Zugl.: Aachen, Techn. Hochsch., Diss., 2008.

CRUZ, M. G. A. Catalisadores baseados em Fe-C mesoporosos para síntese de Fischer-Tropsch. 2017. 97 f. Tese (Doutorado em Engenharia Química)–Centro de Tecnologia, Universidade Federal do Ceará, Fortaleza, 2017. / Submitted by Marlene Sousa (mmarlene@ufc.br) on 2017-09-06T14:51:50Z No. of bitstreams: 1 2017_tese_mgacruz.pdf: 4026668 bytes, checksum: 3c2516a4d0b0ba6bcae042831861b0a6 (MD5) / Approved for entry into archive by Marlene Sousa (mmarlene@ufc.br) on 2017-09-06T15:38:26Z (GMT) No. of bitstreams: 1 2017_tese_mgacruz.pdf: 4026668 bytes, checksum: 3c2516a4d0b0ba6bcae042831861b0a6 (MD5) / Made available in DSpace on 2017-09-06T15:38:26Z (GMT). No. of bitstreams: 1 2017_tese_mgacruz.pdf: 4026668 bytes, checksum: 3c2516a4d0b0ba6bcae042831861b0a6 (MD5) Previous issue date: 2017-02-10 / This work deals with the influence of preparation methods of Fe - containing carbon catalysts for Fischer - Tropsch Synthesis (SFT). For these purposes, two series of solids were prepared. The first series was the Fe - based catalysts supported o n polystyrene mesoporous carbon pretreated at dif ferent calcination temperatures. The second series of materials was the solids prepared by distinct preparation methods. All solids were characterized by X - ray diffract ion (XRD) , Raman spectroscopy, s canning and t ransmission electron microcopies (SEM and TEM), textural properties, elemental composition by X - ray dispersive spectroscopy (EDS), temperature programmed reduction (TPR) and X - ray photoelectron spectroscopy (XPS). It was shown that the preexistent carbides phases obtained in the Fe - containing polymeric mesoporous carbons upon using elevated temperatures of calcinations resulted in a solid with good textural and structural properties. However, these materials were not comp letely reoxidized during the SFT reaction while the formation of carbides through the polymeric carbon reaction with magnetite and  or metallic iron resulted in highly active catalysts for SFT . The second series of materials applied copolymer assisted co - p recipitation of iron precursor (CP) , chemical modification of ferrocene (CM) , sol - gel (SG) and wetness impregnation of iron on polymeric carbon (IM) methods . SG method solid resulted in a conversion of syngas up to 56% and productivity of 34 mg hydrocarbon .g cat - 1 .h - 1 at 240 o C and 20 atm. IM gave a Fe/C based catalyst with the highest exposure of active sites, including surface Fe 3+ and Fe 2+ redox sites with great properties in SFT . CM route enabled the formation of hematite and maghemite nanoparticles on ca rbon, which were reduced in situ to magnetite and iron carbide s, the latt er being the most active for the water - gas - shift reaction (RWGS) reaction. It was found that copolymer assisted CP facilitate d the production of large crystals of magnetite, which suf fered sintering and coking in SFT . Among these methods, SG proved to have superior performance due to the good dispersion of Fe, stable magnetite as well as iron carbide and Fe - doped nitrogen carbon phases production. / A proposta deste trabalho é estudar a influência do método de preparação de catalis adores contendo Fe - carbono para a reação de Fischer - Tropsch (SFT). Para este fim, duas séries de sólidos foram preparadas. A primeira série foi composta de Fe contendo carbono pré - tratados em diferentes temperaturas de calcinação . A segunda série de materi ais é composta por sólidos obtidos por distintos métodos de preparação. Todos os materiais foram caracterizados por difração de raios - X (DRX), e spectroscopia Raman, m icroscopias eletrônicas de varredura e transmissão (SEM e TEM), propriedades texturais, co mposição elementar por espectroscopia de energia dispersiva de raios - X (EDS), redução termoprogramada (TPR) e espectros copia fotoeletrônica de raios - X (XPS). Os resultados revelaram que os carbetos formados nos sólidos de Fe impregnados em carbono poliméri co mesoporoso resultaram em boas propriedades texturais e estruturais. No entanto, estes materiais não foram completamente oxidados durante a reação de SFT, enquanto qu e a formação de carbetos oriundos da reação de magnetita e  ou ferro metálico resultaram em catalisadore s ativos para SFT. A segunda série de materiais aplicou os métodos de co - precipitação assistida do copolímero com o precursor de ferro (CP), modificação química do ferroceno (CM), sol - gel (SG) e impregnação de ferro sobre o carbono poliméric o (IM). O método de preparação SG resultou em uma conversão do gás de síntese de 56% e produtividade de 34 mg hidrocarboneto .g cat - 1 .h - 1 a 240 o C e 20 atm. O método IM gerou um catalisador de Fe/C com sítios ativos bastante expostos, incluindo os sítios redo x Fe 3+ e Fe 2+ superficiais que possuem excelentes propriedades em SFT. A rota CM possibilitou a formação de nanopartículas de hematita e maguemita sobre o carbono, os quais foram reduzidos in situ à magnetita e carbeto de ferro, sendo a última espécie alt amente ativa na reação reversa de shift (RWGS) . A síntese de co - precipitação assistida do copolímero, CP, facilitou a formação de grandes cristais de magnetita, que sofreram sinterização e coqueamento na SFT. Dentre esses métodos, o método SG mostrou desem penho superior aos demais, devido à boa dispersão de Fe bem como à produção das fases magnetita estável e Fe contendo carbono dopado com nitrogênio.

