Estireno

9/17/99

ChE 182 Major 1 Styrene Production
Styrene is the monomer used to make polystyrene, which has a multitude of uses, the most common of which are in packaging and insulated styrofoam beverage cups. Styrene is produced by the dehydrogenation of ethylbenzene. Ethylbenzene is formed by reacting ethylene and benzene, and most benzene is made by hydrodealkylation of toluene, which isobtained as a byproduct of gasoline manufacture. There is very little ethylbenzene sold commercially. Most ethylbenzene manufacturers convert it directly into styrene. The plant at which you are employed currently manufactures ethylbenzene, styrene, and polystyrene. The unit to which you are assigned, Unit 500, converts the ethylbenzene into styrene, producing around 100,000 metric tons per year of 99.8wt % styrene.

Styrene Production Reactions
The reactions for styrene production are as follows:

C6 H 5C2 H 5 ethylbenze ne C6 H 5C2 H 5

→
2

1

C6 H 5C2 H 3 styrene

+

H2

(1)

hydrogen + C2 H 4 ethylene + CH 4 methane

→
4

3

C6 H 6 benzene

(2)

ethylbenze ne C6 H 5C2 H 5 + H2

→

C6 H 5CH 3 toluene

(3)

ethylbenze ne hydrogen

Process DescriptionThe process flow diagram is shown in Figure 1. Ethylbenzene feed is mixed with recycled ethylbenzene, heated, and then mixed with high-temperature, superheated steam. Steam is an inert in the reaction, which drives the equilibrium shown in Equation (1) to the right by reducing the concentrations of all components. Since styrene formation is highly endothermic, the superheated steam also providesenergy to drive the reaction. The reactants then enter two adiabatic packed beds with interheating. The products are cooled, producing steam from the high-temperature reactor effluent. The cooled product stream is sent to a three-phase separator, in which light gases (hydrogen, methane, ethylene), organic liquid, and water each exit in

H-501 steam heater E-501 feed heater

E-502 interheaterR-501 styrene reactor

R-502 styrene reactor

E-503 product cooler

E-504 E-505 V-501 C-501 product product three- comprescooler cooler phase sor separator

P-501A/B waste water pump

T-501 E-506 benzene reboiler toluene column

E-507 P-502A/B V-502 condenser reflux reflux drum pump

T-502 E-508 E-509 P-503 A/B styrene reboiler condenser reflux column pump P-504 A/B benzene toluenepump P-505 A/B P-506 A/B styrene recycle pump pump

29
hps

23 P-506 A/B 19

1 ethylbenzene

2 E-501

3 8

9 C-501 26 P-504 A/B

hydrogen

16 R-501 T-501
FIC

E-507
cw

21

benzene toluene

H-501 7 5 4 lps 6

ratio

10

E-502 25 to steam plant

V-501
17

FIC

V-502

LIC

20

11

P-502 A/B T-502
LIC FIC

E-509
cw

ratio

R-502
12

V-503LIC

15

18

lps

22

E-503
bfw hps cw

E-506
LIC

P-503 A/B

13
lps

bfw

14 E-508 E-505 P-501 A/B 28
lps

P-505 A/B 24 27

styrene

E-504

waste water

Unit 500: Production of Styrene from Ethylbenzene

separate streams. The hydrogen stream is further purified as a source of hydrogen elsewhere in our plant. The benzene/toluene stream is currently returned as afeed stream to our petrochemical facility. The organic stream containing the desired product is distilled once to remove the benzene and toluene and distilled again to separate unreacted ethylbenzene for recycle from the styrene product. The styrene product can spontaneously polymerize at higher temperatures. Since our product styrene is sent directly to the polymerization unit, experiencesuggests that as long its temperature is maintained below 125°C, there is no spontaneous polymerization problem. Since this is below styrene’s normal boiling point, and since low pressure pushes the equilibrium in Equation (1) to the right, much of this process is run at vacuum.

Problem
Recently, Unit 500 has been periodically operating outside of standard conditions. There are significant process...