JPH03161030A - Preparation of porous carbon composite membrane - Google Patents

Abstract

PURPOSE:To form a porous carbon composite film excellent in heat resistance and chemical resistance by heating a support wherein a film composed of a specific composition in formed in an oxidizable gas to apply flame-resistant treatment to the support and subsequently heating the support at 600 deg.C or higher in inert gas. CONSTITUTION:A polymer solution having a polyacrylonitrile type polymer and a heat-decomposable volatile polymer dissolved therein is applied to at least one surface of a sheet like support composed of a carbonaceous fiber to form a film. Subsequently, the support is heated in oxidizable gas to apply flame-resistant treatment to the polyacrylonitrile type polymer in the film and heated to 600 deg.C or higher in an inert gas atmosphere not only to carbonize the polyacrylonitrile type polymer but also to decompose and volatilize the heat-decomposable volatile polymer. As a result, a porous carbon film having pores communicating each other is obtained.

Description

Detailed Description of the Invention [Industrial Application Field 1] The present invention provides a porous carbon composite membrane with excellent heat resistance and chemical resistance that can be used as a filtration membrane for microfiltration, ultrafiltration, and reverse osmosis. Regarding manufacturing methods.

[Conventional technology 1 Inorganic porous membranes have higher heat resistance and better heat resistance than organic polymer membranes.
Filtration membranes that have excellent chemical resistance, such as porous glass membranes, porous ceramic membranes such as alumina-based and silica-based membranes, and carbon-based supports whose surfaces are coated with porous zirconia membranes, have already been proposed.

However, it has been difficult to produce a sol of inorganic particles that can form a filtration layer by coating with a porous support, and it has also been difficult to control the pore diameter. Furthermore, during the drying and firing process of the gel layer adhered to the support, the gel layer tends to become brittle and it is difficult to suppress the occurrence of cracks, and the film is expensive because it has to be thickened to a certain extent.

[Problem to be solved by the invention] Daiki Nikki Nikkei name ITl711 name Ofukyokutjirokugo0
The object of the present invention is to provide a method for producing a porous carbon composite membrane in which a thin porous carbon membrane having penetrating pores with a sharp peak in the range of n1 to 1 nm is formed on a sheet-like support made of carbonaceous material.

[Means for Solving the Problems] That is, the present invention provides a carbonaceous fiber or its precursor fiber on at least one surface of a sheet-like support made of carbonaceous fiber or its precursor fiber.
A polymer solution containing a polyacrylonitrile polymer (A) and a thermally decomposable polymer CB) is applied to form a coating film, and the support on which the coating film is formed is heated in an oxidizing gas. Polyacrylonitrile polymer (A) in the coating film
flameproofed and then heated at 600°C under an inert gas atmosphere.
By heating above to carbonize the polyacrylonitrile polymer (A) and decompose and volatilize the pyrolyzable volatile polymer (B), the coating film is made into a porous carbon film having interconnected pores. This is a method for producing a porous carbon composite membrane.

[Function] In the production method of the present invention, first, a mixed polymer solution is applied on at least one surface of a sheet-like support to form a coating film.

Since the sheet-like support used in the method of the present invention serves as a support for the porous carbon thin film, it is not appropriate that the sheet-like support be homogeneous (inner substance) when the porous carbon thin film is formed. It is desirable that the That is,
The sheet-like support referred to herein is preferably a sheet-like material made of fabric such as woven fabric, knitted fabric, non-woven fabric, or paper material, and does not refer only to a homogeneous film-like material.

Further, the form of the sheet-like product includes not only a film-like product that is simply spread on a flat surface, but also a cylindrical or hollow fiber-like product. The materials that make up the sheet-like support are:
Carbon fibers such as carbon fibers, or precursor fibers of carbon fibers such as flame-resistant fibers that can be made into carbon fibers by firing, are easy to handle, flexible, and even support after firing treatment. It is preferable because it has a large reinforcing effect.

In addition, the surface of the sheet-like support may be flattened with a substance that can be removed later so that the thickness of the coating film formed on the sheet-like support does not vary too much.

In this sense, the sheet-like support as a starting material does not necessarily have to have gaps.

A particularly preferable sheet-like support is one in which the size of the gap (cylindrical equivalent pore diameter when the gap in the material is assumed to be a cylindrical pore) measured with a mercury borosimeter after firing is in the range of 0.1 to 50 μm. be.

The mixed polymer solution used to form a coating film on the surface of this support contains an acrylonitrile polymer (A) having 90 to 100 mol% of acrylonitrile units, and
It is prepared by dissolving a thermally decomposable polymer (B) which is thermally decomposed at a temperature of 0.degree.

