Industrial and Laboratory Alkylations - American Chemical Society

21

Monsanto's E t h y l b e n z e n e Process

A. C. MACFARLANE

Downloaded by CORNELL UNIV on July 29, 2016 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0055.ch021

Monsanto Chemical Intermediates Company, Texas City, TX 77590

E t h y l b e n z e n e i s c o m m e r c i a l l y produced a l m o s t e n t i r e l y as an i n t e r m e d i a t e f o r t h e manufacture o f s t y r e n e . Since only a l i m i t e d amount can be made by t h e s u p e r f r a c t i o n a t i o n o f C p e t r o l e u m a r o m a t i c s , most e t h y l b e n z e n e i s produced by the a l k y l a t i o n o f benzene w i t h e t h y l e n e . The a l k y l a t i o n r e a c t i o n can o c c u r e i t h e r i n t h e vapor phase o r t h e l i q u i d p h a s e . A number o f proven p r o c e s s e s e x i s t . The l i q u i d phase p r o c e s s e s u s i n g aluminum c h l o r i d e c a t a l y s t s a r e c u r r e n t l y t h e most w i d e l y u s e d . The purpose o f t h i s paper i s t o d e s c r i b e a new and improved v e r s i o n o f t h i s l a t t e r p r o c e s s which has been c o m m e r c i a l i z e d . 8

Friedel-Crafts

Chemistry

The o l d e s t method o f a l k y l a t i o n w i t h e t h y l e n e i s t h e l i q u i d phase r e a c t i o n u s i n g anhydrous aluminum c h l o r i d e as the c a t a l y s t . T h i s r e a c t i o n i s a form o f t h e c l a s s i c F r i e d e l - C r a f t s r e a c t i o n and was d i s c o v e r e d i n 1879 by B a l s o h n . Most Lewis and B r o n s t e d a c i d s a r e known t o be a c t i v e f o r o l e f i n a l k y l a t i o n s . Alkylation by H S0it and H P0n was f i r s t shown by I p a t i e f f , e t a l , i n 1936 who extended t h e r e a c t i o n t o i s o p a r a f f i n s . F o r t h e l i q u i d phase a l k y l a t i o n o f benzene w i t h e t h y l e n e , however, aluminum c h l o r i d e i s p r e f e r r e d over the other a c i d s , although a c o - c a t a l y s t or promoter i s u s u a l l y needed t o o b t a i n e f f i c i e n t a l k y l a t i o n . A 1 C 1 when d i s s o l v e d i n benzene c o n t a i n i n g some HC1 forms a complex which can be s i m p l y d e s c r i b e d a s : 2

3

3

H

H

341

Albright and Goldsby; Industrial and Laboratory Alkylations ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

342

INDUSTRIAL


T h i s complex then r e a c t s

AND LABORATORY

with ethylene to give

ALKYLATIONS

ethylbenzene.

The a l k y l a t i o n r e a c t i o n i s c o m p l i c a t e d by the o c c u r r e n c e o f minor s i d e r e a c t i o n s such as c r a c k i n g , p o l y m e r i z a t i o n , hydrogen transfer, etc. However, o f major importance i s the f o r m a t i o n o f polyalkylated products. The f i r s t a l k y l group formed a c t i v a t e s t h e a r o m a t i c n u c l e u s so t h a t the second a l k y l a t i o n proceeds more r e a d i l y than the f i r s t and so on a t l e a s t u n t i l s t e r i c h i n d r a n c e i n t e r v e n e s , although hexaethylbenzene i s q u i t e r e a d i l y formed. T h i s r e s u l t s i n a r e a c t i o n p r o d u c t c o n t a i n i n g a m i x t u r e o f mono, d i , t r i , and h i g h e r e t h y l b e n z e n e s t o g e t h e r w i t h u n r e a c t e d benzene. The r a t i o o f e t h y l e n e t o benzene i n t h e r e a c t o r f e e d c a n , o f c o u r s e , be chosen to maximize the f o r m a t i o n o f monoe t h y l benzene; but the o t h e r p r o d u c t s cannot be e l i m i n a t e d . F o r t u n a t e l y , the r e a c t i o n i s r e v e r s i b l e , e . g . , d i e t h y l benzene w i l l r e a c t w i t h benzene under the i n f l u e n c e o f A 1 C 1 to form monoethylbenzene. 3

CôHsCCaHs^

+

ΟβΗε ^

2

CoHs'L^Hs

T h i s t r a n s a l k y l a t i o n r e a c t i o n p e r m i t s v i r t u a l l y a l l the e t h y l e n e and benzene f e d to the r e a c t i o n system t o appear e v e n t u a l l y as t h e monoethylbenzene p r o d u c t ; the r e a c t i o n was f i r s t demonstrated in 1 8 9 4 . ( 1 ) The e q u i l i b r i u m amounts o f t h e v a r i o u s p r o d u c t s a r e shown i n T a b l e I . The a l k y l a t i o n r e a c t i o n can be performed under two r a t h e r different conditions. I f , f o r example, i n a w e l l - s t i r r e d l a b o r a t o r y s e m i - b a t c h r e a c t o r a g i v e n amount o f e t h y l e n e i s added r a p i d l y to the benzene under g i v e n r e a c t i o n c o n d i t i o n s such t h a t t h e e t h y l e n e i s c o m p l e t e l y a b s o r b e d , i t w i l l be found t h a t the p r o d u c t formed i m m e d i a t e l y a f t e r a l l e t h y l e n e i s added i s r e l a t i v e l y r i c h i n h i g h e r p o l y e t h y l b e n z e n e s and r e l a t i v e l y poor i n t h e d e s i r e d monoethylbenzene. However, i f the same amount o f e t h y l e n e i s added r e l a t i v e l y s l o w l y to a n o t h e r batch o f benzene, t h e r e a c t i o n p r o d u c t w i l l be r e l a t i v e l y r i c h i n monoethylbenzene and poor i n the u n d e s i r e d p o l y e t h y l b e n z e n e s . The r a p i d i n i t i a l a b s o r p t i o n and r e a c t i o n o f e t h y l e n e forms p o l y e t h y l b e n z e n e s u n s e l e c t i v e l y , and t h e slow l i q u i d phase r e a c t i o n o f the p o l y e t h y l b e n z e n e s w i t h u n r e a c t e d benzene r e s u l t s i n an approach towards thermodynamic e q u i l i b r i u m . That i s , although the amounts o f h i g h e r p o l y e t h y l b e n z e n e i s n e g l i g i b l e under thermo dynamic c o n t r o l , t h e y can be c o n s i d e r a b l y under k i n e t i c c o n t r o l .



