Discovery and Development of Olefin ... - ACS Publications

29 Discovery and Development of Olefin Disproportionation (Metathesis)

Downloaded by UNIV LAVAL on July 13, 2016 | http://pubs.acs.org Publication Date: June 3, 1983 | doi: 10.1021/bk-1983-0222.ch029

ROBERT L. BANKS Phillips Petroleum Company, Bartlesville, OK 74004 Heterogeneous catalyst studies and factors that contributed to the discovery of the olefin disproportionation (metathesis) reaction are described. Also provided is a personal commentary on the developments of heterogeneous catalyst technology associated with this intriguing reaction and its commercialization. One of the most f a s c i n a t i n g r e a c t i o n s of hydrocarbons to emerge i n recent years i s the catalyzed d i s p r o p o r t i o n a t i o n or metathesis of o l e f i n s . F i r s t d i s c l o s e d i n 1964 ( 1) , t h i s v e r s a t i l e r e a c t i o n has opened up a new and e x c i t i n g f i e l d of hydrocarbon chemistry. I t has been studied i n research i n s t i t u t i o n s throughout the world, r e s u l t i n g i n more than 2000 p u b l i c a t i o n s , and has been the t o p i c of four i n t e r n a t i o n a l symposiums (2). Commercially, i t i s used f o r the i n t e r c o n v e r s i o n of l i g h t o l e f i n i c hydrocarbons, the backbone of today's petrochemical industry, and f o r the synthesis of o l e f i n s f o r the s p e c i a l t y chemicals market (_3, 4) . Observed i n 1959 during an i n v e s t i g a t i o n i n our l a b o r a t o r y of a new heterogeneous c a t a l y s t composition (1, % 6), t h i s novel r e a c t i o n i s now known to be catalyzed by a number of both heterogeneous and homogeneous systems; the l a t t e r were d i s c l o s e d i n 1967 by Calderon and coworkers a t Goodyear (7) and i n 1968 by Zuech a t P h i l l i p s (8). We r e f e r r e d to the new r e a c t i o n , which can be v i s u s a l i z e d (Figure 1) by the breaking and reformation o f two o l e f i n i c bonds (the type and number o f bonds remaining unchanged), as " o l e f i n d i s p r o p o r t i o n a t i o n . " However, the scope of the r e a c t i o n r a p i d l y broadened to the extent that the term "disproport i o n a t i o n " d i d not s t r i c t l y apply to a l l cases, prompting the uses of a v a r i e t y of names (e.g., " o l e f i n r e a c t i o n " ) . The term " o l e f i n metathesis," introduced by the Goodyear workers (7), covers the broad scope o f the r e a c t i o n and i s now commonly used. Presented i n t h i s paper i s a review o f the heterogeneous c a t a l y s t studies i n our l a b o r a t o r y that l e d to the discovery of the o l e f i n d i s p r o p o r t i o n a t i o n r e a c t i o n , accompanied by personal comments on the development of heterogeneous c a t a l y s t technology associated with t h i s i n t r i g u i n g r e a c t i o n . 0097-6156/8 3/0222-0403$06.00/0 © 1983 American Chemical Society

Davis and Hettinger; Heterogeneous Catalysis ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

HETEROGENEOUS

404

R I I 2

R

3

R ι— C — C — R4 + « R 5— C — C Rg I I R 5 R 7


F i g u r e 1.

R I

Rι

C

Re

C

2

3

C

R

C

Rg

II + II

R6

New

R I _

CATALYSIS

I I

4

^7

o l e f i n reaction.

