JPH1052629A - Molecular sieve carbon film and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare a molecular sieve carbon film having good selective permeability, high strength, and heat resistance by making a carbon film having a carbon content of at least a given value and lots of pores adhere to the surface of a porous ceramic material of a specified shape. SOLUTION: A porous ceramic material such as alumina, silica is used, and the porosity of the material is made 30-80%. A thermosetting resin such as a phenol and a melamine resin is applied on the surface of the material to form a polymer film, and the film is heat-treated at 550-1100 deg.C in a nonoxidative atmosphere. A molecular sieve carbon film having a carbon content of not less than 80% and lots of pores at least 1nm in diameter is prepared. The film can separate and purify a component of a specified molecular size selectively from various mixed gases of different molecular sizes and is good in heat resistance, chemical resistance and has high strength.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molecular sieve carbon membrane used for separating various mixtures and a method for producing the same, and more particularly, to the use of a difference in permeation speed due to the molecular sieve effect of fine pores. The present invention relates to a molecular sieving carbon membrane used for separating and purifying a gas, and a method for producing the same.

[0002]

2. Description of the Related Art Hitherto, as a gas separation membrane having high permeation selectivity, a gas separation membrane made of various polymers such as a polysulfone membrane, a silicon membrane, a polyamide membrane, and a polyimide membrane has been known. These known polymer gas separation membranes have been put to practical use in various fields, but if the mixed gas to be separated contains an organic solvent such as toluene or xylene, the membrane is deteriorated and deteriorated during use. have. Another drawback is that these polymer films are not suitable for use at high temperatures from the viewpoint of heat resistance.

To improve such disadvantages, for example, JP-A-60-179102 and JP-A-1-22
No. 1518 proposes a carbon film obtained by carbonizing an acrylic hollow fiber at a high temperature and a method for producing the same. Also, JP-A-4-11933 and JP-A-5-2
No. 2036 proposes a hollow fiber carbon membrane obtained by carbonizing or partially carbonizing an aromatic polyimide hollow fiber membrane, and a method for producing the same. However, in these carbon films, the gas permeation rate and permselectivity are not sufficient because the microstructure of the carbon material is not sufficiently controlled, and the strength is not sufficient at present. is there.

On the other hand, as a carbon material for gas separation, for example, as disclosed in Japanese Patent Publication No. 6-20546, a pellet-shaped molecular sieve carbon having a number of strictly controlled pores of 1 nm or less is used. Has been developed and has been put to practical use for separating oxygen and nitrogen in air, for example, by utilizing its selective adsorptivity.

[0005] In a carbon membrane as well, if pores can be formed in the carbon layer and the pore structure can be strictly controlled to impart molecular sieving characteristics, molecular sieving that was impossible with conventional membrane separation is possible. It is considered that membrane separation utilizing the action becomes possible. It is also important to increase the strength of the separation membrane and to impart excellent heat resistance.

[0006]

DISCLOSURE OF THE INVENTION The present inventors have intensively studied to solve the above-mentioned problems of the existing separation membrane and completed the present invention. It is to provide a sieving carbon film. Still another object of the present invention is to provide a molecular sieve carbon film having excellent permselectivity, high strength and good heat resistance. Yet another object of the present invention is to provide a method for producing the molecular sieve carbon film of the present invention. Still other objects and advantages of the present invention will become apparent from the following description.

[0007]

SUMMARY OF THE INVENTION The above objects and advantages of the present invention are as follows: a large number of porous ceramics having a porosity of 30 to 80% and a carbon content of 80% or more and a pore diameter of 1 nm or less. It is a molecular sieve carbon film characterized by having pores, and more preferably, the molecular sieve carbon film is a pheno-carbon film.
This is achieved by providing the above molecular sieve carbon film, which is a glassy carbon obtained by pyrolysis of a resin. Further, the molecular sieve carbon film of the present invention is prepared by applying a liquid thermosetting resin to the surface of a porous ceramic body to form a polymer film, and then forming the polymer film in a non-oxidizing atmosphere at a temperature of 550 to 550.
Manufactured by heat treatment in a temperature range of 1,100 ° C,
More preferably, it is produced by a method characterized in that the liquid thermosetting resin is a phenol resin.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The material of the ceramic porous body used in the present invention is, for example, alumina, silica, silica such as mullite or cordierite, alumina or a composition comprising silica, alumina, and other components. A thing etc. can be used conveniently. Further, other oxides such as zirconia and magnesia, carbides and nitrides such as silicon carbide and silicon nitride, or a mixture thereof can also be used.

