Models Modified Redlich-Kwong

Phase compositions of VLLE in the systems glucose + acetone + water + carbon dioxide and carbohydrates + 2-propanol + water + carbon dioxide have been determined experimentally. Like for VLE of related systems from literature, the carbohydrate solubility in a phase rises when the phase becomes more similar to the water-rich lower liquid phase. At the same time separation of different carbohydrates becomes more difficult because selectivity decreases. Theoretically based models can help to find an optimum of capacity and selectivity and to minimize the number of necessary experiments. A simple model based on the Soave-Redlich-Kwong EOS which can reproduce glucose partitioning between the two liquid phases in VLLE in the glucose + acetone + water + carbon dioxide system is presented. 2-Propanol is shown to be a better modifier for these systems than acetone, but denaturation of carbohydrates in the carbohydrate + 2-propanol + water + carbon dioxide system limits industrial applications. 

Other approaches to the computation of solid-liquid equilibria are shown in Table 11.2-3. The Soave-Redlich-Kwong equation of state evaluates fugacities to calculate solid-liquid equilibria,7 while Wenzel and Schmidt developed a modified van der Waals equation of state forthe representation ofphase equilibria. The Wenzel-Scbmidt approach generates fugacities, from which the authors developed a trial-and-error approach to compute solid-liquid equilibrium. Unno et a .9 recently presented a simplification of the solution of groups model (ASOG) that allows prediction of solution equilibrium from limited vapor-liquid equilibrium data. 

In this study, the phase equilibrium in the binary mixtures that are expected to be found in the flash distillation was modeled with the Predictive Soave-Redlich-Kwong (PSRK) equation of state [4], using modified molecular parameters r and q. Five binary ethanol + congener mixtures were considered for new yield values for parameters r and q. The congeners considered were acetic acid, acetaldehyde, furfural, methanol, and 1-pentanol. Subsequently, the model was validated with the water + ethanol binary system, and the 1 -pentanol + ethanol + water, 1-propanol + ethanol + water, and furfural + ethanol + water ternary systems. 

This work proposed the use of the Predictive Soave-Redlich-Kwong (PSRK) model to describe the phase equilibria in the flash distillation, using modified molecular parameters r and q for ethanol. In this way, the PSRK equation of state becomes more empirical, but keeps the predictive capabilities of the model. Furthermore, the introduction of new molecular parameters r and in the UNIFAC model gives more accurate predictions for the concentration of the congener in the gas phase for binary and ternary systems. 

The cubic Soave-Redlich-Kwong equation of state with the modified Huron-Vidal mixing rules developed by Michelsen (herein after assigned the acronym MHV2) is a model that fulfils these requirements and it is very attractive due to its mathematical simplicity details of Huron-Vidal mixing... 

In the middle of the 20 h century, (Redlich Kwong, 1949) published a new model derived from Van der Waals equation, in which the attractive term was modified in order to obtain better fluid phase behaviour at low and high densities ... 

The alpha function a T) used in the SRK equation is often named Socwe s alpha function. The accuracy of this model was tested by comparing vapour pressures of a number of hydrocarbons calculated with the SRK equation to experimental data. Contrary to the Redlich-Kwong equation, the SRK equation was able to fit well the experimental trend. After Soave s proposal, many modifications were presented in the literature for improving the prediction of one or another property. One of the most popular ones is certainly the modification proposed by (Peng Robinson, 1976) (their equation is named PR76 in this chapter). They considered the same alpha function as Soave but coefficients of the m function were recalculated. In addition, they also modified the volume dependency of the attractive term ... 

Long time the original van der Waals EOS did not found industrial applications. Redlich and Kwong (1949) discovered that a modified form was convenient for describing the hydrocarbon mixtures. The model, abbreviated here by RK-EOS, is represented by the relation ... 

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