Enhanced Gasification of Waste Glycerol Over Ni/SiC Catalyst for Fuel Gas Production

Abstract

The amount of waste glycerol from biodiesel production increases sharply due to greater use of this alternative fuel from high cost and adverse environmental effect of conventional fossil fuel. The crude glycerol can convert to fuel gas (mainly CO, H2, and CH4) through thermochemical conversion processes such as gasification and pyrolysis. In this study, pyrolysis and gasification of glycerol waste were studied in a laboratory scale quartz tube reactor using silicon carbide (SiC) as a bed medium. In order to improve the conversion efficiency while minimizing tar formation, nickel catalyst supported by SiC was synthesized using wet impregnation method and used in some trials. It was found during pyrolysis runs that carbon and hydrogen conversion of glycerol increased with temperature of 600–800°C in the range of 18.72–95.33% and 16.26–96.30%, respectively. When varying the air fuel ratio from 0–0.25 at 800°C, complete conversion of crude glycerol may be achieved both for pyrolysis and gasification conditions. This may be due to the dominant of steam gasification reactions from 13.56% moisture content in crude glycerol which controls the overall reactions at that high temperature. However at lower temperature of 600°C, carbon and hydrogen conversion of crude glycerol decreased to 18.72–42.23% and 16.26–35.27%, respectively. Increase in residence time from 1.3–4.0 second did not significantly affect the conversion efficiency for pyrolysis at 600°C which indicated that the kinetic of these decomposition reactions proceed at rapid rates even at the minimum hold time used in this work. Catalytic conversion of crude glycerol with 10% nickel on silicon carbide (Ni/SiC) was performed using pyrolysis condition at 600°C to obtain higher conversion efficiency. The results revealed that non-reduced and reduced catalyst, could increase the production of synthesis gas as much as 1.02 and 0.56 times when compared with non-catalytic process, respectively. It may be suggested from high energy content as well as product gas quality that using Ni/SiC catalyst is suitable for thermal conversion of waste glycerol to fuel gas that may be further utilized with minimum treatment. The obtained synthesis gas may be utilized for direct heat and power or further transformed to other alternatives fuels which help increase value and at the same time minimize the waste management requirement of this industrial waste.