Catalyst Deactivation through Pore Mouth ... - ACS Publications

21 Catalyst Deactivation through Pore Mouth Plugging during Residue Desulfurization

Downloaded by UNIV OF QUEENSLAND on November 1, 2015 | http://pubs.acs.org Publication Date: June 1, 1978 | doi: 10.1021/bk-1978-0065.ch021

F . M . D A U T Z E N B E R G , J. VAN K L I N K E N , K . M. A . P R O N K , S. T . SIE, and J - B . W I J F F E L S * Koninklijke/Shell-Laboratorium, Shell Research B.V., Badhuisweg 3, Amsterdam, The Netherlands

I . Introduction Hydrodesulfurization of residual feedstocks with a high metals content i s a commercial proposition today (1,2). Based on previous work of many investigators (e.g. ref. 3 through 9) Shell's major efforts were focussed on the development of a suitable cata l y s t , for which a better understanding of the ageing phenomena oc curring i n the catalyst p a r t i c l e was needed. The present paper deals with the development of a simple two -parameter model describing the deactivation behaviour of residue desulfurization catalysts. The validity of the model i s being checked against the results of a large number of experiments with a variety of catalysts, two feedstocks and under different opera ting conditions. II. Experimental A. Equipment and Test Conditions Most experiments were performed at a fixed standard temperature and pressure i n bench-scale equip ment (about 100 ml catalyst volume) provided with facilities for recycle of H S-free liquid product (recycle r a t i o : 10 volumes of l i q u i d product per volume of fresh feed). This mode of operation was adopted to ensure good catalyst wetting i n small-scale r e actors. It has been established that i n this way reproducible and meaningful results can be obtained. At the high recycle ratios applied, the kinetics of the system approach that of a continuous stirred-tank system. An essential feature of this system i s that the catalyst deactivates uniformly, i.e., catalyst properties are constant throughout the bed at any time during a run. This i s in contrast with the non-uniform deactivation occurring i n a plug flow reactor (fixed bed without recycle). In the l a t t e r system, a deactivation front gradually proceeds through the catalyst bed. In most experiments we used a space velocity of *+.35 kg fresh feed per kg catalyst per hour, while an exit gas rate of 250 NI H2 per kg fresh feed was maintained. In a few cases we used different laboratory test conditions. These differences have been indicated in the figures and tables. * Present address: Shell Internationale Petroleum Mij B . V . , The Hague © 0-8412-0401-2/78/47-065-254$05.00/0 2

In Chemical Reaction Engineering—Houston; Weekman, V., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

21.

DAUTZENBERG

ET AL.

Deactivation through Pore Mouth Plugging

255

Β


· Feedstocks P r o p e r t i e s o f the Caribbean long residue (Feed I ) and the Middle East long residue (Feed I I ) used as feed stocks i n these s t u d i e s are l i s t e d ir) Table I . C a t a l y s t s Commercial as w e l l as experimental c a t a l y s t s were t e s t e d . I n Table I I we have l i s t e d the compositions o f t h e various c a t a l y s t s . D e t a i l s on shaping and p r e p a r a t i o n a r e a l s o i n cluded i n t h i s t a b l e . C a t a l y s t A has been t e s t e d as 1.5-mm e x t r u dates, but a l s o as 0 . 5 - and 0.8-mm broken p a r t i c l e s . S i m i l a r l y , C a t a l y s t J was t e s t e d as 1.5-mm extrudates and as 0.8-mm p a r t i c l e s . Before t e s t i n g , a l l the c a t a l y s t s were p r e s u l f i d e d i n s i t u . I). C a t a l y s t A c t i v i t y I t has been found t h a t h y d r o d e s u l f u r i z a t i o n o f heavy g a s - o i l f r a c t i o n s i n fixed-bed o p e r a t i o n w i t h a l a r g e product r e c y c l e (simulated s t i r r e d - t a n k o p e r a t i o n ) can be described as pseudo one-and-a-half order i n s u l f u r c o n c e n t r a t i o n , whereas vanadium removal can be described as pseudo f i r s t order i n vanadium c o n c e n t r a t i o n . We t h e r e f o r e used the f o l l o w i n g formula t o c a l c u l a t e c a t a l y s t a c t i v i t y f o r d e s u l f u r i z a t i o n and metal removal: --X—E.SV

k s III.

