Fluid Catalytic Cracking II - ACS Publications - American Chemical

Chapter 20

Concepts for Future Residuum Catalyst Development 1

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P. O'Connor , A. W. Gevers , A. Humphries , L. A. Gerritsen , and P. H. Desai Downloaded by CHINESE UNIV OF HONG KONG on February 14, 2016 | http://pubs.acs.org Publication Date: January 23, 1991 | doi: 10.1021/bk-1991-0452.ch020

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Akzo Chemicals BV, P.O. Box 975, 3800 AZ Amersfoort, The Netherlands Akzo Chemicals, Inc., 3250 East Washington Boulevard, Los Angeles, CA 90023 Akzo Chemicals BV, P.O. Box 15, 1000 AA Amsterdam, The Netherlands Akzo Chemicals, Inc., 13000 Bay Park Road, Pasadena, TX 77058

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4

This paper reviews some main concepts for Resid Catalyst development. In the area of catalyst architecture, the effect of an enhanced accessibility of the active sites by the larger resid molecules, can significantly improve both conversion and bottoms cracking. Several generations of vanadium metal catchers have been developed (1, 2), leading to an improved activity retention at high vanadium levels on catalyst. The recent progress in nickel tolerance with new nickel encapsulation technologies i s just as dramatic. The reduced coke, gas and hydrogen make of these types of catalysts open the road to a significant increase in resid processing. Developments in the zeolite field in terms of non-framework alumina control, leading to super low delta coke zeolites and the advent of enhanced surface activity zeolites, seem promising for the resid cracking field (3). Resid upgrading in the refining industry Several forecasters (4) have predicted that the world's crude reserves are weighted about two to one in favor of heavy versus light crudes. Consequently the inevitable trend is that the average crude processed will become heavier. Market forces, regional demand, environmental considerations and other factors will determine the economics and justification for heavy oil conversion. But it is clear that in the global scene, there will be an increasing supply, of heavy oil.

0097-6156y91A)452-0318$07.25/0 © 1991 American Chemical Society In Fluid Catalytic Cracking II; Occelli, Mario L.; ACS Symposium Series; American Chemical Society: Washington, DC, 1991.

Downloaded by CHINESE UNIV OF HONG KONG on February 14, 2016 | http://pubs.acs.org Publication Date: January 23, 1991 | doi: 10.1021/bk-1991-0452.ch020

20.

O'CONNOR ETAL.

Future Residuum Catalyst Development

319

On t h e o t h e r h a n d , a s t e a d y d e c l i n e i n f u e l o i l c o n s u m p t i o n i n d i f f e r e n t r e g i o n s h a s b e e n r e p o r t e d (5, 6). Increasing supply, c o m b i n e d w i t h d e c r e a s i n g demand f o r o i l , c h a l l e n g e s t h e r e f i n e r i e s t o i n v e s t i g a t e c r e a t i v e s o l u t i o n s t o t h e r e s i d p r o b l e m . The m a i n o b j e c t i v e i s t o convert the heavy r e s i d to d e s i r a b l e t r a n s p o r t a t i o n fuels. Several hydrocarbon processes are a v a i l a b l e f o r upgrading r e s i d : h y d r o t r e a t i n g , F l u i d C a t a l y t i c Cracking (FCC), coking e t c . , some m o r e c a p i t a l i n t e n s i v e t h a n o t h e r s . The m o s t w i d e l y p r e v a l e n t p r o c e s s i s t h e FCC p r o c e s s . T h e r e f o r e a n y a d v a n c e s i n p r o c e s s i n g r e s i d i n FCC u n i t s w i l l h a v e w i d e a p p l i c a t i o n . T h i s p a p e r d e a l s w i t h concepts f o r developments i n r e s i d c r a c k i n g , p a r t i c u l a r l y i n r e s i d FCC d e v e l o p m e n t , e v a l u a t i o n a n d a p p l i c a t i o n . W h e r e a s w o r l d w i d e demand f o r g a s o l i n e i s e x p e c t e d t o r e m a i n m o r e o r l e s s c o n s t a n t , demand f o r m i d d l e d i s t i l l a t e s (diesel, kerosene, j e t f u e l ) i s expected to increase. Resid cracking to y i e l d g a s o l i n e does not always l e a d t o f a v o r a b l e economics. Making midd i s t i l l a t e s f r o m r e s i d h o w e v e r , may o f f e r i n t e r e s t i n g o p p o r t u n i t i e s . Resid

Processing

F r o m a n FCC v i e w p o i n t , t h e r e i s n o t a c l e a r d e f i n i t i o n o f r e s i d c r a c k i n g . I f we c o n s i d e r t h e o v e r a l l r e f i n e r y s c h e m e , a l l m a t e r i a l s n o t q u a l i f y i n g f o r gas o i l t y p e s p e c i f i c a t i o n s a r e r e s i d , w h i c h i n f a c t means t h a t t h e t r a d i t i o n a l FCC f e e d , V a c u u m G a s o i l ( V G O ) , i s n e a r l y 1 0 0 % r e s i d , o r t o be m o r e s p e c i f i c a f u e l o i l . The f a c t t h a t a t r a d i t i o n a l VGO FCC u n i t i s a l s o a " f u e l o i l " c r a c k e r , c a n be i l l u s t r a t e d b y t h e f a c t t h a t p r o c e s s i n g o f VGO in a FCC u n i t i n a r e f i n e r y r u n n i n g on M i d d l e E a s t c r u d e , w i l l r e d u c e t h e h e a v y f u e l o i l p r o d u c t i o n o f t h e r e f i n e r y by a b o u t 10% wt on crude ( 7 ) . F o r c o n v e n t i o n a l VGO c r a c k i n g t h e s h a r p n e s s o f t h e v a c u u m s e p a r a t i o n between t h e f l a s h e d d i s t i l l a t e and r e s i d u e i s n o t r e a l l y important, provided that the undesirable n o n - v o l a t i l e asphalthenes and m e t a l compounds a r e l e f t i n t h e r e s i d u e . E n t r a i n m e n t i s k e p t a t a minimum by a wash o i l s e c t i o n i n t h e v a c u u m u n i t a n d c h e c k e d w i t h a c o l o u r s p e c i f i c a t i o n o n t h e FCC feed. The " r e a l " FCC r e s i d c r a c k i n g s e e m s t o s t a r t , w h e n t h e w a s h o i l s t r e a m i n t h e v a c u u m c o l u m n i s a l s o r o u t e d t o t h e FCC u n i t , o b v i o u s l y t h e c o l o u r o f t h e FCC f e e d w i l l d e t e r i o r a t e s t r o n g l y . D e p e n d i n g on t h e c r u d e o r i g i n , a l r e a d y t h e i n t r o d u c t i o n o f d i r t y w a s h o i l c a n h a v e a s i g n i f i c a n t i m p a c t on t h e m e t a l c o n t e n t o f t h e FCC f e e d a n d h e n c e t h e c a t a l y s t . S e v e r a l d e a s p h a l t i n g p r o c e s s e s o p e n up t h e p o s s i b i l i t y t o c u t d e e p e r , b u t a l s o m o r e s e l e c t i v e i n t e r m s o f a s p h a l t h e n e and m e t a l c o n t e n t i n t o t h e r e s i d . H i g h t e m p e r a t u r e deep f l a s h i n g and vacuum f l a s h i n g o f t h e r m a l l y cracked d i s t i l l a t e a l s o c o n t r i b u t e s to i n c r e a s i n g the percentage of t h e c r u d e , w h i c h c a n be r o u t e d t o t h e FCC u n i t . I n t h e u l t i m a t e c a s e , d e p e n d i n g on t h e f e e d s t o c k o r i g i n and t h e FCC u n i t o p e r a t i o n a l c o n s t r a i n t , e v e n 100% a t m o s p h e r i c r e s i d u e c a n s o m e t i m e s be p r o c e s s e d i n t h e FCC u n i t . ( T a b l e I.)

