Application of New Ammonium-Based Ionic Liquids for Dehydration of Crude Oil Emulsions

Crude oil emulsions are prevalent in the petroleum industries due to diferent natural emulsifers in crude oil. In addition, adding amphiphilic compounds for enhanced oil recovery at high temperatures and pressure under extreme shear stress conditions improved the stability of these emulsions. However, these emulsions are not desirable because they cause diferent operational problems. Herein, this work aims to synthesize and characterize two novel ionic liquids (ILs) and apply them to the dehydration of water-in-crude oil (W/O) emulsions. For that, tetraethylene glycol (TEG) was reacted with thionyl chloride (TC), yielding dialkyl halide (TEC). After that, TEC was reacted with 4-hexylaniline (HA) or 4-tetradecylaniline (TA) in the presence of sodium carbonate, obtaining the amines TC-HA and TC-TA, respectively. Finally, TC-HA and TC-TA were reacted with acetic acid, yielding the corresponding ionic liquids, THA-IL and TTA-IL. Chemical structure, surface tension (ST), interfacial tension (IFT), thermal stability, and micelle size were investigated using various techniques. Te conventional bottle test was used to evaluate the performance of these ILs for dehydration W/O emulsion at diferent crude oil/brine ratios (ranging from 90/10 to 50/50). Te results indicated that the dehydration performance (DP) increased with an increase in IL concentration. In addition, DP improved with increased water contents, reaching 100% for THA-IL and 80% for TTA-IL, respectively, at a crude oil/brine ratio of 50/50. Furthermore, TTA-IL showed higher DP and separated more clear water than THA-IL, which could be linked to its higher ability to reduce IFTdue to a longer alkyl chain than THA-IL. Te results showed that the synthesized ILs could serve as demulsifers in the petroleum industry.


Introduction
Despite eforts being made to search for alternative energy sources for crude oil, such as solar energy, hydrogen resulting from splitting water, and wind energy, crude oil still represents one of the most signifcant global energy sources. In addition, crude oil is an essential resource for various petrochemical industries. Oil demand has continuously climbed during the previous 20 years, rising from 60 to 84 million barrels per day [1]. In the early years of the 21st century, global crude oil demand grew by 3.4% yearly due to the explosive expansion of consumption and industry in emerging countries such as China and India [2]. As conventional oil and gas resources have declined, unconventional resources have been promoted, developed, and utilized, particularly heavy oil and oil sands [3]. Heavy crude oil represents half of the world's oil reserves [4]. However, heavy crude oil production transportation, storage, and refning are associated with many problems. It commonly contains higher amounts of natural emulsifers such as asphaltene, resin, naphthenic acids, and solid particles than light and medium crude oils. Tese components facilitate the formation of very stable emulsions with brine [5][6][7]. Tese emulsions increase crude oil viscosity and cause corrosion in various pieces of equipment such as pipelines, pumps, and tanks. Furthermore, the ions in these emulsions poison downstream catalysts [8,9]. Terefore, dehydration of these emulsions is crucial to avoid these issues. Various methods have been applied to dehydrate crude oil emulsions, including chemical, physical/mechanical, and biological [10,11]. However, using chemicals is the most applicable method due to its low cost and short dehydration time [12,13]. Surface active agents are the most common chemicals used to dehydrate crude oil emulsions. However, they have limitations, such as limited solubility under harsh conditions, e.g., high salinity, high temperature, and toxicity [14][15][16].
Over the past few years, ionic liquids (ILs) have received much attention for dehydrating crude oil emulsions because of their unique properties [12,17]. Due to their ionic nature and organic components, they can work even in harsh conditions where traditional chemicals cannot function [18,19]. In addition, they can dissolve in several organic and organic solvents [20]. Te performance of ILs to dehydrate crude oil emulsion depends on the choice of the appropriate cations and anions. IL performance increases as they migrate across water/oil interfaces and reduce IFT without aggregation [21,22].
For the synthesis of ILs in the current work, frst, tetraethylene glycol (TEG) was reacted with thionyl chloride (TC), producing dialkyl halide (TEC). Following this, TEC was reacted with amines, hexylaniline (HA), or tetradecylaniline (TA), obtaining amines, TC-HA, and TC-TA, respectively. Next, TC-HA and TC-TA were quaternized with acetic acid, yielding the corresponding ionic liquids, THA-IL and TTA-IL. Te yielded ILs were characterized using diferent techniques. Furthermore, the performance of these ILs in dehydration water-in-crude oil emulsions was investigated.
Te novelty of this work is that low-cost raw materials were used to synthesize two new ammonium-based ILs under mild preparation conditions through a short route, which reduced the production cost of the obtained demulsifers when compared with conventional demulsifers such as poly (propylene -b-ethylene oxide). Using synthesized ILs as demulsifers for crude oil emulsion, dehydration will signifcantly solve crude oil emulsion problems in the petroleum industries.

