Anaerobic digestion of lignite represents a promising approach for low-rank coal resource utilization and energy structure optimization, offering broad application prospects. To this end, nano-Fe2O3 modified biochar (NIBC) was synthesized and evaluated against biochar. Synthesis and characterization confirmed the successful loading of nano-Fe2O3 onto biochar, which led to significantly improved material properties (e.g., surface area, porosity, and surface functional groups). Consequently, NIBC substantially enhanced methane production (81.88 ± 6.78%, 4.89 ± 0.41 mL/g), system stability, and substrate degradation. Mechanistic analyses revealed a synergistic reconfiguration of dissolved organic matter, characterized by a shift toward more bioavailable intermediates (tryptophan-like and protein-like components), alongside a marked enrichment of key microbial taxa (e.g., Pseudomonadota, Methanobacteriota, Methanosarcina) and their associated metabolic pathways (e.g., glycolysis, reductive acetyl-CoA pathway). This work elucidates the integrated physicochemical-biological mechanisms by which NIBC enhances lignite anaerobic digestion, revealing previously overlooked cross-scale linkages between material properties, liquid-phase chemistry, and microbial ecology. The findings suggest potential opportunities for the development of biowaste-derived additives and the utilization of low-rank coal resources. Future research could focus on process scale-up, continuous operation, and techno-economic assessment to evaluate the feasibility of such strategies under practical conditions. Overall, this study provides a mechanistic foundation for advancing the clean conversion of lignite and supports the development of more sustainable bioenergy technologies.

Against the backdrop of global climate change, coal seam CO2 geological sequestration technology has garnered extensive attention due to its significant potential. To enhance the CO2 adsorption capacity of coal, the synergistic modification of lignite using supercritical CO2 (ScCO2) and microorganisms has emerged as a promising technical approach, in which temperature regulation plays a pivotal role. Through experimental studies conducted under different temperature conditions, the evolution of coal structure and variations in the liquid-phase environment were systematically analyzed. The experimental results indicate that 40 degrees C is the optimal temperature for the synergistic effects, at which the pore structure of coal is most notably developed, with the specific surface area and total pore volume increasing to 11.253 m2/g and 0.14589 cm3/g, respectively. Concurrently, the oxygen-containing functional groups on the coal surface increased notably, the degree of ordering of the microcrystalline structure was reduced, and the reactivity of the coal matrix was enhanced. Under this temperature condition, microbial metabolism was most active, which efficaciously neutralized the system's acidity and promoted the formation of HCO3- and CO32-, thereby creating favorable conditions for the conversion of CO2 into stable carbonate minerals. In contrast, when the temperature was raised to 45 degrees C, microbial activity was inhibited, leading to a significant reduction in the modification effect. These findings confirm that temperature is a key parameter controlling the efficiency of synergistic carbon sequestration. Future research should further explore the coupling effects of temperature and pressure, as well as microbial metabolic mechanisms, to facilitate the practical application of this technology.

Integrated experimental characterization and molecular simulation systematically reveal the molecular structural evolution from low-rank lignite (DM) to medium-rank fat coal (KL) and its regulatory mechanism on CH4/ CO2 adsorption behaviors. Molecular structure models of coal macromolecules, rigorously validated by NMR spectra, were constructed based on industrial analysis, ultimate analysis, 13CNMR , and XPS data. Molecular dynamics (MD) and grand canonical Monte Carlo (GCMC) simulations were employed to elucidate aggregated structure characteristics and gas adsorption mechanisms. Results demonstrate that DM primarily contains single-benzene or small-naphthalene rings with abundant long aliphatic chains and oxygen-containing functional groups (e.g., carboxyl and hydroxyl), forming a loose porous structure dominated by weak van der Waals interactions. In contrast, KL evolves into naphthalene-anthracene condensed aromatic skeletons, exhibiting significantly enhanced aromaticity, shortened aliphatic chains, and removed oxygen-containing groups. This transformation yields compact aromatic stacking, where it-it interactions dominate the cohesive packing, while residual electrostatic interactions primarily arise from polar functional groups and contribute to gas molecule binding. KL exhibits a substantially higher adsorption capacities for both CH4 and CO2 than DM, with pronounced selectivity toward CO2. This selectivity arises primarily from strong interactions between the CO2 quadrupole moment and aromatic it-electron clouds alongside residual polar functional groups. Elevated temperatures reduce the adsorption capacity of both coals, with DM showing a more significant reduction owing to its weaker adsorption strength. This study elucidates how increasing coal rank enhances gas adsorption efficacy through intensified aromatic condensation and pore densification, providing molecular-level theoretical support for coalbed methane exploitation and CO2 geological sequestration.

