Vapor-liquid equilibria for binary mixtures of carbon dioxide with benzene,toluene and p-xylene

Vapor-liquid equilibrium data for carbon dioxide - benzene, carbon dioxide - toluene, and carbon dioxide - p-xylene were measured for pressures up to 6.5 MPa, and at temperatures of 353 K, 373 K, and 393 K. The solubility of benzene in the dense carbon dioxide vapor phase is higher than that of either toluene or p-xylene. In the liquid phase, carbon dioxide is more soluble in p-xylene than in toluene or benzene. The experimental data obtained were compared with calculations from three correlations: the Peng-Robinson equation, the UNIFAC activity coefficient correlation, and the Perturbed-Anisotropic- Chain Theory (PACT). All three correlations predict phase compositions in good agreement with the experimental data.     

Vapor-liquid and vapor-liquid-liquid equilibria of carbon dioxide/n-perfluoroalkane/n-alkane ternary mixtures

Perfluoroalkanes have numerous applications (e.g., in the medical field and the chemical industry), and their high affinity for carbon dioxide makes them attractive as surfactants and cosolvents. Although research in this area has grown in the past few years, very little phase-equilibrium data is available in the open literature for these systems. In this work, we present, for the first time, predictions of vapor-liquid and vapor-liquid-liquid equilibria of binary and ternary systems of carbon dioxide/n-perfluoroalkane/n-alkane. Our results are based on the SAFT-VR EOS (statistical associating fluid theory of variable range, equation of state), and we study the influence of temperature, pressure, composition, and chain length on the phase diagram. The predicted phase diagrams are based on temperature-independent binary interaction parameters, and no ternary parameters are introduced. Comparisons to the available experimental and molecular simulation data show that the predicted diagrams should provide a good representation of the phase equilibria.     

Liquid-liquid-vapor phase equilibria behavior of certain binary carbon dioxide + n-alkylbenzene mixtures

The liquid-liquid-vapor loci for the binary mixtures CO₂ + n-hexylbenzene, n-heptylbenzene, and n-octylbenzene were experimentally studied. The compositions and molar volumes of the liquid phases are reported along with the pressure and temperature. For these three alkylbenzenes, the nature of the liquid-liquid-vapor loci experiences a transition, with the CO₂ + n-heptylbenzene mixture exhibiting two separate liquid-liquid-vapor branches.     

Vapor-liquid equilibria in binary mixtures formed from hexamethyldisiloxane,toluene and ethanol

Vapor-liquid equilibria have been measured in the binary systems hexamethyldisiloxane-toluene, hexamethyldisiloxane-ethanol and toluene-ethanol between 333.15 and 358.15 K and the results have been correlated using the Wilson equation. All three binary systems exhibit azeotropic behavior in the temperature range studied.     

Correlations for binary phase equilibria in high-pressure carbon dioxide

The high-pressure phase equilibrium in binary mixtures of carbon dioxide and various liquids such as benzene, toluene, m-xylene, chlorobenzene, 1,2-dichlorobenzene, low molecular weight alcohols, amides and a solid, hexachlorobenzene, was modeled using the Peng–Robinson equation of state with quadratic mixing rules. Though the technique of modeling is not new, the key conclusion of the study is that the two adjustable parameters, k_ij and l_ij, vary linearly with the addition of functional groups. In addition, the adjustable parameters are found to be nearly independent of temperature and the same values of k_ij and l_ij can be used for a range of temperatures for the systems considered in the present study.     

Phase equilibria of long-chain polyunsaturated fish oil fatty acid ethyl esters and carbon dioxide,ethane, or ethylene at reduced gas temperatures of 1.03 and 1.13

Phase equilibria of a mixture of long-chain polyunsaturated fish oil fatty acid ethyl esters (FAEEs) with carbon dioxide were measured at 313.2 and 343.2 K, with ethane at 314.0 and 344.6 K, and with ethylene at 290.9 and 318.6 K. The temperatures correspond to reduced gas temperatures of approximately 1.03 and 1.13. The experimental pressures range from 1.6 to 25 MPa. The FAEE mixture is rich in eicosapentaenoic acid ethyl ester (EPA, 52.5 wt.%), and docosahexaenoic acid ethyl ester (DHA, 36.1 wt.%), and a total of 10 components were identified. The experimental temperatures, pressures, solubilities, mass fractions, and calculated equilibrium ratios are reported in tables and graphs. The mass fractions and the equilibrium ratios are reported on a solvent-free basis.     

