Electrodialysis To Concentrate Waste Ionic Liquids: Optimization of

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Electrodialysis to concentrate waste ionic liquids: optimization of operating parameters Haiyang Yan, Chunyan Xu, Wei Li, Yaoming Wang, and Tongwen Xu Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.5b03809 • Publication Date (Web): 29 Jan 2016 Downloaded from http://pubs.acs.org on January 31, 2016

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Industrial & Engineering Chemistry Research

Electrodialysis to concentrate waste ionic liquids: optimization of operating parameters Haiyang Yan1,3#, Chunyan Xu2#, Wei Li3, Yaoming Wang1,3*, Tongwen Xu1*

1

CAS Key Laboratory of Soft Matter Chemistry, Collaborative Innovation Center of Chemistry for Energy Materials, School of Chemistry and Materials Science, University of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China

2

School of Civil & Environmental Engineering, Georgia Institute of Technology, Atlanta, GA, USA

3

#

Hefei ChemJoy Polymer Materials, Co., LTD, Hefei, Anhui,230601, People’s Republic of China

These authors contributed equally to this work.

∗Corresponding authors. Tel.: + 86 551 3601587 (T. W. Xu); E-mail address: [email protected] (Y.M. Wang) and [email protected](T. W. Xu).

ACS Paragon Plus Environment


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Abstract: As a novel solvent, ionic liquids have been used in a series of industrial fields, in which large amounts of waste ionic liquids are generated and need to be concentrated and recycled rather than discharged. The disposal of aqueous ionic liquid solutions may cause environmental issues due to slow degradation and toxicity. Electrodialysis (ED) was proposed here to concentrate dilute aqueous solutions of ionic liquids. The effects of membrane types, applied voltage drop across the ED membrane stack and operating modes, including partial cyclic operation mode and change in volume ratio of concentrate solution to dilute solution (Vc:Vd), were investigated systematically. Results indicate that the membrane type and operating voltage drop across the membrane stack were optimized as CJMC/MA membranes and 10 V, respectively. Also, it shows that the concentration efficiency of volume ratio of 1:8 is superior to that of partial cyclic operation mode since high concentration ratio (4.5), low energy consumption (9.46 kW h/m3) and low water transport (10.3%) can be achieved. In addition, membrane fouling was monitored, which showed that anion exchange membranes were stable in concentrating process. Nevertheless, the absorption of foulants on the membrane surface has some effect on concentrating process, which should be overcome in industrial application. Overall, ED process is a feasible technology to concentrate and recycle the wasted ionic liquids.

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1. Introduction Ionic liquids, as potential room temperature melted salts,1 are one category of the most organic salts, which consist entirely of organic cations such as imidazolium, alkylammonium, or alkylpyridinium

and organic or inorganic anions such as halides,

[CH3COO]−, [BF4]−, [EtOSO3]− and [Ph-COO]−.1−5 There have been a lot of research focusing on ionic liquids during the last decades because of the peculiar properties, such as good non-flammability, high electric conductivity, wide electrochemical windows, excellent catalytic activities and good phase separation performance.4,6 For these reasons, ionic liquids are being applied in a series of fields including catalysis,7 cellulose dissolution,8 organic acid separation and purification,9,10 gas separation11,12 and etc. In industrial application processes, however, large amounts of dilute aqueous solutions of ionic liquids are produced.4 They need to be concentrated and recycled rather than simply discharged since the disposal of aqueous ionic liquid solutions may cause environmental issues due to their slow degradation and toxicity.13 To resolve this imperative problem, only a few recovery methods have been reported such as distillation, CO2 hydrate, and aqueous biphasic systems.13 But the energy consumption is very high and a large number of chemicals are consumed in these recycling processes. Therefore, it is necessary to explore an eco-friendly, energy-saving, and high efficiency technology to improve the recycling performance of waste ionic liquids. Electrodialysis (ED) is an electro-membrane separation process with cation and anion exchange membranes (CEMs and AEMs) arranged in an alternating pattern to form concentrate and dilute compartments.14 Anions and cations in dilute compartment can migrate toward the anode and cathode into concentrate compartment correspondingly under a driving force of electric potential difference.15 Nowadays, ED, as a novel separation process, has been widely used in separating and concentrating fields.16−18 Specifically, ED has also used in separating ionic liquids from a hydrolysate of lignocellulosic biomass8 and recovering ionic liquids from dilute aqueous solutions.4 However, the separation efficiency and concentration ratio in the previous reports were very low, and the recovered solution cannot be reused 3



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directly, which needs to be treated by other concentration process such as evaporation. For instance, the conductivity of concentrate solution in separating ionic liquids from a hydrolysate of lignocellulosic biomass could only be improved to ~3 mS/cm;8 the concentration ratio was as low as ~1.7 in recovering ionic liquids from dilute aqueous solutions.4 Therefore, ED with novel operating parameters is proposed to enhance the concentration efficiency in concentrating ionic liquids from aqueous solutions. Imidazolium ionic liquids are a typical ionic liquid used in industrial production, so that this kind of ionic liquid was concentrated and investigated as a case in this study. And the concentration of other ionic liquids may be similar to the imidazolium ionic liquids. In this study, effects of membrane types, applied voltage drop across the ED membrane stack and operating modes, including partial cyclic operation mode and change in volume ratio of concentrate solution to dilute solution were investigated. In particular, energy consumption, water transport, and concentration ratio were discussed. Furthermore, membrane fouling was investigated to evaluate fouling phenomenon and membrane performance. 2. Experimental section 2.1. Materials. Feed solution, i.e. waste ionic liquids belonged to a classification of imidazole, was provided from a chemical factory in Henan Province, China. The conductivity, soluble solids content (brix) and pH of the feed solution were ~5.7 mS/cm, 2.3% and 7.7, respectively. Membrane types and properties used in the experiment are listed in Table S1. The used chemicals were of analytical grade. Deionized water was used.

