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Separation of inorganic and organic acids from glyoxal by electrodialysis
DESALINATION ELSEVIER
Desalination 140 (2001) 47-54 www.elsevier.com/locate/desal
Separation of inorganic and organic acids from glyoxal by electrodialysis P u n i t a V. V y a s , B . G . Shah, G.S. Trivedi, P . M . G a u r , P. R a y , S.K. A d h i k a r y * Central Salt & Marine Chemicals Research Institute, Bhavnagar 364002, Gujarat, India Tel. +91 (278) 567760, 568923; Fax: +91 (278) 566970, 567562; email: [email protected] Received 12 September 2000; accepted 17 January 2001
Abstract
The electrodialysis(ED) process employing ion-exchangemembraneshas been used mainly for the desalinationof brackish water and concentrationof seawater. Of late ED has become a unique process for the separation of ionic and non-ionic substances from chemical mixtures. In such manufacturingprocesses, glyoxal is produced by the oxidation of acetaldehydewith nitric acid. After the reaction,the product containsnitric acid, acetic acid, glycolic acid, etc., which are to be separated from the mixture. Attempts were made to make use of ED to separate electrolytes from nonelectrolytesand to separatenitric acid and weak organicacids from glyoxal. The experimentalresults obtained from the separation of nitric acid, organic acids and glyoxalunder differentexperimentalconditionsare presentedand discussed. Keywords: Glyoxal; Nitric acid; Acetic acid; Eleetrodialysis; Separation
1. Introduction
The most important industrial applications using electrodialysis (ED) were the production of fresh water from brackish water and brine solutions from seawater. With the development of RO, very few now use ED for desalination. Hence, an alternative application for ED other than desalination has been developed where RO or other membrane processes cannot be applied. ED can be used for purification by deminerali*Corresponding author.
zation of solutions of widely varying industrial fluids found in the food, chemical and pharmaceutical industries [1-3]. Recently El) has become a unique operation for the separation of ionic from non-ionic substances, viz., separation of inorganic salts from cheese whey containing organics such as proteins and sugars, deacidification of fruit juices [4-8], deashing of sugar cane juice, etc. In our earlier communication [9] we reported on the work of separation of sodium formate from a mixture containing sodium formate and pentaerythritol.
0011-9164/01/$- See front matter © 2001 Elsevier Science B.V. All rights reserved PII: S 0 0 1 1 - 9 1 6 4 ( 0 1 ) 0 0 3 5 3 - 8
48
P.V. Vyas et aL / Desalination 140 (2001) 47-54
Glyoxal (CHOCHO) is a highly reactive dialdehyde. Reaction of glyoxal with cellulose, starch and other carbohydrates and hydrocolloids is used in paper manufacture [10]. The reaction of glyoxal with hydrocolloids is being used for the modification of adhesives containing starch, carbohydrates, and other reactive materials. In photography, glyoxal is useful in hardening gelatin, either alone or condensed with diols or amino alcohols. It is used to make a reconstituted tobacco sheet with aroma, taste, and burning characteristics of natural, whole-leaf tobacco. Glyoxal and many of its derivatives have biological activity and hence are useful in medicine, bacteriology and pest control. Glyoxal is useful in leather tanning. Protein treated with glyoxal is more resistant to pepsin than protein treated with formaldehyde. Glyoxal is significantly less toxic than formaldehyde. Glyoxal is produced by the oxidation of acetaldehyde with nitric acid [ 10-12]. Thus, after the reaction, the product contains unreacted nitric acid, acetic acid, glycolic acid, etc., which are to be separated from glyoxal. ED can be used for the separation of electrolytes from non-electrolytes. Thus ED technology was studied to separate nitric and organic acids from glyoxal, which was obtained from a factory in Gujarat, India. In this paper we describe the results of experiments on the separation of nitric and organic acids from glyoxal.
2. Experimental An ED stack was packed with 15 cell pairs of cation and anion-exchange membranes of heterogeneous types, prepared from polyvinyl chloride (PVC)-ion-exchange resin powder in this laboratory [13] forming 15 diluate, 14 concentrate and two electrode compartments. A parallel-cum-series flow in three equal stages was used in the stack. The single effective membrane area of the stack was 80 cm 2. The salient feature
(a)
1 [L~_l_ I I / / I Ilil I I Ill::] ., L _ . . . . . . . . . . . . . . . . . I l:-:Electrode wash (-,0, IN NaAc)
Diluate (glyoxal)
Concentrate (acid)
Glyoxal (diluate)
(b)
............................ -I.......
