CATALYTIC CRACKING OF A GAS OIL DERIVED FROM EASTERN ...

C a t a l y t i c C r a c k i n g o f a Gas O i l "I
Derived from Eastern Canadian O i l Shale

S. H. Ng

S y n t h e t i c F u e l s Research L a b o r a t o r y , CANMET
Energy, Mines and Resources Canada
Ottawa, O n t a r i o , Canada K 1 A OG1

Introduction

Large o i l s h a l e d e p o s i t s have been d i s c o v e r e d i n C e n t r a l and E a s t e r n
Canada.l I n t h e p a s t few years, c o n s i d e r a b l e r e s e a r c h was conducted on E a s t e r n
o i l shales.2-5 Primary l i q u i d products from r e t o r t i n g o f o i l shales are superior
t o Canadian heavy o i l and t a r sand b i t ~ m e n . ~I n a c o n t i n u i n g e f f o r t t o e v a l u a t e
t h e p r o c e s s a b i l i t y o f t h e shale o i l produced, a c a t a l y t i c c r a c k i n g study on i t s
gas o i l f r a c t i o n was r e c e n t l y undertaken a t CANMET. T h i s paper r e p o r t s t h e
primary results.

Experimental Section

The raw s h a l e o i l was produced b y r e t o r t i n g a New Brunswick o i l shale
f r o m A l b e r t Mines n e a r Moncton, New Brunswick. The r e t o r t system i n t h e p i l o t
p l a n t has been r e p o r t e d p r e v i o ~ s l y . ~The s h a l e o i l was d i s t i l l e d under vacuum t o
g i v e t h e gas o i l f r a c t i o n which c o n s t i t u t e d 80 w t % o f t h e feed. For comparison,
a c o n v e n t i o n a l gas o i l was o b t a i n e d f r o m a r e f i n e r y which processes t h e A l b e r t a
crudes t r a n s p o r t e d t o E a s t e r n Canada t h r o u g h t h e I n t e r p r o v i n c i a l P i p e L i n e
(IPPL). The two gas o i l s were analyzed u s i n g ASTM o r o t h e r accepted methods.
The r e s u l t s a r e shown i n Tables I and 11.

Three e q u i l i b r i u m c a t a l y s t s OA-440, Nova 0 and GX-30 o b t a i n e d f r o m
Davison o f Id. R. Grace were used i n t h i s study. P r i o r t o t h e i r c h a r a c t e r i z a t i o n
and t e s t i n g , t h e c a t a l y s t s were decoked a t 590 'C f o r 3 h. S u r f a c e
c h a r a c t e r i s t i c s were determined by b o t h N Z a d s o r p t i o n - d e s o r p t i o n technique and by
mercury porosimetry. Z e o l i t e s u r f a c e areas and z e o l i t e c o n t e n t s were estimated
based on a method r e p o r t e d i n t h e l i t e r a t u r e . 6 T h e i r p h y s i c a l and chemical
p r o p e r t i e s a r e g i v e n i n Table 111.

C a t a l y t i c c r a c k i n g o f t h e gas o i l s was performed i n a m i c r o a c t i v i t y
t e s t (MAT) u n i t w h i c h was m o d i f i e d from t h e ASTM 03907 v e r s i o n . It c o n s i s t s o f a
f i x e d bed q u a r t z r e a c t o r packed w i t h 4.2 g o f c a t a l y s t heated a t 470-530 'C i n a
t h r e e - z o n e f u r n a c e . Feeds were d e l i v e r e d u s i n g a s y r i n g e pump w i t h c a t a l y s t l o i l
r a t i o varying from 2-6 while keeping the hourly weight space v e l o c i t y (WHSV)
c o n s t a n t a t 20 h-1. A f l o w o f n i t r o g e n purge gas a t 20 mL/min was m a i n t a i n e d
throughout t h e 20-min t e s t period. L i q u i d products were c o l l e c t e d i n a glass
receiver cooled i n an ice-water bath whereas the gaseous products were trapped
using water displacement. A f t e r the t e s t , both products were q u a n t i t a t i v e l y
measured b e f o r e a n a l y s i s . The amount o f coke formed on t h e spent c a t a l y s t was
a l s o d e t e r m i n e d . Conversion was c a l c u l a t e d based on t h e f r a c t i o n o f l i q u i d
product having a b o i l i n g p o i n t above 216 'C.

