Naphtha cracker feeds may contain 10-25 wt% aromatic compounds. Removal of these aromatic compounds from the feed to the cracker would offer several advantages: higher capacity, higher thermal efficiency, and less coke formation. In this work, we investigated the separation of toluene from heptane by extraction with ionic liquids. Several ionic liquids are suitable for extraction of toluene from toluene/heptane mixtures. The selectivities for the aromatic/aliphatic hydrocarbon separation with all ionic liquids tested increase with decreasing aromatic content in the feed. The toluene/heptane selectivities at 10% toluene in the feed at T = 40 degrees C and 75 degrees C with several ionic liquids ([emim]HSO4 , [mmim] methylsulfate, [emim] ethylsulfate, [bmim]BF 4 , [emim] tosylate, [mebupy]BF4 , and [mebupy] methylsulfate) are a factor of 1.5-2.5 higher than those obtained with sulfolane, which is a conventional solvent for the extraction of aromatic hydrocarbons from a mixed aromatic/aliphatic hydrocarbon stream. The three most suitable ionic liquids from the ionic liquids tested for the separation of aromatic and aliphatic hydrocarbons are [mebupy]BF4 , [mebupy]CH3SO4 , and [bmim]BF4 and at 75 degrees C also [emim] tosylate. The ionic liquid [mebupy]BF4 is selected for further testing in our extraction pilot plant. Because ionic liquids have a negligible vapor pressure, evaporating the extracted hydrocarbons from the ionic liquid phase could achieve the recovery of the ionic liquid. A conceptual process scheme for the extraction has been set up. Preliminary calculations show that both the investment costs and the energy costs will be considerably lower with ionic liquids than with sulfolane as the solvent.