[0009] The porosity of the porous ceramic body is usually 30
About 80%, preferably 35-70%, most preferably 40-60%. If the porosity is too small, the gas permeability is undesirably reduced. On the other hand, if the porosity is too large, the strength of the support decreases, which is not preferable. Further, the pore diameter of the ceramic porous body of the present invention,
Usually its diameter is 10-100,000 nm, preferably 100-1
0,000 nm, most preferably 500-5,000 nm. The ceramic porous body may be a composite porous body in which the pore diameter near the surface layer of the substrate is reduced by, for example, impregnating the surface of the porous body of the alumina substrate with silica sol.

[0010] The thickness and shape of the ceramic porous body of the present invention are not particularly limited. Since the ceramic porous body plays a role of a support for the carbon film formed thereon, the carbon film only needs to have a strength as a support capable of exhibiting practically sufficient strength. Further, in the case of the molecular sieve carbon membrane, it is necessary to increase the permeability of the component to be separated, so that it is not preferable that the ceramic porous body is too thick.
Further, the shape of the ceramic porous body is extremely important because it determines the shape of the molecular sieve carbon film formed thereon, but may be appropriately selected such as a flat plate shape or a cylindrical shape depending on the purpose.

The molecular sieve carbon film of the present invention has a porosity of 30 to
Closely adheres to 80% ceramic porous body surface, carbon content 80%
% Or more, a molecular sieve carbon film characterized by having a large number of pores having a pore diameter of 1 nm or less. 80% carbon content
In the following, excellent characteristics of carbon such as hydrophobicity and high heat resistance, chemical resistance and solvent resistance cannot be utilized. The carbon content is preferably at least 85%, most preferably at least 90%.

The molecular sieve carbon membrane of the present invention preferably has a bulk density of 0.7 to 1.5 g / cc, more preferably 0.8 to 1.5 g / cc.
1.3g / cc. In the molecular sieve carbon film of the present invention, most of the pores are distributed in a region having a diameter of 1 nm or less, and therefore, have a maximum value of the pore diameter distribution in this region. In the present invention, it is preferable that the pores have a strictly controlled sharp distribution, and it is particularly preferable that the pores are distributed in a range of about 0.3 to 0.7 nm in diameter. In the measurement of the pores of the nanometer order, the nitrogen adsorption method is usually used, and analysis using a t-plot is performed. In this case, the pore diameter that can be analyzed is 0.6 nm or more. It is. For the analysis of finer pores, a molecular probe method is usually used. That is, for example, oxygen (molecular diameter 0.28 nm), ethane (molecular diameter 0.40 nm),
In this method, the pore volume in a predetermined pore diameter range is calculated from the amount of adsorption of a molecule having a known molecular diameter such as isobutane (molecular diameter: 0.50 nm). The molecular sieve carbon film of the present invention has a pore volume obtained by oxygen molecule adsorption of 0.070 to 0.30 cc / g, preferably 0.090 to 0.25 cc / g, and most preferably 0.10 to 0.20 cc.
/ g.

The adsorption of oxygen molecules on the molecular sieve carbon membrane is considered to occur in the pore diameter range of about 0.28 nm to 1.5 nm. However, the adsorption amount of isobutane on the molecular sieve carbon membrane is relatively small. According to the results of t-plot analysis of nitrogen adsorption, most of the pores are considered to be in the range of 1 nm or less.

The thickness of the molecular sieve carbon film of the present invention is usually
It is 1 μm to 5 mm, preferably 2 μm to 1 mm, most preferably 5 to 500 μm.

When the molecular sieve carbon film of the present invention is obtained by thermal decomposition of a phenol resin, the carbon film has a high strength, a uniform distribution of fine pores, and a selective permeability. And particularly preferred.

