Macromolecular Structure Of Coal Research Articles

Permeability and meso-structure evolution of coking coal subjected to long-term exposure of triaxial stresses and high-pressure nitrogen

Permeability and meso-structure evolution of coal are crucially important to the profound understanding of coal–gas interactions in the enhanced coalbed methane recovery and in controlling gas outburst. Very few studies focus on the effect time has on these interactions We performed a series of experiments on the permeability evolution of coking coal subjected to the long-term exposure of triaxial stresses and nitrogen pore pressure. The coking coal seam belongs to a low permeability reservoir with an initial permeability of 10−16 m2. The change tendency of the permeability was divided into types I and II. In type I, coal permeability increased at first then decreased and stabilized at a lower level while only decreasing and stabilization were present in type II. There existed a threshold value (2.0 × 10−19 m2) about the initial permeability to control the tendency transition from type I to type II. The natural logarithm of both the maximum permeability in the increasing phase and the stable permeability in the stabilization phase were closely linear to the natural logarithm of initial permeability. The tendency corresponded to a change of coal structure, which was broken into many small-sized grains by the integrative action of long-term stresses, gas pressure, and gas adsorption. A simple elastic–plastic model was established to explain the destroyed mechanism of the coal macromolecular structure. The results will be helpful in understanding the mechanism of gas outburst in coal mines and gas-coal interactions in enhanced coalbed methane recovery.

Fine Characterization of the Macromolecular Structure of Huainan Coal Using XRD, FTIR, 13C-CP/MAS NMR, SEM, and AFM Techniques.

Research on the composition and structure of coal is the most important and complex basic research in the coal chemistry field. Various methods have been used to study the structure of coal from different perspectives. However, due to the complexity of coal and the limitations of research methods, research on the macromolecular structure of coal still lacks systematicness. Huainan coalfield is located in eastern China and is the largest coal production and processing base in the region. In this study, conventional proximate analysis and ultimate analysis, as well as advanced instrumental analysis methods, such as Fourier transform infrared spectroscopy (FITR), X-ray diffraction (XRD), 13C-CP/MAS NMR, and other methods (SEM and AFM), were used to analyze the molecular structure of Huainan coal (HNC) and the distribution characteristics of oxygen in different oxygen-containing functional groups (OCFGs) in an in-depth manner. On the basis of SEM observation, it could be concluded that the high-resolution morphology of HNC’s surface contains pores and fractures of different sizes. The loose arrangement pattern of HNC’s molecular structure could be seen from 3D AFM images. The XRD patterns show that the condensation degree of HNC’s aromatic ring is low, and the orientation degree of carbon network lamellae is poor. The calculated ratio of the diameter of aromatic ring lamellae to their stacking height (La/Lc = 1.05) and the effective stacking number of aromatic nuclei (Nave = 7.3) show that the molecular space structure of HNC is a cube formed of seven stacked aromatic lamellae. The FTIR spectra fitting results reveal that the aliphatic chains in HNC’s molecular structure are mainly methyne and methylene. Oxygen is mainly –O–, followed by –C=O, and contains a small amount of –OH, the ratio of which is about 8:1:2. The molar fraction of binding elements has the approximate molecular structure C100H76O9N of organic matter in HNC. The results of the 13C NMR experiments show that the form of aromatic carbon atoms in HNC’s structure (the average structural size Xb of aromatic nucleus = 0.16) is mainly naphthalene with a condensation degree of 2, and the rest are aromatic rings composed of benzene rings and heteroatoms. In addition, HNC is relatively rich in ≡CH and –CH2– structures.

