JP3155299B2 - Anion exchanger - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an anion exchanger which is particularly effective for selectively adsorbing nitrate ions.

[0002]

2. Description of the Related Art Nitrate ions are harmful to the human body when contained in drinking water. Particularly in recent years, the problem of acid rain based on industrial exhaust gas, and the increase of nitrate ions contained in groundwater based on agricultural fertilizer or livestock excreta in areas with little rain have become serious problems. This phenomenon is particularly noticeable in Europe where rainfall is low. Further, industrial waste containing nitrate ions is increasing, which is also an important problem from the viewpoint of environmental protection of the earth.

Conventionally, various methods have been known for removing these nitrate ions. For example, the nitrate ion N
A number of techniques have been developed, including a method of decomposing O ₃ ^- into N ₂ and O ₂ , a method of adsorbing and removing by an ion exchange resin, a method of decomposing by anaerobic fermentation, and many others. As a method using a separation membrane, for example, a reverse osmosis membrane method,
There is an electrodialysis method using an ion-exchange membrane, which is used separately according to the purpose and is an important industrialized technology.

[0004]

However, the removal of nitrate ions present in a dilute salt solution such as groundwater by the above-mentioned prior art has problems to be solved. For example, in adsorption removal by an ion exchange resin, a sulfate ion is selectively adsorbed by a normal anion exchange resin, and there is no selective adsorption property to a nitrate ion. Further, the membrane separation method is extremely useful for removing a small amount of nitrate ions in that it can be operated continuously without the need for regeneration, but it is extremely difficult to selectively allow only nitrate ions to permeate the membrane. is there. That is, in the reverse osmosis membrane method, there is no selective permeability to nitrate ions. In the electrodialysis method, when a normal anion exchange membrane is used, sulfate ions, which are polyvalent ions, first selectively permeate the membrane, and there is almost no selective permeability between chloride ions and nitrate ions.
Therefore, the electrodialysis method using an ion-exchange membrane is suitable for so-called deionization as long as a normal anion-exchange membrane is used, but only the nitrate ions can be permeated through the membrane while leaving the necessary ionic species as a mineral component. Did not.

[0005]

Means for Solving the Problems The present inventors have conducted intensive studies on the adsorption and removal of nitrate ions by the above-mentioned anion exchange resin, and have found an anion exchange resin which selectively adsorbs nitrate ions. Came to offer. That is, the present invention is an anion exchanger having an anion exchange group to which a hydrocarbon chain having 4 or more carbon atoms is bonded, which is used for selective ion exchange adsorption of nitrate ions.

In the anion exchanger of the present invention, examples of the anion exchange group to which a hydrocarbon chain having 4 or more carbon atoms is bonded include butyl, amyl, octyl, octadecyl and the like. Linear or branched hydrocarbon chains, alicyclic hydrocarbon chains, aromatic hydrocarbon groups, hydrocarbon chains having an ether bond to them, and hydrocarbons in which some halogen groups that do not participate in the reaction are substituted A chain or the like bonded to at least an anion exchange group, for example, benzyldimethylbenzylammonium base, N-dodecylpyridinium base, benzyldibutylamine base, benzyloctylamine base and the like.

Further, an anion exchange group to which a strongly or weakly basic methyl group having 1 carbon atom is bonded may be bonded together with an anion exchange group to which a hydrocarbon group having 4 or more carbon atoms is bonded. That is, in the anion exchanger of the present invention, the ratio of the anion exchange group having a hydrocarbon chain having 4 or more carbon atoms bonded to the total ion exchange capacity is preferably 50% or more, particularly preferably 70% or more. The anion exchange group itself in such an anion exchanger of the present invention may be a strongly basic anion exchange group or a weakly basic anion exchange group. Specifically, the strongly basic anion exchange group itself has a positive charge irrespective of the pH of the solution such as a quaternary ammonium base, a tertiary sulfonium base, a quaternary phosphonium base, an arsonium base, and a gobalticinium base. The group is not particularly limited as long as it is a group exhibiting anion exchangeability. In general, a quaternary ammonium base is preferably used. Primary, secondary and tertiary amines are used as the weakly basic anion exchange groups.
These weakly basic amino groups need to be used in a dissociated state in order to carry out an ion exchange reaction.

