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     

混合物临界性质的预测

本文基于Heidemann和Khalil的临界状态判别准则,对混合物临界性质进行了预测。为了扩展应用到极性混合物并提高预测质量(尤其是预测临界体积的准确度),本文应用了最近提出的立方型转子链(CCOR)状态方程及局部组成型的CCOR状态方程。按以上二模型及SRK和PR模型对十六组极性和非极性二元及三元混合物计算了临界性质。计算结果表明:CCOR模型应用于极性和非极性体系均能获得良好效果,尤其对临界体积(Vc)的预测,其准碓性较之SRK和PR模型有显著的提高。     

Lee-Kesler方程的计算机应用研究

本文完成了Lee-Kesler对比状态方程的计算机解法,以此为基础进而完成了Lee-Kesler法进行混合物汽液平衡性质计算的程序系统。对迭代初值、收敛性、迭代精度及其他有关情况做了讨论。从实验数据出发,通过参数优化将Lee-Kesler法从烃类扩展到某些特殊体系(如含氢、氮、氨和水等的体系),初步取得了一些满意可用的结果,为利用数据库扩展各种状态方程的应用范围摸索了一条途径。     

含氢混合气体的压缩因子

在高压低温下,含氢混合气体已极大地偏离理想气体,因而必须要求正确地确定这种混合气体的P-V-T关系。本文对混合气体假临界常数的Kay方法进行修正,用此计算对比参数,就可把LK方程延伸使用于含氢混合气体。文中分别用修正Kay方法和GCP方法所得的假临界常数和LK方程对H_2-CH_4-N_2、N_2-H_2、H_2-N_2-CO_2-CO-CH_4等系统的压缩因子进行了计算,并和文献中的实验值作了比较。结果表明,用本文修正Kay方法所得计算值与实验值有更好程度的吻合。     

立方型状态方程用于液体过量体积的计算

用 SRK、PR 和 YU-LU 三个立方型状态方程对常压下的液体混合过量体积进行了关联计算,涉及的体系包括非极性、弱极性、水及羧酸等强极性混合物。对于对称的非极性、弱极性、极性流体混合物获得了良好的结果,但这种计算方法不适用于含水或羧酸的体系。     

丙二烯二氯化膦水解过程的热力学计算及分析

采用相对分子质量法、修正Joback法、Joback法、Lee-Kesler法、Riedel法、Rowlinson-Bondi对应状态法、Benson法估算了丙二烯二氯化瞵水解反应体系相关物质的基本物性参数如常沸点、临界参数和偏心因子,基本热化学性质参数如蒸发潜热、气体热容和液体热容、气体标准摩尔熵、相变熵。利用键能法计算了气体的标准反应热,计算了实际反应条件下的反应热、吉布斯自由能及相关反应的化学平衡常数,并对反应体系的特点进行了分析,估算数据可为理论研究、工程设计与放大及生产提供参考。     

常用临界性质计算公式对伊朗原油馏分油的适用性考察

用实测的伊朗原油24组馏分油的部分物性数据,考察了常用的估算临界性质的七个估算式应用于伊朗原油的适用性,结果表明:估算临界温度的四个计算式的平均相对偏差在1.25%~2.21%之间,其中Sim-Daubert式、Lee-Kesler式和Cavett式的偏差分别是1.25%、1.43%和1.46%,优于Roess式的2.21%。Roess式、Sim-Daubert式和Lee-Kesler式以及Cavett式均可满足工艺计算临界温度的要求。估算临界压力的三个计算式中,Sim-Daubert估算式、Lee-Kesler估算式和Cavett式的平均相对偏差分别为2.31%、6.67%和7.12%,标准偏差分别为为0.109MPa、0.149 MPa和0.142 MPa,Sim-Daubert估算式可以满足工程计算的要求。     

MH状态方程使用DDLC混合规则计算混合物临界轨迹

<正>一、引 言状态方程能否精确地描述流体混合物热力学性质,建立合适的混合规则是一个重要因素.近十年来,许多研究者把局部组成概念引入立方型状态方程,建立了与密度有关的局部组成(DDLC)混合规则,将两类重要的热力学模型——状态方程和活度系数方程联系起来,大大地改善了状态方程应用于高密度区时的柔软性,改进了状态方程描述极性一非极性、含超临界组分等高度非对称体系的精确度.作者将局部组成概念引入多参数的MH状态方程,椎导了MH方程的DDLC混合规则,用于计算高压汽液平衡和二元混合物临界轨迹.本文将介绍后者的计算情况.     

