Optimizing hydrate formation and distribution in the presence of amino acids for CO2 marine sequestration

Abstract

Carbon dioxide (CO₂) marine sequestration by hydrate method is considered as one of the options to effectively achieve carbon reduction. However, the slow rate of hydrate formation becomes a major limiting factor. In view of the gas-water mass transfer problem which is the main obstacle, this paper explored the amphiphilic amino acids to promote the formation of CO₂ hydrate and used low-field nuclear magnetic resonance (LNMR) to conduct an innovative study on its kinetics and spatiotemporal distribution. By comparing the promotion performance of L-methionine (L-met), L-cysteine (L-cys), and L-valine (L-val), the comprehensive kinetic promotion ability of L-met was the highest, reducing the induction time by 60.0%, achieving the maximum water conversion of about 57.0% within only 1 h, and reaching a final CO₂ storage efficiency of 84.6%. LNMR results showed that hydrates were preferentially formed in large and medium pores in the reservoir region. Interestingly, we found that the combined effect of hydrophilic groups and the hydrophobic side chain of L-met not only promoted the rearrangement of water molecules and provided more nucleation sites, but also created a localized CO₂ supersaturated environment and facilitated gas-water redistribution. Meanwhile, L-met promoted the formation of a hydrate porous structure to ensure the continuous formation of hydrates. This study innovatively explored CO₂ hydrate formation behavior in amphiphilic amino acids and laid a theoretical foundation for the realization of CO₂ marine sequestration by hydrate method.