20 / 2023-05-14 10:43:58

Study on the change of free radicals in coal during the process of oxygen isolation and temperature rise

coal spontaneous combustion,functional group,active groups,subtraction map,activation energy

Abstract: In order to study the change law of the most essential free group of middling coal and its pyrolysis kinetics during the anaerobic heating process, thermogravimetric and in-situ infrared experiments were carried out on long flame coal. The infrared spectra of different characteristic temperature points of long flame coal were obtained through data processing, and the variation trend of functional groups at adjacent temperature points was characterized using subtractive spectra. The pyrolysis kinetics analysis was conducted based on the functional group data obtained from in-situ pyrolysis infrared spectrum deconvolution. The results showed that the number of main functional groups in coal showed a decreasing trend, with the smallest decrease in aromatic C=C and only an increase in aromatic C-H content. Reactions or volatilizations of functional groups with weaker stability from 30 ℃ to 266 ℃ result in a decrease in the number of functional groups; From 427 ℃ to 510 ℃, more chemical bond broke, aliphatic, aromatic and more oxygen-containing functional groups began to react, and the decrease of C-C bond content was well correlated with the decrease of aliphatic functional group number (R²=0.99843); The oxygen-containing functional groups such as -OH and C-O at 800 ℃ are basically completely consumed. The activation energy of aliphatic functional groups increases with temperature, and the first, second, and third stages are consistent with unidirectional transport, third, and first order kinetic modes, respectively; The second stage of aromatic C=C follows a second-order reaction mode, with a maximum activation energy of 207.2kJ/mol; The second stage of hydroxyl group is consistent with the second order reaction model, with an activation energy of 72.31 kJ/mol; The first and second stages of C-O are consistent with the first and second order reaction modes respectively. The activation energy increases from 39.46kJ/mol to 52.92kJ/mol, and the Goodness of fit is about 0.98.