Kinetic analysis of the pyrolysis of wood/inorganic composites under non-isothermal conditions

Abstract

The pyrolysis kinetics of wood/inorganic composites was measured using one or two kinds of inorganic modifiers (CaCO3, SiO2–TiO2, and Mg–Al compounds) to study the pyrolysis behavior. Thermogravimetric experiments were carried out under nitrogen conditions and operated at different heating rates, ranging from 10 to 40 K/min. Model-free methods (Starink, Flynne-Wall-Ozawa, and modified Coats-Redfern) were used to evaluate the kinetic parameters, including apparent activation energy (Ea) and reaction order. For the range of conversion fractions investigated (20%-80%), the results yielded Ea values of 114–117 kJ/mol, 151–158 kJ/mol, 174–175 kJ/mol, and 153–156 kJ/mol for the unmodified poplar wood and modified poplar wood composites with CaCO3, SiO2–TiO2, and Mg–Al inorganic compounds, respectively. The corresponding reaction order values were 0.4485–0.8677, 0.0150–0.3694, 0.2021–0.5579, and 0.4336–0.8293, respectively. Wood impregnated with inorganic substances had good chemical modification effect. In addition, the kinetic mechanism function of the wood pyrolysis reaction was also studied. Results show that the heating diffusion mechanism model better describes the entire pyrolysis process of the modified wood compared with the control wood, which could be attributed to difficulty in the heat transfer process because of the thermal barrier effect of the inorganic layer and the resistance of gaseous products during pyrolysis. The stability of the wood/inorganic composites is therefore effectively improved.