Asphaltenes conversion by chemical modification

  • Author / Creator
    Carvalho do Prado, Glaucia H
  • 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.

  • Subjects / Keywords
  • Graduation date
    Fall 2015
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.