A 7A
C
AI
A~
l Acid(¢oneenlrata)
IA
"
.~
_
Mixture of glyoxal & acid
Fig. 1. (a) Schematic flow diagram. (b) Principle of separation of acids from glyoxal. C, cation-exchange membrane; A, anion exchange membrane; A-, anion of nitric or acetic acid.
of the ED stack are given in Table 1, and the flow diagram of the experimental set-up is shown in Fig. 1. The glyoxal solution containing mixture of glyoxal, nitric acid, organic acids (mainly acetic) from the container marked "Diluate" (Fig. la) was circulated through the diluate (treated) compartments of the ED stack. At the same time distilled water from the container marked "concentrate" (Fig. la) was circulated through the concentrate compartments. As mentioned in our previous work [9] and also in some other studies of ED [7,8,14] where experiments were carried out under circulation of diluate and concentrate solutions, the circulation flow rate did not have a significant effect on the performance of ED; in a single-pass flow system,
49
P.V. Vyas et al. / Desalination 140 (2001) 47-54
Table 1 Characteristics of the electrodialysis stack employing ion-exchange membranes No. of pairs
15
Membranes Cation exchange Areal resistance, ~.cm 2 Anion exchange Areal resistance, ~.cm 2
Heterogeneous, sulfonic acid group 3-4 Heterogeneous, quaternary ammonium group 7-8
Effective cross-sectional area of each membrane, cm2 Flow path length, cm Flow path breadth, cm
80 10 8
Cell thickness, cm
0.2
Membrane gaskets and non-conducting netting type spacer gaskets
Built-in flow arrangements made from HDPE sheets
Electrodes Anode and cathode
Expanded titanium metal coated with precious metal oxide
Housing for electrode
Rigid PVC with built-in flow distributor and outlets
Pressing assembly Flow arrangements
Threaded tie rods with nuts Parallel-cum-series
the flow rate does have an effect. All the experiments were carried out at a circulation flow rate of 71/h each for both diluate and concentrate streams by using suitable pumps. A dilute solution o f sodium acetate (-0.1 N) was circulated through the two electrode compartments at the ends to remove the products of electrolysis. Electrical potential was applied between the two electrodes by means o f an A C - D C rectifier (digital type) having a variable current capacity o f 0-10 A and a variable voltage of 0--100V. The circulation o f both treated and concentrate streams was continued until the run was terminated. At regular intervals volumes o f treated and concentrate, current, voltage, etc., were recorded, and the samples were drawn from each stream and analyzed for nitric acid, total acid, glyoxal, etc. Glyoxal present in the solution was estimated as follows: 1 ml o f sample was diluted to 100 ml
with distilled water. To a 25-ml diluted solution, 35 ml o f sodium metaperiodate solution ( - 1 N ) was added and kept at room temperature for 45 min and then titrated against a ~4). 1N N a O H solution using methyl red as the indicator. A blank was run. Thus, the concentration ofglyoxal was estimated as: Glyoxal concentration (%w/v) _ (A-B)×Sx2.9
O)
0.25 where d is the main reading, B the blank reading and S the normality o f the N a O H solution. To determine the concentration of total acid, 25 ml of diluted sample was titrated against -4). 1 N NaOH solution using a phenolphthalein indicator. Nitric acid was estimated by titrating 25ml o f diluted sample with --0.1N N a O H
50
P.V. Vyas et al. / Desalination 140 (2001) 47-54
solution using a thymol blue indicator. The concentrations of total acid and nitric acid were estimated as follows: Total acidity as H N O 3 ( % W/V) or HNO3 (% w/v) equals RxSx6.3
(2)
0.25
where R is the titre value in ml. From the experimental data and the concentrations of total acid in diluate stream, the current efficiency (CE) was calculated as: C a (%) -
W x F x 100
(3)
MxNxQ
where W is the weight of total acid as H N O 3 (g), F is Faraday (26.8 A.h), M is the molecular weight of HNO3, N the number of cell pairs and Q is the amount of electricity (A.h). Energy consumption (E) was determined from voltage, current, duration, etc.
E=f- dt (4)
1000f 1000
d, k W h / m
3
v
where V is the voltage (V), t the time (h), I the current at time t (A) and v is the volume of solution taken for experiment (1). The glyoxal solution used in this study was collected from a local industry. The solution that was analyzed as per the methods described here contained 7.5% (w/v) glyoxal, 2.5% (w/v) HNO3, 10.2% (w/v) acetic acid and 13.4% (w/v) total acid as HNO 3. The experiments were carried out under the fixed potential of 30V (which is the maximum voltage to be applied in our ED stack
containing heterogeneous membranes) at ambient temperature (28-30°C). In the trial experiments, it was noticed that, without changing any stream (diluate and concentrate), it was difficult to achieve the reduction of concentration of total acid beyond 0.7%(w/v) from its original value of 13.2% (w/v) as HNO3. In the absence of any electrical field, diffusion of electrolytes takes place through an ion-exchange membrane under a concentration gradient. Here experiments were carried out in the circulation mode. After some time the concentration of total acid in the concentrate reached such a high value that the back diffusion of acid from concentrate to diluate became the predominant factor in comparison to ion transport from diluate to concentrate, as the current value was very low. Hence, back diffusion was facile at this point, and it was decided to remove all of the solution from the concentrate stream and replace it with distilled water. Three sets of experiments were carried out: • Experiments-I D After 140 min when current dropped nearly to 1 A, the concentrate stream (CO was replaced with distilled water and the experiments were continued until the run was terminated. • Experiments--H - - Two replacements of concentrate streams (C~ and C2) one after 140 min and another after 200 min were done with distilled water. • Experiments--HI-- After four different time intervals, the concentrate streams (C~, C2, C3 and C4) were replaced with distilled water.
