Synthesis and application of new surface active poly (ionic liquids) based on 1,3-dialkylimidazolium as demulsifiers for heavy petroleum crude oil emulsions

Accepted Manuscript Synthesis and application of new surface active poly (ionic liquids) based on 1,3-dialkylimidazolium as demulsifiers for heavy petroleum crude oil emulsions

Abdelrhman O. Ezzat, Ayman M. Atta, Hamad A. Al-Lohedan, Ahmed I. Hashem PII: DOI: Reference:

S0167-7322(17)33517-1 https://doi.org/10.1016/j.molliq.2017.12.081 MOLLIQ 8377

To appear in:

Journal of Molecular Liquids

Received date: Revised date: Accepted date:

3 August 2017 24 November 2017 14 December 2017

Please cite this article as: Abdelrhman O. Ezzat, Ayman M. Atta, Hamad A. Al-Lohedan, Ahmed I. Hashem , Synthesis and application of new surface active poly (ionic liquids) based on 1,3-dialkylimidazolium as demulsifiers for heavy petroleum crude oil emulsions. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Molliq(2017), https://doi.org/10.1016/j.molliq.2017.12.081

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ACCEPTED MANUSCRIPT Synthesis and Application of New Surface Active Poly (ionic liquids) Based on 1,3-Dialkylimidazolium as Demulsifiers for Heavy Petroleum Crude Oil Emulsions Abdelrhman O. Ezzat1, Ayman M. Atta1,2,* Hamad, A. Al-Lohedan 1, and Ahmed I. Hashem3 1

Chemistry department, college of science, King Saud University, Riyadh 11451, Saudi Arabia. 2

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Petroleum Application Department, Egyptian Petroleum Research Institute, Nasr City 11727, Cairo, Egypt. 3

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Chemistry department, faculty of Science, Ain Shams University, Abasia, 11566 Cairo, Egypt.

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Abstract: Application of ionic liquids (ILs) and their polymers (PILs) as

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green chemicals in the petroleum industry is an original area of the research study. This work aims to synthesize new amphiphilic ILs based

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on dialkyl substituted imidazolium cations as a head groups combine with acetate and 4-(trifluoromethoxy) phenyl borate anions. Their surface activity and aggregation behaviors, in toluene and aqueous medium, have

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been investigated by surface tension, particle size distribution and zeta

PT E

potentials measurements. The sizes of aggregates in water and toluene solvents have been investigated from the dynamic light scattering (DLS)

CE

measurements. The demulsification mechanism for the heavy crude oil / water emulsions at low water contents has been estimated from the

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fluorescent optical microscope in the presence of the prepared ILs and PILs. The demulsification performance of ILs and PILs demulsifiers was found to be considerably improved with incorporation of oxyethylene units into hydrophobic imidazolium cations, and increment the content of 4-(trifluoromethoxy)phenyl borate anions. The results confirmed that the PIL has stronger adsorption for asphaltene molecules facilitated the distortion of the asphaltene protective film that stabilized the water-in-oil

1

ACCEPTED MANUSCRIPT emulsion and thus promoting the water droplets coalescence to realize the separation of water from oil. Keywords: Oil-in-water emulsion; Demulsification; Dialkylimidazolium; Ionic Liquids; Amphiphiles. 1. Introduction:

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Ionic liquids, ILs, as a green chemical attracted great attention to replace

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surfactants that used to solve many petroleum problems such as enhanced oil recovery, demulsifiers, corrosion inhibitors, asphaltene and oil spill

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dispersants, refining extraction solvents and catalysts modifiers [1-5]. The undesirable emulsified water and salts with crude oil caused several

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problems in the production, transportation and refining of crude oils industries [6-8]. There are different polymer structures having a wide

amines,

phenol

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range of polymer molecular weights based on mixtures of alkoxylated formaldehyde

copolymer,

polypropylene

oxide,

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polyethylene oxide were used to solve the emulsion problems [9].

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Recently, there is need to design more effective cheap and environmentally friendly chemical demulsifiers to replace the polymer blends demulsifiers. In this respect, IL has been reported among several

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demulsification chemicals and techniques based on nanomaterials,

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ultrasonic, microwaves, bacteria and CO2 [10-14]. IL contains both either amphiphilic cations and anions have strong ability to replace the asphaltene from the surface of water in oil (W/O) or oil in water (O/W) emulsions. They have strong ability to change the stabilization of emulsion either by affecting the interfacial tension [15] or to reduce the dispersion of asphaltene at the surface of emulsion [16]. It was also previously reported that the demulsification rate of ILs was increased by applying of microwave radiation in the destabilization of water-in-oil 2

ACCEPTED MANUSCRIPT (W/O) emulsions [2, 10, 17]. The effect of ILs chemical structures on their efficiencies as new demulsifiers is still ambiguous to select the suitable ILs having high demulsification rate of crude oil emulsions. It is well know that the polymeric materials have great advantages over monomeric materials to apply as oil field chemicals due to their high

PT

activity at lower concentrations, low sensitivity to processing salts pressure and temperature [18]. For these reasons poly (ionic liquids),

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PILs, were recommended to apply as oil field chemicals due to their low volatility, general non-flammability, excellent thermal characteristics,

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higher activity and also minimized any material loss due to leaching [19-

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22].

