Solid Fuel Chemistry最新文献

Macroporous carbon materials (macro-PCMs) were obtained using a matrix synthesis approach which consists in the deposition of pyrolytic carbon (PC) on a matrix of P803 carbon black (CB) during its high-temperature treatment in hydrocarbon medium. The microstructure, morphology, and porous structure of synthesized macro-PCMs were studied using a set of methods, such as transmission and scanning electron microscopy, X-ray diffraction, Raman spectroscopy, low-temperature nitrogen adsorption, mercury porosimetry, and helium pycnometry. It was shown that PC is deposited on the CB matrix surface both in the form of ordered graphene layers and as wedge-shaped particles. Two stages of the macro-PCM formation can be distinguished. At the first stage (α < 0.66 g of PC per g of CB), the most accessible macropores with sizes of >100 nm are predominantly filled with PC and then, at the second stage (α > 0.66 g of PC per g of CB), pores with sizes of <100 nm are also filled. A decrease in the specific pore volume V_>100 from 0.48 to 0.26 cm³/g_CB occurs with volumetric filling of large macropores (>100 nm) between aggregates, while the PC deposition at α > 0.66 g/g leads to a decrease in V_<100 to 0.077 cm³/g_CB and to an almost constant value for V_>100.

When coal resources enter deep mining, the coal body is exposed to a complex geological condition characterized by “high ground stress”, “high osmotic pressure” and “high temperature”. Under such geological conditions, the permeability evolution law of the coal body is determined by the coexistence of multi-phase and multi-field coupling. Moreover, the permeability of the coal body directly impacts the safety of coal mining operations. Thermodynamic coupling tests were conducted on coking coal samples. The scanning electron microscope and high-pressure adsorption instrument were employed to characterize the pore structure and adsorption capacity on the coal surface. Subsequently, the changes in the coal pore structure and gas displacement efficiency before and after the thermodynamic coupling treatment were compared and analyzed. The results demonstrated that, under thermodynamic coupling, the adsorption of CH₄ in the coal rises with the increase in pressure. However, as the temperature increases, the adsorption of CH₄ in the coal exhibits an opposite tendency. With the growth of injection pressure, the replacement ratio of CH₄ decreases linearly. Likewise, with the elevation of temperature, the CH₄ replacement ratio also diminishes. After the thermodynamic coupling, the pore structure of the coal sample is well-developed and the porosity is enhanced. The research findings can offer a theoretical foundation and technical guidance for the study of multi-field coupled gas migration and coal seam gas treatment.

The peculiarities of changes in the composition of SS grade coal prone to spontaneous combustion after its treatment in gas environments of various chemical activities (nitrogen, air, and carbon dioxide) were investigated. The effect of gases on changes in the chemical composition of the coal surface and the adsorption capacity to oxygen during low-temperature oxidation of coal in the air was established. The EPR-spectroscopic data indicated the recombination of free radicals at the initial stages of coal oxidation followed by an intensification of their formation when coal samples were exposed to air. An analysis of changes in the rate of oxygen absorption and the composition of the gas phase indicated the highest sorption activity to oxygen of a coal sample treated in an inert nitrogen environment. The crushing of coal in an atmosphere of air led to the primary oxidation of the native outer surface and a decrease in the sorption capacity to oxygen at the initial stage of its determination. The adsorption of carbon dioxide on an accessible coal surface was accompanied by a transformation of its functional composition and, thereby, a slowdown at the initial stages of oxidation.

To develop a sustainable approach for coal pitch utilization, oxidation of commercial coal pitch in aqueous NaOCl solution was investigated. Effects of feeding methods, reaction temperature and time on coal pitch oxidation conversion rate were investigated. The maximum oxidation conversion rate was 17.4% at the optimized conditions of 50°C and 6 h, with multi-stage feeding method using 75–25–25 mL NaOCl solution. A mathematical regression model is developed to predict the oxidation conversion rate of coal pitch, which can accurately capture the reaction behavior observed in the experimental data (R² = 0.976). The oxidized pitch residue was characterized by FTIR, and the extracted products were analyzed by GC-MS. The results suggest that NaOCl oxidation is an effective treatment under mild conditions, obtaining value-added organic chemicals. Hydroxyls and carbonyls were introduced into the structure of the oxidized coal-pitch; 33 organic-compound products were detected, including value-added chemicals, i.e. naphthalene, phenanthrene, and anthraquinone. Thus, the aqueous NaOCl treatment exhibits a good potential to improve the economy of commercial coal pitch application.

The article presents the results of studies of the distribution of rhenium in black (dictyonema) shales of the Baltic basin in the Kaibolovo–Gostilitsy area located in the Leningrad oblast. Rhenium contents exceeding the levels of minimum industrial concentrations in known types of complex ores have been determined. The distribution of rhenium in the organic and mineral matter of black shales has been studied. The distribution of rhenium in the dictyonema shale formation over the area and in the section of the shale-bearing stratum and the conditions under which rhenium mineralization was formed are described. The rhenium resources in the dictyonema shales of the Russian part of the Baltic basin should be considered as a new unconventional source of this valuable strategic metal.

The distribution and kinetic analysis of catalytic hydrogenation products derived from preasphaltenes (PA) were examined. A kinetic model was developed using the lump kinetic method to simulate the hydrogenation of PA catalyzed by FeS and S. The study revealed that PA is directly converted into asphaltenes (AS) and oil, followed by the further hydrocracking of AS into oil and gas products. At higher temperatures, there is a noticeable regression of PA to char and AS back to PA. Increased temperature and longer reaction time were found to enhance the conversion of PA and the yield of oil and gas products. Under conditions of 400°C and 60 min, the hydrogenation of PA achieved a conversion rate of 75.92% with an oil and gas yield of 32.76%. The hydrogenation conversions from the model corresponded well with experimental data, and the activation energies ranged from 67 to 224 kJ · mol^–1.

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.