S

90 100 110 120 130 140 150 160 R [kmol/h]

Figure 7.11 Nonmonotonic behavior of MeAc reactive distillation column.

with little difficulty. Monotonically decreasing temperature profiles can also be seen for the IPAc system. The material balance lines in Figure 7.10 show how separation is achieved around the decanter.

7.4.3 Type III: BuAc and AmAc

For the BuAc system, acetic acid has the second highest normal boiling temperature and therefore the acid is reacting away in the lower part of the reactive zone, as shown in the upper graph in Figure 7.14. The composition profile in the stripping section clearly shows that the stripper is performing the BuOH/BuAc separation. Because of a large LL envelope, only four rectifying trays are needed to drive the condensate of the top vapor into the LL zone. We also observed that significant conversion occurs in the upper section of the reactive zone where two feeds are located nearby. The concentration effects of these two reactants enhance the reaction in that region. The lower graph in Figure 7.14 shows an almost monotonic temperature because the two reactants are close boiling components with a 1 °C temperature difference in the normal boiling points. The vapor and liquid composition profile in a three-dimensional plot (Fig. 7.10) clearly shows the separation characteristic in the stripping section (along the BuOH/BuAc edge) as well as in the LL envelope.

For the AmAc system, AmOH has the second highest normal boiling point temperature (which is different from the ranking for the BuAc system). In theory, we should consume most of the alcohol in the reactive zone. Because we do not have stringent product specifications on the alcohol, a small amount of AmOH is allowed to leave the reactive zone. Still, the stripping section is performing the separation between HAc/AmAc, as demonstrated in the upper graph in Figure 7.15. Because the AmAc system has a larger LL envelope compared to the BuAc system, only two rectifying trays are required to drive the overhead condensate into the LL zone. A major portion of the reaction takes place in the upper section of the reactive zone where the two feeds are located. However, fewer reactive trays are required to react away the heavy reactant, compared to the BuAc system. A

NFhac&NFBQH

NFhac&NFBQH

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