Liquid emulsion membrane system

Gadekar PT, Mukkolath AV, and Tiwari KK. Recovery of nitrophenols from aqueous solutions by a liquid emulsion membrane system. Sep Sci Technol 1992 27 427 55. 

Mok YS, Lee SC, and Lee WK. Water transport in water-in-oil-in-water liquid emulsion membrane system for the separation of lactic acid. Sep Sci Techrwl 1994 29 743-764. 

Nilsen DN, Hundley GL, Galvan GJ, and Wright JB. Field testing of a liquid-emulsion membrane system for copper recovery from mine solutions. In Bartsch RA, Way JD, eds. Chemical separations with liquid membranes, Washington, DC American Chemical Society, ACS symposium series 642, 1996 329-341. 

Field Testing of a Liquid-Emulsion Membrane System for Copper Recovery from Mine Solutions... 

Table 31.3 gives a few typical examples on recovery of actinides by ELM. Myriad literature reports exist on the use of HDEHP for metal extraction involve ELMs. Comparative studies between column and batch liquid emulsion membrane techniques based on HDEHP/HCl system were carried out to develop a system for the isolation of Th from natural uranium, which showed that, kineticaUy, the equilibrium for thorium separation using batch technique is faster than the continuous column system [37]. The effective separation of Th from natural uranium was found to be independent of time. El-Sherif studied... 

El-Reefy, S.A., El-Sherif, E.A., and Aly, H.F., Recovery of Th from natural uranium using liquid emulsion membrane based on HDEHP-HCl system. J. Radioanal. Nucl. Chem., 1996, 207 129-136. 

Applications of liquid emulsion membranes (LEMs) to biomedical and biochemical systems are reviewed and other potential applications identified. The LEM-mediated downstream processing of small, zwitterionic biochemicals (e.g. amino acids) is examined using chloride ion counter-transport to separate and concentrate the amino acid phenylalanine from stimulated fermentation broth. The effect of agitation rate and osmotic swelling of membranes on separation is shown to be significant. 

LEM systems have also been shown to be successful in separating commodity-type biochemicals such as propionic acid (10) and acetic acid (10,22) and have been used for the preparation of L-amino acids from racemic D,L mixtures by means of enzymatic hydrolysis of amino acid esters (23). In addition to biochemical separations, the work of Mohan and Li showed that enzymes could be encapsulated in liquid emulsion membranes with no deleterious effect on enzyme action (24). Later work by these authors indicated that encapsulated live cells could remain viable and function in the LEM interior phase for period as long as five days (25). 

The versatility of LEMs is clear. From the encapsulation of living cells to the removal of toxic or inhibiting substances, and in their use as a downstream process, liquid emulsion membranes remain a powerful and, as of yet, virtually untapped resource for biochemical engineers. The ability of LEMs to separate and concentrate amino acids demonstrated here gives strength to this observation, and it is anticipated that these systems will enjoy increasing attention in the years to come. 

Figure 9.41 Variation of copper concentration in the raffinate during extraction with a liquid emulsion-membrane complexing agent system.43...

In the early 1970s Li [13] proposed a method that is now called Emulsion (surfactant) Liquid Membrane (ELM) or Double Emulsion Membrane (DEM) (Fig. 3). The name reveals that the three liquid system is stabilized by an emulsifier, the amount of which reaches as much as 5 % or more with respect to the membrane liquid. The receiving phase R, which usually has a smaller volume than the donor solution, F of similar nature, is finally dispersed in the intermediate phase, M. In the next step the donor solution F is contacted with the emulsion. For this purpose, the emulsion is dispersed in the donor solution F by gentle mixing typically in a mixer-settler device. After this step, the emulsion is separated and broken. The enriched acceptor solution is further processed and the membrane liquid M is fed back for reuse. 

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... 

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]. 

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]. 

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... 

Use of Emulsion Liquid Membrane Systems in Chemical and Biotechnological Separations... 

The concept of emulsion liquid membranes (ELM) was first proposed by Li in 1968 [1]. Since their inception in the late 1960s they have been referred to as surfactant liquid membranes, double emulsion membranes or ELM. Regardless of the terminology used, the workings of such systems are as follows they consist of an emulsion formed by an organic solvent and water, which can be stabilized by the addition of surfactant. This emulsion is then contacted with a continuous phase containing the desired solute, stirred to yield globules, and transported across the extremely thin membrane layer that separates internal phase droplets... 

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