JPH05279923A - Method for infusibilizing thermoplastic fiber - Google Patents

Abstract

PURPOSE:To rapidly and uniformly infusibilize thermoplastic fiber by oxidation treatment. CONSTITUTION:Thermoplastic fiber, preferably staple fiber, obtained from a pitch having a high softening point and having >=30mum fiber diameter and 30-500mum weight-average fiber length is brought into contact with an oxidizing gas such as air, oxygen or nitrogen dioxide while applying vibration at >=25Hz frequency and >=1mm amplitude through a vibrator attached to a fluidized bed body to the thermoplastic fiber under fluidized conditions or while indirectly applying the vibration to the thermoplastic fiber by applying the pulsation to the oxidizing gas fed to the fluidized bed. Since the staple fiber having a high packing density, a wide surface area and a fine fiber diameter is brought into direct contact with the oxidizing gas, the infusibilization is rapidly and uniformly carried out. Since the staple fiber has the higher packing density than that of tow-shaped fiber, the production efficiency is remarkably improved.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing spherical activated carbon using fibers of a thermoplastic material such as pitch as a raw material, and in particular, a thermoplastic fiber obtained from pitch or other raw materials can be rapidly and uniformly treated by an oxidation treatment. It relates to a method of infusibilizing.

[0002]

2. Description of the Related Art In recent years, the creation of earth-friendly industrial technology,
Against the background of social excitement such as creation of amenity space, it is required to improve the functionality and shape of activated carbon. And conventional activated carbon, that is, powdered activated carbon,
In order to eliminate the disadvantages of granular activated carbon and activated carbon fibers, spherical activated carbon fibers, that is, activated carbon fiber lumps, have been proposed, and as a method for producing them, as disclosed in JP-A-3-146721, non-thermal There is known a method in which fusible short fibers, that is, pitch fibers that have been infusibilized are spheroidized to obtain spherical fibers, which are further activated.

Generally, in the production of spherical activated carbon using pitch as a raw material, a so-called infusibilizing step is carried out, in which prior to the activation step, thermoplastic pitch fibers are oxidized to make infusible fibers that do not melt even when heated. is necessary.

In general, the infusibilizing step is carried out by adding oxygen or an oxidizing substance to pitch fibers to form intermolecular crosslinks, and a gas or liquid substance such as air is used as the oxidizing substance. This reaction is carried out at a temperature lower than the softening point of the pitch, and since it is an exothermic reaction, strict temperature control, that is, heat removal to prevent melting of the pitch, is required. It has been.

Further, since the degree of progress of infusibilization greatly affects the quality of the activated carbon produced, uniform infusibilization is desired. Since such an infusibilization reaction proceeds from the surface of the pitch fiber, the smaller the pitch fiber diameter and the larger the outer surface area of the pitch, the faster and more uniform infusibilization is expected.

In the method which has been generally tried as a method for making the heat-fusible pitch uniform infusible, a material pitch having a high softening point is used as a pre-step of the activation step in the production of activated carbon to make a substantially uniform infusibilization. The particles are finely pulverized to a particle size to the extent that they are carried out, and the solid-gas reaction of the fine particles is reacted with an oxidizing gas using a kiln furnace or a fluidized bed apparatus. With this method, it is difficult to prevent fusion due to melting of the pitch particles with each other, uniform infusibilization cannot be rapidly performed, and industrialization has not been achieved. Further, the production efficiency of the conventional infusibilizing step of carbon fiber is low in the suspending furnace for tow-shaped fibers and the basket type furnace for chopped strands, and even in the rotary firing furnace for short pitch fibers. Is insufficient.

As a method for rapidly and uniformly infusibilizing a heat-meltable pitch, Japanese Patent Laid-Open Nos. 56-69214 and 56-
As described in Japanese Patent No. 69215, a pitch having a high softening point is added with an aromatic compound having 2 to 3 rings such as naphthalene as an additive, spheroidized, and the additive is extracted with an organic solvent to obtain a pitch sphere. A method is known in which a through hole for an additive is formed to increase the surface area as a porous pitch, thereby facilitating the inflow of an oxidizing gas into the interior and carrying out a crosslinking reaction.

