Formation kinetics & phase stability of double hydrates of C4H8O and CO2/CH4: A comparison with pure systems

Gas hydrate based technology plays a key role in capturing carbon dioxide (CO2) or methane (CH4) gas molecules from its source locations. The parameters like hydrate phase stability, formation kinetics and gas uptake capacity (hydrate yield) are measured for carbon dioxide (CO2) and methane (CH4) at different initial gas pressures. The behaviour is also compared with double hydrates, prepared using 6 mol% of tetrahydrofuran (C4H8O -THF) aqueous solution. Measured thermodynamic phase boundary points for the hydrates with single guest molecules (CO2 or CH4) concur with the literature data. However, the phase stability of double hydrates with THF + CO2/CH4 appeared to be controlled by the stability of THF hydrates. Hydrate formation kinetics is faster in double hydrates than corresponding pure hydrates. Further, the yields in double hydrates with CH4 guest molecule show increasing trends with the gas pressure, whereas, it remains unchanged in double hydrates with CO2 guest molecule beyond some gas pressure. This is attributed to the occupancy of vacant cages by the gas molecules.