Production of Sebacic Acid Using Two-Phase Bipolar Membrane

Jul 27, 2009 - to sebacic acid with a current efficiency of 94% and energy consumption of 2.2 ... Sebacic acid (C10H18O4) is a raw material for produc...
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Ind. Eng. Chem. Res. 2009, 48, 7482–7488

Production of Sebacic Acid Using Two-Phase Bipolar Membrane Electrodialysis Fang Zhang, Chuanhui Huang, and Tongwen Xu* Laboratory of Functional Membranes, School of Chemistry and Materials Science, UniVersity of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China

To produce a water-insoluble acidssebacic acidsin an environmentally friendly manner, two-phase bipolar membrane electrodialysis (TPBMED) was proposed to convert sodium sebacate into sebacic acid in ethanol-water mixtures. The results indicated that BP-C configuration (BP, bipolar membrane; C, cationexchange membrane) was better than the other configurations: BP-A (A, anion-exchange membrane), BPA-C, and BP-A-A. In a TPBMED stack of BP-C configuration, the sodium sebacate could be totally transformed to sebacic acid with a current efficiency of 94% and energy consumption of 2.2 kW h kg-1. The process cost was estimated to be $0.57 kg-1. Nonetheless, to simultaneously dissolve sebacic sodium and sebacic acid, the ethanol content in the mixture was controlled at 60 v/v %, and the maximal concentration of sebacic acid produced was only 0.13 mol dm-3 due to the limit on solubility. 1. Introduction Sebacic acid (C10H18O4) is a raw material for production of nylon, alkyd resins, plasticizers, lubricants, cosmetics, etc.1 Currently, this acid is mainly manufactured from castor oil via caustic pyrolysis. As shown in Scheme 1, the process consumes considerable H2SO4 and discharges Na2SO4-containing solutions. How do we acidify a salt without secondary salt pollution? This is a serious problem endangering our environmental security. To resolve this problem, bipolar membrane electrodialysis (BMED) is a good choice. A bipolar membrane is a composite membrane comprising a cation-exchange layer and an anionexchange layer and can split water into H+ and OH- under reverse bias in a direct current field. BMED is a technique integrating bipolar membrane with electrodialysis and can acidify/alkalize a salt without salt introduction. To date, BMED has been widely used in or studied for application in chemical syntheses, food processing, and environmental protection.2-8 On the basis of water splitting in bipolar membranes, it is not difficult to convert organic salts into organic acids; however, some acids, such as sebacic acid, are hardly or not soluble in water and thus cannot be directly produced in a BMED stack if water is the only solvent. As pointed out by Alvarez et al.,9 BMED had a high stack voltage drop and a significant limit on salt conversion when applied to produce salicylic acid (low solubility in water) in aqueous solutions. To overcome this shortcoming, a mixture of water and an organic solvent can be used as the media for BMED to function in. This strategy has been put forward for application in other ED techniques. Kameche et al.10 produced propionic, butyric, octanoic, and salicylic acids in an ethanol-water medium (up to 50 v/v %) without a significant increase in energy consumption by using conventional electrodialysis. Luo et al.11 developed two-phase electro-electrodialysis (TPEED) for recovering and concentrating citric acid. The results showed that the electro-osmosis and osmosis of water could be properly controlled if the membrane was positioned between water and a mixture of water and organic solvent. Yi and Luo et al.12 coupled backextraction with two-phase electro-electrodialysis to produce lactic acid. They found that the crucial factor affecting lactate conversion was the competition between OH- and lactate ions and that lower * To whom correspondence should be addressed. E-mail: twxu@ ustc.edu.cn.

