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Unformatted text preview: K and 11 bar. Methanol feed of 215.5 mol/s at 320 K and 11 bar to stage 10.
Column operates at 11 atm and has 15 equilibrium stages, with a total condenser and partial
reboiler. Reflux ratio = 7 and bottoms flow rate is set at 197 mol/s. Catalyst for the reaction is
provided in the amount of 204.1 kg/stage only at stages 4 through 11. Kinetic data is given in
Example 11.9, but substitute activities for mole fractions in the kinetic equations. Use
UNIQUAC method for liquidphase activity coefficients, with the binary interaction parameters
in Example 11.9, and RK EOS for vaporphase fugacities.
Find: Distillate and bottoms products, and comparison of results with those of Example 11.9.
Analysis: Kinetic equations for the reaction rates are most often written in terms of component
concentrations, component mole fractions, or component partial pressures (in the case of gasphase reactions). However for liquidphase reactions when the components form a nonideal
solution, chemical equilibrium can only be satisfied when the rate equation is written in terms of
activities (product of mole fraction times liquidphase activity coefficient). For the formation of
MTBE from isobutene and methanol, the Rehfinger and Hoffmann article was developed in
terms of component activities. However, in Example 11.9, component mole fractions are used,
as seen in Eqs. (1) and (2). This assumes that all component activity coefficients are equal to
one. With Aspen Plus, builtin kinetic ratelaw expressions are not available in terms of
activities. Therefore, a FORTRAN subroutine for the ratelaw must be provided. On the
following four pages, the Aspen Plus input data are listed for solving this exercise. Under the
Aspen Plus paragraph REACTIONS RMTBEU REACDIST, reference is made to the usersupplied subroutine RAMTBE. This subroutine is listed on the subsequent five pages, where the
kinetic rate equation is written in terms of activities. The Aspen Plus input data are written to
explore the variation of methanol feed stage. For methanol fed to stage 10, the conversion of
isobutene, when using activities, is 99.5% compared to a 95.6% conversion in Example 11.9,
where mole fractions are used. Analysis: (continued) Exercise 11.23 (continued) Analysis: (continued) Exercise 11.23 (continued) Analysis: (continued) Exercise 11.23 (continued) Analysis: (continued) Exercise 11.23 (continued) Exercise 11.23 (continued)
Analysis: (continued) Analysis: (continued) Exercise 11.23 (continued) Exercise 11.23 (continued)
Analysis: (continued) Analysis: (continued) Exercise 11.23 (continued) Analysis: (continued) Exercise 11.23 (continued) Exercise 11.24
Subject: Reactive distillation of isobutene (IB) with methanol (M), in the presence of nbutene
(NB) to produce MTBE. Chemical equilibrium at each stage that has catalyst.
Given: Mixed butenes feed of 195.44 mol/s of IB and 353.56 mol/s of NB entering stage 11 as
a vapor at 350 K and 11 bar. Methanol feed of 215.5 mol/s at 320 K and 11 bar to stage 10.
Column operates at 11 atm and has 15 equilibrium stages, with a total condenser and partial
reboiler....
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 Spring '11
 Levicky
 The Land

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