Reclamation of Aniline Wastewater and CO2 Capture Using Bipolar

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The reclamation of aniline wastewater and CO2 capture using bipolar membrane electrodialysis Qiuyue Wang, Chenxiao Jiang, Yaoming Wang, Zheng-jin Yang, and Tongwen Xu ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.6b01686 • Publication Date (Web): 29 Aug 2016 Downloaded from http://pubs.acs.org on September 4, 2016

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ACS Sustainable Chemistry & Engineering

The reclamation of aniline wastewater and CO2 capture using bipolar membrane electrodialysis

List of Authors

Mailing Address

Qiuyue Wang

No.96 Jinzhai Road, Baohe district, Hefei, Anhui Province, China

Chenxiao Jiang


Yaoming Wang


Zhengjin Yang


Tongwen Xu*


1

ACS Paragon Plus Environment


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Qiuyue Wang, Chenxiao Jiang, Yaoming Wang, Zhengjin Yang and Tongwen Xu*

CAS Key Laboratory of Soft Matter Chemistry, Collaborative Innovation Center of Chemistry for Energy Materials, School of Chemistry and Material Science, University of Science and Technology of China, Hefei 230026, PR China [email protected] (T. W. X). ABSTRACT: Aniline-contained wastewater and greenhouse gases are two significant environmental issues that threaten the life of human being. In this work, a novel bipolar membrane electrodialysis (BMED)-based process was proposed to treat the aniline waste water and simultaneously capture CO2. Such process consists of pre-desalinization, CO2 capture and aniline removal three steps. Firstly, the pre-desalinization is to remove the salt in saline aniline wastewater because the aniline is neutral in this condition. Secondly, in order to adjust the pH of wastewater and make the aniline positively charged, the CO2 is captured and finally, BMED is used to remove aniline from the feed compartment and then collect in base compartment and simultaneously recover CO2 in acid compartment. The processes are discussed in terms of multi-aniline content, multi-CO2 partial pressure and multi-steps, which clearly indicate the feasibility of the processes with an eco-friendly and low cost way. Keywords:

Aniline, Wastewater, CO2 capture, Electrodialysis, bipolar membrane 2


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■ INTRODUCTION Aniline, as a typical aromatic compound, has been widely used as the intermediate for the manufacturing of various organic compounds such as colorants, agrichemicals, pharmaceutical agents and synthetic resins1, and also exist as the by-product of the petroleum, paper, coal and chemical industries. The aniline could react in the blood and convert hemoglobin into methemoglobin which would prevent the oxygen uptake. Therefore, aniline has a serious effect on human health2. Considering the characteristics of long-term residue, biological accumulation and carcinogenic properties, aniline is listed as one of the 129 kinds of priority control pollutants by US EPA (U.S. Environmental Protection Agency)3, and should be strictly controlled in industrial drainage. Conventionally, several methods have been used for aniline wastewater treatment which include chemical

4, 5

, physical

6, 7

, biological

8-11

and electrochemical12,

13

methods. Biological method is the most widely used, by which aniline can be completely biodegraded into CO2 and N2/NOx. However, the chemical, biological and electrochemical methods can’t achieve the recovery of aniline, and exhaust enormous amount of chemical reagents, which not only increases the operation cost but also causes secondary pollution. For examples, biological method is temperature dependent and inhibited by the toxicity of pollute, especially it is greatly sensitive to the wastewater salt concentration; electrochemical method is clean and easy to be handled but would produce more CO2 which is known as greenhouse gas. Although the physical method can recover aniline, it is not suitable for industrial application 3



