Characterization and Catalyst Development

Chapter 35

Quality Assurance for Purchased Catalysts F. H. Puis

Downloaded by UNIV OF PITTSBURGH on February 12, 2015 | http://pubs.acs.org Publication Date: October 3, 1989 | doi: 10.1021/bk-1989-0411.ch035

Exxon Chemical Company, Baton Rouge, LA 70821-2226

Analytical results of measuring particle sizes of catalyst pellets, depths of metal impregnation through electron microscope scans, and acidic properties through ammo nia chemisorption, are presented here to i l l u s t r a t e the fact that some commercial catalyst replacement charges exhibit quite undesirable quality variations which are causing petrochemical operating costs to be higher than expected. S t a t i s t i c a l process control is being implemented by catalyst manufacturers to detect and eliminate, i f possible, causes of variations in quality. As many depart ments, such as operating, technical, pur chasing, and R&D, become involved in the pursuit of quality, a unified approach to ward the implementation of total quality is being developed through an accreditation procedure for catalyst suppliers.

P e t r o c h e m i c a l i n d u s t r i e s r e q u i r e many d i f f e r e n t t y p e s of c a t a l y s t s a n d a d s o r b e n t s i n p r o c e s s a p p l i c a t i o n s . M a j o r p o r t i o n s o f s u c h r e q u i r e m e n t s a r e b e i n g met t h r o u g h p u r c h a s e s from commercial c a t a l y s t s u p p l i e r s . The i m p o r t a n c e o f c a t a l y s t s t o c h e m i c a l a n d p e t r o c h e m i c a l i n d u s t r i e s c a n n o t be o v e r s t a t e d . D e v i a t i o n s i n c a t a l y s t performance from e x p e c t a t i o n s a f f e c t y i e l d s and f e e d s t o c k u t i l i z a t i o n , g e n e r a t e u n d e s i r a b l e s i d e r e a c t i o n s and b y - p r o d u c t s , i n c r e a s e o p e r a t i n g c o s t s , and r e d u c e c a p a c i t y . The c o s t o f s u c h d e v i a t i o n s f r o m t h e e x p e c t a t i o n s w h i c h were i n c o r p o r a t e d i n t h e p r o c e s s d e s i g n , a r e n o t a l w a y s known a n d c a n e a s i l y e x c e e d t h e c o s t o f a new c a t a l y s t c h a r g e . 0097-6156/89/0411-0384$06.00/0 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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385

When c a t a l y s t c h a r g e s a r e r e p l a c e d , a d d i t i o n a l u n l o a d i n g , l o a d i n g , and h a n d l i n g c o s t s a r e i n c u r r e d and valuable production capacity i s being l o s t . Moreover, e x p e c t a t i o n s f o r improved performances r e s u l t i n g from new c a t a l y s t r e p l a c e m e n t c h a r g e s a r e n o t a l w a y s b e i n g r e a l i z e d . Therefore, i t i s not s u r p r i s i n g that i n the q u e s t f o r q u a l i t y , w h i c h h a s t o u c h e d much o f US i n d u s t r y i n t h e e i g h t i e s ( 1 ) ( 2 ) c a t a l y s t s were among t h e f i r s t p r o d u c t s w h i c h were s i n g l e d o u t f o r s p e c i a l a t t e n t i o n .


r

From OC t o SPC. A new q u a l i t y c o n t r o l (QC) f u n c t i o n f o r E x x o n C h e m i c a l Company was e s t a b l i s h e d a t one o f t h e E x x o n l a b o r a t o r i e s i n 1980. E x x o n R e s e a r c h a n d D e v e l o p ment L a b o r a t o r i e s a t B a t o n Rouge, L o u i s i a n a was c h o s e n , because a s i m i l a r f u n c t i o n a l r e a d y e x i s t e d f o r r e f i n e r y c a t a l y s t s , and b e c a u s e a n a l y t i c a l and p r o f e s s i o n a l c a p a b i l i t i e s a t t h i s l o c a t i o n s u p e r b l y met o u r n e e d s . I n 1984, a s t a n d a r d q u a l i t y c o n t r o l p r o c e d u r e was i n t r o d u c e d f o r a l l p u r c h a s e d f i x e d bed c a t a l y s t s a n d a d s o r b e n t s , e . g . t o be u s e d a t t h e d i s c r e t i o n o f a l l Exxon Chemical worldwide o p e r a t i n g p l a n t s . F i n a l l y , t h i s year, a standard c a t a l y s t supplier a c c r e d i t a t i o n procedure i s b e i n g implemented. P r i m a r y e m p h a s i s i s on t h e i m p l e m e n t a t i o n o f c o n t r o l c h a r t s a n d 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 (SPC) p r o c e d u r e s i n t h e manufacture of commercial c a t a l y s t s i n o r d e r t o improve l o t t o l o t c o n s i s t e n c i e s (3) f o r purchased c a t a l y s t s . F i x e d Bed C a t a l y s t s . N o b l e m e t a l , base m e t a l , and o t h e r types of c a t a l y s t s , i n c l u d i n g alumina, s i l i c a , r e s i n s , c l a y s , z e o l i t e s , and c o m b i n a t i o n s t h e r e o f a r e u s e d i n a l m o s t e v e r y t y p e o f c h e m i c a l and p e t r o c h e m i c a l b u s i n e s s segment. There a r e many d i f f e r e n t p r o c e s s a p p l i c a t i o n s r a n g i n g from t h e g e n e r a t i o n of s u i t a b l e f e e d s t o c k s , a c t u a l c h e m i c a l r e a c t i o n s , and p u r i f i c a t i o n o f p r o d u c t s t o the t r e a t m e n t o f b y - p r o d u c t s t r e a m s . Petrochemical processes require smaller reactors t h a n used i n r e f i n e r i e s . C h e m i c a l r e a c t o r s a r e s i z e d i n the 50 t o 250 c u . f t . r a n g e . Orders f o r replacement c a t a l y s t u s u a l l y r a n g e f r o m 10,000 t o 50,000 l b s , b u t t h e r e a r e many d i f f e r e n t p r o c e s s a p p l i c a t i o n s . C a t a l y s t q u a l i t y i s b e c o m i n g more i m p o r t a n t t h a n i n r e c e n t y e a r s a s many i n d u s t r i e s a t t e m p t t o r e d u c e t h e c o s t o f n o n c o n formance and improve t h e q u a l i t y o f m a n u f a c t u r e d g o o d s . A c h e m i c a l producer has a c h o i c e of e i t h e r s e l e c t i n g an o f f - t h e - s h e l f c a t a l y s t a v a i l a b l e from u s u a l l y s e v e r a l s o u r c e s , or of d e v e l o p i n g a p r o p r i e t a r y c a t a l y s t s u i t e d t o h i s s p e c i f i c p r o c e s s and o p e r a t i n g n e e d s . F i x e d Bed A d s o r b e n t s . S i m i l a r q u a l i t y r e q u i r e m e n t s , a s d i s c u s s e d f o r c a t a l y s t s , a p p l y t o m o l e c u l a r s i e v e s and other adsorbents. Instead of c a t a l y t i c a c t i v i t y , adsorpt i o n c a p a c i t i e s f o r c e r t a i n m a t e r i a l s , such as water, or l i n e a r p a r a f f i n s , are important p r o p e r t i e s of aluminas, c l a y s , and z e o l i t e s when u s e d a s a d s o r b e n t s .


