Abstract Carbon nanotubes (CNTs) were grown catalytically by a chemical vapor deposition method and characterized by a range of techniques. Fe, Ru and Co catalysts supported on the carbon nanotubes were prepared and investigated for their performances in the Fischer-Tropsch synthesis. CNTs were synthesized in a quartz tubular reactor at atmospheric pressure and at temperatures of 700°C over iron supported on CaCO3 using C2H2 as carbon source. Prior to CNT synthesis, the iron catalyst was first reduced under the same conditions (700°C and atmospheric pressure) in a flow of 5% H2 balanced in Argon. The catalyst, for the preparation of the CNTs, was prepared by the incipient wetness impregnation. The purification of the CNTs was performed with 30 wt % HNO3. Characterization of the CNTs using TEM, SEM, HRTEM, BET and TPR revealed that the crude product contained solely CNTs, catalysts particles and support, while no amorphous carbon was observed. The purified product is comprised of an interwoven matrix of tubes that were shown to be multi-walled (MWCNTs). CNT supported FT based catalysts were also prepared by an incipient wetness impregnation method and tested in a plug flow reactor in Fischer-Tropsch synthesis. The TEM images of the different FT catalysts supported on CNTs revealed that the catalyst particles are well dispersed on the surface of the CNTs. The catalyst particles were very iii small, and some residual Fe catalyst material, not removed by the acid treatment, could clearly be seen on the surface of the CNTs. The reduction and metal dispersion properties of the catalysts were investigated through TPR and chemisorption techniques. A TPR study showed three reduction steps for Co catalysts, and addition of Ru to the catalyst decreased the reduction temperature of the catalysts. Gasification of the CNTs was noted to occur at temperatures higher than 600°C. The effect of metal catalyst loading and promoters on the activity and selectivity of CNT supported FT synthesis catalysts was studied under condition of 275°C, 8 bar, CO/H2 = 1/2 and different flow rates. The FT catalysts supported on carbon nanotubes displayed a high CO conversion and excellent stability with time on stream in the Fischer-Tropsch synthesis. Fe catalysts displayed the lowest methane selectivity compared to all other FT synthesis catalysts used in this study.

Due to the combined heavy dependence on crude oil and the unpredictable nature of the associated markets, an alternative means to produce the required hydrocarbon based products is much desired. The Fischer-Tropsch synthesis provides a route to the production of synthetic crude oil by a catalytic reaction between carbon monoxide and hydrogen (collectively referred to as syngas) at moderate temperatures and pressures. First discovered in the early 1900's, the process results in a multitude of products which can supply a range of transportation fuels and petrochemicals. However, knowledge of the reaction process is still not completely understood due to the complex product distribution which is obtained. In order to gain better control over the process outputs, enhancing the understanding of the mechanistic routes which govern the overall reaction is key. A novel route was developed to monitor the number and length of hydrocarbon species which accumulate and grow on the catalyst surface during the reaction by implementing in situ quantitative FTIR spectroscopy. Initially molar absorption coefficients, required in order to quantify the adsorbed hydrocarbon species, were determined utilising a custom made thermogravimetric infrared cell. The resulting absorption coefficients values were then applied to data which was derived from infrared spectra collected for various catalysts during multiple Fischer-Tropsch reactions. The quantitative analysis of the catalyst surface was then compared with reaction data collected using gas chromatography (GC), in order to investigate if a link exists between the surface species and reaction products. Results showed that while no direct link was detected, the observed surface species could be attributed to oxygenate products of the Fischer-Tropsch reaction which are not produced in a detectable amount by GC. The species were shown to reside on both the metal and support material, with the transportation mechanism to the support also investigated.

