Emulsion liquid membranes using hollow

This paper reviews the use of emulsions and microemulsions as liquid membranes with sp ial emphasis placed on the separation of mercury, as Hg(N03)2, from water using oleic acid as the extractant Although emulsion (either macro- or micro-) liquid membranes offer advantages in terms of fast rates of separation, new modes of creating a stabilized liquid membrane utilizing hollow fiber contactors offer comparable flux in a more stable format. The paper wiU start with a review of the basic types of liquid membranes as currently used in research. The discussion will then focus on the author s experience with emulsified liquid membrane systems. The last section of the paper will discuss the obvious next step in liquid membrane technology, the use of emulsion liquid membranes in hollow fiber contactors. 

In this paper an overview of the developments in liquid membrane extraction of cephalosporin antibiotics has been presented. The principle of reactive extraction via the so-called liquid-liquid ion exchange extraction mechanism can be exploited to develop liquid membrane processes for extraction of cephalosporin antibiotics. The mathematical models that have been used to simulate experimental data have been discussed. Emulsion liquid membrane and supported liquid membrane could provide high extraction flux for cephalosporins, but stability problems need to be fully resolved for process application. Non-dispersive extraction in hollow fib er membrane is likely to offer an attractive alternative in this respect. The applicability of the liquid membrane process has been discussed from process engineering and design considerations. 

Hu, S.Y.B. and Wiencek, J.M. (1998) Emulsion-liquid-membrane extraction of copper using a hollow-fiber contactor. AICHE Journal, 44, 570. 

Raghuraman, B. and Wiencek, J.M., Extraction with emulsion liquid membranes in a hollow-fiber contactor, AIChE J., 39, 1885, 1993. 20a. Hu, S.Y. and Wiencek, J.M., Emulsion-liquid-membrane extraction of copper using a hollow-fiber contactor, AIChE J., 44, 570, 1998. 20b. Wiencek, J.M. and Hu, S.Y., Emulsion liquid membrane extraction in a hollow-fiber contactor, Chem. Eng. TechnoL, 23, 551, 2000. 

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 Section 5.4.4, we studied a variety of chemical reaction facilitated separation where the reaction was taking place in a thin liquid layer acting as the liquid membrane Figure 5.4.4 illustrated a variety of liquid membrane permeation mechnisms. Here we will identify first the structural configuration of the liquid membranes as they are used in separators with countercurrent flow pattern (as well as for the cocurrent flow pattern). There are three general classes of liquid membrane structures emulsion liquid membrane (ELM) supported liquid membrane (SLM) or immobilized liquid membrane (ILM) hollow fiber contained liquid membrane (HFCLM). Each will be described very briefly. 

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... 

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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