A M M O X I D A T I O N O F T O L U E N E
A N D X Y L E N E S TO NITRILES
A M M O X I D A T I O N O F T O L U E N E
A N D X Y L E N E S TO NITRILES
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. I l i l l l Süilliilll lili "O u t m o* sO oBIBLIOTHEEK TU Delft
P 1660 5149
A M M O X I D A T I O N O F T O L U E N E
A N D X Y L E N E S TO NITRILES
PROEFSCHRIFT ter verkrijging van
de graad van doctor in de
technische wetenschappen
aan de Technische Hogeschool Delft
op gezag van de rector magnificus,
prof.ir. B.P.Th. Veltman
voor een commissie aangewezen
door het college van dekanen
te verdedigen op
donderdag 18 juni 1981
te 14.00 uur door
Johannes Jacobus Joseph den Ridder
scheikundig ingenieur
geboren te Zevenbergen
Dit proefschrift is goedgekeurd door de promotor
PROF.DRS. P.J. V A N DEN BERG
AAN MIJN OUDERS
AANANS
Voorwoord
De t o t s t a n d k o m i n g van d i t p r o e f s c h r i f t i s m o g e l i j k gemaakt door de i n z e t van
een g r o o t a a n t a l p e r s o n e e l s l e d e n en s t u d e n t e n van de T e c h n i s c h e H o g e s c h o o l .
Langs deze weg w i l i k hen v o o r hun b i j d r a g e h a r t e l i j k danken. D i t g e l d t i n
h e t b i j z o n d e r
de s t u d e n t e n : Hans B r a b e r , Kees T i n t e l , Jan-Kees V i s , Henk van Ingen, J o h n
Bekker en R o b e r t K e l l y , d i e op e n t h o u s i a s t e w i j z e aan d i t onderzoek hebben
meegewerkt;
Loek P e f f e r en Ben N o r d e r v o o r hun a s s i s t e n t i e t e n a a n z i e n van de a n a l y s e
-a p p -a r -a t u u r ;
Wim J o n g e l e e n , J a n van H o l s t en Koos Kamps v o o r h e t tekenwerk en f o t o g r a f i s c h
v e r k l e i n e n van de f i g u r e n ;
S a u l Lemkowitz v o o r h e t c o r r i g e r e n van de E n g e l s e t e k s t ;
C a r o l i n e Monna v o o r h e t t y p e n van h e t m a n u s c r i p t ;
de heer Ph.A. B a t i s t ( T e c h n i s c h e H o g e s c h o o l Eindhoven) en h e t C e n t r a a l
C o n t e n t s
SUMMARY 3
1 INTRODUCTION 5
1.1 S e l e c t i v e gas-phase o x i d a t i o n and ammoxidation i n g e n e r a l 5
1.2 Ammoxidation o f a r o m a t i c h y d r o c a r b o n s 6
1.3 The c a t a l y s t 6
1.4 Aim and scope o f t h e t h e s i s 7
R e f e r e n c e s 8
2 APPARATUS AND ANALYSIS 9
2.1 I n t r o d u c t i o n 9
2.2 Flow a p p a r a t u s 9
2.3 The p u l s e r e a c t o r system 12
2.4 A n a l y s i s s y s t e m 14
R e f e r e n c e s 18
3 EXPERIMENTAL METHODS AND CALCULATION PROCEDURES 19
3.1 I n t r o d u c t i o n 19
3.2 D e f i n i t i o n s 19
3.3 R e a c t o r a s p e c t s 21
3.4 P u l s e t e c h n i q u e 23
3.5 C a l c u l a t i o n methods 26
R e f e r e n c e s 29
4 OXIDATION AND AMMOXIDATION OVER A'-BISMUTH MOLYBDATE CATALYST 30
4.1 I n t r o d u c t i o n 30
4.2 The c a t a l y s t 31
4.3 F l o w e x p e r i m e n t s 31
4.3.1 O x i d a t i o n o f t o l u e n e 31
4.3.2 O x i d a t i o n o f ammonia 34
4.3.3 Ammoxidation o f t o l u e n e 41
4.3.4 Ammoxidation o f b e n z a l d e h y d e 54
4.4 P u l s e e x p e r i m e n t s 55
4.4.1 C a t a l y s t r e d u c t i o n w i t h ammonia 55
4.4.2 C a t a l y s t r e d u c t i o n w i t h ammonia and t o l u e n e 61
4.4.3 R e o x i d a t i o n o f t h e c a t a l y s t 63
4.5 D i s c u s s i o n
R e f e r e n c e s
67
70
5 AMMOXIDATION OVER A SILVER CERIUM VANADATE CATALYST 72
5.1 I n t r o d u c t i o n 72
5.2 The c a t a l y s t 72
5.3 F l o w e x p e r i m e n t s 73
5.3.1 I n t r o d u c t i o n 73
5.3.2 C a t a l y s t a c t i v i t y and s t a b i l i t y 74
5.3.3 K i n e t i c s o f t h e ammoxidation o f t o l u e n e 77
5.3.4 K i n e t i c s o f t h e ammoxidation o f x y l e n e s 87
5.4 P u l s e e x p e r i m e n t s 97
5.4.1 I n t r o d u c t i o n 97
5.4.2 C a t a l y s t r e d u c t i o n w i t h t o l u e n e and ammonia 97
5.4.3 C a t a l y s t r e d u c t i o n w i t h a l t e r n a t i n g ammonia and
t o l u e n e p u l s e s 99
5.4.4 R e o x i d a t i o n o f t h e c a t a l y s t 99
5.5 D i s c u s s i o n 101
R e f e r e n c e s 106
6 FINAL DISCUSSION 107
6.1 B i s m u t h molybdate c a t a l y s t s 107
6.1.1 S t r u c t u r e 107
6.1.2 Mechanism 109
6.1.3 K i n e t i c s 114
6.2 Vanadium b a s e d c a t a l y s t s 116
6.2.1 S t r u c t u r e 116
6.2.2 Mechanism 117
6.2.3 K i n e t i c s 119
R e f e r e n c e s » 123
L I S T OF SYMBOLS 12 5
SAMENVATTING 126
2
Summary
The ammoxidation o f p r o p y l e n e t o a c r y l o n i t r i l e has a l r e a d y been a p p l i e d i n -d u s t r i a l l y f o r s e v e r a l -d e c a -d e s . The i n c r e a s i n g -deman-d f o r a r o m a t i c compoun-ds makes i t w o r t h w h i l e t o d e v e l o p a s i m i l a r p r o c e s s f o r t h e s y n t h e s i s o f a r o m a t i c n i t r i l e s .
A number o f p o s s i b i l i t i e s f o r t h e ammoxidation o f some m e t h y l b e n z e n e s were i n v e s t i g a t e d i n t h i s t h e s i s . F o r t h i s p u r p o s e two c a t a l y s t s were examined w i t h r e g a r d t o a c t i v i t y , s e l e c t i v i t y and s t a b i l i t y . B i s m u t h m o l y b d a t e was chosen bec a u s e o f i t s e x bec e l l e n t p r o p e r t i e s f o r t h e o x i d a t i o n and ammoxidation o f p r o p y
-l e n e , and i n v i e w o f t h e a n a -l o g y between a r o m a t i c and v i n y -l i c m e t h y -l g r o u p s . S i l v e r c e r i u m v a n a d a t e on a s i l i c a c a r r i e r was c h o s e n b e c a u s e o f t h e good p r o p e t i e s o f t h i s c a t a l y s t f o r the o x i d a t i o n o f t o l u e n e t o b e n z a l d e h y d e and b e n z o i c a c i d . Moreover, vanadium-based c a t a l y s t s a r e g e n e r a l l y used f o r t h e o x i d a t i o n o f o - x y l e n e t o p h t h a l i c a n h y d r i d e .