The anion exchanger of the present invention is not particularly limited in its shape and production method as long as it has an anion exchange group to which a hydrocarbon chain having 4 or more carbon atoms is bonded. It can be manufactured using a general manufacturing method of an ion exchange resin. That is, the polymer to which the above-described anion exchange group is bonded is used as the base, but any of a bonding polymer, a polymer polymer, and a crosslinkable polymer can be used without distinction. Preferably, the above-mentioned anion exchange group is bonded to a polymer having a crosslinked structure. As the resin structure, a spherical resin having a normal gel structure, a porous spherical resin obtained by polymerizing in the presence of a poor solvent for the copolymer, and the like are used without any limitation, but in particular, the mechanical strength of the resin and ion exchange A porous spherical resin is preferred because of its high speed. Not only spherical resins, but also fibrous ion exchangers, not spherical but crushed granular materials, woven fabrics, nonwoven fabrics,
Anion exchangers having a membrane shape or the like are also preferably used.

The ion exchange capacity of the anion exchanger of the present invention is generally preferably in the range of 1.0 to 6 meq / g (dry). That is, if the ion exchange capacity is too low, the amount of nitrate ions adsorbed per unit volume becomes small, so that a large amount of ion exchanger is required, which is not economical. On the other hand, if the ion exchange capacity is too large, the mechanical strength of the ion exchanger becomes weak, so that loss due to breakage of the resin during use is large. Needless to say, in this case, it is also industrially possible to use a belt-like membrane ion exchanger as the anion exchanger and continuously immerse it in the treatment liquid to perform regeneration. In addition, not only a membrane but also a fibrous ion exchanger can be effectively used as described above.

The solution containing nitrate ions to be treated with the anion exchanger of the present invention generally contains an aqueous solution containing not more than 1%, preferably not more than 0.1% of nitrate ions, simultaneously with other anions. Often included. In particular, the anion exchanger of the present invention is generally suitable for selectively removing nitrate ions from water having a salt concentration suitable for drinking water. Such a nitrate ion naturally has a cation as a counter ion in the aqueous solution, and it is preferable to remove the cation at the same time. Therefore, a cation exchanger is used simultaneously with the anion exchanger of the present invention. These anion exchangers and cation exchangers and the manner of use may be of a conventionally known mixed-bed type or double-bed type, and are selected according to the purpose and the amount of treated water.

When the anion exchanger of the present invention is used, the strongly basic anion exchange group is usually used in the state where OH ^- is ion-exchanged, but when a weakly basic anion exchange group is present. Is used after being dissociated into hydrochloride, sulfate and the like.

After the nitrate ion is sufficiently adsorbed on the anion exchanger of the present invention, it is treated with a basic aqueous solution such as caustic soda or ammonia water or regenerated with a saline solution or sodium sulfate.

[0013]

The anion exchanger of the present invention can selectively adsorb and remove nitrate ions from a relatively dilute solution in which nitrate ions are mixed together with various anions.

The mechanism by which the specific anion exchange group in the anion exchanger of the present invention selectively adsorbs nitrate ions by ion exchange is not clear, but a hydrophobic group is bonded to the anion exchange group itself. This causes a change in the structure of water in the exchanger, and as a result, from the relationship with the hydration state of nitrate ions, it is considered that nitrate ions were selectively adsorbed to the anion exchanger of the present invention.

