Competitive and synergistic mechanisms of adsorption-hydration during methane storage in the wet ZIF-8 fixed bed

Abstract

The natural gas storage technology based on wet ZIF-8 fixed bed has been proved to have excellent methane storage performance. To reveal the internal competition and synergism mechanism of adsorption-hydration, molecular dynamics technique was employed to simulate the microscopic dynamics process of methane hydrate formation in the ZIF-8 fixed bed with saturated water. Our results indicated that when the diameter of ZIF-8 particles were small, the low water content of the bed would induce the strong adsorption-hydration competition, and apparently inhibit the formation of methane hydrates. When the water content was sufficient, the gas adsorption performance of ZIF-8 solid particles could significantly accelerate the hydrate nucleation, exhibiting the adsorption - hydration synergy. In this case, the hydrate nucleus always took shape outside the region affected by ZIF-8 (within the range of about 10 Å from the surface of ZIF-8) and continuously grew away from the solid surface. Moreover, the simulation results also showed that the particle sizes of ZIF-8 played a vital role on hydrate nucleation/growth velocities and the types of clathrate cages formed, but had little impact on the conversion ratio of water and methane to hydrates.