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Article

The Synthesis and Application of Novel, Star-Shaped Surfactants for the Destabilization of Water in Arabian Heavy Crude Oil Emulsions

by
Abdelrahman O. Ezzat
1,*,
Hamad A. Al-Lohedan
1,
Mohammed Yousef Albarqan
2,
Meshary Abdullah Toraba
2 and
Noorah A. Faqihi
1
1
Surfactants Research Chair, Department of Chemistry, College of Sciences, King Saud University, Riyadh 11451, Saudi Arabia
2
Institute of Refining and Petrochemical Technologies, King Abdulaziz City for Science and Technology, Riyadh 11442, Saudi Arabia
*
Author to whom correspondence should be addressed.
Processes 2023, 11(11), 3162; https://doi.org/10.3390/pr11113162
Submission received: 8 October 2023 / Revised: 26 October 2023 / Accepted: 1 November 2023 / Published: 6 November 2023
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Abstract

:
Water in heavy crude oil (W/O) emulsions, which are stubborn mixtures of immiscible heavy crude oil and brine, are a ubiquitous challenge in the petroleum industry. They cause serious corrosion problems, increase the viscosity of petroleum and make the production cost very high. This phenomenon appears during the production of crude oil and should be treated to maximize the overall profitability of oil production and meet transportation requirement. Surfactants are some of the most useful demulsifiers and play a pivotal role in breaking brine/oil emulsions. Herein, we aimed to combine ethyleneamine units and ethyleneoxide units to prepare star-shaped surfactants and test the effect of this combination on the demulsification performance. First, diethylenetriamine reacted with glycidyl 4-nonyl ether (GNE) through an epoxy ring opening to prepare trinonyl phenoxy diethylenetriamine (TNDT). Then, ethylene oxide units were introduced via the interaction of hydroxyl groups with 2-(2-chloroethoxy)ethanol to form ethoxylated trinonyl phenoxy diethylenetriamine (ETNDT). The chemical structures of the surfactants were verified via FTIR and NMR characteristic techniques. The surfactants were applied as demulsifiers for W/O emulsions. It was found that the introduction of the ethyleneoxide units enhanced the solubility of the water and the demulsification performance of the prepared surfactants. The demulsification efficiency was enhanced via ethoxylation and reached 100% for ETNDT for most of the W/O emulsions.

1. Introduction

One of the most significant challenges during the production, lifting and transportation of oil is the high viscosity of crude oil, especially heavy crude oil [1]. This high viscosity restricts the production rate and increases the energy requirement and, as a result, increases the total production cost [2]. This problem mainly stems from the presence of asphaltene as a natural surfactant in the oil’s composition and the injection of brine, surfactants and polymers in order to enhance the production process [3]. When water comes into contact with oil in the presence of these surface-active agents, different types of emulsions can be formed, such as water in oil (W/O), oil in water (O/W), water in oil in water (W/O/W) and oil in water in oil (O/W/O) [4,5,6,7]. These kinds of emulsions not only increase the production cost but also cause operation obstacles, including poisoning catalysts, pipeline corrosion and the growth of microorganisms [8,9].
Due to the deleterious effects of water/oil emulsions, from the economic and operational perspectives, these emulsions should be broken down to purify crude oil from water contamination [10]. Emulsions can be broken down using commercial methods, including heating, centrifuging, ultrasonication, electrical treatment and chemical treatment [11]. The combination of these methods can optimize the results of the separation process [12]. One of the most common methods for separating water from oil in an emulsion is using a combination of heating, either traditional or microwave, and chemical surface-active compounds which contain both hydrophilic and hydrophobic moieties [13].
Oligomeric surfactants have attracted researchers’ attention as they have unique characteristics [14]. The simplest oligomeric surfactants are gemini surfactants, which have two hydrophilic and two hydrophobic groups in their structure [15]. Another class of oligomeric surfactants are trimeric surfactants, which have superior surface properties and a wide range of applications compared with gemini surfactants [16,17]. Star-shaped surfactants are a class of trimeric surfactants that have three hydrophilic groups and three hydrophobic chains [18,19]. Y. Bi et al. [20] prepared two star-shaped quaternary ammonium surfactants from a melamine core and a hydrophilic quaternary ammonium sub-core. They applied these surfactants for the demulsification of W/O emulsions. They found that star-shaped surfactants have greater water-separation efficiency than traditional linear cationic surfactants.
E. El-Sharaky et al. [21] prepared star-shaped nonionic polymeric surfactants based on maleic anhydride, triethanolamine, polyethylene oxide (EO), polypropylene oxide (PO) and silicone polyether to separate water from crude oil. Their research findings indicated that the star-shaped silicon polymeric surfactants had a higher efficiency as demulsifiers than EO/PO copolymers.
In our previous work [22], ethyleneimine-based surfactants were prepared from the reaction of an LMW polyethyleneimine series with glycidyl 4-nonyl ether (GNE) and applied as demulsifiers for W/O emulsions. The prepared materials broke emulsions quickly, but their single drawback was their low demulsification efficiency for emulsions with high water contents. Surfactants with ethylene oxide units as hydrophilic units were synthesized and applied as demulsifiers for emulsions with high percentages of water and demonstrated high levels of efficiency, but the separation time was long [23,24].
The aim of the present work is to combine ethyleneamine units and ethyleneoxide units to prepare surfactants with high and fast demulsification efficiencies. First, diethylenetriamine was reacted with glycidyl 4-nonyl ether (GNE); then, ethylene oxide units were introduced via an interaction with 2-(2-chloroethoxy)ethanol. The chemical structures of the surfactants were verified using FTIR and NMR, and their surface and interfacial characteristics were studied. The star-like nonionic surfactants were applied as efficient and fast demulsifiers for W/O emulsions.

