Zeolite Synthesis - American Chemical Society

Chapter 38

Studies on the Kinetics of ZSM-23 Crystallization 1

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S. Ernst , R. Kumar , and J. Weitkamp 1

Department of Chemistry, Chemical Technology, University of Oldenburg, Ammerlaender Heerstrasse 114-118, D-2900 Oldenburg, Federal Republic of Germany Institute of Chemical Technology I, University of Stuttgart, Pfaffenwaldring 55, D-7000 Stuttgart 80, Federal Republic of Germany

Downloaded by MONASH UNIV on August 1, 2013 | http://pubs.acs.org Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0398.ch038

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To optimize the synthesis conditions for zeolite ZSM-23 with respect to synthesis time and purity of the pro duct, its crystallization kinetics was studied in de tail by X-ray powder d i f f r a c t i o n and scanning electron microscopy. The following reaction parameters were varied: Temperature, SiO /Al O , OH /SiO , H O/SiO , pyrrolidine/SiO2. Pertinent results are: i) increasing temperature or decreasing Al-content of the gel leads to shorter induction periods and enhanced crystalliza tion rates, ii) a t SiO /Al O = 70 to 150 pure ZSM-23 can be obtained; for lower or higher values other phases may form; iii) an optimum value for OH /SiO seems to exist (ca. 0.1) below which the crystalliza tion rate is slow and above which impurity phases (e.g., C r i s t o b a l i t e ) appear before complete crystallization is achieved and, iv) a minimum concentration of pyrro l i d i n e is required for ZSM-23 to crystallize. Alter natively, the use o f heptamethoniumbromide as template was studied. Its main advantage is the much wider range of SiO /Al O ratios with which ZSM-23 can be synthe sized. -

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ZSM-23 i s a medium pore high s i l i c a z e o l i t e with i n t e r e s t i n g c a t a l y t i c and a d s o r p t i v e p r o p e r t i e s ( 1 - 5 ) . R e c e n t l y , i t s framework topo logy was shown t o have orthorhombic symmetry (Pmmn) with u n i t c e l l parameters o f a = 0.501 nm, b = 2.152 nm and c = 1.113 nm. The pore s t r u c t u r e o f ZSM-23 c o n s i s t s o f l i n e a r , n o n - i n t e r p e n e t r a t i n g chan n e l s with t e a r d r o p shaped openings o f c a . 0.45 χ 0.56 nm {6). I t was proposed t o denote t h i s framework topology as MTT (Mobil-twentyt h r e e ) ( 6 ) . Based on a comparison o f X-ray powder d a t a , i t was suggesteïï t h a t two o t h e r z e o l i t e s , v i z . KZ-1 (_7) and ISI-4 (8) a l s o possess the MTT framework ( 6 ) . The s y n t h e s i s o f ZSM-23 can be accomplished i n the presence o f o r g a n i c templates, v i z . p y r r o l i d i n e ( 1 ) , heptamethoniumbromide (9 10), octamethoniumbromide (JjO), c e r t a T n i m i d a z o l e d e r i v a t i v e s (11) 9

3

On leave from the Inorganic Chemistry Division, National Chemical Laboratory, Pune 411 008, India 0097-6156/89/0398-0560$06.00/0 © 1989 American Chemical Society In Zeolite Synthesis; Occelli, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.


38.

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Kinetics of ZSM-23 Crystallization

