Coal Macerals Research Articles

The influence mechanism of water-liquid CO2 treatment on the hydrophobicity of vitrinite and inertinite

Liquid CO2 has similar properties to non-polar hydrocarbon oils and can be used to achieve hydrophobic aggregation separation of coal macerals. To reveal the influence of the water-liquid CO2 treatment on the interfacial properties of vitrinite and inertinite, the effects of the water-liquid CO2 system on the interfacial properties of vitrinite and inertinite were investigated by SEM, BET, FTIR, and XPS. The results showed that the content of oxygen-containing functional groups on the coal macerals were reduced more significant than the hydrocarbons due to the physical adsorption and chemical extraction of liquid CO2, which led to an increase in the hydrophobicity of vitrinite and inertinite. The higher porosity and specific surface area of inertinite causing the decrease in the content of oxygen-containing functional groups in inertinite was greater than that in vitrinite. This study provides theoretical support for the separation of coal macerals using liquid CO2 hydrophobic agglomerates.

A novel approach to the separation of macerals in inertinite-rich coal: Charged micro-nanobubble flotation

The classification and utilization of coal macerals have become a vital focus for the advancement of the modern coal chemical industry and mineral processing. Flotation is a well-established technique for large-scale mineral separation, but as for maceral separation, it is often limited by a low recovery rate and poor selectivity. This study investigates the utilization of charged micro-nanobubble (CMNB) flotation to separate the vitrinite from a typical low-ash and inertinite-rich coal in Xinjiang. Results show that CMNB flotation demonstrated notable index advantages over conventional flotation. Optimal flotation was achieved by the CMNBs produced from a 0.75 mM sodium dodecyl sulfate (SDS) solution, with a yield, concentrate vitrinite content, and vitrinite recovery of 49.58 %, 74.31 %, and 77.28 %, respectively. It was revealed that the CMNBs not only promoted the aggregation of vitrinite particles but also increased the adhesion of vitrinite particles and their aggregates to conventional flotation bubbles, resulting in enhanced flotation performance.

Microfacies and Paleomire Reconstruction of Coal in the Warukin Formation, Barito Basin, Kandangan Area, South Kalimantan

Abstract The Barito Basin is one of the basins in South Kalimantan and serves as a coal-producing region. One of the coal-bearing formations present in the Barito Basin is the Miocene Warukin Formation. The purpose of this research is to understand the characteristics of coal macerals, including the dominance of macerals and their microfacies, as well as the type and development of the mire where coal is deposited. This information is crucial for the coal geological study in the Kandangan region, South Kalimantan. The methods employed include organic petrography analysis, proximate and ultimate analysis on seams L8, L5, L5B, M16, and MS02 collected using the ply-by-ply method.The results of the subbituminous coal petrography examination in this formation show the dominance of vitrinite ranging between 41.34-74.04% vol, liptinite between 11.61-38.24% vol, inertinite between 2.21-32.32% vol, and mineral matter ranging from 0.17-1.98% vol, predominantly composed of pyrite. The ash content data ranges from 1.36-15.45 (% wt, adb). The sulfur content data ranges from 0.1-0.45 (% wt, daf). Based on the distribution of maceral abundance, coal microfacies can be categorized into five groups: (1) gelovitrinite-rich group, (2) telovitrinite-rich group, (3) liptinite-telovitrinite-rich group, (4) inertinite-rich group, and (5) telovitrinite-inertinite-rich group. The lower section is predominantly characterized by the telovitrinite-inertinite-rich group. In the middle section, the inertinite-rich group takes precedence, alternating with the liptinite-telovitrinite-rich group. The upper segment is primarily marked by the gelovitrinite-rich and telovitrinite-rich groups. The developed paleomire includes repetitions of topogenous mire and ombrogenous mire. The paleomire type is a wet forest swamp under limnic and telmatic conditions. The dominant original vegetation consists of woody plants, although shrubby plants are also found in significant amounts. Moderate to high gelification levels indicate that the peat was constantly inundated with water.

Mechanism of phenols evolution during pyrolysis of Shendong coal macerals swelled with oxygen-containing organic solvents: Experimental and DFT study

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.

