Calculation of infinite dilution activity coefficients by the NRTL and UNIQUAC models

Infinite dilution activity coefficients have been calculated for 42 binary systems using the NRTL and UNIQUAC models. Temperature dependent parameters of the models are used in the calculations. These parameters have been estimated by using excess Gibbs free energy and enthalpy of mixing data simultaneously. The calculated values are compared with experimental infinite dilution activity coefficients obtained by extrapolation of vapor-liquid equilibrium (VLE) data published in the literature. The agreement between the calculated and experimental values is poor for highly nonideal system. The selection of the best model is difficult and may be system dependent.     

环己烷-正庚烷-N,N-二甲基甲酰胺体系液液相平衡测定与关联

采用平衡釜法测定了三元体系(环己烷+正庚烷+N,N-二甲基甲酰胺)在常压不同温度(30,40,50℃)下的液液相平衡数据。实验数据用Bachaman及Othmer-Tobias进行可靠性关联,关联结果表明数据的可靠性较好,根据实验结果绘制了三元相图。对不同温度下的液液平衡实验数据,分别用NRTL和UNIQUAC活度系数方程进行了关联,求得方程的二元交互作用系数,关联结果表明NRTL和UNIQUAC方程对该体系适用较好。由实验数据计算得到衡量N,N-二甲基甲酰胺抽提性能的参数(分配系数、分离因子、选择性系数)。     

Application of NRTL and uniquac models to liquid-liquid systems with halogen salts (Part I)

Binodal curves, tie lines, and plait points for benzene-halogen salt solutions-n-propanol systems were determined, and Othmer-Tobias equation was employed for a system without salt and Eisen-Joffe equation for systems with salt to test consistency. Halogen salt solutions were prepared with aqueous solution of 5% KF, 5% NaCl, 5% NaBr and5% Nal, respectively. Compositions of two splitting phases on liquid-liquid equilibria (L-L-E) condition were calculated and the parameters were estimated by correlating experimental tie lines with the NRTL and the UNIQUAC (or modified UNIQUAC) models. The effects of addition of four halogen salts (KF, NaCl, NaBr, Nal) to benzene-water-n-propanol system were considered.     

含离子液体液液平衡的UNIQUAC模拟

为了解决UNIQUAC模型在关联含离子液体液液平衡数据时,因离子液体的分子结构参数r和q不完全而使其应用受限的问题,文中采用量子化学法计算了近几年报道的液液平衡文献中涉及的8种离子液体的分子结构参数r和q。利用密度泛函理论优化离子液体的分子结构,得到离子液体的最优结构和最优能,然后采用极化连续介质模型计算最优分子结构的体积和表面积,进而得到离子液体分子结构的r和q值。使用含上述数值的UNIQUAC模型关联了20种含离子液体的三元体系在不同温度下的液液平衡数据,并计算出模型的预测值与实验值的均方根偏差,187个连结点数据的均方根偏差值平均为0.011 7。结果表明:计算的离子液体的r和q值用于UNIQUAC方程中能较好地关联三元体系液液平衡数据。     

Calculation of solid-liquid equilibria in aqueous solutions of nitrate salts using an extended UNIQUAC equation

An extended UNIQUAC-Debye-Hückel model is used to predict solid-liquid equilibria for aqueous solutions of nitrate salts with the cations K⁺, Mg²⁺ and Ca²⁺. In addition to a model for activity coefficients in mixed electrolyte solutions, the method requires knowledge of the solubility products of all possible solid phases. Furthermore, some ternary solid-liquid equilibrium data are required.It is shown that the extended UNIQUAC equation can be applied to the calculation of solid-liquid equilibria in the K⁺-Mg²⁺-Ca²⁺-NO₃⁻-H₂O system with good results.A new algorithm for calculation of solid-liquid equilibrium in ionic solutions has been proposed. The number and amount of phases in equilibrium are found by minimization of the total Gibbs function of the system.     

