Chemical Structure Of Coal Research Articles

Effect of pre-oxidation and cooling process on characteristics and mechanism of the coal re-ignition

Based on the engineering background that the sealed fire area is easy to reignite, the reignition characteristics of pre-oxidized coals (POC) after cooling are studied. Predecessors mainly explain this problem from the perspective of pre-oxidation affecting coals pore structure. This paper analyzes the effects of different pre-oxidation temperatures and cooling atmospheres on coal physical and chemical structure. The changes of coals during oxidation-cooling-reoxidation were studied by means of a programmed heating device, low temperature nitrogen adsorption experiment, FTIR and quantum chemical calculation. The results show that the average pore size of the coal cooled in nitrogen at the same pre-oxidation temperature is smaller than that of the coal cooled in dry air, while the spontaneous combustion characteristics of the coal cooled in nitrogen are stronger than those of raw coal, and spontaneous combustion characteristics of coal cooled in air are the opposite. The oxygen-containing functional groups of the coal cooled in nitrogen are pyrolyzed to produce active sites which can exist stably in nitrogen. Then, the rationality of “The active sites tend to be alkyl radical” is analyzed and speculated by molecular orbital theory, and it's found that alkyl radicals can release lots of heat at 30 °C.

Evolution mechanism of coal chemical structure after supercritical CO2 transient fracturing

This study investigates the chemical structural evolution of coal during supercritical CO2 transient fracturing using a self-developed experimental platform. Coal samples with different metamorphic ranks were subjected to transient fracturing under different pressures. Characterization techniques, including X-ray diffraction, Raman spectroscopy, and Fourier transform infrared spectroscopy, analyzed the fractured coal samples. Initially, supercritical CO2 dissolved minerals and non-aromatic structures, rearranging organic compounds. As fracturing intensified, alkanes and substituents rapidly released, causing large aromatic rings to break into smaller ones. The breakage of small aromatic rings created pores and increased aromatic structure dimensions. Moreover, the interaction between fractured small aromatic rings and oxygen atoms in the C=O group facilitated the formation of new C–C bonds, promoting the connection of aromatic rings to form larger structures. In the early stages of fracturing, the molecular structure of coal relaxed, and subsequently, as the fracturing intensified, the hydrogen bonds initially broken could reconnect to aromatic structures to form OH-π interactions, enhancing intermolecular attraction. This promoted molecules to be more inclined to form stable, dense structures. Understanding this evolution mechanism aids in analyzing the transformation of fractured coal pores, thereby enhancing our understanding of the mechanism for improving coal seam permeability using this technology.

Study on the degree of influence of coal chemical structure on its wetting characteristics

The wettability of coal plays a crucial role in determining the effectiveness of mine dust reduction, coal flotation, and coal water slurry preparation. This property is influenced by various factors, including coal structure and liquid properties. To investigate the impact of coal’s chemical properties on its wetting behavior, we employed different experimental to characterize the chemical structures of six types of coal. Utilizing contact angle experiments and gray slope correlation analysis, we determined the correlation between each chemical structure parameter and the wetting characteristics of the coal samples. Our findings revealed that 6#Yangquan anthracite has the lowest wettability and its contact angle is 85.3°. Within the coal’s functional group structure, the CH2 symmetric stretching vibration exhibited the highest correlation (0.944) with coal wetting properties. Regarding the elemental composition of coal, oxygen exhibited a higher correlation with coal-wetting properties (carbonyl oxygen structure, 0.788; phenol hydroxyl and ether oxygen bond, 0.798; carboxyl oxygen structure, 0.734). In the carbon skeleton structure of coal, the protonated aryl carbon exhibited the highest correlation degree of 0.944. These results offer insights into the selection of evaluation indices for assessing the influence of coal wetting characteristics and optimizing the hydrophilic and hydrophobic features of the coal surface.