Effect of supercritical-CO2 interaction time on the alterations in coal pore structure

The supercritical CO2 (S-CO2) interaction time is a vital parameter in CO2 geo-sequestration in coal seams, which is under-evaluated up to date. Through this study, we provide an experimental insight into this aspect by evaluating the effect of S-CO2 interaction time on the coal pore structural alterations. The results revealed that the S-CO2 pre-exposure has a notable impact on the adsorption capacity of coal, in which short-term (order of hours) and long-term (order of weeks) S-CO2-treated coal show less and higher adsorption capacities, respectively, compared to untreated coal. The pore characterisation results infer that both surface area and pore volume are decreased by about 20% after short-term S-CO2 treatment and then show an approximate linear increment with further longer treatment time. Based on the experimental observations, we propose a conceptual model to explain the temporal alterations, in which we elucidate that the complex temporal alterations in coal pore morphology occur due to the combined effect of multiple factors: 1) S-CO2 adsorption-induced coal matrix swelling and consequent pore shrinkage, that causes physical constriction of pores, reducing the surface area and the pore volume, 2) S-CO2-induced plasticization that extracts and mobilizes the low-molecular-weight hydrocarbons, which are entrapped in pore mouths or necks, increasing the number of accessible pores. The resultant overall alteration at a given S-CO2 pre-exposure time depends on the competitive behaviour and the significance of the multiple processes. The proposed model is supported by 1) measuring the S-CO2 adsorption-induced volumetric swelling of the coal matrix, which concludes that 70% of volumetric swelling has already been completed within 24 h of coal-S-CO2 interaction, causing the pore shrinkage and, 2) analysing the FT-IR spectrums, which confirms the S-CO2-induced bond dissociation and substitution, confirming the re-arrangement of coal macromolecular structure that possibly leads to hydrocarbon mobilization and pore structural alterations.

Macromolecular structural response of Wender coal under tensile stress via molecular dynamics

Forty Wender coal macromolecular structures were constructed into a polymer cell, which was stretched with the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS), and Gaussian was used to determine the dissociation energies. The following was learned: the coal macromolecular structure gradually breaks down to form free radicals under tensile stress and micromolecule shedding. Connected and crackable bonds restrict each other, as the breaking of one bond results in the attached bond no longer breaking. The bond breaking sequence was determined according to the chemical bond dissociation energies as aliphatic ether > alkane side chain > aromatic ether > aromatic side chain. The order in which bonds break in each molecule is not consistent with dissociation energy since it is controlled by both the dissociation energy and the angle between the bond length direction and tensile stress direction. As a result, bonds can overcome the energy barrier at certain angles.

Evaluation of the mechanical behaviour of brine+CO2 saturated brown coal under mono-cyclic uni-axial compression

CO2-sequestration and ECBM techniques necessitate injection of CO2 into coal reservoirs that are saturated under various pore fluid conditions, resulting in alterations in mechanical properties. In this study, we evaluate the effect of pore fluid chemistry and the interaction time on the coal mechanical degradation. Uni-axial compressive strength (UCS) tests, ARAMIS photogrammetric analysis, micro-CT imaging, and Fourier transform infrared spectroscopy (FT-IR) are combinedly used to evaluate such alterations and to interpret the causative factors in water, water+CO2, 10% brine+CO2 and 20% brine+CO2 saturated coal. The results indicate that irrespective of the pore fluid chemistry, mechanical parameters including UCS, Young’s modulus and brittleness index reduce significantly in saturated coal, due to moisture adsorption-induced softening effect. The presence of CO2 in pore fluids causes additional alterations in each mechanical property, due to the corrosive chemical interactions occur in acidic environments, CO2 adsorption-induced energy reduction and plasticization-induced alterations in coal macromolecular structure. The direct comparison of FT-IR spectrums of natural and CO2-interacted coal concludes that CO2 interaction causes alterations in the coal macromolecular structure possibly causing the mechanical degradation of coal mass due to plasticization effect and the extraction of pore-constricting hydrocarbons. The volumetric strain analysis and micro-CT image-based 3D-reconstruction infer that water, water+CO2 and 10% brine+CO2 saturation increase the ductile properties of coal, resulting in a dilatancy deformation and extensive fracturing, upon mechanical loading. In contrast, the higher order of NaCl concentrations (i.e. 20% brine) in pore fluid causes NaCl crystallization in coal, resulting in an elevated brittleness and consequently altering the sample deformation, failure pattern and fracturing mechanism. Although, softening effect and chemical interactions cause continues mechanical degradation with increasing saturation time in all saturation conditions, a significant strength reduction occurs at a short-term saturation period and the latter longer saturations have caused only gradual strength reductions, probably due to the rapid CO2 adsorption process on to coal matrix.

