Free Chlorine - University of Illinois Extension

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the heterogeneous reaction between aqueous free chlorine and granular activated carbon. ..... SIT sso. Oxidized sites per unit mass of carbon x k d /4. ,3 P ...... rate of free chlorine removal in a packed bed reactor model makes Equation.
WRC RESEARCH REPORT NO. 103

REDUCTION OF AQUEOUS FREE CHLORINE WITH GRANULAR ACTIVATED CARBON

Makram T. Suidan and Vernon L. Snoeyink U n i v e r s i t y of I l l i n o i s a t Urbana-Champaign Urbana, I l l i n o i s

F I N A L REPORT P r o j e c t No. A-066-ILL

The work upon which t h i s p u b l i c a t i o n i s based was supported i n p a r t by funds p r o v i d e d by t h e U. S. Department o f t h e I n t e r i o r as a u t h o r i z e d under t h e Water Resources Resarch A c t o f 1964, P. L. 88-379 Agreement No. 14-31-0001-5013

UNIVERSITY OF ILLINOIS WATER RESOURCES CENTER 2535 Hydrosystems L a b o r a t o r y Urbana, I l l i n o i s 61801

August 1975

ABSTRACT REDUCTION OF AQUEOUS CHLORINE WITH GRANULAR ACTIVATED CARBON A surface r e a c t i o n r a t e expression was developed t o describe t h e heterogeneous r e a c t i o n between aqueous f r e e c h l o r i n e and g r a n u l a r a c t i v a t e d carbon. This expression was then i n c o r p o r a t e d i n t o a pore d i f f u s i o n model and t h e r e l e v a n t p a r t i a l d i f f e r e n t i a l equations w i t h t h e corresponding boundary c o n d i t i o n s were solved f o r t h e case o f (1) a constant c o n c e n t r a t i o n batch r e a c t o r and ( 2 ) a closed batch r e a c t o r . The s o l u t i o n s were then compared t o s i m i l a r batch data i n o r d e r t o e v a l u a t e t h e pore model constants. A packed bed r e a c t o r model was then solved u s i n g t h e r a t e i n f o r m a t i o n from t h e batch rr~athematical models and experimental data. The p r e d i c t e d r e s u l t s from t h e packed bed model were then compared t o experimental r e s u l t s which were c o l l e c t e d using applicable conditions. The e f f e c t o f p a r t i c l e s i z e on t h e r a t e o f removal o f f r e e c h l o r i n e was i n v e s t i g a t e d both i n batch and packed bed column form. The e f f e c t o f pH on t h e r a t e o f r e a c t i o n was s t u d i e d i n t h e pH range I t was found t h a t t h e pH o n l y a f f e c t s t h e r a t e i n s o f a r as i t o f 4-10. a f f e c t s t h e d i s t r i b u t i o n o f f r e e c h l o r i n e between O C l s and HOC1. Temperature e f f e c t s were a l s o s t u d i e d i n t h e range 2"-35°C. The e f f e c t o f temperature on t h e surface d i s s o c i a t i o n r a t e constant was found t o correspond t o t h e Arrhenius law. Suidan, Makram T. and Vernon L. Snoeyink REDUCTION OF AQUEOUS FREE CHLORINE WITH GRANULAR ACTIVATED CARBON F i n a l r e p o r t t o t h e O f f i c e o f Water Resources Research, Department of t h e I n t e r i o r on Annual A l l o t m e n t P r o j e c t A-066-ILL, August 1975. KEYWORDS: dechl o r i nation/mathernati c a l model /pore d i f f u s i on/packed bed model

ACKNOWLEDGEMENT This r e p o r t represents t h e t h e s i s o f Makram T. Suidan, submitted i n p a r t i a l f u l f i l l m e n t of t h e requirements f o r t h e degree of Doctor of Philosophy i n Environmental Engineering i n C i v i l Engin e e r i n g a t t h e U n i v e r s i t y of I l l i n o i s a t Urbana-Champaign, 1975. The authors wish t o thank Drs. Roger A. Schmitz, Jon C. Liebman and A r t h u r R. Robinson whose i n t e r e s t and many v a l u a b l e sugg e s t i o n s c o n t r i b u t e d a g r e a t deal towards t h e completion o f t h i s investigation.

The i n p u t provided by Drs. Edward S. K. Chian, Paul

A. Jennings, M r . Gerald E. Q u i n d r y and M r . David L. Dunn i s g r a t e f u l l y

acknowledged. T h i s study was supported, i n p a r t , by funds provided by t h e U n i t e d States Departrnent of t h e I n t e r i o r as a u t h o r i z e d under t h e Water Resources Research A c t o f 1964, P u b l i c Law 88-379. The numerical a n a l y s i s was c a r r i e d o u t u s i n g t h e I B M 360/75 computer system o f t h e Computer Services O f f i c e o f t h e U n i v e r s i t y o f I l l i n o i s , Urbana, I l l i n o i s .

i

iv

TABLE OF CONTENTS Page I.

. . . . . . . . . . . . L i t e r a t u r e Review . . . . . . . . . 1. D e c h l o r i n a t i o n w i t h S u l f u r Compounds . 2. D e c h l o r i n a t i o n w i t h Hydrogran Peroxide, Ammonia and Ferrous S u l f a t e . . . . 3. D e c l o r i n a t i o n w i t h A c t i v a t e d Carbon. .

A.

a. b. c. B. 11.

. . . . .

3 5

. . . . .

5

INTRODUCTION

Free C h l o r i n e - A c t i v a t e d Carbon Reactions D e c h l o r i n a t i o n Bed L i f e and Regeneration Rate o f Reaction and Modeling o f D e c h l o r i n a t i o n Beds.

Objective o f

. . . . . . . . . . . . Study . . . . .

. . . . . . . . . . . . . . .

. . . . . . . . . . S u r f ace Reaction Rate Expression . . . . . Model f o r Reaction w i t h i n Carbon Pores . . . Boundary C o n d i t i o n s and Reactor Matherrlati c a l Model s . . . . . . . . . 1. B a t c h R e a c t o r s . . . . . . . . . .

THEORETICALANALYSIS A. B. C.

. . . . .

a.

. . . . . . . . . . . . . . Packed Bed Column Reactor . . . . . a. Approximate Rate Expression . . .

b. c.

2.

Constant Concentration Batch Reactor. . Closed Batch Reactor Nondimensionalized Batch Models.

. .

1 1 1

10 14 16 18

.

19 21

. .

25

. . . .

. . . . . . b. M o d i f i e d Packed Bed Reactor Model . . . c . Nondimensi onal ized Packed Bed Reactor Model . . . . . . . . . . d. Plug Flow Packed Bed Reactor Model . . . . . . . . . . . .

26 26 27 28 29 33 35 35 38

. . A c t i v a t e d Carbon. . . . . . . Free C h l o r i n e Measurement. . Color Measurement . . . . . Free C h l o r i n e S o l u t i o n s . . Experimental . . . . . . . . 1. Batch Experiments . . . a. Closed Batch Experiments . b. Constant Concentration Batch Experiments. . . . . . 2. Packed Bed Column Experiments .

EXPERIMENTAL MATERIALS AND METHODS

A. B. C. D. E.

IV.

RESULTS AND DISCUSSION A. B.

C.

D. E.

F.

C.

. . . . . . . . . .

. . . . . . . . . .

. . . . . . . . . .

. . . . . . . . . .

. . . . . . . . . .

. . . . . . . . . . .

Rate o f C h l o r i n e Disappearance from Blank Reactor. Experiments a t pH 4.0 and 23°C

. . . . . . . Batch Studies . . . . . P a r t i c l e Size E f f e c t Studies PackedBedStudies. . . .

. . 1. . 2. . 3. . Experiments a t pH 10.0 and 23°C. . 1. B a t c h s t u d i e s . . . . . . 2. Packed Bed Studies. . . . .

. . . . . . . .

. . . . . . . .

. . . . . . . .

Experiments a t pH 7 . 6 and 23" . . . . . Temperature E f f e c t Studies a t pH 4.0 and 10.0 P r e d i c t i o n o f Model Constants f o r D i f f e r e n t pH and Temperature Values.

. . . . . . . .

. . . . . . . .

. .

. . . . . . . . . . . . . . . . . . . . . .

. Conclusions . . . . . . Engineering S i g n i f i c a n c e . . F u r t h e r Study. . . . . .

CONCLUSIONS AND RECOMMENDATIONS

A. B.

. . . . . . .

LIST OF REFERENCES.

. . . .

. . . .

. . . ~

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

L I S T OF FIGURES Page

Figure

1.1

NoOH T I T R A T A B L E SURFACE OXIDES PRODUCED BY THE REACTION OF FREE CHLORINE WITH ACTIVATED CARBON

8

REDUCTION I N p-NITROPHENOL ADSORPTION CAPACITY A S A FUNCTION OF THE AMOUNT OF FREE CHLORINE REACTED.

9

. . . . . . . . . . . . .

. . . . . . . . . . . . . . .

.

12

. . . . . . .

22

SCHEMATIC DIAGRAM OF PACKED BED COLUMN REACTOR.

. . . . . . . . . . . . .

31

CHLORINE REDUCTION RATE v s X I N A CCBR, p H 4, 23°C

36

RATE OF CHLORINE DISAPPEARANCE I N BLANK REACTOR.

46

CHLORINE-CARBON (60 x 80 MESH) REACTION I N A 30 MG/LyASC12yCCBRypH4y230C

48

CHLORIME-CARBON (60 x 80 MESH) REACTION I N A 2 0 MG/L, A S C l 2, CCBR, p H 4, 23°C.

49

CHLORINE-CARBON (60 x 80 MESH) REACTION I N A 10 MG/L, A S C l 2, CCBR, p H 4, 23°C

50

CHI-ORINE-CARBON (60 x 80 MESH) REACTION I N A 5 MG/L, A S C12, CCBB, p H 4, 23°C.

51

CHLORINE-CARBON (60 x 80 MESH) REACTION I N A CLOSED BATCH REACTOR, p H 4, 23°C.

54

CHLORINE-CARBON ( 4 5 x 5 0 MESH) REACTION I N A 30 MG/L, A S C12, CCBR, p H 4, 23°C

55

CHLORINE-CARBON ( 4 5 x 5 0 MESH) REACTION I N A CLOSED BATCH REACTOR, p H 4, 23°C.

58

CHLORINE BREAKTHROUGH CURVE, p H 4, 23"C, 60 x 80 MESH CARBON

59

DECHLORINATION BED L I F E .

.

.

SCHEMATIC DIAGRAM OF CARBON PORE.

. . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

.

. . . . . . . . . . . . . . .

. . . . . . .

. . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . .

Page CHLORINE BREAKTHROUGH CURVE, p H 4 , 23"C, 18 x 20 MESH CARBON

. . . . . . . . . . .

CHLORINE AND COLOR BREAKTHROUGH CURVE, p H 3.2-5.8, 23"C, 6 0 x 80 MESH CARBON

. . . . .

CHLORINE CARBON (60 x 80 MESH) REACTION I N A CLOSED BATCH REACTOR, p H 10, 23°C.

. . . . .

CHLORINE BREAKTHROUGH CURVE, p H 10, 23"C, 6 0 x 80 MESH CARBON

. . . . . . . . . . .

CHLORINE-CARBON ( 6 8 x 88 MESH) REACTION I N A CLOSED BATCH REACTOR, p H 7 . 6 , 23°C

. . . . . .

CHLORINE-CARBON (60 x 80 MESH) REACTION I N A CLOSED BATCH REACTOR, p H 7.6, 23°C

. . . . . .

CHLORINE-CARBON ( 6 0 x 80 MESH) REACTION I N A CLOSED BATCH REACTOR, p H 10, 35°C

. . . . . .

CHLORINE-CARBON ( 6 0 x 80 MESH) REACTION It4 A CLOSED BATCH REACTOR, pH 10, 2°C.

. . . . . .

CHLORINE-CARBON ( 6 0 x 80 MESH) REACTION I N A CLOSED BATCH REACTOR, p H 4, 35°C

. . . . . .

CHLORINE-CARBON ( 6 0 x 80 MESH) REACTION I N A CLOSED BATCH REACTOR, p H 4, 35°C

s

EFFECT OF TEMPERATURE ON T H E PARAMETER S S T

. . .

NOTAT ION Packed bed c r o s s - s e c t i o n a l area Pore s u r f a c e area p e r u n i t w e i g h t o f carbon Free c h l o r i n e c o n c e n t r a t i o n p e r u n i t volume o f solution I n i t i a l , b u l k o r i n f l u e n t f r e e c h l o r i n e concentrat i o n f o r c l o s e d batch, c o n s t a n t c o n c e n t r a t i o n b a t c h and packed bed r e a c t o r Reactive s i t e s c o n c e n t r a t i o n p e r u n i t s u r f a c e area o f carbon Adsorbed f r e e c h l o r i n e c o n c e n t r a t i o n p e r u n i t s u r f a c e area o f carbon

CO*

Oxidized s i t e s c o n c e n t r a t i o n p e r u n i t s u r f a c e area o f carbon T o t a l s i t e s c o n c e n t r a t i o n p e r u n i t s u r f a c e area o f carbon

CCBR

Constant c o n c e n t r a t i o n b a t c h r e a c t o r Packed bed a x i a l d i s p e r s i o n c o e f f i c i e n t Free c h l o r i n e pore d i f f u s i o n c o e f f i c i e n t Diameter o f s t r a i g h t c y l i n d r i c a l pore Dirr~ensionlessf r e e c h l o r i n e c o n c e n t r a t i o n i n packed bed model Dimensionless f r e e c h l o r i n e c o n c e n t r a t i o n i n pore model Packed bed r e s i d e n c e t i m e

Dimensionless p o s i t i o n v a r i a b l e used i n packed bed numerical s o l u t i o n Constant i i n expression f o r R(X,C) F i r s t o r d e r r e a c t i o n r a t e c o n s t a n t i n Magee's packed bed column r e a c t o r Free c h l o r i n e - a c t i v a t e d carbon a d s o r p t i o n r a t e constant Free c h l o r i n e - a c t i v a t e d carbon d e s o r p t i o n r a t e constant

MIL T SITE

Surface r e a c t i o n d i s s o c i a t i o n r a t e c o n s t a n t

MIL T SITE

Adsorption-desorption e q u i l i b r i u m constant

M/ L3

Numerator c o n s t a n t i n SSO expression

SITEIM

Dimension1 ess c o n s t a n t i n SSO expression F i r s t o r d e r r a t e o f decay c o n s t a n t Packed bed 1ength Pore h a l f l e n g t h Number o f segments i n t o which packed bed i s subd i v i d e d f o r numerical s o l u t i o n purposes Mass o f carbon p e r u n i t r e a c t o r volume Number o f segments i n t o which h a l f pore i s d i v i d e d f o r numerical s o l u t i o n purposes

2 x number o f pores p e r u n i t w e i g h t o f carbon

Dimensionless p o s i t i o n i n time used i n packed bed numerical s o l h t i o n Free c h l o r i n e mass c o n c e n t r a t i o n per u n i t mass o f carbon Pec 1e t

number

I n i t i a l o r b u l k f r e e c h l o r i n e c o n c e n t r a t i o n per u n i t mass o f carbon f o r closed batch o r CCBR models Negative logl

of equi 1 ibriurn constant

Mass o f f r e e c h l o r i n e reacted per u n i t mass o f carbon Dimensionless p o s i t i o n i n t i m e used i n numerical s o l u t i o n o f pore model Dimensionless r a t e term i n pore model Surface r e a c t i o n r a t e Rate o f f r e e c h l o r i n e decay i n blank Reactor Rate o f c h l o r i n e removal f o r a c o n c e n t r a t i o n o f carbon equal t o m

Free c h l o r i n e mass removal r a t e per u n i t mass o f carbon

=

Dimensionless p o s i t i o n i n space used i n numerical s o l u t i o n o f pore model Rate o f f r e e c h l o r i n e mass a p p l i e d per u n i t mass o f carbon i n packed bed r e a c t o r SIT

2 SST x Lp/Dc

sso

Oxidized s i t e s per u n i t mass o f carbon x k d / 4 ,3 P

SST

T o t a l r e a c t i v e s i t e s p e r u n i t mass o f carbon x k3dp/4

T‘ K

A b s o l u t e temperature Cumulative t i m e f o r b a t c h o r column r u n

T

Bed r e s i d e n c e t i m e i n Magee's model

T

A x i a1 v e l o c i t y through packed bed r e a c t o r

L/T

Pore volume p e r u n i t mass o f carbon

L3/M

Free c h l o r i n e mass r e a c t e d p e r u n i t s u r f a c e area

M/ L~

T o t a l f r e e c h l o r i n e r e a c t e d p e r u n i t mass o f carbon P o s i t i o n v a r i a b l e i n pore model D i s t a n c e v a r i a b l e i n packed bed column model Change from. mean c o n c e n t r a t i o n , C o y a1 lowed i n CCBR experiments Enthal py o f Reaction Dilr~ensionlessd i s t a n c e s t e p used i n numerical s o l u t i o n o f packed bed r e a c t o r model Dimensionless t i m e s t e p used i n numerical s o l u t i o n o f packed bed r e a c t o r model Dimensionless t i m e s t e p used i n numerical s o l u t i o n o f p o r e model Dimensionless d i s t a n c e s t e p used i n numerical s o l u t i o n o f p o r e model Dimensionless p o s i t i o n v a r i a b l e i n packed bed model Packed bed p o r o s i t y

X)-1

Lapow paq p a y ~ duk alqekvleh awl2 s s a l u o k s u a ~ ~ ~ k a Lapow a ~ o du k a l q ~ J~ P A uo !J !sod ssa l u o ksuawka Lapow a ~ o du k a ~

~ P ~ JawkJ P A

ssa luoksuauka

u o k ~ 10s n 40 AJ 1 ~ 0 3 LsA aJn l o s q y

I. INTRODUCTION

Free c h l o r i n e has been used i n water t r e a t m e n t f o r many years. I t s p r i m a r y use i s f o r d i s i n f e c t i o n , a l t h o u g h i t has a number o f o t h e r a p p l i c a t i o n s , such as ammonia removal and t a s t e and odor c o n t r o l .

Free

c h l o r i n e r e s i d u a l i s sometimes i n excess o f d e s i r e d l e v e l s , and conseq u e n t l y i t has t o be removed o r reduced i n c o n c e n t r a t i o n .

T h i s may be t h e

case, f o r example, a f t e r b r e a k p o i n t c h l o r i n a t i o n , e s p e c i a l l y o f wastewater. A number o f i n d u s t r i e s a l s o r e q u i r e c h l o r i n e f r e e water because o f t h e i n t e r f e r e n c e o f c h l o r i n e w i t h some i n d u s t r i a l processes.

These and many

o t h e r reasons i l l u s t r a t e t h e importance o f having a w e l l understood p r o cess f o r t h e rerr~ovalo f f r e e c h l o r i n e from water. A.

L i t e r a t u r e Review

A number o f processes have been developed f o r e l i m i n a t i n g o r r e d u c i n g f r e e c h l o r i n e r e s i d u a l s from water, t h e use o f s u l f u r compounds b e i n g t h e most common.

A c t i v a t e d carbon, hydrogen peroxide, ammonia and

f e r r o u s s u l f a t e have a l s o been used.

Snoeyink and Suidan (1975) conducted

an i n t e n s i v e 1 it e r a t u r e r e v i e w o f t h e s u b j e c t o f d e c h l o r i n a t i o n and some o f t h e m a t e r i a l i n t h i s s e c t i o n was taken from t h a t r e v i e w . 1.

D e c h l o r i n a t i o n w i t h S u l f u r Compounds The most cornlnon procedure f o r r e d u c i n g f r e e c h l o r i n e r e s i d u a l

i n v o l v e s t h e use o f s u l f u r compounds w i t h s u l f u r i n t h e + I V o x i d a t i o n s t a t e . S u l f u r d i o x i d e i s t h e most p o p u l a r among t h e S(+IV) species, t h e m a j o r

reason f o r which appears t o be t h e c o s t o f u s i n g i t .

Dean (1974) has e s t i -

mated t h a t t h e c o s t o f c h l o r i n a t i o n o f a secondary e f f l u e n t f o r d i s i n f e c t i o n f o l l o w e d by d e c h l o r i n a t i o n w i t h SO2 w i l l be on t h e o r d e r o f 1.2 t o 1.3 times as g r e a t as c h l o r i n a t i o n alone. S u l f u r d i o x i d e i s g e n e r a l l y purchased as a l i q u i d which i s then converted t o a gas i n p r e p a r a t i o n f o r adding i t t o water.

The gas d i s s o l v e s

r e a d i l y i n water f o r m i n g s u l f u r o u s a c i d

The H2S03 p a r t i a l l y i o n i z e s t o g i v e HSO;

and SO;,

t r a t i o n s o f these species b e i n g dependent on pH.

w i t h t h e r e l a t i v e concenSodium b i s u l f i t e , NaHS03,

and sodium s u l f i t e , Na2S03, a r e s a l t s which a r e a l s o used as a source of S(+IV) f o r d e c h l o r i n a t i o n b u t these a r e g e n e r a l l y more expensive and l e s s s t a b l e than SO2 (Laubusch, 1971).

A m a j o r advantage i n u s i n g SO2 i s t h a t

t h e equipment used f o r f e e d i n g i t i s t h e same as t h a t used f o r dosing c h l o r i n e (White, 1972).

T h i s s i m i l a r i t y serves t o c u t down on equipment

v a r i a b i l i t y i n a p l a n t and thus t o reduce o p e r a t i o n a l d i f f i c u l t i e s . According t o White ( 1 972), hypochlorous a c i d r e a c t s w i t h SO2 as f o l l o w s :

S02

+

H20

+ HOCl

-+

3 H+

+ 50;

+ ~ 1 -

1.2

w i t h s i m i l a r r e a c t i o n s b e i n g a p p l i c a b l e when t h e o t h e r S(+IV) species a r e used.

Using Equation 1.2 as a b a s i s f o r c a l c u l a t i o n , i t can be shown t h a t

0.9 mg o f SO2 i s r e q u i r e d p e r mg of c h l o r i n e , as C12, reduced.

Similarly,

2.1 mg o f a1 k a l i n i t y as CaC03 i s r e q u i r e d t o r e a c t w i t h t h e H+ produced by

1 I

the reaction.

+

I f t h e H r e s u l t i n g f r o m h y d r o l y s i s o f gaseous C12 when i t

i s added t o t h e water i s i n c l u d e d , a t o t a l o f 2.8 mg o f a1 k a l i n i t y i s r e q u i r e d p e r mg o f c h l o r i n e .

I

I

I ' 1

1

There i s some evidence t h a t t h e r e q u i r e d S(+IV)

dose i s a f u n c t i o n o f t h e composition o f t h e water (Gagen, 1941).

states t h a t i t reacts nearly instantaneously w i t h f r e e chlorine.

1

! I

A search

o f t h e a v a i l a b l e l i t e r a t u r e has n o t r e v e a l e d i n f o r m a t i o n on t h e e f f e c t o f pH, temperature and composition o f t h e w a t e r on t h e k i n e t i c s .