energy consumption could be achieved by lowering the ratio of organic/aqueous phases. To sum up, there are the following advantages when applying electrodialysis in organic-aqueous solutions:13 (1) Water can dissolve more inorganic supporting electrolytes (inorganic acids) than ethanol and keep the electrical resistance under easy control. (2) The organic-aqueous interface is favorable for suppression of co-ion (organic anions) leakage because organic anions are preferentially distributed to the aqueous-organic or organic phase. (3) The organic-aqueous interface favors the reduction of water electro-osmosis and osmosis. In this research, the concept of “two phases” is introduced into BMED for production of sebacic acid in an ethanol-water mixture. Sodium sebacate is used as the model raw material, and the BMED stack performances are evaluated for practical use. 2. Experimental Section 2.1. Materials. The membranes used in the experiments were FT-FAB (anion exchange membrane, FuMA-Tech GmbH, Germany), Neosepta BP-1 (bipolar membrane, Tokuyama Co., Japan), and Neosepta CMX (cation exchange membrane, Tokuyama Co., Japan); their properties are listed in Table 1. All the chemicals were of analytical grade and used as received. Distilled water was used throughout. 2.2. Setup. As shown in Figure 1, there were four configurations considered for construction of a laboratory-scale BMED stack. Take the BP-A-C configuration as an example, a BMED stack of such configuration arranges a bipolar membrane, an anion-exchange membrane, and a cation-exchange membrane between anode and cathode and thus has four separate compartments. Every compartment was connected to a 500 cm3 beaker, allowing for circulation of external solutions by submersible pumps (AP1000, Zhongshan Zhenghua Electronics Co. Ltd., China, with the maximal speed of 27 dm3 h-1). The effective membrane area was 7.07 cm2. The electrodes were made of titanium coated with ruthenium. In the stack of BP-A, BP-A-A, or BP-A-C configuration (Figure 1a-c), sodium sebacate (Na2C10H16O4) and the formed sebacic acid (C10H18O4) are in two separate compartments, so

10.1021/ie900485k CCC: $40.75  2009 American Chemical Society Published on Web 07/27/2009

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-1

The energy consumption E (kW h kg ) was calculated in eq 3:

Scheme 1. Industrial Production of Sebacic Acid

E)

dt ∫ CUIVM

(3)

t

where U (V) is the voltage drop across the BMED stack, I (A) is the current applied, Ct (mol dm-3) is the concentration of sebacic acid at time t, V is the volume of the acid cycle (0.25 dm3), and M is the molar mass of sebacic acid (202.25 g mol-1). 3. Results and Discussion

different solvents can be used to dissolve the two chemicals; i.e., sodium sebacate and sebacic acid are dissolved in water and a mixture of ethanol and water, respectively. In the stack of BP-C configuration (Figure 1d), however, sodium sebacate and sebacic acid exist in one compartment, and thus, a mixture of ethanol and water was chosen as the solvent. For scale-up experiments and cost estimation, a 3-unit stack of BP-C configuration (Figure 1e) was used to convert sebacate sodium. Theoretically, the stack of BP-C configuration has the lowest energy consumption; however, sodium sebacate and sebacic acid coexist in the same solution, so ethanol content in the solution cannot be high if the salt needs to be totally dissolved. To investigate the effects of ethanol content over a wide range and more factors (OH- flux and its enhancement on salt dissociation), BP-A - a configuration competitive with BP-C-was considered in all the experiments except the ones for configuration investigation. LiCl, due to its high solubility in ethanol-water mixtures,14 was added as an electrolyte to reduce the electrical resistance of the mixture and keep the stack voltage relative low and stable even at 100% conversion of sebacate. Na2SO4 was added as supporting electrolyte and electrode rinse. 2.3. Determination of Acid Concentration. The concentration of sebacic acid was determined by titration with a calibrated NaOH solution using phenolphthalein (pH 8-9.8) as an indicator. The concentration of sebacic acid, Csa, was calculated as eq 1: Csa )

COHVOH 2Vsa

(1)

Where, COH (mol dm-3) is the concentration of the calibrated NaOH solution, Vsa (dm3) is the volume of the acid cycle, and VOH (dm3) is the volume of NaOH used for titration. Because sebacic acid is a binary acid, there is a “2” in eq 1. 2.4. Calculation of Current Efficiency and Energy Consumption. The current efficiency η was calculated in eq 2: η)

2(Ct - C0)VF × 100% It

(2)

where Ct and C0 (mol dm-3) are the concentration of sebacic acid at time t and 0, respectively; V (dm3) is volume of the acid cycle; F is Faraday constant (96500 C mol-1); and I (A) is the current applied. Since the volume change in each compartment could be neglected during operation, V was equal to 0.25 dm3.

