No abstract

Volumetric data of nonpolar gaseous mixtures are analyzed in terms of the theory of corresponding states. Special attention is given to an analysis of the second virial coefficient and to the calculation of pseudocritical constants.Second virial coefficients are calculated from experimental data for ten binary systems. These coefficients, with those previously published, are correlated by means of a generalized equation involving three parameters for each component: the critical volume, the reduced temperature, and the acentric factor.Equations are derived for the pseudocritical temperature and pressure of mixtures. These equations are considerably more accurate than those given by Kay's rule. Because of the complexity of the proposed equations for the pseudocritical parameters, a simplified pseudocritical method is presented which is sufficiently accurate for most chemical engineering purposes, especially at reduced temperatures exceeding 1.3.Methods are available for predicting with good accuracy the volumetric properties of nonpolar gases in the pure state, but no method of comparable validity has been reported for mixtures of these gases. The volumetric properties of gaseous mixtures not only are of interest for applications similar to those pertaining to pure gases, but they also are required for accurate determination of phase equilibria and for correct specification of the driving force in separation operations and chemical kinetics. In vapor-liquid equilibria, for example, departure from ideal behavior in the gaseous phase a t high pressures may be at least as large as that in the liquid phase. The P-V-T-y behavior of a gaseous mixture uniquely determines the fugacity for each component at any particular temperature, pressure, and composition, and the fugacities in turn, determine the equilibrium curve.Various methods for predicting the properties of gaseous mixtures have been proposed, but for the most part these have been strictly empirical. While such method8 have been successful in limited cases, large errors often appear in unexpected instances, demonstrating the basic weakness of a purely empirical approach.In view of the inadequacy of the present methods this investigation has attempted to develop equations based as much as possible on available theory while remaining within the realm of engineering utility.The nonideality of gaseous mixtures can be conveniently regarded as consisting of two parts: one part is due to the nonideality of the pure gases and the other to the nonideality of mixing. This paper considers only the second part. The nonideality of pure gases has received much attention previously, and, with the help of corresponding-states correlations, volumetric properties of nonpolar or slightly polar gases can now be predicted accurately. The problem of computing the volumetric properties of a gaseous mixture, therefore, consists of relating the properties of the mixture to the corresponding properties of the pure components. VlRlAL EQUATIONThe volumetric properties of gases are convenie...

Effective critical constants for helium and normal hydrogen have been determined by fitting experimental volumetric data for these gases to the generalized tables of Pitzer. The effective critical temperature and pressure are found to depend on the temperature and on the molecular mass in a simple manner permitting good estimates to be made of effective cribical constants for other quantum gases for which experimental data are scarce (neon, isotopes of helium and hydrogen). Pitzer's tables are used with pseudocritical mixing rules to predict thermodynamic properties of mixtures a t high pressures and low temperatures. Calculated compressibility factors and enthalpies are in excellent agreement with experimental results for dense mixtures of hydrogen-methane, hydrogen-argon, and helium-nitrogen.The volumetric properties of nonpolar or slightly polar fluids have been correlated by Pitzer et al. (7,19,20) using an extended form of the theorem of corresponding states. Pitzer's correlation excludes highly polar fluids and also those light (quantum) gases whose configurational properties must be described by quantum rather than classical statistical mechanics. In this work we describe a simple, semiempirical procedure which, in effect, extends Pitzer's correlation to the quantum gases. This extension may be useful for predicting volumetric and derived thermodynamic properties of neon and isotopes of helium and hydrogen for which experimental data are scarce. More important for technical applications, however, this extension provides a good method for predicting thermodynamic properties of dense gaseous mixtures which contain one or more of thg quantum gases. Such mixtures are common in many technical operations in petroleum and related industries; since these mixtures are frequently at low temperatures and high pressures, deviations from ideal behavior are sometimes very large. The configurational property of most interest for rational design of cryogenic processes is the configurational enthalpy which, at high pressures and low temperatures, may make a significant contribution to the refrigeration load. Optimization of cryogenic separation processes requires accurate enthalpy information and, since experimental enthalpy data for dense mixtures are scarce, it is desirable to be able to predict such enthalpies with confidence. EXTENSION OF PITZER'S C O R R E L A T I O N TO QUANTUM GASESPitzer correlated the compressibility factors of pure gases in terms of two generalized functions, d o ) and z(l), such that Equation (1) is a direct consequence of Pitzer's form of the theorem of corresponding states. The acentric factor, which is a constant for any given gas, is a measure of the importance of noncentral intermolecular forces and for small molecules (for example, nitrogen, methane, argon) it is very nearly zero. The functions .do) and dl) have been tabulated (20).Pitzer's tables are not applicable to the quantum gases when the true critical constants and acentric factor are used in Equation ( I ) , because these gases do...

A corresponding states correlation is presented for the prediction of saturated liquid volumes. Parameters required are the critical temperature, the acentric factor, and a scaling volume. The correlation is valid over the entire useful range of reduced temperatures from 0.2 to 1.0. The full temperature range has not been covered by previous corresponding states correlations. Average absolute deviations in predicted liquid volumes is one‐quarter of 1% for 26 compounds. The correlation is also useful for calculating critical temperatures, pressures, and volumes when experimental critical data are lacking. The proposed method also provides a convenient means for calculating rapidly and accurately the statistical mechanical parameters used in the cell model correlation developed by Renon, Eckert, and Prausnitz.

No abstract