ethanol adsorption
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8/8/2019 Ethanol Adsorption
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ELSEVIERP I 1 : S 0 9 6 0 - 8 5 2 4 ( 9 8 ) 0 0 0 4 8 - 0
Bioresource Technology 66 (1998) 75-78© 1998 Elsevier Science Ltd. All rights reserved
Printed in Great Britain0960-8524/98 $19.00
S h o r t C o m m u n i c a t i o n
S e l e c t i o n o f A d s o r b e n t s t o b e u s e d i n
a n E t h a n o l F e r m e n t a t i o n P r o c e ss .
A d s o r p t i o n I s o t h e r m s a n d K i n e ti cs
Abstrac t
Adsorption equil ibrium assays were carried out in
order to f in d adsorben ts se lec t ive for e thano l to use in
a ferm enta t ion process . Three hydrophobic adsorben ts
- - s i l i ca l i te , ZSM-5 and CMS-5A - - were tes ted .
Resu l t s o f adsorp t ion equ i l ibr ium a t 298 K o f e thano l ,
g lucose , f ruc tose and g lycero l f rom aqueous so lu t ions
o f each s ingle solute are given. E tha no l adsorption
iso therms were descr ibed by Langmuir - type equa t ions .
Som e k inet ic assays o f e thano l adsorp t ion are al so
presen ted . The resu lt s ob ta ined appear to be use fu l for
pract ic ioners on the fermenta t ion-processes f i e ld .
© 1998 Elsevier Science Ltd. All r ights reserved
Key words: e t h an o l ad s o r p t i o n , C M S - 5 A , s i l i c a l i t e ,
Z S M - 5 .
I N T R O D U C T I O N
I n e t h a n o l f e r m e n t a t i o n r e l a ti v e l y h i g h c o n c e n t r a -
t i o n s o f e t h a n o l i n c r e a s e t h e p r o d u c t i n h i b i t i o n
e f f e c t ( M a i o r e l l a et al . , 1 9 8 4 ; L e t o u r n eau & V i l l a ,
1 98 7) . T h i s l i m i ts t h e a m o u n t o f e t h a n o l w h i c h c a n
b e p r o d u c e d p e r u n i t o f ti m e a n d v o l u m e o f
f e r m e n t o r . S e v e r a l m e t h o d s t o i m p r o v e t h e a l c o h o l
p r o d u c t i v i t y b y r e d u c i n g t h e e t h a n o l c o n c e n t r a t i o ni n t h e b r o t h h a v e b e e n s u g g e s t e d ; s u c h a s r e d u c t i o n
o f t h e p r e s s u r e i n th e r e a c t o r ( C y s e w s k i & W i l k e ,
1 9 7 7 ; F i n n & R am a l i n g am , 1 9 7 7 ) , o n - l i n e s o l v en t
e x t r a c t i o n ( M i n e r & G o m a , 1 9 82 ) o r s e l e c ti v e
e t h a n o l a d s o r p t i o n ( M i l e s t o n e & B i b b y , 1 9 8 3 ; L e e &
Wang , 1982 ; P i t t et al . , 1983; Lenck i et al . , 1983) .
C o n t i n u i n g o u r r e s e a r c h o n e t h a n o l i c f e r m e n t a -
t i o n ( B r av o & G o n z f i l ez , 1 99 1 ), w e a r e d ev e l o p i n g a
d e v i c e f o r a f e r m e n t a t i o n p r o c e s s i n a f l u i d i z e d b e d
b i o r e a c t o r w i t h i m m o b i l i z e d c e l l s o f S a cch a r o m yces
cerevisiae i n c a l c i u m - a i g i n a t e , t o g e t h e r w i t h s i m u l t a -
n e o u s e x t r a c t i o n o f t h e p r o d u c t e t h a n o l b y a d s o r p -
t i o n o n t o a n a d s o r b e n t . A n i n it ia l p h a s e o f t h is
s t u d y co n s i s t s o f s c r een i n g p o s s i b l e s o r b en t s . T h e
a i m o f t h e p r e s e n t w o r k w a s t o p r o v i d e r e s u lt s f o r
75
e t h a n o l a d s o r p t i o n o n t h r e e d i f f e r e n t a d s o r b e n t s a s
a n a i d t o w a r d s t h e a s s e s s m e n t o f t h e p o t e n t i a l o f
t h a t p r o ces s .
