Crystallization of Zeolites in the Presence of a Complexing Agent

5 Crystallization of Zeolites in the Presence of a Complexing Agent Part ΙI

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1

GÜNTER H. K Ü H L

2

Mobil Research and Development Corp., Central Research Division Laboratory, Princeton, N. J. A zeolite of increased SiO /Al O ratio crystallizes when the ratio of silicate to tetrahydroxoaluminate in the reaction mixture is raised by complexing aluminum. The equilibrium between the resulting complex and tetrahydroxoaluminate is pH-dependent. All complexing agents investigated but sulfate are effective to varying degrees, but only phytate provides a buffering action comparable to phosphate. Attempts are made to explain the observed effect of these variables: SiO /Al O ratio, pH, cation or cation ratio, silica source, time, concentration, and temperature. The explanation is based on the polymerization-depolymerization equilibrium, the stabilizing effect of certain cations on certain precursors, and the hypothesis that cations determine the way in which precursors are linked to form a zeolite structure. Simple precursors are probably 4-rings, double 4-rings, and double 6-rings. 2

2

2

2

3

3

*Tp he effect of phosphate, arsenate, tartrate, and salicylate on the crystallization of zeolites has been reported previously (17). The influence of other complexing agents is described herein. Zeolite synthesis has been quite empirical. Any information available will help, therefore, to understand the sequence of reactions occurPart I presented as a monograph, "Molecular Sieves," Society of the Chemical Industry, London, 1968. Present address: Mobil Research and Development Corp., Applied Research and Development Division, Paulsboro, N. J. 08066 1

2

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

64

M O L E C U L A R SIEVE ZEOLITES

1

r i n g d u r i n g c r y s t a l l i z a t i o n . I n f o r m a t i o n g a i n e d f r o m zeolite synthesis i n p h o s p h a t e - c o n t a i n i n g r e a c t i o n m i x t u r e s is p a r t i c u l a r l y v a l u a b l e because the p H is c o n t r o l l e d w e l l d u r i n g the entire c r y s t a l l i z a t i o n p e r i o d , a n d the o b s c u r i n g effect of a large excess of silicate c a n b e a v o i d e d . Experimental Reagents. S o d i u m a l u m i n a t e a n d s o d i u m m e t a s i l i c a t e w e r e s u p p l i e d b y A l l i e d C h e m i c a l C o r p . , G e n e r a l C h e m i c a l D i v i s i o n . T h e compositions were 43.3% A 1 0 , 37.7% N a 0 ; 21.9% S i 0 , 24.5% N a 0 . Sodium waterglass, o b t a i n e d f r o m P h i l a d e l p h i a Q u a r t z C o . , h a d the c o m p o s i t i o n 2 8 . 7 % S i 0 , 8 . 9 % N a 0 . C o l l o i d a l s i l i c a sol ( L u d o x L S ) was s u p p l i e d b y d u P o n t de N e m o u r s ; c o m p o s i t i o n : 3 0 . 7 % S i 0 , 0 . 2 3 % N a 0 . O t h e r s o d i u m silicate solutions w i t h different properties w e r e o b t a i n e d f r o m P h i l a d e l p h i a Q u a r t z C o . T h e y c a n b e d e s c r i b e d as f o l l o w s : 2


2

3

2

2

2

2

2

Si0

2

%

Designation Star D

26.5 29.4 36.0 31.4

C

B-W

2

%

Molar Ratio Si0 /Na 0

10.6 14.7 18.0 19.7

2.48 2.06 2.06 1.65

Na 0 2

2

2

Viscosity Centipoise 60 350 70,000 7,000

G l u c o n i c a c i d , as a t e c h n i c a l g r a d e 5 0 % aqueous s o l u t i o n , w a s o b t a i n e d f r o m M a t h e s o n , C o l e m a n , a n d B e l l ; p h y t i c a c i d , as a 7 0 % aqueous s o l u t i o n , f r o m K & K L a b o r a t o r y , P l a i n v i e w , Ν. Y . G e i g y I n d u s t r i a l C h e m i c a l s s u p p l i e d e t h y l e n e d i a m i n e d i ( o - h y d r o x y p h e n y lacetate ) ( Chel D P ). S o d i u m d i e t h a n o l g l y c i n a t e ( D E G N a ) was o b t a i n e d f r o m C h a s . P f i z e r & C o . , Inc. A l l the other c h e m i c a l s w e r e a n a l y t i c a l grade reagents. Preparation of Zeolites. P r e p a r a t i o n was d o n e as p r e v i o u s l y d e s c r i b e d (17). T h e t e m p e r a t u r e was i n the r a n g e 9 0 ° - 1 0 0 ° C . P o l y p r o p y l e n e flasks w e r e u s e d t h r o u g h o u t . T h e final p H w a s m e a s u r e d at a m b i e n t t e m p e r a t u r e after the c r y s t a l l i z a t i o n . A l t h o u g h different f r o m that at r e a c t i o n t e m p e r a t u r e , i t p r o v i d e s a c o n v e n i e n t c o m p a r i s o n b e t w e e n experiments. Crystallization

in the Presence of Complexing

General Considerations.

Agents

I t has b e e n r e p o r t e d p r e v i o u s l y (17)

p h o s p h a t e aids i n the p r e p a r a t i o n of h i g h - s i l i c a zeolites. c o m p l e x e d b y p h o s p h a t e (15)

that

A l u m i n u m is

a n d g r a d u a l l y released f r o m this c o m p l e x ,

t h e r e b y b e c o m i n g a v a i l a b l e for r e a c t i o n w i t h the silicate. U n d e r r e a c t i o n conditions

( p H , temperature)

the c o m p l e x m u s t p r o v i d e a sufficiently

h i g h c o n c e n t r a t i o n of h y d r o x o a l u m i n a t e to enable t h e zeolite to c r y s t a l l i z e . O n the other h a n d , the s t a b i l i t y of the c o m p l e x m u s t b e h i g h e n o u g h to p r o v i d e a l o w e r c o n c e n t r a t i o n of h y d r o x o a l u m i n a t e t h a n w i t h o u t the c o m p l e x i n g agent.