Characterization.
Fourier-transform infrared (FTIR) and nuclear magnetic resonance spectroscopies were employed to verify THA-IL and TTA-IL chemical structures. Te pendant drop technique was used to investigate the surface tension (ST) and interfacial tension (IFT) of THA-IL and TTA-IL at air/water and oil/water interfaces. Termal gravimetric analysis was conducted to investigate THA-IL and TTA-IL thermal stability. Te relative solubility number (RSN) was used to evaluate the solubility properties of THA-IL and TEC-AP as follows: IL (1 g) was dissolved in 30 mL of dioxane: toluene mixture (96 : 4 vol.%). Te obtained solution was treated with double distilled water until the appearance of continual turbidity; at this point, the volume of consumed water in mL equals the RSN. Dynamic light scattering (DLS) was utilized for measuring the micelle size (MS) and polydispersity index (PDI).

Dehydration of W-HCO Emulsions.
Te dehydration of W-HCO emulsions was tested using the conventional bottle test method as follows: the freshly prepared emulsions were transferred to quick-ft cylinders (25 mL), injected with a suitable dose of IL solution (500 mg dissolved in 2 mL of xylene/ethanol volumetric ratio 75/25) via a micropipette, closed, shaken 100 times on an oscillating shaker, and placed in a hot water bath (60°C). Te following equation was used for dehydration performance (DP%) calculation: where DW is a volume of dehydrated water and EW is a volume of emulsifed water.

Synthesis of THA-IL and TTA-IL.
An excess amount of TC was added to TEG (10 g, 51.49 mmol.) gradually at 30°C for 1 h, followed by refux for 4 h. Ten, the excess amount of TC was evaporated under reduced pressure to produce dialkyl chloride (TEC). Following this, a mixture of TEC (28.2 mmol.) and Na 2 CO 3 (1.5 g) with HA or TA (28.2 mmol.) was dissolved in 20 mL of dimethylformamide and stirred at ambient temperature for 5 h. Dimethylformamide was evaporated using a rotary evaporator, and the mixture was dissolved in 2-propanol. Te produced solution was fltered, followed by the evaporation of 2propanol, yielding the corresponding amines, TC-HA and TC-TA. Ionic liquids, THA-IL and TTA-IL, were obtained from reacting amines, TC-HA and TC-TA, respectively, with a stoichiometric ratio of acetic acid. Scheme 1 presents the synthesis route for THA-IL and TTA-IL. A schematic illustration of the synthesis, characterization, and application of THA-IL and TTA-IL in the dehydration of W-HCO emulsions is presented in Figure 1.  [24]. In contrast, the stretching absorption bands of saturated aliphatic C-H appeared at around 2925 cm −1 and 2850 cm −1 [25]. Te stretching bands of the aromatic double band (C�C) occurred between 1620 cm −1 and 1500 cm −1 [26]. Te bending absorption band of aliphatic C-H was observed at 1465 cm −1 . Te stretching bands of C-O-C were noticed at around 1124 cm −1 [27]. In 1 H-NMR spectra (Figures 3(a) and 3(b)), the protons of the alkyl chain were observed between 0.75 and 2.6 ppm, as indicated in the fgure. Te methyl protons of CH 3 COO − were noticed at 1.85 ppm [28], while the protons of TEC were noticed at 3.4 ppm and 3.65 ppm [29]. Te proton of aromatic rings resonated at 7.05 ppm and 7.25 ppm [30], whereas the protons of quaternized amine appeared at 7.85 ppm [31].

Termal Stability of THA-IL and TTA-IL.
Te thermal stability of THA-IL and TTA-IL was evaluated using TGA, as shown in Figure 4. Te decomposition of THA-IL and TTA-IL seems similar, which could be due to their similar chemical structure. Te decomposition up to 150°C is caused by the loss of physisorbed water [32]. Te primary decomposition for both ILs occurred between 150 and 450°C, which could be referred to as the degradation of the alkyl chains and oxyethylene units. Te slight increase in thermal stability of THA-IL can be attributed to its structure containing shorter alkyl chains than TTA-IL [33].

