Improving heavy oil recovery, part (I): Synthesis and surface activity evaluation of some novel organometallic surfactants based on salen-M complexes

Article abstract of DOI:10.1039/d0ra09502h

This study focuses on preparing a new family of organometallic surfactants based on five ion complexes, namely Co2+, Ni2+, Cu2+, Fe3+, and Mn2+. The first step is the preparation of 5-chloromethyl salicylaldehyde (Salen, S). The second step is the formation of sodium alkoxide of Pluronic F-127 (AP). The third step is the formation of the modified AP-Salen (new ligand). This ligand was reacted with the metal chlorides as mentioned earlier to obtain the organometallic surfactants (OMS) named AP-Salen-M complexes. FT-IR, 1H-NMR, SEM, and EDX justified the chemical structure of the as-prepared materials. The surface tension of these surfactants was measured for surfactant solutions at different concentrations to determine the CMC and calculate their surface-active properties. The interfacial tension at CMC was measured against heavy crude oil to predict the availability and use these surfactants in the enhanced oil recovery (EOR) process. From the results, this class of surfactants exhibited good surface-active properties and high efficiency on the interface adsorption; besides, they reduced the interfacial tension in the order between 10-1 and 10-2 mN m-1, which gives a good indication to use these surfactants in EOR application for the heavy crude oil.

Full text of DOI:10.1039/d0ra09502h

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PAPER
Improving heavy oil recovery, part (I): synthesis and
surface activity evaluation of some novel
organometallic surfactants based on salen–M
complexes†
Cite this: RSC Adv., 2021, 11, 1750
ac
S. A. Rizk,b M. A. Betiha,ac S. M. Desoukya
*
M. M. Abdelhamid,
and A. M. Alsabaghac
This study focuses on preparing a new family of organometallic surfactants based on five ion complexes,
namely Co2+ Ni2+ Cu2+ Fe3+ and Mn2+
The first step is the preparation of 5-chloromethyl
,
,
,
,
.
salicylaldehyde (Salen, S). The second step is the formation of sodium alkoxide of Pluronic F-127 (AP).
The third step is the formation of the modified AP–Salen (new ligand). This ligand was reacted with the
metal chlorides as mentioned earlier to obtain the organometallic surfactants (OMS) named AP–Salen–M
complexes. FT-IR, 1H-NMR, SEM, and EDX justified the chemical structure of the as-prepared materials.
The surface tension of these surfactants was measured for surfactant solutions at different
concentrations to determine the CMC and calculate their surface–active properties. The interfacial
tension at CMC was measured against heavy crude oil to predict the availability and use these
surfactants in the enhanced oil recovery (EOR) process. From the results, this class of surfactants
exhibited good surface–active properties and high efficiency on the interface adsorption; besides, they
reduced the interfacial tension in the order between 10ꢀ1 and 10ꢀ2 mN mꢀ1, which gives a good
indication to use these surfactants in EOR application for the heavy crude oil.
Received 8th November 2020
Accepted 2nd December 2020
DOI: 10.1039/d0ra09502h
rsc.li/rsc-advances
oil) remaining in reservoirs aer applying primary and
secondary oil extractions.14,15
1. Introduction
In the past decades, several theoretical and laboratory
studies have been conducted to validate the EOR techniques
such as thermal, chemical, microbial, and miscible ooding
methods. The most widely and promising applied process is
chemical EOR (C-EOR), which was developed since the 1950s.4
Among them, chemically enhanced oil recovery is the most
promising and also the particle method due to the broadness of
the type of chemicals used that accomplish the purpose.2 The C-
EOR includes using alkalis, surfactants, polymers, or a mix of
the previous example, such as surfactant/polymers, alkaline/
surfactant/polymer (ASP), and nano-uids.5 The prominent role
of a surfactant in C–EOR is the change of rock wettability by
reducing the interfacial tension and improvement of water/oil
mobility ratio due to the reduction of ow properties of heavy oil.6
The surfactant approach in EOR via the reduction of the
interfacial tension between oil and water is very important. This
approach leads to a remarkable displacement efficiency of
crude oil as the IFT decreases.7 Agista et al. reported that the
metal nanoparticles could promote the action of the surfactant
to achieve more reduction in IFT.2,8
The heavy crude oil is mainly composed of high molecular
weight paraffin, asphaltenes, and resins and a low concentra-
tion of aromatic and naphthene components.1,2 This oil has an
API of less than twenty and a high viscosity and density. Indeed,
these properties cause low owability in porous media and
pipeline transportation.2,3 Thus, the heavy crude oil production
process faces numerous challenges, including the cost of
production and the nature of the facilities used.2 In general,
several methodologies have been developed to enhance the
percentage of heavy crude oil production from oil wells aer
reducing the reservoir's energy.2 Crude oil production passes
through three different stages: primary, secondary, and tertiary
(enhanced) oil recovery. The primary stage is the extraction of
oil under natural driving forces existing in the reservoir.