Estimation of vapour liquid equilibria of binary systems,carbon dioxide–ethyl caproate,ethyl caprylate and ethyl caprate using artificial neural networks

Vapour liquid equilibrium (VLE) data are important for designing and modeling of process equipments. Since it is not always possible to carry out experiments at all possible temperatures and pressures, generally thermodynamic models based on equations of state are used for estimation of VLE. In this paper, an alternate tool, i.e. the artificial neural network technique has been applied for estimation of VLE for three binary systems viz. carbon dioxide–ethyl caproate, ethyl caprylate and ethyl caprate which are of importance in supercritical extraction. The temperature range in which these models are valid is 308.2–328.2 K and the pressure range is 1.6–9.2 MPa. The average absolute deviation for all the three systems in the estimation of liquid phase mole fraction was 3% or less and less than 0.02% for the vapour phase mole fraction. The error was less compared to that estimated by SRK or Peng Robinsons equation of state.     

High-pressure phase equilibria of binary and ternary mixtures of carbon dioxide,triglycerides and free fatty acids: Measurement and modeling with the GC-EOS

Vapor–liquid equilibria were measured for binary systems including carbon dioxide and free fatty acids such as oleic and linoleic acid, triglycerides as triolein or vegetable oils as sunflower oil, and modelled by the Group Contribution Equation of State (GC-EoS). Binary group parameters used in the calculation and prediction of CO₂–triglycerides systems were obtained from the literature but in the case of CO₂-free fatty acids, binary group parameters were adjusted through a parameterization strategy. At the end, a unique set of parameters could be established to model systems of vegetable oils at high pressures in the presence of CO₂. Moreover, a strategy to calculate the two-phase region in a ternary diagram was also studied. The good correspondence between theoretical and experimental results suggests that the strategy and the set of binary group parameters proposed in this work can be reliable predictive tools for using GC-EoS to describe systems involving vegetable oils with a composition based mainly in free fatty acids and triglycerides, such as those which can be encountered, for example, in oil deacidification processes using supercritical CO₂.     

Phase equilibria experiments and calculations for carbon dioxide + methanol binary system

Vapor-liquid equilibria (VLE) data for the carbon dioxide + methanol system was measured at 293.15, 298.15, 310.15, and 323.15 K. Phase behavior measurements were made in a high-pressure visual cell with variable volume, based on the static-analytic method. The pressure range under investigation was between 4.8 and 95.1 bar. The Soave-Redlich-Kwong (SRK)-EOS coupled with Huron-Vidal (HV) mixing rules and a reduced UNIQUAC model, was used in a semi-predictive approach, in order to represent the phase behavior (critical curve, isothermal VLE) of the system. The topology of the phase behavior of the carbon dioxide + methanol system is satisfactory predicted with the SRK/HV-residual UNIQUAC model.      

High-pressure phase equilibria for chlorosilane + carbon dioxide mixtures

Fluid-phase equilibria, including dew points, bubble points, and critical points were measured for four binary systems composed of a chlorosilane and carbon dioxide. The measurements were carried out in a constant-composition, variable-volume cell equipped with a sapphire window, which allowed visual observation of the phases in the cell. A syringe pump was used to inject the CO₂ into the cell and to control its pressure. Methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, and diethyldichlorosilane up to about 0.14 mol fraction were studied in this apparatus and a total of 243 phase-boundary points were obtained. Displacements in the critical point with respect to pure CO₂ of up to 11.81 MPa and 348.05 K were observed. Modeling of the fluid-phase equilibria for three of the four binary systems was done using the Peng–Robinson equation of state, standard van der Waals mixing rules with two binary interaction parameters, and a φ–φ formulation of the equilibrium. The binary interaction parameters were obtained by fitting the model to the experimental data. The model produced excellent agreement between computed and experimental data. Graphical representations of the modeling results are presented and compared to experimental results. The results indicate that the largest chlorosilane (diethyldichlorosilane) produced the largest shift in critical pressure and critical temperature with respect to pure CO₂.     

