Vapor-liquid behavior

We believe that the SRK equation of state has been pushed to its limits. Some improvements in its ability to describe the behavior of hydrocarbon water-other components systems can probably be made. Some of our earlier work indicated that the vapor liquid behavior of selected organic water systems could be reasonably well described (7, 23). Unfortunately, the results of this work could not be extended beyond the range of data used in the fitting process. 

Measurements of binary vapor-liquid equilibria can be expressed in terms of activity coefficients, and then correlated by the Wilson or other suitable equation. Data on all possible pairs of components can be combined to represent the vapor-liquid behavior of the complete mixture. For exploratory purposes, several rapid experimental techniques are applicable. For example, differential ebulliometry can obtain data for several systems in one laboratory day, from which infinite dilution activity coefficients can be calculated and then used to evaluate the parameters of correlating equations. Chromatography also is a well-developed rapid technique for vapor-liquid equilibrium measurement of extractive distillation systems. The low-boiling solvent is deposited on an inert carrier to serve as the adsorbent. The mathematics is known from which the relative volatility of a pair of substances can be calculated from the effluent trace of the elutriated stream. Some of the literature of these two techniques is cited by Walas (1985, pp. 216-217). 

Generalized Correlations. A simple and reliable method for the prediction of vapor—liquid behavior has been sought for many years to avoid experimentally measuring the thermodynamic and physical properties of every substance involved in a process. Whereas the complexity of fluids makes universal behavior prediction an elusive task, methods based on the theory of corresponding states have proven extremely useful and accurate while still retaining computational simplicity. Methods derived from corresponding states theory are commonly used in process and equipment design. 

The pressure in the reactor PR is calculated explicitly from Eq. (2.74) assuming ideal vapor-liquid behavior... 

Several enhanced distillation-based separation techniques have been developed for close-boiling or low-relative-volatility systems, and for systems exhibiting azeotropic behavior. All these special techniques are ultimately based on the same differences in the vapor and liquid compositions as ordinary distillation but, in addition, they rely on some additional mechanism to further modify the vapor-liquid behavior of the key components. These enhanced techniques can be classified according to their effect on the relationship between the vapor and liquid compositions ... 

The various cases discussed all refer to pressure and temperature conditions that are above the MCP of the binary mixture COj-solvent nevertheless, the presence of solutes has evidently modified the vapor-liquid behavior with respect to the one characteristic of the binary system at least in cases a-c cosolvency and formation of two phases have been observed. Thus, visual observation and powder analysis confirmed our hypothesis of a shift of the MCP induced by the addition of the third component. 

This book presents a state-of-the-art review of this important topic and discusses the use of cubic equations of state to model the vapor-liquid behavior of mixtures of all degrees of nonideality. A special feature of the book is that it includes a disk of computer programs for all the models discussed along with tutorials on their use. With the programs and tutorials, readers can easily reproduce the results reported and test all the models presented with their own data to decide which will be most useful in their own work. 

Use the UNIFAC model to predict the vapor-liquid behavior of the system in the previous problem, and compare the results with the experimental data. 

High pressure vapor-liquid behavior is typically classified into one of five basic types illustrated in Figure 11. (Classification numbering of the systems varies and one additional classification is sometimes added (8,10,17)). If the only area of interest is above the critical point of the lighter component, then the only temperatures of interest are above Cj. As an illustration of type III behavior, a P-x-y diagram of the ethylene-n-propanol... 

LE2 Lee, H.-Y., Yoon, S.-D., and Byun, H.-S., Cloud-point and vapor-liquid behavior of binary and ternary systems for the poly(dodecyl acrylate) + cosolvent and dodecyl acrylate in supercritical solvents, J. Chem. Eng. Data, 55, 3684, 2010. 

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