Stabilizing effect of tetrabutylammonium bromide on CO2 hydrate in kaolinite nanopores: A molecular dynamics study under static and flow conditions

Abstract

The stability of CO₂ hydrate in clay-rich porous media is fundamental to the safety of geological CO₂ storage. While the TBAB is known as hydrate promoter, its stabilizing effect under the combined influence of thermodynamic condition and dynamic flow remains poorly understood. This study systematically investigates the stabilizing effect of TBAB on CO₂ hydrate stability in the kaolinite pores by molecular dynamics simulation across a range of temperature (255–295 K) and pressure gradients (0–50 MPa/nm). It is found that TBAB mitigates hydrate decomposition by forming a continuous, protective TBA⁺-CO₂-H₂O ternary composite structure near the hydrate. Innovatively, it is found that the stabilizing mechanism is non-monotonic with respect to flow. The moderate shear flow could enhance stability by organizing TBA⁺ ions into a more effective barrier, whereas high flow rates disrupt this layer. Similarly, high temperature facilitates the escapement of CO₂ from the ternary composite structure accelerating hydrate decomposition. These molecular-level insights offer crucial guidance for practical applications, informing the selection of favorable temperature conditions and suggesting that moderate injection flow rates may contribute to enhanced storage security. Ultimately, this work provides crucial insights for developing additives to ensure the long-term safety and efficiency of hydrate-based CO₂ storage.