Статьи журнала «Сверхкритические Флюиды: Теория и Практика»

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2007, №4

сс. 43-59

Articles

Key words: ZnO nanoparticles, synthesis, organic compounds, syngas, H2O and CO2 supercritical fluids

When studying oxidation of solid and liquid zinc (Zn)S,L by sub- and supercritical water, supercritical CO2 and mixture of H2O/CO2, formation of (ZnO)n nanoparticles was found out. We have called this process chemical re-condensation (ChR). According to our investigations, nanoparticles of 2÷100 nm, nanoneedles and nanorods with 10÷100-nm diameter and up to 50-µm length, and mechanically strong nanostructured ceramics are formed, depending on the conditions of ChR. The cluster mechanism of ChR triggering was suggested. Kinetic parameters of ChR of (Zn)S,L in H2O were determined. The higher rate of ChR in H2O in comparison with CO2 is probably caused by orientation of dipole molecules of H2O in the field of contact voltage at (Zn)S,L/(ZnO)n boundary and prolongation of the molecule life time at the absorbed state. At ChR of zinc in CO2 carbon is formed together with CO, and in H2O/CO2 mixtures paraffin and aromatic hydrocarbons, alcohols and formaldehyde are formed together with H2 and CO.

2007, №4

сс. 30-42

Articles

Reactions of Ozone with Organic Substrates in Supercritical Carbon Dioxide

D.A. Lemenovskii, S.A. Yurin, V.V. Timofeev, V.K. Popov, V.N. Bagratashvili, Yu.E. Gorbaty, G.P. Brusova, V.V. Lunin.

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Key words: ozone, ozonation of organic substances, supercritical carbon dioxide (SC-CO2), dicyclopentadiene

The new original procedure for preparative reactions of ozone with organic substrates in supercritical (SC) fluids as solvents is proposed. Reactions of ozone with o-isopropenylaniline and dicyclopentadiene as model substrates are investigated, and their products are identified using GC-MS, IR- and NMR-spectroscopies. It is demonstrated that in the case of reaction of ozone with o-isopropenylaniline SC-CO2 not only plays the role of efficient solvent for both ozone and organic substrate, but also stabilizes ozone (prevents its decomposition)  and participates in the process as a co-reactant.

2007, №4

сс. 5-29

Reviews

Key words: light alkanes, methane, ethane, propane, conversion, oxidation, critical point, supercritical water

The features of light alkanes (LA) as prospective raw materials for production of bulk chemicals from natural gas are analyzed. The literature data on methane, ethane, and propane reactions in supercritical (SC) conditions are reviewed. It is demonstrated that both experimental studies of LA transformations under high temperatures and pressures (in supercritical water in particular) and description of their kinetics face serious difficulties. However, SC conditions provide with new opportunities due to specific trends in thermodynamic properties of substances in the nearest neighborhood of their critical point and in supercritical region.

2007, №4

сс. 3-4

Editorial note

2007, №3

сс. 101-102

Information

2007, №3

сс. 98-100

Information

2007, №3

сс. 81-97

Articles

Doppler Spectroscopy of Near-critical Carbon Dioxide in Free Volume and Nanopores

V.N. Bagratashvili, K.P. Bestemyanov, V.M. Gordienko, M.V. Kondratyev, A.N. Konovalov, V.K. Popov.

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Key words: critical point, phase transition, nanopores materials, optical heterodyning, critical opalescence

The comparative study of optical properties of near-critical carbon dioxide in free volume and in nanopores is performed by optical heterodyning of laser light back-scattering. The universal [(Т - Тс)/Тс]0,63 law for temperature dependence of scattering spectral width is obtained for C02 in free volume, while for C02 in nanopores of aerogel and Vycor glass the significant change of scattering parameters is revealed. No alteration in the critical temperature of C02 (detected by the maximum of dynamic scattering) is found in nanopores relative to free volume; the latter is explained by the effect of adsorbed CO2 layer on the nanopore surface.

