Molecular insight into the decomposition mechanism and stability of CO2 hydrate in the symmetric non-flat double-plate porous media system

Abstract

Unveiling the decomposition mechanism and stability of hydrate in porous media sediments is the fundamental issue related to hydrate-based CO2 capture and sequestration. In this work, Molecular Dynamics (MD) simulations were performed to study the decomposition mechanism and stability of CO2 hydrate in the porous media of symmetric non-flat double-plate system and explore its mass transfer process. The model of CO2 hydrate in porous media possessing symmetric non-flat double-plate structure was constructed using square quartz (SiO2) as the single crystal material of porous media, illustrating the decomposition mechanism and stability law of CO2 hydrate in such media system. Simulation results indicate that there exists no pretty noteworthy discrepancy between CO2 hydrate in the symmetric non-flat double-plate porous media system and pure CO2 hydrate at the aspect of the decomposition process and sequence. The decomposition process can be divided into two stages: initial cage destruction and CO2 bubble evolution. The decomposition order proceeds in an outside to inside manner generally, with CO2 hydrate decomposition in the middle layer and diagonal region taking priority. Furthermore, the distance between media layers exerts a prominent influence on CO2 hydrate decomposition, which larger distance motivates the decomposition of CO2 hydrate easier. The results also indicated that, compared with pure water system, the stability of CO2 hydrate is greater in the symmetric non-flat double-plate porous media system, with the extreme values of DC reaching 0.64 times only than pure water system. Additionally, CO2 hydrate displayed a stronger stability in the confined space. These findings are beneficial for understanding the decomposition mechanism and stability of CO2 hydrate and provide an interesting insight into geological CO2 sequestration in sediments.