Geological CO₂ Capture and Storage with Flue Gas Hydrate Formation in Frozen and Unfrozen Sediments: Method Development, Real Time-Scale Kinetic Characteristics, Efficiency, and Clathrate Structural Transition

The climate system is changing globally, and there is substantial evidence that subsea permafrost and gas hydrate reservoirs are melting in high-latitude regions of the Earth, resulting in large volumes of CO ₂ (from organic carbon deposits) and CH ₄ (from gas hydrate reserves) venting into the atmosphere. Here, we propose the formation of flue gas hydrates in permafrost regions and marine sediments for both the geological storage of CO ₂ and the secondary sealing of CH ₄ /CO ₂ release in one simple process, which could greatly reduce the cost of CO ₂ capture and storage (CCS). The kinetics of flue gas hydrate formation inside frozen and unfrozen sediments was investigated under realistic conditions using a highly accurate method and a well-characterized system. The results are detailed over a wide range of temperatures and different pressures at in situ time scales. It has been found that more than 92 mol % of the CO ₂ present in the injected flue gas could be captured under certain conditions. The effect of different relevant parameters on the kinetics of hydrate formation has been discussed, and compelling evidence for crystal-structure changes at high pressures has been observed. It has also been found that temperature rise leads to the release of N ₂ first, with the retention of CO ₂ in hydrates, which provides a secondary safety factor for stored CO ₂ in the event of a sudden temperature increase.