7 Process of Zeolite Formation in the System N a O - A l O - S i O - H O Downloaded by GEORGE MASON UNIV on December 24, 2014 | http://pubs.acs.org Publication Date: August 1, 1974 | doi: 10.1021/ba-1971-0101.ch007
2
2
3
2
2
F R I E D R I C H Ε. S C H W O C H O W and G E R H A R D W. H E I N Z E Farbenfabriken Bayer A G , Leverkusen, West Germany
This paper is aimed at clarification of the change of concen tration with time in the liquid phase before crystallization starts. To find optimum conditions for the commercial pro duction of pure zeolites of the types A and faujasite, the reaction of fine-particle amorphous silica with sodium aluminate solution was studied at 20°, 40°, and 75°C. The liquid phase separated by filtration nucleates the zeolite types A, sodalite, phillipsite, and faujasite, depending on stirring time before liquid-solid separation. Quite similar conditions are observed in precipitated sodium aluminosilicate gels and mother liquor.
Tnterest i n understanding the reaction mechanism of the formation of synthetic zeolites grows with their technical importance. The experi ence gathered for the hydrothermal synthesis of defined zeolites remains restricted to a specific case, until an understanding of the mechanism can be presented. The type of the crystallizing zeolite is predetermined not only by the concentrations of the reaction partners, but also by addi tional factors—Si0 source, precipitation step, digestion of the gels. A c cording to Zhdanov (5), it first is necessary, in order to understand the synthesis, to replace the customary over-all ratios of the reactants by separate concentration data for the 2 phases in the heterogeneous system. Experiments i n the system precipitated sodium aluminosilicate gelsmother liquor make it probable that the lattice type of the crystallizing zeolite is predetermined mainly by the composition of the liquid phase. The importance of the liquid phase is emphasized also by Kerr ( 2 ) using zeolite A crystallization as an example. Our investigations refer to the time-dependent concentration change i n the 2 phases before crystalliza2
102 In Molecular Sieve Zeolites-I; Flanigen, E., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.
7.
SCHWOCHOW
Process of
A N DH E I N Z E
103
Formation
t i o n starts a n d t o zeolite f o r m a t i o n i n the m o t h e r l i q u o r s separated f r o m the respective s o l i d phases. Experimental F o r o u r experiments, w e selected t h e 2 f o l l o w i n g S i 0
2
sources: a m o r
p h o u s p r e c i p i t a t e d s i l i c a (specific surface a r e a : 200 m / g r a m a c c o r d i n g 2
to B E T ) a n d t e c h n i c a l w a t e r glass s o l u t i o n , o f d e n s i t y 1.33 g r a m s / m l , c o n t a i n i n g 1.7 moles o f N a 0 / 1 a n d 5.78 moles o f S i 0 / 1 . 2
Sodium alu-
2
m i n a t e , 1.36 g r a m s / m l , w a s u s e d as a s o l u t i o n c o n t a i n i n g 3.4 moles o f N a 0 / 1 a n d 2.0 moles o f A l 0 / 1 .
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2
2
3
T h e s e p a r a t i o n of s o l i d - l i q u i d phases
w a s effected via filter p a p e r ( S c h l e i c h e r & S c h u l l N o . 5 8 9 ) . W i t h i n the separated l i q u i d phases, S i 0 a c c o r d i n g to c o n v e n t i o n a l c h e m i c a l m e t h o d s . flame
photometry.
Crystalline
2
and A 1 0 2
3
were analyzed
N a 0 was determined b y 2
reaction products
were
identified b y
D e b y e - S c h e r r e r d i a g r a m s ; t h e c o m p o s i t i o n o f t h e m i x t u r e s w a s deter m i n e d b y c o m p a r i s o n w i t h d i a g r a m s o f test samples.
Table I.
