The main aim of this paper is to investigate the possibility of using ionic liquid as a solvent for the separation processes, especially for extraction of azeotropic mixtures i. e. aliphatic from aromatic hydrocarbons. The first step in assessing the ability of selective extraction is to determine the selectivity based on measurements of activity coefficients at infinite dilution. In this work new data of the activity coefficients at infinite dilution for 53 solutes including: alkanes, alk-1-enes, alk-1-ynes, cycloalkanes, aromatic hydrocarbons, alcohols, thiophene, ethers, ketones, acetonitrile, pyridine, 1-nitropropane and water in the ionic liquid: 1-butyl-4-methylpyridinium dicyanamide, [B4MPy][DCA] were determined using GLC technique at wide temperature range from (308.15 to 368.15) K. From the temperature dependence of c113 the partial molar excess Gibbs free energies, DGE; 1 1, enthalpies DHE; 1 1 and entropies TrefDSE; 1 1 at infinite dilution were calculated. Additionally the (gas + liquid) partition coefficients, KL were determined. The selectivities for the many separation problems were calculated and compared to the values from the recent literature for other ionic liquids. The densities of pure ionic liquid were determined over a wide temperature range from (308.15 to 368.15) K. (C) 2013 Published by Elsevier Ltd.