A Microscale Simulation Test for Fluid Catalytic Cracking - ACS

Chapter 13

A Microscale Simulation Test for Fluid Catalytic Cracking P. O'Connor and M. B. Hartkamp

Downloaded by MONASH UNIV on April 15, 2016 | http://pubs.acs.org Publication Date: October 3, 1989 | doi: 10.1021/bk-1989-0411.ch013

Akzo, Chemical Division, Research Centre Amsterdam, P.O. Box 15, 1000 A A Amsterdam, Netherlands

A microscale Fluid Catalytic Cracking (FCC) simulation test is presented, which results in yields and product properties which correspond very well with commercial FCC results. Critical parameters to simulate are the ratio of Catalytic to Thermal cracking and the related chemical composition of the gasoline fraction. Obviously, these parameters are particularly important for the research into FCC product properties and, for instance, for the evaluation of potential octane catalysts. The test conditions for this Microscale Simulation Test (MST) correspond to the low vapor contact times as applied in today's FCC riser technology. An effective feed preheat and feed dispersion is ensured, while the isothermal reactor bed is set to the dominating kinetic temperature in the riser, being approximately the feed catalyst mix temperature. The MST conditions enable the testing of high Conradson Carbon residue feedstocks. Substantially better FCC forecasts can be made with the MST simulation conditions, making this test a very useful tool for catalyst and feedstock evaluations. A g r e a t need e x i s t s f o r r e l i a b l e F l u i d C a t a l y t i c C r a c k i n g performance t e s t s w h i c h can be used f o r t h e e v a l u a t i o n o f f e e d s t o c k s and catalysts. N o t w i t h s t a n d i n g the p o s s i b i l i t y o f d o i n g d e t a i l e d s i m u l a t i o n s w i t h bench o r p i l o t s c a l e r i s e r r e a c t o r s , the t r a d i t i o n a l M i c r o A c t i v i t y T e s t (MAT) remains the main t o o l f o r b a s i c FCC r e s e a r c h and c a t a l y s t and f e e d s t o c k e v a l u a t i o n and m o n i t o r i n g . The shortcomings o f t h e e x i s t i n g ASTM-MAT t e s t and p o s s i b l e a d a p t i o n s t o t h i s r e l a t i v e l y s i m p l e t e s t have been d i s c u s s e d by J.L. Mauleon e t . a l . ( 1 ) . The ASTM-MAT t e s t i s i n f a c t o n l y i n t e n d e d t o determine and compare t h e a c t i v i t y o f c r a c k i n g c a t a l y s t s ( 2 ) , and i s not s u i t a b l e f o r s i m u l a t i n g the r e a l FCC o p e r a t i o n , u s i n g t h e c o n d i t i o n s ( T a b l e 1 ) as d e f i n e d by t h e ASTM ( 3 ) . 0097-6156/89/0411-0135$06.00/0 © 1989 American Chemical Society

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


136

CHARACTERIZATION AND CATALYST DEVELOPMENT

S e v e r a l FCC Research groups have made changes t o t h e s t a n d a r d method, r e s u l t i n g i n many d i f f e r e n t t e s t methods ( 4 ) . F o r i n s t a n c e , a t Akzo R e s e a r c h we i n t r o d u c e d t h e Ketjen-MAT t e s t f o r t h e e v a l u a t i o n of p r o d u c t i o n and development samples ( 5 ) . The K e t j e n MAT t e s t i n c l u d e s a f a s t p r e h e a t , a s h o r t e r c o n t a c t t i m e and a h e a v i e r f e e d s t o c k than t h e ASTM f e e d . A l t h o u g h t h i s t e s t c l e a r l y had i t s advantages, t h e d e v i a t i o n from a c t u a l FCC r i s e r r e a c t o r o p e r a t i n g c o n d i t i o n s s t i l l remained too l a r g e as i l l u s t r a t e d i n f i g u r e 1; The Ketjen-MAT c o n d i t i o n s seem t o s i m u l a t e a FCC bed r e a c t o r , but n o t a r i s e r r e a c t o r . E s p e c i a l l y i n view o f t h e need t o o b t a i n n o t o n l y r e p r e s e n t a t i v e FCC y i e l d s , b u t a l s o more d e t a i l e d i n f o r m a t i o n on t h e p r o d u c t p r o p e r t i e s (RON, M0N, C e t a n e ) , an improved s i m u l a t i o n o f t h e FCC process i s indispensable. Testing