2. Experimental

2.1. Materials and Characterization

Diethylene triamene (DETA), 99% and glycidyl 4-nonylphenyl ether (GNPE), both technical grade (Aldrich company, Steinheim, Germany), ethylene glycol nono-2-chloroethyl ether, 98% (TCI company, Zwijindrecht, Belgium), and xylene, 99.5% (Sinpharm Chemical Reagent Corporation, Shanghai, China), were acquired. ARBREAK 8846 (Baker Petrolite Corporation, Sugar Land, TX, USA) was used as a commercial demulsifier. Its chemical structure is a high-molecular-weight oxyalkylated alkyl phenolic resin. All chemicals were used without further purification. Arabian heavy crude oil (Aramco Co., Riyadh, Saudi Arabia) was also acquired. The crude oil’s specifications were explained in detail, as shown in Table 1. Brine (35,000 ppm) was prepared by dissolving sodium chloride in distilled water.
Nuclear magnetic resonance (NMR) spectra were recorded using a Bruker AVANCE DRX-400 MHz NMR spectrometer. FT-IR was carried out using a Nicolet FT-IR spectrophotometer. A DSA-100 was employed to study the surface activity and IFT (DLS; Zetasizer Nano ZS, Malvern Instrument Ltd., Worcestershire, UK) for zeta potential studies at room temperature [25].

2.2. The Synthesis of Surfactants

(a)
The Synthesis of TNDT:
A solution of 2-((4-nonylphenoxy)methyl)oxirane (8.28 g, 0.03 mol) in dry xylene (40 mL) and DTA (1.03 g, 0.01 mol) was stirred in three-neck round flask via refluxing at 120 °C under a N2 atmosphere for 4 h. After that, the reaction mixture was cooled down and the excess solvent was evaporated using a rotary evaporator. Then, the obtained product was dissolved in isopropanol and liquid–liquid extraction was carried out three times using a saturated NaCl solution. The purified product, a viscous yellow liquid, was obtained by evaporating an isopropanol solvent using a rotary evaporator with the following yield (87%); IR (KBr) ν/cm−1: 3411 (OH &NH), 2960, 2929, 2871 (CH-Ali), 1614 (C=C), 1462 (benzene ring), 1248 (C-O); 1H-NMR (400 MHz, CDCl3-d1) δH: 0.54 (t, 9H, 3CH3), 0.66–0.75 (m, 18H, 9CH2), 0.92–1.18 (m, 18H, 9CH2),1.40–1.60 (m, 6H, 3CH2), 2.40–2.66 (m, 20H, 3CH2-Ar, 4CH2NH, 3CH2N), 3.82–3.85 (m, 6H, 3CH2-O), 3.93–3.97 (m, 3H, 3CH-OH), 5.43 (s,1H,OH), 6.74 (s, 6H, Ar-H), 7.06–7.13 (app. m, 8H, 6Ar-H, 2NH).
(b)
The Synthesis of ETNDT:
A mixture of 2-(2-chloroethoxy)ethanol (3.11 g, 25mmol) and an adduct (4.66 g, 5 mmol) were stirred in presence of NaOH (0.6 g, 15 mmol) and toluene as a solvent for 6 h at 70 °C and then filtered to remove the NaCl. The excess unreacted 2-(2-chloroethoxy)ethanol was evaporated. The title compound appeared as yellowish-brown oil with the following yield (75%): IR (KBr) ν/cm−1: 3405 (OH &NH), 2959, 2930, 2872 (CH-Ali), 1611 (C=C), 1462 (benzene ring), 1248 (C-O); 1H-NMR (400 MHz, CDCl3-d1) δH: 0.56 (t, 9H, 3CH3), 0.65–0.79 (m, 18H, 9CH2), 1.04–1.25 (m, 18H, 9CH2), 1.40–1.56 (m, 6H, 3CH2), 2.69–2.80 (m, 12H, 3CH2-Ar, 3CH2N), 2.89–2.97 (m, 8H, 4CH2NH), 3.57–3.73 (m, 24H, 12CH2-O), 3.88–3.97(m, 6H, 3CH2-O), 4.10–4.12 (m, 3H, 3CH-OH), 5.43 (s,1H,OH), 6.81 (s, 6H, Ar-H), 7.14–7.25 (app. m, 8H, 6Ar-H& 2NH).

