Pure Component Vapor Pressures Research Articles

An improved generalized three-parameter cubic equation of state for pure fluids

An improved simple generalized three-parameter cubic equation of state for pure fluids is proposed to estimate pure component fluid properties by incorporating substance dependent epsilon-function and almost substance independent sigma-function in the generic cubic equation of state, followed by temperature and acentric factor dependent attractive term. The proposed cubic equation of state is utilized to predict critical compressibility factor, liquid molar volume, vapor molar volume, and pure component vapor pressure for several simple hydrocarbons and fatty acid of methyl esters, and the predicted properties are compared with the actual values. In this study, most of the pure fluid properties are considered from literature; however experimentation is carried out for few fatty acid of methyl esters to determine pure fluid vapor pressure at elevated temperature and pressure. The proposed cubic equation of state is found to be accurate in predicting both literature reported and experimentally determined pure fluid properties. The overall performance of the proposed cubic equation of state is also compared with commonly used cubic equations of state and is found to be superior for predicting critical compressibility factors and other pure fluid properties.

P– x data for binary systems using a novel static total pressure apparatus

A new static isothermal vapor–liquid equilibrium (VLE) apparatus, designed for operation at pressures up to 2000 kPa incorporates novel dual-mode piston pumps which, in the micro-mode, can dispense microlitre volumes repeatably. Pure component vapor pressure and VLE measurements for two test systems (water + 1-propanol at 313.17 K and n-hexane + 2-butanol at 329.22 K) showed excellent agreement with literature data. New VLE data are presented for n-dodecane + 1-propanol at 342.8 and 352.7 K, and n-dodecane + 2-butanol at 342.7 and 352.7 K. An accurate new method for finding the cell net interior volume from cumulative injected liquid volumes and corresponding pressures is presented. For systems of high relative volatility the liquid equilibrium composition ( x i ) may differ significantly from the charge composition ( z i ) in the region dilute in the more volatile component. Exact equations for the fractional difference ( z i − x i )/ x i conveniently show the influence of relative volatility, system pressure, vapor space, and vapor non-ideality, and are illustrated for the n-dodecane + 1-propanol system. Equations showing the dependence of the limiting activity coefficient on the virial coefficient values ( B 11, B 12, and B 22) used in their computation indicate that the influence may be considerable for derivatives numerically larger than about 4 × 10 −5 mol cm −3.

The sensitivity of Secondary Organic Aerosol component partitioning to the predictions of component properties – Part 2: Determination of particle hygroscopicity and its dependence on "apparent" volatility

Abstract. A large number of calculations of absorptive partitioning of organic compounds have been conducted, making use of several methods to estimate pure component vapour pressures and activity coefficients (p0 and γi). The sensitivities of the predicted particle properties (density, hygroscopicity, CCN activation potential) to the choice of p0 and γi models and to the number of components used to represent the organic mixture have been systematically compared. The variability in theoretical hygroscopic growth factor attributable to the choice of estimation technique increases with decreasing mixture complexity. Generally there is low sensitivity to the choice of vapour pressure predictive technique. The inclusion of non-ideality is responsible for a larger difference in predicted growth factor, though still relatively minor. Assuming instantaneous equilibration of all semi-volatile on drying the aerosol to 0 % RH massively increases the sensitivity. Without such re-equilibration, the calculated growth factors are comparable to the low hygroscopicity of organic material widely measured in the laboratory and atmosphere. Allowing re-equilibration on drying produces a calculated hygroscopicity greater than measured for ambient organic material, and frequently close to those of common inorganic salts. Such a result has substantial implications on aerosol behaviour in instruments designed to measure hygroscopicity and on the degree of equilibration of semi-volatile components in the ambient atmosphere. The impacts of this variability on behaviour of particles as cloud condensation nuclei, on predicted cloud droplet number and uncertainty in radiative forcing are explored. When it is assumed only water evaporates on drying, the sensitivity in radiative forcing, "ΔF" to choice of p0 and γi estimation technique is low when the particle organic volume fraction is less than 55 %. Sensitivities increase with decreasing component complexity. If all components re-equilibrate on drying, the sensitivity of ΔF increases substantially for organic volume fractions as low as between 16 and 22 % depending on the complexity of the organic composition and assumed aerosol size distribution. The current study ignores the impact of predicted changes in particle size which will increase uncertainty in droplet number and forcing.

