Improvement of continuous hydrate-based CO₂ separation by forming structure II hydrate in the system of H₂ + CO₂ + H₂O + Tetrahydropyran (THP)

Continuous hydrate-based CO₂ separation is a compelling technology both from an environmental and economical perspective. We developed a method to continuously capture and separate CO₂ from a gas mixture with H₂ and determined the time-dependent changes of compositions in the gas and hydrate containing aqueous phases. Tetrahydropyran (THP), a representative water-soluble large molecular guest compound for structure II (sII) clathrate hydrate, was added in the reactor. THP forms hydrates under moderate conditions. The effects of THP mass fraction in the solution, w_THP, on the gas separation was simultaneously investigated by using w_THP = 0.11 and the stoichiometric value for sII hydrate, w_THP = 0.22. The results showed the gas phase hydrogen concentration reached steady state at 0.92 mol fraction from 0.60 in the feed gas. Also, the results demonstrated that sII hydrate has the highest CO₂ loading capacity compared to ionic semi-clathrate hydrate phases. A continuous hydrate-based gas separation with sII hydrate has yet to be investigated. This study provides new experimental evidence which proves that the sII hydrate is the best structure for hydrate-based gas separation.