Synthesis and Characterisation of Ferrisilicate Zeolites

37

Synthesis and Characterization of Zeolites

W.

Inaoka, S. Kasahara. T. Fukushima and K.

Igawa

Chemical Research L a b o r a t o r y , Tosoh C o r p o r a t i o n , 4560 Tonda, Shinnanyo. Yamaguchi 746, Japan ABSTRACT W i t h o u t u s i n g o r g a n i c templates, h i g h s i l i c a z e o l i t e s , ZSM-5, mordenite. f e r r i e r i t e , z e o l i t e L, z e o l i t e o f f r e t i t e / e r i o n i t e , and z e o l i t e Y, have been s y n t h e s i z e d as a s i n g l e phase from t h e r e a c t a n t m i x t u r e s i n Na20-K20-A1 O3 -Si02-H20 system. The c o m p o s i t i o n range o f t h e r e a c t a n t m i x t u r e s s u i t a b l e f o r t h e c r y s t a l l i z a t i o n o f each z e o l i t e spec es was c l a r i f i e d . The s t i r r i n g c o n d i t i o n d i r i n g c r y s t a l l i z a t i o n was c r i t i c a l f o r o b t a i n i n g p u r e z e o l i t e . INTRODUCTION We d e f i n e z e o l i t e s w i t h Si02/A1203 mo a r r a t i o > 5 as h i g h s i l i c a z e o l i t e s . These,

t y p i c a l l y e x e m p l i f i e d by ZSM-5,

catalysts.

p l a y an i m p o r t a n t r o l e as i n d u s t r i a l

S t u d i e s t o a p p l y them as hydrophobic adsorbents

have a l s o been

conducted. From a commercial p o i n t o f view,

i t i s important t o f i n d the conditions f o r

s y n t h e s i z i n g h i g h s i l i c a z e o l i t e s w i t h o u t u s i n g any o r g a n i c templates. a l s o i m p o r t a n t t o s t u d y t h e z e o l i t e f o r m a t i o n mechanism i n v o l v e d [1.2].

It i s For

t h e p r e p a r a t i o n o f z e o l i t e c a t a l y s t s , d e a l u m i n a t i o n i s t h e main t e c h n i q u e . New pores w i t h a d i a m e t e r o f 40-200

8

have been induced i n d e a l u m i n a t i n g z e o l i t e Y

by a h y d r o t h e r m a l t r e a t m e n t . The p r e s e n t paper d e s c r i b e s s y n t h e s i s s t u d i e s f o r t h e h i g h s i l i c a z e o l i t e s w i t h o u t u s i n g o r g a n i c t e m p l a t e s as w e l l as t h e i r characterization. EXPERIMENTAL

SYNTHESIS For each s y n t h e s i s , a r e a c t a n t m i x t u r e was p l a c e d i n a s t a i n l e s s a u t o c l a v e w i t h an a g i t a t o r . 90'-200°C Zeolite

for was

The c r y s t a l l i z a t i o n was c a r r i e d o u t i n a t e m p e r a t u r e range

20-72 h. identified

The s o l i d p r o d u c t was f i l t e r e d , by

powder X-ray

washed and d r i e d .

d i f f r a c t i o n measurement.

a n a l y s i s was conducted by atomic a d s o r p t i o n s p e c t r o m e t r y .

