ba-1971-0101.ch004?src=recsys

4 Zeolite Formation from Synthetic and Natural Glasses

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R. AIELLO, C. COLELLA, and R. SERSALE Istituto di Chimica Applicata, Facoltà di Ingegneria, Università di Napoli, Italy The formation of zeolites from glasses has been investigated systematically. Synthetic sodic glasses with variable SiO / Al O or Na O/Al O ratios have been considered, together with synthetic, alkali-rich glasses obtained by melting natural products—i.e., leucite—with alkalis, and natural glasses (pumices). Zeolites such as zeolite A, Na-P, analcite, basic sodalite, and faujasite have been obtained. The influence of different factors affecting the transformation of glass to zeolite have been examined. The kinetics of zeolite formation have been followed, and the chemical composition of the mother liquors at different reaction times were determined. The existence of a gel as an intermediate stage of the glass-zeolite transformation has been admitted. 2

2

3

2

2

s

TJor a long time, the Institute of Applied Chemistry of Naples University has been systematically investigating the zeolitization process of glasses, either volcanic (7) or synthetic, with composition near (8, 9) or different (4) from that of the natural ones. This paper refers to the most recent results obtained from studying the zeolite formation from synthetic sodic glasses with variable S i 0 / A1 0 or N a 0 / A l 0 ratios, semisynthetic glasses prepared by melting leucite with sodium carbonate, and natural glasses (pumices). 2

2

3

2

2

3

Experimental Synthetic glasses have been prepared by melting and subsequent quenching in distilled water of suitable oxide mixtures. The granulated glasses were oven-dried at 110 °C and subsequently ground. In this way, 2 series of glasses were prepared, thefirstwith N a 0 / A l 0 ratio = 1 and S i 0 / A l 0 ratio variable between 1 and 6, the second with S i 0 / A1 0 ratio = 4 and N a 0 / A l 0 ratio variable between 1 and 4. The 2

2

2

3

2

2

3

3

2

2

2

3

51 In Molecular Sieve Zeolites-I; Flanigen, E., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

52

M O L E C U L A R SIEVE ZEOLITES

1

c o m p o s i t i o n of these glasses, d e t e r m i n e d b y c h e m i c a l analysis, is specified i n the N a 0 - A l 0 3 - S i 0 2 d i a g r a m i n F i g u r e 1. 2

2


sio

A1 0 2

N*2/llfe0b

3

Figure

N o n e of

2

=1

N

a

1. Molecular composition synthetic glasses examined

the samples i n v e s t i g a t e d , tested b y

2 °

of

x-ray, showed

any

presence of arcs. T h e s e m i s y n t h e t i c glasses w e r e o b t a i n e d b y m e l t i n g m i x t u r e s of l e u c i t e f r o m R o c c a m o n f i n a , I t a l y , a n d s o d i u m carbonate.

T h e samples

tested h a v e the m o l e c u l a r c o m p o s i t i o n i n d i c a t e d i n T a b l e I. R i o l i t i c p u m i c e s f r o m L i p a r i , I t a l y ( T a b l e I I ) , s e r v e d as n a t u r a l glass samples. A l l the glasses, w h e n not o t h e r w i s e specified, w e r e s i e v e d at 256 m e s h . G l a s s samples w e r e m i x e d w i t h N a O H solutions of different c o n c e n t r a t i o n i n p e r f e c t l y c l o s e d T e f l o n containers. T h e s e containers w e r e p l a c e d i n a n a i r - t h e r m o s t a t e d o v e n at v a r i a b l e t e m p e r a t u r e f o r a g i v e n t i m e a n d r o t a t e d at 33 r p m . T h e r a t i o b e t w e e n the w e i g h t of the glass a n d the w e i g h t of the w a t e r c o n t a i n e d i n the a l k a l i n e contact s o l u t i o n w a s c o n s i d e r e d as the s o l i d / l i q u i d r a t i o ( S / L ) .

