Phase Behavior and Thermophysical Properties of Athabasca Bitumen and Athabasca Bitumen + Toluene Mixtures in Near-critical Water

The phase behavior and thermophysical properties of heavy hydrocarbons + water at elevated temperatures underpins development and implementation of coordinated production and refining processes, where for example, bitumen is produced by a SAGD method (steam assisted gravity drainage) and the resulting bitumen + water mixtures are then upgraded directly. Supercritical water is an effective solvent for hydrocarbons at high temperatures and reduces coke formation when present during upgrading. In this work, the thermophysical properties and phase behavior of Athabasca bitumen + solvent + water mixtures are investigated and the results are compared to large molecule size hydrocarbons + water binaries available in the literature. Experiments were conducted using a variable-volume X-ray view cell in the broad range of temperature and pressure up to 644 K and 26.2 MPa near the critical point of water. The P-x and PT phase diagrams for pseudo-binaries and pseudo-ternaries of bitumen + solvent + water are constructed and single phase bitumen-rich regions are identified. The solubility of water in the hydrocarbon-rich phase, a key parameter in the design of water-based upgrading reactors, is evaluated to provide a reliable reference for solubility of water in high-molar-mass hydrocarbons. The accuracy of water solubility in the hydrocarbon-rich phase and phase behavior boundaries were validated by reproducing pressure-composition diagrams at fixed temperature and pressure-temperature diagrams for 1-methylnaphthalene + water and toluene + water binaries presented in the literature. Impacts of toluene addition on solubility of water in Athabasca bitumen + water mixtures are described. Furthermore, the density of bitumen phase and the impact of water solubility on the volume of mixing for the bitumen-rich liquid phase are discussed. A simple and robust model is developed to predict solubility of water in ill-defined hydrocarbons below their upper critical end point. An empirical model is also proposed to extend the solubility data to higher temperatures (> 673 K) where the mixtures are reactive. This body of work including phase diagrams, solubility and density data and models are expected to provide essential data to define promising regimes of temperature, pressure and composition for the application of water in hydrocarbon resource processing.