Coal Molecules Research Articles

The Inhibition Effect of CO2-N2 Composite Gas on Spontaneous Combustion of Coal and the Law of Competitive Adsorption in Coal

ABSTRACT The purpose of this study is to study the effect of CO2-N2 composite gas on coal spontaneous combustion index gas and the mechanism of inhibiting coal spontaneous combustion through a competitive adsorption process and to provide theoretical guidance for adopting inert injection fire prevention and control technology in goaf to prevent coal spontaneous combustion. The programmed temperature experiment and gas chromatography were used to analyze the indicator gas after injecting different mixed ratios of CO2 and N2 inert gas. In the whole oxidation heating process (25–300 ℃), the generation of indicator gas and the peak point of gas ratio showed an apparent “Hysteresis phenomenon” and the more significant the proportion of CO2 in the composite inert gas, the more pronounced the “Hysteresis phenomenon.” Even in the CO2-dry air environment, the peak point disappears, indicating that with the injection of N2 and CO2, the coal body is in a more complex gas atmosphere, and a variety of gases are in the process of adsorption and desorption on the inner and outer surfaces of the coal body. The characteristics of the evolution of the spontaneous combustion oxidation process of coal are more complex, directly affecting the coal-oxygen interaction, thus affecting the intuitive combustion oxidation process. Molecular simulation studies the characteristics of coal molecules on CO2, N2, and O2. The results show that the adsorption capacity and adsorption energy of coal molecules on CO2 molecules are more significant than O2 and N2, and there is a competitive adsorption relationship between CO2 and N2 molecules and O2 molecules, and the competitive adsorption capacity of CO2 is more significant than N2. It shows that the composite inert gas can inhibit the coal-oxygen adsorption by competitive adsorption to displace oxygen and achieve the combustion inhibition effect. The experimental and theoretical basis for developing and improving inert gas fire extinguishing technology is provided by studying the index gas after CO2-N2 composite inert gas action and the adsorption capacity and energy in the competitive adsorption process.

Experimental investigation and ReaxFF simulation on pore structure evolution mechanism during coalification of coal macromolecules in different ranks

This analysis revealed the alterations in the pore structure of large organic molecules in coal during the process of coal pyrolysis. Nine models of macromolecular structures in coals, representing distinct coal ranks, have been built. The research results show that along with the increasing coal rank, the average microporous volume of medium rank coal is 0.0287 cm3/g. The average microporous volume of high-grade coal is 0.0662 cm3/g. The micropore volume and specific surface area of coal samples decrease in the order of high rank, low rank, and middle coal. The experimental measurements align with the ReaxFF pyrolysis simulation calculations, indicating a decrease in the hydrogen to carbon ratio and oxygen to carbon ratio of all coal molecules. Additionally, the pore volume and specific surface area exhibit a pattern of initially decreasing and then increasing. The simulation results of gas probes indicate that a majority of the pores with a diameter larger than that of CH4 molecules are found in the macromolecular structure models of low rank coal and medium to high rank coal. The conclusions are useful for us to understand the formation and development process of pores in coal reservoir. A two-dimensional representation of coal’s macromolecular structure was constructed using ChemDraw software. The Forcite module in Materials Studio software was used to perform geometric optimization and annealing kinetics simulation of a two-dimensional macromolecular structure model. The ReaxFF-MD module in Amsterdam Modeling Suite (AMS) 2020 software to model the pyrolysis of XJ coal macromolecules.

Thermodynamic Studies on the Pathway and Mechanism of Coal-Oxygen-Water Coupling Reaction of Low-Temperature Oxidation

ABSTRACT It is imperative to have an in-depth understanding of the pathway and mechanism of coal-oxygen-water coupling reaction during low-temperature oxidation of coal, not only for preventing fires in the coal industry but also for reducing emissions of hazardous gases. In this study, in-situ Infrared spectroscopy characterization and quantum chemical calculations were combined to investigate in detail the chemical interactions between coal, moisture, and oxygen. In-situ infrared oxidation experiments ascertained the types and amounts of hydroxyl, aliphatic hydrocarbon, and carbonyl functional groups in lignite coal samples with varied moisture content during LTO. Subsequently, three typical molecular structures of functional groups mainly involved in the coal-oxygen reaction were chosen as the research representatives, and their reactivity was analyzed using density functional theory (DFT). Thus, the main reaction pathways of these functional groups during the LTO of coal were studied using quantum chemical methods. The results indicated that the moisture in coal significantly affected the coal–oxygen reaction by altering the chemisorption processes in the coal–oxygen combination and the active sites in coal molecules. Quantitative calculation of thermodynamic parameters such as the enthalpy and activation energy showed that moisture had a promoting effect on some reaction steps while hindering others. Moreover, the mechanism of coal-oxygen-water coupling reaction was also explored based on the reaction sequence of intermediate complexes.

