The chemical complexity and diversity of an Athabasca asphaltene sample was described using a series of molecular representations. The molecular representations were created with a Monte Carlo construction method that represented molecules with a series of aromatic and aliphatic groups. After the groups were randomly sampled for a molecule, a connection algorithm linked them together to form molecules consisting of aromatic groups connected by aliphatic chains and thioethers. A sequential nonlinear optimization algorithm was used to select a small subset of molecules that were consistent with elemental, molecular weight, and NMR spectroscopy (both 13C and 1H) data. To accurately represent the analytical data for the asphaltene sample, a minimum of five molecules was needed. On the basis of the results of the sequential optimization, at least 50 molecules in the starting population were required to produce an analytically consistent molecular representation.

Although the mechanism of cracking of distillate fractions is well-known, the reactions that underlay conversion of the residue fractions of petroleum and bitumen are not well defined. Despite the difficulties in analyzing residue fractions in detail, the chemistry of these materials must follow the same elementary reactions as distillates. This paper presents a consistent mechanism for cracking of residues based on the known chemistry of free-radical chain reactions and model compounds. The roles of hydrogen, donor solvents, and added catalysts are then interpreted in this context. The formation of olefin groups from cracking of aliphatic groups gives the potential for addition reactions in the liquid phase. Removal of olefin groups, by reactions with donor solvents or hydrogenation, controls addition reactions and thereby suppresses coke formation. This mechanism suggests that innovative methods to remove or react olefinic groups may allow higher conversion of residues to desirable liquid products.

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.

The coupling of reaction and mass transfer was investigated for the thermal cracking of thin films of an Athabasca vacuum residue. Thin films of the vacuum residue were coated on the interior of a stainless steel tube and then heated to 530 °C using induction heating. Vapor products were swept out of the reaction zone with nitrogen, and reactions in the liquid phase were allowed to proceed to completion. Coke yield, total liquid product, and gas make were determined for initial film thicknesses ranging from 10 to 80 μm. Product qualities of the liquid samples were characterized by high-temperature simulated distillation and microcarbon residue concentration. The coke yield decreased as the film thickness was reduced, while the yield of distillate products (<524 °C boiling point) increased. As the film thickness was reduced, the mode of mass transport shifted from bubbling in thick films to diffusion through a stagnant thin film. These results were consistent with a decrease in the trapping of cracked products in coke as the film thickness was reduced, because of more effective transport of products out of the liquid phase. A mathematical model was developed to analyze the results and to estimate the diffusivity of gases in the reacting liquid phase.

Thermal cracking of Athabasca bitumen at various reaction conditions with and without the presence of steam was investigated to determine if steam has a chemical influence on coking. The reactions were done in 15 mL microautoclave reactors and a 3" diameter fluidized bed coking pilot unit over a range of reaction severity (350-530 °C, 10-60 min reaction time). The differences between reactions with and without steam were investigated by comparing elemental composition of the products and coke yield. The presence of steam decreased coke yield and decreased sulfur removal, and reduced the H/C ratio of the liquid products. Hydrogen exchange from steam to thermally cracked bitumen molecules was tested by doping water with deuterium oxide (D 2 O) and analyzing liquid and coke products by NMR and stable isotope mass spectrometry, respectively. Preferential deuteration of benzylic carbons was observed along with a trend of increasing deuterium transfer to liquids and coke as reaction severity increased. Free-radical, ionic, and physical mechanisms that can account for these experimental results are discussed.