Liquid–liquid extraction of sulfur compounds from heptane with tricyanomethanide based ionic liquids

Liquid–liquid extraction of sulfur compounds from heptane with tricyanomethanide based ionic liquids

Accepted Manuscript Liquid – liquid extraction of sulphur compounds from heptane with tricyanomethanide based ionic liquids Marek Królikowski PII: DOI...

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Accepted Manuscript Liquid – liquid extraction of sulphur compounds from heptane with tricyanomethanide based ionic liquids Marek Królikowski PII: DOI: Reference:

S0021-9614(18)30845-0 https://doi.org/10.1016/j.jct.2018.10.009 YJCHT 5575

To appear in:

J. Chem. Thermodynamics

Received Date: Revised Date: Accepted Date:

14 August 2018 10 October 2018 11 October 2018

Please cite this article as: M. Królikowski, Liquid – liquid extraction of sulphur compounds from heptane with tricyanomethanide based ionic liquids, J. Chem. Thermodynamics (2018), doi: https://doi.org/10.1016/j.jct. 2018.10.009

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Journal of Chemical Thermodynamics Liquid – liquid extraction of sulphur compounds from heptane with tricyanomethanide based ionic liquids Marek Królikowski*

Department of Physical Chemistry, Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland Thermodynamic Research Unit, School of Engineering, University of KwaZulu-Natal, Howard College Campus, King George V Avenue, Durban 4041, South Africa

* To whom the correspondence should be addressed. E-mail: [email protected]

Abstract Liquid–liquid phase equilibrium (LLE) data for the {tricyanomethanide-based ionic liquid (1) + tiophene, or benzothiophene (2) + heptane (3)} ternary systems were experimentally determined at T = 308.15 K and at pressure p = 0.1 MPa. Based on the experimental data, the performance of two tricyanomethanide-based ionic liquids (ILs) in the extraction of thiophene, or benzothiophene from alkanes was determined. In this work three ILs, that is: 1-butyl-1-methylmorpholinium tricyanomethanide, [BMMOR][TCM], 1-butyl-1methylpyrrolidinium

tricyanomethanide,

[BMPYR][TCM]

and

1-hexyl-1-

methylmorpholinium tricyanomethanide, [HMMOR][TCM] have been investigated. The high solubility of sulphur compounds and practical complete immiscibility of heptane in the tested ionic liquids have been observed. The selectivity,

and solute distribution ratio,

derived

from the experimental equilibrium data, were calculated and used to determine the efficiency of these ionic liquids as a solvent for the extraction of sulfur compounds from model fuels. The experimental results have been compared to literature data for other tricyanomethanidebased ILs and were discussed in terms of the selectivity and solute distribution ratio of separation of related systems. The NRTL equation was successfully used to correlate the experimental tie-lines and calculate the phase composition error in mole fraction in the ternary systems. The average root mean squere (RMSD) of the phase composition was less than 0.8 %. Additionally, the oxidative-extractive desulfurization of model fuels has been studied using tricyanomethanide-based ionic liquid (IL): [BMMOR][TCM] and [BMPYR][TCM] and deep eutectic mixture (DES): ([BMMOR] [Br] + diethylene glycol). Model liquid fuel was prepared by dissolving benzothiophene in octane (500 ppm of sulphur). Oxidation in this process was achieved by adding hydrogen peroxide and acetic acid to the mixture. Different parameters such as a type of extractant, extraction time, and oxidant to sulphur molar ratio and temperature were optimized.

Keywords: ternary system; desulfurization; (liquid + liquid) phase equilibria; extraction; ionic liquid

1. Introduction In the last few decades, environmental pollution caused by car fumes containing sulfur oxides is becoming more serious. Diesel fuel combustion products with a high sulfur content are rich in their oxides, which largely pollutes the air and consequently has a detrimental effect on human health. The production of fuels with a reduced sulfur content is a challenge for refineries and many scientific laboratories around the world. Due to the strong limitation of standards for SOx oxides emission to the atmosphere, new, effective and energy-saving technologies for separating these compounds from fuels are being sought [1,2]. The conventional method of effective removal of sulfur compounds, including thiols, thioethers, and disulphides with fuels used on an industrial scale, is hydrodesulfurization (HDS). The undoubted disadvantage of this process is that it requires high temperature and pressure, reduces the octane number of the fuel, and above all is ineffective to remove aromatic sulfur compounds, which account for over 55% of the total sulfur content, such as benzothiophene, dibenzothiophene and their derivatives, and especially 4,6-dimethyl-dibenzothiophene. Rigorous conditions for running a conventional hydrodesulphurization process that generates high costs [3,4] and other limitations cause that alternative methods of deep desulphurization of fuels are being sought that would allow effective separation of sulfur compounds. Alternative

fuel

desulfurization

methods

include

oxidative

desulphurization,

biodesulphurization, extractive desulphurization and adsorption desulfurization [5–7]. Recently, an excellent review on alternative methods of desulfurization was presented in the open literature [8]. Ionic liquids are perceived as an important class of new compounds characterized by specific properties. Particularly low volatility and high values of selectivity coefficients, demonstrated in earlier works, support the use of ionic liquids as alternative solvents in many

branches of the chemical industry, including, among others, extraction processes and environmental clean-up technologies [9–11]. Literature reports show that ionic liquids exhibit high values of selectivity coefficients for the separation of aromatic sulfur compounds (thiophene) from aliphatic hydrocarbons (fuels) compared to classical organic solvents used on an industrial scale (NMP, or sulfolane) [12–15] which, combined with negligible vapor pressure, creates the hope that this type of compounds can be used for separating sulfur compounds from fuels on an industrial scale instead of traditional volatile organic solvents. The best information about the possibility of the separation processes is the selectivity and distribution ratio, parameters obtained from the ternary (liquid – liquid) equilibrium measurements. In the opened literature the imidazolium- [16–21], pyridinium- [22–24], pyrrolidinium- [13,25], morpholinium- [25], ammonium- [26] and piperidinium-based [25,27] ILs have been investigated as a solvent in separation processes. In our laboratory, the liquid– liquid phase equilibria for ternary systems (different ILs + thiophene, or benzothiophene + heptane) have been investigated [25,25,28 –30]. The main aim of this work is to present and discuss the possibility of use tricyanomethanide-base ILs with 1-butyl-1-methylmorpholinium and 1-hexyl-1-methylmorpholinium cations as a solvent in the extraction of sulphur compounds from model fuel. The first step in determining the ability of [BMMOR][TCM] in extraction processes was done based on measurements of activity coefficients at infinite dilution [31]. It was presented that the selectivity value for heptane / thiophene separation process for [BMMOR][TCM] was optimistic and at T = 328.15 K was equal to 73.8, whereas, for [BMPYR][TCM] [32], the selectivity was 43.6 at the same temperature condition. In this work, the liquid–liquid phase equilibrium (LLE) data for the ternary systems of {[BMMOR][TCM] (1) + thiophene, or benzothiophene (2) + heptane (3)} and {[HMMOR] [TCM] (1) + thiophene, or

