One-Step Synthesis of Amphiphilic Nonylphenol Polyethyleneimine for Demulsification of Water in Heavy Crude Oil Emulsions.

The demulsification of water-in-heavy crude oil emulsion with water droplet size in the microscale has drawn great attention because of their high stability and difficulty of separation. In the present work, a series of ethylene amine-based demulsifiers were prepared in one step through the interaction of pentaethylene hexamine, tetraethylene pentamine, and triethylene tetramene with glycidyl 4-nonylphenyl ether. The amphiphilic polyethyleneimine (APEI) abbreviated as DNPA-6, DNPA-5, and DNPA-4 were prepared to adjust their hydrophile-lipophile balances (HLB) to meet the requirement of the demulsification. 1HNMR, 13CNMR, and FTIR spectra were utilized to verify their chemical structures. The surface properties and zeta potential were also investigated. Demulsifier dose, separation time, and HLB values were taken into account to evaluate the demulsification efficiency of the synthesized APEI. The results suggested that the prepared demulsifiers had high ability to reduce the surface and interfacial tensions and also broke successfully water-in-Arabian heavy crude oil emulsions. The demulsification efficiency of DNPA-5 reached 100% for crude oil/water emulsion (90/10 vol %).

Introduction

Recently the high requirement for utilizing surfactants and polymer-based materials in the enhanced oil recovery leads to the formation of water-in-oil (W/O) or oil-in-water (O/W) emulsions.[1,2] Depending on the production scheme, about 80% of the worldwide crude oil is produced in an emulsified form.[3] In the crude oil production, W/O emulsion represents the greatest part of the crude oil. The W/O ratio, origin of the emulsion, and natural emulsifier systems are the main factors that affect the emulsion composition.[4,5] Also, the heavy crude oil reserves are considered to be more complicated when comparing with light and medium reserves. Heavy crude oil has many undesirable properties such as high viscosity, high acidity, and tendency to form stable emulsions; thus, it represents a major challenge for the oil industry.[6,7] In case of heavy crude oil reserves, highly stable W/O emulsions can be produced due to the presence of resins, asphaltenes, naphthenic acids, and fine solids that act as emulsifying agents.[8] The petroleum crude oil and water emulsions cause several economic problems such as pipelines corrosion, microorganism’s growth, and oil viscosity increase. Hence, the isolation of water from crude oil before the refining process is required.[9] The formed emulsion can be broken down mechanically, electrically, and chemically.[4,10] In practice, to get the highest demulsification efficiency, a combination of these techniques should be improved. The combination between heating and chemical demulsifiers is the most broadly used technique.

Demulsifiers have the ability to rapidly separate emulsions into water and oil thanks to their amphiphilic nature with both hydrophobic and hydrophilic moieties. As a result of using demulsifiers, interfacial tension (IFT) between water and oil is reduced and the phase separation is promoted.[11,12] Therefore, they can promote the oil flocculation and coalescence.[13] Amphiphiles based on anionic, cationic, and nonionic are the three classes of demulsifiers. Nonionic demulsifiers are widely used to break O/W or W/O emulsions. Poly(ethylene oxide)–poly(propylene oxide) (PEO–PPO) block co-polymers, poly ethylene oxide (EO), and poly propylene oxide (PO) are some kinds of nonionic surfactants designed for emulsion breaking purposes.[14] Polymeric demulsifiers relied on (PEO) or (PEO–PPO) block copolymers have been widely used due to their good results in the separation of water/oil emulsions, in addition to corrosion reducing.[15,16] One of the main significant factors affecting the demulsification performance of (PEO–PPO) block copolymers is the position of EO to PO units in the copolymers. When (EO) as a hydrophilic part presents in the core and (PO) as a hydrophobilc part present in the tail, the copolymer showed no efficiency; however, PO core and EO tail polymers display the best demulsification efficiency. Also, it was found that increasing the ethylene oxide contents of these kinds of polymeric nonionic surfactants increases their demulsification performance.[17,18] The main drawback of using these kind of nonionic polymers is their high production cost.[19] Polyethylenimine (PEI), is an extremely significant polyelectrolyte, with both linear and branched forms. PEI charge is pH dependent with the highest charge density at low pH than any polyelectrolyte.[20] The main difference between (PEO) or (PEO–PPO) block copolymers and PEI is that PEI can form intra- and inter-chain hydrogen bonds between NH groups. Furthermore, it was found that all intra-chain hydrogen bonds are nonlinear and longer than typical H-bonding.[21]

