Orientador: Ulf Friedrich Schuchardt / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-09T12:55:28Z (GMT). No. of bitstreams: 1 Marciniuk_LeticiaLedo_M.pdf: 1780819 bytes, checksum: 5b109bf0ee256783ab2b668c7fddbc93 (MD5) Previous issue date: 2007 / Resumo: Cinco catalisadores heterogêneos ácidos a base de fosfato e metais trivalentes foram sintetizados para a produção de ésteres metílicos e etílicos de óleos vegetais. Os difosfatos ácidos de latânio, cério, samário, alumínio e ferro foram sintetizados pela reação de soluções ácidas de cloretos ou óxidos dos metais trivalentes com pirofosfato de sódio e caracterizados por TG, área superficial, DRX, IV, análise elementar e RMN-P e Al. Esses compostos mostraram-se altamente eficientes tanto nas reações de transesterificação de óleos vegetais quanto na esterificação de ácidos graxos livres, com rendimentos em ésteres superiores a 95 %. As condições reacionais foram estudadas com óleo de soja e difosfato ácido de lantânio, sendo 2 h de reação na metanólise e 1,5 h na etanólise, 175 °C, razão molar de óleo: metanol 1:12 e óleo:etanol 1:9 e 5 % (m/m) de catalisador. Os sólidos não perdem suas atividades catalíticas na presença de água, comprovado pelos rendimentos em ésters de 90 e 97 % para as reações do óleo de soja com álcoois etílicos 80 e 95 %, respectivamente. Os sólidos podem ser reciclados, porém perdem suas atividades catalíticas a partir da segunda reutilização, devido à lixiviação de fosfatos. Provavelmente, tanto a catálise homogênea quanto a heterogênea estão presentes neste processo / Abstract: Five phosphate-based trivalent metal heterogeneous-acid catalysts have been synthesized for the production of methyl and ethyl ester from vegetable oils. Acids lanthanum, samarium, cerium, aluminium and iron diphosphate were prepared by reacting a sodium diphosphate solution and an acid solution of the trivalent metal chloride or oxide and characterized by TGA, surface area, XRD, FTIR, elemental analysis, NMR-P and Al. These compounds were applied in the production of biodiesel. They are highly active even for the simultaneous transesterification of vegetable oils and esterification of free fatty acids, with yields above 95 %. The reaction conditions were optimized for soybean oil and acid lanthanum diphosphate at 175 °C, for 2 h reaction for methanolysis and 1.5 h for ethanolysis, molar ratio of methanol:oil 12:1 and ethanol:oil 9:1 and 5 % (w/w) of catalyst. The solids are efficient in the presence of water given yields in esters of 90 and 97 % for the transesterification of soybean oil with 80 and 95 % hydrated ethanol, respectively. The catalysts can be recycled, however, they lose their catalytic activities from the second re-use, due to leaching of the phosphate. Probably, both homogeneous and heterogeneous catalysis are envolved in this process / Mestrado / Quimica Inorganica / Mestre em Química

M.Sc. (Chemistry) / The isomerization of short chain olefins on a catalyst containing a H-X zeolite (HZ-1) produces mainly branched olefins at 400°C. At SASOL the catalyst is also used to reduce organic acids present in the feed. Amarked increase in the acid concentration over a period of time has been reported. Other impurities in the reactor feed include short chain alcohols, aldehydes and ketones. This study consisted of kinetic experiments which concentrated on the formation of acids from ketones and aldehydes during the isomerization of 1-hexene on 60/80 mesh HZ-1. The formation of acetic and propionic acid from methyl ethyl ketone was observed. It was also shown that n-butyrealdehyde forms formic acet ic, propionic and n-butyric acid at 400°C. The presence of n-buthanol during the reaction of methyl ethyl ketone enhanced the formation of acid. A supplementary study showed the formation of only acetic acid from acetone. The study of the formation of acids from a 5% methyl ethyl ketone/5% n-buthanol at 400, 300, 250, 200 and 150°C showed an overall decrease in the acid concentration with a lowering in temperature. These results showed the development of a definite maximum in the acid production. The formation of formic acid was also observed at 200 and 150°C. Amechanism for the formation of acids from ketones is proposed and discussed. Other than existing mechanisms this explains the formation of formic, acetic and propionic acid from methyl ethyl ketone. The mechanism includes Bronsted and Lewis acid sites. During this study a method was developed for the analysis of trace quantities of organic acids present in the reaction product. Ion exclusion chromatography was used for the quantitative determination of the different types of acids. Surface studies with nitrogen adsorptics showed a drastic decrease in the surface area during the reactions. Pore volume studies showed remarkably the loss of macropores' with a pore diameter bigger than 3,6 nm. Pikinometry showed the existance of micropores which were unaffected by the reactions. Aneutron activation analysis of HZ-l showed the presence of a great variety of transition elements mainly Scandium, Cobalt and Iron.

