- Email: [email protected]
Relation between mass transfer and operation parameters in the electrodialysis recovery of acetic acid
DESALINATION Desalination 154 (2003) 147-152
ELSEVIER
www.elsevier.com/locate/desal
Relation between mass transfer and operation parameters in the electrodialysis recovery of acetic acid Lixin Yu*, Tao Lin, Qingfeng Guo, and Jihua Hao Department of Chemical Engineering, Tsinghua University, Beijing, 100084, P.R. China Fax +86 (10) 6277-0304; email: [email protected] Received 20 January 2002; accepted 4 September2002
Abstract The recoveryof acetic acid from dilute wastewater by means of bipolar membrane electrodialysis is studied in more detail. The current efficiencyof the electrodialysis recoveryof acetic acid from dilute wastewater is related to the current density and other operation parameters. There exists a highest value of current efficiency at optimal current density. The highest concentration of recovered acid is also related to current efficiency. The experimental data are analyzed on a theoretical basis. Keywords: Electrodialysis; Bipolar membrane; Acetic acid; Recovery
1. Introduction Dilute wastewater containing acetic acid is generated in many chemical processes. Some methods have been tried to recover these acids [1-9]. We have also studied the feasibility of the recovery of acetic acid using bipolar membrane electrodialysis from dilute wastewater in a previous paper [10]. But there remain some problems which have not been fully understood, such as the accurate concentration of acetic acid in the finally treated wastewater, the optimal current density, and the highest concentration of *Corresponding author.
the recovered acetic acid. In this paper these problems have been studied in detail.
2. Experiment The experiment scheme is the same as described in a previous paper and the principle of recovery is shown in Fig. 1 [10]. The acetic ions are transferred through the anion-exchange membranes from the wastewater to the concentrated solution. Then the hydroxyl ions generated from the bipolar membranes neutralize the hydrogen ions left in the wastewater. The size of each membrane is 10 cm x 20 cm, with an
0011-9164/03/$- See front matter © 2003 Elsevier Science B.V. All rights reserved PII: S001 I - 9 1 6 4 ( 0 3 ) 0 0 2 1 6 - 9
148
L. Yu et al. /Desalination 154 (2003) 147-152
water
concentrated aceti I acid
diltllt"
Col ~2¢:1h'II[¢'.[
SO'tLliOIt dmmber
,M"ltl I it )11
chamber
water A
concentrated acetic acid
~. h i¢ solt l m chamber
i ii
o.-!
()11" m.
¢~m~:cntralt~ solulion i chamber i i
iilb
w
cathode
A,Ot I
I I.O
o.-
it,
T
........i j" mo
mo
.... 4-
i!
anode
[ i
i
.................a1,¢~ '~ I 1,O
}
i ii
!-:?
,L
dilute wasteg-ater
.'..........
!i ,,. ........ i~ ........
tt,O i i l l O
ii
?H,o
i,
ii i~,¢~ ii
.A!" ii
4--
" i i? ,
~-"
i, ii 4--
dilute wasle~aler
Fig. 1. Mass transfer in recovery process. Solid arrows: desired mass transfer; dotted arrows: undesired mass transfer. Table 1 Characteristics of anion-exchange membranes
Thickness, mm Ion-exchange capacity, meq/g dry membrane Water content, % Electric resistance, f~ cm2 Burst strength, 10~Pa
Type A
Type B
0.19 1.8
0.18 1.8
22 4.5 >2.0
24 3.5 >2.0
effective area of 7 cm x 14 cm. We have assembled two membrane units in the experiment module. The gap between the two adjacent membranes is 1.5 mm and polypropylene nets are placed in each gap. The linear velocity in the gap can reach 15 cm/s at most. The highest current available for this experiment apparatus is 10 A, corresponding to a current density of 100 mA/ cm 2. The bipolar membranes used in this experiment are BP-I membranes which are produced by Tokuyama and the anion exchange membranes are from Beijing Well Resource Co., whose characteristics are listed in Table 1.
