**2. Literature review**

#### **2.1 Quaternary systems with two aliphatic compounds**

Up to now, a quite wide range of papers dealing with liquid-liquid equilibrium data of hydrocarbon + aromatic + IL ternary systems can be found in literature. These studies are essential to determine the capability of ILs to extract aromatic compounds; however, many other compounds are present in refinery streams, and these compounds can modify the extraction process.

With the aim of analysing the influence of more than one aliphatic compound on the extraction of aromatics, liquid-liquid equilibrium data of several quaternary systems have been published [9–14].

Requejo et al. [9–11] studied the extraction of benzene from its mixtures with octane and decane using tributylmethylammonium bis(trifluoromethylsulfonyl) imide, [N4441][NTf2]; 1-butyl-1-methylpyrrolidinium dicyanamide, [BMpyr] [DCA]; and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, [BMpyr][NTf2], and the results of the quaternary system were compared with those obtained for the ternary systems octane + benzene + IL and decane + benzene + IL.

Using [N4441] [NTf2], the highest values of β were obtained for the ternary system octane + benzene + [N4441] [NTf2], while the β values calculated for the

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

consequently the presence of two alkanes does not seem to affect them [9]. Solute distribution coefficient is similar for both ternary systems octane + benzene + [BMpyr][DCA] and decane + benzene + [BMpyr][DCA] and for the quaternary system octane + decane + benzene + [BMpyr][DCA], while the selectivity for the quaternary system is lower than for the ternary system with decane and

ternary system decane + benzene + [N4441][NTf2] and for the quaternary system are similar. Selectivity values are quite similar for the ternary and quaternary systems;

A different influence was found comparing the ternary systems octane + benzene + [BMpyr][NTf2] and decane + benzene + [BMpyr][NTf2] with the quaternary system decane + octane (1) + benzene (2) + [BMpyr][NTf2] [11]. In that case, both solute distribution coefficients and selectivity are lower for the quaternary system. The extraction of toluene from its mixtures with heptane and cyclohexane, using ethyl-methylimidazolium-based ILs, was studied by Corderí et al. [12–14]. The selected anions were methylsulphate [MSO4], acetate [OAc] and dicyanamide [N(CN)2]. According to their results, solute distribution coefficient clearly follows the trend:

With regard to selectivity, higher values were obtained with [EMim][N(CN)2]. Comparing quaternary systems with the respective ternary ones, the following

i.Solute distribution coefficients for the ternary systems with [EMim][MSO4] are quite similar and higher than those obtained for the quaternary system at higher toluene composition in the hydrocarbon-rich phase. When the toluene concentration in the hydrocarbon-rich phase is lower than 0.2, similar values of β were obtained for the ternary and the quaternary systems.

ii.In the case of [EMim][OAc], β values for the quaternary system are slightly higher than those obtained for the ternary systems independent of the

iii.Similar β values were obtained for the ternary and quaternary systems using

iv.In all cases, selectivity values for the quaternary system are between the

As it can be seen, both solute distribution coefficients and selectivity values can be influenced by the presence of another hydrocarbon in different ways. The lack of more experimental data does not allow us to take general conclusions about the influence of other aliphatic compounds present in the mixture; consequently more

Among all the ILs that have been studied as separation agents, only a small number

of them have shown simultaneously solute distribution coefficients and selectivity higher than sulfolane since, generally, high selectivities are related to low solute distribution coefficients and vice versa. On the other hand, most ILs present quite high viscosity, which make their use difficult in extraction processes. The proper selection of two ILs could lead to a separation agent, whose physical properties and extraction performance overcome those of sulfolane. Therefore, some pairs of ILs have been tested to extract aromatics, mainly benzene or toluene, from their mixtures with alkanes.

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

higher than for the ternary system with octane [10].

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

toluene concentration in the hydrocarbon-rich phase.

**2.2 Quaternary systems with IL mixtures as extraction agents**

results were obtained:

[EMim][N(CN)2].

values of the ternary systems.

experimental data would be necessary.

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

ternary system decane + benzene + [N4441][NTf2] and for the quaternary system are similar. Selectivity values are quite similar for the ternary and quaternary systems; consequently the presence of two alkanes does not seem to affect them [9].

Solute distribution coefficient is similar for both ternary systems octane + benzene + [BMpyr][DCA] and decane + benzene + [BMpyr][DCA] and for the quaternary system octane + decane + benzene + [BMpyr][DCA], while the selectivity for the quaternary system is lower than for the ternary system with decane and higher than for the ternary system with octane [10].

A different influence was found comparing the ternary systems octane + benzene + [BMpyr][NTf2] and decane + benzene + [BMpyr][NTf2] with the quaternary system decane + octane (1) + benzene (2) + [BMpyr][NTf2] [11]. In that case, both solute distribution coefficients and selectivity are lower for the quaternary system.

The extraction of toluene from its mixtures with heptane and cyclohexane, using ethyl-methylimidazolium-based ILs, was studied by Corderí et al. [12–14]. The selected anions were methylsulphate [MSO4], acetate [OAc] and dicyanamide [N(CN)2]. According to their results, solute distribution coefficient clearly follows the trend:

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

With regard to selectivity, higher values were obtained with [EMim][N(CN)2]. Comparing quaternary systems with the respective ternary ones, the following results were obtained:


As it can be seen, both solute distribution coefficients and selectivity values can be influenced by the presence of another hydrocarbon in different ways. The lack of more experimental data does not allow us to take general conclusions about the influence of other aliphatic compounds present in the mixture; consequently more experimental data would be necessary.