Research on microbially enhanced biomethane production from coal has largely focused on the introduction of single microbial sources and functional strains, whereas the roles and synergistic mechanisms of multi-source mixed consortia remain poorly understood. In this study, exogenous microbiota enriched from biogas slurry, activated sludge, and kitchen wastewater were combined with indigenous microorganisms enriched from fresh mine water at a 1:1 volumetric ratio, and anaerobic digestion (AD) experiments were performed using lignite as the substrate to investigate the synergistic mechanisms of multi-source mixed consortia. Compared with the single-source systems, all mixed-cultures exhibited higher methane yields and more stable fermentation performance. Metagenomic analysis revealed increased abundances of hydrolytic and acidogenic taxa (e.g., Bacteroidota and Bacillota) and a decline in competitive sulfate-reducing bacteria, shifting metabolic fluxes toward acetate formation and the CO2-reduction methanogenic pathway. The abundances of key enzymes associated with the acetoclastic pathway—acetate kinase and acetyl coenzyme A (acetyl-CoA) synthetase—increased by 10.4% and 22.36%, respectively, indicating an enhanced acetoclastic methanogenic capacity. Fourier Transform Infrared Spectroscopy (FT-IR) and Excitation-Emission Matrix (EEM) analyses further demonstrated that mixed cultures accelerated the cleavage and solubilization of macromolecular organic matter in coal, leading to increases in fulvic substances and soluble microbial metabolites, alongside decreases in aliphatic and hydroxyl functional groups, collectively suggesting improved coal biodegradability. Overall, the introduction of exogenous consortia optimized community composition, enhanced metabolic functions and substrate availability, and thereby promoted biomethane production during anaerobic digestion. These findings provide important experimental evidence supporting the advancement of microbial-enhanced coalbed methane (MECBM) technology.

Methane production from coal via anaerobic digestion represents a promising biologically driven pathway for low-temperature coal utilization; however, the recalcitrant macromolecular structure of coal and inefficient interspecies electron transfer limit system start-up and methane yield. Direct interspecies electron transfer (DIET) has been proposed as a potentially effective mechanism associated with enhanced electron flux and methanogenesis, yet its role in coal anaerobic digestion remains insufficiently understood. In this study, two conductive material-mediated DIET enhancement strategies (nano-magnetite and carbon nanotubes) together with ethanol supplementation as an exogenous electron donor, were applied to coal anaerobic digestion systems to evaluate their effects on methane production, electrochemical characteristics, and microbial community dynamics. All DIET-enhanced systems exhibited improved methane production and operational stability. Ethanol addition resulted in the fastest system start-up and highest methane production, whereas carbon nanotubes provided the greatest enhancement in electron transfer rate and electron transport system (ETS) activity. Electrochemical analyses showed increased redox activity and reduced interfacial electron-transfer resistance. Microbial analyses revealed that DIET reshaped microbial succession patterns. Conductive material-mediated DIET favored the enrichment of electron-accepting methanogens, including Methanosarcina and Methanothrix, while ethanol promoted a Methanosarcina-dominated pathway with auxiliary enrichment of hydrogenotrophic methanogens. These findings provide insights into distinct DIET-associated microbial and electron-transfer responses in coal anaerobic digestion and may contribute to future process optimization.

