Home – Home – Jornals – Chemistry for Sustainable Development 2023 number 5

The ignition of hard coal grades DG, G, Zh, and K under the action of laser pulses (1064 nm, 120 µs, 1.3 J) was studied for the fractions of microparticles with a narrow size distribution in the range of 0.25-44 µm. The kinetic characteristics of the glow of samples from the entire size range were measured for each coal rank. Three stages of ignition are distinguished for each fraction. The duration of the first stage coincides with the duration of the laser pulse. The duration of the second takes a time interval of 10-15 ms (DG, G and Zh coal ranks) and 3-5 ms (K coal rank). The duration of the third stage is 60-80 ms (DG, G, and G coals) and 20 ms (K coal rank). It has been established that the threshold ignition energy densities (ignition thresholds) at all three stages depend non-monotonically on coal particle sizes. The minimum values of ignition thresholds at all three stages are achieved at particle sizes equal to 2.2 (for DG rank coal), 4.0 (for G rank coal), 0.7 (for Zh rank coal) and 2.0 µm (for K rank coal). Using the results of the proximate analysis of coals, the observed dependences of critical energy densities on the size of coal particles are interpreted.

Two methods for the transition of aqueous solutions of polyvinyl alcohol (PVA) from the liquid state of aggregation to the solid state are considered. Freezing an aqueous solution of PVA at a negative temperature and subsequent thawing at a positive temperature result in the formation of rubber-like cryogels. Another way is chemical crosslinking of kinetically individual PVA macromolecules to spatial networks having elastic properties. Sodium tetraborate was used to structure aqueous PVA solutions. The rheological properties of a two-component aqueous solution of PVA were studied. The study shows that the polymer solution exhibits the properties characteristic of non-Newtonian liquids. The kinetics of gelation of the products of chemical structuring of aqueous PVA solutions with an aqueous sodium tetraborate solution was studied. It is shown that viscosity increases with time as a consequence of chemical interaction. The mechanical properties of carbon-containing composite materials obtained by various methods have been investigated. It has been determined that the most durable materials are those formed by the cryotropic method and those chemically structured after cryogenic treatments. The stress-strain and moisture-resistant properties of carbon materials enable their use as fuel briquettes with a minimum amount of a binder. They can also serve as high-energy fuels for domestic and industrial purposes. The chemical method of structuring a PVA solution can be used for dust control in coal mines.

The procedure for obtaining humic (HA), hymatomelanic (HmA) and fulvic acids (FA) that allows achieving their high yield has been developed and tested with the brown coals of the Kansk-Achinsk and the South Ural basins. The highest yield of humic substances is achieved for naturally oxidized brown coal of the Tisul deposit: HA - 60.9 %, HmA - 11.3 %, FA - 9.6 %. The composition of native brown coals, as well as HA, HmA and FA obtained from them, was studied using proximate and ultimate analysis, FTIR spectroscopy and ¹³C NMR (CPMAS) spectroscopy. It is established that the chemical and structural-group composition of HA, HmA and FA has significant differences. The samples of HmA and FA are characterized by relatively high content of oxygen-containing aliphatic groups with the predominance of carboxylic acids and esters in comparison with HA. Higher content of carbon, hydrogen and aromatic fragments is characteristic of HA. The samples of HmA and FA have similar elemental and structural group composition, however, HmA has a higher content of carbon and aromatic fragments.

Integrated studies of green coke have been carried out by means of X-ray diffractometry, electron microscopy, electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR). It is determined by EPR spectroscopy that two types of radical structures are present in the samples: low-molecular aromatic radicals and conjugated polyaromatic structures in which the unpaired electron is delocalised. Analysis of line shapes in the EPR spectra reveals differences between the green coke samples under investigation. EPR is shown to be highly sensitive method allowing one to follow the changes of molecular structure during the production of green coke. The results obtained in the work with the help of EPR are in good agreement with the results of NMR spectroscopic studies. It is concluded that evaluation of the molecular structure of intermediate coking products is necessary to improve the composition of initial raw material and technological operations.

