Oxidative Methylation of Hydrocarbons with Methane over Rare-Earth Metal Oxide Catalysts

A. Holmen et al. (Editors), Natural Gas Conversion 1991 Elsevier Science Publishers B.V.,Amsterdam

161

O X I D A T I V E M E T H Y L A T I O N OF H Y D R O C A R B O N S W I T H M E T H A N E OVER R A R E - E A R T H M E T A L O X I D E CATALYSTS

T. S O D E S A W A , S. SATO. and F. N O Z A K I D e p a r t m e n t o f A p p l i e d C h e m i s t r y , F a c u l t y of E n g i n e e r i n g , C h i b a U n i v e r s i t y . Chiba 260, Japan SUMMARY O x i d a t i v e m e t h y l a t i o n o f h y d r o c a r b o n s s u c h a s p r o p y l e n e and toluene p r o c e e d s in a m e d i u m w i t h e x c e s s m e t h a n e in the p r e s e n c e of o x y g e n e to g i v e p r o d u c t s w i t h n e w C-C and C = C bonds. In this paper, e f f e c t i v e r a r e c a r t h metal o x i d e c a t a l y s t s f o r the f o r m a t i o n of C 4 - h y d r o c a r b o n s a s I-butene, trans o r c i s - 2 b u t e n e , and 1 , 3 - b u t a d i e n e b y the w a y of o x i d a t i v e m e t h y l a t i o n of p r o p y l e n e w e r e i n v e s t i g a t e d and t h e p l a u s i b l e r e a c t i o n s c h e m e w e r e c o n f i r m e d . INTRODUCTION S i n c e K e l l e r and B h a s i n (ref. 1 ) r e p o r t e d the p o s s i b i l i t y of s y n t h e s i s of C l H 4 and

C2H6 by o x i d a t i v e c o u p l i n g of m e t h a n e o v e r v a r i o u s metal o x i d e s ,

m a n y r e s e a r c h e r s a r e b e g i n n i n g to w o r k in this field. S o f r a n k o el al. h a v e r e c e n t l y s h o w n that in the c a s e of m e t h a n e - p r o p y l e n e in the a b s e n c e of o x y g e n o v e r m a n g a n e s e o x i d e o n s i l i c a , b u t e n e is a p r i m a r y p r o d u c t by way of methyl a d d i t i o n to p r o p y l e n e (ref. 2 ) . H o w e v e r , s t u d i e s c o n c e r n i n g the o x i d a t i v e m e t h y l a t i o n of s o m e o l e f i n s , a r o m a t i c s , and n i t r i l e s c o n t a i n i n g a methyl g r o u p at & - p o s i t i o n o n the e l e c t r o n - a c c e p t i n g f u n c t i o n g r o u p a r e not f u l l y made. I t w a s r e p o r t e d b y u s that the o x i d a t i v e m e t h y l a t i o n of p r o p y l e n e o v e r mclnl o x i d e c a t a l y s t s p r o c e e d s In a m e d i u m w i t h e x c e s s m e t h a n e in the p r e s e n c e o f o x y g e n to g i v e b u t e n e s and 1.3- b u t a d i c n e (ref. 3, 4 ) .

I t was also found that La203

c a t a l y s t d u r i n g the metal o x i d e s tested is most e f f e c t i v e f o r the f o r m a t i o n of C ,-hydrocarbons

s u c h a s l - C p 8 , 1-2-C4H8, c - Z - C q H g , o r 1 .:l-CqHg.

T h e r e f o r e , in

this p a p e r , the o x i d a t i v e m e t h y l a t i o n o f p r o p y l e n e o v e r the o t h e r rare-earth metal o x i d e c a t a l y s t s e x c e p t L a p 3 w a s i n v e s t i g a t e d , U s i n g a c o n v e n t i o n a l flow method a t m o s p h e r i c pressure.

EXPERIMENTAL Preparation of catalysts T h e c a t a l y s t s used h e r e w e r e p r e p a r e d f r o m v a r i o u s c o m m e r c i a l rare-earth metal oxide.

