Chapter 34
Mechanical and Physical Testing of Catalysts Ralph J. Bertolacini
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Research and Development, Amoco Oil Company, Naperville, IL 60566
Proper catalyst specifications for mechanical and physical properties are as important as activity and selectivity. Poor resistance to attrition and crushing can cause pressure drops and expensive unit shutdowns in refining and petrochemical operations. Setting reasonable specifications depends on the development of reliable test procedures and well -characterized reference materials for method development. Statistical control processes can be used to eliminate variations to reduce off -specification catalysts and contractual disputes. These important issues are reviewed and discussed, and subsequent papers in this symposium deal with the specific topics. C a t a l y t i c a c t i v i t y , s e l e c t i v i t y , and t h e r a t e o f d e a c t i v a t i o n are t h e u s u a l c r i t e r i a f o r d e v e l o p i n g , e v a l u a t i n g , and recommending commercial i n d u s t r i a l c a t a l y s t s . These i m p o r t a n t c a t a l y s t p r o p e r t i e s , most o f t e n , a r e p r o p r i e t a r y and d e t e r m i n e d b y the c a t a l y s t u s e r . However, w h i l e t h e s e c a t a l y s t p r o p e r t i e s a r e i m p o r t a n t f o r s u c c e s s f u l commercial performance, t h e y a r e n o t t h e s o l e c r i t e r i a and t h i s i s w e l l r e c o g n i z e d b y t h e c a t a l y s i s community. C a t a l y s t s t a b i l i t y ( 1 ) , a t t r i t i o n r e s i s t a n c e (2-3) . and c r u s h i n g s t r e n g t h (4-5) a r e e q u a l l y as i m p o r t a n t as a c t i v i t y . These m e c h a n i c a l p r o p e r t i e s c a n supersede o u t s t a n d i n g c a t a l y t i c performance and o f t e n a r e t h e l i m i t i n g f a c t o r s f o r u s i n g , and r e g e n e r a t i n g , i n d u s t r i a l c a t a l y s t s . M e c h a n i c a l and p h y s i c a l p r o p e r t i e s are u s u a l l y t i g h t l y s p e c i f i e d by the user. Poor m e c h a n i c a l and p h y s i c a l p r o p e r t i e s a r e c o s t l y problems f o r t h e r e f i n i n g and c h e m i c a l i n d u s t r i e s . Broken c a t a l y s t p a r t i c l e s i n f i x e d b e d r e a c t o r s i n c r e a s e p r e s s u r e drop b y b r i d g i n g i n t e r s t a c i e s between c a t a l y s t p a r t i c l e s w h i c h c a n p l u g t h e bed w i t h d e b r i s coming from above and i n some cases f a c i l i t a t e coke f o r m a t i o n w h i c h f u r t h e r i n c r e a s e s t h e p r e s s u r e drop. F i x e d bed c a t a l y s t s a r e prone t o breakage when they a r e l o a d e d i n t o reactors. L o a d i n g c a n be performed b y p n e u m a t i c a l l y l i f t i n g the 0097-6156/89/0411-0380S06.00/0 c 1989 American Chemical Society
In Characterization and Catalyst Development; Bradley, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
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c a t a l y s t from ground l e v e l i n t o the r e a c t o r o r d r o p p i n g the c a t a l y s t down a s l e e v e so the c a t a l y s t must be rugged. H i g h p r e s s u r e s , h i g h temperatures, and h i g h v e l o c i t y f e e d throughputs a l s o e x e r t a tremendous s t r a i n on the c a t a l y s t p a r t i c l e s . To overcome some o f these problems, c a t a l y s t s are p r e p a r e d i n d i f f e r e n t shapes d e s i g n e d t o r e s i s t f r a c t u r e , s p a l l i n g , and disintegration. C a t a l y s t forms v a r y from p e l l e t s , r i n g s , e x t r u d a t e s , g e o m e t r i c shapes, t o f i n e powders. Each e n g i n e e r e d t o f i t the p r o c e s s and each c a u s i n g problems f o r m e a s u r i n g t h e i r mechanical p r o p e