Kinetic rate of CO2CO2 uptake of a synthetic Ca-based sorbent: Experimental data and numerical simulations

• Grain model was applied modelling the carbonation reaction.
• Fixed bed reactor is a better tool for kinetic study.
• Diffusional limitation of the pellet has been studied using grain model.

This article describes the reactive kinetics of Ca-based synthetic sorbent composed of 25 wt.% mayenite (Ca12Al14O33)(Ca12Al14O33) and CaO with CO2CO2 at temperatures of 1023 K for multiple cycles. The carbonation reaction is a gas–solid reaction system, which generally follows one out of two controlled regimes, namely the kinetic- and product layer diffusion (PLD) controlled regimes. A mathematical model based on the grain model was applied modelling the carbonation reaction.The CO2CO2 capture properties of Ca-based synthetic sorbent were studied in both TGA (thermogravimetric analysis) and fixed bed reactor. Experimental results show that there is considerable effect of the diffusional limitation in the fixed bed reactor in comparison to the TGA study. A large bypass in the conventional TGA could limit its application in kinetic study. Compared to TGA, a fixed bed reactor has well controlled contact between the gas–solid acceptors and being influenced by numerous of factors. Hence, it is found that the fixed bed reactor is a better tool for kinetic study of the carbonation reaction.The mass based pellet model formulated for the sorption process describes the evolution of species mole fractions, pressure, total concentration, temperature, fluxes, and convection within the voids of the porous pellet. The internal effectiveness factors of the carbonation reaction has been calculated for the sorption process. The change in pellet void-fraction due to the formation of the solid CaCO3CaCO3, the diffusion of the gaseous phase through the product layer, and the structural changes of the spherical grains by the inclusion of a variable diffusion coefficient were considered in the pellet model. The nature of the gas–solid reaction system elucidated by the effectiveness factor graph, i.e., the gas–solid reaction system occurs in two different stages: kinetic- and product layer diffusion controlled stages. Hence, by neglecting the product layer diffusion controlled stage for the carbonation reaction might lead to false estimation of concentration profile. Therefore, both the kinetic- and product layer diffusion controlled stages should consider for modelling of the carbonation reaction system.