Zeolites are porous aluminosilicates that occur both naturally and synthetically, having numerous applications in catalysis, adsorption and separations. Despite over a half century of characterization and synthetic optimization of hundreds of frameworks, the exact mechanism of synthesis remains highly contested, with crystallization typically occurring under transport-limited regimes. In this work, a microcrystallization reactor working under segmented oscillatory flow has been designed to produce a semi-continuous flow of zeolite A. The fast injection of the reactants in a mixing section forms droplets of aqueous precursors in a stream of paraffin, dispersing microdroplets and avoiding any clog from occurring in the system. The crystallization occurred in the system at atmospheric pressure and isothermal conditions (65ºC). This allowed for a rather slow crystallization kinetics which was important to study and highlight the different crystallization mechanisms between flow and batch synthesis. The morphology, size distributions, crystallinity, and porosity were examined by ex-situ characterization of the samples by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and N2 Physisorption to support the conclusions drawn. The size distribution of the particles achieved in the flow reactor was conclusively narrower than the distribution achieved in the batch reactor. The average size of the crystals for both synthesis methods is reported as 400 nm and the crystallinity achieved was comparable between the two. However, the morphology was quite different between the two systems, the flow products having a much higher mesoporosity due to the presence of crystal aggregates at high crystallinity when compared to the batch crystals. Finally, extended crystallization times leads to a decline of the crystallinity of the product, which might be explained by the metastable state of zeolites in solution.

Zeolites are porous aluminosilicates that occur both naturally and synthetically, having numerous applications in catalysis, adsorption and separations. Despite over a half century of characterization and synthetic optimization of hundreds of frameworks, the exact mechanism of synthesis remains highly contested, with crystallization typically occurring under transport-limited regimes. In this work, a microcrystallization reactor working under segmented oscillatory flow has been designed to produce a semi-continuous flow of zeolite A. The fast injection of the reactants in a mixing section forms droplets of aqueous precursors in a stream of paraffin, dispersing microdroplets and avoiding any clog from occurring in the system. The crystallization occurred in the system at atmospheric pressure and isothermal conditions (65ºC). This allowed for a rather slow crystallization kinetics which was important to study and highlight the different crystallization mechanisms between flow and batch synthesis. The morphology, size distributions, crystallinity, and porosity were examined by ex-situ characterization of the samples by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and N2 Physisorption to support the conclusions drawn. The size distribution of the particles achieved in the flow reactor was conclusively narrower than the distribution achieved in the batch reactor. The average size of the crystals for both synthesis methods is reported as 400 nm and the crystallinity achieved was comparable between the two. However, the morphology was quite different between the two systems, the flow products having a much higher mesoporosity due to the presence of crystal aggregates at high crystallinity when compared to the batch crystals. Finally, extended crystallization times leads to a decline of the crystallinity of the product, which might be explained by the metastable state of zeolites in solution.

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of Science in Engineering. 