Biomass Gasification: Catalytic Removal of Tars over Zeolites and Nickel Supported Zeolites

Tars have been identified as one of the major impurities associated with biomass gasification fuel gas. Tar buildup can cause blockages, plugging, corrosion, and catalyst deactivation, resulting in serious operational and maintenance problems. Therefore, tar removal is essential to ensure economic and effective fuel gas utilization. This study investigates the catalytic activity of zeolites and nickel supported zeolites for tar removal. Zeolites with varying pore sizes and acidity were tested, to evaluate the effect of pore size and acidity on tar removal. ZY had better catalytic activity due to its larger pore size compared with ZSM5. Catalytic activity of zeolites increased with an increase in the acidity. ZY-5.2, which is more acidic, had better naphthalene conversions compared with ZY-80. Impregnation of nickel on zeolites improved the activity significantly due to the steam reforming ability of nickel. Long-term catalytic activity tests were performed, the results of which showed that nickel-supported ZY-30 and ZY-80 had the best naphthalene conversions, with naphthalene conversions of greater than 99%, followed by nickel-supported ZY-5.2, SiO2/Al2O3, and chabazite. Also, very little loss in activity over a 97 h test period was noticed for nickel-supported ZY-80 and ZY-30, compared with nickel-supported ZY-5.2, SiO2/Al2O3, and chabazite. Characterization of calcined and spent catalysts was performed using X-ray diffraction, thermogravimetric analysis, and surface area analysis, to investigate the lower catalytic activity of nickel-supported ZY-5.2, SiO2/Al2O3, and chabazite. The decreased catalytic activity is attributed to the coke deposition and catalyst surface area.