Kinetic investigation of the catalytic conversion of cellobiose to sorbitol

Abstract

The reaction pathway and the kinetics of the conversion of cellobiose to sorbitol catalyzed by silicotungstic acids combined with ruthenium supported on activated carbon were studied. Two competing reaction pathways starting from cellobiose could be confirmed. The conversion of cellobiose either follows the hydrolysis to glucose or it passes through a hydrogenation of cellobiose to cellobitol (3-β-D-glucopyranosyl-D-glucitol). Cellobitol is subsequently hydrolyzed to sorbitol and glucose. At moderate temperatures of 393K cellobitol becomes the main product with a maximum selectivity of 81%. Raising the reaction temperature to 443K decreases the cellobitol selectivity to 1% while the maximum sorbitol selectivity increases to 75%. Kinetic modeling shows activation energies of 115 and 69kJmol−1 for the hydrolysis of cellobiose and subsequent hydrogenation of glucose. For cellobitol formation followed by hydrolysis 76 and 103kJmol−1 can be determined together with overall higher reaction rates at lower temperatures.