PILs were produced from radical polymerization of polymerizable ILs

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based on vinyl or acryloyl imidazolium, pyridinium or ammonium salts cations combined with numerous organic cations [19]. The PIL colloids

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as amphiphiles were produced to combine the unique properties of ILs

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and the superior dispersity of colloidal particles is still target for modern application of PILs [23]. Considering this potential, it was possible to design amphiphilic PILs for oil field application as demulsifiers [14, 16].

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It is important to consider the balance between hydrophilic and hydrophobic characteristics either in PILs cations or anions during design

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of PILs that played an important role in the demulsification process. 1Alkyl-3-methylimidazolium salts were most popular heterocycles cations that used as ILs due to easy alkylation of commercially available Nmethylimidazoles, relatively low melting points and viscosities, their aromaticity that increased their stability, and easy preparation methods. New method was developed to prepare imidazolium compounds having more than two alkyl chains at atmospheric pressure and to obtain high yields [24]. This method was based on modification of Debus3

ACCEPTED MANUSCRIPT Radziszewski method [25] that reacted the benzil (1,2-diphenylethane1,2-dione) molecule with formaldehyde and two ammonia equivalents to form an imidazole ring. In the present work, new PILs based on novolac resin of phenoxy substituted alkyl imidazolium cations were prepared and used to demulsify different types of crude oil water emulsions. Moreover,

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the demulsification mechanism of the prepared PILs in destabilization of crude oil water emulsions has been investigated. The mechanism is

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focused on the aggregation of asphaltenes and reduction of interfacial tension (IFT) at water/oil interfaces rather than the oil film rupture rate.

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In this regard, the IFT between the Arabian heavy crude oils and PILs

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solutions was evaluated. 2. Experimental

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2.1. Materials

All chemicals used in the preparation of ILs and PILs were purchased

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from Sigma-Aldrich chemicals Co. and they used without further

PT E

purification. Dodecyl amine (DDA), heptyl amine (HA), glyoxal monohydrate, acetic acid and 4-hydoxybenzaldehyde (HBA) were used to

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prepare dialkylimidazolium acetate ionic liquids. Tetraethylene glycol (TEG), 1,2-dichlorodiethyl ether (DCDE) were used to etherify the

AC

prepared ILs. 4-(trifluoromethoxy)phenylboronic acid, formaldehyde ( aqueous solution 37 Wt. %), NaOH and hexamethylenetetramine (HMTA) were used to prepare PILs.

Heavy Arabian crude oil

specifications listed in Table 1, which produced from Ras Tanoura wells by Aramco, Saudi Arabia was used to prepare synthetic emulsions. The total dissolved solids, calcium, magnesium, sodium and chloride contents the seawater collected from the Arabian Gulf are 36170, 522, 1624,

4

ACCEPTED MANUSCRIPT 13416, 23321 mg. L-1, respectively. It was used to prepare synthetic crude oil water emulsions (90/10, 80/20 and 70/30 volume %). 2.2. Preparation methods a) Preparation of ILs

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Amine solution was prepared by mixing of DDA (0.1mol; 18.5 g) or HA (0.1 mol; 11.5 g) in 100 mL of acetic acid aqueous solution ( 50 volume

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%) in ice bath at temperature -4 oC. The aldehyde solution was prepared

SC

by mixing the glyoxal monohydrate (0.05 mol; 3.8 g) with HBA (0.05 mol; 6.1 g) in 100 mL of acetic acid aqueous solution (50 volume %) in a

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separate flask at temperature -4 oC. The aldehyde solution was added to the amine solution under vigorous stirring and heated at 80 oC for 5 h.

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The reaction mixture was washed with diethyl ether to obtain colorless organic phase. The reaction mixture was purified after separation using rotary evaporator to produce dialkyl imidazolium acetate as ILs. The

D

reaction yield percentages of didodecyl imidazolium acetate (DDI) and

respectively.

