Study Of The Adsorption And Desorption Mechanism Of Methane In Coalbed

Methane adsorption and desorption is one of the important research projects in the coalmine safety production, which is an important theoretical basis for study of gas seepage,diffusion, accumulation and outburst. In this dissertation, the absorption and desorptionmechanism of methane on coal was investigated in micro and macro perspectives bytemperature-program desorption experiments, infrared spectroscopy analysis and densityfunction theory. Based the experimental data and theoretical analysis the main content andcontribution are summarized as follows:(1)The temperature is main factor on the desorption process. The macro temperaturefield of methane desorption experiments result shows that the absorption of gas is physicalone without energy level structure. The occurrence of methane on coal is a dynamic process,which includes the adsorption, desorption, diffusion, seepage and accumulation. The increasetemperature will make an increasing amount of methane in coal. The resultant rate from theabsorption rate and desorption rate will be presented to explain the nonlinear dependence ofthe resultant rate and the heating temperature.(2)The main effect on the absorption of methane is dispersion and induction forces.Based on the infrared spectroscopy data of five types of coal samples, the density functionaltheory was used to analyze the kinetics process of adsorption and desorption, The resultsreveal that the bond length, bond angle, dihedral angle and Millikon charges of the gas andcoal molecule structure are changed in this absorption and desorption process, it is mainly dueto the presence of electric field interaction between coal molecules and methane, methanemolecules are polarized and the Millikon charges of coal macromolecular are changed, itfinally reach the electric force equilibrium of coal molecular and methane.(3)A quantitative analysis method on hollow site is presented that using the Millikoncharges to analysis the adsorption site, the coal multilayer adsorption of methane was checked. The key force is the electric field one in the adsorption kinetics, Millikon charges distributionof coal structure is changed obviously in the process, this means that the Millikon chargesdistribution have a significant impact on the adsorption process. According to analysis theMillikon charges, adsorption site of methane will be determined. The calculation ofadsorption potential well depth and adsorption energy implicate that the same adsorption sitemay correspond to multiple adsorption equilibrium structure of methane, which has differentabsorption distance and energy respectively, it has the possibility to multilayer adsorption.(4)The adsorption and desorption kinetics process of methane on coal is the result of theinteraction between macro energy and micro structure. By means of macro experiments dataand micro theory calculation it is found that it has the corresponding relationship betweenmacro regulation and micro mechanism, the change of temperature will change the macroenergy of gas, and it also will affect the adsorption structure. Conversely, micro structure ofadsorption changed will affect the macroscopic pressure and damage the macro structure ofcoal, i.e. the adsorption and desorption process is the interaction one of macro and microfactors.