Crystal growth of clathrate hydrate formed with H₂ + CO₂ mixed gas and tetrahydropyran

Hydrate-based gas separation technology is applicable to the CO₂ capture and storage from synthesis gas mixture generated through gasification of fuel sources including biomass. This paper reports visual observations of crystal growth dynamics and crystal morphology of hydrate formed in the H₂ + CO₂ + tetrahydropyran (THP) + water system with a target for developing the hydrate-based CO₂ separation process design. Experiments were conducted at a temperature range of 279.5-284.9 K under the pressure of 4.9-5.3 MPa. To simulate the synthesis gas, gas composition in the gas phase was maintained around H₂:CO₂ = 0.6:0.4 in mole fraction. Hydrate crystals were formed and extended along the THP/water interface. After the complete coverage of the interface to shape a polycrystalline shell, hydrate crystals continued to grow further into the bulk of liquid water. The individual crystals were identified as hexagonal, tetragonal and other polygonal-shaped formations. The crystal growth rate and the crystal size varied depending on thermodynamic conditions. Implications from the obtained results for the arrangement of operating conditions at the hydrate formation-, transportation-, and dissociation processes are discussed.