Made available in DSpace on 2014-12-17T15:42:06Z (GMT). No. of bitstreams: 1 ReusTR_DISSERT.pdf: 4094188 bytes, checksum: 4969fc6bf4243a6e241302a399783473 (MD5) Previous issue date: 2013-07-22 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The synthesis of MFI-type zeolite membranes was carried by the process in situ or hydrothermal crystallization. We studied the homogenization time of the room temperature and gel filtration just before the crystallization step performed out in an oven, thus obtaining a more uniform zeolite film. The powder synthesized zeolite (structure type MFI, Silicalite) was characterized by several complementary techniques such as Xray diffraction (XRD), scanning electron microscopy (SEM), thermal analysis, temperature programmed desorption (TPD), Fourier Transform infrared spectroscopy (FTIR) and textural analysis by nitrogen adsorption (specific surface area). For the purpose of evaluating the quality of the layer supported on the ceramic support, N2 permeation tests were carried starting from room temperature to 600 ?C, where values were observed values more appropriate permeation from 200 ?C. With the data obtained, it was made into a graph of temperature versus permeation function, the curve of surface diffusion was found. For scanning electron microscopy, we observed the formation of homogeneous crystals and the zeolite film showed no fissures or cracks, indicating that the process of synthesis and subsequent treatments not damaged the zeolite layer on the support. Carried permeation studies were found values ranging from 3.64x10-6 to 3.78x10-6, 4.71x10-6 to 5.02x10-6, to pressures 20 and 25 psi, respectively. And the mixture xylenes/N2 values were between 5.39x10-6 to 5.67x10-6 and 8.13x10-6 to 8.36x10-6, also for pressures of 20 and 25 psi. The values found for the separation factor were 15.22 at 400 ?C in the first experiment and 1.64 for the second experiment at a temperature of 150 ?C. It is concluded that the Silicalite membrane was successfully synthesized and that it is effective in the separation of binary mixtures of xylenes / A s?ntese de membranas zeol?ticas do tipo MFI foi realizada pelo processo de cristaliza??o in situ ou hidrot?rmica. Foi estudado o tempo de homogeneiza??o do gel em temperatura ambiente e filtra??o do mesmo antes da etapa de cristaliza??o efetuada em estufa, obtendo-se um filme zeol?tico uniforme. O p? da ze?lita sintetizada (estrutura tipo MFI, Silicalita) foi caracterizado por diversas t?cnicas complementares, como: difra??o de raios X (DRX), microscopia eletr?nica de varredura (MEV), an?lise t?rmica, dessor??o a temperatura programada (TPD), infravermelho por transformada de Fourier (FTIR) e an?lise textural por adsor??o de nitrog?nio (?rea espec?fica). Com a finalidade de avaliar a qualidade da camada suportada sobre o suporte cer?mico, testes de permea??o com N2 foram efetuados partindo da temperatura ambiente at? 600 ?C, onde foram observados valores mais adequados de permea??o a partir dos 200 ?C. Com os dados obtidos confeccionou-se um gr?fico em fun??o da temperatura versus a permea??o, a curva encontrada foi de difus?o superficial. Por microscopia eletr?nica de varredura, observouse a forma??o de cristais homog?neos e que o filme zeol?tico n?o apresentava fissuras ou rachaduras, indicando que o processo de s?ntese e tratamentos posteriores n?o danificaram a camada de ze?lita sobre o suporte. Realizando estudos de permea??o foram verificados valores que variam entre 3,64x10-6 a 3,78x10-6 e 4,71x10-6 a 5,02x10-6, para press?es de 20 e 25 psi, respectivamente. Para a mistura xilenos/N2 os valores foram de 5,39x10-6 a 5,67x10-6 e 8,13x10-6 a 8,36x10-6, tamb?m para press?es de 20 e 25 psi. Os valores encontrados para o fator de separa??o foram de 15,22 em 400 ?C no primeiro experimento e 1, 64 para o segundo experimento em uma temperatura de 150 ?C. Conclui-se que a membrana Silicalita foi sintetizada com sucesso e que a mesma ? efetiva na separa??o de misturas bin?rias de xilenos

Zeolite nucleation and growth is a complex problem that has been widely investigated but still not completely understood. However, a full understanding of this process is required in order to develop predictive models for the rational design and control of the zeolite properties. The primary objective of this dissertation is to determine the strength of organicinorganic interactions (i.e., the adsorption Gibbs energy) in transparent synthesis mixtures using PFG NMR spectroscopy, in order to provide more information for a better understanding of zeolite nucleation and growth. Three main tasks were conducted in this work. The first was an investigation of the organocation role in precursor mixtures of silicalite-1, where the Gibbs energy of the organocation adsorption on the silica particles was determined at 25 degrees C. The findings showed that small changes in the adsorption Gibbs energy resulting from the differences in the molecular structure of the organocations lead to large changes in both the stability of the precursor particles and the rate of silicalite-1 formation. The second was an in situ PFG NMR investigation of silicalite-1 synthesis mixtures, where the adsorption Gibbs energy was determined at 25 degrees C and 70 degrees C, and the time evolution of silicalite-1 was monitored at synthesis conditions. The findings showed similar adsorption Gibbs energies at 25 degrees C and 70 degrees C. Also, a maximum in the organocation diffusion coefficients was observed during the time evolution of silicalite-1, which was associated with the exothermicendothermic transition occurring during the synthesis. The third was a systematic investigation of silicalite-1 precursor mixtures with varying degrees of dilution, where the effect of the composition of the mixtures on their conductivity, pH and particle size distribution (PSD) was studied. The results showed that conductivity, pH, and PSD are strongly affected by the mixture composition. The main conclusion of this research is that the strength of the organic-inorganic interactions in transparent synthesis mixtures can be determined from experimental data of the organocation self-diffusion coefficients obtained with PFG NMR spectroscopy. The outcome information of this research should contribute to the development of a more detailed molecular-level description of the zeolite nucleation and growth, which is expected to allow the emergence of a new generation of materials by design.

