Propane Clathrate Hydrate Formation Accelerated by Xenon

Experiments are reported that show propane is incorporated into clathrate hydrate cages much more rapidly using propane-xenon mixtures than for pure propane gas. Uptake rates for pure propane type II clathrate hydrate, pure xenon type I clathrate hydrate, and propane and xenon binary type II clathrate were studied for several different synthesis procedures. Upon adding a 0.92 xenon:propane ratio gas mixture to ice particles, the time required for achieving 62% of the theoretical yield of propane enclathration is 20 min, versus 3 days for pure propane. Although the acceleration of clathrate formation decreases as xenon is depleted, enhancement continues even after the composition falls below 3% Xe. It appears that xenon serves to nucleate the dodecahedral 5(12) cages while propane nucleates the larger 5(12)6(4) cages. The type II xenon-propane structure is not only more thermodynamically stable than either pure hydrate; it is also formed much more quickly than propane clathrate, nearly as fast as type I xenon clathrate.