Trickle-Bed Reactors: Dynamic Tracer Tests, Reaction Studies, and

34 Trickle-Bed Reactors: Dynamic Tracer Tests, Reaction Studies, and Modeling of Reactor Performance Downloaded by UCSF LIB CKM RSCS MGMT on September 1, 2014 | http://pubs.acs.org Publication Date: September 16, 1982 | doi: 10.1021/bk-1982-0196.ch034

A. A . EL-HISNAWI and M . P. DUDUKOVIĆ Washington University, Chemical Reaction Engineering Laboratory, St. Louis, MO 63130 P. L . MILLS Monsanto Company, Monsanto Corporate Research, St. Louis, M O 63167

An appropriate model for trickle-bed reactor perfor mance for the case of a gas-phase, rate limiting reactant is developed. The use of the model for predictive calculations requires the knowledge of liquid-solid contacting efficiency, gas-liquid-solid mass transfer coefficients, rate constants and effectiveness factors of completely wetted catalysts, all of which are obtained by independent experiments. The ability of the model to account for changes in liquid physical properties and mass velocities and correctly predict reactor performance is demonstrated using hydrogenation of α-methylstyrene in various organic solvents as a test reaction. T r i c k l e - b e d r e a c t o r s , beds packed w i t h s m a l l porous c a t a l y s t p a r t i c l e s w i t h cocurrent gas and l i q u i d downward flow, a r e used e x t e n s i v e l y i n h y d r o d e s u l f u r i z a t i o n and h y d r o t r e a t i n g o f heavy petroleum f r a c t i o n s as w e l l as i n hydrogénation o f chemicals, o x i d a t i o n o f waste streams and i n fermentations (1, 2,, 3 ) · A l l processes o c c u r r r i n g i n t r i c k l e - b e d s can be d i v i d e d i n t o two c a t e g o r i e s with r e s p e c t to the r a t e l i m i t i n g r e a c t a n t . I n one category, l i q u i d reactant i s n o n v o l a t i l e a t the o p e r a t i n g c o n d i t i o n s used and i s r a t e l i m i t i n g . Reaction then takes p l a c e only on the wetted c a t a l y s t . The second category c o n s i s t s o f processes where e i t h e r a gas r e a c t a n t o r a h i g h l y v o l a t i l e l i q u i d r e a c t a n t i s r a t e l i m i t i n g . Reaction takes p l a c e on both dry and wetted c a t a l y s t but a t d i f f e r e n t r a t e s due t o d i v e r s e t r a n s p o r t l i m i t a t i o n s (4). In e i t h e r case i t i s necessary to know the f r a c t i o n of wetted c a t a l y s t which can be l e s s than u n i t y i n the n o n i n t e r a c t i n g g a s - l i q u i d regime ( t r i c k l e - f l o w ) (2 4^ , 5 ) · order t o p r e d i c t t r i c k l e - b e d performance, besides c o n t a c t i n g e f f i c i e n c y , the knowledge o f v a r i o u s mass t r a n s f e r c o e f f i c i e n t s , g a s - l i q u i d e q u i l i b r i a , k i n e t i c s and c a t a l y s t e f f e c t i v e n e s s a r e a l s o necessary. I

n

9

0097-6156/82/0196-0421$06.00/0 © 1982 American Chemical Society In Chemical Reaction Engineering—Boston; Wei, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1982.

422

CHEMICAL REACTION ENGINEERING

Downloaded by UCSF LIB CKM RSCS MGMT on September 1, 2014 | http://pubs.acs.org Publication Date: September 16, 1982 | doi: 10.1021/bk-1982-0196.ch034

