1-s2.0-0960852494901325-main (1)
TRANSCRIPT
8/20/2019 1-s2.0-0960852494901325-main (1)
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E L S E V I E R
ioresource Technology
4 8 ( 1 9 9 4 ) 3 1 - 3 5
P r i n t e d i n G r e a t B r i ta i n . A l l r i gh t s r e s e rve d
0 9 6 0 - 8 5 2 4 / 9 4 / 7 . 0 0
P R E P A R A T I O N A N D L I Q U I D P H A S E C H A R A C T E R I Z A T I O N O F
G R A N U L A R A C T I V A T E D C A R B O N F R O M R IC E H U S K
T a n z i l H a i d e r U s m a n i , T a m o o r W a h a b A h m a d & A . H . K . Y o u s u f z a i
Industrial Chemicals Research Centre, PCSIR Laboratories Complex, Karachi -- 75280, Pakistan
(Received 2 Au gus t 1993 ; rev i sed vers ion rece ived 23 Octo ber 1993 ; accep ted 26 Octo ber 1993)
bstract
A method for deashing rice husk by alkaline leaching
was developed and optimum deashing to the extent of
93 was achieved. The preparation of granular acti-
vated-carbon from high- and low-ash rice husk was
carried out with zinc chloride as an activating agent as
well as a binder. It was established that granular
activated-carbon of balanced micro-, meso- and macro-
pores and appropriate hardness may be prepared from
low-ash rice husk with 75 zinc chloride as an activa-
ting agent.
Key words: R i c e h u s k , d e a s h i n g , g r a n u l a r a c t i v a t e d -
c a r b o n , i m p r e g n a t i o n r a ti o , z in c c h l o r i d e , l iq u i d p h a s e .
I N T R OD U C T I O N
T h e m a j o r r i c e - p r o d u c i n g c o u n t r i e s i n t h e w o r l d a r e
I n d ia , C h i n a , P a k i s t a n a n d I n d o n e s i a ( M c G r a w - H i l l,
1 9 6 0 ) . I n P a k i s ta n , 4 . 1 4 3 8 m i l l i o n t o n n e s a r e g r o w n
p e r a n n u m (A k h t a r , 1 9 8 6 - 8 7 ), m a i n l y in t h e p r o v i n c e s
o f P u n j a b a n d S i n d h . R i c e h u s k a n d r i c e b r a n a r e
o b t a i n e d d u r i n g t h e i n i t i a l a n d f i n a l p o l i s h i n g o f r i c e ,
r e s p e c t i v e l y . T h e h u s k o r h u l l a c c o u n t s f o r a b o u t
2 0 - 2 3 % o f t h e w h o l e r i ce ( G ri st , 1 9 7 5 ) . T h u s , a n
a p p r o x i m a t e a m o u n t o f 0 8 2 8 8 m i l l io n to n n e s o f ri c e
h u s k i s a v a i l a b l e i n th e c o u n t r y a n n u a l l y . I t i s r o u g h i n
t e x t u r e , a b r a s i v e i n n a t u r e a n d n o t s u i t a b l e f o r a n i m a l
f e e d d u e i t s l o w n u t r i t i v e v a l u e . B e c a u s e o f h i g h a s h
a n d l i g n i n c o n t e n t s , i t i s c o n s i d e r e d u n s u i t a b l e f o r t h e
p u l p a n d p a p e r i n d u s t ry . T h e h u s k p r e s e n t l y h a s s m a ll
i n d u s t r i a l u s e s i n b r i c k k i l n , c h i c k e n l i t t e r a n d a n i m a l
r o u g h a g e . T h i s s i t u a ti o n d e m a n d s a n e x t e n s iv e i n v e st i-
g a t i o n o f t h e e c o n o m i c u t i l i z a t i o n o f t h i s a g r i c u l t u r a l
w a s t e . It m a y b e n e f i t a c o m i t y o f r i c e - p r o d u c i n g , d e v e -
l o p i n g c o u n t r i e s .
