Carbon nanotube processing system and processing method using electrolysis

Abstract

To provide a carbon nanotube processing system and method that reduce an amount of an oxidizing agent necessary for oxidative decomposition of carbon nanotubes for the purpose of lowering an environmental load.SOLUTION: A carbon nanotube processing system includes a water-to-be-treated tank T1 that stores water to be treated containing carbon nanotubes and water, a water-to-be-treated pipe L12 that feeds liquid from the water-to-be-treated tank to a mixed water tank T2, a chloride ion supply source tank T5 that stores a chloride ion supply source, a chloride ion supply source pipe L52 that supplies the chloride ion supply source from the chloride ion supply source tank to the mixed water tank, a treated water pipe L26 that feeds liquid from the mixed water to a treatment tank, and an electrolysis device provided in the mixed water tank.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to sp nanotubes, graphene, carbon nanohorns, fullerenes, and the like. 2 The present invention relates to a system and method for processing carbon nanomaterials, which have a carbon skeleton, and in particular to a processing system and method for carbon nanotubes using electrolysis. [Background technology]

[0002] Carbon nanomaterials such as carbon nanotubes (hereinafter also referred to as CNTs), graphene, carbon nanohorns, and fullerenes are essentially sp 2 These carbon nanomaterials are compounds composed solely of carbon atoms. These nanomaterials exhibit excellent chemical stability, mechanical properties, heat resistance, and electrical properties due to their unique three-dimensional structures, such as cylinders, sheets, spheres, and ellipsoids, and the p-orbital electrons that are distributed over their surfaces. For this reason, they are expected to be used in a wide range of fields, from electronics to medicine, and practical applications are already underway.

[0003] On the other hand, carbon nanomaterials have been known to have extremely small sizes and unusual shapes with high aspect ratios between their major and minor axes, raising concerns about their impact on the environment and living organisms. Therefore, there is a need to develop technologies to treat industrial wastewater containing carbon nanomaterials.

[0004] Patent Document 1 discloses a method of treating a mixture containing carbon nanotubes and water with an aqueous solution of hypochlorous acid or hypochlorite, the concentration of which is 0.1% by weight to 10% by weight.

[0005] Patent Document 2 discloses a method for decomposing a difficult-to-decompose substance in water to be treated, which contains water and a difficult-to-decompose substance consisting of at least one substance selected from nanocarbon materials and difficult-to-decompose organic substances, and includes a step of adding a first oxidizing agent consisting of at least one substance selected from hypohalous acids and salts thereof to the water to be treated, and a step of adding a second oxidizing agent consisting of a sulfur compound containing a peroxide group to the water to be treated.

[0006] However, these methods have the problem of placing a burden on the environment, as one oxidant is used at a high concentration or two oxidants are used in combination. Therefore, the establishment of a treatment method that reduces the burden on the environment has become a challenge. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2019-218218 [Patent Document 2] Patent Publication No. 2021-23869 Summary of the Invention [Problem to be solved by the invention]

[0008] In order to reduce the burden on the environment, it has been desired to reduce the amount of oxidizing agent required for oxidative decomposition of carbon nanotubes. [Means for solving the problem]

[0009] The present disclosure has been conceived in view of the above problems, and provides a system and method for treating carbon nanotubes using a low concentration oxidizing agent.

[0010] Specifically, the carbon nanotube processing system according to the present disclosure includes: a water tank for storing water to be treated containing carbon nanotubes and water; a treated water pipe for sending the treated water from the treated water tank to a mixed water tank; a chloride ion supply tank that stores a chloride ion supply source; a chloride ion supply pipe for supplying the chloride ion from the chloride ion supply tank to the mixed water tank; a treated water pipe for sending the mixed water to a treatment tank; A carbon nanotube processing system characterized by having an electrolysis device in the mixed water tank. [Effects of the Invention]

