Article pubs.acs.org/IECR
Production of Aldonic Acids by Bipolar Membrane Electrodialysis Jiefeng Pan,† Mengjie Miao,† Xi Lin,† Jiangnan Shen,*,† Bart Van der Bruggen,‡ and Congjie Gao† †
Center for Membrane Separation and Water Science & Technology, Ocean College, Zhejiang University of Technology, Hangzhou 310014, P. R. China ‡ Department of Chemical Engineering, KU Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium S Supporting Information *
ABSTRACT: Conventional methods for the synthesis of aldonic acids are typically expensive and complex, generate contaminated water, and generally yield a low purity of the products. In this work, the bipolar membrane electrodialysis (BMED) process was used as an environmentally friendly and efficient method to produce aldonic acids (lactobionic acid and gluconic acid as examples). The influence of cell configuration and current efficiency was investigated. The BMED process was further evaluated on the basis of energy consumption and current efficiency. The experimental results show that the two studied cell configurations (two compartment cell configuration and multichamber cell configuration) were viable to increase the concentration of aldonic acids to a satisfactory level. The multichamber cell configuration stack, consisting of two cation exchange membranes in conjunction with a bipolar membrane, was found more suitable to produce gluconic acid due to lower energy consumption, higher current efficiency, and higher conversion rate. The process with a multichamber cell configuration could increase product conversion rate by about 3.5% and current efficiency by about 4.1% by comparing with the two compartment cell configuration at the same operation conditions, with a minor increase in the energy consumption of below 0.5%.
1. INTRODUCTION Aldonic acids, with the chemical formula HOCH 2 − (CHOH) n−COOH, are generally obtained by alkaline oxidation, degradation, and redox disproportion of poly-, oligo-, and monosaccharides.1 Aldonic acids and their mineral salts are valuable in the pharmaceutical industry and in the food industry.2−4 Currently, the production of aldonic acids has been extensively studied and applied with great achievement, such as gluconic acid (GluA), lactobionic acid (LBA), and xylonic acid. For example, the demand of GluA increases steadily and has reached 60,000 tons per year.5 To obtain pure aldonic acid, the conventional strategy is to convert salt into acid by adding acid or using a cation exchanger. In this procedure, a large number of chemical effluents would be generated, which not only causes a loss of the valuable product but also gives rise to severe damage of the aqueous environment.6,7 As a “green” technology, bipolar membrane electrodialysis (BMED) splits water into protons (H+) and hydroxide (OH−) ions with the help of an electric field. The acid and alkali solution can be formed without introducing any other foreign substances.8,9 BMED has been © XXXX American Chemical Society
widely used to produce organic acids from their corresponding organic salts, and was further developed as an attractive, advanced, and clean separation technology.10−14 Based on exploratory studies on the conversion rate of organic salts to organic acids and bases, two main operation patterns were used to produce aldonic acids.15−17 One is to selectively permeate organic anions through an anion exchange membrane and combine with the hydrogen ions produced by a bipolar membrane. However, organic acids with large molecular size have a low permeability through the anion exchange membrane, which could further increase the stack resistance.18 To solve this problem, Zhang has explored a porous P84 copolyimide anion exchange membrane, which can decrease the membrane stack’s resistance by reducing the resistance of the membranes.19 The second operation pattern is to replace metal cations (from organic salts) with hydrogen ions (supplied by a Received: Revised: Accepted: Published: A
April 12, 2017 June 19, 2017 June 20, 2017 June 20, 2017 DOI: 10.1021/acs.iecr.7b01529 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
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Industrial & Engineering Chemistry Research
