Influence of Superacid Sites in Ultrastable Y ... - ACS Publications

Chapter 2 Influence Y

of

S u p e r a c i d Sites

Zeolites

on

Gas

in

Ultrastable

O i l Cracking

A. Corma, V. Fornés, F. A. Mocholí, J. B. Montón, and F. Rey

Downloaded by PURDUE UNIVERSITY on June 5, 2013 | http://pubs.acs.org Publication Date: January 23, 1991 | doi: 10.1021/bk-1991-0452.ch002

Instituto de Tecnología Química, UPV-CSIC, Universidad Politécnica de Valencia, Camino Vera S/N, 46071 Valencia, Spain

Gasoil Cracking has been carried out on two USY samples with unit c e l l sizes of 24.47 and 24.31 Å, which were steamed at 650° and 650° plus 725°C, respectively. The results were compared with those obtained with the same series of samples after removing most of the extraframework aluminum ( E F A L ) by (NH ) SiF treatment. In the zeolite steamed at lower temperature, the chemical treatment produces a strong decrease on the cracking a c t i v i t y . This decrease is not due to surface framework dealumination, as shown by XPS analysis and n -heptane cracking, but to the absence of EFAL. The removal of EFAL also produces an increase in gas and coke formation. Much less marked effects are observed on the high temperature steamed zeolites after being chemically treated. Gasoil cracking, a c t i v i t y and selectivity of the 24.47 Å USY sample after removing EFAL and being subject to an u l t e r i o r high temperature steaming gives s l i g h t l y less gases and coke and more gasoline than a USY sample with the same unit c e l l size but containing all the EFAL. 4

2

6

Most of the actual refineries are using high octane catalysts based on ultrastable Y zeolite (USY). Ultrastabilization is achieved by increasing the framework S i / A l ratio of the zeolite by either steam (1,2), chemical treatments (3-5) or a combination of both (6) . If a p a r t i a l dealumination of the Y zeolite i s carried out during the manufacturing of the catalyst, the u l t e r i o r dealumination in the FCC unit becomes slower, and more c r y s t a l l i n i t y i s retained. If p a r t i a l l y NH exchanged NHNaY zeolite i s steam calcined, a slow +

4

4

0097-6156/91/0452-0012$06.00/0 © 1991 American Chemical Society In Fluid Catalytic Cracking II; Occelli, M.; ACS Symposium Series; American Chemical Society: Washington, DC, 1991.


2.

CORMA ET AL.