Evolution of pore structure and changes in oxidation characteristics of coal after heating freezing treatment

To study the spontaneous combustion characteristics of preheated coal treated by liquid nitrogen (LN2), surface structure test, thermal analysis experiment and chemical characteristic analysis experiment were used to study the change characteristics of surface structure, oxidation characteristic and chemical structure of coal under the action of LN2 quenching. The results showed that with the increase of preheating temperature, the fractal dimension, specific surface area, pore volume and average pore diameter of the LN2 treated coal (quenched-coal) increase. With the increase of preheating temperature, under the oxidation condition, the CO and CO2 produced at ST of 230 ℃ are 1.19 times and 1.21 times higher than those at ST of 70 ℃. The CO/CO2 emission of quenched-coal is significantly increased, and the secondary oxidation capacity is stronger. Due to the more developed pore cracks of coal under pyrolysis and quenching conditions, the natural characteristics of coal are stronger. The oxygen adsorption capacity and apparent activation energy of pyrolysis coal in the stageⅠ affected by LN2 are stronger. Oxidized coal shows stronger oxidation and heat release ability in the stageⅡ under the action of LN2, resulting in higher apparent activation energy in this endothermic stage. The addition of LN2 blocked the oxidation reaction of preheated coal and sealed the structure of -C = O, –COOH and –OH. The bridge bond –CH2- structure of pyrolysis coal is further destroyed, and the ratio of –CH2/–CH3 is reduced. The increase of alkyl free radicals in pyrolysis coal and alkyl oxygen free radicals in oxidation coal accelerates the spontaneous combustion oxidation of coal. The research results have important guiding significance for the occurrence and prevention of coal reignition disaster after LN2 fire quenching.

Physical Characteristics of Coal Reservoirs and CBM Favorable Area Prediction in the Huaibei Coalfield, Northern China.

To quantitatively characterize middle-high-ranked coal reservoirs, the physical characteristics of seven coal samples from the Huaibei Coalfield in northern China were investigated in detail based on experiments including proximate analysis, coal petrology, low-temperature nitrogen adsorption (LTNA), mercury intrusion porosimetry (MIP), nuclear magnetic resonance (NMR), and methane isothermal adsorption. The results show that coal maceral in the Huaibei Coalfield is dominated by vitrinite, with a large change in the maximum vitrinite reflectance ranging from 0.7 to 2.5%. The various coal metamorphisms can be attributed to the combined influence of magmatic activities of the Tanlu and Taihang Mountains during the Yanshanian. The coal quality can be characterized by medium-high ash yield, low to very low sulfur content, low phosphorus, and medium-high calorific value. From low-ranked coals to medium-ranked coals, the volume of adsorption and seepage pores decreases but the fracture volume increases due to the stronger dehydration and coal matrix shrinkages. From medium-ranked coals to high-ranked coals, adsorption pores have a significant advantage, suggesting a stronger CH4 adsorption capacity. There is a positive correlation among the fixed carbon content, coal rank, and Langmuir volume, which can be attributed to the transformation of coal chemical composition and structure by coal metamorphism. The deep Xiaoxi in the Suixiao coal mining area, deep Nanping, deep Taoyuan-Qinan, deep Pengqiao, northern Zhuxianzhuang in the Suxian coal mining area, deep Renlou-Zhaoji, and Xutuan deep in the Linhuan mining area are predicted to be favorable areas for CBM exploration in the Huaibei Coalfield.

