Polymeric membrane separation

Microporous polymeric membrane separators are characterized by pore sizes in the micrometer scale. Microporous polymeric membrane separators are mainly made of polyethylene (PE), polypropylene (PP), and the combinations of them (PE/PP and PP/PE/PP) because of their high chemical and mechanical stabilities. According to the number of layers, they can be classified into monolayer and multilayer polymeric microporous membranes. 

Ochoa, N., Pagliero, C., Marchese, J., and Mattea, M. (2001) Ultrafiltration of vegetable oils. Degumming by polymeric membranes. Separation and Purification Technology 22-23, 417-422. 

The research on ion-exchange membranes has grown considerably in recent years with the interest in fiiel-ceU technology for the automotive and portable applications [152]. The most promising fuel-cell technology for low temperature operation makes use of a polymeric membrane separating the anode and cathode of an electrochemical cell. 

In order to automate the analysis, these methods frequently combine immobilized enzymes with flow or sequential injection techniques. These methods may include a separation step such as solid-phase extraction, gas diffusion, or pervaporation. The latter is a nonchromatographic separation technique, which selectively separates a liquid mixture by partial vaporization through a nonporous polymeric membrane. Separation is not based on relative volatilities as in distillation, but rather on the relative rates of permeation through the membrane. 

Selective separation of toxic heavy metal ions from waste solutions is frequently required in hydrometallurgical processing (7). Solvent extraction is known to be an useful method to separate such metal ions from solutions. To make a continuous process of such a system, liquid membrane separations have been developed (2, 5). However, the unstability of these systems often pose a problem to practical industrial applications. With respect to the system stability, polymeric membrane separations may be feasible. The problem for the polymeric membrane separations is their poor transport selectivity toward heavy metal ions. Thus a development of the polymeric membrane separation which can show a comparable metal separation ability with the liquid membrane separation is an important issue to perform the practical heavy metal ion separation (4). 

Based upon the above concept, three different types of membrane separation, i.e., (1) liquid membrane separation which utilizes lipophilic anion-exchangers as mobile carriers, (2) polymeric membrane separation in which the anion-exchange sites function as fixed carriers, and (3) polymeric plasticizer membrane separation in which the membrane is composed of polymeric support, membrane plasticizer, and lipophilic anion-exchangers as a novel membrane material are discussed in relation to their transport efficiency and selectivity for separation of heavy metal chloride complexes. 

To enhance the permeation efficiency and selectivity of the polymeric membrane separation, a novel polymeric plasticizer membrane which is composed of cellulose triacetate (CTA) as a membrane support, o-nitrophenyl octyl ether (NPOE) as a membrane plasticizer, and trioctylmethylammonium chloride (TOMAC) as an anion-exchange carrier has been developed. Compared with the poly (vinyl chloride) plasticizer membrane which is widely used for ion-selective electrode, the CTA membrane can contain a larger amount of plasticizer due to a high affinity between CTA and NPOE (25). Thus the plasticizer (NPOE) solubilized in the membrane acts effectively as an organic medium for the carrier mediated membrane separation (25-29). 

The membrane transport experiments were first conducted in a cylindrical dialysis cell (membrane area, 0.8 cm ) shown in Figure 10. The source phase solution was a 250 mL of 0.25 M MgCl2 solution which contained 0.10 mM Pb(II) and Cd(II). The receiving phase was 5.0 mL of pure water. Plots of the EF value versus time for competitive transport of Pb(II) and Cd(II) are presented in Figure 12a. Selective permeation of Cd(II) over Pb(II) was observed, which is consistent with the selectivity obtained for the polymeric membrane separation. The EF for both heavy metals increased with time and reached values of 13.3 and 0.7 for Cd(II) and Pb(II), respectively after 6 h. As shown in Figure 11, the polymeric membrane separation required the permeation time of 40 h to achieve the EF value of 5.8 for Cd(II), whereas such EF value was recorded only after 2 h for the polymeric plasticizer membrane separation. Thus it is evident that the polymeric plasticizer membrane revealed a superior transport efficiency and selectivity to the conventional polymeric anion-exchange membrane. 

This chapter will be dedicated to a state of the art analysis of simulation of polymeric membrane separation processes for post-combustion CO2 capture. 

Interfacial polymerization membranes are less appHcable to gas separation because of the water swollen hydrogel that fills the pores of the support membrane. In reverse osmosis, this layer is highly water swollen and offers Httle resistance to water flow, but when the membrane is dried and used in gas separations the gel becomes a rigid glass with very low gas permeabiUty. This glassy polymer fills the membrane pores and, as a result, defect-free interfacial composite membranes usually have low gas fluxes, although their selectivities can be good. 

