JP2002128859A - Polyurethane foam for collecting heavy metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyurethane foam for collecting heavy metal capable of efficiently adsorbing heavy metals such as chromium, nickel, vanadium, uranium, and cobalt, particularly uranium dissolved in an aqueous solution, particularly in seawater, river, plant waste water or the like. SOLUTION: A polyol component for the polyurethane foam comprises a mixed polyol consisting of a polymer polyol (A) which is obtained by a graft polymerization of an acrylonitrile monomer or a methacrylonitrile monomer to a polypropylene oxide, and a polypropylene oxide/polyethylene oxide copolymer (B), wherein (A)/(B) is in a range of 70/30 to 30/70. The polyurethane foam for collecting heavy metal is subjected to film removing treatment, and a nitrile group present in the polyurethane foam is changed to an amidoxime group by hydroxylamine.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a heavy metal trapping agent capable of efficiently adsorbing heavy metals, for example, chromium, nickel, vanadium, uranium, cobalt, etc., dissolved in an aqueous solution, particularly in seawater, rivers, industrial wastewaters and the like. For polyurethane foams.

[0002]

2. Description of the Related Art For the purpose of purifying and reusing industrial wastewater or recovering useful substances, separation and recovery of trace amounts of heavy metals in an aqueous solution are performed. In Japan, where metal resources are scarce, technologies to separate and recover useful rare heavy metals present in seawater, rivers, irrigation water, mining wastewater, etc. have been developed. An adsorption / separation method using a compound that forms a complex with a compound has been applied.

For example, about 3.3 mg of uranium in 1 m ^{3 of} seawater contains uranyl tricarbonate ion (UO ₂ (CO ₃ ) ₃ ).
^In Japan, where uranium resources are scarce, it is being dissolved in the form of a complex ion called ^4- ), and technology for collecting uranium present in this seawater has been actively developed. As a technique for collecting uranium in this case, it is known that a resin having an amidoxime group exhibits good adsorption ability as an adsorbent for uranium dissolved in seawater.

However, in this adsorbent, since the distribution of the hydrophilic amidoxime group is distributed to the center of the base resin, the entire resin swells, and the mechanical strength is reduced and the absorption and absorption of the amidoxime group are reduced.
A problem remains with sufficient durability in repeated desorption. Therefore, instead of resin, polyethylene fiber,
Alternatively, a nonwoven fabric has been proposed in which a nitrile group is introduced by co-graft polymerization of acrylonitrile / methacrylic acid by a graft polymerization method using radiation based on a polypropylene fiber, and then the nitrile group is converted to an amidoxime group by hydroxylamine. Development of a technology for adsorbing uranium with a nonwoven fabric has been proposed.

[0005] In the adsorption and recovery of heavy metals such as uranium by a nonwoven fabric into which an amidoxime group has been introduced, the target heavy metal or the like cannot be collected efficiently unless a plurality of nonwoven fabrics are stacked and used. . Therefore, a plurality of nonwoven fabrics are stacked and brought into contact with seawater as a collecting material, but most of the fibers constituting the nonwoven fabric exist in a state parallel to the plane direction. The water permeability of water becomes extremely strong in one direction, and the isotropic permeability of water in the nonwoven fabric is necessarily hindered.

[0006] In particular, in collecting uranium dissolved in seawater, the contact amount between the trapping material and the seawater is large, and the seawater permeates through the trapping material quickly, so that the target is collected. It is preferable to collect heavy metals. Therefore, for that purpose, it is necessary that the trapping material has a certain thickness, and that the trapping material has an isotropic permeability inside the trapping material. However, it cannot exhibit a sufficient function for collecting heavy metals and cannot secure a sufficient thickness. Furthermore, the method of manufacturing a nonwoven fabric using a fiber made of polypropylene and introducing an amidoxime group is considerably complicated, and there is a problem that the manufacturing cost is high.

[0007]

Accordingly, the present invention provides
It is an object of the present invention to provide a heavy metal collecting material having isotropic water permeability by an industrially simple method that has solved the above problems. In order to solve this problem, the present inventors have conducted intensive studies and have found that a polyurethane foam, particularly a polyurethane foam that has been subjected to a film-free treatment, is used as a substrate for collecting heavy metals, and a polyol component as a constituent component of polyurethane. Furthermore, it was found that if a nitrile group was present and the nitrile group was amidoximed, heavy metals could be efficiently collected by the amidoxime group present in the polyurethane foam, and the present invention was completed.

