Content Of Oxygen-containing Functional Groups Research Articles

Study on the effects of inorganic salts and ionic surfactants on the wettability of coal based on the experimental and molecular dynamics investigations

Through the evaluation and preparation of a novel inorganic salt composite solution consisting of sodium dodecyl benzene sulfonate (SDBS), the nonionic surfactants polyethylene glycol pisooctyl phenyl ether (Triton X-100), and inorganic salt Na2SO4, based on surface tension, contact angle, settling time, wetting rate, and changes in the surface microstructure and functional groups of coal, this study analyzed the wetting behavior of the solution on coal dust and its adsorption capacity on the surface of coal particles. The results demonstrate that the composite solution of inorganic salts can significantly enhance the wettability of coal samples, reducing the contact angle to 21.54° and lowering the surface tension to 26.10 mN/m. After treatment with the solution, the relative content of oxygen-containing functional groups in the microscopic structure of the coal sample increased to 59.6 % and pores more prominent than 25 nm increased to 34.63 %. Molecular dynamics (MD) simulations of the water-inorganic salt composite solution-coal system are conducted using Materials Studio software, revealing that after the addition of the composite solution, the self-diffusion coefficient (D) of water molecules is 6.3 × 10-9 m2/s, the starting point of the composite solution is 15 Å, and the system's interaction energy increase to 14000 kcal/mol. It further elucidated the modification of the surface molecular structure of coal dust by the inorganic salt composite solution, increasing hydrogen bonds, enhancing wetting, and demonstrating a solid adsorption capability of the inorganic salt composite solution on the surface of coal dust.

Study on the Wettability and Methane Desorption Characteristics of Coal under High Pressure with Different Surfactants.

In the process of coalbed methane extraction, due to the strong hydrophilicity of coal, the surface interaction force between water and the coal matrix is strong. The hydrophobic effect of the coal seam during drainage and pressure reduction is not significant, and adsorbed methane is difficult to desorb. In order to reduce the surface interaction force promoting methane desorption between water and coal, the surfactants NH766, G526, and D001 with a concentration of 0.1% were selected. A pressure of 12 MPa, which is close to that used for the on-site mining of coalbed methane in Baode, was selected as the experimental condition to simulate hydraulic fracturing of high fat coal, and the influence of different surfactants on methane desorption characteristics was analyzed. Combining contact angle experiments and infrared spectroscopy experiments, we explored the changes in wettability of the coal samples. We compared the changes in wettability and methane desorption characteristics and explored the similarities between these changes. The experimental results showed that after NH766 treatment, the content of oxygen-containing functional groups in coal rock decreased by 30%, and the contact angle of the coal matrix surface increased by 10°. Furthermore, its hydrophobicity was enhanced, and the desorption amount increased by 24%. In contrast, the oxygen-containing functional groups in coal rock after G526 and D001 treatments increased by 5% and 16%, respectively, and the contact angle of the coal matrix surface became smaller. Furthermore, its hydrophilicity was enhanced, and the desorption amount was reduced by 12.5% and 20%, respectively. NH766 reduces wettability and promotes methane desorption, and it can be applied to improve CBM extraction efficiency. G526 and D001 enhance wettability and inhibit methane desorption, which make them suitable for dust prevention and gas control in coal mines.

Optimization and Mechanism Study of Bonding Properties of CFRP/Al7075 Single-Lap Joints by Low-Temperature Plasma Surface Treatment