Following World War I I , process research at P h i l l i p s had be come e s s e n t i a l l y research i n c a t a l y s i s and I became involved i n heterogeneous c a t a l y s t studies d i r e c t e d toward improving p e t r o leum r e f i n i n g technology and f i n d i n g more e f f i c i e n t ways to u t i l i z e petroleum resources. The goal of our s p e c i f i c research p r o j e c t i n 1959 was to develop an e f f e c t i v e heterogeneous c a t a l y s t that would r e p l a c e mineral a c i d s used to c a t a l y z e the o l e f i n - p a r a f f i n a l k y l a t i o n r e a c t i o n . That work, i n turn, u t i l i z e d techniques evolving from our e a r l i e r development of a supported chromium oxide p o l y m e r i z a t i o n c a t a l y s t ( P h i l l i p s Marlex P o l y o l e f i n P r o c e s s ) , e s p e c i a l l y the procedures to e l i m i n a t e traces of c a t a l y s t poisons from hydrocarbon feed and the e x p e r i mental system. During the screening of p o t e n t i a l heterogeneous c a t a l y s t compositions f o r a l k y l a t i o n a c t i v i t y , Group VI t r a n s i t i o n metal hexacarbonyls became a v a i l a b l e i n experimental q u a n t i t i e s and we speculated that i f these zero-valent metal compounds could be supported on a high s u r f a c e area s u b s t r a t e , they might e x h i b i t unique c a t a l y t i c p r o p e r t i e s . The key f a c t o r was to support the carbonyl compounds without d e s t r o y i n g t h e i r i n t e g r i t y . A pro cedure, now commonly used i n homogeneous-heterogeneous c a t a l y s t preparations, was developed that consisted of impregnating under vacuum a p r e c a l c i n e d (500 to 600°C) support with a non-aqueous (e.g., cyclohexane) s o l u t i o n of the metal carbonyl and removing, by n i t r o g e n f l u s h i n g followed by a vacuum treatment at a tempera ture s l i g h t l y below the decomposition temperature of the metal carbonyl, the hydrocarbon solvent from the c a t a l y s t (1) . Molybdenum hexacarbonyl supported on high s u r f a c e area gamma alumina was the f i r s t c a t a l y s t prepared by the new technique. In the i n i t i a l t e s t of that c a t a l y s t f o r a l k y l a t i o n a c t i v i t y , we recovered a small amount of l i q u i d product equivalent to l e s s than one per cent of the butene-isobutane feed mixture. However, BGLC (Before Gas L i q u i d Chromatography) a n a l y s i s of t h i s seemingly i n s i g n i f i c a n t amount of product revealed that i t consisted almost e n t i r e l y of 2-pentene rather than products of a l k y l a t i o n or d i m e r i z a t i o n r e a c t i o n s ( i . e . , Ce hydrocarbons). T h i s r e s u l t was both unexpected and p u z z l i n g : N-Butenes/Isobutane ->• 2-Pentene? Thus, the experiment was repeated. D e t a i l e d analyses of the t o t a l e f f l u e n t from the reactor showed that butènes disappeared and that propylene, i n a d d i t i o n to pentenes, was a r e a c t i o n product. Of s i g n i f i c a n c e to us was that propylene and 2-pentene were formed i n n e a r l y equimolar amounts:


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BANKS

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Olefin Disproportionation

N-Butenes

M6(C0) «A1 03. Catalyst 6

2

Propylene + Pentenes + 51% 40%

C+ 9% 6

We concluded that the o l e f i n component of the feed mixture had been d i s p r o p o r t i o n a t e d to homologs of s h o r t e r and longer carbon chains (1). A d d i t i o n a l s t u d i e s with v a r i o u s o l e f i n i c hydrocarbons v e r i f i e d that a new c a t a l y t i c r e a c t i o n had been discovered i n which the o l e f i n i c bonds are c a t a l y t i c a l l y cleaved and recombined i n a h i g h l y s p e c i f i c and e f f i c i e n t manner to form new o l e f i n i c products.


E a r l y C a t a l y s t Developments The d i s c o v e r y of a new r e a c t i o n c a t a l y z e d by a new c a t a l y s t composition prompted the immediate t e s t i n g of other supported t r a n s i t i o n metal carbonyls. Tungsten carbonyl supported on alumina c a t a l y z e d o l e f i n d i s p r o p o r t i o n a t i o n but was l e s s a c t i v e than the molybdenum homolog. Chromium carbonyl behaved as a polymerization c a t a l y s t . No advantage was observed v i a s u b s t i t u t i n g part of the carbonyls with Π-coordinating l i g a n d s . How ever, an i n t e r e s t i n g phenomenon emerged from those s t u d i e s . When ethylene was contacted with Mo(CO)6·AI2O3, cyclopropane was a r e a c t i o n product, Table 1 (1): Table 1.

