A Kinetic Study on the Formation of Aromatics During Pyrolysis of

10 A Kinetic Study on the Formation of Aromatics During Pyrolysis of Petroleum Hydrocarbons ΤΟΜΟΥΑ SAKAI and DAISUKE NOHARA Dept. of Chemical Reaction Engineering, Nagoya City University, 3-1, Tanabedori, Mizuhoku, Nagoya, 467 Japan TAISEKI KUNUGI

Downloaded by CORNELL UNIV on July 19, 2016 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/bk-1976-0032.ch010

Dept. of Synthetic Chemistry, Faculty of Engineering, University of Tokyo, 7-1, Hongo, Bunkyoku, Tokyo, 113 Japan F o r t h e p y r o l y s i s o f p a r a f f i n i e h y d r o c a r b o n s a t 700 - 8 0 0 ° C , y i e l d s of o l e f i n s such as e t h y l e n e , p r o p y l e n e , b u t è n e s , b u t a d i e n e and c y c l o o l e f i n s i n c r e a s e d u r i n g t h e i n i t i a l s t a g e o f t h e r e a c t i o n , p a s s t h r o u g h t h e i r maxima, and l a t e r d e c r e a s e ; y i e l d s o f a r o m a t i c s , h y d r o g e n and methane however i n c r e a s e m o n o t o n i c a l l y t h r o u g h o u t t h e reaction course. S a k a i e t a l . (1) r e p o r t e d p r e v i o u s l y t h e r e s u l t o f a k i n e t i c s t u d y on t h e r m a l r e a c t i o n s o f e t h y l e n e , p r o p y l e n e , b u t è n e s , b u t a d i e n e and t h e s e r e s p e c t i v e o l e f i n s w i t h b u t a d i e n e a t the c o n d i t i o n s s i m i l a r to those of p a r a f f i n p y r o l y s i s , d i r e c t i n g t h e i r a t t e n t i o n on t h e r a t e s o f f o r m a t i o n o f c y c l i c compounds. K i n e t i c f e a t u r e s of the t h e r m a l r e a c t i o n s of t h e s e o l e f i n s a r e summarized i n T a b l e I combined w i t h t h e r e s u l t s o b t a i n e d i n l a t e r i n v e s t i g a t i o n s f o r t h e r m a l r e a c t i o n s o f c y c l o o l e f i n s (2) and b e n z e n e (_3). T h e r m a l r e a c t i o n s o f e t h y l e n e (4,_5) r e q u i r e h i g h e r t e m p e r a t u r e s ( 7 5 0 - 800°C) than the o t h e r o l e f i n s . I n i t i a l reaction produ c t s a r e b u t a d i e n e , 1 - b u t e n e , p r o p y l e n e , e t h a n e and a c e t y l e n e . As t h e y i e l d s o f t h e s e i n i t i a l p r o d u c t s d e c r e a s e w i t h i n c r e a s e d r e s i d e n c e t i m e s , c y c l i c compounds s u c h a s c y c l o p e n t e n e , c y e l o p e n t a d i e n e , c y c l o h e x e n e and b e n z e n e a r e p r o d u c e d . In the case of p r o p y l e n e (6,_7), t h e r e a c t i o n p r o c e e d s 2 - 4 t i m e s f a s t e r t h a n t h a t o f e t h y l e n e ; and e t h y l e n e , m e t h a n e , b u t a d i e n e , b u t è n e s , a c e t y l e n e , and m e t h y l c y c l o p e n t e n e a r e t h e m a i n p r o d u c t s d u r i n g t h e i n i t i a l s t e p ; c y c l o p e n t a d i e n e , c y c l o p e n t e n e , b e n z e n e , t o l u e n e and p o l y c y c l i c compounds h i g h e r t h a n o r e q u a l t o n a p h t h a l e n e a r e p r o d u c t s of secondary r e a c t i o n s . A remarkable f a c t f o r the t h e r m a l r e a c t i o n o f p r o p y l e n e i s t h a t t h e y i e l d s o f f i v e membered r i n g compounds a r e l a r g e r t h a n t h o s e i n t h e c a s e o f e t h y l e n e . D i f f e r e n t f e a t u r e s were observed between the t h e r m a l r e a c t i o n o f 1 - b u t e n e and t h o s e o f c i s - and t r a n s - 2 - b u t e n e s a t 640 - 6 8 0 ° C (jL). In the former case, the r e a c t i o n proceeded mainly i n t h r e e w a y s ; t h e s e w e r e p y r o l y s i s t o methane and p r o p y l e n e , dehydrogenat i o n t o b u t a d i e n e , and p y r o l y s i s t o two m o l e s o f e t h y l e n e ; t h e r a t i o of r a t e s f o r these three r e a c t i o n s are 4 : 3 : 1 , respectively. I n t h e l a t t e r c a s e s , t h e m a i n r e a c t i o n was i s o m e r i z a t i o n between 152

Albright and Crynes; Industrial and Laboratory Pyrolyses ACS Symposium Series; American Chemical Society: Washington, DC, 1976.