This paper studied favorable low-temperature plasma (LTP) surface treatment modes for Carbon Fiber Reinforced Polymer (CFRP)/Al7075 single-lap joints using complex experimental methods and analyzed the failure modes of the joints. The surface physicochemical properties of CFRP after LTP surface treatment were characterized using scanning electron microscopy (SEM), contact angle tests, and X-ray photoelectron spectroscopy (XPS). The influence mechanism of LTP surface treatment on the bonding properties of CFRP/Al7075 single-lap Joint was studied. The results of the complex experiment and range analysis showed that the favorable LTP surface treatment parameters were a speed of 10 mm/s, a distance of 10 mm, and three repeat scans. At these parameters, the shear strength of the joints reached 30.76 MPa, a 102.8% improvement compared to the untreated group. The failure mode of the joints shifted from interface failure to substrate failure. After low-temperature plasma surface treatment with favorable parameters, the CFRP surface exhibited gully like textures, which enhanced the mechanical interlocking between the CFRP surface and the adhesive. Additionally, the surface free energy of CFRP significantly increased, reaching a maximum of 78.77 mJ/m2. XPS results demonstrated that the low-temperature plasma surface treatment led to a significant increase in the content of oxygen-containing functional groups, such as C-O, C=O, and O-C=O, on the CFRP surface.

Hydrolysis-dominated catalytic system: Hydrogen-free hydrogenolysis of lignin from Pd-MoOx/TiO2

Lignin is continuously investigated by various techniques for valorization due to its high content of oxygen-containing functional groups. Catalytic systems employing hydrolysis‑hydrogenolysis, leveraging the synergistic effect of redox metal sites and acid sites, exhibit efficient degradation of lignin. The predominance of either hydrolysis or hydrogenolysis reactions hinges upon the relative activity of acid and metal sites, as well as the intensity of the reductive atmosphere. In this study, the Pd-MoOx/TiO2 catalyst was found to primarily catalyze hydrolysis in the lignin depolymerization process, attributed to the abundance of moderate acidic sites on Pd and the redox-assisted catalysis of MoOx under inert conditions. After subjecting the reaction to 240 °C for 30 h, a yield of 48.22 wt% of total phenolic monomers, with 5.90 wt% consisting of diphenols, was achieved. Investigation into the conversion of 4-propylguaiacol (4-PG), a major depolymerized monomer of corncob lignin, revealed the production of ketone intermediates, a phenomenon closely linked to the unique properties of MoOx. Dehydrogenation of the propyl is a key step in initiating the reaction, and 4-PG could be almost completely transformed, accompanied by an over 97 % of 4-propylcatechol selectivity. This distinctive system lays a new theoretical groundwork for the eco-friendly valorization of lignin.

Adsorption properties and mechanism of Cu(II) on virgin and aged microplastics in the aquatic environment.

Microplastics (MPs) migrate by adsorbing heavy metals in aquatic environments and act as their carriers. However, the aging mechanisms of MPs in the environment and the interactions between MPs and heavy metals in aquatic environments require further study. In this study, two kinds of materials, polyamide (PA) and polylactic acid (PLA) were used as target MPs, and the effects of UV irradiation on the physical and chemical properties of the MPs and the adsorption behavior of Cu(II) were investigated. The results showed that after UV irradiation, pits, folds and pores appeared on the surface of aged MPs, the specific surface area (SSA) increased, the content of oxygen-containing functional groups increased, and the crystallinity decreased. These changes enhanced the adsorption capacity of aged MPs for Cu(II) pollutants. The adsorption behavior of the PA and PLA MPs for Cu(II) conformed to the pseudo-second-order model and Langmuir isotherm model, indicating that the monolayer chemical adsorption was dominant. The maximum amounts of aged PA and PLA reached 1.415 and 1.398 mg/g, respectively, which were 1.59 and 1.76 times of virgin MPs, respectively. The effects of pH and salinity on the adsorption of Cu(II) by the MPs were significant. Moreover, factors such as pH, salinity and dosage had significant effects on the adsorption of Cu(II) by MPs. Oxidative complexation between the oxygen-containing groups of the MPs and Cu(II) is an important adsorption mechanism. These findings reveal that the UV irradiation aging of MPs can enhance the adsorption of Cu(II) and increase their role as pollutant carriers, which is crucial for assessing the ecological risk of MPs and heavy metals coexisting in aquatic environments.

