Supports hollow-fiber

Supported hollow fiber coupled transport pilot plant installed at Wyoming uranium mill -1983... 

The dimensions of the tubular membranes are so large that they have to be supponed whereas the hollow fibers and capillaries are self-supporting. Hollow fibers and capillaries can be prepared ia three different methods ... 

Thermoplastic synthetic polymers are used for preparing semipermeable medical membranes owing to their good mechanical resistance and low density, which make it possible to easily prepare thin self-supporting hollow-fiber membranes, and their low energy requirement and processing costs. In the following, the main features of the commercial semipermeable medical membranes made of synthetic polymers are briefly discussed. 

FIGURE 15.27 Schematic illustration of dip-coating (a) dry porous support hollow fiber membrane, (b) coating bath, (c) oven, (d) hollow-fiber composite membrane. (Adapted from M. Mulder, Basic Principles of Membrane Technology, 2nd edn., Kluwer Academic, Dordrecht, the Netherlands/Boston, MA, 1996.)... 

The most widely used chemically modified PPO in the development of thin film composite membranes is sulfonated polyphenylene oxide (SPPO). The polymer in the acid form as well as salt form has been used by Bikson to produce multilayer composite membranes. These types of membranes have been described to have at least two chemically distinct layers deposited on a porous substrate in a single coating step process. The outer layer forms a protective defect-sealing surface whereas the inner layer is the selective SPPO layer. This layer is adjacent to the porous support membrane. The two top layers are formed simultaneously on top of porous polysulfone support hollow fibers. A coating solution of SPPO in the lithium salt form (SPPO-Li ) and amine functional silicone fluid was coated on top of the polysulfone fibers. These coated fibers were used to construct a hollow fiber separator permeator. 

These gas transfer membranes or membrane contactors employ microporous polypropylene hollow fiber membranes arranged in a modular design. Oxygenated water flows on the shell side of the hollow fibers, and a strip gas (such as nitrogen) or a vacuum is applied to the inside (lumenside), with the hollow fibers acting as a support medium for intimate contact between the water and gas phases. 

Although hollow fibers are thought to be an excellent candidate to be used as support-they are cheap and have a very high surface area to volume (>1000 m m ) - very few reports on hollow-fiber-supported zeolite membranes exist in the open literature. For zeohte membranes, ceramic hollow fibers are preferred because of their mechanical and thermal stability. Recently, Alshebani... 

Liquid Membranes Several types of liquid membranes exist molten salt, emulsion, immobilized/supported, and hollow-fiber-contained liquid membranes. Araki and Tsukube (Liquid Membranes Chemical Applications, CRC Press, 1990) and Sec. IX and Chap. 42 in Ho and Sirkar (eds.) (op. cit., pp. 724, 764-808) contain detailed information and extensive bibliographies. 

The production process for (S)-phenylalanine as an intermediate in aspartame perpetuates the principle of reracemization of the nondesired enantiomer (Figure 4.5) in a hollow fiber/ liquid membrane reactor. Asymmetric hydrolysis of the racemic phenylalanine isopropylester at pH 7.5 leads to enantiopure phenylalanine applying subtilisin Carlsberg. The unconverted enantiomer is continuously extracted via a supported liquid membrane [31] that is immobilized in a microporous membrane into an aqueous solution of pH 3.5. The desired hydrolysis product is charged at high pH and cannot, therefore, be extracted into the acidic solution [32]. 

Huang, D.S., Huang, K.L., Chen, S.P. et al. (2008) Rapid reaction-diffusion model for the enantioseparation of phenylalanine across hollow fiber supported liquid membrane. Separation Science and Technology, 43 (2), 259-272. 

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... 

In the past decade, several novel solvent-based microextraction techniques have been developed and applied to environmental and biological analysis. Notable approaches are single-drop microextraction,147 small volume extraction in levitated drops,148 flow injection extraction,149 150 and microporous membrane- or supported liquid membrane-based two- or three-phase microextraction.125 151-153 The two- and three-phase microextraction techniques utilizing supported liquid membranes deposited in the pores of hollow fiber membranes are the most explored for analytes of wide ranging polarities in biomatrices. This discussion will be limited to these protocols. 

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... 

Zeolite/polymer mixed-matrix membranes can be fabricated into dense film, asymmetric flat sheet, or asymmetric hollow fiber. Similar to commercial polymer membranes, mixed-matrix membranes need to have an asymmetric membrane geometry with a thin selective skin layer on a porous support layer to be commercially viable. The skin layer should be made from a zeohte/polymer mixed-matrix material to provide the membrane high selectivity, but the non-selective porous support layer can be made from the zeohte/polymer mixed-matrix material, a pure polymer membrane material, or an inorganic membrane material. 

The geometries for asymmetric mixed-matrix membranes include flat sheets, hollow fibers and thin-fihn composites. The flat sheet asymmetric mixed-matrix membranes are formed into spirally wound modules and the hollow fiber asymmetric mixed-matrix membranes are formed into hollow fiber modules. The thin-film composite mixed-matrix membranes can be fabricated into either spirally wound or hollow fiber modules. The thin-film composite geometry of mixed-matrix membranes enables selection of different membrane materials for the support layer and low-cost production of asymmetric mixed-matrix membranes utilizing a relatively high-cost zeolite/polymer separating layer on the support layer. 

Metal ions such Cu, Cd, and Pb can be preconcentrated from water samples using liquid membranes containing 40% w/w of di-2-ethylhexylphosphoric acid in kerosene diluent in a PTFE support. The liquid membrane can be coupled on-line to an atomic absorption spectrometer and has been shown to be stable for at least 200 h with extraction efficiencies over 80%, and enrichment factors of 15 can be obtained. A liquid membrane has also been used for sample cleanup and enrichment of lead in urine samples prior to determination by atomic absorption spectrometry [100]. The experimental setup for metal enrichment is shown in Fig. 13.4. Lead was enriched 200 times from urine [80] and several metals were enriched 200 times from natural waters [88]. Using hollow fiber... 

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. 

Fig. 4. Primary liver cells are cultivated on the exterior surfaces of semipermeable capillary hollow fiber membranes. Medium is perfused through the extrafiber space. Through the fibers oxygen supply is supported...

Although several hepatocyte-based Ever support systems have been proposed, there is no current consensus on its eventual design configuration. The most devices used currently are based on conventional hollow fiber membranes, and there are many opportunities for bioengineers to design new bioreactors that will optimize device function, particularly with regard to oxygen and nutrient provision. 

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]. 

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