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CHARACTERIZATION AND

CATALYST DEVELOPMENT


User's Plant Problems At some point i n time, every operating plant must make the d e c i s i o n to replace an e x i s t i n g c a t a l y s t charge because i t has aged due to feedstock poisons, i t s h i s t o r y of high temperatures and chemical r e a c t i o n s , mechanical and chemical degradation and so on (4). Expectations are created with every c a t a l y s t replacement d e c i s i o n that the new charge w i l l perform better than the charge being replaced. When the new c a t a l y s t charge does not meet these expectations, s i g n i f i c a n t f i n a n c i a l losses are i n c u r r e d . T e c h n i c a l e f f o r t s are i n i t i a t e d to i n v e s t i g a t e the causes of nonconformance. Feedstock p r o p e r t i e s , s t a r t - u p procedures, p l a n t operations, and c a t a l y s t p r o p e r t i e s u s u a l l y are being considered. Changed C a t a l y s t P r o p e r t i e s . In s e v e r a l cases, changed plant performance could be traced to changed c a t a l y s t p r o p e r t i e s . The p o t e n t i a l impact of such nonconformance on plant operations i s shown i n Table I. Table I. Nonconforming C a t a l y s t Replacement Charges Nonconformance Lower a c t i v i t y

Impact on Operations Reduced throughput to maintain same conversion Higher a c t i v i t y Reduced throughput due to heat transfer limitation Lower crush strength Pressure drop; increased f i n e s due to reduced p h y s i c a l i n t e g r i t y Higher crush strength Pressure drop; increased f i n e s due to greater b r i t t l e n e s s Higher abrasion l o s s Pressure drop; increased f i n e s when handling, shipping, loading Smaller p a r t i c l e s Bulk d e n s i t y ; p o s s i b l y c h a n n e l l i n g due to unequal s i z e d i s t r i b u t i o n Larger p a r t i c l e s i z e Reduced a c t i v i t y and c a t a l y s t l i f e Larger c r y s t a l l i t e s Reduced a c t i v i t y and c a t a l y s t l i f e Reduced s e l e c t i v i t y Higher l o s s e s ; shorter c y c l e time; poor feedstock u t i l i z a t i o n Lower sieve c a p a c i t y Reduced c y c l e time; shorter l i f e of molecular sieve Performance v a r i a t i o n s of d i f f e r e n t l o t s of the same brand of c a t a l y s t s t i l l are causes of s i g n i f i c a n t plant problems i n the i n d u s t r y . Such experiences j u s t i f y e f f o r t s to develop e f f e c t i v e q u a l i t y c o n t r o l procedures for purchased c a t a l y s t s . Obtaining a c l e a r understanding of required c a t a l y s t p r o p e r t i e s i s a f i r s t step. P l a n t problems and unusual events need to be recorded. The h i s t o r y of c a t a l y s t performance i n the plant i s most valuable to have i n developing c a t a l y s t s p e c i f i c a t i o n s .


