Micellar-enhanced

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].

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... 

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]. 

This technique of MEUF has also been successfully employed for the recovery of thuringiensin [258], removal of cresols [262], extraction of chromate anion [257], removal of dissolved organic pollutants [256], removal of -alcohols [263],preconcentration and removal of iron [260], and preconcentration of aniline derivatives [261].Kandori and Schechter [264] have given a detailed account of selecting surfactants for MEUF. The design characteristics of micellar enhanced utrafilters and cross-flow ultrafiltration of micellar surfactant solutions have been described by Markets et al. [265]. 

Solubilization o-f dissolved organic molecules into micelles is important in detergency (2), emulsion polymerization (65). and micellar—enhanced ultra-fiItration (3), Just to name a -few applications. Solubilization also indirectly a-f-fects many other operations because it o-ften a-f-fects monomer—micelle equilibrium, in-fluencing sur-factant adsorption, wetting, etc. when solubi 1 izable, non—sur-factant species are present in solution. 

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. 

Mg(II) forms a complex with 8-hydroxyquinoline-5-sulfonic acid (37) at pH 9.0 with Tris-HCl buffer, which can be determined by ELD (X x = 388 nm, ka = 495 nm) with micellar enhancement by cetyltrimethylammonium chloride (38). Masking of Ca(II) is achieved by EGTA (19). The method was applied in a SIA system for analysis of natural waters . After elution of the Mg(II) ions adsorbed on an alkali-activated PTFE tube with 0.1 M HCl and addition of A,A -bis(salicylidene)-2,3-diaminobenzofuran (39), the end analysis was by fluorometric determination of the Mg(II) complex (kex =475 nm, kfl = 545 nm). Possible interference of Ca(II) is masked on addition of the chelating agent... 

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. 

In microemulsions, the salinity for which the mixing of oil with a surfactant solution produces a middle-phase microemulsion containing an oil-to-water ratio of 1. In micellar enhanced oil recovery processes, extremely low interfacial tensions result, and oil recovery tends to be maximized when this condition is satisfied. 

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. 

Micellar-Enhanced Detection in Separation Science. In several instances, the use of appropriate surfactant media allows for enhanced and/or new modes for chromatographic detection. Most of the work has been in the area of spectroscopy. For example, it is well known that the presence of suitable surfactant micelles can significantly increase the absorbance of metal complexes (4,8,345). 

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... 

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