried out to observe the morphology of the hydrolysis residues. The results demonstrate that the concentration of hexose produced increased with increasing the solid-liquid ratio of cellulose/water in the hydrolysis process. The maximum concentration of fermentable hexose (37.98 g/L), corresponding to a hexose yield of 11.39%, was achieved at the solid-liquid ratio of cellulose/water of 250 (g/L) at 6 min. Various holes and spherical particles were observed on the surface of hydrolyzed cellulose, which suggests that the dissolving ability of supercritical water was restricted. The results show that many chars were produced as residues, which results in a low-hydrolysis yield but a high-hexose concentration. This study provides an important guide of producing high-concentration solution of hexose from cellulose for fermentation.