r t i e s . C a t a l y s t s f o r e b u l l a t i n g bed r e a c t o r s are s u b j e c t e d t o attrition. Those used f o r r e s i d h y d r o p r o c e s s i n g and c o a l l i q u e f a c t i o n must r e s i s t t u r b u l e n c e , from h i g h gas v e l o c i t i e s as w e l l as e r o s i o n by the ash and i m p u r i t i e s i n the f e e d s t o c k s . F l u i d c a t a l y t i c c r a c k i n g c a t a l y s t s must have good f l u i d i z a t i o n p r o p e r t i e s t o e l i m i n a t e c i r c u l a t i o n problems and excess g e n e r a t i o n o f c a t a l y s t f i n e s w h i c h cause o p e r a t i o n a l and e n v i r o n m e n t a l problems. F l u i d bed c a t a l y t i c c r a c k i n g c a t a l y s t s a r e a l s o s u b j e c t e d t o h i g h temperature d u r i n g steam s t r i p p i n g and r e g e n e r a t i o n , w h i c h f u r t h e r decrease t h e i r r e s i s t a n c e t o attrition. D e v e l o p i n g methods t o p r e v e n t and e l i m i n a t e c a t a l y s t breakage and a t t r i t i o n are as i m p o r t a n t as d e v e l o p i n g h i g h l y a c t i v e and s e l e c t i v e c a t a l y s t s . Good d i a g n o s t i c t e s t s f o r a c c e l e r a t e d a g i n g and p s e u d o e q u i l i b r a t i o n are used t o s i m u l a t e and p r e d i c t c a t a l y s t i n - s e r v i c e performance. Two i m p o r t a n t t e s t s used t o measure p o t e n t i a l c a t a l y s t breakage problems d u r i n g o p e r a t i o n are s i n g l e p e l l e t and b u l k c r u s h i n g s t r e n g t h s . S i n g l e p e l l e t t e s t s are a p p l i c a b l e to p i l l s , e x t r u d a t e s , and spheres. These t e s t s measure the r e s i s t a n c e t o a c o m p r e s s i v e f o r c e and are used f o r q u a l i t y c o n t r o l by the producer. The u s e r u s u a l l y s p e c i f i e s a range o f s t r e n g t h s , f o r example 3-4 p o u n d s / m i l l i m e t e r o f l e n g t h o r d i a m e t e r , o r a s p e c i f i c p e r c e n t a g e a t some minimum s t r e n g t h , f o r example n o t more t h a n 5% below 22 pounds t o t a l . This e l i m i n a t e s s o f t p e l l e t s which c o u l d p u l v e r i z e d u r i n g l o a d i n g o r r e a c t i o n and l e a d t o p r e s s u r e drop problems. B u l k c r u s h measures the a b i l i t y o f the c a t a l y s t t o s u p p o r t the w e i g h t o f the c a t a l y s t bed. T h i s i s d i f f i c u l t t o measure p r e c i s e l y and has not y e t been s t a n d a r d i z e d . T h i s t e s t i s now done on a p r o p r i e t a r y b a s i s . The paper by S. A. B r a d l e y , e t al.((5) addresses a p r o c e d u r e now under c o n s i d e r a t i o n f o r s t a n d a r d i z a t i o n w h i c h , i f adopted, s h o u l d be v a l u a b l e t o c a t a l y s t u s e r s and p r o d u c e r s f o r s p e c i f i c a t i o n and q u a l i t y c o n t r o l . S i m i l a r t o the importance o f m e c h a n i c a l s t a b i l i t y , p h y s i c a l p r o p e r t i e s such as s u r f a c e a r e a , pore s i z e , and pore s i z e d i s t r i b u t i o n , m e t a l d i s p e r s i o n , and s u r f a c e a c i d i t y a r e i m p o r t a n t p a r a m e t e r s , w h i c h the c a t a l y t i c chemist o r e n g i n e e r c o n s i d e r s when d e v e l o p i n g a c a t a l y t i c system. The p h y s i c a l p r o p e r t i e s are o p t i m i z e d t o f i t the c a t a l y t i c a p p l i c a t i o n . Measurement o f t h e s e p r o p e r t i e s , w h i l e not a l l are f u l l y s t a n d a r d i z e d , have been w i d e l y p u b l i s h e d f o r s p e c i f i c c a t a l y t i c systems. The most complete r e v i e w o f these p r o c e d u r e s w i t h examples f o r s p e c i f i c c a t a l y t i c systems and r e f e r e n c e s have been p u b l i s h e d (7-8) .
