Boosting CO ₂ Hydrate Formation in Saline Systems with Cyclopentane Hydrate Seeds and Tetrahydrofuran: Experiments and Implications for Ocean Carbon Sequestration

Hydrate-based ocean carbon sequestration is a highly effective approach to carbon capture and storage (CCS). The key to its success lies in the efficient formation of CO2 hydrates in seawater and their stability. This research integrated macroscopic experiments using CP (cyclopentane) hydrate crystal seeds and THF (tetrahydrofuran) as a combined promoter with microscopic analyses via Raman spectroscopy and scanning electron microscopy (SEM). The goal was to thoroughly examine how different concentrations of the solid–liquid promoters affect CO2 hydrate formation in the saltwater system, ultimately identifying the most effective concentration mix. Additionally, we studied how CO2 hydrates from various systems settle and disperse over time under simulated marine conditions. The results show that the combination of 2.78% CP and 2.78% THF is the most effective, leading to a CO2 gas consumption of 23.28 mmol in the saltwater system, which is 33% higher than in the pure water system, and the average formation rate improves by 40%. CO2 hydrates formed in the saltwater system also show a significant increase in density under a pressure of 5.50 MPa and exhibit superior stability in simulated marine sedimentation experiments. In contrast, CO2 hydrates formed in pure water are more prone to decomposition, which hinders their long-term storage.