- Email: [email protected]
Adsorption of phenol on adsorbent resins and activated carbon: Equilibrium and kinetic studies in batch and open systems
J. Rouquerol and K.S.W. Sing (Editors) Adsorption at the gas-solid and liquid-solid interface © 1982 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
125
ADSORPTION OF PHENOL ON ADSORBENT RESINS AND ACTIVATED CARBoN:EQUILIBRIUM AND KINETIC STUDIES IN BATCH AND OPEN SYSTEMS C.A.COSTA and A.E.RoORIGUES Department of Chemical Engineering,University of Porto,Porto (Portugal)
ABSTRACT Equilibrium adsorption isotherms were determined for the system phenol-water/ adsorbent at 20 C and 60 Clthe adsorbents used were: Duolite ES861,Amberlite XAD4,Ambersorb XE348 and activated carbon Norit PK1-3. Kinetic studies were carried out in batch and open systems (perfectly mixed sorber) in order to obtain the diffusivity of phenol in various adsorbents.The ~nalysis
of kinetic data involves testing of homogeneous and pore diffusion mo-
dels,which are related with the transport phenomena occuring inside the particles and then
depen~
on their porous structure.
INTRODUCTION Phenolic compounds can be found in some industrial effluents in concentrations ranging from 80 to 4000 mg/l.The elimination of these compounds can be achieved by adsorption (ref. 1). Equilibrium,hydrodynamics and kinetic data are needed to a scientific design of adsorption equipmentlone major point for chemical engineers is the design of experiments at the laboratory scale to get that information. In this paper we first present equilibrium data for the adsorption of phenol on several adsorbentslthen kinetic experiments in batch and open systems are shown in order to get data of phenol diffusivity in Duolite ES861 (refs. 2-4)
ADSORPTION EQUILIBRIUM ISOTHERMS Adsorption equilibrium isotherms were obtained for the system phenol-water/ adsorbentladsorbents tested were: Duolite ES861,Amberlite XAD4,Ambersorb XE348 and activated carbon Norit PK1-3. Experiments were carried out in batch systems at temperatures of 20 C and 60 Cl samples were taken
out at equilibrium condi-
tions and phenol analised at 272 nm using an UV Spectrophotometer Unicam SP6-400. In Figure 1 adsorption equilibrium isotherms are shown.
126
q
(mg/g dr solidl
_ _...... -----< >-7
10 4
100
300
sno
Fig. 1. Adsorption equilibrium isotherms for the system phenol/adsorbent. 1-Norit PK1-3(20 Cl;2-Ambersorb XE348 (20 Cl;3-Duolite ES861 (20 Cl;4-Amberlite XAD4 (20 ci , 5-Duolite ES861 (60 C). Experimental points were fitted by a Langmuir equation q=qmKAc/(1+KAcl,where q and c are the phenol concentrations in the solid and liqUid phases, respectively, K is the equilibrium constant and qm is the maximum capacity of the adsorbent. A In Table 1 we summarize the values of K and qm we got from data obtained at A 20 C and 60 C. TABLE 1 Parameters for adsorption eqUilibrium isotherms Adsorbent
qm(mg/g)
K D/mg) A
TCKl
Norit PK1-3 Ambersorb XE348 Duolite ES861 Amberli te XAD4 Duoli te ES861
161.6 133.3 91.7 271.5 35.0
1.24x10- 1 4.2 x10- 2 2.88x10- 3 5.05x10- 3 4.1 x10- 3
293 293 293 293 333
KINETIC STUDIES Experiments were carried out in a basket ad sorber sketched in Figure 2;it can be operated either as a batch adsorber or as a CSTR adsorber.The ad sorber volume is 470 ml and each basket is 7.5 x3 xi cm. The goal of these experiments is the measure of the diffusivity of phenol in Duolite ES851;so the experimental conditions were such that mass transfer resistance in the fluid film around the particles is negligible. Then the stirrer speed was chosen after carrying out the tests shown in Figure 3.
127
Fig. 2. Sketch of the ad sorber and basket (so-called Carberry reactor)
1•
c/c
o
o
00
A
o
~
OA 0
A
o a
o.