In Characterization and Catalyst Development; Bradley, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
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CHARACTERIZATION AND CATALYST DEVELOPMENT
T r a d i t i o n a l l y , f o r p r o p r i e t a r y reasons, i n d u s t r i a l c a t a l y t i c r e s e a r c h e r s have n o t d i s c u s s e d o r d i s c l o s e d in-house methods f o r s e t t i n g t h e m e c h a n i c a l and p h y s i c a l p r o p e r t y s p e c i f i c a t i o n s o f i n d u s t r i a l c a t a l y s t s . However i n 1974, t h e American I n s t i t u t e o f C h e m i c a l E n g i n e e r i n g a t t h e June meeting i n P i t t s b u r g h , devoted a d a y - l o n g symposium on measuring t h e m e c h a n i c a l and p h y s i c a l p r o p e r t i e s o f c a t a l y s t s ( 9 ) . Beaver d e s c r i b e d a m e c h a n i c a l l y d r i v e n p i s t o n apparatus w h i c h gave more r e p r o d u c i b l e r e s u l t s t h a n p r e v i o u s l y d e s c r i b e d hand-operated d e v i c e s f o r shaped c a t a l y s t s ( 1 0 ) . D a r t d e s c r i b e d a p r o c e d u r e f o r measuring c a t a l y s t a t t r i t i o n r e s i s t a n c e , i . e . , a b r a s i o n l o s s f o r formed and shaped c a t a l y s t s (11). Proper sampling procedures f o r developing s t a n d a r d i z e d t e s t s were a d d r e s s e d b y Adams, e t a l . ( 1 2 ) . They p o i n t o u t t h a t p r o p e r s a m p l i n g i s an i m p o r t a n t f a c t o r i n c a t a l y s t t e s t i n g w h i c h i s n o t o f t e n d i s c u s s e d when s e t t i n g c a t a l y s t s p e c i f i c a t i o n s . O f t e n d i s p u t e s between t h e vendor and p u r c h a s e r a r e caused b y poor s a m p l i n g methods. As a r e s u l t o f t h e 1974 American I n s t i t u t e o f Chemical E n g i n e e r i n g , t h e American S o c i e t y f o r T e s t i n g M a t e r i a l s o r g a n i z e d Committee D - 3 2 - - C a t a l y s t s i n J a n u a r y 1975. The e a r l y h i s t o r y and development o f t h e Committee was r e p o r t e d by K i o v s k y ( 1 3 ) , N e a l ( 1 4 ) , and B e r t o l a c i n i ( 1 5 ) . S i m i l a r s t a n d a r d i z a t i o n groups have s i n c e been formed i n Japan, U n i t e d Kingdom, Europe, and t h e S o v i e t Union. T w e n t y - f i v e s t a n d a r d s have been d e v e l o p e d by t h e American S o c i e t y f o r T e s t i n g M a t e r i a l s Committee D - 3 2 - - C a t a l y s t s i n c l u d i n g tests f o r a t t r i t i o n , crush strength, p a r t i c l e s i z e d i s t r i b u t i o n , and v i b r a t e d apparent p a c k i n g d e n s i t y ( 1 6 ) . S t a n d a r d i z a t i o n o f c a t a l y s t t e s t methods w i l l h e l p e l i m i n a t e c o s t l y and u n n e c e s s a r y r e p e a t e d t e s t i n g because t h e a n a l y s e s a r e done by t h e same method w i t h measured p r e c i s i o n and b i a s . This s h o u l d h e l p e l i m i n a t e c o n f l i c t s i n m a i n t a i n i n g q u a l i t y c o n t r o l and s p e c i f i c a t i o n requirements. Q u a l i t y a s s u r a n c e i s an i m p o r t a n t c o n s i d e r a t i o n f o r t h e u s e r and p r o d u c e r . Both a s p e c t s a r e d i s c u s s e d by P u i s (12) i n h i s symposium paper. L o t - t o - l o t v a r i a t i o n s i n purchased c a t a l y s t can be m i n i m i z e d b y a system o f s t a t i s t i c a l p r o c e s s c o n t r o l by t h e c a t a l y s t p r o d u c e r , h i s s u p p l i e r , and t h e u s e r . The s t a t i s t i c a l process helps t o minimize product q u a l i t y v a r i a t i o n s by i n s t i t u t i n g c o r r e c t i v e a c t i o n on a r e a l - t i m e b a s i s t o p r e v e n t t h e production o f o f f - s p e c i f i c a t i o n material. The development and s t a n d a r d i z a t i o n o f r e l i a b l e t e s t p r o c e d