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

320

FLUID CATALYTIC CRACKING II: CONCEPTS IN CATALYST DESIGN

Table

- VGO

Cracking


- HVGO/DAO

I . R e s i d C r a c k i n g i n FCC

- Vacuum G a s o i l c l e a r , no m e t a l s

- Vacuum F l a s h e d d i s t i l l a t e from atmospheric r e s i d

-

- C u t t i n g deeper into the barrel, while trying to avoid excessive a s p h a l t h e n e s and metals

H e a v y VGO, Wash o i l s D e e p F l a s h e d VGO Flashed Cracked residues Deasphalted O i l

- Resid Cracking - Atmospheric

Residue

(AR)

- Crude s e l e c t i o n to avoid excessive asphalthenes and metals Pretreatment t o reduce asphalthenes and m e t a l s

Processability of resids

i n FCC

units

I t i s w e l l known t h a t t h e p r o c e s s i n g o f h e a v i e r , more c o n t a m i n a t e d feedstocks (metals, asphaltenes) tends t o i n c r e a s e t h e p r o d u c t i o n of coke and gas and d e a c t i v a t e s t h e c a t a l y s t . T h i s i s m a i n l y t h e r e s u l t s of( 8 ) : (1) A l a r g e r f e e d f r a c t i o n t h a t does n o t v a p o r i z e under c o n v e n t i o n a l c r a c k i n g c o n d i t i o n s . F o r t h i s r e a s o n r e s i d i n FCC i s s o m e t i m e s d e f i n e d as t h e f r a c t i o n o f t h e f e e d b o i l i n g above an e f f e c t i v e " o u t p o i n t " o f t h e f l a s h i n t h e b o t t o m o f t h e FCC r i s e r . Depending on t h e e x p e c t e d bottom mix t e m p e r a t u r e , c u t p o i n t s o f 5 3 0 u p 560°C a r e m e n t i o n e d i n t h e l i t e r a t u r e . ( 2 ) C o n t a m i n a t i o n b y h e a v y m e t a l s ( V , N i ) . To m a i n t a i n t h e m e t a l c o n t e n t on c a t a l y s t c o n s t a n t , u s u a l l y a l a r g e i n c r e a s e i n c a t a l y s t c o n s u m p t i o n ( f r o m a n a v e r a g e o f 0.15 l b / b b l u p t o a n d a b o v e 0.5 l b / b b l ) i s r e q u i r e d . A l t e r n a t i v e l y s p e c i a l m e t a l r e s i s t a n t c a t a l y s t c a n be a p p l i e d i n o r d e r t o m i n i m i z e c a t a l y s t consumption. A r b i t r a r i l y a metals c o n t e n t ( N i + V) o f above 1500 ppm o n c a t a l y s t i s s o m e t i m e s c o n s i d e r e d t o b e a m e t a l s contaminated r e s i d operation. (3) A h i g h e r c o n c e n t r a t i o n o f b a s i c and p o l a r m o l e c u l e s , i . e . n i t r o g e n compounds t h a t a r e r e a d i l y a d s o r b e d on t o t h e c a t a l y s t a c i d i c s i t e s , l e a d i n g t o an i n s t a n t , b u t temporary d e a c t i v a t i o n . P o l y c y c l i c aromatics a l s o s t r o n g l y c o n t r i b u t e t o coke f o r m a t i o n .


20. O'CONNOR ETAL. (A)


Other poisons as a l k a l i

contaminants

321

(Na, K....).

The h i g h e r c o k e p r o d u c t i o n o f r e s i d f e e d s t o c k s w i l l a l s o t e n d t o i n c r e a s e t h e temperature o f t h e regenerator and hence t h e deactivation of thecatalyst.


F r o m t h e f o r e g o i n g i t b e c o m e s o b v i o u s t h a t t h e FCC p r o c e s s a b i l i t y o f r e s i d f e e d s t o c k a n d t h e c h o i c e o f a p o s s i b l e FCC f e e d p r e t r e a t m e n t ( f o r i n s t a n c e R e s i d H y d r o p r o c e s s i n g ) w i l l depend on t h e feed q u a l i t y and hence i t s o r i g i n . N a b e r e t a l ( 9 ) h a v e d e m o n s t r a t e d t h a t FCC s t i l l h a s a considerable p o t e n t i a l t o remain t h e ( r e s i d ) conversion "workhorse" of t h e o i l i n d u s t r y . A t present about 45% o f t h e world's crude can be e n v i s i o n e d t o b e w i t h i n t h e f r o n t i e r s o f R e s i d FCC ( f i g u r e 1 ) . A p a r t f r o m t h e i m p o r t a n c e o f FCC f e e d p r e t r e a t m e n t a n d FCC u n i t d e s i g n , a l s o t h e i m p a c t o f FCC c a t a l y s t p e r f o r m a n c e i s c r u c i a l t o allow the processing of heavier feeds. The

Catalyst Role i n Resid

FCC

R e v i e w i n g t h e m a i n c h a l l e n g e s i n R e s i d F C C , we c a n e s t a b l i s h t h e a r e a s i n w h i c h FCC c a t a l y s t i m p r o v e m e n t s c a n p l a y a r o l e i n enhancing t h e p r o c e s s a b i l i t y o f resids. (see Table I I . )

(a) V a p o r i z a t i o n and c r a c k i n g o f l a r g e hydrocarbons: T h i s leads t o a poor conversion and higher coke and f u e l gas y i e l d s . I n order t o improve t h e conversion o f l a r g e molecules, new m o d i f i c a t i o n s i n t h e FCC C a t a l y s t A r c h i t e c t u r e a n d A c t i v e S i t e A c c e s s i b i l i t y , a r e r e q u i r e d i n terms o f Pore S i z e and Pore Acidity distribution. (b) C o n t a m i n a t i o n by heavy m e t a l s (V, N i ) : S e v e r a l c a t a l y s t s on t h e market today c o n t a i n s p e c i a l vanadium t r a p s o r vanadium scavengers i n order t o p r o t e c t t h e a c t i v e i n g r e d i e n t s a g a i n s t p o i s o n i n g and/or d e s t r u c t i o n by Vanadium. These " M e t a l Traps" l i m i t t h e m o b i l i t y o f t h e vanadium pentoxide c o m p o u n d s u n d e r FCC c o n d i t i o n s ( 2 , 1 0 ) . T h e n i c k e l p r o b l e m n e e d s t o b e a p p r o a c h e d d i f f e r e n t l y : a n d more r e c e n t l y , p r o g r e s s h a s b e e n made t o w a r d s r e d u c i n g t h e d e h y d r o g e n a t i o n a c t i v i t y o f n i c k e l d i s p e r s e d o n FCC c a t a l y s t s ( 1 1 ) . ( c ) P o i s o n i n g a n d coke f o r m a t i o n by b a s i c a n d p o l a r compounds: High n i t r o g e n r e s i s t a n t c a t a l y s t s and/or n i t r o g e n t r a p s a r e a v a i l a b l e nowadays; u n f o r t u n a t e l y , no r e a l b r e a k t h r o u g h s have b e e n made i n r e d u c i n g t h e e f f e c t o f p o l y c y c l i c a r o m a t i c s (Conradson Carbon C a t c h e r s ? ) . A t present super low d e l t a coke c a t a l y s t s a r e produced t o a l l o w f o r t h e a d d i t i o n a l coke produced by t h e s e p o l y c y c l i c a r o m a t i c s . (d) A c t i v e s i t e p o i s o n i n g by Sodium, P o t a s s i u m ; e t c The S o d i u m r e s i s t a n c e o f t h e a c t i v e i n g r e d i e n t s i n FCC c a t a l y s t s can a l s o be t a c k l e d b y high a c t i v i t y a n d s t a b i l i t y c a t a l y s t s . (e) Severe Hydrothermal regeneration conditions: An i m p r o v e m e n t i n c o k e s e l e c t i v i t y c a n h a v e a l a r g e i m p a c t o n



322


100 IRAN Hy 90

Q UJ

IRAN

ARAB Hy

It

80-

U.J U. 70

KUWAIT

% OF TOTAL

60 E CL CL

WORLD CRUDE RESERVES

50-

>

+

7

45^

SIRTICA

40

ARAB LT

30

'30* EKOFISK ESSIDER

20

STATE OF ART

CURRENT BORDERLINE

SARIR

10 LT.PARAFFINIC ATM. RESIDU i—r~ 0 4 2

8

10

n—r 12

14

" i — i—I— 16 18

20

%WT CCR IN FEED

Figure

1

: R e s i d ( 3 7 0 °C TBP+) p r o p e r t i e s i n r e l a t i o n t o FCC p r o c e s s a b i l i t y (see Ref. 9 ) . Reprinted with permission from N a t i o n a l Petroleum R e f i n e r s A s s o c i a t i o n p u b l i c a t i o n AM-90-42. C o p y r i g h t 1 9 9 0 .



