Home – Home – Jornals – Chemistry for Sustainable Development 2019 number 6

Laser ignition (λ = 1064 nm, τ_i = 120 ms) of the coal samples of different marks from the Kuznetsk coal basin was studied. Three consecutive stages of ignition were detected for all marks of coal. These stages are characterized by the threshold radiation energy densities H_cr⁽¹⁾, H_cr⁽²⁾, H_cr⁽³⁾ which are characteristic for each coal marks. It was established that the first stage involves surface heating and ignition of micro protrusions on coal particles. The duration of this stage does not exceed the time of the laser pulse. At the second stage, volatile matter are observed to evolve and ignite. The duration of combustion depends on the density of radiation energy. Ignition of the nonvolatile residue occurs at the third stage, upon reaching H_cr⁽³⁾; burning time is 40-150 ms. It was demonstrated that the threshold value at the first stage varies only slightly for all coal marks. For bituminous coal, the second threshold decreases with an increase in coalification degree, while the third threshold increases. The second and the third thresholds for lignite are comparable with the values of H_cr⁽²⁾ and H_cr⁽³⁾ for low metamorphic bituminous coals. Experimental results allow us to conclude that ignition occurs at the first and the third stages according to the heterogeneous mechanism, while at the second stage it occurs according to a homogeneous mechanism.

Thermal reactions proceeding through hydrogen transfer from the polyaromatic compounds of coal tar pitch to model organic compounds (nitrobenzene, chlorophenols, and chloraniline) are investigated. Within the temperature range 270-360 ^оC, there is a complete conversion of nitrobenzene into aniline (with a yield of 75-82 %) and condensation products remaining in the pitch. It was found that 4-chlorophenol enters hydrodechlorination starting at a temperature of 300 ^оC and leading to the formation of phenol and condensation products. The reactivity of 2,4-dichlorophenol and 2,4,6-trichlorophenol is higher than that of 4-chlorophenol. The features of the reactions are compared using coal tar pitch and hydroaromatic compounds as hydrogen donors.

The oxidation of biofuel samples with different lignin content (10, 20 and 70 %) was studied. The kinetic parameters of combustion reactions were obtained which allowed us to consider the process as a two-stage one. The sample with 20 % lignin content was shown to have a high reactivity in oxidation reactions.

The properties of the pitch samples obtained through the thermal dissolution of coal were studied using a unit with a flow tubular reactor. Their main differences were analyzed in comparison with coal-tar pitch. It was shown that in terms of elemental composition, extractive pitches are characterized by lower carbon content and a high percentage of oxygen, compared to the traditional binder. Their technological parameters are characterized by increased softening point and low coke residue. These features are a consequence of molecular composition. According to IR and NMR spectroscopy, the aromaticity factor of the alternative binder is relatively low, the organic matter contains a large number of aliphatic groups (-CH₂- and -CH₃), as well as polar oxygen-containing groups such as carbonyl, ether, etc. The latter groups have a negative effect on the rheological properties of extractive pitch. The influence of coal type and coal-oil paste composition on the yield and quality indicators of the pitch-like products of thermal dissolution was analyzed. The use of a coal-solvent mixture with the high percentage of coal is not reasonable because of the high viscosity of final extractive pitches, which hinders the preparation of a homogeneous mixture for the formation of carbon-graphite products.

The influence of the dry (in the air, without water) and wet (in water) method of brown coal grinding on the extraction efficiency and structural group composition of the extracted humic acids (HA) was studied. The samples of liquid and powder humic preparations (HP) from brown coal of the Tisulskoye deposit (Kaychakskiy site) were produced. The samples were obtained using the original set-up, which allowed us to achieve the high yield of HA using ultrafine grinding of the raw material in the dry form or in the aqueous solution of an alkali. The technical characteristics and regimes of equipment operation are presented. All the samples were characterized by means of technical and elemental analysis, ¹³C NMR (CPMAS) and FTIR spectroscopy. Granulometric composition and specific surface area of coal samples after dry and wet grinding were determined. It was established that the wet method allows achieving more complete extraction of HA from brown coal due to an increase in the surface area of the contact between coal and the alkali. Both methods of grinding do not have a significant effect on the structural group composition of extracted HA and their biological activity.

