Análise Econômica

The PFD for the EB process is shown in Figure B.2.1.

Alimentação

A refinery cut of benzene is fed from storage to an on-site process vessel (V-301), where it is mixed with the recycled benzene. From V-301, it is pumped to a reaction pressure of approximately 2000 kPa (20 atm) and sent to a fired heater (H-301) to bring it to reaction temperature (approximately 400°C).

Reação

• R-301

The preheated benzene is mixed with feed ethylene just prior to entering the first stage of a reactor system consisting of three adiabatic packed-bed reactors (R-301 to R-303), with interstage feed addition and cooling. Reaction occurs in the gas phase and is exothermic.

• R-302

The hot, partially converted reactor effluent leaves the first packed bed, is mixed with more feed ethylene, and is fed to E-301, where the stream is cooled to 380°C prior to passing to the second reactor (R-302), where further reaction takes place. High-pressure steam is produced in E-301, and this steam is subsequently used in the styrene unit.

• R-303

The effluent stream from R-302 is similarly mixed with feed ethylene and is cooled in E-302 (with generation of high-pressuresteam) prior to entering the third and final packed-bed reactor, R-303. The effluent stream leaving the reactor contains products, by-products, unreacted benzene, and small amounts of unreacted ethylene and other noncondensable gases.

Troca de Calor e Vaso Flash

The reactor effluent is cooled in two waste-heat boilers (E-303 and E-304), in which high-pressure and low-pressure steam, respectively, is generated. This steam is also consumed in the styrene unit. The two-phase mixture leaving E-304 is sent to a trim cooler (E-305), where the stream is cooled to 80°C, and then to a two-phase separator (V-302), where the light gases re-separated and, because of the high ethylene conversion, are sent overhead as fuel gas to be consumed in the fired heater.

Purificação

T-301

The condensed liquid is then sent to the benzene tower, T-301, where the unreacted benzene is separated as the overhead product and returned to the front end of the process.

T-302

The bottoms product from the first column is sent to T-302, where product EB (at 99.8 mol% and

containing less than 2 ppm diethylbenzene [DEB]) is taken as the top product and is sent directly to

the styrene unit.

The bottoms product from T-302 contains all the DEB and trace amounts of higher ethylbenzenes. This stream is mixed with recycle benzene and passes through the fired heater (H-301) prior to being sent to a fourth packed-bed reactor (R-304), in which the excess benzene is reacted with the DEB to produce EB and unreacted benzene. The effluent from this reactor is mixed with the liquid stream entering the waste-heat boiler (E-303).

A PFD para o processo de EB é mostrado na Figura B.2.1 . Um corte de refinaria de benzeno é alimentado a partir do armazenamento para
um vaso no local de processo ( V - 301 ) , onde é misturado com o benzeno reciclado . V- 301 , é
bombeado para uma pressão de reacção de cerca de 2000 kPa ( 20 atm ) e enviado para um aquecedor de irradiação ( H - 301 )
a trazê-lo até à temperatura de reacção ( cerca de 400 ° C ) . O benzeno pré-aquecido é misturado com a alimentação
etileno , imediatamente antes de entrar no primeiro estágio de um sistema de reactor que consiste em três adiabático -embalados
reatores de leito (R- 301 a R- 303) , com a adição de alimentação interstage e refrigeração. Reacção ocorre nos gases
fase e é exotérmica . A quente, efluente do reator parcialmente convertido deixa o primeiro leito fixo , é
misturado com mais alimentação de etileno , e é alimentado a E - 301 , onde o fluxo é arrefecida até 380 ° C antes de serem
passar para o segundo reactor ( R - 302 ) , onde tem lugar ainda mais reacção . Vapor de alta pressão é
produzido em E - 301 , e este vapor é subsequentemente utilizado na unidade de estireno . A corrente de efluente proveniente
R - 302 é igualmente misturado com a alimentação de etileno e é arrefecida em E - 302 ( com a geração de alta pressão
vapor ) antes de entrar no terceiro e último reactor de leito empacotado , R - 303 .