Application of superomniphobic electrospun membrane for treatment of real produced water through membrane distillation

Abstract

A superomniphobic polyvinylidene fluoride (PVDF-F) membrane was fabricated through electronspinning to obtain an excellent antiwetting and antifouling property for the effective and efficient treatment of real produced water. Compared with pristine PVDF and hydroxyl functionalized PVDF (PVDF-O) membrane, PVDF-F membrane had a larger pore diameter, while its pure water flux was found to be lower than both. Neither liquids with high surface tension (water, ethanol) or low surface tension (sodium dodecyl sulfate (SDS) as surfactant, mineral oil) could wet the PVDF-F surface even up to 3 min of contact. During membrane distillation (MD) of 3.5 wt% of aquoues NaCl solution, PVDF-F could withstand 0.4 mM SDS solution without any wetting as seen from the conductivity of the permeate, which was not the case for the PVDF and PVDF-O membranes. After 18 h of MD operation using produced water, a significantly thick fouling layer was found on the PVDF and PVDF-O membranes containing Ca3(PO4)2, Sr3(PO4)2 and Mg3(PO4)2. However, PVDF-F had a very thin and reversible organic fouled layer, causing only 40% reduction in permeate flux and with a low permeate conductivity of 20 μS cm−1. This layer was easily removed by cleaning using distilled water and 80% of the flux was recovered. On the 2nd and 3rd MD cycle, the reduction in permeate flux was within 10%. The superomniphobic PVDF-F nanofibrous membrane was run for three successful consecutive MD cycles during produced water processing without any significant fouling as well as wetting.