Secondary recovery refers to the increase in the cumulative oil
produced using water and immiscible gas ooding.11–13 Tertiary
recovery or EOR is used for recovering additional oil (residual
aEgyptian Petroleum Research Institute (EPRI), Nasr City, Cairo 11727, Egypt. E-mail:
mahmmoud.mmohamed@gmail.com
bChemistry Department, Faculty of Science, Ain Shams University, 11566, Cairo, Egypt
cEnhanced Oil Recovery Unit (EOR Unit), Nasr City, Cairo 11727, Egypt
† Electronic supplementary information (ESI) available. See DOI:
10.1039/d0ra09502h
In this study, materials that include the surfactant metal
complex moieties are prepared as a new surfactant (OMS) in
different steps. In the rst step, 5-chloromethyl salicylaldehyde
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was prepared by the reaction of salicylaldehyde and formalde- with a molecular weight of 211.28 was collected as a ne pale-
hyde (Salen, S). In the second step, the formation of sodium yellow powder (yield ¼ 91%, 3.60 g).17
alkoxide was carried out by the reaction of Pluronic F-127 with
sodium metal (AP). In the third step, a new ligand was prepared
by the reaction of the alkoxide with the Salen compound to form
a modied AP–Salen (ligand) with other chlorides, including
Co2+, Ni2+, Cu2+, Fe3+, and Mn2+, to achieve the new chemical-
based structure of AP–Salen–M OMS complexes. These
compounds will be characterized via FT-IR, 1H-NMR, SEM, and
TEM. The surface–active properties and interfacial tension
against heavy crude oil might be investigated to predict the
spectrum opportunity to use them in the EOR application.
2.5. Preparation of modied AP–Salen sodium 2-(1-(2-(3-
formyl-4-hydroxyphenoxy)ethoxy)propan-2-yloxy)ethanoate
In a 100 mL round ask (0.002 mol, 12.3 g), alkoxide was reacted
with (0.002 mol, 0.34 g) of 5-chloromethylsalisaldehyde (Salen) in
the presence of ethanol as a solvent to form sodium-2-(1-(2-(3-
formyl-4-hydroxyphenoxy)ethoxy)propan-2-yloxy)ethanolate (modi-
ed AP–Salen). The product was white powder (yield ¼ 89%, 11.5 g).
2.6. Preparation of Schiff base (SB)
In a 100 mL round ask attached with a condenser (0.001 mol,
6.3 g), the modied AP–Salen reacted with (0.001 mol, 0.21 g)
potassium 4-amino benzenesulfonate dissolved in ethanol to
form a Schiff base at 60 ꢁC for 2 h with continuous stirring; the
waxy pale yellow product was obtained (yield ¼ 82%, 5.2 g).
2. Experimental
2.1. Materials
All used chemicals including salicylaldehyde (2-hydrox-
ybenzaldehyde) (98%), formaldehyde solution (37%), Pluronic-F-
127 (polyethylene–polypropylene–polyethylene) block co-polymer
powder, 4-aminobenzenesulfonic acid ($99.0%), zinc oxide
2.7. Preparation of organo-metallic surfactant, OMS
($99.0%), cobalt(II) chloride (97%), nickel(II) chloride (98%), cop- In a 250 mL three-neck ask, with a condenser, nitrogen source,
per(II) chloride (99%), iron(III) chloride (97%), manganese(II) chlo- and thermometer (0.0008 moles, 5 g), SB was reacted with the
ride ($99%), sodium metal, potassium chloride (99%), sodium
sulphite ($98.0%), diethyl ether ($97.0%), benzene ACS reagent
(>99%), ethanol pure ($99.0%), isopropanol ($99.0%), hydro-
chloric acid reagent (37%) were purchased from Sigma Aldrich Co.
corresponding molar ratio of NiCl2, CoCl2, CuCl2, FeCl3, and
MnCl2 individually. The reaction proceeded in ethanol as
a solvent at 60 ꢁC for 8 h to form the organometallic surfactant
OMS. The purication was carried out by removing the ethanol
carefully at 45–55 ꢁC using a rotary evaporator. Then, the
materials were dissolved in isopropyl alcohol individually, and
then the salting-out by the supersaturated NaCl solution was
carried out. The two layers were separated, and then iso-
propanol was distilled off at 60 ꢁC. The color of the products was
waxy greenish-yellow, green apple, brown, black, and dark
brown, respectively (yield was 83% ꢂ 2).
