Fractionation of Asphaltenes in Understanding Their Role in Petroleum Emulsion Stability and Fouling

Abstract

SARA fractionation separates the oil into fractions of saturates (S), aromatics (A), resins (R), and asphaltenes (A) based on the differences in their polarizability and polarity.Defined as a solubility class, asphaltenes are normally considered as a menace in the petroleum industry mainly due to their problematic precipitation and adsorption at oil water and oil-solid interfaces. As a broad range of molecules fall within the group of asphaltenes with distinct sizes and structures, considering the asphaltenes as a whole was noted to limit the deep understanding of governing mechanisms in asphaltene-induced problems.Extended-SARA (E-SARA) is being proposed as a concept of asphaltene fractionation according to their interfacial activities and adsorption characteristics, providing critical information to correlate specific functional groups with certain characteristics of asphaltene aggregation, precipitation and adsorption. Such knowledge obtained is essential to addressing asphaltene-related problems by targeting specific subfractions of asphaltenes for selective removal.2

Role of the porphyrins and demulsifiers in the aggregation process of asphaltenes at water/oil interfaces under desalting conditions: a molecular dynamics study

“…The analysis of this fraction shows that its molecular mass is higher and the amounts of carbon, hydrogen, nitrogen and sulfur are similar to those found in asphaltenes not demonstrating such activity. On the other hand, the amount of oxygen is 3 times higher and can be attributed, thanks to the FTIR analysis (band around 1700 cm −1 ), according to the study, to a more important number of sulfoxides (Yang et al 2015), carboxylic acids, carbonyls and their derivatives (Qiao et al 2017). Once these sub-fractions are separated out, the remaining asphaltenes show almost no emulsion formation and stabilization, thus corroborating the results already found by Yang et al (2014).…”

“…These can be present in crude oil in two forms: naphthenic acids, non-aromatic structures which are mostly found in heavy and immature oils, their origin being indicated as being due to the biodegradation of microorganisms (Meredith et al 2000;Brandal et al 2006); or as end groups of asphaltenes' side chains, which gives them an amphiphilic character (Varadaraj and Brons 2007). By revealing their presence in the fraction responsible for the stabilization of emulsions, we can also immediately see the link with the corrosion of pipelines due to emulsions: The interaction between these acids from the emulsion and the chromium(III) oxide from the surface of stainless steel can also contribute to this unwanted process (Qiao et al 2017).…”

“…Since asphaltenes are defined as a class of solubility (SARA fractionation Jewell et al 1972) rather than a class of molecules with specific properties, only a fraction of the molecules may have emulsifying properties (concomitant presence of hydrophobic and hydrophilic groups), while other fractions are inert (Jarvis et al 2015;Czarnecki and Moran 2005;Czarnecki 2008;Yang et al 2014;Wu 2003). As a result, asphaltenes in general may be wrongly identified as being the only ones responsible for the undesirable stability of crude oil emulsions formed during the desalting process (Kilpatrick 2012;Qiao et al 2017 and the references therein). Such a limitation is, undoubtedly, detrimental to the thorough understanding of these mechanisms.…”

“…Such a limitation is, undoubtedly, detrimental to the thorough understanding of these mechanisms. Qiao et al (2017) proposed a novel fractionation method consisting in separating the asphaltenes on the basis of their adsorption properties at the water/oil interfaces. The fraction showing significant interfacial activity was estimated to be only 2% in the weight of the total amount of isolated asphaltenes.…”

“…Concerning the water/oil interfaces, it has been hypothesized that acid/base interactions within crude oil may be behind the stabilization of emulsions (Fortuny et al 2007;Kilpatrick 2012;Subramanian et al 2017). Molecules capable of forming a network of interactions around water molecules, including hydrogen bonds, are also indicated as being possible targets to reduce such stabilization process (Kilpatrick 2012;Qiao et al 2017).…”