Ultrarapid CO<sub>2</sub> Hydrate Nucleation and Growth Enabled by Magnesium Coupled with Amino Acids as a Promoter
Yan Li, Zhenyuan Yin, Yizhi Rao, Hongfeng Lu, Chenlu Xu, Xuejian Liu, Li Yang, Jianzhong Zhao, Praveen Linga
Abstract
Hydrate-based CO 2 sequestration (HBCS) technology is one promising method for reducing the CO 2 level in the atmosphere for climate mitigation. However, the sluggish kinetics and low conversion rate of the CO 2 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 CO 2 hydrate nucleation and realize the ultrarapid CO 2 growth in the static system. The addition of a Mg sheet speeds up CO 2 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 CO 2 hydrate nucleation and growth. The resulting final CO 2 gas uptake is 78.9 V g / V w compared with 67.8 V g / V w without Mg. However, the t 90 used is significantly shortened to 1.4 h compared with a t 90 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 Mg 2+ 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 Mg 2+ in solution reaching 68 mg/L. Based on the experimental evidence, we propose that the abundant H 2 bubbles released from the surface of the Mg sheet due to corrosion in the acidic environment of CO 2 solution are one critical factor explaining the ultrarapid nucleation observed. Our study demonstrated that employing Mg corrosion to assist the nucleation of CO 2 hydrate is effective in the static system and the coupling of amino acid can further enhance CO 2 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.