Long-flame Coal Research Articles

An investigative and simulative study on the wetting mechanism of alkaline dust suppressant acting on long-flame coal

In order to tackle the issue of excessive coal dust and hydrogen sulfide (H2S) concurrently in underground coal mines, an alkaline dust suppressant was formulated by combining surfactant sodium sec-alkyl sulfonate (SAS60) and sodium carbonate (Na2CO3) at a certain mass ratio, meant for injection into coal seams. This study principally targeted long-flame coal extracted from Hequ County, located in Shanxi Province, China. The objective was to investigate and analyze the underlying process of how alkaline dust suppressants affect the wettability of coal. A comprehensive strategy including contact angle determination, Fourier transform infrared absorption spectrometer(FTIR) analysis, low-temperature nitrogen adsorption tests, scanning electron microscope(SEM) experimental studies, and molecular dynamics simulations was employed for this examination. The results revealed that merging Na2CO3 with SAS60 could reduce the coal’s contact angle. Despite the core structure of the coal surface staying unchanged after alkaline dust suppressant treatment, a rise in the number of hydrophilic functional groups was observed. This count notably surpassed the amount of hydrophobic functional groups, consequently boosting the coal’s hydrophilicity. The permeability of the examined coal specimens was chiefly affected by the existence of macropores and mesopores. Processing with 0.05 wt% SAS60 and 1.0 wt% Na2CO3, the coal acquired additional pores and cracks, causing an upswing of average pore size by 25.79% and a 30.64% increase in the maximum gas adsorption. This facilitated more straightforward infiltration of water into the coal dust. Molecular dynamics simulation outcomes indicated a closer affiliation between coal and water following the incorporation of Na2CO3. It led to a heightened activity in water molecule movement, fortifying intermolecular electrostatic interactions, and fostering the creation of hydrogen bonds. Consequently, this improved the coal’s wettability. The increase in the mass fraction of Na2CO3 directly corresponds to a more considerable enhancement in the solution’s ability to wet the coal. The outcomes of the molecular dynamics simulation validated the experimental results’ precision.

Exploration on the mechanism of enhancing flotation of long-flame coal by diesel modification via oxidation

Low-rank coal is naturally hydrophilic, and the traditional hydrocarbon collectors often have poor performance in its flotation. In this study, the modification of diesel was conducted using an instantaneous gasification-oxidation-condensation device for the expected improvement of collector’s performance. Experimental analyses and interfacial interaction calculation were performed to explore the mechanism of enhancing flotation of long-flame coal by diesel modification. It indicated that the flotation of coal sample can be greatly enhanced by the modified diesel, and a combustible matter recovery of 90.52 % could be attained only consuming 6 kg/t of modified diesel which was far better than the flotation effect consuming 100 kg/t of common diesel. The improved flotation effect of the coal sample could be attributed to the increased polarity of collector from 0.48 % to 9.76 % resulted from the newly added oxygenated functional groups after the oxidation of diesel, which significantly enhanced the adsorption capacity of the collector on the long-flame coal surface reflected by the FTIR and XPS analyses. Furthermore, the calculated results of interfacial interaction between the coal sample and the common/modified diesel suggested that the efficient adsorption of modified diesel on the coal sample was achieved through the bridging role acted by water molecules. This research may give some insight into enhancing flotation of low-rank coal.

Influence of imidazole-based ionic liquid surfactants on the wetting effect of long-flame coals

In order to study the wetting effect of C12MImBF4, C12MImBr and C12MImCl on long-flame coal, and their mechanism of action on coal-water bonding, physical experiments, molecular dynamics simulation and DFT theoretical calculation were combined in this work. It is confirmed that the imidazole ionic liquid surfactant optimizes the wetting effect by forming hydrogen bonds, reducing the surface tension of water, and increasing the number of free hydroxyl groups in coal. After the wettability test, the concentration of 4 g/L of the three ionic liquid surfactants had the best wetting effect on long-flame coal, and the contact angle at this concentration was reduced by more than 40 % compared with water within 0.2 s after dripping on the coal. Due to the difference in the anionic head group of the three surfactants, there are differences in the number and strength of hydrogen bonds formed between the three surfactants and water molecules, the results of wettability C12MImBF4 > C12MImCl > C12MImBr were presented. Combined with these characteristics of imidazole ionic liquids on long-flame coal, the reasonable application in the wet dust removal process of actual coal mine production can optimize the efficiency of droplet capture of coal particles, so as to effectively improve the dust removal capacity.

