Tannic Acid as an Efficient Green Promoter for Methane Hydrate Formation

Natural gas hydrates have been widely recognized as a promising option for natural gas storage and transportation due to their high gas storage density and moderately demanding operating conditions. However, large-scale deployment remains limited by slow hydrate formation kinetics, prolonged induction periods, and insufficient gas storage capacity. Developing efficient and environmentally benign promoters is therefore essential for advancing hydrate-based storage technologies. This work investigates tannic acid, a natural and sustainable compound, as a novel hydrate promoter by integrating high-pressure reactor experiments with molecular simulation. Experimental results demonstrate that, under specific conditions, 5 wt% tannic acid reduces the induction time for hydrate nucleation by approximately 50% and significantly increases both gas uptake and final hydrate yield, confirming its strong promotion capacity. To elucidate the underlying mechanism, molecular dynamics simulations were performed. The simulations verify that tannic acid facilitates efficient nucleation and accelerates subsequent hydrate growth, in agreement with the experimental observations. Mechanistic analysis indicates that tannic acid molecules adsorb onto methane bubble interfaces via their characteristic three-dimensional “hand-shaped” architecture, effectively wrapping the bubbles. This interfacial configuration does not hinder mass transfer; rather, it enhances the transport of methane from the gas phase to the liquid phase, enabling more methane molecules to escape the bubble phase and dissolve into the aqueous phase. Further simulation analysis reveals that tannic acid captures and locally enriches dissolved methane molecules, lowering their mobility and restricting free diffusion in the liquid phase. This confinement leads to the formation of methane-rich microdomains. The resulting “solubilization–capture–enrichment” effect substantially reduces the nucleation energy barrier and promotes rapid formation and growth of hydrate nuclei. Overall, this study clarifies the promoting efficiency of tannic acid across macroscopic and molecular scales and elucidates its microscopic mechanism of action. The findings provide theoretical guidance and new molecular-design insights for developing high-performance, environmentally friendly hydrate promoters suited for chemic al and energy engineering applications.