Theoretical and experimental investigation of CO₂ capture through choline chloride based supported deep eutectic liquid membranes

The supported liquid membranes (SLMs) provide a feasible solution to global warming by combining their high CO₂ interaction with stripping in a continuous and single step process. Herein, deep eutectic solvents (DESs), possible substitutes to ionic liquids (ILs), were used as material to synthesize novel SLMs. The DESs were prepared from choline chloride and urea using three different mole ratios 1:2, 1:1, and 2:1 respectively. The prepared DESs were impregnated into the pores of polyvinylidene fluoride microporous membrane support to form novel DES-SLMs. The DESs-SLMs were tested using pure and mixed gas CO₂ permeability as well as CO₂/N₂ and CO₂/CH₄ separation experiments. Density functional theory calculations were performed to get an insight into the interaction of DES with CO₂ over N₂/CH₄. The complexation energies (Ec) of the DES with CO₂, N₂, and CH₄ were in the order of −29.3, −9.9, and −13.0 kJ/mol, respectively which reflected the high interaction of CO₂ with DES over CH₄ and N₂. The DES with choline chloride to urea molar ratio of 2:1 showed the highest CO₂ permeability of 45.6 Barrer and corresponding CO₂/CH₄ and CO₂/N₂ selectivity of 61.62 and 78.62, respectively. Finally, a comparison with the supported ionic liquid membranes (SILMs) literature showed that the DESs-SLMs presented comparable CO₂ permeability and a significantly high CO₂/CH₄ selectivity which enabled them to surpass the well-known Robeson's upper bound proving their commercial potential. This reflects that the DES-SLMs are a green strategy for carbon capture which can replace the SILMs in practical applications.