M.Sc. (Chemistry) / Please refer to full text to view abstract

M.Tech. / Clinoptilolite possesses acid and base properties, and is hydrothermally stable at high temperatures. It can be reactivated by simple oxidation, and is highly selective due to its unique-shape selectivity. It is also not harmful to the environment and it has shown benefits to soil as well (Mumpton,1977). An initial study of the reactions of methanol amination was done using both natural local and synthetic clinoptilolites. Characterization of each was done before and after modification using XRD, TPD and BET analysis. The BET analysis showed an increase in the surface area and pore diameter of both the natural and synthetic types after acid treatment and calcination. Most interesting of all was the large increase in surface area, where the natural type increased from 16 to 36.7 m 2/g after acid treatment and the synthetic type increased almost 13 times, from 2 to 27.7 m2/g after acid treatment. This effect had a strong influence on the selectivity of methylamines by allowing a larger surface area to be in contact with the feed reagents. The XRD of the treated and untreated natural and synthetic clinoptilolite were compared and discussed. The catalytic properties of zeolites depend on the treatment of clinoptilolite, and the characteristic peaks of natural and the acid treated form can be identified in the XRD plots.The TPD analyses showed that there were two acid sites associated with the clinoptilolite; one weak and one strong. The synthetic clinoptilolite weak acid site also showed a much lower ammonia uptake, than the natural clinoptilolite weak acid site. Clinoptilolite was shown to be successful as a catalyst for the production of dimethylamine with high selectivity. This was attributed to a transition state shape selectivity associated with the clinoptilolite channels. The natural clinoptilolite displayed good selectivities at 400°C and a 5:1 ratio of methanol to ammonia, and gave a high conversion of > 90% ammonia to amines. The synthetic clinoptilolite gave better conversions and lower TMA selectivity than the natural clinoptilolite over a large range of feed ratios and temperatures. This included conversions of over 90% for most ratios (at 400 and 450°C). The natural clinoptilolite gave better results than those obtained using the amorphous clinoptilolite, which is currently used in industry. For example, low TMA selectivity was observed when a ratio of 5:1 or greater (methanol to ammonia) was used. The TMA selectivity is still far lower than the thermodynamic equilibrium selectivities obtained without a catalyst (62%). The catalyst lifetime has been shown to deteriorate with time.