A c t i v a t e d c a r b o n s a r e u n i q u e a n d v e r s a t i l e a d s o r -
b e n t s b e c a u s e o f t h e ir e x t e n s i v e s u rf a c e a r e a , m i c r o -
p o r o u s s t r u c t u r e a n d h i g h a d s o r p t i o n c a p a c i t y . T h e y
a r e a s s u m i n g i n c r e a s i n g i m p o r t a n c e i n t h e c o n t r o l o f
a i r p o l l u t i o n , i n p u r i f y i n g a n d c o n t r o l l i n g t h e g e n e r a l
c h e m i c a l e n v i r o n m e n t , i n c e r t a i n b i o m e d i c a l a p p l i c a -
t i o n s a n d f o r t h e r e m o v a l o f o r g a n ic m a t t e r f r o m w a t e r
a n d w a s t e w a t e r ( M a r t i n , 1 9 8 0 ) . A c c o r d i n g t o a r e c e n t
s u r v e y ( B a n s a l
et al.,
1 9 8 8 ) , t h e a n n u a l p e r c a p i t a c o n -
3 1
s u m p t i o n ( i n k g) o f a c t i v e c a r b o n i s a b o u t 0 5 i n J a p a n ,
0 -4 in t h e U S A , 0 2 in E u r o p e a n d 0 0 3 i n t h e d e v e l o p -
i n g w o r l d , g e n e r a l l y r e f l e c t i n g t h e d e g r e e o f a w a r e n e s s
a m o n g t h e c o m i t y o f n a t io n s f o r a s a f e r a n d c l e a n e r
e n v i r o n m e n t . C a r b o n i s g e n e r a l l y u s e d i n t w o f o r m s ,
p o w d e r e d a n d g r a n u la r . T h e p r i n c i p a l u s e s o f g r a n u l a r
a c t i v a t e d - c a r b o n ( G A C ) a r e i n a i r p u r i f i c a t i o n , s o l v e n t
r e c o v e r y , r e c o v e r y o f g o l d a n d i n c i g a r e t t e f i l t e r s .
A b o u t 8 0 % o f t h e G A C p r o d u c e d w o r l d w i d e is u s e d in
l i q u i d - p h a s e p u r i f i c a t i o n s , a n d t h e r e s t i s u s e d i n g a s -
p h a s e a p p l i c a t i o n s . G A C i s g e n e r a l l y a s s o c i a t e d w i t h
s m a l l p o r e d i a m e t e r a n d l a r g e i n t e r n a l s u r f a c e ,
c o n t r a r y t o t h a t o f t h e p o w d e r e d f o r m w h e r e l a r g e
p o r e s a n d s m a l l e r i n t e r n a l s u r f a c e a r e t h e m a i n
fe a t u re s .
R i c e h u s k ( R H ) , b e i n g h i g h l y s i l i c e o u s i n n a t u r e ,
c o n t a i n i n g 1 7 - 2 3 % a s h , n a t u r a ll y f u r n is h e s a c h a r w i th
l o w f i x e d - c a r b o n c o n t e n t , r e s u l t i n g i n l o w a c ti v it y . B e g
a n d U s m a n i ( 1 9 8 5 ) p r e p a r e d l o w - a s h , p o w d e r e d a c t i -
v a t e d - c a r b o n f r o m r i c e h u s k b y a l k a l i n e l e a c h i n g o f
s il ic a f r o m h i g h - a s h c a r b o n o b t a i n e d b y l o w - t e m p e r a -
t u r e p y r o l y si s in a n i n e r t a t m o s p h e r e . L a t e r , U s m a n i et
al. ( 1 9 9 0 ) d e v e l o p e d a n d p a t e n t e d a p r o c e s s f o r d e a s h -
i n g h i g h - a s h r a w m a t e r i a l s l i k e r i c e h u s k b e f o r e t h e i r
p r o c e s s i n g fo r t h e p r e p a r a t i o n o f a c ti v a t e d c a r b o n . T h e
p r o c e s s o f c h e m i c a l a c t i v a t i o n w a s s t u d i e d i n d e ta i l a n d
z i n c c h l o r i d e w a s f o u n d t o b e t h e b e s t a c t i v a t i n g a g e n t
f o r o b t a i n i n g p o w d e r e d a c t i v a t e d - c a r b o n f r o m i n d i -
g e n o u s a g r o w a s t e s a n d i n f e r i o r w o o d s ( U s m a n i et al.,
1 9 8 8 , 1 9 8 9 ) .
T h i s s t u d y is n o w f u r t h e r e x t e n d e d a n d G A C h a s
b e e n p r e p a r e d f r o m h i g h - a s w e ll as l o w - a s h r ic e h u s k
u s i n g z i n c c h l o r i d e a s a n a c t i v a t in g a g e n t . A p p r o p r i a t e
w o r k i n g c o n d i t i o n s h a v e b e e n e s t a b l is h e d i n th e l i g h t o f
d i f f e r e n t p h y s i c a l a n d c h e m i c a l c h a r a c t e r i s ti c s o f t h e
p r o d u c t s .