2.2. Preparation of 5-chloromethyl salicylaldehyde (Salen)
Hydrochloric acid (37%, 150 mL (4.74 mol)), salicylaldehyde
(0.141 mol, 17.22 g), and formaldehyde (37%, 10.8 mL (0.57 mol)) in
the presence of (0.01%) zinc chloride powder as a catalyst were
prepared. All materials were stirred well in a 250 mL three-necked
ask for 24 h. This ask was attached to two necked asks lled
with sodium chloride, equipped with a glass dropping funnel
charged with sulfuric acid to generate fresh HCl gas through
a silicon rubber line. The product was washed by diethyl ether and
distilled water ratio 1 : 1 (v/v), followed by washing with pure ethanol
and dried (yield ¼ 89%, 13.8 g). The product physical appearance is
white powder.9
2.8. Measures of surface tension, ST
The surface tension of the OMS solutions at the interface was
measured at different temperatures using a Biolin Scientic, Theta
Attention tensiometer embedded with a HP/HT chamber in the
formation of water18 (TDS 19917.1 mg Lꢀ1. Salinity 18 090.6 mg Lꢀ1
,
alkalinity 800.3 mg Lꢀ1, density 1.0202 g mLꢀ1 and pH at 25 C,
ꢁ
8.24). The measured value of surface tension of this formation water
as blank was 68 mN mꢀ1 at 303 K. The data was employed to
calculate the various surface–active and thermodynamic parameters
to predict the behavior of the new type of surfactants (OMS) mole-
cules at the interface (air/liquid) and the bulk of formation water.
2.3. Preparation of alkoxide (AP)
A 100 mL round ask charged with (0.003 mol, 18.6 g) of Pluronic
F127 (polyethylene oxide (100)–polypropylene oxide (67)–poly-
ethylene oxide (100)) block copolymer was dissolved in 30 mL
toluene and 30 mL toluene in the presence of sodium metal
(0.006 mol, 0.14 g) under continuous stirring until the complete
disappearance of the sodium metal,16 and the product participated
in the shape of white powder. The solvent was discarded, and then
dried using a vacuum oven at 70 ꢁC (yield ¼ 74%, 12.84 g).
2.9. Measures of interfacial tension, IFT
The IFT measurements were investigated using a Theta Atten-
tion Tensiometer between heavy asphaltenic crude oil and the
OMS solutions at different temperatures at the CMC concen-
tration.19,20 The crude oil specications were (API gravity at 60
ꢁF,ꢁF 18. Asphaltene content 12.78 wt%, wax 1.91 wt% and
2.4. Preparation of potassium 4-aminobenzenesulfonate
4-Aminobenzenesulfonic acid (0.017 mol, 2.9 g) was dissolved density 0.9887 g Lꢀ1). The data of the tensiometer technique.
in an adequate amount of water and (0.017 mol, 0.95 g) potas- The crude oil drop was injected into a capillary tube containing
sium hydroxide 80 ꢁC with stirring for 4 h. The water evapo- the surfactant solution.21 The measured blank value of IFT of
rated, and the remaining potassium 4-aminobenzenesulfonate crude oil against formation water was 26 mN mꢀ1 at 50 ꢁC. The
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Scheme 1 Preparation of sodium 2-(1-(2-(3-formyl-4-hydroxybenzyloxy)ethoxy)propan-2-yloxy)ethanolate.
values of IFT at the CMC and alcohol effect on their efficiency binding (b) is calculated from the slope of conductivity data
ꢀ
ꢁ
should be used in the excluded study of the chemical ooding of
heavy crude oil.
slope postmicell
slope premicell
the degree of concentration dissociation, and (1 ꢀ a) gives
aer and before the CMC values
give (a);
b values.23
2.10. Measures of conductivity
Conductivity for OMS was measured using an auto-temperature
electrical conductivity meter JENWAY-Japan 4510. The solutions
were thermostated at different temperatures in a thermostated
3. Results and discussion
3.1. Structure conrmation of Salen–M(II) complexes
glass vessel controlled by a temperature controller. CMC values The new family of surfactants in the term of organometallic
for an adequate quantity of surfactant were dissolved in water to surfactants was prepared through different steps. The rst step is
change the surfactant concentration.22 The degree of counterion the preparation of 5-chloromethyl salicylaldehyde (Salen, S). The
Scheme
2 Preparation of potassium sodium (E)-4-(2-hydroxy-5-((2-(2-(2-oxidoethoxy)propoxy)ethoxy)methyl)benzeylideneamino)
benzenesulfonate.