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

5.

Table I. Reaction

Mixture

Molar

Si0 / Al 0s

CA. l Al O

1 2 3 4

4.0 4.0 4.0 4.0

4.0 4.0 4.0 4.0

(10.0) ( 9.0) ( 8.5) ( 8.0)

5 6

4.0 4.0

5.6 11.2

2.05 1.52

7 8 9 10

4.0 4.0 4.0 4.0

2.0 2.0 3.0 3.0

2.48 1.97 1.97 1.47

11 12 13 14

4.0 4.0 4.0 3.74

2.12 4.24 5.29 5.91

3.77 2.38 2.09 1.93

15 16 17 18 19 20

4.0 4.0 3.74 3.74 6.0 6.0

2.04 3.06 3.80 4.75 2.04 3.06

4.35 3.24 2.68 2.34 5.42 3.95

21 22 23

4.0 4.0 4.0

1.02 3.06 5.10

5.67 2.06 1.43

24 25 26

4.0 4.0 4.0

1.02 1.60 2.00

5.68 4.00 3.50

27 28 29 30

4.0 4.0 4.0 4.0

2.0 3.0 3.0 3.0

1.66 1.33 1.17 1.00

31 32 33 34

4.0 4.0 6.0 6.0

1.0 1.0 1.0 1.0

10.28 8.76 10.44 8.94

2


Effect of Complexing Agents in the Preparation of Zeolite Y

No.

2

a 6

65

Crystallization of Zeolites

KUHL

a

2

z

Na 0/ C.A.

Ratios H 0/ Na 0

2

2

a

2

6 6

& b

Crystallization Time, Days

Diphosphate —65 5 —65 7 14 —65 —65 Sulfate 2 —77 —52 6 Oxalate —135 3 4 —170 5 —150 —200 16 Citrate 2 —110 —90 3 6 —80 — —75 EDTA —125 5 —135 6 12 —140 —130 2 —100 2 —110 Gluconate 4 —115 2 —105 —90 5 Chel D P —230 6 —210 6 11 —190 DEG-Na 6 —180 —220 9 —190 23 —220 — Phytate 4 —90 —110 30 14 —90 45 —105

Final pH 12.8 12.55 11.85 —10

Si0 / Al O 2

2

z

3.22 3.31 3.43 Amorphous

12.0 12.0

2.73 2.80

12.2 12.2 13.0(?) 11.95

2.81 3.12 2.98 3.33

12.05 12.35 12.75 10.9

2.93 3.23 3.33 Amorphous

12.4 12.2 12.5 12.6 12.2 12.0

3.04 3.25 3.19 Amorphous 3.27 3.56

12.5 12.2 13.0(?)

2.96 3.02 3.16

12.6 12.6 11.0

3.11 3.27 3.40

12.8 12.5 11.7 9.7

3.15 3.35 3.61 Amorphous

12.6 11.0 11.7 10.7

3.14 3.48 4.34 Mainly amorphous

Complexing agent. p H to which NaA10 -Na4 P2O7 solution was adjusted before addition of N a S i 0 . 2


2

3

66


It appears that the r e a c t i o n m i x t u r e m u s t h a v e a p H of 11 ±

1

0.2 or

h i g h e r for the faujasite structure to c r y s t a l l i z e , w h i c h seems to b e o w i n g to the state of the silicate i n s o l u t i o n . T h e r e f o r e , a c o m p l e x i n g agent for this a p p l i c a t i o n s h o u l d p r o v i d e a f a v o r a b l e e q u i l i b r i u m b e t w e e n its a l u m i n u m c o m p l e x a n d h y d r o x o a l u m i n a t e at a p H of 11 or h i g h e r . T h e h i g h e r the p H , the m o r e h y d r o x o a l u m i n a t e w i l l b e i n e q u i l i b r i u m w i t h the a l u m i n u m c o m p l e x .

It w i l l b e h e l p f u l , therefore, i f t h e c o m p l e x -

i n g agent c a n buffer i n t h e p r o p e r p H range. T h e a b i l i t y of a s a l t - a c i d m i x t u r e to buffer a s o l u t i o n c a n b e d e s c r i b e d best b y the d i s s o c i a t i o n


constants of the a c i d . H o w e v e r , the p K values m a y not a l w a y s b e v a l i d i n the presence of a l u m i n u m because c o m p l e x acids m a y be f o r m e d . M o s t experiments d e s c r i b e d h e r e i n w e r e c o n d u c t e d w i t h a 4.0 S i 0 / 2

A1 0 2

3

m o l a r r a t i o of the m i x t u r e . W i t h o u t c o m p l e x i n g agent, t h e faujasite

p r o d u c t of s u c h a m i x t u r e h a d a S i 0 / A l 0 2

Individual Complexing

Agents.

2

3

r a t i o of 2.81.

Experiments w i t h the

following

c o m p l e x i n g agents are s u m m a r i z e d i n T a b l e I. A p p a r e n t l y , n o t h i n g is k n o w n of

Diphosphate.

the existence

of

a l u m i n u m - d i p h o s p h a t e complexes i n the a l k a l i n e range. I n o u r experiments w i t h d i p h o s p h a t e as the c o m p l e x i n g agent, p a r t of the a l k a l i n i t y w a s n e u t r a l i z e d w i t h H C 1 b e f o r e s o d i u m m e t a s i l i c a t e w a s a d d e d (see

column 4).

D i p h o s p h a t e does h a v e a n effect o n the s i l i c a - t o -

a l u m i n a r a t i o of the p r o d u c t , b u t the p H has to b e c o n t r o l l e d

very

carefully. Sulfate forms

Sulfate.