Effect of supercritical CO2 transient high-pressure fracturing on bituminous coal microstructure

Carbon dioxide phase change fracturing is an effective permeability enhancement technology, and its influence mechanism on the coal microstructure remains to be further investigated. To explore the impact of CO2 fracturing on the coal chemical structure, the self-developed transient high-pressure fracturing of CO2 test platform was independently developed. Based on X-ray photoelectron spectrometer (XPS), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD), the elemental morphology, functional group and crystal structure of the two bituminous coal samples before and after fracturing were analyzed. The results showed that the fracturing process resulted in the disruption of hydrogen bonds within coal, leading to a reduction in the cross-linking density of the coal structure. Moreover, it facilitated the breaking of fatty alkyl side chains and oxygen-containing functional groups, causing the detachment of side chains and shortening of the fatty chains. The interlayer spacing of aromatic layers (d200) of fractured coal decreased, and the average transverse dimension (La), the average stack height (Lc) and the aromaticity (fa) increased. With the improvement of aromaticity, the arrangement between aromatic layers was looser. The volume and basic unit structure of coal crystal nucleus became larger, and the flattening degree increased. The research results contribute to the understanding of the change of coal microstructure under supercritical CO2 transient high-pressure fracturing and provide theoretical support for exploring the methane adsorption capacity of fractured coal.

A study of the relationships between coal heterogeneous chemical structure and pyrolysis behaviours: Mechanism and predicting model

Coal is naturally heterogeneous on chemical structure, which significantly affects its pyrolysis behaviours. However, due to the limit of characterization tools, quantification of the chemical structural heterogeneity and its effects on pyrolysis are still challenging. In this study, a quantification method for chemical structural heterogeneity by Raman mapping technique was firstly proposed, and the heterogeneous chemical structure of coal was investigated. The results show that the distributions of the chemical structure are highly uneven, even though the average structural characteristics are highly similar. Besides, the effects of chemical structural heterogeneity on pyrolysis behaviours were studied. It is found that except for the average structural properties, the chemical structural heterogeneity affects the pyrolysis behaviours significantly. It is attributed to the different pyrolysis mechanisms and uneven distribution of these chemical structures with different reactivity. The effects of the average chemical structures and the chemical structural heterogeneity on the pyrolysis behaviours are independent. Furthermore, new predicting models for pyrolysis behaviours by considering both the average structure and the chemical structural heterogeneity were established and validated. The final models were proved to be adequate to effectively predict the pyrolysis behaviours of raw and blended coals.

Experimental study on changes in components and pore characteristics of acidified coal treated by organic solvents

Chemical solvents could change coal components and effectively enhance conductivity of coal reservoir, which is beneficial to efficient methane extraction. Relationship between coal chemical structure parameters and main functional groups variations affected by acidification and tetrahydrofuran (THF) is investigated through infrared spectroscopy tests and curve peak fitting. Meanwhile, variations in fractal dimensionality and pore structure characteristics are studied by adopting low-temperature nitrogen adsorption tests and Frenkel-Halsey-Hill (FHH) fractal model. Main results are: (1) After extracting raw coal and acidified coal using THF with varying concentrations, absorbance of aromatic hydrocarbon –CH surface and aromatic methyl bond become weaker. While the proportion of substituted aromatic hydrocarbons increases in acidified coal than in raw coal. Acidification treatment could reduce strength of C-O-C absorption peak. Proportion of CH2 and CH3 in raw coal decreases with increasing THF concentration, indicating that THF could react with aliphatic structure to reduce CH2 and CH3 content. Extraction with THF dissolves aromatic structure, lowering C = C content in coal to different degrees. (2) Acidification pretreatment could produce more micropores in coal samples. Micropore contents of acidified coal after THF extraction are all lower than coal sample S, while transition pores and mesopores contents are both higher than those in coal sample S. (3) Fractal dimension D1 of raw coal indicates a relatively linear relationship with specific surface area, while the D1 of acidified coal is less correlated with specific surface area. The factor D2 shows a linear relationship with average pore size. After treatment of THF, average pore size of raw coal increases with D2, while that of acidified coal varies in different degrees with uneven distribution of pore sizes.

