Dehydroxylation of glycerol to propylene glycol over copper-zinc oxide catalysts : effects of catalyst perparation and regeneration

Abstract

Glycerol is a major by-product from vegetable oil transesterification to biodiesel. The increase in biodiesel production results in the marketed surplus of glycerol. The catalytic dehydroxylation of glycerol to propylene glycol is one of the most attractive routes to convert glycerol to high value-added products. In this work, the dihydroxylation of glycerol to propylene glycol was investigated over Cu-ZnO/AI₂O₃ catalysts prepared by different techniques -i.e. incipient wetness impregnation (IWI), co-precipitation (COP), and sol-gel (SG) methods. The prepared catalysts were tested for their catalytic activity in a packed-bed reactor at 250 °C and 500 psig under hydrogen atmosphere. Fresh and spent catalysts were characterized by several techniques including SAA, XRF, XRD, TPR, and TPO. Among the catalysts tested, the impregnated Cu-ZnO/AI₂O₃ catalyst provided the highest catalytic performance which could be due to its low coke formation and high stability of metal on surfaces. Furthermore, causes of the catalyst deactivation were found to be the combination of deposited carbon and sintering of active metals. Therefore, the catalytic of the Cu-ZnO/AI₂O₃ catalysts cannot be recovered by a simple method for coke removal.