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387


Puschass s p e c i f i c a u p n g G e n e r a l c a t a l y s t p r o p e r t i e s , sometimes c a l l e d t y p i c a l a n a l y s e s , a r e u s u a l l y b e i n g p r o v i d e d by v e n d o r s i n s a l e s l i t e r a t u r e . N o m i n a l s i z e and shape o f c a t a l y s t s , compos i t i o n by m a j o r c o m p o n e n t s , i n t e r n a l s u r f a c e a r e a and p o r e v o l u m e , b u l k d e n s i t y , and a v e r a g e c r u s h i n g s t r e n g t h a r e u s u a l l y a v a i l a b l e . The name and d e s i g n a t i o n o f merc h a n t c a t a l y s t s i s b e i n g h i g h l i g h t e d . The s u p p l i e r s o f u s e r - p r o p r i e t a r y c a t a l y s t s a r e r e q u i r e d t o use more e x p l i c i t s p e c i f i c a t i o n s . I n e i t h e r c a s e , t h e c h e m i c a l and p e t r o c h e m i c a l user of a purchased c a t a l y s t does v e i l t o make s u r e t h a t c a t a l y s t q u a l i t y needs a r e u n d e r s t o o d by b o t h s u p p l i e r and u s e r . Q u a l i t y R e q u i r e m e n t s . One c a n s t a t e t h r e e p r i n c i p a l q u a l i t y r e q u i r e m e n t s a s f o l l o w s : ( 1 ) t h e c a t a l y s t must have s u f f i c i e n t p h y s i c a l i n t e g r i t y t o w i t h s t a n d t h e p h y s i c a l f o r c e s w h i c h a r e c r e a t e d when l o a d i n g t h e c a t a l y s t i n t o r e a c t o r s and when s u b j e c t i n g t h e p a r t i c l e s to process c o n d i t i o n s of v a r y i n g temperatures, p r e s s u r e s , v a p o r and l i q u i d mass v e l o c i t i e s , and t o w i t h s t a n d c h e m i c a l a t t a c k , ( 2 ) t h e c a t a l y s t must have t h e p r e s c r i b e d c h e m i c a l p r o p e r t i e s needed t o f u n c t i o n i n t h e d e s i r e d c h e m i c a l r e a c t i o n and ( 3 ) p h y s i c a l and c h e m i c a l p r o p e r t i e s i n t h e i n t e r i o r o f i n d i v i d u a l p a r t i c l e s must p e r m i t a c c e s s o f t h e r e a c t a n t s on a b u l k m o l e c u l a r s c a l e and e x h i b i t s u f f i c i e n t r e a c t i v i t y t o meet t h e r e q u i r e ments s e t by t h e p r o c e s s d e s i g n . S p e c i f i c a t i o n s . P u r c h a s e s p e c i f i c a t i o n s have t o be d e f i n e d f i r s t . Then, q u a l i t y c o n t r o l of c a t a l y s t samples which are r e p r e s e n t a t i v e of the purchased c a t a l y s t l o t s , c a n be i m p l e m e n t e d t o compare a c t u a l c h e m 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 t h the range of v a l u e s s t a t e d i n the purchase s p e c i f i c a t i o n s . A c t i v i t y and s e l e c t i v i t y o f c a t a l y s t s a r e s o m e t i m e s i n c l u d e d i n s p e c i f i c a t i o n s and c a n be m o n i t o r e d i n s m a l l s c a l e s i m u l a t i o n s of c o m m e r c i a l r e a c t o r s , s u c h as i n p i l o t p l a n t s u s i n g s t a n d a r d f e e d s t o c k s o r model compounds. The s t e a m r e f o r m i n g t e s t p e r f o r m e d c o m m e r c i a l l y by C a t a l y s t S e r v i c e s I n c . o f S h e l b y v i l l e , K e n t u c k y i s ment i o n e d as an e x a m p l e . I n f o r m a t i o n on p u r c h a s e d c a t a l y s t s s h o u l d i n c l u d e t h e l o t numbers and d a t e s o f m a n u f a c t u r e , and t h e amount o f w a t e r and o t h e r v o l a t i l e m a t t e r s t i l l c o n t a i n e d on the c a t a l y s t . S p e c i f i c a t i o n s should p r o v i d e data f o r c h e m i c a l a n a l y s e s , and p h y s i c a l - m e c h a n i c a l and p h y s i c a l c h e m i c a l p r o p e r t i e s . The l a t t e r i n f o r m a t i o n s h o u l d i n c l u d e d a t a c o n c e r n i n g t h e a v e r a g e shape and s i z e s o f p a r t i c l e s , including oversized p a r t i c l e s , fines content, and o t h e r m e a s u r e s of p h y s i c a l i n t e g r i t y . An example o f i n f o r m a t i o n w h i c h c o u l d be i n c l u d e d i n p u r c h a s e s p e c i f i c a t i o n s f o r a f i x e d bed c a t a l y s t i s shown i n t h e f o l l o w ing Table I I .


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Table I I .

C a t a l y s t Purchase

Analyses Supplier Catalyst Designation L o t No. & Date M a n u f a c t u r e d Shape a n d N o m i n a l S i z e s CHEMICAL ANALYSES Molybdenum, v t % D N i c k e l , wt% D O t h e r C h e m i c a l A n a l y s e s , ppm PHYSICAL PROPERTIES Crush S t r e n g t h , l b s , r a d i a l D Abrasion R e s i s t a n c e , % Loss D Packed Bulk D e n s i t y D Pore S i z e D i s t r i b u t i o n , by M e r c u r y I n t r u s i o n , D Nitrogen Desorption D P o r e Volume, m l / g S u r f a c e A r e a , m2/g D Ammonia C h e m i s o r p t i o n D

Specifications

ASTM HgthQd

S p e c i f i e d Values Mint Maxt T y p i c a l to

/../.. be r e p o r t e d :