Experimental Measurement of Vapor Pressures and Densities at Saturation of Pure Hexafluoropropylene Oxide: Modeling Using a Crossover Equation of State

Hydrofluoroalkenes, like hexafluoropropylene, can be considered as new working fluids for refrigeration systems and consequently volumetric and critical property data are required. In this study, a vibrating tube densitometer technique was used to determine densities at nine different temperatures between (263 and 358) K, and pressures between (0.04 and 15) MPa. The experimental uncertainties are ±0.0003 and ±0.0006 MPa for pressure, ± 0.02 K for temperature, ± 0.5% (relative) for vapor densities, and ±0.05% for liquid densities. A different equipment based on static method is used for the determination of pure component vapor pressures for temperatures between (231 and 359) K. The experimental uncertainties are ±0.0005 MPa for pressure and ±0.02 K for the temperature. Critical properties have been determined by direct measurement and also from utilization of experimental densities considering the asymptotic scaling law behavior. The Patel−Teja and crossover Patel−Teja equations of state are used to corre...

상용성 화학공정모사기를 활용한 혼합냉매 이용 냉동사이클의 전산모사

Abstract In this study, a computer simulation has been performed for the refrigeration cycle using mixed refrigerants in order to decrease the process stream temperature to -20 o C. Refrigerant supply temperature was assumed to be -30 o C considering the temperature difference as 10 o C with process stream. Peng-Robinson equation of state model was selected for the computer simulation. A new alpha function proposed by Twu et al was used for an accurate prediction of pure component vapor pressure experimental data. One fluid mixing rules were used for the estimation of mixture vapor-liquid equilibria calculations. A commercial process simulator, PRO/II with PROVISION was utilized for the simulation of the overall refrigeration process. In order to minimize the compressor power consumption, we have optimized the two-stage compression system by varying the first stage compressor outlet pressure. Finally, we could obtain the minimum total power 755.7kW at the first stage compressor outlet pressure, 6 bar.Key Words : Refrigeration cycle, Simulation, Mixed refrigerants, Equation of state, Two-stage Compression

Pure Component and Binary Vapor−Liquid Equilibrium + Modeling for Hexafluoropropylene and Hexafluoropropylene Oxide with Toluene and Hexafluoroethane

Experimental pure component vapor pressure data for hexafluoropropylene (R1216) and hexafluoropropylene oxide (HFPO) are presented. Experimental vapor−liquid equilibrium (VLE) data are presented at two temperatures, (273 and 313) K, for four binary systems: R1216 + toluene, HFPO + toluene, hexafluoroethane (R116) + R1216, and R116 + HFPO. The measurements were undertaken using both a “static−analytic” apparatus fitted with a pneumatic rapid online sampler injector (ROLSI) and a “static−synthetic” PVT apparatus. The experimental vapor pressure data were regressed to obtain correlated parameters for the Peng−Robinson (PR) and Soave−Redlich−Kwong (SRK) equations of state with the Mathias−Copeman α function. The binary VLE data were regressed to obtain correlated parameters for three different model combinations: the PR equation of state with the Wong−Sandler (WS) mixing rules, the PR equation of state with the modified Huron−Vidal first-order (MHV1) mixing rules, and the SRK equation of state with the WS mix...