Porosity Characteristics of Coal Seams and the Control Mechanisms of Coal Petrology in the Xishanyao Formation in the Western Part of the Southern Junggar Basin

The porosity characteristics of coal seams serve as a pivotal factor in assessing the development potential of coalbed methane (CBM) resources, significantly influencing the adsorption and permeability capabilities of coal reservoirs, as well as the accumulation, entrapment, and preservation of CBM. In this study, we focused on the coal seams of the Xishanyao Formation in the western part of the southern Junggar Basin (NW China). By leveraging the complementarity of nuclear magnetic resonance (NMR), low-temperature liquid nitrogen experiments, and high-pressure mercury intrusion porosimetry (MIP) in spatial exploration range and precision, we conducted a comprehensive analysis to achieve a fine description of porosity characteristics. Furthermore, we explored the coal petrology factors controlling the pore characteristics of the Xishanyao Formation, aiming to provide geological evidence for the selection of favorable areas and the development potential evaluation of CBM in the study area. The results indicate the following: (1) The total pore volume of the coal samples is 6.318 × 10−3 cm3/g on average, and the micropore volume accounts for a relatively high proportion (averaging 44.17%), followed by the fine pores (averaging 39.41%). The average porosity is approximately 3.87%, indicating good gas storage and connectivity of the coal seams, albeit with some heterogeneity. The coal reservoir is dominated by micropores and fine pores with diameters less than 100 nm, and the pore structure is characterized by low pore volume and high pore area. (2) The pore structure is influenced by both the coalification degree and the coal maceral. Within the range of low coalification, porosity increases with the increase in coalification degree. Building upon this, an increase in the vitrinite content promotes the development of micropores and fine pores, while an increase in the inertinite content promotes the development of meso–macropores. The clay mineral content exhibits a negative correlation with the adsorption pore volume ratio and a positive correlation with the seepage pore volume ratio.

Molecular structure of coal macerals and thermal response behavior of their chemical bonds obtained by structural characterizations and molecular dynamics simulations

Clarifying the microscale reaction mechanism of macerals is crucial for achieving efficient thermal utilization of coals. Herein, we analysed the chemical structures of two coals used in coking for their macerals employing 13C NMR, FTIR, and XPS to build molecules. The pyrolysis behaviours of coals and their macerals were accessed through molecular dynamics of calculating chemical bond characteristics. Results show that inertinite with higher maturity is rich in aromatic, vitrinite with stronger thermal-reactivity is rich in aliphatic, and macerals of coking and gas coal have more advantages in hydrocarbon generation and branch-chain development, respectively. Based on the validated and optimized molecules containing C, H, O, and N elements, it is found that not only the bond lengths of the longest and shortest in macerals from gas coal are greater than those from coking coal, but the thermal response of heteroatom bonds in the former is almost twice that of the later. Moreover, vitrinite and inertinite of coking coal have N–H cleavage to produce active hydrogen in the late stage of bond dissociation, while gas coal lacks this feature. These explain why the pyrolytic properties of different coals and their macerals have variability, guiding the rational selection of coal-based feedstock for industry.

A quantitative investigation on pyrolysis behaviors of metal ion-exchanged coal macerals by interpretable machine learning algorithms

Generalizing the rules from complex processes such as catalytic pyrolysis to guide their process control is always a difficult but attractive task. The influences of ion-exchange of metal ions (Na+, K+, Ca2+, Mg2+, Co2+ and Ni2+) on the pyrolysis behavior of vitrinite and inertinite from Shendong coal were investigated by thermogravimetric analyzer-Fourier transform infrared spectrometer (TG-FTIR), fixed-bed reactor (FBR), gas chromatograph-mass spectrometer (GC-MS) and X-ray diffractometer (XRD). A set of machine learning models was successfully constructed based on random forest, support vector machine, and Gaussian process regression, to quantify the relationships between pyrolysis behaviors and the properties of metals and macerals. The leave-one-out-cross validation showed that there are considerable determination coefficients (R2 > 0.9) between predicted and experimental values for most responses (17 out of 29). By combining genetic programming-based symbolic regression with the black-box algorithm, 23 symbolic regression expressions with high confidence were successfully constructed. This work is a pioneering attempt of optimization in small-scale experiments. By utilizing the highly interpretable models, a demand-orientated (multi-)optimization coal pyrolysis can be achieved. The bi-objective optimization was conducted on the yield of tar and the content of light aromatics in tar, and the results show that Co is the optimal loading metal.

