Flat-sheet supported liquid membrane

Dozol, J.-F., Casas, J., Sastre, A. M., Transport of cesium from reprocessing concentrate solutions through flat-sheet-supported liquid membranes Influence of the extractant, Sep. Sci. Technol, 30, 435-448,1995. 

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. 

Breembroek G.R.M., Witkamp G.J., and Van Rosmalen G.M., Extraction of cadmium with trilaurylamine-kerosine through a flat-sheet-supported liquid membrane. J. Membr. Sci. 146, 195, 1998. 

Table 3.1 Characteristic of some commercially available membranes used as a polymeric support in flat-sheet supported liquid membranes (FS-SLM)... 

Deblay, P., Delepine, S., Minier, M., Renon, H. (1991). Selection of organic phases for optimal stability and efficiency of flat-sheet supported liquid membranes. Sep. Sci. Technol., 26, 97-116. 

FSSLM Flat-sheet supported liquid membrane... 

In another study, the reduction of chromium(VI) to chromium(III) state by hydrazine sulfate in the stripping process of chromium(VI)-loaded organic solutions had received attention. Various SLM technologies were employed, such as flat-sheet-supported liquid membranes, NDSX, and PEHFSD, and in all the aforementioned investigations, the phosphine oxide Cyanex 923 was used as the carrier [25-27]. 

Altin S, Yildirim Y and Altin A (2010), Transport of silver ions through a flat-sheet supported liquid membrane , Hydrometallurgy, 103,144-149. 

Extensive studies including both inner-sphere and outer-sphere complexation of cations were performed with lasa-locid A, which is a small natural ionophore containing a salicylic acid fragment (Figure 1). The ability of lasalocid to form neutral outer-sphere complexes with species like Co(NH3)(5 +, Cr(bpy)3 ", Pt(bpy)(NH3)2 " " allows one to use it as an ionophore for the membrane transport (including chiroselective transport) of such species. The lasalocid ionophore also was shown to be an efficient carrier for toxic water-soluble metal cations such as Pb + and Cd + across artificial flat-sheet-supported liquid membranes, which represent a potential system for separation of these cations. 

Figure 1. Schematic Representation of Different Liquid Membrane Configurations (a) Bulk Liquid Membrane, (b) emulsion liquid membrane, (c) flat-sheet supported liquid membrane, (d) hollow fiber supported liquid membrane.

Figure 3. Representation of the Transport Cell and a Flat Sheet Supported Liquid Membrane.

Through Flat Sheet Supported Liquid Membranes ... 

Transport Measurements. The same Flat-Sheet Supported Liquid Membrane (SLMs) device described by T. Stolwijk et al. (18) and shown in Figure 7 was used for the transport experiments. The volume of both aqueous solutions (feed and stripping) ranged from 45 to 55 mL depending on the glass devices manufactured by Prodilab and Verre Science Companies. The circular membranes were about 15 to 16 cm in area and made of polypropylene Celgard 2500 microporous support (of 25 mm thickness... 

Bhattacharyya, A. et al., Liquid-liquid extraction and flat sheet supported hquid membrane studies on Am(III) and Eu(III) separation using 2,6-bis(5,6-dipropyl-l,2,4-triazin-3-yl)pyridine as the extractant, J. Hazard. Mater. 195, 238, 2011. 

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. 

Di Luccio M, Smith BD, Kida T, Alves TLM, and Borges CP. Evaluation of flat sheet and hollow fiber supported liquid membranes for fructose pertraction from a mixture of sugars. Desalination, 2002 148(1-3) 213-220. 

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. 

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. 

Supported liquid membranes offer excellent selectivity for use in gas separation. The transport of CO2 through an aqueous diethanolamine solution held within a hollow fibre membrane is modelled in this paper. When compared with flat-sheet models, the results demonstrated that radial geometry has to be taken into account in a hollow fibre model. The model was used to simulate the CO2 separation in membrane contactors and the results were compared with experimental data. The discrepancy between the results and the experimental data is thought to be due to the conditions within the membrane contactors, which are far from ideal. 

A simple model for predicting the flux of CO2 through hollow fibre supported liquid membranes has been presented. It has been shown that radial geometry must be considered in order to accurately simulate the flux of the gas through the walls of a hollow fibre and that a flat sheet model is not able to capture this. However, because of... 

Different extraction techniques have been developed. These techniques have been classified as porous and nonporous, based on their structure, as a flat (like a paper sheet with less than 1 pm of thickness) or hollow fiber (200-500 pm i.d.) configuration. Other classification refers to the number of phases involved in the extraction (one-, two-, or three-phase extraction techniques) [186]. A distinction can be based on the nature of the acceptor phase liquid membrane extractions, where the acceptor phase is a liquid, such as supported liquid membrane (SLM) extraction, microporous membrane liquid-liquid... 

Supported Liquid Membranes. A SLM can be fabricated in at least three different geometries. Planar or flat sheet SLMs are very useful for laboratory research and development purposes, but the surface area to volume ratio of flat sheets is too low for industrial applications. Spiral wound and hollow fiber geometries can... 

Supported liquid membrane extraction techniques employ either two or three phases, with simultaneous forward- and back-extraction in the latter configuration. The aqueous sample phase is separated from the bulk organic or an aqueous receiver phase by a porous polymer membrane, in the form of either a flat sheet or a hollow fiber that has been impregnated with the organic solvent phase. The sample phase is continuously pumped, the receiver phase may be stagnant or pumped, and the organic phase in the membrane pores is stagnant and reusable [8-10]. 

Classically, flat-sheet porous PTFE or polypropylene membranes are used as support for the membrane liquid and mounted in holders (cells, contactors) permitting one flow channel on each side of the membrane [1,3,6,8,25]. See Figure 12.1. Such membrane units are typically operated in flow systems and in principle apphcable to aU versions of membrane extraction for analytical sample preparation or sampling. Such a setup can be easily interfaced with different analytical instmments, such as HPLC and various spectrometric instmments, and thereby provides good possibdities for automated operation. Drawbacks of this type of devices are relatively large costs and limited availability, as well as some carryover and memory problems as the membrane units are utilized many times, necessitating cleaning between each extraction. 

In SLM extraction, the most widely applied type of three-phase membrane extraction, the membrane consists of an organic solvent, which is held by capillary forces in the pores of a hydrophobic porous membrane supporting the membrane liquid. Such membrane support can be either flat porous PTFE or polypropylene membrane sheet or porous polypropylene hollow fibers. Typical solvents are long-chain hydrocarbons like n-undecane or kerosene and more polar compounds like dihexyl ether, dioctyl phosphate, and others. Various additives can increase the efficiency of extraction considerably. The stability of the membrane depends on the solubility and volatility of the organic liquids, and it is generally possible to obtain membrane preparations that are stable up to several weeks. 

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