JPS58120818A - Production of porous carbon fiber - Google Patents

Abstract

PURPOSE:Fibers in which the pores have a specific void volume and BET surface area and the reduction in the void volume is low, when dried, is preoxidized, then subjected to oxidative pore-opening treatment under an oxidative atmosphere to produce the titled fiber that is suitable for use in uranium recovery, because of its large surface area and high strength. CONSTITUTION:Porous fibers that have fine pores opening on the fiber surface in which the void volume of the pores with pore diameters of 200-10,000Angstrom is larger than 0.1cc/g, a BET surface area of 1-20m<2>/g and have the void volume reduction of lower than 0.08cc/g, when dried at 120 deg.C for 1hr, are preoxidized and subjected to oxidative pore-opening treatment in an oxidaive atmosphere at over 500 deg.C to give the objective carbon fiber with a pore volume of pores of 200-10,000Angstrom 0.1cc/g larger than.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel method for producing porous carbon fibers.

Activated carbon has long been widely used as an adsorbent for removing impurities in liquids or gases or recovering harmful substances, or as a carrier for catalysts. Activated carbon that has been used for these purposes has been in powder or granular form; however, in recent years, fibrous activated carbon has been developed, and its use has expanded due to its form and adsorption performance.

However, the fibrous activated carbon that has been conventionally obtained is
The diameter of the pores is mostly less than 50x,
Even if there are several hundred pores, most of them have a pore volume of less than O,l ca/9, so they may not be suitable materials depending on the field of use. For example, when fibrous activated carbon with a pore diameter of 50 mm or less is used in a liquid system such as for uranium recovery or battery electrodes, the diffusion rate of the solute in the pores becomes smaller than the diffusion rate of the solute in the liquid. This causes the inconvenience of not being used effectively. Generally, fibrous activated carbon is produced by flame-proofing and activating organic fibers, but even if the activation conditions are varied, it has not been possible to increase the pore diameter suitable for the above-mentioned uses. .

However, in view of the above points, the present inventors conducted extensive research and arrived at the present invention.

The first point of the present invention is that in order to obtain a porous carbon fiber having a pore diameter of zoo-IQQOOX with a pore volume of 0.1 cc79 or more, open micropores exist on the fiber surface. The pore volume of pores with a pore diameter of 200 to 10,000X (hereinafter pore volume refers to the pore volume of pores with a pore diameter of 200 to 10,000X) is 0°l ce/g or more, and the EFT surface area is 1 to 20 tl. /q, and the decrease in pore volume when dried at 120°C for 1 hour is 0.
08 ac/q or less is used as a starting material. Porous fibers with so-called olosed porθ, which do not have openings on the fiber surface, have pores open on the fiber surface that allow material exchange with the outside of the fiber, and It is difficult to obtain porous carbon fibers with a large pore volume in high yield. Further, even if the pore volume is O6l cc/9 or more, if the BIT surface density exceeds 20 as'/g, the fiber becomes brittle and the pores lack stability. On the other hand, if the BIT surface area is less than IR"79 or the pore volume is O, l
If it is less than cc/g, even if it is flame-resistant, carbonized, or oxidized, the effect of the present invention will be insufficient, as pores of 411 m < 2 o □ X or less will mainly be produced. Moreover, porous carbon fibers with a pore volume of O.lee/g or more can only be obtained by using fibers with a pore volume reduction of O.0 acc/9 or less.

For example, a porous fiber produced by fixing the porous structure of a swollen gel thread (13ET surface area 2o~7am7g) obtained by wet spinning acrylic fiber has a 1.20%
Decrease in pore volume after drying for 1 hour at °C is 0.08cc/g
However, even if flameproofing, carbonization, and oxidation treatments are performed on the fiber, stable porous carbon fiber cannot be obtained.