3.1. Effect of Sodium Sebacate Concentration on the Production of Sebacic Acid. As stated in the Experimental Section, the BP-A configuration was applied to all the experiments except the ones for configuration investigation. Figure 2 shows the effect of sodium sebacate concentration on the production of sebacic acid at a current density of 31 mA cm-2 and an ethanol content of 80 v/v %. In the left part of Figure 2a, the yield of sebacic acid increases as time elapses. Furthermore, the yield becomes lower than the ideal value (suppose the current efficiency equals to 100%) during operation, indicating a decrease in current efficiency. It can be ascribed to two main factors: the flux of OH- (generated in cathodic reaction) and the loss of H+ (generated by the water splitting in bipolar membranes). Whether OH- transports into the acid cycle or H+ migrates out of the acid cycle, acid yield decreases and thus current efficiency drops. The right part of Figure 2a shows the final yields of sebacic acid when using different concentrations of sodium sebacate. As the sodium sebacate concentration increases, the acid yield increases initially but levels off gradually afterward. The initial increase can be attributed to an increase in the molar ratio of sebacic anion/OH- when the sodium sebacate concentration rises. Although OH- has a much higher inherent mobility than sebacic anions, it can not acquire the predominance of quantity under the experimental conditions due to the buffer effect of sebacate (addition of OH- favors the dissociation of sebacate) (Table 2, calculated by using the dissociation constants15). Moreover, as sebacate concentration increases, OH- will have less proportion in the solution (Table 2). Naturally, when the ratio of sebacic anion/OH- increases to a certain large value, the negative effect caused by OH- competition is negligible, and thus, the acid yield changes slightly when the sodium sebacate concentration is above 0.3 mol dm-3. Figure 2b illustrates the effect of sodium sebacate concentration on the voltage drop across the stack. Within the first several minutes, the voltage drop decreases with an increase in the concentration of sebacate sodium. This is because under the given conditions the stack electrical resistance decreases as electrolyte (sodium sebacate is also an electrolyte) concentration rises. However, as time elapses, the formed sebacic acid, which is low in electrical conductance, makes the stack electrical resistance increase. There are two voltage leaps during experiment runs. The first leap is attributed to the well-known water splitting in bipolar membranes.16 The second leap is mainly caused by the increase in the concentration of sebacic acid in central compartment. Note that there is another important factor to be considered during the first several minutes. After the depletion of ions in the intermediate layer of bipolar membrane (high in voltage drop at this time), water splitting takes place, and H+ and OH- begin to fill the bipolar membrane and decrease the voltage drop across bipolar membrane gradually. On the other hand, the yield of sebacic acid (not high during the first

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Table 1. Properties of the Membranes Applied to the BMED Stacks membrane

type

thickness (µm)

IEC (meq/g)

area resistance(Ω cm2)

selectivity (%)

FT-FAB Neosepta CMXa Neosepta BP-1b

anion exchange cation exchange bipolar

120 140-200 200

0.8 1.5-1.8

2-4 2.0-3.5

>98

voltage drop (V)

efficiency (%)

1.2-2.2

>98

The area resistance was measured in 0.5 mol dm-3 NaCl, 25 °C. b The voltage drop and efficiency were measured between 1 mol dm-3 NaOH and 1 mol dm-3 HCl, 10 A dm-2, 30 °C. a

Figure 1. BMED stacks of four configurations: (a) BP-A, (b) BP-A-A, (c) BP-A-C, and (d) 1-unit and (e) 3-unit BP-C (BP, bipolar membrane; A, anion exchange membrane; C, cation exchange membrane; (white) water; (grey grid) ethanol-water mixture).

several minutes) leads to an increase in the electrical resistance of the acid compartment. These two counteracting factors result in a relatively constant stack voltage for a period of time. But after the concentrations of H+ and OH- ions reach a balance in the bipolar membrane, the change in stack voltage will depend mainly on the yield of sebacic acid. That is why there comes the second leap in stack voltage. The changing trend of current efficiency in Figure 2c is similar to that of acid concentration in Figure 2a. When sodium sebacate concentration is above 0.3 mol dm-3, all the current efficiencies are close to 90%. As for energy consumption, the lowest value (4.6 kWh kg-1) can be

achieved when sodium sebacate is 0.3 mol dm-3. In our case, energy consumption increases with an increase in stack voltage and a decrease in sebacic acid yield. At the lowest salt concentration, the stack voltage is the lowest (Figure 2b) but the acid yield is also the lowest (Figure 2a). At the highest salt concentration, the acid yield is the largest (Figure 2a) but the stack voltage is high (Figure 2b). As a result, the lowest energy consumption is achieved at a medium salt concentration because it has a moderate acid yield and a not high stack voltage. In view of the performance mentioned above, 0.3 mol dm-3 sodium sebacate will be used in the following experiments.

