Recovery of CH₄from natural gas hydrates using the mixture of carbon dioxide and nitrogen

On the continental margins and in permafrost regions, natural gas such as methane, ethane, propane and large hydrocarbons, which has been expected to replace petroleum energy, exists in solid hydrate form. Because of huge amounts of natural gas in the solid form of Natural Gas Hydrate (NGH), the effective recovery of natural gas from NGH becomes the most important factor on evaluating the economic feasibility in the sense of commercialization. If NGHs could be transformed into CO₂ hydrates, they would suggest double opportunities as energy sources and global warming gas storage sites. Herein, we report the Dual CO₂ sequestration and CH₄ recovery phenomena occurring in NGH layers including sI, sII and sH. For sI CH ₄ hydrate, the resulting outcome of 64% and 85% CH₄ recovery rate achieved by the direct use of CO₂ and N ₂/CO₂ mixtures (8:2) was reported by using Gas Chromatography (GC). In the case of sII and sH CH₄ hydrates, we report dual structure transition to si during swapping phenomena and a cage-specific distribution of guest molecules. A significant change of structure transition due to CO₂s attack induces the considerable increase of CH₄ recovery rate.