benzothiophene (2) + heptane (3)}were determined at T = 308.15 K and pressure p = 0.1 MPa. From the experimental results, the values of selectivity, S, and the solute distribution ratio, β, were calculated and compared with the values of S, and β of other tricyanomethanidebased ILs. In order to increase the efficiency of removing sulfur compounds from fuels (over 90%), desulfurization with the addition of an oxidizing agent is proposed [7, 33–36] which is also the subject of research in this work. Additionally, an extensive analysis of the obtained results will allow for the orientation of future research in the technological direction of choice of ionic liquid and DES, an oxidizing agent, temperature, extraction time, and amount of oxidizing agent on the efficiency of the oxidative desulfurization process with the use of ionic liquids. This part of the experiment is a continuation of latest work on desulphurization of model fuel, also in presence of different oxidizing agents [37].

2. Experimental 2.1. Chemicals and materials The chemicals and ILs used in this work with name, abbreviation, CAS number, supplier, molar mass (M), purity and methods of purification and analysis are presented in Table 1 and 2, respectively. Directly before the experiment, all solvents were stored over freshly activated molecular sieves (5 Å, Type 522, Carl Roth) and the samples of ILs were dried

over

24

h

at

T = 373 K under low pressure, p = 410-3 mbar (Vacuum Drying Oven, Binder, model VD 23, Germany). (Table 1 goes here) (Table 2 goes here) 1-Butyl-1-methylmorpholinium tricyanomethanide, [BMMOR][TCM] and 1-butyl-1-methylpyrrolidinium tricyanomethanide, [BMPYR][TCM] were supplied by IoLiTec Ionic Liquids Technologies GmbH, Germany. 1-Butyl-1-methylmorpholinium bromide, [BMMOR][Br] and 1-hexyl-1-methylmorpholinium tricyanomethanide, [HMMOR][TCM] were synthesized in our laboratory. The procedure of synthesis of [BMMOR][Br] was mentioned in previous publication from our laboratory [38]. Detailed description of the synthesis of [HMMOR][TCM] is given below. 2.1.1. Synthesis of 1-hexyl-1-methylmorpholinium tricyanomethanide, [HMMOR][TCM] To a flask containing 48.18 g of 1-hexyl-1-methylmorpholinium bromide, [HMMOR] [Br] (0.1810 mol, synthesized accordingly to a previously reported procedure [39] [N-methylmorpholinium 21.33g; 1-bromohexane 40.21g; yield 94.6%]), a mass of 20.69 g of sodium tricyanomethanide (0.1830 mol, Io-Li-Tec 98%, 1.01 equivalent, used as received), 100 cm3 of deionized water and 150 cm3 of dichloromethane (POCH/Avantor) were added.

Mixture was stirred at the room temperature for 4 h. The phases were separated. The heavier organic phase was extracted by 10 x 25 cm3 by deionized water to remove the residual salt. The product was further purified by addition of 2 g activated charcoal stirring for 24 h and then filtered. The solvent was removed by rotary evaporation and further dried in vacuum (373 K, 4·10-3 mbar). The product was obtained as 41.92 g of oil. Reaction yield was 83.8%. 1

H NMR δH(500 MHz; CDCl3) ppm: 0.780 (3 H, t, 3JH,H = 6.9 Hz), 1.18 – 1.31 (6 H,

m), 1.61 – 1.69 (2 H, m), 3.054 (3 H, s), 3.24 – 3.37 (6 H, m), 3.83 – 3.92 (4 H, m). 13

C NMR δC(100 MHz; CDCl3) ppm: 13.749, 21.436, 22.152, 25.630, 30.866, 46.995,

59.941, 60.392, 65.971, 121.538. 1

H NMR and

13

C NMR spectra are presented as Fig. 1S in the Supplementary Data

(SD).

2.2.

Apparatus and procedure

2.2.1. Water content The water content of the chemical compounds used in the experimental part of the work was analysed by the coulometric Karl Fischer titration (TitroLine 7500 KF trace, SI Analytics, Germany). The sample of IL, or solvent was dissolved in dry methanol and titrated using chemical reagent, Hydranal™ - Coulomat AG (Fluka). The error on the water content was 5%. The water content in each compound is presented in Table 1 and 2. 2.2.2. Ternary liquid – liquid equilibria (Liquid – liquid) phase equilibria have been determined using a static method. For the determination of the experimental tie-lines, the binary mixtures of (IL + thiophene, or benzothiophene and IL + heptane) and ternary mixtures of (IL + thiophene, or benzothiophene + heptane) with composition inside the immiscibility region were prepared in a jacketed glass

vessel with a volume of 10 cm3. The vessel was tightly closed to prevent evaporation or to pickup of moisture from the atmosphere. The jackets were connected to a thermostatic water bath (LAUDA Alpha A6) to maintain a constant temperature of T = (308.15 ± 0.05) K. The mixtures were stirred for 6 hours using a magnetic stirrer to reach the thermodynamic equilibrium. After getting the phase separation for a minimum of 12 h the mixtures were analysed. For this purpose, the samples of about (0.1–0.3) × 10−3 cm3 were taken from both phases using glass syringes with coupled stainless steel needles. The sample of the phase was placed in an ampoule with a capacity of 2 × 10−3 cm3, closed with a septum cap. Next, in order to avoid phase splitting and to maintain a homogeneous mixture, a volume of 1.0 cm 3 of acetone was added to the samples. In this work, 1-butanol was used as internal standard for the GC-analysis. The analysis was made by only for thiophene, or benzothiophene and heptane. The mass fraction of the IL, which exhibit low vapour pressure, was determined by subtracting the mole fractions of the two other components from one. The operating conditions in the gas chromatograph for the analysis of the composition of phases in the equilibrium state are presented in Table 3. (Table 3 goes here) 2.2.3. Desulfurization of model fuel The experiment was started with the preparation a sample of model fuel with known sulfur content (approximately 500 ppm) by dissolving benzotiophene in octane. The vessels thermostayted at T = 308.2 K or 313.2 K with the magnetic stirrer were used to perform the experiment. In this experiment two ILs: [BMMOR][TCM] and [BMPYR][TCM] and deep eutectic mixture of {[BMMOR][Br] + diethylene glycol} were used as an extractant. To each vessel, a known amount of model fuel and IL, or DES were added. It the first step, the effect of extraction time on efficiency of sulphur removal was investigated. For this

