Wide Range Of State Parameters Research Articles

On the Natyre of the Influence of the Architecture of Molecules on the Thermophisical Properties of Alkane Isomers

Purpose. Performing measurements of sound velocity and density in the liquid phase of hexane isomers on the saturation line in a wide range of state parameters, including the critical region.Methods. Using a precision pulse-phase method for measuring the speed of sound in the liquid phase of hexane isomers and their density with a pycnometer at atmospheric pressure. The paper discusses the results of precision measurements of sound velocity and density in five hexane isomers. The speed of sound was measured on the equilibrium curve in the liquid phase of isomers by the pulse-phase method in the range from -30 to their critical point. The measurement error of the speed of sound did not exceed 1 m/s. Density measurements were performed using a pycnometer at atmospheric pressure in the range from -30 to their normal boiling point with an error not exceeding 0.05%. The results of sound velocity and density measurements were used to study the character of intermolecular forces. The necessity of taking into account the non-covalent chemical interaction of molecules of the studied substances is shown.Results. Sound velocity measurements were performed on the saturation line in the liquid phase of all five hexane isomers in the temperature range from -30 C to the critical temperature of all 5 isomers. The obtained results are used to study the features of the dependence of the energy of intermolecular forces on the parameters of the state in the field of research.Conclusion. It is shown that the energy of intermolecular forces in marginal hydrocarbons and other simple substances is the sum of 3 terms representing: 1) the energy of the dispersive attractive forces proportional to the square of the density; 2) the energy of the repulsive forces proportional to the biquadrate of the density and 3) the energy of weak chemical non-covalent binding forces proportional to the cubic root of the density of matter.

Metoda obliczania jednostkowego składu węglowodorów na podstawie skumulowanego składu frakcyjnego próbek ropy naftowej i kondensatu

The composition of oils is the main source of information that enables the evaluation and modeling of their physical, thermal and chemical properties (including their critical properties) across a wide range of state parameters. The more comprehensively the composition of oils is analyzed, the more precise information is provided for calculations and problem-solving in the field of oilfield mechanics and related areas, such as the extraction, preparation, transportation, and processing of oils and their fractions. The principal constituents of oils are hydrocarbons. Oils contain hydrocarbons of three homologous series: paraffins, naphthenes and aromas. In oils, there may be hydrocarbons of a mixed composition containing both naphthenic and aromatic rings. In addition to hydrocarbons, oils also contain oxygen, sulfur, nitrogen and other constituents. These compounds are the primary elements of asphaltene-resinous substances (ARS) found in oil. They are characterized by high relative densities (often exceeding 1 g/cm3), dark coloration, and relative chemical instability when exposed to elevated temperatures, oxygen, adsorbents, etc. The composition of asphaltene-resinous substances encompasses a wide range of substances. The validity of the proposed technique is justified by the observation that the data of molecular weight, Watson characteristic factor, and experimental density calculated from molar compositions should align on the same surface with a high degree of correlation. In addition, the experimental and calculated values, in terms of molecular composition, of molecular weights should lie on a straight line passing through the origin of coordinates with a slope coefficient equal to unity and exhibit high degree of correlation.

