JPS63296803A - Condensate purification method - Google Patents

Abstract

PURPOSE:To prevent generation of solid iron sticking to the filtrate side of a filter membrane and not to allow lowering the permeation rate of the membrane in purifying condensate of steam in an atomic reactor, by using hollow filament porous membrane with specific equivalent of a functional group in side chains which have cationic exchange function, and with specific mean aperture diameter, percentage of voids and membrane thickness. CONSTITUTION:For instance, a mixture of silicic acid in the form of fine particles, dioctylphthalate (DOP) and pulverized ethylene resin is extruded in a hollow filament form. Extrudate is immersed in trichloroethane for extraction of DOP, further, soaked in an aqueous caustic soda solution to extract finely pulverized silicic acid and obtained hollow porous membrane is sulphonated. The hollow filament porous membrane thus available has cationic exchange group 0.05-5mg of membrane in the side chain, with a mean aperture diameter of 0.01-5mu, voids of 20-80% and a membrane thickness of 10mu-5mm. Application of this membrane enables purification of a condensate from a condenser of boiling water-type atomic reactor.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for efficiently removing iron colloid (crud) from steam condensate generated in a boiling water nuclear reactor using a porous membrane.

[Conventional technology]

The steam generated in a boiling water reactor is typically used to rotate a turbine and generate electricity, and then is condensed in a condenser and used for circulation. Since it contains corrosion products, these must be removed to avoid the generation of radionuclides.

This corrosion product contains several flPb of iron ions as well as several to several tens of pl)b of colloidal iron (cra-sod).

In order to remove this crud, a powdered ion exchange resin (trade name Baudesoxu) has traditionally been used, but recently a method using a hollow fiber porous membrane (for example, Japanese Patent Application Laid-Open No. 87092/1983) ) has been proposed.

However, although the method using a hollow fiber porous membrane has many advantages over the conventional Baudesox method, as a result of practical operation, it has become clear that it has the following problems. In other words, it has become clear that during purification of condensate, iron ions present adhere in solid form to the inner surface of the membrane on the water side, reducing the water permeability of the membrane. The fact that there is a correlation between the solid adhesion of iron to the inner surface of the membrane on the I water side and the decrease in the water permeability of the membrane can be seen by cleaning the inner surface of the membrane with oxalic acid, etc.
This is evident by the almost complete recovery of water permeability. Conversely, even if the undiluted solution side is washed, the water permeability does not recover much.

[Problem that the invention seeks to solve]

The object of the present invention is to establish a more efficient condensate purification method that does not cause a decrease in the water permeability of the membrane.

[Means for Solving the Problems] As a result of intensive research into means for achieving the above object, the inventor found that the object can be achieved by the following means.

That is, in the present invention, the condensate has a functional group having a cation exchange function in the side chain in an amount of 0.05 to 5 milliequivalents per gram of membrane, an average pore diameter of 0.01 to 5 microns, and a porosity of 20. % to 80% and a membrane thickness of 10 microns to 5 mm.

Preferably, the material of the porous membrane is polyolefin, a copolymer of olefin and halogenated olefin, polyvinylidene fluoride, or polysulfone, and at least a portion of the inner and outer surfaces of the membrane and the surface of the pores are provided with a functional material having a cation exchange function. It is preferable to use a hollow fiber porous membrane to which groups are chemically bonded, and the bonding of the functional groups to the porous membrane is as follows:
This may be done directly or may be bonded to a polymer containing a functional group.

More preferably, the membrane material of the porous membrane is polyolefin, the membrane structure has a three-dimensional network structure, and the membrane has a functional material having a cation exchange function over at least a portion or the entire surface of both the inside and outside of the membrane and the surface of the pores. It is preferable to carry out treatment and purification using a hollow fiber porous membrane to which a polymer having groups or functional groups is chemically bonded.

The present invention will be explained in more detail below.

In the present invention, H'' type or metal salt type of sulfonic acid group, carboxylic acid group, and phosphoric acid group are used as the functional group having a cation exchange function.

These functional groups should be present in an amount of 0.05 to 5 milliequivalents per gram of membrane.