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since it is difficult for the clarification between extract regent and aniline. An efficient process for aniline wastewater treatment is urgently needed. And as a primary component of greenhouse gases, the capture of carbon dioxide has a great significance for global warming and environment. The existing CO2 capture technology is mainly based on the reciprocal reaction between CO2 and amino compound such as ethanolamine, diethanolamine, piperazine and pyridine, etc. And the generally used CO2 emission method is thermal-process which breaks the reaction balance of organic amine and carbon dioxide by using the method of heating then makes the carbon dioxide released. But a thermal-process has the following disadvantages: 1). Heating is an energy intensive method which relies on the burning of fossil fuels and the difference between the CO2 released in heating and CO2 capture is very small, so the capture efficiency of this process is too low; 2). Heating process will cause the volatilization of organic amine solution; 3). Since there are sulfur dioxide in flue gas and can form thermostable sulfonic organic amine salt, the heat method can’t realize the regeneration. So, a process can meet the demand of the aniline removal and the capture/emission of CO2 is quite valuable. Bipolar membrane electrodialysis (BMED) is an electrodialysis employing a bipolar membrane, which comprises an anion-exchange layer and a cation-exchange layer and its well-known function is to split water into OH− and H+ under reverse bias in a direct current field. Thus, a BMED process can achieve separation and acid/base production simultaneously. As a novel process, it has been used for the environmental protection, biochemistry industry14 and pharmaceutical industry, especially, for the 4


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regeneration of flue-gas desulfurizing agents 15, 16 and the carbon dioxide clarification and capture

17-19

. It is found that the CO2 capture regent always contain organic

amine20 since the amine group could react with CO2 and form positively charged organic amine (shown in Figure 1(a)). As we all know, aniline is not charged in neutral salt solution, therefore, the wastewater containing aniline cannot be treated directly using BMED or conventional electrodialysis. However, if acid gas such as CO2 is introduced into the aniline wastewater, a reaction between CO2 and aniline will occur according to Figure 1(a), in which aniline will be transformed to positively charged aniline and CO2 will be absorbed inside the solution as HCO3-/CO32- or H2CO3 form. In this case, the aniline wastewater that has reacted with CO2 can be pumped into the BMED process and be treated correspondingly according to the separation mechanism (Figure 1(b)). During the BMED process, the positively charged aniline in the feed compartment moves through the cation-exchange membranes and stays in the base compartment then combines with the OH- produced by the bipolar membrane; at the same time, the HCO3-/CO32- would move through the anion exchange membrane and combine with the H+ produced in acid compartment, which makes the emission of carbon dioxide possible. The process not only can recover the aniline in waste water but also can achieve the capture of carbon dioxide. It thus shows several potential advantages: 1) efficiently treated the aniline salt wastewater under low energy consumption, 2) regenerated the aniline and salt as byproduct with considerable extra value and 3) realize the capture and storage of CO2.

5



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Figure 1. Schematic diagram and mechanism of simultaneous aniline recovery and CO2 capture (a. the reaction between aniline and CO2; b. BMED process of aniline removal) There is about 30 million kilogram aniline 21(nearly 322 million mol) going into the environment every year in the word. Theoretically, if it was treated with this process, about 322 million mol CO2 (equivalent to 14.17 million kilogram) will be captured per year, while the global anthropogenic emission is about 35 billion tons22, which is too much more than we can capture, but it should be noted that aniline wastewater is only one representative and normally produced organic wastes in the industries. A series of organic amine wastewaters are normally produced in the pharmaceutical industry, printing and dyeing industry, and petrochemical industry, such as ethylamine, pyridine, phenylenediamine, p-phenylenediamine etc., which often have strong toxicity and hard to treat due to their high stability. Aniline was just selected as a model for the investigation of the feasibility and research the potential for the treatment of other organic amine wastes using this novel process. Therefore, although 6


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annually aniline wastewater produced is not significant, it would be greatly improved when other organic amines was considered. In order to demonstrate the feasibility of this process, in this work, we have introduced simulated flue gas with different carbon dioxide levels for the treatment of salty wastewater with different concentrations of aniline. The desalting efficiency and removal ratio of aniline will be investigated and the capture of CO2 will be discussed at the same time.

