Hydrogen-Amine Process for Heavy Water Production

3 Hydrogen-Amine Process for Heavy Water Production

Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on May 28, 2018 | https://pubs.acs.org Publication Date: June 1, 1978 | doi: 10.1021/bk-1978-0068.ch003

W. J. HOLTSLANDER Atomic Energy of Canada Ltd., Chemical Engineering Branch, Chalk River Nuclear Laboratories, Chalk River, Ontario W. E . LOCKERBY Atomic Energy of Canada Ltd., Heavy Water Projects, Tunney's Pasture, Ottawa, Ontario

Ammonia-hydrogen or amine-hydrogen exchange is one of the three major chemical systems considered u s e f u l f o r deuterium enrichment processes. The other two being the water-hydrogen sulfide system (GS process) p r e s e n t l y being used to produce the major f r a c t i o n o f the w o r l d ' s heavy water supply and the hydrogen -water system which is c u r r e n t l y under a c t i v e development. Heavy water p l a n t s based on ammonia-hydrogen exchange have operated in France and are being commissioned in I n d i a . The usefulness of amines in place of ammonia was shown by B a r - E l i and K l e i n (_1) in 1962. This work showed amines, p a r t i c u l a r l y methylamine had f a s t e r exchange r a t e s than the comparable ammonia-based system. A t Chalk R i v e r , a f t e r work w i t h the ammonia-hydrogen system showed a water-fed p l a n t d i d not o f f e r any advantage over the GS p r o c e s s , development was s t a r t e d on the amine-hydrogen system. A p a r a l l e l development program f o r the amine process was a l s o i n i t i a t e d by the Commissariat a L ' E n e r g i e Atomique in France and d e t a i l s of the exchange r e a c t i o n work were reported by Rochard and Ravoire ( 2 ) . The amine chosen was methylamine (MA). The advan tages of methylamine over ammonia are f a s t e r deuterium exchange r a t e s , higher hydrogen s o l u b i l i t y and a low vapour pressure. The choice of methylamine over other amines was discussed in d e t a i l by Bancroft and Rae ( 3 ) . The o r i g i n a l c a t a l y s t was the potassium s a l t of methylamine, potassium methylamide (PMA), because of i t s favourable exchange r a t e coupled w i t h reasonable c o s t . Subsequent work forced a m o d i f i c a t i o n o f the c a t a l y s t and the reasons f o r t h i s w i l l be d i s c u s s e d . T h e d e v e l o p m e n t o f t h e amine p r o c e s s a t CRNL p r o c e e d e d in three major areas: c o n t a c t o r development, p r o c e s s c h e m i s t r y and p r o c e s s d e s i g n . Development o f e f f i c i e n t g a s - l i q u i d c o n t a c t o r s was r e q u i r e d t o p r o v i d e h i g h mass t r a n s f e r r a t e s p e r u n i t volume in t h e c o l d t o w e r s (-50°C) where t h e e x c h a n g e r e a c t i o n r a t e is r e l a t i v e l y slow. T h i s program evolved through a s e r i e s o f p i l o t p l a n t c o n t a c t o r s r a n g i n g in s i z e f r o m 5 t o 15 cm d i a m e t e r a t l o w

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0-8412-0420-9/78/47-068-040$05.00/0

Rae; Separation of Hydrogen Isotopes ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

3.