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O e n i t r o g e n a t i o n o f t h e s h a l e vacuum gas o i l (VGO) was done b y b o t h
e x t r a c t i o n i n which d i m e t h y l s u l f o x i d e (DMSO) c o n t a i n i n g 6 w t % ZN s u l p h u r i c a c i d
was used as s o l v e n t , and a d s o r p t i o n i n which an A t t a p u l g u s c l a y was used as
adsorbent.

R e s u l t s and Discussion

Table I shows t h a t t h e q u a l i t y o f t h e s h a l e VGO i s b e t t e r t h a n o r
e q u i v a l e n t t o t h a t o f t h e IPPL gas o i l except i t s n i t r o g e n c o n t e n t s a r e much
I h i g h e r . The b a s i c n i t r o g e n i s u n d e s i r a b l e i n FCC f e e d s t o c k s as i t can n e u t r a l i z e
the acid sites of the cracking catalysts resulting i n a rapid loss of
a c t i v i t y . 7 - 9 The h i g h n i t r o g e n l e v e l i s a l s o r e f l e c t e d b y t h e p o l a r s i n t h e
hydrocarbon t y p e a n a l y s i s ( T a b l e 11). P o l a r s i n t h e s h a l e o i l may a l s o i n c l u d e
oxygen compounds. I f these p o l a r s a r e c o n s i d e r e d c r a c k a b l e , t h e c o n v e r s i o n
c o n s t r a i n t s based on t h e c o m p o s i t i o n a l a n a l y s i s can be e s t i m a t e d a t 80.6 and 81.1
w t % f o r IPPL and shale VGO r e s p e c t i v e l y , assuming t h a t t h e d i a r o m a t i c s and t h e
more h i g h l y condensed s t r u c t u r e s i n c l u d i n g aromatic sulphurs cannot be converted
t o l i g h t products w i t h b o i l i n g p o i n t s l e s s t h a n 216 'C due t o t h e s t a b i l i t y o f
t h e benzene r i n g s .

F i g u r e 1 shows t h e e f f e c t s o f temperature and c a t a l y s t l o i l r a t i o (C/O)
on conversion. S i g n i f i c a n t d i f f e r e n c e s can be seen between t h e two feedstocks.
For IPPL gas o i l , t h e conversion tends t o l e v e l o f f and approaches i t s l i m i t a t
h i g h s e v e r i t y . Furthermore, i t i s l e s s s e n s i t i v e t o t h e temperature change. On
t h e o t h e r hand, f o r s h a l e VGO, t h e c o n v e r s i o n i n c r e a s e s s h a r p l y and l i n e a r l y w i t h
C/O r a t i o and i s f a r below i t s expected l i m i t even a t much h i g h e r s e v e r i t y . The
conversion i s obviously very temperature-dependent. This suggests t h a t the
catalysts were seriously poisoned during cracking by t h e basic n i t r o g e n o f shale
VGO as t h i s t y p e o f p o i s o n i n g i s m a i n l y a s u r f a c e a d s o r p t i o n phenomenon and h i g h
temperature tends t o promote d e s o r p t i o n . Between t h e two c a t a l y s t s , Nova D i s
apparently more a c t i v e i n c r a c k i n g IPPL conventional gas o i l due t o i t s h i g h e r
zeolite content. This agrees w i t h Oavison's m i c r o a c t i v i t y results (Table 111).
However, t h i s t r e n d i s r e v e r s e d f o r s h a l e VGO, w i t h OA-440 b e i n g more a c t i v e .
This suggests t h a t t h e shale o i l c o n t a i n s l a r g e r molecules which do n o t have
access t o the small pores o f t h e z e o l i t e b u t can be cracked by t h e m a t r i x o f
DA-440 which has a l a r g e r pore d i a m e t e r ( T a b l e 111). A s i m i l a r phenomenon was
also observed i n a separate cracking study which deals w i t h other nonconventional
gas o i l s i n c l u d i n g those d e r i v e d from r e s i d s , t a r sand bitumens and heavy o i l s . l 0