2007, №3

сс. 74-80

Articles

Key words: irradiated nuclear fuel, Uranium, liquid and supercritical carbon dioxide, dissolution

The possibility of irradiated nuclear fuel (INF) processing in supercritical and liquid carbon dioxide media is demonstrated using the real INF from nuclear power plants equipped with reactors of RMBK and VVER types.

2007, №3

сс. 67-73

Articles

Key words: desactivation, stainless steel, radionuclides, liquid carbon dioxide, spent nuclear fuel

Combined decontamination method coupling the steam decontamination with the decontamination in liquid carbon dioxide media is tested. A separate use of steam and carbon dioxide decontamination is less effective than the combined method. The surface purified using the combined method is practically free of both initial contaminants and decontaminating compositions.

2007, №3

сс. 57-66

Articles

Key words: supercritical fluid, liquefied gas, carbon dioxide, extraction, radionuclides

The work is devoted to a comparison of extraction processes of metals macro- and microquantities by complexon solutions in supercritical (SC) and liquid CO2. It is demonstrated that in the most cases the regularities of liquid-liquid extraction also serve in extraction by liquid and SC-CO2. The differences between the extraction by "traditional" solvents and by carbon dioxide is mostly kinetic due to a much lower viscosity of the latter in both liquid and SC states. The specific features of metal SFE become significant only in the case of extraction of microquantities.

2007, №3

сс. 48-56

Articles

Key words: carbon dioxide, freon, supercritical fluid, Uranium, Plutonium, irradiated nuclear fuel, extraction

Supercritical freon-22 and liquid freon-134a can dissolve 11÷12 and 19÷25 vol.% of tributylphosphate (TBP), respectively, in dynamic conditions. These solutions efficiently extract nitric acid up to mole ratios [HNO3] : [TBP] from 1.5:1 to 2.3:1. The solution of TBP · nHNO3 adduct in freon-134a efficiently dissolves uranium and mixtures mimicking the irradiated nuclear fuel from reactors of VVER type.

2007, №3

сс. 40-47

Articles

Deactivation in the Media of Supercritical Fluids and Liquified Gases

A.Yu. Shadrin, A.A. Murzin, D.N. Shafikov, V.A. Kamachev.

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Key words: carbon dioxide, freon, Americium, Cesium, Strontium, deactivation

It is demonstrated that supercritical CO2, liquified CO2 and freon-134a can be utilized as a medium for supercritical fluid extraction (SFD). While using for this purpose an enlarged pilot installation, the desactivation of the protective cloths and metallic articles down to the background level in the medium of liquified CO2 is accessible.

2007, №3

сс. 25-39

Articles

Key words: supercritical and liquid carbon dioxide, actinides, fission products, actinide oxides, organic ligands, radionuclide extraction, spent nuclear fuel reprocessing, countercurrent chromatography

The main regularities of actinide recovery from oxide mixtures by supercritical carbon dioxide CO2 (SC-CO2) containing adduct of tri-n-butylphosphate (TBP) and other organic ligands with HNO3 are studied. It was found that effective actinide extraction by such adducts can be achieved even in the absence of SC-CO2. The extraction of Uranium and main fission products (FP) from model spent nuclear fuel (MSNF) was investigated. It was shown that at >99 % of U extraction the principal fractions of 95Zr и 95Nb (up to 90 %) transferred into adduct phase, as well as 131I and partially 103Ru (~30 %), 99Tc (20 %) and lanthanides (Ln) (up to 10 %). A complete separation of U from 137Cs, 85Sr, 140Ba, as well as from the main part of 140La, 141-144Ce and 147Nd can be achieved. Uranium separation from the remaining part of FP is completed by the adduct dissolution in liquid CO2, transfer of the obtained solution to the separation column of planetary centrifuge, and its further processing by countercurrent chromatography (CCC) in dynamic mode.

