Methane and carbon dioxide hydrates are one of the possible forms in which these gases exist in natural coal (for more detailed discussion see Refs [1

2]). In this work

the decomposition of carbon dioxide hydrate in five samples of natural coal differing from each other in metamorphism degree was investigated experimentally. Carbon dioxide hydrate dispersed in coals was synthesized from water adsorbed in these coals. During a linear temperature rise in an autoclave with the coal + hydrate sample the hydrate decomposition manifests itself as a step of increase in gas pressure

accompanied by a decrease/stabilization of the temperature of coal sample. The dependencies of the amount of hydrate formed on initial coal humidity and on gas pressure during hydrate formation were studied. It was demonstrated that each coal sample is characterized by its own humidity threshold below which hydrate formation in natural coal is impossible. With an increase in gas pressure

the amount of water transformed into hydrate increases. For the studied coal samples

the decomposition of carbon dioxide hydrates proceeds within a definite temperature and pressure range

and this range is close to the curve of phase equilibrium for bulk hydrate.