Present and Future Directions in Zeolite Research

I believe that this meeting lends support to that statement. The high degree of representation of petro leum-oriented research organizations is eviden...
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77

Present

and

Future

Directions

in

Zeolite

Research

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W. F. AREY, JR. Esso Research Laboratories, Baton Rouge, La. 70821 Molecular sieve zeolites have become established as an area of scientific research and as commercial materials for use as sorbents and catalysts. Continuing studies on their synthesis, structure, and sorption properties will, undoubtedly, lead to broader application. In addition, crystalline zeolites offer one of the best vehicles for studying the fundamentals of heterogeneous catalysis. Several discoveries reported at this conference point toward new fields of investigation and potential commercial utility. These include phosphorus substitution into the silicon—aluminum framework, the structural modifications leading to "ultrastable" faujasite, and the catalytic properties of sodium mordenite.

/

T h e task of s u m m a r i z i n g the major results of the conference a n d s u g f

A

gesting the f u t u r e d i r e c t i o n of m o l e c u l a r sieve zeolites is n o t a n easy

one.

I n p a r t i c u l a r , i t is d i f f i c u l t to s u m m a r i z e the major results because

there w e r e so m a n y n o t e w o r t h y c o n t r i b u t i o n s .

O b v i o u s a n d substantial

progress is b e i n g m a d e i n a l l the major areas—i.e., synthesis,

structure

a n d m i n e r a l o g y , s o r p t i o n a n d d i f f u s i o n , a n d catalysis. B r e c k m a d e the f o l l o w i n g c o m m e n t

i n the i n t r o d u c t o r y l e c t u r e :

" T h e r e seems to b e a d i r e c t r e l a t i o n b e t w e e n the l e v e l of scientific interest a n d t h e area of m a j o r a p p l i c a t i o n . " I b e l i e v e that this m e e t i n g lends s u p p o r t to that statement.

T h e h i g h degree of representation of p e t r o ­

l e u m - o r i e n t e d research o r g a n i z a t i o n s is e v i d e n t . O n e of the major a p p l i c a t i o n s of c r y s t a l l i n e zeolites is as c a t a l y t i c materials f o r p e t r o l e u m r e f i n i n g processes.

A p r i m e use is i n c a t a l y t i c

c r a c k i n g , w h i c h is the major c o n v e r s i o n process

i n today's

refineries.

A n o t h e r g r o w i n g use is i n h y d r o c r a c k i n g , s u c h as the U n i c r a c k i n g — J H C process, w h i c h gives the refiner a d d e d f l e x i b i l i t y i n oils w h i c h c a n b e processed a n d p r o d u c t s w h i c h c a n b e m a d e . 451

In Molecular Sieve Zeolites-II; Flanigen, E., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

452

M O L E C U L A R SIEVE ZEOLITES

T o date, crystalline zeolite catalysts

have been

II

most effective i n

c a t a l y z i n g c a r b o n i u m i o n reactions s u c h as c a t a l y t i c c r a c k i n g a n d h y d r o c r a c k i n g . O t h e r c a r b o n i u m i o n reactions s u c h as a l k y l a t i o n a n d i s o m e r i ­ z a t i o n also are c a t a l y z e d b y certain f o r m s o f zeolites.

I expect t o see

these a p p l i c a t i o n s e x p a n d — p r o v i d e d suitable catalyst c o m p o s i t i o n s a r e d e v e l o p e d to a l l o w e c o n o m i c a l l y v i a b l e processes.