Au cours de ce travail de thèse, nous avons développé un procédé plasma-catalyse d'élimination de l'acétaldéhyde en utilisant un processus diphasique couplant un catalyseur nano-structuré et a plasma à la pression atmosphérique. L’élaboration du catalyseur nanostructuré a été d'abord étudiée. Puis la performance de dégradation du polluant a été étudiée. Les nanoparticules monodispersées (titane-oxo-alcoxy) sont générées dans le réacteur de sol-gel avec micro-mélange turbulent et déposés sur des plaques de verre ou des billes de verre comme monocouches nanostructurées. Le dépôt de l'argent et de l'or est réalisé par la réduction des ions sous l’irradiation de UV-A. La cinétique de croissance photocatalytiques et de la morphologie des nanoparticules sont étudiés expérimentalement par les méthodes MET, MEB et AFM. Il est également intéressant de discuter du mécanisme de la formation des nanoparticules et d'évaluer son efficacité quantique. Les conclusions expérimentales sont supportées théoriquement par le calcul des spectres d'absorption. Ensuite l'efficacité du processus de couplage d'une décharge à barrière diélectrique et d’un lit fluidisé d'argent et d’or nanostructurés, pour la dégradation d'un polluant modèle (acétaldéhyde CH₃CHO), est étudiée. Dans la première partie, l'efficacité du procédé plasma seul est discutée, en termes de dégradation des polluants et de production de CO et CO₂. Dans la deuxième partie, la dégradation de CH₃CHO ainsi que la production COx sont étudié en fonction du temps de réduction photocatalytique d’Ag+ et d’Au³⁺ ions, qui est liée à la masse d'argent et d’or déposée. Les voies de dégradation des polluants, notamment la chimie homogène dans la phase de plasma et la chimie hétérogène sur la surface, sont discutées. Enfin, la production des sous-produits principaux est présentées et comparées entre les catalyseurs Ag et Au. / During this Phd work, we have developed a plasma-catalytic process of acetaldehyde removal using a diphasic process coupling a nano-structured catalyst and an atmospheric pressure plasma. The elaboration of the nanoparticulate catalyst has been firstly studied. Then its performance coupling with plasma has been investigated. The monodispersed titanium-oxo-alkoxy nanoparticles are generated in the sol-gel reactor with turbulent micromixing and deposited onto glass plates or glass balls as monolayer nanocoatings. The silver and gold deposition is achieved by the ions reduction at UV-A light illumination. The photocatalytic growth kinetics and nanoparticle morphology are studied experimentally by the TEM, SEM and AFM methods. It’s also interesting to discuss the mechanism of the nanoparticles formation and evaluate its quantum efficiency. The drawn conclusions are supported theoretically through the calculation of the absorption spectra. Then the efficiency of the process coupling a dielectric barrier discharge and a fluidized nanostructured silver and gold based bed for the degradation of a model pollutant (acetaldehyde CH₃ CHO) is studied. In the first part, the efficiency of the plasma alone process is discussed, in terms of pollutant removal and CO and CO₂ production. In the second part, CH₃ CHO removal as well as COx production is studied as a function of the photocatalytic reduction time of Ag⁺ and Au³⁺ ions, which is related to the deposited silver and gold mass. The pollutant removal pathways, including homogeneous chemistry in the plasma phase and heterogeneous chemistry on the surface, are discussed. Finally, the production of main by-products is presented and compared between Ag and Au catalysts.

The past two years have witnessed groundbreaking advances in the industrial deployment of olefin metathesis. While metathesis methodologies have been an integral part of the chemical manufacturing landscape for 60 years, implementation in pharmaceutical and specialty chemicals manufacturing represents a new frontier. The imperative to develop greener and more cost-effective manufacturing processes is anticipated to spur further improvements in sustainable synthesis. Advances in catalyst productivity, however, are critical to expansion of the uptake of metathesis methodologies in this and other manufacturing sectors. Key to increased catalyst productivity is elimination of side reactions that lower yield and errode selectivity. Among such reactions, double-bond isomerization is by far most common. Accumulating evidence suggests that unwanted isomerization during olefin metathesis is due to ruthenium species generated via catalyst decomposition. The identification of these species and how they are formed is thus of great importance. Two hydride complexes, RuHCl(CO)(H2IMes)(PCy3) and a dinuclear hydride, are known to form under some circumstances by decomposition of the second-generation Grubbs catalyst, RuCl2(H2IMes)(PCy3)(=CHPh), GII. These complexes have been widely viewed as responsible for unintended isomerization reactions. However, examination of their performance in olefin isomerization under conditions relevant to metathesis reveals that their activity is too feeble to account for the levels of isomerization observed during metathesis. Alternatively, kinetically competent culprits emerge from decomposition studies that reveal unexpected ruthenium products on decomposition of GII during metathesis; specifically, formation of ruthenium nanoparticles. The formation and catalytic non-innocence of RuNPs constitutes a new paradigm in this field, which opens the door to new approaches to prevent or to harness olefin isomerization. Key to prevention, clearly, is circumventing the decomposition pathways that enable ligand stripping from the active catalyst. New approaches to catalyst design that involve use of truncated NHC ligands are also examined. Finally, the power and utility of isomerization when coupled with metathesis is explored. The opportunities and limitations of orthogonal isomerization–metathesis catalysis are examined in the context of the two-step synthesis of cinnamates from 1-allylbenzenes abundant in essential oils. An efficient one-pot, two-catalyst protocol is developed for conversion of these biorenewable feedstocks to high-value-added chemicals.

