Role of the porphyrins and demulsifiers in the aggregation process of asphaltenes at water/oil interfaces under desalting conditions: a molecular dynamics study

Abstract

Breaking water-in-oil emulsions during the refining of crude oils is an important step before any upgrading process is started. Asphaltene molecules are incriminated as playing an important role in this phenomenon. Unraveling the mechanisms behind the affinity between them and water is a key step to understand how to break these emulsions more easily and require lower amounts of demulsifiers. Choosing which demulsifier molecule(s) to use is also primordial, but to do so rationally, one needs to know which are the molecular interactions in place between asphaltenes, porphyrins and water so that demulsifiers are chosen to destabilize a specific physical-chemical interaction. In this paper, we study the interactions arising between asphaltenes and porphyrins and six different molecules potentially displaying a demulsification action in the presence of water/oil interfaces. We demonstrate that the ionic demulsifier molecules present an interesting potential to either interact strongly with water, replacing asphaltenes in this interaction, or to interact with the active sites of asphaltenes, deactivating them and avoiding any asphaltenic interfacial activity. Finally, we also found that although asphaltenes do not migrate spontaneously toward the water/oil interfaces, porphyrins do so rather easily. This indicates that porphyrins do have an important activity at the water/oil interface.

Probing Aggregation Tendencies in Asphaltenes by Gel Permeation Chromatography. Part 2: Online Detection by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry and Inductively Coupled Plasma Mass Spectrometry

“…The composition of the vanadyl porphyrins eluting in the most aggregated region (leftmost plot) spans the largest carbon number range. As aggregation lessens, the carbon number range narrows and the average H/C ratio decreases to almost 1.0, corresponding to species with very little alkylation on the core, tetrapyrrolic porphyrin structure. ,, Increased aggregation correlated to decreased aromaticity and greater abundance of more aliphatic species for all of the heteroatom classes observed. Figure confirms that correlation for three of the most abundant heteroatom classes in the whole asphaltenes.…”

Fractionation and Characterization of Petroleum Asphaltene: Focus on Metalopetroleomics

“…The π-stacking interactions are not strong enough to explain why porphyrins are commonly found within asphaltene aggregates [214]. The formation and stabilization of asphaltene nanoaggregates are dependent on the size of the conjugated core and the eventual presence of polar groups capable of forming H bonds [212,215]. Vanadyl porphyrins, even without polar lateral chains, can interact considerably strongly with asphaltene molecules via the formation of H bonds from the central O atom [194,213].…”

Advances and Challenges in the Molecular Characterization of Petroporphyrins

“…Moreover, calculations show that asphaltene–asphaltene interaction energies are larger than asphaltene–porphyrin interaction energies, which support the idea that trapped compounds and resins preferentially bond to porphyrins rather than asphaltenes in large aggregates. , These conclusions were supported by molecular dynamics calculations that take into account solvent effects, asphaltene diversity, and thermodynamics conditions and concluded that metalloporphyrins do not directly affect asphaltene–asphaltene interactions. ,,, However, polar lateral chains on porphyrin core structures leads to hydrogen bond interactions with both asphaltenes and water, causing reinforcement of π-stacking interactions between asphaltenes. Therefore, the presence of metalloporphyrins may display an interfacial activity and, depending on the solvent, induces either a stronger precipitation in n -heptane or stabilizes aggregate at a water/oil interfaces. ,, …”