W e h a v e f o c u se d o n t h e h y d r o p h o b i c a d s o r b e n t s
s i l i c a l i t e , Z S M - 5 a n d C M S - 5 A b e c a u s e i t c o u l d b e
e x p e c t e d t h a t t h e y w o u l d s h o w h i g h e r s e l e c ti v it y f o re t h a n o l t h a n f o r w a t e r a n d t h e o t h e r c o m p o n e n t s o f
t h e f e r m e n t a t i o n b r o t h . N e v e r t h e l e s s , w e h a v e a l s o
t e s t e d t h e a d s o r p t i o n c h a r a c t e r i st i c s o f s u g a r s a n d
g l y c e r o l o n t o t h e s o li d s in c o n c e n t r a t i o n r a n g e s
u s u a l ly f o u n d f o r t h o s e c o m p o n e n t s i n e t h a n o l i c
f e r m e n t a t i o n p r o c e s s e s .
M E T H O D S
M a t e r ia l s
A d s o r b en t s
T w o s y n t h e t i c s i l i c a m o l ecu l a r s i ev es , s i l i c a l i t e
( U O P ) , Z S M - 5 ( M o b i l C h e m i c a l I n te r n a t i o n a l) a n d
a n a c t i v a t e d c a r b o n m o l e c u l a r s i e v e , C M S - 5 A
( T a k e d a C h e m i c a l I n d u s t r i e s ) , w e r e t e s t e d a s a d s o r -
b en t s . T h e s i ze o f th e p e l l e t i zed cy l i n d r i ca l s o l id s
w a s : 3 × 1 m m f o r p e l l e ts o f Z S M - 5 , 5 × 1 m m f o r
s il ic a l it e a n d 8 × 4 m m f o r C M S - 5 A . B e f o r e e a c h
r u n , Z S M - 5 a n d s i l i c a l i t e w e r e r e g e n e r a t e d b y
w a s h i n g r e p e a t e d l y w i t h u l t r a p u r e b o i li n g w a t e r a n d
d r y i n g a t 2 0 0 - 2 2 0 °C . C M S - 5 A w a s d i r e c t ly u s e d ,
a f t e r w a s h i n g , a s a w e t s o li d , b e c a u s e p r e l i m i n a r y
t e s ts s h o w e d t h a t i t s a d s o r p t i o n c a p a c i t y w h e n w e t
w a s s l i g ht ly h i g h e r t h a n w h e n d r i e d .
A d s o r b a t e s
E t h a n o l , g l u c o se , f r u c t o s e a n d g l y c e ro l w e r e u s e d i n
c o n c e n t r a t i o n r a n g e s l a r g e e n o u g h t o c o v e r a ll l ev e l s
w h i c h t y p i c a ll y a p p e a r i n f e r m e n t a t i o n b r o t h s .
S y n t h e t i c s o l u t io n s i n t h e r a n g e s 0 - 5 0 % ( w /w ) f o r
e t h a n o l - w a t e r m i x tu r e s, 0 - 2 - 1 5 % ( w /w ) fo r g l u c o s e -
w a t e r so l u ti o n s , 0 - 2 - 8 % ( w /w ) f o r f r u c t o s e - w a t e r
a n d 0 . 2 - 0 . 7 % ( w /w ) fo r g l y c e r o l - w a t e r w e r e
p r e p a r e d .
Kinet ic and equi l ibr ium exper iments
T h e e q u i li b ri u m a d s o r p t io n m e a s u r e m e n t s a t
2 5 _ 0 " 1 ° C a n d p H 4 . 0 + 0 . 1 w e r e c o n d u c t e d b y
i m m e r s i n g i n s t o p p e r e d f l a s k s k n o w n m a s s e s o f
a d s o r b e n t a n d s o l u t io n o f i n it ia l s o l u t e c o n c e n t r a -
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76 S h o r t c o m m u n i c a t i o n
t i o n C o. T h e s t i r r e d s o l u t i o n s w e r e a l l o w e d t o r e a c h
e q u i l i b r i u m a n d , a f t e r f i l tr a t io n , c l e a r s a m p l e s w e r e
t a k e n a n d a n a l y s e d i n o r d e r t o d e t e r m i n e t h e
c o n c e n t r a t i o n o f s o l u t e in s o l u t i o n a t e q u i li b r i u m ,
C e .