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diheptyl imidazolium acetate (DHI) liquids were 87.3 and 95.6 %,

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b) Etherification of ILs

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DDI or DHI (0.01 mol) was mixed with TEG (0.01 mol), DCDE (0.02 mol) and NaOH pellets (0.02 mol). The reactants were stirred at the reaction temperature of 120 oC for 4h. The reaction mixture was cooled and poured in acetone solvent to precipitate the NaCl from the reaction. The final product of the reaction was separated from solvent by using rotary evaporator. The reaction yield percentages of etherified di-dodecyl imidazolium acetate (EDDI) and di-heptyl imidazolium acetate (EDHI) liquids were 92.4 and 98.7 %, respectively. 5

ACCEPTED MANUSCRIPT c) Preparation of PILs The polymerization of the prepared ILs was carried out using two stepwise routes by reacting DDI, EDDI, DHI and EDHI either with formaldehyde or HMTA. In this respect, DHI (0.003 mol; 1.25 g) was mixed with HMTA (0.0015 mol; 0.21 g) and 4-(trifluoromethoxy)

PT

phenylboronic acid (0.0015 mol; 0.31 g). The reaction mixture was heated at 120oC with stirring under nitrogen atmosphere. The reaction

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products were purified using rotary evaporator to isolate the final PILs.

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The polymers of DDI and DHI were designated as PDDIB and PDHIB,

EPDIB and EPHIB, respectively.

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respectively. The polymers based on EDDI and EDHI were designated as

The second method to prepare PILs was based on reaction of DDI or DHI

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with formaldehyde in the presence of NaOH as a catalyst. In this respect, DDI (0.01 mol; 4.16 g) was mixed with formaldehyde (0.14 mol) and

D

0.24 mL of NaOH (4 mol/L). The reaction mixture was stirred for 5 h at

PT E

90 oC. The reaction product was washed with aqueous HCl solution (10 volume % ) and water several times to obtain neutral solution. The final product was dried at 70 oC. The polymers of DDI and DHI are designated

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as PDDIF and PDHIF, respectively.

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2.3. Characterization of ILS and PILs The chemical structure of the prepared ILS and PILs was characterized by proton magnetic nuclear resonance, 1HNMR, spectroscopy model a 400MHz Bruker Avance DRX-400 spectrometer. The molar mass of the prepared ILS and PILs was determined by size exclusion chromatography (SEC; Waters 600E pump, Waters WISP 717 sample injector and Alltech 2000ES evaporative light scattering detector and Ultrastyragel columns 6

ACCEPTED MANUSCRIPT with dimensions of 7.8 x 300 mm, 103, 500 and 50 Å). The thermal degradation steps, of the prepared ILs and PILs, were evaluated from thermogravimetric analysis (TGA) and differential thermal analysis (DTA) using Shimadzu DTG-60 M. All samples were run in aluminum pans under a nitrogen atmosphere at a heating rate of 10 °C/min.

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The surface tension measurements of the prepared ILs and PILs in the aqueous solutions were conducted using pendant drop method and

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evaluated using drop shape analyzer (DSA-100). The aggregation of the

SC

prepared ILs and PILs was evaluated in aqueous and toluene by dynamic light scattering (DLS) to determine the hydrodynamic diameter of

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aggregates (nm), polydispersity index (PDI) and zeta potential in aqueous solutions using (Zetasizer Nano ZS, Malvern Instrument Ltd., Malvern,

MA

UK) at 25 oC.

The crude oil water emulsion was confirmed using fluorescent Optical

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microscope (Olympus BX-51 microscope attached with a 100 W mercury

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lamp).

2.4. Demulsification of the crude oil water emulsions

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The demulsification efficiency (%DE) of the of the prepared PILs for crude oil water emulsions was determined at 60 oC as reported in the

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previous work [14, 16]. The prepared PIL was dissolved with solvent mixture of xylene / ethanol (75/25 Vol. %) to obtain PIL concentrations of 70 Wt. %. The PIL solution was injected in the crude oil water emulsion at different concentrations ranged from 50 to 500 mg/L. The blank sample is based on the crude oil emulsions in the absence of IL and PIL dose and presence of solvent (xylene/ethanol; 75/25). The solvent was injected into emulsions at the same concentration doses. 7

ACCEPTED MANUSCRIPT 3. Results and discussion In this work, substituted imidazolium ILs with long side chains are prepared by reacting dialkylimidazolium ILs with HMTA or FA to produce a series of acetate PILs as represented in Scheme 1.