A modification of the alpha function ( α), and the critical compressibility factor ( ζc) in ER (Esmaeilzadeh–Roshanfekr) equation of state

In this study a temperature-dependent function of the attractive term, called the alpha function, and the critical compressibility factor ( ζ c) of the ER (Esmaeilzadeh–Roshanfekr) equation of state have been modified to improve the performance of equation of state. The ER EOS is a new three-parameter equation of state that was developed in 2006 with special attention to application for reservoir fluids. Using these modifications, saturated liquid density, saturated vapor density and vapor pressure of pure components are calculated more accurate than the ER equation of state. The average absolute deviations of the predicted saturated liquid density, saturated vapor density and vapor pressure of pure components with the modified ER (mER) are 0.95%, 1.17% and 1.20%, respectively. Also, the mER, the ER and the Peng–Robinson (PR) equation of state are used to predict dew point pressure for six gas condensate mixtures and bubble point pressure for five LNG mixtures. In order to have an unbiased comparison between these equations of state, van der Waals mixing rules are used without using any adjustable parameters ( k ij = 0). The results show that the mER EOS predicts the dew point pressure and bubble point pressure with best accuracy among the other EoSs.

The third industrial fluid properties simulation challenge

The third industrial fluid properties simulation challenge was held from March to September 2006. As in the previous two events contestants were challenged to predict specific, industrially relevant, properties of fluid systems. Their efforts were judged based on the agreement of the predicted values with previously unpublished experimental data (provided by researchers at ExxonMobil and DuPont). The focus of this contest was on the transferability of modeling methods—the ability to predict properties for materials that are chemically different, or at different state points, to those used in model parameterization and validation. Nine groups attempted to compute bubble point pressures for mixtures of 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea) and ethanol at 343 K, given data for mixtures at 283 K, and given the pure component vapor pressures. They used a range of different techniques including statistical mechanical and molecular simulations-based approaches. Four of the groups were recognized for providing predictions that were significantly more accurate than would be obtained by extrapolation using the NRTL model (the standard engineering approach). Three groups undertook the more challenging “molecular transferability” problem, attempting to predict shear viscosities at two different state points for a range of diols and triols for which little experimental data was available.

Measurement and modelling of hydrogen bonding in 1-alkanol + n-alkane binary mixtures

Two equations of state (simplified PC-SAFT and CPA) are used to predict the monomer fraction of 1-alkanols in binary mixtures with n-alkanes. It is found that the choice of parameters and association schemes significantly affects the ability of a model to predict hydrogen bonding in mixtures, even though pure-component liquid densities and vapour pressures are predicted equally accurately for the associating compound. As was the case in the study of pure components, there exists some confusion in the literature about the correct interpretation and comparison of experimental data and theoretical studies, which is clarified in the present work. New hydrogen bonding data based on infrared spectroscopy are reported for seven binary mixtures of alcohols and alkanes.

Separation of Glycol Ethers and Similar LCST-Type Hydrogen-Bonding Organics from Aqueous Solution Using Distillation or Liquid−Liquid Extraction

Infinite-dilution relative volatilities ( ) were measured at 50 °C and 80 °C using a Rayleigh distillation apparatus for dilute solutions of propylene glycol n-butyl ether (PnB), propylene glycol n-propyl ether (PnP), and dipropylene glycol n-butyl ether (DPnB) dissolved in water and brine (3 wt % NaCl). The data were analyzed to determine infinite-dilution activity coefficients ( ), Henry's Law constants, partial molar enthalpies of mixing, and Setschenow constants. Partition ratios (K values) for extraction of PnP also were measured using 14 hydrophobic organic extraction solvents, including alcohols, ketones, ethers, chlorinated hydrocarbons, aromatics, and aliphatics. An interpretation of molecular interactions in solution is given based on the analysis of activity coefficients, as a function of temperature and salt concentration. General rules are proposed for the class of hydrogen-bonding organic compounds characterized by the presence of a lower critical solution temperature (LCST) in the organic + water phase diagram. The value of αi,water is likely to increase as the temperature increases for stripping volatile LCST-type hydrogen-bonding organics from dilute aqueous solution, provided the pure-component vapor pressure relative to water ( / ) also increases or stays approximately the same. For extraction of LCST-type compounds from aqueous solution, K is likely to increase as the temperature increases, provided that the mutual solubility between phases is low.

