Extension of UNIFAC to high pressure VLE using Vidal mixing rules

The UNIFAC and ASOG group contribution methods are extensively used for predicting vapor—liquid equilibria at low pressures. At higher pressures, these models are not applicable—primarily because there is no consistent way of correcting for vapor phase non-idealities. In this work the UNIFAC model was incorporated in an equation of state framework using Vidal mixing rules. Excellent prediction results are obtained at high pressures for highly non-ideal systems. The method serves as a convenient way to extend the applicability of the group-contribution models to higher pressures.     

顺丁烯二酸酐与邻苯二甲酸二甲酯二元体系在4.00, 8.00和12.00 kPa下的等压气液平衡

采用沸点仪测定了顺丁烯二酸酐和邻苯二甲酸二甲酯二元体系在4.00, 8.00和12.00 kPa下的等压气液平衡数据以及纯DMP组分饱和蒸气压数据, 将实验数据回归得到了纯DMP在417~525 K范围内的Antoine方程. 根据实验平衡温度、 压力和组成数据进一步回归得到NRTL方程参数, 推算出平衡气液相组成, 并利用UNIFAC方程对实验数据进行了预测, 其结果与沸点仪测定结果及NRTL拟合的结果基本相符.     

Vapor pressures and flash points for binary mixtures of tricyclo [5.2.1.0] decane and dimethyl carbonate

Bubble-point vapor pressures, equilibrium temperatures and flash points for binary mixtures of a high energy density hydrocarbon fuel, tricyclo [5.2.1.0^2.6] decane (JP-10), and dimethyl carbonate (DMC) were measured. Correlation between vapor pressures and equilibrium temperatures for each mixture was given by the Antoine equation. The binary system of JP-10 and DMC appears with very large positive deviations of vapor pressure from the Raoult's law. The experimental vapor pressures are correlated and the flash points are then predicted using Scatchard-Hildeband, Van Laar and Wilson models of liquid phase activity coefficients with satisfactory results.     

Estimation of pure component properties: Part 3. Estimation of the vapor pressure of non-electrolyte organic compounds via group contributions and group interactions

A group contribution method for the estimation of the normal boiling point of non-electrolyte organic compounds, which was published earlier, has been the basis for development of subsequent physical property methods. In this work, the model was extended to enable the prediction of vapor pressure data with special attention to the low-pressure region. The molecular structure of the compound and a reference point, usually the normal boiling point, are the only required inputs and enables the estimation of vapor pressure at other temperatures by group contribution. The structural group definitions are similar to those proposed earlier for the normal boiling point, with minor modifications having been made to improve the predictions. Structural groups were defined in a standardized form and fragmentation of the molecular structures was performed by an automatic procedure to eliminate any arbitrary assumptions. The new method is based on vapor pressure data for more than 1600 components. The results of the new method are compared to the Antoine correlative equation using parameters stored in the Dortmund Data Bank, as well as, the DIPPR vapor pressure correlations. The group contribution method has proven to be a good predictor, with accuracies comparable to the correlations. Moreover, because the regression of group contributions was performed for a large number of compounds, the results can in several cases be considered more reliable than those of the correlative models that were regressed to individual components only. The range of the method is usually from about the triple or melting point to a reduced temperature of 0.75–0.8.     

气相色谱法测定多溴联苯的蒸气压

采用气相色谱法,以二氯二苯三氯乙烷(DDT)为参考化合物,测定了6个多溴联苯(PBBs)在不同温度条件下的蒸气压, 然后使用Slide数理统计软件、以最小二乘法回归计算出Antoine方程的A,B,C参数,从而建立了6个PBBs的蒸气压与温度 的关联式。初步探讨了分子连接性指数与蒸气压的相关性,结果发现一阶拓扑指数与蒸气压表现出很好的线性关系,两者 的相关系数的平方大于0.99,标准偏差小于0.08。     

Experimental vapor pressures and maximum-likelihood Antoine-equation constants for 1,1,1-methoxydimethylpropane,thiacyclopentane and 1,4-butanediol

The saturated vapor pressures of the title compounds have been determined by high-precision comparative ebulliometry. A modified maximum-likelihood estimation procedure is used to fit the Antoine equation to the experimental data.     

Study on volatility and flash point of the pseudo binary mixtures of sunflower-based biodiesel + methylcyclohexane

The transesterification of sunflower seed oil was carried out in supercritical ethanol without using any catalyst to produce biodiesel. In the present work, methylcyclohexane was added to enhance the vapor pressure of biodiesel. The vapor pressures of mixtures of biodiesel + methylcyclohexane as a function of temperature were measured by comparative ebulliometry with an inclined ebulliometer. The vapor pressures versus composition at different temperatures were obtained. Experimental data of vapor pressures and equilibrium temperatures were correlated by the Antoine equation. A mathematical model was used to predict the flash point of the pseudo binary mixtures. With the regular solution theory, the predictive flash point displays agreement with the experimental data obtained by closed cup test.     