System Amorphous Silica—Sodium Aluminate
Conditions Prior to Separation of Liquid Phases Temp., °C
Stirring Time, Hours
20
24
Zeolite Crystallizing from Separated Liquid Phases
Composition* of Separated Liquid Phases, _ Mole Ratios, Na 0 Al 0: Si0 2
3.67:
2
1
Main Produce
2
48
4.08:
1
No
: 0.04 Zeolite A
a = 12.29 A 0
20
Impurities
7
No
: 0.06 Zeolite A
a = 12.29iA Q
20
72
6.01:
1
No
: 0.09 Zeolite A
a = 12.30χΑ 0
2
40
3.67:
1
: 0.06 Zeolite A
a = 12.30iA
2% S o d a l i t e
0
4
40
8.92:
1
: 0.22 Zeolite A
a = 12.29 A a
40
8
67.82:
1
:55.58 F a u j a s i t e
40
16
50.00:
1
:74.17
75
2
57.59:
1
:79.13 F a u j a s i t e
a = 25.02iA 0
a = 24.77 A Q
10%
Sodalite
6
9
10% P h i l l i p site 3% Zeolite A
8% P h i l l i p site
The composition of the liquid phase depends on temperature and stirring time, as well as the corresponding zeolite type crystallizing from the separated liquid phases. a = unit cell constant. a
6
Q
In Molecular Sieve Zeolites-I; Flanigen, E., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.
104
MOLECULAR SIEVE ZEOLITES
Concentration
1
Change in the Liquid Phase
F o r o u r investigations o n s o d i u m - a l u m i n i u m - s i l i c a t e — w a t e r m i x t u r e s , w e h a v e selected c o n c e n t r a t i o n ratios i n w h i c h c r y s t a l l i z a t i o n of faujasite is b a s i c a l l y possible.
F i r s t , t h e r e a c t i o n of a m o r p h o u s p r e c i p i t a t e d s i l i c a
w i t h s o d i u m a l u m i n a t e s o l u t i o n w a s i n v e s t i g a t e d , t h e m o l e ratios b e i n g Si0 /Al 0 2
2
= 5, N a 0 / S i 0 = 0.6, a n d H 0 / N a 0 = 40 ( b a s e d o n t h e
3
2
total batch).
2
2
2
I n this system, faujasite is o b t a i n e d i n h i g h p u r i t y after a
f e w hours at 1 0 0 ° C .
I f the r e a c t i o n b a t c h is s t i r r e d at 2 0 ° , 4 0 ° , a n d 7 5 ° C
a n d s u b s e q u e n t l y t h e s o l i d p h a s e is separated f r o m t h e l i q u i d phase b y Downloaded by GEORGE MASON UNIV on December 24, 2014 | http://pubs.acs.org Publication Date: August 1, 1974 | doi: 10.1021/ba-1971-0101.ch007
filtration,
one o b t a i n s — d e p e n d i n g o n t e m p e r a t u r e a n d s t i r r i n g t i m e b e -
fore t h e s e p a r a t i o n of p h a s e s — e i t h e r s o d i u m a l u m i n a t e solutions or sod i u m silicate solutions as t h e l i q u i d phase ( T a b l e I , F i g u r e 1 ) .
These
c o n c e n t r a t i o n points are passed i n t h e l i q u i d phase d u r i n g t h e c o n t i n u o u s course of t h e s y n t h e s i s — f o r e x a m p l e , d u r i n g p r e d i g e s t i o n a n d h e a t i n g . W h i l e the S i 0 / A l 0 2
2
3
becomes p o o r i n A 1 0 2
r a t i o i n t h e s o l i d phase decreases, t h e l i q u i d phase 3
content u n t i l t h e r e is p r a c t i c a l l y n o t h i n g left b u t
sodium hydroxide solution.
T h e s o l u t i o n t h e n changes
over f r o m t h e
a l u m i n a t e side to t h e silicate side, w h i c h means t h a t i n c r e a s i n g q u a n t i t i e s of S i 0
2
are being dissolved i n the sodium hydroxide solution.
Zeolite Crystallization
from the Separated Mother
Liquors
F r o m t h e l i q u i d phases present i n t h e a m o r p h o u s S i 0 - s o d i u m a l u 2
m i n a t e system, i t is possible to o b t a i n c r y s t a l l i n e zeolites w i t h o u t t h e Nafi
C s composition of the total batch (mole ratios) Si0 /Al 0 r 5 Na 0/Si0 =0.6 H 0/Nap =40 2
2
2
3
2
2
Si0
2
Figure 1.
