چكيده به لاتين
Membrane distillation is a process that has been extensively studied for the production of pure water, concentration of solutions, purification of effluent streams. This process is relatively new and has been proposed as a suitable alternative to conventional separation processes such as distillation and reverse osmosis due to its low cost and energy savings.
The aim of this study is to synthesize titanium dioxide nanotubes and then synthesize polyvinylidene fluoride membrane (PVDF) and its modification with titanium dioxide nanotubes for use in the laboratory scale membrane distillation process. Increasing the mechanical properties and porosity of the membranes are intended to improve the efficiency of the membrane distillation.
In this study, titanium dioxide (TNT) nanotubes were first successfully synthesized using titanium dioxide (TiO2) nanoparticles along with sodium hydroxide (NaOH) in autoclave by hydrothermal method. The structure of the synthesized nanotubes was characterized by performing various analyzes such as X-ray diffraction (XRD), scanning electron microscopy (SEM) and field emission electron microscopy (FE-SEM), transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) spectroscopy. The (XRD) spectrum of the samples confirmed the formation of titanium dioxide nanotube structures in the pure anatase phase. The (FE-SEM) images showed that the hydrothermal product was a dense mass of nanotubes. The (TEM) images confirmed formation of the nanotube structure with higher resolution.
The effect of operational parameters such as feed concentration, feed flow intensity and feed temperature was investigated using the experimental design method (CCD RSM-) with 15 experiments and the optimal conditions were determined.
Subsequently, the mixed matrix membranes containing titanium dioxide nanotubes were fabricated using polyvinylidene fluoride (PVDF) polymer and dimethyl acetamide (DMAC) solvent by phase inversion method and their performance were evaluated in vacuum membrane distillation process. The structural properties of the fabricated membranes were evaluated by (SEM), (FE-SEM) and (TEM) analysis and contact angle measurement. The effect of using different concentrations of titanium dioxide nanotubes on the performance of the fabricated membranes in the vacuum membrane distillation process (VMD) was investigated. Pure water flux and salt rejection were measured during the vacuum membrane distillation process.
The results show that the addition of titanium dioxide nanotubes has improved the performance of the mixed matrix membranes by improving membrane structure, such as increasing the size of surface cavities, increasing finger-like cavities, and thus increasing porosity. The fabricated membrane containing 2 wt.% of titanium dioxide nanotubes was recognized as the optimal membrane, which compared to pure membrane, showed about 30% enhancement in pure water flux and (99.9%) salt excretion at temperature of (70 C) and vacuum pressure of (0.8 bar).
The results of this study showed that titanium dioxide nanotubes can improve the structure of the PVDF membrane. Hydrophilic titanium oxide can intensify anti-solvent effect in the phase inversion process. In fact, the presence of hydrophilic titanium dioxide nanotubes can accelerate the infiltration of water into the polymer film and form a membrane with larger pores. As a result, as the amount of nanotubes in the membrane network increases, the porosity of the membranes increases and larger and more elongated finger-like holes are formed, which can increase the amount of flux passing through the membrane.
Other effects of titanium dioxide nanotubes addition into membranes include increasing mechanical strength of the membrane and also increasing salt rejection.
