- Email: [email protected]
Effect of feed characteristics on the separation performances of monovalent and divalent salts by electrodialysis
DESALINATION Desalination 1.58(2003) 95-100
ELSEVIER
www.elsevier.com/locate/desal
Effect of feed characteristics on the separation performances of monovalent and divalent salts by electrodialysis N. Kabay”*, M. Ardab, 1. KurucaovalP, E. Ersoza, H. Kahveci”, M. Can”, S. Dal”, S. Kopuzlua, M. Haner”, M. Demircioglu”, M. Yuksel” f,Depar~tment
qf Chemical
Engineering,
Tel/Fax “Department
Faculty
A 90 (232) 3887600;
of Chemistryq
Faculty
qfEngineering, e-mail:
Ege University,
35100
Dmir:
Turkey
[email protected]
of Science, Ege iJniversity.
35100
IzmiK
Turkey
Received 12 December 2002: accepted 30 December 2002
Abstract In this study, separation performance for monovalent salts (NaCI, KCI) and divalent salts (CaCI, MgCl,) was investigated by electrodialysis at pH 6.0-6.5, 4.0 and 2.0 using constant voltage mode of operation. TS-l-10 electrodialysis equipment (Tokuyama) modified with rotameters was employed in experimental studies. The effect of electrical potential, pH and ion valency on separation performance was studied at room temperature using a constant flow rate. The efficiencies of each run were evaluated as specific power consumption with the electrical energy consumed only in stack. Keywords:
Electrodialysis; Monovalent salts; Divalent salts; Desalination; Feed characteristics; Specific power consumption
1. Introduction Water is the most important natural resource in the world since without it life cannot exist and most industries could not operate. The presence of a safe and reliable source of water is thus an -___-
essential prerequisite for the establishment of a stable community. Electrodialysis and reverse osmosis have been widely applied for many years for the production of drinking and process water in order to reduce the salinity. In electrodialysis process, ion exchange membranes are employed to separate ions
*Corresponding author.
00
1I-91
64/03/$-
See
PII:SOOll-9164(03)00439-9
front matter 0 2003 Elsevier Science B.V. All rights reserved
96
M Kabay ef al.
Desalinalion 158 (2003) 95--/W
2. Experimental
from an aqueous solution by means ofan electrical potential applied [l-7]. When a DC power is applied between two electrodes, the cations move to the cathode and anions to the anode passing through negatively charged cation exchange and anion exchange membranes, respectively. Thus, ion concentrations increase in alternate compartments with a simultaneous decrease of ions in other compartments [2,3]. In our previous studies, the separation performance ofNa” ions from NaCl solution has been investigated by electrodialysis [8]. Most recently, we have reported on demineralization by electrodialysis for monovalent salts and we compared the separation performance of specific power consumption of K’ and Na’ ions as a function of potential and flow rate applied [9]. Removal of calcium and magnesium hardness by electrodialysis was reported elsewhere [IO]. In this study, performance and cost comparisons have been carried out for both monovalent salts (NaCI, KCI) and divalent ones (CaCI, and MgCl,) as a function of solution pH and potential applied.
I I
I
i
j
’
:
I 0
A schematic view of the experimental set-up is shown in Fig. 1 [I 01. This equipment contains a stack with 10 pairs ofNeosepta cation exchange (CMX) and anion exchange (AMX) membranes with a membrane area of 1 dm’. Limiting current density measurements were performed for each solution at pH 6.0-6.5, 4.0 and 2.0 prior to parametric studies. During unsteady state runs, outlet metal ion concentrations and conductivities of dilute streams were measured at a certain periods of time. Tests were continued until the current measured dropped to 0.01 A. 3. Results The concentrations of cations (Na’, K’, Ca” and Mg?+) only in dilute compartment were measured at certain time intervals throughout the experimental studies. The results are presented on charts in dimensionless concentrations, defined as the ratio of concentration at any time to the initial concentration.
__i
4 _ J ---p--
‘I I
I I I I I I I I I I
I
Fig. 1. Batch mode operation of electrodialysis system.
