Application of RDF to Synthesis of Zeolite

21

Application of RDF to Synthesis of Zeolite

Usui, K. Abe, T. Tokita, S. Imafuku and M. Ogawa Mizusawa Industrial Chemicals, Ltd. 1-21, 4-ChomeY Nihonbashi-muromachi, Chuo-ku, Tokyo 103 Japan K.

ABSTRACT The radial-distribution function (RDF) is an effective means for obtaining information on the structure of amorphous material. RDF was applied to the aluminosilicate hydrogels, which were formed by mixing and reacting sodium silicate solution with sodium aluminate solution under stirring, in order to produce NaA-zeolite crystal. It seems that all aluminosilicate hydrogels formed at the mixing, aging and heating process have similar structures comprised mainly of a 4-member chain. INTRODUCTION The radial-distribution function (RDF) specifies the density of atoms or electrons as a function of the radial distance from any reference atom or electron in the system. It can be applied to both crystalline and amorphous materials, and is especially effective for amorphous material. Previously in 1989, we reported the application o f RDF to various zeolites At that time we were interested in the and dealuminated products therefrom [I]. structural changes or decomposition of crystalline zeolites by weak acidtreatment or dealumination of the crystalline zeolites. The present study deals with the application o f RDF to the sodium aluminosilicate hydrogels, which were formed by mixing, aging and heating of sodium silicate solution with sodium aluminate solution under stirring, in order to produce NaA-zeolite crystal. PREPARATION OF SODIUM ALUMINOSILICATE HYDROGELS Raw mater i a1 s The chemical analyses of raw materials, namely sodium silicate solution and sodium aluminate solution, are as follows;

22 K. Usui. K. Abe, T. Tokita, S. Imafuku and M. Ogawa

Sodium s i l i c a t e s o l u t i o n Na20

7.82%

Si02

23.07%

Sp. G r .

Sodium a l u m i n a t e s o l u t i o n Na20 2'3 Sp. G r .

1.324

Mol r a t i o

22.81% 1.516

Mol r a t i o

Si02/Na20

Preparation

17.30%

3.04

of hydrogel

Na20/A1203

1.25

samples

0 3 The sodium s i l i c a t e s o l u t i o n was heated t o 50 C, and 350cm o f t h e s o l u t i o n

was p u t i n t o a beaker o f ca. Idm i n a water-bath. Under s t i r r i n g w i t h a s t i r r e r 3 made o f s t a i n l e s s s t e e l , ca. 260cm o f t h e sodium aluminate s o l u t i o n , which was 0

heated t o 50 C p r e v i o u s l y , was added t o t h e s i l i c a t e s o l u t i o n .

After mixing f o r

5 minutes, an a p p r o p r i a t e volume o f t h e m i x t u r e was taken o u t and f i l t e r e d immediately b y Buchner-funnel under vacuum. 0

0

The cake was washed w i t h about two

volumes o f h o t water (40 -50 C) t o t h e volume o f t h e m i x t u r e on t h e Buchner funnel.

The wet cake o r hydrogel was sample A. 0

The r e s t o f t h e m i x t u r e was

aged f o r 3 hours a t 50 C, a f t e r aging s i m i l a r l y an a p p r o p r i a t e volume o f t h e m i x t u r e was taken o u t and f i l t e r e d . as sample A. 0

The f i l t e r cake was washed b y t h e same way

The wet cake was sample B.

90 C i n two hours.

The r e m a i n i n g m i x t u r e was heated t o

A l s o a f t e r t h e heating, an a p p r o p r i a t e volume o f t h e m i x t u r e

was taken out, and sample D was prepared b y t h e same procedure as samples A and 0

Holding t h e temperature a t 90 C f o r one hour, t h e m i x t u r e o f t h e hydrogel

B.

was changed t o c r y s t a l l i n e NaA z e o l i t e , i.e.

sample D-1.

Furthermore conversely, t h e heated sodium s i l i c a t e s o l u t i o n was added i n t o t h e heated sodium aluminate s o l u t i o n .