Modeling vapor–liquid equilibria of ethanol + 1,1,1,2,3,3,3-heptafluoropropane binary mixtures using PC-SAFT

One objective of the Third Industrial Fluid-Properties Simulation Challenge was the extrapolation of mixture phase equilibrium information obtained from one isotherm to other temperatures. In this work, we present modeling results for the vapor–liquid equilibrium of the ethanol/1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea) mixture obtained with the PC-SAFT equation of state. The required pure-component parameters were determined by fitting pure-component vapor pressures and liquid density data. To get a quantitative description of the mixture, a temperature-independent binary interaction parameter was adjusted to experimental bubble-point data at 283.17 K. Using these parameters, bubble-point pressures at T = 343.13 K were predicted for different concentrations.

Monte Carlo Simulation of Carboxylic Acid Phase Equilibria

Configurational-bias Monte Carlo simulations were carried out in the Gibbs ensemble to generate phase equilibrium data for several carboxylic acids. Pure component coexistence densities and saturated vapor pressures were determined for acetic acid, propanoic acid, 2-methylpropanoic acid, and pentanoic acid, and binary vapor-liquid equilibrium (VLE) data for the propanoic acid + pentanoic acid and 2-methylpropanoic acid + pentanoic acid systems. The TraPPE-UA force field was used, as it has recently been extended to include parameters for carboxylic acids. To simulate the branched compound 2-methylpropanoic acid, certain minor assumptions were necessary regarding angle and torsion terms involving the -CH- pseudo-atom, since parameters for these terms do not exist in the TraPPE-UA force field. The pure component data showed good agreement with the available experimental data, particularly with regard to the saturated liquid densities (mean absolute errors were less than 1.1%). On average, the predicted critical temperature and density were within 1% of the experimental values. All of the binary simulations showed good agreement with the experimental x-y data. However, the TraPPE-UA force field predicts saturated vapor pressures of pure components that are larger than the experimental values, and consequently the P-x-y and T-x-y data of the binary systems also deviate from the measured data.

Vapor–liquid equilibrium, densities and viscosities for the binary system exo- and endo-tetrahydrodicyclopentadiene and pure component vapor pressures

Vapor pressures of exo- and endo-tetrahydrodicyclopentadiene (THDCPD) were measured by using dynamic glass still at T = 335–463 K. The experimental vapor pressures were fitted well with the Antoine equation. Isobaric vapor–liquid equilibria for the binary system exo-THDCPD + endo-THDCPD were determined by a using dynamic method at six constant pressures of 10, 30, 50, 70, 90 and 101.3 kPa. All the VLE data sets were correlated with NRTL model. Additionally, densities and viscosities at 288.15, 298.15, 308.15 and 318.15 K for the same binary mixtures were measured by using a vibrating tube density meter and a precision viscometer, respectively.

THE MODIFIED PGR EQUATION OF STATE: PURE-FLUID PREDICTIONS

ABSTRACT The Park-Gasem-Robinson (PGR) equation of state (EOS) has been modified to improve its volumetric and equilibrium predictions. Specifically, the attractive term of the PGR equation was modified to enhance the flexibility of the model, and a new expression was developed for the temperature dependence of the attractive term in this segment-segment interaction model. The predictive capability of the modified PGR EOS for vapor pressure and saturated liquid and vapor densities was evaluated for selected normal paraffins, normal alkenes, cyclo-paraffins, light aromatics, argon, carbon dioxide, and water. The generalized EOS constants and substance-specific characteristic parameters in the modified PGR EOS were obtained from pure component vapor pressures and saturated liquid and vapor molar volumes. The calculated phase properties were compared with those of the Peng-Robinson (PR), the simplified-perturbed-hard-chain theory (SPHCT), and the original PGR equations. Generally, the performance of the proposed EOS (%AAD of 1.3, 2.8, and 3.7 for vapor pressure, saturated liquid, and vapor densities, respectively) was better than the SPHCT and original PGR equations in predicting the pure fluid properties.

