الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
From the point of increasing awareness of energy cost, an impetus was borne to the de¬velopment of pressure-driven membranes which provide competitive performance, i.e. flux and rejection, at ultra-low pressure than those commercially available. In the present work, novel promising semipermeable cellulose-based membranes working under low pressure were fabricated and tested for desalination of saline water using an UF cell, and the effects of conditions of preparation on their characteristics were studied, as a further step on cost reduction of pure water production.
Previous work on different solvent mixtures used to dissolve CA polymer proved that one certain solvent mixture in which acetone, dioxane and DMF, with DMP as plasticizer gave optimum performance in dialysis ofNaCI and were therefore used in definite proport¬ions to dissolve CA, in the present work. In the preliminary experiments, some other solve¬nt mixtures were also used. The membranes were prepared by the phase inversion process using a casting assembly, followed by deacetylation of half of each membrane sheet. The membranes were then tested in two UF cells for flux and percent rejection determination. The membranes were then characterized by scanning electron microscopy to determine the skin layer thickness and total thickness of the membranes as well as their morphology. Also percent water content was determined.
This thesis consists of four chapters. The first chapter is concerned with the theoretical background. This chapter shows basics of membrane separations, different desalination te¬chniques, including RO as a desalination process, in addition to inter-related factors which affect membrane microstructure and consequently membrane performance. Also, it presen¬ts a literature review about RO membranes with special focus on asymmetric CA membra¬nes. Finally, aim of the work is highlighted. Experimental work is presented in chapter two in which how membranes are coded is clarified. Materials used, method of membrane pre¬paration and membrane characterization are described. Then conditions during membrane preparation and testing are summarized in table form. In the third chapter, results are pres¬ented and are discussed as average values of fluxes and percent rejections as a means of comparison among the membranes. In addition, SEM micrographs are presented to assess the membrane’s various microstructures as a function of the various preparation and test¬ing conditions. This chapter consists of three sections: section (A) shows preliminary expe¬riments that were carried out during which different variables were first investigated for their effect on the salt rejection and water flux. Based on these preliminary experiments, the optimum testing conditions for membranes, i.e. membrane area and time of run were determined. Section (B) pertains to the main experiments carried out based on results of the preliminary study. In this section, the influencing parameters in the overall porosity of an anisotropic membrane were divided under two formulation categories which are compo¬sition formulation parameters and casting formulation parameters. Composition formulati¬on parameters were a) polymer concentration; b) solvent composition; c) additive content, and d) deacetylation process. Casting formulation parameters were a) time of air exposure, i.e. casting time and ET; b) casting solution temperature; c) coagulation bath composition and temperature; d) as-cast membrane thickness; e) angle of membrane immersion in coag¬ulation bath, and f) nature, temperature, and humidity of casting atmosphere. Other param¬eters included a) membrane area; b) operation time (testing time); c) feed pressure, and d) feed concentration. Finally, Section (C) points out the suitability of selected membranes (regarding flux and %rejection) which could be used in either UF or RO applications in
table fonn. The conclusions drawn from the present work plus the recommendations for future work are presented in chapter four.
Results of UF tests showed that the skin layer thickness which is responsible for salt re¬jection, increases with increasing solvent evaporation rate, Le. increasing ET, casting solut¬ion- and coagulation bath- temperatures, and polymer concentration. In addition, the vari¬ation in skin layer thickness increases with increasing polymer concentration and casting solution temperature. At higher polymer concentrations, the membrane microstructure was the prime factor in effecting easy penneation of water than the ET and the thickness of the rejection layer. In general, fluxes of deacetylated CA membranes were considerably higher than acetylated ones. This effect decreases with increasing ET, Le. with increase in the skin layer thickness. In case of deacetylated membrane cast at 21°C casting solution temperat¬ure, 18.5 % polymer concentration, and 2 min ET, the BW membrane could be used as a very efficient UF membrane since its flux was the highest among all the membranes fabri¬cated in this work (11.94 kg/m2hr). It gave an outstanding flux which is by far better than other UF membranes reported in the literature. A wider range of membranes from deacety¬lated CA from a warm casting solution may be fabricated, a few of which can be applied in RO while others were suitable for UF. Decrease in coagulation bath temperature increased water flux and decreased salt rejection. For 0.5 min ET, the best perfonnance at 18.5% CA was attained at lower coagulation bath temJ,>erature coupled with hot casting solution temp¬erature for acetylated (average: 1.83 kg/m hr and 9.8% rejection) and deacetylated (avera¬ge: 6 kg/m2hr and 2.6% rejection) membranes, whereas the best perfonnance at 20.5% CA was obtained at lower coagulation bath temperature coupled with cold casting solution temperature for acetylated (average: 0.035 kg/m2hr and 73% rejection) and deacetylated (average: 0.7 kg/m2hr and 17% rejection) membranes for both SW and BW feeds. Fluxes were higher when using BW than SW. SEM micrographs for cross-sections of produced membranes proved increase of skin layer thickness with increase in solvent evaporation rate. Also, it showed change in the cross-section morphology with variation in preparation conditions.
The best produced membranes suitable for separations of macromolecules by UF are 18400CA membrane (average: flux 4.7 kg/m2hr; rejection 2.8%; polymer concentration 18.5%; casting time 40 sec; ET 0 min, casting solution temperature 15°C; coagulation bath temperature 14°C; RH 50%; air temperature 15°C; acetylated); 18402HD membrane (aver¬age: flux 7.7 kg/m2hr; rejection 0.89%; polymer concentration 18.5%; casting time 40 sec; ET 2 min; casting solution temperature 22°C; coagulation bath temperature 15.3°C; RH 65%; air temperature 15.9°C; deacetylated); 1840.5*HD (average: flux 6.16 kg/m2hr; rej¬ection 3.72%; polymer concentration 18.5%; casting time 40 see; ET 0.5 min; casting solu¬tion temperature 20°C; coagulation bath temperature 9.5°C; RH 66%; air temperature 22.4°C; deacetylated) and 1840.5*CD (average: flux 6.4 kg/m2hr; rejection 2.25%; poly¬mer concentration 18.5%; casting time 40 sec; ET 0.5 min; casting solution temperature 15°C; coagulation bath temperature 9.5°C; RH 62%; air temperature 22.4°C; deacetylated). While the best fabricated membranes suitable for desalination of saline water by RO, pro¬viding working on increasing their fluxes, are 18401HAS (average: flux 0.02 kg/m2hr; rejection 78.81 %; polymer concentration 18.5%; casting time 40 sec; ET 1 min; casting solution temperature 21°C; coagulation bath temperature 14.6°C; RH 64%; air temperature 15.8°C; acetylated; feed concentration 35.6 g/l NaCl); 2040.5*CAS (average: flux 0.04 kg/m2hr; rejection 77.1 %; polymer concentration 20.5%; casting time 40 sec; ET 0.5 min; casting solution temperature 15°C; coagulation bath temperature 9.5°C; RH 69%; air temperature 23.2°C; acetylated; feed concentration 35.6 g/l NaCl) and 2040.5*CAB
(average: flux 0.03 kg/m2hr; rejection 69%; polymer concentration 20.5%; casting time 40 see; ET 0.5 min; casting solution temperature 15°C; coagulation bath temperature 9.5°C; RH 69%; air temperature 23.2°C; acetylated; feed concentration 10.36 g/l NaCl).