JPH04293526A - Separation of nitrate ion - Google Patents

Abstract

PURPOSE:To separate nitrate ions selectively from an aqueous solution containing various other anions in addition thereto by an electrodialyzing method using an ion exchange membrane. CONSTITUTION:A method for separating nitrate ions which is characterized by using in electrodialysis a strong basic anion exchange membrane having at least one hydrocarbon group containing not less than two carbon atoms attached to its anion exchange group.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for selectively separating nitrate ions from an aqueous solution containing various anions by electrodialysis using a specified anion exchange membrane.

0002

BACKGROUND OF THE INVENTION Nitrate ions are ion species that are harmful to the human body if they are contained in drinking water. Particularly in recent years, acid rain caused by industrial exhaust gas and an increase in nitrate ions contained in groundwater caused by agricultural fertilizers or livestock excrement in areas with little rainfall have become serious problems. This phenomenon is particularly noticeable in Europe, where rainfall is low. Furthermore, the amount of industrial waste containing nitrate ions is increasing, and this is also an important problem from the perspective of global environmental conservation.

Conventionally, various methods have been known for removing these nitrate ions. For example, nitrate ion N
A method of decomposing O3 − into NO2 and O2,
Many other techniques have been developed, including methods for adsorption and removal using ion-exchange resins, methods for decomposition by anaerobic fermentation, and others. Further, methods using separation membranes include, for example, reverse osmosis membrane method and electrodialysis method using ion exchange membrane, each of which is used depending on the purpose and is an important technology that has been industrialized.

0004

However, in order to remove nitrate ions present in a dilute salt solution such as groundwater using the above-mentioned conventional techniques, there are problems that must be solved. For example, adsorption and removal of nitrate ions using an ion exchange resin requires a regeneration operation of the resin, which is not only complicated, but also requires treatment of waste liquid after the regeneration. Additionally, the membrane separation method is extremely useful for removing trace amounts of nitrate ions because it does not require regeneration and can be operated continuously, but it is extremely difficult to selectively allow only nitrate ions to permeate through the membrane. be. That is, in the reverse osmosis membrane method, there is no selective permeability to nitrate ions. In electrodialysis, when a normal anion exchange membrane is used, sulfate ions, which are multivalent ions, selectively permeate through the membrane first, and there is almost no selective permeability between chloride ions and nitrate ions. Therefore,
Electrodialysis using an ion-exchange membrane is suitable for so-called deionization, but it is not possible to allow only nitrate ions to pass through the membrane, leaving behind the ionic species necessary as mineral components.

[0005]

[Means for Solving the Problems] In view of the above-mentioned problems, the present inventors have conducted intensive research on the selective removal of nitrate ions by membrane separation method. As a result, they obtained the knowledge that nitrate ions can be selectively separated from an aqueous solution containing multi-component anions by using the anion exchange membrane specified in the electrodialysis method, leading to the completion of the present invention. be.

That is, according to the present invention, a strongly basic anion exchange membrane in which a hydrocarbon group having 2 or more carbon atoms is bonded to an anion exchange group is used to remove different species together with nitrate ions by electrodialysis. A method is provided for selectively separating nitrate ions from an aqueous solution containing anions.

[0007] An anion exchange membrane in which a specific hydrocarbon group is bonded to an anion exchange group as used in the present invention has a chain length of 8 to 28 carbon atoms in the anion exchange group present in the surface layer. A similar anion exchange membrane having alkyl groups bonded thereto is disclosed in Japanese Patent Publication No. 61-18930. However, in Japanese Patent Publication No. 61-18930,
It merely describes an anion exchange membrane that prevents acid leakage through the membrane due to concentration gradients and acid permeation through the membrane due to electrodialysis. There is also no description suggesting that nitrate ions selectively permeate membranes with respect to ions.

The strongly basic anion exchange group possessed by the anion exchange membrane of the present invention includes quaternary ammonium bases,
pH of solutions such as tertiary sulfonium bases, quaternary phosphonium bases, arsonium bases, cobalticinium bases, etc.
Although there are no particular restrictions on the group that exhibits anion exchangeability and has a positive charge regardless of the group, quaternary ammonium bases are generally preferably used. This quaternary ammonium base is generally a methyl group as an alkyl group bonded to a nitrogen atom, such as trimethylbenzylammonium base and N-methylpyridinium base, but dimethylethanolbenzylammonium etc. are also used as an exception. . Also, in tertiary sulfonium bases and quaternary phosphonium bases, a methyl group is generally bonded as the hydrocarbon group.