Although X - and

Y - t y p e faujasite c a n be u s e d i n c a t a l y t i c c r a c k i n g a n d h y d r o c r a c k i n g , the Y - t y p e is p r e f e r r e d f o r p a r a f f f n - o l e f i n a l k y l a t i o n . Y - t y p e faujasite is suit­ Downloaded by UCSF LIB CKM RSCS MGMT on November 30, 2014 | http://pubs.acs.org Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0102.ch077

able for use i n h y d r o i s o m e r i z a t i o n catalysts, b u t synthetic m o r d e n i t e is also a p r o m i s i n g m a t e r i a l . O n the other h a n d , zeolite-based catalysts h a v e not d e v e l o p e d a n y significant interest i n other i m p o r t a n t processes s u c h as c a t a l y t i c r e f o r m ­ i n g , hydrogénation

o f olefins a n d aromatics, h y d r o d e s u l f u r i z a t i o n a n d

h y d r o d e n i t r o g e n a t i o n . T h i s l a c k o f u t i l i t y is a t t r i b u t a b l e , i n part, to the h i g h c r a c k i n g a c t i v i t y e x h i b i t e d b y active z e o l i t e - b a s e d

catalysts.

A t present, the m a j o r interest lies i n catalysts b a s e d o n synthetic X a n d Y - t y p e faujasite a n d s y n t h e t i c m o r d e n i t e . With

this b a c k g r o u n d , I b e l i e v e

that

t h e f o l l o w i n g results

were

h i g h l i g h t s of the m e e t i n g : • T h e s u b s t i t u t i o n o f materials other t h a n s i l i c o n o r a l u m i n u m into the zeolite f r a m e w o r k — p a r t i c u l a r l y the p h o s p h o r u s s u b s t i t u t i o n r e p o r t e d b y F l a n i g e n a n d G r o s e . I t w a s , h o w e v e r , d i s a p p o i n t i n g that this was suc­ cessful w i t h o n l y one large-pore m a t e r i a l , n a m e l y , t y p e L zeolite. • T h e e l u c i d a t i o n o f t h e structures i n v o l v e d i n p r o d u c i n g u l t r a s t a b l e faujasite r e p o r t e d b y M a h e r , H u n t e r , a n d Scherzer. A l t h o u g h t h e d i s ­ c o v e r y o f t h e ultrastable faujasite was r e p o r t e d at t h e 1967 L o n d o n m e e t i n g , these subsequent studies ( a n d w o r k b y G . T . K e r r ) are p o i n t i n g to a n u n e x p e c t e d m e t h o d o f a l t e r i n g the c r y s t a l l i n e f r a m e w o r k . • T h e h i g h a c t i v i t y o f s o d i u m m o r d e n i t e f o r c a t a l y z i n g benzene h y d r o ­ génation as r e p o r t e d b y M i n a c h e v et al. T h i s result is so u n i q u e that a d d i t i o n a l i n v e s t i g a t i o n is w a r r a n t e d . It seems to m e that the above constitute discoveries w h i c h c o u l d l e a d to n e w a n d different c a t a l y t i c materials. T h e c o n t i n u i n g studies o n the m e c h a n i s m s i n v o l v e d i n z e o l i t e s y n ­ thesis are l e a d i n g t o a better u n d e r s t a n d i n g o f the c o n t r o l l i n g factors i n this c o m p l i c a t e d r e a c t i o n system. B u t m o r e remains to be done. T h i s also h o l d s the p r o m i s e o f l e a d i n g to the synthesis o f n e w z e o l i t i c structures. T h e systematic investigations of the structure a n d s o r p t i o n p r o p e r t i e s of n a t u r a l a n d synthetic zeolites are c e r t a i n l y c e n t r a l to t h e b o d y o f k n o w l e d g e that w i l l a i d i n the f u t u r e research a n d u t i l i z a t i o n o f zeolites i n v a r i o u s possible w a y s . N o m e n c l a t u r e is i n f l u e n c e d b y structure. h a v e a better system of n o m e n c l a t u r e .

It w o u l d b e desirable to

H o w e v e r , the q u e s t i o n of just h o w

m u c h "fine s t r u c t u r e " needs to b e d e s c r i b e d m a y b e d i f f i c u l t t o answer.

In Molecular Sieve Zeolites-II; Flanigen, E., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

77.

ARE Y

Directions

in Zeolite

453

Research

M a n y n a t u r a l zeolites h a v e a v a r i a b l e c o m p o s i t i o n . I t m a y b e t h a t t h e degree o f S i - A l o r d e r - d i s o r d e r i n s y n t h e t i c zeolites m a y v a r y w i t h p r e p a ­ ration procedures.

