(2je) Polymer Membrane Technology, Synthesis of Copolymer Membrane with Polystyrene and Divinylbenzene Used in Electrodialysis and It's Applications

Research Interests: polymer membranes have gained an important place in chemical technology and are used in a broad range of applications. The key property that is exploited is the ability of a membrane to control the permeation rate of a chemical species through the membrane. Membrane technologies have developed as one of the main contributors to the resolution of water- related problems over the past two decades. Increasing water scarcity, followed by severe regulations in industrialized countries, have promoted the use of membranes for water and wastewater treatment. From the perspective of wastewater treatment, microfiltration, ultrafiltration, nanofiltration, and reverse osmosis are the most common developed membrane separation techniques applied in industries. Forward osmosis has also been introduced as a recent advance in membrane techniques for wastewater treatment. Many researchers have focused on proper systems to obtain fresh water by purifying and reusing polluted water. Water purification is the process of eliminating disagreeable agents, such as chemicals, organic and biological contaminants from water. Medical applications of membranes are artificial kidneys, artificial lungs, and controlled drug delivery. Wide efforts have been implemented to improve both flux and selectivity of the membranes. A membrane is a discrete, thin interface that moderates the permeation of chemical species in contact with it. This interface may be molecularly homogeneous, that is, completely uniform in composition and structure, or it may be chemically or physically heterogeneous, for example, containing holes or pores of finite dimensions or consisting of some form of layered structure. Furthermore, some researchers have focused on reduce membrane fouling as the most important problem in application of membranes in wastewater treatment. As a result, the performance and commercial markets of membranes have been greatly increased during the past years. The driving force for transport in membrane processes can be a pressure gradient and chemical or electrical potential across the membrane. Membrane processes depend on a physical separation, usually with no phase change and chemicals addition in the feed stream, thus stand out as an alternative wastewater treatment technique to conventional processes (i.e., distillation, precipitation, coagulation/ flocculation, adsorption by active carbon, ion exchange, biological treatment, etc. the low energy consumption, reduction in number of processing steps, greater separation efficiency and higher final product quality are the main attractions of these processes. However, limited resistance of the membranes in terms of chemical, mechanical, and thermal restricts their application. Ion- exchange membranes have been used in various industrial processes, for example, in the electrodialytic concentration of seawater to produce edible salt, as a separator for electrolysis, in the desalination of saline water by electrodialysis, in the separation of ionic materials from non- ionic materials by electrodialysis, in the recovery of acid and alkali from waste acid and alkali solution by diffusion dialysis, in the dehydration of water- miscible organic solvent by pervaporation, etc. thus, various ion- exchange membranes have been developed according to their requirements. Synthesis of copolymer membrane with polystyrene and divinylbenzene produced by free- radical polymerization using suspension technique. The suspension method is highly suitable for a batch process. Commercially available polystyrene is mostly of the atactic variety and, hence, is amorphous in nature. Polystyrene consists generally of linear molecules and is chemically inert. For organic phase: styrene, was used as a monomer, divinylbenzene, was used as a cross-linker, azo-bis-isobutyronitrile, was used as a initiator, and toluene, was used as a diluent. The aqueous phase was prepared by adding gelatin, calcium carbonate as a stabilizer, and sodium sulfate as a surfactant into distilled water as a polymerization medium. The effect of different parameters (initiator, cross-linker and diluent amount, diluent type, agitation speed was studied by varying the polymerization conditions. Direct modification of polymer backbone: for soluble polymers, polyarylene polymers containing aromatic pendant groups on polymer backbones such as poly aryl sulfone, poly aryl ketone, and polyphenylene oxides, the corresponding membranes can be obtained either by introducing anionic or cationic moieties, followed by the dissolving of polymer and casting it into a film. For the preparation of ion exchange membrane, these polymers are attractive as the polymer matrix due to several reasons: i)their high mechanical and thermal stability, good processing stability, relatively high glass transition temperature, low cost, and the ability to chemically modify the polymer backbone via the electrophilic substitution at their aromatic skeletons. However, for membrane preparation with these soluble polymers, its chemical stability is not so good and often needs post treatment, such as crosslinking. Charge induced on the film membranes: the IEM can also be prepared by forming the non-ionic