(35c) Stability and Selectivity of Supported Liquid Membranes with Ionic Liquid for Separation of Organic Liquids by Vapor Permeation

Room temperature ionic liquids (RTILs) have attracted a great deal of attention as green solvents, and are used in many fields of the chemical industry, because of their thermal stability and negligible vapor pressure, which makes them environmentally friendly. Supported liquid membranes (SLMs) are often prepared by immobilizing organic solvent inside a porous structure of polymeric or ceramic membranes, and become a promising alternative to conventional solvent extraction, since they combine the operations of extraction and stripping. However, SLMs have not obtained commercial application in the past 20 years, mainly due to their instability and poor long-term performance. In order to prevent the loss of membrane liquids, we propose a novel approach in which vapor permeation with an ionic liquid filling-type SLM replaces solvent extraction. Since the basic characteristics of RTILs are high surface tension and a lack of detectable vapor pressure, this method provides several possible advantages: no adjacent liquid phase contacts the ionic liquid directly, thus preventing the loss of membrane liquid by the dissolution/dispersion effect, as well as by evaporation. Moreover, the molecular structure of ionic liquid used for SLMs can be designed corresponding with the required physicochemical properties of the desired permeation component in the organic mixtures. The separation of toluene/cyclohexane mixtures was conducted for as long as 550 hours, and the separation factor was kept within the range of 15 to 25, showing good durability in vapor permeation. The use of SLMs with ionic liquid was shown to be a promising method to separate organic/organic or organic/water mixtures.