VAPOR-LIQUID-EQUILIBRIA OF PROPANE AND N-ALKANE CONFORMERS

The vapour-liquid equilibrium of an angular Kihara model of propane is obtained from a very accurate perturbation theory proposed recently. Gibbs ensemble simulations are performed in order to determine the vapour-liquid equilibrium of this model. A comparison of the theoretical and simulation results for the vapour-liquid equilibria shows excellent agreement. In addition it is demonstrated that a simple extrapolation procedure of the theoretical results yields reliable estimates of the critical properties. Vapour-liquid equilibria of n-butane and n-pentane conformers were obtained by the perturbation theory. trans- and gauche-Butane differ in their vapour-liquid equilibria and in their critical properties. However, they do not differ significantly in their second virial coefficient. The critical temperature of gauche-butane is higher than that of the trans conformer by about 6%. For the different conformers of n-pentane similar results are obtained. The conclusion is that the more spherical is a molecule or conformer the higher the reduced critical temperature. The more anisotropic conformers present larger deviations from the principle of corresponding states. The critical temperature of the all-trans and of the all-gauche conformers appear as a lower and upper bound of the critical temperature of the n-alkane. That suggests that a good description of the vapour-liquid equilibria of the n-alkane could be obtained if a representative conformer of the n-alkane system were chosen.