Zeolite Synthesis - American Chemical Society

Chapter 15

Nonaqueous Synthesis of Silica Sodalite

Downloaded by UCSF LIB CKM RSCS MGMT on November 23, 2014 | http://pubs.acs.org Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0398.ch015

D. M. Bibby, N. I. Baxter, D. Grant-Taylor, and L. M. Parker Chemistry Division, Department of Scientific and Industrial Research, Private Bag, Petone, New Zealand

The synthesis of ethylene glycol-silica sodalite from the non-aqueous systems SiO -Na O-ethylene glycol and SiO -Na CO -ethylene glycol is described. Addition of water up to a water/ethylene glycol ratio of 0.05 has no effect, above this sodium metasilicate is produced in increasing amounts until it is the only product at a water/ethylene glycol ratio 0.5. Each sodalite cage contains one ethylene glycol molecule which can be removed by a combination of pyrolysis and high pressure oxidation. These oxidation products can be decapsulated at low pressures to produce a pure s i l i c a sodalite. 2

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We d e s c r i b e h e r e t h e s y n t h e s i s o f s i l i c a s o d a l i t e c o n t a i n i n g e t h y l e n e g l y c o l i n t h e s o d a l i t e cages, a m a t e r i a l r e f e r r e d t o as e t h y l e n e g l y c o l - s i l i c a s o d a l i t e , EG-SS. We a l s o d e s c r i b e a method f o r removing t h e e t h y l e n e g l y c o l t o l e a v e a pure s i l i c a s o d a l i t e . U n l i k e t h e u s u a l systems f o r s y n t h e s i s o f z e o l i t i c m a t e r i a l s ^ ) t h e s e a r e non-aqueous, namely s i l i c a - s o d i u m h y d r o x i d e - e t h y l e n e g l y c o l and s i l i c a - s o d i u m c a r b o n a t e - e t h y l e n e g l y c o l . Our f i r s t s y n t h e s e s were d e s c r i b e d elsewhere ^ ) . S u b s e q u e n t l y , a wide range of a l l o w a b l e r e a g e n t c o m p o s i t i o n s f o r s u c c e s s f u l EG-SS p r o d u c t i o n have been s t u d i e d and t h e c r y s t a l l i s a t i o n f i e l d s a r e p r e s e n t e d h e r e . The a v a i l a b l e e v i d e n c e s u g g e s t s t h a t t h e m a t e r i a l as s y n t h e s i s e d c o n t a i n s one e t h y l e n e g l y c o l m o l e c u l e i n each s o d a l i t e cage. The h i g h temperature w e i g h t l o s s i n t h e r m o g r a v i m e t r i c a n a l y s i s c o r r e s p o n d e d t o n e a r l y two e t h y l e n e g l y c o l m o l e c u l e s p e r u n i t c e l l , w i t h a carbonaceous r e s i d u e i n the b l a c k c a l c i n e d material. A neutron d i f f r a c t i o n study (3) produced d a t a o f such a q u a l i t y t h a t e s s e n t i a l l y one e t h y l e n e g l y c o l m o l e c u l e must be p r e s e n t i n each cage. W i t h a f r e e d i a m e t e r o f t h e s o d a l i t e cage o f about 6 angstrom, t h e s i z e o f t h e m o l e c u l e s t h a t c a n be accommodated i s limited. E t h y l e n e g l y c o l , p r o p a n o l and a l s o t e t r a m e t h y l ammonium i o n s (5) can be e a s i l y e n c a p s u l a t e d . However, m o l e c u l e s such as 2

0097-6156/89/0398-0209$06.00/0 ο 1989 American Chemical Society

In Zeolite Synthesis; Occelli, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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p r o p y l e n e g l y c o l o r g l y c e r o l , which might a l s o be s u i t a b l e s o l v e n t s , would be t o o l a r g e t o f i t c o m f o r t a b l y i n t h e cage.