Molecular dynamics simulation of water absorption and mechanical weakening in coal rocks based on Monte Carlo methods

Aiming at the problem of roadway destabilization in water encountered in the roadway of the back mining roadway of an extra-thick coal seam in Xinjiang Dabei Coal Mine, this paper used molecular dynamics simulation to study the interaction between coal and water and analyzed the adsorption characteristics of water molecules and the change of mechanical properties of coal. Firstly, the model of C181H138N2O24 bituminous coal was constructed by test, the coal-water adsorption was simulated based on the Monte Carlo method, and the coal-water adsorption configuration was analyzed. The results showed that: the saturation adsorption capacity was about 60 water molecules/cell, and the water molecule adsorption was concentrated in the vicinity of oxygen-containing groups and hydrogen atoms; the increase of water molecule content led to the decrease of heat of adsorption and diffusion capacity, and the heat of adsorption decreased by 9.1 %, and the diffusion coefficient of the early stage of adsorption was about three times of that of the final stage; the mechanical parameters of the coal body were significantly decreased, and the bulk modulus, Young's modulus, and shear modulus were respectively decreased by 21.90 %, 36.76 %, and 38.87 %, Poisson's ratio increased by 14.81 %, Poisson's ratio variability was low, volumetric modulus variability was medium, Young's modulus and shear modulus variability was high. The decrease in strength after coal water adsorption is due to the significant volume expansion of the coal body, the saturation expansion rate reaches 12.47 %, and at the same time, the total energy of the coal model decreases, where the weakening effect produced by the changes in the bonding and non-bonding energies results in the decrease in the mechanical strength of the coal molecules, and the weakening of the stability of the coal rock. The results of the study reveal the deformation and damage mechanism of the softening and deformation of the back-mining roadway in contact with water in Xinjiang Dabei Coal Mine, which provides a basis for the subsequent disaster prevention and control.

Exploring the Potential of Coal: Electrolysis and Extraction for Chemical Recovery, Oral Presentation

Formed from the fossilized remains of ancient plants, coal is a combustible sedimentary rock classified as a nonrenewable resource due to its extremely slow formation process. The chemical structure of coal contains diverse types of carbon, including aliphatic carbons, aromatic carbons, and carbonyl carbons [1], [2]. Coal is considered the most economical source of energy; however, its potential as a repository for valuable chemical compounds remains underutilized. Although solvent extraction offers a way to extract specific components from coal, it comes with limited extraction efficiencies and significant environmental, and economic drawbacks.Coal electrolysis is a process that utilizes electricity to break down and oxidize carbon structures in diverse ways, yielding liquid-phase products [3]. One key application of coal electrolysis is the production of hydrogen gas. Traditional methods, such as Indirect coal liquefaction (ICL) and Direct coal liquefaction (DCL), rely on high-temperature and high Pressure (ranging from 200-1450°C, 100-200 atm) respectively. In contrast, the technology known as the “Continuous Coal Electrolytic Cell (CEC)” facilitates the direct conversion of coal into valuable chemicals and liquid fuels at mild temperatures (25-180°C) and low pressures (1-2 atm) [4]. Therefore, this process could potentially be more efficient and less energy-intensive than conventional methods. In the CEC, electric power is applied to a coal-slurry to directly convert the coal into pure clean hydrogen, and organic compounds (liquid form), with minimum CO2 emissions. During the CEC process, the surface of the coal particles (electrolyzed coal char) gets oxidized into lower molecular weight hydrocarbons than coal. Subsequently the electrolyzed coal char undergoes extraction to separate the liquid fuels and/or valuable chemicals. This technology has already proven that temperature and applied current are the most influential factors in maximizing hydrogen production. However, the conditions for obtaining various liquid-phase products have not yet been optimized.In this study, the effect of coal particle size during electrolysis and the subsequent extraction process was explored more in-depth specifically to determine the characteristic of the liquid extracted. Three coal particle size were electrolyzed using Pt-Ir catalyst, followed by extraction using two different solvents. The changes in the main functional groups of coal particles were studied by FTIR, while proximate analysis and carbon structure were analyzed by TGA/DSC and CHNS, SEM and XRD, respectively. Our findings reveal the distribution of sulfur and nitrogen after electrolysis and the benefits of solvent selection since it is known that the solvent influences the interaction between organic and mineral matter. By demonstrating that coal electrolysis, combined with extraction, can remove valuable chemicals, new market opportunities emerge for coal across various applications.[1] D. Jing, X. Meng, S. Ge, T. Zhang, M. Ma, and G. Wang, “Structural Model Construction and Optimal Characterization of High-Volatile Bituminous Coal Molecules,” ACS Omega, vol. 7, no. 22, pp. 18350–18360, May 2022, doi: 10.1021/acsomega.2c00505.[2] X. Gong, M. Wang, Y. Liu, Z. Wang, and Z. Guo, “Variation with time of cell voltage for coal slurry electrolysis in sulfuric acid,” Energy, vol. 65, pp. 233–239, Feb. 2014, doi: 10.1016/j.energy.2013.11.083.[3] S. Chen, W. Zhou, Y. Ding, G. Zhao, and J. Gao, “Coal-Assisted Water Electrolysis for Hydrogen Production: Evolution of Carbon Structure in Different-Rank Coal,” Energy Fuels, vol. 35, no. 4, pp. 3512–3520, Feb. 2021, doi: 10.1021/acs.energyfuels.0c04122.[4] X. Jin and G. G. Botte, “Feasibility of hydrogen production from coal electrolysis at intermediate temperatures,” J. Power Sources, vol. 171, no. 2, pp. 826–834, Sep. 2007, doi: 10.1016/j.jpowsour.2007.06.209.