The

symmetrical 1,3dialkylimidazolium IL is prepared by reacting HBA with

PT

HA or DA in the presence of glyoxal and acetic acid as represented in the experimental section. The resole type of phenoxy 1,3-dialkylimidazolium

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can be produced either by condensation with FA or HMTA. The

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produced oligomers are soluble in common organic solvents and water. The non-soluble oligomers were not produced from these reactions. The

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molecular weights data of the oligomers such as number average molecular weights (Mn), weight average molecular weights (MW) and

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dispersity index (DI=Mw/Mn) are given in Table 2. The molecular weights data (Table 2) confirm that the molecular weight and repeating

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unit of polymer (n) are decreased for the polymers based on di-dodecyl

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more than that based on di-heptyl imidazolium ILs. Moreover, the DI values are increased for the polymers based on di-dodecyl more than that based on di-heptyl imidazolium ILs. These mean that the lowering of

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alkyl carbon number increases the yield of imidazolium cations and molecular weights of oligomers to prevent the curing of resole resins due

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to steric hindrance of alkyl groups having higher carbon number [24, 26]. The produced oligomers based on imidazolium cations are reacted with linking agent based on DCDE and through the active hydrogens of the phenolic ring using TEG to produce etherified derivatives as represented in Scheme 1.

8

ACCEPTED MANUSCRIPT 3.1. Characterization of ILs and PILs The chemical structure of poly (dialkylimidazolium) ILs and their ethers are confirmed from

1

HNMR and their representative spectra are

summarized in Figure 1 a- c. The appearance of singlet peak related to 2H protons of imidazole at 7.87 ppm in all spectra (Figure 1a-c) confirms

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the formation of imidazole rings. The disappearance of peak at 9.97 ppm and appearance of peaks at 7.1 and 8.5 ppm elucidate the substitution of

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imidazolium proton, between two nitrogen and phenoxy group (Figure

SC

1a-c). The appearance of peaks at 4.19 (m, 4H, 2 CH2-N), 1.79 (m, 4H, 2 CH2), 1.62 (s, 3H, CH3), 1.25 (m, 16H, 8 CH2), 0.85 ppm (m, 6H, 2 CH3)

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elucidates the incorporation of diheptyl groups in DHI (Figure 1a). These peaks are also observed for didodecyl groups of DDI (Figure 1 b) to

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confirm the incorporation of dodecyl groups in imidazole rings as represented in Scheme 1. The appearance of multiple peaks at 3.65 ppm

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(-CH2CH2O) in the spectrum of EPHIB (Figure 1c) and all spectra of

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EPHIF, EPDIF and EPDIB (they were not represented here for brevity) confirm the etherification of phenol hydroxyl group with TEG. The appearance of new broad peak at 4.3-4.8 ppm elucidates the presence of

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amine proton cations as represented in scheme 1 and Figure 1c.

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It is very important to study the thermal stability of the prepared PILs before application as oilfield chemicals because the petroleum industry usually needs to expand their operations at elevated temperature [27]. The thermal stability of the prepared ILs is estimated by TGA-DTA measurements as represented in Figure 2 (a-d). The thermal stability of the prepared ILs is confirmed from increasing the initial decomposition temperatures of DHI, DDI and EPDIB as 165, 195 and 285

o

C,

respectively. It was previously reported that the thermal stability of 9

ACCEPTED MANUSCRIPT imidazole based ILs depended on the anion types [28-30]. In the present system, it can be confirmed that the thermal stability of the prepared ILs increases with the increment of the chain lengths of the alkyl substituted imidazole cations. Moreover, the presence of two different types of anions on the same molecule of the prepared PILs increases its thermal

PT

stability. The low thermal stability of ILs based on imidazole cation and acetate anion is referred to the formation of acetic acid that produced

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from the deprotonation of the cation with the further formation of the original base. The formation of acetic acid reduces the thermal stability of

SC

ILs [31]. The remained residue 12 and 22.3 Wt. % of EPDIB and EPHIB

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(Figure 2c and d) after heating up to 800 oC confirm the crosslinking of PILs at high temperature due to presence of methylene links of phenyl

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dialkyl imidazole as substituent.

3.2. Solubility and surface activity of ILs and PILs

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The investigation of the surface activities of the prepared ILs and PILs in

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water and organic solvent is very important to apply as demulsifier in the petroleum industry. The evaluation of the surface activities of ILs and PILs at air/water or oil/water interfaces assist to design the suitable

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chemical structure beside the interpretation the demulsification

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mechanism. In the present system the long chain alkyl substituents imidazolium cations attracted great attention as amphiphilic ILs or PILs that combine both properties of ionic liquids and surfactants [32-34]. The solubility, micellization and adsorption of these ILs in water and organic solvents played important factors to select the appropriate applications in the extraction or oilfield chemicals [35-37]. In this respect, the relative solubility number (RSN) of the prepared ILs and their PILs is measured as reported in the previous work [38] and listed in Table 3. The RSN 10

