SELECTIVE CATALYST FOR SOME ANHYDRIDE SYNTHESES \

J o s é L u i s H e r c e V i g i l ' J u l i o Flores

M a r e c k F r a c z a k '

.

f

DIVISION DE CIENCIAS BASICAS E INGENIERIA Departamento d e Ciencias Básicas

UNIVERSIDAD AUTOMOMA METROPOLITANA Unidad Azcapotzalco

MBxico 16, D.F.

'I'he mechanism for benzene and orto-xilene oxidation f o r ftalic

and maleic anhydride production and their correlations with d

electronic configurations can be summarized by statTng that the

1 ollowing d electronic configurations make possible the corre-

:;pending reaction steps :

chcnli:.;orpt ion of oxygen dl, d 2 , d3, dlo chemisorption of hydrocar:bon do, dl, d 2 , d3, d* , d9, dlo cyc1 ic anhydride formation dl, d2, d3, dlo

'L'hc rc:;ul-ts; 1)resented are the experimental data obtciinerl i or

t h c benzene and o-xi1er.e oxidation on a pilot scale. The stu-

clics have be?n carried out on a fixed bed reactor with a German

irI(lus-tria1 non-porous vanadium-type ctalyst. Additional data ,

1 o r ' oxidaton of 2-buteneY reported in the literature are i n c l u d -

( : ( I iorl comparison purposes.

C o r r e l a t i o n s between the courses of some organic reactions and

-the electronic configur>ations of the transition elements used

< I : ; r : , ~ I : a l y s t f o r these reactions have been employed to propose

I t t c : 1~a:;is f o r catalyst selection. A general criterion for c a t -

, . . ~ l y s t choice for1 benzaldehide hydration, for example, hay be1.n

3

introduced by Dowden (1). Since any catalytic reaction is s1.1;~-

] J O : ; C ~ to proceed through several intermediate staples , i:L i :; I ) ! < I L .-

L;il)le to expect that, f o r a given reaction,there is an a p p r c > p l l i -

a t e composition o f the trasition elements which could acct.1.e1>;1'.

cc2ch of these reaction stages. Once the suitable catalyst C<j1il:-c

cition is determined on the basis of theoretical consideratio!l;:;

and if the experimental results are according with the pre(.Í.j.ct.:'

ones , the assumed reactions mechanism could be said as beir :c t í :

sonle extent confirmed.

'I'hc subject of this communication is the selective oxidation oí

o-xilene, benzene and 2-butene. Chemical equations o f these r c -

action are given in Tab. 1 which also includes the total oxidc~-

t l o n proce,, PPes.

The mechanism o f these reactions have been studied (1-51, hut :

till now no general criterlion for the catalyst choice has JJeriri

formulated. It is know, however, that molecular ox:/gen s t c ~ r l ( ! ;

fort the anhydride formation, and atomic oxygen leads to t i l l : tot^.!'

oxidation (Tab. 1). Kinetic equations presented in the litera-

ture are similar f o r total and partial oxidations (6-9).

U:;ing the correlations between reactions and electronic configTu -~

rations dn o f transition ions, necessaries for stable complexex

formation, it is possible to develop hypothese fop ca.talyst

choices f o r selective hydrocarbon oxidations for anydride syn--

these and also for a better comprehension o f catalyst pr.opc?rtir-:: :

dertermined by experiences with catalysts composed by mixture:>

of metallic ions.

4

-

1 . :;clcc t. i-v i. t.y I or Anhytlridc: - Synthese -

A I I equation to evaluate selectivity can be develop consitleri-ni:

the following experimental facts:

- benzene oxidation with a mixture of V and Mo oxides is not

selective. Spectroscopically (IR) , it was possible to pro-

ve the V = O bonds. Selective oxida-tion is possible only with

reduced catalysts and in these cases the presence of V = O 11as

not been detected.

- the presence of molecular adsorbed oxygen, as superoxide

radical 0, , with Si02 a:; support was proved spectroscopi-

cally by Shvets and Kazansky (10).