[0009] Such an anion exchange membrane of the present invention includes:
If strong basic anion exchange groups are bonded to 1/2 or more of the total ion exchange capacity, even if other weak basic anion exchange groups such as primary amines, secondary amines, and tertiary amines are bonded, good. Therefore, in the anion exchange membrane of the present invention, it is essential that a hydrocarbon group having two or more carbon atoms is bonded to a strongly basic anion exchange group.

In the anion exchange membrane of the present invention, the compound capable of bonding a hydrocarbon group having 2 or more carbon atoms to a strongly basic anion exchange group may be selected depending on the constituents of the ion exchange group. be selected as appropriate. For example, in the case of an anion exchange membrane obtained from a haloalkyl group system, an alkylamine, a trialkylstivine, a trialkylphine, etc. containing at least one kind of alkylamine are used. Furthermore, in the case of anion exchange membranes obtained from vinylpyridine-based membranes, halogen compounds such as alkyl halides are used. Such amines and halogen compounds may be compounds having linear or branched hydrocarbon chains, alicyclics, or aromatic rings, and are reactive tertiary amine compounds with carbon atoms bonded to the nitrogen atom. There is no particular restriction as long as the number of carbon atoms in the hydrogen chain is 2 or more. In addition, the amine compound may have an ether bond or a reactively inactive halogen bonded to it, and the halogen compound is particularly limited as long as it has a reactive halogen group bonded to it and a hydrocarbon group having two or more carbon atoms. Not done. These reactive amine compounds and halogen compounds each react with a polymer membrane having a reactive group to form an anion exchange group having a hydrocarbon group having two or more carbon atoms.

Specifically, tertiary amines having a hydrocarbon group having 2 or more carbon atoms, such as triethylamine, tripropylamine, tributylamine,
A tertiary amine such as N,N-dimethyloctylamine or N,N-dimethylbenzylamine is reacted uniformly or on one side of the membrane. Of course, when reacting on one side of the membrane, it is necessary to react the remaining chloromethyl groups with other amines, such as trimethylamine. In addition, a compound containing a reactive halogen having 2 or more carbon atoms such as butyl bromide, octyl bromide, dodecyl bromide, etc., may be uniformly applied to the polymer membrane of the vinylpyridine-divinylbenzene copolymer, or one side of the membrane or After the entire film is reacted at a low reaction rate, the remaining pyridine groups are reacted with a relatively easily reactive halogen compound such as methyl iodide or methyl bromide.

In the anion exchange membrane of the present invention, the specific anion exchange group bonded to a hydrocarbon group having two or more carbon atoms accounts for 50% or more, preferably 70% of the total ion exchange capacity.
The above ratio may exist uniformly within the film, or may exist non-uniformly. In other words, a specific anion exchange group exists on only one surface of the membrane, and a normal strongly basic anion exchange group exists on the other surface, or a specific anion exchange group exists on both surfaces of the membrane. Both forms are effective, such as a form in which an ion exchange group is present and a normal strongly basic anion exchange group is present inside the membrane, but the most desirable form is to place the specified anion exchange group on one surface of the membrane. In this method, an anion exchange membrane having a thickness of 5 μm to 100 μm is present, and the membrane surface having the anion exchange group is placed over the electrodialysate to perform electrodialysis. Note that 5 of the surface layer of the anion exchange membrane described above
In the thickness of ~100 μm, the anion exchange groups specified in the present invention may be uniformly present, or ordinary strong basic anion exchange groups and weak basic anion exchange groups may be mixed. However, the most desirable embodiment is one in which the specified anion exchange group exists selectively in one surface layer and is distributed within the membrane with a certain gradient.

In the electrodialysis method of the present invention, a cation exchange membrane is used together with the specified anion exchange membrane, but the cation exchange membrane is not particularly limited. Known hydrocarbon-based, fluorocarbon-based, and perfluorocarbon-based cation exchange membranes bonded with strongly acidic cation exchange groups such as sulfonic acid groups can be used without any limitations. In addition, when performing electrodialysis using such an anion exchange membrane and a cation exchange membrane, for example, a water tank type, a clamping type electrodialysis tank, and a conventional clamping type such as a sheet flow type or torture flow type, etc. Any known electrodialysis device can be suitably used. Particularly when electrodialyzing a solution with a low salt concentration, it is desirable to use an electrodialysis tank equipped with a spacer that can maintain the critical current density as high as possible. Furthermore, in order to prevent contamination of the membrane surface, electrodialysis is also effective, in which the electrodes of the electrodialysis tank are periodically reversed to alternately switch between the concentration chamber and the dilution chamber.