In order to know the accurate content of acetic acid in the final treated water, we used an ion chromotographer. The column in the ion chromotographer was the IC-A1 type and the carrier phase was 1 mM potassium hydrogen phthalate solution. 3. Theoretical analysis of mass transfer in the recovery process The mass transfer in this recovering process includes the transfer o f molecules (water molecules and acetic acid molecules) and ions (hydrogen ions, hydroxyl ions and acetic ions) and can be catalogued as desired transfer and undesired transfer. The first one of the desired mass transfer is that of acetic ions through the anion-exchange membranes from the dilute solution chamber to the concentrated solution chamber driven by electric force. The other desired mass transfer is that of the hydroxyl ions, which are generated by the bipolar membranes, and which then take the place of acetic ions in the dilute solution chambers. The third desired transfer is the transfer of water from both sides o f the bipolar
L. Yu et al. / Desalination 154 (2003) 147-152
membrane into the interface of the anionexchange layer and cation-exchange layer of the bipolar membrane. This amount of water will provide the source for splitting to generate hydrogen ions and hydroxyl ions. The last desired transfer is that of hydrogen ions, which are generated inside bipolar membranes and are transported out to the concentrated solution chamber to form acetic acid of higher concentration. The first undesired mass transfer is that of acetic acid molecules driven by the concentration difference between the concentrated solution chamber and the dilute solution chamber. As discussed before [10], if there is no electric field applied, the acetic acid molecules can diffuse through both the bipolar membranes and the anion-exchange membranes. But under an electric field, acetic acid molecules can only pass through the anion-exchange membrane. They could not pass through the bipolar membranes because the acetic acid molecules reaching to the interface of two exchange layers inside bipolar membrane would be split into hydrogen ions and acetic ions. This splitting of acetic acid will not affect the technical aspect of the recovery, but will decrease the current efficiency of the process. The effect of concentration difference on current efficiency can be seen in Fig. 2. When sodium hydroxide is used in the concentrated solution chamber instead of acetic acid, the instant current efficiency is much higher. The second undesired mass transfer is that of hydroxyl ions from the dilute chamber to the concentrated solution chamber. This is more serious when the recovery is almost complete and the ratio of hydroxyl ions to acetic ions is relatively higher than that at the initial stage of recovery (Fig. 2). This transfer of hydroxyl ions will decrease both the current efficiency and the concentration of recovered acid. Another undesired transfer is that of water which is transported through the anion exchange membranes accompanying the transported acetic
ad ~D
_=
149
0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0,1 0 0
0,2
0.4
O. 6
0.8
1
Removal ratio
Fig. 2. Instant current efficiency vs. removal ratio of HAc. xO: sodium hydroxide solution in a concentrated solution chamber; A: acetic acid solution in a concentratedsolution chamber. ions and hydroxyl ions. This transfer of water will finally decrease the concentration of the recovered acetic acid. 4. Results and discussion
4.1. Concentration o f acetic acid in the final treated wastewater By using an ion chromotographer, we can accurately know that the final content can be reduced to as low as 10 ppm. Before this study, only pH had been measured to monitor the terminal of the recovery process. Here we can see that the ion chromotographer is a more accurate method. Some typical experimental data are listed in Table 2. 4.2. Current efficiency vs current density Current efficiency is influenced by current density, flow condition, and the concentration difference between the concentrated and dilute solution chambers. From Fig. 3 we can see that the current efficiency has a maximum value at an optimum current density. Interesting enough, we have determined the zero efficiency point. The current efficiency is calculated according to the following equations:
150
L. Yu et al. / Desalination 154 (2003) 147-152
Table 2 Acetic acid content in the final treated wastewater Batch