F o r t h e e x p e r i m e n t a l work two d i f f e r e n t t e c h n i q u e s were u s e d :
1) The k i n e t i c s o f t h e ammoxidation o f t o l u e n e and x y l e n e s were i n v e s t i g a t e d i n a c o n t i n u o u s l y o p e r a t e d f i x e d b e d r e a c t o r a t c o n d i t i o n s o f 3 5 0 490 °C, a t -m o s p h e r i c p r e s s u r e and space t i -m e s between 0 . 3 - 4 s e c .
2) The r e a c t i v i t y o f t h e c a t a l y s t s i n r e l a t i o n t o t h e i n d i v i d u a l r e a c t a n t s , t o l u e n e , ammonia and oxygen, was s t u d i e d u s i n g a p u l s e r e a c t o r , o p e r a t i n g a t 350 - 450 °C and a t an a b s o l u t e p r e s s u r e o f 2 - 3 b a r .
The main r e a c t i o n s o c c u r r i n g d u r i n g t h e ammoxidation o f t o l u e n e a r e g i v e n i n t h e scheme below:
AMMONIA
TOLUENE BENZONITRILE
U s i n g t h e b i s m u t h m o l y b d a t e c a t a l y s t , a l l t h e s e r e a c t i o n s can be d e s c r i b e d by a r e d o x model, w i t h t h e e x c e p t i o n o f the ammonia o x i d a t i o n . A c c o r d i n g t o s u c h a model, t o l u e n e and b e n z o n i t r i l e r e a c t w i t h c a t a l y s t oxygen (and ad-s o r b e d ammonia) t o form t h e v a r i o u ad-s p r o d u c t ad-s . The r e o x i d a t i o n o f t h e c a t a l y ad-s t w i t h g a s - p h a s e oxygen was f o u n d t o be f a s t r e l a t i v e t o t h e c a t a l y s t r e d u c i n g r e a c t i o n s 1 t o 4. The r a t i o s between t h e r a t e c o n s t a n t s o f r e a c t i o n s 1, 2 and
3 a t 350 - 490 °C were, r e s p e c t i v e l y , a b o u t 1 : 0.2 : 0.2. The maximum y i e l d ob-t a i n e d f o r b e n z o n i ob-t r i l e was a b o u ob-t 60%. A d i s a d v a n ob-t a g e o f ob-t h e b i s m u ob-t h m o l y b d a ob-t e c a t a l y s t i s , t h a t a c o n s i d e r a b l e p e r c e n t a g e o f ammonia (up t o 90%) was o x i d i z e d t o n i t r o g e n . The u n d e s i r a b l e s i d e - r e a c t i o n c o u l d , however, be s u p p r e s s e d t o l e s s t h a n 50% by a d d i n g water t o t h e r e a c t i o n m i x t u r e .
W i t h t h e ammoxidation o f t o l u e n e on t h e s i l v e r c e r i u m v a n a d a t e c a t a l y s t some r e m a r k a b l e d i f f e r e n c e s , r e l a t i v e t o t h e b i s m u t h m o l y b d a t e c a t a l y s t , were obs e r v e d . 1) The o x i d a t i o n o f b e n z o n i t r i l e depended obs t r o n g l y on t h e oxygen c o n -c e n t r a t i o n i n t h e r e a -c t i o n m i x t u r e . 2) The d i r e -c t -c o m b u s t i o n o f t o l u e n e d i d n o t o c c u r , w h i c h means t h a t a t a low c o n v e r s i o n d e g r e e n e a r l y a l l t h e t o l u e n e i s c o n v e r t e d t o b e n z o n i t r i l e . 3) A t an ammonia/toluene r a t i o s m a l l e r t h a n two, l e s s t h a n 10% o f t h e ammonia was c o n v e r t e d t o n i t r o g e n . 4) B e n z o n i t r i l e i n h i b i t e d t h e ammoxidation r a t e o f t o l u e n e .
The k i n e t i c model which b e s t d e s c r i b e s t h e r e a c t i o n s i s b a s e d on a combina-t i o n o f a r e d o x and a L a n g m u i r - H i n s h e l w o o d mechanism. The b a s e s o f combina-t h e model a r e t h a t c a t a l y s t oxygen i s r e s p o n s i b l e f o r t h e f o r m a t i o n o f b e n z o n i t r i l e and t h a t a d s o r b e d g a s - p h a s e oxygen i s r e s p o n s i b l e f o r t h e f o r m a t i o n o f t h e p r o d u c t s o f c o m p l e t e o x i d a t i o n . The maximum y i e l d o b t a i n e d was 75%. R e c y c l i n g o f t h e un-c o n v e r t e d t o l u e n e t o t h e r e a un-c t o r i n un-c r e a s e d t h e y i e l d t o more t h a n 90%.
The r e s u l t s o f t h e p u l s e e x p e r i m e n t s w i t h t h e s i l v e r c e r i u m v a n a d a t e c a t a l y s t a g r e e w e l l w i t h t h e r e s u l t s o b t a i n e d w i t h t h e f i x e d - b e d r e a c t o r . I n t h e absence o f g a s - p h a s e oxygen, h a r d l y any c o m p l e t e r e a c t i o n p r o d u c t s were formed. T h i s c a t a l y s t p r o p e r t y makes i t p o s s i b l e t o c h o o s e f o r a r e g e n e r a t i v e p r o c e s s , w h i c h means t h a t t h e r e o x i d a t i o n o f t h e c a t a l y s t o c c u r s s e p a r a t e l y from t h e o t h e r r e a c t i o n s .
The ammoxidation o f m- and p - x y l e n e on t h e s i l v e r c e r i u m v a n a d a t e i s s i m i l a r t o t h e ammoxidation o f t o l u e n e . U s i n g o - x y l e n e some c o m p l i c a t i o n s a r o s e , however. F i r s t l y , a d e a l k y l a t i o n r e a c t i o n o c c u r r e d , by w h i c h .a c o n s i d e r a b l e p e r c e n t a g e
(up t o 25%) o f b e n z o n i t r i l e was formed. S e c o n d l y , b e s i d e s p h t h a l o n i t r i l e p h t h a -l i m i d e was a -l s o formed, i . e . by an e q u i -l i b r i u m r e a c t i o n w i t h w a t e r and ammonia.
From t h e r e s u l t s o f t h e k i n e t i c r e s e a r c h and t h e p u l s e e x p e r i m e n t s i t was c o n c l u d e d t h a t a n i t r i l e i s formed by a d i r e c t r e a c t i o n between an a c t i v a t e d m e t h y l b e n z e n e m o l e c u l e and a d s o r b e d ammonia. I t i s n o t p r o b a b l e t h a t a l d e h y d e s o r a c i d s a r e formed as i n t e r m e d i a t e s d u r i n g t h e ammoxidation o f t o l u e n e and x y l e n e s on t h e i n v e s t i g a t e d c a t a l y s t s .
1 I N T R O D U C T I O N
1.1 S e l e c t i v e gas-phase o x i d a t i o n and ammoxidation i n g e n e r a l
Many v a l u a b l e i n t e r m e d i a t e s f o r t h e c h e m i c a l i n d u s t r y a r e p r o d u c e d b y p a r t i a l
o x i d a t i o n o f h y d r o c a r b o n s . I n such a way oxygen and n i t r o g e n c a n be i n t r o d u c e d
i n o l e f i n i c and a r o m a t i c compounds t o s y n t h e s i z e a l d e h y d e s , a c i d s and n i t r i l e s .
One o f t h e e a r l y t e c h n i c a l p r o c e s s e s i s t h e o x i d a t i o n o f n a p h t h a l e n e t o
p h t h a l i c a c i d a n h y d r i d e w i t h a vanadium p e n t o x i d e c a t a l y s t , as r e a l i z e d i n
1917- 1918 i n t h e USA (4) and i n 1920 by BASF i n Germany ( 1 1 ) . The vanadium
o x i d e c a t a l y s t was, however, n o t s u i t a b l e f o r t h e s e l e c t i v e o x i d a t i o n o f o l e
-f i n e s .