A s i m i l a r p r o c e d u r e w a s f o l l o w e d in s o m e e x p e r i -
m e n t s w i t h e t h a n o l - w a t e r s o l u t i o n s . I n t h i s c a s e ,
s a m p l e s o f s o l u t i o n w e r e i n t e r m i t t e n t l y t a k e n b y
m e a n s o f a h y p o d e r m i c s y r in g e t h ro u g h a r u b b e r
s e p t u m o n t h e t o p o f th e c l o s e d f la s k. T h e e v o l u t i o n
o f e th a n o l c o n c e n t r a t i o n w i th t i m e w a s d e t e r m i n e d
b y a n a ly s i n g e a c h s a m p l e .
A n a l y t ic a l m e t h o d s a n d m a s s b a l a n c e s
C o n c e n t r a t i o n s o f e th a n o l , c a r b o h y d r a t e s a n d
g l yc e r o l w e r e m e a s u r e d b y H P L C u s in g a n A m i n e x
I o n E x c lu s i o n H P X - 8 7 H B i o R a d c o l u m n a n d
0 "0 1 N H 2 5 0 4 s o l u t i o n a t 6 0° C a s m o b i l e p h a s e a n d
a f l ow r a t e o f 0 .7 c m 3 m i n - l . E l u t e d m a t e r i a l s w e r e
d e t e c t e d u s i n g a W a t e r s d i f fe r e n t ia l r e f r a c t o m e t e r
d e t e c t o r 4 10 ( W a t e r s C h r o m a t o g r a p h y D i v is i on /
M i l l ip o r e C o r p o r a t i o n , 3 4 M a p l e S t r e e t /M i l f o r d ,
M A 0 1 7 5 7 ) .
T h e a d s o r p t i o n u p t a k e C s , g a d s o r b e d s o l u t e / g
s o l id a d s o r b e n t , w a s f o u n d b y a m a s s b a l a n c e o n t h e
a d s o r b e d s p e c i e s, a s s u m i n g w a t e r w a s n o t s i g ni fi -
c a n t l y a d s o r b e d .
W h e n u s in g d r y a d s o r b e n ts , t h e m a s s b a l a n c e
y i e l d e d t o t h e e q u a t i o n :
M ( C o - - C ,, )C s - ( 1 )
S ( 1 O 0 - - C e )
M a n d S b e i n g t h e m a s s ( g ) o f i n i ti a l s o l u t i o n a n d
d r y a d s o r b e n t , r e s p e c t iv e l y .
W h e n u s i n g w e t a d s o r b e n t , t h e f o l l o w i n g e q u a t i o n
w a s u s e d :
M C o - - ( M + S w - - S ) C eCs = (2 )
S ( I O 0 - C e)
S w b e i n g t h e m a s s ( g ) o f w e t a d s o r b e n t .
R E S U L T S A N D D I S C U S S I O N
K i n e t i c s
K i n e t i c e x p e r i m e n t s o n s i li c a li te a n d C M S - 5 A w e r e
c o n d u c t e d a t t w o i n i t i a l e t h a n o l c o n c e n t r a t i o n s :
C o = 1 0 " 1 5 % a n d 5 . 0 9 % ( w / w ) .
F o r b o t h a d s o r b e n ts , t h e d e c r e a s e o f e t h a n o l
c o m p o s i t i o n i n s o lu t i o n w a s s l i g ht ly h i g h e r w h e n t h e
i n it ia l s o l u t io n w a s m o r e c o n c e n t r a t e d . I n g e n e r a l ,
a n i n i t ia l f a s t a d s o r p t i o n o f e t h a n o l f o l l o w e d b y as e c o n d s l o w s t a g e w a s o b s e r v e d . A s i m i l a r p e r f o r m -
a n c e w a s f o u n d w h e n c h e c k i n g th e a d s o r p t i o n o n
Z S M - 5 . A s s u g g e s t e d f r o m t h e k i n e t i c p r o f i l e s , t h e
k i n e t i c r e s u l t s w e r e a s s a y e d t o f i t a f i r s t - o r d e r k i n e t i c
m o d e l :
C t = C o e - k ' (3 )
C t ( % w / w ) a n d k ( m i n 1 ) b e i n g t h e e t h a n o l
c o n c e n t r a t i o n i n s o l u ti o n a t t im e t ( m i n ) a n d t h e
k i n e t i c r a t e c o n s t a n t , r e s p e c t i v e l y .