2.2. ED setup. Figure 1 shows electrodialysis (ED) setup and the membrane stack in detail. The setup was produced by Hefei ChemJoy Polymer Materials, Co., LTD (CJED-9×21-4), which contained the following units: (1) direct current supply (GX1761SL5A, Hangzhou Yuhang Siling Electrical Instrument Ltd., China); (2) ED membrane stack, in which electrodes were made of titanium coated with ruthenium; (3) electrode chamber feed with 0.3 mol/L Na2SO4 (300 mL) as electrode rinse 4


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solution (ERS); (4) concentrate chamber and (5) dilute chamber, in which initial solution is the feed solution, respectively; and (6) submersible pump with a maximum flow rate of 22 L/h (AP1000, Zhongshan Zhenghua Electronics Co. Ltd., China). Specifically, the membrane stack has five cation exchange membranes (CEMs) and four anion exchange membranes (AEMs) with an effective area of 9×21 cm2.The neighboring membranes were separated by a spacer with a thickness of 0.8 mm. Hence, the stack had four repeating units including four concentrate compartments and four dilute compartment. Besides, the stack had an anode compartment and a cathode compartment and the two electrode compartments were connected from the cathode to the anode compartment. To obtain high concentration of ionic liquids, two operation modes in the ED process were carried out. For one, a partial cyclic operation mode was installed as shown in Fig. 2. In this process, the concentrate solution was circulated along with the experiment, and the initial volume was 200 mL; the dilute solution was replaced by new feed with a volume of 200 mL after each batch of treatment. For another, different volume ratios of concentrate solution to dilute solution (Vc:Vd) were studied. In this operation mode, the initial volume of concentrate solution was fixed at 200 mL, the initial volume of dilute solution was designed as 400, 800, 1200 and 1600 mL. The solution in each chamber was circulated for a certain time to eliminate all visible gas bubbles before the operating voltage drop was applied.19 All experiments were performed at a constant voltage drop condition (CV operation mode) and at room temperature of ~25°C. Experimental data, including conductivity of solution in concentrate or dilute chamber, soluble solids content (brix) of solution, and current across the membrane stack, were recorded directly from the screen of indicator of the conductivity meter (DDS-307, Shanghai INESA&Scientific Instrument Co., Ltd), digital hand-held "Pocket" refractometer (PAL-1, ATAGO Co., Ltd) and direct current supply, respectively. Those instruments have a relatively high accuracy (low inherent error). In particular, the deviation of conductivity meter was ±1.0%, the deviation of digital hand-held "Pocket" refractometer was ±0.2%, and the current stability of direct current supply is lower than 0.1%+10mA. Besides, random error was investigated, 5



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and the value of random error was determined by triplicate experimental runs when effect of applied voltage drop and volume ratio of concentrate solution to dilute solution was investigated. Operating time of each experiment was determined by an occasion when the conductivity of dilute solution was reduced to 0.2 mS/cm.

2.3. Energy consumption (E), water transport (WT) and concentration ratio (Cr). The energy consumption, E (kW h/m3), of the ED process can be calculated as eq. 1, t

E=

U ∫ Idt 0

Vd

（1)

where U is the applied voltage drop across the membrane stack; I is the recorded current; t is the overall operating time of a batch of ED experiment; Vd is the initial volume of the dilute solution. The deviation of E is in proportion to the deviation of I caused by the random error, and is inversely proportional to the Vd. WT can be calculated as eq. 2, WT=1-

(Vd )t (Vd ) 0

(2)

where (Vd)t is the volume of dilute solution at the end time of a batch of ED experiment, and (Vd)0 is the volume of dilute solution at time 0. (Vd)0 can be determined accurately by a measuring cylinder, while (Vd)t was determined with a deviation of ±2 mL due to the residual solution in the apparatus. The deviation of water transport can then be calculated from the eq. 2, the more (Vd)0 the lower deviation. Cr can be calculated as eq. 3, Cr =

brixt brix0

(3)

where brixt is the brix of concentrate solution at the end time of a batch of ED experiment; and brix0 is the initial brix of the feed solution (2.3%). The deviation of Cr is in proportion to the deviation of brixt caused by the random error.

2.4. Investigation of anion exchange membrane fouling. Anion exchange membrane (AEM, CJMA membrane) fouling was investigated mainly through ion 6


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exchange capacity (IEC), membrane resistance and morphology. IEC was measured as following: dry membrane samples were accurately weighed and were converted to the Cl– form in 1.0 mol/L NaCl for 2 days at room temperature. Excess NaCl was washed off, and then the samples were immersed in 0.5 mol/L Na2SO4 for 2 days. IEC was finally obtained by determining the amount of exchanged Cl– through titration with 0.01 mol/L AgNO3. The measurement of membrane resistance was conducted by a fast method as described in details in a previous paper.20 Membrane surface morphologies were observed with a scanning electron microscopy (SEM, Sirion 200). Before SEM observation, the samples were dried by heating at 60ºC for 3 h and then coated with gold.