Fischer-Tropsch synthesis is a commercial technology that allows converting synthesis gas, a mixture of CO and H2, into fuels and chemicals. This process could be one of the actors in the reduction of oil dependency of the transportation sector. In fact, it has great potential for producing synthetic fuels also from renewable sources, such as biomass, after its thermochemical conversion (gasification) into synthesis gas. Concerning the quality of a diesel fuel produced with this technology, it has a lower local environmental impact than conventional diesel, since it is practically free of sulphur and nitrogen compounds and yields lower exhaust emissions of hydrocarbons, CO and particulates. The present study focuses on the use of cobalt-based catalysts for the production of diesel. In particular, it looks upon correlation between product selectivities when varying the catalyst properties and the effect of process parameters, such as a low H2/CO ratio, typical of a biomass-derived synthesis gas, and the water partial pressure. Different cobalt-based catalysts, with different properties, such as conventional 3-dimensional porous network supports (γ-Al2O3, α-Al2O3, TiO2, SiO2), Co-loading, preparation technique, etc., were investigated in the Fischer–Tropsch reaction at industrially relevant process conditions. For a set of process conditions, a linear relationship seems to exist between the selectivity to methane (and other light products) and higher hydrocarbons (identified by the industrially relevant parameter SC5+, selectivity to hydrocarbons with more than 4 carbon atoms) indicating a common precursor. Ordered mesoporous materials (SBA-15), characterized by a 1-dimensional mesoporous network, were tested as model supports and showed the possibility of occurrence of CO-diffusion limitations at diffusion distances much shorter than those required for conventional 3-dimensional porous network supports. The linear relationship mentioned above, derived for conventional supports, was shown to be an efficient tool for indicating whether measured selectivities are affected by CO-diffusion limitations. Some of the catalysts were exposed to H2-poor syngas and to external water addition and the effects on the selectivity relationships were investigated. Furthermore, the possibility of internal water-gas shift of a H2-poor syngas with mixtures of Co/γ-Al2O3 and a Cu/ZnO/Al2O3 catalyst was investigated both as a technical solution for direct use of a model bio-syngas in the Fischer-Tropsch synthesis, and as a means to study the effect of indigenous water removal on the reaction rate to hydrocarbons. It was found that removal of indigenously produced water slows down the reaction rate significantly. Lastly, the effect of water partial pressure on the Fischer–Tropsch rate of the Co catalyst supported on narrow-pore γ-Al2O3, on its own, was studied. Inlet water partial pressure was varied by external water vapor addition at different H2/CO molar ratios ranging from 1 to 3. The effect of water showed to be positive on the rate for all the H2/CO ratios, but more significantly at H2-poor conditions. The nature of this positive effect on the rate seems to be unrelated to changes in amounts of amorphous polymeric carbon detectable by temperature-programmed hydrogenation of the spent catalyst. / <p>QC 20120914</p>

Thesis--Leyden. / In Periodical Room.

Zugl.: München, Univ., Magisterarbeit, 2008/2009

Submitted by Eduarda Figueiredo (eduarda.ffigueiredo@ufpe.br) on 2015-03-11T14:35:25Z No. of bitstreams: 2 Dissertação Completa_Rodrigo.pdf: 2042384 bytes, checksum: adeaba5f9e93bef7dcc818744781565e (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) / Made available in DSpace on 2015-03-11T14:35:25Z (GMT). No. of bitstreams: 2 Dissertação Completa_Rodrigo.pdf: 2042384 bytes, checksum: adeaba5f9e93bef7dcc818744781565e (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Previous issue date: 2012-05-31 / A tecnologia de produção de combustíveis sintéticos iniciou seu desenvolvimento a partir de 1919, na Alemanha, tendo o carvão mineral como insumo para a gaseificação. Com o passar dos anos novos insumos foram utilizados, como a biomassa e o gás natural, cada um com rotas tecnológicas próprias. Com o uso do gás natural esta rota tecnológica é conhecida como Gas-To- Liquids (GTL) sendo uma transformação química que gera faixas de hidrocarbonetos líquidos e estáveis à temperatura e pressão ambientes. Este processo tem como etapa principal etapa à reação de Fischer Tropsch (FT), pois transforma gás síntese resultante da reforma do gás natural em hidrocarbonetos líquidos que ao serem refinados tornamse importantes produtos para indústria petroquímica, de transporte e áreas afins. Essa transformação pode ser realizada no próprio local de produção do gás, evitando investimentos e problemas ambientais na construção de gasodutos. No Brasil, o gás natural apresenta crescente incremento da sua produção, e forte aumento das suas reservas, como por exemplo, a descoberta do pré-sal e o gás natural presente pode estar tanto associado quanto não-associado ao petróleo. Devido às estruturas de plataformas normalmente se localizarem em áreas remotas, torna-se custoso o aproveitamento desse gás que é liberado pela produção do óleo, sendo o mesmo queimado ou ventado. Devido às restrições estabelecidas pela legislação ambiental, a queima do gás natural nas plataformas de produção passa a ser problemática e crítica. Este trabalho teve como objetivo desenvolver e avaliar por meio de simulação computacional uma planta de GTL na produção de hidrocarbonetos líquidos via a reação de FT e utilizá-lo na otimização do processo, na busca por um processo com maior capacidade produtiva e com menores gastos energéticos, gerando um melhor aproveitamento do gás natural, produzindo materiais com maior valor agregado. Foram utilizados os softwares de simulação MATLAB® e HYSYS®, que permitiram a analise de resultados satisfatórios para a conversão e distribuição de hidrocarbonetos gerados em comparação com o descrito pela literatura. A qualidade dos hidrocarbonetos gerados foi analisada pela avaliação do diesel obtido.