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Table 2. Calculated Ion Distribution in the Cathode Compartment of BP-A Configuration at 298 Ka COH- (mol dm-3) 0.001

0.01

0.03

CNa2A (mol dm-3) 0.1 0.2 0.3 0.4 0.5 0.1 0.2 0.3 0.4 0.5 0.1 0.2 0.3 0.4 0.5

CHA-/*COH-4

3.9 × 10 7.8 × 10-4 1.2 × 10-3 1.6 × 10-3 1.9 × 10-3 3.9 × 10-6 7.8 × 10-6 1.2 × 10-5 1.6 × 10-5 2.0 × 10-5 4.3 × 10-7 8.6 × 10-7 1.3 × 10-6 1.7 × 10-6 2.2 × 10-6

CA2-/*COH1.0 × 102 2.0 × 102 3.0 × 102 4.0 × 102 5.0 × 102 10.0 20.0 30.0 40.0 50.0 3.3 6.7 10.0 13.3 16.7

a COH-, amount of OH- produced in electrode reaction divided by the solution volume; *COH-, OH- concentration in the solution; solution volume, 0.25 dm3; Na2A, sodium sebacate; HA-, C10H17O4-; A2-, C10H16O42-; pKa1 ) 4.59, pKa2 ) 5.59.15

Figure 2. Effect of sodium sebacate concentration on stack performances: (a) acid yield, (b) the voltage drop across the stack, (c) current efficiency and energy consumption. Experimental conditions: configuration, BP-A; current density, 31 mA cm-2; ethanol content, 80 v/v %; Na2SO4, 0.3 mol dm-3; LiCl, 0.3 mol dm-3; flow rate, 27 dm3 h-1.

3.2. Effect of Current Density on the Production of Sebacic Acid. Figure 3a shows the effect of current density on the production of sebacic acid when using the stack of BP-A configuration at an ethanol content of 80 v/v %. Sebacic acid yield rises as current density increases; however, at a given current density, acid yield becomes lower than the ideal value as time elapses. Similarly, the main causes are the flux of OHand the loss of H+. At higher current densities, more free OHand H+ ions exist in the cathode and salt/acid compartments and compete for the current carriers. Figure 3b shows the effect of current density on stack voltage drop. As current density increases, the voltage drop increases correspondingly. The curves all have two voltage leaps, but,

different from Figure 2b, the curves have no intersection. This is because, at a given amount of sodium sebacate, the higher current density, the higher acid yield and the higher stack electrical resistance. Figure 3c shows the effect of current density on current efficiency and energy consumption. When current density is in the range of 10-50 mA cm-2, the current efficiencies have no significant difference; however, there is a slight drop in current efficiency after current density is more than 40 mA cm-2. This can be ascribed to the flux of OH- since the amount of OH- formed in cathodic reaction is in direct proportion to current density and thus the ratio of sebacic anion/OH- decreases dramatically at high current densities. When it comes to energy consumption, it increases almost linearly as current density increases. Considering the current efficiency and energy consumption, a current density of 31 mA cm-2 is favorable, though longer experimental time is needed to convert the same amount of sebacate. 3.3. Effect of Ethanol Content on the Production of Sebacic Acid. Figure 4 shows the effect of ethanol content on the production of sebacic acid using BP-A configuration. In Figure 4a, the concentration of sebacic acid increases as ethanol content increases. The reason can not be ascribed to the enhancement on the solubility of sebacic acid by addition of ethanol since the produced acid is far from saturation in the corresponding mixture of ethanol and water. In fact, as ethanol content increases, there are two main changes in the system: (1) a decrease in the diffusion of sebacic acid and (2) a decrease in the leakage of H+ due to the decrease in the mobility of H+ and acid dissociation. These two main changes contribute to the increase in acid concentration. However, too much ethanol will make electrolytes dissociate less and thus solution resistance rises dramatically. As shown in Figure 4b, the voltage drop leaps when ethanol content increases above 70 v/v %. Figure 4c shows the effects of ethanol content on current efficiency and energy consumption, which show a similar changing trend as mentioned above. When ethanol content is above 70 v/v %, the current efficiency and especially the energy consumption increase dramatically. To have an acceptable energy consumption, the ethanol content must be controlled under 70 v/v %. 3.4. Effect of Stack Configuration on the Production of Sebacic Acid. To single out the most cost-effective configuration, other configurations (BP-A-A, BP-A-C, and BP-C) need

