A.N. El-hoshoudy, A. Ghanem and S.M. Desouky
Journal of Molecular Liquids xxx (2020) xxx
self-association, which adversely affects the crude oil viscosity [18].
Asphaltene dispersants either adsorbed on to the asphaltene surface
or bonded with the polar moieties in the asphaltene molecule. It is
well known that resin can stabilize asphaltene in the oil media and
the lack of resin content induces asphaltene particles to aggregate and
precipitate, so most of the asphaltene dispersants are designed to
mimic the resin structure [19].
modeled molecules are differentiated into two categories, known as,
“continental” and “archipelago”. The archipelago model comprises
small polyaromatic cores connected by alkyl chains. The continental
model comprises a dominant polyaromatic core bonded to peripheral
substituent side chains [11]. In this work, alkyl imidazolium ionic liquids
and their modified Lewis-acid structure were synthesized. The synthe-
sized ionic liquids have been characterized and evaluated as asphaltene
dispersants since, π-π∗ polar interactions between the Lewis-acid moi-
ety and the basic regions through the asphaltene molecules restrict
the growth of asphaltene deposition through hydrogen bond formation
and electrostatic interaction, which reduces the oil viscosity. The crude
oil characteristics were investigated before and after the ILs treatment.
Viscometric and UV–Vis spectroscopic methods were employed to de-
tect the asphaltene onset precipitation point. Moreover, computational
calculations are performed to inspect the compatibility of ionic liquids
as a function of asphaltene and crude oil molecules.
To the best of our knowledge, this work serves to utilize ILs as green
chemistry agents in the asphaltene dispersion process. Furthermore, the
molecular dynamic simulation was conducted to assess the capability of
ILs as asphaltene dispersants. The commercial outcome of this work can
assist the gas and petroleum industry to handle asphaltene precipitation
through utilizing ILs, leading to ease the processing of heavy oils con-
taining asphaltenes and enhancement of the oil recovery factor. The en-
vironmental outcome encompasses that the ILs are environmentally
friendly candidates compared to traditional dispersion agents. The the-
oretical outcome involves the conductance of MD simulation to investi-
gate the interaction energies between ILs and asphaltene particles, in
addition to the evaluation of ILs ability to disperse the asphaltenes.
Ionic liquids (ILs) containing long alkyl tails (> eight carbon chain)
are effective asphaltene dispersants since they interact with the
asphaltenes and form steric stabilization layers around the asphaltene
molecules [20], leading to the reduction of asphaltene aggregates and
oil viscosity [6]. Acidic ionic liquids were significantly used to prevent
asphaltene from deposition, due to its ability to form hydrogen bonds
and π- π ∗ interactions with asphaltene aggregates [16]. Deep eutectic
solvents and ILs are green chemistry alternatives to surfactants in
many fields, including the petroleum industry as chemical EOR agents
[21–27], chemical synthesis, catalysis, and fuels refining [27–32]. Fur-
thermore, ILs are green media for chemical reactions, alternatives for or-
ganic solvents in catalytic processes [33]. They are an environmentally
friendly candidate, recyclable, non-toxic, non-flammable with low crit-
ical micelle concentration [18,34], non-corrosive agents with unique
surface-active criteria, and remarkable physicochemical properties in-
cluding low vapor pressure [35], and high thermal stability [6,36,22],
so used as green oilfield chemicals [18]. ILs consist of amphiphilic cat-
ions such as imidazolium, ammonium or pyridinium, and organic or in-
organic anions such as halide [36,38]. They can destabilize water in oil
(W/O) or oil in water (O/W) emulsions through dispersing asphaltene
molecules at the interface [32]. Furthermore, they can emulsify heavy
crude oil, boost oil recovery, and reduce residual oil saturation [5] with-
out adverse effects in the porous media [39,40].
