Unraveling the Role of Amino Acid _L-Tryptophan Concentration in Enhancing CO₂ Hydrate Kinetics

Carbon dioxide (CO₂) hydrates have garnered significant interest as a promising technology for CO₂ capture and storage due to its high storage capacity and moderate operating conditions. The kinetics of CO₂ hydrate formation is a critical factor in determining the feasibility of hydrate-based CO₂ capture and storage technologies. This study systematically investigates the promotional effects of the amino acid _L-tryptophan (_L-trp) on CO₂ hydrate formation kinetics and morphology under stirred and unstirred conditions. In the stirred system, experiments were conducted in a high-pressure 100 mL reactor with 0.05, 0.10, and 0.30 wt% _L-trp solution. CO₂ gas uptake kinetics and morphological evolution were monitored using a high-resolution digital camera. Results showed that _L-trp promoted CO₂ hydrate formation kinetics without delay, with rapid CO₂ consumption upon nucleation. Morphological evolution revealed rapid hydrate formation, wall-climbing growth, and dendritic morphology filling the bulk solution. Under unstirred conditions, experiments were performed in a larger 1 L reactor with 0.1 wt% and 0.5 wt% _L-trp solutions to assess the influence of additive concentration on hydrate formation thermodynamics and kinetics. Results demonstrated that _L-trp influenced both thermodynamics and kinetics of CO₂ hydrate formation. Thermodynamically, 0.1 wt% _L-trp resulted in the highest hydrate formation, indicating an optimal concentration for thermodynamic promotion. Kinetically, increasing _L-trp concentration from 0.1 wt% to 0.5 wt% reduced formation time, demonstrating a proportional relationship between _L-trp concentration and formation kinetics. These findings provide insights into the role of _L-trp in promoting CO₂ hydrate formation and the interplay between additive concentration, thermodynamics, and kinetics. The results can inform the development of effective hydrate-based technologies for CO₂ sequestration, highlighting the potential of amino acids as promoters in gas hydrate.