Na[Al(S0 ) ]. 4

2

an anionic complex

with

aluminum

(3),

T h e f o r m a t i o n of this c o m p l e x is s l o w a n d c a t a l y z e d b y

O H " ions. Zeolites p r e p a r e d i n the presence

of sulfate h a v e l o w

Si0 /Al 0 2

2

3

ratios; no effect of sulfate c a n b e seen ( T a b l e I ) . Oxalate.

O x a l a t o a l u m i n a t e complexes

of the t y p e

are a m o n g the best k n o w n a l u m i n u m complexes

(1).

M [A1(C 0 )3] 3

f o u n d that oxalate c a n f o r m 2 c o m p l e x a l u m i n a t e ions. T h e [A1(C 0 ) ]~ 2

4

2

and

[A1(C 0 ) ] " 2

4

3

3

are e x t r e m e l y

2

4

L a c r o i x (18,

stable i n essentially

n e u t r a l solutions; n o t h i n g is s a i d about the s t a b i l i t y of the complexes h i g h e r p H values. T h e p

K 2

19)

complexes at

v a l u e of o x a l i c a c i d (4.19) indicates t h a t this

reagent is not a n effective buffer i n the p r o p e r p H range. B e c a u s e of t h e l o w s o l u b i l i t y of N a C 0 , larger v o l u m e s t h a n n o r m a l h a d to b e u s e d . 2

2

4

L o w - s i l i c a zeolite Y i n s t e a d of zeolite X w a s o b t a i n e d f r o m a n u m b e r of p r e p a r a t i o n s ( T a b l e I ) , i n d i c a t i n g that oxalate is c a p a b l e of r e d u c i n g the c o n c e n t r a t i o n of h y d r o x o a l u m i n a t e to some extent. Citrate.

C a d a r i u , G o i n a , a n d O n i c i u (4)

r e p o r t a n i n f l e c t i o n i n the

t i t r a t i o n c u r v e of a n a l u m i n u m - c i t r a t e s o l u t i o n w i t h h y d r o x y l ions at p H 11-12.

T h i s i n f l e c t i o n d i m i n i s h e s as the ratio of c i t r a t e to a l u m i n u m

increases, a n d disappears at c i t r . / A l =

5. T h e c o m p l e x a c i d f o r m e d at


5.

Crystallization of Zeolites

KUHL

67

l o w c i t r . / A l s h o u l d b e able to buffer i n the d e s i r e d p H r a n g e .

Indeed,

the best b u f f e r i n g a c t i o n is o b s e r v e d at l o w c i t r . / A l ( T a b l e I ) . a c i d itself is a p o o r buffer ( p

K s

=

Citric

5.4). A n ethylenediaminetetraacetate

Ethylenediaminetetraacetate.

com

p l e x of a l u m i n u m has b e e n d e s c r i b e d b y S c h w a r z e n b a c h a n d c o w o r k e r s (22).

Saito a n d T e r r e y (21)

assign the f o r m u l a H [ A l ( H 0 ) E D T A ] to 2

the a c i d f o r m . K e r r ( 12) f o u n d that this c o m p l e x is a c t u a l l y H [ A l ( O H ) 2

EDTA]

w i t h 2 a c i d functions.

T h e a c i d H [ A l ( O H ) E D T A ] forms 2

a

m o n o s o d i u m salt, N a H [ A l ( O H ) E D T A ] , at p H 4.5 a n d a d i s o d i u m salt, N a [ A l ( O H ) E D T A ] , at p H 8.0 u p o n r e a c t i o n w i t h s o d i u m h y d r o x i d e . Downloaded by GEORGE MASON UNIV on December 24, 2014 | http://pubs.acs.org Publication Date: August 1, 1974 | doi: 10.1021/ba-1971-0101.ch005

2

T h e last a c i d h y d r o g e n of e t h y l e n e d i a m i n e t e t r a a c e t i c a c i d has a p

K

of

10.26, w h i c h is q u i t e h i g h c o m p a r e d w i t h most acids. It is a p p r o a c h i n g the v a l u e for arsenic a c i d (11.60) a n d m a y b e c a p a b l e of p r o v i d i n g a l i m i t e d degree of b u f f e r i n g i n the p H range of interest. C o m p a r i s o n of the e x a m p l e pairs 15,16 a n d 19,20 ( T a b l e I )

shows

that a n increase i n t h e ratio of E D T A / A 1 f r o m 1 to 1.5 y i e l d s p r o d u c t s of significantly h i g h e r S i 0 / A l 0 2

2

3

ratios.

A greater excess of

EDTA

appears to h i n d e r the c r y s t a l l i z a t i o n . Gluconate.

G r o s s m i t h (8)

r e p o r t e d the p r e p a r a t i o n of a l u m i n u m

complexes w i t h gluconate. The

s i l i c a - t o - a l u m i n a ratios of

the

faujasite-type

gluconate-containing mixtures ( T a b l e I) Y-range.

T h e final p H values w e r e 12.2 or h i g h e r .

o b t a i n l o w e r a l k a l i n i t i e s , zeolite Β of S i 0 / A l 0 2

the final p H r e m a i n e d the same.

products

from

w e r e i n the h i g h X - or

2

3

=

low

W h e n w e t r i e d to 3.3 c r y s t a l l i z e d , b u t

T h e c r y s t a l l i t e size i n the p r e p a r a t i o n s

w i t h gluconate was generally larger t h a n i n the other examples. Ethylenediamine

di(o-hydroxyphenylacetate).

Since C h e l D P is effec

t i v e for c h e l a t i n g i r o n i n m i l d l y a l k a l i n e s o l u t i o n (7, 13),

i t was

hoped

that a c o m p l e x a n a l o g to the f e r r i c c o m p l e x is f o r m e d w i t h a l u m i n u m . T h e faujasite p r o d u c t s o b t a i n e d w i t h C h e l D P w e r e of a v e r y h i g h c r y s t a l l i n i t y a n d h a d compositions i n the l o w zeolite Y range.

