Substantial Enhancement of Heavy Crude Oil ... - ACS Publications

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Industrial & Engineering Chemistry Research

Research Article

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Substantial enhancement of heavy crude oil dissolution in low waxy crude

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oil in the presence of ionic liquid

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Sugirtha Velusamy1, Sivabalan Sakthivel1, Ramesh Gardas2, Jitendra S. Sangwai1,*

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Gas Hydrate and Flow Assurance Laboratory, Petroleum Engineering Program,

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Department of Ocean Engineering, Indian Institute of Technology Madras,

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Chennai – 600 036, India

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2

Ionic Liquid Laboratory, Department of Chemistry, Indian Institute of Technology Madras, Chennai – 600 036, India

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Corresponding Author:

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Jitendra Sangwai: [email protected]; Phone: +91-44-2257-4825 (Office); Fax: +91-

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44-2257-4802.

1 ACS Paragon Plus Environment


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ABSTRACT

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Enormous production losses has ascended in diverse operational and technical issues

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due to deposition of heavy crude oil (HCO) in various production components like tubing,

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near well bore (skin formation), surface storage tank, pipeline blockage, etc. Existing

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methods employed for the dissolution of HCO are either cumbersome or uses organic

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solvents, which are hazardous to the environment. This study presents finding on the

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enhanced dissolution of HCO using low waxy crude oil (LWC) in the presence of ionic liquid

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(IL). The use of ILs is found to be compatible with the polar moieties in heavy crude oil, such

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as, resins, aromatics and asphaltenes enhancing its dissolution. Twelve ionic liquids were

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tested for the dissolution of HCO using LWC. The dissolution of HCO was performed and

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confirmed using gravimetric analyses, ultraviolet-visible (UV-vis) spectrophotometry,

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Fourier transform-infrared spectroscopy (FT-IR), 13C-nuclear magnetic resonance (13C-NMR)

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and the interfacial tension (IFT) measurements. The total percentage of dissolution of HCO in

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LWC (2:3 wt/wt) with 100 ppm of ionic liquid is found to be increased by a magnitude of

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30% (71% from 41%) of the standard HCO+LWC alone. The increase in solubility (%) of

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HCO+ LWC with organic solvent (used for dilution in UV-vis) in the presence of ILs is

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observed to be a maximum of 38%. The results are further confirmed qualitatively through

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the use of FT-IR and

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determination of IFT substantiating the fact that the ILs possess the tendency to dissolve and

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recover residual oil from production systems and reservoir. In all the above experiments, the

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efficiency of the ILs with a longer alkyl chain and larger ring size is much convincing as

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compared with the rest of the studied ILs.

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C-NMR spectroscopy. These findings are further supported by the

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Key words: 13C-NMR; dissolution; FT-IR; ionic liquid; heavy crude oil; low waxy crude oil;

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UV-vis spectrophotometric technique.


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1. INTRODUCTION

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The growing demand for crude oil has led the oil and gas industries in the pursuit for

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unconventional oil resources rather than the limited conventional stock. However, the

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extraction and storage of heavy oil requires the use of cumbersome techniques for processing,

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storage and transport. The recent past portrays diverse operational and technical issues

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causing enormous production losses ascended as a consequence of deposition of heavy crude

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oil (HCO) (≤ 10 °API gravity) in various production components like tubing, near well bore

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(skin formation), surface storage tank, pipeline blockage, etc.1 The existing methods currently

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employed by the oil and gas industries have become insufficient in addressing the potential

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issues to a profitable extent. This has led to the hunt of advanced cost-effective innovative

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technologies by the petroleum industries to supply the processed hydrocarbons effectively.2-3

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Generally, the heavier fractions of the crude oil hold more of waxes, asphaltenes, resin,

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inorganic materials, biomass, etc., in liquid state when present in the reservoir which starts

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solidifying once it reaches the surface condition due to drop in pressure and temperature.

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These solidified heavier fractions, when transported, start accumulating in the production

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equipments leading to flow assurance issues. The toughest challenge for the industry is to

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confront the considerable quantities of the polar fraction of the aromatics, asphaltene and

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resin.4-5

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The conventional chemical methods for the dissolution of HCO consume huge

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quantities of organic solvents to liquefy or the execution of hot oil/water circulation. The

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common aromatic hydrocarbon solvents used are toluene and benzene, possessing the ability

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to solubilize asphaltene, resin and aromatic moiety of the HCO.6-8 On account of their volatile

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nature, these solvents own a pronounced disadvantage being hazardous to the environment.6

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Moreover, these processes are expensive and may not be easy for practice. Low waxy crude

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oil (LWC), which is commonly produced from various reservoirs, can be used instead of



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conventional chemicals. Hence, an alternative method to improve the dissolution of HCO

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using low waxy crude oil (LWC) along with ionic liquid (IL) forms the objective of the

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study.

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Ionic liquids are fused salts with cation and anion in poor co-ordination with one and

5

another, and have been widely used in several engineering fields, organic synthesis, inorganic

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synthesis, biomass conversion, electrochemical reaction, bitumen recovery, desulfurization,

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enhanced oil recovery, asphaltene degradation, etc.9-18 Purposefully induced minor structural

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variations in the cationic/anionic part of the ionic liquids lead to abrupt modulations in their

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behavior.14-15,19-20 Besides, the ionic liquids show favorable physicochemical properties, such

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as negligible vapor pressure, very good catalytic property, high thermal stability, non-

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flammability, strong hydrogen bond acceptor property and very low melting point.9

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Furthermore, the used ionic liquid can be recycled with little quantity of water and can be

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reused.9-12,13,16

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A few imidazolium based aromatic ionic liquids were employed to investigate the

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dissolution behavior of asphaltene. It was observed that the ionic liquids, such as

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[C4mim]+[Cl-], [C4mim]+[AlCl4]- increased the level of dissolution to a certain extent.21 A

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few researchers investigated the use of ionic liquids, such as [N222]+[AlCl4]-, [N222]+[AlCl4]--

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Ni2+, [N222]+[AlCl4]--Fe2+ and [N222]+[AlCl4]--Cu+ to reduce the viscosity of the heavy oil and

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improving the oil recovery.17 Other investigators also noted an effective functioning of

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Chloro-aluminate (III) ionic liquids with H3PO4 for asphalt degradation and a couple of

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imidazolium ionic liquids ([C2mim]+[BF4]- and [C4mmim]+[BF4]-) for bitumen recovery.13,16-

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17

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possess the capability to reduce sulfur content from 0.75 % to 0.23 %.from the bulk stream of

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heavy crude oil, and consequently achieving greater crude oil recovery. 18 The adhesion force

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between bitumen and silica is found to be reduced with the use of ionic liquids and making

In addition, metal based ionic liquid, 10 % of [BMIM]+[AlCl4]- has been observed to


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the process of separation much easier.22 Similarly, the contact angle and interfacial tension

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(IFT) in bitumen (crude oil)-water system is observed to be reduced in the presence of ionic

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liquids.9,23 The addition of ionic liquids to crude oil/water system has also helped in reducing

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the interfacial tension.24-26

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In the present investigation, the dissolution of HCO is tested and quantified with

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respect to solubility (%) using LWC as solvent in the ratio of 2:3 wt/wt. The dissolution

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studies of HCO using LWC with and without using ILs have been studied and estimated

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quantitatively through gravimetric analysis. To optimize the system to obtain enhanced

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dissolution/recovery of HCO, different strategies have been employed. These include

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elaborate analyses of temperature effect, dissolution time and the concentration of the ILs.

