Molecular dynamic simulations of selective self-diffusion of CH4/CO2/H2O/N2 in coal

2017 Global Conference on Polymer and Composite Materials

材料科学;化学

Song, Y.^1,2 ; Jiang, B.^1,2 ; Li, F.L.^1,2

School of Resources and Earth Science, China University of Mining and Technology, Xuzhou

221116, China^1

Key Laboratory of Coal Bed Methane Resource and Reservoir Formation Process, Ministry of Education, Xuzhou

221008, China^2

关键词: Adsorption energies;    Annealing kinetics;    Canonical monte carlo;    CH4/CO2/H2O/N2;    Diffusion activation energy;    Md calculations;    Self-Diffusion;    Self-diffusion coefficients;   

Others  :  https://iopscience.iop.org/article/10.1088/1757-899X/213/1/012014/pdf
DOI  :  10.1088/1757-899X/213/1/012014

学科分类：材料科学（综合）

来源: IOP

【 摘 要 】

The self-diffusion coefficients (D) of CH4/CO2/H2O/N2at a relatively broad range of temperatures(298.15∼ 458.15K)and pressures (1∼6MPa) under the NPT, NPH, NVE, and NVT ensembles were obtained after the calculations of molecular mechanics(MM), annealing kinetics(AK), giant canonical Monte Carlo(GCMC), and molecular dynamics (MD) based on Wiser bituminous coal model (WM). The Ds of the adsorbates at the saturated adsorption configurations are DCH4CO2H2ON2(NPT, 298.15K, 0.1MPa). The diffusion activation energy (E) is EH2O(1.07kJ/mol)N2(1.82kJ/mol)CO2(2.94kJ/mol)CH4(10.88kJ/mol), indicating that CH4diffusion requires to overcome the highest adsorption energy barrier and N2and H2O to the lowest. The order of different ensembles is DN2(NVE)N2(NVT)≈DN2(NPH)≈DN2(NPT) (TN2(NVE) is remarkable higher than other ensembles when T>418K. The average swelling ratios manifest as H2O (14.7∼35.18%)>CO2(13.38∼32.25%)>CH4(15.35∼23.71%)> N2(11.47∼22.14%) (NPH, 1∼6MPa). There exits differences in D, swelling ratios and E among various ensembles, indicating that the selection of ensembles has an important influence on the MD calculations for self-diffusion coefficients.