AU

and d i i s o p r o p a n o l a m i n e 0 2 ) . Regarding t h e s y n t h e s i s o f ZSM-23 using p y r r o l i d i n e as the o r g a n i c base, t h e r e a r e some c o n t r a d i c t o r y r e p o r t s i n the l i t e r a t u r e : I t i s r e p o r t e d (6_) t h a t i n a p r e f e r r e d s y n t h e s i s o f ZSM-23, sources o f s i l i c a , alumina, c a u s t i c soda and p y r r o l i d i n e a r e r e a c t e d a t 150°C t o 160°C u n t i l the c r y s t a l l i z a t i o n i s complete. On the o t h e r hand, i t has been f r e q u e n t l y s t a t e d (10, 12, 13) t h a t with p y r r o l i d i n e as template, the s y n t h e s i s o f pure ZSM-23 f a i l e d . Instead, ZSM-5 was the major phase formed. Suzuki e t a l . (J4-) have shown t h a t upon v a r i a t i o n o f t h e g e l composition as many as f i v e d i f f e r e n t z e o l i t e s t r u c t u r e s (ZSM-5, ZSM-35, ZSM-39, ZSM-48 and KZ-1) can be s y n t h e s i z e d i n t h e presence of p y r r o l i d i n e (14). Hence, not only the nature o f the o r g a n i c temp l a t e but a l s o tTïê gel chemistry and s y n t h e s i s c o n d i t i o n s have a marked i n f l u e n c e on the s t r u c t u r e o f the c r y s t a l l i n e product. In a r e c e n t s y s t e m a t i c study i t was p o i n t e d o u t t h a t e s p e c i a l l y pH and Na -content have t o be c a r e f u l l y a d j u s t e d i n o r d e r t o a v o i d t h e f o r mation o f phases o t h e r than ZSM-23 ( 4 ) . In an attempt t o o p t i m i z e the s y n t h e s i s o f ZSM-23 i n the presence o f p y r r o l i d i n e , t h e i n f l u e n c e o f t h e g e l composition on the c r y s t a l l i z a t i o n k i n e t i c s was s t u d i e d i n d e t a i l . F o r comparison, some experiments with heptamethoniumbromide as template a r e a l s o i n c l u d e d . +

Experimental A l l s y n t h e s i s experiments were c a r r i e d o u t i n r o t a t i n g s t a i n l e s s s t e e l a u t o c l a v e s with an approximate volume o f 250 cnw. A f t e r each experiment, the a u t o c l a v e s were c l e a n e d with 40 wt.-% HF t o minimize seeding e f f e c t s by r e s i d u a l c r y s t a l l i z a t i o n products. The preparat i o n o f t h e s y n t h e s i s mixture was as f o l l o w s . Fumed s i l i c a with a s u r f a c e area o f c a . 200 m /g (CAB-0-SIL M-5) was mixed with about 90 % o f the t o t a l amount o f d i s t i l l e d water. To t h i s mixture were added subsequently under s t i r r i n g : NaOH p e l l e t s (Merck, p . a . ) , p y r r o l i d i n e ( F l u k a , p.a.) as s t r u c t u r e d i r e c t i n g agent, Α Η ^ ^ · 9 H2O (Merck, p.a.) d i s s o l v e d i n the remaining 10 % water and con c e n t r a t e d s u l f u r i c a c i d (98 wt.-%, Merck, p . a . ) . When heptamethoni umbromide was used as template, a sodium waterglass s o l u t i o n (Merck, 28.5 wt.-% S i 0 , 8.8 wt.-% Na 0, 62.7 wt.-% H 0) and A1 (S04)3 · 16 H 0 were used as the s i l i c a and t h e alumina s o u r c e s , r e s p e c t i v e l y . Heptamethoniumbromide (Ν,Ν,Ν,Ν' ,Ν' ,Ν'-hexamethylheptamethylendiammoniumdibromide; C y D i q u a t ) was prepared from 1,7-dibromoheptane and trimethylamine a c c o r d i n g t o (9). The composition o f the r e a c t i o n mixtures was c a l c u l a t e d as d e s c r i b e d by Rollmann and V a l y o c s i k (15). The mixtures were thoroughly homogenized, f i l l e d i n the a u t o c l a v e s and afterwards r o t a t e d i n a furnace thermostated a t t h e d e s i r e d tem p e r a t u r e . P e r i o d i c a l l y , a u t o c l a v e s were withdrawn from the oven and quenched with c o l d water. The c r y s t a l l i n e products were f i l t e r e d , washed with d i s t i l l e d water, d r i e d a t 120°C i n a i r and afterwards c h a r a c t e r i z e d by X-ray powder d i f f r a c t i o n ( C u K - r a d i a t i o n ) and scanning e l e c t r o n microscopy. Percentage c r y s t a l l i n i t i e s o f ZSM-23 were estimated from the h e i g h t o f the peak a t 2Θ = 22.8°. 2