Source and geological significance of Jurassic asphalt in the Ruoqiang Sag of Southeast Depression, Tarim Basin, Northwestern China

The Southeast Depression of the Tarim Basin has a very low petroleum exploration degree, and currently, no industrial oil and gas have been discovered. Many hydrocarbon shows exist in the Ruoqiang Sag, where hydrocarbon sources and accumulation processes are unclear. Only two potential Jurassic hydrocarbon source rocks developed in the Ruoqiang Sag, the Yangye (J2y) lacustrine mudstone of the Middle Jurassic and the Kangsu (J1k) coal-bearing mudstone of the Lower Jurassic. In this study, the Jurassic asphalt found in the QD1 well, combined with the source rocks of drilling cores and outcrops, was used to explore the possible hydrocarbon source and forming process in the Ruoqiang Sag using oil-source correlation and hydrocarbon accumulation geochronology methods. The asphalts have lower light and heavy rare earth fractionation than the J2y mudstone, and the total rare earth element (ΣREE) content, chondrite-normalized curves, and δEu and Y/Ho values are similar to those of the J1k mudstone, especially for the J1k coal. The n-alkane ratios of the carbon preference index and the odd-to-even preference (OEP) of Jurassic asphalts are greater than 1.0, indicating that its source rock has experienced low thermal evolution. All Jurassic samples have similar source-related biomarkers but different maturity-related parameters, and the thermal evolution degree of asphalt is close to the J1k mudstone and coal but slightly higher than the J2y mudstone. Meanwhile, rhenium–osmium isotopes show the asphalts are formed in 192+30/−45 Ma, which is similar to the J1k sedimentation time. The asphalts contain coal macerals and probably derived from the asphaltene precipitated by the J1k coal during the early coalification. The low abundance of 25-norbornanes with a non- or slight petroleum biodegradation degree indicates the asphalt was generated relatively late and migrated into the J2y formation along the faults, possibly accompanied by the striking activities of the Altyn Tagh Fault during the Neotectonics movement. This study provides evidence for the J1k coal-bearing strata serving as the effective source rock in the Ruoqiang Sag and increases confidence for Jurassic petroleum exploration in the Southeast Depression of the Tarim Basin. The structural and lithological traps near hydrocarbon source stoves, where Jurassic strata were deeply buried and far from the Altyn Tagh Range, are favorable oil and gas exploration targets.

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

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

Conversion of aliphatic structure-rich coal maceral into high-capacity hard carbons for sodium-ion batteries

Pre-oxidation is an effective strategy for preparing high-capacity coal-derived hard carbons. However, the complex molecular structure of coal results in the uncontrollability of oxidation and structural evolution, which hinders the design of high-performance hard carbons. Herein, we are separating macerals to investigate the effects of molecular structural features of coal macerals on their oxidative reactivity, as well as the constitutive relationship between the cross-linked structures of the macerals and the structures of coal-derived hard carbons. According to molecular mechanics and Monte Carlo method simulations, the oxygen adsorption behavior of different coal molecules during increasing temperatures is revealed. The macerals with more aliphatic structures exhibit higher oxidative reactivity and have more adsorbed oxygen in the molecular model, contributing to a more cross-linked structure. The subsequent carbonization process limits the rearrangement of the carbon layers, resulting in a more disordered carbon layer structure and the formation of more ultra-micropores. Experimental results reveal that vitrinite-rich coal-derived hard carbons exhibit a capacity of 330.2 mAh/g higher than inertinite-rich coal-derived hard carbons capacity of 260 mAh/g. This work throws a light on the preparation of high-capacity coal-derived hard carbons, and provides theoretical guidance for other thermochemical research systems.