s

1.5

Ρ The Mechanism o f C a t a l y s t

Deactivation

A major problem i n t h e c a t a l y t i c h y d r o d e s u l f u r i z a t i o n of r e s i dual o i l s i s the d e a c t i v a t i o n o f the c a t a l y s t by m e t a l - c o n t a i n i n g a s p h a l t e n i c species i n the feed. As can be seen from the r e s u l t s of a t y p i c a l d e s u l f u r i z a t i o n experiment presented i n F i g . 1, t h e c a t a l y s t shows a r a p i d i n i t i a l d e c l i n e which i s attended w i t h a f a s t b u i l d - u p o f coke on the c a t a l y s t . A t a r e l a t i v e l y low c a t a l y s t age Θ, as d e f i n e d i n S e c t i o n IV, a s t a t i o n a r y coke l e v e l i s reached. In c o n t r a s t , t h e d e p o s i t i o n o f the i n o r g a n i c remnants o f the hydrocracked asphaltenes (mainly vanadium and n i c k e l s u l f i d e s ) continues and g r a d u a l l y clogs t h e pores i n t h e outer zone o f the c a t a l y s t p a r t i c l e s , as confirmed by e l e c t r o n microprobe analyses o f spent c a t a l y s t samples (see F i g . 2 ) . This causes a slow f u r t h e r l o s s i n d e s u l f u r i z a t i o n a c t i v i t y over a longer p e r i o d o f time. U l t i m a t e l y , the c a t a l y s t becomes t o t a l l y i n a c t i v e f o r d e s u l f u r i z a t i o n because the - s t i l l a c t i v e - inner core has become completely i n a c c e s s i b l e t o t h e s u l f u r - b e a r i n g molecules. IV. D e a c t i v a t i o n o f a S i n g l e C a t a l y s t P a r t i c l e Since t h e d e p o s i t i o n o f metal compounds determines c a t a l y s t l i f e we developed a model i n which we used the d e p o s i t i o n of metals as t h e p r i n c i p a l parameter t o d e s c r i b e t h e d e a c t i v a t i o n phenomena for equilibrium-coked c a t a l y s t . When coke d e p o s i t i o n becomes over-


CHEMICAL REACTION ENGINEERING—HOUSTON

256

PROPERTIES OF FEEDSTOCKS

UOP

Feed

I

II

Origin

Caribbean

M i d d l e East

distillation

%v a t %v a t

5 10 20 30 ho

2v a t

$v a t at %v a t

50


Density, Mol.

°C °C °C °C °C °C

315 337

Î423

372 koQ

**51 1*87

hh3 k&3

0.918i4

d 70A, g / m l

weight

Chemical

352 372 398

527

0.9183 1*88

analysis,

r H,

s, N, Ni, V,

Na,

%w o n f e e d #v o n f e e d %v o n ?iw o n ppm w o n ppm w o n ppm w o n

feed feed feed feed feed

85. 88 1 158 . 2.06 0.312 25 208 7

81*.25 11.32 3.86 0.21 1 1U 1*8 3

TABLE I I CATALYST PROPERTIES Catalyst r e f . no.

Composition

A Β

Support

Metal load %v on support

Particle size/shape

Bulk density

Co/Mo

1* 3/10.9

A1 0

il

0 78 g/ml

AI2O3

-

C

Ni/Mo

1+ 3/10.9

0 58 g/ml

D

Ni/Mo

k

Ε

Ni/Mo

k 3/10.9

0 65 g/ml

Sol-gel A1 0 Sol-gel A1 0 A1 0

F

Co/Mo

k 3/10.9

0 66 g/ml

A1 0

3

G

Co/Mo

U 3/10.9

0 72 g/ml

A1 0

3

H

Ni/Mo

k 3/10.9

0 58 g/ml

A1 0

3

I

Ni/Mo

k 3/10.9

0 58 g/ml

A1 0

3

J

Ni/Mo

2/16

0 58 g/ml

Si0 .Al 0

3

Κ

Ni/Mo

1/8

0 1*1 g/ml

Si0 .Al 0

3

L

Ni/Mo

2/16

0 hi o/ml

Si0 .Al 0

3

1.5 mm beads 1 .5 mm beads 1.5 mm extrudates 1 .5 mm extrudates 1.6 mm extrudates 1 .7 mm beads 1.7 mm beads 1.5 mm extrudates 1.5 mm extrudates 1 .5 mm extrudates

