A Systematic investigation of a surfactant type nano gemini ionic liquid

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Applied Chemistry

A Systematic investigation of a surfactant type nano gemini ionic liquid and simultaneous abnormal salts effects on the crude oil/water interfacial tension Javad Saien, Mona Kharazi, Meysam Yarie, and Mohammad Ali Zolfigol Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b05553 • Publication Date (Web): 13 Feb 2019 Downloaded from http://pubs.acs.org on February 15, 2019

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Industrial & Engineering Chemistry Research

Graphic for manuscript

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Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

A Systematic investigation of a surfactant type nano gemini ionic liquid and simultaneous abnormal salts effects on the crude oil/water interfacial tension Javad Saiena,*, Mona Kharazia, Meysam Yarieb, Mohammad Ali Zolfigolb a

Department of Applied Chemistry, Bu–Ali Sina University, Hamedan 65174, Iran

b

Department of Organic Chemistry, Bu–Ali Sina University, Hamedan 65174, Iran

Abstract Gemini ionic liquids (ILs) are usually known with significant surfactant behavior. Nano materials, on the other hand, are capable of improving interface properties. The current study explores the use of a novel nano gemini imidazolium IL with a molecular structure of four methylene group spacer, for reducing crude oil/water interfacial tension (IFT). The gemini IL was prepared purely by a two steps synthesis method and characterized in different ways. Results revealed that IFT was drastically decreased to 97.8% in the presence of the IL and more decrease was achieved with temperature and pH variations. The high performance of the IL can be attributed to the strong IL amphiphilic nature. The salt effects in the presence of the IL were evaluated with NaCl, MgCl2 as well as their mixture. Results revealed more IFT reduction under salinity conditions because of remarkable found synergism effect, unlike conventional surfactants. The findings encourage the use of seawater IL solutions in chemical enhanced oil recovery. The obtained salt free IFT data were precisely reproduced with the well-known Frumkin adsorption isotherm and the corresponding thermodynamic parameters were obtained at different temperatures. From thermodynamic results, a spontaneous IL adsorption was deduced. Keywords: Gemini ionic liquids; Interfacial tension; Crude oil; Water salinity; Frumkin isotherm

1. Introduction Despite many applied methods in oil recovery, more than two thirds of the oils still remain unrecoverable in mature reservoirs.1 Accordingly, a lot of attempts have been made to develop new methods in enhanced oil recovery.2 Among different ways, chemical enhanced oil recovery (CEOR) methods are profound due to being extremely impressive and low cost.3 CEOR techniques involve injecting special chemicals to alter the reservoir fluid properties in order to mobilize trapped oil in the media. The used chemicals can decrease interfacial tension (IFT) followed by 1 ACS Paragon Plus Environment

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smoothing the mobilization of residual oil in the reservoirs.3 IFT characterizes the cohesive forces dominant between adjacent molecules at the interface of immiscible liquids, stemmed from unbalanced forces of the neighboring molecules.4 Surfactants can significantly reduce the IFT, and one of the widely used techniques in CEOR is the surfactant flooding.5 Although different surfactants types have been examined, the conventional surfactants encounter the problem of losing activity under reservoirs harsh conditions.3 In this regard, many researchers encourage designing new surfactants to be capable of steadily reducing the IFT.3,6,7 Accordingly, ionic liquids (ILs) have gained much attention over recent years. In an abbreviate manner, ILs are a class of organic salts that are in liquid form at ambient or even lower temperatures.8 ILs are generally known as promising noble green substances to replace the traditional toxic materials due to general desired properties e.g. low vapour pressure, high thermal stability, reusability, non-toxic, resistive under brine solutions and minor adsorption on the rock surfaces.9 In addition, a part of ILs exhibit excellent behavior as surfactant, due to their amphiphilic nature and can improve the EOR by lowering IFT of the crude oil/water system and the crude oil/rock.10 They may also be used to dehydrate and to desalinate crude oils as well as in petroleum refining for desulfurizing, denitrogenating and dearomatizing. Additionally, removing depositions of asphaltenes and paraffins with ILs have been tested to dissolve them and good ILs performance has been revealed.11 These properties allow ILs to be used as desired chemicals in ecology and in economical points of view. Accordingly, several investigations have been conducted to examine the effectiveness of ILs. Painter et al.5,12 for instance, reported that Canadian tar sands extra-heavy crude oil may be recovered up to 90% by using imidazolium ILs even at high salinity and that the used IL may be recycled five times. To improve these features, gemini type ILs have recently attracted the attention, due to molecular amphiphilic nature.1,13 These ILs consist of two hydrophobic chains and hydrophilic head groups that are connected by a spacer near or exactly at the head groups.14 Investigations show that compared to mono analog structure ILs and quaternary ammonium cationic surfactants, the molecular structure of gemini ILs, with the same carbon numbers in the alkyl chain, provide desired surface properties as well as better water solubility, aggregation and rheological 2 ACS Paragon Plus Environment