13

Influence of Superacid Sites in USY Zeolites

framework d e a l u m i n a t i o n o c c u r s w h i l e s i l i c o n m i g r a t i o n t o s t a b i l i z e the defects s i t e s takes place (1). Following this procedure, the extraframework aluminum (EFAL) r e m a i n s i n t h e z e o l i t e and i t s e x a c t n a t u r e and t h e r e f o r e i t s c a t a l y t i c r o l e d e p e n d s on t h e method and c o n d i t i o n s u s e d f o r i t s f o r m a t i o n ( 7 , 8 ) . The c a t a l y t i c r o l e o f E F A L during g a s o i l c r a c k i n g i s a matter of d i s c u s s i o n . There a r e s t u d i e s which c l a i m a n e g a t i v e r o l e f o r t h e EFAL component (9) as responsible for a non selective cracking. Others (8,10) c l a i m t h a t some E F A L p l a y s a p o s i t i v e r o l e by e n h a n c i n g t h e B r o n s t e d a c i d i t y o f t h e HF and L F h y d r o x y l g r o u p s . This role i s specially effective i n samples steamed a t moderated t e m p e r a t u r e s (11). The E F A L p r e s e n t i n an e q u i l i b r i u m c a t a l y s t i s i n t h e f o r m o f c o n d e n s e d t y p e s o f a l u m i n a , and i t i s b e l i e v e d (11) t h a t i t i s a c t i v e f o r b o t t o m s c o n v e r s i o n and L i g h t C y c l e O i l (LCO) p r o d u c t i o n , b u t on t h e o t h e r h a n d g i v e s c o k e and d r y gas. In order t o e l i m i n a t e the negative e f f e c t s , a p r o c e d u r e b a s e d on an ( N H ) S i F treatment (4) h a s b e e n c o m m e r c i a l l y d e v e l o p e d w h i c h i s a b l e t o e x t r a c t aluminum w h i l e r e p l a c i n g by s i l i c o n and r e m o v i n g t h e E F A L f r o m t h e zeolite. However, and by f o l l o w i n g t h i s t r e a t m e n t , no more t h a n 40% o f t h e A l c o n t a i n e d i n a Y z e o l i t e c a n be removed u n d e r e c o n o m i c a l l y c o m p e t i n g p r o c e d u r e s (12) . N e v e r t h e l e s s , when t h e p r e d e a l u m i n a t i o n i s c a r r i e d o u t by t h i s p r o c e d u r e , t h e e q u i l i b r i u m c a t a l y s t has s t i l l EFAL p r e s e n t when t h e z e o l i t e becomes f u r t h e r d e a l u m i n a t e d i n the u n i t . I t i s p o s s i b l e t o e l i m i n a t e t h e EFAL formed d u r i n g t h e u l t r a s t a b i l i z a t i o n by s t e a m t r e a t m e n t , b y a c i d l e a c h i n g ( 6 , 1 3 ) . However, t h e p r o c e d u r e w i l l a l s o remove Al f r o m t h e framework, and p r o b a b l y w i l l g e n e r a t e a framework S i / A l g r a d i e n t a l o n g t h e c r y s t a l . I n a p r e v i o u s p a p e r (14) we h a v e shown t h a t b y an adequate t r e a t m e n t o f steam d e a l u m i n a t e d Y z e o l i t e s w i t h ( N H ) S i F i t i s p o s s i b l e t o remove s e l e c t i v e l y t h e E F A L . The p h y s i c o c h e m i c a l c h a r a c t e r i z a t i o n o f t h e s e samples shows t h a t t h e p r e s e n c e o f E F A L i s t h e r e s p o n s i b l e f o r t h e f o r m a t i o n o f s u p e r a c i d s i t e s , as w e l l as f o r t h e n e u t r a l i z a t i o n o f a p a r t o f framework h y d r o x y l s . I n t h i s work we have s t u d i e d t h e e f f e c t of the e l i m i n a t i o n o f t h e E F A L on t h e g a s o i l c r a c k i n g b e h a v i o u r of the z e o l i t e s . 4

4

2

2

6

6

Experimental S a m p l e s USY-1, USY-2 and U1F-25, U2F-15, U2F-35 were obtained f o l l o w i n g the procedure described in the p r e v i o u s paper (14). M o r e o v e r , a new USY s a m p l e (U1F25S) was o b t a i n e d by s t e a m i n g s a m p l e U1F-25 a t 7 5 0 C and 100% s t e a m d u r i n g 5 h o u r s . A c i d i t y m e a s u r e m e n t s were c a r r i e d o u t on w a f e r s o f 10 mg.cm" p r e v i o u s l y d e g a s s e d i n a I.R. c e l l a t 4 0 0 C and 10" Pa, o v e r n i g h t . 6.66.10 Pa o f p y r i d i n e were i n t r o d u c e d i n t o the cell at room temperature. After equilibrium, the samples were a

2

Q

3

In Fluid Catalytic Cracking II; Occelli, M.; ACS Symposium Series; American Chemical Society: Washington, DC, 1991.