1. 2. 3. 4.

tr tr

tr tr

0.25

1.77 3.57

19.4 27.3

50.1 49.3

28.6 19.6

0.8

1.0

rings.

tr tr

0.02 0.09

0.72

11.9

46.8

40.6

0.6

M o l a r r a t i o o f e t h y l groups t o a r o m a t i c Ethylbenzene. T r a c e , l e s s than 0.01 wt %. C a l c u l a t e d from f r e e energy d a t a .

tr tr

tr

0.20

5.7

38.1

tr tr

56.0

Hexa-EB

Penta-EB

0.4

3

Tetra-EB tr

Tri-EB

Di-EB 0.02

2

1.5

EB 22.9

Benzene

Percentage

75.6

1

Weight

0.2

E/B

Molar Ratio

1

LIQUID PHASE *

THERMODYNAMIC EQUILIBRIA OF BENZENE AND ETHYLBENZENES

TABLE I


344

INDUSTRIAL

Commercial

Alkylation

AND

LABORATORY

ALKYLATIONS

Process

Emmet R e i d and h i s c o - w o r k e r s a t Johns Hopkins demonstrated i n the 1920's the p r a c t i c a l i t y o f u s i n g e t h y l e n e f o r e t h y l b e n z e n e p r e p a r a t i o n w i t h the l i q u i d A1C1 c a t a l y s t . I t was, however, Dow Chemical i n t h e U n i t e d S t a t e s who d e v e l o p e d the F r i e d e l - C r a f t s r e a c t i o n w i t h A1C1 i n t o a c o n t i n u o u s e t h y l b e n z e n e m a n u f a c t u r i n g p r o c e s s i n 1937. BASF were a l s o s i m i l a r l y a c t i v e i n Germany i n the 1930"s. Dow showed t h e importance o f HC1 as a promoter and t h e n e c e s s i t y o f m a i n t a i n i n g s t r i c t l y anhydrous c o n d i t i o n s . The Dow p r o c e s s o p e r a t e d a t about 95°C and a t a s m a l l p o s i t i v e pressure. In 1942, w i t h the c u t o f f o f n a t u r a l r u b b e r s u p p l i e s from the P a c i f i c a r e a , a r a p i d i n c r e a s e i n s t y r e n e c a p a c i t y was required. Monsanto o p e r a t e d a p l a n t a t Texas C i t y f o r t h e government t h a t used t h e i r own v e r s i o n o f F r i e d e l - C r a f t s c h e m i s t r y f o r the ethylbenzene s t e p . C a r b i d e a l s o i n s t a l l e d t h e i r own A1C1 p r o c e s s a t I n s t i t u t e , West V i r g i n i a . Dow Chemical expanded t h e i r o r i g i n a l e t h y l b e n z e n e p r o d u c t i o n c a p a c i t y by b u i l d i n g i n Los A n g e l e s , C a l i f o r n i a , and F r e e p o r t , T e x a s . The v a r i o u s e t h y l b e n z e n e p r o c e s s e s , a l t h o u g h having i n d i v i d ual d i f f e r e n c e s , a l l seemed t o have been based on s i m i l a r principles. I n v a r i a b l y p r e s e n t were t h r e e p h a s e s — e t h y l e n e g a s , a r o m a t i c l i q u i d , and a l i q u i d c a t a l y s t complex. R e a c t i o n took p l a c e i n t h e c a t a l y s t complex, and e q u i l i b r i u m was e s t a b l i s h e d between t h e c a t a l y s t complex and the o r g a n i c p h a s e . The l i q u i d r e a c t i o n p r o d u c t was then c o o l e d and the two l i q u i d l a y e r s separated. The lower c a t a l y s t complex l a y e r was r e c y c l e d t o the r e a c t i o n system. A1C1 was l o s t from the system i n two ways, by s o l u b i l i t y i n the o r g a n i c l a y e r and by withdrawal o f a s l i p s t r e a m o f c a t a l y s t complex t o a l l o w a d d i t i o n o f f r e s h c a t a l y s t . The c a t a l y s t complex was then h y d r o l y z e d s e p a r a t e l y t o produce an aqueous A 1 C 1 waste s o l u t i o n and an o r g a n i c l a y e r which was added back t o t h e s y s t e m . The o r g a n i c r e a c t i o n p r o d u c t from t h e a l k y l a t i o n s t e p was washed t o remove d i s s o l v e d A1C1 and HC1. The washed a l k y l a t e was s e p a r a t e d i n t o i t s components i n a s e r i e s o f three d i s t i l l a t i o n columns. T h i s then i s the w e l l proven A 1 C 1 p r o c e s s t h a t i s p r e s e n t l y w i d e l y used i n v e r y l a r g e p l a n t s around the w o r l d . 3