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In Zeolite Synthesis; Occelli, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

562

ZEOLITE SYNTHESIS

R e s u l t s and D i s c u s s i o n Based on p r e l i m i n a r y experiments the f o l l o w i n g standard gel composit i o n was s e l e c t e d f o r f u r t h e r systematic i n v e s t i g a t i o n s : S i O o / A U C ^ +

110, 0 H " / S i 0 = 0.1, H 2 0 / S i 0 = 4 5 , N a / S i 0 = 0.41 and R / S i 0 = 0.45


2

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(R: p y r r o l i d i n e ) . To check the i n f l u e n c e o f c r y s t a l l i z a t i o n temperat u r e on the k i n e t i c s o f ZSM-23 formation from t h i s gel c o m p o s i t i o n , the s y n t h e s i s was conducted a t 160°C, 170°C and 180°C. The r e s u l t s are shown i n F i g u r e 1. I n c r e a s i n g temperature r e s u l t s i n a s h o r t e r i n d u c t i o n p e r i o d and enhanced c r y s t a l l i z a t i o n r a t e s . A t 180°C, comp l e t e l y c r y s t a l l i z e d ZSM-23 can be o b t a i n e d a f t e r about 1 day. The X-ray powder p a t t e r n of a sample s y n t h e s i z e d i n t h i s manner i s shown in F i g u r e 2. The l i n e p o s i t i o n s and r e l a t i v e i n t e n s i t i e s agree very well with p u b l i s h e d data { ] ) . No peaks due to other c r y s t a l l i n e phases c o u l d be observed. The product c r y s t a l l i t e s t y p i c a l l y possess a d i s c l i k e morphology. The d i s c s are almost always intergrown ( c f . F i g u r e 3). In the s y n t h e s i s o f z e o l i t e s the a l k a l i n i t y o f the r e a c t i o n mixture i s one o f the major f a c t o r s which govern n u c l e a t i o n and c r y s t a l growth ( 1 6 , 17). T h e r e f o r e , 0H"/SiÛ2 was v a r i e d i n the range -0.25 to 0.19 by a d j u s t i n g the amount of H2SO4 added to the g e l . Negative values o f 0H"/Si02 simply i n d i c a t e t h a t more moles of a c i d were added t o the gel than o f hydroxide. A p o s s i b l e c o n t r i b u t i o n o f the template to OH' c o n c e n t r a t i o n i s not taken i n t o account. The r e s u l t s are d e p i c t e d i n F i g u r e 4. A p p a r e n t l y , there e x i s t s a minimum value f o r 0H"/Si0o below which c r y s t a l l i z a t i o n o f ZSM-23 i s very slow. I n c r e a s i n g the a l k a l i n i t y (0H"/SiÛ2 up to 0.10) r e s u l t s i n a d r a s t i c a c c e l e r a t i o n o f c r y s t a l l i z a t i o n . A f u r t h e r i n c r e a s e to OH"/ S i 0 2 = 0.19 does not b r i n g about a f u r t h e r enhancement. Rather, a f t e r about 20 hours the c r y s t a l l i n i t y o f ZSM-23 i s no longer improved, i n s t e a d c r i s t o b a l i t e s t a r t s to c r y s t a l l i z e a s impurity phase (not shown i n F i g u r e 4 ) . For g e l s with OH'/SiO? = 0.10 and 0.03 c r i s t o b a l i t e i s o n l y observed f o r extended s y n t h e s i s times a f t e r complete c r y s t a l l i z a t i o n o f ZSM-23. Both, the decrease i n n u c l e a t i o n time and the enhanced r a t e s o f c r y s t a l growth with i n c r e a s i n g OH"/ S i 0 2 r a t i o s can be a t t r i b u t e d to an i n c r e a s e d s o l u b i l i t y of the r e a c t a n t s a t h i g h e r a l k a l i n i t i e s . T h i s r e s u l t s i n a h i g h e r supersat u r a t i o n o f the mother l i q u o r (16). I t i s known from the s y n t h e s i s of o t h e r h i g h - s i l i c a z e o l i t e s (ëTg., ZSM-5 (J8) and ZSM-12 (j9)) t h a t the c r y s t a l l i t e s i z e i n c r e a s e s with d e c r e a s i n g pH o f the g e l . The reason i s the slower r a t e o f n u c l e a t i o n which r e s u l t s i n a s m a l l e r amount o f c r y s t a l s which are formed i n i t i a l l y . Fewer c r y s t a l s can grow to a b i g g e r s i z e b e f o r e the r e a c t a n t s are completely consumed. I t has now been found t h a t t h i s r u l e a l s o holds f o r ZSM-23. F i g u r e 5 shows a scanning e l e c t r o n micrograph o f ZSM-23 produced from a r e a c t i o n mixture with 0H"/Si0o = 0.03. The c r y s t a l s possess the same morphology a s those o b t a i n e d a t OH'/SiOg = 0.10 ( c f . F i g u r e 3) but are about twice as l a r g e . From the v a r i a t i o n o f the OH" conc e n t r a t i o n i n the i n i t i a l g e l , the f o l l o w i n g main c o n c l u s i o n s can be drawn: i ) An optimum value f o r 0H~/Si02 seems to e x i s t ( c a . 0.1) below which the c r y s t a l l i z a t i o n r a t e i s slow and above which i m p u r i t y phases (e.g., c r i s t o b a l i t e ) appear before complete c r y s t a l l i z a t i o n i s achieved and, i i ) the c r y s t a l s i z e o f ZSM-23 can be i n c r e a s e d upon lowering 0H"/Si02 however, the c r y s t a l l i z a t i o n time w i l l i n crease too.