Initial volume of wastewater, ml Initial content of acid in wastewater, wt% Initial content of acetic acid in concentrated solution chamber, wt%a Initial volume of concentrated acid, ml Time for pH of wastewater to reach 7, min Final content of Ac- in treated water, ppm Type of anion-exchange membrane Operation current, A Current density, mA/cm2 Average voltage (total), V Average voltage drop per cell, V Average current efficiency, %
1
2
3
4
5
500 0.2 15
500 0.2 15
500 0.2 15
500 500 2.0 2.0 0.5 M NaOH 0.5 M NaOH
500 47 25 A 2 20.4 14 3-4 30
500 51 36 A 2 20.4 32.5 12-13 26
500 40 10 B 2 20 42 15-17 35
500 94 89 B 3 30.6 27 8-9 39
500 117.5 47 A 3 30.6 60 24-52 42
aFinai concentration of acetic acid is almost the same as the initial concentration because only small amounts of acetic acid were transferred during each experiment. 0.35
~
0.3 025
0.3
i 0.2
0.2
0.15 0,1 O 0.05
0
0 0
10
20
30
40
Current density (mA/cm 2)
Fig. 3. Current efficiency vs, current density. mtF Ear e -
°if 0,4
Nlt
A mF Ei,~ = lira zxt-o N 1 A t where Eave and Eins are the average and instant current efficiency, respectively; m, is the mole amount o f acid transported at time period t; F is the Faraday constant; N is the number o f membrane units (here N=2); I is the operation
I 2
I 4
i 6
I 8
I
I
10
12
14
Linear velocity (cm/s)
Fig. 4. Current efficiency vs. flow rate.
current; Am is the mole amount o f acid transported during time period At. From the above theoretical analysis, we can see the reason to this E vs. I change. At high current densities, the concentration polarization in dilute cell will occur, leading to the increase o f undesired mass transfer o f hydroxyl ions. This will finally decrease the current efficiency. Theoretically the molecular diffusion o f acetic acid across the ion-exchange membranes will only depend on the concentration difference. Thus its flux is a constant. At very low current density, when the transfer flux o f acetic ions
L. Yu et al. / Desalination 154 (2003) 147-152
driven by electric force is equivalent to that of molecular diffusion, the overall current efficiency will become low and even reach 0. So the higher the concentration in a concentrated solution chamber is, or the higher the diffusion coefficient of acetic acid in the membrane is, the higher the current density at zero efficient point will be. The concentration polarization can be indirectly verified by the data in Fig. 4. When increasing the flow rate of the dilute wastewater, the current efficiency is also raised. 4. 3. Highest concentration of recovered acetic acid
The concentration of the recovered acetic acid is effected by the following factors such as current efficiency, water transported with the ions, water transport driven by osmosis pressure, and so on. The competition of hydroxyl ions with acetic ions will lead to low current efficiency (Fig. 2) and also lead to low concentration of recovered acetic acid. These hydroxyl ions combine with hydrogen ions from bipolar membrane and the formed water will dilute the recovered acetic acid solution. If the highest current efficiency is 40% in the present case, the highest acid concentration could be calculated as 70% (wt). When acetic, hydroxyl and hydrogen ions are transported, water will accompany their transport. This will further decrease the concentration of the acid. But the actual number of water molecules per acetic acid molecule is difficult to predict theoretically. Especially when there existing concentration difference across the membrane, water will also transport through the membrane driven by the osmosis pressure. This is also a factor which might influence the final concentration of the recovered acid. This amount of transport by osmotic pressure is also difficult to estimate. For these reasons, it is more practical to calculate through experiments the number of
151
water molecules transported with each acetic acid molecule. In the present study, we have determined that the number o f water molecules accompanying the transport of acetic acid is around 12.
5. Conclusions
The current efficiency in the bipolar membrane electrodialysis process for the recovery of acetic acid from dilute wastewater is theoretically analyzed and experimentally tested. The main factors are current density and concentration of the recovered acetic acid. There is a highest current efficiency for each operation condition. By the ion chromotographer method, we can verify the almost complete removal of acetic acid from the wastewater. The concentration of recovered acetic acid is related to many parameters and needs to be determined by experiments.
