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Effect of aromatic spacer groups and counterions on aqueous micellar and thermal properties of the synthesized quaternary ammonium gemini surfactants
Journal of Molecular Liquids 296 (2019) 111837
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Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq
Effect of aromatic spacer groups and counterions on aqueous micellar and thermal properties of the synthesized quaternary ammonium gemini surfactants S.M. Shakil Hussain a, Muhammad Shahzad Kamal a, *, Mobeen Murtaza b a b
Center for Integrative Petroleum Research, King Fahd University of Petroleum & Minerals, Dhahran, 31261, Saudi Arabia College of Petroleum Engineering, King Fahd University of Petroleum & Minerals, Dhahran, 31261, Saudi Arabia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 9 September 2019 Received in revised form 22 September 2019 Accepted 26 September 2019 Available online 9 October 2019
One of the major challenges for the oil industry in the 21st century is to get the desired surfactants that are soluble in high saline water (220, 000 ppm) and stable at high temperature (100 C). Most commercial surfactants suffering due to hydrolysis at high temperature and the monovalent and divalent reservoir ions leads to surfactant precipitation. In order to address these issues, a new series of cationic gemini surfactants with a different number of aromatic rings in the spacer group as well as different counter ions were synthesized and characterized with the aid of MALDI-TOF MS, FTIR, 1H NMR, and 13C NMR spectroscopy. The effect of number of phenyl aromatic rings in the spacer and counterions on thermal and surface properties was determined. Thermogravimetric results showed the decomposition temperature of all the gemini surfactant near to 300 C which is larger than the existing oilfield temperature (100 C). The insertion of ethoxy units between the lipophilic tail and lipophobic headgroup resulted in good solubility of cationic gemini surfactants in high saline and normal water without cloudiness or precipitation. The critical micelle concentration and the corresponding surface tension were lower for gemini surfactants containing bromide counterions compared to the surfactants containing chloride counterions. The gemini surfactants containing two aromatic phenyl rings in the spacer have lower critical micelle concentration compared to the gemini surfactants with one phenyl ring. The properties of the synthesized cationic gemini surfactants mark them a material of choice for high salinity/temperature reservoirs. © 2019 Elsevier B.V. All rights reserved.
Keywords: Oilfield Quaternary ammonium Gemini Aqueous Thermal stability
1. Introduction Surfactants (surface active agents) are continuously developing for multiple oilfield applications including stimulation, fracturing, wettability alteration, and enhanced oil recovery [1e4]. Surfactants tend to lower the miscibility gap between aqueous and crude oil until a microemulsion is generated to produce an ultralow (103 mN/m) interfacial tension (IFT). Moreover, surfactants also perform as an emulsifier, demulsifiers, wettability modifier, foaming agent, and dispersant agent [5e11]. Gemini surfactants are the unique class of surfactants having two hydrophobic tail and two hydrophilic heads covalently attached through spacer group [12]. Gemini surfactants exhibit distinct properties compared to conventional single tail and single
* Corresponding author. E-mail address: [email protected] (M.S. Kamal). https://doi.org/10.1016/j.molliq.2019.111837 0167-7322/© 2019 Elsevier B.V. All rights reserved.
head material. These properties include low critical micelle concentration (CMC), heat resistant, salt resistance, excellent aqueous solubility, and ultra-low interfacial tension (IFT). Ammonium-based cationic gemini surfactants are successfully applying in multiple oilfield applications [13]. Abo-Riya and coworkers reported the synthesis of 1,2-ethane bis (dimethyl 2(octadecyloxy)-2- oxoethyl ammonium chloride with different hydrophobic tail length and claimed that such kind of cationic gemini surfactants may apply as a petroleum-collecting and dispersing agents [14]. Mao and co-workers studied the effect of counterions on the properties of cationic gemini surfactants as a clean fracturing fluid and emphasized that the viscosity reduction was due to micelle dissociation [15]. Migahed et al. reported the synthesis of 2,2’-(1-aminopropane-1,3-diyl)bis(1-(2-aminoethyl)1-dodecyl-4,5-dihydro-1 H-imidazol-1-ium)dichloride as corrosion inhibitor for X-65 steel dissolution for formation water in deep oil wells and concluded that inhibition efficiency increased with concentration [16].
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The careful selection of each group in the structure of gemini surfactant plays a vital role to obtain desired properties. For instance, surfactants with long hydrophobic tail exhibit high heat stability and lower CMC [17]. However, increasing the length of the hydrophobic tail reduces aqueous solubility of surfactant [18]. The aqueous solubility of the surfactant with a long hydrophobic tail can be achieved by adding ethoxy units (EO) which enhances the surfactants water solubility through hydrogen bonding with water molecules. The presence of amide group [NHC]O] in the gemini surfactant show multiple advantages compared to the gemini surfactant without the amide group. For example, the CMC of the cationic gemini surfactant without the amide group reached from 0.82 mM to 0.18 mM. On the other hand, the CMC of the related cationic gemini surfactant with an amide group reached from 0.19 mM to 0.08 mM. The low CMC of the gemini surfactants containing amide group may attribute to the formation of hydrogen bonding which facilitates the formation of micelles at low CMC [19,20]. The spacer group perhaps the most critical part that identifies the fundamental properties of the gemini surfactants [21]. Within the different kinds of spacer group (rigid, flexible, hydrophilic, hydrophobic, short, long), the surfactant with an aromatic group is the material of choice due to better surface properties associated with the p-p stacking for phenyl spacers. Moreover, the surfactants with aromatic groups are known to attract more aromatics in the reservoir such as asphaltene etc. In this article, we report the synthesis and structure elucidation of amide-based cationic gemini surfactants (12-PhBr-12, 12-PhCl12, 12-BiPhBr-12, and 12-BiPhCl-12) containing mono phenyl and biphenyl rings as an aromatic spacer group with different counterions. The counterions play a significant role in determining thermal and surface/interface properties [22]. The chemical structures were confirmed with the aid of spectroscopic tools including MALDI-TOF-MS, FTIR, 1H and 13C NMR spectra. The effect of number aromatic rings (mono phenyl vs biphenyl) and counterions (Br vs Cl) was identified by means of thermal gravimetric analysis (TGA), aqueous solubility, CMC, surface tension at CMC (gcmc), maximum surface access (гmax), and occupied surface area at the interface of air-water (Amin). The chemical structures were carefully designed and synthesized according to the harsh reservoir conditions. For example, the cationic gemini surfactants were chosen due to their low adsorption on to the carbonate rocks associated with the charge repulsion [23]. A specific number of EO groups were incorporated among lipophilic tail and lipophobic headgroup to achieve better solubility in formation brine (FW), seawater (SW), and deionized water (DW). The amide group was selected because of the excellent thermal and surface properties. 2. Materials and synthesis
MALDI-TOF MS spectra were noted on Bruker SolariX XR instrument in a matrix of Dithranol in dichloromethane. 1H and 13C/NMR readings were obtained on Jeol 1500 spectrometer. The FT-IR studies were conducted on a 16F PerkinElmer FT-IR spectrometer. 2.2. Solubility test Gemini surfactants (12-PhBr-12, 12-PhCl-12, 12-BiPhBr-12, and 12-BiPhCl-12) (15 wt% each) were solubilized in DW, SW, FW, and solubility was noticed with elapse of time. 2.3. Thermal gravimetric analysis (TGA) TA instrument (SDT Q600) was utilized for the TGA experiments. The measurements were conducted with heating at 20 C/min in the presence of nitrogen (100 mL/min). The temperature interval was ranged from 30 C to 500 C. 2.4. Surface tension Surface tensions measurements of (12-PhBr-12, 12-PhCl-12, 12BiPhBr-12, and 12-BiPhCl-12) were conducted on force tensiometer using Wilhelmy plate method. Measurements were done at 60 ± 0.1 C and 30 ± 0.1 C. Before each run, the Wilhelmy plate was rinsed with DW followed by blue flame heating. DW surface tension was also recorded for reference. 2.5. Synthesis 2.5.1. Synthesis of 12-PhBr-12 Synthesis of 12-PhBr-12 is outlined in Scheme 1. The acid (6) (25 g, 36.23 mmol) was reacted with amine (5) (7.40 g, 72.46 103 mol) in a 250 mL RB flask at elevated temperature (160 C) up to 6 h. Sodium fluoride (NaF) (0.15 g, 3.62 mmol) was poured into the reaction mixture to catalyze the experiment. After 6 h, more amine (5) (5.55 g, 54.35 103 mol) was poured into the reaction flask to achieve complete conversion of acid (6) to amide (4) and the experiment was continued for further 4 h (see Fig. 1). Finally, the remaining amine (5) and NaF were extracted to acquire 4 [24]. The compound 4 (20.0 g, 25.84 103 mol) was then further reacted with a,a0 -dibromo-p-xylene (2.73 g, 10.34 103 mol) in absolute EtOH (10 mL) for 50 h at 80 C [25]. Eventually, the reaction mixture was subjected to column chromatography with ethanol (EtOH) mobile phase to acquire 12-PhBr-12 in the shape of viscous oil. 12-PhCl-12, 12-BiPhBr-12, and 12-BiPhCl-12 were synthesized according to same procedure by treating intermediate 4 with a,a0 dichloro-p-xylene, 4,40 -bis(bromomethyl)biphenyl, and 4,40 -bis(chloromethyl)-1,10 -biphenyl, respectively.
