JPS60202703A - Carbon membrane - Google Patents

Abstract

PURPOSE:To obtain the titled carbon membrane having the most excellent resistance to heat and chemicals and excellent separation effect, mechanical strength, and shape stability by combining a porous layer having separative power with a layer having voids whose maximum pore diameter is regulated to a value higher than the specified value and used for controlling permeatioi velocity. CONSTITUTION:A void-structure membrane is obtained by quickening the solidification velocity of a polyacrylonitrile polymer with a wet membrane forming process. The membrane is made resistant to flames without being drawn in an acidic atmosphere, and then carbonized at high temps. in an inert atmosphere. The obtained carbon membrane is composed of dense layers 1 and 2 having separative power and a porous layer 3 having voids whose maximum pore diameter is regulated to >=5mu and used for controlling permeation velocity.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a high-performance separation membrane made of carbon and excellent in form stability and durability.

(Prior art and its problems) Carbon fibers, fabrics, films, etc. have traditionally been used for industrial purposes such as F'RP materials, conductive materials, and heat insulation materials due to their excellent fiber properties, electrical properties, and heat resistance. Widely used as a material.

However, all such carbon materials are mainly made in pursuit of high strength and high rigidity, and carbon materials with defects such as voids were considered to be inferior products.

For example, in the case of Tokkai Fi! No. 57-166354, it was merely used as structure II of filter paper. In other words, it was not possible to separate liquids and gases, and at most it could only separate solids and liquids.

On the other hand, Japanese Patent Publication No. 51-5090 describes a carbon material with a large surface area, that is, a hollow fiber that forms voids in the carbon body and has the function of adsorbing trace substances in gases and liquids. This [t is produced by a method in which a solid fiber obtained by melt-spinning a phenolic resin is partially crosslinked with a crosslinking agent, and then the uncrosslinked portion is eluted with a solvent and the resulting hollow fiber is carbonized. Therefore, it does not have a microporous dense layer and has relatively large voids even near the densest surface, making it extremely brittle, with poor form stability and formability, and due to the linear pressure in practical use. It also has the disadvantage of easily losing its shape. Furthermore, even if a carbon material with such a rough structure is used, the function of a separation membrane cannot be achieved, and the accuracy of so-called ordinary filter paper has been slightly improved. Furthermore, JP-A-54-151622 discloses an inorganic hollow L membrane for fluid separation. This is an inorganic hollow fiber that has giant voids anisotropically in the sense that the direction changes perpendicular to the fiber axis. However, this is a hollow fiber of ceramics such as so-called metals such as nickel and iron, or oxides of these metals, and is not a hollow fiber of carbon, which is usually the subject of debate as to whether it is inorganic or organic. In other words, carbon materials other than diamond do not have a crystalline structure like general inorganic materials, but are clearly different in that they consist of planar molecules made up of six-carbon rings connected in a graphite structure. Because of their structure, carbon materials can form intercalation compounds, and they are used as electrical materials or reinforcing materials by taking advantage of their low specific gravity and superior mechanical properties per weight compared to general inorganic materials. It is well known that And, the fraction 111 made of carbon that has a characteristic structure like this
There has never been an example of 1tl#.

In view of such prior art, the present invention has investigated the fact that a carbon membrane composed of a porous layer having separation ability and a porous layer that controls permeation rate exhibits an extremely excellent separation function. reached.

(Object of the invention) The object of the present invention is to provide a carbon membrane that has outstanding heat resistance, chemical resistance, and pressure resistance, and is also capable of separating solvent and solute or mixed fluid with low pressure loss. shall be.

(Structure of the Invention) (1) A carbon membrane comprising a composite of a porous layer having separation ability and a porous layer controlling permeation rate having voids with a maximum pore diameter of 5 μ or more.

(Description of Structure) The carbon membrane of the present invention can be used, for example, in gas separation, reverse osmosis, ultrafiltration, dialysis, ultrafiltration, and the like.

