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 N2 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.