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c i s - and t r a n s - 2 - b u t e n e , and t h e s e l e c t i v i t i e s o f o t h e r r e a c t i o n s t h a n t h e i s o m e r i z a t i o n w e r e s u p r e s s e d t o l e s s t h a n 10%. C y c l i z a t i o n p r o c e e d e d i n n e a r l y 100% s e l e c t i v i t y i n t h e c a s e of t h e r m a l r e a c t i o n of b u t a d i e n e ( 1 ) , y i e l d i n g 4 - v i n y l c y c l o h e x e n e (VCH) f o r t h e f i r s t s t e p and e t h y l e n e , c y c l o h e x e n e , c y c l o h e x a d i e n e , and b e n z e n e i n t h e s e c o n d a r y s t e p s . Similar highly select i v e c y c l i z a t i o n s were observed f o r t h e r e a c t i o n s between b u t a d i e n e and e t h y l e n e , p r o p y l e n e , 1 - b u t e n e , c i s - 2 - b u t e n e , t r a n s - 2 b u t e n e o r i s o b u t y l e n e ( 1 ) , y i e l d i n g c y c l o h e x e n e (HCH), 4 - m e t h y l c y c l o h e x e n e (MCH), 4 - e t h y l c y c l o h e x e n e , c i s - 4 , 5 - d i m e t h y l c y c l o hexene, t r a n s - 4 , 5 - d i m e t h y l c y c l o h e x e n e or 4 , 4 - d i m e t h y l c y c l o h e x e n e , respectively. B a s e d on t h e a b o v e i n f o r m a t i o n , i t c a n be s a i d t h a t b u t a d i e n e p l a y s an i m p o r t a n t r o l e i n the f o r m a t i o n of c y c l i c compounds i n p y r o l y s i s c o n d i t i o n s . N e x t , i n o r d e r t o l e a r n more a b o u t t h e r a t e s o f d e h y d r o g e n a t i o n of c y c l o h e x e n e s r e s u l t i n g from D i e l s - A l d e r r e a c t i o n s between b u t a d i e n e and o l e f i n s , VCH, HCH and MCH w e r e e a t l i e t ? s u b j e c t e d t o t h e r m a l r e a c t i o n s a t 5 3 0 - 665°C ( 2 ) . The m a i n r e a c t i o n s i n t h e s e c a s e s w e r e r e v e r s e D i e l s - A l d e r r e a c t i o n s and d e h y d r o g e n a t i o n s . DeKydrogenations which are r e l a t e d to the productions of c y c l o h e x a d i e n e and b e n z e n e h o m o l o g u e s w e r e 1 : 10 i n s e l e c t i v i t y a s c o m p a r e d t o t h a t o f t h e r e v e r s e D i e l s - A l d e r r e a c t i o n . An i n t e r e s t i n g o b s e r v a t i o n r e l a t e d t o c y c l i c compound f o r m a t i o n i s t h a t , i n t h e c a s e o f MCH p y r o l y s i s , c y c l o h e x a d i e n e and c y c l o p e n t e n e a r e f o r m e d a t a l m o s t t h e same r a t e s as b u t a d i e n e a n d p r o p y l e n e . So t h a t , i n t h i s c a s e , a b o u t 60% o f MCH i s e m p l o y e d i n t h e f o r m a t i o n o f c y c l i c compounds. T h e r m a l r e a c t i o n o f b e n z e n e (3) p r o c e e d e d a t 800 - 8 5 0 ° C p r o d u c i n g b i p h e n y l and h y d r o g e n . B e n z e n e was t h e most r e f r a c t o r y m a t e r i a l of the f e e d s t o c k s employed i n t h e s e e x p e r i m e n t s . The a d d i t i o n o f 3 - 4 wt% o f n a p h t h a l e n e t o b e n z e n e d i d n o t g r e a t l y a f f e c t the r e a c t i o n k i n e t i c s or product s e l e c t i v i t y . However, when e t h y l b e n z e n e was a d d e d i n t h e same s m a l l amount, f e a t u r e s o f the r e a c t i o n were q u i t e changed. No w h i t e c r y s t a l l i n e p r o d u c t was o b t a i n e d , and i n s t e a d a t a r r y m a t t e r c o v e r e d t h e i n s i d e o f t h e reactor. B a s e d on t h e k i n e t i c d a t a o b t a i n e d a b o v e , a t e n t a t i v e c a l c u l a t i o n was e a r l i e r p e r f o r m e d t o d e t e r m i n e w h e t h e r o r n o t t h e r a t e o f c y c l i c compound f o r m a t i o n i n a c t u a l p y r o l y s i s r e a c t i o n s c a n b e a c c o u n t e d f o r through the D i e l s - A l d e r r e a c t i o n s between b u t a d i e n e and o l e f i n s . The a c t u a l r a t e o f c y c l i c compound f o r m a t i o n was much g r e a t e r t h a n t h e r a t e c a l c u l a t e d f r o m t h e c o n c e n t r a t i o n s o f b u t a d i e n e and o l e f i n s i n t h e a c t u a l p y r o l y s i s c o n d i t i o n s . A l l y l r a d i c a l s were t e s t e d as m a t e r i a l s o r s u b s t a n c e s t h a t cause c y c l i z a t i o n w i t h o l e f i n s . 1 , 5 - H e x a d i e n e ( d i a l l y l ) and d i a l l y l o x a l a t e (DAO) w e r e u s e d a s t h e s o u r c e m a t e r i a l s f o r a l l y l radicals. T h e s e compounds w e r e s u b j e c t e d t o t h e t h e r m a l r e a c t i o n i n the presence of e t h y l e n e , w h i c h r e s u l t e d i n a r a p i d f o r m a t i o n o f f i v e - m e m b e r e d c y c l i c compounds. The r o l e o f a l l y l r a d i c a l f o r t h e f o r m a t i o n o f a r o m a t i c s i n p y r o l y s i s r e a c t i o n i s however s t i l l


