Combustion Kinetics of Secondary Biomass Chars in the Kinetic Regime

In this study, the oxidation of secondary biomass chars, generated from evaporation/decomposition of four bio-oil samples (BTG, Dynamotive, Ensyn, Pyrovac), is investigated under a kinetic control. Weight loss characteristics, consisting of the sequential stages of char devolatilization and oxidation, are qualitatively similar with those of chars produced from wood pyrolysis. However, reactivities are generally quantitatively lower, owing to the highly different morphological properties and the lower inorganic content. A four-step parallel mechanism (versus the two-step mechanism of wood char) describes well the integral and differential measurements for variable heating rates. The devolatilization stage includes three first-order rate reactions with activation energies of 84, 100, and 118 kJ/mol accounting for the release of volatile species amounting to 27-40% of the initial mass (versus about 15% of wood chars). An additional nonlinear step simulates the oxidation stage but requires sample-dependent activation energies (211, 174, 169, and 163 kJ/mol versus 183 kJ/mol of wood char).