9 February, 2017 / Global climate change and other environmental disasters have been attributed to continuous anthropogenic carbon dioxide (CO2) emission into the atmosphere. Today, researchers are constantly seeking measures to reduce anthropogenic CO2 emission. Traditionally, absorption technology with use of monoethanolamine (MEA) is used for separating / capturing of anthropogenic CO2. However, the use of MEA is associated with numerous shortcomings, including inefficient energy usage, high operating and capital cost, amine degradation, solvent loss and excessive equipment corrosion. Alternatively, zeolite based membrane systems are promising technique that prove handy and useful than the traditional processes (absorption with monoethanolamine). However, zeolitic membranes with zeolite coating on the supports (i.e. thin-film supported zeolite membranes) are susceptible to abrasion and thermal shock at elevated temperatures due to temperature mismatch between the supports and the membranes, making them to lose selectivity at early stages. On the contrary, nanocomposite architecture membranes, synthesized via pore-plugging hydrothermal route, are more thermally stable and membrane defects are controlled. Nanocomposite zeolite (sodalite) membranes have been proposed for gas separations, most importantly in the separation of H2/CO2, a major component in pre-combustion carbon capture. In addition, sodalite, a porous crystalline zeolite made up of cubic array of β-cages as primary building block having cage aperture in the range of 0.26 and 0.29 nm, is a potential candidate for the separation/purification of light molecules such as hydrogen which has a cage aperture of 0.27 nm under certain process conditions. In this work, nanocomposite architecture hydroxy sodalite membrane with sodalite crystals embedded within α-alumina tubes were successfully synthesized using the pore-plugging hydrothermal synthesis technique and characterized using techniques such as scanning electron microscopy (SEM) and X-ray diffraction (XRD). The morphology of the synthesized membranes shows that sodalite crystals were indeed grown within the porous structures of the support. Furthermore, Basic Desorption Quality Test (BDQT) and gas separation measurement were conducted to evaluate the quality of the as-synthesized membrane in industrial gas separation applications. The effects of operating variables such as pressure at 1.1 bar, 2.0 bar and 3.0 bar. Also, the effects of temperature were conducted on the nanocomposite membrane at 373 K, 423 K and 473 K. Finally, the gases permeation results were fitted with the well-known Maxwell-Stefan model. Results indicated that, the nanocomposite sodalite / ceramic membrane is a potential candidate for removal of H2 from H2/CO2 mixture. The gas permeation measurement from the one-stage nanocomposite membrane shows that the membrane displayed H2 and CO2 permeance of 3.9 x 10-7 mols-1m-2Pa-1 and 8.4 x 10-8 mols-1m-2Pa-1, respectively. However, the morphology of two-stage nanocomposite membrane shows that the support was more plugged with sodalite crystals and the permeance of H2 and CO2 were 7.4 x 10-8 mol.s-1.m-2.Pa-1 and 1.1 x 10-8 mol.s-1.m-2.Pa-1, respectively. Consequently, the H2/CO2 ideal selectivity for the one-stage nanocomposite membrane improved from 4.6 to 6.5 in the two-stage nanocomposite membrane. In conclusion, the two-stage synthesized membrane shows better improvement. The porous support was well plugged and separation performance was evaluated. However, occluded organic matters present in the cages of hydroxy sodalite could have adverse effect on the gas permeation performance of the membrane. It is expected that an organic-free sodalite supported membrane (such as silica sodalite supported membrane) could out-perform the hydroxy sodalite supported membrane reported in this work in term of membrane flux because there will be enough pore space for gas permeation. / MT2017

Development of sustainable and environmentally friendly chemical processes is of vital importance nowadays. Although there is a palette of different synthetic methods for the formation of epoxides, sulphoxides and sulphones, from both economic and environmental points of view, a direct oxidation with a simple oxidant is highly appreciated. The main goals of the thesis were design and synthesis of novel titanium containing zeolitic materials with the ability to catalyse selective oxidation of sterically demanding organic compounds, particularly epoxidation of cyclic olefins and terpenes and oxidation of bulky thioethers to corresponding sulphoxides and sulphones with hydrogen peroxide as the oxidant. Two novel extra-large pore titanosilicates were prepared by means of hydrothermal synthesis (Ti-CFI, Ti-UTL), three large-pore titanosilicates (Ti-CON, Ti-AFI, Ti-IFR) were prepared using two step deboronation - liquid phase titanium impregnation procedure and two groups of lamellar materials were prepared. One group was based on modified nanosheet TS-1; the other was prepared from Ti-IPC- 1P lamellar precursor, which was prepared by means of top-down transformation of Ti-UTL. Last but not least, the Ti-UTL was transformed into new titanosilicates Ti-IPC-2 (OKO structure) and Ti-IPC-4 (PCR structure) by...