In the present invention, the porous layer having separation ability (hereinafter referred to as layer 1) may be any porous layer having a density sufficient to exhibit the separation function, and usually has an average pore diameter of 1 μm or less, preferably 0.5 μm or less. A microporous dense layer consisting of pores of 5μ or less, more preferably 0.1μ or less, but preferably such a dense layer has a gas permeable or liquid permeable range, e.g. It is a unit, usually number 100.
From the viewpoint of separation ability, it is preferable that the pores be comprised of pores in the range of 1.5 Å or less, and in the case of gases, up to the size of the free volume in which the diffusion rate becomes an issue. Further, the layer 1 does not necessarily have to be uniform, and the average pore size may change as it moves in the thickness direction of the film. The thickness of the densest layer is preferably equal to or greater than the average pore diameter of that layer.

On the other hand, the porous layer that controls the permeation rate (hereinafter referred to as layer 2) in the present invention is a porous layer that greatly contributes to mechanical strength, but is not related to separation ability and is porous to the extent that fluid can move without pressure loss. Although any porous layer may be used as long as the porous layer has a porosity, it is usually a porous layer containing voids with a maximum pore size of 5 μm or more, preferably 10 μm or more. On the other hand, the shape of the void is not particularly limited, but a tubular shape (including a conical shape) is preferable. The shape of layer 2 is preferably one in which tubular voids are arranged in parallel to the thickness direction of the membrane, since this reduces the decrease in mechanical strength of the membrane and increases the permeation rate. This is preferable in that it can greatly improve . The feature of the present invention lies in the membrane structure formed by combining layer 1 and layer 2. A membrane without layer 1 has a limited separation effect and is not only poor in accuracy, but also has the drawbacks of being brittle and having poor durability in terms of mechanical strength and practicality. It is sufficient that there is only one layer 1, and the thickness thereof is preferably 1/2 or less of the total film thickness,
More preferably, it is 1/3 or less, and at least 1/3 of the film thickness.
150. It is preferably 1/30 or more, and from the viewpoint of separation ability and mechanical properties, it is at least 500 people, preferably 0.1 μ or more, more preferably 1 μ or more. Such requirements can be determined as appropriate depending on the desired separation ability and membrane properties.

In the present invention, it is preferable that the layer 1 is present on the front and back surfaces of the membrane because it can be used for separation from any direction and is strong against bending in any direction.

On the other hand, the thickness of the layer 2 is preferably at least 115 or more, preferably 1/2 or more of the film thickness, and preferably occupies the entire area excluding the layer 1. Membranes with such a layer have significantly improved permeation rates compared to membranes without such a layer.

Layers other than layer 1 included in the present invention include layer 2, layer 1
It must be a porous layer consisting of pores with a size greater than or equal to the average pore diameter of the material.

The carbon separation membrane as used in the present invention refers to flat membranes and hollow membranes substantially composed of carbon, and includes both carbonized membranes and graphitized membranes.

Among these, hollow fiber membranes are superior to flat membranes in that when used as a module, the membrane area per unit volume can be increased. Usually the outer diameter is 10μ to 1Qmm, and the hollow rate (
The volume ratio occupied by the hollow part to the entire system is 10 to 90.
%, but the outer diameter is 50 μ to 1 m and the hollow ratio is 50
~80% is 1lllit□, engineering, ayo. ,.

Although the separation membrane of the present invention is such a carbon structure, it is also possible to further coat the structure with another type of membrane, such as a polymer membrane, which improves the separation function, depending on the purpose.

The present invention will be explained with reference to the drawings. Figure 1 is an example of the carbon membrane of the present invention, and a micrograph (200 mm) showing its cross-sectional shape is shown.
0 times). In the figure, layer 1.2 is layer 2, and when observed as a whole, it has a cardboard structure.

The method for manufacturing the carbon separation membrane of the present invention will be explained below.

Examples of polymers for obtaining the raw material membrane for the carbon membrane of the present invention include cellulose, cellulose ester, polyamide, polyester, polyurethane, polyurea, polyimine, polyimide, polyether, polysulfide, polysulfone, polyolefin, polystyrene, polyphenylene, polyacetylene, Examples include polyvinyl alcohol, polyacrylonitrile, pitch, etc., but polyacrylonitrile polymers are particularly preferred from the viewpoint of film strength and morphological stability after firing.