3. Results
and discussion
In all sets of experiments it was observed that the current was initially low but progressively increased within a few minutes to a maximum and then decreased. This variation of current with time was explained in our earlier communication [9].
P.V. Vyas et al. /Desalination 140 (2001) 47-54
In the beginning of each experiment, distilled water was passed through concentrate compartments. Since distilled water has very low electrical conductivity of the order of 10 -6 mhos, the concentrate compartments offered high electrical resistance. With onset of the migration of acids from diluate compartments to concentrate compartments, the concentration of acids was built up in these compartments while that in diluate compartments reduced. As a result, the electrical resistance offered by diluate compartments was continuously increasing and those offered by concentrate compartments were decreasing. The net effect was that overall electrical resistance of the ED stack initially decreased with time, causing an increase in current. After some time the acid concentration in the diluate compartments became sufficiently low to cause an increase in overall electrical resistance of the ED stack, and hence current was found to decrease. The acid concentration vs. duration graphs (Fig. 2) indicated that concentrations of both total acid and HNO3 in diluate compartments initially decreased sharply with time. After 130-140 min, concentration of HNO3 in the diluate compartments became zero, after which the rate of decrease in acid concentration (which contained mostly acetic acid) became gradual.
51
The glyoxal solution used in these experiments contained nitric acid, organic acids (mainly acetic acid). Nitric acid, which is strong, ionizes easily. Organic acids such as acetic acid are mainly weak. The dissociation constant of acetic acid is well known and hence need not be mentioned here. In the beginning of the experiments, transport of HNO3 as ions is faster than acetic acid. During this period, ion transport of acetic acid, though slow as compared to HNO3, also takes place. Hence, acid reduction in the diluate stream was initially faster, and after some time, a 100% reduction of HNO3 could be possible. When all the HNO3 was removed from the glyoxal mixture, the mixture contained glyoxal and acetic acid. Acetic acid being a weak electrolyte, its transport as ions through the membrane was slow and the decrease in acid concentration in the glyoxal mixture was gradual in the later stage. The results are shown in Table 2. As presented in Fig. 3 (curves a), it can be seen that energy consumption increases with time. The rate of energy consumption with time was initially sharp, but after 130-140 min, rates became gradual. Loss of glyoxal vs. duration curves (Fig. 3, curves b) indicate that initially loss was low 180
14
40
~(1)
15£
.............................................................................................................................4
A
30 ;
120 a
"~
8
x".s"
I:o
"6
I t ::'.It'"
b
m
60
10 o, o
30
8 2
0 50
100- 750" 200 25"0" 300''350 Duration(min)
40
Fig. 2. Acid concentration vs. duration curves, a. Total acid; b. HNO3.
0
50
100
150 200 250 300 350 400 Duration(rain)
Fig. 3. a. Energy vs. duration; b. Loss of glyoxal vs. duration. (1) Experiments-I, (2) Experiments-II, (3) Experiments-Ill.
52
P. V. Vyas et al. / Desalination 140 (2001) 4 7 - 5 4
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~
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~t'~
~ P,.
I
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¢,~
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~ p,.
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P.V. Vyas et al. / Desalination 140 (2001) 47-54
when solution contained HNO3. After 130140 min, when concentration of HNO3 in the diluate stream was almost zero, loss of glyoxal became faster. Loss of glyoxal was minimum in Experiments-III where the concentrate streams (C~, C2, C3 and C4) were replaced with distilled water for four different intervals of time. Loss was greater in Experiments-I where the concentrate stream (CO was only replaced with distilled water once. The reduction of acid concentration is due to the transport of ions from diluate compartments to concentrate compartments. Generally, ions are hydrated. With the transport of ions, some water, and possibly some glyoxal, were also transported to the concentrate stream due to diffusion. Due to the diffusion of water and possibly glyoxal, the volume of diluate stream was continuously reduced. This volume change with duration is represented in Fig. 4. The volume change was minimum in Experiments-III. In all experiments there was a sharp increase in volume reduction up to 140 min. During this time, the transport of HNO3 was taking place. HNO3, a strong acid, carries more water with it. Thus, the volume change was sharp in the initial stages. After 140 min the concentration of HNO3 in the diluate stream was zero, and the solution contained only weak organic acids. Therefore, volume reduction was gradual at that stage.
