Multi-stage shrinking core model for thermal decomposition reactions with a self-inhibiting nature

Among the variety of thermal decomposition reactions, some display self-inhibiting behaviour,
where the produced gas negatively influences the reaction progress. Further, a build-up of
internal pressure caused by the product gas may alter the reaction pathway over the reaction
duration in a way that favours a particular pathway over others. Two well-known cases of this
kind of reaction are the thermal decomposition of limestone and gibbsite, in which carbon
dioxide and water vapour are the produced gases, respectively. A multi-stage, multi-reaction,
shrinking core model is proposed for this type of reaction. The model emphasises the role of
the produced gas, not only in the mass transfer rate, but also in the reaction kinetics. It also
includes parallel and series reaction pathways, which allows for the presence of an
intermediate species. The model has been applied to the conversion of gibbsite to alumina, and
it includes the formation of boehmite as an intermediate product. The model results are in
good agreement with experimental data for gibbsite calcination reported in the literature.
Gibbsite conversion, boehmite formation and subsequent consumption, as well as alumina
formation, are successfully simulated. Further, the corresponding kinetic parameters are
estimated for all reactions of interest.