JPH02160923A - Porous carbon fiber and production thereof - Google Patents

Abstract

PURPOSE:To provide the subject fiber having the fine pores of improved radii in the surface layer thereof and useful for adsorbing and separating various substances, etc., by spinning a mixture of an acrylonitrile copolymer and a thermally decomposable copolymer, drawing the prepared fiber and subsequently subjecting the drawn fiber to a flame-resisting treatment, a thermal decomposition treatment and an activation treatment under specific conditions. CONSTITUTION:A mixture of an acrylonitrile copolymer containing >=90mol.% of acrylonitrile and a thermally decomposable copolymer decomposing at a temperature of <=600 deg.C into lower mol.wt. compounds is spun and drawn into an acrylonitrile blend fiber, which is subjected to a fire-resisting treatment in an oxidating gas atmosphere of 200-300 deg.C. The treated fiber is further decomposed in an inert gas atmosphere and subsequently subjected to an activation treatment in an atmosphere of the mixture of an inert gas and an activation gas at 400-1200 deg.C to provide the objective fiber comprising a porous carbon fiber containing >=75wt.% of carbon, having opened fine holes having plural peaks in the radius distribution of the opened fine pores and especially having at least one peak in 10-50Angstrom and 50-1000Angstrom , respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to porous carbon fibers with improved pore diameters on the surface layer.

"Conventional technology" In recent years, porous carbon fiber has been used as an adsorbent material that has high gas and vapor adsorption performance and excellent processability, and has been used for adsorption and recovery of trace organic gases, adsorption and removal of malodorous components, catalytic decomposition ability, and organic electrolyte electrodes. It is widely used as a new functional material.

Porous carbon fibers include those made from organic fibers such as cellulose fibers, polyacrylonitrile fibers, polyvinyl alcohol fibers, and phenol fibers, as well as those made from pitch-based materials. Melting treatment (
In the carbonization process, it is activated in an activation gas such as steam, carbon dioxide, or air (porous treatment).
has been manufactured. The value of 13 E 'I' surface area varies depending on the raw material, but it is approximately 500 to 3000 m2/
in the range of g. These porous carbon fibers each have a porous structure with a peak pore distribution having a pore radius of 50 Å or less.

"Problem to be solved by the invention" However, conventional porous carbon fibers have a pore radius of 50 Å.
Because of its small molecular weight, it has a problem that although it has a relatively small molecular weight, it has excellent adsorption properties from the gas phase, but it is not suitable for adsorbing organic substances, polymers, etc. with a relatively large molecular weight dissolved in the liquid phase.

The present invention was made in view of the above circumstances, and is a porous material suitable for adsorption and separation of relatively large molecular weight substances dissolved in the liquid phase without impairing the adsorption performance of relatively small molecular weight substances from the gas phase. The purpose is to provide carbon fiber.

"Means for Solving the Problems" The present invention provides a porous carbon fiber having a carbon content of 75% by weight or more, which has a plurality of radii of pores formed on the surface of the porous carbon fiber. To solve this problem, the porous carbon fiber has at least one peak in the range of 10 Å or more and 50 Å or less and at least one peak in the range of more than 50 Å and 1000 Å or less among the plurality of peaks. It was used as a means of

"Effect" By having a distribution peak in the range of pore radius of 10 Å to 50 Å, substances with relatively small molecular weights from the gas phase can be adsorbed and separated, and the distribution peak is in the range of more than 50 Å and 1000 Å or less. By having this, substances with relatively large molecular weights can be adsorbed and separated from the liquid phase.

Hereinafter, the porous carbon fiber of the present invention will be explained in detail.

As mentioned above, the porous carbon fiber of the present invention has a carbon content of 75% by weight or more, and a distribution of radii of pores opened in the surface layer in a range of 10 Å to 50 Å, which is larger than 50 Å. It is characterized by having at least one peak within a range of 1000 Å or less.

Here, if the carbon content of the porous carbon fiber of the present invention is less than 75% by weight, it is not defined as a carbon fiber and does not exhibit the effect as a porous carbon fiber.