3

3

3

3

3

3

Disadvantages

o f Commercial

Process

S t y r e n e , and thus e t h y l b e n z e n e , a r e now commodity c h e m i c a l s . Economics have f o r c e d m a n u f a c t u r e r s t o c o n s t r u c t modern, h i g h l y e n g i n e e r e d p r o d u c t i o n u n i t s w i t h c a p a c i t i e s o f 1,000 m i l l i o n pounds/year and h i g h e r . T h u s , the b a s i c c h e m i s t r y and the manuf a c t u r i n g t e c h n i q u e s have t o be c l o s e l y s c r u t i n i z e d i n the l i g h t o f p r e s e n t day raw m a t e r i a l s h o r t a g e s , energy c o s t s , p r o d u c t p u r i t y demands, and e n v i r o n m e n t a l c o n s i d e r a t i o n s . In t h e s e b i l l i o n pound/year p l a n t s , r e l a t i v e l y small improvements can o f t e n l e a d t o i m p o r t a n t money s a v i n g s p r o v i d e d they a r e r e l i a b l e



21.

M A C F A R L A N E

Ethylbenzene

345

Process

and w e l l d e m o n s t r a t e d . In p l a n t s o f t h i s s i z e , not v e r y much u n c e r t a i n t y can be p e r m i t t e d . In some v e r s i o n s o f the e t h y l b e n z e n e m a n u f a c t u r i n g p r o c e s s , F i g u r e 1, a r e l a t i v e l y l a r g e volume o f c a t a l y s t complex, a f t e r c o o l i n g and s e p a r a t i o n from the a l k y l a t e , i s r e c y c l e d through t h e a l k y l a t o r to moderate the temperate r i s e o f t h e e x o t h e r m i c r e a c t i o n by a c t i n g as a heat s i n k . ( 2 ^ , 4 ) The c a t a l y s t c o m p l e x , however, tends to a b s o r b p r e f e r e n t i a l l y t h e h i g h e r p o l y e t h y l benzenes. These a r e then s u b j e c t e d t o a h i g h l y r e a c t i v e e n v i r o n ment a t an e l e v a t e d t e m p e r a t u r e f o r a f a i r l y l o n g a v e r a g e residence time. I t i s , t h u s , not s u r p r i s i n g t h a t such a system tends t o make c o n s i d e r a b l e p o l y m e r s , h i g h b o i l e r s , and t a r s . T h i s not o n l y l e a d s to a s i g n i f i c a n t l o s s i n y i e l d but a l s o to a h i g h e r than n e c e s s a r y usage o f aluminum c h l o r i d e c a t a l y s t , s i n c e the t a r s t i e up the c a t a l y s t i r r e v e r s i b l y and so r e n d e r i t inactive. T h u s , even more o f the c a t a l y s t complex has t o be withdrawn from t h e s y s t e m . The p r e s e n c e o f i n c r e a s e d amounts o f i m p u r i t i e s a l s o tends t o produce a r e l a t i v e l y impure e t h y l benzene p r o d u c t w i t h many o f t h e s e i m p u r i t i e s c a r r y i n g a l l the way through t o the p r o d u c t s t y r e n e . T h i s c a t a l y s t complex stream i s a l s o v e r y c o r r o s i v e and r e q u i r e s h i g h a l l o y m a t e r i a l s o f c o n s t r u c t i o n i n p i p i n g and equipment h a n d l i n g the complex. Improved A l k y l a t i o n

Process

A few y e a r s ago Monsanto a t Texas C i t y , T e x a s , d e c i d e d t o re-examine i t s p o s i t i o n i n e t h y l b e n z e n e m a n u f a c t u r e . Other proc e s s e s were a v a i l a b l e o r were becoming a v a i l a b l e a n d , as we have s e e n , t h e A l CI 3 c h e m i s t r y was q u i t e a n c i e n t . An e x a m i n a t i o n o f the o t h e r p r o c e s s e s r e v e a l e d t h a t they too p o s s e s s e d c e r t a i n serious shortcomings. One o f many p o t e n t i a l problems w i t h a new p r o c e s s i s the r i s k i n v o l v e d i n b e i n g t h e f i r s t t o b u i l d a 1.7 b i l l i o n l b / y e a r EB p l a n t u s i n g a not f u l l y proven t e c h n o l o g y . 1.7 b i l l i o n times a l m o s t a n y t h i n g i s a l o t o f money to be made o r l o s t so we had t o be s u r e t h a t any change was to the most economi c a l process a v a i l a b l e . We c o n c l u d e d t h a t r a t h e r than abandon the o l d A I C I 3 t e c h n o l o g y we ought f i r s t t o g i v e i t a f a i r chance and t r y t o d r a s t i c a l l y improve i t . T h u s , we d e c i d e d t o t a k e a new l o o k a t the b a s i c F r i e d e l - C r a f t s c h e m i s t r y . As a r e s u l t o f t h i s , we have d e v e l o p e d and c o m m e r c i a l i z e d a p r o c e s s u s i n g the b a s i c A1C1 c a t a l y s t but w i t h c h e m i s t r y i n an a r e a c o m p l e t e l y d i f f e r e n t from t h a t p r e v i o u s l y u s e d . T h i s new homogeneous process e l i m i n a t e s o r g r e a t l y reduces most o f t h e problems a s s o c i a t e d w i t h the two-phase s y s t e m . 3

The Monsanto Texas C i t y l a b o r a t o r y d i s c o v e r e d t h a t e t h y l e n e would r e a c t c o m p l e t e l y and v i r t u a l l y i n s t a n t a n e o u s l y w i t h benzene c o n t a i n i n g o n l y a small amount o f d i s s o l v e d A 1 C 1 . The A I C I 3 i s used o n l y once and t h e r e i s no r e c y c l e . In t h i s homogeneous a l k y l a t i o n s y s t e m , c a r e has to be taken t o m i n i m i z e the f o r m a t i o n o f the h i g h e r e t h y l benzenes. These compounds a r e more b a s i c than 3



Dry Benzene

or HC1

Ethyl Chloride

Polyethyl benzenes

Figure 1.

cw

Ethylbenzene alkyhtion (two liquid phases)

Catalyst Complex

Alkylator

Ethylene


Separator

to Wash System

Alkylate

21.