ACCEPTED MANUSCRIPT values are alternative for hydrophile-lipophile balance (HLB) of the surfactants [38] and their value indicated the solubility of the materials in water. It is reported that, the materials having RSN values < 13 is considered insoluble in water, while 1317 is dispersible at low concentrations. The solubility in water is elucidated by a RSN value >

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17. In this respect, all ILs (Table 2) have RSN value more than 17 and decreases with increasing the substituent alkyl chain length from heptyl to

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dodecyl. The PILs show low RSN below 17 to confirm the lower solubility in water due to hydrophobicity of polymer backbone and

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hydrophobicity of 4-(trifluoromethoxy) phenylborate anion (Scheme 1).

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The differences in the solubility between ILs and their PILs can be referred to the assembly of IL cations and anions in aqueous solutions. In

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the present work, the hydrophobicity of the ILs is tuned by variation of the alkyl chain length of imidazolium cations, the type of head-groups

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oxyethylene groups.

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with the insertion of 4-(trifluoromethoxy) phenylborate anion and

The behavior of ILs in aqueous system is investigated from their surface tension and zeta potential measurements.

The surface tension

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measurements of the prepared ILS and PILs are investigated by pendant drop method as reported in the experimental section. The relations

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between surface tension (mN/m) with their concentrations are represented in Figure 3. It was previously reported that, the surface active ILs behave like cationic surfactants and they have great tendency to aggregate more than the conventional cationic surfactants [39]. The aggregation of the ILs and their PILs can be investigated from Figure 3 and determined as critical aggregation concentration (cac; mmol. L-1). Their values are determined from the intersection between the regression straight line of the linearly dependent region and the straight line passing through the 11

ACCEPTED MANUSCRIPT plateau (Figure 3). The cac value of the prepared ILs and PILs are determined and listed in Table 3. The data confirm that the cac values are decreased with increment of alkyl chain length and polymerization of imidazolium cation. Moreover, the ability of ILs to reduce the surface tension at cac, γcac, is increased with the polymerization of imidazolium

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cation, incorporation of TEG unit and increment the carbon number of alkyl substituent from heptyl to dodecyl group. These data elucidate the

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ability of ILs to aggregate with increasing the ILs concentration and decreasing the carbon number of the alkyl substituent [40]. The

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incorporation of 4-(trifluoromethoxy)phenyl borate anion increases both

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the hydrophobicity of the prepared PIL and its aggregation at lower concentrations. The effectiveness of the ILs was expressed by the maximum reduction of surface tension of the water that determined from

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the equation, ∆γ= γwater - γcac; where γwater is the surface tension of water at 25 oC. The ∆γ values of the prepared ILs and PILs are determined in

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water and listed in Table 3. The data confirm the increment of ILs and

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PILs effectiveness to reduce the surface tension and to adsorb at interfaces with increment the chain length of alkyl substituent,

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incorporation of oxyethylene in imidazolium cation and new 4(trifluoromethoxy)phenyl max,

anion.

The

surface

excess

and the minimum area of ILs, Amin, at the aqueous–

AC

concentration, Г

borate

air interface are used to correlate the adsorption of the prepared ILs and PILs with their chemical structures. The surface excess concentration is calculated from surface tension data using the following equation: Г max = (-∂ γ / ∂ ln c)T /RT, where (−∂γ / ∂ ln c)

T

is the slope of the plot of γ

versus ln c at constant temperature (T) and R is the gas constant (in J mol−1 K−1) [41]. The area per molecule at the interface is estimated using the equation: Amin = 1016/ N Гmax, where N is Avogadro’s number. The 12

ACCEPTED MANUSCRIPT data of Гmax, Amin, and (-∂ γ / ∂ ln c) are calculated and summarized in Table 3. The data listed in Table 3 confirm that the PILs form aggregates or micelles at lower concentrations due to increment of the polymer hydrophobicity with the presence of methylene groups and hydrophobic 4-(trifluoromethoxy)phenyl borate anion. Moreover, the presence of these concentration by increment Г

max

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groups increases the tighter packing of PILs at interfaces to increase its and lowering the Amin, values at

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air/water interfaces due to stronger hydrophobic interactions and their denser arrangement of hydrophobic groups [42]. The packing of PILs at

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interfaces can be also referred to increment the hydrophobicity of PIL

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anions that enhances the binding at the aggregate surface. This leads to reduce the electrostatic repulsion between head groups, thereby

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increasing its tendency to aggregate and lowering values of cac [43]. Consequently, the order and surface activity of the prepared ILs and PILs at interfaces are increased with incorporation of oxyethylene unit and 4-(trifluoromethoxy)phenyl