Calculation of vapor-liquid equilibria in aqueous sulfuric acid solutions using the UNIQUAC equation in the whole concentration range

Sulfuric acid has many industrial applications. Its main use can be related to fertilizer manufacture, process with ore, chemical synthesis, liquid effluents treatment and the petroleum refine. A main characteristic of this acid is its behavior depending on concentration. When it is dilute, under molar concentrations of 90%, the solution acts as a strong acid and does not show dehydration power. On the other hand, when it is concentrated, above 90%, its acidic feature is omitted and its dehydration power increases. Due to its importance in chemical process and in view of all works present in the literature, one does not consider both dissociation reactions in the liquid phase and the complex formation reaction in the vapor as one, a thermodynamic model has been developed using Prigogine and Defay Chemical Theory. This model takes into account phase and chemical equilibria, simultaneously, with satisfactory results to calculate vapor-liquid equilibria of H₂O-H₂SO₄ solutions in the whole concentration range and temperatures from 0 to 150 °C.     

Calculation of vapour-liquid equilibria in mixed solvent/salt systems using an extended UNIQUAC equation

A new method for the correlation and prediction of salt effects on VLE is proposed. The model combines a term of the Debye-Hückel type with a modified UNIQUAC equation with concentration-dependent parameters. The model parameters are ion-specific, and no ternary parameters are required.Application of the model to alcohol-water/salt mixtures has shown that the change in vapour phase composition on addition of salt to the liquid phase can be represented with good accuracy. Fifty-four ternary data sets were correlated with a total mean of the absolute deviation in the vapour phase mole fraction of 0.012. Deviations in calculated pressures or temperatures may, however, be rather high, especially at high salt concentrations.The maximum salt concentration for the included data points in the database is 10 mol/kg for 1:1 salts and 6.5 mol/kg for 2:1 salts.     

On the combinatorial part of the UNIFAC and UNIQUAC models

The excess Cibbs energy of liquid mixtures may be predicted using group contribution models (f.ex. UNIFAC and ASOG), or it may be correlated using molecular models such as UNIQUAC. Group contribution models and the UNIQUAC model contain a combinatorial contribution which accounts for size- and shape-effects and a residual contribution which accounts for interactions among groups or molecules. A new expression for the combinatorial contribution is given which yields much improved predictions of the excess Gibbs energy of systems where the residual contribution may be expected to be zero (e.g., mixtures of aliphatic hydrocarbons). It is shown that it is advantageous to incorporate the new combinational expression into future modifications of the UNIFAC model.     

Prediction of vapor-moisture equilibriums for a wood-moisture system using a modified UNIQUAC model

A modified UNIQUAC model has been extended to describe and predict the equilibrium relative humidity and moisture content for wood. The method is validated over a range of moisture content from oven-dried state to fiber saturation point, and over a temperature range of 20-70 °C. Adjustable parameters and binary interaction parameters of the UNIQUAC model were estimated from experimental data for Caribbean pine and Hoop pine as well as data available in the literature. The two group-interaction parameters for the wood-moisture system were consistent with using function group contributions for H₂O, -OH and -CHO. The result reconfirms that the main contributors to water adsorption in cell walls are the hydroxyl groups of the carbohydrates in cellulose and hemicelluloses. This provides some physical insight into the intermolecular force and energy between bound water and the wood material.     

用NRTL方程关联和预测离子液体-醇-水体系的液液相平衡

引 言 离子液体是指在室温或室温附近温度下呈液态的由离子构成的有机熔融盐,其特点是:几乎没有蒸气压,热稳定性好,大多数离子液体可以在高达300℃的温度范围内不分解,还对大量常见的有机物或无机物有良好的溶解性能,用离子液体替代传统的有机溶剂作为反应和分离的介质,也能有效地消除VOCs污染.因此,离子液体的研制和应用受到了广泛的关注[1-3].     

PR方程结合vdW混合法则推算二元及三元HFC/HC混合工质

以PR方程结合vdW混合法则,利用建立的二元相互作用系数kij差值关联模型,对11组二元HFC/HC混合工质及5组三元HFC/HC混合工质（HFC32 / HFC125 / HFC134a,HC290 / HC600a / HFC32,HFC125 / HFC143a / HFC134a,HFC32 / HC290 / HFC227ea,HFC32 / HFC125 / HC290）气液相平衡性质进行了推算,并与文献实验数据比较,对压力计算的平均相对偏差分别为2.225%、8.317%、1.433%、0.403%、1.71%,对气相组分计算的平均绝对偏差分别为0.0086、0.0132、0.0054、0.0071、0.0089。结果表明该方法可用于推算二元及三元HFC/HC混合工质气液相平衡性质。     

On the concentration dependence of the UNIQUAC/UNIFAC models

The UNIQUAC/UNIFAC models can not in general represent vapor-liquid and liquid-liquid equilibria simultaneously with satisfactory results. Recent modifications of the models take into account association and solvation effects by means of chemical theory. However, this approach leads to complicated expressions for the activity coefficients and the improvements are only moderate. A modification of the UNIQUAC/UNIFAC models is presented which takes into account solvation and association by allowing the interaction energies to vary with composition. This approach leads to explicit expressions for the activity coefficients. It is shown that the modified models in simultaneous correlations lead to quantitative representation of vapor-liquid equilibrium data and semi-quantitative representation of binary and ternary liquid-liquid equilibrium data.     