3. Results and discussion 3.1. Effect of membrane types on concentrating process. Due to special polymer and functional groups, different membranes have different performance, and thus different separation/concentration efficiency.21 Three types of commercial membranes, CMV/AMV, CJMC/MA and FKS/FAS membranes, were used to concentrate ionic liquids from industrial wastewater. Initial volumes of concentrate and dilute solutions were 200 and 400 mL, respectively. Operating voltage drop was fixed at 10 V. Fig. 3 shows current-time curves of different membranes in concentrating ionic liquids. The curve of CMV/AMV membranes is lower than that of CJMC/MA membranes at the first 5 min, and FKS/FAS membranes is lower than CMV/AMV membranes, which is due to the reason that membrane resistance of FKS/FAS membranes is the highest, and CJMC/MA membranes is of the lowest value of membrane resistance as can be seen in Table S1. The value of currents of all three kinds of membranes decreases gradually as a function of time, which is attributed to a decrease in the conductivity of dilute solution as shown in Fig. 4(a). Specifically, the current in the case of FKS/FAS shows a stable value from 3 to 10 min. The reason may be that the conductivity of dilute chamber has no obvious decrease compared with other two types of membranes as can be seen in Fig. 4(a). At the latter of 7



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experiment the change trend of CJMC/MA membranes is similar to that of CMV/AMV membranes, which may be due to the similarity of separation rate. However, FKS/FAS membranes have a relatively low separation rate, resulting in a long operating time and a high current value. Fig. 4 shows the change of the conductivity and brix of concentrate or dilute solution during concentrating process. The conductivity of concentrate solution of both CMV/AMV and CJMC/MA membranes can increase from 5.7 to 13.8 mS/cm within a short time of 30 min when the conductivity of dilute solution decreases to below 0.2 mS/cm, while FKS/FAS membranes need a long time (45 min) to reach a conductivity of 13.8 mS/cm as shown in Fig. 4(a). The change trend of brix (Fig. 4(b)) is similar to that of the conductivity. The brix of three kinds of membranes can reach up to 5.3−5.6%. Meanwhile, the concentration ratio can reach 2.3−2.4 (Table 1). Besides, the energy consumption was calculated as shown in Table 1. Energy consumptions of membranes CMV/AMV (9.34 kW h/m3) and CJMC/MA (10.04 kW h/m3) are relatively low, while FKS/FAS membranes have a higher energy consumption of 11.88 kW h/m3 due to the low separation rate as aforementioned. As a common phenomenon in ED, water transport22, 23 has been investigated to evaluate membrane performance. Both forward osmosis and electro-osmosis can cause water transport. During ED operation, the electro-osmosis plays a prominent role in water transport as compared with osmosis17. As the concentration difference increases, forward osmosis occurs and changes more and more intense. The intensification of forward osmosis combined with electro-osmosis will result in the rapid increase in total water transport. However, membranes with a dense polymer network and high steric hindrance can effectively minimize the water molecules transported per ion22,23, which is advantageous for concentrating process. Hence, water transport was investigated to evaluate membrane performance, and the data were listed in Table 1. The water transport of both CMV/AMV and FKS/FAS membranes is 5.5%, which is lower than that of CJMC/MA (8.3%), indicating that CJMA/MC membranes is of an insufficient dense degree. However, the membrane cost of CJMA/MC membranes is only one third of CMV/AMV or FKS/FAS membranes, which is of economically 8


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competitive. Overall, CJMC/MA is the optimal membranes to concentrate ionic liquids under the consideration of high separation rate and the low membrane cost.

3.2. Effect of voltage drop on concentrating process. As a driving force of ED, potential difference (i.e. voltage drop across the ED membrane stack) can influence the migration rate of ions and the concentration rate.24 High applied voltage drop would lead to a high current density in ED process. If current density is over the limiting current density, water molecular in the dilute solution would be dissociated on the surface of membrane to produce H+ and OH− ions,25 which is disadvantageous for ED performance and would enhance energy consumption and decrease the lifespan of the membranes. Hence, the applied voltage drop across the membrane stack was investigated to optimize operating parameter. The CJMC/MA membranes were used. Fig. 5 shows the changing trends of current during the concentrating process when different voltage drops were applied. At the earlier stage of the experiment, the current increases as an increase of voltage drop, which could accelerate the concentration rate and reduce the operating time correspondingly. When the voltage drops are 5, 10 and 15 V, the operating time is 42, 20 and 25 min, respectively. Figs. 6(a) and (b) indicate that the conductivity of dilute solution can be reduced to below 0.2 mS/cm, and the brix of dilute solution can be reduced to ~0. The conductivity of concentrate solution can increase from ~5.7 to ~13.0 when applied voltage drop is 5 or 10 V, and the pH value of concentrate solution increases from 7.7 to 8−9 slightly. When the voltage drop increases to 15 V, the conductivity of concentrate solution increases to a relatively high value of 14.4 mS/cm, and the value of pH in concentrate solution increases rapidly from 7.7 to 11.1 during the concentrating process. The reason may be that the current density in ED stack surpasses the limiting current density, and water in the dilute solution was dissociated as aforementioned. The produced OH− ions are then migrated from the dilute solution to the concentrate solution, resulting in the increase of the pH value and conductivity of concentrate solution. But it cannot 9



