High spin has been shown to be necessary for optimal reactivity of transition metal complexes toward the activation and functionalization of C-H bonds. This thesis presents our examination of the weak-field, tripodal, trianionic tris(pyrrolyl)ethane (tpe) ligand and its complexes. Outer-sphere oxidation of the manganese, iron, cobalt, nickel and zinc complexes of tpe were performed by electrochemical and chemical methods. Electrochemical oxidation occurred at the same potential for each species, suggesting a ligand-based oxidation. The reaction product of chemical oxidation of iron showed oxidation of a pyrrole unit followed by H-atom abstraction to form a dichelated species. Density functional theory calculations confirm these results, and in silico oxidation of the complexes is entirely ligand-based. These results establish that tpe complexes are oxidized at the pyrrolide subunits in outersphere electron transfers, and elucidate minimal metal-ligand electronic communication. The more reactive \([(tpe)Fe(THF)]^−\) anion exhibits rapid binding of three equivalents of tert-butyl isonitrile, while reaction with excess carbon monoxide induces ligand fragmentation to form a species wherein two molecules of carbon monoxide have been reductively coupled. A mechanism based on the observed isonitrile species is proposed. The use of inner-sphere oxidant reagents allows for several stable iron (III) complexes of tpe to be isolated and characterized. Alkyl peroxides and alkyl disulfides, organic azides, and diphenyldiazomethane are all shown to oxidize iron by a single electron. Reaction with organic azides results in the formation of iron (III) amide species, likely as a result of Hatom abstraction. The weak-field of tpe creates a high propensity for forming high-spin iron (III) complexes, to the extent that diphenyldiazoalkane acts as a redox-active ligand and provides a one-electron reservoir to reveal a high-spin \(Fe^{3+}\). Spectroscopic and computational studies were undertaken to rigorously assign the physical oxidation state of iron in all cases. Given the outer-sphere redox liability of the tpe ligand, and the capability for inner-sphere oxidation local to iron, tpe complexes of iron represent a new class of metal-ligand redox activity, wherein the metal and ligand form two separate redox reservoirs, accessible via different mechanisms. / Chemistry and Chemical Biology

Stable isotope of natural gas hydrates provides useful information of their gas sources. We investigated the isotopic fractionation of gas molecules during the formation of synthetic gas hydrates composed of methane and ethane. The gas hydrate samples were experimentally prepared in a pressure cell and isotopic compositions (δ13C and δD) of both residual and hydratebound gases were measured. δD of hydrate-bound molecules of methane and ethane hydrates was several per mil lower than that of residual gas molecules in the formation processes, while there was no difference in the case of δ13C. Effect of temperature on the isotopic fractionation was also investigated and it was found that the fractionation was effective at low temperature.

Enormous amount of latent heat generates/absorbs at the formation/dissociation process of gas hydrates and controlls their thermal condition themselves. In this paper we investigated the effect of ethane concentration on dissociation heat of mixed-gas (methane and ethane) hydrate. It has been reported by researchers that a structure II gas hydrate appears in appropriate gas composition of methane and ethane. We confirmed by using Raman spectroscopy that our samples had the following three patterns: structure I only, structure II only and mixture of structures I and II. Dissociation heats of the mixed-gas hydrates were within the range between those of pure methane and ethane hydrates and increased with ethane concentration. In most cases two peaks of heat flow appeared and the dissociation process was divided into two parts. This can be understood in the following explanation that (1) the sample contained both crystal structures, and/or (2) ethane-rich gas hydrate formed simultaneously from dissociated gas and showed the second peak of heat flow.

Dissociation and specific heats of synthetic methane and ethane hydrates were measured under high-pressure condition by using a heat-flow type calorimeter to understand thermodynamic properties of gas hydrates under submarine/sublacustrine environments. Ice powder was put into the sample cell and pressurized by methane and ethane up to 5MPa and 2MPa, respectively. After the completion of gas hydrate formation, samples were heated from 263K to 288K at the rate of 0.01 K min-1. Large negative peaks of heat flow corresponded to the dissociation of gas hydrates were detected in a temperature range 279-282K at a pressure of 5MPa for methane hydrate and 283-286K at 2MPa for ethane hydrate, respectively. We also obtained the specific heats of gas hydrates in the range 264-276K for methane and 264-282K for ethane under pressure.

