Hydrogenation of benzene to cyclohexane

(1)

,

•

• Nr

:

Laboratorium voor Chemische Technologie

~

..

Verslag behorende

bij het fabrieksvoorontwerp

van

.

...

~~.J;j.~~

..

~.·

...

~5?E.~.~~~~.~ ... ~:.~!:: ... .

onderwerp:

adres:

Roland Holstlaan 1108

2624 JS Delft

opdrachtdatum :

29 maart 1982

(2)

•

, '

Hydrogenation

of

Benzene to Cyclohexane

"

N

ever let

_-

vour schoolin

g

_-~

interf

ere

wi

th your education"

[

"

la

r

k

Twain

M

arjan

G

.

X

ort

ekaas

M

.

S

c.

Rol

a

n

d

Holstlaan

11

08 2624 JS

De

lft

April 29,

1

982

(3)

•

• Summary

This

FVO

d

escri

bes the

catalytic

hyd

ro

f,

en

a

tion

of benzene to cycloh

exa

ne

with

a Pt

/

A

1

2

0

3 cat

a

l

yst

.

The process is

desi

g

ned for

a p

ro

duct

ion

capacity

of 1

00 .

000 m

ton

per

yea

r.

The

con

version

for this

process is al

m

ost

complete. The overall selectivity

is

more

than

99.8% calculated on benzene. The

operating conditiohs in th

e

multi-bed

r

ea

ctor

of

100 C

and

6 at

m

make

this

a vapor phase

reaction.

A

second part o

f

this paper

i

s an

invent

a

ri-sation of

some

comm

e

rci

a

lly

ava

il

ab

l

e p

rocess

es

.

(4)

•

• C

o

ntents

I 11

Introduction

Inventarization of

Processes

for

the

Hydro~enation

o

f

B

enzene

1 .

Hydrogenation

of

B

enzene

2 .

Thermodynamics

and

K

inetic

Da

ta

3. Liqu

i

d phase

Hydrogenation

4. Gas phase

· Hydrosenation

5. The Catalyst

6 .

Ove

r

view of Excistin

g

Processes

7. Econom

i

cs

8 .

Conclus

i

on

111

Design

Considerations

1. Capacity of Factory

2. The Catalyst

3. Spec

i

fications

of

Raw Mate

rial

4 .

Specif

i

cations of

End Product

I

V

p

escription of

Process

Flow

Sheet

V

Ca

l

culations for the

Desi~n

1. The Cata

l

yst Volume

2 .

The

Reactor Volume

3. Pressu

r

e

drop

over the

Reactor

4. Heat

Exchan

ge

rs

5. C

o

mpressors and

Pumps

6. Li

qu

i

d

-

gas

Separator

VI

Safe

t

y and Hea

l

th

V

II

Conclusioï1

V

III

Notation

Appendix

1

Appendix 2

Appendix 3 Appendix

3

11. Appendix

4 Appen

d

ix 5

Appendix

6 Appendix

7 References

1

2 2 2 3 4 4 5 7 9

10

10 1e

1

0

1

0

11

12

13

14

15

17

18

19

25

29

30

31

34

3

6

37

3

9

40 42

(5)

-I

I

-I

I

-I

I

-I

I

.

-I.

Intro

duction

Cyclohexane i

s

very

i~portant

due

to it

s use as

a

raw

material for th

e manufacturin

g

of

nylon,

and

as a solvent

for

v

a

rious f

a

ts,

oils, waxes

,

etc

.

(1)

.

There

are two

di~ferent

ways to produce cyclo

-hexane.

About

70%

of

a

ll cyclohexa

n

e

i

s

obtained by the

hydro

g

enation of benzene. The re

ma

inin

s

3 0%

i

s

r

e

-coveredas

natural cyclo

he

xane by

special

fr

act

io-nation and/or isome

ri

za

tion

processes

(2).

The first

route

produces cyclohex

a

ne of the

hi

s

hest purity,

is

the

most

i

mportant

in in

du

s

tr

y

,

and

wi l l

be

used

in

this

paper for the

desig

n of

a

FVO

.

(6)

•

2

Ir. Inventarization of

Processes for the Hydro

?:e

nation

of

Benzene

.

II.1.

Hydro~enation

of Benzene

Since Sabatier developed

the

first

hydro~enation

process for benzene in 1898, it

has become

the

most

i

mp

ort

ant

route to

produce

cyclohexane (3).

The

main

objéctive

of this part of the paper

is

to compare

techno

l

o

g

ical

and economical aspects of

the

most

important

commercial processes

a

v

ailab

le.

Based

on this

study

an

existin

g

or

a

new

process

will

be chosen for

desi

g

n and

reactor

calculations.

