1997. Catalytic Process Development_A Process Designer's Point of View

7/23/2019 1997. Catalytic Process Development_A Process Designer's Point of View

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E L S E V I E R Catalysis Today 36 (1997) 367-374

C T LYSIS

TOD Y

C a t a l y t ic pr o c e s s de v e l o pm e nt : A pr o c e s s de s i g ne r s

A . B i s i o *

Atro Associates PO. Box 1367 Mountainside NJ USA

p o i n t o f v i e w

P r oc e s s de s igne r s a r e no t m e m be r s o f t he c a t a ly s t

c o m m u n i t y ; f e w h a v e e v e r d e v e l o p e d o r e v e n t e st e d a

c a t a ly s t . H ow e ve r , in a n im por t a n t w a y , t he y a r e t he

f i r s t c u s tom e r s f o r ne w o r im pr ove d c a t a ly s t s . The i r

i n t e r e s t is l im i t e d t o da t a t ha t w i l l e na b l e t he m to m a k e

a s e r i es o f c om ple x de c i s ions a bou t c om m e r c i a l c a t -

a ly t i c r e a c to r sy s t e m s in a m a nuf a c tu r ing e nv i r on -

m e n t . U nde r s t a nd ing the i r ne e ds ( a nd p r e jud i c e s )

shou ld e na b le t he c a t a ly s t c om m uni ty t o de l i ve r

' ne w ' c a t a ly s ts m or e e f f e c t i ve ly .

M os t , i f no t a l l o f the c a t a ly s t s u se d c om m e r c i a l l y

toda y f o r m a nuf a c tu r ing c he m ic a l s a nd pe t r o l e um

r e f in ing w e r e l a r ge ly de ve lope d by t e d ious t r i a l a nd

e r ro r . H undr e ds o f m a n- hou r s ha ve b e e n spe n t i n t he

l a bo r a to r ie s o f u se rs a nd c a t a ly s t ve ndo r s t o de ve lop

a nd e vo lve a c om m e r c i a l l y v i a b l e c a t a ly s t . N o t su r -

pr is ingly , the re i s a growing in te res t in u t i l iz ing more

r a t i ona l a pp r oa c he s t ow a r d t he de ve lop m e n t o f c a t a -

ly s ts , pa r t i c u l a r ly i f one i s t r y ing t o a c h i e ve de s i r a b l e

e nv i r onm e n ta l goa l s .

A r e v i e w o f r e c e n t l i t e r a tu r e on c a t a ly s i s w i l l

unc o ve r tw o in t e r w o ve n s t r ands :

A be l i e f t ha t c a t a ly s ts c a n be de s igne d ; a nd

A s t rong fee l ing , a lmo st mess ian ic , tha t new ca t -

a ly s t s c a n l e a d t o r e duc t ion o f t he po l lu t ion bu r de n

on the e nv i r onm e n t .

I nde e d , a m o s t e l e m e n ta r y l i te r a tu re s e a r c h c ove r -

ing t he pa s t 10 ye a r s w i ll unc o ve r ove r 350 a r t ic l e s a nd

one pa t e n t u s ing t he ph r a se s , de s ign ing c a t a ly s t s o r

*Corresponding author.

des igner ca ta lys ts , in the t i t le and probably severa l

t housa nd tha t u se t he se w or ds ( o r s im i l ar one s ) i n t he

text.

'B e n ign by d e s ign ' i s a c onc e p t ( a lt hough i t w a s no t

o r ig ina t e d by h im ) t ha t ha s be e n pop u la r i z e d i n r e c e n t

ye a r s by P r o f e s so r M a r k D a v i s o f t he C a l i f o r n i a

I n s t it u t e o f T e c hno logy . Le t u s f i rs t c ons ide r b r i e f ly

f r om a p r oc e s s de s igne r ' s v i e w po in t , t he im p l i c a t ions

o f t he c onc e p t ' b e n ign by de s ign ' o r a ' c l e a n t e c hno l -

o g y ' .

To a r r i ve a t a l e ve l o f pe r f o r m a n c e im p l i e d by t he

c onc e p t o f a ' c l e a n t e c hno log y ' r e qu i r e s m or e t ha n j u s t

a n im pr ov e m e n t in t he pe r f o r m a n c e o f a c a t a ly s t , suc h

as a h igher y ie ld or improved se lec t iv i ty . At a mini -

m um , w e m us t a c c e p t t ha t the a r e a o f i n t er e s t is a lw a ys

a m a nuf a c tu r ing s i t e ( c r a d l e - to - g r a ve o r l i f e - c yc l e

th ink ing , w h i l e im por t a n t , a r e no t pa r t o f ou r c on -

s ide r at i ons a t t h i s junc tu r e ) . I f t he po l lu t i on bu r de n on

the e nv i r onm e n t i s t o be r e duc e d , t he n w e m us t

r e c ogn iz e t ha t e ve r y th ing t ha t ha ppe ns o r m a y ha ppe n

w i th in a p l a n t s i te i s li nke d . A c ha n ge in t he m o de o f

ope r a t i on o f a p r oc e s s un i t c a n qu i c k ly c a sc a de

th r ough the ope r a t i on o f t he e m is s ions a nd w a s t e -

m a na ge m e n t sy s t e m s , t he e ne r gy sys t e m s , a nd m a y

e ve n ha ve a n im pa c t on r a w m a te r ia l , p r oduc t s t o r a ge

a nd t r a nspo r t at i on . G a in ing a n u nde r s t a nd ing o f t he se

l i nka ge s a nd the i r c onse que nc e s i s o f p r im e c o nc e r n t o

a process des igner .