Recognition and (semi-)quantitative analysis of REE-bearing minerals in coal using automated scanning electron microscopy

The recognition and quantification of rare earth and yttrium (REY) minerals in coal is extremely important for understanding their geological origin and developing high-efficiency extraction techniques. This study developed an automated image analysis by scanning electron microscopy (AIA-SEM) method for characterizing REY minerals in coal. Carbon and copper were used as grey-scale calibration standard to assure the consistency per experiment and differentiate organic matter and minerals with different brightness. Two critical issues in determining REY including rapid recognition of fine REY-bearing particles and accurate classification and quantification of REY minerals in coal are resolved by (1) establishing grey threshold standard to locate REY-bearing grains and a two-step image scan; (2) developing classification criteria supplemented with spot- and EDS-mapping analysis for questionable particles. By using the established method, a total of 166 REY-bearing mineral grains were identified from 12,930 particles in a medium-volatile bituminous coal (REY concentration: 149.21 ppm; ash yield: 21.25%). It is found that Ca-REE flurocarbonates, monazite, and (Sc, Y)-bearing zircon are the dominant REY species in the studied coal sample. REE-aluminophosphates are also important hosts for REE in coal, with total amounts being >10%. REY minerals are fine in particle size. Over 50% of monazite, xenotime, Ca-REE flurocarbonate, and REE-aluminophosphate have particle size below 5 μm and monazite occurs mostly as submicron particle. Most REY minerals (> 60%) are embedded into coal macerals as included minerals. About 80% of REY-bearing phosphates and zircon are partly or completely encapsulated in clay minerals, whereas more than half of Ca-REY-fluorocarbonates mineral grains is free of other minerals.

Illustrating the effect of physicochemical properties within vitrinite and inertinite on residual carbon formation in drop tube furnace

The high carbon content and poor combustibility of the fine slag produced by the entrained – flow gasification limits its resource utilization. From coal chemistry, residual carbon formation is highly related to the coal macerals. In this study, Meihuajing coal was selected to be separated and enriched macerals by density gradient centrifugation. Different macerals were gasified at 1300 °C and H2O/O2 conditions in the drop tube furnace to collect residual carbon. The results showed that the area shrinkage of inertinite grew to 0.90 at the early stage, but final conversion required a longer induction period to realize. The residual carbon of vitrinite had richer pore structure and larger specific surface area as well as lower degree of aromatization and graphitization than inertinite, resulting in higher reactivity. The present study is important in understanding the relationship between the formation of residual carbon and the structure of coal macerals.

Study on classification separation of low-rank coal macerals using hydrocyclone and enhanced gravity separator

ABSTRACT Efficient enrichment of macerals improves the liquefaction efficiency of low-rank coal. The paper studied the characteristics of Shendong low-rank coal, including proximate and ultimate analyses, size and density compositions, and petrographic analysis, as well as the migration regularity of narrow particle size of low-rank coal macerals in the enhanced gravity field. On this basis, a novel classification separation process for low-rank coal macerals using Krebs hydrocyclone and enhanced gravity separator was proposed. The classification size was determined to be 0.074 mm and Krebs hydrocyclone achieved a satisfactory classification effect with a classification efficiency of 84.72%. Based on the enhanced gravity separation results of macerals from hydrocyclone underflow and overflow, the optimal sorting solutions for underflow and overflow were obtained through response surface analysis, respectively. Through the novel classification separation process, the vitrinite content of clean coal has been increased from 46.60% to 61.33% with an outstanding recovery of 77.40%. The novel classification separation process using hydrocyclone and enhanced gravity separator develops an excellent enrichment effect for low-rank coal macerals, which also provides a prospective approach for the cleaner utilization of low-rank coal.

Coal Structure Characteristics of the 2# Coal Seam in the Jiaozuo Mining Area and Its Geological Dependence.

To clarify the coal structure, spatial distribution, and controlling factors of the 2# coal seam in Jiaozuo mining, the drilling coal samples were collected to observe the coal type and coal structure. The coal macerals were identified by a MPVSP microscope photometer, and the spatial characteristics of the coal structure were obtained through interpreting deep lateral resistivity logging, natural gamma ray logging, density logging, and acoustic logging curves. The influence of coal properties, burial depth, geological stress, and faults on the coal structure were discussed correspondingly. The results exhibit that granulitic-mylonite coal was most developed in the 2# coal seam, followed by primary coal and cataclastic coal; the coal type was dominated by semibright coal, followed by clarain and semidull coal. Granulitic-mylonite, cataclastic, and primary coals were the main components of clarain, semibright coal, and semidull coal, respectively. Higher vitrinite and organic matter contents were conducive to the development of granulitic-mylonite. The coal structure combinations were spatially varied, and the granulitic-mylonite combinations were the most common. Granulitic-mylonite coal was developed in the east and south parts of the study area, and the coal structure was fragmented with a greater burial depth and larger thickness. The geological stress is the fundamental cause of coal structure damage as well as the cutting of faults.

