► Raman parameters on collotelinite and fusinite are different from the corresponding fused char and fusinoid morphotypes. ► The highest differences occurring between collotelinite and corresponding ...fused chars. ► During pyrolysis major structural changes occur in collotelinite. ► Raman parameters of fused char and fusinoid portions are similar.
Raman spectroscopy analyses were carried out on macerals from a set of coals with increasing rank and their corresponding char morphotypes in order to improve the understanding of the structure of coal char produced in a fluidized bed reactor.
The Raman parameters obtained on collotelinite and fusinite are different from those obtained on the corresponding fused char and fusinoid morphotypes. The highest differences occur between collotelinite and corresponding fused chars, suggesting that major structural changes occur in collotelinite during pyrolysis, while those occurring in fusinite are less pronounced.
Raman parameters of the different fused char and fusinoid portions are similar, suggesting that the heat treatment enhanced the formation of similar structures. However, the fused char portions not only display different optical patterns from fusinoid chars but also have slightly higher reflectance.
Peat depositional environments, the sites where and conditions under which peat accumulates, significantly influence a resultant coal's physical properties, chemical composition, and coal utilization ...behavior. Recognition of peat depositional environments for coal is a challenging endeavor because coal's observed compositional properties not only result from a variety of geological processes operating during peat accumulation, but also reflect the influence of adjoining or external depositional sedimentary environments and alteration during later diagenesis and/or epigenesis. The maceral or microlithotype composition of any one layer of peat can be the product of years or decades of plant growth, death, decay, and post-burial infiltration by roots in addition to the symbiotic, mutualistic, parasitic, and saprophytic relationships with non-plant biota, such as arthropods, fungi, and bacteria. The overprint of increasing thermal maturation and fluid migration through time on the resulting coal can make these relationships difficult to recognize. Therefore, published models based on maceral composition alone must be used with great caution. Lipid compositions, even from lipid-poor low-rank coals, can provide important information about depositional environments and paleoclimate, especially if combined with the results of organic petrography and paleontological studies. Just as sulfur derived from seawater provides environmental clues, the ratios of two particularly relevant trace elements rather than a single trace element can be used to interpret peat depositional environments. Epigenetic minerals, as well as their corresponding chemical compositions should not be used for such a purpose; similarly, resistant terrigenous minerals deposited during peat accumulation in many cases should be used with considerable caution. The interactions of the biota present in the peat-forming ecosystem, often determined using palynological and geochemical proxies, and their interpretation in the context of geography and paleoclimate are important means for deciphering peat depositional environments. Overall, a combination of evidence from geochemistry, mineralogy, palynology, and petrology of coal and from stratigraphy, sedimentology, and sedimentary facies of related rocks is necessary for accurate and comprehensive determination of depositional environments. The need for interdisciplinary studies is underscored by peat compositional properties, which have been greatly affected by various processes during the syngenetic, diagenetic or epigenetic stages of coal formation.
•Three maceral-rich fractions were obtained by maceral float-and-sink method.•Pyrolysis behavior of the separated maceral-rich fractions were evaluated.•The tar yield from pyrolysis of ...vitrinite-enriched fraction increased to 15.68 %.•The mechanism of free radical fragments in tar formation was further explored.
An ideal way of clean and efficient utilization of low-rank coal by separating it into different maceral-rich fractions and then choose the appropriate utilizing method based on its composition and structure was proposed. In this paper, the coal sample was successfully separated into vitrinite-enriched coal (VC), inertinite-enriched coal (IC) and mineral-enriched coal (MC) by macro maceral separation method, and the structure and pyrolysis characteristics of different maceral-rich fractions were studied. The XRD analysis revealed that VC exhibited a higher degree of structural disorder, whereas the IC displayed greater aromaticity and graphitization. Raman analysis showed a higher proportion of amorphous carbon structure in VC, indicative of abundant side-chain active components. Conversely, IC contained more ordered aromatic rings and a higher degree of aromatic condensation. FTIR analysis confirmed that VC contained the highest aliphatic hydrocarbon content and aliphatic long-chain structures, while IC showed a lower aliphatic/aromatic ratio. The pyrolysis of different maceral-rich fractions indicated that VC pyrolysis produced the largest amount of tar (15.68 %), which was 4.37 % higher than that of the raw coal’s 11.31 %, and contained a large number of aliphatic hydrocarbons and phenols. In contrast, the tar yield of IC pyrolysis was 1.08 % lower than that of raw coal, and the tar was composed of more polycyclic aromatic hydrocarbons such as biphenyl, naphthalene and benzene series. The maceral macro separation of low-rank coal effectively realizes the separation and enrichment of different type of components in coal, which was beneficial to its subsequent cascade utilization.
