Hydrogen purification via hydrate-based methods: Insights into H2-CO2-CO hydrate structures, thermodynamics, and kinetics

Abstract

Hydrate-based H₂ purification is promising for removing impurities owing to the cage-like structures formed by water molecules. Understanding the competition mechanism of multicomponent gas molecule in hydrate is critical for improving gas purification efficiency. This study investigated the hydrate structure, thermodynamics, and kinetics of ternary gas mixture (H₂–CO₂–CO) from natural gas reforming products. The results identified H₂–CO₂–CO hydrate as type sI and determined the lattice parameters using X-ray diffraction. Raman spectroscopy results confirmed the presence of H₂, CO₂, and CO gas molecules in the hydrate phase. Increasing pressure, compared to cooling, enhanced CO₂ content in hydrate phase. The phase equilibrium conditions and average hydrate dissociation enthalpy (53.47 J/g) were determined using a high-pressure microcalorimeter. Gas chromatography identified that the content of CO₂ in the hydrate was the highest, followed by H₂, and CO was the least abundant. The molecule dynamics simulation results show CO₂ molecule numbers reflected trends in 5¹²6² cages, H₂ numbers correlated with changes in 5¹² cages, while CO numbers showed insignificant variation. Under the gas composition studied, the ability of gas molecules to be incorporated within hydrates decreases in the following order: CO₂, H₂, and CO.