N. Kabay et al. /Desalination
The plots of Na’, K’, Ca” and Mg*+ ions at constants pHs are given in Figs. 2-5. It is observed that the operation time becomes shorter at each pH value as the potential increases. On the other hand, it was obtained that the operation time was shorter at pH 2 than at pH 4.0 and 6.0-6.5 when a potential of 5 V was applied. However, the effect
0
-c--
10
20 Time (min)
30
!iv
-3-
IOV
158 (2003)
40
1.0
s
1.0
2
0.8
2
0.8
$
0.6
$ 6
0.4
i
0.2
u
0.0
10 -&-
5
v
20 Time (min)
-a-
30
40
IOV
Cl
10
(u
5v
0
10
lb-
sv
w 0.0 0
10
20 Time (min)
I+
5v
+
Fig. 2. Dimensionless sodium.
concentration
30
40
IOV
vs. time plots for
2 -=
0.6
2 g
0.4
g
0.2
u
0.0
20 Time (min)
30
-cl-
-a-
30
40
IOV
I
.^
.^ ” _ I
I
I
0
10
pL?-
5v
Fig. 3. Dimensionless potassium.
40
IOV
20 Time (min)
”
1.0 9 !d. 0.8
1.0 --_ 2 0.8
3
97
of pH is negligible at 10 V. The effect of cation valencies on separation performance was apparent and operation time for monovalent salts was shorter than the divalent ones, indicating that the transport of divalent ions is lower than that of monovalent ions [ 111.
3
0
95-100
20 Time (min] -c>-
concentration
30
40
IOV
vs. time plots for
5 Kabay et al. ,’Desalination
98
158 (2003) Y5-100
w 0.0 10
0
-c-
5v
20 Time (min) -o-
30
-G--
IOV
3
1.0
5
1.0
2
0.8
2
0.8
.:
0.6
.E 0.6
g = 0.4 Itl g 0.2 o
0.0 0
10
I-+
sv
20 Time (min) -a-
30
sr
0.4
z g
0.2
w
0.0 0
40
IOV
1.0
3
1.0
I!
0.8
e
0.8
E .; 0.6
.;
0.6
;E 0.4 E g 0.2
g c $ ‘0
0.0
U
0
10
*
_;,,:-
Fig. 4. Dimensionless
5V
20 Time (min) 4)
concentration
30
e-
5v
40
IOV
20 Time (min) -a-
5v
30
30
40
IOV
0.4 0.2 0.0
0
40
20 Time (min)
10
u
5
o
IO
0
40
10
20
30
40
Time (min) 10 v
vs. time
-a-
I plots
for
Fig. 5. Dimensionless
magnesium.
calcium.
A cost comparison for monovalent and divalent salts has been established by calculating specific power consumption (SPC) using Eq. (1).
Specific
5v
-o-
IOV
concentration
power consumption
= __!I.-v,,
vs. time
plots
for
(1)
N. Kubay et al. /Desalination IS8 (N03) 95-100
5rf
0.8
0.0
0.0 > 0
2 --o-- !iv
4 PH
6
u
IOV
8
I 0
I
,
2
4
,
6
8
PH -+
5v
u
IOV
Fig. 6. SPC vs. pH plots for monovalent salts.
0.0 0
2 -Q-
5v
4 PH -c-
6 IOV
8
1
0 -a-
I
I
(
2
4 PH
6
5v
-0--
IOV
I 8 ---J
Fig. 7. SPC vs. pH plots for divalent salts.
The calculated SPC values for each set of pH and potential values for monovalent and divalent salts are exhibited in Figs. 6 and 7, respectively. It was found that the SPC becomes higher when a higher potential is applied. The effect of pH on SPC was very remarkable when the pH increased from 2.0 to 4.0. The SPC value was the highest at pH 2 when 5 and 10 V of potentials were applied. The difference in SPC values at pH 4.0 and 6.0-6.5 was not so large, though. It was also found that the SPC values were larger for divaient ions than those for monovalent ions. 4. Conclusions The separation performance of monovalent and divalent ions was obtained as a function of
pH of the feed solution and potential applied in ED system (TS-I-10). The operation time was short when a high potential was applied. Besides, the operation time for monovalent ions was found to be shorter than that for divalent ions. It was found that specific power consumption (SPC) was influenced by pH of the feed solution and potential applied. Acknowledgements The authors wish to thank Tokuyama Corp., Japan for modification of their standard product (TS-1 - 10). We thank Mr. M. Akcay for metal analyses by AAS.
\;. Kabuy et al.