[0015]

EXAMPLES The contents of the present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

In the experiment of adsorbing nitrate ions in the present invention, NaCl, Na ₂ SO ₄ , NaHCO ₃ , NaN
The anion exchanger of the present invention was immersed in 1 liter of a liquid containing O _{3 at a} concentration of 2.5 mmol / l, and the mixture was stirred to be in an equilibrium state. Thereafter, the eluate was eluted with sodium iodide, and each anion in the eluate was analyzed. ^{_{SO 4 2-, NO 3 -,}} Cl - were respectively analyzed by ion chromatography, HC
O ₃ ^- was determined by titration with 0.1 N hydrochloric acid using methyl orange as an indicator.

Example 1 90 parts of chloromethylstyrene and 10 parts of divinylbenzene having a purity of 55% were dispersed in 1 liter of water using polyvinyl alcohol as a dispersant. To this, 3 parts of benzoyl peroxide was added and heated to 80 ° C. to polymerize styrene-divinylbenzene dispersed in water to obtain a granular resin. Next, this was immersed in a mixed solution of 60 parts of hexane and 40 parts of tributylamine at 60 ° C. for 48 hours. Next, the resin was thoroughly washed with hexane, and then 10%
It was immersed in an aqueous solution of trimethylamine to react with unreacted chloromethyl groups. The anion exchanger obtained after the reaction with tributylamine had an anion exchange capacity of 3.5 meq / g (dry resin), but after the reaction of trimethylamine became 4.2 meq / g (dry resin). Was.

[0018] was equilibrated in the mixed electrolyte solution of the obtained anion exchange resin described above with the above, the respective anion in the ion exchange resin is NO ₃ ^- 82%, C
^{_{l - 12%, SO 4 2-}} 7%, HCO 3 - was 1% or less.

On the other hand, the chloromethylstyrene-divinylbenzene copolymer was immersed in an aqueous solution of trimethylamine to carry out an amination treatment. The obtained anion exchange resin was similarly immersed in a mixed salt solution to equilibrate, then eluted, and each anion in the resin was analyzed. As a ^{_{result, NO 3 - 33%, SO}} 4
^2-42 %, Cl ^- 22%, HCO ₃ was 3%.

Example 2 90 parts of 4-vinylpyridine and 55% pure divinylbenzene were dispersed in water and polymerized in the same manner as in Example 1 to obtain spherical particles. This is butyl bromide 3
The pyridine ring was alkylated by immersion in a 0% methanol solution. Next, this was washed with hydrochloric acid to remove bromine to form a chloride ion form, and then eluted with sodium nitrate to measure an anion exchange capacity. As a result, it was 5.3 meq / g (dry resin). Furthermore, after this equilibrium 0.5N saline adjusted to pH 10, similarly Cl ion exchange resin ^- was analyzed, 4.5 m eq / g
(Dry resin). The obtained anion exchange resin having a weakly basic anion exchange group and a strongly basic anion exchange group coexist with NaCl, Na ₂ S in the same manner as in Example 1.
After equilibrating to a mixed solution of O ₄ , NaHCO ₃ , and NaNO ₃ , each anion in the resin was eluted and analyzed. As a result, 86% of NO ₃ ⁻ , 8% of Cl ⁻ , and 6% of SO ₄ ²⁻ were analyzed. %
In, HCO ₃ ^- was not throat detection N殆.

On the other hand, the 4-vinylpyridine-divinylbenzene copolymer resin obtained above is treated with hexane / methyl iodide
The pyridine ring was N-methylated by immersion in a 4/6 (weight ratio) solution. The ion exchange capacity of the obtained anion exchange resin was 5.4 meq / g (dry resin). When the mixed electrolyte solution was equilibrated and the anions in the resin were analyzed in the same manner as above, NO ₃ ⁻ was 34%, and SO ₄ ²⁻⁴⁸ was analyzed.
%, Cl ^- 17% and HCO ₃ ^- were 1%.

Claims (1)

(57) [Claims] 1. An anion exchanger having an anion exchange group to which a hydrocarbon chain having 4 or more carbon atoms is bonded, which is used for selective ion exchange adsorption of nitrate ion.