ABSTRACT
Liquid membranes are thin liquid layers that separate two miscible phases. They became attractive because diffusivity in the liquid phase is generally three or four orders of magnitude higher than in solid membranes. Liquid membranes are separated into three types: bulk, emulsion, and supported. Bulk-liquid membranes are limited to laboratory use because such configuration is inadequate for practical use. Emulsion liquid membranes were originally proposed by Li (1968) and had an advantage of high permeation rates based on a high surface area per unit volume. Processes utilizing emulsion liquid membranes are more complex because emulsification and demulsification steps are needed before and after the permeation step using multiple emulsions. A supported liquid membrane (SLM), which is a porous solid structure impregnated with liquid, has also been studied. The SLM process has several advantages over other liquid membrane systems, such as simple configuration, low energy consumption, and a reduction in the amount of solvent used. The general characteristics and the current picture of SLM systems are reviewed in other chapters. This chapter focuses on ionic liquids as impregnating liquids. An SLM system using ionic liquids has some variations: ionic liquids diluted by solvents (Marták et al., 2008), the membranes of ionic liquids on porous alumina membranes (Huang et al., 2008), and composite membranes with cellulose triacetate (Jung et al., 2010) and polydimethylsiloxane (Izák et al., 2008). Since most previous research has been conducted using supported ionic liquid membranes (SILMs) absorbed into polymeric membranes, only this type will be described in this chapter. Here we briefly describe the characteristics of ionic liquids.
