Pure Compound Vapor Pressures Research Articles

Prediction of vapor liquid equilibria using COSMOtherm

The COSMO-RS method in its COSMOtherm implementation has been used to predict the vapor liquid equilibria of problem sets 1a and 1b of the first industrial fluid property prediction challenge, i.e. for the mixtures of dimethylether (1) and propene (2) and of nitroethane (1) and propylene glycol monomethyl ether (1-methoxy-2-propanol) (2). Good quality predictions for both systems have been achieved within less than one day of work, using experimental values for the pure compound vapor pressures and predicted activity coefficients for the mixture thermodynamics. In addition to the results reported for the challenge predictions based on predicted pure compound, vapor pressures are reported and discussed in this paper.

Simplification and extension of a predictive group contribution method for estimating heavy organic pure compound vapor pressures: I. Hydrocarbons

In this work, a revision of a predictive model previously proposed by Coniglio for the calculation of pure component vapor pressures by means of the Peng–Robinson equation of state is presented. A new expression for the shape factor m, more suitable for heavy components, has been suggested by Trassy and a simplification of the group contributions is proposed. In this part I, the method is applied to alkanes, naphthenes, aromatic hydrocarbons, alkenes and alkynes. Results obtained on vapor pressures are compared, when possible, to those obtained using the previous versions. A prediction for heavier hydrocarbons is also presented. This new version offers a good compromise between good results and simplicity.

Prediction of vapor pressures of pure compounds from knowledge of the normal boiling point temperature

A simple method for the prediction of vapor pressures of pure compounds from knowledge of the normal boiling point temperature is presented. Typical errors down to 10 −5 bar (1 Pa) are below 20% and are off only by a factor of 2–3 down to 10 −9 bar (10 −4 Pa), which must be considered very satisfactory considering the simplicity of the method and the uncertainty in the very low vapor pressure data. For higher pressures, up to 5 bar, very satisfactory results are obtained with typical errors below 3% but somewhat higher for alcohols.

Vapor pressures of pure compounds using the Peng–Robinson equation of state with three different attractive terms

Accurate representation of pure compounds vapor pressures is required to increase the robustness of equations of state when predicting phase equilibria for mixtures. Using cubic equations of state, this representation largely depends on improving the temperature-dependent attractive term of the equation of state (EOS) to cover data from the triple to critical points. With this purpose, the Peng–Robinson equation of state is applied with three different attractive terms: Mathias, Mathias–Copeman, and Carrier–Rogalski–Péneloux. Experimental vapor pressures for 311 pure compounds (9000 experimental values) have been fitted. The studied compounds include nitrogen compounds, oxides, sulfides, chlorides, oxyhalides, inorganic compounds, alkanes, cycloalkanes, alkenes, alkadienes, alkynes, aromatic hydrocarbons, halogenated alkanes, halogenated cycloalkanes, halogenated alkenes, halogenated aromatic hydrocarbons, alcohols, ethers, aldehydes, ketones, alkanoic acids, esters, phenols, heterocyclic oxygen compounds, heterocyclic nitrogen compounds, hydrocarbon nitrogen compounds, and sulfur compounds. Overall average absolute deviations of 0.416, 0.214 and 0.276% have been found for the resulting Peng–Robinson–Mathias (PRM), Peng–Robinson–Mathias–Copeman (PRMC), and Peng–Robinson–Carrier–Rogalski–Péneloux (PRCRP) equations of state, respectively.

A new cubic equation of state for simple fluids: pure and mixture

A two-parameter cubic equation of state is developed. Both parameters are taken temperature dependent. Methods are also suggested to calculate the attraction parameter and the co-volume parameter of this new equation of state. For calculating the thermodynamic properties of a pure compound, this equation of state requires the critical temperature, the critical pressure and the Pitzer’s acentric factor of the component. Using this equation of state, the vapor pressure of pure compounds, especially near the critical point, and the bubble point pressure of binary mixtures are calculated accurately. The saturated liquid density of pure compounds and binary mixtures are also calculated quite accurately. The average of absolute deviations of the predicted vapor pressure, vapor volume and saturated liquid density of pure compounds are 1.18, 1.77 and 2.42%, respectively. Comparisons with other cubic equations of state for predicting some thermodynamic properties including second virial coefficients and thermal properties are given. Moreover, the capability of this equation of state for predicting the molar heat capacity of gases at constant pressure and the sound velocity in gases are also illustrated.