A t the e n d of

each

e x p e r i m e n t , the solids w e r e c e n t r i f u g e d f r o m t h e m o t h e r l i q u o r s , w a s h e d until p H ^

9, a n d o v e n - d r i e d at 1 1 0 ° C .

T h e f o l l o w i n g a b b r e v i a t i o n s i n d i c a t e the p r o d u c t s o b t a i n e d : X faujasite-type z e o l i t e ( 3 ) ; A = Β =

analcite ( I ) ; I =

Results and

zeolite A ( 2 ) ;

Ρ == z e o l i t e N a - P

= (I);

b a s i c sodalite ( I ) ; U denotes n o c r y s t a l l i z a t i o n .

Discussion

Zeolitization of Synthetic Glasses. T h e f o r m a t i o n areas of some p r o d u c t s , o b t a i n e d i n different c o n d i t i o n s f r o m b o t h series of glasses ( F i g u r e 1 ) , are s h o w n i n F i g u r e s 2 a n d 3. F i g u r e 2 refers to the series

In Molecular Sieve Zeolites-I; Flanigen, E., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

4.

AIELLO E T A L .

Table I. Na 0 2

1.98 2.95 3.94

Formation

Molecular Composition of Semisynthetic Glasses K0

Si0

2

2

0.97 0.94 0.95

Table II.

1 1 1

Symbol Sl s S3

4.05 4.03 4.02

2

Composition of Riolitic Pumices Si0 A1 0 MnO Ti0 Fe 0 FeO CaO MgO Na 0 K 0 H 0 2

2


53

from Glasses

3

2

2

3

2

2

2

70.85% 12.83 0.11 0.15 1.02 1.35 0.83 0.55 4.46 4.70 3.71 100.56

% NaOH in Ihc conlacl solution

". NaOH in the eonlacl solution

Figure 2. Formation areas of products obtained from a-f glasses treated for 36 hours with variably concentrated NaOH solutions and S/L = 1/20, at 80° and 120°C, respectively

« N a O H in t k . contact .olution

% N a O H in t h . contact solution

Figure 3. Formation areas of products obtained from dj-d^ glasses treated at 80°C with variably concentrated NaOH solutions and S/L = 1/20, for 12 and 36 hours, respectively


54


1

of glasses a - f , after t r e a t m e n t w i t h N a O H solutions of v a r i a b l e c o n c e n t r a t i o n f o r 36 hours, w i t h s o l i d / l i q u i d r a t i o =

1 / 2 0 , at 8 0 ° a n d 1 2 0 ° C ,

respectively. Z e o l i t e Ρ is p r e d o m i n a n t at b o t h temperatures.

T h i s zeolite is n o r

m a l l y present i n c u b i c f o r m . T h e t e t r a g o n a l f o r m of zeolite Ρ has b e e n o b t a i n e d p a r t i c u l a r l y f r o m glasses w i t h l o w S i 0 / A l 0 2

2

ratio, w i t h h i g h e r

3

concentrations of t h e a l k a l i n e contact s o l u t i o n a n d at h i g h e r temperatures. A n a l c i t e appears o n l y f r o m s t a r t i n g glasses w i t h h i g h S i 0 / A l 0 2

a n d at h i g h e r temperatures.

2

3

ratio

L o w temperatures f a v o r t h e f o r m a t i o n o f


z e o l i t e A , as w e l l as zeolite X , w h i c h is c o m p l e t e l y absent at 1 2 0 ° C . A t 80 ° C t h e greatest, a l t h o u g h l i m i t e d , y i e l d of zeolite X has b e e n obtained w i t h ratio S i 0 / A l 0 2

2

3

== 4. C o n s i d e r i n g t h e p r a c t i c a l interest

of the synthesis of faujasite g r o u p zeolites, w e s t u d i e d t h e z e o l i t i z a t i o n of m o r e a l k a l i n e glasses ( N a 0 / A l 0 2

a n d e q u a l to 4; glasses d - d 2

2

ratio >

3

1, S i 0 / A l 0 2

2

3

r a t i o fixed

i n F i g u r e 1 ) to investigate t h e influence of

4

the glass a l k a l i n i t y o n t h e y i e l d of zeolite X .

