Degree Of Coalification Research Articles

Flotation separation of maghara coal in Egypt for the removal of hazardous Cr(VI) from industrial wastewater

ABSTRACT Due to its serious toxicity, wastewater contaminated with hexavalent chromium (Cr(VI)) has become an increasing environmental concern. Herein, a novel flotation separation of maghara coal in Egypt for Cr(VI) removal was proposed to separate coal to three types of maceral group fractions including liptinite, vitrinite, and inertinite via controlling in density as a function in the degree of coalification. The results implied that the activated inertinite macerals (AIM) have the highest carbon and lowest nitrogen levels among the entire maceral groups. The Langmuir isotherm model exhibited a high adsorption capacity of the AIM sample (1226. 21 mg/g) compared to pre-flotation separation sample (877.55 mg/g). Therefore, the flotation separation of maghara coal played a vital role in the Cr(VI) removal. The residuary concentration of Cr(VI) after adsorption onto AIM was close to 0.037 mg L−1 at pH = 2, which satisfies the industrial wastewater discharge standard. In addition, the removal of Cr(VI) onto AIM surface has been demonstrated to be highly effective via the adsorption and reduction process. The oxygen-containing functional groups could strengthen the interaction between Cr(VI) and AIM surface through the reducing reactions. The accelerating effect of organic acids was investigated for the capture of Cr(VI) and the efficiency in the presence of tartaric acid was improved up to 99.96% within 48 h compared to other organic acids. Therefore, this research provides a sophisticated strategy for separating coal to highly efficient adsorbents for wastewater remediation.

Mineralogy and Geochemistry of Rare Earth Elements in Carboniferous-Permian Coals at the Eastern Margin of the Ordos Basin.

This article used Carboniferous-Permian coals from the Jungar, Hedong, and Weibei Coalfields in the east of the Ordos Basin as research samples. Characteristics of coal quality, petrology, mineralogy, and geochemistry were analyzed by proximate analysis, inductively coupled plasma mass spectrometry, X-ray fluorescence spectroscopy, X-ray diffraction analysis, scanning electron microscopy-energy spectrum analysis, and incident light microscope. The enrichment regulations, distribution patterns, and occurrences of REY (rare earth element and yttrium) in coal under different geological conditions were compared. Geological significance and the influence of REY were then discussed. The average REY of Permian coal in the eastern margin of the basin is 127.9 μg/g, CC = 1.87, and the average REY of Carboniferous coal is 117.49 μg/g, CC = 1.72, which are within the normal enrichment range. The inorganic affinity of REYs in the study area is strong and mainly occurs in clay minerals and detrital phosphates and correlates well with LREY. The Permian coal sedimentary environment is more oxidized than the Taiyuan formation, and the Carboniferous coal sedimentary environment is noticeably more affected by marine water. With an increasing degree of coalification, the concentration of rare earth elements (REE) in high-rank coal vitrinite is lower than that in inertinite. In contrast, the concentration of REEs in low-rank coal is the opposite. This is because the oxygen-containing functional groups that can combine with REEs in vitrinite reduce significantly, resulting in the loss of trace elements into other forms. The provenance of the northern and central regions of the study area is mainly sedimentary rocks, granite, alkaline basalt, and continental tholeiite, while the southern region is mainly granite and sedimentary rocks.

Organic geochemistry of Palaeogene coals from Greenland and Svalbard

AbstractThe organic geochemistry and coal petrology of Palaeogene coals from northeast Greenland (Thyra Ø Island and Kronprins Christian Land) and central Spitsbergen (Longyearbyen and Grumantbyen) were studied using Rock–Eval and gas chromatography–mass spectrometry, as well as microphotometry and maceral group analyses. Bulk data and biomarker distributions of the coals demonstrate a low coal rank for both, but a lower coalification degree of coals from Greenland (0.49–0.55% VRr) compared to those from Svalbard (0.68–0.75% VRr). Maceral group analyses revealed relatively similar distributions with a strong predominance of vitrinite. The generally high abundance of hopanoids (hopanes/hopenes and hopanoic acids) implies a strong bacterial reworking of the organic matter, whereas sulphur occurrences indicate a marine influence after organic matter deposition. A great variety of higher plant biomarkers was detected in all coals. Distinctive compounds recorded in the coals are aliphatic and aromatic diterpenoids as well as partly hydrogenated picenes, suggesting strong input of conifers and angiosperms. Pristane/phytane ratios indicate that the organic matter in the ancient swamps was deposited in an oxic, fluvio-deltaic setting at both sites. This study provides a detailed geochemical investigation of understudied coals from northeast Greenland. Moreover, it enhances our understanding of probably interrelated Palaeogene depositional settings from Greenland and Spitsbergen in terms of their palaeoecology, primary input into coal swamps, and individual thermal history. Graphical abstract