38. ERNST ET AL.

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F i g u r e 1. S y n t h e s i s o f ZSM-23 from the r e a c t i o n mixture: S i 0 / = 110, 0H"7Si0 = 0.1, H 0 / S i 0 = 45, N a / S i 0 = 0.41, R / S i 0 = 0.45: I n f l u e n c e o f c r y s t a l l i z a t i o n temperature. 2

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F i g u r e 2. X-ray powder p a t t e r n o f ZSM-23 formed from the s t a n dard g e l composition a f t e r c a . 1 day a t 180°C.


ZEOLITE SYNTHESIS


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F i g u r e 4. I n f l u e n c e of 0 H ~ / S i 0 on ZSM-23 c r y s t a l l i z a t i o n (T = 180°C, S i 0 / A l 0 = 110, H 0 / S i 0 = 45, N a / S i 0 = 0.41, R / S i 0 = 0.45). 2

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F i g u r e 5. ZSM-23 c r y s t a l l i t e s grown from a gel w i t h the composit i o n Si02/Al2Û3 = 110, 0 H " / S i 0 = 0.03, H20/SÎ02 = 45, N a / S i 0 = 0.41, R / S i 0 = 0.45 a t Τ = 180°C. +

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The i n f l u e n c e o f the water content o f the g e l on the c r y s t a l l i z a t i o n k i n e t i c s o f ZSM-23 i s shown i n F i g u r e 6. O b v i o u s l y , c r y s t a l l i z a t i o n i s f a s t e r f o r the more c o n c e n t r a t e d systems. T h i s observat i o n can be e a s i l y r a t i o n a l i z e d i f i t i s c o n s i d e r e d t h a t with dec r e a s i n g amount o f water i n the s y n t h e s i s mixtures the c o n c e n t r a t i o n of the r e a c t a n t s and hence pH i n c r e a s e s . T h i s has the same e f f e c t as an i n c r e a s e i n 0H"/SiÛ2 r a t i o , v i z . higher s u p e r s a t u r a t i o n o f the mother l i q u o r . The consequences have been d i s c u s s e d b e f o r e . In order t o optimize the p y r r o l i d i n e c o n c e n t r a t i o n o f the g e l and t o l e a r n more about i t s r o l e i n the s y n t h e s i s o f the MTT framework, the molar r a t i o p y r r o l i d i n e / S i 0 was v a r i e d by adding d i f f e r ent amounts o f the o r g a n i c base t o the r e a c t i o n mixture. I t can be seen from F i g u r e 7 t h a t the c r y s t a l l i z a t i o n o f ZSM-23 becomes f a s t e r i f R / S i 0 i n c r e a s e s . However, a t the h i g h e s t value i n v e s t i g a t e d i n t h i s study ( R / S i 0 = 0.67) c r i s t o b a l i t e s t a r t s t o form before ZSM-23 i s completely c r y s t a l l i z e d . As a r e s u l t , a value o f c a . 0.45 f o r R / S i 0 can be recommended t o achieve both, f a s t c r y s t a l l i z a t i o n and high p u r i t y . I f no p y r r o l i d i n e i s added t o the s y n t h e s i s mixture o n l y c r i s t o b a l i t e c r y s t a l l i z e s , even a f t e r extended s y n t h e s i s times ( c f . F i g u r e 7 ) . T h i s o b s e r v a t i o n suggests t h a t , a t l e a s t f o r t h e g e l composition used i n t h i s study, p y r r o l i d i n e i s e s s e n t i a l i n the n u c l e a t i o n stage o f ZSM-23. In a d d i t i o n a l experiments i t was t r i e d to s y n t h e s i z e ZSM-23 from p y r r o l i d i n e - f r e e r e a c t i o n mixtures using seeds. E i t h e r 1 o r 2 wt.