Comparative study of catalytic conversion of glycerol, a by-product of transesterification, to cyclic hydrocarbons using MCM-22, ZSM-5 and alumina

Abstract

Recently chemical consumption has increased due to the growth of human population and industrialization. Depleting fuel reserves and increase in chemicals rise has led and researcher to focus on alternative bio based chemicals. Glycerol which is produced as a major byproduct from the trans-esterification reaction of fatty acids for producing biodiesel has been used in this work for conversion to value added products. Conversion of glycerol in presence of alumina, MCM-22 (pure silica based mesoporous catalyst) and ZSM-5 (Si-Al based catalyst) is investigated at different temperature and catalyst weight in a fixed bed reactor. The conversion of glycerol was found to be maximum in presence of alumina whereas maximum liquid products were obtained with ZSM-5. GC/MS analysis confirmed the production of Furan compounds in higher fraction with both alumina as well as ZSM-5 showing the importance of acid sites for the glycerol conversion to higher hydrocarbons. The GC/MS analysis of liquid product obtained in presence of catalyst was also observed with high area% of unconverted glycerol. The order is as follow 54% (MCM-22) > 44% (ZSM-5) > 42.2% (Alumina). For the investigation of the conversion for varying catalyst weight (0–3 g with 0.5 g weight difference), reaction temperature were varied between 450 and 550 °C. Different values of n = 0, 1, 2 etc. were used for the fitting of the respective plot. A change in reaction rate and the rate constant indicated that with the change of temperature, reaction rate was increased. The rate constant value obtained between 0.09 and 0.12 h−1. In all cases 450 °C and catalyst weight of 2.5 g was obtained as optimum for higher liquid yield. TGA analysis of spent catalyst also showed that alumina give high yield (∼50% by weight) of coke as compared to ZSM-5 and MCM-22.