2.1. Materials 3. Results and discussion
a,a0 -dibromo-p-xylene, (97%), a,a0 -dichloro-p-xylene (98%), 4,40 -bis(bromomethyl)biphenyl (98%), 4,40 -bis(chloromethyl)-1,10 biphenyl (98%), aluminum oxide (99.99%), glycolic acid ethoxylate lauryl ether (average Mn ~690), NaF (99%), 3-(dimethylamino)-1propylamine (99%), were obtained from Sigma Aldrich. Simulated FW and SW were prepared using salts including MgCl2, CaCl2, Na2SO4, NaHCO3, and NaCl. The salts were purchased from Panreac company and the amount of each salt in the solution is depicted in Table 1. 2.1.1. Elucidation of surfactants structure The chemical structures of the synthesized cationic gemini surfactants (12-PhBr-12, 12-PhCl-12, 12-BiPhBr-12, and 12BiPhCl-12) were elucidated with the aid of spectroscopic tools including MALDI-TOF-MS, FTIR, and 13C/1H NMR instruments. The
Four quaternary ammonium gemini surfactants (12-PhBr-12, 12-PhCl-12, 12-BiPhBr-12, and 12-BiPhCl-12) containing mono and biphenyl rings with different counterions (Br and Cl) were synthesized by treating amine (5) with acid (6) in the presence of the catalytic amount of sodium NaF. In second step, the amide (4) was charged individually with a,a0 -dibromo-p-xylene, a,a0 dichloro-p-xylene, 4,40 -bis(bromomethyl)-1,10 -biphenyl, and 4,40 bis(chloromethyl)-1,10 -biphenyl to obtain 12-PhBr-12, 12-PhCl-12, 12-BiPhBr-12, and 12-BiPhCl-12, respectively (Scheme 1, Fig. 2). 3.1. Structure identification The structure identification is represented for 12-PhBr-12. According to 1H NMR of 12-PhBr-12 (Table 1, Fig. 2), the
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Table 1 1 H NMR data and peak assignment of gemini amphiphiles [15,22,31,32]. Gemini amphiphiles
1
H NMR data (500 MHz, CDCl3, d in ppm)
Hydrophobic Tail
12-PhBr-12 12-PhCl-12 12-BiPhBr-12 12-BiPhCl-12
Ethoxy groups
Amide
Amido-amine
Spacer protons
CH3 (a)
CH2 (b)
CH2 (c)
CH2 (d, j)
(CH2)2 (e)
CH2 (f)
NH (g)
CH2 (h) CH3 (k)
CH2 (i)
CH2 (m)
CH (n)
CH (o)
0.88 0.88 0.88 0.88
1.25 1.26 1.26 1.25
1.57 1.57 1.57 1.57
3.44 3.44 3.44 3.44
3.64 3.64 3.64 3.64
4.02 4.01 4.05 4.03
7.97 8.03 7.90 8.00
3.15 3.13 3.21 3.18
1.72 1.72 1.74 1.73
3.98 3.99 3.99 3.99
7.70 7.70 7.67 7.64
7.36 7.36
Scheme 1. Synthetic scheme of cationic gemini surfactants.
Fig. 1. 1H NMR of intermediate compound (4).
characteristics peaks at d 0.88 ppm and d 1.26 ppm relate to CH3 and CH2 moieties in the lipophilic tail of surfactant [26]. The sharp peaks at d 3.16 ppm correspond to the methyl moieties linked hydrophilic headgroup [-(CH3)2eNeCH2eC6H4eCH2eN-(CH3)2-]. The strong peak at d 3.64 ppm corresponds to the ethoxy groups [-CH2CH2-O-CH2-CH2-O-] [27]. The peak at d 4.02 ppm was associated with the methylene moiety (CH2) connected with carbonyl carbon [-O-CH2-C]OeNH-]. The protons of aromatic benzene ring were coupled with the signals detected at d 7.70 ppm. The singlet peak at d 7.97 ppm may be attributed to amide proton [-OeCH2eC]OeNH] [28e30].
According to 13C NMR of 12-PhBr-12 (Table 2, Fig. 3), the sharp signals at d 14.1 ppm and d 22.6e31.7 ppm linked with CH3 and CH2 moieties presented in the surfactant tail. Methyl (CH3) moieties linked with the hydrophilic headgroup [-(CH3)2eNeCH2eC6H4eCH2eN-(CH3)2-] were confirmed with the peak at d 49.9 ppm. Moreover, two characteristics peaks at d 62.2 ppm and d 66.6 ppm could be linked with the methylene (CH2) groups joined with the hydrophilic headgroup [-CH2Ne(CH3)2eCH2eC6H4eCH2-(CH3)2eNeCH2-] [33]. The strong peak at d 70.4 ppm may be attributed to ethoxy groups [-CH2-CH2-OCH2-CH2-O-]. The peak detected at d 171.1 ppm may be referred to
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characteristics bands at 1544/cm and 1652/cm related with amide I carbonyl and amide II carbonyl group [28]. The peak at 1347/cm and 1463/cm may refer to bending vibration of CH3 and CH2 groups, respectively. Strong signals were detected at 1097/cm that could be coupled with ethoxy moieties [35,36]. The MALDI-TOF MS data of 12-PhBr-12 (Fig. 5) exhibited the highest peak at 680.5 that could be reorganized as a homolytic cleavage of the bond between terminal carbon of spacer and ammonium headgroup. This type of homolytic bond-breaking generate radical cation and showed that the major component of 12-PhBr-12 having 8 ethoxy units and 12 carbons in the surfactant tail.
Fig. 2. 1H NMR of 12-PhBr-12.
