Half-Pancake Bonding in Asphaltenes

Abstract

Aggregation of asphaltenes in petroleum crude oil is a well-known and ongoing problem for petroleum production. Asphaltenes aggregate even in situations where polycyclic aromatic hydrocarbon (PAH) model compounds do not, which implies that there is more to the phenomenon than just π-stacking. Half-pancake bonds involving stable radical PAH have been hypothesized to contribute to asphaltene aggregation (ZhangY. Zhang, Y. Energy Fuels20203490949107). We report density functional theory calculations on half-pancake bonding in asphaltene model compounds. Pancake and half-pancake bonds can be viewed as multi-center generalizations of (common) two-electron covalent bonds and (rare) odd-electron bonds, respectively. In the absence of other effects, we find negligible half-pancake bonding between radical PAH and neutral nonradical PAH. Introducing heteroatoms can produce modestly strong donor-acceptor half-pancake-type interactions. Our results suggest that half-pancake bonding alone is too weak and too rare to drive asphaltene aggregation. However, interactions between stable organic radicals, heteroatoms, and polar groups may contribute to aggregation.

Application of the Y-Rule and Theoretical Study to Understand the Topological and Electronic Structures of Polycyclic Aromatic Hydrocarbons from Atomic Force Microscopy Images of Soot, Coal Asphaltenes, and Petroleum Asphaltenes

“…Nevertheless, interactions between stable radicals, heteroatoms, and polar groups may contribute to aggregation. 98 The implication of localized π-radicals in the formation of π-stacking interactions of radical PAHs as soot precursors has also been investigated. 99 Martin et al 99 found that the σradicals are most reactive and form bonds with other radicals, while partially saturated pentagonal rings form localized πradicals which are highly reactive.…”

“…For this, a theoretical systematic investigation of the molecular orbitals and stability of the three different radicals proposed by Zhang et al (phenalenyl type π-radicals, doubly benzylic radicals, and benzylic radicals) would be necessary. With this objective in mind, recently Janesko and Brothers have reported density functional theory calculations on half-pancake bonding in asphaltene model compounds, finding that that half-pancake bonding alone is too weak and rare to drive asphaltene aggregation. Nevertheless, interactions between stable radicals, heteroatoms, and polar groups may contribute to aggregation .…”

“…With this objective in mind, recently Janesko and Brothers have reported density functional theory calculations on half-pancake bonding in asphaltene model compounds, finding that that half-pancake bonding alone is too weak and rare to drive asphaltene aggregation. Nevertheless, interactions between stable radicals, heteroatoms, and polar groups may contribute to aggregation . The implication of localized π-radicals in the formation of π-stacking interactions of radical PAHs as soot precursors has also been investigated .…”

Virtual Experiments on Real Asphaltenes: Predicting Properties Using Quantum Chemical Simulations of Structures from Non-contact Atomic Force Microscopy

“…While asphaltenes form nanoaggregates at a low concentration in toluene, pyrene and alkylpyrene model compounds do not. , Heteroatoms and persistent organic radicals have been hypothesized to play important roles in asphalene aggregation. We recently used DFT simulations to address one specific hypothesis about the role of radicals in aggregation …”

“…We recently used DFT simulations to address one specific hypothesis about the role of radicals in aggregation. 92 In this section, we explore how simulations of asphaltenes imaged by nc-AFM can give insight into the "parts" of the structures that may be involved in aggregation and interfacial activity. We focus on variations in computed surface electrostatic potentials V s .…”