JPH0588B2 - - Google Patents

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) Fibers, fabrics, films, etc. made of carbon have traditionally been used as industrial materials such as FRP materials, conductive materials, and heat insulation materials due to their excellent fiber properties, electrical properties, and heat resistance. Widely used.

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.

Therefore, when applying such a material to a filtration material, for example, as in JP-A-57-166354,
It was simply used as a constituent fiber 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 uses a carbon material with a large surface area, that is, a carbon material with voids formed in the carbon body.
Hollow fibers that have the function of adsorbing trace substances in gases and liquids are described. This fiber is produced by partially crosslinking a solid fiber obtained by melt-spinning a phenolic resin with a crosslinking agent, then eluting the uncrosslinked portion with a solvent, and carbonizing the resulting hollow fiber. Therefore, it does not have a microporous dense layer and has relatively large voids near the surface, so it is extremely brittle and has poor shape stability and formability, and its shape does not change even when subjected to filtration pressure in practical use. It has the disadvantage of being easily broken down. Furthermore, even if such a carbon material with a rough structure is used, it cannot be expected to separate gas or liquid, and the function can only be obtained with slightly higher precision than that of so-called ordinary filter paper.

In view of the background of the prior art, the present invention was achieved by investigating the fact that a carbon membrane having one or more microporous dense layers exhibits an extremely excellent separation function.

(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 characterized by having at least one microporous dense layer.

(2) A method for producing a carbon film, which comprises carbonizing a film made of a fiber-forming linear polymer and having an orientation coefficient of 0.70 or less as measured by wide-angle X-ray diffraction.

(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.

The microporous dense layer referred to in the present invention may be any porous layer with uniform pore diameters and has a density sufficient to exhibit the above-mentioned separation function, and usually has an average pore diameter of 1 μm.
or less, preferably 0.5μ or less, more preferably
A microporous dense layer consisting of voids of 0.1 μm or less, but preferably such a dense layer is gas-permeable or liquid-permeable, e.g., with an average pore size in the order of Å, and is usually in the order of several Å. From the viewpoint of separation ability, it is preferable to have pores with a diameter of 100 Å or less, and in the case of gases, up to the size of the free volume where the diffusion rate becomes a problem.

A feature of the present invention is that it has at least one such microporous dense layer. Membranes without this layer have a limited separation effect and are not only poor in accuracy, but also have the drawbacks of being brittle and having poor durability in terms of mechanical strength and practicality. Such a dense layer is 1
Of course, the entire film may be a dense layer, but preferably the thickness is 1/2 or less of the total film thickness, more preferably 1/3 or less, and at least 1/3 of the film thickness. /50, preferably 1/30 or more, and
In terms of resolution and mechanical properties, at least
500Å, preferably 0.1μ or more, more preferably
It is 1μ or more. Such requirements can be appropriately determined depending on the desired separation ability and membrane properties.

In the present invention, it is preferable that such a microporous dense layer exists 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. In such a structure, it is preferable in terms of separation performance that a porous layer (which may be within the range of the dense layer) that is coarser than the dense layer exists between the dense layers.

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 outer diameter is 10μ~10mm
The hollow ratio (volume ratio of the hollow part to the whole thread) is 10 to 90%, but the outer diameter is 50 μ to 1 mm.
A material with a hollow ratio of 50 to 80% is more preferable because of its high separation performance.

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 and enhances the separation function, depending on the purpose.

The present invention will be explained with reference to the drawings. FIG. 1 is an example of the carbon film of the present invention, and is a micrograph (3000x magnification) showing its cross-sectional shape. In the figure, 1 and 2 are dense layers,
3 exists between the dense layers 1 and 2, and 1 and 2 are present between the dense layers 1 and 2
It is a coarser porous layer and has a cardboard structure when observed as a whole.

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

The fiber-forming linear polymer in the present invention includes, for example, cellulose, cellulose ester, polyamide, polyester, polyurethane, polyurea, polyimine, polyimide, polyether, polysulfide, polysulfone, polyolefin,
Polymers such as polystyrene, polyphenylene, polyacetylene, polyvinyl alcohol, polyacrylonitrile, and pituti, or copolymers of these may be used alone or in a mixture of two or more of them. Polyacrylonitrile polymers are preferred from the viewpoint of morphological stability.