3.2. Heat stability
Table 2 13 C NMR data showing the values of chemical shift in gemini amphiphiles. Gemini amphiphiles
13
12-PhBr-12 12-PhCl-12 12-BiPhBr-12 12-BiPhCl-12
14.0, 13.9, 13.9, 14.0,
C NMR (CDCl3, d, 125 MHz) 22.5, 22.5, 22.5, 22.6,
25.9, 25.9, 25.9, 25.0,
29.2, 29.2, 29.2, 29.2,
29.3, 29.3, 29.3, 29.4,
29.4, 29.4, 29.4, 29.5,
31.7, 31.7, 31.7, 31.8,
35.7, 35.8, 35.8, 35.7,
49.9, 49.8, 49.4, 49.4,
62.1, 62.1, 62.1, 62.2,
66.6, 66.6, 66.6, 66.9,
70.4, 70.4, 70.4, 70.4,
129.6, 129.7, 126.9, 127.1,
133.8, 133.8, 127.2, 127.3,
171.0 170.9 133.8, 141.1, 170.8 133.9, 141.2, 170.9
Fig. 3. 13C NMR of 12-PhBr-12.
the carbonyl of amide [-C]OeNH-]. According to FTIR results of 12-PhBr-12 (Table 3, Fig. 4), the signals at 3414 cm1 could be coupled with the stretching vibration of the NeH group [34]. Signals at 2854/cm and 2924/cm related with CH2 symmetrical and CH2 asymmetrical bands. Two
The temperature of the carbonate reservoirs reaches up to 100 C, therefore, the applied surfactant must be thermally stable. We studied the thermal stability of the synthesized surfactants (12PhBr-12, 12-PhCl-12, 12-BiPhBr-12, and 12-BiPhCl-12) with the aid of TGA. Fig. 6 showed the TGA thermogram of four gemini
Table 3 FTIR results of the gemini amphiphiles. Gemini amphiphiles
FTIR data (in cm1) (yN-H)
yC-H asym.
yC-H sym.
amide (I)
amide (II)
CH2 (bend)
CH3 (bend)
ethoxy stretch
asym. Stretch
12-PhBr-12 12-PhCl-12 12-BiPhBr-12 12-BiPhCl-12
3414 3413 3415 3414
2924 2924 2923 2925
2854 2850 2851 2855
1652 1651 1653 1654
1544 1542 1541 1543
1465 1466 1464 1465
1348 1349 1347 1350
1097 1098 1097 1099
947 946 945 946
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Fig. 4. FTIR spectrum of 12-PhBr-12. Fig. 6. Thermal degradation curves of gemini amphiphiles determined by TGA.
amphiphiles under nitrogen. All four surfactants showed an initial loss in the range of 5%e10% because of residual water and impurities. A big and sharp loss for all the gemini amphiphiles was detected near to 300 C, exhibiting the degrading effect of heat on the structure of 12-PhBr-12, 12-PhCl-12, 12-BiPhBr-12, and 12BiPhCl-12. The effect of counterion on thermal stability was evaluated for surfactants containing mono phenyl aromatic ring and biphenyl aromatic rings. For instance, 12-PhBr-12 and 12-PhCl-12 have same ethoxy units, same tail length, same spacer, and same hydrophilic headgroup. Therefore, the counterion is the only factor responsible for any change in thermal behavior. The thermal stability of the surfactant with bromide counterion was slightly better than the surfactant with chloride counterion (12-PhCl-12 ˂ 12PhBr-12 and 12-BiPhCl-12 ˂ 12-BiPhBr-12). Similarly, the surfactant-containing biphenyl spacer group exhibited better thermal stability compared to the surfactant with mono phenyl spacer with same counterion (12-PhBr-12 ˂ 12-BiPhBr-12 and 12PhCl-12 ˂ 12-BiPhCl-12) [37]. In general, the counterion and number of aromatic rings do effect the thermal stabilities of the gemini amphiphiles and, overall, all four surfactants degraded near
to 300 C, which is greater than the existing reservoir temperature (100 C).
3.3. Solubility Surfactant solubility in normal and high saline water is the prerequisite for its oilfield application. The divalent and monovalent ions available in the injected water (SW) and reservoir brine (FW) leads to surfactant precipitation. The insertion of EO units increases the aqueous solubility of the surfactants. Such a phenomenon can be explained in terms of hydrogen bonding. The hydrogen of water creates hydrogen bonding with the oxygen of the EO group which ultimately increase solubility. We investigated the solubility of the synthesized cationic gemini surfactants by dissolving them in DW, SW, and FW. The amount of different monovalent and divalent ions is depicted in Table 4. All four cationic gemini surfactants revealed excellent solubility and no phase separation, precipitation, or cloudiness was observed (Fig. 7).
Fig. 5. MALDI-TOF MS of 12-PhBr-12.
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Table 4 The amount of different monovalent and divalent ions in simulated FW and SW. Ions
FW (g/L)
SW (g/L)
Sodium(1þ) ion Calcium (2þ) ion Magnesium (2þ) ion Sulfate (2-) ion Chloride (1-)ion Bicarbonate (1-) ion Total
59.5 19.1 2.5 0.4 132.1 0.4 214
18.3 0.7 2.1 4.3 32.2 0.1 57.7
surface tension reduces with the rise in temperature. Other surface properties such as CMC, surface tension corresponding to CMC (gcmc), maximum surface access (гmax) and minimum area per molecule at air-water interface (Amin) were estimated from the surface tension data. The following equations were used to calculate the surface properties [38]:
гmax ¼
1 nRT
dg dlnC
(1) T
Fig. 7. Snapshot of gemini amphiphiles solutions in SW and FW.
3.4. Surface properties
. Amin ¼ 1018 NA гmax
(2)
The effect of counterions (Cl and Br ) and a number of aromatic phenyl rings on the surface tension of gemini surfactant solutions was measured at two different conditions of temperatures (30 C & 60 C). The surface tension data of the synthesized gemini surfactants at two different temperatures is shown in Fig. 8 to Fig. 9. Other surface properties are also given in Table 5. The surface tension decreases with increasing concentration of surfactant until the critical micelle concentration is reached. There is an insignificant variation in the surface tension upon extra addition of the surfactant beyond CMC. For all discussed gemini surfactants, the
Here dg/dlnC is the slope below CMC in surface tension plot, R represents the gas constant, C is the concentration of the surfactant, T is the temperature, NA Avogadro’s number and n was taken as 3 for the gemini surfactant. The data given in Table 5 provides significant fundamental information about the effect of counterions, the number of phenyl rings, and temperature on the surface properties. For all surfactants, the CMC decreased by increasing the temperature. The reduction in the CMC with temperature is associated with the decrease in the hydration of the hydrophilic group.
Fig. 8. Surface tension of 12-PhBr-12 and 12-PhCl-12 at various temperatures.
Fig. 9. Surface tension of 12-BiPhBr-12 and 12-BiPhCl-12 at various temperatures.
