JP7615745B2 - Method for purifying polyvinylamine resin, method for producing polyvinylamine resin, and polyvinylamine resin - Google Patents

Description

The present invention relates to a method for purifying polyvinylamine resin, a method for producing polyvinylamine resin, and polyvinylamine resin.

Polyvinylamine resins are used in a wide range of applications, including gas adsorbents and anion exchange resins. Polyvinylamine resins are usually obtained by polymerizing monomers containing N-vinyl carboxylic acid amide and hydrolyzing the resulting polymer.

As a method for producing polyvinylamine resin, for example, Patent Document 1 discloses a method in which N-vinylformamide and divinylbenzene are subjected to reverse phase suspension polymerization while being stirred in cyclohexane, and the resulting polymer is hydrolyzed to obtain polyvinylamine resin. Patent Document 2 discloses a method in which N-vinylformamide, divinylbenzene, and acrylonitrile are subjected to suspension polymerization in salt water in the presence of a dispersant, and the resulting polymer is hydrolyzed to obtain polyvinylamine resin.

Japanese Patent Application Publication No. 6-190235 International Publication No. 2016/042846

The methods for producing polyvinylamine resin disclosed in Patent Document 1 and Patent Document 2 do not include a washing step, and therefore the amount of eluted total organic carbon (TOC) in the resulting polyvinylamine resin is not sufficiently reduced.

If the amount of TOC eluted from the polyvinylamine resin is large, the TOC will elute from the polyvinylamine resin into the water treated with this polyvinylamine resin, causing the treated water to fail to meet the TOC standard for its intended use. In addition, the TOC components eluted from the polyvinylamine resin are often basic, causing the pH of the treated water to rise.

The present invention has been made in consideration of these problems, and an object of the present invention is to provide a method for purifying polyvinylamine resin to reduce the amount of TOC eluted. Another object of the present invention is to provide a method for producing polyvinylamine resin with a reduced amount of TOC eluted. A further object of the present invention is to provide a polyvinylamine resin with a reduced amount of TOC eluted.

As described above, no polyvinylamine resin with a reduced amount of TOC elution has been provided up to now.
As a result of extensive research, the present inventors have found that performing steps (1) to (3) described below is effective for reducing the amount of TOC eluted, and have thus arrived at the present invention.

That is, the gist of the present invention is as follows.
[1] A method for purifying a polyvinylamine resin, comprising the following steps (1) to (3) in that order:
Step (1): A step of loading ions onto the polyvinylamine resin with an acid; Step (2): A step of washing the polyvinylamine resin with water; and Step (3): A step of removing ions from the polyvinylamine resin with an alkali. [2] The method for purifying a polyvinylamine resin according to [1], wherein the polyvinylamine resin is a crosslinked resin.
[3] The method for purifying a polyvinylamine resin according to [1] or [2], wherein the acid in step (1) is hydrochloric acid.
[4] The method for purifying a polyvinylamine resin according to any one of [1] to [3], wherein the alkali in the step (3) is an aqueous solution of an alkali metal hydroxide.
[5] A method for producing a polyvinylamine resin, comprising the method for purifying a polyvinylamine resin according to any one of [1] to [4].
[6] A polyvinylamine resin having an elution amount of total organic carbon of 100 ppm or less.

According to the method for purifying polyvinylamine resin of the present invention, it is possible to reduce the amount of TOC eluted from the polyvinylamine resin. Furthermore, according to the method for producing polyvinylamine resin of the present invention, it is possible to obtain polyvinylamine resin with a reduced amount of TOC eluted. Furthermore, the polyvinylamine resin of the present invention has a reduced amount of TOC eluted.

The present invention is described in detail below, but is not limited to the following embodiments and can be modified in various ways within the scope of the gist. In this specification, the expression "~" is used to include the numerical values or physical property values before and after it. In addition, in this specification, "(meth)acrylic" refers to "acrylic", "methacrylic", or both, and "(meth)acrylate" refers to "acrylate", "methacrylate", or both.

