Chapter 10
Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on September 2, 2015 | http://pubs.acs.org Publication Date: September 12, 1988 | doi: 10.1021/bk-1988-0375.ch010
Cracking Metal-Contaminated Oils with Catalysts Containing Metal Scavengers Effects of Sepiolite Addition on Vanadium Passivation Mario L. Occelli Unocal Science & Technology Division, Unocal Corporation, P.O. Box 76, Brea, CA 92621
The addition o f layered magnesium silicate p a r t i c l e s such as sepiolite to a high activity commercial fluid cracking c a t a l y s t (FCC), generates dual-functional cracking c a t a l y s t (DFCC) mixtures t h a t , even when metal contaminated with as much as 1.5 wt% vanadium, are capable o f r e t a i n i n g useful cracking a c t i v i t y (70% conversion) when cracking a light gas oil (with an API gravity o f 29.6) a t m i c r o a c t i v i t y t e s t (MAT) conditions. Improved coke and hydrogen selectivity were also observed. Transport experiments have been used to show that the DFCC enhanced vanadium resistance can be a t t r i b u t e d to the gas phase transport o f this metal from the host c a t a l y s t to the diluent (sepiolite) where it is sorbed and passivated. R e c e n t l y , i t has been reported i n t h e patent l i t e r a t u r e t h a t vanadium (and n i c k e l ) r e s i s t a n c e i n a FCC can be s i g n i f i c a n t l y enhanced by t h e a d d i t i o n o f c e r t a i n d i l u e n t s capable o f a c t i n g as metal scavengers ( 1 - 4 ) . In f a c t , a d d i t i o n o f alumina and a l u m i n a - c o n t a i n i n g m a t e r i a l s w i t h (1_) o r w i t h o u t [2) p a s s i v a t i n g agents (such as Sn o r Sb) o r a d d i t i o n o f n a t u r a l l a y e r e d magnesium s i l i c a t e s (20 as w e l l as a d d i t i o n o f c e r t a i n n a t u r a l z e o l i t e s ( 4 ) can i n h i b i t t h e d e l e t e r i o u s e f f e c t s t h a t metal contaminants ( l i k e "rTi and V) i n gas o i l s have on t h e c r a c k i n g a c t i v i t y and s e l e c t i v i t y o f commercial f l u i d c r a c k i n g c a t a l y s t s (FCC). The a d d i t i o n o f metakaolin microspheres t o improve a commercial c a t a l y s t r e s i s t a n c e to metals p o i s o n i n g has been proposed by B a r t h o l i c (J5). I t i s t h e purpose o f t h i s paper t o r e p o r t and e x p l a i n t h e high r e s i s t a n c e t o metals d e a c t i v a t i o n o f a d u a l - f u n c t i o n c r a c k i n g c a t a l y s t (DFCC) obtained by d i l u t i n g a high a c t i v i t y c r a c k i n g c a t a l y s t (Davison 6RZ-1) w i t h s e p i o l i t e granules 100 χ 325 mesh i n size. S e p i o l i t e (and a t t a p u l g i t e ) a r e f i b r o u s c l a y m i n e r a l s composed o f t e t r a h e d r a l chains o f s i l i c a l a y i n g i n planes j o i n e d together (through shared oxygens) by magnesium (and aluminum) atoms i n octahedral c o o r d i n a t i o n . T h e i r s t r u c t u r e has been d e s c r i b e d i n d e t a i l s by Grim (6). These l a y e r e d magnesium s i l i c a t e s c o u l d °
0097-6156/88/0375-0162$06.00/0 1988 American Chemical Society
In Fluid Catalytic Cracking; Occelli, M.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.
10.
OCCELLI
Catalysts with Metal Scavengers
163
p a s s i v a t e n i c k e l contaminants by forming s t a b l e s i l i c a t e s (_7) s i m i l a r to g a r n i e r i t e . ( G a r n i e r i t e i s a hydrous nickel-magnesium s i l i c a t e s i m i l a r to c h r y s o t i l e w i t h n i c k e l i n octahedral s i t e s . ) Vanadium p a s s i v a t i o n could r e s u l t from the formation of heat s t a b l e vanadates (7_).
Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on September 2, 2015 | http://pubs.acs.org Publication Date: September 12, 1988 | doi: 10.1021/bk-1988-0375.ch010
Experimental M a t e r i a l s and Gas O i l C r a c k i n g . The reference c a t a l y s t used (Davison's GRZ-1 ) i s a h i g h - a c t i v i t y c r a c k i n g c a t a l y s t c o n t a i n i n g about 35% c a l c i n e d r a r e - e a r t h exchanged z e o l i t e Y (CREY). The 100 χ 325 mesh granules of "Spanish S e p i o l i t e " (from TQLSA, S.A.) used t o study metals t r a n s p o r t a t hydrothermal c o n d i t i o n s , have been found to c o n t a i n a c l a y mineral c h a r a c t e r i z e d by a t y p i c a l f i b r o u s s t r u c t u r e , high s u r f a c e area (142 m / g ) , and pore volume (0.68 c c / g ) ; i t s chemical composition i s shown i n Figure 1. This mineral was e s s e n t i a l l y f r e e from phase i m p u r i t i e s and gave an x-ray p a t t e r n i n e x c e l l e n t agreement w i t h JCPDS ( J o i n t Committee on Powder D i f f r a c t i o n Standards) p a t t e r n No. 13-595, see F i g u r e 1. A f t e r steaming (760°C/5h) t h i s c l a y r e t a i n e d 70% of i t s o r i g i n a l BET s u r f a c e area and i t s pore volume remained e s s e n t i a l l y unchanged a t ^0.68 cc/g. C a t a l y t i c e v a l u a t i o n was performed using a m i c r o a c t i v i t y t e s t (MAT) s i m i l a r to the one d e s c r i b e d by C i a p e t t a and Anderson ( 8 ) . The weight h o u r l y space v e l o c i t y (WHSV) was 14-15; the r e a c t o r temperature was 510°C. A c a t a l y s t - t o - o i l r a t i o of 3.5-3.8 was used. The chargestock's s l u r r y o i l (S.O., b.p. >354°C), l i g h t c y c l e gas o i l (LCGO, 232°C < b.p.