The activity of monometallic (Ni/γ-Al₂O₃, Co/γ-Al₂O₃) and bimetallic (Ni-Co/γ-Al₂O₃) catalysts supported on γ-aluminium oxide for dry reforming of methane into synthesis gas was studied. It was determined that the bimetallic catalyst is more active than monometallic. A set of methods (X-ray phase analysis and temperature-programmed reduction with hydrogen) was applied to reveal that the addition of Co to the composition of Ni/γ-Al₂O₃ leads to the formation of a surface bimetallic alloy Ni-Co, which plays an important role in suppressing the formation of carbon deposits on the catalyst surface and increasing its activity.

Preparation and properties of nanostructured composites promising for the development of electrode materials for supercapacitors are considered. The composites are based on carbon fibres made of multiwalled carbon nanotubes (MCNT), filled with the nanoparticles of mixed cobalt and nickel hydroxides which are deposited on the surface and in the channels of these nanotubes. The composition and morphology of nanostructured composites were studied using transmission electron microscopy and X-ray diffractometry, including the method of small-angle X-ray scattering and X-ray fluorescence analysis. The electrochemical properties of the obtained electrode nanocomposite material were considered. It is shown that variations of the cobalt to nickel ratio in the composition of the mixed hydroxide lead to significant changes in the electrochemical properties of composite electrodes. In general, an increase in their capacitance is due to the contribution of the pseudocapacity of nickel-cobalt hydroxides, and the highest capacitance values are achieved with the Co/Ni ratio close to 1 : 1. Analysis of voltammetric curves also revealed a decrease in the specific electric capacity of the electrode material with an increase in scanning rate for samples having a pseudocapacity component, which was obtained by matrix functionalization and the introduction of cobalt and nickel hydroxides, because redox reactions on the electrodes proceed with lower rates than charge accumulation due to the double electrical layer. The functionalization of carbon nanofibres consisting of multilayer carbon nanotubes was carried out by ozonation, followed by the introduction of a hydroxide filler containing transition metal hydroxides. This treatment caused an increase in their specific electric capacity, thus it is promising for the development of highly efficient electrode materials based on carbon matrices.

The texture characteristics of carbon sorbents obtained from coal of five different grades from Kuzbass were studied. The sorbents were prepared through alkaline activation using potassium hydroxide. The alkali-coal mixture was homogenized by mechanical mixing at the KOH/coal mass ratio of 1 : 1. It was shown that the sorbents prepared from coal activated with KOH have a developed porous structure and pronounced microporosity. The structure of micropores is practically independent of coal grade. The contribution from mesopores into the porosity of the sorbents is insignificant and is observed only for fat coal. It was established that the specific surface and pore volume of the sorbents increase with a decrease in the degree of coal metamorphism. The sorbent prepared from subbituminous coal has the highest textural characteristics: its specific surface area is 1340 m²/g, pore volume 0.58 cm³/g. The minimal values are characteristic of lean coal: 780 m²/g and 0.33 cm³/g, respectively.

The synthesis of nanostructured systems based on transition metals and the investigation of their physicochemical properties is one of the urgent problems of material science given the expanding area for the application of these materials. The paper presents the results of the voltammetric study of potentiostatic electrodeposition and anodic oxidation of iron-nickel and iron-cobalt nanostructured systems with glassy carbon electrodes in various electrolytes. It was found that the electrolytic synthesis of these nanostructured systems free of oxide-hydroxide impurities can be carried out in sulphate, ammonia-tartrate and chloride media. According to the voltammetry data, the phases of solid solutions with variable composition are formed during the deposition process, and their anodic dissolution proceeds by the uniform mechanism. Metal deposition rates were compared, and an approach allowing one to calculate the compositions of electrodeposited nanostructured alloys was proposed. The capabilities of anodic and cyclic voltammetry in the characterization of nanometallic deposits were shown.