S yn the t i c r ou t e s t ha t u se h igh ly t ox i c a nd v o l a t i l e

r a w m a te r i a l s , suc h a s phosge ne , m us t be a vo ide d i f

pos s ib le . W he n no t pos s ib l e a nd i f the r a w m a te ri a l s

c a nno t be ge n e r a t e d a s ne e de d , t he de s igne r w i l l ha ve

0920-5861/97/$32.00 Copyright 1997 ElsevierScienceB.V. All rights reserved.

PII

S 0920- 5861( 96 ) 00231- 3


2/8

368

A. B isio/ Catalysis Today 36 1997) 367-374

to have a sophis t ica ted unders tanding of wha t i s

involved in t ranspor t ing an d s tor ing them. Procedu res

tha t protec t pe rsonne l aga ins t exposure to them and

handle acc identa l re leases in a re spons ib le man ner a re

also absolutely vi ta l .

Whether used as a reac t ion media or to fac i l i t a te

separa t ions , the ma gni tud e of the so lvent inventor ies

and the c i rcula t ion ra tes a re impo rtant . Smal l re la t ive

losses (e .g . ,


3/8

A. Bisio / Catalysis Today 36 1997) 367-374

369

Commerc ia l Inpu ts

Screen ing S t ra tegy

I Prel imina r ' Tech nical

A s s e s s m e n t

Labora tory

Screen ing

Kinetic/Thermodynamic

Data

T

Deta i led Techn ica l

Ana lys is

Labora tory Reac tor

Eva lua t ion

Pi lot P lant

Eva lua t ion

I C o m m e r c i a l

Des ign

Fig. 1. M ajor tasks in a m arket-drivencatalytic process develop-

ment program . Adopted from Ref. [2].

Prel iminary

Techn ica l /Commerc ia l

Ana lys is

Technical

A s s e s s m e n t

R e s e a r c h C o n c e p t

Mater ia l Screen ing

Discovery

Labora tory Reac tor

Eva lua t ions

Opt im iza t ion

Se lec t ion o f Sys tem

G o o d S c i e n c e

Pi lot Scale

Opera t ion

I~ ta ikKI I

Techn ica l /Commerc ia l

Ana lys is

C o m m e r c i a l

Des ign

Fig. 2. M ajor tasks in a science-driven catalytic proc ess develop-

ment program . Adopted from Ref. [2].

v e r s i o n . T h e r e f o r e , h i s p r o j e c t i o n s w i l l b e f o r t h c o m -

i n g i f n o t g e n e r o u s a n d h i s c o n c e r n s m i n i m a l .

A s c i e n c e - d r i v e n d e v e l o p m e n t i n v o l v e s i n v e n t i n g a

n o v e l ( o r n e w ) c a t a l y s t t h a t m a y ( o r m a y n o t ) f o r m t h e

b a s i s f o r a p r o f i t a b l e c o m m e r c i a l p l a n t , u n l i k e a

m a r k e t - d r i v e n d e v e l o p m e n t i n w h i c h c a s e a s ig n i f i ca n t

p o r t i o n o f t h e w o r k w i l l b e e x p l o r a t o r y i n n a t u r e ,

b r o a d i n i t s s c o p e , a n d u n c e r t a i n i n o u t c o m e . O n l y

a l i m i t e d d a t a - b a s e m a y e x i s t t o g u i d e t h e s e l e c ti o n o f

i n i t i a l c a t a l y s t c o m p o s i t i o n s , a s s o c i a t e d p r e p a r a t i o n

p r o c e d u r e s , a n d ' t e s t ' r e a c t i o n c o n d i t i o n s ; t h i s c a n

r e s u l t i n t h e p r o c e s s d e s i g n e r b e i n g q u i t e r e l u c t a n t t o

m a k e p r o j e c t i o n s , e v e n c o n s e r v a t i v e o n e s .

T h e m a j o r t a s k s t h a t m u s t b e c o n d u c t e d b e f o r e a

c a t a l y s t a n d t h e a s s o c i a t e d p r o c e s s ( e . g . , r e a c t o r a n d

s u p p o r t s y s t e m s ) a r e p r o j e c t e d t o b e c o m m e r c i a l l y

v i a b l e , a r e s h o w n i n F i g . 2 . T h e k e y t e c h n i c a l h u r d l e s

w i l l i n c l u d e ( a t a m i n i m u m ) :

A n i n i t ia l d i s c o v e r y t h a t r e s u l ts f r o m a h i g h l y

e x p l o r a t o r y l a b o r a t o r y r e se a r c h p r o g r a m ;

E x t e n s i v e l a b o r a t o r y r e a c t o r t e s ti n g ; a n d

D e m o n s t r a t i o n s o n a p i l o t - p l a n t s c a le .