behavior.15,16 Imidazolium-based ILs are the most known IL structure and gemini type it could represent amazing properties because of existing two imidazolium head groups causing them to adsorb more effective at interfaces compared with mono analog structures.16 Further, these ILs are more water-soluble and more stable under high temperature and salinity levels.17 It is noteworthy, although ILs have been successfully examined for the crude oil producing, transporting and refining at lab scale, they have not been investigated as much as need in pilot plants and field scales. Thus, in industry, more works are needed in order to address a number of issues like the choice of the IL, the IL/feed ratio and costs.11 Hence, before any reliable judgment on the oil field application of the ILs, it is critically important to design the ILs, not only to tolerate the harsh salinity conditions but also to reduce more significantly the IFT values. Nano-size materials, on the other hand, has been found with excellent thermo-physical and surface/interface properties.18,19 Based on this and in the continuation of our previous works on using ILs in desulfurization of fuels20,21 as well as in IFT reduction of organic/water systems,22-24 an attempt was made here to use a novel nano gemini IL in reducing IFT of crude oil/water. The molecule of the used IL has four-methylene spacer group and eight carbon in alkyl chain, namely [1,1'-(butane-1,4-diyl)bis(3-octyl-1H-imidazol-3-ium) bromide] and briefly as [C8-4-C8im]Br2 (Figure 1). For a precise study, the IL concentration, temperature and pH effects were considered and critical micelle concentration (CMC) was determined. Salinity effect as another important factor, dominant in reservoirs, was investigated. In order to develop an understanding of the corresponding properties of the IL behavior, the experimental data were reproduced with a wellknown adsorption isotherm. Accordingly, the thermodynamic parameters were obtained. This study is regarded as comprehensive by including real operational conditions. “Figure 1” 2. Experimental 2.1. Materials. Crude oil was from the Iranian southern oil field whose specifications and composition are given in Table 1. Salinity study was performed by using NaCl and MgCl2 from Merck and Fluka. For pH adjusting, NaOH or HCl solutions (1.0×10−1 mol dm−3) were utilized. Details of the provenance and mass fraction purity of chemicals including those for IL synthesis are listed in Table 2. Deionized water with the electrical conductivity of 7.0×10−2 μS cm–1 was “Tables 1 and 2”

used for preparation of aqueous solutions.

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2.2. Synthesis and Characterization of the Nano Gemini IL. The nano gemini IL was prepared through a two steps synthesis method25 as illustrated in Scheme 1. Briefly, 1-octylimidazole was prepared through the reaction of imidazole with 1-bromooctane. Then, the 1-octylimidazole product and 1,4-dibromobutane were used as reagents for the preparation of the gemini imidazolium IL, [1,1'-(butane-1,4-diyl)bis(3-octyl-1H-imidazol-3-ium) bromide].26 The melting point of the white solid product was 313 ± 0.5 K. In Supporting Information, 1H NMR and 13C NMR spectra prove the correct structure of the product. The IL purity was confirmed by giving just the IL peaks in the spectra and none for reactants and/or by-products. In a separate exploration, in order to study the morphology of the product, scanning electron microscopy (SEM) images were taken (Figure 2). The gemini IL has a nano-size structure and the size distribution was within 14 37 nm. The structure of the prepared IL was also characterized by X-ray diffraction (XRD). From obtained pattern (Supporting information), it is obvious that the prepared IL has a crystalline structure with diffraction lines at 2θ = 25.9°, 30.0°, 42.8°, 50.7°, 53.1°, 62.1°, 70.4° and 78.4°. Applying Scherrer equation, D = Kλ/(β cosθ), where λ is the X-ray wavelength of Cu kα (1.54 Å), K is the Scherrer constant with a value of 0.9, β is the peak width at half maximum (FWHM) of the peak in radians and θ is the Bragg diffraction angle, disclosed that the IL has particles size between 27.7 and 51.5 nm (Supporting information).27 “Scheme 1” and “Figure 2” For analyzing the size of the IL aggregates in aqueous solutions, dynamic light scattering (DLS) method was utilized. The measurements by this method known as “hydrodynamic diameter” are different from the size, illustrated by SEM images.28 The DLS report for typical IL concentrations of 1.0×10−2 and 4.0×10−1 mol dm−3 in water (less and more than CMC) are presented in Figure 3. The diameters were within (1 - 7) nm and (1.5 - 8) nm for the considered concentrations. With the IL concentration of 4.0×10−1 mol dm−3, a new size range within (250 - 600) nm was appeared, representing aggregates with a high number of monomers. “Figure 3” 2.3. IFT Measurements. The Pendant drop method was used to measure the IFT of crude oil/water system where oil drops were formed at the tip of a stainless-steel needle with 1.628 mm outer diameter, immersed in the aqueous continuous phase. The apparatus (Fars EOR Technol., CAES10) composed of a syringe pump to form drops in a quartz cell containing the continuous phase. 4 ACS Paragon Plus Environment