2.3. Preparation of W/O Emulsion

Brine as the dispersed phase and Arabian heavy crude oil as the continuous phase were employed in the preparation of a W/O emulsion. In detail, 10%, 30% and 50% by volume of brine were mixed with 90%, 70% and 50% of crude oil, respectively, to achieve an overall percentage of 100%. The mixing process was carried out in a 500 mL beaker, using a homogenizer (BULLIO SR2) at 5000 rpm for 15 min at room temperature in order to simulate emulsion in an oilfield. The emulsion was then transferred into 25 mL glass graduated cylinders with stopper caps.

2.4. Emulsion-Separation Test

Calculated amounts of the demulsifiers were added to the capped cylinders containing the W/O emulsions, and the bottles were shaken by hand for 1 min to ensure that the demulsifiers were mixed well with the emulsions. The emulsion bottles were then incubated in water bath at 60 °C, and the amount of water separated with time was observed and recorded. The demulsification efficiency (D%) was calculated from the following equation:
Demulsification Efficiency % = (Vwater/Vo) × 100
where Vwater is the demulsified water volume and Vo is the water volume in the blank emulsion sample.

2.5. Photographic Study of the Demulsification Process

Ethoxylated trinonyl phenoxy diethylenetriamine (ETNDT) was chosen for this objective, relying on its higher demulsification activity. A freshly prepared 10% W/O emulsion was incubated at 60 °C in a water bath after tge injection of 250 ppm of an ionic liquid solution, also considering a blank sample without treatment. At different time intervals, photographic microscopy photos were taken using an (Olympus BX-51 microscope) for the treated and untreated emulsions after spreading droplets of the emulsions on a glass slide.

2.6. Relative Solubility Number (RSN)

The RSN is a practical method for identifying the hydrophobic–hydrophilic character of a surfactant, and it was carried via the titration of water into a dioxane and toluene solvent system in which the former acted as a polar solvent and the latter acted as a non-polar solvent. The RSN value is defined as the amount of distilled water (in milliliters) required to produce persistent turbidity of (1 g of surfactant dissolved in 30 mL of dioxane/toluene solution, 96:4 vol%).

3. Results

3.1. Characterization of ILs

The target ethoxylated tri-nonyl phenoxy diethylenetriamine (ETNDT) 2 is depicted in Scheme 1. The synthetic route based on tri-nonyl phenoxy diethylenetriamine (TNDT) derivative 1 was carried out by refluxing the substituted phenoxymethyloxirane and diethylenetriamine (DTA) under a N2 atmosphere, followed by mixing them with an excess of monochloroethoxyethanol in the presence of NaOH (Scheme 1).
The structure of the assigned TNDT 1 was verified based on its spectral data. The IR spectrum disclosed absorption bands at ν 3411, 2960, 2929, 2871, 1614, 1462 and 1248 cm−1 which correlated to the OH and NH, aliphatic (-CH), C=C, benzene ring and the (C-O) functionalities, respectively (Figure 1). The 1H-NMR (400 MHz, CDCl3-d1) spectrum revealed a triplet signal at δH = 0.54 ppm corresponding to the methyl protons, three multiplet signals for the methylene protons of the alkyl chain at δH = 0.66–0.75, 0.92–1.18 and 1.40–1.60 ppm and a multiplet signal at δH = 2.40–2.66 ppm due to the CH2-Ar, CH2NH, and CH2N protons. In addition, two multiplet signals at δH = 3.82–3.85 and 3.93–3.97 ppm due to the CH2O and CH-OH protons were identified. Moreover, two singlets were identified at δH = 5.1 and 6.74 ppm for OH and four aromatic protons. In addition, one multiplet at δH = 7.06–7.13 ppm attributed to the remaining aromatic protons overlapping with NH protons (Figure 2).
The structure of ETNDT 2 was verified via the IR spectra and showed more intense characteristic bands at ν 2959, 2910, 2872 and 1248 cm−1; these bands were related to the introduction of new ethoxy groups (Figure 3). Also, the 1H-NMR (400 MHz, CDCl3-d1) spectrum revealed a characteristic signal at δH = 3.60–3.73 ppm corresponding to the methylene protons (CH2O) of the ethoxyethanol moiety (Figure 4).