Ethylbenzene

M A C F A R L A N E

Process

347


benzene, i n a Lewis s e n s e . In f a c t , the t e t r a e t h y l b e n z e n e s a r e p r o b a b l y b a s i c enough to t i e up the small amount o f aluminum c h l o r i d e c a t a l y s t p r e s e n t as a r e l a t i v e l y s t a b l e s a l t , thus s t o p p i n g the a l k y l a t i o n . D o e r i n g , e t a l , ( 5 ) i n 1958 had shown t h a t c a t a l y s t s i n r e a c t i o n s o f t h e F r i e d e l - C r a f t s type r a p i d l y become i n a c t i v a t e d due t o the p r e s e n c e o f h i g h e r a l k y l a t e d b e n z e n e s . F o r example, when working w i t h methyl b e n z e n e s , they showed t h a t a h e p t a m e t h y l benzenium i o n even more b a s i c than penta and hexamethylbenzene c o u l d be formed. T h i s heptamethyl i o n was so b a s i c t h a t i t was even e x t r a c t a b l e by aqueous h y d r o c h l o r i c a c i d ! S i n c e o n l y a small amount o f aluminum c h l o r i d e i s used i n t h i s homogeneous a l k y l a t i o n p r o c e s s , more c a r e has t o be taken t o c o n t r o l the method and r a t e o f a d d i t i o n o f e t h y l e n e t o the benzene. The a l k y l a t i o n r e a c t i o n v e s s e l i s d e s i g n e d t o accommod a t e s i m u l t a n e o u s l y both the v e r y r a p i d e t h y l e n e - b e n z e n e r e a c t i o n and the r e l a t i v e l y slow p o l y e t h y l b e n z e n e t r a n s a l k y l a t i o n r e a c tions. By c a r e f u l d e s i g n o f the r e a c t o r and c o n t r o l o f o p e r a t i n g c o n d i t i o n s , the f o r m a t i o n o f h i g h e r p o l y e t h y l b e n z e n e s can be minimized. The absence o f a c a t a l y s t complex phase has c e r t a i n a d v a n t ages. The a l k y l a t i o n t e m p e r a t u r e i s no l o n g e r l i m i t e d t o the 100°C r a n g e . Much h i g h e r t e m p e r a t u r e s can now be used w i t h o u t e x c e s s i v e y i e l d l o s s e s , t a r f o r m a t i o n , e t c . , and w i t h o n l y a moderate A1C1 usage i n o r d e r t o m a i n t a i n h i g h c a t a l y t i c a c t i v i t y . The use o f h i g h e r t e m p e r a t u r e s i n a l k y l a t i o n a l s o p e r m i t s r e c o v e r y o f the heat o f r e a c t i o n i n a waste heat b o i l e r , g e n e r a t i n g steam a t a u s e f u l p r e s s u r e . T h i s steam has a s i g n i f i c a n t e f f e c t on the e c o n o m i c s . The h i g h e r t e m p e r a t u r e s a l s o p e r m i t d e c r e a s e d use o f aluminum c h l o r i d e . A d d i t i o n a l l y , i t a l s o leads to a l e s s c o r r o s i v e environment. The t r a n s a l k y l a t i o n and i s o m e r i z a t i o n r e a c t i o n s can be s a t i s f a c t o r i l y e x p l a i n e d by t h e S t r e i t w i e s e r mechanism((5). This mechanism proposes a 1 , 1 - d i p h e n y l e t h a n e - t y p e i n t e r m e d i a t e . For example, p a r a - d i e t h y l b e n z e n e . ( F i g u r e 3) Such an i n t e r m o l e c u l a r mechanism i s c o n s i s t e n t w i t h t h e e x p e r i m e n t a l d a t a and does not r e q u i r e the assumption o f a sequence o f i n t r a m o l e c u l a r 1,2 s h i f t s . The decay o f the p o l y e t h y l b e n z e n e s towards e q u i l i b r i u m i s c o n s e c u t i v e and not c o n c u r r e n t . The c a t a l y s t seems t o be a s s o c i a t e d w i t h the most b a s i c c e n t e r ; and when i t r e a c h e s s t e a d y - s t a t e , the c a t a l y s t t r a n s f e r s t o t h e next most b a s i c o n e . There i s a l s o a c o n c u r r e n t i n t r a m o l e c u l a r i s o m e r i z a t i o n such as 1 , 2 , 4 t r i e t h y l benzene g o i n g t o 1 , 3 , 5 t r i e t h y l benzene. T h e r e i s hence a movement towards isomer e q u i l i b r i u m as w e l l as p r o d u c t e q u i l i b r i u m . Monsanto's r e a c t o r l a y o u t , i n s i m p l i f i e d f o r m , i s shown i n F i g u r e 2. Dry benzene, e t h y l e n e , c a t a l y s t , and promoter a r e f e d c o n t i n u o u s l y to t h e r e a c t o r . The a l k y l a t o r e f f l u e n t i s mixed w i t h p o l y e t h y l b e n z e n e s , m a i n l y d i e t h y l benzene r e c y c l e d from the s u b s e quent r e c o v e r y s y s t e m . The t r a n s a l k y l a t o r a l l o w s enough r e s i d e n c e time f o r the p r o d u c t to approach e q u i l i b r i u m . The aluminum 3

American Chemical Society Library 1155 16th St., M-W. Washington, D.C. 20036 Albright and Goldsby; Industrial and Laboratory Alkylations ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

348

INDUSTRIAL

AND

LABORATORY

ALKYLATIONS

Polye thylben zene s Recycle

Ethylene Dry Benzene ' Alkylate

HC1


AlClo

Alkylator Figure 2.