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The equipment was also equipped with an image processing system for analyzing the drop formation and obtaining IFT from the pendant drop profile, a light source to illuminate media, a CCD color camera (4 megapixels) with a macro zoom lens, panel light and a personal computer to run the image processing software were utilized. In the pendant drop method, the balance between gravity and surface forces of a forming drop determines the relationship between the drop profile and the IFT through:29



 g D 2 H

(1)

where D is the equatorial diameter,  is the difference between aqueous and oil phases density and g is the gravitational constant. H is a parameter depending on the shape factor, S  d D , where d is diameter at distance D from drop bottom. The 1 H corresponding values are obtained from a consistent correlation:30 B 1  4a  B3 S 3  B2 S 2  B1S  B0 H S

(2)

where a and Bi (i = 0 to 4) are considered as empirical constants for S that are reported in the literature.30 Upon obtaining a clear image of forming drop at each second; the image was automatically analyzed and the IFT value was reported. The temperature of the quartz cell was adjusted at 298.2, 308.2, 318.2 and 328.2 K with 0.1 K uncertainty. The density of phases at different temperatures was measured by an oscillating U-tube densitometer with automatic viscosity correction (Anton Paar DMA 4500) with the uncertainty of 1.0×10−4 g cm−3 as well as a density hydrometer with uncertainty of 1.0×10−2 g cm−3. To ensure mechanical equilibrium, the constant low oil flow rate of 2.0 mL h−1 was established by means of the syringe pump. To perform experiments, different aqueous solutions of the gemini IL, from 5.0×10−5 to 4.0×10−1 mol dm−3, were prepared. The required gemini IL and salts were weighted with uncertainty of 1.0×10−1 mg. The NaCl salt concentration was within (5.0×10−1 - 1.5) mol dm−3, MgCl2 within (1.0×10−1 - 1.0) mol dm−3, as well as a middle concentration mixture of them, all with standard deviations less than 4.0×10−6 mol dm−3. The used IL solution could be recycled several times with no considerable loss of efficiency. All the experiments conducted at ambient pressure. Details of measured values are given in the Supporting Information.


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The natural pH of about 6.7 was the case for aqueous solutions unless for investigating pH effect for which different pHs from 2.5 to 9.5 were adjusted using mentioned solutions and by means of a Denver bench-top UB-10 pH meter with the accuracy of ±0.01. The measured equilibrium IFT of the crude oil/pure water by this method was 31.8 mN m−1 at 298.2 K. To validate the measurements, the pure water surface tension, at 298.2 K, was obtained as 71.5 mN m−1, close to the reported value in the literature.31 Further, to check the method, the IFT of crude oil/pure water was measured by the alternative drop volume method,23 showing a close agreement. All tests were at least duplicated to ensure consistency and the IFT measurements uncertainty was estimated about ± 0.1 mN m−1. Finally, experiments for emulsion stability were conducted by means of an ultrasonic bath (SONICA 2400ETH S3, 40 kHz, 305 W) to prepare emulsions of crude oil and aqueous solutions containing the gemini IL.

3. Results and Discussion 3.1. Effect of the IL Concentration. Synthesis and application of a nano gemini IL was the main interest of this work. Figure 4, shows that IFT was drastically decreased with the IL concentration and remained constant above the CMC of about 2.0×10−1 mol dm−3, giving IFT as low as 7.0×10−1 mN m−1. A maximum IFT decrease of 97.8% was therefore attained. This amazing effect is due to the strong amphiphilic nature of the IL molecules. At the interface of crude oil/water, the hydrophobic hydrocarbon chains and spacer tend to orient in the oil phase whereas the charged hydrophilic imidazolium rings remain in the aqueous phase.32 Under this arrangement as schematically presented in Figure 5, the IL molecules find the lowest free energy. Brownian motions, as well, help the gemini IL molecules to more easily migrate toward the interface and reduce the IFT upon their adsorption.33 “Figures 4 and 5” Compared to the results in a previous report,3 concerned on a mono analog IL, [C8mim]Cl, Figure 6 shows that the nano gemini IL gives significantly more IFT reduction for the same crude oil/water system (irrespective of the low temperature difference in the experiments and the kind of anion). Based on simple chain surfactant molecules, the electrostatic repulsion between charged head groups disturbs the easy adsorption at the interface; however, the spacer group decreases the repulsions13 and also provides higher CMC value compared to the mono analog IL. The latter case 6 ACS Paragon Plus Environment


