Low-rank Coal Research Articles

Equilibrium study for mercury removal using sub-bituminous coal and its application on ex-gold mining soil contaminated with mercury

Optimizing the potential utilization of low-rank coal, such as sub-bituminous coal (SC), can improve and maintain soil quality and productivity through amelioration technology. This potential is especially in controlling heavy metals such as Hg. This study aimed to examine the geochemistry of SC and the adsorption mechanism of Hg with SC through an adsorption isotherm model approach developed for experimental equilibrium. The geochemical of SC has an atomic composition of C (43.60%), O (40.64%), N (11.96%), Si (1.57%), Al (1.06%), Ca (0.92%), Mg (0.14%) and K (0.11%) and oxide composition dominated by SiO2 (57.07%), as well as O-H and N-H functional groups, C-H C-H, C=C-H, C=O, and C=C-H and minerals (quartz, magnetite, mica and muscovite). Characteristics of SC have a proximate composition (16.99% moisture, 97.81% volatile matter, 69.63% ash, and 28.19% fixed carbon) and chemical properties of pH, EC, CEC, OC, and total N (5.23, 1.38 dS m-1, 35.33 cmol(+) kg-1, 9.81% C, and 0.16% N). The adsorption capacity and coefficient of Hg2+ by SC were 304.32 mg g-1 and 78.67 L kg-1 at pH 1.26 and Hg2+ concentration 100 mg L-1 with a removal efficiency of 76.08%. Hg2+ adsorption isotherms occurred in Langmuir (RL = 0.97 and R² = 1)>Freundlich (1/n = 1.05 and R² = 0.9999) models. The application of 40 t SC ha-1 on ex-gold mining soil contaminated with Hg significantly decreased the total Hg in the soil by 2.50 mg kg-1 and a removal efficiency of 36.37% with increased pH H2O (0.35), OC (0.041% C), and CEC 2.14 cmol(+) kg-1, compared to control.

Oxygen bond cleavage and its migration mechanisms during pyrolysis of naomaohu sub-bituminous coal

Investigating the oxygen bond cleavage and its migration mechanisms during the pyrolysis process of sub-bituminous coals is essential for their classification utilization. The present study employed a fixed-bed pyrolysis technique (temperature range: 350–600 °C) to explore the cleavage of oxygen-containing bonds and subsequent behavior of oxygen migration and transformation during the pyrolysis process of Naomaohu sub-bituminous coal (NSBC). X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy results reveal that the organic oxygen in NSBC predominantly exists as the form of C–O bonds, accounting for 22.81 wt% of the total composition, mainly encompassing hydroxyl, carbonyl, ester, and ether groups. The organic oxygen in the light tar is mainly in the form of phenols, reaching 1.71 wt%, of which methyl substituted phenols is predominant at a final pyrolysis temperature of 600 °C. This can be attributed to the presence of more aryl ether bonds and hydroxyl groups in NSBC, which are prone to cleavage at higher temperatures, resulting in the formation of phenoxyl radicals. Additionally, the higher temperature facilitates the weakening of hydrogen bonds between phenolic hydroxyl groups, thereby enhancing the yield of phenolic compounds. The ester compounds present a decreasing trend with increasing temperature, primarily associated with the cleavage temperature of ester linkers being 350 °C, suggesting that an increase in temperature favors the cleavage of ester bonds. In addition, the cleavage of C–O bonds begins to accelerate significantly during the pyrolysis temperature range of 450–500 °C, subsequently accounting for the pronounced proliferation of phenols within this specific thermal interval. The oxygen content in semi-coke decreased with the increase of temperature, from 85.27 wt% at 350 °C to 37.17 wt% at 600 °C, while the oxygen content in the pyrolysis gas increases from 11.63 wt% at 350 °C to 47.53 wt% at 600 °C, indicating that a significant migration of organic oxygen to the pyrolysis gas during the pyrolysis of NSBC. This study can deepen the understanding of the transformation mechanism of oxygen-containing structure in NSBC pyrolysis process, and provide a theoretical basis for high-grade utilization of low-rank coals.

