o o o _ D a D • — O O o o o o o o f O O O Ol o o o ! _ O o- o o o o o O O O O O O O O O O O O O C o O O O O O O Q O , o f o o o o o o o T o o o o o „ o o~ c1 ( O O O O O O o , _ O O O O O O O C . 0 0 0 0 0 0 0 0 0 • o o o o o 0 0 0 o T O O O O O O O O O V O O O O O O 0 0 0 0 , O O O O O O O O O » ^ 0 O O O O O O O O O , O O O O O O O O O o-o o-o 0 , 0 o-o o-o o-o o-o » 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 , O O O O O O O C V - fw, rtOOOOOOO^. J O O O O O O J ° . - o q •O O O O O O O -O -O -O -O -O -O -O -O -O O O O O O O O O O - O O O O O O O O O 0 0 0 0 0 0 0 0 0 0 0 0 1 o O O O O O O O O O 0 _ O O O O O O O O O O O I O O O O 0 0 o o - o o • 0 0 0 0 0 o o - o o o » O O O O O O 0 0 o o o O O O O ° „0,0„ ° -I O O O O O O O 0 0 0 O O O O O O O O O O ' » O O O O O O O O O C U O O O O O O O O O O , > 0 0 0 0 0 0 0 0 0 -0 -0 -0 -0 -0 -0 -0 -0 -0 -0 , 1 O 0 3 O 3 O O O " 3 3 0 o o / l o o 3 0 0 0 0 o^b o o O O O O O 3 3 O 3 0 0 0 0 0 0 0 3 V o V o V o V o : " T o l o 30o0o0o0o0o S V ' ¿ V o o o o 3 3 3 r 3 - V o W W '
Removal of formic acid from crude acetic acid
by heterogeneous catalytic decomposition
o *• *-vjn © (v O t-» © -J W OD 0s O O -J BIBLIOTHEEK TU Delft P 1630 4276 470518
Removal of formic acid from crude acetic acid
by heterogeneous catalytic decomposition
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
woensdag 15 oktober 1980 te 14.00 uur door
Franciscus Johannes Wubben scheikundig ingenieur geboren te 's-Gravenhage
PROF. IR.W. A. DE JONG
PROF. IR. A. G. MONTFOORT
Aan allen die het tot stand
komen van dit proefschrift
mogelijk hebben gemaakt.
SUMMARY XI
SAMENVATTING X I I I
1. INTRODUCTION 1
1.1 O b j e c t i v e 1
1.2 O u t l i n e o f t h e s i s 2
2. PRODUCTION OF ACETIC ACID AND REMOVAL OF FORMIC ACID
FROM CRUDE ACETIC ACID 3
2.1 P r o d u c t i o n o f a c e t i c a c i d 3 2.1.1 I n t r o d u c t i o n 3 2.1.2 A c e t a l d e h y d e o x i d a t i o n 5 2.1.3 L i q u i d phase o x i d a t i o n o f s a t u r a t e d h y d r o c a r b o n s 7 2.1.4 M e t h a n o l c a r b o n y l a t i o n 8 2.1.5 P o t e n t i a l r o u t e s 10 2.1.6 Economic c o n s i d e r a t i o n s 12 2.2 Removal o f f o r m i c a c i d 13 2.2.1 I n t r o d u c t i o n 13 2.2.2 A z e o t r o p i c d i s t i l l a t i o n 14 2.2.3 C a t a l y t i c d e c o m p o s i t i o n 19 2.2.4 E s t e r i f i c a t i o n 20
3. THERMODYNAMICS AND KINETICS 21
3.1 I n t r o d u c t i o n 21 3.2 Thermodynamics 22 3.3 P o s s i b l e mechanisms and r a t e e x p r e s s i o n s f o r f o r m i c a c i d d e c o m p o s i t i o n 25 3.3.1 I n t r o d u c t i o n 25 3.3.2 D e h y d r o g e n a t i o n on m e t a l s 28 3.3.3 D e h y d r a t i o n on o x i d e s 35 3.3.3 D i s c u s s i o n 36 3.3.5 C o n c l u d i n g remarks 41
4. EXPLORATORY EXPERIMENTS, EQUIPMENT AND PROCEDURES 43 4.1 E x p l o r a t o r y e x p e r i m e n t s 43 4.2 Equipment 44 4.3 A n a l y s i s 46 4.3.1 I n t r o d u c t i o n 46 4.3.2 A n a l y s i s o f w a t e r , f o r m i c a c i d and a c e t i c a c i d 46 4.3.3 A n a l y s i s o f c a r b o n monoxide and c a r b o n d i o x i d e 53 4.4 P r o c e d u r e s 54 4.4.1 C a l c u l a t i o n o f c o n v e r s i o n 54 4.4.2 K i n e t i c measurements 55
5. DECOMPOSITION OF FORMIC ACID IN THE PRESENCE OF ACETIC ACID
AND WATER OVER A COPPER CATALYST 56
5.1 Review o f t h e l i t e r a t u r e 56 5.2 C a t a l y s t c h a r a c t e r i z a t i o n 60
5.3 C a t a l y s t s t a b i l i t y 61
5.4 K i n e t i c s 65
5.5 C o n c l u s i o n s 71
6. DECOMPOSITION OF FORMIC ACID IN THE PRESENCE OF ACETIC ACID
AND WATER OVER A NICKEL CATALYST 72
6.1 Review o f t h e l i t e r a t u r e 72 6.2 C a t a l y s t c h a r a c t e r i z a t i o n 76
6.3 C a t a l y s t s t a b i l i t y 78
6.4 K i n e t i c s 80 6.5 C o n c l u s i o n s 85
7. DECOMPOSITION OF FORMIC ACID IN THE PRESENCE OF ACETIC ACID
AND WATER OVER A V-ALUMINA CATALYST 86
7.1 Review o f t h e l i t e r a t u r e 86 7.2 C a t a l y s t c h a r a c t e r i z a t i o n 89
7.3 C a t a l y s t s t a b i l i t y 89
7.4 K i n e t i c s 92
8.1 I n t r o d u c t i o n 99 8.2 C a t a l y t i c a s p e c t s o f h i g h f o r m i c a c i d c o n v e r s i o n on F - a l u m i n a 99 8.3 A p p l i c a t i o n o f t h e c a t a l y s t s s t u d i e d i n t h e p u r i f i c a t i o n u n i t o f an e x i s t i n g a c e t i c a c i d p l a n t 101 8.3.1 I n t r o d u c t i o n 101 8.3.2 E x i s t i n g p u r i f i c a t i o n u n i t 101 8.3.3 A p p l i c a t i o n o f t h e copper and F - a l u m i n a c a t a l y s t s i n t h e e x i s t i n g f l o w scheme 103 8.3.4 A p p l i c a t i o n o f t h e copper and y - a l u m i n a c a t a l y s t s i n t h e m o d i f i e d f l o w scheme 105 8.3.5 Economic c o n s i d e r a t i o n s 107 8.4 C o n c l u s i o n s 109 APPENDIX 1 : Thermodynamic d a t a 110
APPENDIX 2 : A n a l y s i s o f f o r m i c a c i d , a c e t i c a c i d and water 113 APPENDIX 3 : A n a l y s i s o f c a r b o n monoxide and c a r b o n d i o x i d e 114
APPENDIX 4 : A s s o c i a t i o n i n t h e gas phase 115
LIST OF SYMBOLS AND ABBREVIATIONS 118
XI
SUMMARY
F o r m i c a c i d i s a b y - p r o d u c t i n s e v e r a l r o u t e s f o r p r o d u c i n g a c e t i c a c i d . Removal i s e s s e n t i a l because c o n t a m i n a t i o n by f o r m i c a c i d r e n d e r s a c e t i c a c i d u n s u i t a b l e f o r most a p p l i c a t i o n s and much more c o r r o s i v e than i t o t h e r w i s e would be.
F o r m i c a c i d , a c e t i c a c i d and water form a t e r n a r y s a d d l e p o i n t a z e o t r o p e . T h e r e f o r e a z e o t r o p i c d i s t i l l a t i o n i s a p p l i e d c o m m e r c i a l l y f o r t h e removal o f
f o r m i c a c i d , e s p e c i a l l y when f o r m i c a c i d i s r e c o v e r e d and s o l d . When r e c o v e r y o f f o r m i c a c i d i s n o t e c o n o m i c a l l y f e a s i b l e c a t a l y t i c d e c o m p o s i t i o n i s o f t e n f a v o u r e d as t h e method f o r removal because a z e o t r o p i c d i s t i l l a t i o n has t h e d i s a d v a n t a g e o f a h i g h energy r e q u i r e m e n t . I n d u s t r i a l l y , t h e c a t a l y t i c
decom-p o s i t i o n i s c a r r i e d o u t by ( decom-p a r t i a l ) o x i d a t i o n w i t h a i r o v e r a codecom-pdecom-per s u l decom-p h a t e on a l u m i n a c a t a l y s t ( o x i d a t i o n p r o d u c t s : CO^ and H„C5. However, t h i s p r o c e s s f o r removal has t h e d i s a d v a n t a g e s t h a t the c a t a l y s t i s n o t s t a b l e , i . e . d e a c t i -v a t i o n o c c u r s , and a l s o n o t t o t a l l y s e l e c t i -v e , i . e . some a c e t i c a c i d i s a l s o
decomposed. The o b j e c t i v e o f t h i s s t u d y was t o f i n d a c a t a l y s t which c o u l d d e h y d r o g e n a t e ( p r o d u c t s : CO^ and H^) o r d e h y d r a t e ( p r o d u c t s : CO and H2O) f o r m i c a c i d s e l e c t i v e l y o v e r a s t a b l e c a t a l y s t . To t h a t end, s t a b i l i t y and k i n e t i c measurements were performed w i t h a copper on a l u m i n a c a t a l y s t , a
n i c k e l on a l u m i n a c a t a l y s t and a l u m i n a i t s e l f as t h e c a t a l y s t .
The t h r e e c a t a l y s t s s t u d i e d were a l l v e r y s e l e c t i v e , i . e . d e c o m p o s i t i o n o f a c e t i c a c i d was n o t o b s e r v e d .