Porous carbon fibers having a peak at pore radius distribution force <10 cannot be produced by the method of the present invention;
If the fiber has a peak exceeding that of humans, the fiber strength tends to decrease. If the peak exists only in the range of 10 Å to 50 Å, the same effect as conventional porous carbon fibers can be obtained, and the peak is larger than 50 Å.
If it exists only in the range of less than oooÅ, it will not be suitable for adsorption separation of substances with relatively small molecular weights. The present invention
It is characterized by having both characteristics.

Next, the method for producing porous carbon fibers of the present invention will be explained in detail.

The porous carbon fiber of the present invention is prepared by first adding 9% acrylonitrile to the porous carbon fiber of the present invention.
an acrylonitrile copolymer containing 0 mol% or more;
A mixed solution in which a thermally decomposable copolymer that is thermally decomposed to lower its molecular weight at a temperature of 600°C or lower and a compatibilizer consisting of a block or graft copolymer of both types of polymers added as necessary is dissolved in a solvent. This is then spun and drawn to produce an acrylic blend fiber. Next, the above fibers are
After flameproofing treatment is performed in an oxidizing gas atmosphere at 300°C, carbonization treatment is performed in an inert gas atmosphere at 600°C or higher. At the same time, the thermally decomposable polymer is thermally decomposed, and relatively large pores are opened by the escape of the decomposed low-molecular substances. Furthermore, relatively small pores are opened by activation treatment in a mixed gas atmosphere of oxidizing gas such as water vapor and carbon dioxide gas and inert gas at 400 to 1200°C, and the multiple pore distribution of the present invention is created. A porous carbon fiber having a porous carbon fiber is produced.

The acrylonitrile copolymer used in the present invention is preferably a copolymer containing 90 mol% or more of acrylonitrile and 10 mol% or less of a known monomer copolymerizable with acrylonitrile.

Here, if the copolymer contains less than 90 mol % of acrylonitrile, it tends to cause fusion during the flameproofing treatment and is difficult to carbonize.

Examples of monomers copolymerizable with acrylonitrile include acrylic acid, methacrylic acid, itaconic acid, derivatives of the above acids such as methyl methacrylate and ethyl methacrylate, amide derivatives such as acrylamide and methacrylamide, vinyl acetate, and vinylidene chloride. halogen monomer,
Examples include sulfonic acid derivatives such as sodium methacryl sulfonate and sodium styrene sulfonate. The degree of polymerization of this acrylonitrile copolymer preferably has a specific viscosity in the range of 042 to 0.3.

The thermally decomposable copolymer used in the present invention has a decomposition temperature of 600
It is preferable to use one that thermally decomposes at a temperature below C to lower the molecular weight.
Preferably, those that can be dissolved in the same solvent as the acrylonitrile copolymer are used.

Here, if the decomposition temperature exceeds 600°C, it will not be thermally decomposed in the carbonization process, resulting in the problem that pores will not be formed.

The thermally decomposable copolymer contains 51 mol% or more of vinyl monomers such as vinyl chloride, vinyl alcohol, and vinyl acetate, and acrylate monomers such as methacrylate, methyl methacrylate, ethyl methacrylate, and n-butyl methacrylate. A copolymer containing 49 mol % or less of a monomer other than acrylonitrile is preferably used. The specific viscosity of this thermally decomposable copolymer is 0.2~
Approximately 0.03 is suitable. Setting the specific viscosity to a value close to that of the acrylonitrile copolymer is advantageous when adjusting the solution concentration and viscosity of both types of copolymer.

Generally, when different types of polymers are mixed and dissolved, those with different values of solubility parameters (δ) tend to cause layer separation. Also in the present invention, (δ) of the acrylonitrile copolymer
is about 15,4, and (δ) of the thermally decomposable copolymer is about 9,
Since it is in the range of 0 to 12.2, phase separation is likely to occur. In such cases, it is generally well known to use a block or graft copolymer of different types of polymers as a compatibilizer. Such compatibilizers include 30 mol% or more of acrylonitrile as block and graft copolymers;
Those containing 40 mol % or more of a thermally decomposable copolymer and 10 mol % or less of other copolymerizable monomers are preferably used.

The mixing ratio of the acrylonitrile copolymer, thermally decomposable copolymer, and compatibilizer is 40 to 80% by weight of the acrylonitrile copolymer, 20 to 60% by weight of the thermally decomposable copolymer, and 0% by weight of the compatibilist. A range of 5% by weight is preferred.

