Modelling CO2 adsorption dynamics onto amine-functionalised sorbents: A fractal-like kinetic perspective

In this article we applied a fractal-like Vermeulen model to describe kinetic data selected from literature case-studies for CO2 adsorption onto amine-functionalised sorbents. The statistical analysis based on the Akaike information criterion demonstrated a better fitting performance of the fractal-like model with respect to its canonical counterpart in describing experimental profiles of coverage degree in the entire time range explored. The canonical kinetic model generally provided a satisfying description of dynamic data only in the early stages of the process. The fractal model accounts for the presence of an instantaneous rate coefficient which ranged between orders 10−2 and 1 min−1. Parameters derived from the fractal-like model demonstrated that the diffusion process at the beginning of adsorption is enhanced when the sorbent has a pore network easily accessible for the adsorbate. This happens when the sorbent is characterised by a wider mean pore diameter and greater specific pore volume, and when the process temperature is raised. The heterogeneity parameter of the fractal-like model affects the time-decay of the adsorption rate coefficient. This parameter ranged between 0.16 and 0.85, and it is higher when the porous material is both rapidly occupied by CO2 molecules and displays a wider pore size distribution.