3.2. The Solubility and Surface Activity of TNDT and ETNDT

Solubility and surface activity are key properties of surfactants as they reflect how surfactants function in various applications [26]. A surfactant’s solubility in a specific solvent relies on its hydrophilic and lipophilic balance and the solvent’s polarity. The amphiphilic nature of surfactants causes them to form micelles in bulk solutions and form monolayers at interfaces. The minimum concentration at which surfactants spontaneously form micelles is known as the critical micelle concentration (cmc). Below this concentration, molecules are dispersed in a solution, and above it, they form aggregates [27]. When surfactants are adsorbed at the liquid–air or liquid–liquid interface, they have the ability to lower the surface tension, which is called a surfactant’s surface activity. They achieve this result by directing their hydrophilic heads to the liquid and their hydrophobic tails to air or an immiscible liquid.
Changes in the surface tension (γ) versus different concentrations of TNDT and ETNDT are plotted in Figure 5 to determine different solubility parameters. As can be seen, the figure contains a linear decrease and levels off at the cmc. The cmc values (mol L−1) and (γcac; mN m−1) for TNDT and ETNDT were calculated and are listed in Table 2. As shown in the table, ETNDT had a higher cmc value than TNDT as a result of ethoxylation, which increased the hydrophilicity of the surfactant and, as a result, increased its water solubility [3]. Moreover, TNDT and ETNDT diminished the γ of water to 40 ± 0.4 and 38 ± 0.5, respectively.
Surfactant molecules can arrange at the air–water interface. The density at the interface and other parameters can be determined by figuring out the maximum excess surface concentration (Γmax) and the average minimum surface area per molecule (Amin) at a low concentration [28]. These values were calculated and are listed in Table 2. Gibbs adsorption isotherm equations were employed to detect their values as follows: Γmax = (−∂γ/∂ ln c)T/RT and Amin = 1016/NΓmax, where R is the gas constant (8.314 J mol−1 K−1), T is the temperature (K), γ is the surface tension (mN m−1), NA is the Avogadro constant (6.022 × 1023), c is the surfactant’s concentration and ∂γ/∂lnc is the linear fit slope of the surface tension plot before the cmc [29]. As TNDT has a lower RSN and is more hydrophobic, the TNDT molecules pack tighter at the interface and, as a result, it has a higher Γmax value and a lower Amin value compared with ETNDT (Table 2) [30,31].
To obtain information about the surfactants’ solubility in aqueous solutions, their relative solubility numbers (RSNs) wesre practically determined. This value reflects the degree of solubility of a surfactant in water. As the value becomes higher, the water solubility increases. When RSN < 13, 17 > RSN > 13 or RSN > 17, the surfactant is water insoluble, water dispersed or water soluble [32]. The RSN values for TNDT and ETNDT were 14 and 16.5, respectively (Table 2). These values indicate that both TNDT and ETNDT are water-dispersed surfactants with an increase in the RSN value for ETNDT because of ethoxylation.
As surfactant molecules form micelles at the cmc, the micelles’ charge can be determined using dynamic light scattering (DLS) [33]. The zeta potentials of aqueous solutions of TNDT and ETND at the cmc were measured and are listed in Table 2. The zeta potential values for TNDT and ETNDT were 50 ± 0.9 and 41 ± 0.1, respectively. W. Liu et al. [34] found that in the pH range of 4.0–10.0, the dominant species of N-(2-hydroxyethyl)-N-dodecyl-ethanediamine (NHDE) in its aqueous solution are the double-protonated NHDE2+ (RNH+(CH2CH2OH)CH2CH2NH3+) and the protonated NHDE+ (RNH+(CH2CH2OH)CH2CH2NH2) species. These positively charged species (NHDE2+ and NHDE+) were responsible for the positive charge of the zeta potential in the pH range mentioned. This could be the same for our synthesized surfactants as they have diethylenetriamine and oxyethylene moieties that can form positive charges in their solutions and provide high zeta potential charges. The high values elucidate the stable aggregates of both surfactants. The higher value for ETND can be attributed to the ethoxylation of TNDT. The introduction of the oxyethylene units lessened the unfavorable contact of water with hydrophobic chains and enhanced the stability of the formed micelles in water [23].