[0011] The carbon nanotube treatment system according to the present disclosure can oxidatively decompose carbon nanotubes in the water to be treated using hypochlorous acid. Furthermore, by electrolyzing a chloride ion source in a mixed water tank using an electrolysis device, hypochlorous acid is generated, accelerating the decomposition of carbon nanotubes. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram showing an example of the overall flow of a processing system. [Figure 2] Diagram showing the dissociation of chloride ions depending on pH DETAILED DESCRIPTION OF THE INVENTION

[0013] The carbon nanotube processing system and processing method according to the present disclosure will be described below with reference to drawings and examples. Note that the following description illustrates one embodiment and one example of the present disclosure, and the present disclosure is not limited to the following description. The following description can be modified without departing from the spirit of the present disclosure. In addition, in the following description, "~" indicating a range of component composition means "more than or equal to" or "less than or equal to." In other words, "A%~B%" means "more than or equal to A% and less than or equal to B%."

[0014] Figure 1 shows an example of the overall flow of a treatment system. A tank T1 for treated water, which stores water CW containing carbon nanotubes (hereinafter also referred to as CNTs) and water, may include a water quality measuring device W1. While not shown, the water quality measuring device W1 may include, for example, a pH meter 91, a CNT meter 92, a thermometer 93, a level gauge 94, and a residual chlorine concentration meter 95.

[0015] The raw water CW is sent from the raw water tank T1 to the mixed water tank T2 via the raw water piping L12. The mixed water tank T2 may also include a mixed water quality measuring device W2. The raw water piping L12 may have a raw water feed pump P102 and a raw water feed rate adjustment valve V102 for adjusting the feed rate. The feed rate of the raw water CW may also be determined by one or more indicators, such as the CNT meter 92 and level gauge 94 of the raw water quality measuring device W1 and the mixed water quality measuring device W2.

[0016] The mixed water tank T2 is equipped with an electrolyzer ELM. The anode Ea and cathode Ec of the electrolyzer ELM are immersed in the mixed water tank T2. The anode Ea and cathode Ec may be flat or cylindrical, and are preferably arranged facing each other horizontally or vertically. In particular, a vertical arrangement is more preferable because CNT particles are less likely to accumulate.

[0017] It is preferable to use insoluble electrodes coated with a platinum-based catalyst for the anode Ea and cathode Ec. Insoluble electrodes with platinum-based catalysts have excellent corrosion resistance and electrical conductivity, enabling stable electrolysis over a long period of time. They also exhibit high catalytic activity in the hypochlorous acid production process, enabling efficient reactions. It is also preferable to reverse the polarity of the anode Ea and cathode Ec to prevent the buildup of scale, etc.

[0018] The chloride ion source CL stored in the chloride ion source tank T5 may be solid or liquid. As the chloride ion source CL, chlorides having alkali metals or alkaline earth metals as cations can be used, with sodium chloride being particularly preferred.

[0019] The chloride ion supply tank T5 includes a chloride ion supply pipe L52 for supplying the chloride ion supply CL to the mixed water tank T2. When the chloride ion supply CL is solid, it is supplied from a hopper (not shown) or the like, and the chloride ion supply pipe L52 may have a chloride ion supply amount adjustment valve V502 for adjusting the supply amount. The chloride ion supply tank T5 may include a chloride ion supply measurement device W5.

[0020] When the chloride ion supply source CL is a liquid, the chloride ion supply source pipe L52 may have a chloride ion supply source supply pump P502 and a chloride ion supply source supply rate adjustment valve V502 for adjusting the supply rate.

[0021] Alternatively, the chloride ion supply tank T5 may be provided with an electrolyzer ELM, and hypochlorous acid and sodium hypochlorite produced by electrolyzing the chloride ion supply source CL may be supplied to the mixed water tank T2.

[0022] Hypochlorous acid and sodium hypochlorite can be produced by electrolyzing mixed water MW containing the water to be treated (CW) and a chloride ion source (CL). Hypochlorous acid and hypochlorite ions (OCl-) are strong oxidizing agents and can oxidize and decompose CNTs. Compared to hypochlorite ions (OCl-), hypochlorous acid has a higher oxidizing power, and the higher the proportion of hypochlorous acid present in free chlorine, the more effectively it can decompose CNTs.

