Chemical Reaction Engineering Reviews

3 Contacting Effectiveness in Trickle Bed Reactors

Downloaded by UNIV QUEENSLAND on June 17, 2013 | http://pubs.acs.org Publication Date: June 1, 1975 | doi: 10.1021/ba-1975-0148.ch003

CHARLES

N.

SATTERFIELD

Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Mass. 02139

The

use of trickle

reviewed,

typical

laboratory

and

version

liquid

plug

Models

be based models

pilot

in a trickle

for an ideal rates.

bed

residence

in industrial

conditions

plant

studies

flow reactor

catalyst

time distribution,

are analyzed

critically

limitations

highest

Con-

liquid

performance

wetting

reactant

flow may

characteristics,

or axial dispersion;

and compared.

when

is

recent

comes closest to that

at the

in the vapor phase are considered

/

are summarized.

and to predict

holdup,

processing

are cited, and

bed reactor usually

to explain

on liquid

of transport

reactors

operating

Some

is present

these effects

partially

briefly.

T p h e c e n t r a l p r o b l e m i n d e s i g n , scale-up, a n d u n d e r s t a n d i n g o f t h e A

o p e r a t i o n of t r i c k l e b e d reactors is d e t e r m i n i n g t h e effectiveness

with

w h i c h t h e r e a c t i n g l i q u i d is b r o u g h t i n t o contact w i t h t h e s o l i d catalyst. T h e l i q u i d a n d gas f l o w rates u s e d b y t h e laboratories, p i l o t p l a n t s , a n d c o m m e r c i a l operations v a r y greatly, a n d t h e w i d e r a n g e i n l i q u i d

flow

rate i n p a r t i c u l a r is a p r i m a r y cause of t h e v a r i a t i o n i n b e h a v i o r w i t h scale of o p e r a t i o n . A b r i e f r e v i e w of i n d u s t r i a l p r a c t i c e s a n d t h e reasons therefore sets t h e stage f o r c o n s i d e r a t i o n of t h e effect o f l i q u i d flow rate o n p e r f o r m a n c e a n d f o r c h a r a c t e r i z a t i o n of t h e effectiveness

o f catalyst

c o n t a c t i n g i n a t r i c k l e b e d reactor. Industrial Petroleum Refining. reactor

"Processing T h e t e r m t r i c k l e b e d as u s e d here means a

in which a liquid

phase

a n d a gas p h a s e

flow

cocurrently

d o w n w a r d t h r o u g h a fixed b e d of catalyst p a r t i c l e s w h i l e r e a c t i o n takes p l a c e . T h e s e reactors h a v e b e e n u s e d t o a m o d e r a t e extent i n c h e m i c a l 50 In Chemical Reaction Engineering Reviews; Hulburt, H.; Advances in Chemistry; American Chemical Society: Washington, DC, 1975.

3.

SATTERFIELD

Trickle

Bed

Reactors

51

p r o c e s s i n g , b u t most of the p u b l i s h e d i n f o r m a t i o n a b o u t t h e i r i n d u s t r i a l applications

concerns p e t r o l e u m

processing,

i n p a r t i c u l a r the

hydro-

d e s u l f u r i z a t i o n or h y d r o c r a c k i n g of h e a v y or r e s i d u a l o i l stocks a n d the h y d r o f i n i s h i n g or h y d r o t r e a t i n g of

l u b r i c a t i n g oils.

A c c o r d i n g to

D e e m t e r ( J ) , a t r i c k l e b e d h y d r o d e s u l f u r i z a t i o n process w a s by Vlugter, Hoog,

a n d their co-workers

A m s t e r d a m after W o r l d W a r

van

developed

at t h e S h e l l L a b o r a t o r i e s i n

I I , a n d the

first

commercial

unit

was

b r o u g h t o n stream i n 1955. T h e S h e l l process w a s d e s c r i b e d f u r t h e r b y L e N o b e l and Choufoer

(2).

Similar developments

less s i m u l t a n e o u s l y at other p e t r o l e u m companies. Downloaded by UNIV QUEENSLAND on June 17, 2013 | http://pubs.acs.org Publication Date: June 1, 1975 | doi: 10.1021/ba-1975-0148.ch003

mixed-phase

d e s u l f u r i z e r reactors that w e r e

occurred

Lister (3)

developed

more

or

described

b y the

British

P e t r o l e u m C o . a n d p u t i n t o o p e r a t i o n d u r i n g the 1950's; h e g a v e c o n siderable detail about

various e n g i n e e r i n g

design problems

and

how

t h e y w e r e o v e r c o m e . I n the P r o c e e d i n g s of the v a r i o u s W o r l d P e t r o l e u m Congresses and

w e r e p u b l i s h e d g e n e r a l descriptions

h y d r o d e s u l f u r i z a t i o n processes d e v e l o p e d

U n i o n O i l , a n d other

of the

hydrocracking

b y Chevron, Esso, Gulf,

companies.

T r i c k l e bed processing

is less costly t h a n c o m p l e t e l y

vapor-phase

o p e r a t i o n since less heat is r e q u i r e d for feedstock v a p o r i z a t i o n a n d less gas m u s t be r e c y c l e d a n d h e a t e d to r e a c t i o n t e m p e r a t u r e . trickle bed residual

operation

oils

that

allows t h e p r o c e s s i n g

cannot

react

as

vapors.

of

heavy

Moreover,

distillates a n d

Hydrocracking

processes

are u s u a l l y p r e c e d e d b y a h y d r o d e s u l f u r i z a t i o n r e a c t i o n t h a t reduces t h e content of o r g a n o s u l f u r a n d o r g a n o n i t r o g e n

c o m p o u n d s to a suffi-

c i e n t l y l o w l e v e l so that they c a n be t o l e r a t e d b y t h e h y d r o c r a c k i n g catalyst. I n these processes, as i n l u b r i c a t i n g o i l treatment, t h e r e a c t i o n is b e t w e e n h y d r o g e n a n d a p e t r o l e u m stock, a n d h i g h h y d r o g e n pressures are u s e d i n order to o b t a i n l o n g catalyst l i f e . T h e l u b r i c a t i n g o i l processing

m a y be a s o - c a l l e d h y d r o f i n i s h i n g t h a t r e m o v e s p r i m a r i l y o r g a n i c

sulfur a n d n i t r o g e n c o m p o u n d s a n d i m p r o v e s

c o l o r w i t h little h y d r o -

génation of the p e t r o l e u m feedstock, or i t m a y b e a m o r e severe h y d r o t r e a t m e n t w h i c h causes not o n l y s u l f u r a n d n i t r o g e n r e m o v a l b u t also r i n g hydrogénation a n d subsequent

h y d r o c r a c k i n g of one

or m o r e

of

the s a t u r a t e d rings ( h a v i n g started w i t h a m u l t i p l e - r i n g a r o m a t i c

feed-

stock)

In

some

the

fluid

systems,

to p r o d u c e l u b r i c a t i n g oils of e.g.

h i g h viscosity

some h y d r o d e s u l f u r i z a t i o n reactions,

index.

much

of

present m a y be near or a b o v e t h e c r i t i c a l p o i n t a n d phase b e h a v i o r is uncertain. An

alternate a n d closely r e l a t e d f o r m of

g a s - l i q u i d upflow. processing

of

c o n t a c t i n g is

cocurrent

It a p p a r e n t l y has not b e e n u s e d i n d u s t r i a l l y f o r the

petroleum

fractions, b u t i t has b e e n a p p l i e d i n some

c h e m i c a l operations.

In Chemical Reaction Engineering Reviews; Hulburt, H.; Advances in Chemistry; American Chemical Society: Washington, DC, 1975.

52

CHEMICAL REACTION ENGINEERING

REVIEWS

Chemical and Petrochemical Processing. T r i c k l e b e d reactors h a v e also b e e n u s e d o n a s u b s t a n t i a l scale for c h e m i c a l a n d p e t r o c h e m i c a l processing,

b u t i n f o r m a t i o n is f r a g m e n t a r y .

synthesis of l i q u i d fuels f r o m m i x t u r e s of H

2

I n the F i s c h e r - T r o p s c h a n d C O , v a r i o u s means of

r e m o v i n g the s u b s t a n t i a l heat of r e a c t i o n h a v e b e e n

tried including

r e c y c l e of i n e r t hot o i l t h r o u g h the reactor b e d as w e l l as the use of hot-gas r e c y c l e a n d s l u r r y - t y p e reactors. son (4)

Storch, G o l u m b i c , a n d A n d e r -

t r e a t e d i n d e t a i l t h e c h e m i s t r y a n d t e c h n o l o g y of t h e F i s c h e r -

T r o p s c h synthesis as i t w a s d e v e l o p e d i n G e r m a n y b e f o r e a n d d u r i n g W o r l d W a r I I , together w i t h c o n t r i b u t i o n s f r o m other sources. Downloaded by UNIV QUEENSLAND on June 17, 2013 | http://pubs.acs.org Publication Date: June 1, 1975 | doi: 10.1021/ba-1975-0148.ch003

h o t - o i l r e c y c l e v e r s i o n of this process w a s d e v e l o p e d D u f t s c h m i d a n d co-workers

The

i n the 1930s b y

at I. G . F a r b e n i n d u s t r i e ; t h e y r e l i e d o n

e v a p o r a t i v e c o o l i n g of the hot o i l to r e m o v e a p o r t i o n of the h e a t b y u t i l i z i n g c o c u r r e n t u p f l o w t h r o u g h t h e catalyst b e d .

A later v e r s i o n of

t h e U n i t e d States B u r e a u of M i n e s also o p e r a t e d b y c o c u r r e n t u p f l o w b u t w i t h l i t t l e or no e v a p o r a t i v e c o o l i n g , a n d i t w a s r e g a r d e d as p r o b a b l y m o r e efficient. It w a s r e p o r t e d that this f o r m of c o n t a c t i n g gives better temperature control than trickle-type operation, but the upflow version w a s s h o r t l y thereafter s u p e r s e d e d b y a n e b u l l i a t i n g b e d reactor b e c a u s e of difficulties w i t h catalyst c e m e n t a t i o n i n the fixed b e d .