purpose, the mixtures were stirred for at different period of time, from 20 minutes to 80 minutes and then separated for 12 hours. After that, the upper phase of theses mixture was taken and analyzed using X-ray fluorescence spectrometry Rigaku NEX QC+ apparatus. The measurement uncertainty was estimated to be ± 3−4 ppm. After that, the influence of oxidizing agents such as hydrogen peroxide and acetic acid on the sulfur extraction efficiency was tested. In this part, the mixtures were stirred for 5 minutes, separated for 15 minutes and then analyzed using the same equipment. 2.2.4. Density measurements The density of pure [HMMOR][TCM] was used using was measured using an Anton Paar GmbH 4500 vibrating-tube densimeter (Graz, Austria). The temperature was controlled with two integrated Pt 100 platinum thermometers provided the good precision of (±0.01 K). The densimeter includes an automatic correction for the viscosity of the sample. The apparatus is precise to within 110–5 g·cm-3, and the overall uncertainty of the measurements was estimated to be better than 510–5 g·cm-3. 2.2.5. Viscosity measurements The viscosity of pure [HMMOR][TCM] was performed using an Anton Paar GmbH AMVn (Graz, Austria) programmable viscometer, with a nominal uncertainty of 5 % for viscosities from (0.3 to 2500) mPa·s. During the experiment, temperature was controlled internally to a precision of 0.01 K in a range from (298.15 to 348.15) K. In the measured viscosity range, the diameter of the capillary was 1.6 mm, 1.8 mm, 3.0 mm and 4.0 mm for the following viscosity ranges: (0.3 to 10) mPa·s, (2.5 to 70) mPa·s, (20 to 230) mPa·s and (80 to 2500) mPa·s respectively. Before the experiment, the apparatus was calibrated using the standard provided by the supplier.

3. Results and discussion The main purpose of this research is to present and discuss the separation possibility of new tricyanomethanide-based ILs: [BMMOR][TCM] and [HMMOR][TCM] in the extraction sulphur compound (thiophene, or benzothiophene) from aliphatic hydrocarbons (heptane). For this purpose, the (liquid – liquid) phase equilibria in {[BMMOR][TCM] (1) + thiophene, or benzothiophene (2) + heptane (3)} and {[HMMOR][TCM] (1) + thiophene, or benzothiophene (2) + heptane (3)} ternary systems have been measured at T = 308.15 K and pressure p = 0.1 MPa. The experimental results are collected in Table 4 and Figures 1–4. (Table 4 goes here) (Figure 1 goes here) (Figure 2 goes here) (Figure 3 goes here) (Figure 4 goes here)

The selection of the tested ILs, will allow determination of the effect of the chain length in the morpholinium cation on extraction abilities. Additionally, comparing the experimental data with the literature for [BMPYR][TCM] [25] and [EMIM][TCM] [28] it will be possible to discuss the influence of IL’s cation core on the extraction efficiency of the proposed ILs. From the experimental data it can be noticed, that in the binary {IL (1) + thiophene (2)} system, better solubility was observed in the ionic liquid [HMMOR][TCM], where a miscibility gap was observed up to x1 = 0.175, and worse for [BMMOR][TCM], with a miscibility gap up to x1 = 0.211. For comparison, in binary system with [EMIM][TCM] the immiscibility gap was observed up to x1 = 0.135 [25] and with [BMPYR][TCM] up to x1 = 0.152

[25].

High

solubility of

thiophene

in

[BMIM][TCM], [BPy][TCM]

and

[BMPYR][TCM] were confirmed by (liquid-liquid) phase equilibria measurements presented in Lukoskho et al.[40]. The solubility of benzothiophene in the tested ILs has been shown to be higher in comparison with the solubility of thiophene. For example in the case of [BMMOR][TCM] the immiscibility gap in the system with benzothiophene is observed for the composition range up to x1 = 0.129, whereas in the system with thiophene up to x1=0.114. The reason for this is the presence of stronger π-π interactions between the ionic liquid and benzothiophene compared to thiophene. This conclusion is valid for every also IL for other tricyanemethanide-based ILs [25,28,30]. From the data presented, it is clear that in the {IL (1) + heptane (2)} system a miscibility gap was observed over almost a whole range of ionic liquid molar fraction (from 0.000 to 0.979) for [BMMOR][TCM] and (from 0.000 to 0.969) for [HMMOR][TCM] due to the aliphatic nature of heptane. This observation is also true for other tricyanomethanidebased ILs reported in the literature [25,28,30]. In this work, it has been shown that the increase of the alkyl chain length in the morpholinium cation, and thus the increase in the molar volume, causes the increase of van der Waals interactions between the ionic liquid and heptane

which

increases

the

solubility

of

the

aliphatic

hydrocarbon.

Among

tricyanomethanide-based ILs, the lowest solubility of heptane was observed in binary system with [EMIM][TCM], where a miscibility gap on wide IL mole fraction x1 (from 1,000 to 0.991) was observed [28], and the best solubility, corresponds to the miscibility gap in the molar range of the ionic liquid (from 1,000 to 0.969) was observed for the ionic liquid [HMMOR][TCM]. The phase diagrams in ternary systems (IL (1) + thiophene (2) + heptane (3)} indicate that the area of incompatibility of two liquid phases decreases in the following series: [BMPYR] [TCM] < [HMMOR][TCM] < [BMMOR][TCM] <[EMIM][TCM] as is presented in Figure 5.

(Figure 5 goes here) From comparison of the liquid – liquid phase equilibria measurements in {IL (1) + benzotiophene (2) + heptane (3)} ternary systems, presented in Figure 6, it was shown that the broadest area of immiscibility of two liquid phases is present with Ionic liquid [EMIM][TCM], and the best miscibility was observed for the ionic liquid [HMMOR][TCM]. (Figure 6 goes here) The feasibility of using the entrainer to perform the extraction of thiophene, or benzothiophene from heptane was evaluated by two classic parameters such as the selectivity (S), and the solute distribution ratio (). These parameters are defined by the following expressions:

(1)

(2)

where: x is the mole fraction; superscripts I and II refer to heptane rich phase and IL-rich phase, respectively. Subscripts 2 and 3 refer to thiophene and heptane, respectively. The values

of

S and , calculated from the experimental data, are shown in Table 4, together with the compositions of experimental tie-lines for the tested ternary systems. Both parameters, the selectivity, and solute distribution ratio are presented as a function of the mole fraction of thiophene or benzothiophene in the heptane-rich phase for the investigated systems. It can be noticed that in each case the values of selectivity and solute distribution ratio decrease when the mole fraction of sulphur compound in the raffinate increases.

