Pervaporative desalination application with metal organic framework structure doped hybrid polymeric membranes

Water is the most valuable natural resource for all living things on earth and is of vital importance. Although 75% of the Earth is water, fresh water resources suitable for drinking water and use are quite scarce. The available freshwater resources (0.3%) are decreasing day by day due to drought, climate change, industrialization and increasing population density. Therefore, desalination has become a good solution to deliver clean water to the community, converting salt water into fresh water from the almost unlimited supply of seawater. In this study, pervaporation(PV) process is used for desalination. Pervaporation has attracted a lot of attention due to its low energy consumption, easy operation, low cost, high separation performance and promising features for the separation of mixtures with sensitive and close boiling points. For this purpose, Polyvinyl alcohol (PVA) was synthesized for its superior membrane forming ability, ease of processing, abundant availability and high hydrophilicity in pervaporative desalination process and hydrophobic Polyvinylidine Fluoride (PVDF) which has the advantage of high thermal, chemical and mechanical resistance as well as oxidative resistance. Pervaporative desalination experiments were carried out with hybrid membranes formed by the addition of ZIF-8, which has a zeolitic imidazolate framework structure, high thermal and chemical stability, permanent pore size and shape, and flexibility properties, and HKUST-1, which is a practical and easily synthesizable metal organic framework (MOF) structure with high hydrophilic structure. The effects of ZIF-8 and HKUST-1 added to PVA and PVDF membranes, feed salt concentration and operation temperature on flux and salt removal were investigated. Optimum loading rates, optimum operating temperature and optimum feed salt concentration by weight were determined for both hybrid membranes. In order to improve the flux and desalination performance of these membranes, mixed matrix membranes were obtained by using metal organic framework structures ZIF-8 and HKUST-1 as additives. The effect of feed salt concentration and operation temperature on flux and desalination of hybrid membranes was investigated. Optimum loading rates, optimum operating temperature and optimum feed salt concentration by weight were determined for both hybrid membranes. SEM, FT-IR, XRD, TGA and contact angle analyses were performed for the characterization of the membranes. It was observed that ZIF-8 and HKUST-1 doping exhibited a good dispersion in the membrane. Desalination experiments were carried out based on the experimental parameters giving the best separation and salt rejection. As a result of the experiments, it was observed that membranes containing ZIF-8 and HKUST-1 increased the flux. The highest flux value of 99.94% in the synthesized PVDF / HKUST-1 doped hybrid membrane belongs to the membrane with 0.75% HKUST-1 concentration. In the PVA/ZIF-8 membrane, a ZIF-8 loading rate of 0.2% was found at a temperature of 60 °C and a feed salt concentration of 2 wt%. Pervaporative desalination tests of seawater under optimum operating conditions were carried out and removal performance above 99% was obtained.