■ EXPERIMENTAL SECTION Materials. A BMED stack with two repeat units of BP-C-A configuration was applied in these experiments, in which two anion-exchange membranes (CJMA-1, Table 1), two cation-exchange membranes (CJMC-1, Table 1) and three bipolar membranes (BPM-I, Table 1) with an effective membrane area of 189 cm2 (9 cm width and 21 cm length) were used. The reagents used include aniline, NaCl, Na2SO4, HCl and NaOH. All are AR. and purchased from Sinopharm Chemical reagent Co., Ltd., China. Table 1 Types of membrane and their properties Membrane type

Thickness (µm)

IECa (meq.g-1)

Area resistance (Ω.cm2)

Water uptakeb (%)

Transport number (%)

CJMC-1

160-200

1.5

1.3-1.7

62

0.91

CJMA-1

160-200

1.5

2.8-3.2

46

0.91

TR, BPM-I

160-230

-

-

35-40

-

7



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The data were collected from the product brochure provided by manufacturers a

Anion-exchange membrane and Cation-exchange membrane IEC were determined in meq.g-1 in -

Cl and Na+ form respectively. b

Water uptake/swelling degree were determined by gH2O/gdry

c

Anion-exchange membrane and Cation-exchange membrane area resistance was measured as -

Cl and Na+ form in 0.5M NaCl @T=25 °C .

Setup and equipment. As shown in Figure 1(b), the integrated EDBM stack is composed of two cell triplets, each cell triplet containing an electrode, a feed, an acid and a base compartment regulated by special designed millimeter-thick Silica gel spacers and membranes with an effective area of 189 cm2 (9 cm width and 21 cm length).The electrode made of titanium coated with ruthenium has the same effective area as silica gel spacers and membranes. Figure 2 showed the flowchart and photograph of laboratory-scale experimental equipment. Each chamber was connected with corresponding sealed canister and diaphragm pump (PLD-1205, Shijiazhuang Pulandi Mechanical & Electrical Equipment Co., Ltd., China) via silicone tube. The flow rate was 500 mL/min for the cycle of electrode, feed, acid and base solution, respectively.

8


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Fig 2. (a). A flowchart of the experimental setup and (b). Photo of experiment setup ) The BMED experiment was operated at a constant current density of 10.58 mA/cm2 using a CV/CC regulated power supply (N5772A, Agilent Technologies, Co., Ltd). The samples of feed solution, base solution and acid solution were regularly taken to determine the aniline and sodium concentration of each compartment using ultraviolet spectrophotometer (UV-2550) and ICP (Optima 7300DV, inductively coupled plasma emission spectrometer) method, respectively. Considering the linear range of UV detection and ICP detection, all sample solutions were diluted 100 times before the test. In order to eliminate the potential bubble trapped inside the BMED stack, the solutions need to be circulated for at least 10 min before the experiment. In the experiment, the variation in temperature, pH, conductivity of solution and the potential drop of membrane stack were recorded by temperature sensors (MIK-WRP, Hangzhou Sinomeasure Automation Technology Co., Ltd.), pH meters (SIN-PH160, Hangzhou Sinomeasure Automation Technology Co., Ltd.), conductivity meters 9



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(SIN-TDS210, Sinomeasure, Hangzhou Sinomeasure Automation Technology Co., Ltd.) and a Voltage transmitter (MIK-DZU-0-5V-1000V, Hangzhou Sinomeasure Automation Technology Co., Ltd.) respectively. These data from the transmitters were recorded online every one second and were managed using the data management software. Membranes before and after experiments were characterized by scanning electron microscope (SEM, TM3000, Tabletop Microscope, Hitachi, Ltd.) and ATR-FTIR (Nicolet™ iS™10 FT-IR Spectrometer, Thermo Scientific, USA).