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The techniques, such as ultraviolet-visible (UV-vis) spectrophotometry, Fourier transform-

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infrared spectroscopy (FT-IR),

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interfacial tension are further employed for qualitative analysis of the dissolution of HCO in

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LWC with/without ILs.

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C-nuclear magnetic resonance (NMR) spectroscopy, and

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2. EXPERIMENTAL SECTION

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2.1. Materials

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2.1.1 Heavy crude oil (HCO)

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For the present investigation, HCO and LWC were provided by Oil India Limited

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(OIL), Assam, India. HCO was more of viscous and solid, and LWC appeared to be a very

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light oil. The physical properties of both the HCO and LWC, such as SARA, density, API

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gravity and viscosity are summarized in Table 1.

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2.1.2 Ionic liquids and solvents



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In the present investigation, twelve ionic liquids, four each from three different

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categories (imidazolium, alkyl ammonium, and lactam) were synthesized (Table 2) and

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characterized using 1H NMR (Nuclear Magnetic Resonance) technique as per literature.27-31

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The 1H NMR spectroscopic characterization of all the synthesized twelve different ionic

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liquids are provided in Figure S1-S12 with their synthesis procedures. Among them, four

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ionic liquids namely, 1-butyl-3-methylimidazolium chloride [C4mim]+[Cl-], l-butyl-3-

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methylimidazolium bromide [C4mim]+[Br-], 1-butyl-3-methylimidazolium hydrogen sulfate

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[C4mim]+[HSO4]- and 1- octyl-3-methylimidazolium chloride [C8mim]+[Cl-] belong to the

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aromatic imidazolium family; the second set of four ionic liquids namely, triethylammonium

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sulfate [N222]+[HSO4]-, triethylammonium acetate [N222]+[CH3COO]-, triethylammonium

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phosphate [N222]+[H2PO4]-, tripropylammonium sulfate [N333]+[HSO4]- belong to the aliphatic

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alkyl ammonium group; and the last set of four ionic liquids namely, butyrolactam formate

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[BT]+[HCOO]-,

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[BT]+[C6H13COO]-, caprolactam formate [CP]+[HCOO]- belong to the lactam group. In this

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investigation, the ILs are mainly chosen to compare and contrast their effects with respect to

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the families (inter-family comparison) to which they belong rather than their intra-family

17

comparison. Before commencing the experiments, all the ionic liquids were thoroughly dried

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using a vacuum pump (0.1 Pa) at 353 K for about 24 h. The utilized chemicals for the present

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experimental research are summarized in Table S1.

butyrolactam

acetate

[BT]+[CH3COO]-,

butyrolactam

hexanoate

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2.2 Experimental procedure

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2.2.1 Ionic liquid assisted heavy crude oil dissolution with LWC as a solvent

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Dissolution of HCO was performed in a three necked round bottom flask (500 mL). A

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2:3 wt/wt ratio of HCO:LWC was prepared by adding 48 g of HCO in a 500 mL flask,

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followed by the addition of 72 g of LWC to obtain an overall weight of 120g and a total


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volume of 100 mL. The mixture was then agitated using a magnetic stirrer for better

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interaction of the two crude oils, after which the dissolved crude was separated from the

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undissolved solid material (see the Figure 1 for reference). The same set of experimental

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studies were performed with the addition of 100 ppm (10 mg) of ionic liquid (under nitrogen

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atmosphere) at various conditions, such as, different reaction time within the range of 15-300

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min and temperatures in the range of 298.15 K-358.15 K with an interval of 20 K. The effect

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of concentration (100-10000 ppm) of each ionic liquid was performed individually at 298.15

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K for a reaction time of 60 min. The schematic representation of the experimental procedure

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is shown in Figure 1. Throughout this gravimetric experimental section the uncertainties are

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u(T) = 0.4 K, u(weight)= 0.1 mg, u(IL conc.) = 1 ppm, u(volume) = 0.12 mL. The parameters

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which were fixed during this gravimetric estimation are stirring speed = 1000 rpm and

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volume size = 500 mL round bottom flask and volume of sample = 100 mL of HCO:LWC

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(2:3 wt/wt)+10 mg of IL.

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2.2.2 Standard solutions of HCO:LWC (2:3 wt/wt) for UV-vis study

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Standard stock solution of 1000 ppm of HCO:LWC (in 2:3 wt/wt) mixtures were

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prepared using four different organic solvents. For e.g., 100 mg of HCO:LWC (in 2:3 wt/wt)

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was placed in a 100 mL standard measuring flask and filled up to the mark using organic

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solvent (toluene/hexane/heptane/decane). Subsequently, different concentrations (10-100

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ppm in the interval of 10 ppm) of HCO:LWC solutions were prepared and their λmax (Table

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3) was measured using UV-vis spectrophotometer in the wavelength range of 190-900 nm. At

22

the same λmax, the absorbance of the different concentrations (with regard to 2:3 wt/wt of

23

HCO:LWC) of the solutions was recorded and plotted in the calibration plots (Figure S13)

24

where R2 is > 0.99. The corresponding absorbance values for all the concentration are

25

reported in the in Table S2 with its standard deviation. Henceforth, the term, concentration



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(in ppm), is subsequently referred to the concentration of HCO+LWC (2:3 wt/wt) mixture in

2

the specified solvent.

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2.2.3 Sample solutions of HCO:LWC (2:3 wt/wt) with ILs for UV-vis Study

5

The sample solutions of 1000 ppm of HCO:LWC (2:3 wt/wt) (stock solution) were

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prepared by dissolving 100 mg of HCO:LWC (2:3 wt/wt) and 10 mg of IL (100 ppm of IL) in

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a 100 mL standard measuring flask filled till the mark using the corresponding solvents, in

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the same way as per the aforementioned section 2.2.3 (also see Figure 1). Further dilutions

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made out of the stock solutions were 10, 30, 50 and 70 ppm for the present study. The

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absorbance of all these solutions were measured using UV-vis spectrophotometer and

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compared with the standard solutions so as to calculate the increase in solubility (%) of the

12

HCO+LWC+IL system. Moreover, all the experimental studies were performed in triplets

13

and their average values are reported.

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2.2.4 Preparation of sample for FT-IR and 13C-NMR FT-IR and

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C-NMR spectroscopic techniques were used to understand the

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dissolution of HCO:LWC (2:3 wt/wt) using the typical organic solvents and in the presence

18

of ionic liquid. Samples for these studies were obtained from the bottom sediments (solid) of

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the UV-vis samples (see Figure 1). These solids were washed thoroughly using distilled water

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to remove the ionic liquid, which could be reused later, followed by drying to remove the

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organic solvent and moisture. After complete drying, the samples were separated into two

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portions; one for FT-IR (2 mg) and the other for 13C-NMR (35 mg) analyses. Throughout the

23

experimental investigation, for both the 13C-NMR and FT-IR studies, all the samples (crude

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oil, undissolved residual portion of solvent treated crude oil, undissolved residual portion of

25

the solvent+ionic liquid treated crude oil and dissolved portion of the solvent+ionic liquid


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treated heavy crude oil) and solvent (KBr/CDCl3) quantities have been maintained uniformly

2

to avoid any misleading interpretations of the spectra. The recyclization procedure for the

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ionic liquid is given in the supporting information. The 1H-NMR spectra of the fresh

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[C4mim]+[Cl-] and processed/reused [C4mim]+[Cl-] are given as Figure S14, and there was no

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considerable variation in the peaks observed on their comparison. However the efficiency of

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the recycled IL, [C4mim]+[Cl-] is not insignificant (see supporting information). Similarly, the

7

13

8

solvent+IL (heptane+[CP]+[HCOO]-) treated undissolved residue of HCO:LWC (Figure

9

S15). No other peaks were observed corresponding to the ionic liquid confirming the absence

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C-NMR spectra of the pure IL, [CP]+[HCOO]- was compared with the 13C-NMR spectra of

of the IL in the undissolved residue.