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Scheme 3 Preparation of the Bi-AP–Salen sodium 2-(1-(2-(3-formyl-1,4-hydroxyphenoxy)ethoxy)propan-2-yloxy)ethanolate Ni(II) complex
(OMS).
second step is the formation of sodium alkoxide of Pluronic F-127
S.1 shows the 1H-NMR for 5-chloromethyl salicylalde-
(AP). The third step is the formation of the modied AP–Salen (new hyde (CMS) in (DEMSO, TMS): d ppm, 10.21 (a, 1H, –CHO);
ligand). This ligand was reacted with the metal chlorides, as 14.9 (b, 1H, –OH); 7.6 (c, 3H, Ar CH2–CH2); 4.68 (d, 2H,
mentioned earlier, to obtain the organometallic surfactants (OMS) CH2–Cl).
named AP–Salen–M complexes. The reaction steps are shown in
S.2 the 1H-NMR for sodium alkoxide in (DEMSO, TMS),
Schemes 1–3. The chemical structure was justied by 1H-NMR, FT- d ppm: 3.52 (a, 4H, –O–CH2–CH2–O–); 3.68 (b, 4H, –O–CH2–CH2–
IR, SEM, and TEM of modied AP–Salen sodium 2-(1-(2-(3-formyl- O–); 1.2 (c, 3H, CH3).
4-hydroxyphenoxy)ethoxy)propan-2-yloxy)ethanolate.
Fig. 1 the 1H-NMR for modied AP–Salen in (DEMSO, TMS),
d ppm: 1.19 (a, 3H, CH3); 3.37 (b, 4H, –O–CH2–CH2–O–); 4.3 (c,
2H, CH2–O–); 5.28 (d, 1H, –OH); 10.28 (e, 1H, CHO–); 7.58 (g, 3H,
Ar CH2–CH2).
1
3.2. Nuclear magnetic resonance H-NMR
1
1H-NMR conrmed the molecular structure of the target
Fig. 2 the H-NMR for SB in (DEMSO, TMS), d ppm: 8.9 (a,
product.
1H, –CHN); 2.6 (b, 1H, –OH); 3.4 (4H, –O–CH2–CH2–O–); 7.8 (d,
Fig. 1 1H NMR for 2-hydroxy-5-((2-(2-(2-hydroxyethoxy)propoxy)ethoxy)methyl)benzaldehyde (modified AP–Salen).
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Fig. 2 1H NMR for potassium sodium (E)-4-(2-hydroxy-5-((2-(2-(2-oxidoethoxy)propoxy)ethoxy)methyl)benzylideneamino)benzenesulfonate
(SB).
3H, Ar CH2–CH2); 8.9 (e, 2H, CH2–Cl); 5.3 (f, 1H, –OH); 4.51 (d,
2H, CH2–).
3.3. IR spectroscopy
Fig. 4 shows the IR spectrum of the target product. From Fig. 4,
it can be seen that the absorption peaks at 2924 and 2853 cmꢀ1
are caused by the tensile and bending vibrations of –CH2 and
–CH3, respectively, while the absorption peaks at 1618 and
Fig. 3 the 1H-NMR for organo-metallic surfactants OMS
Ni2+ (DEMSO, TMS): d ppm: 6.83 (d, 2H, Ar-H); 7.59 (s, 2H, Ar-
H).10,11
Fig. 3 1H NMR of the Bi-AP–Salen sodium 2-(1-(2-(3-formyl-1,4-hydroxy-phynoxy)ethoxy)propan-2-yloxy)ethanolate Ni(II) complex.
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minimum surface tension value of 29 and 31 mN mꢀ1 was
pronounced at CMC (9.14 ꢃ 10ꢀ3 mol dmꢀ3) for the Ni–OMS
and Cu–OMS, respectively.