HOLTSLANDER

AND

LOCKERBY

Hydro gen-Amine

Process

41


p r e s s u r e in g l a s s t o a 25 cm s t a i n l e s s s t e e l c o n t a c t o r t h a t o p e r a t e d a t 2 MPa (300 p s i ) f o r b o t h c o l d t o w e r a n d h o t t o w e r testing. F u r t h e r i n f o r m a t i o n on c o n t a c t o r development and process d e s i g n was o b t a i n e d in c o o p e r a t i o n w i t h S u l z e r B r o s . , S w i t z e r l a n d who h a d i n d e p e n d e n t l y c o n s t r u c t e d a p i l o t p l a n t u s i n g a f u l l s c a l e contactor operating a t f u l l process pressure (4). E x t e n s i v e p r o c e s s d e s i g n work and economic e v a l u a t i o n s were done a t CRNL a n d u n d e r c o n t r a c t w i t h i n d u s t r i a l e n g i n e e r i n g f irms. The v e r y e x t e n s i v e c h e m i s t r y p r o g r a m c o n s i s t e d o f d e t e r m i n ing the p h y s i c a l and chemical p r o p e r t i e s o f the system, d e v e l o p i n g h a n d l i n g and a n a l y t i c a l t e c h n i q u e s , d e t e r m i n i n g the r e a c t i v i t y o f the system w i t h p o t e n t i a l i m p u r i t i e s , examining f a c t o r s which a f f e c t the deuterium exchange r a t e , l o o k i n g f o r b e t t e r c a t a l y s t s t o improve the exchange r a t e and s t u d y i n g the s t a b i l i t y o f the c a t a l y s t s o l u t i o n a t process c o n d i t i o n s . This p r o g r a m was v e r y much o f a p i o n e e r i n g one b e c a u s e o f t h e s c a r c i t y o f i n f o r m a t i o n o n s o l u t i o n s o f a l k a l i m e t a l a l k y l a m i d e in a m i n e s in t h e l i t e r a t u r e . I t was n e c e s s a r y t o f i r s t d e v e l o p s u i t a b l e l a b o r a t o r y t e c h n i q u e s t o handle such a r e a c t i v e system s a f e l y and in t h e a b s e n c e o f a t m o s p h e r i c c o n t a m i n a n t s t o o b t a i n meaningful q u a n t i t a t i v e data. The a b s e n c e o f p r e v i o u s l y p u b l i s h e d i n f o r m a t i o n o n r e l a t e d s y s t e m s meant t h a t l i t t l e g u i d a n c e was a v a i l a b l e f o r p r e d i c t i o n o f t h e c h e m i c a l b e h a v i o u r and a l l a s p e c t s o f t h e w o r k had t o b e e x p e r i m e n t a l l y d e t e r m i n e d . D e v e l o p m e n t o f a c o m p l e t e r a n g e o f a n a l y t i c a l m e t h o d s was a m a j o r component o f t h e p r o g r a m . W i t h t h i s l a c k o f b a c k g r o u n d i n f o r m a t i o n , u n f o r e s e e n r e s u l t s were o f t e n observed. A prime e x a m p l e in t h i s w o r k was t h e d i s c o v e r y t h a t h y d r o g e n a t p r o c e s s p r e s s u r e is a r e a c t i v e s p e c i e s ; n o t o n l y in t h e d e u t e r i u m e x c h a n g e r e a c t i o n b u t a l s o c h e m i c a l l y . T h i s is n o t s oint h e c o m p a r a b l e ammonia s y s t e m and was t o t a l l y u n e x p e c t e d . I t was t h i s d i s c o v e r y t h a t n e c e s s i t a t e d t h e d e v e l o p m e n t o f a new c a t a l y s t t o make t h e p r o c e s s v i a b l e . Because the process operates a t h i g h p r e s s u r e (6-13 MPa, d i c t a t e d b y t h e h o s t ammonia p l a n t ) t o o b t a i n e f f e c t i v e mass t r a n s f e r r a t e s , much o f t h e c h e m i s t r y h a d t o b e done a t c o n d i t i o n s w h i c h s i m u l a t e d t h e p r o c e s s . T h i s added t h e c o m p l i c a t i o n o f having t o develop s p e c i a l experimental techniques. T h i s w o r k i l l u s t r a t e s t h e i m p o r t a n c e o f c h e m i s t r y s t u d i e s in p r o c e s s d e v e l o p m e n t . A l t h o u g h d e u t e r i u m e x c h a n g e is t h e c e n t r a l f e a t u r e o f a heavy water process, s u c c e s s f u l development r e q u i r e s d e t a i l e d knowledge o f a l l a s p e c t s o f p r o c e s s c h e m i s t r y . I n many c a s e s t h e s e a r e l a r g e l y unknown b e f o r e h a n d . The c h e m i s t r y w o r k was done b y a number o f g r o u p s a t CRNL and t h r o u g h c o n t r a c t s w i t h t h e U n i v e r s i t y o f A l b e r t a , T r e n t U n i v e r s i t y , R a y l o C h e m i c a l s L t d . in A l b e r t a a n d C h e m i c a l P r o j e c t s L t d . in T o r o n t o . A more d e t a i l e d r e v i e w o f t h i s c h e m i c a l w o r k forms the major p o r t i o n o f t h i s paper.