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hydrophobic

borate

anion

to

avoid

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energetically unfavorable contact of hydrophobic chains with water. It also decreases the electrostatic repulsion between head of imidazolium

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cations. These results conclude that, the disubstituted alkyl imidazolium cations with acetate and 4-(trifluoromethoxy)phenyl borate anions

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behave as surfactants due to its successive adsorption of both cations and anion at interfaces [44]. The data of zeta potentials in the aqueous solutions can be also used to confirm the effect of ILs and PILs chemical structures on their surface charges and performance in the water solutions. It is previously reported that, the ILs behave like potential determining ions as colloid and aggregates [45]. The zeta potential values of the prepared ILs and PILs were determined from DLS measurements and listed in Table 3. It was 13

ACCEPTED MANUSCRIPT noticed that, the zeta potential values are all positive except DHI. Moreover, the values of zeta potential are increased with polymerization and etherification of ILs. These data confirm that the PILs based on dialkyl substituent imidazolium cations have great tendency to form aggregates in the water at lower concentrations. The negative value for

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zeta potential of DHI confirms that the heptyl groups cannot hinder the acetate charges of the formed micelles. The higher zeta potential data of

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EPDIB indicates the 4-(trifluoromethoxy)phenyl borate counter ion bearing disubstituted dodecyl imidazolium cations forms stable aggregate

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solution than their acetate counterparts of DDI [46]. This can be

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correlated to the surface tension measurements that confirm the unfavorable contact of hydrophobic chains with water is avoided by of

oxyethylene

unit

and

hydrophobic

4-

MA

incorporating

(trifluoromethoxy)phenyl borate anion.

D

The aggregation diameter can be also estimated from DLS measurements

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in toluene and water solution from hydrodynamic diameter (Dh, nm) of ILs and PILs solution as shown in Figure 4 and 5 a-c for DDI derivatives as representative samples. It is interest to represent that, the

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prepared ILs and PILs form different size aggregates in water correlated to their chemical structures. The DDI (Figure 4 a) shows small

AC

aggregates having different sizes ranged from 0.1 to 55 nm. The incorporation of oxyethylene unit (EDDI) increases the aggregate sizes Dh value to 89.2 nm with uniform polydispersty index (PDI; 0.188) as represented

in

Figure

5b.

Moreover,

the

polymerization

and

incorporation of 4-(trifluoromethoxy) phenylborate anion increase the Dh value up to 244.3 nm with more uniform aggregates having PDI equals 0.123. The increment of Dh value may be attributed to higher counterion binding and low polarity indices of the 4-(trifluoromethoxy) phenylborate 14

ACCEPTED MANUSCRIPT anion counterparts that increase the interaction between the small size aggregates to form larger aggregates [47]. The data listed in Table 3 depicted that the EPDIB possess higher zeta potential than DDI or EDDI. Hence, the zeta potential and Dh measurements elucidated that the poly (disubstituted imidazolium) cations form higher stable aggregates than its

PT

monomer counterion in aqueous solution. The behavior of DDI, EDDI and EPDIB in nonpolar solvent such as toluene, represented in Figure 5

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a-c, shows different performance than that observed in water (Figure 4a –c). It is observed that the Dh of aggregates reduced from 18.883 µm to

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67 nm after polymerization and etherification of DDI as represented in

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Figures 5 a-c. This means that the hydrophobicity of DDI increases its solubility in nonpolar solvent after conversion to EPDIB (scheme 1).

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These data elucidate that both EDDI and EPDIB have great tendency to act as amphiphiles in both aqueous and nonpolar organic solvents. This behavior encourages the application of the prepared materials as oilfield

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chemicals.

3.3. Demulsification of crude oil water emulsions In our previous work [14, 16], ILs and PILs based on ammonium salts

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were used to separate water from the crude oil emulsions in a long time.

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Moreover, the new demulsification mechanism was proposed to clarify the demulsification mechanism of ILs for crude oil emulsions. It was concluded that [16], the main factor that determine the activity of ILs and PILs to act as demulsifier is the ability of ILs or PILs to disperse in the crude oil emulsion. It was also reported that [13], the water insoluble hydrophobic ILs are more effective as demulsifiers than that soluble in water. It is also very important to consider that, the ILs demulsifiers should have a high molecular volume of IL and cations, a high 15

ACCEPTED MANUSCRIPT polarizability value for the cations, and low molecular refractivity and molecular volume values for the anions [3]. In this respect, EDDI and EPDIB are selected to act as demulsifiers for three types of crude oil water emulsions having W/O emulsion compositions 10/90, 20/80 and 30/70 volume %. The dehydration curves based on emulsification