I n 1948 Hearne and Adams (6) d i s c o v e r e d t h a t a c r o l e i n c o u l d be p r o d u c e d from
a m i x t u r e o f p r o p y l e n e and a i r , u s i n g a c u p r o u s o x i d e c a t a l y s t . However, a
major b r e a k t h r o u g h i n t h e f i e l d o f p a r t i a l o x i d a t i o n was t h e d i s c o v e r y i n 1959
of a b i s m u t h molybdate c a t a l y s t , by t h e S t a n d a r d O i l o f O h i o Company (SOHIO).
The b i s m u t h (phospho)molybdate was found n o t t o be o n l y an e x c e l l e n t c a t a l y s t
f o r t h e o x i d a t i o n o f p r o p y l e n e t o a c r o l e i n , b u t a l s o f o r t h e p r o d u c t i o n o f
b u t a d i e n e from butene and, more i m p o r t a n t , f o r t h e one s t e p p r o d u c t i o n o f
a c r y l o n i t r i l e from a m i x t u r e o f p r o p y l e n e , a i r and ammonia ( 7 ) . The l a t t e r
r e a c t i o n i s c a l l e d t h e ammoxidation o r o x i d a t i v e ammonolysis o f p r o p y l e n e .
In t h e p e r i o d 1950 - 1960 t h e ammoxidation o f a r o m a t i c s a l s o began t o appear
i n t h e l i t e r a t u r e t h r o u g h t h e r e s e a r c h o f Denton e t a l . (2) and Hadley ( 5 ) .
Denton d i d n o t use oxygen i n t h e r e a c t i o n m i x t u r e : ammonia and t h e h y d r o c a r b o n
r e a c t e d w i t h a MoO^ on a c t i v a t e d a l u m i n a c a t a l y s t t o t h e d e s i r e d n i t r i l e . The
c a t a l y s t was r e g e n e r a t e d w i t h a i r . Hadley c o n d u c t e d c o n v e n t i o n a l ammoxidation,
i . e . , i n t h e p r e s e n c e o f m o l e c u l a r oxygen, u s i n g a V^O^ c a t a l y s t .
For t h e p a r t i a l o x i d a t i o n o f h y d r o c a r b o n s t h e use o f a c a t a l y s t i s n e c e s s a r y ,
s i n c e t h e G i b b s f r e e e n e r g y change f o r t h e t o t a l c o m b u s t i o n a l w a y s has a
l a r g e r n e g a t i v e v a l u e t h a n f o r p a r t i a l o x i d a t i o n r e a c t i o n . A c a t a l y s t f o r a
p a r t i a l o x i d a t i o n r e a c t i o n must p r o v i d e o n l y a l i m i t e d amount o f oxygen t o t h e
r e a c t a n t . The c a t a l y s t s w h i c h a r e g e n e r a l l y used f o r s e l e c t i v e o x i d a t i o n c o n
c a t a l y s t s f o r p a r t i a l o x i d a t i o n a r e a l s o d e s c r i b e d , i . e . , s u p p o r t e d rhodium
and r u t h e n i u m c a t a l y s t s ( 1 ) , b u t t h e i r e f f i c i e n c y i s l o w e r t h a n t h a t o f the
m e t a l o x i d e s .
S i n c e t h e d i s c o v e r y o f t h e b i s m u t h m o l y b d a t e c a t a l y s t many s t u d i e s have been
c a r r i e d o u t t o o b t a i n more i n s i g h t o f t h e mechanism o f t h e p a r t i a l o x i d a t i o n
r e a c t i o n and t h e r o l e o f t h e c a t a l y s t . A l t h o u g h c o n s i d e r a b l e p r o g r e s s has been
made d u r i n g t h e l a s t decade, t h e u n d e r s t a n d i n g o f t h e p r o c e s s i s n e v e r t h e l e s s
f a r from c o m p l e t e , and t h e improvement o f t h e p r o p e r t i e s o f a c a t a l y s t s t i l l
p r o c e e d s i n an e m p i r i c a l way.
1.2 Ammoxidation o f a r o m a t i c h y d r o c a r b o n s
The ammoxidation o f a r o m a t i c h y d r o c a r b o n s t o n i t r i l e s has r e c e i v e d much a t t e n
-t i o n i n p a -t e n -t and s c i e n -t i f i c l i -t e r a -t u r e d u r i n g -t h e l a s -t decade. Mos-t p r o c e s s e s
however, a r e s t i l l i n t h e development s t a g e , and o n l y a few n i t r i l e s a r e as
yet p r o d u c e d c o m m e r c i a l l y (e.g. b e n z o n i t r i l e and 1 , 3 - d i c y a n o b e n z e n e ) , u s i n g
ammoxidation.
A number o f a r o m a t i c compounds w i t h a m e t h y l (or e t h y l ) s i d e - c h a i n can be
c o n v e r t e d t o a n i t r i l e v i a a m m o x i d a t i o n . T o l u e n e can be c o n v e r t e d t o
benzo-n i t r i l e , w h i c h i s used i benzo-n t h e s y benzo-n t h e s i s o f b e benzo-n z o c y a benzo-n i benzo-n e r e s i benzo-n s abenzo-nd as a s o l v e benzo-n t
0-, m- and p - x y l e n e y i e l d , r e s p e c t i v e l y , p h t h a l o n i t r i l e , i s o p h t h a l o n i t r i l e and
t e r e p h t h a l o n i t r i l e . P h t h a l o n i t r i l e i s u s e d i n t h e m a n u f a c t u r e o f c o p p e r p h t h a
-l o c y a n i n e p i g m e n t s . I s o p h t h a -l o n i t r i -l e i s a c h e m i c a -l p r e c u r s o r t o D a c o n i -l ,
an a g r i c u l t u r a l c h e m i c a l f u n g i c i d e , and t o m - x y l y l e n e d i a m i n e , w h i c h can be
u s e d i n p o l y a m i d e f o r m u l a t i o n s o r c o n v e r t e d t o i s o c y a n a t e f o r p o l y u r e t h a n e
f o r m u l a t i o n s . T e r e p h t h a l o n i t r i l e i s an i n t e r m e d i a t e i n t h e t e r e p h t h a l i c a c i d
p r o d u c t i o n a c c o r d i n g t o t h e Lummus p r o c e s s ( 3 ) .
In a d d i t i o n N - h e t e r o c y c l i c compounds can be c o n v e r t e d t o t h e c o r r e s p o n d i n g
n i t r i l e s . The ammoxidation o f 3 - p i c o l i n e , f o r i n s t a n c e , y i e l d s n i c o t i n o n i t r i l e ,
w h i c h can be c o n v e r t e d t o n i c o t i n a m i d ( v i t a m i n B^) and n i c o t i n i c a c i d .
In t h i s t h e s i s t h e ammoxidation o f t o l u e n e and x y l e n e a r e s t u d i e d . The
major p a r t o f t h e s t u d y c o n c e r n s t o l u e n e , w h i c h r e p r e s e n t s t h e s i m p l e s t model
component f o r a r o m a t i c ammoxidation.
1.3 The c a t a l y s t
Two d i f f e r e n t t y p e s o f c a t a l y s t s were s e l e c t e d f o r t h i s s t u d y :
a. P u r e b i s m u t h molybdate
b. S i l v e r c e r i u m v a n a d a t e on a s i l i c a c a r r i e r .
