Separation using functional polymeric membranes

Inert membranes are by far the most widely used in polymeric membrane reactors. Since in PIMRs the catalytic function is absent from the membrane, in comparison with PCMRs this type of membrane reactor represents a lower level in process integration. However, because of this and because the membrane modulus can be separated from the vessel where the chemical reaction takes place, PIMRs allow a much wider range of reactor configurations than PCMRs. 

A separator is a porous membrane placed between electrodes of opposite polarity, permeable to ionic flow but preventing electric contact of the electrodes. A variety of separators have been used in batteries over the years. Starting with cedar shingles and sausage casing, separators have been manufactured from cellulosic papers and cellophane to nonwoven fabrics, foams, ion exchange membranes, and microporous flat sheet membranes made from polymeric materials. As batteries have become more sophisticated, separator function has also become more demanding and complex. 

Functionalized polymers are of interest in a variety of applications including but not limited to fire retardants, selective sorption resins, chromatography media, controlled release devices and phase transfer catalysts. This research has been conducted in an effort to functionalize a polymer with a variety of different reactive sites for use in membrane applications. These membranes are to be used for the specific separation and removal of metal ions of interest. A porous support was used to obtain membranes of a specified thickness with the desired mechanical stability. The monomer employed in this study was vinylbenzyl chloride, and it was lightly crosslinked with divinylbenzene in a photopolymerization. Specific ligands incorporated into the membrane film include dimethyl phosphonate esters, isopropyl phosphonate esters, phosphonic acid, and triethyl ammonium chloride groups. Most of the functionalization reactions were conducted with the solid membrane and liquid reactants, however, the vinylbenzyl chloride monomer was transformed to vinylbenzyl triethyl ammonium chloride prior to polymerization in some cases. The reaction conditions and analysis tools for uniformly derivatizing the crosslinked vinylbenzyl chloride / divinyl benzene films are presented in detail. 

Due to the low preparation cost, monolayer polymeric membranes have been widely used as separators for LIBs. However, limited by the relatively single function of mono-layer polymeric membranes with relatively poor puncture strength and thermal stability, monolayer polymeric membranes may not be able to meet many application demands. 

M. Ulbricht published recently a comprehensive overview on the development of polymeric membranes having advanced or novel functions in the various membrane separation processes [121], The author describes novel processing technologies of polymers for membranes, the synthesis of novel polymers with well-defined structure as designed membrane materials, advanced surface functionalization of membranes, the use of templates for creating tailored barrier or surface structures for membranes, and the preparation of composite membranes for the synergistic combination of different functions by different (mainly polymeric) materials. 

As the membrane acts as a separating medium between two flow compartments, these basic functions can be applied to liquid/liquid, gas/liquid and gas/ gas systems, respectively. The physical shape of the membrane strongly depends on the membrane material used. For polymeric systems, these can be flat sheets in a plate-and-frame configuration, spiral-wound modules, and tubular mem-... 

It is well known that the surface chemical and physical properties play a dominant role in the separation characteristics of a membrane. Most of the currently used membranes are made of polymers because they have excellent bulk physical and chemical properties, they are inexpensive, and are easy to process. However, the surface properties of polymers, their hydrophobicity, and their lack of functional groups stand in the way of many other applications (Chan et al. 1996). So far, various polymers have been used for membrane fabrication. However, due to the limited number of polymeric materials on the market, one cannot expect any significant increase in the variety of the membranes offered. What is more, large-scale production of brand-new polymers has not been commercialized during the last decade, nor is it expected to be launched in the near future. These observations have forced material scientists to search for alternative methods to increase the number and variety of membranes being prepared. There are two directions for new membrane manufacturing (i) to modify a polymer in bulk and then prepare the membrane from it or (ii) to prepare the membrane from a standard polymer and then modify its surface. The first method needs the optimization of the membrane formation for the particular derivative separately. The second seems to be less complicated and less expensive, and it can offer a wide variety of new membranes based on one starting matrix. The authors intention is to present the plasma methods for membrane modification and tailor them based on the end-user requests. 

Wang, Y.C., Li, C.L., Lee, K.R. and Liaw, D.J. 2005. Pervaporation separation of aqueous alcohol solution through a carbazole-functionalized norbornenederivative membrane using living ring-opening metathesis polymerization. J Memh S l. 246 59-65. 

A membrane is simply a barrier between two phases. If one component of a mixture moves through the membrane faster than another mixture component, a separation can be accomplished. Polymeric membranes are used commercially for many applications including gas separations, water purification, particle filtration, and macromolecule separations (7-4). There are several important aspects to this definition. First, a membrane is defined based on its function, not the material used to fabricate the membrane. Secondly, a membrane separation is a rate process and the separation occurs due to a chemical potential gradient, not by equilibrium between phases. 

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