混合物临界区域热力学性质研究进展

对近期混合物临界区域热力学性质的研究作了综述,介绍了混合物临界点和临界区域相平衡的实验测定及关联计算,对临界区域热力学性质的研究作了讨论。     

由状态方程计算混合物的临界性质

混合物的临界性质(T_c,P_c和V_c)在高压相态及分离过程计算中具有重要意义.由于实验测定的困难,文献与手册中有关混合物临界性质的数据(与混合物组成有关)极少,如何通过计算确定这些性质成为热力学界所关心的问题之一.混合物的临界性质一般可通过以下三种方法进行估算:(1)通过相包线计算间接确定;(2)由经验或半经验关联式计算;(3)基于严格的临界状态的热力学准则应用状态方程直接计算.第一种方法过于繁琐;而第二种方法普适性较差,且缺乏与汽液平衡计算的热力学一致性;第三种直接计算法可消除上述缺点,因而近年来受到较大重视.Heidemann和Khalil(1980)以及Peng和Robinson(1977)所提出的直接计算法已成功地应用于烃类非极性混合物临界性质的预测.本文的目的主要是将直接法扩充应用至极性混合物临界性质的计算,并改进前人对临界比容的预测.在前阶段工作(徐东海和郭天民,1989)基础上,本文作了较大扩充与修改.按Heidemann和Khalil由Helmholtz自由能导出的下列临界状态判别准则Q△n=0,△n~T△n=1(1)及偏导数矩阵Q中的元素q_(ij)与三次式中三阶偏导数的表达式结合状态方程(可导出逸度f_i表达式)联解方程式(l)和(2)便可求得组成指定的混合物的临界性质.为将直接法扩展应用至极性混合物,作者选用了Leet等(1986)提     

高密度及多组元方阱位能混合物流体的计算机Monte Carlo模拟

<正>流体的热力学宏观性质由其微观结构所支配,因此许多研究者用计算机Monte Carlo模拟(MC)或分子动力学模拟(MD)方法,力求得到流体的微观结构的真实图象,并据此建立推算或预测流体宏观性质的热力学模型.     

Monte Carlo法模拟球形-线性Lennard-Jones流体混合物

本文用Monte Carlo方法对球形-线性Lennard-Jones流体混合物进行了计算机模拟。推导出含有该类线性分子的体系能量、压力和化学位的长程校正公式,并用于NPT系综模拟,研究了组成对体系物性的影响,为进一步模拟链状分子及聚合物体系打下基础。     

近临界区流体相态和热力学性质研究现状及发展趋势

近临界区流体相态和热力学性质的研究是当前化学工程领域受到重视的前沿研究课题。本文扼要介绍了临界现象与临界指数，描述了近临界区流体相态和热力学性质的实验测定与估算方法，并对该领域的研究动态作了讨论。     

流体相平衡研究的进展

本文介绍了国内外有关流体相平衡的理论及实验研究的新进展及展望,其中包活低压、高压汽液平衡及高压PVT关系的实验研究;状态方程、活度系数模型和基团贡献法等流体相平衡的理论研究。作者着重介绍了统计力学方法在这些研究中的应用以及缔合状态方程和连续热力学等新的研究领域。此外,还对诸如高压与临界现象、电解质溶液、表面活性剂系统、含化学反应的相平衡等有希望的领域的研究作了介绍和展望,本文也用了一定的篇幅对近年来迅速发展的计算机模拟技术作了介绍。     

