Selective Recovery of Ethyl Acetate by Air-Sparged Membrane Distillation Using Carbon Nanotube-Immobilized Membranes and Process Optimization via a Response Surface Approach

Ethyl acetate (EA) is an extensively used industrial solvent, and typically, aqueous mixtures containing EA are discarded as hazardous waste. The recovery of EA from wastewater streams would have significant environmental benefits and be a circular economy approach to solvent recycling. However, with a relatively high water solubility (8.3% w/v at room temperature), it remains a challenge. In this paper, we report the recovery of EA from water using air-sparged sweep gas membrane distillation (AS-SGMD) with carbon nanotube-immobilized membranes. A central composite rotatable design was used to study the effect of process parameters on flux and selectivity via conventional SGMD and AS-SGMD. The experiments were run at different operating conditions of temperature, concentration, and flow rate. The flux reached as high as 1.41 kg/m2 h–1, and selectivity as high as 10.8 was obtained. The introduction of air sparging improved the flux by as much as 12% and the selectivity by 17%. The response surfaces of flux and selectivity as a function of operating variables were studied, and regression models were developed. For both regular SGMD and AS-SGMD, the selectivity of EA recovery followed a quadratic model, while the flux showed a linear response. The predicted and experimental responses were in agreement with a R2 value of 0.94. The optimization efforts showed that relatively low temperatures, higher concentrations, and high flow rates favored higher selectivity.