154

INDUSTRIAL AND LABORATORY PYROLYSES Table I. Reactant

A Summary of Rate Data on Thermal

Temperature (°C)

Product

primary

OC

700 - 850

C4H , 1-C4H , C H ,

C=C-C

700 - 850

C

C=C-C-C

640 - 680

6

3

8

C H2, C H , H 2

2

H

2


640 - 680

4

8

2

2

3

6

6640 40

-- 6680 80

550 - 750

550

- 750

OC-OC + OC

510

- 590

o c - o c + oc-c

510

- 590

o c - o c + c=c-c-c

510

- 590

O C - O C + C-OC-C

(cis-)

510

- 590

O C - O C + C-OC-C

(tr-)

510

- 590

510

- 590

530

- 585

C C—C*C Ι" e

cr

Q

(Q)

558855 -- 666655

σ

575

- 650

CH4, H

2

, Q ,

0'©

2

H

6

CH4, H O , ( 0 ) ,

,

2

O.C/.jgj', C H 2

C H

8

2

4

6

cis-C4H , C4H6, cis-C4H8, CH , C H

C H4

8

3

2

6

cr 0 σ cr α

ί J "

ΟΌ'^'

C

CH , C H , H 4

3

6

a σ

or

C H 4

C2H C H 4 ,, 2

6

CC HH 44

4

0 Q C Hσ,0 ®-, C H , 3

C H

6

4

C H

66

3

6

6

CH , 4

2

700

- 850

6

8

4

4

OC-OC + OC-OC

4

6

6

3

C - O C - C (tr-)

C

fy> C H , CH4, H CH4, C H , C4H , C H , 2-C4H 's trans-C H , €4%, CH4, C H 2

C-OC-C (cis-)

6

ΰ Η ,

,

4

6

secondary

4

Pyrene, CH4 H , 2

C H 2

4


2

2

H

4

,

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Reactions of O l e f i n s , Cycloolefins and Benzene ( > mol, sec)

log k

ml

Reaction order

500

600

1.5

-

1.5

1 0

Ε

(kcal/mol)

log^gA (ml, mol, sec)

700

800

-

0.59

1.63

49.6

11.73

-

-

0.86

2.19

63.2

15.06

1.0

-

-1.88

-0.30

61.3

13.47

1.0

-

-0.51

0.95

56.5

13.64

1.0

-

-0.50

0.97

57.2

13.82

24.8

10.41

28.8

10.68

29.7

10.40

52.7

15.67

54.7

15.97

30.6

10.80

45.8

14.06

60.6

15.05

4.84

5.36

2.0

3.40

4.20

2.0

2.54

3.47

2.0

2.00

2.96

2.0

0.77

2.48

2.0

0.50

2.27

2.0

2.14

3.14

2.0

1.11

2.59

1.0

-2.09

-0.12

1.0

-3.09

-1.52

-

48.4

10.60

1.0

-3.57

-1.44

_

65.7

15.01

1.0

-4.02

-2.25

11.50

1.0

-3.41

-1.31

64.9

14.94

1.0

-3.67

-1.69

-

54.9

1.0

-3.94

-1.92

1.0

-3.52

-1.92

-

-

1.0(?)

-

-2.96

-1.80

61.1

13.61

62.4

13.70

49.55

10.49

55.0

9.40


156

INDUSTRIAL AND LABORATORY PYROLYSES

o b s c u r e b e c a u s e t h e c y c l i z e d compounds p r o d u c e d f r o m a l l y l r a d i c a l and o l e f i n s w e r e e x c l u s i v e l y f i v e - m e m b e r e d r i n g compounds d u r i n g t h e i n i t i a l s t a g e o f the r e a c t i o n ( 8 ) . However, i n c o m b i n a t i o n w i t h the i s o m e r i z a t i o n r e a c t i o n s of s u b s t i t u t e d cyclopentenes which are expected to proceed e a s i l y at p y r o l y s i s c o n d i t i o n s , i t i s l i k e l y that a l l y l r a d i c a l s are important intermediates causing the a r o m a t i z a t i o n of o l e f i n s .


