hexadecane with ionic liquids in ternary liquid-liquid phase equilibrium

Journal Pre-proof Separation of thiophene from octane/hexadecane with ionic liquids in ternary liquidliquid phase equilibrium Marcin Durski, Paramespri Naidoo, Deresh Ramjugernath, Urszula Domańska PII:

S0378-3812(20)30013-3

DOI:

https://doi.org/10.1016/j.fluid.2020.112467

Reference:

FLUID 112467

To appear in:

Fluid Phase Equilibria

Received Date: 21 October 2019 Revised Date:

30 December 2019

Accepted Date: 10 January 2020

Please cite this article as: M. Durski, P. Naidoo, D. Ramjugernath, U. Domańska, Separation of thiophene from octane/hexadecane with ionic liquids in ternary liquid-liquid phase equilibrium, Fluid Phase Equilibria (2020), doi: https://doi.org/10.1016/j.fluid.2020.112467. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier B.V.

Author Contribution Statement CRediT author statement Marcin Durski: Metodology, Data curation, Measurements, Figures. Paramespri Naidoo: Conceptualization, Methodology, Supervision, Reviewing and Editing. Deresh Ramjugernath: Supervision, Funding acquisition, Formal analysis. Urszula Domańska: Writing, Calculations.

Fluid Phase Equilib. Separation of thiophene from octane/hexadecane with ionic liquids in ternary liquid-liquid phase equilibrium Marcin Durskia, Paramespri Naidooa, Deresh Ramjugernatha, Urszula Domańskaa,b,* a

Thermodynamics Research Unit, School of Engineering, University of KwaZulu-Natal,

Howard College Campus, King George V Avenue, Durban 4001, South Africa b

ŁUKASIEWICZ Research Network – Industrial Chemistry Research Institute,

Rydygiera 8, 01-793 Warsaw, Poland.

*Corresponding author at Łukasiewicz - Industrial Chemistry Research Institute, Rydygiera 8, 01-793 Warsaw, Poland. Tel.:+48 22 6213115; fax: +48 22 6282741. E-mail address: [email protected] (U. Domańska).

Keywords: Ionic liquids 1-Butyl-1-methylpiperidynium dicyanamide, Tri-iso-butylmethylphosphonium tosylate, Ternary (liquid-liquid) phase equilibrium, Selectivity, Solute distribution ratio, NRTL correlation.

1

ABSTRACT This work is a continuation of the investigations on desulfurization processes, by assessing the applicability of two ionic liquids (ILs), 1-butyl-1-methylpiperidynium dicyanamide, [BMPIP][DCA] and tri-iso-butylmethylphosphonium tosylate,

[Pi4,i4,i4,1][TOS],

for the

separation of thiophene from octane, or hexadecane. The latter two components are used as model substances of the fuel stream. Experimental liquid-liquid phase equilibrium (LLE) data were obtained for four ternary systems {IL + thiophene + octane, or hexadecane} at temperature T = 308.15 K and pressure p = 101 kPa. The DCA-based IL showed better selectivity than the tosylate-based IL in the extraction of thiophene from both alkanes with much lower solute distribution ratio. The selectivity is acceptable in all systems in comparison with currently published data for different ILs. Chromatography analysis showed that the IL was not present in the octane, or hexadecane layer, which simplifies the process of separating the solvent from the hydrocarbon layer. The non-random two liquid (NRTL) model showed satisfactory correlation of the measured phase data.

2

1. Introduction Extractive desulfurization of gasoline using ionic liquids (ILs) is an area of increasing interest as seen in many recent experimental and theoretical works [1-4]. ILs are sustainable alternatives for traditional hydrodesulphurization (HDS) process which is costly due to high temperature and pressure operations and cost of hydrogen. The properties of ILs can be modified by adding to the “cores” of cation and/or an anion the functional groups, which may differ in size, shape, polarity, acidity, etc. Several computational methods have been used to predict the structure of ILs