Molecular Modeling of Supercritical Processes and the Lattice—Gas Model

The existing possibilities for modeling the kinetics of supercritical processes at the molecular level are considered from the point of view that the Second Law of thermodynamics must be fulfilled. The only approach that ensures the fulfillment of the Second Law of thermodynamics is the molecular theory based on the discrete–continuous lattice gas model. Expressions for the rates of the elementary stage on its basis give a self-consistent description of the equilibrium states of the mixtures under consideration. The common usage today of ideal kinetic models in SC processes in modeling industrial chemistry contradicts the non-ideal equation of states. The used molecular theory is the theory of absolute reaction rates for non-ideal reaction systems, which takes into account intermolecular interactions that change the effective activation energies of elementary stages. This allows the theory to describe the rates of elementary stages of chemical transformations and molecular transport at arbitrary temperatures and reagent densities in different phases. The application of this theory in a wide range of state parameters (pressure and temperature) is considered when calculating the rates of elementary bimolecular reactions and dissipative coefficients under supercritical conditions. Generalized dependencies are calculated within the framework of the law of the corresponding states for the coefficients of compressibility, shear viscosity, and thermal conductivity of pure substances, and for the coefficients of compressibility, self- and mutual diffusion, and shear viscosity of binary mixtures. The effect of density and temperature on the rates of elementary stages under supercritical conditions has been demonstrated for a reaction’s effective energies of activation, diffusion and share viscosity coefficients, and equilibrium constants of adsorption. Differences between models with effective parameters and the prospects for developing them by allowing for differences in size and contributions from the vibrational motions of components are described.

Thermal Conductivity Calculation Model for Refrigerant Mixtures in the Vapor Phase

Thermal conductivity measurements of ten refrigerant mixtures (R-404A, R-406A, R-407C, R-409A, R-410A, R-415A, R-507A, R-227ea/R-134a 61.5/38.5, R-227ea/R-134a 88.8/11.2 and R-227ea/R-134a 45/55) in the gas phase are analyzed. The thermal conductivity was studied with the same experimental setup, which improved the reliability of the results, excluding thereby systematic errors caused by using different methods to measure thermal conductivity. The reported experimental data have 1.5 % to 2.5 % uncertainty at 0.95 confidence level with a coverage factor of k = 2. Equations for calculating thermal conductivity depending on temperature and pressure are given for each mixture. The equations for thermal conductivity on the dew line and in the ideal gas state are obtained. A model for predicting thermal conductivity on a wide range of state parameters is proposed based on obtained experimental data and the theory of thermodynamic similarity. A comparison of the experimental data with the calculation model gives the standard deviation at 0.4 % to 2.1 %, which does not exceed the measurement error.

On the nonmonotonous behavior of the thermal properties of fullerene C60 / o-xylene solutions

This paper presents the experimental data for the thermal properties of fullerene C60 / o-xylene solutions over a wide range of state parameters. The density was experimentally measured within a fullerene mass concentration range of 0–0.55% and a temperature range 273 K − 353 K. It was shown that the additives of fullerene C60 reduced the density of o-xylene in the concentration range from 0 to (0.05 ± 0.01) wt.%. The temperature and concentration dependences of the isothermal compressibility and density fluctuations were analyzed. It was demonstrated that the temperature dependences of the density fluctuations show up as practically equidistant lines. This fact can be explained due to thermodynamically similar behavior of fullerene C60 / o-xylene solutions and pure o-xylene. We found that the concentration dependences of the isothermal compressibility and density fluctuations in the concentration range of fullerene 0 ≤ wC6 ≤ 0.2% have zones of extremal changes. The zones coincide in the concentration range of fullerene with a zone of extreme decrease in the density. In our opinion, the reason of a nonmonotonous behavior of the thermal properties of fullerene C60 / o-xylene solutions is the effect of fullerene on the density fluctuations of the base liquid as well as a quasicrystalline structure of a liquid phase.

Prediction of the Viscosity of Liquid Petroleum Products

The article deals with the new technique for predicting the viscosity of liquid petroleum products, which differ significantly in physicochemical properties and fractional composition, in a wide range of state parameters. No specific information is used to predict viscosity other than molar mass, average volume boiling point, and relative density at 20 °C. It is shown that the deviation of the predicted values from the experimental data is comparable to the error of the viscosity measurement. Methods for correcting the calculation results using limited experimental information are proposed. The application of the developed method is advisable in conditions of a lack of empirical information about the petroleum products viscosity. Keywords: viscosity prediction; petroleum products; petroleum fractions.