T h e industrial

scale F i s c h e r - T r o p s c h processes u s e d i n G e r m a n y a n d elsewhere a l l i n v o l v e d c o m p l e t e l y v a p o r - p h a s e o p e r a t i o n , b u t the o i l - r e c y c l e process w a s s t u d i e d i n G e r m a n y i n converters as l a r g e as 50 f t

3

and by

the

U n i t e d States B u r e a u of M i n e s i n a 5 0 - b b l / d a y c a p a c i t y p l a n t ( 5 , 6, 7 ) . A process for synthesis of b u t y n e d i o l ( H O C H C = = C C H O H ) f r o m 2

2

aqueous f o r m a l d e h y d e a n d acetylene uses t r i c k l e b e d flow over a c o p p e r a c e t y l i d e catalyst a n d r e c y c l e of the p r o d u c t s t r e a m for heat r e m o v a l . O n e i n d u s t r i a l reactor was r e p o r t e d to b e 58.5 ft h i g h a n d 4.9 ft i n d i a m e t e r ( 8 ). O t h e r t r i c k l e b e d studies of this r e a c t i o n are g i v e n b y B i l l , a reported by B o n d i (9). K r o n i g ( J O ) d e s c r i b e d a t r i c k l e b e d process t h a t is u s e d i n one or m o r e c o m m e r c i a l plants for selective hydrogénation of acetylene i n o r d e r to r e m o v e i t i n the presence of b u t a d i e n e i n C O p e r a t i o n at 1 0 - 2 0 ° C a n d 2 - 6

kg/cm

2

4

h y d r o c a r b o n streams.

pressure a l l o w s l i q u i d - p h a s e

p r o c e s s i n g w h i c h r e p o r t e d l y gives l o n g catalyst l i f e , u n l i k e

gas-phase

p r o c e s s i n g i n w h i c h p o l y m e r s r a p i d l y b u i l d u p o n the catalyst. A p a t e n t b y P o r t e r (11)

describes some i n t e r e s t i n g o p e r a t i n g aspects

of a t r i c k l e b e d catalyst h y d r o g e n a t o r u s e d to convert a n a l k y l a n t h r a q u i n o n e to the h y d r o q u i n o n e f o r m , w h i c h is one step i n a c y c l i c process for manufacturing hydrogen peroxide.

( U p o n subsequent contact w i t h

o x y g e n , t h e h y d r o q u i n o n e y i e l d s the q u i n o n e p l u s h y d r o g e n

peroxide,

a n d the q u i n o n e is t h e n r e c y c l e d . )


3.

SATTERFIELD

Trickle

Bed

53

Reactors

Recent Experimental Studies.

I n v i e w of t h e w i d e s p r e a d use

of

t r i c k l e b e d reactors o n a v e r y l a r g e scale i n the p e t r o l e u m i n d u s t r y , it is s u r p r i s i n g t h a t so l i t t l e w a s p u b l i s h e d a b o u t the d e v e l o p m e n t , and

o p e r a t i o n of this t y p e of reactor.

design,

A u s e f u l g e n e r a l r e v i e w of

l i q u i d - p a r t i c l e operations b y 0 s t e r g a a r d (12)

gas-

cites the l i t e r a t u r e u p to

a b o u t 1965-1966 o n c o n t a c t i n g b e t w e e n a gas a n d a l i q u i d i n fixed beds. U n f o r t u n a t e l y for present purposes, most of this l i t e r a t u r e is m o r e r e l e v a n t to a b s o r p t i o n systems t h a n to c h e m i c a l reactors. l a b o r a t o r y scale

studies of

reactors w e r e r e p o r t e d (see

specific

A small number

c h e m i c a l reactions

T a b l e I w h i c h also i n c l u d e s a recent, r e p r e -

sentative, l a b o r a t o r y scale, p e t r o l e u m p r o c e s s i n g s t u d y ) . Downloaded by UNIV QUEENSLAND on June 17, 2013 | http://pubs.acs.org Publication Date: June 1, 1975 | doi: 10.1021/ba-1975-0148.ch003

of

in trickle-bed A number

of

other l a b o r a t o r y or p i l o t p l a n t scale studies of p e t r o l e u m r e f i n i n g r e a c tions w e r e d e s c r i b e d b y H e n r y a n d G i l b e r t (23), w h i c h are s u m m a r i z e d i n T a b l e I I .

the most p e r t i n e n t of

I n some t r i c k l e b e d

studies

of

c h e m i c a l reactions, a t t e n t i o n w a s d i r e c t e d p r i m a r i l y to c a t a l y t i c b e h a v i o r or c h e m i c a l k i n e t i c s , a n d these investigations h a v e b e e n o m i t t e d unless some p o r t i o n of t h e w o r k focussed o n p h y s i c a l effects. Comparison with Slurry Reactors. fixed

b e d w i t h two-phase

flow,

T h e p r i n c i p a l a l t e r n a t i v e to a

either u p w a r d or d o w n w a r d , is a s l u r r y

reactor or e b u l l i a t i n g b e d i n w h i c h t h e catalyst p a r t i c l e s , w h i c h m u s t b e s u b s t a n t i a l l y s m a l l e r , are i n m o t i o n .

T h e s e are also sometimes

termed

three-phase fluidized b e d reactors or s u s p e n d e d b e d reactors. T h e s e h a v e the following advantages: temperature control, ( b )

(a)

a h i g h heat c a p a c i t y to p r o v i d e

good

a p o t e n t i a l l y h i g h r a t e of r e a c t i o n p e r u n i t

v o l u m e of reactor i f the catalyst is h i g h l y a c t i v e , ( c ) easy h e a t r e c o v e r y , (d)

a d a p a b i l i t y to either b a t c h or flow p r o c e s s i n g , ( e )

a catalyst that

is r e a d i l y r e m o v e d a n d r e p l a c e d i f its w o r k i n g l i f e is r e l a t i v e l y short, and

(f)

p o s s i b l e o p e r a t i o n at catalyst effectiveness

factors

approaching

u n i t y w h i c h is of s p e c i a l i m p o r t a n c e i f d i f f u s i o n l i m i t a t i o n s cause r a p i d catalyst d e g r a d a t i o n or p o o r e r selectivity. follows:

(a)

T h e i r disadvantages

are as

the residence t i m e d i s t r i b u t i o n patterns are close to those

of a C S T R w h i c h makes i t difficult to o b t a i n h i g h degrees of c o n v e r s i o n except b y s t a g i n g ; ( b )

catalyst r e m o v a l b y

filtration

m a y pose p r o b l e m s

w i t h possible p l u g g i n g difficulties w i t h filters ( a n d the costs of

filtering

systems m a y b e a s u b s t a n t i a l p o r t i o n of the c a p i t a l i n v e s t m e n t ) ; a n d ( c ) t h e h i g h r a t i o of l i q u i d to s o l i d i n a s l u r r y reactor a l l o w s h o m o g e n e ous side reactions to b e c o m e m o r e i m p o r t a n t , i f a n y are possible. I n the t r i c k l e b e d reactor, the catalyst b e d is fixed, the flow p a t t e r n is m u c h closer to p l u g flow, a n d the r a t i o of l i q u i d to s o l i d present is m u c h smaller. I f heat effects are s u b s t a n t i a l , t h e y c a n b e c o n t r o l l e d b y r e c y c l e of t h e l i q u i d p r o d u c t s t r e a m a l t h o u g h this m a y n o t b e p r a c t i c a l if a v e r y h i g h p e r c e n t c o n v e r s i o n is d e s i r e d ( as i n h y d r o d e s u l f u r i z a t i o n ) or i f the p r o d u c t is n o t r e l a t i v e l y stable u n d e r r e a c t i o n c o n d i t i o n s .


The

54

CHEMICAL REACTION

ENGINEERING

Table I.

Reaction

Recent

Reference

O x i d a t i o n of S 0 on w e t t e d C Hydrogénation of c r o t o n a l d e h y d e I s o m e r i z a t i o n of c y c l o p r o p a n e Hydrogénation of « - C H styrene Hydrogénation of benzene Hydrogénation of « - C H styrene Hydrotreating 2

3

3


REVIEWS

H a r t m a n & C o u g h l i n (13) K e n n e y & S e d r i c k s (14,15) Way (16,17) Pelossof {18,19) S a t t e r f i e l d & O z e l (20) G e r m a i n , et al. {21) M e a r s (22) * b

d

F o r ρ = 1.0, 1 k g / m sec = 0.1 cm/se c. Flow over a vertical string of spheres, L calculated for a bed of spheres touching in a square pattern. e

2

6

Table II.

Pertinent Laboratory Scale Petroleum

Reaction

Reference

H y d r o c r a c k i n g of a h e a v y gas o i l H y d r o d e n i t r o g e n a t i o n of v a r i o u s compounds and of a c a t a l y t i c a l l y c r a c k e d l i g h t furnace o i l H y d r o d e n i t r o g e n a t i o n of a lube o i l d i s t i l l a t e

H e n r y & G i l b e r t (23) F l i n n , et al. (24)

Hydrogénation of a r o m a t i c s i n a n a p h t h e n i c lube o i l d i s t i l l a t e

Henry & Gilbert

a

Gilbert & Kartzmark

°There are no data points in original reference; recorded.

