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

This study experimentally measured bubble-point pressures and vapor–liquid equilibrium (VLE) vapor-phase compositions of R134a + CO2 mixtures under low-temperature conditions relevant to liquefied natural gas (LNG) regasification. 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 kij(T) = kij(1) + kij(2)·T + kij(3)/T. 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 kij(1) = −1.09683, kij(2) = 2.14439 × 10–3 K–1, and kij(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. For the independent low-temperature literature VLE data, the AARD decreased from 5.33% to 1.36%. The regressed BIP correlation was further applied to an LNG regasification process simulation using an R134a + CO2 mixed heating medium. The results show that the regressed PR EOS parameters provide experimentally supported thermodynamic inputs for modeling the phase-change behavior of R134a + CO2 mixtures in LNG regasification-relevant temperature ranges.