Este trabalho consiste de um estudo detalhado a respeito da Espectroscopia de Alta Resolução em Sólidos por RMN e da sua aplicação à análise de zeólitas Y e *, sendo utilizadas as técnicas de Rotação em torno do Ângulo Mágico, Desacoplamento e Polarização Cruzada para a obtenção dos espectros de alta resolução. Dedicamos uma atenção especial à interação quadrupolar, existente quando o núcleo apresenta spin > 1/2, devido aos seus efeitos importantíssimos em zeólitas, e procuramos apresentar um material teórico abrangente e acessível sobre o assunto. As análises de zeólitas foram feitas por RMN dos núcleos 29Si, 27Al, 13C e 23Na, o que permitiu a obtenção de uma variada quantidade de informações sobre suas propriedades e modificações ocorridas ao longo dos tratamentos com elas realizados. Todas as medidas foram efetuadas com um espectrômetro desenvolvido em nosso laboratório; o campo magnético utilizado foi de 2T, um valor baixo mas que permite a extração de valiosas informações a respeito dos materiais analisados / This work consists in a detailed study of High Resolution NMR Spectroscopy in Solids and its application to the analysis of zeolites Y and *. In these studies, we have used the techniques of Magic Angle Spinning, Decoupling and Cross Polarization in order to obtain the high resolution spectra. We dedicate a special attention to the quadrupolar interaction, present if the nucleus possesses spin > 1/2, due to its highly important effects in zeolites; we intend to present a comprehensive and wide theoretical material about this subject. Analysis of the zeolites has been performed by NMR of the nuclei 29Si, 27Al, 13C and 23Na, which allowed to obtain a wide range of information about its properties and the changes which occurred during the treatments performed. All measurements were achieved with a home build spectrometer operating at a magnetic field of 2T, which is a low value but allows the extraction of valuable information about the materials under study

A cinza da casca do arroz (CCA) é um resíduo rico em sílica amorfa. Um método simples e de baixo consumo energético para extração desta sílica foi pesquisado, obtendo-se um material com baixo teor de impurezas e alta reatividade, adequado para a síntese de zeólitas e wolastonita (CaSiO3). As zeólitas sintéticas, que não possuem estruturas similares na natureza, são cada vez mais valorizadas no mercado devido a pureza e eficiência em aplicações específicas nas áreas de troca iônica, peneira molecular e catálise. A wolastonita com elevado grau de pureza tem várias aplicações na indústria e agricultura. O mineral wolastonita pode ser formado de várias maneiras na natureza. Em geral é aceito que existem dois processos de formação; os quais envolvem o metamorfismo (calor e pressão) do calcário. Neste trabalho, foi desenvolvido um novo processo para a síntese das zeólitas e da wolastonita, ambas a partir da sílica coloidal da CCA; tendo como objetivo um processo de um menor custo energético, menor número de etapas e menor consumo de reagentes. Foram sintetizadas neste trabalho as zeólitas: A, usada em detergentes, e a ZSM-5, empregada na indústria petroquímica, devido a sua alta seletividade em reações catalíticas e grande estabilidade térmica e resistência aos ácidos. A primeira etapa na síntese da wolastonita foi estudada com o objetivo da formação do hidrossilicato de cálcio (CSH). Contudo, onze hidrossilicatos de cálcio diferentes ocorrem no sistema Ca(OH)2-SiO2-H2O que em uma segunda etapa passam por um tratamento térmico para dar formação a fase wolastonita. / Rice hull ash (RHA) is a industry scrap rich in amorphous silica. A simple and low-energy cost method for the extraction of this silica was researched. A low level of impurity and high reactivity material was produced, which is appropriate for the synthesis of zeolites and wolastonite (CaSiO3). The synthetic zeolites, has not similar structures in nature, and they have been more and more valued in the market due to their purity and efficiency in specific applications like ion exchange, molecular sieve and catalysis areas. High purity wolastonite has many applications in manufacturing and agriculture. The mineral wolastonite can be formed in nature in different ways; it is generally accepted two forming processes, both encompassing limestone metamorphism (heat and pressure). In this work, a new process for the synthesis of zeolites and wolastonite from RHA colloidal silica was developed. Moreover, the process is aimed at lower energy costs, fewer stages and fewer reactants consume. In this work, zeolite A used in detergent and zeolite ZSM-5, employed in the petrochemical industry due to its high selectivity in catalytic reactions and its high thermo and acid stability, were synthesized. The first step of the wolastonite synthesis was studied, with the purpose of obtaining calcium hydrosilicate. Eleven different hydrosilicates occur in the system Ca(OH)2-SiO2-H2O, in the second step, it was annealed to form the wolastonite phase.

