Enhanced CO2 hydrate formation via biopromoter coupled with initial stirring activation

• A method of using initial stirring to activate CO 2 hydrate formation process was proposed. • About 90% of energy consumed for stirring can be saved using proposed method. • Abundant small CO 2 hydrate floccules rapidly formed and filled the entire solution under action of stirring. • CO 2 hydrates are flexible and expandable with strong capillarity-driven action under l -methionine promoter. CO 2 sequestration based on hydrate technology is considered to be the most promising long-term CO 2 sequestration technology. In this study, a method of using initial stirring to activate CO 2 hydrate formation process was proposed in the aim of saving energy and avoiding the problem of stirring shaft stuck, where the stirring only played a role in activating hydrate formation process. Two amino acids, l -Methionine and d -leucine, were chosen as promoters for improving the formation kinetics of CO 2 hydrates, and l -Methionine presents better than d -leucine. When the concentration of l -methionine solution is equal to or greater than 4 mmol/L, even with the initial stirring of 10 rpm within 8 min, T 90 can be shortened to close to or less than 40 min with a high gas consumption of more than 7.3 mmol gas/mL water, where the promoting effect is similar to the condition of continuous stirring of about 100 min, indicating that about 90 % of the energy consumed for mechanical stirring can be saved. Moreover, an interesting phenomenon was observed that CO 2 hydrates firstly nucleated inside the l -methionine solution, and a large number of small hydrate floccules rapidly formed and filled the entire solution under the action of magnetic stirring, which proved the instantaneous excitation effect of stirring on hydrate formation. This work contributes to rethinking the promoting roles of stirring and promoters in CO 2 hydrate formation.