References
[1] B. Saha, S.P. Chopadeand S.M.Mahajani,Recovery of dilute acetic acid through esterification in a reactive distillation column. Catalysis Today, 60(1) (2000) 147-157. [2] M.N.Ingale and V.V. Mahajani, Recovery of acetic acid and propionic acid from aqueous waste stream. Sep. Technol., 4(2) (1994) 123-126. [3] S. Kurum and Z. Fonyo, Comparative study of recoveringacetic acid with energy integratedschemes. Appl. ThermalEng., 16(6) (1996) 487--495. [4] F.L.D. Cloete and A.P. Marais, Recovery of very dilute acetic acid using ion exchange. Ind. Eng. Chem. Res., 34 (7) (1995) 2464-2467. [5] I. Lau and G. Hayward, Recovery of fatty acids by immobilizedsolventextraction.Can. J. Chem. Eng., 68(3) (1990) 376-381. [6] D.J.O'Brien and G.E. Senske,Separationand recovery of low molecularweight organic acids by emulsion liquidmembranes.Sep. Sci.Technol.,24(9-10) (1989) 617-628.
152
L. Yu et al. / Desalination 154 (2003) 147-152
[7] M.N. Ingale and V.V. Mahajani, Recovery of carboxylic acids, C2--C6, from an aqueous waste stream using tributyiphosphate(TBP): effect of presence of inorganic acids and the ir sodium salts. Sep. Technol., 6(1) (1996) 1-7. [8] H. Reisinger and C.J. King, Extraction and sorption of acetic acid at pH above pKa to form calcium magnesium acetate. Ind. Eng. Chem. Res., 34(3) (1995) 845-852.
[9] Y. Li, H. Tian and X. Lu, Recovering acetic acid from waste water from methacrylic acid production by isobutyraldehyde oxidation. Petrochem. Technol., 26(4) (1997) 245-248. [10] L. Yu, Q. Guo, J. Hao and W. Jiang, Recovery of acetic acid from dilute wastewater by means of bipolar membrane electrodialysis. Desalination, 129 (2000) 283-288.
ELSEVIER
www.elsevier.com/locate/desal
Relation between mass transfer and operation parameters in the electrodialysis recovery of acetic acid Lixin Yu*, Tao Lin, Qingfeng Guo, and Jihua Hao Department of Chemical Engineering, Tsinghua University, Beijing, 100084, P.R. China Fax +86 (10) 6277-0304; email: [email protected] Received 20 January 2002; accepted 4 September2002
Abstract The recoveryof acetic acid from dilute wastewater by means of bipolar membrane electrodialysis is studied in more detail. The current efficiencyof the electrodialysis recoveryof acetic acid from dilute wastewater is related to the current density and other operation parameters. There exists a highest value of current efficiency at optimal current density. The highest concentration of recovered acid is also related to current efficiency. The experimental data are analyzed on a theoretical basis. Keywords: Electrodialysis; Bipolar membrane; Acetic acid; Recovery
1. Introduction Dilute wastewater containing acetic acid is generated in many chemical processes. Some methods have been tried to recover these acids [1-9]. We have also studied the feasibility of the recovery of acetic acid using bipolar membrane electrodialysis from dilute wastewater in a previous paper [10]. But there remain some problems which have not been fully understood, such as the accurate concentration of acetic acid in the finally treated wastewater, the optimal current density, and the highest concentration of *Corresponding author.
the recovered acetic acid. In this paper these problems have been studied in detail.
2. Experiment The experiment scheme is the same as described in a previous paper and the principle of recovery is shown in Fig. 1 [10]. The acetic ions are transferred through the anion-exchange membranes from the wastewater to the concentrated solution. Then the hydroxyl ions generated from the bipolar membranes neutralize the hydrogen ions left in the wastewater. The size of each membrane is 10 cm x 20 cm, with an
0011-9164/03/$- See front matter © 2003 Elsevier Science B.V. All rights reserved PII: S001 I - 9 1 6 4 ( 0 3 ) 0 0 2 1 6 - 9
148
L. Yu et al. /Desalination 154 (2003) 147-152
water
concentrated aceti I acid
diltllt"
Col ~2¢:1h'II[¢'.[
SO'tLliOIt dmmber
,M"ltl I it )11
chamber
water A
concentrated acetic acid
~. h i¢ solt l m chamber
i ii
o.-!