Concentration change in the liquid and solid phases dunng the course of zeolite synthesis
In Molecular Sieve Zeolites-I; Flanigen, E., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.
7.
SCHWOCHOW
AND
HEINZE
Process of
Formation
105
Na 0
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2
Si0
2
2°3
Al
Figure 2.
Change of concentration with time and temperature in the 2 phases, using different Si0 sources 2
s i m u l t a n e o u s presence of the a p p r o p r i a t e s o l i d phases.
I f the respective
l i q u i d phases separated f r o m the b a t c h are h e a t e d to 8 5 ° C (24 h o u r s ) , the different zeolite types A , sodalite, faujasite, a n d p h i l l i p s i t e w i l l c r y s t a l l i z e , d e p e n d i n g o n t e m p e r a t u r e a n d s t i r r i n g t i m e p r i o r to the s o l i d l i q u i d separation. T h e s e experiments s h o w c o n c l u s i v e l y that zeolite A a n d sodalite, w h i c h are p o o r e r i n s i l i c a , are o b t a i n e d f r o m the l i q u i d phase i f the solutions r e m a i n o n the a l u m i n a t e side of the c o n c e n t r a t i o n diagram.
It is o n l y after the changeover
of the l i q u i d phase f r o m the
a l u m i n a t e side to the silicate side that faujasite or p h i l l i p s i t e , b o t h r i c h e r i n s i l i c a , are o b t a i n e d .
The S i 0
2
content of the faujasite rises w i t h the
S i 0 / N a 0 r a t i o i n the l i q u i d phase. 2
2
Concentrations Our
in the Liquid Phase for Different Si0
2
findings
Sources
p e r t a i n i n g to the change of c o m p o s i t i o n i n the l i q u i d
p h a s e w i t h t i m e , as discussed i n the first section, are c o n f i r m e d i n essence w i t h i n r e a c t i o n m i x t u r e s w h i c h cause the f o r m a t i o n of faujasites p o o r i n silica—smaller S i 0 / A l 0 2
2
3
a n d larger N a 0 / S i 0 2
2
m o l e ratios i n the t o t a l
batch. F i g u r e 2 shows the change of c o n c e n t r a t i o n w i t h t i m e a n d t e m p e r ature i n the l i q u i d phase for a b a t c h w i t h the m o l e ratios S i 0 / A l 0 2
3.5, N a 0 / S i 0 2
2
=
1.35, a n d H 0 / N a 0 = 2
2
40.
2
3
=
P r i o r to c r y s t a l l i z a t i o n ,
t h e r e a c t i o n m i x t u r e s c o n t a i n i n g a m o r p h o u s s i l i c a or w a t e r glass a p p r o a c h the same final concentrations of S i 0
2
i n the l i q u i d phase. B o t h , h o w e v e r ,
m a y differ w i t h respect to the p o l y m e r i z a t i o n state of the d i s s o l v e d s i l i -
In Molecular Sieve Zeolites-I; Flanigen, E., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.
106
MOLECULAR SIEVE ZEOLITES
1
cate. T h e figures i n T a b l e I I s h o w that o n l y a p a r t of the a v a i l a b l e w a t e r glass is p r e c i p i t a t e d i n g e l p r e c i p i t a t i o n . A s s u c h , the l i q u i d phase contains at least a p a r t of the p o l y m e r i c silicates f r o m the w a t e r glass u n c h a n g e d . O n the other h a n d , the f o r m a t i o n of d i s s o l v e d silicate f r o m
amorphous
s i l i c a a n d s o d i u m h y d r o x i d e results i n essentially m o n o m e r i c
species.
Crystallization
of Faujasite or Phillipsite from Mother
of the Same Analytical
Liquors
Composition
W i t h i n the phase d i a g r a m ( F i g u r e 2 ) , o u r
findings
show a region
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w i t h i n w h i c h faujasite as w e l l as p h i l l i p s i t e m a y c r y s t a l l i z e . W h i c h of the 2 a c t u a l l y p r e d o m i n a t e s i n the c r y s t a l l i z a t i o n m i x t u r e is i n f l u e n c e d b y t h e c h o i c e of the S i 0
2
source.
