Partitioning equilibria in multicomponent surfactant systems for design of surfactant-based extraction processes

Aqueous biphasic systems based on nonionic surfactants have perspective applications in extraction processes, in particular, cloud point extraction of hazardous compounds or high valued products, especially biomolecules. Additives (e.g., ionic surfactants, salts) and variations in pH can significantly affect the surfactant-based separation processes, representing an additional degree of freedom for their optimization. However, there are few systematic studies of phase and partition behavior for these multicomponent surfactant systems.In this study we examined the clouding, phase compositions and partitioning equilibria for aqueous mixed surfactant systems of a nonionic surfactant (Triton X-114), ionic surfactants (cetyltrimethylammonium bromide or sodium dodecyl sulfate) and NaCl, in order to improve the extraction efficiency. Vanillin was used as a model substance at three different pH values, specifically in (partly) dissociated or non-dissociated states. The partition coefficients obtained in the batch experiments were compared to the predictions by the thermodynamic model COSMO-RS. Based on this knowledge a continuous multistep extraction process was carried out.To the best of our knowledge this is the first demonstration of using a mixed surfactant system for continuous countercurrent cloud point extraction.