Application of TraPPE-UA force field for determination of vapor–liquid equilibria of carboxylate esters

The transferability of Lennard–Jones parameters in the united-atom force field known as “transferable potentials for phase equilibria” (TraPPE-UA) is assessed through vapor–liquid equilibria calculations performed on carboxylate esters. In the TraPPE-UA force field, non-bonded interactions are governed by a Lennard–Jones plus fixed point charge functional form. Partial charges are borrowed from the optimized potentials for liquid simulations (OPLS) force field [Briggs, Nguyen, Jorgensen, J. Phys. Chem. 95 (1991) 3315]. No reparameterization of pseudo-atoms occurs in this work. Instead, the molecules of interest are built from pseudo-atoms parameterized in previous installments of the TraPPE-UA force field. Configurational-bias Monte Carlo simulations in the grand canonical ensemble, combined with histogram-reweighing techniques, are used to determine the vapor–liquid coexistence curves, vapor pressures and critical points of the esters methyl acetate, ethyl acetate, methyl propionate and vinyl acetate. Pressure-composition diagrams are calculated for methyl acetate + ethyl acetate at 313.15 K and methyl acetate + methanol at 323.15 K. Average deviations in the saturated liquid densities and critical temperatures from experiment vary from 1.8% (methyl acetate) to 4.2% (vinyl acetate), while the critical densities for all four esters are predicted to within 0.8%. The pressure-composition diagrams for methyl acetate + ethyl acetate and methyl acetate + methanol agree qualitatively with experiment, but quantitative differences exist due to the overprediction of the pure component vapor pressures. For the methyl acetate + methanol system the predicted azeotropic composition of x AcOMe = 0.66 is in good agreement with the experimental value of x AcOMe expt = 0.65 . Analysis of the microstructure of the methyl acetate + methanol mixture shows that the addition of methyl acetate has little effect on the self-association of methanol molecules through hydrogen bonding.

A new cubic equation of state for reservoir fluids

A new three-parameter cubic equation of state is developed with special attention to the application for reservoir fluids. One parameter is taken temperature dependent and others are held constant. The EOS parameters were evaluated by minimizing saturated liquid density deviation from experimental values and satisfying the equilibrium condition of equality of fugacities simultaneously. Then, these parameters were fitted against reduced temperature and Pitzer acentric factor. For calculating the thermodynamic properties of a pure component, this equation of state requires the critical temperature, the critical pressure, the acentric factor and the experimental critical compressibility of the substance. Using this equation of state, saturated liquid density, saturated vapor density and vapor pressure of pure components, especially near the critical point, are calculated accurately. The average absolute deviations of the predicted saturated liquid density, saturated vapor density and vapor pressure of pure components are 1.4%, 1.19% and 2.11%, respectively. Some thermodynamic properties of substances have also been predicted in this work.

Transferable Potentials for Phase Equilibria. 8. United-Atom Description for Thiols, Sulfides, Disulfides, and Thiophene