PT

efficiencies (E %) and dehydration time relations at 60oC are plotted in Figure 6 a-c and summarized in Table 4. The data elucidate that, the

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blank samples cannot separate any water droplet during more than 30 days when heated at the same separation temperature. It was also noticed

SC

that, the EPDIB shows great demulsification efficiency with decreasing

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the emulsion water contents (10/90 Vol. %). The EDDI achieves more demulsification efficiencies and low dehydration times with increasing

MA

the water contents of crude oil emulsions (30/70 Vol. %). The data listed in Table 4 and Figure 6 a-c show that using 250 mg/L of EPDIB reached 100 % of water removal in longer time at 45 minutes when the crude oil

D

water emulsion of 20/80 vol.% is used more than the crude oil water

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emulsions of 10/90 or 30/70 vol.% that achieved dehydration time with 30 minutes. In our previous works [14, 16], the mechanism of crude oil

CE

water demulsification by using PILs depends on their ability to form networks surrounded to the water droplet to coalesce and demulsify from

AC

the crude oil. Careful inspection of data represented in Figure 6 a and c which indicates that the EPDIB networks have the same coalescence rates. Figure 6b shows that the EPDIB networks have low tendency to interact with water droplet at higher concentration using crude oil water emulsion 20/80 vol.%. The EDDI and EPDIB achieve complete dehydration of crude oil emulsion within 1h at 60 oC as represented in Figure 6 and photos recorded in Figure 7. The non-contaminated water (pure water without oil droplet) is observed with EPDIB demulsifier more 16

ACCEPTED MANUSCRIPT than EDDI (Figure 7). The presence of some crude oil contaminates with water during demulsification confirms the good effectiveness of PILs as demulsifier. Optical microscope photos of crude oil water emulsion in the absence and presence of EPDIB are represented in Figure 8 a-c. Fluorescence

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microscopy image of water crude oil emulsions in the presence 100 ppm of EPDIB after 15 minutes is recorded in Figure 9. The optical

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microscope image of crude oil water emulsion (Figure 8 a) shows the

SC

formation of stable W/O emulsions, which possesses low droplet sizes, and low contents of multiple emulsions. It is observed that, the presence

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of EPDIB replaces the asphaltene layer surrounded the water droplet to increase the water droplet sizes (Figure 8b). The increment of

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demulsification times to 15 minutes increases the water droplet sizes to separate by gravity (Figure 8c). The formation of PILs networks

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droplets surfaces as observed from fluorescence microscopy image (Figure 9). It is noticed that, the formed EPDIB networks facilitate their interaction with water using its ions either with imidazolium cations or

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acetate and 4-(trifluoromethoxy) phenylborate anions. It can be also observed that, the EPDIB is highly dispersed in crude oil due to

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increment of its hydrophobicity as confirmed from surface tension and DLS data. These demulsification data elucidate that the presence of two dodecyl hydrophobic group and oxyethylene units in the chemical structure of EDDI and EPDIB increase their dispersion in the crude oil to surround the water droplet in crude oil emulsions. Accordingly, the application of ILs and PILs as demulsifier depend on their great ability to aggregate asphaltene surrounded the W/O emulsion followed by great interaction with water droplet to coalesce with other water droplet. 17

ACCEPTED MANUSCRIPT Moreover, the PILs and ILs show different mechanism than traditional surfactants. The great dispersion of PILs and ILs in the continuous phase facilitates their ability to for network to surround the water-dispersed phase as supported from optical microscope photos. This conclusion is supported by the surface tension measurements and asphaltene dispersion

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efficiencies.

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4. Conclusions:

Dialkyl imidazolium amphiphilic ionic liquids were prepared in the

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presence of acetic acid and polymerized in the presence of formaldehyde or hexamethylenetetramine and 4-(trifluoromethoxy)phenylboronic acid.

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These ILs and PILs were etherified with tetraethylene glycol to produce amphiphilic PILs. The surface tension measurements confirmed that the

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prepared PILs exhibit low cac values and best performance to reduce the surface tension than their monomers. These results conclude that the

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presence of disubstituted alkyl imidazolium cations with acetate and 4-

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(trifluoromethoxy)phenyl borate anions

produce surface active PILs.

