CO₂ gasification of char derived from waste tire pyrolysis: Kinetic models comparison

This work studies the gasification of char derived from waste tire pyrolysis (pCB) by using a thermogravimetric analyzer under CO2/N2 atmospheres (20/80, 25/85 and 30/70 vol%) at different temperatures (825 °C, 850 °C, 875 °C, 900 °C and 925 °C). The main goal is the assessment of three different kinetic models for predicting not only the conversion (X) versus time (t) curve, but also the reaction rate (dX/dt) versus conversion (X) one, with high accuracy. At this respect, the Changing Grain Size Model (CGSM), the Random Pore Model (RPM) and a new model based on the RPM named the Hybrid Modified Random Pore Model (HMRPM) were used. The three models were fitted and the kinetic parameters such as the apparent kinetic constant (Ki(T,pj)), the reaction order (n), the activation energy (Ea) and the pre-exponential factor (A) were determined. The results suggest that the HMRPM is the model with better fitting because its ability to reproduce both conversion (X) and reaction rate (dX/dt); and hence, it is reliable to be integrated in both particle and reactor models, i.e. when the process is being designed and scaled-up. A drastically decrease in the reaction rate at the first stage of conversion (<20%) suggests a possible effect of volatile matter and inorganic compounds contained into the pCB. The n, Ea and A were found to be 0.543, 147.27 kJ/mol and 4.547 × 105 s−1, respectively.