The d e c o m p o s i t i o n r e a c t i o n o f f o r m i c a c i d o v e r the copper on a l u m i n a c a t a l y s t proceeded a l m o s t e x c l u s i v e l y t h r o u g h d e h y d r o g e n a t i o n . The c a t a l y s t p r o v e d t o d e a c t i v a t e : a f a s t d e a c t i v a t i o n t h r o u g h carbon f o r m a t i o n which c o u l d be n u l
l i f i e d by o x i d a t i o n / r e d u c t i o n o f t h e d e a c t i v a t e d c a t a l y s t and a s l o w d e a c t i -v a t i o n w h i c h may be due t o s u b l i m a t i o n o f c o p p e r ( I ) formate and/or s i n t e r i n g . V a r y i n g t h e p a r t i a l p r e s s u r e o f a c e t i c a c i d , w a t e r (above 20 k P a ) , CO^ and had no e f f e c t on t h e r a t e o f f o r m i c a c i d d e c o m p o s i t i o n o v e r t h e copper c a t a
-l y s t . A f r a c t i o n a -l o r d e r r a t e dependency w i t h r e s p e c t t o t h e c o n c e n t r a t i o n o f f o r m i c a c i d was found i n the e x p e r i m e n t a l range s t u d i e d which i s c o n t r a r y t o most p u b l i s h e d d a t a b u t can be c o n s i d e r e d t o be i n a c c o r d a n c e w i t h t h e r e s u l t s o f Van H e r w i j n e n f o r pure f o r m i c a c i d d e c o m p o s i t i o n o v e r a Cu/ZnO
s h i f t c a t a l y s t .
The d e c o m p o s i t i o n r e a c t i o n o v e r t h e n i c k e l c a t a l y s t proceeded p r i m a r i l y t h r o u g h d e h y d r o g e n a t i o n . The CO/CO^ r a t i o o f t h e p r o d u c t gas m i x t u r e d e c r e a s e d w i t h on-stream t i m e which may be a consequence o f i n c r e a s i n g c a r b i d e f o r m a t i o n . Slow d e a c t i v a t i o n o f t h e c a t a l y s t was o b s e r v e d . C o n t r a r y t o t h e copper c a t a
-l y s t a c e t i c a c i d was found t o have a r e t a r d i n g e f f e c t on t h e r a t e . The o r d e r i n f o r m i c a c i d i s z e r o i n t h e e x p e r i m e n t a l range s t u d i e d which i s i n a c c o r -dance w i t h l i t e r a t u r e d a t a .
The r a t e e x p r e s s i o n s found f o r t h e copper and n i c k e l c a t a l y s t s can be c o n s i -dered t o be i n l i n e w i t h t h e g e n e r a l l y a c c e p t e d mechanism o f f o r m i c a c i d d e c o m p o s i t i o n o v e r m e t a l s i n which formate i s t h e i n t e r m e d i a t e .
The d e c o m p o s i t i o n o f f o r m i c a c i d o v e r a l u m i n a proceeded p r i m a r i l y t h r o u g h
de-h y d r a t i o n . Tde-he CO/CO^ r a t i o o f t de-h e p r o d u c t gas m i x t u r e d e c r e a s e d w i t de-h on-stream t i m e and t h e w a t e r - g a s s h i f t r e a c t i o n was found t o i n f l u e n c e t h e CO/CO^ p r o d u c t r a t i o . C a t a l y s t d e a c t i v a t i o n was n o t o b s e r v e d . A c e t i c a c i d had a r e t a r d i n g e f f e c t on t h e r a t e . A f i r s t o r d e r r a t e dependency on f o r m i c a c i d
was d e t e r m i n e d which i s i n a c c o r d a n c e w i t h a mechanism proposed i n t h e l i t e -r a t u -r e i n which gaseous f o -r m i c a c i d -r e a c t s w i t h a p -r o t o n s u p p l i e d by t h e d i s s o c i a t i v e a d s o r p t i o n o f f o r m i c a c i d .
On t h e b a s i s o f an e x i s t i n g p u r i f i c a t i o n u n i t o f an a c e t i c a c i d p l a n t t h e
a p p l i c a t i o n o f a l u m i n a a s t h e c a t a l y s t i s d i s c u s s e d . The advantages o f a l u m i n a o v e r t h e c a t a l y t i c o x i d a t i o n p r o c e s s a r e t h e b e t t e r s e l e c t i v i t y and s t a b i l i t y . These advantages a r e p a r t i a l l y o f f s e t by t h e h i g h e r t e m p e r a t u r e l e v e l and t h e e n d o t h e r m i c h e a t o f t h e r e a c t i o n . Water i s a d e c o m p o s i t i o n p r o d u c t i n b o t h
methods and t h i s g i v e s r i s e t o r e l a t i v e l y h i g h energy r e q u i r e m e n t s i n t h e d i s t i l l a t i o n s o f t h e p u r i f i c a t i o n u n i t . C a l c u l a t i o n s show t h a t f o r t h i s r e a s o n a s t a b l e , s e l e c t i v e , d e h y d r o g e n a t i n g c a t a l y s t w i l l be e c o n o m i c a l l y s u p e r i o r .
X I I I
SAMENVATTING
M i e r e z u u r i s een b i j p r o d u k t b i j v e r s c h i l l e n d e p r o d u k t i e m e t h o d e n van a z i j n z u u r .
V e r w i j d e r i n g van m i e r e z u u r i s n o o d z a k e l i j k omdat v e r o n t r e i n i g i n g met m i e r e -z u u r het a -z i j n -z u u r o n g e s c h i k t maakt voor de meeste t o e p a s s i n g e n en d a a r n a a s t
ook c o r r o s i e v e r dan het zonder m i e r e z u u r zou z i j n .
M i e r e z u u r vormt, tezamen met a z i j n z u u r en w a t e r , een t e r n a i r e a z e o t r o o p . Tene i n d Tene m i Tene r Tene z u u r t Tene v Tene r w i j d Tene r Tene n wordt op industriëlTene s c h a a l a z Tene o t r o p i s c h Tene d Tene s
-t i l l a -t i e -t o e g e p a s -t , v o o r a l i n d i e n he-t m i e r e z u u r a l s b i j p r o d u k -t word-t gewonnen en v e r k o c h t . I n d i e n deze w i n n i n g e c h t e r economisch n i e t a a n t r e k k e l i j k i s wordt vaak een k a t a l y t i s c h e o n t l e d i n g t o e g e p a s t omdat a z e o t r o p i s c h e d e s t i l -l a t i e het n a d e e -l h e e f t van een g r o o t e n e r g i e v e r b r u i k . Op industrië-le s c h a a -l
wordt de k a t a l y t i s c h e o n t l e d i n g u i t g e v o e r d door (partiële) o x y d a t i e met l u c h t o v e r k o p e r s u l f a a t op a l u m i n a a l s de k a t a l y s a t o r ( r e a c t i e p r o d u k t e n : CO^ en 1^0). Nadelen van deze methode z i j n dat de k a t a l y s a t o r n i e t s t a b i e l i s ( d e a k t i v e r i n g t r e e d t op) en ook dat de r e a k t i e o v e r deze k a t a l y s a t o r n i e t g e h e e l s e l e c t i e f i s ( a z i j n z u u r wordt voor een k l e i n g e d e e l t e ook o m g e z e t ) .
Het d o e l van d i t onderzoek was om een s t a b i e l e k a t a l y s a t o r t e v i n d e n d i e m i e r e z u u r s e l e c t i e f kan o n t l e d e n door d e h y d r o g e n e r i n g ( p r o d u k t e n : C0^ en h^) o f door d e h y d r a t a t i e ( p r o d u k t e n : CO en h^O). D e r h a l v e z i j n s t a b i l i t e i t s p r o e v e n en k i n e t i s c h e metingen v e r r i c h t met een koper op a l u m i n a k a t a l y s a t o r , een
n i k k e l op a l u m i n a k a t a l y s a t o r en a l u m i n a z e l f a l s de k a t a l y s a t o r .
De d r i e o n d e r z o c h t e k a t a l y s a t o r e n waren a l l e n z e e r s e l e c t i e f , d.w.z. e r werd geen o n t l e d i n g van a z i j n z u u r waargenomen.
De o n t l e d i n g van m i e r e z u u r o v e r de koper op a l u m i n a k a t a l y s a t o r vond v r i j w e l u i t s l u i t e n d p l a a t s v i a d e h y d r o g e n e r i n g . K a t a l y s a t o r d e a k t i v e r i n g t r a d op; een s n e l l e d e a k t i v e r i n g door k o o l v o r m i n g , d i e e c h t e r opgeheven kon worden door o x y d a t i e / r e d u k t i e van de g e d e a k t i v e e r d e k a t a l y s a t o r , en een langzame d e a k t i
-v e r i n g , d i e t e w i j t e n kan z i j n aan s u b l i m a t i e -van k o p e r ( I ) f o r m i a a t e n / o f s i n t e r i n g . V a r i a t i e van de p a r t i a a l s p a n n i n g van a z i j n z u u r , w a t e r (boven 20 k P a ) , CO,, en had geen e f f e c t op de s n e l h e i d van m i e r e z u u r o n t l e d i n g o v e r de k o p e r k a t a l y s a t o r . Gevonden i s een f r a c t i o n e l e o r d e i n m i e r e z u u r wat n i e t overeenkomt met de meeste l i t e r a t u u r , maar wel met de r e s u l t a t e n van Van
s h i f t k a t a l y s a t o r .
Over de n i k k e l op a l u m i n a k a t a l y s a t o r vond m i e r e z u u r o n t l e d i n g v o o r n a m e l i j k p l a a t s v i a d e h y d r o g e n e r i n g . De CO/CO^ v e r h o u d i n g i n h e t p r o d u k t g a s m e n g s e l nam a f met toenemende p r o c e s t i j d wat een g e v o l g kan z i j n van toenemende c a r b i d e v o r m i n g . Waargenomen werd een langzame d e a k t i v e r i n g van de k a t a l y s a t o r . A z i j n z u u r had een v e r t r a g e n d e w e r k i n g op de r e a k t i e s n e l h e i d , d i t i n t e g e n s t e l -l i n g t o t de k o p e r k a t a -l y s a t o r . De o r d e i n m i e r e z u u r i s n u -l i n h e t o n d e r z o c h t e meetgebied en d i t i s i n overeenstemming met l i t e r a t u u r g e g e v e n s .
De gevonden s n e l h e i d s v e r g e l i j k i n g e n van de k o p e r - e n n i k k e l k a t a l y s a t o r z i j n i n overeenstemming met h e t algemeen g e a c c e p t e e r d e mechanisme van m i e r e z u u r -o n t l e d i n g -over m e t a l e n , w a a r i n f -o r m i a a t h e t i n t e r m e d i a i r i s .
