Activation of pyrolytic tire char with CO2: kinetic study

Abstract

Chars from old tire pyrolysis have been activated with CO2. The chars were obtained by pyrolysis of a waste tire sample in a fixed bed reactor at a temperature of 1000 °C for 3 h. The pyrolytic char, basically the original carbon black plus the tire mineral matter, was ground and sifted to an average particle size obtaining different fractions that were used as raw material in the activation experiments. These experiments were performed in a thermobalance at different temperatures (850, 900, 950 and 1000 °C) in order to determine the activation energy and pre-exponential factor, basic intrinsic kinetic parameters of the activation process. Experimental conditions were optimized to avoid internal and external mass transfer phenomena performing experiments with different particle sizes, at different flow rates and initial weights. Moreover, the tire char activation was found to be a first order reaction with respect to CO2. A kinetic expression for tire activation, based on the random pore model and the structural parameters of the pyrolytic char, was deduced. In addition, with this kinetic model it can also be explained the maximum in reaction rate observed experimentally at conversions around 40%.