Vapor permeation of hydrocarbons through supported liquid membranes based on ionic liquids

Separation of benzene and cyclohexane is one of the most challenging processes in the chemical industry. In our previous paper, we examined the separation of a mixed solution of benzene and cyclohexane using a supported liquid membrane (SLM) based on ionic liquids. In this study, vapor permeation (VP) of benzene/cyclohexane through a SLM using ionic liquids based on 1-alkyl-3-methylimidazolium and quaternary ammonium salts was performed. We examined the effects of ionic liquids and the benzene fraction in the feed on the permeation flux and separation factor, and the stability of the SLM based on ionic liquid. It was found that the sorption step mainly affected the separation factor depending on the hydrophilicity of the ionic liquid. The hydrophilic liquid membrane that used N ,N -diethyl-N -methyl-N -(2-methoxyethyl) ammonium tetrafluoroborate, which showed the highest selectivity of 47.1 for the mixed solution, gave the highest separation factor, 185 for 53 wt.% benzene and 950 for 11 wt.% benzene for the VP, which are superior to the previously reported values obtained by pervaporation. Over 1 month, a steady flux and separation factor were obtained, suggesting that the membrane was extremely stable.

We applied SLMs impregnated with ionic liquids to the VP process for benzene and cyclohexane separation. Benzene selectively permeated the membrane. Permeability was mainly controlled in the membrane by diffusivity. The separation factor increased as the hydrophilicity of ionic liquids increased. The SLM based on ionic liquid shows high membrane stability for one month unlike the conventional SLM impregnated with volatile organic solvent. These experimental results indicate that the application of ionic liquid-supported membranes to the benzene and cyclohexane separation process is promising. To ensure practical availability of ionic liquid-SLMs, molecular design of an ionic liquid is needed for benzene and cyclohexane separation and for a high contact area membrane configuration.