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

Area of Science:

• Thermodynamics
• Materials Science
• Chemical Engineering

Background:

• Gas hydrates, particularly mixed systems like methane-propane, exhibit complex phase behavior.
• The existence and magnitude of the 'memory effect' in gas hydrate nucleation remain controversial.
• Quantifying nucleation phenomena requires statistically robust experimental methods.

Purpose of the Study:

• To investigate the controversial memory effect in methane-propane mixed gas hydrates.
• To systematically quantify the memory effect using a novel high-pressure apparatus.
• To determine the influence of superheating temperature and heating time on the memory effect.

Main Methods:

• Utilized a high pressure automated lag time apparatus (HP-ALTA) capable of 15 MPa isobaric conditions.
• Applied numerous linear cooling ramps to small water samples, recording maximum subcooling for each nucleation event.
• Recorded thousands of nucleation events across multiple sample cells and superheating temperatures.

Main Results:

• A statistically significant bias supporting the memory effect was observed in nucleation phenomena.
• A reduction in most probable subcooling of at least 4 K was necessary for positive memory effect identification in one cell.
• The memory effect's magnitude varied significantly between different sample cells.
• The memory effect's influence increased as superheating temperature decreased.

Conclusions:

• The memory effect in methane-propane gas hydrates is supported by experimental evidence, despite the stochastic nature of nucleation.
• The magnitude of the memory effect is sample-dependent and influenced by superheating conditions.
• Heating time did not show a significant impact on the memory effect within the studied range.