[0023] The temperature of the mixed water MW in the mixed water tank T2 is preferably adjusted to 30°C to 60°C by a temperature adjustment device TC (not shown). If the temperature is below 30°C, the reaction rate slows down, and if the temperature exceeds 60°C, the decomposition of hypochlorite ions progresses. A more preferable temperature range is 35 to 60°C, and even more preferable is 40 to 60°C.

[0024] Furthermore, the temperature control device TC may adjust not only the temperature of the mixed water MW but also the temperature of the water to be treated CW and the chloride ion source CL, thereby reducing the amount of energy used by the temperature control device TC throughout the entire system and controlling the treatment time.

[0025] Figure 2 shows the proportion of chlorine, hypochlorous acid, and hypochlorite ions depending on the pH. A pH below 5 is not practically desirable because it may generate chlorine, which has adverse effects on the human body. Also, at a pH of 9 or higher, free chlorine is converted into hypochlorite ions (OCl), which do not have a high oxidizing power. - ) form, so although the decomposition reaction proceeds, it takes a very long time.

[0026] Therefore, it is preferable to adjust the pH of the mixed water MW to 5-9 using a pH adjusting device pHC. The pH adjusting device pHC is composed of, for example, a pH adjusting acid tank T3 and a pH adjusting alkali tank T4, which will be described later. In this range, hypochlorous acid (HOCl), which has high oxidizing power, is present in the free chlorine, and CNTs can be decomposed more effectively. It is more preferable to adjust the pH range to 6-7. In this range, hypochlorous acid ions (OCl - This is because the proportion of hypochlorous acid present is higher than that of water.

[0027] The reactions occurring at the electrodes and the pH changes are described in detail below. The reactions occurring in the electrolyzer ELM are shown in equations (1) to (3) below.

[0028] Anode: 2Cl - →Cl2+2e - (1) Cl2 + H2O → HClO + HCl (2) Cathode:2H2O+2e - →H2+2OH - (3) The chlorine produced at the anode reacts immediately with water to produce hypochlorous acid and hydrochloric acid. - CNTs can be decomposed by adjusting the conditions, such as hypochlorous acid concentration, pH, and temperature, but when CNT decomposition occurs due to hypochlorous acid, reactions (4) to (6) described below occur, causing the pH to lean toward acid.

[0029] To adjust the pH of the mixed water MW to the acidic side, the amount of pH adjusting acid Ac, such as an organic acid or inorganic acid stored in the pH adjusting acid tank T3, delivered may be determined by the mixed water pH adjusting acid pump P302 in the mixed water pH adjusting acid piping L32 or the mixed water pH adjusting acid amount adjustment valve V302. For example, hydrochloric acid is preferably used as the pH adjusting acid Ac. The pH adjusting acid tank T3 may include a pH adjusting acid water quality measuring device W3.

[0030] Furthermore, when adjusting the pH of the mixed water MW to the alkaline side, the amount of pH-adjusting alkali Al, such as organic alkali or inorganic alkali stored in the pH-adjusting alkali tank T4, delivered may be determined by the mixed water pH-adjusting alkali pump P402 in the mixed water pH-adjusting alkali piping L42 or the mixed water pH-adjusting alkali quantity adjustment valve V402. For example, sodium hydroxide is preferably used as the pH-adjusting alkali Al. The pH-adjusting alkali tank T4 may include a pH-adjusted alkali water quality measuring device W4.

[0031] Furthermore, the pH adjustment device pHC may adjust not only the pH of the mixed water MW but also the pH of the water to be treated CW or the chloride ion source CL. When adjusting the pH of the water to be treated CW, the amount of pH adjusting acid Ac fed may be determined by the water to be treated pH adjusting acid pump P301 or the water to be treated pH acid amount adjustment valve V301 in the water to be treated pH adjusting acid piping L31, and the amount of pH adjusting alkali Al fed may be determined by the water to be treated pH adjusting alkali pump P401 or the water to be treated pH adjusting alkali amount adjustment valve V401 in the water to be treated pH adjusting alkali piping L41.

