In this work, we report for the first time the observation of naturally occurring discotic liquid-crystalline domains of ca. 100 μm in diameter in unreacted heavy fractions of petroleum. Precipitated solids from several bitumen and heavy oil samples exhibited the characteristic optical patterns of liquid crystals when observed under cross-polarized light. Samples included asphaltenes precipitated from Athabasca and Cold Lake bitumen (Canada), Maya heavy crude oil (Mexico), and Safaniya crude oil (Saudi Arabia) and a maltene fraction of Athabasca bitumen. The liquid-crystal domains appeared in asphaltene solids at ∼330 K in a nitrogen atmosphere and disappeared at ∼430 K. Upon cooling and subsequent reheating, the domains did not reappear. Liquid-crystal domains also appeared and then disappeared in the presence of toluene vapor at room temperature. Because the liquid crystals exhibit both thermotropic and lyotropic behavior, they are amphotropic. While amphotropic liquid crystals are known to arise in biological systems, the specific attributes of the liquid-crystal structures observed here are the first reported occurrence of such behavior in nature. The presence of liquid crystals in petroleum solids enriches our understanding of the complex phase and interfacial behavior of these materials and may provide new opportunities for partitioning petroleum.

Complex viscosity and phase-angle measurements for Athabasca bitumen and Maya crude oil were performed with a rotational rheometer using parallel plates and a double gap cylinder in the oscillatory mode over the temperature range of (200 to 410) K. A large range of shearing conditions were applied (frequency of oscillations, shear strain, or stress), and up to three orders of magnitude of variations in measured viscosity values for individual samples at a fixed temperature were obtained. Athabasca bitumen and Maya crude oil were found to be solid-like materials up to (260 to 280) K and (230 to 240) K, respectively. Athabasca bitumen is a non-Newtonian shear-thinning fluid up to (310 to 315) K, whereas Maya crude is a shearthinning fluid up to (280 to 285) K. Both are Newtonian at higher temperatures. Maya crude oil was also found to possess thixotropic behavior. Athabasca bitumen reveals the thermal irreversibility of complex viscosity, if it is heated above 360 K. These rheological behaviors are attributed to the multiphase behavior of these materials over the temperature range of interest, and these results can be used to reconcile the large differences in reported viscosity values for bitumen and heavy oil obtained with diverse viscometers where shear rate and other variables are not controlled. Additional artifacts introduced during measurements are also addressed. Sample variation due to geographical location, depth of formation, and production and postproduction processing can also result in up to three orders of magnitude of differences between the measured "viscosity" of bitumen when the measurement method and temperature are fixed. The flow properties of bitumen and heavy oil are expected to be strong functions of sample source and the hydrodynamics prevailing in situ or in processes at temperatures where non-Newtonian behaviors prevail.

The phase behavior of Athabasca bitumen (Alberta, Canada) was determined from nanofiltered permeates and retentates with pentane-asphaltene mass fractions w A ranging from 0.053 to 0.57, and chemically separated Athabasca pentane maltenes and pentane asphaltenes based on differential scanning calorimetry and rheology measurements from (190 to 570) K at atmospheric pressure. Samples were subject to two sequential heating cycles. Composition, apparent heat-capacity, and phase-angle data were collected and interpreted jointly to define phase diagrams for nanofiltered maltene þ nanofiltered asphaltene pseudobinary mixtures for each heating cycle. These pseudocomponents are shown to behave independently. During the first heating cycle, observed phase transitions for maltenes include: a broad low-temperature glass transition with a T g from (215 to 230) K and a small first-order phase transition with a peak temperature T trs between (320 and 340) K linked to a fraction of Athabasca maltenes undergoing a crystal to liquid transition. These transitions were found in both chemically separated and nanofiltered maltenes. Nanofiltered asphaltenes undergo a two-stage transition from solid to liquid between (260 and 470) K, with the second stage being a glass type transition. The nature of the first stage requires additional study. By contrast, chemically separated pentane asphaltenes undergo a complex transformation from (310 to 530) K comprising overlapping processes including endothermic transitions from solid-to-liquid and solid-to-liquid crystals and an exothermic dissolution of the liquid crystals [Bagheri, S. R., et al. Energy Fuels 2010, 24, 4327À4332]. Athabasca bitumen comprises a minimum of four phases drawn from liquid, crystalline maltene þ glass and/or crystal, and liquid asphaltenes from (260 to 360) K. The phase transition reversibility is discussed, and the phase diagram for Athabasca bitumen is compared with that of Maya crude oil, reported previously [Fulem, M., et al. Fluid Phase Equilib. 2008, 272, 32À41]. Multiphase behavior appears to be a general phenomenon, but phase diagram details appear to vary from feedstock to feedstock.

The standard molar enthalpy of formation in the liquid state for 1-methylimidazole (MeIm) was obtained from combustion calorimetry. The enthalpy of vaporization of the compound was derived from the temperature dependence of the vapor pressure measured by the transpiration method. Additionally, the enthalpy of vaporization for MeIm was measured directly using Calvet-type calorimetry. In order to verify the experimental data, first-principles calculations of MeIm were performed. The enthalpy of formation evaluated at the G3MP2 level of theory is in excellent agreement with the experimental value. The heat capacity and parameters of fusion of MeIm were measured in the temperature range (5 to 370) K using adiabatic calorimetry. The thermodynamic functions for the compound in the crystal and liquid states were calculated from these data. Based on the experimental spectroscopic data and the results of quantum-chemical calculations, the ideal-gas properties for MeIm were calculated by methods of statistical thermodynamics.