Study on the effect of imidazole ionic liquids on the whole process spontaneous combustion characteristics of long-flame coal based on TG–DSC technology

Study on the effect of imidazole ionic liquids on the whole process spontaneous combustion characteristics of long-flame coal based on TG–DSC technology

Enhanced energy efficiency and fast co-pyrolysis characteristics of biogas residues and long-flame coal using infrared heating and TG-FTIR-MS

Co-pyrolysis may enhance the energy efficiency of anaerobic digestion waste (biogas residues), while simultaneously facilitating the clean utilization of coal. A thermogravimetric analyzer (TG), TG-FTIR-MS, and infrared heating technique were employed to investigate the rapid co-pyrolysis properties of long-flame coal (LFC) and biogas residues (BR) in this study. Meanwhile, the effects of temperature on the co-pyrolysis product distributions and compositions were studied in reactors that were heated with electric heating and rapid infrared heating. The co-pyrolysis of LFC and BR had the potential to decrease greenhouse gas emissions, as indicated by the TG-FTIR/MS findings. The co-pyrolysis kinetics were calculated using two models (KAS and FWO); the average Eα values are 176.09 and 187.26 kJ/mol, respectively. Tar yields increased initially in IH (electric heating) and EH (infrared heating) reactors, before declining as the temperature rose. The tar yields are greatest for EH at 500 °C (16.12 wt%) and IH at 600 °C (16.02 wt%). Tar yields generated via infrared heating were greatly higher than those generated by EH at 600–700 ℃. IH has a higher tar yield due to the fact that there are significant synergistic effects between coal and lignin, protein, and lipid at high temperatures. The GC-MS results indicate that IH has promoted the aromatization and ketonization reactions. Moreover, more monocyclic aromatic and bicyclic aromatic products are generated by infrared heating, suggesting an indication of tar quality improvement. An elevated co-pyrolysis temperature results in a greater degree of graphitization in char.

Mild Alkaline-Enhanced depolymerization of Long-Flame coal for the synthesis of Coal-Derived fluorescent carbon dots with application as probes

The intricate composition and structural of low-rank coal have hindered its broad utilization in the field of material science. The study utilized an alkaline hydrothermal method to enhance the depolymerization of long-flame coal and achieve the purification of fluorescent carbon dots for the first time, which were then being employed for the trace detection of Cu2+ or Fe3+ ions. The carbon extraction efficiency reached 58 %, with the carbon dots averaging size of 1.36 ± 0.42 nm, the sp2 hybridized structure of the carbon dots indicated successfully purification under alkaline conditions. After reduction with sodium borohydride, defects in the core region of the carbon dots were repaired, and the C = O functional groups were transformed into O–H groups, leading to an increase in fluorescence intensity. At a concentration of 0.25 g/L of carbon dots, demonstrated high emission intensity at both long and low emission wavelengths, which can be used as LED luminescent material. Furthermore, the application of these carbon dots in detecting heavy metal ions (Cu2+, Fe3+) in aqueous solutions was explored, showing as low as detection limit of ∼ 0.04 μM. This study achieved higher depolymerization of coal and purification of fluorescent carbon dots for use in probe-based detection, providing fresh perspectives on the high-value utilization of low-rank coal.

Construction of a microscopic molecular model of Hongqingliang long-flame coal for potential application in adsorption simulation

The present study aims to develop a tailored microscopic molecular model for analyzing the adsorption properties of Hongqingliang (HQL) coal. The chemical structure of the coal was thoroughly analyzed through the utilization of various techniques, including elemental analysis, Carbon-13 Nuclear Magnetic Resonance spectroscopy (13C NMR), X-ray Photoelectron Spectroscopy (XPS), and Fourier Transform Infrared Spectroscopy (FTIR). Subsequently, a three-dimensional periodic microscopic molecular model for HQL coal was constructed, followed by the development of a 4 nm fracture pore model. To validate the modeling approach, a comprehensive comparative analysis was conducted utilizing nitrogen adsorption isotherms at 77.35 K. The results indicate that the amorphous cell model constructed in Material Studio solely comprises micropores narrower than 1 nm, making it unsuitable for simulating coal's pore characteristics. Conversely, the nitrogen adsorption isotherm of the 4 nm fracture pore model matches actual results. Therefore, to analyze the pore adsorption characteristics of coal, it is necessary to utilize the amorphous cell model to construct a characteristic pore model for coal.