[Method for purifying polyvinylamine resin]
The method for purifying a polyvinylamine resin of the present invention includes the following steps (1) to (3) in this order:
Step (1): A step of loading ions onto the polyvinylamine resin using an acid; Step (2): A step of washing the polyvinylamine resin with water; Step (3): A step of removing ions from the polyvinylamine resin using an alkali.

The TOC elution component from polyvinylamine resin is thought to be non-crosslinked linear polyvinylamine. In the polyvinylamine resin purification method of the present invention, in step (1), the linear polyvinylamine in the polyvinylamine resin is ionized with an acid to make it more soluble in water, and this linear polyvinylamine can be efficiently removed by washing with water in the next step (2). Furthermore, in the next step (3), the adsorbed ions of the polyvinylamine resin ionized with an acid can be removed, so that it is thought that the elution of TOC from the polyvinylamine resin can be suppressed and a polyvinylamine resin with a low amount of TOC elution can be obtained.

(Polyvinylamine resin)
The polyvinylamine resin used in step (1) is obtained by polymerizing a monomer containing N-vinyl carboxylic acid amide (hereinafter, sometimes referred to as a "raw material monomer") and hydrolyzing the obtained polymer. The polyvinylamine resin is preferably a crosslinked resin because it has excellent mechanical strength, is insoluble and infusible, and has excellent handleability.

Examples of N-vinyl carboxylic acid amides include N-vinyl formamide, N-methyl-N-vinyl formamide, N-vinyl acetamide, N-methyl-N-vinyl acetamide, N-vinyl propionamide, N-methyl-N-vinyl propionamide, N-vinyl butylamide, and N-vinyl isobutylamide. These N-vinyl carboxylic acid amides may be used alone or in combination of two or more. Among these N-vinyl carboxylic acid amides, N-vinyl formamide and N-vinyl acetamide are preferred, with N-vinyl formamide being more preferred, due to their excellent atom efficiency and ease of availability and synthesis.

The raw material monomers for polyvinylamine resin may include other monofunctional and polyfunctional monomers in addition to N-vinyl carboxylic acid amide.

The other monofunctional monomer is not particularly limited as long as it is copolymerizable with N-vinyl carboxylic acid amide, and examples thereof include (meth)acrylonitrile, (meth)acrylamide, N-alkyl (meth)acrylamide, N,N'-dialkyl (meth)acrylamide, N,N'-dialkyl amino alkyl (meth)acrylamide, alkyl (meth)acrylate, hydroxyalkyl (meth)acrylate, dialkyl amino alkyl (meth)acrylate, etc. These other monofunctional monomers may be used alone or in combination of two or more. Among these other monofunctional monomers, (meth)acrylonitrile is preferred, and acrylonitrile is more preferred, because of its excellent copolymerizability with N-vinyl carboxylic acid amide.

The polyfunctional monomer is not particularly limited as long as it is copolymerizable with N-vinyl carboxylic acid amide, and examples thereof include aromatic polyvinyl compounds such as divinylbenzene, trivinylbenzene, and divinyltoluene; and poly(meth)acrylates such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, glycerol di(meth)acrylate, and trimethylolpropane tri(meth)acrylate. One of these polyfunctional monomers may be used alone, or two or more of them may be used in combination. Among these polyfunctional monomers, aromatic polyvinyl compounds are preferred, and divinylbenzene is more preferred, since they do not decompose due to hydrolysis or the like and have excellent resistance under acidic and basic conditions.

The content of the other monofunctional monomer in the raw material monomer is preferably 1 part by mass to 100 parts by mass, more preferably 10 parts by mass to 40 parts by mass, per 100 parts by mass of N-vinyl carboxylic acid amide. When the content of the other monofunctional monomer in the raw material monomer is 1 part by mass or more, spherical particles are easily obtained. Furthermore, when the content of the other monofunctional monomer in the raw material monomer is 100 parts by mass or less, the acid adsorption capacity of the polyvinylamine resin is large.

The content of the polyfunctional monomer in the raw material monomer is preferably 0.1 to 100 parts by mass, and more preferably 1 to 20 parts by mass, per 100 parts by mass of N-vinyl carboxylic acid amide. When the content of the polyfunctional monomer in the raw material monomer is 0.1 parts by mass or more, the mechanical strength of the polyvinylamine resin is excellent. Furthermore, when the content of the polyfunctional monomer in the raw material monomer is 100 parts by mass or less, spherical particles are easily obtained.

