JPS6350447B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel method for producing porous carbon fibers. Activated carbon has long been used as an adsorbent for removing impurities in liquids or gases or recovering harmful substances.
It has also been widely used as a catalyst carrier. Activated carbon that has been used for these purposes has been in the form of powder or granules, but in recent years fibrous activated carbon has been developed, and its use has expanded due to its form and adsorption performance. However, in conventionally obtained fibrous activated carbon, most of the pores have a diameter of 50 Å or less, and even if pores of several hundred Å exist, the pore volume is mostly small. Since it was less than 0.1 cc/g, it could not be considered a suitable material depending on the field of use. For example, when the above-mentioned fibrous activated carbon with a pore diameter of 50 Å or less is used in a liquid system such as for uranium recovery or battery electrodes, the diffusion rate of solute in the pores becomes smaller than the diffusion rate of solute in the liquid. This causes the inconvenience that the pores are not used effectively. Generally, fibrous activated carbon is produced by flame-proofing and activating organic fibers, but even if the activation conditions were varied, it was impossible to increase the pore diameter suitable for the above-mentioned uses. . In view of the above-mentioned points, the present inventors conducted intensive research and arrived at the present invention. That is, in the present invention, micropores are formed on the surface of the fiber obtained by adding a pore-forming aid to the fiber-forming stock solution and spinning the yarn, and among the micropores, the diameter of the pores is 200 to 200.
The pore volume of 10,000 Å is 0.1 cc/g or more, the BET surface area is 1 to 20 m ² /g, and the decrease in the pore volume is 0.08 cc/g or less when dried at 120°C for 1 hour. Big and metal content is 1.0
Carbon having a pore volume of 0.1 cc/g or more with a pore diameter of 200 to 10,000 g by flame-retardant treatment of porous acrylic fiber with a weight percent or less, and then oxidation opening treatment in an oxidizing atmosphere at a temperature of 500°C or higher. This is a method for producing porous carbon fiber, characterized by producing fibers. The first point of the present invention is that in order to obtain porous carbon fibers with a pore diameter of 200 to 10,000 Å and a pore volume of 0.1 cc/g or more, micropores opened on the fiber surface must be present. The pore volume of pores with a pore diameter of 200 to 10,000 Å (hereinafter pore volume refers to the pore volume of pores with a pore diameter of 200 to 10,000 Å) is 0.1 cc/g or more,
and the BET surface area is 1 to 20 m ² /g, and 120
℃, the decrease in pore volume when dried for 1 hour was 0.08
Porous acrylic fibers of cc/g squid are used as the starting material. Porous fibers with so-called closed pores, which do not have pores on the fiber surface, have pores on the fiber surface that allow material exchange with the outside of the fiber, no matter how much flame-retardant, carbonization, or oxidation opening treatment is performed. , and it is difficult to obtain porous carbon fibers with a large pore volume in a high yield. Also, even if the pore volume is 0.1cc/g or more, the BET surface area is 20
If it exceeds m ² /g, the fiber becomes brittle and the stability of the pores is lacking. On the other hand, if the BET surface area is less than 1 m ² /g or the pore volume is less than 0.1 cc/g, the effects of the present invention are difficult to obtain even if flame-retardant, carbonization, and oxidation treatments are performed, and the pores of 200 Å or less are mainly affected. It just happens. Also, the decrease in pore volume is 0.08cc/g.
Porous carbon fibers with a pore volume of 0.1 cc/g or more can only be obtained by using the following fibers.
For example, porous fibers produced by fixing the porous structure of swollen gel yarns (BET surface area 20 to 70 m ² /g) obtained by wet spinning acrylic fibers have fine particles when dried at 120°C for 1 hour. decrease in pore volume
If it exceeds 0.08cc/g, flame resistance, carbonization,
Even if oxidation treatment is performed, stable porous carbon fibers cannot be obtained. Such pore volume is 0.1 cc/g or more,
Porous fibers with a BET surface area of 1 to 20 m ² /g and a decrease in pore volume of 0.08 cc/g or less may be prepared by adding a cross-linked water-absorbing agent, which is a pore-forming aid, to the spinning dope for fiber formation. It is produced by adding a resin or a pore-forming stabilizer, or by adding paraffins and extracting the paraffins after thread formation. Examples of fiber-forming polymers include cellulose-based, acrylonitrile-based, and phenol-based fibers, and the aggregate form of fibers may include tow, cotton, filament, spun yarn, nonwoven fabric, woven fabric, paper, etc. depending on the purpose. You can choose from various forms. The porous fiber thus obtained is then subjected to flame resistance. Regarding flame-retardant treatment, if the material is acrylonitrile fiber, it can be heated at 150 to 300℃ in an oxidizing atmosphere containing oxygen, nitrogen dioxide gas, etc., especially in air.
