Kinetics of Hydrogenolysis of Glycerol to Propylene Glycol over Cu-ZnO-Al2O3 Catalysts

A series of Cu-ZnO-Al2O3 catalysts with various metal compositions of Cu/Zn/Al were prepared by the co-precipitation method, and screened for glycerol hydrogenolysis to propylene glycol. The catalyst with a Cu/Zn/Al molar ratio of 1 : 1 : 0.5 exhibited the best performance for glycerol hydrogenolysis, and thus selected for kinetic investigation. Under elimination of external and internal diffusion limitation, kinetic experiments were performed in an isothermal fixed-bed reactor at a hydrogen pressure range of 3.0-5.0 MPa and a temperature range of 493-513 K. Based on a dehydration-hydrogenation two-step hydrogenolysis mechanism, a two-site Langmuir-Hinshelwood kinetic model taking into account competitive adsorption of glycerol, acetol and propylene glycol was proposed and successfully fitted to the experimental data. The average relative errors between observed and predicted outlet concentrations of glycerol and propylene glycol were 6.3% and 7.6%, respectively. The kinetic and adsorption parameters were estimated by using the fourth-order Runge-Kutta method together with the Rosenbrock algorithm. The activation energies for dehydration and hydrogenation reactions were 86.56 and 57.80 kJ·mol−1, respectively.