II.

by heavy

- Severe Hydrothermal Conditions

E

D Other poisons

- Basic and polar compounds

Contamination metals

A Vaporization and cracking of l a r g e hydrocarbon molecules

Table

Resid

Challenges

- Catalyst deactivation/ s t a b i l i t y problems

A c t i v e s i t e poisoning by e.g. Sodium

a c t i v e s i t e poisoning by Nitrogen Coke formation and a c i d s i t e blocking by polyc y c l i c aromatics

C a t a l y s t d e a c t i v a t i o n by Vanadium Dehydrogenation a c t i v i t y of N i c k e l

- High A c t i v i t y and Catalysts

Stability

- Sodium Catcher/Resistance

Nitrogen Catcher/Resistance Conradson Carbon Catcher?

Vanadium Catcher/Resistance Reduction of N i c k e l A c t i v i t y

Catalyst Architecture

and C a t a l y s t Development

Unvaporized feed r e s u l t s i n poor conversion and higher coke and fuelgas production

Processing


324


the a c t i v i t y s t a b i l i t y v i a t h e regenerator temperature High a c t i v i t y and s t a b i l i t y c a t a l y s t s a r e r e q u i r e d .

reduction.


I t i s o b v i o u s t h a t d e p e n d i n g o n t h e t y p e a n d s e v e r i t y o f FCC f e e d pretreatment (Coking, Hydrogenation/Demetallization) and t h e type o f FCC u n i t d e s i g n a n d o p e r a t i n g p h i l o s o p h y t h e p r i o r i t y o f t h e f o r e g o i n g a s p e c t s may d i f f e r c o n s i d e r a b l y . A n i n t e r e s t i n g e x a m p l e i s t h e c o m p a r i s o n b e t w e e n t h e o p e r a t i o n o f FCC u n i t s w i t h a n d without heat removal, (Table I I I . )

A l t h o u g h t h e t a b l e g i v e s a v e r y exaggerated comparison between t h e two c a s e s , i t d o e s c l e a r l y d i s t i n g u i s h t h e i r p r i o r i t i e s . I t i s a l s o c l e a r t h a t i n t h e c a s e o f FCC w i t h h e a t r e m o v a l , t h e f r o n t i e r o f r e s i d p r o c e s s a b i l i t y c a n a t a c e r t a i n moment b e d e t e r m i n e d by t h e c o k e s e l e c t i v i t y o f t h e c a t a l y s t , w h i l e on t h e o t h e r hand t h e c o n v e r s i o n o f r e s i d i n a u n i t w i t h o u t heat removal may a l s o b e l i m i t e d b y t h e m e t a l r e s i s t a n c e o f a c a t a l y s t . Catalyst Accessibility i.

and A r c h i t e c t u r e

D i f f u s i o n and a c t i v e s i t e

accessibility

The a c c e s s i b i l i t y o f a c t i v e s i t e s p l a y s a n i m p o r t a n t r o l e i n t h e a c t i v i t y a n d s e l e c t i v i t y o f FCC. F o r r e s i d c r a c k i n g d i f f u s i o n a n d a c c e s s i b i l i t y e f f e c t s c a n become o f p r i m e i m p o r t a n c e . I n a p r e v i o u s p a p e r ( 7 ) , we h a v e i l l u s t r a t e d t h a t d i f f u s i o n i n FCC t a k e s p l a c e i n t h e n o n - s t e a d y r e g i m e a n d t h a t t h i s e x p l a i n s t h e f a i l u r e o f s e v e r a l a t t e m p t s t o r e l a t e l a b o r a t o r y m e a s u r e m e n t s o n FCC c a t a l y s t s t o t h e o r i e s on s t e a d y s t a t e d i f f u s i o n . A p a r t from t h e d i f f u s i o n a s p e c t s , Nace ( 1 3 ) h a s a l s o i n d i c a t e d t h e l i m i t e d a c c e s s i b i l i t y o f t h e z e o l i t e p o r t a l s u r f a c e area by comparing t h e c r a c k i n g r a t e s o f v a r i o u s m o d e l compounds w i t h a n i n c r e a s i n g number o f n a p h t h e n i c r i n g s o n z e o l i t e a n d a m o r p h o u s FCC c a t a l y s t s , f i g u r e 2. W i t h an i n c r e a s e i n t h e number o f n a p h t h e n i c r i n g s , t h e c r a c k a b i l i t y o f t h e h y d r o c a r b o n m o l e c u l e i n c r e a s e s ( v i d e d a t a w i t h SiO^,AlÔ^ c a t a l y s t ) , w h i l e t h e r e l a t i v e c r a c k i n g r a t e by z e o l i t e s d r o p s o f f due t o t h e l i m i t e d a c c e s s i b i l i t y o f t h e a c i d s i t e s i n t h e zeolite. I t becomes c l e a r t h a t s i g n i f i c a n t c o n v e r s i o n b e n e f i t s c a n be o b t a i n e d b y i n c r e a s i n g t h e a c t i v i t y c o n t r i b u t i o n i n t h e meso p o r e r a n g e ( a b o u t 20 t o 2 0 0 A n g s t r o m d i a m e t e r ) i n a c a t a l y s t , T a b l e I V . R e s u l t s o b t a i n e d f r o m t e s t i n g v a r i o u s c a t a l y s t s w i t h Vacuum g a s o i l (VGO) a n d A t m o s p h e r i c R e s i d u e ( A R ) c o n f i r m t h a t i n d i c a t e d i m p r o v e m e n t o f FCC c o n v e r s i o n .



C a t a l y s t development Category

Operating goal

Catalyst p r i o r i t y

Catalyst to o i l ratio Coke production Regenerator temperature Delta Coke on c a t a l y s t

Tvpicals

Strategy

Table

1. 2. 3. 4.

III.

FCC O p e r a t i n g

RESID-2

"MAXIMIZE CTO"

Super low d e l t a coke Hydrothermal s t a b i l i t y Catalyst a r c h i t e c t u r e Metal resistance

low low high low

Without heat removal

Resid

Strategy

1. 2. 3. 4.

RESID-1

"MAXIMIZE ACTIVITY"

Metal resistance High a c t i v i t y / s t a b i l i t y Catalyst a r c h i t e c t u r e Low d e l t a coke

high high low high

With heat removal


326


Table I V . Impact o f enhanced a c c e s s i b i l i t y


Catalyst

A B C D Development

Mesopore Surface area

Mesopore activity

low high medium high medium

low high medium medium medium

on c o n v e r s i o n

Conversion i n MST t e s t , w t % Delta VGO AR

63 63 62 68 66

63 65 64 74 74

+ + + +

0 2 2 6 8

MST = M i c r o S i m u l a t i o n T e s t ( 1 4 ) ; H i g h T e m p e r a t u r e , S h o r t c o n t a c t T i m e MAT (560°C, 15 s e c o n d s ) VGO = K u w a i t AR = North Sea C a t a l y s t D e a c t i v a t i o n : 5 h r s 788°C, 1 0 0 % s t e a m , 1 5 0 0 ppm N i

A l t h o u g h a n i n c r e a s e i n meso p o r e s u r f a c e a r e a a n d a c t i v i t y w i l l r e s u l t i n an i n c r e a s e i n c o n v e r s i o n and r e s i d c o n v e r s i o n , T a b l e I V a l s o shows t h a t t h e r e i s no s i m p l e c o r r e l a t i o n between t h e o b s e r v e d c a t a l y s t p r o p e r t i e s and these r e s u l t s . A p p a r e n t l y other aspects such as pore s i z e d i s t r i b u t i o n and pore c h e m i s t r y a l s o p l a y an important r o l e . A n o t h e r a s p e c t w h i c h needs t o be c o n s i d e r e d i s t h e e f f e c t o f c a t a l y s t t o o i l r a t i o . I n a c o m m e r c i a l u n i t t h e e f f e c t i v e meso p o r e a c t i v i t y w i l l b e a f u n c t i o n o f t h e meso p o r e a c t i v i t y o f t h e c a t a l y s t and o f t h e c a t a l y s t t o o i l r a t i o (CTO): E f f e c t i v e meso p o r o s i t y = M e s o p o r o s i t y x CTO M e s o p o r o s i t y i s expressed i n terms o f s u r f a c e a r e a as measured by Hg a d s o r p t i o n i n t h e 20 t o 100 A n g s t r o m r a n g e . F i g u r e 3 i n d i c a t e s how t h e e f f e c t i v e meso p o r e a c t i v i t y h a s a s t r o n g e f f e c t o n c o n v e r s i o n o f bottoms i n t h e case o f Atmospheric Residue, w h i l e t h i s e f f e c t i s much l e s s p r o n o u n c e d i n t h e c a s e o f VGO f e e d s t o c k . F o r a c o m m e r c i a l u n i t t h i s i m p l i e s t h a t we n e e d t o e n h a n c e t h e meso p o r e a c t i v i t y w h i l e a v o i d i n g a d r o p i n CTO d u e t o ( f o r i n s t a n c e ) a h i g h e r d e l t a coke o f t h e c a t a l y s t . ii.