T h e absence

of b u f f e r i n g a b i l i t y is e v i d e n t f r o m the fast decrease of the final p H w h e n N a 0 / C . A . is l o w e r e d to 3.5. 2

D e c r e a s i n g a l k a l i n i t y does increase the

c o m p l e x i n g a b i l i t y of C h e l D P for a l u m i n u m , as is e v i d e n t f r o m h i g h e r s i l i c a - t o - a l u m i n a ratio of the p r o d u c t .

the

T h e a m o u n t of C h e l D P

m a y h a v e b e e n a d e q u a t e o n l y i n E x a m p l e 26. Diethanolglycinate.

T h e reagent forms v e r y strong f e r r i c i o n chelates

over a b r o a d p H range, b u t is c o m m o n l y u s e d at p H 9.5 to 12.5. A l t h o u g h no d a t a o n c o m p l e x i n g a l u m i n u m w i t h this reagent h a v e b e e n f o u n d i n the l i t e r a t u r e , the c h e m i c a l s i m i l a r i t y of i r o n a n d a l u m i n u m m a d e i t a c a n d i d a t e for this study. T h e e x p e r i m e n t a l results ( T a b l e I ) i n d i c a t e that a c o m p l e x

between

a l u m i n u m a n d D E G is f o r m e d , as the s i l i c a - t o - a l u m i n a r a t i o of the p r o d -


68


u c t increases w i t h d e c r e a s i n g p H . T h e c o m p o u n d

1

does not buffer t h e

s o l u t i o n , so that c o n t r o l of the p H is difficult. Phytate.

P h y t i c a c i d is the p h o s p h o r i c a c i d ester of i n o s i t o l , h e x a -

hydroxycyclohexane.

E v e r y phosphoric

acid group

contains 2

h y d r o g e n s , so t h a t the c o m p o u n d is e x p e c t e d to buffer. t i o n w i t h a n u m b e r of cations is k n o w n (24)

acidic

Complex forma

but an aluminum complex

has n o t b e e n r e p o r t e d . T h e results of c r y s t a l l i z a t i o n i n the presence of p h y t a t e ( T a b l e

I)

i n d i c a t e t h a t p h y t a t e is b o t h a g o o d c o m p l e x i n g agent a n d a r e a s o n a b l y


g o o d buffer.

Faujasites w i t h s i l i c a - t o - a l u m i n a ratios as h i g h as those

o b t a i n e d i n the presence of p h o s p h a t e a n d tartrate c a n b e p r e p a r e d w i t h this c o m p l e x i n g agent.

T h e b u f f e r i n g a c t i o n of p h y t a t e is better t h a n

that of tartrate, b u t m a y not q u i t e r e a c h that of p h o s p h a t e . Variables

in the Crystallization

of Zeolites

Zeolites u s u a l l y are p r e p a r e d b y m i x i n g silicate a n d a l u m i n a t e s o l u tions a n d h e a t i n g the r e s u l t i n g g e l - s o l u t i o n m i x t u r e u n t i l a c o m p l e t e c r y s t a l l i z a t i o n is o b t a i n e d .

S i n c e zeolites h a v e n o n s t o i c h i o m e t r i c s t r u c

tures w i t h A l s u b s t i t u t i n g f o r S i , the c o m p o s i t i o n of the p r o d u c t d e p e n d s o n the c o m p o s i t i o n of the r e a c t i o n m i x t u r e . L i t t l e is k n o w n a b o u t t h e m e c h a n i s m of zeolite c r y s t a l l i z a t i o n . K e r r (10)

has s h o w n t h a t z e o l i t e A

crystallizes f r o m s o l u t i o n r a t h e r t h a n b y s o l i d - s o l i d t r a n s f o r m a t i o n . same a u t h o r (11)

The

f o u n d i n d u c t i o n p e r i o d s i n the c r y s t a l l i z a t i o n of z e o

lites X a n d Β a n d different g r o w t h rates of the respective n u c l e i . seeding, the i n d u c t i o n p e r i o d ( n u c l e a t i o n ) (5)

c o u l d be eliminated.

By

Ciric

f o u n d that the g r o w t h rate of zeolite A increases w i t h r i s i n g a l k a

l i n i t y , b u t the i n d u c t i o n p e r i o d seems to r e m a i n u n c h a n g e d . N o i n f o r m a t i o n is a v a i l a b l e o n the c o m p o s i t i o n

a n d s t r u c t u r e of

s o l u b l e precursors. W e f e e l t h a t observations m a d e i n b u f f e r e d r e a c t i o n m i x t u r e s are of p a r t i c u l a r v a l u e because the degree of p o l y m e r i z a t i o n of silicate a n d a l u m i n o s i l i c a t e is better c o n t r o l l e d . M o s t of our experiments h a v e b e e n c a r r i e d out i n p h o s p h a t e - b u f f e r e d

m i x t u r e s , a n d i t has to be

t a k e n i n t o c o n s i d e r a t i o n that p h o s p h a t e is also a c o m p l e x i n g agent for aluminum.

S1O2/AI2O3.

The S i 0 / A l 0 2

2

3

r a t i o (R)

of the r e a c t i o n m i x t u r e is

one of the v a r i a b l e s that c o n t r o l the m o n o m e r - p o l y m e r

equilibrium and

the c o m p o s i t i o n of the c r y s t a l l i z i n g f r a m e w o r k s t r u c t u r e ( e x a m p l e : X Y).

-»

T h i s ratio also facilitates f o r m a t i o n of c e r t a i n p r e c u r s o r structures

t h a t are r e q u i r e d for c e r t a i n zeolites to c r y s t a l l i z e . T h e n u m b e r of cations associated w i t h a p r e c u r s o r c a n be r e g u l a t e d b y c h o o s i n g the a p p r o p r i a t e R; e x a m p l e : c r y s t a l l i z a t i o n of zeolite A at R = R =

2 a n d of zeolite X at

4. A r e a c t i o n m i x t u r e m a d e w i t h p h o s p h a t e - b u f f e r e d s o d i u m a l u m i -


5.