M i e r e z u u r o n t l e d i n g o v e r a l u m i n a vond v o o r n a m e l i j k p l a a t s v i a d e h y d r a t a t i e . De CO/CO2 verhouding i n h e t produktgasmengsel nam a f met toenemende p r o c e s t i j d , en gevonden i s d a t de C O - s h i f t r e a k t i e de CO/CO^ v e r h o u d i n g b e i n v l o e d t . E r t r a d geen k a t a l y s a t o r d e a k t i v e r i n g op. A z i j n z u u r had een v e r t r a g e n d e f f e c t op de r e a k t i e s n e l h e i d . Een 1 o r d e k i n e t i e k i n m i e r e z u u r i s gevonden, wat i n 'overeenstemming i s met een i n de l i t e r a t u u r v o o r g e s t e l d mechanisme w a a r i n g a s v o r m i g m i e r e z u u r r e a g e e r t met een p r o t o n , a f k o m s t i g van de d i s s o c i a t i e v e a d s o r p t i e van m i e r e z u u r .
De industriële t o e p a s s i n g van a l u m i n a i s t o e g e l i c h t aan de hand van een z u i v e r i n g s s e c t i e van een b e s t a a n d e a z i j n z u u r f a b r i e k . De v o o r d e l e n van a l u m i n a ten o p z i c h t e van de k a t a l y t i s c h e o x y d a t i e z i j n de b e t e r e s e l e c t i v i t e i t en s t a b i l i t e i t . Deze v o o r d e l e n worden t e n d e l e t e n i e t gedaan d o o r d a t de r e a k t i e endotherm i s en b i j een hogere t e m p e r a t u u r v e r l o o p t . Water i s een o n t l e d i n g s -p r o d u k t b i j b e i d e methoden, hetgeen a a n l e i d i n g g e e f t t o t een r e l a t i e f hoog e n e r g i e v e r b r u i k b i j de d e s t i l l a t i e s i n de z u i v e r i n g s s e c t i e . U i t b e r e k e n i n g e n b l i j k t d a t daarom een s t a b i e l e , s e l e c t i e v e , dehydrogenerende k a t a l y s a t o r u i t economisch oogpunt de v o o r k e u r g e n i e t .
J 1. INTRODUCTION 1.1. OBJECTIVE A c e t i c a c i d i s m a n u f a c t u r e d c o m m e r c i a l l y by t h e l i q u i d phase o x i d a t i o n o f s a t u r a t e d h y d r o c a r b o n s , t h e o x i d a t i o n o f a c e t a l d e h y d e o r by methanol c a r b o n y l a t i o n . E s p e c i a l l y t h e f i r s t two r o u t e s t o a c e t i c a c i d ( they a c c o u n t e d f o r 75 % o f t h e p r o d u c t i o n o f a c e t i c a c i d i n t h e USA i n 1 9 7 3 ( 1 ) ) are c h a r a c t e r i z e d by t h e f a c t t h a t many b y - p r o d u c t s a r e formed.
High and low b o i l i n g b y - p r o d u c t s can be d i s t i l l e d o f f e a s i l y b u t f o r m i c a c i d poses a p r o b l e m , because i t forms a t e r n a r y s a d d l e p o i n t a z e o t r o p e w i t h a c e t i c a c i d and water and cannot be d i s t i l l e d o f f i n t h e normal way. F o r m i c a c i d removal i s e s s e n t i a l because any p r e s e n c e o f f o r m i c a c i d i n
a c e t i c a c i d r e n d e r s t h e f i n a l p r o d u c t u n s u i t a b l e f o r most a p p l i c a t i o n s and much more c o r r o s i v e than i t o t h e r w i s e would be.
Depending on t h e p r i c e o f f o r m i c a c i d , t h e c o n c e n t r a t i o n , and t h e economics o f t h e p r o c e s s f o r r e m o v a l , i t i s removed by a n o n - d e s t r u c t i v e method o r a
d e s t r u c t i v e one. A n o n - d e s t r u c t i v e method i s a z e o t r o p i c d i s t i l l a t i o n , which i s commonly employed b u t has t h e prime d i s a d v a n t a g e o f a h i g h energy r e q u i r e m e n t . A d e s t r u c t i v e method i s t h e c a t a l y t i c d e c o m p o s i t i o n o f f o r m i c a c i d by o x i d a t i o n ( p r o d u c t s : h^O and CQ^) • T h i s method i s a p p l i e d
commer-c i a l l y by t h e C e l a n e s e C o r p o r a t i o n ( 2 ) . The r e a commer-c t i o n i s commer-c a r r i e d o u t i n t h e vapour phase w i t h a i r a t about 200 °C o v e r copper s u l p h a t e on a l u m i n a as t h e c a t a l y s t . D i s a d v a n t a g e s o f t h i s p r o c e s s a r e 1) n o n - s e l e c t i v i t y , i . e . some a c e t i c a c i d i s a l s o decomposed, 2) c a t a l y s t d e a c t i v a t i o n , 3) t h e r e s u l t i n g
l a r g e gas s t r e a m which has t o be p u r i f i e d .
The aim o f t h e s t u d y p r e s e n t e d i n t h i s t h e s i s was t o f i n d a c a t a l y s t which c o u l d dehydrogenate ( p r o d u c t s : H^ and CO^)and/or d e h y d r a t e ( CO and H2O ) the f o r m i c a c i d s e l e c t i v e l y over a s t a b l e c a t a l y s t , t h e r e b y overcoming t h e d i s a d v a n t a g e s o f t h e p r o c e s s mentioned above. The work i n c l u d e d measurements
o f t h e k i n e t i c s o f t h e f o r m i c a c i d d e c o m p o s i t i o n i n t h e p r e s e n c e o f a c e t i c a c i d and water o v e r s e l e c t e d c a t a l y s t s .
1.2. OUTLINE OF THESIS
In c h a p t e r 2 t h e v a r i o u s methods o f p r o d u c i n g a c e t i c a c i d a r e r e v i e w e d a l o n g w i t h methods f o r removal o f f o r m i c a c i d from c r u d e a c e t i c a c i d . In c h a p t e r 3 s e v e r a l t h e o r e t i c a l r a t e e x p r e s s i o n s f o r c a t a l y t i c f o r m i c a c i d d e c o m p o s i t i o n
a r e d e r i v e d and d i s c u s s e d i n r e l a t i o n t o l i t e r a t u r e d a t a . The e x p e r i m e n t a l a p p a r a t u s and p r o c e d u r e s a r e p r e s e n t e d i n c h a p t e r 4. P r e l i m i n a r y e x p e r i m e n t s ( c a t a l y s t s c r e e n i n g ) a r e a l s o d e s c r i b e d i n t h i s c h a p t e r . In c h a p t e r 5 t h e e x p e r i m e n t a l r e s u l t s a r e p r e s e n t e d on t h e d e c o m p o s i t i o n o f f o r m i c a c i d i n t h e
p r e s e n c e o f a c e t i c a c i d and water o v e r a copper on a l u m i n a c a t a l y s t . Chapter 6 and 7 have t h e same s t r u c t u r e as c h a p t e r 5. Chapter 6 d e a l s w i t h a n i c k e l on a l u m i n a c a t a l y s t and c h a p t e r 7 w i t h t h e c a r r i e r i t s e l f , F - a l u m i n a . A c o m p a r i s o n between t h e t h r e e c a t a l y s t s s t u d i e d i s made i n c h a p t e r 8.
Indus-t r i a l a p p l i c a Indus-t i o n s w i Indus-t h Indus-t h e c a Indus-t a l y s Indus-t s s e l e c Indus-t e d a r e a l s o d e s c r i b e d i n c h a p Indus-t e r 8 and compared w i t h e x i s t i n g p r o c e s s e s t o remove f o r m i c a c i d from c r u d e a c e t i c a c i d .
3
2. PRODUCTION OF ACETIC ACID AND REMOVAL OF FORMIC ACID
FROM CRUDE ACETIC ACID
2.1. PRODUCTION OF ACETIC ACID
2.1.1. I n t r o d u c t i o n The t o t a l US a c e t i c a c i d p r o d u c t i o n0 f 950 m i l l i o n kg i n 1975 r a n k s t h i s c h e m i c a l among t h e t o p 20 o r g a n i c i n t e r m e d i a t e s ( 3 ) . T a b l e 2.1 i n d i c a t e s i t s p a t t e r n o f g r o w t h . Year M i l l i o n s o f kg A n n u a l growth r a t e , % 1940 84.55 (1940-1950) 9.0 1950 200.12 (1950-1960) 5.3 1960 336.12 (1960-1970) 10.0 1970 876.47 (1965-1975) 4.3 1975 951.45 (1970-1975) 1.7 T a b l e 2.1. P r o d u c t i o n o f s y n t h e t i c a c e t i c a c i d i n t h e US ( 3 ) . S i g n i f i c a n t end u s e s o f a c e t i c a c i d i n t h e USA a r e l i s t e d i n f i g . 2 . 1 . ( 4 ) . N e a r l y a l l t h e v i n y l a c e t a t e monomer i s used i n t h e m a n u f a c t u r e o f p o l y v i n y l a c e t a t e and c o p o l y m e r s . A l a r g e amount o f t h e p o l y v i n y l a c e t a t e i s c o n v e r t e d t o p o l y v i n y l a l c o h o l and i t s a c e t y l a t e d d e r i v a t i v e , p o l y v i n y l b u t y r a l . A c o n t i n u e d growth i n v i n y l a c e t a t e demand i s e x p e c t e d . On t h e o t h e r hand,
though c e l l u l o s e a c e t a t e i s s t i l l an i m p o r t a n t t h e r m o p l a s t i c and f i b e r c o n s t i t u e n t , i t s growth has now l e v e l e d o u t . The use o f a c e t i c a c i d as a s o l v e n t i n t h e TPA/DMT m a n u f a c t u r e i s r e l a t i v e l y s m a l l b u t r a p i d l y
e x p a n d i n g (4).The end u s e s o f a c e t i c a c i d can v a r y from c o u n t r y t o c o u n t r y .
