Kinetic Model Comparison for Waste Tire Char Reaction with CO2

Abstract

Pyrolysis has proven to be a useful recycling process for waste tires, and pyrolytic char is ∼40% of initial sample weight. To valorize this solid, the activated carbon production has been studied for the last years from a generation point of view. However, there are only few studies about the kinetics of the reaction. In this paper, four gas−solid models have been applied to CO2 activation of tire char: volume model, modified volume model, changing grain size model, and random pore model. The reactions were performed in a thermobalance with a structural and analytically characterized tire char obtained by pyrolysis in a fixed-bed reactor at a temperature of 1000 °C for 3 h. Experimental conditions were optimized to minimize internal and external mass-transfer phenomena performing experiments with different particle sizes, at different flow rates and initial weights. Finally, to obtain the intrinsic kinetic parameters, several experiments were carried out at different partial pressures of CO2 and temperatures, concluding that the random pore model is the most appropriate model to describe the reaction. The tire char activation was found to be a first-order reaction with respect to CO2. The kinetic results reported in this paper can be useful for tire char activation scaling-up and the process engineering design, so that knowledge of the activation energy and the preexponential factor of the chemical reaction is fundamental to perform the chemical reactor design and the optimization of process parameters.