Water content in CO2–CH4 mixtures: New saturation setup and measurements using a quartz-crystal microbalance.

This study presents experimental data on water content in CO2, methane, and their mixtures. A new saturation process was developed using a PVT cell connected to a variable-volume cylinder filled with deionized water. Dry gas with a known composition was injected into the cylinder, and the temperature and pressure conditions were adjusted accordingly. The water content of the saturated gas was then analyzed using a quartz-crystal microbalance (QCM). Various mixtures with different CO2 and methane mole ratios were investigated at different pressures for a given temperature. The PC-SAFT and CPA equations of state were applied to correlate the moisture data. The association scheme employed included 2B, 3B, and 4C types, considering the cross-association between water and CO2. The results for pure methane showed that the water content increased as the pressure decreased across all pressure ranges. However, for pure CO2 above 70 bar, the water content increased due to the condensation behavior of CO2. The same trend was observed for mixtures, where the water content increased with increasing pressure for CO2 mole fractions above 0.74. For all the systems studied, the PC-SAFT and CPA equations of state successfully correlated the water content data using a single constant binary interaction parameter and considering the cross-association between water and CO2.