The cost of comercial cobalt molybdenum and nickel molybdenum catalysts has escalated by a factor of four over the last five years. This has produced a strong.
A Study of D e a c t i v a t i o n and Regeneration of C a t a l y s t s Used i n t h e LC-Fining o f Solvent Refined Coal C. W. C u r t i s , J. A. Guin, R. Nalitham, A. Mohsin, and A. R . T a r r e r
Department o f Chemical Engineering, Auburn U n i v e r s i t y , Auburn U n i v e r s i t y , AL 36849
J. D. P o t t s and K. E. Hastings C i t i e s S e r v i c e Research and Development Company, P.O. Box 3908, Tulsa, OK 74102 Introduction Lummus C i t i e s - F i n i n g (LC-Fining) w a s developed by C i t i e s S e r v i c e over t h e p a s t twenty y e a r s and i s l i c e n s e d by t h e CE Lumus Company. The technology h a s been s u c c e s s f u l l y a p p l i e d t o t h e upgrading of low q u a l i t y petroleum crudes and r e f i n e r y r e s i d u e s . LC-Fining is c u r r e n t l y being a p p l i e d t o t h e upgrading of c o a l e x t r a c t s . The c o s t o f c o m e r c i a l c o b a l t molybdenum and n i c k e l molybdenum c a t a l y s t s h a s e s c a l a t e d by a f a c t o r of f o u r o v e r t h e l a s t f i v e y e a r s . This h a s produced a s t r o n g economic i n c e n t i v e t o r e g e n e r a t e used LC-Fining c a t a l y s t s . The Auburn U n i v e r s i t y r e s e a r c h program w a s undertaken t o o b t a i n d e t a i l e d information on t h e e f f e c t o f v a r i o u s s o l v e n t and SRC t y p e s on t h e d e a c t i v a t i o n of a c o m e r c i a l S h e l l 324 n i c k e l molybdenum c a t a l y s t , t o understand t h e mechanism o f c a t a l y s t d e a c t i v a t i o n i n c a t a l y t i c upgrading of c o a l e x t r a c t s and t o develop e f f e c t i v e r e g e n e r a t i o n methods. Experiment a 1 M a t e r i a l s . The s o l v e n t s used i n t h i s s t u d y were Koppers heavy r e s i d u e c r e o s o t e o i l , hydrogenated t o 7.0%, 7.5% and 8.0% hydrogen and l a b e l e d f o r t h i s study a s " s o l v e n t D , " "solvent C , " and "solvent AB," r e s p e c t i v e l y . The s o l v e n t r e f i n e d c o a l s (SRC) used i n t h i s s t u d y were from (1) Pyro Kentucky f 9 c o a l processed a t t h e W i l s o n v i l l e SRC P i l o t P l a n t u s i n g Kerr McGee c r i t i c a l s o l v e n t deashing a s t h e s o l i d s s e p a r a t i o n method and l a b e l e d a s SRC I-A ( W i l s o n v i l l e Run 161 and 1 6 3 ) ; ( 2 ) Kentucky #9 c o a l processed a t t h e F o r t Lewis, Washington SRC P i l o t P l a n t and l a b e l e d a s SRC I-B; and ( 3 ) F i e s c o a l processed a t t h e W i l s o n v i l l e SRC P i l o t P l a n t a l s o u s i n g Kerr McGee deashing and d e s i g n a t e d a s F i e s SRC (Wilsonville Run 2 0 9 ) . The c a t a l y s t used was S h e l l 324 nickel-molybdenum, 1 / 3 2 inch e x t r u d a t e . The c a t a l y s t w a s p r e s u l f i d e d according t o t h e m a n u f a c t u r e r ' s suggested procedure b e f o r e use. Spent c a t a l y s t s were obtained from t h e CE Lumms LC-Fining PDU ( P r o c e s s Development Unit) o p e r a t i o n i n New Brunswick, N e w J e r s e y . Spent c a t a l y s t A was obtained a f t e r p r o c e s s i n g a 7 0 / 3 0 volume blend o f SRC I-A/solvent AB f o r 28 days, and s p e n t c a t a l y s t B was obtained after p r o c e s s i n g a 50/50 volume blend of SRC I-B/solvent AB f o r 24 days. Elemental a n a l y s e s o f t h e s o l v e n t s and SRC's a r e given i n Table I . Naphthalene ( F i s h e r , s c i n t a n a l y z e d ) and hexadecane ( P f a l t z and Bauer) were used i n t h e model compound hydrogenation r e a c t i o n s . Equipment and Analysis. Batch c a t a l y s t d e a c t i v a t i o n experiments and naphthalene hydrogenation r e a c t i o n s were performed i n tubing bomb r e a c t o r s of volumes o f 46 cc and 17.5 c c , r e s p e c t i v e l y . The tubing bomb w a s immersed i n a f l u i d i z e d sand b a t h Hydmepn Wac rhareerl t n t h e 2'C and was n e i t n t d nt 860 PPM maintained a t 430' t u b i n g bomb through a Nupro f i n e metering v a l v e . Products from t h e naphthalene hydrogenation r e a c t i o n s were analyzed by gas chromatography u s i n g a Varian Model 3700 equipped with a SP2250 column ( 2 . 