JPH0368425A - Method for removing ion - Google Patents

Abstract

PURPOSE:To efficiently remove metal ions or ionic organic components by treating water with a hollow filiform porous membrane in which water permeation velocity peculiar to membrane and average water permeation velocity are regulated to values in specific ranges, respectively, and which has ion exchanging function or chelate adsorbing property. CONSTITUTION:Metal ions or ionic organic components are removed from water by means of filtration by using a hollow filiform porous membrane having a relation of F'/F>==0.50 between a water permeation velocity F'(l/m<2>.hr.kg/ cm<2>) peculiar to membrane measured under the condition where the effect of the length of the membrane is practically negligible and an average water permeation velocity F'(l/m<2>.hr.kg/cm<2>) measured by the length of the membrane of substantial pressure drop at the time of practical use and also having anion- cation exchanging function or chelate adsorbing function. As the above hollow filiform porous membrane, a membrane in which bonding is performed by 0.1-10 milliequivalents per gram of membrane as side chain of chelate radical, etc., can be used.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention produces highly purified water that can be applied to semiconductor and pharmaceutical industries that require ultrapure water, nuclear waste water treatment, etc. This invention relates to a method for removing ions from water.

(Prior Art) Ion exchange resins used for deionization are used in ultrapure water production processes in the semiconductor industry and the like. The present inventors have found that if a hollow fiber porous membrane having anion or cation exchange functionality or chelate adsorption functionality is used instead, the ion removal rate can be increased and colloidal substances can also be removed at the same time. We thought that it would be possible to purify water extremely efficiently. However, in the case of hollow fiber membranes, because the membrane has a length, the differential pressure in each part of the membrane generally varies depending on the pressure drop in the tube part within the hollow fiber, and the life of the membrane tends to be longer or shorter depending on each part. be.

(Problems to be Solved by the Invention) The present invention provides a method for removing ions from water using a hollow fiber-like porous membrane having anion or cation exchange functionality or chelate adsorption ability, in which the lifetime of the membrane is extended as much as possible. It is an object of the present invention to provide a water purification method for the purpose of water purification.

(Means for Solving the Problems) The present invention provides a membrane specific water permeability rate F(i,/rrr·hr−
kg/cd) and the average water permeation rate F' CF, /d・hr− measured at the effective pressure drop membrane length when actually used.
kg/c+1), anion or cation exchange functionality having a relationship of F'/F≧0.50;
Alternatively, the present invention relates to an ion removal method characterized by filtering metal ions or ionic organic components from water using a hollow fiber porous membrane with chelate adsorption functionality.

In general, in the case of a hollow fiber porous membrane, the filtration pressure difference between the inside and outside of the membrane differs in the length direction of the fiber due to pressure loss within the hollow fiber tube. For example, in the case of external pressure filtration and one-end blockage, according to Omobi et al. (Kagakusho 27. (4) 74 (1983)), the average water permeation rate F' of the membrane when length Lm, outer diameter Dm, and inner diameter 2rm is rrr/rd·h (kg/rrf) is expressed by the following formula.

(When one end is closed and external pressure is used for total filtration) Here, F' is the average flux of pure water per unit area when the actual membrane length Lm is /r'I'r・h (kg/po) F is, Membrane-specific flux h/h (kg/rrf)
ρ is the viscosity of water in kg-h/po.

Therefore, in order to set F'/F to 0.50, the outer diameter D,
Either the inner diameter 2r or the membrane length L may be adjusted using the above calculation formula, or may be designed by actual measurement.

In addition, the design can be made in almost the same way in the case of internal pressure and one end closed.

On the other hand, when both ends are open, the pressure drop effect due to the flow of water in the membrane tube is substantially halved, so the effective pressure tU
The membrane length is assumed to be L/2.

When actually assembling the module, the ends of the hollow fibers are sealed with adhesive or the like to seal them from the outside, so the actual water permeation rate of the membrane will differ from the measured value depending on the length of this seal, but this will affect the life of the membrane. There is no essential difference between the two, and the present invention also includes a method in which the filtrate is circulated and filtered in a cross-flow manner under internal pressure, but in practice, increasing the circulation rate has little effect on the adsorption rate. Actually, the differential pressure is 5 kg
/c+fl or less, and the linear velocity is usually used at 1 m/sec or less.

Here, F is the membrane-specific water permeation rate, meaning the filtration rate of fresh water filtered by external pressure or internal pressure method with a pressure difference of kg/cd at a sample length where the membrane length is practically negligible. . If you want to strictly ignore the length of the membrane, it is also possible to change the sample length and calculate by extrapolation.