3.3. The Effects of TNDT and ETND on the IFT of the W/O Interface

Generally, crude oil and brine have relatively high IFT values. Surfactant molecules have the ability to arrange at the interface and lessen the W/O interface. To test the effects of the addition of TNDT and ETND on the IFT value, different concentrations in brine were used, and the IFT values were measured against Arabian heavy crude oil. The data obtained are listed in (Table 3). It can be noticed that both TNDT and ETND decreased the IFT when compared with the blank sample of crude oil with bare brine. It can be noticed that the effect of the surfactants on the IFT is the most important when the demulsifiers’ concentrations were elevated from 0 to 500 ppm. ETND decreased the IFT value greatly as the introduction of the ethyleneoxide units played a crucial role in lowering the IFT value [35]. Also, the combination of the ethyleneamine and ethyleneoxide units may synergize and increase the efficiency of ETND compared with TNDT [22]. Decreasing the IFT is a significant criterion for applying surfactants as demulsifiers because demulsifier molecules replace or compress the rigid film, protecting the emulsion from separation, causing its rupture and finally breaking the emulsion [36,37].

3.4. The Interactions of TNDT and ETND with Asphaltene

Surfactants can play an important role in mitigating asphaltene precipitation by interacting with asphaltene structures and reducing the IFT between asphaltene particles and the surrounding phase [38]. This interaction is also paramount in the demulsification of W/O emulsions in which asphaltene acts as a natural emulsifier [39]. By interacting and dissolving the asphaltene surrounding water droplets in W/O emulsions, the rigid asphaltene film can be removed, and the unfavorable emulsion can be broken. Surfactant–asphaltene interactions can be electrostatic interactions, H-bonding and π-π interactions [3]. Asphaltene has macromolecular structures containing heteroatoms and fused aromatic rings [40]. An H-bonding interaction can take place as the prepared surfactants provide OH and NH, which can form hydrogen bonds with the heteroatoms in the asphaltene’s structure. Additionally, the tribenzene rings in a surfactant’s structure can form π–π bonds with the asphaltene’s aromatic rings. The electrostatic interaction can be tested by measuring the zeta potential of the asphaltene dispersion in the presence of different concentrations of TNDT and ETND [41,42]. As shown from Table 4, the asphaltene’s zeta potential (blank sample) is -40 ± 0.9 mV. This negative charge is formed on the asphaltene’s surface as a consequence of the acidic and basic groups in its structure [41]. By dissolving different amounts of the TNDT and ETND surfactants, the zeta potential charges became positive (Table 4). This great shift in zeta potential values verifies the electrostatic interaction between surfactants that have positive charges with the negatively charged asphaltene. This electrostatic interaction can help remove the rigid asphaltene film surrounding the water droplets in a W/O emulsion, causing its rapture [43].

3.5. The Dehydration of W/O Emulsion Control Samples

The drop dilution method confirmed that all the prepared emulsions were W/O emulsions as they dispersed well in nonpolar organic solvents such as xylene and toluene. In all demulsification experiments, a control sample (untreated with a demulsifier) was considered at the same incubation temperature, 60 °C. Upon inspection, we found that all the prepared emulsions were stable for more than 5 days with no water separation. This stability comes from the high content of asphaltene in Arabian heavy crude oil that acts as a natural emulsifier and increases its mechanical stability by surrounding water droplets. This surrounding activity prevents adjacent water droplets from coalescing. This is why the control samples remain stable for a long time without any water separation.