[0008]

Accordingly, the present invention provides a polymer polyol (A) obtained by graft-polymerizing an acrylonitrile monomer or a methacrylonitrile monomer onto polypropylene oxide, and a polypropylene oxide / polyethylene oxide copolymer (B).
(A) / (B), a mixed polyol in the range of 70/30 to 30/70 is used as a polyol component, and a polyurethane foam is formed by a reaction with an isocyanate compound;
The present invention provides a polyurethane foam for metal collection, wherein a nitrile group present in the polyurethane foam is amidoximed with hydroxylamine after the membrane-free treatment.

That is, the present invention uses a mixed polyol composed of a polymer polyol having a nitrile group introduced therein and a polyalkylene copolymer as a polyol component constituting a polyurethane foam having excellent water permeability,
By reacting with the isocyanate compound, the nitrile group was present in the polyurethane foam from the beginning, and further, the nitrile group was converted to an amidoxime group, and the cell membrane in the polyurethane foam was removed to improve the water permeability. It is characterized by points.

Therefore, according to the present invention, the step of introducing a nitrile group can be omitted by using a polyol component into which a nitrile group has already been introduced as a raw material component of a polyurethane foam. In this regard, for example, it is possible to omit steps such as introduction of a nitrile group by graft polymerization by complicated radiation irradiation, which are performed when introducing an amidoxime group into a nonwoven fabric of polyethylene fiber or polypropylene fiber. And has the advantage of being extremely simple as an industrial production method.

Further, according to the present invention, the water permeability inside the foam is further improved by removing the cell membrane of the polyurethane foam. Therefore, when the polyurethane foam of the present invention is used as a heavy metal collecting material, it is possible to obtain a collecting material having a certain thickness, and for example, has an advantage that an improvement of a contact surface with seawater or the like can be secured. Things.

[0012]

DETAILED DESCRIPTION OF THE INVENTION The polyurethane foam used in the present invention is obtained by reacting a so-called polyol component with an isocyanate compound in the presence of a foaming agent, a foam stabilizer, a catalyst and other auxiliaries. It is.

[0013] In particular, in the polyurethane foam of the present invention, which is a metal collecting material, the polyol component may be
A polymer polyol (A) obtained by graft-polymerizing an acrylonitrile monomer or methacrylonitrile to polypropylene oxide;
A mixed polyol of the polyethylene oxide copolymer (B) is used.

That is, by using a polymer polyol (A) obtained by graft polymerization of an acrylonitrile monomer or methacrylonitrile to polypropylene oxide, a nitrile group can be present in the polyurethane foam from the beginning. is there.

The polypropylene oxide in this case is:
Preferably, the molecular weight is in the range of about 2,000 to 7,000, and the content of acrylonitrile or methacrylonitrile is in the range of about 15 to 25% in the polymer polyol constituting the polyurethane foam. Are preferred.

The polymerization of acrylonitrile or methacrylonitrile with polypropylene oxide is carried out as follows:
It is performed by so-called graft polymerization. That is, by graft polymerization of acrylonitrile and the like, a nitrile group is present in the resin chain, and the reaction with the isocyanate compound reduces the incorporation of the nitrile group into the polyurethane resin. This is because more amidoxime groups will be present in the polyurethane foam.

The polyurethane foam provided by the present invention is based on the fact that the above-mentioned polymer polyol having a nitrile group is used as the polyol component. A so-called mixed polyol using the oxide / polyethylene oxide copolymer (B) is preferably used as the polyol component.

More specifically, the polypropylene oxide / polyethylene oxide copolymer (B) in this case is more preferably a copolymer of polypropylene oxide / polyethylene oxide in a ratio of 30/70 to 70/30. Having a molecular weight of 2000 to 70
Those in the range of about 00 are preferred.

In the polyurethane foam of the present invention, the above-mentioned polymer polyol (A) and a polypropylene oxide / polyethylene oxide copolymer (B)
It is good to use a mixed polymer having a mixing ratio of 70/30 to 30/70, preferably a mixing ratio of 60/40 to 40/60. If the component (B) is less than 30%, the swelling ratio of the polyurethane foam is as low as about 10%, and there is no problem in the strength as a polyurethane foam having excellent dimensional stability, but the polyurethane foam is poor in hydrophilicity.
Even if an amidoxime group is formed, the metal adsorbability will be poor. Further, when the component (B) is 70
%, The swelling rate of the polyurethane foam is 30%
Thus, the strength becomes insufficient. Furthermore, although the hydrophilicity is good, the content of the amidoxime group is small, and the metal adsorbing property is insufficient.