A number of attempts i n i n t e r p r e t i n g t r i c k l e - b e d performance appeared i n the open l i t e r a t u r e (6-14). These s t u d i e s d i d not demonstrate the p r e d i c t i v e a b i l i t y of the proposed r e a c t o r models. Some used the r e a c t i o n data i n t r i c k l e - b e d s to evaluate unknown model parameters i n order to match c a l c u l a t e d and experimental r e s u l t s (7-11). Other s t u d i e s l e f t c e r t a i n observed phenomena unexplained (6-12). The o b j e c t i v e of t h i s paper i s to develop a model f o r a gas reactant l i m i t e d r e a c t i o n i n an isothermal t r i c k l e - b e d r e a c t o r . Model parameters are evaluated by indepen dent means and model's p r e d i c t i v e a b i l i t y i s t e s t e d . Reaction K i n e t i c s Reaction Order, Rate Constants and A c t i v a t i o n Energy ( S l u r r y Reactor). Hydrogentation of α-methylstyrene was s e l e c t e d f o r a t e s t r e a c t i o n . This r e a c t i o n has been s t u d i e d e x t e n s i v e l y by a number of i n v e s t i g a t o r s (6, 11, 14, 15» 17)· Previous s t u d i e s used Pd/A&2C>3 or Pd-black c a t a l y s t s i n α-methylstyrene-cumene mixtures. We wanted to v e r i f y the k i n e t i c s of t h i s r e a c t i o n i n v a r i o u s s o l v e n t s of d i f f e r e n t p h y s i c a l p r o p e r t i e s (cyclohexane, hexane (u.v.), hexane (A.C.S), toluene, 2-propanol) and examine the e f f e c t of Pd c o n c e n t r a t i o n on the r a t e . The above s o l v e n t s were to be u t i l i z e d i n t r i c k l e - b e d r e a c t i o n s t u d i e s a l s o to pro v i d e a range of l i q u i d p h y s i c a l p r o p e r t i e s . The k i n e t i c experiments were performed i n the 2.6 l i t e r semibatch, s t i r r e d s l u r r y r e a c t o r shown i n F i g u r e 1 (with the c a t a l y s t basket No. 10 removed). A known amount of s o l v e n t as w e l l as the known mass of f i n e l y c r u s h e d ( d = 0.005 cm) a c t i v a t e d c a t a l y s t (0.5% Pd and 2.5% Pd on Α ^ Ο β ) were charged i n t o the r e a c t o r . Hydrogen was bubbled through the s l u r r y and a t the beginning of each run a known amount of α-methylstyrene (ams) was i n j e c t e d so that the i n i t i a l c o n c e n t r a t i o n was between 1x10"* (gmol/cm^) and 6xl0~^(mol/cm^). The c a t a l y s t l o a d i n g was between 1 and 2 ( g / l i t ) and the temperature range between 10°C and 35°C was covered. I t was shown that s t i r r i n g r a t e and hydrogen flow r a t e had no e f f e c t on the r e a c t i o n r a t e . The t e s t s done to assure that i n t r i n s i c k i n e t i c r a t e was measured and other experimental d e t a i l s are described by El-Hisnawi (18). p

The r e a c t i o n i s found to be zeroth order w i t h respect to α-methylstyrene and approximately f i r s t order w i t h respect to hydrogen i n a l l s o l v e n t s as shown i n Table I . Reaction dependence on hydrogen i n cyclohexane s o l v e n t i s shown i n F i g u r e 2 and a t y p i c a l Arrhenius p l o t i s presented i n F i g u r e 3. Reaction r a t e i s independent of Pd c o n c e n t r a t i o n ( s t r u c t u r e i n s e n s i t i v e ) i n pure nonpolar s o l v e n t s (cyclohexane, hexane (U.V.)) but becomes s t r u c ture s e n s i t i v e ( i . e . dependent on Pd concentration) i n s o l v e n t s w i t h i m p u r i t i e s or which are more p o l a r . The a c t i v a t i o n energy of 10.2 kcal/mol found i n cyclohexane agreed w e l l w i t h the one determined by Germain et a l . ( 6 ) .

In Chemical Reaction Engineering—Boston; Wei, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1982.


Figure 1.

Experimental equipment for both intrinsic and apparent reaction studies.


6

ι

Ci

δ. » s

ce

F

fi"

>

W H

ι

W

4*

Ο)


2-propanol

Toluene

Hexane (ACS) grade

Hexane (u.v) grade

Cyclohexane

Solvent

Table I .

