JPH03169330A - Composite membrane - Google Patents

Abstract

PURPOSE:To obtain good gas separation characteristics by a method wherein separation layers A and porous layers B are alternately laminated and both surfaces of the laminate are composed of the layers B and the void ratio and pore size of the layers B are within a specific range and the thickness and mean minute pore size of the layers A satisfy a specific formula. CONSTITUTION:In a composite membrane wherein separation layers A taking charge of separation function and porous layers B taking charge of reinforcing function are alternately laminated and both surfaces of the laminate are composed of the porous layers B, the void ratio of the porous layers B of the composite membrane is 30-90% and the mean pore size of the minute pores thereof measured by a mercury porosimeter is 0.01-0.5mum while the relation between the thickness (t) of the separation layers A and the mean pore size PI of the pores thereof measured by the mercury porosimeter is characterized by PI<=(log (t)+2.2)/7.8. As the polymer used in the separation layers A of the composite membrane, there are a silicone polymer and a polyolefin polymer and, as the polymer used in the porous layers B, there is a crystalline polymer. This composite membrane has good gas separation characteristics and has no flaw in membrane constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a composite membrane used for gas separation, solvent separation, etc.

[Conventional technology]

Many methods for separating and purifying substances have been developed and improved over the years. Membrane separation technology is one such technology, and looking at the progress of its improvements, the major trends in technological development are the development of superior membrane materials and the development of thin film technology to increase efficiency.

One direction in thin film technology is to form a thin film on a porous substrate using a coating method or vapor deposition method. Thin film material enters the pores and a substantial thin film cannot be obtained.

In order to avoid this phenomenon, there is a method in which the pores of a porous substrate are filled in advance with a soluble substance to form a thin layer on the surface, and then the soluble substance within the porous substrate is eluted. Difficult to obtain a homogeneous thin layer! Vulnerable. Problems such as the occurrence of pinholes, uneven film thickness, and lack of durability have made it difficult to put it into practical use.

A multilayer composite hollow fiber membrane and its manufacturing method (Japanese Unexamined Patent Application Publication No. 1983-1992
-1404).

[Problem to be solved by the invention]

However, JP-A-62-1404 does not describe a composite membrane structure that is controlled by the porosity, average pore diameter, and thickness of the intermediate layer in order to stably and easily express the function of the intermediate layer. do not have.

As a result of detailed study by the present inventors, in order to fully realize the function of the intermediate layer, the average pore diameter and porosity of the porous membrane and the membrane thickness of the separation membrane must be adjusted to a certain level depending on the thickness of the intermediate layer. It turns out that I need to set it to a range.

[Means to solve the problem]

The gist of the present invention is to provide a composite membrane in which a separation layer A having a separation function and a porous layer B having a reinforcing function are alternately laminated, and both surfaces thereof are composed of porous layers B. The porosity of layer B is 30 to 90μ, and the average diameter of micropores measured with a mercury porosimeter is (LO1 to 115μ).
The composite membrane is characterized in that the membrane thickness t of the separation layer A and the average pore diameter PI of the micropores measured with a mercury porosimeter are in the range of m.

The composite membrane of the present invention has a structure in which a thin separation layer is included within a porous structure. In other words, it consists of an essential layer, and an intermediate layer separates from the very thin olfactory layer, which has a separating function. Basically, one layer of the separation layer A is sufficient, but a multilayer structure of two or more layers can be arbitrarily formed depending on the purpose. In a separation membrane, the most important layer is the layer that performs the separation function, and if it is the outermost layer, there is a risk of damaging the surface during handling, but the composite membrane of the present invention has a structure of three or more layers. There is no such danger because there is a layer having a separation function in the intermediate layer.

In order to fully demonstrate the membrane performance of the porous layer B, which has the reinforcing function of the composite membrane, and the separation layer A, which has the separation function, it is necessary to have a porosity that does not become a resistance to the permeation of the substance to be separated. Its value is approximately 50e6 or more. In order to maintain the mechanical strength of the composite membrane, the porosity of porous layer B is 9.
01 or less is required.

In order to improve the separation performance of the separation layer A which performs the separation function as much as possible, it is necessary to make the thickness of the separation layer as thin as possible.

The present inventors analyzed in detail the relationship between the thickness of the #ll layer and the micropore diameter of the porous layer, and the relationship between the occurrence of defects in the separation layer.

As a result, the micropores in the porous layer need to be at least 11 μm in diameter to avoid increasing the resistance to fluid permeation, and the smaller the better to prevent defects in the separation layer ((
It became clear that the thickness should be 15 μm or less. That is, what is the relationship between the film thickness tμm of the separation layer A and the average pore diameter PI7jm of the small pores measured with a mercury porosimeter? Engineering ≦■ (
The one at log(t)+2-2)z8 is a composite membrane with no defects in separation mA.