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Table 5 Surface properties of GS with various counterions at various temperatures. Surfactant
Solvent
T ( C)
CMC (mmol L1)
gcmc (mN m1)
гmax x 107 (mol m2)
Amin (nm2)
12-PhCl-12 12-PhCl-12 12-PhBr-12 12-PhBr-12 12-BiPhCl-12 12-BiPhCl-12 12-BiPhBr-12 12-BiPhBr-12
DW DW DW DW DW DW DW DW
30 60 30 60 30 60 30 60
0.0214 0.00851 0.0153 0.00846 0.0138 0.00674 0.00887 0.00647
38.9 38.1 37.29 35.63 37.71 35.08 36.258 33.405
7.73 7.51 6.63 6.48 7.30 6.69 7.12 6.96
2.14 2.21 2.50 2.56 2.27 2.48 2.331 2.387
The resulted decreases in hydration at the high temperature promotes micelle formation and reduction in CMC. The critical micelle concentration depends on the interactions among the surfactant molecules in the bulk phase. In most cases, the critical micelle concentration can be reflected by the adsorption of surfactants at the interface. The internal or external changes in conditions that lead towards more closer packing of the surfactant at interface results in a reduction in the surface tension and CMC. A clear trend was observed for all surfactants at both temperatures when the counterion was changed from bromide to chloride. The CMC of the surfactants having bromide as a counterion was low compared to the CMC of the corresponding surfactants having chloride counterions. This behavior was consistent for surfactants with one aromatic phenyl ring and two aromatic phenyl rings as well. The number of phenyl rings in the spacer also affect the CMC of the surfactants. The behavior was also consistent for both types of counterions and at both temperatures. The CMC of surfactants decreased when the number of aromatic rings increased from 1 to 2. Adding two aromatic phenyl rings decreased the CMC due to more conjugation, p-p stacking, and increased hydrophobicity. Among all surfactants, the lowest CMC was observed for 12BiPhBr-12 at 60 C. The gcmc values also decreased by increasing temperature. In addition, surfactants with bromide counterions have lower gcmc compared to the surfactants with chloride counterions. The surfactants containing two aromatic rings also showed lower gcmc values compared to the surfactants with a single aromatic phenyl ring. Maximum surface access decreases with temperature while the area per molecule increases with temperature. The synthesized gemini surfactants showed excellent surface properties that can make them cost-effective in real field applications. The CMC of similar type of surfactants have been reported between 8.0 10 3 mol/L to 12.5 103 mol/L [28].
4. Conclusion Novel amide based cationic gemini surfactants were synthesized and characterized using spectroscopic tools including MALDITOF-MS, FTIR, 1H and 13C NMR spectroscopy. The influence of number of aromatic rings and counterions on thermal and surface properties was investigated. The prepared surfactants offered high thermal stability and excellent surface properties. TGA thermograms revealed the decomposition temperature of all the gemini surfactant near to 300 C which is greater than the existing reservoir temperature (100 C). The surfactants containing biphenyl spacer group found to be more thermally stable compared to the surfactants having mono phenyl spacer group. The insertion of ethoxy units between the lipophilic tail and lipophobic headgroup resulted in excellent solubility of the synthesized gemini surfactants in all kinds of water (FW, SW, and DW) without cloudiness or precipitation. It has been found that the CMC of the gemini surfactants containing bromide counterion was less compared to the surfactants containing chloride counterion. In addition, the CMC of the surfactants decreased when the number of aromatic phenyl
rings increased. We concluded that the synthesized cationic gemini surfactants have significant potential for oilfield application based on their good thermal stability, salt tolerance, and surface properties. Conflicts of interest The authors declare no conflict of interest. Acknowledgment The research was supported by the College of Petroleum Engineering & Geoscience (CPG) at KFUPM through a collaborative project with The University of Texas at Austin. References [1] S.O. Olayiwola, M. Dejam, A comprehensive review on interaction of nanoparticles with low salinity water and surfactant for enhanced oil recovery in sandstone and carbonate reservoirs, Fuel 241 (2019) 1045e1057. [2] M.S. Azad, J.J. Trivedi, Novel viscoelastic model for predicting the synthetic polymer’s viscoelastic behavior in porous media using direct extensional rheological measurements, Fuel 235 (2019) 218e226. [3] S. Ahmed, K.A. Elraies, A.S. Hanamertani, M.R. Hashmet, Viscosity models for polymer free co2 foam fracturing fluid with the effect of surfactant concentration, salinity and shear rate, Energies 10 (2017) 1970. [4] S. Ahmed, K.A. Elraies, M.R. Hashmet, M.S. Alnarabiji, Empirical modeling of the viscosity of supercritical carbon dioxide foam fracturing fluid under different downhole conditions, Energies 11 (2018) 782. [5] A.H. Tantawy, H.I. Mohamed, A.A. Khalil, K.A. Hebash, M.Z. Basyouni, Novel bioactive imidazole-containing polymeric surfactants as petroleum-collecting and dispersing agents: synthesis and surface-active properties, J. Mol. Liq. 236 (2017) 376e384. [6] A.M. Atta, M.M. Abdullah, H.A. Al-Lohedan, A.O. Ezzat, Demulsification of heavy crude oil using new nonionic cardanol surfactants, J. Mol. Liq. 252 (2018) 311e320. [7] A. Aminian, B. ZareNezhad, Wettability alteration in carbonate and sandstone rocks due to low salinity surfactant flooding, J. Mol. Liq. 275 (2019) 265e280. [8] M. Zhao, W. Lv, Y. Li, C. Dai, H. Zhou, X. Song, Y. Wu, A study on preparation and stabilizing mechanism of hydrophobic silica nanofluids, Materials 11 (2018) 1385. [9] H. Seong, G. Kim, J. Jeon, H. Jeong, J. Noh, Y. Kim, H. Kim, S. Huh, Experimental study on characteristics of grinded graphene nanofluids with surfactants, Materials 11 (2018) 950. [10] M. Yazdimamaghani, T. Pourvala, E. Motamedi, B. Fathi, D. Vashaee, L. Tayebi, Synthesis and characterization of encapsulated nanosilica particles with an acrylic copolymer by in situ emulsion polymerization using thermoresponsive nonionic surfactant, Materials 6 (2013) 3727e3741. [11] M.S. Kamal, A novel approach to stabilize foam using fluorinated surfactants, Energies 12 (2019) 1163. [12] F.M. Menger, J.S. Keiper, Gemini surfactants, Angew. Chem. Int. Ed. 39 (2000) 1906e1920. [13] R. Nguele, K. Sasaki, H. Said-Al Salim, Y. Sugai, A. Widiatmojo, M. Nakano, Microemulsion and phase behavior properties of (dimeric ammonium surfactant salteheavy crude oileconnate water) system, J. Unconv. Oil Gas Res. 14 (2016) 62e71. [14] M. Abo-Riya, A.H. Tantawy, W. El-Dougdoug, Synthesis and evaluation of novel cationic gemini surfactants based on guava crude fat as petroleumcollecting and dispersing agents, J. Mol. Liq. 221 (2016) 642e650. [15] J. Mao, X. Yang, Y. Chen, Z. Zhang, C. Zhang, B. Yang, J. Zhao, Viscosity reduction mechanism in high temperature of a gemini viscoelastic surfactant (ves) fracturing fluid and effect of counter-ion salt (kcl) on its heat resistance, J. Pet. Sci. Eng. 164 (2018) 189e195. [16] M. Migahed, M. EL-Rabiei, H. Nady, E. Zaki, Novel gemini cationic surfactants as anti-corrosion for x-65 steel dissolution in oilfield produced water under
