Replacement of CH₄ in hydrate form with CO₂ is a candidate for recovering CH₄ gas from its hydrates and storing CO₂. In this work, microsecond molecular dynamics simulations were performed to study the replacement mechanism of CH₄ hydrate by CO₂ molecules. The replacement process is found to be controlled cooperatively by the chemical potentials of guest molecules, “memory effect”, and mass transfer. The replacement pathway includes the melting of CH₄ hydrate near the hydrate surface and the subsequent formation of an amorphous CO₂ hydrate layer. A large number of hydrate residual rings left after the melting of CH₄ hydrate facilitate the nucleation of CO₂ hydrate and enhance the dynamic process, indicating the existence of so-called “memory effect”. In the dynamic aspect, the replacement process takes place near the surface of CH₄ hydrate rather easily. However, as the replacement process proceeds, the formation of the amorphous layer of the CO₂ hydrate provides a significant barrier to the mass transfer of the guest CH₄ and CO₂ molecules, which prevents the CH₄ hydrate from further dissociation and slows down the replacement rate.

Removal of carbon dioxide is an essential step in many energy-related processes. Here we report a novel slurry concept that combines specific advantages of metal-organic frameworks, ion liquids, amines and membranes by suspending zeolitic imidazolate framework-8 in glycol-2-methylimidazole solution. We show that this approach may give a more efficient technology to capture carbon dioxide compared to conventional technologies. The carbon dioxide sorption capacity of our slurry reaches 1.25 mol l⁻¹ at 1 bar and the selectivity of carbon dioxide/hydrogen, carbon dioxide/nitrogen and carbon dioxide/methane achieves 951, 394 and 144, respectively. We demonstrate that the slurry can efficiently remove carbon dioxide from gas mixtures at normal pressure/temperature through breakthrough experiments. Most importantly, the sorption enthalpy is only −29 kJ mol⁻¹, indicating that significantly less energy is required for sorbent regeneration. In addition, from a technological point of view, unlike solid adsorbents slurries can flow and be pumped. This allows us to use a continuous separation process with heat integration.