B y l i n e a r i z a t io n o f e q n ( 3 ), a n a c c e p t a b l e f it w a s
a c h i e v e d f o r t h e t w o s u c c e s s i v e f i r s t - o r d e r s t e p s .T a b l e 1 s h o w s t h e l i n e a r f i tt e d p a r a m e t e r s , t o g e t h e r
w i t h e x p e r i m e n t a l r e s ul ts . F o r e t h a n o l a d s o r p t i o n o n
s i l ic a l i te a t C o = 1 0 - 1 5 % , a l o w k - v a l u e r e s u l t e d f o r
t h e s e c o n d s t e p , t h i s f a c t s h o w i n g t h a t t h e o v e r a l l
a d s o r p t i o n o c c u r s i n t h e f i r s t s t a g e .
T able 1 . K ine t i c s o f e thano l adsorpt ion o nto s i l i ca li t e and C M S-5A : exper im enta l re su l t s and l inear param eters f it t ed toa tw o- s tage f i r s t order m ode l
S i l ica l i te S i l ica l it e CM S -5 A CM S -5 A
C t t C t t C t t C t t
10.15 0 5"09 0 10-15 0 5"09 09.92 5 4.92 8 10.05 5 4"85 59.75 15 4.81 23 9.93 10 4.71 209.73 35 4.78 39 9.63 50 4.63 359.75 70 4.75 57 9.51 65 4.53 529.79 80 4.74 72 9.50 85 4.49 839"78 110 4.73 90 9.46 105 4.48 1079"76 125 4.71 500 9"40 144 4.42 1379"73 500 9.36 500 4-32 500
C o n s t a n t s o f e q n ( 3 )S t e p 110.15 > C t > 9"75k = 2-55 x 1 0 -3
S t e p 2Ct < 9-75k = 1.26 x 10 .5
C o n s t a n t s o f e q n ( 3 )S t e p 1
5"09 > C t > 4"78k = 2"37 x 10 -3
S t e p 2Ct _< 4-78
k = 1.33 x 10 -4
C o n s t a n t s o f e q n ( 3 )S t e p 1
10.15 > C t > 9"70k = 2"02 x 10 3
S t e p 2Ct < 9-70
k = 2.70 x 10 4
C o n s t a n t s o f e q n ( 3 )S t ep 1
5.09 > Ct > 4.71k = 5.74 x 10 3
S t e p 2Ct < 4.71
k = 4 .80 x 1 0 -4
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Shor t communica t ion 77
T a b l e 2 . A d s o r p t i o n i s o t h e r m s o f e t h a n o l o n t o s i li c a l it e , C M S - 5 A a n d Z S M - 5 a t 2 9 8 K : e x p e r i m e n t a l r e s u l t s a n d
L a n g m u i r - ty p e a d s o r p t i o n p a r a m e t e r s
Silicalite CMS-5A ZSM-5
C~ C~ C~ C¢ Cs C~
1.274 0-016 0.322 0.032 0"365 0.0232-753 0.025 0.753 0.039 0.739 0"0364-700 0.034 2.144 0"055 1'641 0"0457"778 0"051 4.222 0.074 0.614 0.052
11.548 0.056 6.164 0.089 5"539 0'05614.609 0.064 9.705 0.107 7"576 0"05722-109 0.065 13.685 0" 116 13"692 0.05829-704 0.066 26.502 0.115 25"418 0.06440-484 0.072 30.323 0"116 28.921 0"06849-656 0.075 33"078 0.117 39.309 0-071
Langmuir parameters Langmuir parameters Langmuir parametersa = 0.015 a = 0"058 a = 0-095b = 0"179 b = 0"464 b = 1'437Norm = 0"008 Norm = 0-023 Norm = 0-009
Langmuir equation C~ = a'Ce/(1 + b'Ce).