3943-86 4481-85 4179-82 4058-87 4699-87

for 12

instance: 25 15

4284-83 4222-83 3663-84 4824-88

Q u a l i t y CQHtSQl P r o c e d u r e s A c a t a l y s t m a n u f a c t u r e r w i l l have p r o c e d u r e s i n p l a c e t o monitor the q u a l i t y of c a t a l y s t l o t s as these a r e being m a n u f a c t u r e d . To a l a r g e e x t e n t , i t w i l l depend on t h e c u s t o m e r , how much i n f o r m a t i o n c o n c e r n i n g c a t a l y s t p r o p e r t i e s and c a t a l y s t performance i s b e i n g communicated. I n some c a s e s , t h e c a t a l y s t m a n u f a c t u r e r may have i n s u f f i c i e n t i n f o r m a t i o n c o n c e r n i n g t h e intended use f o r the c a t a l y s t b e i n g s o l d . He w i l l base h i s m a n u f a c t u r i n g s p e c i f i c a t i o n s on h i s a s s u m p t i o n s c o n c e r n i n g p o s s i b l e c a t a l y s t uses. The c a t a l y s t u s e r may r e l y on t h e s u p p l i e r ' s q u a l i t y c o n t r o l , o r he may have h i s own q u a l i t y c o n t r o l s f o r catalysts received a t the plant s i t e . Standard Q u a l i t y Control Procedure. A standard q u a l i t y c o n t r o l p r o c e d u r e was e s t a b l i s h e d i n E x x o n C h e m i c a l Company i n 1984. O p e r a t i n g p l a n t s were o f f e r e d i n - h o u s e a s s i s t a n c e f o r d e v e l o p i n g a p p r o p r i a t e purchase s p e c i f i c a t i o n s , and f o r m o n i t o r i n g t h e q u a l i t y o f l o t samples o f purchased commercial c a t a l y s t s and adsorbents. R e p r e s e n t a t i v e L o t Samples a n d A n a l y s e s . S u p p l i e r s o f c a t a l y s t and f i x e d bed a d s o r b e n t a r e b e i n g r e q u e s t e d t o s u p p l y r e p r e s e n t a t i v e l o t samples and a n a l y t i c a l c e r t i f i c a t e s f o r e a c h new p u r c h a s e o r d e r a t t h e t i m e t h e c a t a l y s t i s r e a d y f o r s h i p m e n t . The a n a l y t i c a l r e s u l t s a r e b e i n g compared w i t h u p d a t e d p u r c h a s e s p e c i f i c a t i o n s . QC E x p e r i e n c e . When we a p p l i e d q u a l i t y c o n t r o l s t o p u r c h a s e d c a t a l y s t s w i t h i n E x x o n C h e m i c a l Company, we f o u n d


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s i g n i f i c a n t l o t t o l o t v a r i a t i o n s i n t h e q u a l i t y o f some c a t a l y s t s . S o m e t i m e s , s u c h v a r i a t i o n s were w i t h i n t h e s p e c i f i c a t i o n s , o s c i l l a t i n g between maximum and minimum v a l u e s i n an u n p r e d i c t a b l e f a s h i o n , s o m e t i m e s v a r i a t i o n s were c a u s e d by t h e a b s e n c e o f a p p r o p r i a t e s p e c i f i c a t i o n s T h i s i s i l l u s t r a t e d i n the f o l l o w i n g three examples: PflEUgle - k e n q t h ofi S x t t V t a a t e g A new r e a c t o r c h a r g e o f a 3.2 mm (1/8 i n c h ) e x t r u d e d n i c k e l o x i d e on a l u m i n a c a t a l y s t was compared w i t h t h e p r e v i o u s c h a r g e , b e c a u s e t h e o p e r a t i n g p l a n t o b s e r v e d an i n c r e a s e i n c a t a l y s t c h i p s . These were t h o u g h t t o have c o n t r i b u t e d t o p r e s s u r e drop problems. R e t a i n e d samples of the r e s p e c t i v e c a t a l y s t l o t s were e x a m i n e d . I t was f o u n d t h a t the replacement l o t c o n t a i n e d a h i g h e r percentage of s m a l l e r p a r t i c l e s which r e s u l t e d i n reducing the l e n g t h t o d i a m e t e r r a t i o of c a t a l y s t p a r t i c l e s . The t e s t was c o n d u c t e d by t a k i n g a 125 ml random sample from each r e p r e s e n t a t i v e l o t sample, s o r t i n g i n d i v i d u a l p a r t i c l e s i n e a c h s a m p l e by l e n g t h , and m e a s u r i n g g r o u p s o f 25-50 p a r t i c l e s o f a p p r o x i m a t e l y e q u a l s i z e . T o t a l number o f p a r t i c l e s r a n g e d f r o m 900 t o 1200, r e s p e c t i v e l y . These were d i v i d e d i n t o a b o u t 30 f r a c t i o n s . The a v e r a g e p a r t i c l e l e n g t h was c a l c u l a t e d by d i v i d i n g t h e l e n g t h o f a 260 mm l o n g r u l e r by t h e number o f p e l l e t s , c o u n t e d f o r e a c h f r a c t i o n , w h i c h were l i n e d up a g a i n s t t h e r u l e r . The d a t a i s s u m m a r i z e d i n t h e f o l l o w ing t a b l e . Table I I I .

P a r t i c l e S i z e Measurements

Replacement Lot B 1 % 50 % 23 % 2$ \ 100 % 5.8 mm Average p a r t i c l e l e n g t h Diameter of e x t r u d a t e s 3.2 mm 1.8 A v e r a g e L/D r a t i o o f e x t r u d a t e s

P a r t i c l e S i z e Range Lencrth i n m i l l i m e t e r s > 13.6 5.6 13.5 4.6 5.5 < 4.6

Previous Lot A 17 % 73 % 9 %

I

\

100 % 9.4 mm 3.2 mm 2.9

These a n a l y s e s were r e v i e w e d w i t h t h e s u p p l i e r . The s i z e d i s t r i b u t i o n and t h e l e n g t h / d i a m e t e r r a t i o o f t h e c a t a l y s t were s u b s e q u e n t l y d e f i n e d i n p u r c h a s e s p e c i f i c a tions to eliminate uncontrolled l o t to l o t v a r i a t i o n s . D e p t h o f P a l l a d i u m P e n e t r a t i o n . A new c a t a l y s t c h a r g e , c o n s i s t i n g o f 0.3 wt % p a l l a d i u m on a l u m i n a , e x h i b i t e d h i g h e r a c t i v i t y and l o w e r s e l e c t i v i t y a t g i v e n p l a n t ope r a t i n g c o n d i t i o n s . C h e m 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 t h i s c h a r g e were compared w i t h t h e p r e v i o u s c h a r g e w h i c h had been o p e r a t i n g s a t i s f a c t o r i l y .


