THE VAPOR-LIQUID-EQUILIBRIUM OF N-ALKANES

The vapour-liquid equilibrium of short n-alkanes is considered by usin g perturbation theory. This requires as a previous step obtaining an e quation of state (EOS) for hard flexible models. An EOS for hard-n-alk ane models which shows excellent agreement with computer simulation of hard-n-alkane models with up to 100 carbon atoms is proposed. This EO S is combined with a mean-field term and the vapour-liquid equilibrium of n-alkanes is computed. When theoretical critical densities and pre ssures are plotted as a function of the number of carbon atoms, a maxi mum is found. This is in agreement with experiment. The conditions for the appearance of such a maximum in general chain models are establis hed. Some ways of improving the mean-held theory are suggested.