A Thiele Modulus Approach for Nonequilibrium Adsorption Processes and Its Application to CO₂ Capture

A Thiele modulus-effectiveness factor method was applied to provide insight into the interplay of intraparticle mass transfer and intrinsic adsorption kinetics in nonequilibrium adsorption processes. A full model and two approximate methods were considered. In the approximate methods only the fluid concentration at the exterior surface and the averaged sorbent loading are required as input. Assuming a uniform sorbent loading, an explicit solution for the effectiveness factor for adsorption as a function of the Thiele modulus for adsorption was derived. For each adsorptive system a minimum and maximum Thiele modulus can be calculated, which provide a priori insights regarding the rate-determining step. The approximations were validated against complete numerical solutions for a single particle and their use was compared to a complete particle description within a full reactor-particle model. Results for CO₂ adsorption from flue gas and ambient air showed that the approximations result in a good accuracy for the applications studied.