Kinetics and Physicochemical Morphology Evolution of Low and High-Ash Pyrolytic Tire Char during CO_2 Gasification

摘要

The heterogeneity of waste tire pyrolytic char associated with ash composition and distribution is explored to understand the effect of ash on gasification. In this paper, high-ash tire tread (TT) and low-ash sidewall (SW) were separated to study gasification kinetics and the influence of ash on char physicochemical morphological evolution during CO2 gasification. Morphological development and characterization of chars were studied using N-2 adsorption and scanning electron microscopy coupled with energy dispersive X-ray analysis. Isothermal gasification kinetics were derived from a thermogravimetric analyzer, and described by the shrinking core model (SCM), volumetric model (VM), and the random pore model (RPM). The results showed that TT char has silica-based ash clusters which inhibit gasification, particularly at high conversions. Moreover, TT ash suppresses surface area development and forms an inherent skeletal structure that inhibits particle size reduction during the reaction. In contrast, SW char exhibited significant particle size reduction, and surface area development was more pronounced compared to that for TT char. The surface area for SW char increased until 75% conversion and decreased thereafter, albeit insignificantly, while the TT char surface area decrease was more pronounced after 50% conversion. All chars exhibited significant internal structure development, thus eliminating the SCM as an appropriate model. All models yielded kinetic parameters of nearly the same magnitude, and the RPM was selected as the most suitable model. The activation energy for TT and SW were found to be 177.1 and 163.6 kJ mol(-1), respectively. The model-free method confirmed the reliability of the results. These findings further confirmed the inhibiting nature of tire ash.