JPH05245351A - Hollow fiber microfilter membrane and its production - Google Patents

Abstract

PURPOSE:To provide a filter membrane having not only microfiltration function but also ion exchangeability or chelate bonding ability. CONSTITUTION:A polyethylene powder of 5-20mum and an ion exchange resin or chelate resin particulate of <=20mum are dispersed in a polyvinyl alcohol aq. solution and are spinned to hollow fiber state with an ammonium sulfate as a coagulation bath and after the polyethylene is heat fused, the hollow fiber filter membrane made by holding the ion exchange resin or chelate resin particulate in the porous structure of polyvinyl alcohol with warm water to be eluted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a hollow fiber microfiltration membrane capable of removing both suspended substances and ionic substances in a liquid, for example, removal of clad or metal ions contained in water used for nuclear power plants. The present invention relates to an effective hollow fiber microfiltration membrane and a method for producing the same.

[0002]

2. Description of the Related Art Conventional polyethylene hollow fiber filtration membranes are used mainly by sieving the size of the substance to be removed and the size of the pores present in the membrane. Therefore, in order to remove the substance having a small particle diameter, it is necessary to reduce the pore diameter of the membrane. However, there is a drawback that the flow rate of the liquid is reduced when the pore diameter of the membrane is reduced. Moreover, it is not suitable for removing soluble ions.

In order to remove suspended substances and soluble metal ions in a liquid, it is generally necessary to use a microfiltration membrane and a reverse osmosis membrane or an ion exchange resin tower together. However, especially in nuclear power plants, it is desired to simplify the system due to the problems of used waste and safety, and it is possible to remove suspended substances and metal ions at the same time, and the flow rate of the liquid is large. The appearance of microfiltration membranes is expected.

As ion exchange membranes, ion exchange membranes having no pores for desalting and the like have hitherto been used, but there have been very few reports of membranes having pore diameters corresponding to microfiltration membranes. The polyolefin microfiltration membrane is slightly irradiated with an electron beam and then chemically treated (Japanese Patent Laid-Open No. 64-70108).
No.) and the like have been proposed to give ion exchange capacity after treatment.

[0005]

However, the above-mentioned conventional method causes water swelling property of the basic polyolefin, and it is unavoidable that physical properties and flow rate are lowered. Furthermore, there are significant restrictions on the type and density of functional groups that can be introduced, and it is difficult to obtain a very satisfactory one. Further, when such a method is industrially carried out, it is disadvantageous in terms of equipment and operation. As a result of earnest research to solve such conventional problems, the present inventors disperse fine particles having adsorption ability and ion exchange ability in the porous structure of a porous membrane made of porous hollow fibers of polyethylene. As a result, it was found that a hollow fibrous microfiltration membrane having both excellent selective permeation performance and ion exchange capacity can be obtained, and the present invention was completed. An object of the present invention is to provide a microfiltration membrane having both selective permeation performance and ion exchange ability and a method for producing the same, excluding the conventional drawbacks.

[0006]

Means for Solving the Problems That is, the microfiltration membrane of the present invention is composed of a porous body made of polyethylene and functional fine particles retained in the porous structure, and is a hollow fibrous precision having a pore size of 10 microns or less. It is a filtration membrane. Examples of the functional fine particles include fine powders of ion exchange resins or chelate resins, which are held in a dispersed state between porous structures.

As the method for producing the hollow fiber microfiltration membrane of the present invention, first, a polyethylene (hereinafter referred to as PE) fine powder having a particle size of 5 to 20 microns and ion exchange resin fine particles or a chelate having a particle size of 20 microns or less. Polyvinyl alcohol (hereinafter referred to as P
An aqueous solution is used as the spinning dope, and this spinning dope is
While keeping the temperature at room temperature or 90 ° C. or lower, extrude from the double tube nozzle together with the coagulating liquid in the core portion for 0.1 to 5
After passing through a space layer of 0 cm, coagulate in a coagulation bath and then PVA.
A precursor hollow fiber membrane in which PE fine powder and ion exchange resin fine particles chelate resin fine particles are dispersed is obtained. This is heat-treated or stretch-heat-treated to fuse the PE powder, followed by washing with warm water to elute PVA or stretching after elution.

