Influence Of Microstructure On Gas Adsorption Difference Between Soft And Hard Coal

In order to study the influence of the microstructure to the adsorption law o-f soft coal and hard coal,typical soft and hard coal?anthracite coal and coking coal?were collected from JiuLishan coal mine and PingDing shan coal mine.T-hrough the static adsorption experiment,the adsorption quantity of the soft and h-ard coal at each pressure equilibrium point is obtained,the adsorpion isotherm c-urves were drawn,and the adsorption constants“a”and“b”were obtained,based on the above parameters,the difference of adsorption property between soft and hard coal is compared.The higher the degree of damage is,the greater the diff-erence in the adsorption constant of the soft and hard coal with the same coal rank.For example,the difference of“a”value between Jiu LiShan soft and hard coal is 3.996 ml.g^-1,while that between Pingdingshan soft and hard coal is onl-y 1.484 ml.g^-1.The average degree of fitting of 7 kinds of adsorption models t-o the adsorption of soft and hard coal:D-A>Toth>E-La-ngmuir>L-F>Freundlich>B-ET>Langmuir,the fitting degree of Langmuir adsorption model is the lowest.The difference of molecular structure between soft and hard coals with different metamorphic and deformation was measured by X ray diffraction?XRD?and micro-fourier transform infrared spectroscopy?FTIR?.Finding that all the net spacing d₀₀₂02 of soft is less than that of hard coal,the ductility La and Lc as well as nucleus size La/Lc value of soft coal were higher than hard coal,The content of oxygen functional groups and aliphatic hydrocarbon content of soft coal are lower than hard coal,but the amount of C=C is more than hard coal,which means that the tectonic stress increases the order of the crystal structure of the coal,the volume of the crystal becomes larger,the functional groups fall off,the basic unit structure of the aromatic ring condensation becomes larger,and tends to be flat.With the increase of coal rank,the crystal nucleus has a similar evolution.The changes of these structures further illustrate the existence of dynamic metamorphism.The La/Lc value of grain size can be used as an index to measure the degree of coal metamorphism and to distinguish whether or not it occurs.Through the low temperature liquid nitrogen adsorption and CO₂ adsorption experiment,the specific surface area,pore volume,pore size distribution and adsorption loop type difference of soft and hard coal under 10nm microporous were studied,finding that holes below 2nm contributed most of the coal surface area,and it can also be speculated that some micropore is slit holes between the basic structure unit or cylindrical hole surrounded by the aromatic ring.Molecular dynamics simulation software Materials-Studio was used to simulate the effects of different molecular structure,pore structure and the pore under 2nm on the adsorption of coal.It is found that the increase of ductility is helpful to the adsorption of coal,and the degree of stacking,the oxygen-containing functional groups and defects on the surface of the structure are not conducive to the adsorption,and pore size has a great effect on the adsorption.The adsorption capacity of 1.5nm pore was biggest,the value is6.161g/g,and the adsorption amount of 1nm pore was lowest,the value is 3.990g/g.The adsorption rate and adsorption capacity of the holes under 2nm were significantly higher than that of coal,and can reach equilibrium faster than the latter.At the same time,it is found that the La/Lc value is can be used as a criterion to judge the adsorption property and metamorphism of coal.