Method for producing nitrite ions, and system for producing nitrite ions

Abstract

This invention provides a method for producing nitrite ions by reducing nitrate ions, and also provides a system for producing nitrite ions. [Solution] A method for producing nitrite ions, comprising: (a) contacting a composition containing nitrate ions with manganese ions and an electron donor to obtain a reaction mixture; and (b) irradiating the reaction mixture with light to carry out a reduction reaction of nitrate ions.

Description

Technical Field

[0001] The present invention relates to a method for producing nitrite ions and a nitrite ion production system.

Background Art

[0002] The outflow and accumulation of nitrogen into the environment have become a global problem, and there are concerns about the adverse effects on animals and plants. Ammonia nitrogen (ammonium ion: NH4 , , , ,

[0005] , ), nitrate nitrogen (nitrate ion: NO3 - ), and nitrite nitrogen (nitrite ion: NO2 - ) are regulated by emission standards in the Water Pollution Control Law. These nitrogen compounds are being more strictly regulated from the perspective of environmental protection, and technologies for reducing the concentration of nitrogen compounds are required. As means for removing nitrate nitrogen composed of nitrate nitrogen and nitrite nitrogen, physicochemical methods such as ion exchange, reverse osmosis, electrochemically assisted dialysis, and electroreduction, biological methods, and methods using photocatalysts are known. When reducing the concentration of nitrate ions by a reduction reaction such as electroreduction, nitrite ions are passed through in the process, so this process is an important process in the treatment of nitrogen compounds by reduction reactions.

[0003] The Fenton process using manganese ions is known as a method for decomposing and detoxifying organic pollutants (Non-Patent Document 1). However, the action of manganese ions in the reduction reaction of nitrate ions to nitrite ions was unknown.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present invention aims to provide a method for producing nitrite ions by reducing nitrate ions. Furthermore, the present invention aims to provide a system for producing nitrite ions. [Means for solving the problem]

[0006] In order to solve the above problems, the inventors of this invention conducted diligent research and discovered a method for efficiently producing nitrite ions by a reduction reaction using manganese ions, thereby completing the present invention.

[0007] In other words, the present invention includes the following embodiments. Section 1. A method for producing nitrite ions, (a) A step of contacting a composition containing nitrate ions with manganese ions and an electron donor to obtain a reaction mixture, (b) A step of irradiating the reaction mixture with light to carry out the reduction reaction of nitrate ions. A manufacturing method that includes [the following]. Section 2. The method for producing an electron donor according to claim 1, wherein the electron donor comprises at least one electron donor selected from the group consisting of phenols, lower alcohols, and hydrogen peroxide. Section 3. The method for producing the product according to item 1, wherein the electron donor is an electron donor of phenols. Section 4. The manufacturing method according to any one of items 1 to 3, wherein the reaction temperature of step (b) is 0°C or higher. Section 5. The manufacturing method according to any one of items 1 to 4, wherein the wavelength of light in the light irradiation is 600 nm or less. Section 6. A system for producing nitrite ions, A mixing means for mixing a composition containing nitrate ions, manganese ions, and an electron donor to obtain a reaction mixture, Light irradiation means for irradiating the reaction mixture with light A system that includes [this]. Section 7. The system according to claim 6, further comprising heating means for heating the reaction mixture. Claim 8. The system according to claim 6 or 7, wherein the light irradiation means is means for utilizing sunlight. Claim 9 Use of manganese ions for the production of nitrite ions by reducing nitrate ions.

Advantages of the Invention

[0008] According to the present invention, a new method for producing nitrite ions can be provided. Further, according to the present invention, a new nitrite ion production system can be provided.

Brief Description of the Drawings

[0009] [Figure 1] It is a diagram showing the effect of manganese ions in the nitrate ion reduction reaction. [Figure 2] It is a diagram showing the influence of light irradiation in the nitrate ion reduction reaction by manganese ions. [Figure 3] It is a diagram showing the influence of an electron donor in the nitrate ion reduction reaction. [Figure 4] It is a diagram showing the influence of phenol and hydrogen peroxide in the nitrate ion reduction reaction. [Figure 5] It is a diagram showing the correlation between the amount of phenol and the reactivity in the nitrate ion reduction reaction. [Figure 6] It is a diagram showing the influence of light wavelength in the nitrate ion reduction reaction. [Figure 7] It is a diagram showing the photoreactivity of manganese ions with respect to light wavelength by electrochemical measurement. [Figure 8] It is a diagram showing the photoreactivity of manganese ions with respect to an electron donor by electrochemical measurement.

