Coal Macerals Research Articles

Relationships between the optical properties of coal macerals and the chars resulting from fluidized bed pyrolysis

In this study the values of the RIS axes and parameters were calculated using Kilby's method to the characterization of the textural anisotropy and structure of the basic structural units of coal macerals (collotelinite, fusinite, and macrinite). Their microstructural evolution after having been subjected to fluidized bed pyrolysis at 800°C was investigated, using the same parameters, on their respective char portions (fused char, fusinoids, and inertoids). Thus, this work represents the first attempt to determine the variations of the optical properties of fluidized bed chars.After the thermal treatment, the fusinoids and the inertoids presented similar Rr% values and RIS parameters values, indicating that after pyrolysis these materials are texturally and structurally similar.Collotelinite produced fused chars with a higher reflectance than those resulting from fusinoids and inertoids. Their reflectance increase in lower and decrease in higher rank coals. The highest RMAX%, Rev, and Ram increase occurred in the fused char portions derived from the collotelinite of coals in the 0.86–1.60Rr% range, indicating substantial chemical and spatial rearrangement.

Microstructure of Mid and High Rank Coals from Qinshui Basin, North China and its Contribution to Coalbed Meathane

To better understand the relationship between micro-structures and coalbed methane(CBM), characterisation methods including microscopic photometer, scanning electron microscopy (SEM), mercury porosimetry, nitrogen adsorption at 77K and methane isothermal adsorption were introduced into investigating the adsorption capability of coal reservoir. The results reveal that the micropores volume has a increasing trend with increased vitrinite reflectance. The most favorable pore type is to have good connectivity, very good micro-pores porosity and good adsorption capability. Statistical analysis shows that endo-microfractures are the main type microfractures of Qinshui basin. Based on the results of coal macerals, coal lithotypes, it is found that the bright coal and telocollinites are favorable for endo-fractures formation. Obviously different from the formation of endo-microfracture, exo-microfracture strongly relates to the coal structure. A good match between the fractures and the pores is needed for a favorable CBM reservoir. Based on the evaluation of pore-fracture system, Yangquan is the second CBM commercial area of Qinshui basin.

Mapping the chemistry of resinite, funginite and associated vitrinite in coal with micro‐FTIR

Micro-FTIR mapping is a powerful tool for nondestructive, in situ chemical characterization of coal macerals at high resolution. In this study, the chemistry of resinite, funginite and associated vitrinite is characterized via reflectance micro-FTIR for Cenozoic high volatile C bituminous coals from Colombia. In comparison with the micro-FTIR spectra of vitrinite and inertinite, the corresponding spectra of liptinite macerals in the same coals are characterized by stronger aliphatic CH(x) absorbance at 3000-2800 and 1460-1450 cm⁻¹, but less intense aromatic C=C ring stretching vibration and aromatic CH(x) out-of-plane deformation at 700-900 cm⁻¹. The aliphatic components in resinite have the longest carbon chains and are least branched, bestowing the highest hydrocarbon generation potential on resinite among the three macerals studied. In contrast, funginite exhibits the strongest aromatic character, the highest aromaticity, the lowest 'A' factor values and the lowest C=O/C=C ratios among the three maceral groups. Vitrinite generally displays intermediate chemical characteristics. Reflectance micro-FTIR mapping of coal samples further confirms the aliphatic character of resinite and the aromatic nature of funginite. In addition, chemical mapping of resinite and adjacent vitrinite shows that vitrinite immediately adjacent to resinite displays higher aliphatic CH(x) stretching intensity than more distant vitrinite, suggesting that chemical components from resinite can diffuse over short distances into adjacent vitrinite, specifically causing hydrogen enrichment. It needs to be pointed out, however, that the region of influence is localized and limited to a narrow zone, whose extent likely depends on resinite's properties, such as its size and aliphatic material content. This way, the chemical map of resinite and associated vitrinite provides direct evidence of the intermaceral effects occurring during the peat forming stage or during later coalification. No influence of funginite (primarily fungal spores and sclerotia) on the chemistry of adjacent vitrinite has been demonstrated, which is likely due to the highly aromatic structure of this type of funginite.