In J a p a n , f o r i n s t a n c e , a l a r g e p e r c e n t a g e ( 19?o ) i s used i n t h e f e r m e n t a -t i o n i n d u s -t r y , where i -t i s m i c r o b i o l o g i c a l l y -t r a n s f o r m e d i n -t o a number o f amino a c i d s ( 3 ) . However, s y n t h e t i c a c i d may not be used f o r f o o d s t u f f s i n
market s h a r e 40 v i n y l a c e t a t e p o l y v i n y l a c e t a t e p o l y v i n y l a l c o h o l s p o l y v i n y l b u t y r a l p o l y v i n y l c h l o r i d e -a c e t -a t e r e s i n s a d h e s i v e s , p a i n t s a d h e s i v e s , f i l m s s a f e t y g l a s s s u r f a c e c o a t i n g s s a f e t y g l a s s 23 % c e l l u l o s e a c e t a t e f i b e r s , c i g a r e t f i l t e r s 10 % 12 % 9.5 2.5 % TPA / DMT b u t y l a c e t a t e i s o p r o p y l a c e t a t e a c e t a n i l i d e a c e t i c a n h y d r i d e a c e t y l c h l o r i d e ammonium a c e t a t e c h l o r o a c e t i c a c i d p o l y e t h y l e n e t e r e p h -t a l a -t e a c e t o a c e t i c e s t e r s a c e t y l s a l i c y l i c a c i d a c e t a m i d e 2,4-D and 2,4,5-T a c i d s sodium c a r b o x y -m e t h y l c e l l u l o s e e t h y l c h l o r o - a c e t a t e g l y c i n e s a r c o s i n e t h i o g l y c o l i c a c i d f i b e r s , f i l m s s o l v e n t s f o r perfumes f l a v o r i n g e x t r a c t p h a r m a c e u t i c a l s d y e s t u f f s dye i n t e r m e d i a t e a s p e r i n d y e s t u f f s p l a s t i c i z e r h e r b i c i d e s d e t e r g e n t promoter e m u l s i o n s t a b i l i z e r l a t e x p a i n t s o l v e n t food a d d i t i v e d e t e r g e n t s permanent wave s o l u -t i o n , v i n y l s -t a b i l i z e r t e x t i l e p r o c e s s i n g F i g . 2.1. End u s e s o f a c e t i c a c i d i n t h e US ( 4 ) .
•j
the USA. V i n £ g a r , a 4 ?o s o l u t i o n o f a c e t i c a c i d i n w a t e r , i s produced by the a n c i e n t method o f e t h a n o l f e r m e n t a t i o n . On a g l a c i a l a c e t i c a c i d b a s i s
t h e p r o d u c t i o n i n t h e USA i n 1973 was 36 m i l l i o n k g . ( 1 ) .
The h i g h c o s t o f t h e e t h a n o l f e e d s t o c k , c o u p l e d w i t h t h e problems a s s o c i a t e d w i t h t h e massive q u a n t i t i e s o f water t o be h a n d l e d , makes i t i m p r a c t i c a l f o r l a r g e s c a l e g l a c i a l a c e t i c a c i d m a n u f a c t u r e . S i n c e v i r t u a l l y a l l t h e
s y n t h e t i c a c e t i c a c i d produced c o m m e r c i a l l y i s made by a c e t a l d e h y d e o x i d a t i o n , l i q u i d phase o x i d a t i o n (LPO) o f s a t u r a t e d h y d r o c a r b o n s o r
methanol c a r b o n y l a t i o n , t h e s e r o u t e s a r e b r i e f l y d i s c u s s e d h e r e .
2.1.2. A c e t a l d e h y d e o x i d a t i o n
About 35?o o f t h e US a c e t i c a c i d c a p a c i t y i s based on t h e l i q u i d phase o x i d a t i o n o f a c e t a l d e h y d e . Most o f t h e a c e t a l d e h y d e i s used f o r a c e t i c a c i d m a n u f a c t u r e . Hence, t h e a c e t a l d e h y d e p r o d u c t i o n can be c o n s i d e r e d as t h e f i r s t phase o f a t w o - s t e p p r o c e s s f o r making a c e t i c a c i d . The two main r o u t e s to a c e t a l d e h y d e a r e : 1) t h e l i q u i d phase o x i d a t i o n o f e t h y l e n e , which a c c o u n -ted f o r about two t h i r d s o f t h e w o r l d a c e t a l d e h y d e p r o d u c t i o n i n 1973 ( 1 ) , and 2) t h e vapour phase o x i d a t i o n o f e t h a n o l , which a c c o u n t e d f o r one t h i r d o f t h e w o r l d p r o d u c t i o n i n 1973, but i s r a p i d l y d i m i n i s h i n g i n i m p o r t a n c e . The p r o c e s s f o r t h e p r o d u c t i o n o f a c e t a l d e h y d e from e t h y l e n e was d e v e l o p e d by Wacker Chemie ( twostage p r o c e s s ) and Farbwerke Hoechst A.G. ( s i n g l e -s t a g e ). The f i r -s t c o m m e r c i a l p l a n t -s ba-sed on t h e Wacker p r o c e -s -s , a-s i t i -s commonly c a l l e d , were b u i l t i n Europe i n 1960 ( 5 ) . The p r o c e s s i s based on the f o l l o w i n g r e a c t i o n s : C2H4 + P d C l2 + H20 — CH3CH0 + Pd + 2 HC1 p r o d u c t f o r m a t i o n Pd + 2 C u C l2 — P d C l2 + 2 CuCl Pd o x i d a t i o n 2 C u C l + 2 HCL + \ 02 —*- 2 C u C l2 + H20 C u C l o x i d a t i o n C2H ^ + k 02 — - CH3CH0 o v e r a l l r e a c t i o n With an e x c e s s o f c u p r i c c h l o r i d e p r e s e n t no m e t a l l i c p a l l a d i u m w i l l p r e c i p i -t a -t e ; -then PdCl„ a c -t s as -t h e c a -t a l y s -t . The r e a c -t i o n p r o c e e d s -t h r o u g h a
2-n - complex o f e t h y l e 2-n e w i t h a P d C l ^ i o 2-n . The mai2-n r o l e o f t h e c u p r i c c h l o r i d e i s t o a c c e l e r a t e t h e r a t e o f r e o x i d a t i o n o f e l e m e n t a r y p a l l a d i u m ,
because o x i d a t i o n o f the m e t a l w i t h oxygen i s v e r y s l o w .
The p r o c e s s , c a n be c a r r i e d out i n e i t h e r one or two s t a g e s . The s i n g l e - s t a g e p r o c e s s i s c o n d u c t e d a t 130 °C and 300 kPa; the t w o s t a g e p r o c e s s a t 125 -130 °C and 1 MPa. In the t w o - s t a g e p r o c e s s the a c e t a l d e h y d e produced i n the f i r s t s t a g e i s removed by a d i a b a t i c f l a s h i n g i n a t o w e r . The c a t a l y s t s o l u
-t i o n i s r e c y c l e d from -the f l a s h -tower base -t o -t h e f i r s -t r e a c -t o r v i a -t h e second r e a c t o r where t h e c u p r o u s s a l t i s o x i d i z e d t o t h e c u p r i c s t a t e by a i r .
Both p r o c e s s e s g i v e about 95% y i e l d o f a c e t a l d e h y d e on e t h y l e n e .
Major b y - p r o d u c t s a r e mono-, d i - and t r i - c h l o r i n a t e d a c e t a l d e h y d e s , c a r b o n d i o x i d e , c r o t o n a l d e h y d e and m e t h y l - and e t h y l c h l o r i d e . B y - p r o d u c t r e c o v e r y i s u n e c o n o m i c a l , a l t h o u g h m o n o c h l o r o - a c e t a l d e h y d e r e c o v e r y might be an e x c e p t i o n i n t h e two-stage p r o c e s s ( 5 ) . A c e t a l d e h y d e frorn ethar_K3l i s p r e p a r e d i n d u s t r i a l l y by o x i d a t i o n . T h i s o x i d a -t i o n p r o c e e d s as a h i g h l y e x o -t h e r m i c r e a c -t i o n be-tween a i r and v a p o r i z e d e t h a n o l o f h i g h p u r i t y a t 500 - 550 °C and 100 - 200 kPa o v e r a s i l v e r c a t a l y s t . 2 C2H50 H + 02 — 2 CH3CH0 + 2 H20
C o n v e r s i o n per pass t h r o u g h the r e a c t o r i s about 70% and f i n a l p r o d u c t y i e l d 95?o. B y - p r o d u c t s a r e methane, c a r b o n monoxide and f o r m i c a c i d .
The h i g h c o s t o f t h e e t h a n o l f e e d s t o c k makes t h i s r o u t e f o r p r o d u c i n g a c e t i c
a c i d e c o n o m i c a l l y a t t r a c t i v e o n l y i n c o u n t r i e s where t h e r e i s a s u r p l u s o f e t h a n o l . Much r e s e a r c h has gone i n t o t h e development o f p r o c e s s e s f o r making e t h a n o l from v a r i o u s a g r i c u l t u r a l or f o r e s t waste m a t e r i a l s . T e c h n i c a l l y a c c e p t a b l e r o u t e s have been worked out but t h e h i g h c a p i t a l i n v e s t m e n t f o r a
low c a p a c i t y p l a n t have made t h e s e r o u t e s n o n - c o m p e t i t i v e u n l e s s the s a l e o f v a r i o u s b y - p r o d u c t s j u s t i f y t h e h i g h c o s t s .
The l i q u i d - p h a s e o x i d a t i o n o f a c e t a l d e h y d e w i t h oxygen and manganese a c e t a t e
as t h e c a t a l y s t i s h e l d t o be a c h a i n r e a c t i o n i n w h i c h the i n t e r m e d i a t e p e r a c e t i c a c i d r e a c t s w i t h a c e t a l d e h y d e t o produce a c e t i c a c i d v i a a c e t a l d e -hyde monoperacetate (AMP) o r a complex o f AMP and c a t a l y s t ( 6 ) .
CH CH0 + 02 —*- CHjCOOOH
CH3C000H + CH3CH0 ^ AMP c a t a l y s t
AMP 2 CH3C00H
7 C o n v e n t i a l o x i d a t i o n p r o c e s s e s i n v o l v e a i r o x i d a t i o n o f a s o l u t i o n o f 5 - 15 55 a c e t a l d e h y d e i n a c e t i c a c i d c o n t a i n i n g d i s s o l v e d manganese a c e t a t e a t 50 - 80 °C and 100 - 1000 k P a . P r o c e s s y i e l d on a c e t a l d e h y d e i s t y p i c a l l y 95?^. C h i e f b y - p r o d u c t s a r e formaldehyde and f o r m i c a c i d ( 3 ) . 2.1.3. L i q u i d phase o x i d a t i o n o f s a t u r a t e d h y d r o c a r b o n s . S e v e r a l f e e d s t o c k s may be used a l t h o u g h t h e b e s t y i e l d o f a c e t i c a c i d i s o b t a i n e d w i t h n-butane. The p r o c e s s u t i l i z i n g n-butane was c o m m e r c i a l i z e d by C e l a n e s e C h e m i c a l Co. i n 1952, and i n 1973 butane o x i d a t i o n a c c o u n t e d f o r about 40K o f t h e US p r o d u c t i o n c a p a c i t y o f a c e t i c a c i d ( 4 ) .