2

2

4

1

6

8

10

4 6 é ' 10 %NoOH In thecontact solution 1

1

Figure 4. Zeolite X percentages from d -d glasses treated at 80° C with variably concentrated NaOH solutions and S/L = 1120 for 12 (x) and 36 hours (o) 2

i


4.

Formation

AIELLO E T A L .

from

Glasses

55

T h e f o r m a t i o n areas of some zeolites o b t a i n e d b y t r e a t i n g these glasses w i t h N a O H s o l u t i o n of v a r i a b l e c o n c e n t r a t i o n , s o l i d / l i q u i d r a t i o =

1/20, at 80 ° C for 2 different lengths of t i m e , are s h o w n i n F i g u r e 3.

T h e increase of a l k a l i n i t y i n the s t a r t i n g glass c l e a r l y p r o m o t e s the f a u j a site f o r m a t i o n ; f r o m the m o r e a l k a l i n e glasses, z e o l i t e X forms the s i n g l e e v o l u t i o n phase i n w i d e zones of the zeolite A , seems to b e p r o m o t e d

fields.

Zeolite Ρ formation, unlike

at the expense of z e o l i t e X b y

the

increase of the r e a c t i o n t i m e . T h e glass a l k a l i n i t y also affects the y i e l d of zeolite X f r o m the glass; this is p a r t i c u l a r l y e v i d e n t for short r e a c t i o n t i m e . I n F i g u r e 4, the p e r c e n t a g e of z e o l i t e X i n the solids after 12 a n d Downloaded by GEORGE MASON UNIV on December 24, 2014 | http://pubs.acs.org Publication Date: August 1, 1974 | doi: 10.1021/ba-1971-0101.ch004

36 r e a c t i o n hours has b e e n p l o t t e d against the N a O H c o n c e n t r a t i o n of the contact s o l u t i o n . T h e percentage values w e r e d e t e r m i n e d b y x - r a y q u a n t i t a t i v e a n a l y sis, u s i n g m o l e c u l a r sieve 1 3 X of U n i o n C a r b i d e as reference. T h e m a x i m a of the curves, c o r r e s p o n d i n g to the highest values of the y i e l d , m o v e t o w a r d l o w e r N a O H concentrations of the contact s o l u t i o n as the a l k a l i n i t y of the s t a r t i n g glass increases. T h e m o r e a l k a l i n e glasses ( d d ) 4

3

and

also s h o w a better r e a c t i v i t y t h a n the less a l k a l i n e one ( d ) ; i n fact, 2

the y i e l d of zeolite X o b t a i n e d after 12 h o u r s of r e a c t i o n is c o m p a r a b l e w i t h the y i e l d at 36 hours for the d

3

and d

4

glasses b u t is m u c h i n f e r i o r

for d . 2

The a

values of the zeolite X samples o b t a i n e d f r o m d i - d

0

glasses

4

c o r r e s p o n d to the values of faujasites p o o r i n s i l i c a (zeolites X , S i / A l ratio

1.5)

(3).

This displacement

m a y be r e l a t e d to the b i g p H v a r i a t i o n i n the contact s o l u t i o n p a s s i n g f r o m 0 to 1 %

of N a O H .