Ethylene r e a c t i o n s over group VI metal hexacarbonyls (5)

Alumina impregnated with W(C0) Mo (CO)s Cr(C0) 26 3 1- Butene 71 26 2- Butene 8 28 Propylene 21 Cyclopropane 8 Methylcyclopropane 12 S o l i d Polyethylene 97 Product, wt %

a. b.

6

Tests at 120°C and 500 Secondary r e a c t i o n s .

6

Type of Reaction Dimerization ^ Isomerization ^ Disproportionation Ring c l o s u r e Ring c l o s u r e Polymerization

psig.

This o b s e r v a t i o n was c o n s i s t e n t both with the mechanistic scheme we i n i t i a l l y considered (four-carbon m e t a l l o c y c l e ) and the c u r r e n t l y favored metallocarbene mechanism (2). To shed some l i g h t on the nature of the a c t i v e s p e c i e s , carbon monoxide pressure was monitored; the p a r t i a l l o s s of CO's occurred under both p r e p a r a t i o n (solvent removal) and r e a c t i o n c o n d i t i o n s . At that stage of the c a t a l y s t s t u d i e s (Spring, 1960), Grant C. B a i l e y and I considered the p o s s i b i l i t y that metal oxides, corresponding to the carbonyls, might a l s o e x h i b i t s i m i l a r c a t a l y t i c p r o p e r t i e s . We found that not only d i d supported


HETEROGENEOUS CATALYSIS

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molybdenum and tungsten oxides promote the d i s p r o p o r t i o n a t i o n of o l e f i n s , but they were more a c t i v e than the corresponding c a r bonyls. One of the most a c t i v e of the metal oxide c a t a l y s t s was a commercial cobalt molybdate c a t a l y s t (3% CoO/8% M 0 O 3 / 89% A I 2 O 3 ) , making i t apparent that the d i s p r o p o r t i o n a t i o n r e a c t i o n had been o c c u r r i n g unnoticed i n r o u t i n e hydrocarbon processes. Emphasis i n the l a b o r a t o r y r a p i d l y s h i f t e d to the development of the more a c t i v e oxide c a t a l y s t s . C a t a l y s t compositions and c a t a l y s t a c t i v a t i o n s and pretreatments were i n v e s t i g a t e d . Various o l e f i n i c hydrocarbons were tested and the ranges of r e a c t i o n c o n d i t i o n s (e.g., F i g u r e 2) were e s t a b l i s h e d f o r patent coverage and f o r p r e l i m i n a r y economic e v a l u a t i o n . Evaluation The i n i t i a l i n v e s t i g a t i o n of c o b a l t molybdate c a t a l y s t s provided data f o r conceptual designs and economic a p p r a i s a l s of s e v e r a l of many suggested a p p l i c a t i o n s of o l e f i n metathesis. Economics f o r converting propylene to ethylene and butènes were found to be f a v o r a b l e and i t appeared that the proposed process could be a p p l i e d commercially i n s e v e r a l areas: e.g., balancing o l e f i n production from naphtha c r a c k i n g u n i t s , producing h i g h p u r i t y ethylene f o r chemical p l a n t s i n remote l o c a t i o n s , and combining with a l k y l a t i o n u n i t s to produce higher octane g a s o l i n e . Thus, the d i s p r o p o r t i o n a t i o n of propylene was s e l e c t e d f o r the i n i t i a l development of o l e f i n metathesis technology. Because three o l e f i n s were i n v o l v e d , the name " T r i o l e f i n Process" was chosen. Development E a r l y i n 1962, f o l l o w i n g P h i l l i p s Management's d e c i s i o n to develop the T r i o l e f i n Process, l a b o r a t o r y s t u d i e s were resumed and expanded. In a d d i t i o n to conducting a d e t a i l e d i n v e s t i g a t i o n of cobalt molybdate c a t a l y s t systems, an extensive search f o r other c a t a l y s t compositions a c t i v e f o r o l e f i n metathesis was made. Concurrent with these i n v e s t i g a t i o n s were s t u d i e s designed to expand the scope and explore other a p p l i c a t i o n s of o l e f i n metathesis r e a c t i o n s , P i l o t p l a n t development of T r i o l e f i n Process technology was i n i t i a t e d about s i x months a f t e r l a b o r a tory s t u d i e s had been resumed. The search f o r new c a t a l y s t compositions, conducted by L. F. Heckelsberg, produced a l a r g e l i s t of heterogeneous compositions e f f e c t i v e f o r metathesis r e a c t i o n s (9). A major f i n d i n g of Dr. Heckelsberg was that molybdenum and tungsten oxides supported on high surface area s i l i c a were very a c t i v e f o r o l e f i n metathesis at temperatures s e v e r a l hundred degrees higher than the optimum temperature f o r the alumina-based c a t a l y s t s (10). I n t e r e s t i n g p r o p e r t i e s were e x h i b i t e d by supported rhenium oxide c a t a l y s t s :



