No description available.

No description available.

Heavy hydrocarbon upgrading is attracting more interest amidst growing supply of heavier crudes. These materials, often distinguished by high aromatic and asphaltene contents generate larger volumes of residue upon processing. The present study investigates the potential of partial oxidative cracking in water as an alternative to the conventional thermal cracking or hydrocracking upgrading routes. Sub and supercritical water partial oxidative cracking experiments have been carried out in a batch micro-bomb reactor using model compounds of three to five-membered ring polycyclic aromatic hydrocarbons (PAHs). The goal is twofold; to establish the optimum operating window for the PAH oxidative cracking and to evaluate the reactivity patterns between different PAH compounds. It was found that partial oxidative cracking of PAH depends strongly on reaction temperature and oxidant concentration. Using a 0.38 O/Ostoic atomic ratio (38% of the oxygen needed for complete combustion), phenanthrene and anthracene were converted at short reaction time of 0 min into mostly oxygenated intermediates (DCM solubles) at subcritical water conditions. Under the more reactive supercritical water conditions, ring cleavage products, which include phenols, aromatic acids, ketones and unsubstituted aromatics (DCM solubles) were favoured. Most of these intermediates were formed via middle ring oxygenation which could potentially contribute to higher cracking efficiency upon subsequent thermal treatment. In addition to the target compounds, polymerized materials (DCM insolubles) were also produced under both conditions. A good compromise between the two major product streams was obtained at 400 oC whereby the DCM fraction contains a balanced mixture of oxygenated and cracking compounds. PAHs exhibit higher degree of stability with increasing ring size. A higher reaction temperature of 450 oC was needed in order to convert pyrene and benzo[a]pyrene. The reactivity order with respect to PAH conversion into the desirable DCM soluble fraction was established as follows: anthracene > phenanthrene > pyrene > benzo[a]pyrene.

La cémentation gazeuse à basse pression est un procédé de traitement de surface qui consiste à renforcer des pièces en acier par diffusion d’atomes de carbone provenant de la pyrolyse d’hydrocarbures gazeux. Une partie de l’hydrocarbure craqué est adsorbée sur le métal mais une autre partie réagit en phase gazeuse et conduit, entre autres, à la formation de HAP. Or, de nombreux HAP sont toxiques, voire cancérigènes, et les salariés en charge du nettoyage ou de la maintenance des fours de cémentation peuvent y être exposés. Des expériences de pyrolyse d’acétylène ont été réalisées à 900°C et 8 kPa, conditions proches de celles des procédés de cémentation gazeuse à basse pression. Un réacteur auto-agité par jets gazeux et des réacteurs tubulaires ont été utilisés. A la sortie de la zone réactionnelle, les produits de la pyrolyse ont été analysés. Entre autres, 16 HAP considérés comme des polluants prioritaires par l’Agence de Protection de l’Environnement aux Etats-Unis (US EPA) ont été observés. L’influence du taux de dilution du réactif en entrée et du temps de passage dans le réacteur a été étudiée. Les résultats expérimentaux ont été comparés à ceux obtenus avec un modèle cinétique détaillé. Ce modèle a été développé dans le but de décrire la formation des HAP lors de la pyrolyse d’hydrocarbures légers. Une attention particulière a été portée aux voies de formation des premiers cycles aromatiques et des 16 HAP de la liste de l’EPA. En plus des données expérimentales obtenues dans le cadre de cette étude, le modèle a été validé à partir de données expérimentales de la littérature. Le but de l’étude est de comprendre les phénomènes de formation et de croissance des HAP afin de trouver des conditions opératoires permettant de rendre plus surs les procédés de cémentation gazeuse à basse pression / Low-pressure gas carburizing is a heat treatment process used to harden surface of steel by enriching the metal with carbon atoms coming from pyrolysis of hydrocarbons. At the same time, a wide variety of molecules and radicals are also formed in the gas phase. They react together, leading to the formation of PAHs. PAHs are toxic and even carcinogenic, and activities such as furnace maintenance may thus represent a risk to workers. Experiments of acetylene pyrolysis were carried out in conditions close to low-pressure gas carburizing processes, at 900°C and 8 kPa. Two kinds of reactors were used: a jet stirred reactor and tubular reactors. At the outlet of the reaction zone, products of pyrolysis were analyzed. Among other products, 16 PAHs classified as priority pollutants by the United States Environmental Protection Agency (US EPA) were observed. Influence of residence time and of reactant dilution was studied. Experimental results were compared to those obtained with a detailed kinetic model. This model was developed in order to describe PAH formation during light hydrocarbon pyrolysis. The focus was placed on formation pathways of the first aromatic rings and of the 16 EPA-PAHs. In addition to the experimental data obtained in this study, the model was validated using experimental data from the literature. The aim of the study is to understand the phenomena of PAH formation and growth in order to find operating conditions to make safer the low-pressure gas carburizing processes