Supported Liquid Membrane SLM Extraction

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... 

Several manufacturers introduced products amenable for this solid-supported LLE and for supported liquid extraction (SLE). The most common support material is high-purity diatomaceous earth. Table 1.8 lists some commercial products and their suppliers. The most widely investigated membrane-based format is the supported liquid membrane (SLM) on a polymeric (usually polypropylene) porous hollow fiber. The tubular polypropylene fiber (short length, 5 to 10 cm) is dipped into an organic solvent such as nitrophenyl octylether or 1-octanol so that the liquid diffuses into the pores on the fiber wall. This liquid serves as the extraction solvent when the coated fiber is dipped... 

The principle of a three-phase membrane extraction is illustrated in Figure 1.28. An organic solvent is immobilized in the pores of a porous polymeric support consisting of a flat filter disc or a hollow fiber-shaped material. This supported liquid membrane (SLM) is formed by treating the support material with an organic solvent that diffuses into its pores. The SLM separates an aqueous... 

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. 

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]. 

Affinity of MIP towards the target analyte should be examined prior to fabrication of the chemosensor. Batch binding assays are used to test selectivity of suitable MIPs. Especially, affinity of MIP to compounds, which are structurally related to the target analyte, should be tested. If MIP binds similarly with these compounds as the template, then cross-reactivity is manifested [156], This effect was exploited for determination of adenine and its derivatives with the use of MIP templated with 9-ethyladenine. Nevertheless, the cross-reactivity, if undesired, can be avoided by suitable sample pretreatment, e.g. by interferant extraction with a supported liquid membrane (SLM) coupled to the MIP-PZ chemosensor. The Fluoropore membrane filter of submicrometre porosity can serve that purpose. That way, this membrane holds interferants, thus eliminating the matrix effect. The SLM-involving determination procedure is cheaper than traditional laborious sample pretreatment used to remove the interfering substances. For instance, caffeine [143] and vanillin [157] in food samples have been determined using this procedure. 

Partitioning of components between two immiscible or partially miscible phases is the basis of classical solvent extraction widely used in numerous separations of industrial interest. Extraction is mostly realized in systems with dispergation of one phase into the second phase. Dispergation could be one origin of problems in many systems of interest, like entrainment of organic solvent into aqueous raffinate, formation of stable, difficult-to-separate emulsions, and so on. To solve these problems new ways of contacting of liquids have been developed. An idea to perform separations in three-phase systems with a liquid membrane is relatively new. The first papers on supported liquid membranes (SLM) appeared in 1967 [1, 2] and the first patent on emulsion liquid membrane was issued in 1968 [3], If two miscible fluids are separated by a liquid, which is immiscible with them, but enables a mass transport between the fluids, a liquid membrane (LM) is formed. A liquid membrane enables transport of components between two fluids at different rates and in this way to perform separation. When all three phases are liquid this process is called pertraction (PT). In most processes with liquids membrane contact of phases is realized without dispergation of phases. 

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. 

A supported liquid membrane (SLM) process has been considered, among other possible options, for the reiiK>val of contaminants from groundwater, because of the following advantages of SLM s over competing techniques (solvent extraction, ion exchange, polymeric membrane processes, etc.) ... 

A new and promising way of combining reaction and extraction are supported liquid membranes (SLM). Miyako et al. used SLMs on the basis of different water-immiscible ionic liquids and aliphatic hydrocarbons to achieve pure (S)-ibuprofen together with an enzymatic resolution step (Scheme 8-6). Only the (S)-enantiomer is esterified by the enzyme attached to the feed interface and able to enter the membrane. The ionic-liquid phase allows the selective transport of the more hydrophobic ibuprofen methyl ester from the aqueous-feed phase to the receiving phase. At the inter ce of the receiving phase, the (S)-ibuprofen methyl ester is hydrolysed to (S)-ibuprofen by another lipase. As (S)-ibuprofen is more hydrophilic it is not transported back through the supported ionic-Hquid phase. Best results were achieved with [BMIM]( (CFjSOijiN] as liquid membrane phase and the enzyme combination mentioned in Table 8-3 [85,86]. 

Nitric acid removal from an aqueous stream was accomplished by continuously passing the fluid through a hollow fiber supported liquid membrane (SLM). The nitric acid was extracted through the membrane wall by coupled transport. The system was modeled as a series of (SLM)-continuous stirred tank reactor (CSTR) pairs. An approximate technique was used to predict the steady state nitric acid concentration in the system. The comparison with experimental data was very good. 

One promising technique to accomplish this task Is solid supported liquid membrane (SLM) transfer using new extractants that are selective for actinides of various valencies (1,2). Our previous work p), also has demonstrated the utility of this technique and Is reviewed and extended In this paper. 