leads to observed viscous solutions under CMC, which could improve displacement efficiency in reservoirs and injection fluid may exhibit sweeping behavior like polymers.34 “Figure 6” 3.2. Performance of the IL under Reservoir Conditions. As shown in Figure 7, temperature causes a decrease in IFT under certain IL concentrations. The maximum decrease was about 15.2% for the lowest IL concentration and temperature effect was not significant by increasing IL concentration. At high IL concentrations (around CMC), the interface becomes occupied with no sensible further adsorption even at high temperatures. The general temperature effect in IFT reduction can be attributed to the following reasons:  The mobility of adsorbing molecules rises with temperature, resulting in the breakdown of iceberg structures surrounding the alkyl chain hydrophobic groups and leading to IL hydrophobicity enhancement.35 Further, induced Brownian motion accelerates the adsorption.  Aqueous phase viscosity decreases as temperature increases, simplifying the IL transport from bulk to the subsurface and easily adsorption at the interface.  The molecular agitation of the phases is improved with temperature which in turn causes attenuation of intermolecular forces at the interface.36 Based on observed temperature effects and molecular stability, the dominant high temperature of reservoirs favors operations with the gemini IL. “Figure 7” Regarding pH effect, previous studies indicate that pH can assist the surfactants adsorption and in turn, alters the system IFT.24,37 Here, a pH range of 2.5 - 9.5 was considered with a typical IL concentration of 2.5×10−2 mol dm−3, corresponding to a middle IFT. With this IL concentration, the natural pH of the IL solution was 6.7 and was changed to specified values by using NaOH or HCl solutions. As illustrated in Figure 8, more IFT reductions are corresponding to higher pHs. It is a sensible case in CEOR where use of alkali solutions in the reservoirs is conventional particularly for high acid number crude oils.24,37 This phenomenon can be explained by the known tendency of hydroxyl ions (OH−) to interface adsorption,38 causing the electrostatic repulsive interaction between the IL molecules to diminish and leading to 34.5% more IFT reduction at pH 9.5 compared to natural pH. “Figure 8”


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The influence of water salinity was investigated by using NaCl and MgCl2 as the most abundant salts in seawaters. This is an important case in operational and economical points of view because of the possible use of seawater and other saline waters for injection in reservoirs.39 These salts are present in the most formation waters within the range 10 - 15 wt%.1 The NaCl concentrations of 5.0×10−1, 1.0 and 1.5 mol dm−3 and MgCl2 of 1.0×10−1, 5.0×10−1 and 1.0 mol dm−3 as well as their mixture of respectively 5.0×10−1 and 1.0 mol dm−3 were examined at 298.2 K and natural pH of 6.7. It must be mentioned that the used salts with corresponding concentrations did not alter much the solutions pH. The results depicted in Figure 9 show a remarkable IFT reduction with the used salts. Hence, the maximum IFT reduction was corresponding to the salts mixture that caused IFT to decrease drastically from 8.1 to 3.2 mN m−1 with the IL concentration of 1.0×10−1 mol dm−3. Higher levels of the IL in the presence of salts give very low IFT values (less than 5.0×10−1 mN m−1), out of the apparatus accuracy. Thus, salt addition provides a synergistic effect on the IFT reduction with the IL. This observation is in contrast to conventional surfactants, making the gemini IL as a distinctive alternative in CEOR dealing with harsh salinity conditions.24 It is also worth noting that salts have usually no effect on the non-ionic surfactants; hence, for the ionic surfactants, an optimum point is usually relevant at a specified salt concentration after which IFT remains constant or presents an ascending variation.40,41 In the presence of salt ions, the repulsion between molecules of the IL is weakened. This repulsion, in turn, compresses the two parallel charge layers surrounding the gemini IL head groups, giving a closer arrangement and easier accumulation of the IL molecules.42 Meanwhile, the presence of salts causes a decrease in the surfactants solubility in aqueous phase due to ‘salting-out effect’;43 therefore, migration toward the interface is assisted. “Figure 9” The comparison shown by Figure 10 indicates that with 5.0×10−1 mol dm−3 salt concentration, the influence of MgCl2 is more than NaCl which is due to the more charge density of Mg2+ ions, leading to stronger salting out effect. It is while, at the high salt concentration of 1.0 mol dm−3, the effect of NaCl is more which seems reasonable due to the significant lower density of these salt solutions under the same molarity (See Supporting Information) based on equation (1). Considering these results, it could be generally suggested that addition of the gemini IL to seawaters can provide a suitable injection fluid for CEOR process. “Figure 10” 8 ACS Paragon Plus Environment


