Equilibrium properties of dense hydrogen isotope gases based on the theory of simple fluids

We present a new method for the prediction of the equilibrium properties of dense gases containing hydrogen isotopes. The proposed approach combines the Feynman-Hibbs effective potential method and a deconvolution scheme introduced by Weeks et al. The resulting equations of state and the chemical potentials as functions of pressure for each of the hydrogen isotope gases depend on a single set of Lennard-Jones parameters. In addition to its simplicity, the proposed method with optimized Lennard-Jones potential parameters accurately describes the equilibrium properties of hydrogen isotope fluids in the regime of moderate temperatures and pressures. The present approach should find applications in the nonlocal density functional theory of inhomogeneous quantum fluids and should also be of particular relevance to hydrogen (clean energy) storage and to the separation of quantum isotopes by novel nanomaterials.     

Self consistent equations for calculating ideal gas heat capacity,enthalpy and entropy. III. Coal chemicals

Rehman, Z.U. and Lee, L.L., 1985. Self consistent equations for calculating ideal gas heat capacity, enthalpy and entropy. III. Coal chemicals. Fluid Phase Equilibria, 22: 21–31.Heat capacity, enthalpy and entropy correlations presented in previous studies (Aly and Lee, and Fakeeha et al.) are generalized here to include 37 coal chemicals and 29 additional hydrocarbons. We take into account one additional vibrational contribution in the formulae. The temperature range tested extends from 298.15 to 1000 K. The ideal heat capacity is predicted to within 0.07% for most substances.     

Isothermal (vapour + liquid) equilibria and excess Gibbs free energies in some binary (cyclopentanone + chloroalkane) mixtures at temperatures from 298.15 K to 318.15 K

The vapour pressures of binary (cyclopentanone + 1-chlorobutane, +1,3-dichloropropane, and +1,4-dichlorobutane) mixtures, were measured at the temperatures of (298.15, 308.15, and 318.15) K. The vapour pressures vs. liquid phase composition data have been used to calculate the excess molar Gibbs free energies G^E of the investigated systems, using Barker’s method. Redlich–Kister, Wilson and NRTL equations, taking into account the vapor phase imperfection in terms of the second virial coefficient, have represented the G^E values. No significant difference between G^E values obtained with these equations has been observed.     

Comparison of methods for calculating thermodynamic properties of binary mixtures in the sub and super critical state: Lee–Kesler and cubic equations of state for binary mixtures containing either CO2 or H2S

The (ρ,T,p) and (vapor + liquid) equilibria for fluid mixtures containing either CO₂ or H₂S have been determined from 13 equations of state. The estimated values have been compared with published experimental results. CO₂ and H₂S were used to represent non-polar and polar fluids, respectively. The equations of state investigated were as follows: (a) the Lee–Kesler equation; (b) two equations that included new reference fluids for the Lee–Kesler method; (c) three so-called extended equations of state; and (d) seven cubic equations of state. After adjustment of the binary interaction parameters the predicted values differed from the experimental data by about 0.8% for CO₂ mixtures while for H₂S mixtures the uncertainty was about ±2.8%. Somewhat larger errors, although still lower than ±5%, were obtained for co-existing phase densities; the Lee–Kesler method provided results of the highest accuracy. The cubic equations proposed by Schmidt and Wenzel and Valderrama provide the most reliable predictions of both single and co-existing phase densities. Comparison of the predicted (vapor + liquid) equilibrium with experiment shows that each of the seven cubic equations provides results of similar accuracy and all within ±6%.     

Efficient methods for calculations of compressibility,density and viscosity of natural gases

This study presents two new methods for calculating properties of natural gases. The first is an efficient empirical model to calculate compressibility and density of natural gases containing high amount of heptane plus and none-hydrocarbon components. The model is derived from 2400 measurements of compressibility and density of various gases presented in this study. Accuracy of the model is compared to various equations of state (EOS), corresponding state, and empirical methods. The study shows that the new model is simpler and more efficient than EOS. It eliminates the numerous computations involved in EOS calculations. The new method also eliminates the characterization of the heptane plus fraction and estimation of binary interaction parameters needed for EOS calculations. Experimentally measured density of several gases has been used to study the validity of the proposed method. These measurements indicate that the new method successfully capture the physical trend of changing gas density as a function of pressure, temperature, and composition.The second method is a modification of Lee–Gonzalez–Eakin gas viscosity correlation. The new method accounts for the presence of heptane plus, hydrogen sulfide, and carbon dioxide in natural gases. The proposed method is compared to other EOS-based viscosity model, corresponding state methods, and correlations. The comparison indicates the superiority of the new method over the other methods used to calculate viscosity of natural gases.     

