Construction and Parametric Determination of a Thermodynamic Model for Heterogeneous Nucleation of Tetrahydrofuran Hydrate on Solid Surfaces Based on Classical Nucleation Theory

Introduction: Heterogeneous nucleation at the solid/liquid interface is the rate-limiting step in hydrate formation, yet existing classical nucleation theory (CNT) models rely on empirical parameters and consider only contact angle, neglecting the complex effects of solid surface chemistry, such as surfactant adsorption and modification on interfacial thermodynamics. The mechanistic basis for how solid/liquid interfacial thermodynamic parameters quantitatively effect hydrate nucleation remains unresolved.

Methods: Building upon static nucleation experiments of tetrahydrofuran (THF) hydrate conducted on metal substrates with surfactants, nucleation statistics were analyzed via cumulative nucleation probability, from which experimental nucleation rates and lag times were extracted using an exponential fitting model. Contact angles and interfacial tensions (hydrate/solution, substrate/solution) were measured and combined with Young’s equation and the Berthelot mixing rule to determine solid/hydrate interfacial tensions. These parameters were used to compute critical cluster sizes, nucleation free energy barriers, and kinetic pre-factors. The thermodynamic model was subsequently corrected using Gibbs free energy or availability function approaches to incorporate surfactant-induced interfacial modifications beyond contact angle alone.

Results: Quantitative analysis revealed that solid/liquid and hydrate/liquid interfacial tensions and contact angles exert strong, coupled control over nucleation free energy barriers and critical cluster size, producing orders-of-magnitude variation in predicted nucleation rates across systems. Critically, anionic surfactants were found to suppress heterogeneous nucleation on metal surfaces by elevating the solid/liquid interfacial energy, whereas cationic surfactant promoted nucleation by reducing hydrate/liquid interfacial tension, a differentiated mechanism that kinetic mass-transfer theories alone cannot explain.

Conclusions: A corrected heterogeneous nucleation thermodynamic model was established with experimentally back-calculated parameters, enabling quantitative prediction of nucleation behavior from interfacial properties. This framework provides a mechanistic thermodynamic basis for rationalizing and designing synergistic substrate–surfactant systems for controlled hydrate formation.