In this research, oxidative dehydrogenation of ethane to ethylene was studied over Cr-O and Cr-V-O mixed oxide catalysts through steady-state and dynamic experiments. The catalysts were prepared by the complexation method. By XRD, presence of Cr2O3 phase in Cr-O / and the small Cr2O3 and V2O4 phases of Cr-V-O were revealed. In H2-TPR, both catalysts showed reduction behaviour. From XPS the likely presence of Cr+6 on fresh Cr-O was found. On Cr-V-O, the possible reduction of V+5 and Cr+6 forms of the fresh sample to V+4, V+3 and Cr+3 states by TPR was discovered through XPS. With an O2/C2H6 feed ratio of 0.17, Cr-O exhibited the highest total conversion value of about 0.20 at 447&deg / C with an ethylene selectivity of 0.82. Maximum ethylene selectivity with Cr-O was obtained as 0.91 at 250&deg / C. An ethylene selectivity of 0.93 was reached with the Cr-V-O at 400&deg / C. In the experiments performed by using CO2 as the mild oxidant, a yield value of 0.15 was achieved at 449&deg / C on Cr-O catalyst. In dynamic experiments performed over Cr-O, with C2H6 pulses injected into O2-He flow, the possible occurrence of two reaction sites for the formation of CO2 and H2O was detected. By Gaussian fits to H2O curves, the presence of at least three production ways was thought to be probable. Different from Cr-O, no CO2 formation was observed on Cr-V-O during pulsing C2H6 to O2-He flow. In the runs performed by O2 pulses into C2H6-He flow over Cr-V-O, formation of CO rather than C2H4 was favored.

Na indústria petroquímica, fornos para craqueamento térmico são utilizados para processar hidrocarbonetos leves, como nafta, etano, propano e GLP, a fim de obter-se olefinas, como eteno e propeno. Fornos de craqueamento de etano são de fundamental importância para melhorar os rendimentos globais de uma planta de produção de olefinas. Neste contexto, um modelo matemático de um forno industrial de craqueamento de etano foi desenvolvido utilizando o simulador de processos EMSO para previsão do tempo de campanha. No modelo proposto, um reator de fluxo pistonado multi-secção foi acoplado com um modelo cinético das reações de craqueameto e coqueamento a partir de dados da literatura. Em paralelo, a câmara de radiação do forno foi modelada em fluidodinâmica computacional, através do uso do software Ansys-CFX. Os resultados das simulações no EMSO e no Ansys-CFX apresentaram boa concordância com os dados de literatura e dados industriais. Entre os principais benefícios dos modelos desenvolvidos para aplicação industrial ressaltam-se: i. a possibilidade de avaliar o impacto de contaminantes na corrente de etano que alimenta o forno e prever se ocorrerá uma redução do tempo de campanha; ii. viabilizar uma otimização dos fornos de etano, buscando operá-los em condições otimizadas de tempo de campanha reduzindo o risco de descoques simultâneos; iii. confirmar se reduções de tempo de campanha observados são em função das condições de processo ou se existe algum outro fator que esteja causando desvios em relação às previsões da simulações, iv. avaliar possíveis problemas de má distribuição de calor na câmara de radiação. / In petrochemical industries, steam cracking furnaces are used to process light hydrocarbons like naphta, ethane, propane and LPG in order to obtain olefins, like ethylene and propylene. Ethane steam cracking furnaces are of fundamental importance to improve the overall yields of an olefins production plant. In this context, a model for an industrial steam cracking furnace was developed using the equation-oriented dynamic simulator EMSO. In the proposed model, a multi-section plug flow reactor was coupled with cracking and coking kinetics from literature. Additionally, the radiation chamber was studied by computational fluid dynamics, using Ansys-CFX. The results performed are in good agreement with published and industrial design data. Among the main benefits of the models developed for industrial application, following stand out: i. the possibility to evaluate the impact of contaminants in ethane feed to the furnace and predict some run length reduction; ii. allow an optimization of ethane furnaces, seeking to operate them in optimal conditions of run length reducing the risk of simultaneous decokes; iii. confirm that observed run length reductions are depending on the process conditions, or if there is some other factor that is causing deviations from the simulation predictions, iv. evaluate possible problems due to poor heat distribution in the radiation chamber.

