Thermodynamic stability of gas hydrates and cage occupancy of guest species

Abstract

Natural-gas hydrate field under the deep-ocean floor has become the object of public attention as a potential unconventional energy resource. In addition, the storage and transport systems of natural-gas or hydrogen using gas hydrates, and high-pressure separation of hydrogen from gas-mixtures containing carbon dioxide have been a focus of constant attention as new techniques. In order to proceed toward the realization of them, the studies on physical and chemical properties of gas hydrate crystal have been accelerated. In this article, recent thermodynamic and Raman spectroscopic studies on pure and mixed gas hydrate systems are reviewed with particular emphasis on the cage occupancy of guest species and the structural phase transition.