Molecular insights into the performance of promoters for carbon dioxide hydrate.

ABSTRACT

Hydrate-based CO2 storage is a cost-effective and environmentally friendly approach to reduce carbon emission, and the addition of hydrate promoters has shown a promising avenue for enhancing CO2 hydrate formation. In this work, the promotion mechanism and promotion performance of five different hydrate promoters (denoted as DIOX, CP, THF, THP, and CH) were investigated and compared by first-principles calculations and molecular dynamics simulations. The results show that the hydrate promoters prefer to singly occupy 51264 cages of the sII hydrate, and CO2 molecules can singly occupy 512 cage or multiply occupy 51264 cages. The cohesive energy density indicates that the optimum CO2 storage capacity can reach up to ∼28 wt%. The stabilization effects of hydrate promoters on the hydrate stability should follow the order of CP > CH > DIOX > THF ≈ THP. The hydrate promoters can increase the water-water interactions, and the molecular diffusivity shows that the dynamic stability of the hydrates is THP ≈ CH > CP > DIOX > THF. Further, the hydrate promoters can accelerate the hydrate formation kinetics, which reduce the induction time and increase the nucleation and growth process.