Simultaneous extraction and enrichment of sunset yellow dye in an aqueous two-phase system

Sunset Yellow (SSY) is a neutral dye commonly used in the textile, cosmetic, pharmaceutical and food industries. This is found in the effluent streams of these industries. In this study, the extraction of this dye is analyzed using a polymer-salt aqueous two-phase system (ATPS). Classical extraction processes are based on contacting an organic phase with an aqueous phase. Our focus is on developing a green process where the use of an organic solvent is avoided. Polyethylene glycol of molecular weights 600 and 6000 are chosen as two candidates for the polymer phase and sodium sulfate as the salt phase. The propensity of the dye to selectively transfer into the polymer-rich phase is exploited to study the extraction process. The binodal curves are experimentally obtained using the cloud point method. The composition of salt and polymer was chosen so as to ensure that the volume of the polymer-rich phase is relatively low in the two-phase system. This choice results in obtaining a high concentration of the dye in the polymer-rich phase from a dilute solution of dye in the salt-rich phase. This is a spontaneous energy-efficient process which avoids the use of any other energy-intensive processes such as evaporation. The dye extraction is studied experimentally in batch mode where 75% extraction occurs in 2 h when the mass transfer is only by diffusion. To accelerate the process a milli channel is used under stratified flow conditions where the length scales are decreased, and 77% extraction is achieved in around 3 min. ATPS is characterized by low interfacial tension and obtaining slug flows in a microchannel is a challenge. We show that by using a milli channel we can lower the capillary number and obtain slug flow at higher flow rates. The internal circulations present in the slugs help in an accelerated mass transfer and 85% extraction is achieved in the PEG6000-salt system in 3 min.