53
The results of the experimental data are summarized in Table 2. The following trends can be seen: 1. The best results were obtained with Experiments-III where the concentrate stream was replaced with distilled water at four different time intervals. In these experiments current efficiency was the highest; water transport, glyoxal loss and energy consumption were the lowest. 2. After 140 min, the concentrate (C~) containing 2.1% (w/v) HNO3, 8.9% (w/v)total acid as HNO3 and 0.7% (w/v) glyoxal was removed and replaced by 1360 ml of distilled water. After 200 min, the concentrate (C2) containing 0.05% (w/v) HNO3, 1.3% (w/v) total acid as HNO 3 and 0.3% (w/v) glyoxal was replaced with 1360 ml of distilled water. After 255 min, the concentrate (C3) containing zero HNO3, 0.5% (w/v) total acid and 0.4% (w/v) glyoxal was replaced by 1360 ml of distilled water. Finally, after 305 rain, the concentrate (C4) containing zero HNO 3, 0.1% (w/v) total acid as HNO3 and 0.1% (w/v) glyoxal was replaced by distilled water, and the experiments were continued until the run was terminated. Thus, the final acid concentration in the diluate stream could be reduced to 0.2% (w/v) as HNO3 with minimum loss of glyoxal.
4. Conclusions
450 400 350 E ~ 300
I) )
"5 2~ lo( 5(
0
50
100
150 200 250 Duralion(rain)
300
350
400
Fig. 4. Volume change vs. duration. (1) Experiments-I; (2) Experiments-II; (3) Experiments-Ill.
The ED process using heterogeneous ionexchange membranes prepared at this Institute could be conveniently used for separating nitric acid and acetic acid, etc., from glyoxal. HNO3 concentration in the final glyoxal solution could be brought down from 2.54% (w/v) to 0% (w/v). Total acid concentration in the final glyoxal solution could be brought down from 13.2% (w/v) to 0.2% (w/v). This could be done by operating an ED stack containing 15 cell pairs of heterogeneous cation- and
54
•
•
•
•
P.V. Vyas et al. / Desalination 140 (2001) 47-54 anion-exchange membranes(effective crosssectional area of a single membrane was 80cm 2) by a feed and bleed method in which concentrate streams were changed four times during the experiments. The current efficiency, energy consumption and the loss of glyoxal to achieve the above result were 75.7%, 148 kWh/m 3 and 25%, respectively. By this method, one might finally get six solutions: (1) treated final containing 0.2% (w/v) total acid, 0% nitric acid 7.4% (w/v) glyoxal; (2) concentrate (C~) containing 0.7% (w/v) glyoxal, 2.1% (w/v) HNO3, 8.9% (w/v) total acid as HNO3; (3) concentrate (C2) containing 0.3% (w/v) glyoxal, 0.05% (w/v) HNO3, 1.3% (w/v) total acid as HNO3; (4) concentrate (C3) containing 0.4% (w/v) glyoxal, 0% HNO3, 0.5% (w/v) total acid as HNO3; (5) concentrate (C4) 0.1% (w/v) glyoxal, 0% HNO3, 0.1% (w/v) total acid as HNO3; and (6) a final concentrate containing 0.15% (w/v) glyoxal, 0% HNO3 and 0.5% (w/v) total acid as HNO3. This investigation demonstrates the technical feasibility of separating HNO3 and organic acids from glyoxal. The experiments were carried out with a practical product stream from a local industry, which was interested in 100% separation of inorganic acids and simultaneously maximum possible separation of organic acid from glyoxal.
Acknowledgement The authors are very thankful to the Ministry of Environment and Forests, Government of
India, for funding a project to carry out this research. The authors are also thankful to Mr. Vijayaraghavan for typing the manuscript.
References [1] [2] [3] [4]
Y. Hara, Bull. Chem. Soc. Jpn., 36(11) (1963) 1373. F. Leitz, Environ. Sei. Technol., 10(2) (1979)136. R. Audinos, Rev. Gen. Electr., 88(1) (1989) 858. R.W. Kilbum and H.P. Gregor, US Pat. 3,165, (1965) and 3,265,607 (1966). [5] J.A. Zang; Proc., Symp. on Membrane Processes for Industry, Birmingham, AL, USA, 1966. [6] N.A. Gordona and M.J. Milan, Desalination, 35 (1980) 317. [7] S.K. Adhikary, W.P. Harkare, K.P. Govindan and A.M. Nanjundaswamy, Ind. J. Technol., 21 (1983) 120. [8] S.K. Adhikary, W.P. Harkare, K.P. Govindan, K.C. Chikkappaji, S. Saroja and A.M. Nanjundaswamy, Ind. J. Technol., 25 (1987) 24. [9] B.G. Shah, G.S. Trivedi, P. Ray and S.K. Adhikary, Sep. Sci. Teclmol., 34(16) (1999) 3243. [10] Encyclopedia of Chemical Technology, 3rd ed., K. Othmer, ed., Wiley-Interscience, Vol. 11, 1980, p. 946. [11] K.TsunemitsuandY.Tsujino, US Patent, 3,290, 378 (1966). [12] M. Mugdam and J. Sixt, German Patent 573,721 (1933). [13] P.V. Vyas, B.G. Shah, G.S. Trivedi, P. Ray, S.K. Adhikary and R. Rangarajan, React. Funct. Polymers, 44 (2000) 101. [14] S.K. Thampy, P.K. Narayanan, D.K. Chauhan, S.K. Adhikary and V.K. Indusekhar, Wat. Treatment, 6 (1991) 385.