'l.
o
o
2
3
Fig. 3. Outlet phenol concentration vs reduced time (CSTR) o Stirrer speed- 301 rpm; c =111 mg/l; stoechiometric time- t st=8.52 min 0 A 616 rpm; 0 =111 mg/l; 8.77 min
a
0
875 rpm;
0
0
=115 mg/l;
8.69 min
128 Batch experiments Experimental results obtained in the batch adsorber,in terms of phenol concentration as a function of a real time , t are shown in Figure 4. The runs were carried out for three different initial concentrations, Co of phenol and three different particle diameter,d
Phenol concentration reach a plateau corresponding to the p' equilibrium conditions.
clc
o
o
o
,
2
3
4
5
20
.
tCminl
Fig. 4. Phenol concentration vs time in batch adsorber ~ run 1; + run 2;A run 3; • run 4;C run 5 In Table 2 we summarize the experimental conditions used and the values of diffusivity of phenol in Duolite ESB61,obtained from the homogeneous and pore diffusion models. TABLE 2 Experimenta 1 conditions for adsorption in batch system op (m 2/sec) D 2/sec) Run co(mg/ll dp(cml EO: SQR I(m 1.4x1o-9 1.2x1o- 11 1 B7.3 .060 .96B 6.2 1.4x10- 9 1.4x1o- 11 3.7 2 46.6 .060 .969 1.1x1o- 9 4.3x1o- 12 .41 .060 17.3 .969 3 7.6x1o- 1o B.9x1o- 12 4 .034 1.41 .971 B2.0 1.5x10- 9 7.3x1o- 12 .077 .79 5 B3.5 .971
SQR .145 .069 .141 .034 .126
CSTR experiments Results from runs carried out in open systems (CSTRl are shown in Figure 5. In these experiments the inlet phenol concentration,c changed.
o
and the flowrate.U were
129
+0
o clc
n
D
a
0+
o
D D
00
rt
.5 ~o DO
+ t;\.0 o
o
o
2
3
Fig. 5. Phenol concentration vs reduced time in CSTR experiments a run 1; a run 2;+ run 3 Experimental conditions for the runs carried out in a CSTR are given in Table 3. TABLE 3 Experimental conditions for phenol adsorption in a CSTR Run
Flowrate (ml/min) 100.0
1 2 3
7B.9 7B.9
rpm 511
17.6 4BB.2 100.4
503 510
26.3 2B.1 2B.2
Discussion Results obtained in batch experiments were analised by using two different models: I- Homogeneous model II- Pore diffusion model In Tables 4 and 5 we present the mathematical equations for the models I and II, respectively. These model equations were solved by using the collocation method (ref.5) for the particle radial coordinate;the resulting system of ODEs was then solved with Gear's method (ref.6). In Figure 6 we present the experimental results for run 1 in batch ad sorber together with the predicted curves of clc models I and II.
o
as a function of time obtained·from
The values of DI(or D used in these computations were obtained as follows: p) a- we first calculate a curve clc as a function of e, where 8=0 t/r 2 or 0 t/r 2 o
according to the models I and II
I
p
p
p
130
TABLE 4 Homogeneous model+ Mass balance in the particle
aq(r,t) _ 1 a {2 aq(r,t) - r r a r : r oI H Average particle concentration_ 3 rr p q(t)= ~ q(r,t)r 2dr I" 0 Equilibrium at the interface p q(r p ,t)=f(c(t» . Boundary conditions 1"=0 , a q(r,t)!cl 1"=0
at
r=r p' batch
£(c o-c(t»=(1-£)Q(t) c -c-r dc/dt +(1-£)t/£ 'dq(t»)dt
CSTR Initial conditions
< I"
I"
1"=1"
,q(r.O)=O
p
p
o
,batch
q(r ,O)=f(c )
CSTR
q(r ,o)=f(c(O»
p
0
p
TABLE 5 + Pore diffusion model Mass balance in the particle
a 1 a 2 a c (I", t ) -at{xcp(r,t)+q(r,t)}=x 7 ar:{r 0p a / } Average particle concentration ~r 3 p xcp(r,t)+q(r,t) = 0 lx c p(r,t)+q(r,t)\r2dr
r;
Equi librium
q(r,t)=f(cp(r,t» with c
Boundary conditions
(I" ,t)=c(t) P P 1"=0, ac (r,t)!clr=aq(r,t)Ar=O
p
1"=1" p Batch £(c -c(t»=(1-£)( Xc (r,t)+q(r,t» o p CSTR Initial conditions
I"
<
1"=1"
+
I"
p
,
P
+(1-£)t/£~JXcp(r,t)+q(r,t*
co=c+t dc/dt
Cp (1",0) =0 batch
c
CSTR
C
P p
(I" (I"
P p
,O)=c
0
,O)=c(O)
In the tables above q is the phenol concentration in the particle,c p the phenol
concentration in the pores,c the phenol concentration in the bulk of liquid phase, Co the initial (or inlet) phenol concentration in batch (or CSTR) systems,r is the radial coordinate in the particle,
I"
p
the particle radius,t is the time, X the
particle porosity,£ the adsorber porosity,o
p
is the phenol diffusivity in the pores,
0 the phenol diffusivity in the particle, t is the space time and -1 average quantities.