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3.3. Emulsion Stability. Emulsions are considered as a subdivision of one phase in the form of small droplets in another phase.44 For CEOR applicability, surfactants must be able to reduce IFT in aqueous solutions for solubilizing crude oil in the aqueous phase and forming stable emulsions to improve oil recovery.44 Therefore, emulsification activity of the IL with the criterion of emulsification index were considered. For this purpose, equal volumes (1 cm3) of the aqueous phase with typical gemini IL concentration of 5.0×10−2 mol dm−3 and the crude oil were sonicated in a glass vial for 15 min and then allowed to rest (at 298.2 K). The corresponding emulsification index was obtained from the height ratio of the emulsion region to the total liquid (Figure 11).45 The emulsification indices were 57.5% and 56% after one day and after one week, respectively. Thus, the gemini IL forms remarkable levels of crude oil/water emulsions and adequately stable, implying a proper candidate for EOR. “Figure 11” 3.4. Theoretical Considerations. The IFT data corresponding to the IL concentrations below CMC and under certain temperatures were satisfactorily reproduced with the Frumkin adsorption isotherm. This model is based on the Gibbs dividing interface thermodynamic concepts and emphasizes existing interactions between the adsorbed species at the interface.46 The state equation and the adsorption isotherm are as:47

  2RTΓ m,F ln(1   )   2  bF f  C C  C electrolyte 

1

2



 1

(3)

exp  2 

(4)

where     is the difference between the clean and any IFT values, known as the interfacial pressure;   Γ Γ m,F is the layer coverage of interface, R is the ideal gas constant and Γ m,F is the maximum interface excess (adsorption effectiveness). b F and  are respectively the adsorption equilibrium constant (adsorption tendency) and the parameter of van der Waals molecular interaction. The parameter f  is the average activity coefficient of the ions that is close to unity at extremely low concentrations. Further, C and Celectrolyte are respectively the bulk concentrations of surfactant and inorganic electrolyte (if there is any). The ideal behavior of interface-adsorbed species, corresponding to zero  values, changes the Frumkin isotherm to the Langmuir isotherm. For attractive interactions this parameter will be positive, while a repulsive interaction gives negative values.47 Based on the Gibbs dividing interface definition, when the interface has electro 9 ACS Paragon Plus Environment

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neutral combinations, factor 2 is used for the ionic surface active substances dissociation into the relevant cation and anion.47 The experimental data in the absence of salts (due to inconsistent anions of the IL and the salts) were fitted to equations (3 and 4) using the IsoFit software. To achieve the best fit, the parameters were adjusted by giving minimum value of the objective function of:48

C i  i i=1 C exp,i  m  1 m

OF  

(5)

where difference between the experimental and calculated gemini IL concentration is represented by C i  C exp,i  C cal,i and, the difference between interfacial pressure corresponding to the ith point is i    exp,i+1   exp,i-1  2 . Also,  m    m represents the maximum interfacial pressure. In Figure 12, the solid lines represent the curves obtained from Frumkin model. The corresponding OF values are given in Table 3. “Figure 12” The parameters of the Frumkin model are listed in Table 3. As can be seen, both Γ m,F and  values increase with temperature. This variation of Γ m,F is due to improving the thermal mobility of the adsorbed IL and breakdown of water iceberg structures surrounding the twin alkyl chains. Therefore, the large number of gemini IL molecules are easily adsorbed at the interface leading to higher number of adsorbed molecules. The negative  values suggest repulsion between adsorbed ILs due to the positive head group charges. By increasing the IL interface excess, the electrostatic repulsion between the positive charges becomes greater and the magnitude of the interaction parameter increases. On the other hand, b F is declined by increasing temperature. This parameter is the ratio of the rates of adsorbing species to desorbing at the interface and because of the higher adsorbed molecules as well as higher mobility, the adsorption tendency decreases at elevated temperatures. In addition, the minimum interface area occupied by each molecule, Am , can be obtained by:

Am 

1 Γ m, F N Av

(6)



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where N Av is the Avogadro's number. Temperature causes reasonably smaller Am values since the area corresponding to each molecule is reduced when concentration increases at the interface. “Table 3”  The thermodynamic parameters of the standard free energy of adsorption, G ads , entropy, S

, and energy, U , for the gemini IL were calculated at different temperatures. Based on equilibrium constant values, the adsorption standard free energy as well as the micellization, G m , were calculated from:48,49 b ρ   G ads  2RT ln  F   2 

(7)

G m  RT ln CMC

(8)

where ρ    18 is the water molar concentration at a specific temperature. Meanwhile, the relation between the entropy change associated with the adsorption and IFT at permanent pressure is considered by:50

d    Δ S d T  2 RT Γ

dC C

(9)

where Γ represents the interface excess under a specified bulk concentration. Further, at concentrations below CMC, the associate adsorption change in entropy and the associate adsorption energy change are obtained from:50

 γ  S     T  p ,C

(10)