Low molecular weight (LMW) PEI derivatives were used as low toxic and efficient gene delivery vectors due to their biocompatibility.[22] Biodegradability is one of the most significant characteristics of biocompatible polymers. Biodegradable polymers as environmentally friendly materials have attracted considerable attention for their possible roles as alternatives to nonbiodegradable materials that accumulate in the environment.[23] Also, nonylphenol as a widely used reagent in detergents, emulsifiers, and solubilizers manufacturing was considered as inherently biodegradable material.[24] The linearity of nonylphenol played an important role in its biodegradation. It was found that the higher the branching, the lower the biodegradability.[25]

According to the applications of PEI, ethoxy, hydrophobic, or hydrophilic units can be introduced to its structure.[26] Amphiphilic derivatives of PEI using PEO–PPO block copolymers or nonionic surfactants based on lauryl acid or nonylphenol with different EO units have been studied and applied as demulsifiers for W/O emulsions.[17,27] They were used to control the hydrphile–lipophile balance (HLB) and the amphiphilicity of demulsifiers to be applied for the W/O emulsion system especially when the oil phase is thick.[28−31] Most of PEI-based demulsifiers were prepared through multistep procedures and almost most of them used hyperbranched PEI[2,32,33] while the method used in our paper is a simple single step reaction using linear LMW PEI. The present work aims to prepare new ethyleneimine-based surfactants that are synthesized through the reaction of LMW PEI series with glycidyl 4-nonyl ether (GNE) and utilized as demulsifiers for water-in-heavy crude oil emulsions. The synthesized surfactants were prepared using a simple one step reaction and their chemical structures were ensured by common spectroscopic tools.

Results and Discussions

Characteristic Properties of DNPA-6, DNPA-5, and DNPA-4

Three amphiphilic polyethyleneimine (APEI) demulsifiers based on glycidyl alkyl benzene and ethyleneimine were synthesized as illustrated in Scheme . Fourier transform infrared (FTIR) charts, 1HNMR, and 13CNMR spectra were used to verify their chemical structures. The 1HNMR, 13C NMR, and FTIR spectra for DNPA-6, DNPA-5, and DNPA-4 surfactants are nearly identical due to the similarity in their structures. The integration of the 1HNMR peaks assigned for CH2NH groups certainly differs. For brevity, the interpretation of the FTIR, 1HNMR, and 13C NMR for DNPA-6 are illustrated in Figures , 3 and 4, respectively. The FTIR spectra of DNPA-6 depicted in Figure illustrates that the alcoholic hydroxyl and secondary amine groups of DNPA-6 appeared as broad peak at 3401 cm–1. The disappearance of the two stretching bands of NH2 at 3400 cm–1 confirmed the interaction of the epoxy ring of glycidyl 4-nonylphenyl ether (GNPE) with the two primary amine groups of pentaethylene hexamine. The stretching bands at 2959 cm–1 and 2872 refer to the aliphatic C–H. The stretching band at 1660 cm–1 refers to the aromatic C=C bonds. The 1HNMR spectra (Figure ) of DNPA-6 confirms the presence of methyl groups as multiplet at 0.30–0.42 ppm, and also methylene groups of the nonyl branch are observed as multiplet at 0.44–0.51, 0.7–0.96, 1.12–1.29, and 1.98–2.16 ppm. The formation of the ethylene amine units in DNPA-6, DNPA-5, and DNPA-4 is confirmed from the appearance of new multiplet peaks in the region between 2.25, and 2.45 ppm. The appearance of new peaks as doublet at 3.82 ppm, and multiplet at 3.97 ppm related to CH2O (methylene oxide) and CH attached to alc. OH, and phenoxide, respectively, confirms the epoxy ring opening. The aromatic protons appeared as doublet at 6.52 ppm, and multiplet at 6.82–6.89 ppm. The 13C NMR spectra of DNPA-6 (Figure ) are also used to verify the chemical structures of the prepared APEI demulsifiers. The peaks at 49 and 53 ppm attributed to CH2NH and CH2NHCHOH confirm the interaction of pentaethylene hexamine with GNPE through the epoxy ring opening. Additional details of the other peaks are assigned in the chemical structures of DNPA-6 as illustrated in Figure . The FTIR, 1HNMR, and 13C NMR verify the presence of both ethylene amine and alkyl benzene in the chemical structure of the new synthesized demulsifiers.