Removal of Cr(VI) from aqueous solution using ball mill modified biochar: multivariate modeling, optimization and experimental study

Chromium (Cr(VI)) pollution has attracted wide attention due to its high toxicity and carcinogenicity. Modified biochar has been widely used in the removal of Cr(VI) in water as an efficient and green adsorbent. However, the existing biochar prepared by chemical modification is usually complicated in process, high in cost, and has secondary pollution, which limits its application. It is urgent to explore modified biochar with simple process, low cost and environmental friendliness. Therefore, ball milling wheat straw biochar (BM-WB) was prepared by ball milling technology in this paper. The adsorption characteristics and mechanism of Cr(VI) removal by BM-WB were analyzed by functional group characterization, adsorption model and response surface method. The results showed that ball milling effectively reduced the particle size of biochar, increased the specific surface area, and more importantly, enhanced the content of oxygen-containing functional groups on the surface of biochar. After ball milling, the adsorption capacity of Cr(VI) increased by 3.5–9.1 times, and the adsorption capacity reached 52.21 mg/g. The adsorption behavior of Cr(VI) follows the pseudo-second-order kinetics and Langmuir isotherm adsorption model rate. Moreover, the Cr(VI) adsorption process of BM-WB is endothermic and spontaneous. Under the optimized conditions of pH 2, temperature 45 °C, and adsorbent dosage 0.1 g, the removal rate of Cr(VI) in the solution can reach 100%. The mechanism of Cr(VI) adsorption by BM-WB is mainly based on electrostatic attraction, redox and complexation. Therefore, ball milled biochar is a cheap, simple and efficient Cr(VI) removal material, which has a good application prospect in the field of remediation of Cr(VI) pollution in water.

Probing the molecular interaction between photoaged polystyrene microplastics and fulvic acid

As emerging contaminants, microplastics (MPs) are becoming a matter of global concern, and they have complex interactions with dissolved organic matter (DOM) widely present in aqueous environments. Here, we investigate the molecular interactions between aged polystyrene microplastics (PS-MPs) and fulvic acid (FA) under neutral conditions using a series of analytical techniques. The structural changes of FA and the binding interactions of PS-MPs with FA at a molecular level were explored by fluorescence and FT-IR combined with two-dimensional correlation spectroscopy (2D-COS). Results showed that photoaging of PS-MPs changed the sequence of structural variations with FA. Atomic force microscopy-infrared spectroscopy (AFM-IR) strongly demonstrated that the surface roughness of both pristine and aged PS-MPs greatly increased after FA addition. Meanwhile, AFM-IR and Raman spectroscopy revealed a stronger interaction between aged PS-MPs and FA. The content of oxygen-containing functional groups in PS-MPs increased after aging and after binding with FA, and surface distribution of these functional groups also changed. XPS analyses indicated that the oxygen content in PS-MPs increased after the interaction with FA and the increase in oxygen content was even greater in aged PS-MPs. Overall, these research findings are useful to understand the environmental impacts of DOM-MPs interactions and to address the uncertainty of MPs aging effect on their environmental behavior in aquatic ecosystems.

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.

Study on the mechanism of constructing structure defects on surface of activated carbon with carbon black to promote hydrogen production by thermal-decomposition of methane

Hydrogen production from catalytic decomposition of methane is a promising method of hydrogen production that caters to low-carbon energy sources. The low cost and easy regeneration of carbon-based catalysts is more compatible with the concept of sustainability than metal catalysts. The key problem with catalytic decomposition using activated carbon is the rapid deactivation of the activated carbon due to structural changes caused by the production and accumulation of deposited carbon. Carbon black, on the other hand, exhibits slowly increasing catalytic performance in the catalytic decomposition of methane. Therefore, combining the properties of the two, it is proposed to disperse and load the nano conductive carbon black onto the surface of urea-modified activated carbon, so that the activated carbon can also have self-repairing ability at a later stage. It is shown that the combined application of carbon black loading and urea modification enhances the structural properties of the activated carbon by enriching the microporous structure of the activated carbon surface, increasing the disorder of its crystal structure, and altering the content and concentration of oxygen-containing functional groups on the surface. These microstructural changes combined to enhance the overall catalytic activity of the activated carbon, including its late deactivation time and catalytic performance after deactivation.