U    T S

(11)

 values for the IL are negative, indicating spontaneous As displayed in Table 4, all G ads

adsorption of the gemini IL molecules at the crude oil/water interface. This indicates the greater freedom of the adsorbed species at the interface. By raising the temperature, the absolute standard free energy show decreasing to some extent. In addition, negative G m values and increasing the magnitude with temperature, indicate spontaneous micelle formations and that due to more breakdown of iceberg structures surrounding the IL hydrophobic part at higher temperatures, easier micelles formation are corresponding. “Table 4” 11 ACS Paragon Plus Environment

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The variation of S versus temperature is illustrated in Figure 13. Different trends are corresponding to the complicate temperature effect on adsorbed species at the interface. When surfactant molecules are adsorbed, two factors have dominant influence: limitation of molecular motion at the interface and the hydrophilic and/or hydrophobic groups dehydration by disrupting structured water molecules around the IL molecules.51 With increasing temperature, these factors compete with each other and gemini IL molecules become ordered or disordered at the interface. Here, when temperature increases at a specified IL concentration, disrupting structured water molecules becomes superior. Therefore, for the most gemini IL concentrations, entropy variation raises with temperature until nearby 303.2 K. On the other hand, thermal agitation causes more dehydration of the IL hydrophobic groups at the interface, causing higher van der Waals attraction between hydrophobic groups and leading greater monolayer conformational ordering, corresponding to lower entropy variation.52 Moreover, by increasing the IL concentration, the associated entropy change decreases at a specified temperature. It is since the adsorbed molecules give higher surface density and reduce the adsorbed species mobility. For adsorption energy change, a similar variation trend with temperature is appropriate (Figure 14). The adsorption energy growing is relevant to raising the used energy for neutralizing repulsive interactions between adsorbed species.50 The maximum energy change appears reasonably at about 303.2 K and for the highest used IL concentration. “Figures 13 and 14”

4. Conclusions The feasibility of using a novel nano gemini imidazolium IL surfactant, namely [1,1'-(butane1,4-diyl)bis(3-octyl-1H-imidazol-3-ium) bromide] for reducing the IFT of crude oil/water was studied. The synthesized gemini IL was characterized and a nano-size structure was revealed. The used IL gives low IFT values for the system owing to its unique molecular structure. Temperature assists this phenomenon at low IL concentrations whereas no sensible change was attained at concentrations close to CMC. The emulsification index showed that the gemini IL could form stable emulsions, useful for CEOR applicability. The used IL was much more effective in salty waters with very close to seawaters content which is important in utilizing seawaters for enhanced oil recovery. This abnormal salts effect was



attributed to the fact that salts can neutralize the positive charge of the IL head groups and facile the adsorption at the interface. In this regard, alkaline pHs provide more IFT reduction. To reproduce the experimental data of salt free cases, the Frumkin adsorption isotherm was applied consistently. Accordingly, the maximum interface excess and the adsorbed molecular repulsion were increased with temperature. However, an inverse variation was relevant to the adsorption tendency. The adsorption thermodynamic parameters were determined, confirming that the IL adsorption and micelle formation were spontaneous due to freedom of the hydrophobic part of the gemini IL molecules. Associated entropy and adsorption energy show different variation trends with the IL concentration and temperature. In summary, it can be declared that the used nano gemini imidazolium IL represents a high potential for lowering crude oil/water IFT and that salt addition provides a synergistic effect in IFT reduction. ■ AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] (J. Saien) ■ Supporting Information are given in the file …

Author Contributions The manuscript was written through the contributions of all authors. All authors have given approval to the final version of the manuscript.

Notes The authors declare no competing financial interest. ■ ACKNOWLEDGMENTS The authors wish to acknowledge the Iran National Science Foundation (INSF) for financial support of this work.