(25)

(23)

highest flow rates were not

m o s t c o m m o n t y p e of t r i c k l e b e d p r o c e s s i n g is hydrogénation, a n d most of the subsequent d i s c u s s i o n refers to this t y p e of r e a c t i o n . T h e other r e a c t a n t m a y be essentially a l l i n t h e l i q u i d p h a s e or i n b o t h the l i q u i d and

t h e gas phases, a n d the d i s t r i b u t i o n of reactant a n d p r o d u c t s

t w e e n gas a n d l i q u i d phases m a y v a r y w i t h d e g r e e of c o n v e r s i o n .

beIn a

f e w c i r c u m s t a n c e s , as i n some versions of the F i s c h e r - T r o p s c h process, the l i q u i d is i n e r t a n d serves as a heat-transfer m e d i u m , a n d the r e a c t i o n occurs b e t w e e n reactants i n s o l u t i o n a n d the catalyst. Industrial Operating Conditions. T r i c k l e b e d reactors i n the p e t r o l e u m i n d u s t r y m a y b e o p e r a t e d u n d e r a w i d e v a r i e t y of c o n d i t i o n s t h a t d e p e n d o n t h e properties of the feedstock a n d the n a t u r e of the r e a c t i o n . T h e less r e a c t i v e fractions, w h i c h t e n d to b e i n the h i g h e r b o i l i n g r a n g e and

m o r e viscous at a m b i e n t temperatures, are t y p i c a l l y processed

at

the l o w e r l i q u i d flow rates. R e p r e s e n t a t i v e s u p e r f i c i a l l i q u i d velocities, L , are 1 0 - 1 0 0 f t / h r ( 0 . 8 3 - 8 . 3 k g / m

2

sec for a d e n s i t y of 1) f o r l u b r i c a t -

i n g oils, h e a v y gas oils, a n d r e s i d u a l fractions a n d 1 0 0 - 3 0 0 f t / h r ( 8 . 3 - 2 5


3.

SATTERFIELD

Trickle

Bed

Reactors

55

Laboratory Scale Studies Superficial Flow kg/m

Liquid Rate; sec

2

Gas Flow Rate kg X V J m sec 3

2


0.0043-0.06 0.038 0.26-2.1 1.4-8.7 0.9-3.0 0.08-1.6 0.19-0.76 c

15.4 0.47 3-28

- 0.04^8

28° 0.14-3.3 1.6-7.2

16-55 2-8

G for H plus benzene vapor. Countercurrent flow. A t 100 atm pressure; all other studies at 1 atm. 2

d e

Refining Studies Cited by H e n r y and Gilbert (23) L , kg/m

2

sec

Conversion,

0.07-0.5 lowest : 0.07 l o w e s t : ' 0.035

61-20 9 9 . 8 % [furnace o i l reacted at 371 ° C ( 7 0 0 ° F ) ] 8 0 % [ q u i n o l i n e reacted at 3 1 6 ° C ( 6 0 0 ° F ) ]

a

0.025-0.14 0.025-0.06 0.03-0.25

9 7 - 7 0 % (low t e m p e r a t u r e reaction) 9 8 . 5 - 9 5 % (high t e m p e r a t u r e reaction) 8 0 - 3 0 % (low pressure) 9 5 - 4 0 % (high pressure)

6 6

b

b

%

Taking reactor height as 3 ft; true height was not published.

kg/m

2

sec) for n a p h t h a fractions w h e n c a l c u l a t e d w i t h the a s s u m p t i o n

that the f e e d is e n t i r e l y i n t h e l i q u i d phase.

F o r l i g h t e r fractions, this

is not g e n e r a l l y the case, a n d m u c h of the f e e d is a c t u a l l y present as vapor. T h e hydrogen terms of v o l u m e of H

2

flow-to-liquid

flow

r a t i o is c o m m o n l y expressed i n

[expressed i n s t a n d a r d c u b i c feet (scf ) at s t a n d a r d

t e m p e r a t u r e a n d pressure ( S T P ) ] p e r b a r r e l of f e e d p r o c e s s e d The

(scf/bbl).

s u p e r f i c i a l gas flow rate, G , becomes a b o u t (L) ( s c f / b b l ) G = 5.6 n

w h e r e L is l i k e w i s e i n c m / s e c .

/ cm/sec

R e p r e s e n t a t i v e values are

2000-3000

s c f / b b l for h y d r o d e s u l f u r i z a t i o n of a h e a v y gas o i l , 5000 s c f / b b l

for

h y d r o d e s u l f u r i z a t i o n of a h e a v y r e s i d u e , a n d 5000-10,000 s c f / b b l for a hydrocracker.

F o r m i l d h y d r o g e n t r e a t m e n t , h y d r o f i n i s h i n g , the h y d r o -

gen-to-feedstock

ratios m a y b e c o n s i d e r a b l y s m a l l e r .


56

C H E M I C A L REACTION ENGINEERING REVIEWS

L i s t e r ( 3 ) s u m m a r i z e d the characteristics of seven B r i t i s h P e t r o l e u m C o . d e s u l f u r i z e r s that w e r e d e s i g n e d b e t w e e n 1952 a n d 1962. O p e r a t i n g c o n d i t i o n s r a n g e as f o l l o w s :

l i q u i d h o u r l y space v e l o c i t y

(volume

of

l i q u i d f e d e a c h h o u r p e r v o l u m e of r e a c t o r ) , L H S V , 1.4-8.0 h r " ; oper1

a t i n g t e m p e r a t u r e , 6 9 0 ° - 7 9 0 ° F ( 3 6 5 ° - 4 2 0 ° C ) ; pressure, 50O-1000 p s i g ; r e c y c l e r a t e , 1000-4000 s c f / b b l ; a n d s i n g l e catalyst b e d d e p t h , 8 - 2 1 ft. O n e reactor consisted of t h r e e beds, e a c h 10 ft 10 i n . d e e p ; a s e c o n d u n i t consisted of three i d e n t i c a l reactors

i n series, e a c h

8 ft 9 i n . deep.

R e a c t o r d i a m e t e r s r a n g e d f r o m 4 to 7 ft. Present d a y units m a y be considerably larger, a n d m u l t i p l e - b e d Downloaded by UNIV QUEENSLAND on June 17, 2013 | http://pubs.acs.org Publication Date: June 1, 1975 | doi: 10.1021/ba-1975-0148.ch003

reactors

are f r e q u e n t l y

used.

The

q u a n t i t y of

catalyst is t y p i c a l l y

d i v i d e d i n t o one to five beds, e a c h 1 0 - 2 0 ft d e e p ; i n m u l t i p l e - b e d reactors, h y d r o g e n is i n j e c t e d b e t w e e n the beds for t e m p e r a t u r e c o n t r o l — s o - c a l l e d c o l d shot c o o l i n g .

I n m u l t i p l e - b e d reactors, the catalyst beds m a y

be

e q u a l i n d e p t h . M o r e c o m m o n l y , t h e y increase i n d e p t h as t h e r e a c t i o n p r o c e e d s , a n d the q u a n t i t y of h y d r o g e n i n j e c t e d at e a c h p o i n t is a d j u s t e d i n order to a c h i e v e the d e s i r e d a x i a l t e m p e r a t u r e profile w h i c h is s p e c i fied so as to l i m i t the a d i a b a t i c t e m p e r a t u r e rise a l o n g e a c h b e d to s o m e maximum

[ t y p i c a l l y ~ 2 8 ° C ( 5 0 ° F ) or l e s s ] .

thus increases w i t h

flow

T h e gas-to-liquid ratio

t h r o u g h successive b e d s , a n d the a m o u n t

gas i n j e c t e d for c o o l i n g c a n r e a d i l y e x c e e d t h a t f u r n i s h e d i n i t i a l l y . q u a n t i t y of H

2

f u r n i s h e d u s u a l l y far exceeds t h a t n e e d e d

of The

for s t o i c h i o -

m e t r i c r e a c t i o n , a n d i t is u s u a l l y d e t e r m i n e d p r i m a r i l y b y t h e r e q u i r e ments for t e m p e r a t u r e c o n t r o l a n d p e r h a p s sometimes to h e l p better l i q u i d h e i g h t of

d i s t r i b u t i o n or to p r o l o n g

a single catalyst b e d

catalyst life.

The

achieve

maximum

is d e t e r m i n e d b y t h e i m p o r t a n c e

of

a c h i e v i n g r e d i s t r i b u t i o n of l i q u i d a n d gas after some l i m i t i n g b e d d e p t h is t r a v e r s e d or b y the c r u s h i n g strength of the catalyst. I n present p r a c t i c e , this m a x i m u m seems to b e a b o u t 2 0 - 2 5 ft. R e p r e s e n t a t i v e o p e r a t i n g c o n d i t i o n s for p e t r o l e u m r e f i n i n g processes are t y p i c a l l y t o t a l pressures of 5 0 0 - 1 5 0 0

psi (substantially higher i n a

f e w cases) a n d t e m p e r a t u r e s of 3 4 5 ° - 4 2 5 ° C

(650°-800°F).

Catalyst

p a r t i c l e s are t y p i c a l l y 1 / 8 - 1 / 3 2 i n . ( 0 . 3 2 - 0 . 0 8 c m ) i n d i a m e t e r . O f c o n s i d e r a b l e i m p o r t a n c e i n a n a l y z i n g d a t a o n t r i c k l e b e d reactors is t h e fact t h a t i n p i l o t p l a n t s the 2 - 6 - f t h i g h reactors diameter)

(1-1.5 in. in

are t y p i c a l l y o p e r a t e d at a b o u t the same L H S V

as is u s e d

c o m m e r c i a l l y . F o r a specified v a l u e of L H S V , the t r u e 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 is thus p r o p o r t i o n a l to r e a c t o r

length.

A

large

commercial

r e a c t o r of r e c e n t d e s i g n m a y h a v e as m u c h as 6 0 - 8 0 ft t o t a l d e p t h of catalyst; d a t a f o r this scale-up m a y h a v e b e e n o b t a i n e d i n a p i l o t u n i t at the same L H S V b u t therefore at 1 / 1 0 - 1 / 1 5 of the s u p e r f i c i a l l i q u i d

flow

rate a n d at a c o r r e s p o n d i n g l y l o w e r gas rate. S i n c e the p i l o t u n i t a n d the

commercial

unit may

operate

under

somewhat

different


hydro-

3.

SATTERFIELD

Trickle

57

Bed Reactors

d y n a m i c flow c o n d i t i o n s , t h e i r c o n t a c t i n g efficiencies m a y b e s i g n i f i c a n t l y different.

I n most reports o f l a b o r a t o r y studies o f a n y t y p e o f r e a c t i o n ,

the l i q u i d a n d gas flow rates w e r e m u c h l o w e r t h a n those u s e d

com-

m e r c i a l l y (see T a b l e s I , I I , a n d I I I ) . S o m e o f t h e r e c e n t l y r e p o r t e d l a b o r a t o r y scale studies i n v o l v e d r a p i d e x o t h e r m i c reactions at l o w l i q u i d flow rates; c o n s e q u e n t l y , heat effects w e r e e s p e c i a l l y significant. C a t a l y s t pellets w e r e o n l y p a r t i a l l y w e t t e d , a n d reactants w e r e r e l a t i v e l y v o l a t i l e so that r e a c t i o n o c c u r r e d i n b o t h l i q u i d a n d v a p o r phases (see

below).

