High pressure facilitates delignification of Japanese cedar in supercritical methanol

Abstract

Supercritical methanol is a tool for decomposing woody biomass and dissolving the products under relatively mild conditions. Thus, the use of supercritical methanol—in combination with catalytic hydrogenolysis—in industrial production of biochemicals has been widely studied. However, the contribution of specific methanol properties to wood decomposition remains unclear. In this study, the effect of the pressure on the decomposition of Japanese cedar in supercritical methanol was investigated in a semi-flow reactor. Delignification progressed better at higher pressure, attributable to the ability of methanol to dissolve high molecular weight, lignin-derived oligomers at high pressure. This solubility was strongly correlated with the methanol density. Methanol pressure also affected the product yields, with higher pressure resulting in higher coniferyl alcohol and sugar yields. This is attributable to the fact that the higher pressure facilitated rapid dissolution of the decomposition products and recovery from cell walls, protecting the products from further degradation. The findings of this study will contribute to the establishment of supercritical methanol in industrial production of biochemicals.