Home – Home – Jornals – Chemistry for Sustainable Development 2020 number 6

Laser ignition (1064 nm, 120 μs) of the dispersed particles of different coal marks was studied. For all coal marks, three consecutive ignition stages with characteristic threshold radiation energy densities ( H _cr) for each stage were discovered. With an increase in the rank, the values of the first ignition limit H _cr⁽¹⁾ remain almost constant, the second ignition limit H _cr⁽²⁾ decreases, while the third ignition limit H _cr⁽³⁾ increases. Results of the investigation of kinetic dependencies of flame glow at different ignition stages arising under the action of laser pulses on coal particles are presented. The glow duration at the first ignition stage slightly exceeds the duration of the laser pulse and reaches 150 μs for all marks of coal. The glow duration at the second ignition stage at H = H _cr⁽²⁾ is in the millisecond time interval. With an increase in the energy density of laser radiation, the glow duration at the second ignition stage decreases to the submillisecond range as a result of an increase in the rates of thermochemical reactions. At the third ignition stage at H = H _cr⁽³⁾, the glow duration is 10-100 ms for different marks of coal. It was established that for the studied coals, the glow intensity increases from the moment of exposure to laser pulse. In the submillisecond range, a decrease in glow intensity was observed. The glow amplitude of coals increases linearly with an increase in the energy density of laser radiation.

The samples of native and n -butanol-modified humic acids isolated from brown coals of the Kansk-Achinsk and South Ural coal basins (Russia) were obtained. Their composition and properties were characterized using the methods of elemental, spectral, technical analysis and testing for biological activity. Changes in the structural group parameters of modified humic acids were revealed by means of ¹³C NMR (CPMAS), IR and Raman spectroscopy. The biological activity of native and modified humic acids was evaluated by means of phytotesting with the seeds of Iren wheat. It is shown that modified humic acids are characterized by increased biological activity. This is due to an increase in the relative content of aromatic structural fragments, which is accompanied by an increase in aromaticity index f _a and the ratio of aromaticity to aliphaticity f _ar/al of humic acids.

Phenol adsorption from aqueous solutions on carbon sorbents was studied. The carbon sorbents were prepared from Kuzbass coals by means of chemical activation of raw coals using potassium hydroxide. Coal and potassium hydroxide were mixed by means of impregnation (with a mass ratio of coal/alkali 1 : 1), followed by mixture carbonization at 800 °C with isothermal exposure for 1 h. Phenol adsorption on thus prepared sorbents was shown to be described by Langmuir equation ( R ² ≈ 0.999). Sorption parameters point to the high efficiency of phenol adsorption on carbon sorbents, especially on the sorbent obtained from D coal. It was established that phenol adsorption from aqueous solutions by the sorbents is described by the pseudo-second-order adsorption kinetics model, and the limiting stage is the diffusion of phenol molecules in the microporous space of the sorbent.

The thermal solvolysis of epoxy diane resin (ED-20) and glass and carbon fibre reinforced plastics (FRP) in the medium of coal tar pitch and petroleum pitches was studied. The components of liquid-phase decomposition products were identified by gas chromatography-mass spectrometry; solvolysis residues were characterized. The mechanism of thermal solvolysis of epoxy resin in coal tar pitch and in petroleum pitches was proposed. The possibility of carbon and glass fibre recycling as a result of thermal solvolysis of FRP in coal tar pitch and in petroleum pitches was demonstrated. Coal tar pitch and petroleum pitches were compared as solvents for thermal solvolysis.

The structural, morphological and electrochemical properties of nanocomposite materials obtained by thermal decomposition of cobalt hydroxides and mixed cobalt-zinc hydroxides on the surface of a carbon matrix formed by multi-walled carbon nanotubes (MWCNT) were investigated. The interaction of the solutions of cobalt and zinc sulphates with sodium hydroxide results in the formation of the solid phase which includes cobalt hydroxide and zinc oxide. Subsequent thermal treatment in the air leads mainly to the formation of zinc cobaltate Zn _x Co_{(1 - x )}O _y , in which the relative content of cobalt and zinc can vary within a broad range. The electrochemical properties of synthesized nanocomposite materials were investigated by cyclic voltammetry. Investigation of the electrochemical properties of the synthesized nanocomposite materials by means of cyclic voltammetry showed that the introduction of cobalt oxide into carbon matrix causes an increase in electrical capacitance within the whole range of potential scanning rates (10-80 mV/s). Application of electrode materials based on the carbon/zinc cobaltate composite for manufacture allows an increase in specific capacitance of supercapacitors by a factor of 1.5 and saves cobalt, a material in short supply.