[0032] Furthermore, although not shown, when the chloride ion supply source CL is a liquid, the pH adjustment may be performed by determining the amount of pH adjusting acid Ac sent by the chloride ion supply source pH adjusting acid pump P305 or the chloride ion supply source pH adjusting acid amount adjustment valve V305 in the chloride ion supply source pH adjusting acid piping L35. Furthermore, the amount of pH adjusting alkali Al sent may be determined by the chloride ion supply source pH adjusting alkali pump P405 or the chloride ion supply source pH adjusting alkali amount adjusting valve V405 in the chloride ion supply source pH adjusting alkali piping L45.

[0033] This reduces the fluctuation in pH when the water to be treated CW comes into contact with the chloride ion source CL, thereby enabling the treatment time to be controlled. When the CNT concentration in the mixed water MW falls below the decomposition standard concentration, the treated water is sent from the treated water pipe L26 to the treated water tank T6 by the treated water sending pump P206. If the chloride ion supply source CL is liquid, the amount of liquid sent to the chloride ion supply source tank T5 and the treated water tank T6 may be determined based on the residual chlorine concentration in the treated water TW. The treated water tank T6 may include a treated water quality measuring device W6.

[0034] For example, when the residual chlorine concentration in the treated water TW is higher than the reference concentration, the amount of liquid sent from the treated water pipe L26 to the chloride ion supply source tank T5 may be adjusted by the chloride ion supply source reuse valve V205 in the branch pipe L25. Also, when the residual chlorine concentration in the treated water TW is lower than the reference concentration, the amount of liquid sent from the treated water pipe L26 to the treated water tank T6 may be adjusted by the treated water feed pump P206 or the treated water feed rate adjustment valve V206.

[0035] Treatment to meet effluent standards for treated water TW by reusing chloride ion source CL Not only does this reduce the load on the equipment, but it also reduces the chloride ion source CL and utilities.

[0036] The residual chlorine concentration in the treated water tank T6 may be measured, and the amount of residual chlorine decomposer CD sent from the residual chlorine decomposer tank T7 to the treated water residual chlorine decomposer pipe L76 may be determined by the treated water chlorine decomposer pump P706 and the treated water chlorine decomposer amount adjustment valve V706 until the amount meets the discharge standard. For example, sodium thiosulfate or the like may be used as the residual chlorine decomposer CD. The residual chlorine decomposer tank T7 may include a residual chlorine decomposer water quality measuring device W7.

[0037] The residual chlorine concentration decomposition device can be defined as including the treated water chlorine decomposition agent pump P706 and the treated water chlorine decomposition agent amount adjustment valve V706 in the treated water residual chlorine decomposition agent piping L76 from the residual chlorine decomposition agent tank T7.

[0038] In addition, the amount of liquid sent from the mixed water tank T2 to the treated water tank T1 can be adjusted using the mixed water circulation pump P201 or the mixed water circulation volume adjustment valve V201 in the mixed water circulation pipe L21. It is believed that the decomposition reaction of CNTs proceeds according to the following reaction formulas (4) to (6), and the residual chlorine concentration decreases as the reaction proceeds. Therefore, it is thought that when the residual chlorine concentration falls to a certain value, the decomposition of CNTs will become difficult to proceed. C n + 2n HClO → n CO2+ 2n HCl (4) C n + 2n MClO → n CO2+ 2n MCl (5) C n + 2n M(ClO)2→ n CO2+ 2n MCl2(6) Furthermore, among the three reactions (4) to (6) above, reaction (4) has the highest oxidizing power and the fastest reaction rate. Therefore, to increase reaction (4), it is necessary to efficiently bring the treated water (CW) into contact with the chloride ion source (CL). To promote the decomposition of reaction (4), the residual chlorine concentration in the mixed water (MW) should be adjusted to between 0.3 mg / mL and less than 1 mg / mL. The residual chlorine concentration can be measured by any method, including electrochemical, polarographic, galvanic, and DPD reagent methods. Considering the need to incorporate this into a system, electrochemical and polarographic methods, which allow for continuous in-line measurement, are preferred.

