Types supported liquid membranes

Teramoto M et al. Development of spiral-type supported liquid membrane module for separation and concentration of metal ions. Sep Sci Technol, 1987 22(11) 2175-2201. 

Takeuchi, H., Takahashi, K., Nakano, M. (1990). Separation of heavy metals from aqueous solutions by hoUow-fiber type supported liquid membranes in a continuous regenerating mode. Water Treatment, 5, 222-36. 

FIG U R E 2 7.9 Schematic diagram of a spiral-type supported liquid membrane (SLM) module 1, microporous hydrophobic membrane (support) 2, mesh spacer 3, inlet pipe of feed solution 4, inlet pipe of receiver solution 5, inlet tube of organic membrane solution 6, feed solution 7, organic membrane solution and 8, receiver solution. (Reprinted from Teramoto, M. et al., Sep. Sci. TechnoL, 24, 981-999,1989. With permission from Taylor Francis Ltd.)... 

Fig. 5-2. Three types of the liquid membrane eonfiguration (a) emulsion liquid membrane (b) supported liquid membrane (e) elassieal bulk liquid membrane set-up.

In supported liquid membranes, a chiral liquid is immobilized in the pores of a membrane by capillary and interfacial tension forces. The immobilized film can keep apart two miscible liquids that do not wet the porous membrane. Vaidya et al. [10] reported the effects of membrane type (structure and wettability) on the stability of solvents in the pores of the membrane. Examples of chiral separation by a supported liquid membrane are extraction of chiral ammonium cations by a supported (micro-porous polypropylene film) membrane [11] and the enantiomeric separation of propranolol (2) and bupranolol (3) by a nitrate membrane with a A/ -hexadecyl-L-hydroxy proline carrier [12]. 

Liquid Membranes Several types of liquid membranes exist molten salt, emulsion, immobilized/supported, and hollow-fiber-contained liquid membranes. Araki and Tsukube (Liquid Membranes Chemical Applications, CRC Press, 1990) and Sec. IX and Chap. 42 in Ho and Sirkar (eds.) (op. cit., pp. 724, 764-808) contain detailed information and extensive bibliographies. 

As discussed by Frankemfeld and Li(28) and del Cerro and Boey(29), liquid membrane extraction 28,29) involves the transport of solutes across thin layers of liquid interposed between two otherwise miscible liquid phases. There are two types of liquid membranes, emulsion liquid membranes (ELM) and supported liquid membranes (SLM). They are conceptually similar, but substantially different in their engineering. 

For the sake of discussion, we have divided the separators into six types—microporous films, non-wovens, ion exchange membranes, supported liquid membranes, solid polymer electrolytes, and solid ion conductors. A brief description of each type of separator and their application in batteries are discussed below. 

These types of separators consist of a solid matrix and a liquid phase, which is retained in the microporous structure by capillary forces. To be effective for batteries, the liquid in the microporous separator, which generally contains an organic phase, must be insoluble in the electrolyte, chemically stable, and still provide adequate ionic conductivity. Several types of polymers, such as polypropylene, polysulfone, poly(tetrafluoroethylene), and cellulose acetate, have been used for porous substrates for supported-liquid membranes. The PVdF coated polyolefin-based microporous membranes used in gel—polymer lithium-ion battery fall into this category. Gel polymer... 

In the supported liquid membrane process, the liquid membrane phase impregnates a microporous solid support placed between the two bulk phases (Figure 15.1c). The liquid membrane is stabilized by capillary forces making unnecessary the addition of stabilizers to the membrane phase. Two types of support configurations are used hollow fiber or flat sheet membrane modules. These two types of liquid membrane configuration will be discussed in the following sections. 

Figure 20.2 Different types of membrane contactors, (a) stripper/ scrubber, driving force difference of concentration (b) liquid-liquid extractors, driving force difference of concentration (c) removal of volatiles/gases from liquids, driving force difference of partial pressures (d) direct contact membrane distillation, driving force difference of partial pressures (e) supported liquid membranes, driving force difference of concentrations.

Separations in two-phase systems with one immobilized interface(s) are much newer. The first paper on membrane-based solvent extraction (MBSE) published Kim [4] in 1984. However, the inventions of new methods of contacting two and three liquid phases and new types of liquid membranes have led to a significant progress in the last forty years. Separations in systems with immobilized interfaces have begun to be employed in industry. New separation processes in two- and three-phase systems with one or two immobilized L/L interfaces realized with the help of microporous hydrophobic wall(s) (support) are alternatives to classical L/L extraction and are schematically shown in Figure 23.1. Membrane-based solvent extraction (MBSE) in a two-phase system with one immobilized interface feed/solvent at the mouth of microspores of hydrophobic support is depicted in Figure 23.1a and will be discussed... 

