The role of metalloporphyrins on the physical-chemical properties of petroleum fluids

Abstract

The presence of metalloporphyrins in crude oil has been known by many years now but their role on the physical-chemical properties of petroleum fluids, such as the aggregation of the high-molecular weight phases, remains unknown. In this paper, these properties are studied using different molecular modeling techniques (Molecular Dynamics, Semi-empirical PM7 and Density Functional Theory). This combined methodology allowed us characterizing the nature of these interactions, how it dominates the electronic structure of the stacked molecules and what is their participation on the formation of the nano-, microand macro-aggregates.

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 same XIC is also plotted with the abundance-weighted average H/C ratio as the y -axis instead of relative abundance. The average H/C ratio XIC is shown in red with the y -axis inverted, and it gives us a measure of aromaticity for the N 4 O 1 51 V 1 porphyrin heteroatom class . The aromaticity and H/C ratio are inversely related, so the earliest eluting porphyrins are least aromatic, as confirmed by the (+)­APPI derived isoabundance color-contoured plots of double-bond equivalents vs carbon number for the N 4 O 1 51 V 1 class (Figure , top).…”

“…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 presence of H bonds between porphyrins and asphaltenes by polar lateral chains can enhance π-π interactions, an about twofold increase [213]. 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].…”

Advances and Challenges in the Molecular Characterization of Petroporphyrins

“…A first level is the characterization of the interaction between pairs of compounds including a metal porphyrins. Considering only pairs of compounds or a few numbers of molecules allows implementation of quantum chemistry calculations in order to investigate interactions between metalloporphyrins and resins or asphaltenes model molecules. ,− In particular, a large effort ensued to understand the contributions of π-stacking interactions, hydrogen bonds, , or metal–ligand interactions through direct bonding onto the metal center. ,,− These studies highlight the driving force of porphyrins behaviors into asphaltene aggregates and the balance between π stacking, hydrogen bonds, and metal coordination. In the case of nickel porphyrins, a consensus is reached about the predominance of the typical association scheme through π-stacking interactions, , and the axial binding onto the nickel center strongly depends on the electronic state of the nickel .…”