Peng-Robinson Equation of State for Thermodynamic Properties

Peng-Robinson Equation of State for Thermodynamic Properties 

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Appendix B Peng-Robinson Equation of State for Thermodynamic Properties. 347... 

The converged simulation was done using the thermodynamic method of RKS to estimate the properties. The Peng-Robinson equation of state was used for predicting the equilibrium and liquid properties, and the vapor phase was assumed to be ideal. 

Finally, we must select appropriate methods of estimating thermodynamic properties. lime (op. cit.) used the SRK equation of state to model this column, whereas Klemola and lime (op. cit.) had earlier used the UNIFAC model for liquid-phase activity coefficients, the Antoine equation for vapor pressures, and the SRK equation for vapor-phase fugacities only. For this exercise we used the Peng-Robinson equation of state. Computed product compositions and flow rates are shown in the table below. 

A computer program for calculation of thermodynamic properties using the Peng-Robinson equation of state is available for a nominal fee (Carl L. Yaws, Box 10053, Lamar University, Beaumont, TX 77710, phone/FAX 409-880-8787). The computer program is executable and complete with data files. The program calculates thermodynamic properties at pressures and temperatures that are input by the user. Representative results are shown below ... 

The graphs are based on the Peng-Robinson equation of state (1) as improved by Stryjek and Vera (2, 3). The equations for thermodynamic properties using the Peng-Robinson equation of state are given in the appendix for volume, compressibility factor, fugacity coefficient, residual enthalpy, and residual entropy. Critical constants and ideal gas heat capacities for use in the equations are from the data compilations of DIPPR (8) and Yaws (28, 29, 30). 

This generalized form of the Peng-Robinson equation of state (or other equations of state) can be used to compute not only the compressibility, but also the departure functions for the other thermodynamic properties. This is done using Eqs. 6.4-29 and... 

The equations for solving this problem are the same as in Illustration 6.5-1. Specifically, the final temperature and pressure in the tank should be such that the molar entropy of gas finally in the tank is equal the initial molar entropy (Eq. c of Illustration 6.5-1), and the final molar volume should be such that the correct number of moles of gas remains in the tank (Eq. e of Illustration 6.5-1). The main difference here is that the Peng-Robinson equation of state is to be used in the solution. The general procedure used to calculate thermodynamic properties from the Peng-Robinson equation of state, and specifically for this problem, is as follows ... 

The recently proposed Peng-Robinson equation of state ( 1) incorporates the best features of the Soave (2) treatment of the Redlich-Kwong ( 3) equation into a new model which has some significant advantages over earlier two-parameter equation of state models. The purpose of this contribution is to indicate how the equation performs when it is used for calculating fluid thermodynamic properties for systems of industrial Interest. 

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