[0014]

According to the electrodialysis method of the present invention, trace amounts of nitrate ions can be selectively separated from an aqueous solution containing other anions. Although this mechanism has not yet been fully elucidated, looking at chloride ions and nitrate ions as an example, nitrate ions generally have a harder time moving through an anion exchange membrane than chloride ions. However, the adsorption of nitrate ions into the membrane is greater than that of chloride ions. In the electrodialysis of the present invention, this seems to be the result of the adsorption of nitrate ions to the anion exchange membrane becoming even stronger, but the details are not clear. In addition, other anions such as sulfate ions are naturally easily adsorbed to the membrane and therefore easily permeate through the membrane, but in the electrodialysis method of the present invention, depending on the type of membrane, sulfate ions may be more permeable than nitrate ions, or vice versa. Permeation of sulfate ions may be blocked.

[0015]

EXAMPLES The content of the present invention will be specifically explained below by way of Examples, but the present invention is not limited to these Examples.

Note that in the present invention, the effective current carrying area 1
Neocepta CM-1 (Tokuyama Soda Co., Ltd., trade name) was used as a cation exchange membrane in a 00 cm2 clamping type electrodialysis tank.
Electrodialysis was performed using various anion exchange membranes. The analysis was performed by analyzing each anion by ion chromatography after electrodialysis for a certain period of time. From these results, in order to indicate the mutual permeability of anions, the selective permeability coefficient PX NO3 of nitrate ion NO3 - with respect to anion X - was determined by the following equation.

Example 1 A polymeric film with a thickness of 0.12 mm, which is a copolymer of chloromethylstyrene and divinylbenzene with a purity of about 55%, containing a reinforcing material of polyvinyl chloride with a degree of crosslinking of 20%. The material was used as a raw membrane for producing anion exchange membranes. This is N,N
- It was immersed in a 40% acetone solution of dimethylbutylamine and reacted by heating at 50°C for 24 hours. This membrane had an ion exchange capacity of 0.89 mEq/g (dry membrane). This membrane was then diluted with 1N trimethylamine in acetone 3
12 parts at 30°C by immersion in a solution of 0 parts and 70 parts of water.
The anion exchange membrane (A) obtained by the time reaction has an anion exchange capacity of 2.12 m equivalent/g (dry membrane),
The electrical resistance was 3.2 Ω-cm 2 when measured in 0.5N saline water (25.0° C.). Separately, an anion exchange membrane (B) obtained by reacting the raw membrane for manufacturing an anion exchange membrane with trimethylamine without reacting with N,N-dimethylbutylamine has an ion exchange capacity of 2.14 m equivalent. /g (dry film), and the electrical resistance is 2.
It was 4Ω-cm2.

The obtained two types of anion exchange membranes (A
, B) respectively manufactured by Tokuyama Soda Co., Ltd. using a cation exchange membrane (
Five pairs were assembled with NeoSepta CM-1 (trade name: NeoSepta CM-1) and set in a tightening type electrodialysis tank. In these electrodialyzers, NaCl, Na2 SO4, NaHCO3
and NaNO3 in an equivalent ratio of 1:1:1:1, respectively.
Electrodialysis of a salt solution with a total concentration of 10 milliequivalents was carried out at a constant current density of 100 mA/dm2, and desalination was performed until the concentration was reduced to 1/2. The permselectivity and current efficiency were determined. The results are shown in Table 1.

Example 2 A polymeric film of the present invention was prepared using a polymer film made of a copolymer of 4-vinylpyridine and divinylbenzene with a crosslinking degree of 20% and a film thickness of 0.11 mm. An anion exchange membrane used for electrodialysis was manufactured. That is, this raw film was reacted with the reaction reagents methyl iodide, ethyl iodide, propyl bromide, butyl bromide, amine bromide, and octyl bromide, respectively, as follows. After reacting at 50°C for 16 hours using methanol as a 30% solution, the membrane was taken out and 1
After conditioning with normal hydrochloric acid and 0.5 normal ammonia aqueous solution, it was equilibrated to the measurement solution.

The obtained anion exchange membrane was tested for ion exchange capacity, electrical resistance, and PX under the same conditions as in Example 1.
I asked for NO3. The results are shown in Table 2 according to the reaction reagent of the anion exchange membrane.