M

Ni/Mo

2/16

0 1*8 g/ml

Si0 .Al 0

3

Ν

Ni/Mo

2/16

0 U9 g/ml

Si0 .Al 0

3

0

Ni/Mo

2/16

0 U8 g/ml

Si0 .Al 0

3

Ρ

Ni/Mo

1/8

0 U8 g/ml

Si0 .Al 0

3

Q

Ni/Mo

1/8

0 kk g/ml

Si0 .AI2O3

R

Co/Mo

U.3/10.9

0 61 g/ml

A1

S

Co/Mo

3/10.9

1.5 mm extradâtes 0.8 mn extrudates 0.8 mm crushed beads 1.5 mm beads 1.5 mm extrudates 1.5 mm extrudates 1 .6 mm extrudates 1.7 mm beads 1.7 mm beads 1.5 mm extrudates 0.8 mm crushed extrudates 0.8 mm crushed extrudates 0.9 mm extrudates 1.2 mm extrudates 1.2 mm extrudates 1.2 mm extrudates 1.5 mm extrudates 1 .5 mm extrudates 1.5 mm extrudates

0 77 g/ml

Co/Mo

0 58 g/ml

A1 0

3/10.9

3/10.9

2

2

0 62 g/ml

Particle size/shape

Type

-

3

3

2

3

2

3

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2°3 2

3

partly dried gel partlydried gel partly dried g e l partly dried g e l 1 . 5 mm extrudates 1 . 5 mm extrudates

C a t a l y s t s A, B, and S have been commercially prepared. C a t a l y s t s C through I p l u s c a t a l y s t R have been prepared i n t h e l a b o r a t o r y on commercial supports.



DAUTZENBERG E T A L .

DESULFURIZATION RATE CONSTANT, (ARBITRARY UNITS )


100|-

2^

I

1

1

Ο

0.1

0.2

0.3

0.4

0.5

0.6

1

0.7

Figure 1. Hydrodesulfurization of a Caribbean long residue (feed I)




258

r u l i n g , the model cannot be used. This s i t u a t i o n may a r i s e w i t h a c a t a l y s t operating a t t o o low hydrogen p a r t i a l pressures. For sim p l i c i t y we t h e r e f o r e assume t h a t i n r e s i d u e h y d r o d e s u l f u r i z a t i o n (the i n i t i a l b u i l d - u p o f coke w i l l not be taken i n t o account) only two r e a c t i o n s take p l a c e i n p a r a l l e l : metal removal and hydrode s u l f u r i z a t i o n . S u l f u r i s removed as HgS and ends up i n the gas stream; the product o f the metal-removal r e a c t i o n i s a metal s u l f i d e t h a t i s deposited on the w a l l o f the c a t a l y s t pores. These metal s u l f i d e s reduce the o r i g i n a l d e s u l f u r i z a t i o n a c t i v i t y , but leave the metal-removal a c t i v i t y u n a f f e c t e d ; hence, new d e p o s i t s are formed on top o f o l d l a y e r s . As i n most r e s i d u a l feedstocks vanadium predominates over other metals, i t i s considered t o r e present t o t a l metals. Furthermore, both the d e s u l f u r i z a t i o n and the devanadization r e a c t i o n are d i f f u s i o n a l l y c o n t r o l l e d i n s i d e a catalyst particle. According t o t h i s l i n e o f thought, the concentrations o f t h e metal-bearing compounds decrease towards t h e i n s i d e o f the c a t a l y s t p a r t i c l e , and thus t h e r a t e o f deposit formation i s highest p r e c i s e l y at the pore entrance. As time proceeds, new d e p o s i t s a r e formed on top o f o l d l a y e r s , i n c r e a s i n g t h e i r t h i c k n e s s . Thus, t h e pore r a d i u s i n the periphery o f the c a t a l y s t p a r t i c l e i s reduced. As the pore r a d i u s decreases (which means t h a t t h e surface area per u n i t pore volume i s e n l a r g e d ) , the metal-removal r e a c t i o n zone f u r t h e r recedes t o the outer surface r e g i o n o f the c a t a l y s t p a r t i c l e and a "diaphragm" o f metal s u l f i d e s i s constructed i n t h e mouths o f the pores. We w i l l now d e s c r i b e these e f f e c t s i n q u a n t i t a t i v e terms. At any p o i n t i n a pore*, t h e r a t e a t which the t h i c k n e s s o f the depos i t l a y e r increases (or the r a t e a t which the pore r a d i u s i s reduced) i s p r o p o r t i o n a l t o the volume deposited per u n i t surface area per u n i t time:

