Investigation into the strength and source of the memory effect for cyclopentane hydrate

The memory effect for cyclopentane hydrate formation has been investigated for various degrees of superheating and time periods. It was found that provided the superheating above the equilibrium temperature for cyclopentane hydrates (7.7 °C) was no more than 2–3 °C, we could consistently obtain hydrates much faster during cooling to 0.0 °C than if hydrates were formed from the liquids for the first time. The memory effect did not always disappear with as much as 8.4 °C superheating for 20 min, or with 1.5 °C superheating for 20 h. It was also found that transference of a small amount of water from melted cyclopentane hydrates (made with no more than 2–3 °C superheating) to a much larger amount of fresh water and cyclopentane, with no previous cyclopentane history, initiated cyclopentane hydrate formation significantly faster than using the unspiked fresh water alone. This suggests that the memory effect is in the bulk water phase and is probably due to residual clathrate hydrate structure.

► Cyclopentane hydrate formation is kinetically very slow even at 0.1 °C.
► The memory effect for the reformation of cyclopentane hydrate was found to diminish as superheating increased.
► Results suggest the memory effect is probably due to impurities or residual hydrate structure in the water.