Preparation of acid-resistant PEI/SA composite membranes for the pervaporation dehydration of ethanol at low pH

Pervaporation is an efficient process for recovering bioethanol produced from biomass fermentation, which often contains ethanol, water, and a variety of acids compounds. However, it is still a major challenge to fabricate pervaporation membranes with good acid resistance capability and high separation performance. In order to separate ethanol/water mixtures consisted of inorganic or organic acid over a range of pH environments, we prepared polyelectrolyte multilayer membranes via ionic cross-linking between polyethyleneimine (PEI) and sodium alginate (SA). In this study, PEI and SA were alternatively deposited on ultrafiltration support membrane by using dynamic layer-by-layer (LbL) technique. The ionic cross-linking between the COO− groups of SA and -NH2 groups of PEI has been demonstrated using FTIR. It was found that the multilayer membranes showed high pervaporation performance in acid conditions. The water content could be enriched from 10 wt% to 99.42 wt% (β = 1542) and the permeate flux was 1.203 kg/(m2 h) in the dehydration of ethanol/water mixture with pH = 3 at 60 °C. Long time operations showed that water content in permeate fluctuated above 99.3 wt%, and permeation flux stayed stable around 0.88 kg/(m2 h), which indicated that (SA/PEI)1.5/PAN membrane has promising potential for dehydration of acid feed.