Since the vanadium c o n c e n t r a t i o n i s highest at t h e o u t s i d e o f the c a t a l y s t p a r t i c l e ( C ) , the pore r a d i u s a t t h e entrance r i s reduced f a s t e s t and, a f t e r i n t e g r a t i o n o f the above equation, i s given by: Q

r

=r.(l -Θ), ο

Q

(2)

ι

i n which r-[ denotes the pore r a d i u s o f the f r e s h c a t a l y s t . The " r e l a t i v e c a t a l y s t age" Θ, which c h a r a c t e r i z e s t h e degree o f d e a c t i v a t i o n o f the c a t a l y s t , i s then d e f i n e d by: (3) and i s n u m e r i c a l l y equal t o the f r a c t i o n o f the pore mouth r a d i u s blocked by m e t a l - s u l f i d e d e p o s i t s . * For reasons o f s i m p l i c i t y the pores a r e considered t o be c y l i n ders o f equal s i z e and c i r c u l a r cross s e c t i o n . In Chemical Reaction Engineering—Houston; Weekman, V., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

21.

DAUTZENBERG ET AL.


259

One has t o look the c a t a l y s t i n t o i t s pore mouth i n order t o t e l l i t s age. With a f r e s h c a t a l y s t * t h e pore mouth i s f u l l y open and 0 = 0 . As soon as 0 = 1, t h e c a t a l y s t has o b v i o u s l y d i e d through complete c l o s u r e o f the "diaphragm" o f metal d e p o s i t s . A c a t a l y s t t h a t i s exposed t o t h e f u l l metal c o n c e n t r a t i o n o f the feed (Cp) w i l l have a l i f e which we w i l l d e f i n e as t h e " m i n i mum l i f e " . The minimum l i f e t ime Tjflin i s found from eq. (3): r. rp


mm

-

f

1

1. Ν

k.C^.V^ F dep A c a t a l y s t t h a t i s i n contact w i t h a l i q u i d o f lower metal c o n c e n t r a t i o n s w i l l remain a c t i v e f o r a longer p e r i o d . Since the d e a c t i v a t i o n i s a r e l a t i v e l y slow process, the v a nadium mole balance f o r the pore can be w r i t t e n as:

^{Aff^rkC,

(5)

where 1 denotes the l e n g t h o f t h e pore measured from the outer surface o f t h e p a r t i c l e , l = x y , where y i s the s u p e r f i c i a l l e n g t h of the pore and τ the t o r t u o s i t y . D denotes the d i f f u s i o n c o e f f i c i e n t o f the vanadium-bearing molecules i n t h e pore. The curvature of the s h e l l i n which the metal removal takes p l a c e has been neglected f o r s i m p l i c i t y . For a f r e s h c a t a l y s t r = r £ and eq. (5) may be solved d i r e c t l y to y i e l d :

C =Cq

e

,

H

(6)

where φ i s the T h i e l e modulus d e f i n e d by: = TR

^

and R i s the c h a r a c t e r i s t i c p a r t i c l e r a d i u s . I f , now, expression (6) i s introduced i n t o eq. (1) we f i n d as a f i r s t approximation for the pore r a d i u s o f an aged c a t a l y s t : r=r.(l-0e

K

(7)

) ,

and i f i n t u r n t h i s expression i s introduced i n t o the vanadium balance ( 5 ) , the vanadium c o n c e n t r a t i o n i n s i d e the pores of an aged c a t a l y s t i s found a f t e r i n t e g r a t i o n as: ί

C=C je o

-φ£ R

+9(e

-2φ^ R

-e

-φ£ R

)

)j.

(8)

* Since we neglected the i n i t i a l "build-up o f coke t h i s r e f e r s t o a f i c t i t i o u s s t a t e o f t h e c a t a l y s t where coke has reached i t s steadys t a t e l e v e l , but where no s i g n i f i c a n t metals have been deposited yet, so t h a t the pores are considered t o be s t i l l f u l l y open, 0 = 0 . In Chemical Reaction Engineering—Houston; Weekman, V., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.


