Freezing-Memory Effect of Water on Nucleation of CO₂ Hydrate Crystals

Abstract

We measured the times to nucleate CO 2 hydrates from CO 2 dissolved water under pressure and 8.6 K supercooling using different methods to prepare the water. These times ranged from 50 min to more than 7200 min, depending on the preparation method. The nucleation rates were calculated by fitting the observed nucleation probability distributions to a nucleation rate equation. The nucleation rates significantly increased when the water had previously frozen as ice and melted (freezing-memory effect), except when the meltwater was heated to 298 K before nucleation. The nucleation rates also increased with O 2 -saturated meltwater, but decreased with degassed water.

Generation of micro- and nano-bubbles in water by dissociation of gas hydrates

“…A method to accelerate gas-hydrate formation involves the use of a thermal hysteresis process called the 'memory effect', which is recognized as a shortening of the induction time of gas hydrate nucleation upon recrystallization after the initial crystallization. For example, Parent and Bishnoi [16] and Takeya et al [17] show that the memory effect may occur using meltwater from gas hydrate in the methane (CH 4 )/water system and the carbon dioxide (CO 2 )/water system, respectively. Sloan and Koh [18] summarized the memory effect phenomena, and showed that its behavior was predicted by two previously proposed hypotheses: 1) the hydrate structure remained in solution after hydrate dissociation [16,17], and 2) dissolved gas remained in solution after hydrate dissociation [19].…”

Kinetics of Cyclopentane Hydrate Formation: An Interfacial Rheology Study

“…4.12 and 4.13). Indeed, as demonstrated in other works [38,45], ice can trigger hydrate nucleation because of its hydrogen-bonded crystal structure that is similar to the hydrate crystal structure.…”

“…Multiple researches have evidenced that hydrate nucleation happens at the interface between water and hydrocarbon, where the Gibbs free energy of nucleation is lower. It is explained by the very high concentrations of both hydrate components at this site and the mutual insolubility at low concentrations of hydrocarbons and water [28,38,[44][45][46]. Nowadays, there are basically two conceptual molecular models of hydrate nucleation at the interface: the labile cluster hypothesis and the local structuring hypothesis.…”

“…Two major reasons have been proposed to explain this phenomenon [30,38,45,[48][49][50][51][52]. The first and oldest one is the presence of some sort of residual molecular structures in the aqueous phase that can persist for a long time after dissociation, being transformed in nucleation sites when cooled again.…”

“…In 2000, Takeya et al [45] dissolved CO 2 in water under pressure to analyze the freezing-memory effect. Their experiments showed that the nucleation rates significantly increase when the water is previously frozen as ice and melted, but only if the heat provided to melt water is not too high (below 298 K).…”