and their properties for the desulfurization [5,6] or

denitrogenation of fuels [7,8]. A conductor-like screening model for real solvents (COSMORS) is very helpful in designing new ILs for the desulfurization of fuels [7-9]. An interesting screening approach of ILs for the desulfurization process was recently presented [4,10]. In most petroleum processes, low level of sulfur compounds such as thiophene, benzothiophene, methyldibenzothiophenes, 4,6-dibenzothiophenethiols, thioethers, and disulfides are the key species of interest for extraction. The content of total sulfur compounds in USA and European gasoline and diesel fuels must be at a maximum concentration level of 10 ppm [11,12]. Favorable operating conditions and simpler processing methods are some of the advantages in promoting the use of the ternary liquid-liquid equilibrium (LLE) over other treatments. It was shown in the ternary liquid-liquid equilibrium systems that piperidinium based ILs displayed high selectivities for the desulfurization process [4,13]. Many ILs have already been reported in the literature in form of LLE ternary or activity coefficients at infinite dilution for the desulfurization process [2,13,14-38]. ILs based on the imidazolium, pyridinium and pyrrolidinium cations and on the anions such as thiocyanate, [SCN]-, dicyanamide, [DCA]-, tricyanomethanide, [TCM]- and tetracyanoborate, [TCB]- have been identified as most promising candidates [2,14,15]. 3

Thiophene can be considered as the key substance to be separated from liquid fuel oils. As model compounds, n-alkanes (C7, C8, or C16) are usually tested. The popular [DCA]--based ILs were measured in many works for the separation of thiophene: 1-butyl-1-methylpyrrolidinium dicyanamide, [BMPYR][DCA] [25], 1-ethyl-3methylimidazolium

dicyanamide,

[EMIM][DCA]

[26],

1-butyl-3-methylimidazolium

dicyanamide, [BMIM][DCA] [26], ethyldimethylsulphonium dicyanamide, [S1,1,2][DCA] (extraction from model oil) [26], 1-butyronitrile-3-methylimidazolium dicyanamide, [CpMIM][DCA]

and

1-butyronitrile-2,3-dimethylimidazolium

dicyanamide,

[CpMMIM][DCA] [27]. The tosylate-based ILs are not very popular in extraction processes due to the high melting points of these ILs [28]. Nevertheless, the complete solubility of few tosylate-based ILs in thiophene were observed over a wide range of temperatures and mole fraction of the IL [28]. Determination of activity coefficients at infinite dilution for different solutes and water reported

high

selectivities

for

thiophene/1-butyl-3-methylimidazolium

tosylate,

[BMIM][TOS] [29], and N-hexyl-3-methylpyridinium tosylate, [HM3PY][TOS] [30]. Most of works, presented the analysis of activity coefficients at infinite dilution ( γ 13∞ ), in order to determine the selectivity in separating thiophene from heptane, octane or other hydrocarbons

[25,27,29,30].

Measurements

were

also

performed

for

tri-iso-

butylmethylphosphonium tosylate, [Pi4,i4,i4,1][TOS] [31]. This report is the continuation of our systematic study on desulfurization of fuels. Experimental ternary LLE data for four ternary systems {IL + thiophene + octane, or hexadecane} at T = 308.15 K and pressure p = 101 kPa are presented. Two ILs, 1-butyl-1methylpiperidynium dicyanamide, [BMPIP][DCA] and tri-iso-butylmethylphosphonium tosylate, [Pi4,i4,i4,1][TOS] were used to assess the desulfurization process. The selectivities

4

and solute distribution ratios for the extraction of thiophene from octane, or hexadecane are presented.

2. Experimental

The ILs studied, [BMPIP][DCA] and [Pi4,i4,i4,1][TOS] were obtained from Io-li-tec. The structure, name, abbreviated name, molar mass and mass fraction purity of ILs are listed in Table 1. The density of [Pi4,i4,i4,1][TOS] at temperature T = 308.15 K was 1.061 g⋅cm-3 [31]. The names, suppliers, mass fraction purities, purification method, water content, and CAS numbers of all solvents used are shown in Table 2. Most of the chemicals used were purchased from Sigma Aldrich. The samples of ILs were dried for 72 h at T = 353 K under vacuum, to remove volatile impurities and trace amounts of water. Thiophene, octane and hexadecane were stored over freshly activated 0.3 nm molecular sieves supplied by Merck. The alkanes, octane and hexadecane were chosen as a less measured data to comparison with heptane. The water content was checked using the Karl-Fischer Moisture Titrator MKS 500. The sample of IL, or solvent, was dissolved in methanol and titrated in steps of 0.005 cm3. The error in the water content was ±10