Research on the microscopic mechanism and model applicability differences of CH4 and CO2 adsorption based on molecular dynamics

To verify the accuracy and rationality of the molecular simulation model, the microscopic mechanism of gas adsorption was analyzed and clarified from a microscopic perspective. The effect of molecular models created by direct construction and supercell expansion on the adsorption capacities of CH4 and CO2 has been analyzed. Eight coal-based molecular configurations were created to simulate the isothermal adsorption process of CH4 and CO2 using various coal-based molecular configurations. Using physical experiments, the validity of different construction methods for coal-based molecular structures was verified. The direct construction method was chosen to simulate the effect of various coal-based molecular numbers on the adsorption capacity of CH4 and CO2. The results show that the adsorption capacity of CO2 on coal is greater than that of CH4. The isothermal adsorption curves of CH4 and CO2 in coal-based molecular systems constructed using different methods reveal that the adsorption of methane on coal molecules adheres to the Langmuir monolayer adsorption theory. The adsorption sites for methane increase with the rise in free volume. The structure directly constructed and the supercell expansion directly determines the amount of methane adsorbed by each coal based molecule. The adsorption constants of CH4 and CO2 on the supercell extended structure are more volatile than those on the directly constructed structure, and the structure constructed directly for different coal based molecules is better than the supercell extended structure. The simulation using the direct construction method shows that as the number of coal-based molecules in the molecular configuration increases, The isothermal adsorption quantities of CH4 and CO2 increase linearly. The molecular configuration is not affected by the number of anthracite molecules. Molecular configuration is not affected by the number of anthracite molecules. The rationality of model construction has no obvious relationship with the number of coal based molecules.

Exploring the ultramicropore structure evolution and the methane adsorption of tectonically deformed coals in molecular terms

The mechanical deformation of coals occurring extensively during the geological period (tectonically deformed coals) can directly alter their pore structures and then the storage of coalbed methane. This study in-situ investigated the effects of different mechanical deformations on the ultramicropore structure and the methane adsorption of coal molecules using molecular simulations. The results show that the shear deformation (< 0.23 GPa) of coals was much easier than the compression (~ 20 GPa). Further, the shear deformation can increase the void fraction (200%) and the surface area (30%) of coal molecules, comparing to the reduction of them by the compressive deformation. Accordingly, compression is not benefited to the methane storage (only remaining 14-22% adsorption amount). While, the shear deformation of coals can increase the methane adsorption amount (reaching 42–50 mmol/g). The ~ 7.5 Å is a key pore size to evaluate the effect of the shear deformation on the methane adsorption amount. Also, the adsorption sites for methane depends on the deformation mode of coals (compression: heteroatoms; shear: C atoms). Overall, the strained Wiser (bituminous, medium-rank) coal shows relatively superiority in the methane storage, while the methane adsorption of Wender (lignite, low-rank) coal is much more sensitive to the mechanical strain.

