VAPOR PHASE DEHYDRATION OF GLYCEROL OVER MESOPOROUS SILICA SUPPORTED IRON (III) PHOSPHATE CATALYSTS

Abstract

Surplus glycerol produced during the production of biodiesel is having a detrimental effect on the production of biodiesel which is due to lack of commercial utilities of glycerol which is a major by-product. Conversion of glycerol into value added products can further improve the economics of biodiesel production. Catalytic conversion of glycerol to acrolein and acetol by vapor phase dehydration of glycerol with the help of various solid acid catalysts has been an area of research for commercial utilization of glycerol. In previous studies, several solid acid catalysts have been proposed for these reactions. Dehydration study with mesoporous silica as support are very limited. Here in this study a series of Iron (III) phosphate impregnated on mesoporous silica MCM-41 with varying iron (III) phosphate loading were prepared by incipient wetness impregnation methods. The physiochemical properties of the catalysts such as acidity and morphologies were characterized by N2 adsorption/desorption, surface areas, NH3-temperature programmed desorption (TPD), X-ray diffraction (XRD) and scanning electron microscopy (SEM-EDX). Surface area of mesoporous silica was found to be 1141 m2/g. With increase in weight percentage of FePO4, it was found that the surface area of the impregnated catalysts got reduced significantly. The XRD results confirmed the presence well dispersed FePO4 on MCM- 41. The TPD results revealed that, the presence of moderate acid sites on the catalysts. The catalytic tests were carried out in a continuous flow reactor. Dehydration of glycerol was carried out at 300°C and atmospheric pressure. 20% wt% aqueous solution of glycerol was used for the dehydration reaction. The catalysts amount was kept constant at 1.0 g for all the experiments. The effect of support and various weight per cent of FePO4 loading on vapour phase reaction was studied. Among all the catalysts tested, FePO4 on MCM-41 with Si to Fe ratio 5:1 and P to Fe ratio 1.3:1 showed superior performance for dehydration reactions. FePO4/MCM-41(Si: Fe=5:1) catalyst showed the highest conversion of glycerol along with highest acrolein selectivity. For dehydration of glycerol, the maximum selectivity to acrolein of 82% was obtained with a glycerol conversion of 99% after a reaction time of 5h. Acetol selectivity increased with increase in time for all the catalysts tested reaching maxima of 72%.