Liquid membrane supports

Bulk Liquid Membrane. . . Emulsion Liquid Membrane. Supported Liquid Membrane Dispersion Free Extraction. ... 

Three-phase liquid membrane Supported liquid membrane extraction SLM [6,85]... 

A novel polymeric bicontinuous microemulsion (PBM) membrane, consisting of an interconnecting network of nanometer pore size water channels, was employed as liquid membrane support [13] for the immobilization of new porphyrin carrier [14] for facilitated oxygen transport. Although the membrane resulted to be stable due to the nanoporous structure, a modest (2.3-2.4) O2/N2 selectivity was achieved. 

Some researchers have also used nitrocellulose filters as liquid membrane supports. Mochizuki and Forster (5) used this material as a support for hemoglobin solutions to study the facilitated transport of O2 and CO. Enns (6) used the same support for studying the facilitated transport of CO2 using aqueous solutions of carbonic anhydrase. Donaldson and Quinn (7) utilized both nitrocellulose filters and cross-linked protein membranes as supports to investigate CO2 facilitated transport using enzymatically active liquid membranes. 

Two common liquid membrane support materials, polytetrafluoroethylene and polypropylene, have critical surface tensions of 18 mN/m and 35 mN/m, respectively. Manufacturers often supply critical surface tensions for their porous films. Liquids with a surface tension, y, less than the critical surface tension will probably wet the surface. Therefore, hydrocarbons will wet polypropylene, but water (y = 72 mN/m) will not. Shafrin and Zisman (30) have summarized critical surface tension data for many materials and correlated the data such that critical surface tensions may be estimated from knowledge of the functional groups in the chemical structure of the surface. 

Figure 3 is a schematic representation of a tortuous pore in a liquid membrane support. Lee et al. (33) define the tortuosity, T, as the following ... 

The authors state that while the above definition is used widely, other authors have defined tortuosity as 1/T, T, and l/T as these forms are frequently encountered in expressions for ionic conductivity and mobility through tortuous membranes. Experimental measurement of liquid membrane support tortuosity is described by Bateman et al. 

The mean pore size of a liquid membrane support determines the force which holds the liquid membrane within the pore structure. The Young-Laplace equation (28) relates the force holding a liquid within a cylindrical capillary to the contact angle, the surface tension, and the radius of the pore ... 

As new membranes are developed, methods for characterization of these new materials are needed. Sarada et al. (34) describe techniques for measuring the thickness of and characterizing the structure of thin microporous polypropylene films commonly used as liquid membrane supports. Methods for measuring pore size distribution, porosity, and pore shape were reviewed. The authors employed transmission and scanning electron microscopy to map the three-dimensional pore structure of polypropylene films produced by stretching extended polypropylene. Although Sarada et al. discuss only the application of these characterization techniques to polypropylene membranes, the methods could be extended to other microporous polymer films. Chaiko and Osseo-Asare (25) describe the measurement of pore size distributions for microporous polypropylene liquid membrane supports using mercury intrusion porosimetry. 

In the next section, four chapters describe three main configurations of liquid membranes supported, emulsion, and bulk LM. Each chapter is subdivided into theory and transport mechanisms, module design and experimental techniques, and applications in different fields of chemical, biochemical, environmental, and pharmaceutical separations. 

Substance Application Liquid membrane Support Configuration References... 

Wieczorek, P., Tomaszewska, M. (1997). Transport ofamino acids through liquid membranes supported on novel poly(vinylidenefluoride) porous flat-sheet matrix. Solvent Extr. Ion. Exc., 15, 879-94. 

Liquid membranes supported by hollow fibers are relatively easy to make and operate and the membrane fluxes can be quite high. However, membrane stability is a problem. The variation in coupled transport flux during long-term tests is shown in Figure 9.36. As these results show, actual behavior varies quite widely, depending on the membrane and the complexing agent. However, each curve is quite reproducible. 

If solvent extraction may be considered a source technique, derived liquid-liquid separation techniques include configurations in which an extraction solvent is physically immobilized by a coating or impregnation process onto a solid support such as silica, porous resin beads, or foam [13,84—87]. Other derived techniques include membranes of various configurations bulk liquid membranes, supported liquid membranes, emulsion membranes, and polymer-impregnated membranes [88]. Many derived liquid-liquid techniques have been developed, especially for use in analytical applications [13,60,62,64,75,84,85,87]. In each of these derived techniques, the... 

However, Immobilized liquid membranes supported with porous substrates have two prlmeu y experimental problems loss of solvent and loss or deactivation of the carrier. Matson et al. ( ) prevented evaporative loss of liquid by maintaining the relative humidity of the gas streams in the range of 60 to 90%. Another problem may arise when humidification is used. If solvent condenses out of the feed gas stream onto the ILM and a pressure gradient between the feed and sweep gas stream exists, solvent may flow through the support pore structure leaching the carrier out of the membrane. 

Chaudry, MA., Islam, N.U. Mohammad, D. (1987) Uranium(VI) transport through tri-n-butylphosphate kerosene oil liquid membrane supported in polypropylene film. Journal of Radioanalytical and Nuclear Chemistry, 09 ),n 22. 

Lao,8Sro.2Feo.7Gao.303 a Work by Air Liquide membrane supported on Lao.8Bao.2Feo.703 5 114... 

Supported Liquid Membranes. Supported liquid membranes (SLMs) consist of a hydrophobic, porous plastic sheet or hollow fiber (usually polypropylene or polysulfone). The pores are filled with an organic solvent in which the carrier is dissolved. This membrane separates the aqueous source and receiving phases (Figure 8c). The liquid-containing pores allow transport of the target species via the dissolved carrier, while the plastic sheet offers support for the liquid membrane. Pore sizes generally range from 0.02 to 1.0 pm. 

Rgure 8. Frequently Used Membrane Types. A, B, C, and D are bulk liquid membrane, emulsion liquid membrane, supported liquid membrane, and dual module hollow fiber membrane configurations respectively. (Reproduced with permission from ref. 47. Copyright 1990 CRC Press.)... 

In another study, Navratil etal. (37-39) used undiluted DHDECMP and also 80 volume % of TBP in dodecane as liquid membranes supported in hollow-fiber... 

Figure 5.4.6. (a) Copper stripping with a supported liquid membrane. Copper is selectively concentrated by diffusion across a liquid membrane supported by a porous polymer film, (b) How the membranes work. Copper is concentrated by means of the steps shown, (a) and (b) reprinted, with permission, from Lee et al., AIChE J., 24(5), 860 (1978). Copyright [1978] American Institute of Chemical En neers (AIChE). 

The separation of the two metals will he primarily determined by the ratio of the two distribution coefficients, kmio/k o. exactly as in solvent extraction. Separation of copper from nickel using L1X65N in the liquid membrane using these principles has been studied by Lee et al. (1978). A general review of metal extraction using liquid membranes supported in microporous polymeric membranes is provided by Danesi (1984-85). 

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