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increase the brix of concentrate solution as shown in Fig. 6(b). All brixs can reach 5.2−5.3% when different voltage drops were applied, and all concentration ratios are 2.3 (Table 2). As the voltage drop increases, the energy consumption increases from 3.90 to 19.16 W h/L, as shown in Table 2, which is due to the high current at the earlier stage of experiment. The water transports are also calculated, which decrease from 9.8% to 5.3% due to the reason that high voltage drop can reduce operating time, and thus lower the water transport. In ED concentrating process, low water transport is better for the enhancement of concentration, hence water transport should be reduced to a relatively low value. Overall, the voltage drop is optimized as ~10 V to achieve high concentration rate, relatively low energy consumption and low water transport, and to avoid the dissociation of water in dilute solution.

3.3. Effect of operation mode on concentrating process 3.3.1. Partial cyclic operation mode. To obtain a high concentration of ionic liquids, a partial cyclic operation mode was carried out. In this process the initial volume of concentrate solution was 200 mL, the volume of each step of dilute solution was also 200 mL, and the applied voltage drop across the membrane stack was 10 V. The change in conductivity and brix of concentrate or dilute solution was recorded. The energy consumption and water transport of each step and the concentration ratio were calculated and investigated to evaluate concentrating process. Figs. 7(a) and (b) show the conductivity and brix of dilute solution in each step could be reduced to below 0.2 mS/cm and 0, respectively. Meanwhile, the conductivity of concentrate solution increases gradually from 5.7 to 21.8 mS/cm because of an increase in operating step number; the brix of concentrate solution can increase from 2.3% to 11.0%. Increase speeds of conductivity and brix of the concentrate solution are, however, decreasing as the operating step number increases. This is due that the concentration of concentrate solution is so high that the forward osmosis happens and water in dilute solution is migrated to concentrate solution, thus 10


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decreasing the increase speeds. Table 3 shows a water transport range of 11.0−18.0%, which indicates that the water transport is relatively high in the latter stage of partial cyclic operation, lowering the concentration degree. Besides, Table 3 shows that the energy consumption has a slight increase, the concentration ratio can achieve as high as 4.8 after 11 steps, which is higher than the reported value of ~1.7.4 The operating time of each step increases from 16.5 to 21 min. The reason may be that impurities precipitated on the membrane surface retard the migration of ions. Membrane fouling will be discussed in section 3.4 in detail. In summary, high concentration of concentrate solution can be achieved in the partial cyclic operation mode. For instance, the conductivity of concentrate solution can increase to 21.8 mS/cm; and brix can be enhanced to 11.0%, almost five times of initial feed solution (2.3%). Nevertheless, the water transport and the operating time of each step increase as an increase in step number, lowering the concentration degree. Hence, change in volume ratio of concentrate solution to dilute solution was investigated hereafter.

3.3.2. Change in volume ratio of concentrate solution to dilute solution. Different volume ratios of concentrate solution to dilute solution (Vc:Vd) were carried out as a comparison to the partial cyclic operation mode. The initial volume of concentrate solution was fixed at 200 mL in each experiment, the dilute solution volume was raised from 400 to 1600 mL, and the applied voltage drop across the membrane stack was constant at 10 V. Fig. 8 shows that the current decreases slowly as an increase in the volume of dilute solution. The reason should be that the conductivity of the dilute solution with a larger volume decreases more slowly than that with a smaller volume as a function of operating time as can be seen in Fig. 9(a). Figs. 9(a) and (b) show the conductivity and brix of dilute solution all can be reduced to below 0.2 mS/cm and 0, respectively. The conductivity and brix of concentrate solution increase consistently during the concentrating process when the volume ratios are 1:2, 1:4, and 1:6. However, a slight downtrend of the conductivity and brix of concentrate solution, at the latter stage of 11



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concentrating process, occurs when the volume ratio is 1:8. This can be attributed to the water transport including forward osmosis and electro-osmosis. After running 110 min the brix of dilute solution has been decreased to nearly 0, while that of concentrate solution has achieved the highest value of 10.6%; and the conductivity of dilute solution was lower than 0.395 mS/cm, while that of concentrate solution has achieved the highest value (19.5 mS/cm). As a result, the concentration and osmotic pressure differences between dilute solution and concentrate solution, this moment, were much higher, resulting in the occurrence of forward osmosis, i.e., water is extracted from a lower osmotic pressure solution (dilute solution) into a higher osmotic pressure solution (concentrate solution) by a driving force of osmotic pressure difference26. In addition, electro-osmosis as aforementioned occurred throughout the overall concentrating process. Hence, at the latter stage of concentrating process, there was much more water migrated from the dilute to the concentrate solution, and thus causes a decrease in conductivity and brix. Energy consumption, water transport and concentration ratio were also calculated and listed in Table 4. The energy consumption has no obvious decrease and is in the range of 10.04−9.07 kW h/m3 as the volume ratio changes. Water transport is in the range of 8.3−11.4%, but the increase in volume of concentrate solution increases from 33 to 165 mL dramatically as an increase in the volume of dilute solution, which restricts the concentration degree. Nonetheless, larger volume of dilute solution can lead to a higher concentration ratio (4.5); hence the volume ratio of 1:8 is a better choice. Under this condition, significantly, the conductivity of the concentrate solution can reach the highest value of 19.5 mS/cm at 100 min, and that of the dilute solution can be reduced to 0.5 mS/cm; the brix of concentrate solution can reach the highest value of 10.6%, and that of dilute solution can be reduced to zero. In comparison, in the partial cyclic operation mode, at the total operating time of 100 min the conductivity of concentrate solution can reach up to 19.6 mS/cm, which is close to 19.5 mS/cm in the volume ratio of 1:8; and the brix can reach 8.7% lower than that of volume ratio of 1:8 (10.6%). The reason may be that large amount of ions in the dilute solution have been migrated to the concentrate solution when the volume 12