Magister Scientiae - MSc / Over the recent past, organometallic chemistry has grown and the impact of catalytic applications in various chemical technologies has rapidly evolved from the realm of academic laboratories into full-scale industrial processes. Pyrrole-imine ligands were prepared by condensation of pyrrole-2-carboxylaldehyde with propyl amine, 2,6-diisopropylanaline, poly(propylene) imine dendrimer and 3-aminopropyl-triethoxysilane to give the desired ligands in good yields. These ligands were charaterized via combination of techniques to establish the molecular structure. Microanalysis was performed to confirm the purity of the product. / South Africa

This thesis describes the key steps in the production of high purity (solar-grade) silicon from metallurgical-grade silicon for use in the production of photovoltaic cells as alternative renewable, environmentally benign and cheap energy source. The initial part of the project involves the development and optimization of a small chemical production platform system capable of producing alkoxysilanes from metallurgical-grade silicon as green precursors to solar-grade silicon production. Specifically, the main aim of the study was to synthesize trialkoxysilanes in continuous flow mode, although the synthesis on monosilane was also done in batch mode. The alkoxylation reaction was carried out in a traditional slurry phase batch reactor, packed bed flow tubular reactor and also attempted in a continuous flow falling film tubular reactor. The effect of key parameters which affect the silicon conversion and selectivity for the desired trialkoxysilane were investigated and optimized using ethanol as a reagent model. The synthesis was then extended to the other alcohols namely methanol, n-propanol and n-butanol. Copper catalysts which were tested in the alkoxylation reaction included: CuCl, Cu(OH)2, CuO and CuSO4. CuCl and Cu(OH)2 showed comparable activity in the batch mode but the former was more efficient in the packed bed flow tubular reactor. Cu(OH)2 could be used as a non-halide catalyst but its activity is limited to short reaction cycles (<10 h). The uncatalysed reaction resulted in negligible reaction rates in both types of reactors. High temperature catalyst pre-heating (>500 oC) resulted in a lower rate of reaction and selectivity than when slightly lower temperatures are used (<350 oC) in both reactors, although much difference was noticed in the packed bed flow tubular reactor. Synthesis in the batch reactor needed longer silicon-catalyst activation time, higher pre-heating temperature and higher catalyst amounts as compare to the packed bed flow tubular reactor. Reaction temperature and alcohol flow rate influenced the reaction in both methods. The optimum reaction temperature range and alcohol flow rate was comparable in both reactors (230 to 240 oC) and 0.1mL/min respectively. The effect of alcohol R-group (C1 to C4) on the reaction revealed that conversion and selectivity generally decrease with an increase in carbon chain length in both methods. Ethanol showed highest selectivity (>95% in batch and >97% in flow) and conversion (about 88% in batch and about 64% in flow) as compared to all other alcohols studied showing that it could be the most efficient alkoxylation alcohol for this reaction. Overally, the packed bed flow tubular reactor resulted in higher selectivity to trialkoxysilanes than the batch system. Performing the reaction under pressure resulted in increased conversion but selectivity to the desire trialkoxysilane diminished. Synthesis in a continuous flow falling film tubular reactor was not successful as it resulted in very poor conversion and selectivity. Monosilane was successfully synthesized from the disproportionation of triethoxysilane using homogeneous and heterogeneous catalysts in batch mode. The results obtained from homogeneous catalysis showed that the reaction can be conducted at room temperature. The heterogeneous catalysis method resulted in slow conversion at room temperature but mild heating up to 55 oC greatly improved the reaction. Conducting the reaction under neat conditions produced comparable results to reactions which were carried out using solvents. The disproportionation reaction was best described by the first order kinetic model. The results obtained in this research indicate that the packed bed flow tubular reactor can be utilized with future modifications for continuous flow synthesis of alkoxysilanes as feedstock for the solar-grade silicon production.