天然产物液体组分饱和蒸汽压间接测定实验方法

根据物理化学中的相平衡体系热力学理论设计了间接测定天然产物液体组分饱和蒸汽压数据的实验方法,采用改进的Ellis或Rose平衡釜测定不同压力下高浓度的天然产物溶液汽液平衡数据,推算不同温度下天然产物液体组分的饱和蒸汽压,回归出Antoine方程的各参数A,B,C,建立天然产物液体组分饱和蒸汽压与温度的关联式.应用该方法测定了蒎烷、对孟烷与长叶烯的饱和蒸汽压,所得结果与文献值吻合良好,为天然产物液体组分饱和蒸汽压的实验测定与关联提供了一种便捷的途径.     

Group contribution multifluid lattice theory for simultaneous predictions of thermodynamic properties of pure fluids and mixtures

A unified group contribution (GC) lattice equation of state (EOS) was formulated based on the multifluid approximation of the nonrandom lattice fluid theory. The GC-EOS requires segment size and interaction energy parameter from functional group characteristics. The unique feature of the approach is that a single set of group parameters are used for both pure fluids and mixtures. The approach was found to be quantitatively applicable for predicting thermodynamic properties of real pure fluids and mixtures. Its potential utility was demonstrated for vapor pressures, vapor–liquid coexistence densities of pure fluids and phase equilibrium properties of mixtures including polymeric solutions.     

Isobaric vapor–liquid equilibria of the binary system maleic anhydride and di-isobutyl hexahydrophthalate at 2.67, 5.33 and 8.00 kPa

Isobaric vapor–liquid equilibrium (VLE) data for the binary system maleic anhydride (MAN) + di-isobutyl hexahydrophthalate (DIBE) at 2.67, 5.33 and 8.00 kPa were measured with a modified ebulliometer. Also, saturated vapor pressures of pure DIBE were measured and Antoine constants were obtained. These data were used to calculate equilibrium vapor and liquid compositions for this binary system using the NRTL model. Prediction of the VLE was done with the universal quasi-chemical functional-group activity coefficients (UNIFAC) model. The predicted results generally agree with those from experiment.     

Assessment of systematic errors in measurement of vapor pressures by thermogravimetric analysis

The present study explores the application of the diffusion limited evaporation theory to the estimation of vapor pressure from TG experimental data. A simplified method was developed to calculate the apparent values of the vapor pressure of pure substances from TG data, based on isothermal TG runs with crucibles having different surface areas available for evaporation. Antoine parameters are estimated through a numerical procedure based on a non-linear least square algorithm. The procedure also evaluates the substance diffusivity in nitrogen. The methodology developed might be used for a preliminary screening of the vapor pressure of pure compounds, due to the limited amounts of sample that are necessary and to the limited time frame required for the experimental runs. However, the estimation of diffusivity and vapor pressures values by the TG technique is possible with limited accuracy. Possible sources of error were thoroughly investigated and discussed.     

Estimation of solid vapor pressures of pure compounds at different temperatures using a multilayer network with particle swarm algorithm

Solid vapor pressures (P^S) of pure compounds have been estimated at several temperatures using a hybrid model that includes an artificial neural network with particle swarm optimization and a group contribution method. A total of 700 data points of solid vapor pressure versus temperature, corresponding to 70 substances, have been used to train the neural network developed using Matlab. The following properties were considered as input parameters: 36 structural groups, molecular mass, dipole moment, temperature and pressure in the triple point (upper limit of the sublimation curve), and the limiting value P^S → 0 as T → 0 (lower limit of the sublimation curve). Then, the solid vapor pressures of 28 other solids (280 data points) have been predicted and results compared to experimental data from the literature. The study shows that the proposed method represents an excellent alternative for the prediction of solid vapor pressures from the knowledge of some other available properties and from the structure of the molecule.     

Physical and chemical changes of medicinals in mixtures with adsorbents in the solid state. III. Determination of vapor pressure of solid drugs by steam distillation

The vapor pressures of solid drugs were determined by the steam distillation method. Experiments using a series of benzoic acid derivatives indicated that this method offered consistent and satisfactory values for vapor pressure at about 100 degrees C. The vapor pressures of two nonsteroidal antiinflammatory drugs, flufenamic acid (FFA) and mefenamic acid (MFA), were found to be 3.8 x 10(-3) and 1.8 x 10(-4) mmHg, respectively. These values explain the difference in the rate of change to the amorphous state between mixtures of each with magnesium aluminum silicate (MAS) when they were stored under reduced pressure. It was concluded that the vapor pressures of solid drugs at about 100 degrees C, as determined by steam distillation, may be suitable indices for predicting whether or not these drugs have an inherent propensity to become amorphous readily in mixtures with an adsorbent.     