混合物非平衡气液两相临界流动压力计算模型

气液两相临界流动压力是气液两相输送系统中安全阀尺寸设计、孔口泄漏速率计算的关键参数,现有的临界流动压力计算方法主要是针对单组分流体建立的,对多组分混合物的适用性差。针对这一问题,基于现有的非平衡均相流动(HNE-DS)模型和适用于多组分混合物的Peng-Robinson状态方程,推导了新的非平衡压缩系数表达式;通过拟合实验数据,得到新的临界流动压力比和非平衡压缩系数关联式,建立了改进的HNE-DS模型。结果表明:对于单组分流体,改进HNE-DS模型计算的临界压力比与实验值之间的平均相对偏差为3.3%,较原模型减小了1.6%。对于多组分混合物,改进HNE-DS模型的计算值更接近实际情况。成果为准确计算多组分混合物的临界流动压力提供了依据。     

甲醇-脂肪酸混合物临界参数及酯交换反应条件探讨

超临界甲醇法制备生物柴油反应涉及到拟二元混合物临界参数的计算。操作参数对系统热力学相态的影响直接关系到化学反应的机理,进而决定反应速度和产物转化率。为此,采用基团贡献法与L-B混合规则对甲醇和脂肪酸混合物的临界参数进行了计算。发现采用C-G基团贡献法与L-B混合规则可以较好地描述甲醇和大豆油混合物的临界参数,并且无需考虑相互作用参数。与文献值相比,平均误差为1.7%。据此,对反应器内混合物相态进行分析,讨论了低醇油摩尔比、反应温度和反应压力等条件对反应物相态和甲酯产率的影响。结果对于指导高压法制备生物柴油工艺设计有所帮助。     

Use of velocity of sound in predicting thermodynamic properties of dense fluids from cubic equations of state

In this paper it has been shown that velocity of sound data may be used to obtain constants of a cubic equation of state and then thermodynamic properties can be accurately calculated through the constants extracted from sonic velocity data. Results are presented for estimation of heat capacities, enthalpies, vapor pressures and compressibility factors of some pure vapor and liquid compounds as well as some binary mixtures for pressures up to 100 MPa and temperatures up to 600 K for hydrocarbons from methane to hexadecane. The method will be useful for those mixtures containing heavy compounds for which accurate data on critical constants are not available, but for which the sonic velocity can be measured.     

Modeling the thermal and physical properties of liquid and gas mixtures of Fischer–Tropsch synthesis products

The method of pseudocritical thermodynamic parameters and the Lee-Kesler equation of state are used for calculating the thermal and physical properties of a solution and a mixture of gaseous paraffins that are major constituents of Fischer-Tropsch synthesis products. The dynamic viscosities of a solution and a vapor are modeled using an original procedure proposed by the authors. A surface tension is calculated by the parachor method. The composition of liquid and gaseous products is found using a stable iteration scheme proposed by the authors. The model is tested by a comparison with experimental data from the literature for model mixtures of hydrocarbons. The results of calculating the composition and thermophysical properties of a mixture of paraffins that model the composition of synthesis products at different values of the chain propagation parameter, temperatures, and pressures are presented.     

Die quantitative bestimmung der klinkermineralien mit dem diffraktometer

A simplified diffractometric method for the quantitative determination of the phases tricalcium silicate, dicalcium silicate, tricalcium aluminate and the ferrite phases in portland cements consists of comparing measured intensities with precalculated diffractometric constants of pure clinker minerals. MgO is used as an internal standard. Results obtained by this method on synthetic mixtures and on some Hungarian portland cements are compared with data of chemical analysis. The agreement is satisfactory.     

