New Materials, New Devices, New Solutions: How to Prepare a Membrane

Nowadays, polymeric membranes have been used successfully in a wide range of large-scale indus-trial applications. The use of membranes in industry is primary the result of two developments: (1) in membrane materials and (2) in membrane structures, both followed by the step of large-scale membrane production. The selection of a suited material and a preparation technique depends on the application in which the membrane is to be used (e.g., gas separation, microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO)). In this chapter, a review of up-to-date literature about preparation of polymeric membranes from new materials for different membrane applications by means of phase inversion process is given. The most important part in any membrane separation process is the membrane itself. A mem-brane is a thin barrier that allows selective mass transport (Cabasso, 1987). In some applications such as in gas separation and pervaporation, the membrane material as the dense layer plays a crucial role in membrane separation. In other applications such as in liquid separations, MF or UF, wherein the transport is not based on solution-diffusion mechanism but occurs through a porous membrane by means of a sieving process, the membrane material is not quite as important as the membrane structure. In membrane processes such as NF and RO, for which both transport mecha-nisms (i.e., solution diffusion and sieving) contribute to membrane performance, the choice of mem-brane material is fundamental. In more recent membrane operations, such as membrane contactors, where the membrane is porous and not selective, the only function of the membrane is to act as a barrier between two nonmixable phases (Drioli et al., 2006). In this case, the main requirement is that the membrane must not be wet, and the suited material is chosen on the basis of surface tension properties. Different methods of polymeric membrane preparation have been reported in literature (Strathmann, 1981; Lonsdale, 1982; Nunes and Peinemann, 2001). Membranes can be classified according to their bulk structure, morphology, and application (Figure 1.1). Membranes have either a symmetric (isotropic) or an asymmetric (anisotropic) structure. Symmetric membranes have a uniform structure throughout the entire membrane thickness,