The article reports the results of the study of the morphology, porous structure and electrical capacitance characteristics of highly porous carbon matrices (HPCMs) obtained from coal raw materials with different degrees of metamorphism and nanostructured composites (NSCs) based on them, the surface of which is decorated with gold or manganese oxide nanosized particles (NP), accumulating electrical charge during polarization in the electrolyte via two mechanisms (formation of an electrical double layer (EDL) and involvement of pseudo-capacitance component during Red-Ox reactions on electrodes). The samples of HPCMs were obtained by high-temperature (800 ^oC) alkaline activation (the mass ratio KOH/C = 2 : 1) of fossil coal from the coal basins of the Kemerovo Region and the Republic of Sakha (Yakutia): CAK - based on anthracite of the Kiyzasskiy open-pit mine (Kuzbass), with the highest coalification degree; CBK - based on boghead (a kind of sapropel coal ) from the Taymylyr deposit (Yakutia) with the lowest degree of metamorphism; CDK - based on long-flame coal (Kuzbass) occupying an intermediate position in the metamorphism series. Results obtained by scanning electron microscopy, small-angle X-ray scattering in combination with sorptometry showed that the NSC morphology is largely determined (except for submicron aggregates) by the porous structure of the matrices. The shape of cyclic voltammetry (CVA) curves for HPCMs CDK, CBK and Au-NP filled NSC based on them indicated a significant contribution from EDL into capacitance; the contribution of pseudo-capacitance is observed for the composite MnO_x/CDK electrode. The features of CVA curves for microporous CAK HPCM and NSC based on it are probably caused by hindered diffusion. The specific electrical capacitance is higher as a result of the polarization of CDK and CBK HPCM with large proportions of mesopores, as well as NSCs on their basis, than that resulting from the polarization of microporous CAK and the corresponding composites. For all three HPCMs, the introduction of fillers causes an increase in the electrode capacitance. The effect is more significant for NSCs obtained from hard coals with a low level of metamorphism (an increase up to 1.8 and 1.6 times with respect to the capacitance of initial matrices for NSCs based on CDK and CBK, respectively, according to the impedance measurement data), which is due to a decrease in the active resistance and the charge transfer resistance of the cells, and, in general, to the active component of the impedance.

The morphology of nanoparticles, structural-phase properties, and phase transformations that occur during heating in the nanostructured CoPt and CoPd systems rich in precious metals, obtained by co-reduction of aqueous precursor solutions by hydrazine hydrate, were studied by X-ray phase analysis and X-ray structural analysis, small-angle X-ray scattering, and high-resolution transmission electron microscopy. The results obtained are of interest for the development of the fundamentals of materials science of bimetallic nanoalloys, and provide a key to understand the processes of the formation of FePt, CoPt and FePd nanoalloys while heating intermetallic compounds with a highly ordered structure L1₀, which possess record-setting magnetic and magneto-optical properties.

The work is concerned with the development of a new type of iron-containing catalyst (Ct) based on lignin for the hydrogenation of carbon monoxide. Catalytic systems were obtained by hydrothermal synthesis and studied using a set of physicochemical methods (Fourier transform IR spectroscopy, Raman spectroscopy, low-temperature nitrogen adsorption, elemental analysis, atomic absorption analysis, X-ray phase analysis, X-ray photoelectron spectroscopy, transmission electron microscopy). Brunauer-Emmett-Teller (BET) surface area analysis, elemental analysis, atomic absorption analysis, X-ray fluorescence (XRF), transmission electron microscopy (TEM). It is shown that the formed catalysts are fine-grained, non-pyrophoric, non-hygroscopic, black powders. The catalytic systems are determined to exhibit high activity in carbon monoxide hydrogenation: the conversion is close to 100 %, the productivity with respect to С₅₊ hydrocarbons reaches 131.6 g/(kg Ct ∙ h).

The effect of hydrothermal carbonisation temperature (190-250 °C) on the properties of biochar produced from hydrolytic lignin was studied. Biochar was investigated using a set of physicochemical methods, its elemental, proximate and thermal analysis was carried out. It is shown that an increase in the temperature of hydrothermal treatment has a negative effect on biochar yield but allows obtaining a more thermally stable product with fuel characteristics comparable with those of brown coal.

