Tailoring Urethane-Based Poly(ionic liquid) Membranes for Enhanced Carbon Dioxide Sorption and Separation Performance

Polyurethane-based PILs were synthesized via in situ polymerization using different proportions (95%/5%, 90%/10%, and 80%/20%) of polycarbonate diol (PC) and polytetramethylene glycol (PG) as polyols, dimethylolpropionic acid (DMPA), and hexamethylene diisocyanate (HDI), with BMIM⁺ and TBP⁺ countercations. Gas permeability, CO₂/N₂ and CO₂/CH₄ ideal selectivity, and diffusion and solubility coefficients were determined. Computational simulations were conducted to elucidate the role of urethane moieties and TBP⁺/BMIM⁺ in CO₂ capture. The PIL-PC95-PG5-TBP membrane exhibited the highest CO₂ uptake (106.9 mg of CO₂/g at 30 °C and 10 bar) and the highest CO₂ permeability (38.9 barrer), while the BMIM-based membrane demonstrated superior ideal selectivity (CO₂/CH₄ = 52 and CO₂/N₂ = 82 at 4 bar). Computational simulation results confirmed the absence of chemisorption and highlighted opportunities to further enhance CO₂ affinity in these membranes. PIL membranes showed enhanced CO₂ permeability and selectivity compared to neat PUs and other PILs reported in the literature, demonstrating great potential for gas separation applications.