4 m x 0 . 3 m O.D.), FID d e t e c t i o n and temperature p r o g r a m i n g from 60" t o 165°C a t 5"Clmin. Surface area measurements o f t h e c a t a l y s t s were obtained by n i t r o g e n a d s o r p t i o n . C a t a l y s t 164
p e l l e t s were r e g e n e r a t e d by low, medium and high t e m p e r a t u r e a s h i n g . A f o u r chamber L.F.E. Model 504 low temperature a s h e r (LTA) o p e r a t e d a t 0 . 5 mm Hg oxygen and 250 w a t t s was used f o r t h e LTA experiments. Reaction Procedures. The b a t c h c a t a l y s t d e a c t i v a t i o n s t u d y was performed i n a 46cc t u b i n g bomb a t 430'C and 1250 p s i g i n i t i a l hydrogen p r e s s u r e charged a t 25'C. A 70/30 SRC/solvent c h a r g e (weight b a s i s ) was used w i t h an i n i t i a l f r e s h c a t a l y s t weight of 1.25 g. Four d e a c t i v a t i o n c y c l e s were performed; each c y c l e was followed by a s e p a r a t e hydrogenation r e a c t i o n on a c a t a l y s t a l i q u o t u s i n g a 10 w t . % naphthal e n e i n hexadecane s o l u t i o n r e a c t e d i n a 17.5 cc t u b i n g bomb a t t h e r e a c t i o n c o n d i t i o n s of 410°C and 1250 p s i g . R e s u l t s and D i s c u s s i o n C a t a l y s t D e a c t i v a t i o n . D e a c t i v a t i o n of S h e l l 324 Ni/Mo c a t a l y s t used i n t h e upgradi n g of SRC was examined i n f o u r c y c l e b a t c h d e a c t i v a t i o n experiments u s i n g v a r i o u s SRC/solvent feed b l e n d s . The loss of c a t a l y s t hydrogenation a c t i v i t y a f t e r t h e SRC r e a c t i o n was measured by t h e degree of n a p h t h a l e n e hydrogenation a f t e r each c y c l e . A s shown i n Table 2 , t h e c a t a l y s t showed d e a c t i v a t i o n i n each SRC/solvent system a s measured by a d e c r e a s e i n naphthalene conversion. A comparison of t h e a c t i v i t y l e v e l of t h e f r e s h p r e s u l f i d e d Ni/Mo c a t a l y s t i s a l s o given. Of t h e v a r i o u s combinations of SRC and s o l v e n t employed, t h e SRC I-A/solvent C and SRC I - B / s o l v e n t C systems appear t o have t h e l e a s t c a t a l y s t d e a c t i v a t i o n a f t e r f o u r r e a c t i o n c y c l e s .
When s o l v e n t and c a t a l y s t w i t h no SRC p r e s e n t a r e r e a c t e d i n a s i m i l a r s e t of e x p e r i ments, e s s e n t i a l l y no c a t a l y s t d e a c t i v a t i o n was observed a s measured by changes i n naphthalene c o n v e r s i o n . However, comparisons of t h e e n t i r e product d i s t r i b u t i o n s between t h e f r e s h p r e s u l f i d e d c a t a l y s t and t h e s o l v e n t t r e a t e d c a t a l y s t s showed a d e f i n i t e d i f f e r e n c e a s i l l u s t r a t e d i n Table 3. Less d e c a l i n f o r m a t i o n and more t e t r a l i n formation of t h e s o l v e n t t r e a t e d c a t a l y s t r e p r e s e n t s a d e c r e a s e i n t h e hydrogenation a c t i v i t y of t h e c a t a l y s t a f t e r c o n t a c t w i t h t h e s o l v e n t . T a i l o r i n g o f t h e s o l v e n t and SRClsolvent combination f o r maximal SRC upgrading and minimal c a t a l y s t d e a c t i v a t i o n may be a n important f a c t o r i n c a t a l y t i c upgrading according t o p r e l i m i n a r y evidence. T h i s c e r t a i n l y w a r r a n t s f u r t h e r i n v e s t i g a t i o n . A comparison of t h e f i v e d i f f e r e n t SRC/solvent combinations u s i n g c a t a l y s t prepared i n t h e same b a t c h i n d i c a t e s t h