Effect of removal organic sulfur from coal macromolecular on the properties of high organic sulfur coal

The present work investigated the effect of efficient reduction desulfurization method (potassium tertbutoxide and hydrosilane system) on coal properties. Characteristic changes of high organic sulfur coal were studied utilizing TGA, FTIR and XPS after desulfurization. Results showed that more than 60% organic sulfur was removed, while the calorific value of coal samples decreased slightly and the aromatics in coal macromolecular structure were destroyed little. After treatment, formation of low molecular fragments from aliphatic carbons leaded to the increase of mass loss in TGA. XPS results revealed that some oxygen-containing groups were deoxidized after reduction treatment. The changes of coal properties were mainly attributed to the fracture of branch chain, the reduction of oxidized carbon atoms and side reactions during reduction desulfurization.

Dissolution behavior and chemical characteristics of low molecular weight compounds from tectonically deformed coal under tetrahydrofuran extraction

Tectonically deformed coal (TDC) is formed by complex and variable tectonic stresses. The induced physical-chemical effects result in a variety of chemical compositions and structures in TDCs. In this work, medium volatile bituminous coals with four types of tectonic deformation were selected and extracted with tetrahydrofuran to investigate the dissolution behavior and distribution of low molecular weight compounds in TDCs. The results revealed that a higher degree of tectonic deformation in the coal produces a higher total extraction yield as the total extraction time increases. A diffusion model also establishes a good relationship between the extraction mass and extraction time, and the diffusion coefficient Dobs can be used to describe the extraction kinetics. Chemical analysis of the extracts using column chromatography and GC/MS further found that there are more binding points for forming non-covalent bonds in long chain aliphatic hydrocarbons. So the alkanes with more than 20 carbon atoms are often dissolved at the medium and late stages. Aromatic compounds, which are mostly dissolved at the medium stage, are essentially combined into the coal macromolecular structure by π–π stacking interactions or hydrogen bonds. While a large number of heteroatomic compounds are distributed widely in coals, resulting in diverse dissolution behaviors. Under the tectonic stresses, the type and content of low molecular weight compounds in TDCs increase compared to intact coal. Particularly, an increase in tectonic deformation appeared to produce more aromatic hydrocarbons and long chain alkanes in TDCs, whilst the presence of heteroatomic compounds becomes more complex.

Insight into the macromolecular structural differences between hard coal and deformed soft coal

Coalification and tectonic deformation have significant influence on the macromolecular structure of coal. In this paper, Fourier transform infrared (FTIR) spectral and X-ray photoelectron spectrometer (XPS) measurements were conducted on soft and hard coals with metamorphism varying from bituminous coal to anthracite. Structural parameters were estimated from curve-fitting analysis, and the correlations were established for these parameters. Comparison of microstructural differences was also made between the studied soft and hard coals. The results indicate that both the apparent aromaticity, fa, and the aliphatic structural parameter, A(CH2)/A(CH3), are positively correlated with increasing vitrinite reflectance, Ro. The oxygen-containing groups including carbonyl/carboxyl groups and hydroxy groups are gradually removed with increasing coalification. The enhancement of coalification degree is capable of elevating the atomic ratio of aromatic carbon. The overall evolutionary paths of microstructures in soft and hard coals are briefly described as the increase of aromatic rings, the decline of aliphatic methyl groups and the removal of CO and OH groups, leading to the higher apparent aromaticity (fa) and maturity with coal rank increasing from bituminous coal to anthracite. Comparison of microstructural differences between soft and hard coals suggests that coal macromolecular structure is obviously affected by metamorphism degree and tectonic deformation. For bituminous coal, more CO, OH groups and methyl groups are lost in soft bituminous coal, and tectonic deformation can promote the coalification progress to some degree. As a result, soft bituminous coal contains greater aromatic rings and higher maturity than corresponding hard coal, demonstrating the precocious evolutionary characteristic. However, it is only suitable for bituminous coal and could not be applicable to anthracite based on this study. At the stage of high-rank anthracite, the removal of methyl groups and oxygen-containing groups (CO, OH) is faster in hard anthracites, due to the conversion of more hydroaromatic methyl structures to aromatic rings. Meanwhile, coal macromolecular structure is less affected by tectonic deformation for high-rank coals. Consequently, as compared with soft anthracite, hard anthracite contains greater aromatic rings and less CO and OH groups. Analysis of the microstructural differences between soft and hard coals can be conducive to studying the construction of coal molecular model and the gas transportation within coal.