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(43) Eftekhardadkhah, M.; Øye, G. Correlations Between Crude Oil Composition and Produced Water Quality: A Multivariate Analysis Approach. Ind. Eng. Chem. Res. 2013, 52, 17315-17321. (44) Yuan, C. D.; Pu, W. F.; Wang, X. C.; Sun, L.; Zhang, Y. C.; Cheng, S. Effects of Interfacial Tension, Emulsification, and Surfactant Concentration on Oil Recovery in Surfactant Flooding Process for High Temperature and High Salinity Reservoirs. Energy Fuels 2015, 29, 6165-6176. (45) Amani, H. Evaluation of Biosurfactants and Surfactants for Crude Oil Contaminated Sand Washing. Petrol. Sci. Technol. 2015, 33, 510-519. (46) Birdi, K. Surface and Colloid Chemistry: Principles and Applications, CRC press 2009. (47) Stubenrauch, C.; Fainerman, V.; Aksenenko, E.; Miller, R. Adsorption Behavior and Dilational Rheology of the Cationic Alkyl Trimethylammonium Bromides at the Water/Air Interface. J. Phys. Chem. B 2005, 109, 1505-1509. (48) Möbius, D.; Miller, R.; Fainerman, V. B. Surfactants: Chemistry, Interfacial Properties, Applications, Elsevier 2001. (49) Liu, G.; Gu, D.; Liu, H.; Ding, W.; Luan, H.; Lou, Y. Thermodynamic Properties of Micellization of Sulfobetaine-Type Zwitterionic Gemini Surfactants in Aqueous Solutions–A Free Energy Perturbation Study. J. Colloid Interface Sci. 2012, 375, 148-153. (50) Motomura, K.; Iwanaga, S. I.; Yamanaka, M.; Aratono, M.; Matuura, R. Thermodynamic Studies on Adsorption at Interaces: V. Adsorption from Micellar Solution. J. Colloid Interface Sci. 1982, 86, 151157. (51) Asadabadi, S.; Saien, J.; Khakizadeh, V. Interface Adsorption and Micelle Formation of Ionic Liquid 1-Hexyl-3-methylimidazolium Chloride in the Toluene+ Water System. J. Chem. Thermodyn. 2013, 62, 92-97. (52) Matsubara, H.; Onohara, A.; Imai, Y.; Shimamoto, K.; Takiue, T.; Aratono, M. Effect of Temperature and Counterion on Adsorption of Imidazolium Ionic Liquids at Air–Water Interface. Colloids Surf. A Physicochem. Eng. Asp. 2010, 370, 113-119.


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Tables Table 1. Main specifications and compositions of the used crude oil. Specification/Composition Value Density at 20 °C (g cm–3) 0.915 ° API 20.7 Viscosity at 70 °F (cP) 55 Viscosity at 100 °F (cP) 44 Kinematic viscosity at 70 °F (cSt) 60 Water content (wt%) Nil Salt content (lbs per 1000 bbls) 4 Sulphur content (wt%) 1.63 Flash point (°F) 70 Pour point (°F) 10 Reid vapor pressure (psi) 12.1 Acidity number (mg KOH/g) 0.09 Saturated (wt%) 54.0 Aromatic (wt%) 22.3 Resin (wt%) 6.7 Asphalt (wt%) 7.7 Loss at 200 °C (wt%) 9.3

Table 2. Provenance and mass fraction purity of the used chemicals. Chemical Provenance Mass fraction purity Imidazole Alfa Aesar 0.99 1-Bromooctane Merck > 0.98 1,4-Dibromobutane Alfa Aesar 0.99 Hydrochloric Acid Merck 0.37 Sodium Hydroxide Merck > 0.97 Sodium Chloride Merck > 0.995 Magnesium Chloride Fluka > 0.98

Table 3. Molar concentration of water equilibrium adsorption constant,

ρ  , maximum interface excess, Γ m,F , interaction parameter,  , Frumkin

b F , minimum area occupied by a molecule, Am , and objective function, OF

(Equation 5), for adsorption of the nano gemini IL at different temperatures and under natural pH.

ρ  ×103

Γ m,F ×106

298.2

(mol cm−3) 55.4

(mol m−2) 3.3

308.2

55.2

318.2 328.2

T (K)

bF

Am ×1036

−5.0

(dm3 mol−1) 481.1

(m2) 3.5

4.2

−6.0

213.6

2.8

12.3

54.9

5.3

−8.5

173.9

2.2

15.6

54.5

6.7

−10.0

103.1

1.8

12.4




OF×102 14.7


Table 4. Standard free energy of adsorption, ΔG ads and free energy of micellization G m of the nano gemini IL at different temperatures and under natural pH.

298.2

(kJ mol ) −47.1

G m (kJ mol−1) −3.9

308.2

−44.5

−4.1

318.2

−44.8

−4.3

328.2

−43.3

−4.4

T (K)

ΔG ads −1

Schemes

Scheme 1. A two steps synthetic route to synthesize the gemini imidazolium IL.


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FIGURES

Figure 1. The chemical structures of [1,1'-(butane-1,4-diyl)bis(3-octyl-1H-imidazol-3-ium) bromide].

Figure 2. SEM images of the prepared gemini imidazolium IL.



50 0.001 mol dmˉ³ gemini IL 0.4 mol dmˉ³ gemini IL 40

Intensity (%)

IL molecules 30

Micelle aggregate

20

10

0 0.1

1

10

Size (nm)

100

1000

10000

Figure 3. DLS analysis for different concentration of the gemini IL solutions under natural pH and temperature of 298.2 K.

30

298.2 K 308.2 K 318.2 K

25

328.2 K

IFT (mN m−1)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 28

20

15

10

5

0 0.00001

0.0001

0.001

0.01

0.1

Gemini IL concentration (mol dm−3)

Figure 4. The effect of gemini IL concentrations on the IFT of crude oil/water at natural pH.