II.2. Thermodynamics

and

K

inetic

Data

The

catalytic

hydro

g

enation of

be~ene

to

cyclo-?

hexane is

a very

exother

mic

reaction

(~:~~-51.2

.

k

c

al

/

m

ole) (4).

The operatin

g

conditions

are not

critical

and

can

be taken

in t

he

convential

ran

g

es

.

For

example the pressure

between

1 and

50 atm, and

the temperature

between 50 and

400~

(5).

However

,

to

avoid undesirable

by

-

products

(

methylcyclopen

-tane, benzene iso

me

rization

products),

an

unaccepta-bIe hi

g

h equilibrium

benzene

content

and

hydrocrack-ing, the temperature should be

kept under 230

C

.

Dependin

g

on these

operatin

g

con

d

itions,

the

process can be

c

a

rri

ed out either

in liqui

d

or

mixed

li

qu

i

d

-vapor

phase, or in vapor

pha~e,

in

the

presence of

a

fixe

d bed

of catalyst or

a dispersed

cat

a

lyst.

Because

of th

e

equili

b

riu

m

of

the

re

action

:

(7)

•

3

the conversion

of bel/zene

i

s

g

reater

a

t 101

'

/er

te;npe

r

a

-ture

and

at hi

g

her pressure.

Therefore

most

CO

Gme

r-cia1 processes op

erate a

t

200 C

and 4

0 atm,

in li

qu

id

phase (6,7,8,

9 ,1

0)

,

havin

g

a

con

version

of

more than

99%

.

However, in the last

coupl

e

of

yea

r

s

so~e

ga

s

phase

processes

wer

e

deve

lop

ed

,

operatin

g

at

4

0 0-600

C

and

20-30

atm (11,12).

A

l

so

claimin

g

a

conver-sion

of

more

than.

99%

and

reportin~

no si

g

nificant

by

-product

formation.

These processes use very special

catalysts.

Especially these

l

ast

ga

s

phase

processes

are very

interestin

g

,

but unfortunately not

much

---information is

available.

The

kinetics of

liqui

d

phase

hyd

ro

g

enation have

been studied exten

sive

1y (13,14,15).

N

ot

mu

ch is

pub1ished on the

vapor phase

reaction

s

(16,17).

Because

of the tre

nd

(11,12) towards

gas

phase

pro-cesses, it

would be

int

erest

in

g

to co

m

pare

the

advan~

ta

g

es

and

disaàvan

tages

of

gas

and liquid

phase

processes.

11.3. Liquid

phase Hydro

g

enation

Most

co

mme

rci

a

l

processes

àeve

10ped in

the late

60's are liquid phase

processes. The

oper

at

in

g

con-ditions are temp.

around 200

C

and pressure

around

40 atm. Each

process

-

el

aim

in

g

a specific catalyst.

The advanta

g

es are:

(1)

R

eactor

volu

m

e

i

s

small

(

2 )

Te

m

p.

con

trol

is

eas

y

(3) Liqui

d

s

are

ea

s

ier

to

pump

(4)

A

llo

vIs

h

i

.:;,

h

-

or

de

r

of flexibility in c

apa

city

Some

of

the

disadvanta

2 es a

r

e

:

(1)

I

t is

h

ar

d

to

~:eep

the c

ata

l

ys t

i

n

sus

pens

ion

in

a

ll

part

s

o

f the

li

qu

i

d

e

Th

erefore there

is

a p

o

ssibility of

loc

a

l

hot

spots

,

intro

-ducin

s

r

everse

-

reaction

and sta

rt

o

f

hydro

-crackin

g

.

/&r4/~j~r

v~·

(8)

•

4

(

2)

The

higher pressurcs

requirc

more expensive

equipment.

11.4. Gas

Phase

Hvdropenation

v i

As

said

before

,

the

newer processes available

are

characterized

by

lower

pressures between

1 and

25 atm.

So~e

use

hi

S

h

temp. (40

0 -60

0 C), others

lower temp.

bctwe~n

150 and 250

C

.

They all claim

.

spec

ific

catalysts

bringing about a conversion of

benzene of more than

99%

.

The advantases

are

:

( 1 )

( 2)

1

(3)

(4)

Easier

for continous

operation

There

is

always a

g

ood contact

with

cat

a

lyst

~ss,-chanze

of

a

te

mp

.

run

away

,

anc

less

old-up,

which can

le

ad

to

e;~plosi

ve

ten~p.

Lower operatin

g

pressures

require less

expensive

equipment.

The

d

isa

dvantages are:

(1)

Require

l

ar

g

er reactor

(2)

Theoretically

at

lower

pressure

there

should

be

lo

wer

conversion,

which

means

recircula-tion.

This turns

out to be no problem

in

industrial

proccsses

.

(3)

These processes

need hi

g

h excess of hydro

-gen

(12:1-20:1).