29. BANKS


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while rhenium oxide supported on alumina i s very a c t i v e at room temperatures, on s i l i c a i t d i s p l a y e d two temperatures at which a c t i v i t y maxima occur. Although most c a t a l y s t s that were a c t i v e f o r metathesis contained a t r a n s i t i o n metal, i t was found that magnesium oxide, when treated with carbon monoxide, c a t a l y z e d the d i s p r o p o r t i o n a t i o n of propylene without the b e n e f i t of a promoter (6). These new c a t a l y s t s broadened the e f f e c t i v e temperature range f o r metathesis r e a c t i o n s , a l l o w i n g the s e l e c t i o n , f o r s p e c i f i c a p p l i c a t i o n s , of a r e a c t i o n temperature which f a v o r s metathesis over competing s i d e r e a c t i o n s (e.g., high temperature needed f o r i s o b u t y l e n e metathesis to be the predominant r e a c t i o n ) (6). Following Heckelsberg's d i s c o v e r y of high-temperature metat h e s i s c a t a l y s t s (Spring, 1963), emphasis i n p i l o t plant and l a b o r a t o r y development of the T r i o l e f i n Process was switched from the c o b a l t molybdate c a t a l y s t to s i l i c a - b a s e d c a t a l y s t s . T h i s change f a c i l i t a t e d c a t a l y s t r e g e n e r a t i o n ( p a r t l y e l i m i n a t i n g c o s t l y h e a t i n g - c o o l i n g c y c l e s ) and s i g n i f i c a n t l y reducing r e a c t o r s i z e ( e q u i l i b r i u m conversions were achieved at space r a t e s an order of magnitude h i g h e r ) . The s i l i c a - b a s e d c a t a l y s t s were a l s o more r e s i s t a n t to poisons; i n most cases the a c t i v i t i e s of these c a t a l y s t s were f u l l y r e s t o r e d when the c a t a l y s t poison was removed from the feed (Figure 3) (10). One disadvantage of the s i l i c a - b a s e d c a t a l y s t s was that they had not been commercially produced and procedures and s p e c i f i c a t i o n s f o r commercial product i o n had to be developed. Since s i l i c a i s extremely d i f f i c u l t to form i n t o t a b l e t s or extrudates, a key hurdle was the development of a technique f o r forming p a r t i c l e s of s a t i s f a c t o r y crushing strength without impairing a c t i v i t y or s e l e c t i v i t y . E a r l y l a b o r a t o r y studies showed that the primary d i s p r o p o r t i o n a t i o n products of propylene were ethylene and c i s - and trans-2 -butene; 1-butene and C 5 + product e x t r a p o l a t e d to zero at zero contact time (Figure 4) (_1) . The r e v e r s i b i l i t y of metathesis r e a c t i o n s was a l s o demonstrated. An i n t e r e s t i n g s e l e c t i v i t y phenomenon was observed f o r the d i s p r o p o r t i o n a t i o n of butènes: the conversion of a mixture of 1-butene and 2-butene was higher than the conversion of e i t h e r o l e f i n by i t s e l f . Furthermore, w h i l e the d i s p r o p o r t i o n a t i o n of 1-butene favored the production of ethylene and hexene, a butene mixture r i c h i n 2-butene tended to produce propylene and pentenes, i n d i c a t i n g that the predominant r e a c t i o n occurred between the 1-butene and 2-butene. The r e s u l t s of the above and s i m i l a r studies provided the b a s i s f o r a key c o n t r i b u t i o n that aided the development of o l e f i n metathesis technology at P h i l l i p s : D. L. C r a i n , i n 1963, recognized that product d i s t r i b u t i o n s obtained by d i s p r o p o r t i o n a t i o n of v a r i o u s o l e f i n s and mixtures of o l e f i n s could be e x p l a i n ed by a concerted " f o u r - c e n t e r mechanistic scheme (Figure 5A). T h i s mechanism was proposed i n a l a t e r p u b l i c a t i o n of Bradshaw and coworkers of B r i t i s h Petroleum (11). Although the simple " f o u r - c e n t e r " , or "quasi-cyclobutene," scheme i s no longer the 11


