(695b) Development of a Kinetics Model for Autothermal Pyrolysis in a Fluidized Bed Reactor

Autothermal pyrolysis is achieved by reacting a small amount of oxygen (equivalence ratios of 0.06-0.10) with biomass in a fluidized bed reactor, which partially combusts the products of pyrolysis to overcome the endothermic enthalpy of pyrolysis. Experiments performed at Iowa State have shown that autothermal pyrolysis produces no significant loss in bio-oil yield or quality as compared to traditional non-oxidative pyrolysis. Current experimental data shows that half the heat comes from oxidation of non-condensable gases (NCGs) such as carbon monoxide, methane, ethane, and ethylene and an additional one-quarter comes from oxidation of char. However, currently available kinetic mechanisms for gas-phase combustion of NCGs do not predict significant oxidation at pyrolysis temperatures (400 - 600ËšC). On the other hand, many of the volatile organic compounds that subsequently condense to bio-oil are predicted to readily oxidize at these temperatures, thus prompting a closer examination of the gas-phase kinetics of autothermal pyrolysis.

The role of gas-phase oxidative reactions in providing the enthalpy of pyrolysis during autothermal pyrolysis are explored in this study using both experimental and computational methods. A fluidized bed operated at temperatures between 400-600ËšC was used to estimate the oxidation rates of bio-oil model compounds at equivalence ratios of 0.06. Gas analysis allowed product distributions to be determined. These results were used for modeling oxidative reactions during autothermal pyrolysis.