Argon plasma transport properties at reduced pressures

Argon plasma transport properties at low pressures (0.01 atm) are calculated using a modified Debve length suggested by T. Kihara et al. Electrons and heavy species are treated as two different gases, and the method of calculation is based on the simplified theory (or transport properties developed by R. S. Devoto. A generalized Saha equation is used to calculate the species composition, and experimental data by Y. Itikawa for momentum transfer cross sections are adapted for the evaluation of electron-atom collision cross sections.     

Phase equilibria in systems containing o-cresol,p-cresol,carbon dioxide,and ethanol at 323.15–473.15 K and 10–35 MPa

Phase equilibria in binary and ternary systems containing o-cresol, p-cresol, carbon dioxide, and ethanol have been investigated experimentally at temperatures between 323.15 K and 473.15 K and pressures ranging from 10 MPa to 35 MPa. The experimental results provide a systematic basis of phase equilibrium data, yielding the effect of temperature on the influence of the position of the methyl groups of cresols that are in phase equilibria with carbon dioxide. Based on the different solubilities of the cresol isomers in carbon dioxide, the separation of o-cresol and p-cresol was investigated. The dependence of the separation factor between both cresol isomers on concentration, temperature, and pressure is obtained from experiments in the ternary system, o-cresol+p-cresol+carbon dioxide. The influence of ethanol added to each of the binary systems, cresol isomer+carbon dioxide, in order to enhance the solubility of the cresols in the carbon dioxide-rich phase is also shown. The experimental data have been correlated using seven different equations of state, whereof four explicitly account for intermolecular association: Statistical Association Fluid Theory (SAFT) by Chapman, Gubbins, Huang and Radosz, the SAFT modification by Pfohl and Brunner for near-critical fluids, a modified cubic-plus-association equation of state (CPA EOS) according to the ideas by Tassios et al., and one of the EOS by Anderko. The mixing rule proposed by Mathias, Klotz, and Prausnitz, with two binary interaction parameters per binary system influencing intermolecular attractive forces, is used for all EOS as a basis for an objective comparison of the EOS.     

(Vapour + liquid) equilibria and excess Gibbs free energies of (cyclohexanone + 1-chlorobutane and + 1,1,1-trichloroethane) binary mixtures at temperatures from (298.15 to 318.15) K

The vapour pressures of binary (cyclohexanone + 1-chlorobutane, + 1,1,1-trichloroethane) mixtures were measured at the temperatures of (298.15, 308.15, and 318.15) K. The vapour pressures vs. liquid phase composition data have been used to calculate the excess molar Gibbs free energies G^E of the investigated systems, using Barker’s method. Redlich–Kister, Wilson, UNIQUAC, and NRTL equations, taking into account the vapour phase imperfection in terms of the 2-nd virial coefficient, have represented the G^E values. No significant difference between G^E values obtained with these equations has been observed.     

Excess molar volume and viscosity study for the ternary system tetrahydrofuran (1) + 1-chlorobutane (2) + 2-butanol (3) at 283.15, 298.15 and 313.15 K

This work reports the measured density, ρ, and viscosity, η, values of liquid mixtures of tetrahydrofuran (1) + 1-chlorobutane (2) + 2-butanol (3) at temperatures of 283.15, 298.15 and 313.15 K over a range of mole fractions and atmospheric pressure. Excess molar volume, V^E, viscosity deviations, Δη, and excess free energies of activation of viscous flow, ΔG^*E, have been calculated from experimental data and fitted to Cibulka, Singh et al. and Nagata and Sakura equations. The results were analyzed in terms of the molecular interaction between the components of the mixtures. Excess molar volumes and viscosity deviations were predicted from binary contributions using geometrical solution models, Tsao and Smith; Jacob and Fitzner; Kholer; Rastogi et al.; Radojkovic et al. Finally, experimental results are compared with those obtained by applying group-contribution method proposed by Wu.     

Vapour pressure and excess Gibbs energy of binary 1,2-dichloroethane + cyclohexanone,chloroform + cyclopentanone and chloroform + cyclohexanone mixtures at temperatures from 298.15 to 318.15 K

The vapour pressures of the binary systems 1,2-dichloroethane + cyclohexanone, chloroform + cyclopentanone and chloroform + cyclohexanone mixtures were measured at temperatures between 298.15 and 318.15 K. The vapour pressures vs. liquid phase composition data for three isotherms have been used to calculate the activity coefficients of the two components and the excess molar Gibbs energies, G^E, for these mixtures, using Barker's method. Redlich–Kister, Wilson, NRTL and UNIQUAC equations, taking into account the vapour phase imperfection in terms of the 2-nd virial coefficient, have represented the G^E values. No significant difference between G^E values obtained with these equations has been observed. Our data on vapour–liquid equilibria (VLE) and excess properties of the studied systems are examined in terms of the DISQUAC and modified UNIFAC (Dortmund) predictive group contributions models.     