Crystallization

KUHL

of

69

Zeolites

nate a n d s o d i u m waterglass y i e l d s Z K - 1 4 ( c h a b a z i t e s t r u c t u r e ) at R = 4 ( f i n a l p H 11.85, S i 0 / A l 0 = 3.4) a n d Z K - 1 5 ( s i m i l a r to species S ) at R — 6 ( f i n a l p H 11.65; S i 0 / A l 0 = 4.1). 2

2

2

3

2

2

3

p H . T h e p H influences the p o l y m e r i z a t i o n - d e p o l y m e r i z a t i o n e q u i l i b r i u m of the soluble aluminosilicates—i.e., the average size of these spe cies increases w i t h decreasing p H . T h i s shift i n the size d i s t r i b u t i o n of b u i l d i n g b l o c k s causes different structures to c r y s t a l l i z e ( e x a m p l e : s o d a lite - » A ) . W h e n the p H is v a r i e d i n the presence of p h o s p h a t e , zeolites of the same c r y s t a l structure b u t different S i 0 / A l 0 ratios c r y s t a l l i z e ( e x a m p l e : X - » Y ) . F u r t h e r decrease of the p H c a n cause c r y s t a l l i z a t i o n of a zeolite w i t h a different c r y s t a l structure, e v i d e n t l y r e s u l t i n g f r o m a c h a n g e i n the structure of the p r e c u r s o r ( e x a m p l e : Y - > Z K - 1 5 ) ( T a b l e I I ) . 2

2

3


1 7

1 7

Table II.

Effect of p H

Na 0

Si0

2

P0 2

b

3.55 3.11 2.87 2.72 2.60 a

a

2

Zeolites Obtained

Al 0z

Y Υ (+ Β + ZK-15) Y + Β (+ ZK-15) Z K - 1 5 + trace of Y Z K - 1 5 + trace of Y

Sodium metasilicate as the silica source,

(Product)

2

3.8 4.3 4.8 5.8 6.0

S1O2A / I2O3

=

5.18.

I n the c r y s t a l l i z a t i o n of gallosilicates at 90 ° C , w é o b s e r v e d t h a t every r e a c t i o n m i x t u r e w i t h a final p H h i g h e r t h a n about 12 y i e l d e d a sodalite structure, whereas a faujasite-type m a t e r i a l c r y s t a l l i z e d b e l o w p H 12. It is l i k e l y that, b a r r i n g a n y c o m p l i c a t i o n s , a t y p e of b u i l d i n g b l o c k s a l w a y s w i l l generate the densest structure possible. I n the s o d i u m system, the smallest b u i l d i n g b l o c k that determines a c r y s t a l structure is c o n c e i v a b l y a r i n g of 4 t e t r a h e d r a w i t h associated cations. S u c h 4 - m e m b e r rings c a n c o m b i n e to f o r m the sodalite structure. U p o n decrease of the p H , the p r e d o m i n a n t b u i l d i n g b l o c k m a y b e a d i m e r of the 4 - m e m b e r r i n g , a c u b e , also k n o w n as a d o u b l e 4 - r i n g , consisting of 8 t e t r a h e d r a a n d associated cations. C o n n e c t i n g these species i n the same w a y as the single 4-rings y i e l d s the zeolite A structure. W h e n the p H is l o w e r e d f u r t h e r , the most a b u n d a n t species m a y be a t r i m e r of the 4 - m e m b e r r i n g , a h e x a g o n a l p r i s m d o u b l e 6 - r i n g , w i t h associated cations. C o n n e c t i o n of these precursors w o u l d f o r m the faujasite structure. H o w e v e r , a c o m p l i c a t i o n arises here. I t seems difficult for the faujasite structure to a c c o m m o d a t e 96 h y d r a t e d s o d i u m ions p e r u n i t c e l l . T h e r e f o r e , this structure n o r m a l l y is o b s e r v e d o n l y i f either the n u m b e r of cations is l o w e r e d b y i n c r e a s i n g


70


the S i 0 / A l 0 2

2

3

1

ratio of the r e a c t i o n m i x t u r e or some of the s o d i u m ions

i n the m i x t u r e are r e p l a c e d b y p r e s u m a b l y s m a l l e r h y d r a t e d p o t a s s i u m ions

(25). H o w e v e r , w e f o u n d that b o t h zeolites, X a n d A , c r y s t a l l i z e f r o m a

r e a c t i o n m i x t u r e of R =

2.0 c o n t a i n i n g gluconate.

this w a y a l w a y s has a l o w S i 0 / A l 0 2

Table III. Si0 / AWt Downloaded by GEORGE MASON UNIV on December 24, 2014 | http://pubs.acs.org Publication Date: August 1, 1974 | doi: 10.1021/ba-1971-0101.ch005

2

2.0 2.0 2.06 2.0 2.0 2.0

CtHitOj/ Ah0

2

3

T h e lattice

Preparation of Low-Silica Faujasite Na 0/

Final pH

H 0/ Na 0

2

2

3

3.06 3.06 3.06 3.06 3.57 4.08

Zeolite X f o r m e d i n

ratio ( T a b l e I I I ) .

2

1.67 1.51 1.37 1.18 1.01 0.89

~140 ~200 ~170 ~200 ~200 ~200

a

0

35 25.090 25.132 65 25.064 55 50 25.029 70 25.071 Amorphous

13.0 12.75 12.9 12.5 10.9 9.4

p a r a m e t e r of one of the faujasite structures f r o m these p r e p a r a t i o n s w a s 25.132 A , e q u i v a l e n t to

=

S1O2/AI2O3

2.0 ( 6 ) .

It is d o u b t f u l t h a t the

g l u c o n i c a c i d p l a y s a n y other role t h a n t h a t of a n a c i d . T h e zeolite A structure has not b e e n o b s e r v e d i n gallosilicates. P o s s i b l y , a stable p r e c u r s o r of the c u b e t y p e cannot b e f o r m e d because of t h e larger g a l l i u m . Instead, the t r i m e r is f o r m e d i m m e d i a t e l y , l e a d i n g to the faujasite structure. I f the a s s u m p t i o n is correct t h a t the 3 precursors m e n t i o n e d exist, t h e n every single 4 - r i n g has at least 1 A l , every d o u b l e 4 - r i n g at least 2, a n d every t r i m e r at least 3 A l . T h u s , the highest S i 0 / A l 0 2

r i v e d f r o m these precursors is 6.0.

