JP2000015066A - Humidification membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a humidification membrane for a humidifier, particularly the one capable of being used for a humidifier for a solid polymer fuel cell. SOLUTION: This humidification membrane is made of a vinylidene fluoride resin or of a porous film having a mean flow rate micropore diameter of 0.1-1 μm, a maximum pore diameter of 0.1-3 μm, a porosity of 40-90% and a film thickness of 50-1000 μm. This humidification membrane does not permit water to bleed to a gas side as droplets and has an excellent humidification performance and allows to reduce size of the humidifier. Thus, this humidification membrane can be used in humidifier applications wherein reduction in size is desired such as a humidifier for a solid polymer fuel cell and the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a membrane for a humidifier, and more particularly to a membrane that can be used in a humidifier for a polymer electrolyte fuel cell.

[0002]

2. Description of the Related Art Conventionally, as a humidifier that can be used for an air conditioner or the like, a method of isolating water and air through a membrane and permeating water vapor through the membrane to humidify the air is known. As a humidifying film for this purpose, use of a hydrophobic porous film made of a polymer material or a ceramic material is disclosed in Japanese Patent Application Laid-Open No. 61-27434 and Japanese Patent Application Laid-Open No. 61-27434.
No. -240045 and the like. In particular, JP-A-61-240045 discloses that the average pore size is 0.1%.
It is disclosed that a hydrophobic polymer porous membrane having a thickness of 10 to 10 μm is preferable. However, in this case, there has been a problem that water oozes out to the side of the air when used continuously.

As a method for solving this problem, Japanese Patent Application Laid-Open
Japanese Patent No. 174373 discloses the use of a membrane in which a hydrophobic polymer porous membrane and a non-porous polymer porous membrane are laminated. In JP-A-9-156007, the skeleton of a porous polymer substrate film is coated with a tetrafluoroethylene-based copolymer, and has an average pore size of 0.1 to 1 μm,
It has been proposed to use a continuous pore type porous membrane having a porosity of 60 to 90%.

On the other hand, a polymer electrolyte fuel cell is a power generating element generally composed of a hydrogen ion conductive solid polymer sandwiched between carbon electrodes carrying a platinum catalyst, ie, a polymer electrolyte membrane-electrode junction. It has a structure in which a gas separation membrane member that supports each power generation element from both sides is laminated on the body and each electrode surface. When the solid polymer electrolyte membrane is dried, the ionic conductivity is reduced, and a poor connection between the membrane and the electrode is caused to cause a sharp decrease in output. Therefore, it is necessary to humidify the supply gas. . This battery is expected to be used for mobile objects such as electric vehicles, and it is desired to reduce the size of the device, and to develop a humidifier that has higher humidification performance and can be reduced in size. The use of a porous film made of a tetrafluoroethylene resin as a film for the humidifier is disclosed in JP-A-3-269958. Further, the use of a hollow fiber-like porous membrane to increase the permeable area per unit volume and enhance the humidification performance is disclosed in JP-A-8-273687 and JP-A-8-3.
No. 15838.

However, the humidifying films disclosed in JP-A-7-174373 and JP-A-9-156007 have a problem that the humidifying performance is not sufficient. Further, Japanese Patent Application Laid-Open Nos. Hei 3-269958 and Hei 8-
In the humidifying membrane described in Japanese Patent No. 273687 and Japanese Unexamined Patent Publication No. H8-315838, if water is in contact with water for a long time, water oozes out on the gas-side film surface to generate droplets. There was an inconvenience.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a humidifying film which does not exude water to the gas side as droplets and has excellent humidifying performance.

