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In mining industries, the process combining ultrafiltration (UF) and reverse osmosis (RO) is often used for wastewater treatment, but RO brine discharge is a big issue. Membrane distillation (MD) has been proposed to solve this problem by significantly increasing the water recovery ratio, and recovering minerals. However, membranes with high hydrophobicity targeting for MD, particularly for vacuum membrane distillation (VMD) are still scarce. Hyflon AD is a novel candidate for fabricating membranes for MD. In this paper, the effects of membrane fabrication parameters, such as coating time, heat treatment and pre-filling were investigated and optimized. Membrane morphology, mechanical properties and VMD performance of the composite membranes were tested. The results showed that the hydrophobicity and elongation at break of the membrane were significantly improved after coating. The coating polymer concentration, coating time, heat treatment temperature and heat treatment time for the membrane coated by Hyflon AD40L and Hyflon AD40H, respectively were optimized. Monovalent alcohols can be excellent pre-filling agents to improve membrane performance. Separation performance of the membrane coated by Hyflon AD40H was better than that of the one coated by Hyflon AD40L. [ABSTRACT FROM AUTHOR]

Composite membranes were fabricated by coating three types of highly hydrophobic perfluorinated copolymers (commercial name: Hyflon AD) on poly(vinylidene fluoride) hollow fibers. The membrane properties, including morphologies, pore sizes, porosities, liquid entry pressures (LEPs), mechanical strength, and separation performance (flux, rejection and wettability) in vacuum membrane distillation (VMD) were systematically characterized and investigated. The properties of the fabricated membranes, including pore sizes, pore size distributions, porosities, and LEPs were significantly affected by the viscosity of the coating polymer solution. Coating solutions with lower viscosities caused smaller pore sizes, narrower pore size distributions, lower porosities, higher LEPs and less flux decline in VMD. Particularly, LEP of the membrane coated with a lower viscosity solution (0.46 MPa) was two times higher than that of the uncoated membrane (0.23 MPa). As a result, the anti-wetting property of the composite membrane after coating was significantly enhanced compared with that of the original membrane. The coated composite hollow fiber membranes also showed improved hydrophobicity, mechanical strength and separation performance (water flux and salt rejection). The water contact angle of the membrane increased from 94 to 145° after coating with a lower viscosity solution. [ABSTRACT FROM AUTHOR]

Throughout the world an intensified use of desalination for reducing current and future water scarcity is observed. Despite the enormous benefits of desalination processes, improvements are still required in terms of lower desalted water cost, higher productivity, better water quality and enhanced eco-sustainability of the desalination process. Environmentally sensitive concentrate management is today recognized as a significant hurdle to extensive implementation of desalination technologies. Membrane assisted crystallization (MCr) offers a suitable solution for redesigning desalination process through the treatment of brine streams for the production of salts and water. In this work, three different Hyflon/polyvinylidene fluoride (PVDF) composite membranes were tested in MCr operations. The coating of PVDF membranes with Hyflon allowed increasing membrane surface hydrophobicity. The latter is the membrane essential characteristic when MCr is implemented according direct contact membrane distillation configuration like in the present work. The aim was to analyze the MCr performance in terms of membrane chemical–physical properties and process operating conditions. [ABSTRACT FROM AUTHOR]