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2.2.5 Preparation of samples for IFT measurement of crude oil-water system

13

IFT measurements of crude oil-aqueous ionic liquid solutions were measured using

14

the dynamic contact angle Tensiometer (Dataphysics DCAT 11EC, Germany). The mixture

15

of crude oil (HCO+LWC in 2:3 ratio) and aqueous ionic liquid (100 ppm of IL in distilled

16

water) were stirred forcefully using an electric magnetic stirrer for about 5 h to enable the

17

ionic liquid to take an absolute effect on the crude oil-water system. Following this, the crude

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oil-aqueous ionic liquid solutions were separated into two fractions. The requisite volume of

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aqueous phase and oil phase solutions were separated and further used for the experimental

20

measurements of IFT studies. The obtained IFT values were compared with the standard IFT

21

values of crude oil-water system to understand the effect of ionic liquid in the crude oil-water

22

interface.

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2.3 Analytical methods



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Viscosity data was generated using the Viscometer (Brookfield, model: DV2TLV,

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Spindle: SC4-18, measuring range: 1.5 to 30000 cP). For API gravity, Hydrometer was used

3

to measure the specific gravity (ߛ) (range finder=0.7 to 1.0) from this the API gravity was

4

calculated. Water content of all the synthesized ionic liquids were analyzed using Karl

5

Fischer reagent in Analab Karl Fischer Titrator (Micro Aqua Cal 100, India). Prior to the start

6

of experiments, the instrument was calibrated using distilled water with a titer factor of 5.356

7

(5.356 mg of water can be determined with 1 mL of this titration agent). The instrument has

8

the ability to detect the water content in the range of 10 ppm to 100% using dual platinum

9

electrode through conductometric titration. The characterization of all the synthesized ionic

10

liquids were performed by recording 1H-NMR (Brukar Avance 500 MHz spectrometer)

11

spectra, and using the same instrument, 13C-NMR spectra of the crude oil was performed for

12

the purpose of dissolution study using DMSO or CDCl3 as the solvents. Absorbance of both

13

the standard and sample solutions were measured using UV-visible spectrophotometer

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(JASCO V-650, Japan; accuracy= ±0.2nm; wavelength range= 190 to 900 nm) at the

15

corresponding λmax of the particular solvents. The FT-IR spectrophotometer used in the

16

analyses was a JASCO FT-IR-4100 (Japan) with a maximum resolution 0.9 cm-1 and

17

22,000:1 signal to noise ratio. Dynamic Contact Angle Tensiometer (Dataphysics DCAT

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11EC, Germany) was employed to measure the interfacial tension between crude oil and

19

aqueous ionic liquid system with the use of Wilhelmy platinum-iridium plate, type PT-11, of

20

thickness 0.2 mm and area 3.98 mm2 with an accuracy ±1.5 % at 298.15 ± 0.1 K as the probe.

21

Before beginning the measurement of IFT, the calibration of the instrument was carried out

22

by measuring the surface tension of distilled water. It was observed that the measured surface

23

tension was 71.95 mN/m at the temperature of 298.15 K for deionized water which was in

24

good agreement with the reported value of 71.99 mN/m.32 Similarly, the IFT of a known


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system (hexane/water) was observed to be 50.35 mN/m, which also showed good consistency

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with the literature value of 50.38 mN/m.33

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3. RESULTS AND DISCUSSION In the present investigation, twelve different ionic liquids namely, [C4mim]+[Cl-],

6

[C4mim]+[Br-],

[C4mim]+[HSO4]-,

7

[N222]+[H2PO4]-, [N333]+[HSO4]-, [BT]+[HCOO]-, [BT]+[CH3COO]-, [BT]+[C6H13COO]-,

8

[CP]+[HCOO]- have been used to study their effect on the dissolution of HCO+LWC system.

9

As a first step, dissolution of HCO has been quantitatively estimated using ionic liquid

10

through gravimetric analysis, followed by the detailed dissolution study using UV-vis

11

spectrophotometer, FT-IR,

12

experimentation on the IFT of crude oil-aqueous ionic liquid solution.

13

[C8mim]+[Cl-],

[N222]+[HSO4]-,

[N222]+[CH3COO]-,

C-NMR spectroscopy. This is followed by a brief

13 14

3.1 Dissolution studies of HCO in presence of LWC with ILs using gravimetric analysis

15

The dissolution of HCO using LWC with and without using ILs has been studied and

16

estimated quantitatively through gravimetric analysis. To optimize the system to obtain

17

enhanced dissolution of HCO effectively, different strategies have been employed. These

18

include elaborate analyses of temperature effect, dissolution time and the concentration of the

19

ionic liquids.

20

concentrations (100, 250, 1000, 5000, 10000 ppm) of twelve different ionic liquids were

21

tested with the system of 2:3 wt/wt ratio of HCO:LWC crude oil. It was noticed that, only by

22

using LWC as a solvent, about 41.50 % dissolution of the HCO occurred at the experimental

23

condition of 298.15 K in a reaction time of 60 min. Using ILs, dissolution of HCO in LWC

24

was observed to be increased by a magnitude of 30% (41 to 71%). Figure 2 shows the effect

25

of three different concentrations of twelve different ionic liquids on the enhanced dissolution

Samples were prepared as discussed in the section 2.2.1. Five various



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of HCO at 298.15 K in 60 min of reaction time and remaining data for the rest of the

2

concentrations are given in Table S3. Among the lactam based ionic liquids, the one with the

3

largest ring size has been observed to perform better than the rest of the ionic liquids towards

4

the crude oil dissolution. The reaction temperature has been witnessed as a critical factor in

5

the dissolution of the HCO. The effect of different temperatures on the dissolution of HCO

6

has been analyzed with twelve different ionic liquids of 100 ppm concentration with 60 min

7

of reaction time. Figure 3 illustrates the effect of temperatures on the dissolution of HCO

8

using twelve different ionic liquids at the concentration of 100 ppm and at 60 min reaction

9

time. It is clearly seen that the ionic liquid with greater chain length and size showed better

10

performance in the dissolution of HCO with LWC. As shown in Figure 4, the dissolution of

11

HCO had been executed using LWC as a solvent with the addition of 100 ppm of twelve

12

different ionic liquids at different time durations, such as 15, 60, 300 minutes, and the

13

remaining data for the rest of the time durations are given in Table S4. As anticipated, greater

14

level of dissolution was observed when the mixture was exposed to a longer time. Here, we

15

consider 60 min duration of the reaction time to be the optimum time for the effective

16

dissolution, as further increase in the reaction time did not significantly affect the dissolution.

17

Throughout this study, all the samples were used only in a non-equilibrium state. Few

18

researchers7-8,34-36 have reported the recovery of crude oil from contaminated sand particle

19

using some conventional surfactants/bio surfactants, such as sodium dodecyl sulfate, Triton

20

X-100, Tween 80, Rhamnolipid, Saponin, Surfactin and Serrawettin in different

21

concentrations. It was observed that the addition of such surfactants improved the crude oil

22

recovery to a range of 27-63%. Similarly, few researchers have studied the dissolution of

23

asphaltenes/resins (a fraction of heavy crude oil) with the use of commercially available

24

toluene, heptane, diesel and/or the combination of any two in various ratios, where the

25

authors found the efficiency of dissolution in the range of 13-99% whereas the present study


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showed 57-75% of solubility efficiency, which is more convinced for the dissolution of heavy

2

crude oil than the surfactant methods. Comparison of efficiency of the present crude oil

3

dissolution method with the previously available methods using different surfactants and

4

hydrocarbons is given in Table S5.