Experimental The r e a g e n t s were r e d i s t i l l e d e t h y l e n e g l y c o l (EG) ( l a b o r a t o r y r e a g e n t ) , fumed s i l i c a (Degussa A e r o s i l 200), NaOH ( l a b o r a t o r y grade) and Na2C03 ( l a b o r a t o r y g r a d e ) . A l l r e a c t i o n s were c a r r i e d o u t a t a temperature o f 170°C, f o r p e r i o d s o f up t o 21 days, i n s t a i n l e s s s t e e l v e s s e l s w i t h a g i t a t i o n when t h e v i s c o s i t y was low enough. I n s y n t h e s e s u s i n g NaOH where t h e S 1 O 2 / E G r a t i o was l e s s t h a n 0.1, t h e h y d r o x i d e was added as t h e s o l i d as i t r a p i d l y d i s s o l v e d i n t h e EG a t t h e r e a c t i o n t e m p e r a t u r e . F o r SÎ02/EG r a t i o s between 0.1 and 1.0, t h e NaOH was g e n e r a l l y d i s s o l v e d i n t h e EG p r i o r t o m i x i n g w i t h t h e Si02« F o r r a t i o s above 1.0, NaOH was d i s s o l v e d i n methanol and a s l u r r y w i t h t h e S 1 O 2 was p r e p a r e d . The methanol was t h e n removed a t low temperature (below 50°C) i n vacuo, and t h e a p p r o p r i a t e amount o f EG was added. In syntheses using Na2C03 t h e c a r b o n a t e was mixed i n t o t h e r e a c t i o n m i x t u r e i n a f i n e l y ground anhydrous form. T h e r m o g r a v i m e t r i c a n a l y s i s was p e r f o r m e d on a S t a n t o n R e d c r o f t t h e r m o b a l a n c e i n a f l o w i n g oxygen atmosphere a t a h e a t i n g r a t e o f 10°C/minute. Thermal d e s o r p t i o n / m a s s s p e c t r o m e t r y (TD/MS) was c a r r i e d o u t u s i n g an E x t r a n u c l e a r q u a d r u p o l e mass s p e c t r o m e t e r . ^ ) To a n a l y s e t h e e v o l v e d gases a mass range o f 1 t o 100 was scanned, w h i l e t h e sample was h e a t e d i n a p a r t i a l vacuum ( c a . 0.1 b a r argon) a t 10°C/minute. The h i g h p r e s s u r e o x i d a t i o n s t u d i e s were c a r r i e d o u t i n t e s t v e s s e l s (American I n s t r u m e n t Co.) w i t h a working p r e s s u r e l i m i t o f 1000 b a r a t room temperature and o n l y s l i g h t l y lower a t a t e m p e r a t u r e l i m i t o f 400°C. High p r e s s u r e oxygen (commercial grade) was i n t r o d u c e d from a c y l i n d e r w i t h up t o 140 b a r a v a i l a b l e a t room temperature. The oxygen p r e s s u r e a t 400°C c o u l d be c a l c u l a t e d from values of the c o m p r e s s i b i l i t y f a c t o r a n d the f i l l i n g p r e s s u r e a t room t e m p e r a t u r e . Sample powders were s p r e a d t h i n l y a l o n g the w a l l o f t h e h o r i z o n t a l v e s s e l t o reduce any l o c a l h e a t i n g t o a minimum. Sodium a n a l y s e s were c a r r i e d o u t by flame p h o t o m e t r i c methods after d i s s o l u t i o n o f t h e sample i n HF. X-ray d i f f r a c t i o n was c a r r i e d o u t on s t a n d a r d powder d i f f r a c t i o n equipment. R e s u l t s and D i s c u s s i o n S y n t h e s i s o f E t h y l e n e G l y c o l - S i l i c a S o d a l i t e (EG-SS)· The c r y s t a l l i s a t i o n f i e l d f o r t h e system Si02~Na0H-EG a t 170°C i s shown i n F i g u r e 1. A t low v a l u e s o f t h e r a t i o S 1 O 2 - E G t h e p r o d u c t s were e i t h e r c l e a r s o l u t i o n s or t r a n s l u c e n t g e l s . A t low Na20/EG r a t i o s and h i g h S 1 O 2 / E G r a t i o s no o b v i o u s r e a c t i o n p r o d u c t s were found and t h e m a t e r i a l was s t i l l amorphous a f t e r r e a c t i o n . A t Na20/EG r a t i o s above 0.025 and S 1 O 2 / E G r a t i o s between 0.05 and 0.5 b o t h 3-sodium s i l i c a t e and c r i s t o b a l i t e were formed. Pure EG-SS was formed a t S 1 O 2 / E G r a t i o s between 0.05 and 3.0 and Na20/EG r a t i o s from 0.007 t o 0.4. Mixed EG-SS and amorphous m a t e r i a l was produced up t o a S 1 O 2 / E G r a t i o o f ca.10. Assuming t h a t each s o d a l i t e cage i s o c c u p i e d by one EG


