Cloud point séparation of direct yellow from micellar solutions

Separation of dye traces from aqueous solutions is an important environmental problem. Different physical techniques, including adsorption, sedimentation, flotation, ultrafiltration, reverse osmosis and other chemical techniques are usually used. Dyes can also be removed by the cloud point technique of micellar solutions containing non-ionic surfactants. It was found that the separation of the surfactant-rich phase was very slow and not complete. The separation was far from being in equilibrium. As a result, the concentrations of the surfactant and dye in the aqueous phase after the separation were significantly higher, compared to the expected values. The separation depended upon temperature, time, electrolyte and surfactant. The presence of sodium chloride improved the separation. Yields around 94-96% could be obtained. Oxyethylated nonylphenol and alcohol were suitable surfactants. Low yield of separation (below 40%) were only obtained for RokN8p7 having polyoxyethylene and polyoxypropylene blocks.