-% (based on S i 0 i n the g e l ) o f u n c a l c i n e d ZSM-23 seeds (obtained by c r y s t a l l i z i n g the standard r e a c t i o n mixt u r e ) were added t o a p y r r o l i d i n e - f r e e g e l o f the composition: SiOo/ A 1 0 = 110, 0 H " / S i 0 = 0 . 1 , H 0 / S i 0 = 45, N a / S i 0 = 0.41. A f t e r a u t o c l a v i n g a t 180°C f o r s e v e r a l days, c r i s t o b a l i t e was again the only c r i s t a l l i n e product. These r e s u l t s suggest t h a t p y r r o l i d i n e i s not o n l y important d u r i n g the n u c l e a t i o n stage o f ZSM-23 but a l s o f o r i t s c r y s t a l growth. In t h i s case i t s e f f e c t maybe t h a t o f a pore - f i l l i n g agent. T h i s suggestion i s supported by the f o l l o w i n g rough e s t i m a t i o n : According t o the o r i g i n a l patent (J_), c a l c i n e d ZSM-23 adsorbs about 5.5 wt.-% o f n-hexane ( a t 25°C and P _ h ~ 2.7 kPa). I f t h i s value i s used and simply c o r r e c t e d f o r d e n s i t y d i f f e r ences, one would p r e d i c t a s o r p t i o n c a p a c i t y f o r p y r r o l i d i n e o f c a . 7.2 wt.-%. From the n i t r o g e n content o f most o f t h e a s - s y n t h e s i z e d ZSM-23 samples i n (1) a p y r r o l i d i n e content o f c a . 6.6 wt.-% can be c a l c u l a t e d . Hence, T t i s reasonable t o assume complete o r n e a r l y complete p o r e f i l l i n g o f a s - s y n t h e s i z e d ZSM-23 with p y r r o l i d i n e . From these c o n s i d e r a t i o n s i t can be concluded t h a t p y r r o l i d i n e helps n o t only i n forming the ZSM-23 n u c l e i but a c t s a l s o as p o r e - f i l l i n g agent d u r i n g c r y s t a l growth. When the N a / S i 0 r a t i o i s v a r i e d between 0.17 and 0.25 keeping a l l o t h e r r a t i o s c o n s t a n t , no s i g n i f i c a n t changes i n c r y s t a l l i z a t i o n k i n e t i c s a r e observed. Since the covered range o f N a / S i 0 i s only very r e s t r i c t e d , no c o n c l u s i o n s r e g a r d i n g the i n f l u e n c e o f sodium can be made a t the present stage. It i s claimed (1) t h a t ZSM-23 can be s y n t h e s i z e d with p y r r o l i dine as template witïïin a c e r t a i n range o f aluminium contents ( S i 0 / AI0O3 = 40 - 250). However, upon i n c r e a s i n g the aluminium content o f the r e a c t i o n mixture, c r y s t a l l i z a t i o n r a t e s decrease ( c f . F i g u r e 8 ) . T h i s o b s e r v a t i o n was a l s o made with o t h e r high s i l i c a z e o l i t e s , e.g., 2

