Estimation of pure component properties. Part 4: Estimation of the saturated liquid viscosity of non-electrolyte organic compounds via group contributions and group interactions

A new group contribution method for the prediction of pure component saturated liquid viscosity has been developed. The method is an extension of the pure component property estimation techniques that we have developed for normal boiling points, critical property data, and vapour pressures. Predictions can be made from simply having knowledge of the molecular structure of the compound. In addition, the structural group definitions for the method are identical to those proposed for estimation of saturated vapour pressures. 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 liquid viscosity data for more than 1600 components. Results of the new method are compared to several other estimation methods published in literature and are found to be significantly better. A relative mean deviation in viscosity of 15.3% was observed for 813 components (12,139 data points). By comparison, the Van Velzen method, the best literature method in our benchmarking exercise produced a relative mean deviation of 92.8% for 670 components (11,115 data points). Estimation results at the normal boiling temperature were also tested against an empirical rule for more than 4000 components. The range of the method is usually from the triple or melting point to a reduced temperature of 0.75–0.8. Larger than average deviations were observed in the case of molecules with higher rotational symmetry, but no specific correction of this effect was included in this method.     

Prediction of Antoine constants using a group contribution method

Vapor pressure is one of the important properties necessary for process design. Antoine equation has been widely used to evaluate the vapor pressures. This article deals with the proposal of a method for predicting the Antoine constants using a group contribution method. The 1817 compounds treated here are grouped into six classes. The group contribution parameters for each class have been determined using a regression analysis. The group contribution method with help of experimental normal boiling point has good results for predicting the vapor pressures.     

Estimation of normal boiling points of hydrocarbons from descriptors of molecular structure

Correlations for estimation of thermophysical properties are needed for the design of processes and equipment related to phase equilibria. The normal boiling point (NBP) is a fundamental characteristic of chemical compounds, involved in many correlations used to estimate important properties. Modern simulation packages usually require the NBP and a standard liquid density from which they can estimate all other necessary properties and begin the design of particular processes, installations and flowsheets. The present work contributes a correlation between the molecular structure and the normal boiling point of hydrocarbons. Its main features are the relative simplicity, sound predictions, and applicability to diversified industrially important structures, whose boiling points and numbers of carbon atoms span a wide range. An achievement of particular interest is the opportunity revealed, for reducing the number of the compounds required for the derivation (the learning set), through multivariate analysis and molecular design. The high accuracy achieved by the correlation opens up a possibility for systematic studies of chemical engineering applications in which the effects of small changes are important. This also defines a path towards the more general problem of the influence of uncertainties in calculated thermophysical parameters on the final outcome of computer aided simulation and design.     

Calculations of Freezing Point Depression,Boiling Point Elevation,Vapor Pressure and Enthalpies of Vaporization of Electrolyte Solutions by a Modified Three-Characteristic Parameter Correlation Model

A method was proposed for calculating the thermodynamic properties, freezing point depression, boiling point elevation, vapor pressure and enthalpy of vaporization for single solute electrolyte solutions, including aqueous and nonaqueous solutions, based on a modified three-characteristic-parameter correlation model. When compared with the corresponding literature values, the calculated results show that this method gives a very good approximation, especially for 1-1 electrolytes. Although the method is not very suitable for some solutions with very high ionic strength, it is still a very useful technique when experimental data is scarce.     

Estimation of boiling and melting points of light,heavy and complex hydrocarbons by means of a modified group vector space method

A modified group vector space (GVS) method was developed for estimating the normal boiling points and melting points of alkanes, alkenes, alkynes, and cyclic and aromatic hydrocarbons including their isomers. The present method, based on group contributions as well as topological contributions, can represent the normal boiling points of isomeric compounds accurately. The group parameters for the modified GVS method were obtained from the correlation of the boiling and melting points of 1115 hydrocarbons.     

计算烷烃沸点的新方法-基团键贡献法

根据分子中基团的特性和连接性,将基团贡献法和化学键贡献法结合在一起,发展了一种直接根据分子结构信息计算烷烃沸点的新方法-基团键贡献法,此方法同时具有基团贡献法和化学键贡献法的特点。对753种烷烃(C2～C100)的计算结果表明,沸点计算值与实验值的一致性令人满意,平均误差0.46%。     

Group vector space method for estimating enthalpy of vaporization of organic compounds at the normal boiling point

The specific position of a group in the molecule has been considered, and a group vector space method for estimating enthalpy of vaporization at the normal boiling point of organic compounds has been developed. Expression for enthalpy of vaporization Delta(vap)H(T(b)) has been established and numerical values of relative group parameters obtained. The average percent deviation of estimation of Delta(vap)H(T(b)) is 1.16, which show that the present method demonstrates significant improvement in applicability to predict the enthalpy of vaporization at the normal boiling point, compared the conventional group methods.     

