Research On The Adsorption And Desorption Mechanism Of Coalbed Methane

The desorption mechanism of Coal bed methane (CBM) in coal-based adsorbents is one of the critical problems in today's exploitation of CBM. In view of the lack of theoretical research on desorption home and abroad, the research includes the following several main aspects:1. Based on a survey of the available adsorption equipment, a simulated super-weight equipment of adsorption and desorption is designed, manufactured, tested and used;2. Through super-weight experiments on absorption and desorption of CBM, data of absorption and desorption of the coal in the major CBM exploitation areas in our country are collected;3. Through mathematical analysis,and the fitting of the experimental data, reliable mathematical models of absorption and desorption are derived;4. Through the analysis of adsorbate, sorbent and their interface features, mathematical models reflecting the process of the adsorption and desorption of CBM are derived, using the fundamental theories of physical chemistry, and the established models are checked, the parameters are analyzed and confirmed in terms of physical significance.Conclusions:1. The processes of adsorption and desorption of CBM are irreversible. The process of desorption lags behind that of adsorption;2. The adsorption and desorption curves of CBM are all of ModelⅠof Brunauer adsorption isotherm. The mathematical expressions that fit well into the experimental results(R2≥0.9) include Langmuir equation, exponential function, logarithmic function,and Weibull function, among which Weibull function is of the highest fitting degree(R2≥0.99)with the smallest relative error (Δ<0.5%); 3. Based on the analysis of the Lenard-Jones potential function of medium surface and the use of coverageθfunction, it is established that the intensity of the porous solid sorbent(coal) and the adsorbate(CH4) is determined by the scale of molecules (The width of half pore is r),and that the surface energy distribution of coal, in agreement with Weibull function, is unsymmetrical, thus the mathematical models of adsorption and desorption are derived: V = V0 ?[1?exp(?bPq)] V0 = the largest adsorption amount b= change of adsorption heat q= the unsymmetry of pores4. According to the change factors of adsorption enthalpy (b)in Weibull function model, the desorption is classified into decompression desorption, metathesis desorption, pervasion desorption, heating-up desorption and electromagnetically induced desorption, etc.;5. It is confirmed that desorption amount and adsorption amount of CBM are not interrelated. The relation between desorption amount and pressure can be formulated by mathematical expressions;6. Based on the analysis of the CBM exploitation rate, it is concluded that the rate is solely determined by adsorption heat in desorption process.