Pore

Size Acidity

Distribution

In an i d e a l i z e d s i t u a t i o n one c a n o p t i m i z e s e v e r a l s t a g e s cracking of a r e s i d molecule: Stage

i n the

one : C a t a l y s t s o r b s non v o l a t i l e o r p a r t i a l l y v o l a t i l e r e s i d . L a r g e a s p h a l t h e n e s c r a c k and decompose n e a r l y i n s t a n t a n e o u s l y , and m e t a l s a r e d e p o s i t e d on t h e c a t a l y s t s u r f a c e .


20. O'CONNOR ET AL.

k /


327

ko

4 Si02-A1203 Zeolite


\ \

Accessibility Limitation k

= Cracking r a t e

ko = Cracking r a t e of C16

—i

i

'0

i

i

.i — i —

i—J—-u-

1 2 3 4 Naphthenic r i n g s 12 13 14 16 Carbon number

16

Figure 2

Bottoms,

5

: Active Site

accessibility (13).

wt%

15 VGO

ATM.RESID

CTO * PV-Meso MST a t Figure 3

70 wt%

(20-100 Ad) conversion

: Effective

Mesoporosity

concept.


328


Stage two

: L a r g e h y d r o c a r b o n m o l e c u l e s p r e c r a c k i n meso p o r e s .


Stage three: Hydrocarbon

c r a c k i n g on s u r f a c e o f and i n z e o l i t e

pores.

H e t t i n g e r e t a l (7) have p r e s e n t e d t h i s staged c r a c k i n g concept as a useful m o d e l f o r FCC r e s i d c a t a l y s t d e s i g n ( f i g u r e 4 ) . B a s e d o n t h i s m o d e l we c a n e n v i s i o n a v e r y s p e c i f i c P o r e S i z e A c i d i t y D i s t r i b u t i o n ( f i g u r e 5 ) , w h i c h would b e n e c e s s a r y t o a c h i e v e a n i m p r o v e ment i n r e s i d c o n v e r s i o n . We h a v e n o t e d t h a t r e g a r d i n g t h e n e c e s s i t y o f s p e c i a l l a r g e " L i q u i d c a t c h i n g " (LC) p o r e s , t h e r e i s a v e r y s i g n i f i c a n t impact on coke and f u e l gas s e l e c t i v i t y . F i g u r e 6 s h o w s a n e x a m p l e o f t h e c o k e s e l e c t i v i t y i n t h e MST u n i t w i t h a n o r m a l VGO f e e d s t o c k . A n o t h e r i n t e r e s t i n g f e a t u r e i s t h a t t h e s e LC p o r e s r e s u l t i n a n i n c r e a s e i n t h e o v e r a l c o n v e r s i o n . T h i s e f f e c t i s most pronounced when t h e c a t a l y s t i s i m p r e g n a t e d w i t h N i c e l ( 1 5 0 0 ppm N i c k e l i n MST) and a t h i g h c o k e y i e l d s . From t h i s i t seems o b v i o u s t h a t p o r e mouth b l o c k i n g i s a l s o a f a c t o r i n R e s i d FCC, and t h a t t h e p r e s e n c e o f LC p o r e s c a n b e b e n e f i c i a l i n t h i s r e s p e c t . M e s o p o r e s , a r e e s s e n t i a l f o r r e d u c t i o n o f t h ebottoms y i e l d w i t h a r o m a t i c and/or n a p h t h e n i c f e e d s t o c k s . ( T a b l e V.)

T a b l e V.

Impact

Bottoms y i e l d

o f meso p o r e a c t i v i t y

i n t h e MST a t 4 w t % c o k e '*) A r o m a t i c/Napthen i c Feedstock

Cat.

Cat.

Cat.

A

high zeolite activity l o w meso p o r e activity medium z e o l i t e activity h i g h meso p o r e activity medium z e o l i t e activity h i g h meso p o r e activity

B

C

* MST t e s t

with

1 5 0 0 ppm N i , c a t a l y s t

Paraffinic Feedstock

14.5

11.5

12.0

13.2

11.0

10.5

deactivated

5 h o u r s a t 788°C.


20.

O'CONNOR ETAL.


329

Liquid asphaltene Non-Acidic large pores


1

Acidic Matrix

H+ \//////////////////////////A

H+

iC4. C5=, C3= e t c .

Z e o l i t e P o r t a l S u r f a c e Area Figure 4

Surface Area

Small

: Staged C r a c k i n g Model

(15).

Relative

Pores

Activity

< 20 Ad

"Liquid catching" Large Pores > 100 Ad

Meso P o r e s 30

J

- 100 Ad

L_J I I I I I I I Pore Diameter

Figure 5

1

: Poresize Acidity

i

1

I

I

I

L

• Distribution.



330


T a b l e 5 i n d i c a t e d t h e l a r g e e f f e c t o f m e s o p o r e a c t i v i t y on t h e r e d u c t i o n of bottoms y i e l d w i t h Aromatic/Naphthenic feedstocks. For the p a r a f f i n i c feedstocks t e s t e d , the impact of the z e o l i t e a c t i v i t y i s much more p r o n o u n c e d , and t h e c a t a l y s t w i t h t h e h i g h e s t z e o l i t e a c t i v i t y and l o w e s t mesopore a c t i v i t y g e n e r a t e s t h e lowest bottoms y i e l d . T h e s e r e s u l t s seem t o c o r r e l a t e w e l l w i t h t h e "conceptual p i c t u r e " o f s t a g e d c r a c k i n g a s p r e s e n t e d by H e t t i n g e r ( f i g u r e 5 ) a n d t h e i n f l u e n c e o f m o l e c u l a r s t r u c t u r e ( l a r g e number o f r i n g s v s low number o f r i n g s ) on t h e e f f e c t i v e n e s s o f t h e z e o l i t e a c t i v i t y a s i n d i c a t e d by Nace ( f i g u r e 2 ) . A s a l i e n t p o i n t o f t a b l e 5 i s t h e f u r t h e r r e d u c t i o n of bottoms y i e l d s obtained w i t h a s p e c i a l technology h i g h mesopore a c t i v i t y c a t a l y s t (Cat. C). F i g u r e 7 i l l u s t r a t e s t h a t t h e r e i s an e s s e n t a i l d i f f e r e n c e i n the pore s i z e a r c h i t e c t u r e between c a t a l y s t s produced w i t h t h i s t e c h n o l o g y ( C a t . C) a n d t h o s e p r o d u c e d w i t h t h e o t h e r m a n u f a c t u r i n g t e c h n o l o g i e s ( C a t . A , B ) . W i t h t h e C a t . C T e c h n o l o g y ( h i g h meso p o r e a c t i v i t y c a t a l y s t s ) t h e r e i s a s h i f t t o w a r d s more p o r e s i n t h e " l a r g e r " meso p o r e a r e a (Table IV.) Catalyst Resistance i.