The research determined that the improved heat transfer characteristics of a fluidized bed reactor (FBR) will allow the use of cobalt catalyst for high temperature Fischer-Tropsch synthesis (HTFT). Cobalt was loaded onto a gamma alumina support, the catalyst was characterized using TPR, BET/BJH, XRD, and PSA to track changes in the catalyst morphology. The reactor was characterized to determine the minimum fluidization velocity and the maximum velocity prior to entering lean phase fluidization with pneumatic transport of the catalyst. The highest minimum fluidization velocity was found to be about 2800 sccm, there was no maximum velocity found for the reactor setup. Once characterized, the reactor was operated at pressures of 145, 217.6, and 290.1 psig, a syngas flow rate of 4000 sccm, and at temperatures of 330 and 350 °C. The optimal conditions found in this study were 330 °C and 217 psig. At these conditions CO conversion was 83.53 % for a single pass. Methane, CO2, and light gases (C2 - C4) selectivities were at low rates of 31.43, 5.80, and 3.48 % respectively. Alcohol selectivity at these conditions was non-existent. The olefin and wax selectivities were the lowest of the data set at 7.05 and 3.18 % respectively. Liquid transportation fuels selectivity was the highest at 56.11 %.

L'alumine, utilisée comme support de catalyseurs pour la réaction de Fischer-Tropsch ou pour la conversion de la biomasse, se transforme partiellement en présence d'eau en phases (oxy)hydroxydes à l'origine de fines qui posent problème dans la mise en ¿uvre de procédés en réacteurs de type slurry. Afin de concevoir des catalyseurs plus stables et plus résistants, ce travail de thèse visait à identifier le mécanisme d'hydratation et de dégradation des alumines de transition en phase aqueuse, et à étudier la façon dont des additifs organiques (alcools, polyols) ou inorganiques (Mg, Zr, Ni et Si) permettent de limiter cette dégradation. La conduite d'une étude systématique sur l'hydratation des alumines à 70°C à pression atmosphérique, ou à 150°C en conditions hydrothermales, a permis de définir un mécanisme général en deux étapes: une dissolution de la surface de l'alumine, suivie d'une précipitation, respectivement, d'hydroxydes d'aluminium Al(OH)3 ou de boehmite AlOOH sur les grains d'alumine. Par ailleurs, la dégradation chimique tend à favoriser la dégradation sous contraintes mécaniques. La présence de polyols en phase aqueuse, principalement des molécules à 5 ou 6 atomes de carbone, ralentit la dissolution de l'alumine et inhibe la précipitation de la boehmite. Les ions métalliques utilisés comme dopants de l'alumine ont tous un effet similaire sur la diminution de l'hydratation. Une inhibition totale de l'hydratation est obtenue par greffage de silicium à partir de TEOS. Une étude DRIFT dans la région des vibrations OH suggère que les additifs inorganiques inhibent la dissolution de l'alumine en bloquant des sites Al-OH localisés sur les faces latérales des particules. / Alumina, used as a catalyst support for the Fischer-Tropsch reaction or for the conversion of biomass, partially transforms in presence of water into (oxy)hydroxides phases. The formation of the latter leads to the production of fine particles that may cause plugging problems in the implementation of processes based on slurry bubble column reactors. In order to design more stable and more resistant catalysts, this PhD work aimed at identifying the mechanism of hydration and degradation of transition aluminas in aqueous phase, and to study how organic (alcohols, polyols) or inorganic (Mg, Zr, Ni and Si) additives can limit this degradation. The conduct of a systematic study on the hydration