Lepidodendron dawsonii: functional groups and pyrolysates of compression and fossilized-cuticle (Late Asturian, Canada)

Lepidodendron dawsonii BELL 1938 is an endemic species of Late Asturian age in the Canadian Sydney Coalfield, with conspicuous elongate leaf cushions. The study specimen, 35 cm long and 10 cm wide, represents a dichotomous bough from the tree crown in which the inner part of one side is black and compression-preserved, whereas the one in contact with the entombing rock matrix is dark-amber in colour and fossilized-cuticle preserved. Only stomatal pits and cuticular details are preserved. Comparison of these preservation states, based on Fourier transform infrared (FTIR) spectrometry, and flash pyrolysis gas chromatography mass spectroscopy (Py-GC/MS), demonstrate sufficient differences in chemistry to be able to link the two preservation states with differing pathways of organic matter transformation (diagenesis). The aliphatic-hydrocarbon chains of the cuticles are comparatively shorter and more branched than the longer chains of the compressions. Py-GC/MS results support the presence of hydrocarbon markers of plant cuticles. The high abundances of C1 and -C2 alkylphenols and C1 and -C2 alkylbenzenes in pyrolysates are likely derived from maturing lignin or lignin-like biomacromolecules. We suggest comparison of L. dawsonii’s cuticles with Lepidodendron coal macerals in Chinese Permian Leping coal, and with suberinite.

Molecular models of coal’s organic matter and the reflectance of the macerals: A review

The mean reflectance R o,n of vitrinite and other macerals in coal whose structure is represented by molecular chemical models may be calculated on the basis of the contributions of structural-chemical groups to the molecular refraction, if the relation between the reflection, refraction, and absorption is taken into account on the basis of the Fresnel-Beer law. The findings confirm the relation between the reflectance R o,n and the chemical structure of the coal macerals. Consequently, reliable analysis of the possible chemical transformations in coal may be based on molecular models of the structure.

Influences of chemical structure and physical properties of coal macerals on coal liquefaction by quantum chemistry calculation

Significant progress has been made in the simulation of coal liquefaction by the quantum chemistry calculation among similar rank coals. Three Chinese bituminous coals from Lingwu, Shendong and Pingshuo were chosen as samples and evaluated. By means of density gradient centrifugation, six kinds of coal macerals with greater than 95% purity were obtained. Using Materials Studio 4.0 quantum chemistry software the hydro-liquefaction activity differences were analyzed by the bond orders of six maceral model structures. Calculation results were compared with specific surface area and average pore size data from nitrogen physical adsorption. It showed that the specific surface area of macerals had no direct relation with their liquefaction yield, while their average pore size and liquefaction yield were shown to be positively correlated. Also, chemical bond cleavage activity of coal structure units influenced liquefaction yield. Under the solvent cycle condition, the capacity of coal liquefaction is potentially decided by the efficiency of hydrogenation to stabilize the free radicals, and also by coal pore size. The rapid cycle of solvent increases the liquefaction yield due to more additional fresh solvent added. The chemical structure and physical properties of Shendong coal displayed much better liquefaction capability than other coals examined.

Development of web-based organic petrology photomicrograph atlases and internet resources for professionals and students

With advances in web applications, organic petrography and other related disciplines are in need of updated online resources and educational tools to aid professionals and students in the identification and interpretation of macerals. The U.S. Geological Survey (USGS) Organic Petrology Laboratory along with USGS Eastern Energy Resources Science Center Information Technology staff have developed five web atlases containing images of organic matter in geologic materials: 1. an American Society for Testing and Materials (ASTM) Atlas, 2. an Organic Petrology Taxonomy for International Classification (OPTIC) of Coal Macerals Atlas, 3. an Interactive Gulf Coast Photomicrograph Web Atlas (I-Map), 4. an Organic Material in Shales Atlas (Shale), and 5. an interactive Blue/White/Ultraviolet (UV) Light Atlas (Light). Each web atlas contains images of macerals with associated sample and petrographic data collected by the USGS. These webpages will provide means to preserve and circulate petrographic data collected by the USGS for coal and shale samples from all over the world.

The burning of Gondwana: Permian fires on the southern continent—A palaeobotanical approach

Fossil charcoal has widely been accepted as a direct indicator for the occurrence of palaeo-wildfires. In Upper Palaeozoic sediments of Euramerica and Cathaysia, records of these remains are relatively common and (regionally and stratigraphically) more or less homogeneously distributed in terrestrial sequences. On the other hand, just a few records have been published for the Permian of Gondwana and only recently has it been demonstrated that macroscopic charcoals are also common here. Most Permian macroscopic charcoal from Gondwana is gymnospermous and has been reported from coal-bearing strata. Macroscopic charcoal occurrences are spread out in different sequences and also in distinct stratigraphic intervals in the Permian [e.g., Paraná Basin (Sakmarian/Artinskian of Brazil), Karoo Basin (Artinskian of South Africa), Damodar Basin (Lopingian of India) and Dead Sea area (Changhsingian of Jordan)]. They range from peri-glacial/post-glacial to warm temperate climatic systems throughout the Permian. Macro- and micro-charcoal occurrences are compared to inertinite incidences to support the pyrogenic origin for these coal macerals and to provide an up to date overview on the known evidences of Permian wildfires on Gondwana in space and time.

Characterization of chemical functional groups in macerals across different coal ranks via micro-FTIR spectroscopy

Fourier transform infrared spectra of a suite of coals of varying rank from peat to anthracite were obtained via reflectance micro-FTIR and traditional KBr pellet techniques. With increasing rank of coal samples, KBr-FTIR spectra exhibit rising aromaticity (ratio of CH ar at 3000–3100 or 700–900 cm − 1 versus CH al at 2800–3000 cm − 1 ) and enhanced condensation of aromatic rings (ratio of CH ar versus C=C at ~ 1600 cm − 1 ), whereas the aliphatic chain length (ratio of CH 2 /CH 3 at 2800–3000 cm − 1 ) and the ‘C’ factor (ratio of C=O at ~ 1710 cm − 1 versus (C=O + C=C)) decrease. The ratio of CH al /(CH al + C=C) (i.e., the ‘A’ factor), which reflects the hydrocarbon-generating potential, initially rises at low rank and later decreases in higher-rank coal= ( R o > 0.98%). However, the trends of these semi-quantitative FTIR ratios are difficult to trace in high-rank coals ( R o > 1.50%), probably attributable to limited peak areas and enhanced uncertainties in ratio calculations. The overall evolutionary trends of functional group abundances in bulk coals and their individual macerals are similar; distinct differences in chemical properties, however, exist among maceral groups, and these variations depend on rank. Within the three maceral groups, liptinite generally exhibits the lowest aromaticity, the longest aliphatic chains having the least amount of branching, and the highest ‘A’ factor testifying to the highest hydrocarbon-generating potential. In contrast, inertinite shows the highest aromaticity and degree of condensation of aromatic domains and the lowest hydrocarbon-generating potential. Vitrinite generally exhibits intermediate characteristics between liptinite and inertinite. Compared to KBr spectra, micro-FTIR spectra present better detection capability and stronger signals in the 700–900 cm − 1 region, which allows for close investigation of aromatic CH x out-of-plane deformation modes. The rapid decrease in the peak area ratio at ~ 870 cm − 1 /~ 750 cm − 1 in vitrinite from peat to low-volatile bituminous coal is followed by a significant increase after R o > 1.50%, which indicates the dominance of highly substituted aromatic rings in immature coal's structure, while condensed aromatic domains become prevalent in higher-rank coals (semi-anthracite and anthracite). The increase in coal aromaticity during coalification is attributed largely to the accumulation of condensed aromatic structures in more mature coals. Novel reflectance micro-FTIR mapping is a promising and powerful tool providing high-resolution information on chemical properties of coal macerals relating to parent material and coalification. ► We demonstrate the applicability of micro-FTIR mapping to the study of coal macerals. ► Aromaticity increases and aliphatic chain length decreases with coal rank. ► Highly substituted aromatic rings dominate in immature coal’s structure. ► Condensed aromatic domains are prevalent in higher-rank coals.

Coal macerals separation by reflux classification and thermo-swelling analysis based on the Computer Aided Thermal Analysis

The reflux classifier is a water based device designed for classifying and separating particles using inclined plates. Particles of sufficiently high settling rate are refluxed back to the slurry, while slow settling particles (low density vitrinites) are removed in the overflow. In this study, the reflux classifier was used to separate coal macerals less than 212μm in size. The thermo-swelling characteristics of separated macerals were evaluated on the basis of the Computer Aided Thermal Analysis (CATA) technique with extended volumetric measurements. A suite of maceral concentrates with various densities, ash contents, particle sizes and vitrinite percentages was obtained, which indicated that the reflux classifier can offer an alternative method of macerals separation/concentration without the use of dense media. The pyrolysis experiments of maceral concentrates indicated that the vitrinite-rich macerals showed a higher extent of volumetric swelling, exothermic reactions and thermal conductivity between 400 and 600°C than inertinite-rich macerals. Addition of inertinite to vitrinite concentrates showed that inertinite can suppress volumetric swelling and shift the swelling to a higher temperature during the primary devolatilization, but does not have a significant influence on high temperature contraction. Further observations about the interaction among different maceral groups were also discussed in this study.

Dynamic behaviour of coal macerals during pyrolysis – Associations between physical, thermal and chemical changes

A fundamental study on the behaviour of heating coal macerals has been undertaken using two novel thermal analysis techniques. The apparent specific heat was determined during heating using an inverse calorimetric method (computer aided thermal analysis, CATA) and combined with pressure and displacement measurements to correlate endothermic and exothermic behaviour with measurement of swelling. The second technique used a post-oxidation stage to combust the tars and gases into products which were analysed. This method was used to study the elemental character of volatiles release from coal maceral concentrates in terms of carbon and hydrogen. Extents of swelling and exothermicity during primary devolatilisation were found to be correlated with vitrinite content and were associated with tar evolution. For the highest vitrinite fraction (of 86.4% vitrinite) swelling was initiated at the same temperature range for exothermic reactions, and maximum swelling coincided with the peak release of light gases. Tar evolution was found to change in chemical character (as defined by H/C ratio) during progressive heating, initially rising in the early stages of tar formation (<430°C) to a maximum of 1.24, then gradually decreasing to a minimum of 0.64 at 550°C.

Combining palynofacies and petrography in the study of sub-bituminous tropical coals: A case history from Lower Tertiary coals in Colombia

Colombia contains large coal reserves of Late Cretaceous to Cenozoic age in various sedimentary basins, but little is known about their potential to generate hydrocarbons. In Western Venezuela, coals are known to be potential source rocks for oil and the vicinity of these coals with coal-bearing basins in Colombia has prompted new studies in Colombian tropical coals to develop concepts about their hydrocarbon generating potential. The Paleogene Amagá Formation studied here, although of limited geographical extension, is an ideal field laboratory which contains low-rank coal seams, in which the transformation and preservation state of organic matter permits the assessment of environment and vegetation types existing at the time of peat formation.Several seams up to 1m thick have been analyzed using both bulk seam samples and ply (or lithotype) samples. It is demonstrated that bulk seam samples are not representative for a proper evaluation of the hydrocarbon generation potential of seams. One needs to evaluate all lithotype assemblages within a seam. Proximate analysis and Rock-Eval pyrolysis provide a rapid and cheap way to assess the generation potential of each lithotype. The potentially interesting lithotypes can be further analyzed through the combination of petrographic and palynological observations. These methods permit the comparison of coal macerals with the equivalent palynofacies constituents, provided that a preparation technique especially designed for tropical, sub-bituminous, Tertiary coals is used.The palynofacies technique has proved to be more accurate than petrography in determining the relative proportion of the potentially oil-prone constituents/macerals, which can be hidden or difficult to identify in petrographic polished section. Moreover, the comparison between resinite oil observed in petrography and resins identified in palynofacies may yield indications of early hydrocarbon generation.This methodology provides a fully detailed inventory of coal properties with respect to hydrocarbon generation potential. The use of palynofacies is an additional tool to apprehend the floral composition and paleoenvironment of coals, thereby increasing the geological and geochemical database needed to evaluate their potential. Such a methodology may prove very important to assess the petroleum potential of thicker coal deposits in prospective petroleum provinces, such as the Cerrejon coals in Northern Colombia.

Raman spectroscopy of coal macerals and fluidized bed char morphotypes

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.

Coal Macerals Response to Coal Liquefying Activity Based on SPSS - Take No.11 Coalbed in Antaibao Mine for Example

Coal liquefaction is the available, adoptable method of relieving the energy crisis from crude oil supply in large scale. The coal type and react activity are hot research. In this paper, From the SPSS (Statistical Product and Service Solutions) data correlation analysis and hierarchical clustering graph about the macerals respond to coal liquefaction yield, all the correlation coefficients determine the liquefying activity of submacerals. It shows that every liquefaction intendancy is agreed with the maceral inherent petrology property, and these views have been found in previous study. The results indicated that by means of SPSS method, we can take investigation when there is not proper experiment condition. Compared with painstaking seperating-maceral experiment and the impossible separation to submacerals, it may be a simple, accurate, comprehensively, completely and practically method in a sense.

Fuzzy Comprehensive Evaluation on Relationship of Coal Maceral and Porosity

Porosity where most complicated physicochemical changes in is not only related to coal metamorphic degree but also to the maceral. Relationships of coal maceral and porosity are the main content of this paper. By pressured-mercury testing and polarizing microscope analysis, it is found that vitrinite has higher content of transition pore and inertinite is rich of macroporous, meanwhile the specific pore volume of mesopore and microporous is related to both vitrinite and inertinite. Also, there is a creative found that the method of fuzzy comprehensive evaluation could be used to estimate the relationship of the coal maceral and porosity.

Influence of microwave treatment under a hydrogen or methane atmosphere on the flotability of the macerals in Shenfu coals

The modification of Shenfu coals by a microwave treatment carried out under a hydrogen or a methane atmosphere, and the subsequent maceral separation by flotation, are described in this paper. The surface contact angle and the Zeta potential of the coal macerals were measured both with and without the treatment. The results show that the surface wettability of SFF (Shenfu Fusain) and SFV (Shenfu Vitrain) can be changed by the microwave treatment. An increase in the difference in surface wettability of SFF and SFV causes in a subsequent increase in the enrichment of inertinite and vitrinite. The results of the Zeta potential measurements show that the surface potentials of SFF and SFV are also changed by the treatment.

Petrographic, geochemical, and mycological aspects of Miocene coals from the Nováky and Handlová mining districts, Slovakia

Abstract Fungi have once again become a topic of interest to coal scientists in their roles as agents of maceral formation. Recent works have demonstrated that fungi occur in association with woody remains, resins, and cuticles in coalified materials of a variety of ages, in addition to coal-balls and compression–impression fossils, where they are already well known. These forms, however, have only been viewed as cross-sections along a polished plane. Assigning the fungi to family, much less determining which fungi they represent is very difficult in this orientation. Fungal identifications are necessary to the continuance of this research into the origin of coal macerals because of the need to know if macrinite begins to form prior to incorporation into the peat, which could be demonstrated by its association with symbiotic and parasitic, rather than saprophytic fungi. This study examines the fungal remains recovered from eight coal samples from Miocene-age coals in the Novaky and Handlova mining districts of Slovakia with the aim of making this distinction. These samples were collected in Slovakia as part of the US Geological Survey's World Coal Quality Inventory program and provided to the authors. The samples were processed using the O'Keefe technique for subbituminous coals and mounted for observation in transmitted light. Forms were identified using published works and consultation with a modern mycologist. Forms recovered through palynologic processing were compared to and correlated with forms seen in cross-section under reflected light.

Micro-Raman spectroscopy of carbonized semifusinite and fusinite

Abstract The purpose of the study was to present application of micro-Raman spectroscopy for examination of coal macerals and to characterize the internal structure of semifusinite and fusinite heated at 400–1200 °C, in an argon atmosphere. Examination was performed on inertinite concentrates prepared from three samples of steam and coking bituminous coals ( R r = 0.98–1.42%) from the Upper Silesian Coal Basin of Poland. Fusinite and semifusinite, as well as reactive and non-reactive forms of the latter maceral differ in terms of structural properties, as inferred from the Raman-derived parameters. Behavior of both macerals under heat-treatment is determined by their structural and chemical properties. Carbonization causes rebuilding of macromolecular network of semifusinite and fusinite resulting in the growth of polyaromatic units and, in case of the former maceral, also increases in structural organization. This is followed by significant reflectance increase. Semifusinite carbonized at 1200 °C has larger coherent domains and they are more ordered than in fusinite, which results in higher reflectance value. The A D3 + D4 /A ALL ratio may be used as a measure of inertinite reactivity. Significant relationships between random reflectance ( R r ) of semifusinite and fusinite and the I D1 /I G ratio and position of most Raman bands (G, D1, D2 and D3) for the studied temperature range were found.

Coal Forming Environments of the Third Member of Yacheng Formation of the Paleogene in Qiongdongnan Basin for an Example

Qiongdongnan basin is located in the Southeastern waters area of the Hainan Islands China. In this paper, many methods were used such as sedimentology, coal geology, and geochemistry to study the geochemical characteristics and coal-forming environments of the coal seams in the third member of Yacheng Formation. The results indicate that the coal seams were characterized by thin-beds, multi-layered and unstability forms. Through the analysis of the moisture content, ash content, volatile content, total sulfur, carbons, coal maceral and the maximum reflectivity of the vitrinite, we found that the coals belong to the medium rank bituminous coal, of which the metamorphic grade between the fat coal and coking coal. This result is consistent with that reflected by the volatile content. The coal macerals are mainly desmocollinite, which means the plant lignocellulose tissues have undergone more complete gelation during coalification, so the sedimentary environment should be the light oxidation to reduction. The sediment facies plan of the period of the sedimentation of the third member of Yacheng Formation indicate that the coal seams were mainly formed in the environments both near the sea and the sources such as fan or braided delta plains, or delta front with shallow water where could be easily influenced by the sea water. The general trend of sedimentation showed as transgression, that is, with the intrusion of sea water, the sedimentary environments in the region of interest involved into transitional environments such as fan delta, braided delta and shallow sea, then involved into marine environments such as tidal flat, lagoon and shallow sea.

Chemometric analysis of functional groups in fossil remains of the Dicroidium flora (Cacheuta, Mendoza, Argentina): Implications for kerogen formation

Abstract Studied samples include eight Gondwanan species of the Dicroidium flora: seed ferns (3), conifer (1), cycad-related (1), unknown affinity gymnosperms (2), and one undetermined axis from two Middle to Upper Triassic localities (Cacheuta, Mendoza, central western Argentina). Based on differing preservation states and sample treatments, four sample forms are established: (1) compressions, (2) cuticles, (3) cuticle-free coalified layers, and (4) associated coal samples. The purpose of the study is firstly to analyze the sample forms using Fourier transform infrared (FTIR) spectrometry, contributing to filling an existing gap of chemical information for Gondwanan pant fossil remains. Secondly, semi-quantitative chemical parameters, calculated by area integration of infrared spectra, are treated using principal component analysis to infer statistical groupings as a function of chemical structures (functional groups). From the initial two-component solution, based on the 8 × 41 data matrix, a subset matrix (4 × 29) could be isolated which also yielded a two-component solution (in each case, cumulative explained variance is at least 89%). Results include the distinction between the coaly forms (1) compressions and (3) cuticle-free coalified layers mainly based on the carbonyl contents and branching and length of the hydrocarbon side chains. The highly aliphatic nature of cuticles, which is indicative of biomacromolecules (cutin), is noted. Similarities in functional groups are recorded with types of kerogen and coal macerals. The result enables us to postulate that the functional groups characterizing the different modes of preservation of our fossil remains are likely related to the propensity to generate oil and gas/condensate from the kerogen. Our data have the potential for future studies with implications for chemotaxonomy, molecular taphonomy, and paleoclimatology.