I

White (1972)

The k i n e t i c s o f S(+IV) d e c h l o r i n a t i o n a r e v e r y f a s t .

Because o f

t h e v e r y r a p i d r e a c t i o n k i n e t i c s , m i x i n g i s t h e most i m p o r t a n t parameter t o be considered when S(+IV) compounds a r e t o be used f o r dechl o r i n a t i o n . The r e a c t i o n between S(+IV) and oxygen

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

The e x t e n t t o which i t

proceeds wi 11 i n c r e a s e t h e S(+IV) dose, ,but, more i m p o r t a n t l y , d e p l e t i o n o f d i s s o l v e d oxygen may n e c e s s i t a t e a c o s t l y r e a e r a t i o n s t e p i f d e c h l o r i n a -

1 1

I I

t i o n i s b e i n g a p p l i e d p r i o r t o d i s c h a r g e o f a t r e a t e d wastewater t o r e c e i v i n g waters.

I t a l s o i n d i c a t e s t h e importance o f a v o i d i n g any overdose o f

S(+IV), which may be d i f f i c u l t i n c e r t a i n s i t u a t i o n s . Sodium t h i o s u l f a t e , Na2S203, can a l s o be used i n d e c h l o r i n a t i o n

i I

i

b u t i t r e a c t s more s l o w l y t h a n t h e S(+IV) compounds and i t can c o n t r i b u t e t o sensory e f f e c t s i n v o l v e d w i t h t a s t e and odor (Baker, 1964).

It i s u s u a l l y

employed f o r d e c h l o r i n a t i n g water samples p r i o r t o b a c t e r i o l o g i c a l a n a l y s i s .

1 .

J]

2.

D e c h l o r i n a t i o n w i t h Hydrogen Peroxide, Ammonia and Ferrous S u l f a t e Hydrogen p e r o x i d e has n o t been e x t e r ~ s i v e l yused f o r d e c h l o r i n a t i o n

According t o Mishchenko

a l t h o u g h i t may have some p o t e n t i a l i n t h i s respect.

e t aZ. (1960), t h e f o l l o w i n g r e a c t i o n w i l l t a k e place. HOCl

+ H202

+

O2 (aq)

+

H+

T h i s r e a c t i o n i s n o t thermodynamically l i m i t e d

+

~ 1 -+ ~ ~ 0

(AGO

= -36.3

1.4

k c a l a t 25°C)

b u t t h e k i n e t i c s o f t h e r e a c t i o n w i t h f r e e c h l o r i n e have n o t been w e l l defined.

I n view o f t h e l a c k o f i n f o r m a t i o n about t h e use o f t h i s compound

f o r d e c h l o r i n a t i o n , i t i s obvious t h a t much more remains t o be l e a r n e d i f t h e f e a s i b i l i t y o f u s i n g i t i s t o be f u l l y assessed. According t o White (1972) as we1 1 as o t h e r s , ammonia and f e r r o u s s u l f a t e can be used as d e c h l o r i n a t i n g agents.

Ammonia can be used t o e l i m i -

nate f r e e c h l o r i n e v i a the breakpoint reaction,

o r i t can be used t o c o n v e r t f r e e c h l o r i n e t o combined c h l o r i n e .

A very

l o n g r e a c t i o n time, a p p r o x i m a t e l y 20 minutes i n t h e pH range 7 t o 7.5, must be a l l o t t e d f o r t h e b r e a k p o i n t r e a c t i o n , however (White, 1972). Ferrous i o n , Fe",

can a l s o be used as a d e c h l o r i n a t i n g agent,

b u t i t s use i s l i m i t e d t o s i t u a t i o n s where d e c h l o r i n a t i o n i s f o l l o w e d by a s o l i d s removal step.

When o x i d i z e d by c h l o r i n e , ~e''

i s converted t o

~ e which + ~ i s v e r y i n s o l u b l e and which serves as a good coagulant.

Sedi-

m e n t a t i o n and/or f i l t r a t i o n would be r e q u i r e d t o remove i t f r o m t h e water. According t o White (1972), Fe"

reacts r e a d i l y with f r e e chlorine.

3.

D e c h l o r i n a t i o n w i t h A c t i v a t e d Carbon

a.

Free C h l o r i n e - A c t i v a t e d Carbon Reactions A c t i v a t e d carbon has been used f o r d e c h l o r i n a t i o n f o r some time.

The process was f i r s t i n s t a l l e d i n a m u n i c i p a l water t r e a t m e n t p l a n t a t Reading, England i n 1910.

I t appears t o have been used predorninantly f o r

t h e removal o f f r e e c h l o r i n e , a1 though r e f e r e n c e has been rr~ade t o t h e f a c t t h a t i t wi 11 a1 so remove combined c h l o r i n e (Magee, 1956).

Magee (1 956) was

t h e f i r s t t o conduct an i n t e n s i v e s t u d y o f t h i s process b u t d e s p i t e t h e advancement which he and o t h e r s f o l l o w i n g him have made, much remains t o be l e a r n e d about i t . I n v e s t i g a t o r s (Magee, 1956; P u r i , 1970) have s t u d i e d t h e r e a c t i o n between f r e e c h l o r i n e and carbon and a c c o r d i n g t o t h e i r f i n d i n g s , i t can be d e s c r i b e d by t h e f o l l o w i n g equation: HOCl where C

*

co*

r e p r e s e n t s t h e a c t i v a t e d carbon and CO

on t h e carbon.

*

represents a surface oxide

Magee (1956) showed t h a t when f r e e c h l o r i n e i s i n i t i a l l y con-

t a c t e d w i t h a c t i v a t e d carbon, t h e r e i s an i n i t i a l b u i l d u p o f C1-containing species on t h e carbon surface.

A f t e r a p e r i o d o f time, however, t h e c h l o r i d e s

produced i n t h e r e a c t i o n a r e s t o i c h i o m e t r i c a l l y equal t o t h e f r e e c h l o r i n e removed f r o m t h e aqueous s o l u t i o n i n t h e r e a c t o r .

Snoeyink e t aZ. (1974)

a l s o observed s i m i l a r r e s u l t s . The hydrogen i o n produced i n accordance w i t h Equation 1.6 i s i m p o r t a n t because i t may n e c e s s i t a t e a pH adjustment s t e p subsequent t o

dechlorination.

The problem of a pH decrease becomes more severe i f c h l o r i n e

gas i s used as t h e source o f c h l o r i n e .

+ when

H

added t o water.

C h l o r i n e gas hydrolyzes t o produce

The s t o i c h i o m e t r y o f t h e r e a c t i o n i n Equation 1.6

+ , however.

r e q u i r e s f u r t h e r study w i t h r e s p e c t t o p r o d u c t i o n o f H

Based on

t h i s equation, i t i s p r e d i c t e d t h a t no H+ w i l l be produced i f 0C1' r e a c t s i n p l a c e o f HOC1.

However, 01 son and B i n n i n g ( 1 974) and Snoeyi n k e t a l .

(1974) n o t i c e d a pH drop when OC1- reacted, t h e reason f o r which was n o t determined.

I t may be a t t r i b u t a b l e t o t h e f o r m a t i o n o f a s u r f a c e o x i d e i n

t h e form o f a c a r b o x y l group which subsequently i o n i z e s t o produce t h e H', however (Olson and Binning, 1974).

+

no H

I n experiments c a r r i e d o u t by t h e author,

p r o d u c t i o n was observed when t h e carbonate system was i n e q u i l i , b r i u m

w i t h t h e atmosphere.

Thus, t h e drop i n pH observed by Olson and B i n n i n g

(1974) and Snoeyink e t a t . (1974) c o u l d be a t t r i b u t e d t o C02 d i s s o l u t i o n f rorn t h e atmosphere.

The p r o d u c t i o n o f s u r f a c e oxides v i a Equation 1.6 i s i m p o r t a n t because o f t h e i r e f f e c t on t h e d e c h l o r i n a t i o n r e a c t i o n as w e l l as on t h e a d s o r p t i o n o f o r g a n i c compounds by t h e carbon.

Magee (1956) a t t r i b u t e d t h e

gradual r e d u c t i o n i n e f f i c i e n c y o f d e c h l o r i n a t i o n o f a carbon bed t o t h e gradual p o i s o n i n g o f t h e carbon s u r f a c e w i t h these o x i d e s .

He a l s o observed

t h a t these oxides were u n s t a b l e t o a c e r t a i n degree because CO and C02 were released t o t h e s o l u t i o n .

That t h i s does occur i s f o r t u n a t e because i t prob-

a b l y r e s u l t s i n extended l i f e o f t h e carbon f o r d e c h l o r i n a t i o n . Using t h e a n a l y t i c a l procedure o f Boehm (1966), Snoeyink e t a l . (1974) s t u d i e d t h e accumulation o f a c i d i c s u r f a c e oxides as a f u n c t i o n o f t h e amount o f f r e e c h l o r i n e reacted.

As t h e amount o f c h l o r i n e r e a c t e d

increases, t h e s u r f a c e c o n c e n t r a t i o n o f NaOH t i t r a t a b l e o x i d e s reached a p l a t e a u as can be seen i n F i g u r e 1.1.

A t t h e p l a t e a u value, a p p r o x i m a t e l y

15 mmoles f r e e c h l o r i n e (1.06 g as C12) have r e a c t e d p e r gram o f carbon. Many o f t h e t i t r a t a b l e oxides were r e l a t i v e l y v o l a t i l e i n n a t u r e and c o u l d be removed by d r y i n g a t 105°-l100C o r , a l t e r n a t i v e l y , by d r y i n g and o u t gassing, as shown i n F i g u r e 1.1.

The same s t u d y showed t h a t t h e oxides r e -

rnoved by t h i s procedure had l i t t l e e f f e c t on a d s o r p t i o n o f p h e n o l i c compounds. Only a small f r a c t i o n o f t h e o x i d e s which were produced v i a Equation 1.6 were t i t r a t a b l e w i t h NaOH.

On t h e b a s i s o f t h e r e a c t i o n s t o i -

-

chiometry, a one-to-one correspondence between oxides produced and c h l o r i n e r e a c t e d i s expected.

Such was n o t t h e case, however.

Only 1.5-2 mmoles o f

t i t r a t a b l e oxides were formed f o r 15 mmoles r e a c t e d p e r gram; a l s o t h e i n crease i n oxides was n o t l i n e a r b u t reached a p l a t e a u .

Some o f t h e oxides

were p r o b a b l y evolved w h i l e o t h e r s were n o t t i t r a t a b l e w i t h NaOH.

I t was

a l s o found p o s s i b l e t o n e a r l y double t h e c o n c e n t r a t i o n o f NaOH t i t r a t a b l e o x i d e s by u s i n g t h r e e s e q u e n t i a l t r e a t m e n t s o f t h e carbon w i t h 15 mmoles c h l o r i n e p e r gram, w i t h each t r e a t m e n t being f o l l o w e d by d r y i n g o f t h e carbon. The surface oxides which r e s u l t from r e a c t i o n w i t h c h l o r i n e a l s o a f f e c t a d s o r p t i o n o f o r g a n i c compounds.

F i g u r e 1.2 (Snoeyink e t a l . , 1974)

shows t h e decrease i n c a p a c i t y o f carbon f o r p - n i t r o p h e n o l as a f u n c t i o n o f t h e amount o f c h l o r i n e reacted.

Each t r e a t m e n t w i t h c h l o r i n e was followed

by d r y i n g o f t h e carbon a t 105°-l100C p r i o r t o t h e a d s o r p t i o n s t u d i e s .

The

v a l u e a t 60 mrnoleslg was o b t a i n e d by u s i n g carbon which had been r e a c t e d w i t h 15 mmoles c h l o r i n e p e r gram f o u r times and d r i e d a f t e r each treatment. The decrease i n c a p a c i t y may p o s s i b l y be a t t r i b u t e d t o d e s t r u c t i o n o f t h e

Titretable Acidic Oxides, rnmoles/g

p- N itrophenol Surf ace Concentration, 1 0 ~ r n o l e s / ~

carbonyl f u n c t i o n a l groups o r t o pore blockage by t h e s u r f a c e oxides.

These

r e s u l t s a r e g e n e r a l l y c o n s i s t e n t w i t h those o f Cough1 i n e t aZ. (1 968).

The

e f f e c t on a d s o r p t i o n o f o t h e r types o f o r g a n i c compounds may w e l l be d i f f e r e n t t h a n was observed f o r p - n i t r o p h e n o l , e s p e c i a l l y i f t h e compound w i l l r e a c t s p e c i f i c a l l y w i t h t h e s u r f a c e oxides which a r e formed. I n b a t c h systems, a d i s t i n c t brown c o l o r was found i n s o l u t i o n a f t e r r e a c t i o n o f a p p r o x i m a t e l y 15 mmoles c h l o r i n e p e r gram o f carbon (Snoeyink e t aZ. , 1974).

Boehm (1 966) s i m i l a r l y found brown c o l l o i d a l

m a t t e r i n suspension a f t e r e x t e n s i v e o x i d a t i o n o f carbon.

01 son and B i n n i n g

(1974) observed a s i m i l a r m a t e r i a l and noted t h a t a c e r t a i n p o r t i o n o f i t was n o t adsorbable by carbon.

Snoeyink and Suidan (1975) observed t h a t

t h i s c o l o r appeared i n t h e e f f l u e n t from a carbon d e c h l o r i n a t i o n bed a f t e r about 3 grams f r e e c h l o r i n e , as C l p , bed.

had r e a c t e d p e r gram o f carbon i n t h e

I t should be noted, however, t h a t t h e amount o f c h l o r i n e which must

r e a c t b e f o r e t h e c o l o r i s produced i s near t h e amount t h a t r e a c t s d u r i n g t h e l i f e o f a t y p i c a l d e c h l o r i n a t i o n bed (as d e f i n e d by a p r e s e t breakt h r o u g h c o n c e n t r a t i o n ) as g i v e n by Hagar and F l e n t j e (1965).

If alterna-

t i v e designs o f t h e bed a r e used, t h e p r o d u c t i o n o f c o l o r by t h e carbon bed, r a t h e r t h a n t h e appearance o f c h l o r i n e i n t h e e f f l u e n t o f t h e bed, may s i g n a l t h e need f o r r e g e n e r a t i o n o r replacement o f t h e carbon. b.

Dechl o r i n a t i o n Bed L i f e and Regeneration

.There i s l i t t l e q u a n t i t a t i v e i n f o r m a t i o n a v a i l a b l e on t h e l i f e o f d e c h l o r i n a t i o n beds o r on procedures which w i l l a l l o w t h e p r e d i c t i o n o f bed l i f e under d i f f e r e n t c o n d i t i o n s .

One e x c e p t i o n i s t h e s e t o f curves presented

by Hagar and F l e n t j e (1965) as reproduced i n F i g u r e 1.3,

a l t h o u g h no i n f o r -

m a t i o n i s g i v e n on t h e procedures which were used t o develop these curves. Using a c o n c e n t r a t i o n o f 0.01 mg/R c h l o r i n e t o d e f i n e breakthrough, Hagar and F l e n t j e found bed l i f e t o be a s i g n i f i c a n t f u n c t i o n o f i n f l u e n t c h l o r i n e c o n c e n t r a t i o n , h y d r a u l i c l o a d i n g r a t e , temperature, pH, and p a r t i c l e s i z e of t h e a c t i v a t e d carbon.

C a l c u l a t i o n s made f r o m these curves show t h a t a t an

i n f l u e n t c o n c e n t r a t i o n o f 1 mg/R o f f r e e c h l o r i n e , 1 g o f 8 x 30 U.S. standard mesh carbon w i l l r e a c t w i t h 0.28 and 2.1 g c h l o r i n e when loaded a t r a t e s o f 2 and 1 gpm/ft3, r e s p e c t i v e l y , w h i l e 1 g o f 12 x 40 mesh carbon

w i l l r e a c t w i t h 2.1 and 12.5 g c h l o r i n e when h y d r a u l i c l o a d i n g r a t e s o f 2 and 1 gpm/ft5 a r e used, r e s p e c t i v e l y .

I f 2.1 g c h l o r i n e r e a c t p e r g o f

3 carbon a t t h e 1 g p r r ~ / f t l o a d i n g r a t e , a bed l i f e o f 12.5 y e a r s i s p r e d i c t e d f o r a 2.5 f o o t bed depth.

T h i s p e r i o d o f tirne i s v e r y long, however, and

i t i s expected t h a t a d s o r p t i o n o f o r g a n i c s which would cause a decrease i n

d e c h l o r i n a t i o n e f f i c i e n c y would n e c e s s i t a t e r e g e n e r a t i o n much b e f o r e t h e 12.5 years. Care must be e x e r c i s e d i n u s i n g F i g u r e 1.3.

I f Equation 1.6

c o r r e c t l y r e p r e s e n t s t h e r e a c t i o n , o n l y 5.9 g f r e e c h l o r i n e can r e a c t p e r g carbon b e f o r e each carbon atom has combined w i t h an oxygen atom i f a c t i vated carbon i s assumed t o be 100 p e r c e n t carbon.

But i f each carbon atom

can accept 2 oxygen atoms, t h e n 17.7 g c h l o r i n e / g carbon r e p r e s e n t s t h e maximurn.

The t y p e o f o x i d e formed i s i m p o r t a n t i n t h i s r e s p e c t .

If the

r e a c t i o n were t o proceed t o these l i m i t s , a l l t h e carbon would have been converted t o CO o r C02.

P r i o r t o complete conversion, however, t h e carbon

p a r t i c l e s would fragment w i t h t h e s m a l l e r p a r t i c l e s escaping from t h e bed

lnf luent Chlorine Conc., mg/l

and t h e d a r k c o l o r , as noted above, would a l s o be produced.

I t i s n o t ap-

p a r e n t t h a t F i g u r e 1.3 t a k e s these l a t t e r phenomena i n t o account. One p o s s i b l e mechanism o f r e a c t i o n which c o u l d s i g n i f i c a n t l y a f f e c t bed l i f e and which m e r i t s d i s c u s s i o n concerns t h e c a t a l y t i c d e s t r u c t i o n o f HOCl by carbon as f o l l o w s :

T h i s r e a c t i o n i s therrnodynamically f a v o r e d as can be shown by f r e e energy calculations.

Prell'rninary m o n i t o r i n g o f d i s s o l v e d oxygen d u r i n g d e c h l o r i -

n a t i o n has shown no s i g n i f i c a n t change i n c o n c e n t r a t i o n , however, t h u s r e d u c i n g t h e p r o b a b i l i t y t h a t t h i s r e a c t i o n i s i m p o r t a n t (Snoeyink and Suidan, 1975).

Magee (1956) s i m i l a r l y found no i n c r e a s e i n d i s s o l v e d oxygen concen-

t r a t i o n during dechlorination. The o r i g i n a l a c t i v a t e d carbon d e c h l o r i n a t i o n e f f i c i e n c y can be regenerated by h e a t i n g t h e carbon t o temperatures i n excess o f 500"-700°C (Magee, 1956).

Boehm (1966) and P u r i (1970) noted t h a t carbon must be

heated i n an i n e r t atmosphere t o a temperature exceeding 1000°C i n o r d e r t o e v o l v e a l l oxides, t h u s i n d i c a t i n g t h a t e l i m i n a t i o n o f a l l o x i d e s i s n o t necessary t o r e e s t a b l i s h t h e o r i g i n a l d e c h l o r i n a t i o n e f f i c i e n c y .

A l a r g e w e i g h t l o s s may be noted d u r i n g r e g e n e r a t i o n .

The v e r y

e x t e n s i v e s u r f a c e area of carbon can h o l d a l a r g e number o f o x i d e s and t h e carbon evolved w i t h t h e o x i d e s can be s i g n i f i c a n t .

I f Equation 1.6 i s c o r -

r e c t , f o r example, each p a r t by w e i g h t o f f r e e c h l o r i n e r e q u i r e s 0.17 p a r t s by w e i g h t o f carbon.

Because many o f t h e o x i d e s formed as p r o d u c t s a r e a t -

tached t o t h e carbon, a v e r y s i g n i f i c a n t p o r t i o n o f t h e w e i g h t l o s s w i l l t a k e p l a c e d u r i n g t h e r e g e n e r a t i o n step.

Stuchl i k (Smisek and Cerny, 1970) r e p o r t s t h a t carbon i n pressure d e c h l o r i n a t o r s can be regenerated by steam treatment.

The exhausted bed i s

f i r s t washed w i t h a b a s i c s o l u t i o n t o remove t h e a c i d which has formed d u r i n g ,

the dechlorination reaction.

Then 105"-11 O°C steam, 1 atm gauge pressure,

i s i n t r o d u c e d a t t h e t o p o f t h e bed.

Several hours a r e r e q u i r e d f o r t h e

stearn t o heat t h e bed; steaming i s c o n t i n u e d f o r about 1 h r a f t e r steam f i r s t appears i n t h e e f f l u e n t o f t h e bed. r i n s e d and r e t u r n e d t o o p e r a t i o n .

A f t e r steaming, t h e carbon i s

S t u c h l ik i n d i c a t e s t h a t r e g e n e r a t i o n

t r e a t m e n t s a f t e r t h e f i r s t r e g e n e r a t i o n a r e necessary a f t e r s u c c e s s i v e l y s h o r t e r t i m e i n t e r v a l s and a f t e r a t i m e t h e carbon w i l l r e q u i r e r e p l a c e ment.

He a l s o n o t e s t h a t i n g r a v i t y f e d d e c h l o r i n a t o r s , some r e c o v e r y o f

c a p a c i t y can be achieved by washing w i t h c a u s t i c s o l u t i o n . c.

Rate of Reaction and Modeling o f D e c h l o r i n a t i o n Beds Magee (1956) s t u d i e d t h e r a t e o f r e a c t i o n o f f r e e c h l o r i n e w i t h

carbon i n a column apparatus and claimed t h a t h i s r e s u l t s g e n e r a l l y agree w i t h t h e surface r e a c t i o n being t h e r a t e l i m i t i n g step.

He observed t h a t

an i n i t i a l stage, which he c a l l e d a d i f f u s i o n c o n t r o l l e d stage, was i n e f f e c t p r i o r t o i n i t i a t i o n o f t h e s u r f a c e r e a c t i o n r a t e c o n t r o l l e d step.

The

i n i t i a l phase was observed t o l a s t f o r a p p r o x i m a t e l y 1000 bed volumes when t h e i n l e t c o n c e n t r a t i o n o f f r e e c h l o r i n e was 30 mg/L as C12.

Subsequent t o

t h i s i n i t i a l p e r i o d , he found t h a t t h e removal r a t e c o u l d be d e s c r i b e d by t h e f i r s t o r d e r r a t e equation,

dC dt*

-

kc

which, f o r t h e i n i t i a l c o n d i t i o n s o f c o n c e n t r a t i o n C = Co a t t i m e t* = 0 integrates to,

The t i m e parameter, t*, i n t h i s case r e p r e s e n t s t h e t i m e o f c o n t a c t o f t h e c h l o r i n a t e d water w i t h carbon. Although Magee's (1956) model i s based upon t h e s u r f a c e r e a c t i o n being t h e r a t e l i m i t i n g step, i t i s n o t apparent t h a t t h e d i f f u s i o n cont r o l l e d s t e p can be e l i m i n a t e d from an a c c u r a t e model which d e s c r i b e s t h e reaction.