Investigation of synergistic mechanism of magnesium ions and cationic surfactant in low-rank coal flotation

The effect of magnesium ions on the adsorption of DTAB (Dodecyltrimethylammonium Bromide) surfactants by low-rank coal using adsorption experiments and microscopic mechanism analysis. In addition, the flotation recovery of coal was summarized for application by micro flotation test. The results of adsorption experiments showed that 0.1 mM magnesium ions concentration is optimal, with 12.55 mg/g adsorption capacity. Besides, correlation analysis reveals that the adsorption capacity is positively correlated with temperature, surfactant concentration, reaction time and the magnesium ions density. Adsorption thermodynamics and kinetics experiments indicate that magnesium ions promote adsorption by increasing the adsorption active sites of coal and accelerating the adsorption rate of DTAB on coal. Furthermore, the results of contact angle, zeta potential, model calculations and FTIR (Fourier transform infrared spectroscopy) analyses reveal that magnesium ions and its hydrolysates can adsorb on the coal as a bridge and destroy the stable hydrogen bond on the coal to activate the adsorption, which enhance the negatively charged coal to electrostatically adsorb positively charged DTAB. Moreover, the recovery rate of low-rank coal flotation using DTAB combined with magnesium ions was tested by a micro flotation apparatus, which provides a guidance for the flotation application by saline surfactant solution on coal.

Catalytic Pyrolysis of Naomaohu Coal Using Combined CaO and Ni/Olivine Catalysts for Simultaneously Improving the Tar and Gas Quality

Catalytic pyrolysis of low-rank coal is currently an effective method for producing high-quality tar and gas. In this study, catalytic upgrading of volatiles from Naomaohu (NMH) coal pyrolysis has been conducted in a two-stage fixed-bed reactor using combined CaO and Ni/olivine (Ni-loaded olivine) catalysts. The effect of catalyst distribution modes and catalytic temperature on the tar and gas quality has been investigated. Simulated distillation and GC-MS analysis have been used to investigate the distribution of tar components. The results indicated that the light oil fraction in tar dramatically increased due to the combination of CaO and Ni/olivine. The CaO-Ni/olivine mode is especially better compared to the layouts of the Ni/olivine-CaO mode and the mixed mode. The CaO-Ni/olivine mode ensures a higher light fraction in tar at 69.3% and a light oil fraction at 29.8% at a catalytic temperature of 450 °C, while the heavy tar fraction decreased to 30.7%. Meanwhile, the contents of benzene (heteroatomic substituents) in tar significantly increased from 2.55% to 6.45% compared with the blank test. In this scenario, CaO breaks down macromolecular compounds in tar and cleaves long-chain esters to produce aliphatic hydrocarbons. These hydrocarbons are then dehydrogenated to produce lighter aromatic hydrocarbons over the CaO surface. Subsequently, the volatiles pass through the Ni/olivine catalysis, where ether compounds are produced by means of dehydration reactions. In addition, the CaO absorbs the CO2 in the pyrolysis gas, leading to an elevation of CH4 and H2 concentration. Particularly, the concentration of H2 significantly increased from 16.2% to 30.37%, while the concentration of CO2 significantly decreased from 37.9% to 10.57%. These findings suggest that the usage of combined CaO and Ni/olivine catalysts is beneficial for improving both the tar and gas quality.

Synergistic consideration of co-treatment of sewage sludge, low-rank coal, and straw for sustainable resource utilization and enhanced energy efficiency: a review.

This article provides a comprehensive exploration of the imperative necessity for coupling the utilization of low-rank coal, sewage sludge, and straw. It studies the challenges and limitations of individual utilization methods, addressing the unique hurdles associated with feedstocks. It focused on achieving integrated and sustainable resource management, emphasizing efficient resource utilization, waste minimization, and environmental impact reduction. The investigation extends to the intricate details of reaction processes in co-processing, with a specific emphasis on the drying of raw materials to enhance combustion characteristics. The molding and preparation of feedstock are dissected, encompassing raw material selection, mixing, and the crucial addition of additives and binders. The proportions and homogenization of these feedstocks are intricately examined for uniformity and effectiveness. Furthermore, it presents theoretical approaches for investigating the co-combustion of these diverse feedstocks, contributing a solid foundation for future studies in this dynamic field. The findings presented in it offer valuable insights for researchers, practitioners, and policymakers seeking sustainable solutions in the co-disposal technology of these feedstocks. Therefore, it provides a holistic understanding of the challenges and opportunities in coupling the utilization of these selected feedstocks. By addressing individual limitations and emphasizing integrated resource management, the article establishes the groundwork for sustainable and efficient co-processing practices. The exploration of reaction processes gives a comprehensive framework for future research and application in the field of co-combustion technology. The insights gleaned from this study contribute significantly to advancing knowledge in the sustainable utilization of diverse feedstocks, guiding efforts towards environmentally responsible and resource-efficient practices.

