Soave-Redlich-Kwong equation Predictive

Simulation results, using Soave-Redlich-Kwong equation of state to predict -values. 

Forthe present calculations we have set Cu = 0. The iwo upper curves In Fig. 1.6-2 represent notubilities computed from Eq. (1.6-16) with (he Soave-Redlich-Kwong equation and two different values of 12- The topmost curve corresponds to k,2 = 0 it is a purely predictive result and, although quantitatively poor for the higher pressures, it correctly reproduces (he qualitative features of (he notability enhaucctnent. 

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. 

The Soave-Redlich-Kwong equation is rapidly gaining acceptance by the hydrocarbon processing industry. Further developments, such as that of Peng and Robinson,are likely to improve predictions of liquid density and phase equilibria in the critical region. In general however, use of such equations appears to be limited to relatively small, nonpolar molecules. Calculations of phase equilibria with the S-R-K equations require initial estimates of the phase compositions. 

Use the Soave-Redlich-Kwong equation of state to predict for each phase the density, mixture fugacity coefficients, and enthalpy. Also predict the K-values and compare them to the experimental values derived from the above data. 

An approach to overcome the above mentioned difficulties was the PSRK (Predictive Soave-Redlich-Kwong) equation developed by Holderbaum and Gmehling in 1991 [49, 50], based on the Soave-Redlich-Kwong equation 43]. Its main progress is the use of mixing rules (see Chapter 4) for a significant improvement of the description of mixtures with polar compounds. For the improvement of the pure component vapor pressures, an -function, individual for every substance, was introduced. In the PSRK equation, the Mathias-Copeman approach [51] is used, which is a polynomial extension of the Soave a-function (Eq. (2.163)) ... 

Predictions of saturated liquid densities of pure fluids from the Soave-Redlich-Kwong equation of state and, to a lesser extent, the Peng-Robsinson equation of state deviate from experimental data. This should be expected given the... 

Hoderbaum and Gmehling proposed the Soave-Redlich-Kwong equation of state be combined with UNI FAC and produced the Predictive Soave-Redlich-Kwong (and given the acronym PSRK) equation for which a(x) is given by... 

Neither the Group Contribution Association equation of state nor Soave-Redlich-Kwong equations of state with MHV2 mixing rules are recommended methods to prediet mixture densities. The Peng-Robinson equation of state with classical mixing rules is the more preeise model among the van der Waals family of equation of state to predict molar volumes of mixtures particularly when the volume eorrection has been used as proposed by Peneloux et... 

In the simplest form of phase separation, the stream to be separated is flashed into a vapor product and a liquid product, each having a different composition. Following are examples of single-stage separations of certain mixtures. The distribution coefficients are predicted by the Soave-Redlich-Kwong equation of state (Soave, 1972). 

Phase equilibria calculations from both an Orye-type BWR and the Soave Redlich-Kwong equation of state were compared with data from an LNG plant. Both correlations showed good comparisons with the plant data and experimental data measured by P-V-T, Inc. The enthalpies predicted using the Soave Redlich-Kwong equation of state were poorer than those predicted using the Lee-Kesler correlation. 

Figure A3.3 compares the experimental (corresponding states) results with the predictions from the van der Waals. modified Berthelot, Dieterici, and Redlich-Kwong equations of state.b The comparison is not so direct for the Soave and Peng-Robinson equations of state, since the reduced equation still includes to, the acentric factor. Figure A3.4 compares the corresponding states line, with the prediction from the Soave equation, using four different values of to. The acentric factors chosen are those for H (o> = —0.218), CH4 (to = 0.011),...

For both the Soave and Peng-Robinson equations, the fit is best for uj — 0. The Soave equation, which essentially reduces to the Redlich-Kwong equation when ui — 0, does a better job of predicting than does the Peng-Robinson equation. The acentric factors become important when phase changes occur, and it is likely that the Soave and Peng-Robinson equations would prove to be more useful when 77 < 1. 

The UNIFAC model has also been combined with the predictive Soave-Redlich-Kwong (PSRK) equation of state. The procedure is most completely described (with background literature citations) by Horstmann et al. [Fluid Phase Equilibria 227 157-164 (2005)]. 

Hence, the third parameter, co, implicitly contains information about the vapor pressure, making vapor pressure prediction something like a circular loop. But Soave went beyond this simple observation. Wilson had previously recognized these issues, but his equation met with limited success, especially at low reduced temperatures. Soave was careful to analyze the temperature dependence of his equation of state in great detail at the outset. He achieved this by introducing an adjustable parameter into the attractive contribution of the Redlich-Kwong equation. 

Compared with an experimental value of 982.5 kPa, the best predictions are by the Soave equation and the Redlich-Kwong equation. 

The above results for reflux ratios of 0, 1, and are given in Table 3.3. Also tabulated are data points at other values of reflux ratio, calculated by computer simulation using the Soave-Redlich-Kwong (SRK) equation of state for predicting the X-values. The concentrations are also plotted in Figure 3.4, showing the effect of reflux ratio on separation. In this example, since V, = L, an overall material balance indicates that at any point -i- Xj, = 1. 

The equation performs as well as or better than the Soave-Redlich-Kwong in all cases tested and shows its greatest advantages in the prediction of liquid phase densities.47 The constants, mixing rules, and the expressions for the fugacities and enthalpies for this equation of state are given in Table 14-7. 

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. 

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