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

Highlights: • 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. - Abstract: 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