Ni-, Co- and Ni–Co-containing catalysts for steam reforming of isobutanol were obtained by biochar impregnation with water-alcohol solutions of metal salts. Biochar was synthesised by the hydrothermal carbonisation of cellulose with subsequent thermal treatment of the obtained materials under the conditions of limited oxygen access. The catalysts were characterised using a complex of physicochemical methods (IR spectroscopy, BET, temperature programmable desorption of ammonia, scanning electron microscopy in combination with local electron microprobe analysis, X-ray phase and X-ray fluorescence analysis). It is found that the sample 2.5Ni-2.5Co/C (where the number before the metal symbol means its mass content calculated for the mass of reduced catalyst, %) provides a high yield of hydrogen (58%) from isobutanol reforming.

To develop an effective catalyst for the resource-saving conversion of coal-industry methane into hydrogen-containing gas, the materials Ce_0.2Ni_0.8O_1.2/Al₂O₃ were synthesized, their physicochemical and functional properties were studied depending on the nature of the precursors of active components (nickel(II) nitrate hexahydrate, nickel(II) ammonium oxide) and promoters (cerium(III) nitrate hexahydrate, ammonium cerium(IV) nitrate). It is shown that the nature of the precursor affects the textural and structural characteristics of the samples, their catalytic activity in the steam-carbon dioxide reforming of methane and resistance to the formation of carbon deposits. The optimal composition of precursors (nickel(II) nitrate hexahydrate, cerium(III) nitrate hexahydrate) has been established, the use of which in the synthesis of the Ce_0.2Ni_0.8O_1.2/Al₂O₃ catalyst ensures a decrease in the average particle size of the Ni active component (25 → 6.5 nm) and the degree of catalyst carbonisation (2.9 → 0.5%), high hydrogen yield (95%) at 800 °C in the steam-carbon dioxide reforming of methane.

The effect of the temperature regimes of hardwood sawdust thermochemical treatment (hydrothermal carbonization and torrefaction) on biochar properties and combustion characteristics are investigated. The mass yields of biochars were considered from the viewpoint of the processes that take place during thermochemical treatment, along with the changes in the elemental composition resulting from these processes. The optimal method and temperature regime of thermochemical treatment were determined. The effect of the method and temperature of sawdust thermochemical treatment on the composition of gaseous products from biochar combustion was assessed by FTIR spectroscopy combined with thermogravimetric analysis. Two main stages of biochar combustion were detected: the phase of removal and combustion of volatile substances (up to 400 °C) and the phase of semi-coke combustion (above 400 °C). The analysis carried out by means of FTIR spectroscopy during combustion allowed us to determine the released components of the gaseous mixture and to observe thermochemical decomposition of biochar components in the real time mode. Investigation of biochar combustion showed that an increase in sawdust processing temperature reduces the formation of gaseous products at the first stage of combustion and promotes an increase in the amount of carbon dioxide at the second stage.

Adsorption treatment of industrial wastewater and reservoir water from toxic metals can reduce the anthropogenic load on water bodies. The efficiency of using an adsorbent obtained on the basis of local mineral raw material, namely burnt rock from the Erunakovskoe coal deposit (the Kemerovo Region), to remove heavy metal ions from aqueous solutions is shown. The kinetics of cadmium ion extraction from aqueous solutions, the adsorption models of Freundlich, Langmuir and Dubinin-Radushkevich, and their significance for the description of heavy metal ion recovery from aqueous solutions using burnt rock were studied. The dependence of adsorption on the acidity (pH) of the medium has been established. A maximum adsorption capacity of 30 to 40 mg/g was achieved at pH 12.0. Chemical modification with alkali (NaOH) at pH 12.0 leads to an increase in the degree of cadmium ions extraction. Within the studied concentration range, the Freundlich and Langmuir isotherms are more consistent with the experimental data on the equilibrium adsorption of metal ions on burnt rock, compared to the Dubinin-Radushkevich model.