Embodiments for Carrying Out the Invention

[0010] <Definition of Terms> In this specification, the term "electron donor" refers to a substance that donates electrons to other atoms, molecules, or ions during electron transfer, such as in the formation of a compound, and includes, for example, Lewis bases. It may also include electrons themselves.

[0011] 1. Method for producing nitrite ions The present invention relates to a method for producing nitrite ions, comprising the steps of (a) contacting a composition containing nitrate ions with manganese ions and an electron donor to obtain a reaction mixture, and (b) irradiating the reaction mixture with light to carry out a reduction reaction of nitrate ions.

[0012] 1.1 Process (a) The form of the nitrate ion-containing composition used in the present invention is not particularly limited and may be obtained by known methods, however, from the viewpoint of related technologies, the nitrate ions are preferably derived from nitrogen-containing wastewater. Furthermore, from the viewpoint of improving the efficiency of the reaction, the form is preferably a solution.

[0013] The origin of the manganese ions used in the present invention is not particularly limited and can be obtained from known metal salts. Examples of such metal salts of manganese include manganese(II) chloride, manganese(II) sulfide, manganese(II) sulfate, manganese(II) nitrate, manganese(II) phosphate, manganese(II) carbonate, manganese(II) acetate, or mixtures thereof. Furthermore, the form is not particularly limited and may be particulate, powdered, or in solution. Among these, from the viewpoint of improving the efficiency of the reaction, the form is preferably powdered or in solution. When used as an aqueous solution, the metal salt of manganese is preferably soluble in water, and as such metal salts of manganese, manganese(II) chloride, manganese(II) sulfate, manganese(II) nitrate, manganese(II) acetate, or mixtures thereof are particularly preferred.

[0014] The electron donor used in the present invention is not particularly limited and can include phenols such as phenol and cresol, lower alcohols such as methanol and ethanol, and hydrogen peroxide. Among these, from the viewpoint of reactivity, it is preferable to use phenols or hydrogen peroxide as the electron donor.

[0015] When phenols are used as electron donors, they may be originally present in the composition containing nitrate ions. When the composition containing nitrate ions is wastewater, it is known that phenols may be originally present in the wastewater as organic pollutants. Therefore, the present invention is advantageous in that the amount of phenols supplied is reduced. Furthermore, in the present invention, phenols are thought to be decomposed into carbon dioxide, which is advantageous in that phenols as organic pollutants contained in wastewater are rendered harmless.

[0016] On the other hand, the inventors have found that when phenols are used as electron donors, the efficiency of nitrite ion production decreases in the reaction of step (b) in the presence of hydrogen peroxide. Therefore, when phenols are used as electron donors, it is preferable that the reaction mixture does not contain hydrogen peroxide.

[0017] In the step of contacting a composition containing nitrate ions with manganese ions and an electron donor to obtain a reaction mixture, the mixing order is not particularly limited; one may be added to the other, or both may be added simultaneously. As for the mixing method, any appropriate method such as stirring, shaking, or ultrasonic dispersion can be used.

[0018] 1.2 Process (b) In the present invention, the reaction temperature in step (b) is not particularly limited as long as sufficient conditions are met for the reaction to proceed. In this regard, the inventors previously found that the reaction efficiency improves in a temperature-dependent manner in their study of the Fenton reaction using manganese ions. Therefore, from the viewpoint of improving the efficiency of the reaction, the reaction temperature in the present invention is preferably 0°C or higher, more preferably 5°C or higher, even more preferably 30°C or higher, and particularly preferably 60°C or higher. On the other hand, the reaction temperature is preferably below the boiling point of the solvent, more preferably 90°C or lower, and particularly preferably 80°C or lower.

[0019] In the present invention, the wavelength of light used in step (b) is not particularly limited as long as sufficient conditions for the reaction can be carried out. However, from the viewpoint of improving the efficiency of the reaction, it is preferably 600 nm or less, more preferably in the range of 100 nm to 500 nm, and particularly preferably 200 nm to 400 nm. This generally coincides with the UV-Vis spectrum of an aqueous manganese(II) nitrate solution. In the reaction of the present invention, it is thought that when manganese ions absorb light, the oxidation reaction of manganese ions and the reduction reaction from nitrate ions to nitrite ions proceed due to photoexcitation. Subsequently, electrons are supplied to the manganese ions from an electron donor, and the manganese ions are reduced. Therefore, in the present invention, the wavelength of light used in the light irradiation is preferably in the range in which light absorption by manganese ions occurs.