100
Desalination
References III [21
[31
141
[51
[61
R. Rautenbach and R. Albrecht, Membrane Processes, Wiley, New York, 1989, pp.344350. H. Strathmann, Membrane Handbook, W.S. Winston Ho and K.K Sirkar, Eds., Van Nostrand Reinhold,New York, 1992, pp.2 18-262. H. Strathmann, Application of ion-exchange membranes in industrial processes, Macromol. Chem. Macromol. Symp., 70171 (1993) 363-377. G. Kraaijeveld, V. Sumberova, S. Kuindersma and H. Wesselingh, Modelling electrodialysis using the Maxwell-Stefan description, Chem. Eng. J., 57 (1995) 163-176. J.H. Choi, S.H. Lee and S.H. Moon, Effectsofelectrolytes on the transport phenomena in a cation exchange membrane, J. Colloid Interface Sci., 238 (2001) 188195. E.G. Lee, S.H. Moon,Y.K. Chang, 1.K. Yooand H.N. Chang, Lactic acid recovery using two-stage electrodialysis and its modeling, J. Membr. Sci., 145 (1998) 53-66.
158 (20031 95-l (10
[71
[81
[91
[lOI
[Ill [I21
H.J. Lee, F. Sarfert, H. Strathmann and S.H. Moon. Designing of an electrodialysis desalination plant. Desalination, 142 (2002) 267-286. M. Demircioglu, N. Kabay, E. Ersoz, I. Kurucaovali, C. Safak andN.Gizli, Cost comparison and efficiency modeling in the electrodialysis of brine, Desalination, 136 (2001) 317-323. M. Demircioglu, N. Kabay, I. Kurucaovah and E. Ersoz, Demineralization by electrodialysis (ED)separation performance and cost comparison for monovalent salts, Desalination, 153 (2002) 329-333. N. Kabay, M. Demircioglu, E. Ersoz and 1. Kurucaovali, Removal of calcium and magnesium hardness by electrodialysis, Desalination, 149 (2002) 343-349, Tokuyama Corp., Neosepta-Ion Exchange Membranes, information brochure, Tokyo, Japan, 1999. G. Saracco, Transport properties of monovalent-ion-permselective membranes, Chem. Eng. Sci., 52 ( 1997) 3019.-303 I.
ELSEVIER
www.elsevier.com/locate/desal
Effect of feed characteristics on the separation performances of monovalent and divalent salts by electrodialysis N. Kabay”*, M. Ardab, 1. KurucaovalP, E. Ersoza, H. Kahveci”, M. Can”, S. Dal”, S. Kopuzlua, M. Haner”, M. Demircioglu”, M. Yuksel” f,Depar~tment
qf Chemical
Engineering,
Tel/Fax “Department
Faculty
A 90 (232) 3887600;
of Chemistryq
Faculty
qfEngineering, e-mail:
Ege University,
35100
Dmir:
Turkey
[email protected]
of Science, Ege iJniversity.
35100
IzmiK
Turkey
Received 12 December 2002: accepted 30 December 2002
Abstract In this study, separation performance for monovalent salts (NaCI, KCI) and divalent salts (CaCI, MgCl,) was investigated by electrodialysis at pH 6.0-6.5, 4.0 and 2.0 using constant voltage mode of operation. TS-l-10 electrodialysis equipment (Tokuyama) modified with rotameters was employed in experimental studies. The effect of electrical potential, pH and ion valency on separation performance was studied at room temperature using a constant flow rate. The efficiencies of each run were evaluated as specific power consumption with the electrical energy consumed only in stack. Keywords:
Electrodialysis; Monovalent salts; Divalent salts; Desalination; Feed characteristics; Specific power consumption
1. Introduction Water is the most important natural resource in the world since without it life cannot exist and most industries could not operate. The presence of a safe and reliable source of water is thus an -___-
essential prerequisite for the establishment of a stable community. Electrodialysis and reverse osmosis have been widely applied for many years for the production of drinking and process water in order to reduce the salinity. In electrodialysis process, ion exchange membranes are employed to separate ions
*Corresponding author.
00
1I-91
64/03/$-
See
PII:SOOll-9164(03)00439-9
front matter 0 2003 Elsevier Science B.V. All rights reserved
96
M Kabay ef al.