2

14

FLUID CATALYTIC CRACKING II: CONCEPTS IN CATALYST DESIGN

a

o u t g a s s e d a t t e m p e r a t u r e s o f 250, 350 and 4 0 0 C u n d e r vacuum, and t h e s p e c t r a i n t h e 1800-1300 cm" region r e c o r d e d a t room t e m p e r a t u r e . I n t e n s i t i e s o f t h e bands a t 1540 cm" ( B r o n s t e d s i t e s ) and 1450 cm" (Lewis s i t e s ) and a p p a r e n t e x t i n c t i o n c o e f f i c i e n t s r e p o r t e d by Hughes and W h i t e (15) were u s e d t o d e t e r m i n e t h e amount o f a c i d centers. XPS measurements were performed following the experimental c o n d i t i o n s p r e v i o u s l y p u b l i s h e d (16). Cracking c a t a l y s t s were p r e p a r e d b y d i l u t i n g the z e o l i t e s i n a high surface s i l i c a matrix. A vacuum g a s o i l was cracked a t 482 C i n a t u b u l a r f i x e d bed reactor. The c a t a l y s t t o o i l r a t i o ( g . z e o l i t e / g . g a s o i l ) was v a r i e d b e t w e e n 0.1 and 1.1 g.g" , i n o r d e r t o o b t a i n d i f f e r e n t l e v e l s o f c o n v e r s i o n , t h e t i m e on s t r e a m was a l w a y s k e p t a t 60 s e c o n d s . I n t h i s way i t i s p o s s i b l e t o o b t a i n t h e y i e l d s o f g a s o l i n e , d i e s e l , g a s e s and c o k e , a t d i f f e r e n t l e v e l s o f c o n v e r s i o n , and t h e r e f o r e t o compare t h e s e l e c t i v i t i e s o f t h e d i f f e r e n t c a t a l y s t s a t t h e same l e v e l o f c o n v e r s i o n . The c a t a l y s t s were r e g e n e r a t e d " i n s i t u " a f t e r e a c h e x p e r i m e n t by p a s s i n g 6 ml.h" f l o w o f a i r a t 530°C f o r 5 h o u r s . G a s e s were a n a l y z e d by GC and s e p a r a t e d w i t h a Poropak-Q p l u s s i l i c a c o l u m n . Liquids were a n a l y z e d by S i m u l a t e d D i s t i l l a t i o n . C r a c k i n g o f n - h e p t a n e was c a r r i e d o u t on c a t a l y s t s USY-1 and U1F-25 i n a c o n t i n u o u s f l o w , f i x e d b e d r e a c t o r (15), at 450 C and atmospheric pressure. In a l l e x p e r i m e n t s , 0.223 g o f z e o l i t e c a t a l y s t , and 8.625 g o f n - h e p t a n e were u s e d . W i t h e a c h c a t a l y s t t h e r e a c t i o n was p e r f o r m e d a t 75, 150 and 375 s e c o n d s o f t i m e on s t r e a m . The catalyst was regenerated "in situ" after each e x p e r i m e n t by p a s s i n g f l o w o f a i r a t 5 2 0 C d u r i n g 4 h o u r s , and l i q u i d s were a n a l y z e d b y GC b y means o f a P o r a p a k - Q s i l i c a and a S-30 c o l u m n s r e s p e c t i v e l y . 1

C


1

1

a

a

R e s u l t s and

Discussion

The c h a r a c t e r i s t i c s o f a l l s a m p l e s a r e g i v e n i n T a b l e 1, while acidity measurements at different degassing t e m p e r a t u r e s a r e summarized i n T a b l e 2. Cracking

activity

F i g u r e l a shows t h e a c t i v i t y o f s a m p l e s USY-1 and UF1-25 for gasoil cracking. I t becomes a p p e a r e n t t h a t the extraction of E F A L by the (NH ) SiF treatment has decreased the activity of the zeolite catalyst, e v e n t h o u g h t h e b u l k framework S i / A l r a t i o h a s r e m a i n e d p r a c t i c a l l y unchanged a f t e r t h e c h e m i c a l t r e a t m e n t ( T a b l e 1) . I f one t r i e s t o e x p l a i n t h i s b e h a v i o u r o n l y on t h e b a s e s o f t h e framework A l , and s i n c e t h e g a s o i l c r a c k i n g takes place mainly at the external surface of the z e o l i t e c r y s t a l l i t e s , one c o u l d t h i n k t h a t e v e n t h o u g h t h e b u l k framework S i / A l has n o t been changed by t h e c h e m i c a l 4

2

6



80 85 80 85 65 65 65

USY-1 U1F-25 U1F-25S USY-2 U2F-15 U2F-35 USY-3

FAL/u.c.

