This research has been focused on a study of the ionic liquid (IL) Ammoeng 102 (tetraalkyl ammonium sulfate) as solvent in liquid-liquid extraction. Experimental densities, speeds of sound, and refractive indices of Ammoeng 102 were studied in dependence on temperature at atmospheric pressure, both by conventional techniques. The thermal expansion coefficient of the IL was calculated from the density. Experimental (liquid + liquid) equilibria data (LLE) were obtained for mixtures of (Ammoeng 102 + heptane) from T = (293.15 to 343.15) K and (heptane + toluene + Ammoeng 102) at T = 298.15 K and atmospheric pressure. The experimental results for the binary and ternary systems were well correlated with the NRTL model. Selectivity and distribution ratio values, derived from the tie-line data, were presented. A comparison with other ILs and with sulfolane is included in order to analyze the best separation solvent in a liquid extraction process. (C) 2009 Elsevier Ltd. All rights reserved.