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S.M. Shakil Hussain et al. / Journal of Molecular Liquids 296 (2019) 111837 sweet conditions: combined experimental and computational investigations, J. Mol. Struct. 1159 (2018) 10e22. M. Zhou, Z. Zhang, D. Xu, L. Hou, W. Zhao, X. Nie, L. Zhou, J. Zhao, Synthesis of three gemini betaine surfactants and their surface active properties, J. Taiwan Inst. Chem. Eng. 74 (2017) 7e13. S.S. Hussain, M.A. Animashaun, M.S. Kamal, N. Ullah, I.A. Hussein, A.S. Sultan, Synthesis, characterization and surface properties of amidosulfobetaine surfactants bearing odd-number hydrophobic tail, J. Surfactants Deterg. 19 (2016) 413e420. J. Hoque, P. Kumar, V.K. Aswal, J. Haldar, Aggregation properties of amide bearing cleavable gemini surfactants by small angle neutron scattering and conductivity studies, J. Phys. Chem. B 116 (2012) 9718e9726. S.S. Hussain, M.S. Kamal, Effect of large spacer on surface activity, thermal, and rheological properties of novel amido-amine cationic gemini surfactants, J. Mol. Liq. 242 (2017) 1131e1137. R. Zana, Dimeric (gemini) surfactants: effect of the spacer group on the association behavior in aqueous solution, J. Colloid Interface Sci. 248 (2002) 203e220. A. Laschewsky, K. Lunkenheimer, R.H. Rakotoaly, L. Wattebled, Spacer effects in dimeric cationic surfactants, Colloid Polym. Sci. 283 (2005) 469e479. S. Liu, X. Liu, Z. Guo, Y. Liu, J. Guo, S. Zhang, Wettability modification and restraint of moisture re-adsorption of lignite using cationic gemini surfactant, Colloid. Surf. Physicochem. Eng. Asp. 508 (2016) 286e293. Z. Chu, Y. Feng, A facile route towards the preparation of ultra-long-chain amidosulfobetaine surfactants, Synlett 2009 (2009) 2655e2658. R. Zana, M. Benrraou, R. Rueff, Alkanediyl-. Alpha.,. Omega.-bis (dimethylalkylammonium bromide) surfactants. 1. Effect of the spacer chain length on the critical micelle concentration and micelle ionization degree, Langmuir 7 (1991) 1072e1075. S.S. Hussain, L.T. Fogang, M.S. Kamal, Synthesis and performance evaluation of betaine type zwitterionic surfactants containing different degrees of ethoxylation, J. Mol. Struct. 1173 (2018) 983e989. S.S. Hussain, M.S. Kamal, L.T. Fogang, Synthesis and physicochemical investigation of betaine type polyoxyethylene zwitterionic surfactants containing different ionic headgroups, J. Mol. Struct. 1178 (2019) 83e88.
[28] A.K. Ghumare, B.V. Pawar, S.S. Bhagwat, Synthesis and antibacterial activity of novel amido-amine-based cationic gemini surfactants, J. Surfactants Deterg. 16 (2013) 85e93. [29] A.M. Atta, H.A. Al-Lohedan, M.M. Abdullah, S.M. ElSaeed, Application of new amphiphilic ionic liquid based on ethoxylated octadecylammonium tosylate as demulsifier and petroleum crude oil spill dispersant, J. Ind. Eng. Chem. 33 (2016) 122e130. [30] X. Cui, S. Mao, M. Liu, H. Yuan, Y. Du, Mechanism of surfactant micelle formation, Langmuir 24 (2008) 10771e10775. [31] S.M. Tawfik, Synthesis, surface, biological activity and mixed micellar phase properties of some biodegradable gemini cationic surfactants containing oxycarbonyl groups in the lipophilic part, J. Ind. Eng. Chem. 28 (2015) 171e183. [32] Y. Wang, Y. Jiang, T. Geng, H. Ju, S. Duan, Synthesis, surface/interfacial properties, and biological activity of amide-based gemini cationic surfactants with hydroxyl in the spacer group, Colloid. Surf. Physicochem. Eng. Asp. 563 (2019) 1e10. [33] S.S. Hussain, M.S. Kamal, L.T. Fogang, Effect of internal olefin on the properties of betaine-type zwitterionic surfactants for enhanced oil recovery, J. Mol. Liq. 266 (2018) 43e50. [34] S. Hussain, M.S. Kamal, M. Murtaza, Synthesis of novel ethoxylated quaternary ammonium gemini surfactants for enhanced oil recovery application, Energies 12 (2019) 1731. [35] S.M. Shaban, I. Aiad, H.A. Fetouh, A. Maher, Amidoamine double tailed cationic surfactant based on dimethylaminopropylamine: synthesis, characterization and evaluation as biocide, J. Mol. Liq. 212 (2015) 699e707. [36] A. Al-Sabagh, E. Azzam, S. Mahmoud, N. Saleh, Synthesis of ethoxylated alkyl sulfosuccinate surfactants and the investigation of mixed solutions, J. Surfactants Deterg. 10 (2007) 3e8. [37] P. Patial, A. Shaheen, I. Ahmad, Synthesis, surface active and thermal properties of novel imidazolium cationic monomeric surfactants, J. Ind. Eng. Chem. 20 (2014) 4267e4275. [38] S.S. Hussain, M.S. Kamal, L.T. Fogang, Effect of internal olefin on the properties of betaine-type zwitterionic surfactants for enhanced oil recovery, J. Mol. Liq. 266 (2018) 43e50.
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Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq
Effect of aromatic spacer groups and counterions on aqueous micellar and thermal properties of the synthesized quaternary ammonium gemini surfactants S.M. Shakil Hussain a, Muhammad Shahzad Kamal a, *, Mobeen Murtaza b a b
Center for Integrative Petroleum Research, King Fahd University of Petroleum & Minerals, Dhahran, 31261, Saudi Arabia College of Petroleum Engineering, King Fahd University of Petroleum & Minerals, Dhahran, 31261, Saudi Arabia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 9 September 2019 Received in revised form 22 September 2019 Accepted 26 September 2019 Available online 9 October 2019
One of the major challenges for the oil industry in the 21st century is to get the desired surfactants that are soluble in high saline water (220, 000 ppm) and stable at high temperature (100 C). Most commercial surfactants suffering due to hydrolysis at high temperature and the monovalent and divalent reservoir ions leads to surfactant precipitation. In order to address these issues, a new series of cationic gemini surfactants with a different number of aromatic rings in the spacer group as well as different counter ions were synthesized and characterized with the aid of MALDI-TOF MS, FTIR, 1H NMR, and 13C NMR spectroscopy. The effect of number of phenyl aromatic rings in the spacer and counterions on thermal and surface properties was determined. Thermogravimetric results showed the decomposition temperature of all the gemini surfactant near to 300 C which is larger than the existing oilfield temperature (100 C). The insertion of ethoxy units between the lipophilic tail and lipophobic headgroup resulted in good solubility of cationic gemini surfactants in high saline and normal water without cloudiness or precipitation. The critical micelle concentration and the corresponding surface tension were lower for gemini surfactants containing bromide counterions compared to the surfactants containing chloride counterions. The gemini surfactants containing two aromatic phenyl rings in the spacer have lower critical micelle concentration compared to the gemini surfactants with one phenyl ring. The properties of the synthesized cationic gemini surfactants mark them a material of choice for high salinity/temperature reservoirs. © 2019 Elsevier B.V. All rights reserved.
