Thermal transformations and dissociations in polycrystalline CO₂hydrates

Area of Science:

• Materials Science
• Physical Chemistry
• Computational Chemistry

Background:

• Carbon dioxide (CO2) hydrates are crucial for CO2 sequestration and natural gas recovery.
• The stability of CO2 hydrates is paramount for their practical applications.

Purpose of the Study:

• To investigate the thermal dissociation and cage transformations in polycrystalline CO2 hydrates.
• To establish machine learning frameworks for predicting CO2 hydrate dissociation behavior.

Main Methods:

• High-throughput molecular dynamics simulations.
• Machine learning (ML) models.
• Analysis of cage structures and transformations.

Main Results:

• Melting points of CO2 hydrates are determined by predominant microstructural cages (5^12, 5^12 6^2, 4^1 5^10 6^3).
• Heating induces a reduction in clathrate cages and large-scale reformations via 28 types of cage transformations.
• Water molecule dynamics (removal, insertion, rotation) drive cage transformations, with specific cages (5^12, 5^12 6^2, 4^1 5^10 6^3, 4^1 5^10 6^2) being frequently involved.

Conclusions:

• Thermal dissociation of CO2 hydrates involves extensive, mechanism-driven cage transformations.
• Machine learning frameworks can effectively predict melting points and dynamics of CO2 hydrate dissociation.