Procedures. As aforementioned, the procedure of aniline salt wastewater treatment using BMED and simulated fossil combustion fuel gases can be viewed as three steps: the removal and online transformation salt from the wastewater, the capture of CO2 and ionizion of aniline (Figure 1(a)); and the removal of positively charged aniline by BMED according to Figure 1(b). To investigate the availability of this process, a series of simulated fossil combustion fuel gases with inherent different compositions ( a)100 % CO2, b) 50% N2 + 50% CO2 and c) 70% N2 + 30% CO2 ) were proceeded using pure CO2 and N2 gas. The simulated salty aniline wastewater was prepared with different concentrations of aniline (1000ppm, 2000 ppm and 3000 ppm) with same inorganic salt content (0.1 M NaCl). The simulated aniline salt waste water was filled into feed compartment, pH of 6.5 NaH2PO4/H3PO4 buffer solution in the acid compartment, 0.1 M NaOH in the base compartment and 3% Na2SO4 solution in the two electrode compartments, respectively. To check the leakage or communication between adjacent compartments 10


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and simultaneously exclude the trapped invisible bubbles inside the BMED stack, the solutions were circulated for 20 min before the running of the experiment. Afterwards, the experiments were operated as following three steps (As shown in Figure 3). Step 1. Pre-desalination of aniline salt wastewater. When the solutions were circulating under stable situation, a constant current was supplied on the BMED stack. Under the driven force of current, the aniline in simulated wastewater prepared in our experiment is neutral and would not move, the sodium ions in our feed solution would be attracted to the cathode through the cation-exchange membrane and combine with hydroxyl ions produced by the bipolar membrane and then formed sodium hydroxide in the base compartment; accordingly, the chloride ions in the feed solution would move toward the anode through the anion-exchange membrane and combined with hydrogen ions produced by the bipolar membrane and then formed hydrochloric acid in the acid compartment. With the development of time, the sodium ions and chloride ions in feed solution all moved to corresponding chamber and the goal of pre-desalination was achieved (The conductivity drops to 100 µs/cm). The electro-neutral aniline stays in feed solution.

11



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Fig 3. The operation process chart of treating salty aniline wastewater with capture of CO2 Step 2. The capture of CO2 and ionization of aniline. After pre-desalination, the wastewater mainly contains the neutral aniline which cannot move under the current. By contacting with simulated fuel gases, aniline and CO2 would react and transforms 12


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into positively charged aniline and HCO3-/CO32- or H2CO3 as discussed above. To investigate the influence of fuel gas composition on the wastewater CO2 absorption and recovery, different simulated gases were preceded. The fuel gases were introduced into the feed compartment at the constant flow rate of 0.2 L/min (measured by CO2). To guarantee the absolutely reaction of aniline and CO2, the current would not supply onto the BMED stack until the pH comes to constant state for the feed compartment. Step 3. Removal of the positively charged aniline ions and recovery of the CO2. After the above two steps, the feed was transformed to the charged aniline ions and bicarbonate ions, which is ready for BMED. Under the driven force of current potential, the positively charged aniline ions in feed solution would move toward the cathode through the cation-exchange membrane and combined with hydroxyl ions produced by the bipolar membrane, then get aniline molecules; while the HCO3- in the feed solution would move toward the anode through the anion-exchange membrane and combined with hydrogen ions produced by the bipolar membrane and release carbon dioxide gas. It should be noted that, the simulated fuel gas was continuously input into the feed compartment during the experiment to maintain a constant pH of the wastewater. In summary, the above steps constitute the whole experimental process and realize the following three purposes. 1) The removal of inorganic salt in aniline waste water 2) The capture of CO2 and transformation of aniline in ionic state 13



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3) The removal (or recovery) of aniline from salty aniline waste water and CO2 from flue gas. Calculation formulas and equations. In the aniline removal and recovery process, the most important index is the removal efficiency. For the total procedure, the desalinization rate of feed solution is also a key point. To this issue, we investigated the influence of CO2 partial pressure and initial aniline content on the removal rate for aniline and total desalinization ratio (for three steps) named in ηand ω, respectively. The equations are shown as following:

η = × 100%

ω=

(1)