The present invention is directed to manufacturing yA (
A membrane with a void structure is obtained by forming a membrane under appropriate conditions (thread spinning). For example, in the case of polyacrylonitrile, voids are generated by increasing the solidification rate during wet film formation.

The film containing 1 q of voids thus obtained is carbonized without being stretched, and the carbonization is carried out according to a conventional method. For example, when polyacrylonitrile is used as a raw material polymer, a temperature of 500 to 2000°C is applied to the carbonization treatment.
Before that, an oxidation treatment called flame resistance is performed to achieve stable carbonization.Flame resistance is 150% in an acidic atmosphere.
It is carried out under conditions of -400°C, preferably 200-300°C.

Carbonization is usually carried out under an inert atmosphere such as nitrogen or argon. After such carbonization, graphitization can be carried out by further heat treatment at a high temperature of 2000 to 3000° C. in an inert atmosphere.

(Effect of the invention) The present invention has excellent heat resistance and chemical resistance.

Furthermore, compared to ordinary inorganic membranes, carbon has the characteristic that its porosity can be changed arbitrarily, and it also has excellent separation effects, mechanical properties, and morphological stability.
There is no fear of the membrane structure collapsing during molding or practical use, the separation operation can be performed stably, and it has excellent durability.

The present invention will be further explained below with reference to Examples.

Example 1 10% by weight of an acrylonitrile-styrene copolymer having an acrylonitrile content of 27% by weight was mixed with polyacrylonitrile copolymerized with 2.0% by mole of methyl acrylate and 1.0% by mole of sodium allylsulfonate. A dimethyl sulfoxide solution of the mixture was wet-spun using a core-sheath type die for hollow fibers to obtain undrawn hollow filaments. This filament contained voids.

This hollow fiber was fixed to a metal frame and subjected to hot air treatment at 260° C. for 1 hour in a limited shrinkage state with a shrinkage rate of 10.2% to make it flame resistant. The outer diameter/inner diameter of the obtained flame-resistant hollow fiber is 870μ/79
It was 0μ.

This thread was further heated at 1200±5°C for 4 hours under an argon atmosphere.
Carbonization was performed by firing for 5 minutes, but during carbonization it showed a shrinkage of 21.8%, and the outer diameter/inner diameter was 680μ/620μ.

When we observed the cross section of this carbon separation membrane using an electron microscope, we found that
As shown in Figure 1, the membrane has an extremely dense layer 1 on its outer surface, and a porous layer 1 with a thin dense layer on its inner surface, with a length of approximately 20μ and a thickness of approximately It had a layer 2 in which 8 micron tubular voids were arranged radially. 1I11. The thickness of the dense layer 1 was 1.0 μm, and the dense layer on the surface of the porous layer 2 was 20 OA.

Using this carbon membrane, the permeation rate of various gases can be reduced to 0°5-・C.
Measured at a pressure of 11 l-2. The results are shown below.

P(1-1e)=6. '9x, 10-4cm3-c
m-2・'sea -1-cmf-1g-1 P(N2)-4,1x10- 4cm& -am-2-
8ec ”' 1 -cIllll-1g -1P(02
>-3,7X10-4co+3-cm-2-8eC
-1-cml-1"" I P (CO2> -3,3X10-4cm3-cm-2
-sec-1-cm)Ig-1.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an electron micrograph (2000x magnification) showing an example of the cross-sectional structure of the carbon film of the present invention. In the diagram, 1: Layer 1 (surface part) 2: Layer 1 (It curved part 3: Layer 2 Patent applicant Toshi Co., Ltd. Company procedure amendment (method) % formula % 1, Incident display 1982 Patent Application No. 56248 2, Name of the invention Carbon Film 3, Relationship with the case of the person making the amendment Patent applicant location 2-2-5 Nihonbashi Muromachi, Chuo-ku, Tokyo Number of inventions increased by amendment None 6, Amendment Subject (1) "An example of a cross-sectional structure of a carbon film" in line 9 of page 12 of the present specification is corrected to "shape of a fiber that is an example of a carbon film."

Claims (1)

[Claims] (1) A carbon membrane comprising a composite of a porous layer with separation ability and a porous layer with voids having a maximum pore size of 5 μm or more and controlling permeation rate.