Chain Equation Of State Research Articles

Physicochemical properties of drug-like fluids using thermodynamic models

ABSTRACT In this paper, density, solubility parameter and transport properties viscosity, thermal conductivity and diffusion coefficient at infinite dilution in water (diffusivity) of drug-like fluids including two groups have been calculated. We have studied the modified perturbed hard trimmer chain equation of state combined with statistical model and modified rough hard-sphere (RHS) theory to model the solubility parameter and transport properties of drug-like fluids for temperature ranging from 129.95 to 1090.15 K and atmosphere pressure. From 838 experimental data points examined, the average absolute relative deviation (AARD) of calculated density was found to be 1.05%. In the case of solubility parameter, the new statistical-based model correlated 234 experimental data points with AARD equal to 0.70%. RHS-based model has also been extended to calculated 601, 771 and 261 experimental data points of viscosity, thermal conductivity and diffusivity with AARD equal to 3.11%, 2.12% and 7.69%, respectively.

Corrigendum to “Density and isothermal compressibility of ionic liquids from perturbed hard -sphere chain equation of state” [J. Mol. Liq. 174 (2012) 52–57

Abstract After a careful reconsideration of the article (S. M. Hosseini, M. M. Papari, J. Moghadasi, Journal of Molecular Liquids, 174 (2012) 52–57), several typos are appearing in some of the key equations of this article which would not allow the readers to utilize the underlying equation of state for the calculation of volumetric properties of pure ionic liquids without any problem. Regarding this, Erratum is presented to fix this issue.

Cubic-Plus-Chain (CPC). II: Function Behavior of the Chain-Modified Cubic Equation of State

The cubic-plus-chain (CPC) equation of state framework for nonpolar chain molecules hybridizes the classical cubic equation of state with the chain equation of state from SAFT (Sisco and Abutaqiya ...

Cubic-Plus-Chain (CPC). I: A Statistical Associating Fluid Theory-Based Chain Modification to the Cubic Equation of State for Large Nonpolar Molecules

An equation of state framework for nonpolar chain molecules is proposed that hybridizes the classical cubic equation of state with the chain equation of state from SAFT (Chapman et al., Fluid Phase Equilibria, 1989). The cubic equation of state serves as the physical description of the monomer beads, providing repulsive and attractive character to the segments, and the chain term bonds these monomer segments to form chains of homogeneous beads. Whereas the model molecule of the standard cubic equation of state is a sphere with variable attraction energy and volume but whose fundamental shape remains roughly spherical, the model molecule of the proposed cubic-plus-chain (CPC) equation of state consists of beads bonded covalently to form linear chains. The CPC model molecule is a better representation of chain-like molecules, such as n-alkanes and polymers, and phase behavior modeling with the proposed CPC equation of state shows considerable improvement over the reference cubic equation of state, mainly du...

A perturbed hard-sphere chain equation of state: prediction from boiling point constants

A modified perturbed hard-sphere chain equation of state (EOS) is developed to predict the PVT (pressure, volume, temperature) properties of fluids simply and accurately. Two temperature-dependent parameters, an effective van der Waals covolume and the strength of the attractive forces between two non-bonded segments, appear in this equation. Due to the law of corresponding states, we have correlated these two parameters with very good accuracy. This is done by using the boiling point constants of fluids as scaling constants. Just one adjustable parameter remains, which can be calculated by fitting to a few experimental data. The predicted EOS is tested against the experimental data for a large number of fluids including a number of diatomic and polyatomic inorganic molecules, saturated and compressed hydrocarbons, and a number of olefins and aromatics. The agreement with experiment is very good and within 2%.

Calculation of the Density and Activity of Water in ATPS Systems for Separation of Biomolecules

In this study, the perturbed hard sphere chain equation of state is utilized to calculate the activity of water in binary and ternary solutions of polyethylene glycol (PEG), salt and water. The liquid density of the binary and ternary solutions is also predicted. To estimate the water activity in PEG–water binary systems, a linear correlation is obtained for the binary interaction parameter between water and PEG. Then, using this correlation and without introducing any additional binary parameters, the water activities are predicted in ternary solutions of water, salt and PEG with different molecular weights (MW). Our results show that the mean absolute average relative deviation (AARD %) of water activity for binary PEG–water solutions in 298 K is 0.73 %. In addition, the water activity in ternary solutions of water and two PEGs with different MW is predicted within 0.31 % AARD %. Furthermore, the AARD % for prediction of water activities in binary PEG–water solutions over the temperature range 308–338 K is 0.41 %. Also, the water activities of aqueous two-phase systems are predicted with AARD % = 0.64 %. In this regard, no adjustable parameters were correlated between salt and PEG. Finally, liquid densities were predicted in binary solutions of water–PEG and ternary solutions of water–PEG–salt.

A perturbed Yukawa chain equation of state for refractory liquid metals

The perturbed Yukawa chain equation of state (EoS) has been employed to calculate the liquid density of refractory metals over a wide range of temperatures and pressures. The model uses three independent parameters: m-segment number, σ-segment size, and ε/k-segment energy. For pure components, parameters have been obtained by fitting the models to experimental data on liquid densities. Our calculations on the liquid density of tantalum, rhenium, molybdenum, titanium, zirconium, hafnium and niobium from undercooled temperatures up to several hundred degrees above the boiling point and pressures ranging from 0 to 200 MPa reproduces very accurately the experimental pVT data.