408


•

PROPYLENE

•

1-BUTENE


Ο 2-BUTENE •

1-PENTENE

•

2-PENTENE

•

1-HEXENE

Δ

1-OCTENE

200 300 400 500 600 TEMPERATURE, F. F i g u r e 2 . E f f e c t o f t e m p e r a t u r e on d i s p r o p o r t i o n a t i o n c o n v e r s i o n over cobalt molybdate-alumina. (Reproduced from Réf. 1. Copyr i g h t 1964, American Chemical Society.)

I 0

I 1

L 2

TIME, HOURS Figure 3. Temporary e f f e c t o f c a t a l y s t poisons on s i l i c a based c a t a l y s t s . (Reproduced from Ref. 10. Copyright 1968, American Chemical Society.)


29.

409


BANKS

40

—A

*

trans-2-BUTENE

A

•

35

ζ 2 Η

30

ω ο 2 g h- oc

25

"V^ETHYLENE

Η Ο •

(/> û .


I-

20

cis-2-BUTENE

•

° 15

—

10

—

C

5

+ RESIDUE

Ο >

oc û.

1-BUTENE

A

5

0

•ι 0

10

20

1

1

30

40

1

1 50

60

CONTACT TIME, SECONDS F i g u r e 4. Propylene product d i s t r i b u t i o n at zero contact time. (Reproduced from Ref. 1. Copyright 1964, American Chemical Society.) A. FOUR-CENTER:

I

I

— C= C — - C

= C -

I

*

I

B. CARBENE:

I

M

I I

—c

Η

II

•c

I I

I

— C= C — _ M= C —

m

•c

-c

c— II

c—

c—

II

II

M

c—

I

c—

ι :

—c= c— c— I

— FigureM5. C Mechanistic schemes f o r o l e f i n metathesis.