They behave like surfactants due to successive adsorption of both cations and anion at interfaces. The DLS measurements elucidate that, these new

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ILs and PILs have the ability to form aggregates above the cac in both

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aqueous and toluene solvent with Dh ranged from 0.1−55 nm. The prepared ILs and PILs used as demulsifiers for heavy crude oil emulsions. Results obtained on the current work show that the EPDIB interact with water droplet after aggregation of asphaltene layer that surrounded water droplets with its ions either with imidazolium cations or acetate and 4(trifluoromethoxy) phenylborate anions. It can be also observed that the EPDIB is highly dispersed in crude oil due to increment of its hydrophobicity as confirmed from surface tension and DLS data. The 18

ACCEPTED MANUSCRIPT demulsification data confirm that the presence of two dodecyl hydrophobic group, oxyethylene units in the chemical structure of EDDI and EPDIB facilitate their dispersion in the crude oil to surround the water droplet in crude oil emulsions. Acknowledgment:

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The authors would like to extend their sincere appreciation to the

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Deanship of Scientific Research at king Saud University for its funding

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this Research group NO (RGP-235).

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ACCEPTED MANUSCRIPT Table 1. Arabian heavy crude oil specifications.

Method

Results

API gravity

Calculated

20.8

Specific gravity 60/60(oF)

IP 160/87

0.929

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Test

UOP 46/64

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(Wt%) Asphaltene content, (Wt%)

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IP 143/84

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Heteroatoms (w/w%)

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Mwt (g/mol) Determined from Gel permeation chromatography

2.3

8.3

6350 6.5 49.0

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Aromatic carbon (mol %)

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Wax content,

Determined from 13CNMR

Aromatic hydrogen (mol %)

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7.81

Determined from 1 HNMR

40.5

Aromatics (w%)

29.8

Resins (w%)

21.4

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Saturates (w%)

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Mn g.mol-1 2235 5495 1746 4980

DI= Mw/Mn 1.7 2.3 2.9 3.5

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PDHIF PDHIB PDDIF PDDIB

Mw g.mol-1 3800 12638 5063 17430

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Гmax Zeta Δγ cac γcac × 10 10 compounds RSN potential mN.m (−∂γ/∂lnc)T mmol.L-1 mN.m-1 µmol. 1 (mV) m-2 DHI 18.8 -2.7 12.30 42.0 30.1 8.3 3.40 EDHI 19.3 6.8 14.80 40.0 32.1 12.9 5.20 DDI 17.4 1.4 2.20 32.0 40.1 19.5 8.10 EDDI 18.3 2.1 0.73 24.0 48.1 29.6 12.20 EPDIB 16.3 36.0 0.31 18.0 54.1 32.7 13.30 EPHIB 14.5 44.2 0.12 21.3 50.8 31.2 12.74

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Amin nm2 0.049 0.032 0.020 0.014 0.012 0.013

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EPDIB

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EDDI

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EPHIB

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EDHI

50 100 250 50 100 250 50 100 250 50 100 250

10/90 20/80 30/70 %DE Time %DE Time %DE Time (%) (minute) (%) (minute) (%) (minute) 0 30 120 35 120 12 120 60 120 50 120 35 120 70 120 65 120 10 120 35 120 50 120 25 120 50 120 60 120 40 120 85 120 70 120 75 120 90 120 70 120 100 80 100 85 85 120 100 40 100 60 100 120 85 75 100 120 90 120 100 45 100 65 100 70 100 30 100 45 100 30

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Concentrations (mg/L)

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Scheme 1: Preparation methods of the ILs and PILs

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Figure 1: 1HNMR spectra of a) DDI, b) DHI and c) PDHIB.

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Figure 2: TGA and DTA analyses of a) DDI, b) DHI and c) EPDIB and d) EPHIB . 32

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Figure 3: Relation between surface tension and different concentrations of ILs and PILs in aqueous solutions at 25 oC.

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Figure 4: DLS data of a) DDI, b) EDDI and c) EPDIB in water at 25 oC.

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Figure 5: DLS data of a) DDI, b) EDDI and c) EPDIB in toluene at 25 oC.

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Figure 6: Demulsification kinetics of the crude oil emulsions W/O a) 10/90, b) 20/80 and c) 30/70 in the presence of 250 mg/L of the prepared ILs and PILs at 60 oC.

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Figure 7: Demulsification photos of W/O emulsions a) blank, b) 10/90 in the presence of EPDIB, c) 10/90 in the presence of EDDI, d) 20/80 in the presence of EPDIB, e) and f) 20/80 and 30/70 in the presence of EDDI.

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Figure 8. Optical microscope photo of crude oil/water emulsions after injection 100 mg /L EPDIB after interval times a) 0, b) 15, and c) 25 minutes.

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Figure 9: Fluorescent optical microscope photo of crude oil/water emulsions in the presence of EPDIB.

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Graphical abstract

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New aphiphilic poly(ionic liquids) based on dialkyl imidazolium cations. Fast demulsification efficiencies of heavy crude using PILs as demulsifiers. Aggregation of asphaltene layers surrounded the water droplets.

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