CH4 – Flue gas replacement occurring in sH hydrates and its significance for CH4 recovery and CO2 sequestration

Abstract The CH 4 -flue gas replacement that occurs in structure H (sH) hydrates was investigated, with a primary focus on thermodynamic phase behavior, structure identification, heat flow monitoring, and dissociation enthalpy, for its dual function of CH 4 recovery and CO 2 sequestration. The significant shift in the equilibrium line of the CH 4  + neohexane (2,2-dimethylbutane, NH) hydrates replaced with CO 2 (10%) + N 2 (90%) and CO 2 (20%) + N 2 (80%) indicates that CH 4 molecules in the sH hydrates were significantly exchanged with flue gas mixtures. Furthermore, 13 C NMR spectroscopy revealed that replacement using flue gas occurs without a structural transition, and that CO 2 molecules preferentially attack CH 4 molecules occupied in the medium 4 3 5 6 6 3 cages of sH hydrates. The extent of the CH 4  + NH – flue gas replacement was approximately 74%. During CH 4 – flue gas replacement in sH hydrates, there was no significant change in heat flow associated with the dissociation and subsequent reformation of gas hydrates. Dissociation enthalpies of gas hydrates before and after replacement, measured using a high-pressure micro-differential scanning calorimeter (HP μ -DSC), also supported isostructural replacement with the high extent of reaction. This study reports the first experimental evidence of isostructural CH 4 – flue gas replacement occurring in sH hydrates, and thus, might contribute to extending the potential fields of CH 4 exploitation using a flue gas replacement, into sH natural gas hydrate reservoirs.