New insights into asphaltenes chemistry and structure: Implications for aggregation modelling

Asphaltenes are the heavy fraction of crude oil, defined operationally as being soluble in aromatic solvents (e.g. toluene), but insoluble in n-alkanes (e.g. heptane/pentane). This definition comes from the SARA analysis method, which separates the components of crude oil into saturates, aromatics, resins and asphaltenes based on their solubility and polarity. As a component of crude oil, asphaltenes have historically been viewed as problematic, causing fouling in reservoirs and process equipment such as heat exchangers and marine engines. To better understand their chemistry and structure, many researchers have fractionated asphaltenes based on their solubility in solvents of decreasing aromaticity, yet those studies have provided little clarity on the chemistry-structure relationship. In the current study, a new method of separating asphaltenes based on their interfacial activity at an oil-water interface has been considered. Through this method two subfractions are isolated (a strongly interfacially active and weakly interfacially active) and characterised to highlight differences in their chemistry and how those differences influence their structure in solvents. The main findings of this research are i) differences in aggregate structures between strongly and weakly interfacially active asphaltenes, ii) demonstrating the importance of the fractions molecular architecture, as well as heteroatom content and functional group differences, and iii) developing an understanding of how these fractions behave and interact at interfaces. The research presents new insights to the molecular-level understanding of problematic asphaltene fractions and how those molecular properties govern their aggregation behaviour. The new understandings provide opportunity to design better chemical additives that can be used to stabilise and inhibit asphaltene deposit problems.