Adsorption equilibria of binary gas mixtures on graphitized carbon black

Adsorption equilibria for binary gas mixtures (methane-carbon dioxide, methane-ethane, and carbon dioxide-ethane) on the graphitized carbon black STH-2 were measured by the open flow method at 293.2 K. The experimental pressure range was (0 to 1.6) MPa. The extended Langmuir (EL) model and the ideal adsorption solution theory (IAST) have been adopted to predict the equilibria of binary gas mixtures. The results indicate that gas mixtures adsorbed on the homogeneous surface of STH-2 exhibit the nonideal behavior, which is mainly induced by adsorbate-adsorbate interactions. The real adsorption solution theory (RAST) has been used to analyze the property of the adsorbed mixtures. The activity coefficients have been correlated with the Wilson equation. The investigation demonstrates that the nonideality of adsorbed phase is completely dissimilar with the bulk liquid phase. The adsorption of the heavier component would benefit the adsorption of the lighter component.     

Determination of ethyl glucuronide and fatty acid ethyl esters in hair samples

Hair testing for alcohol biomarkers is an important tool for monitoring alcohol consumption. We propose two methods for assessing alcohol exposure through combined analysis of ethyl glucuronide (EtG) and fatty acid ethyl esters (FAEEs) species (ethyl myristate, palmitate, stearate and oleate) in hair (30 mg). EtG was analysed by liquid chromatography–tandem mass spectrometry, while FAEEs were analysed by gas chromatography–tandem mass spectrometry using electron impact ionization. Both methods were validated according to internationally accepted guidelines. Linearity was proven between 3 and 500 pg/mg for EtG and 30–5000 pg/mg for FAEEs, and the limits of quantification were 3 pg/mg for EtG and 30 pg/mg for each of the four FAEEs. Precision and accuracy were considered adequate, processed EtG samples were found to be stable for up to 96 h left in the injector and processed FAEEs samples for up to 24 h. Matrix effects were not significant. Both methods were applied to the analysis of 15 authentic samples, using the cut‐off values proposed by the Society of Hair Testing for interpretation. The results agreed well with the self‐reported alcohol consumption in most cases, and demonstrated the suitability of the methods to be applied in routine analysis of alcohol biomarkers, allowing monitoring consumption using low sample amounts.     

Fluid multiphase equilibria and critical phenomena in binary and ternary mixtures of carbon dioxide, certain n-alkanols and tetradecane

Experimental results of fluid multiphase equilibria occurring in ternary mixtures of near-critical carbon dioxide, certain n-alkanols and tetradecane are presented. The following n-alkanols were used in this investigation: decanol, octanol, heptanol, hexanol and pentanol. In the ternary systems with decanol, octanol or heptanol a closed loop liquid-vapor two-phase region in the three-phase surface liquid-liquid-vapor was found. As far as the ternary system with decanol is concerned, this phenomenon is in agreement with an earlier and unexpected finding of Patton et al. (1993). In addition, it was also found in this study that the phase diagrams of the ternary mixtures with hexanol or pentanol as the n-alkanol show further complications.     

Vapor-liquid equilibria for benzyl alcohol with carbon dioxide, ethane, or nitrogen at elevated pressures

Vapor-liquid equilibrium (VLE) phase compositions were measured for the binary systems of benzyl alcohol with carbon dioxide, ethane, or nitrogen at temperatures from 333.15 K to 453.15 K and pressures up to 19 MPa. Henry's constants were calculated from the isothermal equilibrium data. The new VLE data were correlated by the Patel-Teja equations of state with three different types of mixing rules. In general, using the one-fluid, two-parameter van der Waals mixing rule yielded the best representation for the investigated systems. The validity of a generalized Soave model was also tested with the equilibrium data of carbon dioxide + benzyl alcohol.     

Vapor-liquid equilibria forn-tetradecane-benzene mixtures at 25 and 50°C

Vapor pressures for the benzene+n-tetradecane system have been measured using a static apparatus. The excess Gibbs free energy was calculated using a modified Barker method and a Pade approximant equation. The selection of the most adequate approximation is discussed. Results are compared with those corresponding to other thermodynamic properties. The activity coefficient of benzene at infinite dilution calculated from these data agrees well with the value obtained from the literature.     

Solid–liquid equilibria for the dimethyl ether + carbon dioxide binary system

A recently built experimental setup was employed for the estimation of the solid–liquid equilibria of alternative refrigerants systems. The behavior of dimethyl ether (DME) + carbon dioxide was measured down to temperatures of 131.6 K. To confirm the reliability of the apparatus, the triple point of the DME was measured. The triple point data measured revealed a good consistency with the literature. The results obtained for the mixtures were corrected by the Rossini method and interpreted by means of the Schröder equation.     

