Hydrolysis of cellulose to glucose by supercritical water and silver mesoporous zeolite catalysts

Abstract

The hydrolysis of cellulose into glucose is a critical step for the conversion of lignocellulosic biomass into fuels and chemical products. The combination of supercritical water hydrolysis in ultrafast reactors, with the subsequent hydrolysis of the cello-oligosaccharides on silver-exchanged mesoporous mordenite zeolite, offers the possibility of a clear enhancement in the conversion of cellulose and in glucose formation. Complete dissolution of cellulose is achieved in the supercritical step and 81.8% of formed oligosaccharides are hydrolyzed in the catalytic step, with a yield into glucose of 77.0%. A fraction of Al is octahedrally coordinated, indicating a distribution of acid sites after the silver exchange. A deactivation of the catalyst between the first and third reaction cycle is observed, with a reduction in hydrolyzed carbon from 81.8% up to 45.6%. However, the selectivity to glucose only varies from 94.1 to 81.8%. Afterwards, the activity remains constant up to the fifth cycle. The presence of Ag(0) particles, together with the formation of coke, are responsible for the partial blockage of the pores of the support and loss of catalytic activity.