D. R. Paul and Y. P. Yampol skii, eds.. Polymeric Gas Separation Membranes, CRC Press, Boca Raton, Fla., 1994. 

Fleece-Back Sheet. A fleece-back sheet is a nonreinforced polymeric membrane that has had a nonwoven mat made of polyester, weighing 101.7—203.4 g/m, laminated to the back of the sheet. The prime use of the fleece-back sheet is in the fully adhered roofing systems. The fleece provides the chemical separator, which eliminates the need for an adhesive that is compatible with the specific membrane or a compatible substrate. 

S. Hwang and K. Kammermeyer, Membranes in Separations,]ohn Wdey Sons, Inc., New York, 1975 good study of membrane transport phenomenon. R. E. Kesting, Synthetic Polymeric Membranes, McGraw-HiU, New York, 1971 good bibhographies. 

Selective gas permeation has been known for generations, and the early use of p adium silver-alloy membranes achieved sporadic industrial use. Gas separation on a massive scale was used to separate from using porous (Knudsen flow) membranes. An upgrade of the membranes at Oak Ridge cost 1.5 billion. Polymeric membranes became economically viable about 1980, introducing the modern era of gas-separation membranes. Hg recoveiy was the first major apphcation, followed quickly by acid gas separation (CO9/CH4) and the production of No from air. 

Leading Examples These apphcations are commercial, some on a very large scale. They illustrate the range of application for gas-separation membranes. Unless otherwise specified, all use polymeric membranes. 

By the time the next overview of electrical properties of polymers was published (Blythe 1979), besides a detailed treatment of dielectric properties it included a chapter on conduction, both ionic and electronic. To take ionic conduction first, ion-exchange membranes as separation tools for electrolytes go back a long way historically, to the beginning of the twentieth century a polymeric membrane semipermeable to ions was first used in 1950 for the desalination of water (Jusa and McRae 1950). This kind of membrane is surveyed in detail by Strathmann (1994). Much more recently, highly developed polymeric membranes began to be used as electrolytes for experimental rechargeable batteries and, with particular success, for fuel cells. This important use is further discussed in Chapter 11. 

Through these processes dissolved substances and/or finely dispersed particles can be separated from liquids. All five technologies rely on membrane transport, the passage of solutes or solvents through thin, porous polymeric membranes. 

In this case study, an enzymatic hydrolysis reaction, the racemic ibuprofen ester, i.e. (R)-and (S)-ibuprofen esters in equimolar mixture, undergoes a kinetic resolution in a biphasic enzymatic membrane reactor (EMR). In kinetic resolution, the two enantiomers react at different rates lipase originated from Candida rugosa shows a greater stereopreference towards the (S)-enantiomer. The membrane module consisted of multiple bundles of polymeric hydrophilic hollow fibre. The membrane separated the two immiscible phases, i.e. organic in the shell side and aqueous in the lumen. Racemic substrate in the organic phase reacted with immobilised enzyme on the membrane where the hydrolysis reaction took place, and the product (S)-ibuprofen acid was extracted into the aqueous phase. 

The solid-liquid separation of shinies containing particles below 10 pm is difficult by conventional filtration techniques. A conventional approach would be to use a slurry thickener in which the formation of a filter cake is restricted and the product is discharged continuously as concentrated slurry. Such filters use filter cloths as the filtration medium and are limited to concentrating particles above 5 xm in size. Dead end membrane microfiltration, in which the particle-containing fluid is pumped directly through a polymeric membrane, is used for the industrial clarification and sterilisation of liquids. Such process allows the removal of particles down to 0.1 xm or less, but is only suitable for feeds containing very low concentrations of particles as otherwise the membrane becomes too rapidly clogged.2,4,8... 

It is possible to separate a soap-LSDA dispersion by ultrafiltration through a polymeric membrane [33]. The filtrate contained sodium and some magnesium ions but no calcium soaps or LSDA. The separated substances on the membrane could be readily dispersed in water in which they retained a high degree of surface activity. 

Novel chiral. separations using enzymes and chiral surfactants as carriers have been realized using facilitated transport membranes. Japanese workers have reported the synthesis of a novel norbornadiene polymeric membrane with optically active pendent groups that show enantio.selectivity, which has shown promi.se in the. separation of propronalol. 

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