Coupled modeling and experimental study of three-stage mass transfer in porous materials: From forced convection to micropore diffusion

Physical adsorption-based carbon capture represents a promising technological pathway for achieving carbon neutrality. The engineering design of carbon capture systems should be optimized based on kinetic processes. However, most current kinetic models lack clear physical interpretability. Both monodisperse and bidisperse pore models are pure diffusion models that neglect forced convection between flue gas and pellets. In this study, we established a three-stage kinetic model that explicitly accounts for macroscopic convection, macropore diffusion, and micropore diffusion processes. The model was validated against experimental data, demonstrating good agreement with observed adsorption behaviors. Based on the modeling results, we proposed an optimized adsorbent design strategy and subsequently synthesized target adsorbents for experimental verification. The results showed remarkable kinetic enhancement, with the adsorption rate increasing significantly when the average particle size was reduced from 4 mm to 0.6 mm. Furthermore, we systematically investigated the influence of crystal diameter (1.25–40 μm) on mass transfer efficiency, revealing a strong size-dependent effect within this range.