Anomalous self-preservation

FIGURE 3.36 Average rates for methane hydrate samples reaching 50% dissociation at 0.1 MPa, following destabilization by rapid release of P. The anomalous preservation regime is between 242 and 271 K. Square symbols experiments in which P is maintained at 2 MPa, Diamonds 0.1 MPa rapid depressurization tests on sll methane-ethane hydrate, showing no comparable preservation behavior at 268 K. (Reproduced from Stern, L.A., Circone, S., Kirby, S.H., Durhan, W., Can. J. Phys., 81, 271 (2003). With permission from the National Research Council.) 

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Self-preservation is the phenomenon where hydrates can remain stable for extended periods outside the hydrate stable region (Figure 3.36). Self-preservation or anomalous self-preservation has been experimentally observed by a numerous researchers (Davidson et al., 1986 Yakushev and Istomin, 1992 Stern et al., 2001a, 2001b, 2003 Takeya et al., 2002 Kuhs et al., 2005 Shimada et al. 2005). However, little is understood of this phenomenon. The ability to increase and prolong the stability of gas hydrates is desirable for gas storage applications. 

As shown in Figure 3.36, the anomalous preservation region is observed over the temperature range 242-271 K on rapid depressurization to 0.1 MPa. This anomalous behavior has been also called anomalous self-preservation. The latter consists of a short rapid dissociation phase with a release of 5-20 vol%... 

Anomalous self-preservation stabilizes methane hydrate and carbon dioxide hydrate particles at atmospheric pressure at 242-271 K for up to 2-3 weeks. This phenomenon can have implications for natural gas storage. 

Methane hydrate has an unclear property called the self-preservation or anomalous preservation effect, i.e., slow dissociation of the hydrate under thermodynamically unstable conditions. This slow dissociation is thought to be caused by a layer of ice covering hydrate surfaces that forms from the dissociated hydrate. However, little is known about this preservation mechanism. For example, it is still unclear that this effect is not observed between 193-240 K but above 240... 

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