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5.2 6 7 8 9 10 11 12 Catalyst loading, lVcat bot

Figure 16.26 (a) Effect of catalyst loading in column base (Wcatbot) on TAC for single reactive tray configuration and (b) tradeoff of operation cost (excluding catalyst cost), capital cost, and catalyst cost.

5.2 6 7 8 9 10 11 12 Catalyst loading, lVcat bot

Figure 16.26 (a) Effect of catalyst loading in column base (Wcatbot) on TAC for single reactive tray configuration and (b) tradeoff of operation cost (excluding catalyst cost), capital cost, and catalyst cost.

Condenser

Condenser

Condenser

Condenser

EtAc 1.50% EtOH 2.18% H20 96.31% HAc 1.04e-03% 60.44 kmol/h

Aqueous Product

Organic Reflux 502.35 kmol/h

Column

Feed to Stripper

EtAc 71.48% EtOH 5.68% H20 22.84% HAc 2.25e-03% 221.54 kmol/h

Organic Reflux 502.35 kmol/h

Column

Duty 6317 kW

EtOH Feed 57.472 kmol/h EtOH 87.0% Water 13.0%

Feed to Stripper

EtAc 71.48% EtOH 5.68% H20 22.84% HAc 2.25e-03% 221.54 kmol/h

EtAc 1.50% EtOH 2.18% H20 96.31% HAc 1.04e-03% 60.44 kmol/h

Aqueous Product

Stripper

Duty 6317 kW

Duty 1979 kW

EtAc 99.00% EtOH 0.91% H20 0.08% HAc 0.01% 47.82 kmol/h

Duty 1979 kW

EtOH Feed 57.472 kmol/h EtOH 87.0% Water 13.0%

EtAc 99.00% EtOH 0.91% H20 0.08% HAc 0.01% 47.82 kmol/h

Figure 16.27 Optimized single reactive tray configuration (reactive distillation single reactive tray) for EtAc production.

intuitively appealing because it has the advantage of easy catalyst replacement. However, simulation results show that, with the same catalyst weight as that of the reactive distillation column (Wcat,RD = Wcat,bot + Wcat trays), the single reactive tray configuration is infeasible for the given purity specification. In fact, the required catalyst loading is 5.2xWcat,RD. Figure 16.25 clearly shows that the acid concentration at the column overhead cannot reach the specification unless a substantial increase in the catalyst loading is made. Thus, the performance of the single reactive tray configuration is not as good as that of the reactive distillation. The conversion is only 93% with the same catalyst loading (1 x Wcat,RD) as opposed to 99% for reactive distillation.

To obtain an improved design for the single reactive tray configuration, the TAC is computed as the amount of catalyst in the column base Wcat,bot is varied. As the catalyst holdup Wcat,bot is increased, the capital and energy costs decrease and the catalyst cost increases. The optimized single reactive tray design gives a catalyst loading of 8.5 x WcatRD, and the energy cost increases by 24% as shown in Figure 16.26. The improved single reactive tray design is demonstrated in Figure 16.27 with an organic phase reflux ratio of 2.27 as opposed to 1.76 for reactive distillation. The optimized single reactive tray configuration has a TAC that is 30% greater than that of the reactive distillation configuration (Fig. 16.28). The result reveals that, despite having almost 90% conversion in the column base for reactive distillation, additional reaction stages are

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