2

3

ratio de-

I n d e e d , no e v i d e n c e has b e e n f o u n d

yet t h a t A a n d X structures occur w i t h lattice parameters s m a l l e r t h a n those c o r r e s p o n d i n g to S i 0 / A l 0 2

s i l i c a sodalite (16, 20)

2

3

=

6.0. H o w e v e r , p r e p a r a t i o n of h i g h

suggests that single 6-rings c o n t a i n i n g 1 A l a n a

e a c h associated w i t h 1 t e t r a m e t h y l a m m o n i u m c a t i o n are precursors

of

s u c h a structure. A t h i g h e r R, decrease of the p H causes a h i g h e r degree of p o l y m e r i z a t i o n of the silicate a n d l o w e r c o n c e n t r a t i o n of r e a c t i v e species r e s u l t i n g i n a slower c r y s t a l l i z a t i o n of zeolite Y , f r e q u e n t l y c o n t a m i n a t e d

with

zeolite B . F u r t h e r decrease of the p H causes Z K - 1 5 to c r y s t a l l i z e . Type of Cation and Cation Ratio. T h e p o l y m e r i z a t i o n - d e p o l y m e r i z a t i o n e q u i l i b r i u m c o n c e i v a b l y c a n b e i n f l u e n c e d b y the s t a b i l i z i n g effect of c e r t a i n cations o n c e r t a i n precursors.

T h e cations present also m a y

d e t e r m i n e the w a y i n w h i c h these b u i l d i n g b l o c k s are j o i n e d to g i v e a f r a m e w o r k structure. R e a c t i o n m i x t u r e s , i d e n t i c a l except for the c a t i o n i n t r o d u c e d w i t h the p h o s p h a t e , y i e l d different p r o d u c t s at the same p H .


5.

Crystallization

KUHL

of

71

Zeolites

W h e n s o d i u m is p r e d o m i n a n t , the faujasite structure c r y s t a l l i z e s ; w h e n p o t a s s i u m is the m a j o r c a t i o n , a zeolite of c h a b a z i t e structure ( Z K - 1 4 ) is formed.

B o t h of these structures c a n b e b u i l t f r o m h e x a g o n a l p r i s m s as

the o n l y b u i l d i n g blocks.

A p p a r e n t l y the presence of the p r e s u m a b l y

s m a l l e r h y d r a t e d p o t a s s i u m ions a l l o w s a denser structure

(chabazite)

to c r y s t a l l i z e . T e t r a m e t h y l a m m o n i u m ions a p p e a r to s t a b i l i z e the precursors t h a t cause the z e o l i t e A structure to c r y s t a l l i z e . T h u s , a zeolite A s t r u c t u r e ( Z K - 4 , Z K - 2 1 , Z K - 2 2 ) is o b t a i n e d f r o m a r e a c t i o n m i x t u r e t h a t w o u l d y i e l d


a zeolite of faujasite structure i f the o n l y cations present w e r e s o d i u m (9,

16). A zeolite of p h i l l i p s i t e structure ( Z K - 1 9 ) (14,

a m i x t u r e of

S1O2/AI2O3

=

17)

is o b t a i n e d f r o m

4 to 6 w h e n the f r a c t i o n of s o d i u m i n a

r e a c t i o n m i x t u r e c o n t a i n i n g s o d i u m a n d p o t a s s i u m is i n the r a n g e 0.5-0.8.

of

T h i s denser structure is t h e r m o d y n a m i c a l l y m o r e stable t h a n

either the faujasite or c h a b a z i t e structure. It seems to p l a y the same role as zeolite Β i n the p u r e s o d i u m system

(II).

W h e n a zeolite crystallizes, the n u m b e r of c a t i o n i c charges i n c o r p o r a t e d i n the z e o l i t e structure is e q u a l to the n u m b e r o f a l u m i n u m atoms i n the zeolite f r a m e w o r k .

O b v i o u s l y , i f o n l y a s m a l l n u m b e r of cations

are a v a i l a b l e , the a m o u n t of a l u m i n u m b e i n g i n c l u d e d i n the zeolite f r a m e w o r k is l i m i t e d .

B y u s i n g cations w h o s e size prevents t h e m f r o m

b e i n g as easily i n c o r p o r a t e d as s o d i u m , one c a n l i m i t the n u m b e r

of

cations effectively a v a i l a b l e for zeolite c r y s t a l l i z a t i o n w i t h o u t affecting the p H of the r e a c t i o n m i x t u r e . If some of these l a r g e cations are i n c o r p o r a t e d i n the c r y s t a l l i z i n g zeolite, t h e y m a y f u r t h e r l i m i t the n u m b e r of c a t i o n i c charges p e r u n i t c e l l , c a u s i n g a d d i t i o n a l increase of the s i l i c a - t o a l u m i n a r a t i o of the p r o d u c t . It is i m p o r t a n t , of course, that the size a n d shape of the l a r g e cations be c o m p a t i b l e w i t h the zeolite structure d e s i r e d . I n o r d e r to p r e p a r e a h i g h - s i l i c a zeolite of faujasite structure ( S i O / a

A1 0 2

3

> 4.5) f r o m a p h o s p h a t e - c o n t a i n i n g m i x t u r e , the n u m b e r of s o d i u m

ions c a n be l o w e r e d b y s u b s t i t u t i n g p a r t of the s o d i u m p h o s p h a t e w i t h the c o r r e s p o n d i n g t e t r a m e t h y l a m m o n i u m p h o s p h a t e , thus r e t a i n i n g the p H ( a n e x a m p l e is g i v e n i n T a b l e V I ). Prepolymerization of Silicate.