5 6

3.2 Dissolution studies of HCO:LWC with and without ILs by UV-vis spectroscopy

7

The absorbance of the standard solutions have been measured using JASCO UV-

8

visible spectrophotometer at their corresponding λmax (as per Table 3) for the HCO:LWC

9

solution in their respective solvent. The standard calibration linear fit plots are shown in

10

Figure S13, i.e., the absorbance of the standard solutions were plotted against their

11

corresponding concentration (in ppm) of the HCO:LWC (in the ratio of 2:3 wt/wt) in the

12

solvents (toluene, hexane, heptane, decane) and obtained regression coefficients (R2) using

13

linear regression.

14

All the sample solutions were prepared and their absorbances were recorded

15

corresponding to their λmax (Table 3) in a particular solvent using the similar approach as the

16

standard solution. All the experiments were performed at the atmospheric pressure (0.1 MPa)

17

and at constant room temperature (298.15 K) maintained using an air conditioner. All the

18

measurements were performed thrice (accuracy within ± 0.001) and the average of these

19

absorbance values was considered for calculating the increase in solubility (%). The

20

absorbances of the sample solutions were compared with the corresponding standard

21

solutions at the same concentration and the increase in solubility in percentage was assessed

22

(Tables S6-S9). Figure 5 shows the performance of twelve different ionic liquids with

23

percentage increase in solubility (±0.1 %) versus concentration (in ppm) of HCO+LWC (2:3

24

wt/wt ratio) mixture in four various solvents and at two different concentrations (30, 70 ppm)

25

of heavy crude oil. Figure S16 shows the comparison of the efficiency of the ILs in terms of 13 ACS Paragon Plus Environment


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1

increase in solubility of HCO:LWC (2:3 wt/wt) in all the studied solvents and at four

2

different concentrations of HCO+LWC solutions.

3

Now, it has been proved that the addition of IL to HCO enhances the dissolution of

4

HCO. The ILs increase the dissolution of HCO to an overall range of 9 to 38 %. Particularly,

5

the combination of heptane and lactam based ILs has been witnessed to cause better

6

dissolution of HCO in the presence of LWC which is about 35-38% of increase in solubility

7

with heptane as a solvent. However, the ILs, such as [C4mim]+[Br-] and [N222]+[H2PO4]-

8

exhibit minimum efficiency in the range of 9% to 14%, with solvents like toluene, hexane

9

and decane. Largely, the ILs [CP]+[HCOO]-, [C8mim]+[Cl-] and [N333]+[HSO4]- have been

10

found to work effectively in all the four different studied solvents. It is to be observed that

11

their efficiency was in the range of 14% to 38% of increase in solubility. Even though four

12

different lactam based ionic liquids improve the dissolution in the range of 18% to 38% in all

13

the four different solvents, unfortunately hexane does not seem to aid in increasing the

14

dissolution at higher concentrations similar to the trend as observed in our previous work.14-

15

15

16

greater ring size of the cation/anion is performing efficiently in reducing the IFT of the crude

17

oil-water system. Accordingly, on comparing [C4mim]+ and [C8mim]+ based on Cl-,

18

[C8mim]+ shows a more better efficiency towards crude oil dissolution. Likewise, [N333]+

19

serves as a better IL than [N222]+ based on [HSO4]- anion. In the same way, caprolactam ILs

20

are better when compared with the butyrolactam ILs with same anion. Generally, in the

21

investigation of the dissolution study of HCO using LWC with ionic liquid, the observed

22

increase in solubility follows the order: Lactam > Imidazolium > Alkyl-ammonium ILs for all

23

the four analyzed solvents. From the Figure 5, it can be concluded that, the solvents like

24

heptane, decane and toluene exhibit highest efficiency for the dissolution of HCO:LWC (2:3

25

wt/wt) with 100 ppm of any ionic liquid. Though our study uses solvent for HCO+LWC

It can be concluded at this instance that the ionic liquid containing lengthier chain and


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1

dissolution in the presence of ILs, the purpose is primarily due to the requirement for the

2

analysis using UV-vis, which could have otherwise been a tedious task. In fact, the

3

gravimetric study (as discussed above) has already shown the increase in solubility of HCO

4

using LWC with small amount of IL.

5 6

3.3 FT-IR spectral analysis

7

The qualitative determination of the dissolution of HCO:LWC (2:3 wt/wt) has been

8

done using FT-IR spectral analysis. At first, the FT-IR spectrum of HCO:LWC (2:3 wt/wt)

9

was recorded using pure KBr. Then undissolved portion of the UV-vis standard solution

10

(HCO+LWC in heptane solvent) was dried thoroughly to remove organic solvent (heptane)

11

and then the spectra was recorded. Similarly, the undissolved portion of the UV-vis sample

12

solutions (HCO+LWC in heptane with 100 ppm of ionic liquid) was washed thoroughly

13

using distilled water to ensure the absence of ionic liquid and dried in the oven 353.15 K,

14

followed by the recording of the FT-IR spectra (see Figure 1). The FT-IR spectra of the

15

dissolved portion of the UV-vis sample solution (undissolved portion of HCO:LWC (2:3

16

wt/wt)) was recorded by collecting the respective sample and the organic solvent was

17

removed using rotary evaporator. The four different spectra were compared with each other

18

and presented in Figure 6 (c) to understand the dissolution behavior of crude oil with the

19

addition of ionic liquid. For this purpose of recording the FT-IR spectra, three different ionic

20

liquids namely, [C4mim]+[Cl-], [N333]+[HSO4]- and [CP]+[HCOO]- have been selected among

21

the three various families and their overall effect on HCO dissolution has been shown in

22

Figure 6.

23

The ILs that showed maximum efficiency in the UV-vis studies were selected for the

24

study of FT-IR analysis. In the Figures 6 (a-c), the peaks observed at 2950 cm-1 and 1450 cm-

25

1

corresponding to the C-H stretching and bending frequencies, respectively, which represent



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

1

alkane (methyl)/alkene (methylene) moiety of HCO. The broad peaks around 3500 cm-1

2

correspond to the alcoholic O-H or water H2O molecule. The strongly absorbed peaks in the

3

regions of 1100 cm-1, 800 cm-1 and 500 cm-1 correspond to the presence of kaolinite

4

(minerals), silicates (sand) and clay, respectively.37-38 From the Figures 6 (a-c), the solvents

5

treated undissolved residual portion of the heavy crude oil reveal significant reduction in the

6

intensity of the peak at 2950 cm-1. It is clearly noticed that the addition of organic solvent

7

aids in improving the dissolution of HCO considerably. Upon the addition of 100 ppm of ILs

8

into the system of HCO+LWC+solvent (undissolved residual portion of the solvent and ILs

9

treated heavy crude oil), further considerable decrement in the intensity of the peak is

10

observed at the same wavenumber 2950 cm-1. FT-IR spectra of the dissolved fraction of the

11

HCO:LWC (2:3 wt/wt) with 100 ppm of IL is shown in Figure 6 (c). It is observed that the

12

dissolved fraction of the HCO:LWC (2:3 wt/wt) exhibits itself to be more pure than the

13

others, i.e., clear C-H stretching and bending frequencies were observed. Thus, it is observed

14

that the addition of IL along with solvent (LWC, heptane or other organic solvents)

15

tremendously enhances the dissolution of the HCO than the system with solvent alone.

