Synergistic effect of temperature and CO2 concentration on the microscopic evolution of CH4-CO2 binary hydrate

The control and reduction of greenhouse gas emissions have become essential for mitigating the global climate crisis. The method of replacing CH4 in hydrate with CO2 is a promising option for both energy recovery and carbon sequestration in the field of natural gas hydrate (NGH) production. However, the microscopic study on the replacement of CH4 hydrate by CO2 remains not comprehensive and thorough, which restricts its potential application. In this work, molecular dynamics (MD) simulations were performed to investigate and quantify the synergistic effect of temperature and CO2 concentration on the CH4-CO2 binary hydrate evolution process. Results demonstrated that higher temperatures or lower CO2 concentrations promote CH4 hydrate dissociation, while lower temperatures or higher CO2 concentrations enhance CO2 hydrate growth. The synergistic effect of various temperature and CO2 concentration on CH4-CO2 binary hydrate evolution are categorized into three patterns: (I) synchronous growth of CH4 and CO2 cages without dissociation; (II) initial CH4 dissociation followed by regrowth, with delayed CO2 cages formation; and (III) complete CH4 dissociation without CO2 growth. Additionally, key mechanistic insights reveal that gaseous CH4 bubbles accelerate hydrate dissociation, while adsorbed CO2 molecules stabilize hydrate structures to favor the growth of CO2 hydrate and inhibit the dissociation of CH4 hydrate. The findings highlight the significant synergistic effect of temperature and CO2 concentration on the microscopic evolution process and results of CH4-CO2 binary hydrate, which provides guidance of methane recovery and carbon sequestration application.