56


1

%NaOH in the contact solution

Figure 5. a variation as function of initial NaOH concentration in the contact solutions for zeolite X samples from d glass treated at 80°C for 36 hours and S/L = 1 /20


G

h

5

10

15

time, h

60

Figure 6. Si0 and Al O concentrations in mother liquors obtained by treatment of d glass at 80°C, with 4% NaOH solution and S/L = 1 /20 at different reaction times; n.d. = not determinable 2

2

s

s

F o r a better u n d e r s t a n d i n g of the g l a s s - z e o l i t e t r a n s f o r m a t i o n m e c h a n i s m , the f o r m a t i o n k i n e t i c of zeolite X f r o m d

3

glass has b e e n f o l l o w e d

w i t h different i n v e s t i g a t i o n t e c h n i q u e s . T h e treatment c o n d i t i o n s of the glass h a v e b e e n 4 % N a O H s o l u t i o n a n d s o l i d / l i q u i d r a t i o 1/20, at 8 0 ° C . F o r this p u r p o s e , a series of i d e n t i c a l g l a s s - s o l u t i o n m i x t u r e s w a s set to react; the m o m e n t the glass w a s a d d e d to e a c h s o l u t i o n ( a l r e a d y p l a c e d i n the T e f l o n c o n t a i n e r a n d t h e r m o s t a t e d at 8 0 ° C ) w a s a s s u m e d as t i m e zero.

E a c h c o n t a i n e r was e x t r a c t e d f r o m the thermostat at the p r o -

g r a m m e d t i m e , a n d the s o l i d w a s s e p a r a t e d f r o m the m o t h e r l i q u o r . Si0

2

and A 1 0 2

3

w e r e d e t e r m i n e d g r a v i m e t r i c a l l y i n the l i q u i d s ; a l u m i n a

w a s p r e c i p i t a t e d u s i n g 8 - h y d r o x y q u i n o l i n e . T h e solids w e r e w a s h e d a n d a s m a l l p a r t w a s u s e d for electron m i c r o s c o p y investigations; the r e m a i n -


4.

Formation

AIELLO E T A L .

from

Glasses

57

i n g p a r t was d r i e d at 1 1 0 ° C a n d s u b s e q u e n t l y e q u i l i b r a t e d at 20 ° C a week on C a ( N 0 ) 3

2

saturated s o l u t i o n .

T h e p e r c e n t a g e of zeolite

for X

( b y x - r a y q u a n t i t a t i v e a n a l y s i s ) a n d the p e r c e n t a g e of w a t e r ( b y 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 ) present i n these solids w e r e t h e n d e t e r m i n e d i n the same t h e r m o s t a t e d r o o m .

T h e e x p e r i m e n t a l results are s u m m a r i z e d


i n F i g u r e s 6, 7, a n d 8.

Figure 7. Crystallization kinetic of zeolite X from d glass treated at 80°C with 4% NaOH solution and S/L = 1/20 s

5

10

15

60 time, h

Figure 8. Percentages of water present in samples obtained from d glass treated at 80° C with 4% NaOH solution and S / L = J /20 at different reaction times 3

F i g u r e 6 shows the variations w i t h t i m e of the silicate a n d a l u m i n a t e concentrations, expressed as S i 0 a n d A 1 0 , i n the m o t h e r l i q u o r . T h e f o r m a t i o n k i n e t i c of zeolite X , o b t a i n e d b y x - r a y q u a n t i t a t i v e analysis, u s i n g m o l e c u l a r sieve 1 3 X of U n i o n C a r b i d e as reference, is r e p o r t e d i n 2

2

3


58


F i g u r e 7.

T h e percentages

1

of w a t e r present i n the solids at different

r e a c t i o n times are r e p o r t e d i n F i g u r e 8. T h e 2 curves i n F i g u r e 6 c a n b e d i v i d e d i n t o 3 periods. I n the first ( u p to a b o u t 1 h o u r ) b o t h curves are ascendent; i n t h e s e c o n d ( u p to a b o u t 2 h o u r s ) t h e r e is a l e v e l i n g off i n b o t h cases, after w h i c h , i n t h i r d p e r i o d , t h e curves d i v e r g e u n t i l t h e y r e a c h p r a c t i c a l l y constant values at the e n d of t h e r e a c t i o n . C o n s i d e r i n g the c u r v e i n F i g u r e 7, zeolite X becomes detectable b y x - r a y shortly after the b e g i n n i n g of the t h i r d p e r i o d . A c o m p a r i s o n of the curves i n F i g u r e s 7 a n d 8 shows, h o w e v e r ,


a d e t e r m i n a b l e a m o u n t of w a t e r i n the solids before t h e t h i r d p e r i o d .

