**3.2 Results and discussion**

*Solvents, Ionic Liquids and Solvent Effects*

**3.1 Chemicals and experimental procedure**

manipulated under inert gas atmosphere.

mixture (checked by <sup>1</sup>

sectional plane.

of 15 K min<sup>−</sup><sup>1</sup>

constant at 1 mL min<sup>−</sup><sup>1</sup>

to obtain a mean value.

The ILs [EMim][NTf2] and [HMim][NTf2] were supplied by IoLiTec GmbH. They were subjected to vacuum and moderate temperature (P = o.2 Pa, T = 343 K) for several days to eliminate water and volatile compounds that could be present. Cyclohexane, heptane and toluene were supplied by VWR Prolabo, and they were used without further purification. Mass purity of all chemicals was higher than 99%. In order to prevent water absorption, all chemicals were kept and

**Figure 1** shows a representation of the quaternary systems studied in this work where grey surfaces represent the miscible areas on the top and the base of the tetrahedron. Due to the very negligible miscibility of these ILs in the aliphatic

phase. For the determination of liquid-liquid equilibrium data, samples of a mixture of the four components were prepared by weight using a Mettler AXE-205 Delta Range balance. In order to select the composition of the initial samples, a sectional plane (SP), in which the mole fraction of the ionic liquid is constant, was selected as it can be seen in **Figure 1**. This sectional plane is perpendicular to the tie lines, and the compositions of the other three compounds involved in the initial quaternary mixtures were selected in such a way that they cover the

The samples were vigorously stirred by using a magnetic stirrer for 6 hours and left to settle down overnight. Afterwards, a sample of each phase was withdrawn

and final temperature of 368.15 K for 4.30 min. The injector and

in the column. Two analyses of each sample were performed

detector were maintained at 553.15 K, and the helium carrier gas flow rate was kept

The compositions of cyclohexane, heptane and toluene were analysed with a Hewlett-Packard 5890 Series II gas chromatograph with a Hewlett-Packard 5971 mass selective detector and a Hewlett-Packard-5MS capillary column (60 m × 0.250 mm × 0.25 μm). Because of the IL negligible vapour pressure, they cannot be analysed by gas chromatography; consequently, their composition was calculated through a mass balance. An empty precolumn was used to avoid the IL that could not be retained by the liner to go into the chromatograph. The temperature programme has initial temperature of 343.15 K for 10.30 min, ramp

with a syringe, and it was analysed by gas chromatography.

*Schematic representation of the quaternary system and the sectional plane (SP).*

H-NRM), no IL is present in the aliphatic hydrocarbon

**72**

**Figure 1.**

From experimental values, solute distribution coefficient, β, and selectivity, S, were calculated by the following equations:

$$\mathfrak{B} = \mathfrak{X}\_3^{\mathrm{II}} / \mathfrak{X}\_3^{\mathrm{I}} \tag{1}$$

$$\mathbf{S} = \mathbf{x}\_3^{\text{II}} \mathbf{x}\_{1\star 2}^{\text{I}} / \mathbf{x}\_3^{\text{I}} \mathbf{x}\_{1\star 2}^{\text{II}} \tag{2}$$


#### **Table 1.**

*Experimental LLE data, solute distribution coefficients, β, and selectivity, S, for the quaternary system heptane (1) + cyclohexane (2) + toluene (3) + [EMim][NTf2] (4).*

where x is the mole fraction; the superscripts I and II indicate the hydrocarbonrich phase and the IL-rich phase, respectively; and the subscripts 1 + 2 refer to the mole fraction of heptane plus cyclohexane and 3 refers to toluene.

**Tables 1** and **2** show the experimental data at 298.15 K, β and S for the system heptane + cyclohexane + toluene + [EMim][NTf2] or [HMim][NTf2], respectively.

As it can be seen from the tables, selectivity is higher using [EMim][NTf2], while higher solute distribution coefficients were obtained using [HMim][NTf2]. Since S > 1 in both cases, [HMim][NTf2] would be the best choice due to β values higher than 1 which facilitate the extraction process, and less solvent and less separation stages would be necessary. **Figures 2** and **3** show the tie lines for the pseudoternary system (heptane + cyclohexane) (1) + toluene (2) + IL (3). The higher β values obtained for the extraction using [HMim][NTf2] are reflected in the positive slope of the tie lines for toluene molar fractions up to 0.45.


#### **Table 2.**

*Experimental LLE data, solute distribution coefficients, β, and selectivity, S, for the quaternary system heptane (1) + cyclohexane (2) + toluene (3) +[HMim][NTf2] (4).*

**75**

**Figure 3.**

**Figure 2.**

*Extraction of Aromatic Compounds from Their Mixtures with Alkanes: From Ternary…*

Selectivity and solute distribution coefficients for the quaternary system heptane + cyclohexane + toluene + [EMim][NTf2] can be compared to the results obtained for the ternary systems heptane + toluene + [EMim][NTf2] and cyclohexane + toluene + [EMim][NTf2] [27]. β values are similar for the ternary and quaternary systems, while S for the ternary system heptane + toluene + [EMim] [NTf2] (between 3 and 24) and the quaternary system are similar and higher than

*DOI: http://dx.doi.org/10.5772/intechopen.86229*

the ternary system with cyclohexane (between 8 and 4).