正丁醇-硫酸铵-水液液平衡数据的测定及关联

采用浊点法和饱和密度法测定了正丁醇+硫酸铵+水部分互溶体系在25℃和60℃下的溶解度数据和液液相平衡数据。在相图的基础上讨论了温度对正丁醇的相形成能力的影响。此外,采用Othmer-Tobias和Bancroft方程以及Setschenow-type方程关联和预测了2个温度下的液液相平衡组成。结果表明:温度升高,二相区增大,结线长度增大,正丁醇相中硫酸铵的质量分数减小,低于0.3%,相应水相中的正丁醇的质量分数降低。2个模型的关联结果与实验结果均吻合较好,偏差均小于1.7%。     

A method for calculation of vapor-liquid and liquid-liquid equilibria

A new parameter, pseudo temperature (T_p) is introduced to solve two-phase equilibrium calculations. The resulting T_p-method has a single set of equations to describe different phase regions encountered in vapor-liquid equilibrium (VLE) and liquid-liquid equilibrium (LLE). It does not require a priori the number of phases existing at equilibrium, and involves a minimization problem having a linear objective function subject to nonlinear constraints, which can be solved by a version of successive linear programming method. T_p-method is tested on typical examples for VLE and LLE, and compared with pseudo pressure (P_p) method of Bullard and Biegler [Computers and Chemical Engineering 17, 95–109 (1993)] for VLE. In each example, several operating conditions are considered to cover both single- and two-phase situations. The results show that T_p-method is successful for both VLE and LLE, and that T_p- and P_p-methods are comparable for VLE.     

Measurement and Prediction of the Solubility of Stearic Acid Polymorphs by the UNIQUAC Equation

The solubility of stearic acid polymorphs B and C in methanol, 2‐butanone, decane and hexane was measured using a precise gravimetric method. Stearic acid is a molecule with 18 carbons that is highly nonideal in solutions and experimental data show strong deviations from the solubility prediction for ideal systems. It is soluble in both polar and nonpolar organic solvents. From experimental solubility, data the solvent mediated polymorphic transition temperature was found around 30°C. From thermal analysis, temperature and heat of transition from form B to form C and also heat of fusion of form C were found to be 49°C, 20 J/g and 240 J/g, respectively. From experimental solubility data the binary parameters of the universal quasi‐chemical (UNIQUAC) model, for stearic acid were calculated. The UNIQUAC solubility predictions compared very closely with the experimental data.     

Isobaric vapour-liquid equilibria of the ternary system hexane-benzene-sulpholane

Isobaric vapour-liquid equilibria for the ternary system hexane-benezene-sulpholane have been determined at 760 mmHg pressure. The data have been compared with those calculated using the NRTL equation. The NRTL constants obtained from the literature were evaluated from ternary liquid-liquid equilibrium data for this system. The agreement between experimental and calculated values is reasonable.     

UNIFAC模型与PRSV方程相结合预测二元及三元系统汽液相平衡

采用Ｗｏｎｇ和Ｓａｎｄｌｅｒ混合规则，将ＰＲＳＶ立方型状态方程与ＵＮＩＦＡＣ活度系数模型相结合，给出一种预测混合物相平衡热力学性质的方法，并用５４个二元体系和９个三元体系的实验数据做了检验，结果表明，该法可以较好地预测二元及三元体系的汽液相平衡。     

Measurement and correlation of liquid-liquid equilibria for polystyrene-cyclopentane and polystyrene-cyclopentane-cyclohexane systems

Liquid-liquid equilibrium data for the polystyrene-cyclopentane binary system and the polystyrene-cyclopentane-cyclohexane ternary system were measured by observing the cloud points at the temperature range in which the systems showed their lower critical solution temperature. The experimental liquid-liquid equilibria were correlated successfully by the UNIFAC-FV model with adjustable parameters.