Structural, morphological and electrochemical properties of the electrode material for supercapacitors which consists of a porous matrix with embedded mixed cobalt-nickel oxide nanoparticles were investigated. The synthesis of nanostructured composite was carried out by thermal decomposition of mixed nickel and cobalt azides on the surface of multi-wall carbon nanotubes. X-ray diffraction analysis and small-angle scattering were used to determine the composition and to estimate the dispersion characteristics of the obtained oxide nanoparticles. Investigation of the electrochemical properties of synthesized electrode materials by means of cyclic voltammetry showed that the growth of their electrical capacity is proportional to an increase in the content of nickel cobaltate NiCo₂O₄ in the composite, while the dependence for cobalt oxide Co₃O₄ is more complicated. Electrode materials based on nanostructured carbon - nickel cobaltate composite С/NiCo₂O₄ provide a significant increase in electrical capacity, compared to the capacity of the original carbon matrix.

The absorption capacity of different types of coal from the largest deposits of West Siberia (Kansk-Achinsk, Kuznetsk and Gorlovskiy basins), composition and content of biogenic elements in the form of cations (K⁺, Na⁺, Ca²⁺ and Mg²⁺) in water-soluble and exchange forms are studied. It is shown that the absorption capacity of coal, as measured by cation exchange capacity, increases with an increase in the coal metamorphism degree in the sequence: anthracite → coal → brown coal, and with an increase in dispersity of carbon particles from coarse size fractions to smaller ones. The major exchange positions in coal are occupied mainly by calcium, which, in turn, negatively affects the ability of coal to participate in the exchange processes with other biogenic elements. The ability of coal to absorb cations from solutions is largely determined not by the geologically caused density and porosity of coal but mainly by the total surface area of particles. The values of the cation exchange capacity of coal are comparable with the values for the most fertile soils of West Siberia (agrochernozems) and their parent rocks (loess-like loam) or even exceed them.

The data on the effect of ozonation on the component composition and chemical properties of spent mineral engine oil are presented. It is shown that as a result of ozonolytic treatment, the relative content of aromatic and unsaturated compounds decreases in the composition of the waste oil, with an increase in the proportion of low-boiling components in the form of alkyl, alkyl ether and alicyclic structures. The content of aliphatic carboxylic acids, ethers and esters with linear and cyclic structure, lactones and anhydrides, which replenish the composition of resinous products, increases. The possibility of waste oil purification from mechanical impurities and resinous products by ozonation was revealed, and the optimal process conditions were determined, which correspond to ozone consumption of about 11 g/kg. The products of ozonation of the used engine oil - purified oil, resins, mineral deposits - can be reused in chemical, petrochemical and construction branches of industry as raw materials or their components.

Nanostructured composites Mn_xO_y/multiwalled carbon nanotubes (MCNT) with a mass ratio of Mn/MCNT 2 : 98; 5 : 95; 10 : 90 were prepared by the reduction of KMnO₄ aqueous solution on the surface of a carbon material (matrix) at a temperature of 25, 60 and 80 °C. Non-ozonized MCNT-1 and ozonized MCNT-2 were used as the carbon matrix. Nanocomposites were studied by means of X-ray phase analysis, small-angle scattering of X-ray radiation, and a complex of electrochemical methods. The influence of the conditions for producing nanocomposites (temperature, ultrasonic radiation) and the filler content on their electrical capacity characteristics were considered. It was determined that the optimal Mn/MCNT ratio was 5 : 95; with an increase in the content of manganese oxides (Mn/MCNT up to 10 : 90) and potential scanning rate higher than 40 mV/s, the electric capacitance of some samples was lower than that of the initial carbon nanotubes. For samples containing non-ozonized multiwalled nanotubes, the highest capacitance was observed for materials obtained at 80 °C; for ozonized samples, the optimum synthesis temperature was 60 °C. For optimized composition and conditions for the preparation of samples, the specific electric capacitance in asymmetric cells exceeds the specific electric capacitance of the electrodes based on the initial matrices by a factor of 1.5-2.9. Using the methods of galvanostatic charge-discharge and impedancemetry, it was established that electrochemical cells with nanocomposite electrodes have a higher capacitance and low internal resistance. It was discovered that sonication of the reaction medium during the preparation of nanocomposites leads to deterioration in the electrical capacity characteristics and to a noticeable increase in the internal resistance of the cells, especially the active component of the impedance.