Impact of Organic Sulfur on Coal Graphitization

AbstractThe utilization of high‐sulfur coal, especially high‐organic coal, has always been a difficult hot spot in the energy field. To study the influence of sulfur in coal on coal‐based graphite products, a series of coal samples with different sulfur content and different degrees of coalification were collected for proximate analysis, ultimate analysis, and sulfur species analysis. The structural characteristics of coal‐based graphite products were analyzed by X‐ray diffraction (XRD). The relationships between the sulfur in coal and the yield (Y), graphitization degree (G), cell diameter (La), and stacking height (Lc) of coal‐based graphite products were explored. The yield of coal‐based graphite ranges from 8.92 % to 64.45 %, and it was found that the yield of coal‐based graphite is not only affected by the degree of coalification, fixed carbon content, and volatile matter content of coal but also significantly inhibited by organic sulfur in coal when the reflectance is less than 2.00 %. The graphitization degree (G) of coal‐based graphite is distributed between 76.02 % and 91.02 %, and positively related to the degree of coalification, and negatively related to the content of volatile matter. Organic sulfur in coal is an unfavorable factor for the graphitization degree (G) of coal‐based graphite. Both the cell diameter (La) and stacking height (Lc) of coal‐based graphite are positively correlated with the degree of coalification and negatively correlated with the volatile matter content in coal. Organic sulfur in coal plays an important inhibitory role on the cell diameter (La) of coal‐based graphite. Still, it has almost no effect on the stacking height (Lc) of coal‐based graphite, resulting in a low ratio of horizontal‐to‐vertical (La/Lc), which is not conducive to the horizontal development of coal‐based graphite cells.

PARAGENETIC RELATIONS OF COAL-BEARING AND OIL- AND GAS-BEARING FORMATIONS (EXAMPLE OF THE DON-DNIEPER TROUGH)

The relationship between coal-bearing and oil-and-gas-bearing formations is a fundamental problem in geology. The aim of this study is to determine the paragenetic relationships between hydrocarbons with coal-bearing sediments. This is achieved through the analysis of hydrocarbon composition, hydrocarbons deposits distribution, connection with petrographic types and degree of coalification of the coal in the Don-Dnieper trough. It provides various examples of the coexistence and palaeogeographic connectivity of coal, oil, and gas-bearing formations, which is a widespread occurrence in many basins worldwide. During both peat accumulation and the transformation of organic matter from peat to coal, the Don-Dnieper trough was located in the equatorial range of paleo-latitudes. This observation is significant because it sheds light on the conditions that existed during the formation of coal in this region. This text describes the petrographic composition and degree of coalification of the concentrated and scattered organic matter in the Don-Dnieper trough. These characteristics determine the formation of liquid and gaseous hydrocarbons. Based on the distribution of hydrocarbon deposits in the Don-Dnieper trough, and their consistency with petrographic coal types and degree of coalification, carboniferous deposits are classified into several categories: coal-bearing, gas-carbon-bearing, coal-gas-bearing, gas-bearing, oil-gas-bearing, gas-oil-bearing, and oil-bearing. The distribution of coal deposits of a certain age, the degree of coalification, and the composition of organic matter are consistent with the presence of liquid or gaseous hydrocarbons. The additional data obtained strongly support the concept of a paragenetic connection between coal-bearing and hydrocarbon-containing formations.