In the present invention, such polymers are appropriately formed into films under film-forming (thread-spinning) conditions suitable for each polymer, but it is important to maintain the orientation of the polymer as much as possible after film formation. This is the point where it becomes carbonized or graphitized. Specifically, it is important to maintain the orientation coefficient at 0.70 or less as measured by wide-angle X-ray diffraction. That is, after the film having such specific orientation characteristics is fired, it forms a structure convenient for use as a separation film.
In particular, when the orientation coefficient is 0.70 or less, a microporous dense layer is formed.

One specific method for maintaining such an orientation coefficient is not to stretch, but there is no need to limit it to this. In short, it is sufficient if the molecular orientation is disordered to the above degree in the state of a polymer film.

Here, the orientation coefficient F(X) is calculated from the half-width H of the intensity curve measured along the Debye ring obtained by wide-angle X-ray diffraction using F(X) = 1-H/180. It is a value.

The smaller the value, the better; an orientation coefficient of 0.60 or less provides a more uniform, porous, dense layer and provides an excellent separation membrane without leakage.

Next, carbonization is carried out according to the usual method.

For example, when polyacrylonitrile is used as a raw material polymer, a temperature of 500 to 2000°C is applied for carbonization treatment, but before that, an oxidation treatment called flameproofing is performed to stably achieve carbonization. Flame resistance is 150-400℃ under acidic atmosphere, preferably
It is carried out under conditions of 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.

The carbon membrane of the present invention includes both carbonized and graphitized membranes.

(Effects of the Invention) The present invention has excellent heat resistance and chemical resistance. Moreover, it has excellent separation effects, mechanical properties, and morphological stability, so there is no fear of the membrane structure collapsing during molding or practical use, allowing stable separation operations, and excellent durability. be.

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

Example 1 A dimethyl sulfoxide solution of polyacrylonitrile copolymerized with 0.3 mol % of itaconic acid was wet-spun using a core-sheath type die for hollow fibers to obtain undrawn hollow filaments. This filament was subjected to wide-angle X-ray diffraction to obtain an intensity curve, but since it was unstretched, crystallization was low and it was difficult to distinguish it from the background, making it impossible to determine the orientation coefficient.

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 22.3% to make it flame resistant. The outer diameter/inner diameter of the obtained flame-resistant hollow fiber is
It was 690μ/620μ.

This thread was further heated to 1200±5℃ under an argon atmosphere.
It was fired for 45 minutes and carbonized. It showed a shrinkage of 14.0% during carbonization, and the outer diameter/inner diameter was 470μ/430μ.

When the cross section of this carbon separation membrane was observed with an electron microscope, it was found that the membrane had extremely dense layers on both sides and a coarse layer between them, as shown in FIG. The thickness of dense layer 1 is 2.5μ, and the thickness of dense layer 2 is
It was 1.0μ.

Using this carbon membrane, the permeation rate of various gases can be reduced to 0.5
The pressure was measured in Kg/cm ² . The results are shown below.

P (He) = 2.3 × 10 ^-4 cm ²・cm ^-2・sec ^-1・cmHg ^-1 P (N ₂ )=1.5×10 ^-4 cm ²・cm ^-2・sec ^-1・cmHg ^-1 P (O ₂ ) = 1.4 × 10 ^-4 cm ² · cm ^-2 · sec ^-1 · cmHg ^-1 P (CO ₂ ) = 1.2 × 10 ^-4 cm ² · cm ^-2 · sec ^-1 · cmHg ^-1 It was hot.

Comparative Example The undrawn hollow filament obtained in Example 1 was
The filament was stretched twice to obtain a stretched hollow filament. The outer diameter/inner diameter of this filament is 325μ/280μ,
The orientation coefficient was 0.86, and the film structure was dense throughout. This hollow fiber was made flame resistant and carbonized in the same manner as in Example 1. The outer diameter/inner diameter of the hollow carbonized fiber obtained is
170μ/145μ, uniformly dense throughout,
It did not have a microporous structure.

Using this fiber, the gas permeation rate was measured in the same manner as in Example 1, but no gas permeation was observed.

[Brief explanation of the drawing]

Figure 1 is an electron micrograph (3000x magnification) showing an example of the cross-sectional structure of fibers constituting the hollow carbon membrane of the present invention.
It is. In the figure, 1: dense layer (surface part), 2: dense layer (back surface part), 3: porous layer.

Claims (1)

[Scope of Claims] 1. A carbon membrane characterized by having at least one microporous dense layer. 2. A method for producing a carbon film, which comprises carbonizing a film made of a fiber-forming linear polymer and having an orientation coefficient of 0.70 or less as measured by wide-angle X-ray diffraction.