Such porous fibers have a pore volume of 0.1 cc79 or more, a BIT surface area of 1 to 20 m''/g, and a decrease in pore volume of 1 cc/g or less.
For example, methods such as adding a cross-linked water-absorbing resin or a pore-forming stabilizer as a pore-forming aid to the spinning dope for fiber formation, or adding paraffins and extracting the paraffins after yarn formation. Manufactured by adopting. Examples of fiber-forming polymers include cellulose thread, acrylonitrile fiber, phenol fiber, etc., and fiber aggregate forms include tow, cotton, filament, spun yarn, non-woven fabric S-woven fabric 1 paper, etc. depending on the purpose. You can choose the form of

The porous fiber thus obtained is then subjected to flame resistance. When the material is acrylonitrile fiber, it is carried out in an oxidizing atmosphere containing oxygen, nitrogen dioxide gas, etc., especially in air, at a temperature of 150 to 300°C, and when the material is cellulose fiber, it is carried out at a temperature of 150 to 300°C. It is preferable to carry out the reaction under an inert atmosphere at ℃ because the yield can be increased. In the case of phenolic fibers, they do not require any special flame-retardant treatment because they have been made infusible themselves.

By the way, in the present invention, the above-mentioned porous fibers are made flame resistant as described above, and in this case, the starting fibers are made of metals, particularly Na, Oa, Mg, Or, Ml, Fe,
Oo.

If Ni, Ou, and Zi are present, it is preferable that their total content (1) (content of one or more metals) be LO weight % or less. That is, the phase contained is 1.0% by weight.
If it exceeds this value, the metal itself acts as an oxidation catalyst during high-temperature butylation, which not only makes it impossible to perform uniform high-temperature oxidation treatment, but also undesirably causes a drop in yield. Therefore, if the starting m-fiber contains an excessive amount of metal, the 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 second 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 the treatment is carried out in an inert atmosphere, the pores tend to close, and the pores in the fiber structure do not open further to the fiber surface, making it difficult to obtain a porous carbon fiber with a large pore volume as in the present invention. Can not.

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. In order to make the pore diffusion coefficient of the solute the same as the solute diffusion coefficient in the liquid, the pore diameter needs to be approximately 100 to 200x or more.
It can be seen that the porous carbon fiber according to the present invention can meet this requirement. A special adsorbent is attached to the porous carbon fiber, and it has excellent performance as a carrier for so-called composite adsorbents that collect various substances from liquids.Since it is carbon-based, it is electrically conductive. This material is particularly useful as an electrode material because it has good chemical properties, low chemical reactivity, and the properties mentioned above in liquid systems. Among them, it is excellent as an electrode material for redox flow secondary batteries, which are currently being developed as secondary batteries.

The pore volume, BIDT surface area, and pore volume reduction used in the present invention are measured and calculated as follows. (1) Pore volume (ce/g) Measured by mercury porosimetry. External absolute pressure P (kg/
cd), calculate the cumulative pore distribution curve from the pore radius (^) determined by the following formula and the actual mercury intrusion volume, and calculate the pore diameter 200X.
200-100OO from the difference in pore volume between
Find the pore volume of A.

Here, γ is the surface tension of mercury (48Q dyne/cx
), θ is the contact angle between mercury and carbon fiber, and is 141°.

(2) BIT surface area (m'/g) BIT from crosstalk such as adsorption of nitrogen gas at the boiling point of liquid nitrogen (77°K)
Required by law.

(3) Pore volume decrease (%) Calculated using the following formula.

Decrease in pore volume = vQ-v Vi Pore volume of sample fiber dried at 120°C for 1 hour Vos Pore volume of sample fiber not subjected to the above drying process Example 1 A cross-linked AN thread copolymer emulsion prepared by copolymerizing methyl acrylate, methylenebisacrylamide, and sodium p-styrene sulfonate was treated with alkali, and the resulting water-absorbing resin water dispersion was treated with 90% AN, 10% The water-absorbing resin was added to the spinning stock solution, which was a rhodan soda aqueous solution of an AN-based polymer containing 50% methyl acrylate, in a proportion of 4% based on the total amount of the AN-based polymer and the water-absorbing resin. The spinning stock solution was adjusted to 0.
The fibers were wet-spun using a 10 m + φ spinneret according to a conventional method, coagulated, washed with water) and stretched, then dried at 120°C for 20 minutes to densify the fibers, and then subjected to moist heat sintering at 125°C for 5 minutes to form a 0. Pore volume of 41 cc/g and 0.04 c
Pore volume reduction of c/9 and lP, BI of #I”/9
A porous acrylic fiber A of 5.0 denier having a surface area of
Fiber B was obtained by washing the fibers thoroughly with water until Hol was no longer observed and drying. The metal content in fiber B is 0.
0 fiber B, which was 1% by weight, was heated at 30°C from 150°C in air.
The temperature was raised to 290°C at a heating rate of /hr to obtain flame-resistant fibers. This flame-resistant fiber was heated from room temperature to 400°C in a nitrogen stream.
The temperature was raised to 850°C at a heating rate of 15 hours.
Switching to a nitrogen stream containing water vapor of M% by volume, oxidizing pore-opening treatment was performed for 2 hours, and after cooling in the nitrogen stream, porous carbon fibers were obtained at a yield of 26%. The pore volume of the porous carbon fiber was measured and found to be 0.55 cc/9.

