Probing Challenges of Asphaltenes in Petroleum Production through Extended−SARA (E−SARA) Analysis

  • Author / Creator
    Qiao, Peiqi
  • Asphaltenes are polyaromatic compounds present in crude oils, which are defined as being soluble in aromatic solvents and insoluble in n−alkanes. The partition of self−associated asphaltene aggregates at oil−solid and oil−water interfaces is the root cause of a number of major problems encountered in oil production and processing. However, it has been noted that not all asphaltene molecules contribute equally to these problems. This thesis focuses on probing properties of the crucial “problematic” asphaltene subfractions using extended−saturates, aromatics, resins, and asphaltenes (E−SARA) analysis.Unlike most studies on asphaltene fractionation based on solubility or density differences, E−SARA analysis provides a unique way to fractionate asphaltenes according to their interfacial behaviors and adsorption characteristics at either oil−solid or oil−water interfaces that is directly linked with problems encountered in petroleum production and processing. Through the E−SARA fractionation based on asphaltene adsorption onto calcium carbonate, the adsorbed asphaltene subfractions were found to contain a higher amount of carbonyl, carboxylic acid or derivative groups than the remaining asphaltenes. Using the E−SARA fractionation based on asphaltene adsorption at oil−water interfaces, the “interfacially active asphaltenes” (IAA) were extracted as asphaltenes irreversibly adsorbed onto emulsified water droplets, while the asphaltenes remaining in the oil phase were considered as “remaining asphaltenes” (RA). Despite the small percentage of IAA (< 2 wt%) in whole asphaltenes (WA), IAA subfractions were found to play an essential role in stabilizing W/O emulsions by forming thick and rigid films at oil−water interfaces with severe aging effects, as opposed to RA which showed no stabilization potential for W/O emulsions. In this thesis research, the effect of solvent aromaticity on the compositions of IAA and RA was studied using toluene and heptol 50/50 as the extraction solvent, respectively. Heptol 50/50, a mixture of n−heptane and toluene at a 1:1 volume ratio, is a less aromatic solvent than toluene. A lower fractional yield (1.1 ± 0.3 wt%) of toluene−extracted IAA (T−IAA) than that (4.2 ± 0.3 wt%) of heptol 50/50−extracted IAA (HT−IAA) was obtained. However, T−IAA exhibited a greater interfacial activity and a higher W/O emulsion stabilization potential than HT−IAA, as shown by the measurements of interfacial tension, interfacial shear rheology, crumpling ratio, and bottle test of W/O emulsion stability. Such differences are attributed to the higher oxygen and sulfur content of T−IAA than HT−IAA, highlighted in the presence of sulfoxide groups as verified by elemental analysis, Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). In contrast to two IAAs, the compositions of two RAs (T−RA and HT−RA) were found to be essentially the same regardless of solvent type used in fractionation. Both RAs had a lower sulfur and oxygen (in particular) content than IAAs, giving rise to their considerable less interfacial activities.Asphaltenes were found to adsorb at oil−water interfaces in the form of asphaltene aggregates. The aggregation kinetics of IAAs and RAs were investigated using dynamic light scattering (DLS), indicating the enhanced asphaltene aggregation by reducing solvent aromaticity. In a given solvent, T−IAA exhibited the strongest aggregation tendency, followed by HT−IAA, then T−RA and HT−RA, following the same trend with their interfacial activities and emulsion stabilization potentials. The interaction forces between immobilized fractionated asphaltenes were measured using an atomic force microscope (AFM). The decreasing solvent aromaticity was found to reduce steric repulsion and increase the adhesion between asphaltenes with asphaltenes adopting a more compressed conformation. IAAs, in particular T−IAA, exhibited stronger adhesion forces than RAs, showing good agreement with the results from DLS measurements. In spite of the small sulfoxide content in asphaltenes, the sulfoxide groups are believed to play a critical role in enhancing asphaltene aggregation in the bulk oil phase. Using E−SARA analysis, the complexity of asphaltenes can be reduced by targeting specific asphaltene subfractions that have critical influences in the relevant systems of interests. The key chemical functionalities that govern asphaltene adsorption and aggregation are identified through the characterizations of fractionated asphaltenes, leading to a better understanding of the related molecular mechanisms. The fundamental findings from this thesis is essential to providing the optimal solutions of asphaltene−related problems in petroleum industry.

  • Subjects / Keywords
  • Graduation date
    Spring 2019
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
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