4

3.477 χ 1 0

3

5 e

-

1

0

'

8

0

0

8 3 5 3 / R T

/

R

T

P

P

H

H

P„ 2

H

H

P„ 2 P„ 2

H

2 0 0 / R T

9 2 8 0 / R T

5.04 χ 1 0 e -

4

7.1 χ 1 0 e -

'

8 0 0 0 / R T

1 0

2.307 χ 10 e -

5

10.25 χ 10 e -

u H

Rate(mol/g Pd s ) ;P 0.5% Pd 2

2.5% Pd

2

1.091 χ 1 0

4.99 χ 1 0

4

e

4

e

-

-

6

8

1

2.724 χ 1 0 e -

0

0

0

0

0

/

/

R

R

T

T

H

P„ 2 H

P„ 2 P„

8 1 8 0 / R T

Same as with 0.5% Pd.

Same as with 0.5% Pd.

(atm)

Summary o f I n t r i n s i c Reaction Rates i n V a r i o u s Solvents


6

34.

EL-HISNAWI ET AL.

•06

α u oo

•04 —

425

Trickle-Bed Reactors

I

1

/

dp s 0.005 cm —

OÙ ω


ce os

υ

on

•01

y

ι P

u

H

Figure 2.

1

•5

1*5 (atm)

2

Reaction rate of AMS hydrogénation as a function of hydrogen partial pressure in cyclohexane.

•05

ι

ι

i

dp m 0.005em

k .04

E s 10.2 kcal/mol.

\ u

00 rj

.03

ce

on

c o υ to

Φ

•02

.015 3.2

I

I

3.3

3.4

1/T

Figure 3.

x ίο

3

Ί

.

3.5

(κ" ) 1

Reaction rate as function of reaction temperature in cyclohexane solvent.



426


C a t a l y s t E f f e c t i v e n e s s F a c t o r (Basket R e a c t o r ) . The e f f e c t i v e n e s s f a c t o r s of the c a t a l y s t p a r t i c l e s to be used i n t r i c k l e bed s t u d i e s were determined i n a stagnant basket r e a c t o r (Figure 1 ) . The p a r t i c l e s were c y l i n d r i c a l extrudates (0.13x0.56 cm) w i t h 0.5% Pd and 2.5% Pd d i s t r i b u t e d i n a s h e l l l a y e r on the o u t s i d e o f the p a r t i c l e . The e f f e c t i v e n e s s f a c t o r s of completely wetted p e l l e t s i n the basket a t d i f f e r e n t temperatures are p r e sented i n F i g u r e 4. The apparent a c t i v a t i o n energy v a r i e d between 4.5 and 5.4 (kcal/mol) c l e a r l y i n d i c a t i n g s t r o n g pore d i f f u s i o n a l e f f e c t s i n a l l s o l v e n t s . However, there was an order of magnitude d i f f e r e n c e i n the e f f e c t i v e n e s s f a c t o r between hexane and c y c l o hexane s o l v e n t .

T r i c k l e - B e d Reactor Model Development Reactor model f o r the t e s t r e a c t i o n of α-methylstyrene hydro génation i s developed based on the f o l l o w i n g assumptions: 1. Reaction occurs only i n the l i q u i d phase on the s o l i d c a t a l y s t . 2. Reaction i s f i r s t order i n gas r e a c t a n t . 3. Gas and l i q u i d stream are i n p l u g flow. 4. Reactor i s i s o t h e r m a l . 5. Gaseous reactant c o n c e n t r a t i o n i n the gas phase i s constant throughout the r e a c t o r . 6. A f r a c t i o n of the c a t a l y s t e x t e r n a l s u r f a c e ( T I C E ) covered by a f l o w i n g l i q u i d f i l m w h i l e the r e s t i s exposed t o a t h i n stagnant l i q u i d f i l m . Assumption 2 was v e r i f i e d by already reported k i n e t i c s t u d i e s . A water cooled r e a c t o r w i t h low feed c o n c e n t r a t i o n s o f α-methylstyrene operated between 15°C and 20°C s a t i s f i e s assumptions 1 and 4 due to low v o l a t i l i t y o f the l i q u i d r e a c t a n t and due to s m a l l o v e r a l l heat e f f e c t s , r e s p e c t i v e l y . Pure hydrogen i n l a r g e excess i s used as the gas feed s a t i s f y i n g assumption 5. Assumption 3 i s s a t i s f a c t o r y as shown by t r a c e r s t u d i e s (19, 20). T r a c e r s t u d i e s , d e s c r i b e d i n the next s e c t i o n , a l s o demonstrate t h a t e x t e r n a l c o n t a c t i n g i s not complete a t lower l i q u i d mass v e l o c i t i e s i n agreement w i t h assumption 6. I t remains to be determined whether the c a t a l y s t s u r f a c e not covered w i t h the f l o w i n g l i q u i d f i l m s or r i v u l e t s i s dry or i n contact w i t h a s t a g nant l i q u i d f i l m . The d i f f e r e n t i a l equations d e s c r i b i n g the model (Ml) and the r e s u l t i n g e x p r e s s i o n f o r c o n v e r s i o n are summarized i n Table IIA. A s i m p l i f i e d model i s developed by assuming n e g l i g i b l e changes of the d i s s o l v e d gas r e a c t a n t along the r e a c t o r . T h i s model (M2) u t i l i z e s the concept of the o v e r a l l gas-flowing l i q u i d - s o l i d and gas-(stagnant l i q u i d ) - s o l i d mass t r a n s f e r c o e f f i c i e n t s . The governing equations and the r e s u l t i n g expres s i o n f o r conversion are summarized i n Table IIB. I


