CO₂ Capture by Supported Ionic Liquid Phase: Highlighting the Role of the Particle Size

CO₂ capture by fixed-bed sorption has been evaluated using Supported Ionic Liquid Phase (SILP) based on the ionic liquid 1-butyl-3-methylimidazolium acetate ([bmim]­[acetate]). The SILP sorbent was prepared with three remarkably different mean particle sizes and characterized by porous texture, morphology, thermal stability, and elemental composition. The thermodynamics and kinetics of the CO₂ capture process has been studied, testing the effects of SILP particle size, sorption temperature, gas flow rate, and CO₂ partial pressure. The CO₂ sorption isotherms at different temperatures were obtained by gravimetric measurements, revealing that the equilibrium sorption capacity is only due to the IL incorporated on the silica support of SILP. The experimental isotherms were successfully fitted to the Langmuir–Freundlich model. Fixed-bed experiments of CO₂ capture were carried out to evaluate the performance of the SILP sorbents at different operating conditions. All the breakthrough curves were well described by a linear driving force model. The obtained kinetic coefficients revealed that the CO₂ sorption rate in fixed-bed linearly increases when decreasing the SILP particle size and increasing the operating temperature. Higher CO₂ partial pressure in the inlet gas stream led to a faster mass transfer rate, affecting both the mass transfer driving force and kinetic coefficient. Aspen Adsorption simulator was successfully applied to model the fixed-bed operation, highlighting the role of the particle size on separation efficiency. Simulations results indicate that at very low CO₂ partial pressure chemical absorption is the controlling step, while increasing that partial pressure shifts the regime toward diffusion into the SILP. This methodology will allow designing CO₂ sorption systems based on SILPs that fulfill the separation requirements at given conditions (CO₂ partial pressure and temperature), minimizing the SILP needs by optimizing the particle size and type of IL.