× 100% (2)

where the η stands for the removal rate of aniline, Cb and Cf stands for the aniline concentration of feed solution before and after treatment respectively. And, as the desalinization ratio of feed solution for the whole process, ω is equivalent to the ratio of sodium concentration after (CNa+ here) and before(C0 here) treatment since the simulated wastewater contained only NaCl as its salt composition. The current efficiency and energy consumption of aniline removal and NaCl desalinization were assessed. The NaCl desalination current efficient and energy consumption is based on the data of step1 while the current efficient and energy consumption of aniline removal is based on the data of step3. When the applied current is fixed, the current efficiency of NaCl desalination ( (%)) and aniline removal ( (%))can be calculated as following equations： ( − ) ∙ ∙ = × 100% (3) ∙ ∙!

14


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=

(#$%&%$' − #$%&%$' )∙∙ × 100% (4) ∙ ∙!

+ where in the feed and (mol/L) are the concentration of element Na

compartment at time t and 0 respectively; Similarly, #$%&%$' and #$%&%$' (mol/L) are

the concentration of aniline in the feed compartment at time t and 0 respectively; V (L) is the volume of the feed compartment; F is Faraday constant (96485 C); I is constant current (the applied current density multiply the membrane effective area); n is repeating unit of the BMED stack (n=2 here); t (min) is test time. The energy consumption of NaCl desalination () (kW h/kg)) and aniline removal () (kW h/kg)) were calculated as following equation:

) = * ( .

+∙,-

/ )∙0∙1 23

) = *

+∙,- . /4563657 )∙0∙14563657 (4563657

(5)

(6)

where U (V) is the voltage drop across BMED stack; M is molar mass of NaCl or aniline. The reactions that take place when carbon dioxide introduced to feed solution can be represented by the following series of equilibria:

15



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The notations g. and aq. refer to the state of the species. Unfortunately, it is difficult to distinguish between the species CO2 (aq) and H2CO3 by analytical means. It is thus usual to lump the concentrations of CO2 (aq) and H2CO3 together and to express this sum as the concentration of a hypothetical species, CO2* (hydrate convention23), then Reactions(1), (2) and (3) are redefined in terms of this hypothetical species24:

The equilibrium relationships between the concentrations of these various species can then be written as:

8 = 8 = 8 =

[:;∗ ]

(8)

>2?; [@ ][@:AB ] [:;∗ ] [@ ][:A;B ] [@:AB ] [# ]

8C = [# ][@ ]

(9) (10) (11)

where D:; stands for the fugacity of carbon dioxide in the gas phase which represent the partial pressure of CO2 in ideal-gas state; The reaction constant of Eq (6), (7), (4) and (5) is assumed to be k1 , k2 , k3 and k4 which can be obtained from Handbook of Chemistry; the[E FC ], [HCFC/ ], [CFC/ ], [EI ], [JI ] and [J ] are 16


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the concentrations of E FC , HCFC/, CFC/ , E I , positive charged aniline ions and electroneutral aniline in the feed solution, respectively. The coefficients are all constant in our process (25℃, 101.325KPa). As the absorption of CO2, the H+ in feed compartment was increasing and reacting with aniline then ionizing it. According to the equilibrium relationships shown above, we can draw the conclusion that a higher CO2 partial pressure can lead the increase of [CO2*] then facilitate the reaction between CO2 and water/aniline then correspond to a lower pH of feed solution while more aniline can react with more H+ and correspond to a higher pH of feed solution. This conclusion also can be confirmed in the results and discussion section.

■ RESULTS AND DISCUSSION Step 1. Pre-desalination of aniline salt wastewater. In order to investigate the desalination efficiency with different contents of aniline, the pH and sodium concentration conductivity change in feed solution, the voltage of membrane stack was discussed in detail in the following. The experiments were operated under a constant current density for a constant removal of salt.