An extension of the transferable potentials for phase equilibria united-atom (TraPPE-UA) force field to thiol, sulfide, and disulfide functionalities and thiophene is presented. In the TraPPE-UA force field, nonbonded interactions are governed by a Lennard-Jones plus fixed point charge functional form. Partial charges are determined through a CHELPG analysis of electrostatic potential energy surfaces derived from ab initio calculations at the HF/6-31g+(d,p) level. The Lennard-Jones well depth and size parameters for four new interaction sites, S (thiols), S(sulfides), S(disulfides), and S(thiophene), were determined by fitting simulation data to pure-component vapor-equilibrium data for methanethiol, dimethyl sulfide, dimethyl disulfide, and thiophene, respectively. Configurational-bias Monte Carlo simulations in the grand canonical ensemble combined with histogram-reweighting methods were used to calculate the vapor-liquid coexistence curves for methanethiol, ethanethiol, 2-methyl-1-propanethiol, 2-methyl-2-propanethiol, 2-butanethiol, pentanethiol, octanethiol, dimethyl sulfide, diethyl sulfide, ethylmethyl sulfide, dimethyl disulfide, diethyl disulfide, and thiophene. Excellent agreement with experiment is achieved, with unsigned errors of less than 1% for saturated liquid densities and less than 3% for critical temperatures. The normal boiling points were predicted to within 1% of experiment in most cases, although for certain molecules (pentanethiol) deviations as large as 5% were found. Additional calculations were performed to determine the pressure-composition behavior of ethanethiol+n-butane at 373.15 K and the temperature-composition behavior of 1-propanethiol+n-hexane at 1.01 bar. In each case, a good reproduction of experimental vapor-liquid equilibrium separation factors is achieved; both of the coexistence curves are somewhat shifted because of overprediction of the pure-component vapor pressures.

Henry’s law constants of methane, nitrogen, oxygen and carbon dioxide in ethanol from 273 to 498 K: Prediction from molecular simulation

Henry’s law constants of the solutes methane, nitrogen, oxygen and carbon dioxide in the solvent ethanol are predicted by molecular simulation. The molecular models for the solutes are taken from previous work. For the solvent ethanol, a new rigid anisotropic united atom molecular model based on Lennard–Jones and coulombic interactions is developed. It is adjusted to experimental pure component saturated liquid density and vapor pressure data. Henry’s law constants are calculated by evaluating the infinite dilution residual chemical potentials of the solutes from 273 to 498 K with Widom’s test particle insertion. The prediction of Henry’s law constants without the use of binary experimental data on the basis of the Lorentz–Berthelot combining rule agree well with experimental data, deviations are 20%, except for carbon dioxide for which deviations of 70% are reached. Quantitative agreement is achieved by using the modified Lorentz–Berthelot combining rule which is adjusted to one experimental mixture data point.

Vapour pressures and excess functions of (3,5; 2,6)dimethylpyridine + n-hexane, n-heptane and n-octane measurement and prediction

The vapour pressures of liquid (3,5; 2,6)-dimethylpyridine + n-hexane; + n-heptane and + n-octane mixtures were measured by a statistic method, respectively, between 263.15–353.15 K at 10 K intervals. The pure component vapour pressures data and those of mixtures were correlated with the Antoine equation. The excess enthalpies, at 303.15 K for those mixtures were measured by an isothermal calorimeter model C80 SETARAM. The molar excess Gibbs energies, calculated from the vapour liquid equilibrium data and the molar excess enthalpies compared satisfactorily with group contribution method (DISQUAC).

Vapor−Liquid−Liquid Equilibria, Azeotropic, and Excess Enthalpy Data for the Binary System n-Undecane + Propionamide and Pure-Component Vapor Pressure and Density Data for Propionamide

Vapor−liquid−liquid equilibria (VLLE), azeotropic, and excess enthalpy (HE) data for the binary system n-undecane + propionamide were measured at temperatures from 359.25 to 416.65 K. Additionally, pure-component vapor pressure and density data for propionamide were determined experimentally. The LLE and VLLE measurements were performed in a stirred glass cell and in a static equilibrium cell with a capability to take small samples from the different phases by using pneumatic micro samplers. For the HE measurements, an isothermal flow calorimeter was used, and the azeotropic data were obtained from distillation experiments using a micro spinning band column. The pure-component vapor pressures and densities were measured with the help of the dynamic method (ebulliometer) and a vibrating tube densimeter, respectively. To the experimental mixture data from this work linear temperature-dependent interaction parameters for the NRTL model were fitted. They can be used to represent the phase equilibrium behavior and excess enthalpies of the investigated system.