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The permeability of light gases in a series of different glassy polymers is analyzed through a thermodynamic-based approach for solubility and diffusivity. The nonequilibrium thermodynamic model for glassy polymers describes the solubility of the different penetrants; diffusivity is given as the product of a mobility factor and a thermodynamic factor. The latter is predicted by the nonequilibrium lattice fluid thermodynamic model, while the mobility coefficient is determined using the experimental permeability data. For rather soluble penetrants (e.g., CO2), a plasticization factor is also accounted for, considering the mobility to depend exponentially on penetrant concentration, as often observed experimentally. The model is able to describe accurately the experimental behavior in a simple and effective way, considering only two adjustable parameters. The mobility coefficient is found to depend on the penetrant size (critical volume) and on the fractional free volume of the polymer matrix, following rather general and reasonable correlations. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2776–2788, 2015

This work investigates the hidden details that are responsible for the practical success of cubic equations of state (EOS) in phase equilibrium calculations. A detailed consideration of the van der Waals method for evaluating the pure compound EOS parameters sheds new light on the reasons why the elimination of the actual critical volume as parameter was also adopted in the Redlich–Kwong and the Peng–Robinson (PR) frameworks. It is shown that an interesting relationship for the critical compressibility factor arising from the Martin–Hou method opens a new door for future exploration of different frameworks. A consideration of the key steps of Soave's reasoning for determining the temperature dependence of the attractive parameter explains the larger success of the Stryjek–Vera modification of PR EOS over the PR EOSs. A reference to the extension of cubic EOS to calculate liquid densities and enthalpies and a ready to use algorithm for the evaluation of the roots of a cubic equation are included for instructional purposes. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2824–2831, 2015

The gene expression programming (GEP) strategy is applied for presenting two corresponding states models to represent/predict the surface tension of about 1,700 compounds (mostly organic) from 75 chemical families at various temperatures collected from the DIPPR 801 database. The models parameters include critical temperature or temperature/critical volume/acentric factor/critical pressure/reduced temperature/reduced normal boiling point temperature/molecular weight of the compounds. Around 1,300 surface tension data of 118 random compounds are used for developing the first model (a four-parameter model) and about 20,000 data related to around 1,600 compounds are applied for checking its prediction capability. For the second one (a five-parameter model), about 10,000 random data are applied for its development, and 11,000 data are used for testing its prediction ability. The statistical parameters including average absolute relative deviations of the results form dataset values (25 and 18% for the first and second models, respectively) demonstrate the accuracy of the presented models. © 2012 American Institute of Chemical Engineers AIChE J, 59: 613–621, 2013

New correlations, based on the rough hard-sphere theory and an extensive literature database, were developed for the determination of the binary diffusion coefficients of liquid and solid solutes in supercritical solvents. The correlations were tested to predict 107 solute-solvent systems with good results. The input data required for the correlations are the solute molecular weight, temperature, density and the solvent basic properties (molecular weight, critical volume, and critical pressure).

We propose the following method for predicting the critical volume from the van der Waals volumes: V c = A x V vdw = 5.36 x V vdw , where A is a universal constant,which can be used to predict the critical volume for a wide variety of substances: alkanes, alkenes, cycloalkanes, alcohols, carboxylic acids, amines, aromats and other. We use van der Waals volumes given in the DIPPR data compilation (Daubert and Danner, 1989). The new predictive method has been compared with two other methods: the Lydersen method (1955), and the Fedors method (1979)

An extensive critical evaluation of available correlations for predicting critical properties of binary defined hydrocarbon as well as some multicomponent hydrocarbon and hydrocarbon-nonhydrocarbon mixtures is presented using all available literature data. The Li method is recommended for critical temperature prediction based upon its accuracy and simplicity, although the Chueh-Prausnitz method is equivalent in accuracy. The Kreglewski method is most accurate for critical pressure prediction. All methods evaluated yielded high errors for the critical properties of methane-containing mixtures. Current correlations on critical volume are discussed, and correlational work on prediction using an excess volume approach is described.

Volumetric data of nonpolar gaseous mixtures are analyzed in terms of the theory of corresponding states. Special attention is given to an analysis of the second virial coefficient and to the calculation of pseudocritical constants. Second virial coefficients are calculated from experimental data for ten binary systems. These coefficients, with those previously published, are correlated by means of a generalized equation involving three parameters for each component: the critical volume, the reduced temperature, and the acentric factor. Equations are derived for the pseudocritical temperature and pressure of mixtures. These equations are considerably more accurate than those given by Kay's rule. Because of the complexity of the proposed equations for the pseudocritical parameters, a simplified pseudocritical method is presented which is sufficiently accurate for most chemical engineering purposes, especially at reduced temperatures exceeding 1.3.

Lennard-Jones force constants calculared from viscosity values at normal pressures for nearly forty nonpolar organic and inorganic substances have been used to develop relationships for the estimation of these constants from the critical temperature and volume of the substance. The product of the critical temperature and volume TcVc was found to correlate linearly with the force constant modulus . When the collision diameter ρ was plotted against the cube root of the critical volume on log-log coordinates, a straight line of slope 5/4 resulted. The corresponding relationship was found to predict ρ values with an average deviation of 3.1% when compared with values calculated from viscosity measurements. The temperature force constant ϵ/κ was found to vary as the 5/6 power of the critical temperature, and the resulting relationship produced an average deviation of 10%.

The van der Waals' constanta a andb evaluated from structural considerations of the unsaturated aliphatic hydrocarbons are used to calculate the critical constants for these types of compounds. For these unsaturated hydrocarbons, both van der Waals' constants are calculated through the additive contribution of unsaturated bonds to the van der Waals' constants of the corresponding saturated aliphatic hydrocarbons calculated according to a method previously proposed (6). With both van der Waals' constants available, the critical temperatures, pressures, and volumes for these types of compounds can be obtained. By use of this approach, the critical temperatures, pressures, and volumes of several olefins, diolefins, and acetylenes have been calculated. These calculated values have been compared whenever possible with values reported in the literature to produce an average percentage deviation of 1.3 for the critical temperature, 3.0 for the critical pressure, and 1.5 for the critical volume. In this comparison questionable literature values have been included, and consequently the reported deviations present the worst possible expectation.