Kinetic study of low temperature oxidation of Athabasca bitumen

Abstract

The principal objective of this study was to provide low temperature oxidation reaction models which are suitable for use in numerical simulators of in situ combustion for the Alberta's Athabasca oil sands. For the first time, in the literature, a systematic study was carried out to investigate the low temperature oxidation reactions of the liquid phase components of bitumen or heavy oils. Athabasca bitumen, free of water and minerals, was oxidized using a stirred semiflow batch reactor. Reactions were carried out in the 60°c to 1S0°c temperature range and at oxygen partial pressures of 40 kPa to 2233 kPa. The total pressures applied in the reactor ranged from 2190 kPa to 4415 kPa. Experimental data were collected in the kinetic subregime. Reactor product gas analysis was carried out using a gas chromatograph and the liquid phase oxidation product was separated into six main components (lumped components): saturates, aromatics, resins I, resins II, asphaltenes and coke. Experimental runs were made at 1S0°C, 135°c, 120°c, 105°c and 60°c, and at each temperature reactions were terminated after varying degrees of oxidation or reaction extent. Time dependent product distribution curves show that the reactions involving the liquid phase components are consecutive. The oxidation reactions were dependent on oxygen partial pressures and were independent of the total pressure in the reactor. Elemental analysis and spectroscopy tests were carried out for selected oxidized bitumen samples in an attempt to understand the chemistry of the complex oxidation reactions. Results of these tests suggest that the liquid phase products were formed through condensation, oxygen incorporation and polymerization reactions. For the first time, in the literature, kinetic models have been established for the liquid phase reaction components involved in the low temperature oxidation reactions of a mixture of complex hydrocarbons. Based on the experimental kinetic data, two main types of reaction models are proposed. These are: i) A non-steady state kinetic model to represent the overall rate of oxygen consumption. This model is second order with respect to oxygen partial pressure. ii) Four non-steady state multiresponse kinetic models representing the oxidation reactions of the liquid phase components. These components include, maltenes, oils, the resins and asphaltenes-coke. The models are first order with respect to the lumped components and fractional order in oxygen partial pressure. The invariant kinetic parameters in the models were estimated using the maximum likelihood techniques. statistically adequate. Proposed models were found.