ME THO D S
I n t h e p r e s e n t s t u d y , r i c e h u s k w a s u s e d i n it s h i g h - a n d
l o w - a s h f o rm s . T h e f o r m e r w a s a l s o u s e d i n it s g r o u n d
f o r m o f p a r t ic l e s i ze 0 - 5 - 1 0 m m . T h e p r o c e s s s e -
q u e n c e ( F i g . 1 ), f o r t h e p r e p a r a t i o n o f G A C ( h i g h / l o w -
a s h ) , c o n s i s t e d m a i n l y o f t h e f o l l o w i n g fi v e s t e p s : (i )
d e a s h i n g o f r i c e h u s k ; ( i i ) c h e m i c a l t r e a t m e n t o f h i g h /
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32
T a n z il H a i d e r U sm a n i T a m o o r W a h a b A h m a d A . H . K . Y o u s u f z a i
R I C E H U S K
Na O H Z nC l 2 Z nC I 2 (R I~C YC L E D)
LOW H _
~[ DEA SHING RICE HU SK '7
7 ~ TRE XrM EN T ,'~[ [
b .
r
V
GR ANUL AR AC T IVAT ED
C A R B O N
( H I G H / L O W A S H )
DRYING I~ ,
HC I
L E A C H I N G /
WAS HING l - ~
CARBONIZATION
Fig. I. Block diagram of the preparation o f granular activated-carbon (high/low-ash) from rice husk.
l ow- a sh r i c e husk ; ( i i i ) e x t r us ion o f t he c he m ic a l l y -
t r e a t e d g e l a t inous m a ss ; ( iv ) c a r bon iz a t i on o f e x t r u de d
gr a nu le s ; a nd ( v ) l e a c h ing , wa sh ing a nd d r y ing o f t he
f in i she d p r od uc t .
T h e p r o d u c t s o b t a i n e d i n e a c h s e t o f e x p e r i m e n t
w e r e e v a l u a t e d b y s t a n d a r d m e t h o d s . T h e e x p e r i m e n t
w i t h h i g h - a n d l o w - a s h f o r m s o f r i c e h u s k s w a s
r e p e a t e d t w i c e i n c lu d i n g t h r e e r e p l i c a te s o f e a c h t r e a t-
m e n t . R e p l i c a t e s w e r e r e p r o d u c i b l e a n d s t a n d a r d
de v ia t i on wa s c a l c u l a t e d whe r e ve r a pp l i c a b l e .
D e a s h i n g o f r ic e h u s k
Ric e husk f r om a husk ing m i l l wa s c o l l e c t e d , s ie ve d a nd
w a s h e d t o f r e e i t f r o m d i r t a n d f o r e i g n m a t e r i a l a n d
dr i e d t o a c ons t a n t we igh t. It wa s t he n r e f l ux e d w i th
d i f f e re n t c o n c e n t r a t i o n s o f s o d i u m h y d r o x i d e s o l u t io n s
f r om 0 .1 t o 7 5% f or 4 h . T he l e a c he d m a te r i a l wa s
t h e n f i l t e r e d , w a s h e d t o n e u t r a l p H a n d d r i e d t o a
c ons t a n t we igh t . Che m ic a l a na lyse s o f t he o r ig ina l a s
w e l l a s e a c h o f t h e l e a c h e d r i c e h u s k s a m p l e s w e r e
c a r r i e d o u t a n d p e r c e n t y i e ld o f d e a s h e d m a t e r ia l e s ta -
b l i she d . I n t he l igh t o f t he c he m ic a l a na lys i s o f de a she d
s a m p l es , a 1 % c o n c e n t r a t i o n o f s o d i u m h y d r o x i d e w a s
f o u n d t o b e a p p r o p r i a t e a n d u s e d i n f u r t h e r s t ud i es .