Preparation and characteristic analysis of graphene based on coal macerals of different rank

Graphene is prepared using the improved Hummers redox method to study the preparation and structural characteristics of coal-based graphene from coal macerals of rank between 0.52 % and 1.98 %. The macerals are separated and enriched by hand sorting, sieving, and isopyknic gradient centrifugation. The crystal characteristics of the macerals, coal-based graphite, and graphene are characterized by XRD, Raman, SEM and TEM. The flake graphene with stable structure, good extensibility, different cell parameters and defects can be prepared from macerals. All the preparation yields are less than 4.0 %. The XRD data shows that after high-temperature graphitization, the layer spacing d002 of each sample is less than 0.3400 nm, and the lamellar crystallite sizes La and Lc are 7.70–21.09 nm and 11.53–16.94 nm, respectively. After the redox reaction, inertinite MLI-GS, YCWI-GS, and vitrinite GMDV-GS have the layer spacing d002, lamellar extendability La, stacking thickness Lc, and average stacking layer Nave that tend to be graphite-like structure. The microcrystalline structure is well developed and stable. Raman also confirmes that inertinite and high-rank vitrinite-derived graphene have fewer structural defects, good ordering, and a high degree of graphitization. The average values of ID/IG and AD/AG of maceral → coal-based graphite → graphene are 0.73 → 0.29 → 1.06, 2.12 → 0.40 → 1.62, indicating a relationship between the structural order: coal-based graphite > maceral > graphene, and between the degree of graphitization: coal-based graphite > graphene > maceral. The SEM and TEM dates show that inertinite tends to form a flat graphene structure with four–six layers, and has good light transmission. The graphene has few folds and warps, good layer extensibility, and high lattice order. The layer spacing at the edge is consistent with the d002 of XRD analysis. Vitrinite, cutinite, and barkinite derived graphene are similar to a kneaded paper balls. The layers are mixed with each other, forming more folds and ripples, and the peeling effect is poor. Only the high-rank GMDV-GS is clean like gauzy graphene, indicating that the micromorphological characteristics of graphene are related to the coal rank and macerals.

Relationship between fluorescence characteristics of coal macerals and excitation time

The fluorescence characteristics of coal macerals can be used as one of the indexes to evaluate the properties of coking coal. In this work, a single-wavelength laser with a wavelength of 360 nm was used as the excitation source to excite the surface of particulate block under a polarizing microscope. Effect of excitation time on fluorescence characteristics of the macerals was studied. The relationship between spontaneous fluorescence intensity and the excitation time of each maceral of six kinds of coking coals show that the fluorescence characteristics of coal macerals are related to the type and metamorphism of coal. The excitation time has a certain effect on the fluorescence parameters of the macerals. By comparing the relative fluorescence intensity values under different excitation times, it is found that the mean relative fluorescence intensity within 15 s can be used as an optical parameter to characterize the structure and metamorphic grade of different macerals. The essence of this method is to express movement of electrons in outer layer of nucleus by macroscopic fluorescence spectrum and relative fluorescence intensity of the initial state value and simplify microscopic complexity into macroscopic and numerical form generally accepted.

Differential heat transfer characteristics of coal macerals and their control mechanism: At the mesoscale

The dynamic heat transfer process of coal with different macroscopic types was characterized by a thermal imaging acquisition system, and the differential control mechanism of maceral composition and distribution on coal heat transfer was revealed. The results show that the temperature distribution in bright and dull coal samples are unimodal compared with the bimodal temperature distribution in semibright and semidull coal. With the extension of the heating time, the difference of the temperature distribution in the samples are first decreased, then increased and finally decreased. According to the evolutionary characteristics of the temperature difference, the heat transfer process can be divided into four stages: rapid temperature rise, slow down, fluctuating temperature rise and dynamic equilibrium. Inertinite is heated up faster, forming a high-temperature region, and vitrinite is heated slowly resulting in a low-temperature region. The temperature rise rate and equilibrium temperature in the low-temperature region are inversely proportional to the distance from the high-temperature region. It is difficult for vitrinite to heat up as vitrinite has the largest specific heat capacity and the smallest thermal conductivity and thermal diffusion coefficient. Therefore, the heat transfer capacity of vitrinite is generally weak, featured by a lower rate of temperature transfer disturbance.

