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
e~KOE~X'~l0E~ld6(K0~)d'(IO€~d'tlO0(IOEIX~~6f1O€~~l
'~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
'
NIW/E*SW3
3 3 3 3 3
3 3
3 3 3 3
-
~
~
~
~
-
~
C
,
-
~
B
~
O
~
B
D
~
I
~
E
D
~
~
~
~
-
-
Nr ~ ~
C
r a ~ o + o ~ n ,
C
~
