Spontaneous generation of stable CO2 emulsions via the dissociation of nanoparticle-aided CO2 hydrate

Abstract

This study finds that CO2 hydrate dissociation spontaneously generates fine-textured emulsions or foams, and that the phase state of CO2 which was used to form hydrate determines the stability of the emulsion or foam when hydrate is dissociated in an aqueous dispersion of hydrophilic silica nanoparticles. This process suggests an energy-efficient method of generating stable emulsions for high-pressure applications without a need for mechanical energy input. We proved experimentally that the CO2 hydrate phase could be used to generate foams and emulsions because the hydrate formation process naturally disconnects a hydrate guest molecule phase from the bulk water phase. During dissociation, easy adsorption of nanoparticles at CO2-water interfaces hinders the coalescence of bubbles. As a result, CO2 emulsions or foams were generated upon the completion of hydrate dissociation. The CO2 emulsions generated remained fairly stable, while the CO2 foams generated became unstable and the buoyant force of the CO2 bubbles led to their coalescence. The concepts experimentally proven here could be applicable to any suitable clathrate compound undergoing a solid to a liquid phase transition.