390



S t a n d a r d a n a l y t i c a l p r o c e d u r e s , i n c l u d i n g CO c h e m i s o r p t i o n , i n d i c a t e d t h a t t h e new c h a r g e a p p e a r e d t o be o f t h e same q u a l i t y a s p r e v i o u s l y u s e d c a t a l y s t . S u b s e q u e n t l y , e l e c t r o n probe scans l e d t o t h e o b s e r v a t i o n t h a t t h e d e p t h o f p a l l a d i u m i m p r e g n a t i o n had c h a n g e d . A c o m p a r i s o n o f t y p i c a l p a l l a d i u m p e n e t r a t i o n s f o r t h e two c h a r g e s i s shown i n T a b l e I V a n d i n F i g u r e s 1 and 2. S u b s e q u e n t a c t i v i t y t e s t s w i t h model compounds were c o n s i s t e n t w i t h t h e r e s u l t s shown i n T a b l e I V a n d p r o v e d t o o u r s a t i s f a c t i o n t h a t t h e new c a t a l y s t was d i f f e r e n t . T a b l e I V . E l e c t r o n P r o b e P d Measurements S c a n n i n g E l e c t r o n P r o b e T r a c e s o f 3 mm SDheres :In C r o s s S e c t i o n (Averacres) D e p t h o f m a j o r Pd p e a k , m i c r o n s T o t a l Pd p e n e t r a t i o n , m i c r o n s

Lot Y 115 570

Lot X 360 770

C a t a l y s t A c i d i t y b v Ammonia C h e m i s o r p t i o n . P l a n t p e r f o r mances b e l o w e x p e c t a t i o n s were r e p o r t e d b y two u n i t s , i n w h i c h t h e o r i g i n a l a l u m i n a b a s e d c a t a l y s t s were r e p l a c e d . S u r f a c e a r e a s p e c i f i c a t i o n s were 150-200 m2/g f o r b o t h c a t a l y s t s . A c i d i t y was measured b y ammonia c h e m i s o r p t i o n u s i n g a r e c o r d i n g vacuum t h e r m o a n a l y z e r w i t h a TGA s a m p l e h o l d e r , a n d was c o r r e l a t e d w i t h BET s u r f a c e a r e a , a s shown i n T a b l e V. I n one c a s e , a c i d i t y needed f o r t h e r e a c t i o n was m a x i m i z e d b y c h a n g i n g t h e s p e c i f i c a t i o n t o 190-200 m2/g surface area. I n the other case, undesirable side react i o n s , t h o u g h t t o be c a u s e d b y e x c e s s i v e a c i d i t y o f t h e c a r r i e r , were m i n i m i z e d b y a d o p t i n g a s u r f a c e a r e a o f 150-160 m2/g a s a new p u r c h a s e s p e c i f i c a t i o n . T a b l e V.

Ammonia C h e m i s o r p t i o n and S u r f a c e A r e a

BET S u r f a c e A r e a Ammonia C h e m i s o r p t i o n Sample m2/g mUUequivalents/gram High A c i d i t y Alumina New r e p l a c e m e n t 0.55 192 New s p e c i f i c a t i o n 190-200 0.46 Replacement charge 147 ( t o o low) P r e v i o u s charge 0.60 198 Low A c i d i t y C a t a l y s t New r e p l a c e m e n t 0.41 153 New manuf. t a r g e t 150-160 -0.56 Replacement charge 196 ( t o o h i g h ) P r e v i o u s charge 0.40 150 Limitations of Quality Control. Q u a l i t y c o n t r o l by det e c t i o n i s b a s e d on t h e i n s p e c t i o n o f f i n i s h e d c a t a l y s t before i t i s being shipped t o t h e customer.



35.

PULS


T

r

i

0 115

570

Pd P e n e t r a t i o n F i g u r e 1.

(microns)

Lower Depth of

Impregnation.


391

392



F i g u r e 2.

Deeper S u b s u r f a c e

Impregnation.



35.

PULS


393

Product not meeting manufacturing s p e c i f i c a t i o n s i s e i ther being recycled, separated f o r other uses, or d i s c a r d e d . A f t e r r e c e i v i n g t h e c a t a l y s t , t h e c u s t o m e r may a p p l y h i s own q u a l i t y c o n t r o l a n d may r e j e c t drums o f c a t a l y s t s w h i c h do n o t meet h i s i n s p e c t i o n criteria. I n f o r m a t i o n d e v e l o p e d d u r i n g a n i n s p e c t i o n c a n be used o n l y f o r t h e next c a t a l y s t o r d e r , assuming t h e p u r c h a s e r w i l l p a s s t h e i n f o r m a t i o n on t o t h e s u p p l i e r . Thus, q u a l i t y c o n t r o l by d e t e c t i o n i s u n s a t i s f a c t o r y , and i s w a s t e f u l due t o p o t e n t i a l d u p l i c a t i o n o f q u a l i t y c o n t r o l e f f o r t s b y b o t h t h e s u p p l i e r and t h e c u s t o m e r . Q u a l i t y c o n t r o l can o n l y d e t e c t , b u t does n o t p r e v e n t , d e v i a t i n g and p o o r e r q u a l i t y from happening. I n this situation, suppliers under-utilize catalyst performance d a t a s i n c e u s e r s u s u a l l y w i l l n o t communicate s u c h i n f o r m a t i o n . U s e r s u n d e r - u t i l i z e t h e know-how i n c a t a l y s t manufacture which s u p p l i e r s c a r e f u l l y guard. The way o u t o f t h i s s i t u a t i o n i s t o i n t r o d u c e a p p r o p r i a t e s t a t i s t i c a l process c o n t r o l procedures i n the manufacturing processes of the s u p p l i e r , h i s s u p p l i e r s , and t h e u s e r . T h r o u g h t h e s e e f f o r t s , s a t i s f a c t o r y a s w e l l as u n s a t i s f a c t o r y performances of i n d i v i d u a l l o t s of c a t a l y s t s c a n be d e t e r m i n e d , a n d l o t t o l o t v a r i a t i o n s o f c a t a l y s t q u a l i t y c a n be i d e n t i f i e d . PKQfluce^s'