T h e b e h a v i o r o f these systems m a y b e s i g n i f i c a n t l y different f r o m those i n w h i c h the r e a c t a n t is e x c l u s i v e l y i n t h e l i q u i d phase ( to w h i c h subseDownloaded by UNIV QUEENSLAND on June 17, 2013 | http://pubs.acs.org Publication Date: June 1, 1975 | doi: 10.1021/ba-1975-0148.ch003

quent discussion pertains).

Table III.

Representative Limiting Flow Conditions for Petroleum Processing Superficial

Reactor

Liquid

kg/m

ft/hr

2

Superficial Gas Velocity kg/m sec" 0

sec

0

to 25.0

300 Pilot plant

0.083

1

6

to 2.5

30

2

0.0132 0.066 0.395 1.97 0.0013 0.0066 0.0395 0.197

0.83

10

Commercial

Velocity

"Values of G were calculated for 1000 and 5000 scf H / b b l ; it was assumed that all hydrocarbon is in the liquid phase. Length of pilot plant reactor was assumed to be 1/10 that of commercial reactor. 2

6

0

1 l b / h r ft = 1 . 3 6 X 10" k g / m sec. 2

3

2

A n o t h e r p r e c a u t i o n i n i n t e r p r e t a t i o n stems f r o m t h e fact t h a t a l m o s t a l l o f the p u b l i s h e d i n f o r m a t i o n o n p e r f o r m a n c e o f i n d u s t r i a l t r i c k l e b e d reactors has dealt w i t h p e t r o l e u m refinery operations s u c h as h y d r o d e sulfurization. reactivities, kinetics.

T h e w i d e s p e c t r u m o f c o m p o u n d s present, w i t h different requires

some

arbitrariness i n describing

the intrinsic

F o r five fractions of a flashed p e t r o l e u m d i s t i l l a t e , B o n d i ( 9 )

r e p o r t e d h y d r o d e s u l f u r i z a t i o n d i f f e r e n t i a l r e a c t i o n rates over a C o / M o / A1 0 2

and

3

catalyst t h a t v a r i e d b y as m u c h as a f a c t o r o f 4 at 4 0 %

conversion

b y a factor o f 7 o r so a t 8 0 % c o n v e r s i o n . I f these a r e a l l t r e a t e d as

one c o m p o u n d i n reactor analysis, t h e effect is t o increase t h e a p p a r e n t o r d e r o f r e a c t i o n . A m i x t u r e o f s e v e r a l species w i t h different r e a c t i v i t y ,


58

CHEMICAL

each exhibiting true

first-order

REACTION ENGINEERING REVIEWS

k i n e t i c s , appears to f o l l o w s o m e h i g h e r

o r d e r r e a c t i o n o v e r a w i d e r a n g e of c o n v e r s i o n since the less r e a c t i v e species persist l o n g e r t h a n the m o r e r e a c t i v e ones. O n t h e other h a n d , a group

of

species

w i t h similar reactivity can frequently be

a d e q u a t e l y w h e n t h e y are d e e m e d to f o l l o w l i m i t e d r a n g e of c o n v e r s i o n .

first-order

treated

kinetics over a

T h e best p r o c e d u r e to f o l l o w varies w i t h

circumstances.


Models for

Design and

Analysis

The Ideal T r i c k l e Bed Reactor.

T h e analysis of t r i c k l e b e d

per

f o r m a n c e u n d e r i d e a l circustances a n d w i t h the a s s u m p t i o n of s i m p l e first-order cases.

k i n e t i c s p r o v i d e s a p o i n t of d e p a r t u r e for analysis of

W e assume the f o l l o w i n g : ( a )

real

p l u g flow of l i q u i d , i.e. n o d i s

p e r s i o n i n t h e a x i a l or r a d i a l d i r e c t i o n ; ( b )

no mass or h e a t t r a n s f e r

l i m i t a t i o n s b e t w e e n gas a n d l i q u i d , b e t w e e n l i q u i d a n d s o l i d catalyst, or i n s i d e catalyst p a r t i c l e s ( t h e l i q u i d s a t u r a t e d w i t h gas at a l l t i m e s ) ; (c)

first-order

i s o t h e r m a l , i r r e v e r s i b l e r e a c t i o n w i t h respect to

(gaseous r e a c t a n t present i n great e x c e s s ) ; pletely bathed w i t h liquid; phase; and (f)

(e)

(d)

catalyst pellets

liquid com

t h e r e a c t a n t c o m p l e t e l y i n the l i q u i d

n o v a p o r i z a t i o n or c o n d e n s a t i o n .

I f w e c o n s i d e r a d i f f e r e n t i a l v o l u m e e l e m e n t across the r e a c t o r a n d set the rate of r e a c t i o n i n t h a t element e q u a l to the d i s a p p e a r a n c e of r e a c t a n t as t h e l i q u i d passes t h r o u g h the element, t h e n : Fc dx

=

in

where F =

l i q u i d flow r a t e i n c m / s e c , c 3

i n entering l i q u i d i n m o l e s / c m , χ = 3

dV = of

rdV

(1)

i n

=

c o n c e n t r a t i o n of r e a c t a n t

f r a c t i o n a l c o n v e r s i o n of r e a c t a n t ,

r e a c t o r v o l u m e i n slice u n d e r c o n s i d e r a t i o n i n c m , a n d r = 3

reaction i n moles/sec

cm

3

of

reactor volume.

rate

I f the r e a c t i o n is

first-order: fc c(l

r = where it =

v

c m of l i q u i d / c m of catalyst p e l l e t v o l u m e sec. 3

v

(2)

— c)

3

Substituting

E q u a t i o n 2 i n E q u a t i o n 1, w e o b t a i n Fc dx in

Since c =

c

i n

(1 —

=

fc (l v

—

e)cdv

x),


3.

Trickle

SATTERFIELD

59

Bed Reactors

or , l

c n

V

i n

^

F

=

fe (l

-c)

T

M

1

-

i

3600fc (l - « )

.

Y

LHSV

Lfh

)

(

3

)

w h e r e V is the v o l u m e of t h e t r i c k l e b e d p a c k e d w i t h catalyst. If t h e same s i m p l i f y i n g assumptions a g a i n h o l d , w e s h o u l d b e a b l e to o b t a i n t h e same values o f t h e r e a c t i o n rate constant k

Y

i n a s t i r r e d autoclave.

f r o m studies

I n the autoclave, w e measure change i n concen-

t r a t i o n w i t h t i m e whereas i n t h e t r i c k l e b e d reactor t h e c h a n g e is i n Downloaded by UNIV QUEENSLAND on June 17, 2013 | http://pubs.acs.org Publication Date: June 1, 1975 | doi: 10.1021/ba-1975-0148.ch003

c o n c e n t r a t i o n w i t h distance. H o w e v e r , t h e a u t o c l a v e a n d t h e t r i c k l e b e d reactor s h o u l d g i v e t h e same v a l u e of k

because t h e r e is a one-to-one

v

c o r r e l a t i o n b e t w e e n t i m e i n t h e autoclave a n d d i s t a n c e t r a v e r s e d i n t h e t r i c k l e b e d . ( F o r a specified f l o w rate, t h e distance t r a v e r s e d is i n v e r s e l y p r o p o r t i o n a l to t h e d y n a m i c l i q u i d h o l d u p , b u t i t is unnecessary t o k n o w this i n t h e i d e a l cease—see subsequent

d i s c u s s i o n o n residence

time

distribution. ) I n the a u t o c l a v e : _

de _

r(v

cat

dt

+ v)

^

m

Vu

q

w h e r e r is m o l e s / ( s e c ) ( c m l i q u i d + c m catalyst i n a u t o c l a v e ) , t> 3

3

v o l u m e of catalyst pellets i n a u t o c l a v e i n c m , v 3

autoclave i n c m , a n d t = 3

m

cat

=

= v o l u m e of l i q u i d i n

t i m e i n sec. B y s u b s t i t u t i n g E q u a t i o n 2 i n

E q u a t i o n 4, w h e r e ( 1 — c) is n o w t h e v o l u m e f r a c t i o n of s o l i d catalyst i n t h e l i q u i d s l u r r y i n the a u t o c l a v e , w e o b t a i n :

dt v

cat

Integration gives:

Although i n principle k

Y

^i"it

Vcatkyt

C final

^liq

from Equation 5 should equal k

y

E q u a t i o n 3, i n p r a c t i c e t h a t d e r i v e d f r o m

from

E q u a t i o n 5 is f r e q u e n t l y

greater t h a n that c a l c u l a t e d f r o m t r i c k l e b e d studies because o f a loss of c o n t a c t i n g effectiveness i n t h e t r i c k l e b e d . B e f o r e this c o n c e p t is d i s c u s s e d , h o w e v e r , other p o s s i b l e reasons f o r these differences s h o u l d b e n o t e d .

Homogeneous

reactions, i f t h e y are

possible, are more likely to be encountered i n the autoclave than i n the t r i c k l e b e d b e c a u s e of the m u c h h i g h e r r a t i o of l i q u i d to catalyst v o l u m e . T h i s c o u l d p o s s i b l y l e a d to v a r i o u s unforeseen

consequences s u c h as


60


m o r e f o r m a t i o n of s i d e - p r o d u c t a n d p o l y m e r s t h a t m i g h t b l o c k

pores.

