Vapor–Liquid Equilibrium Measurements and Binary Interaction Parameter Regression for the Peng–Robinson Equation of State in R134a–CO₂ Mixtures at LNG Regasification Conditions

The measurements were conducted for R134a-rich mixtures containing 8.4–31.6 mol % CO₂ using a 30 mL isochoric equilibrium cell and GC analysis. The measured bubble point and VLE data were used to regress a temperature-dependent binary interaction parameter (BIP) correlation for the Peng–Robinson (PR) equation of state in the form <i>k</i>_<i>ij</i>(<i>T</i>) = <i>k</i>_<i>ij</i>⁽¹⁾ + <i>k</i>_<i>ij</i>⁽²⁾·<i>T</i> + <i>k</i>_<i>ij</i>⁽³⁾/<i>T</i>.

The regression was performed using only the experimental data obtained in this work, while literature VLE data below 300 K were used as an independent reference for comparison. The regressed BIP coefficients were <i>k</i>_<i>ij</i>⁽¹⁾ = −1.09683, <i>k</i>_<i>ij</i>⁽²⁾ = 2.14439 × 10^–3 K^–1, and <i>k</i>_<i>ij</i>⁽³⁾ = 141.824 K. After applying the regressed BIP correlation, the average absolute relative deviation (AARD) decreased from 3.54% to 2.76% for the bubble point pressure data and from 2.35% to 1.99% for the VLE vapor-phase composition data measured in this work, although the improvement was not uniform across all compositions and data points.