()11" m.
¢~m~:cntralt~ solulion i chamber i i
iilb
w
cathode
A,Ot I
I I.O
o.-
it,
T
........i j" mo
mo
.... 4-
i!
anode
[ i
i
.................a1,¢~ '~ I 1,O
}
i ii
!-:?
,L
dilute wasteg-ater
.'..........
!i ,,. ........ i~ ........
tt,O i i l l O
ii
?H,o
i,
ii i~,¢~ ii
.A!" ii
4--
" i i? ,
~-"
i, ii 4--
dilute wasle~aler
Fig. 1. Mass transfer in recovery process. Solid arrows: desired mass transfer; dotted arrows: undesired mass transfer. Table 1 Characteristics of anion-exchange membranes
Thickness, mm Ion-exchange capacity, meq/g dry membrane Water content, % Electric resistance, f~ cm2 Burst strength, 10~Pa
Type A
Type B
0.19 1.8
0.18 1.8
22 4.5 >2.0
24 3.5 >2.0
effective area of 7 cm x 14 cm. We have assembled two membrane units in the experiment module. The gap between the two adjacent membranes is 1.5 mm and polypropylene nets are placed in each gap. The linear velocity in the gap can reach 15 cm/s at most. The highest current available for this experiment apparatus is 10 A, corresponding to a current density of 100 mA/ cm 2. The bipolar membranes used in this experiment are BP-I membranes which are produced by Tokuyama and the anion exchange membranes are from Beijing Well Resource Co., whose characteristics are listed in Table 1.
In order to know the accurate content of acetic acid in the final treated water, we used an ion chromotographer. The column in the ion chromotographer was the IC-A1 type and the carrier phase was 1 mM potassium hydrogen phthalate solution. 3. Theoretical analysis of mass transfer in the recovery process The mass transfer in this recovering process includes the transfer o f molecules (water molecules and acetic acid molecules) and ions (hydrogen ions, hydroxyl ions and acetic ions) and can be catalogued as desired transfer and undesired transfer. The first one of the desired mass transfer is that of acetic ions through the anion-exchange membranes from the dilute solution chamber to the concentrated solution chamber driven by electric force. The other desired mass transfer is that of the hydroxyl ions, which are generated by the bipolar membranes, and which then take the place of acetic ions in the dilute solution chambers. The third desired transfer is the transfer of water from both sides o f the bipolar
L. Yu et al. / Desalination 154 (2003) 147-152
membrane into the interface of the anionexchange layer and cation-exchange layer of the bipolar membrane. This amount of water will provide the source for splitting to generate hydrogen ions and hydroxyl ions. The last desired transfer is that of hydrogen ions, which are generated inside bipolar membranes and are transported out to the concentrated solution chamber to form acetic acid of higher concentration. The first undesired mass transfer is that of acetic acid molecules driven by the concentration difference between the concentrated solution chamber and the dilute solution chamber. As discussed before [10], if there is no electric field applied, the acetic acid molecules can diffuse through both the bipolar membranes and the anion-exchange membranes. But under an electric field, acetic acid molecules can only pass through the anion-exchange membrane. They could not pass through the bipolar membranes because the acetic acid molecules reaching to the interface of two exchange layers inside bipolar membrane would be split into hydrogen ions and acetic ions. This splitting of acetic acid will not affect the technical aspect of the recovery, but will decrease the current efficiency of the