Starting from these facts, it is reasonable to estimate selectiv -

i t y f o r reactions represented on Tab. 1, as:

S = moles M = O moles M - O + moles M=O

2 . Experimental

2.1 Apparatus

Using two flowmeters, streams of dried air and o-xilene (or

benzene) were measured and combined to form a mixture con-

taining about 1% of o-xilene ( o r benzene). The mixture was

preheated andthen introduced to the reactor containing a

V,O, industrial catalyst heated by a mixture of molten salts.

Reactor, c ; i t a l y s T and operational characteristics are summa-

rized in Tab. 2 and Fig. 1.

5

2.2 Analysis

I 1 l . h c ) ; F ~ L ; composition was analyzed measuring the concentratiori:3

o f organic compounds involved (maleic and ftalic a n h y d r > i c l c , ,

Etalide, to1 il-aldehide, etc. ) before, inside and after - t h e

r1eac:torl by flame gas chromatography (VARIAN 1400). I n o r ; T , < ! n I c:

compounds ( C O Z , CO, 0,) were analyzed by thermal conduct.ivi.I:v

chromatograph (VARIAN 1520) after organic compounds and w C 1 t t ’

elimination through a cold and silica gel traps. The d n c J 7 . ; : I

ical system is represented also in Fig. 2. B o t h chromal.opr~.1p?;

were connected to an electronic integrator in order to detcr -

mine concentration values (11-13).

3. I<csult S

Lx;-er>imcnta1. results were treated with different kinetic equa-”

t-ions (11-13) and schemas and then simulated with a cornputc?ll. -

1:etter results were obtained with the following systems for. o-

xilene oxidation

, 3.

.L o-xilene Intermediates “+ Ftalic Anhydride

I + co + coz + 1320

tor benzene oxidation (11)

Benzene __f Maleic Anhydride 4

I + co + co, + €120

‘I’he measured temperature and concentration prof íles are p l o t t e c !

i . n Fig. 3 and 4, using one and two-dimensional models, the 01,-

6

. ( . , I i n c d r e s u l t s w i t h t h e s e t w o m o d e l s were s i m i h r , bu-t: Lhc i wo-

c l i r r r ens iona l model shows a b e t t e r a p p r o a c h .

S = yield of p a r t i a l o x i d a t i o n yield of t o t a l o x i d a t i o n

L x p e r > i m e n t a l a n d c a l c u l a t e d s e l e c t i v i t i e s a re g i v e n i n T a b . 3 .

( : F l l c u l a t e d s e l e c t i v i t i e s k e e p a g o o d a g r e e m e n t w i t h e x p e r i n e ! i t a l

r v . s u l t s , e x c e p t i n t h e case of 2 - b u t e n e , w h e r e t h e e x p e r i m e n t a l

v < I l u c i s 6 % less t h a n t h e c a l c u l a t e d . It c o u l d b e t h o u g h t t h a t

: - ; c l e c t i v i t y may be improved .

4 . D i : ;cur;sion. ______.-._

'I'hc e x p e r i m e n t a l r e s u l t s a l low t h e a u t h o r s t o p r o p o s e t h e fol--

l o w i n g h y p o t h e s e o v e r t h e r e a c t i o n m e c h a n i s m for t h e o x i d a t i o n

o f - l l y d r o c a r b o n s t o a n h y d r i d e s w i t h meta l l ic o x i d e s as c a t a l y s t s :

l r ic>lccular oxygen i s b e i n g c h e m i s o r b e d , h y d r o c a r b o n s r eac t C 1 u i c k l y

w i t h molecular a d s o r b e d o x y g e n , p r o d u c i n g i n t e r m e d i a t c covpouncl:,

;Ind a t o m i c o x v g e n b o n d e d t o metal , t h a t m e a n s , metals a r e b e i n g

o x i d i z e d . T o t a l o x i d a t i o n ~ e q u i r e s a t o m i c o x y g e n f o r m a t i o n , -

bonded t o t h e m e t a l , w h e r e c a t i o n s are b e i n g r e d u c e d a n d t h e n -

t h e c y c l e i s r e p e a t e d .

