Evolution Mechanism Of Nano-pore And Macromolecule In Low And Middle-rank Tectonically Deformed Coals (Tdcs)

There are theoretical and practical significances for the prevention of coal and gas outburst and the occurance/enrichment mechanism to investigate the evolution of nano-pore and macromolecule in tectonically deformed coals?TDCs?.Here,the fluid injection technology and fractal theory were combined to investigate the nano-pore structural and heterogeneous characteristics of TDCs.The response characteristics of organic macromolecules to tectonic deformation were discussed utilizing the spectrum peak separation and fitting analysis.Then,structural alignment of the aromatic clusters in TDCs was revealed through the information extracted from the HRTEM.The Materials studio 2017,Fringe 3D,and Volume 3D were integrated applied to construct the macromolecular model of the mylonitic coal based on the elemental analysis,¹³ C NMR?FTIR and HRTEM.The molecular simulation of CH₄ adsorption onto mylonitic coal was then conducted through GCMC.Additionally,the coal and gas outburst mechanism in mylonitic coal developing area was furtherly clarified combining Steel potential function,microporous size distribution,and heterogeneities in macromolecules and structural defects.The main achievements are as follows:1)The structural deformation profoundly affects the heterogeneity of macropore,mesopore and micropore in coal.The heterogeneity of the adsorption-pores increases while that of the seepage-pores decreases with the increasing tectonic deformation.These exists distinct differences in surface and volume heterogeneity between two microporous segments of 0.3⁰.6 nm and 0.6¹.4 nm in diameter.The effect of different deformation mechanisms on the internal difference of pore size distribution manifests as:Shear deformation>ductile deformation>brittle deformation.The variations of the sample size reduce the effect scale of structural deformation on mesoporous and microporous structures to a certain extent.2)Tectonic deformation promotes the evolution of organic macromolecules in coal.The maturity of coal organic matter increases gradually under the action of mechano-chemistry.The advanced effects from the ductile deformation are stronger than those from the brittle and shear deformation.Mylonization process can promote the rapid exfoliation of oxygen-containing functional groups.Strong ductile shear destroys the side chains and side groups of coal aromatic rings,and accelerates the ordering evolution of coal macromolecular structure.Raman spectrum G peak of TDCs moves towards the high frequency region compared with the primary coals.The differences in D1 and G peak position increase in the cataclastic coal?schistose coal,and scaly coal.The splitting degree of Raman spectrum becomes more significant with the increasing tectonic deformation.Shear tectonic stress can reduce the content of organic sulfur such as sulfide,thioether,dithiol and dithiobenzene series,while ductile deformation has obvious enrichment effect on thiophene sulfur and inorganic sulfur.The fitting results of the Raman second-order indicated that the brittle TDCs are rich in DV and SV defects while ductile TDCs are rich in SW and MV defects.3)Tectonic deformation improves the structural alignment of aromatic clusters of coal.Brittle deformation shortens aromatic clusters.Stress condensation is more obvious under strong shear deformation than brittle deformation.Brittle-and weak shear deformation have little effect on the length of aromatic fringes while strong brittle deformation can increase long aromatic fringes and reduce the short lattice fringes.The proportion of small size aromatic clusters decreases while that of large size aromatic clusters increases with the increase of tectonic deformation.The molecular weight proportion of aromatic clusters decreases with the increasing relative molecular mass of aromatic clusters in TDCs.Both the proportion of aromatic clusters with high molecular weight?500-4499 Da?and the curved fringes increase due to stress condensation.The longer fringes for the scaly,wrinkled,and mylonitic coal accommodate more segments/undulations for curved fringes,consistent with the higher curved fringe percentages for these three types.4)The ultra-structure of the mylonitic coal determines the high risk of gas outburst in the development area.High proportions of large aromatic clusters,widespread development of structural defects,and development of nanoporous specific surface area in mylonitic coal have enhanced its natural methane occurrence ability.Molecular swelling mechanism and heterogeneity of microporous structure promote mylonite to become“soft coal”.The calculation results of the Steel potential function indicated that lack of activated desorption and Knudsen diffusion pores leads to further gas accumulation,increasing the risk of coal and gas outburst.This dissertation highlights the evolution mechanism of nano-pore and macromolecule and constructs the macromolecule model of mylonitic coal.The mechanism of coal and gas outburst in mylonite coal development area was discussed combining the distribution of nanopore,heterogeneity of macromolecule structure,and development mode of structural defects.There are 133 figures,39 tables and 339 references in this paper.