Статьи журнала «Сверхкритические Флюиды: Теория и Практика»

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2021, №1

сс. 17-51

Articles

Effect of Mechanical Pressure on Zinc Oxide Recrystallization in Aqueous Medium during Cold Sintering

Yu.D. Ivakin, A.V. Smirnov, M.N. Kormilitsin, A.A. Kholodkova, A.A. Vasin, M.V. Kornyushin, V.P. Tarasovskii, V.V. Rybalchenko.

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Key words: zinc oxide, cold sintering, recrystallization, solid-phase mobility in an aqueous medium, crystal size distribution, coalescence, surface spreading

An effect of mechanical pressure on the crystal size distribution during the treatment of
zinc oxide in an aqueous medium in the presence of zinc acetate or ammonium chloride as
activating additives was studied by analyzing scanning electron microscopy images. The
results of ZnO cold sintering at 220—296 °C and its thermovaporous treatment (TVT)
without applying mechanical pressure in an autoclave under similar conditions were
compared. It was concluded that due to the presence of the additives in an aqueous
medium, the hydration of the structure increased and the solid-phase mobility was activated,
leading to the redistribution of the mass of crystals. Mechanical pressure during the cold
sintering enhanced the effect of solid-phase mobility activation and led to the predominance
of crystal coalescence in mass transfer. During the TVT with no mechanical pressure
applied, surface spreading as the mass transfer mechanism prevailed. A scheme illustrating
the effect of the aqueous medium on the mass transfer during the recrystallization of
ZnO was proposed.

doi:10.34984/SCFTP.2021.16.1.002

2021, №1

сс. 3-16

Articles

Key words: nanocomposite, single-walled carbon nanotubes, suspensions, supercritical impregnation, polymethylmethacrylate, supercritical carbon dioxide, Raman spectroscopy, thermogravimetry, differential scanning calorimetry

A technique is described for dispersing single-walled carbon nanotubes to obtain stable
suspensions with a high concentration of individual nanotubes in 2-pyrrolidone. The
resulting suspensions were investigated using Raman spectroscopy and were used to
modify poly(methylmethacrylate) samples with average molecular weights 15000 and
996000 g/mol by impregnation in supercritical carbon dioxide. The thermal properties of
the obtained composite materials are studied. It is shown that the glass transition
temperatures of the samples are increased with comparison with the initial polymers.
Glass transition temperatures of composites increased by 26°С and 32°С for PMMA
with an average molecular weight of 15000 and 996000 g/mol accordingly.

doi:10.34984/SCFTP.2021.16.1.001

2020, №4

сс. 74-79

Information

2020, №4

сс. 68-73

Articles

Subcritical Water as Instrument for Production of Oleanolic Acid from the Olive Leaf (Olea Europaea L.)

E.V. Maksimenko, S.S. Khizrieva, S.N. Borisenko, A.V. Lekar, N.I. Borisenko, V.I. Minkin.

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Key words: subcritical water, oleanolic acid, olive leaf, Olea europaea L.

The presented work is aimed at the development technique for production oleanolic acid
(OA) from the oliveleaf (Olea europaea L) using the subcritical water (SBW). For the
first time SBW that serves as a reactant and a solvent has been used to obtain OA in good
yields starting from the olive leaf (Olea europaea L.). This method of preparation of OA
allows one to avoid the use of toxic organic solvents. The good yields of the targeted OA
can be obtained for the period which is 4 times shorter than needed by the traditional
procedures.

doi:10.34984/SCFTP.2020.15.4.006

2020, №4

сс. 60-67

Articles

Laser-Induced Supercritical Water

V.S. Zhigarkov, V.I. Yusupov.

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Key words: supercritical water, laser-induced formation, laser pulse, laser technologies, phase diagram.

