Roles of montmorillonite clay on the kinetics and morphology of CO2 hydrate in hydrate-based CO2 sequestration1

Hydrate-based CO2 sequestration in marine sediments has emerged as a novel sustainable technology for long-term and stable CO2 sequestration. However, the role of clay minerals in CO2 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 CO2 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 CO2 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 CO2 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 CO2 hydrate formation. Upon thermal stimulation, partial CO2 hydrate dissociation was observed within the pure CO2 hydrate stability region for 10.0 wt% Na-MMT suspension, indicating a possible impact of Na-MMT on CO2 hydrate thermodynamics. Moreover, the addition of Na-MMT clay promotes CO2 hydrate dissociation kinetics significantly. This study provides fundamental insights into the interaction between Na-MMT clay and CO2 hydrate, offering new perspectives for designing effective strategies for CO2 sequestration in abundant clay-rich marine sediments.