F r o m phosphate-buffered

mixtures

of i d e n t i c a l c h e m i c a l c o m p o s i t i o n , different zeolites c r y s t a l l i z e d e p e n d i n g o n the degree of p r e p o l y m e r i z a t i o n of the silicate. P o l y m e r i c silicates t e n d to g i v e Z K - 1 5 or zeolites of c h a b a z i t e structure [ l o w - s i l i c a Z K - 1 4 (17)1

i n the same p H range w h e r e m e t a s i l i c a t e causes zeolite Y to c r y s

tallize ( T a b l e I V ) .

T h u s , either the d e p o l y m e r i z a t i o n of waterglass is

s l o w e r t h a n g e n e r a l l y t h o u g h t o r the precursors f o r m e d w i t h p a r t i a l l y d e p o l y m e r i z e d silicate are s t a b i l i z e d sufficiently t o p r e v e n t f u r t h e r r a p i d depolymerization.


72


Table IV.

Effect of Silica Source

Mixture Silica

Source

Metasilicate Waterglass


Colloidal silica sol Table V

SiO,/ Ah0

Ratios

Product H Of Na 0

Na 0/ 4.22 6.46 4.22 4.22 2.82 2.82

Si0 / Al 0 2

2

2

P2O5

3

4.0 6.47 4.0 6.0 4.0 6.0

1

Type

2

63 80 64 61 89 89

3.35 3.33 3.3 3.45 3.55 3.55

2

3

Y Y + Trace Β ZK-14 ZK-15

4.0 4.1

ZK-15 ZK-15

4.6 4.8

contains i n f o r m a t i o n o n t h e c r y s t a l l i z a t i o n of

3.4 4.2

a certain

a l u m i n a t e - p h o s p h a t e m i x t u r e w i t h silicates of different degrees of p o l y merization.

A l t h o u g h n o c o r r e c t i o n w a s m a d e for t h e different S 1 O 2 /

N a 0 ratios of the silicates, the final p H w a s a l w a y s i n a range t h a t w o u l d 2

h a v e a l l o w e d zeolite Y to c r y s t a l l i z e . A t r e n d f r o m Y to Z K - 1 4 to Z K - 1 5 to Β is o b s e r v e d w i t h i n c r e a s i n g degree of p o l y m e r i z a t i o n of t h e silicate used. Table V .

Effect of Degree of Polymerization of the Silicate Si0 /Al 0s 2

=

2

6.0 Si0 / Al O 2

Waterglass B-W C

D Star

Final

pH

Zeolite

12.05 12.1 11.9 11.6

Obtained

2

s

4.09 4.35 4.39 4.76

ZK-14 +

Z K - 1 5 + trace Y ZK-15 ZK-15 Β + trace Z K - 1 5

Time. M o s t zeolite structures are metastable; t h e y are g e n e r a l l y less h y d r o t h e r m a l l y stable the l o w e r t h e i r density is. T h e r e f o r e , w h e n the m o r e o p e n zeolites are k e p t i n t h e i r m o t h e r l i q u o r for a n extended t i m e , t h e y t e n d to r e c r y s t a l l i z e to denser structures. Zeolites of faujasite struc t u r e r e c r y s t a l l i z e i n a s o d i u m system to zeolite B , a n d those of c h a b a z i t e structure are t r a n s f o r m e d i n t h e i r m i x e d s o d i u m - p o t a s s i u m m o t h e r l i q u o r to p r o d u c t s of the denser p h i l l i p s i t e structure. T h e rate of c r y s t a l l i z a t i o n of a c e r t a i n zeolite c r y s t a l structure u s u a l l y decreases w i t h i n c r e a s i n g S i 0 / A l 0 2

2

3

r a t i o . A s K e r r (11)

p o i n t e d out,

a longer c r y s t a l l i z a t i o n t i m e gives the denser m a t e r i a l — e . g . , zeolite

Β—

a c h a n c e to nucleate. T h e c r y s t a l l i z a t i o n rate of zeolite Β is greater t h a n that of zeolite X so that the r e m a i n i n g a m o r p h o u s m a t e r i a l crystallizes m a i n l y to zeolite B . F u r t h e r m o r e , g i v e n sufficient t i m e , the p r e v i o u s l y f o r m e d zeolite X recrystallizes also to zeolite B . T h e n u c l e a t i o n t i m e of zeolite X c a n b e e l i m i n a t e d b y seeding.


5.

Crystallization

KUHL

of

73

Zeolites

A greater r e a c t i o n v o l u m e f r e q u e n t l y results i n a

Concentration.

slightly higher S i 0 / A l 0 2

2

3

r a t i o of the p r o d u c t .

H i g h concentrations of

salts i n h i b i t c r y s t a l l i z a t i o n so t h a t denser materials are o b t a i n e d . Table V I .

Effect of Concentration on Crystallizing Structure

C o n s t a n t s : |£f Al O 2

= 8.0;

+

z

2

Να 0 [(CH,) N] 0 2

Na 0

+


2

H0

Temp.,

2

Na 0 2

+

[(CH ),N] 0 53 43 26 26 s

°C 90 90 95 90

2

\{CH*MÛP0

4

2

_ ~

n

9

Final pH 12.3 12.95 12.6 12.3

,

B

M

5

_

Product YJfoy X + 5% A A + 10% X Sodalite + 1 5 % A Sodalite

Si0 /Al 0z 6.0 4.9 7.4 8.1 2

2

° Only the ( C H ) 4 N added as hydroxide. +

3

T a b l e V I shows the influence of d i l u t i o n i n a N a - ( C H ) 4 N system 3

containing ( C H ) N B r . 3

4

T h e smaller precursors are f o r m e d i n the pres

ence of h i g h e r concentrations

of T M A ions.

