Hydrate Crystalline Cavities and Structures

The information on hydrate structures I and II in this section is derived in large part from the excellent reviews of Jeffrey and McMullan (1967), Davidson (1973), and Jeffrey (1984), with the addition of substantial work on molecular motions reviewed by Davidson and Ripmeester (1984). The structure H material was excerpted from Ripmeester et al. (1987,1988,1991,1994), Udachin et al. (1997b, 2002), Mehta (1996), and Mooijer-van den Heuvel et al. (2001, 2002). 

Of more than 130 compounds that are known to form clathrate hydrates with water molecules, the majority form either si, sll, or sH, with exceptions such as (1) bromine (Allen and Jeffrey, 1963 Dyadin et al., 1991), (2) dimethyl ether (Gough et al., 1974, 1975 Udachin et al., 2001a), (3) ethanol (Brownstein et al., 1967 Calvert and Srivastava, 1967), and (4) very high pressure hydrate phases (Dyadin et al., 1997 Loveday et al., 2001b, 2003b Kursonov et al., 2004). Detailed emphasis is given to si, sll, and sH hydrates since these are by far the most common natural gas hydrate structures. 

The above (l)-(3) exceptions do not involve natural gas compounds and therefore are not described in any detail, but rather just mentioned in passing. The reader is referred to reviews by Davidson (1973), Davidson and Ripmeester (1978), and the papers of Jeffrey (1984), Dyadin et al. (1991), Udachin and Ripmeester (1999) and Udachin et al. (2001a) for further details on the less common hydrate structures of other compounds. The relevance of other compound structures is becoming increasingly of interest in areas of refrigeration, gas storage, and gas separation using clathrate hydrates. 

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