10-6 in mass fraction. The water content in the

solvents used was less than 500 10-6 in mass fraction. To measure the experimental LLE tie-lines, mixture compositions which created twophase layers for these systems were placed into 10 cm3 glass cells, each surrounded with a heating jacket. Coated magnetic stirring bars were used to agitate these mixtures. The vessels were sealed to prevent moisture from the atmosphere entering the cell or losses by evaporation. The jacketed vessels were connected to a thermostatic water bath (PolyScience temperature controller) to maintain a constant temperature T = 308.15 K (±0.1). The mixtures were agitated for 6 h to reach thermodynamic equilibrium and left to settle for about 12 h to

5

allow sufficient phase separation. Next samples of 0.1–0.3 cm3 were withdrawn from both phases using disposable plastic syringes with attached stainless steel needles. A sample of the phase was placed in a 2 cm3 ampoule which was closed with a septum cap. An internal standard was prepared by dissolution of 2-pentanone in 1-propanol in mass ratio 0.054. To each ampoule 1.0 cm3 of internal standard was added to maintain a homogeneous mixture and avoid phase splitting. Due of the low vapor pressure, the ILs used in this work cannot be analyzed by GC. Thus, only thiophene and octane, or hexadecane were analyzed. The mass fraction of the third component, the IL, was calculated by subtracting the mole fractions of the two other components from unity. This was done by taking into account only three important peaks from thiophene, hydrocarbon and 2-pentanone neglecting the co-solvent peak. The compositions were measured using a Shimadzu 2010, gas chromatography equipped with an FID detector and Elit-5MS PerkinElmer column. The GC Solution software was used to obtain the chromatographic areas for thiophene, octane, or hexadecane and the internal standard 2-pentanone. Samples were injected three times, and the average peak area was calculated. Details of the operational conditions of the apparatus are reported in Table 1S in the Supplementary Material. The estimated standard uncertainty in the determination of mole fraction compositions is u(x) = ± 0.005.

3. Results and discussion Tables 3 and 4 report the equilibrium compositions in mole fractions of the experimental tie-line analysis for four ternary systems {[BMPIP][DCA], or [Pi4,i4,i4,1][TOS] (1) + thiophene (2) + octane, or hexadecane (3)} at T = 308.15 K and p = 101 kPa. In the binary {IL (1) + octane (3)} system, liquid miscibility (solubility of octane in the IL) is observed up to a mole fraction of octane x3IL = 0.006, and x3IL = 0.048 for [BMPIP][DCA] and [Pi4,i4,i4,1][TOS], respectively, as well as up to mole fraction of 6

hexadecane, x3IL = 0.008,

and x3IL = 0.04 for

[BMPIP][DCA] and [Pi4,i4,i4,1][TOS],

respectively. The solubility of both hydrocarbons in ILs is much lower in the [BMPIP][DCA] than in [Pi4,i4,i4,1][TOS]. The extracted substance, thiophene is supposed to be very soluble in the IL. The observed value for thiophene is x2IL= 0.790 for [BMPIP][DCA] (for [Pi4,i4,i4,1][TOS], was not measured) at T = 308.15 K. The results are shown in triangular diagrams for each IL and thiophene in Figs. 1- 4. It can be seen that the two-phase region is similar for both ILs measured in this work and in many other previous measurements [13,24,38] and covers almost the entire area of the triangle. The slope of the tie-lines is changing from large contamination of thiophene to the small amounts of the thiophene in the mixture. Better selectivity of the solvent (IL) is always observed for the lower concentration of sulphur-compounds in the ternary system. It can be seen from Tables 3 and 4 that when x2HC , the mole fraction of the thiophene in the hydrocarbon phase, decreases up to 0.2-0.3 or to the lower values, the selectivity increases. The small immiscibility region between [BMPIP][DCA] and thiophene is typical for many ILs [13,16,38]. The diagram presented in Fig. 1 and 3 is very similar to the published earlier

results

for

trifluorotris(perfluoroethyl)phosphate4-(2-methoxyethyl)-

4methylmorpholin-4-ium, [COC2mMOR][FAP] [38]. We assume from the experimental points in ternary systems with the [Pi4,i4,i4,1][TOS] IL (see Fig. 2 and 4) that it will be immiscibility in the binary (IL+ thiophene) system similar to [BMPIP][DCA]-based IL. Unfortunately, because of the large viscosity it was not measured. The desulphurization process lies on the region having low thiophene mole fraction, which is at the lowest part of diagram.

For ILs displaying high selectivity, the positive slopes of the tie-lines over the

concentration range is observed.

