Ionic liquids as alternatives to organic solvents in liquid-liquid extraction of aromatics

The ionic liquids 1-ethyl-3-methylimidazolium ethylsulfate and 1,3-dimethylimidazolium methylsulfate are suitable for extraction of toluene from toluene/heptane mixtures. The selectivity for the toluene/heptane separation using [emim] ethylsulfate increases with decreasing toluene content in the feed, from 13.4 (95% toluene) to 55.3 (5% toluene) at 40 degrees C and from 8 to 35 at 75 degrees C. With [mmim]methylsulfate the selectivity increases from 6 to 67.8 at 40 degrees C and from 11.4 to 55 at 75 degrees C. These selectivities are a factor of 2-3 higher compared to those obtained with sulfolane as the extractant. Because ionic liquids have a negligible vapour pressure, evaporating the extracted hydrocarbons 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 compared to using sulfolane as the solvent.