24 Hydrogenation Function of Fresh and Deactivated Hydrocracking Catalysts: Cyclohexene Hydrogenation
Downloaded by IOWA STATE UNIV on February 18, 2017 | http://pubs.acs.org Publication Date: September 16, 1982 | doi: 10.1021/bk-1982-0196.ch024
S. R. POOKOTE, J. S. DRANOFF, and J. B. BUTT Northwestern University, Department of Chemical Engineering and Ipatieff Laboratory, Evanston IL 60201
A systematic study o f the h i s t o r y o f t h e hydrogenation f u n c t i o n in a s e r i e s o f f r e s h and d e a c t i vated commercial hydrocracking c a t a l y s t s is reported u s i n g cyclohexene hydrogenation as a probe r e a c t i o n . The c a t a l y s t s were hydrocracking c a t a l y s t s , both f r e s h and d e a c t i v a t e d up t o p e r i o d s of two y e a r s . Hydrogenation a c t i v i t y is shown t o be r e l a t e d t o s u l f u r content, while ESR s t u d i e s i n d i c a t e a c o r r e l a t i o n between activity and MO in the c a t a l y s t . A p o s s i b l e mechanism o f d e a c t i v a t i o n is change in the o x i d a t i o n s t a t e o f Mo as induced by s u l f u r deposition. 5+
Hydrocracking c a t a l y s t s a r e b i f u n c t i o n a l i n nature and can be d e a c t i v a t e d by v a r i o u s mechanisms i n c l u d i n g poisoning of t h e a c i d i c f u n c t i o n by bases, formation o f i n a c t i v e s u l f i d e phases, and coke d e p o s i t i o n ( 1 ) . Some general aspects of d e a c t i v a t i o n i n hydrocracking have r e c e n t l y been d i s c u s s e d ( 2 ) . A p a r t i c u l a r problem, addressed here, i s that p r o p e r l y c o n t r o l l e d coke burning for r e g e n e r a t i o n appears t o r e t u r n f u l l a c t i v i t y f o r the a c i d i c f u n c t i o n , however f u l l hydrogénation a c t i v i t y i s not recovered. In t h i s study a s e r i e s o f f r e s h , d e a c t i v a t e d and regenerated hydrocracking c a t a l y s t s were i n v e s t i g a t e d as to hydrogénation a c t i v i t y u s i n g cyclohexene hydrogénation as a probe r e a c t i o n . The d e a c t i v a t e d m a t e r i a l s were obtained from both p i l o t and commercial u n i t s operated f o r p e r i o d s up t o two years. S p e c i f i c s of t h e hydrogénation f u n c t i o n were i n v e s t i g a t e d experimentally a f t e r p r e poisoning a c i d i c a c t i v i t y by NH^ chemisorption. Experimental C a t a l y s t s . The commercial c a t a l y s t s samples, a l l o f s i m i l a r composition, were s u p p l i e d by AMOCO O i l . These c o n t a i n MoO^ and CoO as hydrogénation components. The c r a c k i n g component i s a
0097-6156/82/0196-0283$06.00/0 © 1982 American Chemical Society Wei and Georgakis; Chemical Reaction Engineering—Boston ACS Symposium Series; American Chemical Society: Washington, DC, 1982.
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CHEMICAL REACTION ENGINEERING
c r y s t a l l i n e a l u m i n o s i l i c a t e i n an amorphous Si02/Al2Û3 m a t r i x . Table I g i v e s a d e s c r i p t i o n of m a t e r i a l s i n v e s t i g a t e d . Both p r e s u l f i d e d and n o n p r e s u l f i d e d c a t a l y s t s were i n v e s t i g a t e d ; most r e s u l t s presented-here p e r t a i n to p r e s u l f i d e d samples. The standard pretreatment c o n d i t i o n s were N ,lh,25°C; No-H2S,365 ; N2,lh,25°; N H 3 p u l s e to saturation,25°; N 2 purge,25 . The time employed i n the N2^S step was such t h a t the weight r a t i o of c a t a l y s t to H S was u n i t y . 0
2
2
Reaction. A c o n v e n t i o n a l f l o w r e a c t o r system was used to measure cyclohexene hydrogénation k i n e t i c s a t 150