A comprehensive study of the functional and group compositions of hexane-insoluble coal-tar pitch asphaltenes was carried out by chemical elemental analysis, nuclear magnetic resonance (NMR), infrared spectroscopy (IRS), and thermal analysis, and gas chromatography in combination with mass spectrometry. It was shown that the hydrocarbon skeleton of an average hypothetical asphaltene macromolecule can be considered as a set of condensed aromatic nuclei of the re-condensed type containing 7 rings, which have alkyl substituents and connecting bridges, consisting of 2 carbon atoms on average. Moreover, the structure contains one S, N, or O atom on average per 500, 50, or 167 carbon atoms, respectively, and one hydrogen atom per 2 carbon atoms. The ratio of various structural units in the powder of asphaltenes is as follows: there are 4-5 N- and 1.3-1.7 O-containing structures per one S-containing structure. Sulphur atoms are present in thiophene-like, thermally stable fragments of the structure, and pass into the coke residue without decomposition. Oxygen is in thermally unstable carboxyl and phenolic groups decomposing with the evolution of CO₂, as well as in aromatic esters passing into the coke residue. The data obtained using different methods are in good agreement with each other and will allow modeling the structural unit of coal tar-pitch asphaltene macromolecule.

Asphaltenes as self-organizing supramolecular structures are of great scientific and practical interest. An urgent problem is to reveal the regularities of the directed formation of planar associates of asphaltenes and condensed graphite-like structures. For the purpose of investigating the self-organization of the molecular aggregates of coal-tar pitch asphaltenes, the morphology and structure of the particles of asphaltene powder obtained from coal-tar pitch asphaltenes by method of selectively soluble groups was studied by complex of physicochemical methods. It was shown that the crystal structure of asphaltene powder particles is represented mainly by turbostratic carbon structures. According to XRD data, the coke residue after the thermolysis of asphaltenes is characterized by the presence of crystallites consisting of naphthenoaromatic layers.

The biological activity of humic acids produced from the coals of the Kansk-Achinsk and South Ural basins was evaluated by means of phyto-testing in a series of laboratory and field tests. A connection between the structural group parameters of the organic acids of humic preparations (humic acids) and their biological activity was revealed in the series of field experiments at the sites characteristic of the most widespread technogenic landscapes of Siberia. It was established that in the case when humates are applied at the burrows of open-pit coal mines with the lack of moisture, it is necessary to take into account the hydrophobic-hydrophilic parameters of the preparations. Preparations with the high degree of aromaticity of humic acids are more efficient for the-reclamation of the burrows of brown coal deposits.

Bitumen extraction is a promising project of brown coal processing. It raises the task of identifying and quantifying the components of recoverable bitumen. In this paper, the method of gas chromatography-mass spectrometry is used to solve this problem. The composition of high-molecular fatty acids of brown coal bitumen from the Tyulgan deposit was studied taking into account the patterns of molecular ion fragmentation for the butyl esters of fatty carboxylic acids under ionization by electron impact. The ethanol extract fraction was investigated. The NIST-11 Database and ChemStation D.01.02. software was used to identify the butyl esters of fatty carboxylic acids.