Possibilities of the Molecular Modeling of Kinetic Processes under Supercritical Conditions

Current possibilities of modeling the kinetics of supercritical processes are considered, based on the theory of an absolute rate of the reaction for non-ideal reaction systems, which considers intermolecular interactions that change the effective energy of activation of elementary stages. This allows the theory to describe the rates of elementary stages for arbitrary temperatures and densities of the reagent in different phases. Application of this theory in a wide range of state parameters (pressure and temperature) is examined while calculating elementary bimolecular reactions and dissipative coefficients under supercritical conditions. Generalized dependences within the law of corresponding states are calculated for the compressibility, viscosity, and thermal conductivity coefficients of pure substances and those of the compressibility, self- and mutual diffusion, and viscosity of binary mixtures. The effect density and temperature have on the rates of elementary stages under supercritical conditions is demonstrated for a reaction’s effective energies of activation, diffusion and share coefficients, and equilibrium constants of adsorption. Differences between models with effective parameters and the prospects for developing them by allowing for differences in size and contributions from the vibrational motions of components are described, along with ways of improving the accuracy of describing correlation effects.

Study of the heat conductivity coefficient of heat carriers and working media in a wide range of state parameters

Study of the heat conductivity coefficient of heat carriers and working media in a wide range of state parameters

The effect of fullerene C60 additives on the density of o-xylene

The results of the experimental study of the density of o-xylene/ fullerene C60 solutions in the concentration range 0-0.55 wt.% and temperatures 283-343 K are presented. The density was measured by a pycnometric method with an extended uncertainty of 0.07%. The concentration and temperature dependences of the density of o-xylene/ fullerene C60 solutions were obtained. It was shown that the temperature dependences of the density form a family of almost equidistant straight lines. At the same time, the concentration dependences of the density have a peculiarity that indicates probable structural transformations in the base fluid when a small amount of fullerene C60 is added. It was shown that all concentration dependences of the density of the studied solutions have a minimum in the vicinity of the fullerene concentration of 0.05 wt.% in the entire investigated temperature range. In addition, these dependences consist of two branches with different behavior. Of interest is the phenomenon of the density reduction in the region of small fullerene C60 additives to o-xylene. It is proposed to use an extended scaling model with a universal for non-associated substances crossover function for predicting the density of o-xylene/ fullerene C60 solutions in a wide range of state parameters. Within this model, the pseudocritical parameters of o-xylene/ fullerene C60 solutions were calculated. The authors note that the concentration dependences of the pseudocritical parameters also have a minimum in the vicinity of the fullerene concentration of .0.05 wt.%. The density of o-xylene/ fullerene C60 solutions calculated according to the proposed equations are consistent with the experimental data within the extended uncertainty. The excess molar volume of o-xylene/ fullerene C60 solutions was calculated.

Экспериментальное исследование процесса извлечения органического вещества из твердых горючих ископаемых в широком диапазоне параметров состояния, включая и критическую область

The experimental study of supercritical extraction of the organic substance (OS) from various genetic types of oil shale in a wide range of state parameters was carried out. The dependences of the liquid yield on the temperature at pressure values varying from 3 to 20 MPa were identified. It was found that pressure has a significant effect on the overall degree of organic substance conversion and the liquid yield. With an increase in reactor pressure, the dissolving capacity and the solvent penetration depth increase which contributes to full extraction of soluble components of the organic substance from the porous structure. The results of the study of extraction of the organic substance from oil shale showed that with an increase in pressure the degree of organic substance conversion and the total liquid yield increase by 49-73% and 1,9-3,9 times respectively. The article concludes that variation in thermodynamic parameters of the supercritical fluid extraction process can be used to increase the degree of OS conversion and the liquid yield.

A unified low-parametrical equation used to calculate the viscosity coefficient of liquid, gas, and fluid. Argon. Xenon

A simple unified low-parametric equation has been obtained for describing the coefficient of argon and xenon viscosity in a wide range of state parameters. It is shown that the proposed low-parametric equation for calculating the viscosity coefficient of liquid and gas allows reliable extrapolation beyond the studied region.

