Coupling Amino Acid with THF for the Synergistic Promotion of CO₂ Hydrate Micro Kinetics: Implication for Hydrate-Based CO₂ Sequestration

CO₂ capture and sequestration are broadly recognized as the most effective technology for reducing CO₂ emissions and mitigating global climate change. In this regard, hydrate-based CO₂ sequestration (HBCS) has been proposed as an effective method for long-term safe and stable CO₂ sequestration. It is a promising technology for reducing the concentration of CO₂ in the atmosphere and achieving carbon neutrality. However, one major challenge related to HBCS technology is the lack of understanding of how to improve the formation kinetics of CO₂ hydrate effectively. Herein, in this study, we identified the synergistic promotion effect on CO₂ hydrate formation when a low-dose thermodynamic promoter (tetrahydrofuran, THF) is coupled with an environment-friendly kinetic promoter (l-methionine, l-Met). Based on the kinetic experiments and the morphological observation, 0.6 mol % THF coupled with 0.1 wt %l-Met yields the optimal CO₂ gas uptake. <i>In situ</i> Raman spectra reveal the mechanism of the observed two-step growth behavior at the molecular level, where low-dose THF promotes the initial CO₂-THF sII hydrate nucleation and growth in the solution and l-Met promotes the subsequent CO₂ sI hydrate growth along the surface of the reactor. Our study unveils the underlying synergistic mechanism when thermodynamic and kinetic promoters are coupled for CO₂ hydrate formation. The results provide guidance for the identification and use of novel bio-friendly thermodynamic and kinetic promoters and are beneficial to a series of sustainable hydrate-based technologies when fast CO₂ formation is required.