I



410


accepted mechanism f o r o l e f i n metathesis r e a c t i o n s , i t s e a r l y use i n guiding and planning c a t a l y s t m o d i f i c a t i o n studies and i n extending o l e f i n metathesis to other o l e f i n i c hydrocarbons was extremely b e n e f i c i a l . The e l u c i d a t i o n of the r o l e of double-bond i s o m e r i z a t i o n a c t i v i t y i n metathesis process i s an example of the h e l p f u l n e s s of the four-center mechanism. As the scheme p r e d i c t e d , i n c e r t a i n a p p l i c a t i o n s the elimination, of double-bond i s o m e r i z a t i o n a c t i v i t y ( a c i d i c i s o m e r i z a t i o n s i t e s were destroyed by v a r i o u s mild c a u s t i c treatments) prevented secondary metathesis r e a c t i o n r e s u l t i n g i n very high s e l e c t i v i t y to s p e c i f i c products (5). In c o n t r a s t , i n other a p p l i c a t i o n s (e.g., l i n e a r o l e f i n and neohexene processes) to obtain a high l e v e l of productive metathesis, the mechanistic scheme i n d i c a t e d a need f o r enhanced isomerizat i o n a c t i v i t y ; t h i s was accomplished by a d d i t i o n of a very s e l e c t i v e double-bond i s o m e r i z a t i o n c a t a l y s t to the scheme (5). G. C. Ray and D. L. C r a i n used the scheme to p o s t u l a t e that metathesis r e a c t i o n s could be extended to the cleavage of c y c l i c o l e f i n s with ethylene to y i e l d alpha-omega d i o l e f i n s (Figure 6). The four-center scheme implies that i n theory the number of metathesis r e a c t i o n s i s l i m i t e d only by the number of compounds containing carbon-carbon multitype bonds. P i l o t plant development of T r i o l e f i n Process technology, r e q u i r i n g about four years, i n c l u d i n g e s t a b l i s h i n g p r e f e r r e d feed composition, p u r i f i c a t i o n techniques, c a t a l y s t composition, c a t a l y s t a c t i v a t i o n and regeneration procedures, process condit i o n s , and c y c l e length. C a t a l y s t l i f e was a l s o determined i n repeated c y c l e s and c e r t a i n design premises (e.g., temperature d i f f e r e n t i a l i n the reactor) were demonstrated to be v a l i d . P i l o t p l a n t runs demonstrated that e q u i l i b r i u m conversions and s e l e c t i v i t i e s i n the high 90's were f e a s i b l e (5). Commercial A p p l i c a t i o n s Commercialization of o l e f i n metathesis was accomplished i n 1966 (12). Shawinigan Chemical L t d . , at t h e i r Varennes complex near Montreal, Quebec, brought the P h i l l i p s T r i o l e f i n Process on stream. With an excess of propylene at that l o c a t i o n , Shawinigan had a need f o r polymerization-grade ethylene and highp u r i t y butènes. This presented an i d e a l opportunity f o r a p p l i c a t i o n of the T r i o l e f i n Process. The commercial u n i t was operating at f u l l c a p a c i t y two weeks a f t e r start-up and i t s performance exceeded that p r e d i c t e d by l a b o r a t o r y and p i l o t plant s t u d i e s . Part of the s u c c e s s f u l operation can be a t t r i b u t e d to the very e f f e c t i v e e l i m i n a t i o n of c a t a l y s t poisons from the commercial u n i t . In 1972, operation of the Shawinigan plant was terminated due to a change i n economic c l i m a t e . Another i n d u s t r i a l use of the v e r s a t i l e o l e f i n metathesis r e a c t i o n was commercialized by S h e l l i n 1977. As part of t h e i r h i g h - o l e f i n process, SHOP, they are producing detergent range


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C11-C1O

(i.e., o l e f i n s v i a c r o s s - d i s p r o p o r t i o n a t i o n of heavy and l i g h t o l e f i n f r a c t i o n s over a metathesis c a t a l y s t operating i n the 80-140°C temperature range (13). The l a t e s t (1980) commercial a p p l i c a t i o n of o l e f i n metathesis i s P h i l l i p s Neohexene Process (4). Neohexene, an intermediate i n the synthesis of a perfume musk, i s produced by cross-metathesis of d i i s o b u t y l e n e with ethylene ( i . e . , ethylene cleavage) over a b i f u n c t i o n a l (double-bond isomerization/metathesis) c a t a l y s t system (Figure 7 ) .