Therefore, in the present invention, by setting the ratio of the component (A) / the component (B) to 70/30 to 30/70, the swelling ratio of the urethane foam is suppressed as much as possible, and there is no problem in strength. Thus, it is possible to obtain a polyurethane foam having excellent metal adsorption.

On the other hand, as the isocyanate component forming the polyurethane foam, known ones can be used, and there is no particular limitation, but aromatic, alicyclic, and aliphatic polyisocyanates, and modified polyisocyanates thereof can be used. One or more modified polyisocyanates obtained by the above method are appropriately selected and used.

Examples of the aromatic polyisocyanate include toluene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 2,4
-A mixture of tolylene diisocyanate and 2,6-tolylene diisocyanate, diphenylmethane diisocyanate, naphthalene diisocyanate, triphenylmethane triisocyanate, xylylene diisocyanate, polymethylene polyphenyl diisocyanate, and the like.

Examples of the alicyclic polyisocyanate include cyclohexylmethane diisocyanate and cyclohexane diisocyanate. Examples of the aliphatic polyisocyanate include hexamethylene diisocyanate, cyclohexane methane diisocyanate, and the like. Among these, in the present invention, good results were obtained by using toluene diisodicyanate as the isocyanate compound.

As the catalyst used in the production of the polyurethane foam by the reaction between the polyol component and the isocyanate, for example, amine catalysts, organometallic catalysts, and other known catalysts for foaming polyurethane foams can be used. Is not particularly limited. Examples of such a catalyst include, for example, amine-based catalysts such as triethylenediamine, triethylamine, tripropylamine, triisopropanolamine, tributylamine,
Trioctylamine, N-methylmorpholine, N-ethylmorpholine and the like can be mentioned.

Examples of the organometallic catalyst include tin octylate, tin laurate, dibutyltin dilaurate and the like.

As a foaming agent for producing a polyurethane foam, one or more mixtures of water, trichloromonofluoromethane, dichlorodifluoromethane, methylene chloride, trichlorofluoroethane, trichloroethane and the like can be mentioned.

As the foam stabilizer, a conventionally known organosilicone surfactant is used. However, in the case of the polyurethane foam as the metal collecting material of the present invention, the presence of a hydrophobic substance, such as silicone oil, in the foam is not preferable in the subsequent amidoximation reaction, and therefore, as a foam stabilizer, It is preferable to use a reactive material or a material that can be easily removed by washing.

[0028] The polyurethane foam of the present invention produced as described above is used to ensure the permeability in the foam.
It is preferred to be constituted as a polyurethane foam having a cell density of about 10 to 40 cells / inch, specifically, a maximum of 50 cells / inch.

[0029] In the method for eliminating the film of the polyurethane foam thus produced, there is an alkali method or an explosion method. In the method for eliminating the film of the present invention, it is preferable to carry out the explosion method. When the film is eliminated by the alkali method, the polyurethane foam is denatured, and in the subsequent amidoximation, an undesirable reaction tends to proceed.

More specifically, the film formation by the explosion method is carried out by using a mixed gas of hydrogen / oxygen.
It can be easily implemented using a mixed gas of 70% and an oxygen concentration of 25 to 35%.

Next, the nitrile groups present in the polyurethane foam of the present invention are amidoximed by reaction with hydroxyamine. Specifically, this amidoximation reaction uses a salt of hydroxyamine in a suitable solvent, removes the salt under neutral or weakly alkaline conditions, and reacts a free hydroxyamino group with a nitrile group. It can be carried out by performing amidoximation.

When acrylonitrile and methacrylic acid are polymerized on a polyethylene nonwoven fabric with a graph using γ-rays, and the nitrile group is amidoximed with hydroxylamine, in order to suppress the formation of an imidoxime-forming reaction, Although a single alcohol solvent is used as the solvent, it has been found that in the amidoximation reaction of the present invention, a single solvent of water can sufficiently achieve the object. Accordingly, examples of the solvent used for the amidoximation reaction in the present invention include water, an alcohol, and a mixed solvent of water / alcohol. Among them, the reaction is preferably performed with a single solvent of water.

The water used as the solvent in this case is preferably distilled water or highly ion-exchanged water which does not contain heavy metals, in view of the purpose of the present invention for collecting metals.

