Solubility prediction UNIQUAC

The question remains, however, of whether the solution is in fact infinitely dilute at a solute concentration of xi. Only if this is true is it valid to assume that yi = y - Literature values of solubility data for several compounds in water were used to obtain parameters for the UNIQUAC and NRTL excess Gibbs energy expressions, and y values for these compounds were calculated. The calculated values are compared with inverse solubility data in Table I. The inverse solubility predicts lower values of y in all cases. However, the difference becomes smaller as the solubility decreases, and for compounds with solubility less than 0,5% the difference is less than 10%. It has been shown that these excess Gibbs energy expressions, while very useful, are not the exact representation of the composition dependence of activity coefficient all expressions have difficulty in representing liquid-liquid equilibria (43-44). Thus, extrapolating these expressions to infinite dilution may be in error. It is therefore inconclusive as to the correctness of using the inverse solubility to calculate... 

If the mutual solubilities of the solvents A and B are small, and the systems are dilute in C, the ratio ni can be estimated from the activity coefficients at infinite dilution. The infinite dilution activity coefficients of many organic systems have been correlated in terms of stmctural contributions (24), a method recommended by others (5). In the more general case of nondilute systems where there is significant mutual solubiUty between the two solvents, regular solution theory must be appHed. Several methods of correlation and prediction have been reviewed (23). The universal quasichemical (UNIQUAC) equation has been recommended (25), which uses binary parameters to predict multicomponent equihbria (see Eengineering, chemical DATA correlation). 

One problem limiting the consideration of salt extractive distillation is the fact that the performance and solubility of a salt in a particiilar system is difficult to predict without experimental data. Some recent advances have been made in modeling the X T.E behavior of organic-aqueous-salt solutions using modified UNIFAC, NRTL, UNIQUAC, and other approaches [Kumar, Sep. Sci. Tech., 28(1), 799 (1993)]. 

For the purpose of this case study we will select Isopropyl alcohol as the crystallization solvent and assume that the NRTL-SAC solubility curve for Form A has been confirmed as reasonably accurate in the laboratory. If experimental solubility data is measured in IPA then it can be fitted to a more accurate (but non predictive) thermodynamic model such as NRTL or UNIQUAC at this point, taking care with analysis of the solid phase in equilibrium. As the activity coefficient model only relates to species in the liquid phase we can use the same model with each different set of AHm and Tm data to calculate the solubility of the other polymorphs of Cimetidine, as shown in Figure 21. True polymorphs only differ from each other in the solid phase and are otherwise chemically identical. 

In addition to the experimental results of phase equilibria, the correlation with the widely known GE models was assigned to. It was indicated by many authors that SLE, LLE, and VLE data of ILs can be correlated by Wilson, NRTL, or UNIQUAC models [52,54,64,79,91-101,106,112,131,134]. For the LLE experimental data, the NRTL model is very convenient, especially for the SLE/LLE correlation with the same binary parameters of nonrandom two-liquid equation for mixtures of two components. For the binary systems with alcohols the UNIQUAC equation is more adequate [131]. For simplicity, the IL is treated as a single neutral component in these calculations. The results may be used for prediction in ternary systems or for interpolation purposes. In many systems it is difficult to obtain experimentally the equilibrium curve at very low solubilities of the IL in the solvent. Because this solubility is on the level of mole fraction 10 or 10 , sometimes only... 

For the UNIQUAC equation, there are two adjustable equation parameters for each binary. For the binary that is partially miscible, the best way to determine the two binary parameters is to fit the mutual solubility data. For the completely miscible binaries, useful interaction parameters can be obtained from vie data. However, fitting vie data to within experimental accuracy does not uniquely determine the binary parameters. The choice of a particular set of parameters can have a significant effect on the representation of the ternary lie. For the ternary system of chloroform, water, and acetone at 333°K, for example, the two binary parameters are first determined from mutual solubility data for chloroform and water and then the other binary parameters for the two miscible binaries. Somewhat improved predictions occur by fitting binary parameters to the miscible binaries. Similar predictions have also been found for ternary systems of ethyl acetate, ethanol, and water. 

Then a correlating equation e.g., UNIQUAC, can be used to compute the activity coefficient, Yi for the hydrocarbon in the water phase. In this calculation the hydrocarbon is assumed to be infinitely dilute in the water phase, a reasonable approximation because of its limited solubility. The solubility then follows from equation (8). Table I shows the results of this approximate calculation for the benzene-water-ethanol system. The UNIQUAC equation with the constants of Brandani et al. (9) was used to predict the hydrocarbon activity coefficients. 

Solutions containing carboxylic acids The Wilson model appears to best correlate data for mixtures containing carboxylic acTds, if the components are mutually soluble. (The Wilson model does not predict liquid-liquid phase splitting, as discussed in Sec. 11.2). Otherwise, the UNIQUAC, van Laar, or NRTL model should be used. 

Kaewsichan L, Al-hofersrai O, Yesavage VF, Selim MS. Predictions of the solubility of acid gasses in monoethanolamine (MEA) and methyldiethanolamine (MDEA) solutions using the electrolye-UNIQUAC model. Fluid Phase Equdih 2001 183 184 159-71. 

Tie-line data of the ternary system containing of (water + propionic acid + 1-octanol) were obtained at temperature from (293.15 to 308.15) K. Experimental LLE data of this work analyzed and predicted using UNIQUAC and ASPEN model. The average RMSD value between the observed and calculated mole fractions was 12.94% for the UNIQUAC and ASPEN model. It can be concluded that 1-octanol has high separation factor, very low solubility in water, low cost, high boiling point which may be an adequate solvent to extract propionic acid from its dilute aqueouse solutions. 

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