The work uses the possibility of formation supercritical water (SCW) upon absorption
of a laser pulse with a duration of 8 ns by a 50 nm thick gold film, which is in contact with
water. To estimate the growth of the pressure jump film, we used an approach based on
measuring the acoustic pressure in the far field using a hydrophone based on a lithium
niobate crystal. The temperature jump was estimated using a reference point — the
melting point of gold. It is shown that at a laser pulse energy of 65 mJ, a thin layer of
water in contact with a metal film is in a supercritical state for ~4.5 ns.

doi:10.34984/SCFTP.2020.15.4.005

2020, №4

сс. 49-59

Articles

Key words: milk Thistle fruit, supercritical fluid extraction, carbon dioxide, oil, experiment planning

Milk Thistle [Silybum marianum (L.) Gaertn], which grows in the Republic of Dagestan,
is a promising raw material for obtaining broad-spectrum medicines. Milk Thistle fruit oil,
as a source of higher polyunsaturated carboxylic acids, has anti-inflammatory, woundhealing,
regenerating and antioxidant effects. The process of supercritical fluid extraction
of fatty oil from milk Thistle fruits with carbon dioxide is optimized using a second-order
full-factor uniform plan. The influence of pressure, temperature, and process duration on
the extract yield was evaluated. According to the model used, the optimal conditions are:
a pressure of 41,8 MPa, a temperature of 70 °C, and an extraction time of 140 minutes.
When conducting a confirmation experiment under these conditions, the extract yield
was 25.9 %, which is only 0.5% less than the maximum yield obtained by exhaustive
extraction with n-hexane. The relative error of the model was 1.5%.

doi:10.34984/SCFTP.2020.15.4.004

2020, №4

сс. 39-48

Articles

Key words: organic waste, waste water, purification, concentration, adsorption, microfiltration, supercritical water oxidation

A method for treating wastewater containing organic pollutants has been developed,
including adsorption, membrane concentration and supercritical water oxidation of the
concentrate. It is shown that the introduction of crushed plant waste into wastewater as
sorbents makes it possible to stabilize the process of membrane concentration. The
parameters of the obtained filtrate and the concentrate oxidized in supercritical water
comply with the sanitary standards for discharge into the sewage system.

doi:10.34984/SCFTP.2020.15.4.003

2020, №4

сс. 29-38

Articles

Key words: dispersed system, suspension, milk thistle, subcritical water, extraction

The regularities of the formation of dispersed systems (DS) from extracts of milk thistle
after extraction with water at 150, 200, 250 °C and 5 MPa in a dynamic mode were
studied. The sizes of particles in the obtained DS were determined. It has been established
by high performance liquid chromatography that the particles are formed by silibinin,
silichristin and silidianin. It has been shown that the characteristics of DS particles
depend on the concentration of these compounds in the extract, which makes it possible
to control the size of the formed particles during dynamic extraction.

doi:10.34984/SCFTP.2020.15.4.002

2020, №4

сс. 3-28

Reviews

Key words: thermal conductivity, critical amplitudes, critical point, supercritical fluid, crossover model, heat transfer coefficient

The experimental bases and some aspects of the theory and modeling of transport properties
(thermal conductivity, viscosity, thermal diffusion coefficient) of fluids in the critical and
supercritical regions are considered. Information on the critical thermal conductivity
anomaly (theory and experiment) is analyzed in detail. A brief historical reference is
given on the first experiments on thermal conductivity in the critical region, carried out
mainly by Soviet researchers. The features of measuring the thermal conductivity in the
critical region and various interpretations of its critical anomalies are considered. Various
approaches to describing the critical anomaly in the transport properties of supercritical
fluids, primarily the crossover approach, are discussed. The possibility of representing
critical thermal conductivity anomalies described on the basis of the coupled modes
theory of dynamic critical phenomena, in a simplified version with two critical amplitudes
and with one «cutoff» parameter \(\overline q_D\) (boundary value of the wave number), characteristic
of a particular fluid, is shown. A procedure for determining these specific parameters is
developed on the basis of the corresponding states princi ple. This made it possible to
develop a universal method for describing critical anomalies of transport properties of
supercritical fluids. In a pulse experiment, conditions were found under which anomalies
of properties did not manifest themselves.

doi:10.34984/SCFTP.2020.15.4.001

2020, №3

сс. 103-109

Articles

Solubility Computation of 1,2,4-Thiadiazole Derivatives in Supercritical Carbon Dioxide

N.N. Kalikin, Y.A. Budkov, A.L. Kolesnikov, M.A. Krestyaninov, D.V. Ivlev, M.G. Kiselev.

