(381p) Application of Micropatterned and Chemically Modified PVDF Membranes for the Treatment of Produced Water Via Membrane Distillation

Produced water, specifically fracking wastewater, is considered as one of the principle waste streams from the oil and gas industries. Along with a high concentration of salts, fracking wastewater contains a wide range of harmful contaminants such as heavy metals, emulsified oil, and other organics, which pose serious environmental challenges. According to the Environment America Research & Policy Center, in United States, fracking wells located in seven states generated around 14 billion gallons of wastewater in 2014 and the amount is likely to increase in the future. Some of the techniques used to treat this water include filtration, cyclonic separation, flotation, evaporation, and deep well injection. However, most of these techniques require a large amount of energy for operation. Recently, membrane distillation (MD) has emerged as a promising candidate for treating fracking wastewater due to its energy efficiency. In contrast to other membrane processes where pressure is used as the driving force, MD is a thermal-driven separation process where water from the feed side (hot temperature side) transports to the permeate side (cold temperature side) through a hydrophobic membrane as vapor molecules. As fracking wastewater usually has a higher temperature than ambient temperature, the feed is not required to be heated which makes MD an energy efficient technique. Though MD is an effective way to treat fracking wastewater, flux reduction due to oil fouling of the hydrophobic membrane is a problematic issue. Because of oil fouling, the maintenance costs are high which makes the technique costly. As such, an efficient and cost-effective strategy is required to mitigate the fouling and will have significant economic and environmental impacts.

Previously, most of the strategies employed for mitigating oil fouling have been based on the surface chemistry modification of membranes. Recent studies showed that surface chemistry modification alone is not sufficient to tackle the problem. Membranes modified with a specific, ordered surface pattern exhibited reduction of fouling. The finding that patterning of membrane surfaces can enhance their resistivity towards fouling makes patterning a crucial parameter for membrane design. Based on the prior studies, we hypothesize that the combination of surface chemistry modification and surface patterning will make a membrane surface more effective in combatting oil fouling than either method alone.

In this work, a couple of micropatterns were imparted onto the surface of commercial polyvinylidene fluoride (PVDF) membranes by thermal embossing followed by the UV photopolymerization of a sulfobetaine zwitterionic polymer to the PVDF membrane surface as the antifouling coating. Profilometry and SEM were used for characterizing the pattern replication, whereas the surface chemistry modification was characterized by ATR-FTIR and contact angle. The modified membranes were tested in a custom membrane distillation system to compare their water flux performance and fouling resistance to the pristine membrane.