Permeability liquid membranes

Ionic liquids have already been demonstrated to be effective membrane materials for gas separation when supported within a porous polymer support. However, supported ionic liquid membranes offer another versatile approach by which to perform two-phase catalysis. This technology combines some of the advantages of the ionic liquid as a catalyst solvent with the ruggedness of the ionic liquid-polymer gels. Transition metal complexes based on palladium or rhodium have been incorporated into gas-permeable polymer gels composed of [BMIM][PFg] and poly(vinyli-dene fluoride)-hexafluoropropylene copolymer and have been used to investigate the hydrogenation of propene [21]. 

Kcurentjes et al. (1996) have also reported the separation of racemic mixtures. Two liquids are made oppositely chiral by the addition of R- or S-enantiomers of a chiral selector, respectively. These liquids are miscible, but are kept separated by a non-miscible liquid contained in a porous membrane. These authors have used different types of hollow-fibre modules and optimization of shell-side flow distribution was carried out. The liquid membrane should be permeable to the enantiomers to be separated but non-permeable to the chiral selector molecules. Separation of racemic mixtures like norephedrine, ephedrine, phenyl glycine, salbutanol, etc. was attempted and both enantiomers of 99.3 to 99.8% purity were realized. 

Antibiotics are used to treat bacterial infection [41]. Some antibiotics act directly on cell membranes of micro-organisms, with consequent alteration of permeability and leakage of intracellular components. Antibiotics affect cell membranes and thus also the liquid membrane, with the possibility of change in oscillation. 

The concept of the pH electrode has been extended to include other ions as well. Considerable research has gone into the development of these ion-selective electrodes over the years, especially in studying the composition of the membrane that separates the internal solution from the analyte solution. The internal solution must contain a constant concentration of the analyte ion, as with the pH electrode. Today we utilize electrodes with 1) glass membranes of varying compositions, 2) crystalline membranes, 3) liquid membranes, and 4) gas-permeable membranes. In each case, the interior of the electrode has a silver-silver chloride wire immersed in a solution of the analyte ion. 

As in most membranes, the liquid membrane must have selective permeability to specific solutes. The overall mechanism of solute transfer consists of three steps (1) extraction of the solute into the liquid membrane ... 

Polymers are permeable to liquids having similar solubility parameters. Several different celts have been designed to measure the permeability of membranes to gases and vapors. 

Simple lipophilic cations, like ammonium ions bearing long hydrocarbon chains, allow anion extraction into an organic phase and render liquid membranes permeable to anions by an anion exchange (antiport) process. Such carriers effect, for instance, selective transport of amino acid carboxylates [6.3] against inorganic anions like chloride. 

Permeability of Cesium through Supported Liquid Membranes... 

In this chapter membrane preparation techniques are organized by membrane structure isotropic membranes, anisotropic membranes, ceramic and metal membranes, and liquid membranes. Isotropic membranes have a uniform composition and structure throughout such membranes can be porous or dense. Anisotropic (or asymmetric) membranes, on the other hand, consist of a number of layers each with different structures and permeabilities. A typical anisotropic membrane has a relatively dense, thin surface layer supported on an open, much thicker micro-porous substrate. The surface layer performs the separation and is the principal barrier to flow through the membrane. The open support layer provides mechanical strength. Ceramic and metal membranes can be either isotropic or anisotropic. 

Wijers, M.C., Jin, M., Wessling, M. and Strathmann, H. (1998) Supported liquid membranes modification with sulfonated poly(ether ether ketone) - permeability selectivity and stability Journal of Membrane Science, 147, 117. 

Ramakul, P., Prapasawad.T., Pancharoen, U. and Pattaveekongka, W. (2007) Separation of radioactive metal ions by hollow fiber-supported liquid membrane and permeability analysis. Journal of the Chinese Institute of Chemical Engineers, 38, 489. 

Yang, X.J., Fane, A.G. and Soldenhoff, K. (2003) Comparison of liquid membrane processes for metal separations Permeability, stability, and selectivity. Industrialsl Engineering Chemistry Research, 42, 392. 

Oxygenation of water or water suspension such as blood can be done by (1) blowing oxygen gas into the liquid via a porous membrane and (2) bubbleless oxygenation via a gas-permeable (nonporous) membrane. Both the methods have... 

Miscible Liquid Behavior. Further concerning osmotic behavior, there is the behavior of, say, two miscible liquids, or miscible liquid components, but with each separated from the other by a semipermeable membrane, more permeable to one liquid than the other. Movement of the more permeable liquid phase to the less permeable liquid phase will occur, building up a pressure difference. However, there will likely be membrane leakage from the latter phase to the former, in the reverse direction, eventually producing the same equilibrium composition on both sides of the membrane. This brings up the relative permeation of two miscible liquids from a zone of composition on the one side of a membrane... 

The problem of the interactions between membrane and absorbent solution interests, for instance, the removal of CO2. Reactive absorption liquids, such as amines, that are used for this type of removal, usually wet polyolefin membranes. Wettability depends on the surface tension of the liquid, membrane material, contact angle, and pore properties of the membrane. Possible solutions to this problem are to employ more resistant membrane materials, to use different absorbent liquids, and to deposit a nonporous layer on the membrane surface that prevents any passage of the liquid through pores. In order to do not increase too much the resistance to the mass transport, the layer has to be thin and highly permeable to the gaseous species. The dense skin can be useful also for avoiding any possible contamination of the feed gas by the absorbent (Figure 38.4). 

In some disciplines, certain multiple emulsions have been termed liquid membrane systems, as the liquid film which separates the other liquid phases acts as a thin semi-permeable film through which solute must diffuse moving from one phase to another. There are, therefore many potential practical applications of multiple emulsions. 

Y. Wang, Y. S. Thio, and F. M. Doyle, Formation of Semi-permeable Polyamide Skin Layers on the Surface of Supported Liquid Membranes, J. Membr. Sci., 147, 109-116 (1998). 

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