P o t e n t i a l Uses Technology f o r a number of a p p l i c a t i o n s of o l e f i n metathesis has been developed (3, 40 . At P h i l l i p s , p o t e n t i a l processes f o r producing isoamylenes f o r polyisoprene s y n t h e s i s and long-chain l i n e a r o l e f i n s from propylene have been through p i l o t plant development. In the area of s p e c i a l t y petrochemicals, p o t e n t i a l i n d u s t r i a l a p p l i c a t i o n s i n c l u d e the p r e p a r a t i o n of numerous o l e f i n s and d i o l e f i n s . High s e l e c t i v i t i e s can be achieved by s e l e c t i o n of c a t a l y s t and process c o n d i t i o n s . The development of new c l a s s e s of c a t a l y s t s allows the metathesis of c e r t a i n f u n c t i o n a l o l e f i n s (4, 14). The metathesis of alkynes i s a l s o f e a s i b l e (15). Fundamental C o n t r i b u t i o n s Worldwide s t u d i e s over the past two decades o f o l e f i n metat h e s i s c a t a l y s t s and r e a c t i o n s have played a s i g n i f i c a n t r o l e i n the advancement of the science of both heterogeneous and homogeneous c a t a l y s i s . The i n f l u e n c e o f the heterogeneous c a t a l y s t s u b s t r a t e s , metal components, l i g a n d s ( i n c l u d i n g chel a t i n g p o l y o l e f i n s added to the feed, F i g u r e 8), and c a t a l y s t m o d i f i c a t i o n s and pretreatments have provided i n s i g h t s i n t o heterogeneous c a t a l y s i s . Rate-temperature p r o f i l e s show that maximum metathesis a c t i v i t i e s occur at approximately 100 C lower than the maximum H-D exchange r a t e s over the corresponding subs t r a t e , i n d i c a t i n g a r e l a t i o n s h i p between proton m o b i l i t y and metathesis a c t i v i t y (6). Generally, c a t a l y t i c models are based upon s t u d i e s i n v o l v i n g homogeneous systems, with l i t t l e , i f any, b a s i s f o r the e x t r a p o l a t i o n to heterogeneous c a t a l y s t s . However, i n the case of o l e f i n metathesis, the homogeneous c a t a l y s t s a r e s t r i k i n g l y s i m i l a r to t h e i r heterogeneous counterparts; a vast m a j o r i t y of these c a t a l y s t s c o n t a i n molybdenum, tungsten, or rhenium as h a l i d e s , oxides, or carbonyls. Further s i m i l a r i t i e s i n r e a c t i o n conditions and s u s c e p t i b i l i t y to photo-assistance make t h i s r e a c t i o n i d e a l f o r e s t a b l i s h i n g r e l a t i o n s h i p s between heterogeneous and homogeneous c a t a l y s t s . T h i s was demonstrated r e c e n t l y by the r e s u l t s of very d e t a i l e d k i n e t i c and mechanistic s t u d i e s , conducted by s e v e r a l groups of i n v e s t i g a t o r s , which 9


412



Figure 6.

CH CH

CH

3

CH

3

- C - CH = C - C H

3

C H

Synthesis of alpha-omega d i o l e f i n s .

3

+

CH = C H 2

3

CH

C H - C - CH = CH

2

3

METATHESIS

It

CH

3

C H

2

+

3

CH =C-CH 2

3

3

ISOMERIZATION CH

3

CH -C-CH -C 3

2

3

=CH + CH 2

CH*

2

=CH

2

M —

NO

NET

REACTION

METATHESIS Figure 7.

Neohexene process chemistry.

TIME ON STREAM, MINUTES Figure 8. E f f e c t of 1,5-cyclooctadiene on a c t i v i t y of tungsten oxide-silica catalyst. (Reproduced from Ref. 5. Copyright 1979, American Chemical Society.)


29.

BANKS


413

i n d i c a t e a s i n g l e - s t e p metallocarbene mechanism (Figure 5B) f o r both the homogeneous and heterogeneous catalyzed metathesis reactions (2). The p o t e n t i a l r e l a t i o n s h i p of v a r i o u s types of o l e f i n r e a c t i o n s i n an area of fundamental i n t e r e s t . While molybdenumand tungsten-containing c a t a l y s t s promote metathesis of o l e f i n s , chromium-containing c a t a l y s t s tend to polymerize them. The s i m i l a r i t y of these three Group VI t r a n s i t i o n metals leads to the s p e c u l a t i o n that v a r i o u s o l e f i n r e a c t i o n s might proceed through mechanistic schemes that only have s u b t l e d i f f e r e n c e s (16). A very general philosophy concerning mechanisms i n the i n t i m a t e l y r e l a t e d f i e l d s of metathesis and p o l y m e r i z a t i o n i s now emerging.