42

S E P A R A T I O N O F H Y D R O G E N ISOTOPES

Process

Chemistry


The p r o c e s s l i q u i d , m e t h y l a m i n e , must c o n t a i n a d i s s o l v e d c a t a l y s t t o p r o v i d e an a c c e p t a b l e d e u t e r i u m e x c h a n g e r a t e . This c a t a l y s t is p r e p a r e d b y d i s s o l v i n g p o t a s s i u m m e t a l in t h e m e t h y l amine. The p o t a s s i u m s l o w l y d i s s o l v e s t o g i v e a b l u e s o l u t i o n t y p i c a l o f a l k a l i m e t a l s in ammonia o r a m i n e s . Blue

Yellow +

Κ + C H N H + K , K~, e" - + KNHCH + % H 3 2 * ' solv 3 2 0

0

0

I n a m i n e s w i t h p o t a s s i u m F l e t c h e r e t a l Ç5,6) a t CRNL h a v e shown t h i s c o l o u r t o be due t o a n e q u i l i b r i u m b e t w e e n p o t a s s i u m a n i o n s and s o l v a t e d e l e c t i o n i o n p a i r s . The b l u e c o l o u r e d s o l u t i o n s l o w l y decomposes t o g i v e t h e y e l l o w p o t a s s i u m m e t h y l a m i d e s o l u t i o n and hydrogen. A l k a l i m e t a l a l k y l a m i d e s d i s s o l v e d in a m i n e s a r e s t r o n g b a s e s and a r e v e r y r e a c t i v e c h e m i c a l l y . They r e a c t v i g o r o u s l y w i t h a i r and w a t e r s o t h a t s p e c i a l t e c h n i q u e s a r e r e q u i r e d when h a n d l i n g and s t u d y i n g t h e s e s y s t e m s . Some o f t h e more i m p o r t a n t r e a c t i o n s w i t h i m p u r i t i e s e n c o u n t e r e d in t h e p r o c e s s a r e l i s t e d below. CH^NHK + H 0

CH NH

2

CH^NHK + 0

3

2

+ ΚΟΗΨ

-> KCN+, CH NCH=NCH , ΚΟΗΨ

2

3

3

Κ Potassium D ime t h y 1 f ο rmamid i d e 0

π CH NHK + CO

CH^NHK + C 0

HC-lji- CH Ψ ( p o t a s s i u m N - m e t h y l f ormamide) Κ 0 2

-> C^NHC-ΟΚΨ(carbamate) 0

2CH NH 3

2

+ C0

CH NHK + N H 3

0

2

3

·> CH NHC-O CH NH®(carbamate) 3

-> C H N H 3

3

2

+ KNH^

A l l o f t h e s e r e a c t i o n s h a v e b e e n s t u d i e d in v a r y i n g d e g r e e s o f d e t a i l t o d e t e r m i n e t h e i d e n t i t y o f t h e p r o d u c t s and t h e e f f e c t t h e y h a v e on t h e p r o c e s s . The m a j o r c o n s e q u e n c e o f t h e s e r e a c t i o n s is d e s t r u c t i o n o f c a t a l y s t t h u s r e d u c i n g t h e e x c h a n g e r a t e , and p r o d u c i n g i n s o l u b l e s o l i d s t h a t may c a u s e d e p o s i t i o n



3.

HOLTSLANDER

H y dro gen-Amine

A N D LOCKERBY

Process

43

and b l o c k a g e o f e q u i p m e n t . I t is t h e r e f o r e a r e q u i r e m e n t t h a t t h e s e i m p u r i t i e s b e m a i n t a i n e d a t an a c c e p t a b l y l o w l e v e l in t h e process t o a v o i d these problems. An a r e a o f p r o c e s s c h e m i s t r y t h a t was e x t e n s i v e l y s t u d i e d b o t h a t C h a l k R i v e r and by S a n f o r d , P r e s c o t t and Lemieux a t Raylo C h e m i c a l s , Edmonton was t h e t h e r m a l s t a b i l i t y o f t h e PMA-MA system. Thermal decomposition occurs t o y i e l d t h r e e major p r o d u c t s : h y d r o g e n , p o t a s s i u m d i m e t h y l f o r m a m i d i d e (PDMFA) a n d ammonia, 2CH NH 3

