LIQUID PHASE CONVERSION OF GLYCEROL TO PROPANEDIOL OVER Cu/MgO CATALYST: SYNTHESIS, CHARACTERIZATION AND REACTION PARAMETER STUDY

Abstract

Catalytic conversion of glycerol into glycols (1, 2-propanediol and 1, 3-propanediol) by hydrogenolysis is very promising route for glycerol utilization. MgO supported Cu based catalysts with different Cu metal loadings were prepared by co-precipitation method. The physiochemical properties of the catalysts were characterized by various techniques such as BET surface area, X-ray diffraction (XRD), temperature programmed reduction (TPR), temperature programmed desorption (TPD) and scanning electron microscopy (SEM) methods. Surface area of pure MgO was 104 m2/g. It was found that specific surface area decreased with increase in Cu metal loading up to 25% which may be due to the formation of CuO clusters on the MgO support which might be blocking the pores of MgO. The XRD result showed the formation of Cu oxides along with Mg oxides and the peaks intensity suggested the crystalline structure of Cu/MgO catalyst.TPR result revealed that all the Cu/MgO catalyst undergoes reduction at 350oC. NH3-TPD revealed the acidic characteristics of Cu/MgO catalysts. SEM images showed the morphology of prepared Cu/MgO catalysts. At 5-20 wt % loading, the agglomeration of the catalyst is observed results in formation of big lumps, whereas at 25 wt% metal loading rod shape structure is observed. Catalytic activity was tested in a Teflon lined stainless steel autoclave. Hydrogenolysis of glycerol was carried out at 210o C temperature, 45 bar H2 pressure. The 20% (v/v) aqueous solution of glycerol and 1.6g catalyst was used for hydrogenolysis. The product was collected after a reaction time of 12 h. Among all the catalysts tested Cu catalyst with a metal loading of 25 % showed maximum glycerol conversion of 88.17 % with 91.7 % selectivity towards 1, 2-PDO. Small amount of ethylene glycol (EG), acetol and other products were also detected. As 25% Cu/MgO catalyst showed better activity, so this catalyst was used to evaluate the reaction parameters. The activity of glycerol conversion was tested at different reaction temperature and it was found that the glycerol conversion increased from 72% to 88% as the temperature increased from 190 oC to 210 oC and the selectivity for 1, 2-PDO also increased up to 210 oC. Further increase in temperature from 225 oC to 240 oC the conversion of glycerol slightly increased but the selectivity towards the 1, 2-PDO is decreased from 91 % to iv 83% at high temperatures. At different reaction pressure, it was found that as pressure is increased from 1.5 to 4.5 MPa the conversion of glycerol increases from 49% to 88%.Then further increased in pressure to 6 MPa the conversion decreases to 81% and 1, 2-PDO selectivity was found to be in the range of 85% to 91% in all cases. At different catalyst weight, it was found that the glycerol conversion increased from 67 % to 95 % with increase in catalyst loading from 6-10 wt% and selectivity towards 1, 2-PDO was found to be in range of 86-91%. At different glycerol concentration, it was found that conversion of glycerol decreased from 88% to 38% with increase in glycerol concentration from 10 wt% to 60 wt% and selectivity towards 1, 2-PDO decreases from 91% to 84%. Characterization results suggested that the activity of Cu/MgO catalyst depended on particles size of Cu and MgO, Catalyst having smaller particle size were more active for hydrogenolysis of glycerol.