The polymerization method for the raw material monomers including N-vinyl carboxylic acid amide can be a known polymerization method, and known additives such as polymerization initiators and dispersants necessary for polymerization can also be used.

(Step (1))
Step (1) is a step of loading ions onto a polyvinylamine resin using an acid.

Examples of acids include hydrochloric acid, hydrobromic acid, sulfuric acid, and nitric acid. These acids may be used alone or in combination of two or more. Among these acids, monovalent acids are preferred because they have a large degree of swelling of the polyvinylamine resin and excellent cleaning properties, with hydrochloric acid and hydrobromic acid being more preferred, and hydrochloric acid being even more preferred.

The acid is usually used as an aqueous solution. The concentration of the acid in the aqueous acid solution is preferably 2% by mass to 25% by mass, and more preferably 4% by mass to 15% by mass. When the acid concentration is 2% by mass or more, ions can be loaded efficiently. Furthermore, when the acid concentration is 25% by mass or less, loading due to shrinkage of the polyvinylamine resin can be suppressed.

The amount of the acid used in step (1) is preferably 1 to 10 equivalents, more preferably 3 to 6 equivalents, relative to the acid adsorption capacity of the polyvinylamine resin. When the amount of the acid used is 1 equivalent or more, the cleaning efficiency of the polyvinylamine resin is excellent. Furthermore, when the amount of the acid used is 10 equivalents or less, the loading time can be shortened.
The acid adsorption capacity of a polyvinylamine resin is the amount of acid ions that can be adsorbed by the polyvinylamine resin per unit mass of the polyvinylamine resin, and is determined by titration.

Methods for loading ions onto polyvinylamine resin using acid include, for example, a column method in which a column is filled with polyvinylamine resin and acid is passed through it; and a batch method in which polyvinylamine resin and acid are placed in a container and stirred. Of these methods, the column method is preferred because it has excellent efficiency in loading ions onto polyvinylamine resin relative to the amount of acid used.

In the column method, the acid passing rate is preferably SV1 hr ^-1 to 10 hr ^-1 , and more preferably SV3 hr ^-1 to 7 hr ^-1 . When the acid passing rate is SV1 hr ^-1 or more, the efficiency of loading ions onto the polyvinylamine resin is excellent. When the acid passing rate is SV10 hr ^-1 or less, the operability of passing the acid is excellent.

The temperature when loading ions into the polyvinylamine resin with acid is preferably 10°C to 50°C, more preferably 20°C to 30°C. If the temperature is 10°C or higher, the load can be easily handled. Furthermore, if the temperature is 50°C or lower, deterioration of the polyvinylamine resin due to heat can be avoided.

(Step (2))
Step (2) is a step of washing the polyvinylamine resin that has been subjected to step (1) with water.
The water used for washing is preferably water that does not contain ions, such as desalted water, pure water, or ultrapure water.

The amount of water used is preferably 20 to 300 times the amount (volume) of polyvinylamine resin, and more preferably 50 to 180 times. When the amount of water used is 20 times or more, the cleaning effect of polyvinylamine resin is excellent. When the amount of water used is 300 times or less, the cleaning efficiency of polyvinylamine resin is excellent.

Methods for washing polyvinylamine resin with water include, for example, a column method in which a column is filled with polyvinylamine resin and water is passed through it; and a batch method in which polyvinylamine resin and water are placed in a container and stirred. Of these methods, the column method is preferred because it has excellent washing efficiency for polyvinylamine resin relative to the amount of washing water.

In the column method, the water passing rate is preferably SV1 hr ^-1 to 10 hr ^-1 , and more preferably SV3 hr ^-1 to 7 hr ^-1 . When the water passing rate is SV1 hr ^-1 or more, the washing efficiency of the polyvinylamine resin is excellent. Furthermore, when the water passing rate is SV10 hr ^-1 or less, the operability of passing the liquid is excellent.