In Europe, N a t i o n a l D i s t i l l e r s ( now BP C h e m i c a l s L t d . ) has c o m m e r c i a l i z e d a p r o c e s s u s i n g naphtha as t h e raw m a t e r i a l . I t s o x i d a t i o n can be e f f e c t e d a t l o w e r t e m p e r a t u r e s and p r e s s u r e s . The p r o d u c t c o m p o s i t i o n from n a p h t h a , however, i s f a r more complex and t h e s e p a r a t i o n o f a c e t i c a c i d i s more
e x p e n s i v e . The c h e m i s t r y o f t h e l i q u i d phase o x i d a t i o n o f n-butane a t h i g h e r t e m p e r a t u r e s i s v e r y complex ( 7 , 8 ) . Rll R-R 1 . C00' H
V
2 R-R00 2 R00 2 RCH2 00-+ X + o2 + RH R-R0, R R 2 R-R R00R R00R HX C00H H i n i t i a t i o n p r o p a g a t i o n RC 0 II RCH20H 0„ t e r m i n a t i o n The i n i t i a l s t e p i s t h e f o r m a t i o n o f a b u t y l r a d i c a l ( by l i g h t , heat o r i n i t i a t o r ), which r e a c t s w i t h oxygen t o a p e r o x y r a d i c a l . The p e r o x y r a d i c a l r e a c t s w i t h n-butane t o g i v e a new b u t y l r a d i c a l and h y d r o p e r o x i d e .M a i n l y t h e secondary b u t y l r a d i c a l i s formed w h i c h , a f t e r s c i s s i o n i n a
h y d r o x y l r a d i c a l and an a l k o x y r a d i c a l , can r e a c t t o a c e t a l d e h y d e ( s c i s s i o n ) , 2 - b u t a n o l ( hydrogen a d d i t i o n ) and m e t h y l e t h y l ketone ( r e a c t i o n w i t h r a d i c a l ). These p r i m a r y p r o d u c t s can be o x i d i z e d t o a c e t i c a c i d . B e s i d e s a - s c i s s i o n t o a c e t a l d e h y d e a l s o ƒ} - s c i s s i o n o c c u r s which
g i v e s p r o d u c t s such as m e t h a n o l , e t h a n o l , p r o p i o n i c a c i d and a c e t o n e .
F o r m a t i o n o f p r i m a r y b u t y l r a d i c a l s g i v e s r i s e t o p r o d u c t s l i k e f o r m i c a c i d , p r o p i o n i c a c i d and b u t y r i c a c i d .
K e e p i n g i n mind t h a t any r a d i c a l can r e a c t w i t h most components o f the
r e a c t i o n m i x t u r e and t h a t a l c o h o l s can g i v e e s t e r s w i t h a c i d s , i t w i l l be c l e a r t h a t t h e r e a r e many b y - p r o d u c t s . D e s p i t e t h i s f a c t t h e p r o c e s s i n i t s e l f i s a f l e x i b l e one; by c h a n g i n g o p e r a t i n g c o n d i t i o n s i t i s e i t h e r p o s s i b l e t o m a n u f a c t u r e o n l y a c e t i c a c i d ( y i e l d about 57?o ) w i t h some
n o n - r e c o v e r a b l e b y - p r o d u c t s , or t o produce a c e t i c a c i d w i t h r e c o v e r e d b y - p r o d u c t s e.g. a c e t a l d e h y d e , a c e t o n e , m e t h a n o l , m e t h y l e t h y l k e t o n e , e t h y l a c e t a t e .
Normal o p e r a t i n g c o n d i t i o n s a r e 150 - 225 C and 3 - 8 MPa.
The o x i d a t i o n i s c a r r i e d out w i t h o u t a c a t a l y s t ( Chemische Werke H u l s (9) )
or w i t h c o b a l t a c e t a t e as a c a t a l y s t ( C e l a n e s e Corp. / Akzo Zout Chemie ). W i t h manganese as a c a t a l y s t more f o r m i c a c i d i s formed ( 1 0 ) .
2.1.4. M e t h a n o l c a r b o n y l a t i o n
Two t e c h n o l o g i e s based on methanol c a r b o n y l a t i o n have been c o m m e r c i a l i z e d . A c e t i c a c i d l i q u i d phase s y n t h e s i s from methanol and c a r b o n monoxide u s i n g cobaltouB i o d i d e as a c a t a l y s t was d e v e l o p e d by BASF. The f i r s t p l a n t s came i n t o o p e r a t i o n i n Europe i n 1960 and i n the USA i n 1966.
The BASF r e a c t i o n system o p e r a t e s a t 210 - 250 °C and 50 - 70 MPa.
In 1968 P a u l i k & Roth (11) r e p o r t e d the d i s c o v e r y o f a new i o d i d e - p r o m o t e d rhodium c a t a l y s t o f such h i g h a c t i v i t y t h a t methanol c a r b o n y l a t i o n c o u l d t a k e p l a c e a t a t m o s p h e r i c p r e s s u r e . Monsanto d e v e l o p e d the p r o c e s s and c o m m e r c i a l i z e d i t i n 1970. In 1973 15?o o f the US a c e t i c a c i d c a p a c i t y was
based on methanol c a r b o n y l a t i o n .
E f f e c t upon r e a c t i o n r a t e
R e a c t i o n v a r i a b l e C o b a l t c a t a l y s t system Rhodium c a t a l y s t system
F i r s t o r d e r Zero o r d e r
pCO Second o r d e r Zero o r d e r
I F i r s t o r d e r F i r s t o r d e r
Co or Rh V a r i a b l e F i r s t o r d e r
9
The c h e m i s t r y o f t h e BASF and Monsanto p r o c e s s e s i s p r o b a b l y v e r y s i m i l a r
but d i f f e r e n t r e a c t i o n k i n e t i c s have been o b s e r v e d i n d i c a t i n g d i f f e r e n t r a t e d e t e r m i n i n g s t e p s ( see t a b l e 2.2 ), which i n t u r n c o u l d i m p l y c o m p l e t e
l y d i f f e r e n t mechanisms ( 1 2 ) . The s i g n i f i c a n t d i f f e r e n c e i s t h a t t h e c o b a l t -c a t a l y z e d r e a -c t i o n i s s t r o n g l y dependent on b o t h -c a r b o n monoxide p r e s s u r e
and methanol c o n c e n t r a t i o n whereas t h e r h o d i u m - c a t a l y z e d r e a c t i o n i s n o t . The i m p o r t a n t c o m m e r c i a l i m p l i c a t i o n i s t h e h i g h e r methanol c o n v e r s i o n i n the rhodium system.The p o s t u l a t e d r e a c t i o n mechanism f o r t h e r h o d i u m c a t a l y -zed r e a c t i o n i s as f o l l o w s : 1. CH3OH + HI C H3I + H20 ^Rh c o m p l e x j 2. C H3I + |Rh c o m p l e x s l o w CH. Rh c o m p l e x I + CO CH, I J Rh complex.CO I I CH, I J C=0 I Rh c o m p l e x CH, I 3 Rh c o m p l e x I I CH, I 3 Rh complex.CO I I CH, I J C=0 I Rh c o m p l e x H20 CH3COH + j^Rh c o m p l e x j + HI M e t h a n o l i s r a p i d l y c o n v e r t e d t o m e t h y l i o d i d e w h i c h r e a c t s w i t h t h e rhodium ( I ) complex t h r o u g h o x i d a t i v e a d d i t i o n t o produce a s i x - c o o r d i n a t e a l k y l - r h o d i u m ( I I I ) s p e c i e s . R a p i d i n s e r t i o n o f c a r b o n monoxide i n t o t h e r h o d i u m - a l k y l bond o c c u r s t o y i e l d an a c y l - r h o d i u m ( I I I ) complex. F i n a l l y t h e r e a c t i o n i s c o m p l e t e d by r e a c t i o n o f t h e a c y l
rhodium ( I ) complex. The mechanism o f t h i s r e a c t i o n i s s t i l l b e i n g i n v e s t i -g a t e d (12,13,14,15). The same t y p e o f rhodium complexes a r e used f o r the h y d r o f o r m y l a t i o n o f o l e f i n s t o a l d e h y d e s ( 1 6 ) .
The Monsanto p r o c e s s o p e r a t e s a t 150 - 200 °C and p r e s s u r e s up t o 6.6 MPa. Y i e l d o f a c e t i c a c i d i s 99?o on methanol and 90% on c a r b o n monoxide ( 1 1 ) . P r o c e s s y i e l d f o r t h e BASF p r o c e s s i s l o w e r , v i z . 85?» on methanol and 59?o
on c a r b o n monoxide ( 1 7 ) .
The low a c e t i c a c i d y i e l d on CO m a i n l y r e f l e c t s the low c o n v e r s i o n o f t h i s raw m a t e r i a l (65%). B y - p r o d u c t f o r m a t i o n i n the Monsanto p r o c e s s i s much l o w e r which a c c o u n t s f o r the h i g h e r m e t h a n o l s e l e c t i v i t y t o a c e t i c a c i d .
In b o t h p r o c e s s e s the main b y - p r o d u c t i s c a r b o n d i o x i d e produced by the water gas s h i f t r e a c t i o n ( methanol i s u s u a l l y d i l u t e d w i t h water t o s u p p r e s s m e t h y l a c e t a t e f o r m a t i o n ). Other p r o d u c t s o f the BASF p r o c e s s a r e methane, f o r m i c a c i d , e t h a n o l , p r o p i o n i c a c i d , p r o p i o n a l d e h y d e , b u t y r a l d e h y d e and
b u t a n o l , w i t h p r o p i o n i c a c i d making up about 50% o f t h e t o t a l l i q u i d by-p r o d u c t .
One o f t h e major problems i n methanol c a r b o n y l a t i o n i s t h e d i f f i c u l t s e p a r a -t i o n o f o r g a n i c i o d i d e and a c e -t i c a c i d . Much r e s e a r c h i s f o c u s e d on -t h i s p o i n t ( 1 8 , 1 9 ) .
2.1.5. P o t e n t i a l r o u t e s
R e s e a r c h and development on new a c e t i c a c i d p r o c e s s e s i s s i g n i f i c a n t . E f f o r t s have been f o c u s e d on:
1) u s i n g o t h e r f e e d s t o c k s f o r a c e t i c a c i d p r o d u c t i o n , e.g. n-butene and p r o p y l e n e o x i d a t i o n i n the l i q u i d and vapour phase.
