Yan-Ping Chen

Calculation of the solid solubilities in supercritical carbon dioxide using a modified mixing model

Abstract The Peng–Robinson equation of state and a modified Huron–Vidal type mixing model with a volume correction term are applied in this study to calculate the solid solubilities of aromatic, fatty acid and heavy alcohol compounds in supercritical carbon dioxide. The UNIFAC activity coefficient model with its optimally fitted binary interaction parameters is used in this study. A volume correction term is employed, and its parameters are correlated as functions of the solid molar volume for both non-polar and polar systems. The effect of the sublimation vapor pressure on the calculation of solid solubilities in supercritical carbon dioxide is examined. The sublimation vapor pressures for heavy compounds are fitted in this study to yield the optimally calculated results of the solid solubility. Reasonable sublimation vapor pressures are obtained and their values are well correlated by the Antoine equation. A generalized calculation model is proposed in this study which gives satisfactory results of the solid solubility in supercritical carbon dioxide for both the binary and ternary systems.

Application of a volume-translated Peng-Robinson equation of state on vapor-liquid equilibrium calculations

A volume-translated Peng-Robinson (VTPR) equation of state (EOS) is developed in this study. Besides the two parameters in the original Peng-Robinson equation of state, a volume correction term is employed in the VTPR EOS. In this equation, the temperature dependence of the EOS energy parameter was regressed by an improved expression which yields better correlation of pure-fluid vapor pressures. The volume correction parameter is also correlated as a function of the reduced temperature. The VTPR EOS includes two optimally fitted parameters for each pure fluid. These parameters are reported for over 100 nonpolar and polar components. The VTPR EOS shows satisfactory results in calculating the vapor pressures and both the saturated vapor and liquid molar volumes. In comparison with other commonly used cubic EOS, the VTPR EOS presents better results, especially for the saturated liquid molar volumes of polar systems. VLE calculations on fluid mixtures were also studied in this work. Traditional van der Waals one-fluid mixing rules and other mixing models using excess free energy equations were employed in the new EOS. The VTPR EOS is comparable to other EOS in VLE calculations with various mixing rules, but yields better predictions on the molar volumes of liquid mixtures.

Correlation of the mutual diffusion coefficients of binary liquid mixtures

Abstract A correlative UNIDIF model for the mutual diffusion coefficients of binary liquid mixtures is developed using statistical thermodynamics and the absolute reaction rate theory. In this model, a mole fraction average of the logarithm of the pure-component limiting diffusion coefficients is taken as a reference term. The model expresses the excess part of the diffusion coefficient relative to this reference term in a form similar to that of a UNIQUAC equation which comprises two parts due to the combinatorial and residual contributions. The combinatorial part depends on the molecular sizes and shapes. The residual part includes two binary interaction parameters, which are obtained from data regression, for each binary mixture. Mutual diffusion coefficients of nonpolar+nonpolar, nonpolar+polar and polar+polar fluid mixtures are correlated in this study. Optimal binary interaction parameters are presented. Correlation results using the UNIDIF model for mutual diffusion coefficient are satisfactory and are superior to those from other methods.

Vapor-liquid equilibria at elevated pressures of binary mixtures of carbon dioxide with methyl salicylate, eugenol, and diethyl phthalate

Abstract A semi-flow type apparatus was used to measure the vapor–liquid equilibria (VLE) of CO2 with methyl salicylate, eugenol, and diethyl phthalate binary mixtures at 308.15, 318.15, and 328.15 K over the pressure range from 1.4 to 13 MPa. New VLE data for these binary mixtures are presented and the Henrys constants were determined from these results. The Soave–Redlich–Kwong and the Peng–Robinson equations of state, and the van der Waals, Panagiotopoulos–Reid and Huron–Vidal mixing rules are used to correlate these VLE data. It is shown that both equations of state with the van der Waals mixing rules and two adjustable parameters give satisfactory correlation results.

A group contribution correlation of the mutual diffusion coefficients of binary liquid mixtures

Abstract A group contribution method is developed on the basis of the UNIDIF model [Y.D. Hsu, Y.P. Chen, Fluid Phase Equilibria 152 (1998) 149–168] for the correlation of the mutual diffusion coefficients of binary liquid mixtures. In this group contribution UNIDIF (GC-UNIDIF) model, a mole fraction average of the logarithm of the infinite dilution limiting diffusion coefficients is taken as a reference term. The model expresses the excess part of the diffusion coefficient relative to this reference term in a form similar to that of a UNIFAC equation with two parts due to the combinatorial and residual contributions. The combinatorial part depends on the molecular sizes and shapes. The residual part includes two binary interaction parameters, which are obtained from generalized data regression, for each pair of functional groups. Optimal group interaction parameters are presented. The mutual diffusion coefficients of binary liquid mixtures are calculated for non-polar+non-polar, non-polar+polar and polar+polar fluid mixtures in this study. The calculation results using the GC-UNIDIF model for mutual diffusion coefficient are satisfactory. This model also requires lesser number of parameters than other correlative methods.

