The Experimental and Modeling Study on the Effect of Ethane in Helium-Rich Natural Gas on the Thermodynamic Equilibrium of Hydrate Formation in the Presence of Tetrahydrofuran

Hydrate-based gas separation (HBGS) is a new method for extracting helium from helium-rich natural gas (HNG). The ethane in HNG affects the thermodynamic equilibrium hydrate formation pressure (<i>Peq</i>), and <i>Peq</i> is crucial to the application of HBGS for extracting helium. In this work, the <i>Peq</i> of the HNGs with different ethane contents (0.5 mol%, 1.0 mol%, and 10 mol%) and the solutions with different tetrahydrofuran (THF) contents (5 wt%, 10 wt%, and 19 mol%) at different temperatures were experimentally investigated through the isothermal pressure search method. Ethane and THF have a competitive effect on hydrate formation. A new thermodynamic model was proposed to predict the <i>Peq</i> of different HNG-THF solution systems. The effect of ethane on <i>Peq</i> can be quantitatively described, and the <i>Peq</i> of HNGs can be accurately predicted by the model in this work. The average relative deviation of the model for predicting <i>Peq</i> of HNGs in different THF aqueous solution systems is less than 3%. The results of this study can guide the operating conditions for the optimization of extracting helium from HNGs by the HBGS process.