.

Magee found t h a t t h e r e a c t i o n r a t e c o n s t a n t was i n v e r s e l y pro-

p o r t i o n a l t o t h e p a r t i c l e s i z e o f carbon, an o b s e r v a t i o n which i s incons i s t e n t w i t h t h e s u r f a c e r e a c t i o n being r a t e c o n t r o l 1i n g because t h e t o t a l s u r f a c e area o f an adsorbent g e n e r a l l y v a r i e s v e r y 1 i t t l e w i t h p a r t i c l e size.

What Magee f a i l e d t o n o t e was t h a t t h e i n v e r s e p r o p o r t i o n a l i t y be-

tween k and p a r t i c l e diameter i n d i c a t e s a d i f f u s i o n c o n t r o l l e d mechanism i n t h e case o f a f i r s t o r d e r s u r f a c e r e a c t i o n (Levenspiel, 1972).

Addi-

t i o n a l ly, Magee r e p o r t e d t h a t t h e r e a c t i o n r a t e doubled f o r a temperature i n c r e a s e o f 20°C f o r t h e range 0 t o 90°C.

T h i s temperature e f f e c t corresponds

t o an a c t i v a t i o n energy o f 5.5 t o 8.6 kcal/mole, values which correspond t o those g e n e r a l l y a t t r i b u t e d t o a d i f f u s i o n c o n t r o l l e d r e a c t i o n r a t e ( H e l f f e r i c h , 1962). Magee (1956) found t h e r a t e c o n s t a n t t o be an i m p o r t a n t f u n c t i o n o f pH, w i t h t h e v a l u e a t pH 4-5.5 being f o u r times g r e a t e r than t h e v a l u e a t pH 8.5-10;

marked d i f f e r e n c e s i n t h e e f f i c i e n c y o f d i f f e r e n t types o f

carbon were a l s o observed.

Magee's (1956) model does n o t t a k e i n t o account t h e p o i s o n i n g , o r r e d u c t i o n i n r e a c t i o n r a t e , which o c c u r s as t h e e x t e n t o f t h e r e a c t i o n i n creases.

The data on which he based h i s model were t a k e n a f t e r a s i g n i f i -

c a n t aniount o f c h l o r i n e had r e a c t e d w i t h t h e carbon and i t was assurned t h a t a f u r t h e r r e d u c t i o n i n r a t e as t h e r e a c t i o n proceeded would be n e g l i g i b l e . Equation 1.9 t h u s p r e d i c t s t h a t a d e c h l o r i n a t i o n bed o p e r a t i n g under a g i v e n s e t o f c o n d i t i o n s w i l l produce a g i v e n q u a l i t y o f e f f l u e n t i n d e f i n i t e l y , and t h i s p r e d i c t i o n i s c o n t r a r y t o observed r e s u l t s . Kovach (1971) proposed t h e use o f bed h a l f - l e n g t h (bed l e n g t h r e q u i r e d t o reduce t h e i n f l u e n t c o n c e n t r a t i o n by one h a l f ) f o r t h e d e s i g n of a c t i v a t e d carbon d e c h l o r i n a t i o n beds. h i s d a t a were c o l l e c t e d .

No i n f o r m a t i o n was p r o v i d e d on how

As s t a t e d p r e v i o u s l y , Magee (1956), and Snoeyink

and Suidan ( 1 975) observed t h a t d e c h l o r i n a t i o n columns o p e r a t e a t an unsteady state, a t l e a s t i n i t i a l l y .

Consequently, i t i s meaningless t o even propose

t h e use o f bed h a l f - l e n g t h f o r t h e design o f such r e a c t o r s . 6.

O b j e c t i v e o f Study Preliminary i n v e s t i g a t i o n s i n d i c a t e t h a t t h e design o f a c t i v a t e d

carbon d e c h l o r i n a t i o n r e a c t o r s on a steady s t a t e b a s i s i s v e r y erroneous and may l e a d t o e x c e s s i v e over-design.

The o b j e c t i v e o f t h i s s t u d y was t o de-

v e l o p a t h e o r e t i c a l l y sound model f o r t h e d e c h l o r i n a t i o n process. The model u t i l i z e d a proposed t h e o r e t i c a l l y d e r i v e d s u r f a c e react i o n r a t e e x p r e s s i o n based on Langmuir-Hinshelwood k i n e t i c s .

This reaction

r a t e e x p r e s s i o n was i n c o r p o r a t e d i n t o a pore d i f f u s i o n model.

Closed and

c o n s t a n t c o n c e n t r a t i o n b a t c h r e a c t o r d a t a were t h e n used t o e v a l u a t e

-paqenleAa

OSLP

aJaM s q 3 a j j a a ~ n q ~ ~ a d u j' aa q~ n ~ ~ ~ a dj w o asuo!.q3unj q aJP

a q w u o k q ~ aa ~3 ~ j ~ nayq s

PUP

L q ~ h l s n j j l payq yqoq a3uks ' L L L P U ~ ~ .sanlPA ~d quaJajjLp ~ o p aj q p n l m a aJaM squeqs

-uo3 Lapow ' a u ~ ~ o l ya3a J j j o uokq~sodtuoz~ ayq uo ~d j o q 3 a j j a ayq j o a s n ~ z ~ a g

'sqLnsaJ p a q 3 k p a ~ dy pqpp ~ ~ q u a w ~ ~ a6u[~~dwo:, dxa Lq s q 3 a j j a JaqatuPkp alz~kquredJ

q

~

~

O ~paqsaq SPM

. y 3 e o ~ d dp~a s o d o ~ dayq j o L q k p ~ ayq l ~ ~L j p a ~ 02 ~ q e p[ ~ q u a w p a d x a~

S U L P ~paqsaq P

uayq aJaM s a ~ ~ ny 63 n o ~ y q y ~ apaq3kp ~q

-LJPAam13 ayq ~ 3 k p a ~oqd Lapow paq p a y ~ ~P duk p a q ~ ~ o d ~ o SPM 3 u l Lapow a ~ o d

11.

THEORETICAL ANALYSIS

The r e a c t i o n between aqueous f r e e c h l o r i n e and g r a n u l a r a c t i v a t e d carbon i s heterogeneous i n n a t u r e .

A f r e e c h l o r i n e molecule has f i r s t t o

m i g r a t e t o an a c t i v a t e d carbon s i t e .

T h i s t r a n s p o r t i n v o l v e s b u l k and sur-

f a c e f i l m t r a n s p o r t which a r e f u n c t i o n s o f t h e hydrodynamics o f t h e r e a c t o r and f i n a l l y pore d i f f u s i o n , s i n c e a c t i v a t e d carbon i s h i g h l y porous w i t h p r a c t i c a l l y a l l t h e r e a c t i v e s u r f a c e s i t u a t e d i n s i d e t h e granule.

In this

study, i t was assumed t h a t t h e major r e s i s t a n c e t o f r e e c h l o r i n e t r a n s p o r t occurred i n t h e a c t i v a t e d carbon pore.

T h i s assumption was v e r i f i e d e x p e r i -

mental l y by r u n n i n g i d e n t i c a l c l o s e d batch c h l o r i n e - a c t i vated carbon e x p e r i ments under d i f f e r e n t m i x i n g c o n d i t i o n s .

For low m i x i n g r a t e s , t h e r a t e of

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

As t h e

m i x i n g r a t e was f u r t h e r increased, t h e c o n c e n t r a t i o n vs. t i m e curves c o i n c i d e d i n d i c a t i n g t h a t above a minimum m i x i n g i n t e n s i t y , no a p p r e c i a b l e b u l k o r s u r f a c e f i l m t r a n s p o r t r e s i s t a n c e was present.

I n a l l b a t c h experiments

c a r r i e d o u t i n t h i s study, t h e m i x i n g i n t e n s i t y was m a i n t a i n e d w i t h i n t h e range where no e x t e r n a l t r a n s p o r t r e s i s t a n c e was observed.

I t was f u r t h e r

assumed t h a t t h e outward d i f f u s i o n o f r e a c t i o n p r o d u c t from t h e a c t i v a t e d carbon pores d i d n o t i n t e r f e r e w i t h t h e f o r w a r d f r e e c h l o r i n e d i f f u s i o n . T h i s assu~nption i s u s u a l l y t r u e i n d i l u t e systems such as t h e one s t u d i e d here. The assumption t h a t a l l r e s i s t a n c e t o t r a n s p o r t occurred w i t h i n t h e a c t i v a t e d carbon pores i s v e r y commonly employed i n t h e s t u d y o f react o r kinetics.

Petersen (1 965) s t a t e d t h a t " c o n c e n t r a t i o n d i f f e r e n c e s be-

tween t h e b u l k f l u i d phase and t h e e x t e r n a l s u r f a c e o f a c a t a l y t i c p e l l e t

19

owing t o e x t e r n a l d i f f u s i o n l i m i t a t i o n s i s never observed i n t h e absence o f corresponding l a r g e r c o n c e n t r a t i o n g r a d i e n t s w i t h i n t h e p e l l e t . " A.

Surface Reaction Rate Expression The r e a c t i o n between f r e e c h l o r i n e and a c t i v a t e d carbon can be

d e s c r i b e d by (Magee, 1956; P u r i , 1970):

+ HOCl

C*

-t

CO*

+ H+

+ C1-

1.6

where C* r e p r e s e n t s an a c t i v a t e d carbon r e a c t i o n s i t e and CO* r e p r e s e n t s a s u r f a c e o x i d e on t h e carbon.

The above r e a c t i o n i s heterogeneous and i t

was assumed t h a t i t proceeds by a simple r e v e r s i b l e a d s o r p t i o n - d e s o r p t i o n s t e p f o l l o w e d by a simple i r r e v e r s i b l e d i s s o c i a t i o n step.

C*

+ HOCl

kl

2

CHOCl*

k2 3 CHOCl*

+

CO*

+ H+

+ C1-

where CHOCl* r e p r e s e n t s an adsorbed f r e e c h l o r i n e molecule and kl, K2, M/SITE*T-L and k3, M/SITE*T*L a r e r a t e constants.

2.2 2 L /SITE*T,

Here L, M y T and SITE

stand f o r l e n g t h , mass, t i m e and s u r f a c e s i t e , r e s p e c t i v e l y . Some o f t h e r e a c t i v e carbon s i t e s a r e o x i d i z e d as t h e s u r f a c e r e a c t i o n proceeds.

Plagee (1956) observed t h a t some o f these o x i d e s were

r e l e a s e d t o t h e s o l h t i o n as C02 and CO.

When such a r e l e a s e occurred, i t

was assumed t h a t t h e s i t e was regenerated.

*

o f s u r f a c e s i t e s , Ct, sites yields

remains c o n s t a n t .

As a r e s u l t , t h e t o t a l number

A m a t e r i a l balance on t h e s u r f a c e

=

C*

+ CO*

+ CHOCl*

2.3

I n t h e above equation, t h e symbols r e f e r t o t h e c o n c e n t r a t i o n s o f t h e r e s p e c t i v e species.

The u n i t s f o r a l l f o u r s u r f a c e species a r e SITE/L

2

.

I n t h i s study, t h e d i s s o c i a t i o n s t e p of t h e s u r f a c e r e a c t i o n was assumed t o be r a t e l i m i t i n g , and consequently t h e a d s o r p t i o n - d e s o r p a t i o n s t e p was assumed t o be a t e q u i l i b r i u m .

T h i s i s expressed by

where C r e p r e s e n t s t h e f r e e c h l o r i n e c o n c e n t r a t i o n , M/L'.

When t h e term

f o r C* as expressed i n Equation 2.3 i s s u b s t i t u t e d i n Equation 2.4,

CHOCl*

i s solved t o be

Since t h e a d s o r p t i o n - d e s o r p t i o n s t e p was assumed t o be a t e q u i l i b r i u m , t h e n t h e r a t e o f p r o d u c t i o n o f c h l o r i d e i o n s i s equal t o t h e r a t e o f f r e e c h l o r i n e removal, - R c

T h i s i s expressed by

Rc

-

- k3C C + k4

(c;

-

CO*)

3 where Rc r e p r e s e n t s t h e r a t e o f f r e e c h l o r i n e g e n e r a t i o n , M/L *T, and k4 r e p r e s e n t t h e a d s o r p t i o n - d e s o r p t i o n e q u i l i b r i u m c o n s t a n t , M/L k2/kl

3

g i v e n by

. A c t i v a t e d carbon c o n t a i n s i m p u r i t i e s such as oxygen, hydrogen and

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

In

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

due t o s t r a i n s a c q u i r e d d u r i n g manufacture.

I n t h i s study, however, t h e I t was a l s o assumed t h a t

carbon s u r f a c e was assumed t o be homogeneous.

c h l o r i d e and hydrogen i o n s produced by t h e s u r f a c e r e a c t i o n do n o t occupy any o f t h e r e a c t i v e s i t e s .

As a r e s u l t , t h e y were n o t i n c l u d e d i n an over-

a l l r e a c t i v e s i t e s m a t e r i a l balance. B.

Model f o r Reaction w i t h i n Carbon Pores The pores o f an a c t i v a t e d carbon g r a n u l e a r e a s e r i e s o f t o r t u o u s ,

i n t e r c o n n e c t e d paths o f v a r y i n g c r o s s - s e c t i o n a l areas.

Consequently, i t

would n o t be f e a s i b l e t o d e s c r i b e d i f f u s i o n w i t h i n each o r any o f t h e pores. I n t h i s study, i t was assu~iied t h a t t h e pore volume o f a carbon g r a n u l e was made up o f s t r a i g h t c y l i n d r i c a l open ended pores o f l e n g t h 2 L

P

.

The h a l f l e n g t h , L

and diameter P o f each such pore being equal t o o n e - s i x t h t h e

P' average diameter o f t h e g r a n u l e (Levenspiel, 1972).

Both open ends o f a

pore a r e exposed t o t h e b u l k f r e e c h l o r i n e c o n c e n t r a t i o n .

Because o f t h a t ,

symmetry e x i s t s i n a pore and, consequently, i t i s s u f f i c i e n t t o c o n s i d e r o n l y h a l f o f such a pore f o r t h e purpose o f a n a l y s i s ( F i g u r e 2.1). L e t Y be t h e p o s i t i o n v a r i a b l e as measured from pore mouth, and c o n s i d e r a d i f f e r e n t i a l element o f w i d t h AY p o s i t i o n e d a t a d i s t a n c e Y f r o m t h e pore mouth.

{

A m a t e r i a l balance on C l e a d s t o

Flux o f } c in

+

{ Rate o f Generation

of

=

c

-

Rate o f o Af cCc u r n u l a t i o n ~

which c o u l d be r e w r i t t e n e x p l i c i t l y as

{

Flux o f } c out

2 where Dc represents t h e d i f f u s i v i t y o f f r e e c h l o r i n e i n t h e pore, L / T y and t represents t h e t i m e dimension.

D i v i d i n g by AY and l e t t i n g AY tend t o zero,

Equation 2.8 reduces t o

L e t W be t h e mass o f f r e e c h l o r i n e r e a c t e d per u n i t area o f pore surface, M/L

2

.

Then a d i f f e r e n t i a l m a t e r i a l balance on C and W y i e l d s

L e t n be t h e number o f h a l f pores per u n i t weight o f a c t i v a t e d

3

carbon, V be t h e pore volume per u n i t weight o f carbon, L / M y g i v e n by 7rd 2 P (+) (L ) (n), and A be t h e pore s u r f a c e area per u n i t weight o f carbon, P P 2 Equation 2.10 L /M, g i v e n by ( r d p ) (Lp) ( n ) . M u l t i p l y i n g Equation 2.9 by V P' by A and s u b s t i t u t i n g Equation 2.6 f o r Rc leads t o P

where P and Q r e p r e s e n t t h e mass c o n c e n t r a t i o n o f f r e e c h l o r i n e p e r u n i t mass o f carbon and t h e mass o f f r e e c h l o r i n e r e a c t e d p e r u n i t mass o f car-, bony r e s p e c t i v e l y .

S i m i l a r l y SST and SSO r e p r e s e n t t h e number o f t o t a l and

+.

o x i d i z e d r e a c t i v e s i t e s p e r u n i t mass o f carbon, r e s p e c t i v e l y , each mu1 tip l i e d by t h e q u a n t i t y

Also, kg i s equal t o k4 mu1 t i p 1 i e d by Y

P The s u r f a c e r e a c t i o n terms i n Equations 2.11 and 2.12 a r e a

f u n c t i o n o f t h e o x i d i z e d r e a c t i v e s i t e s , SSO.

.

S r ~ o e y i r ~ek t aZ. (1974) presented

d a t a d e s c r i b i n g t h e accumulation o f NaOH t i t r a t a b l e s u r f a c e oxides as a Their

f u n c t i o n of t h e amount o f c h l o r i n e r e a c t e d per u n i t w e i g h t o f carbon.

data, as reproduced i n F i g u r e 1.1, c o u l d n o t be used t o a r r i v e a t a t h e o r e t i c a l e x p r e s s i o n f o r SSO s i n c e o n l y some of these o x i d e s were measurable by t h e i r technique and because t h e i r d a t a r e p r e s e n t an average e f f e c t over a carbon g r a n u l e and n o t a l o c a l i z e d e f f e c t as SSO r e p r e s e n t s .

As a r e s u l t ,

an e m p i r i c a l e x p r e s s i o n was adopted f o r SSO which d e s c r i b e s t h e general shape o f t h e d a t a shown i n F i g u r e 1.1.

sso

k7

= +

2.13

klOQ

I n a d d i t i o n i t a l l o w s f o r more f r e e c h l o r i n e t o r e a c t w i t h t h e carbon w i t h o u t much i n c r e a s e i n t h e s u r f a c e o x i d e s once t h e l e v e l o f these s u r f a c e o x i d e s became a p p r e c i a b l e .

T h i s i s i n agreement w i t h Magee's (1956) obser-

v a t i o n t h a t more C02 and CO was i n t h e e f f l u e n t from packed bed a c t i v a t e d carbon r e a c t o r s as t h e i n f l u e n t f r e e c h l o r i n e c o n c e n t r a t i o n t o these r e a c t o r s was increased. S u b s t i t u t i n g t h e expression f o r SSO g i v e n by Equation 2.13 i n t o Equations 2.11 and 2.12 l e a d s t o t h e general pore model

-ap - - at

C.

P + k8

(SST

-

Boundary C o n d i t i o n s and Reactor Mathematical Model s The pore mathematical model developed i n t h e p r e v i o u s s e c t i o n

d e s c r i b e s t h e r e a c t i o n and t r a n s p o r t mechanisms t a k i n g p l a c e i n s i d e t h e pores o f a c t i v a t e d carbon granules.

To s o l v e these equations, however,

boundary c o n d i t i o n s a r e needed t o r e l a t e t h e c o n d i t i o n s i n t h e b u l k of t h e s o l u t i o n t o those i n s i d e a pore.

I n addition, i n i t i a l conditions are

a l s o r e q u i r e d t o d e s c r i b e t h e s t a t e o f t h e systerr~j u s t p r i o r t o t h e s t a r t o f the reaction. The i n i t i a l c o n d i t i o n s needed t o s o l v e Equations 2.14 and 2.15 a r e independent o f t h e t y p e o f r e a c t o r under c o n s i d e r a t i o n and depend on t h e s t a t e o f P and Q a t t h e , s t a r t o f an experiment.

Assuming t h a t f r e s h

carbon was used, then t h e i n i t i a l c o n d i t i o n on Q becomes

The i n i t i a l c o n d i t i o n on P was obtained from t h e steady s t a t e s o l u t i o n o f Equation 2.14 w i t h Q s e t t o zero.

The use o f such an i n i t i a l c o n d i t i o n as-

sumes t h a t t h e c o n c e n t r a t i o n p r o f i l e f o r P i n s i d e a pore develops r e l a t i v e l y f a s t compared t o t h e speed o f t h e s u r f a c e r e a c t i o n . i s g i v e n by

This i n i t i a l condition

The pore rnodel used i n t h i s study assumes a s t r a i g h t c y l i n d r i c a l pore w i t h both open ends exposed t o t h e b u l k f r e e c h l o r i n e concentration. Because o f t h e symmetry o f such a pore, the boundary c o n d i t i o n a t t h e h a l f l e n g t h o f a pore i s given by

for t > - 0,

The second boundary c o n d i t i o n describes t h e c o n c e n t r a t i o n P a t t h e pore mouth.

This boundary c o n d i t i o n i s a f u n c t i o n o f t h e type o f r e -

a c t o r f o r which t h e pore d i f f u s i o n model i s solved. 1.

Batch Reactors

a.

Constant Concentration Batch Reactor The constant c o n c e n t r a t i o n batch r e a c t o r , CCBR, assumes t h a t the

b u l k s o l u t i o n i s i n f i n i t e i n volume thus r e s u l t i n g i n a constant concentrat i o n o f f r e e chlorine i n the bulk solution.

Consequently, t h e boundary

c o n d i t i o n a t pore mouth f o r a CCBR i s given by C

=

Co

1 , f o r t >- 0, or

P

=

Y = 0

0

where Co i s t h e f r e e c h l o r i n e concentration i n t h e bulk, MIL given by V

P

x Co.

3

and Po i s

The mathematical model f o r a CCBR i s t h e r e f o r e g i v e n by Equations 2.14, b.

2.15,

2.16,

2.17,

2.18 and 2.19.

Closed Batch Reactor

A c l o s e d b a t c h r e a c t o r , sometimes known as a s i m p l e o r f i n i t e b a t c h r e a c t o r , assumes a f i n i t e b u l k s o l u t i o n volume i n which t h e a c t i v a t e d carbon i s w e l l mixed.

When t h e pore d i f f u s i o n model i s solved f o r such a

r e a c t o r , t h e boundary c o n d i t i o n a t pore mouth r e q u i r e s a f r e e c h l o r i n e mat e r i a l balance t o s u p p l y a l i n k between t h e carbon pore phase and t h e b u l k s o l u t i o n phase.

Because o f t h i s , an expression, Rrcy f o r t h e r a t e o f f r e e

c h l o r i n e removal from t h e s o l u t i o n phase i s needed.

This expression i s given

by

where m r e p r e s e n t s t h e c o n c e n t r a t i o n o f activat.ed carbon p e r u n i t r e a c t o r volume, M/L

3 and Rrc has t h e u n i t s o f M/L 3 .T.

