Molecular Dynamics Simulation Study Of Factors Influencing Carbon Dioxide Hydrate Formation

Replacement of natural gas hydrate with carbon dioxide is an important method to realize effective methane extraction and carbon dioxide storage.Storage of carbon dioxide in the form of hydrate is a green way to achieve carbon emission reduction.As a common gas hydrate,the study of the formation process of CO₂ hydrate is of great significance for the basic research and gas storage of hydrate.This article adopts the method of molecular dynamics simulation system of CO₂ hydrate formation is established,the research object,the molecular concentration,pressure,temperature and additives on the hydrate formation,the influence of different components in the process of simulating structure change,exercise behavior and system parameters such as energy,write hydrate cage structure recognition algorithm,to explore the mechanism of CO₂ hydrate formation from the molecular level.The simulation results show that many types of cages are generated in the CO₂ hydrate system,among which 4¹5¹⁰6² cages are the most numerous and exist stably under the experimental conditions.The formation rate and amount of CO₂ hydrate are sensitive to the concentration of guest molecules.Increasing the concentration of guest molecules can shorten the induction time of hydrate nucleation and increase the amount of hydrate formation.The formation of CO₂ hydrate is sensitive to the change of temperature.The decrease of temperature can effectively promote the formation of CO₂ hydrate,while the change of pressure has little effect on the formation of CO₂ hydrate.The simulation results show that both Na Cl and KCl can inhibit the formation of CO₂ hydrate,and the tetrahedral cluster structure of water molecules is destroyed by the electrostatic action of ions.The higher the mass concentration of salt ions,the less the number of hydrate cages.The inhibition effect of the two inorganic salts on the formation of CO₂ hydrate is Na Cl>KCl.In the simulation group,the optimum concentration of ethylene oxide（EO）to promote the formation of CO₂ hydrate is 12 wt%.When the concentration is lower than 12 wt%,the promotion effect increases with the increase of EO concentration.When higher than 12 wt%,ethylene oxide can still promote the formation of carbon dioxide hydrate,but the promotion effect decreases,and more ethylene oxide hydrate will be generated in the system.Thetrahydrofuran（THF）can effectively promote the formation of CO₂ hydrate,significantly shorten the induction time of hydrate nucleation,and increase the number of hydrate cages in the system.However,when the mass concentration of THF increased from 5 wt%to 10 wt%,the promoting effect of THF decreased,the number of system CO₂ cages decreased,and the number of THF cages increased.The promoting effect of two kinds of small organic molecules on the formation of carbon dioxide hydrate at the same mole fraction is THF>EO,the research results have a certain guiding significance for the balance between the amount of accelerator and the use effect.