The hydrogenation of ethylene reaction was studied over small catalyst beds of powdered nickel, nickel spheres, alumina supported nickel, powdered copper, and platinum wire. The reactor was positioned between the pole faces of an electromagnet, so that a magnetic field of strengths up to 10⁴ gauss could be applied across the catalyst bed. The reaction was studied at conditions of constant flow over the temperature range of 25° C to 550°C. The reaction rate was measured by means of a gas chromatograph, which had the sampling port installed in the system. Two magneto-catalytic effects were studied in this work: (i) the change in catalytic activity of a ferromagnetic catalyst as it is heated through its Curie temperature (internal magneto-catalytic effect); (ii) the change in catalytic activity of either a ferromagnetic or non-ferromagnetic catalyst, due to the presence of an external magnetic field (external magneto-catalytic effect). A clearly observable internal magneto-catalytic effect was found for the runs done on the ferromagnetic catalyst, nickel, which has an approximate Curie temperature of 360°C. In order to confirm this effect, runs were done over the temperature range of 300°C to 500°C on the non-ferromagnetic catalysts, copper and platinum. No change in reaction rate was found near 360°C, as was found using a nickel catalyst. No external magneto-catalytic effect was observed at any temperature. The hydrogenation of ethylene was found to be a rapidly self-poisoning reaction at temperatures above 100°C. Published literature indicates that at moderately high temperatures, desorption of reacting ethylene complexes off the catalyst surface causes the decrease in reaction rate. In this work a significant mole fraction of methane was detected in the reactor effluent gas, at temperatures above 300°C, and an accompanying carbon deposit was observed to form on the catalyst surface. The rapid decrease in catalytic activity at high temperatures was believed to be due to this carbon deposit. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

The reactivity of copper chloride (CuC1[subscript x], 1 < x < 2) towards chlorine and its catalytic activity in the chlorination of propane have been studied. The oxidation of copper (I) chloride by chlorine was found to be diffusion controlled after the first 25% of reaction. For the chlorination of propane, CuC1 was catalytically inactive, CuC1₂ was active, but the maximum activity was found in the range CuC1₁․₅ to CuC1₁․₈ with two peaks at roughly CuC1₁․₅₇ and CuC1₁․₇₈. Both reactions appear to have an active centre in common — a Cu⁺ ion which is capable of accepting a proton. The phase of maximum catalytic activity is a highly defective CuC1₂ phase containing such centres. The mechanism for the catalytic chlorination involves the homolytic splitting of C₃H₈ and stabilization of surface radicals through proton transfer into the bulk. No compound other than CuC1 and CuC1₂ was found in the CuC1x system by X-ray powder studies. However, the results of X-ray powder, electrical conductivity and magnetic susceptibility studies provide convincing evidence for the existence of a defective CuC1₂ phase with interstitial cations as well as a cation-deficient CuC1 phase in CuC1x. Furthermore, these results are consistent with a structural change at x ∼1.63 as suggested also by the kinetic studies. While the present work shows many interesting features of the CuC1x system, there is plenty of room for further exploration in this hitherto virtually unknown field. Suggestions for future work related to the present findings are outlined in this thesis. / Science, Faculty of / Chemistry, Department of / Graduate