Correlation densities of ionic liquids based on perturbed Yukawa chain equation of state

The perturbed Yukawa chain equation of state (EoS) is formulated based on Barker and Henderson's liquid state perturbation theory. The model uses three independent parameters: m-segment number, σ-segment size and ε/k-segment energy. For pure components, parameters have been obtained by fitting the models to experimental data on liquid densities. Analytical expressions for Helmholtz energy and compressibility factor of perturbed Yukawa chain EoS were derived using a hard sphere chain reference. The Yukawa potential where λ = 1.8 is exploited for its ability to mimic the Lennard Jones potential. In this study, we employed this model to calculate the liquid density of 25 ionic liquids. The results show excellent agreement with the experimental data for nearly all substances over all ranges of conditions. The average absolute deviation compared with experimental data is 0.22%.

A Molecular-Based Model for Normal Fluid Mixtures: Perturbed Lennard-Jones Chain Equation of State

The perturbed Lennard-Jones chain (PLJC) equation of state, previously used for pure fluids, is extended to normal fluid mixtures. The PLJC equation utilizes the hard-sphere chain mixture as the reference system, while the perturbation term is derived based on the first-order variational theory. Binary vapor−liquid equilibrium data of a wide range of fluids were well described by this model through the use of one binary parameter kij. We showed that the PLJC equation of state was able to predict vapor−liquid equilibrium fairly accurately using binary data. Also, the PLJC equation is able to model retrograde condensation and liquid−liquid−vapor three-phase equilibrium of ternary mixtures without the need to reevaluate binary parameters. Theoretical phase equilibrium compositions were determined through an isothermal−isobaric flash calculation based on global minimization of the Gibbs free energy using a genetic algorithm.

Simple equation of state for hard‐sphere chains

AbstractA simplified thermodynamic perturbation theory‐dimer framework is used to derive an equation of state for hard‐sphere chains. The accuracy of the equation is tested against simulation data for hard‐sphere chains containing up to 201 hard‐sphere segments. A comparison is also presented with the results of other more sophisticated hard‐sphere chain equations of state. The equation reproduces the compressibility factor of hard‐sphere chains obtained from molecular simulation with a reasonable degree of accuracy. The equation can potentially form the theoretical backbone of an equation of state for real chainlike molecules. From a practical perspective, it has the advantage of being considerably simpler than alternative hard‐sphere chain equations.

Heat capacity of polymer melts from the polymer chain-of-rotators equation of state

Recently, the chain-of-rotators equation of state derived from the rotational partition function was extended to polymers. Values of the three equation of state (EOS) parameters were obtained from fitting with experimental pressure-volume-temperature data and the parameters were correlated with the structure of the polymer repeat unit. In this article, the residual molar heat capacity derived from an EOS is added to the ideal gas heat capacity from Benson's group contribution method to obtain the polymer molar heat capacity at constant pressure, C p . Predictions from the polymer chain-of-rotators (PCOR) using correlated parameters are compared with those obtained from PCOR, Sanchez-Lacombe, Flory-Orwoll-Vrij, and the perturbed-hard-sphere chain equations of state using parameters fitted from experimental data. Deviations of calculated C p from the formula of van Krevelen for liquid polymers are likewise presented. With the correlations developed for its parameters, the PCOR offers the advantage of predicting the C p for polymer melts from just the knowledge of the polymer's structure.

Heat capacity of polymer melts from the polymer chain‐of‐rotators equation of state

Recently, the chain-of-rotators equation of state derived from the rotational partition function was extended to polymers. Values of the three equation of state (EOS) parameters were obtained from fitting with experimental pressure–volume–temperature data and the parameters were correlated with the structure of the polymer repeat unit. In this article, the residual molar heat capacity derived from an EOS is added to the ideal gas heat capacity from Benson's group contribution method to obtain the polymer molar heat capacity at constant pressure, Cp. Predictions from the polymer chain-of-rotators (PCOR) using correlated parameters are compared with those obtained from PCOR, Sanchez–Lacombe, Flory–Orwoll–Vrij, and the perturbed-hard-sphere chain equations of state using parameters fitted from experimental data. Deviations of calculated Cp from the formula of van Krevelen for liquid polymers are likewise presented. With the correlations developed for its parameters, the PCOR offers the advantage of predicting the Cp for polymer melts from just the knowledge of the polymer's structure. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:841–848, 1998

Applicability of the Perturbed Hard Chain Equation of State for Simulation of Distillation Processes in the Oleochemical Industry. Part I: Separation of Fatty Acids

Abstract Fatty acids constitute an important group of chemicals with extensive end-use markets, either for their direct uses or for the intermediate uses of their numerous derivatives. These oleochemical products are currently purified or fractionated using distillation at subatomspheric pressures. Due to the increasing interest of the pharmaceutical industry in some fatty acids with high purity, supercritical fluid extraction followed by appropriate fractionation steps are also employed. It would therefore be convenient to utilize a single thermodynamic model that is capable of predicting all thermodynamic properties needed, and covering the whole pressure range which is currently applied in both industries. Different equations of state and activity coefficient models were scanned, and the perturbed hard chain equation of state (PHC-EOS) provided results which are as good as those obtained using activity coefficient models, and in some cases better. Since there are very scarce experimental data on the be...

Superheating Limit of Boiling n‐Hexane Spinodal Decomposition Versus Nucleation Process

AbstractTwo predicative theories for superheating limits of a boiling liquid are considered in this work. In the nucleation picture, classical homogeneous nucleation theory is used to calculate superheating temperature at various pressures. In spinodal decomposition picture, stability limits are taken as the superheating temperature. A perturbed‐hard chain equation of state was developed and used for the purpose of calculating mechanical stability limit. Calculations are done for the case of normal hexane at different pressures and compared with experimental results. Classical nucleation theory gives good prediction at negative and smaller pressures. While near critical pressure, spinodal picture seems to be more accurate.