Prominent Structural Dependence of Quantum Capacitance Unraveled by Nitrogen-Doped Graphene Mesosponge.

Porous carbons are important electrode materials for supercapacitors. One of the challenges associated with supercapacitors is improving their energy density without relying on pseudocapacitance, which is based on fast redox reactions that often shorten device lifetimes. A possible solution involves achieving high total capacitance (Ctot), which comprises Helmholtz capacitance (CH) and possibly quantum capacitance (CQ), in high-surface carbon materials comprising minimally stacked graphene walls. In this work, a templating method is used to synthesize 3D mesoporous graphenes with largely identical pore structures (≈2100 m2 g-1 with an average pore size of ≈7nm) but different concentrations of oxygen-containing functional groups (0.3-6.7 wt.%) and nitrogen dopants (0.1-4.5 wt.%). Thus, the impact of the heteroatom functionalities on Ctot is systematically investigated in an organic electrolyte excluding the effect of pore structures. It is found that heteroatom functionalities determine Ctot, resulting in the cyclic voltammetry curves being rectangular or butterfly-shaped. The nitrogen functionalities are found to significantly enhance Ctot owing to increased CQ.

Spontaneous combustion properties and quantitative characterization of catastrophic temperature for pre-oxidized broken coal under stress

Coal Spontaneous Combustion (CSC) is one of the most important natural disasters in coal mining safety production. To deeply restore the real state of CSC left in goaf during the face mining of coal mines, the experiments are carried out to simulate the oxidation characteristics of coal left in goaf under the coupling of the stresses (0 MPa, 4 MPa, 8 MPa) and the pre-oxidation temperatures (25 °C, 70 °C, 120 °C, 180 °C) employing the load-pressure-based device equipped with temperature-programmed. The oxidation characteristic parameter of CO gas generation, the O2 consumption rate, the apparent activation energy (Ea), and the critical temperature(T1) are calculated. It is found that both the pre-oxidation temperature and the stress have a promotion range for coal spontaneous combustion, and although they inhibited each other beyond the promotion range, they still show a promotion result. The pre-oxidation temperature and stress mainly affect the content of oxygen-containing functional groups and the permeability, thus influencing the process of coal spontaneous combustion. Based on the engineering application, a cusp catastrophe model is established to predict the catastrophic temperature of coal spontaneous combustion, and it is verified that the catastrophic temperature could correctly characterize the transition of coal spontaneous combustion, and it is found that the catastrophic temperature lagged behind the critical temperature, which provides sufficient time and space for the prevention and control of coal spontaneous combustion.

Rapid preparation of porous carbon by Flash Joule heating from bituminous coal and its adsorption mechanism of methylene blue

Porous carbon is an extensively used adsorbent for the removal of dye. However, the conventional high-temperature carbonization and activation method with prolonged heating and annealing process was complicated, energy-consuming and polluting, which greatly limit the large-scale production. In this study, rapid and efficient preparation of porous carbon by the Flash Joule heating (FJH) method was realized for the first time using three bituminous coal samples with different degrees of metamorphism. The preparation process was completed in less than 1 s without chemical treatment, the process was more environmentally friendly. The physical and chemical properties of porous carbon were analyzed and the adsorption mechanism of porous carbon on methylene blue (MB) was investigated. The results showed that the specific surface area of porous carbon prepared by Shuozhou (PC-SZ), Gujiao (PC-GJ) and Changzhi (PC-CZ) could reach 601.95, 361.91 and 256.33 m2·g−1, respectively. The diversity in chemical properties of coal with different metamorphic degrees leads to the different properties of porous carbon. PC-SZ had a higher content of oxygen-containing functional groups and defects. The adsorption experiments indicate that PC-SZ had the best adsorption capacity on MB. The adsorption process was fitted by pseudo-second-order model commendably. It was found that more lattice defects and larger interlayer spacing made PC-SZ to become an excellent adsorbent of methylene blue (MB). Therefore, FJH can be an innovative approach for preparing porous carbon with excellent adsorption properties and is expected to achieve large-scale production.