Correlation of solid solubility for biological compounds in supercritical carbon dioxide: comparative study using solution model and other approaches

Abstract Solid solubility of biological compounds in supercritical carbon dioxide was calculated using the solution model approach. These biological solutes include steroids, antioxidants, xanthines, drugs and heavy aromatic compounds. The regular solution model coupled with the Flory–Huggins equation was employed. The molar volume of the solute in the supercritical phase was optimally fitted for each biological compound using the experimental solubility data. With two parameters in the solution model, satisfactory results of solid solubility were obtained which are comparable to those calculated from the equation-of-state method or semi-empirical equations with more adjustable parameters. The parameters in the solution model also show regular correlation with the pure component property of the complex solutes.

Vapor–liquid equilibria of carbon dioxide with ethyl benzoate, diethyl succinate and isoamyl acetate binary mixtures at elevated pressures

Abstract Vapor–liquid equilibrium (VLE) data of CO 2 with ethyl benzoate, diethyl succinate, and isoamyl acetate binary mixtures were measured by a semi-flow type apparatus at 308.15, 318.15, and 328.15 K over the pressure range from 1.0 to 13 MPa. New VLE results for CO 2 with esters are presented and the Henrys constants are determined. These VLE data were also correlated using the Soave–Redlich–Kwong and the Peng–Robinson equations of state with various types of the van der Waals, composition-dependent and Huron–Vidal mixing rules. It is shown that both equations of state with the van der Waals mixing rules and two adjustable parameters give satisfactory correlation results.

Development of an equation of state for the square-well chain molecules of variable well width based on a modified coordination number model

An equation of state (EOS) is developed according to the statistical associating fluid theory (SAFT) model. The dispersion term in the new EOS is derived by a modified coordination number equation. This modified coordination number expression gives correct results at low density and close-packed regions. It also agrees well with the computer simulation results for square-well (SW) fluids. A modified expression of the chain term compressibility factor for the SW fluid with variable well width is proposed in this study. Comparison of the calculated compressibility factors with molecular simulation data for tangent hard sphere chains and SW chains indicates that the new EOS yields satisfactory results and relatively smaller deviations than those from other equations. Finally, the new EOS is employed on real fluid systems of n-alkanes. For each pure fluid, four EOS parameters are regressed. These pure fluid parameters yield reasonable correlation with the molecular weight for n-alkanes up to n-eicosane. The pure fluid properties are well calculated by the new EOS. Prediction of the saturated vapor pressures of higher carbon number alkanes also shows satisfactory results. The new EOS developed in this study is consistent with the molecular simulation data for SW fluids with variable well width. It is simple in mathematical form, and is applicable from small molecular weight compounds to long chain molecules.

Vapor-liquid equilibria of the binary mixtures 2-butanone + t-pentanol, t-pentanol + butyl acetate and 2-propanol + diethyl ketone at 101.3 kPa

Abstract Vapor–liquid equilibria have been measured at 101.3 kPa for three binary mixtures of 2-butanone+t-pentanol, t-pentanol+butyl acetate and 2-propanol+diethyl ketone. The isobaric T–x–y data have been reported and the thermodynamic consistency has been examined. Calculations of the non-ideality of the vapor phase have been made with the second virial coefficients determined by the Tsonopoulos correlation. Various activity coefficient models have been used to correlate the experimental data. Satisfactory results have been obtained and optimally fitted binary parameters are presented.

Measurements of the Heat Capacity and Solid-liquid Equilibrium of Water-Potassium Chloride and Water-Magnesium Chloride Binary Mixtures

The eutectic and liquidus temperatures of water-potassium chloride and water-magnesium chloride systems were measured using DSC in this study. The plots of liquidus temperatures as a function of composition show good agreement with partially available literature data. The measured eutectic temperatures of water-potassium chloride and water-magnesium chloride mixtures are –11.1 °C and –33.2°C, respectively. The heating curve of the eutectic mixture of water-potassium chloride was also used to confirm the eutectic temperature. The eutectic compositions of water-potassium chloride and watcr-ma~ncSIUI1\ chloride systems are 19.5 wt% KCI and 21.6 wt% MgCl2, respectively. The eutectic composition of water-potassium chloride was also estimated from the eutectic fraction data. In comparison with the available literature data, the DSC measurement and the eutectic fractional transformation methods provide consistent and accurate results. The solid state heat capacity data of the nearly eutectic binary mixtures were also evaluated from the measured DSC data.