Experimental S e v e r a l methods a r e known f o r t h e g e n e r a t i o n o f a l l y l r a d i c a l . James and T r o u g h t o n (9) commented on t h e p h o t o l y s e s o f d i c y c l o p r o p y l k e t o n e , p r o p y l e n e , 1 - b u t e n e , and c y c l o p r o p a n e and r a d i o l y s i s of d i a l l y l k e t o n e . M c D o w e l l and S i f n i a d e s (10) and James and Kambanis (11) o b t a i n e d t h e a l l y l r a d i c a l f r o m p h o t o l y s e s o f c r o t o n a l d e h y d e and d i a l l y l o x a l a t e a t l o w t e m p e r a t u r e s , r e s p e c t i v e l y . A l - S a d e r and C r a w f o r d (12) o b t a i n e d a l l y l r a d i c a l s by t h e r m o l y s i s of 3 , 3 - a z o - 1 - p r o p e n e . Some o f t h e a b o v e m a t e r i a l s may however h a v e s e v e r a l d i s a d v a n t a g e s s u c h as p r e l i m i n a r y i s o m e r i z a t i o n o f r e a c t a n t s , c o n c o m i t a n t g e n e r a t i o n o f o t h e r r e a c t i v e s p e c i e s , comp l e x i t y o f t h e s u c c e s s i v e and c o m p e t i n g r e a c t i o n s , and d i f f i c u l t y i n raw m a t e r i a l p r e p a r a t i o n s . At r a t h e r e l e v a t e d temperatures, i t i s thought t h a t d i a l l y l produces a l l y l r a d i c a l s s o l e l y d u r i n g the very i n i t i a l stage of the p y r o l y s i s . DAO was employed as t h e s o u r c e m a t e r i a l f o r a l l y l r a d i c a l s f o r r e a c t i o n s t o be i n v e s t i gated a t lower temperatures. The p u r i t y o f d i a l l y l s a m p l e was more t h a n 9 9 . 4 wt% by gas chromatographic a n a l y s i s a f t e r d i s t i l l a t i o n w i t h a spinning-band r e c t i f i c a t i o n c o l u m n o f 60 s t a g e s . The m a i n i m p u r i t y was 1 - h e x e n e . DAO was s y n t h e s i z e d and d i s t i l l e d a c c o r d i n g t o a method r e p o r t e d i n t h e l i t e r a t u r e ( 1 3 ) . P o l y m e r i z a t i o n g r a d e e t h y l e n e was u s e d w i t h o u t p u r i f i c a t i o n s . I m p u r i t i e s i n the e t h y l e n e sample were methane and e t h a n e i n 0 . 0 1 and 0 . 0 7 m o l %, r e s p e c t i v e l y . Nitrogen f r o m a c y l i n d e r was d e o x y g e n a t e d by p a s s i n g i t t h r o u g h a r e d u c e d c o p p e r g a u z e a t 250°C f o l l o w e d by d r y i n g i n a s i l i c a g e l column. A c o n v e n t i o n a l f l o w - t y p e r e a c t i o n s y s t e m was u s e d f o r r e a c tions at atmospheric pressure. The l i q u i d s a m p l e was v a p o r i z e d a t 0 ° C w i t h t h e a i d o f n i t r o g e n and e t h y l e n e f l o w s , and t h e r e s u l t i n g mixtures then entered the r e a c t o r . The r e a c t o r was a n a n n u l a r q u a r t z c y l i n d e r o f 200 mm l e n g t h and 1 0 . 6 mm i . d . , e q u i p p e d c o a x i a l l y w i t h a t h e r m o w e l l o f 7 . 2 mm o . d . The r e a c t o r was p o s i t i o n e d i n a n e l e c t r i c a l l y h e a t e d b r a s s b l o c k o f 180 mm l e n g t h , 18 mm i . d . , and 55 mm o . d . The t e m p e r a t u r e p r o f i l e o f t h e r e a c t o r was m e a s u r e d f o r e a c h r u n , and t h e r e s i d e n c e t i m e s o f t h e r e a c t a n t s w e r e d e t e r m i n e d by t h e method o f Hougen and Watson ( 1 4 ) . I n l e t and o u t l e t g a s e s w e r e a n a l y z e d by u s e o f f l a m e - i o n - d e t e c t o r gas c h r o m a t o g r a p h s e q u i p p e d w i t h 50 m c a p i l l a r y c o l u m n s c o a t e d w i t h s q u a l a n e and d i - n - b u t y l m a l e a t e a t 50 and 0 ° C , r e s p e c t i v e l y . 1