[0020] Manganese ions are known to absorb light in relatively long wavelength regions. In this respect, the reaction of the present invention appears to be capable of using sunlight. Using sunlight is advantageous from the standpoint of energy consumption.

[0021] In the present invention, depending on the progress of the reaction, steps (a) and (b) may be repeated after step (b). Therefore, a composition containing nitrate ions, an electron donor, and manganese ions if necessary may be supplied to the reaction mixture after step (b) to obtain a further reaction reaction.

[0022] 2. Nitrite ion production system The present invention also relates to a system for producing nitrite ions, which includes means for carrying out the above-described method for producing nitrite ions. Therefore, the examples in the following description are merely examples and are not particularly limited as long as the conditions for carrying out the above-described method for producing nitrite ions can be met, and can be modified as appropriate without changing the essence of the invention.

[0023] 2.1 Configuration of a nitrite ion production system One embodiment of the present invention relates to a system for producing nitrite ions, comprising a mixing means for mixing a composition containing nitrate ions, manganese ions, and an electron donor to obtain a reaction mixture, and a light irradiation means for irradiating the reaction mixture with light.

[0024] The manufacturing system of the present invention may include a means for supplying a composition containing nitrate ions, and a means for supplying manganese ions and an electron donor to the composition containing nitrate ions. Each supply means may supply each component individually or a mixture thereof. Each supply means may also include a mechanism for controlling the supply amount of each component according to the progress of the reduction reaction. The supply means for supplying the electron donor may also be an electrode.

[0025] The mixing means for mixing a composition containing nitrate ions, manganese ions, and an electron donor to obtain a reaction mixture is not particularly limited, but may include, for example, a stirring bar or impeller, a sonicator, a shaker, or a mixer.

[0026] The light irradiation means is not particularly limited, but examples include light-emitting diodes (LEDs), laser diodes (LDs), xenon lamps, fluorescent lamps, incandescent lamps, metal halide lamps, and high-pressure mercury lamps. The wavelength of the light emitted by the light irradiation means is preferably 600 nm or less, more preferably in the range of 100 nm to 500 nm, and particularly preferably 200 nm to 400 nm. Furthermore, from the viewpoint of energy consumption, the light irradiation means may also be a means that utilizes sunlight.

[0027] The manufacturing system of the present invention may further include heating means to promote the reduction reaction, for example, heating means such as an electric heating wire. If the manufacturing system of the present invention includes heating means, it may further include a temperature sensor and a temperature control means.

[0028] The manufacturing system of the present invention may also include gas separation means for removing CO2 gas and the like generated by the reaction, discharge means for discharging the reaction mixture after the reaction, filters, and the like. [Examples]

[0029] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way to these examples.

[0030] 1. Nitrite ion (NO2) - ) quantitative analysis Generated NO2 - The colorimetric analysis of 4,4'-diaminodiphenylsulfone and N-1-naphthylethylenediamine dihydrochloride was performed using a UV-Vis analyzer (APEL, PD-3500UV) and the Saltzman colorimetric method (measurement wavelength: 542 nm). To 2 mL of sample solution, 80 μL of 1.0 M HCl aqueous solution, 160 μL of a 50 vol. ethanol solution of 0.1% 4,4'-diaminodiphenylsulfone, and 80 μL of 0.5% N-1-naphthylethylenediamine dihydrochloride were added and mixed. The light absorption of the resulting colored solution was then measured using a UV-Vis analyzer.

[0031] Example 1 In a test tube (φ30 × 200 mm), 3 mL of 1.0 M Mn(NO3)2 aqueous solution or NaNO3 aqueous solution and 27 mL of pure water were added to make a total volume of 30 mL. Then, 20 μmol of phenol was added and the mixture was stirred for 30 minutes in a 30°C warm bath. After that, the mixture was irradiated for 4 hours with visible light or ultraviolet-visible light with a wavelength cutoff filter (L42: HOYA Corporation) using a 300 W xenon lamp. The results are shown in Figures 1 and 2. It can be seen that nitrite ions are generated in the presence of manganese ions, depending on the light irradiation time.

