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1.
Vapor-liquid equilibrium of binary CO2-organic solvent systems (ethanol, tetrahydrofuran, ortho-xylene, meta-xylene, para-xylene)
Željko Knez, Mojca Škerget, Ljiljana Ilić, Christoph Lütge, 2008, original scientific article

Abstract: High pressure vapor-liquid phase equilibrium data (P-T-x-y) for the binary mixtures of organic solvent (ethanol, tetrahydrofuran, o-xylene, m-xylene, p-xylene) with CO2 have been measured at temperatures 313.2, 333.2, 353.2 K and pressures from 1 to 14 MPa using a static-analytic method. For the systemsethanol-CO2 and tetrahydrofuran-CO2, the experimental data at 313.2 and333.2 K are in a good agreement with literature data. The experimental results have been correlated by the Peng-Robinson equation of state in combination with van der Waals one fluid mixing rule with two adjustable parameters.
Keywords: chemical processing, high pressure technology, carbon dioxide, ethanol, tetrahydrofuran, xylene, vapor-liquid equilibrium, experimental data, PR equation of state
Published: 01.06.2012; Views: 1389; Downloads: 70
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2.
Estimation of solid solubilities in supercritical carbon dioxide: Peng-Robinson adjustable binary parameters in the near critical region
Mojca Škerget, Zorka Novak-Pintarič, Željko Knez, Zdravko Kravanja, 2002, original scientific article

Abstract: The density dependence of the binary parameters of the Peng-Robinson equation of state in near the critical region was examined. Published solubility data of eight compounds in pure CO2 have been fitted to the Peng-Robinson equation in combination with one and two parameters van der Waals mixing rules and in combination with the three parameter density dependent mixing rule of Mohamed and Holder. A systematic study has been done to determine the influence of different terms in the mixing rules. In order to obtain density dependence, binary parameters were calculated for each isotherm at particular experimental point separately in the way to equalise experimental and calculated solubility data. The system was formulated as an equation-oriented model and solved by means of a nonlinear programming optimisation algorithm. For all compounds the binary interaction parameters thus obtained were found to vary strongly with pressure in the range from 75 bar to approximately 150 bar, i.e. near the critical end point (CEP) of the low temperature branch of the three phase solid-liquid-gas (SLG) curve. At higher pressures, the parameter is practically independent on pressure. In general, for the systems investigated, kij increases linearly with increasing density and reaches a constant value at higher densities in the range from 700 to 800 kg/m3, depending on the system under investigation.
Keywords: solid liquid equilibria, equation of state, mixing rules, binary parameters, near critical region, nonlinear programming, thermodynamic model, supercritical fluids, CO2, solubility
Published: 01.06.2012; Views: 1421; Downloads: 74
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3.
Calculation of thermophysical and thermochemical properties during hydrocarbon combustion
Jurij Avsec, Franc Zgaga, Milan Marčič, 2002, original scientific article

Abstract: A mathematical model is presented for computing the chemical and thermophysical properties in the process of combustion of natural gas. To identify the parameters of state of combustion products, their composition hasto be known, which may be determined from chemical equilibrium. The computation is performed with the use of chemical potentials and statistical thermodynamics, featuring all important molecular contributions (translation, rotation, vibration, and intermolecular potential energy). A thermal equation of state with two virial terms is used. The real gas mixture is treated as consisting of four components: carbon dioxide, nitrogen, carbon monoxide, and water. Virial coefficients are dependent on temperature and mole fractions of the real components. Mixed terms are taken into account. The caloric equation of state is based on statistical thermodynamics for an ideal gas. Corrections are made in accordance with the second law of thermodynamics and the thermal equation of state. As the whole computation is based on matrix algebra, increasing the number of components presents no problems. We tested our model in the high-pressure region (100 bar) and the low-pressure region (1 bar), in the temperature range 500 - 6000°K. Our model is compared with other analytical models presented in the literature and shows relatively good agreement. At the same time we tested the influence of real conditions on the chemical and thermophysical properties of combustion products.
Keywords: statistical thermodynamics, thermodynamical properties, combustion of natural gas, mathematical models, thermodynamic functions of state, equation of state, virial coefficients
Published: 01.06.2012; Views: 1229; Downloads: 76
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4.
Phase equilibrium measurements and data correlation for the ternary system oleic acid + 1-octanol + carbon dioxide
Chiara Giulia Laudani, Mateja Primožič, Željko Knez, Maja Leitgeb, 2009, original scientific article

Abstract: A study of the high-pressure phase equilibria in the ternary system oleic acid/1- octanol/supercritical CO2 was performed to obtain information for optimization of enzymatic synthesis of n-octyl oleate. Equilibrium data were measured at temperatures of 308.15, 323.15 and 343.15 K over a pressure range from 1 to 25 MPa. Two different apparatuses: a Variable Volume View Cell and a Batch Stirred Tank were used employing synthetic and static-analytic measurement methods, respectively. The measured solubility of dense CO2 in the binary liquid mixture oleic acid/1-octanol covered the range from 0.0781 to 0.7686 of CO2 molar fraction. CO2 solubility increased with increasing pressure up to 10 MPa. At higher pressures, no significant increase was observed. The Soave-Redlich-Kwong equation-of-state (SRK-EoS) with quadratic mixing rules was successfully used for data correlation in the whole P-T-x region studied.
Keywords: data correlation, 1-octanol, oleic acid, supercritical carbon dioxide, Soave-Redlich-Kwong equation-of-state, vapor-liquid equilibria
Published: 05.07.2017; Views: 484; Downloads: 52
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