Enhanced CO2 Hydrate Formation Using l -methionine and SiO2 Nanoparticles as Combined Kinetic Promoters

Abstract Hydrate-based CO2 storage requires green kinetic promoters that can accelerate hydrate formation while maintaining favorable growth morphology and reuse stability. In this study, l-methionine (l-Met) and l-Met + SiO2 nanoparticle systems were investigated for CO2 hydrate formation through kinetic measurements and direct morphological observation. l-Met significantly promoted hydrate formation, with 0.100 wt % identified as the optimum single-promoter concentration. The enhancement was closely associated with the formation of a porous wall-climbing hydrate layer, which improved gas–liquid contact and sustained hydrate growth through capillary-assisted water supply. Introducing SiO2 nanoparticles into the optimized l-Met system further enhanced the formation kinetics within an appropriate concentration range, with the 0.100 wt % l-Met + 0.10 wt % SiO2 formulation selected for the subsequent five-cycle evaluation based on the combined mean performance of induction time, final normalized gas consumption, and t90. Morphological observations showed that SiO2 did not redirect the wall-climbing growth induced by l-Met toward a pathway dominated by bulk hydrate formation; instead, it acted mainly as an auxiliary promoter by supplying additional heterogeneous nucleation sites within the existing wall-climbing growth route. Five consecutive formation-dissociation cycles showed that the combined system maintained favorable hydrate-forming performance without fresh promoter addition. These results demonstrate that l-Met + SiO2 is an effective and reusable promoter system for CO2 hydrate formation.