2007, №3

сс. 5-24

Reviews

Supercritical Fluid Extraction of Radionuclides

B.F. Myasoedov, Yu.M. Kulyako, A.Yu. Shadrin, M.D. Samsonov.

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Key words: supercritical and liquid carbon dioxide, organic ligands, radionuclides, actinides, actinide oxides, radionuclide extraction, spent nuclear fuel

The developments in supercritical fluid extraction (SFE) of radionuclides progressed since 1990's are reviewed. The possibility of extraction of radionuclides using supercritical and liquid carbon dioxide (SC- and L-CO2) containing different organic ligands from solutions, different matrixes as well as from mixtures of metal oxides was stated. Perspectives of SFE utilization for the reprocessing of spent nuclear fuel (SNF) are discussed. The latter is very promising as a possibility to diminish the production of highly radioactive aqueous and organic solutions, which are formed as by-products in existing technologies of SNF reprocessing.

2007, №3

сс. 3-4

Editorial note

2007, №2

сс. 93-93

Information

2007, №2

сс. 78-96

Articles

Key words: water-salt systems, supercritical fluids, immiscibility of liquid phases, salt solubility, phase diagrams

General features of the phase behavior of systems "water-salt" of different types in sub- and supercritical conditions are analyzed. Type 1 systems are characterized by the increasing solubility of non-volatile component (salt) at rising temperature, whereas in type 2 systems the solubility decreases. An existence of homogeneous unsaturated fluid and of fluid equilibrium with solid salt components at temperatures above the critical temperature of water at any pressures is a distinguishing feature of water-salt systems of type 2. An appearance of supercritical fluid in the systems of type 1 is observed only above the critical temperature of salt. Review of available experimental data permits to establish both the general features of salt solubility behavior in binary systems of various types and some distinctive properties of hydrothermal solubility of the salts of type 2 in aqueous solutions of type 1 salts. Special attention is paid to the processes of heterogenization of supercritical fluid saturated with the salts of type 2 when the salt of type 1 is added and to an influence of immiscibility phenomena, which are common in the hydrothermal salt solutions on fluid phase heterogenization.

2007, №2

сс. 70-77

Articles

Key words: molecular dynamics, supercritical conditions, computer simulation, structural and dynamic characteristics, water solutions of methanol

The analysis of structural and dynamic characteristics of methanol - water mixtures with the method of molecular dynamics was performed for sub- and supercritical parameters. The range of concentrations of methanol in water, corresponding to the maximum of a heat capacity of these mixtures under normal conditions were investigated. It was revealed that water structure is totally destroyed in supercritical solutions methanol - water at the range of concentrations different from the maximum of its heat capacity. However, certain stabilization of water was observed in the region corresponding to this maximum.

2007, №2

сс. 55-69

Articles

Key words: supercritical water, computer modeling, hydrogen bond

The interaction potential that includes non-electrostatic constituent of hydrogen bond is adopted for the modeling of water state in sub- and supercritical conditions. Molecular dynamic approach is used to calculate radial distribution functions, intrinsic energy, topology of the hydrogen bond network and its temporal behavior in different points of the supercritical region of the phase diagram. Effects of parameters of state (temperature, pressure, density) upon the structural and dynamic properties of water are analyzed.

2007, №2

сс. 20-54

Reviews

Key words: aqueous solutions; critical point; equation of state; Krichevskii parameter; partial molar volume; supercritical water; water

The results of the study of thermodynamic properties of infinite dilution aqueous solutions (IDS) near the critical point (CP) of pure water using the Krichevskii parameter and the properties of water are reported. The values of the Krichevskii parameter for aqueous hydrocarbon, alcohol, salt, and gas have been calculated by using the available critical lines and phase diagrams data. The derived values of the Krichevskii parameter have been used to study thermodynamic and structural properties of the IDS in the critical and supercritical regions.