Macromolecular Structure Of Maceral Composition In Hancheng Mine Area

Coal-bed methane（CBM）is a kind of combustible organic gas mainly composed of methane in coal seams.In the process of coalification,due to the differences of coal-forming materials and coal-forming environment,the maceral of coal rocks in each coal seam is quite different,and the maceral of coal rocks has a great influence on the structure and adsorption of coal body.Therefore,in order to improve the understanding of the influence of coal rock maceral on the adsorption of CBM,and to provide theoretical guidance for favorable area prediction and CBM mining.In this paper,different coal rock maceral samples（vitrinite rich and inertinite rich）in hancheng mining area are taken as the research object.Basic geological data of hancheng mining area are collected.Combined with basic experimental test results and computer molecular simulation technology,the following understandings are obtained after comprehensive analysis:1.The FTIR,XPS and ¹³C-NMR spectra of XS coal samples of vitrinite rich group and SSP coal samples of inertinite rich group were fitted by peak splitting,and qualitative and semi-quantitative analysis was conducted.（1）Aromatic structure absorption band get ortho 2 replace content of Vitrinite-rich coal samples is more than Inertinite-rich coal samples,the content of ortho three replace were similar,while the content of benzene five replace is rich coal vitrinite sample more dominant;From the absorption band of oxygen-containing,It can be seen functional groups that the content of CH₃symmetrical bending vibration of coal samples in vitreous group is significantly higher than that in inertinite group.The absorption zone of fat structure indicates that the content of methylene in two coal samples is higher than that of methyl.The hydroxyl absorption band indicates that the molecular structure of-OH in XS and SSP coal samples is mostly hydroxy-hydroxyl association structure rather than free state.（2）According to the XPS analysis,the main existing forms of nitrogen in the two coal samples are pyrrole and pyridine nitrogen,and the total content of pyrrole and pyrrole is more than 75%,followed by a small amount of quaternary nitrogen and nitrogen oxides,of which the nitrogen oxides may be the product of the long-term oxidation of pyrrole and pyridine in the air.The sulfur element analysis showed that the sulfur in XS coal sample was mainly thiophene sulfur and sulfoxide sulfur,and the SSP coal sample was mainly thiophene,Sulphoxides and Sulfone sulfur（3）¹³C nuclear magnetic map can be seen that the peak position mainly concentrated in the 0 to 50ppm and 110-140ppm,and the content of Vitrinite-rich coal samples is slightly higher than Inertinite rich coal samples.The reason may be the SSP coal sample′s degree slightly higher than the XS coal sample.By analyzing ¹³C nuclear magnetic map and combining with carbon atoms in nuclear magnetic resonance（NMR）chemical shift attribution table,calculate 12structure parameters of Vitrinite-rich coal samples and Inertinite-rich coal samples.Thus draws the average bridge peripheral of Vitrinite-rich coal samples is 0.29,the Inertinite-rich coal samples is 0.34.2 The initial model was constructed and the final model was corrected by combining ACDLab software and Material Studio software based on the data analysis of the graph experiment.（1）According to the result of the above analysis to build initial plane structure model of Vitrinite-rich coal samples and Inertinite-rich coal samples,the rich vitrinite XS coal sample regard 2 and 3 aromatic compounds as primary structure.But,SSP coal samples of inertinite rich group is given priority to with condensation degree of 3 aromatic compounds,and add a small amount of condensation degree of 4 and 5 of the aromatic ring.Through constantly adjust to connecting method and sequence of each functional group until the experimental measured spectra was consistent with model simulation spectra.In the end,we can say that this model is perfect.（2）I made the optimization of molecular mechanics geometric and molecular dynamics annealing to the final structure model,and got the lowest energy configurations of vitrinite-rich coal samples and inertinite-rich coal samples.We can see clearly structure that through the optimized geometry optimization and annealing model chemical bonds occurred different degrees of torsion,bending,look more compact.By comparing the previous energy to after optimization,the valence electrons and the bonding can have greatly reduced,the reduce of the valence electrons can mainly depend on key expansion reduction,bond Angle can have increased slightly.It indicates that the molecular structure of coal sample changes from a planar structure to a more stable three-dimensional structure after the torsion and bending of chemical bonds.л-лinteraction between aromatic ring is more stable in the form of nearly parallel arrangement.（3）Testing the final structure by ¹³C-NMR spectra comparison,the truth and contrast density,the content of C,H,O,N and S elements and element analysis.,Results showed that the macromolecular structure of XS coal sample of vitrinite rich group and SSP coal sample of inertinite rich group can better reflect the main structural characteristic parameters of the coal sample,so it is considered that the coal sample constructed is more reasonable.3、The optimal periodic structure model was studied by saturation adsorption and isothermal adsorption in Material Studio8.0 software,and the following conclusions were obtained:（1）From the transformation energy in the process of saturating adsorption that vitrinite rich coal samples and Inertinite rich coal samples to methane and carbon dioxide,energy we can know that adsorption rely mainly on the effect of van der Waals energy,electrostatic energy effect is small,the methane adsorption no hydrogen bonding,while CO₂ adsorption with hydrogen bond to the role.The hydrogen bonding is stronger in the inertinite rich coal than in the vitrinite rich coal.The adsorption belongs to physical adsorption,adsorption concentration performance is more obvious the inertinite rich coal sample.We can know from saturated adsorption data that the CO₂ adsorption capacity is higher than methane adsorption.（2）According to the isothermal adsorption simulation data,the adsorption amount decreases with the increase of temperature,and the sensitivity of vitrinite rich coal samples to temperature is greater than that of inertinite rich coal samples.With the increase of pressure,the adsorption capacity presented a three-stage change characteristics of"fast suction-slow suction-dynamic balance".Under the same temperature and pressure,carbon dioxide are more easily adsorbed by coal samples than methane.The vitrine-rich coal samples and the inertine-rich coal samples were placed in the same temperature and coordinate system.According to the data comparison,in the studied four temperature points,the methane and carbon dioxide adsorption capacity of the vitrine-rich coal samples was higher than that of the inertine-rich coal samples.The results of binary isothermal adsorption show that the CO₂ has stronger adsorption competitiveness than the CH₄.