Liquid membrane system

In general, high selectivities can be obtained in liquid membrane systems. However, one disadvantage of this technique is that the enantiomer ratio in the permeate decreases rapidly when the feed stream is depleted in one enantiomer. Racemization of the feed would be an approach to tackle this problem or, alternatively, using a system containing the two opposite selectors, so that the feed stream remains virtually racemic [21]. Another potential drawback of supported enantioselective liquid membranes is the application on an industrial scale. Often a complex multistage process is required in order to achieve the desired purity of the product. This leads to a relatively complicated flow scheme and expensive process equipment for large-scale separations. 

As the main disadvantage of liquid membrane systems is the instability over a longer period of time, another approach would be to perform separation through a solid membrane [22]. Enantioselective polymer membranes typically consist of a nonse-lective porous support coated with a thin layer of an enantioselective polymer. This... 

In this chapter, novel oscillations observed with liquid membrane systems by the present authors [22-25] will be introduced, and the mechanisms for the oscillation are clarified by using VITIES, taking into consideration ion transfer reactions and adsorptions at two aqueous-membrane interfaces. The mechanism of the spontaneous potential oscillation in a liquid membrane system proposed by Yoshikawa et al. is also discussed briefly. 

Curve 1 in Fig. 5 gives an example of the oscillation of membrane current observed with the liquid membrane system as in Eq. (3) by applying a constant AFwi-w2 of —0.48 V and measuring the time course of the current through the LM, /wi-w2- The cell used was the same as that used for the measurement of the potential oscillation, except a tetraphenyl-arsonium ion selective electrode [26,27], TPhAsE, was employed as a reference electrode in LM of NB ... 

Typically, transport experiments have been performed using a U-tube apparatus in which a solvent such as chloroform, containing the macrocyc-lic carrier, is placed in the tube so that it separates two aqueous phases the source phase containing the metal ion(s) to be transported and the receiving phase into which the transported ions are deposited. A diagrammatic representation of a liquid membrane system is shown in Figure 9.4. 

Efficient extraction of proteins has been reported with reverse micellar liquid membrane systems, where the pores of the membrane are filled with the reverse micellar phase and the enzyme is extracted from the aqueous phase on one side of membrane while the back extraction into a second aqueous phase takes place at the other side. By this, both the forward and back extractions can be performed using one membrane module [132,208]. Armstrong and Li [209] confirmed the general trends observed in phase transfer using a glass diffusion cell with a reverse micellar liquid membrane. Electrostatic interactions and surfactant concentration affected the protein transfer into the organic membrane and... 

In order to develop the liquid membrane techniques, i.e., emulsion Hquid membrane (ELM), supported liquid membrane (SLM), non-dispersive extraction in hollow fiber membrane (HFM), etc., for practical processes, it is necessary to generate data on equilibrium and kinetics of reactive extraction. Furthermore, a prior demonstration of the phenomena of facilitated transport in a simple liquid membrane system, the so-called bulk liquid membrane (BLM), is thought to be effective. Since discovery by Li [28], the liquid membrane technique has been extensively studied for the separation of metal ion, amino acid, and carboxyHc acid, etc., from dilute aqueous solutions [29]. 

The emulsion liquid membrane for cephalosporins relies essentially on facilitated transport. There are basically, however, two types of facilitated transport in emulsion liquid membrane system, i. e.. Type I and Type II facilitation. In the first type, the concentration gradient of the membrane soluble solute/permeate... 

Fig. 6. Ty pical concentration profile in a supported liquid membrane system...

Two principal approaches for the demulsification of the loaded emulsion are chemical and physical treatments. Chemical treatment involves the addition of a demulsifier to the emulsion. This method seems to be very effective. However, the added demulsifier will change the properties of the membrane phase and thus inhibits its reuse. In addition, the recovery of the demulsifier by distillation is rather expensive. Therefore, chemical treatment is usually not suitable for breaking emulsion liquid membrane, although few examples of chemical demulsification have been reported for certain liquid membrane systems [88]. 

Since the first uphill (active) transport membrane sensor was proposed in 1986/ this method has already been demonstrated for several liquid membrane systems " by exploiting synthetic molecules, such as methyltrioctylammonium chloride (92 dicyclohexyl-18-crown-6 (93 K" ), and dibenzoyl-... 