16 17

3.4 13C-NMR spectral analysis

18

Similar to the FT-IR spectral studies, the undissolved portion of the UV-vis standard

19

(without ILs) and sample solutions (with ILs) has been considered for recording of 13C-NMR,

20

after removing from them the used solvents and ionic liquid, respectively (refer section 3.3).

21

The obtained spectra have been compared with the 13C-NMR of the HCO:LWC (2:3 wt/wt)

22

crude oil to get a better understanding of the dissolution behavior of HCO:LWC (2:3 wt/wt)

23

with and without IL in the presence of solvent (heptane). The Figure 7 (a) illustrates the

24

recorded 13C-NMR spectra of the HCO:LWC (2:3 wt/wt) using CDCl3 as a solvent. Figure 7

25

(b) shows the

13

C-NMR spectra of the solvent (heptane) treated undissolved residues of the


Page 16 of 36

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1

HCO:LWC (2:3 wt/wt), while Figure 7 (c) displays the 13C-NMR spectra of the undissolved

2

residue of the solvent (heptane)+IL ([CP]+[HCOO]-) treated HCO:LWC (2:3 wt/wt). For this

3

study, [CP]+[HCOO]- ionic liquid was selected to understand its effect on HCO:LWC (2:3

4

wt/wt) dissolution, due to its peak performance noticed in UV-vis analysis (see Figure 5).

5

Numerous peaks has been observed for the 13C-NMR spectra (Figure 7 (a)) of the HCO:LWC

6

(2:3 wt/wt), wherein the peaks in the region of 10-55 ppm belong to the aliphatic

7

methylene/methyl carbons and the peaks in the region of 120-140 belong to the aromatic

8

carbons. In Figure 7 (b), once the HCO:LWC (2:3 wt/wt) is treated with heptane, the peaks in

9

the region (aliphatic methylene/methyl) 10-50 ppm steadily diminished, whereas the aromatic

10

peaks disappeared almost rapidly as it contained very minor quantity of undissolved carbon.

11

This signifies that crude oil is still present undissolved in the sample, which requires an even

12

more efficient method to solubilize it more effectively. Figure 7 (c) shows the complete

13

disappearance of the peaks in the aromatic region and a nearly clean-swept aliphatic region.

14

Hence, it is clear that the ionic liquid assist in the solubilization process of HCO:LWC (2:3

15

wt/wt) significantly. The

16

with the UV-vis and FT-IR studies. Undissolved crude oil is a complex mixture of clay,

17

minerals, sand particles, etc. Its presence in the samples can be handled either by increasing

18

the amount of organic solvents or their combination with ILs causing further enhancement in

19

its dissolution. Moreover, neither the ILs nor the organic solvent can cause any dissolution of

20

the rest of the solid particles other than the crude oil which require the use of suitable

21

mechanical methods for their removal.

13

C-NMR spectral analyses, therefore, exhibit consistent results

22 23

3.5 Effect of ILs on the IFT of crude oil-water systems

24

Large number of crude oil reserves become mature leaving behind huge amount of

25

unrecoverable trapped oil even after primary and secondary recovery techniques.39 Reduction



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

1

of interfacial tension (IFT) is one of the essential requirement for the successful application

2

of enhanced oil recovery (EOR) operations. Reduction in IFT of crude oil-water system also

3

indicate possible removal of crude oil from production facilities.40

4

The interfacial tension of the HCO:LWC (2:3 wt/wt)-water system was accomplished

5

with and without the addition of ionic liquid (100 ppm concentration) and as a function of

6

temperature from 298.15 K to 318.15 K with 10 K interval at atmospheric pressure (0.1

7

MPa). Figure 8 presents the influence of twelve different ionic liquids (aromatic imidazolium,

8

aliphatic alkyl ammonium and lactam group of ionic liquids) on the interfacial tension of

9

HCO:LWC (2:3 wt/wt)-water system at three different temperatures of 298.15, 308.15 and

10

318.15 K with 100 ppm of IL concentration at 0.1 MPa. It is noticed that the interfacial

11

tension of neat HCO:LWC (2:3 wt/wt)-water system is 37.15 mN/m at 298.15 K whereas

12

upon addition of 100 ppm of IL further reduction in the interfacial tension was observed to

13

20.18 to 27.86 mN/m. This shows a positive impact of addition of small quantity of IL for the

14

IFT reduction of HCO:LWC (2:3 wt/wt)-water system. The effect of temperature on the IFT

15

of HCO:LWC (2:3 wt/wt)-water is further performed. It has been noticed that increase in

16

temperatures causes a linear reduction in IFT to a considerable magnitude. Moreover the

17

addition of 100 ppm of [CP]+[HCOO]- (lactam based IL) is found to reduce the IFT to 20.18

18

mN/m from 37.15 mN/m at 298.15 K. Likewise, the addition of 100 ppm of imidazolium

19

based aromatic ionic liquid, [C8mim]+[Cl-] reduces the IFT to 26.06 mN/m from 37.15

20

mN/m. Subsequent to the above observations, the concentration of ammonium based

21

aliphatic ionic liquid [N333]+[HSO4]- from 0 ppm to 100 ppm is observed to reduce the IFT to

22

25.96 mN/m from 37.15 K. It can be concluded at this instant that the ionic liquid containing

23

lengthier chain and greater ring size of the cation/anion is performing efficiently in reducing

24

the IFT of the crude oil-water system. Overall, the order for the efficiency of the three

25

different category of ionic liquids is: Lactam > Imidazolium > Alkyl-ammonium ILs. The


Page 18 of 36

Page 19 of 36

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1

reason behind the greater efficiency of lengthier chain/larger ring containing ionic liquid

2

could be due to the increase of van der Waals force of interactions between the alkyl group of

3

HCO:LWC (2:3 wt/wt) crude oil and alkyl chain of ionic liquid occupying at the interface of

4

HCO:LWC (2:3 wt/wt)-water system.41 Correspondingly, few researchers42-45 have studied

5

the IFT of crude oil-water systems with the addition of some ionic liquids and surfactants,

6

such

7

Fluorosurfactant, Triton X-100 and Triton X-405. A comparison chart of the IFT results of

8

this present study with the previously reported IFT values of crude oil+water systems upon

9

addition of IL/surfactants is presented as Table S10. They noticed a decreasing trend in the

10

IFT values upon addition of ILs/surfactants in the lower concentrations. However, the ILs

11

reported in the present work showed better and consistent IFT reduction than the other

12

reported ILs/surfactant at the concentration of 100 ppm, furthermore, the increase in the

13

concentration of these ILs would improve the efficiency further. Hence, their contribution

14

could be considered as an alternative to the conventional surfactants. Moreover, the ionic

15

liquids used here are structurally similar to the surfactant kind of the structure.

as

[C12mim]+[Cl-],

[C8mim]+[Cl-],

[C12Py]+[Cl-],

[C8Py]+[Cl-],

Zonyl

FSE

16

In the case of lactam ILs, the degree of interaction with HCO increases and improves

17

the dissolution process to a larger extent which is mainly due to the presence of a strong

18

electron withdrawing carbonyl group (-C=O) that forms a part of the cationic moiety. This

19

electron withdrawing group enhances the positive character of the cationic part of the ILs (at

20

N- atom), thereby causing greater HCO-ILs interactions compared to the other system of ILs

21

without the –C=O group. Hence, it can be interpreted that the ILs with greater positive

22

character of the cationic part will have a greater tendency to solubilize the greater polar

23

fractions (resins and asphaltenes containing large numbers of heteroatoms) of the crude oil,

24

all of them possessing at least one lone pair of electrons which are susceptible to interactions.

