Mechanism and kinetics of guest exchange in sII hydrate – Flue gas replacement as revealed by experimental and computational approaches for hydrocarbon recovery and CO2 sequestration.

[Display omitted] • Kinetic guest exchange in sII hydrate-flue gas replacement was investigated. • The sII hydrate-flue gas replacement occurred iso-structurally. • The higher pressure enhanced guest exchange with CO 2 in both small and large cages. • The competitive inclusion of CO 2 and N 2 in the small (512) cages was observed. • The size and dispersive movement of the guest molecules affected the lattice parameter. In this study, the kinetics of guest exchange in sII (CH 4 (90%) + C 3 H 8 (10%)) hydrate – flue gas (CO 2 (20%) + N 2 (80%)) replacement was investigated to elucidate the replacement mechanism and guest exchange characteristics for hydrocarbon recovery and CO 2 sequestration. The Rietveld refinement of Powder X-ray diffraction (PXRD) patterns of the replaced hydrates at two pressures (11.0 MPa and 17.0 MPa) demonstrated that sII hydrate – flue gas replacement occurred iso-structurally. The time-dependent guest compositions in the hydrate phase and the cage occupancy of guest molecules were examined to understand the effect of pressure on guest exchange behaviors. The increased CO 2 inclusion in both the small (512) and large (51264) cages at a higher pressure resulted in the larger production of CH 4 and C 3 H 8 and a lower N 2 /CO 2 ratio in the hydrate phase. The slower inclusion rate and lower N 2 occupancy in the small (512) cages at a higher pressure during replacement were observed due to the competitive inclusion of CO 2 and N 2 in the small (512) cages. The molecular dynamics (MD) simulation demonstrated that the expansion or shrinkage of hydrate cages caused by guest exchange has a significant impact on the lattice parameter of the replaced hydrates and it was influenced by not only the average molecular size of guest molecules in each cage but also the dispersive movement of the guest molecules in each cage. [ABSTRACT FROM AUTHOR]