Dyes separation by means of cross-flow ultrafiltration of micellar solutions

Separation of organic dyes from micellar solutions was studied in a cross-flow SEPA CF Osmonics module. Several model dyes (methylene blue, mordant black 11 and mordant black 17) were investigated. Sodium dodecylsulfate (SDS), hexadecyltrimethylammonium bromide (CTAB), oxyethylated coconut fatty acid methyl esters (OMC-10) and binary mixtures of ionic and nonionic surfactants were used as surfactants. Membranes made of cellulose acetate (CQ), polysulfone (PES) and polyvinylidene fluoride (PVDF) (cut-off 15–30 kDa) were used. Ultrafiltration of micellar solutions could be considered as a research method, helpful in determining important parameters such as: (i) the micelle loading and (ii) micelle binding constant used to characterize micellar solutions, and (iii) the distribution coefficient employed in extraction studies. It was found that the type of surfactant is the main factor affecting the rejection. The best separation of the dyes was obtained when the ionic surfactant, charged opposite to dye, was used alone or in the mixture with the nonionic surfactant. Moreover, the introduction of nonionic surfactant into ionic surfactants decreased the CMC of mixed micelles and then the concentration of surfactants in the permeate.