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Concept
Carbon dioxide clathrate
Résumé
Carbon dioxide hydrate or carbon dioxide clathrate is a snow-like crystalline substance composed of water ice and carbon dioxide. It normally is a Type I gas clathrate. There has also been some experimental evidence for the development of a metastable Type II phase at a temperature near the ice melting point. The clathrate can exist below 283K (10 °C) at a range of pressures of carbon dioxide. CO2 hydrates are widely studied around the world due to their promising prospects of carbon dioxide capture from flue gas and fuel gas streams relevant to post-combustion and pre-combustion capture. It is also quite likely to be important on Mars due to the presence of carbon dioxide and ice at low temperatures.
The first evidence for the existence of CO2 hydrates dates back to the year 1882, when Zygmunt Florenty Wróblewski reported clathrate formation while studying carbonic acid. He noted that gas hydrate was a white material resembling snow and could be formed by raising the pressure above a certain limit in his H2O - CO2 system. He was the first to estimate the CO2 hydrate composition, finding it to be approximately CO2•8H2O. He also mentions that "...the hydrate is only formed either on the walls of the tube, where the water layer is extremely thin or on the free water surface... (from French)" This already indicates the importance of the surface available for reaction (i.e. the larger the surface the better). Later on, in 1894, M. P. Villard deduced the hydrate composition as CO2•6H2O. Three years later, he published the hydrate dissociation curve in the range 267 K to 283 K (-6 to 10°C). Tamman & Krige measured the hydrate decomposition curve from 253 K down to 230 K in 1925 and Frost & Deaton (1946) determined the dissociation pressure between 273 and 283 K (0 and 10°C). Takenouchi & Kennedy (1965) measured the decomposition curve from 45 bars up to 2 kbar (4.5 to 200 MPa). The CO2 hydrate was classified as a Type I clathrate for the first time by von Stackelberg & Muller (1954).
On Earth, CO2 hydrate is mostly of academic interest.
Source officielle
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