25

Consequently, it is assumed that the ionic liquids, as well as the heteroatoms of the



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

1

asphaltene/resin, separate from the rest of the unit which are merely the hydrocarbons that

2

can get easily dissolved in the solvent. The positive charge on the lactam ILs would be

3

delocalized around the N-C=O part which keeps the ILs in active mode enabling their

4

reaction with heavy crude oil. Moreover, these lactam based ILs structurally possess high

5

polar moieties which could possess better ability to improve the dissolution of heavy crude

6

oil to a larger extent. Proposed mechanism for the enhanced dissolution of HCO in LWC with

7

the presence of ILs is shown in Figure 9.

8 9

4. CONCLUSION

10

In this present investigation, ionic liquid assisted heavy crude oil dissolution was

11

described quantitatively through gravimetric analyses with the addition of low waxy crude oil

12

as a solvent. Investigations on the effect of temperature, time and concentration for the

13

dissolution of HCO using LWC with ILs have been presented. Twelve different ionic liquids

14

from three various families with a concentration of 100 ppm were used. Through gravimetric

15

analysis, the dissolution of heavy crude oil is found to increase up to 71% from 41%, with

16

100 ppm of ILs. The various experiments carried out in this investigation confirmed the

17

enhancement in the dissolution of HCO using LWC with ionic liquid through the use of three

18

analytical techniques, such as UV-vis spectrophotometry, FT-IR spectroscopy and 13C-NMR

19

spectroscopy. It was observed that that the ionic liquid with lengthier alkyl chain /larger ring,

20

such as [CP]+[HCOO]-, [C8mim]+[Cl-], [N333]+[HSO4]- with 100 ppm concentration are

21

performing better than the other studied ionic liquids. From UV-vis analysis, ionic liquid with

22

the combination of heptane as a solvent works efficiently for the dissolution of the

23

HCO:LWC (2:3 wt/wt). It could be specified that a HCO with LWC along with a small

24

amount of ionic liquid was efficient to enhance the dissolution effectively, as compared to a

25

conventional organic solvents alone. The interaction between ionic liquid and the polar 20 ACS Paragon Plus Environment

Page 20 of 36

Page 21 of 36

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1

fractions in heavy crude oil could be ascribed as a reason towards improved dissolution of

2

HCO+LWC in the presence of ionic liquid, whereas the absence of any IL does not seem to

3

cause the anticipated dissolution.

4 5

ACKNOWLEDGMENT

6

The authors would like to acknowledge IIT Madras for extending its financial support

7

throughout this research work. The authors would also like to thank Oil India Limited for

8

providing crude oil samples and their SARA analysis. The authors would also like to thank

9

Mr. Pratap K. Chhotaray for providing a few ionic liquids for the study.

10 11

SUPPORTING INFORMATION AVAILABLE

12

List of chemicals used for the ILs synthesis (Table S1), Standard calibration

13

absorbances values in different solvents (Table S2), Comparison of the efficiency of the ILs

14

in terms of the increase in concentration and time (Table S3-S4), Comparison of efficiency of

15

the present crude oil dissolution method with the previously available methods (Table S5),

16

UV-vis absorbance values comparison of standard and sample solution (Table S6-S9),

17

Comparing the IFT results of this present study with the reported IFT values of water and

18

crude oil+water systems (Table S10), The 1H NMR characterization of all the ILs (Figure S1-

19

S12), Standard calibration curve (Linear fit) for different solvents (Figure S13), Comparison

20

of the 1H-NMR spectra of pure [C4mim]+[Cl]- and processed/reused [C4mim]+[Cl]- (Figure

21

S14).

22

(HCO+LWC+heptane+[CP]+[HCOO]-) and pure [CP]+[HCOO]- (Figure S15). This

23

information is available free of charge via the Internet at http://pubs.acs.org/.

Comparison

of

the

13

C-NMR

spectra

of

undissolved

24


residual

HCO


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

1 2 3 4 5 6 7

Page 22 of 36

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33. Zeppieri, S.; Rodriguez, J.; de Ramos, A. L. L.; Interfacial tension of alkane + water systems. J. Chem. Eng. Data. 2001, 46, 1086-1088.

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34. K. Urum.; S. Grigson.; T. Pekdemir.; S. McMenamy. A comparison of the efficiency

16

of different surfactants for removal of crude oil from contaminated soils.

17

Chemosphere. 2006, 62, 1403-1410.

18

35. C. C. Lai.; Y. C. Huang.; Y. H. Wei.; J. S. Chang. Biosurfactant-enhanced removal of

19

total petroleum hydrocarbons from contaminated soil. J. Hazard. Mater. 2009, 167,

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609-614.

21 22

36. C. I. Oseghale.; F. O. Ebhodaghe.; Asphaltene deposition and remediation in crude oil production: solubility technique. J. Eng. Applied. Sci. 2011, 6 (4), 258-261.

23

37. Painter, P. C.; Coleman, M. M.; Jenkins, R. G.; Whang, P. W.; Walker Jr, P. L.

24

Fourier transform infrared study of mineral matter in coal. A novel method for

25

quantitative mineralogical analysis. Fuel. 1978, 57, 337-344.



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38. Painter, P. C.; Rimmer, S. M.; Snyder, R. W.; Davis, A. A fourier transform infrared

2

study of mineral matter in coal: The application of a least squares curve-fitting

3

program. Appl. Spectrosc. 1981, 35, 102-106.

4

39. Gong, H.; Xin, X.; Xu, G.; Wang, Y. The dynamic interfacial tension between

5

HPAM/C17H33COONa mixed solution and crude oil in the presence of sodium

6

halide. Colloids Surf. A. 2008, 317, 522-527.

7 8

40. Nilsson, S.; Lohne, A.; Veggeland, K. Effect of polymer on surfactant flooding of oil reservoirs. Colloids Surf. A. 1997, 127, 241-247.

9

41. Smit, B.; Schlijper, A. G.; Rupert, L. A. M.; van Os, N. M. Effects of chain length of

10

surfactants on the interfacial tension: molecular dynamics simulations and

11

experiments. J. Phys. Chem. 1990, 94, 6933-6935.

12

42. Hezave, A. Z.; Dorostkar, S.; Ayatollahi, S.; Nabipour, M.; Hemmateenejad, B.

13

Investigating the effect of ionic liquid (1-dodecyl-3-methylimidazolium chloride

14

([C12mim] [Cl])) on the water/oil interfacial tension as a novel surfactant. Colloids

15

Surf. A. 2013, 421, 63-71.

16

43. Hezave, A. Z.; Dorostkar, S.; Ayatollahi, S.; Nabipour, M.; Hemmateenejad, B. Effect

17

of different families (imidazolium and pyridinium) of ionicliquids-based surfactants

18

on interfacial tension of water/crudeoil system. Fluid Phase Equilib. 2013, 360, 139-

19

145.

20

44. Hezave, A. Z.; Dorostkar, S.; Ayatollahi, S.; Nabipour, M.; Hemmateenejad, B.

21

Dynamic interfacial tension behavior between heavy crude oil and ionic liquid

22

solution (1-dodecyl-3-methylimidazolium chloride ([C12mim][Cl] + distilled or

23

saline water/heavy crude oil)) as a new surfactant. J. Mol. Liq. 2013, 187, 83-89.