Prediction of vapor pressures and enthalpies of vaporization of organic compounds from the normal boiling point temperature

Recently, our Laboratory proposed a model for the prediction of vapor pressures of organic compounds that requires only the knowledge of the normal boiling point of the compound involved, and a compound specific K_f for which generalized expressions for several classes of organic compounds as functions of the normal boiling point and the molecular weight were developed.In this work our model is compared with the one proposed in Lyman's book, which is similar to our model but uses different K_f values. The results indicate that our model provides very satisfactory results in the temperature range from the melting up to the normal boiling point and up to the critical, where no hydrogen-bonding is involved. Also, it is proven that the accuracy of our model is much better than that proposed by Lyman, especially for the high molecular weight compounds.Finally, our model is used for the prediction of enthalpies of vaporization at the normal boiling point. Excellent results are obtained that are comparable or better than those obtained with two recommended models in “The Properties of Gases and Liquids” book, where the latter, however, require as input information except from the normal boiling point the critical properties of the compound involved as well.     

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.     

Evaluation of correlations for prediction of the normal boiling enthalpy

Ten analytical models were used to calculate the enthalpy of vaporization of fluids at the boiling temperature. The correlations considered were six specific expressions valid only at that temperature, and four general correlations valid for any temperature. Most of these models require as inputs the critical properties and the acentric factor, but one of the specific models requires only the molecular weight (and, obviously, the boiling temperature). One of the models is a correlation requiring a molecular Lennard–Jones parameter and the acentric factor as inputs. Results for 290 fluids are compared with the values given by the DIPPR project.     

拟静态法测定混合溶剂的汽化热和汽化熵

讨论了沸点升高法测定混和溶剂化热和汽化熵的原理，并用拟静态法测定了乙醇－丙酮，并－四氯化碳和苯，甲苯三组混和溶剂在不同组成下的正常沸点，根据沸点数据求得了混和泶微分汽化热和汽化熵，实验结果表明，二元混和溶剂与理想溶液偏离不大时，其正常汽化熵符合Ｔｒｏｕｔｏｎ规则。     

Prediction of the molar volume at the normal boiling point

A group contribution method for the prediction of the molar volume at the normal boiling point has been developed. The method can be used for organic and inorganic compounds. It cannot be used for elements and diatomic molecules. Group contributions are shown for a wide variety of hydrocarbons, organic halogen compounds, organic oxygen compounds, organic nitrogen compounds, organic sulfur compounds, organic boron compounds, organic silicon compounds, miscellaneous organics, and many inorganic compounds.Contrary to the corresponding states methods for the prediction of molar volumes, knowledge of critical properties, acentric factors, and reference volumes is not needed.     

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.     

Vapor pressure of 1,1,1,2,3,3,3-heptafluoropropane

A total of 84 vapor pressure data points for 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea) have been measured in the temperature range from 243 to 375 K. The maximum total pressure uncertainty of these data is estimated to be within ±1 kPa. The purity of the sample used in this work is 99.9 mol%. Based on this data set, a vapor pressure equation for HFC-227ea has been developed. The root-mean-square (RMS) deviation of the experimental data from the vapor pressure equation is 0.057%. The normal boiling point of HFC-227ea was also determined.     

The temperature dependence of mercury saturated vapor pressure over the whole range of its liquid state

The Boltzmann distribution with normalization with respect to the boiling point was used to calculate the temperature dependence of vapor pressure, which included the temperature and heat of boiling only. A refined equation of mercury vaporizability with mutually consistent characteristics such as vapor pressure and the temperature and heat of boiling was obtained. The equation correctly described this dependence over the whole liquid state range, including the critical point.     

Calculation of normal boiling points for alkane isomers by a second order group contribution method

Second order groups are introduced into the group contribution method proposed by Tu to calculate the normal boiling points of alkanes from C₁ to C₁₀. The present method can well distinguish between the normal boiling points of alkane isomers. The absolute average error is 1.24 K.