In Table 5, the selectivity and solute distribution ratio for ILs tested in this work, as well as for other ILs with similar structure are presented. (Table 5 goes here) Both parameters are presented for the molar fraction of the organic sulphur compound in rich phase in heptane,

= 0.05. It gives the opportunity to compare S and β to the one

reference point for each IL from the systems and give an opportunity to compare the values of the selectivity and efficiency coefficient. Otherwise, the selectivity values and the efficiency coefficient depend on the position of the first measured tie-line of the ternary system. It can be noticed, that the selectivity in both separation processes, undertaken increase with an increase of the alkyl chain length in the morpholinium cation. For thiophene / heptane at T = 308.15 K, the selectivities are 55 and 67 for [BMMOR][TCM] and [HMMOR][TCM], respectively. Moreover, the selectivity values are higher for benzothiophene/heptane than for thiophene/heptane system. This is due to the fact that much better solubility of benzothiophene in the ionic liquid-rich phase was observed. Generally speaking, the separation in the systems thiophene, or benzothiophene / heptane, described by the selectivity for [BMMOR][TCM] and [HMMOR][TCM] are not as optimistic as for other tricyanomethanide-based

ILs,

presented

earlier.

For

example

the

selectivity

in

thiophene/heptane system for [EMIM][TCM]28 at T = 308.15 K was reported as S = 171, or for [BMPYR][TCM] at T = 298.15 K, the selectivity was S = 121.1. Summarizing, for a series of tricyanomethanide-based ILs, the selectivity in thiophene / heptane increases in the following order: [BMMOR][TCM] (S = 55 at T = 308.15 K) < [HMMOR][TCM] (S = 67.0 at T = 308.15 K) < [BMPYR][TCM] [25] (S = 121.2 at T = 298.15 K) < [EMIM][TCM] [28] (S = 171.0 at T = 308.15 K). Moreover, the selectivity in benzothiophene / heptane at T = 308.15 K increases from [BMMOR][TCM] (S = 78.5) < [HMMOR][TCM] (S = 87.1) <

[BMPYR][TCM] [38] (S = 152.0) < [EMIM][TCM] [28] (S = 221.4). The selectivity for [BMMOR][TCM] is fairly close to previously published values for [COC2MPIP][NTf2] [27] and [COC2MPYR][FAP] [13] determined at T = 298.15 K. Not only selectivity is very important parameters from the point of view of the liquidliquid extraction, but also the solute distribution ratio, β. It is high value indicates the good solubility of aromatic sulphur compounds in fuels. It also depends on the amount of solvent used in the process, and thus affects the size of the solvent recovery installation and the cost of the process itself. As shown in Table 5, the solute distribution ratio for tricyanomethanide-based ILs for thiophene / heptane systems increase in order: [EMIM][TCM] (β = 1.97 at T = 308.15 K) < [BMMOR][TCM] (β = 2.16 at T = 308.15 K) < [BMPYR][TCM] (β = 3.18 at T = 298.15 K) < [HMMOR][TCM] (β = 3.00 at T = 308.15 K), whereas for benzothiophene / heptane system the value of this parameter determined at T = 308.15 K, increase as follows: [BMMOR][TCM] (β = 2.41) ⁓ [HMMOR][TCM] (β = 2.42) < [EMIM][TCM] (β = 2.94) < [BMPYR][TCM] (β = 5.48). As we can see from the above data, the solute distribution ratio in the system with thiophene is the highest for [HMMOR][TCM], tested in this work. For all ionic liquids compared in this work, β is greater than 1, which indicates the possibility of using these ionic liquids in separation processes with good results. The aim of the next part of the experimental work is to determine the influence of many factors, i.e. the type of extractant, extraction time and temperature as well as the type and amount of oxidant on the sulphur extraction efficiency from the model fuel. The following extractant were tested: [BMMOR][TCM], [BMPYR][TCM] and deep eutectic mixture ([BMMOR][Br] + diethylene glycol, x1 = 0.2). The experiments were performed at two

temperatures T = (308.15 and 318.15) K. The experimental results are presented in Table 6 and Figure 7. (Table 6 goes here) (Figure 7 goes here) It can be noticed, that in each case, with an increase of the time of extraction, the amount of sulphur which are extracted increases. For example when [BMMOR][TCM] was used as an extractant, after 20 minutes of extraction at T = 308.15 K, 41.7 % of sulphur were extracted, while when the extraction was performed for 80 minutes at the same temperature condition, the yield of extraction was 64.7 %. Moreover, at the higher temperature the amount of sulphur extracted was higher for each extractant tested. As for example, the extraction efficiency for [BMPYR][TCM] increases from 44.7 % at T = 308.15 K to 55.2 % at T = 318.15 K after 20 minutes of extraction. The highest extraction efficiency, equals to 69.1 %, was recorded for [BMMOR][TCM] at T = 318.15 K after 80 minutes of extraction and the lowest when deep eutectic mixture ([BMMOR][Br] + diethylene glycol) was used. In this case, the highest amount of sulphur, equals to 25.1 % was extracted at T = 318.15 K and after 80 minutes of extraction. This value is almost three-times lower than that for [BMMOR][TCM] at the same time and temperature conditions. In order to improve the efficiency of sulphur removal, the oxidizing agent was added to the mixture. In this work, the desulphurization of model fuel was performed in presence of hydrogen peroxide and acetic acid. The influence of the amount of oxidizing agent on extraction efficiency was determined. The experimental results at T = 318.15 K are presented in Table 7 and Figure 8. (Table 7 goes here)