27 24 5 9 9 9 8

2.447 2.445 2.428 2.431 2.431 2.431 2.430

0

a nm

1

Physicochemical

1053 1055 1078 1074 1073 1074 1076

Si-0

26 24 6 10 10 10 8

FAL/u.c.

2

EFAL

18 2 21 25 14 4 41

Framework Si/Al

6 7 35 21 21 21 23

c h a r a c t e r i s t i c s o f t h e samples

3

—

1.3 5.0 13.9

-

0.72 4.8

XPS Surface S i / A l

From u n i t c e l l p a r a m e t e r a n d F i c h t n e r - S m i t t l e r e q u a t i o n ( 2 0 ) . From S i - 0 a s y m m e t r i c s t r e t c h i n g f r e q u e n c y a n d Sohn e t a l . e q u a t i o n ( 2 1 ) . C a l c u l a t e d f r o m F A L (1) a n d t o t a l aluminum b y c h e m i c a l a n a l y s i s .

Crist. %

1.

Sample

Table


16

FLUID CATALYTIC CRACKING H: CONCEPTS IN CATALYST DESIGN

t r e a t m e n t , t h e ( N H ) S i F , b e s i d e s removing t h e EFAL has d e a l u m i n a t e d p r e f e r e n t i a l l y t h e framework o f t h e s u r f a c e of the c r y s t a l l i t e s . In order t o check t h a t p o s s i b i l i t y t h e s u r f a c e S i / A l r a t i o o f s a m p l e s USY-1 and U1F-25 h a v e b e e n m e a s u r e d by XPS and t h e r e s u l t s a r e g i v e n i n T a b l e 1. T h e y show t h a t , a s h a s b e e n p r e v i o u s l y p r e s e n t e d (17,18), i n t h e c a s e o f steam d e a l u m i n a t e d samples, a s e n s i b l e amount o f E F A L m i g r a t e s to the surface of c r y s t a l l i t e s decreasing the surface S i / A l r a t i o with respect to that of the bulk. The XPS a n a l y s i s o f t h e 4


Table

2.

2

6

B r o n s t e d and L e w i s a c i d i t y , m e a s u r e d a s mmols o f p y r i d i n e a d s o r b e d a t d i f f e r e n t temperatures Bronsted

SAMPLE

USY-1 U1F-25 U1F-25S USY-2 U2F-15 U2F-35 USY-3

a

Lewis a

250°C

350 C

400 C

167 302 10 26 134 145 14

109 169 5 16 80 74 7

60 101 4 8 30 23 4

250°C

52 23 4 23 83 27 15

fl

350 C

fi

400 C

40 19 2 15 75 25 6

35 19 2 9 68 25 4

z e o l i t e a f t e r the (NH ) SiF treatment o f t h e steamed sample, does n o t i n d i c a t e u n e q u i v o c a l y a p r e f e r e n t i a l d e a l u m i n a t i o n o f t h e framework a t t h e s u r f a c e . I n f a c t , the s u r f a c e S i / A l r a t i o i s c l o s e , but s l i g h t l y lower, t h a n t h a t o f t h e b u l k , s o m e t h i n g w h i c h c a n be e x p l a i n e d by t h e r e m a i n i n g 2 E F A L p e r u n i t c e l l w h i c h h a v e n o t b e e n extracted. The XPS results are i n favor of the hypothesis t h a t the (NH ) SiF has been used t o e x t r a c t E F A L and v e r y l i t t l e , i f any, i n e x t r a c t i n g framework A l f r o m t h e c r y s t a l l i t e s s u r f a c e . However, on t h e b a s e s o f t h e XPS r e s u l t s we can not c o m p l e t e l y r u l e d out the p o s s i b i l i t y o f a framework d e a l u m i n a t i o n a t t h e s u r f a c e and t h e r e f o r e t o r e j e c t c o m p l e t e l y t h e h y p o t h e s i s made above. What becomes c l e a r , however i s t h a t , e v e n i f a c e r t a i n d e p l e t i o n o f t h e FAL h a s o c c u r r e d a t t h e s u r f a c e o f t h e c r y s t a l l i t e s , most o f t h e b u l k framework S i / A l r a t i o has remained p r a c t i c a l l y unchanged. T h e n , i f we perform a c r a c k i n g r e a c t i o n w i t h a r e a c t a n t , n-heptane, which can e a s i l y penetrate i n s i d e o f the z e o l i t e , i f the s i t e s a s s o c i a t e d t o framework A l a r e t h e o n l y r e s p o n s i b l e f o r t h e c r a c k i n g we s h o u l d n o t e x p e c t d i f f e r e n c e s i n a c t i v i t y b e t w e e n s a m p l e s USY-1 and U1F-25. I n any c a s e , i t i s c l e a r t h a t i n t h i s case the s u r f a c e e f f e c t claimed f o r t h e g a s o i l w o u l d be n e g l i g i b l e . 4

