Liquid membrane system configurations

Figure i.i Three configurations of liquid membrane systems hulk (BLM), supported (immobilized) (SLM or ILM), and emulsion (ELM). F is the source or feed phase, E is the liquid membrane, and R is the receiving phase. 

Selectivity parameters, needed for the BOHLM or BAHLM module design and their determination techniques, are analyzed. Selectivity can be controlled by adjusting the concentration, volume, and flow rate of the LM phase. Such control of the selectivity is one of the advantages of the bulk liquid membrane systems in comparison with other liquid membranes configurations and Donnan dialysis techniques. The idea of dynamic selectivity and determination techniques are presented and discussed. 

Chapter 8, written by R. Tandhch, presents the field of wastewater treatment considering BLM, ELM, and SLM configurations of liquid membrane systems. 

Ultra-thin liquid membranes can be fabricated down to 1 pL in thickness. Ultra-thin liquid membranes can be formed in the skin layer of an porous asymmetric polymer membrane by methods in which the liquid is selectively deposited in the skin rather than the backing support. The wide variety of pore sizes and membrane configurations available in asymmetric membranes allows for good flexibility in the design of ultra-thin liquid membrane systems. 

Kandwal, P., Ansari, S.A., Mohapatra, P.K., A highly efficient supported liquid membrane system for near quantitative recovery of radio-strontium from acidic feeds. Part II Scale up and mass transfer modeling in hollow fiber configuration, J. Membr. Sci. 405 06, 85, 2012. 

Microporous membrane liquid-liquid extraction (MMLLE) is a two-phase extraction setup. In MMLLE procedures, the membrane material and format (FS and HF), extraction units, and system configurations are identical to those described in SLM (Section 4.4.1.2).63 The two-phase HF-MMLLE system is identical to that used in Section 4.4.3, although sometimes with minor differences. In contrast to three-phase SLM extraction, MMLLE employs a microporous membrane as a miniaturized barrier between two different phases (aqueous and organic). One of the phases is organic, filling both the membrane pores (thus making the membrane nonporous) and the compartment on one side of the membrane (acceptor side). The other phase is the aqueous sample on the other side of the membrane (donor side). In this way, the two-phase MMLLE system is highly suited to the extraction of hydrophobic compounds (log Ko/w > 4) and can thus be considered a technique complimentary to SLM in which polar analytes (2 < log Ko/w < 4) can be extracted. 

A liquid membrane configuration, which is much used for technical applications, is the emulsion liquid membrane (ELM) systems where the acceptor phase is dispersed as a colloid phase, each colloid drop surrounded by a thin organic, surface active phase. This principle does not seem to have been used for analytical sample preparation, probably due to the difficulty of quantitatively recovering the disperse acceptor phase. 

The rising need for new separation processes for the biotechnology industry and the increasing attention towards development of new industrial eruyme processes demonstrate a potential for the use of liquid membranes (LMs). This technique is particularly appropriate for multiple enzyme / cofactor systems since any number of enzymes as well as other molecules can be coencapsulated. This paper focuses on the application of LMs for enzyme encapsulation. The formulation and properties of LMs are first introduced for those unfamiliar with the technique. Special attention is paid to carrier-facilitated transport of amino acids in LMs, since this is a central feature involved in the operation of many LM encapsulated enzyme bioreactor systems. Current work in this laboratory with a tyrosinase/ ascorbate system for isolation of reactive intermediate oxidation products related to L-DOPA is discussed. A brief review of previous LM enzyme systems and reactor configurations is included for reference. 

A new type of configuration, the flowing liquid membrane (FLM) was studied by Teramoto et al. [20]. In this case, the membrane liquid phase is in motion as the feed and strip phase. In this type of system a plate-and-frame and spiral-wound configuration with flat membrane was used. The scheme of the FLM configuration is drawn in Fig. 7.3A. The hquid phase flows (FLM) between two hydrophobic microporous membranes. The two membranes separate the hquid membrane phase from feed and strip phases. In Fig. 7.3B, it is reported the classical plate-and-frame module employed for the separation of ethylene from ethane [20]. The liquid membrane convection increased the membrane transport coefficient in gas separation. However, the membrane surface packing density (membrane surface area/ equipment volume) is much lower in spiral-wound system than in hollow fiber. 

To the best of my knowledge, Xenakis and Tondre [12] were the first to use the term microemulsion liquid membrane with reference to a system using an oil-in-water microemulsion to separate oil-soluble components in a U-tube configuration. In a closely related publication [13], the same authors showed the generality of the idea by reversing the transport, using water-in-oil microemulsions to separate and to concentrate water-soluble solutes. 

Indeed, one matter of concern in the development of new polymer ionic membranes lies in the fact that their high conductivity is often associated with amorphous, low-viscosity phases. Therefore, in their conductive form, these membranes behave like soft solids with poor mechanical stability their direct use in LPBs may give rise to those problems commonly met in conventional liquid electrolyte systems, such as leakage, loss of interfacial contacts and short circuits. Under these circumstances, one of the most useful feature of LPBs, namely the solid-state configuration, would then be lost. Consequently, it is of key importance to assure that the polymer electrolyte membrane maintains good mechanical properties even in its conductive state. 

Un, Koparal, and Ogiitveren (2007a) developed a membrane reactor (depicted in Figure 14.5) with a unique design and electrode configuration for gas—liquid reaction systems for the direct electro-oxidation of SO2 to H2SO4. In this reactor, dissolved SO2 is oxidized at a platinum expanded mesh anode with a counter electrode made of titanium. This inner-cell process uses a cylindrical electrochemical reactor with a reported high removal efficiency >93%. 

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