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

Abstract

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 R 2 value of 0.94. The optimization efforts showed that relatively low temperatures, higher concentrations, and high flow rates favored higher selectivity.

Omniphobic, Bilayer Carbon Nanotube-Immobilized Fluorinated (FAS) Membranes for Bioethanol Recovery at High Concentrations via Membrane Distillation

“…The wetting property of membranes when exposed to increasing ethanol concentrations is an important consideration. , The contact angle at higher ethanol concentrations is an important parameter. This was performed using liquid droplets (4 μL) which were dropped on the membrane surface using a Hamilton microsyringe (0–10 μL), and a stage-mounted video camera was used to record its picture. ,,, A minimum of five readings was taken, and the average contact angle was reported. Based on the findings presented in Figure a, the PTFE demonstrated a water contact angle of approximately 120° and very minimal wetting resistance to ethanol.…”

“…Thermogravimetric analysis (TGA) was performed for the modified and unmodified samples using the PerkinElmer Pyris 7 TGA system ,,, and is displayed in Figure S3. Thermogravimetric analysis (TGA) was performed to study the thermal stability of modified and unmodified samples.…”

“…Here, P f is the feed side vapor pressure and P p is the permeate side vapor pressure. The vapor pressures of ethanol and water were calculated using the Antoine equation. ,,, Experimental fluxes were used for both ethanol and water to determine the mass transfer coefficient. k values are important to explain the permeation of solvents through membrane pores. k = J / ( P normalf − P normalp ) …”

“…Higher ethanol flux and separation factors are desired for better performance. Permeate separation index is an important expression to relate between flux and separation factor. ,,, This is expressed as below permeate separation index 0.25em ( PSI ) = α J where α is the separation factor and J is the ethanol flux. Since the separation factor is a dimensionless variable, PSI is expressed in the same units as the flux, which is expressed as kg/m 2 ·h.…”

“…The membrane samples, cut into 0.5 cm long pieces, were carboncoated for SEM imaging, following previously established protocols. 23,45,46,48,49 Figure 3 displays SEM images of both the unmodified PTFE membrane (control) and the modified membranes. In Figure 3a, the original PTFE membrane surface reveals interconnected pores and a relatively rough texture.…”