1

Page 23 of 28

Figure 5. A schematic presentation of the nano gemini IL orientation at the interface of crude oil/water system.

40

35

[C₈mim]Cl [C₈-4-C₈im]Br₂

30

IFT (mN m−1)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


25

20

15

10

5

0 0.00001

0.0001

0.001

0.01

0.1

1

IL concentration (mol dm−3)

Figure 6. Comparison between the effects of the nano gemini IL at 298.2 K and a mono analog IL3 at 295 K and under natural pH.



no IL 2.5 . 10 ⁻⁴ mol dm⁻ᶟ 5.0 . 10 ⁻ᶟ mol dm⁻ᶟ 2.5 . 10 ⁻² mol dm⁻ᶟ 1.0 . 10 ⁻¹ mol dm⁻ᶟ 4.0 . 10 ⁻¹ mol dm⁻ᶟ

35

30

5.0 . 10 ⁻⁵ mol dm⁻ᶟ 1.0 . 10 ⁻ᶟ mol dm⁻ᶟ 1.0 . 10 ⁻² mol dm⁻ᶟ 5.0 . 10 ⁻² mol dm⁻ᶟ 2.0 . 10 ⁻¹ mol dm⁻ᶟ

IFT (mN m−1)

25

20

15

10

5

0 295

300

305

310

315

320

325

330

T (K)

Fig. 7. IFT variation as a function of temperature in the presence of different gemini IL concentration and under natural pH. 26

24

22

IFT (mN m−1)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 28

20

18

16

14

12

10 2

3

4

5

6

7

8

9

10

pH

Figure 8. IFT versus pH under typical gemini IL concentration of 2.5×10−2 mol dm−3 at 298.2 K.


Page 25 of 28

30 Salt free 0.1 mol dm⁻ᶟ MgCl₂ 0.5 mol dm⁻ᶟ NaCl

25

1.0 mol dm⁻ᶟ MgCl₂

1.5 mol dm⁻ᶟ NaCl 0.5 mol dm⁻ᶟ MgCl₂ and 1.0 mol dm⁻ᶟ NaCl

IFT (mN m−1)

20

15

10

5

0 0.001

0.01

0.1

Gemini IL concentration (mol

dm−3)

1

Figure 9. IFT versus gemini IL concentration in the presence of salts at 298.2 K and under natural pH.

30

Salt free 0.5 mol dm⁻ᶟ NaCl 0.5 mol dm⁻ᶟ MgCl₂

25

1.0 mol dm⁻ᶟ NaCl 1.0 mol dm⁻ᶟ MgCl₂ 0.5 mol dm⁻ᶟ MgCl₂ and 1.0 mol dm⁻ᶟ NaCl

20

IFT (mN m−1)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


15

10

5

0 0.001

0.025


0.1

dm−3)

Figure 10. IFT at different gemini IL concentrations in the presence of salts at 298.2 K and under natural pH.



crude oil phase emulsion

aqueous phase

after one day

after one week

Figure 11. Phase behavior of crude oil/water solutions with typical gemini IL concentration of 5.0×10−2 mol dm−3 at 298.2 K and under natural pH.

30 298.2 K 308.2 K

25

318.2 K 328.2 K 20

Π (mN m−1)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 28

15

10

5

0 0.00001

0.0001

0.001

0.01


0.1

dm−3)

Figure 12. Curves from Frumkin model at different temperatures and under natural pH.


1

Page 27 of 28

0.25

no IL 0.00005 mol dm⁻ᶟ 0.00025 0.001 0.005 0.01 0.025 0.05 0.1

∆S·103 (J K−1 m−2 )

0.20

0.15

0.10

0.05

0.00 298.2

303.2

308.2

313.2

318.2

323.2

328.2

T (K)

Figure 13. Entropy change as a function of temperature for different gemini IL concentrations at natural pH.

100

no IL 0.00005 mol dm⁻ᶟ 0.00025 0.001 0.005 0.01 0.025 0.05 0.1

80

∆U ·103 (J m−2 )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


60

40

20

0 298.2

303.2

308.2

313.2

318.2

323.2

328.2

T (K)

Figure 14. Energy change as a function of temperature for different gemini IL concentrations under natural pH.



Graphic for the manuscript

Research highlights 

The surfactant type gemini imidazolium IL was satisfactorily synthesized and revealed a nano-size structure.



The IL provided strong crude oil/water IFT reduction for the aim of CEOR.



The salts abnormal effects caused extremely IFT decrease by using the IL, in contrary to conventional surfactants.



Stable emulsions of crude oil/water appeared in the presence of the IL.



The Frumkin adsorption isotherm was consistently applied to the data and the thermodynamic parameters were obtained.


Page 28 of 28

A Systematic investigation of a surfactant type nano gemini ionic liquid

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