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157

R e s u l t s and D i s c u s s i o n


In the p r e s e n t i n v e s t i g a t i o n , the thermal r e a c t i o n s of d i a l l y l o r DAO i n e x c e s s n i t r o g e n o r e t h y l e n e w e r e c o n d u c t e d i n a flow system. Information concerning the r e a c t i o n s of the a l l y l r a d i c a l w i t h o l e f i n s were o b t a i n e d , e s p e c i a l l y t h e r e a c t i o n s r e s u l t i n g i n t h e f o r m a t i o n o f C 5 c y c l i c compounds. The d e t a i l e d product d i s t r i b u t i o n s are given for v a r i e d conversion l e v e l s . The p r i m a r y and s e c o n d a r y p r o d u c t s a r e c l e a r l y s e p a r a t e d . A r e a c t i o n scheme i s p r o p o s e d t o e x p l a i n q u a l i t a t i v e l y t h e f o r m a t i o n o f p r i mary and s e c o n d a r y p r o d u c t s . T h e r m a l R e a c t i o n o f D i a l l y l . O v e r a l l mass b a l a n c e s f o r t h e p y r o l y s i s experiments of d i a l l y l i n excess n i t r o g e n g e n e r a l l y were w i t h i n 9 6 - 99 %. I t was c o n f i r m e d t h a t t h e e f f e c t o f t h e q u a r t z s u r f a c e o n t h e r e a c t i o n was n e g l i g i b l e u n d e r t h e p r e s e n t c o n d i tions. The c o n v e r s i o n o f t h e r e a c t a n t h a s b e e n d e f i n e d a s t h e r a t i o o f t h e sum o f t h e p e a k a r e a s o f p r o d u c t s t o t h a t o f a l l p e a k a r e a s o f t h e gas c h r o m a t o g r a m . T y p i c a l k i n e t i c r e s u l t s are l i s t e d i n Table I I , i n which the p r o d u c t d i s t r i b u t i o n s a r e p r e s e n t e d as the weight per cent of the i n d i v i d u a l p r o d u c t s i n t h e t o t a l p r o d u c t s e x c l u d i n g C 1 2 and h i g h e r compounds. A k i n e t i c m o d e l b a s e d on t h e 3 / 2 - o r d e r f i t s t h e e x p e r i m e n t a l results. From A r r h e n i u s p l o t s , t h e o v e r a l l r e a c t i o n r a t e c o n s t a n t was o b t a i n e d as k = 1 0 1 3 . 5 e x p ( - 4 4 , 5 0 0 / R T ) m l l / 2 m o l " / s e c " . The e x a m i n a t i o n o f t h e p r o d u c t d i s t r i b u t i o n v s . r e s i d e n c e t i m e c u r v e s a t f o u r t e m p e r a t u r e l e v e l s r e v e a l e d t h a t t h e same mechanism a p p l i e d f o r t h e r e a c t i o n w i t h i n t h e p r e s e n t e x p e r i m e n t a l c o n d i t i o n s , so t h a t , i n F i g u r e 1, the p r o d u c t d i s t r i b u t i o n v s . c o n v e r s i o n curves were a d o p t e d . From F i g u r e 1 , i t i s c l e a r t h a t t h e p r i m a r y p r o d u c t s o f t h e thermal r e a c t i o n of d i a l l y l are e t h y l e n e , propylene, 1-butene, b u t a d i e n e , 1 - p e n t e n e , c y c l o p e n t e n e , c y c l o p e n t a d i e n e , and 1 , 3 , 5 h e x a t r i e n e , and t h e s e c o n d a r y p r o d u c t s a r e 1 , 3 - c y c l o h e x a d i e n e and benzene. T r a c e amounts o f m e t h a n e , p r o p a n e , and 1 , 4 - p e n t a d i e n e were a l s o f o u n d i n some e x p e r i m e n t s . No h y d r o g e n was d e t e c t e d by a n i t r o g e n c a r r i e r gas c h r o m a t o g r a p h w i t h MS 5A c o l u m n . The f o r m a t i o n o f C12 compounds was n o t i c e d a t l o w t e m p e r a t u r e s . A small amount o f l i q u i d p r o d u c t was f o u n d i n t h e s e p a r a t o r t u b e a f t e r 50 o r more e x p e r i m e n t a l r u n s . The a v e r a g e m o l e c u l a r w e i g h t o f t h e l i q u i d p r o d u c t was 428 b a s e d on t h e method o f H i l l ( 1 5 ) . By e x t r a p o l a t i n g t h e c u r v e s i n F i g u r e 1 t o z e r o c o n v e r s i o n , the molar r a t i o s of formation of i n d i v i d u a l products at the i n i t i a l s t a g e of the r e a c t i o n were approximated as l i s t e d i n Table I I I , i n w h i c h t h e amount o f e t h y l e n e was t a k e n a s u n i t y . From T a b l e I I I and F i g u r e 1, t h e r a d i c a l c h a i n mechanism o f t h e t h e r m a l r e a c t i o n o f d i a l l y l i s p r o p o s e d as f o l l o w s . 1

Initiation:

1.

c=c-c~c-c=e

(i)

2

2 c=c-o


1

Albright and Crynes; Industrial and Laboratory Pyrolyses ACS Symposium Series; American Chemical Society: Washington, DC, 1976. 94.58

The r e m a i n d e r c o n s i s t s o f s e v e r a l m i n o r p r o d u c t s s u c h a s m e t h a n e , propane, 1,4-pentadiene, e t c .

94.58

4.31

17.55

0.00

8.02

2.40

2.80

9.76

b)

excluded.

91.04

2.77

12.92

3.16

8.33

3.25

3.63

9.27

8.24

F o r m a t i o n o f C^2 and h i g h e r compounds i s

94.09

0.42

6.62

9.85

9.10

12.96

8.45

32.92

8.58

6.44

0.140

620

Diallyl

a)

b

Total >

13.59

1,3,5-Hexatriene

0.00

6.73

Cyclopentadiene

Benzene

-

Cyclopentene

6.62

3.43

5.51

1-Pentene

1,3-Cyclohexadiene

4.76

11.93

Butadiene

7.67

9.94

1-Butene

32.14

30.97

Propylene

31.12

9.29

7.12

2.07

0.386

580

of

8.16

0.437

0.314

540

Ethylene

P r o d u c t d i s t r i b u t i o n ) , wt %

0.075

C o n v e r s i o n , wt %

500

E x p e r i m e n t a l D a t a on P y r o l y s i s

0.273

3

Typical

Residence time, sec

T e m p e r a t u r e , °C

T a b l e II.



