Kinetic Study of Catalytic Conversion of Cellulose to Sugar Alcohols under Low-Pressure Hydrogen

摘要

Efficient hydrolytic hydrogenation of cellulose to sugar alcohols under low H-2 pressures has remained a challenge. This article deals with the conversion of cellulose by using a carbon-supported Ru catalyst under H-2 pressures as low as 0.7-0.9MPa (absolute pressure at room temperature). Kinetic studies revealed that the Ru catalyst not only enhances the hydrolysis of cellulose to glucose and hydrogenation of glucose to sugar alcohols (sorbitol and mannitol), but also the degradation of sugar alcohols to C-2-C-6 polyols and gasses. The degradation path limits the total yield of sugar alcohols to less than 40%. The yield of sugar alcohols is theoretically improved by increasing the ratio of the reaction rates of the cellulose hydrolysis, which is the rate-determining step in the reaction, to the decomposition. Thus, a mix-milling pretreatment of cellulose and the Ru catalyst together selectively accelerated the hydrolysis step and raised the yield up to 68%, whereas the addition of acids in the cellulose conversion was less effective as a result of promotion of side-reactions. These results demonstrate superior applicability of the mix-milling treatment in the depolymerization of cellulose to its monomers.