F' is actual ¥tM, which means the average water permeation rate over the length,
This is a value calculated by measuring by internal pressure or external pressure method based on the actual length of the membrane and dividing it by the membrane area (e) of the sample membrane.

In this case, F' and F need to be carried out using the same filtration method and temperature.

In the present invention, F'/F is 0.50 or more, preferably 0.
．． Set to 75 or higher.

Below this range, the life will be shortened, which will be disadvantageous in actual batch or continuous operation.

The hollow fiber porous membrane with anion or cation exchange functionality or chelate adsorption functionality used in this invention is preferably a porous base membrane made of polyolefin, a copolymer of olefin and halogen, or polysulfone. A porous membrane in which an anion exchange functional group, a cation exchange functional group, or a functional group having chelate adsorption functionality is chemically bonded to the inner and outer surfaces of the membrane and at least a portion of the surface of the pores inside the membrane. The functional group may be bonded directly to the base film, or may be bonded to a polymer containing the functional group. It is also possible to use a membrane in which a functional group is indirectly added to the membrane surface or pore surface by methods such as coating or surface polymerization treatment.

More preferably, the material of the base membrane is a polyolefin, and the membrane structure is a porous membrane having a three-dimensional network structure, and cations or It is preferable to carry out processing and purification using a porous membrane to which a functional group having an anion exchange function, a functional group having a chelate adsorption function, or a polymer having these functional groups is chemically bonded.

Examples of the functional group having a cation exchange function in the present invention include a sulfone group, a carboxyl group, and an H+ type phosphoric acid group including polyvalent and chelate groups. As a functional group having an anion exchange function, R-N"(CH3)U011-.R-N"(C1ls)z(CJ40H)
Examples include OH--RN(C1h)z. (here,
R represents a hydrocarbon group. ) Also, as a chelate group, R-CH2X −+ CHz
COO II) z etc.

Each of these functional groups has a concentration of 0.1 per gram of porous membrane.
It must be contained in an amount of ξ equivalents to 10 milliequivalents, preferably 0.1 to 5 milliequivalents. If it is below this range, the ion removal ability of the membrane will decrease, and if it exceeds this range, other properties of the membrane, such as mechanical properties, will decrease.

The average pore diameter of the porous membrane is selected from the range of 0.01 m to 5 m, preferably 0.01 m to 1 m. If it is smaller than this range, the water permeability is not sufficient for practical performance, and if it is larger than this range, ion removal becomes a problem.

There are many methods for measuring the average pore diameter, but in the present invention, we use the air permeation method between dry and wet membranes when changing the air pressure, which is usually called the air flow method, which is described in ASTM F-316-70. Conforms to the method of measuring from flux.

The porosity of the porous membrane is 20% to 80%, preferably 40%
-80% is used.

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.

Various pore structures can be formed in the porous membrane that serves as the base material depending on the molding method.For example, if the base polymer is polysulfone, after making a mixed solution using a solvent etc.
A three-dimensional network structure membrane can be obtained by employing a so-called wet method in which hollow fibers are discharged from a nozzle and shaped with a coagulant or the like. In the case of polyolefins, stretching methods,
It is also possible to make a porous membrane by a so-called etching method, which is made by chemical treatment after electron beam irradiation, but the pore structure is more difficult than the straight-through pore structure obtained by a stretching method or an etching method. For example,
292 Publication, Special Publication No. 40-957 and Special Publication No. 4
Preferred from the viewpoint of practical performance are those having a three-dimensional network structure formed by the microphase separation method or mixed extraction method disclosed in Japanese Patent No. 7-17460.

In particular, it is preferable to use a film having the structure shown in Japanese Patent Application Laid-Open No. 55-131028.

As a method for introducing a functional group having a cation exchange function into the side chain of the polymer constituting the base film, a known method is adopted.For example, as a method for introducing a sulfone group into the side chain of polyethylene, Methods include reacting with sulfuric anhydride in a non-reactive solvent or sulfuric acid, or reacting with sulfuric anhydride in a gaseous state, but after irradiating the polyethylene film with an electron beam,
A method in which styrene is grafted and then the above-mentioned sulfonation is carried out is preferable in terms of physical properties.

Further, when introducing a carboxylic acid group, for example, 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 a gas phase.