混合工质临界性质的推算研究

采用五种不同的方法计算了四种不同二元混合工质的临界温度和临界压力,研究对比不同方法在推算二元混合临界性质时的精度。其中Peng-Robinson（PR）方程和Soave-Redlich-Kwong（SRK）方程,两种状态方程结合Heidemann等提出的临界点判据计算得到的临界参数与实验结果吻合较好。两种经验公式,改进的Chueh-Prausnitz（MCP）方法和Redlich-Kister方法,以及径向基函数神经网络（RBFNN）在计算混合工质的临界性质时也都有着较高的计算精度。对于临界温度的计算,PR方程、SRK方程、MCP方程、Redlich-Kister方程以及径向基函数神经网络计算结果的绝对平均偏差的最大值分别为1.82%、1.73%、0.95%、0.17%和0.20%。对于临界压力的计算,通过PR方程、SRK方程、MCP方程、Redlich-Kister方程以及径向基函数神经网络计算的绝对平均偏差的最大值分别为6.07%、5.04%、3.49%、1.90%以及0.67%。     

非电解质液体混合物表面张力的统计热力学模型

运用Davis模型导出一个统计热力学的表面张力模型．对22个双组分体系的表面张力作了推算和关联,总平均相对偏差分别为5.45％和1.95％.并利用关联双组分体系得到的参数值,直接推测了三组分体系的表面张力,平均相对偏差为2.21％.结果令人满意.表明该方法简单、精确,便于工程应用．     

CORRELATION OF CRITICAL LOCI FOR FLUID MIXTURES

The hard-sphere three-parameter equation of state proposed in our previous investigation was applied to correlate binary critical loci of alkane-alkane, aromatic-aromatic, hydrocarbon-inorganic gas and systems containing oxygenated hydrocarbons including those exhibiting type Ⅲ behaviors as classified by van Konynenberg and Scott. A new procedure was also presented which simplified mathematical manipulations and permitted the reduction of the computation time.Results were compared with those obtained by Patel-Teja equation with temperature-dependent binary interaction parameters. Significant improvements were achieved by the proposed equation with temperature-dependent parameters.In addition parameters obtained from the critical locus calculations were used to predict vapor-liquid equilibria of hydrogen-carbon monoxide and hydrogen-carbon dioxide systems. Prediction accuracies were found to be very satisfactory.     

线型聚乙烯-丙烷体系在超临界条件下临界点的计算

根据Koningsveld等人推广的Flory-Huggins关于高聚物溶液理论,提出了用聚乙烯-丙烷体系标样的超临界流体相平衡浊点线实验值来模拟计算临界点的方法.结果表明,该计算方法简便,计算结果与实验数据基本相符.     

THE CALCULATION OF CRITICAL PROPERTIES OF MIXTURES FROM EQUATIONS OF STATE

The rigorous critical state criteria based on Helmholtz free energy is used with equations of state fordirect calculation of critical properties(T_c,P_c and V_c)of 44 binary and 5 ternary systems.Special at-tention is paid to systems containing polar component(s)and the improvement in critical volume prediction.For extending this method to polar systems,the recently developed Cubic Chain-of-Rotators equation ofstate has been applied.As compared with SRK and PR equations of state,the improvement in V_c pre-diction is most impressive.     

ESTIMATION OF CRITICAL PROPERTIES OF BINARY MIXTURES USING GROUP CONTRIBUTION METHODS

A new method for estimating critical temperature (T_c), critical pressure (P_c), and critical volume (V_c), of both nonpolar and polar binary mixtures displaying continuous critical loci is proposed. The methodology is based on the group contribution concept for estimation of critical constants of pure compounds, and the combining rule concept for estimation of mixture properties. Lydersen group contribution method is used to demonstrate the application of this methodology. The combining rules are formulated and their adjustable parameters are determined using 43 nonpolar and polar binary mixtures including 417 data points for (T_c), 390 data points for (P_c), and 219 data points for (V_c), respectively. The method is then evaluated with 15 independently selected binary mixtures containing hydrocarbons, alcohols, ethers, amine, carbon dioxide, nitrous oxide, sulfur dioxide, chloroform, and hydrogen sulfide. The average deviations of the estimated (T_c), (P_c), (V_c) are 1.60%, 7.26%, and 3.64%, respectively. The present procedure does not require experimentally adjusted interaction parameters for estimation of the critical properties of a given binary mixture.     