carried out at a temperature of The second point of the present invention is to keep the metal content of the porous acrylic fibers to 1.0% by weight or less. In the present invention, the above-mentioned porous acrylic fiber is made flame resistant as described above, but in this case, the starting fiber is made of metals, particularly Na, Ca, Mg, Cr, Mn,
If Fe, Co, Ni, Cu, and Zn are present, their total content (content of one or more metals)
is preferably 1.0% by weight or less. That is,
If the content exceeds 1.0% by weight, the metal itself acts as an oxidation catalyst during high-temperature oxidation, which not only prevents uniform high-temperature oxidation treatment but also undesirably causes a drop in yield. Therefore, if the starting fiber contains an excessive amount of metal, the metal content should be adjusted to 1.0% by weight or less by extracting it with an acid or the like before making it flameproof. The third point of the present invention is to subject the flame-resistant fibers as described above to an oxidative hole-opening treatment in an oxidizing atmosphere at a temperature of 500° C. or higher. As the oxidizing atmosphere, an atmosphere containing an oxidizing gas such as carbon dioxide, water vapor, or oxygen, combustion waste gas, or the like is used. When treated in an inert atmosphere, the pores tend to close,
The pores in the fiber structure do not open further to the fiber surface, making it impossible to obtain a porous carbon fiber with a large pore volume as in the present invention. The porous carbon fiber produced by the above method can be used for various purposes by taking advantage of its characteristic performance, but is particularly suitable for use in liquid systems. To make the pore diffusion coefficient of the solute the same as the solute diffusion coefficient in the liquid, the pore diameter should be approximately 100 to 200.
Å or more, and it can be seen that the porous carbon fiber according to the present invention can meet this requirement. The porous carbon fibers are impregnated with a special adsorbent and have excellent performance as a carrier for so-called composite adsorbents for collecting various substances from liquids. Furthermore, since it is carbon-based, it has good conductivity, low chemical reactivity, and the above-mentioned properties in liquid systems, making it particularly useful as an electrode material. Among them, it is excellent as an electrode material for redox flow secondary batteries, which are currently being developed as secondary batteries. Pore volume, BET surface area used in the present invention,
The decrease in pore volume was measured and calculated as follows. (1) Pore volume (cc/g) Measured by mercury intrusion method. Based on the difference in pore volume between pore diameters of 200 g and 10,000 Å, the cumulative pore distribution curve was determined from the pore radius (Å) determined by the following formula for the external absolute pressure P (Kg/cm ² ), the actual mercury intrusion volume, and the cumulative pore distribution curve. Find the pore volume between 200 and 10,000 Å. γ=-2γcosθ/P where γ is the surface tension of mercury (480dyne/cm),
θ is the contact angle between mercury and carbon fiber, and is assumed to be 141°. (2) BET surface area (m ² /g) Obtained by the BET method from the nitrogen gas adsorption isotherm at the boiling point of liquid nitrogen (77〓). (3) Pore volume reduction (%) Calculated from the following formula. Decrease in pore volume = V ₀ −V V; Pore volume of sample fiber dried at 120°C for 1 hour V ₀ ; Pore volume of sample fiber not subjected to the above drying process Example 1 Acrylonitrile (hereinafter referred to as AN) , methyl methacrylate, methylenebisacrylamide,
A cross-linked AN copolymer emulsion prepared by copolymerizing sodium p-styrene sulfonate was treated with an alkali, and the resulting water-absorbing resin water dispersion was diluted with 90%
AN, an anti-thread stock solution that is a Rodan soda aqueous solution of AN polymer containing 10% methyl acrylate.
The water absorbent resin was added at a ratio of 4% based on the total amount of the AN polymer and the water absorbent resin. The spinning stock solution
Wet spinning was performed using a 0.10 mmφ spinneret according to a conventional method, followed by coagulation, washing with water, and stretching, and then spinning at 120°C.
