Multivessel heteroazeotropic batch distillation

A multivessel operation to recover water in the decanter aqueous phase, the entrainer (vinyl acetate) in a middle vessel, and acetic acid in the bottom is explored in this section. The most 

TABLE 13.11 Comparison of Results from Batch Rectifier and Multivessel Operations. 

The extremely simple batch operating sequence that is exactly the same as the one used in the previous section is implemented. The bateh operating sequence is again summarized below. 

Step 1 Charge the total mixture to be separated into the bottom of the column together with some entrainer. In the simulation results the feeds include 2.0 kmol of acetic acid, 2.5 kmol of water, and 1.0 kmol of entrainer. Note that no initial distribution of material into the decanter and the middle vessel is used in the dynamic simulations to reduce total batch time. 

Step 2 Start the heat-up of the column and put all controllers (Stage 23 temperature control, organic phase level control, top column pressure control, and decanter temperature control) on automatic mode. Note that, in this operation, the total reflux period has been eliminated to reduce batch time. 

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Figure 13.35 Overall control strategy for the heteroazeotropic batch distillation system with multivessel.

S. Skouras, S. Skogestad, Separation of ternary heteroazeotropic mixtures in a closed multivessel batch distillation-decanter hybrid, Chem. Eng. Proc. 43 (2004) 291-304. 

If components of a mixture form a heteroazeotrope or by the addition of an entrainer (E) a heteroazeotrope can be formed, the azeotropic composition can be crossed by decantation. In the pharmaceutical and fine chemical industries batch processes including the batch heteroazeotropic distillation (BHD) are widely applied. As far as we know the BHD was exclusively applied in the industry in batch rectifiers (equipped with a decanter) in open operation mode (with continuous top product withdrawal). The batch rectifier (BR) was investigated with variable decanter holdup by Rodriguez-Donis et al. (2002) and with continuous entrainer feeding by Modla et al. (2001, 2003) and Rodriguez-Donis et al. (2003), respectively. Recently the BHD was extensively studied for the BR and multivessel columns by Skouras et al. (2005a,b). 

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