Scheme 1

Synthesis Route of DNPA-6, DNPA-5, and DNPA-4

Figure 2

FTIR spectra of DNPA-6.

Figure 3

1H NMR spectra of DNPA-6 in CDCl3 solvent.

Figure 4

13C NMR spectra of DNPA-6 in CDCl3 solvent.

Solubility and Surface Activity of the Prepared APEI

The surface activity and the solubility of surfactants affect strongly their industrial applications.[34] The surface tension measurements were carried out to investigate the impact of the chemical structures of the synthesized surfactants on their surface properties. Also, critical micelle concentration (cmc) and surfactant inter- and intra-molecular interactions in the bulk solution and at air/water interface are investigated.

At cmc, the surfactant molecules adsorbed on the solution surface reach equilibrium and at the same time form aggregates (micelles) in the solution bulk. In order to determine cmc, the relation between (ln c; mol/L) and the surfactant surface tensions in aqueous solutions is plotted as shown in Figure . The values of cmc (mol. L–1) and surface tensions at cmc (γcac; mN m–1) of DNPA-6, DNPA-5 and DNPA-4 surfactants are indicated from Figure and listed in Table . The data showed that DNPA-6 has the highest cmc value, whereas DNPA-4 has the lowest one. This is attributed to the relatively highest hydrophilic part in DNPA-6, and the lowest in DNPA-4 while DNPA-5 was in between. Furthermore, DNPA-6 had the greatest ability to reduce water surface tension due to the strong hydrogen bond between water and the highest number of amino groups, which decrease the interaction between water molecules and that between surfactant molecules.[35]

Figure 5

Surface tension isotherm of DNPA-4, DNPA-5, and DNPA-6.

Table 1

Surface Activity Parameters, HLB, and Zeta Potential of DNPA-6, DNPA-5, and DNPA-4 at 25 °C

compound	cmc (mM)	(−∂γ/∂ ln c)T	γcmc (mN/m)	Γmax × 10–6 (mol/m2)	Amin (nm2/molecule)	HLB	zeta potential (mv)
DNPA-6	0.32	15.06	34 ± 0.5	6.08	0.27	9.58	56.8 ± 0.7
DNPA-5	0.19	16.1	37 ± 0.5	6.5	0.25	8.98	70.60 ± 1
DNPA-4	0.091	18.7	39 ± 0.5	7.5	0.22	8.29	74.6 ± 1

The theoretical solubility of the prepared surfactants can be evaluated by calculating the hydrophilic–lipophilic balance (HLB).[36] The HLB of surfactant can be easily calculated using Griffin and Davies equations.[37,38] Also, by calculating the HLB values of surfactants, we can easily expect their potential applications.[39] For nonionic surfactants having HLB below 8, they are considered to be water insoluble. While those which have 8 < HLB > 11 are dispersed in water at low concentrations. Additionally, nonionic surfactants with HLB values more than 11 are water soluble. The HLB values of DNPA-6, DNPA-5, and DNPA-4 are 9.58, 8.98, and 8.29, respectively. These values suggest that at low concentrations, the synthesized surfactants are water soluble. In addition, the solubility and the polarity of the synthesized surfactants can be ordered as DNPA-6 > DNPA-5 > DNPA-4.