To

e v i d e n c e this finding, the w a t e r amounts i n the solids at different r e a c t i o n times not a t t r i b u t e d to a d s o r p t i o n b y zeolite X are i n d i c a t e d i n F i g u r e 9 as s h a d e d area. T h i s w a t e r is, i n o u r o p i n i o n , r e l a t e d to the

Figure 9. Upper curve as Figure 8. Lower curve: water percentages adsorbed by zeolite X in the same solids. Shaded area shows water percentages connected with gel

Figure 10. Electron micrographs. Samples obtained from d at 80°C with 4% NaOH solution and S/L = 1/20 for 80 (A) and 120(B) minutes 3


4.

Formation

AIELLO E T A L .

from

Glasses

59

presence of a g e l as i n t e r m e d i a t e stage i n the c r y s t a l l i z a t i o n process of zeolite X . T h e e l e c t r o n m i c r o g r a p h s i n F i g u r e 10, together w i t h t h e scales of n o n r e a c t e d

glass, s h o w

phase, a m o r p h o u s

the presence

of

a semitransparent g e l - l i k e

to the electron d i f f r a c t i o n .

R e f e r r i n g a g a i n to

the

curves i n F i g u r e 6, the first p e r i o d ( u p to a b o u t 1 h o u r ) has b e e n i n t e r p r e t e d as the i n i t i a l stage of the glass d i s s o l u t i o n ; the s e c o n d ( u p to a b o u t 2 h o u r s ) as the p e r i o d of gel f o r m a t i o n . A1 0 2

3

I n the first p e r i o d , the

r a t i o i n the m o t h e r l i q u o r r e m a i n s p r a c t i c a l l y constant

Si0 / 2

around

values of 3.4-3.6 because of a p r o b a b l e d i f f e r e n t i a l d i s s o l u t i o n of

the

glass. T h e g e l f o r m a t i o n begins a b o u t the e n d of the first p e r i o d , f o l l o w Downloaded by GEORGE MASON UNIV on December 24, 2014 | http://pubs.acs.org Publication Date: August 1, 1974 | doi: 10.1021/ba-1971-0101.ch004

i n g the s a t u r a t i o n i n S i 0

and A 1 0

2

the second p e r i o d the S i 0

2

2

of the s o l u t i o n . C o n s i d e r i n g t h a t i n

3

and A 1 0 2

3

concentrations r e m a i n almost c o n -

stant a n d t h e i r r a t i o is near that f o u n d i n the first p e r i o d , w e d e d u c e t h a t the S i 0 / A l 0 2

2

3

r a t i o of t h e g e l is a r o u n d t h e values of 3.4-3.6 g i v e n

above. A g a i n r e f e r r i n g to F i g u r e 6, w e n o t i c e that w i t h i n 2 to 3 h o u r s , the A1 0 2

3

concentration

concentration

begins

remains

to decrease c o n s i d e r a b l y , w h i l e the

p r a c t i c a l l y constant.

This

indicates

g i n n i n g of f o r m a t i o n of zeolite X n u c l e i i n the gel. f o r m a t i o n shows a r a t i o S i 0 / A l 0 2

2

a t t r i b u t e d to the g e l ; the S i 0 / A l 0 2

2

=

3

3

the

Si0

2

be-

T h e zeolite X i n

2.3, s m a l l e r t h a n the v a l u e w e

ratio i n zeolite X does not seem to

v a r y d u r i n g t h e w h o l e process of zeolite c r y s t a l l i z a t i o n . I n a d d i t i o n , t h e results s h o w n i n F i g u r e 9 suggested to us the presence of g e l i n successive stages of the process.