Trichloroethylene (TCE) is one of the most common groundwater pollutants in the United States. The EPA estimated that between 9% and 34% of the drinking water sources in the United States may contain TCE. The United States Environmental Protection Agency set a maximum contaminant level at 5 µg/L of trichloroethylene for drinking water. This study investigated the feasibility of removing TCE from water by sorption to ZSM-5 and advanced oxidation to destroy the TCE on the zeolite. Aqueous oxidation of TCE with Fenton's reagent was shown to be efficient for the destruction of TCE. The quantified by-products were cis-DCE and trans-DCE. ZSM-5 rapidly removed TCE from water. A Freundlich isotherm was created for the uptake of TCE by ZSM-5. Once TCE was sorbed to ZSM-5, preliminary experiments showed that the oxidation was able to destroy the TCE while producing the same by-products.

As zeólitas são amplamente utilizadas pela indústria em diferentes processos. Nos processos relacionados à conversão térmica do carvão, as zeólitas encontram aplicação, por exemplo, como suporte de catalisadores para a Síntese de Fischer-Tropsch, ou mesmo como adsorventes de efluentes líquidos ou de gases poluentes. No entanto, a microporosidade da zeólita limita a difusão dos produtos e dos reagentes ocasionando um transporte de massa lento e um longo tempo de residência, aumentando a possibilidade de reações secundárias, formação de coque e desativação do catalisador. Uma das maneiras de superar essas limitações é a introdução de um sistema secundário de poros, através da reestruturação da rede cristalina com modeladores de estruturas ou ataques químicos básicos e ácidos nas zeólitas de modo a formar materiais hierárquicos ou mesoporosos. Neste trabalho, foram investigadas três rotas para promover a mesoporosidade em zeólitas do tipo Y. Primeiramente foi realizada a síntese da zeólita hierárquica através da modificação com líquidos iônicos. O segundo método empregado foi o processo de dessilicação, utilizando hidróxido de sódio como base e, por último, a desaluminação com ácido oxálico. As zeólitas mesoporosas foram caracterizadas através de análises de área específica (BET), distribuição de tamanho de poros (BJH), difração de raios X (DRX) e redução à temperatura programada (TPR-H2). Dentre os métodos adotados, os resultados para DRX e BET mostraram que o tratamento de dessilicação destruiu a cristalinidade da zeólita, acarretando no abandono dessa rota de investigação. A síntese com líquido iônico se mostrou eficiente para a formação de mesoporos e, conforme a distribuição de tamanho de poros, seu sistema apresentou-se ordenado de maneira hierarquizada. A desaluminação não danificou a estrutura da zeólita, porém foi obtido um aumento pouco expressivo em seu número de mesoporos. A reação de esterificação foi utilizada, como modelo, para avaliar o efeito dos mesoporos sobre a atividade catalítica da reação. A reação de esterificação ocorreu a 70°C por 1 h, utilizando ácido acético e álcoois com diferentes tamanhos de moléculas. Em comparação à zeólita de partida (CBV720 - Zeolyst), a criação da mesoporosidade na zeólita através dos líquidos iônicos resultou em um aumentou na conversão de ácido acético para os álcoois etílico (em 17,65%), isopropílico (em 8,42%) e isobutílico (em 2%). Para a zeólita mesoporosa sintetizada por desaluminação, houve um acréscimo de 10,93% e 2,11% na conversão para os álcoois etílico e isopropílico, respectivamente. Os resultados mostraram que a presença de mesoporosidade influenciou positivamente o desempenho das zeólitas Y na reação modelo de esterificação, mostrando-se um excelente mecanismo a ser aplicado para facilitar o transporte de massa nos poros da zeólita, especialmente para a síntese feita com o emprego de líquidos iônicos. / Zeolites are widely used by industry in different processes. In processes related to the thermal conversion of coal, the zeolites find application, for example, as catalyst support for the Fischer-Tropsch Synthesis, or even as adsorbents of liquid effluents or pollutant gases. However, the small pore diameter of the zeolite limits the diffusion of the products and the reactants causing slow mass transport and a long residence time that increase the possibility of secondary reactions, coke formation and catalyst deactivation. One of the ways to overcome these limitations is the introduction of a secondary pore system by restructuring the crystal lattice with structural modellers or basic chemical and acidic attacks on zeolites to form hierarchical or mesoporous materials. In this work, three routes were investigated to promote mesoporosity