The molecular sieve carbon film of the present invention is prepared by applying a liquid thermosetting resin to the surface of a porous ceramic material to form a polymer film, and then heat-treating the film in a non-oxidizing atmosphere at a temperature of 550 to 1100 ° C. Can be manufactured.

In the present invention, a pretreatment such as immersing the ceramic porous body made of the above-mentioned material in a solution of silica sol, alumina sol or the like and then drying it, if necessary,
After adjusting the pores of the support, a liquid thermosetting resin may be applied. The solvent for the silica sol and the alumina sol is not particularly limited, but isopranol, ethylene glycol, water and the like can be suitably used. Also,
The content of ceramic particles such as silica and alumina is usually 10 to 40%, preferably 20 to 35%.

In the present invention, the liquid thermosetting resin is applied to the surface of the ceramic porous body by, for example, applying the ceramic porous body to a solution in which the thermosetting resin is dissolved in an organic solvent or an aqueous solution of the thermosetting resin. It is good to soak. Also,
The resin film can also be formed by applying a thermosetting resin solution thinly and uniformly with a spray gun or the like. The concentration of the liquid resin may be appropriately selected according to the coating method to be used, the target film pressure, and the like.

Examples of the thermosetting resin used in the present invention include phenol resin, melamine resin, urea resin, and furan resin. Phenol resins can be roughly classified into
And novolak resins and other special phenolic resins and modified products. A melamine resin is a colorless and transparent water-soluble resin obtained by reacting melamine with an aldehyde, usually formaldehyde, in the presence of a basic catalyst, and shows thermosetting properties. The urea resin is a colorless and transparent water-soluble resin obtained by reacting urea with formaldehyde in the presence of an acid catalyst or a basic catalyst. The furan resin is an initial condensate of furfuryl alcohol, a furfural resin or a modified resin thereof, and the initial condensate of furfuryl alcohol is soluble in alcohol if it has a low viscosity. And even those having a high viscosity are soluble in solvents such as ethyl acetate and acetone.

As described above, the thermosetting resin used in the present invention is easy to handle at the time of production, has a high carbonization yield, easily controls pores, and has a carbon film. Phenol resins are preferred in terms of high strength and the like, and the following granular phenol resins are particularly preferred.

The granular phenolic resin applied to the present invention is disclosed in JP-B-62-3021 or JP-B-62-30211.
No. 30213, which discloses a reactive granular resin containing a condensate of a phenol and an aldehyde as a main component, and (A) spherical primary particles having a particle size of 0.1 to 150 μm; Containing the secondary aggregates and (B)
At least 50% by weight of the whole is a size that can pass through a 100-Tyler mesh sieve, and (C) methanol solubility is 50% by weight or more, and (D) a value determined by liquid chromatography as free The phenol content is 500 ppm or less. It is characterized by the following.

Most of the granular phenolic resin has a particle size.
0.1 to 150 μm primary particles or secondary aggregates thereof, at least 50% by weight, preferably 90% by weight of the whole
It is large enough to pass through a 100 Tyler mesh sieve, but distributed to have a peak between 1 and 50 μm.

The particulate phenol resin applied to the present invention has a free phenol content of 500 ppm or less, substantially 100 ppm or less, as measured by liquid chromatography. In addition, as measured by GPC (gel permeation chromatography), it is a polymer having a weight average molecular weight in terms of polystyrene of 1000 or more, but substantially melts or fuses when held at a temperature of 100 ° C. for 5 minutes. Things.

The particulate phenolic resin applied to the present invention has a methanol solubility represented by the following formula 1 of 50% by weight when heated and refluxed in substantially anhydrous methanol.
Or more, preferably 70% by weight or more, most preferably 90% by weight or more. When the methanol solubility is less than 50% by weight, it is difficult to prepare a phenol resin solution using an organic solvent, and therefore, it is impossible to form a resin film on a ceramic support.

[0025]

S = {(W ₀ −W ₁ ) / W ₀ } × 100 W ₀ : weight of the resin used (g) W ₁ : weight of the resin remaining after heating and refluxing (g) S: the weight of the resin Resin methanol solubility (wt%)

In the present invention, the solvent for dissolving the thermosetting resin is not particularly limited as long as the thermosetting resin resin such as methanol, acetone and tetrahydrofuran can be uniformly dissolved. Some thermosetting resins become water-soluble by adjusting the molecular weight. In such a case, an aqueous solution can be used.

