Hydrogenolysis of glycerol to propylene glycol by in situ produced hydrogen from aqueous phase reforming of glycerol over SiO2–Al2O3 supported nickel catalyst

Abstract

In the present work, the reactions of glycerol's aqueous phase reforming (APR) and Aqueous Phase Hydrogenolysis (APH) in a batch reactor containing SiO2–Al2O3 supported 65% Ni catalyst are performed. The effect of: i) the reaction time (30–240min), ii) the operating temperature (200–240°C), iii) the glycerol concentration (1 or 10wt.%), iv) the catalyst weight (0.5–10g) and v) the gas to liquid phase volume ratio (1.4 or 5ml/ml) on: a) the gaseous and liquid product selectivities and b) the glycerol's conversion is investigated. The main gaseous products are found to be H2, CH4 and CO2, while the main liquid products are found to be propylene glycol (PG), ethylene glycol (EG), ethanol and acetol. Glycerol's conversion increases with the reaction evolution and the increase of the temperature, reaching a plateau. It is found that hydrogen yield is maximized at short reaction times, low glycerol concentrations and increased gas to liquid phase volume ratios, reaching up to 23.5%. On the contrary, the PG yield is favored under the inverse conditions, reaching up to 22%. The higher conversion to gaseous products is found to be ~73.6% and the higher conversion to liquid products ~35.6%. It is also found that, the increased catalyst concentration favors the C–C bond cleavage and the formation of ethylene glycol, ethanol and CH4.