Figure 1. Product distribution vs. conversion for pyrolysis of diallyl


ΟΙ

h-»

CO

δ"

ι

ο

ο

>

S

Ο

160



Propagation:

(ID

2.

C=C-C-

+

I

C=C-C

3.

c=c-c-

+

I

e=c-e-c-c-e-c-c=c

(III)

c=c-c-c-c-c-c-c=c

(IV)

+

C=C-C-C-C=C

4.

III

5.

III

Û*

+ c=c-c=c

6.

III

Ο

+ c=e-e-c-

7.

III

Ô

+ c=c-c-c

8.

IV

9.

Cr +

I

+

I

10. 11.

o*

c=c-c-c-cc=c-c-

+ c=c +

c=c-c-c-c-c

£5

+ c=c-c-c-c-c-

Ο

+

13.

ό c=c-c- c - o

c=c-c-

14.

c=c-c- c-c- +

c=c-c-c-c

15.

c=c-c- c-

C= C - C - C

12.

16. 17.

+

II

H>

+ c=c + +

II II

C=C-C=C-C=C

+

Η·

c=c-c= c-c=c

18. 19.

H-

20.

Η·

c

+ 1

C=C-C-C-C-C

+

I

C=C-C-C-C-C-

c=c-c- c-c-c

C=C-C-

22.

c=c-c- c-c-c-

C=C-C-C-

II

2H-

+

21.

23.

+ c=c-c=c

+

η 1

+

C=C-C +

C=C

Ρ·

Termination : 24.

H-

25.

H-

26. 27.

+ + 2R+

RH PH RR PR

28.

PP 2PThe i n i t i a t i o n r e a c t i o n i s assumed t o b e t h e d e c o m p o s i t i o n o f d i a l l y l i n t o two a l l y l r a d i c a l s . L o s s i n g e t a l . ( 1 6 ) , R u z i c k a and B r y c e (17) and A k e r s and T h r o s s e l l (18) a l s o s u g g e s t e d t h e same i n i t i a t i o n r e a c t i o n . An a l l y l r a d i c a l g e n e r a t e d by r e a c t i o n 1 a b s t r a c t s hydrogen from the parent molecule to produce propylene as i n r e a c t i o n 2 . E x i s t e n c e of the 1 , 5 - h e x a d i e n y l r a d i c a l ( I I ) i s s u p p o r t e d b y R u z i c k a and B r y c e (17) a n d James and T r o u g h t o n ( 9 ) .



10.

SAKAi

ET AL.