process. The effect of concentration difference on current efficiency can be seen in Fig. 2. When sodium hydroxide is used in the concentrated solution chamber instead of acetic acid, the instant current efficiency is much higher. The second undesired mass transfer is that of hydroxyl ions from the dilute chamber to the concentrated solution chamber. This is more serious when the recovery is almost complete and the ratio of hydroxyl ions to acetic ions is relatively higher than that at the initial stage of recovery (Fig. 2). This transfer of hydroxyl ions will decrease both the current efficiency and the concentration of recovered acid. Another undesired transfer is that of water which is transported through the anion exchange membranes accompanying the transported acetic
ad ~D
_=
149
0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0,1 0 0
0,2
0.4
O. 6
0.8
1
Removal ratio
Fig. 2. Instant current efficiency vs. removal ratio of HAc. xO: sodium hydroxide solution in a concentrated solution chamber; A: acetic acid solution in a concentratedsolution chamber. ions and hydroxyl ions. This transfer of water will finally decrease the concentration of the recovered acetic acid. 4. Results and discussion
4.1. Concentration o f acetic acid in the final treated wastewater By using an ion chromotographer, we can accurately know that the final content can be reduced to as low as 10 ppm. Before this study, only pH had been measured to monitor the terminal of the recovery process. Here we can see that the ion chromotographer is a more accurate method. Some typical experimental data are listed in Table 2. 4.2. Current efficiency vs current density Current efficiency is influenced by current density, flow condition, and the concentration difference between the concentrated and dilute solution chambers. From Fig. 3 we can see that the current efficiency has a maximum value at an optimum current density. Interesting enough, we have determined the zero efficiency point. The current efficiency is calculated according to the following equations:
150
L. Yu et al. / Desalination 154 (2003) 147-152
Table 2 Acetic acid content in the final treated wastewater Batch
Initial volume of wastewater, ml Initial content of acid in wastewater, wt% Initial content of acetic acid in concentrated solution chamber, wt%a Initial volume of concentrated acid, ml Time for pH of wastewater to reach 7, min Final content of Ac- in treated water, ppm Type of anion-exchange membrane Operation current, A Current density, mA/cm2 Average voltage (total), V Average voltage drop per cell, V Average current efficiency, %
1
2
3
4
5
500 0.2 15
500 0.2 15
500 0.2 15
500 500 2.0 2.0 0.5 M NaOH 0.5 M NaOH
500 47 25 A 2 20.4 14 3-4 30
500 51 36 A 2 20.4 32.5 12-13 26
500 40 10 B 2 20 42 15-17 35
500 94 89 B 3 30.6 27 8-9 39
500 117.5 47 A 3 30.6 60 24-52 42
aFinai concentration of acetic acid is almost the same as the initial concentration because only small amounts of acetic acid were transferred during each experiment. 0.35
~
0.3 025
0.3
i 0.2
0.2
0.15 0,1 O 0.05
0
0 0
10
20
30
40
Current density (mA/cm 2)
Fig. 3. Current efficiency vs, current density. mtF Ear e -
°if 0,4
Nlt
A mF Ei,~ = lira zxt-o N 1 A t where Eave and Eins are the average and instant current efficiency, respectively; m, is the mole amount o f acid transported at time period t; F is the Faraday constant; N is the number o f membrane units (here N=2); I is the operation
I 2
I 4
i 6
I 8
I
I
10
12
14
Linear velocity (cm/s)
Fig. 4. Current efficiency vs. flow rate.
