Measurement and Theoretical Calculation of CO₂ Solubility Data in Liquid CH₄ + C₂H₆ Mixtures at Cryogenic Temperatures

Abstract

In the liquefied natural gas (LNG) industry, CO2 needs to be removed to 50 ppm to avoid CO2 freeze-out under cryogenic conditions. However, in LNG produced from unconventional natural gas that is rich in ethane, the allowance of CO2 may be much higher due to the much higher CO2 solubility than that in conventional LNG. Considering that CO2 solubility data in liquid CH4 + C2H6 mixtures are still quite lacking, a static solid–liquid equilibrium experimental setup is built to measure the CO2 solubility data. The experiments are carried out at the temperature range of 148–203 K, covering an ethane content of 0–100%. The experimental results are compared with theoretical calculated results based on equations of state and Gibbs–Helmholtz relation. CO2 solubility in the CH4 + C2H6 mixture increases exponentially with increasing temperature. The addition of ethane significantly increases the CO2 solubility in the entire temperature zone, indicating that the purification specification of CO2 in natural gas with high ethane content can be significantly enlarged, and it is easier to achieve carbon removal by cryogenic distillation. Furthermore, the increase in CO2 solubility in the CH4 + C2H6 mixture approximates a logarithmic relationship to the C2H6 content.