Mtbe Control

The two fresh feedstreams to the column are a pure methanol steam and a C4 stream containing the reactive isobutene and the nonreactive n-butene. The bottoms from the column is mostly MTBE. The distillate is mostly n-butene.

15.1.1 Steady State

Figure 15.1 gives the steady-state conditions and equipment parameters found in Aspen Plus. The methanol and the C4 stream are both fed on stage 10 at the bottom of the reactive

Reactive Distillation Design and Control. By William L. Luyben and Cheng-Ching Yu Copyright # 2008 John Wiley & Sons, Inc.

Figure 15.1 The MTBE Aspen Plus steady-state conditions.

Figure 15.1 The MTBE Aspen Plus steady-state conditions.

zone (stages 4-10) of a column with 15 total trays (17 stages in Aspen notation with the reflux drum being stage 1). Figures 15.2 and 15.3 give composition and temperature profiles, respectively.

The dynamic simulation was converged to a steady-state condition after the control structure discussed in Section 15.1.2 was installed. The results (Fig. 15.4) are essentially the same as those found in Aspen Plus (Fig. 15.1). The flowrate of the C4 stream is specified to be the same (1976 kmol/h), but the methanol feed is slightly smaller (768 kmol/h in the dynamic steady state vs. 776 kmol/h in the original steady state). The bottoms MTBE flow-rate and purity are the same, but the distillate flowrate is slightly smaller (1361 kmol/h in the dynamic steady state vs. 1385 kmol/h in the original steady state). The reason for this difference is the slightly higher purity of the distillate: 93.0 mol% n-butene in the dynamic steady state versus 91.8 mol% n-butene in the original steady state. The distillate contains less methanol (5.7 vs. 6.6mol%), so less methanol needs to be fed.

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