Water binary pairs

For ternary and higher order mixtures, we have usually assumed that the interaction parameters for the non-water binary pairs in the water rich phase are identical to the vapor (hydrocarbon rich liquid phase) interaction parameters. Some work has been done on changing all water phase interaction parameters we concluded that predicted results were not improved enough to warrant the expenditure of time required to develop the additional parameters. A third interaction parameter for the hydrocarbon rich liquid could also be determined. Again, our work indicated that little improvement resulted from using this third parameter. Additional work is being done on both points. 

These binary interaction parameters were obtained using the program VDW.EXE described in Appendix D.3, and the data files am200.dat, mw250.dat, and aw250.dat, respectively, for acetone-methanol, methanol-water, and acetone-water binary pairs.)... 

More Complex Mixtures. AH the sequences discussed are type I Hquid systems, ie, mixtures in which only one of the binary pairs shows Hquid—Hquid behavior. Many mixtures of commercial interest display Hquid—Hquid behavior in two of the binary pairs (type II systems), eg, secondary butyl alcohol—water—di-secondary butyl ether (SBA—water—DSBE), and water—formic acid—xylene (92). Sequences for these separations can be devised on the basis of residue curve maps. The SBA—water—DSBE separation is practiced by ARGO and is considered in detail in the Hterature (4,5,105,126). 

Ternary-phase equilibrium data can be tabulated as in Table 15-1 and then worked into an electronic spreadsheet as in Table 15-2 to be presented as a right-triangular diagram as shown in Fig. 15-7. The weight-fraction solute is on the horizontal axis and the weight-fraciion extraciion-solvent is on the veriical axis. The tie-lines connect the points that are in equilibrium. For low-solute concentrations the horizontal scale can be expanded. The water-acetic acid-methylisobutylketone ternary is a Type I system where only one of the binary pairs, water-MIBK, is immiscible. In a Type II system two of the binary pairs are immiscible, i.e. the solute is not totally miscible in one of the liquids. 

A second type of ternary electrolyte systems is solvent -supercritical molecular solute - salt systems. The concentration of supercritical molecular solutes in these systems is generally very low. Therefore, the salting out effects are essentially effects of the presence of salts on the unsymmetric activity coefficient of molecular solutes at infinite dilution. The interaction parameters for NaCl-C02 binary pair and KCI-CO2 binary pair are shown in Table 8. Water-electrolyte binary parameters were obtained from Table 1. Water-carbon dioxide binary parameters were correlated assuming dissociation of carbon dioxide in water is negligible. It is interesting to note that the Setschenow equation fits only approximately these two systems (Yasunishi and Yoshida, (24)). 

Before describing variations in the critical points in the four-component water-gas shift mixture it is instructive to examine the critical points in the various binary mixtures. There are six binary pairs to consider. 

Figure 1. Critical lines in water-gas shift binary pairs...

The introduction of this parameter for each aqueous binary pair means that the interaction between the water molecule and the gas molecule in the aqueous liquid phase is much different from that in the nonaqueous phases. For all the aqueous binaries which have been examined in this study, the temperature -dependent interaction parameters take on negative values at ambient temperature and monotonically increase as temperature increases. This indicates that the attraction energy between the water molecular and the other molecules decreases as the temperature increases. 

Since pentane and water exhibit immiscibility, we might consider decantation as the first step. If it worked, it would be an inexpensive one to carry out. But a rigorous three-phase equilibrium calculation predicts that, in the presence of acetone and methanol, the small water fraction in the feed does not form a second liquid phase so we reject this idea. The calculation also reveals that the feed mixture is almost at the azeotropic composition for the pentane/methanol binary pair. 

Most of the ternary or pseudoternary wstems used in extraction are of two types one binary pair has hmited miscibility (termed a type 1 system), or two binary pairs have limited miscibility (a type 11 system). The water -h acetic acid -I- methyl isobutyl ketone (MIBK) system... 

Biddulph and Kalbassi (1988) investigated the distillation of the ternary system methanol(l)-l-propanol(2)-water(3). In separate experiments they determined the numbers of transfer units for each binary pair that makes up the ternary system. Estimate the number of transfer units for the ternary system at total reflux if the composition of the liquid leaving the tray is... 

In this section we have considered liquid-liquid equilibrium in binary mixtures, and in ternary mixtures in which there was limited mutual solubOity between only one pair of components (for example, the methyl isobutyl ketone + water binary mixture in the methyl isobutyl ketone + water + acetone system). In fact, liquid-liquid equilibria can be more complicated than this when two of three binary pairs in a ternary-mixture, or all three of the binary pairs, have limited solubility. Such systems can be described by... 

When carrying out a batch distillation on a binary mixture it is very useful to have a quick and user-friendly analysis of the overheads. It is even better if the analysis can be performed on the plant without the need to take a sample to the laboratory and the process operator has a continuous record of the progress of the batch. A record of this sort can be provided by an on-line specific gravity (i.e. density corrected for temperature) meter. Many binary pairs such as mixtures of methanol, acetone and THF with water have large density differences between the organic distillate and water. This property can be used to control the split between reflux and product flow rates. 

