La gazéification de la biomasse permet d’obtenir un gaz de synthèse riche en CO et H2 utilisable pour la production d’électricité, de biocarburants ou de composés chimiques. Ce procédé permet de palier à l’épuisement des ressources fossiles. L’utilisation de boues d’épuration comme ressources de biomasse assurerait à ce type de déchets organiques une valorisation énergétique. Cependant, les boues contiennent une forte charge minérale (entre 30 et 50% massique). Cette fraction est composée d’une vingtaine d’oxyde notamment la silice, la chaux et l’oxyde de phosphore, P2O5 (plus de 15%).Les boues sont des systèmes complexes très peu étudiés jusqu'à présent. Il est donc nécessaire de connaitre le comportement en température des inorganiques afin de mesurer leur impact lors du processus de gazéification et de se prémunir contre les risques de corrosion et de pollution du gaz liés à leur présence. - Dans un premier temps, les températures de liquidus de deux fractions minérales de boues ont été déterminées. Il s’avère que celles-ci, comprises entre 1257°C et 1358°C, sont dans la plage opératoire d’un gazéifieur à lit entrainé. De plus, une étude menée sur le binaire SiO2-P2O5 a permis d’améliorer les bases de données thermodynamiques. - Dans un second temps, les études thermodynamiques et cinétiques de volatilisation du phosphore ont mis en évidence le faible relâchement en température du phosphore grâce à la formation de phases réfractaires associant l’oxyde de phosphore et la chaux tel que Ca3(PO4)2 et Ca9Fe(PO4)7. La volatilité des inorganiques des boues est inférieure à 0.5% massique. - Enfin, l’interaction entre les inorganiques liquides et plusieurs céramiques réfractaires a été étudiée, par des essais de corrosion statique et dynamique. Un matériau, constitué d’alumine et d’oxyde de chrome, s’est révélé être un excellent candidat pour le garnissage du réacteur de gazéification. / Synthesis gas can be obtained by biomass gasification. It is composed of CO and H2 and can be used for the production of electricity, organic coumpounds and biofuels. The use of sewage sludges allows exploiting this kind of waste as biomass resources. However, sewage sludges contain a large percentage of minerals (30 to 50 % wt) composed of at least 20 different oxides including silica, lime and phosphorous oxide, P2O5 (15 % wt of the minerals). Mineral matters of sludges are complex and not well known. So, it is necessary to study their behaviour in function of temperature to understand their impact during gasification process and avoid gas pollution and corrosion of the ceramic refractories. Firstly, liquidus temperatures of two different mineral matters were determined. The result shows that these temperatures, between 1257 and 1358°C, are in the operating range of the gasifier. Thus, a study of the binary system SiO2-P2O5 had enabled to enhance thermodynamic databases. Secondly, thermodynamic and kinetic studies, confirmed the low release of P2O5 in function of temperature due to the formation of refractory compounds like Ca3(PO4)2 and Ca9Fe(PO4)7. Release of inorganics from the sludge is less than 0.5 % wt. Finally, interaction between slag and different ceramic refractories was studied. Static and dynamic trials were performed to choose the most resistant ceramic refractory. One of them composed of alumina and chrome oxide proved to be a good choice to build the gasifier wall.

Doctor of Philosophy / Department of Chemical Engineering / Keith L. Hohn / Vanadium phosphorous oxide (VPO) is traditionally manufactured from solid vanadium oxides by synthesizing VOHPO[4subscript][dot in middle of line]0.5H[2subscript]O (the precursor) followed by in-situ activation to produce (VO)[2subscript]P[2subscript]O[subscript]7 (the active phase). These catalysts considerably improve their performance when prepared as nanostructured materials and this study discusses an alternative synthesis method based on sol-gel techniques capable of producing nanostructured VPO. Vanadium(V) triisopropoxide oxide was reacted with ortho-phosphoric acid in tetrahydrofuran (THF). This procedure yielded a gel of VOPO[4subscript] with interlayer entrapped molecules. The gels were dried at high pressure in an autoclave with controlled excess and composition of THF-2-propanol mixtures. The surface area of the obtained materials was between 50 and 120 m[2superscript]/g. Alcohol produced by the alkoxide hydrolysis and incorporated along with the excess solvent reduced the vanadium during the drying step. Therefore, after the autoclave drying, the solid VOPO[4subscript] was converted to the precursor; and, non-agglomerated platelets were observed. Use of additional 2-propanol increased the amount of precursor in the powder but reduced its surface area and increased its crystallite size. In general, sol-gel prepared catalysts were significantly more selective than the traditionally prepared materials, and it is suggested that the small crystallite size obtained in the precursor influenced the crystallite size of the active phase increasing their selectivity towards maleic anhydride. The evaluation of these materials as catalysts for the partial oxidation of n-butane at 673 K under mixtures of 1.5% n-butane in air yielded selectivity of 40% at 50% conversion compared to 25% selectivity at similar level of conversion produced by the traditionally prepared catalysts. Variations in the catalytic performance are attributed to observed polymorphism in the activated materials, which is evidenced by remarkable differences in the intrinsic activity. All precursors and catalysts were characterized by IR, XRD, SEM and BET, and the products of the catalytic tests were analyzed by GC.