7

The characteristic parameters, selectivity (S) and solute distribution ratio (β) for the measured mixtures were calculated for the potential application in the separation of thiophene from hydrocarbons. The parameters S and β are defined as follows:

S=

x2II ⋅ x3I x2I ⋅ x3II

(1)

x2II β= I x2

(2)

where x is the mole fraction; superscripts I and II refer to the octane, or hexadecane– rich phase and the IL–rich phase, respectively. Subscripts 2 and 3 refer to thiophene and hydrocarbon (octane, or hexadecane). The values of β and S are listed in Tables 3 and 4. The values of S and β are different for the different tie-lines. The average parameters for all tielines of the system, SAv = ΣS/n and βAv = Σβ/n (where n is a number of tie-lines) obtained in this work are compared to a few reported literature data in Table 5 [13,18,20-22]. Unfortunately, the ILs investigated in this study do not exhibit the best criteria when compared to those reported in Table 5 for the desulfurization of fuels. The measured [BMPIP][DCA] shows selectivity (SAv = 103.2) with very low solute distribution ratio (βAv = 0.025) in the ternary system {IL + thiophene + octane}. The solute distribution ratios are much better for [BMIM][OTf] (SAv = 43.9, βAv = 1.82) [22], or for [OHOHIM][NTf2] (SAv = 40,3, βAv = 0,498) at T = 308 K [22], or for [HMIM][SCN] (SAv = 80.17, βAv = 1.82) at T = 298 K and p = 88 kPa [20]. Much better results were obtained for hexadecane. The measured [BMPIP][DCA] shows selectivity (SAv = 159.4) with low solute distribution ratio (βAv = 0.02). In the ternary system {IL + thiophene + hexadecane} the best literature results were shown for [BMIM][OTf] (SAv = 209 and βAv = 0.925) [22]. The other ILs presented in Table 5 revealed 8

selectivity lower than 70 [21,22]. Quite interesting results with hexadecane were obtained in this work for [Pi4,i4,i4,1][TOS] with selectivity (SAv = 109.5) and a solute distribution ratio of (βAv = 0.99). The

ILs discussed in this work revealed the largest selectivity at the lowest

concentration of thiophene, which supporting its use only for deep desulphurization, unfortunately with very low solute distribution ratio. There is possible a comparison of the systems {IL + thiophene + octane} with the system {IL + thiophene + hexadecane}. As we can see from Table 5 there is an influence of the chain of hydrocarbon on the selectivity and solute distribution ratio. The selectivity increases and the distribution coefficient comes down when the chain of the hydrocarbon increases from octane to hexadecane. It is evident from the reported data in Tables 3 and 4 that there is no IL in the hydrocarbon phase. This is an important information for industrial applications, as it allows for less costly methods of extraction and solvent recovery. The extraction characteristic parameters obtained in this work are compared to some previously described in the open literature at mole fraction of sulphur compound in the hydrocarbon-rich phase, x2HC = 0.05. The best values were observed in the literature for the [EMIM][TCM], measured by us earlier, in the system of {IL+ thiophene + heptane} at T = 308 K (S0.05 = 171.0 and βo.o5 = 1.97 [39]. The other interesting values from the literature for systems with heptane are: for [HMIM][TCB] (S0.05 = 45.9 and βo.o5 = 2.88 at T = 308 K [24], and for [BMPYR][CF3SO3] (S0.05 = 76.5 and βo.o5 = 1.88 at T = 308 K [24], In this work [BMPIP][DCA] shows selectivity (S0.05 = 118.1 ) with solute distribution ratio (β0.05 = 0.02) in the ternary system {IL + thiophene + octane} and (S0.05 = 215) with solute distribution ratio (β0.05 = 0.001) in the ternary system {IL + thiophene + hexadecane}.

9

Much better results were observed for [Pi4,i4,i4,1][TOS] (S0.05 = 28.06) with solute distribution ratio (β0.05 = 1.83) in the ternary system {IL + thiophene + octane} and (S0.05 = 148.9) with solute distribution ratio (β0.05 = 1.14) in the ternary system {IL + thiophene + hexadecane}. Nevertheless, the results obtained for the DCA-based IL, measured in this work, are interesting for their selectivity with not useful in technological use too small solute distribution ratio. This comparison for thiophene and different systems is made for two different temperatures (298.15 and 308.15) K, but the influence of temperature on the LLE ternary is not great.