Chemical

38 W. Inaoka, S. Kasahara, T. Fukushima and K. Igawa

DEALUMINATION NaY of Si02/A1203 = 5.6 was dealuminated by ion exchanges i n NH4N03 solution, calcination and HC1 treatment. The final Si02/A1203 ratio was 680 by chemical analysis. The pore size distribution was measured by N2 adsorption, Hg porosimetry and electron microscopy. The details have been described previously [ 3 ] . RESULTS AND DISCUSSION High silica zeolites, ZSM-5, mordenite, ferrierite, zeolite L, zeolite offretite/erionite, and zeolite Y, could be crystallized as a single phase. Clinoptilolite and dachiardite, which have almost the same composition as natural mordenite, were not crystallized. Zeolite L and zeolite offretite/erionite were crystallized not in Na' but in a bialkali Na+-Kt system. Fig.1 is a triangular diagram of the Na20-A1203-Si02 system which shows the reactant composition range for each zeolite species as a single phase. The composition of mother liquor of zeolite slurry was found to be almost Na20.3SiO2.nH20. The vertical line shows the Si02/A1203 ratio of zeolite. Therefore, it is possible to calculate the Si02/A1203 ratio of zeolite crystallized from the reactant composition, that is, the value on the vertical line where the vertical line and the line passing through the reactant composition and Si02/Na20 = 75/25 intersect. The maximum Si02/A1203 ratio of zeolite was 50 and the solid product with Si02/A1203 > 50 was crystalline silicates such as kenyaite and quartz. The starting material, especially the silica source, and the stirring condition during crystallization were found to affect not only the rate of crystallization but also the crystallization area of high silica zeolites, while water content in a reactant mixture was found not to be critical. ZSM-5 ZSM-5 was the most siliceous zeolite synthesized in this experiment and its Si02/A1203 ratio could be varied widely from 20 to 50 by changing the reactant composition, mainly the Si02/A1203 ratio. ZSM-5 was crystallized under stirring condition not under static condition. Typical synthesis conditions for ZSM-5 were as follows: the composition of reactant mixture is 6Na20'A1203'50Si02'1250H20 and the crystal 1 ization occurred at 165OC for 72 h under stirring with peripheral speed of 1 m/s. The apparent activation energy for synthesizing ZSM-5 with SiO2/Al203 = 25 was 16.9 kcal/mol for nucleation and 21.9 kcal/mol for crystallizatioh, compared with 25.6 kcal/mol and 19.4 kcal/mol synthesized by using tetrapropylammonium (TPA) ion, respectively [ 4 ] .

Synthesis and Characterization of Zeolites 39

F i g . 1. z e o l it e s .

Composition diagram f o r t h e r e a c t a n t f o r s y n t h e s i s o f h i g h s i l i c a

SiO2

A

7

VAIratio of

20

\

coexisting phase: quartz, sodium polysilicate, Z S M - ~

coexisting phase: analcime

Na2O

__t

F i g . 2. Composition diagram f o r t h e r e a c t a n t and s u i t a b l e t e m p e r a t u r e f o r s y n t h e s i s o f h i g h s i l i c a mordenite.

40 W. Inaoka, S. Kasahara, T. Fukushima and K. Igawa

The difference in activation energy for nucleation suggests that there are many more nuclei created in the Na' system than i n the TPA' system. MORDENITE Mordenite with Si02/A1203 ratio of 10-20 was synthesized and crystallization conditions were studied in detail [ 5 ] . Fig. 2 is a triangular diagram showing reaction conditions and products. The circled area designates the region in which pure mordenite is obtained, mordenite of a given composition is produced along the dashed line, and figures on the dashed line give Si02/A1203 ratios. Temperature affects not only the rate of crystal1 ization but also the crystallization area of high silica mordenite. Mordenite was crystallized irrespective of stirring and static condition. The crystal size was controlled from 0.05 to 3 um in diameter by changing stirring condition and temperature.

FERRIERITE Ferrierite with but under stirring ferrierite is very be extended by the the 'K utilization Na' ion.

Si02/A1203 ratio of 12-20 was crystallized not under static condition. The region of reactant composition suitable for limited in the Na20-A1203-Si02 system (Fig. 1). but it can copresence of 'K ion in the reactant mixture. Table 1 shows factor and ferrierite has a higher affinity for K+ than for

Table 1. Reactant and ferrierite composition 'K utilization reactant mixture ferrierite Si02/A1203 Na/A1 K/A1 % Si02/A1203 Na/A1 K/A1 19.6 19.6 19.4 18.5

1.41 1.24 0.70 1.04

0.35 0.82 1.05 0.69

Synthesis conditions : H20/Si02

18.2 17.4 17.9 17.2 =

0.65

0.22

0.21 0.31

0.37 0.79 0.91 0.69

100 96 87 100

20, 18OoC for 72 h under stirring condition.