of alumina at 70°C under atmospheric pressure, or at 150°C in hydrothermal conditions, allowed defining a general two-step mechanism: a dissolution of the surface of alumina, followed by a precipitation of, respectively, aluminum hydroxides (Al(OH)3) or boehmite (AlOOH) on alumina grains. Furthermore, the chemical degradation tends to promote the degradation under mechanical stress. The presence of polyols in aqueous phase, mainly molecules with 5 or 6 carbon atoms, slows down the dissolution of alumina and inhibit the precipitation of boehmite. Metal ions used as dopants of alumina all have a similar effect on the decrease of hydration. A total inhibition of hydration is obtained by grafting silicon using TEOS. A DRIFTS study in the OH vibration region suggests that inorganic additives inhibit the dissolution of alumina by blocking Al-OH sites located on the lateral facets of the particles.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / Este trabalho teve como objetivo sintetizar catalisadores metÃlicos de ferro suportados em carbono ativado a base de polÃmeros para sÃntese de Fischer-Tropsch. A preparaÃÃo dos catalisadores foi realizada pelo mÃtodo de impregnaÃÃo a umidade incipiente, utilizando soluÃÃo aquosa de nitrato de ferro nonahidratado para obtenÃÃo de amostras com, aproximadamente, 55% de ferro. Duas amostras foram preparadas (FeCP1 e FeCP2) e caracterizadas por fluorescÃncia de raios-X por energia dispersiva (EDXRF), difraÃÃo de raios-X (DRX), medidas de fisissorÃÃo de nitrogÃnio, espectroscopia fotoeletrÃnica de raio-X (XPS), microscopia eletrÃnica de varredura (SEM-EDS) e reduÃÃo à temperatura programada (TPR). As amostras foram submetidas tambÃm a testes catalÃticos, utilizando-se diferentes condiÃÃes de temperatura (513, 528 e 543 K), pressÃo (20, 25 e 30 atm) e razÃo molar H2:CO de 1 e 0,5. Os dados de EDXRF evidenciaram considerÃvel diferenÃa no teor de metal impregnado entre os dois catalisadores; o FeCP2 apresentou teor prÃximo ao esperado enquanto o catalisador FeCP1 ficou aquÃm do desejado. Os difratogramas obtidos por DRX mostraram um maior grau de cristalinidade da amostra FeCP2, enquanto FeCP1 e os dois suportes (CP1 e CP2) apresentaram-se como semi-cristalinos. Para o catalisador FeCP2, apresentaram-se duas fases ativas presentes, α-Fe2O3 e γ-Fe2O3; jà no FeCP1, hà apenas α-Fe2O3. A anÃlise das caracterÃsticas texturais revelou que, apÃs a introduÃÃo metÃlica no suporte, houve decrÃscimo nos valores de Ãrea especÃfica, volume de poros e diÃmetro de poros, sendo mais perceptÃvel para o catalisador FeCP2. As curvas de XPS expuseram os grupos funcionais oxigenados presentes na superfÃcie dos suportes, bem como a presenÃa do Fe+3 como fase ativa predominante em ambos os catalisadores. O espectro de ambos os catalisadores apresentou tambÃm um pico satÃlite que sugere a presenÃa de um outro estado de valÃncia do ferro semelhante ao que se tem no carbeto de ferro. As imagens obtidas por SEM exibiram forma e superfÃcie irregulares, sendo as partÃculas presentes no FeCP2 maiores que a do FeCP1 devido a sua cristalinidade. Os dados de EDS demonstraram que, aproximadamente, metade do percentual de ferro presente no catalisador encontra-se na superfÃcie. Pode-se inferir tambÃm por essa anÃlise, utilizando-se seu espectro, a presenÃa de carbeto de ferro na superfÃcie do catalisador. As curvas de TPR evidenciaram uma maior estabilidade do catalisador FeCP2 mediante o FeCP1, por este ter apresentado trÃs etapas de reduÃÃo do Ãxido de ferro e nÃo duas, como apresentada para aquele Ãltimo. O teste catalÃtico expÃs a melhor eficiÃncia do catalisador FeCP2 para a produÃÃo de hidrocarbonetos na faixa de C5-C9, para as mesmas