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A new version of CPA (cubic-plus-association) equation of state (EOS) for associating fluids is proposed. This equation takes the Nasrifar–Moshfeghian (NM) cubic EOS as a frame for representing the physical interactions of fluid molecules and also an associating term from the bonding term of statistical associating fluid theory (SAFT). The resulting EOS contains five adjustable parameters, three in physical term and two in association-based term. The parameters are determined using vapour pressures and saturated liquid densities of pure associating fluids. The excellent saturated liquid density is obtained for four pure associating fluids including primary alcohols (methanol, ethanol and 1-butanol) as well as water. The total average absolute deviations of the calculated values of densities from the experimental data are within 1.71%. The present model is compared with the original CPA EOS. Results show that our model agrees well with the original one. [ABSTRACT FROM PUBLISHER]

The main aim of the present study is to modify the attractive part of van der Waals-type EOS to model the volumetric ionic liquids and their mixtures. The present study uses the Carnahan–Starling (CS) repulsion term and also focuses on introducing a variable parameter in the attractive term of modified vdW-type EOS. Investigation of the results obtained revealed that this variable is a function of temperature. Our results also show that employment of CS repulsion term together with an appropriately chosen exponent in the attractive term of EOS will greatly improve the accuracies of the calculated densities of various ionic liquids. The average absolute deviation (AAD) of the calculated densities from the experimental ones for 848 data points of pure ionic liquids was found to be 0.36. Further, in the case of mixtures, for 1014 data points the AAD was 0.20. [ABSTRACT FROM AUTHOR]

This paper addresses a method for predicting the participating constants in the Ihm-Song-Mason (ISM) equation of state (EOS) for normal fluids from the enthalpy of fusion and liquid density at freezing point as scaling constants. The corresponding states principle has been used to estimate the second virial coefficient B2 (T). α(T) and b(T), the two other temperature-dependent constants apprearing in the equation of state are calculated using scaling rules. The heat of fusion (ΔHfusion) and fusion density (ρf) are employed to construct a corresponding states correlation for the aforecited parameters. The ISM EOS has been applied to to predict the volumetric properties of several substances including: noble gases, diatomic molecules, hydrocarbons and aromatics. The outcomes of the computations have been compared with literature data. Results obtained in the present work are in good harmony with those given in the literature. [ABSTRACT FROM AUTHOR]

It is the purpose of the present work to predict thermodynamic properties of alkali metals including lithium, sodium, potassium, rubidium, and cesium over a wide range of PVT space using a statistically-based equation of state (EOS). The EOS is that of Ihm-Song-Mason (ISM) EOS. The second virial coefficient, which plays a vital role in the EOS, is calculated from a corresponding states correlation with two scaling constants including latent heat of vaporization and molar density both at triple point. Further the second virial coefficient of lithium is calculated by using an accurate pair potential energy for singlet and triplet sates. The first quantum correction has been considered for calculating the second virial coefficient of lithium. Other two temperature-dependent parameters required by the ISM EOS are determined by the usage of Lennard-Jones (12-6) model potential. The calculated results are compared with literature data. The overall agreement between our results and literature values is remarkable. [ABSTRACT FROM AUTHOR]

A statistically-based equation of state (EOS) proposed by Tao and Mason was applied to four light fluids including 4He, Ne, H2 and CH4. The best intermolecular pair potentials were taken to evaluate the second virial coefficients of four aforecited systems. For CH4 and Ne the first quantum correction, and for He and H2, up to the second quantum correction were performed on the classical second virial coefficient. The calculated second virial coefficients were applied to Tao–Mason (TM) EOS to predict the density of four systems in both subcritical and supercritical regions. Agreement with experiment was excellent for all four systems. [ABSTRACT FROM PUBLISHER]

Abstract: This paper addresses a method for predicting the participating constants in equation of state (EOS) for compressed polymeric fluids using two scaling constants. The theoretical EOS undertaken is Ihm–Song–Mason (ISM), which is based on the Weeks–Chandler–Anderson (WCA), and the two constants are the surface tension γg and the molar density ρg, both at the glass transition point. There are three temperature-dependent quantities that are required to use the EOS: the second virial coefficients B2(T), an effective van der Waals co-volume, b(T) and a correction factor, α(T). The second virial coefficients are calculated from a two-parameter corresponding states correlation, which is constructed with two constants as scaling parameters, i.e., the surface tension γg and molar density ρg. This new correlation has been applied to the ISM EOS to predict the volumetric behavior of polymer melts including polypropylene (PP), poly(ethylene oxide) (PEO), polystyrene (PS), poly(vinyl methyl ether) (PVME), and polycarbonate bisphenol-A (PC) at compressed states. The operating temperature range is from 311.5 to 603.4K and pressures up to 200.0MPa. Other two-temperature-dependent parameters α(T) and b(T) appearing in the ISM EOS, are calculated by scaling rules. It was found that the calculated volumes agree well with the experimental values. A collection of 421 data points has been examined for the aforementioned polymers. The average absolute deviation between the calculated densities and the experimental densities is of the order of 0.6%. The newly obtained correlation has been further assessed through a detailed comparison against previous correlations proposed by other researchers. [Copyright &y& Elsevier]

Abstract: It is the purpose of this paper to determine the volumetric properties of some ionic liquids (ILs) using the modified version of Tao–Mason (TM) equation of state (EOS). The studied ILs include the cations: imidazolium, phosphonium, pyridinium, pyrrolidium and anions: tetrafluoroborate, bis(trifluoromethylsulfonyl) imide, and hexafluorophosphate. The densities of these compounds were calculated by the usage of the modified TM EOS at several temperatures and pressures. The most important parameter in this EOS is the second virial coefficient which is calculated from a two-parameter corresponding states correlation along with two constants enthalpy of vaporization and molar density both at 298K. The other remaining parameters (i.e., α(T) and b(T)) that appeared in the EOS were calculated from simple equations. Novelty of this work is the modification of the original TM EOS and usage of enthalpy of vaporization and molar density instead of critical and Boyle parameters in the original TM EOS. The good harmony between the calculated and literature density values of ILs confirms the ability of the modified TM EOS in predicting volumetric properties of this class of fluids. Overall average absolute deviation (AAD) of the calculated densities from 3394 experimental data points is 1.48%. [Copyright &y& Elsevier]