Statistical Study of the Memory Effect in Model Natural Gas Hydrate Systems

Abstract

A high pressure automated lag time apparatus (HP-ALTA) was used for the investigation of the controversial memory effect in methane-propane mixed gas hydrates. The instrument can apply a large number of linear cooling ramps to a small volume of sample water under an isobaric condition of up to 15 MPa and record the maximum achievable subcooling for each cooling ramp. Over a hundred nucleation events were recorded for each of the several superheating temperatures used for the dissociation of the gas hydrate in a sample. In total, four different sample cells were used, and the effect of heating time was also studied for two of the four sample cells. A difference between two stochastic nucleation probability distributions was systematically and unambiguously quantified in terms of the most probable difference in the maximum achievable subcoolings. The protocol offers by far the most statistically robust method of quantification of the magnitude of the memory effect in each sample. From the analysis of several thousands of nucleation events, the following conclusions were made: (1) Even though the nucleation phenomena were intrinsically stochastic, a clear bias was observed which supported the existence of the memory effect. In particular, a reduction in the most probable subcooling of at least 4 K was required for positive identification of the memory effect for one of the sample cells. (2) The reduction increased as the superheating temperature was lowered. (3) The magnitude of the memory effect varied substantially among the sample cells used. (4) No significant effect of the heating time was observed in the range studied.

Some current challenges in clathrate hydrate science: Nucleation, decomposition and the memory effect

“…These early observations appear to have been forgotten, but in more recent times memory effects have been observed quite regularly as discussed by Sloan [50], who also promoted the residual structure hypothesis discussed below. Many other researchers have contributed results and suggestions for mechanisms as recently reported by Sowa and Maeda [51]. We think that one can safely conclude that the memory phenomenon has been well documented and supported by many trained observers over a period of more than 100 years.…”

“…In 2015, Sowa and Maeda offered ''Even though the nucleation phenomena were intrinsically stochastic, a clear bias was observed which supported the existence of the memory effect" [51]. This suggests very modest progress in explaining the memory phenomenon, however, they did suggest three leading candidates for explaining the memory effect, and categorized, the by now better defined, deterministic variables suggested by Parent and Bishnoi [54].…”

A 3-In-1 Approach to Evaluate Gas Hydrate Inhibitors

“…The sample was then heated just above hydrate-liquid-vapor equilibrium temperature, at the experimental pressure, to dissociate the initial hydrate [25]. Discussion on crystal formation history is beyond the scope of this paper, but interested readers are referred to the literature on this topic as applied to gas hydrates [27][28][29][30].…”

Kinetics of Cyclopentane Hydrate Formation: An Interfacial Rheology Study

“…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.…”

“…Sowa and Maeda [48], in turn, used a high pressure automatic lag time apparatus (HP-ALTA) to test the memory effect in ethane-propane mixed gas hydrates by four different boats. They concluded that the memory effect do exist, but its amount varied among the boats.…”