162 Various rare e a r t h oxide catalysts modified with Na 0 were obtained by an impregnation method. Each cata'lyst was calcined in air at 973 K for 2 h. Prior t o the reaction, the pretreatment for the activation of catalysl was performed at 973 K fo~'0.5 h in a flow of nitrogen and oxyeen. and then for 1.5 h in a stream o f nitrogen alone. Reaction test The reaction was carried o u t using

a

conventional f l o w method

at

atmospheric

pressure. The reaction conditions were as follows; reaction temperature: T=773973 K , partial pressure o f methane: P(CH4)=88.6 kPa, partial pressure o f propylene: P(C~Hg)=8.44 kPa, partial pressure o f oxyeen: P(o2>=4.22 kPa.

The

products were analyzed by gas chromatography. The surface area o f various rare earth oxide catalysts was measured by a conventional BET method. Results and Discussion Various rare earth metal oxide catalysts Table 1 shows the typical results o f the reaction on various rare carth metal oxide catalysts. The yield was calculated on the basis of conversion o < propylene to the each product. As is shown in Table 1 , the L n 2 0 3 catalyst is mosl effective for the reaction at relatively higher temperature above 923 K than the other rare earth metal oxides. In addition, the L a 2 0 3 calalysts modified with Na2O in the range o f 1 t o 5 wtX exhibited much more activity for C4 formation than the La203 catalyst vithout Na20 (ref. 3 , 4 ) .

I t was a l s o

found that there is no relationship between thc surface area o f rare earth m e t a l oxide and the activity for C4 formation by way of oxidative methylation.

As to C 4 distribution, both La 0 and Sm203 calalysts produce more 2 - C 4 H 8 than 2 3

TABLE I

Oxidative methylation o f propylene over various rare earth metal oxide

BET Surface

Co nve rs i on

Yield (XI

Di s (ri b u t ion (XI

( X )

Area m2/e-Cat La2O3 Sm203

Ce02

C4H.C. COfCO

CH4

C3Hs

l-C4H( t-2-C4H~c-2-C4H8 1,3-C4Hg

23.6

44.1

18.2

20.4

17.3

2.41

6.89

3.78

11.4

1.01

1.59

7.68

10.7

45.3

31.6

23.2

25.8

19.5

0.97

6.64

23.2

18.2

55.5

6.1

6.3

32.2

14.3

29.3

54.6

8.0

8.6

28.8

57.6

7.6

7.7

27.1

13.3

Nd203

1.30

1.80

4.89

Gd203

3.03

1.55

6.89

9.17 12.5

a)Reaction temperature: 923 K , data at 60 min, W/F=4.67 (e-Cat.h/mol).

163

T

m 2

C4-hydrocarbon yields over various rare earth metal oxide catalysts C4-hydrocarbon Yield

(%)

7?:1 K

823 K

873K

923 K

La2 03

-

-

1 .o

6.89

sm2 03

2.45

2.58

Ca tal ys t

-

CeOZ Nd20 3 GdZO s

2.46

3.28

973 K

1.54

1.59

1.53

0.43

0.97

2.67

1.80

1.80

1.89

1.55

a) Da’ta at 60 min, W/F=4.67 (g-Cat.h/mol)

the other C4 hydrocarbons. On the other hand, in the cases o f CeO?, Nd203, and GdzO3

catalysts. the ratios o f l - C 4 t 1 1 and 1 . 3 - C 4 H 6

are larger than those o f the

other C, hydrocarbons.

Active catalysts at lower reaction temperature

In order to find out active catalysts for the oxidative methylation, the I-ractions were carried out at lower temperatures below 923 K. The results were summarized in Table 2. As can be seen from Table 2. i t is clear that both La 0 2 3 and CcOz catalysts l o w e i . activity below 873 K compared with S m 2 0 3 o r G d 2 0 3 . Therefore, further investigation concernig the reaction using S m 0 catalysts was per f o r m e d .

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i

G.E. Keller and M . M . Bhasin, J . Catal., 73 (1984) 9-19.,

2

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3

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.1

T. Sodesawa, S. Sato. and F. Nozaki, 1989 International Chemical Congress of Pacific Basin Societies, Honolulu, Hawaii, U . S . A , December 17-20, 1989, Preprints of 3tl Symposium on Methane Activation, Conversion and Utilization,

PP. 124-125.