CH4 recovery and CO2 sequestration using flue gas in natural gas hydrates as revealed by a micro-differential scanning calorimeter

• The extent of the replacement was improved due to the enclathration of N2 in small cages.
• The dissociation enthalpies of the replaced gas hydrates were measured.
• There was no noticeable heat flow change during the CH4–flue gas replacement.
• The replacement could occur without significant destruction of gas hydrates.

The CH4–flue gas replacement in naturally occurring gas hydrates has attracted significant attention due to its potential as a method of exploitation of clean energy and sequestration of CO2. In the replacement process, the thermodynamic and structural properties of the mixed gas hydrates are critical factors to predict the heat flow in the hydrate-bearing sediments and the heat required for hydrate dissociation, and to evaluate the CO2 storage capacity of hydrate reservoirs. In this study, the 13C NMR and gas composition analyses confirmed that the preferential enclathration of N2 molecules in small 512 cages of structure I hydrates improved the extent of the CH4 recovery. A high pressure micro-differential scanning calorimeter (HP μ-DSC) provided reliable hydrate stability conditions and heat of dissociation values in the porous silica gels after the replacement, which confirmed that CH4 in the hydrates was successfully replaced with flue gas. A heat flow change associated with the dissociation and formation of hydrates was not noticeable during the CH4–flue gas replacement. Therefore, this study reveals that CH4–flue gas swapping occurs without structural transitions and significant hydrate dissociations.