condiÃÃes de temperatura, pressÃo e razÃo molar. Entretanto, a diminuiÃÃo da razÃo molar desfavoreceu a obtenÃÃo de hidrocarbonetos pesados. / The aim of this work was to synthesize iron catalysts supported on polymer-based activated carbons, for the Fischer-Tropsch synthesis. The preparation of the catalysts was performed by incipient wetness impregnation method using an aqueous solution of iron nitrate nonahydrate to obtain samples with approximately 55 % of iron. Two samples were prepared (FeCP1 and FECP2) and characterized by energy dispersive X-ray fluorescence (EDXRF), X-ray diffraction (XRD), nitrogen adsorption measurements, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM-EDS) and temperature-programmed reduction (TPR). The samples were also submitted to catalytic tests using different conditions of temperature (513, 528 and 543 K), pressure (20, 25 and 30 atm), and H2:CO molar ratio of 1 and 0.5. EDXRF data showed considerable difference in content of impregnated metal for both catalysts. FeCP2 exhibited an iron load close to the value expected while FeCP1 presented an iron load significantly lower than expected. XRD patterns showed a higher degree of crystallinity of the sample FeCP2, whereas FeCP1 and both supports used (CP1 and CP2) were found to be semi-crystalline. FeCP2 catalyst presented two active phases, α-Fe2O3 and γ-Fe2O3, while FeCP1 showed only one phase, α-Fe2O3. The analysis of the textural characteristics revealed a decrease in the values of the specific area, pore volume and pore diameter after the introduction of the metal into the support, which was more noticeable with the FeCP2 catalyst. XPS patterns indicated oxygen functional groups on the support surface and the presence of Fe+3 as the predominant active phase on both catalysts. The spectrum of both catalysts also showed a satellite peak which shows the presence of another valence state similar to the iron carbide. Images obtained by SEM revealed irregular shape and surface, being the particles present in FeCP2 greater than those on FeCP1 due to the crystallinity of the former. EDS data showed that approximately half of the iron percentage present in the catalyst bulk is on the surface. The presence of iron carbide on the catalyst surface can be inferred by using this spectrum analysis too. TPR graphics demonstrated a higher stability of the FeCP2, due to the three-step reduction of iron oxide instead of two as shown for the FeCP1. According to the results of the catalytic tests FeCP2 exhibited a better efficiency for the production of hydrocarbons in the C5-C9 range, for the same conditions of temperature, pressure and molar ratio. However, the decrease in the molar ratio disfavors the production of heavy hydrocarbons.

Submitted by Isaac Francisco de Souza Dias (isaac.souzadias@ufpe.br) on 2016-05-02T17:40:30Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação Mestrado_Victor Vital L Bezerra.pdf: 2015533 bytes, checksum: 69f4ce642504e6d617f898f6de8e138c (MD5) / Made available in DSpace on 2016-05-02T17:40:30Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação Mestrado_Victor Vital L Bezerra.pdf: 2015533 bytes, checksum: 69f4ce642504e6d617f898f6de8e138c (MD5) Previous issue date: 2015-02-27 / PRH-28 / ANP / Como principal reação da tecnologia Gas-to-Liquids (GTL), a síntese de Fischer-Tropsch (SFT) surge como alternativa expoente para enriquecimento da cadeia do gás natural. Utilizando uma unidade de bancada que possibilita a reação e a análise dos produtos formados, foram realizadas reações a pressão constante de 2,0 MPa e relação molar de gás de síntese H2:CO=2:1. Foi investigado o uso de catalisadores sólidos, não promovido (20%Co/γ-Al2O3) e