To explore the aggregation behavior at cmc for DNPA-6, DNPA-5, and DNPA-4 in water and at the air/water interface, particle size and zeta potential were measured as displayed in Figures and 7, respectively. The aggregates hydrodynamic diameter (Dh; nm) and polydispersity index (PDI) values increased with increasing the hydrophilic ethylene amine part (Figure ). This indicates that DNPA-6 forms aggregates with different sizes and needs high concentration to reach cmc, whereas DNPA-5 and DNPA-4 need lower one. The surface charges of the surfactant aggregates can be also determined from their zeta potential values.[40] As displayed in (Figure a–c), the aggregates of all prepared surfactants had positive charges with increasing the zeta potential value of DNPA-4 than DNPA-5 and DNPA-6. This result is in agreement with the particle size value. As the zeta potential value increases, the repulsion between the formed aggregates increases and their stability in the aqueous solution increases to give a suspension with law particle size.[41] The data obtained from the particle size and zeta potential measurements confirm that DNPA-6, DNPA-5, and DNPA-4 form different aggregates (micelles) in the bulk water solution. The maximum excess surface concentration (Γmax) and the average minimum surface area per molecule (Amin) are the two parameters used to study the adsorption of surfactants at the air/water interface at low concentration. Their values for DNPA-6, DNPA-5, and DNPA-4 are listed in Table . Γmax and Amin values give an indication to the packing density of surfactant molecules at the air/liquid interface.[42] They can be calculated utilizing the Gibbs adsorption isotherm equations 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 concentration of ethyleneimine surfactants, and ∂γ/∂ln c is the linear fit slope of the surface tension plot before the cmc.[43] It was noticed that the Gibbs surface excess Γmax gradually reduced with the lengthening the ethylene amine hydrophilic chain in the surfactant molecules, while the minimum surface area Amin showed a converse trend, suggesting that surfactants with longer hydrophilic chain have lower packing densities at the air/water interface.

Figure 6

DLS histograms of (a) DNPA-6, (b) DNPA-5, and (c) DNPA-4 at their cmc and 25 °C.

Figure 7

Zeta potential of (a) DNPA-6, (b) DNPA-5, and (c) DNPA-4 at their cmc and 25 °C.

The Effect of DNPA-4, DNPA-5, and DNPA-6 on the IFT of W/O Interface

The IFTs of oil/water interface with different concentrations of DNPA-6, DNPA-5, and DNPA-4 in the aqueous phase were studied to explore the demulsification mechanism. As shown in Table , all of the prepared demulsifiers reduced IFT of heavy oil and sea water interface compared with the blank sample with no demulsifier. The data verify that DNPA-6 and DNPA-5 had greater tendency to reduce the IFT than DNPA-4. Therefore, the increment in the ethylene amine units may increase the surfactant adsorption on the oil/water interface. When comparing with the demulsification data in Table , it is observed that decreasing the IFT is essential for proceeding the demulsification. At high demulsifier concentration, the molecules can be strongly absorbed on the surface of water droplet and replace or compress the interfacial film causing it to cleave, and the droplets to unite forming larger ones and causing emulsion breaking.[44]

Table 2

IFT of the Heavy Crude Oil/Water Interface with Different Demulsifier Concentrations in the Aqueous Phase at 25 °C

demulsifier	concentration (mg L–1)	IFT (mN/m)
DNPA-6	0	33.5 ± 1
	250	23.5 ± 0.8
	500	19 ± 0.5
	1000	11 ± 0.1
DNPA-5	0	33.5 ± 1
	250	23.3 ± 0.8
	500	20.2 ± 0.5
	1000	11.7 0.1
DNPA-4	0	33.5 ± 1
	250	26 ± 0.5
	500	21.5 ± 0.5
	1000	15 ± 0.4

