The Overriding Chemical Principles that Define Asphaltenes

TLDR

Asphaltenes are defined by solubility classification, but this operational definition and debate over molecular weight have obscured the chemical and structural parameters that govern the asphaltene fraction. The study investigates asphaltenes using multiple techniques to elucidate structure–property relationships. The authors compare asphaltene molecular size to the aromatic‑to‑saturated carbon ratio. They conclude that asphaltene structure is governed by a balance between π‑stacking of fused aromatic rings, which reduces solubility, and steric disruption by alkane groups, which increases solubility.

Abstract

Asphaltenes are defined in terms of their solubility classification. This operational definition combined with the previous controversy over asphaltene molecular weight have obscured the governing chemical and structural parameters that define the asphaltene fraction. Here, asphaltenes are investigated by several techniques to elucidate relations between structure and properties. In particular, the asphaltene molecular size is compared to the ratio of aromatic to saturated carbon. The conclusion is obtained that asphaltene molecular structure is governed by the balance between the propensity of fused aromatic ring systems to stack via π-bonding, reducing solubility, vs the steric disruption of stacking due alkane groups, increasing solubility.