Hydrocarbon Generation From Pyrolysis Of Low-Rank Coal And Its Molecular Dynamics

Low-rank coal accounts for about 50%of the total coal reserves in China.Since it contains high organic matter,a large amount of hydrocarbon substances will be produced during its pyrolysis,so the hydrocarbon generation process of low rank coal and the mechanism of hydrocarbon generation process pyrolysis is explored,which has positive significance for coal industrial production and clean utilization of coal processing.In response to the above problems,the chemical molecular structure of Xianfeng Mine lignite was selected as the research object of this study.Through Fourier infrared spectroscopy experiments（FTIR）,solid-state nuclear magnetic resonance experiments(¹³C NMR),X-ray photoelectron spectroscopy experiments（XPS）and elemental analysis experiments,the chemical molecular structure of Xianfeng Mine lignite was characterized and its molecular structure model was established;The optimal 3D system model was obtained by structural optimization,and the model was analyzed for energy evaluation and rationality.By the golden tube thermal simulation experiments in the closed system,the change process of pyrolysis products,kinetic parameters of gas products and hydrocarbon generation patterns of low coal grade coals under different heating rate conditions were studied;By Reaxff MD molecular dynamics simulation means,the molecular structure model of Xianfeng Mine lignite was calculated by the warming pyrolysis simulation,and the hydrocarbon generation process was analyzed by the dynamic evolution of products and molecular structure visualization tracking.The main insights obtained in this study are as follows:（1）The experimental results of chemical structure characterization of Xianfeng mine lignite show that the structure of organic matter functional groups in coal is dominated by fatty side branching structure and aromatic structure,and contains more oxygen-containing functional groups.In the aromatic structure,the trisubstituted structure is dominated,and a small amount of disubstituted and pentasubstituted structures are supplemented;the oxygen-containing functional groups are mainly carboxyl and hydroxyl groups;the fatty structure is dominated by methylene and hypomethyl groups.The physical density and radial distribution function were used to verify the rationality of the molecular model,and the results indicated that the established three-dimensional molecular structure model could better reflect the chemical structure characteristics of the lignite of Pioneer Mine at room temperature.（2）The results of the gold tube thermal simulation experiments were shown that the variation of the total gaseous hydrocarbon yield was characterized by an increase followed by a decrease.The analysis of the individual yields of hydrocarbon gases shows that the yield of gaseous hydrocarbons in the hydrocarbon generation process gradually decreases with the increase of their molecular weight.Comparing the yield changes under different heating rates,it shows that the lower heating rate can better ensure the full pyrolysis of coal.According to the changes of organic matter maturity and gaseous hydrocarbon yield during coal pyrolysis and hydrocarbon generation,the hydrocarbon generation process was divided into four stages:immature,mature,highly mature and over mature.（3）Reaxff MD simulation results were shown that in the lower temperature range,the hydrocarbon generation process is dominated by the primary reaction of coal,mainly the breakage of macromolecular structure and the shedding of active functional groups.In the higher temperature range,secondary reactions dominate,with further tar decomposition and strong aromatic structure condensation reactions.The generation of CH₄ is mainly related to the formation of-CH₃ radicals by shedding methyl groups;the generation of CO₂ is mainly related to the shedding of carboxyl groups and hydroxyl groups;the generation of H₂ is mainly related to the dehydrogenation reaction of fatty structures such as methyl groups and hydroxyl groups;the generation of H₂O is mainly related to the shedding of hydroxyl groups and some oxygen-containing functional groups.Thus the process of coal pyrolysis to produce hydrocarbons is the process of free radical shedding and remodeling is also illustrated.