Influence
of Ionic Liquids on the Aggregation and
Preaggregation Phenomena of Asphaltenes in Model Solvent Mixtures
by Molecular Dynamics Simulations and Quantum Mechanical Calculations:
The Effect of Cation’s Shape and Size
posted on 2024-02-15, 08:04authored byRafaela
N. Martins, Lucas G. Celia-Silva, João P.
Prates Ramalho, Pedro Morgado, Eduardo J. M. Filipe, Luís F. G. Martins
The
merits of ionic liquids (ILs) as additives to influence the
solid–liquid behavior of asphaltenes in crude oil models have
been well-established in specialized literature. The direct interaction
between ionic liquids and asphaltenes is recognized as a key factor
for the role played by these additives in the asphaltene aggregation
process, which depends on the structural details of the ionic liquids
used (and also on the model considered for the asphaltenes). In a
previous paper, we presented a systematic molecular dynamics study
of the effect of 1-alkyl-3-methyl imidazolium-based ionic liquids
on the asphaltene preaggregation phenomenon, focusing on the effect
of the alkyl chain length of the cation and on the size of the anion.
In this work, this study is extended to evaluate the effect of the
shape and size of the cation head. The preaggregation phenomena in
toluene/n-heptane mixtures and the asphaltene/IL
interactions are studied here by molecular dynamics simulations and
density functional theory (DFT) calculations, using N-alkylpyridinium, N-alkyl isoquinolinium, and 1-alkyl-3-methyl
benzimidazolium chloride ILs, with alkyl chains containing between
4 and 10 carbon atoms as additives. These additives show a general
dispersing effect in n-heptane-rich systems, with
the N-alkyl isoquinolinium-based ILs with longer
alkyl chains (especially C8 but also C10) being
the most active ones. The asphaltene/IL interaction is found to be
enhanced by cations with two condensed aromatic rings instead of one,
which seems to highlight the importance of the π–π
stacking contact. However, the most interactive family of ILs (1-alkyl-3-methyl
benzimidazolium chloride) is also the one that induces asphaltene
aggregation, especially for shorter alkyl side chains (with 33% larger
aggregates than the systems without additive for mixtures with equal
proportions of the two solvents), probably representing a binder effect
for asphaltenes. Although by molecular simulation, the N-alkyl isoquinolium-based ILs showed the clearest dispersing effect
toward asphaltenes and the most intense interactions with them, they
also presented the lowest interaction energies of the asphaltene–IL
dimers obtained by DFT, and this was found to be the consequence of
a specific cation–anion interaction only for this family of
ILs, which is close to a covalent bond. This work is a valuable addition
to the understanding of the molecular interactions that govern asphaltene
aggregation in the presence of additives, and contributes to the selection
and design of better additives to prevent or induce asphaltene aggregation
in crude oil.