Effects of supercritical CO2 on micropores in bituminous and anthracite coal

The effects of supercritical CO2 (ScCO2) on coal micropores play a critical role in determining the CO2 capacity of coalbeds. To investigate the effects of ScCO2 on micropores in coals of different ranks under a range of temperature and pressure conditions, CO2 sequestration processes are replicated using a ScCO2 geochemical reactor. Four samples of coal of different ranks are exposed to ScCO2 and water for 240 h at 62.5 °C and 15 MPa, and CO2 adsorption tests, Fourier transform infrared spectroscopy, and X-ray diffraction are performed to determine the volume and pore size distribution of the micropores, the types and contents of the organic groups, and the aromatic crystallite structures of the coal samples before and after the ScCO2-H2O treatment. The influence of the chemical structure and the organic groups of the coal on the coal micropores is then studied. Micropores with widths <0.46 nm are mainly associated with the inter-layer spacing of the aromatic layers. Swelling caused by ScCO2 detaches heterocycles and non-condensed polynuclear aromatics of high-volatile bituminous coal, resulting in slight increases in the volume of micropores with widths <0.46 nm. The falling off of cross-links with low bond energies caused by swelling and the formation of CArCAr cross-links between the aromatic layers caused by polyaddition reactions together cause a decrease in the volume of micropores with widths <0.46 nm in semi-anthracite and anthracite coal. Micropores with widths >0.46 nm are pores in the macromolecular structure of coal and are known as intermolecular pores, and their volumes are determined by the directional arrangement of aromatic crystallites and the aliphatic hydrocarbon chain length. The broken bonds caused by ScCO2 in high-volatile bituminous coal form new aliphatic or aromatic compounds via addition and polyaddition reactions. These processes increase the directional arrangement of aromatic crystallites, resulting in a decrease in the volume of micropores with widths >0.46 nm. As the coal rank increases, the aliphatic hydrocarbon chain length gives priority to the macromolecular structure of coal after the ScCO2 treatment, resulting in an increase in the volume of micropores with widths >0.46 nm in semi-anthracite and anthracite coal.

Feasibility study of reduction removal of thiophene sulfur in coal

The present work investigated an effective reductive desulfurization method for thiophene sulfur in high organic sulfur coal utilizing the potassium tert-butoxide/hydrosilane. Maximum decreases of 65.8% and 64.2% in organic sulfur for Xinyu coal and Guxian raw coals were, respectively obtained under the optimized conditions of the molar ratio of reductive assistant to sulfur of coal (15), treatment time (80 min), temperature (215 °C). According to the results of XPS, more than 80% mercaptan, sulfoether and thiophene on the raw coals surface were removed without destroying the macromolecular structure of coal. Sulfur on treated coal surface samples mainly existed in the form of sulfonate and sulfone due to the hydrolysis and oxidation of intermediate products generated in the reduction desulfurization reaction. These findings confirmed the possibility of effective removal for thiophene sulfur in coal utilizing the reductive system, which could give a reference for thiophene sulfur removal of high organic sulfur coal.

Effect of solvent extraction pretreatments on the variation of macromolecular structure of low rank coals

In order to understand the effects of solvent pretreatment on the inherent macromolecular structure of low rank coal, Xilinguole lignite (XLL) and Shenfu sub-bituminous coal (SFC) were extracted by tetrahydrofuran (THF) Soxhlet extraction, carbon disulfide/N-methyl-2-pyrrolidone (CS2/NMP) mixed solvent extraction and thermal dissolution, respectively. The extracted coals were characterized by diffuse reflection FT-IR spectroscopy (DRIFT), thermogravimetric analysis (TGA), mercury intrusion method (MI) and swelling ratio determination. The results indicated that the extraction resulted in the arrangement and reassociation of coal inherent macromolecules. THF Soxhlet extraction and CS2/NMP mixed solvent extraction can relax the macromolecular structure of coal to varying degrees by changing the non-covalent bond cross-linking, especially the distribution of hydrogen bond interactions. However, thermal dissolutions at high temperature mainly increased the covalent cross linking of coal macromolecules, especially for XLL. Swelling of all extracted coals was limited by Fickian diffusion, and the extracted coal showed lower swelling activation energy than the corresponding raw coals.

