Home – Home – Jornals – Chemistry for Sustainable Development 2023 number 3

The distributions of bioorganic components, as well as compounds of anthropogenic and mixed origins, have been studied in the sediments and water of the Parshikha Bay of the brackish Lake Chany (the Novosibirsk Region). The contribution of the main sources of organic matter in water and bottom sediments was estimated relying on the compositions of identified compounds (acyclic, aromatic and naphthenic hydrocarbons, acyclic and alicyclic oxygenated organic compounds, steroids, bicyclic sesquiterpenoids and pentacyclic triterpenoids). The composition of these objects has been established to be formed mainly due to the compounds of biogenic and mixed origin. The ratio of odd to even alkanes is equal to unity, the presence of cyclohexanes and drimanes, which are not characteristic of recent precipitation, indicates the presence of petroleum products. Household compounds - triphenylphosphates and phthalates, which are used as plasticizers in the production of polymer materials, have also been identified.

In this work, the samples of α-fractions isolated from the pitches of different grades (B, B1, V) obtained from an industrial sample of coal tar are studied. The main numerical characteristics obtained from the Raman spectra of the isolated α-fractions are calculated and analysed. A direct relationship is established between the content of defects in graphite-like crystallites and the pitch softening temperature.

The production of high-purity lithium hydroxide (LiOH) solution by electrochemical conversion of soluble lithium salts (membrane electrolysis) was tested on semi-industrial scale. Stainless steel (cathode) and lead (anode) were used as electrode materials. Lithium sulphate solution was utilised as anolyte and water - as catholyte. During membrane electrolysis, water oxidation takes place in the anode compartment with the formation of gaseous oxygen and protons. Lithium ions permeate through the cationic membrane into the cathode compartment, where gaseous hydrogen and hydroxide ions are formed as the products of water decomposition on the cathode, so lithium hydroxide gets concentrated up to 33-36 g/dm³ with respect to lithium oxide. Electrolysis efficiency is 50-55 % for one process cycle. Sulphuric acid formed in the anode compartment may be then neutralised by adding lithium carbonate, and the formed lithium sulphate may be re-used in membrane electrolysis, which means anolyte recycling. Five successive electrolysis cycles with recycled anolyte allow an increase in the degree of lithium ion transfer from the anode to cathode compartment to 95-98 %. It is established that, in addition to lithium, other metal ions (sodium, potassium, calcium, etc. ) and sulphate ions migrate through the cation-exchange membrane into the cathode compartment from anolyte solution. To evaluate the quality of the obtained lithium hydroxide monohydrate (LiOH · H₂O), lithium hydroxide solutions obtained both by membrane electrolysis and by the traditional lime causticisation process were evaporated. Comparison between the concentrations of impurity ions in lithium hydroxide monohydrate samples obtained using different methods shows that the product of better purity may be synthesized from lithium sulphate solution by membrane electrolysis.

A compact mechanism based on elementary radical reactions is proposed for the temperature conversion of methane-ethane mixtures. The kinetic model relying on this mechanism describes the literature data on the conversion of methane and ethane at millisecond time intervals in the temperature range 600-1400 °C. Within the kinetic model, the time dependences of the concentrations of hydrogen, ethylene, acetylene and benzene on the temperature and on the methane/ethane ratio in the initial mixture are determined in the isothermal approximation. Using the proposed mechanism for the calculations of axisymmetric gas dynamic flows of reagents mixture, the yields of hydrogen and valuable unsaturated hydrocarbons in a non-isothermal tubular reactor are determined.

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The results of studies on changes in the chemical composition and structure of doped titanium hydroxide during thermal treatment are analysed. It is shown that anatase is formed at first under heating in all cases, and with further increase in temperature or in the duration of thermal treatment it is transformed into rutile. The temperature of the start of anatase-rutile transition depends on the type of doping component. The transition proceeds not abruptly at a certain temperature but gradually over a wide temperature range, while both compounds can exist simultaneously. At a constant temperature, the proportion of rutile increases with an increase in the duration of thermal treatment. It is concluded on the basis of the conducted studies that the samples of titanium dioxide in the presence of doping components represent the broad classes of non-stoichiometric compounds with different crystal structures, and the transition of anatase to rutile is not a polymorphic transformation of the 1^st kind but it is a consequence of various chemical processes involving the release of anionic and/or cationic impurities into the gas or solid phases.

