Distillation ternary mixtures

Dribicka and Sandall (1979) distilled ternary mixtures of benzene (1), toluene (2), and ethylbenzene (3) at total reflux in a wetted wall column made from stainless steel and of 2.21-cm inside diameter (<7). A schematic diagram of the column is shown in Figure 8.13. Samples of the vapor and liquid phases were taken from various points along the column. During one of their experiments the vapor phase at a height of 300 mm from the bottom of the column had the composition... 

The use of a ternary mixture in the drying of a liquid (ethyl alcohol) has been described in Section 1,5 the following is an example of its application to the drying of a solid. Laevulose (fructose) is dissolved in warm absolute ethyl alcohol, benzene is added, and the mixture is fractionated. A ternary mixture, alcohol-benzene-water, b.p. 64°, distils first, and then the binary mixture, benzene-alcohol, b.p. 68-3°. The residual, dry alcoholic solution is partially distilled and the concentrated solution is allowed to crystallise the anhydrous sugar separates. 

Fig. 3. Residue curve map for a ternary mixture with a distillation boundary mnning from pure component D to the binary azeotrope C.

The overwhelming majority of all ternary mixtures that can potentially exist are represented by only 113 different residue curve maps (35). Reference 24 contains sketches of 87 of these maps. For each type of separation objective, these 113 maps can be subdivided into those that can potentially meet the objective, ie, residue curve maps where the desired pure component and/or azeotropic products He in the same distillation region, and those that carmot. Thus knowing the residue curve for the mixture to be separated is sufficient to determine if a given separation objective is feasible, but not whether the objective can be achieved economically. 

FIG 13-59 (Continued) Distillation region diagrams for ternary mixtures. 

Table 11.10 presents some heuristics for using complex distillation columns to separate a ternary mixture into its pure component products. On the basis of these heuristics and those for simple columns, suggest two sequences containing complex columns that can be used to separate the mixture described in Table 11.9 into relatively pure products. 

A ternary mixture of mole fraction ethanol of 0.15, ethyl acetate of 0.6 and methanol 0.25 is to be separated into relatively pure products. Sketch a system of distillation columns and mixer arrangements in the triangular diagram to carry out the separation by exploiting the shift in the distillation boundary with pressure. Sketch the flowsheet corresponding with this mass balance. 

Jso-propyl alcohol is very difficult to dry satisfactorily. The water binary mixture, boiling at 80.35°, contains 12.1 per cent of water by weight. The ternary mixture with benzene, boiling at 66.5°, contains 73.8 per cent benzene, 18.7 per cent iso-propyl alcohol and 7.5 per cent water. Hence by adding 120 g. of dry benzene to 100 g. of the iso-propyl-water binary, and distilling off until the temperature reaches 82°, there will remain 55 to 60 g. of nearly dry iso-propyl alcohol. The commercial anhydrous alcohol was used in this preparation. 

The model of a multicomponent batch distillation column was derived in Sec. 3.13. For a simulation example, let us consider a ternary mixture. Three products will be produced and two slop cuts may also be produced. Constant relative volatility, equimolal overflow, constant tray holdup, and ideal trays are assumed. 

Alatiqi presented (I EC Process Design Dev. 1986, Vol. 25, p. 762) the transfer functions for a 4 X 4 multivariable complex distillation column with sidestream stripper for separating a ternary mixture into three products. There are four controlled variables purities of the three product streams (jCj, x, and Xjij) and a temperature difference AT to rninirnize energy consumptiou There are four manipulated variables reflux R, heat input to the reboiler, heat input to the stripper reboiler Qg, and flow rate of feed to the stripper Lj. The 4x4 matrix of openloop transfer functions relating controlled and manipulated variables is ... 

Fig. 1. Three thermally coupled distillation schemes for the separation of ternary mixtures...

Five composition groups were studied in the low-pressure device, four composition groups in the high-pressure device as shown in Figure 3. The choice of the composition of the ternary mixtures was made in order to be representative of the different part of the reactive distillation column from bottom to top. 

This example considers distillation of a reacting ternary mixture in an open batch distillery with flowing sweep gas. From this example, one can see the determination of reactive azeotropes and reactive arheotropes . The considered hypothetical reaction is... 

Similar patterns of behavior can be observed in reactive distillation columns or other integrated reaction separation processes with fast reversible reactions [11, 23] as illustrated in Fig. 5.3 for a pure rectifying column with a ternary mixture and a reaction of type 2B A + C taking place in the liquid phase. However, due to the reaction equilibrium the profiles consist of a single concentration front, which is clearly different from the nonreactive problem illustrated in Fig. 5.2. 

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