Enhancing CO₂ separation from N₂ mixtures using hydrophobic porous supports immobilized with...

The main obstacles in adopting solvent-based CO₂ capture technology from power plant flue gases at the industrial scale are the energy requirements for solvent regeneration and their toxicity. These challenges can be overcome using new green and more stable ionic liquids (ILs) as solvents for post-combustion CO₂ capture. In the current study, tributyl-tetradecyl-phosphonium chloride [P₄₄₄₁₄][Cl] as an IL, was immobilized on hydrophobic porous supports of polypropylene (PP), polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE) at 298 ± 3 K and pressures up to 2 bar. The surface morphology indicated homogenous immobilization of the IL on the membrane support. Supported ionic liquid membranes (SILMs) were tested for CO₂ permeability and CO₂/N₂ selectivity. None of the SILMs exhibited IL leaching up to 2 bar. The PTFE-based SILM performed better than other supports with minimum loss in water contact angle (WCA) and achieved good antiwetting with a maximum CO₂ permeability and selectivity over N₂ of 2300 ± 139 Barrer and 31.60 ± 2.4, respectively. This work achieves CO₂ permeability about two-fold more than other works having CO₂/N₂ selectivity range of 25-35 in similar SILMs. The diffusivity of CO₂ and N₂ in [P₄₄₄₁₄][Cl] was measured as 3.64 ± 0.18 and 2.01 ± 0.09 [10^-8 cm² s^-1] and CO₂ and N₂ solubility values were 9.79 ± 0.47 and 0.19 ± 0.001 [10^-2 cm³(STP) cm^-3 cmHg^-1], respectively. The high values of Young's modulus and tensile strength of the PTFE support-based SILM (234 ± 12 MPa and 6.07 ± 0.31 MPa, respectively) indicated the long-term application of SILM in flue gas separation. The results indicated phosphonium chloride-based ILs could be better solvent candidates for CO₂ removal from large volumes of flue gases than amine-based ILs.