The study of adsorption of n-alkanes in zeolite pores represents both a fundamental problem in molecular thermodynamics and also a problem with substantial industrial importance. Until mid 19th century, adsorption was mainly used for purification processes such as removal of H2S and mercaptans from natural gas and organic matter from water. However, with the emergence of molecular sieves, especially zeolites, adsorption processes have become an attractive alter- native to distillation in large scale separation of mixtures that have low relative volatility into streams each enriched in one of the components. The pore di- ameters of molecular sieves are of the order of molecular diameters and hence selective adsorption can be achieved by both a difference in adsorbate-adsorbent interactions of various species and obstruction by the pore walls to some of the species in the mixture. The existing adsorption theories such as Henry’s law, Langmuir adsorption model and BET isotherm are incapable of predicting the adsorption isotherms of n-alkanes in zeolite pores. The reason is that in microporous adsorbents, the sorbate molecular mechanisms are influenced by geometrical constraints also. This limitation in the use of theory can be overcome by developing a molecular model and using computers to mimic the real system. This nature of simulation is called molecular simulations. With the development of advanced algorithms, improved force-field parameters and very high computational power of present day computers, molecular simulations have become an important tool in studying adsorption on micro-porous materials. Adsorption experiments of mixtures of long chain alkanes into silicalite under liquid phase conditions show selectivity inversion and azeotrope formation. These effects are due to the subtle interplay between the size of the adsorbed molecules and pore topology of the adsorbent. The underlying molecular mechanisms responsible for selective uptake of one of the components cannot be obtained from experiments but can be realized through simulations. Therefore, in this study, the selective uptake of lighter component during liquid phase adsorption of C14/C15 and C15/C16 n-alkane binary mixtures in the zeolite silicalite is understood through configurational bias grand canonical Monte Carlo (CB- GCMC) molecular simulation technique and a course-grained siting analysis. The simulations are conducted under conditions of low and high loading. The siting pattern of the adsorbates inside the zeolite pores is used to explain the selectivity as seen in experiments.

Cette étude se situe dans le cadre des recherches menées par le CEAEA sur la production massive d'hydrogène, sans émission de gaz à effet de serre, via un cycle thermo-chimique de décomposition de l'eau couplé à une source de chaleur à haute température d'origine nucléaire. Dans le cas particulier du cycle dit« Iode-Soufre», on doit extraire H2 à partir d'un mélange H2/HI/H20 très corrosif, opération pour laquelle des procédés membranaires ont été proposés. L'objectif de ce travail est le développement de membranes zéolithiques de type MFI susceptibles d'être utilisées dans ce contexte. Nous présentons les différents matériaux utilisés, la méthodologie de synthèse de couches minces de Silicalite-1 et de ZSM-5 synthétisée sans structurant organique, les techniques de caractérisation des membranes. Une étude cinétique nous a permis d'optimiser et de contrôler les conditions d'obtention de ces couches minces déposées sur des substrats tubulaires en Ti02 et plans en Al2O3-α. De nombreuses expériences de perméation ont été réalisées, pour des gaz simples (H2, He, Ar, N 2, C02, SF6) et des mélanges gazeux (H2/H20/Ar) et (H2/H20/HI/Ar). Les effets de la température, de la pression amont, de l'épaisseur et de la longueur de la couche mince ainsi que du gaz vecteur ont été étudiés en détail. Il apparaît que la présence de molécules d'H20 dans le système joue un rôle prépondérant sur la perméation des autres molécules. / In the general context of massive and "carbon free" hydrogen production studies, the aim of this work was the development of zeolitic MFI membranes for hydrogen extraction and separation. The methodology of synthesis, the membranes characterization techniques as well as the permeation experimental setup are presented. Optimization and control of the elaboration of Ti02 supported Silicalite-1 and template free ZSM-5 membranes have been reached. Details of the full kinetic study that we performed are given. Numerous permeation experiments, involving pure gas (H2, He, Ar, N2, C02, SF6) and mixtures (H2/H20/Ar) and (H2/H 20/HI/Ar) have been carried on. The effects of temperature, feed pressure, thickness and length of the membranes, as well as the role of the sweeping gas have been emphasized. In the case of gas mixtures, the presence of H20 molecules appears to be a predominant factor.