When a single solvent of water is used as the reaction solvent, it is preferable to use a surfactant or the like in combination in order to allow the reaction solution to sufficiently penetrate into the voids of the polyurethane foam. Examples of such a surfactant include sodium dioctyl sulfosuccinate, polyethylene glycol lauryl ether, and acetylene glycol derivative, and the amount of the surfactant is preferably about 0.01 to 0.1%.

When a water / alcohol mixed solvent is used as the reaction solvent, the alcohols include:
Methanol, ethanol, isopropanol, and the like can be given. In this case, the concentration of the alcohol is 3 to 60.
% Can be used.

The amidoximation reaction is more specifically described as follows:
In a solution of hydroxylamine hydrochloride or hydroxylamine sulfate, or a mixed solution of alcohol / water, under a neutral or weakly alkaline condition, a polyurethane foam which has been subjected to a film-free treatment is preferably at about 65 to 85 ° C, preferably about 65 to 85 ° C. Can be carried out by heating to about 75 to 80 ° C.

The reaction time is not particularly limited, and it is sufficient that a sufficient time is taken for completing the amidoximation reaction, and usually 60 to 240 minutes is sufficient.

As the alkali substance used to convert the hydroxylamine salt into a free amine, inorganic hydroxides such as sodium hydroxide and potassium hydroxide are preferably used, and among them, sodium hydroxide is particularly preferable. Good to do.

The concentration of hydroxylamine used in the amidoximation reaction may be any as long as it has a concentration capable of converting nitrile groups present in the polyurethane foam into amidoximation, and specifically, hydroxylamine hydrochloride or hydroxylamine hydrochloride. As hydroxylamine sulfate, 10
It is preferable to use a solution having a concentration of g / L to 70 g / L and react the polyurethane foam at about 10 g per liter.

In the above-mentioned amidoximation reaction of the nitrile group with hydroxylamine, it is particularly preferable to forcibly circulate the reaction solution in the polyurethane foam. If the polyurethane foam is left alone in the reaction solution, a difference in the reaction conditions occurs between the foam surface and the inside, making it difficult to obtain a uniform amidoximation reaction.

As such a reaction vessel, for example, a cheese dyeing machine, an Overmeyer dyeing machine, a drum dyeing machine or the like which is used as a dyeing reactor for textile products can be suitably used. It is to be noted that a good result is obtained when the reaction is carried out in a state where air is shut off as much as possible for the purpose of suppressing side reactions.

It has been found that a good result is obtained when a decompression device is attached to the reaction vessel in order to efficiently remove the air in the polyurethane foam and uniformly replace the reaction solution throughout the polyurethane foam.

In the polyurethane foam amidoximated as described above, an amidoxime group for trapping a so-called heavy metal by a chelate bond is present in the polyurethane foam, and the cell membrane is made non-membrane. The water permeability inside the foam is extremely good.

When the polyurethane foam obtained by the present invention is used as a heavy metal collecting material, the shape is not particularly limited. For example, the shape may be a shape easily penetrated by seawater or the like, and such a shape may be a plate-like or rope-like shape, or a small-sized cube or the like. In the case of adopting a plate-like shape, it is sufficient that the foam has a thickness of about 10 mm. In the case of a cube, one side is 5 mm.
A cubic foam of about 10 cm to 10 cm is preferable.

[0045]

The present invention will be described in more detail with reference to the following examples, but the scope of the present invention is not intended to be limited by these examples.

Example: A glycerin-based polypropylene oxide-based polymer polyol (A) containing 21% of acrylonitrile and having a hydroxyl value of 56.1, and a hydroxyl value of 56.1 added to glycerin with ethylene oxide / propylene oxide = 50/50. The mixed polyol of the polyalkylene oxide (B) was reacted with toluene diisocyanate according to a conventional method to obtain a polyurethane foam having a density of 0.029. Next, the obtained foam was removed from the cell membrane by an explosion method using a mixed gas of hydrogen: oxygen = 2.2: 1 to obtain a polyurethane foam without a membrane.

Then, 50 g of a solvent, hydroxylamine hydrochloride was placed in a glass beaker made of Pyrex (registered trademark).
/ L and sodium hydroxide at a ratio of 28.8 / L and mixed well. A sample having a size of 4.0 cm × 5.0 cm × 4.0 cm was prepared from the non-film-formed polyurethane foam obtained above, and immersed in a beaker containing the above-mentioned mixed solution to perform amidoximation. The polyurethane foam of the present invention was produced.