For IPPL gas o i l , favourable and optimum gasoline y i e l d (54 w t % ) i s
o b t a i n e d a t about 73% c o n v e r s i o n beyond which o v e r c r a c k i n g seems t o t a k e p l a c e .
The g a s o l i n e y i e l d decreases s l i g h t l y w i t h i n c r e a s e d temperature a t c o n s t a n t
conversion. Between t h e two c a t a l y s t s , OA-440 i s s l i g h t l y more s e l e c t i v e f o r
g a s o l i n e p r o d u c t i o n . T h i s does n o t n e c e s s a r i l y mean t h a t i t produces a b e t t e r
g a s o l i n e , i n terms o f h i g h e r octane number, as OA-440 i s n o t an octane-enhancing
c a t a l y s t b u t Nova D i s . I t i s known t h a t t h e dealuminated u l t r a - s t a b l e Y z e o l i t e
c a t a l y s t s USY) y i e l d h i g h e r octane g a s o l i n e b y p r o d u c i n g more o l e f i n i c
compounds,jl compared w i t h t h e r a r e e a r t h exchanged Y z e o l i t e c a t a l y s t s (REY).
For s h a l e VGO, t h e g a s o l i n e y i e l d i n c r e a s e s l i n e a r l y and monotonously w i t h
c o n v e r s i o n w i t h o u t obvious e f f e c t s o f t e m p e r a t u r e and c a t a l y s t . The e x p e r i m e n t a l
maximum g a s o l i n e y i e l d i s l e s s t h a n 30 w t % w h i c h i s unacceptably low.

The coke y i e l d s o f t h e two gas o i l s i n c r e a s e e x p o n e n t i a l l y (IPPL) o r
linearly (shale o i l ) with conversion. A t constant conversion, higher temperature

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f o r t h e same c a t a l y s t tends t o l o w e r t h e coke y i e l d because C / O r a t i o can be
reduced t o achieve t h e same conversion. C o n t r a r y t o t h e l i t e r a t u r e , l l Nova D

( U S Y ) y i e l d s more coke t h a n i t s c o u n t e r p a r t DA-440 ( R E Y ) i n c r a c k i n g s h a l e VGO

whereas f o r IPPL gas o i l , Nova D shows s l i g h t l y b e t t e r o r e q u i v a l e n t coke
s e l e c t i v i t y t h a n DA-440. A s i m i l a r phenomenon was a l s o observed i n a s e p a r a t e
cracking study involving other nonconventional feedstocks.10 It i s thus believed
t h a t the superiority o f USY catalysts over REY catalysts w i t h respect t o coke
s e l e c t i v i t y depends a l s o on t h e n a t u r e o f t h e feedstock.

I t has been observed t h a t a l i n e a r c o r r e l a t i o n e x i s t s between the
second-order c o n v e r s i o n (conversion/[lOO - c o n v e r s i o n ] ) and t h e coke y i e l d . The
l i n e a r r e l a t i o n s h i p i s expected based on t h e e q u a t i o n s proposed by W o l l a s t o n
e t a1.12 For IPPL gas o i l , t h e s t r a i g h t l i n e s a t d i f f e r e n t temperatures pass
through the o r i g i n i n d i c a t i n g that a l l the oke formed results from c a t a l y t i c
c r a c k i n g and i s t h e r e f o r e " c a t a l y t i c " coke.f3 However, f o r shale VGO, t h e
s t r a i g h t l i n e s i n t e r s e c t t h e x-axis a t d i f f e r e n t coke values. These values
o b t a i n e d a t 0% c o n v e r s i o n r e p r e s e n t n e i t h e r " c a t a l y t i c " coke n o r "contaminant"
coke s i n c e t h e n i c k e l and vanadium contents o f t h e c a t a l y s t s are r a t h e r l o w
(Table 111). This suggests t h a t they belong t o t h e " a d d i t i v e " coke r e s u l t i n g
from t h e b a s i c n i t r o g e n o€ t h e s h a l e gas o i l which c o n t a i n s l i t t l e Conradson

-carbon another p o s s i b l e p r e c u r s o r f o r t h e " a d d i t i v e " coke.13 The " a d d i t i v e "

coke found i s independent o f t h e c a t a l y s t t y p e and i s e s t i m a t e d a t 1.47, 1.25,

1.09 and 0.97 w t % a t 470 'C, 490 'C, 510 'C and 530 'C, r e s p e c t i v e l y .