Mechanism of enhanced microfine low-rank coal flotation by jet slurry conditioning

ABSTRACT Microfine low-rank coals are subject to metamorphic changes that hinder their floatability, impeding their clean and efficient utilization. The objective of this study was to refine the jet-slurry technique to enhance the floatability of microfine low-rank coals. Furthermore, advanced methods including Focused beam reflectance measurement (FBRM), high-sensitivity microelectromechanical balancer (DCAT), Fourier transform infrared spectrometer (FTIR), and scanning electron microscope (SEM) were employed to dissect the physicochemical effects of jet slurring on microfine low-rank coal particles. The study found that as the concentration of microfine coal particles increased, surface reagent adsorption initially rose and then fell with greater feed volumes. In contrast, adhesion forces displayed an inverse trend. Optimal results were achieved with a feed volume set at 25 L/min. This phenomenon is attributable to multiple regulatory factors. Within certain limits, intensifying conditioning promotes particle agglomeration, curtails fine gangue mineral coverage, boosts sodium dodecyl sulfate (SDS) adsorption, diminishes microfine coal wettability, and better kerosene-coal particle mixing. However, at excessive jet speeds (30 L/min), substantial physical pressure variances and mechanical dispersion forces arise, undermining SDS or kerosene’s chemical adsorption to coal or modified coal, thus reducing reagent attachment. The aforementioned study demonstrates that within certain parameters, jet slurring significantly betters coal-gangue separation, thereby amplifying the flotation efficacy of microfine low-rank coals. This research offers strategic insights into microfine low-rank coal flotation processes and lays a theoretical groundwork for the selection of suitable techniques and reagents.

Correlation between the structure of low-rank coal and its yield and characteristics of thermal dissolution extracts

To investigate the effect of structure difference of coals on its yield and characteristics of thermal dissolution extracts (TDEs), four Xinjiang low-rank coals were chosen for thermal dissolution extraction using 1-methylnaphthalene (1-MN) as the solvent at 380 °C. The low-rank coals were divided into TDEs consisting of deposit (DP) precipitated at room temperature in 1-MN and soluble (SL) dissolved in 1-MN, along with a minor proportion of liquid and gas products, as well as residue. The results showed that TDEs yields of Qidaowan (QDW), Heishan (HSC) and Runbei (RBC) coal samples increased with the increase of volatiles. However, almost the same TDEs yield was obtained for Hefeng coal (HFC) as RBC despite of higher volatiles content of the former. Further analysis suggested that both higher volatiles content and aromatic carbon ratio contributed to the formation of TDEs when 1-MN was used as the solvent. Besides, significant differences of carbon types for the above coal samples were observed, wherein, HFC possessed the lowest aromatic carbon of 45.59%, yet the value for all the DPs and SLs were above 60%, falling in the range of 60%-68% and 66%-71%, respectively. Furthermore, the aromatic ring cluster of DPs was composed of 2–3 rings, while that for SLs was 1–2 rings on average. Moreover, the TDEs obtained from coals with higher oxygen content were also characterized by a relatively higher oxygen content, and a higher content occurred on DPs. The molecular weight, polydispersity index and methylene chain length of DPs and SLs located in the range of 1000–1800 amu, 2.0–4.4, and 0.8–2.3, respectively. And it was found that good caking properties similar to coking coals occurred on the DPs and SLs, ranging from 88 to 97. Results also exhibited that there was a positive synergistic effect for caking index of DP & SL mixture. This work provides a theoretical basis for low-rank coal as an alternate to coke coal by thermal dissolution extraction.

Preparation of an additive using tannic acid for enhancing rheological properties of coal-water slurry

ABSTRACT Low-rank coal is an ideal future development coal for coal-water slurry (CWS) due to its abundant resource, but low-rank coal is tougher to produce slurry than high-rank coal. Herein, a new-type macromolecular additive, tannic acid grafted carboxymethyl cellulose sodium (TAC), was designed and prepared to enhance the rheological properties of CWS using Hongshaquan coal in Xinjiang (Coal-HSQ). This work shows that trace amounts of TAC can effectively improve the fluidity of CWS in comparison with calcium lignosulfonate (CLS). Through contact angle and a novel surface characterization method in this field called microscopic infrared imaging, the analyses reveal the hydrophobicity of the Coal-HSQ surface modified by TAC is improved, which is beneficial for enhancing the fluidity of CWS. The apparent viscosity of CWS can be reduced to the lowest point (674.8 mpa·s), as CWS slurry concentration is 55 wt% and TAC addition is only 0.2 wt%. Finally, the highest slurry concentration of CWS prepared with 0.2 wt% TAC can be increased to 56.3 wt%.

