Omniphobic braid-reinforced hollow fiber membranes for DCMD of oilfield produced water: The effect of process conditions on membrane performance

Recent efforts to realize appropriate hollow fiber membranes (HFMs) for treatment of complex wastewater such as oilfield produced water (PW) have resulted in designing unique surfaces like the omniphobic, for use in membrane distillation (MD) to combat pore wetting and fouling/scaling. However, HFMs, despite their unique advantages, suffer from mechanical inadequacies. The use of polyethylene terephthalate (PET) braid support to strengthen HFMs is gaining attraction for filtration membranes, although their application in MD is scarce. Herein, we report a pioneering omniphobic PET braid-reinforced HFMs (OBRMs) for application in direct contact membrane distillation (DCMD) of PW. The effects of feed type, feed flow rate, feed temperature, and prolonged testing on performance OBRMs are reported. From the obtained findings, a thin polymer (PVDF) layer (∼68 μm) with a single-layer finger-like structure allowed for good vapor flux (up to 15 kg/m2h) while omniphobic skin layer was instrumental in keeping oils and surfactants at bay. Complex PW feed is shown to have more adverse effect on strength of OBRMs than saltwater. Increased temperature negatively affects tensile strength while a turbulent flow regime keeps foulants at bay and mitigates fouling-assisted deterioration. Prolonged testing for nine DCMD cycles (72 h) of treating PW recorded flux recovery up to 85 %, with salt rejection remaining above 99.9 %, a total organic carbon (TOC) rejection up to 98 % and a decline in tensile strength of used membranes by 6.5 %.