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Figure 3. Effect of current density on stack performances: (a) acid yield, (b) the voltage drop across the stack, (c) current efficiency, and energy consumption. Experimental conditions: configuration, BP-A; ethanol content, 80 v/v %; Na2SO4, 0.3 mol dm-3; LiCl, 0.3 mol dm-3; sodium sebacate, 0.3 mol dm-3; flow rate, 27 dm3 h-1.

to be examined. As discussed above, 0.3 mol dm-3 sodium sebacate and 70 v/v % ethanol-water mixture are two favorable conditions for running a TPBMED of BP-A configuration, but these two conditions can not be attained in the case of BP-C configuration. In a stack of BP-C configuration, the saturation concentration of sebacic acid is about 0.13 mol dm-3 in a 60 v/v % ethanol-water mixture, and the concentration of LiCl should not be more than 0.2 mol dm-3 due to the salting out effect. Therefore, to have the identical conditions for comparison of the four configurations, the concentrations of sodium sebacate and LiCl were selected as 0.13 and 0.2 mol dm-3, respectively. Figure 5 shows the voltage drops for BP-A, BP-A-A, BPA-C, and BP-C (1-unit and 3-unit) configurations. The voltage

Figure 4. Effect of ethanol content on stack performances: (a) acid yield, (b) the voltage drop across the stack, (c) current efficiency and energy consumption. Experimental conditions: configuration, BP-A; current density, 31 mA cm-2; Na2SO4, 0.3 mol dm-3; LiCl, 0.3 mol dm-3; sodium sebacate, 0.3 mol dm-3; flow rate, 27 dm3 h-1.

drops of BP-A-A and BP-A-C configurations are higher than that of BP-A configuration since additional monopolar membranes and compartments add to the electrical resistance of BMED stack. Further, the BP-A-C configuration exhibits a higher voltage drop than the BP-A-A configuration especially in the later period of time, and this is mainly because electrolytes migrate into the feed compartment in the case of BP-A-A configuration but migrate out in the case of BP-A-C configuration. Among the four configurations, BP-C (1-unit) configuration has the lowest voltage drop not only because it has only two membranes and three compartments but also because the ions migrating across the monopolar membrane are Li+ and Na+, instead of the ions with low mobility-sebacic anions. For the same configuration, BP-C, the voltage drop increases dramatically when the repeating unit number rises to three due to the

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Figure 5. Voltage drops for different configurations: BP-A, BP-A-A, BPA-C, and BP-C. Experimental conditions: current density, 31 mA cm-2; ethanol content, 60 v/v %; Na2SO4, 0.3 mol dm-3; LiCl, 0.2 mol dm-3; sodium sebacate, 0.13 mol dm-3; flow rate, 27 dm3 h-1. Table 3. Estimation of Process Cost configuration repeating units current density (mA cm-2) experiment time (min) ethanol content (v/v %) effective membrane areaa (cm2) Na2SO4 concentration (mol dm-3) LiCl concentration (mol dm-3) fluid flow speed (dm3 h-1) sebacate sodium (mol dm-3) sebacic acid (mol dm-3) current efficiency (%) energy consumption (kW h kg-1) process capacity (kg y-1) electricity charge ($ kW-1 h-1) energy cost for sebacic acid ($ kg-1) energy cost for the peripheral equipment ($ kg-1 × 10-2) total energy cost ($ kg-1) membrane lifetime and the amortization of the peripheral equipment (y) monopolar membrane price ($ m-2) bipolar membrane price ($ m-2) membrane cost ($) stack cost ($) peripheral equipment cost ($) total investment cost ($) amortization ($ y-1) interest ($ y-1) maintenance ($ y-1) total fixed cost ($ y-1) total fixed cost ($ kg-1) total process cost ($ kg-1)