Product d i s t r i b u t i o n f o r t h e two f e e d s t o c k s a t 50% c o n v e r s i o n i s shown
i n Table I V . It can be seen t h a t t h e s h a l e VGO produces more gases, l e s s
g a s o l i n e and much more coke compared w i t h IPPL gas o i l . The h i g h decant o i l
y i e l d (39 w t % ) f o r IPPL VGO may be m i s l e a d i n g as t h e m a j o r i t y o f i t s p r e c u r s o r
i s crackable a t h i g h e r s e v e r i t y . A t 73% conversion, t h i s value drops t o 8 w t %
r a i s i n g t h e g a s o l i n e y i e l d f r o m 35 t o 54 w t %.

Three methods have been used t o achieve h i g h e r conversion o f t h e shale
o i l . The f i r s t i s t o c r a c k with GX-30, a v e r y a c t i v e c a t a l y s t because o f i t s
higher z e o l i t e c o n t e n t . The o t h e r methods i n v o l v e upgrading o f gas o i l s by
removing some o f t h e n i t r o g e n compounds u s i n g e i t h e r DMSO/acid e x t r a c t i o n o r
A t t a p u l g u s c l a y a d s o r p t i o n . One disadvantage o f t h e r e j e c t i o n methods i s t h e
accompanying l o s s o f the hydrocarbon value. Table V shows t h e weight r e c o v e r y
and the n i t r o g e n contents o f t h e upgraded feedstocks. It i s evident t h a t t h e
c l a y method i s s u p e r i o r t o the e x t r a c t i o n technique s i n c e i t removes almost 50%
more b a s i c n i t r o g e n f o r t h e same recovery. T a b l e V I shows a comparison o f
c r a c k i n g y i e l d s o f raw and t r e a t e d f e e d s t o c k s cracked a t v a r i o u s c o n d i t i o n s w h i l e
keeping c a t a l y s t l o i l r a t i o constant at 6. For the untreated shale o i l , although
t h e use o f GX-30 r e s u l t s i n some improvement over DA-440 i n c o n v e r s i o n and
gasoline y i e l d , t h e coke y i e l d i s unacceptably high. E v i d e n t l y , DMSO r a f f i n a t e
shows b e t t e r performance t h a n t h e raw s h a l e o i l whereas t h e c l a y t r e a t e d s h a l e
o i l i s the best due t o i t s lowest basic n i t r o g e n content.

Let us consider two approaches i n f u r t h e r e v a l u a t i o n o f t h e data: one
involves cracking o f t h e raw shale o i l as a whole whereas t h e other involves the
separation o f the shale o i l i n t o two fractions p r i o r t o individual cracking under
t h e same c o n d i t i o n s . I n t h e l a t t e r case, t h e recovered f r a c t i o n c o n t a i n s l e s s
n i t r o g e n and i s t h e r e f o r e b e t t e r i n q u a l i t y whereas t h e r e j e c t e d f r a c t i o n i s
assumed, f o r s i m p l i c i t y , t o be u n c o n v e r t i b l e e i t h e r because o f i t s h i g h n i t r o g e n
l e v e l o r a r e f r a c t o r y n a t u r e . One can c a l c u l a t e t h e i r c r a c k i n g y i e l d s on a

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" t o t a l o i l " basis by m u l t i p l y i n g t h e y i e l d s , based on t h e recovered p o r t i o n , w i t h

t h e weight f r a c t i o n o f recovery. The r e s u l t s a r e i l l u s t r a t e d i n F i g . 2. Here,
t h e increases i n conversion and g a s o l i n e y i e l d s o f t h e t r e a t e d s h a l e o i l s over
those o f t h e u n t r e a t e d ones r e f l e c t t h e n e t poisoning e f f e c t on t h e c a t a l y s t b y
the basic nitrogen.