Polymer A used for the separation layer ▲ in the composite membrane of the present invention
Examples include silicone rubber, silicone-based polymers such as copolymers of silicone and polycarbonate, polyolefin-based polymers such as poly-4-methylbentene-1, linear low-density polyethylene, bar 7 loloalkyl-based fluorine-containing polymers, and polyurethane-based polymers. Polymers, cellulose polymers such as ethyl cellulose, polyphenylene oxide, poly-4-vinylpyridine, and copolymers or blends of these polymer materials can be mentioned.

As the polymer B' used for the porous layer B, any polymer may be used as long as it is a material that can be made porous by a stretching operation, such as polyethylene, polypropylene, poly-4-methylpentene-1, etc. Preferred are polyolefins, polyvinylidene difluoride, tetrafluoroethylene, and other crystalline polymers.

The composite membrane of the present invention is manufactured as follows.

To form the composite, polymer B' and polymer A' are alternately formed into a sandwich shape at a melt-forming temperature of 150° C. to 300° C. and a draft of 5 to 9000° C.

The unstretched multilayer composite film formed by melting and forming the composite film is subjected to a resin treatment if necessary, and then the polymer B' is layer-stretched to make it porous. The method of stretching to make porous layer is to cold stretch from 10 to 2004, hot stretch to make the total stretching ratio 30 to 400, and finally heat set to make only porous layer B which has reinforcing function porous. A method in which the small pores are stabilized by oxidation is preferred.

〔Example〕

Examples will be explained below.

Examples 1 and 2 A polymer material with a density (L 9 6 8 t/cc and a melt index value of 5.0) was used as the polymer material supplied to the inner and outer layers of a hollow fiber manufacturing nozzle having three discharge ports arranged concentrically. No. 5 high-density polyethylene (Mitsui Petrochemical @
(Hisex 2200J) was spun at a discharge temperature of 165°C and a winding speed of 205 m/min using segmented polyurethane (Tecoflex gG-soA, Thermedex) as the polymer material supplied to the intermediate layer. The obtained hollow undrawn yarn has an inner diameter of 250 μm, and is coated from the innermost layer to each AI5 μm. It consisted of three concentrically arranged layers with a thickness of 15μ and 14μm. This hollow undrawn yarn was annealed at 115° C. for 1 hour.

Then, the annealed yarn was heated to 60% at room temperature (Example 1),
1204 (Example 2) was carried out in two ways. I did a heat setting inside.

The membrane performance of the composite hollow fiber membrane thus obtained was evaluated, and the results shown in Table 1 were obtained. The pore volume (porosity) was measured using a mercury porosimeter, and from the relationship between the pore diameter and the pore volume, the pore diameter when the pore volume was 172 was taken as the average pore diameter PI. The ratio of the oxygen permeability coefficient to the nitrogen permeability coefficient was measured to determine the separation coefficient α, and the film thickness of the separation layer was measured by electron W4 microscopic observation.

From Table 1, even in the case of the example with deviation b, the condition of PI≦PIC is satisfied, and a good gas content g! It can be seen that it shows the coefficient.

Comparative Examples 1 and 2 Using the same polymer as in Example 1, the discharge temperature was 165°C,
Spinning was carried out at a winding speed of 133 ml min. The obtained hollow undrawn yarn has an inner diameter of 270 μm, and a distance of 18 μm from the innermost layer.
It consisted of three concentrically arranged layers with thicknesses of 1, 0 μm and 16 μm. This hollow undrawn yarn was annealed at 115° C. for 1 hour. Next, the annealed yarn was heated to 40% at room temperature (Comparative Example 1), and 5004 was heated to 50%
Hot stretching was carried out in a casing with a temperature of 0.00 mm, and heat setting was further carried out in a heating furnace at 120°C. Table 1 shows the removal performance of the composite hollow fiber membrane obtained.

Koichiza〈, the separation coefficient is [lL94mata[19B,
It can be seen that the original separation coefficient of the separation membrane is not expressed.

[Effects of invention]

As is clear from the results of the examples, a composite membrane in which the average pore diameter and porosity of the porous layer and the membrane thickness of the separation layer meet the claimed requirements has good gas separation properties and has no defects in the membrane structure. It can be seen that it is a composite membrane with no

Claims (1)

[Scope of Claims] A composite membrane in which a separation layer A having a separation function and a porous layer B having a reinforcing function are alternately laminated, and both surfaces thereof are composed of the porous layer B, the porous layer of the composite membrane The porosity of B is 30 to 90%, the average pore diameter of micropores measured with a mercury porosimeter is in the range of 0.01 to 0.5 μm, and the film thickness t of separation layer A and the micropores measured with a mercury porosimeter are in the range of 0.01 to 0.5 μm. A composite membrane characterized in that the relationship between the average pore diameter PI of pores is PI≦1/7.8 (log(t)+2.2).