Chemical Design Ethylbenzene

1.0 IN TRODUCTION TO PRODUCTION OF ETHYL BENZENE

1.5 PROCESS SELECTION

In order to produce ethyl benzene as a desired product, there are a few process available which are by unique process of toluene, super fractionation of mixed aromatic hydrocarbon and alkylation of benzene with ethylene.The most suitable process for production ethyl benzene is alkylation of benzene with ethylene. This process produce high purity of ethyl benzene as a main product compared to other manufacturing process. Less of pure ethylene and benzene has been used in this process. This process also has low operating condition and the cost of production is lower than other process. 1.6 REACTION SCHEME THERMODYNAMIC

thyl benzene is produced by alkylation of benzene with ethylene, illustrated by the following chemical reaction!

C" H" C# H$ C" H%C# H% benzene ethylene ethylbenzene &enzene alkylation process, for the production of ethyl benzene, consists of three basic steps. The alkylation reaction takes place at high pressure and low temperature. Typically, ethylene!benzene molar ratios between '.(% and '.# are used. The reactor inlet temperature is controlled by recycling a small portion of the reactor effluent. In transalkylation step, in which poly ethyl benzene at presence of benzene are converted to ethyl benzene on a reverse alkylation process. Transalkylation takes place in a separate reactor . Then in separation step, in which unreacted benzene, poly ethyl benzenes and other components enter benzene recovery column and separated from each other. The bottom for the benzene recovery column is sent to a product column, where ethyl benzene of ) **.*+ purity is taken overhead. or this reason # distillation columns has been used. The final product is obtained in liquid phase.

2.1 CHEMICAL DESIGN FOR DISTILLATION COLUMN

2.2 INTRODUCTION

STREAM 17 FLOWRATE : 13, 321.5 kg/hr COMPONENT : Benzene ,

STREAM 1'

Eh!"#enzen$ T%&"ene

FLOWRATE : 2(,3(5.) kg/hr COMPONENT : Benzene, Eh!"#enzene, 1,(*+ Eh!"#enzene

STREAM 1FLOWRATE : 11 2(.5 kg/hr COMPONENT : Benzene, Eh!"#enzene, 1,(*+ Eh!"#enzene

igure (! -istillation column T/'( -istillation column is use to produce high purity of liquid product at operating condition. 0ince this criteria is crucial, therefor e a suitable distillation column need to be chosen wisely since it will effects the purity and amount of production. The purpose of T/'( is to separate the ethylbenzene others chemical in stream (1. 2s a result , ethyl benzene discharged from the top of T/'# as a liquid together with other light component. The bottom outlet of T/'# contains no benzene.

3ame

4nit

8apor fraction Temperature :ressure ;olar flow

9 k:a kmol30T23T The equilibrium constant can be calculated as follows !

Table 1 : Ki value for stream 16

+i, b 0.0000084 0.96363 0.030#2

*iXi,t

i

@i 0.9993 0.00918 '.7$% 0 '.((* '.'#

@i, t (.''% (.7 '

dew

T

use b ? 1(.$

Table 2 : Ki value for stream 17

Table 3 : Ki value for stream 18

#.$

DL2TI8 8>L2T2LITI0 Delative volatility,G is the volatility separation factor in vaporliquid system. In other words, it is the volatility of one component divided by the volatility of the other. The greater the value of G, the easier will be the desired separation. The relative volatility can

be calculated between any two components in a mixture. &ased on @ values the relative volatility can be expressed as belows

which is subscript L@ for light key and B@ is for heavy key. The component separated are called light key, which more volatile . The component more volatile than light key are called light key components and will be present in the bottom in small amount. The component less volatile than the heavy key are called heavy component and will be present in the distillate in small amount.5Heankoplis,#'($6. Light component is the component of feed mixture which is desired to be kept out of the bottom product while heavy key component is a component of feed mixture which is desired to be kept out of the top product. Thus, the selection of key component is as below! Light key ? &enzene Beavy key ? thylbenzene 9omponent

@i, f

Gf

&enzene

'.7

%$".#"

thylbenzene

'.((*

(

(,$-iethylbenzene

'.'#

'.("1

T#"e ( : 0 "&e %r re4 1'

9omponent

@i, t

Gt

&enzene

(.''%

'.%*

thylbenzene

(.7

(

(,$-iethylbenzene

'

'

T#"e 5 : 0 "&e %r re4 17

9omponent

@i, b

Gb

&enzene

'.''%

'.''%

thylbenzene

(.'7%

(

(,$-iethylbenzene

'./

'.#1

T#"e ' : 0 "&e %r re4 1-

The following approximation may be used to calculate the average relative volatility !

