Characteristics of bio-tar catalytic cracking by char’s inherent Fe2O3 and K2O for biomass gasification process

In this research, a newly-designed micro fluidized bed reaction analyzer (MFBRA) was used to evaluate the catalytic activity of char's inherent Fe2O3 and K2O on bio-tar in Ar at temperatures of 1023 K, 1073 K, 1123 K, and 1173 K. The adopted samples of char and tar were obtained by biomass pyrolysis in Ar at 1273 K. Fe2O3- and K2O-loaded char were prepared by doping metal oxides on the demineralized char samples to simulate the inherent metal oxides in char. The real-time cracking properties of tar were examined and compared on the basis of the analyzer's high heating rate, quick sample loading at the predetermined temperature, and online analysis of gas products. The results show that both Fe2O3 and K2O displayed obviously catalytic activity by improving tar conversion and reaction rate, and lowering activation energy (Ea). Compared to K2O at 1173 K, Fe2O3-loaded char promoted the generation of H2, CO, CO2, CH4, C3H6, and the total gas products with the conversion ratio (XFe2O3/K2O) of 2.04, 1.02, 1.24, 1.32, 1.56, and 1.12, respectively. However, it suppressed the formation of C2H6 with the XFe2O3/K2O of 0.43. Meanwhile, the maximum generation rates for CO, CO2, CH4, and the total gas products improved to different extent. During tar catalytic cracking, Fe2O3 suppressed carbon deposition on the char surface because of the larger specific area after experiments. Finally, the generation Ea of CH4, H2, CO, CO2, C3H6 and the total gas products by Fe2O3-loaded char further decreased drastically and that of C2H6 increased obviously. All of these indicated the catalytic activity of the inherent Fe2O3 in char was better than K2O.