Fabrication and characterization of superhydrophobic PDMS composite membranes for efficient ethanol recovery via pervaporation

Abstract

Bio-ethanol, clean and renewable, has proved to be a promising alternative energy resource to replace conventional fossil fuels. In its continuous production via the fermentation–pervaporation process, hydrophobic polymer membranes such as polydimethylsiloxane (PDMS) have been developed to enrich ethanol from dilute fermentation broth. However, the efficiency of current ethanol recovery via pervaporation is not high enough for large-scale bioethanol production. To address this issue, we separately fabricated two types of lotus-inspired PDMS composite membranes to combine the beneficial properties (low surface energy and super-hydrophobicity) of superhydrophobic lotus leaves with the pervaporation process and optimized the separation performance. First, we prepared lotus leaf powder/PDMS mixed matrix membranes (MMMs) to exploit the intrinsic properties of lotus leaf’s material. In addition, polydivinylbenzene (PDVB)-coated PDMS composite membranes were fabricated to mimic and make use of the properties coming from the lotus leaf’s hierarchical structure. The morphology, surface chemistry, and pervaporation performance were systematically investigated for all the membranes. And results showed that MMMs at 1.5 wt% lotus powder loading displayed the ideal dispersion condition and increased the total flux of pervaporation process by 22% (750 g∙m−2∙h−1, 6 wt%, 37 °C). For the PDVB-coated PDMS membrane, the hierarchical roughness was successfully established on the PDMS surface, which resulted in a super-hydrophobic surface with water contact angle higher than 150°. As PDVB also has preferential adsorption for ethanol, the PDVB-coated PDMS membrane showed a higher ethanol recovery performance with the separation factor and total flux increased by 13% and 30%, respectively. Therefore, it was demonstrated that PDVB coating is an effective method to fabricate superhydrophobic membranes and both the two lotus-inspired strategies are feasible in optimizing pervaporation performance for ethanol recovery.