Catalytic Effect of Iron and Nickel on Gas Formation from Fast Biomass Pyrolysis in a Microfluidized Bed Reactor: A Kinetic Study

Isothermal pyrolysis of rice husk catalyzed by iron and nickel was conducted in a microfluidized bed reactor to investigate the forming characteristics and kinetics of the main gas components. Results indicated that both Fe and Ni showed a catalytic effect on the releasing behavior of gaseous products during rice husk pyrolysis. The forming reaction rate of H-2 and CO2 was significantly promoted with the addition of Fe or Ni, while that of CH4 was inhibited. For CO, Ni showed a positive effect while Fe showed a negative effect on its forming rate. The char evolution of rice husk was also influenced by the presence of Fe and Ni from the SEM-EDX and BET results. The model fitting method was used to calculate the kinetics of gas releasing to further investigate the effect of Fe and Ni, and the most probable reaction mechanism was obtained based on the relative error between experimental and calculated conversion fraction. Corresponding to the changing trend of reaction rate, the obtained activation energies for the gas components changed with the addition of Fe and Ni. More specifically, the apparent activation energies for H-2 and CO2 reduced from 91.15 and 35.15 kJ/mol to 67.72 and 30.44 kJ/mol for Fe-RH and to 55.13 and 33.99 kJ/mol for Ni-RH, while that for CH4 increased from 40.65 kJ/mol to 51.71 and 46.65 kJ/mol with Fe and Ni as catalyst, respectively. The apparent activation energy for generating CO increased from 34.50 to 37.15 kJ/mol in the case of adding Fe, while its value decreased from 34.50 to 30.26 kJ/mol with the presence of Ni. Further comparing the activation energies, the catalytic performance of Fe and Ni was noted during biomass pyrolysis, while the catalytic performance differed for different gas components.