Hollow fiber membrane based separation liquid membranes

Nonselective membranes can assist enantioselective processes, providing essential nonchiral separation characteristics and thus making a chiral separation based on enantioselectivity outside the membrane technically and economically feasible. For this purpose several configurations can be applied (i) liquid-liquid extraction based on hollow-fiber membrane fractionation (ii) liquid- membrane fractionation and (iii) micellar-enhanced ultrafiltration (MEUF). 

Pabby, A.K. and Sastre, A.M. (2006) Hollow-fiber membrane based separation technology performance and design perspectives, in Solvent Extraction and Liquid Membranes Fundamental and Application in New Materials (eds Cortina and Aguilar), Marcel Dekker, New York. 

In liquid separation, hollow fiber membranes based on PBI have shown excellent performance for pervaporation dehydration of organic liquids. For example, a dual layer PEI-PBI hollow fiber membrane with an outer selective layer of PBI showed better performance than most other polymeric membranes in pervaporation dehydration of ethylene glycol. Sulfonation modifications of PBI membranes have demonstrated excellent separation efficacies in the dehydration of acetic acid. Studies have shown that PBI hollow fiber membranes were effective in separating chromates from solutions. Also, PBI nanofiltration hollow fiber membranes are promising candidates as forward osmosis membranes. In gas separation, recent studies sponsored by the Department of Energy at Los Alamos National Laboratories and SRI International demonstrated potential applications of PBI membranes in carbon capture and Hj purification from synthesis gas streams at elevated temperatures. H2/CO2 selectivity > 40 has been achieved at H2 permeability of 200 GPU at 250°C. ... 

Kitiyanan, B., O Haver, J.H., Harwell, J.H. and Sabatini, D.A. (2000) The use of liquid-liquid-extraction in hollow fiber membrane for the removal of organic contaminants from aqueous surfactant streams. In J.F. Scamehorn and J.H. Harwell (eds), Surfactant-Based Separations Science and Technology, ACS Symposium Series 740. American Chemical Society, Washington, DC, pp. 76-89. 

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). 

Hollow membrane fibers are required for many medical application, e.g. for disposable dialysis. Such fibers are made by usmg an appropriate fiber spinning technique with a special inlet in the center of the spinneret through which the fiber core forming medium (liquid or gas) is injected. The membrane material may be made by melt-spinning, chemical activated spinning or phase separation. The thin wall (15-500 xm thickness) acts as a semi-permeable membrane. Commonly, such fibers are made of cellulose-based membrane materials such as cellulose nitrate, or polyacrylonitrile, polymethylmethacrylate, polyamide and polypropylene (van Stone, 1985). 

Much effort has been expended in attempting to use membranes for separations. Reverse osmosis membranes are used worldwide for water purification. These membranes are based on size selectivity depending on the pores used. They do not have the ability to selectively separate target species other than by size. Incorporation of carrier molecules into liquid membrane systems of various types has resulted in achievement of highly selective separations on a laboratory scale. Reviews of the extensive literature on the use of liquid membrane systems for carrier-mediated ion separations have been published [15-20]. A variety of liquid membranes has been studied including bulk (BLM), emulsion (ELM), thin sheet supported (TSSLM), hollow fiber supported (HFSLM), and two module hollow fiber supported (TMHFSLM) types. Of these liquid membranes, only the ELM and TMHFSLM types are likely to be commercialized. Inadequacies of the remaining... 

Chen H, Ohuskovic G, Majumdar S, and Sirkar KK. Immobilized glycerol-based liquid membranes in hollow fibers for selective CO2 separation from CO2-N2 mixtures. J. Mem. Sci. 2001 183 75-88. 

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. 

S. Mukhopadhyay, Dispersion and emulsion based liquid membrane systems in hollow fiber contactor, in S.A. Ansari, A.K. Pandey, P.K. Mohapatra, A. Goswami (eds.), Proceedings of Theme Meeting on Membrane Separation for Fuel Cycle Applications, BARC, Mumbai, India, September 16-18, 2013, p. 11. 

Distillation and related vapor-liquid processes are by far the most widely used molecular separation processes in the petroleum, natural gas, petrochemical, and chemical industries, as mentioned earlier. It is highly unlikely that adsorption will ever rival distillation in frequency of use, but adsorption will continue to m e inroads into its domain. Adsorption s serious competition for the separations for which it is now used would seem to come chiefly from membrane-based processes, and especially fixed-membrane processes. For example, Monsanto s Prism hollow-fiber-based process has been commercialized in a number of hydrogen-upgrading applications, and a growing number of other applications are being pursued. 

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