Influences of surface active-groups on the exothermic properties and oxidation of coal molecules

In this study, coal samples' reactive group contents were changed using extractants, and the effects of the reactive group contents spontaneous coal combustion were investigated using infrared spectroscopy, thermogravimetry/derivative thermogravimetry, and differential scanning calorimetry. The results showed that the coal samples' hydroxyl group contents decreased in the order ethylenediamine (3.832 %) > N-methyl-2-pyrollidone mixed solution (2.091 %) > petroleum ether (0.882 %) > toluene (0.495 %) and that the hydroxyl group content was inversely related to the characteristic temperature point. RDG analysis showed that ethylenediamine formed N–H–O hydrogen bonds with hydroxyl-group-bearing molecules, coal molecules formed C–H–O hydrogen bonds with NMP molecules, petroleum ether generated a cumulative dispersive force with aliphatic side chains, and toluene molecules' benzene rings formed a very stable spatial structure with coal molecules' benzene rings. The thermogravimetry/derivative thermogravimetry curves showed that because the characteristic temperature points of the extracted coal samples moved to the high-temperature region from T5 onward, the coal samples had to be heated to a higher temperature to reach the energy required for the reaction. From the DSC thermograms, the exergy decreased in the order toluene (110.68 J/g) > NMP (110.52 J/g) > ethylenediamine (78.29 J/g) > petroleum ether (65.45 J/g). With increasing temperature from T1 to T6, the Pearson correlation coefficients of the alcoholic and phenolic hydroxyl groups were calculated at −0.7, −0.72, −0.93, −0.84, −0.8, −0.8, and −0.93 and −0.72, −0.91, −0.83, −0.79, −0.815, and −0.91, respectively, indicating that the hydroxyl group content influenced the coal's spontaneous combustion more than the other groups' contents.

Microscopic mechanism of oxygen consumption inhibitor delaying the oxidation of coal

In order to inhibit the coal-oxygen complex that triggers spontaneous coal combustion, a retardant consisting of sodium alginate solution, sodium bicarbonate, inorganic salt MgCl2 and deoxidiser that can achieve multiple effects of hysteresis and oxygen depletion was developed. Taking the sulfur-containing side-chain reactive group of coal molecule -CH2-SH as the object of study, the Gaussian 16W procedure and density-functional-transfer theory (DFT) were applied to investigate the electrostatic potential and reaction tendency, oxygen adsorption capacity, front-line orbitals, natural bonding capacity, and oxygen adsorption capacity of the reactive group before and after the formation of the complexes with Na+ and Mg2+, using the solvation effect at the level of B3LYP/6-31G(d, p), respectively. The changes of electrostatic potential and reaction tendency, oxygen adsorption, front orbitals, natural bonding orbitals and charge transfer before and after the formation of complexes between -CH2-SH reactive groups and Na+, Mg2+, respectively. Comparative analysis of the interaction with oxygen before and after the formation of coordination blocking structure of coal and inorganic salts in gaseous environment, aqueous environment and retarded oxygen-depleting sodium alginate blocking solution environment, respectively. The calculated results show that the side chain of the aromatic ring of the raw coal is the active site for easy adsorption of oxygen, and the stability of the coordination blocking structure is significantly enhanced under the environment of hysteretic oxygen-depleting sodium alginate gel blocking agent, and the adsorption of oxygen before and after the coal molecule combines with Na+ and Mg2+ is the weakest under the environment of hysteretic oxygen-depleting sodium alginate gel blocking agent; The absolute value of the HOMO orbital energy increases the most, and the energy level difference (ELUMO - EHOMO) of the complexes increases the most; the natural bonding orbital analysis reveals that the lone pair of electrons of S atoms in -CH2-SH under the environment of hysteresis oxygen depletion sodium alginate gel blocker has a strong coordination effect with Na+ and Mg2+. In the hysteresis oxygen depletion sodium alginate gel resist environment, the stability of the coordination blocking structure is strengthened due to the moderateness of the dielectric constant, and its oxygen depletion also reduces the number of O2 molecules, which further reduces the adsorption and collision chances between the two, and a more desirable blocking effect can be obtained. The results reveal the micro-mechanism of the hysteresis oxygen depletion inhibitor in preventing spontaneous combustion of coal, which can provide a reference for further improving the inhibition effect of the inhibitor.

