Polymeric Membranes for Molecular Separations

Ulbricht M and Susanto H (2009), Polymeric membranes for molecular separations , in Drioli E and Giomo L, Membrane Operations, Innovative Separations and Trans/owrafioni, Wemheim, Wiley-VCH, 19-43. 

This is followed by a chapter on polymeric membranes that discusses the current achievements and challenges on membranes for molecular separation in liquid phase. 

A new area of polymer science termed nano-macromolecular chemistry [Eirich, 1993] also has relevance to future polymer blend technology and application. Langmuir-Blodget techniques allow for the formation of films of one molecule thickness. Utilizing polymerizable molecules for these films, a polymer molecule or network can yield a film with the thickness of several nanometers. Alternating layers comprised of different polymers could be prepared to yield specific optical or electrical properties. Polymerization of calix-arenes to yield molecular sieving membranes for gas separation has been discussed by Conner et al. [1993]. 

There is a growing interest in the development of gas separation membranes based on materials that provide better selectivity, thermal and chemical stability than those which already exist (i.e. polymeric membranes). Carbon membranes offer the best candidates for the development of new membrane technologies, because of their stability and molecular sieving capabilities. The most notable advantages of carbon membranes have been recently reviewed [8] in comparison to those of polymeric membranes, in order to highlight the factors that make carbon membranes very attractive and useful as separation tools. Table 11.2 inserted in the errd of the chapter summarizes the performance of carbon membranes for the separation of mixtures of permanent gases as reported in the literature. 

Adsorption systems employing molecular sieves are available for feed gases having low acid gas concentrations. Another option is based on the use of polymeric, semipermeable membranes which rely on the higher solubiHties and diffusion rates of carbon dioxide and hydrogen sulfide in the polymeric material relative to methane for membrane selectivity and separation of the various constituents. Membrane units have been designed that are effective at small and medium flow rates for the bulk removal of carbon dioxide. 

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