[0007]

Means for Solving the Problems In view of the above-mentioned problems of the prior art, the present inventors have studied a porous film made of an organic polymer having a different composition and structure. The present invention was found to have excellent humidification performance without oozing out of water, leading to the present invention. That is, the present invention
(1) It is made of a vinylidene fluoride resin, has an average flow pore diameter of 0.1 to 1 μm, a maximum pore diameter of 0.1 to 3 μm, a porosity of 40 to 90%, and a film thickness of 50 to 1000 μm.
A humidifying membrane, comprising a porous membrane,
(2) The humidifying membrane according to the above (1), comprising a vinylidene fluoride-based resin in which at least 98 wt% is composed of vinylidene fluoride units, and (3) the ratio of the average flow pore diameter to the maximum pore diameter is 1.0 to 1.0. (1) the humidifying membrane according to (1), wherein the porous membrane is in the form of a hollow fiber membrane;
The membrane for humidification as described in (5), wherein the porous membrane has an inner diameter of 0.3 to 5.0 m.
(6) the humidifying membrane according to the above (4), which is a hollow fiber membrane of
Use of the membrane of (1) above in a humidifier for a polymer electrolyte fuel cell.

Hereinafter, the present invention will be described in detail. As the vinylidene fluoride resin constituting the humidifying membrane of the present invention,
In addition to vinylidene fluoride homopolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene Copolymer, vinylidene fluoride-fluoroethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-hexafluoroacetone copolymer, vinylidene fluoride-perfluorovinyl ether Copolymers, vinylidene fluoride-ethylene-tetrafluoroethylene copolymers, and vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymers are exemplified. These may be used alone, or a mixture of these polymers may be used. Above all, a polymer comprising at least 98% by weight of vinylidene fluoride units is particularly preferable since it has high heat resistance and can be brought into contact with hot water and gas at a relatively high temperature.

[0009] The average flow pore diameter of the porous membrane in the present invention is in the range of 0.1 to 1 µm. When the average flow pore size is less than 0.1 μm, the humidifying performance is inferior because the moisture transmission rate is reduced. On the other hand, when the average flow pore diameter exceeds 1 μm, water tends to seep into the gas side as droplets. Preferably, it is 0.1 to 0.7 μm, more preferably 0.2 to 0.5 μm.

In the present invention, the maximum pore size of the porous membrane is 0.1.
It is in the range of 1-3 μm. If the maximum pore size is less than 0.1 μm, the humidifying performance is inferior because the moisture transmission rate is reduced.
If the maximum pore diameter exceeds 3 μm, the pores are too large and water tends to seep into the gas side as droplets. Preferably, 0.15 to 2 μm, more preferably 0.2 to 1 μm
m.

The average flow pore diameter and the maximum pore diameter in the present invention are defined as the impregnation liquid having a surface tension of 22.3 dynes / c based on the description of ASTM F316-86.
m. It is a value measured using denatured ethanol at 25 ° C. In the present invention, the ratio of the average flow pore diameter to the maximum pore diameter is preferably from 1.0 to 3.0. When this ratio exceeds 3.0, the liquid droplets tend to seep onto the gas-side film surface. Particularly preferably, 1.0 to
2.0.

Further, the porosity of the porous membrane of the present invention is 40 to 40%.
It needs to be 90%. If the porosity is less than 40%, the number of moisture permeation paths is reduced, and the humidification performance is reduced. on the other hand,
If it exceeds 90%, it becomes difficult to control the amount of humidification, and it is difficult to obtain mechanical strength that can withstand the operating pressure. Further, the thickness of the porous membrane of the present invention is in the range of 50 to 1000 μm. If it is less than 50 μm, the mechanical strength of the film is not sufficient,
If it exceeds 1000 μm, the humidification performance will decrease. Preferably it is 70-500 micrometers, and 100-300 micrometers is especially preferable.

In the conventional method using a tetrafluoroethylene resin, the gas is humidified by diffusing water vapor in the porous membrane, and the pore size of the porous membrane is set within a specific range, so that the inside of the porous membrane can be immersed. Liquid water is prevented from entering and water is prevented from seeping out to the gas side. This method is considered to have insufficient humidification performance because humidification depends only on the diffusion of water vapor.