Desalination 140 (2001) 47-54 www.elsevier.com/locate/desal
Separation of inorganic and organic acids from glyoxal by electrodialysis P u n i t a V. V y a s , B . G . Shah, G.S. Trivedi, P . M . G a u r , P. R a y , S.K. A d h i k a r y * Central Salt & Marine Chemicals Research Institute, Bhavnagar 364002, Gujarat, India Tel. +91 (278) 567760, 568923; Fax: +91 (278) 566970, 567562; email: [email protected] Received 12 September 2000; accepted 17 January 2001
Abstract
The electrodialysis(ED) process employing ion-exchangemembraneshas been used mainly for the desalinationof brackish water and concentrationof seawater. Of late ED has become a unique process for the separation of ionic and non-ionic substances from chemical mixtures. In such manufacturingprocesses, glyoxal is produced by the oxidation of acetaldehydewith nitric acid. After the reaction,the product containsnitric acid, acetic acid, glycolic acid, etc., which are to be separated from the mixture. Attempts were made to make use of ED to separate electrolytes from nonelectrolytesand to separatenitric acid and weak organicacids from glyoxal. The experimentalresults obtained from the separation of nitric acid, organic acids and glyoxalunder differentexperimentalconditionsare presentedand discussed. Keywords: Glyoxal; Nitric acid; Acetic acid; Eleetrodialysis; Separation
1. Introduction
The most important industrial applications using electrodialysis (ED) were the production of fresh water from brackish water and brine solutions from seawater. With the development of RO, very few now use ED for desalination. Hence, an alternative application for ED other than desalination has been developed where RO or other membrane processes cannot be applied. ED can be used for purification by deminerali*Corresponding author.
zation of solutions of widely varying industrial fluids found in the food, chemical and pharmaceutical industries [1-3]. Recently El) has become a unique operation for the separation of ionic from non-ionic substances, viz., separation of inorganic salts from cheese whey containing organics such as proteins and sugars, deacidification of fruit juices [4-8], deashing of sugar cane juice, etc. In our earlier communication [9] we reported on the work of separation of sodium formate from a mixture containing sodium formate and pentaerythritol.
0011-9164/01/$- See front matter © 2001 Elsevier Science B.V. All rights reserved PII: S 0 0 1 1 - 9 1 6 4 ( 0 1 ) 0 0 3 5 3 - 8
48
P.V. Vyas et aL / Desalination 140 (2001) 47-54
Glyoxal (CHOCHO) is a highly reactive dialdehyde. Reaction of glyoxal with cellulose, starch and other carbohydrates and hydrocolloids is used in paper manufacture [10]. The reaction of glyoxal with hydrocolloids is being used for the modification of adhesives containing starch, carbohydrates, and other reactive materials. In photography, glyoxal is useful in hardening gelatin, either alone or condensed with diols or amino alcohols. It is used to make a reconstituted tobacco sheet with aroma, taste, and burning characteristics of natural, whole-leaf tobacco. Glyoxal and many of its derivatives have biological activity and hence are useful in medicine, bacteriology and pest control. Glyoxal is useful in leather tanning. Protein treated with glyoxal is more resistant to pepsin than protein treated with formaldehyde. Glyoxal is significantly less toxic than formaldehyde. Glyoxal is produced by the oxidation of acetaldehyde with nitric acid [ 10-12]. Thus, after the reaction, the product contains unreacted nitric acid, acetic acid, glycolic acid, etc., which are to be separated from glyoxal. ED can be used for the separation of electrolytes from non-electrolytes. Thus ED technology was studied to separate nitric and organic acids from glyoxal, which was obtained from a factory in Gujarat, India. In this paper we describe the results of experiments on the separation of nitric and organic acids from glyoxal.
2. Experimental An ED stack was packed with 15 cell pairs of cation and anion-exchange membranes of heterogeneous types, prepared from polyvinyl chloride (PVC)-ion-exchange resin powder in this laboratory [13] forming 15 diluate, 14 concentrate and two electrode compartments. A parallel-cum-series flow in three equal stages was used in the stack. The single effective membrane area of the stack was 80 cm 2. The salient feature
(a)
1 [L~_l_ I I / / I Ilil I I Ill::] ., L _ . . . . . . . . . . . . . . . . . I l:-:Electrode wash (-,0, IN NaAc)
Diluate (glyoxal)
Concentrate (acid)
Glyoxal (diluate)
(b)
............................ -I.......
