Modelling CO 2 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 102 and 1 min1. 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.