A New Approach to Investigation of vdW Type of Equations of State

A new approach to the investigation ofvdW type of equations of state (EOS) is developed by embedding a vapor pressure equation and a saturated liquid volume equation into vdW type EOS, which resuits in a new function A^s(T). The A^s(T) possesses the properties of an attractive parameter A(T), and if an EOS is accurate in the whole PVT space, then its numerical wahie equal8 A(T). As a useful tool for investigating EOS, the A^s(T) has been used to make comparisons among RKS, PRSVII, PT and ALS EOS, and to indicate where the shortcomings of the EOS are coming from. Based or. the A^s(T), a possible way to develop at real predictive equation of state is also suggested.     

Calculation of excess molar volumes with different cubic equations of state and different mixing rules

The effects of the simple composition-dependent combining rules (conventional, Adachi-Sugie and van Laar-Stryjek-Vera-type) and Huron-Vidal-NRTL mixing rules and different cubic equations of state (Redlich-Kwong, Soave-Redlich-Kwong, Peng-Robinson and Peng-Robinson-Stryjek-Vera) on excess molar volume correlation are examined. The results obtained for some asymmetric non-ideal mixtures indicate very good agreement between correlated and experimental data in all cases when Huron-Vidal-NRTL mixing rules are coupled with the Peng-Robinson-Stryjek-Vera equation of state.     

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

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.     

Simulation-based equations of state for the Lennard-Jones fluid: Apparent success and hidden failure

In this work, we utilize concepts from bifurcation theory to pinpoint hidden defects in accurate multiparameter simulation-based equations of state for the Lennard-Jones (LJ) fluid. The proposed bifurcation diagrams track the evolution of volume roots as temperatures vary at constant pressure. We critically evaluate four distinct types of LJ-based equations of state: modified Benedict-Webb-Rubin equation (with three different parameter sets), Kolafa and Nezbeda, Mecke et al, and Thol et al. For each model, we mainly construct two bifurcation diagrams at subcritical and supercritical isobars. The unphysical behaviors associated with the studied equations involve spurious two-phase separation regions, distorted volume-temperature behavior, unphysical branches, unphysical turning points, and multiplicity in volume roots. Our proposed bifurcation diagram provides a reliable and simple technique to pinpoint hidden defects in equations of state-based merely on temperature, volume, and pressure without the need of their partial derivatives or thermodynamic potentials.     

Correlation of high-pressure phase equilibria in the retrograde region with three common equations of state

Phase equilibria in the retrograde regions were calculated for the methane — n-decane binary system and for a realistic natural-gas system (methane - Kensol-16). Calculations were performed using three equations of state (EOS): Peng-Robinson, Redlich-Kwong-Soave and Perturbed-Hard-Chain; calculations were compared to experiment. Liquid-drop-out curves and pressure-temperature diagrams were calculated between 301 and 369 K and pressures to 90 MPa. The binary system was represented best by the Peng-Robinson EOS. For the natural-gas system, the Perturbed-Hard Chain equation yielded the best results, although all equations of state showed appreciable deviations. Good results could only be obtained when binary coefficients were fitted to the experimental retrograde data.     

A systematic approach for the efficient estimation of interaction parameters in equations of state using binary vle data

A systematic and computationally efficient approach for the estimation of the interaction parameters in equations of state using binary vapor liquid equilibrium (VLE) data is presented. Initially, the best set of interaction parameters is estimated by implicit least squares. Subsequently, the VLE calculations are performed using these parameters. Based on the quality of the fit it is decided whether these estimates suffice or implicit maximum likelihood estimation should be performed to obtain the statistically best values. Estimation subject to the liquid phase stability constraint is performed when erroneous phase behavior is computed. The approach is illustrated with typical examples.     

基于不同状态方程预测气体水合物相平衡条件

气相逸度的计算结果会直接影响气体水合物相平衡条件的预测精度。基于Chen-Guo模型,选取RK、SRK、PR以及PT四种状态方程计算逸度,分别对甲烷、乙烷以及二氧化碳三种不同气体水合物在不同温度范围内的相平衡条件进行计算。结果表明：纯水条件下,RK方程最适合预测甲烷水合物相平衡条件,而PR方程更适合预测乙烷及二氧化碳水合物相平衡条件;对于冰中,SRK方程适合预测甲烷水合物的相平衡条件,PR方程适合预测乙烷水合物的,而RK方程更适合二氧化碳水合物的;对于甲烷水合物,低于218.2 K的预测是导致模型预测精度偏低的原因;对于乙烷水合物,需要提高低于230.2 K的预测精度;对二氧化碳水合物而言,提高对低于270.7 K的预测可以进一步提高模型预测精度。     

Generalization of the effects of solvent–polymer interactions with linear multiparameter equations

A quantitative generalization of the indices of swelling process of polymers, containing the nonhydrocarbon groups (polyurethanes, fluoropolymers) in organic solvents, as well as of the process of dissolution of poly(methy1 methacrylate) was successfully realized by means of multiparametric equations, which take into account the solvents capacity for specific and nonspecific solvation of polymers and solvents' molar volumes. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Twenty‐one new theoretically based cubic equations of state for athermal hard‐sphere chain pure fluids and mixtures