t o D e a c t i v a t i o n by

Metals

S t r a t e g i e s to reduce vanadium e f f e c t s

There a r e s e v e r a l good r e v i e w a r t i c l e s w h i c h c o v e r t h e r e s e a r c h o f t h e m e c h a n i s m o f v a n a d i u m d e a c t i v a t i o n o f FCC c a t a l y s t s ( s e e 2, 8). B a s i c a l l y the vanadium present i n the l a r g e metal porphorin m o l e c u l e s i s d e p o s i t e d o n t h e o u t e r s u r f a c e o f t h e c a t a l y s t , due to the f a s t decomposition of these molecules. A t h i g h t e m p e r a t u r e s and i n t h e p r e s e n c e o f s t e a m , v a n a d i u m b e c o m e s m o b i l e a n d m o v e s i n t o o t h e r p a r t s o f t h e c a t a l y s t . I n a FCC u n i t t h i s t a k e s p l a c e d u r i n g t h e r e g e n e r a t i o n p h a s e ( a v e r a g e 700°C a n d 5 - 2 5 % s t e a m a t m o s p h e r e ) . V a n a d i u m o x i d e VÔ^ formed d u r i n g r e g e n e r a t i o n c a n r e a c t w i t h t h e z e o l i t e , REÔ^, Na a n d AÔ-* p r o m o t i n g d e s t a b i l i z a t i o n and c o l l a p s e o f t n e z e o l i t e s t r u c t u r e (16, 17). Even i n the case t h a t a very s t a b l e z e o l i t e i s a b l e t o w i t h s t a n d t h i s a t t a c k , a c t i v i t y l o s s e s c a n o c c u r due t o n e u t r a l i z a t i o n o f t h e z e o l i t e and m a t r i x a c i d s i t e s . FCC c a t a l y s t d e v e l o p m e n t t o r e d u c e t h e e f f e c t o f v a n a d i u m h a s been aimed a t r e d u c t i o n of vanadium m o b i l i t y : the a p p l i c a t i o n of s p e c i a l i n g r e d i e n t s i n t h e c a t a l y s t w h i c h f u n c t i o n as m e t a l s c a v e n g e r s o r m e t a l c a t c h e r s . I n t h e p a s t ( 2 , 10) t r a n s p o r t e x p e r i m e n t s w e r e u s e d t o show t h a t d u r i n g s t e a m - a g i n g , i n t r a p a r t i c l e t r a n s f e r o f v a n a d i u m o c c u r s a n d t h a t m i g r a t i n g v a n a d i u m c a n be i r r e v e r s i b l y s o r b e d by a m e t a l t r a p s u c h as s e p i o l i t e ( 2 ) i n t h e form of a heat s t a b l e vanadate. A s i m p l e v a n a d i u m m o b i l i t y t e s t c a n be s e t u p , i n w h i c h t h e vanadium which migrates from vanadium-loaded c a t a l y s t towards n o n - v a n a d i u m l o a d e d c a t a l y s t c a n be m e a s u r e d u n d e r c a t a l y s t a g i n g ( u s u a l l y steaming) conditions (2). The m e t h o d we a p p l i e d i s a s f o l l o w s : The c a t a l y s t i s s i e v e d i n t o a c o a r s e a n d a f i n e f r a c t i o n . The c o a r s e f r a c t i o n o f t h e c a t a l y s t (PSD > 7 5 yum) i s i m p r e g n a t e d h o m o g e n e o u s l y w i t h a b o u t 4 0 0 0 ppm v a n a d i u m fey a t r a d i t i o n a l p o r e v o l u m e i m p r e g n a t i o n method.



O'CONNOR ET AL.


1

58

60

62

64

66

68

70

72

CONVERSION, WT% Figure 6

: Selectivity

b e n e f i t of improved pore

architecture.


331

332


A f t e r t h i s both f r a c t i o n s a r e mixed t o g e t h e r a g a i n , and t h e m i x t u r e i s s t e a m e d i n a f i x e d b e d f o r 5 h o u r s a t 7 8 8 o r 830°C, w i t h 1 0 0 % steam. The steamed m i x t u r e i s t h e n s i e v e d a g a i n and t h e vanadium c o n t e n t o f t h e c o a r s e f r a c t i o n ( P S D > 7 5 yum) i s m e a s u r e d . T h i s a p p r o a c h m i n i m i z e s t h e e f f e c t s o f c a t a l y s t a t t r i t i o n phenomena on t h e v a n a d i u m m o b i l i t y d e t e r m i n a t i o n . The

vanadium m o b i l i t y

(VM) i s t h e n d e f i n e d a s f o l l o w s : V

C- s t a r t

-

V

C- e n d


VM ( % > = _

:

*

1

0

0

V start

^C^

start =

Vanadium l e v e l o f c o a r s e f r a c t i o n m i x i n g a n d s t e a m i n g (ppm w t )

( > 7 5 yum), b e f o r e

^C^

end

Vanadium l e v e l o f coarse f r a c t i o n m i x i n g a n d s t e a m i n g (ppm w t )

( > 75 yum) a f t e r

The and

f o l l o w i n g t a b l e (Table VI.) , s h o w s a n e x a m p l e o f v a n a d i u m i t s dependence on c a t a l y s t c o m p o s i t i o n .

=

Table V I . R e d u c t i o n o f vanadium

Catalyst

USY USY USY

mobility

mobility

Vanadium m o b i l i t y (% V m i g r a t i o n )

+ Active A1 0 2°3 + A c t i v e kUO* L 0 + MTT*) 2 3 L

L

?

U

*) MTT = A m e t a l t r a p ,

61.5 52.7 33.0

as d e s c r i b e d i n Reference (18).

I n FCC u n i t s w h i c h e x h i b i t a h i g h t e n d e n c y t o v a n a d i u m t h e a p p l i c a t i o n o f m e t a l t r a p s can be v e r y b e n e f i c i a l .

migration,

Factors that

FCC u n i t s

i n f l u e n c e vanadium m o b i l i t y

i n commercial

are:

1. T h e o x i d a t i o n s t a t e o f t h e v a n a d i u m ( s e e a l s o 2 ) 2. R e g e n e r a t o r t e m p e r a t u r e ; i t h a s b e e n o b s e r v e d t h a t t h e v a n a d i u m m o b i l i t y c a n d o u b l e w i t h A0°C r e g e n e r a t o r t e m p e r a t u r e ( s e e figure 8). 3. T h e p r e s e n c e o f s t e a m a n d c a r b o n o n c a t a l y s t . 4. T h e v a n a d i u m l e v e l a n d t h e c a t a l y s t r e p l a c e m e n t o n i n v e n t o r y .



20. O'CONNOR ET AL.


333

F i g u r e 8 i l l u s t r a t e s t h e e f f e c t o f t e m p e r a t u r e on v a n a d i u m m o b i l i t y ( m e a s u r e d o n e q u i l i b r i u m c a t a l y s t s f r o m t h r e e FCC u n i t s ) a n d t h e l a r g e impact of c e r t a i n u n i t v a r i a b l e s . For t h e s e measurements t h e c o a r s e e q u i l i b r i u m c a t a l y s t was t e s t e d i n a m o b i l i t y t e s t u s i n g t h e method d e s c r i b e d a b o v e by s u b s t i t u t i n g s i e v e d c o a r s e e q u i l i b r i u m c a t a l y s t f o r vanadium impregnated c a t a l y s t . I n case o f a r e l a t i v e l y low vanadium m o b i l i t y , t h e d e a c t i v a t i o n by v a n a d i u m w i l l be l e s s , and so w i l l be t h e e f f e c t o f i n c o r p o r a t i n g a m e t a l t r a p . S t i l l i t a l s o a p p e a r s t o be i m p o r t a n t t o a d d r e s s t h e s t r a t e g y t o combat vanadium i n t h i s c a s e . I f vanadium i s o n l y p r e s e n t on t h e o u t e r l a y e r and i n t h e l a r g e r p o r e s o f a c a t a l y s t , t h e e f f e c t on z e o l i t e d e a c t i v a t i o n m i g h t be d e c r e a s e d . H o w e v e r o w i n g t o deactiv a t i o n of a c i d s i t e s i n these mesopores, the bottoms c r a c k i n g p o t e n t i a l o f t h e c a t a l y s t s w i l l be s t r o n g l y a f f e c t e d . Thus t h e presence of vanadium c a t c h i n g c a p a b i l i t y i n these l a r g e r pore r e g i o n s becomes e s s e n t i a l . T h i s i s c l e a r l y v i s i b l e w i t h more r e s i d in the feestock. S i n c e t h e method o f m e t a l i m p r e g n a t i o n w i l l a l s o have a l a r g e impact o n t h e p r o f i l e o f v a n a d i u m d e p o s i t i o n o f t h e c a t a l y s t , we c l e a r l y need t o r e v i e w t h i s a s p e c t of c a t a l y s t t e s t i n g . V i a c y c l i c m e t a l i m p r e g n a t i o n a n d c a t a l y s t d e a c t i v a t i o n , we c a n a p p r o a c h " R e a l - W o r l d " c o n d i t i o n s f a r b e t t e r . (Table VII.)

Table V I I . E f f e c t of

C o n v e r s i o n i n MST,

%

accessibility

wt 1 0 0 % VGO

Catalyst

66

A

Catalyst B "Accessible"

*) 5 0 0 0 ppm method.