6
The b i s m u t h molybdate c a t a l y s t s were used i n a l a r g e number o f l a b o r a t o r y
s t u d i e s (8, 9, 12), and t h e y may be c o n s i d e r e d as one o f t h e b e s t d e f i n e d
c a t a l y s t s i n p a r t i a l o x i d a t i o n r e a c t i o n s . A b i s m u t h m o l y b d a t e c a t a l y s t i s
t h e r e f o r e v e r y s u i t a b l e f o r s t u d y i n g t h e e x p e c t e d a n a l o g y between t h e
d a t i o n o f t o l u e n e and b e t t e r known r e a c t i o n s , l i k e t h e o x i d a t i o n and
ammoxi-d a t i o n o f p r o p y l e n e anammoxi-d t h e o x i ammoxi-d a t i o n o f t o l u e n e . A ammoxi-d i s a ammoxi-d v a n t a g e o f t h e p u r e
b i s m u t h m o l y b d a t e s i s t h e i r p o o r m e c h a n i c a l s t r e n g t h w h i c h l i m i t s t h e i r use
t o l a b o r a t o r y s t u d i e s .
F o r t h e p a r t i a l - o x i d a t i o n o f a r o m a t i c compounds o t h e r t y p e s o f c a t a l y s t s were
d e v e l o p e d . A c c o r d i n g t o t h e p a t e n t l i t e r a t u r e a m a j o r i t y o f t h e s e c a t a l y s t s
c o n t a i n vanadium o x i d e as t h e b a s i c compound and one o r two o t h e r m e t a l
o x i d e s . F o r t h i s r e a s o n t h e second c a t a l y s t , a s i l v e r c e r i u m v a n a d a t e on
s i l i c a , was s e l e c t e d f o r t h i s s t u d y . T h i s c a t a l y s t i s d e s c r i b e d by D u t c h S t a t e
M i n e s i n a p a t e n t i n w h i c h t o l u e n e i s o x i d i z e d t o b e n z a l d e h y d e and b e n z o i c
a c i d ( 1 0 ) .
Of s p e c i a l i n t e r e s t i n t h i s s t u d y was the q u e s t i o n whether t h e ammoxidation
o f t o l u e n e and x y l e n e p r o c e e d s i n a s i m i l a r way on d i f f e r e n t t y p e s o f c a t a l y s t ,
o r t h a t a t each c a t a l y s t a n o t h e r mechanism o c c u r s .
1.4 Aim and scope o f t h e t h e s i s
The aim o f t h i s s t u d y was t o i n v e s t i g a t e t h e k i n e t i c s and mechanism o f t h e
ammoxidation o f t o l u e n e and x y l e n e . Two d i f f e r e n t t y p e s o f c a t a l y s t s were
u s e d i n o r d e r t o examine what s i m i l a r i t i e s e x i s t e d between t h e c a t a l y s t and,
i n p a r t i c u l a r , whether s i m i l a r o r d i f f e r e n t mechanisms o c c u r r e d .
F o r t h i s r e s e a r c h two a p p a r a t u s were a v a i l a b l e (Chapter 2 ) . A c o n t i n u o u s
f l o w s y s t e m was used t o s t u d y the k i n e t i c s under s t a t i o n a r y c o n d i t i o n s .
Ex-p e r i m e n t s w i t h a Ex-p u l s e a Ex-p Ex-p a r a t u s were Ex-p e r f o r m e d t o s t u d y t h e r e a c t i o n o f one
o r two components w i t h t h e c a t a l y s t under n o n - s t a t i o n a r y c o n d i t i o n s .
C h a p t e r 3 d e a l s w i t h t h e e x p e r i m e n t a l methods and t h e c a l c u l a t i o n p r o c e d u r e s .
I n t h e same c h a p t e r t h e r a t h e r c o m p l i c a t e d p u l s e t e c h n i q u e i s d i s c u s s e d .
The e x p e r i m e n t a l r e s u l t s o b t a i n e d w i t h t h e b i s m u t h m o l y b d a t e c a t a l y s t a r e
d e s c r i b e d i n C h a p t e r 4. The l a r g e r p a r t o f t h e e x p e r i m e n t s c o n c e r n s t h e
ammoxidation o f t o l u e n e , t h e l e s s e r p a r t t h e o x i d a t i o n o f ammonia.
The c a t a l y t i c p r o p e r t i e s o f t h e s i l v e r c e r i u m v a n a d a t e c a t a l y s t a r e d e s
-c r i b e d i n C h a p t e r 5. S t u d i e d were t h e ammoxidation o f t o l u e n e and x y l e n e .
I n t h e f i n a l c h a p t e r (Chapter 6) t h e e x p e r i m e n t a l r e s u l t s o f C h a p t e r s 4
References
1. C a n t , N.W., H a l l , W.K., J . C a t a l . , 22^, 310 (1971).
2. Denton, W.I., B i s h o p , R.B., C a l d w e l l , H.P., Chapman, H.D., I n d . Eng. Chem.
42_, 796 (1950).
3. G e l b e i n , Ä.P., S z e , M.C., W h i t e h e a d , R.T., H y d r o c a r b o n P r o c e s s i n g , 211,
S e p t . 1973.
4. G i b b s , H.P., Conover, C , C A . 13,134,230 (1919).
5. H a d l e y , D.J. ( D i s t i l l e r s Co.), U.S. P a t e n t 2,846,462 (1958).
6. Hearne, G.W., Adams, M.L. ( S h e l l Development C o . ) , U.S. P a t e n t 2,451,485
(1948).
7. I d o l , J.D. ( S t a n d a r d O i l C o . ) , U.S. P a t e n t 2,904,580 (1958).
8. K e u l k s , G.W., J . C a t a l . , 22, 19 (1971).
9. M a t s u u r a , I . , J . C a t a l . , 33, 420 (1974).
10. M u l l e r , F.S. ( S t a m i c a r b o n N.V.) N e t h . P a t e n t 6514683 (1965).
11. Wohl, A . ( B A S F ) , DRP 379,822 (1916).
12. Wragg, R.D., Ashmore, P.G. , Hockey, J.A. , J . C a t a l . , 22./ 19 (1971).
2 A P P A R A T U S AND A N A L Y S I S
2.1 I n t r o d u c t i o n
Two a p p a r a t u s were b u i l t f o r t h e e x p e r i m e n t a l p a r t o f t h i s r e s e a r c h : a c o n
-t i n u o u s f l o w s y s -t e m and a p u l s e d f l o w r e a c -t o r .
The c o n t i n u o u s f l o w s y s t e m was u s e d f o r e x p e r i m e n t s under s t a t i o n a r y c o n
-d i t i o n s an-d c o n t a i n e -d a p l u g f l o w r e a c t o r . The l a t t e r i s p r e f e r r e -d t o a f l u i -d
bed because o f i t s s i m p l e f l o w p a t t e r n . A l t h o u g h a f l u i d bed i s homogeneous
i n t e m p e r a t u r e , t h e c o m p l e x i t y o f i t s f l o w p a t t e r n r e n d e r s t h e i n t e r p r e t a t i o n
o f r e s u l t s more d i f f i c u l t t h a n w i t h a p l u g f l o w r e a c t o r . The r e a c t i o n c o n
-d i t i o n s a p p l i e -d a r e c l o s e t o t h e c o m m e r c i a l v a l u e s ( 4 ) . As t h e a i m o f t h e
r e s e a r c h i s t h e s t u d y o f t h e k i n e t i c s o f t h e h e t e r o g e n e o u s r e a c t i o n s on t h e
c a t a l y s t s u r f a c e , i t i s n e c e s s a r y t o meet a number o f r e q u i r e m e n t s , s u c h as
t h e absence o f p o r e and f i l m d i f f u s i o n l i m i t a t i o n s , t h e absence o f t e m p e r a t u r e
g r a d i e n t s , e t c . These a s p e c t s w i l l be d i s c u s s e d i n C h a p t e r 3. I n t h i s c h a p t e r
the hardware w i l l be d e s c r i b e d .