2) making heterogeneous v a r i a t i o n s on e x i s t i n g homogeneously c a t a l y z e d l i q u i d phase p r o c e s s e s , e.g. the e t h y l e n e vapour phase o x i d a t i o n t o a c e t a l d e h y d e , t h e vapour phase o x i d a t i o n o f s a t u r a t e d h y d r o c a r b o n s and t h e vapour phase methanol c a r b o n y l a t i o n .
3) e l i m i n a t i n g a p r o c e s s s t e p , e.g. t h e d i r e c t o x i d a t i o n o f e t h y l e n e t o
a c e t i c a c i d i n t h e vapour phase and d i r e c t p r o d u c t i o n o f a c e t i c a c i d from s y n t h e s i s g a s .
Only the n-butene r o u t e has been r e p o r t e d t o be f u l l y p i l o t e d by Chemische Werke H u l s (20) and by Bayer ( 2 1 ) . The m o t i v e f o r u s i n g nbutene as a f e e d
-s t o c k f o r a c e t i c a c i d p r o d u c t i o n i -s t h e p o t e n t i a l growth i n the a v a i l a b i l i t y o f n-butene as one o f the p r o d u c t s o f naphtha c r a c k i n g .
11
a t 180 - 245 °C and 1.5 - 3 MPa over a t i t a n i u m / v a n a d i u m o x i d e c a t a l y s t . A c e t i c a c i d y i e l d i s r e p o r t e d t o be l o w , v i z . 46?¿ ( 2 2 ) , a l t h o u g h i n more r e c e n t p a t e n t l i t e r a t u r e h i g h e r y i e l d s have been mentioned ( 2 3 , 2 4 ) .
C o p r o d u c t s a r e m a i n l y f o r m i c a c i d and m a l e i c a c i d .
The Bayer p r o c e s s i s a two-step l i q u i d phase r e a c t i o n i n which t h e n-butenes
a r e c o n v e r t e d w i t h a c e t i c a c i d i n t o s e c - b u t y l a c e t a t e and then o x i d i z e d . The f i r s t s t e p i s c a r r i e d o u t a t 100 - 120 °C and 1500 - 2500 kPa i n t h e p r e s e n c e o f a c i d - r e a c t i n g s i l i c a t e s o r i o n exchange r e s i n s . The second s t e p t a k e s p l a c e a t 180 - 220 °C and 4 - 7 MPa. A c e t i c a c i d y i e l d i s 58%. The e x p e c t e d s h o r t a g e o f s u p p l y o f £ropylene_ has made 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 e t i c a c i d ( now ) o f academic i n t e r e s t o n l y . V a n a d i u m / t i n / t u n g s t e n o x i d e (25) o r molybdenum o x i d e (26) a r e f a v o u r e d as c a t a l y s t s . A c e t a l d e h y d e i s known t o be a p r i m a r y p r o d u c t o f c a t a l y t i c va£our_ph_as_e £xidation £f_et.h^lene o v e r p a l l a d i u m ( 2 7 ) . P a l l a d i u m c h l o r i d e on a c t i v e c o a l has been r e p o r t e d (28) t o g i v e a c e t a l d e h y d e a t v e r y h i g h e f f i c i e n c y ( > 90% ) i n t h e vapour phase o x i d a t i o n o f e t h y l e n e .
For a r e v i e w o f vapour phase o x i d a t i o n o f h y d r o c a r b o n s up t o 1972 see
H u c k n a l l ( 2 9 ) .
Vanadium t e t r o x i d e i s p r e f e r r e d t o t h e o t h e r o x i d e s o f vanadium as a c a t a l y s t f o r t h e vapourjh_as_e_o>^id_atio_n_o_f s_aturat_ed_ h y d r o c a r b o n s .
O x i d e s o f phosphorus and o f molybdenum improve t h e y i e l d ( 3 0 ) . Y i e l d i s comparable w i t h t h e l i g u i d phase o x i d a t i o n ( 50 - 60 % ). M a l e i c a c i d i s a major b y - p r o d u c t .
The va£Ourj3h_as_e_ca_rbjanyl^a£io_n_of_ me_tha_np_l_over a s u p p o r t e d l i q u i d phase
c a t a l y s t ( rhodium complex p l u s i o d i d e promotor on c a r b o n ) e x h i b i t s t h e same k i n e t i c s as t h e homogeneous a n a l o g ( 1 4 ) . I f t h e c a t a l y s t i s s t a b l e t h i s may become an i m p o r t a n t r o u t e t o a c e t i c a c i d i n t h e f u t u r e . Among t h e many c o m b i n a t i o n s o f n o b l e m e t a l / t r a n s i t i o n m e t a l o x i d e s t e s t e d a p a l l a d i u m / v a n a d i u m p e n t o x i d e c a t a l y s t gave t h e b e s t r e s u l t s f o r t h e d i r e c t _ o x i d a t i o n o f e t h y l e n e t o a c e t i c a c i d . A c e t i c a c i d y i e l d i s low ( 10- 25 % ) but a c e t i c a c i d p l u s a l d e h y d e y i e l d i s h i g h ( 60 - 90 % ) (31,32,33). Directj£oduc_tion_ 2/_a£etic a c i d _ f r o m s y n t h e s i s ^ gas has been a c c o m p l i s h e d by
B h a s i n (34) o v e r a r h o d i u m - s i l i c a g e l c a t a l y s t a t 250 °C and h i g h p r e s s u r e s . T h i s c a t a l y s t has a r e l a t i v e l y h i g h a c e t i c a c i d p r o d u c t i o n and c o m p a r a t i v e l y minor amounts o f e t h a n o l , a c e t a l d e h y d e and methane a r e formed.
The f o r m a t i o n o f m e t h y l f o r m a t e from s y n t h e s i s gas over p o t a s s i u m m e t h o x i d e
2.1.6. Economie c o n s i d e r a t i o n s
Based on p u b l i s h e d c o s t d a t a f o r p r o d u c i n g a c e t i c a c i d Lowry and A g u i l o (1) c a l c u l a t e d t h e t o t a l f i x e d c a p i t a l i n v e s t m e n t , t r a n s l a t e d i n t o a c e t i c a c i d p r o d u c t i o n c o s t i n 1973 f o r a 180 m i l l i o n kg p e r y e a r p l a n t , t o be between
$ 0.03 and $ 0.08 p e r kg a c e t i c a c i d p r o d u c e d .
The v a r i a b l e c o s t s which a r e s t r o n g l y raw m a t e r i a l and energy-dependent a r e p r o b a b l y g r e a t e r than $ 0.10 p e r kg a c e t i c a c i d p r o d u c e d ( i n 1 9 7 3 ) .
C o n s e q u e n t l y t h e economics o f a c e t i c a c i d t e c h n o l o g i e s depends p r i m a r i l y on raw m a t e r i a l e f f i c i e n c y as w e l l as on energy c o n s e r v a t i o n . O v e r a l l y i e l d o f
p r o d u c i n g a c e t i c a c i d from e t h y l e n e i s h i g h (90?í) so t h e r e i s l i t t l e room f o r improvement. P r o c e s s y i e l d s f o r t h e LP0 o f s a t u r a t e d h y d r o c a r b o n s i s l o w ; 50-57 % u s i n g n-butane and 40?í f o r n a p h t h a . T h i s d i s a d v a n t a g e has been o f f s e t by t h e r e c o v e r y and s a l e o f a v a r i e t y o f b y - p r o d u c t s . The Monsanto p r o c e s s
f o r methanol c a r b o n y l a t i o n has c l e a r a d v a n t a g e s o v e r t h e BASF p r o c e s s ; h i g h e r e f f i c i e n c y and l o w e r c a p i t a l i n v e s t m e n t due t o t h e m i l d e r r e a c t i o n c o n d i t i o n s . Any new v a r i a t i o n on t h e t h r e e c o m m e r c i a l i z e d r o u t e s must have the same o r h i g h e r e f f i c i e n c y , o r must o f f e r a v e r y s u b s t a n t i a l r e d u c t i o n i n
equipment c o s t s t o a c h i e v e a s i g n i f i c a n t a d v a n t a g e .
A l l t h e new r o u t e s based on e t h y l e n e , n-butane and methanol mentioned i n 2.1.5. have e f f i c i e n c i e s comparable w i t h t h e c o m m e r c i a l i z e d r o u t e s so t h e y are p o t e n t i a l c a n d i d a t e s f o r p r o d u c i n g a c e t i c a c i d i n t h e f u t u r e .
n-Butene b e i n g a b y - p r o d u c t o f naphtha c r a c k i n g t o produce e t h y l e n e , i t w i l l not become a major raw m a t e r i a l f o r p r o d u c i n g a c e t i c a c i d even i f t h e r o u t e v i a n-butene i s c o m m e r c i a l i z e d .
I t i s d i f f i c u l t t o p r e d i c t f u t u r e p r i c e developments f o r e t h y l e n e , n-butane
or m e t h a n o l . Monsanto a l r e a d y c l a i m s t h a t t h e i r p r o c e s s has t h e b e s t economics f o r p r o d u c i n g a c e t i c a c i d ( 3 6 ) . Rhône-Poulenc I n d u s t r i e s S.A. i s b u i l d i n g a 225 m i l l i o n k g / y e a r p l a n t i n F r a n c e based on t h e Monsanto p r o c e s s ( 3 7 ) . I t w i l l come on s t r e a m i n 1980.
Union C a r b i d e (38) and Akzo Zout Chemie (39) a n t i c i p a t e d t h a t t h e butane raw m a t e r i a l p o s i t i o n would be c o m p e t i t i v e enough: Union C a r b i d e expanded i t s
p l a n t by 90 m i l l i o n kg i n 1977 and Akzo by 50 m i l l i o n kg i n 1978.
I f o i l and n a t u r a l gas s u p p l i e s d i m i n i s h i n t h e f u t u r e i t i s p o s s i b l e t h a t i n d u s t r i a l c h e m i c a l s w i l l be i n c r e a s i n g l y based on c o a l . Then t h e methanol c a r b o n y l a t i o n r o u t e t o a c e t i c a c i d o r p o s s i b l y t h e d i r e c t s y n t h e s i s o f a c e t i c
13
2.2. REMOVAL OF FORMIC ACID
2.2.1. INTRODUCTION
W i t h t h e e x c e p t i o n o f t h e Monsanto c a r b o n y l a t i o n r o u t e many b y - p r o d u c t s are formed i n t h e v a r i o u s a c e t i c a c i d p r o c e s s e s . T h e r e f o r e l a r g e p u r i f i c a t i o n s e c t i o n s a r e n e c e s s a r y . High and l o w b o i l i n g s u b s t a n c e s can be d i s -t i l l e d o f f e a s i l y b u -t -t h e s e p a r a -t i o n o f f o r m i c a c i d from a c e -t i c a c i d and
w a t e r i s d i f f i c u l t because t h e m i x t u r e has a t e r n a r y s a d d l e p o i n t a z e o t r o p e . In some p r o c e s s e s , e.g. t h e H u l s p r o c e s s f o r vapour phase o x i d a t i o n o f n-butene and i n naphtha o x i d a t i o n , t h e f o r m i c a c i d i s r e c o v e r e d as a by-p r o d u c t , b u t i n most o t h e r by-p r o c e s s e s f o r m i c a c i d i s by-p r e s e n t i n r e l a t i v i t y
s m a l l c o n c e n t r a t i o n s and i s n o t r e c o v e r e d . A t y p i c a l m i x t u r e o b t a i n e d i n n-butane LPO a f t e r removal o f e s t e r s and e t h e r s i s p r e s e n t e d i n t a b l e : 2.3.
