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

The formation of gas hydtates 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 CO2 and CH4 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 CO2 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 CO2 hydrate did not intersect near the dissociation point of CO2 hydrate.