The surface tension at CMC for Co–OMS, Fe–OMS, and Mn–
OMS was 32, 33, and 34 mN mꢀ1, respectively, and the CMC was
situated between 37.1 and 18.4 mol dmꢀ3 for them. The
surface–active properties of the OMS aqueous solution are
described in terms of two items: surface effectiveness (pCMC
)
and adsorption efficiency (PC20). These two parameters were
calculated using eqn (1) and (2):
pCMC ¼ go ꢀ gCMC(t)
PC20 ¼ ꢀlog C20
(1)
(2)
Fig. 4 FTIR for the prepared materials (I) Salen, S, (II) sodium alkoxide,
where go is the surface tension of the formation water (blank) 68
mN mꢀ1 and gCMC(t) is the minimum surface tension at the
CMC and different temperatures. The term C20 points to the
concentration of the OMS at which the surface tension is
reduced by 20 mN mꢀ1. The minimum concentration as
adsorption efficiencies (PC20) was reached with the minimum
concentration. The surface pressure or effectiveness was in the
maximum value with Ni–OMS and Cu–OMS (38.4 and 36.4 mN
mꢀ1, respectively).
That means these two surfactants have effectiveness higher
than the other OMS surfactants (Co–OMS, Fe–OMS, and Mn–
OMS). These results show that Ni–OMS and Cu–OMS can
effectively saturate any interface, thereby showing surface
attributes with required exibility and favorably low interfacial
tension.24–26 The surfactant molecules lower the surface tension,
which contribute towards a quantitative investigation showing
the Ni–OMS and Cu–OMS concentration that continuously
adsorbed onto the aqueous solution interface (air/aqueous). So
that, the concentration values less than the CMC can be
completely ignored. From surface tension versus the natural
logarithm of the OMS concentration plots just below the CMC,
the maximum surface excess concentration (Gmax) is calculated
by the Gibbs adsorption equation, (3).
(IV) SB MOS–Co2+
.
1492 cmꢀ1 are caused by the vibrations of the benzene ring
skeleton. The absorption peak at 1256 cmꢀ1 corresponds to the
vibration of the ester group, and the absorption peak near
1184 cmꢀ1 is related to the vibration of the sulfonic acid
group.12
The peak at 1097 cmꢀ1 is attributed to the presence of the
SO– group. The small absorption peaks at 710 and 632 cmꢀ1
correspond to the SO group.32,33
3.4. SEM/EDX investigation
The X-ray diffractograms were carried out using an XPERT X-ray
diffractometer equipped with a silicon detector and X-ray
accelerating voltage 18 kV with a magnication of 1448ꢃ.
Fig. 5(a)–(e) shows the EDX diagram and the K orbital metal
in the OMS surfactants in the solid phase. The metals in the
complex structures were as following; 20.4, 11.92, 10.21, 15.74,
and 3.70 against MOS–Ni2+, MOS–Co2+, MOS–Cu2+, MOS–Fe2+,
and MOS–Mn2+, respectively. The SEM images show the shape
of MOS–Ni2+, MOS–Co2+, MOS–Cu2+, MOS–Fe2+, and MOS–
Mn2+, which look like layers, needles, brain, scales, and leaves,
respectively.
From the SEM/EDX results, it can be concluded that the used
metal was successfully embedded by the chemical reaction to
form the new family of the organo-metallic surfactants OMS.
The H1NMR, FTIR, and SEM/EDX justied the chemical
structure of the new family of surfactants as we expected.
ꢂ
ꢃ
1
dg
Gmax ¼ ꢀ
(3)
nRT dðln CÞ
t
dg
dðln CÞ
where
is the slope of the pre-CMC line in the plots
(Fig. 6). R is the universal gas constant equal (8.314 J Kꢀ1
molꢀ1), T is the temperature in Kelvin and g is the surface
tension value, mN mꢀ1 27,28 The Gibbs adsorption coefficient (n)
.
is a function of the number of constituent species that are
adsorbed at the interface and is taken as two values for the
anionic surfactant system.29
3.5. Gibbs adsorption isotherm and thermodynamic
properties of the OMS
2
˚
The minimum area Amin occupied per surfactant molecule A
The g–ln C adsorption isotherm of the OMS solutions at
different temperatures is plotted in Fig. 6. By increasing the
concentration of the surfactant, the surface tension decreases
until the change is a constant, and this point indicates the
critical micelle concentration (CMC). At higher concentrations
than the critical change, the aqueous/air interface becomes
completely saturated with monolayers named as Gibbs
adsorption monolayers. This layer is promoting the formation
of spherical micelles in the bulk of the solution phase. The
per molecule at the air/aqueous interface is the inverse
proportion with +ve values (Gmax), as shown in the following
equation:
1016
Amin
¼
:
(4)
N ꢃ Gmax
wherein N is the Avogadro's number, and Gmax is the maximum
surface excess concentration (mol mꢀ2).30 The Gmax values of Ni–
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Fig. 5 The SEM and EDX of the OMS for (a) Co2+, (b) Mn2+, (c) Ni2+, (d) Cu2+ and (e) Fe3+
.