Na indústria petroquímica, fornos para craqueamento térmico são utilizados para processar hidrocarbonetos leves, como nafta, etano, propano e GLP, a fim de obter-se olefinas, como eteno e propeno. Fornos de craqueamento de etano são de fundamental importância para melhorar os rendimentos globais de uma planta de produção de olefinas. Neste contexto, um modelo matemático de um forno industrial de craqueamento de etano foi desenvolvido utilizando o simulador de processos EMSO para previsão do tempo de campanha. No modelo proposto, um reator de fluxo pistonado multi-secção foi acoplado com um modelo cinético das reações de craqueameto e coqueamento a partir de dados da literatura. Em paralelo, a câmara de radiação do forno foi modelada em fluidodinâmica computacional, através do uso do software Ansys-CFX. Os resultados das simulações no EMSO e no Ansys-CFX apresentaram boa concordância com os dados de literatura e dados industriais. Entre os principais benefícios dos modelos desenvolvidos para aplicação industrial ressaltam-se: i. a possibilidade de avaliar o impacto de contaminantes na corrente de etano que alimenta o forno e prever se ocorrerá uma redução do tempo de campanha; ii. viabilizar uma otimização dos fornos de etano, buscando operá-los em condições otimizadas de tempo de campanha reduzindo o risco de descoques simultâneos; iii. confirmar se reduções de tempo de campanha observados são em função das condições de processo ou se existe algum outro fator que esteja causando desvios em relação às previsões da simulações, iv. avaliar possíveis problemas de má distribuição de calor na câmara de radiação. / In petrochemical industries, steam cracking furnaces are used to process light hydrocarbons like naphta, ethane, propane and LPG in order to obtain olefins, like ethylene and propylene. Ethane steam cracking furnaces are of fundamental importance to improve the overall yields of an olefins production plant. In this context, a model for an industrial steam cracking furnace was developed using the equation-oriented dynamic simulator EMSO. In the proposed model, a multi-section plug flow reactor was coupled with cracking and coking kinetics from literature. Additionally, the radiation chamber was studied by computational fluid dynamics, using Ansys-CFX. The results performed are in good agreement with published and industrial design data. Among the main benefits of the models developed for industrial application, following stand out: i. the possibility to evaluate the impact of contaminants in ethane feed to the furnace and predict some run length reduction; ii. allow an optimization of ethane furnaces, seeking to operate them in optimal conditions of run length reducing the risk of simultaneous decokes; iii. confirm that observed run length reductions are depending on the process conditions, or if there is some other factor that is causing deviations from the simulation predictions, iv. evaluate possible problems due to poor heat distribution in the radiation chamber.

Na indústria petroquímica, fornos para craqueamento térmico são utilizados para processar hidrocarbonetos leves, como nafta, etano, propano e GLP, a fim de obter-se olefinas, como eteno e propeno. Fornos de craqueamento de etano são de fundamental importância para melhorar os rendimentos globais de uma planta de produção de olefinas. Neste contexto, um modelo matemático de um forno industrial de craqueamento de etano foi desenvolvido utilizando o simulador de processos EMSO para previsão do tempo de campanha. No modelo proposto, um reator de fluxo pistonado multi-secção foi acoplado com um modelo cinético das reações de craqueameto e coqueamento a partir de dados da literatura. Em paralelo, a câmara de radiação do forno foi modelada em fluidodinâmica computacional, através do uso do software Ansys-CFX. Os resultados das simulações no EMSO e no Ansys-CFX apresentaram boa concordância com os dados de literatura e dados industriais. Entre os principais benefícios dos modelos desenvolvidos para aplicação industrial ressaltam-se: i. a possibilidade de avaliar o impacto de contaminantes na corrente de etano que alimenta o forno e prever se ocorrerá uma redução do tempo de campanha; ii. viabilizar uma otimização dos fornos de etano, buscando operá-los em condições otimizadas de tempo de campanha reduzindo o risco de descoques simultâneos; iii. confirmar se reduções de tempo de campanha observados são em função das condições de processo ou se existe algum outro fator que esteja causando desvios em relação às previsões da simulações, iv. avaliar possíveis problemas de má distribuição de calor na câmara de radiação. / In petrochemical industries, steam cracking furnaces are used to process light hydrocarbons like naphta, ethane, propane and LPG in order to obtain olefins, like ethylene and propylene. Ethane steam cracking furnaces are of fundamental importance to improve the overall yields of an olefins production plant. In this context, a model for an industrial steam cracking furnace was developed using the equation-oriented dynamic simulator EMSO. In the proposed model, a multi-section plug flow reactor was coupled with cracking and coking kinetics from literature. Additionally, the radiation chamber was studied by computational fluid dynamics, using Ansys-CFX. The results performed are in good agreement with published and industrial design data. Among the main benefits of the models developed for industrial application, following stand out: i. the possibility to evaluate the impact of contaminants in ethane feed to the furnace and predict some run length reduction; ii. allow an optimization of ethane furnaces, seeking to operate them in optimal conditions of run length reducing the risk of simultaneous decokes; iii. confirm that observed run length reductions are depending on the process conditions, or if there is some other factor that is causing deviations from the simulation predictions, iv. evaluate possible problems due to poor heat distribution in the radiation chamber.

