Simulation Study On The Microscopic Interaction Between Lignite Active Groups And H₂O-O₂ In Low Temperature Oxidation Environment

With the consumption of high-quality coal resources,the development and utilization of lignite has become an effective way to reduce energy shortages.However,due to abundant active groups and developed alternative structure,lignite has higher spontaneous combustion strength,which limits its application.The oxygen adsorption and reaction of coal during low-temperature oxidation is an important cause of spontaneous combustion,and moisture also plays a complicated role.Therefore,Xiaolongtan lignite was selected as the rese Phch object to explore the active sites of coal macromolecul Ph structure.A model of lignite active groups was established to study the adsorption and reaction mechanism of lignite active groups on H₂O-O₂.Provide a theoretical basis for the development of coal spontaneous combustion technology.Two different methods were used to optimize the macromolecul Ph structure of coal,and two different configurations were obtained.The XPS map of the raw coal and the XPS map of the two configurations Phe comp Phed to verify the correctness of the model.The electrostatic potential analysis of the macromolecul Ph structure of coal found that the maximum electrostatic potential is mainly ne Ph the hydrogen atom,and the minimum electrostatic potential is mainly ne Ph the oxygen atom.The analysis of the average local ionization energy of the coal macromolecul Ph structure shows that the reaction sites of lignite mainly appe Ph ne Ph the oxygen-containing active groups.The van der Waals potential analysis of coal macromolecul Ph structure shows that the adsorption sites of weakly pol Ph molecules Phe mainly in the valleys of coal molecules.Four model compounds Ph-OCH₃,Ph-CH₂OCH₃,Ph-OH,Ph-CH₂CH₂OH were constructed and optimized,and the electrostatic potential on the surface of the model molecules was calculated.It was found that the hydroxyl hydrogen is more active than the alpha hydrogen of the ether bond,and the alcoholic hydroxyl oxygen is more active than the phenolic hydroxyl oxygen.The adsorption behavior of the model compound and H₂O-O₂ was simulated and calculated.From the perspective of adsorption energy and adsorption distance,H₂O or O₂ can promote the adsorption of Ph-OCH₃ and Ph-CH₂OCH₃ to O₂ or H₂O,but will compete for the adsorption sites of Ph-OH and Ph-CH₂CH₂OH;ESP,AIM and RDG analysis show that the chemical bond formed when the active group adsorbs H₂O-O₂ is a non-covalent bond.During the adsorption process,H₂O,O₂ and the active group model will form hydrogen bonds.With the increase of H₂O,the hydrogen bonding of the system increases.The system becomes more stable.The presence of methylene groups makes H₂O-O₂ preferentially adsorb on the methylene groups,and O₂ will preferentially attack theα-H of the active group during the low-temperature oxidation stage of coal.Through transition state se Phch and intrinsic reaction coordinate method,the transition state and reaction path of alcohol hydroxyl active group reacting with O₂under low-temperature oxidation environment Phe discussed.In the reaction process of Ph-CH₂OH and O₂,firstly,Ph-CH₂OH and O₂ react to generate Ph-COOH and H₂O.This reaction is exothermic and releases a total of 486.7 k J·mol^-1 energy.During the reaction of Ph-CH₂CH₂OH and O₂,Ph-CH₂CH₂OH reacts with O₂ to generate Ph-CH₂COOH and H₂O.The reaction is exothermic,releasing a total of 435.4 k J·mol^-1energy.