11.5. The

Gatalyst

1 are

Ramsey

The

m

o

nickel, or nickel, platinum or

st

i

mportant hydrogenation

catalysts

_p~ladium,

used

-preferably on

a support such as

alu~ina,

silica,

kieselguhr

,

or

inor~anic

oxides, alone or in

combi-nations. Some processes use

a

catalyst slurry (4).

The use of

a nickel

-

containin

g

catalyst could

be

a disadvantage,

because

of the fact that nici<el

is

sensitive to sulfurous compounds, possibly

con-tained in the

benzene

concentl~ate.

On the otherb

a

nà

(9)

•

5

The

se

lectivi

ty

of

a

ll th

ese

c

a

taly

s

ts

i

s

ve

ry

high (more th

an 99

.8

%

). Only very

sma

ll

amounts

of

by-products

(;.;CP)

rnay

be produced, '.'/hich can

be

m

ini-mized

throu

gh

use of

suitable operatin

g

conditions.

The

amount

o

f

cat

a

ly

st

in

the

r

eacto

r(

s)

will

depend

on the

quality of the fee

d s

tocks.

The

life of

the

different

cat

a

lyst

s

have

b

een

reported in

liter~ture

anywhere between

1 and

7 years.

11.6. Overview

of

excistin

g

o

roc

esses

The co

mme

rci

a

lly

avaiIabIe processes

main

I

y

differ

in

the way they remove t

he h

i

g

h

exother~ic

heat ~6f ~eaction. Si~pIified

they c

an be

divided

into two

cate

g

ori

es

:

(1)

Processes empIoyin

g

in

d

ir

ect

w

a

t

e

r coolin

g

in

the reactor(

s)

.(IF

P

-

p

r

ocess

,

HA

-

84 ,

ARCO

-

pro

-c

ess,

and

DS~-process) .

(2 )

Processes

recyclin

s

portion of fee

d

or

product

~ ~.

to the re

a

ctor to

assist

in controllin

g

the

reactor te

mp

.

(

Ae

r

osa

t-

p

roc

ess

,

tlycl

r

a

-

process

,

and

H

oudry-process).

~

M

r ,/

~

A

short

des

cri

p

tio

n and

fIow~Sheet

of

each

process w

i l l

follow below.

Insti tute Fr

an

c

a

i

s

du

Petro

l

e

(6). Fi

g

ure

1. v----Hydro

g

enation is

almost co

mp

lctely achieve

d

in

a

liqui

d

phase

r

eactor

.

Hea

t in

excess

i

s

re~oved

~

\

in

an

exchan

ge

r

where

10VI

p

ress

u

r

e stcam

i

s p

ro

du

c

ed

.

o

A small c

a

talvtic

DOt

ac

t

s a

s

finishin

n

reactor

.

A

f ter

... ,l. I".J

...

L

condens

_ _ _ _ _ _ _ _ _ _ _ _

a

tion,

the

reactor

e

f

l

uent

i

s f

l

a

shcè in

IIP

separator

.

A

stabilizer

re

moves

hydro~en-rich

ga

s

.

Practically stoic

h

io

met

ric

yields

of

c

yclohexane

fro

m

(10)

I

•

6

r~-84

by Sinclair

Re

search, Inc.(7). Fi3ure

2. Benzene and

hydro~en

are preheated

to reaction

temperatures

(

200 C) by exchanain

(J t...>

g

f

irst with reactor

effluent and then with

steam. The

re

a

ctants flow

throu

gh

a

fixed

bed of precious

l

catalyst

which completely hydro

g

enates

the benzene

to

cyclo-hexane

.

The

reaction

temp.

is

efficiently controlled

by using

the

hi

g

h'

heat

release

to

ge

nerate stea

m

.

The

entire

hydrogenation is effected in a

s

in

gle

reactor.

The

reactor

effluent is exchanSed, cooled

a

nd flashed

at system pressure.

A

portion of th

e

separator vapors is use

d

as hY

J

ro

ge

n

recycle

gas

.

The stabilizer bottoms is the hi

gh

purity

cyclo-hexane product

.

Hydrar by Universal Oil Pro

du

cts

Co

.CB).

Fi

g

ure

3. Benzene feed, recycle cyclohexane and fresh

and

recycle

hydrogen are brou

g

ht to reaction

te

mp

.

and

1. charged

to

~ ~.

exchanaina

~ ~ ~ 0

the re

actor

.

The reactor effluent,

af ter

heat with the feed, is charged to the

A

portion of the cyclohexane from the

~

<;

~

,separa

t

or

.

separator

i

s

recycled

to the reactor to assist in

the control of the

reaction temp.

Product

cyclo-hexane

is

flashed

and/or stabilized to

remove li

g

ht

hydrocarbons

.

DSM

by Stamicarbon

B

.V.Cll).