S

EL-HisNAWi

ET AL.



34.


427


428


4

ι

1—I

I I I II

'

ι

3 X

c, 2

2.5% pa

J

' 40

10

ι ι ι t 60 M

S Figure 4c.

Catalyst effectiveness factor as a function of thiele modulus (ψ) in cyclohexane.


34.

EL-HISNAWI

Table I I . IIA.

Model Equations

Model Ml

dC " SL Ί Γ " U


429


ETAL.

n

k

(Tl)

a

» v- e » > B *W'CE C A,LS - n (Ι-ε,,ΧΙ-η^) k„ ν C A, gLS B' ~ 'CE' v

x

A T C

dC (T2)

a

\S

k

«Ws*

LS

(C

gLS V S

C

)

k

v

n

""V

n

(T3)

C

C

E A,LS

k

(T4)

C

A,e- A,gLS " v " " V ^ C E * A,gLS

C (z)

(T5)

a

ao

2-0

C

n

"

Equilibrium feed

(T6)

Non-equilibrium feed

(T7)

(

A,L *> 2 »

C

0

X

ao "SI, a L nk d-e)c v

( 1 A e

-V {—ÎTH-} k S gLS ex

CE

(

η k V *LS

''ex n

a

^LS LS λ - 1+ (ka) g*

k

\S

v

V

Oca) L t

.

)

+ 1

0

S

ex

1+ k

(T8)

S

LS ex


(T9)


430


Table I I . IIB.

Model Equations

(continued)

Model M2 dC

' SL dT "

n

U

k

s

a

k

gLS V S

C

( C

LS

a

k

CE c"A AT .C -n L S "k „ν ( l - e jB (ΐ-ru,) CE C A,gLS Λ

« d-e*>B

C

A,e- A,LS

(C

)

C

X

e

α

C

(z)

L — SL

U

k

n

v

A,e- A,gLS> "

η

k

(Tll)

C

CE A,LS

C

v

A,gLS

(η k

C

V

A

'

CE

'CE

)

A

(T12)

(T13)

αο

ζ « 0

" B X„ - 7Γ—^ ao

Π

"

(T10)

(T14)

e

1 + (Bi)

t

(Bi)

D

J


34.

EL-HiSNAWi ET AL.

431



The equipment used i n t r a c e r s t u d i e s i s presented i n F i g u r e 5 while d e t a i l s a r e given elsewhere (20). I t has already been shown that c o n t a c t i n g e f f i c i e n c y determined by equation (2) i s i n good agreement w i t h the values i n f e r r e d from r e a c t i o n s t u d i e s (22, 23). I n t h i s study the data base was f u r t h e r expanded u s i n g the a d d i t i o n a l f i v e hydrocarbon s o l v e n t s . The e x i s t i n g data f o r dynamic s a t u r a t i o n (dynamic holdup d i v i d e d by bed p o r o s i t y ) i n the t r i c k l e - f l o w regime (18, 20, 21, 24, 25) can be c o r r e l a t e d by the f o l l o w i n g equation: ω

- ο ΛΟΙ η 0.344 -0.197 = 2.021 Re^ Ga^ n

β

/ 0

v (3)

