方型状态方程在高压相平衡中的研究及应用

对近年来状态方程的研究及其在高压相平衡计算中的应用状况作了综述分析。以ＰＲＳＶ方程为基础，通过实际计算考察和评价不同混合规则在复杂体高压汽液平衡、超临界流体／固体体系相平衡计算中的性能     

PREDICTION OF PHASE EQUILIBRIA IN BINARY MIXTURES USING AN IMPROVED EQUATION OF STATE AND A THEORETICALLY CONSISTENT MIXING RULE

Prediction of thermodynamic properties and phase equilibria in fluid mixtures using a simple cubic equation of state is still a challenging problem. In this paper, we have predicted vapor/ liquid phase equilibria of several binary fluid mixtures using our previously developed improved Peng-Robinson equation of state and a theoretically consistent mixing rule. Our mixing rule combines the mixing rule of Wong-Sandier with a physically based combination rule. Mixtures are composed of nonpolar, nonassociating polar and associating polar fluids. Comparisons of theoretical predictions with experimental data show a very good performance of our approach in describing vapor/liquid phase equilibria of several mixtures, namely, carbon dioxide/ propane, ethane/hexane, butane/methanol, benzene/methanol, acetone/methanol, methanol/ ethanol, methanol/1-butanol, methanol/water and ethanol/water.     

VAPOR-LIQUID EQUILIBRIA BY EXTENDED SOAVE EQUATION OF STATE

The Soave[1]equation of state is extensively accepted because of its accuracy andsimplicity.In 1988,Tan et al.[2]suggested a modification by introducing atemperature-dependent factor to parameter"b"on the basis of statistical meaning,anda good accuracy was obtained for supercritical fluids as well as fluids approaching criti-cal conditions but not for mixtures.In the previous work,an extended Soave equa-tion of state[3]has been proposed to improve the prediction of liquid density.In thispaper,the extended equation is used to calculate vapor-liquid equilibria of mixtures atsubcritical conditions.     

单参数Wilson方程预测C_9-DMP体系汽液平衡

根据实测γ~∞_1用单参数Wilson方程预测均三甲苯-DMP和偏三甲苯-DMP二元体系汽液平衡,并推算均三甲苯-偏三甲苯-DMP三元体系的汽液平衡,与实测数据比较,均获得良好结果。     

改进SRK方程提高正构烷烃饱和蒸气压和液体体积预测精度

<正>引言 在化学工程和油藏工程的相平衡和其他热力学性质计算中,两参数立方型SRK方程应用最为广泛。然而,在某些情况下由SRK方程预测的饱和蒸气压出预测的液体体积偏差较大,无法满足工程计算的需要,必须改进方程,提高其预测精度。1 饱和蒸气压的改进 SRK方程可以写为 p=RT/（V-b）-(a(T)）/V(V+b) （1）     

PHASE EQUILIBRIA OF THE CYCLOHEXANE-TOLUENE-SULFOLANE AND HEXANE-TOLUENE-SULFOLANE TERNARY SYSTEMS

Liquid-liquid equilibrium data for two ternary systems were obtained. The experimental data were measured for cyclohexane-toluene-sulfolane at 17, 25 and 50°C, and for hexane-toluene-sulfolane at 18 and 25°C. The NTRL and UNIQUAC models were used to correlate the experimental results and to calculate the phase compositions of the ternary systems. The agreement between the experimental results and the fitted values was equally good with both of the models.     

VAPOUR LIQUID EQUILIBRIA IN STRONG ELECTROLYTE SOLUTIONS BY THE CORGC EQUATION OF STATE

The capability of chain-of-rotalor group contribution equation of state (CORGC EOS) in prediction of vapour-liquid equilibria for electrolyte solutions is discussed. A new approach is considered in which salt is considered as a single component and therefore, there is no ion in the solution. The interaction parameters between water and 50 salts are determined and reported. The parameters are temperature dependent and thus, vapour-liquid equilibria calculations can be achieved at moderate temperature. The percent average absolute deviation for prediction of vapour pressure and osmotic coefficient for 50 aqueous solutions are equal to 0.89 and 16.7, respectively. Comparison between the calculated results and experimental data has been performed.     