Table 3

Demulsification Efficiency for DNPA-6, DNPA-5, and DNPA-4 at 60 °Ca

		crude oil/water composition
		90/10		70/30		50/50
compound	dosage (ppm)	η %	t (min)	η %	t (min)	η %	t (min)
DNPA-6	250	10	140	13	180	40	60
	500	60	120	13	150	48	45
	1000	80	100	33	130	80	40
DNPA-5	250	10	120	25	170	20	75
	500	80	120	33	150	44	60
	1000	100	100	33	120	76	50
DNPA-4	250	5	140	33	150	10	90
	500	12	120	33	120	24	75
	1000	25	120	46	100	56	65
ARBREAK 8846	250	35	400	100	380	100	300
	500	48	370	100	350	100	240
	1000	62	350	100	300	100	190

The blank sample (at 0 ppm of demulsifier) showed no water separation for more than 2 weeks at 60 °C.

APEI Interactions with Asphaltene

APEI interaction with asphaltene as an important factor in the demulsification process was investigated using zeta potential (mV) measurements for asphaltene dispersions in different solvents in the presence of different surfactants concentrations.[45,46] The charge on the asphaltene surface originates from the presence of acidic or basic functional groups by dissociation or protonation, respectively. Also, the presence of resins attached to the asphaltene molecules are in charge of the asphaltene isoelectric point at different pHs.[45] As shown in Table , the zeta potential value of asphaltene in the absence of APEI has a negative value (−43.35 mV) which is converted to positive in the presence of different concentrations of DNPA-6, DNPA-5, and DNPA-4. These data extremely verify the strong interaction between asphaltene particles and different APEI, and as a result, APEI can replace the asphaltene aggregates at the water/oil interface forming lower elastic films favoring coalescence of the dispersed water droplets.[47]

Table 4

DLS Data for APEI Interaction With Asphaltene at Different Concentrations

		zeta potential (mv)
compound	conc. (ppm)	APEI	asphaltene	asphaltene/APEI
DNPA-6	250	56.8 ± 0.7		27.74 ± 0.3
	500			27.74 ± 0.3
	1000			27.74 ± 0.3
DNPA-5	250	70.6 ± 1	–43.35 ± 0.5	30.79 ± 0.32
	500			30.79 ± 0.32
	1000			30.79 ± 0.32
DNPA-4	250	74.6 ± 1		33.25 ± 0.35
	500			33.25 ± 0.35
	1000			33.25 ± 0.35

Demulsification of Crude Oil/Water Emulsion

Different emulsion breakers are generally tested through a bottle test method by adding the given emulsion breaker to the sample of the emulsion. DNPA-6, DNPA-5, DNPA-4, and a commercial demulsifier (ARBREAK 8846) were dissolved separately in toluene/ethanol (75/25 wt %) and then injected to 25 mL of the previously prepared emulsion at different concentrations ranging from 250 to 1000 ppm. The demulsification performance as a function of time was observed.[1] The emulsion breaking process is depicted in Scheme . Oil was the continuous phase of the synthesized emulsions while water was the dispersed phase and that was confirmed by the drop test method. The emulsion droplet sizes were noticed using the optical microscopy photographs as represented in Figure a, which indicate the formation of microscaled emulsion. A blank bottle, without the addition of any demulsifier and with the equivalent volume of the toluene/ethanol solvent, was used to observe the emulsion stability at the same demulsification conditions (60 °C). The demulsification efficiencies (η %) with different concentrations of DNPA-6, DNPA-5, DNPA-4, and ARBREAK 8846 and at various time intervals are listed in Table . As shown in Figure b,c, optical microscopy photographs were taken for crude oil/water separation at different time intervals. The effect of several factors including HLB value, demulsifier concentration, effect of water content, and effect of contact time on demulsification efficiency were studied. Water separation photos of W/O emulsions (50:50 vol %) are shown in Figure to ensure the ability of the prepared APEIs to act as demulsifiers.

Scheme 2

Possible Demulsification Mechanism Using DNPA-6, DNPA-5, and DNPA-4 Demulsifiers

Figure 9

Optical microscopy images of crude oil/water emulsion (90/10 vol %) in (a) blank after 3 weeks, (b) after 30 min 500 ppm of DNPA-5 and (c) after 60 min.