A p u l s e f l o w system i s used t o s t u d y t h e r e d u c t i o n o x i d a t i o n p r o p e r t i e s o f
t h e c a t a l y s t . I t i s g e n e r a l l y assumed t h a t c a t a l y s t oxygen i s i n v o l v e d i n t h e
s e l e c t i v e gas phase o x i d a t i o n and ammoxidation p r o c e s s o v e r m e t a l o x i d e s . I n a
p u l s e system i t i s p o s s i b l e t o s t u d y t h e r e a c t i o n o f each i n d i v i d u a l compound
w i t h t h e c a t a l y s t a t d i f f e r e n t d e g r e e s o f r e d u c t i o n . Because o f t h e n o n s t a t i o n
-a r y c o n d i t i o n s , however, t h e i n t e r p r e t -a t i o n o f t h e r e s u l t s i s d i f f i c u l t . T h i s
d i f f i c u l t y a l s o a p p l i e s t o t h e c o r r e l a t i o n o f p u l s e and f l o w e x p e r i m e n t s .
2.2 F l o w a p p a r a t u s
A d i a g r a m m a t i c f l o w s h e e t o f t h e a p p a r a t u s i s shown i n F i g u r e 2-1. E x c e p t f o r
t h e r e a c t o r t h e e n t i r e a p p a r a t u s i s made o f s t a i n l e s s s t e e l 316. The f e e d
m i x t u r e from t h e gas f l o w c o n t r o l u n i t [1] may c o n s i s t o f a i r , n i t r o g e n , neon
and ammonia. A l l gases e x c e p t a i r a r e o b t a i n e d from c y l i n d e r s ( r e s e a r c h grade) ;
no f u r t h e r p u r i f i c a t i o n was f o u n d n e c e s s a r y . F o r t h e a c c u r a t e c o n t r o l o f t h e
~ 1
c 6
T 7
Figure 2-1 Diagrammatic flowsheet of the apparatus
1. Gas flow control unit
2. Saturators
3. Switch valve (6-way)
4. Reactor
5. Condensor
6. Sample valve (10-way)
7. Analysis system
(P.F.D. 112) a r e used i n t h e range o f 2-200 cm^/min. N i t r o g e n o r a i r a r e
p a s s e d t h r o u g h d o u b l e w a l l e d t h e r m o s t a t e d s a t u r a t o r s [ 2 ] , w h i c h a r e f i l l e d
w i t h t o l u e n e , x y l e n e o r w a t e r . The d e s i r e d p a r t i a l p r e s s u r e c a n be o b t a i n e d by
a d j u s t i n g and c o n t r o l l i n g t h e t e m p e r a t u r e o f t h e s a t u r a t o r . The gas l e a v i n g t h e
v a p o r i z e r i s c o m p l e t e l y s a t u r a t e d w i t h v a p o u r . T h i s c o m p l e t e s a t u r a t i o n i s
e f f e c t e d by v a r y i n g t h e l i q u i d l e v e l i n t h e s a t u r a t o r above a c e r t a i n minimum
v a l u e . No change i n t h e gas c o m p o s i t i o n i s found i n t h e c a s e t h a t t h e s a t u r a t o r
i s more t h a n h a l f f i l l e d . A f t e r t h i s t h e gas m i x t u r e p a s s e s a C a r l e s i x - p o r t
v a l v e [3] and i s f e d t o t h e r e a c t o r [ 4 ] . The p r o d u c t gas p a s s e s a g a i n t o t h e
s w i t c h v a l v e [ 3 ] , a C a r l e t e n - p o r t sample v a l v e [ 6 ] , and f i n a l l y t o a condensor
[ 5 ] . I n t h e c o n d e n s o r (280 K) h y d r o c a r b o n v a p o u r s a r e c o l l e c t e d and a r e s u b
j e c t e d t o s e n s i t i v e q u a l i t a t i v e a n a l y s i s . The sample v a l v e [6] has two sample
l o o p s (0.5 cm^), w h i c h a r e used by e i t h e r t h e f e e d o r t h e p r o d u c t gas, d e p e n d i n g
on t h e p o s i t i o n o f t h e s w i t c h v a l v e . B o t h v a l v e s a r e p l a c e d i n an a i r t h e r m o s t a t
a t a b o u t 510 K t o a v o i d c o n d e n s a t i o n o f r e a c t i o n p r o d u c t s and t o e n s u r e a c o n
-s t a n t q u a n t i t y o f ga-s i n t h e -sample l o o p -s . A l l f e e d and p r o d u c t l i n e -s t o t h e
two samples v a l v e s a r e h e a t e d t o a b o u t 370 K and 520 K, r e s p e c t i v e l y , t o a v o i d
c o n d e n s a t i o n o f h y d r o c a r b o n s and w a t e r .
The c o n s t r u c t i o n o f t h e r e a c t o r i s shown i n F i g u r e 2-2. From i n t r o d u c t o r y
k i n e t i c e x p e r i m e n t s i t was found t h a t s t a i n l e s s s t e e l i s c a t a l y t i c a l l y a c t i v e
f o r t h e o x i d a t i o n o f ammonia a t a t e m p e r a t u r e e x c e e d i n g about 670 K. F o r t h i s
r e a s o n t h e r e a c t o r [2] i s made o f q u a r t z . To a v o i d p r o b l e m s w i t h the p a c k i n g
o f t h e q u a r t z t u b e a t a h i g h t e m p e r a t u r e , t h e tube i s p l a c e d i n a s t a i n l e s s
s t e e l tube w i t h an i n n e r d i a m e t e r o f 10 mm [ 4 ] . The c a t a l y s t bed [5] i s 8-10
cm l o n g and c o n s i s t s o f c a t a l y s t p a r t i c l e s d e l u t e d w i t h c r u s h e d q u a r t z p a r t i c l e s
o f t h e same s i e v e f r a c t i o n (0.4-0.6 mm i n most o f t h e e x p e r i m e n t s ) . Two t h i n
t h e r m o c o u p l e s (0.5 mm) a r e mounted i n t h e a x i s o f t h e c a t a l y s t bed t o r e g i s t e r
p o s s i b l e t e m p e r a t u r e d i f f e r e n c e s w i t h i n t h e bed and between c a t a l y s t and r e a c t o r
w a l l . The r e a c t o r i s p l a c e d i n a f l u i d bed o f s i l i c o n c a r b i d e p a r t i c l e s [10] t o
a s s u r e good h e a t exchange and a c c u r a t e t e m p e r a t u r e c o n t r o l .
I n a c c o r d a n c e w i t h Van d e r W i e l e ' s s u g g e s t i o n (6) t h e 'post c a t a l y t i c volume'
was m i n i m i z e d . The i n n e r d i a m e t e r o f t h e r e a c t o r tube d e c r e a s e s t o 2 mm
immediate-l y a f t e r t h e c a t a immediate-l y s t bed, and t h e r e a c t o r i s p immediate-l a c e d j u s t above t h e a i r
thermo-s t a t w h i c h c o n t a i n thermo-s t h e thermo-sample v a l v e f o r t h e a n a l y thermo-s i thermo-s thermo-sythermo-stem. T h i thermo-s m i n i m i z a t i o n
o f t h e 'post c a t a l y t i c volume' was done t o s u p p r e s s s u r f a c e i n i t i a t e d homogeneous
r e a c t i o n s , as were r e p o r t e d by D a n i e l and K e u l k s ( 2 ) .