The average e r r o r f o r the 105 data p o i n t s i s -7.1% w i t h a standard d e v i a t i o n o f the e r r o r o f 26.1%. The data (65 points) for e x t e r n a l c o n t a c t i n g e f f i c i e n c y i n the t r i c k l e - f l o w regime (11, 18, 20, 21) can be c o r r e l a t e d by: n

ι t i l t> 0.146 „ -0.071 = 1.617 R e Ga

C E

L

„v (4)

L

E v a l u a t i o n o f L i q u i d - S o l i d Contacting

Efficiency

T r a c e r methods proposed by Schwartz e t a l . (19) and Colombo et a l . (21) were used t o determine t o t a l and e x t e r n a l c a t a l y s t c o n t a c t i n g e f f i c i e n c y . These techniques have been d e s c r i b e d elsewhere (22). T o t a l c o n t a c t i n g e f f i c i e n c y , ï)ç d e f i n e d as the f r a c t i o n of t o t a l ( e x t e r n a l and i n t e r n a l ) c a t a l y s t area contacted by l i q u i d can be obtained by: 9

β

(K } (u } A app l a l n a TF μ u (K ) " ( la~ ιΜ^ρ A

L F

m

( d i f f e r e n c e i n f i r s t moment f o r adsorbing and nonadsorbing t r a c e r impulse response i n t r i c k l e - f l o w ) ( d i f f e r e n c e i n f i r s t moment o f the above two t r a c e r s i n l i q u i d f i l l e d column a t same l i q u i d flow-rate) (1)

and i t has been shown t o be u n i t y i n the hydrocarbon systems used (20, 22). E x t e r n a l c o n t a c t i n g e f f i c i e n c y , n , d e f i n e d as the f r a c t i o n o f e x t e r n a l c a t a l y s t area i n contact with f l o w i n g l i q u i d i s obtained a s : C E

_r eo'app Λ (D ) , M eo

m

η

0Ε

LF T T

(apparent e f f e c t i v e d i f f u s i v i t y i n t r i c k l e - f l o w ) ( e f f e c t i v e d i f f u s i v i t y i n l i q u i d f i l l e d column) ^2)

where the d i f f u s i v i t i e s a r e e x t r a c t e d from the v a r i a n c e o f the impulse response. Tracer s t u d i e s a l s o give i n f o r m a t i o n on dynamic holdup (22).




432


34.

EL-fflSNAWI ET

AL.


433


w i t h an average e r r o r of -2.5% and standard d e v i a t i o n of the e r r o r of 8.7%. Both dynamic s a t u r a t i o n and l i q u i d - s o l i d c o n t a c t i n g e f f i c i e n c y are found to c o r r e l a t e w e l l w i t h l i q u i d mass v e l o c i t y , not to c o r r e l a t e w i t h Reynolds number alone, to i n c r e a s e w i t h i n c r e a s e d l i q u i d v e l o c i t y and t o decrease w i t h i n c r e a s e d p a r t i c l e diameter. Surface t e n s i o n f o r c e s do not seem to p l a y a r o l e i n t r i c k l e - f l o w regime but become important i n the high g a s - l i q u i d i n t e r a c t i o n (pulsing) regime. Equations (3) and (4) e s t a b l i s h a r e l a t i o n s h i p between c o n t a c t i n g e f f i c i e n c y and dynamic s a t u r a t i o n : 0.244 "CE

=

(5)

