Thermal Cracking Reactions of Model Compounds of Asphaltenes

• Author / Creator

  Alshareef, Ali Haider

• Resolution of reaction pathways to coke formation during the upgrading of heavy resources, such as the vacuum residue fraction of bitumen, is hampered by the extreme complexity of these materials. Alternatively, probing the molecular–level reactions and cracking kinetics of model compounds that incorporate structures known to be present in the asphaltenes was shown to provide more quantitative information. The objective of this research is to investigate the thermal cracking and coking reactions in the condensed liquid phase of especially synthesized model compounds of asphaltenes.
  The model compounds used in this study are of three distinct chemical structures: archipelago structures made of three aromatic systems linked by two ethano bridges, alkylpyrene compounds with different side–chain lengths, and cholestane–benzoquinoline compounds substituted with different aromatic groups. All of the compounds have high molecular weights, within a range of 530–770 g/mol, to ensure they remain in the liquid phase at the reaction conditions.
  The pure compounds and binary mixtures of them were thermally cracked using thermogravimetric analysis to obtain cracking kinetics and coke yields. Microreactor experiments on selective samples provided the conversion of parents, and nature and selectivity of products. Analysis using a number of chromatographic and spectroscopic techniques showed that initial fragments from the model compounds add to other fragments and to the parent via alkyl–alkyl and alkyl–aryl addition reactions to build larger archipelago structures. In addition to the labile bonds that were expected to crack, strong bonds such as alkyl–pyrene bonds also cracked, likely facilitated by unimolecular rearrangement processes. The archipelago compounds formed much more addition products, and subsequently more coke, than the other two families of compounds or their phenyl analogs. Within each family, minor structural changes were found to greatly influence the coke yield, with the reactivity of the parent and its initially formed products, as well as the intermolecular associations, as observed with polarized light microscopy, as the main controlling factors. The activation energy of the cracking reactions, on the other hand, fell within a narrow range for each family of compounds suggesting that similar bonds dominate cracking.

• Subjects / Keywords

  • Model compounds
  • Chemical structure
  • Thermal cracking
  • Ashaltenes
  • Pyrolysis

• Graduation date

  Spring 2012

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3SX64M7P

• 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.