燃料馏分油气－液相平衡常数的测定与关联

实沸点蒸馏原油获得燃料馏分油。采用拟静态法测定不同沸程的22种燃料馏分油在系列温度下的泡点蒸气压，用Antoine方程关联蒸气压与温度的关系。在泡点压力分别为10 kPa、30 kPa、50 kPa、80 kPa和101.325 kPa时，按虚拟组分处理法计算了燃料宽馏分油中各虚拟组分的气-液相平衡常数，关联了气-液相平衡常数与虚拟组分的沸点以及相平衡温度、压力的关系，得到的表达式可以计算常压沸点范围在348.15 K至623.15 K间燃料宽馏分油的气-液相平衡常数，经180个数据点回归检验，平均误差为4.5%。     

Thermogravimetry as a screening tool for the estimation of the vapor pressures of pure compounds

A simplified approach was developed to estimate the vapor pressure of pure compounds from experimental data obtained by isothermal thermogravimetric (TG) analysis. A numerical procedure was developed to estimate the Antoine parameters of the substance by the analysis of isothermal TG data. The results of the experimental validations carried out evidenced that at least a preliminary estimation of vapour pressures of pure substances by the analysis of TG data is possible. The limited time and the reduced amounts of sample required for the experimental runs make the technique attractive with respect to the conventional and more accurate techniques for vapor pressure assessment.     

Prediction of liquid viscosities of phosphorus-containing compounds by Souders' method

Souders' method of predicting the viscosities of liquid compounds from structural information has been extended to include the contribution from the phosphorus atom. The phosphorus contribution has been predicted from the critical pressure to be 67.1. The prediction method has been tested using data available on 15 phosphorus-containing compounds. The results are comparable with those reported in the literature for group contribution methods in general.     

Isobaric Vapor-Liquid Equilibria and Densities for the System Ethyl 1,1-Dimethylethyl Ether + 2-Propanol

Vapor-liquid equilibrium (VLE) data at 50, 75, and 94 kPa have been determined for the binary system ethyl 1,1-dimethylethyl ether + 2-propanol, in the temperature range 323-344 K. The measurements were made in an equilibrium still with circulation of both the vapor and liquid phases. Excess volumes have been also determined from density measurements at 298.15 K. The system exhibits positive deviation from ideal behavior and azeotropic behavior in the range of experimental pressures. The excess volume of the system is negative over the whole mole fraction range. The activity coefficients and boiling points of the solutions were well correlated with the mole fraction by the Wohl, Wilson, UNIQUAC, NRTL equations and predicted by the UNIFAC group contribution method. Excess volume data were correlated using the Redlich-Kister expansion.     

Predicting vapor–liquid equilibria of fatty systems

In the present work, a group contribution method is proposed for the estimation of the vapor pressure of fatty compounds. For the major components involved in the vegetable oil industry, such as fatty acids, esters and alcohols, triacylglycerols (TAGs) and partial acylglycerols, the optimized parameters are reported. The method is shown to be accurate when it is used together with the UNIFAC model for estimating vapor–liquid equilibria (VLE) of binary and multicomponent fatty mixtures comprised in industrial processes such as stripping of hexane, deodorization and physical refining. The results achieved show that the group contribution approach is a valuable tool for the design of distillation and stripping units since it permits to take into account all the complexity of the mixtures involved. This is particularly important for the evaluation of the loss of distillative neutral oil that occurs during the processing of edible oils.The combination of the vapor pressure model suggested in the present work with the UNIFAC equation gives results similar to those already reported in the literature for fatty acid mixtures and oil–hexane mixtures. However, it is a better tool for predicting vapor–liquid equilibria of a large range of fatty systems, also involving unsaturated compounds, fatty esters and acylglycerols, not contemplated by other methodologies. The approach suggested in this work generates more realistic results concerning vapor–liquid equilibria of systems encountered in the edible oil industry.     

Isobaric Phase Equilibria in the Binary Systems Ethyl 1,1-Dimethylethyl Ether + 1-hexene and + Cyclohexene at 94.00 kPa

Abstract

Consistent vapor-liquid equilibrium has been determined for the binary systems 1-hexene + ethyl 1,1-dimethylethyl ether (ETBE) and ethyl 1,1-dimethylethyl ether + cyclohexene at 94.00 kPa. The two systems present slight positive deviations from ideal behavior, can be considered to behave like regular solutions and do not present azeotropic behavior. Pure component vapor pressures are also reported for 1-hexene and cyclohexene. The phase equilibrium of the systems was correlated well by the Wilson, UNIQUAC, and NRTL models and reasonably predicted by the UNIFAC group contribution method. The boiling points of the binary systems were correlated with the Wisniak-Tamir equation.