ZEOLITE L AND ZEOLITE OFFRETITE/ERIONITE 'K ion is necessary for the crystallization of pure zeolite L and of pure offretite/erionite (o/e), because their framework structure is based on the cancrinite cage occupied by the 'K ion [ 6 ] . The )'KtaN(/ ratio in the reactant composition was 0.6-0.8 for obtaining pure zeolite L and 0.2-0.8 for zeolite o/e. Si02/A1203 ratio of zeolite L and of o/e was 5-7 and 6-10, respectively. The intergrowth of offretite and erionite in zeolite o/e was confirmed by electron diffraction patterns.

Synthesis and Characterization of Zeolites 41

ZEOLITE Y High s i l i c a z e o l i t e Y has been b e l i e v e d t o be a t y p i c a l z e o l i t e which can be c r y s t a l l i z e d o n l y under s t a t i c c o n d i t i o n w i t h seed c r y s t a l s o r by a g i n g t h e r e a c t a n t m i x t u r e a t low temperature [ 7 ] . process shown i n Fig.3, a l u m i n o s i l i c a t e gel,

However,

according t o t h e Tosoh

u s i n g c l e a r aqueous n u c l e i s o l u t i o n and homogeneous

h i g h s i l i c a z e o l i t e Y w i t h a Si02/A1203 r a t i o o f up t o

6.2 c o u l d be c r y s t a l l i z e d under s t i r r i n g c o n d i t i o n w i t h i n a s h o r t t i m e [ 8 ] . I t has been observed by TEM, NMR and a d s o r p t i o n measurements t h a t z e o l i t i c n u c l e i 0

w i t h a f a u j a s i t e s t r u c t u r e (50 A ) a r e formed i n c l e a r aqueous s o l u t i o n l e a d i n g a l u m i n o s i l i c a t e g e l t o h i g h s i l i c a z e o l i t e Y. hypothesis

that

zeolite

crystallization

These r e s u l t s s u p p o r t t h e

originates

from

liquid

phase

aluminosilicates. DEALUMINATION OF ZEOLITE Y

Dealumination i s an i m p o r t a n t process t o i m -

prove t h e thermal s t a b i l i t y and r e s i s t a n c e t o a c i d o f z e o l i t e . T h i s i s one o f t h e main t e c h n i q u e s f o r p r e p a r i n g z e o l i t e c a t a l y s t s (US-Y).

New p o r e s

(mesopores) have been i n t r o d u c e d d u r i n g hydrothermal t r e a t m e n t ( F i g . 4 ) . were d i r e c t l y confirmed b y e l e c t r o n microscopy.

which

The d e n s i t y o f mesopores de-

pended on t h e degree o f d e a l u m i n a t i o n and t h e s i z e d i s t r i b u t i o n o f mesopores 0

w i t h t h e i r maximum d e n s i t y a t about 100 A i n diameter being deduced from t h e images agree approximately w i t h those o b t a i n e d by Hg p o r o s i m e t r y measurement. Mesopores may be c r e a t e d from t h e m i g r a t i o n o f S i atoms from t h e framework o f z e o l i t e toward A1 vacancies, which

makes s t r u c t u r a l d e f e c t s . The i d e a i s sup-

p o r t e d by t h e f i n d i n g t h a t mesopores were n o t observed i n Y dealuminated w i t h SiC14.

REFERENCES 1 F. Y. Dai, M. Suzuki, H. Takahashi and Y. Saito. Proc. 7 t h I n t e r n . Z e o l i t e Conf., (1986)223. 2 V. P. S h i r a l k a r and A. C l e a r f i e l d , ZEOLITES, 9(1989)363. 3 H. H o r i k o s h i , S. Kasahara, T. Fukushima, K. I t a b a s h i , T. Okada, 0. Terasaki and D. Watanabe, Nippon Kagaku K a i s h i , No.3(1989)398. 4 A. Erdem and L. B. Sand, J. Catal., 60(1979)241. 5 K. I t a b a s h i , T. Fukushima and K. Igawa, ZEOLITES, 6(1986)30. 6 D. W. Breck, Z e o l i t e M o l e c u l a r Sieves, John Wiley and Sons, New York (1974)77. 7 H. K a c i r e k and H. Lechert, J. Phys. Chem., 79(1975)1589. 8 S. Kasahara, K. I t a b a s h i and K. Igawa, Proc. 7 t h I n t e r n . Z e o l i t e Conf., (1986)185.