[0039] Turbidity (NTU, FTU, kaolin) and absorbance of visible light at a wavelength of 700 nm can be used as indicators of CNT concentration. The measured value may be corrected for pH, temperature, etc. [Example]

[0040] In Example 1, 20 mL of a mixture (0.1 mg / mL) of multilayered CNTs (manufactured by Fuji Film Wako Co., Ltd.) and water, 50 mL of a 20% aqueous solution (50 mg / mL) of sodium chloride (manufactured by Fuji Film Wako Co., Ltd.), and 30 mL of pure water were added to a glass bottle to prepare a 10% sodium chloride, 0.02 mg / mL CNT dispersion. Pt-coated anode and cathode electrodes facing each other were immersed in the dispersion and electrolysis was performed under electrolysis conditions of 1 A / dm2 while the solution was heated to a predetermined temperature using a heater. A small amount of 10% hydrochloric acid was intermittently added to adjust the pH to 6.5-7. When the hypochlorous acid concentration reached the predetermined concentration, electrolysis was stopped and the solution was allowed to stand. The detailed control protocol is listed in Table 1. The electrolysis was temporarily stopped every 5 minutes, the pH was adjusted to 7, and then electrolysis was resumed. The control method is not limited to this method; acid addition in real time based on changes in the pH sensor value is also possible.

[0041] In Comparative Example 1, 2 mL of a mixture (0.1 mg / mL) of multi-layered CNT (manufactured by Fuji Film Wako Co., Ltd.) and water, 0.06 mL of an aqueous solution (50 mg / mL) of sodium hypochlorite pentahydrate (manufactured by Fuji Film Wako Co., Ltd.), and 7.94 mL of pure water were added to a glass bottle, and the resulting solution contained 0.3 mg / mL of free chlorine and CN. A 0.02 mg / mL dispersion was prepared and allowed to stand at room temperature (25°C) without adjusting the pH with hydrochloric acid.

[0042] The evaluation was carried out using a spectrophotometer (Shimadzu UV-3600) to measure the change in absorbance at a wavelength of 700 nm over time. The evaluation time differed depending on the temperature conditions, but the evaluation index was the change in absorbance per hour (ΔAbs. / h), which was used as the CNT decomposition rate to determine superiority or inferiority.

[0043] [Table 1]

[0044] Table 2 shows the results of examples and comparative examples under other conditions.

[0045] [Table 2]

[0046] Comparative Example 1 uses commercially available sodium hypochlorite instead of electrolysis, but the reason for the difference in performance from the Examples is that the pH is not adjusted, making the solution alkaline, and OCl - In contrast, in each example, the pH was adjusted to 6.5 to 7, which increased the HClO ratio and therefore increased the CNT decomposition rate.

[0047] Among the examples, the decomposition rate tended to be faster as the temperature increased, and the decomposition rate also tended to be faster as the concentrations of hypochlorous acid and salt (residual chlorine) increased. [Industrial Applicability]

[0048] The carbon nanotube treatment system and method using electrolysis described in the present disclosure can be suitably used to decompose carbon nanotubes in wastewater containing carbon materials. [Explanation of symbols]

