Sequestering carbon dioxide into complex structures of naturally occurring gas hydrates

Area of Science:

• Geochemistry
• Materials Science
• Environmental Science

Background:

• Vast methane (CH4) hydrate reserves exist in continental margins and permafrost.
• Converting CH4 hydrates to carbon dioxide (CO2) hydrates offers dual benefits: CH4 resource and CO2 storage.

Purpose of the Study:

• Investigate the guest-induced swapping phenomenon in structure I (sI) and structure II (sII) CH4 hydrates.
• Assess the potential for CO2 sequestration using this hydrate conversion process.

Main Methods:

• Spectroscopic analyses were employed to study the swapping phenomenon in sI and sII CH4 hydrates.
• Experiments utilized direct application of binary N2+CO2 guests and pure CO2 guests for comparison.

Main Results:

• A direct N2+CO2 guest mixture yielded an 85% CH4 recovery rate in sI CH4 hydrates, surpassing the 64% rate with pure CO2.
• The N2+CO2 method eliminates the need for CO2 separation and purification.
• sII CH4 hydrates underwent a spontaneous structure transition to sI during CO2 replacement, increasing CH4 recovery due to altered cage dynamics.

Conclusions:

• The direct use of N2+CO2 mixtures for CH4 hydrate conversion is a promising, economically feasible approach for simultaneous CO2 sequestration and CH4 recovery.
• Understanding guest-cage interactions in hydrate structures is crucial for developing effective hydrate-based technologies.