The r a t e o f c h l o r i n e removal,

, expressed i n terms o f P i s g i v e n by R r ~

where R

rP

x V . rc P due t o a c t i v a t e d carbon was

has t h e u n i t s T-I and i s equal t o R The r a t e o f c h l o r i n e removal, R

r c' summed o v e r t i m e i n c o n j u n c t i o n w i t h t h e r a t e o f c h l o r i n e disappearance, Rdy

owing t o f a c t o r s o t h e r than a c t i v a t e d carbon t o p r o v i d e t h e pore mouth

boundary c o n d i t i o n f o r a c l o s e d batch r e a c t o r .

c

=

co +

I ( J = ~~ Y I Y o t

m V D

P

0

Rd has t h e u n i t s o f M/L t

P

=

3

T.

-

=

~ ~ ) f do r ~t ;> 0, Y =

o

2.22

Equation 2.22 expressed i n terms o f P becomes

m V D

-

Po

VpRd)dt;

-

2.23

f o r t > 0, Y = 0

0

where Co represents t h e i n i t i a l b u l k c o n c e n t r a t i o n o f f r e e c h l o r i n e and Po i s g i v e n by Vp x Co. The mathematical model f o r a closed batch r e a c t o r i s t h e r e f o r e g i v e n by Equations 2.14, c.

2.15,

2.16,

2.17,

2.18 and 2.23.

Nondimensionalized Batch Models The two batch r e a c t o r models developed above were nondimensional-

i z e d u s i n g t h e dimensionless time, 0; distance, 5; and c o n c e n t r a t i o n , G, variables.

and

These diliiensiorll ess v a r i a b l e s were defined as

G = -P

2.26

0

S u b s t i t u t i n g t h e above dimensionless v a r i a b l e s i n t h e CCBR model leads t o

G G P + ~ kg

-aG - - ae

3 ae

GP

=

O

GPO + kg

(SIT

(SIT

-

-

1

+ k10 Q )

+

a2G -

ac2

1 + k10 Q )

Q = 0 ; f o r 0 = 0, O -< [ < - 1

a2G -

-

'IT = GPO + kg

at2

and

G

=

1;

0;

f o r 0 = 0,

f o r 0 >- 0 ,

2.29

o 2

5

5

1

c = O

2.32

where SIT and kg a r e two d i m e n s i o n l e s s v a r i a b l e s o b t a i n e d f r o m SST and k7, 3

r e s p e c t i v e l y , t h r o u g h mu1t i p 1 i c a t i o n o f each by t h e q u a n t i t y

5

Dc The nondimensionalized mathematical model f o r a c l o s e d b a t c h r e a c t o r i s i d e n t i c a l t o t h e CCBR model e x c e p t f o r t h e boundary c o n d i t i o n g i v e n by E q u a t i o n 2.32 which i s r e p l a c e d by

2.

Packed Bed Column Reactor When t h e pore d i f f u s i o n model i s s o l v e d i n c o n j u n c t i o n w i t h a

packed bed r e a c t o r model, then t h e p o r e mouth f r e e c h l o r i n e c o n c e n t r a t i o n

30

i s o b t a i n e d through a m a t e r i a l balance on f r e e c h l o r i n e i n t h e l i q u i d phase o f the reactor.

The r a t e o f c h l o r i n e r e d u c t i o n , i n t h i s case, i s s t i l l ex-

pressed by Equation 2.20. The column r e a c t o r considered i n t h i s s t u d y i s a packed bed react o r w i t h a x i a l dispersion.

I t c o n s i s t s o f a c y l i n d r i c a l tube, t i g h t l y

packed w i t h a c t i v a t e d carbon.

Aqueous c h l o r i n e was pumped a t a steady r a t e

i n t o one end o f t h e column and o u t t h e o t h e r . I n most d e c h l o r i n a t i o n a p p l i c a t i o n s , a v e r y low e f f l u e n t c h l o r i n e concentration i s desirable.

Consequently, an a x i a l d i s p e r s i o n t e r m i s

needed i n t h e mathematical model o f such a bed t o b e t t e r p r e d i c t t h e l o w e r e f f l u e n t c o n c e n t r a t i o n s f r o m such a r e a c t o r (Levenspiel

, 1972).

The impor-

tance o f a x i a l d i s p e r s i o n i s discussed i n more d e t a i l i n t h e s e c t i o n on R e s u l t s and Wiscussion. To develop t h e governing e q u a t i o n d e s c r i b i n g t h e f r e e c h l o r i n e c o n c e n t r a t i o n l e v e l s along a packed bed r e a c t o r , c o n s i d e r t h e schematic diagram f o r such a r e a c t o r as g i v e n i n , F i g u r e 2.2. c r o s s s e c t i o n a l area o f t h e bed, L',

Let A represent the

Lb r e p r e s e n t t h e d e p t h o f t h e bed, L,

and z be t h e p o s i t i o n v a r i a b l e as measured from t h e . e n t r a n c e en.d o f t h e bed.

A d i f f e r e n t i a l m a t e r i a l balance on f r e e c h l o r i n e l e a d s t o

'

C i n by B u l k ) Transport

+.

'

+

C i n by A x i a l Dispersion

C Generated by) Carbon

=

which c o u l d be r e w r i t t e n e x p l i c i t l y as

1 -

C o u t by Bulk) Transport

Rate o f Accumulation of C 1

-

'

C o u t by A x i a l Dispersion

where C r e p r e s e n t s t h e f r e e c h l o r i n e c o n c e n t r a t i o n , M/L< a c t u a l l i q u i d v e l o c i t y t h r o u g h t h e packed bed, L/T,

E

v represents the

represents the i n t e r -

p a r t i c l e p o r o s i t y o f t h e packed carbon and DA r e p r e s e n t s t h e a x i a l d i s p e r s i o n coefficient,

2 L /T.

I t i s i m p o r t a n t t o n o t e t h a t C and P a r e r e l a t e d by P =

C V

and t h a t Equation 2.35 i s v a l i d o n l y a t Y = 0. D i v i d i n g Equation 2.35 P by Az and l e t t i n g Az t e n d t o z e r o *leads t o

The boundary c o n d i t i o n s f o r a packed bed r e a c t o r w i t h a x i a l d i s p e r s i o n have been t h e s u b j e c t o f c o n t r o v e r s y f o r some tirne.

The boundary

c o n d i t i o n s adopted i n t h i s s t u d y assume t h a t t h e packed bed extends f r o m z =

-rn

t o z = +- w i t h t h e r e a c t i v e a c t i v a t e d carbon s i t u a t e d between z = 0

and z = Lb.

I t was a l s o assumed t h a t t h e bed was packed w i t h an i n e r t o r

nonreactive material i n the regions

-

< z < - 0 and Lb < z


Nondimensional i z e d Packed Bed Reactor Model The packed bed rnatherrlatical rnodel was nondin~ensionali z e d u s i n g

02 spea 1 Lapou ~ e 3 ~ q . e u a y 2 e u ~ o u e apaq ~ pay 3ed ay2 uk saLqP!..ieh ssaLuo!.suauLp ahoqe ay2 6uk3n2 lq.sqns

0

r e p r e s e n t s t h e mass o f f r e e c h l o r i n e a p p l i e d p e r Lb LL U u n i t t i m e p e r u n i t mass of carbon; H, g i v e n by - , r e p r e s e n t s t h e average v

where S, g i v e n by

r e s i d e n c e t i m e o f t h e s o l u t i o n i n t h e bed and Pe r e p r e s e n t s t h e P e c l e t numvLb b e r and i s g i v e n by D~ and Pe i s dimensionless. mixing i n the reactor.

The u n i t s f o r S and H a r e T

-1

and T, r e s p e c t i v e l y ,

The P e c l e t number i s a measure o f t h e degree o f When Pe i s s m a l l , t h e packed bed r e a c t o r approaches

a c o m p l e t e l y mixed r e a c t o r and when Pe tends t o i n f i n i t y ,

i t approaches a

plug f l o w reactor. d.

Plug Flow Packed Bed Reactor Model Under c e r t a i n f l o w c o n d i t i o n s , t h e a x i a l d i s p e r s i o n c o e f f i c i e n t ,

DA3 and a c c o r d i n g l y t h e m i x i n g t e r m g i v e n by t h e i n v e r s e o f t h e P e c l e t num-

b e r t a k e s m a l l values.

I n such a case, t h e c o n t r i b u t i o n o f DA t o t h e s o l u -

t i o n o f t h e packed bed model becomes n e g l i g i b l e and, consequently, i t may be more c o n v e n i e n t t o s o l v e t h e packed bed model w i t h DA s e t t o zero, l e a d i n g t o a plug flow reactor.

The mathematical model d e s c r i b i n g such a r e a c t o r

i s o b t a i n e d f r o m t h e packed bed w i t h a x i a l d i s p e r s i o n mathematical model by s e t t i n g DA equal t o zero.

Thus t h e nondimensionalized p l u g f l o w mathe-

m a t i c a l model i s g i v e n b y aF -aa-rF+ - -aa

-

1 - S

R(X,F)

. A L s ~ o ~ paukjap A ~ J ~ se awes ay3 aJe

?3

pue L 'H 'S 'X

'-J

aJayM

j

I

111. A.

EXPERIMENTAL MATERIALS AND METHODS

A c t i v a t e d Carbon The a c t i v a t e d carbon used i n t h i s s t u d y was bituminous base

F i l t r a s o r b 400 (Calgon C o r p o r a t i o n , P i t t s b u r g h , PA).

The a c t i v a t e d carbon

was prepared by mechanical g r i n d i n g f o l l o w e d by s i e v i n g i n t o a number o f p a r t i c l e s i z e ranges.

The carbon was t h e n washed w i t h deionized water, f i r s t

i n a beaker and t h e n i n a f l u i d i z e d bed, t o e l i m i n a t e f i n e s . q u e n t l y d r i e d a t 105°-1100C.

I t was subse-

The s p e c i f i c c h a r a c t e r i s t i c s o f t h e carbon

a r e g i v e n i n t h e m a n u f a c t u r e r ' s b u l l e t i n (Calgon C o r p o r a t i o n , 1969). B.

Free C h l o r i n e Measurement The DPD Ferrous T i t r i m e t r i c Procedure (standard Methods, 1970) was

used t o determine t h e c o n c e n t r a t i o n o f aqueous c h l o r i n e . r u n a t pH 10.0,

For experiments

samples were a c i d i f i e d p r i o r t o f r e e c h l o r i n e measurements.

A 5 ml b u r e t was used f o r t h e t i t r a t i o n . T h i s a n a l y t i c a l t e c h n i q u e was found t o be a c c u r a t e and r e p r o d u c i b l e down t o a f r e e c h l o r i n e c o n c e n t r a t i o n o f 0.1 mg/!L, as C12.

For c h l o r i n e

c o n c e n t r a t i o n s h i g h e r t h a n 3 mgle, as C12, t h e samples were d i l u t e d i n o r d e r t o l o w e r t h e measured c o n c e n t r a t i o n s t o a range o f 1-2 mg/Q, as C1

2'

where t h e end p o i n t o f t h e t i t r a t i o n was b e s t d e t e c t e d . C.

C o l o r Measurement A q u a n t i t a t i v e measure o f t h e brown c o l o r o f t h e s o l u t i o n was

made f o r one

CCBR and one column experiment.

T h i s measurement was made a t

270 nm w i t h an ACTA I 1 1 U V - v i s i b l e Spectrophotometer u s i n g a 10 cm l i g h t p a t h (Beckman Instruments, I n c . ,

Ful l e r t o n , CA).

These measurements were

e v a l u a t e d r e l a t i v e t o t h e blank and i n f l u e n t c h l o r i n e s o l u t i o n as was appl i c a b l e. The appearance o f brown c o l o r was a l s o v i s u a l l y d e t e c t e d i n some CCBR and packed bed experiments. D.

Free C h l o r i n e S o l u t i o n s Stock f r e e c h l o r i n e s o l u t i o n s were prepared by making a p p r o p r i a t e

d i l u t i o n s o f t h e household bleach, Clorox.

Free c h l o r i n e s o l u t i o n s were

prepared by adding measured volumes o f t h e s t o c k f r e e c h l o r i n e s o l u t i o n , and 5 m l o f a pH 7.4 phosphate b u f f e r (14.3 g KH2P04 p l u s 68.8 g K2HP04/E o f b u f f e r s o l u t i o n ) p e r 1 i t e r o f d e i o n i z e d water.

The carbonate system o f

t h e s o l u t i o n s was always s e t c l o s e t o e q u i l i b r i u m w i t h t h e atmosphere a t t h e o p e r a t i n g pH o f t h e r e a c t o r by t h e a d d i t i o n o f c a l c u l a t e d amounts o f Na2C03 and NaHC03. NaOH s o l u t i o n s .

Adjustments o f pH were made as necessary u s i n g H C I and

A Beckman Electromate pH Meter (Beckrnan Instruments, I n c . ,

F u l l e r t o n , CA) was used f o r pH measurement. E.

Experimental

1.

Batch Experirr~ents For t h e experiments r u n a t room temperature, no temperature con-

t r o l was used and t h e temperature v a r i e d between 22.5"-23.5"C a mean.

For experiments r u n a t 35°C a Magni Whirl Constant Temperature

Bath (Blue M E l e c t r i c Co., Z°C,

w i t h 23°C as

Blue I s l a n d , I L ) was used and f o r experiments a t

a c o n s t a n t temperature c o l d room was used.

For b a t c h experiments c a r r i e d o u t a t pH 4.0,

where t h e b u f f e r

c a p a c i t y o f t h e s o l u t i o n s i s weak, a F i s h e r Automatic T i t r i m e t e r ( F i s h e r S c i e n t i f i c Co., t h e run.

P i t t s b u r g h , PA) was used t o m a i n t a i n c o n s t a n t pH d u r i n g

M NaOH s o l u t i o n was used t o c o n t r o l pH i n t h i s case. A 0.5 -

o t h e r pH values i n v e s t i g a t e d , 7.6 and 10.0,

For

the b u f f e r capacity o f the solu-

t i o n s was s u f f i c i e n t l y s t r o n g t o p e r m i t manual pH c o n t r o l .

A l l batch reac-

t o r s were covered w i t h f o i l t o exclude l i g h t and t o t h u s p r e v e n t photodecomposition o f t h e c h l o r i n e . Two t y p e s o f b a t c h experiments were c a r r i e d o u t i n t h i s study, c l o s e d and c o n s t a n t c o n c e n t r a t i o n . a.

Closed Batch Experiments Four l i t e r s o f s o l u t i o n were used; t h e o n l y substance added t o

t h e r e a c t o r a f t e r s t a r t i n g t h e t e s t was NaOH for pH c o n t r o l .

A b l a n k reac-

t o r c o n t a i n i n g a l l reagents except a c t i v a t e d carbon w a s r u n t o determine t h e r a t e o f disappearance o f f r e e c h l o r i n e owing t o f a c t o r s o t h e r t h a n r e a c t i o n w i t h a c t i v a t e d carbon. The r e a c t o r s , i n c l u d i n g t h e blank, were mixed u s i n g T - l i n e L a b o r a t o r y S t i r r e r s ( T a l boys E n g i n e e r i n g Corp., s t i r r i n g rod.

Emerson, NJ) and a T e f l o n

The speed o f m i x i n g was c o n t r o l l e d by a v a r i a b l e A u t o t r a n s -

former (STACO, Inc.,

Dayton, OH).

The s t i r r i n g speed was m a i n t a i n e d a t

764-917 rpm as measured by a B i d d l e I n d i c a t o r (James G. B i d d l e Co.,

Plymouth

Meeting, PA). A f t e r t h e s o l u t i o n s were mixed f o r about 3 hours, a c t i v a t e d carbon was added t o t h e r e a c t o r s ; t h e i n i t i a l c o n c e n t r a t i o n o f c h l o r i n e was measured j u s t p r i o r t o carbon a d d i t i o n .

b.

Constant C o n c e n t r a t i o n Batch Experiments The second t y p e o f b a t c h experiment c a r r i e d o u t i n t h i s s t u d y

was a c o n s t a n t c o n c e n t r a t i o n b a t c h r e a c t o r , CCBR.

I n t h i s type o f experi-

ment, o n l y two l i t e r s o f s o l u t i o n were used and b o t h t h e r e a c t o r and t h e b l a n k were mixed a t 61 0 rpm u s i n g t h e sarrle equipment d e s c r i b e d i n t h e p r e vious section. A l l t h e CCBR experiments were conducted a t room temperature, 23"C,

and a t pH 4.0.

The pH was m a i n t a i n e d a t 4.0 u s i n g t h e F i s h e r

Automatic T i t r i m e t e r d e s c r i b e d p r e v i o u s l y . A c t i v a t e d carbon was added t o t h e r e a c t o r s a f t e r t h e s o l u t i o n s were mixed f o r 3 hours.

The i n i t i a l f r e e ' c h l o r i n e c o n c e n t r a t i o n was mea-

sured j u s t p r i o r t o carbon a d d i t i o n .

I n t h i s experiment, t h e f r e e c h l o r i n e

c o n c e n t r a t i o n was m a i n t a i n e d c o n s t a n t a t C o y and t h e r a t e o f r e a c t i o n was determined as a f u n c t i o n o f t h e mass o f c h l o r i n e r e a c t e d p e r u n i t w e i g h t o f carbon, X.

T h i s was accomplished by a l l o w i n g t h e f r e e c h l o r i n e concentra-

t i o n i n t h e b u l k t o d r o p from Co + AC t o Co

-

AC and t h e n adding more s t o c k

c h l o r i n e s o l u t i o n t o b r i n g t h e c o n c e n t r a t i o n back t o Co + AC. used f o r AC were about 0.5-1.0

mg/R.

The values

The r a t e o f c h l o r i n e r e d u c t i o n was

e s t i m a t e d f r o m a few measurements o f c h l o r i n e c o n c e n t r a t i o n as t h i s concen-

+

t r a t i o n dropped from Co and m a i n t a i n e d a t pH 4.0,

AC t o Co

-

AC.

A stock c h l o r i n e solution, buffered

and a n o t h e r pH 4.0 s o l u t i o n which was b u f f e r e d

b u t v o i d o f any c h l o r i n e , were used t o b r i n g t h e c h l o r i n e c o n c e n t r a t i o n i n t h e r e a c t o r back t o Co + t h e r e a c t o r constant.

A C y

and t o m a i n t a i n t h e volume o f t h e s o l u t i o n i n

Both t h e e s t i m a t e d r a t e and t h e v a l u e o f X were

a d j u s t e d by s u b t r a c t i n g t h e e f f e c t o f c h l o r i n e decay as observed i n t h e blank r e a c t o r . 2.

Packed Bed Column Experiments The o t h e r t y p e o f experiment was t h e u p f l o w packed bed r e a c t o r .

The i n f l u e n t s o l u t i o n was prepared i n 60 l i t e r batches and i t was s t a b i l i z e d by m i x i n g f o r a t l e a s t 3 hours p r i o r t o a p p l y i n g i t t o t h e carbon. An FMI p o s i t i v e displacement l a b pump ( F l u i d Metering, Inc., N Y ) was used t o p r o v i d e a steady i n f l u e n t f l o w r a t e .

Tygon t u b i n g was

used f o r t h e t r a r ~ s r n i s s i o no f t h e i n f l u e n t a r ~ de f f l u e n t f l o w s . colurnns were made from P l e x i g l a s s .

Oyster Bay,

The carbon

A s u f f i c i e n t l y l a r g e r a t i o o f column

diameter t o p a r t i c l e diarrleter was used t o a v o i d w a l l e f f e c t s .

I n t h e case

o f 18 x 20 U.S. Standard mesh s i z e carbons t h i s r a t i o was 27.6 w h i l e i t was 73.8 f o r t h e 60 x 80 carbon.

A minimum depth o f 10 column diameters o f

Ottawa sand was packed ahead o f and a f t e r t h e carbon i n t h e column.

This

sand had t h e same p a r t i c l e s i z e as t h e a c t i v a t e d carbon and was i n e r t t o chlorine.

I t s purpose was t o c o n t r o l t h e f l o w regirne t h r o u g h t h e carbon

s e c t i o r ~o f t h e r e a c t o r a r ~ das such j u s t i f y t h e boundary c o n d i t i o n s used i n t h e packed bed w i t h a x i a l d i s p e r s i o n rr~atherrlaticalmodel .

'

IV.

RESULTS AND DISCUSSION

The procedure f o l l o w e d i n t h i s s t u d y was t o f i t t h e numerical s o l u t i o n o f t h e b a t c h mathematical models t o c o r r e s p o n d i n g experimental batch data.

The c o n s t a n t s SIT, k8, kg and k10 were e v a l u a t e d t h r o u g h a

t r i a l and e r r o r f i t o f t h e data. signed t h e v a l u e 6 x

The d i f f u s i v i t y c o e f f i c i e n t ,

cm2/min a t 23°C.

D c y

was as-

T h i s v a l u e i s an o r d e r - o f -

magnitude e s t i m a t e f o r s i m i l a r molecules i n l i q u i d s ( F o g l e r , 1974) and was used f o r b o t h HOCl and OC1'.

( C a l c u l a t i o n o f Dc f o r HOCl by t h e Wilke-

Chang model, which a l s o g i v e s an order-of-magnitude 2 cm /min).

estimate [Bird e t a l . ,

The v a l u e used f o r V

was P 0.94 c c / g as o b t a i n e d from t h e m a n u f a c t u r e r ' s b u l l e t i n (Calgon Corp., 1969). 19601 gave a v a l u e o f 1.12 x

The v a l u e o f L

was always taken as o n e - s i x t h o f t h e a r i t h m e t i c mean o f t h e P p a r t i c l e s i z e range.

A.

Rate o f C h l o r i n e Disappearance f r o m Blank Reactor The r a t e o f disappearance o f f r e e c h l o r i n e from t h e b l a n k r e a c t o r s

was observed t o f o l l o w f i r s t o r d e r k i n e t i c s r a t h e r c l o s e l y . f r o m two b l a n k experiments a r e shown i n F i g u r e 4.1.

The r e s u l t s

The d a t a e x h i b i t i n g

t h e h i g h e r s l o p e r e p r e s e n t a 4 l i t e r , pH 4.0 and 35°C b l a n k experiment, w h i l e t h e d a t a from t h e second experiment were o b t a i n e d a t pH 4.0 and 23°C. As a r e s u l t o f t h e l i n e a r i t y shown by t h e d a t a on a semi-log p l o t , t h e t e r m

Rd f o r t h e decay r a t e i n t h e boundary c o n d i t i o n appearing i n Equations 2.22, 2.23 and 2.33 was r e p l a c e d by

where kd i s t h e f i r s t o r d e r r a t e c o n s t a n t , T 3 c o n c e n t r a t i o n , MIL

.

, and C i s t h e f r e e c h l o r i n e

The v a l u e of kd f o r t h e pH 4.0,

35°C experiment was

c a l c u l a t e d t o be 0.00003 min-l, w h i l e i t was found t o be 0.0000134 min" t h e pH 4.0,

23°C experiment.

for

S i m i l a r data were o b t a i n e d f o r pH 10.0 b l a n k

experiments c a r r i e d o u t a t 23" and 35°C. The values o f kd c a l c u l a t e d from t h e two pH 10.0 b l a n k e x p e r i ments were equal t o t h e v a l h e obtained from t h e 23"C, pH 4.0 d a t a .