The acrylonitrile polymer (A) used in the present invention is
It is 90 to 100 mol% of acrylonitrile and 0 to 10 mol% of a monomer copolymerizable with acrylonitrile or a copolymer.

Specific examples of copolymerizable monomers include acrylic acid, methacrylic acid, itaconic acid and derivatives thereof, such as methyl acrylate, ethyl acrylate, pendyl acrylate, methyl methacrylate, ethyl methacrylate, etc.; acrylamide, methacrylamide, etc. Amide derivatives; vinyl acetate; halogenated monomers such as vinyl chloride and vinylidene chloride; sulfonic acid derivatives such as sodium methacrylsulfonate and sodium styrene sulfonate; and the like.

The degree of polymerization of the acrylonitrile polymer (A) is preferably one having a specific viscosity in the range of 0.1 to 0.4. When the specific viscosity is lower than 0.1, the toughness of the coating film decreases and cracks are likely to occur. On the other hand, if it is higher than 0.4, the viscosity of the solution is high, it tends to gel, and it becomes difficult to produce a uniform thin film, which is not preferable.

The thermally decomposable volatile polymer (B) has a temperature of 600° C. or lower and can be dissolved in the solvent of the acrylonitrile polymer (A). Such pyrolytically volatile polymers (
Specific examples of B) include aromatic vinyl monomers such as styrene, α-methylstyrene, and vinyltoluene; aliphatic vinyl monomers such as vinyl chloride, vinyl alcohol, and vinyl acetate; methyl methacrylate, and ethyl methacrylate. , a methacrylate monomer such as n-butyl methacrylate; or a homopolymer consisting of 51 mol% or more of these monomers and 49 mol% or less of other copolymerizable monomers other than acrylonitrile. Examples include copolymers.

The degree of polymerization of the thermally decomposable volatile polymer (B) is such that the specific viscosity is 0.1.
A value in the range of 0.4 to 0.4 is preferred because it facilitates adjustment of the viscosity of the acrylonitrile polymer (A) and the mixed dispersion.

The solvent used to prepare the polymer solution is a common one for the acrylonitrile polymer (A), the pyrolytically volatile polymer (B), and the optionally added compatibilizer (C). It can be a solvent. Examples of such solvents include dimethiacetamide, dimethylformamide, dimethylsulfoxy, and the like.

When preparing a polymer solution, the solubility parameter δ of the acrylonitrile polymer (A) is usually around 15.4, and that of the thermally decomposable volatile polymer (B) is 9 to 12.
Many are in the 2 range. For this reason, they often have poor compatibility with each other, so depending on the combination of the acrylonitrile polymer (A) and the pyrolyzable volatile polymer (B), it may be necessary to further mix a compatibilizer (C) to make them compatible with each other. It is possible to improve compatibility.

The compatibilizer (C) is a substance that exhibits a compatibility effect with both the polymer (A) and the polymer (B), and if it exhibits a compatibility effect, it may be a low-molecular substance such as an oligomer. A variety of materials are used, ranging from polymer materials to polymer materials. in particular,
Compatible with the acrylonitrile polymer (A) or identical to the polymer (A). Segment (a) composed of a monomer of Polymers contained in the same polymer chain, such as block copolymers or graft copolymers, are used.

Such a block or graft copolymer can be produced by a known method, for example, the method described in Japanese Patent Publication No. 61-39978.

The compatibilizer (C) makes the dissolved phases of the acrylonitrile polymer (A) and the thermally decomposable polymer (B) into small dispersed particles in the polymer solution, and stabilizes the resulting polymer solution. It has the effect of

Furthermore, this compatibilizer (C) not only increases the compatibility effect in the polymer solution, but also controls the size of the dispersed phase (agglomerated particles) of the pyrolytically volatile polymer (B), which becomes the island component in the coating film. do. That is, the size of the aggregated particles of the pyrolytically volatile polymer (B), which is the basis of the pore diameter of the finally obtained thin film, is controlled. Therefore, the amount of compatibilizer (C) used is related to the size of the pores in the final thin film, and if the amount used is not large, the pore size will be reduced and the pore size distribution will be changed. Make it smaller.

The preferred mixing ratio of each component when preparing a polymer solution for forming a film on a support is 10 to 90% by weight of the acrylonitrile polymer (A), preferably 20% by weight.
~80% by weight, pyrolyzable volatile polymer (B) lO ~90%
, preferably 20 to 80% by weight, and the compatibilizer (C) is O to
20% by weight, preferably 0 to 10% by weight [however (A)
The total amount of components (B) and (C) is 100% by weight.