The thick organic-rich shale in the Mesoproterozoic Xiamaling Formation in the Yanshan area is a potential target for shale gas exploration. A field profile survey revealed several sets of diabase intrusions in the Xiamaling Formation, and these intrusions impacted oil and gas accumulation. This work focuses on the Mesoproterozoic Xiamaling Formation in the Xuanhua Basin in the Yanshan area. On the basis of actual measurements and experimental analysis of the section, the influence of a diabase intrusion with a thickness of approximately 6 m on the hydrocarbon generation capacity of the surrounding rock was analysed. The diabase can be classified as island arc alkaline basalt that intruded at 1367.7±50.7 Ma and was emplaced through at least two superimposed magma injections. In this study, the Neoproterozoic prototype basin in the Xuanhua Basin is divided into five evolutionary stages. Volcanic eruption activity was very frequent during the deposition of the Xiamaling Formation, the diabase intruded in a back-arc extensional environment at the end of the deposition of the Xiamaling Formation, and the diabase was formed by rapid thinning of the crust and upwelling of deep mantle-derived magma in the back-arc extensional environment. With the diffusion of heat following the intrusion of the high-temperature magma, the temperature of the surrounding rock increased sharply, greatly promoting the thermal maturation and consumption of organic matter in the surrounding rock, ultimately resulting in a gradual decrease in the organic carbon content with decreasing distance from the diabase.In this study, a model of the influence of diabase on the hydrocarbon generation capacity of the overlying organic-rich shale was established, a conceptual model of shale gas accumulation and enrichment in the Mesoproterozoic Xiamaling Formation in the Xuanhua Basin was established.

The biodegradability of coal is significantly constrained by its recalcitrant aromatic structure, which poses a fundamental challenge to its anaerobic digestion for methane production. This study proposes an innovative green pretreatment method for coal using vermicomposting. A systematic investigation evaluating gas production performance and microstructural evolution across different pretreatment durations (10, 30, 60 days) demonstrated that the 30-day condition yielded the highest methane production (175.54 +/- 23.53 mu mol & sdot;g-1). The physicochemical structural analysis revealed that earthworm activity effectively removed unstable aliphatic side chains from the coal. This promoted the evolution of the EC30 coal sample into a more ordered and bioavailable structure, thereby creating favorable conditions for microbial colonization and enzymatic hydrolysis. Further analysis revealed that methane yield correlated more strongly with microcrystalline structural parameters (d002 and Lc) than with surface chemical properties, suggesting that the physical structure of coal plays a critical role in the methanogenic process. This study identifies 30 days as the optimal pretreatment duration. From the perspective of microcrystalline structure evolution, it elucidates the physical mechanism underlying coal biotransformation, thereby providing novel theoretical and methodological support for the energy recovery from complex organic matter.

Understanding the diffusion behavior of methane under high-temperature and high-stress conditions is important for the exploitation of deep coalbed methane (CBM). In this study, the influencing factors and variation patterns of the methane diffusion coefficient under simulated in situ formation conditions and conventional conditions were investigated using five columnar coal samples (depths: 2744-3017 m) collected from the Yulin area of the Ordos Basin. The results demonstrate that the diffusion coefficient decreases exponentially by up to 78.3% with increasing confining pressure (20.0-50.0 MPa) but increases exponentially by up to 222.6% with increasing gas pressure (15.0-30.0 MPa) and by up to 59% with increasing temperature (45-75 degrees C). The diffusion coefficient parallel to the bedding planes is significantly greater than that perpendicular to the bedding planes by a factor of 25-42 (average of 35). The initial diffusion coefficient fitted by the time-dependent diffusion model under conventional conditions is three orders of magnitude greater than that under in situ conditions. Furthermore, an increase in methane gas pressure leads to a gradual increase in the initial diffusion coefficient, accompanied by an increase in the decay parameter. A higher proportion of macropores within the coal samples correlates with a larger initial diffusion coefficient. These findings contribute to a more comprehensive theoretical framework for the development of deep CBM resources.

