posted on 2024-05-15, 18:23authored byJunghoon Mok, Jonghyuk Lee, Wonjung Choi, Yohan Lee, Yongwon Seo
Guest
replacement technology in the natural gas hydrate layer represents
a cutting-edge approach for achieving carbon neutrality. In this study,
a thorough analysis of the kinetics and mechanisms involved in CH4–CO2 replacement in structure H (sH) hydrates
was conducted. An sH hydrate containing CH4 and methylcyclopentane
exhibited a greater extent of CH4–CO2 replacement than that case of structure I (sI) hydrate under identical
CO2 injection pressures. Time-dependent measurements obtained
via powder X-ray diffraction (PXRD) and 13C nuclear magnetic
resonance (NMR) spectroscopy demonstrated that nearly half of the
initial sH hydrate underwent a structural transformation to become
an sI hydrate within the first hour after CO2 injection.
This accelerated structural transition altered the guest distribution
within the hydrate phase, resulting in improved CH4 recovery
and CO2 storage relative to isostructural CH4–CO2 replacement in sI. The experimental results
revealed a replacement mechanism by which the injected CO2 molecules initially preferred the medium cages of the sH hydrate
to replace CH4 molecules. Upon exceeding a critical CO2 concentration, destabilization of the sH hydrate occurred,
leading to the rapid formation of a new sI hydrate with gas molecules
from the surrounding vapor phase. The study findings enrich our understanding
of the guest exchange behaviors of sH hydrates, with potential implications
for enhanced CO2 storage in natural gas hydrates.