Adsorbents of 4-chlorophenol from long-flame coal activated by potassium hydroxide

The purpose of the work was to evaluate the adsorption capacities of carbon materials (CMs) from long-flame coal with respect to 4-chlorophenol (CPh) and the influence of CMs preparation temperature under alkali activation at a low KOH/coal ratio (1 g/g). The CMs were obtained by heating coal with KOH to specific temperatures ranging from 350 to 8250C with a 1-hour holding time. Specific surfaces of all pores (SDFT), micropores (Smi), ultramicropores (Sumi), and supermicropores (Ssmi) were determined using nitrogen adsorption-desorption isotherms. The kinetics and isotherms of CPh adsorption as well as the maximum capacities (ACPh(m))were measured at 250C. Temperature was found to be a key factor in the formation of CMs nanoporosity and their ability to adsorb CPh. As the temperature increases, the SDFT, Smi, and Ssmi values increase monotonically, while Sumi exhibits an extreme change with a peak at 6000C. The adsorption kinetics followed the second-order model, reaching equilibrium within 2 hours. About half of CPh was absorbed in the first minute. The rate-determining step was identified as the interaction of CPh with the adsorption centers. The adsorption isotherms were best described by the Langmuir model. The ACPh(m) capacity was found to increase with temperature from 32.3 mg/g to 486 mg/g, a 15-fold increase, corresponding to an SDFT increase by 138 times. The ACPh(m) values exhibited an S-shaped dependence on SDFT, Smi, and Ssmi, indicating the non-uniform formation of adsorption centers with surface development. This was attributed to the molecular structure reorganization of CMs, which is also influenced by the activation temperature.

N, S co-doped coal-based hard carbon prepared by two-step carbonization and a molten salt template method for sodium storage

Hard carbon, known for its abundant resources, stable structure and high safety, has emerged as the most popular anode material for sodium-ion batteries (SIBs). Among various sources, coal-derived hard carbon has attracted extensive attention. In this work, N and S co-doped coal-based carbon material (NSPC1200) was synthesized through a combination of two-step carbonization process and heteroatom doping using long-flame coal as a carbon source, thiourea as a nitrogen and sulfur source, and NaCl as a template. The two-step carbonization process played a crucial role in adjusting the structure of carbon microcrystals and expanding the interlayer spacing. The N and S co-doping regulated the electronic structure of carbon materials, endowing more active sites. Additionally, the introduction of NaCl as a template contributed to the construction of pore structure, which facilitates better contact between electrodes and electrolytes, enabling more efficient transport of Na+ and electrons. Under the synergistic effect, NSPC1200 exhibited exceptional sodium storage capacity, reaching 314.2 mAh g-1 at 20 mA g-1. Furthermore, NSPC1200 demonstrated commendable cycling stability, maintaining a capacity of 224.4 mAh g-1 even after 200 cycles. This work successfully achieves the strategic tuning of the microstructure of coal-based carbon materials, ultimately obtaining hard carbon anode with excellent electrochemical performance.

Effect of cavitation treatment of coal-water slurries on a droplet average size in a jet

Relevance. Transition to environmentally friendly energy technologies, due to modern requirements for environmental protection, involves the search and creation of new energy sources, including fuels. One of the ways to meet these requirements and maintain the same level of energy production by thermal power plants is the transition to multicomponent fuels. The most promising and affordable boiler fuels from the point of view of energy, ecology and economy are coal-water slurries. In this regard, the study of the properties and characteristics of such fuels is relevant in many countries. Aim. Experimental studies of the effect of the coal-water fuel cavitation treatment duration on a droplet average size in a jet after spraying with a pneumatic nozzle and substantiation of the efficiency of such approach for practical application. Object. Experimental studies were carried out with coal-water slurries based on long-flame coal (D grade) with addition of 10 and 20 wt % by weight of pyrogenetic liquid. A slurry, consisting of just coal and water, without the addition of pyrogenetic liquid, was used as a reference sample. Method. The coal-water slurries were prepared in a rotary hydrodynamic cavitation generator. A pneumatic nozzle with external mixing was used to spray the coal-water slurries. The average size of fuel droplets after spraying was determined using the Interferometric Particle Imaging method. Results. Experiments on the preparation of coal-water slurries with pyrogenetic liquid showed an increase in the dynamic viscosity of the fuel. An increase in the duration of treatment of the slurries in a rotary hydrodynamic cavitation generator reduced the viscosity by 54%. The average size of droplets in the jet was reduced by 22%.