promovido (0,5%Pt-20%Co/γ-Al2O3) e um sistema estruturado (0,5%Pt-20%Co/γ-Al2O3-micromonólito), observando a influência da temperatura (185 a 230ºC) e velocidade espacial (0,3 a 1,2 mol.gcat-1.h-1). Constatou-se que nas reações da SFT ao se utilizar o catalisador Co/γ-Al2O3, nas condições operacionais de temperatura e velocidade espacial investigadas, foram obtidas variações na conversão de CO (3,4 a 56%), e nas seletividades de CH4 (4,4 a 23,5%); de CO2 (1,1 a 3,0%); de C2-C4 (0,8 a 2,7%) e de C5+ (76,5 a 95,6%), e uma probabilidade de crescimento da cadeia (α) de 0,81 a 0,94. Para o catalisador Co-Pt/γ-Al2O3, em diferentes condições operacionais de temperatura e velocidade espacial, foram obtidas variações na conversão de CO (3,7 a 99,8 %), e nas seletividades de CH4 (3,7 a 23,8%); de CO2 de (0,7 a 11,0 %); de C2-C4 de (1,1 a 4,4%) e de C5+ (71,9 a 95,2%), e uma probabilidade de crescimento da cadeia (α) de 0,79 a 0,93. A adição da platina não alterou a estrutura do catalisador, mas favoreceu na redução dos óxidos de cobalto. Observou-se que para todos os catalisadores investigados neste trabalho, o aumento da temperatura acarretou um aumentou na conversão de CO, entretanto favoreceu a formação de metano. A diminuição da velocidade espacial, de modo geral, acarretou em um aumento na conversão de CO. Quando comparados os catalisadores sólidos, nas mesmas condições operacionais, o catalisador promovido por platina apresentou uma maior atividade catalítica. Quando comparado o catalisador estruturado com o catalisador sólido, não houve grande diferença na atividade catalítica, entretanto o catalisador estruturado apresentou uma maior afinidade para formação e C5+. O sistema estruturado apresentou um excelente controle na dispersão do calor formado na reação. / As main reaction technology Gas-to-Liquids (GTL), the Fischer-Tropsch synthesis appears as an alternative to valorize the natural gas chain. Using a bench unit, reactions were carried out at constant pressure of 2.0 MPa, molar ratio syngas H2:CO=2:1. It was investigated the use of solid catalysts, not promoted (20%Co/γ-Al2O3) and promoted (0,5%Pt-20%Co/γ-Al2O3) and a structured system (0,5%Pt-20%Co/γ-Al2O3-micromonolite). The influence of temperatures (185 to 230°C) and space velocity (0,3 to 1,2 mol.gcat-1.h-1) were studied. It was found that in the FTS reactions, using the catalyst Co/γ-Al2O3 in operating conditions of temperature and space velocity investigated variants were obtained in CO conversion from 3.4 to 56%, and the selectivity to CH4 4.4 to 23,5%; CO2 1,1 to 3,0%; C2-C4 0,8 to 2,7% and the C5+ from 76,5 to 95,6%, and the chain growth probability (α) 0,81 to 0,94. Results of the Pt-Co/γ-Al2O3 show CO conversion from 3,7 to 99,8% were obtained, and the selectivity from CH4 3,7 to 23, 8%; CO2 0,7 to 11,0%; C2-C4 1,1 to 4,4% C5+ from 71,9 to 95,2%, and the chain growth probability (α) from 0.79 to 0,93. The addition of platinum not altering the structure of the catalyst, but favored in the reduction of cobalt oxides. It was observed that for all catalysts studied in this work, the increase in temperature led an increased of CO conversion, however favored the formation of methane. The reduction of space velocity, generally, resulted in an increase of CO conversion. When comparing the solid catalysts, under the same operating conditions, the catalyst promoted by platinum showed higher catalytic activity. The structured catalyst when compared with the solid catalyst, did not differences in catalytic activity, however, the structured catalyst had a higher affinity for formation for C5+. The structured system showed excellent control in heat dispersion formed in the reaction.

