Superior separation of industrial oil-in-water emulsions utilizing surface patterned isotropic PES membranes

Abstract

Developing polymeric membranes for oily wastewater treatment has attracted great interest over the last few years. However, the low permeance and poor fouling resistance are considered the most challenging issues. Introducing topographic patterns on the membrane surface to increase active area and surface roughness is one practical strategy for reducing membrane fouling. Here, isotropic polyethersulfone (PES) membranes with line patterns and continuous sponge-like porous structure were prepared using phase separation micro-molding processes. Various techniques were used to characterize the morphologies and physicochemical properties of the as-prepared membranes. The surface wettability of the membranes was evaluated by measuring contact angle of a water drop in air and of industrial crude oil under water. The as-prepared membranes separation and antifouling performance were assessed using water permeance, oil rejection, and flux recovery ratio after emulsion filtration. The results showed that the patterned PES membrane has superior hydrophilic and antifouling capabilities, with a lower static water contact angle (CA) of 32° as compared to a flat PES membrane (CA = 39°). Furthermore, the patterned membrane had pure water permeance (PWP) of 8036 ± 65 L·h−1·m−2·bar−1, which was ∼ 68 % greater than that of the flat PES membrane. This is mainly attributable to the discernible increase in the membrane pore size distribution and the enhancement in membrane surface hydrophilicity due to the increase in surface roughness as a result of micro-patterning. The patterned membranes showed superior separation efficiency (>99.0 %) and permeance (7031 ± 65 L·h−1·m−2·bar−1) for the oil-in-water emulsion of 0.1 g·L−1. At a higher concentration of crude oil-in-water emulsion (50 g·L−1), the patterned PES membranes achieved promising permeance of 90 L/h.m2.bar and 99.9 % rejection. Furthermore, the flux recovery ratio of the patterned membrane exceeded 91 % after three consecutive cycles of dead-end filtration and backwashing with water, demonstrating the benefit of using micro-patterned membranes for treating high concentration and industrial oil-in-water emulsions.