[0049] T1 Untreated water tank T2 Mixing Water Tank T3 pH Adjusting Acid Tank T4 pH Adjusting Alkaline Tank T5 Chloride ion source tank T6 Treated Water Tank T7 Residual chlorine decomposition agent tank W1 Treated water quality measuring device 91 pH meter 92 CNT meter 93 Thermometer 94 Liquid level gauge 95 Residual chlorine concentration meter W2 Mixed water quality measuring device W3 pH adjusted acid water quality measuring device W4 pH Adjustment Alkaline Water Quality Measuring Device W5 Chloride ion source measuring device W6 Treated water quality measuring device W7 Residual chlorine decomposition agent water quality measuring device L12 Treated water piping L21 Mixed water circulation piping L25 branch piping L26 Treated water piping L31 To be treated water pH adjustment acid piping L32 Mixed water pH adjustment acid piping L35 Chloride ion supply source pH adjustment acid piping L41 Alkaline piping for adjusting pH of treated water L42 Mixed water pH adjustment alkaline piping L45 Chloride ion supply source pH adjustment alkaline piping L52 Chloride ion supply piping L76 Treated water residual chlorine decomposition agent piping P102 Treated water transfer pump V102 Treated water flow rate adjustment valve P201 Mixed Water Circulation Pump V201 Mixed Water Circulation Volume Adjustment Valve P206 Treated water transfer pump V205 Chloride Ion Source Recycle Valve V206 Treated Water Flow Rate Adjustment Valve P301 Acid pump for adjusting pH of treated water V301 Treated Water pH Adjustment Acidity Adjustment Valve P302 Mixed Water pH Adjustment Acid Pump V302 Mixed Water pH Adjustment Acidity Adjustment Valve P305 Chloride ion source pH adjustment acid pump V305 Chloride ion source pH adjustment Acid amount adjustment valve P401 Alkaline pump for adjusting pH of treated water V401 Treated water pH adjustment alkalinity adjustment valve P402 Mixed Water pH Adjustment Alkaline Pump V402 Mixed Water pH Adjustment Alkaline Amount Adjustment Valve P405 Chloride ion supply source pH adjustment alkaline pump V405 Chloride ion supply source pH adjustment Alkali amount adjustment valve P502 Chloride ion source supply pump V502 Chloride ion supply source supply amount adjustment valve P706 Treated Water Chlorine Decomposition Pump V706 Treated water chlorine decomposition agent amount adjustment valve TC temperature control device pHC pH adjustment device CW Treated water MW mixed water Ac pH adjusting acid Al pH adjusting alkali CL Chloride ion source TW treated water CD Residual chlorine decomposition agent

Claims

1. a water tank for storing water to be treated containing carbon nanotubes and water; a treated water pipe for sending the treated water from the treated water tank to a mixed water tank; a chloride ion supply tank that stores a chloride ion supply source; a chloride ion supply pipe for supplying the chloride ion from the chloride ion supply tank to the mixed water tank; a treated water pipe for sending the mixed water to a treatment tank; A carbon nanotube processing system characterized by having an electrolysis device in the mixed water tank.

2. 2. The carbon nanotube processing system of claim 1, wherein the chloride ion source is a solid.

3. 2. The carbon nanotube processing system according to claim 1, wherein the chloride ion source is an aqueous solution containing chloride ions.

4. 2. The carbon nanotube processing system according to claim 1, further comprising a temperature adjusting device for adjusting the temperature of the mixed water in the mixed water tank.

5. 2. The carbon nanotube processing system according to claim 1, further comprising a pH adjusting device for adjusting the pH of the mixed water in the mixed water tank.

6. the treated water pipe is connected to a treated water tank; 2. The carbon nanotube treatment system according to claim 1, further comprising a residual chlorine concentration decomposition device for decomposing residual chlorine in the treated water in the treated water tank.

7. 4. The carbon nanotube processing system according to claim 3, wherein the treated water pipe has a branch pipe.

8. a contacting step of contacting water to be treated containing carbon nanotubes and water with a chloride ion source to obtain mixed water; a concentration adjusting step of adjusting the residual chlorine concentration in the mixed water in the contact step to 0.3 mg / mL or more and less than 1 mg / mL; The method for treating carbon nanotubes further comprises an electrolysis step of electrolyzing the mixed water.

9. 9. The method for treating carbon nanotubes according to claim 8, further comprising a temperature adjusting step of adjusting the temperature of the mixed water to 30 to 60°C.

10. 9. The method for treating carbon nanotubes according to claim 8, further comprising a pH adjusting step of adjusting the pH of the mixed water to 5 to 9.

11. 9. The method for treating carbon nanotubes according to claim 8, further comprising a step of adjusting the temperature of the water to be treated and / or the chloride ion source before the contacting step.

12. 9. The method for treating carbon nanotubes according to claim 8, further comprising a step of adjusting the pH of the water to be treated and / or the aqueous solution containing chloride ions before the contact step.

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