refers to
131 1.
c/c
,
o .0 I
\
\ 0 \ "\ 0 \
.5
',0
',0 '
<,
0
..........
--0.....
.......-0--
o
.2
o
2
3
4
tCminJ
Fig. 6. Comparison between experimental results [run 1,batch adsorberJ and predicted values from homogeneous model C---J and pore diffusion modelC---J. b-for each c/c
e. plot e
o
we get,from the experimental curve, t
curve, c-we
versus time,t
exp
and from the simulated 2
exp
Jfrom the slope of this graph we obtain DI/r p and
finally DICor DpJ. The fitting is not good for short times [ref.7J;so the values of DICand DpJ given in Table 2 are the best fitted values in the sense of the least square method. REFERENCES
2 3 4 5 6 7
A.E.Rodrigues,C.A. Costa and F. Almeida,Proc. Water Industry'81,Brighton,UK, June 1981 ,pp.429- 434. H. Spahn and E.U. Schlunder,Chem.Eng.Sci.,30[1975J529-537. L. Westerley and J.C. Turner,Trans.lnst.Chem.Eng.,54[1976J89-94. I. Neretnieks,Chem.Eng.Sci.,31[1976J107-114. J. Villadsen and M. Michelsen,Solution of Differential Equation Models by Polynomial Approximation,Prentice Hall,1978,p.143. A. Hindmarsh,Gear-ordinary differential equation system solver, Lawrence Livermore Laboratory Report UCID-30001,Dec.1974. R. Peel,A. Benedek and C. Crowe.AIChE Journal,27C1981J26-32.
125
ADSORPTION OF PHENOL ON ADSORBENT RESINS AND ACTIVATED CARBoN:EQUILIBRIUM AND KINETIC STUDIES IN BATCH AND OPEN SYSTEMS C.A.COSTA and A.E.RoORIGUES Department of Chemical Engineering,University of Porto,Porto (Portugal)
ABSTRACT Equilibrium adsorption isotherms were determined for the system phenol-water/ adsorbent at 20 C and 60 Clthe adsorbents used were: Duolite ES861,Amberlite XAD4,Ambersorb XE348 and activated carbon Norit PK1-3. Kinetic studies were carried out in batch and open systems (perfectly mixed sorber) in order to obtain the diffusivity of phenol in various adsorbents.The ~nalysis
of kinetic data involves testing of homogeneous and pore diffusion mo-
dels,which are related with the transport phenomena occuring inside the particles and then
depen~
on their porous structure.
INTRODUCTION Phenolic compounds can be found in some industrial effluents in concentrations ranging from 80 to 4000 mg/l.The elimination of these compounds can be achieved by adsorption (ref. 1). Equilibrium,hydrodynamics and kinetic data are needed to a scientific design of adsorption equipmentlone major point for chemical engineers is the design of experiments at the laboratory scale to get that information. In this paper we first present equilibrium data for the adsorption of phenol on several adsorbentslthen kinetic experiments in batch and open systems are shown in order to get data of phenol diffusivity in Duolite ES861 (refs. 2-4)
ADSORPTION EQUILIBRIUM ISOTHERMS Adsorption equilibrium isotherms were obtained for the system phenol-water/ adsorbentladsorbents tested were: Duolite ES861,Amberlite XAD4,Ambersorb XE348 and activated carbon Norit PK1-3. Experiments were carried out in batch systems at temperatures of 20 C and 60 Cl samples were taken
out at equilibrium condi-
tions and phenol analised at 272 nm using an UV Spectrophotometer Unicam SP6-400. In Figure 1 adsorption equilibrium isotherms are shown.