Transalkvlator

Alkyhtor reactor scheme (single liquid phase)

c

Figure 3.

Disproportionation of p-diethylbenzene


21.

M A C F A R L A N E

Ethylbenzene

Process

349

c h l o r i d e c a t a l y s t i s f e d to t h e a l k y l a t o r i n v e r y small amounts together with the feed m a t e r i a l s . The a l k y l a t e d hydrocarbon p r o d u c t i s no l o n g e r s a t u r a t e d w i t h A 1 C 1 . The A1C1 f e d i s used once t h r o u g h o n l y . The m a t e r i a l l e a v i n g t h e t r a n s a l k y l a t o r i s a d i a b a t i c a l l y f l a s h e d by s i m p l e p r e s s u r e r e d u c t i o n ( F i g u r e 4 ) . The f l a s h e d o r g a n i c s and HC1 a r e r e c o v e r e d and r e c y c l e d t o t h e a l k y l a t o r while o f f - g a s i s f l a r e d o r burned. With h i g h p u r i t y e t h y l e n e , t h e o f f - g a s stream i s v e r y small s i n c e a l l the e t h y l e n e i s r e acted. However, w i t h low p u r i t y e t h y l e n e , t h e o f f - g a s becomes s i g n i f i c a n t and has a p p r e c i a b l e f u e l v a l u e . Recovery and r e c y c l e o f HC1 a l l o w s c o n t r o l o f t h i s o p e r a t i n g v a r i a b l e o v e r a wide range w h i l e s t i l l m a i n t a i n i n g v e r y low u s a g e . The major v e s s e l s i n t h e r e a c t i o n system a r e c o n s t r u c t e d o f b r i c k - l i n e d carbon steel. The use o f h i g h e r a l l o y s i s r e q u i r e d o n l y f o r r e l a t i v e l y s h o r t runs o f p i p e and f o r the a l k y l a t o r w a s t e - h e a t b o i l e r .


3

Purification

o f Crude

3

Ethylbenzene

The p u r i f i c a t i o n o f t h e l i q u i d a l k y l a t e from t h e r e a c t i o n system i s done i n a c o n v e n t i o n a l f a s h i o n ( F i g u r e 5 ) . Before f e e d i n g the c r u d e e t h y l b e n z e n e t o d i s t i l l a t i o n , t h e aluminum c h l o r i d e and t h e r e s i d u a l HC1 must be c o m p l e t e l y removed. Water washing a c c o m p l i s h e s most o f t h i s t a s k ; f i n a l t r a c e s a r e removed by a c a u s t i c soda t r e a t m e n t . This process i s completely r e l i a b l e , i s f r e e from e m u l s i o n f o r m a t i o n , and t h e r e i s no downstream f o u l i n g o r c o r r o s i o n t o worry a b o u t . The washed a l k y l a t e i s f e d t o a s e r i e s o f t h r e e d i s t i l l a t i o n columns where benzene, e t h y l b e n z e n e , and d i e t h y l b e n z e n e - t r i e t h y l benzene m i x t u r e s a r e removed as overhead p r o d u c t s . The benzene i s r e c y c l e d t o the benzene d r y i n g column b e f o r e f e e d i n g a g a i n to the a l k y l a t o r . The d i e t h y l benzene m i x t u r e i s r e c y c l e d t o t h e transalkylator. The bottoms from the l a s t column i s what we c a l l "flux o i l . " This c o n s i s t s mainly of diphenyl ethanes. The amount o f t h i s m a t e r i a l i s good measure o f the o v e r a l l p r o c e s s y i e l d . The y i e l d l o s s i n t h i s p r o c e s s , depending on the a l k y l a t i o n system d e s i g n and c o n t r o l , i s between 0 . 6 and 0 . 9 l b f l u x o i l per 100 l b e t h y l b e n z e n e . Steam i s g e n e r a t e d by w a s t e - h e a t boilers. These t o g e t h e r w i t h t h e a l k y l a t i o n r e a c t o r w a s t e - h e a t b o i l e r a c c o u n t f o r 90 p e r c e n t o f the energy r e q u i r e d f o r t h e e n t i r e ethylbenzene u n i t . Catalyst

Manufacture

The aluminum c h l o r i d e c a t a l y s t f o r the a l k y l a t i o n p r o c e s s may be purchased m a t e r i a l o r t h e aluminum c h l o r i d e may be prepared i n s i t u . For l a r g e p l a n t s p r e p a r a t i o n i n s i t u from cheap powdered aluminum and anhydrous HC1 j s p r e f e r r e d ; however, e t h y l c h l o r i d e i s j u s t as e f f e c t i v e as HC1 a l t h o u g h more expensive. A small supplementary a g i t a t e d v e s s e l i s used t o



HC1

Benzene Ethylene Catalyst 1 Steam

Zone

Condenser

Flash-gas Absorber

Flash

Alkylationflowdiagram

Polyethylbenzene Recycle

TransAlky la tor

Figure 4.