BP-A BP-A-A BP-A-C BP-C 3-BP-C 1 31 90 60 7.07 0.3 0.2 27 0.13 0.016 65 5.0 4.28 0.1 0.50

1 31 90 60 7.07 0.3 0.2 27 0.13 0.022 91 3.8 6.07 0.1 0.38

1 31 90 60 7.07 0.3 0.2 27 0.13 0.024 97 3.8 6.46 0.1 0.38

1 31 90 60 7.07 0.3 0.2 27 0.13 0.025 99 2.6 6.47 0.1 0.26

3 31 180 60 7.07 0.3 0.2 27 0.13 0.13 94 2.2 17.82 0.1 0.22

0.025 0.019

0.019 0.013 0.011

0.525 0.399 3 3

0.399 0.273 0.231 3 3 3

135

135

135

135

135

1350 1.05 1.58 2.37 3.95 1.32 0.32 0.4 2.04 0.48 1.00

1350 1.15 1.73 2.60 4.33 1.44 0.35 0.43 2.22 0.37 0.76

1350 1.15 1.73 2.60 4.33 1.44 0.35 0.43 2.22 0.34 0.74

1350 1.05 1.58 2.37 3.95 1.32 0.32 0.4 2.04 0.32 0.59

1350 3.15 4.73 7.09 11.82 3.94 0.94 1.18 6.06 0.34 0.57

a The effective membrane area is the working area of each piece of membrane.

increase in membrane and compartment numbers and sebacic acid yield. Note that the voltage drop falls again in the end in the case of the 3-unit-BP-C configuration. This is because sebacate sodium is almost completely converted to sebacic acid and thus the surplus of H+ leads to a decrease in the electrical resistance of the solution. As concerns the current efficiency (Table 3), BP-A has the lowest value (65 ( 5%) since other configurations can effectively suppress the negative effect of OH- flux: (1) BP-A-A

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Figure 6. Sodium sebacate (left), the product solution from TPBMED (middle), and the finally obtained sebacic acid (right).

has a buffer compartment for OH- flux and its current efficiency reaches 91 ( 5%; (2) BP-A-C has a cation-selective membrane and a buffer compartment and its current efficiency reaches 97 ( 5%; (3) BP-C has a cation-selective membrane and its current efficiency reaches 99 ( 5% (1-unit BP-C) and 94 ( 5% (3unit BP-C). As for the energy consumption, 3-unit BP-C has the lowests2.2 kW h kg-1. The process cost is estimated according to the literature,17 and the results are listed in Table 3. The process cost for 3-unit BP-C is only 0.57 $ kg-1; naturally, the cost can be lower if more repeating units are positioned between the electrodes. 3.5. Separation and Concentration of Sebacic Acid. The finial product from TPBMED is a mixture of sebacic acid and LiCl. Although LiCl is soluble in both water and ethanol, sebacic acid is almost not soluble in water: 0.1 g in 100 cm-3 of water.15 Accordingly, sebacic acid can be obtained by (a) evaporating ethanol-water mixtures, (b) dissolving the mixture of LiCl and sebacic acid in water, (c) sedimentating sebacic acid, and (d) drying the product. By following the procedure above, sebacic acid powder can be obtained, as shown in Figure 6. According to the analysis by atomic absorption spectroscopy, the metal elements in the final product (sebacic acid powder) are Li and Na, and their contents are less than 1.71% and 0.59%, respectively. 4. Conclusions To run a two-phase bipolar membrane electrodialysis for production of sebacic acid, such parameters as ethanol content, electrolyte usage, salt concentration, and current density, should be kept moderate. As proved by the experimental results, the TPBMED of the BP-C configuration is a cost-effective means to produce sebacic acid in view of its high solubility for sebacic acid and acceptable process cost. Ethanol can dissolve sebacic acid but its content should be controlled under 70 v/v % for the sake of energy consumption. Further, ethanol content is also a limiting factor on acid concentration due to the solubility issue, so a better solvent remains exploited if higher sebacic acid concentration is pursued. The loss of Li ions exist in all stack configurations because they can transfer through cation exchange membranes as counterions and anion exchange membranes as co-ions. Although the loss of Li ions was not significant in our experiments, it will add to the cost if Li ions are not recycled for a long-term run. Measures should be taken to recycle Li ions or keep Li ions from loss.