Desalinalion 158 (2003) 95--/W
2. Experimental
from an aqueous solution by means ofan electrical potential applied [l-7]. When a DC power is applied between two electrodes, the cations move to the cathode and anions to the anode passing through negatively charged cation exchange and anion exchange membranes, respectively. Thus, ion concentrations increase in alternate compartments with a simultaneous decrease of ions in other compartments [2,3]. In our previous studies, the separation performance ofNa” ions from NaCl solution has been investigated by electrodialysis [8]. Most recently, we have reported on demineralization by electrodialysis for monovalent salts and we compared the separation performance of specific power consumption of K’ and Na’ ions as a function of potential and flow rate applied [9]. Removal of calcium and magnesium hardness by electrodialysis was reported elsewhere [IO]. In this study, performance and cost comparisons have been carried out for both monovalent salts (NaCI, KCI) and divalent ones (CaCI, and MgCl,) as a function of solution pH and potential applied.
I I
I
i
j
’
:
I 0
A schematic view of the experimental set-up is shown in Fig. 1 [I 01. This equipment contains a stack with 10 pairs ofNeosepta cation exchange (CMX) and anion exchange (AMX) membranes with a membrane area of 1 dm’. Limiting current density measurements were performed for each solution at pH 6.0-6.5, 4.0 and 2.0 prior to parametric studies. During unsteady state runs, outlet metal ion concentrations and conductivities of dilute streams were measured at a certain periods of time. Tests were continued until the current measured dropped to 0.01 A. 3. Results The concentrations of cations (Na’, K’, Ca” and Mg?+) only in dilute compartment were measured at certain time intervals throughout the experimental studies. The results are presented on charts in dimensionless concentrations, defined as the ratio of concentration at any time to the initial concentration.
__i
4 _ J ---p--
‘I I
I I I I I I I I I I
I
Fig. 1. Batch mode operation of electrodialysis system.
N. Kabay et al. /Desalination
The plots of Na’, K’, Ca” and Mg*+ ions at constants pHs are given in Figs. 2-5. It is observed that the operation time becomes shorter at each pH value as the potential increases. On the other hand, it was obtained that the operation time was shorter at pH 2 than at pH 4.0 and 6.0-6.5 when a potential of 5 V was applied. However, the effect
0
-c--
10
20 Time (min)
30
!iv
-3-
IOV
158 (2003)
40
1.0
s
1.0
2
0.8
2
0.8
$
0.6
$ 6
0.4
i
0.2
u
0.0
10 -&-
5
v
20 Time (min)
-a-
30
40
IOV
Cl
10
(u
5v
0
10
lb-
sv
w 0.0 0
10
20 Time (min)
I+
5v
+
Fig. 2. Dimensionless sodium.
concentration
30
40
IOV
vs. time plots for
2 -=
0.6
2 g
0.4
g
0.2
u
0.0
20 Time (min)
30
-cl-
-a-
30
40
IOV
I
.^
.^ ” _ I
I
I
0
10
pL?-
5v
Fig. 3. Dimensionless potassium.
40
IOV
20 Time (min)
”
1.0 9 !d. 0.8
1.0 --_ 2 0.8
3
97
of pH is negligible at 10 V. The effect of cation valencies on separation performance was apparent and operation time for monovalent salts was shorter than the divalent ones, indicating that the transport of divalent ions is lower than that of monovalent ions [ 111.
3
0
95-100
20 Time (min] -c>-
concentration
30
40
IOV
vs. time plots for
5 Kabay et al. ,’Desalination
98
158 (2003) Y5-100
w 0.0 10
0
-c-
5v
20 Time (min) -o-
30
-G--
IOV
3
1.0
5
1.0
2
0.8
2
0.8
.:
0.6
.E 0.6
g = 0.4 Itl g 0.2 o
0.0 0
10
I-+
sv
20 Time (min) -a-
30
sr
0.4
z g
0.2
w
0.0 0
40
IOV
1.0
3
1.0
I!
0.8
e
0.8
E .; 0.6
.;
0.6
;E 0.4 E g 0.2
g c $ ‘0
0.0
U
0
10
*
_;,,:-
Fig. 4. Dimensionless
5V
20 Time (min) 4)
concentration
30
e-
5v
40
IOV
20 Time (min) -a-
5v
30
30
40
IOV
0.4 0.2 0.0
0
40
20 Time (min)
10
u
5
o
IO
0
40
10
20
30
40
Time (min) 10 v
vs. time
-a-
I plots
for
Fig. 5. Dimensionless
magnesium.
calcium.