Eight new hard‐sphere equations of state (EOS's) were obtained from molecular simulation data for the pair correlation function g_HS(σ) vs. packing fraction η and combined with three theoretical schemes to obtain 21 new cubic EOS's for athermal hard‐sphere chains (AHSC's). The eight new hard‐sphere EOS models successfully reproduced isotropic fluid compressibility factor Z_HS and g_HS(σ) vs. η simulation data and predicted metastable liquid Z_HS vs. η and virial coefficients up through B₁₀. Moreover, calculated Z vs. η and reduced second‐virial coefficient vs. chain length m were compared with molecular simulation data for chains up to m = 201 for a set of representative (eight of twenty‐one) chain equations. Z vs. η for three AHSC binary mixtures was also successfully predicted. The results indicate that the new cubic EOS's give a satisfactory representation of simulation data for chain fluids and can be used to develop theoretically based cubic EOS's for “real” fluids including attractive effects. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1677–1690, 2015     

Prediction of ethane and CO2 solubilities in heavy norma paraffins using generalized-parameter soave and peng-robinson equations of state

A study was made of the abilities of the Soave and Peng-Robinson equations to represent the phase behavior of ethane + n-paraffin and CO₂ + n-paraffin systems. These equations are capable of describing the phase behavior of such systems; however, the level of precision obtained varies with the degree of complexity used in representing the interaction parameters in the mixing rules employed. For ethane/C0₂ with n-paraffins extending from C₃ to n-C₄₄, an uncertainty of about 1 % is obtained for bubble point pressures (or about 0.005 mole fraction for solubilities) when two system-specific interaction parameters per isotherm are used. Simple generalized correlations are presented for the equation-of-state interaction parameters which allow prediction of the bubble point pressures with an expected uncertainty of about 5.7% (0.014 in mole fraction).     

Taking advantage of available cubic equations of state

All available simple cubic equations of state (EOS) are developed for specific representations. An effort has been made to take advantage of these existing equations for binary vapor-liquid equilibrium (VLE) as well as density calculations by assigning different EOS to different components of the mixture under consideration. A four-parameter cubic equation was used for combining the equations in the calculation. The effect of substance-dependent Ω_ac on vapor-liquid equilibrium calculations was further investigated, using two sets of mixing rules. A criterion for selection of equations for VLE calculation by means of the proposed approach was suggested. The improvement in the prediction of liquid volumes for binary mixtures based on the fitting of pure component liquid volumes was very satisfactory.     

一个修正的多参数状态方程

从统计热力学的观点出发，结合经验的状态方程，对方程参数作出适当的修正，得到一个改进的适用范围广的多参数状态方程。结果表明，修正的状态方程精度较高。     

Calculation of pure saturation properties using cubic equations of state

A robust algorithm is outlined for the solution of the classical non-linear isofugacity problem by using equations of state (EOS). The procedure suggested is free of numerical pitfalls from the triple point to the critical point. The combination of differential stability (spinodal curve) and zero pressure reference concepts yields an automatic initialization of the calculations inside a region of convergence where the EOS can always predict pure compound vapor pressures at a given temperature.     

Prediction of thermodynamic properties of polymeric liquids using a new equation of state

In this paper, we have used a simple equation of state (EoS) to predict the density for polymeric liquid mixtures at different temperatures, pressures, and compositions. The excess molar volumes of these mixtures have been also calculated using this equation of state. Also, we have computed isothermal compressibility. A wide comparison with experimental data has been made for each thermodynamic property. The values of statistical parameters between experimental and calculated properties show the ability of this equation of state in reproducing and predicting different thermodynamic properties for studied polymeric mixtures.     

甲基叔丁基醚的状态方程

利用公开发表的实验数据开发了甲基叔丁基醚（MTBE）的状态方程,方程以Helmholtz自由能为显式、以温度和密度为自变量。方程计算饱和蒸气压的不确定度430 K以下为1.0%,随着温度的升高,由于缺少实验数据不确定度增大为2.0%。方程计算密度的不确定度由液相区的0.2% 变到临界区和气相区的1.0%。方程计算能量相关物性（如比热容和音速）的不确定度为0.5%。临界区,除了饱和蒸气压,方程计算所有其它热力学性质的不确定度都较高。正如文中分析,本文方程不但能准确的复现实验数据,而且方程的外推性也是合理的。文中对方程进行了详细的分析。     

PRSV: The stryjek-vera modification of the peng-robinson equation of state. Parameters for other pure compounds of industrial interest

Pure - compound - parameters for the Stryjek-Vera modification of the Peng-Robinson equation of state, PRSV, are reported for sixty-nine additional compounds of industrial interest. Errors in the reproduction of pure compound vapor pressure are normally below 1% at reduced temperatures lower than 0.7 At reduced temperatures higher than 0.7, for a few compounds for which data are scarce, errors are somewhat higher than 1%.