CO2 sequestration trade-offs in polycrystalline hydrate stability

Abstract Natural gas hydrates (NGHs) offer significant potential for energy recovery and carbon sequestration, yet the thermal stability of polycrystalline CH4-CO2 hydrates (PCCHs) which is critical for CO2-based NGH exploitation, remains poorly understood. Here, we unravel CO2’s role in reshaping the thermal dissociation behaviors of PCCHs via high-throughput molecular dynamics (MD) simulations and machine learning (ML). We demonstrate that CO2 reduces the stability of PCCHs, with a 20% increase in CO2 concentration lowering the melting point by approximately 6 K. Microstructural analysis reveals that this destabilization arises from CO2-induced distortion of 512 cage and formation of unconventional metastable cages. Thermal dissociation occurs via cage transformations and dissociations, where 4151062 and 51262 cages act as hubs for solid–solid restructuring pathway. Crucially, CH4 guest molecules facilitate simpler, faster cage transformations than CO2, which requires complex rearrangements. We further develop a GBDT ML model that accurately predicts PCCH melting points using microstructural information, identifying 512, 51262, and 51063 cages as key predictors. This model provides a practical tool for guiding CO2-based NGH exploitation and designing hydrate storage systems. These insights advance the molecular-level understanding of hydrate stability for CO2 sequestration and NGH recovery. Graphical Abstract