OMS and Cu–OMS were found to be 74.23 ꢃ 10ꢀ10 and 57.56 ꢃ benecial to microemulsions, resulting in lower interfacial tension
10ꢀ10 mol dmꢀ3, respectively. The values of the minimum area and improved oil attraction capacity.31,32
2
˚
occupied by the surfactant molecule were 2.24 A per molecule for
The electric conductivity was measured at different concen-
2
˚
Ni–OMS and 1.87 A per molecule for Co–OMS, which are very trations and temperatures to determine two terms. The rst
close to each other. The low value of Amin shows the improved oil- term is the determination of CMC for the OMS as an ionic
displacing capacity per surfactant molecule. The property is molecule (Fig. 6). The second term is the calculation of the ionic
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Fig. 6 g–ln C isotherm for the OMS, (a) at 20 ꢁC, (b) at 35 ꢁC, (c) at 50 ꢁC.
molecule mole fraction (a) of the counterion to determine the ions of Na+ and K+ associated with the micelles and is a signicant
degree of binding (b) of the ionic surfactant molecule. The factor in calculating the free energy of the micellization of the ionic
values of (b) are listed in Table 2. The degree of counter ion surfactant solution. The (b) values for OMS decrease with the
binding (b) of OMS is calculated from the ratio of the slopes of increase in temperature. As seen in Table 2, with the increase in
the two linear lines of the conductivity plot (Fig. 7). The (b) value temperature, the electrostatic repulsion of counter ion decreases;
of the aqueous solution indicates the negatively charged counter this maybe lead to an increase in the thermodynamic stability of
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Table 1 Surface active properties and thermodynamic parameters for OMS at different temperatures
Temp., CMC, mol
PC20, mol
dmꢀ3
gCMC, mN
pCMC, mN
Gmax ꢃ
10ꢀ10
Amin
ꢃ
ID
M. wt ꢁC
dmꢀ3
mꢀ1
mꢀ1
102
DGmic, kJ molꢀ1 DGads, kJ molꢀ1
OMS–Ni 6458.7 20
OMS–Co 6458.9
OMS–Cu 6463.5
OMS–Fe 6455.8
9.14 ꢃ 10ꢀ3
18.4 ꢃ 10ꢀ3
9.14 ꢃ 10ꢀ3
37.1 ꢃ 10ꢀ3
37.1 ꢃ 10ꢀ3
4.03
3.73
4.03
3.43
3.43
29
32
31
33
34
38.4
35.4
36.4
34.4
33.4
74.23
88.92
57.56
57.96
77.80
2.24
1.87
2.89
2.87
2.13
ꢀ22.65
ꢀ20.94
ꢀ22.65
ꢀ19.24
ꢀ19.24
ꢀ27.83
ꢀ24.93
ꢀ28.98
ꢀ25.18
ꢀ23.54
OMS–
Mn
6454.9
SB
6391
45.3 ꢃ 10ꢀ3
4.59 ꢃ 10ꢀ3
9.14 ꢃ 10ꢀ3
4.59 ꢃ 10ꢀ3
18.4 ꢃ 10ꢀ3
18.4 ꢃ 10ꢀ3
3.34
4.33
4.03
4.33
3.73
3.73
35.7
25
29
27
30
31.7
42.4
38.4
40.4
37.4
35.4
64.31
64.31
65.90
46.84
52.80
52.40
2.58
2.58
2.52
3.55
3.15
3.17
ꢀ18.76
ꢀ25.58
ꢀ23.81
ꢀ25.58
ꢀ22.02
ꢀ22.02
ꢀ23.70
ꢀ25.58
ꢀ23.82
ꢀ25.58
ꢀ22.02
ꢀ22.02
OMS–Ni 6858.7 35
OMS–Co 6858.9
OMS–Cu 6863.5
OMS–Fe 6855.8
OMS–
Mn
6854.9
32
SB
6800
45.3 ꢃ 10ꢀ3
2.30 ꢃ 10ꢀ3
4.59 ꢃ 10ꢀ3
2.28 ꢃ 10ꢀ3
18.4 ꢃ 10ꢀ3
18.4 ꢃ 10ꢀ3
3.34
4.63
4.33
4.64
3.73
3.73
33.2
21.5
25
23.6
27
34.2
45.9
42.4
43.8
40.4
37.8
77.41
46.84
65.90
44.86
49.62
49.22
2.15
3.55
2.52
3.70
3.35
3.37
ꢀ19.72
ꢀ29.12
ꢀ27.24
ꢀ29.15
ꢀ23.45
ꢀ23.45
ꢀ19.72
ꢀ38.92
ꢀ33.68
ꢀ38.91
ꢀ31.59
ꢀ31.13
OMS–Ni 6858.7 50
OMS–Co 6858.9
OMS–Cu 6863.5
OMS–Fe 6855.8
OMS–
Mn
6854.9
29.6
SB
6800
21.6 ꢃ 10ꢀ3
3.66
30
37.4
44.06
3.77
ꢀ23.02
ꢀ31.50
micelle formation—further ease in enhancing the thermodynamic the two processes, micellization and adsorption, are sponta-
