Anti-fouling performance investigation of micron-submicron hierarchical structure PVDF membranes in water-in-oil emulsion separation

Membrane technology was widely used in the field of oil-water separation. In the process of water-in-oil emulsion treatment, surface contamination of hydrophobic and lipophilic membranes was a difficult problem. Therefore, the effect of hydrophobic membrane surface micro-rough structure on oil-water separation performance and its anti-fouling behavior has been investigated as a major focus of current research. Superhydrophobic-superoleophilic polyvinylidene fluoride (PVDF) membranes with micron-submicron hierarchical structure were prepared by combining thermally induced phase separation (TIPS) with rolling embossing. The influence of the roller temperature on the structure and performance of the membrane were discussed. The best achieved superhydrophobicity with a high water contact angle (WCA) of 154.8° and rolling angle (SA) of 1.9°, which was similar with lotus-effect. Meanwhile, the N2 flux was 197 L m−2 s−1 and LEP was 4.08 bar. Besides, the tensile strength of PVDF membrane was 1.89 MPa. The embossed membrane showed good lipophilicity, and the residence time of kerosene on the membrane surface was only 0.14 s. PVDF membranes with lotus leaf effect showed excellent demulsification performance and high recyclability in water in oil emulsion. The oil flux and rejection rate were 1258 L m−2 h−1 and 99.14%, respectively. In the separation experiment of PVDF membranes in diesel emulsion containing inorganic pollutant CaCO3, the results showed that the anti-fouling effect of PVDF membranes by cross-flow filtration method was obviously better than that by dead-end filtration method. When the operating temperature and pressure were 0.1 MPa and 45 °C, respectively, embossed membrane showed relatively excellent separation performance in cross-flow filtration. This study provided some guidance for the anti-fouling performance of roughened surface superhydrophobic-superoelophilicity membrane in oil-water separation experiment.