Insight into influence of degradation metabolism of Firmicutes on the microstructure of anthracite coal

Promoting the permeability of deep, low-permeability coal seams through biological means is currently a research hotspot for enhancing the efficiency of coalbed methane extraction. In this study, we selected anthracite coal from Sihe Mine for microbial anaerobic degradation culture experiments. The effects of adding functional microorganisms on the microstructure of anthracite coal were analyzed by high-throughput sequencing of samples before and after the cultivation and microcharacterization experiments of coal samples. The results showed that the maximum methane migration during the period of biodegradation reached 0.640 mL/g coal, and the cumulative migration of the whole cycle was as high as 1.318 mL/g coal. 16S rRNA high-throughput sequencing results indicated that the bacterial community structure had undergone significant succession after the biodegradation experiments, and that the Firmicutes represented by Bacillus(82.41% of the total) occupied the dominant niche. Metabolic pathway analysis based on Kyoto Encyclopedia of Genes and Genomes (KEGG) database showed that the degradation of aromatic compounds by microorganisms appeared to be significantly enhanced by the addition of nitrogen sources. Also, the relative abundance of a number of key metabolic enzyme genes capable of catalyzing the oxygen-containing functional groups into the structure of the coal molecule and the de-cyclization reaction were increased. Fourier Transform Infrared Spectrometer (FTIR) experiments revealed that biodegradation stimulated by nitrogen source reduced the aromaticity of coal by 59.62% and enhanced the hydroxyl functional group content by 1.822 times. Mercury pressure and low-temperature nitrogen adsorption experiments showed that the micropore pore volume of the treated coal decreased by 34.09%, and the macropore pore volume accounted for an increased 168.28%, with an average pore size increment of 60.72 nm. Therefore, the nitrogen source can stimulate Firmicutes on the degradation of polycyclic aromatic hydrocarbon and increase the content of oxygen-containing functional groups, which might promote the development of pores in coal and make the difficult-to-desorption methane migrates rapidly. This study investigated the effect of nitrogen source on the degradation of coal by Firmicutes. This will help improve the efficiency of gas extraction and ensure the safety of coal mine production.

Reactive behaviors and mechanism of methane/coal dust hybrid explosions inhibited by NH4H2PO4 and (NH4)2HPO4: A combined ReaxFF-MD and DFT study

Understanding the explosion-inhibition mechanism of methane/coal dust mixtures at the atomic level is crucial. This study employed ReaxFF-MD and DFT calculations to investigate the inhibitory effects of NH4H2PO4 and (NH4)2HPO4 on methane/coal dust explosions. The research examined macroscopic products, chemical bonds, key reaction pathways, and intermediate products. Furthermore, the evolution mechanism of coal molecules involved in the explosion-inhibition reaction was elucidated. The results indicate that NH4H2PO4 inhibits CO2 generation, while (NH4)2HPO4 enhances H2O production. Additionally, the inhibitors affect not only the initial reaction steps of CH4 but also absorb reactive radicals (•H/•O/•OH) and intermediate products (•CH3/CH2O). Compared to NH4H2PO4, the inhibition cycling reactions of (NH4)2HPO4 exhibit greater diversity. Increasing inhibitors’ mass fraction promotes competing reactions among free radicals, which diminishes the inhibition effect on CH4 dehydrogenation, leading to oscillations in explosion-inhibition efficiency. The inhibitors also delay the bond-breaking time for both the aliphatic bond and the ether-oxygen bridge of coal molecules, thereby prolonging the ring-opening reaction time of these molecules.

Imidazole ionic liquid effects on coal swelling behavior and pyrolysis characteristics: Experiment and molecular simulation

In view of low-rank coal conventional swelling solvent large pollution and the clean efficient utilization of coal, the effects of imidazole ionic liquid (IL) pretreatment with different anion groups as green solvent on coal thermal expansion and pyrolysis performance were investigated. IL interacts with coal molecules, destroying the hydrogen bonds, resulting coal expansion. Different anion groups have different modification effects, [Bmim]Cl has the best swelling effect, which is 17.37 % higher than raw coal, and the best modification time is 24 h. In addition, IL modification has a catalytic effect on coal pyrolysis, which can significantly reduce the maximum weight loss temperature and increase tar content. Coal solvent pretreatment provides a good theoretical basis for application of swelling and pyrolysis. The reduction of thermochemical reaction temperature not only reduces the content of heavy groups in pyrolysis products, but also provides new ideas for carbon emission reduction.

