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

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 & mu;m. 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.