The influence of the concentration of cobalt introduced into HZSM-5 on its acidic and catalytic properties in the transformation of ethanol into high-octane components of motor fuels has been studied in the plug-flow unit within the temperature range of 300-450 °С. The unmodified НZSM-5 zeolite is shown to be highly selective to aromatization products (27.5-47.6 %) and С₁-С₃ alkanes (25.8-37.1 %). A significant increase in selectivity to isomerisation products (from 17.2-19.8 to 34.0-42.7 %) is established for cobalt-modified (1.0-3.0 wt. %) zeolite catalysts within the temperature range 300-350 °C. The highest increase in the selectivity of modified catalysts to aromatisation products (32.7-40.7%) is observed within the temperature interval of 400-450 °С. The effect of modification on the acid properties of HZSM-5 zeolite has been studied using the temperature-programmed desorption of ammonia. It is shown that the changes of the catalytic properties of HZSM-5 zeolite are connected with a considerable decrease in the concentration of strong Brensted acid centres (from 538 to 317 µmol/g), with the formation of new stronger Lewis acid centers (37-80 µmol/g) including cobalt ions and acid-base Co^δ+-O^δ- type pairs capable of strong polarization and activation of C-H bonds in the intermediates. Selectivity to the products of isomerisation and aromatization on the modified catalysts is regulated by cobalt concentration and process temperature. The highest selectivity to isomerisation products (42.7 %) is achieved over the 2 % Co/HZSM-5 catalyst at a temperature of 300 °C. The catalysate obtained over the 2 % Co/HZSM-5 catalyst at 300 °С corresponds to Euro-5 standard in the content of isoparaffin (56.4 %) and aromatic (29.8 %) hydrocarbons, benzene (0.6 %) and olefins (1.1 %).

The increasing concern for environmental sustainability and the need for efficient and green chemical synthesis have driven the development of alternative methods for producing new compounds. In this study, we have synthesized a series of novel 2H-chromene derivatives using a one-pot multicomponent reaction under ultrasound sonication. The use of ultrasound sonication is a green and efficient synthetic method that utilizes sound waves to initiate chemical reactions. We optimized various reaction parameters, such as solvent, temperature, catalyst amount, and reaction time, to identify the best reaction conditions for the synthesis of the derivatives. The synthesized compounds were characterized using analytical techniques such as IR, mass, ¹H and ¹³C NMR spectra, which confirmed the molecular structures of the derivatives. Furthermore, the antioxidant activities of the synthesized derivatives were evaluated and compared to those of ascorbic acid. The IC50 values of the derivatives were promising, indicating their potential as antioxidants. Overall, this study demonstrates the effectiveness of ultrasound sonication as a green and sustainable approach to the synthesis of novel compounds with potential biological activities. The use of one-pot multicomponent reactions also adds to the efficiency and simplicity of the synthesis method. These findings may have important implications for the development of new and sustainable chemical synthesis methods in the future.

Ferulic acid (FA) is a phenolic substance widespread in plants and exhibiting a wide range of potential therapeutic effects, such as antimicrobial and anti-inflammatory, and useful in the treatment of diabetes, lung and cardiovascular diseases. Methanol extracts from the fresh leaves of 40 species from the Lamiaceae family growing in the outdoor collections of the Botanical Garden of the Komarov Botanical Institute of the Russian Academy of Sciences (BIN RAS, Saint-Petersburg) and the experimental station "Otradnoye" BIN RAS (Leningrad region) have been investigated. Ferulic acid was detected in 18 species under investigation, related to the subfamilies Lamioideae Harley ( Betonica grandiflora Willd., Galeobdolon luteum Huds., Lamium album L., Sideritis taurica Steph. ex Willd., Stachys byzantine K. Koch) and Nepetoideae Kostel. ( Clinopodium vulgare L., Hyssopus officinalis L., Lavandula angustifolia Mill., Meechania urticifolia (Miq.) Makino, Melissa officinalis L., Mentha piperita L., Monarda didyma L., Nepeta bucharica Lipsky, Nepeta grandiflora M. Bieb., Origanum vulgare L., Prunella laciniata (L.) L., Salvia desertum L., Salvia officinalis L., Thymus serpillum L.). Ferulic acid was not detected in the representatives of Ajugoideae Kostel. и Scutellarioideae Caruel subfamilies. For 7 species, FA was detected for the first time. The content of FA in the representatives of Lamiaceae subfamily varied within a broad range from 0.01±0.00 mg/g ( Meechania urticifolia ) to 6.68±1.30 mg/g ( Melissa officinalis L.). The high ferulic acid content was established in the Nepetoideae subfamilty in the species Melissa officinalis (6.68±1.30 mg/g) and Origanum vulgare L. (6.07±1.90 mg/g).