Nonaqueous Synthesis ofSilica Sodalite


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m o l e c u l e (a u n i t c e l l c o m p o s i t i o n Si-j 2 Ο 2 4 · 2EG), t h e S 1 O 2 / E G r a t i o o f t h e p u r e EG-SS i s 5.81. Above t h i s r a t i o i t i s i n e v i t a b l e t h a t EG-SS w i l l be mixed w i t h o t h e r p r o d u c t s , u s u a l l y u n r e a c t e d material. I n p r a c t i c e t h i s work shows t h a t pure EG-SS c a n be formed up t o S i 0 / E G = 3 w i t h i n t h e r e a c t i o n times used h e r e . As F i g u r e 1 shows, as t h e amount o f EG i n t h e system f a l l s , t h e r a t i o Na20/EG h a s t o i n c r e a s e f o r s u c c e s s f u l EG-SS s y n t h e s i s . F o r S 1 O 2 / E G r a t i o s below 0 . 4 t h e c a l c u l a t e d S i 0 2 / N a 2 0 r a t i o v a r i e s from ca. 3 t o ca.10. F o r S i 0 / E G above 0 . 4 t h e S i 0 2 / N a 2 0 r a t i o c a n i n c r e a s e from c a . 10 t o a maximum o f c a . 50. Thus a s t h e amount o f EG i n t h e system f a l l s , t h e p r o p o r t i o n o f Na20 r e q u i r e d f o r s u c c e s s f u l s y n t h e s i s o f EG-SS a l s o f a l l s . 2


