Reactive Distillation Column Cl

The temperature on stage 31 is controlled by manipulating the reboiler heat input with a 1-min dead time. Relay-feedback testing and Tyreus-Luyben settings give Kc=038 and T/= 7.9 min with a 100 K temperamre transmitter span and a reboiler heat input range from 0 to twice the steady-state value. 

The reflux-drum level is controlled by the distillate. The reflux ratio is controlled by measuring the distillate flowrate, sending this signal to a multiplier ( Ratio ) and sending the output signal to the setpoint of the reflux flow controller. The base level is controlled by manipulating the bottoms flowrate. 

---

Figure 9.7 gives the flowsheet of the process. There is a prereactor upstream of the reactive distillation column Cl. The flowsheet contains three distillation columns (one reactive) and there are two recycle streams (methanol and water). The design of the prereactor and reactive column is based on the study of Subawalla and Fair. ... 

The reactor effluent is fed into a 35-stage reactive distillation column (Cl) on Stage 28. Catalyst is present on Stages 7-23. The reactor effluent is fed five trays below the reactive zone. A methanol stream if fed at the bottom of the reactive zone (Stage 23). The flow rate of the methanol fed to the reactive column is 235 kmol/h. 

The control structure for the prereactor and reactive distillation column Cl is shown in Figure 14.7, The control structure for the extractive distillation column C2 and the methanol recovery column C3 is shown in Figure 14.8. 

Figure 5.12 gives the flowsheet for the entire process. The distillate from the reactive distillation colmnn Cl has a methanol concentration of 28.1 mol%. It is fed into the two-column pressiu e-swing methanol recovery system. Equipment sizes and economic data are given in Table 5.3. 

Trichloro-l,3,5-triazine (1 37 g, 0.15 mol) and 2-chloro-3-isobutoxypropyl bis(2,3-dichloropropyl) phosphite (126 g, 0.3 mol) in a 500-mL flask equipped with a short distillation column, were stirred and slowly heated to 110°C under reduced pressure while low-boiling by-products were collected (33 g theoretical amount 41 g). NMR spectra showed this to be mainly 1,2,3-trichloropropane, the expected byproduct, />-Toluencsulfonic acid (1 g) was added and the mixture heated at 125 °C until dealkylation of the isobutoxy groups was observed, by NMR spectra, to be complete. The product was very viscous and was taken up in toluene (300 mL) some product was lost due to foamover. The toluene was then distilled off under reduced pressure to give a resin-type product crude yield 107 g (100%) mol wt of solid 714.0 (34.7 % Cl, 8.7 % P, 2 reactive OH groups). The product was taken up in Voranol 490 (polyalcohol mixture 41 g) and used to prepare polyurethane foams. 

Figure 8.25 gives composition profiles in reactive column Cl. Note the low concentration of methanol in the lower part of the column and the fairly high concentration of one of the reactants (2M2B) in the same zone. This is below the reactive trays, which are stages 7-23. Figure 8.26 shows the temperature profile. The reflux ratio is 4, which gives a bottoms purity of 99.2 mol% TAME and a distillate impurity of 0.1 ppm TAME. 

The reactor and column Cl are identical to those used in the pressure-swing process. The methanol-containing distillate Di 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 (reflux-dmm temperature = 326 K). Reboiler heat input is 5.96 MW. The overhead vapor is condensed and it is the C5 product stream. 

---