Prediction of binary and ternary critical properties using deiters' equation, hard sphere and hard convex body equations of state

The use of recently developed equations of state for critical phenomena is examined. Deiter's equation is incapable of accurately predicting the gas-liquid critical properties of mixtures of dissimilar size molecules whereas a hard convex body equation does not yield significantly better results than asimple hard sphere equation. In many cases a 'hard sphere + attractive term' equation can predict the critical properties of Type II mixtures to within experimental error. This conclusion is valid for a wide range of component molecules. However, an adjustable parameter is usually required to optimize agreement. Type II liquid-liquid properties can also be accurately calculated but the same precision can not be obtained for Type III phenomena. Some calculations for CHF3 + alkane mixtures are reported which exhibited Type III behavior. In this work the critical properties of CF4+CHF3+CH4 over a wide range of temperature and pressure and calculated. The results illustrate the potential of theory to classify the phase behavior of ternary mixtures