Thermodynamic property prediction for high molecular weight molecules based on their constituent family

Abstract

A method for predicting the critical temperature of high molecular weight molecules is proposed. The method is based on a modification of the functional form of the Joback method and the use of constituent functional group trends. To demonstrate the predictive capability of the method several pure fluids and their binary mixtures with CO2 are studied. In particular, diglyme, triglyme and tetraglyme whose molecular weights range from 134 to 222, are shown to reveal excellent predictions between 3 and 9% deviation for saturated liquid densities. Application to vapor–liquid phase equilibria for CO2-glyme systems exhibit 4–8% deviation in saturated liquid densities and 1% for vapor densities. For the system of oleic acid + CO2, pure component parameters from the method allow the correlation of the vapor pressure of oleic acid and the solubility of H2 in oleic acid with a BWR type of equation of state and temperature dependent interaction parameters. Solubility of CO2 in triolein is also well correlated. The critical temperature of a polyalkylene glycol with a molecular weight of 1100 is predicted to be 842 K, whereas the prediction by of the Joback method predicts 8541 K, and so cannot be used in equation of state calculations. The pure component properties predicted with the new functional form of the Joback method also allow reliable correlation of CO2-polyalkylene glycol vapor–liquid equilibria.