A t pH

4.0,

HOCl i s t h e predominant f r e e c h l o r i n e species w h i l e i t i s 0 ~ 1 -a t pH

10.0.

Since t h e same value o f kd was o b t a i n e d a t these two pH values a t

23"C,

i t was assumed t h a t t h i s same v a l u e holds a t i n t e r m e d i a t e pH values

where t h e c h l o r i n e s o l u t i o n i s made up o f m i x t u r e s o f t h e two f r e e c h l o r i n e species.

Also, s i n c e t h e same v a l u e o f kd was o b t a i n e d f o r t h e two pH 10.0

experiments a t 23" and 35"C, i t was assumed t h a t t h i s same v a l u e holds f o r b l a n k experiments c a r r i e d o u t a t t h e same pH b u t a t 2°C. Blank experiments were a l s o c a r r i e d o u t i n c o n j u n c t i o n w i t h CCBR experiments.

I n t h i s case, however, t h e v a l u e o f Rd a t o n l y one concentra-

t i o n , namely C o y was needed. B.

Experiments a t pH 4.0 and 23°C

1.

Batch S t u d i e s Four d i f f e r e n t c o r ~ s t a r ~c to n c e n t r a t i o n b a t c h r e a c t o r , CCBR, e x p e r i -

ments were c a r r i e d o u t a t pH 4.0 and 23°C ( F i g u r e s 4.2,

4.3, 4.4 and 4.5).

I n a l l f o u r experiments, 50 mglk o f 60 x 8 0 mesh carbon were used. b u l k c o n c e n t r a t i o n s , Co,

The

i n these f o u r experiments were maintained a t an

average c o n c e n t r a t i o n o f 30, 20, 10 and 5 mg/k.

The b u l k c o n c e n t r a t i o n i n

Reaction Rate, mgl!-min

Reaction Rate, mg/Q-min

Reaction Rate, mg/l-min

each o f these experiments was a l l o w e d t o v a r y between Co + AC and Co i n o r d e r t o a r r i v e a t an e s t i m a t e o f t h e r a t e o f c h l o r i n e removal. values o f AC used were 1.0,

0.75,

-

AC

The

0.5 and 0.5 mg/R f o r t h e 30, 20, 10 and

5 mg/R b u l k c o n c e n t r a t i o n CCBR experiments, r e s p e c t i v e l y . The 20 mg/R b u l k c o n c e n t r a t i o n experiment ( F i g u r e 4.3) was r e peated t h r e e t i m e s t o t e s t t h e r e p r o d u c i b i l i t y o f t h e d a t a .

This reproduci

b i l it y was considered t o be v e r y s a t i s f a c t o r y . C o n s i s t e n t w i t h t h e s u r f a c e r e a c t i o n r a t e e x p r e s s i o n g i v e n by Equation 2.6,

t h e r a t e o f C h l o r i n e removal f o r a s p e c i f i c v a l u e o f X i n -

creased w i t h i n c r e a s i n g b u l k c o n c e n t r a t i o n .

The r a t i o o f t h i s i n c r e a s e

was h i g h when t h e 10 and 5 mg/R d a t a were compared ( F i g u r e s 4.4 and 4.5) b u t tended t o decrease as t h e b u l k c o n c e n t r a t i o n i n c r e a s e d as i s e v i d e n t frorn t h e 30 and 20 rng/R d a t a ( F i g u r e s 4.2 and 4.3). Brown c o l o r appeared i n s o l u t i o n a f t e r t h e r e a c t i o n o f 4.2 and 3.8 grams o f f r e e c h l o r i n e p e r gram o f carbon i n t h e 30 and 20 mg/R b u l k c o n c e n t r a t i o n CCBR experiments shown i n F i g u r e s 4.2 and 4.3.

The o t h e r two

CCBR experiments c a r r i e d o u t a t b u l k c o n c e n t r a t i o n s o f 10 and 5 mg/R ( F i g u r e s 4.4 and 4.5) were stopped p r i o r t o t h e emergence o f any v i s i b l e brown c o l o r . The c o n t i n u o u s curves i n F i g u r e s 4.2,

4.3,

4.4 and 4.5 r e p r e s e n t

t h e r a t e o f c h l o r i n e removal f o r 50 mg/R o f 60 x 80 mesh carbon as a f u n c t i o n o f X, as p r e d i c t e d by t h e rnathernatical model f o r t h e CCBR.

The values

o f t h e model c o n s t a n t s f o r these curves were 0.0035 cm, 0.007, 0.000017, 2.66 and 380 f o r L

SIT, kg, k g and klO, respectively. P' I n t h e case o f t h e 5 mg/R b u l k c o n c e n t r a t i o n experiment ( F i g u r e

4.5),

t h e model underestimated t h e r a t e f o r values o f X g r e a t e r t h a n 1 g/g.

*

I

No a t t e m p t was made t o c o r r e c t f o r t h i s because d a t a from o t h e r pH 4.0,

I

23'C experiments were w e l l p r e d i c t e d u s i n g t h e above model constants.

1

Two c l o s e d b a t c h experiments were c a r r i e d o u t a t pH 4.0 and a temperature o f 23°C.

I n b o t h experiments, t h e i n i t i a l c o n c e n t r a t i o n o f f r e e

c h l o r i n e , as C12, and t h e a c t i v a t e d carbon c o n c e n t r a t i o n were 30 mg/R and 10 mg/R, r e s p e c t i v e l y . rnesh s i z e .

The carbon used i n b o t h experiments was 60 x 80

F i g u r e 4.6 shows t h e r e s u l t s o f t h e two experiments and i t can

be noted t h a t r e p r o d u c i b i 1 it y i s excel 1e n t . The same vallres of t h e rr~odel c o n s t a n t s used i n p r e d i c t i n g t h e CCBR

1 ,

Ij 1

d a t a i n F i g u r e s 4.2,

I I

v a l u e used f o r kd, i n t h i s case, was 0.0000134 min-' As can be seen frorn F i g u r e s 4.2,

I I

4.3,

4.4,

The

as e x p l a i n e d e a r l i e r . 4.5 and 4.6,

t h e two

b a t c h mathematical models were a b l e t o p r e d i c t r a t h e r c l o s e l y t h e experimental b a t c h d a t a when b o t h model s err~ployed t h e sarrle values of t h e rnodel constants. 2.

P a r t i c l e Size E f f e c t Studies

1 1

4.4 and 4.5 when used i n t h e c l o s e d b a t c h r e a c t o r

mathematical model r e s u l t e d i n t h e continuous c u r v e i n F i g u r e 4.6.

I

I

4.3,

To t e s t t h e a b i l i t y o f t h e pore d i f f u s i o n mathematical model t o p r e d i c t p a r t i c l e s i z e e f f e c t s , another c o n s t a n t c o n c e n t r a t i o n b a t c h e x p e r i ment was c a r r i e d o u t a t pH 4.0 and 23°C.

The b u l k f r e e c h l o r i n e concentra-

t i o n i n t h i s case was maintained on t h e average a t 30 mg/R; 50 mg/R o f 45 x 50 mesh carbon were used. i 3

i

J

F i g u r e 4.7. solution.

The r e s u l t s o f t h i s experiment a r e shown i n

T h i s experiment was stopped when brown c o l o r was observed i n T h i s brown c o l o r became v i s i b l e a f t e r 3.6 grams o f c h l o r i n e had

r e a c t e d p e r gram o f a c t i v a t e d carbon.

I n t h i s experiment a q u a n t i t a t i v e

Chlorine Concentration, mg/f

Reaction Rate, mg/l-min

measure o f t h e c o l o r o f t h e samples was made a t 270 nrn u s i n g a 10 crrl l i g h t p a t h ( F i g u r e 4.7).

The absorbance o f t h e f r e e c h l o r i n e s o l u t i o n p r i o r t o

t h e a d d i t i o n o f carbon was 0.14.

A t t h e p o i n t when brown c o l o r became

v i s i b l e (X = 3.6) t h e absorbance of t h e s o l u t i o n was 0.91. The model c o n s t a n t s k8 and k10 a r e independent o f L and kg a r e d i r e c t l y p r o p o r t i o n a l t o t h e square o f L

whereas SIT P (see s e c t i o n I 1 ,C.2.c).

P Consequently, t h e v a l u e s o f SIT and kg f o r t h e 45 x 50 mesh carbon ( L

=

P 0.0055 cm) were e v a l u a t e d f r o m t h e c o r r e s p o n d i n g v a l u e s o f SIT and kg f o r

t h e 60 x 8 0 mesh carbon t o be 0.01728 and 6.568 r e s p e c t i v e l y . The above v a l u e s o f t h e model c o n s t a n t s were used t o p r e d i c t t h e r a t e o f f r e e c h l o r i n e removal vs. X c u r v e f o r t h e 45 x 50 mesh carbon and t h e r e s u l t s a r e shown as a c o n t i n u o u s c u r v e i n F i g u r e 4.7.

As i s obvious

f r o m t h e f i g u r e , a r a t h e r good correspondence was o b t a i n e d between t h e e x p e r i m e n t a l and p r e d i c t e d d a t a i n d i c a t i n g t h a t t h e model i s v a l i d f o r predicting particle size effects. I t i s i n t e r e s t i n g t o n o t e f o r b o t h t h e experimental and p r e d i c t e d

d a t a i n F i g u r e s 4.2 and 4.7 t h a t a t l o w v a l u e s o f X, t h e r a t e of f r e e c h l o r i n e removal f o r t h e 60 x 80 mesh carbon i s a p p r e c i a b l y l a r g e r than t h a t f o r t h e 45 x 50 mesh carbon.

When X i s zero, t h e e f f e c t i v e n e s s f a c t o r ( t h e

r a t i o o f t h e a c t u a l r a t e t o t h a t r a t e o b t a i n e d i f a l l t h e carbon s u r f a c e was exposed t o t h e b u l k f r e e c h l o r i n e c o n c e n t r a t i o n ) f o r t h e 60 x 80 mesh carbon was computed t o be 0.0921 w h i l e t h a t f o r t h e 45 x 50 mesh carbon was found t o be 0.0586.

T h i s d i f f e r e n c e , however, tends t o decrease as

X increases; t h e mathematical model p r e d i c t s t h a t when 3 grams o f c h l o r i n e have r e a c t e d w i t h one gram of carbon, t h e r a t e f o r t h e 45 x 50 mesh carbon

-

57

i s 97.3 p e r c e n t t h a t o f t h e 60 x 80 mesh carbon and t h e corresponding e f f e c t i v e n e s s f a c t o r s were computed t o be 0.94 and 0.966,

respectively.

This

o b s e r v a t i o n i s c o n s i s t e n t w i t h t h e f a c t t h a t as t h e e f f e c t i v e r e a c t i v i t y o f t h e s u r f a c e decreases, t h e e f f e c t i v e n e s s f a c t o r f o r b o t h p a r t i c l e s i z e s tends towards one.

Also, s i n c e t h e i n i t i a l e f f e c t i v e n e s s f a c t o r was found

t o be much l o w e r t h a n one, a mathematical model t h a t does n o t i n c l u d e p o r e d i f f u s i o n e f f e c t s would n o t be i n o r d e r . To f u r t h e r check on t h e a b i l i t y o f t h e p o r e model t o p r e d i c t p a r t i c l e s i z e e f f e c t s , a c l o s e d batch experiment was c a r r i e d o u t a t pH 4.0 and 23"C, w i t h 45 x 50 mesh s i z e carbon.

The i n i t i a l f r e e c h l o r i n e con-

c e n t r a t i o n and a c t i v a t e d carbon c o n c e n t r a t i o n were 30 mg/R and 10 mg/R, r e s p e c t i v e l y , and t h e r e s u l t s a r e shown i n F i g u r e 4.8. The c o n t i n u o u s c u r v e i n F i g u r e 4.8 r e p r e s e n t s t h e c o n c e n t r a t i o n l e v e l s as p r e d i c t e d by t h e c l o s e d b a t c h mathematical model f o r t h e same v a l u e s o f SIT, kg, k g and k10 used i n t h e CCBR mathematical model t o pre,

diet t h e 45 x 50 mesh carbon d a t a i n F i g u r e 4.7. was once more 0.0000134 rnin-'

.

The v a l u e used f o r kd

Examination o f F i g u r e 4.8 shows t h a t t h e

model underestimated t h e e f f e c t o f p a r t i c l e s i z e b u t t h e d i s c r e p a n c i e s were not drastic. 3.

Packed Bed S t u d i e s A c t i v a t e d carbon packed bed experirrlents were c a r r i e d o u t i n o r d e r

t o e v a l u a t e t h e accuracy o f t h e packed bed rrlathematical model f o r p r e d i c t i n g t h e b e h a v i o r o f such r e a c t o r s . The d a t a shown i n F i g u r e 4.9 r e p r e s e n t t h e e f f l u e n t c o n c e n t r a t i o n

Chlorine

Concentration, mg / q

Time, hr FIG. 4.9

CHLORINE BREAKTHROUGH CURVE, pH 4, 23O C CARBON

, 60 x 80

MESH

vs. t i m e f o r a packed bed e x p e r i m e n t w h e r e i n t h e i n f l u e n t c o n c e n t r a t i o n , pH, t e m p e r a t u r e and f l o w r a t e were 20 mg/R, 4.0, 23OC and 32.78 cc/min 2 (4.26 gpm/ft ), r e s p e c t i v e l y . The carbon, 1.49 g of 60 x 8 0 mesh, was packed i n a 1.55 cm i n t e r n a l d i a m e t e r column. p o r t i o n o f t h e bed, Lb was 1.65 cm.

The l e n g t h o f t h e carbon

The bed p o r o s i t y was assumed t o be

0.43 based on p r e v i o u s d e t e r m i n a t i o n s made u s i n g p a r t i c l e s o f s i m i l a r shape ( F a i r et aZ., 1968).

I n i t i a l l y , t h e e f f l u e n t pH r o s e t o 5.2,

apparently

owing t o a d s o r p t i o n o f p r o t o n s by t h e carbon, and a f t e r a b o u t one hour i t decreased t o 3.6. towards 4.0.

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

Brown c o l o r was observed i n t h e e f f l u e n t a f t e r a b o u t 275

hours a t w h i c h t i m e an average o f 3.45 grams o f c h l o r i n e , as C12, had r e a c t e d w i t h each gram o f carbon.

Using t h e c o n s t a n t c o n c e n t r a t i o n b a t c h

r e a c t o r model, i t was p r e d i c t e d t h a t 3.6 grams o f f r e e c h l o r i n e , as C12, would have r e a c t e d w i t h a gram o f carbon exposed t o 20 mg/R o f f r e e c h l o r i n e (column i n f l u e n t c o n c e n t r a t i o n ) . The f o u r p r e d i c t e d c u r v e s f o r t h e 60 x 8 0 mesh carbon shown i n F i g u r e s 4.2,

4.3,

4.4 and 4.5 were used t o o b t a i n t h e a l g e b r a i c f i t , R(X,C).

U s i n g t h i s a l g e b r a i c f i t and an a x i a l d i s p e r s i o n c o e f f i c i e n t ,

D A Y

2 o f 1 cm /min

( L e v e n s p i e l , 1972), t h e packed bed mathematical model was s o l v e d t o p r e d i c t t h e b r e a k t h r o u g h c u r v e f o r t h e same c o n d i t i o n s used i n o b t a i n i n g t h e d a t a i n F i g u r e 4.9.

The p r e d i c t e d c u r v e shown a s a c o n t i n u o u s l i n e i n t h e same

f i g u r e followed the data r a t h e r w e l l i n d i c a t i n g the v a l i d i t y o f using batch d a t a t o p r e d i c t column performance. The packed bed mathematical model was a l s o s o l v e d f o r v a l u e s o f 2 t h e a x i a l d i s p e r s i o n c o e f f i c i e n t , DAY o f 2, 3 and 4 cm /min.

The s o l u t i o n s

61

were i n i t i a l l y d i f f e r e n t from t h e s o l u t i o n shown i n F i g u r e 4.9 b u t a f t e r about 40 hours, t h i s d i f f e r e n c e became n e g l i g i b l e .

The v a l u e o f DA o f

2 1 cm /min was s e l e c t e d s i n c e i t gave b e t t e r f i t o f t h e d a t a .

A l l t h e data

presented i n t h i s s t u d y were c o r r e l a t e d u s i n g t h i s model. T h i s model was a1 so solved assuming p l u g f l o w ( i .e.

, DA

= 0).

T h i s s o l u t i o n r e q u i r e d t h e use o f a d i f f e r e n t numerical technique, as o u t 1 i n e s i n Appendix A, which proved t o be more c o s t l y t h a n t h e s o l u t i o n i n c l u d i n g t h e a x i a l d i s p e r s i o n term.

No a p p r e c i a b l e d i f f e r e n c e was observed

2 between t h e s o l u t i o n s f o r DA equal t o z e r o and DA equal t o 1 cm /min. To f u r t h e r t e s t t h e a b i l i t y o f t h e model t o p r e d i c t p a r t i c l e s i z e e f f e c t s , another packed bed experiment was run, t h i s t i m e u s i n g 18 x 20 mesh carbon (see F i g u r e 4.10).

The i n f l u e n t c o n c e n t r a t i o n , pH and temper-

a t u r e i n t h i s experiment were t h e same as t h e p r e v i o u s column experiment. 2 The f l o w r a t e was 83.9 cc/min (4.06 gpm/ft ); 8.92 g o f carbon were packed i n a 2.54 cm i n t e r n a l diameter column y i e l d i n g a bed l e n g t h o f 4 cm. I n i t i a l l y , t h e e f f l u e n t pH r o s e t o 5.3 and a f t e r one hour i t dropped t o 3.5.

Afterwords, t h e pH r o s e s t e a d i l y towards 4.0.

Brown c o l o r

was observed i n t h e e f f l u e n t a f t e r about 395 hours a t which t i m e an average o f 2.3 grams o f c h l o r i n e , as C12, had r e a c t e d w i t h each gram o f carbon. Using t h e CCBR model, i t was p r e d i c t e d t h a t 2.84 grams o f c h l o r i n e as C12 would have r e a c t e d w i t h a gram o f carbon l o c a t e d a t t h e e n t r a n c e o f t h e column under c o n d i t i o n s o f o p e r a t i o n o f t h e bed. Assuming t h a t t h e i n t e r n a l p a r t i c l e p o r o s i t y does n o t v a r y w i t h p a r t i c l e s i z e , and u s i n g an e x p e r i m e n t a l l y determined value f o r m ( w e i g h t o f a c t i v a t e d carbon p e r u n i t volume o f packed bed), t h e bed p o r o s i t y i n t h i s

Effluent Concentration, mg/X

case was c a l c u l a t e d , based on t h e 60 x 80 mesh carbon bed p o r o s i t y t o be 0.476. The pore l e n g t h , L

f o r t h e 18 x 20 mesh carbon i s 0.0153 cm. P' For t h i s pore l e n g t h , SIT and kg were c a l c u l a t e d t o be 0.1343 and 51.05, respectively.

The c o n s t a n t s k8 and kg remain unchanged a t 0.00001 7 and

380 r e s p e c t i v e l y , as t h e y a r e independent o f pore l e n g t h . values, t h e a l g e b r a i c f i t , R(X,C),

Using these

was o b t a i n e d u s i n g f o u r CCBR model r u n s

a t b u l k c o n c e n t r a t i o n s o f 5, 10, 20 and 30 mg/R.

T h i s a l g e b r a i c f i t was

2 then used along w i t h an a x i a l d i s p e r s i o n c o e f f i c i e n t o f 1 cm /min i n t h e packed bed mathematical model t o p r e d i c t t h e breakthrough curve f o r t h e same c o n d i t i o n s a p p l i c a b l e t o t h e d a t a i n F i g u r e 4.10. The p r e d i c t e d c u r v e i s shown i n F i g u r e 4.10 as a continuous l i n e . Correspondence between t h e p r e d i c t e d c u r v e and t h e data was r a t h e r good, once more i n d i c a t i n g t h e v a l i d i t y o f t h e model i n p r e d i c t i n g p a r t i c l e size effects. I t i s i n t e r e s t i n g t o add here t h a t f o r f r e s h carbon, an e f f e c t i v e ness f a c t o r o f 0.0209 was computed f o r t h e 18 x 20 mesh carbon.

This e f -

f e c t i v e n e s s f a c t o r increased as t h e r e a c t i o n proceeded and was 0.625 when 3 grams o f f r e e c h l o r i n e had r e a c t e d w i t h one gram o f carbon. U n f o r t u n a t e l y , no q u a n t i t a t i v e measurement o f c o l o r was made f o r t h e packed bed column experiments i n F i g u r e s 4.9 and 4.10.

The d a t a shown

i n F i g u r e 4.11 r e p r e s e n t t h e e f f l u e n t c o n c e n t r a t i o n vs. t i m e from a 60 x 80 packed bed experiment c a r r i e d o u t a t 23OC f o r which c o l o r measurements were made, however. E i g h t grams o f carbon were packed i n 2.54 cm i n t e r n a l diameter

-

9-

P

Flow Rate 4.25 gpm/ft2 Bed Length = 3.3 cm lnf luent Concentration = 18-23 m9/1 = 270 nm Chlorine Measurement I Absorbance Measurement

-

0.9

8-

-

7-

-

6-

-0.6

5-

-0.5

4-

-0.4

3-

-0.3

2-

-

0.8

0.7

0.2

-0.1

IOo

60

120

180

240

300

360

0 420

Time, hr. FIG. 4.1 1

CHLORINE AND COLOR BREAKTHROUGH CURVE , pH 3.2 -5.8, 23OC MESH CARBON

, 60 x 8 0

column.

The average l e n g t h o f t h e carbon p o r t i o n o f t h e bed was 3.3 cm

2 and t h e i n f l u e n t f l o w r a t e was m a i n t a i n e d a t 87.5 cc/min (4.25 gprn/ft ) . I n t h i s experiment t h e carbon was h e l d i n p l a c e by a l a y e r o f g l a s s wool on each s i d e . cm g l a s s beads.

The g l a s s wool was i n t u r n supported by t i g h t l y packed 0.2 The i n f l u e n t f r e e c h l o r i n e c o r ~ c e n t r a t i o nv a r i e d between

18 and 23 mg/R, and t h e i n f l u e n t pH ranged from 3.2 t o 5.8.

This experi-

rr~entwas v e r y c r u d e l y prepared as i t was i n t e n d e d f o r t h e purpose o f p r e l i m i n a r y investigation only.

It i s r e p o r t e d here o n l y because c o l o r mea-

surements o f t h e e f f l b e n t samples were made.

The absorbance, a measure

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

E.

t i m e i s shown i n F i g u r e 4.11. Brown c o l o r was observed i n t h e e f f l u e n t a f t e r about 288 hours, a t which t i m e t h e absorbance o f t h e e f f l u e n t was measured a t 0.7.

