Calculation of the Phase Equilibrium of CO2–Hydrocarbon Binary Mixtures by PR-BM EOS and PR EOS

Abstract

The phase equilibrium data of CO2–hydrocarbon binary mixtures are important for the design and operation of CO2 flooding, coal liquefaction, and supercritical extraction processes. Numerous pieces of binary phase equilibrium data have been obtained. Thus, models for the accurate calculation of binary and multicomponent mixtures must be developed on the basis of existing data. In this work, 3578 vapor–liquid phase equilibrium data points for 10 CO2–hydrocarbon binary mixtures, including CO2–butane, CO2–pentane, CO2–isopentane, CO2–hexane, CO2–benzene, CO2–heptane, CO2–octane, CO2–nonane, CO2–decane, and CO2–undecane, were collected. The PR and PR-BM equations of state (EOS) in combination with relevant mixing rules were used to calculate the phase equilibrium data of the CO2–hydrocarbon binary mixtures. The binary interaction parameter kij in the PR EOS was temperature independent, whereas parameters in the PR-BM EOS were functions of temperature. Thus, the phase equilibrium data and other thermodynamic properties of the binary and multicomponent mixtures at different temperatures and pressures can be calculated by using the parameters obtained in this work. The PR-BM EOS performed better than the PR EOS, and the average absolute deviations over the temperature range of 255.98–408.15 K calculated by the PR EOS and PR-BM EOS were less than 5.74% and 3.36%, respectively. The results calculated by the two EOS were compared with those calculated by other models, such as PPR78, PR + LCVM + UNIFAC, KIE + PR EOS + HV, and PSRK. The phase equilibrium data of CO2–butane–decane, CO2–hexane–decane, and CO2–octane–decane ternary mixtures were calculated by the two EOS. The average overall deviations for the CO2 mole fractions calculated by the two EOS were less than 7.66%.