T h e s c o p e a n d i n t e n s i t y o f t h e p i l o t - p l a n t d e m o n -

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

u n c e r t a i n t ie s o f t h e p r o c e s s d e s i g n e r . I f a n s w e r s a r e

n o t f o r t h c o m i n g ( o r b e t t e r y e t , a n t i c i p a t e d a n d v o l u n -

t e e r e d ) , t h e d e v e l o p m e n t w i l l s t a ll .

R e g a r d l e s s o f w h e t h e r a p r o g r a m i s p e r c e i v e d t o b e

m a r k e t d r i v e n o r s c i e n c e d r i v e n , s o m e e x p e r i m e n t a l

d a t a a t e a c h s t a g e o f a p r o g r a m w i l l b e v i e w e d b y a

p r o c e s s d e s i g n e r a s p a r t i c u l a r l y c r it i ca l . I n m y e x p e r i -

e n c e , u n d e r s t a n d i n g t h e i m p l i c a t i o n s o f th e :

cha rac te r i s t i c s of the ca ta lys t ,

p r o t o c o l f o r m a n u f a c t u r e o f t h e c a t a l y s t, a n d

c o n t e m p l a t e d ( p r o j e c t e d ) c o m m e r c i a l r e a c t o r , a r e

c r i ti c a l t o t h e s u c c e s s o f t h e p r o g r a m .


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370 A. B isio/ Catalysis Today 36 1997) 367-374

Table 1

Characteristics of industrial heterogeneous catalysts a

Activity

Selectivity

Stability

Morphology

Mechanical

Thermal

Regenerability

Manufacturability

Reactor productivity/operatingconditions

Undesirable/competitive eactions

Poisoning, fouling, sintering, phase transfor-

mation

Form, g rain size, filling density

Strength/crushing/attrition abrasion/erosion

Therm al conductivity, specific heat

Activity, selectivity,mech anical strength

Reproducibility

Adopted from Ref. [9].

T h e a p p a r e n t s i m i l a r it y o f F i g s . 1 a n d 2 m a y b e

m i s l e a d i n g t o s o m e . T h e e n g i n e e r i n g a n a l y s e s d o n e

b e t w e e n e a c h o f t h e in d i c a t e d s t a g e s a n d t h e c o m -

m e r c i a l d e s i g n a r e , in m y e x p e r i e n c e , q u i t e d i f f e r e n t,

f o r m a r k e t - d r i v e n a n d s c i e n c e - d r i v e n p r o g r a m s . A

c o m m e r c i a l d e s i g n n o t o n l y a d d r e s s e s e q u i p m e n t ,

s y s t e m s , a n d p h y s i c a l l a y o u t , b u t a l s o c a t a l y s t p r e -

p a r a t i o n o n a c o m m e r c i a l s c a l e , s a f e o p e r a t i n g p r o -

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

e t c . I n a s c i e n c e - d r i v e n p r o g r a m , m a n y o f t h e s e w i l l b e

d o n e f o r t h e ' f i rs t t i m e ' o n a c o m m e r c i a l s c a l e .

W h e n i n a s e r i e s o f s t u d i e s o n e i g n o r e s o r m i n i -

m i z e s th e i m p o r t a n c e o f s t u d y i n g s o m e c h a r a c t e r i st i c s

o f t h e c a t a l y s t ( T a b l e 1 ) b y e i t h e r a s s u m i n g t h e a n s w e r

o r r e a s o n i n g b y a n a l o g y , o n e i s a s k i n g f o r f u t u r e

d i f fi c u lt ie s . F o r e x a m p l e , t h e m o r p h o l o g y o f a c a t a l y s t

i s o f t e n c r i t i c a l t o t h e s e l e c t i o n o f t h e c o m m e r c i a l

r e a c t o r s y s t e m . T h e p h y s i c a l f o r m o f a c a t a ly s t a n d i t s

g r a i n s i z e m u s t b e s u i t e d t o t h e p r o j e c t e d r e a c t o r .

U n f o r t u n a t e l y , t h e f o r m , g r a i n s i z e , a n d f i l li n g d e n s i t y

o f a c a t a l y s t a r e a l l r e l a t e d t o i t s p o r e v o l u m e ; t h e r e -

f o r e , c h a n g e s i n w h a t a p p e a r t o b e u n i m p o r t a n t p h y -

s i c a l p r o p e r t i e s m a y h a v e a c o m p l e x i n t e r a c t i o n o n

ca ta lys t ac t iv i ty and , pa r t i cu la r ly , s e l ec t iv i ty .

