Preparation and separation characteristics of polyelectrolyte complex membranes containing sulfated carboxymethyl cellulose for water–ethanol mixtures at low pH

Novel polyelectrolyte complexes based on sulfated carboxymethyl cellulose and chitosan were prepared, containing strongly charged (sulfate (OSO₃)) and weakly charged (carboxylate (COO^?)) groups (SPECs). SPEC homogeneous membranes (SPECMs) for the pervaporation dehydration of ethanol–water mixtures were investigated. The chemical structures and compositions of SPECMs were characterized by Fourier transform infrared spectroscopy and X-ray photoelectron spectra. The swelling behavior and separation performance of SPECMs in low pH feed were evaluated. It was found that the SPECMs containing OSO₃ groups were resistant to acidic feeds and showed very good separation performance even in low pH feed. For instance, the water content in permeate for SPECM-0.35 reached as high as 95.8 wt%, which was much higher than the 60 wt% for SPECM-0 in the dehydration of water–ethanol mixtures with pH 2. The result was attributed to the interplay between the stable complexation formed by OSO₃ groups and the improved ionization degree of COO^? groups in SPECMs. Moreover, the SPECMs maintained their operation stability against acidic feeds. The SPECMs could find considerable potential application in the pervaporation dehydration of acidic feeds, especially for enhancing the conversion of ester condensation.