Catalytic dehydroxylation of glycerol to propylene glycol over Cu-ZnO/Al₂O₃ catalyst: effect of feed purity

Abstract

Biodiesel is now regarded as an economical alternative because of the decrease in petroleum reserves. Nevertheless, in the production of biodiesel by a typical transesterification process, up to 10% glycerol is produced as a by-product. As biodiesel production is expanding, the crude glycerol generated has also been produced in large quantities. For this reason, the transformation of glycerol into more valuable chemicals, such as propylene glycol, is suggested as a value-added product. In this research, the dehydroxylation of glycerol to propylene glycol was investigated over Cu-ZnO/Al2O3 catalyst with different purity feedstocks—refined glycerol, yellow glycerol, technical glycerol, and crude glycerol. The catalyst was tested for its catalytic activity and selectivity in a continuous flow fixed bed reactor at 523 K, 500 psig, WHSV of 3 h-1, and H2 to glycerol molar ratio of 4. The result showed that refined glycerol had the lowest concentration of impurities followed by yellow grade glycerol, technical grade glycerol, and crude glycerol. In line with the impurity contents, the conversion of glycerol and selectivity of propylene glycol decreased in the following order: refined glycerol > yellow grade glycerol > technical grade glycerol > crude glycerol. ICP-EOS indicated that Na and K contaminated in feedstocks deposited on the catalysts and they may poison the catalysts, thus lowering the catalytic activity.