Molecular Survey of Strongly and Weakly Interfacially Active Asphaltenes: An Intermolecular Force Field Approach

Subfractionation of asphaltenes based on their interfacial activity has begun to highlight critical differences between those asphaltenes that are strongly interfacially active (IAA) and the remaining asphaltenes (RA). Following the methods of petroleomics, representative structures of the two asphaltene fractions were determined, reflecting differences in abundant heteroatom groups, carbon number, double-bond equivalents, and single-core/multicore motifs. Using atomistic-potential-based grid-search methods, the intermolecular interactions between asphaltene-asphaltene and asphaltene-solvent (water, heptane, and toluene) were rapidly screened to identify the most favorable and therefore most likely intermolecular interactions to occur. Asphaltene-water interactions were stronger for IAA (abundance-weighted average interaction energy of -9.29 kJ/mol) than for RA (-6.32 kJ/mol), with hydrogen bonding more significant in the IAA-H2O interaction. Dimer interactions of IAA-IAA were stronger than RA-RA, and from the top 100 most favored interactions, the contribution to the total interaction energy was almost exclusively van der Waals for RA-RA (only 3% electrostatic), while for IAA-IAA, electrostatic interactions (9%) and hydrogen bonding (2%) were significant contributors in the most favored interactions. As the relative contribution of the electrostatic interaction increased, the dimer orientation less resembled that of a p-p stack. With the conception of petroleomics and large structural databases, the grid-search method is a useful atomic/molecular screening approach that provides an ideal triaging tool to rapidly assess a wide range of different molecular structures and interactions. The method is complementary to the more computationally expensive precision molecular modeling tools that are not suited to such workflows.

Automated summary

Subfractionation of asphaltenes based on interfacial activity has revealed critical differences between strongly interfacially active asphaltenes (IAA) and remaining asphaltenes (RA), with variations in molecular structures and interactions.