4. Data correlation The experimental tie lines data were correlated with the NRTL equation [40,41]. The equations and algorithms used for the calculation of the compositions in both phases followed the method described in literature [41]. The objective function F(P), was used to minimize the difference between the experimental and calculated compositions:

n

[

] [

] [ 2

] [

]

F ( P ) = ∑ x 2I exp − x 2Icalc (PT ) + x3I exp − x 3Icalc (PT ) + x 2II exp − x 2IIcalc (PT ) + x3II exp − x 3IIcalc (PT ) i =1

2

2

2

(3) where P is the set of parameters vector, n is the number of experimental points, x 2I exp , x 3I exp Icalc and x2i (PT ) , x3Icalc (PT ) are the experimental and calculated mole fractions of one phase and

x 2II exp , x 3II exp and x 2IIcalc (PT ) , x3IIcalc (PT ) 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

10

component of both liquid phases for each ternary system. These binary parameters were obtained for all data simultaneously (binaries and ternaries) with a constant value for the nonrandomness parameter α (chosen for the best correlation). The model results including the parameters and root mean square deviations (RMSD) are listed in Table 6. The RMSD was calculated according to the equation:

[

]

  exp calc 2 RMSD =  ∑∑∑ xilm − xilm / 6k   i l m 

1/ 2

(4)

where x is the mole fraction and the subscripts i, l, and m designate the component, phase, and tie-line, respectively. The Rosenbrock simplex method was used to minimise the objective function [42]. The compositions calculated from the correlations are included in Figs. 1- 4. The experimental tie-lines and the phase composition in mole fraction for the ternary systems were calculated with an average root mean square deviation (RMSD) of 0.009.

5. Conclusions New ternary liquid-liquid phase equilibrium data were measured for the extraction of thiophene from octane, or hexadecane using two ILs at temperature T = 308.15 K and pressure p = 101 kPa. The viability of [BMPIP][DCA] and [Pi4,i4,i4,1][TOS] as suitable solvents was analyzed with respect to the slope of the tie-lines in the phase diagram of thiophene with octane, or hexadecane. The data presented in this work revealed satisfying results compared to many previous studies, especially with [Pi4,i4,i4,1][TOS] in the ternary system {IL + thiophene + hexadecane}. The best separation efficiency was obtained for deep desulfurization of liquid fuels (for the low sulfur concentration in the feed). Unfortunately, the solute distribution ratio for the [BMPIP][DCA] is too small and this ionic liquid is not 11

suitable for the extraction of thiophene. The experimental data in this work were regressed using the NRTL activity coefficient model. Acknowledgments This work has been supported by the National Science Centre (NCN) in Poland in the years 2017–2020 (UMO-2016/23/B/ST5/00145).

CRediT author statement Marcin Durski: Metodology, Data curation, Measurements, Figures. Paramespri Naidoo: Conceptualization, Methodology, Supervision, Reviewing and Editing. Deresh Ramjugernath: Supervision, Funding acquisition, Formal analysis. Urszula Domańska: Writing, Calculations.

Nomenclature gij

molar energy of interaction between i and j (J mol-1)

k

number of parameters

n

number of experimental points

P

the set of parameters vector

S

selectivity

T

equilibrium temperature (K)

∆T

estimated error of temperature (K)

x

mole fraction

Greek letters αij

nonrandomness NRTL parameter

12

β

solute distribution ratio

Subscripts calc

calculated value

exp

experimental value

i

component

T

temperature

I, II

phases

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Table 1 Properties of the ionic liquids investigated: structure, name, abbreviated name, supplier, CAS number, molar mass (M), mass fraction purity (as stated by the supplier) and purification method.* Structure

Name, abbreviation, M/ supplier, CAS (g·mol-1)

1-Butyl-1methylpiperidinium dicyanamide, [BMPIP][DCA], Io-li-tec, CAS: 827033-52-3 Tri(isobutyl)methylphosphonium tosylate , [Pi4,i4,i4,1][TOS], Io-li-tec, CAS: 344774-05-6

222.34

Mass fraction purity /water content (mass fraction) >0.970/ <500x10-6

388.55

>0.950/ <500x10-6

*Purification method: Low pressure 72h, 340K, Analysis: Karl Fisher method.