The alterations in soil organic carbon transformation and bacterial community structure in mining areas induced by coal dust of different coalification degrees

The alterations in soil organic carbon transformation and bacterial community structure in mining areas induced by coal dust of different coalification degrees

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 characterization of coal with different coalification degrees: a combined study from FT-IR, Raman, 13C NMR spectroscopy and modelling

While extensive research has been conducted on the evolution of coal's molecular structure during coalification, the heterogeneity and complexity of coal continue to impede the accurate and precise quantitative characterization of its structural evolution mechanism. In this study, the organic matter source, coal quality, carbon skeleton structure, and functional group occurrence of coal at different coalification stages have been determined using maceral identification, vitrinite reflectance, industrial quality, elemental analysis, and spectral analysis. Four molecular models have been created through computer-aided molecular design. The results indicate that the hydrogen atoms in the benzene ring structure reduce as coalification increases. The content of aliphatic compounds gradually decreases, while the length of aliphatic side chains first decreases (Ro,max<1.81%) and then increases (Ro,max>1.81%). Moreover, the chemical structure of coal tends to mature and stabilize, as the degree of coal crystallization increases, and the oxygen-containing groups gradually decrease. Therefore, aromatization increases with the condensation reaction dominating in the late stage of coalification. After intensive attempts to determine the chemical bond mode between aromatic carbon, aliphatic side chain, and oxygen functional group, the final molecular structure models are presented as C188H165O13N3 (F-1), C182H161O9N5 (J-1), C195H153O10N3 (T-1), and C193H129O7N3 (W-1). Furthermore, the mechanism of coalification is discussed based on the variation of the side chains and chemical bonds. According to the adsorption heat of functional groups, the methane adsorption capacity increases as the degree of coalification increases. The inflection point of methane adsorption capacity is at Ro,max>1.80%. This study provides a theoretical framework to understand the molecular structure evolution of coals at varying degrees of metamorphism. Additionally, it proposes a reliable method for characterizing coal molecular structures with high accuracy.

Chemical Structure Characteristics and Model Construction of Coal with Three Kinds of Coalification Degrees.

The coal structure is extensively used for studying the properties of coal, and the construction of accurate and reliable coal structure models can promote these researches. In this study, Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) were used to analyze the changes in the coal structure as a function of the coalification degree, and a semiquantitative model construction method based on FTIR, XRD, and X-ray photoelectron spectroscopy (XPS) analyses was proposed. With an increase in the coalification degree, the size of the aromatic cores in the coal increased. During the conversion from lignite to bituminous coal, the content of aliphatic structures increased, while the content of oxygen-containing functional groups (OFGs) significantly decreased. Conversely, during the conversion from bituminous coal to anthracite, the content of aliphatic structures decreased while the content of OFGs slightly increased. The calculated FTIR spectra of the coal structure models were consistent with the experimental FTIR spectra, which confirmed the accuracy of the models. Furthermore, the models successfully explained the microscopic mechanism underlying the differences in the wettability of the coal samples with varying coalification degrees. The construction method and coal structure models in this study will be more widely applied in future research.

Research on how acidification affects the coal's microscopic pore structure in the Guizhou mining region

AbstractBy eliminating their minerals, acidification technology makes coal seams more permeable. Acidification technology were conducted in the Farr and Qinglong mining areas using a mixed acid solution to study the impact of acidification technology on increasing the permeability of primary structural coals in the Guizhou region, China. The microphysical and chemical structure of the coal samples before and after acidification transformation was compared using X‐ray diffraction, scanning electron microscope, mercury intrusion porosimetry, and Fourier transform infrared spectrometry experiments. The results show that after acidification, the volatile matter content is reduced by 4.2% and 16.25%, the carbon content is increased, the degree of coalification is deepened, the gas content of the coal seam is elevated, and the gas source is more abundant. The minerals on the surface are dissolved to different degrees, and the pores and cracks are dredged, so that the surface of the coal samples shows better connectivity, which is conducive to the diffusion and transport of coalbed methane. The volume and pore diameter of the macropore and mesopore in the Farr coal samples were improved after acidification, and the fractal structure was more prominent, the pore connectivity was good, and the pore diameter of the Qinglong coal samples was greatly increased. The content of oxygen‐containing functional groups increased by 11.2% and 2.1%, respectively, which is conducive to the desorption of coalbed methane after acidification, and with the increasing degree of metamorphism of the coal samples, the higher the content of oxygen‐containing functional groups was and the less pronounced the effect of acidification. Acidification technology can effectively remove the minerals in the coal body and has a good effect on penetration enhancement, and the results of the study can provide certain theoretical references for the penetration enhancement of coal seams in Guizhou mining areas.