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Key words: solubility, free energy of solvation, 1,2,4-thiadiazole derivatives, supercritical carbon dioxide, density functional theory, group contribution methods

In this paper we present the results of the solvation free energy computation, based on
the classical density functional theory, for the set of 1,2,4-thiadiazole derivatives in the
supercritical carbon dioxide medium at three temperatures: 308.15, 318.15 and 328.15 K.
Basing on the obtained values we determined the solubility values of the compounds. We
found a correlation between the magnitude of the quadrupole moment of the compound
molecule and its free energy of solvation.

doi:10.34984/SCFTP.2020.15.3.011

2020, №3

сс. 87-102

Articles

Key words: water, water fluid, parameters of state, temperature, density, ideal gas, incompressible liquid, supercritical fluid, solubility, dielectric constant, ionic product

The influence of state parameters on the properties of water fluids is analyzed from the
point of view of their correspondence to simple models of an ideal gas and an incompressible
liquid. The main characteristics of the areas, in which the physical state of the fluid
qualitatively differ, have been determined as (1) rarefied steam; (2) «before-critical» water,
(3) sub-critical water; (4) dense steam; (5) supercritical fluid; (6) gas close to ideal. The
boundaries of these regions are set by the values of temperature and density, which determine
the ratio of the energies of thermal motion and intermolecular interactions. The areas of
practical utilization of water fluids depending on the density, dielectric constant and ionic
product, which determine their properties as a solvent, reaction medium, reactant, and
catalyst for various types of processes, are briefly characterized.

doi:10.34984/SCFTP.2020.15.3.010

2020, №3

сс. 73-86

Articles

Key words: supercritical antisolvent preci pitation technique, supercritical carbon dioxide, yttrium-iron garnet, thermodynamics, kinetics

In this paper, the authors synthesized and studied the phase formation of yttrium-iron
garnet (YIG) using the supercritical antisolvent preci pitation technique (SAS) at the
initial stage for the first time. The effect of supercritical CO2 on the solution of acetates
in the quasi-equilibrium state causes an abnormally high mobility of the structure elements.
As a result, it becomes possible to form the equilibrium phase of the YIG solid product
directly (without the appearance of transition oxides) at temperatures much lower than
by solid-phase synthesis. The temperature decrease is due to a significant decrease in the
activation energy of the solid solution.

doi:10.34984/SCFTP.2020.15.3.009

2020, №3

сс. 62-72

Articles

Transformation of Vanillin in Sub- and Supercritical Propanol-2

A.D. Ivakhnov, I.S. Shavrina, D.S. Kosyakov, I.O. Dumanskii.

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Key words: propanol-2, vanillin, supercritical conditions, phenols, gas chromatography

The sequence of product formation and kinetic regularities of vanillin transformation in
propanol-2 medium at different temperatures and duration of the process in a static mode
are investigated. The vanillin conversion products were determined using gas
chromatography-mass-spectrometry method. At a high degree of vanillin conversion
(up to 100 %), a relatively small number of compounds are formed, the main of which
are substituted phenols and their derivatives, such as vanillyl alcohol and its isopropyl
ether, guaiacol, creosol (2-methoxy-4-methylphenol), and homocatechol (3,4-
dihydroxytoluene). A scheme of reci procal transformations of intermediate compounds
is proposed.

doi:10.34984/SCFTP.2020.15.3.008

2020, №3

сс. 49-61

Articles

Key words: impregnation, polymethylmethacrylate, carbamazepine, supercritical CO2

In this work we performed an impregnation of polymethylmethacrylate with carbamazepine
in SC-CO2 medium. Impregnation was carried out at two temperatures of 75 °C and
105 °C and SC-CO2 density equal 1.3 of its critical value. In the first stage, in order to
define the kinetic parameters of CO2 sorption by polymer matrix, we applied high pressure
NMR spectroscopy. Two impregnated polymethylmethacrylate samples were obtained
upon impregnation process and further they were analyzed by Raman spectroscopy and
powder X-Ray diffraction.
Basing on the results of Raman spectroscopy we found that both impregnated samples
contain carbamazepine, at that its concentration in polymethylmethacrylate impregnated
at 105 °C is in ∼2.7 times higher than in polymethylmethacrylate processed at 75 °C. It
was also discovered that carbamazepine does not crystallize in the confinement of polymer
matrix. Its solution in polymethylmethacrylate is formed instead. Moreover, processing
temperature also affects on conformational state of carbamazepine molecules entrapped
into polymer matrix.

doi:10.34984/SCFTP.2020.15.3.007

2020, №3

сс. 41-48

Articles

Influence of Temperature and Pressure on the Structure of Polymeric Catalysts Synthesized in Subcritical Water

M.E. Markova, A.A. Stepacheva, Yu.Yu. Kosivtsov, A.I. Sidorov, V.G. Matveeva, M.G. Sulman.