A cost comparison for monovalent and divalent salts has been established by calculating specific power consumption (SPC) using Eq. (1).
Specific
5v
-o-
IOV
concentration
power consumption
= __!I.-v,,
vs. time
plots
for
(1)
N. Kubay et al. /Desalination IS8 (N03) 95-100
5rf
0.8
0.0
0.0 > 0
2 --o-- !iv
4 PH
6
u
IOV
8
I 0
I
,
2
4
,
6
8
PH -+
5v
u
IOV
Fig. 6. SPC vs. pH plots for monovalent salts.
0.0 0
2 -Q-
5v
4 PH -c-
6 IOV
8
1
0 -a-
I
I
(
2
4 PH
6
5v
-0--
IOV
I 8 ---J
Fig. 7. SPC vs. pH plots for divalent salts.
The calculated SPC values for each set of pH and potential values for monovalent and divalent salts are exhibited in Figs. 6 and 7, respectively. It was found that the SPC becomes higher when a higher potential is applied. The effect of pH on SPC was very remarkable when the pH increased from 2.0 to 4.0. The SPC value was the highest at pH 2 when 5 and 10 V of potentials were applied. The difference in SPC values at pH 4.0 and 6.0-6.5 was not so large, though. It was also found that the SPC values were larger for divaient ions than those for monovalent ions. 4. Conclusions The separation performance of monovalent and divalent ions was obtained as a function of
pH of the feed solution and potential applied in ED system (TS-I-10). The operation time was short when a high potential was applied. Besides, the operation time for monovalent ions was found to be shorter than that for divalent ions. It was found that specific power consumption (SPC) was influenced by pH of the feed solution and potential applied. Acknowledgements The authors wish to thank Tokuyama Corp., Japan for modification of their standard product (TS-1 - 10). We thank Mr. M. Akcay for metal analyses by AAS.
\;. Kabuy et al.
100
Desalination
References III [21
[31
141
[51
[61
R. Rautenbach and R. Albrecht, Membrane Processes, Wiley, New York, 1989, pp.344350. H. Strathmann, Membrane Handbook, W.S. Winston Ho and K.K Sirkar, Eds., Van Nostrand Reinhold,New York, 1992, pp.2 18-262. H. Strathmann, Application of ion-exchange membranes in industrial processes, Macromol. Chem. Macromol. Symp., 70171 (1993) 363-377. G. Kraaijeveld, V. Sumberova, S. Kuindersma and H. Wesselingh, Modelling electrodialysis using the Maxwell-Stefan description, Chem. Eng. J., 57 (1995) 163-176. J.H. Choi, S.H. Lee and S.H. Moon, Effectsofelectrolytes on the transport phenomena in a cation exchange membrane, J. Colloid Interface Sci., 238 (2001) 188195. E.G. Lee, S.H. Moon,Y.K. Chang, 1.K. Yooand H.N. Chang, Lactic acid recovery using two-stage electrodialysis and its modeling, J. Membr. Sci., 145 (1998) 53-66.
158 (20031 95-l (10
[71
[81
[91
[lOI
[Ill [I21
H.J. Lee, F. Sarfert, H. Strathmann and S.H. Moon. Designing of an electrodialysis desalination plant. Desalination, 142 (2002) 267-286. M. Demircioglu, N. Kabay, E. Ersoz, I. Kurucaovali, C. Safak andN.Gizli, Cost comparison and efficiency modeling in the electrodialysis of brine, Desalination, 136 (2001) 317-323. M. Demircioglu, N. Kabay, I. Kurucaovah and E. Ersoz, Demineralization by electrodialysis (ED)separation performance and cost comparison for monovalent salts, Desalination, 153 (2002) 329-333. N. Kabay, M. Demircioglu, E. Ersoz and 1. Kurucaovali, Removal of calcium and magnesium hardness by electrodialysis, Desalination, 149 (2002) 343-349, Tokuyama Corp., Neosepta-Ion Exchange Membranes, information brochure, Tokyo, Japan, 1999. G. Saracco, Transport properties of monovalent-ion-permselective membranes, Chem. Eng. Sci., 52 ( 1997) 3019.-303 I.