It is not preferable that the amount of the pyrolytically volatile polymer (B) added is less than 10% by weight, since it is difficult to obtain continuous pores in the final thin film. As the amount of polymer (B) added increases, the number of communicating pores increases, and if the amount added exceeds 80% by weight, it becomes difficult to control the size of the communicating pores.

As the amount of compatibilizer (C) added increases, the amount of polymer (A
) and the polymer (B) increase, and the size of the aggregated phase of the pyrolytically volatile polymer (B) in the coating decreases. Therefore, when the amount of compatibilizer (C) added increases, the pore diameter in the porous carbon thin film after firing becomes smaller.

However, if the amount added exceeds 20% by weight, the effect of addition becomes saturated, so a mixing amount up to 20% by weight is sufficient.

The concentration of the weight substance (including the compatibilizer (C)) in the polymer solution is preferably 0.1 to 20% by weight, and 1 to 20% by weight.
More preferably, it is 15% by weight. When the concentration of the polymer in the mixed solution is less than 0.1% by weight, the amount of the polymer solution permeated into the porous support increases, making it difficult to form a uniform thin film. Moreover, if it exceeds 20% by weight, the viscosity is high and the fluidity is reduced, and the film thickness tends to become thick, making it difficult to form a thin film.

Application of the polymer solution onto the surface of the sheet-like support may be carried out by dipping the sheet-like support into the polymer solution. In this case, coating films are formed on both surfaces of the sheet-like support. When applying the polymer solution to one side of the sheet-like support, the polymer solution can be applied using a brush, a doctor blade, or the like, or sprayed using a spray gun.

? The polymer solution applied onto the surface of the sheet-like support may be formed into a coating film by a wet method in which it is coagulated using a coagulating liquid, washed, and dried, or it can be formed into a coating film by evaporating the solvent to dryness. A dry method may also be used. Both processes have advantages and disadvantages, and either process can be used. To put it bluntly, the dry method, which has a simple process, is suitable for small-volume production, and the wet method is suitable for large-scale production.

As for the thickness of the coating film, ! A suitable thickness is about 100 μm. It is difficult to form a coating film with a thickness of less than 1 μm on a sheet-like support without producing defects such as holes. Moreover, if the thickness of the coating film exceeds 100 μm, the permeation resistance of the porous carbon thin film increases, making it difficult to use.

The support on which the coating film has been formed in this way is then heat-treated in an oxidizing gas atmosphere (gas containing 02, 03, S, NO, SO, etc.), usually in air, to remove the coating film. The acrylonitrile polymer (A) is subjected to flame-retardant treatment. As for the heating temperature, is it a thermally decomposable volatile polymer? B) at a temperature within a range that does not substantially undergo decomposition, usually from 200 to 300
℃ range. Although the processing time depends on the processing temperature, it is usually 0.1 to 10 hours.

In addition, when performing flameproofing treatment, it is desirable to fix the sheet-like support by placing it on a conveyor or the like so that the sheet-like support does not undergo deformation. If the sheet-like support is deformed, cracks may occur in the 7I membrane, which is undesirable. The coated support is then heated at 400-2000°C.
in an inert gas (N2, Ar, He, etc.) atmosphere or in an inert gas and an oxidizing gas (HCI, H20, Co, 0.0
carbonization treatment is performed in a mixed gas of By carbonizing the acrylonitrile polymer (A), the coating film becomes a porous carbon thin film having open pores. Further, when the sheet-like support is a precursor fiber of carbon fiber, it is converted into carbonaceous fiber in this process.

The porous carbon composite membrane produced in this way has a porous carbon thin film having continuous pores with a small pore size distribution on at least one surface of a sheet-like support made of carbonaceous material such as carbon fiber. Formed and composed. Although the porous carbon membrane is extremely thin, this composite membrane has practically sufficient handling strength due to the sheet-like support.

〔Effect of the invention〕

The porous carbon composite membrane produced by the method of the present invention has a very sharp pore diameter distribution determined from a pore volume differential curve measured by mercury intrusion method, and therefore exhibits high separation performance. It exhibits high water permeability due to the large number of pores per unit membrane area and thin membrane thickness.

In addition, since the entire composite membrane is carbonaceous, it has high heat resistance and high chemical stability, and exhibits strong resistance to most chemical solutions in all PL regions.