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Key words: heterogeneous catalysts, subcritical synthesis, hypercrosslinked polystyrene

The current paper is devoted to the study of the influence of temperature and pressure
of subcritical synthesis on the structure of polymeric supports and the composition of
the active phase of the synthesized catalysts. During the investigation, the optimal
synthesis conditions were chosen for the deposition of the metal-containing phase on
the surface of hypercrosslinked polystyrene.

doi:10.34984/SCFTP.2020.15.3.006

2020, №3

сс. 35-40

Articles

Key words: carbon dioxide, supercritical condition, solvatochromic parameters, dyes, polarity, donor-acceptor properties, temperature, pressure

Kamlet—Taft solvatochromic polarity parameters are determined for carbon dioxide in
sub- and supercritical state at 22, 40, 60 and 80 °С and 10,0—30,0 MPa. As solvatochromic
indicators, 2,6-di phenyl-4-(2,4,6-triphenyl-1-pyridino)-phenolate (Reichardt’s betaine)
and benzophenone were used to determine ET, and to determine β and π parameters,
respectively, 4-nitrophenol and 4-nitroanisole were used. It was found that the values of
the parameters characterizing the polarity and donor-acceptor properties of CO2 are
practically independent of the state parameters, since these properties are determined by
the structure of the molecule.

doi:10.34984/SCFTP.2020.15.3.005

2020, №3

сс. 27-34

Articles

Key words: supercritical antis olvent preci pitation, carbon nanotubes, polymer composites

The possibility to obtain polyurethane—carbon nanotube composites using supercritical
antisolvent preci pitation (SAS) is demonstrated. The influence of solvent, polymer concentration
in the solution, spraying nozzle and suspension flow rate on composites
preparation efficiency and morphology is investigated.

doi:10.34984/SCFTP.2020.15.3.004

2020, №3

сс. 21-26

Articles

Catalytic Conversion of Bio-Oil into Aromatics in the Medium of Supercritical Solvent

A.A. Dmitrieva, A.A. Stepacheva, M.A. Monzharenko, Yu.Yu. Kosivtsov, A.I. Sidorov, M.G. Sulman, V.G. Matveeva.

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Key words: bio-oil, conversion, transition metals, propanol-2, supercritical solvent

This paperis devoted to the study of the catalytic conversion of bio-oil obtained by the
pyrolysis of pine wood waste using supercritical propanol-2. The method proposed in
this work is suitable for the production of monoaromatics mixture from the pyrolysis
liquid. The oxygen removal degree was found to beca. 80 %.

doi:10.34984/SCFTP.2020.15.3.003

2020, №3

сс. 11-20

Articles

The Formation of the Supramolecular Structure of the Composite Aerogels Based on Sodium Alginate and Chitosan

N.A. Gorshkova, O.S. Brovko, I.A. Palamarchuk, A.D. Ivakhnov, K.G. Bogolitsyn, N.I. Bogdanovich, D.G. Chukhchin.

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Key words: sodium alginate, chitosan, supercritical drying, aerogel, interpolymer complex, furacilin

Composite aerogel materials based on the alginate-chitosan interpolyelectrolyte
complex with calcium carbonate using supercritical fluids were obtained. Aerogels have
developed mesoporous structure. The specific surface area of the samples is 400 m2g-1,
the average pore size is 19.3 nm, and the total pore volume is 1.93 cm3g-1. New
materials are superadsorbents. 1 g of aerogel retains 60 g of liquid while maintaining
its shape. The possibility of using the obtained composite aerogels to create wound
coatings with the inclusion of an antiseptic medicinal substance (furacilin) was
shown. It was found that for all samples of aerogels, the furacilin release profile from
the aerogel matrix corresponds to the dynamics of controlled release. It was shown
that within 5 hours there is almost complete release of furacilin (88—95 %) from the
aerogel matrix, which is due to the developed surface of the material.

doi:10.34984/SCFTP.2020.15.3.002

2020, №3

сс. 6-10

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