(Figure 8 goes here) It was shown, that with an increase of the amount of oxidizing agent (oxidant to sulphur molar ratio, S/O) from 1:1 to 1:4, the amount of extracted sulphur increases in each case. For example, the yield of extractions equal to 68.3 % when [BMMOR][TCM] was used as an extractant and the S/O is 1:1. This value for [BMPYR][TCM] is equal to 59.4 % and 24.1 % when the deep eutectic mixture was used. When S/O was 1:4, the efficiency of sulphur extraction is higher and equal to 76.0 % for [BMMOR][TCM], 64.0 % for [BMPYR][TCM] and 25.5 % for ([BMMOR][Br] + diethylene glycol) was used. As expected, the addition of oxidizing agent improves the efficiency of sulphur extraction. For example, for [BMMOR][TCM] without it, the highest efficiency (69.1 %) was observed at T = 318.15 K after 80 minutes of extraction. When extraction was performed in presence of (H2O2 + CH3COOH, the amount of sulphur extracted was equal to 76 % (for S/O = 1:4). Surprisingly, when the deep eutectic mixture was used as an extractant, the efficiency of sulphur extraction was at a low level, even if the oxidizing agent was used. The experimental results show that when extraction was performed in an oxidizing environment, better results are obtained, but not as promising as declared in the literature for the same oxidizing agents [36]. It is worth mentioning that the knowledge of the physicochemical properties such as density and viscosity, are very important to design extraction processes with IL. The experimental density and viscosity of [HMMOR][TCM] at a wide temperature range and at p = 0.1 MPa are presented in Table 8. (Table 8 goes here)

The comparison of the density and viscosity for series tricyanomethanide-based ILs at T = 308.15 K at pressure p = 0.1 MPa are collected in Table 9. (Table 9 goes here) It is worth to highlight, that the tricyanomethanide-based ILs exhibit very low viscosities, what is desirable from the point of view of use extraction process on the industrial scale. The lowest viscosity was determined for [EMIM][TCM] and the highest for morpholinium-based IL, tested in this work. The viscosity for TCM-based IL increases in the following order: [EMIM][TCM] < [BMIM][TCM] < [BMPYR][TCM] < [BMMOR][TCM] < [HMMOR] [TCM]. The viscosity of [BMIM][TCM] (η = 18.5) is slight lower than that for [BMPYR][TCM] (η = 20.6 mPa·s). Although, the viscosity of [BMMOR][TCM] (η = 118.4 mPa·s) is more than 6-times higher than for [BMIM][TCM]. Among tricyanomethanide-based ILs, the highest viscosity was measured for [HMMOR][TCM] (η = 158.1 mPa·s at T = 308.2 K), despite this, this value is significantly lower than the viscosity for other morpholiniumbased ILs, for example [EMMOR][EtSO4] (η = 2425 mPa·s at T = 313.15 K) [41]. The density of [BMMOR][TCM] (ρ = 1.06079 g·cm-3 at 308.2 K) is slight lower than those measured for [EMIM][TCM] (ρ = 1.07393 g·cm-3) [52]. The lowest density was reported for [BMPYR][TCM] (ρ = 1.00076 g·cm-3) [59]. The density of [HMMOR][TCM] (ρ = 1.03333 g·cm-3) is similar to those for [BMIM][TCM] (ρ = 1.04000 g·cm-3) [57]. Generally speaking, the density in the series of tricyanomethanide-based ILs increases in the following order: [BMPYR][TCM] < [HMMOR][TCM] ⁓ [BMIM][TCM] < [BMMOR][TCM] < [EMIM] [TCM].

4. Modelling The non-random liquid equation, NRTL, developed by Renon and Prausnitz [42] was used to correlate the experimental data. The equations and algorithms used in the calculation of the compositions of liquid phases follow the method used by Wales [43]. The objective function F(P), was used to minimize the difference between the experimental and calculated compositions: (3)

where P is the set of parameters vector, n is the number of experimental points, and and

, ,

,

,

are the experimental and calculated mole fractions of one phase , and

,

are the experimental and calculated mole

fractions of the second phase. The binary parameters of each constituent were regressed by minimizing the square of the differences between the experimental and calculated mole fractions of each component of both liquid phases for each ternary system. These binary parameters were obtained for the all data points together (binaries and ternaries) and presented in Table 10. (Table 10 goes here) In this work, the value of NRTL parameter, αij, was fixed at a value of 0.2, which has given the best results of the correlation. The NRTL parameters for the tested ternary systems have been calculated for tie-lines in the liquid phase. The correlated parameters obtained using the NTRL model along with the root mean square deviations (RMSD) are also given in Table 10. The RMSD values, which can be taken as a measure of the precision of the correlation, were calculated according to the following equation:

(4)

where x is the mole fraction; the subscript i, l and m provide a designation for the component, phase and the tie-line, respectively. The value k designates the number of tie-lines. The compositions calculated from the correlations are included in Figures 1–4. The correlation results, obtained for the four systems under work were satisfactory. The experimental and calculated LLE values agree relatively well. The lowest value of the RMSD equal to 0.005 was noticed for {HMMOR][TCM] (1) + thiophene (2) + heptane (3)} and the highest, equal to 0.008 was for {[BMMOR][TCM (1) + benzothiophene (2) + heptane (3)} ternary system.

5. Conclusions In this work, the ability of two ILs: [BMMOR][TCM] and [HMMOR][TCM] to selectively extract sulphur compounds (thiophene and benzothiophene) from model fuel (heptane) is investigated based on the liquid – liquid phase equilibria measurements at T = 308.15 K and p = 0.1 MPa. From experimental LLE data for four ternary systems: {[BMMOR][TCM], or [HMMOR][TCM] (1) + thiophene, or benzothiophene (2) + heptane (3)} the values of selectivity, S and solute distribution ratio, β were calculated and compared to the available literature data. It was observed that the selectivity values are higher for benzothiophene/heptane than for thiophene/heptane system. This is due to the fact that much better solubility of benzothiophene in the ionic liquid-rich phase was observed. Moreover, the selectivity value increases with an increase of the alkyl chain length in the morpholinium cation. Additionally, the separation in the systems thiophene, or benzothiophene / heptane, described by the selectivity for [BMMOR][TCM] and [HMMOR][TCM] are not as optimistic as for other tricyanomethanide-based ILs, presented earlier. Compared to literature data, the selectivity in both separation processes: thiophene / heptane and benzothiophene / heptane increases in the following order: [BMMOR][TCM] < [HMMOR][TCM] < [BMPYR][TCM] < [EMIM][TCM]. The experimental data have been successfully described using NRTL equation with the highest root mean square deviation (RMSD) of 0.008 for {[BMMOR][TCM] (1) + benzothiophene (2) + heptane (3)} ternary system. Moreover, the influence of the extraction time, temperature and amount of oxidizing compound on the efficiency of sulphur extraction were investigated. With the increase of the time of extraction, the amount of sulphur which are extracted increases. The highest extraction efficiency, equals to 69.1 %, was recorded for [BMMOR][TCM] at T = 318.15 K after 80 minutes of extraction and the lowest when deep eutectic mixture ([BMMOR][Br] +

diethylene glycol) was used. At higher temperature, the amount of sulphur extracted was higher for each extractant tested. Moreover, the addition of oxidizing agent improve the efficiency of sulphur extraction, but not as significantly as reported in the opened literature. Additionally,

synthesis

and

basic

physicochemical

characterization

of

[HMMOR][TCM] have been investigated at wide temperature range. It was noticed that in the series of tricyanomethanide-based ILs the density increases in the following order: [BMPYR] [TCM] < [HMMOR][TCM] ⁓ [BMIM][TCM] < [BMMOR][TCM] < [EMIM][TCM], whereas the viscosity increases as follows: [EMIM][TCM] < [BMIM][TCM] < [BMPYR][TCM] < [BMMOR][TCM] < [HMMOR][TCM].