Keywords: Oilfield Quaternary ammonium Gemini Aqueous Thermal stability
1. Introduction Surfactants (surface active agents) are continuously developing for multiple oilfield applications including stimulation, fracturing, wettability alteration, and enhanced oil recovery [1e4]. Surfactants tend to lower the miscibility gap between aqueous and crude oil until a microemulsion is generated to produce an ultralow (103 mN/m) interfacial tension (IFT). Moreover, surfactants also perform as an emulsifier, demulsifiers, wettability modifier, foaming agent, and dispersant agent [5e11]. Gemini surfactants are the unique class of surfactants having two hydrophobic tail and two hydrophilic heads covalently attached through spacer group [12]. Gemini surfactants exhibit distinct properties compared to conventional single tail and single
* Corresponding author. E-mail address: [email protected] (M.S. Kamal). https://doi.org/10.1016/j.molliq.2019.111837 0167-7322/© 2019 Elsevier B.V. All rights reserved.
head material. These properties include low critical micelle concentration (CMC), heat resistant, salt resistance, excellent aqueous solubility, and ultra-low interfacial tension (IFT). Ammonium-based cationic gemini surfactants are successfully applying in multiple oilfield applications [13]. Abo-Riya and coworkers reported the synthesis of 1,2-ethane bis (dimethyl 2(octadecyloxy)-2- oxoethyl ammonium chloride with different hydrophobic tail length and claimed that such kind of cationic gemini surfactants may apply as a petroleum-collecting and dispersing agents [14]. Mao and co-workers studied the effect of counterions on the properties of cationic gemini surfactants as a clean fracturing fluid and emphasized that the viscosity reduction was due to micelle dissociation [15]. Migahed et al. reported the synthesis of 2,2’-(1-aminopropane-1,3-diyl)bis(1-(2-aminoethyl)1-dodecyl-4,5-dihydro-1 H-imidazol-1-ium)dichloride as corrosion inhibitor for X-65 steel dissolution for formation water in deep oil wells and concluded that inhibition efficiency increased with concentration [16].
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The careful selection of each group in the structure of gemini surfactant plays a vital role to obtain desired properties. For instance, surfactants with long hydrophobic tail exhibit high heat stability and lower CMC [17]. However, increasing the length of the hydrophobic tail reduces aqueous solubility of surfactant [18]. The aqueous solubility of the surfactant with a long hydrophobic tail can be achieved by adding ethoxy units (EO) which enhances the surfactants water solubility through hydrogen bonding with water molecules. The presence of amide group [NHC]O] in the gemini surfactant show multiple advantages compared to the gemini surfactant without the amide group. For example, the CMC of the cationic gemini surfactant without the amide group reached from 0.82 mM to 0.18 mM. On the other hand, the CMC of the related cationic gemini surfactant with an amide group reached from 0.19 mM to 0.08 mM. The low CMC of the gemini surfactants containing amide group may attribute to the formation of hydrogen bonding which facilitates the formation of micelles at low CMC [19,20]. The spacer group perhaps the most critical part that identifies the fundamental properties of the gemini surfactants [21]. Within the different kinds of spacer group (rigid, flexible, hydrophilic, hydrophobic, short, long), the surfactant with an aromatic group is the material of choice due to better surface properties associated with the p-p stacking for phenyl spacers. Moreover, the surfactants with aromatic groups are known to attract more aromatics in the reservoir such as asphaltene etc. In this article, we report the synthesis and structure elucidation of amide-based cationic gemini surfactants (12-PhBr-12, 12-PhCl12, 12-BiPhBr-12, and 12-BiPhCl-12) containing mono phenyl and biphenyl rings as an aromatic spacer group with different counterions. The counterions play a significant role in determining thermal and surface/interface properties [22]. The chemical structures were confirmed with the aid of spectroscopic tools including MALDI-TOF-MS, FTIR, 1H and 13C NMR spectra. The effect of number aromatic rings (mono phenyl vs biphenyl) and counterions (Br vs Cl) was identified by means of thermal gravimetric analysis (TGA), aqueous solubility, CMC, surface tension at CMC (gcmc), maximum surface access (гmax), and occupied surface area at the interface of air-water (Amin). The chemical structures were carefully designed and synthesized according to the harsh reservoir conditions. For example, the cationic gemini surfactants were chosen due to their low adsorption on to the carbonate rocks associated with the charge repulsion [23]. A specific number of EO groups were incorporated among lipophilic tail and lipophobic headgroup to achieve better solubility in formation brine (FW), seawater (SW), and deionized water (DW). The amide group was selected because of the excellent thermal and surface properties. 2. Materials and synthesis
MALDI-TOF MS spectra were noted on Bruker SolariX XR instrument in a matrix of Dithranol in dichloromethane. 1H and 13C/NMR readings were obtained on Jeol 1500 spectrometer. The FT-IR studies were conducted on a 16F PerkinElmer FT-IR spectrometer. 2.2. Solubility test Gemini surfactants (12-PhBr-12, 12-PhCl-12, 12-BiPhBr-12, and 12-BiPhCl-12) (15 wt% each) were solubilized in DW, SW, FW, and solubility was noticed with elapse of time. 2.3. Thermal gravimetric analysis (TGA) TA instrument (SDT Q600) was utilized for the TGA experiments. The measurements were conducted with heating at 20 C/min in the presence of nitrogen (100 mL/min). The temperature interval was ranged from 30 C to 500 C. 2.4. Surface tension Surface tensions measurements of (12-PhBr-12, 12-PhCl-12, 12BiPhBr-12, and 12-BiPhCl-12) were conducted on force tensiometer using Wilhelmy plate method. Measurements were done at 60 ± 0.1 C and 30 ± 0.1 C. Before each run, the Wilhelmy plate was rinsed with DW followed by blue flame heating. DW surface tension was also recorded for reference. 2.5. Synthesis 2.5.1. Synthesis of 12-PhBr-12 Synthesis of 12-PhBr-12 is outlined in Scheme 1. The acid (6) (25 g, 36.23 mmol) was reacted with amine (5) (7.40 g, 72.46 103 mol) in a 250 mL RB flask at elevated temperature (160 C) up to 6 h. Sodium fluoride (NaF) (0.15 g, 3.62 mmol) was poured into the reaction mixture to catalyze the experiment. After 6 h, more amine (5) (5.55 g, 54.35 103 mol) was poured into the reaction flask to achieve complete conversion of acid (6) to amide (4) and the experiment was continued for further 4 h (see Fig. 1). Finally, the remaining amine (5) and NaF were extracted to acquire 4 [24]. The compound 4 (20.0 g, 25.84 103 mol) was then further reacted with a,a0 -dibromo-p-xylene (2.73 g, 10.34 103 mol) in absolute EtOH (10 mL) for 50 h at 80 C [25]. Eventually, the reaction mixture was subjected to column chromatography with ethanol (EtOH) mobile phase to acquire 12-PhBr-12 in the shape of viscous oil. 12-PhCl-12, 12-BiPhBr-12, and 12-BiPhCl-12 were synthesized according to same procedure by treating intermediate 4 with a,a0 dichloro-p-xylene, 4,40 -bis(bromomethyl)biphenyl, and 4,40 -bis(chloromethyl)-1,10 -biphenyl, respectively.