Sustainable energy recovery from mixed agri-food waste by hydrothermal carbonisation: Mechanistic evaluation of the evolution of product characteristics

To address aggravating climate concerns and enhance bioenergy production, mixed agri-food waste (MAFW) was upgrade into high quality solid biofuel using hydrothermal carbonisation (HTC), demonstrating the potential to convert low-quality biowaste into valuable bioenergy resource. The influence of reaction temperature (190–230 °C), residence time (1–5 h) and solid loading (5–20 %) on the evolution of hydrochar and process water (PW) characteristics were systematically investigated to gain mechanistic insight into the HTC process of MAFW. In addition, an assessment of the valorisation option(s) for MAFW PW was conducted to guide the development of a conceptual HTC-based biorefinery system for sustainable bioenergy production. Results demonstrated that high HTC reaction severity (increased reaction temperature and residence time) enhanced the fuel characteristics of the hydrochar except for nitrogen content, which increased by ⁓86 % at the most severe HTC operating condition. Furthermore, the concentration of organic compounds in the PW showed a significant decrease as the reaction severity increased, except for total phenol content which showed a consistent increase. Meanwhile, the concentration of organic compounds in the PW increased as the solid loading increased. Overall, MAFW PW is rich in organic matter but relatively low in nutrients. Based on the analysis of the hydrochar and PW characteristics at different HTC operating conditions, it was revealed that dehydration, decarboxylation, aromatisation and Maillard reaction constitute primary reaction mechanisms influencing the HTC conversion of MAFW. Although higher reaction severity yielded a high degree of coalification in MAFW hydrochar, a medium reaction severity was conducive for producing high-quality solid biofuel. Additionally, medium solid loading yielded ample solid yield and a moderate organic matter concentration in the PW. To efficiently valorise the MAFW PW, a multistage process involving the combination of wet oxidation, anaerobic digestion and nutrient recovery was proposed. The findings presented in this study offer valuable referential information for improving the fuel quality of hydrochar obtained from MAFW and guiding the development of a sustainable strategy to harness the energy potential of MAFW via HTC.

NANOSTRUCTURED COMPOSITES BASED ON MATRICES OBTAINED FROM COAL RAW MATERIALS FOR DEVELOPMENT OF ELECTRODE MATERIALS FOR SUPERCAPACITORS

The article reports the results of the study of the morphology, porous structure and electrical capacitance characteristics of highly porous carbon matrices (HPCMs) obtained from coal raw materials with different degrees of metamorphism and nanostructured composites (NSCs) based on them, the surface of which is decorated with gold or manganese oxide nanosized particles (NP), accumulating electrical charge during polarization in the electrolyte via two mechanisms (formation of an electrical double layer (EDL) and involvement of pseudo-capacitance component during Red-Ox reactions on electrodes). The samples of HPCMs were obtained by high-temperature (800 °C) alkaline activation (the mass ratio KOH/C = 2 : 1) of fossil coal from the coal basins of the Kemerovo Region and the Republic of Sakha (Yakutia): CAK - based on anthracite of the Kiyzasskiy open-pit mine (Kuzbass), with the highest coalification degree; CBK - based on boghead (a kind of sapropel coal ) from the Taymylyr deposit (Yakutia) with the lowest degree of metamorphism; CDK - based on long-flame coal (Kuzbass) occupying an intermediate position in the metamorphism series. Results obtained by scanning electron microscopy, small-angle X-ray scattering in combination with sorptometry showed that the NSC morphology is largely determined (except for submicron aggregates) by the porous structure of the matrices. The shape of cyclic voltammetry (CVA) curves for HPCMs CDK, CBK and Au-NP filled NSC based on them indicated a significant contribution from EDL into capacitance; the contribution of pseudo-capacitance is observed for the composite MnOx/CDK electrode. The features of CVA curves for microporous CAK HPCM and NSC based on it are probably caused by hindered diffusion. The specific electrical capacitance is higher as a result of the polarization of CDK and CBK HPCM with large proportions of mesopores, as well as NSCs on their basis, than that resulting from the polarization of microporous CAK and the corresponding composites. For all three HPCMs, the introduction of fillers causes an increase in the electrode capacitance. The effect is more significant for NSCs obtained from hard coals with a low level of metamorphism (an increase up to 1.8 and 1.6 times with respect to the capacitance of initial matrices for NSCs based on CDK and CBK, respectively, according to the impedance measurement data), which is due to a decrease in the active resistance and the charge transfer resistance of the cells, and, in general, to the active component of the impedance.