C a t a l y s t p o i s o n i n g w o u l d also p r o b a b l y cause t h e t w o r e a c t o r systems to b e h a v e differently. I n the a u t o c l a v e , p o i s o n i n g w o u l d o c c u r u n i f o r m l y o v e r a l l the catalyst p a r t i c l e s w h e r e a s i n the t r i c k l e b e d poisons w o u l d u s u a l l y be

adsorbed

p r e f e r e n t i a l l y onto the top-most

catalyst layers

l e a v i n g most of the b e d c l e a n for t h e m a i n r e a c t i o n . T h e net effect c o u l d w e l l be a slower drop i n reactivity w i t h time i n the trickle b e d than w o u l d be e x p e c t e d f r o m the a u t o c l a v e studies. T h e d i s t r i b u t i o n of p o i s o n t h r o u g h a n i n d i v i d u a l catalyst p a r t i c l e m a y also b e a f u n c t i o n of p a r t i c l e s i z e as w e l l as of t i m e a n d e n v i r o n m e n t . Downloaded by UNIV QUEENSLAND on June 17, 2013 | http://pubs.acs.org Publication Date: June 1, 1975 | doi: 10.1021/ba-1975-0148.ch003

I f the r e a c t i o n is n o t a c t u a l l y

first-order,

the values of k

v

as c a l c u -

l a t e d f r o m E q u a t i o n s 3 a n d 5 s h o u l d b e t h e same i f the other a s s u m p tions h o l d a n d i f c o m p a r i s o n is b e i n g m a d e for the same i n i t i a l a n d concentrations.

I n g e n e r a l this m a y n o t b e the case, b u t , f o r

final many

systems of interest w h e r e a h i g h percent of c o n v e r s i o n is n o t r e q u i r e d , t h e k i n e t i c s of the r e a c t i o n m a y be r e p r e s e n t e d satisfactorily as a

first-

o r d e r process e v e n w h e n the t r u e k i n e t i c s are s u b s t a n t i a l l y different. E q u a t i o n 3 is the same expression t h a t is o b t a i n e d for single-phase f l o w except t h a t k

y

is b a s e d o n catalyst p e l l e t v o l u m e a n d h e n c e a f a c t o r

( 1 — c ) appears. N o t e t h a t l i q u i d h o l d u p as s u c h , or t h e t r u e r e s i d e n c e t i m e of l i q u i d i n t h e reactor, does n o t a p p e a r i n this expression. N e i t h e r does the aspect r a t i o of t h e reactor ( r a t i o of l e n g t h to d i a m e t e r ) .

The

significance of these points is discussed b e l o w . Contacting

Effectiveness

A t sufficiently l o w l i q u i d a n d gas flow rates, the l i q u i d t r i c k l e s over t h e p a c k i n g i n essentially a l a m i n a r film or i n r i v u l e t s , a n d t h e gas c o n t i n u o u s l y t h r o u g h the v o i d s i n the b e d .

T h i s is sometimes

flows

termed

the gas c o n t i n u o u s r e g i o n or h o m o g e n e o u s flow, a n d i t is the t y p e that is u s u a l l y e n c o u n t e r e d i n l a b o r a t o r y a n d p i l o t scale operations.

A s gas

a n d / o r l i q u i d flow rates are i n c r e a s e d , one encounters b e h a v i o r w h i c h is d e s c r i b e d as r i p p l i n g , s l u g g i n g , or p u l s i n g

flow,

a n d this m a y

c h a r a c t e r i s t i c of t h e h i g h e r o p e r a t i n g rates e n c o u n t e r e d

be

in petroleum

p r o c e s s i n g . A t h i g h l i q u i d rates a n d sufficiently l o w gas rates, the l i q u i d p h a s e becomes continuous a n d the gas passes i n the f o r m of b u b b l e s — this is sometimes t e r m e d d i s p e r s e d b u b b l e

flow.

T h i s is c h a r a c t e r i s t i c of

some c h e m i c a l p r o c e s s i n g i n w h i c h l i q u i d rates are s u b s t a n t i a l , b u t t h e g a s - t o - l i q u i d ratios are c o n s i d e r a b l y b e l o w those e n c o u n t e r e d i n m u c h petroleum processing.

F l o w patterns a n d t h e transitions f r o m one f o r m

to a n o t h e r as a f u n c t i o n of gas a n d l i q u i d flow rates w e r e d e s c r i b e d b y s e v e r a l authors a n d w e r e r e c e n t l y s u m m a r i z e d b y Sato a n d c o - w o r k e r s (26).


3.

Trickle

SATTERFIELD

Bed

61

Reactors

I f d a t a are o b t a i n e d o v e r a r a n g e of l i n e a r velocities i n a t r i c k l e b e d , i t is u s u a l l y f o u n d that k

v

as c a l c u l a t e d f r o m E q u a t i o n 3 increases

as the l i q u i d flow rate is i n c r e a s e d . I n different terms, i f b o t h h a n d L are d o u b l e d

( w h i c h keeps L H S V c o n s t a n t ) , the p e r c e n t c o n v e r s i o n is

increased although E q u a t i o n 3 predicts there should be

no

change.

F u r t h e r m o r e , i n t h e absence of c o m p l i c a t i o n s as c i t e d a b o v e , the v a l u e of k at the h i g h e s t flow rates approaches the v a l u e o b t a i n e d i n a s t i r r e d y

autoclave

where

the

catalyst is c o m p l e t e l y

surrounded

with

liquid.

C l e a r l y , i n most t r i c k l e b e d reactors there is a loss i n w h a t is t e r m e d c o n t a c t i n g effectiveness

b e l o w t h a t w h i c h c a n b e o b t a i n e d i n the i d e a l


reactor, a n d this loss is greatest at t h e lowest l i q u i d flow rates. I n the past, designers

of t r i c k l e b e d reactors

fact t h a t c o n t a c t i n g effectiveness

generally used

improves w i t h l i q u i d

flow

b u i l t - i n factor of safety b y s c a l i n g - u p f r o m p i l o t p l a n t to p l a n t size o n t h e basis of e q u a l values of L H S V .

the

rate as a commercial

Since commercial reac

tors m a y b e 5 - 1 0 times longer t h a n p i l o t u n i t s , this w o u l d r e s u l t i n p l a n t units o p e r a t i n g at 5 - 1 0 times the 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 u s e d i n the p i l o t plants for t h e same v a l u e of L H S V .

H o w e v e r , the s i t u a t i o n w a s

c o n f u s e d b y t h e f a c t that i n some cases, as r e p o r t e d b y Ross (27),

the

c o m m e r c i a l u n i t p e r f o r m e d m o r e p o o r l y t h a n t h e p i l o t p l a n t u n i t i n spite of the use of h i g h e r l i n e a r l i q u i d velocities. T h i s a p p a r e n t l y w a s c a u s e d b y p o o r e r l i q u i d d i s t r i b u t i o n a n d was c h a r a c t e r i z e d b y t h e l i q u i d h o l d u p w a s p o o r e r i n the large u n i t (27).

finding

that

(This method

of

scale-up is u n l i k e l y to i n t r o d u c e difficulties f r o m mass transfer l i m i t a t i o n s unless the catalyst p a r t i c l e size is i n c r e a s e d at the same t i m e w h i c h , h o w e v e r , the designer m a y b e t e m p t e d to d o i n o r d e r to a v o i d excessive pressure d r o p . ) L e t us n o w use the t e r m a p p a r e n t r e a c t i o n r a t e constant,

fc , app

to

refer to the v a l u e of the r e a c t i o n r a t e constant as c a l c u l a t e d f r o m E q u a t i o n 3 or the e q u i v a l e n t , a p p l i e d to results f r o m a r e a l t r i c k l e b e d , a n d r e t a i n the s y m b o l

k

y

to refer to the i n t r i n s i c v a l u e .

We

shall

now

consider m e t h o d s of p r e d i c t i n g the effect of t h e l i q u i d flow r a t e o n k . &vv

B o n d i (9) to cause fc

app

infinity.

developed

a n e m p i r i c a l r e l a t i o n s h i p of s u c h a f o r m as

to a p p r o a c h ky as t h e s u p e r f i c i a l l i q u i d v e l o c i t y

approaches

H i s e q u a t i o n , expressed i n terms of r e a c t i o n rate constants, i s : 1 app

F o r a n u m b e r of systems, 0.5 < 2/3.

ky b
k,t

A reactor efficiency c a n t h e n b e defined as ( t /1 p

t

=


m

and

where t

v

m

) 100 w h e r e :

(14)

Œ(t)dt

Γ ο

is the residence t i m e as c a l c u l a t e d f r o m E q u a t i o n 13 t h a t

w o u l d p r o d u c e t h e same f r a c t i o n a l c o n v e r s i o n as t h a t f o u n d

experi

mentally. E q u a t i o n s 12 a n d 13 treat the system as t h o u g h i t w e r e h o m o g e n e o u s and

thus k' =

k (l y

— e)/H

sec" w h e r e the h o l d u p H is a s s u m e d to b e 1

constant w i t h l e n g t h a n d , strictly, n e e d not b e k n o w n . H o w e v e r , i t c a n b e c a l c u l a t e d f r o m the E(t) and

f u n c t i o n b y the expression H =

t (F/V), m

i t p r o v i d e s a u s e f u l measure of catalyst c o n t a c t i n g . F o r l a r g e c o m

m e r c i a l reactors, tracer measurements a p p e a r to be the o n l y p r a c t i c a b l e w a y to d e t e r m i n e h o l d u p . R e a c t o r efficiency c a n also b e defined e q u i v a l e n t l y as the r a t i o of the l e n g t h of a n i d e a l ( p l u g

flow)

reactor to t h a t of a r e a l

reactor

r e q u i r e d to p r o d u c e the same specified p e r c e n t c o n v e r s i o n w h e r e the true v a l u e of k' c a n b e c a l c u l a t e d f r o m E q u a t i o n 12. A n e x a m p l e of t h e use of this m e t h o d to a n a l y z e t r i c k l e b e d p e r f o r m a n c e M u r p h r e e et al.

(32).

For 90%

p i l o t reactor o p e r a t e d at 9 0 %

efficiency a n d t h a t a c o m m e r c i a l d e s u l -

f u r i z a t i o n reactor o p e r a t e d at 4 0 - 6 0 % poor operation and 7 0 - 8 0 %

was g i v e n b y

c o n v e r s i o n , t h e y f o u n d that a s m a l l efficiency u n d e r c o n d i t i o n s

of

efficiency u n d e r g o o d o p e r a t i n g c o n d i t i o n s .