a t s o l v e n t AB i n c o n c e r t w i t h t h e S R C ' s used may have a more pronounced d e a c t i v a t i n g e f f e c t than t h a t of s o l v e n t C. The d e a c t i v a t i o n behavior p l o t t e d i n terms of t h e n a p h t h a l e n e conversion a f t e r each c y c l e i s given i n F i g u r e 1. S i n c e coking o c c u r s a t high carbon l o a d i n g s , e l e v a t e d r e a c t i o n t e m p e r a t u r e s and c o n d i t i o n s o f hydrogen s t a r v a t i o n , experiments w e r e performed t o i n v e s t i g a t e t h e e f f e c t of each of t h e s e parameters on c a t a l y s t d e a c t i v a t i o n a t t h e SRC/solvent r e a c t i o n temperature. D e a c t i v a t i o n d a t a h a s been o b t a i n e d w i t h a r a n g e of SRC l o a d i n g s i n two c y c l e hydroprocessing r e a c t i o n s . The e f f e c t of i n c r e a s e d SRC loadi n g on c a t a l y s t a c t i v i t y i s evident a f t e r one c y c l e and becomes more pronounced a f t e r two. C a t a l y s t a c t i v i t y d e f i n i t e l y d e c r e a s e s w i t h i n c r e a s e d SRC l o a d i n g s ( F i g u r e 2 ) . Experiments were a l s o performed a t c o n s t a n t SRC l o a d i n g a t e l e v a t e d temperatures and a t c o n d i t i o n s i n v o l v i n g b o t h e x c e s s and l i m i t e d hydrogen. Experiments u s i n g SRC I - A and SRC I-B with s o l v e n t AB and f r e s h p r e s u l f i d e d c a t a l y s t s show high l e v e l s of a c t i v i t y a t 430'C a f t e r one c y c l e which r a p i d l y dropped o f f t o e s s e n t i a l l y no a c t i v i t y a t 5OO0C ( T a b l e 4 ) . Hydroprocessing r e a c t i o n s were performed The c a t a l y s t s used were b o t h t h e u s i n g 1250 p s i g hydrogen and no hydrogen a t 500'C. spent c a t a l y s t s from t h e LC-Fining PDU o p e r a t i o n and f r e s h p r e s u l f i d e d c a t a l y s t . A 45% i n c r e a s e was observed i n t h e hydrogenation a c t i v i t y l e v e l of t h e f r e s h s u l f i d e d c a t a l y s t w i t h hydrogen p r e s e n t a s opposed t o no hydrogen b e i n g p r e s e n t . No d i f f e r ence i n c a t a l y s t a c t i v i t y was observed f o r t h e spent c a t a l y s t r e g a r d l e s s of hydrogen
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presence, A more s u b s t a n t i a l e f f e c t of t h e hydrogen presence would most l i k e l y be observable a t lower p r o c e s s i n g temperatures. Deactivation Mechanism. Regeneration of spent c a t a l y s t s from t h e LC-Fining PDU o p e r a t i o n was attempted u s i n g c o n t r o l l e d o x i d a t i o n a t t h r e e temperature l e v e l s : low, 'U5OoC i n a n e x c i t e d oxygen atmosphere; medium,370°C with a n a i r atmosphere; and h i g h , 95OoC a l s o w i t h a i r atmosphere. A histogram o f t h e r e g e n e r a t i o n l e v e l s achieved a f t e r o x i d a t i o n or g r i n d i n g a r e shown i n Figure 3. The hydrogenation a c t i v i t y of b o t h s p e n t c a t a l y s t A and B i s low b e f o r e o x i d a t i v e t r e a t m e n t , w i t h c a t a l y s t A showing Spent c a t a l y s t B can be g r e a t e r d e a c t i v a t i o n (PDU r u n a t 70/30 SRC/solvent r a t i o ) . e s s e n t i a l l y regenerated t o i t s o r i g i n a l a c t i v i t y l e v e l a s based on naphthalene conversion by a combination of medium temperature a s h i n g followed by p r e s u l f i d i n g . P r e s u l f i d i n g a l o n e p r o v i d e s s i g n i f i c a n t r e g e n e r a t i o n f o r s p e n t c a t a l y s t B and a d e f i n i t e i n c r e a s e i n a c t i v i t y of s p e n t c a t a l y s t A. P r e s u l f i d i n g of t h e spent c a t a l y s t p e l l e t s apparently increased t h e c a t a l y s t a c t i v i t y b y activating o r s u l f i d i n g s i t e s which had l o s t t h e i r a c t i v i t y d u r i n g t h e c o a l e x t r a c t upgrading r e