In this thesis, geometry is used as a basis for conducting experiments aimed at growing and arranging inorganic minerals on curved interfaces. Mineralisation is directed using crystalline and liquid-crystalline metallic soaps and surfactant/water systems as templates.¶ A review of the history, syntheses, structure and liquid crystallinity of metallic soaps and other amphiphiles is presented as a foundation to understanding the interfacial architectures in mesostructured template systems in general.¶ In this study, a range of metallic soaps of varying chain length and cation type are synthesised and characterised to find potentially useful templates for mineral growth. These include alkaline-earth, transition metal, heavy metal and lanthanide soaps. These are systematically characterised using a variety of analytical techniques, including chemical analyses, x-ray diffraction (XRD) infrared spectroscopy (IR) and differential scanning calorimetry (DSC). Their molecular and crystal structures are studied using transmission electron microscopy (TEM), cryo-TEM, electron diffraction (ED), electron paramagnetic spin resonance (EPR), absorption spectroscopy (UV-VIS), high resolution laser spectroscopy, atomic force microscopy (AFM), nuclear magnetic resonance spectroscopy, scanning electron microscopy (SEM), electron dispersive x-ray analysis (EDXA), thermal gravimetric analysis (TGA) and magnetic measurements. Models for the molecular and crystal structures of metallic soaps are proposed. The soaps are predominantly lamellar crystalline or liquid crystalline lamellar rotor phases with tilted and/or untilted molecular constituents. These display evidence of varying degrees of headgroup organisation, including superstructuring and polymerisation. A single crystal structure is presented for a complex of pyridine with cobalt soap. Simple models for their structure are discussed in terms of their swelling properties in water and oils. Experiments are also presented to demonstrate the sorbent properties of aluminium soaps on oil spills.¶ The thermotropic liquid crystallinity of alkaline earth, transition metal, heavy metal and lanthanide soaps is investigated in detail. This is done to assess their suitability as templates, and to document their novel thermotropic behaviour, particularly the relatively unknown lanthanide soaps. Liquid crystalline behaviours are studied using high-temperature XRD (HTXRD), hot-stage optical microscopy and DSC. Models for a liquid crystalline phase progression from crystals to anisotropic liquids are discussed in terms of theories of self-assembly and interfacial curvature. The terminology required for this is drawn from various nomenclature systems for amphiphilic crystals and liquid crystals. General agreement with previous studies is reported for known soaps, while liquid crystallinity is demonstrated in the lanthanide and some non-lanthanide soaps for the first time. A general phase progression of crystalline lamellar through liquid crystalline lamellar to non-lamellar liquid crystalline is discussed in terms of models concerned with the molecular and crystal structures of the soaps and their phase transitions via headgroup and chain re-arrangements.¶ Experiments aimed at guiding growth of metal sulfides using metallic soaps as templates are described, and a model for this growth is discussed. Metal sulfides have been successfully grown by reacting crystalline and liquid crystalline transition metal and heavy metal soaps with H2S gas at room temperature and at elevated temperature. These have been characterised using XRD, TEM, ED and IR. Sulfide growth is demonstrated to be restricted and guided by the reacting soap template architecture. Zinc, cadmium, indium and lead soaps formed confined nanoparticles within the matrix of their reacting soap template. In contrast, curved and flat sheet-like structures, some resembling sponges were found in the products of sulfided iron, cobalt, nickel, copper, tin and bismuth soaps. A model to explain this behaviour is developed in terms of the crystal and liquid crystal structures of the soaps and the crystal structures of the metal sulfide particles.¶ Liquid crystalline iron soaps have been subjected to controlled thermal degradation yielding magnetic iron oxide nanoparticles. Some XRD and TEM evidence has been found for formation of magnetic mesostructures in heat-treated iron soaps. Models for the molecular and liquid crystalline structure of iron soaps, their thermotropic phase progression and eventual conversion to these magnetic products are discussed. Systematic syntheses of mesoporous silicates from sheeted clays are discussed.¶The templates that have been used are cationic surfactants and small, organic molecular salts. Experiments are reported where a cooperative self-assembly of surfactant/water/kanemite plus or minus salt and oils yields 'folded sheet materials' (FSM'S). Templating of kanemite has also been achieved using cobalt cage surfactants. A theoretical prediction of the specific surface areas and specific volumes of homologous sets of FSM's gave excellent agreement with measured values. The geometry and topology of the mesostructures are discussed. A theoretical model is also discussed regarding the curvature found in the sheets of natural clays , and results of templating clays and silica using metallic soaps are presented. Experiments and a model for low temperature nucleation and growth of microporous silicalite-1 are described in terms of silica templating by water clathrates.¶ Finally, the problem of finding minimal surface descriptions of crystal networks is addressed. Combinatoric methods are used to disprove the existence of possible embeddings of type I and II clathrate networks in non-self intersecting periodic minimal surfaces. The crystal network of the clathrate silicate, melanophlogite is successfully embedded in the WI-10 self-intersecting surface. Details of a previously unreported, genus-25 periodic surface with symmetry Im3m are discussed.