JPH03123642A - Ion-exchange fiber and purification of aqueous solution using same - Google Patents

Abstract

PURPOSE:To obtain an ion-exchange fiber having a large specific surface area and indicating an excellent ion-exchange capacity by treating the surface of the fiber with hydrogen peroxide. CONSTITUTION:After ion-exchange fiber is manufactured it is treated with hydrogen peroxide having a concn. of about 2-10% at room temp. for 0.5-500 hours. Since hydrogen peroxide is fairly highly reactive, it is sufficient to treat the fiber with such a solution as to permit its immersion. The ion-exchange fiber thus treated is entirely swollen due to a finely evolved gas in the solution and due to the oxidative reaction and the surface of the fiber is etched to cause subtle irregularities thereon and its specific surface area becomes very large. For this reason, the activating area contributing to the ion-exchange or adsorption becomes large and the water content is somewhat increased, leading to a more excellent ion-exchange capacity.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides an ion exchange fiber that has a large specific surface area due to a specific surface treatment and therefore exhibits excellent ion exchange ability, and a nuclear power plant using the same. .

The present invention relates to a method for treating impurities contained in water and wastewater in thermal power plants, pharmaceutical companies, etc., and particularly relates to a method for purifying an aqueous solution using a precoat filter.

[Prior Art] Conventionally, in precoat type filters for purifying water and wastewater in nuclear power plants, thermal power plants, etc., powdered ion exchange resin has been used as a precoat material.

Precoat filtration is a general term for a method in which a filtration layer with a certain thickness is formed using a precoat material on some kind of support, and the water to be treated passes through that layer to remove impurities contained therein. There is a method in which a powdered ion exchange resin is precoated on a support element by hydraulic pressure, and the water to be treated is passed through the layer to purify it, and this device is called a precoat filter.

This precoat material is backwashed and replaced with a new precoat material when the differential pressure during water flow reaches a certain value. However, in many cases, the specified differential pressure is reached before the ion exchange capacity of the precoat material is effectively used up, and the differential pressure is rate-limiting at the time of backwashing.

Particularly at nuclear power plants, the waste precoat materials that are backwashed and recovered are all subject to storage and storage because they contain radioactive materials, and the ever-increasing number of such materials has become a new social problem.

Therefore, for the purpose of reducing waste, it has become necessary to lengthen the period from precoating to backwashing (the lifespan of water sampling with one precoat material) as long as possible. This is not just a matter of preventing the differential pressure rise of the precoat material and extending the water sampling life; it is meaningless unless the quality of the treated water is equal to or better than that of existing materials.

If it were possible to improve the quality of treated water, it would also be highly effective in significantly reducing radiation exposure for nuclear power plant workers.

As a method to deal with this, it was considered to improve the precoat material, and the use of ion exchange fibers as the precoat material was devised (Japanese Patent Laid-Open No. 55-67384).

[Problems to be Solved by the Invention] However, these ion exchange fibers are only effective at preventing the precoat material from physically cracking, and are not capable of achieving the above object.

In order to practically extend the precoat life, the precoat layer composed of an ion exchanger is required to have an appropriate porosity and not be compacted when water is passed through it. Moreover, for ion exchange or adsorption, the larger the area of the active surface in contact with the water to be treated, the more impurities can be adsorbed.

Although it has been considered that ion exchange fibers could be used to meet these requirements, no consideration has been given to increasing the specific surface area of the ion exchange fibers themselves through post-treatment. There wasn't.

The present invention eliminates the drawbacks of the prior art, provides an ion exchange fiber that has a larger specific surface area than conventional ion exchange fibers, and exhibits superior ion exchange ability, and purifies aqueous solutions using the ion exchange fiber. The purpose of the present invention is to provide an aqueous solution purification method that extends the filtration life of precoat and improves the quality of treated water compared to conventional methods.

[Means to solve the problem] That is, the present invention has the following configuration.

(1) Ion exchange fibers characterized by surface treatment with hydrogen peroxide.