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F o r v a l u e s o f S Î 0 2 / E G above 1 t h e r e a c t a n t m i x t u r e h a s t h e a p p e a r a n c e o f a d r y powder. A l t h o u g h EG h a s a h i g h vapour p r e s s u r e a t 170°C and was r a p i d l y and u n i f o r m l y d i s t r i b u t e d t h r o u g h o u t t h e r e a c t a n t s , i t was c l e a r from p r e l i m i n a r y e x p e r i m e n t s i n t h e s e " d r y " systems t h a t t h e NaOH c o u l d n o t be u n i f o r m l y d i s t r i b u t e d . I t was f o r t h i s reason t h a t the procedure of mixing the S 1 O 2 w i t h the a p p r o p r i a t e amount o f NaOH d i s s o l v e d i n methanol was a d o p t e d . The p r e s e n c e o f any s m a l l r e s i d u a l amounts o f methanol i n t h e r e a c t a n t s a f t e r d r y i n g i n vacuo d i d n o t appear t o be d e t r i m e n t a l . In t h e system S i 0 2 ~ N a 0 H - E G , water may be p r e s e n t i n t r a c e amounts as an i m p u r i t y o r as a p r o d u c t o f a r e a c t i o n between NaOH and EG t o form sodium g l y c o l a t e . I n an i n v e s t i g a t i o n i n t o t h e p o s s i b i l i t y t h a t water a c t s as a c a t a l y s t , EG-SS was s y n t h e s i s e d from a system where sodium m e t a l was d i s s o l v e d i n r e d i s t i l l e d EG b e f o r e b e i n g mixed w i t h S 1 O 2 p r e v i o u s l y d r i e d a t 500°C. No d i f f e r e n c e s were o b s e r v e d i n t h e r a t e o f f o r m a t i o n o f t h e EG-SS o r i n t h e p u r i t y o f t h e p r o d u c t . However, t h e e x p e r i m e n t a l d i f f i c u l t i e s o f e n s u r i n g complete removal o f water from t h e system are such t h a t , as y e t , a c a t a l y t i c r o l e f o r water c a n n o t be e n t i r e l y eliminated. The e f f e c t t h e d e l i b e r a t e a d d i t i o n o f water on t h e c r y s t a l i z a t i o n o f s i l i c a s o d a l i t e was i n v e s t i g a t e d i n a s e p a r a t e s e r i e s o f e x p e r i m e n t s where i n c r e a s i n g amounts o f water were added t o t h e system. A d d i t i o n o f water up t o w a t e r / e t h y l e n e g l y c o l r a t i o s of 0.05 h a d no o b s e r v a b l e e f f e c t , x - r a y d i f f r a c t i o n showing 100 percent s i l i c a sodalite. Above t h i s r a t i o i n c r e a s i n g amounts o f meta sodium s i l i c a t e were formed u n t i l t h i s became t h e o n l y p r o d u c t a t w a t e r / e t h y l e n e g l y c o l r a t i o s above 0.5. The e f f e c t o f Na2C03 on t h e S i 0 2 ~ N a 2 0 - E G system was i n v e s t i g a t e d because o f t h e r e p o r t e d ( ) s y n t h e s i s o f c a n c r i n i t e from h y d r o t h e r m a l systems c o n t a i n i n g Na2C03. However, we found no p r o d u c t h e r e o t h e r than EG-SS. F i g u r e 2 shows t h e c r y s t a l l i s a t i o n f i e l d f o r EG-SS i n t h e system S i 0 2 - N a 2 C 0 3 - E G . W i t h i n the c o m p o s i t i o n range s t u d i e d , t h e r e appears t o be no upper boundary t o the a l l o w a b l e Na20/EG r a t i o o v e r a range o f v a l u e s o f S 1 O 2 / E G from c a . 0.03 t o ca.2. C o n s i d e r i n g t h e l i m i t e d s o l u b i l i t y o f Na2C03 i n EG, t h i s i s perhaps n o t s u r p r i s i n g . The EG i s e s s e n t i a l l y s a t u r a t e d a t room t e m p e r a t u r e a t Na20/EG r a t i o s > 0 . 0 2 ( ) . Above t h e s a t u r a t i o n r a t i o t h e Na2C03 a c t s a s an i n e r t d i l u e n t . Although r e a c t i o n p e r i o d s were l i m i t e d t o 21 d a y s , t h e r e was no i n d i c a t i o n t h a t p r o d u c t s o t h e r t h a n EG-SS would form. As s e e n i n F i g u r e 3, powder X-ray d i f f r a c t i o n showed t h a t EG-SS Ί

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Figure 2.


SiO /EG versus Na O/EG

for the system SiO :Na CO


:EG.


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20.0

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Figure 3. X-ray powder d i f f r a c t i o n patterns f o r EG-SS prepared from the Si0 :NaOH:EG system

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p r o d u c t s from b o t h systems (NaOH and Na2C03) were e x t r e m e l y crystalline. I n s p e c t i o n o f a pure EG-SS sample by s c a n n i n g e l e c t r o n m i c r o s c o p y showed r e g u l a r c u b o c t a h e d r a up t o 25 m i c r o n s i n d i a m e t e r ( F i g u r e 4 ) . C h e m i c a l a n a l y s i s o f t h e p r o d u c t s from e i t h e r system showed e s s e n t i a l l y no i n c o r p o r a t i o n o f sodium u n l e s s a l u m i n i u m was p r e s e n t , when sodium was p r e s e n t i n amounts a p p r o p r i a t e t o b a l a n c e t h e framework c h a r g e , as has been r e p o r t e d previously( , 8) 2