260

By t h i s method o f p e r t u r b a t i o n u s i n g t h e r e l a t i v e c a t a l y s t age Θ as t h e p e r t u r b a t i o n parameter the equation f o r the r a t e o f change of the pore r a d i u s can be solved t o any d e s i r e d degree o f accuracy, together w i t h t h e mole balance o f t h e vanadium-bearing molecules over the pore. E x p r e s s i o n (8) i s an approximation f o r the exact pro f i l e n e g l e c t i n g terms o f order 0 and h i g h e r . The c o n c e n t r a t i o n on the o u t s i d e o f the c a t a l y s t p a r t i c l e C serves as a l i n k between the " i n s i d e " and the "outside happening". The e f f e c t i v e n e s s f o r metal removal o f the c a t a l y s t decreases w i t h i n c r e a s i n g age owing t o the p l u g g i n g o f the pore mouths. The e f f e c t i v e n e s s f a c t o r i s d e f i n e d as the r a t i o o f the r a t e o f metal removal f o r the aged c a t a l y s t t o t h a t f o r f r e s h c a t a l y s t : 2


Q

π Γ

ί

D

(

3 Î

)

1

= 0,

0=0

and can be c a l c u l a t e d d i r e c t l y from t h e s o l u t i o n (expressions (7) and (8)) t o give : η = m

1 -0

(10)

i f terms o f order 0^ and higher are neglected . V. Metal Removal and C a t a l y s t L i f e i n a (Simulated) Stirred-Tank Reactor The d e c l i n e i n metal-removal a c t i v i t y o f c a t a l y s t used i n s i mulated s t i r r e d - t a n k r e a c t o r experiments may now be evaluated u s i n g the vanadium weight balance: SV.(V

-V ) =η .k °.V (11 ) f Ρ m ν ρ I f the e f f e c t i v e n e s s f a c t o r i s approximated by n =1 - 0, expression (11) can be i n t e g r a t e d w i t h respect t o time u s i n g r e l a t i o n s (3) and (U) t o y i e l d : k k m

- i - = d τ . mm

+

_X-) e_i._X_.e sv sv

2

#

( 1 2

)

By means o f expressions (10), (11) and (12) i t can be d e r i v e d that the metal content o f t h e product ( f o r i n s t a n c e , Vp) as a f u n c t i o n o f the a c t u a l on-stream time t ( i n hours) i s given by: V

V ° .13)

V Ρ

mm

According t o eq. ( 1 3 ) , a p l o t o f (V^/Vp)^ against run time should be l i n e a r , which indeed proved t o be t r u e f o r a l l our experimental data obtained so f a r . F i g u r e 3 shows a few t y p i c a l examples. * From a more e l a b o r a t e s o l u t i o n we found n = 1 - 0 + -^0 up t o order 0 . As 0 values o f p r a c t i c a l i n t e r e s t are smaller than 0.5 (see s e c t i o n V ) , t h e simple s o l u t i o n represents an e x c e l l e n t ap proximation . 2

m


21.

DAUTZENBERG E T

AL.


ι [i


DIAMETRICAL LINE SCAN

0

200

400

600

800

1000

Figure 2. Electron-probe microanalyses of a deac tivated catalyst; semiquantitative vanadium and sul fur concentration profiles

OPEN SYMBOLS: CARIBBEAN LONG RESIDUE (FEED I ) CLOSED SYMBOLS: MIDDLE EAST LONG RESIDUE ( FEED H )

Δ Ne H

200

400

NL/Mo/AL 0 2

3

Ο Ν» Ν

NL/Mo/Si02-Al 0

•

Co/Mo/AL 0

Νβ Β

600

2

2

3

3

800 1000 RUN HOURS

Figure 3. Vanadium removal during hydrodesulfurization of Caribbean and Middle East long residues


261

262


From the i n t e r c e p t o f the p l o t w i t h the ordinate k ° can be c a l c u l a t e d , u s i n g the vanadium balance (eq. 11) at time zero: v

