Supramolecular Assembly Model for Aggregation of Petroleum Asphaltenes

Abstract

The components of petroleum asphaltenes exhibit complex bridged structures comprising sulfur, nitrogen, aromatic, and naphthenic groups linked by alkyl chains. These components aggregate in crude oil and toluene over a wide range of concentrations and temperatures, exhibit strong adhesion to a wide range of surfaces, occlude components that are otherwise soluble, are porous to solvents, and are elastic under tension. None of these properties is consistent with an architecture dominated only by aromatic stacking by electrostatic and/or van der Waals forces, often called π–π stacking. We propose an alternate paradigm based on supramolecular assembly of molecules, combining cooperative binding by Brønsted acid–base interactions, hydrogen bonding, metal coordination complexes, and interactions between cylcoalkyl and alkyl groups to form hydrophobic pockets, in addition to aromatic π–π stacking. A range of architectures are suggested, which almost certainly occur simultaneously, including porous networks and host–guest complexes. The latter may include organic clathrates, in which occluded guest molecules stabilize the assembly of a cage, as methane does in gas hydrates. This model has a number of implications for analysis of asphaltene mixtures and predicting asphaltene phase behavior and transport properties.

Asphaltene adsorption on quartz sand in the presence of pre-adsorbed water

“…Self-aggregation, whether at interfaces or in solution, is understood to result from - stacking of the asphaltene polycyclic aromatic regions [9], although electrostatic and Hbonding contributions involving water have also been identified in model asphaltene systems [10][11][12]. This latter view supports other results from simulation and experiment, that low water concentrations promote asphaltene nanoaggregation in toluene solution [13], which is suggested to involve intermolecular H-bonded water bridges and asphaltene heteroatoms, e.g.…”

Waxes in asphaltenes of crude oils and wax deposits

“…However, the traditional methods used to isolate asphaltenes by adding 40 volumes in excess of low boiling point paraffin hydrocarbons can produce a fraction which is contaminated with a significant amount of waxes (Chouparova and Philp 1998;Thanh et al 1999;Liao et al 2006;Acevedo et al 2009;Coto et al 2011). The presence of paraffin hydrocarbons in asphaltenes can be explained by their coprecipitation as a result of low solubility in low molecular weight n-alkanes (Thanh et al 1999;Coto et al 2011), by interaction between the alkyl lateral chains (C 7 -C 10 ) of asphaltenes with high molecular weight n-alkanes (Garcia and Carbognani 2001;Stachowiak et al 2005;Ganeeva et al 2014), and by their adsorption and/or occlusion inside asphaltene aggregates (Liao et al 2005(Liao et al , 2006Acevedo et al 2009;Gray et al 2011). Now, it is well-known that the asphaltenes exist as three-dimensional aggregates due to the strong intermolecular forces such as hydrogen bonding and p-bonding (Murgich 2002) and even at very low concentration as 50-150 mg/L in a good solvent such as toluene (Mullins et al 2012).…”

Aggregation study of asphaltenes from colombian Castilla crude oil using molecular simulation

“…The polydisperse model, although more accurate in describing the real nature of the system, implies more compute time and propose a technical difficulty in determining the actual forces that intervene in asphaltene aggregation. Recently developed theories are inclined to consider a supramolecular model for asphaltene aggregation that even include the content of heavy metals in the molecule structure, a feature often neglected due to the low fraction of these elements in the structural analysis of asphaltenes [13]. This level of detail allows depicting the association behavior of asphaltenes observed experimentally.…”