S t i c h e r a n d B a c h r e a c h e d analogous

conclusions

s t u d y i n g the r e a c t i o n b e t w e e n k a o l i n i t e a n d p o t a s s i u m h y d r o x i d e T h e use of a n a t u r a l p r o d u c t w i t h S i 0 / A l 0 2

2

3

ratio =

(10).

4 as a r a w

m a t e r i a l for the p r e p a r a t i o n of synthetic glasses has also b e e n s t u d i e d . L e u c i t e w a s m e l t e d w i t h s o d i u m carbonate to o b t a i n the S i , s , a n d s 2

glasses (see

3

E x p e r i m e n t a l ) . T h e s e glasses w e r e s u b m i t t e d to the z e o l i t i z a -

t i o n process i n sodic e n v i r o n m e n t , w i t h c o n d i t i o n s s i m i l a r to those u s e d for the s y n t h e t i c glasses c o n s i d e r e d above. T h e zeolites so far o b t a i n e d f r o m these glasses ( A , X , P , a n d I ) are not different f r o m those o b t a i n e d f r o m glasses c o n t a i n i n g o n l y s o d i u m ( F i g u r e s 2 a n d 3 ) . G o o d y i e l d s of zeolite X h a v e b e e n o b t a i n e d e s p e c i a l l y f r o m

the

glass richest i n s o d i u m ( s ) ; this is p r o b a b l y because of the h i g h e r a l k a 3

l i n i t y of the glass a n d the greater d i l u t i o n i n the glass of p o t a s s i u m present i n the s t a r t i n g leucite. Zeolitization of N a t u r a l Glasses.

T h e research o n the z e o l i t i z a t i o n

of n a t u r a l glasses has b e e n d e v o t e d essentially to the i n v e s t i g a t i o n of the most f a v o r a b l e c o n d i t i o n s for the c r y s t a l l i z a t i o n of the v a r i o u s zeolites obtainable. V o l c a n i c glasses a p p e a r r e m a r k a b l y versatile for the c r y s t a l l i z a t i o n of different zeolites, p r o v i d e d that the c o n d i t i o n s of treatment i n a l k a l i n e e n v i r o n m e n t are chosen p r o p e r l y . W e h a v e p a i d p a r t i c u l a r a t t e n t i o n to



60


10

1

15 20 25 %NaOH in the contact solution

Figure 11. Formation areas of products obtained from pumices (Lipari) at 65° C for 60 hours with various S/L ratios and variably concentrated NaOH solutions

100

5

30

40

50

60

70 time.h

Figure 12. Crystallization kinetics of zeolite X from pumices at 3 different finenesses, treated at 65°C with S/L = 1/25 and 18% NaOH solution Fraction passing at 320 mesh: (1) 100% (2) About 50% (3) About 25% t h e f o r m a t i o n of faujasite-type zeolites.

Starting from riolitic pumices

( T a b l e I I ) , z e o l i t e X , e v e n i f o b t a i n a b l e at a b o u t 8 0 ° C , is a l w a y s a c c o m p a n i e d at this t e m p e r a t u r e b y other phases ( 5 ) .

A t lower temperatures,

the f o r m a t i o n of z e o l i t e X is f a v o r e d i n r e l a t i o n to the other phases; this is i n agreement w i t h the results of B a r r e r et al. ( I ) o n the f o r m a t i o n fields of faujasite-type zeolite f r o m gels.

A s a n e x a m p l e , the f o r m a t i o n areas


4.

AIELLO E T A L .