The f l o w a p p a r a t u s i s o p e r a t e d s e m i - a u t o m a t i c a l l y . A programmable i n t e g r a t o r
( I n f o t r o n i c s CRS 304) w i t h e i g h t e x t e r n a l commands i s used f o r t h e p n e u m a t i c
s w i t c h i n g o f t h e v a l v e s . I n t h i s way samples o f t h e f e e d and p r o d u c t s t r e a m
can be t a k e n a t any d e s i r e d t i m e i n t e r v a l . The t e m p e r a t u r e o f t h e r e a c t o r can
be changed a u t o m a t i c a l l y w i t h s t e p s o f 5-2 5 K, by means o f t h e a c t i v a t i o n o f
a s e r v o - m o t o r , w h i c h i s b u i l t i n t o t h e t h y r i s t e r t e m p e r a t u r e c o n t r o l l e r o f t h e
f l u i d bed.
A f t e r each s e r i e s o f e x p e r i m e n t s t h e d a t a a r e c o l l e c t e d and r e c o r d e d on
punch c a r d s , a f t e r w h i c h c o n v e r s i o n s , s e l e c t i v i t i e s , mass b a l a n c e s e t c . a r e
c a l c u l a t e d u s i n g a F o r t r a n computer programme. The r e s u l t s a r e s t o r e d on a
Figure 2-2 Reactor construction
1. Reactor inlet tube
2. Quartz reactor tube (inner diameter 6 mm)
3. Quick-fit gasket
4. Tube (stainless steel)
5. Catalyst
6. Quartz wool
7. Reactor outlet tube
8. Air inlet tube
9. Distributor plate
10. Fluid bed
11. Electrical heating
12. Isolating material
2.3 The p u l s e r e a c t o r s y s t e m
F i g u r e 2-3 r e p r e s e n t s a d i a g r a m m a t i c f l o w s h e e t o f t h e p u l s e a p p a r a t u s . The
p u l s e i n j e c t i o n system c o n s i s t s o f two p u l s e v a l v e s [ 2 , 3 ] , a s w i t c h v a l v e [1]
12
6
Figure 2-3 Diagrammatic flowsheet of the pulse system
1. Switch valve
2. S3. Pulse valves
4. Injection assembly
5. Reactor
6. Analysis system
and an i n j e c t i o n assembly f o r s y r i n g e s [ 4 ] , a l l p l a c e d i n an a i r t h e r m o s t a t a t
400 K. T h i s c o n s t r u c t i o n a v o i d s c o n d e n s a t i o n o f h y d r o c a r b o n s and w a t e r , and a
c o n s t a n t number o f moles o f r e a c t a n t s i s a s s u r e d . The c a r r i e r gas used i n most
o f t h e e x p e r i m e n t s i s h e l i u m , w h i c h i s f r e e d from t r a c e s o f oxygen by means o f
a r e d u c e d BTS c a t a l y s t . The c a r r i e r gas p a s s e s t h e p u l s e v a l v e s [2, 3] s u c c e s
-s i v e l y and f l o w -s v i a t h e -s w i t c h v a l v e i n t o t h e a n a l y -s i -s -sytem. The p u l -s e ga-s
may c o n s i s t o f any d e s i r e d c o m p o s i t i o n o f t o l u e n e , w a t e r , oxygen, ammonia,
hydrogen and h e l i u m . The gas f l o w c o n t r o l u n i t used f o r t h i s p u r p o s e i s s i m i l a r
t o t h a t d e s c r i b e d i n t h e p r e v i o u s s e c t i o n . F o r t h e d o s i n g o f t h e l i q u i d
com-pounds, a s a t u r a t o r i s a g a i n used.
When a p u l s e v a l v e i s s w i t c h e d , t h e c o n t e n t s o f t h e l o o p i s t r a n s p o r t e d by
t h e c a r r i e r gas s t r e a m t o t h e a n a l y s i s system. I t depends on t h e p o s i t i o n o f
t h e s w i t c h v a l v e [3] whether t h e p u l s e p a s s e s t h e r e a c t o r b e f o r e i t e n t e r s t h e
a n a l y s i s s y s t e m (a s o - c a l l e d p r o d u c t p u l s e ) , o r whether i t e n t e r s d i r e c t l y (a
The a p p a r a t u s i s o p e r a t e d s e m i - a u t o m a t i c a l l y . A g a i n a programmable i n t e g r a t o r
( I n f o t r o n i c s CRS 304) i s used t o a c t i v a t e t h e t h r e e v a l v e s ( C a r l e s i x - p o r t ) and
t o v a r y t h e r e a c t o r t e m p e r a t u r e . Feed and p r o d u c t p u l s e s can be g i v e n w i t h any
d e s i r e d t i m e i n t e r v a l and sequence. O n l y t h e c o m p o s i t i o n o f t h e p u l s e g a s e s has
t o be changed by hand. The p r e s e n c e o f two p u l s e l o o p s w i t h d i f f e r e n t volumes
(0.5 and 2.5 cm^) i s n e c e s s a r y when t h e c a t a l y s t i s r e d u c e d and r e o x i d i z e d
a l t e r n a t e l y and when t h e i n f l u e n c e o f p u l s e s i z e on t h e c o n v e r s i o n l e v e l has
t o be s t u d i e d .
The r e a c t o r i s a s t a i n l e s s s t e e l t u b e ( i n n e r d i a m e t e r 4 mm), w h i c h i s p l a c e d
i n a f l u i d bed o f s i l i c o n p a r t i c l e s f o r a c c u r a t e t e m p e r a t u r e c o n t r o l (T c o n s t a n t
w i t h i n 1 K) . The c a t a l y s t bed (1 cm ) c o n s i s t s o f 250-500 mg c a t a l y s t p a r t i c l e s
d i l u t e d w i t h c r u s h e d q u a r t z p a r t i c l e s ( s i e v e f r a c t i o n 0.4-0.5 mm) and i s p l a c e d
between two p l u g s o f q u a r t z w o o l .
The a n a l y s i s system used f o r t h e q u a n t i t a t i v e d e t e r m i n a t i o n o f t h e p u l s e
com-p o s i t i o n i s d e s c r i b e d i n t h e n e x t s e c t i o n .
The t h e o r y o f o p e r a t i o n o f t h e p u l s e t e c h n i q u e i s d i s c u s s e d i n C h a p t e r 3.
2.4 A n a l y s i s s y s t e m
The a n a l y s i s systems f o r t h e f l o w and p u l s e a p p a r a t u s a r e v e r y s i m i l a r . The
q u a n t i t a t i v e d e t e r m i n a t i o n o f t h e components i n a sample t a k e s p l a c e i n t h r e e
o n - l i n e gas chromatographs ( F i g u r e 2-4). The c a r r i e r gas s t r e a m s p l i t s i n t o two
p a r t s a t t h e a n a l y s i s s y s t e m o f t h e p u l s e a p p a r a t u s . One h a l f o f t h e gas s t r e a m
i s p a s s e d t h r o u g h a gas c h r o m a t o g r a p h w i t h a flame i o n i z a t i o n d e t e c t o r ( G . C . - l ) .
The o t h e r h a l f p a s s e s t h r o u g h two gas chromatographs i n s e r i e s (G.C.-2 and
G.C.-3), b o t h w i t h a t h e r m a l c o n d u c t i v i t y d e t e c t o r .
A t t h e a n a l y s i s system o f t h e f l o w a p p a r a t u s t h e s p l i t t i n g o f t h e c a r r i e r
gas s t r e a m i s o m i t t e d because o f t h e use o f a t e n - p o r t v a l v e w i t h two sample
Figure 2-4 Analysis system
1. OV-101 column
2. Porapak-N column
3. Mol. si eves column
4. Flame ionization detectors
5. S6. Thermal conduct, detectors
l o o p s . A sample o f e i t h e r t h e f e e d o r p r o d u c t s t r e a m i s t a k e n by s w i t c h i n g
the v a l v e , by w h i c h t h e c o n t e n t s o f one l o o p f l o w s t o G.C.-l and t h e c o n t e n t s
o f t h e o t h e r l o o p f l o w s t o G.C.-2 and G.C.-3, u s i n g a d i f f e r e n t gas s t r e a m .