T h e same m e t h o d of analysis was also a p p l i e d b y C e c i l et al. (33)

in a

s t u d y of the d e s u l f u r i z a t i o n of gas o i l or r e s i d u a l f u e l o i l i n a s m a l l p i l o t r e a c t o r at l i q u i d rates of 3 5 - 1 5 0 0 l b / h r f t

2

( a b o u t 0.05-2.2 k g / m

2

sec).

T h e c o n c e p t of reactor efficiency as u s e d h e r e m a y b e subject t o m i s i n t e r p r e t a t i o n since i t is v e r y sensitive to t h e p e r c e n t c o n v e r s i o n

chosen

for c o m p a r i s o n at h i g h degrees of c o n v e r s i o n . T h u s , a m o d e r a t e degree of d e v i a t i o n f r o m p l u g flow b e h a v i o r c a n be i n s i g n i f i c a n t at 9 0 % v e r s i o n b u t serious at 9 9 %

con

conversion.

T h i s a p p r o a c h demonstrates the effect of R T D o n reactor

effective

ness, b u t i t does not address itself d i r e c t l y to c o n t a c t i n g per se; the p o r t i o n of the b e d that is not c o n t a c t e d effectively cannot b e i d e n t i f i e d .

The

use of E q u a t i o n s 12 a n d 13 is r i g o r o u s l y correct i f t h e r e a c t i o n is s t r i c t l y


68


first-order

a n d i f t h e r e are n o r a d i a l c o n c e n t r a t i o n gradients. A s e m p h a

sized b y Schwartz and Roberts

(34),

the d e s i r e d R T D is t h a t of

the

l i q u i d e x t e r n a l to the catalyst pores, b u t a tracer m e a s u r e m e n t u s e d to d e t e r m i n e t h e Ε ( ΐ ) c u r v e w i l l u s u a l l y i n c l u d e as w e l l some c o n t r i b u t i o n f r o m the l a r g e i n t e r n a l h o l d u p w h i c h exhibits itself i n t h e f o r m

of

increased tailing. A x i a l Dispersion. A s a n a l t e r n a t i v e to the use of R T D , s m a l l d e v i a tions f r o m p l u g flow c a n b e d e s c r i b e d i n s t e a d b y the a x i a l d i s p e r s i o n m o d e l w h i c h i n v o l v e s o n l y one p a r a m e t e r , the a x i a l d i s p e r s i o n coefficient, w h i c h is u s u a l l y expressed as a P e c l e t n u m b e r . T h e d i s p e r s i o n coefficient Downloaded by UNIV QUEENSLAND on June 17, 2013 | http://pubs.acs.org Publication Date: June 1, 1975 | doi: 10.1021/ba-1975-0148.ch003

is o b t a i n e d b y a s s u m i n g t h a t a l l the m i x i n g processes i n v o l v e d f o l l o w the same f u n c t i o n a l r e l a t i o n s h i p as F i c k ' s l a w s regardless of the a c t u a l m e c h a n i s m , a n a s s u m p t i o n that becomes i n c r e a s i n g l y d u b i o u s w i t h l a r g e degrees of d e v i a t i o n f r o m p l u g flow b e h a v i o r . R T D measurements i n t r i c k l e b e d s are better fitted b y a t w o - p a r a m e t e r cross-flow m o d e l s u c h as that u s e d b y H o o g e n d o o r n a n d L i p s ( 3 5 ) , H o c h m a n a n d E f f r o n ( 3 6 ) , a n d others. T h i s m o d e l assumes that the h o l d u p consists of stagnant pockets a n d l i q u i d i n p l u g flow, a n d the t w o adjustable p a r a m e t e r s are t h e f r a c t i o n of t h e t o t a l l i q u i d i n p l u g flow a n d a n e x c h a n g e coefficient. Roberts

(34)

Schwartz and

m a d e a d e t a i l e d c o m p a r i s o n of the effect o n p r e d i c t e d

reactor performance

of v a r i o u s R T D d a t a c o r r e l a t e d i n terms of

the

d i s p e r s i o n m o d e l vs. the cross-flow or a n e q u i v a l e n t m o d e l . I f one takes the R T D d a t a of H o c h m a n a n d E f f r o n , w h i c h are p r o v i d e d i n b o t h f o r m s , for representative reactor cases c o r r e s p o n d i n g to R e

L

values of

8 a n d 66, t h e r a t i o of r e q u i r e d catalyst v o l u m e c a l c u l a t e d b y the d i s p e r s i o n m o d e l to that c a l c u l a t e d b y the cross-flow m o d e l is 1.03-1.09 at 80%

c o n v e r s i o n a n d 1.11-1.22 at 9 0 %

conversion.

T h i s suggests that

t h e a x i a l d i s p e r s i o n m o d e l m a y b e the m o r e conservative i n general. It is also a d e q u a t e for i n i t i a l estimates- as to w h e t h e r d e v i a t i o n f r o m p l u g flow w i l l b e significant i n a n y specific case. M e a r s (22, h/d

v

28)

presents the f o l l o w i n g c r i t e r i o n for the m i n i m u m

r a t i o that is r e q u i r e d i n o r d e r to h o l d the reactor l e n g t h to w i t h i n

5 % of t h a t n e e d e d for p l u g

flow.

h 20m C ~r > - 5 — In 77— a Jre Wut i n

p

where P e

L

=

d L/Di p

- v

(15) n

L

a n d m is the o r d e r of r e a c t i o n . T h u s , the m i n i m u m

r e a c t o r h e i g h t increases w i t h the o r d e r of r e a c t i o n , a n d i t is v e r y sensitive to f r a c t i o n a l c o n v e r s i o n at h i g h degrees of c o n v e r s i o n . H o c h m a n a n d E f f r o n (36)

r e p o r t e d d i s p e r s i o n d a t a for

cocurrent

m e t h a n o l a n d n i t r o g e n flow of 6 0 0 - 5 0 0 0 l b / f t h r ( 0 . 8 - 7 k g / m 2

2

sec) i n

a 6 - i n . c o l u m n p a c k e d w i t h 3 / 1 6 - i n . glass spheres. P e c l e t n u m b e r s for the l i q u i d v a r i e d f r o m a b o u t 0.15 at R e = 4 to a b o u t 0.40 at R e == 70 w i t h L

L


3.

SATTERFIELD

considerable

Trickle

scatter.

Bed

69

Reactors

A p p a r e n t l y there w e r e significant, b u t r a n d o m ,

v a r i a t i o n s i n d i s p e r s i o n f r o m p o i n t to p o i n t a n d d a y to d a y . T h e effect of gas rate ( u p to 8.35 c m / s e c ) w a s s m a l l . T h e s e values of P e

L

are 1 / 3 to

1/6 those for single-phase l i q u i d flow at the same R e y n o l d s n u m b e r a n d can

be c o m p a r e d to P e = 2 for f u l l y d e v e l o p e d single-phase t u r b u l e n t

flow

i n p a c k e d beds. C h a r p e n t i e r a n d c o - w o r k e r s

reported P e

L

(37,

38, 39)

likewise

values for t r i c k l e flow d o w n to a n o r d e r of m a g n i t u d e less

t h a n t h a t for single-phase flow at t h e same l i q u i d R e y n o l d s n u m b e r , b u t w i t h m u c h scatter.

E q u a t i o n 15 demonstrates that, for r e p r e s e n t a t i v e

l a b o r a t o r y scale t r i c k l e b e d reactors of the o r d e r of a foot or so i n l e n g t h , Downloaded by UNIV QUEENSLAND on June 17, 2013 | http://pubs.acs.org Publication Date: June 1, 1975 | doi: 10.1021/ba-1975-0148.ch003

a x i a l d i s p e r s i o n m a y cause a significant d e v i a t i o n f r o m p l u g flow b e h a v i o r w h e n conversions are r o u g h l y 9 0 % or m o r e . T h e r e are a b o u t

15 other r e p o r t e d studies of l i q u i d - p h a s e a x i a l

d i s p e r s i o n , b u t these g e n e r a l l y i n v o l v e d c o u n t e r c u r r e n t a i r - w a t e r systems, almost i n v a r i a b l y w i t h R a s c h i g r i n g a n d o c c a s i o n a l l y w i t h

Berl

s a d d l e p a c k i n g , a n d f r e q u e n t l y w i t h flow c o n d i t i o n s outside the r a n g e of interest i n t r i c k l e b e d reactors. A s u m m a r y l i s t i n g w a s g i v e n b y M i c h e l l and

F u r z e r (40)

w h o also p r e s e n t e d a r e c o m m e n d e d c o r r e l a t i o n b a s e d

o n c o n s i d e r a b l e w o r k of t h e i r o w n . Re',

T h i s involves a Reynolds number,

b a s e d o n the i n t e r s t i t i a l r a t h e r t h a n o n the s u p e r f i c i a l v e l o c i t y w h i c h

m u s t therefore be c o m b i n e d w i t h a n expression for t h e d y n a m i c h o l d u p , H, t

to relate s u p e r f i c i a l a n d i n t e r s t i t i a l velocities. T h e r e l a t i o n s h i p s a r e : Pe

L

=

(Re ') - Ga-°0

L

7 0

— (0.68)Re °- Ga-°- ad

H

t

80

L

44

w h e r e G a is the G a l i l e o n u m b e r , d g p /^ , 3

p

i n the d e f i n i t i o n of R e

L

(16)

3 2

c

2

(17)

p

a n d the l i q u i d v e l o c i t y u s e d

2

is the s u p e r f i c i a l v e l o c i t y . T h e s e r e l a t i o n s h i p s r e p -

resent a refinement over s i m i l a r correlations d e v e l o p e d K u n i g i t a (41)

a n d O t a k e a n d O k a d a (42).

by Otake and

R e p r e s e n t a t i v e values of P e

L

for c o u n t e r c u r r e n t a i r - w a t e r flow t h r o u g h 0.25-in. R a s c h i g rings are 0.25 at R e

=

L

10 a n d 0.5 at R e

L

=

100 (43),

values w h i c h are r e a s o n a b l y

close to those r e p o r t e d b y H o c h m a n a n d E f f r o n . P e c l e t n u m b e r s for the gas phase, as r e p o r t e d b y H o c h m a n a n d E f f r o n , w e r e c o r r e l a t e d b y the e x p r e s s i o n : Pe for R e

G

G

=

1.8Re - - 10-° G

0

7

0 0 5 R e

L

values of 11 a n d 22 a n d for a range of R e

T h i s leads to P e

G

(18) L

values f r o m 5 to 80.

values one to t w o orders of m a g n i t u d e less t h a n those

e n c o u n t e r e d i n single-phase gas flow, w h i c h are a t t r i b u t e d , as w a s s u g gested earlier b y D e M a r i a a n d W h i t e (44),

to the gas p h a s e " s e e i n g "

agglomerates of particles c o v e r e d w i t h a b r i d g e of l i q u i d as a n effectively


70


l a r g e r p a r t i c l e . T h i s e x p l a n a t i o n is s u p p o r t e d b y the facts t h a t w e t p a c k i n g i n the absence of

flowing

l i q u i d gives a l a r g e increase i n d i s p e r s i o n

over d r y p a c k i n g a n d t h a t P e

decreases w i t h i n c r e a s e d R e .