A f t e r m i x i n g f o r 5 minutes, corresponding

t o sample A, t h e hydrogel sample was prepared as sample C. 0

Each hydrogel sample was s t o r e d i n an a i r - t i g h t vessel under r e f r i g e r a t i o n

( 7 C ) u n t i l i t was dispatched t o t h e Toray Research Center f o r t h e measurement o f RDF. The c o n d i t i o n s f o r t h e s y n t h e s i s o f NaA z e o l i t e were as f o l l o w s ; Molar r a t i o f o r t h e r e a c t i o n was Na20/Si02 1.20, H20/Na20

Si02/A1203 2.00 and

40.00.

RESULTS Samples A, B, D and D - I were observed under a scanning microscope (SEM). SEM photographs o f t h e s e samples a r e shown i n F i g s . 1 through 4. The chemical analyses o f t h e hydrogels and c r y s t a l sample are shown i n Table 1.

The

Application of RDF to Synthesis of Zeolite 23

Chemical analyses (%) of t h e h y d r o g e l s and c r y s t a l

Table 1.

Sample A Na20

15.77

Si02 2'3 H20(+) H20(-) IIO'CX~~

Si02/A1203

*

Sample B

*

Sample D

Sample D - I

Sample C

16.46

16.12

17.54

15.68

44.76

42.22

41.77

36.09

43.91

27.55

29.18

28.73

30.68

28.87

11.92 68.98(1)

12.14 65.87(1)

13.38 66.80

13.92

11.54 74.55

65.31(2)

66.00(2)

2.757

2.455

2.467

-

1.996

2.581

Molar r a t i o

F i r s t , i n o r d e r t o i n v e s t i g a t e changes i n hydrogel samples d u r i n g RDF measurement over a l o n g p e r i o d o f ca. 5 hours, samples A and B were measured f o r RDF t w i c e s e q u e n t i a l l y ; t h e moisture, H20(-), was a l s o determined t w i c e , i .e.

b e f o r e RDF and a f t e r RDF, t h e former i s s u f f i x e d as ( 1 ) and t h e l a t t e r i s s u f f i x e d as ( 2 ) .

The m o i s t u r e ( % ) o f samples A and B are shown i n Table 1; no

s i g n i f i c a n t changes a r e recognized.

Also no s i g n i f i c a n t d i f f e r e n c e i n RDF i s

shown among these samples ( 1 ) s and (2)s, as shown i n F i g s . 5 and 6. The m o l a r r a t i o o f Si02/A1203 o f hydrogels and c r y s t a l are i n reasonable agreement with p r e v i o u s works

(3, (3)

and (4).

The r a d i a l - d i s t r i b u t i o n f u n c t i o n curves o f a l l samples a r e shown i n F i g s . 5 through 10. other.

The RDF p a t t e r n s o f samples A, B, C and D a r e v e r y s i m i l a r t o each

Every hydrogel shows a s i g n o f t h e Si(A1)-0 bond a t t h e r a d i u s o f 1.6-

1.7A as a t r a c e o f a shoulder i n Figs. 5 through 10. Since t h e main peaks a r e 3.25A,

4.2-4.6A

and 7.OA,

t h e most reasonable u n i t

s t r u c t u r e o f t h e sodium a l u m i n o s i l i c a t e hydrogel i s t h e 4-member c h a i n i l l u s t r a t e d i n F i g . 11. shown i n F i g . 12.

Many 4-member chains e a s i l y f o r m s o d a l i t e cages as

I n t h e case o f a s i m p l e r s i l i c a s t r u c t u r e , t h e double 4-

member r i n g (cube) was recognized b y Sakka e t a1 (5). I t i s e n t i r e l y unexpected t h a t even a f t e r h e a t i n g , i n o t h e r words o n l y one

hour b e f o r e c r y s a l l i z a t i o n , no s i g n o f c r y s t a l l i z a t i o n appeared.

I n our n e x t

s t u d y we would l i k e t o f i n d t h e m i s s i n g l i n k between t h e hydrogel and t h e crystal.

