Molecular Simulation Of The Effect Of Ring Compound-Accelerators On The Coal Bed Methane Hydrate

Coal bed methane reserves are abundant,and the use of hydrate based technology for gas separation can make it an important potential new energy for development.In turn,this paper uses molecular simulation methods to study the stability of CBM hydrates in different simulation systems.The main models of the research include:methane-nitrogen CBM hydrate,in cyclopentane,tetrahydropyran,tetrahydrofuran are used as a promoter to build methane-nitrogen coalbed methane hydrates,and methane-nitrogen coalbed methane hydrate with different methane proportions under cyclopentane accelerator.The main research work and results are as follows:(1)Through quantum chemistry and molecular dynamics simulations,calculate the stabilizing energy of CH₄ and N₂ in the formed SII mixed gas hydrate crystal holes,respectively.And compare the difference between the stability of mixed gas hydrate and single-component gas hydrate.It was found that CH₄molecules are suitable for 5¹² crystal holes,and N₂ molecules can exist in both 5¹²and 5¹²6⁴ crystal holes.From the viewpoint of stability,it can be seen that the micro structure of the obtained CBM hydrate is related to the guest molecular class involved in the construction of the CBM hydrate lattice.(2)Through the molecular dynamics simulation,simulate the difference in the stability of CBM hydrate when the same number of methane molecules and nitrogen molecules occupied small crystal cavities under the action of three different types of accelerators.For the methane-nitrogen CBM hydrate containing THP that cannot achieve good promotion,the destruction of the hydrogen bond network structure of the H₂O molecule leads to the decomposition of the coal bed methane hydrate,and the destruction of the hydrogen bond network structure appears from the outer layer to the inside the layer gradually evolves.Due to the destruction of the hydrogen bonding network structure,some methane molecules and nitrogen molecules are enriched or escaped with different degrees of chaos.For methane-nitrogen CBM hydrate,cyclopentane is a good accelerator.Compared with THF,methane molecules and nitrogen molecules can generate a more stable cell structure under the same temperature and pressure simulation environment.(3)Simulated the stability of CBM hydrates with different component concentrations under the cyclopentane accelerator,and compared the influence of the occupancy of cyclopentane on the stability of CBM hydrates.When the occupancy rate of cyclopentane is less than one,the large crystal hole is vacant,and the spatial mean square displacement of the nitrogen molecules that can exist in the small crystal hole and the large crystal hole vacancy position are not fixed,so the CBM hydrate structure collapses.And when the occupancy rate of methane molecules is greater than the occupancy rate of crystal holes of nitrogen molecules.The small molecular diameter of the methane molecule causes the size of the unit cell to be further increased,and the stability of the interconnected hydrogen bonding network structure decreases,which increases the probability of the CH₄molecule diffusing between the crystal holes,thereby reducing the stability of the hydrate.