Surface Activity of THA-IL and TTA-IL.
Te surface activity is an essential parameter for demulsifer selection, where its molecules can migrate through a continuous phase, reaching the crude oil/brine interface and replacing the naturally occurring rigid flm. Tis replacement facilitates the coagulation of water droplets, leading to emulsion dehydration [7,34,35]. A pendant drop technique was used to measure the ST and IFT of THA-IL and TTA-IL at air/ water and oil/water interfaces. Tis technique is one of the primary and most feasible methods for measuring IFT [36]. Figure 5 shows ST against the natural logarithm of THA-IL and TTA-IL concentrations. ST decreases as concentrations increase, reaching critical micelle concentration (CMC). After that, ST remains constant with increasing IL concentrations, indicating micelle formation. THA-IL and TTA-IL surface activity parameters are shown in Table 1. Te surface excess concentration (Γ max ) and the minimum surface area occupied per molecule are used to indicate surface-active compounds' behavior. Gibbs adsorption isotherm equations were used to calculate these parameters: where R is the general gas constant, T is the measurement temperature in Kelvin, ((−zc)/(zlnc)) T is the straight line slope in Figure 5, and N is Avogadro's constant. Te lower CMC value of TTA-IL shows its lower solubility in water than THA-IL, which could be ascribed to its chemical structure, where it has longer alkyl chains than THA-IL [14,34]. Te higher Γ max value and the lower A min value of TTA-IL confrm its greater tendency to self-assemble at the air/water interface than in bulk aqueous solution. Tese data also indicated that TTA-IL molecules could pack themselves tighter than THA-IL molecules [37,38].   [40]. Furthermore, a decrease in the MS value of THA-IL indicates its tighter packing than in TTA-IL.
However, nonionic surfactants are commonly used as additives to reduce IFT; their performance is afected signifcantly under harsh conditions, e.g., high salinity and high pressure [28,41]. Te synthesized ILs can act as nonionic surfactants due to the presence of oxyethylene units and alkyl chains. Moreover, these ILs can work even under harsh conditions due to their ionic nature. Te IL ions can neutralize salts' ions, leading to their molecule accumulation at the oil/water interface, decreasing IFT [22]. In this respect, the IFT at the crude oil/brine interface was measured, as presented in Table 2. THA-IL and TTA-IL showed efcient performance in reducing IFT, where their performance increased as their concentrations increased. THA-IL and TTA-IL reduced IFT at this interface from 33.5 mN//M to 4.2 mN//M and 3.6 mN//M at 1000 ppm, respectively. Te data indicated that TTA-IL showed higher relative IFT reduction performance, which is due to a longer alkyl chain than that of THA-IL, where increasing the alkyl chain length improves the accumulation of IL molecules at the crude oil/ brine interface, thus reducing IFT [42].

Dehydration Performance of THA-IL and TTA-IL.
However, poly (propylene -b-ethylene oxide) copolymers are one of the most applied demulsifers for crude oil dehydration [43]; they have some drawbacks, e.g., high production cost and low performance under harsh conditions [44]. Tis work focused on synthesizing two novel ILs under mild synthesis conditions through a short route. Teir dehydration performance was evaluated using the conventional bottle test at 60°C, as reported in the Experimental section. Te type of prepared emulsion was confrmed using the drop dilution method. Te dispersion of all prepared emulsions in low polar organic solvents, e.g., toluene and chloroform, with no dispersion in water, confrmed the formation of water-in-oil (W/O) emulsions. Te stability of the prepared emulsions was tested by dealing with the blank samples at the same sample condition except for the addition of IL. Te blank samples were placed in a hot water bath (60°C). Tese samples showed no separation for a couple of weeks, indicating the stability of the prepared emulsions. Figure 7(a) illustrates the microscopy photo of blank emulsion droplets after two weeks with an average diameter of 2 µ, indicating these emulsions' stability. Table 3 shows the dehydration performance (DP) of THA-IL and TTA-IL and dehydration time (DT) for various W/O emulsion ratios at 60°C. Te data show that the DP increased as the THA-IL and TTA-IL concentrations increased. Moreover, the DT decreased as the concentration increased. Figures 8(a)-8(c) display the DP of TTA-IL at diferent concentrations versus DT. Te data showed increased DP and DT as the crude oil ratio decreased. Increasing the IL concentration in W-HCO emulsion enhances the number of its molecules adsorbed at a crude oil/brine interface, weakening and rupturing the asphaltene and resin natural flm, thus facilitating water droplet coalescence. 47           Journal of Chemistry However, THA-IL and TTA-IL exhibited high DP; they take long dehydration time compared to conventional demulsifers, which could be linked to their ionic nature, where their presence in ionic form obstructs their difusion in a continuous phase (crude oil) [12].
Due to an environmental issue, selecting an efective demulsifer for dehydrating clean water is essential when the obtained water is disposed of in the environment [12]. Figures 9(a) and 9(b) show optical images of dehydrated water using THA-IL and TTA-IL in diferent concentrations at a crude oil/brine ratio 50/50. As depicted in Figure, THA-IL and TTA-IL can dehydrate clean water. However, TTA-IL succeeded in dehydrating more clean water than THA-IL, which may be due to its higher ability for IFT reduction than THA-IL due to the presence of a longer alkyl chain than that of THA-IL [14]. Tese results suggest that TTA-IL can be efectively applied to dehydrate clean water in the petroleum industry.