Supported liquid membranes were one of the first types of liquid membranes published in 1967 [1, 2]. There are several types of SLM, which have an origin in three basic approaches ... 

Dense inorganic or metallic membranes for gas separation are usually ion-conducting materials, while membranes with carriers are polymers or supported liquid membranes (SLM). For transport through these materials, different flux equations should be applied. Figure 4.2 sums up and generalizes the various types of transport, which may take place in gas-separation membranes [21]. 

Nonporous membrane techniques involve two or three phases separated by distinct phase boundaries. In three-phase membrane systems, a separate membrane phase is surrounded by two different liquid phases (donor and acceptor) forming a system with two phase-boundaries and thus two different extraction (partition) steps. These can be tailored to different types of chemical reactions, leading to a high degree of selectivity. The membrane phase can be a liquid, a polymer, or a gas, and the donor and acceptor phases can be either gas or hquid (aqueous or organic). Liquid membrane phases are often arranged in the pores of a porous hydrophobic membrane support material, which leads to a convenient experimental system, termed supported liquid membrane (SLM). There are several other ways to arrange a hquid membrane phase between two aqueous phases as described below. 

Teramoto M, Matsuyama H, Nakai K, Uesaka T, and Ohnishi N. Eacilitated uphill transport of eicosapentaenoic acid ethyl ester through bulk and supported liquid membranes containing silver nitrate as carrier A new type of uphill transport. J Mem Sci, 1994 91(1-2) 209-213. Teramoto M, Matsuyama H, and Ohnishi N. Selective facilitated transport of benzene across supported and flowing liquid membranes containing silver nitrate as a carrier. J Mem Sci, 1990 50 269-278. 

However, ELMs are quite difficult to prepare and after transport, the oil droplets have to be separated and broken up to recover the receiving phase. Compared to the ELM, the BLMs are easier to operate. The supported liquid membranes (SLM) are categorized into two types of supports, namely, a flat-sheet supported liquid membrane (FSSLM) or a hollow fiber supported liquid membrane (HFSLM). Here a polymeric filter with its pores filled with the organic phase acts as membrane. The three different types of liquid membranes have already been schematically represented in Chapter 29. A schematic representation of a hollow fiber semp is shown in Figure 31.2. 

Supported liquid membranes comprised the bulk of the published literature on the transport studies of metal ions across thin polymeric films [16,56-59]. Several literature reports on actinide transport across supported liquid membranes using various types of extractants viz., acidic extractants, neutral extractants and amine extractants are discussed below. 

Shukla, J.P., Kumar, A., and Singh, R.K., Effect of solvent type on neutral macrocycle facilitated transport of uranyl ions across supported liquid membranes using dicyclohexano 18-crown-6 as carrier. Radiochim. Acta, 1992, 57 185-194. 

In the biomedical applications outlined by Ward et al. (7 ), more so than in any other separation application of synthetic polymeric membranes, the goal is to mimic natural membranes. Similarly, the development of liquid membranes and biofunctional membranes represent attempts by man to imitate nature. Liquid membranes were first proposed for liquid separation applications by Li (46-48). These liquid membranes were comprised of a thin liquid film stabilized by a surfactant in an emulsion-type mixture. Wtille these membranes never attained widespread commercial success, the concept did lead to immobilized or supported liquid membranes. In... 

Table 3.4 Stability of the supported liquid membranes as a function of the kind of counterion and of the type of organic solvent...

Liquid membranes can be of three types—bulk liquid membrane, immobilized on a solid supported hquid membrane, and liquid membrane as double emulsions. Of these three types, ELMs can achieve much higher mass transfer area than the other two membranes. ELMs were first used by Li [1] for separation of hydrocarbons. Since then, considerable work has been done to demonstrate qualitatively the feasibihty of performing separations with specific formulations. 

Table 7.3 shows a classification of the liquid membranes on the basis of the configuration and module types employed in gas separation. The liquid membranes can be divided in three main classes (i) supported liquid membrane (SLM), (ii) bulk liquid membrane (BLM), and (iii) supported ionic liquid membrane (SILM). 

Promising results are shown by recently developed integrated SLM-ELM [84, 85] systems. These techniques are known as supported liquid membrane with strip dispersion (SLMSD), pseudo-emulsion-based hollow fiber strip dispersion (PEHFSD), emulsion pertraction technology (EPP), and strip dispersion hybrid Hquid membrane (SDHLM). AH techniques are the same the organic phase (carrier, dissolved in diluent) and back extraction aqueous phase are emulsified before injection into the module and can be separated at the module outlet. The difference is only in the type of the SLM contactors hoUow fiber or flat sheet and in the Hquid membrane (carrier) composition. These techniques have been successfuUy demonstrated for the removal and recovery of metals from wastewaters. Nevertheless, the techniques stiU need to be tested in specific apphcations to evaluate the suitabUity of the technology for commercial use. 

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