1 , 0 2

Discussion

of R e a c t i o n Studies i n a T r i c k l e - B e d

Reactor

R e a c t i o n s t u d i e s were performed i n the apparatus shown i n F i g u r e 5. Both 0.5% Pd and 2.5% Pd c a t a l y s t s were used i n cyclohexane and A.C.S. grade hexane s o l v e n t s . In F i g u r e 6 experimental r e s u l t s f o r c o n v e r s i o n as a f u n c t i o n of l i q u i d s u p e r f i c i a l v e l o c i t y are compared to the p r e d i c t i o n s of model Ml f o r the 0.5% Pd c a t a l y s t and cyclohexane s o l v e n t . Equa t i o n (4) i s used to p r e d i c t c o n t a c t i n g e f f i c i e n c y . The c o r r e l a t i o n of Dwivedi and Upadhyay (26) i s used to evaluate f l o w i n g l i q u i d to s o l i d mass t r a n s f e r c o e f f i c i e n t , k^s, and the c o r r e l a t i o n of Goto and Smith (24) i s used t o determine the g a s - l i q u i d v o l u m e t r i c mass t r a n s f e r c o e f f i c i e n t , (ka)g£. The B i o t number on the i n a c t i v e l y wetted s u r f a c e , B i - kgLS Vp/D ex, of 7 i s based on the assumed stagnant l i q u i d f i l m mean thxckness of 0.01 cm. F i g u r e 6 (curve 1) i l l u s t r a t e s that the a v a i l a b l e mass t r a n s f e r c o r r e l a t i o n s are inadequate i n p r e d i c t i n g the observed e x p e r i mental r e s u l t s . T h i s i s to be expected s i n c e these c o r r e l a t i o n s are based on data obtained i n absence of r e a c t i o n . I t i s known that t r a n s p o r t c o e f f i c i e n t s are enhanced by the presence of r e a c t i o n and t h i s has been shown i n t r i c k l e - b e d s a l s o (27). This n e c e s s i t a t e s i n t r o d u c t i o n of two enhancement f a c t o r s : E\ f o r the f l o w i n g l i q u i d - s o l i d mass t r a n s f e r c o e f f i c i e n t , k^s, and E2 f o r the v o l u m e t r i c g a s - l i q u i d mass t r a n s f e r c o e f f i c i e n t , ( k a ) j t . Comparison of experimental and p r e d i c t e d c o n v e r s i o n when the t r a n s p o r t c o e f f i c i e n t s as c a l c u l a t e d from the c o r r e l a t i o n s are m u l t i p l i e d by v a r i o u s assumed values of t h e i r r e s p e c t i v e enhance ment f a c t o r s i s a l s o shown i n F i g u r e 6. Agreement w i t h data seems only a c h i e v a b l e when both Εχ and E2 are l a r g e r than u n i t y . The b e s t f i t (minimizing the sum of the squares of the d e v i a t i o n s ) of the data i s obtained w i t h Εχ - 2.5, E2 - 5.7 and B i n =5.2 (dashed l i n e i n F i g u r e 6 ) . The s i m p l i f i e d lumped parameter model (M2) can a l s o be used to match the data of F i g u r e 6. T h i s suggests the f o l l o w i n g c o r r e l a t i o n s f o r the o v e r a l l mass t r a n s f e r c o e f f i c i e n t s i n presence of r e a c t i o n . s

D

e

g



434


U g (cm/sec) L

Figure 6. Predicted and experimental reactor conversions as a function of liquid superficial velocity. [Model Ml]—Bi = 5.2. Key: A, experimental results. D


34.

23.0

Sc

0 , 4 L

435


EL-HiSNAWi ET AL.

1.3

1^

(6)


(7)

Model p r e d i c t i o n s a r e now t e s t e d a g a i n s t experimental r e s u l t s f o r cyclohexane s o l v e n t and 2.5% Pd c a t a l y s t , hexane (A.C.S. grade) s o l v e n t and 0.5% Pd and 2.5% Pd c a t a l y s t . The r e s u l t s a r e presented i n F i g u r e s 7-9. The p r e d i c t i o n s o f model Ml a r e based on unchanged enhancement f a c t o r s f o r the l i q u i d s o l i d and g a s - s o l i d mass t r a n s f e r c o e f f i c i e n t s o f « 2.5 and E 2 = 5.7, r e s p e c t i v e l y . Both models match r e a c t o r performance w e l l i n the same s o l v e n t (cyclohexane) but on a d i f f e r e n t c a t a l y s t (Figure 7 ) . However, the simpler model (M2) p r e d i c t s r e a c t o r performance b e t t e r i n a d i f f e r e n t s o l v e n t (hexane) on both c a t a l y s t s (Figures 8-9). T h i s suggests that t r a n s p o r t c o e f f i c i e n t s k and kgLg obtained from equations (6) and (7) and used i n model M2 a r e l e s s a f f e c t e d by change i n r e a c t i o n r a t e s than the enhancement f a c t o r s Εχ and E 2 which a r e used with model Ml. The assumption that the f r a c t i o n (1-TICE) °f e x t e r n a l c a t a l y s t s u r f a c e i s dry, as used by some other i n v e s t i g a t o r s (11), r e s u l t s i n a very l a r g e B i p which cannot e x p l a i n o r even match the observed experimental r e s u l t s . Dryout o f a c a t a l y s t s u r f a c e appears p o s s i b l e only when much l a r g e r temperature gradients a r e present. On the other hand the assumption o f TlcE 1 everywhere leads to u n r e a l i s t i c dependence o f mass t r a n s f e r c o e f f i c i e n t s on l i q u i d v e l o c i t y . Matching the data w i t h a s i n g l e parameter model (an o v e r a l l mass t r a n s f e r c o e f f i c i e n t ) r e s u l t s i n too high an e f f e c t o f v e l o c i t y on such a parameter and i n the l o s s o f model predictive a b i l i t y for d i f f e r e n t solvents. s