h e m i c a l t r e a tm e n t a n d e x t r u s i o n m e t h o d o l o g y
O n e h u n d r e d g r a m s o f h i g h -a s h r i c e h u s k i n i ts o r i g in a l
p a n i c l e s i z e ( G ) a n d i t s g r o u n d f o r m o f 0 - 5 - 1 0 m m
( G 1 ) w e r e w e i g h e d a n d m i x e d w i t h 2 5 , 5 0 , 7 5 a n d 1 0 0
g o f z i n c c h l o r i d e d i s s o l v e d i n 3 0 0 m l o f 5 % H C I i n
s e p a r a t e s e ts o f e x p e r i m e n t s. T h e s e s a m p l e s w e r e t h e n
s lowly he a t e d i n a s t e a m - j a c ke t e d , g l a s s l i ne d ve sse l
w i th c on t inuous s t i r r i ng t o a da r k ge l a t i nous m a ss /
p u tt y . T h i s s e t o f e x p e r im e n t s w a s a l s o c a r d e d o u t w i t h
low-ash r ice husk (L) in i t s or igina l par t ic le s ize . The
pe ne t r a t i on va lue s o f h igh- a s we l l a s l ow- a sh r i c e husk
p u t t i e s w e r e m e a s u r e d b y a S e t a U n i v e r s a l S t a n d a r d
P e n e t r o m e t e r (B S 4 1 6 4 - 1 9 8 7 ; w e ig h t u s e d = 5 0 g ,
t e m pe r a tu r e = 30 C , t im e = 5 s ).
E a c h o f t h e h i g h - a n d l o w - a s h p u t t i e s w a s t h e n
e x t r ude d t h r ough a s t a in l e s s s t e e l d i e ha v ing ho l e s o f
2 .5 m m d i a u n d e r a h y d r a u l ic p re s s u r e o f 2 8 1 0 - 5 6 2 0
k g / c m 2 (Mu r t i , 1976) .
P r o c e s s i n g o f g r a n u l e s
T h e e x t r u d e d g r a n u l e s w e r e f ir s t d r i e d a t 1 0 5 °C a n d
the n c a r bon iz e d i n a s t a in l e s s s t e e l ve s se l i n a n i ne r t
a t m o s p h e r e a t 5 0 0 - 5 5 0 ° C f o r 2 h ( U s m a n i et al.
1 9 9 2 ), a n d t h e n r e f l u x e d w i t h 7 5 0 m l o f 1 0 % H C I f o r 4
h . E a c h s a m p l e w a s t h e n f i l te r e d , w a s h e d f r e e o f a c id
a n d c h l o r i d e io n s a n d d r i e d t o a c o n s t a n t w e i gh t .
P r od u c t c h ar ac t e r i z a t i on
T he por e - spa c e pe r 100 g ( Ja in & Sha r m a , 1971) , ba l l
p a n h a r d n e s s n u m b e r ( A S T M , 1 9 7 9 ) , p e r c e n t y i e l d ,
r e a g e n t r e c o v e r y a n d a s h c o n t e n t s ( B e v ia et al . 1984)
o f t h e s e s a m p l e s w e r e d e t e r m i n e d . T h e a c ti v it y o f t h e s e
sa m ple s wa s e va lua t e d a ga ins t a dsor ba t e o f i od ine ,
m e thy l e n e b lue a n d m o la s se s (Sne l l & Hi l t on , 1969 ;
Da ndy , 1977) .
R E S U L T S A N D D I S C U S S I O N
T a ble 1 shows the c he m ic a l a na lyse s o f t he o r ig ina l a s
w e l l as s a m p l e s d e a s h e d w i t h v a r io u s c o n c e n t r a t i o n s o f
s o d i u m h y d r o x i d e . R e d u c t i o n o f a s h a n d l i g n i n w a s
ne g l ig ib l e i n i ti a ll y a nd t he n i nc r e a se d w i th a n i nc r e a se
i n a l k a l i c o n c e n t r a t i o n . O p t i m u m d e a s h i n g o f R H t o
t h e e x t e n t o f 9 3 % w a s a c h i e v e d a t 1 % a l k al i c o n c e n t r a -
t i o n . T h e p e r c e n t a g e o f a - c e l l u l o s e a l t e r e d w i t h t h e
a lkal i c onc e n t r a t i on , a tt a in ing a va lue o f 71 .75% a t 1%
a lka l i . T a b l e 1 a l so shows a r e gu l a r de c r e a se i n y i e ld
wi th i nc r e a s e i n a lka li c on c e n t r a t i on . I n t he l igh t o f t h i s
c he m ic a l a na lys i s ( h ighe r a - c e l l u lose a nd l ow- a sh
c o n t e n t) , 1 % N a O H c o n c e n t r a t i o n w a s s e l e c t e d f o r u s e
in f u r th e r s t ud i e s .