G

However,

L

gas-phase d i s p e r s i o n is not of c o n c e r n o r d i n a r i l y i n t r i c k l e b e d p r o c e s s i n g . M e t h o d s of e s t i m a t i n g w h e n s i g

Mass and Heat Transfer Effects.

n i f i c a n t c o n c e n t r a t i o n gradients exist b e t w e e n gas a n d l i q u i d ,

between

l i q u i d a n d s o l i d , or w i t h i n the porous catalyst are t r e a t e d elsewhere I n t e r n a l diffusion l i m i t a t i o n s are c o m m o n l y the catalyst effectiveness

(45).

expressed i n terms

of

factor, η, w h i c h is defined as t h e r a t i o of t h e

o b s e r v e d rate of r e a c t i o n to t h a t w h i c h w o u l d b e o b s e r v e d i n the absence Downloaded by UNIV QUEENSLAND on June 17, 2013 | http://pubs.acs.org Publication Date: June 1, 1975 | doi: 10.1021/ba-1975-0148.ch003

of a n y i n t e r n a l c o n c e n t r a t i o n or t e m p e r a t u r e gradients. M e t h o d s of e s t i m a t i n g η h a v e n o w b e e n d e v e l o p e d i n great d e t a i l (46, 47).

For a

first-

order reaction, internal diffusion w i l l be insignificant if (rf /2) r(l- ) 2

p

where c

s

c

1

( 1 9 )

is the c o n c e n t r a t i o n of the k e y reactant i n the l i q u i d ( u s u a l l y

t h e d i s s o l v e d gas)

at the s o l i d - l i q u i d interface.

U n l e s s the size of the

d i f f u s i n g molecules is c o m p a r a b l e to that of the pores, Deff=— τ

(20)

w h e r e θ is the catalyst v o i d f r a c t i o n a n d τ is the tortuosity factor w h i c h u s u a l l y has a v a l u e of ~ 4 ( extreme values for the u s u a l catalyst s t r u c tures are a b o u t 2 - 7 ) .

Effectiveness factors for c o m m e r c i a l h y d r o d e s u l

f u r i z a t i o n reactors are t y p i c a l l y 0.36-0.6 for catalyst p a r t i c l e s 5 - 6 m m i n d i a m e t e r , w h i c h is a m i l d d e g r e e of diffusion l i m i t a t i o n . C o n s i d e r n o w some effects that m a y o c c u r i f reactant is present i n b o t h the l i q u i d a n d the v a p o r phases.

T h e m a x i m u m steady-state t e m

p e r a t u r e difference b e t w e e n the center a n d the outside of a catalyst p e l l e t , Δ Γ , occurs w h e n diffusion is sufficiently l i m i t i n g so that reactant c o n c e n t r a t i o n i n the p e l l e t center approaches zero. Δ

Γ

=

^ - Δ # ) Α

ί

ΐ

£

Then

(48)

1

( 2 1 )

λ w h e r e λ is the t h e r m a l c o n d u c t i v i t y of the porous s o l i d . E v e n w i t h a h i g h l y e x o t h e r m i c r e a c t i o n , i t is u n l i k e l y that Δ Γ w i l l exceed m o r e t h a n a f e w degrees i f the pores r e m a i n filled w i t h l i q u i d , unless the gas is m u c h m o r e s o l u b l e t h a n h y d r o g e n i n most l i q u i d s . A n e x a m p l e illustrates t h i s : take the e n t h a l p y c h a n g e and

a hydrogen

s o l u b i l i t y of

on reaction 10~

4

- Δ Η = 5 Χ 10

g mole/cm , 3

4

which would


cal/mole require

3.

SATTERFIELD

Trickle

Bed

71

Reactors

e l e v a t e d pressure i n t y p i c a l h y d r o c a r b o n s . terms are D

e f f

= 2 X 10'

5

T y p i c a l values of the other

cm /sec and λ = 3 X 10' 2

cal/sec cm°K.

4

ΔΓ

is 0.33°C. If pores are filled w i t h v a p o r , h o w e v e r , t e m p e r a t u r e differences i n the h u n d r e d s of degrees are q u i t e possible b e c a u s e D

eit

values for v a p o r s

are t h r e e to f o u r orders of m a g n i t u d e greater t h a n those for solutes a n d gas-phase concentrations are not l o w e r e d b y as large a factor.

The key

l i m i t i n g c o m p o n e n t is t h e n u s u a l l y v a p o r i z e d reactant r a t h e r t h a n h y d r o gen. R e p r e s e n t a t i v e c o n d i t i o n s are as f o l l o w s : — Δ Η = 5 Χ 1 0 (this is n o w p e r m o l e of v a p o r i z e d r e a c t a n t ) , D

ett

=

4

cal/mole

10" c m / s e c , c 2

2

s

=

3 X 10~ ( r e p r e s e n t i n g v a p o r i z e d reactant present i n s m a l l m o l e f r a c t i o n Downloaded by UNIV QUEENSLAND on June 17, 2013 | http://pubs.acs.org Publication Date: June 1, 1975 | doi: 10.1021/ba-1975-0148.ch003

5

but superatmospheric 50°C.

total pressure),

a n d λ as before.

ΔΓ

becomes

T h i s s i t u a t i o n w i l l not d e v e l o p , of course, i f the reactant does not

h a v e a n a p p r e c i a b l e v a p o r pressure. If a r e a c t i o n is s u b s t a n t i a l l y d i f f u s i o n - l i m i t e d w h e n pores are

filled

w i t h l i q u i d reactant, t h e n circumstances that cause the pores to b e c o m e filled

i n s t e a d w i t h v a p o r i z e d reactant c a n cause a m a r k e d increase i n

r e a c t i o n rate w h i c h is associated w i t h the m a r k e d increase i n d i f f u s i v i t y . I n d e e d , this was f o u n d e x p e r i m e n t a l l y b y S e d r i c k s a n d K e n n e y i n a s t u d y of the hydrogénation of c r o t o n a l d e h y d e .

(15)

L i q u i d - p h a s e reac-

t i o n c o u l d p r e s u m a b l y s w i t c h to v a p o r - p h a s e r e a c t i o n at a c r i t i c a l v a l u e of t h e l o c a l l i q u i d flow r a t e b e l o w w h i c h the heat e v o l v e d c o u l d l o n g e r b e c a r r i e d a w a y b y the

flowing

liquid.

w i t h l i q u i d flow to cause t e m p e r a t u r e i n s t a b i l i t i e s i n v a r i o u s w a y s . m a i n a n d co-workers

(21)

no

T h i s effect c a n i n t e r a c t Ger-

d e s c r i b e d a c y c l i c a n d i r r e g u l a r b e h a v i o r of

a t r i c k l e b e d i n w h i c h α-methylstyrene was h y d r o g e n a t e d

to

this c o u l d b e e x p l a i n e d p l a u s i b l y b y p o s t u l a t i n g that c o m p l e t e l y

cumene; wetted

pellets h a d l o w r e a c t i o n rates whereas p a r t l y w e t t e d pellets g r e w hotter because of insufficient heat transfer to

flowing

l i q u i d , w h i c h l e d to h i g h

a c t i v i t y a n d f o r m a t i o n of p o l y m e r i c b y - p r o d u c t s .

These i n turn reduced

c a t a l y t i c a c t i v i t y , w h i c h a l l o w e d the p e l l e t to b e c o m e c o o l a n d w e t t e d again.

R e m o v a l of p o l y m e r b y s o l u t i o n i n the

flowing

liquid

allowed

a c t i v i t y to b e restored a n d the c y c l e to r e c o m m e n c e . Q u a n t i t a t i v e analysis of these types of c o u p l i n g effects m i g h t b e v e r y h e l p f u l i n r e v e a l i n g p o s sible causes of i n s t a b i l i t i e s i n t r i c k l e b e d reactors i n general. Summary

and

Conclusions

M a n y factors of i m p o r t a n c e i n t h e d e s i g n a n d c h a r a c t e r i z a t i o n of t r i c k l e b e d reactors h a v e not b e e n c o v e r e d i n this r e v i e w . T h e s e i n c l u d e a d e s c r i p t i o n of the h y d r o d y n a m i c flow regions, c h a r a c t e r i z a t i o n of p r e s sure d r o p a n d l i q u i d h o l d u p , a n d mass transfer l i m i t a t i o n s t h a t m a y exist b e t w e e n gas a n d l i q u i d , b e t w e e n l i q u i d a n d s o l i d , or w i t h i n t h e


72

CHEMICAL REACTION ENGINEERING

REVIEWS

catalyst p a r t i c l e s . C o n d i t i o n s i n w h i c h r e a c t a n t is d i s t r i b u t e d b e t w e e n t h e l i q u i d a n d v a p o r phases c a n g i v e r i s e t o b e h a v i o r characteristics w h i c h were only mentioned.

