A cubic perturbed, hard sphere equation of state which combines the hard sphere expression of Scott and the empirical attractive term of Redlich and Kwong with two temperature dependent parameters has been successfully applied to the calculation of pure component properties and vapor-liquid equilibrium values. SCOPEA well-behaved equation of state can represent and predict thermodynamic properties of pure components and mixtures, including vapor-liquid equilibrium values which are important in equipment design for separation processes. Many attempts have been made in recent years to improve the applicability of simple analytical equations of state such as those proposed by van der Waals and by Redlich and Kwong for chemical engi-neering applications. Special attention has been given to the modification of the repulsive term RT/(V-h). The objective of this study is to apply a new and simple perturbed, hard sphere equation of state to thermodynamic properties and vaporliquid equilibrium calculations and to compare the calculated results with those obtained from other equations of state recently proposed in the literature. CONCLUSIONS AND SIGNIFICANCEThe new perturbed, hard sphere equation used in this studycombines the analytical expression of Scott for the hard sphere compressibility factor and the empirical attractive term of the Redlich-Kwong (RK) equation of state. This equation possesses the qualities of realism and simplicity of the RK equation, contains only two temperature dependent parameters and remains a cubic one in terms of density (or volume). It is much simpler to use than the equations proposed by De Santis et al. (1976) and Oellrich et al. (1978). The calculated results obtained for five pure component properties (vapor pressure, saturated liquid and vapor volumes, latent heat of vaporization and second virial coefficient) indicate that the new equation vields lower deviatians from the literature values than the two more complicated equations mentioned above. Comparisons made on vapor-liquid equilibrium (VLE) values for five binary systems at thirty-two isothermal conditions indicate that the new equation yields better representation of the data than the methods of Soave (1972) and Peng-Robinson (PR) (1976). Some of the binary data w e d by De Santis et al. (1976) for testing their equation were also used in this study. The calculated results indicate that the new equation yields lower deviation in the calculated values of pressure. Comparisons were also made on VLE values for a ternary system at two isothermal conditions between the calculated results obtained by the new equation and the method of Soave (1972). The new equation again yields better results.Ever since van der Waals (1873) proposed his equation, the v d w equation, many modifications have been made in the literature to improve his model. One of the most successful ones was the two-parameter empirical equation proposed by Redlich and Kwong (1949):

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The temperature-dependent parameters Qa and 6 of the Redlich-Kwong equation of state evaluated from vapor pressures and saturated liquid volumes for 13 pure components were correlated in terms of 7r. The coefficients of these correlations were further generalized in terms of . The generalized correlations have been successfully used to compute the 3 and Qb values for seven arbitrarily selected components other than those included in the generalization. The applicability of the values computed from the generalized equations was further demonstrated by evaluation of pure-component properties and by the calculation and prediction of vapor-liquid equilibria data for eight binary systems at 32 isothermal conditions.

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