Modeling Vapour Pressure Using Compound Specific Cohesion Factor Relationship

Abstract

Major factor in the success of predictive capability of cubic equations of state (CEOS) is the temperature dependency of the cohesion factor. Accurate prediction of vapour pressure is the yardstick for comparing various cohesion factor relationships. For polar and weekly polar compounds generalized expression fails to perform well in predicting vapour pressure using CEOS. The best alternate to improve this is to introduce compound specific parameter in cohesion factor model. So, four compound specific models were compared in the present study. Two of themodels were having single additional parameter and the remaining had two compound specific parameters. We use a simple method to obtain parameters for each compound. Behavior at supercritical conditions was also compared and it was found that the alpha function having exponential form behaves satisfactorily. Modified Trebble–Bishnoi type of cohesion factor model emerged as the best amongst the compared models. Family specific generalized expressions were also proposed. These expressions would be useful in the absence of experimental vapour pressure data. Compound specific parameters for nearly 300 compounds are listed in the paper and can be utilized for the modeling of phase equilibrium of the mixtures of these compounds.