T a b le 2 shows the e f f e c t o f im pr e gna t ion r a t i o ( I R)
o f a c t i v a t i n g a g e n t ( A A ) o n t h e a v e r a g e p e n e t r a t i o n
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A c t i v a t e d c a r b o n f r o m r ic e h u s k
Tab le 1 . Che mica l analysis and y ield o f orig ina l and a lka l i- leached d ee hus k
3 3
Na OH Yie ld a -Ce l lu lo se L ignin Ash Ext rac t ives Pentosans
(%) (%) (%) (%) (%) (% ) (%)
0 00 100 0 35 88 36 38 18 90 1 16 21 21
0-10 94 0 38 01 35 90 18 04 1 09 22 35
0-25 82 0 43 66 33 14 17 26 0 98 23-02
0-50 80 0 48 81 30 26 13 75 0 73 23 97
0 75 66 0 69 05 22 46 5 57 0 65 24-25
1 0 62 0 71 75 18 69 1-25 0 58 24-67
1 25 61 0 72 51 17 51 1 23 0 52 25 50
2 5 56 0 70 25 17 35 1-22 0'3 3 24 62
5 0 53 4 70 45 17'25 1 22 0 '34 24 00
7 5 47 2 70 07 17'24 1 21 0 '37 24-23
Tab le 2 . Effect o f impregn at ion rat io with zinc chloride IR) on average penetrat ion va lue APV) and true y ield
Sample Impreg na t ion Average Yie ld Ash True y ie ld Reagent
cod e ra t io pene t ra t io n va lue (%) conten t (a f t e r a sh recovery
(%) (mm) (%) deduc t ion) (%)
( )
G H 1 a 25 . . . . .
GH 2 50 4 20 56 80 50 09 26 00 70 93
GH 3 75 4 95 55 00 49 50 27 80 72 88
G H 4 100 5 05 54 73 49 17 27 83 75 55
G IH 1 25 4 60 52 95 50 05 25 45 67 98
G1 H2 50 5 00 52 00 49 22 26 78 71 30
G1 H3 75 5 40 53 30 48 19 27 62 73 25
G 1H 4 100 5-50 54 50 48 15 28 26 74 50
LH 1 25 3 80 35 13 2 95 34-09 68 '39
LH 2 50 5-50 35 67 2 88 34-64 71 '75
LH 3 75 5 80 35 87 2 51 34-96 74 '10
LH 4 100 5 80 34 25 2 42 33 42 75 '33
~H 1-H 4 d enotes d i f fe ren t impregn a t ion ra t ios o f zinc ch lor ide g iven in co lum n 2 ( s ee a lso M ethods ) .
- -
no resul t , see text .
v a l u e ( A P V ) o f t h e p u t t i e s u s e d f o r g r a n u l iz a t io n . I t
s h o w s t h a t w i t h t h e i n c r e a s e in I R , th e A P V o f th e
p u t t y g e n e r a l l y i n c r e a s e d ( A h m a d et al. 1 9 9 2 ) .
Sample Bulk True Pore
F u r t h e r , i t s h o w s t h a t i n g r o u p G t h e r e i s n o p u t t y c o d e d e n si ty d e n si ty s p ac e
f o r m a t i o n a t 2 5 % I R , w h e r e a s f o r m a t i o n o f p u t t y a n d ( g /c m 3) ( g /c m 3) ( p e r 1 0 0 g )
t h e r e a f t e r i t s g r a n u l i z a t i o n w a s a c h i e v e d w i t h 2 5 % I R
i n t h e G 1 a n d L g r o u p s . H e n c e f o r t h , s t u d ie s o n l o w - G H 1 - - - - - -
a s h R H w e r e p e r f o r m e d o n l y w i t h t h e o r i g in a l - si z e G H 2 0 .5 4 4 4 1 .9 6 19 1 33
p a r t i c l e s . G H 3 0 . 5 3 5 9 1 . 9 9 13 1 3 6
G H 4 0 4 6 0 2 2 2 3 0 7 1 7 4
I n e i t h e r c a s e , y i e l d i n c r e a s e d w i t h t h e i n c r e a s e i n I R
o f z i n c c h l o r i d e ( N a c c o & A q u a r o n e , 1 9 7 8 ) . H o w e v e r , G 1 H 1 0 -6 5 93 1 .1 5 93 6 5
G 1 H 2 0 - 6 6 3 5 1 . 87 2 1 9 7
a p h e n o m e n o n o f a s h r e d u c t i o n w a s o b s e r v e d i n t h e s e G 1 H 3 0 .6 4 05 1 .8 19 8 1 01
s a m p l e s w i t h a n i n c r e a s e i n I R o f t h i s p a r t i c u l a r A A G 1 H 4 0 . 5 0 14 2 . 13 5 6 1 5 3
( E 1 - S h o b a k y & Y o u s s e f , 1 9 7 8 ) . R e a g e n t r e c o v e r y L H 1 0 . 5 3 80 1 . 80 2 0 1 2 9