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ratio is 1:8, while in the partial cyclic operation mode just six steps have been performed and a limited number of ions be migrated when the operating time is 100 min as can be seen in Fig. 7. When the operating time prolongs to 140 min, the 8th step in the partial cyclic operation mode was performed, the conductivity of concentrate solution can increase to 21.2 mS/cm, which is higher than 19.5 mS/cm (volume ratio of 1:8), and the brix can reach 9.9% lower than that of volume ratio of 1:8 (10.6%).The reason for the high conductivity maybe that some water in the dilute solution were dissociated at the latter stage of each step, and the produced OH− ions were migrated and enriched in concentrate solution, enhancing the conductivity of concentrate solution. The low value of brix can be ascribed to high water transport (12.6%, the average value of eight steps in front), which is higher than the value of volume ratio of 1:8 (10.3% as shown in Table 4) and dilutes the concentration of ionic liquids in the concentrate solution. In the partial cyclic operation mode, the brix of concentrate solution can reach as high as 10.6% after the operating time of 165 min, obviously higher than the case of 100 min as aforementioned. Besides, the energy consumption of volume ratio of 1:8 is 9.46 kW h/m3 and is lower than that of the partial cyclic operation mode (>10 kW h/m3). Overall, the concentration performance of volume ratio of 1:8 is superior to the partial cyclic operation mode under the consideration of high brix of 10.6%, high concentration ratio of 4.5, low water transport of 10.3%, and low energy consumption of 9.46 kW h/m3. After ED concentrating process, the ionic liquids can be further concentrated by other concentrating processes such as the mechanical vapor recompression (MVR) to achieve a high purity, so as to be reused in industrial application.

3.4. Investigation of the fouling of anion exchange membrane. Anion exchange membrane (AEM) in ED process is easy to be fouled by organic or other foulants.27−29 The foulants tends to be absorbed on the surface of membrane by electrostatic interaction,30 which would increase the membrane resistance and affects the migration of anions from the dilute solution to the concentrate solution. Hence, the AEM fouling should be taken into consideration after long-time running. Therefore, the properties 13



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of CJMA membrane after running 11 times were investigated to evaluate the membrane fouling through ion exchange capacity (IEC), images of scanning electron microscopy (SEM), and membrane resistance. As a comparison, the properties of fresh CJMA membrane were also investigated. Table S2 shows that the IEC value of the membrane after experiment is 0.95 meq/g, which is equal to the pristine membrane. It indicates that the polymer structure of anion exchange membrane has not been degraded by ionic liquids; the membrane performance is relatively stable for the concentration of ionic liquids. Fig. 10 shows the SEM cross-section and surface of membranes before and after experiment, large amounts of foulants are clearly observed on the dilute side of membrane, while a small quantity of foulants is observed on the concentrate side. The reason should be that the foulants generally are negatively charged, and tends to be accumulated and absorbed easily on the dilute side of AEM under an electric field in ED process. However, the absorbed foulants are disadvantageous for the migration of ions, followed by increasing the operating time of each experiment as described in Table 3. Hence, in industrial separation process, the problem of foulants should be overcome to achieve high separation efficiency. Besides, the membrane resistances were measured in two ways to investigate the influence of ionic liquids on membrane resistance during the ED process. For one thing, fresh and fouled membranes were measured by the regular method used in the measurement of commercial membrane, i.e. before the measurement membranes were immersed in 0.5 mol/L NaCl for 12 h. For another, to eliminate the influence of NaCl on membrane resistance, the samples were immersed in water for 12 h and then be measured. The results listed in Table S2 indicate that the fouled membrane after being immersed in water has a lower membrane resistance (1.14 Ω cm2) than the fresh membrane resistance after immersion in NaCl (2.04 Ω cm2). It can be attributed to the reason that large amounts of conductive ions in the ionic liquids are accumulated inside the membrane, enhancing the conductivity of the fouling membrane. Overall, the basic properties of membrane have no obvious change in concentrating ionic liquids process under consideration of stable IEC and low membrane resistance. 14


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Nevertheless, the absorption of foulants on the membrane surface, especially on the dilute side, is an unavoidable problem, which lowers the migration of ions from the dilute solution to the concentrate solution, and should be solved in industrial application.