Mechanism study of replacing adsorbed O2 molecules in different pore sizes under different CO2/N2 inert gas conditions

Injecting inert gases into the goaf is a crucial method for inhibiting coal spontaneous combustion. Research has verified that the co-injection of CO2 and N2 provides a more effective control measure compared to a single gas, but the microscopic mechanism underlying the synergistic displacement of O2 by CO2 and N2 remains unclear. Injecting inert gases into the goaf is a crucial method for inhibiting coal spontaneous combustion. Research has verified that the co-injection of CO2 and N2 provides a more effective control measure compared to a single gas, but the microscopic mechanism underlying the synergistic displacement of O2 by CO2 and N2 remains unclear. Here, for the constructed multi-scale aperture slit model, the Grand Canonical Monte Carlo simulation (GCMC) and Molecular Dynamics (MD) simulation are used to investigate the mechanism of displacing adsorbed O2 molecules under different CO2/N2 inert gas conditions. The results indicate that CO2 and N2 aggregated on opposing sides of the coal molecules and dispersed within the slit layer, respectively. At 1 nm pore size, the relative concentration of O2 for optimal displacement was 1.054. The absolute value of the average binding energy is small when the CO2:N2 gas ratio is 80:20 and 40:60 at 2 nm and 4 nm apertures, respectively. This suggests that as the aperture size increases, the displacement effect on O2 shifts towards a higher proportion of N2, with a more conspicuous replacement effect as the aperture widens. The smaller pores ranging from 1-2 nm predominantly feature CO2 displacing adsorbed state O2, while larger pores exceeding 2 nm primarily N2 facilitate the transportation of free state O2.

Experimental and molecular simulation study on the influence of chain length and anion structure of ionic liquids on the wettability of highly hydrophobic bituminous coal

The wettability of bituminous coal is critical for the coal dust suppression and can be apparently modulated by ionic liquids. However, the modulation mechanism still remains elusive. Here, a combination of macroscopic experiments, mesoscopic characterization, and microscopic simulations (quantum mechanics and molecular dynamics) are leveraged to parse the effect on the wettability of coal dust surfaces of three novel ionic liquids ([C12MIm]Br, [BMIm]Br, [BMIm]Cl) featuring the varying chain lengths and anions in the coal-water system. The results show that the selected ionic liquids exert a distinct bridging function from traditional surfactants which invoke the hydrogen bonding interaction. This ionic liquids-mediated bridging mechanism heavily depends on their chain length structure, which can firstly penetrate deeply the internal pores of coal dusts and then adsorb on the coal surfaces to rapidly strike a dynamic equilibrium. Ionic liquids interacting with coal dust can primarily reduce the energy difference between polar and nonpolar interactions within coal dust, thereby enhancing the electrostatic interactions between coal dust and water molecules and effectively improving coal dust wetting properties. These findings provide a theoretical basis for the rational design of high-performance ionic liquids for coal mine dust control.

Micromechanism of the effect of coal functional groups on the catalytic/esterification reaction of acetic acid

Acidification modification has proven to be a successful approach for enhancing the permeability of low-permeability coal seams and increasing coalbed methane extraction. To explore the influence of acetic acid on the organic structure of coal, a combined approach of experimental research and quantum chemical calculation is employed to examine the reaction mechanism of coal organic structure in response to acetic acid. Fourier transform infrared spectroscopy reveals a reduction in the content of hydroxyl and C–O bonds in the treated samples, along with the appearance of an absorption peak of C=C bonds. This demonstrates that the main site of acetic acid acidification modification on coal molecules is the hydroxyl functional group. Therefore, glycerol can be used as a simplified model of coal molecules for further investigation. In addition, three typical functional groups (phenyl, hydroxyl, amino) are selected as the research objects. The electronic density topological properties, molecular surface electrostatic potential, Mayer bond orders and CM5 charge of coal molecules were calculated based on quantum chemical theory. This reveals the intrinsic strength of each chemical bond between single atoms in a molecule, thereby predicting potential reaction pathways between acetic acid and coal molecules. The micro-mechanism of acetic acid catalyzing/esterifying the organic structure of coal is studied using transition state methods. The computational results show that there are two main modes of reaction between acetic acid and coal molecules: (1) acetic acid catalyzes the dehydration reaction of coal molecules; (2) acetic acid reacts with coal molecules to form ester intermediates, followed by decomposition through various reactions. Among the 14 reaction pathways, acetic acid provides protons or groups to trigger the dehydration of coal molecules. Interestingly, it is found that the overall hydroxyl group participates in the reaction is easier than the individual hydrogen atom on the hydroxyl group, and the overall carboxyl group participates in the reaction is easier than the individual hydroxyl group. This indicates that the higher the overall atomic reactivity of acetic acid, the lower the reaction barrier. Compared with catalytic reactions, acetic acid tends to undergo esterification reactions with hydroxyl groups, with the phenyl ring functional group significantly affecting the reaction barrier. The introduction of various oxygen-containing functional groups like ketone, aldehyde, and ester in the reaction products will hinder the adsorption of non-polar methane, reduce the adsorption capacity of coal seams for gas, and play an essential role in promoting gas desorption. The research findings can provide theoretical guidance for the organic acidification modification of low-permeability coal seams to enhance gas permeability and coalbed methane extraction.