( R R ) i n c r e a s e d g r a d u a l l y w i t h t h e i n c r e a s e o f I R i n L H 2 0 . 5 3 7 7 1 . 83 0 3 1 31
b o t h t h e c a s e s a n d g e n e r a l l y r a n g e d b e t w e e n 6 8 a n d L H 3 0 .5 2 9 9 1 .9 9 73 1 39
7 5 % . T h i s a g r e e s w e ll w i t h t h e s t u d y o f A h m a d et al. L H 4 0 . 5 2 2 2 2 . 1 6 9 6 1 4 5
( 1 9 9 0 ) u s i n g t h e s a m e A A w i t h a n o t h e r r a w m a t e ri a l.
T a b l e 3 s h o w s t h a t i n b o t h h i g h - a n d l o w - a s h s a m -
p l es , b u l k d e n s i t y g e n e r a l l y d e c r e a s e d a n d t r u e d e n s i t y
i n c r e a s e d r e s u l ti n g in a n e n h a n c e d p o r e - s p a c e w i t h t h e
i n c r e a s e o f IR . I n t h e c a s e o f t h e G 1 g r o u p , t h e r e s u lt -
a n t p o r e - s p a c e w a s s o m e w h a t l o w e r i n al l t h e s e
c a r b o n s , a p p a r e n t l y d u e t o t h e i r i n c r e a s e d b u l k a n d
Table 3 . Di f ferent physica l characterist ics o f act ivated
ca rb o n s
Ball-Pan
hardness no .
BPH)
3 05
3 51
53 04
2 '05
25 56
6 1 ' 2 5
6 2 ' 3 2
2 0 ' 0 0
93 00
94 50
95 60
c o m p a r a t i v e l y l o w e r t r u e d e n s it ie s . T h i s h i g h e r b u l k
o b t a i n e d i n g r o u p G 1 s a m p l e s h a d r a t h e r a p o s it i v e
e f f e c t i n i n c r ea s i n g t h e c o m p a c t n e s s o f t h e s e g r a n u l e s
a s m a y c l e a r ly b e s e e n b y th e i r h i gh B P H a s c o m p a r e d
t o G c l as s sa m p l e s . T h e d a t a o n B P H f u r t h e r s h o w s t h a t
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34
T a n z i l H a i d e r U s m a n i , T a m o o r W a h a b A h m a d , A . H . K . Y o u s u f z a i
T a b l e 4 A d s o r p t i v e / s u r f a c e c h a r a c t e r i s t ic s o f a c t iv a t e d c a r b o n s
Sample Iodine no.
code (mg/g)
Methylene Molasses Surface area of Surface area of Surface area of
blue no. value pores > 10 A pores > 15 A pores > 28 A
(mg/g) (m2/g) (m2/g) (m2/g)
GH1
GH2 537
GH3 633
GH4 675
GIH1 397
GIH2 423
G1H3 537
G1H4 744
LH1 941
LH2 1059
LH3 1148
LH4 1232
109 298 486 312 144
169 495 576 484 238
199 663 615 569 319
96 410 355 272 198
101 442 379 289 213
189 657 486 541 317
214 696 679 613 335
172 420 864 492 202
189 466 974 542 225
306 498 1057 876 238
375 550 1136 1073 265
in the high-ash classes (G and G1 ), none of the samples
was able to attain the minimum standard o f hardness of
95 required for GAC (ASTM, 1979), even though at
higher IR, BPH numbers increased in somewhat higher
proportion. However, in the case of samples of group
L, except at an IR of 25 , all the GAC samples
attained a similar BPH value. The prominent increase
in hardness obtained between samples LH1 and LH2
may be correlated well with the sudden increase in
APV (Table 2) of their putties from 3-80 to 5-50
(Usmani
et al . ,
1992). An overview of Tables 2 and 3
shows that GAC samples prepared from high-ash RH
could not gain sufficient strength, probably because
their cellulosic contents were lower than those of low-
ash samples. The binding action of zinc chloride seems
to be the contributing factor as it is effective on the
cellulosic portion of the raw material rather than on the
ash (Ts'ai & Chaung, 1942).