fr t Q

t o kpfr

Variations

F i x e d bed c a t a l y s t s a r e m a n u f a c t u r e d i n n o n - c o n t i n u o u s p r o c e s s e s . V a r i a t i o n s i n t h e q u a l i t y have been o b s e r v e d from l o t t o l o t and from p e l l e t t o p e l l e t . C a t a l y s t M a n u f a c t u r e . Many b a t c h a n d s e m i c o n t i n u o u s processing steps are required. A t y p i c a l flow plan f o r a c a t a l y s t manufacturing plant includes the preparation and p u r i f i c a t i o n o f raw m a t e r i a l s , m a n u f a c t u r e o f c a t a l y s t s u p p o r t m a t e r i a l s as powders, d r y i n g , s i z i n g , f o r m i n g , i m p r e g n a t i o n , c a l c i n i n g , r e d u c t i o n and s t a b i l i z a t i o n , s c r e e n i n g and p a c k a g i n g o p e r a t i o n s . Some o f t h e operations a r e c a r r i e d out i n r e p e t i t i v e batches as s m a l l a s 500 t o 1,000 l b s . C a t a l y s t q u a l i t y i s a f f e c t e d i n a l l of the operations. A d j u s t m e n t s b e i n g made t o a n y o f t h e s e p r o c e s s i n g s t e p s a f f e c t o t h e r d o w n s t r e a m o p e r a t i o n s . An a d j u s t m e n t b e i n g made t o c o r r e c t a s i n g l e c a t a l y s t p r o p e r t y w i l l a f f e c t o t h e r p r o p e r t i e s . F o r i n s t a n c e , an i n c r e a s e i n t h e c r u s h strength through a p p l i c a t i o n of higher forming pressure w i l l reduce the s i z e of macro-pores. With these f a c t s i n mind, i t i s n o t s u r p r i s i n g t h a t c a t a l y s t p r o p e r t i e s u s u a l l y v a r y i n some way f r o m one l o t t o t h e n e x t . S t a t i s t i c a l Process

Control

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 (SPC) i s u s e d i n a c c o r d a n c e w i t h t h e p r i n c i p l e of p r e v e n t i o n i n s t e a d o f d e t e c t i o n by m e a s u r i n g v a r i a b l e s a n d a t t r i b u t e s on a r e a l - t i m e b a s i s .



394


This a l l o w s t h e manufacturer t o take c o r r e c t i v e a c t i o n s as s o o n a s s t a t i s t i c a l l y s i g n i f i c a n t d e v i a t i o n s from a n aim a r e b e i n g d e t e c t e d d u r i n g t h e manufacturing p r o c e s s . The o p e r a t o r s h o u l d n o t have t o d e c i d e f r e q u e n t l y t o what v a l u e s i n d i v i d u a l o p e r a t i n g p a r a m e t e r s s h o u l d be a d j u s t e d , i . e . w i t h i n ranges as b e i n g s p e c i f i e d i n t h e r e c i p e s , thus a l l o w i n g f o r a r b i t r a r y v a r i a t i o n s t o occur between many u p p e r a n d l o w e r c o n t r o l p o i n t s . S p e c i f i c t a r g e t s f o r manufacturing v a r i a b l e s and f o r a t t r i b u t e s o f raw a n d i n t e r m e d i a t e m a t e r i a l s c a n be d e f i n e d t h r o u g h t h e a p p l i c a t i o n o f c o n t r o l c h a r t s when the m a n u f a c t u r i n g p r o c e s s o v e r a l l i s balanced and i n c o n t r o l . By u s i n g s u c h t a r g e t s , t h e o p e r a t o r c a n r e d u c e s t a r t - u p times f o r c a t a l y s t batches and c a n m a i n t a i n , t h r o u g h SPC ( 5 ) a more s t e a d y o p e r a t i o n , i n w h i c h u n c o n t r o l l e d m a n u f a c t u r i n g v a r i a t i o n s w i l l be m i n i m i z e d . E s s e n t i a l l y a l l c a t a l y s t m a n u f a c t u r e r s have t a k e n s t e p s i n r e c e n t y e a r s t o t r a i n l a b o r a t o r y and manufact u r i n g p e r s o n n e l i n t h e a p p l i c a t i o n o f SPC, a n d t o make m o d i f i c a t i o n s t o t h e m a n u f a c t u r i n g f a c i l i t i e s t o improve Cpk, t h e p r o c e s s c a p a b i l i t y i n d e x ( 6 ) . D a t a c o l l e c t i o n and a n a l y s i s on c o n t r o l c h a r t s a r e u s u a l l y f i r s t s t e p s f o r i m p l e m e n t i n g SPC. P

