Bubble nucleation as a non-equilibrium phase transition in CO2/CH4 Hydrates.

Gas hydrate dissociation is a complex non-equilibrium process involving coupled lattice destabilization, gas release, and bubble nucleation, which plays a key role in methane recovery and CO2 sequestration. However, the microscopic mechanism linking hydrate melting and gas-phase formation in multicomponent systems remains unclear. In this work, we employ molecular dynamics simulations to investigate the thermodynamic behavior and bubble nucleation mechanism during the thermal dissociation of heterogeneous CO2/CH4 hydrates. The results show that hydrate melting is a cooperative phase transition governed by the collapse of the hydrogen-bond network, with the apparent melting temperature under continuous heating increasing monotonically with CH₄ fraction. The bubble nucleation process proceeds through three distinct stages: induction, nucleation transition, and stabilization. A strong coupling between hydrate melting and bubble formation is identified, indicating that gas nucleation is directly controlled by lattice dissociation. Comparative analysis reveals a competitive mechanism between CH4 and CO2. CO2 facilitates nucleation by lowering the apparent melting temperature, whereas CH₄ dominates bubble growth due to its higher supersaturation and lower de-solvation barrier. Furthermore, a CO2-induced interfacial enrichment layer is observed, which reduces interfacial tension and suppresses the back-diffusion of CH4, thereby significantly enhancing CH4 aggregation efficiency. This leads to the formation of a "pseudo-core-shell" structure, in which CH4 occupies the bubble core while CO2 is enriched near the interface. In addition, a long short-term memory (LSTM) model is employed to predict the temporal evolution of bubble growth, demonstrating high accuracy and consistency with molecular dynamics results. These findings provide a comprehensive microscopic picture of hydrate dissociation and bubble nucleation in multicomponent systems, offering new insights into non-equilibrium phase transitions and interfacial phenomena in condensed matter systems.