LIQUID PHASE HYDROGENOLYSIS OF GLYCEROL OVER SUPPORTED METAL CATALYSTS

Abstract

Biodiesel is a liquid transportation fuel derived from fatty acids obtained from renewable resources such as vegetable oils and animal fats. The fuel crisis in the 21 century due to uncertain supply of fossil fuels increased the demand for biodiesel. The worldwide production of biodiesel is estimated to exceed 180 million tonnes by 2016 at a growth rate of 42% per year. Approximatcly 10% of the total biodiesel produced is crude glycerol. Surplus amount of glycerol produce needs to convert into the valuable chemicals. Among the various processes of glycerol conversion to vaIn added chemicals, hydrogenolysis of glycerol tol,2-propanediol (I ,2-PDO) has attracted significant interest. In this work, a series of monometallic (Cu, Co. Ni, Fe. Zn) and bimetallic (Cu-Zn,Cu-Fe, Co-Zn, Co-Fe and Co-Ni) catalysts supported on MgO were prepared and evaluated for liquid phase hydrogenolysis of glycerol. The physico-chemical properties of the catalysts were determined by various characterization techniques such as BET surface area, NH—temperature programmed dcsorption (NI h-TPD), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Catalytic activity and I ,2-PDO selectivity obtained over different catalysts were compared at 210°C. 4.5 MPa pressure. Results showed that the catalytic activity for monometallic catalyst followed the order: Cu>Co>Ni>Zn>Fe. Among these catalyst, Cu/MgO showed very high glycerol conversion of 96.40%, with 92% selectivity to I ,2-PI)O. Maximum 1 ,2-PDO selectivity of 100% is achieved over Zn and Fe catalyst. The maximum yield of 93.4% was obtained for 50wt %Cu-Zn(7:3)/MgO. The influence and interaction of reaction parameters such as reaction temperature, glycerol concentration and reaction time on glycerol conversion and product selectivity was also studied and the results are represented as contour and 3D surface graphs using Response Surface Methodology (RSM). %• The model developed fitted well with the experimental data. 1'he values of of regression coefficient (R) obtained for glycerol conversion and 1,2-PDO selectivity were 0.98 and 0.95 respectively. Results showed that, among the various reaction parameters studied, temperature had the greatest influence on glycerol hydrogenolysis reaction. Design expert software was used to optimize the reaction parameters in order to maximize the glycerol conversion and I ,2-PDO selectivity. The optimal values of reaction parameters obtained were: reaction temperature 2 12°C, glycerol concentration 20 wt%, catalyst loading 7 wt% and reaction time 12 h.