4. Conclusions The ionic liquids with a brix of 2.3% are effectively concentrated by electrodialysis (ED). Membrane types were optimized as CJMC/MA membranes in consideration of high concentration rate and low membrane cost. The optimal operating voltage drop across the ED membrane stack was optimized as ~10 V to achieve high concentration rate (30 min), low energy consumption (10.04 kW h/m3) and low water transport (8.3%), and to avoid the dissociation of water in dilute solution. In addition, the effect of operation modes, including partial cyclic operation mode and change in volume ratio of concentrate solution to dilute solution, on concentrating process was investigated. Results indicate that the concentration performance of volume ratio of 1:8 is superior to the partial cyclic operation mode due to high brix (10.6%), high concentration ratio (4.5), low water transport (10.3%) and low energy consumption (9.46 kW h/m3). Besides, fouling of anion exchange membrane was investigated through a comparison of membrane properties between fresh membrane and fouled membrane. It was found that the basic properties of membrane have no obvious change because of stable ion exchange capacity and low membrane resistance. However, the absorption of foulants on the membrane surface especially on the dilute side was observed. The foulants can decrease the concentration performance and should be taken into consideration in industrial application. Hence, further studies are needed for pretreatment of the waste ionic liquids to resolve the problem of membrane fouling in order to achieve a relatively stable ED performance in concentrating waste ionic liquids.

Acknowledgements 15



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This project was supported bythe National Natural Science Foundation of China (Nos. 21476220, 21490581,21106140), One Hundred Person Project of

the Chinese

Academy of Sciences and National High Technology Research and Development Program 863 (No. 2015AA021001).

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References [1] Li, H.; Meng, H.; Li, C. X.; Li, L. S. Competitive transport of ionic liquids and impurity ions during the electrodialysis process. Desalination 2009, 245, 349. [2] Meng, H.; Li, H.; Li, C. X.; Li, L. S. Synthesis of ionic liquid using a four-compartment configuration electrodialyzer. J. Membr. Sci. 2008, 318, 1. [3] Wang, X. L.; Nie, Y.; Zhang, X. P.; Zhang, S. J.; Li, J. W. Recovery of ionic liquids from dilute aqueous solutions by electrodialysis. Desalination 2012, 285, 205. [4] Himmler, S.; König, A.; Wasserscheid, P. Synthesis of [EMIM]OH via bipolar membrane electrodialysis–precursor production for the combinatorial synthesis of [EMIM]- based ionic liquids. Green Chem. 2007, 9, 935. [5] Herrmann, S. New synthetic routes to polyoxometalate containing ionic liquids: an investigation of their properties. Springer, 2015. [6] Haerens, K.; De Vreese, P.; Matthijs, E.; Pinoy, L.; Binnemans, K.; Vander Bruggen, B. Production of ionic liquids by electrodialysis. Sep. Purif. Technol. 2012, 97, 90. [7] Zhao, D. B.; Wu, M.; Kou, Y.; Min, E. Ionic liquids: applications in catalysis. Catal. Today. 2002, 74, 157. [8] Trinh, L. T. P.; Lee, Y. J.; Lee, J. W.; Bae, H. J.,; Lee, H. J. Recovery of an ionic liquid [BMIM]Cl from a hydrolysate of lignocellulosic biomass using electrodialysis. Sep. Purif. Technol. 2003, 120, 86. [9] Lopez, A. M.; Hestekin, J. A. Separation of organic acids from water using ionic liquid assisted electrodialysis.Sep. Purif. Technol. 2013, 116, 162. [10] Lopez, A. M.; Hestekin, J. A. Improved organic acid purification through water enhanced electrodeionization utilizing ionic liquids. J. Membr. Sci. 2015, 493, 200. [11] Kárászová, M.; Kacirková, M.; Friess, K.; Izák, P. Progress in separation of gases by permeation and liquids by pervaporation using ionic liquids: A review. Sep. Purif. Technol. 2014, 132, 93. [12] Zhao, W.; He, G. H.; Zhang, L. L.; Ju, J.; Dou, H.; Nie, F; Liu, H. J. Effect of water in ionic liquid on the separation performance of supported ionic liquid membrane for CO2/N2. J. Membr. Sci. 2010, 350, 279. [13] Li, Z. Y.; Pei, Y. C.; Wang, H. Y.; Fan, J.; Wang, J. J. Ionic liquid-based aqueous two-phase 17