Waste-heat Boiler

w

Alkylator

Off-gas

Χ


Alkylation -•Product To Wash System

Separator

Ο 2

Ε*

6

>

F

Ο

%

F

>

CO

21.

M A C F A R L A N E

Ethylbenzene

Process

Benzene Drying Column

351 Distillation

Recycle Benzene Ethylbenzene

Benzene


Ethylene

Flux O i l

CZ=H Catalyst Preparation

Figure 5.

A1C1

3

Ethylbenzeneflowdiagram

• C2H5CI «• C H5'C H5 + Catalys t Complex • A l k y l a t e 6

2

(or HC1)

C

Figure 6.

2

H

5

Catalyst complex preparation


352

INDUSTRIAL

AND

LABORATORY

ALKYLATIONS

p r e p a r e t h e c a t a l y s t i n t h e form o f t h e heavy l i q u i d c a t a l y s t complex o f f i x e d c o m p o s i t i o n [ 0 Η ^ Η ι , · Α ΐ 2 Π ~ ] ( F i g u r e 6 ) . T h i s i s a most c o n v e n i e n t way to h a n d l e , pump, and meter the a d d i t i o n o f the A 1 C 1 c a t a l y s t to t h e a l k y l a t o r , where i t promptly d i s s o l v e s i n the benzene m i x t u r e g i v i n g a c o m p l e t e l y homogeneous solution. 2

5

6

+

7

3

Spent C a t a l y s t

Disposal

The aluminum c h l o r i d e c a t a l y s t used i n the a l k y l a t i o n i s f i n a l l y r e j e c t e d from t h e system as an a c i d i c aqueous s o l u t i o n . T h i s b y - p r o d u c t A 1 C 1 i s u s u a l l y b e s t used f o r waste water t r e a t ment. S a l e o r use o f t h i s m a t e r i a l i s o f t e n as an alum o r copperas s u b s t i t u t e i n water c l a r i f i c a t i o n . I t i s a l s o used i n U . S . m u n i c i p a l sewage t r e a t m e n t p l a n t s , where a v a l u a b l e s i d e e f f e c t i s phosphate r e m o v a l . In Japan i t i s c o n v e r t e d t o p o l y aluminum c h l o r i d e (PAC) and used f o r water t r e a t m e n t . O t h e r uses f o r t h i s aqueous aluminum c h l o r i d e stream e x i s t . The Monsanto Texas C i t y p l a n t chooses t o use an e v a p o r a t i v e t r e a t m e n t f o r aqueous A 1 C 1 e f f l u e n t from t h e wash s y s t e m . ( 7 } T h i s c o n c e n t r a t e s the A1C1 and r e c o v e r s the HC1 as m u r i a t i c acid. T h i s l a t t e r m a t e r i a l i s , o f c o u r s e , v e r y u s e f u l i n the r e g e n e r a t i o n o f z e o l i t e water t r e a t i n g b e d s . An a d d i t i o n a l advantage o f t h e e v a p o r a t i v e t r e a t m e n t i s t h e freedom o f t h e c o n c e n t r a t e d b y - p r o d u c t A1C1 from p o s s i b l e o r g a n i c c o n t a m i n a t i o n . The i n c r e a s e d markets f o r aqueous aluminum c h l o r i d e c o u p l e d w i t h t h e d e c r e a s e d A 1 C 1 r e q u i r e m e n t s i n t h e homogeneous a l k y l a t i o n p r o c e s s a r e such t h a t d i s p o s a l o f t h i s b y - p r o d u c t i s not f o r e s e e n as a p r o b l e m .


3

3

3

3

3

Kinetic

Modeling

T h i s homogeneous v e r s i o n o f t h e c l a s s i c F r i e d e l - C r a f t s A 1 C 1 c h e m i s t r y has a n o t h e r i n t e r e s t i n g b y - p r o d u c t ; t h a t i s , t h e development o f an a c c u r a t e k i n e t i c model o f the r e a c t i o n . Earlier attempts t o model the r e a c t i o n w i t h t h e heavy c a t a l y s t complex phase p r e s e n t were u n s a t i s f a c t o r y . The i n f o r m a t i o n used i n b u i l d i n g t h e p r e s e n t m o d e l , and i t might be added f o r d e s i g n i n g the p l a n t , was g a i n e d from a o n e - l i t e r l a b o r a t o r y a u t o c l a v e opera t i n g under s e m i - b a t c h c o n d i t i o n s and a l s o from a f u l l y automated bench u n i t u s i n g r e a c t o r s w i t h d i a m e t e r s o f 1 1/2 i n c h e s . The m o d e l i n g work went hand i n hand w i t h t h e new i n s i g h t g a i n e d i n t o t h e chemical r e a c t i o n s t a k i n g p l a c e i n the s y s t e m . Two i m p o r t a n t p r e m i s e s made were f i r s t , t h a t t h e a l k y l a t i o n was an i r r e v e r s i b l e r e a c t i o n w i t h t r a n s a l k y l a t i o n a s e p a r a t e and independent r e a c t i o n , and s e c o n d , t h a t t h e r e a c t i o n r a t e o f molec u l a r e t h y l e n e i n the l i q u i d was not r a t e c o n t r o l l i n g as l o n g as the c o n c e n t r a t i o n s o f t h e h i g h e r p o l y e t h y l b e n z e n e s were low. This a l l o w e d t h e k i n e t i c c o n s t a n t s f o r the t r a n s a l k y l a t i o n model t o be e v a l u a t e d from t r a n s a l k y l a t i o n d a t a ; when t h e combined a l k y l a t i o n 3


21.