A nuclear magnetic resonance study of the critical region has been made in ethane which was chosen as the working substance for its convenient critical temperature and pressure. Standard radio frequency pulse techniques were used to measure the spin-lattice relaxation time T₁ and the self diffusion constant D by the method of spin echoes. A spectrometer having good stability and very flexible timing circuits was designed and constructed. An automatic temperature control system capable of holding the sample temperature constant to better than 0.01° C for long periods of time was also designed and constructed. The spin-lattice relaxation time in ethane has been measured along the vapor pressure curve over the entire liquid temperature range as well as in the equilibrium vapor from 0° C to the critical temperature (Tc =32.32° C) and in the dense gas from Tc to 60°C. In the liquid T₁ rises rapidly with increasing temperature and goes through a maximum at about 0°C after which it begins to fall. In the vapor T₁ is always less than in the liquid and increases with increasing temperature. In the dense gas above Tc the relaxation time decreases slowly with increasing temperature. These results are compared with the conventional theory for relaxation in liquids and dense gases. The theory gives the relaxation rate 1/T₁ in terms of three relaxation mechanisms: the dipole-dipole intermolecular interaction the dipole-dipole intramolecular interaction and the spin-rotational interaction. In view of the gross approximations made in the theory a very reasonable fit to the experimental data is obtained. For the low temperature liquid the dipole-dipole interactions are sufficient to account for the relaxation. At high temperatures the spin-rotational interaction seems to contribute significantly to the relaxation and near the critical point it is the dominant relaxation mechanism. No anomalous behaviour was observed in the relaxation near the critical point and to within the error of measurement it is adequately described in terms of changes in density and self diffusion constant. T₁ was also measured in dilute ethane gas over a temperature range of 180°K to 300°K. It was observed that T₁ is proportional to density ρ and the temperature dependence of T/ρ is about T⁻¹˙³⁷. Measurements of the diffusion constant reveal that for low temperatures the product Dρ for liquid ethane varies approximately as T³. As the temperature approaches the critical temperature there appears to be anomalous behaviour in D. For both the liquid and vapor the product Dρ begins to decrease and goes through a minimum and then increases rapidly as the critical point is reached. Oxygen has been added to these samples to decrease their relaxation time and this may well be an impurity effect. Particular attention was devoted to the question of the equilibrium state in the critical region and measurements were made on the time taken to achieve equilibrium. The approach of the ratio of liquid to vapor density to its equilibrium value was found to vary in a roughly exponential manner with a time constant of the order of several hours. Sufficient time was allowed after changing the sample temperature for equilibrium to be established and all measurements of diffusion constant and spin-lattice relaxation time reported here are thought to be equilibrium values. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The aim is to produce aliphatic liquid hydrocarbons using heterogeneous ethylene oligomerization. Thiscould potentially produce renewable synthetic fuels. Heterogeneous catalysis has some advantages overhomogeneous catalysis regarding some sustainability aspects. To achieve this, a setup was built using a heatedfixed bed reactor with an in-situ has chromatography to study conversion and gaseous products, and ex-situGC as well as NMR for analyzing liquid products. Ethylene was oligomerized on a commercial ZSM-5 zeoliteunder varying temperature conditions and feed gas dilution with hydrogen or helium. The gas and liquidproducts were analyzed and evaluated. Additionally, the ZSM-5 was studied at different silica to alumina ratios. The thesis discusses how conversion, liquid yield and selectivity of gas products using GC together withanalysis of liquid products using H-NMR can be used as a simple and quick evaluation. The liquid product isevaluated by the distribution of olefinic and aromatic hydrocarbon species using the hydrogen signal area inthe characteristic chemical shifts of olefinic and aromatic hydrogen. At 250-400oC, 6 bar of ethylene, with andwithout feed dilution, and WHSV of 204 h-1, conversion was consistently above 95% for the diluted 400oCruns. Though the liquid yield fell to around 6%, compared to the best yield at 18% for the pure 300oC run.Diluting the feed had a positive effect on increasing olefinic hydrogen signal while decreasing aromatichydrogen signal. The difference between diluting with H2 or helium had a surprisingly small effect. Decreasingthe Si/Al ratio had no significant effect on performance, while increasing the Si/Al ratio made the zeolite loseits catalytic ability. With a pure ethylene feed the lowest aromatic hydrogen signal was found at 350oC, whilethe olefinic signal did not vary too much with temperature. With diluted feed the higher temperature did leadto a lower olefinic hydrogen signal and higher aromatic hydrogen signal.