A 7A
C
AI
A~
l Acid(¢oneenlrata)
IA
"
.~
_
Mixture of glyoxal & acid
Fig. 1. (a) Schematic flow diagram. (b) Principle of separation of acids from glyoxal. C, cation-exchange membrane; A, anion exchange membrane; A-, anion of nitric or acetic acid.
of the ED stack are given in Table 1, and the flow diagram of the experimental set-up is shown in Fig. 1. The glyoxal solution containing mixture of glyoxal, nitric acid, organic acids (mainly acetic) from the container marked "Diluate" (Fig. la) was circulated through the diluate (treated) compartments of the ED stack. At the same time distilled water from the container marked "concentrate" (Fig. la) was circulated through the concentrate compartments. As mentioned in our previous work [9] and also in some other studies of ED [7,8,14] where experiments were carried out under circulation of diluate and concentrate solutions, the circulation flow rate did not have a significant effect on the performance of ED; in a single-pass flow system,
49
P.V. Vyas et al. / Desalination 140 (2001) 47-54
Table 1 Characteristics of the electrodialysis stack employing ion-exchange membranes No. of pairs
15
Membranes Cation exchange Areal resistance, ~.cm 2 Anion exchange Areal resistance, ~.cm 2
Heterogeneous, sulfonic acid group 3-4 Heterogeneous, quaternary ammonium group 7-8
Effective cross-sectional area of each membrane, cm2 Flow path length, cm Flow path breadth, cm
80 10 8
Cell thickness, cm
0.2
Membrane gaskets and non-conducting netting type spacer gaskets
Built-in flow arrangements made from HDPE sheets
Electrodes Anode and cathode
Expanded titanium metal coated with precious metal oxide
Housing for electrode
Rigid PVC with built-in flow distributor and outlets
Pressing assembly Flow arrangements
Threaded tie rods with nuts Parallel-cum-series
the flow rate does have an effect. All the experiments were carried out at a circulation flow rate of 71/h each for both diluate and concentrate streams by using suitable pumps. A dilute solution o f sodium acetate (-0.1 N) was circulated through the two electrode compartments at the ends to remove the products of electrolysis. Electrical potential was applied between the two electrodes by means o f an A C - D C rectifier (digital type) having a variable current capacity o f 0-10 A and a variable voltage of 0--100V. The circulation o f both treated and concentrate streams was continued until the run was terminated. At regular intervals volumes o f treated and concentrate, current, voltage, etc., were recorded, and the samples were drawn from each stream and analyzed for nitric acid, total acid, glyoxal, etc. Glyoxal present in the solution was estimated as follows: 1 ml o f sample was diluted to 100 ml
with distilled water. To a 25-ml diluted solution, 35 ml o f sodium metaperiodate solution ( - 1 N ) was added and kept at room temperature for 45 min and then titrated against a ~4). 1N N a O H solution using methyl red as the indicator. A blank was run. Thus, the concentration ofglyoxal was estimated as: Glyoxal concentration (%w/v) _ (A-B)×Sx2.9
O)
0.25 where d is the main reading, B the blank reading and S the normality o f the N a O H solution. To determine the concentration of total acid, 25 ml of diluted sample was titrated against -4). 1 N NaOH solution using a phenolphthalein indicator. Nitric acid was estimated by titrating 25ml o f diluted sample with --0.1N N a O H
50
P.V. Vyas et al. / Desalination 140 (2001) 47-54
solution using a thymol blue indicator. The concentrations of total acid and nitric acid were estimated as follows: Total acidity as H N O 3 ( % W/V) or HNO3 (% w/v) equals RxSx6.3
(2)
0.25
where R is the titre value in ml. From the experimental data and the concentrations of total acid in diluate stream, the current efficiency (CE) was calculated as: C a (%) -
W x F x 100
(3)
MxNxQ
where W is the weight of total acid as H N O 3 (g), F is Faraday (26.8 A.h), M is the molecular weight of HNO3, N the number of cell pairs and Q is the amount of electricity (A.h). Energy consumption (E) was determined from voltage, current, duration, etc.
E=f- dt (4)
1000f 1000
d, k W h / m
3
v
where V is the voltage (V), t the time (h), I the current at time t (A) and v is the volume of solution taken for experiment (1). The glyoxal solution used in this study was collected from a local industry. The solution that was analyzed as per the methods described here contained 7.5% (w/v) glyoxal, 2.5% (w/v) HNO3, 10.2% (w/v) acetic acid and 13.4% (w/v) total acid as HNO 3. The experiments were carried out under the fixed potential of 30V (which is the maximum voltage to be applied in our ED stack
containing heterogeneous membranes) at ambient temperature (28-30°C). In the trial experiments, it was noticed that, without changing any stream (diluate and concentrate), it was difficult to achieve the reduction of concentration of total acid beyond 0.7%(w/v) from its original value of 13.2% (w/v) as HNO3. In the absence of any electrical field, diffusion of electrolytes takes place through an ion-exchange membrane under a concentration gradient. Here experiments were carried out in the circulation mode. After some time the concentration of total acid in the concentrate reached such a high value that the back diffusion of acid from concentrate to diluate became the predominant factor in comparison to ion transport from diluate to concentrate, as the current value was very low. Hence, back diffusion was facile at this point, and it was decided to remove all of the solution from the concentrate stream and replace it with distilled water. Three sets of experiments were carried out: • Experiments-I D After 140 min when current dropped nearly to 1 A, the concentrate stream (CO was replaced with distilled water and the experiments were continued until the run was terminated. • Experiments--H - - Two replacements of concentrate streams (C~ and C2) one after 140 min and another after 200 min were done with distilled water. • Experiments--HI-- After four different time intervals, the concentrate streams (C~, C2, C3 and C4) were replaced with distilled water.