Reflection I t i s i n t e r e s t i n g to r e f l e c t on those f a c t o r s that might have contributed to a p a r t i c u l a r s c i e n t i f i c d i s c o v e r y . In the case of o l e f i n d i s p r o p o r t i o n a t i o n , Hanford's law (rephrased) c e r t a i n l y a p p l i e s : " I f you want to f i n d something new, you have to t r y something new" (17). We were i n v e s t i g a t i n g a newly a v a i l a b l e compound f o r c a t a l y t i c behavior, and devised a new technique f o r preparing new c a t a l y s t compositions. A l s o , we were u t i l i z i n g r e l a t i v e l y newly developed p u r i f i c a t i o n methods to s i g n i f i c a n t l y reduce the l e v e l of c a t a l y s t poison i n the feed and experimental system. Improved a n a l y t i c a l techniques were a v a i l a b l e . A p o s s i b l e f a c t o r was the r e l a t i v e l y m i l d a c t i v i t y of the supported molybdenum hexacarbonyl c a t a l y s t ; heterogeneous c a t a l y s t s now known to be very a c t i v e f o r promoting metathesis r e a c t i o n s were used i n e a r l i e r c a t a l y s t research, both at P h i l l i p s and elsewhere, but, because of competing r e a c t i o n s , the metathesis r e a c t i o n had not been recognized. However, perhaps the most s i g n i f i c a n t f a c t o r was " s e r e n d i p i t y . "

Acknowle dgment s In a d d i t i o n to those acknowledged i n the text and r e f e r e n c e s , many other people at P h i l l i p s have made important c o n t r i b u t i o n s to the development of heterogeneous metathesis c a t a l y s i s . Contributions by other research groups, p a r t i c u l a r l y those i n the academic s e c t o r , to t h i s new f i e l d are c r e d i t e d i n v a r i o u s review a r t i c l e s , e.g., r e f e r e n c e ( 2 ) .

Literature Cited 1. 2. 3.

Banks, R. L . ; Bailey, G. C. Ind. Eng. Chem., Prod. Res. Develop, 1964, 3, 170-173. Banks, R. L. "Catalysis" (Specialists Periodical Reports) Kemball, C., Ed.; The Chemical Society, London, 1981 Vol. 4, 100-129. Banks, R. L. J . Mol. Catal. 1980, 8, 269-276.


HETEROGENEOUS

414

4. 5. 6. 7. 8. 9. 10.


11. 12. 13. 14. 15. 16. 17.

CATALYSIS

Banks, R. L . ; Banasiak, D. S.; Hudson, P. S.; Norell, J . R. J . Mol. Catal. 1982, 15, 21-33. Banks, R. L. Chemtech, 1979, 9, 494-500. Banks, R. L. Amer. Chem. Soc. Pet. Chem. Prepr. 1979, 24(2), 399-406. Calderon, N.; Chen, H. Y.; Scott, K. W. Tetrahedron Letters 1967, 34, 3327-3329. Zuech, E. A. Chem. Commun. 1968, 1182. Heckelsberg, L. F . ; Banks, R. L . ; Bailey, G. C. Ind. Eng. Chem. Prod. Res. Develop. 1969, 8, 259-261. Heckelsberg, L. F . ; Banks, R. L.; Bailey, G. C. Ind. Eng. Chem. Prod. Res. Develop. 1968, 7, 29-31. Bradshaw, C. P. C.; Howman, E. J.; Turner, L. J. Catalysis 1967, 7, 269-276. Chemical Week, July 16, 1966, 77 and July 23, 1966, 70. Freitas, E. R.; Gum, C. R. CEP, January 1979, 73-76. Pennella, F . ; Banks, R. L.; Bailey, G. C. Chem. Commun. 1968, 23, 1548-1549. Boelhouwer, C.; Verkuijlen, E. Amer. Chem. Soc. Pet. Chem. Prepr. 1979, 24(2), 392-393. Banks, R. L . ; Bailey, G. C. J. Catalysis 1969, 14(3), 276-278. Chemtech, 1980, 10(3), 129.

RECEIVED

November 29,

1982


Discovery and Development of Olefin ... - ACS Publications

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