[0032] Example 2 In a test tube (φ30 × 200 mm), 3 mL of 1.0 M Mn(NO3)2 aqueous solution and 27 mL of pure water were added to make a total volume of 30 mL. Then, an organic substrate (120 μmol formic acid, 120 μmol methanol, 20 μmol or 40 μmol phenol) was added and the mixture was stirred for 30 minutes in a 30°C warm bath. After that, the mixture was irradiated for 4 hours with visible light or ultraviolet-visible light at λ>300, 420, 520, and 600 nm using a 300 W xenon lamp equipped with a wavelength cutoff filter (no filter, L42, Y52, R60: HOYA Corporation). For comparison, the reaction was also carried out with 20 μmol of phenol and 600 μmol of hydrogen peroxide added under conditions of visible light irradiation from a 300 W xenon lamp (λ>420 nm) equipped with a wavelength cutoff filter L42. The results are shown in Figures 3 to 6. Figures 3 and 4 show that nitrite ions are generated even when electron donors other than phenol are used. On the other hand, when phenol and hydrogen peroxide are present simultaneously, the generation of nitrite ions decreases. Figure 5 shows that the generation of nitrite ions correlates with the amount of electron donor. Furthermore, Figure 6 shows that the generation of nitrite ions increases or decreases depending on the wavelength of irradiated light, and this roughly matches the UV-Vis spectrum of the Mn(NO3)2 aqueous solution. This suggests that the manganese ions absorbed light, which facilitated the reduction reaction from nitrate ions to nitrite ions and the oxidation reaction of manganese ions. It is also thought that electron supply from electron donors such as phenol acted on the reduction of manganese ions.

[0033] Example 3 Anion exchange membrane (NEOSEPTA ASE: strongly basic Cl type, electrical resistance 2.6 Ω·cm) 2Using a two-chamber cell separated by a film thickness of 0.15 mm, a Pt wire was placed at the anode and cathode, and a silver / silver chloride (Ag / AgCl) electrode was used as a reference electrode. 45 mL of 0.1 M Mn(NO3)2 aqueous solution was added to each cell and stirred for 30 minutes. Then, an organic substrate (180, 675, or 900 μmol of formic acid, 180 μmol of methanol, 30 μmol of phenol, or no organic substrate) was added to the cathode side. Using a 300 W xenon lamp equipped with a wavelength cutoff filter (no filter, L42, Y52, R60: HOYA Corporation), the lamp was switched on and off every 5 seconds while irradiating with visible light or ultraviolet-visible light at λ > 300, 420, 520, and 600 nm, and the photoresponse was observed. The results are shown in Figures 7 and 8. Under all conditions, an increase in reduction current (photoresponse: downward current increase) was observed only during light irradiation. This is thought to be due to the occurrence of redox reactions under light irradiation, resulting from the oxidation of manganese ions and reduction of nitrate ions, and the observation of a photoreduction current due to the electrochemical reduction of manganese ions. On the other hand, when phenol was added, the value of the photoreduction current decreased significantly. This is thought to be because, in addition to the reduction of manganese ions by electrochemical electron supply from the cathode side, direct reduction by phenol also occurred, resulting in a smaller photocurrent value.

Claims

1. A method for producing nitrite ions, (a) A step of contacting a composition containing nitrate ions with manganese ions and an electron donor to obtain a reaction mixture, (b) A step of irradiating the reaction mixture with light to carry out the reduction reaction of nitrate ions. A manufacturing method that includes [the following].

2. The manufacturing method according to claim 1, wherein the electron donor comprises at least one electron donor selected from the group consisting of phenols, lower alcohols, and hydrogen peroxide.

3. The manufacturing method according to claim 1, wherein the electron donor is a phenol electron donor.

4. The manufacturing method according to any one of claims 1 to 3, wherein the reaction temperature of step (b) is 0°C or higher.

5. The manufacturing method according to claim 4, wherein the wavelength of light in the light irradiation is 600 nm or less.

6. A system for producing nitrite ions, A mixing means for mixing a composition containing nitrate ions, manganese ions, and an electron donor to obtain a reaction mixture, Light irradiation means for irradiating the reaction mixture with light A system that includes [this].

7. The system according to claim 6, further comprising a heating means for heating the reaction mixture.

8. The system according to claim 6 or 7, wherein the light irradiation means is a means of utilizing sunlight.

9. The use of manganese ions for the production of nitrite ions by reducing nitrate ions.

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