Research on the Inhibitory Effect of Hydrated Phase Change Materials on Spontaneous Combustion in Coal

In order to study the effect of hydrated phase change materials on the suppression of spontaneous combustion in coal, a thermogravimetric experiment and a reaction activation energy analysis experiment were conducted to explore the changes in the combustion characteristic parameters, characteristic temperature, and activating energy of gas coal, long-flame coal, meagre coal, and lean coal before and after adding hydrated phase change materials. The research results indicated that hydrated phase change materials increased the characteristic temperature point of the coal samples and had effective inhibitory effects on different stages of the oxidation process. However, the effect was best at low temperatures, as hydrated phase change materials undergo phase change and absorb heat when heated at low temperatures, isolating coal from contact with oxygen. The activating energy increased by 1.138–23.048 KJ·mol−1 and the mass loss was reduced by 1.6%–9.3% after inhibition of the coal samples, indicating that the oxidation rate of the various coal samples was slowed down and, thus, spontaneous combustion can be suppressed through the use of hydrated phase change materials. At the same time, this material reduced the combustibility indices of meagre coal and lean coal, as well as the comprehensive combustion indices of long-flame coal and gas coal.

Enhancement of CH4/N2 separation capacity of coal-based porous carbons via hydrothermal coupled KOH activation

The separation of CH4 and N2 is an important technology for the effective utilization of low-concentration CBM. To improve CH4/N2 separation properties of coal-based porous carbons, Shaanxi long-flame coal was hydrothermally treated followed by KOH activation for the preparation of porous carbons. The impact of hydrothermal treatment on the pore structure and CH4/N2 separation properties of porous carbons was investigated. The results show that hydrothermal decomposes the macromolecular structure of coal, which enlarges the pore size of the raw coal and facilitates the KOH penetrate deeper into the coal particles. Meanwhile, more release of methylene/methyl groups and in-stiu growth of carbon nanotubes develop the pore structure during the activation process of treated coal. The pore structure of porous carbons can be precisely controlled by adjusting the water-coal ratio in the hydrothermal process. Among them, C-TC1.25 shows a 22% increase in CH4 adsorption capacity over C-RC, which is mainly due to a significant increase in the micropore volume at 0.5–1.0 nm and generation of carbon nanotubes as gas transport channels. At 298 K and 101 kPa, C-TC1.25 exhibits a CH4 adsorption capacity reaching 1.72 mmol/g, which surpasses that of most known adsorbents, while the IAST selectivity is as high as 5.5. The breakthrough experiment confirms that the porous carbons effectively enable separation of CH4/N2 mixed gas. Kinetic studies show the CH4 adsorption process on C-TC1.25 conform to the pseudo-first-order model and exhibit surface-attached physical adsorption.

Exploring carbon dioxide generation in combustion of long-flame coal in Huating mining area by using ReaxFF MD

Coal combustion contributes to 44% of global fuel CO2 emissions. Until now, there has less effective means to study the generation mechanism of carbon dioxide. To approach the generation mechanism of CO2 in coal combustion process at atomic level, the structure information of long-flame coal from Huating mining area, Gansu, China was characterized by ultimate analysis, 13C NMR and XPS. According to these information, one new average structure model was established, its parameters are consistent with the experimental results. Then reactive force field (ReaxFF) molecular dynamics (MD) simulations in 2000–3500 K were performed. Four types of intermediates (Rn–O, Rn–CHO, Rn–CO2, and C2O2) that correspond to four generation routes of CO2 were obtained from the ReaxFF MD simulations. The intermediates can generate CO2 through attacks from oxygen-containing radicals or cleavage of the C–C bond. Rn–O and Rn–CHO can generate CO as intermediates. The oxidation route of acetylene, which first oxidised into C2O2 and then further oxidised into CO2, was analysed using density functional theory (DFT) calculations at the M062X/6–311** level. The DFT results demonstrate the precision of ReaxFF MD calculations. The results can improve the understanding of CO2 generation during coal combustion.

Study on the oxidized gas production characteristics and spontaneous combustion tendency of pre-oxidized water-soaked coal in lean-oxygen environments.

