Ternary distillation

The entrainer recovery column takes the distillate stream, from the azeo-column and separates it into a bottoms stream of pure water, and a ternary distillate stream for recycle to column 2. The overall material balance line for column 3 is shown in Figure 19b. This sequence was one of two original continuous processes disclosed in 1915 (106). More recendy, it has been appHed to other azeotropic separations (38,107,108). 

Table 6.3. Input Data for Ternary Distillation (Simple Model/...

Table 6.4. Results For Ternary Distillation (Simple Model)8...

Figure 6.6. Ternary Distillation (Simple Model) with Off-cut Production (Case 2) a) Accumulated Distillate Composition and Reflux Ratio Profile b) Instant Distillate Composition and Reflux Ratio Profile1.

Table 6.7. Results for Ternary Distillation (Detailed Dynamic Model)"1.

Stichlmair, J., J.R. Herguijuela, Separation regions and processes of zeotropic and azeotropic ternary distillation, AIChEJ, 38,1523-1535,... 

Vogelpohl (193) and Medina et al. (203) applied the diffusional interaction method for predicting ternary distillation composition profiles using binary data. They achieved this by eliminating the first two steps and assuming that all the mass transfer resistance is in the vapor. This procedure was shown to give excellent agreement with experimental data for dissimilar components. Biddulph and Kalbassi (194), however, report some discrepancies between prediction and experiment due to this assumption. 

Any higher alcohols that may have formed in the process from traces of higher olefins present in the propylene feed are absorbed from the azeotrope into mineral oil, in which isopropanol is insoluble. Pure isopropanol is obtained by ternary distillation of the cleaned water azeotrope with the appropriate proportion of added di-isopropyl ether. The ternary azeotrope (Table 19.2) is the top product from the column, and pure isopropanol is removed from the bottom (see Section 16.4 for related information). 

Isopropanol formation is thought to proceed via an intermediate isopropyl carbocation generated by interaction with water and the acid catalyst, which is then hydrated with water. Recovery is by distillation, to the 91% azeotrope, or by ternary distillation of the azeotrope to 100% isopropanol. 

Example 8.8.1 Ternary Distillation in a Wetted Wall Column... 

Repeat Example 8.8.1 (ternary distillation in a wetted wall column) using the linearized equations to calculate the molar fluxes but following the suggestion given in the second paragraph of Section 8.8.3 for estimating the multicomponent mass transfer coefficients in terms of the binary mass transfer coefficients. 

Gorak and Vogelpohl (1985) present an experimental study of ternary distillation in a packed column. The system used was methanol(l)-2-propanol(2)-water(3) and the column was 0.1 m wide and filled with Sulzer CY packing. Use the nonequilibrium model to simulate their experiments. Investigate the sensitivity of the simulation results to the thermodynamic model parameters. Write an article in the format required by Separation Science Technology that summarizes your calculations. 

Gorak, A. and Vogelpohl, A., Experimental Study of Ternary Distillation in a Packed Column, Separ. Sci. Technol., 20, 33-61 (1985). 

It is possible to extend the Margules correlation to multicomponent mixtures although the expressions become more complicated, they depend still on the same, binary interaction parameters. See Perry (1963), Wohl (1946, 1953), Sevems (1955), Chien and Null (1972). For ternary distillation, the activity coefficient at the reference temperature is given for component 1 by ... 

Table 6.3 Specified Design Variables Ternary Distillation...

Consider the overall mass balances around a ternary distillation column ... 

Example 6.14 Rate-Based Ternary Distillation Calculations... 

The following results were obtained for tray n from a rate-based calculation of a ternary distillation at 1 atm involving acetone (1), methanol (2), and water (3). Vapor and liquid phases are assumed to be completely mixed. 

Stichlmair, J., J.R. Fair, J. L. Bravo, 1989, Separation of azeotropic mixture via enhanced distillation, Chem. Eng. Progress, 85(1), 63-69 Stichlmair, J., J. R. Herguijuela, 1992, Separation regions and processes of zeotropic and azeotropic ternary distillation, AIChEJ, 38, p. 1523-1535 Stichlmair, J. G., J. R. Fair, 1999, Distillation, Principles and Practice, Willey-VCH Strathmann, H., 1990, Membrane and Membrane Separation Processes, Ullmann s Encyclopaedia of Industrial Chemistry, vol. A16 Taylor, R., Krishna, R., 2000, Modelling reactive distillation, Chem. Eng. Sci., 52, 993-1005... 

The concept of minimum reflux is more complex in azeotropic distillation, because of the high non-ideal behaviour and distillation boundaries. For the special case of ternary distillation, the analysis may be simplified. It is useful to mention that the minimum reflux is linked with the concept of distillation pinch. This represents a zone of constant phase composition, so that the driving force becomes very small. Consequently, the number of necessary stages for separation goes to infinite. Similarly, there is a minimum reboil rate. In this respect, three classes of limiting separations may be distinguished (Stichlmair and Fair, 1999). Figures 9.36 to 9.38 present concentration profiles obtained by simulation with an ideal system benzene-toluene-ethyl-benzene. 

Agrawal, R. and Z.T. Fidkowski, Are thermally coupled distillation columns always thermodynamically more efficient for ternary distillations Industrial and Engineering Chemistry Research, 1998, 37(8) 3444 3454. 

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