By t h e

t i m e brown c o l o r became v i s i b l e i n t h e column e f f l u e n t , an average o f 3.15 grams o f c h l o r i n e , as C12, had r e a c t e d w i t h each gram o f carbon.

It i s

i n t e r e s t i n g t o n o t e t h a t i n t h e case o f t h e 60 x 80 mesh carbon packed bed experiment shown i n F i g u r e 4.9,

brown c o l o r was observed i n t h e e f f l u e n t

a f t e r 275 hours which i s r a t h e r c l o s e t o t h e 288 hours r e q u i r e d f o r c o l o r emergence i n t h i s experiment.

Using t h e c o n s t a n t c o n c e n t r a t i o n b a t c h r e -

a c t o r model, i t was p r e d i c t e d t h a t 3.605 g o f f r e e c h l o r i n e , as C12, would have r e a c t e d w i t h a gram o f carbon l o c a t e d a t t h e e n t r a n c e o f t h e column i f i t were assumed t h a t b o t h i n f l u e n t c o n c e n t r a t i o n and pH were h e l d con-

s t a n t a t 20 mg/R and 4.0. When t h e r e s u l t s o f t h i s experiment were compared t o t h e o t h e r pH 4, 60 x 80 mesh carbon column experiment shown i n F i g u r e 4.9,

i t was

found t h a t j u s t p r i o r t o t h e emergence o f brown c o l o r i n t h e e f f l u e n t , t h e amount o f c h l o r i n e r e a c t e d p e r gram o f carbon l o c a t e d a t t h e mouth of t h e bed was almost t h e same.

However, t h e average amount o f c h l o r i n e r e a c t e d

p e r gram o f carbon i n t h e bed was much l o w e r due t o t h e f a c t t h a t t h e c a r bon column used f o r t h e r e s u l t s shown i n F i g u r e 4.11 was about t w i c e as l o n g as t h e one used i n t h e experiment shown i n F i g u r e 4.9.

Based on t h i s

o b s e r v a t i o n , i t c o u l d be s t a t e d t h a t more e f f i c i e n t use o f t h e carbon i s a t t a i n e d by r e s o r t i n g t o s h o r t e r carbon columns. T h i s colurrln experinlent was c o r ~ t i n u e da f t e r brown c o l o r was observed i n t h e e f f l u e n t .

As t h e experirrlent proceeded, t h e c o l o r i n t h e ef-

f l u e n t t u r n e d t o b l a c k and became rrluch more i n t e n s e as t h e carbon i n t h e bed s t a r t e d t o fragment and l e a v e t h e bed i n t h e e f f l u e n t .

A f t e r about 360

hours, t h e experiment was stopped a f t e r a h i g h head l o s s developed i n t h e bed. Using t h e a l g e b r a i c f i t , R(X,C),

developed f o r t h e 60 x 80 mesh

carbon, pH 4, and 23°C column experiment i n F i g u r e 4.9, 2 c o e f f i c i e n t , DA o f 1 cm /min and a bed p o r o s i t y ,

E,

an a x i a l d i s p e r s i o n

o f 0.43,

t h e packed bed

model was solved t o p r e d i c t t h e breakthrough c u r v e assuming an i n f l u e n t conc e n t r a t i o n o f 20 rng/R. i n F i g u r e 4.11.

The p r e d i c t e d c u r v e i s shown as a continuous l i n e

A r a t h e r good c o r r e l a t i o n between t h e p r e d i c t e d curve and

t h e d a t a was o b t a i n e d c o n s i d e r i n g t h e crude manner i n which t h i s e x p e r i rr~entwas c a r r i e d o u t .

Note t h a t beyond 288 hours, c o l o r was observed i n

t h e e f f l u e n t and e v e n t u a l l y carbon f i n e s began appearing i n t h e e f f l u e n t . Beyond t h i s p o i n t , t h e rrlodel i s n o t expected t o p r e d i c t t h e e f f l u e n t q u a l i t y as i t does n o t account f o r carbon f i n e s l e a v i n g t h e bed.

As can be

.

seen from F i g u r e 4.11,

t h e p r e d i c t e d values a r e much 1ower than t h e e x p e r i -

mental d a t a i n t h i s range. C.

Experiments a t pH 10.0 and 23°C HOCl i s a weak a c i d w i t h a pKa o f 7.6 a t 23"C:(Morris,

a c c o r d i n g l y , a t pH values above 7.6, chlorine.

1968) and,

OC1- i s t h e predominant species of f r e e

I n o r d e r t o determine how t h i s species r e a c t s w i t h carbon, ex-

periments were c a r r i e d o u t a t a pH o f 10.0. 1.

Batch S t u d i e s Three c l o s e d b a t c h r e a c t o r experiments were c a r r i e d o u t a t pH

10.0 and 23°C and t h e r e s u l t s a r e shown i n F i g u r e 4.12.

I n t h i s case, 4.21

g NaHC03 and 0.53 g Na2C03 were added p e r l i t e r o f s o l u t i o n t o minimize pH changes owing t o e n t r y o f C02 i n t o t h e s o l u t i o n from t h e atmosphere.

In

a l l t h r e e experiments 20 mg/R o f 60 x 80 mesh a c t i v a t e d carbon were added. I n i t i a l f r e e c h l o r i n e c o n c e n t r a t i o n s were 37.0,

28.6 and 13.6 mg/R.

The d i f f u s i o n c o e f f i c i e n t , Dc, f o r OC1- was assumed t o be t h e same as t h a t used f o r HOC1, namely 6 x

l o m 4 cm2/min.

For a v a l u e of L

P equal t o 0.0035 cm, corresponding t o 60 x 80 mesh carbon, t h e c l o s e d b a t c h model was s o l v e d t o p r e d i c t t h e c o n c e n t r a t i o n l e v e l s i n t h e r e a c t o r as a f u n c t i o n o f time. found t o be 0.0018, kg. klO,

The values of t h e model c o n s t a n t s f o r t h i s case were 0.000017,

0.684,

380 and 0.0000134 min-'

f o r SIT, kg,

and kd, r e s p e c t i v e l y , and t h e r e s u l t s a r e shown i n F i g u r e 4.12.

As i s obvious from F i g u r e 4.12,

a r a t h e r good p r e d i c t i o n was o b t a i n e d f o r

t h e t h r e e c o n c e n t r a t i o n vs. t i m e curves.

The v a l u e s o f k8 and kI0 were

Chlorine Concentrat ion, r q / l

n o t changed f r o m those used t o d e s c r i b e t h e pH 4, 23°C data.

It i s possi-

b l e , however, t h a t an e q u a l l y good f i t c o u l d have been o b t a i n e d i f a l l f o u r c o n s t a n t s , SIT, kg, kg and k

had v a l u e s o t h e r t h a n w'ere used f o r t h e pH

10'

4, 23°C data. 2.

Packed Bed S t u d i e s The d a t a shown i n F i g u r e 4.13 r e p r e s e n t a breakthrough c u r v e f o r

a packed bed experiment w i t h an i n f l u e n t pH o f 10.0.

The i n f l u e n t concen-

t r a t i o n , temperature, and f l o w r a t e were 20 mg/R, 23OC and 32.78 c c l m i n 2 (4.26 gpm/ft ), r e s p e c t i v e l y .

The carbon, 2.35 grarns o f 60 x 80 mesh, was

packed i n a 1.55 cm i n t e r n a l d i a m e t e r column.

The l e n g t h o f t h e carbon

p o r t i o n o f t h e bed, Lb, was 2.6 cm and t h e p o r o s i t y was a g a i n assumed t o be 0.43.

The e f f l u e n t pH remained a t 10.0 w i t h no n o t i c e a b l e v a r i a t i o n d u r i n g

t h e run.

The experiment was stopped a f t e r 250 hours p r i o r t o t h e appearance

of brown c o l o r . Using t h e v a l u e s f o r t h e c o n s t a n t s o b t a i n e d from t h e b a t c h d a t a was o b t a i n e d .

Using t h i s

2 e x p r e s s i o n and an a x i a l d i s p e r s i o n c o e f f i c i e n t o f 1 cm /min,

t h e packed

a t pH 10.0,

t h e a l g e b r a i c expression, R(X,C),

bed model was solved; t h e p r e d i c t e d breakthrough c u r v e i s shown as a cont i n u o u s l i n e i n F i g u r e 4.13.

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

n o t q u i t e as good as was observed a t p ~ . 4 0, . b u t i t i s considered s a t i s f a c t o r y f o r most purposes.

D.

Experiments a t pH 7.6 and 23' The pK o f t h e HOCl i s 7.6 a t 23°C ( M o r r i s , 1968). a

The s o l u t i o n

Effluent Concentration, mg/t

~ J L M ~ u a ~ s k s u oavle 3 e ~ e psky pup ~d

ayJ quasavldavl s a u l e n a s a y l

-.SA

( 8 - 1 u o k ~ ~ n baas) g y " u e ~ s s u 3 aJevl

. i l a n k ~ s a d s a v l ' 1 ~ 9 - pue ~ ~ O O -40O 6 Y pue

11s

vlo~3eavly ~ q e qpas013 ayJ 6 u b n ~ o suk pasn avlaM sanlen awes ay3 c K ~ ~ u a n b a s u o ~ :O.OL

~d Je se 0.b ~d 7e awes aqJ avlaM Py pue

coLy

c8y 40 sanlen ay?

JP~J

paMoys e ~ e p~equaw~vladxa 40 s k s K ~ e u b .uokgnlos uk v l a y ~ a 6 opaqskxa ~ sak3ads asay?. y ~ o quayM pasn

SPM

anLen awes s k 4 ~'JLnsavl P sb up^/ lu3 0 1 x g aq z PcJuak3k44a03 u o k s n j j k p a y l

o~ pawnsse avlaM -130 pue 1 3 0 ~o

aukvloly:,

aavlj

aavlj

L P L J ~ U~ ~J L Mpasn

L P L J L U ~UP

y ? . ! ~U

OJ

C

Ja

avlaM uoqvle:,

O ~ J ~ U ~ U~L Upasn O ~

' P L ' P avln6kj u~ u ~ o y savle

auLwvlaJap

pavl ksap

alms ayJ 40 3/6w c j ~c

avlaM uoqvle:,

~

avln6rj ~

-

~

ysalu 08 x 09 40 3/6w 0 1

40 sJlnsavl ayJ c~uau.~kvladxa J S J L ~ ayJ

Y3LLjM

SPM J L

a s n w a q pue u o q n 10s e y3ns uk ~ e n b aavlP

UI

- 130

pup 1 3 0 ~40 s u o k ~ ~ v l ~ u a 3 uayq o 3 a s n e ~ a q6 u ! . ~ s a vloj ~ p a ~ ~ a l aSPM s g * 40 ~ ~d

CHLORINE-CARBON ( 6 0 x 80 MESH) REACTION IN A CLOSED BATCH REACTOR, p H 7 6 , 23OC

7 -

Chlorine Concentration, mg / t

.a 9 UI Q

0 0

0

=4 T 0

-i n mz m w I 0 0 0 D N

IU

0

;(3

a3

P

0

0

Z

CI

m

0 x

OD

0

m V)

I

Y

;(3

z! 3 0

0

-" -, OD

0

m D

0 --I

-

0

0 0

Z

z D

-

0

IU

6

0

V)

m

0 a3

3

0

I ;(3

m B

0 --I

-

0 ;(3

-

P

0

-

0

U1

IU

0

IU U1

w

0

E.

Temperature E f f e c t S t u d i e s a t pH 4.0 and 10.0 Temperature i s expected t o a f f e c t b o t h t h e d i f f u s i v i t y and t h e

r e a c t i o n r a t e constants.

The e f f e c t o f temperature on d i f f u s i v i t y i n a p o r e

was assumed t o be s i m i l a r t o t h a t i n f r e e s o l b t i o n .

The e x p r e s s i o n used f o r

p r e d i c t i n g t h e e f f e c t o f temperature on Dc was ( F o g l e r , 1974)

where

LI

i s t h e v i s c o s i t y , MIL-T, and

T

i s t h e a b s o l u t e temperature,

OK.

Two c l o s e d b a t c h experiments were r u n a t pH 10.0 and 35°C as shown i n F i g u r e 4.16. and 24.8 mg/R.

The i n i t i a l f r e e c h l o r i n e c o n c e n t r a t i o n s were 38.1

Two o t h e r experiments were c a r r i e d o u t a t t h e same pH b u t

a t a temperature o f 2°C as shown i n F i g u r e 4.17.

I n t h i s case t h e i n i t i a l

f r e e c h l o r i n e c o n c e n t r a t i o n s were 39.3 and 24.4 mg/R.

A l l f o u r experiments

were performed w i t h 20 mg/R o f 60 x 80 mesh carbon. The v i s c o s i t y of water a t 2"C, 23°C and 35°C i s 1.6728, 0.9358 and 0.7225 c e n t i p o i s e s , r e s p e c t i v e l y ( P e r r y , 1950). a base v a l u e f o r Dc of 6 x 1 o

- ~cm2 /,in

Using these values and

a t 23"C, t h e v a l u e s o f Dc were c a l -

t o be 3.12 x l

2°C and 35"C,

The c l o s e d b a t c h model was s o l v e d t o p r e d i c t

respectively.

~ and 8.04~ x

l o m 4 cm2/min

c u l a t e d , u s i n g Equation 4.2,

at

t h e c o n c e n t r a t i o n l e v e l s and t o determine t h e r e m a i n i n g c o n s t a n t s ; a r a t h e r good f i t was o b t a i n e d f o r SIT and kg values o f 0.0009 and 0.00267 and 1.0157 a t 35"C, r e s p e c t i v e l y .

and 0.342 a t Z°C,

The v a l u e s o f k8 and k10

were t h e same as f o r t h e pH 4.0 and 10.0 s t u d i e s a t 23°C.

The f i r s t o r d e r

40 2 0 mg / \ Carbon

35 30 25

20 15

10 5

0 0

20

40

60

80

100

120

140

Time, hr

FIG. 4.16

CHLORINE- CARBON ( 6 0 x 8 0 MESH) REACTION IN A CLOSED BATCH REACTOR, p H 10, 35O C

Chlorine Concentration, m g / 1

r a t e o f decay constant, kd, was found t o be e s s e n t i a l l y t h e same, 0.0000134 min'l,

f o r t h e t h r e e d i f f e r e n t temperatures a t pH 10.0. Two o t h e r closed batch experiments were c a r r i e d o u t a t pH 4.0 and

a temperature o f 35°C.

I n t h e f i r s t experiment 20 mg/R o f 60 x 80 mesh c a r -

bon was used and t h e i n i t i a l f r e e c h l o r i n e c o n c e n t r a t i o n was 37.8 mg/R. r e s u l t s a r e shown i n F i g u r e 4.18.

Only 10 mg/R o f 60 x 80 mesh carbon was

used i n t h e second experiment shown i n F i g u r e 4.19; c o n c e n t r a t i o n was 27.3 mg/R.

The

the i n i t i a l f r e e chlorine

The r a t e o f decay a t pH 4.0 and 35°C was found

t o be h i g h e r than t h a t a t 23OC a t t h e same pH; kd was evaluated t o be 0.00003 min-I i n t h i s case.

A good f i t o f t h e data was obtained when t h e f i n i t e batch model was solved f o r values o f SIT and kg o f 0.01039 and 3.947, i s apparent i n Figures 4.18 and 4.19.

r e s p e c t i v e l y , as

I n t h i s case a l s o , t h e values o f k8

and k10 were t h e same as a t 23OC. SIT and kg cannot be regarded as s u r f a c e r e a c t i o n r a t e constants 2 /D Consequently, i n o r d e r t o study P c t h e e f f e c t o f temperature on t h e s u r f a c e r e a c t i o n r a t e SST and k7 are t h e because t h e y both i n c l u d e t h e term L

proper terms t o be analyzed. temperature data, loglO

.

Figure 4.20 shows an Arrhenius p l o t o f t h e

SST _vl. 1/T.

The t h r e e values o f SST a v a i l a b l e a t

pH 10.0 f a l l on a s t r a i g h t l i n e , and t h e two values o f SST a t pH 4.0 form a l i n e p a r a l l e l t o t h e previous one.

Based on these l i m i t e d data, t h e a c t i -

v a t i o n energy f o r k3, t h e o n l y r a t e c o n s t a n t which i s p a r t o f SST, can be c a l c u l a t e d t o be 5.3 k c a l .

The constant, kg, c o n t a i n s t h e a d s o r p t i o n -

d e s o r p t i o n e q u i l i b r i u m constant, k4, and i t l i k e l y v a r i e s w i t h temperature. I n t h i s study, however, i t was assumed t h a t k8 and k10 d i d n o t v a r y w i t h

Chlorine

Concentration, m g / \

Sky7 6 u p n

1 dxa (9915-)

' [ P ~ YO ' P JO

r

'

o

'~ L J O~ L ~ ~ PJO ~ J Ad~ey7uaUP

0 1 + 11 ~ d ) 01 0 1 x 1880'0 + €P€'O] L

(Lid -

- e ~ a d o a ?JO s u o k 7 3 u n ~se '

1-

u p

6Ly

.hue 4;

pue

6oLy

x

s

a~ndw0301pasn aq

=

(L'H~)LSS

' ukw ' 1 ~ sant6 07 padolanap aJaM 1-

pue 8y uo a ~ n ~ e ~ a d40w a73a44a ~ a47

The dimensionless r a t e constants, SIT and k

used i n t h e numeri9' c a l s o l u t i o n o f t h e two b a t c h models can be o b t a i n e d f r o m t h e values o f SST and kg g i v e n by Equations 4.3 and 4.4 u s i n g t h e f o l l o w i n g two equations, 5 2 5 . 2 7 2 ~10 x p ~ Lx x S S T SIT

=

and

9

=

SIT

x

380

where p- i s t h e a b s o l u t e v i s c o s i t y a t temperature T i s t h e pore h a l f l e n g t h , crn.

4.7

7,c e n t i p o i ses,

and L

P

Because k8 and k

and 380, r e s p e c t i v e l y , Equations 4.3-4.7

were c o n s t a n t a t 0.000017 10 can be used t o c a l c u l a t e t h e r e -

maining parameters necessary f o r d e s c r i b i n g t h e performance o f c l o s e d and c o n s t a n t c o n c e n t r a t i o n b a t c h r e a c t o r s as w e l l as packed bed columns u s i n g F i l t r a s o r b 400 carbon.

83

V. A.

CONCLUSIONS AN13 RECOMIYENDATIONS

Conclusions 1.

Batch experimental d a t a can be used t o p r o v i d e t h e i n f o r m a t i o n

necessary f o r t h e design o f packed bed a c t i v a t e d carbon d e c h l o r i n a t i o n r e actors.

I n t h i s s t u d y t h e s u r f a c e r e a c t i o n r a t e c o n s t a n t s appearing i n t h e

pore d i f f u s i o n model were evaluated from batch experimental data.

These

c o n s t a n t s were then s u c c e s s f u l l y used t o p r e d i c t packed bed column behavior.

2.

I n t h i s s t u d y an a l g e b r a i c r a t e expression, R(X,C),

was used

t o simp1 i f y t h e packed bed r e a c t o r mathematical model by e l i m i n a t i n g t h e dimension a l o n g t h e carbon pore from t h e model.

T h i s r a t e e x p r e s s i o n was

o b t a i n e d by a l g e b r a i c a l l y f i t t i n g c o n s t a n t c o n c e n t r a t i o n b a t c h r e a c t o r r a t e d a t a vs. X; t h e amount o f c h l o r i n e r e a c t e d p e r u n i t w e i g h t o f carbon.

The

use o f such an expression was p o s s i b l e because t h e two b a t c h models p r e d i c t e d t h a t , f o r f i x e d pH, temperature and p a r t i c l e s i z e , t h e r a t e o f c h l o r i n e r e moval was a f u n c t i o n o f o n l y t h e b u l k c o n c e n t r a t i o n and t h e amount o f c h l o r i n e a1 ready r e a c t e d w i t h t h e carbon.

3.

Pore d i f f u s i o n was found t o be v e r y i m p o r t a n t , e s p e c i a l l y

when t h e carbon was r e l a t i v e l y f r e s h .

As t h e e x t e n t o f r e a c t i o n increased,

t h e s u r f a c e r e a c t i o n became t h e r a t e c o n t r o l l i n g s t e p as was shown i n t h e case o f t h e 60 x 80 and 45 x 50 mesh carbon CCBR experiments. 4.

The r a t e o f c h l o r i n e removal was found t o be v e r y s e n s i t i v e

t o p a r t i c l e s i z e , decreasing w i t h i n c r e a s i n g g r a n u l e diameter.

This i s a

d i r e c t consequence t o t h e irrlportance o f p o r e d i f f u s i o r l as a r a t e c o n t r o l l i n g mechanism e s p e c i a l l y f o r low values o f X.

The mathematical model was

s u c c e s s f u l l y used t o p r e d i c t p a r t i c l e s i z e e f f e c t s f o r b o t h b a t c h and packed bed r e a c t o r s . 5.

An a n a l y s i s o f t h e d a t a showed t h a t t h e r e a c t i o n r a t e ap-

proaches z e r o a s s y r n p t o t i c a l l y , r a t h e r t h a n a steady s t a t e v a l u e as has been r e p o r t e d by Magee ( 1 956).

I n terrns o f t h e parameters used i n t h i s ' model i t

was found t h a t kg/k10 was equal t o S I T which means t h a t as t h e amount o f c h l o r i n e r e a c t e d p e r gram o f carbon i n c r e a s e s , t h e s u r f a c e r e a c t i o n t e r m approaches zero. 6.

The pH was o b s e r v e d . t o i n f l u e n c e t h e r e a c t i o n r a t e o n l y as

f a r as i t a f f e c t s t h e d i s t r i b u t i o n o f f r e e c h l o r i n e between HOCl and 0 ~ 1 ~ . T h i s f i n d i n g made i t p o s s i b l e t o use r e a c t i o n r a t e c o n s t a n t s o b t a i n e d sepa r a t e l y f o r HOCl and 0 ~ 1 -t o a r r i v e a t t h e r a t e c o n s t a n t s a p p l i c a b l e t o m i x t u r e s o f t h e two f r e e c h l o r i n e species.

7. constant, k

3'

The e f f e c t o f temperature on t h e s u r f a c e d i s s o c i a t i o n r a t e was found t o f o l l o w t h e A r r h e n i u s model.

Based on l i m i t e d

data, t h e a c t i v a t i o n energy f o r k j was found t o be 5.3 k c a l f o r b o t h HOCl and OC1-. 8.

Brown c o l o r was observed i n s o l u t i o n a f t e r e x t e n s i v e o x i d a -

t i o n o f t h e carbon.

The emergence o f t h e brown c o l o r was observed i n b o t h

c o n s t a n t c o n c e n t r a t i o n b a t c h and i n packed bed experiments.

L i t t l e infor-

m a t i o n was o b t a i n e d on t h e emergence o f t h e brown c o l o r , b u t based on t h e l i m i t e d d a t a a v a i l a b l e , between 2.8 t o 4.2 grams o f c h l o r i n e had t o r e a c t w i t h a gram o f carbon b e f o r e t h e c o l o r was v i s i b l e .