2

+ CH^NHK + 2 H + CH N=CHNKCH + N H ^ 2

3

3

The r a t e o f t h i s r e a c t i o n h a s b e e n d e t e r m i n e d o v e r t h e r a n g e of p r o c e s s c o n d i t i o n s . A s a r e s u l t t h e optimum h o t t o w e r t e m p e r a t u r e o r i g i n a l l y s e t a t 70°C ( 3 ) b a s e d on p r e l i m i n a r y d e c o m p o s i t i o n d a t a was r e d u c e d t o 40^C. The d e c o m p o s i t i o n r e a c t i o n h a s two p r o c e s s e f f e c t s ; i t r e s u l t s in a l o s s o f c a t a l y s t t h a t r e q u i r e s make-up and i t p r o d u c e s ammonia and PDMFA b o t h o f w h i c h must be removed. The ammonia must b e removed b e c a u s e o f i t s r e a c t i o n w i t h PMA f o r m i n g p o t a s s i u m amide w h i c h h a s a l i m i t e d s o l u b i l i t y (0.06 mmoles/g). Removal o f PDMFA is o f l e s s importance b u t i t w i l l e v e n t u a l l y b u i l d up t o a c o n c e n t r a t i o n t h a t e x c e e d s i t s s o l u b i l i t y (3.3 mmoles/g @ -40°C) a n d w i l l p r e c i p i t a t e . I n t h e s t u d y o f ways t o r e d u c e t h e d e c o m p o s i t i o n r a t e a n u n e x p e c t e d s i d e r e a c t i o n was d i s c o v e r e d . S i n c e h y d r o g e n was a p r o d u c t o f t h e d e c o m p o s i t i o n , one o f t h e p o s t u l a t e d f i r s t s t e p s w a s d e h y d r o g e n a t i o n o f t h e PMA t o a m e t h y l e n i m i n e , CH NHK t CH =NK + 3

2

I f t h i s p o s t u l a t e d i n t e r m e d i a t e s t e p was r e v e r s i b l e t h e n a h i g h hydrogen p a r t i a l p r e s s u r e might i n h i b i t t h e d e c o m p o s i t i o n . Since t h e p r o c e s s o p e r a t e s most e f f e c t i v e l y a t h i g h h y d r o g e n p r e s s u r e i t was e s s e n t i a l t o i n v e s t i g a t e t h e 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 f u l l p r e s s u r e range. High hydrogen p r e s s u r e d i d reduce t h e d e c o m p o s i t i o n r a t e b u t t h e r e s u l t s were v e r y e r r a t i c and t h e e x p e r i m e n t s were p l a g u e d b y t h e i r r e p r o d u c i b l e a p p e a r a n c e a n d disappearance of white p r e c i p i t a t e s . Workers a t Raylo Chemicals showed t h e h y d r o g e n was r e a c t i n g w i t h t h e PMA-MA s o l u t i o n t o g i v e p o t a s s i u m h y d r i d e w h i c h was i n s o l u b l e . CH NHK + H 3

2

t CH NH 3

2

+ ΚΗΨ

The a p p a r e n t r e d u c t i o n in t h e r m a l d e c o m p o s i t i o n r a t e was due t o r e m o v a l o f PMA f r o m s o l u t i o n . T h i s r e a c t i o n t o f o r m KH does n o t o c c u r in t h e ammonia s y s t e m and was n o t e x p e c t e d in m e t h y l a m i n e . A r e a c t i o n b e t w e e n KNH2 a n d h y d r o g e n d o e s o c c u r in ammonia a t v e r y h i g h hydrogen p r e s s u r e , b u t g i v e s t h e s o l v a t e d e l e c t r o n (the b l u e s o l u t i o n ) r a t h e r than a h y d r i d e p r e c i p i t a t e (7,8).