=here is Gf

? relative volatility of light key to heavy key at feed of column

Gt

? relative volatility of light key to heavy key at top of column

Gb

? relative volatility of light key to heavy key at bottom of column

9omponent

GL@,B@ eed

&enzene L@ 56 thylbenzene5B@6 (,$ -iethylbenzene

".#"

Top '.%*

Table #.(#, G average value for all stream

&ottom '.''%

( '.("1

Gavg

( 

'.$$7 (

(

'.#1

'.##$

#.% DL4E D2TI> The minimum reflux ratio can be estimated by using the method of approximation evolved by 9olburn 5(*$(6 and the exact procedure of 4nderwood 5(*$16. The equation can be express as belows

Gi

? relative volatility of component i with respect to some reference

Dm

? minimum reflux rati

Ei,d

? concentration of component i in the tops at minimum reflux

 is the root of the following equation

xi,f ? concentration of component i in the feed q ? depends on the condition of the feed The value of q is given by

Bv,feed ? Latent heat of the feed 9p,feed ? 0pecific heat of the feed

T

7/." 9

Tbubble

7/." 9

0pecific heat

(//.% J 0T2H0 ;inimum stages

α

√ αLF αLD α LW 2



,a

 √ ( 6.26 )( 0.56 )( 0.005 ) 2

 2.83

X LK X HK

¿

X HK X LK

¿ ¿ ¿b log ¿ N m=¿ 0.9943 0.0054

¿ ¿

0.8964 0.00168

¿ ¿b log ¿ ¿¿

/m  11.#6 sta(es !eoetial sta(es

R = 0.408 =0.29 R + 1 0.408+ 1 Rmin 0.272 = =0.213 Rmin +1 0.272+ 1 Nm =0.49 N 11.76

N

=0.49

N =24 theoretical stages( 23 trays + 1 reboiler)

LOCATION OF FEED TRAY

log

( )(

Ne ! = 0.206log [ Ns D

xf , HK xf , LK

)(

)

2

Xb, LK ] Xd , HK

=here EL@,- ? mol fraction of light key in distillate EB@,- ? mol fraction of heavy key in distillate EB@,& ? mol fraction of heavy key in bottom EL@,& ? mol fraction of light key in bottom Ga ? average relative volatility of light key

log

(

Nr 101.1 =0.206log [ Ns 170.2

)(

0.6244 0.3373

)(

0.8964 0.00168

)] 2

Nr = 0.47 Ns 3r  3s?# $ '.$73s  3s? #$ 3s? ("./# This mean feed tray is (" trays from top

#.1 9>L4;3 I9I39F The prediction of overall column efficiency can be obtained from the correlation given by >A9onnell below!

=here Ma ? the molar average liquid viscosity, m3s  1(5.(  Aerge e4;er&re  113.( C/3-'.( ?

Component

5 

5 B

X

F

7ean isosit" 2

isosit"

&m/sm )

&m/sm2)

Benzene

328.49

182.48

0.6244

0.22

0.13#

t!"lben

410.$8

219.6#

0.33#3

0.1$

0.0$1

1,4

-

-

0.0381

3.6

Thus the average µa can be calculated as below µa

=

'.(/7  '.'%(  '.(/7

? './#% >verall efficiency is '

?%(  /#.% log5'./#%x /.$"#6 ? $*./$ +

2.) N@MBER OF ACT@AL STAES #! &ng e % %er"" r! een!, E%

=

n&4#er % 6e" r! / n&4#er % &" r!

N&4#er % &" r!  23 / .()33 = ('.'2  (' r!