Polarizable and flexible model for ethanol

A polarizable, flexible model for ethanol is obtained based on an extensive series of B3LYP/6-311++G(d,p) calculations and molecular dynamics simulations. The ethanol model includes electric-field dependence in both the atomic charges and the intramolecular degrees of freedom. Field-dependent intramolecular potentials have been attempted only once previously, for OH and HH stretches in water [P. Cicu et al., J. Chem. Phys. 112, 8267 (2000)]. The torsional potential involving the hydrogen-bonding hydrogen in ethanol is found to be particularly field sensitive. The methodology for developing field-dependent potentials can be readily generalized to other molecules and is discussed in detail. Molecular dynamics simulations of bulk ethanol are performed and the results are assessed based on comparisons with the self-diffusion coefficient [N. Karger et al., J. Chem. Phys. 93, 3437 (1990)], dielectric constant [J. T. Kindt and C. A. Schmuttenmaer, J. Phys. Chem. 100, 10373 (1996)], enthalpy of vaporization [R. C. Wilhoit and B. J. Zwolinski, J. Phys. Chem. Ref. Data, Suppl. 2, 2 (1973)], and experimental interatomic distributions [C. J. Benmore and Y. L. Loh, J. Chem. Phys. 112, 5877 (2000)]. The simultaneous variation of the atomic charges and the intramolecular potentials requires modified equations of motion and a multiple time step algorithm has been implemented to solve these equations. The article concludes with a discussion of the bulk structure and properties with an emphasis on the hydrogen bonding network.     

Molecular simulation of vapor–liquid equilibria of toxic gases

In this paper, we derived the potential parameters for three toxic gases, hydrogen sulfide, phosgene and nitrous oxide, modeled by the effective Stockmayer potential model proposed by Gao et al. [Fluid Phase Equilib. 137 (1997) 87]. The vapor–liquid equilibria (VLE) of these substances have been extensively investigated over a wide range of temperatures by the Gibbs ensemble Monte Carlo (GEMC) technique. The simulated saturated densities and pressures are in good agreement with experimental data. The critical properties obtained by regression of the simulated data also agree well with the experimental values. The present work demonstrates that the effective Stockmayer potential can describe well the toxic gases concerned.     

Modelling the VLE properties using van der Waals-type equation of state

The vapour–liquid equilibrium (VLE) properties of polar and non-polar fluids have been modelled by the use of two modified van der Waals (vdW)-type equations of state (EOSs). In this article, a revised method is applied to the above-mentioned EOSs to improve the representation of VLE properties of different class of fluids. In this respect, the repulsion parameter b is considered to be temperature dependent and also a temperature-dependent revision factor α(T) is introduced to the liquid fugacity coefficient expression derived from traditional isothermal integration to reproduce the vapour pressure (P^s) of pure liquids. The present method is also extended to represent the VLE properties of binary mixtures containing noble gases, refrigerants and hydrocarbons. This method outperforms the original vdW-type EOSs in predicting the VLE and pressure-volume-temperature (PVT) properties of 22 pure substances and 7 binary mixtures.     

Theory of dynamic light scattering by polymers and gels

It is shown under very general conditions that the intermediate scattering function for the generalized Rouse—Zimm model always takes the simple form G(K, t) α exp[?K²(k_BT/f)t], when the scattering vector K becomes sufficiently large. (Here k_B is Boltzmann's constant, T is the absolute temperature and f is the individual bead friction factor.) A microscopic formulation for the bulk modulus and friction factor density of a gel network is incorporated into the viscoelastic continuum model of Tanaka et al. The resulting expression for the apparent long-wavelength diffusion coefficient of the gel is D_G = (k_BT/f)2(1 - 2/Φ), where Φ is the network functionality.     

Correlation for prediction of vapor pressures of pure fluids incorporating renormalization group formulations with corresponding-states principle

A simple correlation for predicting the vapor pressures of coal liquids between the freezing and critical points, and extending to normal fluids, has been developed on the basis of renormalization group theory and phenomenological scaling theory. The Clapeyron equation has been reduced to the integral form

to represent vapor pressure using a generalized correlation developed by Sivaraman et al. (1983) for the prediction of latent heats of vaporization of normal fluids and coal-liquid model compounds. L*, the dimensionless latent heat of vaporization, andΔz, the difference between the compressibility factors of the saturated vapor and liquid, are given by the corresponding-states correlations

and

based on the formulations of Pitzer et al. (1955). A simple expression for the latent heat of vaporization developed by Torquato and Stell (1982) is incorporated into this correlation. The vapor-pressure correlation has been tested successfully for 23 pure-component systems including aromatic and heterocyclic compounds often found in coal liquids and shale oil in the region 0 〈 ε = (T_c-T)/T_c 〈 0.69. The deviations in the predicted vapor pressures are in the range 0.11–5.45%.     

