Development and Analysis of a Program for Phase-Equilibrium Calculations Using the Peng-Robinson Equation of State

Ekrem Alagoz

Ekrem Alagoz Turkish Petroleum Corporation, R&D Department, Söğütözü, Nizami Gencevi Caddesi No:10, 06510 Çankaya/Ankara, Turkiye

Keywords: Peng-Robinson EOS, Phase-equilibrium, Binary mixture, Ternary mixture, Gibbs free energy

Abstract

This paper presents a program for isothermal and isobaric phase-equilibrium calculations using the Peng-Robinson equation of state (EOS). The program utilizes successive substitution for both single-phase stability analysis and two-phase flash, and allows for multiple initial guesses and variable input parameters for flexibility. The program is designed to be easily modified to accommodate changes in the number of components, overall composition, temperature, pressure, critical temperature and pressure, acentric factors, binary interaction parameters, convergence criteria, and maximum numbers of iterations for iteration loops. The program is then used to analyze the phase behavior of various mixtures, including a binary mixture of n-hexane and n-hexatriacontane, and a ternary mixture of CO2-n-C4-n-C10 at 180°F and 1700 psia. The results show the bubble- and dew-point curves for the binary mixture, as well as the effect of the binary interaction parameter on the Gibbs energy and phase envelope. The ternary phase diagram for the CO2-n-C4-n-C10 mixture is also presented, along with a Gibbs free energy plot of equilibrium two-phase compositions. Overall, this program and its results have important implications for a variety of fields, including chemical engineering and materials science.

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