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Apart from sebacic acid, other water-insoluble organic acids can be prepared by applying this technique. We believe that TPBMED will gradually play an important role in the sustainable development of organic chemical industry. Acknowledgment Financial support from the Natural Science Foundation of China (No. 20636050) and Significant and Key Foundation of Educational Committee of Anhui Province (nos. KJ2007A016 and KJ2008A69) is greatly appreciated. Literature Cited (1) Xia, Q.; Zhang, F. B.; Zhang, G. L.; Ma, J. C.; Zhao, L. Solubility of sebacic acid in binary water + ethanol solvent mixtures. J. Chem. Eng. Data 2008, 53, 838. (2) Mafe’, S.; Ramy´rez, P.; Alcaraz, A. Electric field-assisted proton transfer and water dissociation at the junction of a fixed-charge bipolar membrane. Chem. Phys. Lett. 1998, 294, 406. (3) Saxena, A.; Gohil, G. S.; Shahi, V. K. Electrochemical membrane reactor: single-step separation and ion substitution for the recovery of lactic acid from lactate salts. Ind. Eng. Chem. Res. 2007, 46, 1270. (4) Onishi, N.; Osaki, T.; Minagawa, M.; Tanioka, A. Alcohol splitting in a bipolar membrane and analysis of the product. J. Electroanal. Chem. 2001, 506, 34. (5) Wilhelm, F. G.; Pu¨nt, I.; van der Vegt, N. F. A. Asymmetric bipolar membranes in acid-base electrodialysis. Ind. Eng. Chem. Res. 2002, 41, 579. (6) Huang, C. H.; Xu, T.W.; Feng, H. Z.; Li, Q. H. Win-Win coupling in electrodialysis with bipolar membranes (EDBM) for cleaner production. Ind. Eng. Chem. Res. 2009, 48, 1699.

(7) Bazinet, L.; Lamarche, F.; Ippersiel, D. Bipolar membrane electrodialysis: applications of electrodialysis in the food industry. Trends Food Sci. Technol. 1998, 9, 107. (8) Xu, T. W.; Huang, C. H. Electrodialysis-Based Separation Technologies: A Critical Review. AIChE J. 2008, 54, 3147. (9) Alvarez, F.; Alvarez, R.; Coca, J.; Sandeaux, J.; Sandeaux, R.; Gavach, C. Salicylic acid production by electrodialysis with bipolar Membranes. J. Membr. Sci. 1997, 123, 61. (10) Kameche, M.; Xu, F. N.; Innocent, C.; Pourcelly, G. Electrodialysis in water-ethanol solutions: Application to the acidification of organic salts. Desalination 2003, 154, 9. (11) Luo, G. S.; Shan, X. Y.; Qi, X.; Lu, Y, C. Two-phase electroelectrodialysis for recovery and concentration of citric acid. Sep. Purif. Technol. 2004, 38, 265. (12) Yi, S. S.; Lu, Y. C.; Luo, G. S. Separation and concentration of lactic acid by electro-electrodialysis. Sep. Purif. Technol. 2008, 60, 308. (13) Huang, C. H.; Xu, T. W.; Zhang, Y. P.; Xue, Y. H.; Chen, G. W. Application of electrodialysis to the production of organic acids: State-ofthe-art and recent developments. J. Membr. Sci. 2007, 288, 1. (14) Aurbach, D. Nonaqueous Electrochemistry; Marcel Dekker, Inc.: New York, 1999, 53. (15) Speight, J. G. Lange’s handbook of chemistry (16th); McGrawHill book Co.: New York, 2005. (16) Wilhelm, F. G.; van der Vegt, N. F. A.; Strathmann, H.; Wessling, M. Comparison of bipolar membrane by means of chronopotentiometry. J. Membr. Sci. 2002, 199, 177. (17) Strathmann, H.; Koops, G. H. Process economics of electrodialytic water dissociation for the production of acid and base. In Handbook on Bipolar Membrane Technology; Kemperman, A. J. B., Ed.; Twente University Press: Enschede, The Netherlands, 2000; pp 191-220.

ReceiVed for reView March 24, 2009 ReVised manuscript receiVed July 3, 2009 Accepted July 13, 2009 IE900485K