CO ₂ Sequestration by Hydrate Formation under Simulated Permafrost Conditions

Carbon Capture and Storage (CCS) is regarded as one of the critical technologies to achieve the goals of carbon peaking and carbon neutrality. As an emerging CCS method, storage of CO2 as hydrates in permafrost has gained increasing attention. This approach benefits from the natural low-temperature, high-pressure, and porous environment of permafrost, which promotes the formation of CO2 hydrate. In addition, CO2 hydrates have high thermodynamic stability, robust mechanical integrity, and considerable gas storage capacity. This study evaluated the feasibility of CO2 storage as gas hydrates in permafrost by simulating permafrost conditions in the Qilian Mountains. The optimal CO2 storage depth was determined to be 200 m. At this simulated permafrost depth, an induction time of 39 min and a formation rate of 0.16 mmol·min–1 were observed, with the storage capacity reaching 109.28 V·V–1 after a single pressurization. CO2 hydrates showed high stability, with a dissociation duration of 490 min and an average dissociation rate of 0.14 mmol·min–1 at room temperature and pressure. Multistage pressurization enhanced the peak hydrate formation rate by 84% and improved the CO2 storage capacity to 413.81 V·V–1, with an overall enhancement of 278%. The study reveals that the formation of a CO2 hydrate follows a cycle of nucleation, localized dissociation, and reformation governed by interfacial CO2 concentration. Dissociation begins at CO2 hydrate edges through the thermally triggered disruption of host–guest interaction. Subsequently, the dissociation front propagates radially inward. This study provides a theoretical foundation for the development of CO2 hydrate-based storage technology in permafrost regions.