126
q
(mg/g dr solidl
_ _...... -----< >-7
10 4
100
300
sno
Fig. 1. Adsorption equilibrium isotherms for the system phenol/adsorbent. 1-Norit PK1-3(20 Cl;2-Ambersorb XE348 (20 Cl;3-Duolite ES861 (20 Cl;4-Amberlite XAD4 (20 ci , 5-Duolite ES861 (60 C). Experimental points were fitted by a Langmuir equation q=qmKAc/(1+KAcl,where q and c are the phenol concentrations in the solid and liqUid phases, respectively, K is the equilibrium constant and qm is the maximum capacity of the adsorbent. A In Table 1 we summarize the values of K and qm we got from data obtained at A 20 C and 60 C. TABLE 1 Parameters for adsorption eqUilibrium isotherms Adsorbent
qm(mg/g)
K D/mg) A
TCKl
Norit PK1-3 Ambersorb XE348 Duolite ES861 Amberli te XAD4 Duoli te ES861
161.6 133.3 91.7 271.5 35.0
1.24x10- 1 4.2 x10- 2 2.88x10- 3 5.05x10- 3 4.1 x10- 3
293 293 293 293 333
KINETIC STUDIES Experiments were carried out in a basket ad sorber sketched in Figure 2;it can be operated either as a batch adsorber or as a CSTR adsorber.The ad sorber volume is 470 ml and each basket is 7.5 x3 xi cm. The goal of these experiments is the measure of the diffusivity of phenol in Duolite ES851;so the experimental conditions were such that mass transfer resistance in the fluid film around the particles is negligible. Then the stirrer speed was chosen after carrying out the tests shown in Figure 3.
127
Fig. 2. Sketch of the ad sorber and basket (so-called Carberry reactor)
1•
c/c
o
o
00
A
o
~
OA 0
A
o a
o.
'l.
o
o
2
3
Fig. 3. Outlet phenol concentration vs reduced time (CSTR) o Stirrer speed- 301 rpm; c =111 mg/l; stoechiometric time- t st=8.52 min 0 A 616 rpm; 0 =111 mg/l; 8.77 min
a
0
875 rpm;
0
0
=115 mg/l;
8.69 min
128 Batch experiments Experimental results obtained in the batch adsorber,in terms of phenol concentration as a function of a real time , t are shown in Figure 4. The runs were carried out for three different initial concentrations, Co of phenol and three different particle diameter,d
Phenol concentration reach a plateau corresponding to the p' equilibrium conditions.
clc
o
o
o
,
2
3
4
5
20
.
tCminl
Fig. 4. Phenol concentration vs time in batch adsorber ~ run 1; + run 2;A run 3; • run 4;C run 5 In Table 2 we summarize the experimental conditions used and the values of diffusivity of phenol in Duolite ESB61,obtained from the homogeneous and pore diffusion models. TABLE 2 Experimenta 1 conditions for adsorption in batch system op (m 2/sec) D 2/sec) Run co(mg/ll dp(cml EO: SQR I(m 1.4x1o-9 1.2x1o- 11 1 B7.3 .060 .96B 6.2 1.4x10- 9 1.4x1o- 11 3.7 2 46.6 .060 .969 1.1x1o- 9 4.3x1o- 12 .41 .060 17.3 .969 3 7.6x1o- 1o B.9x1o- 12 4 .034 1.41 .971 B2.0 1.5x10- 9 7.3x1o- 12 .077 .79 5 B3.5 .971
SQR .145 .069 .141 .034 .126
CSTR experiments Results from runs carried out in open systems (CSTRl are shown in Figure 5. In these experiments the inlet phenol concentration,c changed.
o
and the flowrate.U were
129
+0
o clc
n
D
a
0+
o
D D
00
rt
.5 ~o DO
+ t;\.0 o
o
o
2
3
Fig. 5. Phenol concentration vs reduced time in CSTR experiments a run 1; a run 2;+ run 3 Experimental conditions for the runs carried out in a CSTR are given in Table 3. TABLE 3 Experimental conditions for phenol adsorption in a CSTR Run
Flowrate (ml/min) 100.0
1 2 3
7B.9 7B.9
rpm 511
17.6 4BB.2 100.4
503 510
26.3 2B.1 2B.2
Discussion Results obtained in batch experiments were analised by using two different models: I- Homogeneous model II- Pore diffusion model In Tables 4 and 5 we present the mathematical equations for the models I and II, respectively. These model equations were solved by using the collocation method (ref.5) for the particle radial coordinate;the resulting system of ODEs was then solved with Gear's method (ref.6). In Figure 6 we present the experimental results for run 1 in batch ad sorber together with the predicted curves of clc models I and II.