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1

45. Karnanda, W.; Benzagouta, M. S.; AlQuraishi, A.; Amro, M. M. Effect of

2

temperature, pressure, salinity, and surfactant concentration on IFT for surfactant

3

flooding optimization. Arab. J. Geosci. 2013, 6, 3535-3544.

4 5

FIGURE CAPTION:

6 7

Figure 1. Flowchart for the experimental procedure involving the dissolution of HCO using LWC in addition to the ILs.

8 9 10 11 12

Figure 2. Comparison of the efficiency of the ILs in terms of the increase in concentration of the ILs. Solubility of HCO in LWC (2:3 wt/wt) with the addition of IL at 298.15 K temperature for 60 min. [C4mim]+[Cl-]; [C4mim]+[Br-]; [C4mim]+[HSO4]-; [C8mim]+[Cl-]; [N222]+[HSO4]-; [N222]+[H2PO4]-; [N222]+[CH3COO]-; [N333]+[HSO4]-; [BT]+[HCOO]-; [BT]+[CH3COO]-; [BT]+[C6H13COO]-; [CP]+[HCOO]-.

13 14 15 16 17 18

Figure 3. Comparison of the efficiency of the ILs in terms of the increase temperature. Solubility of HCO in LWC (2:3 wt.wt) with the addition of 100 ppm IL at four different temperature for 60 min. Without ILs; [C4mim]+[Cl-]; [C4mim]+[Br-]; [C4mim]+[HSO4]-; [C8mim]+[Cl-]; [N222]+[HSO4]-; [N222]+[H2PO4]-; [N222]+[CH3COO]-; [N333]+[HSO4]-; [BT]+[HCOO]-; [BT]+[CH3COO]-; [BT]+[C6H13COO]-; [CP]+[HCOO]-.

19 20 21 22 23

Figure 4. Comparison of the efficiency of the ILs in terms of the increase in dissolution time. Solubility of HCO in LWC (2:3 wt/wt) with the addition of 100 ppm IL at 298.15 K temperature. Without ILs; [C4mim]+[Cl-]; [C4mim]+[Br-]; [C4mim]+[HSO4]-; [C8mim]+[Cl-]; [N222]+[HSO4]-; [N222]+[H2PO4]-; [N222]+[CH3COO]-; [N333]+[HSO4]-; [BT]+[HCOO]-; [BT]+[CH3COO]-; [BT]+[C6H13COO]-; [CP]+[HCOO]-.

24 25 26 27 28 29 30

Figure 5. Comparison of the efficiency of the ILs in terms of increase in solubility of HCO:LWC (2:3 wt/wt) in all the mentioned solvents involved in the present investigation at two different concentrations of HCO+LWC solutions. Base line of 0 % solubility is for standard solution. [C4mim]+[Cl-]; [C4mim]+[Br-]; [C4mim]+[HSO4]-; [C8mim]+[Cl-]; [N222]+[HSO4]-; [N222]+[H2PO4]-; [N222]+[CH3COO]-; [N333]+[HSO4]-; [BT]+[HCOO]-; [BT]+[CH3COO]-; [BT]+[C6H13COO]-; [CP]+[HCOO]-. Here the ILs is used in 100 ppm concentration.

31 32 33 34 35 36 37

Figure 6. FT-IR spectra of (a) HCO:LWC (in 2:3 wt/wt), HCO:LWC (in 2:3 wt/wt)+heptane (residue HCO), HCO:LWC (in 2:3 wt/wt)+heptane+[C4mim]+[Cl-] (residue HCO); (b) HCO:LWC (in 2:3 wt/wt), HCO:LWC (in 2:3 wt/wt)+heptane (residue HCO), HCO:LWC (in 2:3 wt/wt)+heptane+[ N333]+[HSO4]- (residue HCO); (c) HCO:LWC (in 2:3 wt/wt), HCO:LWC (in 2:3 wt/wt)+heptane (residue HCO), HCO:LWC (in 2:3 wt/wt)+heptane+[CP]+[HCOO](residue HCO) and HCO:LWC (in 2:3 + wt/wt)+heptane+[CP] [HCOO] (dissolved HCO). 27 ACS Paragon Plus Environment


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

Page 28 of 36

1 2 3

Figure 7. 13C-NMR spectra of (a) HCO:LWC (in 2:3 wt/wt); (b) HCO:LWC (in 2:3 wt/wt) +heptane (residue HCO); (c) HCO:LWC (in 2:3 wt/wt)+heptane+[CP]+[HCOO]- (residue HCO). Here CDCl3 solvent is used to prepare 13C-NMR sample.

4 5 6

Figure 8. Interfacial tension of HCO+LWC (2:3 wt/wt)-water in the presence of various ILs at 100 ppm concentration and at three different temperatures 298.15 K, 308.15 K, 318.15 K.

7 8 9 10

Figure 9. Proposed mechanism for the enhanced dissolution of HCO in LWC with the presence of ILs. Dotted lines indicate the interaction between ILs and heteroatoms of asphaltene/resin present in the HCO; Green color represents the ILs; Orange color is the asphaltene/resin moiety of the HCO.

11 12 13

Table 1. SARA analysis, API gravity and viscosity report of HCO and LWC. + Density API Crude Composition At gravity oil Ar (%) Re (%) As (%) S (%) 298.15±0.1 K

HCO 26.4±1.93 64.8±2.40 4.1±0.85 4.7±1.32 0.9971±0.12 LWC 20.4±0.20 76.2±0.15 3.0±0.17 0.4±0.17 0.9001±0.10 + 14 S: Saturates; Ar: Aromatics; Re: Resins; As: Asphaltenes.

10.40±0.11 25.57±0.08

Viscosity at 298.15±0.1 K 22.8±0.11

15 16 17

Table 2. List of synthesized ionic liquids Cation Anion Name

C4H 9

[Cl-]

N

N

[Br-] [HSO4]-

C8H17

[Cl-]

N H N

N [HSO4][H2PO4][CH3COO]-

Abbreviation

1-butyl-3-methylimidazolium chloride l-butyl-3-methylimidazolium bromide 1-butyl-3-methylimidazolium hydrogen sulfate 1- octyl-3-methylimidazolium chloride

[C4mim]+[Cl-]

Water content (in ppm) 2569

[C4mim]+[Br-]

3205

[C4mim]+[HSO4]-

2965

[C8mim]+[Cl-]

3295

Triethyl ammonium sulfate [N222]+[HSO4]Triethylammonium phosphate [N222]+[H2PO4]Triethylammonium acetate [N222]+[CH3COO]-


3526 4521 4026

Page 29 of 36

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


[HSO4]-

Tripropylammonium sulfate

[N333]+[HSO4]-

3895

H N

H

H N O

[HCOO]Butyrolactam formate [CH3COO] Butyrolactam acetate [C6H13COO] Butyrolactam hexanoate

[BT]+[HCOO][BT]+[CH3COO][BT]+[C6H13COO]-

3832 3376 3129

H

H N O

[HCOO]-

[CP]+[HCOO]-

4127

Caprolactam formate

1 2 3 4

Table 3. List of solvents used to HCO:LWC (in 2:3 wt/wt) dissolution and its corresponding λmax S.No Solvents CAS No. Source Purity λmax (nm) 1 Toluene 108-88-3 Merck 99% 288 2 n-Hexane 110-54-3 Merck 99% 229 3 n-Heptane 142-82-5 Merck 99% 226 4 n-Decane 124-18-5 Aldrich 95% 227

5 6



1 2 3 4

Figure 1. Flowchart for the experimental procedure involving the dissolution of HCO using LWC in addition to the ILs.

