Simultaneous hydrolysis and hydrogenation of cellobiose to sorbitol in molten salt hydrate media

Abstract

The hydrolysis and hydrogenation of cellobiose (4-O-β-D-glucopyranosyl-D-glucose) in ZnCl₂·4H₂O solvent was studied to optimize the conditions for conversion of lignocellulose (the most abundant renewable resource) into sorbitol (D-glucitol). Water at neutral pH does not allow hydrolysis of cellobiose under the conditions of the experiments (up to 125 °C, 4 h), but relatively fast hydrogenation of cellobiose into 3-β-D-glucopyranosyl-D-glucitol over a Ru/C catalyst in the presence of H₂ takes place. In ZnCl₂·4H₂O hydrolysis does take place in the range of temperatures studied (75–125 °C) and simultaneously hydrogenation (H₂, Ru/C), though at a lower rate than that in neutral water. Thus, a one-pot conversion of cellobiose into sorbitol is possible. The hydrolysis is the rate limiting reaction, but the selectivity to sorbitol is determined by the rate of hydrogenation. Under optimal conditions the yield of sorbitol is ≥95%. The kinetic pathways are discussed.