24 K. Usui, K. Abe. T. Tokita, S. Irnafuku and M. Ogawa

SEM p h o t o g r a p h s o f sample A

Fig.1.

Fig.

2.

SEM p h o t o g r a p h s o f sample

B

Application of RDF to Synthesis of Zeolite 25

F i g . 3.

SEM photographs o f sample D

F i g . 4.

SEM photographs of

sample D - I

26

K.Usui, K. Abe, T. Tokita, S. Imafuku and M. Ogawa

Z

0

H

I-

u

Z 3

Fig.

5

RDF

of A ( I ) / A ( 2 )

LL Z 0 n

I3

m

H

a

I-

m

H

0 _I

6

H

0

a a

z

0

I 1

t-

u

z

3

LL

2 0

+ 3

I-i

RDF o f B ( 1 ) a n d B(2)

Fig.

6

m

H

a

t-

Ln 1-4

0

-I

a

1-1

0

a

Z

0

H

t-

u

z

3 LL

z

0

H

RDF o f A ( 1 ) ,B( 1 ) m i Fig.

7

(0 t o 10A)

t-

3

m

H

U

I-

m t-I

0

A

Q

H

0 Q

a

Application of RDF to Synthesis of Zeolite 27

z

0

6 00,

b-I

I

Cl 2

3

4.001

!I.

z

n

I-I

8

RDF o f

,B l)'D-l t o 20A)

2.001

1-

2 1-1

CC

0 POI

I 1

0

-2 001

,I - 4 000

4 000

-

.

I ow

J

.

I 2 wo

I

I

I6

z

0

I--I

9

RDF o f

sample C

I-

$

I4

CII I-

cn

1-1

0

z

0

H

t-

u Z

3

LL

Z 0

H

Fig.10

RDF o f

s amp e D

2 t

I4

oc in L1-1

0 J

<

CI

0

-=I U

I

0

wo

i

28 K. Usui, K. Abe, T.Tokita. S. Imafuku and M. Ogawa

F i g . 11

Scheme o f 4-membered c h a i n

F i g . 12 S o d a l i t e cage formed by t h e 4-membered c h a i n

CONCLUSION

Every sodium a l u m i n o s i l i c a t e hydrogel formed a f t e r mixing, aging and even a f t e r h e a t i n g o f aluminate i n t o s i l i c a t e s o l u t i o n o r v i c e versa has a s i m i l a r u n i t s t r u c t u r e c o m p r i s i n g a four-membered c h a i n i l l u s t r a t e d i n F i g . 11. hydrogel showed s i g n o f a S i ( A 1 ) - 0 bond a t t h e r a d i u s o f 1.6-1.7A,

Each

as a t r a c e of

a shoulder i n F i g s . 5 through 10. REFERENCES 1. K. Abe, S. Kojima, M. Ogawa, K. Usui and T. Nakazawa, The a p p l i c a t i o n o f r a d i a l d i s t r i b u t i o n f u n c t i o n t o v a r i o u s z e o l i t e s and dealuminated p r o d u c t s therefrom, Recent Research Report, ZEOLITES FOR THE N I N E T I E S , 8 t h I n t . Z e o l i t e Conf., Amsterdam, J u l y 9-14, 1989, p.231/2 2. M. Ogawa, K. Abe, K. Usui and T. Nakazawa, Nippon Kagaku K a i s h i , 1989 (1989) 358/63 3. C. L. Angel1 and W. H. Flank, M o l e c u l a r Sieves-11, Am. Chem. SOC. (1977) p.194 4. D. W. Breck, Z e o l i t e , John W i l e y & Sons I n c . (1974) p.337 5. I. Hasegawa and S. Sakka, S i l i c a t e Species w i t h Cagelike S t r u c t u r e i n S o l u t i o n s and Rapid S o l i d i f i c a t i o n w i t h Organic Q u a t e r n a r y Ammonium Ions, Z e o l i t e Synthesis (ACS Symposium S e r i e s 398) Am. Chem. SOC., Washington, DC 1989, p.140/51