T h e r e f o r e , i t seems that

T M A ions s t a b i l i z e not o n l y the precursors of the A - t y p e s t r u c t u r e , p r e s u m a b l y d o u b l e 4-rings, b u t also, at h i g h e r concentrations, s i n g l e 4-rings a n d 6-rings. T h e same n u m b e r of T M A ions m a y b e r e q u i r e d for s t a b i l i z a t i o n of either p r e c u r s o r ; this explains the c o n c e n t r a t i o n effect. Temperature.

T e m p e r a t u r e influences the

polymerization-depoly-

m e r i z a t i o n e q u i l i b r i u m . H i g h e r temperatures cause denser m a t e r i a l s to c r y s t a l l i z e . S e l b i n a n d M a s o n (23)

r e p o r t e d t h a t t h e y h a d to use a l o w e r

t e m p e r a t u r e to o b t a i n the gallosilicate a n a l o g of zeolite X .

Temperatures

a b o v e 70 ° C caused a gallosilicate of sodalite structure to c r y s t a l l i z e . C o u n t l e s s examples for the t e m p e r a t u r e effect are g i v e n i n the l i t e r a t u r e (see,

e.g., Ref. 2 ) .

Conclusions M o s t c o m p l e x i n g agents for a l u m i n u m d o not h a v e the b u f f e r i n g a b i l i t y d e s i r e d to a i d i n the c r y s t a l l i z a t i o n of h i g h - s i l i c a zeolites.

O f the

reagents d e s c r i b e d i n this p a p e r , o n l y p h y t a t e is s i m i l a r i n p e r f o r m a n c e to phosphate.

U s e of a n o n b u f f e r i n g c o m p l e x i n g agent i n c o m b i n a t i o n

w i t h p h o s p h a t e as buffer appears w o r t h w h i l e . O b s e r v a t i o n s m a d e i n zeolite synthesis w o r k c a n be e x p l a i n e d b y the sequence of reactions: C o n d e n s a t i o n of a l u m i n o s i l i c a t e ( a n d s i l i c a t e )


74


1

to form polymers, ring closure, stabilization of certain ring structures by cations to form soluble precursors, combination of precursors under the influence of cations to give nuclei, and finally crystal growth.


Literature Cited (1) Bailar, J. C., Jr., Jones, Ε. M., Inorg. Syn. 1939, 1, 35. (2) Barrer, R. M., Baynham, J. W., Bultitude, F. W., Meier, W. M., J. Chem. Soc 1959, 195. (3) Behr, B., Wendt, H., Z. Elektrochem. 1962, 66, 223. (4) Cadariu, I., Goina, T., Oniciu, L., Studia Univ. Babes-Bolyai, Ser. Chem. 1962, 7, 81. (5) Ciric, J.,J.Colloid Interface Sci. 1968, 28, 315. (6) Dempsey, E., Kühl, G. H., Olson, D. H., J. Phys. Chem. 1969, 73, 387. (7) Freedman, H. H., Frost, A. E., Westerback, S. J., Martell, A. E., Nature 1957, 179, 1020. (8) Grossmith, F., Brit. Patent 949,405 (1964). (9) Kerr, G. T., Inorg. Chem. 1966, 5, 1537. (10) Kerr, G. T., J. Phys. Chem. 1966, 70, 1047. (11) Ibid., 1968, 72, 1385. (12) Kerr, G. T., unpublished data. (13) Kroll, H., Knell, M., Powers, J., Simonian, J.,J.Am. Chem. Soc. 1957, 79, 2024. (14) Kühl, G. H., Am. Mineralogist 1969, 54, 1607. (15) Kühl, G.H.,J.Inorg. Nucl. Chem. 1969, 31, 1043. (16) Kühl, G. H., 158th Meeting, ACS, New York, September, 1969. (17) Kühl, G. H., "Molecular Sieves," p. 85, Society of the Chemical Industry, London, 1968. (18) Lacroix, S., Bull. Soc. Chim. France 1947, 408. (19) Lacroix, S., Ann. Chim. 1949, 4, 5. (20) Meier, W. M., Baerlocher, Ch., Helv. Chim. Acta 1969, 52, 1853. (21) Saito, K., Terrey, H., J. Chem. Soc. 1956, 4701. (22) Schwarzenbach, G., Gut, R., Anderegg, G., Helv. Chim. Acta 1954, 37, 937. (23) Selbin, J., Mason, R. B.,J.Inorg. Nucl. Chem. 1961, 20, 222. (24) Vohra, P., Gray, G. Α., Kratzer, F. H., Proc. Soc. Exptl. Biol. Med. 1965, 120, 447. (25) Wolf, F., Fürtig, H., East German Patent 58,957 (1967). RECEIVED February 4, 1970.

Discussion Brian D. McNicol (Koninklijke/Shell Laboratorium, Amsterdam, Netherlands) : Was there any evidence of tetrahedral framework substitution by arsenic or phosphorus? G. H. Kiihl: No. John Turkevich (Princeton University, Princeton, N . J. 08540): Is the phosphate incorporated into the zeolite structure in those cases where phosphate is used to buffer?


5.

KUHL

Crystallization

of

Zeolites

75

G . H . K u h l : I have never encountered phosphate substitution i n the f r a m e w o r k . H o w e v e r , the zeolite A s t r u c t u r e has b e e n f o u n d w i t h u p to one Ρ p e r sodalite c a g e i n t e r c a l a t e d . J . A . Rabo ( U n i o n C a r b i d e C o r p . , T a r r y t o w n , Ν. Y . 1 0 5 9 1 ) :

You

suggested that l a r g e cations l i m i t the A l content to l o w e r levels. D o y o u h a v e a n y examples for this effect w i t h l a r g e a l k a l i cations? G . H . K u h l : T h e examples are g i v e n i n the p a p e r ( T a b l e V I , T M A ions, a n d p o s s i b l y R e f . 25, w h e r e s m a l l e r h y d r a t e d K ions a p p e a r to p e r +


m i t c r y s t a l l i z a t i o n of l o w - S i z e o l i t e X ) .


Crystallization of Zeolites in the Presence of a Complexing Agent

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