Biodesulfurization of high sulfur fat coal with indigenous and exotic microorganisms

Abstract Coal is the most abundant fossil fuel in the world and its combustion accompanies with the emission of SOX, which is responsible for serious environmental problems. To reduce the emission of SOX is essential for clean fuel. In the present study, indigenous microorganisms acclimatized from fat coal itself and exotic microorganisms from sewage sludge were used for coal biodesulfurization. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and Raman spectral analysis were used to investigate the structural change of fat coal during the bioleaching. Results showed that kaolinite and quartz were the main minerals, and pyrite was the main inorganic sulfide in fat coal. After 36-day biodesulfurization, the total sulfur in fat coal decreased from 5.07% to 2.77% and 2.75%, and the pyritic removal was 77.68% and 87.88% with indigenous and exotic microorganisms, respectively. The exotic microorganisms were more effective to oxidize the pyrite than the indigenous microorganisms. But both microorganisms did not interact with the organic sulfur, which existed as C S bond in fat coal. FT-IR analyses showed the damage of kaolinite structure, indicating potential microbial effect on kaolinite, which has not been reported before. Raman spectral analysis was for the first time used to investigate the changes of coal macromolecular structure during the bioleaching. FT-IR and Raman spectra confirmed the changes of aromatic C H, O H bonds, which led to the increase of carbon crystallinity index.

Heterocyclic sulfur removal of coal based on potassium tert-butoxide and hydrosilane system

The present work investigated the feasibility of heterocyclic sulfur (HS) removal for coal utilizing potassium tert-butoxide and hydrosilane system. Changes of sulfur forms with treatment time in Xinyu (XY) coal were determined by XANES. Results showed that reductions of total sulfur and organic sulfur for XY coal were 55% and 53%, respectively. >85% sulfoether and thiophene sulfur were removed after treated for 4 h, suggesting that the HS could be removed to a high extent from coal. However, contents of sulfonate and sulfonic ester increased with treatment time due to the hydrolysis and oxidation of intermediate products containing SiS bands. Furthermore, it indicated that the HS could be removed selectively from coal without destroying the macromolecular structure of coal based on analysis of desulfurization mechanism. These findings suggested that the desulfurization of refractory HS in coal could be obtained using the potassium tert-butoxide/hydrosilane reductive system, which provided a reference for desulfurization of high organic sulfur coal.

Microbial Degradation of Coal into a Value Added Product

ABSTRACTMicrobial treatment has been considered as an economic, effective and environment safe way of processing coal via degradation of the macromolecular network into simpler, low molecular weight products. The present work is intended to observe the feasibility of microbial attack on reject coal, having high ash content (65% ash). The results indicated that microorganisms were able to change and modify the macro molecular structure of reject coal. This paper summarizes the potential ability of the microorganisms to beneficiate reject coal and to make a value-added product, humic acid from reject coal. This work describes the status of current and the probable directions of the future research.

Coal macromolecular structural characteristic and its influence on coalbed methane adsorption