Fig 4. The conductivity and pH variation in feed solution as a function of time before 17



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CO2 capture As shown in Figure 4, the conductivity in feed solution decreased with the lapse of time and attained the minimum at around 2600 seconds. It suggests that the pre-process can achieve the aim of desalination for salty waste water with different concentrations of aniline. It can be also observed that the concentration of aniline does not have an obvious influence on the desalination, and the tiny difference in desalting time among different aniline waste water shown in Figure 4 can be imputed to the initial differences in salty content. As time goes, the pH of feed solution with 1000ppm and 2000ppm aniline decreased while it is relatively stable for the solution with 3000ppm aniline. We consider this as the combined effect of the ion leakage of ion exchange membrane and aniline dissociation because the pH drop may be caused by the greater hydrogen ion leakage through the anion exchange membrane than hydroxyl ion leakage through the cation exchange membrane. Especially, a higher concentration of aniline would get a relatively stable pH since it can dissociate more hydroxyl ions and neutralize the hydrogen ions from the leakage of ion exchange membranes. In this step, the change of aniline content in feed solution should be paid close attention. It is a main index for demonstrating that the process cannot realize the removal of aniline without introducing the CO2. The aniline concentrations during the pre-desalination process were recorded in the respective acid/base/feed compartment at time 0 (“Initial”), 20 min (“20 min”) and the end of this step (“Final”). The results were shown in Table 2. It can be observed that there was some loss for the aniline in 18


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the feed solution while the aniline was not charged on this occasion. The relative loss ratio increases with the initial aniline content. Such loss of aniline can mainly be attributed to the adsorption of ion exchange membrane since very little aniline in the acid or base compartment was detected. The adsorption of aniline can be assumed equally due to the same the membrane area at the different initial aniline content, so the relative loss ratio increased with decreased aniline content. In practical application, such loss can be avoided by pretreatment of the membranes with aniline waste. It can also be alleviated if the membranes were used several times25. Table 2 Aniline concentrations of the solutions during the pre-desalination step times 1000 ppm Aniline

2000 ppm Aniline

3000 ppm Aniline

+ 0.1M NaCl

+ 0.1M NaCl

+ 0.1M NaCl

Acid

Feed

Base

Acid

Feed

Base

Acid

Feed

Base

CInitial (mg/L)

0

693.92

0

0

1660.49

0

0

2619.79

0

C20 min (mg/L)

0

670.91

14.41

0

1603.56

48.33

0

2573.76

28.95

CFinal(mg/L)

0

535.25

41.06

16.84

1448.52

32.58

83.45

2315.77

73.76

In short summary, the first step can effectively remove the inorganic salt in aniline waste and the tiny loss of aniline mainly attributes to the adsorption of ion exchange membrane and can be alleviated or ignored by pretreating the membranes with feed solution.

Step 2. The capture of CO2 and ionization of aniline. As mentioned above, step 2 is 19



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to conform the neutral aniline into positive charge with CO2 .Figure 5(a) showed the pH variation of feed solutions at the aniline content of 3000ppm when fuel gas with different CO2 partial pressure was introduced. It could be found that the wastewater pH decreased gradually when the fuel gas was pumped into the feed compartment. Due to the higher CO2 partial pressure, 100% and 50% fuel gas operation stabilized at a lower pH compared to the 30% case, since a higher CO2 partial pressure would facilitate the reaction between CO2 and water/aniline as discussed in Calculation formulas and equations part. Just like the trend shown in Figure 5(a), there isn’t relevance between the pH variation of samples and the CO2 partial pressure of fuel gases introduced

Figure 5. (a) The pH variation of feed solution (3000ppm aniline) with time when fuel gas with different CO2 partial pressure was introduced and (b) Variation of the pH 20


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and conductivity of solutions with different aniline content neutralized with pure CO2.