Figure 10

Water separation Photographs of crude oil/water emulsions (50:50 vol %) for different concentrations (in ppm) of (a) DNPA-6, (b) DNPA-5, and (c) DNPA-4.

Hydrophile–Lipophile Balance “HLB” Effect

Studying the HLB values gives a strong indication to the surfactant solubility and the demulsification performance. As shown in Table , the HLB values of DNPA-6, DNPA-5, and DNPA-4 are 9.58, 8.98, and 8.29, respectively. Surfactants with high HLB values have longer hydrophilic parts and are more soluble in aqueous phase (dispersed phase) than those with law HLB values. After the addition of demulsifers to the prepared emulsion, those with high HLB will move toward the water/oil interface and will have more thermodynamic stability at the interface of the water droplets than those with law HLB.[48] As a consequence of such stability, demulsifier molecules arrange a continuous hydrophilic pathway among the dispersed water droplets, and as a result, the interfacial film surrounding the water droplets is removed. Therefore, DNPA-6 with longer ethylene amine hydrophilic part is the best demulsifying agent while DNPA-4 shows the worst performance as shown in Table .

Influence of the Demulsifier Concentration

The demulsifier dose is one of the most notable parameters managing the adsorption of demulsifiers at the interface.[49] The applied commercial and prepared demulsifier doses were 250, 500, and 1000 ppm. The increase in the demulsifier concentrations lead to big enhancement in the demulsification process and as a result big amount water was separated from the emulsion. The demulsification efficiencies of DNPA-6, DNPA-5, DNPA-4, and ARBREAK with different concentrations are shown in Table . For the commercial demulsifier, ARBREAK 8141, the demulsification efficiencies increased with the increasing concentration in only crude oil/water emulsion (90/10 vol %) while showing the same efficiency for other emulsion compositions with different concentrations. It reached 100% demulsification efficiencies for crude oil/water emulsion (50/50 and 70/30 vol %), although it took more time to reach equilibrium than that taken by the synthesized demulsifiers. The synthesized DNPA-6 and DNPA-5 showed higher demulsification rate and efficiency for the crude oil/water emulsion (90/10 vol %) than that for the commercial demulsifier. Increasing the demulsifier dose for all synthesized demulsifiers, from 250 to 1000 ppm leads to a remarkable increment in the demulsification efficiency. This can be assigned to the increment in the demulsifier adsorption on the W/O interface which progressively substitute the asphaltene (native emulsifiers) and reduce the mechanical stability of the interfacial film which eventually result in its displacement and then water droplets collapsing.

Effect of Contact Time

As mentioned before, the demulsifiers break the emulsion either by combining with asphaltene molecules surrounding the water droplets or by replacing them.[50,51] First, the demulsifier molecules move from the solution bulk toward the oil/water interface. Then, they arrange themselves to break the rigid film. As a result, coalescence of water droplets occurs.[52,53] Thus, the coalescence process of the emulsion begins to happen prior to the phase separation. Therefore, the amount of water separated from the emulsion for the synthesized and the commercial demulsifiers increases with time as shown in Table . DNPA-6, DNPA-5, and DNPA-4 showed a relatively high demulsification rate than the commercial demulsifier. In Figure , the contact time is plotted against the demulsification efficiencies of different doses of all of the synthesized demulsifiers using crude oil/water emulsion (90/10 vol %). It is indicated from Figure that the water separation time of crude oil/water emulsion (90/10 vol %) was the nearly the same for DNPA-6 and DNPA-5 (100 min), while it was longer for DNPA-4 (140 min). Also, it was found that as the demulsifier concentration increases, the separation time decreases and the separation efficiency increases for all synthesized demulsifiers. DNPA-5 reached 100% demulsification efficiency when injected with a concentration 1000 ppm. The difference in the demulsification rate and efficiency between the prepared demulsifiers may be due to the number of ethylene amine units in the chemical structure of each demulsifier which plays a great role in the adsorption of demulsifier molecules on the water/oil interface.[54] ARBREAK 8141 (Figure d) took more time to reach equilibrium than DNPA-6, DNPA-5 (100 min), and DNPA-4. DNPA-5 showed the highest demulsification rate and efficiency among the synthesized and the commercial demulsifiers for crude oil/water emulsion (90/10 vol %) (Figure b).