Results of the IR spectroscopic investigation of brown coal from different deposits of Russia and Mongolia are presented. The obtained IR spectroscopic data indicate the presence of complex structures in brown coals containing aliphatic and aromatic hydrocarbon fragments, fragments of oxygen-containing heteroaromatic compounds, as well as oxygen-containing functional groups (carbonyl, hydroxyl, ether). It was found that the aromaticity index f _a calculated from the results of IR spectroscopy has a linear correlation with the quality indicators of brown coal - the yield of volatiles (V^daf), fixed carbon (C_fix ) and the H/C atomic ratio.

In order to develop new catalysts based on carbon nanotubes (Taunite) with deposited bimetallic oxide nanoparticles for oxidative desulphurization, a series of samples with the composition M₁M₂O _x /Taunite (M₁M₂ = CeMo, CuMo, CeCu) was prepared by incipient wetness impregnation. The properties of the catalysts were studied by means of FTIR spectroscopy and thermal analysis combined with mass spectrometry. The effects of the nature of a metal precursor and the oxidative treatment of the support on the functionalization of the support surface and support thermal stability were studied. Decomposition of supports with deposited bimetals was determined to start at a temperature lower by 210-285 °C than in the case of non-modified support. The stability of Taunite support against thermal decomposition increases in the following series of metal cations: CuMo < CeMo < CeCu < support without M₁M₂. The optimal precursors of bimetals for the synthesis of a promising nanosized catalyst M₁M₂O _x /Taunite were selected.

The utilization of ash and slag from coal-fired power plants to ensure their environmental safety was considered. A comprehensive technology is proposed to utilize wastes of solid fuel combustion from thermal power plants and regional industrial wastes along with CO₂ emissions produced at thermal power plants, which is relevant under the Paris Climate Agreement signed by Russia. A low-waste process of energy generation and the production of substituents of natural materials for various purposes may be arranged by combining the production of free calcium and magnesium oxides from the mineral part of fuel burnt in the steam boiler, dry ash removal from the boiler and electrostatic precipitators, chemical saturation of the oxides with carbon dioxide from coal combustion products leading to the formation of thermodynamically stable carbonates. Integrated carbonation of basic components of ashes from the power plant during the mineralization of CO₂ emissions enhances the consumer properties of ash and slag and provides the reduction of CO₂ emission by 3-5 %, which is equivalent to an increase in power plant efficiency by 1.5-2 %. Involvement of regional resources (power plant ash and slag and other facilities, construction waste from housing renovation programs, etc .) in the chemical recycling process can increase the degree of power plant wastelessness up to 70-90 % without turning to expensive technologies of carbon capture and storage (CCS). The possibility to solve the multifactor utilization task for solid and gaseous products of different kinds within a single technological process ensures the commercial attractiveness of this proposal.

The composition of the products of mechanical treatment (MT) of a mixture of brown coal and water (1 : 1) at MT temperature of 80, 120, 160, 200 °С was investigated. MT of the water - coal system was carried out with the help of AGO-2 installation in the atmosphere of argon. Mechanical treatment at increased temperatures promotes the destruction of the organic component of brown coal. It is demonstrated that an increase in MT temperature causes a decrease in methane yield and an increase in the yield of bitumoid. The content of resins and asphaltenes in bitumoids was determined to increase with an increase in MT temperature. The ignition and combustion characteristics of the products of mechanically treated coal-water mixture were studied.

The petrographic composition of sapropelite coal from different deposits of Russia was investigated. It was revealed that the studied samples contain more than 75 % of macerals of the liptinite group, 8 to 24 % macerals of the vitrinite group, and minor amount of the group of inertinites (mainly fusinite), not more than 1-2 %. To determine the genetic maturity of the studied sapropelite coal, the reflectivity of vitrinite was determined. It was established that the vitrinite reflection index in the samples varies within a relatively narrow range from 0.27 % (the sample from the Charchik deposit) to 0.41 % (the sample from the Taimylyr deposit).

Statistical analysis of the material according to the composition of ash-forming elements in coal from the Kaa-Khem deposit ( n = 43) including the data previously obtained by other researchers was carried out. The study samples of coal have a low ash content on average (ash content A^d is 11.8 %), with a relatively high content of CaO (17.4 mass %) and Fe₂O₃ (16.6 mass %). Regression analysis of the data by means of the least-squares allowed us to reveal correlations between ash content and the content of elements. The dependences of the element’s contents in coal [E _i ] and ash [E _i ]^A were estimated over a broad range of ash content values A^d (3-51 %). The types of diagrams for Si, Al, Ti, K, Na differ from those for Fe, Ca, Mg, S. It is demonstrated that the main carriers for Si, Al, Ti, K, Na in the studied coals are mineral inclusions of allothigenic origin. The authigenic mineral formations of coals contain mainly the carriers of Fe, Ca, Mg, S.