Mechanism And Effect Analysis Of Curcumin Inhibiting Coal Spontaneous Combustion

China is rich in coal resources,while there are fewer high-quality coal seams,and the risk of coal spontaneous combustion（CSC）increases as the depth of coal seam mining increases.Therefore,in order to reveal the microscopic reaction characteristics of CSC and develop effective technical methods to control CSC,a series of thermodynamic theoretical and experimental studies were carried out in this paper,focusing on the reaction characteristics of free radicals during coal oxidation and the mechanism of curcumin inhibition CSC.The mechanism of curcumin（CUR）inhibiting CSC was revealed by quantum chemical calculations from two perspectives:free radical scavenging mechanism and metal chelating mechanism.The active sites of CUR molecules for scavenging free radicals were analyzed by molecular orbital analysis,charge distribution,and electrostatic potential.The reaction path and thermodynamic characteristics of CUR molecules for scavenging key active radicals during coal oxidation were studied.The activation energies required for CUR to scavenge hydrocarbon radicals（Ar-CH₂·）,peroxy radicals（Ar-CH₂OO·）,ether oxygen radicals（Ar-CH₂O·）and carbonyl radicals（Ar-C·=O）were 39.383,16.753,2.626,and 31.506 k J/mol,respectively,with corresponding heat releases of 42.008,31.506,99.769,and 39.383 k J/mol,respectively.The results of thermodynamic parameters show that the CUR molecules can spontaneously remove the key active free radicals that promote the free radical chain reaction process at room temperature,effectively inhibiting free radical chain reaction and reducing heat storage.The formation of coordination bonds between CUR molecules and metal ions was analyzed through natural bond orbital analysis,charge distribution and transfer.The interaction between CUR molecules and metal ions was discussed through atom in molecule（AIM）theory and interaction region index IRI analysis.The results show that there is a coordination interaction between CUR molecules and metal iron ions,forming coordination bonds,and CUR molecules can chelate metal iron ions effectively.CUR can prevent the occurrence of CSC by causing the loss of the ability to transfer electrons of the transvalent metal ions,weakening their catalytic effect on the radical reactions during coal oxidation,and reducing the generation of free radicals.Therefore,CUR molecules can play a multiple inhibitory role in preventing and hindering CSC.The changes of free radicals in coal samples before and after CUR treatment were analyzed by electron paramagnetic resonance spectrometer.The results show that the coal samples treated with CUR have lower g-factor values and free radical concentrations.The changes of pore structure and oxygen adsorption of coal samples before and after CUR treatment were tested by automatic specific surface porosity analyzer.The results show that the coal samples with CUR were less likely to contact with oxygen,and the adsorption capacity for oxygen was weakened.The oxygen consumption and gas release patterns of coal samples before and after CUR treatment were studied by programmed temperature experiment device and gas chromatograph.The results show that the oxygen consumption capacity and the production of CO and CO₂gas is reduced of coal samples after CUR treatment.The quality characteristics of coal samples before and after CUR treatment were discussed by synchronous thermal analyzer.The results show that the addition of CUR reduces the weight loss rate and delays the spontaneous combustion process of coal.All the above experimental results show that CUR has a good inhibiting effect on the spontaneous combustion characteristics of coal.