Below this range, the water permeability of the membrane will be reduced, and above this range, other properties of the membrane, such as mechanical properties, will be reduced.

The average pore size of the porous membrane should be in the range of 0.01 microns to 5 microns. If it is smaller than this range, the water permeability will not be sufficient for practical performance, and if it is larger than this range, leakage of the cladding will occur, which poses a problem.

There are many methods for measuring the average pore diameter, but in the present invention, we use the air permeation flux of dry membrane and wet membrane when changing the air pressure, which is usually called the air flow method, which is described in AsTM F316-70. Comply with the method of measurement from

The porous membrane used has a porosity in the range of 20% to 80%. Here, the porosity is measured by immersing the membrane in a liquid such as water in advance, then drying it, and measuring the weight change before and after that. Porosity values outside the above range are unfavorable in terms of permeation rate and mechanical properties.

As the material for the membrane used in the present invention, most of the materials currently on the market can be used, such as cellulose (di or tri) acetate, polysulfone, polyvinylidene fluoride, and polyamide.

Examples include polyethylene, polypropylene, ethylene-4-modified tyrene copolymer, and the like. Polysulfone has the greatest effect of containing a cation exchange function.

This is the case when a relatively hydrophobic membrane such as polyolefin is used.

The pore structure of the porous membrane can be formed in various ways depending on the molding method. For example, polysulfone is prepared by making a mixed solution using a solvent, etc., and then discharging it from a nozzle in the form of a hollow fiber.
A film with a three-dimensional mesh structure can be obtained by employing a so-called wet method of molding with a coagulant or the like. In the case of polyolefin, it is possible to make a porous membrane by a so-called stretching method or an etching method created by chemical treatment after electron beam irradiation. Rather than a through-hole structure, a tertiary pore structure formed by a microphase separation method or a mixed extraction method as shown in, for example, Japanese Patent Publication No. 59-37292, Japanese Patent Publication No. 40-957, and Japanese Patent Publication No. 47-17460, etc. Although a material having an original network structure is preferable in terms of practical performance, the method should not be limited to this method. Especially JP-A-55-1.3102
By using a porous membrane having the structure shown in Publication No. 8, it was possible to achieve an excellent purification method that could not be obtained using conventional techniques.

A known method can be used to introduce a functional group having a cation exchange function into the side chain of the polymer constituting the membrane. For example, methods for introducing sulfonic acid groups into the side chains of polyethylene include reacting with sulfuric anhydride in a non-reactive solvent or sulfuric acid, or reacting with sulfuric anhydride in a gaseous state.

Alternatively, a method may be used in which styrene is irradiated with an electron beam or the like, then grafted, and then the above-mentioned sulfonation is performed.

Further, when introducing a carboxylic acid group, a method is used in which the film is irradiated with an electron beam or the like in advance, and then acrylic acid is grafted in the gas phase.

In order to introduce the functional groups into the side chains of the polymer constituting the membrane, it is possible to introduce them before forming the membrane, but after forming the membrane, it is possible to introduce the functional groups into the side chains of the polymer constituting the membrane. , a method of chemically adding bonding is preferred. Although it is desirable that the functional groups be added to each surface of the membrane as uniformly as possible, there are cases where it is better to preferentially add the functional groups to the inner surface of the membrane.

The amount of functional groups having a cation exchange function in the present invention refers to milliequivalents per gram of membrane, and 1 gram of membrane here is a value based on the fairly macroscopic weight of the membrane, for example. It does not refer to the weight of only a portion of the surface or inside of the membrane. In order to add a functional group having a cation exchange function while maintaining the membrane's excellent mechanical properties, it is preferable to have the functional group present as uniformly and preferentially as possible on the surface of the pores of the membrane. Naturally, partial heterogeneity is allowed. Therefore, the meaning of 1 gram of membrane here refers to the value measured evenly over the entire surface of the membrane, and does not mean the weight from an extremely microscopic point of view.