Vapor-liquid equilibria for polyisobutylene solutions

Vapor sorption isotherms in binary solutions of polyisobutylene (PIB), (M_η = 4.7 × 10⁶ g/mol) in hydrocarbons (cyclopentane; cyclohexane; n-heptane; 2,2-dimethyl butane; and 2,2,4-trimethyl pentane) and chlorinated methanes [carbon tetrachloride (CCI₄) and chloroform (CHCI₃)] have been determined at 23.5°C using the piezoelectric sorption method. The polymer-solvent interaction parameter χ obtained agrees with previously published values determined by using gas-liquid chromatography and a quartz-helix vapor sorption apparatus. The Flory theory of corresponding-states has been applied to the experimental results through the χ parameter and affords a good prediction of the concentration dependence of χ for solutions of chloroform, carbon tetrachloride, n-heptane, and 2,2-dimethyl butane in PIB. The experimental values of \documentclass{article}\pagestyle{empty}\begin{document}$ [\partial (a_1 /\psi _1 )/\partial a_1 ]_{T,P} $\end{document} for the PIB solutions are constant over the measured concentration range, for example \documentclass{article}\pagestyle{empty}\begin{document}$ [\partial (a_1 /\psi _1 )/\partial a_1 ]_{T,P} $\end{document} = ?4.1 for CCI₄, ?3.65 for CHCI₃, ?3.0 for 2,2-dimethyl butane and n-heptane, ?2.7 for 2,2,4-trimethyl pentane, ?2.7 for cyclohexane, and ?1.7 for cyclopentane, where a₁ is the solvent activity and ψ₁ is the solvent segment fraction. The correlations between the values of \documentclass{article}\pagestyle{empty}\begin{document}$ [\partial (a_1 /\psi _1 )/\partial a_1 ]_{T,P} $\end{document} and the theories of Guggenheim, Miller, Huggins, and Flory are discussed.     

Equations for describing liquid-vapor phase equilibria in binary mixtures

Three forms of equations for describing experimental data on liquid and vapor pressures, depending on temperature and composition at phase equilibria in binary mixtures, are proposed and evaluated. It is determined that the form of equation depends on the relationship between the temperature of a mixture and the critical temperatures of the components of the mixture. Exact data on the phase equilibria in nitrogenoxygen, nitrogen-argon, and oxygen-argon mixtures [1] are approximated to assess the effectiveness of the equations’ forms. It is found that the equations also allow us to determine the phase composition at a given temperature and pressure and temperatures of phases at a given pressure and composition.     

Calculations of phase equilibria for mixtures of triglycerides,fatty acids,and their esters in lower alcohols

The objects of study were mixtures containing triglycerides and lower alcohols and also the products of the transesterification of triglycerides, glycerol and fatty acid esters. The Redlich-Kwong-Soave equation of state was used as a thermodynamic model for the phase state of the selected mixtures over wide temperature, pressure, and composition ranges. Group methods were applied to determine the critical parameters of pure substances and their acentric factors. The parameters obtained were used to calculate the phase diagrams and critical parameters of mixtures containing triglycerides and lower alcohols and the products of the transesterification of triglycerides, glycerol and fatty acid esters, at various alcohol/oil ratios. The conditions of triglyceride transesterification in various lower alcohols providing the supercritical state of reaction mixtures were selected.     

Vapor-liquid equilibria for polybutadiene and polyisoprene solutions

Vapor-liquid equilibria in binary solutions of hydrocarbons (n-hexane, benzene, toluene, cyclohexane) and chlorinated methanes [carbon tetrachloride (CCl₄), chloroform (CHCl₃), and dichloromethane (CH₂Cl₂)] in polybutadiene (PBD) and polyisoprene have been determined at 23.5°C by using the piezoelectric sorption method. The weight-fraction activity coefficient of solvent (a₁/w₁) in cis-PBD (98% cis-1,4 addition) and random cis-trans-PBD (r-PBD, 34.3% cis-1,4 addition; 54.3% trans-1,4 addition; 11.4% vinyl-1,2 addition) are almost equal for CCI₄, CHCI₃, CH₂CI₂, benzene, and toluene solutions, while the values of a₁/w₁ in n-hexane and cyclohexane solutions in cis-PBD are larger than those in r-PBD solutions. The values of a₁/w₁ for solutions of hydrocarbons and chlorinated methanes in cis-1,4 polyisoprene (95% cis-1,4 addition) have been compared with those for cis-PBD.