Mechanisms of Asphaltene Aggregation: Puzzles and a New Hypothesis

Abstract

In petroleum science, asphaltenes are well-known as the most refractory fraction of crude oil and remain infamous for problems in production, transportation, and refining processes. Hence, they have been continuously analyzed and modeled over more than half a century. Defined only by solubility and characterized by an extremely complex and diverse molecular composition, asphaltenes lack discriminative molecular descriptions and definitive chemical characteristics. Most of the historic research has focused on representative structures in an attempt to yield physical and chemical models of asphaltenes, and thus, conflicting theories of bonding structures and aggregation interactions remain. This review focuses on the aggregation behavior of asphaltenes and attempts to rationalize a structure−property relationship to asphaltene aggregate thermal stability. Herein, the chemical and physical bonding properties of asphaltenes and the contradictory interpretations of their nature and composition are examined, particularly as they impact formation and stability of asphaltene aggregates. We propose a new hypothesis involving free radical interactions, i.e., pancake bonding, as an additional significant contributor to the bonding structure and formation of aggregates in asphaltenes that is consistent with the latest findings based on Fourier transform ion cyclotron resonance mass spectrometry and non-contact atomic force microscopy techniques. Various structural features of polycyclic aromatic hydrocarbons contributing to this interaction involving a stable free radical are highlighted, and suggestions for future research are presented.

Commercial Investigation of the Ebullated-Bed Vacuum Residue Hydrocracking in the Conversion Range of 55–93%

“…The presence of free radicals in the asphaltene fractions was documented in several recent studies, 83 − 86 and their possible participation in the mechanism of asphaltene aggregation and sediment formation was addressed. 87 …”

“…On the other hand, the higher aromaticity (density) suggests the presence of free radicals, which can be more stable. 87 All these factors facilitate the asphaltene aggregation and sediment formation that can take place in the ebullated-bed vacuum residue hydrocracking.…”

Nondestructive Analysis of Mummification Balms in Ancient Egypt Based on EPR of Vanadyl and Organic Radical Markers of Bitumen

“…Also, carbonaceous radicals are present in all kerogeneous materials and originate from the maturation of biomolecules during tens to hundreds of million years of geological evolution. They are also present in asphaltene of all bitumen samples, whether or not of the marine origin . These radicals are absent in more recent biological materials, so that the presence of both VO-P and radicals in the complex mixture of embalming materials is a very sensitive marker of the presence of a bitumen component in this black material.…”

The Oscillatory Spinning Drop Technique. An Innovative Method to Measure Dilational Interfacial Rheological Properties of Brine-Crude Oil Systems in the Presence of Asphaltenes

“…This is generally due to the formation of a rigid, viscoelastic layer with high mechanical resistance to flow in the film [10,62]. The actual case is somehow complex because this film is composed of natural surfactants from petroleum, such as asphaltenes, resins, and naphthenic acids, as well as particles of inorganic solids or waxes present in the system [52,56,[62][63][64].…”