V o

£ _ sv 1»0 c v.-ν P Furthermore T £ 5 "the minimum l i f e t i m e , can now be c a l c u l a t e d from the slope of the l i n e a r p l o t . I t w i l l be c l e a r t h a t t h e r e l a t i v e c a t a l y s t age 9 can now be determined u s i n g expression ( 1 2 ) , i n t r o d u c i n g T i and k ° , two parameters which have been measured e x p e r i m e n t a l l y by f o l l o w i n g the vanadium content o f t h e l i q u i d product. Long before the c a t a l y s t has l i v e d through i t s a c t i v e p e r i o d the d e s u l f u r i z a t i o n a c t i v i t y has decreased c o n s i d e r a b l y , reaching a p o i n t where f i n a l l y the d e s u l f u r i z a t i o n a c t i v i t y i s seen t o drop r a p i d l y t o a very low l e v e l (point Β i n F i g . 2 ) . At t h i s p o i n t the c a t a l y s t has reached an age ( T g ^ T j ) which w i l l be r e f e r r e d t o as the s t a r t o f a c c e l e r a t e d d e c l i n e . As i l l u s t r a t e d i n F i g . U, a c a t a l y s t w i l l reach Tg^jj when the e f f e c t i v e n e s s f o r metal removal n has dropped t o 0 . 5 · I n F i g . h we have p l o t t e d the values o f n at T g ^ p f o r v a r i o u s c a t a l y s t s and t e s t s c o n d i t i o n s as a f u n c t i o n o f e x p e r i m e n t a l l y estimated T g ^ p from the d e s u l f u r i z a t i o n performance. On the b a s i s o f these obser v a t i o n s we used n 0 5 as a new d e f i n i t i o n of T g ^ j ) . For simulated s t i r r e d - t a n k experiments the f o l l o w i n g expression can then be d e r i v e d , which allows us t o c a l c u l a t e Tg^-p f o r d e s u l f u r i z a t i o n , u s i n g experimental metal-removal data: k

=

ν

f


m

n

m

n

v

m

m

m

SAD

mm

=

#

f

0.53

ii. • ^ 0.1U

V

f

Ρ

,15)

sv

V

The v a l i d i t y o f expression ( 1 5 ) , based on the c a t a l y s t poremouth plugging model, has been demonstrated i n many experiments performed w i t h Caribbean as w e l l as Middle-East long residues as feeds, i r r e s p e c t i v e o f the c o n d i t i o n s used. VI. E f f e c t o f M e t a l D e p o s i t i o n on the D e s u l f u r i z a t i o n A c t i v i t y According t o t h e proposed model the d e c l i n e o f the d e s u l f u r i z a t i o n a c t i v i t y o f a c a t a l y s t i s governed by t h e d e p o s i t i o n o f metals present i n the feed. Therefore i t i s expected t h a t c a t a l y s t d e s u l f u r i z a t i o n a c t i v i t y i s a f u n c t i o n o f the r e l a t i v e c a t a l y s t age Θ. This t h e s i s was t e s t e d f o r a set of experiments i n which the Caribbean long r e s i d u e (feed I) was processed over 1 .5-mm Co/Mo/ ΑΙρΟβ extrudates ( c a t a l y s t no. R) at v a r i o u s space v e l o c i t i e s , v i z . -lèïl 2 . 0 and 1.0 k g . k g - . h ~ . * In t h i s expression the more elaborate expression f o r n has been used. 1

1

m


21.

DAUTZENBERG


ET AL.

263

CARIBBEAN LONG RESIDUE ( FEED I )

Ο

MIDDLE EAST LONG RESIDUE (FEED H )

EXPERIMENTAL η

η

AT POINT Β


0.81-

®

SEE

FIG. 1

1.5

2.0 T

Exp.

Catalyst

Particle

SAO *

R

C

L

A

T

,

V

E

SCALE

Remarks

Ref.

Composition

diam., mm

1 2 3

A A A

C0/M0/AI2O3

0.5 0.8 1.5

granules granules Extr.

k 5

Β Β

C0/M0/AI2O3

0.8 0.8

Extr. Extr.

low-pressure experiment high-pressure experiment

6 7

C D

N1/M0/AI2O3 N1/M0/AI2O3

0.8

granules Beads

8 9

Ε F

N1/M0/AI2O3 C0/M0/AI2O3

1.5 1.5

Extr. Extr.

-

10

G

C0/M0/AI2O3

1.6

Extr.

