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Compressibility Factor (compressibility + factor)

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Chemistry	100%

Selected Abstracts

Transferable intermolecular potentials for carboxylic acids and their phase behavior

AICHE JOURNAL, Issue 2 2010
Amir Vahid
Abstract Transferable step potentials are characterized for 39 carboxylic acids. The reference potential is treated with discontinuous molecular dynamics, including detailed molecular structure. Thermodynamic perturbation theory is used to interpret the simulation results and to provide an efficient basis for molecular modeling and characterization of the attractive forces. Four steps are used for representation of the attractive forces with only the first and last steps varied independently. The two middle steps are interpolated such that each site type is characterized by three parameters: the diameter, ,, the depth of the inner well, ,1, and the depth of the outer well, ,4. The depths of the attractive wells are optimized to fit experimental vapor pressure and liquid density data. Generally, the vapor pressure is correlated to an overall 43% average absolute deviation (% AAD) and the liquid density to 5% AAD. The deviations tend to be largest for the higher molecular weight acids. These deviations are larger than the errors previously encountered in characterizing organic compounds, but carboxylic acids present exceptional challenges owing to their peculiar dimerization behavior. Simultaneous correlation of vapor pressure, vapor compressibility factor, and phase equilibria of water + carboxylic acids place several constraints on the nature of the potential model, with the parameters of the present model representing a reasonable tradeoff. In other words, our model represents minimal deviations for vapor pressure, vapor compressibility factor, and phase equilibria of all acids simultaneously while varying the parameters ,, ,1, ,4, ,CC(dimerizing site bonding energy), ,AD(acceptor-donor bonding energy), and KHB(hydrogen bonding volume) for the acid O and OH site types. The present model is characterized by one acceptor and one dimerizing site on the carbonyl oxygen and one acceptor and one donor site on the hydroxyl oxygen. The acceptor and donor are capable of interacting with water while the dimerizing site is not. With this model, the saturated vapor compressibility factor of acids with seven or fewer carbons is near 0.5 while higher carbon ratios lead to a compressibility factor approaching 1.0. To compensate for the high vapor pressure deviations of the transferable potential model, a correction is introduced to customize the molecule-molecule self interaction energy. This adaptation results in deviations of 3.1% for vapor pressure of the pure acid database. To validate the behavior of the model for carboxylic acids in mixtures, 33 binary solutions were considered. Acids in this database ranged from formic to hexadecanoic. The average absolute deviation in bubble pressure for aqueous acid systems is 4.4%, 10.5% for acid + acid systems, and 4.7% for acid + n-alkane systems without a customized interaction correction. When applying the correction, deviations were 2.4% for aqueous systems, 2% for acid systems, and 2.8% for acid + n-alkane systems. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source]

Extension to mixtures of two robust hard-sphere equations of state satisfying the ordered close-packed limit

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2001
Cyrus Ghotbi
Abstract Two new hard-sphere EOS are proposed and tested using the same attractive potential terms used by the SAFT EOS. Generalized expressions for the pair RDF at contact value, the compressibility factor, and the excess chemical potentials have been derived. Extension to mixtures is tested using three mixing rules for multicomponent hard-sphere fluids. The proposed EOS combined with the Santos et al. and the Barrio-Solana mixing rules reproduced the compressibility factors and the excess chemical potentials more accurately than the Boublik-Mansoori-Camahan-Starling-Leland (BMCSL) EOS. However the pair RDF at contact value had larger deviations than those obtained with the BMCSL EOS. The combination of the proposed equations and the Barrio-Solana mixing rule gave an accurate reproduction of the compressibility factor for binary hard-sphere fluids with high diameter ratio even in the low concentration regions of the larger spheres. Deux nouvelles équations d'état de sphères dures sont proposées et vérifiées à l'aide des m,mes termes potentiels attractifs utilisés pour l'équation d'état de SAFT. Des expressions généralisées pour le RDF pair à la valeur de contact, le facteur de compressibilité et les potentiels chimiques d'excès ont été calculées. L'extension à des mélanges est vérifiée à l'aide de trois régies de mélange pour fiuides à sphères dures multi-composants. Les équations d'état proposées, combinées aux règles de mélange de Santos et al. et de Barrio-Solana, reproduisent les facteurs de compressibilité et les potentiels chimiques d'excès de façon plus précise que l'équation d'état de Boublik-Mansoori-Camahan-Starling-Leiand (BMCSL). Cependant, le RDF pair à la valeur de contact a des écarts plus grands que ceux obtenus avec l'équation d'état de BMCSL. La combinaison des équations proposées et la régle de mélange de Barrio-Solana donne une reproduction exacte du facteur de compressibilité pour des fluides de sphères dures binaires ayant un rapport de diamètre important m,me dans les régions de faible concentration de sphères les plus grandes. [source]

Correlations of supercritical temperature of fluid alkali metals

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2008
Ramasamy Balasubramanian
Abstract The supercritical temperature, the maximum attainable temperature of superheating and the critical compressibility factor of caesium, rubidium and potassium are correlated through the generalised van der Waals equation of state. This three-parameter equation differs from the known van der Waals equation of state by the modified expression for molecular pressure. For caesium, rubidium and potassium, the ratios of the supercritical temperature to the maximum attainable temperature of superheating are estimated. Our estimation results are in agreement with experimental data. It has been established that caesium, rubidium and potassium obey the single-parameter law of corresponding states with the ratio of the supercritical temperature to the maximum attainable temperature of superheating as the thermodynamic similarity parameter. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd. [source]