Ionic Liquid Confined in Mesoporous Polymer Membrane with Improved Stability for CO2/N2 Separation

Supported ionic liquid membranes (SILMs) have a promising prospect of application in flue gas separation, owing to its high permeability and selectivity of CO₂. However, existing SILMs have the disadvantage of poor stability due to the loss of ionic liquid from the large pores of the macroporous support. In this study, a novel SILM with high stability was developed by confining ionic liquid in a mesoporous polymer membrane. First, a mesoporous polymer membrane derived from a soluble, low-molecular-weight phenolic resin precursor was deposited on a porous Al₂O₃ support, and then 1-ethyl-3-methylimidazolium tetrafluoroborate ([emim][BF₄]) was immobilized inside mesopores of phenolic resin, forming the SILM under vacuum. Effects of trans-membrane pressure difference on the SILM separation performance were investigated by measuring the permeances of CO₂ and N₂. The SILM exhibits a high ideal CO₂/N₂ selectivity of 40, and an actual selectivity of approximately 25 in a mixed gas (50% CO₂ and 50% N₂) at a trans-membrane pressure difference of 2.5 bar. Compared to [emim][BF₄] supported by polyethersulfone membrane with a pore size of around 0.45 μm, the [emim][BF₄] confined in a mesoporous polymer membrane exhibits an improved stability, and its separation performance remained stable for 40 h under a trans-membrane pressure difference of 1.5 bar in a mixed gas before the measurement was intentionally stopped.