Synthesis of low silica/alumina zeolite membranes in a flow system

Thesis Type: Postgraduate

Institution Of The Thesis: Orta Doğu Teknik Üniversitesi, Faculty of Engineering, Department of Chemical Engineering, Turkey

Approval Date: 2007




Zeolite A-type membranes are usually synthesized from hydrogels and rarely synthesized from clear solutions mostly in batch systems. Few studies were carried out using semi-continuous systems for zeolite A membrane synthesis. Zeolite A membranes are mainly used in pervaporation processes for separation of water from water/organic mixtures because of their hydrophilic property. In this study, zeolite A membranes were synthesized on -alumina supports from a clear solution with a molar composition of 49Na2O: 1Al2O: 5SiO2: 980H2O. Synthesis was done both in a batch system and in a flow system in which solution was circulated through the support under atmospheric pressure. Effects of synthesis temperature, time, flow rate and seeding on membrane formation were investigated. The membranes were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), single gas permeation measurements and pervaporation tests. In batch system, pure zeolite A membranes having cubic form of zeolite A was obtained for the syntheses carried out at 60°C for 24 h and 80°C for 8 h. Thicknesses of the membranes synthesized at 80°C and 60°C were about 2 m and 4 m, respectively. N2 permeances were 2*10-8 mol/m2sPa and 8*10-8 mol/m2sPa for of the membranes synthesized in the batch system at 60°C and 80°C, respectively. When synthesis was carried out in flow system pure and continuous zeolite A membranes were obtained for all conditions. Membranes synthesized at 60°C and 80°C had thicknesses of about 1.5 and 2 m, respectively. Lower N2 permeations were obtained for the membranes synthesized in flow system. It was observed that flow rate and seeding did not significantly affect the thickness of the membrane layer. The membranes synthesized in this study are significantly thinner than the membranes reported in the literature. Single gas permeation tests at 25°C for the membranes showed that comparable membranes with the ones in literature were obtained in this study. For a double layer membrane synthesized in flow system at 80°C for 8h separation factor about 3700 was obtained for the separation of 92:8 (wt.%) ethanol/water mixture at 45°C.