(2) When purifying the aqueous solution with a precoat filter,
Powdered ion exchange resin and the above (1) as pre-coat material
A method for purifying an aqueous solution, characterized by using the ion exchange fiber described in .

The present invention will be explained in detail below.

The form of the ion exchange fiber used in the present invention is not particularly limited (
Any type of ion-exchange polymer may be used as long as it has a fiber form, but fibers made of an ion-exchange polymer and a reinforcing polymer are particularly preferred from the viewpoint of effectively suppressing the compaction of the pre-coat layer in order to extend the life of the pre-coat material. It is preferable that there be.

The mixing mode of the ion-exchange polymer and the reinforcing polymer is not particularly limited, but for example, core-sheath type fibers, multi-core blends, and multi-core composites in which the ion exchange polymer is the main component of the sheath component and the reinforcing polymer is the core component. Fibers are preferably used. In particular, multifilamentary composite fibers are preferred because they have sufficient mechanical strength, are effective in preventing compaction, and have a large specific surface area as an ion exchanger.

Ion exchange polymers include, but are not limited to, polystyrene, polyacrylic, and polyamide.

Examples include polymers in which ion exchange groups are introduced into polyester-based, polyvinyl alcohol-based, polyphenol-based, poly-α-olefin-based compounds, and the like. In particular, a polymer obtained by introducing an ion exchange group into a crosslinked and insolubilized polystyrene compound is preferable because it is excellent in ion exchange performance and chemical stability, which are extremely important in the present invention.

In addition, examples of the reinforcing polymer include poly-α-olefin, polyamide, polyester, polyacrylic, etc., but the reinforcing polymer is not limited thereto. Among these, poly-α-olefin is preferred because it has excellent chemical resistance for producing ion-exchange fibers. Examples of the poly-α-olefin include, but are not limited to, polyethylene, polypropylene, poly-3-methylbutene-1, poly-4-methylpentene-1, and the like.

The diameter of such ion exchange fibers is preferably 15 to 100 μm from the viewpoint of having a high specific surface area and preventing compaction of the precoat layer. More preferably 20-70μm1, especially 30-70μm1
Most preferred is 50 μm (dry).

In addition, the fiber length is set to 0.0 mm for the purpose of maintaining an appropriate porosity of the precoat layer. 1-1 mm is preferred. More preferably, 0.15 to 0.6 mm, most preferably 0.2 to 0.4 mm.

The cross-sectional shape of this fiber may be circular or various other shapes.

The powdered ion exchange resin used in the present invention preferably has a particle size of 1 to 250 μm, more preferably an average particle size of 60 μm or less. Specifically, we use ion exchange resins made by introducing ion exchange groups into styrene-divinylbenzene copolymers, which have excellent chemical stability and ion exchange performance, or ion exchange resins made from acrylic acid-based monomer divinylbenzene copolymers, down to powder. It can be crushed.

The ion exchange group of the ion exchange fiber and powdered ion exchange resin in the present invention means an anion exchange group and a cation exchange group.

As the anion exchange group, a strongly basic anion exchange group obtained by treating a haloalkylated product with a tertiary amine such as trimethylamine, and a secondary or lower amine such as isopropylamine, diethylamine, piperazine, and morpholine can be used. Examples include weakly basic anion exchange groups obtained by the following, but strongly basic anion exchange groups are preferable from the viewpoint of treatment performance in the present invention.

As the cation exchange group, sulfonic acid groups, phosphonic acid groups, carboxylic acid groups, aminocarboxylic acid groups such as iminodiacetic acid groups, etc. are preferably used, and sulfonic acid groups are more preferable in terms of processing performance in the present invention.

