Silica supported chromium oxide catalysts, known as Phillips catalysts, are used in the production of over 40% of the world's high-density polyethylene. The original catalyst comprised CrO(_3) impregnated onto silica. Due to the carcinogenic nature of chromium(VI), chromium(m) catalyst precursors which are oxidised during calcination are now preferred. Two such precursors have been employed throughout the studies reported in this thesis; one is prepared by the aqueous impregnation of a silica support with basic chromium(in) acetate, whilst the other comprises a dry-blended mixture of chromium(m) acetylacetonate with silica. Calcination of the two precursors has been studied using a combination of temperature-programmed quadrupole mass spectrometry and infrared spectroscopy. The chromium(III) acetylacetonate precursor is postulated to disperse near its melting point and react via an acetate intermediate. Both precursors may therefore be expected to produce the same catalyst following calcination. The study of subsequent CO reduction of these calcined catalysts by quadrupole mass spectrometry supports this observation. The reduction is found to proceed via a Langmuir-Hinshelwood mechanism, both precursors demonstrating the same behaviour. Activation energies for the catalyst reduction have been determined from the corresponding Arrhenius plots. Quadrupole mass spectrometry techniques have identified 1-hexene production during the early stages of polymerization using the CO reduced catalysts. This indicates the formation of a chromacyclopentane intermediate species which may also be involved in the mitiation of polymerization. The continuous fragmentation of the catalyst support and polymer growth have been investigated using contact mode and phase-imaging atomic force microscopy. Non-equilibrium plasma oxidation of the two catalyst precursors has been studied by quadrupole mass spectrometry. An active catalyst is obtained from the chromium(m) acetate catalyst, however the dry-blended chromium(in) acetylacetonate precursor is unable to achieve the dispersion required, and the oxidised species are inactive for ethylene polymerization.

En France, les besoins annuels en matériaux granulaires pour le secteur du BTP sont proches de 400 millions de tonnes dont 96% sont d'origine naturelle. Il est donc inéluctablement nécessaire de trouver des solutions alternatives dites éco-responsables notamment par la valorisation de sous-produits industriels (SPI) tels que les sédiments de dragage. Les sédiments de dragage marins sont désignés comme matière première secondaire dans le cadre de cette étude. Cependant, ces derniers peuvent présenter des niveaux de pollution variables, avec présence de matières organiques (5% à 30%), une teneur en eau relativement élevée (50% à 200%) et une granulométrie assez fine (≤ 300 µm). Ce qui requiert, de mettre en place, en vue d'une utilisation efficiente, des procédés de traitement qui permettront in fine d'améliorer certaines propriétés physico-chimiques du matériau. L'objectif de nos travaux porte sur le traitement physique et thermique des sédiments de dragage puis leur valorisation dans les matrices cimentaires. Nous menons d’abord une étude bibliographique autour de la problématique posée. Au plan expérimental divers études sont conduits : caractérisation physico-chimique, les effets du traitement sur les propriétés des sédiments, l'impact probable de la présence des sédiments dans les matrices cimentaires. Les matériaux cimentaires formulés seront par la suite analysés et caractérisés à quatre échelles: physico-chimique, mécanique, durabilité et environnementale. Une analyse des résultats mécaniques permet de suivre l'activité des sédiments et d'implémenter des lois de formulation adaptées. / In France, construction sector annual needings for granular materials are close to 400 million tonnes, of which 96% are natural origin. Therefore it becames highly necessary to find alternatives solutions, in particular by valorisation of industrial by-products (IBP) such as dredging sediments. Marine sediments are designated as a secondary raw material in this study. However, the latter may present some levels of pollution, with the presence of organic matter (5% to 30%), relatively high water content (50% to 200%) and a fairly fine granulometry (≤ 300 µm). Currently, research target to use them as a supplementary mineral addition in concrete after efficient methods of treatment that improve some physico-chemical properties. The aim of this this study is to establish a profitable methodology for the use of sediments in cementitious matrix. We first lead a bibliographical review on this subject. At the experimental level, a physico-chemical characterization was carried out, determining the major parameters to be considered, the effects of the treatment on material properties, the likely impact of the presence of sediments in the cementitious matrix, and an experimental methodology to quantify these various effects. The cementitious materials formulated will be analysed and characterized at four scales: physico-chemical, mechanical, durability and the environmental impact. An analysis of the mechanical results makes possible to assess the activity of this material and to implement adapted formulation laws.

