Extractive Column C2

Methanol-containing distillate Dj from the top of the reactive column is fed to stage 6 of a 12-stage extraction column. Water is fed on the top tray at a rate of 1050 kmol/h and a temperature of 322 K, which is achieved by using a cooler (heat removal = 1.24 MW). The column is a simple stripper with no reflux. The column operates at 2.5 atm so that cooling water can be used in the condenser (decanter temperature = 326 K). Reboiler heat input is 5.96 MW.

The overhead vapor is condensed and fed to a decanter in which the two liquid phases are separated. The organic phase is the chemically inert C5s, and the aqueous phase is mostly water.

This column is designed by specifying a very small loss of methanol in the overhead vapor (0.01% of the methanol fed to the column) and finding the minimum flowrate of extraction water that achieves this specification. Adding more than 10 trays or using reflux did not affect the recovery of methanol. The bottoms is essentially a binary

Length meter

Block C1 : Liquid Composition Profiles

Block C1 : Liquid Composition Profiles

Figure 14.3 Composition profiles in reactive column.

Btock CI: Temferature Profle

Btock CI: Temferature Profle

Stage

Block C2 Temperature PioBe

Block C2 Temperature PioBe

SI age

methanol/water mixture (23.5 mol% methanol), which is fed to the methanol recovery column.

Figure 14.5 gives the column temperature profile, which shows a sharp temperature break over a small number of trays. There is a large temperature difference between the upper section above the feed (^300 K) and the stripping section below the feed 370 K). This will affect the control system used in the column, as discussed in the next section.

The column base and the decanter are sized to provide 5 min of holdup when 50% full under steady-state conditions. The column diameter is 1.74 m.

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