Cd in natural water using a liquid membrane system with 2-acetylpyr-idine benzoylhydrazone as carrier. Transport processes across the membrane were optimised... 

A permeation liquid membrane system Seawater GFAAS, Modified ... 

M. D. Granado-Castro, M. D. Galindo-Riano and M. Garcia-Vargas, Separation and preconcentration of cadmium ions in natural water using a liquid membrane system with 2-acetylpyridine benzoylhydrazone as carrier by flame atomic absorption spectrometry, Spectrochim. Acta, Part B, 59(4), 2004, 577-583. 

A. Aouarram, M. D. Galindo-Riano, M. Garcia-Vargas, M. Stitou and F. El YoLisli, A permeation liquid membrane system for determination of nickel in seawater, Talanta, H, 2007, 165-170. 

PEI derivatives have proven to be effective carriers of cations in liquid membrane systems (404). This technology led to the development of ion-exchange resins (405), which are also suitable for extracting uranium from seawater (406). 

The study of the ion transfer through artificial liquid membrane systems is important for the elucidation of the ion transfer through biological membranes. In this respect, the Interface between two inmiscible electrolyte solutions (ITIES) constitutes a biomimetic medium suitable for studying several fundamental processes, ranging from biocatalysis to cellular respiration of photosynthesis, and many others [18-22], The first studies of liquid/liquid interfaces (L/L) under the application of an external potential were carried out by Gavach et al. [23], laying the basis for the current electrochemical treatments of ITIES. 

Keller, O.C., Poitry, S. and BufHe, J. (1994) A hollow fibre supported liquid membrane system for metal speciation and preconcentration calculation of the response time. J. Electroanal. Chem., 378, 165-175. 

Yang, Q. and Kocherginsky, N.M. (2007) Copper removal from ammoniacal wastewater through a hollow fiber supported liquid membrane system Modeling and experimental verification. Journal of Membrane Science, 297, 121. 

Yang, Q. and Chung, T.S. (2007) Modification of the commerdal carrier in supported liquid membrane system to enhance lactic add flux and to separate L, D-lactic acid enantiomers. Journal of Membrane Science, 294, 127. 

In emulsion or liquid membrane systems, the volume ratio approaches one of the limiting values r -> 0 and r - 00, and the distribution potential becomes independent of r [vii]. 

Similarly to the induction or the inhibition of the current oscillation at a biomembrane with a sodium channel , the current oscillation observed with the liquid membrane system of Equation (37) without any channel proteins can be induced by acetylcholine ion, Ach" ", or inhibited by such rather hydrophobic ions as alkylammonium ions and glutamate. 

Much effort has been expended in attempting to use membranes for separations. Reverse osmosis membranes are used worldwide for water purification. These membranes are based on size selectivity depending on the pores used. They do not have the ability to selectively separate target species other than by size. Incorporation of carrier molecules into liquid membrane systems of various types has resulted in achievement of highly selective separations on a laboratory scale. Reviews of the extensive literature on the use of liquid membrane systems for carrier-mediated ion separations have been published [15-20]. A variety of liquid membranes has been studied including bulk (BLM), emulsion (ELM), thin sheet supported (TSSLM), hollow fiber supported (HFSLM), and two module hollow fiber supported (TMHFSLM) types. Of these liquid membranes, only the ELM and TMHFSLM types are likely to be commercialized. Inadequacies of the remaining... 

Design of cation selectivity of crown ethers as carriers in liquid membrane systems 86PAC1453. 

General properties of liquid membrane systems have been a subject of extensive theoretical studies. Six basic mechanisms of transport are schematically shown in Figure 13.2. In a simple transport (Figure 13.2a), solute passes through due to its solubihty... 

According to the scheme of the compartments in the liquid membrane system in Figure 13.5b, all local diffusion fluxes of M species from ktok+1 compartment can be defined by a phenomenological Equation 13.41 corresponding with the first Pick s law for diffusion ... 

The Madonna Berkeley (ver.3) solver of ODE, the set of parameters, and initial conditions describing a liquid membrane system (listed in Table 13.2) were applied to numerically investigate the properties of CPS. The main relations resulting from the computations were time-dependent values of (1) the concentration profiles of transported and antiported species in a liquid... 

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