9.

L i t t l e , ifany, m i x i n g o c c u r r e d i n t h e packed bed r e a c t o r

experiments c a r r i e d o u t i n t h i s study.

T h i s was shown by t h e almost

i d e n t i c a l r e s u l t s o b t a i n e d from s o l v i n g t h e packed bed model w i t h t h e a x i a l 2 d i s p e r s i o n c o e f f i c i e n t , DAY equal t o 1 cm /min and w i t h DA equal t o zero. However, a x i a l d i s p e r s i o n may prove t o be i m p o r t a n t when packed bed d e c l o r i n a t i o n r e a c t o r s a r e r u n under c o n d i t i o n s o t h e r t h a n those s t u d i e d here. B.

Engineering S i g n i f i c a n c e 1.

The p a r t i c l e s i z e o f t h e carbon used i n a packed bed r e a c t o r

has an i m p o r t a n t i n f l u e n c e on t h e behavior o f a c t i v a t e d carbon d e c h l o r i n a t i o n reactors.

Because t h e r a t e o f c h l o r i n e removal i n c r e a s e s w i t h de-

c r e a s i n g p a r t i c l e s i z e , s h o r t e r columns c o u l d be used t o achieve a g i v e n r e moval e f f i c i e n c y when s m a l l e r carbon g r a n u l e s a r e used.

T h i s advantage

should be balanced, however, a g a i n s t t h e i n c r e a s e d c o s t o f o b t a i n i n g g r a n u l a r carbon small e r t h a n t h a t a v a i l a b 1 e commercial l y and t h e i n c r e a s e d head 1oss t h a t accorr~panies such a decrease i n carbon s i z e . 2.

The d e s i g n o f a d e c h l o r i n a t i o n carbon column should t a k e b o t h

t h e breakthrough e f f l u e n t c h l o r i n e c o n c e n t r a t i o n and t h e appearance o f c o l o r i n the e f f l u e n t i n t o consideration.

The carbon l o c a t e d a t t h e mouth

o f t h e packed bed i s always exposed t o t h e h i g h e s t c h l o r i n e c o n c e n t r a t i o n i n t h e bed and, as a r e s u l t , t h e e x t e n t o f r e a c t i o n a t t h e mouth o f t h e bed w i l l l i k e l y determine when t h e bed s t a r t s p r o d u c i n g c o l o r .

I f a column i s

t o o long, c o l o r w i l l appear i n t h e e f f l u e n t p r i o r t o t h e emergence o f an undesirable c h l o r i n e concentration.

I n such a case, t h e average amount o f

c h l o r i n e r e a c t e d p e r grarrl o f carbon may be much l e s s t h a n t h e amount t h a t has r e a c t e d w i t h t h e carbon l o c a t e d a t t h e entrance o f t h e packed bed. t h e d e s i g n of a d e c h l o r i n a t i o n bed, i t w i l l be necessary t o balance t h e

In

c o s t o f more f r e q u e n t replacement o f s h a l l o w beds w i t h t h e c o s t o f more i n e f f i c i e n t use o f t h e carbon when l o n g e r beds a r e employed.

T h i s aspect r e -

mains t o be f u r t h e r e v a l u a t e d however. C.

F u r t h e r Study 1.

The e f f e c t o f t h e presence o f o r g a n i c compounds on t h e r a t e

o f uptake o f f r e e c h l o r i n e by a c t i v a t e d carbon has n o t been i n v e s t i g a t e d . T h i s i s a v e r y i m p o r t a n t parameter which i s v e r y d i f f i c u l t t o e v a l u a t e because o f t h e wide v a r i a b i l i t y o f t h e t y p e o f o r g a n i c compounds p r e s e n t i n w a t e r and wastewater, and because o f t h e p o s s i b i l i t y t h a t f r e e c h l o r i n e may r e a c t w i t h sorrle o f t h e adsorbed and nonadsorbed organic.compounds.

The

model developed i n t h i s s t u d y should t h u s be used o n l y as a b a s e l i n e i n any d e s i g n c a l c u l a t i o n s , and a f a c t o r o f s a f e t y should be used t o p r o t e c t a g a i n s t s h o r t f i l t e r r u n s owing t o t h e presence o f o r g a n i c m a t t e r and t h e e n t r a i n ment o f p a r t i c u l a t e m a t t e r p r e s e n t i n t h e water by t h e carbon.

Further re-

search i s needed t o e v a l u a t e t h e e f f e c t o f t h e presence o f o r g a n i c omp pounds on t h e process o f d e c h l o r i n a t i o n and t o g i v e g u i d e l i n e s f o r f a c t o r s o f s a f e t y t h a t a r e needed when d i f f e r e n t k i n d s o f w a t e r a r e a p p l i e d t o t h e carbon.

2.

Only one carbon was used i n t h i s study.

Other carbons have

d i f f e r e n t p u r i t y , s u r f a c e a r e a and pore volume c h a r a c t e r i s t i c s and t h e e f f e c t o f t h e d i f f e r e n t c h a r a c t e r i s t i c s o f o t h e r carbons on t h e r e a c t i o n r a t e c o n s t a n t s remain t o be e v a l u a t e d .

3.

Commercial a c t i v a t e d carbon i s u s u a l l y manufactured t o i n c l u d e

a wide range o f p a r t i c l e

sizes.

B e f o r e a carbon column i s p u t t o use, i t

i s u s u a l l y f l u i d i z e d and t h e n a l l o w e d t o s e t t l e d by g r a v i t y .

Such a procedure

.

r e s u l t s i n a s t r a t i f i e d bed and t h e d e s i g n o f such a bed should t a k e t h i s s i z e s t r a t i f i c a t i o n i n t o account.

F u r t h e r r e s e a r c h i s needed t o e v a l u a t e

1

t h e performance o f such beds when c h l o r i n a t e d water i s a p p l i e d t o them e i t h e r

i

i n t h e downflow o r t h e u p f l o w mode.

LIST OF REFERENCES Baker, R. A,, " D e c h l o r i n a t i o n and Sensory Controls," Jour. American Water Works Assoc. 56, 1578 (1 964). B i r d , R. B., Stewart, W. E. and L i g h t f o o t , E. N., John W i 1ey & Sons, Inc., New York (1 960).

Transport Phenomena,

B i s c h o f f , K. B., "A Note on Boundary C o n d i t i o n s f o r Flow Reactors," Chem. Eng. Science, 1 6 , 131 (1961 ). Boehrr~, H. P., "Chemical I d e n t i f i c a t i o n o f Surface Groups," Ad7)ances i n Catalysis, D. D. E l e y e t a l . (eds), 16, 179-272, Academic Press, New York (1 966). Calgon Corp., "Calgon A c t i v a t e d Carbon Product," P i t t s b u r g h , PA (1 969).

B u l l e t i n No. 20-2a,

Coughlin, R. W., Ezra, F. and Tan, R. N., " I n f l u e n c e o f Chemisorbed Oxygen i n A d s o r p t i o n i n t o Carbon from Aqueous S o l u t i o n , " J . ColZ. I n t e r f a c e S c i . 28, 386 (1968). Dean, R. B., " T o x i c i t y o f Wastewater D i s i n f e c t a n t s , " News of EnvironmentaZ Research i n Cincinnati, U. S. Environmental P r o t e c t i o n Agency, C i n c i n n a t i , Ohio, J u l y 5 (1974). F a i r , G. M., Geyer, J. C. and Okun, D. A., Water and Wastewater Engineering, Vol. 2, John Wiley & Sons, I n c . , New York (1968). Fog1e r , H. S. , The Elements of Chemica Z Kinetics and Reactor Calculations, P r e n t i c e - H a l 1 , I n c . , New J e r s e y (1 974). Hagar, D. G. and F l e n t j e , M. W., "Removal o f Organic Contaminants by Granular Carbon F i l t r a t i o n , " Jour. Amer. Water Works Assoc. 57, 1440 ( 1 965). H e l f f e r i c h , F. G.,

Ion Exchange, McGraw-Hi 11, New York (1 962).

Kovach, J. L., "Activated-Carbon D e c h l o r i n a t i o n , " November ( 1 971 )

.

Ind. Water Eng., October/

Lapidus, L. , Digital Computations for Chemical Engineers., McGraw-Hi 1 1 , New York (1962). Lawbusch, E. J., Chapter i n Water Q u a l i t y and Treatment, 3 r d e d i t i o n , American Water Works Assoc. , McGraw-Hi 11 , New York (1 971 )

.

L e v e n s p i e l , O., Chemical Reaction Engineering, John W i l e y & Sons, I n c . , New York (1972).

1I

Magee, V., "The A p p l i c a t i o n o f Granular A c t i v e Carbon f o r D e c h l o r i n a t i o n o f Water Supplies," Proc. Soc. Water Treat. Exam 5, 17 ( 1 956).

I

{

Mishchenko, K. P., F l i s , I. E. and Kastodina, V. A., "Thermodynamic Chara c t e r i s t i c s o f Aqueous S o l u t i o n s o f Hydrogen P e r i o x i d e and I t s Reaction w i t h C h l o r i n e a t D i f f e r e n t Temperatures," Zhur. Priklad. Khim 33, 2671 (1960). I n Chem. Abstracts 55, 9023 (1961).

1

M o r r i s , J. C., Chapter i n Water and Wastewater Engineering, G. M. F a i r e t a l . (eds.), 2, John Wiley & Sons, Inc., New York (1968).

I

i

Olson, L. L. and Binning, C. C., " I n t e r a c t i o n o f Aqueous C h l o r i n e w i t h A c t i v a t e d Carbon," Chapter i n Chemistry of Water Supply Treatment and Distribution, A. Rubin (ed. ) , Ann Arbor Science Publ ishers ( 1 974). Perry, J. H.

, Chemical

I

Petersen, E. E,

i

1 i

I

i I j

I

1 I

1 i

Engineering Handbook, McGraw-Hi 11 , New York ( 1 950).

, Chemical

Reaction Analysis, Prentice-Hal 1 , New York ( 1 965).

P u r i , B. R., "Surface Complexes on Carbons," Chemistry and P h ~ s i c sof Carbon, P. L. Walker ( e d . ) , Vol. V I , 191-282, M. Dekker, New York (1970). Srni s k y M. and Cerny, S., Active Carbon: Manufacture, Properties and Applications, E l s e v i e r Pub1 is h i n g Co., New York ( 1 970). Snoeyink, V. L., L a i , H. T., Johnson, J. H. and Young, J. Fa, " A c t i v e Carbon: D e c h l o r i n a t i o n and t h e A d s o r p t i o n o f Organic Compounds", Chapter i n Chemistry of Water Supply, Treatment and Distribution, A. Rubin, ed., Ann A r b o r Science Publ -i shers ( 1 974). Snoeyink, V. L. and Suidan, M. T., Chapter i n Disinfection of Water and Wastewater, J. D. Johnson (ed. ), Ann Arbor Science Publ i s h e r s (1975).

Standard Methods for the Examination of Water and Wastewater, 1 3 t h e d i t i o n , American Publ i c H e a l t h A s s o c i a t i o n , New York (1 970). White, G. C., Ohio (1972).

Handbook of Chlorination, Van Nostrad Reinhold Co.,

Cincinnati,

APPENDIX A SOLUTIONS OF BATCH AND PACKED BED MODELS I n t h i s study, an i m p l i c i t f i n i t e d i f f e r e n c e scheme was used t o s o l v e t h e mathematical models as d e s c r i b e d by s e t s of n o n l i n e a r p a r t i a l d i f f e r e n t i a l equations.

T h i s appendix c o n t a i n s t h e f i n i t e d i f f e r e n c e equa-

t i o n s used and an o u t l i n e o f t h e s o l u t i o n procedures. 1.

Closed and Constant C o n c e n t r a t i o n Batch Reactors Equations 2.27,

2.28,

2.29,

behavior o f a c l o s e d b a t c h r e a c t o r . zero and one. each b e i n g 1/N.

2.30,

2.31 and 2.33 d e s c r i b e t h e

The d i s t a n c e v a r i a b l e

5 v a r i e s between

T h i s range was d i v i d e d i n t o N segments, t h e l e n g t h , Ar, o f L e t r designate t h e p o s i t i o n o f each segment.

Thus when r

i s zero, i t p o i n t s t o t h e mouth o f t h e pore and when i t i s N i t r e f e r s t o t h e h a l f l e n g t h o f a pore.

A dimensionless t i m e s t e p Aq, was a l s o s e l e c t e d .

L e t q stand f o r q a p o s i t i o n i n time, t h e n t h e dimensionless t i m e i s g i v e n by qi. i=l The d i f f e r e n c e equations s e l e c t e d t o express t h e d i f f e r e n t derivatives are

.

L e t R r e p r e s e n t t h e nondimensionalized s u r f a c e r a t e expression f o r f r e e chlorine reduction

The s u r f a c e r e a c t i o n r a t e , R, e v a l u a t e d a t t i m e s t e p q + 1 was expressed i n terms o f t h e r a t e a t t i m e s t e p q by

S u b s t i t u t i n g Equations A.1,

A.2,

A.3,

A.4, A.5 and A.6 i n t o t h e c l o s e d b a t c h

mathematical model, t h e f o l l o w i n g two d i f f e r e n c e equations a r e o b t a i n e d

Equations A.7 and A.8 a r e used t o e v a l u a t e G and Q a t p o s i t i o n s t e p r and t i m e s t e p q + 1.

The Equation A.7 when r equals N i s i d e n t i c a l t o Equation

A.7 except i n t h i s case, GrmlYqcl

i s equal t o Grcl

,q+l

because o f t h e sym-

m e t r y expressed by t h e boundary c o n d i t i o n i n Equation 2.31. A t t h e mouth o f t h e pore, when r = 0, p r o p e r boundary c o n d i t i o n i s g i v e n by

Equation A.9 c o n s t i t u t e s t h e f i r s t e q u a t i o n of t h e s e t g i v e n by Equation A.7. was s e t t o z e r o f o r a l l values r,o To o b t a i n The i n i t i a l d i s t r i b u t i o n o f G r y o , an approximate d i s t r i A t the s t a r t o f the solution, Q

o f r.

b u t i o n was o b t a i n e d by s o l v i n g Equation 2.30 assuming GPO t o be much s m a l l e r than k8.

T h i s d i s t r i b u t i o n was t h e n c o r r e c t e d by a repeated s o l u t i o n of

aR and (-) s e t t o zero. A f t e r t h e c o r r e c t Qryq aQ r,q i n i t i a l d i s t r i b u t i o n o f G was obtained, t h e model was t h e n solved a c c o r d i n g

Equation A. 7 w i t h Qr,q+l

,

t o t h e f o l 1owi ng procedure. ( i)

Equation A.8 was solved f o r QrYqcl by s e t t i n g Gryq+l

equal

Gryq.

( i i)

The v a l u e s o f QrYqcl o b t a i n e d i n s t e p ( i ) were then used i n

s o l v i n g Equation A.7 f o r GrYqcl. (iii) recal culate Q (iv)

The values o f Gr,q+l r,q+l

o b t a i n e d i n s t e p ( i i ) were then used t o

'

The v a l u e s of Qr,q+l

t o r e c a l c u l a t e Gr,q+l.

o b t a i n e d i n s t e p ( i i i ) were t h e n used

93

The above scheme was repeated u n t i l convergence was achieved.

In

t h i s study, however, i t was found t h a t , i f s u f f i c i e r ~ t l ysmall t i m e steps, Aq were employed, two i t e r a t i o n s were s u f f i c i e n t t o achieve good convergence. The reason f o r t h i s begin t h e slow change i n t h e p r o f i l e o f G. The s o l u t i o n o f t h e CCBR model was e x a c t l y t h e sarne as t h e one o u t l i n e d above except, i n t h i s case, G

i s always equal t o one and conse-

O

Y

~

q u e n t l y Equation A.9 i s d e l e t e d . 2.

Packed Bed Column Reactor w i t h A x i a l D i s p e r s i o n Equations 2.49,

2.50,

2.51,

2.52, 2.53 and 2.54 d e s c r i b e t h e be-

h a v i o r o f a packed bed column r e a c t o r w i t h a x i a l d i s p e r s i o n .

The d i s t a n c e

v a r i a b l e a v a r i e s between zero and one.

T h i s range was d i v i d e d i n t o M seg-

ments, t h e l e n g t h Ah o f each being 1/M.

L e t h designate t h e p o s i t i o n o f

each segment.

Thus when h i s zero, i t p o i n t s t o t h e entrance o f t h e carbon

bed and when i t i s equal t o M y i t r e f e r s t o t h e e x i t o f t h e bed. A dirnensionless t i m e s t e p Ap was a l s o selected.

Let p represent

D

a p o s i t i o n i n tirne, t h e dimensionless t i m e i s g i v e n by

npi. i= l The d i f f e r e n t equations s e l e c t e d t o r e p r e s e n t t h e d i f f e r e n t

derivatives are

S i m i l a r l y t h e r a t e o f c h l o r i n e r e d u c t i o n , R(X,F),

a t time step p + 1 was

expressed i n terms o f t h e r a t e a t time step p by

I S u b s t i t u t i n g Equations A.10,

A.11,

A.12,

A.13 and A.14 i n t o t h e packed bed

mathematical model, t h e f o l l o w i n g two d i f f e r e n c e equations were obtained

I

1

Equations A.15 and A.16 were used t o e v a l u a t e F and X a t p o s i t i o n h and t i m e p + 1.

The e q u a t i o n f o r h equal t o M i s i d e n t i c a l t o Equation i s equal t o Fh+l ,p+l.

A.15 except, i n t h i s case, Fh-l,p+l

T h i s i s because

o f t h e boundary c o n d i t i o n , a t t h e end o f t h e r e a c t o r , g i v e n by Equation 2.54. A t t h e e n t r a n c e o f t h e bed, t h e boundary c o n d i t i o n g i v e n by Equation 2.53 c o n t r i b u t e s t h e f i r s t e q u a t i o n t o t h e s e t o f e q u a t i o n s d e s c r i b e d by Equat i o n A.15.

This equation i s (Ah Pe

+

-

1 ) Fo,p+l

,p+l

=

Ah Pe

A. 17

A t the s t a r t o f the solution, X values o f h.

was s e t equal t o z e r o f o r a l l h,o To o b t a i n an i n i t i a l d i s t r i b u t i o n o f Fh,o, t h e a x i a l d i s p e r -

s i o n t e r m i n Equation 2.49 was dropped and t h e remaining e q u a t i o n was solved by

I n theaboveF

0 ,o

issetatone.

Once t h e i n i t i a l values o f F and X were d e f i n e d , t h e f i n i t e h ,o h,o d i f f e r e n c e equations were solved i n a manner i d e n t i c a l t o t h a t d e s c r i b e d p r e v i o u s l y f o r t h e CCBR model. 3.

P l u g Flow Packed Bed Reactor Equations 2.55,

2.56,

2.57,

o f a p l u g f l o w packed bed r e a c t o r .

2.58 and 2.59 d e s c r i b e t h e behavior D e f i n i n g y t o be equal t o

u s i n g t h e method o f c h a r a c t e r i s t i c s , t h e system i s

T

-

a and

As was done i n t h e case o f t h e packed bed r e a c t o r w i t h a x i a l d i s p e r s i o n , t h e d i s t a n c e v a r i a b l e a was subdivided i n t o M equal segments, t h e l e n g t h , Ah, o f each b e i n g 1/M.

Here a l s o h was used t o d e s i g n a t e t h e p o s i -

t i o n o f a segment. A dimensionless t i m e s t e p

w was a l s o s e l e c t e d . W

Let w represent

1 A w i The Rungei= l K u t t a - G i l l method (Lapidus, 1962) was used t o s o l v e t h e p l u g f l o w mathemati-

a p o s i t i o n i n t h e y dimension, then y i s g i v e n by

c a l model g i v e n by Equations A.19 and A.20.