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systems and their applications in green separation processes. Trends Anal. Chem. 2010, 29, 1336. [14] Xu, T. W.; Huang, C. H. Electrodialysis-based separation technologies: A critical review. AIChE J. 2008, 54, 3147. [15] Marder, L.; Bernardes, A. M.; Ferreira, J. Z. Cadmium electroplating wastewater treatment using a laboratory-scale electrodialysis system. Sep. Purif. Technol. 2004, 37, 247. [16] Zhang, Y.; Pinoy, L.; Meesschaert, B.; Van der Bruggen, B. Separation of small organic ions from salts by ion‐exchange membrane in electrodialysis. AIChE J. 2011, 57, 2070. [17] Jiang, C. X.; Wang, Y. M.; Zhang, Z. H.; Xu, T. W. Electrodialysis of concentrated brine from RO plant to produce coarse salt and freshwater. J. Membr. Sci. 2014, 450, 323. [18] Wang, Y. M.; Zhang, Z.; Jiang, C. X.; Xu, T. W. Electrodialysis process for the recycling and concentrating of tetramethylammonium hydroxide (TMAH) from photoresist developer wastewater.Ind. Eng. Chem. Res. 2013, 52, 18356. [19] Wang, X. L.; Wang, Y. M.; Zhang, X.; Feng, H. Y.; Li, C. R.; Xu, T. W. Phosphate recovery from excess sludge by conventional electrodialysis (CED) and electrodialysis with bipolar membranes (EDBM). Ind. Eng. Chem. Res. 2013, 52, 15896. [20] Xu, T.W.; Yang, W. H. Fundamental studies of a new series of anion exchange membranes: membrane preparation and characterization. J. Membr. Sci. 2001, 190, 159. [21] Xu, T. W. Ion exchange membranes: state of their development and perspective. J. Membr. Sci. 2005, 263, 1. [22] Rottiers, T.; Ghyselbrecht, K.; Meesschaert, B.; Van der Bruggen, B.; Pinoy, L. Influence of the type of anion membrane on solvent flux and back diffusion in electrodialysis of concentrated NaCl solutions. Chem. Eng. Sci. 2014, 113, 95. [23] Lu, H. Y.; Lin, C. S.; Lee, S. C.; Ku, M. H.; Hsu, J. P.; Tseng, S.; Lin, S. H. In situ measuring osmosis effect of Selemion CMV/ASV module during ED process of concentrated brine from DSW. Desalination 2011, 279, 278. [24] Walker, W. S.; Kim, Y.; Lawler, D. F. Treatment of model inland brackish groundwater reverse osmosis concentrate with electrodialysis—Part II: Sensitivity to voltage application and membranes. Desalination 2014, 345, 128. [25] Tanaka, Y. Concentration polarization in ion-exchange membrane electrodialysis—the 18


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events arising in a flowing solution in a desalting cell. J. Membr. Sci. 2003, 216, 149. [26] Valladares Linares, R.; Li, Z.; Sarp, S.; Bucs, S. S.; Amy, G; Vrouwenvelder, J. S. Forward

osmosis niches in seawater desalination and wastewater reuse. Water Res. 2014, 66, 122. [27] Lindstrand, V.; Sundström, G.; Jönsson, A. S. Fouling of electrodialysis membranes by organic substances. Desalination 2000, 128, 91. [28] Lee, H. J.; Hong, M. K.; Han, S. D.; Cho, S. H.; Moon, S. H. Fouling of an anion exchange membrane in the electrodialysis desalination process in the presence of organic foulants. Desalination 2009, 238, 60. [29] Lee, H. J.; Hong, M. K.; Han, S. D.; Shim, J.; Moon, S. H. Analysis of fouling potential in the electrodialysis process in the presence of an anionic surfactant foulant. J. Membr. Sci. 2008, 325, 719. [30] Langevin, M. E.; Bazinet, L. Ion-exchange membrane fouling by peptides: a phenomenon governed by electrostatic interactions. J. Membr. Sci. 2011, 369, 359.

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Captions of Figures and Tables Figures Fig. 1.Schematic ED setup containing (1) direct current supply, (2) membrane stack with four repeating units, (3) electrode chamber, (4) concentrate chamber, (5) dilute chamber, and (6) submersible pump. Note: ERS is electrode rinse solution. Fig. 2. Schematic diagram of partial cyclic operation mode, in which ED stack is shown in Fig. 1 in detail. Fig. 3.Current-time curves of different types of membranes in concentrating ionic liquid. Notes: Applied voltage drop across the membrane stack is 10 V; volume ratio of initial concentrate solution to dilute solution is 1:2. Fig. 4.Change in the conductivity (a) and brix (b) of concentrate/dilute solution using different membranes in ED. Notes: C is the concentrate solution; D is the dilute solution; applied voltage drop across the membrane stack is 10 V; and volume ratio of initial concentrate solution to dilute solution is 1:2. Fig. 5.Current-time curves using different voltage drops across the membrane stack to concentrate ionic liquid. Notes: The used membranes are CJMC/MA membranes, volume ratio of initial concentrate solution to dilute solution is 1:2. Fig. 6.Change in the conductivity (a) and brix (b) of concentrate/dilute solution using different voltage drops across the membrane stack to concentrate ionic liquid. Notes: C is the concentrate solution; D is the dilute solution; the used membranes are CJMC/MA membranes; and volume ratio of initial concentrate solution to dilute solution is 1:2. Fig. 7. Change in the conductivity (a) and brix (b) of concentrate/dilute solution as an increase in step number. Note: The used membranes are CJMC/MA membranes; applied voltage drop across the membrane stack is 10 V; the volume of initial concentrate solution is 200 mL; and the volume of each step of dilute solution is 200 mL. Fig. 8.Current-time curves of different volume ratios of initial concentrate solution to dilute solution. 20


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Note: The used membranes are CJMC/MA membranes; applied voltage drop across the membrane stack is 10 V; Vc is the initial volume of concentrate solution; and Vd is the initial volume of dilute solution. Fig. 9.Change in the conductivity (a) and brix (b) of concentrate/dilute solution as an increase in the volume ratio of initial concentrate solution to dilute solution. Note: The used membranes are CJMC/MA membranes; applied voltage drop across the membrane stack is 10 V. Fig. 10.SEM images of anion exchange membrane including (a) cross-section of fresh membrane, (b) cross-section of fouled membrane, (c) surface of fresh membrane, (d) concentrate side of fouled membrane, and (e) dilute side of fouled membrane.

