Development of underwater superoleophobic polyamide-imide (PAI) microfiltration membranes for oil/water emulsion separation

Fouling of microfiltration membranes by the adhesion of oil onto the membrane surface and/or penetration into its pores is a major challenge for effective treatment of oily wastewater. In this study, polyamide-imide (PAI) was used to make hydrophilic and underwater superoleophobic microfiltration membranes via non-solvent induced phase separation technique. Membranes were modified with hydrophilic additives, including polyethylene glycol (PEG, 0.4 and 6 kDa) and polyvinylpyrrolidone (PVP, 10 and 360 kDa) to improve their hydrophilicity further. Oil rejection experiments were conducted for three consecutive cycles at a very low transmembrane pressure (0.5 bar) to evaluate the reusability of the synthesized membranes. The use of additives resulted in a wide range of membrane morphology, porosity, pore size, and surface chemical property, which affected the permeation rate and flux recovery. However, all synthesized membranes showed > 98% oil rejection with permeation rate as high as 210 Lm(-2) h(-1). Membranes modified with PEG 0.4 kDa, PEG 6 kDa, and PVP 10 kDa had underwater oil contact angle (OCA) above 150 degrees and showed almost 98% flux recovery ratio. In the case of PVP 360 kDa, a lower flux recovery was observed due to a reduced oleophobic property (OCA = 124 degrees). This study proposes a facile approach for the production of high-performance oil-rejecting membranes without employing complex surface modification methods.