CONTRIBUTIONS TO THE THEORY OF GLASS FORMATION AND THE GLASSY STATE*

An attempt has been made to assimilate the most important results of recent glass research into a theory of glass formation and the glassy state and to discuss it in relation to present knowledge of physics, chemistry, and colloidal chemistry. The formation of glass from the liquid state, in contrast to crystallization, is a continuous path from the liquid, through the viscous (supercooled) to the brittle state. The transformation point (Tjp) represents the boundary temperature between viscous and brittle glass, at which boundary the property-temperature coefficients more or less suddenly change. Property values are influenced by thermal history which can not be explained by mechanical strains. Therefore, while a melt is cooled, an inner change of state, dynamic aggregation, is assumed which takes more and more time as the transformation point is approached and is completely checked at lower temperatures. The question of the thermodynamic stability of the glassy state thus becomes a problem. The difference between “unchecked” (lasting) and “checked” displacements of state is explained with respect to a series of properties. From measurements of the viscosity and of the electric conductivity at temperatures from 1300 down to 300°C, it is shown that the liquid or viscous state follows a simple hyperbolic law, according to which these properties can only continue down to a lower limiting temperature (7V) above the absolute zcro point. The brittle state begins at the transformation point and follows a new law, knowledge of which is made more difficult by sooner or later “checking” the displacements of state. From the previous two different laws, it follows that brittle glass is something other than a supercooled liquid. The transformation point can not be thermodynamically explained. Molecular kinetic considerations make it appear to be that temperature at which densest packing with a cessation of free molecular kinetic motion of the particles is reached. Changes in the brittle state are explained from an atom-kinetic point of view (shrinking of particle volumes) provided no changes in the state of aggregation occur. Dynamic aggregation takes place by the formation of primary and secondary particles. The structure of secondary particles is compared to a roll of coins and this picture is used to explain negative expansion under pressure, peculiarities in expansion curves, and the beginning of brittleness. According to colloidal chemical considerations, the glassy or viscous states represent a solution of secondary particles as the disperse phase in a dispersing medium of primary particles and individual molecules, and the transformation point represents the boundary temperature between viscous and brittle glass paralleled by the gelatinizing temperature characteristic of the change from a sol to a gel. Support for the colloidal-chemical conception is obtained from observations on rapidly cooled glass melts and from reaction kinetic. Changes of property in the brittle and viscous states are proportional to the logarithm of the time, z, a law which is also found in elastic after-working, in isothermal dissociation of carbonates, and in some other instances. This law can he deduced from v. Smoluchowski's theory of coagulation. The disappearance of, double refraction of chilled glasses due to annealing (cooling) can also be linked to the log Z law.     

A CONTRIBUTION TO THE PREDICTION OF PHASE SEPARATION IN BRANCHING CONDUITS

A phenomenological model for phase separation in branching conduits (Hwang el al., 1988) has been extended and improved. These modifications involve new models for the phase distribution at the inlet of a branching junction corresponding to four different flow regimes, and a correction for flooding in vertical junctions. This mechanistically-based model gives good agreement when compared with representative experimental data.     

立方型状态方程用于蒸发热的计算

推导出立方型状态方程计算纯流体蒸发热的新公式,该计算式的特点是式中含有能量参数对温度的导数 da/dT,而与 a(T)无关。根据这一公式对立方型状态方程推算蒸发热进行了比较分析,提出a(T)与 da/dT 相互独立的计算方法,并用 Peng-Robinson 方程对70多种物质(包括烃、醇、卤代烃、酮、无机气体等)进行了关联计算,蒸汽压和蒸发热的平均相对误差分别为0.70%和1.33%。     

NON-CUBIC EQUATION OF STATE FOR PHASE EQUILIBRIUM CALCULATIONS

A new non-cubic equation of state is proposed for calculation of the thermodynamic properties ofnonpolar and polar fluids and their mixtures,including,saturated vapor pressure,saturated liquid volume,saturated vapor volume,heats of vaporization and vapor-liquid equilibria.The new equation is derived from thegeneralized van der Waals partition function in which the repulsive terms are expressed with the Carnahan andStarling equation for hard spheres,and the attractive terms are made up of the dispersive energy and theChemical association energy. The rules of dependence of parameters α and σ and on temperature are considered broadly so that the newequation yields good agreement with experimental saturated properties of 20 nonpolar and 27 polar fluids in therange of reduced temperatures of 0.5 to 1.0 The new equation with parameters group-contributed generally givessatisfactory predictions on saturated properties. Correlations of vapor-liquid equilibrium data for alcohol-containing systems by using van d     

GENERALIZED SEMI-EMPIRICAL NON CUBIC EQUATION OF STATE FOR THE REPRESENTATION OF PROPERTIES OF PURE SUBSTANCES

The analytical equation of state first introduced by Ponce and Renon was modified. At a given temperature, the addition of a corrective term in virial form yields an equation with four parameters. All parameters are assumed temperature dependent and properties of pure substances can be represented with 11 parameters. A corresponding state form using the characteristic parameters T_c, P_c, ω was developed. It yields an improvement in representation of molar volumes compared with the generalized cubic (Soave, Peng-Robinson) and non cubic (Simonet) equations. Enthalpy can also be calculated.     