=

Conclusions Dynamic t r a c e r t e s t s can be used t o determine dynamic holdup and c a t a l y s t c o n t a c t i n g which i n t r i c k l e - f l o w regime can be c o r r e l a t e d w i t h Reynolds and G a l l i l e o number. A simple r e a c t o r model f o r gas l i m i t i n g r e a c t a n t when matched t o experimental r e s u l t s f o r one s o l v e n t and one c a t a l y s t a c t i v i t y p r e d i c t s r e a c t o r performance w e l l f o r d i f f e r e n t c a t a l y s t a c t i v i t i e s and i n other s o l v e n t s over a wide range o f l i q u i d v e l o c i t i e s .




436


EL-msNAWi

ET AL.



34.


437

438



Figure 9.

Reactor conversion as junction of liquid superficial velocity (hexane solvent). Bi = 8.6. Key is the same as in Figure 8. D


34.

EL-HiSNAWi ET A L .

439


Legend o f Symbols a Bi

D

- i n t e r f a c i a l area (see s u b s c r i p t s f o r meaning) - B i o t number on i n a c t i v e l y wetted or dry c a t a l y s t k

< gLS V /De p

S

e x

)

5 i ^ - B i o t number on a c t i v e l y wetted c a t a l y s t ( k

v

s

o

r

k

V

D

LS p/°e e x s p / e S x) S reactant c o n c e n t r a t i o n i n l i q u i d l i q u i d reactant c o n c e n t r a t i o n d i f f u s i v i t y o f gaseous reactant i n the l i q u i d phase e f f e c t i v e d i f f u s i v i t y o f gaseous reactant i n the c a t a l y s t pellet - e f f e c t i v e mean p a r t i c l e diameter (6 V p / S ) - G a l l i l e o number ( d 3 g P L / U L ) - dynamic l i q u i d holdup - s t a t i c e x t e r n a l l i q u i d holdup - adsorption e q u i l i b r i u m constant - r a t e constant per u n i t c a t a l y s t volume - mass t r a n s f e r c o e f f i c i e n t ( i s i n g l e o r m u l t i p l e s u b s c r i p t ) - t o t a l r e a c t o r length - Reynolds number (dp u g Ρχ/μΐ.) - Schmidt number ( U I / P L D ) - e x t e r n a l area of c a t a l y s t p a r t i c l e - liquid superficial velocity - p a r t i c l e volume - volume o f the a c t i v e c a t a l y s t l a y e r - l i q u i d reactant conversion - a x i a l coordinate - bed p o r o s i t y - c a t a l y s t e f f e c t i v e n e s s f a c t o r (completely wetted p e l l e t ) - t o t a l contacting e f f i c i e n c y " external contacting e f f i c i e n c y - parameter (eq. T9) - f i r s t mement o f the impulse response - liquid viscosity - l i q u i d density - p e l l e t modulus ( V / S ) A / D - a c t i v e s h e l l modulus ( V / S A /D - dynamic s a t u r a t i o n (%/eg) - gas reactant A - adsorbing t r a c e r - apparent value - at gas-liquid equilibrium - gas-liquid - l i q u i d - i n a c t i v e l y wetted s o l i d - liquid - liquid filled - l i q u i d a c t i v e l y wetted s o l i d - nonadsorbing t r a c e r - l i q u i d feed c o n d i t i o n s - o v e r a l l (gas-active l i q u i d - s o l i d ) - two phase flow - l i q u i d r e a c t a n t (a-methylstyrene) e