44

SEPARATION

OF

HYDROGEN

ISOTOPES

The gas l i q u i d c o n t a c t o r w o r k a t C h a l k R i v e r was done a t 2 MPa and m i s s e d t h e h y d r i d e r e a c t i o n . A l o w p r e s s u r e c o n t a c t o r was u s e d b e c a u s e t h e mass t r a n s f e r c o e f f i c i e n t was l i q u i d phase c o n t r o l l e d and c o u l d be r e l i a b l y e x t r a p o l a t e d t o h i g h e r p r e s s u r e s . I t was o n l y through the chemistry study the r e a c t i v i t y of hydrogen w i t h p o t a s s i u m m e t h y l a m i d e came t o l i g h t . The h y d r i d e r e a c t i o n had m a j o r p r o c e s s i m p l i c a t i o n s . B e c a u s e o f t h e l o w KH s o l u b i l i t y t h e n e t r e a c t i o n a t p r o c e s s h y d r o g e n p r e s s u r e s was t o t h e r i g h t so t h a t t h e m a j o r p o r t i o n o f t h e c a t a l y s t was t a k e n o u t o f s o l u t i o n as t h e h y d r i d e . T h i s is shown in F i g u r e 1. T h e r e is l i t t l e t e m p e r a t u r e e f f e c t on t h e r e a c t i o n , w h i c h o c c u r s t o g i v e a s i m i l a r shape o f s o l u b i l i t y v e r s u s p r e s s u r e f r o m -30°C t o +50°C. The e f f e c t o f t h e l o w maximum c a t a l y s t s o l u b i l i t y in s o l u t i o n s a t p r o c e s s p r e s s u r e was t o r e d u c e t h e c o l d t o w e r e x c h a n g e e f f i c i e n c y t o a b o u t h a l f t h a t m e a s u r e d a t 2 MPa. A f t e r d i s c o v e r y o f t h e h y d r i d e r e a c t i o n an e x t e n s i v e p r o g r a m was i n i t i a t e d t o f i n d a method o f i n h i b i t i n g t h e r e a c t i o n . A v e r y l a r g e number o f c h e m i c a l a d d i t i v e s and a l t e r n a t i v e s y s t e m s were investigated. Work a t C h a l k R i v e r showed t h e a n a l o g o u s r e a c t i o n o c c u r r e d w i t h s o d i u m m e t h y l a m i d e in m e t h y l a m i n e and w i t h s o d i u m and p o t a s s i u m d i m e t h y l a m i d e in d i m e t h y l a m i n e . I t d i d not occur w i t h l i t h i u m methylamide or w i t h cesium methylamide, but l i t h i u m m e t h y l a m i d e is a v e r y p o o r c a t a l y s t f o r d e u t e r i u m e x c h a n g e and c e s i u m is e x p e n s i v e . I t was f o u n d , h o w e v e r , t h a t when l i t h i u m was added t o PMA in m e t h y l a m i n e t h e r e a c t i o n w i t h h y d r o g e n d i d n o t o c c u r , a t l e a s t in t h e r a n g e o f h y d r o g e n p a r t i a l p r e s s u r e s o f i n t e r e s t to the heavy water p r o c e s s . T h i s is shown in F i g u r e 2 where PLMA r e p r e s e n t s e q u i m o l a r p o t a s s i u m - l i t h i u m m e t h y l a m i d e . T h i s d i s c o v e r y s o l v e d one o f t h e m a j o r p r o c e s s p r o b l e m s b u t r e q u i r e d t h e answer t o many q u e s t i o n s s u c h as t h e e f f e c t o f added l i t h i u m on t h e e x c h a n g e r e a c t i o n , t h e r e a c t i o n s w i t h i m p u r i t i e s , t h e t h e r m a l d e c o m p o s i t i o n r e a c t i o n , and t h e optimum l i t h i u m concentration. E x c h a n g e r a t e s w e r e s t u d i e d in t h e l a b o r a t o r y a t C h a l k R i v e r u s i n g a s m a l l r a p i d l y s t i r r e d e x c h a n g e c e l l where t h e t r a n s f e r o f d e u t e r i u m f r o m h y d r o g e n t o m e t h y l a m i n e was m o n i t o r e d w i t h an onl i n e mass s p e c t r o m e t e r . L a r g e - s c a l e e x c h a n g e w o r k was done in t h e 25 cm p i l o t p l a n t c o n t a c t o r . K i n e t i c e x c h a n g e d a t a u s i n g a s i n g l e - s p h e r e a b s o r b e r was a l s o o b t a i n e d by P r o f e s s o r F.D. O t t o a t t h e U n i v e r s i t y o f A l b e r t a . I n i t i a l w o r k showed t h e PLMA e x c h a n g e c a t a l y s t gave e q u a l o r somewhat h i g h e r r a t e c o n s t a n t s and t r a y e f f i c i e n c i e s t h a n PMA. However, s u b s e q u e n t more d e t a i l e d w o r k has shown t h e e x c h a n g e r a t e c o n s t a n t is d e p e n d e n t on t h e amount o f l i t h i u m added and d e c r e a s e s w i t h i n c r e a s i n g l i t h i u m c o n c e n t r a t i o n . T h i s is shown in F i g u r e 3. The t e m p e r a t u r e c o e f f i c i e n t o f t h e e x c h a n g e r e a c t i o n was f o u n d t o be t h e same f o r b o t h t h e PMA and PLMA s y s t e m s w i t h an a c t i v a t i o n e n e r g y o f 28 k j o u l e s / m o l e , t h e same a s was f o u n d e a r l i e r by R o c h a r d f o r t h e PMA s y s t e m ( 2 ) .



3.

HOLTSLANDER

Hydrogen-Amine

A N D LOCKERBY

45

Process

MAXIMUM CATALYST CONCENTRATION

(m moles/g)

8

10

12

14

16

18

20

22

24

26

28

30

PRESSURE (MPa)

Figure 1.