T h i s p r o c e d u r e r e s u l t s i n a d e c r e a s e o f t h e e x p e r i m e n t a l e r r o r . A d d i t i o n a l l y
G.C.-l c a n be o p e r a t e d c o m p l e t e l y i n d e p e n d e n t l y from G.C.-2 and G.C.-3.
The c o n d i t i o n s o f t h e a n a l y t i c a l s y s t e m o f t h e f l o w a p p a r a t u s a r e shown i n
T a b l e 2-1, whereas t h e chromatograms a r e shown i n F i g u r e s 2-5, 2-6 and 2-7.
G . C . - l : H e w l e t t P a c k a r d 5720
Flame I o n i s a t i o n D e t e c t o r ; Temperature: 573 K
Column: S u p p o r t : Chromosorb G-HP, 80-100 mesh
L i q u i d Phase: 3% OV-101
M a t e r i a l : S t a i n l e s s S t e e l , DCMS t r e a t e d *
L e n g t h : 4 m, I n n e r d i a m e t e r : 2.1 mm
3 -1
C a r r i e r Gas F l o w : 20 cm min
Temperature: 433 K
A n a l y s i n g Time: 10 min (ammoxidation o f t o l u e n e )
20 min (ammoxidation o f p - x y l e n e )
G.C.-2: Thermal C o n d u c t i v i t y D e t e c t o r ; Temperature: 383 K
B r i d g e C u r r e n t : 150 mA
Column: P a c k i n g : Porapak N, 80-100 mesh
M a t e r i a l : G l a s s
L e n g t h : 2 m. I n n e r d i a m e t e r : 3 mm
C a r r i e r Gas Flow: 28 c m
3min
1He STP, c o n t . 200 ppm NH
Temperature : 383 K
A n a l y s i n g Time: 10 m i n u t e s
G.C.-3: Thermal C o n d u c t i v i t y D e t e c t o r ; Temperature: 333 K
B r i d g e C u r r e n t : 150 mA
Column: P a c k i n g : M o l . S i e v e s 5A, 80-100 mesh
M a t e r i a l : S t a i n l e s s S t e e l , DCMS t r e a t e d *
L e n g t h : 4 m, I n n e r d i a m e t e r : 4 mm
n -1
C a r r i e r Gas Flow: 28 cm
Jmin He STP, c o n t . 200 ppm NH.
T e m p e r a t u r e : 333 K
A n a l y s i n g Time: 10 m i n u t e s
*DCMS: d i m e t h y l d i c h l o r o s i l a n e
The a n a l y t i c a l c o n d i t i o n s f o r t h e p u l s e a p p a r a t u s a r e t h e same e x c e p t f o r t h e f l o w r a t e o f t h e c a r r i e r gas s t r e a m , w h i c h i s g i v e n a t t h e s e r i e s o f e x p e r i m e n t s ( C h a p t e r s 4 and 5 ) . G . C . - l i s u s e d f o r t h e s e p a r a t i o n o f t h e h y d r o c a r b o n s : e.g. benzene, t o l u e n e , b e n z o n i t r i l e , t o l u n i t r i l e and b e n z o d i n i t r i l e . G.C.-l i s t e m p e r a t u r e programmable, which i s u s e f u l a t s p e c i a l p r o d u c t c o m p o s i t i o n s . A t n o r m a l c o n d i t i o n s t h e a n a l y s i s i s p e r f o r m e d i s o t h e r m a l l y . The p e a k s a r e r e c o r d e d ( F i g u r e 2-5) , and t h e peak a r e a s a r e d e t e r m i n e d w i t h a d i g i t a l i n t e g r a t o r ( I n f o t r o n i c s CRS 304). On G.C.-2 ' a i r1, c a r b o n d i o x i d e , ammonia and w a t e r a r e s e p a r a t e d . ' A i r ' s t a n d s
f o r a m i x t u r e o f oxygen, n i t r o g e n , neon and c a r b o n monoxide. The s e p a r a t i o n o f t h e p o l a r compounds ammonia and water i s , however, much more c o m p l i c a t e d t h a n one would e x p e c t . V e r b r u g g e (5) and A'Campo e t a l . (1) d e s c r i b e d t h e a n a l y s i s o f p o l a r compounds on p o r o u s p o l y m e r gas c h r o m a t o g r a p h i c columns. Non-l i n e a r r e s p o n s e i s r e p o r t e d due t o ' c o m p e t i t i v e ' a d s o r p t i o n o f water and
ammonia on t h e column m a t e r i a l . I n o u r c a s e t h i s r e s u l t s i n a p r o n o u n c e d t a i l i n g o f t h e ammonia peak ( F i g u r e 2-6a), a peak w h i c h p r o b a b l y c o n t a i n s some w a t e r
o r i g i n a t i n g f r o m a p r e v i o u s sample o r from t h e w a t e r c o n t a i n e d i n t h e c a r r i e r
gas stream. T h i s phenomenon may cause l a r g e s y s t e m a t i c e r r o r s i n b o t h t h e
ammonia and w a t e r c o n c e n t r a t i o n d e t e r m i n a t i o n s . I n a d d i t i o n t o t h i s
ammonia-w a t e r i n t e r a c t i o n , t h e i n t e g r a t i o n o f a t a i l i n g ammonia peak i s a l s o r a t h e r
i n a c c u r a t e , a l t h o u g h modern i n t e g r a t o r s may p a r t l y overcome t h i s p r o b l e m . A
l a r g e improvement o f t h e p e r f o r m a n c e o f G.C.-2 i s r e a c h e d by a d d i n g ammonia
c o n t i n u o u s l y t o t h e c a r r i e r gas so t h a t w a t e r a d s o r p t i o n i s p r e v e n t e d . A
chromatogram w i t h 200 ppm i n t h e c a r r i e r gas s t r e a m i s shown i n F i g u r e 2-6b.
The peak a r e a s a r e d e t e r m i n e d w i t h a programmable i n t e g r a t o r ( I n f o t r o n i c s CRS
304) .
G.C.-3 i s used f o r t h e a n a l y s i s o f neon, oxygen, n i t r o g e n and c a r b o n monoxide.
Because n i t r o g e n i s formed from t h e o x i d a t i o n o f ammonia, i t c a n n o t be used
as an i n t e r n a l s t a n d a r d . F o r t h i s p u r p o s e neon i s added t o t h e f e e d m i x t u r e .
Carbon d i o x i d e , ammonia and w a t e r a r e n o t e l u t e d by t h e column ( m o l e c u l a r
s i e v e L i n d e 5A); t h e r e f o r e p e r i o d i c r e g e n e r a t i o n i s n e c e s s a r y . The r e s u l t i n g
chromatogram i s r e c o r d e d (see F i g u r e 2-7), and t h e peak a r e a s a r e i n t e g r a t e d
( I n f o t r o n i c s CRS 309).
A t a l o w mole f r a c t i o n o f a component i n t h e d e t e c t o r , t h e peak a r e a o f t h e
component i n t h e chromatogram i s p r o p o r t i o n a l t o i t s m o l a r q u a n t i t y i n t h e
sample. The q u a n t i t y o f each component i n t h e f e e d o r p r o d u c t sample c a n be
c a l c u l a t e d u s i n g t h e r e l a t i o n :
P. = f..A. (2.1)
l
l
i
i n w h i c h P., and A^ a r e , r e s p e c t i v e l y , t h e p a r t i a l p r e s s u r e , t h e r e s p o n s e
f a c t o r and t h e peak a r e a o f component i .