A specific method for producing ion exchange fibers is to crosslink and insolubilize the polystyrene portion of a multicore mixed or composite fiber made of a polystyrene compound and poly-α-olefin with a formaldehyde source under an acid catalyst, and then to insolubilize the polystyrene portion by a known method. A method for producing mixed fibers by impregnating poly-α-olefin fibers with styrene-divinylbenzene and introducing ion exchange groups after copolymerization, polyacrylonitrile/polyamide/polyester Examples include, but are not limited to, methods of introducing ion exchange groups into fibers etc. by chemical modification methods, grafting methods, etc.

Here, it is important in the present invention that after producing the ion exchange fiber by the above method, it is treated with hydrogen peroxide.

Hydrogen peroxide is usually preferably used in the form of an aqueous solution, and its concentration is arbitrary, but is 0.01 to 50%, preferably 0.
．． It is preferably about 1 to 20%, more preferably about 0.2 to 10%. This is because if the concentration is too low, the surface treatment effect will be small, and if the concentration is too high, the ion exchange groups will decompose, the physical strength of the fiber will decrease, and it will take a considerable amount of time to wash after treatment, which has many disadvantages. It is.

The reaction temperature is usually 5 to 90°C, but preferably around room temperature. In addition, the processing time depends on the concentration and temperature, but is usually 0.
．． It is preferable to carry out the treatment for 5 to 500 hours.

The treatment method is arbitrary, but since hydrogen peroxide is quite reactive, it is sufficient to soak the fibers in a solution just enough to soak them.

Ion-exchange fibers treated with hydrogen peroxide swell as a whole due to the oxidation reaction with the microscopic gases generated in the solution, resulting in subtle unevenness and etching on the fiber surface, resulting in a very large specific surface area. Therefore, the active sites that contribute to ion exchange or adsorption are expanded, and the water content is also slightly increased, resulting in even better ion exchange ability.

Here, the combination of ion exchange fiber and powdered ion exchange resin as the precoat material in the present invention is [Fc, Ral
, [Rc, Fal, [Fc, Rc.

Fal [Fc, Fa, Ral [Fc, Rc, R
al [Rc, Fa, Rako [F c,
Rc, F a.

Ral etc. are preferable considering the improvement of the outlet water quality, and especially for the purification of waste water of nuclear power plants, [Fc, Rc, Ral etc.
is most preferred. Here, Fc and Fa mean cation and anion exchange fibers, respectively, and Rc and Ra mean powder cation and powder anion exchange resin, respectively.

In the present invention, the ratio of the ion exchange fiber to the total amount of the precoat material is preferably 10 to 60% in terms of dry weight. More preferably 15 to 50%, still more preferably 20%
~40%. This means that if the fiber content is too low, the precoat layer will have a moderate porosity, compaction prevention effect, and high specific surface area. This is because the quality of the treated water will be poor, although the water will increase.

The ratio of cation exchanger/anion exchanger in the precoat material of the present invention is preferably in the range of 1/10 to 10/1, but particularly for purification of wastewater from nuclear power plants, it is in the range of 1/2 to 1/2.
10/1 is preferred.

The pre-coating material can be used in any way, for example, stirring and mixing powdered cation/anion exchange resin and ion exchange fiber in water to form a flock, or using powdered cation/anion exchange resin and ion exchange fiber to form a flock.
After stirring and mixing the anion exchange resin in water to form a flock, ion exchange fibers are mixed and stirred to form a flock. Methods of precoating in one step using the usual method, method of step (multistage) precoating, method of precoating with body feed Various combinations can be considered, such as a method in which a powdered cation/anion exchange resin is stirred and mixed in water, precoated as a flock, and then an overprecoat method in which ion exchange fibers dispersed in water are precoated. Here, from the point of view of operation and maintenance management, it is preferable to carry out one-step precoating using a conventional method.

However, in order to further improve the life of the precoat material, the step precoat method, overcoat precoat method,
Alternatively, it is effective to combine this method with a precoat method that takes into consideration a filtration mechanism such as changing the mixing ratio of fibers and resin in the precoat layer.

Further, a dispersant such as a surfactant may be added during stirring and mixing.

