Pyrolysis characteristics and kinetic analysis of rice husk

Abstract

In this work, the thermo-gravimetric and differential thermo-gravimetric curves of rice husk at different heating rates (20, 40, 60, 80 and 100 °C min⁻¹) were obtained using a thermo-gravimetric analyzer under nitrogen atmosphere. The pyrolysis characteristics of rice husk were analyzed. The fitted Gaussian function peaks showed that the pyrolysis mass loss of rice husk can be characterized by three independent reactions. The devolatilization index D was calculated, and the effect of different experimental statuses on the pyrolysis of rice husk was discussed. The kinetic parameters of rice husk were calculated using iso-conversional models and distributed activation energy models (DAEMs). The kinetic parameters obtained by differential Friedman method and integral Ozawa method were found to be 224.85 kJ mol⁻¹ and 220.06 kJ mol⁻¹, respectively. The apparent activation energies for pyrolysis were not fixed value and continuously fluctuated with the increase in conversion rate. The kinetic parameters, obtained using the Kissinger method, were relatively simple and could not represent the variation trends of variables. Six different probability density functions for DAEMs were used to compute the pyrolysis kinetic parameters. The energy compensation effect existed between the activation energy and the frequency factors. It can be concluded from a comprehensive F test and the amount criterion test (Akaike information criterion test) that the Weibull model is more appropriate to study the pyrolysis of rice husk. Finally, the apparent activation energy, calculated using the Weibull model, was calculated to be 131.97 kJ mol⁻¹, whereas the reaction order was 3.2.