F o r a p r o c e s s d e s i g n e r t h e r e p r o d u c i b i l i t y o f t h e

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

l u a t i o n o f t h e l a b o r a t o r y a n d p i l o t - p l a n t d a t a . W e a r e

a l l a w a r e t h a t t h e p e r f o r m a n c e o f a c a t a l y s t d e p e n d s o n

h o w i t h a s b e e n m a n u f a c t u r e d ; s e e m i n g l y , s m a l l d i f -

f e r e n c e s in t h e p r o c e d u r e c a n h a v e a m a r k e d i m p a c t o n

t h e p e r f o r m a n c e o f a c a t a l y s t . H o w e v e r , I h a v e b e e n

i n v o l v e d i n s e v e r a l d e v e l o p m e n t p r o g r a m s w h e r e

s i g n i f ic a n t e f f o r t a n d t i m e h a d t o b e d e v o t e d t o r e p r o -

d u c i n g ' t h e b a t c h ' o f t he c a t a l y s t t h at p e r f o r m e d v e r y

w e l l m o n t h s b e f o r e . W h e n t h i s h a p p e n s , a p r o g r a m

c a n b e s e r i o u s l y d i sr u p t e d ; i f i t o c c u r s m o r e t h a n o n c e ,

p a r t i c u l a r l y w h e n s t u d i e s ar e b e i n g c o n d u c t e d i n p i l o t

u n i ts , t h e p r o g r a m i s i n j e o p a r d y o f b e i n g t e r m i n a t e d .

T h e l i f e o f a c a t a l y s t ( n u m b e r o f r e g e n e r a t i o n s a n d

h o u r s o n - l i n e ) w i l l d e t e r m i n e m a n y i m p o r t a n t f a c t o r s

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

p r o j e c t e c o n o m i c s . U n f o r t u n a t e l y , l a b o r a t o r y p r o -

g r a m s a n d p i l o t - p l a n t t e s t s w i l l n o t ( a t l e a s t f o r a

p r o c e s s d e s i g n e r ) y i e ld u n e q u i v o c a l i n f o r m a t i o n a b o u t

t h e c a t a l y s t l i fe , w h i c h o n l y a c o m m e r c i a l e x p e r i e n c e

w i l l . T h e r e f o r e , t h e d e v e l o p m e n t p r o g r a m s h o u l d

g e n e r a t e i n f o r m a t i o n a b o u t e a c h o f t h e p a t h w a y s ,

e .g . , po i soning , foul ing , s in te r ing , e t c . t ha t can spec i -

f i c a ll y i m p a c t t h e l i f e o f th e c a t a l y s t u n d e r s t u d y a n d

h o w o n e g o e s a b o u t t o r e c o v e r a c t i v i t y [ 3 , 4 ] . P r o j e c -

t i o n s a b o u t t h e c a t a l y s t l i f e a r e m o r e r e l i a b l e i n a

m a r k e t - d r i v e n p r o g r a m .

A l a r g e n u m b e r o f d i v e r s e r e a c t o r t y p e s a r e u s e d

c o m m e r c i a l l y . I n t e x t b o o k s , t h e r e i s a t e n d e n c y t o

d i s c u s s t h e s e i n i d e a l i z e d t e r m s s u c h a s P F R A a n d

C S T R S . A f e e l i n g f o r t h e r i c h n e s s a n d v a r i e t y o f

Table 2

There is a comp lex nteraction between the catalyst and the reactor a

Reac tor type Residence time distribution Catalyst

Fluid(s) Solid Activity Tem perature

Fixed bed PF Batch f(t) f(Z,R)

Fluid bed PF CST, STR f(t) 'Uniform'

Slurry CST or PF CST, STR f(t) 'Uniform'

Gauze 'PF/CST' Batch f(t) 'Uniform'

Trickle bed 'PF' Batch f(0 f(ZvR)

Mo ving bed PF PF Constant f(Z,R)

Transport line PF PF Constant f(Z)

a Adopted from Ref. [1].


5/8

A. Bisio / Catalysis Today

c o m m e r c i a l r e a c t o r s i s e s s e n t ia l ; t h i s c a n b e o b t a i n e d

f r o m a s t u d y o f t h e p a t e n t l i t e r a t u r e o r a c a r e f u l

r e a d i n g o f R e f . [ 5] .

W h a t i s i m p o r t a n t f o r t h e p r o c e s s d e s i g n e r a n d

u l t i m a t e l y t h e o p e r a t o r o f t h e p l a n t i s t h e c o m p l e x

i n t e r a c t i o n b e t w e e n t h e c a t a l y s t , t h e r e a c t a n t s a n d

p r o d u c t s , a n d t h e r e a c t o r ( T a b l e 2 ). T h e p h a s e r e l a -

t ions in the reac t ion space , e .g . , so l id- l iquid , a re

c r i t i c a l t o b o t h t h e s e l e c t i o n a n d t h e d e s i g n o f a

r e a c t o r . T h e y a r e p a r t i c u l a r l y i m p o r t a n t w h e n , t o

o p t i m i z e c o n v e r s io n a n d y i e ld , a n u m b e r o f r e a c t o rs

a r e c o m b i n e d ( i n t e r c o n n e c t e d ) i n t o a r e a c t o r s y s t e m .

