Hydrogenolysis of glycerol to propylene glycol in continuous system without hydrogen addition over Cu-Ni catalysts

Abstract

A series of Cu, Ni and Cu-Ni catalysts with 20wt% of each metal, supported on Al2O3 and ZSM-5, was prepared by wet impregnation method and tested in glycerol hydrogenolysis to 1,2-propanediol (propylene glycol) using a WHSV of 2h−1 at 250°C, and pressure of 40bar for 6h. Without external hydrogen, the reaction pathway involves glycerol dehydration to acetol, with simultaneous reforming to H2 and CO2; this hydrogen generated in situ is used for the hydrogenation of acetol to propylene glycol. Under these conditions, the CuNi/Al2O3 and CuNi/ZSM-5 catalysts exhibited the highest glycerol conversion, 80% and 85%, respectively, with propylene glycol yield around 25%. With external hydrogen, all catalysts showed higher glycerol conversion (>90%) and the monometallic Cu catalysts presented higher conversion to liquid and propylene glycol yield than the bimetallic ones; the Cu/Al2O3 showed the highest yield to propylene glycol (70%). The activity of the catalysts was correlated with their metallic dispersion and also the support acidity.