current; Am is the mole amount o f acid transported during time period At. From the above theoretical analysis, we can see the reason to this E vs. I change. At high current densities, the concentration polarization in dilute cell will occur, leading to the increase o f undesired mass transfer o f hydroxyl ions. This will finally decrease the current efficiency. Theoretically the molecular diffusion o f acetic acid across the ion-exchange membranes will only depend on the concentration difference. Thus its flux is a constant. At very low current density, when the transfer flux o f acetic ions
L. Yu et al. / Desalination 154 (2003) 147-152
driven by electric force is equivalent to that of molecular diffusion, the overall current efficiency will become low and even reach 0. So the higher the concentration in a concentrated solution chamber is, or the higher the diffusion coefficient of acetic acid in the membrane is, the higher the current density at zero efficient point will be. The concentration polarization can be indirectly verified by the data in Fig. 4. When increasing the flow rate of the dilute wastewater, the current efficiency is also raised. 4. 3. Highest concentration of recovered acetic acid
The concentration of the recovered acetic acid is effected by the following factors such as current efficiency, water transported with the ions, water transport driven by osmosis pressure, and so on. The competition of hydroxyl ions with acetic ions will lead to low current efficiency (Fig. 2) and also lead to low concentration of recovered acetic acid. These hydroxyl ions combine with hydrogen ions from bipolar membrane and the formed water will dilute the recovered acetic acid solution. If the highest current efficiency is 40% in the present case, the highest acid concentration could be calculated as 70% (wt). When acetic, hydroxyl and hydrogen ions are transported, water will accompany their transport. This will further decrease the concentration of the acid. But the actual number of water molecules per acetic acid molecule is difficult to predict theoretically. Especially when there existing concentration difference across the membrane, water will also transport through the membrane driven by the osmosis pressure. This is also a factor which might influence the final concentration of the recovered acid. This amount of transport by osmotic pressure is also difficult to estimate. For these reasons, it is more practical to calculate through experiments the number of
151
water molecules transported with each acetic acid molecule. In the present study, we have determined that the number o f water molecules accompanying the transport of acetic acid is around 12.
5. Conclusions
The current efficiency in the bipolar membrane electrodialysis process for the recovery of acetic acid from dilute wastewater is theoretically analyzed and experimentally tested. The main factors are current density and concentration of the recovered acetic acid. There is a highest current efficiency for each operation condition. By the ion chromotographer method, we can verify the almost complete removal of acetic acid from the wastewater. The concentration of recovered acetic acid is related to many parameters and needs to be determined by experiments.
References
[1] B. Saha, S.P. Chopadeand S.M.Mahajani,Recovery of dilute acetic acid through esterification in a reactive distillation column. Catalysis Today, 60(1) (2000) 147-157. [2] M.N.Ingale and V.V. Mahajani, Recovery of acetic acid and propionic acid from aqueous waste stream. Sep. Technol., 4(2) (1994) 123-126. [3] S. Kurum and Z. Fonyo, Comparative study of recoveringacetic acid with energy integratedschemes. Appl. ThermalEng., 16(6) (1996) 487--495. [4] F.L.D. Cloete and A.P. Marais, Recovery of very dilute acetic acid using ion exchange. Ind. Eng. Chem. Res., 34 (7) (1995) 2464-2467. [5] I. Lau and G. Hayward, Recovery of fatty acids by immobilizedsolventextraction.Can. J. Chem. Eng., 68(3) (1990) 376-381. [6] D.J.O'Brien and G.E. Senske,Separationand recovery of low molecularweight organic acids by emulsion liquidmembranes.Sep. Sci.Technol.,24(9-10) (1989) 617-628.
152
L. Yu et al. / Desalination 154 (2003) 147-152
[7] M.N. Ingale and V.V. Mahajani, Recovery of carboxylic acids, C2--C6, from an aqueous waste stream using tributyiphosphate(TBP): effect of presence of inorganic acids and the ir sodium salts. Sep. Technol., 6(1) (1996) 1-7. [8] H. Reisinger and C.J. King, Extraction and sorption of acetic acid at pH above pKa to form calcium magnesium acetate. Ind. Eng. Chem. Res., 34(3) (1995) 845-852.
[9] Y. Li, H. Tian and X. Lu, Recovering acetic acid from waste water from methacrylic acid production by isobutyraldehyde oxidation. Petrochem. Technol., 26(4) (1997) 245-248. [10] L. Yu, Q. Guo, J. Hao and W. Jiang, Recovery of acetic acid from dilute wastewater by means of bipolar membrane electrodialysis. Desalination, 129 (2000) 283-288.