Selection of ionic liquids for the extraction of aromatic hydrocarbons from aromatic/aliphatic mixtures

The separation of aromatic hydrocarbons (benzene, toluene, ethyl benzene and xylenes) from C4 to C10 aliphatic hydrocarbon mixtures is challenging since these hydrocarbons have boiling points in a close range and several combinations form azeotropes. 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 toluene/heptane selectivities at 40 -C and 75 -C with several ionic liquids, [mebupy]BF4, [mebupy]CH3SO4, [bmim]BF4 (40 -C) and [emim] tosylate (75 -C), are a factor of 1.5–2.5 higher compared to those obtained with sulfolane (Stol/hept=30.9, Dtol =0.31 at 40 -C), which is the most industrially used solvent for the extraction of aromatic hydrocarbons from a mixed aromatic/aliphatic hydrocarbon stream. From these five ionic liquids, [mebupy]BF4 appeared to be the most suitable, because of a combination of a high toluene distribution coefficient (Dtol=0.44) and a high toluene/heptane selectivity (Stol/hept =53.6). Therefore, with [mebupy]BF4 also extraction experiments with other aromatic/aliphatic combinations (benzene/n-hexane, ethylbenzene/n-octane and m-xylene/n-octane) were carried out. The aromatic/aliphatic selectivities were all in the same range, from which it can be concluded that the toluene/heptane mixture is a representative model system for the aromatic/aliphatic separation. D 2005 Elsevier B.V. All rights reserved.