W h i l e m a n y t e x t b o o k s d i s c u s s g i v e n s p e c if i c f l o w a n d

t h e r m a l c o n d i t i o n s , c e r t a i n r e a c t o r s a s ' i d e a l ' , n e v e r -

t h e l e s s a r o b u s t r e a c t o r d e s i g n m u s t , a t a m i n i m u m ,

addres s :

F o r m a t i o n o f f l o w p a t t e r n s i n t h e r e a c t o r , e . g ., d e a d

z o n e s , s h o r t - c i r c u i t f l o w s , a n d c h a n n e l i n g ;

T r a n s p o r t p r o c e s s e s i n t h e i n d i v i d u a l p h a s e s i n t h e

r e a c t o r , e . g . , a x i a l b a c k m i x i n g ;

T e m p e r a t u r e a n d c o n c e n t r a t i o n p r o f i l e s t h a t a r e a

r e s u l t o f t r a n s p o r t r e s i s t a n c e i n , a n d b e t w e e n

phases ;

S e g r e g a t i o n p r o c e s s e s ;

I n c o m p l e t e m i x i n g o f r e a ct a n ts ;

A c c o m m o d a t i o n o f c a t a ly s t a c t iv i ty ; a n d

D e a c t i v a t i o n .

I n m y j u d g m e n t , t h e b e s t d i s c u ss i o n o f t h e c o m p l e x

i n t e r a c ti o n s t h a t a p r o c e s s d e s i g n e r m u s t c o p e w i t h c a n

b e f o u n d i n [ 1 ] . T h o s e w h o c a n o b t a i n a r e a s o n a b l e

m a s t e r y o v e r t h e m a t e r i a l i n t h i s t e x t ( p a r t i c u l a r l y ,

s i n c e i t w a s n o t w e l l p r o o f r e a d ) a r e p r e p a r e d t o

a d d r e s s t h e c h a l l e n g e o f t h e c u r r e n t l i t e r a t u r e .

I n t h i n k i n g a b o u t c a t a l y s t p r o c e s s d e v e l o p m e n t , i t i s

u s e f u l t o c o n s id e r w h a t m e a n i n g f u l i n f o r m a t i o n c a n b e

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

p i l o t - p l a n t r e a c t o r s ( T a b l e 3 ) . I n p r a c t i c e , t h e s c o p e

o f t h e l i s t e d s t u d i es o f t e n o v e r l a p , s o m e t i m e s s i g n if i -

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

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

e x p e r i e n c e a n o r g a n i z a t i o n h a s w i t h t h e n a t u r e o f t h e

c a t a l y s t - r e a c t o r c o m b i n a t i o n u n d e r s tu d y . F o r e x a m -

p l e , L u r g i ( a w e l l - e s t a b l i s h e d l i c e n s o r o f m e t h a n o l

c a t a l y s t s a n d p r o c e s s t e c h n o l o g y ) w o u l d , i n m y j u d g -

m e n t , a p p r o a c h t h e d e v e l o p m e n t o f a n F C C c a t a l y s t

v e r y d i f f e r e n t l y f r o m h o w E x x o n ( a p i o n e e r i n F C C

t e c h n o l o g y ) w o u l d . T h e c o n v e r s e w o u l d b e t ru e , in m y

36 1997) 367-3 74 371

Table 3

Applicability of laboratory-scale reactors to the development of

catalytic processes

Objective of st ud y Understanding nformation sought

Catalyst screening

Param eter screening

Reaction network

Kinetic parameters

Catalyst life

Process 'optimization'

Scaleup"

Developm ent of catalyst candidates

Identification of reaction variables

Characterization of reactio n pathways

(in a lumped sense)

Development of a 'kinetic model'

Impa ct of operating conditions

Def'me best combination' of catalyst and

conditions

Validation o f critical reactor design issues

a Scaleup studies can be conducted in a variety of units, e.g., pilot

plants, comm ercialunits and hydraulic mockups; the issues being

studied will determine what unit is used. Adopted from Ref. [6].

j u d g e m e n t , i f E x x o n w e r e t o u n d e r ta k e t h e d e v e l o p -

m e n t o f a m e t h a n o l p r o c e s s a n d c a t a l y s t .

D e s i g n o f a r e a c t o r i s f a c i l i ta t e d b y t h e a v a i l a b i l i t y

o f a m a t h e m a t i c a l m o d e l t h a t c o m b i n e s i n f o r m a t i o n

o n r e a c t i o n t h e r m o d y n a m i c s , k i n e t i c s , a n d t r a n s p o r t -

k i n e t i c i n t e r a c t i o n s , e . g . , h e a t a n d m a s s t r a n s f e r

e f f e c t s . T h e e x p e r i m e n t a l i n p u t s n e e d e d t o s u p p o r t

t h e d e v e l o p m e n t o f t h e m o d e l c a n b e o b t a i n e d f r o m

s t u d i e s i n l a b o r a t o r y - s c a l e r e a c t o r s y s t e m s . T h e t r a d i -

t i o n a l a p p r o a c h ( w h i c h i s t h e o n l y a p p r o a c h u n d e r -