A Study on the Adsorption of Rhodamine B onto Adsorbents Prepared from Low-Carbon Fossils: Kinetic, Isotherm, and Thermodynamic Analyses.

The aim of this study was to obtain a series of activated carbon samples by the chemical activation of low-rank coal. The precursor was impregnated with a NaOH solution. Activated carbons were characterized by determining their textural parameters and content of surface oxygen functional groups and by using an elemental analysis. The carbons were tested as potential adsorbents for the removal of liquid pollutants represented by rhodamine B. The effectiveness of rhodamine B removal from water solutions depended on the initial concentration of the dye, the mass of rhodamine B, and the pH and temperature of the reaction. The isotherm examination followed the Langmuir isotherm model. The maximum adsorption capacity of the rhodamine B was 119 mg/g. The kinetic investigation favored the pseudo-second-order model, indicating a chemisorption mechanism. The thermodynamic assessment indicated spontaneous and endothermic adsorption, with decreased randomness at the solid-liquid interface. The experiment revealed that a 0.1 M HCl solution was the most effective regenerative agent.

From abandoned mines to carbon sinks: Assessing the CO2 storage capacity of Austrian low-rank coal deposits

This study represents the first assessment of CO2 storage potential in Austrian coal seams. Coal samples were taken from Fohnsdorf and Leoben abandoned coal mines, with particular emphasis on the Fohnsdorf coal since Leoben coal reserves were largely mined during previous coal production. Several methods were used to compare coal characteristics, including Rock-Eval pyrolysis (RE), organic petrography, and low-pressure N2 and CO2 sorption measurements. Both Fohnsdorf and Leoben coal samples show low sulfur and ash yields, as well as correspondingly high total organic carbon (TOC) contents. The pyrolysis Tmax and vitrinite reflectance values agree with a low coal rank for both sites. According to the N2 adsorption measurements at 77 K, low-lying mire coals from Fohnsdorf show a higher BET-specific surface area (BET-SSA) and BJH pore volume compared to raised-mire coals from Leoben. However, sapropelic shales and high-ash coals from Leoben show the highest BET-SSA and BJH pore volumes of all investigated samples and considerably exceed the N2 adsorption volumes of pure coals from both locations (N2 uptake up to 16 cm3/g; avg. for all samples 5.4 cm3/g). In contrast, the mean adsorbed CO2 uptake measured at 273 K and ∼ 1 bar followed the order of Fohnsdorf low-lying mire coals > Leoben raised-mire coals > Leoben sapropelic coals and shales, ranging at ∼0.8 mmol/g, ∼0.7 mmol/g, and ∼ 0.2 mmol/g, respectively. This shows that BET-SSA and BJH equations did not allow for adequate estimation of CO2 adsorption capacity trends in the investigated sample set. Furthermore, based on the existence of a hysteresis loop between CO2 adsorption and desorption branches for all investigated samples, the occurrence of weak chemisorption phenomena during CO2 adsorption is indicated. This effect helps to increase CO2 uptake and storage safety since the chemisorption process is not fully reversible upon pressure decrease. Ultimately, the theoretical CO2 sequestration potential of the remaining unmined Fohnsdorf coal reserves was estimated at 4.65 million tons, with an additional potential for enhanced coal bed methane production due to the gas-rich nature of Fohnsdorf coals with an estimated 1.2 billion m3 of CH4 in place.