To address the challenge of poor compatibility between fracturing fluid thickeners and microbial metabolism in biogenic coalbed methane(CBM)reservoir stimulation,this study developed a multidimensional evaluation system en-compassing gel-breaking efficiency,pore structure modification,and metabolic activation.Using this framework,the syn-ergistic mechanisms of methane enhancement by three thickeners—guar gum,xanthan gum,and modified cellulose—were systematically compared.Gel-breaking agents comprising microbial consortia and ammonium persulfate were used to as-sess the viscosity degradation kinetics of the thickeners at 0.4%concentration.Xanthan gum and guar gum exhibited su-perior viscosity reduction,with final viscosities of 3.5 mPa·s and 2.3 mPa·s after 60 hours,significantly outperforming modified cellulose(4.8 mPa·s).Polyacrylamide was excluded due to its resistance to biodegradation,with a residual vis-cosity of 8.6 mPa·s.Anaerobic co-fermentation experiments with lignite and thickeners revealed that the xanthan gum system achieved a cumulative gas production of 321 mL,representing increases of 40.8%and 205.7%over guar gum and modified cellulose,respectively.Improved Gompertz model fitting indicated a maximum gas production potential 4.7 times that of the control lignite group.Pore structure characterization showed that xanthan gum reduced the specific sur-face area of lignite by 28.4%and expanded the mesopore volume to 0.047 cm3/g.Fourier transform infrared spectroscopy(FTIR)analysis confirmed its role in promoting the cleavage of aliphatic chains and aromatic structures,thereby releasing soluble organic matter.Three-dimensional fluorescence spectroscopy further revealed that xanthan gum increased the con-tent of soluble organic matter in the fermentation broth,providing sufficient substrates for microbial metabolism.Metage-nomic analysis demonstrated that xanthan gum specifically enriched the aceticlastic methanogen Methanothrix and signi-ficantly upregulated the acetate decarboxylation pathway.The expression level of the key gene K00925 reached 356.8,notably higher than that in the guar gum system(259.9).Moreover,the total abundance of related functional genes in-creased by more than 20%.This study established a multidimensional evaluation framework integrating gel-breaking per-formance,pore structure modification,and metabolic activation,elucidating the structure-function relationship of thicken-er-microbe synergy.The results demonstrate that xanthan gum enables simultaneous optimization of reservoir physical properties and reconstruction of microbial metabolic networks,offering theoretical and technical support for the develop-ment of bio-compatible fracturing fluids.

This study introduces a novel earthworm-driven pretreatment a strategy to enhance coal anaerobic fermentation for methane bioconversion. Through comparative analyses of gas production dynamics, physicochemical properties, and microbial metabolic pathways between earthworm-pretreated coal (EPC) and untreated coal (UC), the mechanisms underlying earthworm-mediated enhancement of coal anaerobic fermentation were systematically elucidated. Results demonstrated that earthworm pretreatment significantly accelerated the fermentation process (gas production peak advanced by 3 days) and increased cumulative methane yield by 61.59 % (121.82 +/- 8.61 mu mol g- 1). The initial rise and subsequent decline in enzymatic activity indicated coal-induced oxidative stress in earthworms, followed by effective scavenging of reactive intermediates. Earthworms promote coal biodegradation through fragmentation and enzymatic hydrolysis (e.g., cellulase and ligninase), which destabilize aromatic structures, liberate alkanes, and catalyze structural reorganization of coal matrix. These processes significantly modify the physicochemical architecture of coal, enhancing its specific surface area and porosity to promote microbial substrate accessibility. Furthermore, earthworm mucus secretions and excretions optimise carbon-nitrogen coupling within the system, amplifying resource utilization efficiency. FTIR and XPS analyses demonstrated that EPC retained aliphatic carbon chains while exhibiting a significant increase in oxygencontaining functional groups (C=O, COO-), indicating preferential degradation of macromolecular organics by earthworms and the subsequent release of bioavailable small-molecule carbon sources. This study systematically elucidates the dual physical-biochemical mechanisms by which earthworms enhance coal anaerobic fermentation, providing theoretical foundations and practical guidance for developing efficient and sustainable coal biomethanation technologies.

Geological CO2 sequestration is currently one of the main effective pathways to achieve industrial carbon reduction. The adsorption of CO2 by coal is a unique storage method for carbon sequestration in underground coal reservoirs. This study conducts isothermal adsorption experiments on high-rank coal reservoirs with strong gas adsorption capacity in the southeastern part of the Qinshui Basin, exploring the CO2 adsorption mechanism, adsorption characteristics, and adsorption capacity of coal reservoirs under different temperature and pressure conditions (especially supercritical conditions). The following conclusions are drawn: (1) The amount of CO2 sequestered by coal seams exhibits a negative temperature effect, and the overall trend of adsorption corresponds to the Langmuir adsorption potential; however, under the same temperature and pressure conditions, high-rank coal has a CO2 adsorption capacity 1.5 to 2 times that of CH4. (2) Due to the adsorption characteristics of coal for CO2, various models need to be adopted to simulate adsorption characteristics across different temperature and pressure stages. In subcritical conditions, the single-layer adsorption theory Langmuir model and the multilayer adsorption characteristic Freundlich model, along with the Tempkin model considering adsorption heat, explain the changes in adsorption characteristics during the CO2 adsorption process by coal. In supercritical conditions, an improved D-R model is used to explain the adsorption mechanism of different pores through micropore-filling effects. (3) Finally, based on actual geological data and experimental adsorption amounts, the conventional adsorption model or improved D-R model is applied to predict and assess the CO2 sequestration potential of the coal reservoirs in the study area. This study provides theoretical and practical reference significance for understanding the CO2 adsorption sequestration characteristics and quantifying sequestration amounts in deep coal reservoirs.