EVALUATION OF THE ORIGINAL AND THE MODIFIED LEE-KESLER EQUATION OF STATE

In this work, the Lee-Kesler equation of state has been used together with the extended corresponding states principle. In order to improve the predictability of the equation in a more narrow acentric factor range, two new reference fluids have been chosen. The parameters in the Lee-Kesler equation have been estimated for the two reference fluids, CFC12 (dichlorodifluoromethane) and HFC134a (1,1,1,2-tetrafluoroethane), with the Error-in-Variables Model. This model allows both dependent and independent variables to be subject to errors.

Calculations have been made for the two reference fluids as well as for other compounds, and the predicted thermodynamic properties have been compared with experimental values. Comparative calculations have also been carried out for some of the previously suggested modifications of the Lee-Kesler correlation.     

用兰纳-琼斯位能和单参数Wilson方程预测汽液平衡

根据兰纳-琼斯位能提出计算Wilson方程中同类分子间能量参数gii的一个简便方法,用于单参数Wilson方程可成功地预测二元体系气液平衡,预测精度与已有方法相当,且仅需要纯物质的Tc,Pc,Zc数据。     

A GENERALIZED EQUATION OF STATE FOR POLAR AND NON-POLAR FLUIDS BASED ON FOUR-PARAMETER CORRESPONDING STATES THEOREM

A new generalized equation of state for polar and non-polar fluids based on the corresponding states theorem is developed, f n addition to two critical parameters, four parameters are required; two for the calculation of volumetric properties and two for the calculation of pressure and departure functions. Parameteres for more than 100 polar and non-polar fluids are given. Comparison with the existing generalized state equations showed that the new method, in general, shows a better agreement with the experimental data. The absolute average deviation is 0.48% for the vapor pressure and 0.32% for the saturated liquid volume.     

THE CORRELATION AND PREDICTION OF THE VISCOSITIES OF MIXTURES OVER A WIDE RANGE OF PRESSURE AND TEMPERATURE

A generalized corresponding states principle (GCSP) based on the known properties of two reference fluids has been used to correlate the viscosities of fluid mixtures over a wide range of pressure and temperature. It is shown that good predictions of the viscosities for a variety of mixtures can be obtained with this method. Asymmetric mixtures, however, require the use of one adjustable constant. Comparisons with the TRAPP method are shown and the advantages and limitations of the two methods are discussed.     

A NEW CORRELATION FOR THE PARAMETERS IN A VAN DER WAALS-TYPE EQUATION OF STATE FOR SIMPLE LIQUIDS

We present a new method based on a corresponding-states approach to evaluate the equation-of-state parameters of a van der Waals-type equation of state which is valid for simple, non-polar molecules, both spherical and non-spherical, and their mixtures. The proposed method, which has been tried on fourteen liquids, predicts well pure component liquid molar volumes over a large temperature range. The method's predictive capability of the excess thermodynamic functions (G^E, H^E, and V^E) has also been tested on fourteen liquid mixtures and the results compare favorably with those of other more sophisticated treatments.     

PHASE EQUILIBRIA IN THE H2/CH4 SYSTEM AT TEMPERATURES FROM 92.3 TO 180.0 K AND PRESSURES TO 140 MPa*

Experimental measurements of liquid-vapor phase equilibria in the system H₂/CH₄ are reported for ten temperatures in the range 92.3 to 180 K, and pressures to 140 MPa. The mixture critical line and the pressure-temperature trace of the three-phase region solid-liquid-vapor have been located. The three-phase region and the critical line intersect at T = 91.5 K and P = 147 MPa to form an upper critical end point. Experimental results have been compared with predictions of three equations of state, Peng-Robinson, Reclich-Kwong and Deiters, and with calculations based on statistical mechanical perturbation theory.     

PERFORMANCE OF FIVE EQUATIONS OF STATE FOR THE PREDICTION OF VLE AND DENSITIES OF NATURAL GAS MIXTURES IN THE DENSE PHASE REGION

This paper examines the degree of uncertainty of five Equations of State (EOS) for the prediction of densities in the dense phase region which is beyond the ranges of pressure and temperature originally specified for these equations. Predicted densities were compared with measured values for different hydrocarbon mixtures including a rich mixture. The results show that the GERG equation of state, originally specified for the range of P -8 C, outperforms all other equations in the region up to P=30 MPa and T > -8 C. In this range, its mean deviation from measured values of densities was found to be less than -0.015% and standard deviation ( ) also less than 0.015%. The AGA-8 equation, which identified several regions of pressures and temperatures with different uncertainties, also performed quite well with a mean deviation of -0.2% and less than 0.4% in the region up to P=30 MPa. The other equations showed relatively high deviation: ~2.7% for BWRS,-5.1% for PR and 2.5% for RKS. Unlike GERG and AGA-8, however, these three equations can also be used to predict the vapour-liquid-equilibrium (VLE). VLE predictions were compared with measured values for eight binary mixtures of methane (C1) and ethane (C2). It is recommended to use PR for VLE prediction, as quite good agreement between measured data and prediction by PR was demonstrated.