| Summary: | Clathrate hydrates of gases are ice-like, supramolecular compounds formed when a relatively small, hydrophobic gas, such as methane, hydrogen, hydrogen sulfide, carbon dioxide, etc., comes into contact with water under particular conditions of pressure and temperature. Such guest molecules are enclathrated into hydrogen-bonded water cages with definite geometries (structures sI, sII, sH, etc.) which depend mainly on the guest species, but all share a common building block, the pentagonal dodecahedra (512) composed by 12 pentagonal faces which define a cavity.[1] Methane can be stored in hydrate form at very high concentrations, thus making hydrates a very promising means for safely and effectively storing and transporting natural gas. Moreover, a huge amount of methane is buried as hydrates deep into the ocean bottom or in the permafrost. Also, thermodynamics allows to foresee a process of extraction of methane from field hydrates while carbon dioxide is pumped in to replace extracted methane.[2] Last, but not least, also hydrogen has recently been shown to be entrapped in clathrate form, which form the basis of a possible revolution in the shift to a real "hydrogen economy".[3] Methane hydrate formation has been shown to be heavily promoted by surfactants, and this effect has been ascribed to the solubilizing effect of micelles.[4] In the present work, we performed conductimetric and gas uptake studies under controlled pressure and temperature conditions.[5] As a result, we show that surfactant micelles are not responsible for the observed promotion, and surfactant molecules act well below their CMC's to boost methane enclathration. Both anionic and cationic surfactants were studied, some of which were designed and synthesized in our laboratory, and a preliminary knowledge of structure-activity relationships is illustrated.[6] The stabilization of methane hydrates makes it feasible the application of this technology to methane storage and transportation
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