Pressure-assisted vacuum filtration fabrication of polymer membranes with enhanced selectivity for the separation of an ethanol/carbon dioxide mixture

The membrane performance and effectiveness of fabrication are significant factors that determine the industrialization of membranes. In this study, a pressure-assisted vacuum filtration method was proposed to fabricate a sub-100 nm thin composite membrane using a homemade polyamide for the separation of an ethanol/carbon dioxide (CO₂) mixture. Because during bioethanol fermentation, a large amount of CO₂ can be produced, forming fermentation tail gas with vaporized ethanol, which should be separated to recover ethanol and reduce greenhouse CO₂ emissions. The fabrication conditions, including the size of the polymer coil and feed pressure, were investigated in detail. Characterization using a dynamic laser scatterometer and low-field nuclear magnetic resonance (NMR) was conducted to reveal the membrane properties. The membrane performance obtained by the pressure-assisted vacuum filtration method was compared with that obtained by the solution casting method, which was demonstrated to be 40 % higher. Meanwhile, when a smaller pore size of the substrate was used, a 56 nm thick composite membrane was obtained with an ethanol/CO₂ selectivity of 18 and an ethanol permeance of approximately 35000 GPU (1960 Barrer). Finally, the effects of the operating parameters, such as the feed concentration and stability, on the membrane performance were investigated. This study provides a valuable reference for the fabrication of ultrathin polymer membranes.