The oxidation characteristics and spontaneous combustion (SC) tendency of raw long-flame coal (RC), water-soaked 200-day coal (S200), pre-oxidized water-soaked coal at 200°C (O200S200), and pre-oxidized soaked coal at 300°C (O300S200) in an oxygen-poor environment were investigated using a programmed warming system. The results show that pre-oxidation water-soaked treatment (PWT) promotes the coal-oxygen complex reaction and increases the rate of coal oxygen consumption (OCR) and the rate of carbon and oxygen compound production. The rate of CO and CO2 production of the water-soaked (WS) coal increased by 0.329mol·(cm3·s)-1 and 0.922mol·(cm3·s)-1, respectively, compared with that of the original coal sample. PWT reduces the activation energy of coal in the low-temperature oxidation stage (the maximum difference can be up to 110.99kJ/mol) and enhances the oxidizing and heat-releasing capacity. There was a synergistic effect between the pre-oxidation (PO) and WS treatment, and the lowest comprehensive determination index of the SC propensity of coal in O200S200 samples was 831.92 which was 4.72 lower than that of RC samples, presenting a more SC tendency. Low oxygen concentration has an inhibitory effect on the oxidation characteristic parameters of coal, and the apparent activation energy of the low-temperature oxidation stage of pre-oxidized water-soaked coal (PWC) increased to 206.418kJ/mol at 3% oxygen concentration. The lower the oxygen concentration of the anoxic environment, the lower the risk of SC of the coal samples. The results of the study can provide theoretical guidance for the identification and prevention of SC disasters in coal seams with shallow burial and close spacing.

Changes in the stability of coal microstructure under the influence of weak electromagnetic fields

The article presents experimental results of research concerning the action of weak electric and magnetic fields on physicochemical transformations in samples of hard coal with a previously destabilized microstructure. The actions of electric and magnetic fields are fundamentally different by many parameters. It has been shown that after treatment with a weak electric field, coal posted an electret potential with an anomalously continuous charge relaxation. Compared to untreated coal samples, the rate of methane emission from methane-saturated samples is maximum for long-flame coal and decreases as it approaches anthracite. The electric field stimulates the grinding of microparticles, a decrease in the maximum gas outlet temperature, a decrease in the enthalpy value in the formation of a new phase, and an increase in the chemical activity of treated coal samples. Fundamentally different results were obtained with magnetic stimulation of coals. In X-ray diffractograms of coal powders after magnetic treatment, the values of the maxima of the main peaks are the largest in comparison with the original samples and those treated with an electric field, which is consistent with an increase in the size of microparticles in a magnetic field. There is an increase in the heat of combustion and a decrease (by 5 times) in the loss of coal mass during heating.

Comparative Experimental Study on the Cracking Effect of Liquid Nitrogen Freeze-Thaw Cycles between Anthracite and Long-Flame Coal.

In order to explore the differences in the cracking effect of freeze-thaw cycles on coal of different coal grades, this study used liquid nitrogen to carry out freeze-thaw cycle cracking experiments on coal samples of anthracite and long-flame coal with two degrees of metamorphism. By combining a low-temperature nitrogen adsorption experiment and scanning electron microscopy, the surface cracks and pore structure development of water-saturated coal samples before and after freeze-thaw cycles were tested. Scanning electron microscope (SEM) test results show that the freeze-thaw cycle has an obvious destructive effect on the coal matrix. After three freeze-thaw cycles, the anthracite coal sample is obviously damaged, the coal sample is damaged, and the coal chips are peeled off. The surface of a long-flame coal sample is rough, the structure is loose, and the damage of the coal body is more serious by a freeze-thaw cycle. The results of the low-temperature nitrogen adsorption experiment show that the freeze-thaw cycle can effectively promote the development of the pore structure of the coal body. After three freeze-thaw cycles, the specific surface area growth rates of anthracite and long-flame coal samples are 69.57 and 49.13%, respectively. The pore volume growth rates were 73.01 and 35.54%, respectively. The increment of specific surface area and pore volume of the anthracite coal sample is lower than that of the long-flame coal sample, but the growth rate of specific surface area and pore volume of the anthracite coal sample is higher than that of the long-flame coal sample.