u r e s r e q u i r e s an ample s u p p l y o f w e l l - c h a r a c t e r i z e d r e f e r e n c e m a t e r i a l s . These samples a r e used f o r r o u n d - r o b i n t e s t s by p a r t i c i p a t i n g l a b o r a t o r i e s i n t h e method development. A r e l i a b l e s e t o f r e f e r e n c e m a t e r i a l s a r e a v a i l a b l e from t h e N a t i o n a l Bureau o f S t a n d a r d s . These s p e c i a l r e f e r e n c e m a t e r i a l s a r e d e s c r i b e d b y Haines i n t h i s symposium s e r i e s . The Bureau has packaged t h e m a t e r i a l s i n an a p p r o p r i a t e s i z e and s e c u r e c o n t a i n e r . P r o d u c e r and u s e r l a b o r a t o r i e s have t h e s e r e f e r e n c e m a t e r i a l s a v a i l a b l e t o c r o s s - c h e c k r e s u l t s and r e s o l v e d i f f e r e n c e s i n s p e c i f i c a t i o n a n a l y s e s . These r e f e r e n c e s t a n d a r d s a r e a v a i l a b l e a t a reasonable cost. The s t a n d a r d i z a t i o n o f a l l o f these p r o c e d u r e s f o r a n a l y z i n g c a t a l y s t s has been t h e g o a l o f ASTM Committee D-32. R e f e r e n c e
In Characterization and Catalyst Development; Bradley, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
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p r o c e d u r e s have been e s t a b l i s h e d and s u p p o r t i n g d a t a may be o b t a i n e d from ASTM. By 1992, the f r e e - w o r l d c a t a l y s t market c o u l d r e a c h f o u r b i l l i o n dollars; and the U n i t e d S t a t e s p r o j e c t i o n i s e s t i m a t e d t o be two b i l l i o n ( 1 8 ) . I t i s d i f f i c u l t t o e s t i m a t e how much o f an impact improved methods f o r e n g i n e e r i n g improved m e c h a n i c a l and p h y s i c a l p r o p e r t i e s w i l l have on t h e s e f i g u r e s , b u t we can e x p e c t t h a t a l l c a t a l y s t s w i l l be checked t o meet the s p e c i f i c a t i o n s o f the u s e r and the q u a l i t y c o n t r o l program o f the p r o d u c e r .
LITERATURE CITED 1. 2. 3. 4. 5. 6. 7. 8.
9. 10. 11. 12. 13.
14. 15. 16. 17. 18.
National Petroleum Refiners Association, Questions and Answers Refining Technology, Farrar, G. L . , Ed.; National Petroleum Refiners Association, Washington, DC, 1982, p 52. Ibid., p 154, 1982. Ibid., p 151, 1983. Ibid., p 129, 1983. Ibid., p 102, 1984. Bradley, S.; Pretzer, E., Koves, W. J., Bulk Crush Testing of Catalysts. Prep. Am. Chem. Soc.,; Div. Pet. Chem. 1988, 33 (4), p 557-561. Introduction to Characterization and Testing of Catalysts. Anderson, J . R. and Pratt, K. C., Academic Press, Inc., Florida, 1985. "Characterization of Catalysts," Baker, A., Kohler, M. A., Handbook of Heat and Mass Transfer. Vol. 3, Catalysis, Kinetics, and Reactor Engineering, Cheremesenoff, N. P., Ed.; Gulf Publishing Co., Houston, Texas, 1989, p 3-62. Weller, S. W., Standardization of Catalyst Test Methods. Vol 70, No. 143, AIChE Symposium Series, AIChE New York, 1974. Beaver, E. R., Ibid., p 1-4. Dart, J. C., Ibid., p 5-8. Adams, C. R., Sartor, A. F., and Welch, J. G., Ibid., p 4954. Kivosky, J. R., Oral Communication, Proceedings of the International Symposium in the Relations Between Heterogenous and Homogeneous Catalytic Phenomena, Brussels, October 1974. Neal, A. H., Preparation of Catalysts II, B. Delman, Ed.; Elsevier, Amsterdam, 1979, p 719. Bertolacini, R. J., Neal, A. H., Preparation of Catalysts III. G. Poncelet, Grange, P., Jacobs, P. A., Eds.; Elsevier, 1983, p 767. ASTM Standards on Catalyst: Third Edition, 1988 American Society for Testing Materials, Philadelphia. Puis, F. H., Quality Assurance for Purchased Catalysts. Prep. Am. Chem. Soc., Div. Pet. Chem. 1988, 33 (4), p 56871. Chem Week; June 29, 1988; p.21.
Received April 27, 1989
In Characterization and Catalyst Development; Bradley, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
