Membrane extraction technology

Membrane Exctraction Technology, London, U.K., http //www.membrane-extraction-technology.com. 

Membrane units can be purchased either from Global FLA Inc. (Fox Island, Washington), or from die mechanical workshop at the Chemical Center at Lund University (Lund, Sweden). Process-scale membrane units can be designed by Membrane Extraction Technology Ltd (London, UK). 

Membrane Extraction Technology product brochure (www.membrane-extraction-... 

Unfortunately at present not many of either type of membranes are available commercially, but undoubtedly many more will appear on the market in the near future. Corrrmercially available SRNF irKlude the SelRO membranes (Koch Membrane Systerrrs, USA), Starmem membranes (Membrane Extraction Technologies, UK), SolSep membranes (SolSep, The Netherlarrds), and Desal-5 and Desal-5-DK membranes (GE/Osmomics, USA) designed for aqueous applications, as well as for SRNF. 

Data was obtained for three organic solvents, ethyl acetate, toluene and methanol - these solvents are commonly used in the pharmaceutical and chemical industries. STARMEM 122, an asymmetric OSN membrane with an active layer of polyimide, in a dry form but with a lube oil soaked into the membrane as a preserving agent, with a nominal MWCO of 220 g-moh (manufacturers data) was supplied by Membrane Extraction Technology Ltd (UK). 

Membrane Extraction. An extraction technique which uses a thin Hquid membrane or film has been introduced (80,81). The principal advantages of Hquid-membrane extraction are that the inventory of solvent and extractant is extremely small and the specific interfacial area can be increased without the problems which accompany fine drop dispersions (see Membrane technology). 

In order to maintain a definite contact area, soHd supports for the solvent membrane can be introduced (85). Those typically consist of hydrophobic polymeric films having pore sizes between 0.02 and 1 p.m. Figure 9c illustrates a hoUow fiber membrane where the feed solution flows around the fiber, the solvent—extractant phase is supported on the fiber wall, and the strip solution flows within the fiber. Supported membranes can also be used in conventional extraction where the supported phase is continuously fed and removed. This technique is known as dispersion-free solvent extraction (86,87). The level of research interest in membrane extraction is reflected by the fact that the 1990 International Solvent Extraction Conference (20) featured over 50 papers on this area, mainly as appHed to metals extraction. Pilot-scale studies of treatment of metal waste streams by Hquid membrane extraction have been reported (88). The developments in membrane technology have been reviewed (89). Despite the research interest and potential, membranes have yet to be appHed at an industrial production scale (90). 

Membrane extraction offers attractive alternatives to conventional solvent extraction through the use of dialysis or ultrafiltration procedures (41). The choice of the right membrane depends on a number of parameters such as tlie degree of retention of the analyte, flow rate, some environmental characteristics, and tlie analyte recovery. Many early methods used flat, supported membranes, but recent membrane technology has focused on the use of hollow fibers (42-45). Although most membranes are made of inert polymers, undesired adsorption of analytes onto the membrane surface may be observed, especially in dilute solutions and when certain buffer systems are applied. 

In membrane extraction, the treated solution and the extractant/solvent are separated from each other by means of a solid or liquid membrane. The technique is applied primarily in three areas wastewater treatment (e.g., removal of pollutants or recovery of trace components), biotechnology (e.g., removal of products from fermentation broths or separation of enantiomers), and analytical chemistry (e.g., online monitoring of pollutant concentrations in wastewater). Figure 18a shows schematically an industrial hollow fiber-based pertraction unit for water treatment, according to the TNO technology (263). The unit can be integrated with a him evaporator to enable the release of pollutants in pure form (Figure 18b). 

For the membrane array of cytokine expression, the general procedures (Amersham Pharmacia Biotech R D Systems SuperArray Inc., Bethesda, MD Clontech Laboratories, Inc., Palo Alto, CA) include RNA extraction, reverse transcription into biotin- or radioisotope-labeled cDNA, hybridization with about 20 to several hundred different cDNA prespotted membranes, and signal detection using fluorescence or radioactive methods (L3). As an example, Fig. 4 and Table 4 show different chemokine genes upregulated in allergic asthmatic patients compared with normal controls, based on membrane array technology (SuperArray). 

Improvement of membrane separation technology has resulted in the isolation of MFGM-enriched material from commercially available products. A phospholipid-rich fraction can be extracted from whey (Boyd et al., 1999) and buttermilk (Sachedva and Buchheim, 1997) with a reported yield of 0.25 g of phospholipids/g of protein in buttermilk (Sachdeva and Buchheim, 1997). Microfiltration of whey derived from the Cheddar cheese process, using 0.2 pm ceramic filters results in a fraction containing two major phospholipids, phosphatidylcholine and phosphatidylethanolamine, and lesser amounts of phosphatidylinositol, phosphatidylserine, sphingomyelin and cerebrosides (Boyd et al., 1999). The phospholipid fraction separated from the total lipids contains a larger proportion of mono- and polyunsaturated fatty acids (mainly oleic, Cig i and linoleic, C ) compared to the total lipid and the neutral lipid fraction (Boyd et al., 1999). 

