Chemical engineering properties of phase equilibria for mixed solutions are essential in separation processes such as distillation, absorption, and extraction. When determining the activity coefficients of a non-ideal solution, methods for determining the activity coefficients using information related to atomic groups that compose the molecules without using measured values are called group contribution methods. The ASOG method and the UNIFAC method are representative methods. The UNIFAC method is a modified version of the ASOG method, and basically uses the same procedures. Here, we will consider the derivation of the activity coefficients by a group contribution method, by taking the ASOG method as an example. (H. Taguchi)
When performing vapor-liquid equilibrium calculations, activity coefficient models such as the Wilson method and the NRTL method, or equation of state models such as the SRK method and the Peng-Robinson method are commonly used. The advantage of the former models is that they provide calculation accuracy for non-ideal solutions. The advantages of the latter models are that they enable estimations to be done with only a limited number of parameters, and that they provide reliable results in the critical region. On the other hand, regarding their disadvantages, the former models necessitate parameter fitting using actual measurement data, and the latter models have a limited applicability to non-ideal solutions. Here, we will introduce together with information from the scientific literature, features and points of caution regarding the PSRK method which is a group contribution model that compensates for these respective problems. (H. Taguchi)
It is known that dissolving a nonvolatile solute such as sugar in a solvent increases the boiling point of the solution compared to that of the pure solvent. This is called boiling point elevation or vapor pressure depression. The degree of the boiling point elevation is determined by the boiling point elevation constant, which is a constant specific to the solvent. For this reason, it is possible to experimentally determine the molar mass of the solute dissolved in the solvent by making use of the boiling point elevation constant. Here, we will derive the boiling point elevation constant and examine its range of applicability. (H. Taguchi)
Water is an indispensable substance for life forms and also in industrial plants. It is used in various applications such as in solvents, cooling mediums, and heating mediums. Since water is an important and familiar substance, it is widely used as a standard for physical units, and knowing these values is also important for judging the validity of various calculation results. The vapor pressure of water is an extremely important physical property, but it is difficult to memorize approximate values because of its strong nonlinearity. Here, we will introduce an approximate method for calculating the vapor pressure of water, which can be easily memorized and readily applied. (H. Taguchi)
Vapor pressure is the most important of the physical properties used in process design. Although latent heats of vaporization were often estimated using vapor pressure data before, recently, it seems that less attention has been paid to this due the spread of simulators. Here, we have summarized the relationships between the B value of the Antoine equation, latent heat of vaporization, and the boiling point. (Y. Kumagae)
One of the factors that complicate handling distillation separation processes is the azeotropic phenomenon. A system which forms an azeotropic mixture cannot be separated into pure components by ordinary distillation. Therefore, various measures such as chemical absorption, the addition of a third component, pressure changes, reactive distillation and the like have been devised since long ago to deal with this issue. Here, we will discuss the effect of pressure and of adding a third component on the azeotropic composition. (H. Taguchi)
Although there are many actual measurement data on binary azeotropic mixtures, there are currently few data for ternary systems and prediction is difficult. It is time-consuming and inefficient to check all regions even when conducting experiments. Here, we will introduce a rule of the thumb which seems to be effective for the purpose of estimating ternary azeotropic points. (H. Taguchi)
The vapor-liquid equilibrium calculations using activity coefficient models such as the Wilson and NRTL models are widely practiced and have a number of successful applications. Binary parameters are required in order to use activity coefficient models, and they are generally determined from actually measured vapor-liquid equilibrium data. On the other hand, even when vapor-liquid equilibrium data is not measured, it is possible to estimate vapor-liquid equilibrium with relatively high accuracy when azeotropic data can be used. Here we will consider a method for estimating the binary parameters of an activity coefficient model using azeotropic data, and examine the accuracy of this method. (H. Taguchi)
First, we introduced a vapor-liquid equilibrium estimation method from azeotropic data as an estimation method of vapor-liquid equilibrium in the absence of measured values (Tips #1109). Here, we will introduce a vapor-liquid equilibrium estimation method when liquid-liquid equilibrium data can be used. The liquid-liquid equilibrium data is usually in a lower temperature region than the vapor-liquid equilibrium. (Y. Kumagae)
Physical property data is extremely important for performing process design and plant data analysis. Physical properties include equilibrium physical properties (pure substance vapor pressure, vapor-liquid equilibrium, specific heat, heat of evaporation, etc.) and transport properties (viscosity, thermal conductivity, diffusion coefficients). Among these, the pure substance vapor pressure is significantly important as it is the basis for estimating other physical property values. We will introduce a parameter determination method for the Antoine equation which is often used for pure substance vapor pressure calculations. (Y. Kumagae)
