Separation of CO2 from the CO2/N2 mixed gas through ionic liquid membranes at the high feed concentration

Separation of CO2 from the CO2/N2 mixtures through ionic liquid membrane was carried out in this study. The CO2 volume fractions (XCO2XCO2) at feed side were 0.3–0.5. The microporous polyvinylidine fluoride (PVDF) membrane and two species of ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf2N]), were used as the material for supported membrane and room temperature ionic liquids, respectively. The PVDF membranes were impregnated with the ionic liquids. The total pressures at the feed side were varied from 1.05 to 1.21 atm. The experiment was performed under constant temperature at 40 °C. The gas flow rates of CO2/N2 mixed gas at feed side were varied in range of 100–300 ml min−1. The effects of total pressure difference, the total flow rate at the feed side and the CO2 concentration were investigated. It was found that the higher permeability of CO2 was obtained from the lower total pressure differential conditions. The feed flow rates do not have the significant effect on permeability of N2. The [bmim][PF6] and [bmim][Tf2N] liquid membrane are given the equivalent CO2/N2 selectivity for XCO2XCO2=0.5 even though the feed gas flow rate was adjusted. The carrier saturation inside the ionic liquid membrane at high CO2 concentration and high pressure difference constrain the permeation of CO2. The highest selectivity was obtained in the case of XCO2XCO2=0.3 at constant total pressure difference and feed gas flow rate.

► Increasing total pressure at feed side, decreasing CO2 permeabilities.
► Facilitated transportation plays an important role for CO2 permeation.
► The fluorinated anions of ionic liquid acts as the carriers.