Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Modelling of Asymmetric Membrane Formation by Dry Casting Method(Izmir Institute of Technology, 2001) Özbaş, Bülent; Alsoy Altınkaya, SacideMany polymeric membranes are produced by phase inversion technique invented by Loeb and Sourirajan in 1962. One of the most challenging problems in membrane industry is to produce membranes with desirable structural characteristics which cause best performance for a specific application. The solution of this problem is facilitated by the development of mathematical models. The polymeric membrane formation process is a complicated process due to phase separation, simultaneous heat and mass transfer mechanisms controlled by complex thermodynamic and transport properties of polymer solutions. In this work, a fully predictive mathematical model developed by Alsoy (1998) was used to describe the mechanisms of membrane formation by dry casting method. Model equations consist of coupled unsteady state heat and mass transfer equations, film shrinkage as well as complex boundary conditions especially at polymer gas interface. A key component of the model is incorporation of multicomponent diffusion coefficients that consist of thermodynamic factors and self-diffusivities. The predictions from the model provide composition paths, temperature and thickness of the membrane. The beginning of phase transition was determined when compositions paths were plotted on the phase diagram. The model was applied to cellulose acetate/acetone/water system which is commonly used for asymmetric membrane formation. The model was used as a tool to optimize membrane formation process by investigating the effect of gas phase conditions, initial thickness and composition of the cast solution on the final membrane structure. The predictive ability of the model was evaluated by comparison with the data obtained from gravimetric measurements. Structural studies were conducted using scanning electron microscopy. Also, the permeability of prepared membranes to water vapor was measured using steady state technique. Both experimental and predicted results indicated that morphologies ranging from dense nonporous to asymmetric ones, in which a dense skin layer is supported by a porous layer, can be obtained with dry cast technique.Master Thesis The Use and Characterization of Composite Alumina-Titania Membranes for Gas Separation(Izmir Institute of Technology, 2002) Topuz, Berna; Çiftçioğlu, MuhsinThe preparation, characterization and pure gas permeation of sol-gel derived alumina and silica membranes were investigated in this work. The effects of various parameters on sol particle size and unsupported membranes pore structure were investigated by laser light scattering particle size and N2 adsorption-desorption analysis .-alumina membranes were prepared on ZrO2 supports by successive dipping into boehmite sols. Almost proportional decreases in sol particle size and membrane pore diameter were determined with increasing acid content during the boehmite sol preparation. Increasing the H+/Al3+ mole ratio from 0.1 to 0.25 caused the hydrodynamic particle size and BJH pore size to decrease from 65 to 30 nm and 3.6 to 2.9 nm, respectively. The pore size increased from 2.8 nm to 3 nm upon increasing the calcination temperature from 500 to 600oC. Unsupported membranes were heat treated in the 200 to 1200 oC range for the characterization of the phase structure. Boehmite was the dominant phase below 500 oC, gamma being the dominant phase up to 900 oC and pure .-Al2O3 phase was obtained upon heat treatment at 1200oC. Pinhole and crack free alumina membranes about 3 .m (double layer) in thickness were observed from SEM pictures with insignificant infiltration. The CO2 permeability through the double layer .-Al2O3 membrane calcined at 600 oC was about 2.25*10-7 mol/m2.s.Pa, and had a slight pressure dependence which may indicate Knudsen Diffusion and Laminar Flow as the effective transport mechanisms. Upon the calcination of a similar double layer alumina membrane at 500oC, the CO2 permeability decreased to 1.51*10-8 mol/m2.s.Pa and was independent of pressure. Silica membranes were prepared by a sol-gel technique. These sols were prepared by acid catalysed hydrolysis and condensation of tetraethylorthosilicate in the presence of a solvent. The effects of processing parameters like the acid type and amount utilized during sol preparation, sol aging, heat treatment conditions, dipping time on the membrane pore structure and the permeation of pure gases were investigated. The supported membranes were heat treated in the 50-400 oC range. The N2 and CO2 permeabilities of silica membranes varied in the 2.2 * 10-10 . 2.7 * 10-8 mol / m2.s.Pa and 1.2*10-9 . 6.95*10-8 mol / m2.s.Pa range for single layer membranes dipped for 10 seconds into the sol. The sols became viscous and gelled in 16 hours at 50 oC. The O2 permeability increased with aging time. The optimum dipping time during processing was determined to be 10 seconds. The permeabilities of these membranes increased significantly with the sol acid content. The thickness of the silica membranes were determined to be about 2.m and significant infiltration into the support was observed from the SEM pictures.