Conversion of biomass to 1,2-propanediol by selective catalytic hydrogenation of lactic acid over silica-supported copper

It is shown that it is possible to produce 1,2-propanediol (a high demand commodity chemical) in high yields via the vapor-phase catalytic hydrogenation of biomass-derived lactic acid. This catalytic process provides an environment-friendly route for the production of 1,2-propanediol from renewable resources. Reaction kinetics measurements were conducted for the vapor-phase hydrogenation of lactic acid over silica-supported copper at total pressures between 0.10 and 0.72 MPa and temperatures between 413 and 493 K. Lactic acid is hydrogenated over Cu/SiO2 under these reaction conditions to predominately 1,2-propanediol, with formation of smaller amounts of 2-hydroxy propionaldehyde, propionic acid, and propyl alcohols. Deactivation of the Cu/SiO2 catalyst does not appear to be significant under these reaction conditions. The production of 1,2-propandiol is favored at higher hydrogen partial pressures. At 473 K and a hydrogen partial pressure of 0.72 MPa, complete conversion of lactic acid was observed, with 88 mol% of the lactic acid converted to 1,2-propanediol. A reaction scheme for lactic acid conversion is proposed involving the dissociative adsorption of lactic acid to form an adsorbed alpha-hydroxy acyl species that undergoes successive hydrogenation steps to form adsorbed 2-hydroxy propionaldehyde species and then adsorbed alpha-hydroxy alkoxy species. These alkoxy species react with surface hydrogen to form 1,2-propanediol. The formation of 2-hydroxy propionaldehyde appears to be in equilibrium with 1,2-propanediol at the reaction conditions of the present study. (C) 2002 Elsevier Science B.V. All rights reserved.