The PVA used in the present invention preferably has a polymerization degree of 500 to 5000 and a saponification degree of 75% to 100.
% Is used, and more preferably the degree of polymerization is from 800 to 50.
00, a saponification degree of 97% to 100% is used.

The functional resin is not particularly limited, and fine powder such as cation exchange resin, anion exchange resin or chelate resin is used depending on the purpose. PVA /
The PE ratio is used in the range of 1/1 to 1/9. It is preferably 1/2 to 1/5. PVA /
When PE is larger than 1/1, PE is not fused by heat treatment, and when it is smaller than 1/9, spinning becomes difficult. The composition ratio of the ion exchange resin fine particles or the chelate resin fine particles is preferably in the range of 1% to 50% with respect to PE. 1%
In the following, the ion exchange performance and adsorption performance are difficult to develop,
If it is 50% or more, the practical strength of the hollow fiber membrane cannot be obtained.

The concentration of PVA in the spinning dope is not particularly limited, but is usually within the range of 3% to 20%. It is also possible to add a water-soluble component to the spinning dope for the purpose of forming a pore-forming agent, a thickener, and the like. Examples of the water-soluble component include ethylene glycol, diethylene glycol, polyethylene glycol, polyethylene oxide, polyvinylpyrrolidone, boric acid, borax, urea, calcium chloride and the like.

The coagulating bath and the coagulating liquid of the core may be any as long as they are non-solvents of PVA and compatible with water, but aqueous solutions of inorganic salts, methanol, ethanol, acetone, etc. are usually used, especially sodium sulfate aqueous solution or ammonium sulfate. Aqueous solutions are suitable. It is also possible to put an alkaline additive such as ammonia in the coagulating liquid.

Regarding the elution conditions of PVA, washing treatment with warm water or boiling water enables complete washing of PVA and further maintenance of the membrane structure. Cleaning at a temperature higher than that is performed by a pressure system, but it is not practical because it is a pressure system, and since the treatment temperature is close to the melting point of PE, the membrane structure changes. Further, when the treatment is carried out at a temperature lower than that of hot water, the cleaning of PVA becomes insufficient, resulting in a significant decrease in the liquid flow rate. The hollow fibrous microfiltration membrane having ion exchangeability obtained by the method of the present invention generally has a cross-sectional structure composed of three layers of outer and inner relatively dense layers and a finger-like void layer therebetween. However, when boric acid is added to the spinning dope and ammonia or the like is added to the coagulating liquid, it has a homogeneous porous structure. The outer surface and the inner surface have pores of 10 μm or less, and further, the ion exchange resin particles or the chelate resin particles are dispersed in the three layers or in the homogeneous pores.

[0013]

Example 1 PVA having a polymerization degree of 2400 and a saponification degree of 98%
And PE fine powder (FLOWSEN UF, trade name of Steel Chemical Industry Co., Ltd.) and a strong cation exchange resin crushed with a ball mill (DIAION PK228 manufactured by Mitsubishi Kasei Co., Ltd., hereinafter IER).
-Abbreviated as SC), PVA / PE / IER-
A spinning stock solution having a composition of SC / water of 1/3 / 0.6 / 9.7 and a weight concentration of 7% / 21% / 4.2% / 68% was prepared with a kneader, and the spinning stock solution was prepared at room temperature. The mixture was extruded into a coagulation bath consisting of a 40% ammonium sulfate aqueous solution with a core liquid consisting of a 40% ammonium sulfate aqueous solution, and a dry-wet spinning process was performed. Obtained PVA / PE / IE
After wet heat treating the R-SC hollow fiber membrane in an aqueous solution of ammonium sulfate,
It was washed with water, dried, and heat-treated at 190 ° C. for 30 seconds, and then PVA was washed and eluted with boiling water. The resulting PE / IER-SC hollow fiber membrane had an outer diameter of 1200 microns and an inner diameter of 600 microns, and an air permeation rate of 2.1 liters / (min · cm ² ·.
(Kg / cm ^2)), bubble point (methanol) showed a 0.42 kg / cm ^2, neutral salt decomposition capacity 0.7
It was meq / g. The pure water permeation rate was 3650 liters / (m ² · h · (kgf / cm ² )). As a matter of course, the obtained hollow fiber membrane had good compatibility with water and could obtain good water permeability simply by wetting with water.

