JPH10330173A - Production of carbon molecular sieve - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a carbon molecular sieve only through calcination without a special material and/or a complicated treatment, by carbonizing an aromatic polyimide resin. SOLUTION: The aromatic polyimide resin as the material for this molecular sieve is preferably an aromatic polyimide resin in which one of an aromatic carboxylic acid or an aromatic diamine contains >=1 wt.% of an aliphatic carbon based on the total numbers of carbons. Any apparatuses capable of calcination in an inert atmosphere as removing generated gases are useful as the apparatus for calcination (carbonization) of the material. It is preferable that the increasing speed of the calcination temperature is <=10 deg.C/min. and the calcination temperature is >=800 deg.C. The thus produced molecular sieve must have the maximum absorption volume ratio of carbon dioxide to methane gas of >=3 and the equilibrium absorption volume ratio of carbon dioxide to methane gas at 0 deg.C under the atmospheric pressure of >=4 so as to obtain the pore diameter and its distribution both suitable for separation of carbon dioxide and methane gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing molecular sieve carbon, and more particularly, to an industrial method for producing molecular sieve carbon having a pore diameter and a pore diameter distribution suitable for separating carbon dioxide gas and methane gas. The present invention relates to an advantageous production method.

[0002]

2. Description of the Related Art Conventionally, zeolite and carbon have been known as adsorbents having a molecular sieving effect of separating according to molecular diameter, and these are used for gas separation and purification. By the way, zeolite-based molecular sieves are inferior in heat resistance and chemical resistance, and have a drawback that they do not exhibit a molecular sieve effect in the presence of a polar substance because of their strong selective adsorption to polar molecules such as water. ing. In contrast, molecular sieve carbon is excellent in heat resistance and chemical resistance, and can exert a molecular sieve effect regardless of polarity.

[0003] The molecular sieve carbon is usually activated carbon 1-3
It is characterized by having a small and narrow pore size distribution of 0.3 to 0.7 nm while having micropores of nm. Therefore, in industrial production of molecular sieve carbon, control of the pore size is most important. Since it is difficult to control the size and distribution of the micropores in accordance with the target gas, a method of controlling the pore size is to obtain the target pore size distribution by combining various raw materials and additives. Various attempts have been made.

[0004] By the way, a gas having a molecular diameter of less than carbon dioxide, such as an exhaust gas or a landfill gas, is prepared from a mixed gas composed of carbon dioxide and a gas having a molecular diameter of less than that and a gas having a molecular diameter of more than methane. In order to efficiently separate an organic gas having a high utility value after recovery, such as a gas having a molecular diameter equal to or larger than methane gas, by adsorption and removal, the molecular diameter of carbon dioxide gas is 0.33 nm and the molecular diameter of methane gas is 0. A molecular sieving carbon having an average pore size of between .38 nm and a narrow pore size distribution, and capable of efficiently separating carbon dioxide gas or a gas having a molecular size smaller than that from a gas having a molecular size exceeding carbon dioxide gas is required. It is. However, such molecular sieve carbon has hardly been achieved by conventional techniques as described below. Here, the molecular diameter indicates the minimum diameter of the molecule.

JP-A-5-319813 discloses that a phenol resin or a raw material thereof is added with a modifier such as pitch and carbonized under an inert atmosphere so that the average pore diameter obtained by a molecular probe method is about 0.3. A method for producing molecular sieve carbon having a 4 nm and a sharp pore size distribution is disclosed. However, such molecular sieve carbon is not suitable for separating carbon dioxide gas having a molecular diameter of 0.33 nm and methane having a molecular diameter of 0.38 nm by a molecular sieve effect. Here, the molecular probe method is to apply the Dubinin-Astakhov equation to the adsorption isotherm of a plurality of gases having different molecular diameters to determine the ultimate adsorption volume of each gas. This is a measurement method for determining the pore size distribution as corresponding to the above.

Japanese Patent Publication No. 3-72006 and Japanese Patent Publication No. 4-1288 describe that a synthetic resin composite such as a polyvinyl alcohol-based resin, a melamine resin, and a phenol resin is used as a raw material and carbonized and activated at 500 to 700 ° C. A method for producing molecular sieve carbon is disclosed. However, such molecular sieving carbon has a pore diameter distribution having a maximum value of 1 nm or less, but has a wide distribution of pore diameters of up to 20 nm, so that it can be used for separation utilizing an adsorption rate. It is not suitable for separation by molecular diameter.

[0007] JP-A-3-40912 discloses that carbonaceous mesophase is carbonized and activated at 500 to 1100 ° C.
Although a method for producing molecular sieve carbon is disclosed, the same applies to such molecular sieve carbon.

