Studying the thermo-oxidative stability of chars using pyrolysis-combustion flow calorimetry

A method to estimate the thermo-oxidative stability of chars is proposed using pyrolysis-combustion flow calorimetry. The temperature of char degradation is measured for different oxygen fractions (from 0.01 to 0.4, i.e. from 0 to 40%) into the pyrolyzer. Then the thermo-oxidative stability versus the oxygen fraction is modelled using a simple phenomenological equation. Two parameters have been calculated: the first one predicts the temperature of char degradation in “pure” oxygen and the second one corresponds to the sensitivity of the char degradation temperature to the oxygen fraction. These two parameters allow comparing the chars obtained from different materials after various pyrolysis procedures. Rough relationships between these two parameters and the elemental composition of char are identified. Phosphorus allows improving the thermo-oxidative stability of chars as expected but its effect is nonlinear. Lignocellulosic materials lead to chars with low thermal stability even when the phosphorus content is high. Finally, the obtained results show that the char elemental composition is not the only parameter influencing its thermo-oxidative stability.