Clay nanoflakes and organic molecules synergistically promoting CO2 hydrate formation

Abstract

Carbon dioxide (CO2) reduction is an urgent challenge worldwide due to the dramatically increased CO2 concentration and concomitant environmental problems. Geological CO2 storage in gas hydrate in marine sediment is a promising and attractive way to mitigate CO2 emissions owning to its huge storage capability and safety. However, the sluggish kinetics and unclear enhancing mechanisms of CO2 hydrate formation limit the practical application of hydrate-based CO2 storage technologies. Here, we used vermiculite nanoflakes (VMNs) and methionine (Met) to investigate the synergistic promotion of natural clay surface and organic matter on CO2 hydrate formation kinetics. Induction time and t90 in VMNs dispersion with Met were shorter by one to two orders of magnitude than Met solution and VMNs dispersion. Besides, CO2 hydrate formation kinetics showed significant concentration-dependence on both Met and VMNs. The side chains of Met can promote CO2 hydrate formation by inducing water molecules to form a clathrate-like structure. However, when Met concentration exceeded 3.0 mg/mL, the critical amount of ammonium ions from dissociated Met distorted the ordered structure of water molecules, inhibiting CO2 hydrate formation. Negatively charged VMNs can attenuate this inhibition by adsorbing ammonium ions in VMNs dispersion. This work sheds light on the formation mechanism of CO2 hydrate in the presence of clay and organic matter which are the indispensable constituents of marine sediments, also contributes to the practical application of hydrate-based CO2 storage technologies.