Cons-iclering t h e s e h y p o t h e s e s t h e most i m p o r t a n t ~ h a r a c t ~ ! ~ ~ ; . ~ ~ ; ~ ~ ~ c ~

o í . t h e c a t a l y s t for se l ec t i . ve h y d r o c a r b o n o x i d a t i o n s e c m t o be:

c a p a c i t y for m o l e c u l a r o x y g e n c h e m i s o r p t i o n a n d c a p a c i t y f o r -

quick o x i d a t i o n a n d r e d u c t i o n . S i n c e metal.lic c a t i o n s nc.cd tc

7

h < l V C <I rid" o r b i - t a l for molecular oxygen chcnlisorp-tion as su1Icr'-

ox i ( I < > nn-i.on 0, (1 .0 ) , -then dl cctions nay be employed. Mo:: t L ) !

l.110 c , t - t < - l l y : . ; t t o r ;Inhydride synthese arc p r e p a r c d :;upl'c)r't i r l j i , t. t : ( > : : ( l

ions over metallic oxides. The necessity to use several ion:; ii:

the same catalyst can be justified as follows: catalyst mus t ch(,;:

i : ;o r lbe hydrocarbons and must be multi-functional because i-t ac--

celerates.areaction series to form intermediates. The mulli-

functional characteristics and some analogies with organic s T ; J ' i -

t l lcse perrnit the proposal of reaction mechanisms explainiv t ! i ~

selective oxidation which till now, has not been fully eluci(lL1?-c, !

O-xylene oxidation can be considered as an illustrative example

f o r catalyst choice.

i'llc r;up,p,c:;tcd mechanism is shown on Fig. S. This f i g u r e impl . lc : ,

L l l < ~ t catalysts must satisfy the following conditions: catalysts

nu:; I' form complexes with aromatic products and must f o r m a

structure with two atoms of oxygen which are coordinated w i t i ;

the 'cation through double bonds. These conditions are satis1 L ' t i

by the following cations:

v+2 y +3 +4

Y Y M0 Y Y +4 +5

y w + 4 , y VYl . +5 +4

I l owever , only the stable states under oxidation-reduction corlc!i -

t i o n s of the selective oxidation reaction, can be considered as

thc appropriate ones.

' j '¿lb. 4. shows the atomic configurations of metallic c;ltionr; --

tha t can be employed for the different steps of o-xilene oxic!7-

- I i . o n to f t a l i c a n h y d r i d e b a s e d o n t h e p r o p o s e d m e c h a n i s m (9).

A:; a c o n c l u s i o n i t c a n t h e r e f o r e b e said t h a t a vanadiun] i > : < i ( ~ w

rnu:-;t u n d o u b t e d l y p a r t i c i p a t e as a b a s i c oompound of t h e c a t a l y s t ,

b e c a u s e , as i t i s s e e n i n T a b . 4 , i t i s a c a t a l y s t for a11 r e a r -

t i o n s t e p s . ' T h i s c a t a l y s t c l c t i o n c a n b e a l s o a c h i e v e d by o-ther

metal l ic o x i d e s o f p r o u p V I . E x p e r i m e n t a l r e s u l t s c o n f i r m t h i s

p r e d i c t i o n ( 2-5 1 .

For a c a t a l y s t m i x t u r e of V-Mo o r V-W o x i d e s , i t i s n e c e s s a r y

l-llat thc.y p r e s e n t a s t r u c t u r e i n w h i c h d i f f e r e n t o x i d a t i o n s t a t e s

re i n c l u d e d a n d t h a t t h e y m u s t n o t d i s a p p e a r i n a i r r e v e r s i b l e

w [ - ~ y . V 2 0 , or M O O , a l o n e c a n n o t s a t i s f y t h e s e cond i t ion : ; Lieca:i';e

thcy a r e t r a n s f o r m e d d u r i n g t h e r e d u c t i o n p r o c e s s . I Jhosp1~a te ,

s u l l ' h s t e a n d Sora te a d d i t i o n s i n c r e a s e t h e s t a b i l i t y o f t h e t l i f -

J c : r e n t o x i d a t i o n s t a t e s of I' and Plo ( 1 9 - 2 1 )

I t i s n e c e s s a r y t o p o i n t out: t h e p r e s e n c e of a n a p p r e c i a b l e q u a n -

t i t y of V4+ i o n s i n V20,, e\ren when t h e V20, i s of h i g h p u r i t y .

