Producción de estireno

Energy Balances and Numerical Methods Design Project Styrene Production
Process Description Figure 1 is a preliminary process flow diagram (PFD) for the styrene production process evaluated in the Fall semester 1999 in ChE 40. In this process, styrene is manufactured by the dehydrogenation of ethylbenzene in Unit 500. The reaction is endothermic, reversible, and limited by equilibrium. Reactionoccurs at high temperature (800 - 950 K) and low pressure (0.4 - 1.4 bar) in order to shift the equilibrium to the right to favor styrene production. The raw material is ethylbenzene, which is preheated in E-501 to a saturated vapor. This is then mixed with steam (produced from the fired heater H-501) to provide the heat of reaction and to serve as an inert diluent to help shift the reaction tothe right. The steam to ethylbenzene ratio entering R501 in Stream 6 ranges between 6 and 12. Steam also tends to limit side reactions and helps to extend catalyst life by reducing coke formation on the catalyst. In reactor R-501 the process uses a proprietary iron catalyst that minimizes (but does not eliminate) side reactions at higher temperatures. For simplicity, assume that the only sidereaction that occurs in R-501 is the hydrogenation of ethylbenzene to form toluene and methane. The primary reaction is equilibrium limited and is assumed to approach 80% of equilibrium. The selectivity of the toluene side reaction is a function of reactor temperature. The reactor effluent, Stream 7, is cooled in E-502 to produce steam and then enters a three-phase separator (V-501). The bottomphase of V-501 is waste water stream (Stream 11), which must be decanted and sent for further processing before discharge. Stream 9 leaves the top of the separator and contains all the light gases (methane and hydrogen) and can be used as a fuel gas. Stream 10 contains most of the toluene, ethylbenzene, and styrene. Stream 10 flows through a pressure reducing valve and then enters a distillationtrain (T-501 and T-502) where most of the toluene is removed at the top of first column (T-501) in Stream 17. The remaining toluene and all the ethylbenzene and styrene leaving the bottom of this column in Stream 15 enter the second column (T-502). From T-502, Stream 20 is recycled and mixed with fresh ethylbenzene before the reactor. The bottom product of T-502 leaving in Stream 18 contains thestyrene leaving Unit 500. Process Details Feed Streams Stream 1: Stream 4: fresh ethylbenzene, assume available as a liquid at 30EC. low-pressure process steam available from elsewhere in the plant, to be superheated and used as diluent and heat source for mixture entering reactor in Stream 6.

H-501 steam heater

E-501 feed preheater

R-501 styrene reactor

E-502 product cooler

P-501A/Bwaste water pump

V-501 threephase separator

T-501 toluene column

E-503 condenser

E-504 reboiler

V-502 reflux drum

T-502 styrene column

E-505 condenser

E-506 V-503 reboiler reflux drum

P-502 A/B P-503 A/B styrene toluene pump pump

20
hps

1 ethylbenzene

2 E-501

3

6 R-501 E-503 9
cw

DistillationTrain 16 T-501 P-503 A/B V-502 13 V-501 E-505 17hydrogen methane

toluene

H-501 5 4 Lps Air ng
cw

7 E-502 8

10

12

cw

T-502 14 E-504
lps

V-503 19

11

15

21 E-506
lps

styrene 22 P-502 A/B

18 23 P-501 A/B

waste water

Unit 500: Production of Styrene from Ethylbenzene

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Effluent Streams Stream 9: light-gas stream of hydrogen and methane with traces of water vapor and small amounts of ethylbenzene andtoluene. Take credit as a fuel gas for hydrogen and methane in this stream only. 99% pure toluene with small amounts of ethylbenzene and styrene. The toluene in Stream 17 is at least 95% of the toluene produced. This stream can be sold as byproduct, but it should not exceed 2% of styrene production. styrene crude product of at least 99.0 wt% purity, 100,000 metric tons/yr, with small amounts of...