Roles of montmorillonite clay on the kinetics and morphology of CO2 hydrate in hydrate-based CO2 sequestration.

[Display omitted] • Delamination and the electric field induced by clay particle shortens induction time. • Delayed growth kinetics observed in clay suspension with increasing mass fraction. • Water migration and clay agglomeration yielded the stratification of CO 2 hydrate and clay layer. • Heterogeneous spatial distribution of CO 2 hydrate observed in formation and dissociation. Hydrate-based CO 2 sequestration in marine sediments has emerged as a novel sustainable technology for long-term and stable CO 2 sequestration. However, the role of clay minerals in CO 2 hydrate formation and dissociation in clay-rich sediments, which are widely distributed in the South China Sea, remains controversial due to a lack of experimental evidence. This study investigates the effect of a representative clay mineral, sodium montmorillonite (Na-MMT), on the nucleation and growth kinetics of CO 2 hydrate in suspensions with a msass fraction below 20.0 wt%. The kinetic experiments reveal that Na-MMT significantly reduces the induction time due to the additional nucleation sites provided by the delamination of clay particles and the induced surface electric field. While the average growth rate of CO 2 hydrate is reduced by ∼72 % for Na-MMT mass fraction above 5.0 wt%. Morphologically, hydrate-clay stratification and gas-tunneling behaviors were observed, providing explanations for the retarded kinetics. The mass transfer of CO 2 from the gas phase to the liquid phase is impeded by the high viscosity of the suspension and the clay-induced strongly-polarized water layer, which retards the overall kinetics of CO 2 hydrate formation. Upon thermal stimulation, partial CO 2 hydrate dissociation was observed within the pure CO 2 hydrate stability region for 10.0 wt% Na-MMT suspension, indicating a possible impact of Na-MMT on CO 2 hydrate thermodynamics. Moreover, the addition of Na-MMT clay promotes CO 2 hydrate dissociation kinetics significantly. This study provides fundamental insights into the interaction between Na-MMT clay and CO 2 hydrate, offering new perspectives for designing effective strategies for CO 2 sequestration in abundant clay-rich marine sediments. [ABSTRACT FROM AUTHOR]