Strategy

B a s i c l y we may d i s t i n g u i s h two main l i n e s o f FCC t e s t i n g : 1. S c r e e n i n g , whereby t h e main o b j e c t i v e i s t o d i s c r i m i n a t e ; 2. F o r e c a s t i n g , where t h e p r i o r i t y i s t o f o r e c a s t t h e a c t u a l FCC performance. I n t h e l a t t e r c a s e , t h e need f o r a c o r r e c t FCC s i m u l a t i o n i s e v i d e n t , however, a l s o f o r s c r e e n i n g purposes i t i s a t t r a c t i v e t o s t a r t from a f i r m base o f s i m u l a t i o n c o n d i t i o n s , and then t o adapt e i t h e r t h e c a t a l y s t p r e t r e a t m e n t o r f e e d s t o c k i n o r d e r t o enhance the d i f f e r e n c e s i n performance. U s i n g v a r i a t i o n s i n t e s t i n g c o n d i t i o n s f o r s c r e e n i n g remains a v i a b l e o p t i o n ; t h e p r e s e n t ASTM-MAT c o n d i t i o n s f o r i n s t a n c e a r e such t h a t "Hydrogen T r a n s f e r " (De Jong ( 6 ) ) i s s t r o n g l y a m p l i f i e d . However, t h e r e a r e a few drawbacks: f i r s t o f a l l t h e l i n k w i t h commercial FCC o p e r a t i o n becomes weak, and s e c o n d l y t h e f r e q u e n t s w i t c h i n g o f t e s t c o n d i t i o n s can be d e t r i m e n t a l f o r t h e a v a i l a b i l i t y and t h e r e p r o d u c i b i l i t y o f t h e t e s t . From t h e f o r e g o i n g i t becomes c l e a r t h a t t h e n e x t two p o i n t s a r e e s s e n t i a l i n o r d e r t o improve m i c r o s c a l e FCC t e s t i n g : 1. E s t a b l i s h i n g a good FCC s i m u l a t i o n . In g e n e r a l we a r e t r y i n g t o s i m u l a t e an "average" o r a " r e p r e s e n t a t i v e " FCC u n i t . The t e s t r e s u l t s need t o be c o n f r o n t e d w i t h commercial d a t a . 2. A d a p t i n g c a t a l y s t p r e t r e a t m e n t o r f e e d s t o c k f o r s c r e e n i n g p u r p o s e s , w h i l e m a i n t a i n i n g t h e l i n k t o commercial FCC performance. I n t h e n e x t s e c t i o n h i g h l i g h t s o f our work l e a d i n g t o a new FCC M i c r o s c a l e S i m u l a t i o n T e s t (MST) a r e p r e s e n t e d . E s t a b l i s h i n g a good FCC s i m u l a t i o n The q u e s t i o n "What do we want t o s i m u l a t e ? " i s so complex t h a t we a r e s u r e t h a t a l s o o u r answer i s f a r from complete. The c r i t e r i a we use f o r j u d g i n g t h e s i m u l a t i o n s a r e :


13. O'CONNOR & HARTKAMP

TABLE 1 .

MAT TEST VS COMMERCIAL OPERATING CONDITIONS Commercial FCC

MAT Ketjen

MAT Total *

no

N2

N2

> 2% St

no

fast

fast

fast

Contact time, s Catalyst Vapour

75

50

5-15

2-10

14

4

2-4

0.5-5

WHSV

16

12

40-100

60-200

483 ?

483 ?

510-550 ?