2

4

6

2

6


CORMA ET AL.



Conversion (%)

Conversion (%)

Conversion (%)

F i g u r e 1. G a s - o i l c r a c k i n g a c t i v i t y o f samples USY-1 ( • ) a n d U1F-25 ( • ) ; b) USY-2 ( • ) , U2F( • ) a n d U2F-35 ( A ) ; c) USY-3 ( • ) a n d U1F-25S


18


R e s u l t s f r o m F i g u r e 2, show t h a t s a m p l e U1F-25 i s a b o u t 30% l e s s a c t i v e t h a n s a m p l e USY-1 f o r n-heptane cracking. T h i s r e s u l t c l e a r l y shows t h a t t h e sites associated to framework A l are not the only ones r e s p o n s i b l e f o r t h e c r a c k i n g a c t i v i t y , and a l s o t h a t t h e d i f f e r e n c e s i n g a s o i l a c t i v i t y given i n Figure l a are r e l a t e d w i t h t h e p r e s e n c e o f t h e EFAL. I n t h e p r e v i o u s p a p e r (14) we h a v e shown t h a t t h e ( N H ) S i F t r e a t m e n t o f r e l a t i v e l y low t e m p e r a t u r e s t e a m e d s a m p l e s p r o d u c e s an i n c r e a s e i n t h e i n t e n s i t y o f t h e HF and L F h y d r o x y l s due t o e x c h a n g e o f c a t i o n i c species (A10 , A1(0H) , e t c . . ) by protons, as well as an increase i n the Bronsted a c i d i t y m e a s u r e d by p y r i d i n e adsorption-desorption (Table 2). On t h e o t h e r hand, t h e ( N H . ) S i F t r e a t m e n t , removes n o t o n l y t h e E F A L s p e c i e s g i v i n g non a c i d i c OH g r o u p s a t 3670 and 3610 cm but a l s o those species d i r e c t l y or i n d i r e c t l y responsible f o r the v e r y s t r o n g a c i d h y d r o x y l g r o u p s a t 3600 and 3525 cm" (14,19). A f t e r the acidity measurements (pyridine a d s o r p t i o n - d e s o r p t i o n i n T a b l e 2 ) , i t becomes a p p a r e n t t h a t i f o n l y t h e a c i d s i t e s a s s o c i a t e d t o t h e HF and LF hydroxyls were a c t i v e f o r c r a c k i n g , t h e a c t i v i t y of s a m p l e U1F-25 s h o u l d be h i g h e r t h a n t h a t o f s a m p l e USY1. S i n c e t h e c o n t r a r y i s o c c u r r i n g , we h a v e t o c l a i m an important r o l e of those very strong Bronsted a c i d s i t e s a s s o c i a t e d t o h y d r o x y l s a p p e a r i n g a t 3600 and 3525 cm" , whose t u r n o v e r number w i l l be h i g h e r t h a n t h a t o f t h e c l a s s i c a l HF and LF h y d r o x y l b a n d s a s s o c i a t e d t o a c i d sites. The p r e s e n c e o f t h o s e s u p e r a c i d s i t e s h a s b e e n r e l a t e d w i t h t h e p r e s e n c e o f EFAL s p e c i e s e i t h e r as i n the form of amorphous silica-alumina, and/or by i n t e r a c t i o n o f c a t i o n i c E F A L s p e c i e s and B r o n s t e d (HF and LF) a c i d s i t e s ( 1 4 , 1 9 ) . I n any c a s e , i f a USY c r a c k i n g c a t a l y s t i s p r e p a r e d by s t e a m - c a l c i n a t i o n f o l l o w e d by an ( N H ) S i F treatment t o remove EFAL, t h e a c t i v i t y o f t h e t r e a t e d c a t a l y s t w i l l be l o w e r t h a n t h a t o f t h e c h e m i c a l l y u n t r e a t e d one. When t h e c h e m i c a l t r e a t m e n t i s a p p l i e d t o a s a m p l e p r e v i o u s l y steamed a t a h i g h e r t e m p e r a t u r e (725°C) , which would simulate the zeolite i n an equilibrium c a t a l y s t , o n l y a v e r y s m a l l , i f any, d e c r e a s e i n a c t i v i t y i s o b s e r v e d ( F i g . l b ) . The f a c t t h a t when t h e s t e a m i n g temperature i s high (> 7 0 0 C ) , t h e B r o n s t e d s i t e s of e n h a n c e d a c i d i t y (bands a t 3600 and 3525 cm" ) are not o b s e r v e d ( 8 ) , and o n l y t h e HF and L F b a n d s a r e p r e s e n t (8) , w i l l e x p l a i n t h e a c t i v i t y b e h a v i o u r o b s e r v e d f o r s a m p l e s USY-2 and U2F-35. I t r e m a i n s one s e t o f s a m p l e s t o be d i s c u s s e d , and t h i s i s t h e s a m p l e U1F-25 a f t e r s t e a m i n g a t 7 5 0 C (U1F25S) and an USY s a m p l e o f s i m i l a r u n i t c e l l s i z e (USY-3) . This treatment would simulate the behaviour of a 4