s t o o d b y a n o v e r w h e l m i n g m a j o r i t y o f p r o c e s s

d e s i g n e r s , i n c l u d i n g t h e w r i t e r) i n v o l v e s i n t e r p r e t a ti o n

o f s t e a d y - s t a t e o r q u a s i - s t e a d y - s t a t e r e a c t o r p e r f o r -

m a n c e d a t a f r o m w h i c h k i n e t i c r a t e e q u a t i o n c o n s t a n t s

a r e e v e n t u a l ly e x t r a c t e d b y p a r a m e t e r e s t im a t i o n t e c h -

n i q u e s . W h i l e i t i s k n o w n t h a t s u c h d a t a c a n b e

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

p r o c e s s d e s i g n e r w i l l b e s a t is f ie d i f th e k i n e t i c e x p r e s -

s i o n s a r e b a s e d o n a n u n d e r s t a n d i n g o f t h e p r i n c i p a l

c h e m i c a l p a t h w a y s ( i n a l u m p e d s e n s e ) . F o r t u n a t e l y ,

t h e e x t e n s i v e s tu d i e s o f M o b i l a n d r e l a t e d a c a d e m i c

s t u d ie s p u b l i s h e d i n [ 7] , s u m m a r i z e i n a u s e a b l e f o r m ,

h o w t o g o a b o u t o b t a i n i n g a r e a c t i o n n e t w o r k f o r

m i x t u r e s o f r e a c t a n t s.

C o n t i n u o u s -f l o w l a b o r a t o r y r e a c to r s c a n b e b r o a d l y

c l a s si f i e d b y t h e f l o w p a t t e r n o f t h e g a s , l i q u i d , a n d

sol id phases (F ig . 3) ; quant i t a t ive in t e rpre ta t ion of

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

f lo w , is m u c h m o r e c o m p l e x a n d n o t a s s tr a i g h t f o r w a r d

c o m p a r e d t o t h a t o b t a in e d f r o m r e a c t o rs w h o s e f lo w

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


6/8

372 A. B isio/ Catalysis Today 36 1997) 367-374

i N o n - s t ~ s t m I

I

I

Fig. 3. Classification of multiphase laboratory reactors. Adopted from Ref. [6].

[ 8] . M a k i n g a p r o j e c t io n o f t h e p e r f o r m a n c e o f a

c o m m e r c i a l r e a c t o r f r o m s t u d i e s i n a l a b o r a t o r y

r e q u i r e s , a t a m i n i m u m , c a l c u l a t i o n o f

m a s s b a l a n c e s ,

o n e e n e r g y b a l a n c e , a n d

f o r c e b a l a n c e s f o r e a c h f l u i d i n t h e r e a c t o r.

I n a d d i t io n , o n e m u s t d e c o u p l e t h e k i n e t i c s f o r t h e

r e a c t i o n n e t w o r k f r o m t h e d e a c t i v a t i o n o f c a t a l y s t

ac t iv i ty .

M e a n i n g f u l a n d u s e f u l d a t a ( u s e f u l t o a p r o c e s s

d e s i g n e r ) c a n b e s t b e o b t a i n e d i n c o n t i n u o u s i s o t h e r -

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

l o w p r e s s ur e d r o p . C o n t i n u o u s m i c r o r e a c t o r s m e e t i n g

t h e s e c r i t e r i a a r e a v a i l a b l e t o d a y a t a r e a s o n a b l e c o s t ;

m o d e r n m i c r o r e a c t o r s y s t e m s i n c o r p o r a t e :

R e l i a b le m a s s f l o w m e t e r s w i t h a 1 / 2 - 1 % a c c u r a c y

u p t o 5 0 a t m ;

P C - b a s e d c o n t r o l s y s t e m s ; a n d

C o n t i n u o u s a n a l y t i c a l c a p a b i l i t y f o r s t r e a m s c o n -

t a i n i n g g a s e s , l i q u i d s , a n d s e m i s o l i d s , e . g . , w a x e s .

F o r t u na t e l y , t h e c a p a b i l it y o f t h e e q u i p m e n t n e e d e d

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

t i n u e s t o i m p r o v e .

T h e n a t u r e o f t h e s m a l l - s c a l e r e a c t o r ( T a b l e 4 ) t o b e

u s e d d e p e n d s b o t h o n t h e o b j e c t iv e s o f t h e s t u d y

( T a b l e 3 ) a n d t h e n u m b e r o f p h a s e s i n v o l v e d i n t h e

r e a c t i o n s y s t e m . T h e r e c o m m e n d a t i o n s g i v e n i n

T a b l e 4 w e r e d e v e l o p e d f r o m p r a c t i c a l a n d t h e o r e ti c a l

r e a s o n i n g s t h a t a r e t o o l e n g t h y t o b e g i v e n h e r e

( u n f o r t u n a t e l y , t h e o n l y t h o r o u g h d i s c u s s i o n , k n o w n

t o t h e w r i t e r, o f t h e r e a s o n i n g s u p p o r t i n g t h e s e r e c o m -

m e n d a t i o n s i s i n a p r o p r i e t a r y r e p o r t [ 1 0 ] ) . T h e g u i -

d a n c e g i v e n i n T a b l e 4 s h o u l d o n l y b e r e g a r d e d a s a