In the present invention, a thermosetting resin film is formed by immersing the ceramic support in a thermosetting resin solution and then drying it under appropriate conditions, removing the solvent and curing the resin.

The thus obtained thermosetting resin film on the ceramic support is carbonized at 550 to 1,100 ° C. in a non-oxidizing atmosphere to obtain the molecular sieve carbon film of the present invention. The carbonization temperature is preferably between 600 and 950 ° C, most preferably between 700 and 900 ° C. If the carbonization temperature is higher than 1,100 ° C., the pores of the molecular sieve carbon film shrink due to heat shrinkage, and the transmittance is undesirably reduced. If the temperature is lower than 550 ° C., carbonization is not sufficient, the selective overactivity is low, and the heat resistance, chemical resistance and the like are not preferable.

The non-oxidizing atmosphere in this case is, for example, an atmosphere of nitrogen, argon, helium or the like, and a case containing a small amount of a weakly oxidizing gas such as carbon dioxide or water vapor is also included in the scope of the present invention. .

The rate of temperature increase until reaching the maximum treatment temperature in the carbonization step is not particularly limited, but is preferably
The temperature is 5 to 300 ° C / H, most preferably 30 to 180 ° C / H. The atmosphere at the time of carbonization, the temperature rise rate, the maximum temperature, the holding time at the maximum temperature, etc. depend on the type and pore structure of the ceramic support, the type and properties of the thermosetting resin, the pore structure of the target carbon film, etc. The optimal conditions are selected in consideration of the above. In general, it is preferable to raise the temperature to a relatively high temperature in order to form finer pores.However, if the maximum temperature is too high, the pores become too fine, and the pore volume also decreases, so that gas permeability is low. Is undesirably reduced.

The molecular sieve carbon film obtained by the present invention is usually in the form of a flat film or a cylinder, and adheres to the surface of a ceramic porous body having a porosity of 30 to 80%, and has a carbon content of 80% or more. Thus, there are many pores having a pore diameter of 1 nm or less.

[0032]

The molecular sieve carbon film of the present invention has a porosity of 30.
~ 80% of ceramic porous body surface, carbon content
Since there are many pores of 80% or more and pore diameter of 1 nm or less, it can be used as a separation material to efficiently separate and purify only components with a specific molecular diameter from various mixed gases with different molecular diameters. it can. Moreover, it has excellent heat resistance and chemical resistance and high strength, and can be effectively used for separating various hydrocarbons and corrosive gases. Specifically, for example, a mixed gas of nitrogen and oxygen, a mixed gas of methane and hydrogen, a mixture of hydrocarbon isomers such as xylene isomers, butane isomers, and butene isomers, a mixture of propane and propylene, and a mixture of benzene and cyclohexane It can be used for the separation of a mixture, a mixed gas of hydrogen and carbon monoxide, a mixed gas of nitrogen and carbon dioxide, a mixed gas of argon and oxygen, and is extremely useful in practical use.

[0033]

EXAMPLES As to the gas permeability of a separation membrane, a permeability coefficient P or a permeation speed R defined by the following formulas 2 and 3 is usually used as an index. The permeability of various gases of the separation membrane can be represented by the magnitude of the permeability coefficient or the permeability speed. In the present invention, it was defined separation factor R ₁ / R ₂ as an indicator of the separation performance of the gas mixture.

[0034]

## EQU2 ## Permeability coefficient P = QL / (p ₁ -p ₂ ) At

Equation 3] permeation rate R = P / L = Q / (p 1 -p 2) At Q: Gas permeation amount ^{[cm 3] (0 ℃,} 1 atm) p _1: the high-pressure side gas pressure [cmHg] p ₂ : Low pressure side gas pressure [cmHg] A: Film area [cm ² ] L: Film thickness [cm] t: Time [sec]

The physical properties of the present invention were measured as follows.