[0014]

Example 2 PVA having a polymerization degree of 1200 and a saponification degree of 99%
PVA / PE / PEG / I using the same raw material as in Example 1 except that polyethylene glycol (hereinafter abbreviated as PEG) having an average molecular weight of 1000 and boric acid were used.
ER-SC / water / boric acid 1/4/1 / 0.8 / 11 /
The composition is 0.05 and the weight concentration is 5.6% / 22.4% /
A spinning stock solution of 5.6% / 4.5% / 62% / 0.28% was prepared with a kneader, and the spinning stock solution kept at 50 ° C. was 40% ammonium sulfate aqueous solution with a 5 cm air gap from the double tube nozzle. Was co-extruded into a coagulation bath consisting of 1) together with a core liquid consisting of a 40% ammonium sulfate aqueous solution containing 1% ammonia, and dry-wet spinning was performed. The obtained PVA / PE / IER-SC / PEG / boric acid hollow fiber membrane was wet heat treated in an aqueous solution of ammonium sulfate, washed with water, dried, and heat treated at 190 ° C. for 1 minute, and then PV in boiling water.
A was washed and eluted. The PE / IER-SC hollow fiber membrane obtained had an outer diameter of 1000 microns and an inner diameter of 500 microns,
Air permeation rate 3.0 liters / (min · cm ² · (k
g / cm ² )), the bubble point (methanol) is 0.
12 kg / cm ² and a neutral salt decomposition capacity of 0.7 me
It was q / g.

[0015]

Example 3 The same PVA and PE as in Example 1 and a strong anion exchange resin (Diaion SA10A manufactured by Mitsubishi Kasei Co., Ltd., hereinafter referred to as IER-SA) crushed by a ball mill were used, and PVA / PE / IER-SA was used. / 1/4 of water
0.8 / 11 composition and weight concentration 6% / 24% / 4.8
% / 65% stock solution for spinning was prepared in a kneader and spun as in Example 1. Obtained PVA / PE / IER-SA
The hollow fiber membrane was subjected to wet heat treatment in an aqueous solution of ammonium sulfate, washed with water, dried, heat treated at 190 ° C. for 30 seconds, and then washed and eluted with PVA by boiling water. The obtained PE / IER-SA hollow fiber membrane had an outer diameter of 1000 microns and an inner diameter of 600 microns, and an air permeation rate of 1.2 liters / (min · cm ² · (kgf
/ Cm ² )), bubble point (methanol) is 0.8
7 kg / cm ² and a neutral salt decomposition capacity of 0.7 meq
/ G.

[0016]

As described above, the filtration membrane of the present invention is
In addition to the function of microfiltration to remove suspended components in liquid, it has ion exchange and chelate binding properties, so soluble components such as ions in liquid can be efficiently removed at the same time, and the effect is extremely large. .. Further, according to the method of the present invention, a polyethylene hollow fiber microfiltration membrane having such an ion-exchange or chelate-binding property is prepared from polyethylene fine powder and ion-exchange resin fine particles or chelate resin fine particles using polyvinyl alcohol. It can be easily manufactured by spinning a spinning dope of the following into a hollow fiber, followed by heat treatment and washing with warm water.

Claims (3)

[Claims] 1. A hollow fiber microfiltration membrane having a pore size of 10 μm or less, which is composed of a porous body made of polyethylene and functional fine particles retained in the porous structure. 2. The hollow fibrous microfiltration membrane according to claim 1, wherein the functional fine particles are an ion exchange resin or a chelate resin. 3. Polyethylene powder of 5 to 20 microns and functional fine particles of 20 microns or less are dispersed in a polyvinyl alcohol aqueous solution and spun into hollow fibers in a coagulation bath, and polyethylene is heat-sealed and then polyvinyl alcohol is added. A method for producing a hollow fiber microfiltration membrane, which comprises washing with warm water to elute.