60% VGO/ 40% N o r t h Sea 66

68

AR

71

vanadium c a t c h e r

V metal

level,

i m p r e g n a t i o n by a c y c l i c

deactivation

The r o u t e o f c a t a l y s t d e a c t i v a t i o n v i a a c y c l i c m e t a l i m p r e g n a t i o n and d e a c t i v a t i o n method has p r o d u c e d s i g n i f i c a n t improvements i n a p p r o a c h i n g r e a l i s t i c v a n a d i u m and n i c k e l p r o f i l e s o v e r t h e c a t a l y s t p a r t i c l e s . From e l e c t r o n m i c r o p r o b e a n a l y s e s o f N i and V l o a d e d c a t a l y s t i t has been e s t a b l i s h e d t h a t a f t e r pore volume s a t u r a t i o n , N i and V a r e r a t h e r homogeneously d i s t r i b u t e d o v e r t h e c a t a l y s t . I n c y c l i c i m p r e g n a t e d c a t a l y s t s , N i i s m a i n l y p r e s e n t on t h e c a t a l y s t s u r f a c e . I n c o n t r a s t a vanadium p r o f i l e over the p a r t i c l e i s f o u n d . I n t h e c a s e t h a t no s t e a m i s a p p l i e d i n t h e regeneration stage of the c y c l i c d e a c t i v a t i o n procedure, the V remains mainly c o n c e n t r a t e d a t t h e s u r f a c e o f t h e c a t a l y s t p a r t i c l e s . Other methods a s i m a g i n g SIMS ( 1 9 ) a n d L u m i n e s c e n c e ( 2 0 ) a r e a l s o b e i n g a p p l i e d t o m o n i t o r and compare t h e N i and V d i s t r i b u t i o n o f d e a c t i v a t e d


334


catalysts versus commercially deactivated equilibrium catalysts. C a r e f u l s e l e c t i o n of the d e a c t i v a t i o n c o n d i t i o n s (metals per c y c l e , r e g e n e r a t o r t e m p e a t u r e , % wt s t e a m i n c a n a l s o a l l o w us t o d i s t i n g u i s h b e t w e e n c a t a l y s t d e a c t i v a t i o n by m e t a l s and by h y d r o t h e r m a l e f f e c t s . ( T a b l e V I I I . )


Table V I I I .

Conversion

loss

M e t a l s t o l e r a n c e by

(wt % i n

Catalyst

Zeolite

g K Akzo Akzo

Z-14 US LZ-210 ADZ-40 ADZ-41

Low m e t a l s : 1000 ppm H i g h m e t a l s : 3 0 0 0 ppm

V, V,

cyclic

deactivation

MST) Low m e t a l s cycles 2.8 2.4 2.3 2.6

High metals cycles 5.5 4.8 3.5 3.0

500 ppm N i lOOOppm N i

I t c a n be o b s e r v e d t h a t t h e m a g n i t u d e o f c o n v e r s i o n l o s s o f 1 t o 2 p o i n t s MST p e r 1000 ppm V c o r r e s p o n d s q u i t e w e l l w i t h c o m m e r i c a l d a t a . N o t e t h a t t h i s i s o n l y t r u e f o r V l e v e l s b e l o w 5 0 0 0 ppm t h a t i s , a t r e l a t i v e l y low V l e v e l s . ii.

Nickel effects

and e n c a p s u l a t i o n

I n t h e e i g h t i e s , m o r e a n d m o r e FCC u n i t s p r o c e s s e d n i c k e l r i c h feedstocks, e s p e c i a l l y n i c k e l r i c h p a r a f f i n i c atmospheric r e s i d s f r o m t h e N o r t h Sea and A s i a P a c i f i c s o u r c e s . A l t h o u g h n i c k e l has o n l y a m a r g i n a l e f f e c t on c a t a l y s t d e a c t i v a t i o n , n i c k e l i t s e l f i s a c t i v a t e d e s p e c i a l l y on a l u m i n a s u r f a c e s and works as a d e h y d r o g e n a t i o n agent c a t a l y z i n g t h e r e a c t i o n s f o r m i n g c o k e , gas and e s p e c i a l l y h y d r o g e n ( 2 ) . A l s o as a c o n s e q u e n c e o f t h e h i g h e r l o c a l i z e d c o k e f o r m a t i o n , b l o c k i n g of t h e p o r e s w i l l t a k e p l a c e , r e s u l t i n g i n a l o s s o f a c t i v i t y . A p a r t f r o m t h e u s e o f Sb o r B i p a s s i v a t o r s on t h e c a t a l y s t s i d e , up to v e r y r e c e n t l y t h e o n l y approach has been t o m i n i m i z e t h e a c t i v e a l u m i n a s u r f a c e i n t h e c a t a l y s t and c o n s e q u e n t l y s a c r i f i c e bottoms conversion for nickel resistance. A new t e c h n o l o g y o f c a t a l y s t p r o d u c t i o n ( 1 1 ) i s c a p a b l e o f g e n e r a t i n g m a t e r i a l s i n w h i c h t h e n i c k e l a c t i v i t y as d e h y d r o g e n a t i o n a g e n t h a s been s t o p p e d by a m u l t i - s t e p s t r a t e g y . ( T a b l e I X . )




O'CONNOR ET AL.

Mobility 35 -Unit A 30 -A

25

5h 788 St A 5h 830 St

Similar Catalysts

A

Unit C A

-

Unit A: High T, Low Inv

-

20

A

Unit B. C: Low T, High Inv

15 Unit B 10

i

0

i

i

1

i

1

i

1

i

1

i

2000 4000 6000 Vanadium on cat, ppm.wt Figure 8

335

: V a n a d i u m M o b i l i t y on

FCC

catalysts.


336


Table

Silica

Rich Surface

Alumina r i c h

Surface


Zeolite

I X . S t r a t e g y t o combat N i c k e l

Formation o f l a r g e c r y s t a l l i t e s and stable inert Ni-silicates Encapsulation of nickel i n non-active alumina t e t r a h e d r a l s t r u c t u r e s Non-framework A l u m i n a C o n t r o l (ADZ)

Figure 9 demonstrates t h e c l e a r b e n e f i t o f n i c k e l encapsulation i n r e d u c i n g t h e a c t i v i t y f o r h y d r o g e n p r o d u c t i o n . The o b s e r v e d R l ^ O ^ e f f e c t on hydrogen p r o d u c t i o n , i s r e l a t e d t o t h e f o r m a t i o n o f z e o l i t e s u r f a c e non-framework alumina. P r o g r e s s i n n i c k e l t o l e r a n c e o f FCC c a t a l y s t w i t h t h e s e new t e c h n o l o g i e s i s a t l e a s t a s d r a m a t i c as i n v a n a d i u m t o l e r a n c e ( 2 ) . C o m m e r c i a l FCC o p e r a t i o n s w i t h n i c k e l o n e q u i l i b r i u m c a t a l y s t ( a b o v e 2 0 0 0 ppm) w i t h o u t t h e u s e o f p a s s i v a t o r , h a v e become f e a s i b l e . T h i s new t e c h n o l o g y a l s o a l l o w s f u r t h e r o p t i m i z a t i o n o f t h e m e s o p o r e a c t i v i t y , t h e c o n c e p t u a l f i g u r e 10 i l l u s t r a t e s t h i s p o i n t , w h i c h now h a s b e e n c o n f i r m e d i n c o m m e r c i a l FCC o p e r a t i o n s ( 2 1 ) . As w i t h v a n a d i u m u n d e r r e l a t i v e l y l o w m o b i l i t y c o n d i t i o n s , n i c k e l remains mainly deposited i n t h e larger pores o f t h e c a t a l y s t . Hence t o i n v e s t i g a t e n i c k e l e f f e c t s as r e a l i s t i c a l l y as p o s s i b l e , C y c l i c D e a c t i v a t i o n (CD) methods a r e recommended. T a b l e X: d e m o n s t r a t e s t h i s , s h o w i n g how t h e c a t a l y s t r a n k i n g c a n b e i n f l u e n c e d by t h e d e a c t i v a t i o n procedure used.

T a b l e X. I n f l u e n c e o f c a t a l y s t procedure.

Method

pore volume impregnation

Catalyst

*)

MST y i e l d Conversion H

2 Dry gas Gasoline Bottoms Coke C =/C t o t 4

4

r a n k i n g by type

LCMR

ES

0.16 3.1 44.2 13.1 3.4 0.63

0.22 3.1 44.0 12.2 3.8 0.70

of deactivation

cyclic deactivation LCMR

ES

70 % w t

0.17 3.0 44.0 14.2 4.2 0.60


0.15 2.5 45.2 12.6 3.7 0.65

20. O'CONNOR ET AL.


337

*) C a t a l y s t C h a r a c t e r i s t i c s : LCMR : M i n i m u m m e s o p o r e a c t i v i t y w i t h MR m e t a l t r a p ES : H i g h m e s o p o r e a c t i v i t y w i t h ADVANCE t e c h n o l o g y C a t a l y s t R e s i s t a n c e t o D e a c t i v a t i o n by O t h e r Other c a t a l y s t poisons


1. 2.

besides n i c k e l

Poisons

and vanadium a r e :

Poisons which n e u t r a l i z e o r d e s t r o y a c i d s i t e s , as f o r i n s t a n c e sodium, potassium, n i t r o g e n . P o i s o n s ( s u c h a s b a s i c a n d p o l a r compounds i n t h e f e e d ) w h i c h p r i m a r i l y enhance t h e f o r m a t i o n o f coke and hence i n d i r e c t l y a l s o cause t h e d e a c t i v a t i o n o f t h e c a t a l y s t .