cm2 with a size of 11 cm × 27 cm, the actual photo as shown in Figure S2. The experiments were run in batch recycle mode: the raw solution was received at the salt tank, and the acid tank was fed by deionized water. A 0.3 M sodium sulfuric solution was used as the electrolyte rinsing solution for both electrode compartments. The initial volume of the solution in each feed tank (the diluate and concentrate feed tanks) was 500 mL. The solution was pumped into the BMED stack and circulated through each compartment at a flow rate of 40 L/h. The power supply connected to the BMED stack delivered a constant voltage (15 V). Figure 2 shows the design of the BMED stack and number of membranes in detail. The compartments in every unit were isolated by spacers with a thickness of 0.70 mm. The electrodes were made of titanium coated with ruthenium. The arrangement of the two compartment cell configuration is shown in Figure 2a and consists of a bipolar membrane operating in conjunction with a cation membrane. The multichamber cell is shown in Figure 2b and consists of two cation membranes in conjunction with a bipolar membrane. For two compartment cell configuration, the NaR solution (15%, 20%, 25%, or 30%) and water are pumped into a closed loop at a flow rate of 40 L/h, respectively. For the multichamber cell, the NaR solution is first fed to the chamber between the two cation membranes and the product from this loop is then circulated through the acid compartment. Every compartment is connected with an external reservoir for a continuous recirculation, centrifugal pumps are used to circulate the solutions, and their flow rates are controlled by flow meters. The multichamber cell configuration possesses an ability to obtain higher concentration of acid in a salt/acid stream than a standard two compartment cation cell. Meanwhile, with a higher current efficiency, the same salt/ acid composition can be generated alternately through the cell. 2.3. Analytical Methods. 2.3.1. Stack Resistance Assessment. The stack resistance is calculated according to Ohm’s law. The corresponding currents are measured and recorded by a conductivity meter (F3-Standard Kit, Mettler-Toledo, Switzerland) under the constant voltage (15 V). 2.3.2. Conductivity Assessment. The conductivity in each compartment was measured and recorded by a conductivity meter (F3-Standard Kit, Mettler-Toledo, Switzerland). To evaluate the product purity, samples were taken from the acid compartment and the sodium concentration was analyzed by using ion chromatography (792 Basic IC, Metrohm, Switzerland). The energy consumption data including the voltage and current during the experiment were measured directly by a regulated CV/CC power supply (WYL 1703×2, Hangzhou Siling Electrical Instrument Ltd., China). 2.3.3. Efficiency Assessment. The efficiency of the operation was evaluated through the current efficiency, acid recovery, and specific energy consumption. In the BMED process, with one mole electrical charges for acid or base production, the total charge passed in the system generally reflects the utilization rate of current, which was defined as the current efficiency and calculated with eq 1:
bipolar membrane); the cations are removed by a cation exchange membrane.20−22 The two cell configuration BPMED stack consists of repeating units (a bipolar membrane, a cation exchange membrane, and another bipolar membrane). However, remaining cations are inevitable in this operation pattern, which makes it difficult to obtain a high-purity product. This operation pattern is a main stream approach to produce organic acids due to the advantage of its lower energy consumption. In this work, lactobionic acid and gluconic acid are studied as examples of aldonic acids. The technical validity of BMED to produce these aldonic acids was explored and analyzed. In order to further improve the process performance and obtain a high-purity product, a novel multichamber cation cell configuration of the BMED stack was also explored and optimized for producing gluconic acid.
2. EXPERIMENTAL SECTION 2.1. Materials. Sodium gluconate (Glu-Na) and sodium lactobionate (LB-Na) were supplied by Chernger Biotechnology Co. Ltd. (China) with a purity of 99%. A bipolar membrane Bp-1E and a cation exchange membrane CMX were supplied by Astom (Japan). The properties of these membranes are shown in Table 1. All chemicals were analytical grade and used as received. Deionized water was used throughout the experiments. Table 1. Main Characteristics of Mono- and Bipolar Membranes Used in the Experimentsa membrane
thickness (mm)
ion exchange capacity (mequiv/ g)
area resistance (Ω/cm2)
Bp1E CMX
0.20−0.35 0.17
1.5−1.8
3.0
current efficiency (%) >98
a
Data are collected from the product brochure provided by the manufacturer.
2.2. Experimental Setup. A laboratory-scale experimental setup was built, shown in Figure 1. Five repeat units were installed inside the BMED stack, and every repeat unit contains a bipolar membrane and one or two cation exchange membranes. The effective area of every membrane was 189
η=
z(Ct − C0)VtF × 100% NIt
(1)
C0 and Ct are the concentration of H+ (mol/L) in the salt compartment at time 0 and t (s) respectively. z is the ion’s absolute valence (1 for H+ ions). Vt is the circulated volume of H+ solution at time t, F is Faraday’s constant (96,500 C/mol), I
Figure 1. Schematic diagram of the experimental setup. B
DOI: 10.1021/acs.iecr.7b01529 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
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Figure 2. Schematic structure of BMED stack: (a) two compartment cation cell; (b) multichamber cation cell.