Contribution of surface roughness and oxygen-containing groups to the interfacial shear strength of carbon fiber/epoxy resin composites

The interfacial shear strength (IFSS) between carbon fibers (CFs) and the matrix is crucial to the performance of CF-reinforced polymer composites. To evaluate the contribution of mechanical interlocking and chemical anchoring at the interfaces of a polyacrylonitrile-based CF (TORAYCA T800SC-12000-10E)-reinforced epoxy resin (EP: bisphenol A type epoxy resin and tetrafunctional epoxy resin) composites, the surface roughness and content of oxygen-containing functional groups of the CFs were respectively altered by ammonia treatment and electrochemical oxidation. The results showed that ammonia treatment increased the surface roughness without much change to the surface elemental composition, while electrochemical oxidation increased the number of surface oxygen groups without changing the surface roughness. The IFSS of CF/EP composites was tested by the micro-droplet method. The relationships between IFSS, and surface roughness and oxygen content were obtained by linear fitting. The results showed that in the interfacial bonding of CF to epoxy resin, the contribution of chemical anchoring to the IFSS is larger than that of mechanical interlocking.

Effects of Microstructure and Chemical Composition on the Visual Characteristics of Flattened Bamboo Board

Flattened bamboo board is a new type of bamboo-based panel with various colors that maintains the natural texture of bamboo, and is gradually being used in indoor home decoration. Revealing the influence mechanism on the visual effect of flattened bamboo boards is the key to improving the processing of such boards for household materials. This study employed visual physical quantity measurement methods, field emission scanning electron microscopy, FTIR spectroscopy, and XPS to investigate the visual physical quantities, morphology, and chemical composition of flattened bamboo boards. The results showed that compared with the control samples, the bamboo outer layer boards were dark brown, with the largest ΔE* (38.55), while the outer boards were reddish-brown, with the largest a* (8.82). The inner boards were yellow-red and showed a lower ΔE* (6.55). Due to the elevated density, abundant inclusion, and wax, the bamboo outer layer board exhibited the highest glossiness and darkest color, followed by the outer board and the inner board. The FTIR spectroscopy revealed that hemicellulose decomposed, and the relative content of lignin increased, leading to color changes in the flattened bamboo boards. The bamboo outer layer board was the darkest due to changes in C=C bonds at 1600 cm−1 and 1509 cm−1. The surface color of the outer board was mainly red, which may be caused by C–O bonds at 1239 cm−1. The surface of the inner board was mainly yellow, which may be caused by the C–H stretching vibration of lignin at 1108 cm−1. XPS analysis showed that the proportion of C1 and O1 increased, while C2, C3, and O2 decreased, indicating that hemicellulose degraded at high temperatures, which increased the relative lignin content. Changes in the relative content of oxygen-containing functional groups and SiO2 in the flattened bamboo board were important factors responsible for the change in visual physical quantities.

Effect of Solvent Treatment on the Composition and Structure of Santanghu Long Flame Coal and Its Rapid Pyrolysis Products.

Easily soluble organic components in Santanghu long flame coal (SLFC) from Hami (Xinjiang, China) were separated by CS2 and acetone mixed solvent (v/v = 1:1) under ultrasonic condition, and the extract residue was stratified by carbon tetrachloride to obtain the light raffinate component (SLFC-L). The effect of solvent treatment on the composition and structure of the coal and its rapid pyrolysis products was analyzed. Solvent treatment can reduce the moisture content in coal from 9.48% to 6.45% and increase the volatile matter from 26.59% to 28.78%, while the macromolecular structure of the coal changed slightly, demonstrating the stability of coal's complex organic structure. Compared with raw coal, the relative contents of oxygen-containing functional groups and aromatic groups in SLFC-L are higher, and the weight loss rates of both SLFC and SLFC-L reached the maximum at about 450 °C. In contrast, the loss rate of SLFC-L is more obvious, being 33.62% higher than that of SLFC. Pyrolysis products from SLFC at 450 °C by Py-GC/MS are mainly aliphatic hydrocarbons and oxygenated compounds, and the relative contents of aliphatic hydrocarbons decreased from 48.48% to 36.13%, while the contents of oxygenates increased from 39.07% to 44.95%. Overall, the composition and functional group in the coal sample were changed after solvent treatment, resulting in a difference in the composition and distribution of its pyrolysis products.