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F i g u r e 6. I n f l u e n c e of the water c o n t e n t on c r y s t a l l i z a t i o n k i n e t i c s (T = 180°C, Si02/Al203 = 110, 0 H " / S i 0 = 0.1, N a / S i 0 0.41, R / S i 0 = 0.45). +

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F i g u r e 7. I n f l u e n c e o f R/SiÛ2 on the c r y s t a l l i z a t i o n k i n e t i c s (T = 180°C, S i 0 2 / A l 0 = 110, 0 H " / S i 0 = 0.1, H 0 / S i 0 = 45, N a / S i 0 = 0.41). 2

3

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ZEOLITE SYNTHESIS


568

F i g u r e 8. I n f l u e n c e of aluminium c o n t e n t on the c r y s t a l l i z a t i o n of ZSM-23 (T = 180°C, 0 I T / S i 0 = 0.1, H 0 / S i 0 = 45, N a / S i 0 = 0.41, R / S i 0 = 0.45). +

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38. ERNST ET AL.

569


ZSM-5 ( 2 0 - 22) and ZSM-12 (19, 2 3 ) . The r e v e r s e i s known f o r t h e s y n t h e s i s o f low s i l i c a z e o l i t e s : Due t o an i n c r e a s e d s i l i c a con t e n t i n t h e s y n t h e s i s g e l , the v i s c o s i t y o f the mixture i s i n c r e a s e d , which r e s u l t s i n a decreased c r y s t a l l i z a t i o n r a t e . As a p o s s i b l e e x p l a n a t i o n o f these o b s e r v a t i o n s i t i s assumed t h a t i n c o r p o r a t i o n of aluminium i n t o the framework o f ZSM-23 i s a d i f f i c u l t p r o c e s s , l i k e i t i s f o r ZSM-5 (20). T h i s i s u n d e r l i n e d by t h e decrease o f t h e c r y s t a l l i t e s i z e o f ZS"M 23 with i n c r e a s i n g aluminium c o n t e n t o f the g e l : F o r S102/A12Ο3 = 110, t h e c r y s t a l l i t e s a r e about 2 μηι i n l e n g t h ( c f . F i g u r e 3) whereas i t d i m i n i s h e s t o l e s s than 1 μηι f o r SiÛ2/ ΑΊ2Ο3 = 70 ( c f . F i g u r e 9 ) . These phenomena a r e i n agreement with o b s e r v a t i o n s made e a r l i e r i n t h e s y n t h e s i s o f ZSM-5 (20, 22, 24) and ZSM-12 (]9) and seem t o be o f a more general v a l i d i t y i n t h e synthesis of high-silica zeolites. The r e s u l t s d e p i c t e d i n F i g u r e 8 f u r t h e r i n d i c a t e t h a t , the more s i l i c e o u s t h e s y n t h e s i s mixtures a r e , the e a r l i e r C r i s t o b a l i t e s t a r t s t o form. Hence, i f a ZSM-23 with r e l a t i v e l y high S i 0 / A l 2 0 3 r a t i o i s t o be s y n t h e s i z e d , a c a r e f u l o p t i m i z a t i o n o f c r y s t a l l i z a t i o n time and, perhaps c r y s t a l l i z a t i o n temperature should be made t o o b t a i n pure products. I n c r e a s i n g the aluminium c o n t e n t o f t h e g e l t o S i O o / A ^ O j r a t i o s below c a . 50 a l s o y i e l d s ZSM-23 b u t contaminated with ZSM-b o f a p e c u l i a r morphology ( F i g u r e 10). It i s c l a i m e d (9) t h a t with C y d i q u a t as template ZSM-23 can be s y n t h e s i z e d i n a mucïï broader range o f S102/A12Û3 r a t i o s than i t i s p o s s i b l e with p y r r o l i d i n e . T h e r e f o r e , complementary s y n t h e s i s experiments were conducted with Cy-diquat. In a gel with the composition 0H"/Si02 = 0-3, N a / S i 0 = 0.59, R /SiOo = 0.15 the aluminium cont e n t was v a r i e d such as t o o b t a i n SÎ02/A1203 r a t i o s between 60 and °°. From a l l s y n t h e s i s r u n s , pure and h i g h l y c r y s t a l l i n e ZSM-23 was obt a i n e d a f t e r 1 t o 4 days a t 160°C under a g i t a t i o n . A t y p i c a l X-ray powder p a t t e r n o f a ZSM-23 sample s y n t h e s i z e d i n t h i s way (SiU2/ Al2Ο3 = 140) i s shown i n F i g u r e 11. The r e s o l u t i o n o f t h e p a t t e r n i s c o n s i d e r a b l y improved. Note, f o r example, t h a t the f i r s t somewhat broad peak o f ZSM-23 s y n t h e s i z e d with p y r r o l i d i n e ( c f . F i g u r e 2) s p l i t s i n t o two sharp l i n e s ( t h i s d i f f e r e n c e a l s o remains a f t e r c a l c i n a t i o n i n a i r a t 540°C). One c o u l d expect, t h a t the sharper l i n e s are due t o a l a r g e r c r y s t a l s i z e . However, as i t can be seen from F i g u r e 12, t h i s i s not t h e case. ZSM-23 produced from systems con t a i n i n g Cy-diquat has a p l a t e - l i k e h a b i t with c r y s t a l l i t e s i z e s around o r below 1 μπι. Hence, the reasons f o r the improved r e s o l u t i o n of t h e XRD p a t t e r n s a r e n o t c l e a r a t the moment. One c o u l d s p e c u l a t e t h a t ZSM-23 o b t a i n e d from p y r r o l i d i n e c o n t a i n i n g systems has some amorphous m a t e r i a l o c c l u d e d i n the pores, r e s u l t i n g i n a poorer c r y s t a l l i n i t y . T h i s should r e s u l t i n d i f f e r e n t a d s o r p t i v e and c a t a l y t i c p r o p e r t i e s o f ZSM-23 prepared with d i f f e r e n t templates.