If the mixing ratio of the acrylonitrile copolymer is less than 40% by weight, the carbonization yield will be too low and it is not economical, and if it exceeds 80% by weight, the proportion of closed pores will be large and will not contribute to adsorption. Causes problems.

When the mixing ratio of the thermally decomposable copolymer is less than 20% by weight, the pores are not opened on the surface layer of the fibers, but remain closed, and no adsorption performance is exhibited. If the amount exceeds 60% by weight, the carbonization yield will decrease, making it economically undesirable.

The above-mentioned state of closed pores becomes clear by measuring the density using the density gradient tube method. That is, if pores are not formed on the surface of the fiber, this can be determined by the fact that the density gradient preliquid flows into the pores and the carbon fiber density decreases. In addition, the amount of the thermally decomposable copolymer mixed is 20% by weight or more, preferably 25% by weight or more.
When pores are opened on the surface layer surface by mixing more than % by weight, the density liquid flows into the pores and the fiber density increases, indicating that the pores are opened on the surface layer surface of the fibers. When the mixing ratio of the thermally decomposable copolymer increases, the pore volume increases while the pore radius remains constant, that is, the adsorption capacity increases.

In the present invention, the compatibilizer is essential when the acrylonitrile copolymer and the thermally decomposable copolymer are mixed at the time of melting, but each of them is dissolved individually and immediately before spinning, a compatibilizer that does not require a driving part is used. When mixing using a static kneader, a compatibilizer is not necessarily required.

The effect of adding the above-mentioned compatibilizer is of course to increase the compatibility effect, but also to control the size of the dispersed phase of the thermally decomposable copolymer by adjusting the amount of the compatibilizer mixed. The purpose is to determine the size of the pores. When the amount of the compatibilizer is adjusted while the mixing amount is constant, the size of the dispersed phase becomes smaller as the amount of the compatibilizer increases, and the radius of the pores generated during the carbonization process is reduced. However, the effect will be saturated even if the amount exceeds 5% by weight, so the mixing amount should be 5% by weight.
It is preferable that it is less than or equal to In addition, when mixing without adding a compatibilizer and using a known static crosstalk element that does not require a driving part,
The size of this dispersed phase is controlled by the number of elements in the kneading element.

As a solvent for dissolving these polymers, organic solvents such as dimethylformamide, dimethylacetamide, and dimethylforposide are preferably used.

The viscosity of the mixed solution in which the above polymer was dissolved in this solvent was 5.
The falling ball viscosity measured at 0° C. is preferably in the range of 200 to 800 poise. This viscosity reduces the concentration of the mixed solution to 15
The above range can be adjusted by changing the content within the range of 30% by weight. If the concentration of this mixed solution is low and the falling ball viscosity is lower than 200 voids, the stability of spinning will decrease. Further, if the concentration of this mixed solution is high and the falling ball viscosity is higher than 800 voids, the p overpressure etc. will increase and the spinning operability will tend to deteriorate, which is not preferable.

The above mixed solution is discharged from a normal circular nozzle. The mixed solution is further dispersed due to the flow in the conduit and the shear stress when being discharged from the nozzle. The discharged mixed solution is
After traveling in the air, it is solidified by being introduced into a coagulating liquid or by being directly discharged into a coagulating liquid.

A mixed solution of water and a solvent is usually used as the coagulating liquid. An aqueous solution having a solvent concentration of 60 to 85% by weight and a temperature of 30° C. or lower is preferably used. Outside the above range, the fibers tend to be brittle. It is preferable to make the solidification rate relatively slow because phase separation proceeds more slowly and formation of defect structures is also prevented.

Next, the coagulated fibers are sequentially washed in warm water and hot water. Stretching is performed in multiple stages, and the stretching is performed at a stretching ratio of 3 times or more, preferably 5 times or more. Thereafter, by drying on a heating roll, an acrylonitrile blend fiber with a dense structure is produced. The fineness of this fiber is preferably 3 denier or less, preferably 1.5 denier or less. During the above-mentioned spinning process, each polymer undergoes phase separation and forms independently entangled fibrils.

This acrylonitrile blend fiber has a temperature of 200~
Flameproofing treatment is performed in an atmosphere (usually in air) containing an oxidizing gas (NO2, 02, 03, 81 NO2, etc.) at 300°C. Here, if the treatment temperature is less than 200° C., it will take a long time to generate a flame-resistant structure, and if it exceeds 300° C., runaway reactions will easily occur and fusion will occur.