Figure 8

Demulsification efficiencies of different concentrations of (a) DNPA-6, (b) DNPA-5, (c) DNPA-4, and (d) ARBREAK 8846 against time for crude oil/water emulsion (90/10 vol %) at 60 °C.

Conclusions

In this paper, we studied the demulsification efficiencies of three novel APEI. They were synthesized by the reaction of Pentaethylen hexamine, tetraethylene pentamine, and triethylene tetramine with GNPE in a single step reaction through epoxy ring opening mechanism to give DNPA-6, DNPA-5, and DNPA-4, respectively. Their chemical structures were ensured by common spectroscopic tools including FTIR, 1HNMR, and 13CNMR. The prepared surfactants successfully declined the surface tension and the IFT of water/heavy crude oil interface. At cmc, the particle size and zeta potential were determined to investigate the agglomeration size and the charge on the formed micelles. The potential of DNPA-6, DNPA-5, and DNPA-4 to lower IFT and the positive surface charge on their surfaces demonstrated that they can be utilized as demulsifiers for water/heavy crude oil emulsions and their behavior was examined. The demulsification conditions were optimized to reach the maximum water removal ratio with the shortest settling time. The demulsification performance reached 100% for DNPA-5 for crude oil water emulsion (90/10 vol %) in 100 min. The demulsification performance data indicate the potential application of DNPA-6, DNPA-5, and DNPA-4 as demulsifiers in oilfields.

Experimental Section

Materials

Pentaethylene hexamine, tetraethylene pentamine, triethylene tetramene, and GNPE were purchased from Aldrich company and used without further purification. Xylene (99.5%) was purchased from Sinpharm Chemical Reagent Corporation. ARBREAK 8846 is a commercial demulsifier produced by Baker Petrolite Corporation. Chemically, ARBREAK 8846 is mainly based on a high-molecular weight oxyalkylated alkylphenolic resin. Riyadh refinery unit; Aramco Co. was the supplier for Arabian heavy crude oil with specifications listed in Table . The heavy crude oil and sea water, gathered from Arabian Gulf at Dammam coast, were utilized to prepare synthetic emulsions with the ratios of (90/10, 70/30, and 50/50 vol %) heavy crude oil/water.

Table 5

Arabian Heavy Crude Oil Specifications

test	method	results
API gravity	calculated	20.8
specific gravity 60/60 (°F)	IP 160/87	0.929
wax content, (wt %)	UOP 46/64	2.3
asphaltene content, (wt %)	IP 143/84	8.3
Mw (g/mol)
determined from gel permeation chromatography		6350
heteroatoms (w/w %)		6.5
aromatic carbon (mol %)
determined from 13CNMR		49.0
aromatic hydrogen (mol %)
determined from 1HNMR		7.81
saturates (wt %)		16.3
aromatics (wt %)		25.3
resins (wt %)		48.1

Synthesis of Demulsifiers

Three APEI were synthesized in a single-step reaction by mixing pentaethylene hexamine (10 mmol, 2.32 g) or tetraethylene pentamine (10 mmol, 1.89 g) or triethylene tetramine (10 mmol, 1.46 g) -dissolved separately in 50 mL of xylene- with GNPE (20 mmol, 5.52 g) in three-necked flasks. The reaction mixtures were heated to 120 °C under vigorous stirring under a nitrogen atmosphere for 4 h. Then, the reaction mixtures were cooled down, and the solvent was distilled off using rotary evaporator. The remaining product was dissolved in isopropanol and then salted out with supersaturated NaCl solution to remove the unreacted ethyleneimine. The organic layer was separated and isopropanol was distilled off to obtain viscous brown liquids of dinonylphenoxy pentaethylenehexamine, dinonylphenoxy tetraethylenepentamine, and dinonylphenoxy triethylenetetramine (DNPA-6, DNPA-5, and DNPA-4, respectively) according to Scheme .