H o w e v e r , i t w o u l d b e of interest to d e t e r m i n e w h a t

effect t h e o r d e r - d i s o r d e r has o n a d s o r p t i v e a n d / o r c a t a l y t i c p r o p e r t i e s . S e v e r a l years a g o , i t w a s felt that c a t a l y t i c studies u s i n g c r y s t a l l i n e zeolites w o u l d d r a m a t i c a l l y a i d i n u n r a v e l i n g some of t h e mysteries o f catalysis.

T h i s w a s because t h e c r y s t a l l i n e zeolites h a d a m o r e u n i f o r m

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surface t h a n a m o r p h o u s materials a n d t h e structure c o u l d b e w e l l d e ­ fined.

S o m e of t h e luster of this h o p e appears to b e f a d i n g s l i g h t l y . It

seems that t h e " a c t i v e sites" h a v e a s p e c t r u m o f intensities rather t h a n b e i n g of a u n i f o r m character.

N e v e r t h e l e s s , c r y s t a l l i n e zeolites s t i l l offer

one o f the best vehicles f o r s t u d y i n g t h e f u n d a m e n t a l s o f heterogeneous catalysis. C a t a l y s t s b a s e d o n m o l e c u l a r sieve zeolites w i l l c e r t a i n l y c o n t i n u e t o b e of m u c h interest i n p e t r o l e u m r e f i n i n g . I m p r o v e m e n t s c a n b e e x p e c t e d as t i m e goes o n . R a d i c a l l y different zeolite structures

offer t h e m o s t

c h a n c e of major i m p r o v e m e n t s . S e v e r a l authors have i n d i c a t e d t h e l i k e l i ­ h o o d o f o b t a i n i n g r a d i c a l , c a r b a n i o n , a n d other n o n c a r b o n i u m i o n reac­ tions over zeolite catalysts.

P u r s u i t of this p o s s i b i l i t y m a y p r o v e f r u i t f u l .

Separations w e r e one o f t h e first uses of m o l e c u l a r sieve zeolites. A l t h o u g h some i s o - n o r m a l h y d r o c a r b o n separations plants are o p e r a t i n g , g r o w t h i n this area has n o t b e e n large.

Separations b a s e d o n i n h e r e n t

a d s o r p t i v e b e h a v i o r ( r a t h e r t h a n sieve a c t i o n ) interest.

are b e c o m i n g of m o r e

T h i s is t r u e n o t o n l y o f t h e s e p a r a t i o n o f d i m e t h y l n a p h t h a l e n e s

(as r e p o r t e d b y H e d g e at this m e e t i n g )

b u t also of x y l e n e

isomers.

Separations of this t y p e to p r o d u c e streams of interest i n c h e m i c a l s m a n u ­ facture could grow. A s m e n t i o n e d b y B r e c k i n t h e i n t r o d u c t o r y lecture, m o l e c u l a r sieve zeolites s h o u l d find use i n v a r i o u s p o l l u t i o n c o n t r o l a p p l i c a t i o n s .

Both

t h e i r sorbent a n d c a t a l y t i c properties m a k e t h e m t e c h n i c a l l y f e a s i b l e as agents f o r v a r i o u s aspects of p o l l u t i o n c o n t r o l a n d abatement. I n s u m m a r y , c r y s t a l l i n e zeolites offer n o t o n l y u s e f u l articles o f c o m ­ m e r c e b u t also a n i n t e r e s t i n g research area i n v o l v i n g m a n y different s c i ­ entific d i s c i p l i n e s . U n d o u b t e d l y , t h e f u t u r e w i l l r e v e a l m o r e a b o u t these u n u s u a l materials, p e r h a p s e v e n i n w a y s n o t c l e a r l y foreseen at present. R E C E I V E D November 23,

1970.

In Molecular Sieve Zeolites-II; Flanigen, E., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.