Effect of hydrogen on PMA solutions at 296°Κ

MAXIMUM CATALYST CONCENTRATION (m moles/g)

12

14

16

18

20

22

24

26

28

30

PRESSURE (MPa)

Figure 2.

Effect of hydrogen on PMA and PLMA

catalyst solutions at 296°Κ



46

SEPARATION O F H Y D R O G E N ISOTOPES

Figure 3.

Effect of lithium-potassium mole ratio on exchange rate. Stirred exchange cell at 203°K.



3.

HOLTSLANDER

AND

LOCKERBY

Hydrogen-Amine

Process

47

A s e c o n d exchange r e a c t i o n t h a t o c c u r s in b o t h t h e PMA and PLMA s y s t e m is d e u t e r i u m e x c h a n g e b e t w e e n t h e amino- and m e t h y l groups o f methylamine. T h i s r e a c t i o n was s t u d i e d in d e t a i l b y H a l l i d a y and B i n d n e r (9) a t CRNL and is more t h a n 1000 t i m e s s l o w e r than the amino-group-molecular hydrogen exchange. W h i l e i t d o e s r e s u l t in a s l o w b u i l d u p o f d e u t e r i u m in t h e m e t h y l g r o u p o f t h e p r o c e s s l i q u i d , i t does n o t c o n s t i t u t e a p r o c e s s p r o b l e m . The s o l u b i l i t y - t e m p e r a t u r e r e l a t i o n s h i p o f PLMA ( F i g u r e 4) is o p p o s i t e t o t h a t o f e i t h e r PMA o r LMA ( l i t h i u m m e t h y l a m i d e ) , s h o w i n g a somewhat l o w e r s o l u b i l i t y a t t h e l o w t e m p e r a t u r e and a much h i g h e r s o l u b i l i t y a t h i g h t e m p e r a t u r e s . The s o l u b i l i t y is a l s o m a r k e d l y d e p e n d e n t on t h e l i t h i u m c o n c e n t r a t i o n a s shown in F i g u r e 5. A s t h e amount o f l i t h i u m i n c r e a s e s t h e t o t a l s o l u b i l i t y increases rapidly. I n f a c t systems w i t h h i g h l i t h i u m r a t i o s y i e l d e d c l e a r s o l u t i o n s w i t h a s a l t c o n t e n t c l o s e t o 30% by w e i g h t . The e f f e c t o f added l i t h i u m on t h e t h e r m a l s t a b i l i t y o f t h e s o l u t i o n is shown in F i g u r e 6. The s o l u t i o n is more s t a b l eint h e presence of l i t h i u m w i t h the h a l f - l i f e f o r an equimolar potassiuml i t h i u m s o l u t i o n b e i n g h i g h e r (100 d a y s ) a t 40°C t h a n a PMA s o l u t i o n (25 d a y s ) . I n t h e h e a v y w a t e r p r o c e s s w h e r e t h e s o l u t i o n is c i r c u l a t i n g b e t w e e n c o l d and h o t t o w e r s t h e t i m e s p e n t a t 40°C is o n l y a f r a c t i o n o f a c t u a l t i m e in t h e p r o c e s s so t h a t t h e p r a c t i c a l h a l f - l i f e o f t h e s o l u t i o n is g r e a t e r t h a n t h e 100 d a y s m e a s u r e d in t h e l a b o r a t o r y . The p r o d u c t s o f d e c o m p o s i t i o n a r e t h e same as f r o m PMA w i t h t h e a d d i t i o n o f l i t h i u m d i m e t h y l f o r m a m i d i d e . The ammonia formed r e a c t s i n d i s c r i m i n a t e l y w i t h l i t h i u m and p o t a s s i u m s a l t s t o p r e c i p i t a t e L i N H 2 and KNH2. I n a d d i t i o n , i t was f o u n d t h a t t h e amide s a l t s c o - p r e c i p i t a t e d m e t h y l a m i d e a l o n g w i t h them t h u s f u r t h e r r e m o v i n g a c t i v e c a t a l y s t f r o m t h e s o l u t i o n . F o r t h i s r e a s o n t h e p u r i f i c a t i o n s y s t e m m u s t m a i n t a i n t h e ammonia a t a c o n c e n t r a t i o n b e l o w 0.06 mmole/g w h i c h c o r r e s p o n d s t o t h e amide s o l u b i l i t y . S a n f o r d a t R a y l o has demonstrated a s i m p l e p u r i f i c a t i o n method b a s e d o n d i s t i l l a t i o n o f a s i d e s t r e a m t o remove ammonia and c o n v e r t a m i d e s b a c k t o m e t h y l a m i d e s . MNH

