Surface Modification of PVDF Membranes for Treating Produced Waters by Direct Contact Membrane Distillation.

Direct contact membrane distillation (DCMD) has been conducted to treat hydraulic fracturing-produced water using polyvinylidenedifluoride (PVDF) membranes. Tailoring the surface properties of the membrane is critical in order to reduce the rate of adsorption of dissolved organic species as well as mineral salts. The PVDF membranes have been modified by grafting zwitterion and polyionic liquid-based polymer chains. In addition, surface oxidation of the PVDF membrane has been conducted using KMnO₄ and NaOH. Surface modification conditions were chosen in order to minimize the decrease in contact angle. Thus, the membranes remain hydrophobic, essential for suppression of wetting. DCMD was conducted using the base PVDF membrane as well as modified membranes. In addition, DCMD was conducted on the base membrane using produced water (PW) that was pretreated by electrocoagulation to remove dissolved organic compounds. After DCMD all membranes were analyzed by scanning electron microscopy imaging as well as Energy-Dispersive X-Ray spectroscopy. Surface modification led to a greater volume of PW being treated by the membrane prior to drastic flux decline. The results indicate that tailoring the surface properties of the membrane enhances fouling resistance and could reduce pretreatment requirements.