' 1 ' 1 1 ~ t h e r m o d y n a m i c a l s t a b i l i t y of V,O, i s n o t c o m p l e t e , t l ; c . l t is,

i t i s t r a n s f o r m e d i n t o a n o n - s t o i c h i o m e t r i c o x i d e , w i t h oxygen

v o i d s p a c e s . This p h e n o m e n o n e x p l a i n s t h e i m p o r t a n t c a t a 1 y t i . c :

p r o p e r t i e s of V,O,. A p p l y i n g t h e same a r g u m e n t s , i t i s alFr -

l ' o s s i b l e t o s u g g e s t o x i d a t i o n m e c h a n i s m s for 2 bu tene and benzc -

n e i n a s imilar way t h a n t h a t for o - x i l e n e . F o r m a t i o n of benzo-

q u i n o n e c o u l d be proposed a s i n t e r m e d i a t e s t e p f o r maleic anhy-

( ] p i d e s y n t h e s i s (15). With a similar e l e c t r o n i c c o n f i g u r a t i o n

t h L l t of t h e c a t a l y s t f o r o - x i l e n e o x i d a t i o n , me ta l l i c c a t i o n s

m u s t b e p r e s e n t i n o r d e r t o acce lera te t h e r e a c t i o n s t e p s f o r -

9

Plechanisms for c a t a l y t i c o x i d a t i o n of o - x i l e n e , b e n z e n e < : I ; .

J J U ~ ~ I L ~ are p r o p o s e d by a n a l o g i e s w i t h o t h e r . o r ~ g c ~ ~ ~ i . L : .J:: 1 1 j - 1

' I ' ~ I ( > rrlc:carlisrrls axle based on t he oxygen chemi . so rp - t ion I : > ; r ,

( . )xygen. L x p e r i m e n t a l s e l e c t i v i t i e s t e n d e d o u t t o bc i n I

l e n t a g r e e m e n t w i t h t h e s e l e c t i v i t i e s p r e d i c t e d t h r o u g h 4.hl b '

posed mechanisms.

'The a u t h o r s t h a n k t h e v a l u a b l e s u g g e s t i o n s g i v e n by 1'i-c:. . I :

A. Campero and Prof. Dr. M . Maubert and t h e economic s l J ] ~ ~ ' " ' J ¡ '

I : k ~ e DAAD (Germany) .

10

1~ . 7 .

3 .

4 .

5 .

6 .

7 .

8 .

9.

1 0 .

1 2 .

1 2 .

1 3 .

14 .

1 8 .

1 9 .

2 0 .

2 1 .

Dowden, D . A . Chem. Eng . P rogr . Symp. S e r . 6 3 , 7 3 , p.90 ( 1 9 6 7 )

Pl<aY>golis, L.Y. Adv. Cat. 14. 4 2 9 ( 1 9 6 3 )

Voge, H.H., Adams, R . L . Adv. C a t . 1 7 , 1 5 1 ( 1 9 6 9 )

H u c k n a l l , D . I . , S e l e c t i v e O x i d a t i o n of H y d r o c a r b o n s , Academic I'ress London, ( 1 9 7 4 )

M a r g o l i s , L .Y. C a t . Rev. 8 , 2 4 1 ( 1 9 7 3 )

' h e h a n , B . S . , S u r i , I . K . J. I n d . Res. 1 8 B , 1 4 7 ( 1 9 5 9 )

I o f f e , I . I . , L i u b a r s k i i , A . G . Kin . E Kat. 3 - 2 6 ( 1 9 6 2 )