Prediction of the Condensation Behavior of Natural Gas: A Comparative Study of the Peng−Robinson and the Simplified-Perturbed-Hard-Chain Theory Equations of State

For the prediction of the condensation behavior of natural gas, one has to select an equation of state (EoS) which will be accurate in the temperature and pressure range of interest (10 < P/bar < 70 bar and 250 < T/K < 310). Another requirement of the selected EoS is that it easily can be adapted to a characterization procedure for the heavy-end fraction. For that purpose, two equations were tested: the Peng−Robinson (PR), which is one of the most applied cubic EoS, and the simplified-perturbed-hard-chain theory (SPHCT) equation, which is one of the simplest EoS based on sound statistical mechanical principles. In the underlying study, their predictive capabilities for the prediction of saturated vapor pressures of pure compounds and vapor/liquid equilibrium pressures for binary mixtures are compared. Only components present in natural gas are considered. In addition, new pure-component parameters for the SPHCT EoS for n-alkanes are evaluated. Also a method to find the characteristic energy for non-n-alk...

Application of cubic equations of state to the fit of vapor pressures of pure components

A simplified technique is proposed for the application of cubic equations of state (EOS) to the calculation of vapor pressures of pure compounds and the method can be adapted to any EOS capable of predicting coexisting vapor and liquid phases. The procedure approximates vapor pressures using the zero-pressure liquid fugacity in the low temperature range, allowing a direct estimation of the parameters of a temperature cohesion function α( T r ). Estimation of the whole vapor pressure curve, from low temperatures to the critical point, is possible using minimal information about saturation states. The technique proposed here is illustrated for a generalized form of the cubic EOS.

Extension of EOS non‐iterative methods to density calculations: Correlation of saturated molar volumes and heats of vaporization

AbstractSoave's direct calculation procedures for the vapor pressure of pure compounds with cubic equations of state (EOSs), have been extended to the calculation of phase densities at saturation for Peng‐Robinson (PR) type EOSs. These universal relations have been used to propose EOS‐based correlation methods for the pure compound saturated liquid and vapor molar volumes, at temperatures higher than the normal boiling point. The methods yield satisfactory results independently of the molecular nature of the chemical under consideration. The results for phase densities are used to correct the heats of vaporization predicted by the ZVPR‐EOS. Complete relative error information is provided for calculated heats of vaporization and correlated vapor and liquid phase molar volumes for more than one hundred compounds of industrial interest.

Heteroazeotropy and Analytical Models for Phase Equilibria

Heteroazeotropy in binary systems is of theoretical interest because it provides a physical relation between vapor−liquid (VLE) and liquid−liquid (LLE) equilibria. Criteria for localization of the vapor phase composition in heteroazeotropic points for nonassociating and low-pressure binary systems are established. It is shown that the localization of heteroazeotropic compositions cannot be made without assumption of a model for the liquid phase, although it can be roughly approximated from pure compound vapor pressure information. The developed criteria are illustrated using well-known activity coefficient models such as the Wohl expansion and the NRTL and Gothard models. It is also shown that solution of the problem must be accompanied by a global phase stability analysis.

Calculation of pure saturation properties using cubic equations of state

A robust algorithm is outlined for the solution of the classical non-linear isofugacity problem by using equations of state (EOS). The procedure suggested is free of numerical pitfalls from the triple point to the critical point. The combination of differential stability (spinodal curve) and zero pressure reference concepts yields an automatic initialization of the calculations inside a region of convergence where the EOS can always predict pure compound vapor pressures at a given temperature.

Gas/Particle Partitioning of Organic Compounds to Environmental Tobacco Smoke: Partition Coefficient Measurements by Desorption and Comparison to Urban Particulate Material

Certain organic compounds in environmental tobacco smoke (ETS) can cause respiratory diseases and lung cancers. The behavior and health effects of ETS will depend upon how each of these compounds is distributed between the gas and the particulate phases. ETS particles were collected on a filter. Semivolatile organic compounds were desorbed from the filter at 20 °C using a flow of clean nitrogen at 60% relative humidity. The desorption was followed with time. Volatile, lower molecular weight compounds were released quickly; less volatile compounds were desorbed slowly. A diffusion model was used to estimate gas/particle partition coefficient (Kp) values. The n-alkane and polycyclic aromatic hydrocarbon (PAH) data agreed with prior measurements for ETS by another method. New data for four nitrogen-containing compounds were obtained. At a given pure compound vapor pressure, PAHs were sorbed more strongly than the n-alkanes. The Kp value for nicotine was unusually large, probably due to a significant degree of protonation of the nicotine in the ETS phase. For carbazole, however, which cannot be protonated, Kp was very similar to what would be predicted for a PAH of the same vapor pressure. After normalization for the fraction of organic matter in the particulate phase, the ETS data for PAHs agreed well with data for PAHs sorbing to urban particulate material (UPM). This is consistent with the interpretation that partitioning to both ETS and UPM is absorptive in nature.