2

6


+

2

6

1

1

4

2

6

Q

1

a



2.

CORMA ET AL.


Conversion 10

(%)

r

T.O.S. (s) F i g u r e 2. USY-1 ( O )

N-heptane c r a c k i n g a n d U1F-25 ( • ) .

activity

of

samples


19

20

FLUID CATALYTIC CRACKING H: CONCEPTS IN CATALYST DESIGN

c l a s s i c a l USY z e o l i t e a f t e r c h e m i c a l t r e a t m e n t t o remove a l l E F A L and u l t e r i o r e q u i l i b r i u m i n t h e u n i t . Results f r o m F i g u r e l c , show t h a t s a m p l e U1F-25S p r e s e n t a s i m i l a r a c t i v i t y t h a t USY-3. Cracking

Selectivity

I n F i g u r e 3 t h e y i e l d s f o r g a s e s , g a s o l i n e , d i e s e l and coke a t d i f f e r e n t l e v e l s o f c o n v e r s i o n a r e g i v e n f o r s a m p l e s USY-1 and U1F-25. I t c a n be s e e n t h e r e t h a t when extracting t h e EFAL o f t h e lower t e m p e r a t u r e steam d e a l u m i n a t e d s a m p l e (U1F-25), t h e s e l e c t i v i t y t o g a s e s and c o k e i n c r e a s e s w h i l e t h a t t o g a s o l i n e and diesel decreases. S i n c e t h e ( N H ) S i F t r e a t m e n t o f s a m p l e USY1 produces the disappearance of the s t r o n g Bronsted a c i d s i t e s , and t h e i n c r e a s e o f t h e i n t e n s i t y o f t h e HF and L F h y d r o x y l bands, t h e n e t r e s u l t o f t h e c h e m i c a l t r e a t m e n t i s an i n c r e a s e i n t h e d e n s i t y o f c l a s s i c a l framework a c i d sites. T h i s , i n t u r n , w i l l make t h e s a m p l e more s i m i l a r t o one s t e a m e d a t a l o w e r t e m p e r a t u r e a n d t h e r e f o r e more s i m i l a r t o a sample w i t h a u n i t c e l l s i z e h i g h e r t h a n 24.47 A. R e s u l t s f r o m F i g u r e 4 shows t h a t when g a s o i l c r a c k i n g i s c a r r i e d o u t on s a m p l e s w i t h h i g h u n i t c e l l sizes (> 24.47 A) t h e s e l e c t i v i t y t o g a s e s and coke i n c r e a s e s when i n c r e a s i n g u n i t c e l l s i z e , w h i l e t h a t t o g a s o l i n e and d i e s e l d e c r e a s e s . These results would s u g g e s t t h a t Y z e o l i t e c a t a l y s t s w i t h low a c i d s t r e n g t h , i . e . z e o l i t e Y w i t h h i g h d e n s i t y o f a c i d s i t e s a n d low d e n s i t y o f s u p e r a c i d s i t e s (3600 and 3525 cm" ) , n o t o n l y are less active for cracking, but the cracking s e l e c t i v i t y b e h a v i o u r w i l l a p p r o x i m a t e more t o t h a t o f s a m p l e