The solvent conditions for the amidoximation reaction were water / methanol 50/50 and 100/0 (water alone). When only water was used as the reaction solvent, sodium dioctyl sulfosuccinate was used in combination to promote the penetration / diffusion of the reaction solution into the polyurethane foam.

The ratios of the components (A) and (B) in each of the examples and the reaction solvents thereof are shown in Table 1 below.

[0050]

[Table 1]

Metal Collection Test: Using the polyurethane foam produced as described above, a heavy metal collection test was performed as follows. That is, 500 g of a solution prepared by dissolving 2.5 g of a copper sulfate pentahydrate aqueous solution (manufactured by Kanto Chemical Co., Ltd .: reagent grade) in 1 L of ion-exchanged water was weighed, and the solution was prepared in Examples 1 to 10 described above. Then, 4 g of each amidoximated polyurethane foam was immersed and left for 7 days. After the completion of the immersion, the polyurethane foam was taken out, washed well with water, and dried, and the collection rate of copper sulfate of the polyurethane foam was determined. The measurement of the collection rate was determined by two methods of X-ray fluorescence and atomic absorption in order to examine differences in analysis methods. As a target product, a polyurethane foam (blank product) not subjected to amidoximation treatment was similarly immersed. The results were as described in Table 2 below.

[0052]

[Table 2]

As can be seen from the results in the above table, the amount of metal ions adsorbed is determined based on the total of the affinity of polyurethane foam for water in water and the amount of conversion from acrylonitrile to amidoxime groups. And the polymer polyol (A) in Examples 3 to 8,
70/30 to 30 in (A) / (B) with the polypropylene oxide / polyethylene oxide copolymer (B)
It can be seen that polyurethane foams using mixed polyols in the range of / 70 show good metal collection rates.

[0054]

As described above, in the polyurethane foam as a metal collecting material provided by the present invention, a nitrile group is present in the polyurethane foam from the beginning by a simple method, and the nitrile group is converted into an amidoxime group. It is characterized in that the water permeability in the foam is improved by removing the cell membrane in the polyurethane foam.

Therefore, according to the present invention, for example, a step of introducing a nitrile group by graft polymerization by irradiation of radiation, which is performed when introducing an amidoxime group into a nonwoven fabric made of polypropylene fibers, can be omitted. And has the advantage of being extremely simple as an industrial production method.

Further, according to the present invention, by removing the cell membrane of the polyurethane foam, the water permeability inside the foam is further improved. Therefore, as a collecting material,
It is possible to have a certain thickness.

In particular, the present invention relates to a polymer polyol (A) obtained by graft-polymerizing an acrylonitrile monomer or a methacrylonitrile monomer onto polypropylene oxide as a polyol component constituting a polyurethane foam, and a polypropylene oxide / polyethylene oxide copolymer (B). ) And (A) / (B) are 70
/ 30 to 30/70 is used, and by using the mixed polyol component in such a range, the swelling ratio of the urethane foam is suppressed as much as possible, and there is no problem in strength. In addition, it becomes possible to obtain a polyurethane foam having good hydrophilicity and excellent metal adsorption.

Therefore, when the metal trapping material of the present invention is present in seawater, the amount of contact between the trapping material and the seawater increases, and the seawater quickly flows through the polyurethane foam as the trapping material. To Penetrate. Therefore, as compared with a conventional trapping material in which nonwoven fabrics are stacked, for example, there is an advantage that a sufficient function can be exhibited for trapping uranium, which is a rare metal present in seawater.

Continued on front page F-term (reference) 4G066 AB05A AB09A AC24B AD07B BA22 CA46 CA49 CA50 DA07 DA08 EA20 4J034 BA03 DA01 DB03 DC50 DG09 DQ05 DQ16 HA01 HA06 HA07 HC03 HC12 HC13 HC22 JA01 KC17 KD02 KE02 LA01 LA16 LA02 LA04

Claims (1)

[Claims] 1. A polymer polyol (A) obtained by graft-polymerizing an acrylonitrile monomer or a methacrylonitrile monomer onto polypropylene oxide, and a polypropylene oxide / polyethylene oxide copolymer (B) have a ratio (A) / (B) of 70. / 30-30 / 7
A polyurethane foam for metal collection, wherein a polyurethane foam containing a mixed polyol in the range of 0 as a polyol component is subjected to film-free treatment, and a nitrile group present in the polyurethane foam is amidoximed with hydroxylamine.