C a t a l y s t User. A n a l y s i s of consecutive l o t s of purchased c a t a l y s t i s u s u a l l y a f i r s t s t e p which customers c a n t a k e t o d e t e r m i n e how c a t a l y s t p r o p e r t i e s o s c i l l a t e between u p p e r a n d l o w e r s p e c i f i c a t i o n v a l u e s . T h i s i s i l l u s t r a t e d i n F i g u r e s 3 a n d 4. The two c o n t r o l c h a r t s shown c o n t a i n t h e v a l u e s o f r e d u c e d n i c k e l c o n t e n t o f c o n s e c u t i v e l o t s o f s i m i l a r n i c k e l c a t a l y s t s . Both c a t a l y s t s c o n t a i n a b o u t 50 wt % N i O a n d a r e p r e r e d u c e d . In t h e f i r s t f i g u r e , large l o t t o l o t v a r i a t i o n s c a n be o b s e r v e d , a l t h o u g h t h e c a t a l y s t meets i t s s p e c i f i c a t i o n s o f 40-60 wt % N i O a n d 40-60% r e d u c t i o n . However, i t s q u a l i t y w i t h r e s p e c t t o r e d u c e d N i v a l u e c o u l d be c o n s i d e r e d t o be o u t o f c o n t r o l . An X-bar v a l u e o f 29.0 wt % N i i s b e i n g c a l c u l a t e d . The s e c o n d c a s e r e p r e s e n t s more r e c e n t d a t a . H e r e , q u a l i t y w i t h r e s p e c t t o reduced N i v a l u e i s i n c o n t r o l through the probable a p p l i c a t i o n of appropriate t a r g e t s f o r o p e r a t i n g v a r i a b l e s i n c a t a l y s t m a n u f a c t u r e . An X-bar v a l u e o f 31.3 wt % N i i s b e i n g c a l c u l a t e d . S i m i l a r o b s e r v a t i o n s c a n be made c o n c e r n i n g o t h e r c h e m i c a l and p h y s i c a l c a t a l y s t p r o p e r t i e s . Not a l l variations i nquality w i l l adversely affect catalyst p e r f o r m a n c e . However, t h e p r i c e o f n o n c o n f o r m a n c e , i n many c a s e s , i s unknown. C a t a l y s t M a n u f a c t u r e r , The n e x t s t e p i s f o r t h e m a n u f a c turer t o generate c o n t r o l c h a r t s o f i n d i v i d u a l data ( s u c h a s X- o r I - c h a r t s a n d R - c h a r t s ) f r o m w h i c h a v e r ages, upper and lower t h r e e - s i g m a l i m i t s and ranges between c o n s e c u t i v e d a t a c a n be d e t e r m i n e d . M a n u f a c t u r i n g o b s e r v a t i o n s a n d e v e n t s a r e a l s o l i s t e d on t h e s e c o n t r o l


395


PULS

CONTROL CHART nc iv du

X-c harl

5

40 I


35

1 V\VA

30 25

/ f

/

/ A

20

A

—J

I*

•

P anqc >s

20 15 10 5 0

k

s

J

r

// \

N

I I \ I

UCL= 36.3

-> \

v

\

\I

\ —

V

\1

—

X = 29.0

y 1

\ v.

/

LCL= 21.7

*-chart)

(1

UCL= 12.2

f

\\

R = 5

Figure

10

15

20

Catalyst Production Lot Numbers

3. L o t t o L o t V a r i a t i o n s

25

Within

3.9

30

Specifications.

CONTROL CHART nc iv du als

X-c tia rt

40. 35 .

UCL= 34.0 X = 31.3

30.

LCL= 28.6

f

25. 20.

anges (Ft-chart)

20. 15 . 10. 5. 0

s

40

Figure

\

45

s50

55

60

Catalyst Production Lot Numbers

4.

65

I n C o n t r o l Through M a n u f a c t u r i n g

UCL=

4.9

R =

1.4

70

Targets.



396


c h a r t s , i n order t o determine assignable causes of dev i a t i o n s . T h i s leads t o t h e development o f c o r r e c t i v e a c t i o n s a i m e d a t e l i m i n a t i n g unwanted v a r i a t i o n s . I n a d d i t i o n t o X - c h a r t s a n d R - c h a r t s , CUSUM c h a r t s a r e s o m e t i m e s u s e d . T r e n d s c a n be d e t e c t e d s o o n e r when u s i n g CUSUM c h a r t s . More r e c e n t l y , t h e u s e o f EWMA, e x p o n e n t i a l l y weighted moving a v e r a g e s , i s b e i n g s u g g e s t e d as b e i n g e a s i e r t o u s e on t h e f a c t o r y f l o o r . S o u r c e s o f p r o c e s s v a r i a n c e c a n be q u a n t i f i e d a n d ranked through s t a t i s t i c a l d e s i g n o f experiments. R e l a t i o n s between v a r i a n c e s o f p r o c e s s i n p u t a n d o u t p u t c a n be d e v e l o p e d . I n t h i s way, t h e e f f e c t o f l a b o r a t o r y a n a l y s e s , a s w e l l a s o f p a r a l l e l o r s e q u e n t i a l manufact u r i n g s t e p s , on t h e o v e r a l l v a r i a n c e f o r a c a t a l y s t c a n be d e t e r m i n e d . Supplier

Accreditation

Procedure

The s u p p l i e r - u s e r o r v e n d o r - v e n d e e r e l a t i o n s h i p , a s i t p e r t a i n s t o q u a l i t y , i s w e l l described i n the American N a t i o n a l S t a n d a r d ' s ANSI/ASQC Q90-1987 t o Q94-1987. The s t a n d a r d s a r e t e c h n i c a l l y e q u i v a l e n t t o t h e ISO 9000 t o ISO 9004 s e r i e s o f t h e i n t e r n a t i o n a l Q u a l i t y Management and Q u a l i t y A s s u r a n c e S t a n d a r d s . The recommended q u a l i t y system s p e c i f i e s q u a l i t y p o l i c y , o r g a n i z a t i o n , authori t y , p e r s o n n e l , management r e v i e w , a n d s o o n . Twelve c h e m i c a l p r o d u c e r s r e c e n t l y c o o p e r a t e d w i t h the American S o c i e t y f o r Q u a l i t y C o n t r o l and i s s u e d a M a n u a l o f Good P r a c t i c e s . An e x t e n s i v e b i b l i o g r a p h y i s included i n the booklet ( 7 ) . Our c u r r e n t v i e w s on how t o i m p l e m e n t a c a t a l y s t s u p p l i e r a c c r e d i t a t i o n p r o c e d u r e a r e a s f o l l o w s . A team c o n s i s t i n g of representatives of t e c h n i c a l , a n a l y t i c a l , p l a n t o p e r a t i o n and p u r c h a s i n g f u n c t i o n s v i s i t s w i t h t h e supplier's equivalent representatives prior t o placing a m a j o r o r d e r , o r a t c e r t a i n i n t e r v a l s . The m e e t i n g w i l l have t h e f o l l o w i n g f i v e p a r t a g e n d a : Table V I .