印刷电路板式换热器内超临界甲烷流动换热特性模拟

印刷电路板式换热器（printed circuit heat exchanger,PCHE）作为一种新型高效微通道换热器,将其应用在LNG浮式储存与气化装置（FSRU）上具有非常大的潜力。对超临界甲烷在PCHE通道中的流动和传热特性进行了数值模拟,结果表明：传热系数随温度先增大后减小,并在准临界温度（202～212 K）处达到峰值;压降随温度先保持不变,然后在准临界温度附近急剧上升,之后随温度增大的趋势变缓;当温度在准临界温度附近时,低质流密度下增大热通量会恶化传热;不同压力下传热系数均在准临界温度处达到峰值;温度低于准临界温度时,压力对压降的影响可以忽略,温度高于准临界温度时,压降随压力增大而显著降低;压力由6.4M Pa提高到8.5 MPa时,传热最大降低32.5%,压降最大降低28.5%;开发的换热和压降关联式平均误差分别为5.6%和4.2%。     

Prediction of ternary azeotropes

Interaction constants for binary azeotropic mixtures have been used in conjunction with binary azeotropic information to predict ternary azeotropic compositions and temperature. The method operates within a general classification of liquids based on their hydrogen bonding capabilities, and therefore may be used to predict ternary azeotropic information of a wide variety of mixtures.     

Supercritical Fluid Chromatography Applied to the Characterization of a Siloxane-Based Gas Chromatographic Stationary Phase

Abstract

Supercritical fluid chromatography using n-pentane as a mobile phase and Porasil C as a column packing was applied to the characterization of Dow-Corning 710 fluid, a commonly used gas chromatographic stationary phase. Under the experimental conditions, decomposition of the polymer was observed on columns of alumina, and derivatized Porasil packings were found to be unstable. Linear pressure programming variables were studied at 206 and 216°C by normalizing the total analysis time on a fixed length of column. A series of homologous polymer components was used to demonstrate the effects upon resolution of density-isotherm nonlinearity associated with the mobile phase. The results showed that optimal temperature conditions existed for the use of linear pressure programming, with the choice of temperature conditions dependent upon the molecular weight range. Operational guidelines are suggested. Mixed solvent behavior was investigated for this separation. The effect of changing the polarity of the mobile phase by adding 0 to 20% v/v isopropanol to n-pentane was studied under isothermal and isobaric conditions. The alcohol was shown to change adsorption characteristics and alter critical constants. The effect upon the critical constants appeared to conform to Kay's approximation. The results suggest that mixed solvents can be used to speed up separations for mixtures having components of widely different adsorption energies. The pseudocritical concept using Kay's approximation was tested for its qualitative ability to estimate state effects when solvents are mixed. The effect of temperature upon migration behavior was compared for equimolar amounts of isopropanol and methanol, each in n-pentane. Kay's approximation appeared to be useful for qualitative predictions regarding changes in critical pressure. However, an attempt to predict density isotherm behavior for 20 % isopropanol in n-pentane relative to pure n-pentane suggested that Kay's approximation may not be as useful for predicting criticla temperature effects.     

Zustandsgrößen und Transportkoeffizienten von binären Gasgemischen — II: Die Zweier-Wechselwirkung zwischen gleichen und ungleichen Molekülen

A method is presented for the accurate calculation of the intermolecular pair potential parameters for unlike molecules. Precise equations are derived for the force constants ?₁₂ and σ₁₂ of a Lennard-Jones-(6, δ)-potential. For a repulsive exponent value δ = 12 these constants are evaluated for 16 binary mixtures of different molecular structure and for all noble gas binaries. The results are compared with empirical literature-values and with values calculated from well-known combining rules. The agreement with empirical data is in some cases excellent especially for the noble gas binaries.     

Pseudocritical heat transfer inside vertical tubes

Heat transfer to fluids with pressures slightly above the critical is strongly influenced by the variation of the fluid properties occurring in the so-called pseudocritical region. The heat transfer can either be improved or reduced, depending on the flow conditions. The improvement is due to the enhanced heat transport caused by the increased heat capacity of the fluid. In the case of reduced heat transfer the turbulence is weakened by gravitational effects. In the present paper the heat transfer due to the complex interaction between gravity and turbulence in the so-called pseudocritical region is predicted by a numerical solution of the conservation equations for a turbulent pipe flow. The numerical results are compared with published experimental data for an electrically heated vertical pipe with the fluid R12.     

Conductometric studies on the dissociation constants of phosphoric acid in methanol-water mixtures

The dissociation constants of phosphoric acid have been determined in methanol-water mixtures (8.0–87% by weight of methanol) by the method suggested by Gelb. The results have been verified by Fuoss—Kraus method. Δ⁰ values of HClO₄, KClO₄ and KH₂PO₄ (and hence of H₃PO₄) in mixed solvents have been determined in the usual way. The role of solvents on the dissociation constants has been discussed.