+ CH NH

2

3

2

-> CH^NHM + N H ^

From t h e f u n d a m e n t a l p o i n t o f v i e w t h e q u e s t i o n a r i s e s o f how l i t h i u m m o d i f i e s t h e p r o p e r t i e s o f t h e s o l u t i o n . L i t h i u m m e t h y l a m i d e b y i t s e l f in m e t h y l a m i n e s o l u t i o n is a v e r y p o o r c a t a l y s t w i t h a n e x c h a n g e r a t e l e s s t h a n 1% o f t h a t o f PMA. The w o r k r e p o r t e d in t h i s p a p e r s u g g e s t s t h a t p o t a s s i u m and l i t h i u m m e t h y l a m i d e e x i s t in s o l u t i o n a s a c o m p l e x r a t h e r t h a n a s i m p l e m i x t u r e o f t h e two s a l t s in s o l u t i o n . S u c h a c o m p l e x in e q u i l i b r i u m w i t h t h e two m e t h y l a m i d e s is shown b e l o w . K Li (NHCH ) ^±2KNHCH 2

2

3

4

3

+ 2LiNHCH

2

E v i d e n c e f o r s u c h a c o m p l e x in s o l u t i o n is s u m m a r i z e d in F i g u r e 7. The t o t a l l y o p p o s i t e s o l u b i l i t y - t e m p e r a t u r e r e l a t i o n s h i p

American Chemfcar

Society Library

16th St. N. Isotopes w. Rae; 1155 Separation of Hydrogen ACS Symposium Series; American Chemical Washington, DC, 1978. Washington, D. C.Society: 20038


SEPARATION O F HYDROGEN ISOTOPES

Figure 4.

Solubility of methylamides



HOLTSLANDER

Figure

Hydrogen-Amine

A N D LOCKERBY

5. Solubility

of

potassium-lithium methylamine

Process

methylamide

in


SEPARATION

O F HYDROGEN ISOTOPES


1000

Figure 7.

Evidence that PLMA is a complex



3.

HOLTSLANDER

AND

LOCKERBY

Hydrogen

Amine

Process

51

i n d i c a t e s a c o m p l e x r a t h e r t h a n a m i x t u r e . The I R a n d X - r a y s p e c t r a obtained i n Glinthard's l a b o r a t o r y i n t h e Swiss F e d e r a l I n s t i t u t e o f T e c h n o l o g y u n d e r c o n t r a c t t o S u l z e r shows u n i q u e s p e c t r a f o r PLMA r a t h e r t h a n a sum o f a l l t h e l i n e s f r o m PMA a n d LMA. C o n d u c t i v i t y d a t a o b t a i n e d a t CRNL shows a d i f f e r e n t t e m p e r a t u r e b e h a v i o u r f o r PLMA t h a n f o r PMA o r LMA. The r e a c t i v i t y i s d i f f e r e n t t h a n PMA a n d t h e v a p o u r p r e s s u r e d a t a o b t a i n e d b y Sanford a t Raylo Chemicals i n d i c a t e s a d i f f e r e n t species i n s o l u t i o n t h a n e i t h e r o f t h e two component s a l t s . A l l o f these o b s e r v a t i o n s a r e c o n s i s t e n t w i t h a complex r a t h e r than a s i m p l e mixture. Conclusion I t h a s been demonstrated t h a t p o t a s s i u m - l i t h i u m methylamide i s a s u p e r i o r c a t a l y s t f o r t h e amine-hydrogen heavy water p r o c e s s . I t does n o t r e a c t w i t h hydrogen, and I t has a f a v o u r a b l e deuterium e x c h a n g e r a t e , good s o l u b i l i t y a n d a n a c c e p t a b l e t h e r m a l decomposition rate. A p a t e n t h a s b e e n g r a n t e d f o r t h i s new c a t a l y s t (10). The a m i n e - h y d r o g e n p r o c e s s i s r i c h i n c h e m i s t r y , much o f i t p r e v i o u s l y unknown. The p r a c t i c a l a s p e c t s o f t h e c h e m i s t r y w h i c h d i r e c t l y affect theprocess, i . e . , the preparation of catalyst, t h e r e a c t i v i t y o f t h ec a t a l y s t s o l u t i o n w i t h process ingredients and p r o c e s s i m p u r i t i e s , t h e d e u t e r i u m e x c h a n g e p r o p e r t i e s , t h e t h e r m a l s t a b i l i t y have been t h o r o u g h l y i n v e s t i g a t e d . The p r o c e s s c h e m i s t r y s t u d i e s p r o v i d e a f i r m b a s i s f o r t h e p r o c e s s , however t h e r e i s s t i l l many f u n d a m e n t a l a s p e c t s o f c h e m i s t r y o f t h e s y s t e m w h i c h c o u l d be a f e r t i l e a r e a f o r f u r t h e r b a s i c r e s e a r c h . As a r e s u l t o f t h e s u c c e s s a c h i e v e d i n t h e t h r e e a r e a s o f development, t h a t o f g a s - l i q u i d c o n t a c t o r s , p r o c e s s c h e m i s t r y and p r o c e s s d e s i g n , t h e amine-hydrogen heavy water p r o c e s s h i s reached t h e p o s i t i o n w h e r e t h e n e x t s t a g e i s commitment o f a p r o t o t y p e p l a n t , and t h u s i s now b e i n g p u r s u e d . Acknowledgement s We a c k n o w l e d g e t h e c o n t r i b u t i o n s o f D r . H.K. Rae a n d A.R. B a n c r o f t who d i r e c t e d t h e p r o c e s s d e v e l o p m e n t p r o g r a m a n d for t h e i r review of t h i s manuscript. We a l s o a c k n o w l e d g e D r s . J . F . P r e s c o t t a n d E.C. S a n f o r d a t R a y l o C h e m i c a l s a n d R.E. J o h n s o n a n d R.P. D e n a u l t o f t h e C h e m i c a l E n g i n e e r i n g B r a n c h , CRNL f o r t h e i r m a j o r c o n t r i b u t i o n t o t h e e x p e r i m e n t a l w o r k a n d t o D r . J.P. M i s l a n a n d c o - w o r k e r s o f t h e G e n e r a l C h e m i s t r y B r a n c h , CRNL, who d i d much o f t h e a n a l y t i c a l m e t h o d s d e v e l o p m e n t .