1. 2. 3. 4. 5.

Supplier

Accreditation

Agenda f o r C a t a l y s t U s e r a n d S u p p l i e r V i s i t Topic Provide estimate of p o t e n t i a l purchases Review p r e v i o u s a n a l y s e s , c a t a l y s t performance, and c a t a l y s t s p e c i f i c a t i o n s R e v i e w i m p l e m e n t a t i o n o f c o n t r o l c h a r t s a n d SPC Review p r e v i o u s t o t a l q u a l i t y performance N o t i f y s u p p l i e r o f e v a l u a t i o n r e s u l t s and provide f i n a l i z e d purchase s p e c i f i c a t i o n s .

T h i s s u p p l i e r a c c r e d i t a t i o n p r o c e d u r e i s aimed a t a c h i e v i n g p r o g r a m s o f c o n t i n u e d improvement i n q u a l i t y t h r o u g h SPC i m p l e m e n t a t i o n i n c a t a l y s t m a n u f a c t u r e .


35. PULS


397


I n w o r k i n g w i t h c a t a l y s t s u p p l i e r s we a r e l e d t o t h e u n d e r s t a n d i n g t h a t SPC p r o c e d u r e s and c o n t r o l c h a r t s c a n be a p p l i e d t o t h e p r e p a r a t i o n o f s m a l l e r b a t c h e s o f f i n i s h e d c a t a l y s t s such a s used i n c h e m i c a l i n d u s t r i e s . D a t a c o l l e c t e d f o r c o n s e c u t i v e c a t a l y s t l o t s show t h a t q u a l i t y c o n s i s t e n c y has i m p r o v e d s i g n i f i c a n t l y a f ter introducing c o n t r o l charts i n c a t a l y s t manufacture. Rewards f o r t h i s c o u r s e o f a c t i o n a r e s e e n i n more c o n s i s t e n t c a t a l y s t q u a l i t y , e v e n t u a l l y reduced a n a l y t i c a l c o s t s , and o p p o r t u n i t i e s t o d e v e l o p p r e f e r r e d supp l i e r s t a t u s t o meet t h e s p e c i a l needs o f t h e c u s t o m e r ' s i n d i v i d u a l chemical u n i t . Conclusions Lot t o l o t v a r i a t i o n s i n the q u a l i t y of purchased f i x e d bed c a t a l y s t s a r e c a u s i n g s i g n i f i c a n t p l a n t p r o b l e m s f o r petrochemical catalyst users. Conventional q u a l i t y c o n t r o l procedures f a l l short o f c u r r e n t needs t o i m p r o v e t h e c o n s i s t e n c y o f p u r c h a s e d c a t a l y s t q u a l i t y and a r e b e i n g s u p p l e m e n t e d b y t h e u s e o f c o n t r o l c h a r t s and 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 . E s s e n t i a l l y a l l c a t a l y s t m a n u f a c t u r e r s have t a k e n s t e p s i n t h e s e p a s t c o u p l e o f y e a r s t o i m p l e m e n t SPC i n t h e i r m a n u f a c t u r i n g p r o c e s s e s , i n o r d e r t o improve t h e consistency of c a t a l y s t properties. The q u a l i t y o f p u r c h a s e d f i x e d bed c a t a l y s t s a n d adsorbents i s important. A supplier a c c r e d i t a t i o n procedure i s b e i n g implemented. ASTM Methods f o r c a t a l y s t a n d z e o l i t e a n a l y s e s and A m e r i c a n and I n t e r n a t i o n a l S t a n d a r d s f o r q u a l i t y c o n t r o l and q u a l i t y a s s u r a n c e f o r m t h e c o r n e r s t o n e s o f t h e f o u n d a t i o n upon w h i c h f u t u r e c a t a l y s t s u p p l i e r - c a t a l y s t u s e r r e l a t i o n s h i p s w i l l be c o n s t r u c t e d . Literature Cited 1. 2. 3. 4. 5. 6.

7.

Garvin, David A. Managing Quality; The Free Press, Macmillan Inc.: New York, NY, 1988 Peters, Tom The New Wasters of Excellence; Nightingale-Conant Corporation (Audiocassette Programs), Chicago, 1986 Crosby, P h i l i p B. Quality is Free: New American Library, New York, 1979 Bartholomew, C. H. Chem. Eng. Nov 12, 1984, 91, 96. Oakland, John S. S t a t i s t i c a l process Control, A Practical Guide: Heineman Professional Publishing Ltd: London, 1986 Small, Bonnie B. S t a t i s t i c a l Quality Control Hand book, by Western E l e c t r i c C o . , I n c . : 1956; Eleventh Printing by Delmar Printing Company, Charlotte, NC, 1985 Quality Assurance for the chemical and Process In dustries, ft Manual of good Practices; American Soci ety for Quality Control: Milwaukee, WI, 1987

Received January 26, 1989 In Characterization and Catalyst Development; Bradley, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

Characterization and Catalyst Development

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