The washing time with water in the column method is preferably 1 to 4 days, more preferably 2 to 3 days. If the washing time with water is 1 day or more, the washing effect of the polyvinylamine resin is excellent. Furthermore, if the washing time with water is 4 days or less, the washing efficiency of the polyvinylamine resin is excellent.

In the column method, the water may be passed continuously or intermittently, i.e., the water may be passed without being passed for a desired period of time. When the water is passed continuously, the water passing speed may be changed during the process. When the water is passed intermittently, the water may be passed intermittently at different water passing speeds. In addition, between passes of the water, immersion washing may be performed in which the polyvinylamine resin is left to stand in washing water for a predetermined period of time.

The temperature when washing polyvinylamine resin with water is preferably 10°C to 50°C, more preferably 20°C to 30°C. If the temperature is 10°C or higher, the washing efficiency of polyvinylamine resin is excellent. Furthermore, if the temperature is 50°C or lower, deterioration of polyvinylamine resin due to heat can be avoided.

(Step (3))
The step (3) is a step of removing adsorbed ions from the polyvinylamine resin that has been subjected to the step (2) with an alkali.

Examples of alkalis include alkali metal hydroxides such as sodium hydroxide, lithium hydroxide, and potassium hydroxide. These alkalis may be used alone or in combination of two or more. Among these alkalis, sodium hydroxide and potassium hydroxide are preferred, with sodium hydroxide being more preferred, because they have excellent solubility in water of the carbonate that is generated when handled in air.

The alkali is usually used as an aqueous solution. The concentration of the alkali in the aqueous alkaline solution is preferably 2% by mass to 40% by mass, and more preferably 4% by mass to 15% by mass. When the alkali concentration is 2% by mass or more, ions can be efficiently removed. Furthermore, when the alkali concentration is 40% by mass or less, the load due to shrinkage of the polyvinylamine resin can be suppressed.

The amount of alkali used is preferably 1 to 10 equivalents, and more preferably 3 to 6 equivalents, relative to the acid adsorption capacity of the polyvinylamine resin. If the amount of alkali used is 1 equivalent or more, the residual ions can be reduced. Furthermore, if the amount of alkali used is 10 equivalents or less, the loading time can be shortened.

Methods for removing ions from polyvinylamine resin using alkali include, for example, a column method in which a column is filled with polyvinylamine resin and an alkali is passed through it; and a batch method in which polyvinylamine resin and an alkali are placed in a container and stirred. Of these methods, the column method is preferred because it has a superior efficiency of removing ions from polyvinylamine resin relative to the amount of alkali used.

In the column method, the alkali passing rate is preferably SV1 hr ^-1 to 10 hr ^-1 , and more preferably SV3 hr ^-1 to 7 hr ^-1 . When the alkali passing rate is SV1 hr ^-1 or more, the efficiency of removing ions from the polyvinylamine resin is excellent. Also, when the alkali passing rate is SV10 hr ^-1 or less, the operability of passing the liquid is excellent.

The temperature when removing ions from polyvinylamine resin with alkali is preferably 10°C to 50°C, more preferably 20°C to 30°C. If the temperature is 10°C or higher, the operability of ion removal is excellent. Furthermore, if the temperature is 50°C or lower, deterioration of the polyvinylamine resin due to heat can be avoided.

(Other processes)
The method for purifying a polyvinylamine resin of the present invention may include other steps in addition to steps (1) to (3) as long as the effects of the present invention are not impaired. The other steps may be before step (1), between steps (1) and (2), between steps (2) and (3), or after step (3). The other steps may be either single or multiple.
For example, the step (3) may be followed by a finishing step of washing the polyvinylamine resin with water. This finishing step is carried out by washing the polyvinylamine resin with water such as desalted water, pure water, or ultrapure water, similarly to the step (2). The finishing step is usually carried out until the washing water becomes neutral (pH 6 to 8).

[Method of producing polyvinylamine resin]
The method for producing a polyamine resin of the present invention includes the above-mentioned steps (1) to (3) and, if necessary, other steps. The details of the steps (1) to (3) and other steps are as described above.

[Polyvinylamine resin]
The polyvinylamine resin of the present invention has a TOC elution amount of 100 ppm (ppm by mass) or less. The polyvinylamine resin of the present invention preferably has a TOC elution amount of 50 ppm or less.

