Continuous production of 1,2-propanediol by the selective hydrogenolysis of solvent-free glycerol under mild conditions

BACKGROUND: The conversion of glycerol to value-added derivatives is now critical, owing to the large surplus of glycerol from biodiesel production. The main objective of this work is to develop a novel process for converting solvent-free glycerol to 1,2-propanediol. RESULTS: Several catalysts were screened for aqueous-phase hydrogenolysis of glycerol in an autoclave. The most effective catalysts (Ni/Al2O3, Cu/ZnO/Al2O3) were further tested for vapor phase hydrogenolysis in a fixed-bed. Ni/Al2O3 did not prove as effective for the production of 1,2-propanediol because of the high selectivity to CH4 and CO. Over Cu/ZnO/Al2O3 glycerol was mainly converted to the desired 1,2-propanediol and the reaction intermediate acetol. The production of 1,2-propanediol was favoured at higher hydrogen pressure. At 190 degrees C and 0.64MPa, near complete conversion of glycerol was achieved with 1,2-propanediol selectivity up to 92%. In addition, a higher concentration (between 43.4%, and 0.8%) of acetol was detected and an approximately stoichiometric relationship was found between acetol and 1,2-propanediol. CONCLUSION: 1,2-propanediol can be produced with high yields via the vapor phase hydrogenolysis of glycerol over Cu/ZnO/Al2O3. Furthermore, the mechanism of 1,2-propanediol formation is suggested to proceed mainly through an acetol route over Cu/ZnO/Al2O3 (C) 2008 Society of Chemical Industry