The same principle of operation as described above is applicable also to liquid-liquid extraction where an aqueous liquid and an organic liquid contact each other inside the contactor for extraction of a solute selectively from one phase to another [6-8]. The critical breakthrough pressure for liquid-liquid system could be calculated by Equation 2.1, except that the term A would now be the interfacial tension between the two liquids. Further variation of membrane contacting technology is called gas membrane or gas-gap membrane where two different liquid phases flow on either side of the membrane, but the membrane pores remain gas filled [9-10]. In this situation two separate gas-hquid contact interfaces are supported on each side of a single membrane. 

A historical perspective on aqueous-organic extraction using membrane contactor technology is available in Refs. [1,6,83]. The mechanism of phase interface immobilization was first explored in Ref. [84], while application of membrane solvent extraction for a commercial process was first explored in Ref. [85]. Two aspects of liquid-liquid contact in membrane contactors that are different from typical gas-liquid contact are (1) the membrane used could be hydrophobic, hydrophdic, or a composite of both and (2) the membrane mass transfer resistance is not always negligible. Ensuring that the right fluid occupies the membrane pores vis-a-vis the affinity of the solute in the two phases can minimize membrane resistance. These aspects have been discussed in detail in Refs. [6,86,87]. 

As a part of our comprehensive programme on membrane technology, we evaluated nondispersive solvent extraction (NDSX) with a hydrophobic microporous hollow fiber contactor (HFC) for the separation and removal of actinides [1,10-12]. As the separation and recovery of actinides from different sources is paramount to radiotoxicity, there is a constant need for advances in the field. Among recently developed technologies, membrane extraction using microporous hollow fibers is particularly... 

The mass-transfer efficiencies of various MHF contactors have been studied by many researchers. Dahuron and Cussler [AlChE 34(1), pp. 130-136 (1988)] developed a membrane mass-transfer coefficient model (k ) Yang and Cussler [AIChE /., 32(11), pp. 1910-1916 (1986)] developed a shell-side mass-transfer coefficient model (ks) for flow directed radially into the fibers and Prasad and Sirkar [AIChE /., 34(2), pp. 177-188 (1988)] developed a tube-side mass-transfer coefficient model (k,). Additional studies have been published by Prasad and Sirkar [ Membrane-Based Solvent Extraction, in Membrane Handbook, Ho and Sirkar, eds. (Chapman Hall, 1992)] by Reed, Semmens, and Cussler [ Membrane Contactors, Membrane Separations Technology Principle. and Applications, Noble and Stern, eds. (Elsevier, 1995)] by Qin and Cabral [MChE 43(8), pp. 1975-1988 (1997)] by Baudot, Floury, and Smorenburg [AIChE ]., 47(8), pp. 1780-1793 (2001)] by GonzSlez-Munoz et al. [/. Memhane Sci., 213(1-2), pp. 181-193 (2003) and J. Membrane Sci., 255(1-2), pp. 133-140 (2005)] by Saikia, Dutta, and Dass [/. Membrane Sci., 225(1-2), pp. 1-13 (2003)] by Bocquet et al. [AIChE... 

Bandini, S. Gostoli, C. Concentrating aqueous solutions by gas membrane extraction. Proceedings of Euromembrane 95 Conference, European Society for Membrane Science and Technology Bath, UK, 1995 Vol. 2, 19-24. 

Lin, S. H., Pan, C. L., Leu, H. G. (1999). Liquid membrane extraction of 2-chlorophenol from aqueous solution. Journal of Hazardous Materials 65 289-304. Raghuraman, B.J., Tirmizi, N.P., Kim, B.-S., Wiencek, J. M. (1995). Emulsion Liquid Membranes for Wastewater Treatment Equihbrium Models for Lead- and Cadmium-di-2-ethylheyl Phosphoric Acid Systems. Environmental Science and Technology 29 979-984. Liu, H. J., Wu, Q. S., Ding, Y. P., Liu, L. (2004). Biomimetic synthesis of metastable PbCrO4 nanoparticles by emulsion liquid membrane system with carrier and coupled treatment of Pb(II) and Cr(VI) wastewaters. Hrtij Chimica Sinica 62 946-950. 

Figure 5 Operating principle of extractive membrane bioreactor technology...

Utilization of Membrane Separation Technology for Purification and Concentration of Anserine and Carnosine Extracted from Chicken Meat... 

If anserine and camosine contained in the chicken meat can be purified at low cost using membrane separation technology, they can be promising components of a wide variety of functional foods. In this study, to add extra value to the discarded hen meat and utilize it, a membrane separation process that can purify anserine and carnosine contained in extract from the chicken meat was developed and its efficiency was demonstrated. 

Interfaces between aqueous phase and the volumes confined by amphiphilic molecules [288]. In vitro, these refer to lipid vesicles and micelles, lipid lamellae, cubic and hexagonal phases, Langmuir-Blodgett (LB) films, which are important in colloid science and in extraction technology. In vivo, these are the surfaces of biological membranes. 

For application of membrane contactors in nuclear science and technology, snch processes like MD and membrane extraction-stripping were tested. A very important part of research in this field was devoted to liqnid membranes that also employ membrane contactors to form snpported liquid membranes (SLMs) [130],... 

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