Abstract The hydrogen-amine process f o r heavy water p r o d u c t i o n employs a deuterium i s o t o p e exchange r e a c t i o n between hydrogen and m e t h y l amine c o n t a i n i n g a d i s s o l v e d alkali metal methylamide c a t a l y s t .



52

SEPARATION OF HYDROGEN ISOTOPES

This system is c h e m i c a l l y v e r y r e a c t i v e and a d e t a i l e d understand ing o f all aspects of the process chemistry was r e q u i r e d . T h i s understanding was made more difficult by the l a c k of i n f o r m a t i o n in the literature on this o r similar systems. The m a j o r i t y of the work was of a p i o n e e r i n g n a t u r e . For example, a h i t h e r t o unknown s i d e r e a c t i o n of hydrogen at process pressure w i t h the original exchange c a t a l y s t was d i s c o v e r e d . The s u c c e s s f u l development of a new c a t a l y s t r e s t o r e d the viability of the process so that commercial a p p l i c a t i o n is now f e a s i b l e and is being pursued. Literature

Cited

(1) (2)

Bar-Eli, K . and Klein, F.S., J. Chem. S o c . , 3803, (1962). Rochard, E . and R a v o i r e , J., J. Chem. P h y s . , 68, 1183, (1971). (3) B a n c r o f t , A . R . and Rae, H.K., Atomic Energy of Canada L i m i t e d , Report AECL-3684, (1970). (4) Wynn, Ν . , paper no. 57 Isotope Separation Symposium ACS/CIC C o n f . , (June 1977). (5) F l e t c h e r , J.W., Seddon, W . A . , Jevcak, J. and Sopchyshyn, F.C., Chem. Phys. Lett., 18, 592, (1973). (6) F l e t c h e r , J.W., Seddon, W.A. and Sopchyshyn, F.C., Can. J. Chem., 51, 2975, (1973). (7) K i r s c h k e , E.J. and Jolly, W . L . , I n o r g . Chem. 6, 855, (1967). (8) Bödddeker, K . W . , Land, G . , and Schindewolf, U., Angew Chem. ( I n t . E d . ) 8, 138, (1969). (9) H a l l i d a y , J.D. and B i n d n e r , P.E., Can. J. Chem. 54, 3775 (1967). (10) H o l t s l a n d e r , W.J., and Johnson, R.E., U n i t e d States P a t e n t , 3995017, (November 30, 1976). RECEIVED September 7, 1977


Hydrogen-Amine Process for Heavy Water Production

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