Effect of water immersion pressure on oxidation characteristics and spontaneous combustion characteristics of long-flame coal

Coal seam water injection has an obvious effect on coal dust prevention. The high-pressure water environment of coal seam water injection changes the structure of coal which brings new effects on the characteristics of coal spontaneous combustion disaster. To reveal the effects of water immersion pressure on the oxidation characteristics of long-flame coal, coal samples immersed in water at 0.1 MPa, 2.5 MPa, 5.0 MPa, 7.5 MPa and 10.0 MPa were prepared. Four experiments were conducted to study the changes in oxidation characteristics and its main reasons. The results showed that elevated water immersion pressure promoted the spontaneous combustion tendency of coal, and the composite judgment index of coal decreased to 521.1. Coal immersed in pressurized water entered the stages of oxygen-absorbing oxidation and thermal decomposition earlier than coal immersed in atmospheric pressure water. The specific surface area and average pore diameter of coal immersed in high-pressure water increased, where the pore volume proportion of mesopores of the coal immersed in water at 10.0 MPa increased by 138.5 % compared with that of the coal immersed in atmospheric pressure water. The elevated water immersion pressure prompted coal to produce further aliphatic hydrocarbons and hydroxyl groups, which improved the low-temperature oxidation capacity.

Перетворення довгополуменевого вугілля в нанопористий вуглецевий матеріал при карбонізації з гідроксидом калію

DOI: 10.31081/1681-309X-2024-0-2-32-43 Specialty 161. U.D.C. 552.576.1: 66.040.2: 661.183.2 CONVERTING LONG-FLAME COAL INTO NANOPOROUS CARBON MATERIAL DURING CARBONISATION WITH POTASSIUM HYDROXIDE © V.O. Kucherenko, Doctor of Chemical Scienses, Y.V. Tamarkina, Ph.D. in Chemical Sciences, A.V. Redko (L.M. Litvinenko Institute of Physical-Organic and Coal Chemistry of the National Academy of Sciences of Ukraine, 02160, Kyiv, Kharkiv Highway St., 50, Ukraine) The article is devoted to the study of changes in the supramolecular and porous structure of longflame coal during its transformation into a nanoporous material in the process of carbonisation with potassium hydroxide at a low KOH/coal ratio RKOH = 1.0 g/g. Samples of carbonaceous materials (CM) were prepared in argon by heating (4 deg/min) to a given temperature t (in the range of 350-825 °C), isothermal holding for 1 h, cooling, alkali washing, and drying. The samples are denoted as СM(t). The yield and elemental composition of CM were determined. The supramolecular structure of the CM was studied by XRD (Bruker D8). The interlayer distance in crystallites d002, height Lc, average diameter La and crystallite volume Vc, intensity I002 of the reflex (002) were determined. Based on the low-temperature (77 K) nitrogen adsorptiondesorption isotherms by the 2D-NLDFT-NS method, the integral and differential dependences of the specific surface area of SDFT (m2/g) and the pore volume V (cm3/g) on the average pore diameter (D, nm) were calculated (SAIEUS software). From these, the volumes of ultramicropores (Vumi), supermicropores (Vsmi), and micropores (Vmi) were calculated. The total pore volume was calculated from the amount of nitrogen adsorbed at a relative pressure of p/p0~1.0. Similarly, the specific surfaces of ultramicropores (Sumi), supermicropores (Ssmi), and micropores (Smi) were determined. It has been established that under conditions of alkaline carbonisation with KOH, long-flame coal is converted into СM with a yield of 45.3-70.2 %, a specific surface area of up to 1530 m2/g and a total volume of adsorbing pores of up to 1.091 cm3/g. With increasing temperature, the carbon content of CM decreases from 77.2 % to 71.3 % (at 500 °C), and then increases to 85.9 % (at 825 °C). The oxygen content increases to a maximum at 500 °C due to reactions in which KOH is a donor of Oatoms, and then decreases due to thermal destruction of functional groups and condensation reactions that increase the size of polyarenes of the secondary framework of the СM and form single Car-Car bonds between them. The main changes in the supramolecular structure occur above 400 °C and lead to an increase in d002 from 0.407 nm to 0.446 nm, a decrease in Lc from 0.872 nm to 0.699 nm, and an increase in the size of polyarenes La from 1.46 nm to 3.30 nm. Judging by the ~3-fold decrease in the I002 intensity, the crystallite content decreases significantly with increasing temperature, and the degree of amorphousness of the spatial framework of the CM increases. It was found that the thermally initiated reactions of coal with KOH form mainly pores with D ≤ 5 nm. With increasing temperature, the total pore volume and micropore volume increase monotonically. The values of Vumi and Vsmi increase up to 600 °C, and at 600-825 °C, the volume of Vumi decreases, since ultramicropores (D ≤ 0.7 nm) are transformed into supermicropores (D = 0.7-2.0 nm) due to the burnout of pore walls. The proportion of ultramicropore volume is maximum (23.9 %) in the sample СM(600). The proportion of the specific surface area of ultramicropores is maximum (56.3 %) in СM(500). The proportion of the micropore surface is dominant (92.6-97.0 %) in the CM obtained at t≥450 °C. The distributions of pore volume and specific surface area are characterised by maxima corresponding to subnanopores with D ≤ 1 nm, supermicropores and mesopores with D = 3-5 nm. For the СM samples obtained at 450-750 °C, there are no supermicropore maxima, but their formation occurs. It was determined that the most microporous CM are formed at 785-825 °C and are characterised by a specific surface area of 1514-1522 m2/g, a pore volume of 1.047-1.091 cm3/g, and a micropore surface area of 1415-1443 m2/g, which is not less than 93 % of the total surface. Keywords: long-flame coal, alkaline treatment, carbonisation, carbonaceous material, supramolecular structure, porosity. Corresponding author Y.V. Tamarkina, e-mail: tamarkina@nas.gov.ua

