Product recovery in surfactant-based separation processes: Pervaporation of toluene from concentrated surfactant solutions

Aqueous micellar two-phase systems have been proposed for the cloud point extraction (CPE) of hazardous compounds or high valued products from aqueous solutions. The efficiency of the CPE strongly depends on the reuse of surfactant as well as the product recovery from the coacervate phase. In this work the membrane process pervaporation was successfully applied to remove contaminants from concentrated surfactant solutions. Experimental results show that a polyoctylmethylsiloxane membrane is the most suitable membrane to separate toluene from a 20 wt% Triton X-114 solution. Furthermore, it is demonstrated that trans-membrane fluxes decrease with increasing surfactant concentration. In case of toluene no correlation between concentration and depletion rate was observed. However, it was observed, that the viscosity of the solution is highly influenced by toluene concentration and thus, effects the efficiency of the pervaporation process. To improve the pervaporation performance the influence of temperature and volumetric flow rate on the depletion rate was investigated. The toluene depletion from surfactant-rich solution increases from 30.2% to 55.1% after 200 min by optimising these parameters. The presented results show that the product recovery after the cloud point extraction can successfully be fulfilled by pervaporation. Compared to alternative separation methods no loss of surfactant or excessive foaming was observed in any of the experiments.