A novel method to improve the gas storage capacity of ZIF-8

Abstract

In this work a novel method for enhancing the gas storage capacity of metal-organic frameworks (MOFs), i.e. saturating the MOF with a suitable quantity of water and forming hydrates in it, was proposed. Commercialized ZIF-8 was adopted as it is very stable under an atmosphere of water. The adsorption and hydrate formation behaviors of methane in wet ZIF-8 with five different water contents (0.0%, 16.3%, 27.7%, 30.6%, and 35.1%, mass percentages) were investigated under hydrate formation conditions and the storage capacities of both ZIF-8 frameworks and ZIF-8 particle beds were determined. Our results show that hydrates can form in wet ZIF-8 pores and thus increase the overall storage capacities of both ZIF-8 frameworks and ZIF-8 particle beds remarkably. The contribution of hydrates to the total gas uptake of a ZIF-8 framework can be as high as 45%. Compared with dry ZIF-8 frameworks, the net storage capacity of the wet analogue with a water content of 35.1% increases from 5.954 to 9.304 mmol g À1 at 269.15 K and 2.85 MPa, in other words, raised by more than 56%. The ideal volume storage capacity of the wet ZIF-8 framework can achieve more than 190 V/V at 3.0 MPa or so, 7% higher than the DOE target (180 V/V) for methane storage. In addition, our SEM measurements and XRD analysis demonstrate that ZIF-8 is stable during the saturation and hydrate formation processes, illustrating that it can be used repeatedly.

Methane Hydrate in Confined Spaces: An Alternative Storage System

“…On the contrary, hydrophobic MOFs promote methane hydrate formation, although the hydrate growth takes place in the external surface or in the interparticle space (see Figure ). These systems where water is excluded from the inner cavities (for instance ZIF‐8) can be used as a dual system with methane physisorption in the inner empty cavities and methane hydrate formation in the interparticle space, the extend of hydrate formation being tailored by the amount of water incorporated ,…”

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

“…Specifically, Mu et al reported that the methane storage capacity of one kind of MOF (ZIF-8) can be increased to 45% with the formation of methane hydrate in the ZIF-8. 38 Such a significant increase in gas sorption raises the possibility of two contributions: the inclusion of gas in the gas hydrates' water cages and the inclusion of gas in the intrinsic micropores of MOFs. These two different mechanisms for molecular capture might indicate a new strategy for gas storage and separation, which could lead to more complex patterns from mutual interactions.…”

Separation of Methane/Ethylene Gas Mixtures Using Wet ZIF-8

“…The difference between the adsorption amounts of C 2 H 4 and CH 4 shows great promise for their separation. In addition, Mu et al 11 measured the adsorption and hydration behavior of CH 4 in wet ZIF-8 with five different water contents under hydrate formation conditions, and the overall storage …”