2. Experimental
Several studies reported the use of ILs as asphaltene dispersants. Hu
and Guo [41] reported the reduction of asphaltenes precipitation and
enhancement of the crude oil stability through ILs. Fan et al. [42] used
ILs for heavy oil upgrading. They found that ILs, [(Et)NH][AlCl−3 ],
could reduce apparent viscosity, and asphaltene content, owing to the
formation of C\\S bonds between ionic liquids and organic sulfur in
heavy oil [43]. Fan et al. [44] reported that the synergetic effect of
butylimidazolium Ils with metal chloride could decrease the crude
oil viscosity and asphaltene content by 78%. Boukherissa et al. [14]
screened the capability of ionic liquids as asphaltene dispersants for
heavy crude oil. Rezaee Nezhad et al. [16] stated the utilization of UV–
Visible spectroscopy to investigate the dispersion of petroleum
asphaltenes through new acidic ILs based on 3-(2-carboxybenzoyl)-1-
methyl-1H-imidazol-3-ium chloride. Subramanian et al. [6] apply
imidazolium ILs for reducing the viscosity of asphaltenic heavy oil.
Ezzat et al. [32] use new amphiphilic imidazolium-based ILs for distor-
tion of the asphaltene protective film that stabilized the formulation of
the water-in-oil emulsion through interfacial reduction. Xu et al. [15] re-
ported that poly(maleic acid amide-co-vinyl acetate) copolymers with
aromatic and aliphatic pendant groups act as effective asphaltene dis-
persants. Most of the published literature investigate the experimental
evaluation of ILs in asphaltene dispersion and viscosity reduction; how-
ever, few efforts focused on the mathematical modeling [13], as well as
theoretical and computational assumptions [45]. In this regard,
Takanohashi et al. [17] use molecular dynamics (MD) simulation to in-
vestigate the interaction energy through asphaltene globules [11].
Diedenhofen and Klamt [46] implemented COSMO-RS solvation to ex-
plore the activity coefficients of ILs. Tian Tang [11] explores the effect
of side-chain length on the asphaltene aggregation through MD simula-
tions. Hernández-Bravo et al. [47] use density functional theory (DFT)
and MD to investigate the effect of ILs as asphaltene dispersants. MD
simulation provides insights on the interaction mechanism between
asphaltene molecules and the ILs to design optimally functionalized
molecules [6,48]. Owing to the complexity of the asphaltene structure,
various modeled molecules have been supposed to represent the
asphaltenes structure. Depending on their molecular geometries, these
2.1. Materials and characterization
Methyl imidazole (≥95%); Ethyl imidazole (≥95%); Butyl imidazole
(≥95%); 1-chlorohexadecane (≥97%, GC); Acetonitrile (Fluka); Ethyl ac-
etate ≥99.5%); Toluene ≥99% analytical reagent. All chemicals were ana-
lytical grade supplied from Merck and used without further treatment
unless otherwise stated. The heavy oil sample used in this research
was provided by the West Bakr oil company after an agitation of one
hour to ensure homogeneity. Table 1 summarizes the group composi-
tion analysis (SARA) analysis of the crude oil sample according to
ASTMD2007–932 in addition to other physical properties [34]. FT-IR
bands were identified in the range of 400–4000 cm−1 on the
American FTS-3000 FT-IR spectrometer using KBr discs (supplied by
Scharlab). 1H NMR shifts were screened with D2O solvent and
tetramethylsilane (TMS) standard on a Bruker-NMR 400 MHz spec-
trometer, then identified by Mestre Nova software for peaks
Table 1
Physical properties and Group composition (SARA) analysis of crude oil.
Physical properties
Test
Method
Result
Density, g/cc @ 15.6 o C
API o
Molecular Weight
Pour point, °C
ASTM D5002
0.9351
19.6
329.2
12
1.2
5
–
ASTM D97
UOP-64
ASTM D95
ASTM D4294
ASTM D445
Wax Content, wt%
Water content, v%
Sulfur content, ppm
18,350
104.8
Viscosity, cP at 40 o
C
Group composition (SARA) analysis
Saturates
Aromatics
Resin
29.7
35.9
22.3
12.1
Asphaltene
2