Ethylbenzene

M A C F A R L A N E

Process

353

t r a n s a l k y l a t i o n model was f i t t e d to a l k y l a t i o n d a t a , o n l y the r e l a t i v e r e a c t i o n r a t e s o f the benzene, e t h y l b e n z e n e and p o l y e t h y l benzenes had to be e v a l u a t e d i n terms o f the p r o c e s s variables. The r e s u l t i n g k i n e t i c model e x t r a p o l a t e s c o r r e c t l y t o extreme v a l u e s o f r e a c t i o n c o n d i t i o n s and a l s o a c c u r a t e l y f i t s the a r e a o f p r a c t i c a l i n t e r e s t now used i n the o p e r a t i n g plant. Choice o f Operating

Conditions

The major v a r i a b l e s c o n t r o l l i n g the a l k y l a t i o n and t r a n s a l k y l a t i o n r e a c t i o n s a r e as f o l l o w s : TABLE

II

A 1 C 1 Catalyst Concentration HCl Promoter C o n c e n t r a t i o n Temperature R e s i d e n c e Time E/B M o l a r R a t i o ( E t h y l Groups/Benzene Pressure


3

Rings)

The d e t a i l e d mathematical model o f the chemical r e a c t i o n s has r e v e a l e d t h e p r e s e n c e o f c e r t a i n r e l a t i v e l y sharp optima f o r these r e a c t i o n v a r i a b l e s . I f , f o r example, i t i s d e s i r e d t o reduce t h e A 1 C 1 usage t o a minimum v a l u e , then the k i n e t i c model can be used t o show the e f f e c t o f each o f the v a r i a b l e s on t h e A I C I 3 c a t a l y s t c o n c e n t r a t i o n . To make t h e comparison e f f e c t i v e , i t s h o u l d be made a t the same q u a l i t y o f a l k y l a t e . T h i s , f o r example, can be c o n v e n i e n t l y e x p r e s s e d as the c o n c e n t r a t i o n o f t e t r a e t h y l b e n z e n e i n the product. I t w i l l be r e c a l l e d t h a t i n t h e homogeneous system the amounts o f h i g h e r p o l y e t h y l b e n z e n e s must be s e v e r e l y r e s t r i c t e d because o f t h e i r r e l a t i v e l y basic nature. F i g u r e 7 shows a p l o t o f p e r c e n t t e t r a e t h y l b e n z e n e v e r s u s temperature a t v a r i o u s A 1 C 1 usages. The graph shows t h a t a t g i v e n p e r c e n t a g e the A 1 C 1 requirements can be reduced by i n c r e a s e s i n t e m p e r a t u r e . For s i m p l i c i t y o f p r e s e n t a t i o n , the o t h e r v a r i a b l e s have been h e l d c o n s t a n t . 3

3

3

S i m i l a r l y , F i g u r e 8 shows the e f f e c t o f l i q u i d r e s i d e n c e time on the A 1 C 1 requirements. The graphs showing t h e e f f e c t s o f the o t h e r v a r i a b l e s on A I C I 3 usage a l l show t h e same t y p e o f c u r v e s w i t h f a i r l y p r o nounced b r e a k p o i n t s . I t i s , o f c o u r s e , most advantageous t o operate at or c l o s e to the b r e a k p o i n t s . The homogeneous a l k y l a t i o n p r o c e s s a l l o w s a s u r p r i s i n g l y wide range o f o p e r a t i o n . Changes i n one o r more o f the v a r i a b l e s can be used t o m i n i m i z e a n o t h e r o f the v a r i a b l e s . T h u s , t h e r e a c t i o n c o n d i t i o n s can be t a i l o r e d t o o p t i m i z e the economics f o r a p a r t i c u l a r s e t o f l o c a l conditions. For example, a p l a n t can be d e s i g n e d to o p t i m i z e t o t a l c o s t c o n s i d e r i n g c a p i t a l , raw m a t e r i a l s , c a t a l y s t , and 3


INDUSTRIAL


354

AND

LABORATORY

ALKYLATIONS

Tetra E B , wt. %

Temperature, ° C

Figure 7.

Alkylator—effect of temperature



21.

M A C F A R L A N E

Ethylbenzene

Process

Tetra E B , wt. %

Residence Time, minutes

Figure 8.

Alkyhtor—effect of residence time


355

356

INDUSTRIAL

AND

LABORATORY

ALKYLATIONS

utilities. Once the p l a n t i s b u i l t i t can be o p e r a t e d f o r minimum c o s t w i t h o p e r a t i n g c o n d i t i o n s changed as r e q u i r e d by c h a n g i n g e n e r g y and raw m a t e r i a l c o s t s . The homogeneous a l k y l a t i o n p r o c e s s i s a l s o a d a p t a b l e t o t h e use o f d i l u t e e t h y l e n e s t r e a m s . Here t h e a l k y l a t i o n p r e s s u r e has t o be somewhat h i g h e r , but the p r o c e s s i n g i s q u i t e s i m i l a r . A modern s t y r e n e f a c i l i t y i s c u r r e n t l y under c o n s t r u c t i o n i n A u s t r a l i a u s i n g t h i s d i l u t e C Hi* homogeneous a l k y l a t i o n p r o c e s s . 2