For comparison, we measured the pore volume of carbon fibers prepared by heating the above-mentioned flame-resistant fibers from room temperature to 850 °C in a nitrogen stream at a heating rate of 400 °C/11 r.
The value was as low as 0.07 cc/g.

Comparative Example 1 The method for producing porous acrylic fiber A in Example 1 was the same, but the amount of IJ & aqueous resin was changed to a BIT surface area of 20 m
Decrease in pore volume to exceed '/9 0.0Bee
Either 6.7% was added and spun so that the yarn was less than /9, or one yarn breakage occurred and a satisfactory yarn could not be obtained.

Comparative Example 2 The method of producing porous acrylic fiber A of Example 1 was adopted, and 1.0% of water-absorbing resin was added to give a pore volume of 0.09 c.
Porous fibers with a BIT surface area of 2.4 #1''/g and a pore volume reduction of o, o2cc, /9 were 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% based on yarn, but the pore volume was less than 0.08 cc/gL.

Example 2 1 water absorbent resin was prepared using the same method as for making fiber A in Example 1.
．． Added 5%, pore volume 0.14 (4/g, BIT surface f
il 3-6111'/g, pore volume reduction 0.03c
c/9 porous fibers were made and subjected to the same post-treatment as Fiber B in Example 1 to obtain porous fibers with a yarn yield of 19%, but the pore volume of the fibers was Ool 3 cc/ It was 9.

Example 3 The same method as in Example 1 was used to make the fiber insert, but 5% of a water-absorbing resin of 1/2 the size was added to create a pore volume of 0.25 c.
Example 1 in which porous fibers with a BIT surface area of 16 m'/9 and a decrease in pore volume of 0.3 cc/9 were obtained.
By performing the same post-treatment as Fiber B, porous fibers with a pore volume of 0.26 cc/Q could be obtained at a yield of 23% based on fibers.

Comparative Example 3 Same manufacturing method as porous acrylic fiber A of Example 1 except that no water-absorbing resin was added, the drying and densification step was omitted, the wet heat relaxation treatment temperature was 110°C, and the drying temperature was 100°C. Three types of microporous 5-denier acrylic fibers (0, D, l) with a fibril structure were prepared, and the same acid treatment, flame resistance 1 carbonization, and high temperature oxidation treatment as in Example 1 were performed to obtain porous carbon fibers. Obtained. Acrylic fiber 0. Table 1 shows the performance of zero raw material fibers and porous carbon fibers D and E, which were produced using different coagulation bath compositions during spinning.

Comparative Example 4 The acid treatment conditions of the porous acrylic fiber A made in Example 1 were changed to produce fibers F with different metal contents.

Fibers A, F, and G were subjected to flameproofing, carbonization, and activation treatments in the same manner as in Example 1 to produce porous carbon fibers. Fiber A, which had a metal content of 1.2% by weight, had a low yield, large unevenness of activation, and part of the fiber was burned out.
It was not possible to make uniform porous carbon fiber. Fiber A, B, ? .

Table 2 summarizes the determination results of the metal content, yield, and activation spots of G.

Patent applicant: Toyobo Co., Ltd.

Claims (1)

[Claims] There are open micropores on the fiber surface, and the pore volume of those with a pore diameter of 200 to 100X is 0°1 cc.
Is it 7q or more and has a BIT surface area of 1 to 20 v? /
A porous fiber whose pore volume decreases when dried at 120°C for 1 hour is not more than oacc/g is flame-resistant treated and then oxidized and opened in an oxidizing atmosphere at 500°C or higher. A method for producing porous carbon fibers characterized by producing carbon fibers having a pore diameter of 200 to 1 OOOOA and a pore volume of 0.1 cc/q or more through pore treatment 0