The operating conditions for passing the condensate through the hollow fiber porous membrane are within a known range. In the case of condensate treatment, a filtration method called an external pressure method is usually used, so the pressure difference between the raw water side and the method is 5 kg/cut or less. During filtration, in order to prevent the water permeability of the membrane from decreasing over time, that is, to remove the crud that adheres to the outer surface of the hollow fiber porous membrane, backwashing with air or vibration operation can be performed.

EXAMPLES The present invention will be explained below with reference to examples, but they are not intended to limit the invention.

〔Example〕

Example 1.2 and Comparative Example 1 22.1 parts by weight of finely divided nibucyl silicate VN3LP), 55.0 parts by weight of dioctyl phthalate (DOP),
Polyethylene resin powder [Asahi Kasei S-360 grade] 2
After premixing 3.0 parts by weight of the composition, it was extruded into a hollow fiber shape with an inner diameter of 0.7 m and a thickness of 0.25++n using a 30 mm twin-screw extruder. I-) DOP
Extruded. Furthermore, after extruding the fine powder of silicic acid by immersing it in a 40% aqueous solution of caustic soda at a temperature of 60°C for about 20 minutes, washing with water,
Dry. The obtained hollow fiber porous membrane was immersed in an ethylene dichloride-anhydrous sulfuric acid solution (concentration 8.9%).
The reaction was carried out at .degree. C. to obtain Example membranes 1 and 2 having properties as shown in Table 1. In addition, the properties of Comparative Example Membrane 1 without sulfonation treatment are also shown.

(Margins below) Table 1 ■) Initial water permeability after treating tap water with an ultrafiltration membrane with a molecular weight cut off of 6,000 (differential pressure 1 kg/c + J)2
) A sulfonic acid (-3OJ) type porous membrane is placed in an aqueous calcium chloride (IN) solution to achieve equilibrium, and the hydrogen chloride produced in the solution is reduced to 0. IN caustic soda aqueous solution (force value f)
titrate using phenolphthalein as an indicator,
The value X (cc) of the dry weight in the calcium salt state was obtained for the three types of membranes, and an I-passage test was conducted under the following conditions.

Table 2 (Operating conditions) Overspeed (external pressure method) 0.62 ″'/+1 Temperature 25°C Length of membrane used (m) 1 After passing water through 220011R under the above conditions, the properties of the membrane are shown in the table below. That's right.

Table 3 (Membrane properties after test) γp overspeed retention rate 2) 85 95 96
65I) Calculated from the dry weight of the membrane before and after washing with oxalic acid.

It has been confirmed that this adhered sample is 99% iron.

2) Ratio of initial water permeability before and after operation 3) Example membrane 2-A is -8O3H type 4) Example membrane 2-B is -3O3Na type As shown in the table, the membrane surface was sulfonated. All of the example membranes had less iron adhesion than the comparative example membranes, and the retention rate of water permeability of the membranes was also much lower.

Example 3 and Comparative Example 2 Finely powdered silicic acid, 22.1 parts by weight of butyl VN 3 LP), 55.4 parts by weight of dioctyl phthalate (DOP), polypropylene resin powder [manufactured by Sumitomo Chemical, A S-171A]
) After premixing 22.5 parts by weight of the composition, it was extruded into a hollow fiber shape with an inner diameter of 0.7 mm and a thickness of 0.25 mm using a 30 mm twin screw extruder, and then 1,1.1-trichloroethane [
chlorocene VG (trade name)] for 60 minutes, and then
P was extruded. Further, the product was immersed in a 40% aqueous solution of caustic soda at a temperature of 60° C. for about 20 minutes to extrude the fine powder of silicic acid, followed by washing with water and drying. The obtained porous polyethylene film consisting of a three-dimensional network structure was heated at 100 KGy in a nitrogen atmosphere using an electron accelerator (acceleration voltage 1.5 MeV, electron beam current 1 mA).
and immersed in a 50% aqueous acrylic acid solution (containing 0.2511 t% of Mohr's salt) in which the dissolved oxygen was reduced to below 0.1 ppm and reacted at 25°C for 1 hour = 13
~ Ta. As a result, the cation exchange capacity is 3.7 milliequivalents/
Example 3 having a Gram membrane was obtained.

