Micellar-enhanced ultrafiltration

In the short term, we do not expect chiral membranes to find large-scale application. Therefore, membrane-assisted enantioselective processes are more likely to be applied. The two processes described in more detail (liquid-membrane fractionation and micellar-enhanced ultrafiltration) rely on established membrane processes and make use of chiral interactions outside the membrane. The major advantages of these 

6 Poly (l-[dimethyl(10-pinanyl)silyl]prop-l-yne) (PDPSP) 

Chiral Separation Techniques A Practical Approach, Second, completely revised and updated edition 

Edited by G. Subramanian Copyright 2001 Wiley-VCH Verlag GmbH ISBNs 3-527-29875-4 (Hardcover) 3-527-60036-1 (Electronic) 

6 Enantiomer Separations using Designed Imprinted Chiral Phases 

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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). 

Ultrafiltration of micellar solutions combines the high permeate flows commonly found in ultrafiltration systems with the possibility of removing molecules independent of their size, since micelles can specifically solubilize or bind low molecular weight components. Characteristics of this separation technique, known as micellar-enhanced ultrafiltration (MEUF), are that micelles bind specific compounds and subsequent ultrafiltration separates the surrounding aqueous phase from the micelles [70]. The pore size of the UF membrane must be chosen such, that the micelles are retained but the unbound components can pass the membrane freely. Alternatively, proteins such as BSA have been used in stead of micelles to obtain similar enan-tioselective aggregates [71]. 

Fig. 5-17. Principle of micellar-enhanced ultrafiltration (MEUF). The d-enantiomer of a racemic mixture is preferentially bound to the micelles, which are retained by the membrane. The bulk containing the 1-enantiomer is separated through the membrane [72].

Nonbiological methods for removal of trichloroethylene from water are also being studied. These include the use of a hollow fiber membrane contactor (Dr. A.K. Zander, Clarkson University), photocatalysis by solar or artificially irradiated semiconductor powders (Dr. G. Cooper, Photo-catalytics, Inc.), and micellar-enhanced ultrafiltration (Dr. B.L. Roberts, Surfactant Associates, Inc.). 

Lipe, K. M., Sabatini, D. A., Hasegawa, M. A., and Harwell, J. H., Micellar Enhanced Ultrafiltration and Air Stripping for Surfactant-Contaminant Separation and Surfactant Reuse Ground Water Monitoring Remediation, Winter, pp. 85-92. 

Micellar enhanced ultrafiltration (MEUF) is a recently proposed technique to separate dissolved organic compounds from aqueous streams [256-258]. In this process, surfactant is added to an aqueous stream containing organic solute for forming micelles in order to solubilize the target compound. The subsequent concentration and purification of the target compound is achieved by ultrafiltration by optimizing the process parameters [259-261]. 

In aqueous surfactant solutions, either by circumstance or design, non—surface active organic species may be present. Examples are oil recovery, where crude oil is present, or micellar—enhanced ultrafiltration, where micelles are being used to effect a separation of dissolved organic pollutants from water. The ability of mixed micelles to solubilize organic solutes has received relatively little study. In addition, the solubilization of these compounds by micelles may change the monomer—micelle equilibrium compositions. 

Biologically friendly ionic surfactants can be added to the wastewater at concentrations above the threshold value beyond which the surfactants self-assemble to form micelles. The resulting micelles can trap the hydrocarbon wastes since the hydrocarbon solutes prefer the hydrocarbon interior of the micelle over the aqueous environment outside. In addition, ionic wastes in the water adsorb to the polar heads of the surfactants (see Fig. 8.1). The resulting waste-laden micelles can then be removed more easily using ultrafiltration methods. Such a process, known as micellar-enhanced ultrafiltration (MEUF), can be made continuous, scalable, cost effective, and environmentally friendly (through the use of biodegradable surfactants). 

Beolchini, F., Pagnanelli, F., De Michelis, I. and Veglib, F. (2006) Micellar enhanced ultrafiltration for arsenic(V) removal effect of main operating conditions and dynamic modeling. Environmental Science and Technology, 40(8), 2746-52. 

Enormous advances and growth in the use of ordered media (that is, surfactant normal and reversed micelles, surfactant vesicles, and cyclodextrins) have occurred in the past decade, particularly in their chromatographic applications. New techniques developed in this field include micellar liquid chromatography, micellar-enhanced ultrafiltration, micellar electrokinetic capillary chromatography, and extraction of bioproducts with reversed micelles techniques previously developed include cyclodextrins as stationary and mobile-phase components in chromatography. The symposium upon which this book was based was the first major symposium devoted to this topic and was organized to present the current state of the art in this rapidly expanding field. 

Equilibrium Solubilization of Benzene in Micellar Systems and Micellar-Enhanced Ultrafiltration of Aqueous Solutions of Benzene... 

An automated vapor pressure method has been used to obtain highly precise values of the partial pressure of benzene as a function of concentration in aqueous solutions of sodium dodecylsulfate (at 15 to 45 C) and 1-hexadecylpyridinium chloride (at 25 to 45 C). Solubilization isotherms and the dependence of benzene activity on the intramicellar composition are inferred from the measurements and related to probable micellar structures and changes in structure accompanying the solubilization of benzene. Calculations are made to determine the efficiency of micellar-enhanced ultrafiltration (MEUF) as a process for purifying water streams contaminated by benzene,... 

The mobility of solute species in aqueous media and the transfer of these solutes to other phases can be greatly influenced by their association with ordered entities such as surfactant micelles. Thus, the effectiveness of micellar-enhanced ultrafiltration (MEUF) in removing organic (1 -4) and metal ion ( 5, 6)... 

Iqbal, J., Kim, H.-J., Yang, J.-S., Back, S., and Yang, J.-W. 2007. Removal of arsenic from groundwater by micellar-enhanced ultrafiltration (MEUF). Chemosphere, 66 970-6. 

The micellar-enhanced ultrafiltration MEUF technique, based on addition of surfactants and chelating agents to complex and enhance removal of undesirable compounds, show considerable promise in membrane degumming applications. The natural substances such as phospholipids act as surfactants to form large micelles that will be rejected by the membrane. 

Scamehorn, J.F. Christian, S.D. El-Sayed, D.A. Uchiyama, H. Younis, S.S. Removal of divalent metal cations and their mixtures from aqueous streams using micellar enhanced ultrafiltration. Sep. Sci. Technol. 1994, 26, 809-830. 

Ligand-Modifled Micellar-Enhanced Ultrafiltration for Metal Ion Separations... 

G. Pozniak, 1. Gancarz, and W. Tylus. Modified poly(phenylene oxide) membranes in ultrafiltration and micellar-enhanced ultrafiltration of organic compounds. Desalination, 198(l-3) 215-224, October 2006. 

The other approach utilizes the surfactants for separation purposes and the possibility of removal of metals in the process of micellar-enhanced ultrafiltration (MEUF) [100-103]. MEUF can be applied to separate the micellar phase using membranes with a pore size smaller than the micellar diameter. In such a process, surfactant is added to an aqueous... 

Landaburu-Aguirre, J., Garcia, V, Pongrdcz, E., Keiski, R., The removal of zinc from synthetic wastewaters by micellar-enhanced ultrafiltration Statistical design of experiments, Desalination 240, 262, 2009. 

Xiarchos, I., Jaworska, A., Zakrzewska-Trznadel, G., Response surface methodology for the modelling of copper removal from aqueous solutions using micellar-enhanced ultrafiltration, J. Membr. Sci. 321, 222, 2008. 

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