In order to reduce the amount of TOC eluted from a polyvinylamine resin to 100 ppm or less, the method for purifying a polyvinylamine resin of the present invention may be used.
The amount of TOC eluted from the polyvinylamine resin is measured by the method described in the Examples section below.
In the measurement of the amount of TOC elution in the Examples described later, the amount of TOC elution increases with time as the storage period progresses. However, according to the present invention, the amount of TOC elution can be suppressed to 100 ppm or less, preferably 50 ppm or less, even after a storage period of 14 days.

The polyvinylamine resin obtained by the polyvinylamine resin purification method of the present invention, the polyvinylamine resin obtained by the polyvinylamine resin manufacturing method of the present invention, and the polyvinylamine resin of the present invention are suitable for water treatment, and are particularly suitable for drinking water treatment, since the amount of TOC eluted is reduced.

The present invention will be described in more detail below using examples, but the present invention is not limited to the description of the following examples as long as it does not deviate from the gist of the invention.

(Method of measuring the amount of TOC elution)
For the polyvinylamine resins obtained in Examples 1 and 2 and Comparative Examples 1 and 2, the amount of TOC eluted (ppm) was measured by the following procedure.
2 BV of demineralized water was added to the polyvinylamine resin that had been drained using a centrifuge to make a slurry, to which 0.28 BV of 2N-HCl aqueous solution was added and the mixture was left to soak at 25°C for 1 hour. The polyvinylamine resin slurry was drained using a centrifuge to obtain a partially HCl-treated resin. Next, 10 mL of the drained partially HCl-treated resin and 20 mL of ultrapure water were added to a 100 mL Erlenmeyer flask and shaken at 40°C for 14 hours. After completion of the process, the supernatant was sampled and the TOC was measured using a TOC-L manufactured by Shimadzu Corporation.
This test was carried out by changing the storage period of the drained polyvinylamine resin to 0, 7 and 14 days.

[Production Example 1]
292 parts by mass of demineralized water, 195 parts by mass of ammonium sulfate, and 5.00 parts by mass of polydiallyldimethylammonium chloride aqueous solution (polymer concentration 18% by mass, weight average molecular weight 500,000) were charged into a separable flask, stirred, and dissolved to form a polymerization bath. 100 parts by mass of N-vinylformamide, 8.97 parts by mass of divinylbenzene, 19.2 parts by mass of ethyl acetate, 19.2 parts by mass of acrylonitrile, and 0.64 parts by mass of 2,2'-azobis(2,4-dimethylvaleronitrile) (product name "V-65", Fujifilm Wako Pure Chemical Industries, Ltd.) as an azo-based polymerization initiator were mixed to form a monomer solution. The monomer solution and the polymerization bath were mixed and stirred at 100 rpm while replacing the inside of the separable flask with nitrogen. After 30 minutes, the temperature was raised, and polymerization was performed at 40 ° C. for 100 minutes, then at 50 ° C. for 1 hour, and then at 60 ° C. for 30 minutes. After polymerization, the mixture was filtered, washed, and filtered to obtain hydrous polymer spherical particles. 100 parts by mass of the reaction product thus obtained was placed in a separable flask, and 150 parts by mass of a 24% by mass aqueous solution of sodium hydroxide was added, followed by hydrolysis at 90° C. for 8 hours with stirring. The mixture was washed and filtered to obtain hydrous polyvinylamine resin spherical particles.

[Example 1]
200 g (308 mL) of the polyvinylamine resin obtained in Production Example 1 was packed into a glass column, and 1,538 mL (5 BV) (4.3 equivalents relative to the acid adsorption capacity) of a 2N-HCl aqueous solution (HCl concentration: 7.3 mass %) was passed through the column at 25° C. and SV5 hr ⁻¹ to convert the polyvinylamine resin to HCl.
Next, 1538 mL (5 BV) of desalted water was passed through at SV 5 hr ^- for washing, and excess hydrochloric acid solution was removed. Next, the HCl-modified polyvinylamine resin was stored in desalted water at 25°C for 18 hours while still packed in the glass column. Next, 9230 mL (30 BV) of desalted water was passed through at SV 5 hr ^-1 at 25°C for washing, and washing was further repeated once more. The time required for washing was 49 hours in total.
Then, 1538 mL (5 BV) (4.3 equivalents to the acid adsorption capacity) of a 2N-NaOH aqueous solution (NaOH concentration: 8% by mass) was passed through the column at 25° C. and SV5 hr ⁻¹ to remove chloride ions from the resin in the column.
Then, desalted water was passed through the column for 5 hr ⁻¹ until the outlet liquid became neutral, to purify the polyvinylamine resin.