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I t i s d i f f i c u l t t o d e t e r m i n e t h e r o l e o f t h e EG i n t h e s e s y s t e m s . C l e a r l y i t i s a r e a c t a n t s i n c e , a t t h e l i m i t , t h e amount o f EG p r e s e n t g o v e r n s t h e y i e l d of EG-SS. A t low S 1 O 2 / E G r a t i o s i t would appear t h a t EG had a s i m i l a r s o l v a t i o n b e h a v i o u r t o t h a t o f water i n t y p i c a l hydrothermal z e o l i t e syntheses. However, a t h i g h S 1 O 2 / E G r a t i o s a p o s s i b l e c o m p a r i s o n would be w i t h p n e u m a t o l y s i s ^ ) where r e a c t i o n s t a k e p l a c e n o t i n e x c e s s s o l v e n t b u t i n t h e p r e s e n c e o f s m a l l amounts o f r e a c t i v e v o l a t i l e s w h i c h t r a n s p o r t t h e r e a c t a n t s t o the c r y s t a l l i s i n g s u r f a c e . T h i s i s s u p p o r t e d by t h e f o r m a t i o n o f r e l a t i v e l y l a r g e r e g u l a r c r y s t a l s o f EG-SS, s u g g e s t i n g t h a t they grow from s o l u t i o n , and i n d i c a t e s t h a t t h e EG does a c t as a s o l v e n t t o t r a n s p o r t the s i l i c a t o t h e c r y s t a l l i s i n g s u r f a c e . This solvent need n o t n e c e s s a r i l y be more than a t h i n l a y e r over the growing s u r f a c e as l o n g as t h e r e i s s u f f i c i e n t t o b r i d g e t h e amorphous s i l i c a p a r t i c l e s and t h e EG-SS c r y s t a l s . As t h e S 1 O 2 / E G r a t i o i n t h e r e a c t a n t s approaches t h e c o m p o s i t i o n a l l i m i t o f 5.81, and a l a r g e p r o p o r t i o n o f t h e EG i n i t i a l l y p r e s e n t becomes i n c o r p o r a t e d i n t o t h e EG-SS s o l i d , t h e Na20/EG r a t i o i n c r e a s e s r a p i d l y . E v e n t u a l l y t h e Na20/EG r a t i o r i s e s t o the p o i n t where a p p a r e n t l y no f u r t h e r EG-SS f o r m a t i o n o c c u r s . At t h i s p o i n t , t h e r e m a i n i n g EG i s presumably s a t u r a t e d w i t h sodium s i l i c a t e and c o n d i t i o n s become u n f a v o u r a b l e f o r f u r t h e r c o n v e r s i o n o f t h e amorphous s i l i c a . I t s h o u l d be n o t e d t h a t z e o l i t e s w i l l form from r e a c t a n t g e l s w i t h v e r y low water c o n t e n t s a l t h o u g h r e a c t i o n r a t e s a r e low. A l s o , t h e c o n v e r s i o n o f t h e z e o l i t e c h a b a z i t e i n t h e absence o f added water t o g i v e a range o f o t h e r more compact framework s t r u c t u r e s has been r e p o r t e d . P a r t i c u l a r l y r e l e v a n t was t h e c o n v e r s i o n o f a s i l i c a c e o u s sodium-form o f c h a b a z i t e t o nosean (sodalite) at ca. 300°C. ( 1 2 )

