The critical properties, the normal boiling temperature, and the acentric factor of 200 ionic liquids have been determined using an extended group contribution method, which is based on the well-known concepts of Lydersen and Joback and Reid, that was developed by the authors. The method does not require any additional data besides knowledge of the structure of the molecule and its molecular mass. Because experimental critical properties of ionic liquids are not available, the accuracy of the method is checked by calculating the liquid density of the ionic liquids considered in the study for which experimental data are available in the literature. The results show that the values determined for the critical properties, the normal boiling temperature, and the acentric factor are sufficiently accurate for engineering calculations, generalized correlations, and equation of state methods, among other applications.

Vapor−liquid equilibrium of eight binary mixtures containing an ionic liquid and carbon dioxide have been tested for thermodynamic consistency. A method proposed by one of the authors has been modified to be applied to this special situation in which the gas phase contains practically one component (carbon dioxide) while the liquid phase contains both components in a wide concentration range. The method is based on the Gibbs−Duhem equation and on appropriate combination of equations of state, mixing rules, and combining rules. The Peng−Robinson equation of state with the Wong−Sandler mixing rules including the Van Laar model for the excess Gibbs free energy required in the mixing rules, are used. The experimental data were obtained from literature sources, and the adjustable parameters were found by minimizing the errors between predicted and experimental bubble pressure. It is shown that the proposed modified consistency test is accurate enough to decide about the thermodynamic consistency of this type of data.