[Example 2]
The polyvinylamine resin was purified in the same manner as in Example ¹ , except that the storage time of the HCl-treated polyvinylamine resin was changed from 18 hours to 16 hours, and the condition of passing the desalted water through the HCl-treated polyvinylamine resin was changed from 9230 mL at SV ⁵ hr to 24600 mL (80 BV) at SV 10 hr.

[Comparative Example 1]
The polyvinylamine resin obtained in Production Example 1 was used as it was.

[Comparative Example 2]
250 g (384.6 mL) of the polyvinylamine resin obtained in Production Example 1 was packed into a glass column, and 1923 mL (5 BV) of desalted water was passed through at 25° C. and SV 5 hr ⁻¹ . Then, 1923 mL (5 BV) of methanol was passed through at 25° C. and SV 5 hr ^{−1. Then, 1923 mL (5 BV) of desalted water was passed through at 25° C. and SV 5 hr −1 to} purify the polyvinylamine resin.

The results of measuring the TOC elution amount of the polyvinylamine resins obtained in Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Table 1.

As can be seen from Table 1, the polyvinylamine resins obtained in Examples 1 and 2 having steps (1) to (3) had a reduced amount of TOC elution.
On the other hand, the polyvinylamine resin obtained in Comparative Example 1, which does not include steps (1) to (3), had a large amount of TOC eluted. The polyvinylamine resin obtained in Comparative Example 2, which was washed with methanol and desalted water, also had a large amount of TOC eluted, and it was not possible to reduce the amount of TOC eluted.

As mentioned above, it is believed that the TOC elution component from polyvinylamine resin is non-crosslinked linear polyvinylamine. In Examples 1 and 2, it is believed that efficient cleaning with water was achieved by ionizing linear polyvinylamine with an acid to make it more soluble in water. On the other hand, linear polyvinylamine has low solubility in methanol, and it is believed that no cleaning effect was obtained in Comparative Example 2.

The polyvinylamine resin obtained by the polyvinylamine resin purification method of the present invention, the polyvinylamine resin obtained by the polyvinylamine resin manufacturing method of the present invention, and the polyvinylamine resin of the present invention are suitable for water treatment, and are particularly suitable for drinking water treatment, since the amount of TOC eluted is reduced.

Claims (6)

A method for purifying a polyvinylamine resin , comprising the following steps (1) to (3) in order:
the amount of acid used in the step (1) is 1 equivalent to 10 equivalents relative to the acid adsorption capacity of the polyvinylamine resin;
The method for purifying a polyvinylamine resin, wherein the alkali in the step (3) is an aqueous solution of an alkali metal hydroxide .
Step (1): A step of loading ions onto the polyvinylamine resin using an acid; Step (2): A step of washing the polyvinylamine resin with water; Step (3): A step of removing ions from the polyvinylamine resin using an alkali. The method for purifying a polyvinylamine resin according to claim 1, wherein the polyvinylamine resin is a crosslinked resin. The method for purifying a polyvinylamine resin according to claim 1 or 2, wherein the acid in step (1) is hydrochloric acid. The method for purifying a polyvinylamine resin according to any one of claims 1 to 3, wherein in the step (2), passing water through a column and immersion washing in which the polyvinylamine resin is left stationary in water are performed. A method for producing a polyvinylamine resin, comprising the method for purifying a polyvinylamine resin according to any one of claims 1 to 4. The method for producing a polyvinylamine resin according to claim 5, wherein the polyvinylamine resin produced has an elution amount of total organic carbon of 100 ppm or less.