Removal of Occluded Ethylene G l y c o l . Since the s m a l l e s t cross s e c t i o n o f t h e EG m o l e c u l e i s g r e a t e r than t h e f r e e d i m e n s i o n o f t h e 6-window o f t h e s o d a l i t e cage, t h e r e m o v a l o f o c c l u d e d EG t o y i e l d a p u r e S 1 O 2 s o d a l i t e was n o t s t r a i g h t f o r w a r d . I n i t i a l l y removal was attempted by c a l c i n a t i o n i n a i r o r i n oxygen b u t t h e s o d a l i t e became b l a c k , w i t h t h e e v o l u t i o n o f l a r g e amounts o f v o l a t i l e s , and i t remained b l a c k even a f t e r b e i n g h e a t e d t o 900°C f o r s e v e r a l d a y s . The f o r m a t i o n o f a r e s i s t a n t b l a c k p r o d u c t on c a l c i n a t i o n i s i n c o n t r a s t t o a n o t h e r r e p o r t ^ ) that c a l c i n a t i o n o f EG-SS i n a i r a t 500°C y i e l d e d a w h i t e p r o d u c t . T h e r m o g r a v i m e t r i c a n a l y s i s showed t h a t t h e m a j o r i t y o f t h e EG was l o s t b u t a s i g n i f i c a n t carbonaceous r e s i d u e remained. The X - r a y d i f f r a c t i o n p a t t e r n o f t h e b l a c k s i l i c a s o d a l i t e showed no change e x c e p t t h a t t h e peaks became s i g n i f i c a n t l y b r o a d e r . T h i s suggests t h e g e n e r a t i o n o f some degree o f s t r u c t u r a l d i s o r d e r o r t h e


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Figure 4. Scanning electron micrograph of EG-SS prepared from the SiO :NaOH:EG system.