On the other hand, in the present invention, the use of a porous membrane having a specific pore structure made of a vinylidene fluoride resin enables suppression of seepage of water and improvement of humidification performance. That is, in the present invention, the porous membrane is made of a vinylidene fluoride-based resin having a higher affinity for water than the tetrafluoroethylene resin, and a specific pore structure is controlled. Thereby, by the holding force based on the surface tension, it is possible to suppress the water from seeping out to the gas side even when the water enters the pores inside the membrane, and to control the moisture without depending only on the diffusion of water vapor. It is presumed that excellent permeation performance is exhibited because permeation is possible.

In the present invention, the membrane may take any form such as a hollow fiber membrane or a flat membrane. However, when a membrane module is used, the membrane area per unit volume is large. It is particularly preferred that there is. In the case of a hollow fiber membrane,
Its inner diameter is preferably 0.3-5 mm,
It is particularly preferred that it is 0.5 to 4 mm. 0.3mm
If it is less than 1, the operating pressure rises remarkably due to pressure loss in the fluid flowing inside the hollow fiber, and the humidifier becomes large in order to cope with it. Further, when the thickness exceeds 5 mm, the membrane area per unit volume decreases when the membrane module is formed.
Humidification performance is reduced.

The porous membrane of the present invention is prepared by, for example, mixing a vinylidene fluoride resin with an organic liquid and an inorganic powder, followed by melt molding, and then extracting the organic liquid and the inorganic powder from the molded product. In the above, the organic liquid and the inorganic powder can be obtained by adjusting the types and the mixing ratio thereof. As the inorganic powder, the average primary particle diameter is 0.0
0.5 to 0.5 μm, specific surface area in the range of 50 to 300 m ² / g, and the volume% of methanol in which the powder is completely wetted
It is particularly preferable to use a hydrophobic silica having a (MW value) of 40% or more. As the organic liquid, it is particularly preferable to use an organic liquid having a solubility parameter (SP value) in the range of 8.5 to 9.5. Further, as the composition, by appropriately adjusting the vinylidene fluoride resin to a range of 25 to 45% by volume, the organic liquid material to a volume of 45 to 70% by volume, and the inorganic powder to a range of 10 to 20% by volume, A porous membrane having the characteristics of the average pore diameter and the maximum pore diameter of the present application can be obtained.

When the porous membrane is incorporated in a humidifier, the membrane area per unit volume can be increased and sufficient humidification performance can be obtained by using it in the form of a membrane module. For example, FIG. 1 shows an example of a hollow fiber membrane module. A membrane bundle 5 in which a number of hollow fiber membranes are bundled is placed in a housing 6, and both ends of the membrane bundle 5 are partitioned by partition plates 1 and 2.
The housing 6 is provided with at least two openings 3 and 4 in the housing 6. By flowing gas into the hollow fiber and flowing water from one opening 3 to the other opening 4 of the housing, it becomes possible to humidify the gas through the hollow fiber membrane. The form of the membrane module is not particularly limited, and can take a known form.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail by way of examples. The physical properties shown in this example are as follows:
The following measurement method was used. 1. Weight average molecular weight (Mw) Molecular weight in terms of polystyrene by GPC GPC measuring apparatus: LS-8000 manufactured by Toyo Soda, column: GMHXL, solvent: DMF, column temperature: 40 ° C. 2. Composition ratio (% by volume) It was calculated from the value obtained by dividing the added weight of each composition by the true specific gravity. 3. 3. Porosity Porosity (%) = (pore volume / porous membrane volume) × 100 where pore volume = water-containing weight−absolute dry weight Specific surface area (m ² / g) Measured by BET adsorption method. 5. Average flow pore diameter (μm) (half-dry method) Measured by ASTM F316-86. 6. Maximum pore size (μm) (bubble point method) Measured according to ASTM F316-86. 7. Breaking elongation (kg / cm ² ) Breaking strength (%) ASTM D88 using an Instron type tensile tester
2 (Strain rate 2.0 (mm / mm · mi)
n)) 8. 8. Dissolution parameter (SP value) Calculated from the following formula (Small's formula) SP value = dΣG / M d: specific gravity, G: molar index constant 0.2% by volume of methanol (MW value) at which the powder is completely wetted Silica is collected in a beaker, and 50 ml of pure water is added. Methanol is added below the liquid surface with electromagnetic stirring, and the point where no silica is observed on the liquid surface is defined as the end point, and the following equation is calculated from the required amount of methanol.