Orientador: Gustavo Paim Valença / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-07-27T17:48:45Z (GMT). No. of bitstreams: 1 Goncalves_EmersonSarmento_M.pdf: 6577943 bytes, checksum: 7f0584919df305f521c9d43f2ec3654a (MD5) Previous issue date: 2001 / Resumo: A partir do gás de síntese (que constitui uma mistura gasosa de óxidos de carbono e hidrogênio), pode-se obter hidrocarbonetos, álcoois e aldeídos. Estes podem ser obtidos também através da via petroquímica. Portanto, a produção desses compostos a partir do gás de síntese constituem vias alternativas que podem ser exploradas em função de aspectos econômicos existentes no mercado. Este fato tem motivado um interesse renovado pelo aprofundamento do conhecimento acerca da reação de Fischer- Tropsch. Além disso, é possível transformar gás de síntese resultante de transformações ocorridas com o metano, em produtos com maior valor agregado. O problema proposto é a análise sistemática de possíveis catalisadores eficazes no aumento da especificidade de um produto desejado. No caso particular desse trabalho, a atenção é direcionada a três produtos: metano, metanol e etileno. Na literatura, são apresentados diversos catalisadores para essas reações. Por exemplo, Ni, Pd, FelW são catalisadores seletivos para a reação de metanação. Fe, Co e Ru, são catalisadores seletivos para a formação de hidrocarbonetos e álcoois com mais de 2 átomos de carbono. Cu, Pt e Pd são catalisadores seletivos para a formação de metanol e poliálcoois. O fato de a reação de Fischer-Tropsch apresentar grande diversidade de produtos é coerente com a variedade de mecanismos propostos. Cada um deles é capaz de justificar satisfatoriamente o espectro de produtos formados, mas a evidência usada para sustentar as teorias individuais é usualmente indireta e pode, algumas vezes, ser interpretada em mais de uma rota. Segundo descrições usuais, há três principais categorias, no tocante ao que acontece inicialmente com o monóxido de carbono: na primeira, ele quimissorve dissociativamente e é sucessivamente hidrogenado; na segunda, o CO adsorve associativamente e é sucessivamente hidrogenado; na terceira, a molécula não dissocia e se insere entre ligações metal-hidrogênio ou metal-carbono. Neste trabalho a metodologia de análise das etapas elementares utiliza o formalismo baseado na conservação da ordem de ligação e em Potenciais de Morse (BOC-MP), desenvolvido por E. Shustorovich. Este formalismo aplicado a outras reações resultou em valores para a entalpia de adsorção e energia de ativação de etapas elementares dentro de 10 kJ morl dos valores experimentais. O método estima as entalpias de adsorção qas espécies e a energia de ativação das etapas envolvidas em cada rota de reação. Em reações tais como a oxidação do CO, hidrogenólise do etano, hidrogenação do eteno e decomposição catalítica da hidrazina, o método apresentou bastante sucesso, com erros inferiores a 15% com relação aos valores obtidos experimentalmente. O trabalho consiste em identificar as espécies envolvidas na reação e equaclOnar as entalpias de adsorção de cada espécie e a energia de ativação de cada etapa elementar da reação em função das entalpias de adsorção dos átomos de carbono, oxigênio e hidrogênio apenas. Em seguida, procede-se com análise dos resultados de energia de ativação versus entalpia de adsorção de carbono e de oxigênio. A análise é baseada primeiramente em comparações duas a duas de etapas que apresentem valores de fatores pré-exponenciais com a mesma ordem de grandeza. Busca-se com essa análise as faixas em que cada etapa é predominante, isto é superficies que favorecem uma ou outra etapa. Subseqüentemente, procede-se com o agrupamento das diversas etapas de cada conjunto de etapas, ou rotas de reação, visando determinar regiões ou domínios dos mínimos locais de energia de ativação. Identifica-se dessa maneira as diversas faixas onde cada uma das diversas reações podem ocorrer, de tal maneira a serem identificados os catalisadores ótimos para as diversas reações estudadas. Desta etapa, parte-se para a comparação com resultados experimentais apresentados na literatura procurando-se mostrar onde cada catalisador está localizado. Dependendo dos resultados encontrados será possível sugerir novos domínios ( catalisadores) para outras reações decorrentes dos mesmos reagentes. Uma conseqüência da análise proposta é a sugestão de desenvolvimento de novos catalisadores para reações com gás de síntese e do projeto de catalisadores eficazes na transformação de gás de síntese em produtos com maior valor agregado. Os resultados mostram que, num certo sentido, a forma como o CO quimissorve sobre a superficie metálica é decisiva para o tipo de produto final. A seqüência de etapas elementares que leva à síntese de metanol concorre principalmente com a seqüência de metanação. Desde a primeira até a última etapa, catalisadores de cobre estarão bastante associados à manutenção da ligação CO e sva hidrogenação, bem como das espécies subseqüentes, até o metanol. Platina e paládio apresentam também certa tendência para síntese de metanol. Ferro e níquel estão associados à quebra da ligação CO e são catalisadores de síntese de Fischer- Tropsch e metanação, respectivamente / Abstract: The Fischer- Tropsch synthsis is an altemative route for the production of hydrocarbons, alcohol and aldehydes, chemicals that may also be obtained in a petrochemical route. The final decision on the use of either route depends on economic aspects of local markets. Nonetheless, there has been a renewed interest in the Fischer- Tropsch reaction, particularly as petroleum becomes scarce in many parts of the world and methane-derived syngas may be obtained ITom renewable sources. The present work proposes a detailed analysis of different sequence of elementary steps for the Fischer- Tropsch reaction that may take place on different surfaces, in the search of an increase in product selectivity. As a case study, attention is directed to three products: methane, methanol and ethylene. For example, Ni, Pd, Fe/W are selective catalysts for the methanation reaction while Fe, Co or Ru are selective catalysts for the production of hydrocarbons and alcohols with more than two carbon atoms. Cu, Pt e Pd are selective catalysts for the methanol synthesis and for the formation of polyalcohols. In order to explain the wide variety of products obtained in the Fischer- Tropsch reaction, different sequence of steps are proposed. Each of them is in agreement with the formation of a product, but the evidence used to support individual theories is usually indirect and may be ambiguous. In any event, it is well accepted that CO is involved in three possible steps, namely, dissociative chemisorption with subsequent hydrogenation; non-dissociative chemisorption with subsequent hydrogenation; or insertion ofthe undissociated molecule into either a metal-hydrogen or a metal-carbon bonds. In this work the analysis of elementary steps is based on the bond order conservation and Morse Potentials method (BOC-MP), developed by E. Shustorovich. The method estimates the adsorption enthalpies of the species and the activation energy of the each elementary step. The BOC-MP formalism has been used for reactions such as the CO oxidation, hydrogenolysis of ethane, hydrogenation of ethylene and catalytic decomposition of hydrazine, with errors in activation energy less than 15% of experimental values. First, the possible species involved in all steps were identified and the equations to calculate the adsorption enthalpy of each species as a function of the adsorption enthalpies of O, C and H (Qo, Qc and QH) were written. Then, the elementary steps of each reaction and the equation for the activation energy of each step were written as a function of the adsorption enthalpies of C, O and H. The activation energy was then analysed as a function ofthe adsorption enthalpy ofC and O. Related steps with the same pre-exponential factors are then compared in the search of regions or domains where each step is favoured. Subsequently, alI steps were grouped together and domains of Qo and Qc where local minimum of activation energy exist can be identified. These domains correspond to different catalysts used for each product. There is a good agreement between the surfaces suggested by the present method and real catalysts. Thus, the proposed methodology is able to identify possible surfaces to be used as prospective catalysts for a given reaction or modifications ofthe surface structure ofworking catalysts. The results show that, in a sense, the manner as CO chemissorb over the metalic surface is decisive to the type of final product. The sequence of elementary steps which drive to the methanol synthesis compete principalIy with the sequence of reaction of methanation. From first untillast step, catalysts of copper is very associated at mantainance of bond CO and its hidrogenation, welI as of subsequent species, until methanol. Platinum e paladium also show toa a tendency to methanol synthesis. lron and nickel are associated to break the CO bond and are catalysts ofFischer- Tropsch synthesis and methanation, respectively / Mestrado / Desenvolvimento de Processos Químicos / Mestre em Engenharia Química

To date there has been much work carried out in the field of surface science to gain a better understanding of the fundamentals of a wide range of catalytic systems and reactions. The central theme of this thesis relates to cobalt based Fischer-Tropsch synthesis (FTS) with particular focus on the structure, composition and surface chemistry of CoPd bimetallic systems and on the interaction of Co with oxide support materials. In the work described in this thesis MEIS and STM are used to examine the growth of Co on Pd{111} and to characterise the structure of CoPd alloys created by thermal treatment of thin Co films. MEIS investigations indicate that Co grows initially as an fcc overlayer, but beyond a few layers, a stacking fault exists resulting in hcp growth. On annealing between 550 and 700 K, a previously unreported ordered surface alloy is observed giving rise to a p(2 x 1) structure which is concluded to be the surface termination of an ordered CoPd bulk alloy. At higher annealing temperatures, long range Moiré structure is observed by STM which MEIS reveals to correspond to a Pd-rich alloy. MEIS is used to investigate adsorbate induced segregation effects at CoPd surfaces on Pd{111}. The adsorption of O2, CO, H2 and CO/H2 mixtures (syngas) were all examined on a range of bimetallic surfaces. Oxygen adsorption on CoPd alloys strongly segregates cobalt to the surface as a result of the facile oxidation reaction. The behaviour of the components of syngas was more complex with the most noticeable effects being observed on surfaces which were more defect rich. The growth, annealing behaviour and adsorption properties of Co particles on oxide and mixed oxide surfaces are examined using MEIS and TPD.

The entrainment rate of Ferrosilicone (FeSi) particles was measured in a 140 mm perspex column with air as the fluidising medium. Two different types of FeSi were used, namely atomised FeSi, which is mostly spherical in shape with smooth surfaces, and milled FeSi, which is irregular with rough surfaces. Both the FeSi mixtures had the same solid density and the similar average particle diameters ranging from 38 µm to 50 µm. The size and density of these particles put them on the border between Geldart A and Geldart B powders, similar to the high temperature Fischer-Tropsch catalyst. The atomised FeSi had a slightly higher concentration in fines (8.6% vs 1.8%), but except for the difference in particle shape, the two mixtures had otherwise very similar physical properties. A substantial difference in entrainment rate was measured between the atomised and milled FeSi, where the atomised had an entrainment rate of about six times higher than the milled FeSi throughout the range of superficial velocities tested. It was shown that the higher entrainment rate cannot be attributed only to the higher fines concentration, but that the difference in particle shape had a significant effect on the entrainment rate. Several two dimensional shape characterisation techniques were used in attempt to quantify the difference between the atomised and the milled FeSi. Of these the particle circularity managed to differentiate the best between the two particle mixtures. The circularities of the atomised and the milled FeSi were found to be 0.782 and 0.711 respectively. The measured circularity was used instead of a sphericity to adjust for the effect of particle shape on the terminal velocity of the particles. The adjusted terminal velocity was then used in the elutriation rate constant correlations to see which of the popular correlations in literature predicts the entrainment rate of the FeSi the best. All of the correlations gave a poor performance in predicting the measured entrainment rates. The two correlations that performed the best were that of Choi et al. (1999) (AARE = 72.6%) and Geldart et al. (1979) (AARE = 79%). It was concluded that single particle drag and single particle terminal velocities are not adequate to incorporate the effect of particle shape on entrainment rate. The method i by which shape affects entrainment rate therefore deserves further investigation. Further studies should also be done to develop a three dimensional shape descriptor that predicts bulk behaviour better. / Dissertation (MEng)--University of Pretoria, 2008. / Chemical Engineering / unrestricted

Energy carriers, such as coal, natural gas and biomass, can be converted by Fischer-Tropsch technology into synthetic crude (syncrude). Fischer-Tropsch derived syncrude can then be refined to transportation fuels, such as motor-gasoline, jet fuel and diesel fuel. These fuels meet the same specifications as crude oil derived transportation fuels. Conventional refining technologies have to be adapted to deal with Fischer-Tropsch syncrudes, because they differ significantly from crude oil with respect to composition. Some of the key differences are the high concentration of oxygenates and olefins and absence of sulphur in Fischer-Tropsch syncrude. Imposing a crude oil refining methodology on syncrude can lead to unwieldy and expensive refineries. Yet, despite an abundance of literature of Fischer-Tropsch synthesis, there is little literature that deals with the refining of Fischer-Tropsch syncrude. The present study investigated current refining practice for both crude oil and Fischer-Tropsch syncrude in order to identify fundamental differences in their refining focus and conversion behaviour. This was followed by a critical evaluation of the compatibility of syncrudes from high temperature Fischer-Tropsch (HTFT) and low temperature Fischer-Tropsch (LTFT) synthesis with the chemistry and catalysis of various conversion processes. The conversion processes that were evaluated include isomerisation, oligomerisation, etherification, alkylation, metathesis, hydrogenation, hydroisomerisation, hydrocracking, catalytic cracking, coking, thermal cracking, catalytic reforming and dehydration. The recommendations from the technology evaluation provided the foundation for the development of Fischer-Tropsch syncrude based refinery designs. Refinery designs were developed to determine configurations that would maximise the production of on-specification motor-gasoline, jet fuel and diesel fuel respectively. It could be shown that less complex refinery designs were required to refine Fischer-Tropsch syncrude to motor-gasoline and jet fuel, than were required for crude oil refining. It was also shown that on a molecular level Fischer-Tropsch syncrude is unsuited for maximising the production of Euro-4 type diesel fuel. The present study illustrates the advantage of considering fundamentals in developing refineries specifically for Fischer-Tropsch syncrude, rather than imposing crude oil design practises on Fischer-Tropsch syncrude refinery designs. / Thesis (PhD (Chemical Engineering))--University of Pretoria, 2008. / Chemical Engineering / unrestricted