11 12

H I

NÎ/M0/AI2O3 Ni/Mo/Al 0

1.7

Beads Beads

13

J J J J

Ni/Mo/Si02.Al203

K L M Ν 0 Ρ Q

Ni/Mo/Si0 .Al203 Ni/Mo/Si0 .Al 03 Ni/Mo/Si0 .Al 03 Ni/Mo/Si02.Al 03 Ni/Mo/Si02.Al203 Ni/Mo/Si02.Al203 Ni/Mo/Si02.Al 0

1U 15

16 17 18 19

20 21 22 23

Figure 4.

2

1.5

1.7

3

0.8

2

2

2

2

2

2

2

3

shape

-

-

SV =U.O kg.kg-1 .h-1 SV = h.O kg.kg-1.h-1

1.5 1.5

granules Extr. Extr. Extr.

0.8 0.8 0.9 1 .2 "1.2 1.3 1.6

granules granules Extr. Extr. Extr. Extr. Extr.

SV =U.O kg.kg-1.h-1 SV = U . 0 kg.kg-1. -1

1.5

h

Effectivity of vanadium removal at point B* for various catalysts and test conditions



264

For a l l three space v e l o c i t i e s we p l o t t e d (Vf/Vp)^ versus t and found s t r a i g h t l i n e s i n agreement w i t h eq. ( 1 3 ) from which we subsequently c a l c u l a t e d the i n i t i a l vanadium content, Vp° "the o v e r a l l f i r s t - o r d e r r a t e constant, k ° , and the minimum l i f e t i m e of c a t a l y s t s , T i . These were found t o be constant w i t h i n about 10 % which i s about the experimental u n c e r t a i n t y . We t h e r e f o r e conclude t h a t the pore-mouth plugging model i s u s e f u l as a t o o l t o p r e d i c t f o r i n s t a n c e TSAD at low space v e l o c i t i e s from experiments at r a t h e r h i g h space v e l o c i t y . Since we know the i n i t i a l vanadium i n product, Vp°, f o r each space v e l o c i t y and T j _ , we can c a l c u l a t e the r e l a t i v e c a t a l y s t age, Θ, as a f u n c t i o n of run time t u s i n g eq. ( 1 2 ) . In order t o compare the d e s u l f u r i z a t i o n a c t i v i t i e s on a common s c a l e , we w i l l define a r e l a t i v e catalyst a c t i v i t y for d e s u l f u r i z a t i o n : 5

v

m

n


9

m

1

s

k (0 S

n

(16)

=0.25)'

Since the i n i t i a l d e s u l f u r i z a t i o n r a t e constant i s r a t h e r d i f f i c u l t t o determine a c c u r a t e l y the d e s u l f u r i z a t i o n a c t i v i t y at 0 = 0 . 2 5 has been chosen as reference a c t i v i t y . For a l l t h r e e space v e l o c i t i e s we subsequently p l o t t e d the r e l a t i v e c a t a l y s t a c t i v i t y for d e s u l f u r i z a t i o n as a f u n c t i o n o f 0 (see F i g . 5 A ) . The f i g u r e shows t h a t i r r e s p e c t i v e of the space v e l o c i t y a p p l i e d the same p l o t i s obtained. Encouraged by these r e s u l t s , we analysed i n the same way runs performed at d i f f e r e n t pressures and temperatures. We a l s o compared d i f f e r e n t feedstocks. The r e s u l t s have been p l o t t e d i n F i g . 5 B through 5D. F i g u r e 5 c l e a r l y shows t h a t , although the pore-mouth plugging model does not provide a t h e o r e t i c a l expression f o r the dépendance of n on 0, i t i s p o s s i b l e t o d e r i v e a unique r e l a t i o n between η and 0, which appears t o be independent of space v e l o c i t y , p r e s s u r e , temperature and pressure. This not only confirms our t h e s i s , but i t a l s o demonstrates t h a t 0 i s the c o r r e c t l i f e parameter t o d e s c r i b e c a t a l y s t ageing behaviour. s

s

L i s t o f Symbols r = a c t u a l pore r a d i u s r = pore mouth r a d i u s r£ = pore r a d i u s i n f r e s h c a t a l y s t C = molar vanadium c o n c e n t r a t i o n , i n s i d e the pore C = i b i d , o u t s i d e the c a t a l y s t p a r t i c l e Cf = i b i d , i n the feed ^dep d e p o s i t i o n volume per mole vanadium k = f i r s t - o r d e r s u r f a c e r e a c t i o n r a t e constant f o r vanadium removal k = pseudo f i r s t - o r d e r r e a c t i o n r a t e constant f o r vanadium removal at r e l a t i v e c a t a l y s t age 0

m m m kmol.m-3 kmol.m-3 kmol.m-3 m^.kmol

Q

0

=

5-1

v

kg.kg"