Organic matter (OM) type critically controls the hydrocarbon generation potential and organic pore development in black shales. However, maceral variation in lacustrine shales and its control on ...hydrocarbon generation potential and organic pore development are not yet well understood. In this study, 15 Chang 7 Member shale samples of the Yanchang Formation, Ordos Basin, were investigated with organic petrography, Rock-Eval pyrolysis, and a scanning electron microscope to study the maceral composition, hydrocarbon generation potential, and organic pores in this black shale succession. The results show that the studied shales are in the oil window (Ro~0.70%). OM belongs to Type I and Type III kerogen, as demonstrated by Rock-Eval pyrolysis. Macerals in the Chang 7 Member shales are composed of amorphous OM, alginite, sporinite, liptodetrinite, vitrinite, inertinite, and solid bitumen. Amorphous OM and alginite are major hydrocarbon-generating macerals, and their content determines the hydrocarbon potential of shales. Secondary organic pores were not observed in the studied Chang 7 Member shales due to either a low thermal maturity or a dominance of terrigenous OM. Maceral variation can affect the reliability of using Rock-Eval Tmax as a thermal maturity indicator. This study provides important insights into maceral control on hydrocarbon generation and organic pore development in black shales, calling for a critical evaluation of OM in black shale successions with organic petrography.
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•Shendong coal macerals is swelled by acetic acid, ethanol and acetone, respectively.•Based on the coal structure and Py-GC/MS, pathways of phenols formation are proposed.•The ...reaction energy of phenols generation pathway is carried out by using DFT.•The PCXC yield derived from VD-AT and ID-EA is 43.63 g/kg and 34.19 g/kg, separately.•Among seven pathways of VD-AT, Path 3 exhibits the lowest energy of −148.38 kJ/mol.
Phenols are the important high value-added chemical product of coal tar, and exploring the release behavior of phenols is crucial for clarifying the coal pyrolysis mechanism and regulating the product distribution. The aim of this paper is to investigate the effects of swelling on the pyrolytic properties of de-ashed vitrinite (VD) and de-ashed inertinite (ID). VD and ID prepared by Shendong coal were characterized by 13C NMR, XPS and FTIR to explore physicochemical properties. Acetic acid (AA), ethanol (EA) and acetone (AT) were employed to prepare the swelled VD (VD-AA, VD-EA and VD-AT) and swelled ID (ID-AA, ID-EA and ID-AT). Kinetic analysis was carried out using thermogravimetry, the pyrolysis characteristics and distribution of pyrolysis products were analyzed by fast pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS) and fast pyrolysis fixed bed. Combining with density functional theory (DFT), the possible pyrolysis pathways of phenols generation were proposed. As a result, the macromolecular structures of VD and ID are constructed. TG and kinetic analysis exhibit that swelling promotes the pyrolysis of VD and ID, and the activation energy of the second stage is VD > VD-EA > VD-AT > VD-AA and ID > ID-EA > ID-AT > ID-AA, respectively. Py-GC/MS analysis exhibits that the selectivity of phenol, cresol, xylenol and catechol decreases to 17.53 % (VD-AA) and 12.18 % (ID-AT). By analyzing and comparing the distribution of the full component of Py-GC/MS, seven possible pathways of cresol generation are proposed. DFT calculation exhibits that Path 3 of VD-AT, which produces cresol via sequential decarboxylation, ether bond cleavage, decarbonylation, aliphatic side chain removal and dehydroxylation, demonstrates the lowest reaction energy of −148.38 kJ/mol.
•The separation mechanism of macerals was explored at a multi-scale.•The properties difference between macerals was analyzed to determine the separation entry point.•The in-situ change in surface ...morphology of macerals after reagents adsorption was explored using AFM.•The interaction force and attachment performance demonstrated a difference in reagent absorption on the surfaces of macerals.•Results show that reagents caused a variable change in the surface hydrophobicity of vitrinite and inertinite.
The precise separation of macerals is the premise and foundation for the efficient utilization of coal resources, and flotation is the separation method with the greatest industrial potential. The differences in the surface hydrophobicity of macerals provide the basis for flotation, but the complexity of their surface properties makes separation challenging. In this study, sub-bituminous coal was used to obtain vitrinite and inertinite, and a detailed analysis was carried out on the samples. The surface morphologies of vitrinite and inertinite were observed in the QITM (quantitative imaging) mode of AFM (atomic force microscope) to explore the adsorption of the reagents. The effect of the reagents on the interaction forces between the coal particles and bubbles was measured to reveal the change in hydrophobicity. The attachment performance of macerals under different reagent treatments was investigated using a laboratory-built apparatus. Overall, the results demonstrated that the difference in zeta potential between vitrinite and inertinite was a viable approach for separating the macerals. CTAB adsorption on coal samples changed the surface morphology and the interaction force between particles and bubbles. Interestingly, CTAB adsorption on the gas–liquid interface decreased the interaction force. Vitrinite and inertinite attachment performances were enhanced when Al3+ and SDS were used simultaneously.
It is a challenge to accurately characterize the caking behavior of coal after thermal softening and its reaction mechanism. In this work, the formation behavior of metaplast during coal macerals ...coking was investigated using high-temperature confocal laser scanning microscopy and high-temperature small-amplitude oscillatory shear rheometer, the source of diversities in thermal fluidity of coal was revealed by thermogravimetric-mass spectrometry analysis and kinetic-thermodynamic theory calculations. The results showed that although vitrinite was the generator of metaplast in the thermoplastic stage, the expansion rate of vitrinite from coking coal is more than 70% greater than that from gas coal for two consecutive times. Moreover, the total weight loss of vitrinite from gas coal was about 1.262 times higher than that from coking coal, but the latter exhibited more generous aliphatic groups in pyrolysis products. In the thermal flow interval, the reaction activation energy of vitrinite and inertinite from coking coal and gas coal was 271.0 ± 0.7, 302.0 ± 1.5, 241.0 ± 0.1 and 300.25 ± 1.55 kJ/mol, respectively. Eventually, the kinetic and thermodynamic mechanism parameters of raw coal and macerals had favorable correspondence regularity, and macerals with the most prominent parameters would be dominant in the overall thermal properties of raw coal.
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•The active softening of vitrinite is the main source of the thermal fluidity of coal.•The formation of metaplast in the pyrolysis process of coking coal has multiple stages.•The maximum expansion capacity of vitrinite from coking coal is 7 times that from gas coal.•Structural evolution strongly influences the thermal stability of coals and their macerals.•The thermal properties of raw coal are controlled by macerals with strong pyrolysis expressiveness.
Samples from the Devonian succession in the Sifa-1X well located mid-way between the Egyptian Faghur Basin and the Libyan Cyrenaica Platform were examined in this study. The distribution of liptinite ...group macerals was investigated under reflected and transmitted light microscopy. Diverse and abundant liptinites of terrigenous and marine origin were identified. The palynological investigations included analysis of the miospores assemblages and palynofacies categories by multiple statistical approaches in addition to calculation of the sedimentation rates. These analyses signified four miospores biotopes and three palynofacies biotopes that were used to assess the ramps of paleoclimatological and paleoenvironmental changes during sedimentation. These biotopes were used to define a model of liptinite maceral distribution throughout the Devonian in the study area. The model suggested two different phases of basinal dynamics in terms of climate, sea level, and sedimentation rates, namely an Early-Middle Devonian transgressive phase and a Late Devonian regressive phase. Conditions during the Early-Middle Devonian transgressive phase were oxic to dysoxic with low sedimentation rates and oxic during the Late Devonian regressive phase. Oxygen depletion was under the threshold required to induce significant preservation of the quantity and quality of organic matter, including liptinite macerals. The redox conditions were confirmed by trace element analysis. The high oxygen level affected both the quantity and quality of the liptinite macerals and greatly reduced the preservation of the amorphous organic matter. The quality of the organic matter varied from kerogen type I, II, mixed types II/III and type III. The mixture of these kerogen types was assessed by organic elemental and pyrolysis gas chromatography analyses. In addition, the entire Devonian succession in the Sifa-1X well is in the oil window, as also indicated by miospore coloration. This indicates that the organic matter in the Devonian strata have the potential to generate oil and gas.
•The Devonian sediments from the Western Desert include significant amounts of liptinite.•The liptinite Distribution is studied based on analysis of palynofacies and miospores.•The statistical analysis of miospores and palynofacies revealed several biotopes.•Highest liptinite quality occurs in the palynofacies biotope in the E. to M. Devonian.•Dysoxic-oxic conditions with low sedimentation rate existed in this palynofacies biotope.
Organic liquids are used to prepare the density medium to produce clean coal composites for coal quality and coking test evaluations during the coal exploration stage. Perchloroethylene (PCE) is ...commonly used as a density medium for this procedure; however, it has been shown before that PCE affects Gieseler Fluidity and Ruhr Dilatation indices of coal, as well as the quality of the resulting coke. It was also found that PCE has a negative effect on the coking properties of coals with a high inertinite content. This paper investigates the adsorption of PCE on various coal maceral surfaces using micro-Fourier Transform Infrared Spectroscopy (micro-FTIR) analysis to observe the changes in the absorbance of the double carbon bond C = C (C = C absorbance peak is used as a marker to indicate the presence of PCE) before and after PCE was applied onto their surfaces. The micro-FTIR mapping of absorbance intensity of the C = C bond on coal macerals showed an increasing trend in the presence of these bonds on the surface of all macerals with the time after exposure to the PCE. The SEM- energy-dispersive X-ray spectroscopy was used to analyze the composition of minerals associated with fusinite and semifusinite, as they were filling the pores in these macerals.
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•The purity of vitrinite and inertinite separated by hydrothermal float-sink reached more than 75% and 60%.•The asynchronous graphitization development of coal macerals resulted in ...the density difference.•The combination of experiment and calculation updated the separation mechanism of macerals.
It is of great significance to reveal the specific separation behavior of macerals for realizing the classification and utilization of coal resources. In this article, the separation mechanism of macerals during coal upgrading was investigated experimentally and computationally based on an improved hydrothermal float-sink method combined with various characterization approaches. The apparent morphology, endogenous mineral and aromatic structural differences of macerals were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and high-resolution transmission electron microscope (HRTEM). Materials Studio was applied to calculate the adsorption conformation, energy, charge density difference and bonding tendency of heavy media with functional groups in coal to elucidate the interaction between macerals and heavy liquids. The results show that the float-sink procedure with water bath heating instead of the previous strong acid inhibitor can achieve a purity of more than 75% and 60% for vitrinite and inertinite, respectively. Further refinement of coal particle size can enhance the yield of vitrinite with lightweight, which is less dense due to its lower aromatization than inertinite. In addition, the partial distribution of characteristic functional groups in coal on the surface of inertinite enhances the adsorption between it and heavy liquid, thereby affecting the separation behavior. Therefore, the mechanism of separation and enrichment of macerals by the float-sink method lies in the density difference of individual components and the interaction between the functional groups of each maceral and ZnCl2 solution.
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