Batch distillation diagram

Simple Batch Distillation Constant a, with Trays or Packing, Constant BoUup, and with Reflux [129] Using x-y Diagram... 

Figure S.2 Batch distillation of benzene-toluene at constant reflux ratio, Example 5,3, ia-e) McCabe-Thiele diagram for progressively reducing still concentration to 0.13 mole fraction benzene.

Hgwe 5.3 (Continued) Batch distillation of benzene-toluene with Wriable reflux ratio, Example 5.4. (o-e) McCabe-Thiele diagram fcr progressively increasing reflux ratio to 13 1. 

Rgure 8-35. Batch distillation constant reflux ratio after McCabe-Thlele diagram. Revised/adapted and used by permission, Schweitzer, PA Handbookaf Separation Techniques for Chemical Engineers, McGraw-Hill Book Co. (1979) also reprinted by special permission, Chem. Eng. Jan. 23 (1961), p. 134., 1961 by McGraw-Hill, Inc., New York. 

Ethanol, with a boiling point of 78.3°C, has a vapor pressure of 760 mmHg at this temperature and consequently forms a higher mole fraction in the vapor space above a heated ethanol/water mixture than it does in the liquid phase. Condensation of the alcohol-enriched vapor mixture obtained in this way produces a solution of ethanol in water again, but now enriched in the concentration of ethanol. In a laboratory batch distillation the process described above may be carried out very easily, but this only achieves a limited (by the liquid-vapor composition diagram) improvement in concentration of ethanol obtained with each repetition of the distillation (Eig. 16.5a). Also, as the distillation proceeds, the concentration of alcohol in the distilling vessel becomes depleted. Consequently there is also a gradual depletion in the alcohol concentration obtained in the vapor, and the condensate from this. Despite these problems, many small distilleries still use batch distillation to raise the alcohol concentrations to the requirement of their product [44]. 

For the production of relatively pure products by batch distillation, the stillpot is usually augmented by a multistage rectification column with reflux. Shown in Figure 12.19 is a flow diagram for a typical batch distillation process. The feed in this example contains components A, B, and... 

FIGURE 12.20 Upper quadrant of a McCabe-Thiele diagram for batch distillation at constant reflux. Four theoretical stages shown. 

If a batch distillation is carried out at variable reflux ratio, it is possible u> maintain a constant purity of distillate and to do this until blocked by material balance limitations, A McCabe-Thiele diagram illustrating this method of operation is shown in Fig. 5.5-11. The value of xu is kept constant, and the slope of the operating line is varied in accordance with the overall material balance, The figure shows the conditions at time 0 and time t. Note that the three equilibrium stages include the stillpot. 

Eqrration (5.1-55) formrrlates the so-called residuum line of a hqttid. This line describes the change of the state of the liqttid phase during batch distillation as shown in the triangrrlar concentration diagram in Fig. 5.1-14. The states of the coexistent vapor phase lie on a tangent to the residuum line. 

In practice, the process of batch distillation is represented in diagrams shown in Fig. 5.1-15. Here, the concentrations in the gas and hquid phase are plotted vs. the relative amormt of distillate. It is important to note that the intermediate boiling... 

At any specific time Eq. t9-26i represents a straight line on a y-x diagram The slope will be IVV, and the intercept with the y = x line will be Xq. Since either x or L/V will have to vary during the batch distillation, the operating line will be continuously changing. 

Figure 9-5. McCabe-Thiele diagram for multistage batch distillation with constant IVD, Example 9-2...

The batch distillation column can also be operated with variable reflux ratio to keep x constant. The operating Eq. 19-261 is still valid. Now the slope will vary, but the intersection with the y=x line will be constant at Xp,. The McCabe-Thiele diagram for this case is shown in Figure 9-7. This diagram relates Xs to Xp). Since Xp, is kept constant, the calculation procedure is somewhat different. 

A7. When there are multiple stages in batch distillation, the calculation looks like the McCabe-Thiele diagram for several... 

The simplest batch distillation method is the straight takeover approach, without reflux, often called a Rayleigh distillation. This is the traditional moonshine still" tedinique, in which a batch of material is charged to a kettle (stillpot), brought to boiling, and the vapor condensed as it passes over from the stillpot. A diagram of this type of operation is shown in Fig. 5.5-9. 

Fig. 2-56. McCabe-Thiele-diagram for calculating the number of theoretical stages for the batch distillation of a binary mixture.

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