Coalbed Methane Enrichment Regularity and Model in the Xishanyao Formation in the Santanghu Basin, NW China

The Santanghu Basin is a typical low-rank coal-bearing basin in northwest China, with abundant coalbed methane (CBM) resources. However, the understanding of the main controlling factors and reservoir formation models of CBM in low-rank coal is still insufficient, which has restricted the exploration and development of CBM in this region. In this paper, the CBM enrichment controlling factors and enrichment models are analyzed based on the aspects of sedimentary environment, reservoir characteristics, sealing conditions, and hydrogeological conditions after systematically analyzing the geological characteristics of coal measures. The research results indicate that the coal seams of the Xishanyao Formation in the Santanghu Basin are stably developed, with the main macerals being vitrinite and a lower degree of coalification belonging to low-rank coal; the highest content of CBM can reach 7.17 m3/t, and the methane is mainly composed of biogenic gas supplemented by thermogenic gas; the roof lithology of the coal seam is mainly mudstone and siltstone, with good sealing conditions. Finally, two enrichment modes of coalbed methane in slope zones are proposed, namely, the CBM enrichment in the slope zone and the CBM enrichment by fault-hydraulic plugging. The results of this study can serve as a guide for the exploration and development of the deep-buried coalbed methane in the low-rank coal areas.

VOLCANISM AS AN IMPORTANT FACTOR IN THE FORMATION OF THE MATERIAL-PETROGRAPHIC COMPOSITION OF COAL

A comparative description of the geological conditions of the formation of the Neogene coal deposits of the Pannonian Basin (Hungary) and the Transcarpathian Depression (Ukraine) is given on the example of the Visonta and Ilnytsia coal deposits. The aim of the study was to determine the role of volcanism in the formation of the petrographic composition, qualitative indicators and geochemical characteristics of the coal of the Ilnytsia deposit. For the first time, a comparative analysis of the conditions of formation and occurrence of coal seams, qualitative composition and geochemical characteristics of coal deposits located in the Pannonian Basin and the Transcarpathian Depression was carried out with regard to the role of volcanism in the formation of their material and petrographic composition. The scientific novelty of the obtained results lies in the substantiation of the connection between the facts of the increased content of sodium oxide and the specific nature of the geochemical composition of rare elements in the Ilnytsa brown coal with the volcanic processes that occurred simultaneously with the peat accumulation. The study of the geological conditions of formation and the material and petrographic composition of coal of the same age from two deposits showed that with practically the same degree of coalification and similar facies conditions of formation, there is a noticeable difference in the conditions of occurrence and characteristics of coal. The Ilnytsia deposit is characterized by the alternation of coal seams and coal beds with tuffaceous material. The peculiarity of the Ilnytsia coal is the lower content of components of the huminite group and better preservation of their structure, the presence of mineral impurities of tuffogenic material and opals in the composition, higher ash content with less watering of the peatland, increased content of sodium oxide, different nature of geochemical composition of rare and scattered elements. This indicates that one of the factors of differences between the studied coals is volcanism, which manifested itself in the Ilnytsia deposit synchronously with peat accumulation.

Evaluation and Optimization of Multi-Parameter Prediction Index for Coal Spontaneous Combustion Combined with Temperature Programmed Experiment

Coal spontaneous combustion (CSC) is a serious threat to the safe mining of coal resources, and the selection of suitable gas indicators to predict the CSC state is crucial for the prevention and control of coal mine fires. In this paper, the temperature-programmed experiment of CSC was first carried out to analyze the gas components and compositions in the oxidative pyrolysis process of three coal samples (lignite, long-flame coal, and lean coal) with different coalification degrees. Subsequently, the spontaneous combustion tendency of these three coal samples was evaluated. Finally, through the variation of gas concentration, gas concentration ratio, and fire coefficient with coal temperature, the indicators suitable for predicting the spontaneous combustion of coal were preferred, and a multi-parameter indicator system was established to make a comprehensive judgment on the spontaneous combustion status of coal. The results show that coal rank is negatively correlated with oxygen consumption rate. The higher the coalification degree of coal, the slower the oxidation reaction and the later the characteristic temperature point appears. The lignite selected in this experiment is a type of coal that is more prone to spontaneous combustion than long-flame coal and poor coal, and the CO concentration, C2H6/CH4, and second fire coefficient R2 can be used as the main indicators for predicting CSC, while the other gases, olefin-alkane ratio and fire coefficient can be used as auxiliary indicators. To some extent, the research content can effectively and accurately determine the stage and degree of coal spontaneous combustion, which has a certain guiding role in predicting CSC.