This study was carried out with Beypazari trona ore having a grade about 85 % trona (Na2CO3.NaHCO3.2H2O). The main target of the study is the determination of calcinations and leaching parameters, which are the two main unit operations in the production of soda ash (Na2CO3) from trona ore. Calcination parameters / calcination duration, calcination temperature and particle size were determined by using three different heat treatment systems, namely laboratory type muffle furnace, up draught furnace and microwave oven. As an alternative, wet type microwave-induced calcination which completes the decomposition of trona in solution was also investigated. Thirty minutes of calcination time was sufficient for complete calcination of &amp / #8211 / 6.35 mm trona sample at 175 &deg / C with the muffle furnace. Calcination of trona with microwave treatment was completed in a shorter time. The nature of thermal reactions and structural changes of trona during calcination were elucidated by TG (Thermogravimetry), DTG (Derivative Thermogravimetry), SEM (Scanning Electron Microscope) and XRD (X-ray diffraction) analysis. The effect of heat treatment on grindability, specific surface area and decrepitation of trona were also investigated. In the last stage of the study, leaching parameters / leaching time, leaching temperature and pulp density were determined for both uncalcined and calcined samples. 80 % leach recovery was obtained in 4 minutes for &amp / #8211 / 6.35 mm particle size of uncalcined sample in 25 % pulp density while 100 % leach recovery was reached for the calcined samples under the same conditions.

Afin de miser sur un nucléaire durable les recherches sur les cycles du futur doivent évoluer vers une co-gestion de l’ensemble des actinides et mieux, leur co-conversion. La préparation de solides mixtes intégrant l’uranium et le plutonium est actuellement privilégiée par voie oxalique. Cependant, l’utilisation de peroxydes mixtes comme précurseurs d’oxydes mixtes parait une voie alternative. En effet, la découverte récente de nombreux nano-clusters de peroxydes ou peroxo-oxalates d’uranyle, stabilisés par des cations mono- ou di- ou tri-valents permet d’envisager l’obtention de peroxydes mixtes. Ce travail a pour objectif de former des peroxydes mixtes d’uranium (VI) et de lanthanide (III), utilisé comme analogue des actinides (III), afin d’obtenir, in fine, des oxydes mixtes uranium-lanthanide par traitement thermique. L’examen du système UO22+/NH4+/O22-/C2O42- a permis, non seulement, d’affiner le diagramme d’existence des peroxydes et peroxo-oxalates d’uranyle et d’ammonium en fonction des concentrations des réactifs et du pH mais également d’obtenir douze nouvelles phases cristallines. A partir de pH 9 des phases amorphes précipitent et conduisent, après échange avec le néodyme (III) et calcination, à la formation d’oxydes mixtes homogènes qui intègrent 20 à 30% de néodyme au sein de l’oxyde final. Finalement l’utilisation de cations non labiles thermiquement a permis l’obtention de nouvelles phases U-Ca ou U-Rb. / In order to improve nuclear energy industry sustainability, future research needs to focus on the use of co-management of actinides and their co-conversion. The synthesis of uranium/plutonium mixed oxide by oxalic approach is currently the preferred method. Nevertheless the use of mixed peroxides, like precursors of mixed oxides, is considered as an alternative pathway.In fact, the recent advances on several uranyl peroxides or pero-oxalates nano-clusters stabilized by mono-, di- or tri-valent cations has permitted to investigate the formation of mixed peroxides. This study aims to investigate the formation of mixed uranium (VI) and lanthanide (III) peroxides leading to the formation of uranium-lanthanide mixed oxides, by heat treatment. Lanthanide (III) are used as actinides (III) analogs. The study of the UO22+/NH4+/O22-/C2O42- system allowed us to (i) refine the domains of existence of uranyl and ammonium peroxide and peroxo-oxalates as a function of reactive concentrations or pH (ii) obtain twelve news crystalline phases. At pH 9 and above, amorphous phases precipitated and after neodymium (III) exchange and calcination, led to the formation of mixed oxides. Mixed oxides can thus incorporate from 20 to 30% of neodymium. Finally the use of non thermically labile cations permits the formation of new U-Ca or U-Rb phases.