Based on t h e data obtained from n i t r o g e n r e j e c t i o n methods ( e x t r a c t i o n
I o r a d s o r p t i o n ) , l i n e a r c o r r e l a t i o n can be e s t a b l i s h e d between t h e c r a c k i n g

r e s u l t s , i n terms o f conversion and g a s o l i n e y i e l d , and t h e basic n i t r o g e n
c o n t e n t (1750-4600 ppm) o f MAT feeds. A c r a c k i n g s t u d y was a l s o made on t h e
blends prepared from IPPL and raw s h a l e o i l . The d a t a p o i n t s o b t a i n e d f r o m t h i s
d i l u t i o n method appear t o coincide w i t h those from r e j e c t i o n methods over the

same b a s i c n i t r o g e n range. T h i s suggests t h a t t h e r e j e c t e d p o r t i o n o f t h e raw
shale o i l would have been cracked i f t h e c a t a l y s t had not been poisoned by t h e
basic nitrogen i n the f i r s t place. Also, the basic nitrogen content o f the shale

o i l , r a t h e r than i t s compositional d i f f e r e n c e s from t h e IPPL gas o i l , i s t h e
determining factor f o r the cracking yields. Following the trends created by the
d i l u t i o n method, the shale o i l produces a cracking r e s u l t s i m i l a r t o t h a t o f IPPL

a t t h e same b a s i c n i t r o g e n l e v e l , i. e . , 72 vs 73.5 w t % i n c o n v e r s i o n and 51 v s
5 3 w t % i n g a s o l i n e yield..at 510 'C and a c a t a l y s t / o i l r a t i o o f 4.

Acknowledgement

The authors would l i k e t o thank Dr. T. de B r u i j n and Dr. J. K r i z o f
CANMET f o r many v a l u a b l e d i s c u s s i o n s and suggestions.

REFERENCES

(1) Duncan, D. C. O i l Shale (Eds. Yen, T. F.; C h i l i n g a r i a n , G. V.), 1 9 7 6 , p.19,
E l s e v i e r , New York.

( 2 ) Furimsky, E.; Synnott, J . ; Boorman, R. S.; S a l t e r , R. S. Fuel Process.

Technology, 1984, S, 293-306.

( 3 ) Boorman, R. S.; S a l i b , P. F.; G i l d e r s , R . ; Gemmell, D. E. Can. I n s t . Min.,
Proc. 3 r d Meeting, F r e d e r i c t o n , N. B. 1982.

( 4 ) Karman, D.; K r e s t a , S. PREPRINTS, D i v . o f P e t r o l . Chem., ACS, 1987, g ( l ) ,
94-96.

( 5 ) S a l i b , P. F.; Barua, S. K.; Furimsky, E. Can. J. Chem. Eng. 1986, g ( 6 ) .
1001-1007.

( 6 ) Johnson, M. F. J. C a t a l . 1978, 52, 425-431.

( 7 ) Fu, C. M.; S c h a f f e r , A. M. I n d . Eng. Chem. Prod. Res. Dev. 1985, E ( 1 ) . 68.

( 8 ) Scherzer, J.; McArthur, D. P. O i l Gas J. Oct. 27, 1986, pp 76.

( 9 ) Scherzer, J . ; McArthur, D. P. Ind. Eng. Chem. Res. 1988, ZJ(9), 1571-1576.

I ( 1 0 ) Ng, S. H. Unpublished r e s u l t s .

( 1 1 ) R i t t e r , R. E.; C r e i g h t o n , J . E.; C h i n , D. S.; R o b e r i e , T. G; Wear, C. C.
2,Catalagram, Davison, 1986,
5.

( 1 2 ) Wollaston, E. G.; H a f l i n , W. J . ; Ford, W. D; D'Souza, G. J. Hydrocarbon
Process. 1975, g ( 1 9 ) , 93.

( 1 3 ) Cimbalo, R. N.; F o s t e r , R . L.; Wachtel, S . J. O i l Gas J. 1972, s ( 2 0 ) , 112.

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T a b l e I. Feedstock I n s p e c t i o n Data

.....................................................................