Effect of demineralization on waste tire pyrolysis char physical, chemical characteristics and combustion characteristics

Waste tire carbon black particles (CBp) are the main pyrolysis products of waste tires (WT), and CBp is difficult to use directly. This work mainly focuses on the physicochemical and combustion characteristics of demineralized CBp (DCBp) to explore the resourceful utilization of CBp resources in large quantities. This work also provides a comprehensive comparison with CBp and other carbon-based solid fuels. The results show that most of the minerals in CBp can be removed by chemical demineralization treatment (Ash content of DCBp <0.11 %). DCBp has a more developed pore structure than CBp. The deashing process affects the degree of loosening and stacking of the graphitic carbon microcrystalline structure, and the relative content of oxygen-containing functional groups in CBp to a minor extent. The deashing process leads to a decrease in the relative strength of the cross-linked stable structure and an increase in the disordered structure of carbon in CBp. The volatile fraction to fixed carbon ratio of DCBp is only 0.0467, and a large number of catalytic alkali metal elements and alkaline earth metal elements are removed in the demineralization process, which makes the early combustion of DCBp more difficult. As the combustion reaction proceeds, the internal pores of the particles are opened, and the micropores and mesopores in DCBp provide a larger surface area for the reaction. In addition, the decrease in the relative strength of the cross-linked stable structure and increases in the disordered structure of carbon can increase the intermolecular collision frequency during the combustion process, thus improving the burnout characteristics of DCBp. The above results indicate that DCBp has the potential to be used as fuel for large-scale resource utilization.

Influences of Evolution of Pore Structures in Tectonic Coal under Acidization on Methane Desorption.

Experiments on corrosion reactions of pulverized coal with monomeric and polymeric (mixed) acid solutions reveal that monomeric acids are listed in a descending order as HF, HCl, and CH3COOH according to their corrosion effects on tectonic coal collected in Faer Coal Mine (Liupanshui City, Guizhou Province, China). In addition, the optimal mixing ratio of mixed acids is 6% HCl + 6% HF + 3% CH3COOH + 2% KCl. The mineral grains filled in pores in coal samples treated with mixed acid solutions are dissolved, so the porosity increases. The volumes of transition pores and mesopores are obviously affected by acidization, and some transition pores are transformed into mesopores and macropores to form dissolved pores. At the same time, inkbottle-shaped pores reduce, while slit pores or open pores increase. The coal samples after acidization show a higher aromatization degree and an increased relative content of oxygen-containing functional groups, with a generally lower hydroxyl content, so the methane (CH4) adsorption capacity of coal declines, which promotes CH4 desorption. The control effect of pore structures after acidization reactions on CH4 desorption was revealed from perspectives of the diffusion coefficient (Kn), adsorption volume (ω), average pore-throat ratio (PT), and average sinuosity (τav). That is, CH4 molecules in tectonic coal after acidization turn from Knudsen diffusion to transitional diffusion, the adsorption volume of CH4 molecules shrinks, the average pore-throat ratio decreases, and the average sinuosity reduces, which promotes CH4 desorption from tectonic coal.

Spontaneous Combustion Characteristics of Activated Carbon Modified via Liquid Phase Impregnation during Drying.