On the other hand, an anion exchange functional porous membrane is produced by irradiating a porous membrane made of a polyolefin or a copolymer of an olefin and a halogenated olefin with ionizing radiation, and then grafting styrene in the gas phase, resulting in chloromethylation. After that, it is obtained by adding an organic amine.

The functional groups can be introduced into the side chains of the polymer constituting the base membrane before being formed into a membrane, but after being formed into a membrane, the functional groups can be introduced into the side chains of the polymer constituting the base membrane. A method of chemically adding bonding to at least a portion is preferred. It is desirable that the functional groups are bound to the membrane and pore surfaces as uniformly as possible.

The amount of functional groups in the present invention refers to the equivalent weight per gram of porous membrane, and 1 gram of membrane here refers to a value based on the fairly macroscopic weight of the membrane, for example, the amount of functional groups on the membrane surface. It does not refer to the weight of only a part or part of the inside. In order to bond functional groups while maintaining the membrane's excellent mechanical properties, it is preferable to make the functional groups exist as uniformly and preferentially as possible on the surface of the pores of the membrane. Homogeneity is acceptable. Therefore, the meaning of 1 g of membrane here indicates the value measured evenly over the entire surface of the membrane, and does not mean the weight from an extremely microscopic viewpoint.

In addition, the equivalent of a functional group refers to the number equivalent of a functional group here. Therefore, for example, if the functional group is iminodiacetic acid group,
One mole of it is 2 milliequivalents.

A porous membrane having a thickness of 10uI11 to 5+++m, preferably 100μffl to 2IIIIl is suitably used in the present invention.

(Example and Comparative Example) Fine powder silicic acid (Aerosil P-972), dibutyl phthalate (DBP), polyethylene resin powder (
5H-800 grade (manufactured by Asahi Kasei) were premixed, and then extruded into a hollow fiber shape using three types of nozzles of different sizes in a twin screw extruder for 30 days.
．． 1-Trichloroethane [Chlorocene vG (product name)]
The DBP was extracted by immersion in the water for 60 minutes. Further temperature 60
It was immersed in a 40% aqueous solution of caustic soda at °C for about 20 minutes to extract the fine powder of silicic acid, then washed with water and dried.

An electron accelerator (pressure voltage 1.5 MeV) was applied to the obtained porous membrane.
, 100KG under nitrogen atmosphere using electron beam current 1mA)
After electron beam irradiation with y, styrene (containing 10% divinylbenzene) was almost completely grafted in the gas phase, washed, dried, and sulfonated with SO in EDC.
Porous Jl (A), (B) (above examples), (C)
(Comparative example) was obtained.

Here, the amount of sulfone groups in the example membrane was determined as follows.

[Quantification of sulfone group]

The sulfonated porous membrane was immersed in IN HCIaq to form H-type, washed with water, and then immersed in 1N CaCltaq to remove the liberated HCI. Titration was performed using IN Na0Haq and phenonylphthalein as an indicator.

The properties of the three types of porous membranes obtained in this way are as follows.
Shown in the table.

Table 1 below: Table (1) Measured values with the length changed and the membrane length effect set to 0 by the extrapolator. Measured with UF filtered fresh water.

25℃, initial value, external pressure.

(2) Measure with UF filtration with one end closed. external pressure.

25-'C, initial value.

The three types of porous membranes thus obtained were soaked in fresh water containing lppm of cupric chloride filtered through UF at a filtration pressure of 0.
．． When copper ions were filtered out one by one using an external pressure method at 4 kg/cd to a membrane length of 1 m, the following values were obtained.

Margin below Table 2 Calligraphy (spontaneous) Heisei 2 years February 2 days

Claims (2)

[Claims] (1) Membrane specific water permeability rate F (l/m^2・hr・kg/c) measured under conditions where the effect of membrane length can be virtually ignored
m^2) and the average water permeation rate F' (l/m^2・hr・kg/
cm^2), anion or cation exchange functionality having a relationship of F'/F≧0.50;
Alternatively, a method for removing ions, which comprises filtering metal ions or ionic organic components from water using a hollow fiber porous membrane with chelate adsorption functionality. (2) The hollow fiber porous membrane has an anion exchange functional group, a cation exchange functional group, or a chelate group as a side chain on a base membrane made of polyolefin, a copolymer of olefin and halogen, or polysulfone. Average pore size 0.01-5 0.1-10 milliequivalents bound per gram of membrane
The method for removing ions according to claim 1, wherein the membrane has a porosity of 20 to 80% and a thickness of 10 to 5 mm.