Fi

g

ure

4. At a pressure of 25 to 30

~

.

al-m ana a

temp. of

about 400 C, benzene is

al

m

ost completely converted

tp

cyclohexane

with

a

n

overall

eff

iciency

better

than

99%

.

A

noble

l

cata

ly

st

i

s

used.

On

l

y

a

m

inor

quantity of by

-

produ

c

t

is for

m

ed, furt

he

r

purification of th

e

cyclohexan

e

is

not

necessary.

(11)

•

11.7.

•

7 ARCOby ARCO

Tech~olo~y

Inc

.

(1

2 )

.

fi~ure 5.

A

preheated

f~ixture

of benzene

anti hyd

ro

ge

n

is

c

a

t

a

l

ytica

ll

y hydro

g

enated

in

the v

ap

or

phase

over

a special

no

b

l

e metal catalyst to produce essentia

ll

y

co

mp

let

e

conversion

.

The specially

desi~ned

re

acto

r

assures complete

benzene

conversion

by providin

g

plug flow

and a

l

so e

li

m

inates the

need

to recycl

e

cyclo

hexane for

~eat

control by

g

eneratin

g

steam

instea

d

.

The reactor

eff

l

uent exchan

g

es heat

with

t

he

feed

t

hen

is cooled

bef

or

e

enterin

g

the

li

qu

i

d

-gas

separator.

Aros

a

t

by The

Lu

mmus Co

.

(

9 )

.

Fi

gu

r

e

6.

Fresh

feed benzene

i

s

m

ix

ed

wit

h

r

ecyclohexa

ne,

~

make

-

up

hyd

ro

g

en

and

rec

ycle

hydrogen

,

and charg

ed

to

the reactor.

The product

cyclo

hexane

flows to

th

e

st

abi

liz

e

r

t

o

remove li

gh

t hydrocarbon

g

ases.

Pro

duct cyclo

hexane

is

coo

l

ed and sent to

storaSe

.

Ho

udr

y by Air

P

r

oducts

&

Chem

ical

s

Inc

.

(

l

O)

.

Fi

gure

7. Benzene, hy

d

ro

g

en and

cyclohex

a

ne

pro

duct

are

heated to

r

eact

io

n temp

.

by exchange

with

reactor

effluent.

The exot

he

r

m

ic

heat of

re

act

ion is re

m

oved

or controlle

d

by

heat

exchan

g

e

to

feed and

recycle

streams

.

The

liqui

d cyclohexane product

is

further

purified by

stripping of

the

light

gases

.

Economics

Because

cyclo

hexane and

~enzene

sell

i

or

abo

ut

the same pric

e

on

a

volume basis

,

the expansion

in

wei

gh

t throu

gh

hy

d

ro

s

en

a

tion

provides

a

n

a

rrow

m

ar

-gin

for

profit.

There

is

every

inc

en

tive

t

o

mi

nim

iz

e

d

ir

ect costs

a

s

weIl

as c

a

pit

a

l

lo

ad

(indirect

cost

s

)

.

Therefore

a ti

g

ht

,

easil

y

operabIe

,

a

nd yet

safe

(12)

•

• '

.

•

8

A

co

mparison between

th

e

above described processes

will

be

made

based on the

(scarce)

infor~ation

provided

in the sited references. It

will not be possible to

calculate the investment

and~manufacturins

costs

,

because of the

differences

in

plant capacities

a

nd the

date of infor

mat

ion

available

.

Fi~ures

are calculated

for process

ut

ili

ties

,

based

on

a capacity of

1

00 .

000 mt

on

per

year

.

/

steam

coolin

s

process

_Po\'l~

(cre

d

i

t)

';[~ter

k':!h

h

k~h

m

.~_ . ... ~ ___ J .

-

-IFP

15.

2 (1

8600)LP

68 HA

-

84

48

(

5270)

73 Hy

d

r

a

r

_-

-AReO

26 .7

(150

00 )LP

84 DSI

·I

20 (12GO

O

)LP

5

0 Arosat

43 .5

(235

60)LP

20

I

Houdry

25 .

8

I

433

30 /

...

T

ab

le 1 :

on

100. 000 mton

c

y

clo

hexane

er year

.

Process

ut~~es.

based

~cr.., ~1If...4.~

A __

~

'?

/tu~

th .... , ...

....:~J

No

conclusion c

an be drawn

for the

direct

costs

~

based

on the re

su

lts in

table

1. These

results

vary

widely, dependin

g

on

design

rather than

ga

s

or

liquid

phase process.

S

inc

e there are

no

fi

g

ure3 on investment costs

,

in

g

eneral

c

an be

sa

i

d

that

Dater

i

a

l

and

equip~ent

for

gas

phase processes

w

i l l

be sli

Z

h

l

y

che

aper

than

for

liqui

d

phase

processes

,

caused

by

lower operatin

g

(13)

•

9

r-11.8.

