Preparation of ionic liquid-immobilized siloxane membranes by vapor-phase transport and anion exchange

Using the sol-gel method, we developed ionic liquid (IL)-immobilized siloxane membranes from ionic alkoxysilanes (silylated ILs). The developed membranes were adapted for the separation of inorganic and organic gases and organic liquid mixtures. In this study, we developed a new method for preparing IL-immobilized siloxane membranes using vapor-phase transport and anion exchange techniques. First, a siloxane membrane containing chloropropyl groups was prepared in a porous Al2O3 tube. The membrane was brought into contact and reacted with 1-methylimidazole vapor at 353 K. AgCl precipitation, and Cl 2p3/2 X-ray photoelectron spectroscopy revealed that the chloropropyl group was successfully converted into an imidazolium-type IL structure. Next, the membrane was immersed in aqueous HN(SO2CF3)2 to exchange the anion from Cl− to (CF3SO2)2N−. The change in permselectivity through the membranes before and after the vapor-phase transport and anion-exchange treatments was confirmed by steam/H2 and toluene/N2 separation tests. The developed techniques exhibit excellent potential for preparing a wide variety of IL-immobilized siloxane membranes.