650-750

470-480

470-480

490-530

500-540

ASTM


137

A Microscale Simulation Test

Feed dispersion Preheat

Catalyst temp, C Initial Mix Exit Source:

540-580

Reproduced w i t h p e r m i s s i o n from r e f . 1. C o p y r i g h t 1985 O i l and Gas J o u r n a l .

Catalyst

Separation •520 C

-Bed

level

'Isothermal" - 480 C

660 C

-Riser

700 C FCC Bed Reactor

-560 C

FCC Riser Reactor

F i g u r e 1. K e t j e n MAT s i m u l a t e s FCC bed r e a c t o r .


138



1. 2. 3. 4.

C o n v e r s i o n l e v e l (C/0 s e l e c t i o n ) . Bottoms C o n v e r s i o n . LPG O l e f i n i c i t y (C=3/C3, C4=/C4). F u e l gas-make and t h e r a t i o t h e r m a l / c a t a l y t i c c r a c k i n g (C2-minus/ iC4). 5. G a s o l i n e y i e l d . 6. G a s o l i n e c o m p o s i t i o n . 7. Coke make and D e l t a Coke l e v e l . U s i n g e q u i l i b r i u m c a t a l y s t from commercial FCC u n i t s , we m o d i f i e d t h e MAT r e a c t o r c o n d i t i o n s i n o r d e r t o meet t h e s i m u l a t i o n c r i t e r i a . T h i s work was complemented with ARCO p i l o t r i s e r p l a n t t e s t s , e x p l o r i n g t h e i n f l u e n c e o f t h e main p r o c e s s parameters such as r e s i d e n c e t i m e , m i x i n g , r e a c t o r temperature and t e m p e r t u r e p r o f i l e . C r i t i c a l parameters t o s i m u l a t e a r e t h e r a t i o o f C a t a l y t i c t o Thermal c r a c k i n g and t h e r e l a t e d c h e m i c a l c o m p o s i t i o n o f t h e g a s o l i n e f r a c t i o n . These parameters a r e p a r t i c u l a r l y i m p o r t a n t f o r the e v a l u a t i o n o f t h e octane p o t e n t i a l o f c a t a l y s t s and feedstocks (7). A l s o f o r t h e ARCO P i l o t R i s e r t h i s i s t h e c a s e , but by d r a s t i c a l l y a d a p t i n g t h e o p e r a t i n g c o n d i t i o n s ( T a b l e 2) i t i s p o s s i b l e t o a c h i e v e t h e c o r r e c t FCC g a s o l i n e c o m p o s i t i o n . For m i c r o s c a l e t e s t i n g , a c c e p t i n g t h e f a c t t h a t t h e MAT i s n e a r l y an i s o t h e r m a l t e s t , we chose t o t a k e t h e c a t a l y s t mix temperature as t h e o p e r a t i n g temperature o f o u r new t e s t . T h i s f o l l o w s t h e approach o f J.L. Mauleaon e t . a l . ( 1 ) , s t r e s s i n g t h e importance o f t h e mix temperature above t h a t o f t h e r i s e r e x i t . The ARCO P i l o t riser tends t o c o n f i r m t h e importance o f t h e mix t e m p e r a t u r e . I n g e n e r a l t h e mix temperature i s 25 t o 45 degrees C e l s i u s h i g h e r than t h e r i s e r e x i t temperature. A l s o f o r a good s i m u l a t i o n t h e c o n t a c t time o f t h e t e s t has t o be reduced. A 15 seconds r u n t i m e (2-4 seconds vapor c o n t a c t t i m e ) g i v e s y i e l d breakdowns and t r e n d s which c o r r e s p o n d v e r y w e l l w i t h t h e a c t u a l FCC d a t a (see example T a b l e 3 ) . U s i n g t h e MST t e s t we have been a b l e t o s i m u l a t e v a r i o u s Commercial FCC o p e r a t i o n s w i t h a t e s t mass b a l a n c e o f 96 t o 100%. An i n t e r e s t i n g p o i n t t o note i s t h a t t h e g a s o l i n e c o m p o s i t i o n s o b t a i n e d from t h e ASTM and Ketjen-MAT d e v i a t e s i g n i f i c a n t l y from the commercial FCC r e s u l t s . A t o o low g a s o l i n e o l e f i n i c i t y and a t o o h i g h degree o f b r a n c h i n g o f t h e p a r a f f i n and o l e f i n compounds i s found. The MAT g a s o l i n e can be a n a l y s e d w i t h t h e "Anderson" GC-method (see ( 8 ) , ( 9 ) ) . In o u r case we a p p l i e d a m o d i f i e d extended method. The commercial and P i l o t R i s e r g a s o l i n e were a n a l y s e d w i t h a d e t a i l e d GC-PIAN0 method developed by Akzo Research. As a s i m p l e measure f o r t h e Degree o f B r a n c h i n g (DOB) o f g a s o l i n e we make use o f t h e iC6/nC6 r a t i o . From o u r GC d a t a base we f i n d that t h i s r a t i o c o r r e l a t e s reasonably w e l l w i t h the o v e r a l l gasoline branching of the p a r a f f i n s ( i P / P ) , DOB = iC6/nC6