In order to investigate the effect of coalification on coal macromolecular structure, the combination of Raman spectroscopy and low-pressure N2 gas adsorption (LP-N2GA) was adopted to explore the chemical and physical characteristics of selected samples ranging from bituminous C to anthracite. Raman structural parameters, including band position, band area ratio (AD1/AG) and band position difference (G-D1) of G band and D1 band were derived from curve-fitting analysis. Methane adsorption properties of these samples were measured, and correlations between these Raman parameters and coalbed methane adsorption capacity (VL) were also established. The results indicate that D1 band generally shifts to the lower wavenumbers decreasing from 1365 cm−1 to 1339 cm−1, while G band shifts to higher wavenumbers ranging from 1578 cm−1 to 1609 cm−1 with increasing coal rank. The values of G-D1 increase, but the band area ratio (AD1/AG) declines with the increase of Ro. Pore parameters, including the BET SSA and pore volume, show a polynomial relationship with G-D1, but a reduction for AD1/AG. The increase of graphitization and the order degree of aromatic structures in coal can enhance the porosity in coal. The evolution of coal macromolecular has significant impact on methane adsorption, which displays a U-shape correlation with Raman parameters. Coalbed methane adsorption is not only related to the physical structures, but also to the chemical characteristics, which should be taken into account in practice.

The effects of CO2 on organic groups in bituminous coal and high-rank coal via Fourier transform infrared spectroscopy

The interactions between supercritical CO2 and coal and their effects on changes in the coal pore structure and organic groups play a critical role in the CO2 geological storage-enhanced coalbed methane recovery. To investigate the effects of supercritical CO2 on organic groups in coals of different ranks and its mechanisms under different temperature and pressure conditions, CO2 sequestration processes in bituminous coals and high-rank coals were replicated using a high-pressure reactor. Four coal samples of different ranks were exposed to supercritical CO2 and water under three temperatures and pressures for 240 h. Fourier transform infrared spectroscopy was used to provide semiquantitative ratios and Fourier transform infrared spectra of coal samples before and after the supercritical CO2–H2O treatment. The results show that interactions between supercritical CO2 and coal were controlled by the coal macromolecular structure, and semianthracite is the inflection point of interaction characteristics for coal samples of different ranks. Bituminous coal, including high- and low-volatility bituminous coal, has a low degree of condensation of its aromatic structure, and its aromatic nuclei can facilitate addition reactions. Swellings primarily break cross-links between aromatic nuclei in the same aromatic layer. These characteristics favor the polymerization addition of aliphatic side chains of aromatic nuclei, causing an increase in the degree of condensation of the aromatic structures in bituminous coal. High-rank coals including semianthracite and anthracite have a high degree of condensation of their aromatic structures, and the aromatic nuclei favor substitution reactions. Swellings primarily break cross-links connecting different aromatic layers, and bond dissociation reactions and sulfuration reactions are more significant for high-rank coal. These characteristics cause a decrease in the degree of condensation of the aromatic structure in high-rank coal. Temperature and pressure have a great impact on interactions between supercritical CO2 and coal and are controlled by the reaction types of the organic groups. With the increase in experimental temperature and pressure, the changes in the organic group content can be classified as the descending type, the rising type, the lower opening parabola type, and the upper opening parabola type. 45.0°C and 10 MPa is the inflection point of the changes in the organic group content. Descending- and rising-type changes favor addition, bond dissociation, and sulfuration reactions, which are endothermic. The reaction rate of supercritical CO2 and the organic groups increases, and the effects caused by temperature and pressure decrease as the temperature and pressure increase. Lower opening parabola- and upper opening parabola-type changes favor substitution, oxidation, and addition polymerization reactions, which are exothermic. These changes were significantly affected by a variety of reactions and were suppressed by high temperature and pressure. When the temperature is ≤45.0°C and the pressure is ≤10 MPa, supercritical CO2 has remarkable effects on alkyl and hydroxy groups and has a stronger effect on bituminous coal. When the temperature is &gt;45.0°C and the pressure is &gt;10 MPa, supercritical CO2 has remarkable effects on oxygen- and sulfur-containing groups and has a greater effect on high-rank coals.

Chromatographic separation of alkylated depolymerized Neyveli lignite

The study of macromolecular structure of coal has been subjected to intense research. Neyveli lignite was depolymerized using phenol and phosphotungstic acid and the resultant product was subsequently alkylated. The t-butylated depolymerized lignite exhibited enhanced extractability in organic solvents. The t-butylated depolymerized lignite was fractionated into different components using column chromatography (CC). Three major compounds were isolated and were characterized by FTIR, 1H NMR and Mass spectral techniques.

