Direct detection of H2 in hydrates for separating H2 from CO2 in pre-combustion gases: Comparison of pure water systems and cyclopentane or tetrahydropyran-containing systems

Toward the pre-combustion H 2 /CO 2 gas separation, the inclusion of hydrogen (H 2 ) in clathrate hydrates was experimentally observed. Three hydrate-forming systems were investigated with ex-situ Raman spectroscopy for the characterization of H 2 +CO 2 hydrate, H 2 +CO 2 +cyclopentane (CP) hydrate and H 2 +CO 2 +tetrahydropyran (THP) hydrate. The observed Raman bands in H 2 +CO 2 hydrate indicate a single occupancy of H 2 in both large and small cavities of structure I hydrate, whereas Raman bands of H 2 +CO 2 +CP hydrate and H 2 +CO 2 +THP hydrate are consistent with the single occupancy of H 2 in small cavities of structure II hydrate. Time-dependent Raman spectroscopic measurements indicate the release of H 2 from hydrate cages with time. In-situ Raman spectroscopic measurements in a closed H 2 +CO 2 +water system revealed the changing gas phase compositions, achieving the H 2 /CO 2 separation. Both H 2 and CO 2 were detected as components of the hydrate phase, which coexists with a mixed gas phase. Based on the obtained results, implications for H 2 /CO 2 gas separation are discussed.