Parameters Affecting the Formation of 1,2-Propanediol from Glycerol over Ru/SiO2 Catalyst

The production of 1,2-propanediol from renewable glycerol in hydrogen atmosphere is of high interest. In this study the reaction was performed in the presence of 5 wt %Ru/SiO2 catalyst and the effects of reaction temperature, hydrogen pressure and glycerol concentration were investigated. The catalytic results indicate that increased temperature and pressure favor glycerol conversion and propylene glycol selectivity. Glycerol conversion remains almost constant with water dilution, but 1,2-propanediol selectivity increases due to the function of water as a solvent and the suppression of side reactions, such as degradation and polymerization. At the optimum reaction conditions (T = 240 degrees C, P = 8 MPa H-2, pure glycerol feedstock, catalyst/glycerol ratio = 0.006, reaction time = 5 h) glycerol conversion reaches the value of 21.7% along with 60.5% 1,2-propanediol selectivity. The activity of the catalyst does not change in two consecutive runs, while propylene glycol selectivity slightly decreases due to the formation of overhydrogenolysis products (propanols). The reaction pathways over Ru/SiO2 catalyst were explored using intermediate and final products as reactants. The production of 1,2-propanediol is favorable as it is formed with high selectivity from acetol and its overhydrogenolysis to propanols is very limited. The results suggest that ethylene glycol is a primary product originating from the direct degradation of glycerol.