Systems which have a ternary C.S.T. Refer to Fig. 2.9. In this case, the curve through the plait points Pi, P2, P3, P4, and Pb reaches a ternary maximum at Pe, which then becomes a true ternary C.S.T. The curve continues through P5 to P7, the binary C.S.T. Projections of the isotherms onto the base of the figure are indicated in Fig. 2.10. It is clear that for temperatures between that at P7 and Pe, such as that at isothermal solubility curves, with two plait points, Pb and P5, while the binary pairs show individually complete miscibility. An example of this type of system is that of water-phenol-acetone with a ternary C.S.T. at 92 C., and a binary C.S.T. (water-phenol) at 66 C. (42). 

Much more complex equilibria may arise, as in the case of the system succinic nitrile-ether-water at 2 C. (42), where, while the binary pairs behave as do A, B, and C of Fig. 2.17, three separate, isothermally invariant ternary areas exist. Compound formation will further complicate the equilibria. 

Most investigations of azeotropes have dealt with binary or ternary mixtures. The binary pairs of a multicomponent mixture may separately form azeotropes, but these are submerged by die possible azeotropes involving the Aril mixture. It is sometimes possible to utilize binary pair azeotrope information in estimating Are role that a multicomponent azeotn will play in the distillation separation. As an exariqile, the ethanol-water system exhibits a minimum boiling azeotrope. At atmospheric pressure, the boiling points are... 

For illustrating of the second case, the component system of a reactive distillation system for the production of butyl acrylate (see Zeng et al.") will be used here as an example. Butyl acrylate is produced by an esterification reaction of acrylic acid and butanol with a byproduct of water. The total system includes four components acrylic acid (AA), butanol (BuOH), butyl acrylate (BA), and water. The base-property method was chosen as NRTL-HOC because AA is known to have vapor association. There are a total of six binary pairs in the whole component system. In these six binary pairs, built-in model parameters can be found for the four pairs of AA-BuOH, AA-H2O, BuOH-BA, and BuOH-HaO. The model parameters of the remaining two pairs (AA-BA and BA-H2O) need to be estimated by using the group-contribution method of UNIFAC before any simulation ran can be done. 

From the above analysis, by looking into the iso- and equivolafility curves and the binary VLE diagrams for the IPA-entrainer and the water-entrainer pairs, it is concluded that... 

Calculate the LLE for the ternary di-isopropyl-ether/acetic-acid/water using NRTL and the BIPs available for the three binary pairs in the simulator databank. Conpare the prediction with ternary T T F data for this system at 24.6°C [131. 

The DME-water binary system exhibits two liquid phases when the DME concentration is in the 34% to 93% range [2]. However, upon addition of 7% or more alcohol, the mixture becomes conpletely miscible over the complete range of DME concentration. In order to ensure that this non-ideal behavior is simulated correctly, it is recommended that binary vapor-liquid equilibrium (VLE) data for the three pairs of components be used in order to regress binary interaction parameters (BIPs) for a UNIQUAC/UNIFAC thermodynamics model. If VLE data for the binary pairs are not used, then UNIFAC can be used to estimate BIPs, but these should be used only as preliminary estimates. As with all non-ideal systems, there is no substitute for designing separation equipment using data regressed from actual (experimental) VLE. 

A useful diagnostic option for checking VLE models is also available in the MMSP programs. Most VLE models are based on binary parameters. The data used in obtaining the binary parameters may be very limited and/or at conditions removed from those of interest. Therefore, it is wise to examine the predictions of the model for the binary pairs before attempting a multicomponent simulation. This option in MMSP will use the VLE model to produce y-x, T-x-y, P-x-y, a-x, and K-x diagrams for the binary systems. Two of these plots for the acetone-water system are shown in Figure 8. 

As Table 11.1 makes clear, LLE values change with changes in temperature. For practically insoluble materials like the benzene-water binary in Table 11.1 both solubilities increase slightly with increasing temperature. (The solubility of benzene in water increases by a factor of 1.5 and that of water in benzene by a factor of 9 as the temperature increases from 0 to 70°C.) This behavior is observed for most practically insoluble liquid pairs. 

Prus and Kowalska [75] dealt with the optimization of separation quality in adsorption TLC with binary mobile phases of alcohol and hydrocarbons. They used the window diagrams to show the relationships between separation selectivity a and the mobile phase eomposition (volume fraction Xj of 2-propanol) that were caleulated on the basis of equations derived using Soezewiriski and Kowalska approaehes for three solute pairs. At the same time, they eompared the efficiency of the three different approaehes for the optimization of separation selectivity in reversed-phase TLC systems, using RP-2 stationary phase and methanol and water as the binary mobile phase. The window diagrams were performed presenting plots of a vs. volume fraetion Xj derived from the retention models of Snyder, Schoen-makers, and Kowalska [76]. 

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