An empirical correlation for the third virial coefficient of nonpolar gases is developed. The correlation requires a knowledge of the critical temperature, critical pressure and acentric factor of the compounds for the prediction of third virial coefficients in the absence of experimental data. The use of the correlation for mixtures of nonpolar gases, including quantum gases, requires one binary parameter for each binary interaction. Predictions are in good agreement with reported experimental data and with the values obtained with existing correlations. HASAN ORBEY and J. H. VERA Department of Chemical EngineeringMcGill University Montreal, Quebec, Canada H3A 2A7 SCOPEThe pressure explicit virial equation of state, truncated after the second virial coefficient, is a useful expression for the calculation of thermodynamic properties of gases a t conditions such that the reduced volume is greater than 2. According to recent studies (De Santis and Grande, 1979), the addition of the third virial coefficient extends the applicability of the virial equation to conditions of temperature and pressure for which the reduced volume is greater than 1.3.Empirical correlations for the third virial coefficient (Chueh and Prausnitz, 1967a; Pope et a]., 1973; De Santis and Grande, 1979) are either of limited applicability or require extensive information to characterize the compound. This work presents a generalized correlation for the third virial coefficient of pure and mixed nonpolar compounds, including quantum gases, using critical temperature, critical pressure and acentric factor, similar to the successful empirical correlations for second virial coefficient (Pitzer and Curl, 1957;Tsonopoulos, 1974Tsonopoulos, ,1979. CONCLUSIONS AND SIGNIFICANCEThird virial coefficients for nonpolar gases, including quantum gases, have been correlated using three characteristic parameters for each compound. These three parameters are the same required by successful correlations for the second virial coefficient, i.e., the critical temperature, the critical pressure and the acentric factor. This fact allows the use of the virial equation up to densities of the order of 0.75 the critical density using the same information that previously did not allow one to go beyond 0.5 the critical density. Third virial coefficients of mixtures of nonpolar gases, including quantum gases, may be predicted using one binary interaction parameter. Within the accuracy of the experimental information on the third virial coefficients, the new correlation performs as well as the more complex expressions existing in the literature.The pressure explicit virial equation of state may be written as where B is the second virial coefficient, C is the third virial coefficient, etc. The virial coefficients are only a function of temperature for a given compound. In principle, they may be obtained from potential functions for intermolecular interactions.In macroscopic terms, following the three parameter corresponding states theorem, nonpolar fluids may be characterized b...

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Applicability of the equation of state models for modeling and simulation of phase equilibrium in polymer production processes is investigated. The flash separation of unreacted ethylene from polyethylene is used as a prototype for simulation. First, three equation of state models (statistical associating fluid theory, Sanchez−Lacombe, and an augmented Soave−Redlich−Kwong cubic equation of state) are comparatively used to correlate pure component volumetric, calorimetric, and phase equilibrium properties for ethylene and polyethylene. Next, they are tested for correlation of vapor−liquid equilibrium of ethylene + low-density polyethylene mixtures. Finally, a two-stage flash problem that mimics the separation process in the low-density polyethylene production is simulated using the three models. Each equation of state model has some unique characteristics that affect the outcome of modeling pure component as well as mixture behavior. The advantages and disadvantages of each model are discussed.