High-temperature rheological behavior and non-isothermal pyrolysis mechanism of macerals separated from different coals

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.

Biosorption of some elements by algae from a cutinite-rich coal and its effect on organic geochemical composition: A case study from Abu Thora, Sinai, Egypt

A Carboniferous-age unique cutinite-rich coal seam at Wadi Abu Thora in Sinai, Egypt, was subjected to biosorption extraction of uranium (U) and thorium (Th) by five native algal species. These algal species were used in the biosorption process with the coal acting as a cultivation substrate. The concentration of U and Th was measured before and after the biosorption process. The five algal species used included Sarconema filofirms, Ulva Lactuca, Sargassum detofiulum, Caulerpa prolifera, and Cystoseira osmundacea, in addition to the yeast Saccharomyces cerevisiae. Two species, namely Caulerpa prolifera and Cystoseira osmundacea, were able to grow and adhere well to the coal particles as indicated by the microscopic examination in fluorescence mode. The above two species showed a capability to biosorb U and Th completely followed by Sarconema filofirms (56.7%, 18.7 ppm), Ulva Lactuca (49.4%, 16.3 ppm), and Sargassum detofiulum (40.3%, 13.3 ppm). These three species were successful in the uptake of U, alongside Saccharomyces cerevisiae, which showed a greater capability (58.2% or 19.2 ppm U). Biosorption by Caulerpa prolifera and Cystoseira osmundacea algae is an effective procedure to extract U and Th from this coal. Coal macerals played an important role in U precipitation, reflecting the structure of the compound that contains the U. Extraction of U and Th by biosorption resulted in changes in the cutinite-rich coal sample. Geochemical evaluation of the treated samples reflects a change in their chemical structure with the partial or complete removal of carboxyl/carbonyl-only groups in addition to the n-alkane chains. Pyrolysis data indicated shorter n-alkane-alkene compounds and smaller ratios. Data show that algae play a role in the biotransformation of absorbed organic matter composition by type and quantity. Finally, these compositional changes may produce more mature organic matter from the parent sample.

Pore Structure and Adsorption Characteristics of Maceral Groups: Insights from Centrifugal Flotation Experiment of Coals.

Coal has various types of macerals, which have different pore structures and adsorption properties that change with coal's thermal metamorphism. In-depth study of the characteristics of different coal macerals, especially the pore structure and adsorption properties, can better predict the coal reservoir gas storage capacity and migration ability. In this study, the sub-samples enriched in a specific maceral group with different coal ranks and particle sizes were obtained by centrifugal flotation experiments. Then, experiments containing low-temperature N2 isotherm adsorption (LT-N2GA), low-temperature CO2 isotherm adsorption (LT-CO2GA), and methane isothermal adsorption were carried out on the sub-samples to quantitatively analyze the evolution characteristics of pore structure and adsorption properties of different maceral groups. The results showed the following: (1) The separation effect of the light maceral groups by centrifugal flotation experiments increased with the decrease of particle sizes, which were treated with the heavy liquid of low and medium densities, while that of the heavy maceral groups had the relatively best separation effect in the particle sizes of 0.1-0.125 mm, which were treated with the heavy liquid of high densities. (2) The vitrinite-enriched samples had more ultra-micropores (mainly within the diameter range of 0.4-0.65 nm), while the inertinite enriched samples had more mesopores and transition pores (mainly within the diameter range of 40-50 nm). (3) For the low-rank coal, inertinite had more potential methane adsorption capacity. However, for the medium- and high-rank coal, vitrinite had more potential methane adsorption capacity. (4) For the low-rank coal, the adsorption potential and adsorption space increased with the increase of the inertinite content, while the adsorption potential, adsorption space, and surface free energy for the medium- and high-rank coal increased with the increase of vitrinite content. It is expected that the results can deepen the understanding about the gas storage capacity and migration ability and be used in the prevention of gas outburst and the reduction of carbon emission.