in Y type zeolites. First, the hierarchical zeolite was synthesized through the modification with ionic liquids. The second method used was the desilication process, using sodium hydroxide as the base and, finally, the desalumination method with oxalic acid. The mesoporous zeolites were characterized by specific surface area analysis (BET), pore size distribution (BJH), X-ray diffraction (XRD) and temperature programmed reduction (TPR-H2). Among the methods adopted, the results for XRD and BET showed that the desilication treatment destroyed the crystallinity of the zeolite, leading to the abandonment of this research route. The synthesis with ionic liquid was efficient for the formation of mesopores and, according to the pore size distribution, its system was hierarchically ordered. The desalumination did not damage the zeolite structure, but a small increase in its number of mesopores was noted. The esterification reaction was used to evaluate the effect of mesopores on the catalytic activityof the reaction. The esterification reaction occurred at 70°C for 1 h using acetic acid and alcohols with different sizes of molecules. Compared to the starting zeolite (CBV720 - Zeolyst), the creation of mesoporosity in the zeolite through the ionic liquids resulted in an increase in the conversion of acetic acid for the reaction conducted with ethyl (17.65%), isopropyl (8.42%) and isobutyl alcohols (2%). For the mesoporous zeolite synthesized by desalumination, there was an increase of 10.93% and 2.11% in the conversion to the ethyl and isopropyl alcohols, respectively. The results showed that the presence of mesoporosity positively influenced the performance of the zeolites Y in the esterification model reaction, showing an excellent mechanism to be applied to facilitate the mass transport in the zeolite pores, especially for the synthesis made with the use of ionic liquids.

Biodiesel is a re-emerging biofuel as an alternative to the traditional petroleum derived diesel. There are however, several factors that currently hinder the widespread uptake. Majority of the biodiesel are currently produced from edible oils thereby sparking the food versus fuel debate, the cost of feedstock is significantly high, there are problems experienced in the traditional production process and the resulting fuel is of inadequate quality. This work focused on addressing the issue of poor cold flow properties to improve the overall quality of biodiesel. The skeletal isomerisation of linear fatty acid methyl esters (FAMEs) into branched chain isomers, using solid acid catalysts, appears to be the most comprehensive solution in enhancing the cold flow properties of biodiesel. However, obtaining high branched chain yields, mitigation of undesired side reactions, achieving shorter reaction times, using fewer processing steps and lower operating conditions have still not been achieved to a large extent. Moreover, no studies were found to date investigating isomerisation of FAMEs as a continuous process. A trickle bed reactor (TBR) system has been identified to be an effective continuous reactor. Its key features of being a three phase system and allowing a high degree of contact between the reactant and the catalyst offering a high conversion per unit volume provides an encouraging opportunity to lower reaction times, reaction steps and conditions whilst increasing branched chain yields. This thesis explores the use of the TBR system, for the first time, to enhance the cold flow properties of biodiesel through molecular modification using zeolite beta catalyst with Si/Al ratios of 180 and 12.5. A range of reactions have been investigated including isomerisation, dewaxing (hydroisomerisation and hydrocracking) and decarboxylation on biodiesels derived from camelina, palm and coconut oils. Significant progress has been made in this research area with a 7 °C drop in MP being achieved upon the dewaxing of the coconut biodiesel at 250 °C, 1.01 bar pressure, 0.2 ml/min LF and 37.5 ml/min GF. To achieve greater drops in melting points it has been suggested to investigate mesoporous catalysts as they will ensure greater facilitated molecular access to the active sites, resulting in a higher conversion by preventing pore blockages. All in all, a series of key findings and serendipitous discoveries have brought to surface an array of new challenges as well as paving the way for a host of exciting opportunities for future research. The ability to continuously produce high quality renewable fuel offers a fascinating prospective for various industrial associates such as Argent Energy, Olleco, Neste Oil and ConocoPhillips.