17

Table 2 Properties and purity of the original materials used in this study. Compound

Supplier

Mass fraction purity/ Analysis water content (mass

CAS Number

Method

fraction)a* Octane

Merck

0.990/<100 x 10-6

GC

111-65-9

Hexadecane

Sigma

0.990/<100 x 10-6

GC

544-76-3

0.990/<100 x 10-6

GC

110-02-1

0.995/<100 x 10-6

GC

107-87-9

0.990/<100 x 10-6

GC

71-23-8

0.990/<100 x 10-6

Karl Fischer 67-56-1

Aldrich Thiophene

Sigma Aldrich

2-Pentanone

Sigma Aldrich

1-Propanol

Sigma Aldrich

Methanol

Sigma Aldrich

*Purification method: molecular sieves.

18

Table 3 Compositions of experimental tie lines in mole fractions, selectivity, S and solute distribution ratios, β for the ternary systems {[BMPIP][DCA], or [Pi4,i4,i4,1][TOS] (1) + thiophene (2) + octane (3)} at T = 308.15 K, and pressure p = 101 kPa.a Hydrocarbon - rich phase x1HC x2HC

IL - rich phase S x1IL x2IL [BMPIP][DCA] 0.000 0.994 0.000 0.000 0.038 0.880 0.099 119 0.000 0.130 0.724 0.271 363 0.000 0.185 0.667 0.320 108 0.000 0.352 0.521 0.472 145 0.000 0.472 0.457 0.536 85.7 0.000 0.508 0.431 0.565 109 0.000 0.698 0.338 0.657 56.9 0.000 0.797 0.280 0.710 18.1 0.000 0.896 0.262 0.733 17.0 0.000 0.961 0.229 0.767 10.4 0.000 1.000 0.210 0.790 0.000 [Pi4,i4,i4,1][TOS] 0.000 0.000 0.952 0.000 0.000 0.101 0.762 0.174 24.2 0.000 0.138 0.685 0.243 21.4 0.000 0.166 0.650 0.290 24.3 0.000 0.221 0.581 0.361 22.3 0.000 0.337 0.495 0.453 16.8 0.000 0.348 0.474 0.468 15.1 0.000 0.405 0.399 0.533 11.3 0.000 0.474 0.324 0.604 9.31 0.000 0.571 0.278 0.653 7.11 0.000 0.674 0.229 0.689 4.11 0.000 0.775 0.144 0.770 2.6 a Standard uncertainties are: u(x) = ±0.005; u(T) = ± 0.1 K; u(p) = ± 1 kPa.

19

β

0.006 0.022 0.006 0.016 0.009 0.013 0.010 0.017 0.049 0.048 0.077 1.72 1.76 1.75 1.63 1.34 1.34 1.32 1.27 1.14 1.02 0.99

Table 4 Compositions of experimental tie lines in mole fractions, selectivity, S and solute distribution ratios, β for the ternary systems {[BMPIP][DCA], or [Pi4,i4,i4,1][TOS] (1) + thiophene (2) + hexadecane (3)} at T = 308.15 K, and pressure p = 101 kPa.a Hydrocarbon - rich phase x1HC x2HC

IL - rich phase S x1IL x2IL [BMPIP][DCA] 0.000 0.000 0.992 0.000 0.000 0.115 0.923 0.074 190 0.000 0.222 0.695 0.298 149 0.000 0.293 0.639 0.359 433 0.000 0.402 0.542 0.452 134 0.000 0.466 0.521 0.477 273 0.000 0.564 0.379 0.615 79.2 0.000 0.604 0.351 0.647 212 0.000 0.680 0.317 0.678 79.8 0.000 0.794 0.303 0.696 181 0.000 0.905 0.258 0.737 15.5 0.000 0.946 0.235 0.759 7.22 0.000 1.000 0.210 0.790 [Pi4,i4,i4,1][TOS] 0.000 0.000 0.960 0.000 0.000 0.116 0.872 0.120 114 0.000 0.129 0.852 0.141 136 0.000 0.165 0.828 0.166 140 0.000 0.214 0.803 0.186 62.1 0.000 0.261 0.758 0.230 54.3 0.000 0.381 0.584 0.408 82.9 0.000 0.419 0.508 0.480 55.5 0.000 0.520 0.437 0.548 33.7 0.000 0.587 0.396 0.594 41.8 0.000 0.661 0.367 0.627 53.6 0.000 0.709 0.299 0.692 31.6 0.000 0.777 0.252 0.736 17.6 0.000 0.853 0.203 0.778 7.06 0.000 0.906 0.146 0.835 4.56 a Standard uncertainties are: u(x) = ±0.005; u(T) = ± 0.1 K; u(p) = ± 1 kPa.