[0008] JP-A-7-81915 and JP-A-6-144818 disclose spinning pitch, making it infusible,
A method for producing powdered or fibrous molecular sieve carbon which is calcined and activated is disclosed. However, such molecular sieve carbon has a pore size distribution of 0.28 nm or more and 0.4 or more.
Although it is within the range of less than 3 nm, it is not a sufficiently narrow range, so that it is not suitable for separating gas having a molecular diameter of carbon dioxide gas or less and gas having a molecular diameter of methane or more.

Japanese Unexamined Patent Publication (Kokai) No. 59-230638 discloses a process for producing molecular sieve carbon having a pore diameter of 0.4 to 0.5 nm, characterized by impregnating a raw non-coking coal with a water-soluble organic substance. A method is disclosed. However, such a molecular sieve carbon is not suitable for separating gas having a molecular diameter equal to or less than carbon dioxide gas from gas having a molecular diameter equal to or more than methane gas because the average pore diameter is too large.

Japanese Unexamined Patent Publication (Kokai) No. 63-139909 discloses molecular sieve carbon having a pore size of about 0.5 nm and a narrow pore size distribution, using a vinylidene chloride copolymer as a raw material. . However, such a molecular sieve carbon is not suitable for separating gas having a molecular diameter equal to or less than carbon dioxide gas from gas having a molecular diameter equal to or more than methane gas because the average pore diameter is too large.

Japanese Patent Application Laid-Open No. 1-221518 discloses that a high-molecular polymer, preferably a polyacrylonitrile-based polymer is spun into a hollow fiber and subjected to sintering and activation after cross-linking and oxidation treatment for obtaining a heat-resistant structure. Further, there is disclosed a method for producing molecular sieve carbon having a hollow carbon membrane fiber shape, which is fired at 900 to 1200 ° C. However, since such molecular sieve carbon has a pore diameter that adsorbs methanol, it is estimated that methane and carbon dioxide gas are also easily adsorbed,
Therefore, it is not suitable for separating both gases.

JP-A-50-161485 discloses that a waste of Saran, which is a copolymer of poly (vinylidene chloride) and vinyl chloride, is heat-distilled, and further a sintering agent such as coal tar pitch and an organic substance such as Avicel. And then calcining at 400 to 900 ° C. after the addition of the granulating agent. And in the case of this manufacturing method,
It is possible to obtain molecular sieve carbon that adsorbs carbon dioxide gas but does not adsorb methane, but requires special raw materials and complicated processing.

[0013]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a molecule which can be produced simply by firing without the need for special raw materials or complicated processing. Most of the pores have a molecular diameter of 0.33 nm for carbon dioxide and a molecular diameter of methane for efficient separation of a gas having a molecular diameter of less than carbon dioxide and a gas having a molecular diameter of greater than methane. It is an object of the present invention to provide a method for producing molecular sieve carbon having a narrow pore size distribution such as between 0.38 nm.

[0014]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that the above object can be easily achieved by using a specific polymer compound as a precursor of molecular sieve carbon. Was obtained. The present invention has been achieved based on the above findings, and the gist of the present invention resides in a method for producing molecular sieve carbon characterized by carbonizing an aromatic polyimide resin.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
In the method for producing molecular sieve carbon according to the present invention, an aromatic polyimide resin is used as a raw material. By using such a specific raw material, an industrially advantageous production method of merely firing is adopted, for example, a molecular sieve carbon having a pore diameter and a pore diameter distribution suitable for separating carbon dioxide gas and methane gas. Can be obtained.

The aromatic polyimide resin is usually obtained from an aromatic carboxylic acid and an aromatic diamine, and a typical example thereof is a condensation type polyimide comprising pyromellitic anhydride and diaminodiphenyl ether ("Vespel" manufactured by DuPont). ) And polyetherimide ("Ultem" of GE, USA). In the present invention, an aromatic polyimide in which either the aromatic carboxylic acid or the aromatic diamine contains 1% or more of aliphatic carbon with respect to the total number of carbon atoms is preferable.

A commercially available aromatic polyimide resin as described above is, for example, pyromellitic dianhydride / 4,4-diaminodiphenyl ether / diaminodimethylbiphenyl in a molar ratio of 2: 1: 1. A polymerized polyimide film (“NOVAX” manufactured by Mitsubishi Chemical Corporation) may be used. In such a polyimide, diaminodimethyl biphenyl contains 4.3% of aliphatic carbon with respect to the total carbon number. In addition, 4,4 '-[2,2-bis (4-
[Oxyphenyl) propane] diphthalic dianhydride / phenylene-diamine in a molar ratio of 1: 1 and a polyetherimide film (“Sumilite FS-1400” manufactured by Sumitomo Bakelite Co., Ltd.). In such a polyetherimide, 4,4 '-[2,2-bis (4-oxyphenyl) propane] diphthalic dianhydride contains 8.1% of aliphatic carbon with respect to the total number of carbon atoms. . The film-like molecular sieve obtained from the above-mentioned film is usually used after being pulverized, but its use as a film-like molecular sieve is also expected.