3.6. The Dehydration of W/O Emulsions Using TNDT and ETND

Dehydration processes using TNDT, ETND and ARBREAK 8846 as commercial demulsifiers were studied using the bottle test method [44]. First, 25 mL of synthesized W/O emulsions with 10%, 30% and 50% percentages of water were added separately to graduated glass bottles. Second, surfactant materials were dissolved in a toluene/ethanol mixture to form a 30% solution of surfactants in (75/25 wt%) toluene/ethanol. The surfactants solutions were then added to the emulsion bottles to achieve concentrations of 0, 250, 500 and 1000 ppm. To examine the D%, the bottles were incubated at 60 °C in a water bath. A temperature of 60 °C was chosen to carry out the dehydration study as it is the temperature of oil when extracted from high-pressure wells [45]. The volume of water separated over time was recorded to study dehydration. Microscopy images of the W/O emulsions (Figure 6) for the W/O emulsion (10/90 V%) indicated that water particles filled most of the area, suggesting that oil is the dispersed phase and the emulsion is of the w in o type. Moreover, the most frequently observed particles were below 1 µm for the emulsion before the addition of a demulsifier (Figure 6a). Many parameters affecting the dehydration process were investigated and are described below.
(a)
Relative Solubility Number (RSN)
The dispersed phase of an emulsion may be water or oil depending on the type of emulsion, whether it is water in oil or oil in water, respectively [46]. The amphiphilicity of a surfactant molecule allows it to disperse in either the water phase or oil phase. Measuring the RSN for the prepared materials provided a practical data on their hydrophilic–lipophilic balance [32]. The lower RSN values indicated the easier dispersion of surfactant molecules in crude oil [47]. The RSN values for TNDT and ETNDT were 14 and 16.5, respectively (Table 2). Both values were below 17, indicating the hydrophobicity of both TNDT and ETNDT, so both surfactants easily dispersed in the crude oil as a dispersed phase of the prepared emulsions and thus reached the W/O interface quickly. After reaching the interface, the thermodynamic stability of surfactant at the interface is another factor that is crucial for the dehydration process. Surfactants with higher RSN values are likely more thermodynamically stable at W/O interfaces [48]. This stability aids in forming continuous hydrophilic channels to allow water droplets to combine and enlarge in size and finally separate from the emulsion. Therefore, ETNDT, which has a higher RSN value, had greater dehydration performance than TNDT, which has a lower RSN value (Table 5).
(b)
Demulsifier dose effect
The concentration of the demulsifier is one of the most significant parameters governing the adsorption of molecules at the W/O interface [49]. The effect of concentration on the dewatering performances for TNDT and ETNDT and ARBREAK 8846 is outlined in Table 5. Three concentrations were used for this study: 250, 500 and 1000 ppm. It is obvious that increasing the demulsifier dosage leads to dramatic increases in the dewatering efficiency as more molecules are adsorbed at the W/O interface. These molecules replace the native emulsifiers and decrease the mechanical stability of the rigid film surrounding the water droplets. As a consequence, the film becomes thinner and finally collapses. Adjacent water droplets combine and finally settle down due to gravity [50]. It was also observed that the D% was very high for ETNDT compared with TNDT in all emulsion types because of ethoxylation, which helps form more hydrophilic channels between water droplets, finally leading to separation. The D% of ETNDT reached 100% for all types of emulsions compared with TNDT, which only demonstrated full water separation for W/O emulsions with 10% water. The dewatering efficiency of ARBREAK 8846 was better than TNDT for the W/O emulsion (50/50 and 30/70), but it took long time to separate the emulsion, while ETNDT was better than ARBREAK 8846 at 500 and 1000 ppm. Both TNDT and ETNDT were better for the 10/90 W/O emulsion, and this indicates that the surfactants prepared in our lab can be used commercially for separating 10/90 W/O emulsions.

3.7. The Effect of Contact Time

Dewatering mechanisms include moving the surfactant molecules in the oil (continuous phase) to reach the W/O interface and T = then gaining access to the interface, replacing the rigid film and forming connecting channels for water droplets to finally break the emulsion [51,52]. This is why the process requires time to reach its maximum efficiency. The rate of the dewatering process with respect to time in minutes was recorded and is listed in Table 4. It was found that increasing the mixing time increases the water volume separated from the emulsion. Figure 7a,b shows the demulsification rates of a W/O emulsion (50/50 V%) when using TNDT and ETNDT, respectively. The equilibrium time lengths for TNDT and ETNDT were 60 min and 25 min, respectively. This indicates higher separation kinetics for ETNDT than TNDT. Additionally, the efficiency of ETNDT was higher than TNDT in almost all emulsion compositions (Figure 7 and Table 4). This could be because the introduction of ethylene oxide units into ETNDT greatly lowered the IFT and caused thermodynamically stable adsorption at the W/O interface.
(c)
The effect of demulsifier on the size of water droplets
In order to study how the addition of a demulsifier affects the size of water droplets, an optical microscope was employed. A blank sample was of a 10/90 V% W/O emulsion was considered to determine how small the size of the emulsion was as a reflection of its stability. A sample treated with 250 ppm of ETNDT was investigated after 10 min and 20 min to detect how the surfactant affected the size of emulsion in order to act as demulsifier. For the blank sample, the water droplet size for almost all the emulsions was below 1 µm (Figure 6a). A microemulsion is very stable and difficult to separate. That is why it lasted for more than 5 days with no noticeable separation. The size of the water droplets increased significantly after an injection of ETNDT and settled for 60 min (Figure 6b,c). The size of water droplets increased to the size range (5 to 10 µm) after 10 min (Figure 6b) to reach 60 µm after 20 min (Figure 6c).
The hydrophobicity of ETNDT molecules facilitates their fast movement in a continuous oil phase. The ethyleneamine and ethyleneoxide units in the ETNDT’s structure caused the molecules to be adsorbed onto the interface. At the same time, the molecules can interact and neutralize the negative charge of a rigid asphaltene film and deteriorate the structure of the stable film. These all lead to replacing the film and reducing the IFT and finally rupturing the asphaltene films surrounding water droplets. The hydrophilic parts of the demulsifier’s structure, the ethyleneamine and ethyleneoxide units, form channels that connect water droplets after the rigid film’s rupture. This leads to an increase in the size of the water droplets and finally the separation of the emulsion.
The higher ethyleneoxide content in ETNDT than TNDT increased its efficiency, as is obvious in Table 4. Additionally, it is obvious from the separation images of the dewatering bottles (Figure 8) that the water separated from the W/O emulsion (30/70 V%) was clean with a low oil content. Separated, clean water with little oil residual does not require further purification. This has substantial importance from environmental and economic perspectives since the discharging of this water may not have harmful effects on the environment and if it requires extra treatment, the treatment will be simple.

