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Asphaltenes conversion by chemical modification Open Access


Other title
acid demetalation
Friedel-Crafts alkylation
Type of item
Degree grantor
University of Alberta
Author or creator
Carvalho do Prado, Glaucia H
Supervisor and department
De Klerk, Arno (Chemical and Materials Engineering)
Examining committee member and department
Millan-Agorio, Marcos (Imperial College London)
Chen, Weixing (Chemical and Materials Engineering)
Hall, Dennis (Chemistry)
Semagina, Natalia (Chemical and Materials Engineering)
Department of Chemical and Materials Engineering

Date accepted
Graduation date
Doctor of Philosophy
Degree level
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.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
PRADO, G. H. C. and DE KLERK, A. Halogenation of oilsands bitumen, maltenes, and asphaltenes. Energy & Fuels 2014, 28(7), 4458-4468.PRADO, G. H. C. and DE KLERK, A. Alkylation of asphaltenes using a FeCl3 catalyst, Energy & Fuels 2015, DOI: 10.1021/acs.energyfuels.5b01292.PRADO, G. H. C. and DE KLERK, A. Demetalation of Metallophthalocyanines by Mild Halogenation without Disrupting the Tetrapyrrole Macrocycle, Paper accepted for publication in Fuel, DOI: 10.1016/j.fuel.2015.08.013

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