Characterizations of DNPA-6, DNPA-5, and DNPA-4

To investigate the chemical structure of the synthesized DNPA-6, DNPA-5, and DNPA-4, nuclear magnetic resonance (NMR) characterizations were done on a Bruker AVANCE DRX-400 MHz NMR spectrometer using a CDCl3 solvent.

FTIR spectra were recorded with a Nicolet FTIR spectrophotometer in a wavenumber range of 4000–400 cm–1. All samples were mixed well with ground KBr and form pellets after pressing.

The cmc and the surface tension were measured for different concentrations of the prepared APEI demulsifiers in seawater by pendant drop method using a drop shape analyzer (DSA-100). Also, the IFTs of oil/water interface with different demulsifier concentrations in aqueous phase were measured using (DSA-100).

The hydrodynamic diameter (nm), PDI, and zeta potential (mV) of the surfactant aggregates at cmc for different concentrations of DNPA-6, DNPA-5, and DNPA-4 prepared using 0.001 M KCl aqueous solution were determined using dynamic light scattering (DLS) (Zetasizer Nano ZS, Malvern Instrument Ltd., Malvern, UK) at 25 °C. The asphaltene zeta potential was investigated by the dispersion of 1.5 mL asphaltene solution (50 mg sonicated for 15 min in 15 mL absolute ethanol) in 100 mL of 0.001 M NaNO3 aqueous solution. The effect of adding different concentrations of APEI demulsifiers on the asphaltene zeta potential were also carried out.

The formation of water-in-crude oil emulsions was verified using a fluorescent optical microscope (Olympus BX-51 microscope attached with a 100 W mercury lamp).

Preparation of Water/Crude Oil Emulsion

In a 500 mL beaker, the crude oil was homogenized at 5000 rpm and 25 °C while adding water gradually to the oil. After adding the calculated amount of sea water, the emulsion was left for 30 min under homogenization to ensure the formation of one phase emulsion. Different ratios of crude oil to water emulsions were prepared (50:50, 70:30, and 90:10). The droplet sizes of the prepared emulsions were measured by dispersing 50 mg of each emulsion in 10 mL of toluene, and the data were displayed in Figure . The emulsion droplet diameters were 576.8, 487.7, and 455.5 nm for 50:50, 70:30, and 90:10 W/O emulsions, respectively. The prepared emulsions showed high stability at 60 °C for more than 2 weeks.

Figure 1

Droplet sizes of the different water/oil emulsions (a) 50/50, (b) 70/30, and (c) 90/10.

Hydrophile–Lipophile Balance (HLB)

In order to calculate the HLB of the synthesized APEI, the following equation was utilized; HLB = 20 × MH/(MH + ML), where MH and ML are the formula weight of the hydrophilic and lipophilic (hydrophobic) portions of the molecule.[55]

Demulsification Performance Study

To study the demulsification efficiency for each emulsion used in this study, 25 mL quick-fit measuring cylinders were used. The demulsifiers’ solutions were prepared by dissolving each demulsifier in xylene/ethanol mixture (75/25 vol %). Different concentrations of ARBREAK 8846 as a commercial demulsifier were prepared under the same conditions for DNPA-6, DNPA-5, and DNPA-4 in order to compare the demulsification performance. Each demulsifier with different concentrations were then injected into the 25 mL cylinders containing different emulsion types. To ensure the complete homogeneity of the demulsifiers and the emulsion solution, the mixture was shacked vigorously for 1 min. The demulsification process was then noticed and studied at different time intervals after placing the bottles in a water bath at 60 °C. In each set of experiments, a blank sample was considered in order to ensure the stability of the prepared emulsions at 60 °C. The demulsification efficiencies (η %) for different compositions of crude oil and water emulsions at 60 °C were determined as described in the former wok.[56] The η % was determined according to the relation η % = Vs/Ve, where Vs is the water volume separated at a specific time and Ve is the total emulsified water.