Table 4 depicts activity or adsorptive capability of
the activated carbons against adsorbates of different
molecular dimensions, corresponding to surface areas
of por es> 10, 15 and 28 A respectively (Bonnevie-
Svendsen, 1975). In Table 4 the development of micro-
and mesopores, as indicated by the iodine and MB
numbers, was somewhat low in both the cases of high-
ash RH carbons (G and G1). Contrary to that of high-
ash, quite prominent increases in iodine and MB
numbers were found in low-ash carbons (L). In both
cases, iodine and MB numbers show a pattern of
increase, with a sudden variation in their mesoporos ity
at 75 IR. As far as macroporosity of these carbons
determined by molasses decolorization is concerned, it
was found to be d ependent on IR in both the cases and
increased with it.
This work shows that optimum deashing of rice husk
to the extent of 93 is achieved by refluxing it with 1
sodium hydroxide solution. Granular activated-carbon
of good quality, appropriate hardness, and balanced
micro-, meso- and macropores may be prepared from
low-ash rice husk in its original particle size with 75
zinc chlor ide as an activating agent.
R E F E R E N C E S
Ahmad, T. W., Usmani, T. H. & Ahmad, S. Z. (1990). Acti-
vated carbon from indigenous inferior woods 2. Activa-
tion temperature, time and particle size influence. Pak. J.
Sci. Ind. Res., 33 (4), 177-80.
Ahmad, T. W., Usmani, T. H. & Mumtaz, M. (1992). A
process for the production of granular activated carbon
from indigenous woods. Pakistan patent (filed).
Akhtar, R. (1986-87). Pak i s tan Year Boo k . East and West
Pub. Co., Karachi/Lahore, p. 519.
ASTM (1979).
Standard Tes t Me thods Jbr Bal l -Pan H ardness
of Act iva ted Carbon, Vol . 15.01. ASTM, Philadelphia, PA.
Bansal, R. C., Donnet, J. B. & Stoeckli, F. (1988). Act i ve
Carbon. Marcel Dekker, New York.
Beg, M. A. A. & Usmani, T. H. (1985). Low ash activated
carbon from rice husk. Pak. J. S ci. Ind. Res., 28 (4),
282-7.
Bevia, F. R., Rico, D. P. & Gomis, A. E M. (1984). Activated
carbon from almond shells.
Ind. Eng. Chem., Prod. Res.
Dev.,
23, 266-71.
Bonnevie-Svendsen, M. (1975).
Sorption and Filtration
Methods for Gas and Water Puri f icat ion.
Noordhoft-
Leyden, pp. 275-6.
BS: 4164 (1987). Appendix -- E. Determination and pene-
tration. British Standard Institution, London.
Dandy, A. J. (1977). Production and characterization of acti-
vated carbon from agricultural waste products and wood
charcoals. Ne w Zea land J . Sci. , 20, 291-5.
EI-Shobaky, G. A. & Youssef, A. M. (1978). Chemical acti-
vation of charcoals. Surface Technology, 7, 209-16.
Grist, D. H. (1975). Rice. Longmans, Green & Co., London,
p. 382.
Jain, K. D. & Sharma, M. K. (1971). Preparation of activated
carbon from basmati rice husk. J. Indian Chem. Soc. , 4 8
(12), 1155-60.
Martin, R. J. (1980). Activated carbon product selection for
water and waste water treatment. Ind. Eng. Chem., Prod.
Res. Dev., 19 (3), 435-41.
Mc Graw -Hil l Encycloped ia of Science an d Technology, VoL
i1 1960) .
McGraw-Hill, New York, pp. 562-3.
Murti, H. (1976). Granular activated carbon. Ger. Often.
2,624, 779, 16 Dec. 1976.
Nacco, R. & Aquarone, E. (1978). Preparation of active
carbon from yeast. Carbon, 6, 31-4.
Snell, E D. & Hilton, C. L. (1969). Encyclopedia of Industr ial
Chem ical Analys is, John Wiley, New York, Vol. 1, p. 557;
Vol. 8, pp. 148-9.
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