Dual Promotional Effect of l‑Tryptophan and 1,3-Dioxane on CO₂ Hydrate Kinetics in Seawater under Static/Unstatic Conditions for Carbon Capture and Storage Application

CO₂ hydrates hold promising applications, including as a medium for carbon storage in oceanic sediments, as a result of their high storage capacity. However, the presence of high salinity in sediments is likely to affect the CO₂ hydrate kinetics. To counter this challenge, the CO₂ hydrate formation, dissociation, and deep morphology have been investigated in seawater (SW) under static and non-static conditions. Moreover, the effect of a kinetic promoter [1000 ppm of l-tryptophan (l-tryp)] and a thermodynamic promoter (5 wt % 1,3-dioxane) and dual promotional effects of kinetic and thermodynamic promoters (1000 ppm of l-tryp + 5 wt % 1,3-dioxane) have also been studied. In situ Raman spectroscopy was used to probe the real-time CO₂ dissolution in seawater in the presence of 1,3-dioxane. The CO₂ uptake in seawater for the static system was estimated to be in the following order (20 h): CO₂ (30.5 ± 5.0 mmol/mol) > CO₂ + 1000 ppm of l-tryp (30 ± 1.20 mmol/mol) > CO₂ + 1,3-dioxane + 1000 ppm of l-tryp (26.2 ± 7.1 mmol/mol) > CO₂ + 1,3-dioxane (21.1 ± 6.1 mmol/mol). In comparison, for the non-static system, the CO₂ uptake in seawater was estimated to be in the following order (20 h): CO₂ + 1000 ppm of l-tryp (67.8 ± 2.20 mmol/mol) > CO₂ + 5 wt % 1,3-dioxane (49.3 ± 7.0 mmol/mol) > CO₂ + 5 wt % 1,3-dioxane + 1000 ppm of l-tryp (42.9 ± 4.8 mmol/mol) > CO₂ (39.5 ± 4.1 mmol/mol).