Fractal characteristics for coal chemical structure: Principle, methodology and implication

Despite coal chemical structure's importance as the organic backbone for hydrocarbon production, the fractal characteristics for coal chemical structure remains unexplored. Therefore, this paper proposed a novel method to calculate the fractal dimension Df for coal chemical structure. The principle and methodology of the proposed method were deduced and summarized in detail. This method was applied to calculate the fractal dimension Df for the coal chemical structure from lignite to anthracite. The research results indicate that the fractal dimension Df for coal chemical structure decreases first and then increases with coalification. The turning point of the variation trend of fractal dimension Df and coalification corresponds to the second coalification jump (maximum vitrinite reflectance Ro, max = 1.30 %). This study has achieved the micro characterization on coal chemical structure at molecular scale, which has potential application value on the functional properties analysis and molecular synthesis design of coal-based material research fields.

Chemical structure effects on coal pyrolyzates and reactions by using large-scale reactive molecular dynamics

The relationship between the coal chemical structure and its thermal reactivity is vital to understand coal pyrolysis behaviors. In order to explore chemical structure effects on pyrolysis process, five large-scale coal models of different ranks were constructed and simulated with ReaxFF MD simulations by a combined approach of high performance computing and cheminformatics based reaction analysis in this work. The qualitative temperature mapping results between ReaxFF MD simulations and thermogravimetry experiments were obtained for the first time through the detected covalent bond breaking, which suggests a promising scheme to map the simulation results to the real world. Importantly, the typical structures in coal can be used as the indicators to predict pyrolysis stages, weight loss profiles and major pyrolyzate distributions from the atomistic level. The starting temperature of coal thermal decomposition is anchored by the parameters of falO in 13C NMR representing alkyl ether amounts; and the largest phenol tar generation links closely to the faP NMR parameter; meanwhile methoxy groups determine the initial generation of CH3 radicals and CH4 at relatively low temperature. Additionally, the dynamic profiles of Car-Car bonds and the second increasing trend for CH3 radicals have strong relationship with recombination reactions. With the reasonable coal structures, the large-scale ReaxFF MD simulation alone can complement experimental observation comprehensively to understand the complex coal thermal chemistry and used as a preliminary screening approach to select the coal type or rank for industrial utilization.

Molecular dynamics simulations and experimental study of the effects of an ionic surfactant on the wettability of low-rank coal

The surfactants sodium dodecyl benzene sulfonate, dodecyl dimethyl betaine, and dodecyl trimethyl ammonium bromide were used to study the effect of an ionic surfactant on coal wettability. A lignite-surfactant-water system was constructed using the Wender coal chemical structure model and Materials Studio molecular simulation software, and the static potential of a single molecule was determined by quantum chemical calculations. The initial and equilibrium configurations of the system, relative concentration distribution, and mean-square displacement (MSD) of water molecules were analyzed thoroughly. Additionally, the surface tension and contact angle of aqueous surfactant solutions with different mass concentrations were measured to analyze the relationship between concentration and the rate of reduction of surface tension and of contact angle. The analysis showed that when the surface static potential of the lignite molecule was larger than that of water molecules, the water molecules were easily attracted and exhibited a wetting phenomenon. The water-surfactant-coal system gradually tended from an initial unstable state to a stable state with low energy. Specifically, the hydrophilic groups in the surfactant were tilted toward the water phase and the hydrophobic chains were adsorbed on the surface of coal, which helped enhance the wettability of the coal. The relative concentration distribution range of the SDBS was 26–52 Å, which was wider than the other two surfactants. Additionally, the MSD curve showed that the diffusion coefficient of the water molecules in the water-SDBS-coal system reached a maximum value of 4.23 × 10−2, resulting in accelerated wetting of the coal body. When the SDBS mass concentration was 3%, the surface tension decreased to the minimum value (21.86 mN/m) and the minimum contact angle was 16.12°. Based on the simulation results and experimental test data, the wettability of the three surfactants to lignite was SDBS > BS-12 > DTAB. The findings of this study help to better understand the wetting mechanism of surfactants on lignite, which is conducive to the rapid screening of surfactants with strong wetting ability on lignite, expanding the use of surfactants, and is of great significance to the control and prevention of coal dust pollution.