In the production method according to the present invention, the apparatus used for calcining (carbonizing) the raw material is an inert atmosphere,
Any device can be used as long as it can be fired while removing gas generated from the raw material polymer compound. For example, raw material pellets are filled in a quartz glass boat, and a siliconite furnace is used.
The above-mentioned molecular sieve carbon can be produced only by raising the temperature to 000 ° C. and holding for 60 minutes.

In the above calcination, the heating rate is not particularly limited. However, if the heating rate is too high, the pore diameter becomes large when decomposed gas is generated, so that the separation ability between carbon dioxide gas and methane gas is increased. It is difficult to obtain a molecular sieved carbon having a sharp pore size distribution excellent in carbon. Therefore,
The heating rate is preferably 10 ° C./min or less, more preferably 1 to 5 ° C./min. The firing temperature is not particularly limited as long as carbonization can be achieved, but if the firing temperature is too low, the pore size distribution of the molecular sieve carbon is generally widened, and the ability to separate carbon dioxide and methane is reduced. .
Therefore, the firing temperature is preferably 800 ° C. or higher, more preferably 900 ° C. or higher.

According to the production method of the present invention, molecular sieve carbon having novel pore distribution characteristics can be obtained. That is, according to the present invention, since the pore diameter and the pore diameter distribution are appropriate for separating carbon dioxide gas and methane gas, the ultimate adsorption volume of carbon dioxide gas (Woc: ml / g) and the ultimate adsorption volume of methane gas (Wom: ml / g) g) (Woc / Wom) is 3 or more, and the equilibrium adsorption volume (W
ac: ml / g) and equilibrium adsorption volume of methane gas (Wam: ml / g)
A novel molecular sieve carbon having a ratio (Wac / Wam) of 4 or more to g) can be obtained. The above Woc / Wom is preferably 3 or more, more preferably 6 or more, and Wac / Wam
Is preferably 4 or more, more preferably 8 or more.

Incidentally, the performance evaluation of molecular sieve carbon is as follows.
It can be performed by measuring an isothermal adsorption curve. When the component gas required to be separated by adsorption from the mixed gas is a carbon dioxide gas or less, that is, carbon dioxide, oxygen, nitrogen, helium, or the like having a molecular diameter of 0.33 nm or less, the largest molecular diameter is obtained. It is sufficient to measure the carbon dioxide adsorption capacity. The gas component required to be separated without being adsorbed from the mixed gas has a molecular diameter equal to or greater than methane, that is, a molecular component of 0.1 or more.
In the case of an organic gas such as methane, ethane, ethylene, and propane having a molecular diameter of 38 nm or more, it is sufficient to measure the adsorption capacity of methane gas having the smallest molecular diameter. And
The ratio of the obtained adsorption capacity of carbon dioxide to the adsorption capacity of methane represents the separation performance of adsorbing gas having a molecular diameter equal to or smaller than carbon dioxide in the mixed gas and not adsorbing gas having a molecular diameter equal to or larger than methane.

The above pore distribution characteristics can be determined, for example, in the following manner. That is, first, an adsorption capacity measuring device (for example, “Omni Soap 100C” manufactured by Coulter Inc.)
X ") and the adsorption capacities of carbon dioxide and methane at 0 ° C. are measured by a constant volume method. That is, gas is introduced stepwise from a vacuum into a sample cell filled with a sample,
At each stage, the relationship between the pressure (P) when the adsorption reaches equilibrium and the equilibrium adsorption volume (W) obtained by converting the adsorption capacity into a liquid volume is measured. When the gas pressure reaches the atmospheric pressure at the end of the measurement, the equilibrium adsorption volumes (Wac: ml / g) and (Wam: ml / g) of carbon dioxide gas and methane gas at 0 ° C. and atmospheric pressure are measured.

Next, the following Dubinin-Astakov equation, which is said to be suitable for the analysis of micropores of 1 nm or less, is applied to the results obtained as described above.
When each of the above gases reaches a saturated vapor pressure at 0 ° C., the volume that the gas can adsorb, that is, the ultimate adsorption volume (Woc: ml / g), which is the total pore volume that the gas can adsorb, and ( (Wom: ml / g).

[0024]

W = Wo exp (-(RTln (Po / P) / E) ⁿ )

In the above equation, R is a gas constant, T is a temperature, Po is a saturated vapor pressure at a predetermined temperature, E is a characteristic energy of adsorption, and n is a constant determined by the type of adsorption. Is 2.

