煤体甲烷吸附解吸机理研究

发布时间：2018-07-09 10:15

本文选题：温度场 + 密度泛函理论　；参考：《西安科技大学》2014年博士论文

【摘要】：甲烷吸附与解吸是研究瓦斯扩散、渗流、累积和防治煤与瓦斯突出的重要理论基础，是煤矿安全生产的重要研究课题之一。本文通过温度场下甲烷气体两次解吸实验、煤体红外光谱实验和密度泛函理论（DFT）分别从宏观能量和微观结构两方面对煤体中甲烷气体的吸附与解吸机理进行了研究，发现宏观规律和微观量化计算结果之间具有相关性。通过实验数据分析和理论计算完成的主要工作如下：（1）温度是甲烷气体解吸的最重要影响因素。通过宏观温度场下甲烷气体的两次解吸实验分析，结果表明甲烷气体的吸附为物理吸附，没有能级结构。甲烷气体在煤体中的赋存是一个同时包含吸附、解吸、扩散、渗流和累积的动态过程，温度升高会导致煤体中的甲烷气体吸附速度和解吸速度同时增大，解吸气体含量增多，对此动态过程，提出了综合速度概念，综合速度由吸附速度和解吸速度合成，该速度与温度之间是非线性关系。（2）煤对甲烷气体的吸附力为诱导力与色散力。在五种煤样红外光谱数据分析的基础上，采用密度泛函理论（DFT）对瓦斯吸附和解吸进行动力学分析，发现在吸附和解吸过程中，甲烷气体和煤体大分子结构键长、键角、二面角以及密立根电荷的变化，发现吸附过程主要是由于煤分子和甲烷分子之间存在电场相互作用，甲烷分子在吸附过程中被极化，煤大分子自身密立根电荷量也重新分布，煤分子和甲烷分子最终达到电场力相互平衡，吸附力为诱导力各色散力。（3）提出了采用密立根电荷量定量分析吸附空位的方法，对煤体甲烷气体多分子层吸附理论进行了验证。通过对吸附过程的动力学分析，结果显示在吸附过程中起主要作用的是电场力，，整个煤体结构中的密立根电荷量分布发生了明显变化，即分子结构中的电荷分布对煤的吸附性有重要影响，故以密立根电荷量作为煤对甲烷气体的吸附空位的判定依据。计算了甲烷气体的吸附能和吸附势阱深度，发现在同一吸附空位附近有多个吸附平衡位置，对应的吸附距离和吸附能都不同，说明甲烷气体存在多层吸附的可能性。（4）甲烷气体的吸附与解吸动力学过程是宏观能量和微观结构之间相互作用的共同结果。通过宏观实验结论和微观理论分析相互验证，研究宏观规律和微观机理之间的对应关系，温度变化引起甲烷气体宏观能量变化，同时会对甲烷气体的微观吸附结构产生影响，而微观吸附结构的变化又反过来影响宏观压强和煤体结构，即解吸和吸附是宏观因素和微观因素共同作用的结果。
[Abstract]:Methane adsorption and desorption is an important theoretical basis for the study of gas diffusion, seepage, accumulation and prevention of coal and gas outburst, and is one of the important research topics of coal mine safety production. In this paper, the adsorption and desorption mechanism of methane gas in coal is studied from macroscopic energy and microcosmic structure by means of twice desorption experiment of methane gas under temperature field, infrared spectrum experiment of coal and density functional theory (DFT). It is found that there is a correlation between macroscopic law and microscopic quantitative calculation results. The main works are as follows: (1) temperature is the most important factor of methane desorption. Through two desorption experiments of methane gas under macroscopic temperature field, the results show that the adsorption of methane gas is physical adsorption, and there is no energy level structure. The occurrence of methane gas in coal body is a dynamic process including adsorption, desorption, diffusion, seepage and accumulation. The increase of temperature will lead to the increase of adsorption rate and desorption rate of methane gas in coal body and the increase of desorption gas content. For this dynamic process, the concept of synthetic velocity is put forward, which is composed of adsorption speed and desorption velocity, which is nonlinear with temperature. (2) the adsorption force of coal to methane gas is induced force and dispersion force. Based on the analysis of infrared spectrum data of five kinds of coal samples, the density functional theory (DFT) was used to analyze the kinetics of gas adsorption and desorption. It was found that in the process of adsorption and desorption, the bond length and bond angle of methane gas and coal macromolecular structure were long. With the change of dihedral angle and Millikan charge, it is found that the adsorption process is mainly due to the electric field interaction between the coal molecule and methane molecule, the methane molecule is polarized during the adsorption process, and the charge amount of the coal macromolecule itself is also redistributed. Finally, coal and methane molecules reach the equilibrium of electric field force, and the adsorption force is inductive force. (3) the method of quantitative analysis of adsorption vacancy by Milliken charge quantity is proposed. The multilayer adsorption theory of methane gas from coal is verified. Through the kinetic analysis of the adsorption process, the results show that the electric field force plays a major role in the adsorption process, and the distribution of the Milliken charge in the whole coal structure has changed obviously. That is, the charge distribution in the molecular structure has an important effect on the adsorption of coal, so Millikan charge is used as the basis for judging the adsorption vacancy of methane gas by coal. The adsorption energy and potential trap depth of methane gas are calculated. It is found that there are many adsorption equilibrium sites near the same adsorption vacancy, and the corresponding adsorption distance and adsorption energy are different. (4) the adsorption and desorption kinetics of methane gas is the result of the interaction between macroscopic energy and microstructure. The corresponding relationship between macroscopic law and microscopic mechanism is studied through the mutual verification of macroscopic experimental conclusion and microscopic theoretical analysis. The change of temperature leads to the change of macroscopic energy of methane gas, and at the same time, it has an effect on the microstructure of methane gas adsorption. The change of microcosmic adsorption structure in turn affects the macroscopic pressure and the coal structure, that is, desorption and adsorption are the result of both macro and micro factors.
【学位授予单位】：西安科技大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TD712;TD713

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