C

oncl

us

i

on

~~

(IN

Considerin

g

the

ab

o

ve

infori

;lat

ion

,

& vé~por

phas

e

process, si

m

il

a

r

to

that of

ARCO

/

wil

l

be

used

for

process

d

esi

g

n

and

re

a

ctor c

a

lc

u

l

at

io

ns

.

'Ihe vapor

p

hase

process is

chosen for

se

veral

reasons.

Fir

s

t,

the

r

e

is

a

r

ecent

tren

d

i

n

industry

tO\'/ard these

type o

f

processes

(DSL,

She

ll,

ëSSO

).

Eventhou

gh

these 'proce

sses seal-:'I

to

becoile

incr

eas

-in

g

l

y

i

mportant, not

mu

ch infor

ma

tion i

s

available

.

Furt

he

r,

the

m

os

t

i

Dp

ort

a

nt

advantage

of

a

vapor phase

p

roc

ess

i

s

the reduce

d

ri

sk

for

te

mpe

ra

-ture runa

ways

,

c

aus

in

g

explosions.

The

te~p.

is

easier

to co

nt

ro

l

in

a

li

qu

i

d

phase

r

eactor

,

but

once the te

mp

.

Boes up

,

i

t

will

go so

fast

,

t

ha

t i t

is i

mp

os

sib

l

e

to

stop

it

.

When

the

te~p .

zets above

,

230 C

,

t

he

r

eve

r

se

re

e.

C tion '

,

vill

p

r

odl.<ce hyG

ro

:;en

.

.("tt..JJ/~

~ .~~

---The hydro

g

en

a

t

that

te

mp

.

w

i l l ini

t

i

ate

hydrocracking~

c

aus

in

g

even

h

i

ghe

r te

D

peratures

,

p

ro

duc

in

g m

ore

hyd~en,

etc

.

In

the

g

as phase

,

t

h

i

s

te

mp

.

run

away

wi

l l

g

o

so

m~ch

slower

,

th

a

t i t c

an be

controlled

.

Thirdly,

t

he

new

ga

s phase processes

a

re

so ad

-vanced,

that even

at

l

ower pressur

es

,

ths

conv

ers

ion of

b

enzene

is

mo

r

e than

99 .

8%

.

This

i

mp

lie

s

th

at

sepa

-ration of

benzene out of the

product strea

m

is

not

necessary.

The

mu

lti-

bed

r

ea

ctor is

desi

g

ned

i

n such way

, t

ha

t

bord

the

temper

atu

r

e

of eachA

does

n't excee

d

2

1

0

C. This

is

ac

h

i

eved

by

re

m

ovin

g

the heat of

re

a

c

t

ion

by

injectin

g

col

d

cyclo

hexane

i

n

beh.'een

the

beds

.

Ofcour

se

t

his process has

SOile d

isadv

a

nta

g

es

.

A

lar

ge

r

re

actor vo

l

u@e w

i l l

be necessary

.

A

l

so an excess

o

f hy

d

ro

ge

n

a

n

d

cyclohexane

wi

ll

be re

q

u

ir

ed

,

but

can

be rec

y

cle

d

.

All t

h

e

se

consi

óe

r

at

ion

s

l

ead to the

desi~n

of a

simple

and easy

to operate

,

but

yet safe and efficient

(14)

•

1

0

111. Design Considerations

111.1. Capacity of Factory

The

capacit

y

of the

factovy will be

100.

000 mton

cyclohexane

pe

r

year.

Based

on

330 stearn days

,

this

will

re

qu

ire

3.26 kg/s

of

benzene to produce

3 .5

0 k

g

/s

cyclohexane.

111.2. The Catalyst

The

cat

alyst, Pt

/

AI

2

0

3 ,

described by Aben

(16),

is

used for this

des

i

g

n.

l t

is rea

s

onable

to assume

,

that this

c

atalyst

ha

s

an extremely high

se

lectivity

of more than

99 .

8%

.

Cyclol1exane will be the unique

product

.

N

either inter

med

iate nor

by

-pro

ducts

will

be formed.

111.3. Specifications of

Raw Ma

teri

a

l

Hydro

g

en:

will be

pure.

r---'

Benzene

:

vlill be

obtaine

d

com~~1e~,

con-tainin

g

less th

an

1 ppm unpurities.

---111.4.

Specificat

i

ons of

E

nd

Product

Hi

gh

purity

cyclohexane

will be produced, having

(15)

I

.

•

11

I

V

.

Descript

i

on of

P

r

ocess F

l

ow

Shee

t

The process

will be

descrihed usin

8 flow

sheet

of

fi

g

ure 8

.