Unified low-parametrical equation used to calculate the viscosity coefficient of argon

Using the previously obtained dependence of excess viscosity on internal energy density and low-parametric unified equation of state for calculation of thermodynamic properties of liquid, gas, and fluid, the equation for the excess viscosity of argon in the range of the “mixed” mechanism of momentum transfer in the shear flow was derived. Different versions of approximation of excess viscosity dependence on the density of interaction energy were compared, and the optimal version of this dependence was determined. A simple unified low-parametric equation was obtained for describing the coefficient of argon viscosity in a wide range of state parameters. It is shown that the proposed low-parametric equation for calculating the viscosity coefficient of liquid and gas allows reliable extrapolation beyond the studied region.

Enthalpy and numerical simulation of phase transitions in a Zr–C system

An approximate method for calculating the enthalpy of a Zr–C system in a wide range of state parameters (including the liquid phase) is proposed. The dynamics of phase transitions upon laser heating of Zr–C samples is simulated numerically based on the results of calculating enthalpy. Typical calculated thermograms of heating and cooling are presented; they demonstrate the possibility of identifying the phase-transition temperatures in experiments with laser heating from characteristic features of the thermograms.

Dynamic and Static Characteristics of Drug Dissolution in Supercritical CO2 by Infrared Spectroscopy: Measurements of Acetaminophen Solubility in a Wide Range of State Parameters

In this work we use infrared spectroscopy to investigate solubility properties of a bioactive substance in supercritical CO2 (scCO2). By using acetaminophen as a model compound, we show that the method can provide high sensitivity that makes it possible to study solubility at small concentrations, up to 10–6 mol·L–1. This method also allows one to investigate the kinetics of the dissolution process in supercritical solvent. Our measurements at two different points of the (p,T) plane ((40 MPa, 373 K) and (40 MPa, 473 K)) have shown significant difference in the kinetic mechanisms of acetaminophen dissolution at these two states: at higher temperature the dissolution process in scCO2 has two steps: (i) “fast” step when the acetaminophen concentration in scCO2 quickly reaches (70 to 80) % of the saturation level and (ii) a subsequent “slow” step where the acetaminophen concentration slowly increases up to the saturation level. However, at lower temperature, the dissolution process has only one, “slow” step.

AQUA AMMONIA ELECTROLYTIC CHARACTER AND TPP COOLANT CONDUCTOMETRIC QUALITY CONTROL UNDER HIGH TEMPERATURES AND PRESSURES

To improve the operational conductometric steam quality control at the TPP, CHPP, and NPP, the technique for NaCl and NH4OH concentration in the saturated and superheated steam of the high- and supercritical pressure steam generators is developed, and a device for its implementation is offered. The error of determination in the range of the concentrations specific for the operated power plants is estimated. The equations describing the behavior of the thermodynamic dissociation constant, and limiting equivalent conductance of NH4OH in a wide range of state parameters that can be used in calculating the concentrations according to the proposed technique, as well as in water chemistry organization and management, are proposed. The assessment of the approximation error of dependences for the experimental data on the dissociation constants and limiting equivalent conductance is given.

Isochoric heat capacity and the T-ρ dependence of refrigerants of a propane series

An analysis of the principles of thermodynamic properties of refrigerants of a propane series is per- formed over a wide range of state parameters, including the critical range.

