The separation of ethylbenzene from styrene by distillation is very energy-intensive, because of the low relative volatility (1.3–1.4). 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 liquid–liquid 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 (2.4–2.6) were obtained with ILs containing aromatic cations, and anions with localized electrons. The largest capacities (0.45–0.6 for styrene) were obtained for ionic liquids with delocalized electrons in the anion and large alkyl chain length in both cation and anion.