Type II EtAc and IPAc

Very similar composition profiles are observed for the IPAc system and, again, most of the conversion takes place in the column base of the reactive distillation column (Fig. 7.13). The separation in the stripper is quite straightforward, and high purity IPAc can be achieved 

Before leaving this section, it should be pointed out that the type III flowsheet is probably the most general configuration for acetic acid esterification. In addition to BuAc and AmAc systems, the production of w-propyl acetate, isobutyl acetate, isoamyl acetate, and -hexyl acetate also fall into this category when economic factors arc taken into consideration. 

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Type II EtAc and IPAc. The type II flowsheet differs from type I in that the reactive zone extends to the column base of the first column (called the reactive distillation column) therefore, a much larger holdup is expected in the bottom of the reactive distillation column (Fig. 7.2). The column base holdup is taken to be 10 times that of a reactive tray holdup. We also assume the feed ratio of the reactant can be changed, which leads to the following optimization variables Nr, Ns, Nrx, fVFheavy. NFiight, and FR. 

Next, the RGAs are computed for variable pairings. The results show that for type I (MeAc) and type II (EtAc and IPAc) flowsheets, the composition is controlled with the heat inputs and the feed ratio is used for temperature control. However, for the type IB flowsheets (BuAc and AmAc), the acetate composition is maintained by changing the feed ratio and the tray temperature is controlled using the heat input (Table 13.5). The variable pairing in Table 13.5 indicates that severe nonlinearity will be encountered for the MeAc system and possibly also the AmAc systems. The multiplicity analysis in Figure 13.4 reveals that both input-output pairs (Xd.HzO-Gj and Tn-FR) show input multiplicity for the MeAc system. For the AmAc system, the 2fB,AmAo-FR pair also exhibits input multiplicity. The accompanying difficult control problem cannot be prevented if we choose to control product composition for the MeAc system. 

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