Impact of chemical structure of coal on coke quality produced by coals in the similar category

In order to study the association of coke quality with the little fluctuation of chemical structure of the coal, three coals (C1, C2 and C3) from the similar category were employed to prepare coke in a 10 kg-scale coke oven. The status-oriented (G value, inorganic and organic component, etc.) and process-oriented (fluidity, volatile release, etc.) properties of the three coals are assessed. The association of coal chemical structure with these properties and final coke quality is clarified based on the experimental results by 13C NMR, Raman, etc. Clearly, the three coals from the similar category produce cokes with different properties. Chemical structure information obtained from 13C NMR and Raman shows that large aromatic clusters (higher far, Ca, etc.) with short chain hydrocarbon (lower CH2/CH3), and low graphitization degree (lower AG/AD, PG-D) of coal are not favorable for the coke strength. On the one hand, these structural properties determine the low vitrinite reflectance of coal and restrict the crosslinking reaction that may assist in the formation of the turbostratic carbon structures and affect coke strength. On the other hand, large aromatic clusters but short chain hydrocarbon are difficult to be depolymerized to form mobile components or transferable hydrogen-rich radical donor or acceptor. The development of the fluidity is insufficient to enhance coke strength, which is manifested by narrow plastic range, high temperature zone of thermoplastic stage, and low fluidity. In addition, defected structures (high GR+VL+VR and IGR+VL+VR/ID) in coal contribute to the high reactivity of corresponding coke. The unprotonated aromatic carbons (farN) may correspond to these defected structures in aromatic macromolecular. The results assist in establishing the association of apparent coal property and coke strength with coal chemical structure. The findings also support the assessment and prediction of coke strength for different coals, in particular, for coals that may fall into the similar category according to their similar apparent property.

Effect of self-diverting acid viscosity and the chemical structure of coal under different acid environment

In order to solve the poor water infusion problem for low permeability coal seams, this paper studied the self-diverting acid to uniformly distribute acid. The results show that massive Ca2+ generated by the reaction between HCl and calcite can enhance the crosslinking of micelles. With the increase of HCl concentration, the viscosity increased and then decreased, which could be divided into “low viscosity zone” (0.1%–2%), “viscosity rapid increase zone” (2%–5%) and “viscosity decrease zone” (5%–15%). After treated with self-diverting acid, the fracture width and connectivity of coal was increased. Massive clay minerals were dissolved, the distribution range of pore size and pore volume gradually increased, and a large number of pores caused by corrosion appeared. Due to the influence of viscosity, the wettability of self-diverting acid for the coal was gradually reduced during infusion process. However, compared with distilled water, the overall wettability of coal still increased by 6.91%.

Relationship between Thermal Conductivity and Chemical Structures of Chinese Coals.

Three different ranks of Chinese coals were investigated on the thermal conductivity and corresponding molecular structure by thermal analyzer, 13C NMR, and HRTEM techniques. The thermal conductivity of coals measured in room temperature first shows a decrease, then a slight increase, and finally a sharp increase with increasing coalification. Ranging from 30 to 150 °C, increasing the temperature slightly improves the thermal conductivity of coals with varying degrees. Water with a higher thermal conductivity than air contributes to the thermal conductivity of porous coal samples. The value of thermal conductivity is higher along coal bedding planes than when perpendicular to beddings, which indicates the anisotropy of coal thermal conductivity. The anisotropy degree increases with the rank of coals and is affected by clay minerals when coals adsorb water. Molecular structure analysis shows that polycondensed aromatic ring related to lattice vibration contributes to the increase of thermal conductivity. The aliphatic bridges among aromatic clusters ensure the continuity of atom vibrations and contribute to energy transport, but the free-ended side chains have the opposite effect. The relative ordered distributions of lattice fringes of anthracite, which were higher than those of bituminous coal, enhance the anisotropy of thermal conductivity.