r

2

+

+

2

Conclusions Z e o l i t e ZSM-23 can be r e a d i l y s y n t h e s i z e d with p y r r o l i d i n e as orga nic template and fumed s i l i c a as s i l i c a source. P y r r o l i d i n e seems t o i n t e r v e n e i n t h e n u c l e a t i o n and c r y s t a l growth p r o c e s s , i n t h e l a t t e r case most probably as p o r e - f i l l i n g agent. By proper o p t i m i z a t i o n of t h e g e l composition and the s y n t h e s i s c o n d i t i o n s , ZSM-23 can be s y n t h e s i z e d i n l e s s than one day. The s y n t h e s i s o f ZSM-23 has some



570

ZEOLITE SYNTHESIS

F i g u r e 9. C r y s t a l l i t e morphology o f ZSM-23 s y n t h e s i z e d from a gel with Si0 /A12Ο3 = 70. 2

F i g u r e 10. ZSM-5/ZSM-23 mixture obtained from a g e l with S1O2/ A12Û3 = 50.


38. ERNST ET AL.



ζ LU

10

15

20

25

30

35

40

ANGLE 2 θ, deg

F i g u r e 11. T y p i c a l X-ray powder p a t t e r n o f ZSM-23 (SiU2/Al2Ο3 140) o b t a i n e d with Cy-diquat as template.

F i g u r e 12. T y p i c a l c r y s t a l l i t e morphology o f ZSM-23 prepared from g e l s c o n t a i n i n g Cy-diquat as template.


572

ZEOLITE SYNTHESIS

f e a t u r e s i n common with t h e s y n t h e s i s o f ZSM-5 and ZSM-12: i ) i n c r e a s i n g the a l k a l i n i t y o f t h e gel reduces t h e c r y s t a l l i z a t i o n time and the c r y s t a l l i t e s i z e o f t h e product and i i ) i n c r e a s i n g t h e Si02/ Al2Ο3 r a t i o i n t h e gel enhances t h e r a t e o f c r y s t a l l i z a t i o n . Hence, these o b s e r v a t i o n s seem t o be o f a more general v a l i d i t y i n t h e syn t h e s i s o f h i g h - s i l i c a z e o l i t e s . With Cy-diquat as template, ZSM-23 can be s y n t h e s i z e d i n a much broader range o f SiO^/Al2Ο3 r a t i o s and with b e t t e r r e s o l v e d powder p a t t e r n s . However, t h i s template i s n o t commercially a v a i l a b l e and i t s p r e p a r a t i o n r e q u i r e s c o s t l y r e a c t a n t s .


