Development and characterization of chemically stabilized ionic liquid membranes-Part I: Nanoporous ceramic supports

Stabilization of a room temperature methylimidazolium cation based ionic liquid (IL) into the pores of ceramic nanofiltration (NF) membranes was achieved by means of a novel in situ, pressure assisted imbibition/reaction method. The complete coverage of the nanopores void space by the synthesized IL phase, introduced an additional parameter that was pursued in parallel to the challenge of stabilization. The purpose was to develop hybrid membranes that will exhibit solely the gas solvation/diffusion properties of the IL. A silane functionalized ionic liquid phase of 1-methyl-3-(1-trialkoxysilylalkyl) imidazolium as cation and hexafluorophosphate as anion, was first synthesized and subsequently grafted onto the pore surface. The CO2/CO separation performance of the modified membranes was quite significant. The maximum CO2/CO separation factors achieved were 11 at 30 °C, 25 at 50 °C, 12 at 100 °C and 5 at 230 °C. The respective CO2 permeability values were 226, 520, 715 and 2000 Barrer. The stability of the developed membranes has been verified, in 3 sequential cycles of heating/cooling, in the temperature range between 25 and 250 °C and under a differential pressure up to 0.5 MPa.

Research highlights▶ A silanised ionic liquid of imidazolium cation retains the enhanced CO2 solvation characteristics over other gas species. ▶ Grafting of the silanised ionic liquid into a ceramic nanofiltration membrane pores enhances the stability of the ionic liquid phase. ▶ The grafted ionic liquid membrane performs at temperatures up to 250 °C. ▶ The maximum CO2/CO separation performance was 25 and was observed at 50 °C.