a c t i o n and removal of hydrocarbon d e p o s i t s . Grinding t h e s p e n t c a t a l y s t p e l l e t s t o -200 mesh provides increased a c t i v i t y f o r b o t h spent c a t a l y s t s p o s s i b l y by exposing f r e s h a c t i v e s i t e s . Both high temperature and low t e m p e r a t u r e a s h i n g show s l i g h t i n c r e a s e s i n t h e a c t i v i t y of spent c a t a l y s t B , b u t none f o r s p e n t c a t a l y s t A. The r a t e o f carbonaceous m a t e r i a l removal from t h e s p e n t c a t a l y s t s d u r i n g medium temperature o x i d a t i o n i s shown i n F i g u r e 4 . A f t e r f o r t y h o u r s of o x i d a t i o n , spent c a t a l y s t B p e l l e t s and p e l l e t s of b o t h s p e n t c a t a l y s t A and B ground t o -200 mesh reached constant weight. However, n i n e t y hours a r e r e q u i r e d f o r spent c a t a l y s t A t o r e a c h c o n s t a n t weight. These r e s u l t s i n d i c a t e t h a t s p e n t c a t a l y s t A o b t a i n e d from a h i g h e r SRC loading i n PDU feed may have more carbonaceous m a t e r i a l blocking t h e p o r e s . The carbonaceous m a t e r i a l may a l s o b e more r e f r a c t o r y . Surface a r e a a n a l y s e s were performed u s i n g b o t h s p e n t c a t a l y s t s A and B and c a t a l y s t s A and B regenerated by medium t e m p e r a t u r e o x i d a t i o n followed by s u l f i d i n g . The s u r f a c e a r e a s b e f o r e and a f t e r t r e a t m e n t and t h e naphthalene conversions o b t a i n e d a r e given i n T a b l e 5 . A d i r e c t c o r r e l a t i o n between s u r f a c e area and hydrogenation a c t i v i t y of t h e c a t a l y s t is observed and is shown i n F i g u r e 5 . Spent c a t a l y s t s o b t a i n e d a f t e r f o u r b a t c h r e a c t i o n c y c l e s o f SRC I-B/solvent AB and F i e s SRC/Solvent D were r e g e n e r a t e d i n t h e same manner as t h e spent c a t a l y s t s o b t a i n e d from t h e PDU o p e r a t i o n . By medium temperature a s h i n g followed by p r e s u l f i d i n g , t h e batch deactivated c a t a l y s t s a r e regenerated t o e s s e n t i a l l y t h e i r o r i g i n a l a c t i v i t y l e v e l . Medium temperature o x i d a t i o n a l o n e of t h e b a t c h d e a c t i v a t e d c a t a l y s t s g i v e s p a r t i a l b u t n o t complete c a t a l y s t r e g e n e r a t i o n .
To determine t h e e f f e c t of m e t a l s d e p o s i t i o n on c a t a l y s t d e a c t i v a t i o n , a s h obtained from Kentucky 19 c o a l w a s added t o s o l v e n t C and b a t c h d e a c t i v a t i o n experiments were performed. The degree of c a t a l y s t d e a c t i v a t i o n a t v a r y i n g a s h c o n c e n t r a t i o n s is shown i n F i g u r e 6. Summary. Batch experiments a s w e l l as r e s u l t s from LC-Fining c a t a l y t i c upgrading of c o a l e x t r a c t s i n d i c a t e d e a c t i v a t i o n of t h e S h e l l 324 Ni/Mo c a t a l y s t i n t h e presence of SRC. A t increased l e v e l s o f SRC l o a d i n g , d e a c t i v a t i o n i n c r e a s e s . The c h i e f cause of c a t a l y s t d e a c t i v a t i o n appears t o b e coking. The S h e l l 324 c a t a l y s t can b e subs t a n t i a l l y regenerated a f t e r t h e upgrading r e a c t i o n by medium temperature a s h i n g followed b y p r e s u l f i d i n p . Acknowledgement Auburn University g r a t e f u l l y acknowledges t h e support of C i t i e s S e r v i c e Research and Development Company f o r t h i s work.
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I
Table 1 A n a l y s i s of S o l v e n t s and SRC
Solvent A/B Elemental c o n t e n t , w t % Carbon Hydrogen Oxygen Nitrogen Sulfur Ash, w t % D i s t i l l a t i o n , OF 276.8 336.2 395.6 435.2 464.0 500.0 582.8 647.6 674.6 746.6 820.4
Solvent C
Solvent D
91.28 7.03 0.88 0.69 0.27
91.6 7.5 C0.5 0.36 0.19
91.48 8.01