M e t h o d s of c h a r a c t e r i z i n g t h e c o n t a c t i n g

effectiveness of t r i c k l e b e d reactors, h o w e v e r , are c e n t r a l to p r e d i c t i n g their performance

a n d the recent

developments

reviewed here

give

p r o m i s e of p u t t i n g these m e t h o d s of c h a r a c t e r i z a t i o n o n a m u c h m o r e f u n d a m e n t a l basis t h a n heretofore. Acknowledgments


Discussions w i t h a n d comments f r o m m a n y individuals, i n c l u d i n g Peter Kehoe, D a v i d W . Mears, George Roberts, a n d Thomas K . Sher w o o d , are g r e a t l y a p p r e c i a t e d . Nomenclature S o m e s y m b o l s that w e r e u s e d o n l y o n c e are d e f i n e d at p o i n t of use a n d are n o t i n c l u d e d i n this list. c

=

D

=

D dp F G Ga g H

B= = = = = .= «=

h k

= =

l

c

c o n c e n t r a t i o n , g m o l e / c m ; c , c o n c e n t r a t i o n at l i q u i d - s o l i d interface m o l e c u l a r d i f f u s i v i t y , c m / s e c ; D f f , effective d i f f u s i v i t y i n p o r ous catalyst ( E q u a t i o n 2 0 ) a x i a l d i s p e r s i o n coefficient, c m / s e c catalyst p a r t i c l e d i a m e t e r , c m l i q u i d flow rate, c m / s e c ( E q u a t i o n s 1 a n d 3 ) gas s u p e r f i c i a l flow rate, c m / s e c at S T P or k g / m sec G a l i l e o n u m b e r , d g p / / x ( E q u a t i o n s 16 a n d 17) c o n v e r s i o n constant h o l d u p , c m l i q u i d / c m e m p t y r e a c t o r v o l u m e ; ff , free d r a i n i n g or d y n a m i c h o l d u p h e i g h t of reactor, c m , or d e p t h of p a c k e d b e d , c m first-order r e a c t i o n rate constant; fc , i n t r i n s i c first-order r e a c t i o n rate constant p e r u n i t v o l u m e of catalyst p e l l e t , c m l i q u i d / c m catalyst p e l l e t v o l u m e sec; fc , a p p a r e n t v a l u e as f o u n d e x p e r i m e n t a l l y ; fc = fc (l — e)/H, sec" ( E q u a tions 12 a n d 13 ) ; fc A v = c o n t a c t i n g effectiveness l i q u i d s u p e r f i c i a l flow rate, c m / s e c or k g / m sec l i q u i d h o u r l y space v e l o c i t y , v o l u m e of l i q u i d f e d t o r e a c t o r e a c h h o u r p e r v o l u m e of reactor, = 3600 L/h hi' o r d e r of r e a c t i o n P e c l e t n u m b e r f o r l i q u i d phase, d L/Di r a t e of r e a c t i o n , g m o l e / s e c c m reactor v o l u m e R e y n o l d s n u m b e r f o r l i q u i d flow = d^Lp/μ; R e f o r gas flow = dpGp/μ temperature, ° C t i m e , sec 3

s

2

e

2

3

2

p

c

2

3

2

3

f

v

3

3

apP

7

1

v

apP

L = LHSV =

2

1

m Pe^ r Ret,

= — = =

Τ t

— =

p

3

g


3.

SATTERFiELD

V

Trickle

73

Bed Reactors

—

reactor volume, c m

= = =

v o l u m e o f catalyst pellets i n a u t o c l a v e , c m volume of l i q u i d i n autoclave, c m fractional conversion of reactant

ν c

= =

η

=

μ Ρ

= =

k i n e m a t i c v i s c o s i t y = μ/ρ v o i d f r a c t i o n i n catalyst b e d , same as f r a c t i o n o f r e a c t o r v o l u m e n o t o c c u p i e d b y c a t a l y s t p a r t i c l e s ; ( 1 — c) = r a t i o o f c a t a lyst p e l l e t v o l u m e to e m p t y reactor v o l u m e effectiveness factor, r a t i o o f a c t u a l rate o f r e a c t i o n i n a p o r o u s c a t a l y s t to t h a t w h i c h w o u l d o c c u r i f p e l l e t i n t e r i o r w e r e a l l e x p o s e d t o reactants at t h e same c o n c e n t r a t i o n a n d t e m p e r a t u r e as t h a t e x i s t i n g a t t h e outside surface o f t h e p e l l e t v i s c o s i t y , poises density, g / c m

τ θ

= =

t o r t u o s i t y factor ( E q u a t i o n 2 0 ) v o i d f r a c t i o n i n p o r o u s catalyst p a r t i c l e

ucat #iiq

χ

3

3

3


Greek

3

Literature Cited 1. van Deemter, J. J., Chem. Reaction Eng., 3rd Eur. Symp., 1964, 215. 2. LeNobel, J. W., Choufoer, J. H., Proc. 5th World Pet. Congr. Sect. III, Paper 18, Fifth World Petroleum Congr., New York, 1959. 3. Lister, Α., Chem. Reaction Eng., 3rd Eur. Symp., 1964, 225. 4. Storch, H . H., Golumbic, N., Anderson, R. B., "The Fischer-Tropsch and Related Syntheses," Wiley, New York, 1951. 5. Crowell, J. H., Benson, Η. E., Field, J. H., Storch, Η. H., Ind. Eng. Chem. (1950) 42, 2376. 6. Benson, Η. E., Field, J. H., Bienstock, D., Storch, Η. H., Ind. Eng. Chem. (1954) 46, 2278. 7. Kastens, M. L., Hirst, L. L., Dressler, R. G., Ind. Eng. Chem. (1952) 44, 450. 8. Brusie, J. P., Hort, Ε. V., "Kirk-Othmer Encyclopedia of Chemical Tech nology," 2nd ed., Vol. 1, p. 609, Interscience, New York, 1967. 9. Bondi, Α., Chem. Tech. (March 1971) 185. 10. Krönig, W., 6th World Pet. Congr., 1963, Sect.IV,Paper 7. 11. Porter, D. H., FMC Corp., U.S. Patent 3,009,782 (1961). 12. Østergaard, K., Adv. Chem. Eng. (1968) 7, 71. 13. Hartman, M., Coughlin, R. W., Chem. Eng. Sci. (1972) 27, 867. 14. Kenney, C. N., Sedricks, W., Chem. Eng. Sci. (1972) 27, 2029. 15. Sedricks, W., Kenney, C. N., Chem. Eng. Sci. (1973) 28, 559. 16. Way, P. F., Ph.D. Dissertation, Massachusetts Institute of Technology, 1971. 17. Satterfield, C. N., Way, P. F., AIChE J. (1972) 18, 305. 18. Pelossof, Α. Α., Ph.D. Dissertation, Massachusetts Institute of Technology, 1967. 19. Satterfield, C. N., Pelossof, Α. Α., Sherwood, T. K., AIChE J. (1969) 15, 226. 20. Satterfield, C. N., Őzel, F., AIChE J. (1973) 19, 1259. 21. Germain, A. H., LeFebvre, A. G., L'Homme, G. Α., ADV. C H E M . SER. (1974) 133, 164. 22. Mears, D., Chem. Eng. Sci. (1971) 26, 1361.



74

C H E M I C A L REACTION ENGINEERING

REVIEWS

23. Henry, H. C., Gilbert, J. B., Ind. Eng. Chem. Process Des. Dev. (1973) 12, 328. 24. Flinn, R. Α., et al., Hydrocarbon Process Pet. Refiner (1963) 42 (9), 129. 25. Gilbert, J. B., Kartzmark, R., Proc. Am. Inst. Pet. (1965) 45 (3), 29. 26. Sato, Y., Hirose, T., Takahashi, F., Toda, M., Hashiguchi, Y., J. Chem. Eng. Jpn. (1973) 6, 315. 27. Ross, L. D., Chem. Eng. Prog. (1965) 61 (10), 77. 28. Mears, D. E., ADV. CHEM. SER. (1974) 133, 218. 29. Puranik, S. S., Vogelpohl, Α., Chem. Eng. Sci. (1974) 29, 501. 30. Hobler, T., "Mass Transfer and Absorbers," Engl. transl., pp. 219-230, Pergamon, London, 1966. 31. Wijffels, J.-B., Verloop, J., Zuiderweg, F. J., ADV. CHEM. SER. (1974) 133, 151. 32. Murphree, Ε. V., Voorhies, Α., Mayer, F. X., Ind. Eng. Chem. Process Des. Dev. (1964) 3, 381. 33. Cecil, R. R., Mayer, F. X., Cart, Jr., Ε. N., unpublished data. 34. Schwartz, J. G., Roberts, G. W., Ind. Eng. Chem. Process Des. Dev. (1973) 12, 262. 35. Hoogendoorn, C. J., Lips, J., Can. J. Chem. Eng. (1965) 43, 125. 36. Hochman, J. M., Effron, E., Ind. Eng. Chem. Fundam. (1969) 8, 63. 37. Charpentier, J. C., Prost, C., LeGoff, P., Chem. Eng. Sci. (1969) 24, 1777. 38. Bakos, M., Charpentier, J. C., Chem. Eng. Sci. (1970) 25, 1822. 39. Charpentier, J. C., Prost, C., LeGoff, P., Chim. Ind. Genie Chim. (1968) 100, 653. 40. Michell, R. W., Furzer, I. Α., Chem. Eng. J. (1972) 4, 53. 41. Otake, T., Kunigita, E., Kagaku Kogaku (1958) 22, 144. 42. Otake, T., Okada, K., Kagaku Kogaku (1953) 17, 176. 43. Furzer, I. Α., Michell, R. W., AIChE J. (1970) 16, 380. 44. De Maria, F., White, R. R., AIChE J. (1960) 6, 473. 45. Satterfield, C. N., AIChE J., (1975) 21, 209. 46. Petersen, Ε. E., "Chemical Reaction Analysis," Prentice-Hall, Englewood Cliffs, N.J., 1965. 47. Satterfield, C. N., "Mass Transfer in Heterogeneous Catalysis," paperback edition, Dept of Chemical Engineering, Massachusetts Institute of Tech nology, Cambridge, 1970. 48. Prater, C. D., Chem. Eng. Sci. (1958) 8, 284. RECEIVED December 4, 1974. Work supported by the National Science Foun dation.


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