The kinetics and mechanism of hydrogen evolution on the FeSi₂ electrode in 0.25-1.0 M NaOH solutions have been studied by polarisation and impedance measurements. The cathodic polarisation curves of iron disilicide in the studied solutions are characterized by a Tafel region with constants a and b equal to (-0.78)-(-0.72) and (-0.133)-(-0.128) V, respectively. The impedance spectra of FeSi₂ at the potentials of the Tafel region represent a capacitive semicircle with a displaced centre, which corresponds to an asymmetric maximum in the graph of phase angle dependence on the logarithm of the alternating current frequency; the magnitude of the electrode impedance in all solutions changes in accordance with the course of the polarization curves. To describe the hydrogen evolution reaction on iron disilicide, an equivalent electrical circuit was used, the Faraday impedance of which consists of series-connected charge-transfer resistances and a parallel circuit responsible for the adsorption of atomic hydrogen on the surface and its diffusion into the depth of the electrode material; the circuit also includes the electrolyte resistance and the double-layer capacitance impedance, which is modeled by a constant phase element. It is shown that the results of polarization and impedance measurements for the FeSi₂ electrode are in satisfactory agreement with the discharge-electrochemical desorption mechanism, in which both stages are irreversible and have unequal transfer coefficients; for adsorbed atomic hydrogen, the Langmuir adsorption isotherm is satisfied; simultaneously with the reaction of hydrogen evolution, the reaction of hydrogen absorption by the electrode material proceeds with diffusion control. It has been found that iron disilicide in an alkaline electrolyte is characterised by the low overvoltage of hydrogen evolution, and it is a promising electrode material for the electrolytic production of hydrogen.

High-molecular oil fractions exhibiting the initiating effect, nontypical for these oil objects, on the model reaction of cumene radical oxidation were investigated by means of microcalorimetry. It is shown for some objects that the initiators appear in the high-molecular fractions of oil in the course of their isolation from native oils by n-hydrocarbons. An insignificant correlation is established between the content of nickel, vanadium, and vanadylporphyrins and initiating activity. The initiators have been found in freshly isolated ‘acid resin’ fractions, which lose their initiating ability during storage due to chemical condensation processes. This method may be considered as a test for the content of inhibitors or initiators of radical oxidation in oil objects.

Intense coal mining at the territory of our country, related to the growing amounts of exported fuel, promotes the development of logistic infrastructure but at the same time causes a worsening of the environmental situation near coal mining enterprises. One of the ways to cope with the surfaces that generate dust, in particular fine coal dust particles, is surface treatment with hydrophobising organosilicon emulsion. However, the problem connected with enhancing the hydrophobicity of coatings formed by the emulsion has not been solved yet. This parameter is estimated by determining the wetting angle. The efficiency of modification and the coalescing ability of various additives in the aqueous emulsions of organosilicon liquid GKZh-94 are evaluated in the present work from changes in the wetting angle. The dependences of film wettability changes on the modifying and coalescing agents, and on their amount in the emulsion are demonstrated. The dependences of wetting angle changes on the amounts of the modifying and coalescing agents in the emulsion are plotted on the basis of the polynomial approximations of functions. It is established that preliminary modification of the emulsifier causes an increase in the hardness of polyvinyl alcohol, which hinders coalescence of particles in the emulsion. It is also determined as a result of a comparative analysis that the best wetting angle values are detected for the emulsions with the emulsifier modified with a small amount of glutaric aldehyde, with the high concentration of ethylene glycol as a coalescing agent. The use of glutaric aldehyde in the amount of 0.1-0.25 % and ethylene glycol in the amount of 3-6 % of the total mass of emulsion will allow an increase in the wetting angle of the formed coatings to 125°.

Currently, the chemical nickel plating process is one of the most popular electroplating methods compared to others due to a number of advantages. However, the production process generates a significant amount of spent chemical nickel plating solutions, which poses a threat of environmental pollution. To solve this problem, the possibility of regenerating the spent solution of chemical nickel plating from one of the industrial enterprises of Udmurtia by the reagent method was studied. Sodium carbonate was chosen as the precipitant for nickel ions, the amount of which was determined from potentiometric titration curves; the most complete precipitation of nickel ions occurs at pH 10. It has been established by IR spectroscopy that nickel hydroxide salts are formed as a result of the interaction of the spent electrolyte with the precipitant. The results of thermogravimetric and differential thermal analysis of the precipitate showed three endothermic effects: at temperatures up to 100 °C, it corresponds to dehydration; at 280±10 °C - to the removal of a part of chemisorbed water and carbonates; at 420 °C - to the final removal of water. As a result of heat treatment of the hydroxocarbonate precipitate, a black fine powder of nickel (II) oxide is obtained, the IR spectrum of which has a set of bands characteristic of this compound. Two variants of the technological scheme for the regeneration of spent electrolytes for the preparation of initial working solutions for chemical nickel plating from nickel (II) hydroxocarbonate and nickel oxide are proposed. The quality of the obtained solutions was checked by applying a nickel coating on brass products. The thickness of the coating was measured by scanning electron microscopy. It has been established that the highest quality coating is obtained using an electrolyte prepared from nickel hydroxocarbonate.