Fromment, G.F. I n g . En&. Chem. 5 9 , 1 8 ( 1 9 6 7 )

K r i p y l o , P. Chem. Tech . 3 3 , 6 , 2 9 9 ( 1 9 8 1 )

S c h v e t s , V . A . , Kanzansky. V . B . J. C a t . 2 5 , 1 2 3 ( 1 9 7 2 )

HYusser , F., L u f t , G . , Chimie Tech. 1 0 , 5, 4 5 3 ( 1 9 8 1 )

I-Isusser, F. , D i s s e r t a t i o n , T . H . D a r m s t a d t ( 1 9 7 8 )

Bijhning, K . H . D i p l o m a r b e i t , T . H . D a r m s t a d t ( 1 9 8 1 )

Gerrnain, J . E . B u l l . Soc. Chim. F r a n c e 1 8 4 4 ( 1 9 6 9 )

Nakamura, M . , Kawai, J. F u j i w a r a , Y . , J . Cat. 3 4 , 345 ( 1 9 7 4 )

H e r t e n , cT., Fromment, G.F . Ind. Eng. Chem. P r o c e s s Desi.gn and Dev. 7 , 5 1 7 ( 1 9 6 8 )

Haase, H . Ch imie - Ing . Techn . 44, 9 8 7 ( 1 9 7 2 1

F r i e d r i c h s e n , W., Chemie Ing . Tech . 41., 1 7 , 9 6 7 ( 1 9 6 9 )

R i l e y , H.L., Ramansky, A. US P a t e n t 3 2 2 6 3 3 8 ( 1 9 5 9 )

G i l l i s , E . , Boesman, E . Phys. S t a t . Sol. 1 4 , 3 8 9 ( 1 9 7 0 )

11

S "

H \ ,

C I I

H \ 7 3

C I I

+ A n + "_ >

H 6 \ 4- C " C

II IC "

\

/

'Of + 1' (114 1) 03 4- 3H20 + 6M

C

I1 *- Q

la + + + 1 2 i ( n + 1 ) ---.-+ 4CO 44ki 0+7 214

(11-1) 2 2

13

Reactor a n d C a t a l y s t Charac tcr l is tcs . ______ ~ "" "" .. ~ . " "- - ______

O-xilene System Lenzene S y s t e m ~-~

Feed composition 0.5 - 4 o r t o x i l e n e 0.5 - 1 : I . i r 93 - 99.5

2.2 - ij 0.5 - 1 33 - 99.5

pressure 1 feed tempera-tura 350 - 356 350 - 365 cool ing; system 350 - 370 350 - 370 reac tor l ength 3 r eac to r d i ame te r 0.05 0.05 c a t a l y s t V205-K2S04 V205-Mo03

? 3

composition Heyden-Regensburg A l u s u i s S e form r i n g r i n g l e n g t h 7 x 10-3 5 x lo-? I

diameter 7 x 10-3 5 x 1[>--3 11,

dens i ty 1.87 x l o 3 1.68 X 103 bed dens i ty 1 .05 x 103 1.106 x 1-03 k. ' r i:I

bcd poros i ty o. 56 O. 34

1.7 , - , , 'LC,

" .

T A B L E 3

S e l c c t i v i t y

Ilenzene

O-xilene

2-butene

68 78 66

Ecact ion steps

Hydrocarbon chemisorption x x x x

Molecular oxJgen chemisorption x x x

C'ycl ical oxidat i on x x x . .. "" .

14

I

5-

2 -

II -- . .

F I G . 1

4 F i l t e r

!

F I G . 2 I

U - " ."

5 .-

2 -

0 -

I

o n

O. G

O 4

o. z

FIG. 4

.. _ _ _ - .- . __._._". _..- .._..__.." """ I"

i

t

16

C) It O

G X

I 0.: 0-0 +

o= 0 + X O

h)

Z - i - 3 :

+ h' O N

II O

1 n X - 0 O

+ N

O X

o-" O II

X O

td3 -X

FIG. 5

17