Separation and structural characterization of groups from a high-volatile bituminous coal based on multiple techniques

Although considerable progress has been made in revealing the coal macromolecular structure via solvent extraction, there remains a challenge in elucidating the coal structure due to low extraction yields of coal, poor selectivity of extraction solvents, and complexity of extracts. In this work, a high-volatile bituminous coal was successfully separated into seven groups (G1–G7) with less diversity within each class using multistep extraction followed by column chromatography. The total extraction yield (dmmf) reached up to 56% and the structural characteristics of the seven groups were identified and investigated with a series of analytical techniques. The results showed that the individual groups had a rather unique composition and their chemical properties were different in elemental composition, functional groups, aromatic cluster size, number and length of the alkyl side chains, and degree of order, which resulted in differences of their pyrolysis reactivities. Aliphatic hydrogen accounted for 99% of total hydrogen in n-heptane eluted fraction (G4) but the aliphatic degree in the extract residue (G1) was only 35.7%. The ratios of aromatic bridgehead carbon were 0.32, 0.30, and 0.27 for G1, CCl4 insoluble fraction (G2), and n-heptane insoluble fraction (G3), respectively. Additionally, total volatiles achieved 99.8, 98.1, 98.2, 89.0, and 60.0%, respectively during pyrolysis of G4, toluene eluted fraction (G5), ethyl acetate eluted fraction (G5), methanol eluted fraction (G7), and G3 at end temperature of 800°C, which were substantially higher than those for G1 and G2. In comparison with the partition of coal structure using maceral components, the proposed separation method provides an efficient and convenient investigating for structural exploration and these data can be combined to create structures that are cognitive of the structural diversity present. Through this, exploration of the complex conversion mechanism of coals would become more accessible during pyrolysis, gasification, liquefaction, and coking processes.

Effects of Metamorphism and Deformation on the Coal Macromolecular Structure by Laser Raman Spectroscopy

Metamorphism and deformation significantly affect the macromolecular structure of coal. In this study, experiments were conducted using coal samples with different metamorphic degrees and deformation types from different regions of Hebei, Henan, Shanxi, and Anhui province, followed by laser Raman spectral analysis. The results indicated that the Raman spectrum of all coal samples consist of two characteristic peaks, namely the D peak and the G peak, ranging from 1336.7 cm–1 to 1360 cm–1 and from 1591.2 cm–1 to 1600.6 cm–1, respectively. Simultaneously, with the metamorphic degree of coal increasing, certain change rules were observed in both strong and weak tectonically deformed coals: G and D peaks were gradually separated and the sharpness of these peaks was clearly enhanced. In addition, the D-peak position, full width at half maximum for the G-peak (fwhm-G), and the intensity ratio between the D and G-peaks (ID/IG) decreased, but the G-peak position and d(G–D) values increased, while the analysis resu...

Effect of heat reflux extraction on the structure and composition of a high-volatile bituminous coal

Heat reflux extraction (HRE) process with cyclohexanone (CYC) in a high-performance mass transfer extractor was applied to dissolve Shenmu-Fugu high-volatile bituminous (SFHB) coal for the first time to afford extract (E) and extract residue (ER) from the extraction. SFHB, E, and ER were characterized by elemental analysis, solid-state 13C NMR spectrometry, FTIR spectrometry, XRD, SEM, and TG-FTIR to elucidate the effect of HRE on the evolution of functional groups and macromolecular structure of coal during extraction. The soluble portion in SFHB was 24.37% in the course of HRE with CYC. The aromaticity of SFHB derived from both curve-fitting of 13C NMR and FTIR spectra was obviously increased after extraction suggesting that most of the aliphatic fractions were extracted during HRE process. It was clarified that the substituted degree of aromatic ring in SFHB became low but the substituents on aromatics were larger after extraction. Due to irreversibly swelling crystal structure of SFHB, its interlayer spacing became larger and the stacking height of crystallite decreased after extraction. Moreover, significant amounts of volatile matters were extracted, which caused relatively lower mass loss rate and contents of gaseous products (CO2, aliphatic moieties, CH4, and CO) of ER than SFHB during main pyrolysis stage.