To investigate the process efficiency to treat different kind of wastewaters, a series of simulated wastewater with aniline content of 1000, 2000, and 3000ppm was input into feed compartment. In this case, pure CO2 was used. The conductivity and the pH change were recorded and illustrated in Figure 5(b). It is obviously to find that with the capture of carbon dioxide (shown in Figure 1(a)), the conductivity of the feed solution increases and pH decreases. A higher aniline concentration can promote the reaction between aniline and CO2, then cause the trend that a higher initial concentration of aniline corresponds a higher conductivity rising rate and stable value. Meanwhile, the color of the data points represents the pH of the feed solution, owning to the alkaline aniline (as shown in Reaction (5) ), a higher initial concentration of aniline corresponds to a higher pH throughout the procedure of CO2 capture (pH1000 ppm 50% CO2 > 100 % CO2.

Figure 6.The variation of the pH and conductivity in feed solutions introduced different fuel gas during BMED The influence of CO2 partial pressure and initial aniline content on the removal rate for aniline and total desalinization ratio (for three steps) is shown in Table 4. And the corresponding calculation formulas are shown in experimental section. Here the 24


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treatment time corresponded to that the stack voltage become stable (all aniline in feed solution was nearly moved out). It can be observed that for all cases, the aniline can be absolutely removed (the removal ratio can attain as high as 100%). But the time for this is different: it increases with initial aniline content but decreases with partial pressure of CO2. For example, at the case of pure CO2, the time for 1000ppm, 2000ppm and 3000ppm are 473s, 562s, 802s, respectively; while at the case of 1000ppm as an example, the time is 530s, 519s and 473s for different CO2 partial pressure such as 30%, 50% and 100% respectively. The explanations can be the same as the above: the high aniline concentration needs more time to remove while the high partial pressure CO2 can promote the protonization reaction. From the point of desalination ratio, the analyses can be the same. All the cases can get a desalination ratio more than 94%, some processes (such as the process 1000ppm aniline introduced 30% CO2) even get a desalinization ratio of 100% when take no account of the detection limit of ICP. It can thus confirm that the process can realize the desalination of wastewater effectively. Table 4. The removal time, removal ratio and desalination ratio at different CO2 partial pressure and aniline content Aniline Content

PCO2

Removal Time

1000 ppm 1000 ppm 1000 ppm 2000 ppm 3000 ppm 3000 ppm 3000 ppm

30% 50% 100% 100% 30% 50% 100%

530 s 519 s 437 s 562 s 1504 s 1454 s 802 s

Removal ratio (aniline) 100% 100% 98.68% 99.86 99.74% 100% 100%

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Desalinization ratio (NaCl) 100% 100% 99.69% 96.51% 96.82% 97.35% 96.74%


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Membrane fouling. Considering the absorption of aniline on the surface of membrane may cause membrane fouling, the SEM images of membranes before and after treatment were taken. As shown in Fig 7, neither cation exchange membrane nor anion exchange membrane shows an appreciable difference in their surface after being used. Those membranes shown below have a clear surface because the aniline absorbed in the membrane can be removed by the driven force of current after ionization.

Figure 7.The SEM images of membranes before and after being used

Figure 8. (a) The ATR-FTIR spectra of CJMA-1 membrane before and after used (b) The ATR-FTIR spectra of CJMC-1 membrane before and after used The ATR-FTIR spectra of membranes before and after being used was shown in 26


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Figure 8, in which we can find that the IR absorption peaks of those membranes do not show a big difference. The difference of absorption value shown in Figure 8 (b) is mainly caused by the thickness difference of membranes. Thus, we can draw the conclusion that during the whole process, the structure and composition of membranes are kept stable. It also can find that there is no characteristic absorption band of amine groups (3300cm-1~3500cm-1) in the ATR-FTIR spectra of membranes before and after being used. It thus suggests that there is no adsorbed aniline on the membranes at last. On the bases of the SEM images and ATR-FTIR spectra of membranes before and after being used, the membrane fouling in our membrane is not serious.