Process for desulfurization and demineralization of low rank coal using oxidation assisted froth floatation technique

This study reports the desulfurization and deashing of Hangu coal by air oxidation assisted froth floatation technique applying performic acid (H2O2+HCOOH) as co-oxidant and Fe ions as catalysts in aqueous solution. This process led to the removal of up to 78.08% of total sulfur (TS) and 50.3% of ash at 60 °C, 30 min, a 2:2 ratio of H2O2+HCOOH (v/v), and 0.10% of Fe ions concentration. The sulfur and ash removal followed Fenton mechanism, wherein hydrogen peroxide (H2O2) dissociated into hydroxyl ions (OH-) and hydroxyl radicals (OH.), facilitated by the dissociation of ferrous ions (Fe2+). The reaction of HCOOH with OH. resulted in the formation of performic acid or peroxyl radical, selectively oxidizing sulfur compounds to sulfone and sulfoxide. In the subsequent phase, coal froth floatation was employed with the addition of surfactant i.e. Triton X-100 (TX-100) and collector i.e. diesel oil (DO), resulting in the removal of up to 49.83% of TS and 43.79% of ash. This was achieved under optimized conditions, specifically with a concentration of 400 ppm solution of TX-100 in the solution and a volume of 0.2 mL for DO. The emulsion of TX-100 and DO for the floatation of coal is a suitable option because TX-100 established polar interactions and hydrogen bonding with the oxidized functionalities of coal, whereas the hydrocarbons of diesel oil get attached to the unoxidized coal matrix through hydrophobic interaction. Onwards, simultaneous oxidation assisted by froth floatation in a two-step batch process at pre-optimized parameters resulted in TS and ash removal of 88.8% and 82.6%, and 62.2% and 39.3% in the froth and tailings, respectively. SEM, FTIR and XRD analyses revealed structural and morphological changes, modifications in chemical functionalities and mineralogical changes in the coal sample. The process can be scaled up for the up-gradation of low grade coal for industrial and power generation purposes.

Enhancing visible-light-driven photocatalytic degradation of nitric oxide with lignite-derived graphene quantum dots/BiOBr heterojunctions

In this work, lignite was used to prepare value-added graphene quantum dots (L-GQDs) via the chemical oxidation process. The prepared L-GQDs were then hybridized with bismuth oxybromide (BiOBr) to form composite photocatalysts by a semi-solvothermal method. The composites catalytically degraded NO under visible-light irradiation. Multiple characterizations demonstrated that L-GQDs were successfully deposited onto BiOBr without changing the valence states of the elements in BiOBr. The addition of L-GQDs not only boosted the NO removal efficiency from 48.44% to 80.17%, but also significantly improved the environmental friendliness of the catalyst. Experimental investigations and theoretical calculations confirmed the formation of a type II heterojunction between L-GQDs and BiOBr. Such a heterojunction facilitated the separation of photogenerated electrons and holes, thus enhancing the photocatalytic activity. Furthermore, the prepared composite catalyst demonstrated good stability, maintaining 94.40% of its original photocatalytic activity after five cycles. The synthesis and environmentally conscious application of the value-added L-GQDs in this work provides a cleaner alternative for utilizing low-rank coals.

Pyrolyzed coal base high surface area and mesoporous activated carbon for methyl violet 2B dye removal: Optimization of preparation conditions and adsorption key parameters

Herein, a low-grade Malaysian coal namely Merit Karpit coal (MRTKC) was transformed into high surface area mesoporous activated carbon (MRTKC-AC) via pyrolysis-assisted ZnCl2 activation. A numerical optimization approach rooted in the Box-Behnken design (BBD) was employed to determine the best operational conditions such as A: dosage of MRTKC-AC (ranging from 0.02 to 0.1 g/100 mL), B: the pH of the solution (varying from 4 to 10), and C: the contact time (ranging from 5 to 25 min). A notable surface area of 1229.1 m2/g and a distinctive mesoporous structure with an average pore diameter of 2.9 nm was achieved at optimum impregnation ratio (1 MRTKC: 2 ZnCl2), heating temperature 500 °C, and residence time 60 min. Moreover, the application of MRTKC-AC was evaluated through the removal of methyl violet (MV) from the aqueous environment. The comprehensive equilibrium and kinetic adsorption analyses showed that the adsorption of MV by MRTKC-AC matched closely to the Langmuir isotherm model, while the kinetic behavior was suitably described by the pseudo-second order model. Thus, the maximum adsorption capacity (qmax) for MV dye onto MRTKC-AC was ascertained to be a substantial 238.6 mg/g. The MV dye adsorption mechanism onto MRTKC-AC surface indicates various dye–adsorbent interactions: electrostatic attraction, p–p interaction, and H-bonding. This work shows that Malaysian low-rank coal is an economical precursor for producing low-cost and efficient mesoporous activated carbon with substantive surface area.