F o r t h e f i r s t t y p e o f p o i s o n s , we c a n e i t h e r t r y t o a p p l y t h e same approach as w i t h vanadium; meaning s p e c i f i c c a t c h e r s o r o f f e r a s u f f i c i e n t excess of a c i d s i t e s : s a c r i f i c i a l s i t e s i n order t o reduce t h e r e l a t i v e impact o f t h e p o i s o n i n g . F o r i n s t a n c e , i n t h e case o f a n i t r o g e n r e s i s t a n t c a t a l y s t , u s u a l l y t h e c a t a l y s t design w i l l i n v o l v e a r e l a t i v e l y h i g h r a r e - e a r t h and h i g h z e o l i t e c o n t e n t catalyst with the option of additional s a c r i f i c i a l sites i nthe form o f a c t i v e alumina (12). O b v i o u s l y s u c h a t y p e o f f o r m u l a t i o n c o u l d h a v e some n e g a t i v e c o n s e q u e n c e s f o r t h e c a t a l y s t : p r i m a r i l y a h i g h e r c o k e make a n d p r o b a b l y a l s o some o c t a n e p e n a l t y . W i t h r e g a r d s t o s o d i u m we a l s o n e e d t o c o n s i d e r t h e s t a b i l i t y r e s i s t a n c e o f t h e z e o l i t e . F o r t u n a t e l y , some o f t h e n e w e r z e o l i t e s are able t o maintain t h e i r s t r u c t u r a l i n t e g r i t y , i n t h e presence of h i g h sodium l e v e l s . However, t h e a c i d s i t e s p r e s e n t r e m a i n s t i l l v e r y s u s c e p t i b l e t o n e u t r a l i z a t i o n by sodium. We c a n a l s o d i s t i n g u i s h a f e w l i n e s o f a p p r o a c h r e g a r d i n g c a t a l y s t p o i s o n s which d e a c t i v a t e t h e c a t a l y s t by coke f o r m a t i o n , t h a t i s by b l o c k i n g o f pores and t h e c a t a l y s t a c t i v e s i t e s , 1.

Conversion o f these coke p r e c u r s o r s p r i o r t o t h e formation o f t h e c o k e . I t i s t o some e x t e n t d e b a t a b l e w h e t h e r t h i s c a n b e d o n e . Some i m p r o v e m e n t s a r e p o s s i b l e u s i n g a n i m p r o v e d c a t a l y s t pore a r c h i t e c t u r e and a c i d i t y d i s t r i b u t i o n . 2. A d a p t c a t a l y s t d e s i g n t o m i n i m i z e t h e e f f e c t o f c o k e o n c a t a l y s t . T h i s i s a n a s p e c t w h i c h c l e a r l y d e s e r v e s a t t e n t i o n , a s we m i g h t expect s i g n i f i c a n t d e p o s i t i o n o f coke i n t h e very beginning o f t h e r i s e r when p r o c e s s i n g r e s i d s . 3. R e d u c e t h e c a t a l y t i c c o k e f o r m a t i o n o f t h e c a t a l y s t i n o r d e r t o a l l o w some r o o m f o r t h e a d d i t i o n a l c o k e f o r m e d b y t h e s e p o i s o n s . I n t h i s a p p r o a c h we a c c e p t t h a t t h e e x t r a c o k e f o r m e d i s u n a v o i d a b l e , a n d t h a t we n e e d t o c o m p e n s a t e b y i m p r o v i n g t h e c o k e selectivity of the catalyst. The m a i n s t r a t e g i e s f o r a d d r e s s i n g are summarized i n Table X I .

these

types

of catalyst

poisons


338


O A c t i v e A1203 • No A1203


"Ni-Activating"

• A c t i v e A1203 including ADVANCE Technology

Ni-Encapsulation" _J

0

i

I

2

4

RE203,

i

I

L_

i

6

8

%wt on Y MST at 70%wt Conversion 1500 ppm Ni, 5h 788 100%St

Figure

9

: Hydrogen p r o d u c t i o n

vs Catalyst

design.

--- A c t i v e A1203

COKE

Traditional

A c t i v e A1203 Advance Technology

MST LCS

- Optimum Where ?

Test

1500 ppm N i 5h 788 S t . K u w a i t VGO

MESOPORE ACTIVITY Figure

10

: Coke s e l e c t i v i t y

v s Mesopore

activity.


20.

Table XI.


Type o f

339


O'CONNOR ETAL.

Strategies for addressing

Poison

catalyst

Strategy

Examples

poisons

Remarks

Poisons which n e u t r a l i z e or destroy acid sites

Na, K, nitrogen

s p e c i f i c poison catchers sacrificial sites: high

not s u c c e s s f u l yet n e e d t o compensate f o r cokeselectivity

Poisons which deactivate s i t e s and b l o c k p o r e s by e x t r a coke formation

b a s i c and polar compounds

convert coke precursors min. effect o f c o k e on catalyst reduce catal y t i c coke formation

special acidity

pore distr.

n e e d t o compensate f o r coke selectivity

We c a n c o n c l u d e t h a t a n i m p r o v e m e n t i n c o k e s e l e c t i v i t y p l a y s a n important r o l e i n the s t r a t e g i e s t o cope w i t h b o t h type of p o i s o n s . Catalyst Selectivity

and

Stability

As d i s c u s s e d i n t h e p r e v i o u s s e c t i o n s any i m p r o v e m e n t s i n c o k e s e l e c t i v i t y c a n be u t i l i z e d t o e x t e n d t h e f r o n t i e r s o f r e s i d p r o c e s s i n g as s e v e r a l t y p e s o f p o i s o n s i n t h e r e s i d f e e d , most o f a l l the p o l a r hydrocarbons w i l l i n c r e a s e the coke formed. A l s o f o r f u e l g a s we c a n o b s e r v e t h a t n o n - o p t i m a l v a p o r i z a t i o n a n d c r a c k i n g c o n d i t i o n s w i t h r e s i d w i l l s t r o n g l y enhance gas f o r m a t i o n . A low c o k e and gas c a t a l y s t i s h e n c e a b i g p l u s f o r r e s i d p r o c e s s i n g . (Table XII.) T a b l e X I I . Low

Zeolite

A c t i v e AlÔ^ Catalyst Architecture

c o k e and

gas

catalyst

N o n - f r a m e w o r k c o n t r o l (3), a l s o low coke w i t h m e d i u m / h i g h REÔ^ levels. F u e l g a s d e c r e a s e s w i t h h i g h e r REÔ^ levels M o d i f i e d s u r f a c e c h e m i s t r y t o r e d u c e c o k e and g a s f o r m a t i o n (11, 20) S p e c i a l pore s i z e A c i d i t y D i s t r i b u t i o n r e d u c e s c o k e and gas formation


340


B a s e d o n t h e " i d e a l i z e d o b j e c t i v e s " o u t l i n e d i n T a b l e X I I L , we c a n a r r i v e a t t h e f o l l o w i n g c a t a l y s t c h a r a c t e r i s t i c s f o r optimum coke and g a s r e d u c t i o n RESID-1

Minimum g a s

RESID-2

Minimum coke

Medium r a r e e a r t h z e o l i t e w i t h medium t o h i g h mesopore a c t i v i t y . Low r a r e e a r t h z e o l i t e w i t h l o w mesopore a c t i v i t y .


