Molecular Dynamics Simulation Of TBAB Semi-clathrate Coalbed Methane Hydrate

With the rapid development of our country's economy,our country's energy consumption is increasing day by day,leading to a series of energy shortages and environmental pollution problems.In response to the country's call for the development of a"low-carbon economy",the use of new energy is particularly important.As a new energy source,natural gas hydrate has become a hot spot for scholars from all over the world.Coal-bed methane is an unconventional natural gas with abundant reserves.However,due to technical limitations,the methane in coal-bed methane has not been rationally used,resulting in a lot of waste of resources.Using the hydrate method to separate gas can improve the utilization rate of coalbed methane,and has unique advantages over traditional gas separation methods.Tetrabutylammonium bromide(TBAB)semi-clathrate hydrate has good stability compared to type I and type II hydrates under the same conditions.The related experiments have been fully studied,but no one has studied the dynamics of its microstructure.Study mechanism.In this study,molecular dynamics simulation was used to analyze the internal microstructure of TBAB semi-clathrate hydrate.Based on the first principles of molecular dynamics,the Monte Carlo method was used to fill the gas in the coalbed methane as guest molecules into the hydrate.In,construct single-component gas hydrate,two-component gas hydrate and three-component gas hydrate models respectively.After optimizing the model,perform molecular dynamics simulation under the canonical ensemble(NVT),and analyze the final conformation,Radial distribution function,mean square displacement,hydrogen bond and interaction energy and other parameters,to study the influence of temperature,guest molecule occupancy and guest molecule interactions on the stability of hydrates,and provide for the development and utilization of coalbed methane Theory support.The main research content and conclusions of this article are as follows:(1)When the set temperature is 220K,240K,260K,280K and 300K,the stability difference of hydrates is analyzed through simulation.When the hydrate is in a low temperature state,it is bound by the hydrogen bonds between water molecules,and the guest molecules move in the hydrate cage.The hydrate cage structure remains intact and the symmetry is good,indicating that low temperature is conducive to the stable existence of the hydrate;(2)Simulate the influence of four kinds of crystal hole occupancy on the stability of hydrate.The occupancy rate is set to 100%,75%,50%and 25%respectively,and it is found that when the occupancy rate of the crystal cavity is above 75%,the hydrate exhibits good stability;when the occupancy rate of the crystal cavity is less than 50%,the hydrate is stable Sex will decline rapidly;(3)Simulating the difference in stability of the three hydrates under the same conditions when methane,nitrogen,and oxygen act as guest molecules.Through comparison,it is found that the stability of methane hydrate is relatively good.This is because the size of the methane molecule is closer to the size of the empty cage of the hydrate,and the support effect of the empty cage is better,which improves the overall stability of the hydrate;(4)Construct four different ratios of methane and nitrogen double-component hydrates,and compare and analyze the stability differences of the four types of hydrates through molecular dynamics simulation.It is found that the hydrates formed under the 44CH₄+4N₂system are the most stable.However,it is not that the higher the methane concentration,the better the stability of the double-component hydrate,and it is also related to the interaction between CH₄and N₂;(5)Through simulation and comparison of the stability of four different ratios of methane,nitrogen,and oxygen three-component hydrates,it is found that when the hydrates are in a stable state,the hydrate with the ratio of 5CH₄+14N₂+29O₂ has the best stability;When the hydrate is in the decomposition state,the hydrate with the ratio of 29CH₄+14N₂+5O₂has the lowest degree of decomposition.