Acknowledgement Funding for this research was provided by the National Science Centre, Poland in years 2016 – 2019 (Grant No. 2015/17/D/ST5/01330). Author wishes to thank Dr. Maciej Zawadzki for synthesis of [HMMOR][TCM].

TABLES Table 1 Chemical compounds used in the experimental part of this work. Chemical name

CAS Number

Supplier

Acetone

67-64-1

Benzothiophene

Purification and analysis methods

Purity (mass fraction)

Water content/10-6

POCH/Avantor

0.995

95

95-15-8

Sigma-Aldrich

0.98

84

1-Butanol

71-36-3

POCH/Avantor

0.995

76

Diethylene glycol

111-46-6

Sigma-Aldrich

0.99

116

Heptane

142-82-5

Sigma-Aldrich

0.99

78

Hydrogen peroxide

7722-84-1

POCH/Avantor

0.30

Octane

111-65-9

Sigma-Aldrich

0.99

65

molecular sieves GC/Karl-Fischer

Thiophene

110-02-1

Sigma-Aldrich

0.99

77

molecular sieves GC/Karl-Fischer

molecular sieves GC/Karl-Fischer molecular sieves GC/Karl-Fischer molecular sieves GC/Karl-Fischer molecular sieves GC/Karl-Fischer molecular sieves GC/Karl-Fischer

Table 2 List of investigated ionic liquids: structure, name, abbreviation of name, molar mass (M), purity, water content, purification and analysis methods. Structure

Name, abbreviation, supplier

CAS Number

M/ g·mol-1

Purity (mass fraction)

Water content / 10-6

1-Butyl-1methylmorpholinium bromide

crystallization, 75174-77-5

238.17

>0.98

215

[BMMOR][Br]

low pressure, 373 K, 24 h NMR

own synthesis

1-Butyl-1methylmorpholinium tricyanomethanide

Purification and analysis methods

1620828-20-7

248.33

0.98

370

[BMMOR][TCM]

low pressure, 373 K, 24 h NMR

Io-Li-Tec

1-Hexyl-1-methylmorpholinium tricyanomethanide

276.38

>0.98

335

[HMMOR][TCM]

low pressure, 373 K, 24 h NMR

own synthesis

1-Butyl-1-methylpyrrolidinium tricyanomethanide [BMPYR][TCM] Io-Li-Tec

878027-72-6

232.33

0.98

420

low pressure, 373 K, 24 h NMR

Table 3 Operating conditions in the gas chromatograph for the analysis of composition of phases in the equilibrium state Element

Characteristic

Description

Column

Type

BP20 (Polyethylene glycol) SGE Analytical Science, length 30 m, inner diameter 0.53 mm, film thickness: 1.0 µm

Carrier gas

Helium

Flow

5 mL·min-1

Oven

Temperature program

373.15 K, 5 min  (45 K∙min-1) 473.15 K, 4 min

Injector

Injection volume

0.5 l

Split ratio

10:1

Temperature

423 K

Type

Flame ionization detector (FID)

Temperature

493 K

Detector

Table 4 Compositions of experimental tie-lines, selectivity, (S) and solute distribution ratios, (β) for ternary systems {[BMMOR][TCM], or [HMMOR][TCM] (1) + sulfur compound (2) + heptane (3)} at T = 308.15 K and p = 0.1 MPaa Hydrocarbon – rich phase

