Blended hydrate seed and liquid promoter for the acceleration of hydrogen hydrate formation

Abstract

The slow formation rate of hydrogen clathrate hydrate is one of the most challenging factors impeding the utilization of clathrate hydrate as a hydrogen storage media. Blending of a hydrate seed solution and a liquid phase thermodynamic promoter is introduced in this study to promote the formation of hydrogen hydrates for safe hydrogen storage. Cyclopentane hydrate seeds induced instantaneous growth of cyclopentane + hydrogen mixed hydrates by providing nucleation sites for hydrate formation. Increasing the amount of hydrate seeds accelerated the formation rate of hydrates at the early stage of the reaction because the surface area of hydrate crystals increased. However, the total storage capacity was not so high because the diffusion of hydrogen molecules into empty cages of pre-constructed hydrate crystals was difficult. This diffusion limitation was overcome by the addition of the cyclopentane liquid phase promoter for the simultaneous formation of cyclopentane and hydrogen hydrates with their porous vertical growth. Tetrahydrofuran, one of the most commonly used organic promoters for hydrogen hydrates, was not suitable for the blended hydrate seed and liquid promoter system because its miscibility with water hindered the formation of hydrogen-bond cages and did not induce vertical growth of porous hydrates. This study provides insights into the role of liquid promoter blended with hydrate seeds in enhancing formation of hydrogen hydrates as sustainable hydrogen storage.