HCO concentration (%)

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

Page 30 of 36

75 70 65 60 55 50 100

5 6 7 8 9 10

1000 Concentration of ILs (ppm)

10000

Figure 2. Comparison of the efficiency of the ILs in terms of the increase in concentration of the ILs. Solubility of HCO in LWC (2:3 wt/wt) with the addition of IL at 298.15 K temperature for 60 min. [C4mim]+[Cl-]; [C4mim]+[Br-]; [C4mim]+[HSO4]-; [C8mim]+[Cl-]; [N222]+[HSO4]-; [N222]+[H2PO4]-; [N222]+[CH3COO]-; [N333]+[HSO4]-; [BT]+[HCOO]-; [BT]+[CH3COO]-; [BT]+[C6H13COO]-; [CP]+[HCOO]-.

11 12


Page 31 of 36

85 HCO concentration (%)

75 65 55 45 35 298.15

318.15

2 3 4 5 6 7

338.15

358.15

Temperature (K)

1

Figure 3. Comparison of the efficiency of the ILs in terms of the increase temperature. Solubility of HCO in LWC (2:3 wt.wt) with the addition of 100 ppm IL at four different temperature for 60 min. Without ILs; [C4mim]+[Cl-]; [C4mim]+[Br-]; [C4mim]+[HSO4]-; [C8mim]+[Cl-]; [N222]+[HSO4]-; [N222]+[H2PO4]-; [N222]+[CH3COO]-; [N333]+[HSO4]-; [BT]+[HCOO]-; [BT]+[CH3COO]-; [BT]+[C6H13COO]-; [CP]+[HCOO]-.

8 9 80 HCO concentration (%)

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


70 60 50 40 30 15

10 11 12 13 14 15

60 Time (min)

300

Figure 4. Comparison of the efficiency of the ILs in terms of the increase in dissolution time. Solubility of HCO in LWC (2:3 wt/wt) with the addition of 100 ppm IL at 298.15 K temperature. Without ILs; [C4mim]+[Cl-]; [C4mim]+[Br-]; [C4mim]+[HSO4]-; [C8mim]+[Cl-]; [N222]+[HSO4]-; [N222]+[H2PO4]-; [N222]+[CH3COO]-; [N333]+[HSO4]-; [BT]+[HCOO]-; [BT]+[CH3COO]-; [BT]+[C6H13COO]-; [CP]+[HCOO]-.

16 17



40 Increase in solubility (%)

35 30 25 20 15 10 5 30ppm

70ppm

toluene

30ppm

70ppm

30ppm

70ppm

30ppm

hexane heptane Concentration of crude oil (ppm)/Organic solvents

70ppm

decane

1 2 3 4 5 6 7 8

Figure 5. Comparison of the efficiency of the ILs in terms of increase in solubility of HCO:LWC (2:3 wt/wt) in all the mentioned solvents involved in the present investigation at two different concentrations of HCO+LWC solutions. Base line of 0 % solubility is for standard solution. [C4mim]+[Cl-]; [C4mim]+[Br-]; [C4mim]+[HSO4]-; [C8mim]+[Cl-]; [N222]+[HSO4]-; [N222]+[H2PO4]-; [N222]+[CH3COO]-; [N333]+[HSO4]-; [BT]+[HCOO]-; [BT]+[CH3COO]-; [BT]+[C6H13COO]-; [CP]+[HCOO]-. Here the ILs is used in 100 ppm concentration.

9

120 Transmittance (%)

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

Page 32 of 36

HCO:LWC (2:3) Heptane+HCO:LWC (2:3) (Residue HCO) + Heptane+HCO:LWC (2:3)+[BMIM] [Cl] (Residue HCO)

100 80 60 40 20 0 3500 3000 2500 2000 1500 1000

500

-1

Wavenumber (cm )

(a)


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HCO:LWC (2:3) Heptane+HCO:LWC (2:3) (Residue HCO) + Heptane+HCO:LWC (2:3)+[Pr3NH] [HSO4] (Residue HCO)

Transmittance (%)

120 100 80 60 40 20 0

3500 3000 2500 2000 1500 1000

500

-1

Wavenumber (cm )

(b) HCO:LWC (2:3) Heptane+HCO:LWC (2:3) (Residue HCO) + Heptane+HCO:LWC (2:3)+[CP] [HCOO] (Residue HCO) + Heptane+HCO:LWC (2:3)+[CP] [HCOO] (Dissolved HCO)

120 Transmittance (%)

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


100 80 60 40 20 0 3500

3000

2500

2000

1500

1000

500

-1

Wavenumber (cm )

1 2 3 4 5 6 7 8

(c) Figure 6. FT-IR spectra of (a) HCO:LWC (in 2:3 wt/wt), HCO:LWC (in 2:3 wt/wt)+heptane (residue HCO), HCO:LWC (in 2:3 wt/wt)+heptane+[C4mim]+[Cl-] (residue HCO); (b) HCO:LWC (in 2:3 wt/wt), HCO:LWC (in 2:3 wt/wt)+heptane (residue HCO), HCO:LWC (in 2:3 wt/wt)+heptane+[ N333]+[HSO4]- (residue HCO); (c) HCO:LWC (in 2:3 wt/wt), HCO:LWC (in 2:3 wt/wt)+heptane (residue HCO), HCO:LWC (in 2:3 wt/wt)+heptane+[CP]+[HCOO](residue HCO) and HCO:LWC (in 2:3 + wt/wt)+heptane+[CP] [HCOO] (dissolved HCO).

9


50.297 39.111 38.878 34.760 34.271 32.065 29.800 29.501 22.801 20.777 19.165 14.103 11.414

77.418 77.163 76.908

Page 34 of 36

(a)

190

180

170

160

150

140

130

120

110

100

180

170

160

150

140

130

120

110

100

90

80

70

60

50

40

30

20

ppm

77.413 77.158 76.903 49.935 49.914 41.358 38.982 38.746 36.095 34.630 34.142 31.924 31.878 31.583 29.654 29.475 29.353 29.038 27.942 27.659 26.887 25.221

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

136.275 131.224 130.437 130.380 128.343


(b)

190

90

80

70

60

50

40

30

20

ppm

(c)

1 2 3 4

Figure 7. 13C-NMR spectra of (a) HCO:LWC (in 2:3 wt/wt); (b) HCO:LWC (in 2:3 wt/wt) +heptane (residue HCO); (c) HCO:LWC (in 2:3 wt/wt)+heptane+[CP]+[HCOO]- (residue HCO). Here CDCl3 solvent is used to prepare 13C-NMR sample.

5 6


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


Interfacial tension (mN/m)

Page 35 of 36

1 2 3 4

38 33 28 23 18

Ionic Liquids (ILs)

Figure 8. Interfacial tension of HCO+LWC (2:3 wt/wt)-water in the presence of various ILs at 100 ppm concentration and at three different temperatures 298.15 K, 308.15 K, 318.15 K.

5 X-

X-

H R H N

R H H NH

N

X-

H O R H H H S R H X-

6 7 8 9 10

H R X H H H S R

XN

H

H R X-

Figure 9. Proposed mechanism for the enhanced dissolution of HCO in LWC with the presence of ILs. Dotted lines indicate the interaction between ILs and heteroatoms of asphaltene/resin present in the HCO; Green color represents the ILs; Orange color is the asphaltene/resin moiety of the HCO.

11



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

1 2

Graphical Abstract: Schematic experimental methods for the dissolution of heavy crude oil

3

using low waxy crude oil with or without ionic liquids

4 5 6


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Substantial Enhancement of Heavy Crude Oil ... - ACS Publications

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