CO₂ Hydrate Nucleation Kinetics Enhanced by an Organo-Mineral Complex Formed at the Montmorillonite–Water Interface

Abstract

In this study, we investigated experimentally and computationally the effect of organo-mineral complexes on the nucleation kinetics of CO₂ hydrate. These complexes formed via adsorption of zwitter-ionic glycine (Gly-zw) onto the surface of sodium montmorillonite (Na-MMT). The electrostatic attraction between the −NH₃⁺ group of Gly-zw, and the negatively charged Na-MMT surface, provides the thermodynamic driving force for the organo-mineral complexation. We suggest that the complexation of Gly-zw on the Na-MMT surface accelerates CO₂ hydrate nucleation kinetics by increasing the mineral–water interfacial area (thus increasing the number of effective hydrate-nucleation sites), and also by suppressing the thermal fluctuation of solvated Na⁺ (a well-known hydrate formation inhibitor) in the vicinity of the mineral surface by coordinating with the −COO^– groups of Gly-zw. We further confirmed that the local density of hydrate-forming molecules (i.e., reactants of CO₂ and water) at the mineral surface (regardless of the presence of Gly-zw) becomes greater than that of bulk phase. This is expected to promote the hydrate nucleation kinetics at the surface. Our study sheds new light on CO₂ hydrate nucleation kinetics in heterogeneous marine environments, and could provide knowledge fundamental to successful CO₂ sequestration under seabed sediments