A Molecular Dynamics Study on Xe/Kr Separation Mechanisms Using Crystal Growth Method

The separation of xenon/krypton gas mixtures is a valuable but challenging endeavor in the gas industry due to their similar physical characteristics and closely sized molecules. To address this, we investigated the effectiveness of the hydrate-based gas separation method for mixed Xe-Kr gas via molecular dynamics (MD) simulations. The formation process of hydrates facilitates the encapsulation of guest molecules within hydrate cages, offering a potential strategy for gas separation. Higher temperatures and pressures are advantageous for accelerating the hydrate growth rate. The final occupancy of guest molecules and empty cages within 5¹², 5¹²6⁴, and all hydrate cages were thoroughly examined. An increase in the pressure and temperature enhanced the occupancy rates of Xe in both 5¹² and 5¹²6⁴ cages, whereas elevated pressure alone improved the occupancy of Kr in 5¹²6⁴ cages. However, the impact of temperature and pressure on Kr occupancy within 5¹² cages was found to be minimal. Elevated temperature and pressure resulted in a reduced occupancy of empty cages. Predominantly, 5¹²6⁴ cages were occupied by Xe, whereas Kr showed a propensity to occupy the 5¹² cages. With increasing simulated pressure, the final occupancy of Xe molecules in all cages rose from 0.37 to 0.41 for simulations at 260 K, while the final occupancy of empty cages decreased from 0.24 to 0.2.