Key words: critical point, crossover theory, supercritical fluids, scaling, equation of state, Widom lines
This review provides a detailed description of the main provisions of the modern non-classical theory of critical phenomena in pure fluids, based on the hypothesis of scale invariance (scaling). The main types (parametric and six-term or renormalized Landau expansion), theoretically based, crossover equations of state (EoS) of pure fluids and their application to describe the anomalous behavior of thermodynamic properties near and supercritical fluids are described in detail. It is shown that the crossover model of EoS covers all the characteristic features of the scaling behavior of the thermodynamic properties of pure fluids in the asymptotic region of the critical point (CP) in the form of simple power laws with universal critical exponents and transforms into the classical EoS (in particular, the Landau expansion) far from the critical (fluctuation) region. A detailed comparison of the predictions of the crossover model of EoS with experimental data on thermodynamic properties for a wide class of supercritical fluids in a wide range of temperatures and pressures is presented. Crossover EoS of pure fluids were used to quantify the boundary of the region ofinfluence of critical fluctuations on thermodynamic properties, i.e., to estimate the contribution of the fluctuation component to the experimentally observed anomalous of the thermodynamic properties of supercritical fluids. An interpretation of supercritical phase transitions (Widom lines) is given on the basis of the concept of large-scale critical fluctuations and the crossover theory. The review also considers dynamic crossover phenomena to describe the effect of fluctuations on the critical increase in transport properties (thermal conductivity, conductivity temperature, and viscosity) near and in supercritical fluids.
doi:10.34984/SCFTP.2023.18.4.001
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ГОСТ
7.0.100-2018
Influence of critical fluctuations on the thermodynamic and transport properties of supercritical fluids. Non-classical crossover equations of state / – Текст : непосредственный // Сверхкритические Флюиды: Теория и Практика.. – 2023. – Т. 18. – № 4. – С. 3-67. - DOI: 10.34984/SCFTP.2023.18.4.001
TRANSLIT
Vliyanie kriticheskih fluktuacij na termodinamicheskie i transportnye svojstva sverhkriticheskih flyuidov. neklassicheskie krossovernye uravneniya sostoyaniya / – Tekst : neposredstvennyj // Sverhkriticheskie Flyuidy: Teoriya i Praktika.. – 2023. – Т. 18. – № 4. – S. 3-67. - DOI: 10.34984/SCFTP.2023.18.4.001
En
. Sverhkriticheskie Flyuidy: Teoriya i Praktika, 4, 3-67 (2023). https://doi.org/10.34984/SCFTP.2023.18.4.001
Key words: isopropanol, water, oxides, dehydration, dehydrogenation, reduction.
Transformations of a series of simple oxides (Al2O3, SiO2, La2O3, CeO2, PrO2) during their treatment in an autoclave with isopropanol (i-C3H7OH) under supercritical (SC) conditions and subcritical water vapor were studied. It has been shown that at 350 °C in the presence of water vapor, a more intense decrease of specific surface areas and the transition of some of them (oxides of aluminum, lanthanum and praseodymium) into hydroxides occur. Under the influence of i C3H7OH for 6 hours at 350 °C almost complete conversion of PrO2 occurs, accompanied by its reduction and partial transition to hydroxide. In the case of CeO2, no transformations in both media (i C3H7OH, water vapor), including a decrease in specific surface area, hydration and reduction, were observed. The differences in the behavior of CeO2 and PrO2 are explained by the difference in the values of the 4th ionization potential of the Ce and Pr atoms and, as a consequence, in the binding energies of oxygen in higher oxides. The formation of products of various reactions of i-C3H7OH was detected, the composition of which depends on the type of oxide being processed. The most intense transformation of i-C3H7OH occurs in the presence of Al2O3; in this case, dehydration products (propylene, diisopropyl ether) are formed predominantly. In the presence of La, Ce and Pr oxides, the dehydrogenation process is more intense with the formation of acetone and hydrogen (maximum in the presence of La2O3). The catalytic nature of the isopropanol decomposition in the presence of the studied simple oxides has been established. SiO2, which does not have pronoun- ced acid-base and redox properties, exhibits the least activity in the decomposition of i- C3H7OH. It has been suggested that when oxides are treated with SC isopropanol, their structuring occurs under the action of water vapor, which is a product of the transformation of i-C3H7OH. The catalytic activity of the autoclave material (stainless steel) in the decomposition of i C3H7OH along both routes — dehydration and dehydrogenation — was noted.
doi:10.34984/SCFTP.2023.18.4.002
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ГОСТ
7.0.100-2018
Transformations of simple oxides and reactions of isopropanol during their interaction under supercritical conditions / – Текст : непосредственный // Сверхкритические Флюиды: Теория и Практика.. – 2023. – Т. 18. – № 4. – С. 68-84. - DOI: 10.34984/SCFTP.2023.18.4.002
TRANSLIT
Vzaimodejstvie prostyh oksidov s izopropanolom pri temperature vyshe kriticheskoj / – Tekst : neposredstvennyj // Sverhkriticheskie Flyuidy: Teoriya i Praktika.. – 2023. – Т. 18. – № 4. – S. 68-84. - DOI: 10.34984/SCFTP.2023.18.4.002
En
Transformations of simple oxides and reactions of isopropanol during their interaction under supercritical conditions. Sverhkriticheskie Flyuidy: Teoriya i Praktika, 4, 68-84 (2023). https://doi.org/10.34984/SCFTP.2023.18.4.002
Key words: carbamide, ammonia, water-oxygen fluid, oxidation, hydrolysis
The transformations of carbamide in a water-oxygen fluid (at a carbamide concentration of 0.29—0.39 mol/l, oxygen excess coefficient OR = 0.98—1.25, mole fraction of water 70.0—91.3 %) was studied in a reactor periodic type when heated to 873 K at a rate of 1 K/min. It has been shown that the transformations proceed via the mechanism of parallel and sequential reactions, including carbamide hydrolysis, formation and decomposition of cyanuric acid, oxidation of ammonia and products of cyanuric acid decomposition. From the analysis of the time dependences of temperature and pressure, it follows that the oxidation of carbamide occurs predominantly heterogeneously on the surfaces of the reactor wall and the Pt—Rh/Pt-thermocouple inserted into the center of the reaction volume. It has been established that excess oxygen (OR = 1.25) or the addition of NaOH leads to an increase in the fraction of nitrogen converted into N2 and prevents the formation of cyanuric acid. The influence of the concentration of reagents on the ratio of carbamide conversion pathways and the dynamics of heat release is discussed.
doi:10.34984/SCFTP.2023.18.4.003
Cite
ГОСТ
7.0.100-2018
Peculiarities of carbamide hydrolysis and oxidation in water-oxygen fluid / – Текст : непосредственный // Сверхкритические Флюиды: Теория и Практика.. – 2023. – Т. 18. – № 4. – С. 85-96. - DOI: 10.34984/SCFTP.2023.18.4.003
TRANSLIT
Osobennosti gidroliza i okisleniya karbamida v vodokislorodnom flyuide / – Tekst : neposredstvennyj // Sverhkriticheskie Flyuidy: Teoriya i Praktika.. – 2023. – Т. 18. – № 4. – S. 85-96. - DOI: 10.34984/SCFTP.2023.18.4.003
En
. Sverhkriticheskie Flyuidy: Teoriya i Praktika, 4, 85-96 (2023). https://doi.org/10.34984/SCFTP.2023.18.4.003