To fully advance our understanding of hydrocarbon conversion chemistry requires powerful analytical methods to qualitatively and quantitatively characterize complex petroleum fractions at the molecular level. In the absence of such tools, an alternative solution is to model the molecular composition of hydrocarbon mixtures with limited analytical data. The objective of this study is to integrate modeling techniques with conventional and advanced petroleum characterization methods to derive the composition of middle distillate fractions at the molecular level. In the present approach, analytical petroleum characterization data are used as input to computationally generate a mixture of representative molecules that mimics the properties of the real sample. The representing molecules are constructed according to coherent chemical/thermodynamic criteria by Monte Carlo sampling of a set of statistical functions assigned to each possible molecular feature. The assembled mixture is built on a large set of chemical species and is further optimized with the principle of Maximum Entropy. The approach is applied to simulating two middle distillates differing significantly in hydrocarbon type composition and origin. The samples are experimentally characterized by standard and advanced analytical methods: density, simulated distillation, elemental analysis, hydrocarbon types/distributions and sulfur compound speciation by two-dimensional gas chromatography with flame ionization detector (GC × GC−FID) and sulfur chemiluminescence detector (GC × GC−SCD), and 13 C nuclear magnetic resonance (NMR), to obtain sufficient information for parameter fitting and model validation. Simulation results showed that the model is capable of generating representative mixtures that reasonably match the actual physical samples in analytical properties and carbon number distributions.
Thermal processing and hydrotreatment are used to decrease
the
viscosity of Alberta bitumen. However, changes in bulk properties,
such as API gravity and viscosity, do not correlate to the gravimetric
content of maltenes and asphaltenes. Thus, the work herein employs
an extrography separation that yields asphaltene fractions enriched
with distinct structural motifs and aggregation tendencies to investigate
if changes in viscosity could be linked to the transformation or survival
of specific asphaltene compounds and/or extrography fractions. Samples
with limited change in viscosity upon thermal processing display minor
changes in the gravimetric distribution of the extrography fractions,
specifically polarizable species (Tol/THF/MeOH fraction). Ultrahigh-resolution
mass spectrometry analysis demonstrates that such samples reveal neither
a significant decrease in chemical polydispersity nor a change in
the relative content of multicore/archipelago structural motifs post
thermal treatment. Conversely, hydroprocessed samples with a pronounced
viscosity reduction feature a remarkably lower chemical polydispersity
and increased content of single-core (island) structural motifs. Polarizable
asphaltene fractions from severely hydrotreated samples feature S-containing
species with a low aromaticity, which on the basis of their molecular
composition suggests that they are composed of the expected, alkyl
substituted, geologically stable thiophenic cores (e.g., benzothiophene)
as well as “unexpected” sulfides and sulfoxides. Collectively,
the results suggest that the high viscosity of thermally upgraded
samples could be correlated to the survival of asphaltene species
with high heteroatom content (up to five heteroatoms per molecule)
and persistent, high abundance of archipelago structural motifs. Thus,
it is suspected that nanoaggregation of such fractions prevents their
transformation into lighter products.
This study deals with a systematic investigation of the fluid catalytic cracking (FCC) performance of a bitumen-derived virgin heavy gas oil (HGO) in the presence of its counterpart from bitumen-derived synthetic crude oil (SCO). The objective is to determine the amelioration effect on yield and product slate by the addition of the premium SCO HGO. The 343–525 °C cut virgin bitumen HGO was obtained from distillation of a raw Athabasca oil sands bitumen. It was then blended with different amounts of the 343 °C+ fraction of commercial SCO. Four HGO blends were prepared containing 75, 64, 61, and 48 v% of SCO HGO. Each HGO blend, as well as 100% SCO HGO, were catalytically cracked at 500 and 520 °C using a bench-scale Advanced Cracking Evaluation (ACE) unit. The results show acceptable FCC performance of bitumen virgin HGO when an adequate amount of SCO HGO is added. However, the resulting liquid product may need some quality improvement before use. Several observations, including catalyst poisoning by feed nitrogen and the refractory nature of virgin HGO, are evident and help to explain some observed cracking phenomena.
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