Surfactant solutions ultrafiltration

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]. 

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. 

Ultrafiltration was utilised for catalyst recovery first for enzymes [62, 63] and later for polymer enlarged homogeneous catalysts [64]. The molecular weight of a homogeneous catalyst itself is usually too low in comparison to the molecular weight cut-off of standard ultrafiltration membranes of 5000 or 10 000 Da. By embedding the catalyst in a surfactant micelle the same effect is obtained as with immobilisation of the catalyst at a soluble polymer molecule or a small polymer particle. Ultrafiltration of surfactant solutions is an established technique that is often applied for complete removal of traces of small... 

An ultrafiltration technique, first described by Hutchinson and Schaffer [52] has been used by several workers [38, 53-56]. In a typical experiment a portion of the equilibrated surfactant solution containing a known amount of solubilizate and surfactant is passed through a membrane which is impermeable to micelles but which allows free passage of solubilizate molecules. Filtrand and filtrate are then analysed to determine the composition of the micellar and free phases. As with the equilibrium dialysis technique the selection of a suitable membrane is essential for the success of the technique. 

Paatz, K., J. Rollin, Ultrafiltration of aqueous surfactant solutions (in German), Wiss. Z.-Tech. Hochsch. Kothen, 1991,5, 95-99. 

An organic phase can be used several times provided the sample feed (fermentation broth) does contain cells or cell debris. Presence of such contaminants may render it necessary to regenerate the organic phase for its prolonged use. A literature survey suggests that the knowledge available on the recovery and reuse of surfactants is very little. However, the removal of surfactants from the stripping aqueous solution can be achieved by filtration and then can be recycled [10]. Use of ultrafiltration was also shown to be a successful technique for the separation of surfactants from reverse micellar solution [203]. 

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]. 

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). 

Ergican, E., Gecol, H. and Fuchs, A. (2005) The effect of co-occurring inorganic solutes on the removal of arsenic (V) from water using cationic surfactant micelles and an ultrafiltration membrane. Desalination, 181(1-3), 9-26. 

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)... 

Ultrafiltration of whey is a major membrane-based process in the dairy industry however, the commercial availability of this application has been limited by membrane fouling, which has a concomitant influence on the permeation rate. Ultrasound cleaning of these fouled membranes has revealed that the effect of US energy is more significant in the absence of a surfactant, but is less markedly influenced by temperature and transmembrane pressure. The results suggest that US acts primarily by Increasing turbulence within the cleaning solution [91]. 

In this type of extraction, micellar structures are retained by correctly selecting the ultrafiltration (UF) membrane (Scamehorn et al., 1988). Hydrophobic species are solubilized within the micelles, but surfactant monomers in equilibrium with the micelles can penetrate the membrane along with the free solutes in equilibrium with those solubilized in the micelles. Whereas several uses for this technique have been suggested, such as the collection of radioactive uranium and plutonium present in acid wastes during nuclear plant decommissioning, from our point of view its principal use is in enantiomeric separation (Overdevest et al., 1998). 

C.S. Kedari, S.S. Pandit, S.C. Tripathi, Extraction of Am(III) from aqueous nitrate solutions into micellar pseudo phase of anionic or non-ionic surfactant and separation by ultrafiltration, J. Membr. Sci. 341, 2009, 122-130. 

A flow chart of this general process is illustrated in Figure 5.11. Surfactant and alkaline coupler solutions are combined to form a solution wherein surfactant and coupler form mixed micelles. This solution is then acidified and the coupler is reprotonated to create metastable coupler (nano)particles. Excess salt is then removed by washing (ultrafiltration or dialysis). Steric stabilization may be imparted by adding polymeric stabilizers or nonionic surfactants at the initial or final process stages. 

Substances that are solubilized in surfactant micelles can be separated by ultrafiltration through membranes whose pores are smaller in diameter than the micelle size. For a membrane molecular weight cutoff from 1 to 50kDa, the rejections are 98%. The stream of water-containing monomeric molecules of surfactant (permeate) flows through the membrane. The remaining solution (retentate) contains solutes solubilized in micelles. The MEUF process is used for the separation of organic substances and various ions, the latter after their previous complexation. 

A novel series of water-soluble amphoteric cyclocopolymers containing the pH-responsive hydrophobic monomer, iV,iV-diallyl-iV-methylamine [2424-01-3], and the sulfobetaine monomer, 3-(iVA -diallyl-iV-methylammonio)-propanesulfonate, have been prepared in 0.5 M NaCl aqueous solution (pH 4.0), using 2-hydroxy-l-[4-(hydroxyethoxy)phenyl]-2-methyl-l-propanone (Ir-gacure 2959) as the free-radical photoinitiator (165). Equilibrium dialysis experiments demonstrated that they could be utilized to control the sequestration of organic foulants and thus have potential application as polymeric surfactants in micellar-enhanced ultrafiltration processes for water purification. 

Extraction and concentration schemes based on analyte solnbilization in cationic surfactant micelles, such as miceUar-assisted extraction, coacervative extraction (CAE) [6], micellar-enhanced ultrafiltration (MEUF), smd actant-assisted transport of solutes across bquid membranes (LSM), smd actant-mediated solid-phase extractions (MSPEs), and micellar sobd-phase microextractions (MSPMEs), can be cited [3],... 

Colloid-enhanced ultrafiltration (CEUF) is a separation technique based on the use of colloids able to bind multivalent metal ions by electrostatic interactions. The colloidal solution is then filtered under pressure through a UF membrane with a pore size smaller than the size of the colloid, producing a purified water stream (permeate) and a concentrated stream containing almost all of the colloid and metal ions (retentate) (Dunn et al, 1989). CEUF can be distinguished in micellar-enhanced ultrafiltration (MEUF), if the colloidal species is a micelle-forming surfactant, and in polyelectrolyte-enhanced ultrafiltration (PEUF) when the colloidal species is a polyelecrolyte. 

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