polymer films firstly, subsequently by the introduction of charged functional groups onto the formed polymer films either directly by grafting of a functional monomer or indirectly by grafting non-functional monomer followed by functionalization reaction. Both porous and non- porous membranes can be used as the film substrates. Typical examples of grafting substrates include hydrocarbon polymer membrane of polyethylene, polypropylene, polyalkene non- woven fabrics, and fluorocarbon polymer films of polyvinylidene fluoride and polytetrafluoroethylene. For the grafting agents, there are two major categories: functional monomers such as acrylic acid, methacrylic acid that can be directly attached to the substrate as charged functional groups and non-functional monomers such as styrene, glycidyl methacrylate(the ester of methacrylic acid and 2,3-epoxy-propanol that bears a reactive epoxy group) and vinylbenzyl chloride that can be further chemically modified into the ion-exchangeable. Radiation-induced graft copolymerization is well known for its merits and potential to transform the chemical and the physical properties of pre-existing polymeric materials without altering their intrinsic properties. Using this method cation exchange membrane for electrodialysis application was early prepared by grafting of methacrylic acid onto preformed polyethylene. Another type of membranes prepared by grafting of fluorinated monomers such as methyl trifluoro-propionoate onto polytetrafluoroethylene films was found to be promising for electrodialysis processes as the use of fluorinated monomer imparted more chemical stability to membrane. The crystalline and amorphous components influence polymer properties in as much as the molecular weight of a polymer is influenced by that of the various fractions which make the polymer. The properties of a polymer such as density, modulus, hardness, permeability and heat capacity will be largely affected by its crystallinity. For a partially crystalline polymer, its crystalline and amorphous regions will exhibit different properties, even though both the regions are chemically the same. Permeability depends on the extent and rate of penetration of liquid or vapor molecules through the polymer matrix which, in turn, depend on the physical structure of the polymer. Crystalline polymers, in general, are far less permeable than the amorphous variety. Thus, we could say that as the polymer crystallinity increases the permeability decreases. Permeability and, hence, crystallinity, have some effect on the chemical degradation of the polymer. The acid hydrolysis of cellulose, for example, takes place at the amorphous regions with more case than at the crystalline regions. Membrane technology is becoming increasingly important due to high efficiency, low cost, and easy manipulation, and membranes are widely used in diverse fields including substance separation and purification, environment protection and remedy, and energy conversion and storage. Basic membrane research includes a number of scopes, including membrane surface modification and its relation to membrane characterization, membrane formation and structure on transport properties, theoretical analyses of membrane transport phenomena, experimental results on membrane permeation and selectivity, membrane fouling and its effect on membrane performance, membrane adsorber/ membrane chromatography, membrane modules and their impact on device performance, and membrane processes/ applications with a focus on the role of the membrane. In this special issue, we focus on the membrane formation and applications. In water and wastewater treatment, membrane technology has been recognized as the key technology for the separation of contaminants from polluted sources. Membranes are selective barriers that separate two different phases, allowing the passage of certain components and the retention of others. The driving force for transport in membrane processes can be a pressure gradient and chemical or electrical potential across the membrane. Membrane processes depend on a physical separation, usually with no phase change and chemicals addition in the feed stream, thus stand out as an alternative wastewater treatment technique to conventional processes (i.e., distillation, precipitation, coagulation/ flocculation, adsorption by active carbon, ion exchange, biological treatment, etc. the low energy consumption, reduction in number of processing steps, greater separation efficiency and higher final product quality are the main attractions of these processes. However, limited resistance of the membranes in terms of chemical, mechanical, and thermal restricts their application. Membrane based water treatment technologies lead the desalination industry due to their lower energy requirements compared to thermal evaporative processes. Electrodialysis is another membrane- based process that has held a small but stable share in treatment of low- salinity waters. Driven by a potential gradient, it has higher water recovery rates, fewer pre- and post- treatment steps, and is easily adjustable for varying feed water quality compared to reverse osmosis systems. Current membrane technology enables electrodialysis to be economically advantageous for small to medium sized plants processing salinities of 1000- 5000 mg/L total dissolved solids.