Binaiy interaction parameters

We will refer to this one-binaiy-interaction-parameter-per-pair version of the van der Waals mixing rules (eqns. 3.3.4, 3.3.6, and 3.3.8) as the IPVDW model. 

In using simulation software, it is important to keep in mind that the quality of the results is highly dependent upon the quality of the liquid-liquid equilibrium (LLE) model programmed into the simulation. In most cases, an experimentally validated model will be needed because UNIFAC and other estimation methods are not sufficiently accurate. It also is important to recognize, as mentioned in earlier discussions, that binary interaction parameters determined by regression of vapor-liquid equilibrium (VLE) data cannot be relied upon to accurately model the LLE behavior for the same system. On the other hand, a set of binaiy interaction parameters that model LLE behavior properly often will provide a reasonable VLE fit for the same system—because pure-component vapor pressures often dominate the calculation of VLE. 

The above equations perniit calculation of To do the calculation, one requires values for the critical temperatures, critical pressures, and acentric factors of the pure components. Also needed are estimates for the binaiy interaction parameteR and ilr,2. 

Table 4.6 shows the calculated value of the UNIQUAC and NTRL binaiy interaction parameters for the mixture TBA + 2-ethyl-l-hexanol and NBA + 2-ethyl-1-hex-anol using universal values for the UNIQUAC and NTRL parameters. The mixture non-randomness parameter in the NTRL eqnation was fixed at 0.3. The valnes of r and q used in the UNIQUAC equation are presented in Table 4.7. The UNIQUAC structural parameters r and q were calculated from group contribution data that has been previously reported (Abrams and Pransnitz, 1975). The UNIQUAC and NTRL equations were i...

The binary interaction parameters are evaluated from liqiiid-phase correlations for binaiy systems. The most satisfactoiy procedure is to apply at infinite dilution the relation between a liquid-phase activity coefficient and its underlying fugacity coefficients, Rearrangement of the logarithmic form yields... 

In contrast to the NRTL-SAC model, the UNIFAC model developed by Fredenslund et. al. [29] divides each molecule into a set of functional groups that interact with each other on a binaiy basis and whose interactions are combined together to describe the global liquid phase interaction between molecules. Because the segments in UNIFAC are based on functional groups it is possible to model a system provided that all of the molecular structures are known. The problem with pharmaceutical sized molecules is that existing UNIFAC parameter tables do not contain many of the group interaction parameters that are necessary, and even when they do, the interactions are fitted to a database of chemicals that are much smaller and simpler than pharmaceuticals, and typically fail to represent them adequately. 

Here, X is a generic mole fraction and can refer to any phase. When subscripts i and J are identical in Eq. (1.3-32) or (1.3-33), the parameters refer ro a pure component. When they are different, die parameters are called interaction parameters and diese dqx on the properties of the binaiy i-J mixture as indicated by the subscripts. To estimate these interaction parameters, we use combining rules, for example. 

FIGURE 1.3-2 ConqxMhion dependence of fugacity coefficient of hydrogen sulfide in binaiy mixtures with ethane at 300 K. Curves labeled V are for superheated vapors at 15 bar, those labeled L are for subcooled liquids at 50 bar. All curves are computed ftxnn the Soave-Redlich-Kwong equation, with values of interaction parameter k,2 as shown. 

Binaiy liquid-liquid equilibrium data for the system water + 2-butanol, temaiy liquid-liquid equiUbrimn data for the system water + acetone + 2-butanol, and qua-temaiy liquid-liquid equihbrimn data for the system water + acetone + 1-butanol + sodium acetate were used for estimation of the eneigy interaction parameters of the NRTL model for the activity coefficient. The estimation piocednres nsed the Aspen. With these parameters, the experimental data were correlated. 

Treiner and co-workers [81] measured partitioning of 1-pentanol to elucidate the micellar composition of two aqueous mixed anionic surfactant solutions (sodium decyl sulfate -I- sodium peifluorooctanoate and sodium dodecyl sulfate + sodium perfluorooctanoate). The partition coefficient exhibited a maximum in hydrocarbon-rich mixtures in both mixed micellar solutions. The synergistic effect was attributed to hydrocarbon-fluorocarbon repulsive interaction and found to be in accord with the regular solution model using interaction parameters determined for binaiy surfactant solutions. 

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