Modeling CO2 adsorption dynamics within solid amine sorbent based on the fundamental diffusion-reaction processes

Abstract

A rigorous dynamic adsorption model, considering the realistic diffusion-reaction processes of CO2 adsorption onto the amine functionalized mesoporous silica, was proposed in this work. Three fundamental adsorption steps at different length scales were took into account in model development and a numerical algorithm was developed to solve the coupled partial differential equations of the multi-scale model. TGA (Thermal Gravity Analysis) experiments at different temperatures and CO2 partial pressures were conducted to acquire the dynamic adsorption curves for model fitting and validation. The simulation results based on the proposed model agreed well with the experimental data under all conditions. Through the developed model, the species distribution, mass transfer phenomena and reaction mechanisms at different scales within the sorbent were quantitatively predicted. The results indicated that the bulk of the sorbent captured CO2 simultaneously, and no adsorption front was observed. After the very early stage, the whole sorbent reacted with CO2 uniformly. Further mass transfer resistance analysis showed that chemical reaction was the rate-limiting step, and CO2 diffusion in the amine layer would play an important role in the later stage of adsorption, especially at high temperatures or high CO2 partial pressures. These findings provided a quantitative insight into dynamic evolution of CO2 adsorption within the sorbent particle, which would guide the design of sorbents with optimal pore features and amine loadings.