The p r o g r e s s i n c o k e s e l e c t i v i t y a n d b o t t o m s o r r e s i d c r a c k i n g i s i l l u s t r a t e d i n Table X I I I below:

Table X I I I . Resid conversion a t constant

RC,

coke

R e s i d c o n v e r s i o n = 1 0 0 - b o t t o m s - c o k e , i n MST RC

Base

D e l t a RC

79.3

ADVANCE DEV-1*) DEV-2*)

80.6 82.8 83.8

RE-USY c a t a l y s t w i t h m e d i u m m e s o p o r e a c t i v i t y , a t 788°C, 1 0 0 % s t e a m a n d 1 5 0 0 ppm N i . *) E x p e r i m e n t a l l a b o r a t o r y samples

1.3 3.5 4.5

deactivated

5 hours

I t i s c l e a r t h a t the z e o l i t e d e l t a c o k e w i l l have a s t r o n g e f f e c t on t h e r e g e n e r a t o r t e m p e r a t u r e a n d h e n c e o n t h e c a t a l y s t d e a c t i v a t i o n . D e p e n d i n g o n t h e t r e n d i n FCC r e g e n e r a t o r t e m p e r a t u r e s , t h e a s p e c t o f h y d r o t h e r m a l s t a b i l i t y m i g h t become o f g r e a t e r importance. I t h a s been o b s e r v e d t h a t , t h e i n d i r e c t e f f e c t o f d e l t a coke on c a t a l y s t d e a c t i v a t i o n , a n d t h e d i r e c t e f f e c t o f d e l t a c o k e o n the b l o c k i n g o f a c i d s i t e s ( e a r l y ) i n t h e r i s e r seems t o b e a prime f a c t o r , which dominates conversion and s e l e c t i v i t y e f f e c t s i n a r e s i d type of operation. Future

Perspectives

From t h e f o r e g o i n g c h a p t e r s i t s h o u l d be c l e a r t h a t t h e development o f a s u c c e s s f u l FCC r e s i d c a t a l y s t d e p e n d s o n s e v e r a l a s p e c t s t h e r e l a t i v e p r i o r i t i e s o f which w i l l be determined by t h e r e f i n e r y o b j e c t i v e s , f e e d s t o c k , FCC u n i t c o n f i g u r a t i o n a n d l i m i t a t i o n s . S t i l l , i t i s worthwhile t o distinguish certain "idealized objectives" i n o r d e r t o f o c u s t h e c a t a l y s t development i n t h i s f i e l d . The advances i n r e s i d F C C c a t a l y s t d e v e l o p m e n t u p t o now h a v e b e e n m a i n l y i n t h e f i e l d of metal tolerance (metal traps), while also progress has


20. O'CONNOR ETAL.

b e e n made i n c r a c k i n g t h e l a r g e r h y d r o c a r b o n m o l e c u l e s . F o r t h e f u t u r e we n e e d t o a d d r e s s some o t h e r c r i t i c a l p o i n t s upon i n t h i s r e v i e w as ( T a b l e X I V . )

T a b l e X I V . Some f u t u r e


341


touched

challenges

- How t o r e d u c e t h e f o r m a t i o n a n d t h e d e t r i m e n t a l e f f e c t o f t h e f e e d c o k e o r c o k e f o r m e d b y p o l a r compounds - Development o f t r a p s f o rp o i s o n s , w i t h o u t n e g a t i v e l y a f f e c t i n g the c a t a l y s t s e l e c t i v i t y - A c c e s s i b i l i t y and e f f e c t i v e n e s s o f vanadium t r a p p i n g - Further r e d u c t i o n o f " c a t a l y t i c " coke and f u e l gas p r o d u c t i o n i n o r d e r t o a l l o w more room f o r r e s i d p r o c e s s i n g - Cracking of c e r t a i n " d i f f i c u l t " molecules

I t i s a l s o c l e a r t h a t a g o o d u n d e r s t a n d i n g o f t h e FCC p r o c e s s o b j e c t i v e s , l i m i t a t i o n s and c o n f i g u r a t i o n w i l l be o f c r u c i a l i m p o r t a n c e f o r t h e d e v e l o p m e n t o f a n o p t i m i z e d r e s i d FCC c a t a l y s t formulation. REFERENCES

1. See f o r example: (a) M.L. O c c e l l i and J.V. Kennedy i n GB 2.116.062 A (1983) (b) M.L. O c c e l l i and J.V. Kennedy i n US 4.465.588 (1984) (c) M.L. O c c e l l i and H.E. Swift i n US 4.466.884 (1984) (d) M.L. O c c e l l i i n US 4.615.996 (1986) (e) J . I . de Jong i n US 4.519.897 (1985) 2. M.L. O c c e l l i i n " F l u i d Catalyst Cracking: Role i n Modern Refining", ACS Symposium Series, v o l 375, M.L. O c c e l l i , Ed. ACS Washington D.C., p 162 (1989). 3. See f o r example: (a) J . Scherzer i n " C a t a l y t i c Materials: Relationship between structure and r e a c t i v i t y , ACS Symposium Series, v o l 248 T.E., Whyte, R.A.D. Betta, E.G. Derouane and R.T.K. Baker, E d i t o r s , ACS Washington D.C., p 157 (1983) (b) R.J. P e l l e t , C.S. Blackwell and J.A. rabo; J . C a t a l y s i s 114, 71-89 (1988) (c) B. de Kroes, C.J. Groenenboom and P. O'Connor; "New Z e o l i t e s i n FCC", Akzo Catalyst Symposium 1986, May 25-28, The Netherlands. H.Th. R i j n t e n , and H.J. Lovink e d i t o r s . 4. See f o r example: G.J. Thompson, R.H. Hensen, C.N. Cabrera and E.J. Houde; "Processing requirements and economic analysis of Heavy Oil and syncrude r e f i n i n g " , i n the 12th World Petroleum Congres, Houston 1987, John Wiley & Sons ltd.



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5. C. Carter; NPRA Annual meeting 1986, AM-84-27 6. J.A. Dudley; AIChe 1989, Spring National Meeting, Houston 7. P. O'Connor and F.W. van Houtert; "The role of diffusion in bottoms conversion", Akzo Catalyst Symposium 1986, May 25-28, The Netherlands. H.Th. Rijnten and H.J Lovink editors. 8. J . L . Mauleon and J.B. Sigaud; "Characterization and selection of heavy feeds for upgrading through fluid catalytic cracking process" in the 12th world Petroleum Congress, Houston 1987, Hohn Wiley & sons Ltd. 9. J.E. Naber, P.H. Barnes and M. Akbar; J . P . I . Petroleum Refining conference, Tokyo - Japan, October 1988. 10. M.L. Occelli and J.M. Stengel in "Fluid Catalytic Cracking: Role in Modern Refining", ACS Symposium Series, vol 375, M.L. Occelli, Ed. ACS Washington D.C., p 195 (1989). 11. C. Lam, P. O'Connor and C . P . Smit; "The Advance Catalyst Series", Akzo Catalyst Symposium 1988, May 29-June 1, The Netherlands, H.J. Lovink editor. 12. J. Scherzer and d.P. McArthur; "Catalytic Cracking of High Nitrogen Petroleum Feedstocks: Effect of Catalyst Composition and Properties", Ind. Eng. Chem. Res. 1988, 27, p 1571-1576. 13. D.M. Nace; Ind. Eng. Chem. 9 (2), 203, 1970. 14. P. O'Connor and M.B. Hartkamp in "Characterization and Catalyst Development", ACS Symposium series, vol 411, S.A. Bradley, M.J. Gatturo and R . J . Bertolacini, editors ACS Washington DC, p 135 (1989). 15. P. Hettinger in "Fluid Catalytic Cracking: Role in Modern Refining", ACS Symposium Series, Vol 375, M.L. Occelli, editor ACS Washington DC, p 308 (1989). 16. M.L. Occelli and J.M. Stencel in "Zeolite as Catalysts, sorbents and Detergent Builders" H.G. Karge and J . Weitkamp, editors Elsevier, p 127 (1989). 17. M.L. Occelli and J.M. Stencel in "Zeolites, Facts, Figures, Future", P.A. Jacobs, P.A. Vanjarter, editor Elsevier, part B p 1311, 1989. 18. C. Groenenboom in "Zeolites as Catalysts, Sorbents and Detergent Builders", H.G. Karge, editor Elsevier, p 199, 1989. 19. D.P. Leta and E.L. Kugler; "Secondary Ion Mass Spectranetry Proc. Int. Conf.", 6th 1987, p 373 (1988). 20. MM.L. Occelli; Journal of Catalysis, 96, 1985, 2, p 363-370. 21. A.W. Gevers, P. O'Connor and E. Brevoord; "Advance: an exceptional FCC Catalyst desing", Akzo Catalysts South American Catalyst Seminar, 1989, October 19-20, 1989, H.J. Lovink editor. RECEIVED October 5, 1990


Fluid Catalytic Cracking II - ACS Publications - American Chemical

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