Effect of Sophorolipid Adsorption on the Coal Microstructure: Experimental and Wettability Mathematical Model Discussion.

Green biosurfactants are emerging as a promising area of research. However, there is a limited focus on the adsorption and wetting characteristics of biosurfactants on coal dust. This study explores the effects of sophorolipid (SL) biosurfactants on the microstructure and wettability of different coalification degree coal. The microstructure parameters of SL adsorbed on coal dust were measured using a surface tensiometer, contact angle analyzer, and particle size analyzer. The results indicate that SL has the lowest critical surface tension, leading to a 9.25° decrease in the contact angle for low-rank bituminous coal (YZ-LRBC). Furthermore, SL significantly altered the particle size distribution of lignite (NM-LC) and YZ-LRBC. The pore size structure of SL-infiltrated coal dust was quantified using a specific surface area analyzer, revealing a decrease in the specific surface area and an increase in the average pore size. The infrared analysis demonstrated that SL permeation significantly increased the percentage of hydrophilic functional groups (hydroxyl structures) while reducing the hydrophobic functional groups (aliphatic hydrocarbon and aromatic structure). Based on the measured microstructure parameters, a regression equation for contact angle was established: [contact angle (°)] = 73.800 - 0.860 × [D10 (nm)] + 4.280 × [specific surface area (m2/g)]. Notably, the characteristic particle size D10 had a significant negative effect on the contact angle, while the specific surface area had a significant positive effect. These findings provide a theoretical foundation for the application of biosurfactants in water injection to reduce dust and improve the wetting efficiency.

Competitive adsorption law of multi-component gases during CO2 displacement of CH4 in coal seams

The CO2 enhanced coal bed methane recovery technology provides an excellent way to mitigate the greenhouse effect and energy crisis. The features and mechanism of CO2/CH4 competitive adsorption in the coal rock matrix have a critical impact on the production of CBM. For CO2/CH4 competitive adsorption process components and pressure changes, a multi-component gases competitive adsorption experiment was carried out with CO2 and CH4 binary gases as the study objects, and a multi-component adsorption model was developed by the expanded Langmuir equation. Based on the principles of molecular dynamics and thermodynamics, important parameters such as the average free range of gas molecules and adsorption potential are introduced to explain the competitive adsorption behavior from multiple perspectives and explore the competitive adsorption law of CH4 and CO2 under multiple component conditions, so as to provide some theoretical basis and field guidance for improving the extraction effect of CH4 in coal seams. The results show that: Under two critical conditions (100%CO2 +0%CH4 and 0%CO2 +100%CH4), the Langmuir volumes of CO2 for HN 1/3 coking coal and HL weakly caking coal respectively are 2.21 and 3.01 times higher than those of CH4; the overall adsorption capacity of binary gas is in between the adsorption capacities of both critical conditions and increases with increasing CO2 concentration in the gas source ratio; using E-L equation for binary gas component partitioning, the CH4 partition curves were all below CO2, the concentration of free-phase CH4 was always higher than that in the adsorbed phase, and coal samples had stronger adsorption ability for CO2 than CH4. CO2 has a stronger adsorption potential at the surface for HL weakly caking coal. CH4 has a slightly stronger adsorption potential at the surface for HN 1/3 coking coal. The higher coalification degree of the coal sample, the stronger the adsorption ability for CH4 and the weaker the adsorption ability for CO2. The slope of the overall adsorption curve of multi-component gases is analogous to the slope of the component with a high ratio of gas or strong adsorption capacity; the capacity of one-component adsorption for dual gas is closely related to the partial pressure of the free-phase gas and the separation factor α21. When the concentration ratio of CH4/CO2 in free phase is y2/y1 =α21, the concentration of both gases in adsorption phase is 50%, and α21 correlation is weakened, then the free phase gas partial pressure is dominant and there is a threshold value makes CH4 and CO2 adsorption capacity equal; when y2/y1 <α21, the coal preferentially adsorbs CO2 in the binary gas; when y2/y1 >α21, the coal preferentially adsorbs CH4 in the binary gas.