F o r example, amorphous S i 0
solved i n sodium hydroxide solution ( 1 0 %
dis-
2
N a O H ) and commercially
a v a i l a b l e w a t e r glass s o l u t i o n are p r e c i p i t a t e d w i t h s o d i u m a l u m i n a t e s o l u t i o n at 2 5 ° C u n d e r e q u a l c o n d i t i o n s ( m o l e ratios S i 0 / A l 0 2
Na 0/Si0 2
2
=
2, a n d H 0 / N a 0 = 2
2
2
3
=
5,
40 i n the t o t a l b a t c h ) . A f t e r h e a t i n g
to 1 0 0 ° C ( w i t h i n 30 m i n u t e s ) , the 2 l i q u i d phases c o n t a i n the same c o n centrations of N a 0 , A 1 0 , S i 0 , a n d H 0 ( T a b l e I I I ) . A f t e r s e p a r a t i o n 2
Table II.
2
3
2
2
Change of Silica Concentration with Time in the Liquid Phases Using Different S i 0 Sources 2
Si0 Concentration (g/l) . . ^ . in Separated Liquid Phases stirring Time Prior to Liquid-Solid System: Amorphous System: Water GlassSeparation, Temp., 40° C Si0 -Sodium Aluminate Sodium Aluminate 2
n i
2
20). 2
2
3
(2) In addition, the dissolved silica must be present in a monomeric state predominantly, because otherwise phillipsite crystallizes as the main product. The favorable influence of a predigestion step on the faujasite syn thesis is known. If dissolvable silica is used, the effect of predigestion is clearly recognizable from the experiments reported in Table II, build ing up a sufficiently high S i 0 concentration in the liquid phase. In the case of rapid precipitation of gels from water glass solutions, the effect of the predigestion step cannot be the one just described. Predigestion causes the silicate micels to equilibrate within the gel in such a manner that afterward monomeric silica is split off during dissolving. Hence, it is possible to avoid the time-consuming step either by using reactive silicates for gel precipitation, such as Na Si0 · 5 H 0 ( 1 ), or by con verting a priori unsuitable silicate solutions, such as technical water glass, via depolymerization to solutions with reactive silica (3), carrying out the gel precipitation thereafter. 2
2
3
2
Literature Cited (1) (2) (3) (4) (5)
Andrews, Ε. B., Kerr, J., Whittam, T. V., Ger. Patent 1,269,111 (1964). Kerr, G. T., J. Phys. Chem. 1966, 70, 1047. Schwochow, F. E., Heinze, G. W., unpublished work. Wieker, W., Z. Anorg. Allgem. Chem. 1969, 366, 139. Zhdanov, S. P., "Molecular Sieves," p. 62, Society of the Chemical Indus try, London, 1968.
RECEIVED January 29, 1970.
In Molecular Sieve Zeolites-I; Flanigen, E., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.
108
MOLECULAR SIEVE ZEOLITES
1
Discussion Hans Villiger ( M a r t i n s w e r k G m b H , B e r g h e i m , G e r m a n y ) : Y o u m e n t i o n p h i l l i p s i t e as a f r e q u e n t l y - o c c u r r i n g i m p u r i t y . Is this r e a l l y so, or do y o u use a different n o m e n c l a t u r e ?
To
m y knowledge,
Barrer-Pl
or
L i n d e Β is o b s e r v e d d u r i n g the synthesis of L i n d e X . P h i l l i p s i t e tends to g r o w i n p o t a s s i u m - b e a r i n g systems r a t h e r t h a n the p u r e s o d i u m system. Friedrich Schwochow:
O u r d e s i g n a t i o n " p h i l l i p s i t e " means a c r y s
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t a l l i n e z e o l i t e w i t h the structure of t h e m i n e r a l p h i l l i p s i t e , w h i c h i n o u r r e a c t i o n system necessarily occurs i n the s o d i u m f o r m .
In Molecular Sieve Zeolites-I; Flanigen, E., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.