The arylation of readily accessible N-tosyl hydrazones has been achieved using arynes generated in situ under mild conditions. The resulting N-tosyl-N-aryl hydrazones undergo a one-pot Fischer indole reaction on the addition of acid, giving a synthesis of protected indoles that avoids handling unstable intermediates and arylhydrazines. A new route to functionalised 2-(trimethylsilyl)phenyl triflate aryne precursors via Suzuki cross-coupling has been developed. The method allows the incorporation of a wide range of aryl and heteroaryl groups and reactions of arynes generated from these novel precursors have been demonstrated, including a cyclotrimerisation and a fluorenone synthesis. Work was also undertaken on aryne σ-insertion reactions. The addition of benzyne to ynamides was found to result in its net insertion between the nitrogen and acetylene species. The reaction proceeds from attack at the terminal carbon in an analogous manner to C(sp)–O insertions.

Fischer-Tropsch synthesis is the technology for converting fuel feedstocks such as natural gas and coal into transportation fuels and heavy hydrocarbons. There is scope for research and development into integrated processes utilising synthesis gas for the production of a wide range of hydrocarbons. For this purpose there should be strategies for the development of Fischer-Tropsch processes, which consider both economic and technological feasibilities. The aim of this study was to optimize Fischer Tropsch Plants in order to produce gasoline and gas oil by investigating the benefits of recycling & co-feeding of unconverted gas, undesired compounds, and lighter hydrocarbons over iron-based catalysts in order to save on capital and operating costs. This involved development of FT models for both two-phase and three-phase reactors. The kinetic parameters for these models were estimated using optimization with MATLAB fitting to experimental data and these models were then applied to ASPEN HYSYS flowsheets in order to simulate nine different Fischer-Tropsch plant designs. The methodology employed involved qualitative modelling using Driving Force Analysis (DFA) which indicates the necessity of each compound for the Fischer-Tropsch reactions and mechanism. This also predicts each compounds influence on the selectivity of different products for both two-phase and three-phase reactors and for both pure feeding and co-feeding arrangements. In addition, the kinetic models for both two-phase and three-phase reactor were modified to account for parameters such as the size of catalyst particles, reactor diameter and the type of active sites used on the catalyst in order to understand and quantify their effects. The kinetic models developed can describe the hydrocarbon distributions consistently and accurately over large ranges of reaction conditions (480-710K, 0.5-2.5MPa, and H2/CO ratio: 0.5-2.5) over an iron-based catalyst for once-through processes. The effect of recycling and co-feeding on the iron-based catalyst was also investigated in the two reactor types. It was found that co-feeding unwanted compounds to synthesis gas increases the production of hydrocarbons. This recycling and co-feeding led to an increase in H2/CO feed ratio and increased selectivity towards C5+ products in addition to a slightly increased production of light hydrocarbons (C1-C4). Finally, the qualitative model is compared with the quantitative models for both two-phase and three-phase reactors and using both pure feeding and co-feeding with the same reactor conditions. According to the detailed quantitative models developed, in order to maximize hydrocarbon production pressures of 2MPa, temperatures of 450K and a H2/CO feed ratio of 2:1 are required. The ten different Fischer-Tropsch plant cases were based on Fischer-Tropsch process. FT reactor models were built in ASPEN HYSYS and validated with real FT plant data. The results of the simulation and optimization supported the proposed process plant changes suggested by qualitative analysis of the different components influence. The plants involving recycling and co-feeding were found to produce higher quantities of gasoline and gas oil. The proposed heuristic regarding the economic scale of the optimized model was also evaluated and the capital cost of the optimized FT plant reduced comparison with the real FT plant proposed by Gerard. Therefore, the recycling and co-feeding to FT reactor plant was the best efficiency to produce both gasoline and gas oil.

