الفهرس 
Introduction and Review of literatureOnly 14 pages are availabe for public view
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Abstract
Reverse osmosis membrane provides a developed method for desalination of salt water and seawater. Interest in synthetic RO membranes and membrane processes is rapidly growing. Recently, RO membranes have been increasingly introduced as an effective and economical means for separation and purification of liquids. Membrane technologies do not involve phase change (evaporation then condensation) but used membrane as a barrier for selective permeation of water molecules and reject salts and others contamination. There are a number of polymer materials used in RO membranes for water desalination, the two major polymers are cellulose acetates and polyamides. Two main different techniques have been devolved for the production of polymeric RO membranes, namely (i) the phase separation technique for asymmetric membranes (cellulose acetate) and (ii) the interfacial polymerization technique used for production of composite thin film membranes (polyamide). In spite of the advantages of membrane based desalination process, membrane fouling remains a serious problem limiting the widespread use of membranes in water purification applications. Fouling refers to irreversible precipitation (inorganic, organic materials, suspended particles or bacteria) on the membrane surface and pores, which leads to blocking of pores resulted in a decrease in water flux and an increase in hydraulic resistances.
The main objective of this work is concerned with preparation of modified RO membranes with good antifouling properties which resist the bacterial adhesion on the membrane surface for using in salt water desalination.
To achieve this goal, this work is divided into two main parts:
The first part concerned with the synthesis of polyamide reverse osmosis membrane and its subsequent modification by zwitterionic homopolymer to improve the biofouling properties. To perform this goal, there are several steps were done. The first step in this process was the preparation of microporous polysulfone support membrane using phase inversion technique. Polysulfone (PSu) was dissolved in N,N-dimethyl formamide in presence of polyvinyl pyrrolidone as pore former. The polymer solution was casted onto glass plate using casting knife with 150 µm thickness, then the glass plate with the casted film immediately immersed into non-solvent bath (distilled water) for precipitation without any evaporation. After primary phase separation and membrane formation, the membrane was separated from the glass plate, washed with fresh distilled water and left in distilled water bath for at about 24 h for removing the solvent and water-soluble polymer, then the membrane is ready to cover with the polyamide selective thin layer by the second step (interfacial polymerization).
The interfacial polymerization was carried out between phenylenediamine dissolved in the aqueous phase and trimesoyl chloride dissolved in organic phase (n-Hexane) on the surface of the support membrane to obtain selective thin film polyamide layer. The third step was separate synthesis of zwitterionic polymer of 2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide [MEDSAH] by free radical solution polymerization. The forth step is dynamic coating of the zwitterionic polymer P[MEDSAH] onto the polyamide RO membrane in the filtration cell by in-situ filtration of the coating polymer in the crossflow filtration system. In order to verify the formation of membranes layers (support and selective thin film) and coating layer, they were characterized using FT-IR, SEM, AFM, and Confocal Laser Scanning Microscope (CLSM) were investigated. The RO membrane performance such as water flux, salt rejection and tendency to fouling were evaluated. The support polysulfone membrane was characterized using SEM, showing microporous structure of membrane surface, after polyamide formation on the support polysulfone membrane the morphology greatly different showing ridge valley structure characterized to successful interfacial polymerization of polyamide. The comparison of polyamide and polysulfone layers using FT-IR showing different band for polyamide at 1661 cm−1, that is characteristic of amide C=O stretching vibrations and a peak at 1730 cm-1 assigned to stretching vibrations of C=O group of carboxylic acid aroused from the hydrolysis of the acid chloride on the surface of polyamide layer accompanied with broad band at 3380 cm-1 assigned to OH stretching vibration.
After coating the zwitterionic polymer onto the polyamide membrane surface the coated layer was characterized with FT-IR showing absorption peaks at 963 cm-1 and 1040 cm-1 which are characteristic to quaternary ammonium (QA) and sulfonate (SO3-) groups of the P(MEDSAH) polymer respectively. SEM and AFM showing smoother surface for coated polyamide than uncoated polyamide membranes. Contact angle measurements largely decreased from about 78o to 35o when the coating concentration increasing from 0 to 800 mg/l and the membrane became more hydrophilic than the unmodified membrane.
Performance of coated and uncoated membranes indicating improved water flux and salt rejection properties by increasing the coating polymer concentration till certain value, afterward the water flux was declined due to blocking of the porous by the coating layer. The coated RO membrane by zwitterionic polymer significantly improved the antifouling properties of the membrane, which appear from the figures of Confocal Laser Scanning Microscopy that showed a significantly reduced number of bacteria attached to the surface of the modified membrane.
The second part of this work concerned with the preparation of cellulose acetate RO membranes with and without nanoparticles of chitosan. Phase inversion technique was used to prepare these membranes and different parameters that affect the membrane performance such as compositions of casting solution (cellulose acetate or cellulose triacetate and nanochitosan particles), evaporation time, annealing temperature, and applied pressure were studied. Different ratio of chitosan nanoparticles (1-8 %) relative to the solid content were added to CA casting solution. FT-IR indicated successful incorporation of nano particles into the membrane matrix. TGA and DSC showing there is no negative effect of nanochitosan on the thermal propertied of the base membrane.
The results of RO measurements indicated that by addition of nano chitosan particles the water flux largely increased with enhanced effect on the salt rejection of the membranes. The water flux for blank CA membrane increased from 6 l/m2.h to about 18 l/m2.h by increasing nanochitosan to 2% from the total solution, with increasing the salt rejection from 89% to 94% for 35 g/l NaCl model solution. The membranes of CA that contains nano particles of chitosan showed better resistance for bacterial adhesion as SEM Figures appeared. Different RO membranes were applied to test the desalination of different sources of salt water such as standard sea water, Medditerian (front of Alexandria) sea water and Qarun Lake water. The results indicated salt rejection about 98.5 for Qarun Lake and about 97.7 for standard and Alex sea water
Effect of blending of cellulose acetate with cellulose triacetate (CTA) was studied and the results showed enhanced water flux and salt rejection than pure CA membranes. The best composition ratio was CA: CTA (70:30). The morphology of the blend membranes presented from SEM showed the formation of asymmetric membranes with the macrovoid structure of the cross-section of the membrane. The effect of addition of nanochitosan particles showed decreased in salt rejection for all membranes that contain CTA with large increase in water flux.
The effect of addition of chitosan in the soluble form (soluble in formic acid) to CA membrane indicated largely increase in the water flux with decline in salt rejection of 35g/l NaCl aqueous solution.