Quantum Chemistry Calculation Study on Chain Reaction Mechanisms and Thermodynamic Characteristics of Coal Spontaneous Combustion at Low Temperatures

Abstract

The coal spontaneous combustion phenomenon seriously affects the safety production of coal mines. Aiming at the problem of complex coal molecular structure and incomplete reaction sequences at present, the mechanisms and thermodynamic parameters of coal spontaneous combustion chain reactions were explored by combining experimental detections and molecular simulations. First, the active groups on the surface of coal were obtained by Fourier transform infrared spectroscopy (FTIR), mainly including methyl (−CH3), methylene (−CH2), methyne (−CH), phenolic hydroxyl (−ArOH), alcohol hydroxyl (−ROH), carboxyl (−COOH), aldehyde (−CHO), and ether (−O−), and the coal molecular models containing functional groups and radicals were established. According to the charge density, electrostatic potential, and frontier orbital theories, the active sites and active bonds were obtained, and a series of reactions were given. The thermodynamic and structural parameters of each reaction were explored. In the chain initiation reaction stage, O2 chemisorption and the self-reaction of radicals play a leading role. In this stage, heat gradually accumulates and various radicals begin to generate, where the intramolecular hydrogen transfer reaction of a peroxide radical (−C–O–O·) can produce the key hydroxyl radical (−O·). In the chain propagation reaction stage, O2 and −O· continuously consume active sites to accelerate the reaction sequences and increase the temperature of coal, and index gases such as CO and CO2 generate, causing the chain cycle reactions to gradually form. The chain termination reaction stage is the formation of stable compounds such as ethers, esters, and quinones, which can inhibit the development of chain reactions. The results can further explain the reaction mechanism of coal spontaneous combustion and provide references for the development and utilization of chemical inhibitors.

Study of Butylated Hydroxytoluene Inhibiting the Coal Oxidation at Low Temperature: Combining Experiments and Quantum Chemical Calculations

“… 21 The COLT is a chain reaction process, which can be divided into chain initiation, chain propagation, and chain termination reactions. 4 In the chain initiation reaction stage, a large number of free radicals participate in a variety of reactions and release a large amount of heat, which is the key stage of the chain reaction. 4 , 53 Therefore, the active free radicals in the chain initiation stage were mainly considered in this paper, including alkyl free radicals (·CH 3 , R–·CH 2 ), oxygen free radicals (R–O·), peroxy free radicals (R–OO·), and hydroxyl free radicals (·OH).…”

“…The theory holds that coal spontaneous combustion is caused by coal oxidation at low temperature (COLT), which is due to the physical adsorption, 11 chemical adsorption, 12 and oxidation at room temperature. 4 , 13 When the heat accumulates and cannot dissipate in time, the coal spontaneous combustion occurs. 14 − 16 On the basis, Li 17 , 18 put forward the theory of the free-radical reaction in 1996 and predicted the gas production mechanism in the process of COLT, and he believed that the active groups in coal can produce active free radicals and react with oxygen after fracture, resulting in COLT.…”

“…At present, the coal is still the main production energy and raw material in the world, accounting for 30% of the world’s energy consumption, while Asia’s coal consumption accounts for about 75% of the world. , China is rich in coal resources, accounting for more than 67.5% of disposable energy, but the quality is poor. The low-grade coal is about 190 billion tons, accounting for 41.18% of the total coal reserves. − Coal spontaneous combustion is a common disaster phenomenon in the process of coal mining, storage, and utilization. Coal spontaneous combustion will produce toxic and harmful gases such as CO, CO 2 , SO 2 , and NO.…”

“…For a long time, scholars have carried out a lot of research on the mechanism of coal spontaneous combustion, and coal-oxygen compound theory has been most widely recognized. The theory holds that coal spontaneous combustion is caused by coal oxidation at low temperature (COLT), which is due to the physical adsorption, chemical adsorption, and oxidation at room temperature. , When the heat accumulates and cannot dissipate in time, the coal spontaneous combustion occurs. − On the basis, Li , put forward the theory of the free-radical reaction in 1996 and predicted the gas production mechanism in the process of COLT, and he believed that the active groups in coal can produce active free radicals and react with oxygen after fracture, resulting in COLT. Wei used the electron spin resonance technology to determine the change law of free radicals under different coal types and fragmentation degrees and deduced the chain reaction mechanism of COLT.…”

Experimental and Quantum Chemical Study on the Inhibition Characteristics of Glutathione to Coal Oxidation at Low Temperature

“…Coal is one of the major fossil energy sources in the world, dominating the energy consumption of all countries and influencing the industrialization process of society at all times. − Nonetheless, owing to the depth of coal mining increases, the geothermal influence is progressively enlarging and coal spontaneous combustion accidents occur now and again. − Serious coal spontaneous combustion accidents not only lead to the waste of coal resources and increase the pressure on environmental protection but also cause irreversible damage to equipment, while critically threatening the personal and property safety of operators. , Consequently, it is of great practical significance to take necessary and effective measures to prevent and control coal spontaneous combustion and ensure coal mine safety production.…”