Desalination, clathrate hydrates

In addition to the use of existing hydrates, it has also been suggested that clathrate hydrates could find applications in storage and separation technology. Bardhun showed in 1962 the viable application of hydrates in desalination of sea water, while hydrates have also been investigated as a method for the storage and transport of methane without the use of high-pressure containers. 

Chloride ions easily replace water molecules in the butane clathrate hydrate, and counter-cations can occupy the voids in the lattice. This is one of the reasons why the hydrate crystallization method proved unsuccessful for desalination of sea water. 

R. W. Bradshaw,]. A. Greathouse, R. T. Cygan,B. A. Simmons, D. E. Dedrick,andE. H. Maj-zoub. Desalination Utilizing Clathrate Hydrates, Sandia Report, SAND2007-6565 (2008). 

Steric criteria are also valuable to explain the formation of liquid hydrate clathrates (Fig. 3, 16.2.2.1). They appear for molecules having dimensions between the free diameters of the largest voids of types I and II structures, d, 2 and dn,2- The situation is the same for double liquid hydrates, but here a type I structure is theoretically possible in some cases, e.g., CHjBr, COS and CH3I. For molecules with dimensions >690 pm, no hydrates are formed. This selectivity in encaging certain molecules but not others has been used for fractionation of natural gas by clathration and for desalination of sea water "... 

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