Spontaneous combustion characteristics are important issues for the safe operation of the wet-modified activated carbon drying process. The spontaneous combustion characteristics of activated carbon modified via liquid phase impregnation were fully investigated in this study. The modified activated carbon was prepared using columnar activated carbon and 4-amino-1,2-butanediol solution. Physical properties and surface functional group analyses were performed for activated carbon before and after modification. The ignition temperature of activated carbon before and after modification was then characterized using the methods of GB/T20450-2006, thermogravimetry-derivative thermogravimetry (TG-DTG), and TG-mass spectrometry (TG-MS). At the same time, the activation energy of activated carbon before and after modification was calculated by using thermodynamic analysis. Furthermore, a new self-designed test platform was introduced to investigate the spontaneous combustion characteristics of wet-modified activated carbon under the drying temperatures of 150, 175, 180, and 210 °C. The results show that the specific surface area of Brunauer, Emmett, and Teller (BET) is decreased by 368 m2·g-1, the total volume of pore size is decreased by 0.17 cm3·g-1, and the content of oxygen-containing functional groups is decreased by 0.071 mmol/g compared with row activated carbon. The ignition temperatures of the sample before modification characterized by the three methods are 483, 596, and 599 °C, respectively. The ignition temperatures of the sample after modification are 489, 607, and 611 °C, respectively. The activation energy of the modified activated carbon is increased by 35 kJ/mol compared to the original activated carbon. It is concluded that the temperature that triggers the modified activated carbon combustion during the drying process is between 175 and 180 °C, and the heat is mainly gathered at the longitudinal center of the combustion chamber through the investigation of spontaneous combustion experiments. The results in this study can contribute to safe production to prevent combustion in the process of modifying activated carbon during the drying process.

Influence of Long-Term Immersion in Water at Different Temperatures on Spontaneous Combustion Characteristics of Coal.

The effect of hydrothermal coupling on the risk of spontaneous combustion of coal (SCC) soaked at different water temperatures was studied. The results showed that the porosity and permeability of coal increased significantly after immersion in water at different temperatures. The increase at a water temperature of 30 °C was the largest, the porosity was 22.77% higher, and the permeability was 3.44 times that of raw coal. The relative content of oxygen-containing functional groups, aliphatic functional groups, and hydroxyl functional groups reached 1.8-4.5, 1.1-4.4, and 0.7-1.48 times that of raw coal after soaking in water at different temperatures. The increase ratio of functional groups is the largest under the water temperature of 30 °C. The activation energy of coal samples soaked at water temperatures of 30 and 45 °C decreased by 9.4 and 2.9%, respectively. Under the condition that the coal sample temperature was lower than 110 °C, the highest oxygen consumption rate and heat release rate were coal samples soaked at water temperatures of 30 °C, and the lowest was raw coal. When the coal temperature was higher than 170 °C, all coal samples soaked in different water temperatures are higher than that of raw coal, and the water temperature of 30 °C is the highest. The risk of spontaneous combustion of coal is highest after long-term soaking at 30 °C water.

Hygroscopicity of coal powders with different ranks

The hygroscopicity of coal powder is one of the crucial factors that determine its moisture content, which significantly affects its adhesion, flowability, charge properties, and combustion behavior. In this study, the effects of coal particle size, ambient temperature, and relative humidity on the hygroscopicity of coal powders with different ranks were investigated through experimental methods. The results indicated that an increase in coal particle size resulted in a moderate reduction in the maximum moisture adsorption capacity and a substantial increase in the effective moisture adsorption time of the coal powder. As the coal particle size increased from 19 to 21 μm to 6310–6941 μm, the maximum moisture adsorption capacities of the coal powders decreased by 0.28–0.54 times, while their effective moisture adsorption times increased by 1.47–1.68 times. The maximum moisture adsorption capacities of the coal powders increased dramatically with increasing ambient relative humidity, whereas the impact of temperature on their maximum moisture adsorption capacities was not significant. The hygroscopicity of coal powders varied significantly among different ranks. Low-rank coal such as lignite and subbituminous showed strong moisture adsorption ability, while high-rank coal such as anthracite exhibited moderate moisture adsorption ability, and middle-rank coal such as medium volatile bituminous showed the weakest moisture adsorption ability. FTIR spectra analysis and pore testing results revealed that the content of oxygen-containing functional groups and the distribution characteristics of internal pores were critical factors causing the difference in hygroscopicity of the coal powders. The practical value of this study lies in its potential to determine the moisture adsorption rate and the maximum moisture adsorption capacity of coal powder under specific environmental conditions, which is essential for evaluating the moisture status, transportation efficiency and combustion performance of coal powder.