For example, Woc / Wom = 15 indicates that the pore volume of carbon dioxide gas having a molecular diameter of 0.33 nm or more is 15 times the pore volume of methane gas having a molecular diameter of 0.38 nm or more. , Meaning that most pores have an extremely narrow pore diameter distribution in the range of 0.33 to 0.38 nm. Wac / Wam = 23 means that the pore volume at which carbon dioxide gas can be adsorbed at atmospheric pressure 0 ° C. is 23 times the pore volume at which methane gas can be adsorbed at atmospheric pressure 0 ° C.

The above-mentioned molecular sieve carbon obtained by the production method according to the present invention is obtained by converting a mixed gas composed of carbon dioxide and organic gas such as exhaust gas and landfill gas into carbon dioxide and a gas having a molecular diameter smaller than that. It is useful for separating organic gas having a molecular diameter exceeding carbon dioxide, and is expected to have great potential in the future for recovery of carbon dioxide that causes global warming and recovery of organic gas that can be effectively used.

[0028]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the present invention. In addition, the measurement of the adsorption capacity of molecular sieve carbon was performed by the method described above. That is, a gas is introduced stepwise from a vacuum into a sample cell filled with a sample, and the pressure p when the adsorption reaches an equilibrium in each step.
And the equilibrium adsorption volume W obtained by converting the adsorbed gas into a liquid, and the equilibrium adsorption volume (Wa) at atmospheric pressure and Dubi
The ultimate adsorption volume (Wo) in the nin-Astakov equation was determined.

Example 1 Pyromellitic dianhydride / 4,4-diaminodiphenyl ether / diaminodimethylbiphenyl in a molar ratio of 2: 1:
A 76 μm thick film (“NOVAX” manufactured by Mitsubishi Chemical Corporation) made of the polyimide polymerized in 1 was used as a raw material. In such a polyimide, diaminodimethyl biphenyl contains 4.3% of aliphatic carbon with respect to the total carbon number.

A quartz glass boat is filled with the above-mentioned raw materials, and is used in a siliconite furnace at 9 ° C./mi under an Ar atmosphere.
After the temperature was raised to 900 ° C. at a heating rate of n, it was carbonized by holding for 30 minutes to obtain molecular sieve carbon. Table 1 shows the measurement results of the adsorption volume. The molecular sieve carbon obtained in this example had characteristics of Woc / Wom = 5.4 and Wac / Wam = 7.8, and the separation performance of carbon dioxide gas and methane gas was extremely good.

Example 2 Thickness of polyetherimide prepared by polymerizing 4,4 '-[2,2-bis (4-oxyphenyl) propane] diphthalic dianhydride / phenylene-diamine at a molar ratio of 1: 1 A 25 μm film (“Sumilite FS-1400” manufactured by Sumitomo Bakelite Co., Ltd.) was used as a raw material. Such polyetherimides are 4,4 '-[2,2-bis (4
[Oxyphenyl) propane] diphthalic dianhydride contains 8.1% of aliphatic carbons relative to the total carbon number. Then, in the same manner as in Example 1, the temperature was raised to 950 ° C. to carbonize. Table 1 shows the measurement results of the adsorption volume. The molecular sieve carbon obtained in this example was Woc / Wom = 9.9, Wac
/Wam=15.3, and the separation performance of carbon dioxide gas and methane gas was extremely good.

[0032]

[Table 1]

[0033]

According to the present invention described above, a gas having a molecular diameter of carbon dioxide or less can be selectively produced by an easy method of firing (carbonizing) in an inert atmosphere without performing complicated processing. It is possible to produce molecular sieve carbon having an extremely narrow pore size distribution that adsorbs and does not adsorb organic gas having a molecular diameter greater than methane.

Claims (4)

[Claims] 1. A method for producing molecular sieve carbon, comprising carbonizing an aromatic polyimide resin. 2. The aromatic polyimide resin according to claim 1, wherein any one of aromatic carboxylic acid and aromatic diamine contains 1% or more of aliphatic carbon with respect to the total number of carbon atoms. Production method. 3. The method according to claim 1, wherein the carbonization is performed by firing at a temperature rising rate of 10 ° C./min or less to 800 ° C. or more in an inert atmosphere. 4. The molecular sieve carbon, wherein the ratio of the ultimate adsorption volume of carbon dioxide gas to the ultimate adsorption volume of methane gas is 3 or more,
The ratio of the equilibrium adsorption volume of carbon dioxide to the equilibrium adsorption volume of methane gas at 0 ° C. atmospheric pressure is 4 or more.
The production method according to any one of the above.