4. Conclusions

Two new star-shaped surfactants were prepared, characterized and applied for dewatering W/O emulsions. The surfactants were prepared by reacting diethylenetriamine with GNPE via a simple epoxy ring opening to obtain TNDT, which was then ethoxylated to obtain ETNDT. The oxyethylene groups in ETNDT led to increases in the molecules’ water solubility and Amin values and decreases in their Γmax concentrations at the water–air interface. Both TNDT and ETNDT formed stable micelles in aqueous solutions with zeta potential values of 41 mV and 50 mV, respectively. The positive charges of the micelles attracted the negatively charged asphaltene structures. TNDT and ETNDT decreased the IFT value of a W/O emulsion, with the latter having higher effectiveness. Both TNDT and ETNDT demulsified the 10/90 W/O emulsion with high efficiency (100%) at a low dose (250 ppm). Only ETNDT dehydrated the 30/70 and 50/50 W/O emulsions with D% = 100%. The combination of ethyleneamine and ethyleneoxide units in the ETNDT structure enhanced the kinetics and demulsification efficiency against emulsions with different compositions.

Author Contributions

Conceptualization, methodology A.O.E.; software, M.Y.A. and M.A.T.; validation, formal analysis A.O.E., M.Y.A., N.A.F. and M.A.T.; investigation, H.A.A.-L.; resources, A.O.E.; data curation, A.O.E. and N.A.F.; writing—original draft preparation, A.O.E., M.Y.A. and M.A.T.; writing—review and editing, N.A.F.; visualization, H.A.A.-L.; supervision, H.A.A.-L.; project administration, A.O.E. and H.A.A.-L.; funding acquisition, A.O.E. and H.A.A.-L. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Deputyship for Research & Innovation, Ministry of Education in Saudi Arabia grant number IFKSURC-1-0217.

Data Availability Statement

The data presented in this study are available upon request from the corresponding author.

Acknowledgments

The authors extend their appreciation to the Deputyship for Research & Innovation, Ministry of Education in Saudi Arabia, for funding this research (IFKSURC-1-0217).

Conflicts of Interest

The authors declare no conflict of interest.

