Voprosy khimii i khimicheskoi tekhnologii (Issues of Chemistry and Chemical Technology)

14-21

Authors: A.G. Atapin, V.G. Nefedov

In this work, the effect of current density, surface tension, viscosity and density of the solution on the size of oxygen bubbles evolved during the electrolysis of aqueous sodium hydroxide solutions with a concentration of 2 to 16 mol L–1 is investigated. Experiments showed that the size of the bubbles increases with the current density that contradicts the Fritz formula. This suggests that the conditions of thermodynamic equilibrium of bubbles on an electrode surface cannot be used to determine the detachable sizes of the bubbles formed during water electrolysis. All other things being equal, the bubble sizes increases with increasing concentration and viscosity of the electrolyte. Besides, the value of electrolyte supersaturation is much less than that required to form a spherical nucleus, but it is sufficient to form a bubble through the stage of a flat nucleus. It is shown that it is possible to predict the change in the size of bubbles with the growth of current density and electrolyte concentration when using the theory of a flat nucleus. Calculations show that the growth of the bubbles on the electrode surface occurs through two stages. In the first stage, the bubbles grow on a constant base due to changes in wetting angles. In the second stage, after reaching thermodynamic equilibrium of wetting angles, the growth occurs with decreasing wetting angles and diameters of attachment of the bubbles to the electrode, up to detachment of the bubbles from the electrode surface.

27-33

Authors: O.Y. Horniichuk, N.S. Kariaka, V.O. Trush, S.S. Smola, T.Y. Sliva, N.V. Rusakova, V.M. Amirkhanov

The binuclear rare earth coordination compounds based on bis-chelating carbacylamidophosphate (CAPh) – tetramethyl(2,2,3,3,4,4-hexafluoro-1,5-dioksopentan-1,5-diyl)-bis-amidophosphate (H2L) were synthesized for the first time. A synthesis procedure for obtaining coordination compounds of general formula Ln2L3Phen2 (where Ln3+=Nd3+, Eu3+, Y3+, and Phen=1,10-phenanthroline) was developed. Based on the data of NMR, IR and electronic spectroscopies, the composition of the synthesized compounds was determined. It was established that CAPh ligand is coordinated to metal ions in deprotonated form (L2–) via oxygen atoms of carbonyl and phosphoryl groups. Thermogravimetric study of the europium complex showed its thermal stability up to about 200C. It was stated that upon UV irradiation the obtained neodymium and europium complexes exhibit luminescence in IR and visible regions, respectively. Luminescence excitation spectra of the complexes specifies to effective sensitization of lanthanide luminescence by organic ligands. The ratio between the intensities of the bands of the f–f transitions in the luminescence spectrum of the obtained europium complex points to low symmetry of central ions in coordination environment.

42-47

Authors: M.M. Zipunnikov

The aim of this work was to study the operating characteristics of the membrane-free electrolysis water decomposition for high-pressure hydrogen and oxygen production and ensure a maximum yield of the potassium ferrates as a target product without using expensive electrode metals. An electrode assembly consisting of two electrodes, steel 3 (passive, i.e. gas-releasing) electrode and porous Fe active (i.e. gas-oxidizing) electrode, was used. An aqueous solution of potassium hydroxide (25%) was used as an electrolyte. To assess the efficiency of the formation of potassium ferrates, the effects of the current density (in the range of 0.008 A/cm2 to 0.03 A/cm2) and the number of the complete redox cycles on the density of the electrolyte were studied. It was determined that the density of an electrolyte increased from 1.23 g/ml to 1.26 g/ml after 10 complete cycles. This indicates an increase in the concentration of potassium ferrates in the course of the electrolysis process at the current density of 0.015 A/cm2. A decrease in the current density below 0.01 A/cm2 leads to a decrease in the rates of the gases release (both H2 and O2) and ferrate ions formation which is a critical condition for potassium ferrates formation taking into account their tendency for self-decomposition. The change of the Gibbs energy was determined taking into consideration the initial potential of hydrogen and oxygen evolution. Recommendations were given that concern the application of the developed method of ferric acid salts production to use them as an oxidizing agent in the process of waste-water treatment.