15. BIBBYETAL.


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g e n e r a t i o n o f d e f e c t s a r i s i n g from the i n t e r n a l f o r c e s g e n e r a t e d by the d e c o m p o s i t i o n p r o d u c t s o f t h e EG, which w i l l have a g r e a t e r volume than t h a t o f t h e p a r e n t m o l e c u l e . Water g e n e r a t e d d u r i n g t h e d e c o m p o s i t i o n may a l s o promote some s t r u c t u r a l breakdown. A d e t a i l e d i n v e s t i g a t i o n of the v o l a t i l e decomposition products p r o d u c t s was c a r r i e d o u t u s i n g TD/MS. The r e s u l t s o f h e a t i n g a sample o f EG-SS a t 10°C/minute a r e shown i n F i g u r e 5. A t c a . 400°C t h e r e was r a p i d e v o l u t i o n o f l a r g e q u a n t i t i e s o f water, c a r b o n monoxide, c a r b o n d i o x i d e , and hydrogen. The b l a c k carbonaceous p r o d u c t c l e a r l y s t i l l c o n t a i n e d oxygen as c a r b o n o x i d e s s t i l l c o n t i n u e d t o be e v o l v e d as t h e temperature was i n c r e a s e d , p e a k i n g a g a i n between 600°C and 700°C. Carbon monoxide p r o d u c t i o n c o n t i n u e d t o r i s e from c a . 800°C (not shown h e r e ) , p o s s i b l y due t o t h e r e d u c t i o n o f t h e S 1 O 2 framework by t h e i n t i m a t e l y a s s o c i a t e d carbonaceous m a t e r i a l . The carbonaceous p r o d u c t a l s o dehydrogenated a t t h e h i g h e r t e m p e r a t u r e s , t h e y i e l d o f hydrogen p e a k i n g between 600°C and 700°C. The l a c k o f s u c c e s s i n removing t h e r e m a i n i n g carbonaceous m a t e r i a l by o x i d a t i o n i n a i r i s n o t s u r p r i s i n g i n view o f t h e d i a m e t e r o f t h e 6 - r i n g opening ( c a . 2.3 A) and c r o s s - s e c t i o n a l d i a m e t e r o f t h e oxygen m o l e c u l e (2.8 A ) . However, t h e r e have been s t u d i e s (10,11) o f t h e e n c a p s u l a t i o n i n z e o l i t e s o f m o l e c u l e s which, under normal c o n d i t i o n s o f temperature and p r e s s u r e , c o u l d n o t t h a t oxygen can be p e n e t r a t e t h e framework. e n c a p s u l a t e d i n t h e s o d a l i t e cage o f zeolite-Α and t h a t argon and k r y p t o n ( d i a m e t e r s 3.8 and 3.9 A r e s p e c t i v e l y ) c a n be e n c a p s u l a t e d in sodalite.^ ^ A sample o f EG-SS was p y r o l y s e d i n vacuo a t a h e a t i n g r a t e o f ca. 2°C/minute from 300°C t o 700°C. The r e s u l t a n t b l a c k p r o d u c t was t h e n t r e a t e d w i t h h i g h p r e s s u r e oxygen f o r 15 minutes a t c a . 400°C. A f t e r t h i s t r e a t m e n t , t h e d e c a p s u l a t e d p r o d u c t s e v o l v e d on h e a t i n g were a n a l y s e d u s i n g TD/MS. A f t e r t h e f i r s t t r e a t m e n t , o n l y c a r b o n d i o x i d e and a s m a l l amount o f oxygen were e v o l v e d w i t h no i n d i c a t i o n of c a r b o n monoxide. R e p e a t i n g t h e h i g h p r e s s u r e oxygen p r o c e d u r e produced a sample which e v o l v e d both oxygen and c a r b o n d i o x i d e i n s i m i l a r q u a n t i t i e s ( F i g u r e 6 ) . A f t e r 5 c y c l e s , a sample was p r o d u c e d which e v o l v e d m a i n l y oxygen and which was a l i g h t grey i n colour. A f t e r p y r o l y s i s , i t appeared t h a t most o f t h e s o d a l i t e cages s t i l l c o n t a i n e d some carbonaceous m a t e r i a l . On t r e a t m e n t w i t h oxygen a t h i g h t e m p e r a t u r e s , some degree o f oxygen e n c a p s u l a t i o n o c c u r r e d w i t h t h e oxygen r e a c t i n g w i t h t h e c a r b o n t o g i v e c a r b o n dioxide. As shown i n F i g u r e 6, t h i s décapsulâtes from 400°C. On r e p e a t i n g t h e c y c l e , t h e same r e a c t i o n o c c u r r e d b u t t h i s time t h e r e were more i n i t i a l l y empty s o d a l i t e cages which now became o c c u p i e d w i t h oxygen o n l y and thus on d e c a p s u l a t i o n b o t h oxygen and c a r b o n d i o x i d e e v o l v e d . The r a t i o o f oxygen t o c a r b o n d i o x i d e i n c r e a s e d w i t h each c y c l e as t h e carbonaceous m a t e r i a l was removed as c a r b o n d i o x i d e . Water was n o t o b s e r v e d as any water formed from hydrogen a s s o c i a t e d w i t h t h e carbonaceous r e s i d u e would be d e s o r b e d a t 400°C or lower d u r i n g t h e h i g h p r e s s u r e oxygen t r e a t m e n t as t h e water m o l e c u l e r e a d i l y p a s s e s through t h e 6 - r i n g o p e n i n g . The c o l o u r o f the m a t e r i a l darkened s l i g h t l y d u r i n g d e c a p s u l a t i o n . T h i s was p r o b a b l y due t o t h e g a s - s a t u r a t e d s o d a l i t e h a v i n g a h i g h e r


ZEOLITE SYNTHESIS


218

Figure 6. Ion signal versus temperature for pyrolysed EG-SS containing encapsulated 0« and CCL.



15.

BIBBY ET AL.