161

Another r e a c t i o n of a l l y l r a d i c a l Table I I I . Molar R a t i o of i s an a d d i t i o n t o t h e p a r e n t m o l e P r o d u c t s a t Zero Conver c u l e , i . e . , r e a c t i o n 3 , to form s i o n R e l a t i v e to Ethylene I I I , w h i c h undergo hydrogen s h i f t on P y r o l y s i s o f D i a l l y l to produce IV, i . e . , r e a c t i o n 4. 1 The a p p r e c i a b l e amount o f C5 Ethylene compounds ( 1 - p e n t e n e , c y c l o p e n 2.22 Propylene t e n e , and c y c l o p e n t a d i e n e ) o b t a i n e d 0.46 1-Butene as p r i m a r y p r o d u c t s l e a d s t o t h e 0.54 Butadiene p o s t u l a t i o n of s e v e r a l r e a c t i o n s of 1-Pentene 0.20 C9 r a d i c a l s d e s i g n a t e d a s I I I o r 0.22 Cyclopentene Cyclopentadiene 0.36 IV. They a r e r e a c t i o n s 5 - 8 . Radi c a l s produced i n these r e a c t i o n s 0.37 1,3,5-Hexatriene undergo e i t h e r u n i m o l e c u l a r s c i s 1,3-Cyclohexadiene 0 s i o n or bimolecular r e a c t i o n with 0 Benzene I to form 1-pentene, c y c l o p e n t a d i e n e , and o t h e r p r i m a r y p r o d u c t s as shown i n r e a c t i o n s 9 - 1 5 . T h e s e schemes a r e p a r t l y i n l i n e w i t h t h e one o f R u z i c k a and B r y c e ( 1 7 ) . D i s a g r e e m e n t s e x i s t i n t h a t (a) n e i t h e r m e t h y l c y c l o p e n t e n e n o r h y d r o g e n was d e t e c t e d , (b) f o r m a t i o n o f methane was n e g l i g i b l y s m a l l , and ( c ) a l l C5 com pounds w e r e o b t a i n e d a s p r i m a r y p r o d u c t s i n t h e p r e s e n t s t u d y a s compared t o f i n d i n g s o f R u z i c k a and B r y c e . Among t h e 0$ compounds p r o d u c e d , o n l y 1 , 3 , 5 - h e x a t r i e n e i s t h e primary product. R e a c t i o n 16 i s p r o p o s e d f o r i t s f o r m a t i o n . James and T r o u g h t o n (9^) o b t a i n e d e t h y l e n e and 1 , 3 , 5 - h e x a t r i e n e as t h e p r i m a r y p r o d u c t s i n t h e i r s t u d y on t h e r e a c t i o n o f d i a l l y l w i t h t h e e t h y l r a d i c a l a t 134 - 1 7 5 ° C . Furthermore, they o b t a i n e d 1 , 3 - c y c l o h e x a d i e n e as a s u c c e s s i v e p r o d u c t . R e c e n t l y O r c h a r d and T h r u s h (19) r e p o r t e d t h e t h e r m a l i s o m e r i z a t i o n o f 1 , 3 , 5 - h e x a t r i e n e t o 1 , 3 - c y c l o h e x a d i e n e a t c a . 400°C and t h e c o n s e c u t i v e f o r m a t i o n o f benzene a t c a . 550°C. In the present work, 1,3-cyclohexadiene ( r e a c t i o n 17) and b e n z e n e ( r e a c t i o n 18) w e r e o b t a i n e d a s t h e secondary p r o d u c t s . The h y d r o g e n atom p r o d u c e d i n r e a c t i o n s 1 2 , 16 and 18 i s c o n s i d e r e d t o r e a c t w i t h t h e p a r e n t m o l e c u l e i n two ways a s shown i n r e a c t i o n s 19 and 2 0 . T h e s e r a d i c a l s decompose t o p r o d u c e t h e a l l y l r a d i c a l and p r o p y l e n e i n r e a c t i o n 21 and t h e b u t e n y l r a d i c a l and e t h y l e n e i n r e a c t i o n 2 2 . R e a c t i o n 23 i s p r o p o s e d b e c a u s e C12 i h i g h e r compounds w e r e n o t i c e d i n the p r o d u c t s . Ρ· r e p r e s e n t s s u c h o l i g o m e r s . The t e r m i n a t i o n r e a c t i o n s a r e d e s c r i b e d by r e a c t i o n s 2 4 - 2 8 ; R« r e p r e sents a l l r a d i c a l species. The f a c t t h a t no c y c l o h e x e n e was d e t e c t e d i n t h e p r e s e n t e x periments suggests that the r a t e of c y c l i z a t i o n through D i e l s A l d e r r e a c t i o n b e t w e e n formed b u t a d i e n e and o l e f i n s i s s m a l l e r t h a n t h e r a t e o f c y c l i z a t i o n c a u s e d by t h e r e a c t i o n o f a l l y l r a d i c a l w i t h o l e f i n s at these temperatures. a n
-(V-r-—A—r

5 Conversion x,

°

C4H6

%

10

Product distribution OS. decomposition of DAO in excess ethylene

l i n e s obtained i n such r e l a t i o n s h i p correspond to the r a t e s of formation of the r e s p e c t i v e p r o d u c t s . The c o n c e n t r a t i o n s o f a l l y l r a d i c a l i n t h e p r e s e n t e x p e r i ments w e r e e s t i m a t e d by means o f t h e r a t e e q u a t i o n b e l o w . A second-order r a t e constant kg f o r recombination of a l l y l r a d i c a l t o d i a l l y l was a p p r o x i m a t e d t o be 5 . 0 x 1 0 ^ 1 / m o l - s e c by e x t r a p o l a t i o n f r o m t h e v a l u e r e p o r t e d by G o l d e n e t a l . ( 2 2 ) . The r a t e o f d i a l l y l f o r m a t i o n was o b t a i n e d f r o m t h e l i n e a r r e l a t i o n s h i p b e t w e e n t h e c o n c e n t r a t i o n o f d i a l l y l and t h e r e s i d e n c e t i m e a s mentioned above. This r a t e i s s u b s t i t u t e d i n the f o l l o w i n g equat i o n i n order to c a l c u l a t e the a l l y l r a d i c a l c o n c e n t r a t i o n . d[diallyl]/dt

=

k

0

[allyl-]

2

The c o n c e n t r a t i o n o f e t h y l e n e and t h e c a l c u l a t e d c o n c e n t r a t i o n o f a l l y l r a d i c a l w e r e employed i n t h e r e a c t i o n mechanism p o s t u l a t e d i n the preceeding s e c t i o n to estimate the o v e r a l l r a t e constants of the r e a c t i o n s of a l l y l r a d i c a l w i t h e t h y l e n e to produce both c y c l o p e n t e n e and 1 - p e n t e n e . Experimental r a t e s of formations of c y c l o p e n t e n e and 1 - p e n t e n e w e r e o f c o u r s e a l s o u s e d i n t h e s e c a l culations . E x p e r i m e n t a l e v i d e n c e i n d i c a t e s a d i s t i n c t d i f f e r e n c e between t h e r a t e o f f o r m a t i o n o f c y c l o p e n t e n e and t h a t o f 1 - p e n t e n e . Over-


174


_ 8 Ο CD CO

.

0

•

1.30

1.35

1.40

(1/T)X10*


Figure 9. Arrhenius plots for the overall reaction of allyl radical with ethylene to cyclopentene and 1-pentene formation

Figure 10.

