Hydrogenolysis of glycerol to 1,2-propanediol in a continuous flow trickle bed reactor

Abstract

BACKGROUND: Hydrogenolysis of glycerol to glycols in continuous flow three phase reactors is of practical importance due to the need to give value to huge amounts of surplus glycerol. Thermodynamic and kinetic aspects must be revised for a proper design. The system was studied in a trickle-bed reactor using copper chromite and Cu/Al2O3 as catalysts. RESULTS: Phase equilibrium and flow pattern were verified. Solid, liquid and gas phases were present, with the liquid phase in ´trickling´ flow. Catalysts were characterized by inductively coupled plasma (ICP), nitrogen sortometry, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), temperature programmed reduction (TPR) and pyridine thermal programmed desorption (TPD). The average reaction rate was found to be practically constant under different process conditions. A theoretical analysis indicated that the resistance to the transfer of hydrogen from the gas to the liquid phase dominated the overall kinetics. Selectivity to 1,2-propanediol varied with temperature, with a maximum at 230°C (97%). Selectivity was a function of the catalyst acidity. When the pressure was increased the selectivity to 1,2-propanediol was increased, up to 97% at 14bar. Higher pressures did not modify this value. CONCLUSIONS: Optimum reaction conditions for maximum selectivity to 1,2-propanediol with Cu-based catalysts are 230°C and 14bar. System kinetics are, however, dominated by the gas-liquid mass transfer resistance.