Hydrates, also known as clathrates, are solid crystalline compounds resembling ice, composed of cages of hydrogen-bonded water molecules with small non-polar molecules, typically gas molecules, trapped inside. Hydrates are formed at low temperatures and high pressure; e.g. CO2 hydrates require temperatures between 0 and 10 °C and pressures 10 to 60 bar.
The clathrate hydrate-based desalination process involves contacting an electrolyte solution (salt water) and a guest compound (hydrate-forming gas) under suitable pressure and temperature conditions, leading to a phase change of water from liquid to solid and the formation of solid hydrates. Because of the salt-removing effect observed in the hydrate formation process, the crystalline structure of the hydrates formed from saltwater is free from salts and other impurities, which are concentrated in the liquid phase, without disturbing the morphology of the hydrate crystal.
The salt-free hydrates are mechanically separated from the salt-rich liquid phase (e.g. filtration or centrifuge) and then dissociated into fresh water and the guest compound by pressure reduction, heating or both. The hydrate-forming gas can be reused to form new hydrates.
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