Energy diagram related to reaction of allyl radical with ethylene


10. SAKAI ET AL.


c=c-e-* + c = c «

30

175

JlrQ--^ »

£ ) +H.

c=c-c-c-e-*

-30


+ C=C

C=C-C-C-C + C=0

a l l r e a c t i o n r a t e c o n s t a n t s f o r the f o r m a t i o n s of c y c l o p e n t e n e and 1 - p e n t e n e s h o u l d be d i f f e r e n t i n t h e same manner. Moreover, the t e m p e r a t u r e d e p e n d e n c i e s o f t h e s e two o v e r a l l r a t e c o n s t a n t s a r e i l l u s t r a t e d i n F i g u r e 9 ; the o v e r a l l a c t i v a t i o n energy f o r the f o r m a t i o n o f c y c l o p e n t e n e and t h a t o f 1 - p e n t e n e w e r e f o u n d t o be 1 1 . 5 and 1 6 . 7 k c a l / m o l e , r e s p e c t i v e l y . The d i f f e r e n c e o f t h e s e two a c t i v a t i o n e n e r g i e s , i . e . , 5 k c a l / m o l e , c o r r e s p o n d s t o 4 k c a l / mole o b t a i n e d i n F i g u r e 5 f o r the r e a c t i o n of d i a l l y l i n e x c e s s ethylene. R e f e r r i n g t o t h e r e a c t i o n mechanism p o s t u l a t e d a b o v e , i t c a n be s a i d t h a t t h e r a t e - d e t e r m i n i n g s t e p o f t h e o v e r a l l r e a c t i o n i s not the a d d i t i o n r e a c t i o n of a l l y l r a d i c a l s to ethylene. Above a l l , t h e i m p o r t a n t f a c t i s t h a t a c t i v a t i o n e n e r g i e s o f 1 1 . 5 and 1 6 . 7 k c a l / m o l e w e r e needed f o r r e a c t i o n s t e p 33 o r 35 a n d t h a t of 34, r e s p e c t i v e l y . From t h e h e a t c o n t e n t o f s t a b l e a l l y l r a d i c a l (38 k c a l / m o l e ) and e t h y l e n e ( 1 2 . 5 k c a l / m o l e ) , t h e e n e r g y content of the r e a c t i o n i n t e r m e d i a t e which i s converted to c y c l o p e n t e n e and 1 - p e n t e n e i s n o t s m a l l e r t h a n 62 - 67 k c a l / m o l e . This h i g h energy content of the i n t e r m e d i a t e s t r o n g l y supports the p r e d i c t i o n of a hot 4 - p e n t e n y l r a d i c a l i n the p r e s e n t s t u d y . Step 33 p r o c e e d s r e a d i l y i n t h e c a s e o f h o t 4 - p e n t e n y l r a d i c a l a s s t a t e d i n t h e p r e c e e d i n g s e c t i o n . The same s i t u a t i o n e x i s t s f o r s t e p 34 b e c a u s e t h e h e a t c o n t e n t o f v i n y l r a d i c a l i s a s h i g h as 67 - 69 k c a l / m o l e ( 3 2 ) . T h u s , t h e e x i s t e n c e o f t h e h o t 4 - p e n t e n y l r a d i c a l was r e c o n f i r m e d d u r i n g t h e r e a c t i o n o f an a l l y l r a d i c a l with ethylene. F i g u r e 10 i l l u s t r a t e s t h e h e a t c o n t e n t s o f k e y r a d i c a l s s u c h as r e p o r t e d i n t h e l i t e r a t u r e ( 2 3 , 2 6 , 2 8 , 3 3 ) . A c t i v a t i o n energies obtained i n the present i n v e s t i g a t i o n f o r r e a c t i o n s s t a r t i n g from a l l y l r a d i c a l p l u s e t h y l e n e t o c y c l o p e n t e n e and 1 - p e n t e n e f o r m a t i o n f i t the diagram c o n s i s t e n t l y . This f i g u r e strongly supports t h e c o n c l u s i o n s t h a t i t i s i m p o s s i b l e t o p r o d u c e any l i n e a r ( c y c l i z e d ) C5 r a d i c a l s f r o m s t a b l e c y c l o p e n t y l ( 4 - p e n t e n y l ) r a d i c a l s , and t h a t , i n t h e c a s e o f t h e r e a c t i o n o f a n a l l y l r a d i c a l w i t h e t h y l e n e , i t i s p o s s i b l e t o p r o d u c e b o t h c y c l i z e d and l i n e a r C5 compounds a t t h e same t i m e .

Abstract A summary of rate data is given for the systematic study of the formation of cyclic compounds during thermal reactions of olefins or of olefins with butadiene. As a next step in order to investigate cyclization at pyrolysis conditions, the reactions of allyl radicals with olefins were studied kinetically. 1,5-Hexadiene (diallyl) and diallyl oxalate (DAO) were employed as source


176


materials for allyl radical generation. Thermal reactions of pure d i a l l y l and of d i a l l y l or DAO i n the presence of excess ethylene were conducted at 430 - 700°C to obtain cyclopentene and other olefins. The rate of cyclopentene formation was relatively large, but C cyclic compounds were not found in appreciable amounts. The reaction mechanism is discussed kinetically for the formation of cyclopentene from an allyl radical and ethylene. 6

Literature Cited


(1)

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