Mechanism Of Key Active Groups On Variation Laws Of CO₂/CO During Low-temperature Oxidation Of Coal

China is the country most seriously affected and threatened by spontaneous combustion of coal seams in the world.Spontaneous combustion of coal often induces gas and coal dust explosions and other particularly serious malignant accidents,so the prevention of spontaneous combustion of coal is an important means to ensure the safety of coal mines.The prediction and forecasting of coal spontaneous combustion by monitoring the change pattern of indicator gases produced during the low temperature oxidation of coal is an effective method to prevent coal spontaneous combustion.Since the low temperature oxidation of coal mainly produces CO and CO₂,CO and CO₂ are used as commonly used indicator gases for predicting coal spontaneous combustion.Existing studies related to CO and CO₂ generation during low-temperature oxidation have mainly been studied using programmed warming experiments under air atmosphere,however,coal can generate CO and CO₂ through oxidation,pyrolysis,and desorption pathways.Among the above three gas production paths,the oxidation path is the heat-producing reaction and is the path that can truly reflect the state of coal spontaneous combustion.To this end,this paper designs a thermostatic oxidation experimental method that can exclude the effects generated by desorption as well as pyrolysis,and investigates the variation patterns of CO and CO₂concentrations,kinetic properties and CO₂/CO ratio generated by the oxidation path using raw coal and pyrolysis coal.An in-depth analysis of the intrinsic mechanism of CO₂/CO ratio change is carried out by combining various microscopic characterization tools,and a CO₂/CO-based prediction index system is established under the guidance of the mechanism.The main research content of the thesis and the results obtained are as follows.Coal desorption and pyrolysis gas production can interfere with the CO and CO₂produced in the oxidation path.The effect of desorption and pyrolysis can be effectively eliminated by the difference between the gas in air and N₂ atmosphere,and the variation pattern of CO and CO₂generated under the oxidation path can be obtained.On this basis,the rates of CO and CO₂ production as well as their activation energies were calculated,and the activation energies obtained based on the difference were 59.488 k J/mol and 60.086 k J/mol for the production of CO and CO₂ under the oxidation path,respectively,and 50.525 k J/mol and 50.529 k J/mol for the production of CO and CO₂ under the oxidation path obtained based on the pyrolysis of coal.The combined analysis leads to the conclusion that the rates of CO and CO₂ production from the oxidation pathway is not only temperature dependent but also related to the number of reactive groups involved in the reaction,especially the number of reactive groups gradually took control as the temperature increased.Combined with the infrared analysis,it is concluded that the process of coal low temperature oxidation gas production is the reaction of methylene（hypo-methylene）and oxygen in coal to produce oxygen-containing intermediate products,and then the decomposition of oxygen-containing intermediate products to produce CO and CO₂.The reaction between coal methylene（hypo-methylene）and oxygen is the controlling step of coal low-temperature oxidation gas production,which directly affects the amount and rate of CO and CO₂ production in coal low-temperature oxidation process,therefore,under the conditions of excluding The conditions of desorption as well as pyrolysis gas production result in the same apparent activation energy of CO and CO₂ production from the oxidation path.CO₂/CO can eliminate airflow disturbance and truly reflect the state of coal spontaneous combustion.The CO2/CO ratio is the most commonly used indicator to determine the spontaneous combustion of coal,and the CO2/CO ratio generated by the oxidation path was experimentally derived to be around 3.In addition,the active sites generated from coal pyrolysis strongly affect the concentrations of CO and CO₂at the beginning of oxidation,but they barely influence their ratio which is always about 3.However,temperature still has a large effect on CO₂/CO,as shown by the gradual participation of different reactive groups in the coal at different temperatures to divide CO₂/CO into three stages during the oxidation process:slow oxidation stage,accelerated oxidation stage and fast oxidation stage.The results show that the methylene linked to several benzene rings and the active sites generated by pyrolysis will continue throughout the oxidation process,the essence of the reaction is that the methylene reacts with oxygen.The methylene is the key reactive group affecting the ratio,and the oxidation intermediates are the precursor that produces CO and CO2,resulting in CO2/CO tending to 3.The essence of the effect of temperature on the CO₂/CO ratio is the gradual participation of different reactive groups in the reaction leading to the change of the ratio,according to which the process of the low-temperature oxidation of coal to produce CO and CO₂ can be divided into three stages,and the critical temperature range and dry cracking temperature range of coal samples in the warming process can be determined accordingly.The CO₂/CO ratio was selected as the main index for predicting and forecasting the spontaneous combustion of coal in MDL,and the early warning index system for spontaneous combustion of coal in MDL mine was established by combining the single gas indicators and alkane ratio.Figure 42 Table 14 Reference 120...