Ultrarapid CO2 Hydrate Nucleation and Growth Enabled by Magnesium Coupled with Amino Acids as a Promoter

Hydrate-based CO2 sequestration (HBCS) technology is one promising method for reducing the CO2 level in the atmosphere for climate mitigation. However, the sluggish kinetics and low conversion rate of the CO2 hydrate hindered its practical applications. This study presents an innovative approach by coupling magnesium (Mg) with an amino acid l-leucine (l-Leu) to speed up the CO2 hydrate nucleation and realize the ultrarapid CO2 growth in the static system. The addition of a Mg sheet speeds up CO2 hydrate nucleation, resulting in an induction time less than 10 s compared with traditional ∼10 h in a static system. The coupling Mg sheet with l-Leu (1.0 wt %) shows optimal synergistic promotion effects on both CO2 hydrate nucleation and growth. The resulting final CO2 gas uptake is 78.9 Vg/Vw compared with 67.8 Vg/Vw without Mg. However, the t90 used is significantly shortened to 1.4 h compared with a t90 of 13.0 h without Mg. We further analyzed the possible promotion mechanism of Mg using a series of analytical methods, including Mg sheet surface morphology observation with element composition analysis, gas phase compositions analysis by GC and Mg2+ concentration in aqueous phase by ICP-MS. Corrosion of the Mg sheet surface is observed based on SEM images. A significant reduction of Mg is identified in the element composition analysis with additional C and N after corrosion. A small trace of hydrogen (∼1%) is identified in the gas phase with the Mg2+ in solution reaching 68 mg/L. Based on the experimental evidence, we propose that the abundant H2 bubbles released from the surface of the Mg sheet due to corrosion in the acidic environment of CO2 solution are one critical factor explaining the ultrarapid nucleation observed. Our study demonstrated that employing Mg corrosion to assist the nucleation of CO2 hydrate is effective in the static system and the coupling of amino acid can further enhance CO2 hydrate kinetics. The developed method can also be utilized for other hydrate-based technologies, such as flue gas separation and hydrogen storage, by coupling Mg with suitable promoters.