Universal surface modification by aldehydes on polymeric membranes for isopropanol dehydration via pervaporation

This work reports a novel and facile aldehyde modification method to transform polymeric hollow fiber membranes for pervaporation dehydration of alcohols and biofuels with much enhanced separation performance and chemical stability. A universal approach consisting of hyper-branched polyethyleneimine (HPEI) pre-treatment and aldehyde modification was proposed and successfully applied to various polymeric membranes such as Torlon^®, Ultem^®, and PES hollow fibers with greatly improved separation performance. The surface modified hollow fibers were characterized by positron annihilation spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and water contact angle measurements, etc. Results show the HPEI pre-treatment not only mitigates surface defects but also augments membrane hydrophilicity favoring water transport, while the cross-linking reaction between HPEI and aldehydes tightens polymeric chains and enhances selectivity. Besides, the newly molecularly designed membranes display satisfactory separation performance at various feed temperatures and compositions as well as good long-term stability. This study may open up new perspectives to design advanced pervaporation membranes by synergistic combination of the super reactivity and unique chemical interactions from HPEI and aldehydes.