A Novel Theory for Predicting Critical Constants and the α Function for Pure Polymers

Abstract

The cubic equation of state (CEoS) requires critical temperature (T c ), critical pressure (P c ), and the alpha (R) function for all components including polymers before it can be used for the prediction of phase behavior and thermodynamic properties for the system. For nonpolymers or conventional components, T c , P c , and R usually are available in databanks. However, this is not the case for polymers since their critical point is not measurable and they lack vapor pressures for the derivation of the R function. As a result, the task of finding CEoS critical constants as well as the R function for polymers becomes extremely challenging in the case of polymeric systems. A rigorous theory requiring only the liquid density data of the pure polymer is successfully developed in this work for the accurate prediction of the critical temperature, the critical pressure, and the R function for the pure polymer for use in all types of cubic equations of state. The proposed theory extends the application of cubic equations of state to polymer systems in a very simple fashion.

The New Method for Correlation and Prediction of Thermophysical Properties of Fluids. Critical Temperature

“…The equations acquired by this method are simple, understandable, and accurate. Cubic equation of state − is closely related to critical properties of pure substances, and thus it is also a way to obtain critical parameters. In addition, by employing molecular descriptors from computer simulation of molecular mechanics, Wakeham provided a new correlation for the estimation of critical parameters of hydrocarbons and achieved high precision.…”