(1)

The B r a n c h i n g o f g a s o l i n e o l e f i n s , however, does n o t v a r y much, notwithstanding the l a r g e v a r i a t i o n s i n branching o f t h e g a s o l i n e paraffins (Fig. 2).


13. O'CONNOR & HARTKAMP

TABLE 2 .

ARCO PILOT RISER TEST CONDITIONS Standard Riser


139


Contact time,s Catalyst Regenerator Temp,C Catalyst temp, C Initial Mix Exit

TABLE

Modified (PRT)

Commercial FCC unit

2-10

25

10

650

700

650-750

520

700

650-750

520

545

540-580

520

520

500-540

3.

MST SIMULATION OF FCCUNIT MST

FCC TRX= 5 2 8

c

CT0

6.9

YIELDS, %WT FUELGAS LPG GASOLINE LCO BOTTOMS COKE

3.5 17.3 46.4 17.6 10.5 4.7

CONVERSION, %wt

71.9

71.9

DELTA COKE

0.68

0.69

0.79 0.60

0.80 0.62

93.4

93.3

C3=/C3 C4=/C4 RON (GC)

6

3.3 19.4 45.0 18.0 10.1 4.2


140


Gsln data from Commercial and P i l o t Riser tests. 0

r°;oo *°

p


+

a n a

ff

i n s

Olefins i0/0

/

D0B6 = iC6 / nC6 5

7

9

11

13

DEGREE OF BRANCHING, DOB-6 F i g u r e 2. G a s o l i n e B r a n c h i n g

and DOB f a c t o r .

ARCO PILOT RISER 70%WT CONV.

o\°

1

%

e?om o

o

o ° 0

0

o o

0

o "-a. °co

1.5

2.0

GASOLINE OLEFINICITY

2.5 (0/P)

F i g u r e 3. Degree o f B r a n c h i n g v s O l e f i n i c i t y .



13.