As zeólitas têm recebido grande atenção acadêmica e industrial devido às suas características ácidas e estruturais. A estrutura da zeólita pode ser utilizada para conduzir uma reação catalítica na direção do produto desejado, evitando assim reações paralelas. Porém, essa mesma estrutura cria restrições difusivas com relação ao acesso aos sítios ativos no interior dos microporos. Neste trabalho foram estudados dois métodos de criação de mesoporos (térmico e básico) com o intuito de modificar a acessibilidade aos sítios catalíticos das zeólitas. A reação de hidroisomerização do n-heptano foi selecionada para avaliar as zeólitas após a criação de mesoporosidade. O tratamento térmico (via calcinação em temperaturas elevadas) foi utilizado para as zeólitas do tipo ZSM-5, Mordenita e Ferrierita, tendo sido observado um aumento pouco significativo na mesoporosidade. Este tratamento promoveu, porém, uma significativa desaluminização das amostras, acompanhada da formação de quantidades importantes de espécies de Al extra-rede (ALER), o que se refletiu num bloqueio parcial dos mesoporos gerados e dos microporos preexistentes, e na redução na densidade de sítios ácidos das amostras. A ampliação da escala do tratamento térmico (aumento da quantidade tratada de 2 g para 30 g) não se mostrou reprodutível, gerando menos mesoporos do que o observado no preparo em pequena escala. O tratamento básico (via dessilicação por meio de NaOH), ao contrário do anterior, promoveu a formação de mesoporos gerando menos quantidade de ALER e se mostrou mais reprodutível quando da ampliação da escala. O desempenho dos catalisadores Pt/Al2O3+zeólita na reação de hidroisomerização do n-heptano foi influenciado pela densidade de sítios ácidos fortes e pela estrutura porosa da zeólita. Com relação ao efeito dos tratamentos térmico e básico sobre o desempenho dos catalisadores à base de ZSM-5, os resultados mostraram que o comportamento do catalisador submetido ao tratamento básico (Pt/Al2O3+BZSM-5/85-2) foi similar ao do tratado termicamente (Pt/Al2O3+TZSM-5/1000-2) com relação à distribuição de produtos na reação de hidroisomerização do n-heptano, particularmente com relação aos produtos leves e aos isômeros monorramificados. No entanto, a presença mais significativa de mesoporos na zeólita após tratamento básico (BZSM-5/85-2), se refletiu num leve favorecimento à formação dos isômeros birramificados / Zeolites have received great academic and industrial attention due to their acidic and structural characteristics. The structure of the zeolite can be used to conduct a catalytic reaction selectively to the desired product, thus avoiding undesirable side reactions. However, this structure could create diffusive restrictions regarding the access to the active sites inside the micropores. In this work two methods of mesopores generation (thermal and basic) were studied in order to modify the accessibility of the catalytic sites of the zeolites. The reaction of hydroisomerization of n-heptane was selected to evaluate the modified zeolites. The thermal treatment was employed for ZSM-5, mordenite and ferrierite zeolites and a negligible increase in mesoporosity has been observed. However, this treatment produced a significant dealumination of the samples along with the reduction of the acid sites density and the formation of significant quantities of extraframework Al species (EFAL), which resulted in a partial blockage of the pre-existent micropores and of the mesopores generated. Furthermore, the scale-up of the thermal treatment (increasing the amount of treated sample from 2 g to 30 g) was not reproducible, producing less mesopores than that was observed in the small-scale preparation. The basic treatment with NaOH solution was also tested for ZSM-5 zeolite. It increased significantly the mesoporosity of the zeolite and formed less amount of extra-framework aluminum. Moreover, it was more reproducible when larger amounts of sample were treated. The performance of Pt/Al2O3 + zeolite catalysts in hydroisomerization/hydrocracking of n-heptane was influenced by both the strong acid sites density and the pore structure of the zeolite. As to the effect of the thermal and basic treatments on the performance of the ZSM-5-based catalysts, the results showed that the behavior of that the basically treated samples was similar to those of heat-treated was similar regarding the product distribution particularly with respect to light hydrocarbons and monobranched C7 isomers. However, the larger mesoporosity of sample basically treated slightly favored the formation polybranched isomers