Notice bibliographique
Résumé
Canadian oilsands bitumen contains one of the highest amounts of asphaltenes (16-20 wt %) among all crude oils. Asphaltenes are the lowest value fraction of bitumen. It differs from the other fractions of bitumen because of its insolubility in paraffinic solvents. Asphaltenes are insoluble in paraffinic solvents because their molecules can aggregate and also because they have high molecular mass, high heteroatom content, and presence of large ring structures. Asphaltenes could be converted into more valuable products by modifying the properties responsible for insolubility in paraffinic solvents. The disaggregation of asphaltenes molecules by different chemical conversions was considered in this study. The objective was to explore new conversion strategies that were not already being applied by industry. The work focused on three conversion pathways: halogenation, Friedel-Crafts alkylation, and donor-acceptor reaction by acid treatment. Halogenation reactions had the objective of weakening π-π stacking of aromatic sheets in asphaltenes. Even though ~5 wt % increase of lighter boiling fractions was observed, the products were harder (penetration hardness). The solubility of asphaltenes in various solvents decreased after halogenation reaction. These changes could benefit road paving applications, but not oil upgrading, althouth it was observed that halogenation could demetalate porphyrins in bitumen and maltenes. In order to gain a better fundamental understanding of the influence of halogenation, hardness and demetalation of porphyrins were investigated with model compounds. The results showed that hardness was caused mainly by increased hydrogen bonding. A 74 % decrease of the nickel content in model compounds was observed due to acid-base and metal-ligand equilibrium disruption by bromine. The work also suggested that chloride salts originally present in bitumen could potentially influence coke chemistry and coke yield during bitumen upgrading. Friedel-Crafts alkylation had the objective of disrupting hydrogen bonding in asphaltenes by removal of alcohol groups or convertion of alcohol groups into ethers. The study employed FeCl3 as catalyst and o-xylene and methanol as alkylating agents, targeting alkylation of alcohols and thiols specifically. Alkylation of asphaltenes with o-xylene resulted in 6 % conversion of asphaltenes to maltenes and an increase of 9 % in straight run distillate and vacuum gas oil. Alkylation of asphaltenes with methanol was not beneficial. Model compounds were used to understand the chemistry and observed results. Alkylation of 2-naphthol showed that the two dominant reactions were dimerization of 2-naphthol and coordination with iron. Alkylation with methanol resulted in chlorination of the product by the catalyst. Alkylation of dibenzyl ether showed that ether bonds were cleaved by FeCl3 catalyst, which was followed by C-alkylation with o-xylene. The slight conversion of asphaltenes into maltenes is better explained by C-alkylation after ether cleavage than hydrogen bonding disruption. Disruption of metal-bridged structures in asphaltenes was also investigated. Divalent metals responsible for keeping smaller molecules together were removed with hydrochloric acid. The total of divalent metals removed from asphaltenes was about 2600 μg/g, iron was the metal most affected by acid washing. Around 8 % of asphaltenes could be converted into maltenes. The micro carbon residue of asphaltenes after demetalation decreased from 45 to 40 wt %. This investigation also highlighted the potential role of phenolic to phenoxide conversion in the formation of emulsions. The new conversion strategies investigated did not result in significant asphaltenes to maltenes conversion, but the investigation contributed to the fundamental understanding of asphaltenes conversion, and in particular, reactions involving halogens and acidic compounds.
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Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,002 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».