Figure 3. Resistance of the entire BMED stack and the conductivity of the feed liquid as a function of time, at different mass fractions (GluA and LBA).
is the current (assumed constant, A), and N is the number of repeating units. The integral energy consumption E (kWh kg−1) was calculated by extrapolating the results for the production of 1 kg of acid in the following equation:
E=
∫0
t
UI dt CtVtMb
membrane and solution, and the resistance across the bipolar membranes.23 Here, the Stack resistances were determined with two compartment cell configuration. As shown in Figure 3, the stack resistances of the BMED stack show a “U” shape as a function of operation time in the electrodialysis process. In the initial stage, the resistance of the BMED stack abruptly declines in the first 5 min because the bipolar membranes release a lot of protons (H+) and hydroxide (OH−) ions into the solution. Afterward, the BMED stack obtained a steady state in the intermediate phase: the resistance of the BMED stack remained invariable, indicating that the ion transfer was at steady state.24 Finally, the decrease of the concentration of sodium ions in the feed compartment increases the membrane stack resistance. Figure 3A also indicates that the resistance of the BMED stack decreases with the salt concentration due to the reduction of the conductivity of the salt solution with the concentration of ions (Figure 3B). The resistance is close to unity when the mass fraction of salts solution is above 25% before 10 min. This is due to a slight decrement in the dissociation degree of the salt solution with increasing salt concentration. Furthermore, when LBA is used, the resistance is higher than that when GluA is used. Since the molar mass of sodium lactobionate (398 g/ mol) was almost twice that of sodium gluconate (218.14 g/
(2)
where U is the voltage across the BMED stack (15 V), and Mb is the molecular weight of the acid. The conversion rate of product from the salt solution was calculated as follows: W=
CtVt × 100% N0
(3)
whereN0 is the initial amount of salt (mol) in the feed compartment.
3. RESULTS AND DISCUSSION 3.1. Stack Resistance. The resistance of the membrane stack includes the Donnan resistance at all solution−membrane interfaces, the diffusion resistance in both the cation exchange C
DOI: 10.1021/acs.iecr.7b01529 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
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Figure 4. Effect of sodium gluconate and sodium gluconate on BMED process with different mass fractions.
the increasing mass fractions of salts, because the migration process occurring in the two salt solutions is similar. In summary, almost no difference can be seen in the performance of BMED to prepare gluconic acid and lactobionic acid in the high concentration range, and the design of the synthesis process is very similar. However, for low mass fractions, the resistance of the membrane reactor is different, and the process parameters are different, so the process should be designed separately. 3.3. The Multichamber Cation Cell. The design of the two compartment cation cell can decrease the energy consumption and reduces the production costs. However, a loss of product purity and a decrease of the conversion rate due to the competitive migration in the process are inevitable.2,5 To overcome this weakness, Huang et al.26 designed a multichamber cation cell to solve this problem by adding a cation exchange membrane (BM−C−C). For the type of BM−C−C, the BMED stack of that configuration possesses a lower voltage drop, and the H+ is generated in the process of electrolysis and can easily migrate through the cation-selective membrane into the salt compartment and decrease the electrical resistance. In this cell, a high energy efficiency was obtained in the preparation of sodium hydroxide and sulfuric acid by sodium sulfate. In this study, a novel multichamber cation cell for preparing GluA was designed (Figure 2), and its current efficiency and conversion rate were calculated and compared with those of a two compartment cation cell, as shown in Figure 5. It can be seen that, with the increase of the conversion rate of gluconic acid, the current efficiency of the multichamber cell is slightly different compared to that of the two compartment cation cell before the mass fraction of 75%. After that, the current efficiency of the two compartment cation cell decreased rapidly. This indicates that the migration rate of sodium ions through the cation exchange membrane is low. However, for the multichamber cell, a rapid decrease of the current efficiency occurred when the conversion rate reached 85%. This shows that the design of the multichamber cell can enhance the sodium ion migration. In addition, the time dependency of the BMED stack current efficiency was calculated as shown in Figure 6. The treatment time of the multichamber design was prolonged by more than
