Ionic liquids (ILs) can be used to replace conventional solvents in liquid−liquid extractions of aromatic hydrocarbons. An IL-based extraction process requires fewer process steps and less energy consumption, provided that the mass-based aromatic distribution coefficient and/or the aromatic/aliphatic selectivity are higher than those of the current state-of-the-art solvents such as sulfolane. Only a small number of ionic liquids are able to combine higher mass-based distribution coefficients with selectivities comparable to or higher than those of sulfolane. The most suitable ILs from our analysis are [bmim]C(CN)3, [3-mebupy]N(CN)2, [3-mebupy]C(CN)3, and [3-mebupy]B(CN)4. The mass-based distribution coefficients with these four ILs for benzene, toluene, and p-xylene are factors of 1.2−2.5 higher than those with sulfolane, and the aromatic/aliphatic selectivities are up to a factor of 1.9 higher than with sulfolane. Based on the performed analysis, it can be concluded that industrial application of ILs for aromatics extraction has not yet materialized because only four of the total of 121 investigated ILs are considered suitable for aromatic/aliphatic separation. Most of the reported ILs do not provide higher mass-based aromatic distribution coefficients and/or higher aromatic/aliphatic selectivities than those achieved by conventional solvents such as sulfolane.

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The separation of ethylbenzene from styrene by distillation is very energy-intensive, because of the low relative volatility (1.3À1.4). Extractive distillation is a promising alternative to separate the close boiling mixture, in which the solvent selection is crucial for the process feasibility. In this work, an ionic liquid screening study by liquidÀliquid equilibrium (LLE) experiments has been performed to investigate whether ionic liquids (ILs) show potential to separate ethylbenzene from styrene by extractive distillation. The screening method by LLE experiments was validated by VLE experiments for several ILs. The performance of the ILs was compared with the benchmark solvent sulfolane, which displays a selectivity of ∼1.6. Several ILs outperform sulfolane with selectivities up to 2.6. From the results of the LLE experiments, it was concluded that there is a clear tradeoff between capacity and selectivity. ILs with a high capacity usually have a low selectivity, whereas ILs with high selectivity exhibit low capacity. Both cation and anion structure strongly influence the performance. The highest selectivities (2.4À2.6) were obtained with ILs containing aromatic cations, and anions with localized electrons. The largest capacities (0.45À0.6 for styrene) were obtained for ionic liquids with delocalized electrons in the anion and large alkyl chain length in both cation and anion.

Isobaric vapor–liquid equilibrium (VLE) data have been measured for the ternary system (ethylbenzene + styrene + sulfolane) and the three constituent binary systems under vacuum [(5, 10, and 20) kPa]. The VLE data of the binary system (ethylbenzene + styrene) measured in this work are thermodynamically consistent according to the Herington area test and the point test method contrary to the low pressure VLE data about this system available in the literature. The binary VLE data were described well by the nonrandom two-liquid (NRTL) model. The relative volatility of the system (ethylbenzene + styrene) increases in the presence of sulfolane from 1.4 up to values of 2.2. The ternary system could only be well-correlated when using the ternary VLE data in combination with the binary VLE data as input for the regression of the NRTL binary interaction parameters.

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