Measurement of pure hydrogen and pure carbon dioxide adsorption equilibria for THF clathrate hydrate and tetra-n-butyl ammonium bromide semi-clathrate hydrate

In this work, gas adsorption equilibria for H2 and for CO2 with THF clathrate hydrate particles and with tetra-n-butyl ammonium bromide (TBAB) semi-clathrate hydrate particles (250–355 μm) were measured. The structures of the TBAB semi-clathrate hydrates were confirmed with Raman spectroscopy and with differential scanning calorimetry. The THF clathrate hydrate particles had the largest adsorption (ca. 13.7 mmol-H2/mol-host) at 269 K among all of the hydrates studied. H2 adsorption at 269 K for 2.6 mol% TBAB semi-clathrate hydrate (type-B rich) was ca. 6.9 mmol-H2/mol-host and that for 3.7 mol% TBAB semi-clathrate hydrate (type-A rich) was ca. 3.4 mmol-H2/mol-host. For CO2, THF clathrate hydrate had higher adsorption capacity (ca. 68.5 mmol-CO2/mol-host) than type-A (ca. 16.3 mmol-CO2/mol-host) or type-B (ca. 29.0 mmol-CO2/mol-host) semi-clathrate hydrate. Type-B TBAB semi-clathrate hydrate had a larger Langmuir constant ratio (CCO2/CH2)(CCO2/CH2) than that of THF hydrate. The selectivity of type-B TBAB semi-clathrate hydrate implied by the Langmuir constant ratio can be expected to be large, however the results need to be confirmed with gas mixtures and other conditions including effect of semi-clathrate hydrate particle size.