3. Results
and discussion
In all sets of experiments it was observed that the current was initially low but progressively increased within a few minutes to a maximum and then decreased. This variation of current with time was explained in our earlier communication [9].
P.V. Vyas et al. /Desalination 140 (2001) 47-54
In the beginning of each experiment, distilled water was passed through concentrate compartments. Since distilled water has very low electrical conductivity of the order of 10 -6 mhos, the concentrate compartments offered high electrical resistance. With onset of the migration of acids from diluate compartments to concentrate compartments, the concentration of acids was built up in these compartments while that in diluate compartments reduced. As a result, the electrical resistance offered by diluate compartments was continuously increasing and those offered by concentrate compartments were decreasing. The net effect was that overall electrical resistance of the ED stack initially decreased with time, causing an increase in current. After some time the acid concentration in the diluate compartments became sufficiently low to cause an increase in overall electrical resistance of the ED stack, and hence current was found to decrease. The acid concentration vs. duration graphs (Fig. 2) indicated that concentrations of both total acid and HNO3 in diluate compartments initially decreased sharply with time. After 130-140 min, concentration of HNO3 in the diluate compartments became zero, after which the rate of decrease in acid concentration (which contained mostly acetic acid) became gradual.
51
The glyoxal solution used in these experiments contained nitric acid, organic acids (mainly acetic acid). Nitric acid, which is strong, ionizes easily. Organic acids such as acetic acid are mainly weak. The dissociation constant of acetic acid is well known and hence need not be mentioned here. In the beginning of the experiments, transport of HNO3 as ions is faster than acetic acid. During this period, ion transport of acetic acid, though slow as compared to HNO3, also takes place. Hence, acid reduction in the diluate stream was initially faster, and after some time, a 100% reduction of HNO3 could be possible. When all the HNO3 was removed from the glyoxal mixture, the mixture contained glyoxal and acetic acid. Acetic acid being a weak electrolyte, its transport as ions through the membrane was slow and the decrease in acid concentration in the glyoxal mixture was gradual in the later stage. The results are shown in Table 2. As presented in Fig. 3 (curves a), it can be seen that energy consumption increases with time. The rate of energy consumption with time was initially sharp, but after 130-140 min, rates became gradual. Loss of glyoxal vs. duration curves (Fig. 3, curves b) indicate that initially loss was low 180
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Fig. 3. a. Energy vs. duration; b. Loss of glyoxal vs. duration. (1) Experiments-I, (2) Experiments-II, (3) Experiments-Ill.
52
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P.V. Vyas et al. / Desalination 140 (2001) 47-54
when solution contained HNO3. After 130140 min, when concentration of HNO3 in the diluate stream was almost zero, loss of glyoxal became faster. Loss of glyoxal was minimum in Experiments-III where the concentrate streams (C~, C2, C3 and C4) were replaced with distilled water for four different intervals of time. Loss was greater in Experiments-I where the concentrate stream (CO was only replaced with distilled water once. The reduction of acid concentration is due to the transport of ions from diluate compartments to concentrate compartments. Generally, ions are hydrated. With the transport of ions, some water, and possibly some glyoxal, were also transported to the concentrate stream due to diffusion. Due to the diffusion of water and possibly glyoxal, the volume of diluate stream was continuously reduced. This volume change with duration is represented in Fig. 4. The volume change was minimum in Experiments-III. In all experiments there was a sharp increase in volume reduction up to 140 min. During this time, the transport of HNO3 was taking place. HNO3, a strong acid, carries more water with it. Thus, the volume change was sharp in the initial stages. After 140 min the concentration of HNO3 in the diluate stream was zero, and the solution contained only weak organic acids. Therefore, volume reduction was gradual at that stage.