Solvation of Electrolytes and Nonelectrolytes in Aqueous Solutions

A new theory of electrolyte and nonelectrolyte solutions has been developed which, unlike the Debye-Hückel method applicable for small concentrations only, makes it possible to estimate thermodynamic properties of a solution in a wide range of state parameters. One of the main novelties of the proposed theory is that it takes into account the dependence of solvation numbers upon the concentration of solution, and all changes occurring in the solution are connected with solvation of the stoichiometric mixture of electrolyte ions or molecules. The present paper proposes a rigorous thermodynamic analysis of hydration parameters of solutions. Ultrasound and densimetric measurements in combination with data on isobaric heat capacity have been used to study aqueous solutions of electrolytes NaNO3, KI, NaCl, KCl, MgCl2, and MgSO4 and of nonelectrolytes urea, urotropine, and acetonitrile. Structural characteristics of hydration complexes have been analyzed: hydration numbers h, the proper volume of the stoichiometric mixture of ions without hydration shells V(2h), compressibility β(1h), and the molar volume of water in hydration shells V(1h), their dependencies on concentration and temperature. It has been shown that for aqueous solutions the electric field of ions and molecules of nonelectrolytes has a greater influence on the temperature dependence of the molar volume of solution in hydration shells than a simple change of pressure. The cause of this effect may be due to the change in the dielectric permeability of water in the immediate vicinity of hydrated ions or molecules. The most studied compounds (NaCl, KCl, KI, MgCl2) have been studied in a wider range of solute concentrations of up to 4-5 mol/kg. Up to the complete solvation limit (CSL), the functions V(1h) = f(T) and β(1h) = f(T) are linear with a high correlation factor, and the dependence Y(K,S) = f(β1V1*) at all investigated concentrations of electrolytes and nonelectrolytes up to the CSL enables h and β(h)V(h) to be determined on the basis of relationships obtained in the study. The behavior of nonelectrolyte solutions is no different from that of electrolyte solutions, although it is possible to trace the difference between hydrophobic and hydrophilic interactions.

Simulation of the supramolecular organization and permittivity of methanol over a wide range of state parameters, including the supercritical region

Supramolecular structure models were suggested to describe the permittivity of methanol over a wide range of state parameters from the melting point to the supercritical region. The models were based on the quasi-chemical model of a nonideal associated solution. The permittivity and dipole correlation factor of methanol were calculated over the temperature range 177–593 K at pressures from 0.1 to 20 MPa for two supramolecular structure models. Methanol molecules formed chain associates according to the first model and chain and cyclic aggregates according to the second one. Both models successfully described the experimental data on pure methanol, but the inclusion of cyclic aggregates was necessary for consistency with models of methanol solutions in various solvents over the entire composition range. The thermodynamic and structural parameters of supramolecular aggregates were calculated. The particle-size distributions of aggregates and other integral and differential characteristics of association over the whole range of fluid methanol state parameters were determined for the first time.

Theory for the determination of activity coefficients of strong electrolytes with regard to concentration dependence of hydration numbers

A new theory of electrolyte solutions is discussed which, as opposed to the Debye–Huckel method valid for relatively small concentrations only, enables one to describe the thermodynamic properties of electrolyte solutions over a wide range of state parameters. The novelty of the proposed theory is that it takes into account the dependence of hydration numbers upon concentration, the fact that failed to attract much attention before. The applicability of the theory to the calculation of activity coefficients of some electrolytes (LiCl, NaCl, KCl, RbCl, and CsCl) is demonstrated. A method is proposed for the determination of the thermodynamic parameters of solvation of separate ions.

Thermal equation of state for real gas in a wide range of state parameters, including the critical region

The compressibility factor was calculated in a wide range of parameters including the critical region using the equations of state obtained previously for real gas and conditions and limitations formulated by the authors for the form (structure) of the equation of state. It was determined that maximal deviations of compressibility factor values calculated by these analytical equations from the experimental (tabulated) values occur mainly within the critical region. A corresponding correction was introduced into the initial equation, and the analytical equation accurately describing experimental data in a wide range of real gas state parameters, including the critical region, was derived. It was shown by the example of analysis of high-accuracy experimental data on thermal properties of helium in the critical region that data description by the proposed analytical equation is at least as good as that obtained by the equation of fluctuation theory (scaling). It is shown that the proposed equation meets the classical conditions at the critical point.