Formation

from

61

Glasses

of some zeolites from riolitic pumices at 65°C are shown in Figure 11. In this case, because of the fixed chemical composition of the starting glass, the NaOH concentration in the contact solution and the solid/liquid ratio are considered variables. The shaded area refers to the conditions which permit zeolite X to be obtained unaccompanied by other phases. Figure 11 shows the influence of the solid/liquid ratio on the type of zeolite obtained. This ratio, evidently varying the S i 0 and A1 0 concentrations in the mother liquor, also influences the zeolite formation rate; with the lower solid/liquid ratios, the crystallization has not begun yet at 60 hours. Another factor which evidently affects the crystallization kinetic of the zeolites from glasses, considering that the glass dissolution is an essentially superficial reaction, is the fineness of the starting glass. For this purpose, the crystallization kinetics of zeolite X from pumices at 3 different finenesses, all treated at 65 °C with 18% NaOH solution and with solid/liquid ratio = 1/25, are reported in Figure 12. The curves were obtained by x-ray quantitative analysis, always referring to molec ular sieve 13X of Union Carbide.


2

2

3

Acknowledgment The authors thank E N I (Ente Nazionale Idrocarburi) for financial help and A. Annetta and B. Terracciano for their help in carrying out some of the experiments. Literature Cited (1) Barrer, R. M., Baynham, J. W., Bultitude, F. W., Meier, W. M., J. Chem. Soc. 1959, 195. (2) Breck, D. W., Eversole, W. G., Milton, R. M., Reed, T. B., Thomas, T. L., J.Am. Chem. Soc. 1956, 78, 5963. (3) Breck, D. W., Flanigen, Ε. M., "Molecular Sieves," p. 53, Society of the Chemical Industry, London, 1968. (4) Colella, C., Aiello, R., Chim. Ind. 1970, 52, 151. (5) Franco, E., Aiello, R., Rend. Accad. Sci. Fis. Mat. 1969, 36, 1. (6) Loewenstein, W., Am. Mineralogist 1942, 39, 92. (7) Sersale, R., Ann. Chim. Rome 1959, 49, 1111. (8) Sersale, R., Rend. Accad. Sci. Fis. Mat. 1961, 28, 317. (9) Sersale, R., Silicates Ind. 1960, 11, 1. (10) Sticher, H., Bach, R., Helv. Chim. Acta 1969, 52, 543. RECEIVED January 30,

1970.

Discussion Harry Robson ( Esso Research Laboratory, Baton Rouge, La. ) : You state that the composition of zeolite X produced is constant throughout


62


1

the c r y s t a l l i z a t i o n . T h e r m o d y n a m i c a l l y , w e s h o u l d expect t h a t S i 0 / A l 0 2

of t h e c r y s t a l s h o u l d c h a n g e as t h e c o m p o s i t i o n changes.

2

of t h e m o t h e r

Is i t possible that the crystals i n i t i a l l y f o r m e d

are

3

liquor

annealed

d u r i n g the r e m a i n d e r of the c r y s t a l l i z a t i o n treatment to p r o d u c e a u n i form product? R. A i e l l o : T h e c e l l constant of the i n i t i a l a n d final crystals was p r a c t i c a l l y i d e n t i c a l . W e therefore believe this to m e a n that o u r system w a s not i n t h e r m o d y n a m i c e q u i l i b r i u m . G. Tsitsishvili (Academy

of Sciences of the G e o r g i a n S S R , T b i l i s i ,


U S S R ) : W e h a v e s y n t h e s i z e d zeolites P , A , a n d faujasite u s i n g n a t u r a l o b s i d i a n a l u m i n o s i l i c a t e s , r e o l i t e a n d p e r l i t e . B y r e g u l a t i o n of t h e c r y s t a l l i z a t i o n process, i t is possible to o b t a i n p r o d u c t s w i t h different ratios w i t h i n one t y p e of zeolite. Izv. Akad.

Nauk

Si/Al

D e t a i l s of these results are p u b l i s h e d :

USSR, Inorg. Mater.

1965,

1, 285; 1966, 2, 1306;

5, 1848.


1969,

ba-1971-0101.ch004?src=recsys

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