Anaerobic digestion (AD) of coal to produce biogas represents a promising strategy for clean coal utilization and the reduction of greenhouse gas emissions. However, the complex structure and resistant organic matter in bituminous coal limit the microbial activity, resulting in low biogas yields. This study evaluates the impact of rhamnolipid biosurfactant on the AD of bituminous coal at concentrations of 0.1 %, 0.3 %, and 0.5 %. The results show that 0.1 % rhamnolipid significantly increases biogas production, yielding 164.66 mL, which represents a 120.10 % increase compared to the untreated control (74.82 mL). The rhamnolipid reduces liquid surface tension, correspondingly improving coal wettability and mitigating particle agglomeration, which facilitates a better microbial interaction with coal surfaces. Parallel factor analysis (PARAFAC) identified protein- and humic-like substances as the primary fluorescent components in the fermentation broth. A decrease in fluorescence intensity indicates an effective degradation of coal's functional groups and aromatic structures. Additionally, rhamnolipid enhanced bacterial diversity, particularly Bacteroidota, Bacillota, and Spirochaetota, which are beneficial to degradation of organic matter. The acetate methanogenic pathway was suppressed, while the CO2 reduction and methylotrophic methanogenic pathways were promoted. Finally, rhamnolipid facilitated transmembrane transport and ATP synthesis. These findings highlight a novel approach to improve biogas production from bituminous coal through an application of biosurfactants.

Coalbed Methane Bioengineering, an emerging interdisciplinary field, utilizes microbial action to convert organic matter in coal seams into methane. This approach is gaining attention due to its potential to enhance energy efficiency and promote environ mental friendliness. However, accurately predicting the microbial hydrocarbon generation potential in different regions is challenging. This study aims to utilize machine learning techniques, specifically Random Forest (RF) and SHapley Additive exPlanations (SHAP) analysis, to identify and assess the key factors affecting the production of coalbed biogas. By conducting anaerobic fermentation experiments on coal samples from 12 regions across three provinces in China, this study analyzed 72 characteristics, including coal quality parameters, pore structure, and microbial community structure. A Random Forest-based model was developed to estimate the methane production by microorganisms during anaerobic fermentation of coal. After hyperparameter optimization with Grid Search (GS), the model achieved accuracies of 80%, precision of 87%, recall of 79%, and an F1 score of 73%. This study applies SHAP analysis to interpret model predictions at both global and local levels, enhancing transparency. Through interpretation, it was determined that Methanothrix, Methanosarcina, Vad and Sedimentibacter contribute the most to the estimation process. This is the first study to develop and interpret a machine learning model for estimating microbial hydrocarbon generation capabilities based on coal reservoir parameters and specific microbial community structures. The research offers both theoretical insights and practical guidance for assessing coalbed biogas reserves and surpasses conventional methods, paving the way for unconventional natural gas exploitation with substantial theoretical and practical relevance.

The pore–fracture structure of deep coal deposits is highly important for the potential evaluation, investigation, and utilization of deep coalbed methane resources. This study used methods such as low-pressure CO2 adsorption, low-temperature N2 adsorption, high-pressure mercury intrusion porosimetry, scanning electron microscopy, and optical microscopy to describe the pore–fracture structure of deep coal reservoirs at multiple scales and to discuss the development features, complexity, and influence on permeability of the pore–fracture structure of coal reservoirs. The results showed that there were significant differences in the pore volume and specific surface area (SSA) of the coal specimens with respect to the distribution of pore diameters. The micropore volume and SSA accounted for the largest proportions (85.93