Study on the Influence Mechanism of the Key Active Structure of Coal Molecules on Spontaneous Combustion Characteristics Based on Extraction Technology

The molecular structure of coal is complex, and the existing research methods are limited, so it is difficult to clarify its influence mechanism on the spontaneous-combustion characteristics of coal. In this paper, the previous extraction, FTIR, TPR, TG-DSC and other experimental results are combined to analyze the extraction weakening effect and the correlation analysis of the spontaneous-combustion characteristic parameters of raffinate coal. The results show that extraction can destroy the connection bond of coal molecules, change the content of dominant active groups in the coal spontaneous-combustion reaction, increase the lower limit of the key temperature nodes of coal spontaneous-combustion or extend the temperature range, resulting in an increase in the ignition-point temperature of coal and a decrease in coal quality. This paper will provide a theoretical basis for the study of the microscopic mechanism of coal spontaneous-combustion and then provide new ideas for the development of an active prevention and control technology for coal spontaneous-combustion.

Consolidation performance and mechanism of composite dust suppressant based on graft modification

AbstractTo solve the severe coal dust pollution and dust hazards in underground coal mines, this study utilized graft copolymerization modification technology and compound technology to develop a mining composite consolidation dust suppressant. On this basis, analysis of its consolidation wettability and dust suppression mechanism was conducted through characterization tests and molecular dynamics simulation methods. The results show that polyacrylamide (PAM) had been successfully grafted onto the soybean protein isolate (SPI) molecule, and form a SPI‐PAM complex. After the dust suppressant acted on the coal dust surface, it utilized its wealthy hydrophilic groups, for the adsorption of water molecules and the positive amide group for binding to produce a large area of agglomeration of coal dust particles at the interface, exhibiting good wetting and consolidation into a shell. At the same time, molecular dynamic simulation verified that the diffusivity of water molecules in the dust suppressant‐coal system was 0.30Å2/ps, decreased by 43.3%, and the interaction energy with coal molecules was −200.27 kcal/mol, absolute value increased by 41.35%, which made the dust suppressant molecules more easily adsorb and agglomerate on the surface, demonstrated an excellent solidification and dust suppression effect.

Molecular simulation of the effect of water content on CO2, CH4, and N2 adsorption characteristics of coal

The objective of this work was to investigate the sorption behavior of gases, namely CO2, CH4, and N2, by molecules of coal sampled from Linglu mine under different water inclusion rates. To this end, the adsorption, diffusion, adsorption heat, and potential energy distribution characteristics of the gases in the coal pores at different water inclusion rates were analyzed using molecular dynamics and grand canonical ensemble Monte Carlo methods. The results showed that the adsorption relationship of the coal molecules on CO2, CH4, and N2 exhibited a downtrend followed by an uptrend when the water content was increased from 0 to 3.6%. The adsorption amount of CO2 was approximately twice as much as those of CH4 and N2, indicating that the competitive adsorption advantage of CO2 compared with those of CH4 and N2 was unaffected by the water content. The trend in the average heat of adsorption was generally consistent with the trend in the density of coal molecules under different moisture contents. Under the same conditions, the diffusion coefficient within a coal molecule was negatively related to the water content in the system. The layer spacing of the water molecules (2.875 Å) was greater than the liquid–water layer spacing, indicating the formation of a water molecule layer at this point, which inhibited gas adsorption. This study lays a theoretical foundation for further investigating the microscopic mechanism of coal–water interaction.