P. .r.o.p.e.r.t.i e. .s. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .I.P.P.L. . . . . . . . . . . . . . . . .S.h.a.l.e. . .

"API 24.2 25.0
A n i l i n e p o i n t , 'C 93.7 80.0

Conradson carbon, w t % 0.43 0. i a
T o t a l n i t r o g e n , ppm 1150
7150

B a s i c n i t r o g e n , ppm 310 4570 'I
0.66 0.52
Total sulphur, wt % 65.0 17.3
V i s c o s i t y a t 40 'C, cSt
S i m u l a t e d d i s t i 11a t i o n , 'C

IBP 305 209

10% 369 290
50% 444 394

90% 538 489

FBP 594 536

T a b l e 111. P r o p e r t i e s o f C r a c k i n g C a t a l y s t s

.....................................................................

.P.r.o.p.e.r.t.i e. .s. . . . . . . . . . . . . . . . . . . . . . . . . . .C.I.A.-4.4.0. . . . . . . .N.o.v.a. .D. . . . . .G. X. .-3.0. . . . 'I
I
Type RE Y USY REY
BET s u r f a c e area, m2/g 75.0 95.5 107.5
43.7 66.8
Z e o l i t e s u r f a c e area, m2/g 7.3 48.4 10.8
Relative zeolite content, w t % 0.245 0.257
a. 1
Pore volume, mL/g 280 355
141 0.266 538
iAvg. p o r e d i a m e t e r , 374 400
42.1 208 33.1
V, ppm 24.42 . 351 24.39
N i , ppm 70 78
114
!Al2O3, w t % 45.3
24.28
Unit c e l l dimension,
72
Microactivity (Davison), w t %

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Table I V . Comparison o f Product Y i e l d s a t 50% Conversion*

Gas o i l I PPL Shale
Catalyst DA-440 DA-440

R. .e.a.c.t.o.r. .t e. m. .p.e.r.a.t.u.r.e.,. . '.C. . . . . . . . . . . . . . . .4.7.0. . . . . . . . . . . . . . . . .5.3.0. . . . . . . . .

Total dry gas, w t % 1.0 3.5

I c3 + c4, w t % 8.5 13.0

C 5 t gasoline, w t % 35.0 30.0

Light cycle oil, wt % 14.0 27.0

Decant o i l , w t % 39.0 20.5

Coke, w t % 2.6 6.6

* Extrapolated data

Recovery, w t % 100 85.3 86.1
T o t a l n i t r o g e n , ppm 7150 5618 3496
B a s i c n i t r o g e n , ppm
4570 3007 1745

Table VI. C r a c k i n g Y i e l d s ( w t % ) a t C / O = 6

________________________________________----------------------
c 5+
Shale o i l Typ. Catalyst Conver- Coke

. . . . . . . . . . . . . . . . .C. . . . . . . . . . . . . . . . . . . . . . .s.i.o.n. . . . . . . .G. .a.s.o.l.i n. e. . . . . . . . . . .

Raw 510 DA-440 45.0 25.2 6.5

DMSO t r e a t e d 510 DA-440 53.2 31.7 6.4

Clay t r e a t e d 510 DA-440 65.3 40.0 6.4

Raw 530 DA-440 47.9 26.5 6.6

Raw 530 GX-30 59.8 31.7 9.1

C l a y t r e a t e d 530 DA-440 70.0 42.5 6.4

1242

eo

50
70

60 40

CI 30

- /470. C I I 20
50
2 3 4 I
v
56 I'
s
50
t
40
3 40

1

9

c eo

.0-

v,
L

> 70
c

0

0

60

30
50

40 20
1 2 34 5 6

CataJyst/Oi I Rat i o

Figure 1. E f f e c t s of temperature and c a t a l y s t / o i l r a t i o
on conversion.

1243

I

I

I I 11 II II

12 3 4 5 6 7

40 I

' I1 I I I1 II I I

lo I 7
1234 5 6

Catalyst/Oil Ratio

Figure 2 . Conversions and g a s o l i n e y i e l d s of raw and t r e a t e d
s h a l e gas oils c a l c u l a t e d on t o t a l o i l b a s i s .

1244