Larsson N, Berhanu T, Megersa N, Jdnsson jA. An automatic field sampler utihsing supported liquid membrane (SLM)— Apphed for on-site extraction of s-tiiazine herbicides and degradation products in an agricultural region of Ethiopia. Int J Environ Anal Chem 2011 91 929-944. 

Indeed, the tuneable properties of ILs associated with their environment-friendly perception have increased their investigation as alternative reaction media to replace traditional organic solvents in organic synthesis [11-13], catalytic reactions [12-16], electrochemical applications [17-19], biochemistry [20-24], and material engineering [25], It has also been reported that ILs can be used in extraction and as liquid phase in supported liquid membranes (SLMs) for the separation and recovery of organic compounds, metals, and gases [26-31]. 

The liquid membrane (LM) concept combines solvent extraction (SX) and membrane-based technologies, enabling both extraction and back-extraction in a single step with reduced consumption of extractants and diluents. For these reasons, separation based on LMs can be viewed as a promising alternative to traditional SX. The LM separation approach involves mass transfer of a target chemical species between two solutions (i.e., feed and receiver solutions) separated by an immiscible LM [1]. The main types of LMs are bulk liquid membranes (BLMs), emulsion liquid membranes (ELMs), supported liquid membranes (SLMs), and polymer inclusion membranes (PIMs). 

Supported liquid membranes (SLMs) consisting of 5% tri-n-octylphosphine oxide (TOPO) dissolved in di-w-hexylether/n-undecane (1 1) have been used in the simultaneous extraction of a mixture of three stUbene compounds (dienestrol, diethylstilbestrol, and hexestrol) in cow s milk, urine, bovine kidney, and liver tissue matrices [183]. The efficiencies obtained after the enrichment of 1 ng/1 stilbenes in a variety of biological matrices of milk, urine, liver, kidney, and water were 60-70, 71-86, 69-80, 63-74, and 72-93%, respectively. A new method to contribute to the discrimination of polyphenols including resveratrol with synthetic pores was proposed [184]. The work [185] evaluated two types of commonly available chiral detectors for their possible use in chiral method development and screening polarimeters and CD detectors. Linearity, precision, and the limit of detection (LOD) of six compounds (trans-stilbene oxide, ethyl chrysanthemate, propranolol, 1-methyl-2-tetralone, naproxen, and methyl methionine) on four common detectors (three polarimeters and one CD detector) were experimentally determined and the limit of quantitation calculated from the experimental LOD. trans-Stilbene oxide worked well across all the detectors, showing good linearity, precision, and low detection limits. However, the other five compounds proved to be more discriminating and showed that the CD detector performed better as a detector for chiral screens than the polarimeters. 

Hollow fiber-based extraction can be used for the determination of freely dissolved phenols or total concentration of phenols in environmental water samples. Liu et al. [199] applied hollow fiber-based supported liquid membrane (SLM) coupled with HPLC to the determination of freely dissolved chlorophenols in water samples. In this equilibrium sampling through membranes, freely dissolved chlorophenols were successfully determined in model solutions of humic acids and at low-ppb levels in river and leachate waters. 

In our laboratories, research and development studies have been conducted on the separation of uranium and various lanthanides by common extractants (carriers) and of actinides by crown ether carriers using different types of liquid membrane systems. Also our studies have been directed toward determining optimal support systems for supported liquid membranes (SLM) which may offer improved flux... 

The use of 13a in the extraction process or in the transport through supported liquid membranes (SLMs) allows to recover more than 98% of the cesium cation present in solution, making this derivative extremely attractive for declassification of nuclear wastes. Ligand 13a was dso used for the selective detection of cesium in ISEs and ISFETs with very high selectivity and low detection limit. Very recently, we anchored calix[4]arene-crown-5 and -crown-6 derivatives on silica-gel via hydrosilanization and we were able to separate by chromatography potassium or cesium fi"om other alkali metal ions with high efficiency. ... 

One could use the liquid inunobilized in the pores for separation of liquid mixtures as well, provided the feed liquid and the permeate (strip) liquid are immiscible with the liquid membrane in the pores (Figure 8.1.49(b)). Such membranes are called supported liquid membranes (SLMs). However, at the pore mouths, the two immiscible phases contact each other. The liquid membrane phase has some solubility, however small, in the feed/strip liquid phase. Therefore the life of the liquid membrane is limited (see Kowali and Sirkar (2003) for a brief review), and periodically it needs to be regenerated (Yang and Kocher-ginsky, 2006). The liquid membrane is most likely to have extractants used with the emulsion liquid membranes or solvent extraction in the case of chemically complexing extractants. 

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