Molecular Structure Evolution Of Low Rank Coal And CO Generation Under The Action Of Temperature And Pressure

More and more coal mine detected carbon monoxide excess safety limitation in the coal mine production, bring potential safety hazard of coal mine runing. In this paper, the stress and strain experiment were carried out of CJZ(Cuijiazhai Coal Mine) lignite coal and LNC(Linnjnchang Coal Mine) gas coal under the temperature of 50, 150 and 250℃. At the same time, gas generated was tested; elemental composition of the samples before and after the experiment was determined, coal molecular structure was analyzed byusing Raman spectroscopy, X-ray diffraction, nuclear magnetic resonance, fourier infrared spectroscopy, X-ray photoelectron spectroscopy, solid carbon nuclear magnetic analysied; coal macromolecular structure was constructed, molecular mechanics and dynamics was carried out. The analysis of the evolution characteristics of molecular structure before and after the experiment, reveals the generation mechanism of carbon monoxide.The results are as follows:(1) CJZ coal occurs in the Xiahuayuan Formation of the Jurassic System, geological structure is priority to fault. Its maceral composition is mainly desmocollinite and fusinite. Macro-fractures develop on the sample, and its pore size is mainly big hole. LNC coal occurs in the Shanxi and the Taiyuan Formation of the Carbon-Permian System and normal faults develop in it. The composition of coal maceral is given priority to with telinite and fusinite. Micro fractures develop on it and its pore size is mainly micropores.(2) Ductile deformation happened on CJZ samples under all three temperature points; while for LNC samples, brittle deformation happened under the condition of 50 and 150℃ and ductile deformation at 250℃. Under three temperature points, both of the two samples generated oxygen; and carbon monoxide generationed under 150 and 250℃,. After the experiment, d002 of coal molecular structure increase slightly, while La and Lc decreased slightly; meanwhile, G peak of CJZ samples move to high frequency region under the condition of 250℃, and that of LNC samples move to low frequency area under the condition of 150 and 250℃, it indicates that the pressure and temperature may cause the microcrystalline structure unit broken, and causes the change of aromatic ring structure. After the experiment, porosity, adsorption borehole volume and diffusion hole aperture of CJZ samples reduced and its diffusion distributed capacity increase. For LNC samples, porosity, diffusion hole borehole volume and aperture decreases, absorbed pore volume increase.(3) After experiment, aliphatic side chains branched chains of CJZ samples increased, at the same time cycloalkanes formed; and aromatic ether of oxygen functional groups reduce more; and LNC samples may formed long chain structure of aliphatic side chains, oxygen containing functional groups in the aliphatic decreased. And the macromolecular structure models of the samples before and after the experiment were build.(4) The coal molecular structure mechanics and dynamics simulations show that, corresponding to the raw coal, total energy of CJZ samples decreases, while that of LNC samples increased, this demonstrated that CJZ samples is moving to the stable state and LNC samples to unstable state. By analyzing bond length and bond energy, count carbon monoxide may be derived from carbonyl fall off, or may also comes from the reaction of oxygen oxidation the free radicals and generate carbon monoxide.(5) The burial curve of two coal mines are in the shape of “W” and ”V”, respectively, on the basis of different situations to found carbon monoxide excessive at the two coal mines, combined with their geological evolution histories and conditions of CO generation, it is presumed that the original carbon monoxide of Cuijiazai Coal Mine may formed in Late Jurassic Period to the Early Cretaceous Period(the Yanshan Movement). And that of may generated at three periods, that is, the Late Permian Period to Middle Triassic Period(Indo-Chinese epoch), the Late Triassic Period to the Early Cretaceous Period(the early and middle Yanshanian Movement), and the early Cretaceous Period and the late Cretaceous Period(late Yanshan movement).