Phase Behavior and Thermophysical Properties of Peace River Bitumen + Propane Mixtures from 303 K to 393 K

Propane and mixtures including propane as a principal component are among the leading potential candidates for co-injection along with steam for improving the process and environmental efficiency of oil sands bitumen production processes. Phase diagrams and thermophysical property data enable technologies for the development and optimization of such processes. In this work, phase behavior, phase composition, and phase densities of propane + Peace River bitumen mixtures are reported in the temperature range 303 to 393 K at pressures ranging from 1 to 6 MPa. The phase behavior of this pseudobinary mixture can be categorized as Type III according to the van Konynenburg–Scott nomenclature. Pressure–temperature at fixed composition, and pressure–composition at fixed temperature phase diagrams, and pressure–temperature phase projections are presented, along with saturated compositions and densities of the coexisting bitumen-saturated propane liquid (L₁) and propane-saturated bitumen liquid (L₂) phases. Saturated L₁ and L₂ phases are both significantly less dense than liquid water phases at the same temperatures and pressures, and the volumes of mixing, particularly for the L₁ phase, are large and negative. This data set provides a benchmark for process development and process design calculations for ongoing bitumen production and deasphalting applications

Forced and Diffusive Mass Transfer between Pentane and Athabasca Bitumen Fractions

Forced and diffusive mass transfer between pentane and Athabasca bitumen fractions was investigated at 297 K. Mutual diffusion coefficients were obtained using a free diffusion technique, where time-dependent composition profiles were jointly fit to obtain composition-dependent values. Because the density difference between pentane and Athabasca bitumen is significant, the density gradient was accounted for explicitly in the data analysis. Forced mass-transfer measurements were made by placing a high shear impeller in the pentane-rich phase adjacent to the pentane−feedstock interface. Mass-transfer coefficients were evaluated independently on the basis of the movement of the interface with time and changes in the bulk composition of the well-mixed pentane-rich phase above the interface. Because bitumen fractions are only partially soluble in pentane, the impact of the asymptotic assumptions, complete miscibility and complete immiscibility, on mass-transfer coefficient values obtained was assessed and found to fall within experimental error. The dependence of mass-transfer coefficients upon the shear rate and impeller-interface distance was also evaluated. Mass-transfer rates are shown to range from the diffusion limit at low shear rates and large impeller-interface distances to values consistent with those obtained from pertinent correlations for forced mass transfer under turbulent conditions at higher shear rates. The results suggest that bitumen−pentane mass transfer in reservoirs and surface facilities is likely to be diffusion-limited

Mesoscale Organization in a Physically Separated Vacuum Residue: Comparison to Asphaltenes in a Simple Solvent

Physical separation of heavy oils and bitumen is of particular interest because it improves the description of the chemical and structural organization in these industrial and challenging fluids (Zhao, B.; Shaw, J. M. Composition and size distribution of coherent nanostructures in Athabasca bitumen and Maya crude oil. Energy Fuels 2007, 21, 2795−2804). In this study, permeates and retentates, differing in aggregate concentrations and sizes, were obtained from nanofiltration of a vacuum residue at 200 °C with membranes of varying pore size. Elemental composition and density extrapolations show that aggregates are best represented as <i>n</i>-pentane asphaltenes, while the dispersing phase corresponds to <i>n</i>-pentane maltenes. Small-angle X-ray scattering (SAXS) measurements are processed, on this basis, to calculate the size and mass of the aggregates. Aggregates in the vacuum residue are similar in size and mass to asphaltenes in toluene, and temperature elevation decreases the size of the aggregates. Wide-angle X-ray scattering (WAXS) highlights a coherent domain observed for fluids containing aggregates, corresponding to aromatic stacking described for dry asphaltenes. The scattered signal in this region, not observed in maltenes, grows as aggregate content increases, and the signal persists up to 300 °C. A generic behavior of aggregation in the vacuum residue is depicted, from nanoaggregates to large fractal clusters with high aggregation numbers, that is similar to the organization in toluene

Gold Core Nanoparticle Mimics for Asphaltene Behaviors in Solution and at Interfaces

Asphaltenes are a poorly defined class of self-assembling and surface active molecules present in crude oils. The nature and structure of the nanoaggregates they form remain subjects of debate and speculation. In this exploratory work, the surface properties of asphaltene nanoaggregates are probed using electrically neutral 5 nm diameter gold-core nanoparticles with alkyl, aromatic, and alkanol functionalities on their surfaces. These custom synthesized nanoparticles are characterized, and their enthalpies of solution at near infinite dilution and the interfacial tensions of solutions containing these nanoparticles are compared with the corresponding values for Athabasca pentane asphaltenes. The enthalpies of solution of these asphaltenes in toluene, heptane, pyridine, ethanol, and water are consistent with the behavior of gold-alkyl nanoparticles. The interfacial tension values of these asphaltenes at toluene–water and (toluene + heptane)–water interfaces are consistent with the behavior of gold-biphenyl nanoparticles as are the tendencies for these asphaltenes and gold-biphenyl nanoparticles to “precipitate” in toluene + heptane mixtures. Gold-alkyl nanoparticles are minimally surface active at toluene–water and (toluene + heptane)–water interfaces and remain dispersed in all toluene + heptane mixtures. The behavior of these asphaltenes in solution and at interfaces is inconsistent with the behavior of gold-<i>n</i>-alkanol nanoparticles. The outcomes of this formative work indicate potential roles for aromatic submolecular motifs on aggregate surfaces as a basis for interpreting asphaltene nanoparticle flocculation and interfacial properties, while alkyl submolecular motifs on aggregate surfaces appear to provide a basis for interpreting other aspects of asphaltene solution behavior. A number of lines of inquiry for future work are suggested