Many parts of the world are facing water crises due to the lack of clean drinking water. Growing industrialization in many areas and extensive use of chemicals for various concerns has increased the burden of deleterious contaminants in drinking water especially in developing countries. It is reported that nearly half of the population in developing countries suffers from health problems associated with lack of potable drinking water as well as the presence of microbiologically contaminated water [1] . Synthetic and natural organic contaminants are considered among the most undesirable contaminants found in water. Various treatment processes are applied for the removal of organic contaminants from water including reverse osmosis membranes, ion exchange, oxidation, nanofiltration, and adsorption. The adsorption process is a widely-used technology for the removal of organic compounds from water. In this work, the adsorption of chloroform and methyl tertiary butyl ether (MTBE) onto granular zeolites was investigated. Zeolites were specifically chosen because they have shown higher efficiency in removing certain organics from water than granular activated carbon (GAC). Batch adsorption experiments to evaluate the effectiveness of several granular zeolites for the removal of MTBE and chloroform from water were conducted and the results compared with GAC performance. Results of these batch equilibrium experiments showed that ZSM-5 was the granular zeolite adsorbent with the greatest removal capacity for MTBE and chloroform from water, and outperformed GAC. Fixed-bed adsorption experiments with MTBE and chloroform were performed using granular ZSM-5. Breakthrough curves obtained from these column experiments were used to understand and predict the dynamic behavior of fixed bed adsorbers with granular ZSM-5. The ii film pore and surface diffusion model (FPSDM) was fit to the breakthrough curve data obtained from the fixed bed adsorption experiments. The FPSDM model takes into account the effects of axial dispersion, film diffusion, and intraparticle diffusion mechanisms during fixed bed adsorption. Generally, good agreement was obtained between the FPSDM simulated results and experimental breakthrough profiles. This study demonstrated that film diffusion is the primary controlling mass transfer mechanism and therefore must be accurately determined for good breakthrough predictions.

Microporous catalysts belong to a class of materials that exhibit pore networks in the molecular dimension, that is, channel diameters less than 2 nm. The industrially most important microporous catalysts are zeolites, which are crystalline aluminosilicates and consist of interlinked alumina (AlO4) and silica (SiO4) tetrahedra forming pores and cavities of molecular dimensions. Zeolites can act as very strong solid acids and function as heterogeneous catalysts in various industrial processes used to obtain polyethylene terephthalate (PET) or polyvinyl chloride (PVC). They are crucial for products with a significant market demand such as plastics used in bottles, packaging materials and household consumable goods as well as for coatings of pharmaceutical pills and detergents. Recently, zeolites have been found to have increased applications in aqueous and biphasic reactions that use reactants derived from biomass to arrive at petrochemical products. Thus, surface acidity in zeolites is crucial to understand to tune parameters such as activity and selectivity of zeolite catalysts to optimize product distributions. The objective of this dissertation was to validate the use of non-invasive nuclear magnetic resonance (NMR) techniques to characterise surface acidity in zeolites by benchmarking the NMR results to various more established zeolite characterisation techniques, such as Fourier transform infrared (FTIR) spectroscopy and temperature-programmed desorption (TPD). Furthermore, the use of the tapered element oscillating microbalance (TEOM) to characterise internal and external acidity in zeolites was explored. IR and TPD techniques were used to assess important acidity parameters such as type, number, location and strength of acid sites of ZSM-5 zeolites with varying silica-alumina ratio (SAR = SiO2/Al2O3). The use of NMR relaxation time analysis of pyridine adsorbed in ZSM-5 was then explored as a model system to study surface acidity in microporous materials. Correlation with pyridine TPD results suggested that NMR relaxation time analysis probes the effective strength of pyridine adsorption sites, which varies with SAR. NMR relaxation time analysis was then further shown to be applicable to characterise non-acidic surface properties such as the hydrophilic and hydrophobic surface character. Lastly, the NMR techniques developed at high magnetic field strength (300 MHz) were transferred to a portable, low-cost benchtop low-field (43 MHz) magnet and shown to be applicable for base probe molecules other than pyridine, that is, ammonia (NH3) as well as zeolite framework types other than ZSM-5, that is, chabazite (CHA).

Orientador: Leandro Martins / Banca: Regina Célia Galvão Frem / Banca: Dilson Cardoso / Resumo: Glycerol is the major by-product of biodiesel production. This organic compound has received much attention in recent years due to its growing supply, which has easily surpassed the demand. Therefore, there is a relevant necessity to find a destination for this product. Dehydration reaction is one of the most interesting and challenging routes, which produces acrolein in the presence of an acid catalyst. In order to have a catalytic dehydration of glycerol with high conversion and acrolein selectivity, it's important to develop an efficient acid catalyst. This outlook will be achieved from the coherent combination of several physicochemical characteristics of the catalyst, such as suitable acid strength and porosity. With respect to acidity control, the isomorphous substitution of heteroatoms in zeolite framework may reduce the Brønsted acidity, resulting in decreased coke formation during the catalytic reaction. With respect to porosity, it's possible to obtain hierarchically structured zeolites, which play an important role in molecular diffusion. In this way, the study of the synthesis of MWW and FER lamellar zeolites, incorporated with gallium and boron atoms is proposed. Lamellar zeolites are very interesting materials because they can be exfoliated, enhancing accessibility to active sites. The MWW and FER zeolites were synthesized with boron, aluminum and gallium atoms. The XRD patterns of the samples show that different heteroatoms induce the formation of different cry... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: O glicerol, coproduto da reação de transesterificação da síntese do biodiesel, tem recebido muita atenção nos últimos anos devido a sua ascendente oferta, que tem facilmente superado a sua demanda. Surge, portanto, a necessidade de se encontrar uma destinação adequada a este produto como forma de melhor aproveitamento e também para agregar valor à cadeia produtiva do biodiesel. A desidratação é uma das rotas mais interessantes e desafiadoras, a qual produz acroleína na presença de um catalisador ácido. Para que a reação catalítica de desidratação do glicerol ocorra com alta conversão e seletividade à acroleína, há a necessidade de desenvolvimento de um catalisador ácido eficiente. Isto ocorrerá a partir da combinação de várias características físico-químicas adequadas do catalisador, tais como a força ácida e a porosidade. Com relação ao controle da acidez, há a possibilidade de substituição isomórfica de heteroátomos que diminuem a acidez de Brønsted, o que poderia resultar na diminuição da formação de coque durante a reação e, consequentemente, em um melhor desempenho catalítico. Com relação à porosidade, há a possibilidade de se obter uma zeólita hierarquicamente estruturada, característica importante para solução das limitações difusionais do glicerol que apresenta diâmetro cinético da mesma ordem de grandeza dos poros das zeólitas. Desta forma, é proposto o estudo da síntese das zeólitas lamelares MWW e FER, incorporadas com átomos de gálio e boro. As zeólitas lamelares... (Complete abstract click electronic access below) / Mestre

