Quantitative Characterization And Modeling Of Coal Molecular Structure In Huangling Mining Area

Coal is composed of aggregates with complex structure.The characterization of coal molecular structure directly affects the evaluation of coal reservoir and the enrichment mechanism of coalbed methane.Scholars at home and abroad have done a lot of research on the macromolecular structure of coal with different rank,and built a variety of models.It provides a theoretical basis for the basic research of coal chemical structure and heat conversion technology.Based on the field sample collection,indoor test methods of analysis and numerical simulation research,the geological evolution history of coal measures in Huangling mining area and the molecular structure of No.2 coal seam of Jurassic Yan 'an Formation were studied by the aid of element analysis,industrial analysis,XRD,FTIR and 13CNMR,XPS and simulation software(Petromod 1D,Materials Studio 8.0).It shows that(1)Mesozoic Jurassic yanan group of coal seams in huangling mining area since late Triassic,the main 3?4 times of "settlement-up" process.The maximum buried depth of 2077?2148m at the end of early cretaceous.Coal has the maximum heat temperature at the end of early cretaceous respectively 115? for Wayaopu Formation,113? for Fuxian Formation,109? for No.3 Coal Seam and 107? for No.2 Coal Seam of Yan 'an Formation.The evolution process of hydrocarbon generation corresponds to three stages:protogenic gas(vitrinite reflectance is less than 0.3%),thermogenic gas(vitrinite reflectance evolves to 0.67%-0.74%)and secondary biogenic gas(buried depth of coal measures is less than 1292-1328m and heating temperature is less than 75?.(2)Huangling coal is mainly benzene ring disubstituted and benzene ring tetrasubstituted.Oxygen containing functional group main forms of carboxyl,carbonyl,hydroxyl and ether.Carbon forms are mainly aromatic carbon.Nitrogen forms mainly in pyridine nitrogen and pyrrole nitrogen.Sulfur forms mainly for thiophene type sulfur,sulfoxide type sulfur and mercaptan sulfur.Hydroxyl group is mainly hydroxyl ether oxygen,followed by self-associating hydroxyl bond.More methylene than methylene.(3)The bridge carbon ratio of Huangling coal is in the range of 0.163?0.191.The distance between aromatic layers,the elongation of aromatic layers.The stacking height and the number of stacking layers are in the range of 3.52?3.61A,19.22?23.96A,15.05?16.72A and 4.18?4.69,respectively.(4)The molecular formula of HL2-4 coal in Lingling mining area is C₁₅₇H₁₂₅O₂₈N₂.The simulated density is 1.25g/cm³.The three-dimensional sense of the structure model is enhanced and the total energy of the model is reduced after optimization.Bond expansion energy and van der Waals energy play a very important role in maintaining the structure of HL2-4 coal in Huangling mining area.Hydrogen bonds mainly exist between molecules.The results of molecular structure characterization of coal in Huangling mining area provide a basis for revealing the structural evolution of coal in the process of biogasification.