2.1. Materials 3. Results and discussion
a,a0 -dibromo-p-xylene, (97%), a,a0 -dichloro-p-xylene (98%), 4,40 -bis(bromomethyl)biphenyl (98%), 4,40 -bis(chloromethyl)-1,10 biphenyl (98%), aluminum oxide (99.99%), glycolic acid ethoxylate lauryl ether (average Mn ~690), NaF (99%), 3-(dimethylamino)-1propylamine (99%), were obtained from Sigma Aldrich. Simulated FW and SW were prepared using salts including MgCl2, CaCl2, Na2SO4, NaHCO3, and NaCl. The salts were purchased from Panreac company and the amount of each salt in the solution is depicted in Table 1. 2.1.1. Elucidation of surfactants structure The chemical structures of the synthesized cationic gemini surfactants (12-PhBr-12, 12-PhCl-12, 12-BiPhBr-12, and 12BiPhCl-12) were elucidated with the aid of spectroscopic tools including MALDI-TOF-MS, FTIR, and 13C/1H NMR instruments. The
Four quaternary ammonium gemini surfactants (12-PhBr-12, 12-PhCl-12, 12-BiPhBr-12, and 12-BiPhCl-12) containing mono and biphenyl rings with different counterions (Br and Cl) were synthesized by treating amine (5) with acid (6) in the presence of the catalytic amount of sodium NaF. In second step, the amide (4) was charged individually with a,a0 -dibromo-p-xylene, a,a0 dichloro-p-xylene, 4,40 -bis(bromomethyl)-1,10 -biphenyl, and 4,40 bis(chloromethyl)-1,10 -biphenyl to obtain 12-PhBr-12, 12-PhCl-12, 12-BiPhBr-12, and 12-BiPhCl-12, respectively (Scheme 1, Fig. 2). 3.1. Structure identification The structure identification is represented for 12-PhBr-12. According to 1H NMR of 12-PhBr-12 (Table 1, Fig. 2), the
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Table 1 1 H NMR data and peak assignment of gemini amphiphiles [15,22,31,32]. Gemini amphiphiles
1
H NMR data (500 MHz, CDCl3, d in ppm)
Hydrophobic Tail
12-PhBr-12 12-PhCl-12 12-BiPhBr-12 12-BiPhCl-12
Ethoxy groups
Amide
Amido-amine
Spacer protons
CH3 (a)
CH2 (b)
CH2 (c)
CH2 (d, j)
(CH2)2 (e)
CH2 (f)
NH (g)
CH2 (h) CH3 (k)
CH2 (i)
CH2 (m)
CH (n)
CH (o)
0.88 0.88 0.88 0.88
1.25 1.26 1.26 1.25
1.57 1.57 1.57 1.57
3.44 3.44 3.44 3.44
3.64 3.64 3.64 3.64
4.02 4.01 4.05 4.03
7.97 8.03 7.90 8.00
3.15 3.13 3.21 3.18
1.72 1.72 1.74 1.73
3.98 3.99 3.99 3.99
7.70 7.70 7.67 7.64
7.36 7.36
Scheme 1. Synthetic scheme of cationic gemini surfactants.
Fig. 1. 1H NMR of intermediate compound (4).
characteristics peaks at d 0.88 ppm and d 1.26 ppm relate to CH3 and CH2 moieties in the lipophilic tail of surfactant [26]. The sharp peaks at d 3.16 ppm correspond to the methyl moieties linked hydrophilic headgroup [-(CH3)2eNeCH2eC6H4eCH2eN-(CH3)2-]. The strong peak at d 3.64 ppm corresponds to the ethoxy groups [-CH2CH2-O-CH2-CH2-O-] [27]. The peak at d 4.02 ppm was associated with the methylene moiety (CH2) connected with carbonyl carbon [-O-CH2-C]OeNH-]. The protons of aromatic benzene ring were coupled with the signals detected at d 7.70 ppm. The singlet peak at d 7.97 ppm may be attributed to amide proton [-OeCH2eC]OeNH] [28e30].
According to 13C NMR of 12-PhBr-12 (Table 2, Fig. 3), the sharp signals at d 14.1 ppm and d 22.6e31.7 ppm linked with CH3 and CH2 moieties presented in the surfactant tail. Methyl (CH3) moieties linked with the hydrophilic headgroup [-(CH3)2eNeCH2eC6H4eCH2eN-(CH3)2-] were confirmed with the peak at d 49.9 ppm. Moreover, two characteristics peaks at d 62.2 ppm and d 66.6 ppm could be linked with the methylene (CH2) groups joined with the hydrophilic headgroup [-CH2Ne(CH3)2eCH2eC6H4eCH2-(CH3)2eNeCH2-] [33]. The strong peak at d 70.4 ppm may be attributed to ethoxy groups [-CH2-CH2-OCH2-CH2-O-]. The peak detected at d 171.1 ppm may be referred to
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characteristics bands at 1544/cm and 1652/cm related with amide I carbonyl and amide II carbonyl group [28]. The peak at 1347/cm and 1463/cm may refer to bending vibration of CH3 and CH2 groups, respectively. Strong signals were detected at 1097/cm that could be coupled with ethoxy moieties [35,36]. The MALDI-TOF MS data of 12-PhBr-12 (Fig. 5) exhibited the highest peak at 680.5 that could be reorganized as a homolytic cleavage of the bond between terminal carbon of spacer and ammonium headgroup. This type of homolytic bond-breaking generate radical cation and showed that the major component of 12-PhBr-12 having 8 ethoxy units and 12 carbons in the surfactant tail.
Fig. 2. 1H NMR of 12-PhBr-12.
3.2. Heat stability
Table 2 13 C NMR data showing the values of chemical shift in gemini amphiphiles. Gemini amphiphiles
13
12-PhBr-12 12-PhCl-12 12-BiPhBr-12 12-BiPhCl-12
14.0, 13.9, 13.9, 14.0,
C NMR (CDCl3, d, 125 MHz) 22.5, 22.5, 22.5, 22.6,
25.9, 25.9, 25.9, 25.0,
29.2, 29.2, 29.2, 29.2,
29.3, 29.3, 29.3, 29.4,
29.4, 29.4, 29.4, 29.5,
31.7, 31.7, 31.7, 31.8,
35.7, 35.8, 35.8, 35.7,
49.9, 49.8, 49.4, 49.4,
62.1, 62.1, 62.1, 62.2,
66.6, 66.6, 66.6, 66.9,
70.4, 70.4, 70.4, 70.4,
129.6, 129.7, 126.9, 127.1,
133.8, 133.8, 127.2, 127.3,
171.0 170.9 133.8, 141.1, 170.8 133.9, 141.2, 170.9
Fig. 3. 13C NMR of 12-PhBr-12.
the carbonyl of amide [-C]OeNH-]. According to FTIR results of 12-PhBr-12 (Table 3, Fig. 4), the signals at 3414 cm1 could be coupled with the stretching vibration of the NeH group [34]. Signals at 2854/cm and 2924/cm related with CH2 symmetrical and CH2 asymmetrical bands. Two
The temperature of the carbonate reservoirs reaches up to 100 C, therefore, the applied surfactant must be thermally stable. We studied the thermal stability of the synthesized surfactants (12PhBr-12, 12-PhCl-12, 12-BiPhBr-12, and 12-BiPhCl-12) with the aid of TGA. Fig. 6 showed the TGA thermogram of four gemini
Table 3 FTIR results of the gemini amphiphiles. Gemini amphiphiles
FTIR data (in cm1) (yN-H)
yC-H asym.
yC-H sym.
amide (I)
amide (II)
CH2 (bend)
CH3 (bend)
ethoxy stretch
asym. Stretch
12-PhBr-12 12-PhCl-12 12-BiPhBr-12 12-BiPhCl-12
3414 3413 3415 3414
2924 2924 2923 2925
2854 2850 2851 2855
1652 1651 1653 1654
1544 1542 1541 1543
1465 1466 1464 1465
1348 1349 1347 1350
1097 1098 1097 1099
947 946 945 946
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Fig. 4. FTIR spectrum of 12-PhBr-12. Fig. 6. Thermal degradation curves of gemini amphiphiles determined by TGA.