O'CONNOR & HARTKAMP


141

F i g u r e 3 shows the s t r o n g r e l a t i o n between the DOB and the o l e f i n i c i t y (0/P) of g a s o l i n e , which we f i n d based on the GC-PIANO a n a l y s i s of about 200 P i l o t R i s e r and Commercial FCC g a s o l i n e samples i n our g a s o l i n e database. The d i f f e r e n c e between RON and MON g a i n s o b t a i n e d w i t h low hydrogen t r a n s f e r USY c a t a l y s t s , as i l l u s t r a t e d i n f i g u r e 4, can be e x p l a i n e d w i t h t h i s phenomenon ( 7 ) . F i g u r e 5 demonstrates how the c o r r e c t g a s o l i n e c o m p o s i t i o n can be o b t a i n e d by s e t t i n g the MST t e m p e r a t u r e a t the l e v e l of t h e r e a c t o r r i s e r f e e d c a t a l y s t mix t e m p e r a t u r e . Based on t h e f o r e g o i n g we i n t r o d u c e d the new M i c r o S i m u l a t i o n Test (MST) i n our c a t a l y s t r e s e a r c h , i n e a r l y 1987. S t a n d a r d i z e d t e s t c o n d i t i o n s aiming a t an "average" FCC u n i t a r e g i v e n i n T a b l e 4. O b v i o u s l y f o r an o p t i m i z e d s i m u l a t i o n the MST t e m p e r a t u r e p r o f i l e s d e v i a t e v e r y s i g n i f i c a n t l y from the "average" FCC. One of t h e prime advantages of the new t e s t i s t h a t i t e n a b l e s us t o make s u b s t a n t i a l l y b e t t e r f o r e c a s t s i n terms of product p r o p e r t i e s , because of the congruent l i n k of MST, ARCO P i l o t r i s e r (PRT) and the commercial FCC r i s e r o p e r a t i o n ; i . e . o c t a n e p r e d i c t i o n s see f i g u r e 6. A l s o because of the h i g h t e m p e r a t u r e i t i s p o s s i b l e t o p r o c e s s h i g h Conradson Carbon c o n t a i n i n g r e s i d u e f e e d s t o c k s . A t p r e s e n t we have gone up about 8% wt CCR i n the t o t a l f e e d s t o c k . Some remarks on FCC

kinetics

The r e s u l t s o b t a i n e d i n our s e a r c h f o r o p t i m a l s i m u l a t i o n c o n d i t i o n s can a l s o be i n t e r p r e t e d i n terms of the e f f e c t of r e a c t o r c o n d i t i o n s on the c r a c k i n g k i n e t i c s . For i n s t a n c e the f o r m a t i o n of a r o m a t i c s i n the gasoline f r a c t i o n i n c r e a s e s s i g n i f i c a n t l y w i t h the r e a c t o r t e m p e r a t u r e , w h i l e the r a t e of a r o m a t i c s f o r m a t i o n remains r e l a t i v e l y c o n s t a n t , see f i g u r e 7. T h i s seems t o i n d i c a t e t h a t mono-aromatics s h i f t i n g from the f e e d t o the g a s o l i n e range due t o s h a t t e r i n g of l a r g e m o l e c u l e s can be enhanced by h i g h e r r e a c t o r bottom t e m p e r a t u r e s .

70%WT CONV 85

o oc

0.5

1.0

1.5

GASOLINE OLEFINICITY F i g u r e 4. G a s o l i n e vs

(0/P) Olefinicity.



15 14 RA CH

CD i—i

13 12

O LU RE


-MST 560C

10 9

LL

8

CD LU Q

PRT ARCO r i s e r 545-520 C

540C

k 11

CD

70%WT CONV.

l^-ASTM/Ketjen

-----H \

PRT

\

7 6 \ COMMERCIAL \ "*'"-•• 5 i ii i 1.0 1 .5 2.0 0.5 GASOLINE OLEFINICITY (0/P) F i g u r e 5. MST G a s o l i n e C o m p o s i t i o n .

TABLE 4 .

MST - Microscale Simulation Test Conditions PRT Riser

Feed dispersion Preheat Contact time, s Catalyst Vapour Catalyst temp, C Initial Mix Exit

Commercial FCC

MST

N2

N2

> 2% St

fast

fast

fast

10

15

2-10

1-5

1-4

0.5-5

650-750

700

560

545

550-560

540-580

520

550-560

500-540


O'CONNOR & HARTKAMP


MOTOR OCTANES


Commercial FCC Gasolines PIANO

ARCO Pilot Rise Gasolines

• O C T A N E MODEL

GC - MST MST Gasolines Accurate

' MST RON and MQN

predictions

F i g u r e 6. MST RON and MON p r e d i c t i o n s .

59

61 63 65 67 69 71 73

75

CONVERSION, %WT F i g u r e 7. A r o m a t i c s i n FCC g a s o l i n e .


144


Demar e t . a l . (10) s t r e s s t h e need f o r such a t h e r m a l shock i n order t o convert the asphaltenes present i n the feed. On t h e o t h e r hand, t h e above may a l s o mean t h a t t h e i n i t i a l t h e r m a l d e h y d r o g e n a t i o n o f n a p h t h e n i c compounds i n FCC f e e d i s a s t e p which determines t h e q u a n t i t y o f hydrocarbons which can be c o n v e r t e d to a r o m a t i c s by hydrogen t r a n s f e r .