1. Measurement of pore volume, pore diameter distribution and porosity The pore volume and pore diameter distribution of the molecular sieve carbon membrane and the ceramic support of the present invention are as follows. It was measured by a press-fitting method (Poseiza 9810, manufactured by Shimadzu). Also, the pore diameter is 100 mm
The following is the nitrogen adsorption and adsorption method (manufactured by Nippon Bell, Bellsop 28)
Was measured by Analysis of measurement results requires a pore diameter of 2.0
The Dolimore-Heal method was applied in the range of 20 nm, and the Micropore Analysis method was applied in the range below 2.0 nm. In calculating the pore volume per unit weight of the carbon membrane having a pore diameter of 1 nm or less, the pore volume of the ceramic support was measured in advance, and the pore volume of the ceramic support used in the present invention was 1 nm or less. It was confirmed that it was substantially 0. From this, the measured pore volume with a pore diameter of 1 nm or less was attributed to the pore volume of the molecular sieve carbon membrane on the ceramic support. After the nitrogen gas adsorption measurement was completed, the sample was calcined at 700 ° C in air to remove the carbon film. Was determined. Furthermore,
By measuring the adsorption amounts of oxygen (pore diameter 0.28 nm), ethane (0.40 nm), and isobutane (0.5 nm) at 25 ° C., the pore volume at which these gases can be adsorbed was determined. The porosity of the ceramic support of the present invention was determined by a mercury porosimetry.

2. Measurement of carbon content The carbon content was measured with an element analyzer (CHN CORDER, TM-3 type) manufactured by Yanagimoto Seisakusho.

3. Measurement of gas permeation rate The gas permeation rate of the molecular sieve carbon membrane was measured by a gas permeability measuring apparatus shown in FIG. That is, length 10
A sample 6 in the form of a tubular membrane having a diameter of 0 mm and an outer diameter of 10 mm was set in a permeation cell 5 in a thermostat 7, and a pure gas or a mixed gas was supplied from a gas cylinder 1. At that time, the gas pressure is 2 to 6 at
m, 1 atm on the downstream side, and the gas flow rate was measured by the flow meter 18. The temperature set in the thermostat 7 was kept at 35 ° C. Quantification of the separated gas flowing out of the upstream outlet pipe 8 and the downstream outlet pipe 9 was performed, respectively. Hereinafter, specific examples will be described.

Example 1 A particulate phenol resin having an average particle diameter of 20 μm (manufactured by Kanebo: Bellpar S-895) was dissolved in methanol to prepare a 20% by weight methanol solution. This solution has an outer diameter of 10 mm, a thickness of 1 mm, a length of 100 mm, and an average pore diameter of 1 μm.
m, 35% porosity cylindrical porous alumina tube (Mitsui grinding wheel: Multi-Polaron) suspended by thread, 200mm / min
The resin was immersed in the phenol resin solution at a constant speed, and pulled up again at the same speed. After drying the sample at 80 ° C. for 5 hours,
The above operation was repeated, and the phenol resin film was applied four times. The same operation was repeated to produce five samples (Sample 1,
2, 3, 4, 5).

Each of the immersed and dried samples is placed in an electric furnace, heated to a predetermined temperature in a nitrogen gas atmosphere at a heating rate of 60 ° C./h, kept at the temperature for 1 hour, and then cooled. Then, a carbon film was produced.

Using the sample prepared as described above,
The permeation rates of various gases were measured. Table 1 shows the results. Table 2 shows the results of calculating the gas separation coefficient from the experimental results in Table 1. From Tables 1 and 2, it can be seen that the sample 1 carbonized at 520 ° C. has a high gas permeation rate but little separation performance. In samples 2, 3, and 4, it can be seen that the gas permeation rate decreases as the carbonization temperature increases, but the permeation rate ratio increases. It can be seen that the gas permeation rate of 1,200 ° C carbonized sample 5 was too small and was not suitable as a separation membrane.

(Example 2) Outer diameter 10 mm, thickness 1 m, length 100 m
m, average pore diameter 1μm, porosity 35% cylindrical porous alumina tube (manufactured by Mitsui Grinding Stone: Multipore) is immersed in a silica sol solution (Nissan Chemical Industries: Sno-Tex EG-ST) for 30 minutes, and then pulled up Dried in air. Next, a particulate phenol resin having an average particle diameter of 20 μm (manufactured by Kanebo: Bellpar S-895) was dissolved in methanol to prepare a 20% by weight methanol solution. In this solution, a silica-coated ceramic support or a silica-coated ceramic support was immersed in a phenol resin solution in the same manner as in Experiment 1, and pulled up again at the same speed. After the sample was dried at 80 ° C. for 5 hours, the above operation was repeated, and a phenol resin film was applied a predetermined number of times. The same operation was repeated to produce four samples (samples 8, 9, 10, and 11).

