In this work measurements and modeling of new phase equilibria data for systems related to natural gas processing were performed. A high-pressure apparatus functioning in the static synthetic mode was used to measure P–T–x data for the systems methane + methanol + 2,2′-[ethane-1,2-diylbis­(oxy)] di­(ethan-1-ol) (triethylene glycol (TEG)) (0.0333 methanol/0.9667 TEG wt fraction) and carbon dioxide + methanol + TEG (0.0333 methanol/0.9667 TEG wt fraction) at 303.16 and 323.15 K. Validation of the experimental technique was performed through measurement of P–T–x data for methane + TEG, methane + methanol, and carbon dioxide + water + TEG (0.0350 water/0.9650 TEG wt fraction) test systems from T = 298.15 to 323.15 K. The data were modeled using the Peng–Robinson equation of state with the Wong Sandler mixing rules (PRWS), the Cubic Plus Association (CPA) model, and the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) model, and predictions were performed with the predictive Soave–Redlich–Kwong (PSRK) model. For the methane + methanol + TEG and carbon dioxide + methanol + TEG systems, the PRWS model correlation yielded the best fit to the experimental data compared to the PC-SAFT and CPA models with a maximum absolute average relative deviation in pressure (AARD­(P)) not exceeding 0.0309.

Limited phase equilibria data exist for multicomponent systems encountered in the natural gas processing industry. To address this gap, bubble point measurements were performed for methane + propane + methanol; methane + propane + (2,2′-[ethane-1,2-diylbis-(oxy)] di(ethan-1-ol) or triethylene glycol); methane + propane + methanol + triethylene glycol systems in the temperature range of 283.16 to 323.16 K and a pressure range of 0.78 to 13.79 MPa. A visual synthetic high-pressure cell comprising a sapphire tube of 33 cm 3 working volume was used. The new experimental P-T-x data were modeled using the Cubic Plus Association (CPA) model and the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) model. Model correlations with the CPA model yielded better results than those with the PC-SAFT model, with a maximum absolute average relative deviation in pressure of 6.97% and 7.33%, respectively. The CPA model predictions based on binary parameters alone do not adequately describe phase behavior of multicomponent systems.