Relations between Asphaltene Structures and Their Physical and Chemical Properties:  The Rosary-Type Structure

Abstract

The proposition of the hypothesis-relating structure with properties of asphaltenes is a very important endeavor. In view of their complexity, being an intricate mixture of high-molecular-mass compounds, experimental and theoretical procedures must be designed to check whether the structures proposed are consistent with expected and found behavior. During recent years, a structural characteristic of asphaltene, whereby the several polycyclic systems present in them are joined by flexible aliphatic chains, has been proposed by several authors. For simplicity, we will refer to this as the rosary-type structure. In this paper, using both reported as well as new experimental and theoretical results, an attempt is made to show how asphaltene properties, such as molecular-mass distribution, molecular fragmentation, solubility, adsorption, trapping of molecules, solvent swelling, and aging, could be accounted for in terms of the above rosary-type structures.

Waxes in asphaltenes of crude oils and wax deposits

“…Asphaltenes are defined according to their solubility, i.e., as the fraction of the crude oil which is soluble in toluene and precipitates in low boiling point alkanes (n-pentane, n-heptane). Two of the representative structures for the asphaltene molecules belong to the ''island'' and ''archipelago'' structures (Groenzin and Mullins 2000;Acevedo et al 2007). According to ''island'' structure, the most dominant part of the molecule is a planar polycyclic aromatic system containing on average 7 aromatic rings, and this aromatic system has poor alkyl substitution.…”

“…The mean molecular weight for ''island'' asphaltenes is 750 with a distribution 500-1000, and the mean size is 2 nm (Mullins et al 2012). The ''archipelago'' model (Acevedo et al 2007;Strausz et al 2008) represents several fused ring systems that are interconnected by alkyl chains. These two molecular structures probably coexist, and the debate is now centered on their proportions and specific roles in an asphaltene mixture.…”

Natural Surfactants from Venezuelan Extra Heavy Crude Oil - Study of Interfacial and Structural Properties

“…Therefore, Table 5 shows the percentage of AcJ present in maltenes, asphaltenes, and acid-free asphaltenes. As can be seen, asphaltenes show the highest concentration of acids, suggesting that the AcJ are trapped by the asphaltene molecules which act as molecular traps, because these compounds are linked by hydrogen bonds, among other kind of interactions (π-π interactions) (Acevedo et al 2007). On the other hand, acid-free asphaltenes (ASA) show a higher interfacial tension than AJ indicating that the acids were removed at least almost completely from the asphaltenes.…”

Characterization of Crude Oils and the Precipitated Asphaltenes Fraction using UV Spectroscopy, Dynamic Light Scattering and Microscopy

“…Molecules of the asphaltene fraction are dispersed in crude oil as stabilized colloids, and they can form aggregates by steric efect according to their sizes, polar characteristics, and solvent polarity [35].…”