mol), the ion amount of the sodium lactobionate was much lower than that of the sodium gluconate solution at the same mass fraction. The corresponding trend can also be seen in Figure 3B. At the preliminary stage, the conductivity shows a decrease due to the continuous migration of sodium ions. At the last stage of BMED progress, the sodium ions were almost entirely removed from the feed compartment and a small fraction of lactobionic acid was dissociated. H+ ions were migrated from feed compartment, which led to a slight increase of the conductivity. 3.2. Current Efficiency and Energy Consumption in BMED. To further estimate the suitability of the BMED for practical application, the current efficiency and the specific energy consumption were calculated with a two chamber cell configuration (Figure 4). The energy consumption of the process was represented as the energy consumption per mole of produced acid. The current efficiency represents the ratio of electrical charges required for the organic acid production to the overall electrical charge passing through the system. It can be observed that the current efficiency increases with increasing salt concentration. The increasing trends of current efficiency were attributed to the following factors: (a) the migration of sodium ions is further accelerated due to the increase of the sodium concentration difference on both sides of the cation exchange membrane;25 (b) with the increase of the salt concentration, the decrease of the BMED stack resistance resulted in an increase of the current efficiency. Figure 4 also shows that, with an increase of the salt concentration, the gluconic acid and lactobionic acid production have the same trend of energy consumption and current efficiency. Furthermore, the difference energy consumption between the two processes was obvious. This can be explained as follows: on the one hand, sodium gluconate contains a higher fraction of ions than sodium lactobionate at the same mass fraction. On the other hand, the dissociation constant of gluconic acid (pKa = 3.62) is lower than that of lactobionic acid (pKa = 3.80), so the formed gluconic acid is more stable, not conducive to dissociation and the migration of sodium ions. However, the salt solution resistance gradually decreases the overall membrane stack resistance with the increase of the salt concentration; and the difference between the values of two processes tends to be narrowed down with D
DOI: 10.1021/acs.iecr.7b01529 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
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Figure 7. Evolution in current efficiency and conversion rate at different mass fractions of GluNa for different cell configurations.
Figure 5. Current efficiency of the entire BMED stack with regard to the conversion rate of GluA for different mass fractions and configurations.
Figure 8. Sodium content with regard to mass fraction of GulNa. Figure 6. Time dependency of the current efficiency of BMED stack for different configurations.
slightly higher stack resistance due to the addition of a cation exchange membrane, the energy consumption is very similar, as shown in Table 2. This can be explained by the fact that, for the
25% compared with that of the two compartment design, with the same concentration of sodium citrate. The reduction of the current efficiency for the multichamber process is slower than that of the two compartment design, and the current efficiency of each time point is also higher. Furthermore, the advantage of the multichamber cell can be demonstrated based on Figure 7. To compare the effects of the two types of cell configuration, the increasing trend of the current efficiency and conversion rate is similar to the increase of the concentration as it refers to the same ion migration process. However, the configuration of the multichamber cell has a better performance, regardless of the current efficiency or conversion rate, than the two compartment cation cell. Although the advantage seems not obvious, the calculated residual quantity (Na+ in the acid compartment) from the conversion rate can explain the benefits of the multichamber cell, as shown in Figure 8. The Na+ residual quantity was significantly lower than that of the two compartment cation cell, especially for 10% and 20% of GulNa, which was reduced to less than 200 ppm. Furthermore, the advantage of the multichamber cell was more obvious with respect to the increase of the GluA concentration. Compared with the two compartment cation cell, although the multichamber cell has a
Table 2. Energy Consumption with Regard to Mass Fraction of GulNa energy consumption (kWh/kg)
a
cell
10%a
20%a
30%a
multi standard
0.474 0.468
0.447 0.444
0.424 0.422
Mass fraction.
multichamber cell, the salt/acid stream exhibits a higher concentration of acid than a two compartment cell configuration. Alternatively the cell can be used to generate the same salt/acid composition at a higher current efficiency,27 and the energy consumption gap between the two configurations becomes more narrow. In conclusion, the BMED stack with multichamber design can effectively improve the product conversion rate while without losing energy efficiency.