stability of microemulsion. In the anionic moiety of OMS, the neous. However, DGads was observed to be more negative in
micelle formation occurs by a combined effect of the electrostatic comparison to DGmic. The net results show that the adsorption is
repulsive interactions between the polar head groups that prevent more favorable to the OMS molecules than the micellization
the formation of the large micelles and the attractive hydrophobic process. The negative values of DGmic increase with temperature,
forces between the hydrocarbon tail chains aiding in aggregation. showing that the tendency of surfactant molecules to form
Hence, the micellization is necessarily an association–dissociation micelles improved due to a reduction in surfactant CMC by
process that allows the coexistence of micelles and surfactant temperature (Table 1). As a result of the CMC decrease with the
molecules. The Gibbs free energy change of micellization (DGmic
)
increase in temperature in the experimental range, the tendency of
for the OMS surfactant solution with the multivalent cations is OMS molecules to aggregate is evident at a lower concentration in
calculated using the following equation.33
the aqueous solution. The more negative value of DGads increases
due to an increase in the curvature of the air-aqueous surface. This
means that the number of available vacancy sites for adsorption is
increased, and more OMS molecules should be adsorbed at the
interface with temperature elevation. The surfactant enhances
microemulsion at the CMC concentration. The results of DGmic
and DGads are ꢀve values, and then OMS molecules formed
a stable microemulsion phase and also exhibited effective inter-
facial interactions with the surrounding media. The inspection of
DGmic ¼ (1 + b)RT ln CMC
(5)
The values of DGmic, as are seen in Table 1, are negative for
all OMS surfactants at different temperatures. The b value is
a measure of the counterions present in the stern layers, which
counterbalance the electrostatic forces of repulsion among
polar head groups.34–36 As temperature increases, the value of
b increased showing an increased tendency to micellization in
the bulk phase. As a result, DGmic was observed to increase on
the negative side with a temperature rise, showing increased
micellization spontaneity. That means that the OMS molecule is
just added to the aqueous phase, and the surfactant molecules
initially adsorb at the interface. The Gibbs free energy of
adsorption (DGads) is determined using the following equation:
Table 2 Measurements of b conductivity mS for OMS at different
temperatures ꢁC
b conductivity, mS
ID
20 ꢁC
35 ꢁ
C
50 ꢁ
C
MOS–Ni2+
MOS–Co2+
MOS–Cu2+
MOS–Fe3+
MOS–Mn2+
SB
1.36
1.65
1.90
2.14
2.26
2.55
2.47
2.59
2.86
3.01
3.12
3.38
2.89
3.05
3.18
3.42
3.78
3.90
DGads ¼ DGmic ꢀ [6.023pCMCAmin] ꢃ 10ꢀ3
.
(6)
The negative values of DGads show the tendency of the
adsorption of the OMS molecules at the interface. By investi-
gation of the thermodynamics parameters of OMS molecules,37
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Fig. 7 Conductivity, mS ꢃ 103 and concentration, ꢀln C at 50 ꢁC.