This example membrane 3-A (-COOH type) and 3-
B (-COONa type) and Comparative Example Membrane 2 without grafting treatment were operated under the same filtration conditions as in the above example, and water was passed for 2500 hours. The properties of the membrane showed the following values.

Table 4 1) The physical properties of Example Membranes 3-A and 3-B and Comparative Example Membrane 2 are as follows.

Outer diameter (m) 1.20 1.20 1.2
0 Inner diameter (m) 0.72 0.72 0.
71 Average pore diameter (μ) 0.30 0.30 0
．． 30 Porosity (%) 59 59 60
Note that the grafting equivalent of acrylic acid was determined by the gravimetric method.

〔Effect of the invention〕

By applying the present invention to the purification of nuclear condensate, it is possible to prevent the formation of solid iron that adheres to hollow fiber membrane filtration methods, and there is virtually no decrease in water permeation rate, resulting in a longer service life. It started to peel off.

Patent applicant: Asahi Kasei Kogyo Co., Ltd. = 15- Procedural amendment (voluntary) July 31, 1985 Director General of the Patent Office Kunio Ogawa 1, Indication of the case 1988 Patent Application No. 13164.0 2, Invention Name Condensate purification method 3, relationship with the case of the person making the amendment Patent applicant Asahi Kasei Kogyo Co., Ltd. 4, 1-2-6 Dojimahama, Kita-ku, Osaka-shi, Osaka (003), Insert the following sentence between lines 16 and 17 on page 9 of the detailed description of the amendment.

"Furthermore, it is also effective to modify the functional group that has a cation exchange function in the hollow fiber porous membrane into a salt type, such as iron, before actually treating the condensate." Letter (spontaneous) September 1, 1986 Kunio Ogawa, Commissioner of the Patent Office 1, Indication of the case Patent Application No. 1.3164 of 1988
0 No. 2, Name of the invention Method for purifying condensate 3, Relationship with the case of the person making the amendment Patent applicant 1-2-6-4 Dojimahama, Kita-ku, Osaka-shi, Osaka Prefecture [Details of the invention] Explanation j, Request 5, Contents of amendment (1) From the last line of page 4 to the first line of page 5 of the specification, “having a cation-exchanging functional group” has been replaced with “having a sulfonic acid group or "having a sulfonic acid group, or a sulfonic acid group or a sulfonic acid group" is corrected.

(2) "Ru." in the 8th line of page 5 of the same book has been changed to "Ru." The fact that even if the content of functional groups is small and ρ, the pollution prevention effect is large and the effect is sustainable. Therefore, sulfonic acid groups and sulfonic acid groups are particularly preferred.''

(3) On page 8, line 3, "radiation" is corrected to "irradiation."

(4) In the 1st case on page 8, line 6 of the same page, replace "in the case" with "in the case,
For example,” he corrected.

(5) On page 13 of the same page, in the last line, "contains salts)" was changed to [
(contains 0.25 mol of trimethylolpropane trimethacrylate per 1 mol of trimethylol salt and acrylic acid)
I am corrected.

that's all

Claims (3)

[Claims] (1) After condensing the steam generated in a boiling water reactor in a condenser, 0.05 to 5 milliequivalents of functional groups with a cation exchange function are added to the side chains of the condensate per gram of membrane. and an average pore diameter of 0.01 to 5 microns,
Porosity 20% to 80%, film thickness 10 microns to 5
A method for purifying condensate, which is characterized by passing it through a hollow fiber-like porous membrane having a diameter of 1.5 mm. (2) The hollow fiber porous membrane is made of polyolefin, a copolymer of olefin and halogenated olefin, polyvinylidene fluoride, or polysulfone, and the functional group is present on at least a portion of the inner and outer surfaces of the membrane and the surface of the pores. A method for purifying condensate according to claim 1, which comprises: (3) The method for purifying condensate according to claim 2, wherein the hollow fiber porous membrane is made of polyolefin and its pore structure is a three-dimensional network structure.