Thermogravimetric investigation of five brown coal samples from various deposits in Russia and Mongolia was carried out in the inert and oxidizing media. A comparative analysis of the data obtained allowed us to reveal that brown coal of the Kangalasskoe deposit has higher thermal stability. This is confirmed by a higher yield of solid residue from pyrolysis in the inert atmosphere, lower yield of volatile substances, and the shift of the maximum of thermochemical decomposition of coal substance to higher temperatures. Temperature limits (ignition temperature for particles and the final temperature at which the coke residue burns out) of thermal degradation of the organic mass of the studied brown coals in the oxidizing medium were determined. It was demonstrated that brown coal samples were characterized by increased reactivity with respect to oxygen. It was established that the ignition temperature increases with an increase in the carbon content (С^daf) in the samples and a decrease in the yield of volatiles (V^daf), while the final temperature of the oxidation process significantly correlates with the aromaticity index f _a of the organic mass of coal.

Thermal decomposition of brown coal from the Baganuur deposit in Mongolia and gas coal from the Ulug-Khem deposit in Tuva was studied using thermogravimetry (TG) and differential thermogravimetry (DTG). The stage-by-stage thermal decomposition was revealed under the conditions of programmed heating to 900 °C with different rates in the argon atmosphere. Using the model-free and isoconversion methods of Ozawa-Flynn-Wall (OFW) and Kissinger-Akahira-Sunos (KAS), the dependence of the activation energy on the degree of coal decomposition was established, and the kinetic parameters of pyrolysis were determined. Within the range of coal conversion degrees from 0.1 to 0.9, the average values of pyrolysis activation energies for brown coal and gas coal were 186 and 239 kJ/mol (OFW method), 182 and 238 kJ/mol (KAS method), respectively. The kinetic compensation effect during coal pyrolysis was observed. This may be due to the multicomponent and multifunctional composition of coals.

The group and component composition of n-heptane and alcohol-benzene extracts of bitumen obtained from the brown coal of the Tyulgan deposit were investigated. Application of ¹³С NMR spectroscopy (CPMAS) and IR Fourier spectroscopy, gas chromatography-mass spectrometry, liquid chromatography allowed us to determine that n-heptane and alcohol-benzene extracts are represented by similar groups of substances: alcohols, phenols, alkanes, small amounts of carboxylic acids and aromatic compounds, esters, unsaturated hydrocarbons. The substances of these groups are distributed in these extracts to different extents, with the prevalence of compounds of aliphatic nature. A number of biologically active susbtances were identified in the extracts: tetra-, hexa-, octadecanouc acids, butylparabene, ferruginol, eicosane.

The dissolution of trinitrotoluene (TNT) in a low-melting nitramine, diethanolnitramine dinitrate (DINA), was studied, and a phase diagram for the TNT/DINA system was built. The enthalpy of TNT dissolution in DINA within the temperature range 55-75 °С was measured. The yields of condensed carbon (CC), detonation nanodiamonds (DNDs) and DND content in CC versus the composition of TNT/DINA cast melts upon detonation in a blasting chamber were experimentally studied. The yield of CC was found to linearly decline with decreasing TNT content in the composition, with the content of the diamond phase in CC going through the maximum. The highest yield of DNDs was achieved when the TNT content in the mixture was close to the eutectic (~40 %).

Fluorination of lanthanum oxide with ammonium fluoride is studied. Among all the known rare earth elements, lanthanum oxide is most commonly used as a stabilizing catalyst component, in particular in the hydrogenation of heteroatomic compounds of biofuel. Previous thermodynamic and thermogravimetric studies point to the multistage fluorination of La₂O₃ with ammonium fluoride. The reaction kinetics is correctly described by the kinetic equation of a contracting sphere with the activation energy equal to 33.65 kJ/mol. The X-ray phase analysis of the formed crystal phase showed that complex fluorides like (NH₄)₃La₂F₉∙H₂O and (NH₄)₃LaF₆∙0.5H₂O are formed as impurities during the interaction of La₂O₃ with NH₄F in addition to the major product (LaF₃).

The effect of various methods of physical action on the processes of extraction and organic synthesis is considered. The results of the authors’ works are summarized, and it is demonstrated that the methods of mechanochemical, ultrasonic and microwave activation provide an increase in the yield of target products, a decrease in the volume of solvents used, in time and energy consumption, compared to traditional processes.