References

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Processes 11 03162 sch001
Scheme 1. The synthesis of ETNDT derivatives.
Scheme 1. The synthesis of ETNDT derivatives.
Processes 11 03162 sch001
Processes 11 03162 g001
Figure 1. IR spectrum of TNDT.
Figure 1. IR spectrum of TNDT.
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Processes 11 03162 g002
Figure 2. 1H-NMR spectrum of TNDT.
Figure 2. 1H-NMR spectrum of TNDT.
Processes 11 03162 g002
Processes 11 03162 g003
Figure 3. IR spectrum of ETNDT.
Figure 3. IR spectrum of ETNDT.
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Processes 11 03162 g004
Figure 4. 1H-NMR spectrum of ETNDT.
Figure 4. 1H-NMR spectrum of ETNDT.
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Processes 11 03162 g005
Figure 5. Variations in surface tension with different aqueous concentrations of the TNDT and ETNDT surfactants at 25 °C.
Figure 5. Variations in surface tension with different aqueous concentrations of the TNDT and ETNDT surfactants at 25 °C.
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Processes 11 03162 g006
Figure 6. Optical microscopic images of a (10/90 V%) W/O emulsion of (a) a blank emulsion sample and a sample treated with 250 ppm of ETNDT after (b) 10 min and (c) 20 min.
Figure 6. Optical microscopic images of a (10/90 V%) W/O emulsion of (a) a blank emulsion sample and a sample treated with 250 ppm of ETNDT after (b) 10 min and (c) 20 min.
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Processes 11 03162 g007
Figure 7. Demulsification kinetics of (a) TNDT and (b) ETNDT for (a) W/O emulsion (50/50 V %) at 60 °C.
Figure 7. Demulsification kinetics of (a) TNDT and (b) ETNDT for (a) W/O emulsion (50/50 V %) at 60 °C.
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Figure 8. Water separation photos of W/O emulsions (30/70 vol%) using (a) TNDT and (b) ETNDT with different concentrations (in ppm).
Figure 8. Water separation photos of W/O emulsions (30/70 vol%) using (a) TNDT and (b) ETNDT with different concentrations (in ppm).
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Table 1. The properties of the Arabian heavy crude oil.
Table 1. The properties of the Arabian heavy crude oil.
TestResults
API gravity20.8
Specific gravity 60/600.929
Wax content (wt%)2.3
Asphaltene content (wt%)8.3
Heteroatoms (wt%)6.5
Aromatic carbon (mol %)49.0
Aromatic hydrogen (mol %)7.81
Saturates (wt%)40.5
Aromatics (wt%)30.8
Resins (wt%)22.3
Table 2. Surface activity parameters, RSN and the zeta potentials of the ETNDT and TNDT surfactants at 25 °C.
Table 2. Surface activity parameters, RSN and the zeta potentials of the ETNDT and TNDT surfactants at 25 °C.
Compoundcmc (mM)(−∂γ/∂ ln c)Tγcmc (mN/m)Δγ
mN m−1		Γmax × 10−6 (mol/m2)Amin (nm2/Molecule)RSNZeta Potential (mv)
ETNDT0.2348.3634 ± 0.538 ± 0.51.31.2216.550 ± 0.9
TNDT0.1438.8532 ± 0.540 ± 0.42.620.631441 ± 0.1
Table 3. IFT and interfacial pressure values of the brine/O interface using different concentrations of the TNDT and ETNDT surfactants in brine at 25 °C.
Table 3. IFT and interfacial pressure values of the brine/O interface using different concentrations of the TNDT and ETNDT surfactants in brine at 25 °C.
DemulsifierConcentration (mg L−1)IFT (mN/m)Ω
(mN m−1)
TNDT033.50
2502112.5
50012.521
10001122.5
ETNDT033.50
2501419.5
5006.527
1000528.5
Table 4. The zeta potential values of an asphaltene dispersion at different concentrations of TNDT and ETNDT.
Table 4. The zeta potential values of an asphaltene dispersion at different concentrations of TNDT and ETNDT.
CompoundConc. (ppm)Zeta Potential (mv)
SurfactantAsphalteneSurfactant/Asph
TNDT250
500
1000		41 ± 0.1 24 ± 0.2
26 ± 0.1
30 ± 0.3
ETNDT250
500
1000		50 ± 0.9−40 ± 0.935 ± 0.5
35 ± 0.6
39 ± 0.4
Table 5. Demulsification performances of TNDT, ETNDT and ARBREAK 8846 demulsifiers for different W/O emulsions at 60 °C.
Table 5. Demulsification performances of TNDT, ETNDT and ARBREAK 8846 demulsifiers for different W/O emulsions at 60 °C.
W/O Emulsion
 10/90 30/70 50/50
CompoundDosage (ppm)D%t (min)D%t (min)D%t (min)
TNDT2501006014802070
5001004525602670
10001004525556060
ETNDT2501004094508630
500100301004510030
100010030984510025
ARBREAK 884625030420100375100310
50042360100330100255
100065360100280100180
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Ezzat, A.O.; Al-Lohedan, H.A.; Albarqan, M.Y.; Toraba, M.A.; Faqihi, N.A. The Synthesis and Application of Novel, Star-Shaped Surfactants for the Destabilization of Water in Arabian Heavy Crude Oil Emulsions. Processes 2023, 11, 3162. https://doi.org/10.3390/pr11113162

AMA Style

Ezzat AO, Al-Lohedan HA, Albarqan MY, Toraba MA, Faqihi NA. The Synthesis and Application of Novel, Star-Shaped Surfactants for the Destabilization of Water in Arabian Heavy Crude Oil Emulsions. Processes. 2023; 11(11):3162. https://doi.org/10.3390/pr11113162

Chicago/Turabian Style

Ezzat, Abdelrahman O., Hamad A. Al-Lohedan, Mohammed Yousef Albarqan, Meshary Abdullah Toraba, and Noorah A. Faqihi. 2023. "The Synthesis and Application of Novel, Star-Shaped Surfactants for the Destabilization of Water in Arabian Heavy Crude Oil Emulsions" Processes 11, no. 11: 3162. https://doi.org/10.3390/pr11113162

APA Style

Ezzat, A. O., Al-Lohedan, H. A., Albarqan, M. Y., Toraba, M. A., & Faqihi, N. A. (2023). The Synthesis and Application of Novel, Star-Shaped Surfactants for the Destabilization of Water in Arabian Heavy Crude Oil Emulsions. Processes, 11(11), 3162. https://doi.org/10.3390/pr11113162

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