用微扰理论、平均球近似结合统计缔合流体理论建立纯流体的状态方程

分别采用微扰理论和平均球近似（MSA）处理实际流体偶极──偶极间的相互作用,结合统计缔合流体理论（SAFT）处理氢键缔合相互作用,建立了一个纯缔合流体的状态方程．用分子链节微观参数分别关联了37种纯缔合流体（水、醇、酸和胺）的饱和液相密度和饱和蒸汽压．结果表明：采用微扰理论处理偶极──偶极相互作用的关联结果明显优于平均球近似,与分子模拟数据比较,结论一致．     

用密度泛函理论研究非极性混合流体表面性质

应用密度泛函理论研究了二元非极性混合流体的表面性质.分子作为球形链处理,不同分子内的两链节相互作用以硬核Yukawa势能表示.为了避免计算中势能作用数值积分截断导致的误差,采用了合理的长程校正方法.根据微扰理论建立了流体的状态方程以计算汽液相平衡.从纯流体汽液相平衡数据回归得分子的链节作用参数ε/k、d和m_s,这些参数预测纯流体表面张力时可获得较好结果.继而引入混合参数k_ij表示不同分子链节作用情况,计算了6种非极性混合流体的汽液相平衡、表面张力、表面密度剖面.结果表明,本方法应用于二元非极性流体混合物时汽液表面张力计算值与实验值符合良好,同时显示某些二元混合流体表面区可能出现组分的相对富集现象.     

IMPROVING CUBIC EQUATIONS OF STATE FOR HEAVY RESERVOIR FLUIDS AND CRITICAL REGION

It is shown that by considering the “b” parameter in a cubic equation of state (EOS) as acentric factor/temperature-dependent, liquid densities especially for heavy compounds and the region near the critical point can be estimated more accurately. The proposed equation can also be used for accurate estimation of critical compressibility factors of different compounds, Although the method is applied to Peng-Robinson equation of state (PR-EOS), it can be used for any other cubic equation of state. The proposed method is particularly useful for phase equilibrium calculations of reservoir fluids. The proposed equation requires critical temperature, critical pressure and acentric factor as the input parameters. The proposed equation of stale estimates properties of liquids, vapor-pressure and critical compressibility factors with greater accuracy for pure compounds and mixtures as well as light and heavy compounds found in reservoir fluids.     

Thermodynamics of shear‐induced phase transitions for multicomponent fluid mixtures

A thermodynamic approach for modeling the phase equilibrium of multicomponent fluid mixtures under the influence of an applied shear rate (shear stress) is presented. This approach is based on assuming that, for the modeled mixtures, the viscosity variation with shear rate can be well‐described by using a power law. This framework is then used for predicting the influence of shear rate on the critical temperature, critical pressure, and spinodal curve of several Newtonian multicomponent hydrocarbon mixtures; giving as a result that for these kind of mixtures and depending on the composition, the critical temperature exhibits both an upward and downward shift with shear rate, whereas the critical pressure always exhibits a downward trend. Both a suppression of the liquid–liquid transition and shrinkage of the spinodal curves (mixing effect) are also predicted. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4383–4389, 2013     

A molecular thermodynamic approach to the prediction of phase equilibria in reservoir simulation

Highly asymmetric molecules interacting during miscible-gas processes of oil recovery are responsible for the form of the reservoir fluid phase diagrams, from which feasible displacement conditions can be chosen. In order to fit the expermental fluid phase behavior, current reservoir models employ classical equations of state which cannot easily account for the polydisperse and asymmetric nature of such systems. Using a continuous thermodynamics extension of the Simplified Perturbed Hard-Chain Theory (SPHCT) equation of state of Kim et al. (1986), an alternative molecular method for representing these equilibria in reservoir-fluid systems is presented. The approach yields results which compare well with both experimental data and classical calculation procedures.