*Tie lines for the quaternary systems heptane + cyclohexane + toluene + [EMim][NTf2].*

*Tie lines for the quaternary systems heptane + cyclohexane + toluene + [HMim][NTf2].*

*Extraction of Aromatic Compounds from Their Mixtures with Alkanes: From Ternary… DOI: http://dx.doi.org/10.5772/intechopen.86229*

Selectivity and solute distribution coefficients for the quaternary system heptane + cyclohexane + toluene + [EMim][NTf2] can be compared to the results obtained for the ternary systems heptane + toluene + [EMim][NTf2] and cyclohexane + toluene + [EMim][NTf2] [27]. β values are similar for the ternary and quaternary systems, while S for the ternary system heptane + toluene + [EMim] [NTf2] (between 3 and 24) and the quaternary system are similar and higher than the ternary system with cyclohexane (between 8 and 4).

*Solvents, Ionic Liquids and Solvent Effects*

**x1**

**<sup>I</sup> x2**

where x is the mole fraction; the superscripts I and II indicate the hydrocarbonrich phase and the IL-rich phase, respectively; and the subscripts 1 + 2 refer to the

**Tables 1** and **2** show the experimental data at 298.15 K, β and S for the system heptane + cyclohexane + toluene + [EMim][NTf2] or [HMim][NTf2], respectively. As it can be seen from the tables, selectivity is higher using [EMim][NTf2], while higher solute distribution coefficients were obtained using [HMim][NTf2]. Since S > 1 in both cases, [HMim][NTf2] would be the best choice due to β values higher than 1 which facilitate the extraction process, and less solvent and less separation stages would be necessary. **Figures 2** and **3** show the tie lines for the pseudoternary system (heptane + cyclohexane) (1) + toluene (2) + IL (3). The higher β values obtained for the extraction using [HMim][NTf2] are reflected in

**Hydrocarbon-rich phase IL-rich phase β S**

0.776 0.149 0.095 0.03 0.112 1.49 11.05 0.688 0.168 0.099 0.038 0.193 1.35 8.43 0.631 0.142 0.097 0.034 0.287 1.26 7.46 0.544 0.170 0.099 0.045 0.334 1.17 5.79 0.458 0.164 0.076 0.041 0.416 1.10 5.85 0.368 0.175 0.071 0.052 0.459 1.00 4.43 0.264 0.177 0.062 0.061 0.513 0.92 3.29 0.182 0.183 0.049 0.069 0.554 0.87 2.70 0.675 0.245 0.087 0.053 0.115 1.44 9.45 0.590 0.258 0.090 0.065 0.198 1.30 7.13 0.527 0.240 0.078 0.059 0.286 1.23 6.87 0.431 0.265 0.070 0.070 0.347 1.14 5.67 0.352 0.254 0.065 0.074 0.417 1.06 4.63 0.164 0.279 0.039 0.102 0.510 0.92 2.88 0.593 0.327 0.081 0.076 0.116 1.45 8.50 0.478 0.362 0.070 0.090 0.206 1.29 6.76 0.351 0.369 0.056 0.100 0.332 1.18 5.45 0.158 0.376 0.031 0.124 0.456 0.98 3.37 0.507 0.409 0.066 0.095 0.121 1.44 8.20 0.398 0.445 0.059 0.115 0.204 1.30 6.30 0.259 0.464 0.040 0.131 0.319 1.15 4.87 0.420 0.495 0.056 0.121 0.120 1.41 7.30 0.159 0.548 0.025 0.159 0.326 1.11 4.28 0.330 0.585 0.045 0.150 0.118 1.39 6.51 0.229 0.615 0.031 0.158 0.199 1.28 5.41 0.161 0.741 0.019 0.194 0.135 1.38 5.83

*Experimental LLE data, solute distribution coefficients, β, and selectivity, S, for the quaternary system heptane* 

**II x3**

**II**

**II x2**

mole fraction of heptane plus cyclohexane and 3 refers to toluene.

the positive slope of the tie lines for toluene molar fractions up to 0.45.

**<sup>I</sup> x1**

**74**

**Table 2.**

*(1) + cyclohexane (2) + toluene (3) +[HMim][NTf2] (4).*

*Tie lines for the quaternary systems heptane + cyclohexane + toluene + [EMim][NTf2].*

**Figure 3.**

*Tie lines for the quaternary systems heptane + cyclohexane + toluene + [HMim][NTf2].*

Regarding the quaternary system heptane + cyclohexane + toluene + [HMim] [NTf2], the experimental data of the ternary systems heptane + toluene + [HMim] [NTf2] and cyclohexane + toluene + [HMim][NTf2] can also been found in literature [28]. In that case, both β and S are higher for the quaternary system, which implies that, in some cases, the addition of another component can enhance the extraction of the aromatic compound.

Solute distribution coefficient and selectivity can be compared to those obtained using 1-ethyl-3-methylimidazolium methylsulphate, [EMim][MSO4] [13]; 1-ethyl-3-methylimidazolium dicyanamide, [EMim][N(CN)2] [14]; or 1-ethyl-3-methylimidazolium acetate ionic liquid, [EMim][OAc] [12]. Solute distribution coefficient follows the following trend:

[HMim][HNTf2] > [EMim][HNTf2] > [EMim][N(CN)2] > [EMim] [OAc] > [EMim][MSO4].

β values obtained with ionic liquids with NTf2 anion are significantly higher, reaching values greater than one in the case of [HMim][HNTf2]. Regarding the selectivity, the trend is

[EMim][N(CN)2] > [EMim][MSO4] > [EMim][HNTf2] > [EMim] [OAc] > [HMim][HNTf2].

Since selectivity and solute distribution coefficient do not follow the same trend, the selection of the most adequate IL should be a compromise between these two factors affecting extraction process.