Fre

sh

benzene

(1)

together with

~ake-up (3)

and

recycle

(1

4)

hyd

ro

gen

are preheated to

reaction

te~pe

rature (10

0 C)

by

~xchanging

with

reactor

effluent

i

n

the

fee

d

-

product

exchanger H

l.

The exother

m

ic

heat of

re

a

ction

i

s

re

moved by

injectin

g

col

d

(3

0 C)

cyclo

hexane

(7,8,9)

in

between

t

he bros

of the

specially

eles

i

E;

ned mu

l

ti

-

b

ed re

actor

(

R

l) •

One t

h

ir

d

of

the

eff

l

ent

fro~

the reactor i

s

cooled

to

90 C

by

exchan

g

in

g

with

the

feed

.

The re

-maining stream

o

f

effluent is

a

l

so cooleel to

90 C

in

heat exc

hanger

~3,

parallel to

H

l.

The

two

strea~s

co

m

e to

gether and are

cooled to

30 C

in

heat exchanger

H4

.

Subsequen~ly

the tot

a

l coole

d

effluent is

se)a

r

ated

i

nto hydro

ge

n

gas anel

li

qu

i

d

cyc

l{)l~e:cc.ne

in

a

· lic-

:

Lèid

-gas sepa

rator

drum

(Vl)

.

· The exce

ss

hydro

gen gas

i

s

recycl

ed

to the feed

stream.

A

portion of t

he

cycloh

exane

i

s

recycle

d

to

he

inj

ected

in betwe

en

t

he

re

a

ctor

beds

.

The

other

port

i

on

(16)

"

.

f

i

,

i

i i". )_~I

r.

"

•

'I i [. ~

•

• ,

•

Recycle Walerelof ~ Hl

8

30 Cl Hl ~ (15 '.lATERSTOF ---~~----~ ... (12 )

PROCESSCHEMA VAN CYCLOHEXAANPRODUCTIE VIA BENZEEN HYDROGENATIE

o

Slroomnumm.r

~

T.mpe~gluur

InOC

8

Ef·f. d,.uk I nol .. , Horjon G. Korl.koo. Fabrl.k.vooron\w.rp No. 2535 Apr I I 1962

(17)

I

--

--.---

-

.

---~

.... - ... - - - -..

~

...

~

.. . _.-... _.-....

-~

. .. . -_ ... ..- . . . _0"

•

1

2 V. Calcul

a

tions for

t

he

Des

i

g

n

V

.l.

The C

a

talyst

V

ol

ume

The

design

of

the

r

ea

ctor

for the

hydro~enation

of

benzene

in the

g

as phase

is

based

on

the kine

tic

in

fo

r

ma

tion

provi

d

e

d

by

Abe

n (1

6)

.

For

a

productio

n

of

1

00 .

0

0 mton

cyclo

hexa

ne

pe

r

3

year

, 7.

8

catal

ys

t

Pt

/

A

1

2

0

3 is

re

quired

.

This

r}

calcul

a

tion (appen

d

i

x 2)

i

s based on

t

he E

iven L

HSV

---for

Pt

/

A

1

2

0

3 un

de

r t

he fo

llo

w

i

n

g

assumptions

:

(1)

L

HSV

is

based on

a

constant t

empe

r

atu

r

e

of

1

00

C. (2)

Linear extr

apo

l

at

ion

can be use

d

to

ge

t

a

1

00 %

conversion.

Thes

e

assu

mp

tions have

been

m

ade re

al

izin

g

t

hat

in

reality

there

w

i l l

be a

te

m

perature increase over

the

re

act

or.

A

lso

th

e

r

e

wil

l

be a d

if

fus

i

on

li

m

it

a

-tion

for higher conversion

s

.

The

f

ir

st effect will

re

qu

ire Ie

ss

cataly

st

,

bec

a

use the reaction r

ate

in

cre

ases

at higher te

mpe

r

ature

. The

diffusion

li

mitat

ion

will require

more

c

atalyst

.

The

i

mpa

ct of

each effect

,

however,

is

unkno

wn

.

V.2.The

Rea

ctor

Volu

me

The

lar

g

e heat of r

ea

ction is

aprobl

em

.

Espe

cial

-ly

since the

te

mperature

may

not

excee

d 230

C,

to

pre

-ven

t

undesired

by-p

ro

du

ct

s

.

To achieve

a tempera

ture

below

230 C, a

mu

lti-b

ed

re

a

ctor is

desi

g

ned,

coole

d

by

injectin

g

cold c

y

clo

hexane

in

between the beds

.

The calculati

ons a

r

e

bas

e

d

on

the

fact

t

ha

t the

re

a

ction r

a

t

e

co

nstant

i

s

in

depe

n

dent

of

the hydro

-c

a

r

b

on

s

(1

6 ):

(18)

I ... _ - -... -... ,

.~-.'