' m a j o r i t y o p i n i o n ' ; s i t u a t i o n s o f t e n e x i s t w h e r e

l a b o r a t o r y r e a c t o r s o t h e r t h a n t h o s e r e c o m m e n d e d

i n T a b l e 4 a r e a b e t t e r a l t e r n at i v e . F o r e x a m p l e , m a n y

f in e c h e m i c a l m a n u f a c t u r i n g p r o c e s s e s u t i l iz e b a t c h o r

Table 4

A laboratory reactor is not a comm ercial reactor

Objective of study Solid-gas Solid-liquid Solid-gas-liquid

Catalyst screening PFR PFR STR (batch) STR (semi-batch)

Parameter screening CSTR CST R STR (batch) STR (semi-batch)

Reaction network CSTR CSTR Trickle bed CST R

Kinetic parameters CSTR CSTR Trickle bed CST R

Catalyst life CSTR PFR CSTR PFK Trickle bed CSTR

Process 'optimization' CSTR PFR CST R PFR Trickle bed CST R

Scaleup PFR fluidized bed PFR slurry Trickle bed slurry


7/8

A. Bi sio/ Catalysis Today 36 1997) 367-374 373

sem i-ba tch ag i ta ted reac tors . In these cases , the objec -

t i ve s o f a s t udy m a y be a c h i e ve d m or e e f f i c i e n t ly

th r ough the u se o f s im i l a r l a bo r a to r y r e a c to r s .

O ne m us t a lw a ys r e m e m be r t ha t t he sm a l l - s c a l e

e xpe r im e n ta l s t ud i es e nv i s ion e d in Ta b le 4 ge ne r a t e

da t a ; t he y do no t de m ons t r a t e a c om m e r c i a l r e a c to r .

F o r e xa m ple , a C S TR i s r a r e ly u se d i n a c om m e r c i a l

p r oc e s s , s im p ly be c a use f o r a g ive n p r oduc t ion r a t e a

C S T R w i l l ha ve l a r ge r vo lum e tha n a p lug - f low re a c -

to r ( o f t e n c os t i ng m or e ) . H ow e ve r , f o r m a ny sm a l l -

sca le s tudies , CSTRs a re opt ima l s ince :

R a t e s c a n be de r ive d d i r e c t l y f r om s im p le m a te ri a l

ba lances ;

The t e m pe r a tu r e a nd p r e s su r e a r e un i f o r m ;

P a r a m e te r s f o r r e a c t i ve k ine t i c s a nd c a t a ly s t de c a y

can be separa ted; and

C ond i t i ons i n t he r e a c to r do no t va r y by pos i ti on ;

the re fore , the tr anspor t r e s is tances a t phase boun d-

a r ies and wi th in a ca ta lys t can be es t ima ted .

The m e r i t s a nd de m e r i t s o f t he C a r be r r y S p inn ing

B a ske t , B e r ty i n t e r na l r e c yc l e r e a c to r o r e x t e r na l

r e c yc l e C S TR ha ve be e n e x t e ns ive ly d i s c us se d i n

the l i t e r atu r e ; e xpe r i e nc e a nd pe r sona l p r e jud i c e o f t e n

are the bas is for makin g a ch oice in a spec i f ic s itua t ion .

F o r e xa m ple , I do no t l i ke da t a f r om a B e t ty r e a c to r

s inc e one c a nno t be c e r t a in t ha t ga s a nd l i qu id a r e

r e c yc l e d i n kn ow n ( c a l c u la t e d ) p r opo r t ions .

The de ve lopm e n t o f c a t a ly s t s a nd p r oc e s s sy s t e m s

ba se d on t h e m invo lve s m a n ipu la t i on o f a l a r ge num -

be r o f va r ia b l e s ; t he m os t im p or t a n t o f t he se be ing t he

f o l low ing :

C om pos i t i on o f t he c a t a ly s t ;

P r oc e du r e u se d to m a nu f a c tu r e t he c a t a ly s t ; a nd

N a tu r e o f t he e nv i r onm e n t t he c a t a ly s t i s e xpose d

to (e .g . , r eac tants , poison, opera t ing condi t ions) .

S im i l a r ly , c a t a ly s t pe r f o r m a nc e i s a c om pos i t e o f

reac t ion ra te , y ie lds and se lec t iv i ty , ca ta lys t l i f e , and

the pu r i t y o f t he d e s i r e d p r oduc t ( s ).