Table 3 IFT in formation water for the OMS against heavy crude oil
3.6. Interfacial tension, IFT
IFT, mN mꢀ1 at different temp., ꢁ
C
The interfacial tension is a crucial term to evaluate the effec-
tiveness of the surfactant molecules to benecial in the appli-
cation to enhance oil recovery (EOR).39–42 The lower IFT values of
IFT mean there is more remarkable ability to solubilize the oil,
furthermore enhancing the microemulsion phase.43 The
microemulsion is effectively displacing the oil trapped in the
pore throats of the reservoir. The IFT was measured for the OMS
in the formation of water at CMC and (20 to 70 ꢁC) against heavy
crude oil. The results of the IFT are listed in Table 3. The data
showed that the IFT values decreased with the increase in
temperature, and they are situated between 10ꢀ1 and 10ꢀ2 mN
mꢀ1. These results are considered suitable for using these
surfactants in the EOR applications. The OMS–Ni and OMS–Cu
pronounced the minimum value of IFT to 10ꢀ2 mN mꢀ1 at 50
and 70 ꢁC. OMS–Co, OMS–Fe, and OMS–Mn exhibited IFT in the
Surfactant
20
35
50
70
Blank sample
OMS–Ni
OMS–Co
OMS–Cu
OMS–Fe
28
26
25
23
4 ꢃ 10ꢀ1
8 ꢃ 10ꢀ1
4 ꢃ 10ꢀ1
9 ꢃ 10ꢀ1
8 ꢃ 10ꢀ1
2 ꢃ 10ꢀ1
5 ꢃ 10ꢀ1
1 ꢃ 10ꢀ1
7 ꢃ 10ꢀ1
6 ꢃ 10ꢀ1
7 ꢃ 10ꢀ2
4 ꢃ 10ꢀ1
6 ꢃ 10ꢀ2
5 ꢃ 10ꢀ1
4 ꢃ 10ꢀ1
2 ꢃ 10ꢀ2
2 ꢃ 10ꢀ1
1 ꢃ 10ꢀ2
3 ꢃ 10ꢀ1
2 ꢃ 10ꢀ1
OMS–Mn
the aggregation and adsorption properties of surfactant systems
contributes towards the proper formulation of the surfactant in
different systems and applications, such as in oil solubilization
and displacement processes.38 OMS could be used to give signi-
cant potential in the eld of enhanced oil recovery (EOR).
order 10ꢀ1 mN mꢀ1 and so on at 70 C.
ꢁ
As shown in Fig. 8 and Table 3, the IFT decreased slightly by
increasing the temperature.
Fig. 8 g IFT, mN mꢀ1 at different temperatures, T ꢁC.
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These results were obtained due to the temperature increase,
which increases the free energy of surfactant molecules in the
solvent and helps to push them to adsorb on the interface.44 The
increase in the surfactant molecule on the interface increases the
ability of the surfactant to solubilize the oil phase to form micro-
emulsion; further, the production of oil should be increased.
Acknowledgements
The authors would like to thank EPRI-EOR unit, which was
established according to The Joint-Granted Project and collab-
oration contract no. 56/2015 between the Academy of Scientic
Research and Technology (ASRT) and the Egyptian Petroleum
Research Institute (EPRI).
3.7. Particle size characteristics [dynamic light scattering
(DLS)]
References
DLS is a light scattering technique where a laser is shown
through the aggregation of micelles, which causes the laser light
to scatter (Rayleigh scattering). Because the micelles moving
under Brownian motion, uctuations in the scattering were
measured at specic time intervals, which are then connected to
an autocorrelation function. A diffusion coefficient is then
determined using the Mie theory (based on this autocorrelation
function and the refractive index of the sample), followed by the
micelle size using the Stokes–Einstein equation. Immediately, at
CMC, the micelles were sized using the dynamic light scattering
(DLS) technique. DLS is a well-established and widely used
method for determining the size and polydispersity of micelles
aggregation within a sample. From the data of DLS, the micelle
size and zeta-potential of MOS aggregation are listed as: MOS–
Ni2+ (88.79 nm and 7.36 mV), MOS–Co2+ (81.43 nm and 7.93 mV),
MOS–Cu2+ (35.33 nm and 18.2 mV), MOS–Fe3+ (70.56 nm and
11.1 mV), MOS–Mn2+ (15.54 nm and 8.22 mV). It was found that
the size of the micelle of these families of surfactants is between
15.54 and 88.79 nm, whereas the results of zeta-potential (7.36
and 18.2 mV) are for all MOS–M complexes.
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points:
(1) A new family of surfactants based on Salen–M complexes
named MOS–Ni2+, MOS–Co2+, MOS–Cu2+, MOS–Fe3+, and MOS–
1
Mn2+ were prepared. H NMR, FTIR, and SEM conrmed the
chemical structure of these surfactants.
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Conflicts of interest
There are no conicts to declare.
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