- ." ... - - . - ... -....

~

... - . . _ . - . -- .. - .. -.. - -...

-

.

~--

.. - --

.

-.----

-

--~-

. . .

-

--~--

-

...

-.--

-

-~-.

--.

•

13 bPH

k = 1<: _____

2 __

o

( 1 )

1

+

bp'I I

2 Therefore we c

a

n

as

su

m

e t

h

a

t t

he

conv

e

r

s

ion is

a

linear

function of t

h

e te

mpe

r

a

t

u

r

e

:

\(

%

)

100

26 o

.

..

10

0

21

0

5

3

0 T

(

C

)

The outlet te

mp

er

a

tur

e of

53 0 C

i

s the

t

e

m

pe

-rature

under a

d

i

ab

atic con

d

i tio

n

s

a

n

d

100~~

c

onve

r-sion,

calcul

a

te

d b

y tri

a

l

a

n

d e

rror (

append

i

x 3)

.

In order

that the t

e

m

pe

rature (

w

it

h safety

mar

g

in)

doesn't exc

e

d

21 0 C

in t

he

r

ea

ctor,

we

need 4 catalyst

beds. The

results

of the c

a

lcul

a

tions

are

summ

a

rized

in

t

ab

l

e

2.

V.3~Pressure

dro

p

over t

h

e

R

ea

c

t

or

For calculatin

g

t

h

e tot

a

l

pres

s

ure

d

ro

p ov

er

the reactor, the

e

x

pre

s

sion o

f E

r

gun

(1

9 ) i

s used

for each

bed. The

result

is

a

total pre

ss

ur

e

d~op

of

1.3 atm (appendix

4).

b

~

/

..---b~d

2 bw

3 Ued

4

3 _1'2

_.

₀

2 .

0

2 n

1.

8 V

( r.1 )

.

~

( ~I _I_,))

₂

₆

26

2

6

?'1 _~'--' m ₍_C₎

1

00

1

00

1

00

1

00

.1. •

ln

T

(C)

21

0

2

1

0

21C)

1 5:J

out

CH.

(

r.

101 e)

0

5

7.

5

r-ï '1

53 .

3

:J::>.L+

lnj

Ta

b

le

2 :

C

al

c

u

l

at

i

ons

f

or r

ea

ctor

b

cd

s

.

(19)

•

14

• V.4.

Hea

t

Exchan~ers

• There

arc

a tot

a

l of

fOl1r he

a

t exc

h

o

.

n

,r,

ers in

this process,

which

will

be described below

.

111 :

Feecl-Proeluct

E

xchan

;:z

er

:

• In this

hèat exchan

g

er the feed

streaD

is

pre

-•

•

• heated

from

30 tó 1

00 C

with

part

of the

reäctor

effluent

(222.2

mo

lel

s)

.

The

other part of the

product

stream

is

cooled

down

in

heat exchan

g

er

H3

.

Both parts are cooled

down

from 15

0 to

90 C

.

Usin

g

data from appendix 5 anel

6 ,

the

re-quired surface area for this

heat

exchan

s

er is:

T

ln

U A L

Q

I-I2:

Coolin

p;

of recycl

e Ily

p

:ro

o:

en

:

*"

This

heat exchan

g

er

is necessary to cool

down

Q.

the recycle

hydrogen strem

f

ro

m

35 to 30 C. This

stream is sli

gh

tly

heated by

co

mpressor

2. Need 2.69

kg/s

cool water of

20 C to

accomp

lish

the cooling.

T

ln

=

U

₌

Q

₌

A

₌

~h

0

=

2

16.4

C

845

Cm

2

lVI

200.8 kW

14.5

r,1

2

2 .

6

9 k

g

/s

i 1.-" LOJ J

,."

' i j

l

L

J

(~e

1

t. •• ' • , , u ... ,.·, ,;.I ;

(20)

•

15 H3:Coolinp

of

Product

stream

:

This heat exchan

g

er

has

to cool

down the

other

part of the reactor

effluent fro

m

15

0 to

90 C. Cool water

of

4

0 C (from

H

4)

g

eneratin

z

134 C

ste

am

is

used for coolin

g

.

TIn

=

1

9 .1

C

U

=

845 Cm

2 /\1

Q A 6434. 5 k\'l 2

=

398.7 m

!J1 h')o=

2.67 k

g

/

s

L

H4

:

Add

ition

2

1 Product

stre&~

cool

e

r:

This heat

exchan

ge

r cools down the

p

ro

du

ct

stream fro

m

90 to

30 C

,

usin

g

2 0 C

cool

wa

ter.

TIn

=

1

8 .

2 C

2

U =

845 C

n

/ 1:1 n "< =

14

9

1. 8 kW

A

=

9

7 m

2

!J1

_h

0 =

20.0 k

g

/

s

2

(21)

•

1

6

V.5.