O ne m igh t b e l i e ve , i n v i e w o f t h is c om ple x i ty , t ha t

c a t a ly s t de ve lopm e n t p r og r a m s w ou ld be ne f i t f r om the

use o f c a r e f u l l y p l a nne d e xpe r im e n ta l de s igns t ha t

pe r m i t c onc lu s ions t o be d r a w n th r ough a r i go r ous

s ta t i s t ica l ana lys is o f the da ta . In recent yea rs , doze ns

o f ' c o o k b o o k s ' o n h o w t o u s e e x p e r im e n t a l de s ig n s

ha ve be e n pub l i she d ; ' c ook so f tw a r e ' t ha t f a c il i t at e s

the des ign and ana lys is of exper iments i s a lso ava i l -

a b l e. H o w e ve r , f a r too f e w s tud ie s , i n m y e xpe r i e nc e ,

u t i l i z e e ve n a s e m b la nc e o f a n e xpe r im e n ta l de s ign .

F o r e xa m ple , I r e c e n t ly s tud i e d ove r 2000 p a t e n t s on a

c om m e r c i a l r e a c t i on o f i n t e r e s t t o a c l i e n t . I n on ly

a bou t 50 o f t he pa t e n t s do t he r e po r t e d c onc lu s ions

a bou t t he r e sponse s e xpe c t e d f r om c ha nge s i n t he

process fac tor s have any s ta t i s t ica l bas is .

W hi l e he t e r oge ne ous c a t a ly s t s c a nno t ye t be

de s igne d , a n unde r s t a nd ing o f t he i r be ha v io r su f f i c ie n t

f o r t he de s ign a nd ope r a t i on o f c om m e r c i a l p r oc e s se s

tha t a r e e nv i r onm e n ta l l y ' a c c e p t a b l e ' , i s i n ou r g r a sp

toda y . H ow e ve r , de ve lop ing a nd c onduc t ing e xpe r i -

menta l s tudies tha t genera te use fu l da ta requi res

answer ing the ques t ion (be fore s ta r t ing a s tudy) :

w hy i s t he s tudy be ing done ? The na tu r e o f t he

phe nom e na to be s tud i e d a nd the p r o j e c t i on o f c om -

m e r c i a l pe r f o r m a nc e t ha t w i l l be m a de f r om the

exper imenta l da ta , i s of c r i t ica l impor tance . Only

w he n th i s ha s be e n c l e a r ly e s t a b l i she d c a n t he be s t

m e thod f o r a n e xpe r im e n ta l s t udy be c hose n . O the r -

wise , the s tudy may resul t in da ta which i s of l i t t le

va lue a nd , un f o r tuna t e ly , m a y be m i s l e ad ing ; a s m a ny

studies do

A r e a d ing l i s t m a y be m or e a pp r op r i a t e f o r m a ny

tha n a s e t o f r e f e re nc e s ; in m y judg m e n t t he f o l l ow ing

are pa r t icu la r ly re levant to the i ssues revi ewe d in th is

ar t ic le .

A c k n o w l e d g e m e n t s

I w ou ld l i ke t o e xp r e s s m y g r a t i tude t o m a n y e xpe r t s

a nd f r i e nds ( p r oc es s de s igne r s) w h o he lpe d m e in t he

p r e pa r a t i on o f t h i s a r t ic l e by p r ov id ing ke y in f o r m a -

t i on o r r e v i e w ing the t e s t . I w ou ld e spe c i a l l y l i ke t o

tha nk G ia nn i A s t a r i t a , M or de c ha i H e r skow i t z a nd

R e ue l S h inna r ; how e ve r , t he pa s s ion w i th w h ic h som e

of t he v i e w s a r e e xp r e s se d i s so l e ly t he r e spons ib i li t y

of the author .

References

[1] J.J. Carberry, Chemical and Catalytic Reaction Engineering,

McGraw-Hill, New York, NY, 1976.

[2] L.L. Fassbender et al., Catalysis by Design: A Coordinated

Approach to Catalyst Research and Development. Paper

presented at the AIChE summer meeting, Philadelphia, PA,

1989.


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[3] G.E Froment, Fixed Bed Reactor Design, in S.L. Whitaker

and A.E. Cassano (Eds.), Concepts and Design of Chemical

Reactors, Gordon and Breach, New York, NY, 1986, pp. 179-

212.

[4] C.E Fmment and K.B. Bischoff, Chemical Reactor Analysis,

2nd edn., Wiley, New York, NY, 1990.

[5] K.D. Henkel, Reactor Types and their Industrial Applications,

in Ullmann's Encyclopedia of Industrial Chemistry, 5th edn.,

Vol. B-4., VC H Publishers, Weinheim, 1992, pp. 87-120.

[6] P.L . Mi lls et al., Rev. Chem . Eng., 8 (19 92) 139.

[7] A.M. SapI and EJ. Krambeck (Eds.) , Chemical Reactions in

Complex Mixtures, The Mobil Workshop, Van Nostrand

Reinhold, New York, NY, 1991.

[8] P. Trambou ze, C hemical Reactors: D esign, Engineering,

Operations, Gu lf Publishers, Houston, TX, 1988.

[9] M.P . Dudukovic, Reac tion Eng ineering for Multiphase

Catalyzed Systems, AIChE Continuing Education Lecture

Notes, New York, NY, 1993.

[10] Catalytica Associates Report, in A Practical Guide to Catalyst

Testing, Study No. 4186TE9, 1987.

Documents

1997. Catalytic Process Development_A Process Designer's Point of View