Autoxidation of Oilsands Bitumen: Applied, Model Compounds and Microfluidic Study

  • Author / Creator
    Siddiquee, Muhammad Nurunnabi
  • Canada has the world’s largest oilsands reserves. Part of the reserves is being considered as marginal and is not profitable to recover using current technology. Autoxidation (oxidation with air) is a potential upgrading strategy to produce more valuable products from the oilsands derived bitumen at low cost. Bitumen hardening, however, is a potential challenge to make the upgrading process viable. The interest of this study was to get a better fundamental understanding to prevent or reduce hardening as a generic problem faced by low temperature free radical conversion processes. The research documented in this thesis comprises four different studies to advance the knowledge in the field. In the first study, bitumen was autoxidized at different temperatures and times to understand the extent of hardening and corresponding chemical and physical changes due to autoxidation. Although bitumen hardening was anticipated, it was severe with an order of magnitude increase in both penetration hardness and viscosity after autoxidation at 130 °C for 229 hours. The relative aliphatic to aromatic hydrogen losses were 18:1, 30:1 and 32:1, respectively, for the bitumen autoxidation of 6 hours at 140, 150 and 160 °C. Hydrogen disproportionation occurred during autoxidation of bitumen indicating unsaturation that led to free radical addition and heavier product formation. Model compounds representing different hydrocarbon and heterocyclic compound classes were autoxidized in the second study to understand the compounds responsible for oxidative addition that potentially caused bitumen hardening and the mechanism to form addition products. The results revealed that naphthenic‒aromatic compounds, pyrrolic O‒containing compounds and pyrrolic N‒ containing compounds were susceptible to form heavier products. Five‒membered naphthenic‒aromatic hydrocarbons, indene and indan, were more prone to oxidative addition than even their pyrrolic analogues, indole and 2,3‒dihydroindole, which were known to be prone to oxidative addition. In all the instances, higher molecular weight products were C–C coupled by free radical addition. The third study put special emphases on the controlling of product selectivity at near constant conversion via manipulating oxygen availability by changing the hydrodynamics of a microfluidic reactor. Increasing oxygen availability in the liquid phase at near constant conversion, constant oxygen partial pressure and constant temperature increased the ketone–to–alcohol selectivity in primary oxidation products by an order of magnitude from less than 1:1 to 14:1. A crucial insight that came from the study of oxidation selectivity was that ketone–to–alcohol selectivity in primary oxidation products was an indicator of oxygen availability in the liquid phase during oxidation and the likelihood of free radical addition. In the fourth study, engineering aspects of liquid phase autoxidation were studied experimentally to confirm the oxygen level in the bulk liquid phase during the liquid phase autoxidation. Only in extreme cases, when a very high oxidation rate causes the reaction system to become severely mass transfer limited and does the oxygen level in the bulk liquid reach zero, oxidation takes place in the film. Low oxygen availability could potentially lead to increased formation of addition products, since there is insufficient oxygen to drive free radical termination by oxidation to final products. The study confirmed that liquid phase oxidation was kinetically controlled during the induction period of autoxidation of indan and reached complete saturation with air (19.2 kPa O2) during this period. Liquid phase autoxidation was limited by mass transfer after the induction period and oxygen level decreased in the liquid phase. It was possible to determine to what extent oxidation took place in the film and in the bulk phases. The reaction rate threshold was 2.6×10-3 (mol/m3.s) or 3.4×10-6 (mol/m2.s) for the reaction to occur in the film instead of the bulk. The oxygen concentration in the bulk liquid phase was measured experimentally, while performing autoxidation, instead of relying on theory to predict the liquid phase oxygen concentration. Due to the experimentally challenging nature of these measurements there is a dearth of literature on this topic. In conclusion, the main contributions made by this thesis are: (i) identifying the main compound classes responsible for free radical addition reactions with an explanation based on their reaction pathways, (ii) demonstrating how oxygen availability can be used to control oxidation selectivity independent of conversion by manipulating reactor hydrodynamics, and (iii) modifying the current theoretically predicted threshold for oxidation in the film based on the Hatta-number by performing in situ liquid phase oxygen measurements during autoxidation.

  • Subjects / Keywords
  • Graduation date
    Spring 2016
  • 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.