Laboratory investigation on gas slippage phenomenon in coal sample and its research significance

The gas slippage effect (GSE) of coal is associated with the coalbed methane (CBM) wells' productivity. Through the helium permeability experiment of five coal samples with different vitrinite reflectance, characteristics of gas permeability variations in coal samples with different coalification degrees are analyzed, the influence of coalification degrees, coal pore structures, and different gases on GSE is revealed, and the impact of GSE on the CBM wells productivity is discussed. It indicatess that the gas permeability of coal varies with the pore pressure in a negative power function and a gas slippage coefficient of coals declines with the rise of Klinkenberg permeability by a negative power function. With the ascend of vitrinite reflectance of coal, there is an asymmetric “U-shaped” change trend in GSE. The GSE in coal with different vitrinite reflectance is mostly govern by the pore diameter distribution of coal. The slippage parameter of gas is consistent with the evolution law of coal pore structures during coal metamorphism. The slippage coefficient of different gases is obtained. On this basis, the prediction model of CBM well production considering GSE is established, and the impact degree of GSE on CBM well productivity is revealed.

Reaction heat effect and change characteristics of key groups in coal-oxygen intrinsic reaction path.

The intrinsic reaction of coal with oxygen in the process of low-temperature oxidation is the main reaction path leading to self-heating and spontaneous combustion of coal. Most of the existing studies regard the coal oxidation as an overall reaction, ignoring the multi-path characteristics of coal low-temperature oxidation, and it is difficult to accurately explore the intrinsic reaction characteristics between coal with oxygen. Therefore, the low-temperature oxidation process of coal was studied by using a C80 microcalorimeter and in situ FTIR technology from the macro and micro levels. The "profile subtraction method" was used to study the coal-oxygen intrinsic reaction process, and the reaction heat effect and the change characteristics of key functional groups in the process were analyzed. Furthermore, the gray correlation analysis method was used to study the relevant characteristic parameters in the reaction process and grasp the essential structure-activity relationship. The experimental results show that, compared with the overall reaction process in air atmosphere, the change in the heat release of the coal-oxygen intrinsic reaction path has changed to different degrees, and the change in the slow oxidation stage is the most significant (the heat absorption decreases by 70.1-90.9%). In addition, the characteristic temperature points show different degrees of advance, of which the initial exothermic temperature point is the largest (about 21-46 °C), which directly leads to a significant shortening of the slow oxidation stage (30.1-47.4%). The changes of functional groups in the intrinsic reaction path are more regular. With the increase of temperature, the oxygen-containing functional groups -C=O and the aliphatic hydrocarbon functional groups -CH2- and -CH3 showed a fluctuating trend of increasing and decreasing, respectively. The oxidation heat-contributing functional groups of coal are mainly related to the degree of metamorphism and the functional group reaction characteristics during the reaction. With the deepening of coalification degree, the main heat-contributing functional groups as a whole showed the change rule of oxygen-containing functional groups → aliphatic hydrocarbon functional groups → aromatic hydrocarbon functional groups. In addition, the change of -OH content in the three coal samples has a high correlation with the change of the total heat release of coal.

Structure of coal-bearing sections of swampy coastal-marine lowlands of the Kama coal basin in the territory of the Tatarstan

The paper considers sections of the Visean coal-bearing formation of the Kama coal basin on the territory of the western slope of the South Tara arch. The sections are composed of coals, mudstones, siltstones, and sandstones, which were formed under continental conditions at the beginning of the Visean. The rocks of the coal-bearing formation were formed within the coastal shallow-marine plain with a lacustrine-marsh type of sedimentation. The formation of coals occurred during the formation of isolated swampy lakes on the surface of the floodplain lowlands. The source of organic matter was tree-like and herbaceous vegetation that develops in waterlogged lake water bodies in a hot, wet humid climate. According to the degree of coalification, coals belong to brown coals, their composition is dominated by a black, structureless, amorphous mass of coalified plant matter (fusen). As impurities, there are large fragments of plant remains belonging to the groups of intertinites and macerals. The coals are enriched in mineral, ash components, represented by kaolinite and finely dispersed quartz grains. Ash content will not exceed 20%.