Temperature-Dependent Efficacy of Typical Five-Membered Heterocyclic Promoters in sII CO₂ Hydrate Growth: A Molecular Dynamics Simulation Study

To facilitate CO₂ storage via hydrates, five-membered heterocyclic additives are considered effective promoters to accelerate the hydrate growth rates. Performing molecular dynamics simulations, this study systematically investigates and compares the temperature-dependent promotional efficacy of cyclopentane (CP), tetrahydrofuran (THF), and pyrrolidine (PRD) on sII CO₂ hydrate growth. The results show that the promotional efficacy of CP remains low at temperatures ranging from 264 to 274 K, whereas those of THF and PRD weaken and strengthen with increasing temperature, respectively. According to the independent gradient model based on Hishfeld partition (IGMH) analysis, the intensive interactions between promoter and water molecules in both diffusion and adsorption stages dominate the hydrate growth rate. The subpar promotional efficacy of CP is attributed to its excessive self-diffusion rate and poor interaction with water molecules. The elevated self-diffusion rate with increasing temperature in the diffusion stage should be responsible for the promotional efficacy of THF, whereas that of PRD is governed by the delicate balance between PRD-water and water-water interactions in the adsorption stage. This study elucidates the molecular dynamics underpinning the efficacy of five-membered heterocyclic promoters, a revelation poised to invigorate technologies centered on CO₂ hydrate-based methods.