As the precoat support used in the present invention, all the usual shapes of precoat filters such as cylindrical and single-leaf type filters and filtration supports used in ion exchange filtration can be used. The existing method can be applied as is.

Further, the thickness of the precoat layer is about 2 to 20 mm,
Preferably it is about 3 to 10 mm. In the present invention, the passage speed of the aqueous solution to be treated to the precoat layer is 1 to 20 m.
/hr, and when the pressure loss reaches about 2 kg/al, it is backwashed in the usual manner and the support is used repeatedly.

The pre-coat material of the present invention using ion-exchange fibers with a large specific surface area and powdered ion-exchange resin has a significantly longer life than conventional pre-coat materials, and has enabled further improvement in water quality. It has a thin pre-coated filtration layer,
It is formed from a flock of powdered ion-exchange resin with ion-exchange fibers as the core, and has an integrated and durable structure.The mixture of ion-exchange fibers gives it an appropriate bulk and allows water to pass through. It prevents the phenomenon of compaction, maintains the porosity necessary for ion exchange or adsorption, and because the fiber itself has a very effective ion exchange function, impurities in the aqueous solution to be treated are not wasted between the particles of the entire precoat layer. This is because the surface of the ion-exchange fiber is extensively etched by hydrogen peroxide treatment and has a large specific surface area, so the ion-exchange ability of the ion-exchange fiber itself is extremely low. The fact that it has excellent properties further improves the effectiveness of the precoat material.

Examples are shown below, but the present invention is not limited thereto.

[Example] (Example 1) A cut fiber was obtained by cutting a spun multicore sea-island composite fiber [sea component polystyrene/island component polyethylene = 50150 (number of layers 16)] into a length of 0.3n++n. 1 part by weight of the cut fiber was added to a crosslinking/sulfonation solution consisting of 7.5 parts by volume of commercially available primary sulfuric acid and 0.07 parts by weight of paraformaldehyde, and reacted at 90°C for 4 hours.
After further reacting at 100°C for 3 hours, it was washed with water. Next, a cation exchange fiber having sulfonic acid groups was obtained by treating with an alkali and then activating with hydrochloric acid. (Exchange capacity: 3.5 milliequivalents/g-Na, fiber diameter: approximately 40 μm) The exchange capacity was measured by the following method.

Add 1 g of this cut fiber to 50 ml of sodium hydroxide at 0.0 IN and stir for 2 hours, weigh out exactly 5 ml, and calculate by neutralization titration.

In addition, the above-mentioned cut fibers converted to Na type were thoroughly immersed in ion-exchanged water, dehydrated using a household centrifugal dehydrator, measured for weight (W), and then completely dried in a dryer at 60°C for 48 hours. The weight was measured (Wo) and the water content was determined from the following formula.

Water content = (W-Wo)/W.

The cation exchange fiber had a moisture content of 1.6.

Weigh out 0.125g (dry weight) of this ion exchange fiber, and weigh out 1100pp of amorphous iron (ferric hydroxide).

The mixture was placed in a flask with 25 ml of an aqueous solution (average particle size: 3.6 μm) and stirred for 2 hours. Thereafter, it was filtered through a G1 glass filter, and the filtrate was subjected to UV measurement, and the amorphous iron adsorption rate was determined by comparing the value at a wavelength of 550 nm with that of the stock solution.

Next, 20 g (dry weight) of the above ion exchange fiber was weighed out and added to 200 ml of 5% hydrogen peroxide solution at room temperature.
The ion exchange fiber of the present invention was obtained by soaking the fiber for a period of time and then thoroughly washing with pure water.

When I measured the water content and exchange capacity, they were 1.9.3.5 respectively.
milliequivalent/g-Na.

The amorphous iron adsorption rates of the hydrogen peroxide-treated ion-exchange fibers of the present invention were also investigated in exactly the same manner as the untreated fibers, and the results are shown in Table 1.