Modeling and simulation of coal gasification on an entrained flow coal gasifier

In this paper, the recent researches and developments on coal gasification modeling and simulation are described. Numerical models for the three chemical processes such as devolatilization, char gasification, and gas-phase reaction are reviewed and discussed for further development to improve accuracy. Recently the devolatilization models to describe the coal chemical structure with a simple expression have been proposed and validated on the laboratory-scale flames. It is essential to precisely model char gasification reaction as a rate-determining step and the formulation of the active sites sharing by the mixture and the pore structure formation are important in the modeling. It will become significant to take the elementary reactions into account in the gas phase reaction model. Large-eddy simulation of coal gasification on the laboratory-scale entrained flow gasifier is performed to demonstrate the numerical procedure. Results show the predicted temperature distribution qualitatively agrees with the experiment. Moreover, the gas-liquid-solid three-phase reacting flow simulation is preliminarily performed to capture the molten slag flow behavior within the gasifier. It is revealed that the three-phase simulation can give insight into the complex multiphase and multiphysics phenomena taking place within the gasifier to assess the design and the operating condition.

Controlling mechanism of coal chemical structure on biological gas production characteristics

To find the effect of coal chemical structure on biogas production, Lignite B was collected and extracted with nitrogen methylpyrrolidone (NMP), acetone and 0.60 mol/L NaOH. Simultaneously, methanogenic bacteria were enriched, and gas production experiments involving solvent extraction from residual coal and secondary gas production experiments involving coal were performed. The characteristics of biogas production, microcrystalline structure and coal chemical structure were analyzed. The results showed that the biogas production capacity of residual coal extracted by different solvents differed. The biogas production capacity of residual coal extracted by 0.60 mol/L NaOH was severely inhibited. The biogas production capacity of residual coal extracted by NMP and acetone was enhanced compared with that of raw coal. In contrast, primary residual coal still exhibits potential for methane production, but the methane production efficiency was reduced. Changes in the microcrystalline structure and functional groups of residual coal showed that solvent extraction increases the spacing and stacking height of the aromatic lamellae of coal, reduces the hydroxyl, methyl, methylene and aromatic hydrocarbon levels in coal, loosens the macromolecular network structure of coal, and enhances the connectivity of pores and fissures, thus allowing methane-producing bacteria to enter the coal mass and create favorable conditions for gas production through interactions between the two. X-ray photoelectron spectroscopy measurements showed that the secondary gas production increased the C content on the coal surface, decreased the O content and the O/C ratio, thus promoting the consumption of oxygen-containing functional groups on the coal surface to further produce gas.

Effects of Supercritical CO2 Treatment Temperature on Functional Groups and Pore Structure of Coals

The buried depth of a coal seam determines the temperature at which CO2 and coal interact. To better understand CO2 sequestration, the pore structure and organic functional groups of coal treated with different ScCO2 temperatures were studied. In this study, three different rank coals were treated with ScCO2 at different temperatures under 8 MPa for 96 h in a geochemical reactor. The changes in pore structure and chemical structure of coal after ScCO2 treatment were analyzed using mercury intrusion porosimetry, attenuated total reflection Fourier transform infra-red spectroscopy, fractal theory, and curve fitting. The results show that the enhancement effect of ScCO2 on pore structure of coal becomes less significant as the increase of buried depth. In most of the treated coal samples, the variation proportion of mesopores decreased and the variation proportion of macropores increased. In the relatively higher rank coals, the degree of condensation (DOC) of aromatic rings decreased after treatment with ScCO2. The DOC values showed a U-shape relationship with temperature, and the aromaticity showed a downward trend with increasing temperature. The chemical structural changes in the relatively lower rank coal sample were complex. These findings will provide an understanding of mechanisms relevant to CO2 sequestration with enhanced coalbed methane recovery under different geothermal gradients and for different ranks of coal.