The f - v a l u e s o f t h e gaseous compounds a r e d e t e r m i n e d by m i x i n g one component
w i t h h e l i u m i n a w e l l - k n o w n r a t i o and i n t h e range o f t h e e x p e r i m e n t a l
compo-s i t i o n . From t h i compo-s r a t i o and t h e t o t a l p r e compo-s compo-s u r e i n t h e compo-sample l o o p (or p u l compo-s e
l o o p ) t h e p a r t i a l p r e s s u r e o f t h e component i s c a l c u l a t e d . A f t e r m e a s u r i n g t h e
peak a r e a , t h e f - v a l u e i s c a l c u l a t e d u s i n g e q u a t i o n 2.1. The f - v a l u e s o f t h e
l i q u i d components a r e d e t e r m i n e d s i m i l a r l y , t h e t h e r m o s t a t e d s a t u r a t o r s b e i n g
used t o e f f e c t a c c u r a t e d o s i n g . Knowing t h e t e m p e r a t u r e o f t h e s a t u r a t o r t h e
p a r t i a l p r e s s u r e o f t h e compound c a n be c a l c u l a t e d , u s i n g v a p o u r p r e s s u r e
-t e m p e r a -t u r e d a -t a from -t h e l i -t e r a -t u r e ( 3 ) .
References
1. A'Campo, C.P.M.G., Lemkowitz, S.M., V e r b r u g g e , P., B e r g , P . J . van den, J . Chromatogr. 203, 271 (1981). 2. D a n i e l , C., K e u l k s , G.W., J . C a t a l . , 24, 529 (1972). 3. I n t e r n a t i o n a l C r i t i c a l T a b l e s , V o l . 3, M c G r a w - H i l l (1928). 4. O ' D o n n e l l , J.P., B u t l e r , R.M., Simpson, L.B., ( E s s o ) , U.S. p a t . 3.462.476 (1969). 5. V e r b r u g g e , P., T h e s i s , D e l f t (1979). 6. W i e l e , K. van d e r . T h e s i s , D e l f t (1976).
18
3 E X P E R I M E N T A L METHODS AND C A L C U L A T I O N P R O C E D U R E S
3.1 I n t r o d u c t i o n
The a i m o f t h e e x p e r i m e n t s w i t h t h e c o n t i n u o u s f l o w system was t o s t u d y t h e
k i n e t i c s o f t h e h e t e r o g e n e o u s gas phase ammoxidation o f t o l u e n e and x y l e n e .
I n o r d e r t o g e t r e l i a b l e i n f o r m a t i o n from t h e e x p e r i m e n t a l d a t a c e r t a i n r e
-q u i r e m e n t s must be met. A p a r t i c u l a r r e -q u i r e m e n t i s t h a t t h e i n f l u e n c e o f t h e
t r a n s p o r t phenomena must be e x c l u d e d . I n t h i s c h a p t e r t h e s e r e q u i r e m e n t s w i l l
be b r i e f l y d i s c u s s e d .
The p u l s e t e c h n i q u e p r o v i d e s i n f o r m a t i o n about t h e c a t a l y s t p r o p e r t i e s
under non-steady s t a t e c o n d i t i o n s , making t h e i n t e r p r e t a t i o n o f t h e r e s u l t s
r a t h e r d i f f i c u l t . Because o f t h e s e p r o b l e m s a d i s c u s s i o n o f t h e major a s p e c t s
o f t h e p u l s e system and i t s t h e o r y i s u s e f u l .
F i n a l l y i n t h i s c h a p t e r t h e c a l c u l a t i o n method i s d e s c r i b e d , w h i c h i s u s e d
f o r t h e k i n e t i c m o d e l l i n g o f t h e e x p e r i m e n t a l d a t a from t h e f l o w a p p a r a t u s .
3.2 D e f i n i t i o n s
A number o f terms w h i c h a r e used r e g u l a r l y i n t h e n e x t c h a p t e r s t o c h a r a c t e r
-i z e t h e c a t a l y t -i c p r o c e s s a r e d e f -i n e d as f o l l o w s :
a) The c o n c e n t r a t i o n o f each component i n t h e f e e d and p r o d u c t m i x t u r e i s
e x p r e s s e d as i t s p a r t i a l p r e s s u r e i n terms P a s c a l s . The p a r t i a l p r e s s u r e s o f
a l l components a r e measured a t a t e m p e r a t u r e o f 500 K. W i t h t h e a i d o f t h e
i d e a l gas law t h e d a t a can be e a s i l y c o n v e r t e d t o moles/m^.
b) The r e a c t i o n r a t e i s d e f i n e d a s :
d P.
R. =
— (Pa.cm /s/g) (3.1)
1
d W/F
f l o w r a t e (cmJ/s) o f t h e f e e d a t S t a n d a r d Temperature (293 K) and P r e s s u r e
(100 k P a ) . The r a t i o W/F i s c a l l e d t h e space time (t ), with the dimension o f g.s/cm . To t r a n s f o r m Tg t o t h e more u s u a l d i m e n s i o n o f s e c . t h e v a l u e o f W/F
has t o be d i v i d e d by t h e b u l k d e n s i t y o f t h e c a t a l y s t . T h i s was n o t done b e c a u s e o f t h e v a r i a b l e p a c k i n g o f t h e c a t a l y s t bed and t h e use o f q u a r t z p a r -t i c l e s a s a d i l u -t i o n m a -t e r i a l . To compare o u r space -t i m e v a l u e s w i -t h -t h e l i t e r a t u r e t h e f o l l o w i n g b u l k d e n s i t i e s can be u s e d :
B i s m u t h m o l y b d a t e : p = 1 g/cm3
C e r i u m s i l v e r v a n a d a t e : p = 0.5 g/cm3
c) The c o n v e r s i o n , s e l e c t i v i t y and y i e l d a r e e x p r e s s e d i n mole % and a r e c a l c u l a t e d as f o l l o w s : PA 'Fe C o n v e r s i o n o f comp. A = (1 - ,e —) . 100 • (3.2) A, o' o P .F - P .F S e l e c t i v i t y o f comp. A t o B= ( '°pB '° °) . 1 0 0 (3.3) A,o' o A,e' e P .F - P .F Y i e l d o f comp. B from A = (B,S p6 ^ — ^ — - ) . 100 (3.4) A,o" o In t h e s e r e l a t i o n s F and F a r e t h e v o l u m e t r i c f l o w r a t e s (cm^/s) o f r e s p e c -e o ' ^ t i v e l y t h e p r o d u c t and t h e f e e d m i x t u r e . The d i f f e r e n c e between F and F i s
e o c a u s e d by t h e p r e s s u r e d r o p o v e r t h e c a t a l y s t bed and by an i n c r e a s e o f t h e number o f moles due t o the c h e m i c a l r e a c t i o n s . The r a t i o o f F / F i s c a l c u l a t e d
e o from t h e mass b a l a n c e o v e r t h e i n e r t component neon.
F .P = F .P (3.5) e Ne,e o Ne,o
d) F o r t h e p u l s e e x p e r i m e n t s t h e p r o p e r t i e s o f t h e c a t a l y s t a r e measured r e l a t i v e t o i t s oxygen c o n t e n t . F o r t h i s p u r p o s e a d e g r e e o f r e d u c t i o n i s de-f i n e d :
number o f moles removed from t h e c a t a l y s t
Degree o f r e d u c t i o n = — — • — — — — — — — — — — — number o f moles o f 0^ p r e s e n t i n t h e o x i d i z e d c a t a l y s t (3.6) In t h i s r e l a t i o n t h e oxygen o f t h e c a r r i e r m a t e r i a l ( e . g . s i l i c a ) i s o f c o u r s e n o t c o n s i d e r e d . 20
!["Najnowsze prądy w poezyi naszej", Piotr Chmielowski, Lwów -Warszawa 1901 ; "Dramat Polski doby najnowszej", Piotr Chmielowski, Lwów 1902 : [recenzja]](data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACH5BAEAAAAALAAAAAABAAEAAAICRAEAOw==)