Since the porous carbon composite membrane of the present invention has the above-mentioned excellent property 8-, it can be used for various purposes, such as the separation and purification of pyrodiene, polymers, etc. in the pharmaceutical industry, gas separation in the chemical industry, especially organic It can be used for gas separation and purification.

Furthermore, it can be effectively used in the clarification of alcoholic beverages, soft drinks, soy sauce, vinegar, etc. in the food industry.

[Example] Hereinafter, the present invention will be specifically explained with reference to Examples. In addition,
"Parts" in the following description indicate parts by weight.

1) The specific viscosity of the polymer is 0.1g of the polymer. It was dissolved in 100 ml of dimethylformamide containing IN rhodan soda and measured at 25°C in a conventional manner.

2) The pore size of the porous carbon composite membrane is CARLO
．． Measured using ERBA Borosimeter 200,
The pore diameter was determined as a cylindrical equivalent diameter.

3) Heat resistance was determined by dynamic calorimetry analysis (TGA) of the porous carbon composite membrane.
) in an air atmosphere at a heating rate of 10° C./min.

4) The water permeation rate was determined by measuring the permeation amount of water per unit time that passed through the membrane at a pressure of 1 kg/cm 2 from one side of a prototype module with an effective area of 10 cm x 10 cm.

Synthesis Example 1 Preparation of compatibilizer (C1) A portion of cyclohexanone peroxide (Peroxa H, manufactured by NOF Co., Ltd.) was mixed with methyl methacrylate (hereinafter referred to as MMA).
), 800 parts of pure water and 1 part of Verex OTP (manufactured by NOF ■) as an emulsifier were added to the reaction vessel, and after sufficiently purging with inert gas, the mixture was kept at 40°C and Rongalit 0.76 part and sulfuric acid aqueous solution to pH3
After that, polymerization was started. Continue stirring until 15
The first stage emulsion polymerization was completed in 0 minutes.

Next, in the second stage, 72 parts of acrylonitrile (hereinafter abbreviated as AN) was added to this emulsion, the temperature was raised to 70°C, stirring was continued for 150 minutes, and 4 parts of sodium sulfate was added. was added and stirred for 30 minutes to complete the polymerization.

The polymer was taken out, filtered, washed with water and dried to obtain a block copolymer (compatibilizer (C1)'). The polymerization rate of this compatibilizer was 65.7%, and the specific viscosity was 0.19.

Synthesis Example 2 Preparation of compatibilizer (C2) 1 part of cyclohexanone peroxide (Peroxa H, manufactured by NOF Corporation) was dissolved in 100 parts of MMA, and 800 parts of pure water was dissolved.
and Pellex OTP as an emulsifier (manufactured by NOF Corporation)
After adding 1 part to the reaction vessel and thoroughly replacing with inert gas,
After maintaining the temperature at 40° C. and adjusting the pH to 3 with 0.76 parts of Rongalit and an aqueous sulfuric acid solution, polymerization was started.

Stirring was continued to complete the first stage emulsion polymerization in 120 minutes.

Next, in the second stage, 0 parts of AN6 and 10 parts of vinyl acetate (hereinafter abbreviated as VAc) were added to this emulsion, the temperature was raised to 70°C, stirring was continued for 150 minutes, and 4 parts of Glauber's salt was added. was added and stirred for 30 minutes to complete the polymerization. The polymer was taken out, filtered, washed with water, and dried until the polymerization rate was 65% and the specific viscosity was 0. l8 composition AN30 mol%/MMA65 mol%
/vAc5 mol% block polymer (compatibilizer (C2)
) was obtained.

Examples 1 to 4 Carbon fiber as a support with a basis weight of 200 g/m2 and a thickness of 30
A 0 μm plain woven fabric was prepared. The gap size of this support measured with a mercury porosimeter is 0.5 to 1.0 μm.
Met.

Acrylonitrile (hereinafter abbreviated as AN) 98 mol%
and 60 parts of a 7-acrylonitrile copolymer (AI) with a specific viscosity of 0.24, which is composed of 2 mol% of methacrylic acid (hereinafter abbreviated as MAA), and 99 mol of methyl methacrylate (hereinafter abbreviated as MMA). % and 40 parts of a pyrolytically volatile polymer (81) with a specific viscosity of 0.21 composed of 1 mol % of methyl acrylate (hereinafter abbreviated as MA), addition of a compatibilizer (C1). The four polymer solutions shown in Table 1 were prepared with varying amounts ranging from 0 to 10 parts. The solvent used is dimethylformamide (hereinafter referred to as
The polymer concentration (total amount of components (A1) to (CI)) of the polymer solution was set to 10% by weight using DMF (abbreviated as DMF).