Literature cited 1. Mauleon, J . L . and Courcelle, J . C . ; OGJ , Oct. 21, 1985, p 64-70. 2. Shankland, R.V. and Schmitkons; Proc. API 27 (III), 1947. 3. ASTM D-3907-86; Method for testing FCC catalysts by micro-activity test. 4. Parker, G.A. Ashton, A.G. van Catrer, G.D.L.; Katalistiks' FCC Symposium 1987, June 1987. 5. Ketjen Test Method - MAT. 6. De Jong, J.I.; Ketjen Catalyst Symposium '86, May 1986. 7. O'Connor, P; 2nd Ketjen South American Catalyst Seminar, October 1987. 8. Anderson, P.C.; Sharkey, J . M . ; Walsh, R.P.; J . Inst. of Petrol. 58, (1972), p 83-93. 9. Conkright, W.A.M.; Butler, M.M. and Harter, D.A.; Ketjen Catalyst Symposium '86, May 1986. 10. Demar, M.; T r i k i , A; van Franck, J . P . ; OGJ, Sept. 15, 1988, p 95-99. APPENDIX D e s c r i p t i o n o f t h e MST t e s t By means o f a s y r i n g e pump 1 gram o f f e e d s t o c k i s charged over t h e c a t a l y s t which i s p l a c e d i n t h e r e a c t o r i n t h e f u r n a c e . The c a t a l y s t i s p l a c e d i n t h e r e a c t o r i n an a n u l a r bed w i t h an i n t e r n a l d i a m e t e r of 9 mm and an o u t e r diameter o f 14 mm. The c e n t e r o f t h e bed i s f i l l e d w i t h a s t a i n l e s s s t e e l p r e h e a t e r . The shape o f t h e bed p r e v e n t s a temperature drop over t h e c a t a l y s t bed d i a m e t e r . I t a l s o i n c r e a s e s t h e s u r f a c e o f c a t a l y s t c o n t a c t i n g the w a l l , which h e l p s to p r e v e n t t h e c a t a l y s t from d r o p p i n g o u t o f t h e r e a c t o r . A f t e r 15 seconds f e e d i n g t i m e t h e c a t a l y s t i s s t r i p p e d w i t h n i t r o g e n f o r 15 minutes. The l i q u i d p r o d u c t i s c o l l e c t e d i n a g l a s s p r o d u c t r e c e i v e r t h a t i s c o o l e d w i t h a m i x t u r e o f d r y - i c e and acetone f o r t h e f i r s t 50 seconds. A f t e r t h a t the m i x t u r e i s r e p l a c e d by i c e and water. The gaseous p r o d u c t f l o w s t h r o u g h t h e r e c e i v e r t o t h e gas c o l l e c t i o n b o t t l e where i t i s c o l l e c t e d over water t o g e t h e r with the stripping nitrogen. A gas sample i s t a k e n by r e f i l l i n g t h e gas c o l l e c t i o n b o t t l e w i t h water and l e a d i n g t h e gas t h a t i s d i s p l a c e d by t h e water t h r o u g h the gas sample tube. A n a l y s i s o f gases, l i q u i d p r o d u c t and coke on c a t a l y s t s p e r m i t t h e c a l c u l a t i o n o f c o n v e r s i o n and p r o d u c t s e l e c t i v i t y . P r o c e s s f l o w schemes o f t h e MST and P i l o t R i s e r T e s t s a r e g i v e n i n f i g u r e s 8 and 9.


13.

O'CONNOR & HARTKAMP

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SUPPLY SYRINGE

FEED FLOW CONTROLLER PRESSURE TRANSDUCER ' 4-WAY ••' S L I D E VALVE k

NITROGEN VESSEL

GAS SAMPLE TUBE

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A Microscale Simulation Test for Fluid Catalytic Cracking - ACS

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