Vapour—liquid equilibrium in binary mixtures formed by benzene or cyclohexane with 1-chloropropane or 1-chlorobutane

The vapour—liquid equilibria (VLE) for the binary systems formed by 1-chloropropane with benzene and cyclohexane at 308.15 K and 318.15 K, and for systems formed by 1-chlorobutane with the same hydrocarbons at 308.22 K, 328.27 K and 348.31 K have been determined by a total pressure ebulliometric method. The accuracy of these results was proved by comparing the heat of mixing data calculated from these VLE results with those obtained by direct measurements (Amaya, 1961; Grolier et al., 1973). The experimental data and the results of correlation by means of the Redlich—Kister equation are given. The systems with benzene were found to be nearly ideal, while those with cyclohexane exhibit positive deviations (G^E = 220–260 J mole^?1 for an equimolar mixture). New vapour pressure versus temperature data for 1-chlorobutane are reported.     

Surface tension of non-ideal binary and ternary liquid mixtures at various temperatures and p = 81.5 kPa

Experimental surface tensions for binary mixtures (1,2-ethandiol + water), (1,2-ethandiol + acetonitrile), and (acetonitrile + water) at temperatures of 283.15 K, 298.15 K, and 308.15 K and the ternary mixture (1,2-ethandiol/water/acetonitrile) at 298.15 K have been measured with the Du Noüy ring tensiometer. The surface tension of the above mentioned binary and ternary systems were correlated with empirical and thermodynamic based models. The methods of Pando et al. and Ku et al. were used to correlate the ternary surface tension data. The Fu et al., Kalies et al. and Wang et al. models were also applied to predict surface tension in the ternary system. The mean average absolute deviations obtained from the comparison of experimental and calculated surface tension values for ternary system with three models are less than 2.4%, which leads to concluding that these models show a good accuracy in different situations in comparison with other predictive equations.     

Comment on “Towards the development of theoretically correct liquid activity coefficient models”

The “New activity coefficient model” recently proposed by Lin et al. is shown to be identical to the special, homogeneous case of the COSMOSPACE model [A. Klamt, G.J.P. Krooshof, R. Taylor, AlChE J. 48 (2002) 2332–2349]. Also the proof of theoretical shortcomings of the UNIQUAC method as well as the demonstration of the striking agreement of this model with corresponding lattice Monte Carlo simulations presented by Lin et al. have already been presented in the same paper in a very similar way.     

Diffusion of hydrogen atoms in spherical vessels

A previously developed model for active species concentration profiles in infinite cylindrical systems has been extended to include the spherical system. The model couples the processes of diffusion to and reaction at the wall. Predictions of time buildup under conditions of homogeneous production by light, and time decay after extinguishing the light source, are made for H atoms. Such predictions require a knowledge of the wall recombination coefficient and the binary diffusion coefficient for H in heat bath gas. The model is experimentally tested by measuring the first-order decay constants of H at room temperature in various pressures (10-1500 torr) of six heat bath gases. The atomic concentration is monitored by Lyman-α absorption photometry. The results show good agreement with model predictions in the various heat bath gases up to ～400 torr and depend only on one parameter,γ, the recombi-nation coefficient. This should be contrasted with the earlier work where slight variation in γ was invoked. The rate constants at pressures higher than 400 torr are consistently higher than model predictions.     

Improved binary parameters using GA for multi-component aromatic extraction: NRTL model without and with closure equations

Application of genetic algorithm (GA), which leads to globally optimal binary interaction parameters from multi-component liquid–liquid equilibrium data, has been recently demonstrated for some ternary, quaternary and quinary systems. The binary interaction parameters are related to each other through the closure equations. In this work, the binary interaction parameters based on non-random two liquid (NRTL) activity coefficient model have been estimated using GA, without and with closure equations for 65 multi-component aromatic extraction systems: 53 ternary, 9 quaternary and 3 quinary systems. Parameters that satisfy the closure equations exhibit better root mean square deviations than those that do not satisfy the closure equations. Root mean square deviation value without implementation of closure equations is 0–80% better than literature as compared to 0–90% better with implementation of closure equations.