Solid Fuel Chemistry最新文献

The article considers the methods of fulvic acid (FA) extraction from brown coals by the Tyurin–Forsyth method and by liquid-phase extraction with n-butyl alcohol. The data of technical and elemental analysis and IR and ¹³C NMR spectroscopy of the obtained fulvic acid samples and their fractions are presented. A comparative characterization of the obtained fulvic acids is carried out. It was established that the fulvic acid fractions obtained by the Tyurin–Forsyth method had a higher aromaticity index ( f_ar = 32.79–61.54%) than the fulvic acids obtained by liquid-phase extraction with n-butyl alcohol ( f_ar = 20.64%). Conclusions were made on the possibility and efficiency of using the liquid-phase extraction method with n-butyl alcohol for extracting brown coal fulvic acids.

The combustion behavior of a wet mixture of sludge from a pulp and paper plant and municipal waste was analyzed through complementary experiments. The collected mixed sludge was first naturally dried to decrease its initial moisture percentage to 5–9%. Pure water with mass proportions between 30 and 60% was added to the naturally dried samples to analyze their combustion behavior. Thermogravimetric experiments were carried out with the dried and humidified samples under air and at heating rates between 5 and 100 K/min. The thermogravimetric profiles and the heat flows of the dried and humidified samples were compared. The emissions of CO, CO₂, and total hydrocarbons were measured during further combustion experiments carried out at isothermal temperatures of 600, 700, 800, and 900°C.

To explore the impact of mine water composition on the spontaneous combustion properties of coal samples, the physicochemical characteristics of untreated raw coal (RC) and coal samples soaked in mine water (SC) were comparatively analyzed. The findings indicate that the chemical components of mine water significantly influence the spontaneous combustion behavior of coal. Electron microscopy experiments demonstrated noticeable changes in the surface morphology and pore structures of SC, leading to an increased oxidation rate and a heightened risk of spontaneous combustion. Energy dispersive spectroscopy (EDS) analysis revealed a decrease in carbon content alongside an increase in oxygen and sulfur concentrations on the SC surface, further facilitating the spontaneous combustion process. Simultaneous thermal analysis experiments indicated that characteristic temperatures, such as pyrolysis and ignition points of SC, were generally lower than those of RC, suggesting a stronger propensity for spontaneous combustion. ¹³C NMR results showed a higher content of oxygen-containing functional groups in SC compared to RC, although the aromatic carbon content remained similar. A comprehensive evaluation suggests that SC exhibits an enhanced tendency towards spontaneous combustion. Additionally, programmed temperature experiments revealed that temperatures at which SC generated spontaneous combustion indicator gases were consistently lower than those observed for RC, reinforcing the conclusion that SC possesses a higher spontaneous combustion tendency. In summary, soaking coal samples in mine water substantially increases their spontaneous combustion risk by modifying their physicochemical properties.

The article presents the results of a study of unoxidized and naturally oxidized (weathered) brown and hard coals of early diagenesis and humic acids (HAs) and fulvic acids (FAs) obtained from them. Using ¹³C NMR (CP/MAS) spectroscopy, it was found that the structural-group composition of the isolated HAs was determined by the composition of the original coals (R² = 0.81), and it affected the magnitude of biological activity using wheat seeds as an example (R² = 0.75). The structural-group composition of the isolated FAs was weakly related to the composition of the original coals, and it was more homogeneous. The high quantitative yield and biological activity of HAs and FAs from unoxidized and oxidized brown coals allowed us to recommend them for agriculture. The HAs and FAs from oxidized coals had low biological activity, and they can be considered as technical reagents.

The property of the coal surface to be wetted with various liquids is important for many technological processes of coal mining, sorting, processing, and transportation. In this work, we used the determination of the contact angle of the coal surface and the filtration of liquid through a layer of coal powder to characterize the wettability. The influence of changes in the chemical composition and porosity of coals in the series of their metamorphism on the wettability characteristics was estimated. It was shown that the wettability and filtration properties of coals exhibited an extreme dependence with a minimum at the middle stage of metamorphism.