A mesoporous carbon sorbent modified with sulphosalicylic acid by adsorption from aqueous solutions has been synthesized. The optimal modification parameters were selected: the ratio, concentration, the duration of impregnation and heat treatment stages, and pH. The physicochemical properties of the samples have been studied: textural characteristics, qualitative and quantitative composition of surface functional groups, the amount of applied modifier, adsorption and desorption properties. The adsorption characteristics of the studied samples with respect to organic dyes methylene blue and methanyl yellow are determined. It has been established that during desorption for 48 h, ~68 and ~82% of the initial concentration of sulphosalicylic acid applied to the sample pass into the aqueous solution, modelling the intestinal medium and into ethanol, respectively. In this case, a decrease in the pH of the initial solutions by 6 units is observed. High antibacterial properties of the modified carbon sorbent towards Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, and Klebsiella pneumoniae have been established in vitro .

Compositions for the formation of three-component elastic cryogels based on the aqueous solutions of polyvinyl alcohol (PVA) and potato starch are proposed. It is shown that the viscosity of aqueous solutions depends both on the kind of polymer and on the total content of polymers in the system. The elasticity modulus of three-component cryogels depends on the concentration of starch in them and increases from 5 to 15 kPa with the addition of starch in the amount of 1-5 wt%. By introducing a dispersed material (soil) into the matrix of two-and three-component cryogels, due to the high adhesion of the polymer to the filler, the filled cryogels were obtained, with the elasticity modulus 16 times higher than that of cryogels without the filler. The introduction of potato starch in the amount of 5 wt% into PVA cryogel caused an increase in the time of its complete drying by 24 h, and an increase in its destruction during exposure in water by 5% within a week. Two-component cryogels exhibited sharply different types of behaviour during storage in water: PVA cryogel did not lose its mass, while mass loss by the cryogel of potato starch was 11% within a week. A decrease in the mass of three-component cryogels by 75-89% due to the loss of moisture and destruction was demonstrated in the soil test under the action of aboriginal soil microflora. The mass loss by the two-component cryogel based on PVA was 60%. Soil testing for phytotoxicity after the destruction of three-component cryogels revealed a decrease in the germination capacity of white mustard ( Sinapis alba L.) by 2-10% with respect to the reference experiment, depending on starch content, while for the reference two-component PVA cryogel the corresponding decrease was by 18%. Cryostructuring of the upper soil layer by PVA cryogel caused an increase in the dry above-ground mass of plants by 3.2% in comparison with the reference, while the cryogel with potato starch caused an increase by 7.1%, and cryogel based on PVA and potato starch gave 9.4%.

Methanation process, or selective hydrogenation of carbon oxides, is described. The chemical foundations of the process and the features of the formation of reaction products are considered, depending on the catalyst used. The advantages of catalytic systems based on carbon materials and disadvantages of the catalysts on oxide substrates for the production of synthetic methane are evaluated. Nickel-containing carbon catalysts based on birch activated carbon and microcellulose were obtained by incipient wetness impregnation and hydrothermal synthesis, and proposed for the selective hydrogenation of carbon monoxide (СО). The synthesized samples were studied by optical emission spectroscopy with inductively coupled plasma, low-temperature nitrogen adsorption, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, thermogravimetric analysis. The influence of the substrate and the method of catalyst synthesis on CO conversion and methane yield from the selective hydrogenation of CO was studied, and the optimal size of NiO and Ni(OH)₂ crystallites, the precursors or the active phase, was determined. It is shown that the best carbon monoxide conversion and methane yield from methanation reaction are achieved in the presence of nickel-containing microcellulose-based carbon sample obtained by hydrothermal synthesis.

An algorithm is presented for identifying potential production chains for resource-based regions relying on patent analytics, in particular, applying patent landscape report creation approaches and peer review, which in the future, after their economic justification, can become the foundation for the new strategy of innovative development for a resource-based region. Within this strategy, it is planned to create new high-tech economy sectors in the field of coal mining and coal processing.

The breadth of the use of activated carbons (AC) in many areas of economy, ecology and defense of the country is shown. The unique physicochemical characteristics of AC are denoted, and their modern determination is presented. It is established that the Russian Federation is currently lagging far behind industrialised countries in the output of AC production. Attention is paid to the coals of Kuzbass as a raw material for the large-tonnage production of AC. Various technologies for manufacturing active coals on this basis are considered.