21



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Tables Table 1. Energy consumption (E), water transport (WT) and concentration ratio (Cr) after experiments using different types of membranes in concentrating ionic liquid. Note: The operating times of the cases of CMV/AMV, CJMC/MA and FKS/FAS were 30, 30 and 45 min, respectively. Table 2. Energy consumption (E), water transport (WT) and concentration ratio (Cr) after experiments using different voltage drops across the membrane stack to concentrate ionic liquid. Table 3. The energy consumption (E), water transport (WT) and operating time of each step and the change in concentration ratio (Cr) in partial cyclic operation mode. Table 4. Energy consumption (E), water transport (WT) and concentration ratio (Cr) after experiments using different volume ratios of initial concentrate solution to dilute solution.

22


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Fig. 1 .

23



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Fig. 2

24


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Page 25 of 37

Fig. 3

4.0 3.5

CMV/AMV CJMC/MA FKS/FAS

3.0 2.5

I (A)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2.0 1.5 1.0 0.5 0.0 0

10

20

30

T (min)

25


40

50


Fig. 4

Conductivity (mS/cm)

(a)

14 12 10 8 6 4 2 0

CMV/AMV-C CMV/AMV-D

0

5

10

15

20

CJMC/MA-C CJMC/MA-D

25

30

35

FKS/FAS-C FKS/FAS-D

40

45

T (min)

(b) 6 Brix (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 37

5 4 3 2 1 0

CMV/AMV-C CMV/AMV-D

0

5

10

15

20

CJMC/MA-C CJMC/MA-D

25

30

35

T (min)

26


FKS/FAS-C FKS/FAS-D

40

45

Page 27 of 37

Fig. 5

6.0 5.5

5V 10V 15V

5.0 4.5 4.0 3.5

I (A)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


3.0 2.5 2.0 1.5 1.0 0.5 0.0 -0.5 0

5

10

15

20

25

30

35

T (min)

27


40

45


Fig. 6


(a) 16 14 12 10 8 6 4 2 0

5V-C 5V-D

0

5

10

15

20

10V-C 10V-D

25

30

15V-C 15V-D

35

40

45

T (min)

(b) 6 Brix (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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5 4 3 2 1 0

5V-C 5V-D

0

5

10

15

20

10V-C 10V-D

25

30

T (min)

28


15V-C 15V-D

35

40

45

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Fig. 7

(a)

25

1C 7C

2C 8C

3C 9C

4C 10C

5C 11C

6C


20 15 10

1D 7D

2D 8D

3D 9D

4D 10D

5D 11D

6D

5 0 0

20

40

60

80

100 120 140 160 180 200

T (min)

(b)

12

1C 7C

2C 8C

3C 9C

4C 10C

2D 8D

3D 9D

5C 11C

6C

10 8

Brix (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


6 4

1D 7D

4D 10D

5D 11D

6D

2 0 0

20

40

60

80

100 120 140 160 180 200

T (min)

29



Fig. 8

4.0 3.5

Vc:Vd=1:2 Vc:Vd=1:4

3.0

Vc:Vd=1:6 Vc:Vd=1:8

2.5

I (A)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

2.0 1.5 1.0 0.5 0.0 0

10 20 30 40 50 60 70 80 90 100 110 120 130 140

T (min)

30


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Fig. 9


(a) 21 18 15 12 9 6 3 0

1:2-C 1:2-D

0

10

20

30

40

50

1:4-C 1:4-D

60

70

80

1:6-C 1:6-D

1:8-C 1:8-D

90 100 110 120 130 140

T (min)

(b)

10 8

Brix (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


6 1:2-C 1:2-D

4

1:4-C 1:4-D

1:6-C 1:6-D

1:8-C 1:8-D

2 0 0

10

20

30

40

50

60

70

80

90 100 110 120 130 140

T (min)

31



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Fig. 10

32


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 1 Membrane types

E (kW h/m3)

WT (%)

Cr

CMV/AMV CJMC/MA FKS/FAS

9.34 10.04 11.88

5.5±0.5 8.3±0.5 5.5±0.5

2.4 2.3 2.3

33



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Table 2. Voltage drop (V)

E (kW h/m3)

WT (%)

Cr

5 10 15

3.90±0.16 10.04±0.16 19.16±0.15

9.8±0.5 8.3±0.5 5.3±0.5

2.3±0.1 2.3±0.1 2.3±0.1

34


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Table 3. Step number 3

E(kW h/m ) a WT (%) Cr Operating time (min)

1

2

3

4

5

6

7

8

9

10

11

10.25 11.5 1.6 16.5

10.15 11.0 2.4 17.5

10.38 12.0 2.7 18.0

10.21 13.0 3.2 17.5

10.18 13.5 3.6 18.5

10.84 13.5 3.8 17

10.75 13.0 4.1 17.5

10.53 13.5 4.3 18

10.65 15.0 4.5 19.5

10.66 16.0 4.7 19.5

10.52 18.0 4.8 21

a

The deviation is ±0.5.

35



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Table 4 Vc: Vd

E (kW h/m3)

WT (%)

Cr

1:2 1:4 1:6 1:8

10.04±0.16 9.56±0.12 9.07±0.11 9.46±0.10

8.3±0.5 10.9±0.3 11.4±0.2 10.3±0.1

2.3±0.1 3.3±0.1 4.0±0.1 4.5±0.1

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Electrodialysis To Concentrate Waste Ionic Liquids: Optimization of

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