CA C Downloaded by UCSF LIB CKM RSCS MGMT on September 1, 2014 | http://pubs.acs.org Publication Date: September 16, 1982 | doi: 10.1021/bk-1982-0196.ch034

a

D

E

dp GaL % Hgg k ki L Re^ v

SCL

S ugL Vp V X(X ζ ε η T)Q ^CE λ μ y PL φ φ cop A a app e g£ gLS L LF LS na ο s TF α e x

s

Β

L

3

" -

A

S

ex

2

2

p

L

A

p

V

e x

s

E

e x

V

E


440



Acknowledgements Support o f the Chemical Reaction E n g i n e e r i n g Laboratory i n which t h i s work was performed by Amoco O i l , Monsanto Company and S h e l l Development i s t r u l y a p p r e c i a t e d .

Literature Cited 1. Germain, Α . ; L'Homme, G. Α . ; Lefebvre, Α. "Chemical Engineering of Gas-Liquid-Solid Catalytic Reactions"; L'Homme, G. Α . , E d . ; Cebedoc, Liege, 1978, ρ 265. 2. Satterfield, C. Ν. AIChE J. 1975, 21, 209. 3. Goto, S.; Levec, J.; Smith, J. M. Cat. Rev.-Sci. Eng. 1977, 15, 187. 4. M i l l s , P. L.; Duduković, M. P. Chem. Eng. S c i . 1980, 35, 2267. 5. Gianetto, Α . ; Baldi, G . ; Specchia, V . ; Sicardi, S. AIChE J. 1978, 24(6), 1087. 6. Germain, Α . ; Lefebvre, Α . ; L'Homme, G. A. Adv. Chem. 1974, 133, 164. 7. Sedricks, W.; Kenney, C. N. Chem. Eng. S c i . 1973, 38, 559. 8. Goto, S.; Smith, J. M. AIChE J. 1975, 21, 714. 9. Levec, J.; Smith, J. M. AIChE J. 1976, 22, 159. 10. Satterfield, C. N . ; Ozel, F. AIChE J. 1973, 19, 1259. 11. Herskowitz, M . ; Carbonell, R. G . ; Smith, J. M. AIChE J. 1979, 25, 272. 12. Koros, R. M. Proc 4th Int. Symp. React. Eng. Dechema, Heidelberg, 1976, V o l . 1, ρ Ι Χ - 3 7 2 . 13. Germain, Α . ; Crine, M . ; Marchot, P . ; L'Homme, G. A. ACS Symp. Ser. 1978, V o l . 65, ρ 411. 14. Turek, F.; Lange, R. Chem. Eng. S c i . 1981, 36, 569. 15. Ma, Y. H. D.Sc. Thesis, MIT, 1966. 16. White, D. E.; Litt, M . ; Heymuch, G. J. I&EC Fundamentals 1974, 13, 143. 17. Jawad, A. Ph.D. Thesis, Univ. Birmingham, England, 1974. 18. El-Hisnawi, A. A. D.Sc. Thesis, Washington University, St. Louis, 1981. 19. Schwartz, J. G . ; Weger, E.; Duduković, M. P. AIChE J. 1976, 22, 953. 20. M i l l s , P. L . D.Sc. Thesis, Washington Univ. St. Louis, 1980. 21. Colombo, A. J.; Baldi, G . ; Sicardi, S. Chem. Eng. S c i . 1976, 31, 1101. 22. M i l l s , P. L.; Duduković, M. P. AIChE J. 1981, 27, 893. 23. M i l l s , P. L.; Duduković, M. P. 2nd World Congress on Chem. Eng. Montreal, October 1981, V o l . 3, ρ 143. 24. Goto, S.; Smith, J. M. AIChE J. 1975, 21, 706. 25. Charpentier, J. C. "Chemical Engineering of Gas-Liquid-Solid Catalyst Reactions"; L'Homme, G. Α . , E d . ; Cebedoc, Liege, 1979; ρ 78. 26. Dwivedi, P. Ν . ; Uphadhyay, S. Ν. I&EC Process Des. Develop. 1977, 16, 157. 27. Baldi, G . ; Sicardi, S. Chem. Eng. S c i . 1975, 30, 617. Received April 27, 1982.


Trickle-Bed Reactors: Dynamic Tracer Tests, Reaction Studies, and

Recommend Documents