During the above-mentioned flameproofing treatment (oxidation step), the fibers are controlled so that substantially no shrinkage occurs. Excessive shrinkage during the oxidation step is undesirable because it reduces the strength properties of the resulting fibers.

Excessive stretching also tends to cause fluff and fiber breakage.

It is important to control the elongation in the oxidation step within a range of 0 to 15%. In this oxidation step, the nitrile group portion of the acrylonitrile blend fiber undergoes condensation and ring formation, creating a nonflammable structure and stabilizing it against heat.

After the above oxidation step, the temperature is 600°C or higher, preferably 600°C or higher.
The flame-retardant fibers are carbonized in an inert gas (N2, Ar, I-Ie, etc.) atmosphere at 1200° C. under 0 to 20% elongation. Here, if the treatment temperature is less than 600°C, the formation of porosity will be insufficient, and the treatment temperature will be 120°C.
When the temperature exceeds 0°C, the pore volume shows no tendency to decrease.

In this step, the fibril structure of the thermally decomposable copolymer is thermally decomposed into low molecular weight substances, monomers, etc. and removed, thereby forming relatively large pores.

Furthermore, by performing activation treatment at 400 to 1200°C in a mixed gas atmosphere of 20 to 80% by volume of an activating gas such as water vapor, carbon dioxide, or air, and 20 to 20% by volume, relatively small pores are formed. Open a hole. Here, if the treatment temperature is lower than 400'C, small pores will not be made porous, and if the treatment temperature is higher than 1200C, small pores will not be made porous due to thermal contraction. In addition, the capacity of the activated gas in the mixed gas is 20
If it is less than % by volume, it will take a long time to make it porous.
When the amount is more than 80% by volume, it becomes difficult to control the pore size.

The porous carbon fiber of the present invention is manufactured through the above steps.

"Example" Hereinafter, the present invention will be specifically explained using examples.

(Example) Acrylonitrile (hereinafter abbreviated as AN) 98 mol%,
60% by weight of AN copolymer with a specific viscosity of 0.24 consisting of 2% by mole of methacrylic acid (hereinafter abbreviated as MAA) and 99% by mole of methyl methacrylate (hereinafter abbreviated as MMA).
, 1 mol% of methyl acrylate (hereinafter abbreviated as MA),
From a block copolymer with a specific viscosity of 0.19 consisting of 40 mol% of AN and 60 mol% of MMA for 100 parts by weight of a mixture of both copolymers consisting of 40% by weight of a thermally decomposable copolymer with a specific viscosity of 0.21. 5 parts by weight of the compatibilizer were mixed and dissolved in dimethylpolamide (hereinafter abbreviated as DMF) as a solvent so that the solution concentration of the mixture of the three was 26% by weight to obtain a mixed solution.

This mixed solution was spun by a dry-wet spinning method using a nozzle hole diameter of 0.15 mm. The distance from the nozzle surface to the solidified liquid level was approximately 5 mm.

An aqueous solution of 75% by weight DMF at a temperature of 2° C. was used as a coagulating liquid. The fibers coagulated by this coagulation solution were washed in warm water at 60° C. and stretched twice.

Next, the film was stretched twice in hot water at 98°C. After bowing, the film was dried with a hot roll at 160°C, and further stretched by 1.5 times when passing through a hot roll at 180°C, resulting in a total stretching ratio of 6 times. As a result, the fineness was 12 apr and the number of filaments was 3.
000 AN-based blend fibers were produced.

This fiber was continuously treated in a flameproofing furnace in an air atmosphere having a temperature gradient of 210°C to 255°C to obtain a flameresistant fiber.

Next, relatively large pores were opened by thermally decomposing the thermally decomposable polymer in a nitrogen atmosphere having a temperature gradient of 300 to 600°C. Furthermore, in a mixed gas atmosphere of 50% by weight of nitrogen gas and 50% by weight of water vapor, 9%
Relatively small pores were formed by performing the activation treatment at 00°C.

The characteristics of the obtained porous carbon fiber are shown below.