-30ITF 23- DL2TI8 ;>L2D ;200

0.13#

Component

feed

Distillate

bottom

7ola ei(!t &(mol)

Benzene

0.6244

0.9943

0.0016

#8.11

" ,liq# id

&:(m3) 8#6

8 t!"lben

0.33#3

1,4

0.0381

0.00$4 0

0 .8964 0.1024

106.1# 134.22

866 862

Relative Molar Mass, RMM

RMM = Ʃ ( Component mole fraction x Molecular weight)

RMM at feed =(0.6!!x"#.$$) % (0.&&"&x$06.$") % (0.0&#x$&!.) =#'.0 g*mol

RMM at +istillate(op -roduct)

=(0.!& x"#.$$) % (0.00'! x$06.$6') % (0 x$&!.$#$) ="#.& g*mol

RMM at ottom -roduct

=(0.00$6# x"#.$$) % (0.0#6! x$06.$") % (0.$0! x$&!.) =&.& g*mol +ensit/ top

i1uid densit/, 2 = (0.!&x#"6) % (0.00'!x#66) % (0x#6)

= #"!.06 g*m&

3apor densit/, 23 = ("#.& g*mol * .! m&*mol)("& 4* &'!.! 4) ($.0' 5ar * $5ar)

= .# g*m&

.$$ C7M8 +9:M;;R

he important factor that affects the column diameter is vapor flowrate. he vapor velocit/ should 5e 5elow than which would cause excessive li1uid entrainment or high pressure drop. o estimate the maximum allowa5le superficial vapor velocit/, we use owenstein ($6$) e1uation<

or diameter column a5ove than $ m, plate spacing of 0.& to 0.6 m will normall/ 5e used, and 0.! m ($' in.) can 5e taen as an initial estimate.

(Coulson > Richardon, 00&) 9n this design, taing plate spacing as 0.& m, the allowa5le superficial vapor velocit/, calculated is<

1

"l − "$ 2 ¿ "$ 2 ❑ %$ = (−0.171l t + 0.27 l t −0.047 ) ¿

1

874.06− 2.82 2 ¿ 2.82

%$ =(−0.171 ( 0.3 )❑+ 0.27 ( 0.3 )− 0.047 ) ¿ 2

?'./#7

he column diameter, + c can 5e determined from the e1uation <

+c =

?here 3 = the maximum vapor rate,g*s

:5ove the feed point,

3apor flowrate, 3n = + (R % $)

3n = $& &$.' g*h (0.!0#% $)

i1uid flowrate, = $# "'6.6" g*h

n = 3n @ +

elow the feed point, n = $# "'6.6" A $& &$.' ='!&'.$"g*h

i1uid flowrate, m = n % 

m = '!&'.$"% ! &!'.

=  "#$.0" g*h

=  "#$.0" g*h x ($ h * &600 s)

= #." g*s

3apor flowrate, 3m = m @ ?

3m =  "#$.0" @$$ 0!.'

= $# "'6.'" g*h

= $# "'6.'" g*h x ($ h * &600 s)

= '.$ g*s

Dc

=

√

(

)

4 5.21 & 2.82 8.27

(

)(

) ? '.%/ m

Column area,:c can 5e calculated using<

'c =

& ( 0.53 ) 4

? '.## m

#

2

2.12 COL@MN E9T Wh%& %n6erng he kr %r n! &;;%r, he %"&4n hegh n #e "&"e6 &ng he e&%n #e"% D =r! ;ng  2> D =N%. ge  1> =;"e hkne> C%"&4n hegh  =('>=.3> D =.3  2> D =('*1>=.5>  1(.'25 4  1'.) 4 =n"&6ng 1G e! %r>

.$ C7M8 B;9B

?ithout considering the sirt or an/ support, the column height can 5e calculated using the e1uation 5elow<

5/ nowing<

the plate thicness is 'mm tra/ spacing is 0.!m

Column height = (8o. stage )(tra/ spacing) % (tra/ spacing x )

% (8o. stage @ $)(plate thicness)

Column height = (6&)(0.!) % (0.! x ) % (6&A$)(0.00')

= 6.&$ m

= #.! m (including $0D safet/ factor)

.$& E7MM:RF  CB;M9C: +;E98

9n chemical design, it focuses on the internal part of distillation column which specificall/ a5out the pacing, feed location stages of column and others.

+ew point emperature (top)

#$.!C

u55le point emperature (5ottom) $!'.!C

u55le point temperature (feed) "&.6 C

Minimum num5er of stages $$."6 stages

Reflux ratio 0.!0#

eed point location ra/ 6

8um5er of theoretical stages ! stages

verall tra/ efficienc/

0.!&!

8um5er of actual tra/s !6 tra/s

Column diameter 0.'&m

Column height $6.0m