Each of the immersed and dried samples was placed in an electric furnace, heated to 600 ° C. at a rate of 60 ° C./h in a nitrogen gas atmosphere, kept at that temperature for 1 hour, and then cooled. A carbon film was produced. The carbon content of the carbon film was 88.0 for all samples.
It was in the range of ~ 89.0%.

Using the sample prepared as described above,
Table 3 shows the results of measuring the permeation rates of various gases,
Table 4 shows the value of the separation coefficient R ₁ / R ₂ calculated from the results in Table 3.
Shown in A sample with one film formation has a high gas permeation rate and has almost no separation performance. As the number of film formations increased, the gas permeability decreased and the separation performance improved. In particular, the permeation rate of a gas having a large molecular diameter was greatly reduced. In sample 10, O ₂ / N ₂ , CO ₂ /
The separation factor for N ₂ was 5.7 and 19. In sample 11,
The separation coefficient of C ₃ H ₆ / C ₃ H ₈ was as large as 134.

Example 3 Using the sample 10 of Example 2, CO ₂
Table 5 shows the results of a permeation test of a mixed gas of 19.1 mol% and 80.91 mol% of N ₂ . As shown in Table 5, the pressure on the gas supply side was set to three conditions of 2, 4, and 6 atmospheres.
It was a constant value of 1 atm.

Table 5 shows that Sample 10 showed good values for the separation coefficients of nitrogen and carbon dioxide within the range of the pressures tested, indicating that separation was possible.

[Brief description of the drawings]

FIG. 1 Gas permeability measuring device

[Explanation of symbols]

 1. Gas cylinder 2. Pressure regulating valve 3. Pressure gauge 4. Two-way cock 1 5. 5. Transmission cell Sample 7. Constant temperature bath 8. 8. Upstream outlet piping Downstream outlet piping 10. Three-way cock 1 11. Three-way cock 2 12. Three-way cock 3 13. Three-way cock 4 14. Two-way cock 2 15. Two-way cock 3 16. Pressure regulating valve 2 17. Vacuum pump 18. Gas chromatograph

[Table 1]

[Table 2]

[Table 3]

[Table 4]

[Table 5]

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[Procedure amendment]

[Submission date] December 4, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 7

[Correction method] Change

[Correction contents]

Claims (8)

[Claims] 1. A molecular sieve carbon which is in close contact with the surface of a ceramic porous body having a porosity of 30 to 80% and has a large number of pores having a carbon content of 80% or more and a pore diameter of 1 nm or less. film. 2. The molecular sieve carbon film according to claim 1, wherein the molecular sieve carbon film is made of glassy carbon obtained by thermal decomposition of a phenol resin. 3. The molecular sieve carbon film according to claim 1, wherein a coating layer of silica sol, alumina sol or the like is formed on the surface of the ceramic porous body, and a molecular sieve carbon film adheres to the surface. 4. A molecular sieve carbon film according to claim 2, wherein a coating layer of silica sol, alumina sol or the like is formed on the surface of the ceramic porous body, and a molecular sieve carbon film adhered to the surface. 5. A molecule characterized in that a liquid thermosetting resin is applied to the surface of a ceramic porous body to form a polymer film, and then heat-treated in a non-oxidizing atmosphere at a temperature range of 550 to 1,100 ° C. Manufacturing method of sieved carbon film. 6. The method according to claim 5, wherein the liquid thermosetting resin is a phenol resin. 7. The molecular sieve carbon according to claim 5, wherein a coating layer of silica sol, alumina sol or the like is formed on the surface of the ceramic porous body, and then a phenol resin is applied to the surface. Manufacturing method of membrane. 8. The molecular sieve carbon according to claim 6, wherein a coating layer of silica sol, alumina sol or the like is formed on the surface of the ceramic porous body, and then a phenol resin is applied to the surface. Manufacturing method of membrane.