Phase Equilibria of CO₂ and CH₄ Hydrates in Intergranular Meso/Macro Pores of MIL-53 Metal Organic Framework

Abstract

The formation of gas hydrates in porous media is expected to bring out beneficial properties for gas storage and separation. Appropriate combined use of both gas hydrate and highly porous metal organic frameworks (MOFs) can be useful for achieving advances in the field of gas storage and separation. This makes understanding the behavior of gas hydrates in the confining pores of MOF crucial. The formation and phase equilibria of CO 2 and CH 4 hydrates in MOF were investigated using MIL-53 MOF through low-temperature synchrotron high-resolution powder diffraction (HRPD) and P−T traces. MIL-53 has both intrinsic micropores and intergranular meso/macropores. Gas hydrate forms in meso/ macropores, and its thermodynamic behavior is relatively inhibited compared to its behavior in bulk phase due to reduced water activity. However, a strong CO 2 dissolution appeared instead of gas hydrates in the intrinsic micropores of MIL-53. This led to a notable phenomenon in which the cooling and heating lines in the P−T trace curves of CO 2 hydrate did not intersect near the dissociation point of CO 2 hydrate.

Illuminating solid gas storage in confined spaces – methane hydrate formation in porous model carbons

“…the dissociation in the confined nanospace is slightly promoted compared to the bulk system. This observation can be attributed to the geometric change of water activity in the confined nanospace as described by Handa et al 10 A similar behaviour was observed for gas hydrates confined in metal-organic-framework MIL-53(Al) 26 and porous glasses. 27…”

Promoting Methane Hydrate Formation for Natural Gas Storage over Chabazite Zeolites

“…Although the difference in dissociation temperature (system without zeolite versus system with zeolite) is nearly commensurate with the precision of the HP-DSC (±0.5 °C), the trend is distinct for each zeolite with small deviations. Studies in the literature found that a decrease in hydrate dissociation temperature correlates to thermodynamic inhibition, which can be caused by hydrates forming in a confined space, such as the interparticle spacing, restricting the water activity and in consequence shifting the phase envelope. , To reiterate, the pores of both zeolites in this study (∼0.74 nm, shown in nitrogen adsorption isotherms at 77 K in Figure S5) are too small for hydrate formation (structure I unit cell size 1.2 nm) to take place within the pores; thus, the formation is most likely taking place in the interparticle spacing.…”

Methane Hydrate in Confined Spaces: An Alternative Storage System

“…Kim et al. evaluated the methane hydrate formation in metal organic framework MIL‐53 . Despite the presence of microporosity, methane hydrates could only form in meso‐ and macropores due to steric restrictions (MIL‐53 pores are ≈0.6 nm while sI hydrate lattice is ≈1.2 nm).…”