Compressors

A

couple

of

co~preGsors

a

re

ne

c

essary

to

brin

g

hydro~en

(both

r

ecyc

l

e and

~ake

up)

at

the ri

2 ht operatin

B

pressure

.

Assum

ed

i

s that

hy

d

ro

e

en

is

an

i

dea

l

gas

.

1he ad

i

abatic

d

is

-ch

arp,e

te

mpe

rature is (2

0 ) :

i!..:J

(~)

I<

1

= 'I'

2

1

( k=

1.

4 f

or

2 at

.

sases

)

C

l:

_P

₁

=

1 atm

P2

= 6

at

m

Tl

=

1 8 C

'r

₂

=

30 C

C2

:

_P1

=

3.4 atm

P2

= 6

atm

Tl

=

3

0 C

T

=

35 C

2 Pu

m

2s

The fresh

benzene and

the recycl

e

cyclohex

a

ne

re

qu

ire

re

g

ular centrifu

ga

l

pu

m

ps

to

b

rin

g

t

he

liqui

d

to

o

p

eratin

g

pressure

,

and

to

pump

i t

around

in

the syste

m

.

In

genera~ pumps

do

not

gene

r

ate

th

a

t muc

h

heat

( 24~

that they

s

i

g

nifi-can

tly heat

the li

qu

i

d

s

.

Therefore

,

this part

is

(22)

•

17

V.6. Liquid~eas

Separator

Finally, the

strea~

of hydro

Se

n

E

as

and

li

qu

i

d

cyclohexane needs

to

be

separated.

S

inc

e

t

he

solubi-lity of

hydro

g

en

g

as

in

the

cyclo

hexane

i

s

so low

(appendix 7),

strippin

s

will not

be

necessary.

A

re

gu

lar L/G

separator

dru~

will be sufficient.

The

volume

stream

of liqui

d

is

about

1.2 m

3 /s

and

that

of the

g

as is

2 .

9 m

3 /s

.

Therefore, the L/G

drum

(23)

•

- - - -- - - -- - - -- - - -- -

-18

Vl.Safety

a

nd

Hea

lth

(25)

Th

e

treshol~

li

m

it

va

l

ue

(

T

L

V)

for

cyclo

hexane

is 1

0

5 0 mg

/

m

3 .

W

ith

prolon

c

e

d

exposure

at

1

050 ~3

/

~3

and

m

ore, cyclohex

ane may

cause

irrit

at

ion

to

eyes

and skin

.

A

t

high

cQDc

entrati

on, it i

s an.anesthe

tic

and narcosis

may

occur.

Overall,

cyclo

hexane

i

s

not

dangerous to

your health.

The opposite is true for

b

enzene.

This

is

a

po:isonous

substance with

acu

te

an~

chronic toxic

ef

-f

_ec

t

_s.

Th

_e

mI

1.J

V"

1 S '

3

.

2 rng r

/

3 (.

1

n

U~

::51-'.

..

)

.

""

1

ne

s

h '

0

rt

:

t

e

r

:-:1

effect

s

of in

ha

lation, in

ge

stion, or

skin

contact of

benzene

a

r

e

i

rmed

iatel

y

apparent.

Howeve

r,

the

effe

cts

of chronic exposure to lower levels is not.

In

several tests, benzene i

s

found

to

be a

very

serio

us

carcino

ge

nic co

mp

ound,

hav

in

g

caused

deaths

i

n the

past.

Al

l

exposures

(

ma

lfu

n

cti

ons

,

ma

int

e

n

an

ce)

shou

l

d

be

avo

i

ded.

Hydro~en

gas

i

s

not

con

sidered

toxic, but

it

c

an

cause suffocation

by exclusion

of

a

ir.

The

ma

in

dan

g

er

li

es

in its

extreme

f

la

mma

bility

with oxy

g

en

or

a

ir.

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inc

e

hydro

g

en

i

s

odorless an

d

c

o

l

or

l

ess

, i t

is not

easi

l

y

d

etect

ab

l

e

.

Therefore

p

r

ecautions

should

(24)

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.

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II. Conclu

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i

o

n

Th

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s FVO turns out to

be a

rather si

m

ple

,

but

ne

v

e

rt

he

l

ess realistic picture of a

process for

t

he hydr

o

g

enatio

n

of benzene to cyclohexane

.

Only

t

h

e cooli

n

g

of the product stream could have

been

sol

v

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a

l i t t l

e

more

e

l

e

ga

n

t

.

Ho

weve

r,

the.purpose of th

i

s FVO

,

to

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a

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ee

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g

f

o

r

and

excersize in des

i

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and

c

a

lculatio

n

of

a che

m

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, i

s ach

i

eved

.

been

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