Membrane materials for gas separations span a wide range including polymers, metals, ceramics and composites. Our aim is to create economical hydrothermally stable membranes that can provide high H₂-CO₂ separation at a temperature of 300 degree Celsius, for application in the water-gas shift reactor process. The present work describes the development of novel silica and silica-titania membranes from the controlled oxidative thermolysis of polydimethylsiloxane. The scope of this thesis is fabrication of membranes, material characterization and preliminary gas permeation tests (35-80 degree Celsius) on PDMS derived silica membrane films. The developed membranes can withstand up to 350 degree C in air. High permeabilties of small gas penetrants like He, H₂ and CO₂ have been observed and fairly high separation factors of O₂/N₂=3, H₂/N₂= 14 and H₂/CH₄=11 have been obtained. As the temperature of operation increases, the permeability of hydrogen increases and the separation factor of H₂ from CO₂ increases. The silica membranes exhibit gas separation factors higher than the respective Knudsen values. Additionally, design and construction of a new high temperature gas permeation testing system is described, which will cater to gas permeation tests at temperatures up to 300 degree Celsius for future work. The thesis also includes a detailed plan for future studies on this topic of research.

This collection of studies focuses on a PCO system for the oxidation of a model compound, ethanol, using an adsorption-enhanced silica-Ti02 composite (STC) as the photocatalyst; studies are aimed at addressing the optimization of various parameters including light source, humidity, temperature, and possible poisoning events for use as part of a system for gaseous trace-contaminant control system in closed-environment habitats. The first goal focused on distinguishing the effect of photon flux (i.e., photons per unit time reaching a surface) from that ofphoton energy (i.e., wavelength) of a photon source on the PCO of ethanol. Experiments were conducted in a bench-scale annular reactor packed with STC pellets and irradiated with either a UV -A fluorescent black light blue lamp O·max=365 nm) at its maximum light intensity or a UV -C germicidal lamp O.·max=254 nm) at three levels of light intensity. The STC-catalyzed oxidation of ethanol was found to follow zero-order kinetics with respect to C02 production, regardless of the photon source. Increased photon flux led to increased EtOH removal, mineralization, and oxidation rate accompanied by lower intermediate concentration in the effluent. The oxidation rate was higher in the reactor irradiated by UV -C than by UV-A (38.4 vs. 31.9 nM s-1 ) at the same photon flux, with similar trends for mineralization (53.9 vs. 43.4%) and reaction quantum efficiency (i.e., photonic efficiency, 63.3 vs. 50.1 nmol C02 ~mol photons-1 ). UV-C irradiation also led to decreased intermediate concentration in the effluent compared to UV -A irradiation. These results demonstrated that STC-catalyzed oxidation is enhanced by both increased photon flux and photon energy. The effect of temperature and relative humidity on the STC-catalyzed degradation of ethanol was also determined using the UV-A light source at its maximum intensity. Increasing ii temperature from 25°C to 65°C caused a significant decrease in ethanol adsorption (47.1% loss in adsorption capacity); minimal changes in EtOH removal; and ·a dramatic increase in mineralization (37.3 vs. 74.8%), PCO rate (25.8 vs. 53.2 nM s-1 ), and reaction quantum efficiency (42.7 vs. 82.5 nmol C02 J..Lmol phontons-1 ); intermediate acetaldehyde (ACD) evolution in the effluent was also decreased. By elevating the reactor temperature to 45°C, a -32% increase in reaction quantum efficiency was obtained over the use ofUV-C irradiation at room temperature; this also allowed for increased energy usage efficiency by utilizing both the light and heat energy of the UV-A light source. Higher relative humidity (RH) also caused a significant decrease (16.8 vs. 6.0 mg EtOH g STCs-1 ) in ethanol adsorption and dark adsorption 95% breakthrough times (48.5 vs.16.8 hours). Trends developed for ethanol adsorption correlated well with studies using methanol as the target VOC on a molar basis. At higher RH, ethanol removal and ACD evolution were increased while mineralization, PCO rate, and reaction quantum efficiency were decreased. These studies allowed for the development of empirical formulas to approximate EtOH removal, PCO rate, mineralization, and ACD evolution based on the parameters (light intensity, temperature, and RH) assessed. Poisoning events included long-term exposure to low-VOC laboratory air and episodic spikes of either Freon 218 or hexamethylcyclotrisiloxane. To date, all poisoning studies have shown minimal (0-6%) decreases in PCO rates, mineralization, and minimal increases in ACD evolution, with little change in EtOH removal. These results, while studies are still ongoing, show great promise of this technology for use as part of a trace contaminant control system for niche applications such as air processing onboard the ISS or other new spacecrafts.

No description available.