Acknowledgments F i n a n c i a l support by Deutsche Forschungsgemeinschaft and Fonds d e r Chemischen I n d u s t r i e i s g r a t e f u l l y acknowledged. R a j i v Kumar i s g r a t e f u l t o DAAD f o r a r e s e a r c h f e l l o w s h i p . The authors thank Mrs. S. Hesselmann f o r t e c h n i c a l a s s i s t a n c e .

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Cited

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Plank, C.J.; Rosinski, E.J.; Rubin, M.K. U.S. Patent 4 076 842, 1978. 2. Bendoraitis, J.G.; Chester, A.W.; Dwyer, F.G.; Garwood, W.E. Proc. 7th Intern. Zeolite Conf., 1986, p 669. 3. Wu, E.L.; Landolt, G.R.; Chester, A.W. Proc. 7th Intern. Zeo lite Conf., 1986, p 547. 4. Ernst, S.; Kumar, R.; Weitkamp, J. Catalysis Today 1988, 3, 1-10. 5. Ernst, S.; Kokotailo, G.T.; Kumar, R.; Weitkamp, J. Proc. 9th Intern. Congr. Catalysis, 1988, p 388. 6. Rohrman, Jr., A.C.; LaPierre, R.B.; Schlenker, J.L.; Wood, J.D.; Valyocsik, E.W.; Rubin, M.K.; Higgins, J.B.; Rohrbaugh, W.J. Zeolites 1985, 5, 352 - 354. 7. Parker, L.M.; Bibby, D.M. Zeolites 1983, 3, 8 - 11. 8. Takatsu, K.; Kawata, N. Europ. Patent Appl. 102 497, 1984. 9. Valyocsik, E.W. U.S. Patent 4 490 342, 1984. 10. Casci, J.L. Proc. 7th Intern. Zeolite Conf., 1986, p 215. 11. Zones, S.I. U.S. Patent 4 483 835, 1984. 12. Barri, S.A.I. UK Patent Appl. GB 2 190 910 A, 1987. 13. Casci, J.L.; Lowe, B.M.; Whittam, T.V. U.S. Patent 4 528 171, 1985. 14. Suzuki, K.; Kiyozumi, Y.; Shin, S.; Fujisawa, K.; Watanabe, H.; Saito, K.; Noguchi, K. Zeolites 1986, 6, 290 - 298. 15. Rollmann, L.D.; Valyocsik, E.W. Inorganic Syntheses 1982, 22, 61 - 68. 16. Barrer, R.M. Zeolites 1981, 1, 130 - 140. 17. Jacobs, P.A.; Martens, J.A. Synthesis of High-Silica Alumino silicate Zeolites; Elsevier Science Publishers: Amsterdam, Oxford, New York, Tokyo, 1987; p 70. 18. Ref. 17, p 74. 19. Ernst, S.; Jacobs, P.Α.; Martens, J.A.; Weitkamp, J. Zeolites 1987, 7, 458 - 462. 20. Rollmann, L.D.; Valyocsik, E.W. Europ. Patent Appl. 21 675, 1981.


38. ERNST ET AL. Kinetics of ZSM-23 Crystallization

21. 22. 23. 24.

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Chao, K.-J.; Tasi, T.C.; Chen, M.-S.; Wang, J.J. J. Chem. Soc., Faraday Trans I 1981, 77, 547. Rommanikov, V.N.; Mastikhin, V.M.; Hoćevar, S.; Drźaj, B. Zeolites 1983, 3, 311. Shou-He, X.; Hexuan, L. 7th Intern. Zeolite Conf., Preprints of Poster Papers 1986, 25. Mostowicz, R.; Sand, L.B. Zeolites 1983, 3, 219. December 22, 1988


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