Energy consumption and current efficiency. Based on the calculation method shown in experimental section, the energy consumption and current efficiency of aniline removal and desalinization are shown below:

Fig.9 The current efficiency and energy consumption for NaCl desalination

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Fig.10 The current efficiency and energy consumption for aniline removal As shown in Fig.9, the current efficiency and energy consumption of desalination do not shows a significant difference between wastewaters with different concentrations, while in terms of aniline removal (as shown in Fig.10), a higher initial concentration corresponds to a higher current efficiency and a relative lower energy consumption. The reason is that during this process the aniline loss caused by membrane absorption is almost stable (absorbed 100-300 ppm aniline), and it would be a small amount versus a higher aniline concentration. Considering the current efficiency and energy consumption above, our process performs better when treating an aniline wastewater with a higher concentration. In the aniline removal issue, a minimum energy consumption (2.86 kW h/kg) can be obtained when treating the wastewater with 2000ppm aniline, which is much lower than the data for Electro-Fenton and peroxi-coagulation processes12 (6 kW h/m3, TOC removed 47%, aniline concentration is 1000 ppm) and a little higher than the data for degradation of aniline by plate and rod electrode Fered-Fenton Reactors13 (0. 0025 kW h/L equal to 2.68 kW h/kg, the aniline concentration is 0.01mol/L). Although degradation of aniline by plate and rod electrode Fered-Fenton Reactors can get an energy 28


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consumption lower than BMED, it needs a treatment of more than 30 min to get a remove rate of aniline higher than 95%; besides, it cannot recover the aniline. It should be mentioned that the energy consumptions shown above were calculated using the voltage drops across the whole BMED stack. So the electrode reaction consumption would increase the energy consumption of our process. If the repeat units of our BMED stack were increased and make the contribution of electrode reaction consumption negligible, the energy consumption of aniline removal/recovery would be decreased. The energy consumption also can be further decreased by optimizing the performance of membranes, changing the concentration of feed solution or using thinner spacer.

■ CONCLUSIONS To treat the aniline salt wastewater, the economic and advanced process called bipolar membrane electrodialysis was used and CO2 fuel gas as the greenhouse gas is introduced to react with aniline wastewater. On one aspect, the process would not only successfully remove the inorganic salt and aniline from the wastewater, but also accompany with the CO2 capture and re-storage from the fuel gas. On the other aspect, the process would also realize the useful resources reclamation in the wastewater, since the salt would be recovered as corresponding base and acid byproduct instead of solid waste, and the aniline would also be recovered as the industry raw materials instead of the decomposition from oxidation reaction. The wastewater with different compositions introduced different fuel gas was evaluated using BMED, suggesting 29



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that tall both the dissolved anilines and inorganic salt can be effectively removed: a removal ratio for aniline is higher than 98.68% and a desalinization ratio is higher than 96.51%). Obviously, BMED is a feasible process for the treatment of wastewater with high concentrations of salt and aniline. It is also wondered that, this process can be extended to other system where key neutral component in wastewater can react with CO2.

■ AUTHOR INFORMATION Corresponding Author *Tel.: +86 0551-63601587. Fax: +86 0551-63601587. E-mail: [email protected] (T.W.X.). Notes The authors declare no competing financial interest.

■ ACKNOWLEDGMENT This project was supported in part by the National Natural Science Foundation of China (Nos. 91534203, 21490581, 21476220), National High Technology Research and Development Program 863 (No. 2015AA021001) and One Hundred Person Project of the Chinese Academy of Sciences (2015-43-D). ■ SUPPORTING INFORMATION AVAILABLE CO2 release curve is available free of charge via the Internet at http://pubs.acs.org. 30


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■ Table of Contents


Qiuyue Wang, Chenxiao Jiang, Yaoming Wang, Zhengjin Yang and Tongwen Xu*

Synopsis A novel bipolar membrane electrodialysis-based process was proposed to treat the salty 1aniline waste water and simultaneously capture CO2.

TOC Graphic

33


Reclamation of Aniline Wastewater and CO2 Capture Using Bipolar

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