54-57

Authors: A.S. Krvavych, V.R. Hamada, R.T. Konechna, A.O. Mylyanych, L.R. Zhurakhivska, I.R. Buchkevych, V.P. Novikov

The kinetics of extraction of phenolic compounds from Adonis vernalis was investigated in this work. To this end, the process was carried out under different hydrodynamic conditions and different extent of grinding of the plant. Quantitative determination of the overall content of phenolic compounds in extracts was performed by spectrophotometric method. The extraction proceeds more efficiently under the conditions of continuous stirring than after the infusion; this is associated with an internal character of diffusion. An optimal diameter of components was determined for the best extraction of phenolic compounds. The extraction of Adonis vernalis is recommended to perform using 70.0% ethyl alcohol at the boiling point. The diameter of the components should be equal ~1.6 mm. Under these conditions, the concentration of phenolic compounds was 0.9200.118 g L–1.

65-70

Authors: T. Luk'yanenko, O. Shmychkova, L. Dmitrikova, L. Borschevich, A. Velichenko

It is shown that anionic surfactants, sodium laureth sulphate in particular, are included in electrodeposited lead dioxide. The content of organic substance in the composite coating can vary from 3.4 to 12.5 wt.%. The change in deposition conditions (temperature, pH and anodic current density) allows controlling the content of surfactant in the resulting oxide. The electocatalytic activity of the materials involved was investigated in respect to the oxygen evolution reaction and the electrochemical oxidation of 4-chlorophenol. The calculated value of Tafel slope is 229 mV dec–1 for non-modified PbO2, while it is 178 mV dec–1 for composite of PbO2 with 10.2 wt.% of sodium laureth sulfate. According to absorption spectra, the initial solution of 4-chlorophenol is characterized by two peaks at 220 and 280 nm. At first, the electrolysis leads to a decrease in the peak at 220 nm, a slight increase of the peak at 280 nm and the appearance of the plateau at 240–270 nm. This is caused by a decrease in the concentration of 4-chlorophenol and accumulation of benzoquinone in the solution. A further increase in the electrolysis duration results in the disappearance of the peaks at 220 and 280 nm and the reduction of the plateau at 240–270 nm due to a decrease in the concentrations of both 4-chlorophenol and benzoquinone. Already after 4 hours of electrolysis, the aromatic compounds are completely destroyed with the formation of only aliphatic electrolysis products (mainly maleic acid), that was evidenced by high performance liquid chromatography. The processes of electrooxidation of 4-chlorophenol on lead dioxide and PbO2-based composite materials proceed qualitatively in the same way and differ only in the rate.

77-83

Authors: B. Minaev, О. Aksimentyeva, O. Lut, O. Shevchenko

The electrochemical oxidation of tyrosine in acidic aqueous solutions on a platinum electrode was studied by the method of cyclic and linear voltammetry in conjunction with quantum-chemical calculations. It was determined that electrooxidation of the cation of tyrosine occurs irreversibly, the maximum current of electrooxidation is observed in the potentials range of 1.09–1.21 B (Ag/AgCl) (at pH value of 1.7). The maximum current linearly depends on the concentration of a depolarizer in the solution. Based on the analysis of voltammeter curves, the kinetic parameters of tyrosine electrooxidation (diffusion coefficient, rate constant and Semerano diagnostic criterion and the activation energy of the process) were calculated. The main thermodynamic characteristic functions (entropy, Gibbs energy change, enthalpy of formation), and quantum-chemical constants (total energy, energy of boundary molecular orbitals) are calculated. Based on the obtained experimental results, identification of the products of electrooxidation and quantum-chemical calculations, it was established that the electrooxidation of tyrosine in an acidic medium occurs via the hydroxyl group which is directly linked to the benzene ring; the process is accompanied by the cleavage of two electrons and two protons to form 2-amino-3-(4-oxocyclohexa-2-5-dinyliden) propanoic acid.