This polymer solution was poured into a hole with a hole diameter of 0. A spray nozzle with a diameter of 5 mm was used to spray onto one side of the carbon fiber plain weave support. The spray amount was 300 cc/m''.

Carbon fiber plain fabrics sprayed with four types of polymer solutions were fixed on all sides to a stainless steel perforated plate, and
It was dried and solidified for about 2 hours in a vacuum dryer at a temperature of .degree. C. to form a thin film about 30 .mu.m thick on the surface of each carbon fiber plain weave. This carbon fiber plain woven fabric was treated in an air atmosphere at a temperature of 230°C for 3 hours with all four sides set on a perforated plate.
The polyacrylonitrile copolymer part has a flame-resistant structure. Then, in a nitrogen gas atmosphere, it was heated from room temperature to 1000℃ for 50 minutes.
The mixture was heated to 1000° C. for 20 minutes, and then carbonized at 1000° C. for 20 minutes to thermally decompose the pyrolyzable volatile polymer to make the thin film portion porous to produce a porous carbon composite membrane.

The thickness of the porous carbon thin film part in these composite membranes is approximately 2
It was 0 μm. In addition, the evaluation results of the pore diameter of the thin film part, water permeation rate, and heat resistance of the obtained porous carbon composite membrane were evaluated in the first
Shown in the table.

From Table 1, it can be seen that as the amount of compatibilizer (C1) added increases, the maximum value of the pore radius becomes smaller.

Also, Figure 1 shows these four types of porous carbon composites. The pore volume differential curve of the composite film is shown.

Table 1 Examples 5-7 Specific viscosity 0, composed of 96 mol% AN, 3 mol% MA and 1 mol% intacoic acid (hereinafter abbreviated as ZA).

23 AN/MA/ZA copolymer (A2) and MMA
Specific viscosity 0 composed of 87 mo% and MAI 3 mole%
．． Three types of polymer solutions were prepared by adding a thermally decomposable polymer (B2), which is a MMAAlMA copolymer of No. 20, and a compatibilizer (C2) in the amounts shown in Table 2. Dimethylacetamide (hereinafter abbreviated as DMAc) was used as a solvent and dissolved so that the polymer concentration (total amount of components (A1) to (C1)) was 8%.

As a support, carbon fiber has a basis weight of 180 g/m" and a thickness of 5.
The gap measured with a 00 μm mercury borosimeter is 0.5
Using a nonwoven fabric of ~1.0 LLm, 400 cc/g of the polymer solution shown in Table 2 was applied to one side using a spray gun.
m" to form a solution layer with a thickness of 400 μm on one side of the nonwoven fabric. The solvent was evaporated in an inert atmosphere at a temperature of 200°C to form a coating film with a thickness of about 30 μm. The four sides of this nonwoven fabric were fixed. Then, it was subjected to flameproofing treatment for 3 hours in an air atmosphere at a temperature of 240°C.Then, it was subjected to a carbonization treatment for IO minutes at a temperature of 900°C in a nitrogen atmosphere.

Table 2 shows various performances of the obtained porous carbon composite membrane.

Table 2 4.

[Brief explanation of the drawing]

Figure 1 shows pore volume differential curves obtained by measuring the porous carbon composite membranes produced in Examples 1 to 4 by mercury intrusion method, and Figure 2 shows the pore volume differential curves obtained by measuring the porous carbon composite membranes produced in Examples 1 to 4. This is a pore volume cumulative distribution curve obtained by measuring a porous carbon composite membrane by mercury porosimetry, and FIG. 3 is a schematic cross-sectional view of the porous carbon composite membrane of the present invention.

Claims (1)

[Claims] 1) A polyacrylonitrile polymer (A) and a pyrolytically volatile polymer (B) are dissolved on at least one surface of a sheet-like support made of carbonaceous fibers or their precursor fibers. A coating film is formed by coating the polymer solution, and the support on which the coating film is formed is heated in an oxidizing gas to flameproof the polyacrylonitrile polymer (A) in the coating film,
Next, the polyacrylonitrile polymer (A) is carbonized by heating to 600°C or higher in an inert gas atmosphere, and the thermally decomposable polymer (B) is decomposed and volatilized to open the pores communicating with the coating film. A method for producing a porous carbon composite membrane, characterized in that the porous carbon membrane has a porous carbon membrane comprising: 2) Claim 1, wherein a compatibilizer (C) for the polymer (A) and the polymer (B) is further dissolved in the polymer solution.
Manufacturing method described.