Experimental Study on Combined Microwave-Magnetic Separation-Flotation Coal Desulfurization.

In order to reduce the content of sulfur and ash in coal, improve the desulfurization and deashing rates, a combined experiment method of microwave magnetic separation-flotation was proposed for raw coal. The desulfurization and deashing rates of three experiment methods, namely, single magnetic separation, microwave magnetic separation, and microwave magnetic separation-flotation, were compared. Taking the microwave magnetic separation-flotation experiment method as the main line, the effects of the microwave irradiation time, microwave power, grinding time, magnetic field intensity, plate seam width, foaming agent dosage, collector dosage, and inhibitor dosage on desulfurization and deashing were discussed, and the mechanism of microwave irradiation on magnetic separation and flotation was revealed. The results show that under the conditions of a microwave irradiation time of 60 s, a microwave power of 80% of the rated power (800 W), a grinding time of 8 min, a plate seam width (the plate seam width of a magnetic separator sorting box) of 1 mm, a magnetic field intensity of 2.32 T, a foaming agent dosage of 90 g/t, a collector dosage of 2125 g/t, and an inhibitor dosage of 1500 g/t, the desulfurization and deashing effect is the best. The desulphurization rate is 76.51%, the sulfur removal rate of pyrite is 96.50%, and the deashing rate is 61.91%. Microwaves have the characteristic of selective heating, and the thermal conductivity of organic matter in coal is greater than that of mineral. Microwave irradiation can improve the reactivity of pyrite in coal, pyrolyze pyrite into high-magnetic pyrite, improve the magnetic properties, and improve the magnetic separation effect. Therefore, microwave irradiation plays a role in promoting magnetic separation. Through microwave irradiation, the positive and negative charges in coal molecules constantly vibrate and create friction under the action of an electric field force, and the thermal action generated by this vibration and friction process affects the structural changes in oxygen-containing functional groups in coal. With the increase in the irradiation time and power, the hydrophilic functional groups of -OH and -COOH decrease and the hydrophilicity decreases. Microwave heating evaporates the water in the pores of coal samples and weakens surface hydration. At the same time, microwave irradiation destroys the structure of coal and impurity minerals, produces cracks at the junction, increases the surface area of coal to a certain extent, enhances the hydrophobicity, and then improves the effect of flotation desulfurization and deashing. Therefore, after the microwave irradiation of raw coal, the magnetic separation effect is enhanced, and the flotation desulfurization effect is also enhanced.

Evolution of macromolecular structure during coal oxidation via FTIR, XRD and Raman

The analysis of the macromolecular structure and morphology in coal during oxidation is the basis to explore the mechanism of spontaneous combustion. To explore the evolutionary rules of coal macromolecular structure during oxidation, Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), and Raman Spectroscopy (Raman) were employed to analyze the coal samples with different oxidation degrees. The results revealed that the oxidation action led to the decrease of the aliphatic structures and aromatic hydroxyl groups in coal, while promoting the formation of oxygen-containing functional groups and aromatic structures. It also led to a relative increase of free hydroxyl groups linked to hydrogen bonds. The aromatic layer spacing (d002) decreased with increasing oxidation degree, while the microcrystal stacking height (Lc), the aromatic layer diameter (La), the average number of crystal stacking layers (n) generally increased. It indicated that small aromatic ring molecules in coal could undergo continuous polymerization during oxidation to form a single aromatic layer structure. The variation of Raman spectrum parameters exhibited a consistent decreasing trend in WD/WG, ID/IG, AD/AG, and A(GR+SL)/AG value, indicating an increase in the vibration of sp2 hybridization carbon atoms within the lattice structure of coal. Conversely, PG-D, AS/AD and A(GR+VL+VR)/AD value increased overall, suggesting that small aromatic rings decreased in content during oxidation while polymerizing into larger aromatic rings. The coal structure underwent a brief stage of disordered evolution during oxidation, followed by removal of impurity structures and condensation of aromatic structures due to increasing oxidation temperatures, ultimately leading to a highly ordered crystalline state. The oxidation process significantly influenced the development of coal's aromatic structure, particularly in less metamorphic coal. The research findings provide a theoretical basis for analyzing the underlying mechanism behind spontaneous combustion induced by coal oxidation.