No description available.

Thesis (M.S.)--University of Nevada, Reno, 2005. / "May, 2005." Includes bibliographical references (leaves 75-78). Online version available on the World Wide Web.

Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisors: Dionisios G. Vlachos and Raul F. Lobo, Dept. of Chemical Engineering Includes bibliographical references.

Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisor: Dionisios G. Vlachos, Dept. of Chemical Engineering. Includes bibliographical references.

No description available.

Zeolites are microporous crystalline materials, which are widely used in catalysis, adsorption, and ion-exchange processes. However, in most cases, the synthesis of novel zeolites as functional materials still relies on trial-and-error methods, which are time consuming and expensive. Therefore, the motivation for this thesis work is to understand the zeolite synthesis mechanismand further develop knowledge for manipulating zeolite properties and ultimately the rational design of porous materials. This work focused on formation of silicalite-1 (pure-silica ZSM-5) from basic aqueous solutions containing tetraorthosilicate (TEOS) as silica source, and tetrapropylammonium (TPA) cations as the organic structure-directing agent. The presence of silica precursor particles with size of 2-5 nm in these mixtures prior to and during hydrothermal treatments have been observed through dynamic light scattering (DLS), small-angle X-ray (SAXS) and transmission electron microscopy (TEM). However, to quantify composition and the molecular structure transformation of these silica precursor particles during zeolite synthesis is still a technical challenge. Another important yet unresolved question is how organocations interact with these nanoparticles and direct zeolite nuclei. Unlike many studies performed analyzing the inorganic phase (silica) present in synthesis mixtures, this study quantified the organocation-silica particle interaction and its ultimate effect on zeolite growth mainly through probing the behavior of the organocations. Pulsed-field gradient (PFG) NMR was used to capture the mobility change of organocations, and was complemented with scattering measurements (DLS, SAXS) on the silica nanoparticles. On the basis of the measurement results, the thermodynamic and kinetic properties of the organic-inorganic interaction were derived. Upon aging at room temperature, this interaction manifested as binding of TPA onto the silica particles due to electrostatic interactions, and such binding behavior can be well described by the Langmuir adsorption model. Upon hydrothermal treatment, a fraction of TPA adsorbed at room temperature dissociates from the growing silica nanoparticles and the corresponding desorption profiles were fitted well by the pseudo-second order kinetic model. The addition of tetramethylammonium (TMA) as "competitors" promoted TPA desorption kinetics and hindered silica nanoparticle growth due to stronger association of TMA with particles than that of TPA. Finally, the TPA adsorption strength increased via addition of monovalent salts with increasing ionic size whereas that of TMA shows an opposite trend. This suggests one potential route for tuning the organic-silica precursor particle interactions and thus possibly affecting some kinetics steps in the synthesis.

Recent work in the areas of zeolite membranes and mixed matrix membranes have inspired the development of isotropic microporous mixed matrix (ZeoTIPS) membranes, consisting of high-selectivity zeolite particles suspended in a cellular, microporous polymer matrix formed by thermally induced phase separation (TIPS). The particles form nanoporous connections between the cellular voids in the matrix, and can carry out separations independent of the choice of polymer matrix. Existing water purification and gas separation membranes have a variety of drawbacks, including durability, chemical instabilities, cost, flux, and formation difficulty. ZeoTIPS membranes address each of these drawbacks while yielding high selectivity. Included in this work are theoretical predictions of ZeoTIPS membrane performance along with models and experiments designed to gain fundamental knowledge that can be used to develop these membranes. This dissertation discusses how zeolite particles influence the processes of droplet coarsening and pore formation in thermally induced phase separation by disrupting flow fields as well as changing local compositions and viscosities. Additionally, a mathematical model is presented, leading to understanding of the ZeoTIPS formation process. Polymers used in these membranes must have acceptable interactions with the zeolite particles and desired mechanical properties, but must also be able to undergo thermally induced phase separation with a non-hazardous diluent under reasonable processing conditions. Furthermore, processing conditions such as cooling rate are of vast importance in forming ZeoTIPS membranes, but the required conditions can be difficult to obtain. Thus, development of these membranes has required extensive experimental research to determine feasible polymer--diluent systems for forming the microporous matrix and to develop methods of formation. / text