Methane generation is intrinsically linked to the energy conversion processes that take place during the anaerobic decomposition of coal. This study investigates the differences in energy metabolism of bio-methane production from coal samples with different ranks during anaerobic fermentation. Four coal samples (BYH, ML, SQ, and QD) were selected for anaerobic fermentation experiments, and methane yields, heat release, changes in small-molecule organic compounds, and microbial community structures were analyzed using gas chromatography, microcalorimetry, and other techniques. The results show that the BYH coal sample, which can generate abundant degradable organic substrates, has the highest methane yield and heat release, with peak reaction heat and gas production values reaching 32.539 J/g and 65.05 mu mol/g, respectively. Microbial community analysis reveals that the high abundance of Geobacter and Methanoculleus in the BYH system enhances the direct inter-species electron transfer (DIET) and hydrogenotrophic methanogenesis pathways. In contrast, the SQ system, dominated by Methanothrix and Macellibacteroides, generates more aromatic large-molecule organic compounds and has lower methanogenesis efficiency. By providing theoretical foundations, this research aids in improving the coal bio-methanation process, thus contributing to the efficient utilization and environmental sustainability of coal resources.

Biogas production was conducted using samples from different coal beds and laboratory-domesticated microbes to investigate the effect of the addition of benzoic acid on biogas production. Furthermore, the response properties of produced organic substances at different gas production stages were analyzed with ultraviolet-visible (UV-Vis) spectroscopy and three-dimensional fluorescence spectroscopy. The results showed that adding benzoic acid significantly enhanced the microbial gas production with different rank coals. Obvious spectroscopic differences were observed in the gas production effects and liquid-phase composition across varying rank coals. The UV-vis spectroscopy findings indicated that soluble organic matter gradually increased in molecular weight during gas production, leading to increased aromatization and an increase in aromatic ring substituents with hydrogen and oxygen functional groups. Fluorescence spectroscopy revealed changes in protein-like substances during gas production, indicating the involvement of humic acid-like substances from coal in microbial gas production. The results of the fluorescence index supported the biological origin of humic acid during the gas production process. Benzoic acid augmentation promoted biogas production in different coal grades, and distinct differences were observed in the organic spectral properties during gas production, suggesting that the metabolic pathways of the same microbes acting on different coal grades vary.

The influence of clay mineral content on biogenic gas production in coal seams remains insufficiently understood. This study systematically investigated the mechanisms by which clay minerals affect biogas production in low- and medium-rank coals by integrating simulated biogas production experiments with multidimensional analytical techniques, including infrared spectroscopy, X-ray diffraction, scanning electron microscopy, gas chromatography–mass spectrometry, fluorescence spectroscopy, and metagenomic analysis. The results demonstrated that in low-rank coal, increasing the clay content from 2.78 to 4.75 g per 20 g of coal reduced the biogas yield from 6.30 to 3.47 mL/g. Conversely, in medium-rank coal, increasing the clay content from 1.66 to 2.65 g per 20 g of coal enhanced the biogas yield from 3.45 to 5.28 mL/g. These contrasting outcomes are primarily attributed to the distinct mechanistic roles of clay minerals across coal ranks. In low-rank coal, the hydration-induced swelling of clay minerals intensified pore blockage, impeded gas diffusion, decreased the abundance of genes involved in propionate degradation, and suppressed microbial metabolic activity, ultimately limiting methane production. In contrast, in medium-rank coal, clay minerals facilitated the enrichment of key functional microbial taxa, such as Acetobacteroides and Methanoculleus, promoted the degradation of fatty acids, hydroxyls, and amines, and enhanced the activity of acidogenic and methanogenic pathways, thereby increasing methane yield. This study elucidates the microbial mechanisms underlying the regulatory role of clay minerals in biogas production, offering new theoretical insights into the origin of coalbed methane (CBM) and providing a scientific foundation for optimizing biogenic CBM recovery.