Методичний підхід до обґрунтування способу газифікації кам’яного вугілля для виробництва синтетичних моторних палив

The aim of the article is to substantiate the most suitable method of gasification of Ukrainian hard coal for further production of synthetic motor fuel. For this substantiation, a methodical approach has been developed, the use of which has allowed to obtain the following results. As a raw material base, the article recommends long-flame coal of the Western Donbass, located on the territory of the Dnepropetrovsk region, where powerful enterprises for the extraction and enrichment of coal operate. The most common methods of coal gasification in the world are analyzed: Lurgi (counter-current steam-oxygen gasification of large-lump coal (or briquettes) in a stationary bed), Siemens (direct-flow steam-oxygen gasification in the pulverized coal stream), Texaco (direct-flow oxygen gasification in the flow of coal-water pulp). For each of these methods, material balances have been developed; the composition and quality of the generated gas, the possibilities of organizing the production of the necessary energy resources, the level of emissions of harmful substances into the atmosphere and wastewater discharge have been evaluated. A methodology for calculating the composition of generator gas is proposed, which takes into account the composition of the blast (content of oxygen, water vapor or water). All calculations were performed for an enterprise with a coal capacity of 550 thousand tons of working weight per year. Based on the calculations and comparison of their results, the Texaco method is recommended for industrial implementation. The advantages of this method are as follows: the absence of a stage of steam production for gasification, the scarcity of the water cycle, which practically excludes the formation of wastewater, and the possibility of using contaminated water from other sources for gasification; the highest total content of hydrogen and carbon monoxide in the resulting synthesis gas; the maximum assimilated capacity of production reactors and the largest number of capacities created in the world using this technology; utilization of the heat of the resulting gas to obtain a large amount of electric and thermal energy.

Analyzing the flotation kinetics of long-flame coal slurry using water-soluble emulsified collector mixtures

This article investigates the variations in flotation responses of long-flame coal using emulsified collector mixtures, utilizing various flotation kinetic (FK) models for analysis. The fitting process was carried out using the Origin software. The Fourier transform infrared spectroscopy (FTIR) results indicated that as the number of adjacent H atoms increased, the absorption peak on the surface of long-flame coal, processed by various emulsified collector mixtures, gradually shifted towards short-wave numbers. Moreover, the X-ray photoelectron spectroscopy (XPS) results suggested that COC/COH groups on the coal surface could form hydrogen bonds with oxygen-containing functional groups (OCFGs) in the surfactant molecular structure. Furthermore, the hydrophobic groups of the benzene ring in 4-dodecyl phenol (4-DDP) could adsorb onto the coal surfaces through π-π bonds, enhancing the surface hydrophobicity of long-flame coal. Moreover, the flotation performance of long-flame coal was significantly improved using the emulsified mixture of kerosene and 4-DDP, achieving a peak recovery of 39.86 %. The second-order model with a rectangular distribution of floatability led to an excellent fitting to the flotation process of long-flame coal when employing the emulsified mixtures.