s s t e a m e d a t low t e m p e r a t u r e s . T h e n , we do n o t s e e any a c t i v i t y and selectivity b e n e f i t , from t h e p o i n t o f v i e w o f t h e f r e s h c a t a l y s t by introducing , i n f r e s h USY c r a c k i n g c a t a l y s t a z e o l i t e i n w h i c h most o f t h e E F A L h a s b e e n removed. I n t h e c a s e o f t h e h i g h e r t e m p e r a t u r e steamed sample USY-2, t h e ( N H ) S i F treatment does not produces b i g changes i n s e l e c t i v i t y but a s m a l l d e c r e a s e i n d r y gases and d i e s e l ( F i g . 5) . T h i s i n d i c a t e s t h a t the alumina t y p e EFAL formed a t h i g h t e m p e r a t u r e s p l a y s a p o s i t i v e r o l e f o r c r a c k i n g b o t t o m s , b u t a l s o p r o d u c e s more d r y gases. I n t h e c a s e o f z e o l i t e U1F-25S, t h e r e s u l t s from F i g u r e 6 show t h a t t h i s s a m p l e p r o d u c e s l e s s g a s e s and c o k e and more g a s o l i n e t h a n s a m p l e USY-3. T h e s e r e s u l t s w o u l d be i n a g r e e m e n t w i t h t h e h y p o t h e s i s made a b o v e , t h a t a l u m i n a t y p e EFAL, w h i l e b e i n g a c t i v e f o r b o t t o m s conversion i s less selective for gasoline and more s e l e c t i v e f o r g a s e s and c o k e .


4

2

6

1

4

2

6


CORMA ET AL.



2.

F i g u r e 3. S e l e c t i v i t y t o g a s e s , C I + C2, G a s o l i n e , D i e s e l , Coke a n d Butene/Butane ratio o f samples USY-1 ( • ) a n d U1F-25 ( • ) i n g a s - o i l c r a c k i n g .


21


F i g u r e 4. S e l e c t i v i t y t o Gases, G a s o l i n e , and Coke v e r s u s A l / u . c . o f USY s a m p l e s on c r a c k i n g a t 60% c o n v e r s i o n l e v e l .

Diesel gas-oil


CORMA ET AL.



2.

F i g u r e 5. S e l e c t i v i t y t o G a s e s , C I + C2, G a s o l i n e , D i e s e l , Coke a n d Butene/Butane r a t i o of samples USY-2 ( • ) , U2F-15 ( • ) a n d U2F-35 ( • ) i n g a s - o i l cracking.


23



24

F i g u r e 6. S e l e c t i v i t y t o G a s e s , C I + C2, G a s o l i n e , D i e s e l a n d Coke f o r s a m p l e s USY-3 ( • ) a n d U1F-25S ( • ) i n gas-oil cracking.


2. CORMA ET AL.

25


Acknowledgments F i n a n c i a l support by the g r a t e f u l l y acknowledged.

CICYT (project

MAT 88-0147)

is


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Influence of Superacid Sites in Ultrastable Y ... - ACS Publications

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