Cubic Equation of State for Pure Compound Vapor Pressures from the Triple Point to the Critical Point

A new procedure is proposed for obtaining the temperature dependence of the attractive energy parameter of equations of state (EOS's) . The procedure can be applied to two-parameter cubic and noncubic EOS's, and it is used for the Peng−Robinson (PR) EOS. The modified form of the PR-EOS, the ZVPR-EOS, can accurately reproduce the vapor pressure for a wide variety of pure compounds from the triple point to the critical point. The experimental information required for each pure compound is the acentric factor, the normal boiling point temperature, and the temperature and pressure coordinates at the critical and triple points. Tables of parameters and complete vapor-pressure relative-error information are provided for more than 100 compounds of industrial interest. Additionally, for the PR-EOS, Soave's noniterative calculation procedures have been extended to the low-temperature range.

Modeling the thermodynamic properties of CFC and HCFC compounds, and the vapor-liquid equilibria of CFC and HCFC mixtures and CFC/HCFC-hydrocarbon mixtures, with the perturbed anisotropic chain theory (PACT)

The Perturbed Anisotropic Chain Theory (PACT) is used to model the vapor pressure and liquid density of pure CFC and HCFC compounds, and the vapor-liquid equilibria of binary and ternary CFC and HCFC mixtures and CFC/HCFC-hydrocarbon mixtures over a wide range of temperature and pressure. The phase behavior of nineteen binary and three ternary mixtures is predicted with very good accuracy compared with experimental data. Two widely used cubic equations of state, the Peng-Robinson and the Soave-Redlich-Kwong equations, are used for comparison. The overall deviation between cubic equation predictions and experimental data is twice the deviation between PACT predictions and experimental data. Using one temperature-independent binary adjustable parameter excellent correlation of the experimental data is obtained for all three equations.

Predicting the vapor pressures of pure compounds by using the wagner equation

A method is proposed for calculating the empirical constants of the Wagner equation written in the simplified form ▪ The calculation of the three constants A, B, C hinges on two values of the Riedel parameter, α( T r), evaluated at the critical temperature and at the normal boiling temperature, respectively. Both these values are obtained from generalized correlations which require knowledge of the critical constants T c and P c and the normal boiling temperature T b only. The reliability of the method is evaluated by predicting the vapor pressure data of nearly 50 compounds which are representative of several classes of compounds, including strongly polar molecules and bifunctional compounds. A comparison is made with some well-known literature predictive relations. As a by-product, the new method gives the enthalpy of vaporization of pure compounds in the temperature range below T b.

PRSV: The stryjek‐vera modification of the peng‐robinson equation of state. Parameters for other pure compounds of industrial interest

AbstractPure ‐ compound ‐ parameters for the Stryjek‐Vera modification of the Peng‐Robinson equation of state, PRSV, are reported for sixty‐nine additional compounds of industrial interest. Errors in the reproduction of pure compound vapor pressure are normally below 1% at reduced temperatures lower than 0.7 At reduced temperatures higher than 0.7, for a few compounds for which data are scarce, errors are somewhat higher than 1%.

Generalization of Soave's direct method to calculate pure-compound vapor pressures through cubic equations of state

Soave's direct method to calculate pure substance vapor pressures is extended to the general cubic equation of state. The new algorithm to obtain vapor pressures through any cubic equations of state is proposed.

Reduction of total-pressure vapor—liquid equilibrium data. Common pitfalls encountered

Common problems encountered in the reduction of total-pressure vapor—liquid equilibrium data are illustrated by the application of the Barker and the Mixon—Gumowski—Carpenter methods to thirteen test systems which range from almost ideal to highly non-ideal behavior. The data reduction results are strongly influenced by the way the pure compound vapor pressures are handled, by the equation of state used, and by the objective function and convergence techniques used. Criteria are given for the successful measurement and reduction of total pressure vapor—liquid equilibrium data.

Ultrahigh Vacuum Quartz Spring Microbalance for Determination of Evaporation Rate and Vapor Pressure

An ultrahigh vacuum quartz spring mass sorption microbalance was designed and fabricated to measure the evaporation rates of low volatility substances, e.g., lubricants considered for space applications. The balance is accurate to ±7.2×10−4 g. Optimum test temperatures range from room ambient to 120°C. The evaporation rates are used to calculate the vapor pressures by the Langmuir equation. The observed vapor pressures of pure organic compounds were found to agree closely with those calculated and extrapolated according to applicable temperature-vapor-pressure relationships. Typical data are given on the evaluation of a conventional lubricating oil considered for space application.

Equilibrium constants from a modified Redlich-Kwong equation of state

A modified Redlich-Kwong equation of state is proposed. Vapor pressures of pure compounds can be closely reproduced by assuming the parameter a in the original equation to be temperature-dependent. With the introduction of the acentric factor as a third parameter, a generalized correlation for the modified parameter can be derived. It applies to all nonpolar compounds. With the application of the original generalized mixing rules, the proposed equation can be extended successfully to multicomponent-VLE calculations, for mixtures of nonpolar substances, with the exclusion of carbon dioxide. Less accurate results are obtained for hydrogen-containing mixtures