MW value = {X / (50 + X)} × 100 X: amount of methanol used (ml) The value of “volume% of methanol” required “pure water 50 ml” of “required amount of methanol (ml)”. The ratio is based on the sum of the amount of methanol (ml).

[0020]

Example 1 A humidifying membrane was manufactured by the following method. M
W value 50% average primary particle diameter 16 nm, specific surface area 110 m
² / g hydrophobic silica (Aerosil R-972 (trade name)) 14.2% by volume, diethylhexyl phthalate (S
P value: 8.9) 48.5% by volume, dibutyl phthalate (S
P value: 9.4) 4.4% by volume was mixed with a Henschel mixer, and vinylidene fluoride homopolymer (Mw = 242,000) (Kuha Chemical Industry KF polymer # 1000) was added thereto.
(Trade name)) 32.4% by volume was added and mixed again with a Henschel mixer.

The mixture was mixed with a 30 mmφ twin screw extruder to form pellets. The pellets were formed into a hollow fiber shape by a hollow fiber manufacturing apparatus equipped with a 30 mmφ biaxial extruder and a hollow fiber spout. The formed hollow fiber material is
It was immersed in 1,1, -trichloroethane for 1 hour to extract diethylhexyl phthalate and dibutyl phthalate, and then dried.

Next, the hollow fiber was immersed in a 50% ethyl alcohol aqueous solution for 30 minutes, transferred to water and immersed for 30 minutes to hydrophilize the hollow fiber. After further immersing in 70% aqueous solution of 20% caustic soda for 1 hour to extract hydrophobic silica,
Washed with water and dried. The performance of the obtained polyvinylidene fluoride porous membrane was as follows: average flow pore size: 0.4 μm, maximum pore size:
0.7 μm, the ratio of the average flow pore diameter to the maximum pore diameter is 1.75, the outer diameter is 2.00 mm, and the inner diameter is 1.10 mm
And the porosity was 66.0%.

The module shown in FIG. 1 was constructed using the porous membrane. The effective yarn length in the membrane module is about 60cm
The number of yarns was set such that the membrane area was 0.2 m ^{2 based} on the inner diameter. 70 ° C inside the hollow fiber membrane of the module
Was flowed at a flow rate of 10 m / sec, and hot water of 70 ° C. was flowed from the outside of the hollow fiber membrane in a direction opposite to the flow of the air. At this time, the amount of moisture in the air at the entrance and the exit was measured, and the humidification amount was determined from the difference.

As a result, the humidification amount was 150 g / min · m
^{Was 2} . At this time, the water pressure from the outer surface of the membrane is
Although 0.2 kg / cm ^{2 was} applied, no water droplets bleed out on the inner surface of the film.

[0025]

Example 2 Except that the mixing ratio was changed with 32.2% by volume of vinylidene fluoride homopolymer, 14.3% by volume of hydrophobic silica, 44.5% by volume of diethylhexyl phthalate, and 9.0% by volume of dibutyl phthalate. A polyvinylidene fluoride porous membrane was obtained in the same manner as in Example 1. The performance of the obtained polyvinylidene fluoride porous membrane was as follows: average flow pore diameter: 0.2
μm, maximum pore diameter: 0.4 μm, ratio of average flow pore diameter to maximum pore diameter is 2.0, and hollow fiber membrane inner diameter: 0.7 m
m, hollow fiber membrane outer diameter: 1.2 mm, film thickness: 0.25 mm,
The porosity was 70%.