The paper presents the results of an assessment of the influence of coals’ structural features on their proneness to spontaneous combustion. Fifteen samples of hard coals and anthracite from different deposits of the Russian Federation were used as objects of study. Based on the deconvolution of coal vitrinite Raman spectra, a structural index characterizing the ratio between amorphous and crystallite forms of carbon compounds has been identified. It is noted that this index differs significantly for coals with a close stage of metamorphism. For the studied coals, the activity to ozone was determined for two types of sites that are differing in the rate of deactivation when interacting with it. It is shown that the activity of sites of the first type (with a higher deactivation rate when interacting with ozone) grows with an increase in the proportion of crystalline carbon in the coals’ vitrinite. Whereas, the activity of sites of the second type (with a low rate of deactivation) generally decreases. The kinetic parameters of coal combustion (ignition temperature and activation energy) were estimated according to their thermogravimetric analysis in the air environment. It is shown that with an increase in the proportion of amorphous carbon compounds in vitrinite of coals, both the ignition temperature and the activation energy of coal combustion decrease, which altogether leads to an increase of a risk of spontaneous combustion.

The distribution of organic chlorine in the fractions of semicoking resin of the oil shale from the Perelyubskoye deposit was studied. The highest concentrations of organochlorine compounds were determined in the resin fractions with boiling ranges of 100–120, 140–160, 240–260, and 280–320°C. Based on the experimental data, possible ways of further use of shale resin were proposed.

The sedimentation in high-paraffin oil with the addition of different resins and an inhibiting additive was studied. It was found that the amount of oil sediment decreased with an increase in the concentration of resins in oil with a lower surface tension and a large number of heteroatomic components. With an increase in the fraction of resins with a higher content of polysubstituted aromatic structures, an increase in the amount of oil sediment and a decrease in the efficiency of the inhibiting additive were observed. With an increase in the amount of oil resin additives, the fraction of low-molecular-weight n-alkanes in the composition of asphalt–resin–paraffin deposits (ARPD) decreased and the average sizes of paraffin hydrocarbon aggregates decreased.

The article presents the results of studying resins isolated from the liquid cracking products of sulfur tar from the Omsk Oil Refinery. Thermal treatment was carried out at 500°C for 15, 30, 45, and 60 min. It was found that the yield of coke increased with the duration of tar cracking due to the condensation of resins into asphaltenes and then into coke. Changes in the structural-group parameters of resins in the course of cracking process were established using ¹H NMR spectroscopic data, elemental composition, and the results of molecular weight measurements. Averaged resin molecules became more condensed, and they were characterized by an increased concentration of aromatic fragments and a decrease in the numbers of naphthenic fragments and aliphatic substituents. The set of data on changes in the composition of cracking products together with an analysis of sulfur distribution in the products indicated a significant contribution of sulfur-containing structural fragments of resins to the accumulation processes of thiophene derivatives. It was shown that the cracking of resins was accompanied by the formation of a wide range of low-molecular-weight sulfur-containing compounds in the composition of oils.

The paper presents the results of the initiation of chemical transformations of humic acids (HAs) in a barrier discharge plasma. The HAs were treated with ammonia vapor in the presence of various gas atmospheres like ethylene, air, oxygen, carbon dioxide, and mixtures with argon. A decrease in the number of paramagnetic centers after treatment of HAs in a barrier discharge was revealed using EPR spectroscopy, which indicated the recombination of free radicals in their structure. As revealed by IR spectroscopy, the intensity of an absorption band at 1383 cm^–1 corresponding to the NO₃ group increased when HAs were exposed to discharge plasma in air. When HAs were treated with ammonia vapor in an argon atmosphere, ammonium humate, which is completely soluble in water, was formed.