To address the unclear evolution patterns of gas products and micro-mechanisms underlying low-rank coal pyrolysis, this study systematically elucidated the multi-dimensional correlation among pyrolysis gas components, yields, isotope composition, and coal structural evolution via high-pressure autoclave closed-system pyrolysis experiments. Results showed that: During pyrolysis, CO2 concentration consistently decreased, while CH4 concentration significantly increased. For heavy hydrocarbon gases, the yield of alkane components gradually rose and peaked before the critical threshold of Ro,max = 2.0 %, then dropped sharply beyond this threshold; alkene components, however, rapidly attenuated to negligible levels shortly after initial generation. The evolution of CO2 and CH4 yields exhibited distinct "three-stage" differential characteristics. Mathematical modeling revealed that CH4 yield followed an exponential growth function, while CO2 yield conformed to a logarithmic growth function. Additionally, this study uncovered the synergistic evolution patterns between coal proximate analysis parameters and pyrolyzed solid residues, verifying a carbonization path where mobile phases (volatiles, moisture) are progressively expelled, and refractory carbon structures gradually solidify. Coal structural evolution indicators exhibited divergent trends before and after Ro,max = 1.3 %; similarly, S13C values of pyrolyzed alkanes (CH4 and C2H6) and these coal lipid-chain structure indicators also showed inflection points at Ro,max = 1.3 %, confirming that S13C-CH4 and S13C-C2H6 can serve as sensitive proxies for lipid-chain evolution. Specifically, S13C values of CH4 and C2H6 first decreased (13C-depleted) then increased (13C-enriched), reaching minima near Ro,max = 1.3 %; in contrast, S13C values of propane remained consistently 13C-enriched throughout thermal maturation. These isotopic behavior stems from the synergistic interplay of three factors: uneven carbon isotope distribution between aromatic cores and aliphatic side chains in coal macromolecules, differential C-C bond cleavage propensities of lipid-like side chains, and thermal maturation-driven fractionation effects. Notably, the cyclization-polymerization of aromatic rings releases 13C-enriched components into gaseous hydrocarbons, whereas later-stage thermal evolution not only accelerates aromatic ring decomposition but also incorporates the liberated 13C-collectively driving a sharp increase in S13C values of pyrolytic heavy hydrocarbon gases. Furthermore, the SD value of CH4 displayed a polynomial positive correlation with Ro,max, reflecting thermally induced deuterium isotope fractionation. This research deepens the understanding of micro-scale reaction mechanisms in low-rank coal pyrolysis, provides theoretical support for targeted regulation of reaction products across different thermal stages, and offers quantitative tools (via established mathematical models) for predicting gas yield characteristics during coal maturation.

This study explores the microbial degradation mechanisms and molecular structural transitions of coal during the bioconversion process. We built macromolecular structure models of coal samples at various stages of anaerobic fermentation by analyzing its elemental makeup, carbon framework, surface groups, and pore changes, and using molecular simulation. Experimental results indicate that: the pore size of the coal sample increased from 3.04 nm to 5.0 nm, accompanied by a slight increase in the interlayer spacing d002 of the aromatic layers, with a decrease in both the microcrystalline extension La and the stacking height Lc, suggesting the disruption of the coal sample's microcrystalline structure. During the biogas production process, the molecular structural transformations are primarily focused on the side chains, specifically characterized by a reduction in - CH2 - groups within the aliphatic chains, consumption of - OH groups, and the formation of - COOH groups. Notably, the cleavage of benzene rings occurs at the initial stage of biogas production, while the degradation of naphthalene rings takes place during the biogas production peak, indicating that the aromatic structures significantly influence the biogas production process in lignite. GC-MS analysis of the fermentation liquid revealed that benzene compounds are the main constituents, suggesting that the degradation of naphthalene rings occurs through an open-ring mechanism rather than a direct degradation pathway. During microbial fermentation, the model's total potential energy drops significantly, making it more stable. This change increases non-six-membered rings and lattice defects, affecting the coal's pore structure and reducing its surface fractal dimension.

This study pioneers the application of magnetite in anaerobic digestion of lignite, achieving dual enhancement of biomethane production and coal-derived waste valorization. At an optimal dosage of 2 g, magnetite increased cumulative methane yield by 55.4 % compared to the control, driven by selective enrichment of electroactive bacteria such as norank_f_Synergistaceae and Proteiniclasticum, alongside DIET-driven methanogens dominated by Methanosaeta at 86.29 % abundance. Concurrently, magnetite induced structural modification of lignite through degradation of recalcitrant aliphatic hydrocarbons and a 53.5 % increase in specific surface area from 7.772 to 11.924 m2/g, collectively improving the combustion efficiency of residual coal. These findings establish magnetite as a bifunctional catalyst that unlocks the bioenergy potential of low-rank coals while converting residual waste into cleaner solid fuels. The strategy offers coal-intensive regions a sustainable pathway to integrate biogas production with circular coal waste management.