Supported liquid membranes applications

F igure 8.3. Schematic representation of a hollow fiber contactor set up used for supported liquid membrane applications. Flow directions in a hollow fiber module (a), single fiber (b), and hollow fiber set up for simultaneous extraction and stripping. (Reproduced with permission from Ansari etal, 2011a). 

As described above, the application of classical liquid- liquid extractions often results in extreme flow ratios. To avoid this, a completely symmetrical system has been developed at Akzo Nobel in the early 1990s [64, 65]. In this system, a supported liquid-membrane separates two miscible chiral liquids containing opposite chiral selectors (Fig. 5-13). When the two liquids flow countercurrently, any desired degree of separation can be achieved. As a result of the system being symmetrical, the racemic mixture to be separated must be added in the middle. Due to the fact that enantioselectivity usually is more pronounced in a nonaqueous environment, organic liquids are used as the chiral liquids and the membrane liquid is aqueous. In this case the chiral selector molecules are lipophilic in order to avoid transport across the liquid membrane. 

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. 

Other applications of supported liquid membranes have been related to metal speciation. For example, recently a system for chromium speciation has been developed based on the selective extraction and enrichment of anionic Cr(VI) and cationic Cr(III) species in two SLM units connected in series. Aliquat 336 and DEHPA were used respectively as carriers for the two species and graphite furnace atomic absorption spectrometry used for final metal determination. With this process, it was possible to determine chromium in its different oxidation states [103]. 

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. 

Chiarizia, R. Horwitz, E.P. Rickert, P.G. Hodgson, K.M. Application of supported liquid membranes for removal of uranium from groundwater, Sep. Sci. Technol. 25 (1990) 1571-1586. 

Until quite recently, most of me facilitated transport results reported in me literature were obtained with supported liquid membranes held by capillarity in microporous films. The instability of these membranes has inhibited commercial application of me process. Three factors contribute to mis instability and me consequent loss of membrane performance over time ... 

Figure 1 Two-parameter examination of range of applicability of ion exchange and solvent extraction techniques with a semilogarithmic plot of metal concentration in g/L versus solution flowrate in m /hr. IX = ion SX = solvent extraction LSM = surfactant liquid membrane SSLM = solid supported liquid membrane [8].

Cukrowska E, Chimuka L, Nsengimana H, and Kwaramba V. Application of supported liquid membrane probe for extraction and preconcentration of organotin compounds from environmental water samples. Anal. Chim. Acta 2004 523 141-147. 

Chiarizia, R., Application of supported liquid membranes for removal of nitrate, technetium (VII) and chromium (VI) from ground-water. J. Membr. Sci., 1991, 55 39-64. 

An important number of references have been published dealing with many applications of supported liquid membranes. Mathematical modeling of the process has been developed and it can be generalized and applied to the determination of the response of different systems containing more than one solute. After evaluation of the parameters, process optimization can be applied using common optimization procedures, as described in the text. 

One of the first applications of TSOSs was reported in 2002. Davis and his team have shown that an amine-derived imidazolium salt can capture carbon dioxide by forming a ammonium carbamate [28], Primary amine functionalized imidazolium salts have also been used for facilitating C02 transport through a supported liquid membrane showing high selectivity and high stability for CH4/C02 separation [50] (Fig. 18). 

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... 

The porosity of the support refers to the percentage of the total volume which is void space. The porosity determines the total volume of the liquid membrane which can be immobilized in the pore volume. The volume of liquid membrane solvent and the carrier solubility determine the maximum amount of carrier which can be immobilized in the membrane. Increasing the amount of carrier in the membrane will increase the solute fluxes. The strength of the functional dependence of the solute flux on carrier concentration will depend on whether the facilitated transport system is reaction or diffusion limited. Consequently, a high porosity support is desirable for liquid membrane applications. 

Liquid impregnated (or immobilized) in the pores of a thin microporous sohd support is defined as a supported liquid membrane (SLM or ILM). The SLM may be fabricated in different geometries. Flat sheet SLM is useful for research, but the surface area to volume ratio is too low for industrial applications. Spiral-wound and hoUow-fiber SLMs have much higher surface areas of the LM modules (103 and 104 m /m, respectively [23]). The main problem of SLM technology is the stability the chemical stability of the carrier, the mechanical stability of porous support, etc. 

Parthasarathy N, Buffle J, Capabilities of supported liquid membrane for metal speciation in natural waters application to copper speciation. Anal. Chim. Acta 1994 284 649-659. 

Izatt KM, Bradshaw JS, Lamb JD, Bmening RL, Emulsion and Supported Liquid Membranes. In Araki T, Tsukube H, Eds., Liquid Membranes Chemical Applications. CRC Press, Boca Raton, FL, 1990 123-140. 

Supported Liquid Membranes AND Their Modifications Definition, Classification, Theory, Stability, Application AND Perspectives ... 

Supported liquid membrane stability and lifetime limit the industrial application of this separation technique. Therefore, the stability of these membranes needs to be enhanced drastically. A proper choice of the operating and membrane composition factors might improve the lifetime of SLM systems. 

Ashraf Chaudry, M., Ahmad, S., Malik, M. T. (1997). Supported liquid membrane technique applicability for removal of chromium from tannery wastes. IfOste Management 17 211-218... 

Valenzuela, F., Basualto, C., Tapia, C., Sapag, J. (1999). Application of hoUow-fiber supported liquid membranes technique to the selective recovery of a low content of copper from a Chilean mine water (Short communication). Journal of Membrane Science 155 163-168. 

---