Continuous coalescence and separation of oil-in-water emulsion via polyacrylonitrile nanofibrous membrane coalescer

Abstract

Coalescence separation is an energy-efficient, physical separation method to enable the reuse of oil from oil-in-water (O/W) emulsions, which are widely found in industrial wastewater. However, traditional coalescers are generally ineffective in separating fine, emulsified oil droplets. Here, we applied the polyacrylonitrile (PAN) nanofibrous membrane possessing a three-dimensional network structure and high porosity to separate oil droplets smaller than 10 µm. We demonstrated that oil pieces floated on the surface of the discharged fluid. The continuous separation conducted under a flow rate of 40 mL/min was steady and with a separation ratio greater than 99.9% and a pressure drop of less than 25 kPa. In addition, an analysis of the amount of oil during the continuous operation indicated that the oil droplets did not form a cake layer, which would otherwise foul the membrane and hinder its long-term use. Moreover, the continuous separation of the surfactant-stabilized O/W emulsion with a SPAN20 concentration of 2 wt% in dodecane exhibited a high performance comparable to that of the surfactant-free emulsion. In conclusion, the PAN nanofibrous membrane exhibited excellent performances for the coalescence of fine oil droplets, demonstrating the industrial applicability of nanofibrous membranes for continuous O/W emulsion coalescence and separation.