Molecular Dynamics Study on the Regulation of Carbon Dioxide Hydrate Nucleation and Growth by Sodium Dodecyl Benzene Sulfonate

Technologies based on natural gas hydrates are regarded as highly promising new approaches for capturing carbon dioxide from fuel and flue gas mixtures, carbon dioxide sequestration, cold energy storage, and seawater desalination. However, because of the slow formation kinetics of carbon dioxide hydrates and the low conversion rate of water into hydrate, the practical applications of these technologies remain limited. In this paper, molecular dynamics simulations are employed to separately construct a pure water system without additives and a composite system containing the anionic surfactant sodium dodecylbenzenesulfonate (SDBS), in order to investigate the regulatory role of SDBS in the nucleation and growth stages of carbon dioxide hydrates. By analyzing the hydrate formation state through the F4 order parameter and the number of cages, we find that, in the presence of SDBS, the growth trends of F4 and the number of cages are more stable, which may be attributed to the partial embedding of SDBS molecules, enhancing the structural stability of hydrate cages and promoting the formation of a hydrogen-bond network. However, under the current simulation time scale, in one simulation case the bubble does not completely dissipate because of the influence of interfacial tension. This phenomenon indicates that, while SDBS promotes hydrate formation, it may also introduce additional complexity by excessively stabilizing the bubble, suggesting that the balance between bubble stability and promoter effectiveness still requires further investigation. This study elucidates, at the molecular level, the dynamic regulatory mechanism of SDBS on hydrate formation, and the results not only deepen the understanding of surfactant action mechanisms but also provide a key theoretical basis and new design ideas for the future design of high-performance hydrate promoters or inhibitors.