This result, in which the adsorption rate of amorphous iron was improved without any change in exchange capacity, showed that the ion exchange fibers treated with hydrogen peroxide had a significantly larger specific surface area than those without treatment.

(Example 2) Commercially available powder cation exchange resin [“Powdex”-PC
H (Organo Co., Ltd.), has a sulfonic acid group. exchange capacity 5.0 meq/g] and a commercially available powdered anion exchange resin [“Powdex”-PAO (Organo Co., Ltd.),
It has a trimethylammonium group. The hydrogen peroxide-treated ion exchange fiber produced in Example 1 was added to a mixture having an exchange capacity of 3.2 meq/g at a ratio of 30% of the total amount, so that the cation/anion ratio was 6/ Adjusted to be 1.

Using a column (50 cylinder diameter) equipped with an acrylic support plate inside, a filter paper was placed on the support plate, and the floc was deposited thereon for precoating.

The total amount of flock body is 1.96g (approximately 1.0kg/rr
f). From the top, the differential pressure limit of pre-coat material in a nuclear power plant is shown by using a prepared simulated liquid containing 5 ppm of amorphous iron (ferric hydroxide, average particle size 3.6 μm) in terms of iron at a flow rate of 8 m/hr. The average iron removal rate was determined from the measurement of filtration time (precoat life) and iron concentration.

The experimental results are shown in Table 2.

(Comparative Example 1) An experiment was carried out in exactly the same manner as in Example 2, except that ion exchange fibers that had not been treated with hydrogen peroxide were used.

The experimental results are shown in Table 2.

(Comparative Example 2) An experiment completely similar to Example 2 was conducted except that ion exchange fibers were not used.

The experimental results are shown in Table 2.

As a result, the mixed system with ion-exchange fiber is very effective in suppressing the rise in differential pressure and improving the water quality of the water to be treated, compared to the conventional system using only powdered ion-exchange resin. It was found that hydrogen treatment increases the specific surface area and improves ion exchange performance, thereby further improving its effectiveness as a precoat material.

This is caused by an oxidation reaction with the minute gases generated in the hydrogen peroxide solution, which causes the entire fiber to swell, the surface of the fiber to be etched, and the specific surface area to be extremely large (and the active points that contribute to ion exchange or adsorption to spread). This is thought to be due to the effect of

[Effects of the Invention] The present invention has a structure in which the entire fiber swells slightly due to the oxidation reaction with the minute gas generated in the hydrogen peroxide solution, and the fiber surface is etched, resulting in a very large specific surface area (i.e., ion exchange or adsorption). The ion exchange fiber has a large specific surface area due to the effect of expanding the active sites contributing to the growth and slightly increasing the water content, and in the solution processing method using the ion exchange fiber, the ion exchange fiber becomes the core of the powdered ion exchange resin. By creating a flock body and imparting appropriate porosity and compressive strength, the life of the precoat material can be dramatically extended, and the excellent ion exchange performance of the fibers with a large surface area can also improve the quality of treated water. I made it.

This is a very simple method that can be used as is in the usual precoating method, and is also very effective.

According to the present invention, the waste volume of variously used precoat materials for water treatment can be reduced, and radiation exposure to workers, which is a concern particularly in nuclear power plants, can be dramatically reduced.

The liquid to be treated to which the present invention is applied is not limited to only those that use a precoat filter;
It is particularly effective for wastewater from nuclear power plants and thermal power plants.

Wastewater from nuclear power plants and thermal power plants refers to circulating condensate and
Examples include fuel pool water, desalination equipment backwash wastewater, steam generation blow water, wet water separator drain water, cavity water, suppression pool water, and core water, among which it is particularly effective in purifying nuclear condensate. show.

Claims (2)

[Claims] (1) Ion exchange fibers characterized by surface treatment with hydrogen peroxide. (2) When purifying the aqueous solution with a precoat filter,
Powdered ion exchange resin as pre-coat material and claim (1)
) A method for purifying an aqueous solution, characterized by using the ion exchange fiber described in (1).