o
as a function of time obtained·from
The values of DI(or D used in these computations were obtained as follows: p) a- we first calculate a curve clc as a function of e, where 8=0 t/r 2 or 0 t/r 2 o
according to the models I and II
I
p
p
p
130
TABLE 4 Homogeneous model+ Mass balance in the particle
aq(r,t) _ 1 a {2 aq(r,t) - r r a r : r oI H Average particle concentration_ 3 rr p q(t)= ~ q(r,t)r 2dr I" 0 Equilibrium at the interface p q(r p ,t)=f(c(t» . Boundary conditions 1"=0 , a q(r,t)!cl 1"=0
at
r=r p' batch
£(c o-c(t»=(1-£)Q(t) c -c-r dc/dt +(1-£)t/£ 'dq(t»)dt
CSTR Initial conditions
< I"
I"
1"=1"
,q(r.O)=O
p
p
o
,batch
q(r ,O)=f(c )
CSTR
q(r ,o)=f(c(O»
p
0
p
TABLE 5 + Pore diffusion model Mass balance in the particle
a 1 a 2 a c (I", t ) -at{xcp(r,t)+q(r,t)}=x 7 ar:{r 0p a / } Average particle concentration ~r 3 p xcp(r,t)+q(r,t) = 0 lx c p(r,t)+q(r,t)\r2dr
r;
Equi librium
q(r,t)=f(cp(r,t» with c
Boundary conditions
(I" ,t)=c(t) P P 1"=0, ac (r,t)!clr=aq(r,t)Ar=O
p
1"=1" p Batch £(c -c(t»=(1-£)( Xc (r,t)+q(r,t» o p CSTR Initial conditions
I"
<
1"=1"
+
I"
p
,
P
+(1-£)t/£~JXcp(r,t)+q(r,t*
co=c+t dc/dt
Cp (1",0) =0 batch
c
CSTR
C
P p
(I" (I"
P p
,O)=c
0
,O)=c(O)
In the tables above q is the phenol concentration in the particle,c p the phenol
concentration in the pores,c the phenol concentration in the bulk of liquid phase, Co the initial (or inlet) phenol concentration in batch (or CSTR) systems,r is the radial coordinate in the particle,
I"
p
the particle radius,t is the time, X the
particle porosity,£ the adsorber porosity,o
p
is the phenol diffusivity in the pores,
0 the phenol diffusivity in the particle, t is the space time and -1 average quantities.
refers to
131 1.
c/c
,
o .0 I
\
\ 0 \ "\ 0 \
.5
',0
',0 '
<,
0
..........
--0.....
.......-0--
o
.2
o
2
3
4
tCminJ
Fig. 6. Comparison between experimental results [run 1,batch adsorberJ and predicted values from homogeneous model C---J and pore diffusion modelC---J. b-for each c/c
e. plot e
o
we get,from the experimental curve, t
curve, c-we
versus time,t
exp
and from the simulated 2
exp
Jfrom the slope of this graph we obtain DI/r p and
finally DICor DpJ. The fitting is not good for short times [ref.7J;so the values of DICand DpJ given in Table 2 are the best fitted values in the sense of the least square method. REFERENCES
2 3 4 5 6 7
A.E.Rodrigues,C.A. Costa and F. Almeida,Proc. Water Industry'81,Brighton,UK, June 1981 ,pp.429- 434. H. Spahn and E.U. Schlunder,Chem.Eng.Sci.,30[1975J529-537. L. Westerley and J.C. Turner,Trans.lnst.Chem.Eng.,54[1976J89-94. I. Neretnieks,Chem.Eng.Sci.,31[1976J107-114. J. Villadsen and M. Michelsen,Solution of Differential Equation Models by Polynomial Approximation,Prentice Hall,1978,p.143. A. Hindmarsh,Gear-ordinary differential equation system solver, Lawrence Livermore Laboratory Report UCID-30001,Dec.1974. R. Peel,A. Benedek and C. Crowe.AIChE Journal,27C1981J26-32.