Dehydration Mechanism.
Te dehydration mechanism of crude oil emulsions using ILs occurs via two main steps: difusion of IL in the continuous phase followed by adsorption of IL molecules at the oil/water interface [45,46]. In

Journal of Chemistry
W/O emulsions, the difusion of IL in crude oil as a continuous phase takes a long time due to the ionic nature of ILs obstructing their dispersion in crude oil. Te number of molecules adsorbing at the crude oil/brine interface increases as IL concentrations increase. Te adsorption of these IL molecules at this interface occurs due to their orientation, where the hydrophilic part is oriented toward brine. In contrast, the lipophilic part is oriented toward crude oil. As a result, the hydrophilic and hydrophobic parts interact with crude oil components and water molecules via diferent interactions. Tese interactions include hydrogen bonding between oxyethylene units in IL and those in natural asphaltene and resin flms. In addition, these interactions include Van der Waals and π-π stacking between alkyl chains and phenyl rings of ILs and corresponding in asphaltene rigid flms [47]. Tese interactions neutralize the imbalanced forces between water and crude oil phases and result in IFT reduction (Table 2), thus facilitating asphaltene interfacial flm rupture and water droplet coalescence. Furthermore, the interaction of IL ions with the opposite salt ions (in the brine) reduces the repulsion of IL molecules at the crude oil/brine interface, and thus, it facilitates IL molecule accumulation at this interface [22]. Such interactions reduce IFTand facilitate IL molecules' penetration into the asphaltene rigid flm. When IL molecules penetrate this rigid flm, they change their chemical properties, disrupting and softening it and encouraging its replacement. Te replacement of this flm destabilizes the emulsion droplets, allowing water droplet coalescence. Figures 7(b) and 7(c) show microscopic photos of an emulsion containing TTA-IL 500 ppm after 2 and 3 hrs. Te fgure illustrates how the emulsion droplet size increased over time due to the coalescence of tiny water droplets into a larger one.

Conclusion
Two novel ILs were synthesized and applied to W/O emulsions dehydration. First, TEG was converted to dialkyl halide (TEC) using TC. Following this, TEC was reacted with HA or TA to obtain the corresponding amines, TC-HA and TC-TA. Next, ILs, THA-IL and TTA-IL, were obtained by reacting TC-HA or TC-TA with a stoichiometric ratio of acetic acid. Ten, the synthesized ILs, THA-IL and TTA-IL, were characterized using FTIR, 1 H-NMR, TGA, and DLS. For crude oil emulsion dehydration, surface activity is crucial. Te surface activity parameter showed that THA-IL and TTA-IL exhibited efcient ST and IFT reductions. Moreover, TTA-IL showed higher performance than THA-IL, possibly due to longer alkyl chains of TTA-IL than those of THA-IL.
Tanks to the surface activity of THA-IL and TTA-IL, their performance in the dehydration of W/O emulsions was investigated. Both ILs showed signifcant performance in crude oil emulsion dehydration. Teir performance improved with concentration. Furthermore, TTA-IL displayed higher DP and shorter DT than THA-IL, possibly due to the longer alkyl chains of TTA-IL that increase difusion into a continuous phase (crude oil). Te frst step in dehydration involves IL difusion, followed by adsorption at the oil/water interface. Due to their ionic nature, IL difusion in crude oil can take a long time. However, alkyl chains and aromatic rings in synthesized ILs facilitate their difusion in crude oil. Te adsorption of THA-IL and TTA-IL at the oil/water interface occurs via diferent interactions, including hydrogen bonding, van der Waals, π-π stacking, and electrostatic interactions. Tese interactions weaken the asphaltene rigid flm and facilitate its replacement allowing water droplet coalescence.

Data Availability
All data were included in the manuscript.

Conflicts of Interest
Te authors declare that they have no conficts of interest.