Orientador: Mario de Jesus Mendes / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Campinas / Made available in DSpace on 2018-07-17T00:50:54Z (GMT). No. of bitstreams: 1 Santos_OneliaAparecidaAndreodos_M.pdf: 5044753 bytes, checksum: 4d24d41e569f872f9de1eb02687ec8d3 (MD5) Previous issue date: 1986 / Resumo: A reação de síntese de Fischer - Tropsch tem merecido uma grande atenção pelo seu interesse tecnológico e científico. Naturalmente este interesse está, em grande parte, associado ao problema da escassez do petróleo, na medida em que a síntese de Fischer - Tropsch oferece uma rota adequada para a transformação de combustíveis sólidos em combustíveis líquidos e gasosos e em insumos básicos da industrIa petroquímica. Dada a estrutura do mercado brasileiro, este interesse está essencialmente dirigido para a substituição do óleo diesel e do óleo combustível. A experiência mostra que, através de uma seleção adequada do catalisador e das condições operatórias,é possível alterar, dentro de certos limites, a distribuição dos produtos obtidos na reação de síntese. Neste trabalho é apresentada uma discussão sobre a natureza dos catalisadores usados na síntese de Fischer-Tropsch, assim como o mecanismo da reação, com ênfase nos catalisadores à base de ferro. Pretende-se com esta discussão, identificar algumas possíveis vias para o desenvolvimento de catalisadores otimizados, mais ativos e mais seletivos, para determinadas frações de produtos (gasolina, diesel, olefinas, etc). É ainda apresentada uma descrição da instalação desenvolvida para a coleta de dados cinéticos na síntese de Fischer - Tropsch, e discutidas, com base em resultados preliminares, as dificuldades encontradas, em particular no que respeita à análise das misturas complexas obtidas como produto da reação. / Abstract: The Fischer-Tropsch synthesis reaction has received great attention due to its scientific and technological interest. This interest arises mostly in association with the dwindling of petroleum reserves, and because the Fischer - Tropsch synthesis offers an appropriate route for the transformation of solid fuels into liquid or gaseous fuels, as well as basic chemicals for the petrochemical industry. Considering the structure of the Brazilian market, this interest is essencially directed for the substitution of diesel and fuel oil. Accumulated experience with the synthesis reaction shows that it is possible to alter, within certain limits, the distribution of the products obtained. In this work a discussion is presented on the nature of the catalysts used in the Fischer - Tropsch synthesis, as well as on the reaction mechanism, with emphasis on catalysts based on iron. The aim of this discussion is to establish possible schemes for the development of optimized catalysts, with better activity and selectivity for desired product fractions(gasoline, diesel, olefins,etc). It is also presented the description of an experimental equipment developed for collecting kinetic data on the Fischer - Tropsch synthesis, and discussed the difficulties that were met in the preliminary tests, particularly with reference to chemical analysis of the products of reaction. / Mestrado / Mestre em Engenharia Química

Please read the abstract in the dissertation / Dissertation (MSc)--University of Pretoria, 2013. / gm2014 / Chemistry / Unrestricted