Comprehensive evaluation of low-temperature oxidation characteristics of low-rank bituminous coal and oil shale

The coexistence of coal and oil shale mining conditions exacerbates the complexity of coal spontaneous combustion (CSC) prevention, so conducting in-depth research on the spontaneous combustion characteristics of coal, oil shale, and their mixed samples is necessary. A programmed heating system simulated the low-temperature oxidation process of bituminous coal and oil shale under different air volumes. It was found that CO concentration, C2H4 concentration, and Graham's fire coefficient (R1, R2) can be used as indicator gases to predict the CSC process. Compared with oil shale and mixed samples, bituminous coal has a higher CO production rate, oxygen consumption rate, heat release intensity, and lower apparent activation energy during the slow oxidation stage. Meanwhile, bituminous coal also has lower peak values of minimum float coal thickness, lower limit oxygen concentration, and maximal air leakage intensity, which means that bituminous coal in the goaf is more prone to oxidation. However, the abundant free hydrogen bonds in oil shale can stabilize the hydrogen-deficient functional groups of bituminous coal, which weakens the oxidation ability of the mixed sample during the accelerated oxidation stage. In addition, the increased air volume fraction increases the oxygen adsorption efficiency of the mixed sample throughout the low-temperature oxidation process, which means that the M70 sample has a higher CSC risk. The results have enriched the research on the spontaneous combustion characteristics of coal, oil shale, and mixed samples, which may strengthen the management and control of CSC in coal and oil shale co-mining mines.

Computational and experimental approaches into molecular structure mechanism of ZQV coal and the COx gas releases during pyrolysis

Understanding the structural features of coal and its reactive behaviors in thermal processing is the fundamental to achieve high-efficiency utilization of coal. However, the molecular structural features and the evolution characteristics at atomic scales in thermal processing remain unclear in the microscopic views, particularly for the low-rank coals, which usually exhibits high oxygen content with a variety of oxygen-containing organic functional groups and gets lots of CO/CO2 release during pyrolysis. This research provides a comprehensive analysis of the ZaoQuan vitrinite (ZQV) bituminous coal's structural attributes and its pyrolysis-induced reactivity, which is crucial for optimizing the thermal conversion of low-rank coals. The structural parameters characteristics and molecular structures of ZQV have been revealed based on series of materials characterizations and molecular modeling calculations. The single molecular description of ZQV was conceptualized to be C209H132O41N2 under the average molecular approximation, and the particle models with size about 10 nm was also been obtained. Based on the built molecular models, reactive force field molecular dynamics (ReaxFF MD) simulations then provided insights into the dynamic behavior of molecular structures under pyrolysis conditions. Experimental validation corroborates the computational predictions, revealing a strong coherence between observed gas products and those derived from simulation data. Crucially, this study vividly captures the dynamic migration patterns of oxygen-containing groups during coal's thermal decomposition, thus contributing to the understanding of gasification processes. The release mechanisms for CO and CO2 are systematically dissected, proposing three and two distinct pathways respectively. These findings not only consolidate the molecular narrative of coal's structure and pyrolysis reactivity but also serve as a reliable foundation for interpreting the COx evolution of low-rank coals. Our integrated approach propels the scientific comprehension of coal pyrolysis and is anticipated to inform the development of more effective coal utilization pathways and thermal treatment technologies.

Investigation of the microscopic mechanism of H2O adsorption by low-rank coal slit pores through GCMC and MD simulations

This study investigates the influence of pore structure on H2O adsorption in low-rank coal (LRC) models at a molecular level, employing variously sized LRC slit-pore models·H2O adsorption behavior is analyzed across different pore sizes ranging from 0.001 to 100 kPa fugacity, by employing the Grand canonical Monte Carlo (GCMC) method and molecular dynamics (MD) simulations to explore saturated adsorption kinetics. The findings indicate a positive correlation between H2O adsorption levels and both fugacity and pore diameter. Furthermore, at constant pore diameter, the adsorption heat increases exponentially with increasing adsorption levels. Notably, H2O adsorption in LRC slit pores exhibits multilayer adsorption characteristics. First, adsorption occurs as monomolecular layers on the LRC surface, transitioning to secondary adsorption sites formed by previously adsorbed H2O molecules with increasing fugacity, ultimately saturating the pores. This adsorption process exhibits a correlation with a shift in potential energy distribution from high to low potential energy directions. Moreover, the ordering of H2O molecule arrangements between hydrogen atoms, oxygen atoms, and H2O molecules decreases with increasing pore diameters. Larger pore diameters correspond to increased H2O molecule diffusion, the stronger interaction between the LRC slit pores and H2O molecules but reduced interaction with individual H2O molecules. Overall, this study establishes a theoretical foundation for further studies on coal pore wetting and offer valuable insights for studies aimed at reducing dust and preventing gas outbursts.

