Highly-selective separation of CO2 from N2 or CH4 in task-specific ionic liquid membranes: Facilitated transport and salting-out effect

Abstract

Developing high-performance membranes for selective separation of CO2 is still a focus point in light of massive CO2 emission. Salting-out effect is an useful method for maximizing CO2 separation performance in membranes by inhibiting permeation of inert gases (N2 and CH4). In this work, we designed a class of fluorion-based protic ionic liquids (FPILs) and characterized their chemical structures. Aqueous FPIL solutions were prepared and their densities as well as viscosities were measured. Supported ionic liquid membranes (SILMs) immobilized with FPIL solutions were prepared, and the permeability of CO2, N2 and CH4 were determined under humidified condition. Facilitated transport of CO2 and salting-out effect on N2 and CH4 in FPIL solutions were found. High CO2 permeability (up to 2572 barrers) and superior CO2/N2 and CO2/CH4 selectivity (up to 774 and 387, respectively) were obtained at 40 °C and 0.1 bar of CO2 partial pressure in [DMAPAH][F] solution of 40 wt% water. In addition, effects of CO2 transmembrane pressure, water content and operating temperature on gas permeation as well as facilitated transport mechanism and salting-out effect were systemically invesgated. This work offers a new strategy for designing ILs-based membranes for efficient seperation of CO2.