Molecular Characterization of Remnant Polarizable Asphaltene Fractions Upon Bitumen Upgrading and Possible Implications in Petroleum Viscosity

Abstract

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.

Molecular Characterization of Aged Bitumen with Selective and Nonselective Ionization Methods by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry. 3. Investigation on Molecular Fractions Obtained by Gel Permeation Chromatography

“…Therefore, they hypothesized that the nanoaggregation prevents the transformation of these species into lighter products . It is also in accordance with the work of Chacón-Patiño et al, demonstrating that photooxidation of asphaltene-dominant blends results in the production of almost no water-soluble organic carbon, which could potentially be attributed to the aggregation behavior of asphaltenes . It could be also supposed that most oxidation sites have already been used up in the HMW fraction.…”

Maltene and Asphaltene Contributions to the Formation of Water-Soluble Emerging Contaminants from Photooxidation of Paving Materials

“…These molecular features promote strong nanoaggregation, with direct implications for asphalt binder rheological properties , and the photo-transformation of these species in the built environment. We hypothesize that species with strong aggregation trends tend to remain stable during irradiation, similar to their noted survival upon advanced hydroconversion processes …”

“…This trend of TOC production could potentially be attributed to the aggregation (self-association) behavior of asphaltenes. The ability of asphaltenes to self-aggregate could potentially prevent the asphaltenes from leaching organic carbon into water when exposed to solar irradiation. , Moreover, a previous report demonstrated the sample-dependent production of water-soluble species from asphaltenes. Abundant water-soluble species were observed from the irradiation of Athabasca bitumen asphaltenes.…”

“…We hypothesize that species with strong aggregation trends tend to remain stable during irradiation, similar to their noted survival upon advanced hydroconversion processes. 68 The solubility fractions from coal tar sealant show markedly different trends of heteroatom content and composition. The coal tar sealant native maltenes are rich in HC species (∼92% RA) and depleted in O 1 , N 1 , and S 1 classes (<7% RA).…”

“…Thus, the maltenes are thought to form a continuous phase with the asphaltenes, in which alkane insolubles (asphaltenes) are "dispersed". This idea, along with the fact that asphaltenes feature an intrinsic tendency to self-aggregate and form supramolecular networks, 52,55,78 which can protect asphaltenic compounds from photooxidation and even thermal cracking/ hydroconversion, 68 suggests that the blending of asphaltenes with maltenes makes them more readily available to photooxidation. 79,80 These findings are in agreement with the results in Figure 4, in which photooxidation of the 9:1 and 1:1 blends, for both asphalt binder and coal tar sealant, resulted in the production of highly oxidized water-soluble species.…”