CATALYST: C o / M o / A l 0


2

CATALYST. Co/Mo/Al20 (NeB) FEED: MI DOLE EAST LONG RESIDUE ( FEED S ) 3

3

(Νδ R) FEED : CARIBBEAN LONG RESIDUE (FEED I) SYMBOL

WHSV, kq. kg. h"

Ο • Δ

1

EACH DIFFERENT SYMBOL REFERS TO A DIFFERENT PRESSURE

4.35 2.0 1.0

0.0 0.2 0.4 0.6 0.8 1.0

0.0 0 2 0.4 0.6 OM 1X> θ

θ

Q Figure 5a. Relationship between relative catalyst activity for desulfurization and relative catalyst age. Runs at various space velocities.

b Figure 5b. Relationship between relative catalyst activity for desulfurization and relative catalyst age. Runs at different pres sures.




266

CATALYST: Co/Mo/A 1^3 (N« S) FEED: CARIBBEAN LONG RESIDUE (FEED I) • STANDARD TEMPERATURE Δ ST. - 2 5 ° C Ο ST. - 4 5 ° C

Figure 5c. Relationship between rehtive catalyst activity for desulfurization and relative catalyst age. Runs at various tempera tures.

CATALYST: C o / M e / A ^ O g (Ne R) FEED: Ο CARIBBEAN L0M6 RESIDUE ( FEEO I ) Δ MIDOLE EAST LONG RESIDUE ( FEED S )

Figure 5d. Relationship between rehtive catalyst activity for desulfurization and relative catalyst age. Runs with different feed stocks.


21.



267

= pseudo 1 . 5 t h - o r d e r r e a c t i o n r a t e constant f o r s u l f u r removal at r e l a t i v e c a t a l y s t age Θ kg.kg- .h-1(?wS)-§ t = run time h Θ = r e l a t i v e c a t a l y s t age Tmin minimum l i f e t i m e o f c a t a l y s t h SAD c a t a l y s t age at the s t a r t o f a c c e l e r a t e d d e c l i n e h SV = space v e l o c i t y kg.kg" .h-1 Vf = vanadium content o f t h e feed ppm(w) Vp = vanadium content of t h e product at c a t a l y s t age Θ ppm(w) Sf = s u l f u r content o f the feed %w Sp = s u l f u r content o f t h e product a t c a t a l y s t age Θ %w n = c a t a l y s t e f f e c t i v i t y f o r metal removal n = relative catalyst activity for desulfurization

k

s

1

=

T

=


1

m

f

s

Literature Cited (1) Van Ginneken, A.J.J., van Kessel, M.M., Pronk, K.M.A., and Renstrom, G . , O i l and Gas Journal, A p r i l 28, 1975, p. 59-63. (2) Yamamoto, M.D., Oil and Gas Journal, May 16, 1977 p. 146-165. (3) Hoog, H., K l i n k e r t , H . G . , and Schaafsma, Α., P e t r o l . R e f i n . , (1953) 32 (No. 5), 137. (4) Le Nobel, J.W., and Choufoer, J.H., 1st World Petroleum Congress (1959), Section III, p. 233 paper 18. (5) Van Zoonen, D . , and Douwes, C.Th., J. Inst. of P e t r . , (1963) 49 383. (6) Van Deemter, J.J., Proc. 3rd Eur. Synro. Chem. Reaction Eng., (1964) 215. (7) Larson, O.A., and Beuther, Η., Div. Petr. Chem. ACS Preprints, Pittsburg, (1966) B-95. (8) Newson, E. J., Div. Petr. Chem. ACS Preprints, Chicago, (1970) A141. (9) Moritz, K.H. et. al., Japan Petr. Inst. Fuel Oil Desulfurization Symposium Tokyo, Japan, March (1970).


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