Zeolite membranes are attractive materials to separate gas and liquid mixtures. MFI is a widely studied zeolite type due to its ease of preparation and comparable pore size with the molecular size of many substances. In this study MFI type membranes were synthesized over porous &amp / #945 / -Al2O3 supports and characterized with XRD, SEM and gas permeation measurements. In the first part of this study the effect of soda concentration of the synthesis solution on the membrane morphology and crystal orientation was investigated. The synthesis was carried out from solutions with a molar composition of (0- 6.5)Na2O:25SiO2:6.9TPABr:1136H2O at 150oC. At soda concentrations between 0.45 and 1.8 the membrane layers with (h0h)/c-directed orientation were obtained. At lower and higher soda concentrations membrane layer formed from randomly oriented crystals. The (h0h)/c-oriented membranes showed H2/n-C4H10 ideal selectivities of 478 and 36 at 25&deg / C and 150&deg / C, respectively.In the second part, MFI membranes were synthesized from mixtures with different concentrations of template molecules. Tetrapropylammonium hydroxide, tetrapropylammonium bromide or mixture of both types were used as template. The nucleation period, the size of MFI crystals, membrane thickness decreased as the tetrapropylammonium hydroxide concentration increased. Besides conversion of SiO2 in the synthesis solution to MFI passed through a maximum with increasing concentration of tetrapropylammonium hydroxide in the synthesis solution. When tetrapropylammonium bromide was used as template thicker membranes were obtained. In the third part MFI type membranes with a thickness of 1.5-2 &amp / #956 / m were synthesized by mid-synthesis addition of silica to the synthesis medium. The membranes synthesized with and without mid-synthesis addition of silica have n-C4H10/i-C4H10 ideal selectivities of 47 and 8 at 100oC, respectively. The change of composition during the synthesis increases the crystal growth rate and the size of the crystals forming the membrane, thus better quality membranes can be obtained by mid-synthesis addition of silica to the synthesis medium. In the last part of this study, thin MFI type zeolite membranes were synthesized in a recirculating flow system at 95&deg / C on the inner side of the tubular &amp / #945 / - alumina supports. A membrane synthesized by two consecutive synthesis steps had a separation selectivity of 38 and 86 for equimolar mixtures of n- C4H10/CH4 and n-C4H10/N2 at 25oC, respectively. The membrane selectively permeated large n-C4H10 over small CH4 and N2, suggesting that the separation is essentially adsorption-based and the membrane has few nonselective intercrystalline pores.

abstract: Ordered mesoporous materials have tunable pore sizes between 2 and 50 nm and are characterized by ordered pore structures and high surface areas (~1000 m2/g). This makes them particularly favorable for a number of membrane applications such as protein separation, polymer extrusion, nanowire fabrication and membrane reactors. These membranes can be fabricated as top-layers on macroporous supports or as embedded membranes in a dense matrix. The first part of the work deals with the hydrothermal synthesis and water-vapor/oxygen separation properties of supported MCM-48 and a new Al-MCM-48 type membrane for potential use in air conditioning systems. Knudsen-type permeation is observed in these membranes. The combined effect of capillary condensation and the aluminosilicate matrix resulted in the highest separation factor (142) in Al-MCM-48 membranes, with a water vapor permeance of 6×10-8mol/m2Pas. The second part focuses on synthesis of embedded mesoporous silica membranes with helically ordered pores by a novel Counter Diffusion Self-Assembly (CDSA) method. This method is an extension of the interfacial synthesis method for fiber synthesis using tetrabutylorthosilicate (TBOS) and cetyltrimethylammonium bromide (CTAB) as the silica source and surfactant respectively. The initial part of this study determined the effect of TBOS height and humidity on fiber formation. From this study, the range of TBOS heights for best microscopic and macroscopic ordering were established. Next, the CDSA method was used to successfully synthesize membranes, which were characterized to have good support plugging and an ordered pore structure. Factors that influence membrane synthesis and plug microstructure were determined. SEM studies revealed the presence of gaps between the plugs and support pores, which occur due to shrinking of the plug on drying. Development of a novel liquid deposition method to seal these defects constituted the last part of this work. Post sealing, excess silica was removed by etching with hydrofluoric acid. Membrane quality was evaluated at each step using SEM and gas permeation measurements. After surfactant removal by liquid extraction, the membranes exhibited an O2 permeance of 1.65x10-6mol/m2.Pa.s and He/O2 selectivity of 3.30. The successful synthesis of this membrane is an exciting new development in the area of ordered mesoporous membrane technology. / Dissertation/Thesis / Ph.D. Chemical Engineering 2011