Room temperature ionic liquids (RTILs) have been discovered as very promising media for acetylene-ethylene separation. In this work, propyne and propylene solubility behaviors in dialkylimidazolium-based RTILs bearing various kinds of anions have been investigated for the feasible extraction process of propyne from propylene mixture. Solubility-molar volume relationship supported by thermodynamic analysis indicated that physical absorption mechanism plays dominantly in determining the propylene solubility. Meanwhile, unlike the acetylene solubility, which is controlled almost exclusively by hydrogen bonding interaction (chemical interaction) between the anion of RTIL and the solute, the solubility of propyne is a result from a tradeoff between chemical and physical interactions. Generally speaking, the trend of the ideal absorption selectivity for propyne over propylene is close to the acetylene-ethylene case where the higher the hydrogen bond basicity and the smaller the molar volume of RTIL results in the greater the selectivity for propyne. (C) 2011 Elsevier Ltd. All rights reserved.