Effects of coal molecular structure on adsorption and diffusion behaviors of coalbed methane

doi:10.11949/j.issn.0438-1157.20151780

Abstract

Abstract:

The effects of microcrystal structures, such as the extension of basic structural unit (L_a) and the number of basic structural unit (N), as well as the surface structures including different types of defects and oxygen-containing functional groups, on the adsorption and diffusion of coalbed methane were investigated. The adsorption amounts were simulated by using the Monte Carlo (MC) method, and the diffusion coefficients of coalbed methane were simulated by using molecular dynamics (MD) simulation. All of the simulations were conducted in the condition of 303 K and 10 MPa. It can be concluded that the adsorption capacity of methane on unit mass of coal decreases with N increasing, as well as the existence of defects and oxygen-containing functional groups. The diffusion coefficient of methane increased with L_a extending and shows a complex process influenced by increasing N. The existence of single-defect and C O was favorable of diffusion of coalbed methane. The coalbed methane was easy to diffuse in larger pore of coal. Finally, the micro model of coalbed methane diffusion for the coal particles of radial heterogeneous was proposed base on the micro-influenced factors and macro performance of the migration of coalbed methane.

Key words: coal molecular structure, coalbed methane, adsorption, diffusion, molecular simulation

摘要：

对煤的芳香单元延展度、芳香单元堆砌层数以及包括不同缺陷和含氧官能团类型的表面结构对煤层气吸附与扩散的影响进行了研究。采用Monte Carlo模拟方法及分子动力学模拟方法分别得到了煤层气的吸附量与扩散系数,模拟温度为303 K,压力为10 MPa。研究结果表明,单位质量的煤对甲烷的吸附量随着芳香单元堆砌层数的增加而降低,缺陷和含氧官能团的存在不利于甲烷的吸附。甲烷的扩散随着芳香单元延展度的增加呈现出一个N形的复杂变化过程,单缺陷和羰基的存在有利于煤层气的扩散,煤结构中大的裂隙更有利于煤层气的扩散。最后,基于煤层气的微观影响因素和宏观运移行为提出了煤颗粒径向不均质的煤层气扩散微观模型。

关键词: 煤分子结构, 煤层甲烷, 吸附, 扩散, 分子模拟

CLC Number:

O647.32

WANG Baojun, ZHANG Lina, LING Lixia, ZHANG Riguang. Effects of coal molecular structure on adsorption and diffusion behaviors of coalbed methane[J]. CIESC Journal, 2016, 67(6): 2548-2557.

王宝俊, 章丽娜, 凌丽霞, 章日光. 煤分子结构对煤层气吸附与扩散行为的影响[J]. 化工学报, 2016, 67(6): 2548-2557.

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