Weight p e r c e n t Mole p e r c e n t
Water 33 61 7
F o r m i c a c i d 5 3 6
A c e t i c a c i d 61 34 2
Heavy ends 1 0 5
t a b l e 2.3 Crude a c i d c o m p o s i t i o n ( n-butane LPO )
N o n - d e s t r u c t i v e as w e l l as d e s t r u c t i v e removal can be a p p l i e d i n t h i s c a s e . Commercial methods t o remove f o r m i c a c i d from a c e t i c a c i d a r e :
1) a z e o t r o p i c d i s t i l l a t i o n
2) c a t a l y t i c d e c o m p o s i t i o n
3) e s t e r i f i c a t i o n w i t h subseguent d i s t i l l a t i o n
As i t i s n e c e s s a r y n o t o n l y t o remove t h e f o r m i c a c i d b u t a l s o t o d e h y d r a t e the a c e t i c a c i d a c o m b i n a t i o n o f t h e two p u r i f i c a t i o n s i s o f t e n u s e d . Permanganate, c h r o m i c compounds ( CrO^, K^Cr^O-^ ) , s u l p h u r i c a c i d , phos-p h o r i c a c i d o r a c o m b i n a t i o n o f t h e s e c h e m i c a l s a r e u s u a l l y s u phos-p phos-p l i e d i n t h e
f i n i s h i n g column t o remove c o n t a m i n a n t s i n c l u d i n g t r a c e s o f f o r m i c a c i d l e f t i n t h e p r o d u c t a f t e r a p p l i c a t i o n o f one o f t h e above mentioned methods t o remove l a r g e r c o n c e n t r a t i o n s o f f o r m i c a c i d .
2.2.2. A z e o t r o p i c d i s t i l l a t i o n
Tx diagrams f o r f o r m i c a c i d a c e t i c a c i d , f o r m i c a c i d w a t e r and a c e t i c a c i d -water a t 101.3 kPa a r e g i v e n i n f i g . 2.2,2.3 and 2.4 ( 4 0 ) . F o r m i c a c i d and a c e t i c a c i d do n o t form an a z e o t r o p e b u t t h e vapour and l i q u i d l i n e s a r e v e r y c l o s e so s e p a r a t i o n i s p o s s i b l e b u t t e d i o u s ( 4 1 , 4 2 , 4 3 ) . A c e t i c a c i d and water a l s o form no a z e o t r o p e . F o r v a p o u r - l i q u i d e q u i l i b r i u m d a t a see
S e b a s t i a n i & L a c q u a n i t i (44) who a l s o r e v i e w e d t h e a v a i l a b l e l i t e r a t u r e d a t a up t o 1967. 120 116 100 20 4 0 6 0 8 0 100 • Weight%> formic acid
F i g . 2.2 T-x diagram f o r
15
The f o r m i c a c i d - w a t e r system has a maximum b o i l i n g a z e o t r o p e a t 107.6 C. The a z e o t r o p i c m i x t u r e c o n t a i n s 57.6 mole % f o r m i c a c i d . (43,45,46,47,48). The main cause o f the n o n - i d e a l i t y o f the system i s the f o r m a t i o n o f low o r d e r m o l e c u l a r c l u s t e r s ( dimers or t r i m e r s ) i n t h e l i q u i d as w e l l as i n
t h e vapour phase. For t h e a s s o c i a t i o n i n t h e gas phase see appendix 4. The v a p o u r - l i q u i d e q u i l i b r i u m o f the t e r n a r y system has been measured by A r i s t o v i c h e t a l . (42) and W i s n i a k & Tamir ( 4 9 ) . There i s a d i f f e r e n c e between the two r e p o r t e d a z e o t r o p i c c o m p o s i t i o n s . S i n c e the a c c u r a c y o f the
a n a l y s i s i s b e t t e r f o r the d a t a o f W i s n i a k & Tamir t h e i r r e s u l t s a r e g i v e n h e r e : 36.3 mole % I^O, 46.9 mole % f o r m i c a c i d and 16.8 mole % a c e t i c a c i d . The b o i l i n g p o i n t o f the t e r n a r y s a d d l e p o i n t a z e o t r o p e i s 107.0 °C; see f i g . 2.5. F i g . 2.5 I s o t h e r m a l s a t 101.3 kPa f o r t h e w a t e r - f o r m i c a c i d - a c e t i c a c i d system ( 4 9 ) . B = b i n a r y a z e o t r o p e T - t e r n a r y a z e o t r o p e
The a z e o t r o p e makes i t i m p o s s i b l e t o s e p a r a t e the m i x t u r e i n t o t h e t h r e e pure components by d i r e c t d i s t i l l a t i o n ; t h e r e f o r e a z e o t r o p i c d i s t i l l a t i o n i s used i n which an added e n t r a i n e r forms an a z e o t r o p e w i t h one component w i t h
a lower b o i l i n g p o i n t than any o t h e r o f the components i n t h e m i x t u r e . The b o i l i n g p o i n t s o f water (100°C) and f o r m i c a c i d (10U.6°C) b e i n g very c l o s e , t h e r e a r e two ways t o s e p a r a t e the t e r n a r y m i x t u r e by a z e o t r o p i c d i s t i l l a t i o n : 1) removal o f f o r m i c a c i d by a z e o t r o p i c d i s t i l l a t i o n w i t h subsequent d i r e c t d i s t i l l a t i o n o f a c e t i c a c i d and w a t e r , 2) removal o f w a t e r
by a z e o t r o p i c d i s t i l l a t i o n w i t h subsequent d i r e c t d i s t i l l a t i o n o f f o r m i c and a c e t i c a c i d .
E n t r a i n e r s f o r f o r m i c a c i d u s u a l l y form a b e t t e r a z e o t r o p e w i t h water ( 5 0 ) . T h i s means t h a t a f t e r the s e p a r a t i o n o f w a t e r , t o g e t h e r w i t h f o r m i c a c i d , the m i x t u r e has t o be s e p a r a t e d i n t o i t s pure components (N.B. f o r m i c a c i d
forms a maximum b o i l i n g a z e o t r o p e w i t h w a t e r ) . T h e r e f o r e the n o r m a l , more s e l e c t i v e , p r o c e d u r e i s t o d e h y d r a t e the c r u d e a c i d s f i r s t and then t o s e p a r a t e the a c i d s .
Requirements f o r a good e n t r a i n e r f o r d e h y d r a t i o n a r e : 1) a z e o t r o p e f o r m a t i o n w i t h w a t e r .
2) b o i l i n g p o i n t o f the a z e o t r o p e must be s u f f i c i e n t l y lower than the
b o i l i n g p o i n t o f f o r m i c a c i d .
3) no f o r m a t i o n o f a z e o t r o p e w i t h f o r m i c a c i d and a c e t i c a c i d . 4) no r e a c t i o n w i t h f o r m i c o r a c e t i c a c i d .
5) low s o l u b i l i t y i n w a t e r .
At f i r s t benzene was used as an e n t r a i n e r but i t has t h e d i s a d v a n t a g e t h a t i t a l s o formes an a z e o t r o p e w i t h a c e t i c a c i d and w i t h f o r m i c a c i d , t h e l a t t e r w i t h a b o i l i n g p o i n t (71.05 °C) very c l o s e t o the benzene-water a z e o t r o p e
(69.25 C) ( 5 1 ) . The recommended 1,2 d i c h l o r o - e t h a n e e x i h i b i t s a l m o s t t h e same b e h a v i o u r ( a z e o t r o p e f o r m a t i o n w i t h f o r m i c a c i d ).
A c c o r d i n g t o Hunsmann & Simmrock (51) who s t u d i e d many e t h e r s as e n t r a i n e r s the b e s t one f o r t h i s system i s e t h y l n - b u t y l e t h e r ( B.P. a z e o t r o p e : 76.0°C,
w a t e r c o n t e n t : 10.6 w e i g h t % ).
Other commonly used e n t r a i n e r s f o r the d e h y d r a t i o n a r e e t h y l a c e t a t e ,
n - p r o p y l a c e t a t e and n - b u t y l a c e t a t e . High b o i l i n g e n t r a i n e r s l i k e the l a t t e r two u s u a l l y g i v e a z e o t r o p e s w i t h l a r g e w a t e r c o n t e n t s but they a l s o g i v e r i s e to p r o c e s s c o n t r o l p r o b l e m s . For i n s t a n c e , any e x c e s s o f e n t r a i n e r r e g u i r e d
f o r the a z e o t r o p e a p p e a r s i n t h e bottom. Moreover, any d e f i c i e n c y c r e a t e s a d i s p r o p o r t i o n a t e e f f e c t i n t h e e f f i c i e n c y o f s e p a r a t i o n because o f i t s r a p i d s t r i p p i n g from the l o w e r p a r t o f the column. Thus a t i g h t e n t r a i n e r c o n t r o l has t o be m a i n t a i n e d i n the column ( 5 2 , 5 3 ) .
17
The l o s s o f e n t r a i n e r may be m i n o r , e.g., i n p r o l o n g e d i n d u s t r i a l o p e r a t i o n s
o n l y 0.5-1.0 k g . o f n - b u t a n o l p e r t o n o f a c e t i c a c i d d e h y d r a t e d may have t o be added as make-up. T h i s i s e s t e r i f i e d t o n - b u t y l a c e t a t e i n t h e s y s t e m , and o n l y a v e r y s m a l l amount ends up i n t h e a c e t i c a c i d produced ( 5 4 ) .