After drying for 20 minutes to densify the fiber, it was subjected to moist heat relaxation treatment at 125°C for 5 minutes to obtain a pore volume of 0.41cc/g and a pore volume of 0.04
A 5.0 denier porous acrylic fiber A with a pore volume reduction of cc/g and a BET surface area of 12 m ² /g was obtained. Fiber A was treated in 0.5N HCl at 50°C for 30 minutes, thoroughly washed with water until no Hcl was observed, and then dried to obtain Fiber B. The metal content in fiber B is
It was 0.1% by weight. Fiber B in air from 150℃ to 30℃
The temperature was raised to 290°C at a heating rate of °C/hr to obtain flame-resistant fibers. This flame-resistant fiber was heated from room temperature to 850°C in a nitrogen stream at a rate of 400°C/hr, then switched to a nitrogen stream containing 15% by volume of water vapor, subjected to oxidation opening treatment for 2 hours, and then heated in a nitrogen stream. After cooling, porous carbon fibers were obtained with a yield of 26%. When the pore volume of the porous carbon fiber was measured, it was 0.55cc/
It was hot at g. As a comparison, we measured the pore volume of the carbon fiber prepared by heating the above-mentioned flame-resistant fiber from room temperature to 850°C in a nitrogen stream at a heating rate of 400°C/hr, but the pore volume was as low as 0.07 cc/g. Ta. Comparative Example 1 The method for producing porous acrylic fiber A in Example 1 was the same, but the amount of water-absorbing resin was changed to exceed the BET surface area of 20 m ² /g, and the pore volume was reduced.
Although 6.7% was added so that the concentration was 0.08 cc/g or less, yarn breakage occurred and a satisfactory yarn could not be obtained. Comparative Example 2 The method for producing porous acrylic fiber A in Example 1 was adopted, and 1.0% of water absorbing resin was added to reduce the pore volume.
A porous fiber with a BET surface area of 2.4 m ² /g and a pore volume reduction of 0.02 cc/g was prepared, and acid treatment,
Flameproofing, carbonization, and high-temperature oxidation treatments were performed in the same manner as in Example 1 to obtain porous carbon fibers with a yield of 21%, but the pore volume was only 0.08 cc/g. Example 2 Using the same method as for making fiber A in Example 1, 1.5% of water-absorbing resin was added, resulting in a pore volume of 0.14 cc/g, a BET surface area of 3.6 m ² /g, and a decrease in pore volume of 0.03 cc/g. A porous fiber was prepared and subjected to the same post-treatment as Fiber B in Example 1 to obtain a porous fiber with a yield of 19% based on yarn, but the pore volume of the fiber was 0.13 cc/g. Example 3 Same method as making fiber A in Example 1, but with 1/
Add 5% of water-absorbing resin of size 2 to increase the pore volume.
A porous fiber with a BET surface area of 16 m ² /g and a pore volume reduction of 0.03 cc/g was obtained. The same post-treatment as for Fiber B in Example 1 was carried out, and porous fibers with a pore volume of 0.26 cc/g were obtained at a yield of 23% based on yarn. Comparative Example 3 No water-absorbing resin was added, the drying and densification process was omitted, and the moist heat relaxation treatment temperature was 110°C and the drying temperature was 100°C.
Three types of microporous 5-denier acrylic fibers (C, D, E) having a fibrillar structure were produced using the same manufacturing method as porous acrylic fiber A of Example 1, except that
The porous carbon fiber was prepared and subjected to the same acid treatment, flame resistance, carbonization, and high temperature oxidation treatment as in Example 1 to obtain a porous carbon fiber. Acrylic fibers C, D, and E were produced using different coagulation bath compositions during spinning. Table 1 shows the performance of the raw material fibers and porous carbon fibers.

[Table] Comparative Example 4 The acid treatment conditions of the porous acrylic fiber A made in Example 1 were changed to obtain fibers F and G with different metal contents, and the fibers A, F, and G were flame-resistant in the same manner as in Example 1. transformation,
Carbonization and activation treatments were performed to produce porous carbon fibers. Fiber A had a metal content of 1.2% by weight.
The yield was low, the activation was highly uneven, and some of the fibers were burnt out, making it impossible to produce uniform porous carbon fibers. Table 2 summarizes the metal content, yield, and activation spot determination results for fibers A, B, F, and G.

【table】

Claims (1)

[Claims] 1 Open micropores exist on the surface of the fiber obtained by adding a pore-forming aid to the spinning stock solution for fiber formation and spinning the fiber, and among these micropores, those with a pore diameter of 200 to 10,000 Å have a pore volume of 0.1 cc/g or more, and the BET surface area is 1 to 20 m ² /g, the decrease in the pore volume is 0.08 cc/g or less when dried at 120°C for 1 hour, and the metal content is 1.0% by weight or less. The porous acrylic fiber is flame-resistant treated and then oxidized to open the pores in an oxidizing atmosphere at 500℃ or higher to reduce the pore diameter.
A method for producing porous carbon fibers, which comprises producing carbon fibers having a pore size of 200 to 10,000 Å and a pore volume of 0.1 cc/g or more.