219


r e f r a c t i v e i n d e x than t h a t of the d e c a p s u l a t e d m a t e r i a l . The l i g h t s c a t t e r i n g power of the s a t u r a t e d s o d a l i t e would, t h e r e f o r e , be h i g h e r and as a r e s u l t the powdered sample appeared l i g h t e r i n colour. S i n c e c a r b o n d i o x i d e décapsulâtes from 400°C, an extended t r e a t m e n t i n h i g h p r e s s u r e oxygen a t t h a t temperature s h o u l d be e f f e c t i v e i n removing the carbonaceous r e s i d u e i n one s t e p . A p y r o l y s e d sample of s i l i c a s o d a l i t e was h e a t e d a t 400°C i n h i g h p r e s s u r e oxygen f o r 64 h o u r s . The gases s u b s e q u e n t l y d e c a p s u l a t e d c o n t a i n e d p r e d o m i n a n t l y oxygen w i t h a s m a l l amount of c a r b o n dioxide. T h i s experiment c o n f i r m s t h a t d u r i n g the h i g h p r e s s u r e t r e a t m e n t c a r b o n d i o x i d e can d e s o r b and be r e p l a c e d by oxygen. However, the sample was s t i l l b l a c k a f t e r 64 hours and s u b s t a n t i a l l y l o n g e r times - o r p o s s i b l y h i g h e r temperatures would be r e q u i r e d f o r a l l of the c a r b o n t o be o x i d i s e d and f o r the c a r b o n d i o x i d e t o be d e s o r b e d and r e p l a c e d w i t h oxygen. C a u t i o n has t o be used i n the h i g h p r e s s u r e t r e a t m e n t . As the s t r u c t u r e becomes d e p l e t e d of c a r b o n i t tends t o c o l l a p s e t o an amorphous s o l i d i f temperatures and p r e s s u r e s a r e i n c r e a s e d t o o rapidly. Conclusion The c r y s t a l l i s a t i o n f i e l d s f o r s y n t h e s i s of s i l i c a s o d a l i t e from two non-aqueous systems have been d e t e r m i n e d . The s i l i c a s o d a l i t e s y n t h e s i s e d i s i n a form c o n t a i n i n g e t h y l e n e g l y c o l i n the s o d a l i t e cages. I t has a l s o been shown p o s s i b l e t o remove the e t h y l e n e g l y c o l from the s o d a l i t e cages u s i n g a c o m b i n a t i o n o f p y r o l y s i s f o l l o w e d by r e p e a t e d c y c l e s o f h i g h temperature, h i g h p r e s s u r e oxidation. Acknowledgments We

thank N e i l M i l e s t o n e f o r h e l p f u l and c o n s t r u c t i v e

comments.

References

1.

Barrer, R.M., "Hydrothermal Chemistry of Zeolites"; Academic Press: New York, 1982. 2. Bibby, D.M. and Dale, M.P. Nature 1985, 317, 157. 3. Richardson, J.W. Jr., Pluth, J.J., Smith, J.V., Dytrych, W.J. and Bibby, D.M., J. Phys. Chem. (In Press). 4. Parker, L.M. and Patterson, J.E., Report No. 2330, DSIR, Chemistry Division, New Zealand, 1983. 5. Baerlocher, C. and Meier, W.M., Helv. Chim. Acta 1969, 52, 1853. 6. Perry, J.H. and Chilton, C.H., "Chemical Engineers Handbook", McGraw H i l l : New York, 1973. 7. Stephen, H. and Stephen, Τ., "Solubility of Inorganic and Organic Compounds"; Pergamon Press: New York, 1963, Vol. 1, Part 1. 8. van Erp, W.A., Kouwenhoven, H.W. and Nanne, J.M., Zeolites 1987, 7, 286. 9. Ciric, J., J. Colloid and Interface Sci., 1968, 28, 315.


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10. Fraenkel, D., Ittah, B. and Levy, Μ., "Zeolites", Eds. Drzaj, B., Hocevar, S. and Pejovnik, S., Elsevier Science Publishers: Amsterdam, 1985. 11. Barrer, R.M. and Vaughan, D.E.W., J. Phys. Chem. 1971, 32, 731.


RECEIVED December 22, 1988


Zeolite Synthesis - American Chemical Society

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