Glycerol hydrogenolysis on heterogeneous catalysts

Aqueous solutions of glycerol were hydrogenolysed at 180 °C under 80 bar H2-pressure in the presence of supported metal catalysts in an attempt to selectively produce 1,2- and 1,3-propanediol. Catalysts (Cu, Pd, Rh), supports (ZnO, C, Al2O3), solvents (H2O, sulfolane, dioxane) and additives (H2WO4) were tested to improve reaction rate and selectivity to the target molecules. The best selectivity (100%) to 1,2-propanediol was obtained by hydrogenolysis of water solution of glycerol in the presence of CuO/ZnO catalysts. To improve the selectivity to 1,3-propanediol the reaction was conducted with rhodium catalysts with tungstic acid added to the reaction medium. The best result in terms of conversion and selectivity to 1,3-propanediol (1,3-PDO/1,2-PDO = 2) was obtained by operating in sulfolane. The presence of iron dissolved in the reaction medium was also beneficial for the selectivity to 1,3-PDO. A mechanism was proposed to account for the effect of these different parameters.