amphiphiles under nitrogen. All four surfactants showed an initial loss in the range of 5%e10% because of residual water and impurities. A big and sharp loss for all the gemini amphiphiles was detected near to 300 C, exhibiting the degrading effect of heat on the structure of 12-PhBr-12, 12-PhCl-12, 12-BiPhBr-12, and 12BiPhCl-12. The effect of counterion on thermal stability was evaluated for surfactants containing mono phenyl aromatic ring and biphenyl aromatic rings. For instance, 12-PhBr-12 and 12-PhCl-12 have same ethoxy units, same tail length, same spacer, and same hydrophilic headgroup. Therefore, the counterion is the only factor responsible for any change in thermal behavior. The thermal stability of the surfactant with bromide counterion was slightly better than the surfactant with chloride counterion (12-PhCl-12 ˂ 12PhBr-12 and 12-BiPhCl-12 ˂ 12-BiPhBr-12). Similarly, the surfactant-containing biphenyl spacer group exhibited better thermal stability compared to the surfactant with mono phenyl spacer with same counterion (12-PhBr-12 ˂ 12-BiPhBr-12 and 12PhCl-12 ˂ 12-BiPhCl-12) [37]. In general, the counterion and number of aromatic rings do effect the thermal stabilities of the gemini amphiphiles and, overall, all four surfactants degraded near
to 300 C, which is greater than the existing reservoir temperature (100 C).
3.3. Solubility Surfactant solubility in normal and high saline water is the prerequisite for its oilfield application. The divalent and monovalent ions available in the injected water (SW) and reservoir brine (FW) leads to surfactant precipitation. The insertion of EO units increases the aqueous solubility of the surfactants. Such a phenomenon can be explained in terms of hydrogen bonding. The hydrogen of water creates hydrogen bonding with the oxygen of the EO group which ultimately increase solubility. We investigated the solubility of the synthesized cationic gemini surfactants by dissolving them in DW, SW, and FW. The amount of different monovalent and divalent ions is depicted in Table 4. All four cationic gemini surfactants revealed excellent solubility and no phase separation, precipitation, or cloudiness was observed (Fig. 7).
Fig. 5. MALDI-TOF MS of 12-PhBr-12.
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Table 4 The amount of different monovalent and divalent ions in simulated FW and SW. Ions
FW (g/L)
SW (g/L)
Sodium(1þ) ion Calcium (2þ) ion Magnesium (2þ) ion Sulfate (2-) ion Chloride (1-)ion Bicarbonate (1-) ion Total
59.5 19.1 2.5 0.4 132.1 0.4 214
18.3 0.7 2.1 4.3 32.2 0.1 57.7
surface tension reduces with the rise in temperature. Other surface properties such as CMC, surface tension corresponding to CMC (gcmc), maximum surface access (гmax) and minimum area per molecule at air-water interface (Amin) were estimated from the surface tension data. The following equations were used to calculate the surface properties [38]:
гmax ¼
1 nRT
dg dlnC
(1) T
Fig. 7. Snapshot of gemini amphiphiles solutions in SW and FW.
3.4. Surface properties
. Amin ¼ 1018 NA гmax
(2)
The effect of counterions (Cl and Br ) and a number of aromatic phenyl rings on the surface tension of gemini surfactant solutions was measured at two different conditions of temperatures (30 C & 60 C). The surface tension data of the synthesized gemini surfactants at two different temperatures is shown in Fig. 8 to Fig. 9. Other surface properties are also given in Table 5. The surface tension decreases with increasing concentration of surfactant until the critical micelle concentration is reached. There is an insignificant variation in the surface tension upon extra addition of the surfactant beyond CMC. For all discussed gemini surfactants, the
Here dg/dlnC is the slope below CMC in surface tension plot, R represents the gas constant, C is the concentration of the surfactant, T is the temperature, NA Avogadro’s number and n was taken as 3 for the gemini surfactant. The data given in Table 5 provides significant fundamental information about the effect of counterions, the number of phenyl rings, and temperature on the surface properties. For all surfactants, the CMC decreased by increasing the temperature. The reduction in the CMC with temperature is associated with the decrease in the hydration of the hydrophilic group.
Fig. 8. Surface tension of 12-PhBr-12 and 12-PhCl-12 at various temperatures.
Fig. 9. Surface tension of 12-BiPhBr-12 and 12-BiPhCl-12 at various temperatures.
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Table 5 Surface properties of GS with various counterions at various temperatures. Surfactant
Solvent
T ( C)
CMC (mmol L1)
gcmc (mN m1)
гmax x 107 (mol m2)
Amin (nm2)
12-PhCl-12 12-PhCl-12 12-PhBr-12 12-PhBr-12 12-BiPhCl-12 12-BiPhCl-12 12-BiPhBr-12 12-BiPhBr-12
DW DW DW DW DW DW DW DW
30 60 30 60 30 60 30 60
0.0214 0.00851 0.0153 0.00846 0.0138 0.00674 0.00887 0.00647
38.9 38.1 37.29 35.63 37.71 35.08 36.258 33.405
7.73 7.51 6.63 6.48 7.30 6.69 7.12 6.96
2.14 2.21 2.50 2.56 2.27 2.48 2.331 2.387
The resulted decreases in hydration at the high temperature promotes micelle formation and reduction in CMC. The critical micelle concentration depends on the interactions among the surfactant molecules in the bulk phase. In most cases, the critical micelle concentration can be reflected by the adsorption of surfactants at the interface. The internal or external changes in conditions that lead towards more closer packing of the surfactant at interface results in a reduction in the surface tension and CMC. A clear trend was observed for all surfactants at both temperatures when the counterion was changed from bromide to chloride. The CMC of the surfactants having bromide as a counterion was low compared to the CMC of the corresponding surfactants having chloride counterions. This behavior was consistent for surfactants with one aromatic phenyl ring and two aromatic phenyl rings as well. The number of phenyl rings in the spacer also affect the CMC of the surfactants. The behavior was also consistent for both types of counterions and at both temperatures. The CMC of surfactants decreased when the number of aromatic rings increased from 1 to 2. Adding two aromatic phenyl rings decreased the CMC due to more conjugation, p-p stacking, and increased hydrophobicity. Among all surfactants, the lowest CMC was observed for 12BiPhBr-12 at 60 C. The gcmc values also decreased by increasing temperature. In addition, surfactants with bromide counterions have lower gcmc compared to the surfactants with chloride counterions. The surfactants containing two aromatic rings also showed lower gcmc values compared to the surfactants with a single aromatic phenyl ring. Maximum surface access decreases with temperature while the area per molecule increases with temperature. The synthesized gemini surfactants showed excellent surface properties that can make them cost-effective in real field applications. The CMC of similar type of surfactants have been reported between 8.0 10 3 mol/L to 12.5 103 mol/L [28].
4. Conclusion Novel amide based cationic gemini surfactants were synthesized and characterized using spectroscopic tools including MALDITOF-MS, FTIR, 1H and 13C NMR spectroscopy. The influence of number of aromatic rings and counterions on thermal and surface properties was investigated. The prepared surfactants offered high thermal stability and excellent surface properties. TGA thermograms revealed the decomposition temperature of all the gemini surfactant near to 300 C which is greater than the existing reservoir temperature (100 C). The surfactants containing biphenyl spacer group found to be more thermally stable compared to the surfactants having mono phenyl spacer group. The insertion of ethoxy units between the lipophilic tail and lipophobic headgroup resulted in excellent solubility of the synthesized gemini surfactants in all kinds of water (FW, SW, and DW) without cloudiness or precipitation. It has been found that the CMC of the gemini surfactants containing bromide counterion was less compared to the surfactants containing chloride counterion. In addition, the CMC of the surfactants decreased when the number of aromatic phenyl
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