4. CONCLUSION In this study, the BMED process for preparing lactobionic acid and gluconic acid at different concentrations was investigated. E
DOI: 10.1021/acs.iecr.7b01529 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
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(10) Wang, Y. M.; Huang, C. H.; Xu, T. W. Which is more competitive for production of organic acids, ion-exchange or electrodialysis with bipolar membranes? J. Membr. Sci. 2011, 374, 150. (11) Shen, J. N.; Yu, J.; Liu, L. F.; Lin, J. Y.; Van der Bruggen, B. Synthesis of quaternary ammonium hydroxide from its halide salt by bipolar membrane electrodialysis (BMED): effect of molecular structure of ammonium compounds on the process performance. J. Chem. Technol. Biotechnol. 2014, 89, 841. (12) Huang, C. H.; Xu, T. W.; Zhang, Y. P.; Xue, Y. H.; Chen, G. W. Application of electrodialysis to the production of organic acids: Stateof-the-art and recent developments. J. Membr. Sci. 2007, 288, 1. (13) Shen, J. N.; Huang, J.; Liu, L. F.; Ye, W. Y.; Lin, J. Y.; Van der Bruggen, B. The use of BMED for glyphosate recovery from glyphosate neutralization liquor in view of zero discharge. J. Hazard. Mater. 2013, 260, 660. (14) Zhang, X. Y.; Lu, W. H.; Yang, P. B.; Cong, W. Application of response surface methodology to optimize the operation process for regeneration of acid and base using bipolar membrane electrodialysis. J. Chem. Technol. Biotechnol. 2008, 83, 12. (15) Bailly, M. Production of organic acids by bipolar electrodialysis: realizations and perspectives. Desalination 2002, 144, 157. (16) Jaime-Ferrer, J. S.; Couallier, E.; Viers, P.; Durand, G.; Rakib, M. Three-compartment bipolar membrane electrodialysis for splitting of sodium formate into formic acid and sodium hydroxide: Role of diffusion of molecular acid. J. Membr. Sci. 2008, 325, 528. (17) Roux-de Balmann, H.; Bailly, M.; Lutin, F.; Aimar, P. Modelling of the conversion of weak organic acids by bipolar membrane electrodialysis. Desalination 2002, 149, 399. (18) Wang, Y. M.; Huang, C. H.; Xu, T. W. Optimization of electrodialysis with bipolar membranes by using response surface methodology. J. Membr. Sci. 2010, 362, 249. (19) Zhang, C.; Xue, S.; Wang, G.; Wu, C.; Wu, Y. Production of lactobionic acid by BMED process using porous P84 co-polyimide anion exchange membranes. Sep. Purif. Technol. 2017, 173, 174. (20) Ran, J.; Wu, L.; He, Y. B.; Yang, Z. J.; Wang, Y. M.; Jiang, C. X.; Ge, L.; Bakangura, E.; Xu, T. W. Ion exchange membranes: New developments and applications. J. Membr. Sci. 2017, 522, 267. (21) Jin, K.; Hu, J.; Jin, S.; Gao, C. Industrial study on gluconic acid production by bipolar membranes. Technol. Water Treat. 2011, 37, 60. (22) Gutierrez, L. F.; Bazinet, L.; Hamoudi, S.; Belkacemi, K. Production of lactobionic acid by means of a process comprising the catalytic oxidation of lactose and bipolar membrane electrodialysis. Sep. Purif. Technol. 2013, 109, 23. (23) Fu, L. L.; Gao, X. L.; Yang, Y.; Aiyong, F.; Hao, H. W.; Gao, C. J. Preparation of succinic acid using bipolar membrane electrodialysis. Sep. Purif. Technol. 2014, 127, 212. (24) Feng, H.; Huang, C.; Xu, T. Production of tetramethyl ammonium hydroxide using bipolar membrane electrodialysis. Ind. Eng. Chem. Res. 2008, 47, 7552. (25) Zhang, K.; Wang, M.; Wang, D.; Gao, C. J. The energy-saving production of tartaric acid using ion exchange resin-filling bipolar membrane electrodialysis. J. Membr. Sci. 2009, 341, 246. (26) Huang, C.; Xu, T.; Jacobs, M. L. Regenerating flue-gas desulfurizing agents by bipolar membrane electrodialysis. AIChE J. 2006, 52, 393. (27) Mani, K. N. Electrodialysis water splitting technology. J. Membr. Sci. 1991, 58, 117.
The performance of BMED technology for synthesis of GluA and LBA is similar for high mass fractions (above 25%), but has a large difference at low mass fractions (below 20%). Different membrane stack configurations (the multichamber cell and two compartment cell configuration) were used in preparing GluA. The multichamber cell was found to have a better current efficiency, higher conversion rate, and significantly lower Na+ residual quantity without losing any energy efficiency.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.7b01529. Plot of time dependency of buffer room pH for GluA production and photo of electrodialysis stack containing clapboard and membranes (PDF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Jiangnan Shen: 0000-0003-1384-6139 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The project was supported by the National Natural Science Foundation of China (Grant 21676249), National High Technology Research and Development Program 863 (Grant 2015AA030502), and Natural Science Foundation of Zhejiang Province (Grant LY16B060013).
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REFERENCES
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DOI: 10.1021/acs.iecr.7b01529 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
