Preparation of high-performance pervaporation membranes for ethanol dehydration using a layer-by-layer self-assembly method

To achieve fuel-grade purity (≥99.5 ​wt%), raw bioethanol needs to be purified. Adopting pervaporation membrane for bioethanol enrichment can greatly reduce the energy consumption compared with distillation. However, this requires the membrane having a high flux and high water to ethanol selectivity as well as good stability. In this study, a layer-by-layer self-assembled composite pervaporation membrane was prepared by alternately dip-coating polyallylamine hydrochloride (PAH) and sodium alginate (SA) solutions on the surface of a polyacrylonitrile (PAN) microfiltration membrane. The membrane flux and separation performance under different feed conditions are measured independently, and the results are mutually independent. These tests are conducted as short-term experiments to evaluate the membrane's separation performance under specific feed conditions. By optimizing the concentrations of PAH and SA, best separation performance of the composite membranes was obtained with a flux of 2.02 ​kg ​m⁻² ​h⁻¹ and a water to ethanol separation factor of 10993 using a 90 ​% ethanol water solution as feed at 70 ​°C. The composite membrane showed good stability in water. When keeping all other conditions unchanged, the feed ethanol concentration is adjusted to 50 ​wt%, the membrane flux increase to 12.61 ​kg ​m⁻² ​h⁻¹, and the water concentration in the permeate reach 99.7743 ​wt%.