Example 3 A polymer membrane consisting of a copolymer of chloromethylstyrene and divinylbenzene with a purity of 55%, containing a reinforcing cloth of polyvinyl chloride, and having a crosslinking degree of the resin portion of 8% was coated on one side. This single side was reacted with a 20% methanol solution of tributylamine at 50° C. for 24 hours. When the ion exchange capacity of the obtained membrane was measured, it was found to be 0.84 meq/g (dry membrane). Next, this membrane was immersed in a 1N trimethylamine aqueous solution containing 30% acetone, and the resulting anion exchange membrane (A) had an ion exchange capacity of 2.05 m equivalent/
g (dry film), the electrical resistance was 2.9 Ω-cm 2 , and the water content (hereinafter the same) based on the dry film was 0.24. For comparison, the anion exchange membrane (B) reacted only with dolimethylamine has an ion exchange capacity of 2.16.
m equivalent/g (dry film), electrical resistance 1.6 Ω-cm2,
The water content was 0.32.

These two types of anion exchange membranes (A, B)
Desalting was carried out by electrodialysis using the same conditions as in Example 1, and the permselectivity between each anion was determined. The results are shown in Table 3.

Example 4 A polymer film having a thickness of 0.2 mm and having a polyethylene reinforcing network as a reinforcing material, made of a terpolymer of chloromethylstyrene-styrene-divinylbenzene (degree of crosslinking: 10%) was used as the raw film. This chloromethyl group-containing polymer film was immersed in the reaction bath shown in Table 4.
After reacting at ℃ for 24 hours, the membranes (NO) 1, 2, 3 and 4 were immersed in a mixed solution of 1N acetone and water (30:70) to remove the remaining chloromethyl groups. was bound with trimethylamine.

Regarding these five types of anion exchange membranes,
In the same manner as in Example 1, the ion exchange capacity and electrical resistance were measured, and the permselectivity between anions was determined. The results are shown in Table 4.

Example 5 The anion exchange membrane reacted with octyl bromide in Example 2 was further treated with 40 parts of methyl iodide and 60 parts of hexane.
An anion exchange membrane was prepared by immersing the membrane in the same solution at room temperature for 12 hours. This anion exchange membrane has an electrical resistance of 8.8Ω
-cm2, and the ion exchange capacity was 1.9 m equivalent/g (dry membrane). Further, using this anion exchange membrane, the selective permselectivity of anions was determined using the same conditions and method as in Example 1. The results are shown in Table 5.

Example 6 The following formula

An aromatic condensation polymer having the unit was chloromethylated using chloromethyl ether and SnCl2 to introduce a chloromethyl group. Next, a solution was prepared by dissolving this chloromethyl group-introduced polymer in a solvent of N-methylpyrrolidone to a concentration of 20%, and this was cast onto a flat plate, and the solvent was scattered to form a 0.1 m
It was made into a film of m. The film was immersed in a 10% methanol solution of dioctylamine to react with the chloromethyl groups. The obtained anion exchange membrane had an ion exchange capacity of 0.25 m equivalent and 1 g (dry membrane). Furthermore, this anion exchange membrane was
The anion exchange membrane obtained by immersion in the water mixed solution had an ion exchange capacity of 1.1 m equivalent/g (dry membrane).

Using this anion exchange membrane, the anion permselectivity was determined in the same manner as in Example 1. As a result, PClNO3 = 2.3, PHCO3NO3 =
12.5, PSO4 NO3 =3.5.

For comparison, the same procedure as in Example 1 was carried out using an anion exchange membrane obtained by reacting the above-mentioned chloromethyl group-containing polymer film with trimethylamine without reacting with octylamine. The anion permselectivity was determined by the method. As a result, PClNO3 =1.3
, PHCO3NO3 =4.0, PSO4NO3 =
It was 0.4.

Example 7 A film made of a styrene-divinylbenzene-4-vinylpyridine copolymer was immersed in a methanol solution of butyl bromide and reacted at 50°C for 24 hours to add butyl groups to the pyridine ring. Combined. An anion exchange membrane was manufactured. This anion exchange membrane has an ion exchange capacity of 1.30
m equivalent/g (dry film), electrical resistance is 10.5Ω-cm2
, the moisture content based on the dry film was 0.11. In addition, using this anion exchange membrane, NaCl, NaNO3, NaHCO3 and N
a2 SO4 mixed solution of 1:1:1:1, Na+
A solution having a concentration of 10 milliequivalents and a solution having a concentration of 50 milliequivalents were desalted by electrodialysis. Table 6 shows the anion permselectivity determined from these results.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

[Table 3]

[0033]

[Table 4]

[0034]

[Table 5]

[0035]

[Table 6]

Claims (1)

[Claims] Claim 1: From an aqueous solution containing different types of anions together with nitrate ions, by electrodialysis using a strongly basic anion exchange membrane in which a hydrocarbon group having two or more carbon atoms is bonded to an anion exchange group. A method for selectively separating the nitrate ions.