E q u i l i b r i u m
A d s o r p t i o n o f e t h a n o l
Ethanol adsorption equilibrium results on to silica-
lite, ZSM-5 and CMS-5A from ethanol-water
mixtures are given in Table 2. The shape of the
isotherms displays the adsorption type favourable in
all cases. Therefore, a Langmuir-type equation was
used to represent equilibrium adsorption. Values of
model parameters, a and b, were determined by
fitting the experimental data to the proposed
equation, using the program SigmaPlot ScientificGraphing System. The magnitude of the norm is
also shown in Table 2.
The asymptotic uptakes at ethanol adsorption
equilibrium, a / b , increase in the order: 0-068
(ZSM-5)<0.084 (silicalite)<0.126 (CMS-5A). The
calculated saturation capacities of silicalite and
ZSM-5 are smaller than those given by Farhadpour
(Farhadpour & Bono, 1988) and Milestone
(Milestone & Bibby, 1983), respectively, for the
same systems at similar temperatures: 0-131g
ethanol/g microcrystalline silicalite and 0-12 g
ethanol/g microcrystalline ZMS-5. The discrepancy
might be due to the use of pelletized adsorbents,which diminishes the hyd rophobicity by the presence
of the agglomerant. The content of A1203 in the
adsorbent ZSM-5, even while low, could justify the
observed capacity difference between ZSM-5 and
silicalite.
Concerning the CMS-5A equilibrium adsorption
data, we have not found any references in the litera-
ture. For the purpose of comparison, Lee and Wang
(1982) found an adsorption capacity value of 0.13 g
ethanol/g adsorbent for the adsorption of ethanol on
to a conventional activated carbon.
A d s o r p t i o n o f g lu c o se , f r u c to s e a n d g l yc e ro l
An experimental adsorption study of the systems
glucose-water, fructose-water and glycerol-water
was made. No measurable adsorption of glucose,
fructose and glycerol on silicalite and ZSM-5 was
found. However, a maximal adsorption of glucose
(0"011g glucose/g adsorbent), fructose (0.010g
fructose/g adsorbent) and glycerol (0-014 g glycerol/g
adsorbent) on CMS-5A was found.
The non-adsorption of substrate, together with a
good selectivity for ethanol, make the use of silica-
lite or ZMS-5 as sorbents in removing ethanol from
fermentation broths attractive. The CMS-5A sieve
shows minimal adsorption of substrate. We alsochecked the multicomponent adsorption of ethanol,
glucose and fructose on to this adsorbent. The
results (not shown) indicated that the adsorption of
ethanol did not decrease significantly from the
binary to the multico mponent, while the ad sorption
of the substrates glucose and fructose in the multi-
component system was even lower than in their
respective binary systems. In conclusion, the adsor-
bents screened in this work seem to be promising to
use in ethanol fementation processes. Nevertheless,
we should stress that the results of this preliminary
study correspond to batch processes and these donot mimic the conditions which would be found in a
real fermentation. Further work would be needed to
examine aspects of mass transfer.
R E F E R E N C E S
Bravo, P. & Gonz~ilez, G. (1991). Continuous ethanolfermentation by immobilized yeast cells in a fluidized-bed reactor. J. Chem . Tech. Biotechnol. , 52, 127-134.
Cysewski, G. R. & Wilke, C. R. (1977). Rapid ethanolfermentat ions using vacuum and cell recycle. Biotechnol.Bioeng., 19, 1125-1143.
Farhadpour, F. A. & Bono, A. (1988). Adsorption fromsolution of nonelectrolytes by microporous crystallinesolids: ethanol-water/silicalite system.Journal of Colloidand Interface Science, 124, 209-227.
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A. Cart6n, G. Gonz~i lez Benito*,
J . A. Rey & M. de la Fuente
Department of Chemical Engineering,Faculty of Sc iences, University o f Valladolid,47011 Valladolid, Spain
(Rec e iv ed 1 4 Ju ly 1 9 9 7; r ev i sed v e r s io n r ece iv ed6 F eb ru ary 1 9 9 8 ; accep t ed 1 2 F eb ru ary 1 9 9 8 )
* A u t h o r t o w h o m c o r r e s p o n d e n c e s h o u l d b e a d d r e s s e d .
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