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The calcination of calcium carbonate in a cement or a lime kiln uses approximately two to four times the theoretical quantity of energy predicted from thermodynamic calculation depending upon the type of the kiln used (1.4 x 10^6 Btu/ton theoretical to 6 x 10^6 Btu/ton actual). The objective of this research was to attempt to reduce the energy required for the calcination by 1. decreasing the calcination temperature of calcium carbonate, and/or 2. increasing the rate of calcination at a specific temperature. Assuming a catalytic enhancement of 20 percent in the industrial applications, an energy savings of 300 million dollars annually in the United States could be reached in the cement and lime industries. Three classes of compounds to date have shown a positive catalytic effect on the calcination of calcium carbonate. These include alkali halides, phospho- and silico-molybdate complexes, and the fused carbonates system.

L'utilisation du kaolin calciné, sous forme de métakaolin, comme matériau pouzzolanique pour le mortier et le béton a suscité une attention considérable ces dernières années. Le travail actuel décrit les résultats d'un projet de recherche lancé pour étudier la calcination d'un kaolin local sous diverses températures (650-950°C) et durées (2, 3 et 4 heures) qui ont produit le métakaolin avec une activité pouzzolanique élevée. L'activité pouzzolanique a été évaluée par des méthodes de la chaleur d'hydratation et la résistance à la compression à 28 jours. L'activité maximale a été obtenue à une température de 850°C pendant 3 heures. Les résultats observés établissent qu'une augmentation de la chaleur d'hydratation et de la résistance à la compression a été obtenue lorsque le ciment Portland Ordinaire a été remplacé par 10% de métakaolin. L'utilisation du ciment ternaire améliore la résistance au jeune âge et à long terme. La durabilité a été également améliorée où une meilleure résistance des mortiers à l'attaque des acides a été observée. / The utilisation of calcined clay, in the form of metakaolin as a pozzolanic material for mortar and concrete has received considerable attention in recent years. The present work describes the results of a research project initiated to study the calcination of a local kaolin at various temperatures (650-950°C) and durations (2, 3 and 4 hours) to produced a metakaolin with a high pozzolanic activity. The pozzolanic activity was assessed by 28-days compressive strength and hydration heat methods. The maximum identified activity was obtained at 850°C for 3 hours duration. The observed results establish that an increase of both hydration heat and compressive strength was obtained when ordinary Portland cement was replaced by 10% metakaolin. The use of ternary blended cement improves the early age and the long-term compressive strength. The durability was also enhanced as better acidic resistance was observed.

The main function of a pyroscrubber in petroleum coke calcining process is to oxidize the carbonaceous contents, including hydrocarbon volatiles, of the exhaust gas from the calcination kiln, so as to leave no more than small traces of unburned volatiles, solid carbon, ashes, or emissions (e.g. CO, NOx and SOx) in the flue gas finally discharged. To maximize the energy recovery and reduce pollutant emission from the pyroscrubber, 3-D computational models are developed using FLUENT to simulate the combustion and thermal-flow phenomena inside the pyroscrubber. The results show the 3-D behavior of the flow, the reaction inside the pyroscrubber, effect of different amounts of air injection with respect to combustion efficiency, energy output and NOx emission. A multistage burning strategy is introduced and studied and results show it successfully cuts emission without compromising energy output. A particle combustion model with the homogeneous gas combustion model is also developed and incorporated to investigate CO emission.

Calcined coke is the best material for making carbon anodes for smelting of alumina to aluminum. Calcining is an energy intensive industry and a significant amount of heat is wasted in the calcining process. Efficiently managing this energy resource is tied to the profit margin and survivability of a calcining plant. 3-D computational models are developed using FLUENT to simulate the calcining process inside the long slender kiln. Simplified models are employed to simulate the moving petocke bed with a uniform distribution of moisture evaporation, devolatilization, and coke fines entrainment rate with a conjugate radiation-convection-conduction calculation. The results show the 3-D behavior of the flow, the reaction inside the kiln, heat transfer and the effect of the tertiary air on coke bed heat transfer. The ultimate goals are to reduce energy consumption, recover waste-heat, increase thermal efficiency, and increase the product yield.