93-103

Authors: L.K. Patrylak, S.O. Zubenko, S.V. Konovalov, V.A. Povazhnyi

Butyl esters of fatty acids are used in engineering and are considered as potential biodiesel fuel. The difficulty of separation of products, obtaining by alkaline transesterification of oils, causes the pure attention of researchers to this one-stage of synthesis of butyl esters. The difficulty of separating the products obtained by alkaline transesterification of vegetable oils leads to the limited attention of researchers to this one-step route of the synthesis of butyl esters. The aim of this work was to compare the characteristics of the alkaline transesterification of sunflower oil on hydroxide and water-free alkoxide catalysts and to interpret the observed features from the point of view of reaction mechanism. Transesterification was carried out at the temperature of 20 and 40C using potassium butoxide, methoxide and hydroxide. The highest equilibrium yield of butyl esters (up to 96%) was achieved when potassium butoxide was used, whereas it did not exceed 85% for the case of potassium hydroxide. The third order of reaction was determined. The reaction rate constants and apparent activation energies were calculated. The activation energies were found to be almost equal for both used alkoxides (30.5 kJ mol–1). The features of the formation of glycerol layer were studied; this layer appeared during transesterification using potassium butoxide. Alkaline solutions of catalysts in butanol were studied by IR-spectroscopy. The degeneracy of valence vibrations of OH-groups in the region of about 3300 cm–1 was observed with as an increase in the potassium butoxide concentration. This may be due to the formation of associates of butanol and butoxide. The fundamental differences between reaction stages of methanolysis and butanolysis, caused by low dissociation degree of potassium butoxide in low polar butanol, were discussed. The ways of the formation of potassium glyceroxide and its role in the further course of the process were considered.

112-117

Authors: Yu.V. Pohorenko, A.A. Nahorny, R.M. Pshenychnyi, A.O. Omel'chuk

It has been found that the solid solutions of heterovalent substitution, MxPb1–xSnF4–x (0

126-134

Authors: L.V. Sysa, K.V. Stepova, M.A. Petrova, A.Z. Kontsur

Clay-based materials are promising adsorbents for removal of various pollutants from wastewater. This work is aimed to study the changes in structure and adsorption capacity of microwave-treated bentonite after adsorption of lead(II) ions. The structural investigation of the microwave-treated sample reveals that a partial destruction of silica skeleton takes place, and new surface nucleation centers are formed during microwave processing. The adsorption of Pb2+ on natural bentonite occurs on heterogeneous adsorption sites, whereas the removal of lead on microwave-treated sample is accompanied by the formation of plumbophyllite microcrystals. The natural and microwave-treated adsorbents were tested for lead adsorption in batch experiments. The results were fitted according to Langmuir, Freundlich, Toth, Redlich-Peterson, and Langmuir-Freundlich isotherms of adsorption. The microwave-treated samples revealed substantially higher efficiency towards the removal of lead, their maximal adsorption capacity was 114.7 mg g–1, whereas natural samples showed only 31 mg g–1.

143-152

Authors: A.B. Surovtsev, A.G. Paios, M.P. Dyachenko, I.A. Mandzyuk

The article presents the results of the study on the past-like highly filled compositions and the assessment of their rheological properties using a rotational viscometer of a cone-plane system. Dispersed filler in the initial form of potassium chloride or in its surface-modified form (prepared by the precipitation of the oligomeric products of glycerolysis of polyethylene terephthalate on the surface of the particles) was introduced into the paste-like composition as a main component. The composition also included an additional filler (fine aluminum powder), oligomeric rubber SCDN-N together with a plasticizer as a binder and a surfactant. The effects of the preparation technology, composition and nature of the components on the viscosity of the compositions were evaluated in the range of the shear stresses of 1 to 30 kPa and the temperatures of 293 to 323 K. Along with the use of a surfactant and the addition of dioctylphthalate as a plasticizer, the developed modification of the filler surface (by means of pre-encapsulating its particles with oligomeric glycerolysis products of polyethylene terephthalate) allows significantly increasing the degree of filling of the paste-like composition, the dynamic viscosity close to the viscosity of the original oligomeric rubber being maintained.

160-167

Authors: E.B. Khobotova, V.I. Larin, Yu.S. Kaliuzhna, O.G. Storchak

The mineralogical composition of the samples of slag-alkaline binders prepared on the basis of blast-furnace slags and various alkaline components was determined. X-ray diffraction and electron-probe microscopy were used to investigate the slag-alkaline binders under consideration. The obtained results indicated the advisability of the utilization of dump blast furnace slag in the production of slag-alkaline binders that significantly expands the raw materials base of binders' fabrication and their nomenclature. It was determined that the mineralogical composition of slag-alkaline binders based on blast furnace slag dump occupy an intermediate position between the Portland cement and slag-alkaline binders based on granulated blast furnace slag. Sodium-containing phases, the products of hydration solidification, carbonates and anhydrous aluminum silicates of Ca and Mg are the main minerals of the solidification of slag-alkaline binders. The high activity of slag-alkaline binders based on slags and soda-alkaline melt was observed.