IL – rich phase

S

β

[BMMOR][TCM] (1) + thiophene (2) + heptane (3) 0.000

0.000

1.000

0.980

0.000

0.020

0.000

0.075

0.925

0.805

0.157

0.038

51.0

2.09

0.000

0.171

0.829

0.697

0.272

0.031

42.5

1.59

0.000

0.261

0.739

0.621

0.355

0.024

41.9

1.36

0.000

0.318

0.682

0.545

0.430

0.025

36.9

1.35

0.000

0.335

0.665

0.526

0.449

0.025

35.7

1.34

0.000

0.397

0.603

0.500

0.478

0.022

33.0

1.20

0.000

0.469

0.531

0.456

0.524

0.020

29.7

1.12

0.000

0.528

0.472

0.425

0.557

0.018

27.7

1.05

0.000

0.583

0.417

0.413

0.570

0.017

24.0

0.98

0.000

0.707

0.293

0.373

0.610

0.017

14.9

0.86

0.000

0.837

0.163

0.332

0.657

0.011

11.6

0.78

0.000

0.897

0.103

0.280

0.707

0.013

6.2

0.79

0.000

0.950

0.050

0.258

0.732

0.010

3.9

0.77

0.000

0.983

0.017

0.244

0.745

0.011

1.2

0.76

0.000

1.000

0.000

0.211

0.789

0.000

0.79

[BMMOR][TCM] (1) + benzotiophene (2) + heptane (3) 0.000

0.000

1.000

0.980

0.000

0.020

0.000

0.066

0.934

0.820

0.152

0.028

76.8

2.30

0.000

0.152

0.848

0.708

0.265

0.027

54.8

1.74

0.000

0.231

0.769

0.635

0.341

0.024

47.3

1.48

0.000

0.307

0.693

0.560

0.417

0.023

40.9

1.36

0.000

0.381

0.619

0.526

0.451

0.023

31.9

1.18

0.000

0.456

0.544

0.469

0.512

0.019

32.1

1.12

0.000

0.520

0.480

0.434

0.549

0.017

29.8

1.06

0.000

0.607

0.393

0.413

0.570

0.017

21.7

0.94

0.000

0.679

0.321

0.388

0.595

0.017

16.5

0.88

0.000

0.738

0.262

0.354

0.629

0.017

13.1

0.85

0.000

0.817

0.183

0.312

0.674

0.014

10.8

0.82

0.000

0.888

0.112

0.217

0.770

0.013

7.5

0.87

0.000

0.937

0.063

0.171

0.818

0.011

5.0

0.87

0.000

1.000

0.000

0.126

0.874

0.000

0.87

[HMMOR][TCM] (1) + thiophene (2) + heptane (3) 0.000

0.000

1.000

0.969

0.000

0.031

0.000

0.041

0.959

0.833

0.124

0.043

67.5

3.02

0.000

0.071

0.929

0.787

0.172

0.041

54.9

2.42

0.000

0.119

0.881

0.744

0.221

0.035

46.7

1.86

0.000

0.215

0.785

0.599

0.370

0.031

43.6

1.72

0.000

0.291

0.709

0.523

0.443

0.034

31.7

1.52

0.000

0.363

0.637

0.452

0.523

0.025

36.7

1.44

0.000

0.450

0.550

0.406

0.569

0.025

27.8

1.26

0.000

0.540

0.460

0.332

0.640

0.028

19.5

1.19

0.000

0.621

0.379

0.307

0.670

0.023

17.8

1.08

0.000

0.668

0.332

0.299

0.678

0.023

14.7

1.01

0.000

0.720

0.280

0.284

0.692

0.024

11.2

0.96

0.000

0.761

0.239

0.274

0.703

0.023

9.6

0.92

0.000

0.817

0.183

0.243

0.733

0.024

6.8

0.90

0.000

0.871

0.129

0.221

0.759

0.020

5.6

0.87

0.000

0.897

0.103

0.203

0.781

0.016

5.6

0.87

0.000

0.926

0.074

0.188

0.801

0.011

5.8

0.87

0.000

0.968

0.032

0.180

0.815

0.005

5.4

0.84

0.000

1.000

0.000

0.175

0.825

0.000

0.83

[HMMOR][TCM] (1) + benzotiophene (2) + heptane (3) 0.000

0.000

1.000

0.969

0.000

0.031

0.000

0.057

0.943

0.838

0.136

0.026

86.5

2.39

0.000

0.132

0.868

0.743

0.233

0.024

63.8

1.77

0.000

0.229

0.771

0.610

0.367

0.023

53.7

1.60

0.000

0.316

0.684

0.521

0.457

0.022

45.0

1.45

0.000

0.389

0.611

0.449

0.529

0.022

37.8

1.36

0.000

0.454

0.546

0.408

0.571

0.021

32.7

1.26

0.000

0.524

0.476

0.359

0.620

0.021

26.8

1.18

0.000

0.616

0.384

0.309

0.671

0.020

20.9

1.09

0.000

0.705

0.295

0.290

0.690

0.020

14.4

0.98

0.000

0.786

0.214

0.261

0.720

0.019

10.3

0.92

0.000

0.866

0.134

0.231

0.750

0.019

6.1

0.87

0.000

0.926

0.074

0.186

0.804

0.010

6.4

0.87

0.000

0.967

0.033

0.155

0.840

0.005

5.7

0.87

0.000

1.000

0.000

0.114

0.886

0.000

a

0.89

Standard uncertainties u are: u(x) = 0.003 for compositions of the hydrocarbon-rich

phase, u(x) = 0.005 for compositions of IL-rich phase, u(T) = 0.02 K, u(p) = 0.5 kPa.

Table 5 The experimental and literature values of selectivity, (S), and distribution ratio, (β), of ionic liquids in the processes of separating sulphur compounds from aliphatic hydrocarbons (model fuel). IL

Separation process

T/K

S0,05

β0,05

[EMIM][TCM] [28]

heptane / tiophene

308.15

171.0

1.97

[EMIM][TCM] [28]

heptane / benzothiophene

308.15

221.4

2.94

[EMIM][SCN] [26]

heptane / tiophene

298.15

~ 1500

0.64

[EMIM][EtSO4] [44]

heptane / tiophene

298.15

~ 150

1.80

[EMIM][NTf2] [18]

heptane / tiophene

298.15

74.5

1.95

[EMIM][AcO] [45]

hexane / thiophene

298.15

131.0

1.53

[EMIM][DEP] [46]

hexane / thiophene

298.15

43.5

2.58

[EMIM][FAP] [47]

heptane / tiophene

298.15

78.0

3.30

[BMIM][NO3] [48]

heptane / tiophene

298.15

75.0

2.20

[BMIM][CF3SO3] [49]

heptane / tiophene

298.15

35.0

1.20

[BMIM][BF4] [50]

heptane / tiophene

298.15

298.0

1.70

[BMIM][SCN] [51]

heptane / tiophene

298.15

280.0

2.10

[BMPYR][TCM] [25]

heptane / tiophene

298.15

121.2

3.18

[BMPYR][TCM] [30]

heptan / benzotiofen

308.15

152.0

5.48

[BMPYR][TCB] [25]

heptane / tiophene

298.15

72.1

3.20

[BMPYR][CF3SO3] [38]

heptane / tiophene

308.15

76.5

1.88

[BMPYR][CF3SO3] [38]

heptane / benzothiophene

308.15

111.1

2.89

[BMPYR][FAP] [25]

heptane / tiophene

298.15

50.1

3.70

[BMMOR][TCM]

heptane / tiophene

308.15

55.0

2.16

[BMMOR][TCM]

heptane / benzothiophene

308.15

78.5

2.41

[HMMOR][TCM]

heptane / tiophene

308.15

67.0

3.00

[HMMOR][TCM]

heptane / benzothiophene

308.15

87.1

2.42

[HMIM][TCB] [38]

heptane / benzothiophene

308.15

78.8

5.14

[COC2MPYR][FAP] [13]

heptane / tiophene

298.15

51.5

2.90

[COC2MPIP][FAP] [13]

heptane / tiophene

298.15

51.0

3.60

[COC2MMOR][FAP] [13]

heptane / tiophene

298.15

96.0

2.50

[COC2MPYR][NTf2] [27]

heptane / tiophene

298.15

67.5

2.26

[COC2MPIP][NTf2] [27]

heptane / tiophene

298.15

55.0

2.40

[COC2MMOR][NTf2] [27]

heptane / tiophene

298.15

105.0

1.80

Table 6

Extraction efficiency of model fuel (sulfur content: 500 ppm) with different extractant as a function of extraction times and temperature. Extractant