Co-pyrolysis of low-rank coal and rice stalk: A comprehensive study on product distributions, product properties, and synergistic effects

Co-pyrolysis of low-rank coal and rice stalk is an important way to achieve hierarchical and efficient utilization of energy. This work explored how blend ratios (0–100 wt%) and temperatures (773–1073 K) affect pyrolysis product distribution and characteristics. The results showed that a higher rice straw ratio (80 wt%) significantly reduced the yield of char (22.38–26.9 wt%) compared with 20 wt% of rice straw at different temperatures. The yield and physicochemical properties of target products were closely related to process parameters, which can provide a promising opportunity to acquire desired products by reaction conditions optimization. Co-pyrolysis was able to inhibit the production of large aromatic ring structures in char. High temperature promoted the generation of cross-linked structures, which was influenced by the blend ratio. The synergistic effects of BET surface area and pore volume were most pronounced when the J content was 40 wt% at 873 K, and their increments were 59.6 m2/g and 0.027 cm3/g, respectively. For the char derived from lower rice straw proportions (0, 20, and 40 wt%), the main combustion range and the maximum combustion rate temperature showed a progressive shift towards higher values with temperature increasing. The research is valuable of guiding high-value utilization of agricultural residues and energy transitions.

Experimental investigation on pore characteristics of vitrain and durain in low rank coal based on fractal theory

The macro petrographic compositions and its pore characteristics of coal reservoir play critical role in the accumulation and development of coalbed methane (CBM). In this paper, the pore characteristics of vitrain and durain were analyzed through the experiment and fractal theory. The results indicated that the micropores and microfractures develop in vitrain, and that transitional pores develop in durain. The pore volume and specific surface area (SSA) of vitrain are larger than those of durain, with the micropore SSA of vitrain being 35% higher than that of durain. The threshold pressure and tortuosity of vitrain are greater than that of durain, but the mean pore size of vitrain is smaller than that of durain. The fractal dimension D1 of vitrain is greater than that of durain, while the fractal dimension D2 is opposite, indicating that the pore surface of vitrain is coarser, and the pore structure of durain is more complex. The fractal dimension Dk of vitrain is larger than that of durain, the mean fractal dimension Ds of vitrain is smaller than that of durain, which shows that the diffusivity of vitrain is weak but the seepage capacity is strong due to the developed fractures. The difference in material composition and pore characteristics between vitrain and durain provides a new understanding for the development of CBM in low rank coal.

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.

Effect of Carboxyl Group Position on Assembly Behavior and Structure of Hydrocarbon Oil-Carboxylic Acid Compound Collector on Low-Rank Coal Surface: Sum-Frequency Vibration Spectroscopy and Coarse-Grained Molecular Dynamics Simulation Study.

In this work, the assembly behavior and structure of a compound collector with different carboxyl group positions at the low-rank coal (LRC)-water interface were investigated through coarse-grained molecular dynamics simulation (CGMD) combined with sum-frequency vibration spectroscopy (SFG). The choice of compound collector was dodecane +decanoic acid (D-DA) and dodecane +2-butyl octanoic acid (D-BA). CGMD results showed that the carboxyl group at the carbon chain's middle can better control the assembly process between carboxylic acid and D molecules. SFG research found that the carboxyl group at the carbon chain's termination had a greater impact on the displacement of the methyl/methylene symmetric stretching vibration peak, while the carboxyl group at the carbon chain's middle had a greater impact on the displacement of the methyl/methylene asymmetric stretching vibration peak. The spatial angle calculation results revealed that the methyl group's orientation angle in the D-BA molecule was smaller and the carboxyl group's orientation angle in the BA molecule was bigger, indicating that D-BA spread more flatly on the LRC surface than D-DA. This meant that the assembled structure had a larger effective adsorption area on the LRC surface. The flotation studies also verified that the assembly behavior and structure of D-BA with the carboxyl group at the carbon chain's middle at the LRC-water interface were more conducive to the improvement of flotation efficiency. The study of interface assembly behavior and structure by CGMD combined with SFG is crucial for the creation of effective compound collectors.