Asphaltene Subfractions Responsible for Stabilizing Water-in-Crude Oil Emulsions. Part 2: Molecular Representations and Molecular Dynamics Simulations

Abstract

After successful isolation of the most interfacially active subfraction of asphaltenes (IAA) reported in part one of this series of publications, comprehensive chemical analyses including ES-MS, elemental analysis, FTIR and NMR were used to determine how the molecular fingerprint features of IAA are different from those of the remaining asphaltenes (RA).Compared with RA, the IAA molecules were shown to have higher molecular weight and higher contents of heteroatoms (e.g., three times higher oxygen content). The analysis on the elemental content and FTIR spectroscopy suggested that IAA contained a higher content of high polarity sulfoxide groups which were not present in the RA. The results of ES-MS, NMR, FTIR and elemental analysis were used to construct average molecular representations of IAA and RA molecules. These structures were used in molecular dynamic (MD) simulation to study interfacial and aggregation behaviors of the proposed representative molecules. MD simulation study showed little affinity of representative RA molecules to the oil/water interface while the representative IAA molecules had a much higher interfacial activity, which corresponds to the extraction method. The aggregation of IAA molecules in the bulk oil phase and their adsorption at oil/water interface were not directly related to the ring system but rather to the associations between or including sulfoxide groups. The IAA molecules self-assembled in solvent, forming supramolecular structures and a porous network at the oil/water interface as suggested in our previous work. The results obtained in this study provide a better understanding of the role of asphaltenes in stabilizing petroleum emulsions.

Fractionation of Asphaltenes in Understanding Their Role in Petroleum Emulsion Stability and Fouling

“…86 The molecular weight distribution of IAA peaked within the range of 1,000-1,200 Da, while the average molecular weight of RA was centered at about 700-750 Da, which is in good agreement with recent asphaltene studies. 30 The elemental analysis showed similar carbon, hydrogen, nitrogen, and sulfur contents for two subfractions; however, the oxygen content of IAA (5.54 wt%) is three times higher than that of RA (1.68 wt%).…”

“…It was reported that rather than whole asphaltenes, only a subfraction of asphaltenes is more likely the real contributor to the stabilization of W/O emulsions. 26,[80][81][82][83][84][85][86] The asphaltenes adsorbed onto clays have also been found to be different in composition from whole asphaltenes. 70,[75][76][77] Therefore, it is important to find ways to extract and study these particular species from asphaltenes, which are mainly responsible for the relevant issues of interest.…”

Molecular Interactions between a Biodegradable Demulsifier and Asphaltenes in an Organic Solvent

“…39 Several recent studies highlighted chemical and structural differences between asphaltenes that strongly adsorb at the oil-water and oil-solid interfaces and those remaining in the bulk oil. 40,41,42 An extended SARA analysis 33 where asphaltenes are fractionated and characterized according to their adsorption affinity confirmed differences between adsorbed asphaltenes and whole asphaltenes. In particular, asphaltenes strongly partitioned at the oil-water interface contain a particularly high oxygen content, which led to the increased presence of sulfoxide groups.…”

A multiscale method for simulating fluid interfaces covered with large molecules such as asphaltenes

“…Only very recently have molecular dynamics simulations been applied to the study of asphaltenes at the oil/water interface. Mikami et al [124], Liu et al [125], as well as Yang et al [126] used atomistically-detailed simulations to study this system. In [124,125], the previously mentioned QMR-based model asphaltenes were employed, whereas in [126], two different model asphaltenes were proposed based on experimental measurements and used in simulations.…”

“…Mikami et al [124], Liu et al [125], as well as Yang et al [126] used atomistically-detailed simulations to study this system. In [124,125], the previously mentioned QMR-based model asphaltenes were employed, whereas in [126], two different model asphaltenes were proposed based on experimental measurements and used in simulations. These studies highlight the significant challenge encountered when using an atomistically-detailed approach: one is either confined to very few asphaltene molecules [126] or very short timescales [124,125] due to the high computational cost.…”