Extraction time / min

amount of sulfur extracted / % T = 308.15 K

T = 318.15 K

20

41.7

65.4

40

56.4

67.9

60

62.7

68.3

80

64.7

69.1

20

44.7

55.2

40

48.1

58.4

60

52.8

59.4

80

54.1

60.0

[BMMOR][Br] +

20

16.7

22.6

diethylene glycol

40

18.8

23.3

60

19.0

24.1

80

19.4

25.1

[BMMOR][TCM

[BMPYR][TCM]

Table 7 Extraction efficiency of model fuel (sulfur content: 50010-6) with different extractant in presence of oxidizing agent (hydrogen peroxide + acetic acid) as a function of oxidant to sulphur molar ratio (S/O) at temperature T = 318.15 K and pressure p = 0.1 MPa. amount of sulfur extracted / %

S/O [BMMOR][TCM]

[BMPYR][TCM]

[BMMOR][Br] + diethylene glycol

1:1

68.3

59.4

24.1

1:2

69.6

62.5

24.9

1:3

73.2

62.8

25.3

1:4

76.0

64.0

25.5

Table 8 Density and viscosity of [HMMOR][TCM] over a wide temperature range and at pressure p = 0.1 MPa.a

a

T/K

ρ / g·cm-3

η / mPa·s

293.15

1.04268

459.2

298.15

1.03957

309.8

303.15

1.03645

218.4

308.15

1.03333

158.1

313.15

1.03022

117.9

318.15

1.02713

90.06

323.15

1.02406

70.51

328.15

1.02101

56.52

333.15

1.01798

44.11

338.15

1.01496

37.21

343.15

1.01196

30.95

348.15

1.00896

353.15

1.00598

standard uncertainties u are as follows: u(x1) = 110-4; u(ρ) = 510-4 g·cm-3; ur(η) = 5 %;

u(T) = 0.1 K.

Table 9 The comparison of the density and viscosity of different tricyanomethanide-based ILs at T = 308.2 K at pressure p = 0.1 MPa. Ionic liquid [EMIM][TCM]

ρ / g·cm-3 52

η / mPa·s

1.07393

10.5854

1.074353

10.3255

1.07454 [BMIM][TCM]

[BMPYR][TCM]

1.0398252

18.4556

1.040656

18.9758

1.0400057

19.2057

1.00078 (308.1 K)52

20.659

1.0007659 [BMMOR][TCM] [HMMOR][TCM] (this work)

1.0607932

118.457

1.03333

158.1

Table 10 Binary interaction parameters and root mean square deviation (σx) for the NRTL equation for ternary systems {[BMMOR][TCM], or [HMMOR][TCM] (1) + tiophene, or benzothiophene (2) + heptane (3)} at T = 308.15 K, p = 0.1 MPa. Parameter ij = ji = 0.2 NRTL parameters Components

RMSD σx

[BMMOR][TCM] (1) + thiophene (2) + heptane (3) 1-2

1930.4

58458

1-3

5659.7

15880

2-3

3023.3

1378.3

0.006

[BMMOR][TCM] (1) + benzothiophene (2) + heptane (3) 1-2

4703.9

68148

1-3

7127.3

15240

2-3

756.20

5067.7

0.008

[HMMOR][TCM] (1) + thiophene (2) + heptane (3) 1-2

-861.03

60820

1-3

4123.0

15883

2-3

5056.2

-1327.2

0.005

[HMMOR][TCM] (1) + benzothiophene (2) + heptane (3) 1-2

1581.0

66983

1-3

5262.3

14960

2-3

3448.0

600.52

0.006

FIGURES CAPTION Figure 1. Plot of the experimental tie-lines (●, solid lines) for the LLE of the {[BMMOR][TCM] (1) + thiophene (2) + heptane (3)} ternary system at T = 308.15 K and p = 0.1 MPa. The corresponding tie-lines correlated by means of the NRTL equation (○, dotted lines). Figure 2. Plot of the experimental tie-lines (●, solid lines) for the LLE of the {[BMMOR][TCM] (1) + benzothiophene (2) + heptane (3)} ternary system at T = 308.15 K and p = 0.1 MPa. The corresponding tie-lines correlated by means of the NRTL equation (○, dotted lines). Figure 3. Plot of the experimental tie-lines (●, solid lines) for the LLE of the {[HMMOR][TCM] (1) + thiophene (2) + heptane (3)} ternary system at T = 308.15 K and p = 0.1 MPa. The corresponding tie-lines correlated by means of the NRTL equation (○, dotted lines). Figure 4. Plot of the experimental tie-lines (●, solid lines) for the LLE of the {[HMMOR][TCM] (1) + benzothiophene (2) + heptane (3)} ternary system at T = 308.15 K and p = 0.1 MPa. The corresponding tie-lines correlated by means of the NRTL equation (○, dotted lines). Figure 5. The comparison of the experimental and literature tie-lines for the LLE of the {[cation][TCM] (1) + thiophene (2) + heptane (3)} ternary system at T = 308.15 K and p = 0.1 MPa: (●—●) [BMMOR][TCM]; (○- -○) [HMMOR][TCM]; (▲···▲) [BMPYR] [TCM] [25]; (□-·-·□) [EMIM][TCM] [28]. Figure 6. The comparison of the experimental and literature tie-lines for the LLE of the {[cation][TCM] (1) + thiophene (2) + heptane (3)} ternary system at T = 308.15 K and p = 0.1 MPa: (●—●) [BMMOR][TCM]; (○- -○) [HMMOR][TCM]; (▲···▲) [BMPYR][TCM] [Error! Bookmark not defined.]; (□-·-·□) [EMIM][TCM] [28].

Figure 7. Plot of the extraction time on sulfur removal for different extractant at temperature T = 308.15 K (full points) and T = 318.15 K (empty points) at pressure p = 0.1 MPa: (●,○) [BMMOR][TCM]; (♦,◊) [BMPYR][TCM]; (▲, ) ([BMMOR][Br] + diethylene glycol). Figure 8. Plot of the amount of oxidant on sulfur removal for different extractant at temperature T = 318.15 K at pressure p = 0.1 MPa: (○) [BMMOR][TCM]; (◊) [BMPYR][TCM]; ( ) ([BMMOR][Br] + diethylene glycol). IL, or DES was added to the model oil in a volume ratio of 1:3.

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

HIGHLIGHTS > LLE data for {[BMMOR][TCM] + thiophene / benzothiophene + heptane) were determined. > The S andβ for the extraction of thiophene / benzothiophene from heptane were presented. > Results of S andβ were compared with available literature. >The NRTL model satisfactorily correlates the LLE data. > The synthesis and physicochemical properties of [HMMOR][TCM] are presented. > Oxidative desulphurization with ILs and DES are investigated.

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