As was mentioned b e f o r e , t h e D i s t i l l e r s Co. i n t h e U.K. ( now BP C h e m i c a l s
L t d ) uses naphtha as t h e raw m a t e r i a l f o r t h e l i q u i d phase o x i d a t i o n t o a c e t i c a c i d . F o r t h e removal o f w a t e r , t h e b u l k component, t h e y employ a c o m b i n a t i o n o f s o l v e n t e x t r a c t i o n and a z e o t r o p i c d i s t i l l a t i o n ( 5 5 , 5 6 ) . ( f i g . 2.6.) The f e e d o f wet a c i d s i s c o n t a c t e d c o u n t e r c u r r e n t l y w i t h a s o l
-v e n t t h a t e x t r a c t s t h e a c i d s , l e a -v i n g t h e b u l k o f water t o e x i t i n t h e r a f f i n a t e s t r e a m . The e x t r a c t , c o n t a i n i n g o n l y a s m a l l amount o f w a t e r , p a s s e s t o an a z e o t r o p i c d i s t i l l a t i o n column i n which t h e s o l v e n t now a c t s as an e n t r a i n e r f o r t h e w a t e r , w i t h which i t l e a v e s o v e r h e a d . The d r y a c i d s a r e
removed a t t h e bottom. The s o l v e n t and water l e a v e a t t h e t o p and a r e s e p a -r a t e d . The s o l v e n t l a y e -r i s s p l i t i n t o a -r e f l u x t o t h e d i s t i l l a t i o n column and a r e c y c l e t o t h e e x t r a c t o r . The aqueous l a y e r i s combined w i t h t h e r a f f i n a t e from t h e e x t r a c t i o n column and b o t h a r e p a s s e d t o a s t r i p p i n g column f o r r e c o v e r y o f t h e s m a l l amount o f d i s s o l v e d s o l v e n t . solvent r e c y c l e w e t acids • - d r y acids
(ST
w a t e r effluent F i g . 2.6 Combined s o l v e n t e x t r a c t i o n - a z e o t r o p i c d i s t i l l a t i o n p r o c e s s ( 5 5 ) . 1 - e x t r a c t i o n column. 2 - a z e o t r o p i c column, 3 - s t r i p p i n g column, 4 - s e p a r a t o r .There a r e more o p e r a t i o n s n e c e s s a r y i n t h i s p r o c e s s t h a n i n normal a z e o t r o p i c d i s t i l l a t i o n b u t t h e key t o t h i s p r o c e s s i s t h e l a r g e p r o p o r t i o n o f t h e w a t e r s e p a r a t e d i n t h e e x t r a c t i o n s t e p w i t h t h e e x p e n d i t u r e o f v i r t u a l l y no e n e r g y .
As a r e s u l t t h e a z e o t r o p i c column i s much s m a l l e r than i t o t h e r w i s e would be. A l r e a d y i n 1963 Brown (57) came t o t h e c o n c l u s i o n t h a t , f o r a 50 % s o l u t i o n o f a c i d s i n w a t e r , t h e combined method o f s o l v e n t e x t r a c t i o n and a z e o t r o p i c d i s t i l l a t i o n was more economic than a z e o t r o p i c d i s t i l l a t i o n a l o n e . R i c k e r
& K i n g (58) r e v i e w e d t h e use o f s o l v e n t e x t r a c t i o n f o r t r e a t m e n t o f waste-w a t e r s from a c e t i c a c i d m a n u f a c t u r e waste-where i t i s u n d o u b t e d l y more economic t h a n a z e o t r o p i c d i s t i l l a t i o n a l o n e , b u t w i t h r i s i n g energy c o s t s t h i s combi-n a t i o combi-n o f s o l v e combi-n t e x t r a c t i o combi-n w i t h a z e o t r o p i c d i s t i l l a t i o combi-n w i l l become more
and more c o m p e t i t i v e f o r p r o c e s s s t r e a m s w i t h r e l a t i v e l y low water c o n t e n t . As can be seen i n f i g . 2.2 t h e v o l a t i l i t y o f f o r m i c a c i d r e l a t i v e t o a c e t i c a c i d i s c l o s e t o u n i t y . In t h e whole c o n c e n t r a t i o n range A l p e r t & E l v i n g
(41) r e p o r t e d v a l u e s between 1.15 and 1.35 and C o n t i e t a l . (43) r e p o r t e d
v a l u e s between 1.27 and 1.52. T h i s makes t h e s e p a r a t i o n d i f f i c u l t and f o r t h a t r e a s o n a z e o t r o p i c d i s t i l l a t i o n i s a l s o a p p l i e d f o r t h e s e p a r a t i o n o f f o r m i c and a c e t i c a c i d ( i n t h i s c a s e i t i s n o t n e c e s s a r y b u t c o n v e n i e n t ). Water n o t s u f f i c i e n t l y removed i n t h e d e h y d r a t i o n s t a g e can i n f l u e n c e t h i s
a z e o t r o p i c d i s t i l l a t i o n i n a n e g a t i v e way and i s t h e r e f o r e removed by a d d i n g a c e t i c a n h y d r i d e . C o n t i e t a l . (43) recommended c h l o r o f o r m as e n t r a i n e r f o r t h i s s y s t e m . I t forms an a z e o t r o p e w i t h f o r m i c a c i d b u t n o t w i t h a c e t i c a c i d . The a z e o t r o p e b o i l s a t 59.1°C and has a f o r m i c a c i d c o n t e n t o f 10 w e i g h t ?•. S i n c e t h i s low f o r m i c a c i d c o n t e n t i s u n f a v o u r a b l e , Hunsmann & Simmrock (51)
i n v e s t i g a t e d many o t h e r e n t r a i n e r s and found t h a t 1 - c h l o r o n-butane ( B.P. a z e o t r o p e : 69.4 °C, f o r m i c a c i d c o n t e n t : 22.9 w e i g h t % ) and 1,2 d i c h l o r o -ethane ( B.P. a z e o t r o p e : 77.4 C, f o r m i c a c i d c o n t e n t : 22.4 w e i g h t % ) were the b e s t ones.
.19
2.2.3. C a t a l y t i c d e c o m p o s i t i o n
The h e t e r o g e n e o u s c a t a l y t i c d e c o m p o s i t i o n o f f o r m i c a c i d has been s t u d i e d by many w o r k e r s i n t e r e s t e d i n the f u n d a m e n t a l a s p e c t s o f h e t e r o g e n e o u s c a t a l y s i s . The o x i d a t i o n o f f o r m i c a c i d i n s o l u t i o n s by many d i f f e r e n t s u b s t a n c e s has
a l s o been i n v e s t i g a t e d e x t e n s i v e l y . However, not much r e s e a r c h has been done on the s e l e c t i v e c a t a l y t i c d e c o m p o s i t i o n o f f o r m i c a c i d i n the p r e s e n c e o f a c e t i c a c i d and w a t e r . The s o u r c e s o f a v a i l a b l e d a t a a r e r e s t r i c t e d t o the p a t e n t l i t e r a t u r e .
S u z u k i (59,60,61) p a t e n t e d removal o f f o r m i c a c i d by p a s s i n g i t i n the l i q u i d phase (0.5 w e i g h t % f o r m i c a c i d i n a c e t i c a c i d ) o v e r 5 w e i g h t % Pd on s i l i c a -a l u m i n -a or -a l u m i n -a -a t 50 °C, i n the p r e s e n c e or -absence o f -a i r . R e s i d e n c e
t i m e was about 1 h. D e a c t i v a t i o n was o b s e r v e d ; a d d i t i v e s t o p r e v e n t d e a c t i -v a t i o n were a l s o p a t e n t e d ( 6 2 ) .
O x i d a t i o n i n the l i q u i d phase by P d ( I I ) has been p a t e n t e d (63) and the k i n e -t i c s have been measured ( 6 4 ) . The o x i d a -t i o n was no-t -t o -t a l l y s e l e c -t i v e ( 6 4 ) . A l s o , i t has been been r e p o r t e d t h a t some p h o s p h i n e complexes o f p a l l a d i u m
( I I ) and o t h e r group V I I I m e t a l s decompose f o r m i c a c i d i n a c e t i c a c i d
s o l u t i o n s ( 6 5 , 6 6 ) .
P l a t i n u m has been r e p o r t e d t o decompose f o r m i c a c i d s e l e c t i v e l y but s l o w l y a t t e m p e r a t u r e s below 200°C ( 6 7 ) . T h i s r e a c t i o n was c a r r i e d out i n the vapour phase i n the p r e s e n c e o f a i r . Above 200 °C a c e t i c a c i d was a l s o decom-posed. K i f f (68) f r e e d a c e t i c a c i d o f t r a c e s o f f o r m i c a c i d by o x i d a t i o n o v e r
a m e t a l molybdate c a t a l y s t a t 300 °C. The C e l a n e s e Corp. (2) p a t e n t e d a p r o c e s s i n which f o r m i c a c i d i s s e l e c t i v e l y decomposed by o x i d a t i o n i n t h e vapour phase a t 150-225 C by a c a t a l y s t c o n s i s t i n g o f 0.05 w e i g h t % o f a m e t a l s a l t , p r e f e r a b l y copper s u l p h a t e , on a l u m i n a .
In German p a t e n t no 1117558 (69) a method i s d e s c r i b e d i n which a group V I I I m e t a l on a c t i v e c a r b o n was used t o decompose f o r m i c a c i d s e l e c t i v e l y a t molar
f e e d r a t e s o f f o r m i c a c i d between 6 x 10 and 6 x 10 ^ kmole/s.kg c a t a l y s t a t 100-200 C. With a l u m i n a or s i l i c a as the c a r r i e r the a c t i v i t y was l o w e r .
D e a c t i v a t i o n o f the c a t a l y s t was a l s o r e p o r t e d . P l a t i n u m on s i l i c a a t 220 °C and 500 kPa was used by W o l f ( 7 0 ) . A R u s s i a n p a t e n t (71) mentiones Nii-Cr„0-,
0
as the c a t a l y s t a t 180-190 C. Sennewald e t a l . (72) used a c a t a l y s t o f
0.05-2 w e i g h t % Pd, 0.05-1 w e i g h t % Au and 1-15 w e i g h t % NaOAc on s i l i c a
a t 150-200 ^C a t the same molar f e e d r a t e s as mentioned above t o decompose x As a l r e a d y mentioned i m p l i c i t l y i n c h a p t e r 1 we i n c l u d e i n the p h r a s e
!["Wśród trudności i konfliktów (Działalność Związku Zawodowego Literatów Polskich od września 1945 do października 1946)", Krzysztof Woźniakowski, "Rocznik Komisji Historycznoliterackiej PAN w Krakowie" T.21 (1984) : [recenzja]](data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACH5BAEAAAAALAAAAAABAAEAAAICRAEAOw==)