This thesis is dedicated to the exploration of fluid phases confined in nanoporous materials using Nuclear Magnetic Resonance (NMR) techniques, with an aim to benefit catalysis research. Included in this report are studies of pure fluids and their mixtures, confined in titania and silica catalyst supports. These investigations are conducted at industrially-relevant, high-temperature (≥ 180 °C) and high-pressure conditions (up to 13 bar), made possible by a pilot-scale chemical reactor unit, designed to operate inside the strong magnetic fields of an NMR spectrometer. NMR spectroscopy, relaxation and pulsed field gradient (PFG) diffusion experiments were performed on each of the systems discussed in this report. Cyclohexane was initially studied inside a porous titania catalyst support at 188 °C and various pressures up to 13 bar. The adsorption and desorption processes of the cyclohexane were observed, revealing a number of previously unobserved phenomena. In addition to an overall, averaged diffusion coefficient, a slow diffusion coefficient was observed within the PFG NMR data attributable to surface diffusive processes occurring within the material. Additionally, T1 relaxation studies were found to provide experimental evidence for the differing configurations of adsorbed layers on the adsorption and desorption branch of the isotherm. Cyclohexane was subsequently studied alongside fluorobenzene in a series of silica catalyst supports of 6 nm, 10 nm and 20 nm pore size. In doing this, it was hoped that the multiple phenomena observed in the titania experiments might be deconvoluted, allowing a greater level of insight. The diffusivities of the fluids were found to differ significantly between the materials, and greater evidence was found of the slow-diffusing surface phase in each of the materials. Additionally, concentrations of cyclohexane and fluorobenzene in the gas and adsorbed layers inside the pore space were calculated via the results of the PFG NMR experiments, providing a map of confined phase behaviour. Competitive adsorption effects were found to become more significant, the smaller the pore size of the material. The results of the cyclohexane and fluorobenzene in silica studies were modelled, using approaches available in the literature, which were found to give varying levels of prediction. The data set acquired in this thesis was found to provide a useful standard, against which current and future models of confined phase behaviour might be verified.

Orientador: Carlos Kenichi Suzuki / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-11T16:06:32Z (GMT). No. of bitstreams: 1 Nunes_ClaudiaCarvalho_M.pdf: 7074659 bytes, checksum: 4dec2d1e75a640341af023ba7541f5cb (MD5) Previous issue date: 2008 / Resumo: O sistema binário sílica titânia, SiO2-TiO2,apresenta grande interesse tecnológico devido as suas propriedades: ultra-baixo coeficiente de expansão térmico e alto índice de refração. As propriedades são dependentes da quantidade de dopante presente no material. A SiO2-TiO2 é usada na indústria de componentes fotônicos, tais como, lentes, micro-lentes, espelhos e fibras ópticas especiais. Um importante material óptico para litografia no extremo ultravioleta (EUVL) é caracterizado por concentrações próximas a 8 % em peso de TiO2, com estrutura amorfa e transparente num amplo espectro da região UV, visível e IV. A indústria óptico-eletrônica necessita de fibras ópticas sensoras com alto índice de refração. Este tipo de fibra pode ser obtido através da fabricação de uma fibra de SiO2-TiO2. Amostras com concentrações que variam de 1 a 14 % em peso TiO2 fabricadas pelo método do aerosol em chama foram caracterizadas quanto a suas propriedades estruturais e ópticas. As amostras com concentrações superiores a 7,5 % em peso apresentaram-se translúcidas ou opacas, e com estrutura octaédrica segundo dados de XANES (Absorção de Raios-X próximo à estrutura da borda). A difração de raios-X identificou a fase anatásio da titânia como estrutura octaédrica. Através de tratamentos térmicos a altas temperaturas em chama (> 1500 ºC) obtivemos amostras transparentes no visível, amorfa, contendo 8,2 % em peso. Foi obtido um material com índice de refração de 1,48 para concentração de 10 % em peso de TiO2. Portanto a SiO2-TiO2 é viável para a fabricação de uma fibra com alto índice de refração / Abstract: The binary SiO2-TiO2 system presents a great technological importance due to its special properties: ultra low thermal expansion and high refractive index. The properties depend on the amount of dopant present in material. The SiO2-TiO2 is used for the components of photonic industries, such as lenses, mirrors and special fiber optics. As an important optical material for extreme ultraviolet lithography (EUVL), it is characterized by concentrations of ~ 8 wt. % of TiO2, with amorphous structure and transparent for a large UV, visible and IR spectra. The optoelectronic industries needs optical fiber sensor that presents high refractive index. This kind of fiber can be produce by SiO2-TiO2 fiber production. Samples with concentrations varying in the range 1 to 14 wt. % TiO2 made by flame aerosol technique were characterized in terms of structural and optical properties. As-consolidated samples with concentrations up to 7.5 wt. % TiO2 presented itself translucent or opaque with octahedral structure, according to XANES data (X-ray absorption near-edge structure). The anatase phase of titania was identified by X-ray diffraction patterns. However, by high temperature flame heat treatments (> 1500 ºC), it was possible to obtain transparent SiO2-TiO2 materials in the visible range with concentration up to 8.2 wt. % TiO2. The material presents refractive index 1.48 with concentration about 10 wt. % TiO2. Therefore SiO2-TiO2 is feasible to fibers fabrication with high refractive index / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica