Les carburants liquides actuels sont principalement issus du raffinage du pétrole. Cependant, leur remplacement par des carburants de nouvelle génération, renouvelables, dérivant de la biomasse et plus propre apparait comme une nécessité économique et environnementale. Les buts sont de réduire la dépendance au pétrole dont le prix augmente et les réserves diminuent, et limiter les émissions de dioxyde de carbone (gaz à effet de serre). L'adaptation des motorisations actuelles à ces nouveaux carburants nécessite une connaissance approfondie de leur cinétique de combustion et de la nature et des concentrations des polluants formés lors de leur utilisation. Les activités de recherche sur les carburants alternatifs destinés au secteur aéronautique ont ainsi considérablement augmenté ces dernières années. Dans le cadre de cette étude nous nous sommes intéressés à la solution « carburants de synthèse » qui offrent des perspectives encourageantes pour le futur. Des études cinétiques d’oxydation ont été menées en réacteur auto-agité par jets gazeux (JSR) sur une large gamme de conditions expérimentales à l’Institut de Combustion Aérothermique Réactivité et Environnement sur le campus du CNRS d’Orléans. Ces études ont été menées dans un premier temps sur des hydrocarbures purs qui pourraient être de bons candidats comme molécules-modèles pour représenter la part des iso-paraffines dans un kérosène de synthèse. Ces molécules sont des isomères de l’iso-octane utilisé comme tel jusqu’à maintenant. Dans un second temps, des études ont été menées sur trois kérosènes de synthèse dont un SPK fournit par l’IFP, un CtL (Sasol) et un GtL (Shell). Les analyses par spectrométrie d’absorption infrarouge à transformée de Fourier (IRTF) et par chromatographie en phase gazeuse (CPG-FID-TCD-MS) nous ont permis de mesurer les profils de concentration des réactifs, des produits finals et des intermédiaires stables en fonction de la température. Des mécanismes cinétiques détaillés adaptés aux composés étudiés ont été développés et validés par confrontation avec les résultats expérimentaux. / Current liquid fuels are mainly from petroleum refining. However, replacing them with new-generation alternatives fuels, renewable, from biomass and cleaner appear to be an economic and environmental necessity. Goals are to reduce petroleum dependency whose price increases and supplies decreases, and limit emissions of carbon dioxide (greenhouse gas emissions). The adaptation of existing engines to these new fuels requires a thorough knowledge of their kinetic of combustion and the nature and concentrations of pollutants formed during their use. Research activities on alternative fuels for the aviation industry have considerably increased in recent years. In this study we are interested in the "synthetic fuels" solution that offers encouraging prospects for the future. Studies on the kinetic of oxidation were carried out in a Jet Stirred Reactor (JSR) over a wide range of experimental conditions at the Institute of Combustion Aerothermal Reactivity and Environment on the campus of the CNRS of Orléans. These studies were initially conducted on pure hydrocarbons which could be good candidates as models molecules to represent the isoparaffins cut in a synthetic kerosene. These molecules are isomers of iso-octane used as such until now. In a second step, studies were conducted on three synthetic kerosene, a SPK provided by IFP, a CtL (Sasol) and GTL (Shell). Analyses by Fourier transform infrared spectrometry (FTIR) and by gas chromatography (GC-FID-TCD-MS) allowed us to measure the concentration profiles of reactants, stable intermediates and finals products as a function of temperature. Detailed kinetic mechanisms adapted to the studied compounds have been developed and validated by comparison with experimental results.

En raison de la raréfaction des ressources de pétrole et des variations des prix avec le contexte géopolitique, la réaction de catalyse de Fischer-Tropsch qui permet la production d’hydrocarbures à partir du mélange syngas des gaz CO et H2 en présence d’un catalyseur à base de fer ou de cobalt, présente aujourd’hui un regain d’intérêt tant de la part des industriels que des académiques. Bien que découverte en 1923 par les allemands Franz Fischer et Hans Tropsch, les mécanismes qui entrent en jeu lors de cette réaction et les paramètres importants des propriétés des catalyseurs demeurent encore incertains. Dans ce contexte, les travaux présentés dans cette thèse visent à étudier l’impact de paramètres tels que la structure cristallographique et la forme de nano-objets de cobalt, phase active du catalyseur pour cette réaction. Ceci passe par la synthèse de catalyseurs modèles à base de nano-objets de cobalt et l’étude de leurs propriétés catalytiques. Dans un premier temps, la préparation d’un catalyseur à base de cobalt présentant une structure cristallographique hcp et une morphologie anisotrope a été réalisée, via une voie de synthèse par décomposition d’un précurseur organométallique de cobalt, conduisant à la formation de nano-objets de cobalt anisotropes. Puis, des tests catalytiques ont été réalisés en réacteur slurry, en collaboration avec un partenaire industriel, l’IFP-EN. Cela a permis la réalisation de tests Fischer-Tropsch en conditions proches des conditions industrielles réelles. Ces études ont permis de mettre en évidence la très grande stabilité de ces catalyseurs en comparaison à des catalyseurs de référence.Enfin, différents catalyseurs à base de cobalt, supportés sur des supports originaux de type macrostructurés permettant une meilleure gestion des échanges thermiques de la réaction, ont été préparés et leurs propriétés catalytiques étudiées sur un réacteur de type lit-fixe, mis en œuvre durant cette thèse. / Due to the decreasing the oil resources, and because of the the fluctuations of the price as a result of the geopolitical context, the Fischer-Tropsch synthesis, that enables the production of hydrocarbons form the syngas mixture (CO and H2) in the presence of a catalyst based on cobalt or iron, has recently gained a renewed interest from industrial as well as form the academic communities. Although this reaction was discovered in 1923 by the Germans Franz Fischer and Hans Tropsch, the mechanisms that come into play during this reaction and the crucial properties of the catalyst properties remain uncertain. In this context, the work presented in this thesis, aims to investigate the impact of parameters such as the crystallographic structure and the shape of the cobalt nano-objects, which is the active phase of the catalyst for this reaction. For this purpose, model cobalt nano-objects were synthetized and their catalytic properties were studied. As a first step, a cobalt based catalyst exhibiting an hcp crystallographic structure and an anisotropic shape was prepared via a synthetic route involving the decomposition of an organometallic precursor of cobalt and leading to the formation of anisotropic cobalt nano-objects. Catalytic tests were then conducted in a slurry reactor, in collaboration with an industrial partner, IFP-EN. This collaboration allowed performing catalytic studies under conditions that are very close to the actual industrial conditions. These studies revealed an increased stability of these catalysts compared to reference catalysts that deactivate with time. Finally, several cobalt-based catalysts, supported on innovative supports, such as macrostuctured supports, allowing a better control of the exothermicity, were prepared and their catalytic properties studied on a fixed-bed reactor that was set up during the course of this thesis work.

Student Number : 0303610W - PhD thesis - School of Chemistry - Faculty of Science / Mesoporous MCM-48 was synthesized and used as a template to synthesize mesoporous carbon (MC) materials. Polystyrene, the carbon source, together with sulfuric acid and toluene were added to the template (160 oC for 6 h) and this procedure generated a low surface area carbon supported/MCM-48 material. A repeat addition and carbonization step was needed to form the precursor carbon/MCM-48 material that was pyrolysed at 900 oC to generate graphitic mesoporous carbon materials. After removal of the silica template, mesoporous carbons were characterized by XRD, HR-TEM, Raman spectroscopy and surface area analysis. The effect of the amount of polystyrene as well as the role of the pyrolysis temperature on the final product was investigated. This synthesis methodology can readily be controlled to produce partially ordered graphitic mesoporous carbon supports with predictable pore width and surface area. The methane selectivity was low (below 6%) and stable, and the overall olefin fraction was found to be good for all the supported catalysts studied. The potassium promoter increased the hydrocarbon chain growth to C68 giving α-1 and α-2 both between 0.79 and 0.90 for all supported catalysts with an exception of MCM-48 supported Fe catalyst that selectively produced hydrocarbons up to C28.

Thesis (M. Ing. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2008.

The use of transition metal catalysts - either homogeneous (discrete well-defined metal complexes) or heterogeneous (more poorly-defined metal surfaces) - play an important role in the transformations of small substrates into larger, value-added compounds. Although heterogeneous catalysts have the greater industrial applicability, there has been enormous interest in homogeneous transition metal systems for effecting selective transformations of small substrate molecules. The bulk of these homogeneous systems are mononuclear. Perhaps surprisingly, very little research has focuses on systems with adjacent metal centres. Binuclear systems possess adjacent metals that may interact and possibly lead to transformations not observed in monometallic systems. It is this opportunity for adjacent metal involvement in substrate activation that is the focus of this dissertation. the goal of this research is to gain an increased understanding of metal-metal cooperativity and adjacent metal involvement in substrate transformations; how can adjacent metal involvement lead to substrate activation not seen in monometallic counterparts, and what role does each metal play in these interactions, particularly when the two metals are different. Throughout this dissertation examples of transformation unique to systems with at least two metals are presented and examined with a particular focus on the roles of the two metals and any associated binding modes in these transformations. In addition, by comparing the RhOs, RhRu and IrRu systems, the influence of metal substitution is also examined. For example, diazoalkane activation and C-c bond formation promoted by the Rh-based systems is investigated, the roles of the adjacent metals of the IrRu system in the conversion of methylene groups to oxygenates is examined, and the unusual geminal C-H bond activation of olefinic substrates is explored. Overall, the work presented within this thesis adds to the growing understanding of adjacent metal cooperativety, leading us toward a more rational approach to the design of homogeneous homo- and heterobimetallic catalysts, heterogeneous catalyst and nanoparticle catalysts for selective substrate transformations.

This study focuses on upgrading biomass derived syngas for the synthesis of liquid fuels using Fischer-Tropsch synthesis (FTS). The process includes novel gasification of biomass via a tri-reforming process which involves a synergetic combination of CO2 reforming, steam reforming, and partial oxidation of methane. Typical biomass-derived syngas H2:CO is 1:1 and contains tars that deactivate FT catalyst. This innovation allows for cost-effective one-step production of syngas in the required H2:CO of 2:1 with reduction of tars for use in the FTS. To maximize the performance of the tri-reforming catalyst, an attempt to control oxygen mobility, thermal stability, dispersion of metal, resistance to coke formation, and strength of metal interaction with support is investigated by varying catalyst synthesis parameters. These synthesis variables include Ce and Zr mixed oxide support ratios, amount Mg and Ni loading, and the preparation of the catalyst. Reaction conditions were also varied to determine the influences reaction temperature, gas composition, and GHSV have on the catalyst performance. Testing under controlled reaction conditions and the use of several catalyst characterization techniques (BET, XRD, TPR, XAFS, SEM-EDS, XPS) were employed to better explain the effects of the synthesis parameters. Applications of the resulting data were used to design proof of concept solar powered BTL plant. This paper highlights the performance of the tri-reforming catalyst under various reaction conditions and explains results using catalyst characterization.

No description available.

In this study, the feasibility of a NaA zeolite membrane for the gas phase separation of steam and hydrogen mixtures was determined. The Fischer-Tropsch (FT) process, which produces high value fuels and chemicals from coal and natural gas, can be greatly improved upon by the selective removal of water from the FT reactor product stream. According to the FT reaction kinetics, the rate of reaction increases with the partial pressure of hydrogen but is adversely affected the presence of water in the reactor product stream. Chemisorbed water on the surface of the metal catalysts also enhances deactivation due to sintering and fouling. The use of a zeolite membrane reactor is well equipped to serve the purpose of in-situ water removal as it can facilitate the separation of chemical components from one another in the presence of catalytic reactions. The LTA type zeolite membrane NaA or zeolite 4A, in particular, is well suited for the separation of polar (H2O) from non-polar (H2) molecules because of its high hydrophilicity. NaA has also been identified as an excellent candidate for selective water removal applications due its high adsorption affinity and capacity for water. The NaA membrane used in this study was manufactured by means of the in-situ crystallisation method where the growth of crystals on the inside surface of a centrifugally casted a-alumina support was favoured. Scanning electron microscopy (SEM) analyses performed on the membrane after a double hydrothermal synthesis indicated that the surface topology was rough and that the zeolite crystals formed were not uniform in size. Overall, the membrane thickness varied between 6.5 and 8.0 flm. An evaluation of the membrane quality was made possible through permeation experiments involving SF6 and Hz. The calculated Hz/SF6 permselectivity in this study was found to be 9.78, which despite being higher than the Knudsen diffusion selectivity of 8.54, confirmed the presence of intercrystalline defects or non-zeolitic pores in the membrane. Experiments concerning pure component and binary mixture permeation of steam and hydrogen through the supported NaA membrane were conducted over a temperature range of 115°C to 160 °c for binary hydrogen/steam mixtures, 25°C to 160°C for pure hydrogen and 130°C to 170°C for pure steam. For the permeation of pure component hydrogen, a local maximum in its permeance having a value of 224 x 10'°8 mol.m,z.s'!.Pa'! was reached at a system pressure and temperature of 6.875 bar and 75°C respectively. For the permeation of pure component steam through NaA, the effects of capillary condensation in the pores and defects of the zeolite membrane resulted in a decrease in steam permeance as a function of absolute pressure for temperatures lower than 160 °c. Once the effects of capillary condensation had receded, maxima in the steam permeances as a function of temperature corresponding to values of 70 x 10,08, 65 X 10,08 and 75 x 10,08 mol.m•2.s'I.Pa'l were found for the 182.5, 197.5 and 222.5 kPa isobars respectively. These observations collaborated well with the description of surface diffusion with permeation taking place in the Langmuir (strong adsorption) regime. Permeation experiments through NaA as function of temperature were conducted for a 90 mol% steam -10 mol% hydrogen (90-10) binary mixture as well as for a 60-40 mixture of these two. At low temperatures the permeation of hydrogen was completely suppressed by the condensed steam resulting in an almost perfect separation. The Kelvin equation was used to estimate the pore size of the defects which was found to range between 1.86 and 2.45 nm. The temperature range over which these defects in the membrane were assumed to become unblocked (i.e. assuming when the first breakthrough of hydrogen occurred), were determined to be between 140 to 148 °c and between 128 to 130 °c for the 90-10 and 60-40 mixtures respectively. The mixture selectivities (towards water) between 115 °c and 130 °c were found to be immensely high (much greater than 1000) for both the 90-10 and 60-40 mixtures, while the ideal selectivities were calculated to be less than lover the same temperature range. At 140 °c, the selectivity towards water for the 9010 mixture was still greater than 1000; however for the 60-40 mixture at this temperature, an inversion of selectivity towards H2 had already taken place. The breakthrough in H2 permeance occurs at a much lower temperature when the feed mixture contains a lower concentration of water. Since the partial pressure of steam will be reduced, larger pores will become unblocked at lower temperatures according to the Kelvin equation. / Thesis (M. Ing. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2008.

In this study, the feasibility of a NaA zeolite membrane for the gas phase separation of steam and hydrogen mixtures was determined. The Fischer-Tropsch (FT) process, which produces high value fuels and chemicals from coal and natural gas, can be greatly improved upon by the selective removal of water from the FT reactor product stream. According to the FT reaction kinetics, the rate of reaction increases with the partial pressure of hydrogen but is adversely affected the presence of water in the reactor product stream. Chemisorbed water on the surface of the metal catalysts also enhances deactivation due to sintering and fouling. The use of a zeolite membrane reactor is well equipped to serve the purpose of in-situ water removal as it can facilitate the separation of chemical components from one another in the presence of catalytic reactions. The LTA type zeolite membrane NaA or zeolite 4A, in particular, is well suited for the separation of polar (H2O) from non-polar (H2) molecules because of its high hydrophilicity. NaA has also been identified as an excellent candidate for selective water removal applications due its high adsorption affinity and capacity for water. The NaA membrane used in this study was manufactured by means of the in-situ crystallisation method where the growth of crystals on the inside surface of a centrifugally casted a-alumina support was favoured. Scanning electron microscopy (SEM) analyses performed on the membrane after a double hydrothermal synthesis indicated that the surface topology was rough and that the zeolite crystals formed were not uniform in size. Overall, the membrane thickness varied between 6.5 and 8.0 flm. An evaluation of the membrane quality was made possible through permeation experiments involving SF6 and Hz. The calculated Hz/SF6 permselectivity in this study was found to be 9.78, which despite being higher than the Knudsen diffusion selectivity of 8.54, confirmed the presence of intercrystalline defects or non-zeolitic pores in the membrane. Experiments concerning pure component and binary mixture permeation of steam and hydrogen through the supported NaA membrane were conducted over a temperature range of 115°C to 160 °c for binary hydrogen/steam mixtures, 25°C to 160°C for pure hydrogen and 130°C to 170°C for pure steam. For the permeation of pure component hydrogen, a local maximum in its permeance having a value of 224 x 10'°8 mol.m,z.s'!.Pa'! was reached at a system pressure and temperature of 6.875 bar and 75°C respectively. For the permeation of pure component steam through NaA, the effects of capillary condensation in the pores and defects of the zeolite membrane resulted in a decrease in steam permeance as a function of absolute pressure for temperatures lower than 160 °c. Once the effects of capillary condensation had receded, maxima in the steam permeances as a function of temperature corresponding to values of 70 x 10,08, 65 X 10,08 and 75 x 10,08 mol.m•2.s'I.Pa'l were found for the 182.5, 197.5 and 222.5 kPa isobars respectively. These observations collaborated well with the description of surface diffusion with permeation taking place in the Langmuir (strong adsorption) regime. Permeation experiments through NaA as function of temperature were conducted for a 90 mol% steam -10 mol% hydrogen (90-10) binary mixture as well as for a 60-40 mixture of these two. At low temperatures the permeation of hydrogen was completely suppressed by the condensed steam resulting in an almost perfect separation. The Kelvin equation was used to estimate the pore size of the defects which was found to range between 1.86 and 2.45 nm. The temperature range over which these defects in the membrane were assumed to become unblocked (i.e. assuming when the first breakthrough of hydrogen occurred), were determined to be between 140 to 148 °c and between 128 to 130 °c for the 90-10 and 60-40 mixtures respectively. The mixture selectivities (towards water) between 115 °c and 130 °c were found to be immensely high (much greater than 1000) for both the 90-10 and 60-40 mixtures, while the ideal selectivities were calculated to be less than lover the same temperature range. At 140 °c, the selectivity towards water for the 9010 mixture was still greater than 1000; however for the 60-40 mixture at this temperature, an inversion of selectivity towards H2 had already taken place. The breakthrough in H2 permeance occurs at a much lower temperature when the feed mixture contains a lower concentration of water. Since the partial pressure of steam will be reduced, larger pores will become unblocked at lower temperatures according to the Kelvin equation. / Thesis (M. Ing. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2008.

Liquid transportation fuels can be produced by gasification of carbon containing biomass to syngas( a gaseous mixture of CO and H2) with subsequent conversion of the syngas to fuels. One possible process is the so called mixed alcohols synthesis, which produces a mixture of ethanol and higher alcohols. Another possible process is the reaction of syngas to Fischer-Tropsch liquids, mainly diesel fuel. This study examines the economics of syngas, ethanol and diesel fuel production from lignocellulosic biomass (southern pine residues). The process is modeled with Aspen Plus, a process simulation software package. The process is simulated for plant sizes between 715 and 2205 dry tons/day. The feedstock moisture content is varied between 20% and 50% and the feedstock costs are varied between $30/dry ton and $80/dry ton. The influences of the examined variables on the minimum product selling price are determined. The economic effects of an integration of the mixed alcohols and the FT diesel process with a kraft mill are also evaluated.