Composite Promoter System for Enhancing the Formation Kinetics of Tetrahydrofuran-Methane sII Hydrates under Static Conditions

Abstract This study developed a composite promotion system (sodium cocoyl glycinate (SCG) + phosphatidylcholine (PC-70) + graphene) suitable for static conditions, aiming to enhance the kinetics of sII-type hydrate formation and CH4 storage performance. The effects of thermodynamic promoter (TP) types, concentrations, and the addition levels of PC-70 and graphene on hydrate formation were systematically investigated. Experimental results indicate that under static conditions (500 ppm of SCG), tetrahydrofuran (THF) significantly outperforms other common soluble TPs (such as 1,3-dioxolane, 1,3-dioxane, cyclopentylamine (CPA), and tetrahydropyran (THP)) in accelerating CH4 hydrate formation. As the THF concentration increases from 5.0 mol % to 6.18 mol %, both hydrate gas storage capacity and formation kinetics show continuous improvement. Moderate addition of PC-70 effectively promotes hydrate crystal growth; however, its promoting effect weakens and begins to inhibit nucleation when the concentration exceeds 0.5 wt %. The introduction of trace amounts of graphene (500 ppm) significantly increases hydrate nucleation sites, reducing the induction time from 1.02 to 0.08 min. At 283.15 K and an initial pressure of 7.2 MPa, this composite system enables instantaneous hydrate nucleation, achieving a gas storage capacity of 110 v/v within 16 min─equivalent to 97% of the theoretical capacity. Furthermore, the incorporation of graphene not only effectively suppresses foam formation during hydrate decomposition but also accelerates the rupture and dissipation of existing foam. This research provides systematic experimental evidence and mechanistic insights for developing efficient, controllable, and low-energy CH4 hydrate storage and transportation enhancement technologies.