Q 3 1 V N I W 8 3 1 S I WVU30Hd 3HP 3kl3HH Sd31SN klOd 0 3 I l 3 L N f l 0 3 N 3 S I 0837 30 3 f l 7 V A W 7 1 1 N f l 8 3 1 V q d 3 H SI S l H l 'YO N 3 H l ONV Sd3PSN dO 3fl7VA M3N V SOV3Y WVH3OHd 3 H l N011fl70S 3 H l -SO S M O I l f l 3 3 X 3 Sc93BSN W31-fV ( B T m O I J ) P V W ~ O d73QOW N I S V = 0 l N ( O l o B Z d % l V W 8 0 J 1300W N I S V = 6N BQIm6Z3BPVWt10S 130OW N 1 SV = 8N f O $ * B Z d l l V W k f O J 1300W M I SV = 1 I S (OTeOZdBIVHHOJ d 3 1 S 3WH1 SS37NOISN3HICl = MU f B T m 0 Z J )1WNYOJ 1/9# H 0 1 3 V 3 8 M I N098V4 dO N O I d V N l M 3 3 N 0 3 = NOWYV3 (0I"OZJPIWWkJOd W3 H I O M 3 7 4 l V H 3 8 0 d = 1X (Of '0Zd!lVW'e10d N % W / Z s ~ l d 3l N 3 1 3 B J d 3 0 3 A l I A I S f 7 J J I O = VO dOBmOZ3)IVk18B3 H 3 / 3 3 3bJfllOA 3HOd = AdX ( 0 7 " O Z d ) IVWYOJ 7B9H N O l I V H l N 3 4 Y O 4 Y7n8 = 0 3 Q O P I l l V W 8 O J SlN3W3H3MI Y O X N J I A H 3 A 3 G31NHHd 0 1 N O l l f l 7 0 S 3 H I & 9 V l J 1NIkId W = X N I I ( 0 1 II l V H I J O J o ~ ~ n m x383 n l s d g n s a w l do m a w n ~= S ~ ~ A S M BOX IIBVWHOJ 3 8 0 6 J l V H N I SlM3W93S 4 0 kl38WflN = N

n a - f ~ m= ~ K ) B 3flNIlM03 4 1 (H8Q*(Z+*HO)*YO+(Z**HO)+)IOscZ)= FI)V ( I 1 3 * ( (Z**HO)+d8Q*fZ**HCl )*YOl-d8*(Z+*HO) = (I 10 ( Q Y + O d X ~ f 1 ) 3 ) / ( 1 ) 3 * 1 1 S = YU i28*t8Y+OdX*f1)3))/0Y*lIS = kIUO N b l = I 4 1 OQ OZ'1 = r 91 0 0 Y€i*'Z=( J N l l Q 3nNIlN03 6 YO=( I) l V UO=I lnv ~ N ~ T =6 I oa I - N = JN N / ' 1 = HQ 3flNILN03 Z I ( I X * W l ) H S 0 3 Q + ( I X 4 W l ? H N I S Q * ( bJ1)HNVlO- = ()I13 NsHO = I X N'I = x ZI oa ~8Y/11SlIHOSO = H I I-N = I N 03*AdX = OdX HlflOW 3HOd LV N O I l V d l N 3 3 N 0 3 SS3lNOISN3MIQ 3 H l S I OdX 3 100000'0*03 = 0 3 33/SW3 0 1 1/9W WON4 031kI3AN03 S I 0 3 3 0 1 1 tZbS10V3kI 6Y ( Z b 5 f 0 V 3 N 8Y ( Z b S ) Q V 3 8 11s t z C s ) a v w UQ (Zb5Y0W3H NOgIlV3 ( Z b S ) O Q 3 H i x fzbslavqa va ( z a 5 ) o v 3 a AdX ( Z b 4 ) O V 3 8 0 3 CZb5)OV38 XNII (Ib5)UV3kj Sd3lSN ( I b 5 1 a V 3 8 N LKbS)Ot(3tl f f X S b 8 ' S f 3 1 P ~ l V ~ 1~sQt ~ f ( X S b 8 * 5 1 3 ~ 9 ~ I ) l V W Y 0 0d5 1 ( 0 1 " O Z J l l v W ~ O JZ ( O I I l l V W ~ O JT OIYb6Nb8N l V 3 8 t1JdOt)ZIl30Nn l i p 3 N NOWW03 Q a T 3 b V b 7 V b f l V b S D NOWWfl3 II O E ~ S 0 2

b f T O E ? B b ( l O € ~ ~ V b ( T O E ) l V b ( l O~ €I O ~ ~€ b~ 3 ' t l Q b ~ 1 0 € ) H ~ C l l 4 f I ~ E l d b I T O E ? 1 H ' f 1 0 E ) ~ b ( 1 ~ € ? 1 3 bNnISN3WIO ~~~€~3 (2-QbH-V)8$1V3H

I13IldWI

tBY+OdX*(1991T / ( (1( H ~IO d X ~ O l Y + ' T ~ / ( l ) H * O d X * b ) I - l I S 1 ~ ( 1 1 9 = ( I I d NN'T = 1 5 , 00 Sd31SN.T = f f OZ OQ ET I X N I l = 111 (/'rNIW-l/3W 3AVklr'XS'rW9/H3 '33He1WVnT 'X+'rW3/W3 ' W ~ ~ I ' ~ W V I ' X ~ ~ I N I 3WW 1 1 s r X 9 ' / / f l V W Y 0 4 TZ (TZb9)3AIHM '0 = W3dldV -0 = H I 1 COT'OZj'r = 01X r'01'07d'r = bYr'X11: '/'OT'OZ~'r = 83 rbOI'OZj'r = lISrrXZ6 b / r O 1 * O Z d r ~ S I d31S 3 W I l 3 H l r b X Z Q '/'Ol'OZd'tSI d31S 3 3 N V l S l O 3 H l r ' X Z L ' / / W r r O I e O Z ~ ' r S I N O l l Q Y l N 3 3 N 0 3 NO0dV3 3 H l r ' X Z 9 '/'IH~ r ' 0 T a 0 Z 3 ' t S 1 H13N31 380d 3 H l r ' X Z G '/'tNIW/Z**W3 1'01'023' 0 S I A l I A I S f l J J I O 3 H l o 'XZ3 '/'rWVtI3/33 rrOT'OZdr I S I 3WfllOA 3dOd 3 H l I'XZE '/r0T'023€ ' r S 1 HlflOW 28Od I V N O I l W k I l N 3 3 N 0 3 SS3lNOISN3WIO 3 H l r l 'XZ'/'t33/Sh'Vd3 rZ '01'073'1 S I N O I l V l l ~ N 3 3 N 0 3Y l n f l 3 H l 0 ' X Z ' / ~ 0 1 1 I S I 3 d 0 d V 3 d S l N 3 H 3 3 S JO ll3QWflN ~ H I I ' X Z ~ I V W ~ OOJT 0 1 Y '6U' 8 x 1

-

r

rlIS'YO'HOrN08MV3rlX'VO'AdXrOdX'03rN~OI~9~311~M (8'GT311VWIlOJ 3ftNIlN03 '0 = t I 1 H NNbT= I E 00 3'LIOd JO ON3 0 1 SH333tl N ' 3 8 0 d dO HlnClW 0 1 S'H333Y NN N/'1 = HO "I: = ( N N 1 1 3 'I = ( N N 1 3 1+N = NN n04'Z = (T-N)lV >a = ( I - N I n v 3flNIlN03 na = 4 1 1 7 v no = ( 1 1 f l V I N ' T = I 8 OB (I/' rNIW-lI9WrT ' X S ' ~ * S I ~ ' I S I 3 l V d 1 V l l I N l 3HlrrXZ)lVWk10J 3nNIlNO3 31Vd C81r91311dM ((Z*a7Xl+HQ+'Z)T / N 0 0 ~ V 3 * 0 d X ~ V Q ~ ( ' € - I T 1 3 ~ ' 3 + ~ Z I C J= - 1 31VY 3nNILN03 ( Y 1 1 3 = 0113 N I T = )I LZ 00 Y I a I M 1 11V3

001 €

3

8

81: 91

L1

0N3

dQlS (71 €1 0 1 03 YCIe'Z = 1T-Nl7V na = r l - ~ ~ n v 3flluI1N03 42 YO = fI)lV Ma = c r ~ n w l N b l = I S Z 00 Y0(ZbG10V3ki 31 01 03 (0'83'Sd31SNlJI Sd31SNI T6S)0V3H 3nNBlN03 O Z 0 = 111 ~ ~ V ~ ~ ~ ~ Y W V ~ W ~ ~ W ~ ~ W I I ~ O S T O Z 01 03 (XNII'3NoIIIIzJI I+ 111 = 1x1 V0/tZ+*lX~+UO + H I 1 = Wll N/OdX#33liWV = 33liWV 3flNI1N03 11 (

IlH + 33YWV = 33YWV S N b T = 1 T P 00 1-N = SN + (NNIH) = 33aWV

'Z/((NIH

( N 0 8 ~ V 3 * V O ) / ( Z * * l X ) * Y O 8 3 1 V l i + W 3 ~ H V = W38WV

/N0flllV3*OdX*VO*( tNNlTLSrt'E

-

(T )19*'3

((Z#*lXI*H04'ZIT + CZ119-9= 31PX 3nNllN03 & (11T3 = 1113 fI11H = tI)H AIN'T = i L oa

w a I u 17~3 3nNIINO3 9 (IlHya*(I)1H*(z**nal*na + c110 = crfe ~(I)H8a*X~-'1l/(~IlH+1 I H H - I 9 - I 1 3 I I d O + l Y 0 = (HITH tIfHYO*(I)TH*(Z8*H09*YCI (IIW = ( I 1 B N b T = I 9 00 YIUIlii 37v3 (NN13*YO-(118 = ( 1 F f l 3flNllM03 4 C ((1 IH-4 IllH)*( I)HklO*YOl + ( 1 )3* ( ' T + ( I)9d0*Y0)-(1 lef*Xa)*(Z~~HU) = ( 1 18 ((199li0*(Z**HaI*Y0+(Zt1bHrl)+)1a~'Z)= CI)V N'T = I 5 00 3flNIIN03 3 ~ ( I ) F Y ~ * Y O - ~ I ) / ~ ( ~ I ~ H I)'~J)*Y~+(IHI ~ ( I ~ H ~ ~ - I= I~ I ) I H ((Z**((I)HrOdX*01N+*TllT * ~ 8 N + O d X * ( I ) 3 l l / ( ~ 9 9 ~ O d X r 0 r b Y= - (IIHYO (Zs*(8Y+OdX*(I 139)T / ( ( ( 1 1 H ~ O d X * O ~ ) 1 + * 1 I / ( I ) H ~ O d X ~ 6 N - l I S ) ~ 8=) 1(113Ya

-

OT# (2'5)0V3lJ 6Y ( z 8 s 1 a v 3 8 8 Y 47'S)QV32J I I S tZ'SilffV3kl Y O ~ Z ~ S B O V ~ ~ bd0€IklV3(Zb~)BV3U 7X(Zs4)QV3b VO(Z4S)OV3H AdXtZ4S?BV3kl 03(265)QV3kf XNI I 1 I 6 S 1 0 V 3 8 Sd31SN0 1 ' 5 10V3Y NtKbGlCiV32i f IXS'8'42313~1VWkJOJ 1 5 1 F(XS'B'ST3)9bXTllVWUOJ OST ( 0 1 "024) lVW80J Z ( 0 1 1 1 lVWU04 T 0?#'6Y69Y I V 3 8 l m J J O ~ P Z k l 3 0 N n7 I V J NN NOWW03 B B 8 9 ' ~ b l V ' f l V ' S 8 NOWW03

C TOE 1 SbZ ' ~ T O E ~ Q ' ~ P O ~ B ~ V ~ ~ T O € B ~ ~ ~ ~ ~ T O E ~ V ~ ~ I O € ~ ~ ; ~ ' f I O E ~ H ' ~ 7 0 E ? 1 H ' I I O f ~ b l b ~ I I 0 € ~ T 3 ' ~ 1 O E 'N1O3I S N 3 H I Q 97-0'W-V18*7V38 hI3lldWI 0 3 1 V N I W Y 3 1 SI WV890lid 3 H l 3d3HM Sd31SN HO4 d 3 l i 3 l N n 0 3 N 3 S I 0 8 3 1 -30 3 f l I V A V 7 I I N n 03hVqdEIk4 S I SIHL " # a N 3 H l QNV Sd31SN 30 3 f l l V A M3N V SOV38 WV830kid 3 H l NOHln7OS 3 H l 3 8 S N O I l f i 3 3 X 3 Sd31SN 8 3 1 3 V ~ O T ' O Z J l b V H k l O J NIW/K 33NV2iV3ddVSIO 3 N I M Q l H 3 8 0 3 b N V l S N 0 3 31VY l430t!O l S H I j = d I U S 0 0 1 * O Z J ) l V W 8 O J 1380W N I SV = OTX ( O ~ * O Z J ? I V W ~ ! O J 130OW N I SV = 6Y COPmOZd)lVWUOJ 13QOW M I SV = 8Y d O I m O Z J ) l V W k l O J 13BOW N I SV = I I S BO'BIeO/J BIVWklO4 d 3 1 S 3 W I I SS37N011SN3G-J1 0 = )10 IO~'O?'J~IVW~O~ 1/9W 8 0 1 3 V 3 8 NP NOWWY3 40 N O I l V H B N 3 4 N Q 3 = M08HV3 (OTeOZ4lIVWklOJ W3 H13N3-i J l V H 380d = 7X (O?'OZJBIVWHO3 N I W / Z s * N 3 l N 3 I 4 1 J 3 3 0 4 A l I A I S n j d I Q = VO (OKeOZJ)%VWdQd W3/34 3WlllOA 3 Y 0 d = AdX CQP'OZJ I I V W l i C J 7/3W N O E l V 8 l N 3 3 N O 3 Y 7 n Q 9 V I I I N I = 0 3 ( 0 1 1 IlVWHOJ SlN3W3H3NI NCl X N T I Akl3A3 0 3 1 N I l 4 d S I M B I l n l Q S 3 H l 5 ! 3 V 1 ~1 N I N d V = X N I I ( 0 1 I I lVW8OJ 0 3 1 n 3 3 X 3 38 0 1 S d 3 1 S 3WII JO li38HflN = Sd31SN tO'BIIlbVW8Od 3HOd 37VH N1 ShN3H93S 9 0 83flWnN = N

3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3

' / ' O I ' O Z J b t S 1 6 3 1 5 3 W I l 3 H l r 'XZ8 '/'Ol'OZJ'tSI d31S 3 3 N V l S 1 0 3 H l o b X Z L ' / ' / o ' O T m O Z J b t S I h O l l V 8 l N 3 3 N 0 3 N098V3 3 H l o 4 X Z 9 '/'ow3 r ' O l m O Z J b r S I H13N31 3&0d ~ H I I ' X Z S ' / ' o N I w / z ~ * w ~ I'OK'OZJ'B SI A ~ I A I S ~ J J ~~ H~ I P X Z + '/'1WvH3/33 B ' O I ' 0 2 9 ' 0 S I 3WnlOA 3 8 0 6 3 H l r 'XZE '/'OK*OZJE ' r S I HlnOW 3 8 0 d 1 V N O I l V k l l N 3 3 N U 3 SS37NOISN3WIQ 3H.loZ CXZC/6033/SWvlJ3 12 'OK'OZJ't S I NOIlVkllN33N03 YInB 3 H l r ' X Z ' / ' O l I I S l 3 8 0 d V 3 d S.lN3H33S JO d38WflN 3 H l r e X Z ) l V W k 1 0 J 6 1 dIHlS'01YC6Y'8YT ' 0

'lIS'Y~'HO'NOQHV3b1X'VO'AdX'OdX'03'N~OTb913il~M (//b~NIW-1/9W01 'XSb8'G13'r S I 31Va 3 V I l I N I 3 H I o b X Z lIVWklOJ 8 1 3nNIlM03 9 1 32~H(81'9)3118W f ( Z a * 3 X )*HO*'Z)T /NOQ8V3*0dX*VCI8l ' € - ( I ) r 3 * * 4 + ( 2 1 3 - 1 = 3 l V 8 3nNILN03 L 1 0 1 1 ~ 3= [ U K I N & K = Y 11 oa NIUIkl1 l 1 V 3 nct-f1w = ( m a 3 n N I l N 0 3 ST t 8 H a a ( Z ~ a H C ) ~ Y O + ( Z ~ r o : H a ~ + Y O t m Z= 1 -( 1 ) V I 1 ) 3 * ( (Z**HQ)+88a*FZ**HO ) 1 ( r Y Q ) - t l t l * ( Z t r g H C 1 F Y Q = ( II'd (Za*(8Y+OdX*[I)91I/~YtIIS = HHO (8Y+OdX*(I)3J/(113*IIS = M b l = I ST 00 0 Z b 1 = f 9 1 ClCl YQ#'Z = fJN17V 3flNlbPdP3 6

no

= (II-IV

na = c 1 1 n v JN8T= I 6 OQ I - N = JN N = Nhl 3nNIlN03 21 ( 1X~WllHSO30+(IXeWllHNISO*(W.lI H N t l l O - = ( Y 1 3 YsHa = I X N'1=Y ZT 0 0 N / ' l = Ha ~W.kS)lVBSO= W l 8M/11S HIS O3sAdX = OdX HlflOW 3HOd l t l N C l I l t l t l l N 3 3 N 0 3 SS33NOZSN3WIO 3 H . l S l OdX T 0 0 0 6 0 ' 0 ~ 0 3 = 03 33/SW3 0 1 I/3W WON3 CI3.lH3AN03 SI 03 dI8lSIZ'S)0~38

-

3 3

7nNllN03 9 (I)HlIa*(I )IH*(Zt*HO)*)IO*( IIB = 1 1 18 ((I)HNQ*OdX~YQ-'l)/t(I)H+(~I)HT * ( I )HVCl-( ( 1 13-4 1)13)*(I )3tlO+(I lII)8YO8OdX = C I ITH II)HaU*(I llH*(l*sHCl)~)IO-( I)@ = (I 10 NN'Z-I 9 00 lJIQIa1 17W3 3flNIlN03 S 4 t( I IH-( I I I H I *13~aurg:~a1 ~ + t 1 ~ 3 * ( - 1 + ( 1 1 3 a a * ~ a ) - t 1 i ~ 1 r n o 1 t t z * r= l t(~I oI )R 4 (I )SYO*(Z**HO)*YQ+( ZIr~HCIl+YQ*'Z)- = t I IV NN'Z=I 5 00 3nNI IN03 f ( (1 )H8a*OdX*YO-'I)1 / ( t (I ) H * f IIHIJO-(I lIJ)*OdX*UO+4 I IH) = ( 1 IIH P ( Z * 4 ( ( I )H*OlY+'l)fdt(8)I*OdX*( 1 ) 9 1 ) / ( 1 ) 3 * - = ( I IHHa (Z*a(QY+0dX*(I)3))1 /((tI)H*OT~+'l)/(IfH~6Y-IIS)88Y = (I13da ~ 8 Y + 0 d X * ( I ) 3 ) / ( ( t I l H ~ O I ) 1 + ' T ) / ( I ) H s 6 U - l 1 S I 9 = (1)a NN'I-I f 110 Q O / I Z * ~ l X l * Y Q * d I H l S * H O * ~ 1 1 3 - f 113*Ha = (I 18 Sd31SN41=ff 82 00 YO*AdX+W3+HCl = (1 )V na = m i w MQ*AdX*W3- = tI)nV YO9'1 = ( N ) l V YO = ( w n v 3flNliN03 0 YO = ( I ~ l V no = tI1flV dN6Z=l 8 UO S S "I = (113 '0 = (1)H 3ftN11NU3 O S tI-IIY13 = (IIN19 ' 0 = (1I)OH I-Z+N = IIY NO1 = H 05 OQ I+N = NN 100000'*N08YV3 = W3 "0 = w3awv '0 = HI1 ( / r33/W3 ' 3 N 0 3 r Z 'X9'rNIW-7/3W 32Wtir6XX' rW3/W3 '33V'IWWrT 'Xf'rW9/M3 'W3kI'1WVrbX6'rN1~ 3WIlr'X9a//11VH~OJ 1% tIZ'91iI11~M I-XIUII = III t rNIW/l r 601'023' r = INVlSN03 31VY 3NIddl8lS r 'XZZ '/'Ol'OZdr, I 0IY r'01'023' r = 6UrLXZI ~ / ~ Q I * O Z == It3X ~~ r 'OI*OZJ6 I = 1 IS r ' X Z 6

CALL T R I D I R DO 7 I = l , t J N HLIl = HlII) G(1) = Gl(1) 7 CONTINUE R A T E = ( - G I ( 3 )+4.*G1(2 1-3.4G14 1 ) )*DA*XPO*CAKBUN/ 112m*DH*(XL**2J) AMREM = AMREM+RATE*OK* ( X L * * 2 ) / ( D A * C A R B O N ) AMKEC = [ H ( l I + H ( N N ) ) / Z , DO 11 I = 2 r N AMREC = AMREC+H( 1 ) 11 C O N T I N U E AMREC = AMREC/N TIM = TIH+DK*(XL**~I/IIA CN = G ( l ) * C D I I T = IIT41 I F ( IIT*NE.IINX)GO TO 20 WRITE ( 6 , 1 5 0 ) T I M , AMREM,AMREC*KATE&N I I T = 0 20 CONT1NUE R E A D ( 5 , l I NSTEPS I F ( N S T E P S m E Q . O I G 0 TO 14 K E A D ( S r Z 1 DK GO T O 55 14 STOP END

3.

Packed Bed Reactor

N = NUMBER O F SEGMENTS I N P A C K E D BED F O R M A T ( I 1 O I N S T E P S = NUMBER OF T I M E S T E P S T O BE E X E C U T E D FORMAT4 1 1 0 ) I N D E X = A P R I N T FLAG, THE S O L U T I O N I S P R I N T E D 10) E V E R Y I N D E X DK I N C R E M E N T S FORMAT (I 6 0 = I N F L U E N T C O N C E N T R A T I O N M G / L FORMAT ( 2 0 0 1 0 ) DA = A X I A L D I S P E R S I O N C O E F F I C I E N T C M * * 2 / M I N FORMAT120-10) X L = B E D L E N G T H CM F O R M A T ( 2 0 . 1 0 J FORMAT420.10) A R E A = P A C K E O B E D C R O S S - S E C T I O N A L A R E A CM**2 XPORO = P O R O S I T Y F O R M A T ( 2 0 , l O ) VOLUME FORMAT ( 2 0 - 10 1 CARBON = GRAMS O F CARBON I N ONE C U B I C CM O F HED

'O1°OZJ' r S I NOIlVHPN33N03 N08HV3 3 H l o d X Z ' / ' ~sW3 B ' + O I O O Z d ' ~5 1 H19N37 Q3g ~ H I I ' X Z ~ / ' B N I W / Z * * W S ~ ' O ~ " O ~ ~ € ' B SI I N 3 1 3 1 3 4 3 0 3 NOIS83dSIQ 7VIXV 3 H P s e X Z ' / ' Z ~ 3 3 / S l d V H 3 8 'QBaOZda r S I NO11V8lN33N03 H l f l B 3 H l b ' X Z T '/'OII'r S I Q38 N I S l N I O d JO kI38WnN 3 H k r 4 X Z I l V W H O J 0 1 YO'Hal ~ A ' M O ~ J ' Q ~ H V ' O ~ Q ~ X ' P I O ~ ' ~ ~ V ~Q~0~I 6X9~) 3V1OI 8~MO ~ ' N (OdOdX+V3NV)/M07J = A Z-dN = TN l + N = dN N / ' I = Ha T0000Oo0*Q3 = 0 3 3 3 / S H 9 0 1 183H WOVJ 03lH3ANO9 S I 0 3 3 3nNILNO3 66 (I)f'X~TSTCSlClV311 6 ' 1 = 1 66 OQ

no ~ Z ~ S I O V ~ H

M o l d (Z'SlQV3ll V3HV (Z'S)QV3'd O'dOdX 1Z65)0V31J NOg8V3 (Z4G)CIV3ki 1 X (Zb510V3ki va B Z ~ S ~ Q W ~ ~ 0 3 (Z'SIOV38 X3UNI t I ' G I O V 3 M Sd31SN ( I 6 S ) 0 ~ 3 k I N f1°S110V3tl ~QoS13'XP0%~lVW~ ZO S IJ f8"ST3)PVWklOd 1 5 1 60XS08'513)9'XlllVWU03 051 f O 1 " O Z J ~ l V W ~ O zd ~ O 1 I ~ l v W l . f OTJ t I J J O t )ZH3aNn 1 1 V 3 dM NOWW03 8' I d b V ' l V ' n V ' S B NOWN03 06)f'X61TOC)Sbb(10€tZXZ

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'~TO€BQ'6TCE)V'CT0E~dW3I'(T0E)7Vb 4TOE1nV NOISN3WIB (2-O'H-V)8*lV3H 11317dMI 8 3 1 V N I W831 S 1 WVH9Otld 3#8 383HM S d 3 l S N HOJ 03N31Nf703N3 S I OM32 JO 3fl7Vh V 111Nfl 0 3 1 V 3 d 3 8 S I SIHP "Ha N3HP ONV Sd31SN kJOJ 3nlWA M3N V SQV3H WV830dd 3 H l N O % l f l l O S J H l JO S N O I l n 3 3 X 3 Sd31SN ti31dV (8'513ElVW8Od 3 N I S f l QW3W 38W S l N V I S Y 6 3 3H.L aNV N I W / ' I 38V NOISS3kldX3 31V8 3 H 1 804 S l l N n 3 H l ( 3 ' X l k l NOISS3ktdX3 31V8 31VH8397V 3 H l 'dOd S l N V l S N 0 3 3 N I N = ( I l f ' X fO1 "0ZdFlVWdQd d3PS 3 W I P SS31NOISN3WIQ = Ma (OT0OZJ)IVW80d 31Vd MOlJ l N 3 f l 7 3 N I 1 V L O l = M o t 3

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