Next, a membrane module was constructed in the same manner as in Example 1, and the amount of humidification was measured. As a result, the humidification amount is 1
It was 00 g / min · m ² . At this time, the water pressure from the outer surface of the film was 0.3 kg / cm ^2, but no water droplets bleed out on the inner surface of the film.

[0027]

Example 3 Except that the mixing ratio was changed to 32.5% by volume of vinylidene fluoride polymer, 14.3% by volume of hydrophobic silica, 45% by volume of diethylhexyl phthalate and 8.2% by volume of dibutyl phthalate. A polyvinylidene fluoride porous membrane was obtained in the same manner as in Example 1. The performance of the obtained polyvinylidene fluoride porous membrane was as follows: average flow pore diameter: 0.3 μm.
m, maximum pore diameter: 0.54 μm, the ratio of the average flow pore diameter to the maximum pore diameter is 1.8, and the hollow fiber membrane inner diameter: 2.5 m
m, hollow fiber membrane outer diameter: 4.0 mm, film thickness: 0.75 μm,
The porosity was 70%.

Next, a membrane module was constructed in the same manner as in Example 1, and the amount of humidification was measured. As a result, the humidification amount was 7
It was 0 g / min · m ² . At this time, the water pressure from the outer surface of the membrane was 0.3 kg / cm ² ,
There was no seepage of water droplets on the inner surface of the film.

[0029]

Comparative Example 1 A membrane module similar to that of Example 1 and shown in FIG. 1 was constructed using a hollow fiber membrane-like porous membrane made of tetrafluoroethylene resin. The porous membrane has an average flow pore diameter of 0.4 μm, a maximum pore diameter of 1.4 μm, a ratio of the average flow pore diameter to the maximum pore diameter of 3.5, a yarn inner diameter of 0.7 mm, and a yarn outer diameter of 1. 2mm, film thickness 0.25m
m, the porosity was 70%.

As a result of measuring the humidification amount, the humidification amount was 25 g /
min · m ² . At this time, the water pressure from the outer surface of the film was 0.2 kg / cm ^2, but no water droplets bleed out on the inner surface of the film.

[0031]

Comparative Example 2 Using vinylidene fluoride homopolymer (Kureha Chemical KF Polymer # 1000 (trade name)), average flow pore size: 1.0 μm, maximum pore size 4.0 μm, average flow pore size with respect to maximum pore size A ratio was 4.0, and a hollow fiber membrane having a hollow fiber membrane inner diameter of 0.7 mm, a hollow fiber membrane outer diameter of 1.5 mm, a film thickness of 0.4 mm, and a porosity of 85% was obtained.

A membrane module similar to that of Example 1 was constructed except that the porous membrane was used. Next, at the moment when water pressure was applied from the outer surface of the film to measure the humidification amount in the same manner as in Example 1, water droplets bleed out on the inner surface of the film. Therefore, appropriate humidification was not possible.

[0033]

The film for humidification of the present invention has excellent humidification performance without water oozing as droplets on the gas side. Therefore, the humidifier can be miniaturized, and particularly, can be suitably used in humidifier applications where miniaturization is desired, such as a humidifier for a polymer electrolyte fuel cell.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an example of a case where the film of the present invention is in the form of a practical module.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Partition plate 2 Partition plate 3 Opening 4 Opening 5 Hollow fiber membrane bundle made of polyvinylidene fluoride 6 Housing

Claims (1)

[Claims] An average flow pore size of 0.1 to 1 μm, and a maximum pore size of 0.1 to 3 μm, comprising a vinylidene fluoride resin.
m, the porosity is 40 to 90%, and the film thickness is 50 to 100.
A humidifying membrane comprising a porous membrane having a thickness of 0 μm.