Molecular mechanisms by which tetrahydrofuran affects CO2 hydrate Growth: Implications for carbon storage

Abstract

Gas hydrates have attracted significant fundamental and applied interests due to their important role in various technological and environmental processes. More recently, gas hydrates have shown potential applications for greenhouse gas capture and storage. To facilitate the latter application, introducing chemical additives into clathrate hydrates could help to enhance hydrate formation/growth rates, provided the gas storage capacity is not reduced. Employing equilibrium molecular dynamics, we study the impact of tetrahydrofuran (THF) on the kinetics of carbon dioxide (CO2) hydrate growth/dissociation and on the CO2 storage capacity of hydrates. Our simulations reproduce experimental data for CO2 and CO2 + THF hydrates at selected operating conditions. The simulated results confirm that THF in stoichiometric concentration does reduce CO2 storage capacity. This is not only due to the shortage of CO2 trapping in sII hydrate 512 cages, but also because of the favored THF occupancy in hydrate cages due to preferential THF − water hydrogen bonds. An analysis of the dynamical properties for CO2 and THF at the hydrate-liquid interface reveals that THF can expedite CO2 diffusion yielding a shift in the conditions conducive to CO2 hydrate growth and stability to lower pressures and higher temperatures compared to systems without THF. These simulation results augment literature experimental observations, as they provide needed insights into the molecular mechanisms that can be adjusted to achieve optimal CO2 storage in hydrates.