SYNTHESIS AND CHARACTERIZATION OF SUPPORTED Cu-Ni AS ACTIVE CATALYST FOR LIQUID PHASE REACTION

Abstract

Superfluous glycerol from biodiesel production could not only flood the current market for glycerol but also negatively impact the economic viability of biodiesel. Finding new outlets for glycerol consisting of high value-added products can contribute to biodiesel promotion. Catalytic conversion of glycerol into glycols by hydrogenolysis and esterification of glycerol with acetic acid to obtain monoacetin, diacetin and triacetin is very promising route for glycerol utilization. In earlier studies, several catalysts have been proposed for these reactions. The information regarding the bimetallic catalysts is very limited. Here in this study a series of Cu, Ni monometallic and Cu-Ni bimetallic catalysts supported on A1203 and activated carbon with varying metal loading were prepared by incipient wetness impregnation methods. The physiochemical properties of the catalysts, such as specific surface areas, crystal phases, reduction behaviour, acidity and morphologies were characterized by N2 adsorption/desorption, X-ray diffraction (XRD), temperature programmed reduction (TPR), NH3-temperature programmed desorption (TPD) and scanning electron microscopy (SEM-EDX). Surface area of activated carbon and alumina was 808 and 151 m2/g, respectively. It was found that the surface area of the impregnated catalysts was reduced significantly. In case of Cu-Ni bimetallic catalysts, surface area was lower with respect to the monometallic catalysts may be due to the formation of solid mixed oxide solution. The XRD results confirmed the formation of mixed oxide particles on the bimetallic catalysts. The TPR results revealed that the presence of a second metal lowered the reduction temperature of Cu or Ni catalysts, significantly. The catalytic tests were done in the batch 250 ml Teflon coated stainless steel batch reactor. Hydrogenolysis of glycerol was carried out at 250°C and 10 bar H2 pressure and liquid phase esterification of glycerol was carried out at 120°C at atmospheric pressure. The 40 % (v/v) aqueous solution of glycerol was used for hydrogenolysis. For hydrogenolysis and esterification reaction, the catalysts amount was kept fixed at 0.25 g and 0.1 g, respectively. The effect of support as well as metal loading on liquid phase reaction was studied. Among all the catalysts tested, Cu-Ni bimetallic catalysts supported on 7-A1203 showed superior performance in both reactions. Cu-Ni/A1203 (Cu: Ni=3:l) catalyst showed the highest conversion of glycerol in both the cases. For hydrogenolysis of glycerol, the maximum selectivity to 1,2-PDO of 98% was obtained with a glycerol conversion of 27% after a reaction time of 5h. In case of esterification of glycerol over Cu-Ni/A1203 (Cu: Ni=3:1) catalyst the maximum glycerol conversion was 45% with a diacetin and triacetin selectivity to 62.86% and 11.46%, respectively.