Conclusions I t i s c o n c l u d e d t h a t e l i m i n a t i o n o f the s e p a r a t e c a t a l y s t complex phase i n the A1C1 a l k y l a t i o n p r o c e s s adds s i g n i f i c a n t l y to i t s a t t r a c t i v e n e s s . In a d d i t i o n t o the ease w i t h which a l i q u i d phase c a t a l y s t can overcome any p o i s o n i n g and g e t back on s t r e a m , t h e new homogeneous p r o c e s s can o p e r a t e a t h i g h e r t e m p e r a t u r e s and r e c o v e r the heat o f r e a c t i o n t o g e n e r a t e steam. I t can a l s o o p e r a t e i n a l e s s c o r r o s i v e environment w h i l e p r o d u c i n g an e t h y l b e n z e n e p r o d u c t o f e x c e p t i o n a l p u r i t y and can reduce t h e amount o f aluminum c h l o r i d e r e q u i r e d s e v e r a l f o l d . The p a y o f f i n any development such as t h i s i s i n u l t i m a t e plant operation. T h i s p r o c e s s was c o n c e i v e d i n the l a b o r a t o r y and s c a l e d up w i t h a good u n d e r s t a n d i n g o f t h e b a s i c c h e m i s t r y . The new a l k y l a t i o n p r o c e s s has been i n o p e r a t i o n a t M o n s a n t o ' s Texas C i t y p l a n t s i n c e F e b r u a r y 1974. T y p i c a l operating data a r e shown i n T a b l e I I I . I t i s b e l i e v e d t o be t h e w o r l d ' s largest s i n g l e - t r a i n a l k y l a t o r (Figure 9). I t has a demonstrated c a p a c i t y o f 30% to 115% o f d e s i g n and has o p e r a t e d e x t r e m e l y smoothly s i n c e s t a r t u p w i t h o u t p r o c e s s o r m e c h a n i c a l p r o b l e m s . O p e r a t i o n s have been c h a r a c t e r i z e d by low maintenance c o s t s and low c a t a l y s t u s a g e . We a r e w e l l p l e a s e d w i t h t h i s p r o c e s s and b e l i e v e i t t o be the b e s t proven a l k y l a t i o n a v a i l a b l e . Five companies have r e c e n t l y s e l e c t e d t h i s p a t e n t e d p r o c e s s (8) f o r i n s t a l l a t i o n around the w o r l d ; i n c l u d i n g Pemex a t t h e i r new complex a t La C a n g r e j e r a .


3

Acknowledgement The a u t h o r wishes t o e x p r e s s h i s a p p r e c i a t i o n t o h i s c o workers on t h i s p r o j e c t , p a r t i c u l a r l y t o F. A p p l e g a t h and L. E. Dupree, f o r t h e i r s u g g e s t i o n s and a s s i s t a n c e w i t h t h i s paper.

Abstract The majority of the ethylbenzene manufactured in the world i s produced by the c l a s s i c a l Friedel-Crafts reaction involving the ethylation of benzene in the presence of aluminum chloride as a c a t a l y s t . It has been customary f o r the aluminum chloride to be present in f a i r l y large amounts as a separate heavy


M A C F A R L A N E

Ethylbenzene

Process

357


21.

Figure 9.

Single train alkylator used to produce 1.7 billion pounds of ethylbenzene per year


INDUSTRIAL

TABLE

AND

LABORATORY

ALKYLATIONS

III

TYPICAL OPERATING DATA ETHYLBENZENE FROM BENZENE AND ETHYLENE


Feed R e q u i r e m e n t s ,

l b / l b Ethylbenzene

(100% B a s i s )

Ethylene Benzene Co-Products,

lb/lb

0.267 0.742 Ethylbenzene

Steam Aluminum C h l o r i d e Catalysts

and C h e m i c a l s ,

Sol.,

25%

lb/lb

0.99 0.008

Ethylbenzene

Aluminum C h l o r i d e Anhydrous HC1 (a) C a u s t i c Soda (100% B a s i s )

0.0019 0.0006 0.00065

(a) May s u b s t i t u t e e t h y l c h l o r i d e on a mole f o r mole b a s i s . Utilities,

per lb

Ethylbenzene

Steam (200 p s i g ) Fuel ( L H V ) , Btu C o o l i n g Water (16°F R i s e ) , l b s P r o c e s s and B o i l e r Feed W a t e r , l b s E l e c t r i c i t y , kwh

0.037 832 23 1.11 0.013


21.

M A C F A R L A N E

Ethylbenzene

Process

359

catalyst complex phase which i s subsequently separated from the alkylated organics layer and continuously recycled to the alky l a t o r . This catalyst complex phase has been found to be not only unnecessary but actually harmful i n obtaining maximum y i e l d s , purity, and minimum catalyst usage. This paper describes the s i n g l e - t r a i n Monsanto ethylbenzene unit i n s t a l l e d at Texas City having a capacity of 1.7 b i l l i o n pounds a year. Literature Cited (1) (2) (3)


(4) (5) (6) (7) (8)

Radziewanoski, C., Ber., 27, 3235 (1894). Hornibrook, J . N., Chem. and Ind., May 19, 1962, p. 872. Donaldson, J . W., "ETHYLENE," Chapter 11 (edited by S. A. M i l l e r ) Benn London 1969. Albright, L. F., Process f o r Major Addition Type P l a s t i c s and Their Monomers, McGraw-Hill, 1974. Doering, W. Von E., et. al., Tetrahedron, 1958, Vol. 4, p. 178. Streitweisser, Α., and Reif, L. J . , Am. Chem. S o c , 1960, 82, 5003. Campbell, D. N. This Book, Next Chapter, 1977. U.S. Patent 3,848,012 (Nov. 12, 1974) to Monsanto Company. U.S. Patent 3,899,545 (Aug. 12, 1975) to Lummus Company.


Industrial and Laboratory Alkylations - American Chemical Society

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