Carbon content 80.0wt% Nitrogen 〃 139 Horn single fiber strength 3.2g/d 〃 Elongation 13% BET surface area 806m'/g Pore radius 11 people, 105 people Total pore volume 0.3 cm! '/g, 0.4c
m'/g FIG. 1 shows the pore radius distribution curve of the above example. The pore distribution with a radius of 11 people is calculated from the methanol adsorption isothermal adsorption curve by assuming a cylindrical model in the formula of Ke(!vin) and C
It was obtained using the method of Raneton et al., and the radius was 10
The pore distribution of the five people is a distribution curve determined as a cylinder equivalent radius by the mercury intrusion method (Porosimeter 200 manufactured by CARLOERBA).

As is clear from the characteristic values and FIG. 1, the pore radius distribution peaks at 11 and 105 cases. Thus, a porous carbon fiber having the features of the present invention was produced.

The analytical equipment and analytical method used in the analysis will be described below.

Elemental analysis was performed using a differential thermoconductivity cell using a Yanagimoto Cl-IN coder, model MT-II.

The pore structure was measured by the mercury intrusion method (Porosimeter 200 manufactured by CA RL O. ERBA) for relatively large pores of 100 to 1000, and the radius was determined by calculating the equivalent radius of a cylinder. In addition, in small pores and pores from 10 to 30, from the methanol isothermal adsorption curve, Ke
It was calculated by assuming a cylindrical model in the Qvin equation and using the method of Cronston et al.

The BET surface area was calculated based on the BET equation from the methanol isothermal adsorption curve.

The single fiber strength was measured using a Tensilon VTM ■ model with a sample length of 25 mm.

"Effects of the Invention" The present invention provides a porous carbon fiber having a carbon content of 75% by weight or more, which has multiple peaks in the radius distribution of pores formed on the surface layer of the porous carbon fiber. However, since it is a porous carbon fiber characterized by having at least one peak in the range of 10 Å or more and 50 Å or less and in the range of more than 50 Å and 1000 Å or less, it exists in the liquid phase. It is possible to adsorb and separate substances with relatively large molecular weights present in the gas phase and substances with relatively small molecular weights present in the gas phase. Therefore, the porous carbon fiber of the present invention has the effect of adsorbing and separating substances with relatively large molecular weights, in addition to adsorbing and separating substances with relatively small molecular weights, which have conventionally been able to be adsorbed and separated. .

"Additional notes" Embodiments of the present invention include the following.

(1) When mixing and dissolving an acrylonitrile copolymer and a thermally decomposable copolymer, 0 to 5% by weight of the block or graft copolymer of both is used as a compatibilizer to form a dispersed phase of the thermally decomposable polymer. 3. The method for producing porous carbon fibers according to claim 2, wherein the size of the porous carbon fibers is controlled.

(2) The thermally decomposable copolymer is a copolymer containing 1 mol% or more of methacrylate, methyl methacrylate, ethyl methacrylate, or n-butyl methacrylate and 49 mol% or less of a monomer other than acrylonitrile. The method for producing porous carbon fiber according to claim 2.

(3) The porous structure according to claim 2, wherein the compatibilizer is a block copolymer containing 50% by weight or more of methyl methacrylate, 40% by mole or less of acrylonitrile, and 10% by mole or less of other copolymerizable monomers. A method for producing quality carbon fiber.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the distribution of pore radius in an example of the porous carbon fiber of the present invention. Applicant Mitsubishi Rayon Co., Ltd.

Claims (2)

[Claims] (1) A porous carbon fiber having a carbon content of 75% by weight or more, in which the radius distribution of pores opened on the surface layer of the porous carbon fiber has multiple peaks, and the multiple peaks A porous carbon fiber characterized by having at least one peak in the range of 10 Å or more and 50 Å or less and in the range of 50 Å or more and 1000 Å or less. (2) Acrylonitrile made by mixing, spinning and stretching an acrylonitrile-based copolymer containing 90 mol% or more of acrylonitrile and a thermally decomposable copolymer that thermally decomposes at a temperature of 600°C or lower to reduce the molecular weight. system blend fiber,
Flameproofing treatment is performed in an oxidizing gas atmosphere at 200 to 300°C, then thermal decomposition is performed in an inert gas atmosphere, and further 400°C
2. The method for producing porous carbon fibers according to claim 1, wherein the activation treatment is performed in a mixed atmosphere of an inert gas and an activating gas at a temperature of 1,200°C.