20

β

0.008 0.003 0.009 0.003 0.008 0.004 0.014 0.005 0.013 0.005 0.053 0.111 1.03 1.09 1.01 0.87 0.88 1.07 1.15 1.05 1.01 0.95 0.98 0.95 0.91 0.92

Table 5 A summary of results from previous related literature for LLE with sulfur compounds: β and S are solute distribution ratio of sulfur compound and selectivity, respectively. LLE system

T/K

SAv

βAv

Ref.

[BMPIP][DCA]

IL+thiophene+octane

308

103.2

0.025

This work

[Pi4,i4,i4,1][TOS]

IL+thiophene+octane

308

12.38

1.27

This work

[BMPIP][DCA]

IL+thiophene+hexadecane

308

159.4

0.02

This work

[Pi4,i4,i4,1][TOS]

IL+thiophene+hexadecane

308

109.5

0.99

This work

[BMIM][OTf]

IL+thiophene+octane

308

43.9

1.25

[22]

[HMIM][SCN]

IL+thiophene+octane

298

80.2

1.82

[20]

[OHOHIM][NTf2]

IL+thiophene+octane

308

40.3

0.498

[22]

[OHOHIM][NTf2]

IL+thiophene+hexadecane

308

63.2

0.400

[22]

[BMIM][OTf]

IL+thiophene+hexadecane

308

209.0

0.925

[22]

[EMIM][EtSO4]

IL+thiophene+hexadecane

298

50.5

0.82

[21]

[EMIM][MeSO3]

IL+thiophene+hexadecane

298

56.3

1.09

[21]

IL

21

Table 6 Regressed binary interaction parameters set, nonrandomness parameter αij and root mean square deviation (σx) for the NRTL equation for the ternary systems {[BMPIP][DCA] or [Pi4,i4,i4,1][TOS] (1) + thiophene (2) + octane, or hexadecane (3)} at T= 308.15 K, p = 101 kPa. IL

ij

gij/J·mol–1

gji/J·mol–1

αij

σx

octane [BMPIP][DCA]

[Pi4,i4,i4,1][TOS]

12

-4470.01

19493.46

13

9130.96

13221.44

23

5505.10

-2659.85

12

-5639.80

13207.06

13

29139.08

11553.98

23

4974.70

-3164.41

0.3

0.008

0.3

0.012

0.3

0.009

0.3

0.009

hexadecane [BMPIP][DCA]

[Pi4,i4,i4,1][TOS]

12

-4372.69

19355.21

13

24668.42

9868.71

23

9646.41

-4530.85

12

-5039.03

14339.31

13

18308.80

13051.45

23

11480.12

-5607.23

22

Captions to the figures

Fig. 1. Plot of the experimental (●, solid lines) versus calculated with NRTL equation (ο), red lines) for the composition tie lines of the ternary system {[BMPIP][DCA] (1) + thiophene (2) + octane (3)} in mole fractions at T = 308.15 K, p = 101 kPa. Fig. 2. Plot of the experimental (●, solid lines) versus calculated with NRTL equation (ο), red lines) for the composition tie lines of the ternary system {[Pi4,i4,i4,1][TOS] (1) + thiophene (2) + octane (3)} in mole fractions at T = 308.15 K, p = 101 kPa. Fig. 3. Plot of the experimental (●, solid lines) versus calculated with NRTL equation (ο), red lines) for the composition tie lines of the ternary system {[BMPIP][DCA] (1) + thiophene (2) + hexadecane (3)} in mole fractions at T = 308.15 K, p = 101 kPa. Fig. 4. Plot of the experimental (●, solid lines) versus calculated with NRTL equation (ο), red lines) for the composition tie lines of the ternary system {[Pi4,i4,i4,1][TOS] (1) + thiophene (2) + hexadecane (3)} in mole fractions at T = 308.15 K, p = 101 kPa.

23

Fig. 1.

24

[Pi4,i4,i4,1][TOS] Fig. 2.

25

Thiophene 0

1

0.1

0.9

0.2

0.8

0.3

0.7

0.4

0.6

0.5

0.5

0.6

0.4

0.7

0.3

0.8

0.2

0.9

0.1 0

Hexadecane 1

0.9

0.8

0.7

0.6

0.5

Fig. 3.

26

0.4

0.3

0.2

0.1

1 0 [BMPIP][DCA]

[Pi4,i4,i4,1][TOS] Fig 4.

27

Declaration of interests x☐ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: