Coal Macerals Research Articles

Effect of multi-intensification on the liberation of maceral components in coal

In order to achieve high-quality coal resources in western China, this study focused on a coal sample from the Shangwan Coal Mine, owned by the China Shendong Group, and employed scanning electron microscopy (SEM), mineral liberation analysis (MLA), and maceral component quantitative analysis for investigating the coal sample’s liberation characteristics and crack distribution patterns after pre-grading and microwave processing. The results show that the physical properties of coal maceral components significantly affected the related enrichment performances, and many intra-group and inter-group cracks were produced under the induction of microwave radiation. The cracks then developed and stopped growing among the different maceral components and mineral components, thereby inducing selective and random pulverization along the crack growth direction in further pulverization process and effectively enhancing the liberation properties of different components. Using the Sandbox method, the fractal dimension of the cracks on the particle surface was calculated to be 1.01, which confirmed the self-similarity of the cracks on the coal surface. Multi-intensification maceral liberation also yielded favorable grading performances. The inertinite content was the highest (75.23%) in grade-3 product, while the vitrinite content was the highest (66.3%) in grade-1 product; the corresponding enrichment ratios were 2.15 and 1.59, respectively. Moreover, the ash content in grade-2 product was the lowest, which dropped by 3.61% compared with that in raw coal sample.

Study on geological controls and enrichment models of coalbed methane in the Wuwei Basin in eastern North Qilian, northwestern China

The Wuwei Basin is located in the Gansu Corridor, which has abundant coalbed methane resources of 2.75 × 1011 m3. However, a low degree of coalbed methane exploration exists, and only a few wells have been drilled in local regions due to insufficient understanding of coalbed methane enrichment and its main controlling factors. This study analyzed the controlling factors of coalbed methane enrichment, including coal reservoir characteristics, hydrogeological conditions, and the original sedimentary environment of the coal-bearing strata. The results showed that the main coal seams were developed in the Taiyuan Formation, and were mostly concentrated in the Yingpan Sag in the south and the Ermahu Sag in the north of the study area. The macrolithotype of the coals in this basin was mainly semi-bright coal with a medium to high rank. Coal macerals were mainly vitrinite, ranging between 65.1% and 91.6% (averaged 81.70%), followed by liptinite, ranging between 1.9% and 29.5% (averaged 8.82%), and inertinite, ranging between 0.2% and 16.5% (averaged 3.66%). Mineral contents varied from 2.5% to 15.1% (averaged 6.16%). The macrolithotype and microlithotype of the Taiyuan Formation coals were favorable for coalbed methane formation. Through comparative analysis of moisture content, ash yield, gas content, and coal-forming sedimentary environments, it was found that the coal formed in the lagoon environment had a higher gas content and lower ash yield than that of the coal formed in the tidal flat environment. The high contents of total dissolved solids in aquifers around coal seams (1.75–16.70 g/L) reflected the closed hydrodynamic environment and were favorable for the preservation of coalbed methane in the Yingpan Sag. Considering various controlling factors (i.e., structure, sedimentation and hydrogeology), three coalbed methane enrichment models were proposed. The model of coalbed methane enrichment in the synclinorium was the most favorable for the enrichment of coalbed methane in the Yingpan Sag.

Nanoindentation study of macerals in coals from the Ukrainian Donets Basin

Abstract. This article discusses the mechanical properties of macerals in Carboniferous coals from the Ukrainian Donets Basin, covering a maturity range from 0.62 to 1.47 %Rr (vitrinite reflectance). The inherent inhomogeneity of geological samples requires characterization at the micro-/nanoscale, and hence material parameters, such as hardness H and reduced elastic modulus Er, were obtained from twelve coal specimens via nanoindentation tests. Different material properties and maturity trends were acquired for the individual maceral groups (vitrinite, inertinite, liptinite). The results indicate that apart from maturity, multiple factors like microstructural features and depositional environment control the mechanical properties of macerals in coals. H and Er of vitrinites show a complex relationship with maturity due to additional influence of microstructural features such as nanoporosity or mineral inclusions and complex changes in the organic matter structure with increasing rank. The mechanical behaviour of inertinites is mainly controlled by the prevailing conditions (temperature, exposure) during paleo-wildfires. Er and H of liptinites are strongly influenced by transformational processes related to devolatilization at low to medium rank, as well as later hydrocarbon generation. Variations in the depositional environment (e.g. increased organic S content due to marine influence) might play an additional role.

The evolution of nanopores and surface roughness in naturally matured coals in South China: An atomic force microscopy and image processing study

The coals in South China has not been well investigated because the coal mines are small in volume compared with the well-known large-scale coal accumulations in North China, thus the nature of such coals is of significance to study. The nanopore characteristics and surface roughness of 14 coal samples that have experienced low degrees of tectonic deformation as a naturally matured coal series in South China were addressed. Atomic force microscopy (AFM) and image processing were applied in a study of relationships between nanopore development, surface roughness, and thermal maturity (indicated by vitrinite reflectance; Ro = 0.65%–4.43%) in the naturally matured coal series. The results show that areal porosities of the coal samples are 0.78%–9.33%, with mean pore sizes of 7.9–27.9 nm. There were three main stages of pore evolution related to thermal maturity, with Ro values of <1.3%, 1.3%–3.7%, and >3.7%. Pore number, areal porosity, and mean pore size follow a cyclical downward/upward trend across the three stages. Arithmetical mean (Ra) and root-mean-square (Rq) surface roughness values are 1.69–17.74 nm and 2.24–28.81 nm, respectively. Ra and Rq values of coal samples with relatively low thermal maturity (Ro < 1.3%) are controlled mainly by coal maceral and mineral composition, whereas values for coals with relatively high thermal maturity (Ro > 1.3%) are controlled by nanopore development. Thermal maturity is an important factor that influences the nanopore and surface roughness characteristics of naturally matured coals in South China.

Petrographic and chemical reactivity assessment of Indian high ash coal with different biomass in fluidized bed co-gasification

The reactivity of coal and biomass has been evaluated by comparing the optical and chemical changes in feed material prior and after the co-gasification. The proximate, ultimate, GCV, low-pressure N2 sorption isotherm, micropetrography, SEM and EDX spectroscopy analyses are carried out to assess the reactivity of blends of high ash Indian coal and biomass. The relative changes in parameters like surface area, pore size, and pore volume have been correlated with reacted percentage area of coal macerals and cellulose-lignin cellular structures of biomass. The Optimas image processing software is being used to mark the reacted portion of organic constituents and calculated the reactivity percentage. The bottom ash of pure coal has shown the least reacted organic matters, indicating inefficiency of high ash coal due to a large amount of inorganic and inertinite contents that is resisting the oxidation. The reactivity percentage is determined by the petrographic and SEM images, and varies from 36.34 to 99.64% and 6.61–96.22%, respectively. It is summarised that the estimation of percentage alteration of macerals and other micro-organic constituents can be used as one of the practical approaches for the assessment of the reactivity of coal and biomass. The blending ratio 6:4 of coal and press mud has shown the highest reactivity (>99.64%). The values of petrographic and SEM reactivity have shown good correlations with the carbon contents, unreacted vitrinites, mineral matters and biomass remnants. These relations have been taken into account to formulate the proposed petrographic empirically calculated reactivity (RPEC). The focus has also been made to investigate the influence of feed composition on carbon conversion and heating value of the product gas.

Petrographic Controls on Pore and Fissure Characteristics of Coals from the Southern Junggar Coalfield, Northwest China

The productive potential of coalbed methane projects is controlled by pore and fissure characteristics, which are intrinsically related to coal petrology. This work attempts to identify the influence of petrographic factors on the development of pore and fissure systems in the southern Junggar Coalfield, Northwest China. Here, Middle Jurassic coal (lignite and subbituminous) petrology in coal seam No. 45 of the southern Junggar Coalfield (SJC) is studied with respect to the characteristics of pore and fissure structure with the aid of optical microscopes, scanning electron microscopy, mercury intrusion porosimetry, and nuclear magnetic resonance analysis. Maceral analysis shows coals at the SJC are dominated by vitrinite (38–87 vol %), with moderate quantities of inertinite (1–28 vol %) and liptinite (0.5–30 vol %). Decomposition of plants occurs under slightly oxic–anoxic conditions, with good tissue retention. Four types of coal facies are classified using petrographic indices, comprising (1) lower delta plain marsh, (2) lower delta plain fen, (3) upper delta plain wet forest swamp; and (4) piedmont plain moor. Pores and fissures are generally observed in telinite, collotelinite, fusinite, and semifusinite in SJC coals, indicating that the generation of pores and fissures is strongly influenced by coal macerals. Pore and fissure structures of coals in coal facies (1) appear weakly connected, whereas those in coal facies (2) reveal good connectivity. Coals in coal facies (3) and (4) show moderate connectivity between pore and fissure structure. Therefore, pore and fissure structures are significantly controlled by coal facies. This work provides practical recommendations and implementation methods for petrological studies in future coalbed methane exploration/development in the SJC. This study also serves to predict the physical properties of pores and fissures and interpret the control mechanism of coalbed methane production using coal petrology.

Methane adsorption characteristics and its influencing factors of the medium-to-high rank coals in the Anyang-Hebi coalfield, northern China

The variation of coal rank in the Anyang-Hebi (Anhe) coalfield has the phenomenon of anti-Hilt law, which makes the coalfield distinctive for coalbed methane exploration research. The methane adsorption characteristics and influencing factors of the medium-to-high rank coal samples of the Shanxi Formation in this coalfield were analyzed. The results indicate that the Langmuir volume ( VL) of coals in the shallow western part of the Anhe coalfield is generally higher than that in the deep eastern part. The coal rank and the coal macerals are the dominant factors that influence the methane adsorption capacity of coals in this anti-Hilt law area. The methane adsorption capacity, represented by VL, first increases and then decreases with the coal rank, and the highest VL value corresponds to the maximum vitrinite reflectance of ∼2.1%. The adsorption capacity has a positive correlation with the vitrinite and the moisture content, a negative relationship with the inertinite content. In general, the adsorption capacity of coal samples shows a “V-shaped” change with the ash yield, and the lowest VL value corresponds to the ash yield of ∼9%. A prediction model of the gas content of the Anhe coalfield was proposed based on changes of the methane adsorption capacity and principal component analysis. Areas with a critical depth ranging from 400 m to 700 m are suggested to be methane enrichment regions for coalbed methane exploration in the Anhe coalfield.

Coalification and fuel analysis of the Lower Carboniferous Thora coal seam in the Bedaa- Gebel Hazbar- Gebel Nukhul district, Sinai, Egypt

Twenty channel coal samples were collected and examined along 15 km throughout the outcrops of coal-bearing shale horizon in the middle part of the Abu Thora Formation in Sinai. The coal seam varies in thickness between 20 cm and 72 cm (averaging 55 cm). Fuel analysis shows the shaly coal facies is three times more dominant than the coal facies in the studied area. The type of coal is very low-grade with ash contents (d.b.; dry-base) of about 55% which is a poor quality for industrial use. The high ash content reflects the planner mire of the rheotrophic system during peat accumulation. Coalification paleo-temperature was relatively high of averaging 108.9 °C which could be attributed to additional thermal heating by the Jurassic sill capping the Abu Thora Formation especially within the western area of Gebel Hazbar. The studied coal is classified as medium rank ortho-bituminous based on the average vitrinite reflectance, gross calorific values, volatile matter, and fixed carbon. Vitrinite genesis and exinite genesis during developments of coal macerals are the two main pathways of the studied coal samples that are attributed to well preserved vascular plants under dominant anoxic waterlogged swampy conditions.

Jurassic coal maceral and deposition rate of peat in the northern Qaidam Basin

Jurassic coal maceral and deposition rate of peat in the northern Qaidam Basin

RaMM (Raman maturity method) study of samples used in an interlaboratory exercise on a standard test method for determination of vitrinite reflectance on dispersed organic matter in rocks

RaMM (Raman maturity method) is a thermal maturity tool for humic macerals in coals or as dispersed organic matter (DOM), expressed in equivalent vitrinite reflectance (EqVR). The EqVR values are based on a recently established calibration according to multi-linear regressions of selected parameters from Raman spectra of vitrinite and inertinite in a suite of Australian coals with vitrinite reflectance (VR) in the range 0.4–2.5%. The study contributes to the application of Raman spectroscopy for thermal maturity determinations as applicable to the petroleum exploration industry and researched by many groups worldwide.A suite of samples to apply the technique was made available from an interlaboratory round robin exercise on application of ASTM D7708, a method for determination of VR of DOM in sedimentary rocks. This exercise involved the distribution of two sets of six unknown rock samples to all participating laboratories. Collated VR results from some samples of the first set, having high maturities and low organic matter (OM) contents, showed a disturbingly high degree of scatter. Although general agreement exists between RaMM determinations and the average of ‘mean random’ VR values determined at the various laboratories, some important differences emerged for some samples in the range EqVR = 1.2–1.8%.On RaMM diagrams, which involve plots of EqVRs derived from the two regression equations defining the method, the pattern of distribution of vitrinite and inertinite changes with thermal maturity for ‘normal’ coals and with OM composition in subhydrous versus perhydrous coals.Most of the round robin samples contained solid bitumens having reflectances close to those of the associated vitrinite. Measurements taken from solid bitumen were avoided as much as possible, but because the RaMM study was done in air medium, some contamination of the humic maceral data was inevitable. Many of the solid bitumens and other potentially complicating components such as Tasmanites-related alginite can be identified on the RaMM diagram and eliminated from RaMM results for lower maturity samples (EqVR < 1.4%) whereas solid bitumen and humic macerals appear to provide similar EqVR for higher maturity samples (EqVR > 1.8%).The humic DOM of marine samples having EqVR >1.0% has spectral properties that differ from those of humic macerals of the same maturity in terrestrially deposited rocks; this could possibly explain any discrepancies between RaMM EqVR and VR data for the marine rocks.The presence of contaminating solid bitumen with reflectance similar to that of vitrinite, is the main complicating factor for thermal maturity evaluation using either VR or RaMM analyses of gas shales and tight oil reservoir rocks. To enable the best results from RaMM studies of these types of rocks, a preliminary study of the solid bitumen component should be carried out to determine its field on the RaMM diagram with the object of eliminating contaminating solid bitumen data from EqVR calculations.

Enrichment of reactive macerals in coal: its characterization and utilization in coke making

Macerals in coal are of different types: reactive and inert. These macerals are differ in their physical and chemical properties. Column flotation method has been used to separate the reactive macerals in a non-coking coal. The enriched coal is then characterized in order to understand the changes in the coking potential by different techniques. It is then used in making of metallurgical coke by proper blending with other coals. Enriched coal enhance the properties of metallurgical coke. This shows a path of utilization of non-coking coal in metallurgical coke making.

INFLUENCE OF COAL MACERALS ON BIOMETHANE PRODUCTION

In order to investigate the influence of coal macerals on biomethane production, two types of coal samples were collected respectively from Malan mine in Gujiao and Shaqu mine in Liulin, Shanxi. The vitrinite, inertinite and liptinite were separated by the methods of hand picking and float-and-sink test. Meanwhile, biomethane production experiments using the raw coal samples, vitrinite-rich coal samples, inertinite-rich coal samples as substrates were carried out in the laboratory. Finally, the fourier transform infrared spectrometer (FTIR) was used to analyze the relationship between the macerals and biomethane production. The results show that vitrinite-rich coal samples have the largest biomethane production followed by raw coals samples and inertinite-rich coal samples. Vitrinite-rich coal samples have the highest contents of aliphatic hydrocarbon and lowest degree of aromatization, while inertinite-rich coal samples have the least contents of aliphatic hydrocarbon and highest degree of aromatization. Therefore, the contents of aliphatic hydrocarbon and aromatization degree in coal with different macerals are important indicators of influencing the biomethane production potential.

An Investigation on Floatability Behavior of Coal Macerals In Flotation Process and Reagent Type Optimization at Central Alborz Coal Washing Plant

ABSTRACT In this study, effects of petrographic composition and particle size on flotation process were investigated. Samples were taken from rougher and cleaner cells of central Alborz coal washing plant (Iran). Petrographic study of the feed into flotation circuit with different size fractions showed that an increase in particle size tends to decrease vitrinite and inertinite macerals percentage while increasing that of liptinite. Petrographic analysis of different size fractions of rougher and cleaner cell concentrates showed that, with increasing particle size, vitrinite macerals were reduced but liptinite macerals showed an increase. Evaluation of the cell operation revealed that over 62% of tailings was composed of reactive macerals in coking process, including vitrinite and liptinite. The petrographic study showed that, with the same frother, by applying gasoline as a collector, yield, and total recovery increased by 3.5% and 3%, respectively, as compared to those when kerosene served as collector. Continuing with gasoline as collector, total circuit recovery increased by 2.2% when methyl isobutyl carbinol (MIBC), rather than pine oil, served as frother. Based on petrographic studies and percentages of reactive macerals, the optimal reagents were found to be gasoline (as collector) and MIBC (as frother).

Depositional model for peat swamp and coal facies evolution using sedimentology, coal macerals, geochemistry and sequence stratigraphy

As one of the most important source rocks and reservoirs of unconventional natural gas, the sedimentary environment and mode of peat swamp (the predecessor of coal seam) is important to the coal seam’s spatial distribution, material composition, hydrocarbon generation potential, reservoir physical properties, etc. To reveal the depositional characteristics and history of environmental change in a terrestrial basin during a period of peat accumulation, the Middle Jurassic aged #7 coal from Gaoquan in the Qaidam Basin (NW China) was investigated using sedimentology, maceral composition, geochemistry and sequence stratigraphy. Based on identification of the sedimentary shoreline break belt, wave energy depletion point and position of wave base, the peat swamp system can be subdivided into (1) lakeside plain, (2) low energy lakeshore, (3) high energy lakeshore, and (4) shallow lake subfacies. A new method for determining coal facies is proposed based on the combination of environmental parameters including oxidation-reduction levels, energy conditions and the influence of terrigneous sediments. The evolution of the coal seam shows that peat was deposited mainly in the low energy lakeshore and lakeside plain subfacies. Five types of sequence stratigrpahic surface and two types of parasequence were identified. Forced lake regressions and normal lake regressions are attributed as the causes of sequence boundaries. The sequence stratigraphic framework comprises six sequences and corresponding system tracts, and the curve of base-level for each demonstrates a characteristic initial period of slow rising followed by fast rising and then returning to slow rising. A model indicating the relationship among base-level changes, coal facies evolution, and the environmental features in the swamp is proposed that shows the environmental features of the swamp were controlled by both base-level changes and coal facies. Accompanying depositional environment changes from a lakeside plain to lakeshore and shallow lake caused by increasing rate of base-level rise, water paleosalinity, acidity and the percentage of woody plants decrease, and the bog type alters from the low marsh to raised bog.

Identification and nanoporosity of macerals in coal by scanning electron microscopy

Recent applications of scanning electron microscopy (SEM) to shale resource plays at magnifications of <500–>80,000× have reported nanoporosity in organic matter with limited interpretations of organic matter type. Macerals, inclusive of kerogen and solid bitumen, are recognized and distinguished in reflected white and epifluorescent light in coal and shale samples at magnifications of 200–750×. The objectives of this study are to identify macerals by SEM and evaluate which macerals contain primary and secondary nanoporosity. Since coals are organic rich with a better chance of identifying adjacent maceral types than when dispersed in shales, broad ion beam milled samples of humic and sapropelic (boghead and cannel) coals ranging in rank from peat to semianthracite were examined in backscattered electron (BSE) mode at low magnification (≤2,500×) to identify maceral type. Once identified, macerals were examined at higher magnifications of 1200–75,000× to assess maceral nanoporosity.Manipulation of the accelerating voltage to 10kV in BSE mode of a high volatile bituminous humic coal durain lithotype sample revealed a contrast between maceral groups (vitrinite, inertinite, liptinite), with limited identification of individual maceral types. Vitrinite maceral subgroups telovitrinite and detrovitrinite are distinguished based on their relative gray scale appearance compared to other macerals and occurrence as bands or groundmass, respectively. The liptinite macerals alginite, sporinite and cutinite are distinguished based on dark relative gray level and their shape. The liptinite maceral bituminite/amorphinite was recognized by dark relative gray level and occurrence as groundmass in a boghead coal. The inertinite macerals fusinite and semifusinite are recognized by light gray level appearance compared to other macerals and bogen structure but are not distinguishable separately. Macerals dispersed in shale, lacking the subtle contrast of adjacent macerals, are much more difficult to identify.Even though porosity is revealed at high magnification in BSE mode, too high of a magnification (>15,000×) prohibits identification of maceral types. The best approach is to examine samples at a lower magnification (e.g., 650×) at 10kV accelerating voltage in BSE mode to identify the maceral type and then go to a higher magnification at 1–2kV accelerating voltage to observe nanoporosity.Primary nanoporosity is observed within coal macerals at low rank (peat and subbituminous), but decreases in amount with increasing rank. Primary microporosity occurs as woody cell lumens in semifusinite and fusinite macerals. Secondary nanoporosity develops in post-oil solid bitumen in shale beginning below the peak of the oil window with a lack of nanoporosity at lower thermal maturity. Compared to the abundant nanoporosity of post-oil solid bitumen in shale, only trace amounts of nanoporosity is observed in other macerals in coals of high volatile bituminous rank and higher under the SEM.The emphasis of this study was the identification and nanoporosity of macerals in coal by SEM. The same results may extend to the same macerals in shale. Knowledge of organic matter porosity distribution by maceral type and development by thermal maturity provides insight for coalbed methane, shale gas and tight oil production potential.

An expert system based on hybrid ICA-ANN technique to estimate macerals contents of Indian coals

Coal, as an initial source of energy, requires a detailed investigation in terms of ultimate analysis, proximate analysis, and its biological constituents (macerals). The rank and calorific value of each type of coal are managed by the mentioned properties. In contrast to ultimate and proximate analyses, determining the macerals in coal requires sophisticated microscopic instrumentation and expertise. This study emphasizes the estimation of the concentration of macerals of Indian coals based on a hybrid imperialism competitive algorithm (ICA)–artificial neural network (ANN). Here, ICA is utilized to adjust the weight and bias of ANNs for enhancing their performance capacity. For comparison purposes, a pre-developed ANN model is also proposed. Checking the performance prediction of the developed models is performed through several performance indices, i.e., coefficient of determination (R 2), root mean square error and variance account for. The obtained results revealed higher accuracy of the proposed hybrid ICA-ANN model in estimating macerals contents of Indian coals compared to the pre-developed ANN technique. Results of the developed ANN model based on R 2 values of training datasets were obtained as 0.961, 0.955, and 0.961 for predicting vitrinite, liptinite, and inertinite, respectively, whereas these values were achieved as 0.948, 0.947, and 0.957, respectively, for testing datasets. Similarly, R 2 values of 0.988, 0.983, and 0.991 for training datasets and 0.989, 0.982, and 0.985 for testing datasets were obtained from developed ICA-ANN model.

Online analysis of initial volatile products of Shenhua coal and its macerals with pyrolysis vacuum ultraviolet photoionization mass spectrometry

Initial volatile products from pyrolysis of Shenhua coal and its macerals were investigated by using online pyrolysis-vacuum ultraviolet photoionization mass spectrometry (Py-VUVPI-MS). The fragment-free spectra of initial volatile products were measured during the temperature-programmed pyrolysis of the samples, and the intensity profiles of the initial volatile products as the function of temperature were detected. Mononuclear aromatics and phenols are the primary constituents of initial volatile products along with alkenes, n-alkyl naphthalene, n-alkyl naphthol, etc. The relative content of phenols evolved from coal macerals shows the order of vitrinite>raw coal>inertinite and that of polycyclic aromatic hydrocarbons (PAHs) exhibits the opposite trends. The different relative content in initial volatile products can be attributed to the different structures of coal macerals. The main source of phenols is the thermal decomposition of the oxygen-containing functional groups. PAHs come from two parts: thermal decomposition of coal macromolecular and free PAHs in mobile phase. This work provides a method for online analysis of initial pyrolytic products from coal by Py-VUVPI-MS.

Effects of coal rank on physicochemical properties of coal and on methane adsorption

For the thorough research on coal metamorphism impact on gas adsorption capacity, this paper collected and summarized parameters of experimental adsorption isotherms, coal maceral, proximate analysis and ultimate analysis obtained from National Engineering Research Center of Coal Gas Control and related literatures at home and abroad, systematically discussed the coal rank effect on its physicochemical properties and methane adsorption capacity, in which the coal rank was shown in Vitrinite reflectance, furthermore, obtained the Semi-quantitative relationship between physicochemical properties of coal and methane adsorption capacity.

65 石炭微細組織成分の形状がコークス品質に及ぼす影響(コークス品質,抽出物添加)

65 石炭微細組織成分の形状がコークス品質に及ぼす影響(コークス品質,抽出物添加)

Maceral controls on porosity characteristics of lithotypes of Pennsylvanian high volatile bituminous coal: Example from the Illinois Basin

Porosity characteristics of vitrain, clarain, durain, and fusain lithotypes of the Springfield Coal Member of the Petersburg Formation and the Danville and Hymera Coal Members of the Dugger Formation from the Illinois Basin were investigated with a special emphasis on the control of coal macerals on pore-size distribution. These Pennsylvanian coals are of high volatile bituminous rank and have vitrinite reflectance ranging from 0.51 to 0.60%. The lithotypes studied show decreasing values of Brunauer-Emmett-Teller surface area, and micro- and mesopore volumes from vitrain through clarain and durain to fusain. Within the mesopore size range, vitrain and clarain are dominated by pore-size widths of 4 to 10nm, whereas durain and fusain have more volume for pores larger than 20nm. In contrast to mesopores, micropore sizes are very similar for all lithotypes, averaging 1.37 to 1.39nm. In addition to differences among lithotypes, there are significant differences in pore characteristics among the three coals studied, with largest surface areas and pore volumes documented for the Hymera, followed by the Danville and the Springfield. A strong relationship exists between surface area, mesoporosity, and microporosity and maceral composition, with vitrinite having a very strong positive correlation, liptinite having a weak positive correlation, and inertinite having a strong negative correlation. Negative correlations of total porosity with vitrinite and liptinite and positive correlations with inertinite suggest that among the maceral groups, pores in inertinite contribute most to the total porosity. The Fourier transform infrared spectrometry technique demonstrates that fusains from the three coals studied have higher aromaticity and a higher degree of aromatic ring condensation and lower hydrocarbon potential than the other lithotypes, whereas chemical differences between vitrain, clarain, and durain are less distinct. In addition, there is a relationship between aromaticity of the lithotypes and surface area and mesopore and micropore volumes.