Impact of tectonic deformation on coal methane adsorption capacity

Tectonic deformation can cause significant changes in the physical and chemical structures of coal by damaging the macrostructure and macromolecular composition. For thorough research on the coal tectonic deformation impacts on gas adsorption capacity, this paper collected and summarized the parameters of experimental adsorption isotherms and coal macerals, conducted proximate and ultimate analyses, and systematically discussed the adsorption properties of different structures of coals and the influence of temperature and pressure on coal adsorption. Furthermore, the semi-quantitative relationships between the structural parameters of coal and its methane adsorption capacity are explored. The results show that (1) due to different tectonic stresses, the molecular and porous structures of different types of tectonic coal exhibit significant differences (e.g. sample N25, which is in a fault zone, has the highest methane adsorption capacity), and (2) coal methane adsorption capacity decreases along with increasing temperature. At a pressure of 12 MPa, primary coal (N32) showed Langmuir volume (VL) values of 15.38, 9.58, and 7.86 cm3/g and Langmuir pressure (PL) values of 3.82, 2.07, and 1.81 MPa at temperatures of 30°C, 50°C, and 70°C, respectively. (3) The Langmuir volume appears to have a linear relationship with parameters ID1/IG, Al/OX, and A-factor, as well as a parabolic curve relationship with fa, thereby illustrating that increases of apparent aromaticity can raise CH4 adsorption on coal.

Effect of Igneous Intrusions on Low-temperature Oxidation Characteristics of Coal in Daxing Mine, China

ABSTRACT In order to investigate the effect of igneous intrusions on low-temperature oxidation characteristics of coal, metamorphic coal samples affected by igneous intrusions and normal coal samples were collected from Daxing Mine. The thermal effect of coal at a low temperature was studied by Thermogravimetric analysis and Differential scanning calorimetry (TG-DSC). The oxidation kinetics experiment was used to analyze the oxygen consumption, the index gas, the crossing point temperature (CPT) and apparent activation energy of coal. Compared with normal coal, the metamorphic coal had lower weight loss rate and higher oxygen absorption rate due to igneous intrusions. At the same time, the metamorphic coal absorbed less heat at low-temperature stage and entered the exothermic stage first, and the total heat release in the whole stage was larger. The author also found that the initial exothermic temperature of coal decreased obviously due to igneous intrusions. In addition, metamorphic coal had lower apparent activation energy because of igneous intrusions, which indicated that the molecular structure of coal became easy to be activated, and the energy needed for activation became lower. Fourier transform infrared spectroscopy (FTIR) analysis suggested igneous intrusions changed the chemical structure of coal and increased the branching degree and short aliphatic chains. Moreover, metamorphic coal consumed more oxygen and produced more carbon monoxide, ethylene and ethane, with lower crossing point temperatures, which concluded that the igneous intrusions accelerated the oxidation reaction of coal at low-temperature stage and increased the spontaneous combustion risk of Daxing coal.

Structural and pyrolysis behaviors analysis of coal pretreated with a weak acid

ABSTRACT Mineral matters are essential components of coal and significantly affect its thermal conversion process. To investigate the effects of the minerals on the structures and pyrolysis behaviors, three middle/low-rank Xinjiang coals were mildly pretreated with a weak organic acid with low concentration. We evaluated the physicochemical properties and mineral matters of raw and acid-pretreated coals and analyzed their pyrolysis behaviors. The results indicated that the chemical structure of coals changed slightly; their physical pore structure enlarged; the content of metal cations decreased obviously. The minerals are adverse to conducting the depolymerization and decomposition reaction at the temperature lower than 300 °C. With the temperature increasing, the minerals exhibit excellent catalytic performance and reduce the release of gaseous products (H2O, CO2, H2, C1~C3) mainly from the polycondensation and secondary reaction. The coal rank and the content of coal ash could affect the catalytic performance.