53
The results of the experimental data are summarized in Table 2. The following trends can be seen: 1. The best results were obtained with Experiments-III where the concentrate stream was replaced with distilled water at four different time intervals. In these experiments current efficiency was the highest; water transport, glyoxal loss and energy consumption were the lowest. 2. After 140 min, the concentrate (C~) containing 2.1% (w/v) HNO3, 8.9% (w/v)total acid as HNO3 and 0.7% (w/v) glyoxal was removed and replaced by 1360 ml of distilled water. After 200 min, the concentrate (C2) containing 0.05% (w/v) HNO3, 1.3% (w/v) total acid as HNO 3 and 0.3% (w/v) glyoxal was replaced with 1360 ml of distilled water. After 255 min, the concentrate (C3) containing zero HNO3, 0.5% (w/v) total acid and 0.4% (w/v) glyoxal was replaced by 1360 ml of distilled water. Finally, after 305 rain, the concentrate (C4) containing zero HNO 3, 0.1% (w/v) total acid as HNO3 and 0.1% (w/v) glyoxal was replaced by distilled water, and the experiments were continued until the run was terminated. Thus, the final acid concentration in the diluate stream could be reduced to 0.2% (w/v) as HNO3 with minimum loss of glyoxal.
4. Conclusions
450 400 350 E ~ 300
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Fig. 4. Volume change vs. duration. (1) Experiments-I; (2) Experiments-II; (3) Experiments-Ill.
The ED process using heterogeneous ionexchange membranes prepared at this Institute could be conveniently used for separating nitric acid and acetic acid, etc., from glyoxal. HNO3 concentration in the final glyoxal solution could be brought down from 2.54% (w/v) to 0% (w/v). Total acid concentration in the final glyoxal solution could be brought down from 13.2% (w/v) to 0.2% (w/v). This could be done by operating an ED stack containing 15 cell pairs of heterogeneous cation- and
54
•
•
•
•
P.V. Vyas et al. / Desalination 140 (2001) 47-54 anion-exchange membranes(effective crosssectional area of a single membrane was 80cm 2) by a feed and bleed method in which concentrate streams were changed four times during the experiments. The current efficiency, energy consumption and the loss of glyoxal to achieve the above result were 75.7%, 148 kWh/m 3 and 25%, respectively. By this method, one might finally get six solutions: (1) treated final containing 0.2% (w/v) total acid, 0% nitric acid 7.4% (w/v) glyoxal; (2) concentrate (C~) containing 0.7% (w/v) glyoxal, 2.1% (w/v) HNO3, 8.9% (w/v) total acid as HNO3; (3) concentrate (C2) containing 0.3% (w/v) glyoxal, 0.05% (w/v) HNO3, 1.3% (w/v) total acid as HNO3; (4) concentrate (C3) containing 0.4% (w/v) glyoxal, 0% HNO3, 0.5% (w/v) total acid as HNO3; (5) concentrate (C4) 0.1% (w/v) glyoxal, 0% HNO3, 0.1% (w/v) total acid as HNO3; and (6) a final concentrate containing 0.15% (w/v) glyoxal, 0% HNO3 and 0.5% (w/v) total acid as HNO3. This investigation demonstrates the technical feasibility of separating HNO3 and organic acids from glyoxal. The experiments were carried out with a practical product stream from a local industry, which was interested in 100% separation of inorganic acids and simultaneously maximum possible separation of organic acid from glyoxal.
Acknowledgement The authors are very thankful to the Ministry of Environment and Forests, Government of
India, for funding a project to carry out this research. The authors are also thankful to Mr. Vijayaraghavan for typing the manuscript.
References [1] [2] [3] [4]
Y. Hara, Bull. Chem. Soc. Jpn., 36(11) (1963) 1373. F. Leitz, Environ. Sei. Technol., 10(2) (1979)136. R. Audinos, Rev. Gen. Electr., 88(1) (1989) 858. R.W. Kilbum and H.P. Gregor, US Pat. 3,165, (1965) and 3,265,607 (1966). [5] J.A. Zang; Proc., Symp. on Membrane Processes for Industry, Birmingham, AL, USA, 1966. [6] N.A. Gordona and M.J. Milan, Desalination, 35 (1980) 317. [7] S.K. Adhikary, W.P. Harkare, K.P. Govindan and A.M. Nanjundaswamy, Ind. J. Technol., 21 (1983) 120. [8] S.K. Adhikary, W.P. Harkare, K.P. Govindan, K.C. Chikkappaji, S. Saroja and A.M. Nanjundaswamy, Ind. J. Technol., 25 (1987) 24. [9] B.G. Shah, G.S. Trivedi, P. Ray and S.K. Adhikary, Sep. Sci. Teclmol., 34(16) (1999) 3243. [10] Encyclopedia of Chemical Technology, 3rd ed., K. Othmer, ed., Wiley-Interscience, Vol. 11, 1980, p. 946. [11] K.TsunemitsuandY.Tsujino, US Patent, 3,290, 378 (1966). [12] M. Mugdam and J. Sixt, German Patent 573,721 (1933). [13] P.V. Vyas, B.G. Shah, G.S. Trivedi, P. Ray, S.K. Adhikary and R. Rangarajan, React. Funct. Polymers, 44 (2000) 101. [14] S.K. Thampy, P.K. Narayanan, D.K. Chauhan, S.K. Adhikary and V.K. Indusekhar, Wat. Treatment, 6 (1991) 385.