In the conventional method in which the raw material pitch having a high softening point is made into a porous pitch and then made infusible with an oxidizing gas as described above, since the diameter of the through hole of the additive formed in the pitch sphere is small, the pitch is formed by air. However, it has a drawback that it takes a long time to prevent the melting and to make it infusible. In addition, the manufacturing process is complicated by a large number of steps such as a dissolution pelletizing step using an additive, a spheroidizing step, an additive extracting step, a drying step, and an infusibilizing step, and the additive and the organic solvent are added. Since it is necessary to use, it is difficult to ensure economic efficiency, and since it becomes difficult to uniformly extract and infusibilize when the particle size of the pitch spheroidized product is increased,
The particle size of the resulting activated carbon is small, and therefore the pressure loss is high in using the activated carbon, the use is limited to the use of a specific use form, for example, the use such as a fluidized bed, and the activation mainly proceeds on the particle surface. However, there is a problem that the amount of activated carbon obtained per unit volume is small.

Further, the pitch fiber and the infusibilized fiber which are the objects of the present invention are brittle and difficult to handle. This is important and it is difficult to ensure economics if the fibers are too brittle.

[0010]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned problems of the prior art in making thermoplastic fibers used for the production of activated carbon fiber lumps infusibilized by oxidation treatment. Another object of the present invention is to provide an infusibilizing method which can prevent fusion of fibers due to melting of each other with high productivity, enable rapid and uniform infusibilization of fibers, and prevent breakage of fibers.

[0011]

Means for Solving the Problems In the present invention, when thermoplastic fibers are rapidly and uniformly infusibilized by an oxidation treatment, thermoplastic short fibers having a weight average fiber length of 30 to 500 μm are subjected to vibration under flowing conditions. The above object is achieved by a method for infusibilizing a thermoplastic fiber, which is characterized in that the short fiber is brought into contact with an oxidizing gas to be oxidized while being added.

Examples of the thermoplastic fibers used in the present invention include thermoplastic fibers used in the production of activated carbon fibers made from coal-based pitch, petroleum-based pitch, polyacrylonitrile, phenol resin and the like. As a raw material of the thermoplastic fiber, a pitch having a high softening point is preferable, and a pitch having a high softening point includes coal tar pitch which is a raw material, or petroleum tar pitch, which is distilled, filtered, refined, heat treated, solvent fractionated, hydrogenated, etc. It is a heat-meltable pitch that can be produced by carrying out the steps singly or in combination, and the components that inhibit spinning such as low boiling point volatile components and insoluble solids in the pitch are removed, and the micropores are expressed. An optically isotropic or anisotropic spinning pitch suitable for is preferable, but is not particularly limited thereto. Basically,
Any thermoplastic material for spinning may be used as long as it does not contain solids or gas under spinning conditions and has uniform flow characteristics.

In the present invention, a thermoplastic material, preferably a raw material pitch having a high softening point, is processed into short fibers. Hereinafter, the present invention will be described with respect to pitch fibers, but the present invention is not limited thereto. The processing into pitch short fibers is usually obtained by fiberizing pitch by extrusion spinning or centrifugal spinning method to obtain pitch fibers, crushing this, and shortening it. The fiber diameter of the pitch fiber is preferably about 30 μm or less. When it is thicker than 30 μm, a homogeneous crosslinked structure cannot be obtained, and a homogeneous activated carbon cannot be obtained in the fiber cross-section direction.

The weight average fiber length of the pitch short fibers is preferably 30 μm to 500 μm. If the length is shorter than 30 μm, the short pitch fibers are bonded to each other due to the adhesive force between the particles to form a large lump, and gas channeling occurs. It is not possible to sufficiently bring them into contact with each other, so that the heat removal by the oxidizing gas becomes insufficient and it is impossible to prevent the melting of the pitch. If it is longer than 500 μm, the short fibers are liable to be entangled with each other and the fluidity is significantly deteriorated.It is difficult to make uniform contact with the gas even if vibration is applied to the short fibers, and heat removal by oxidizing gas is performed. Is insufficient, and melting of the pitch cannot be prevented.

In the present invention, the addition of vibration to the pitch short fibers and the contact between the pitch short fibers and the oxidizing gas can be carried out by using a fluidized bed apparatus, and a so-called vibrator having a vibrator attached to the fluidized bed body is used. It can be performed in a vibrating fluidized bed apparatus. In this case, the preferable frequency is 25Hz or more, and the amplitude is 1
mm or more. Alternatively, a method may be used in which the short pitch fibers are indirectly vibrated by pulsating the oxidizing gas flowing into the short pitch fiber layer through a gas dispersion plate. About this, a thing suitable for the final form of the target activated carbon can be selected. Examples of the oxidizing gas used in the present invention include, but are not limited to, air, oxygen, nitrogen dioxide and the like, or a mixed gas atmosphere containing at least one or more of them.

To produce spherical activated carbon from the infusible short fibers obtained by the method of the present invention, the infusibilized short fibers are spheroidized into an arbitrary particle size by a granulator used for rolling granulation and the like, and then carbonized. Proceeding to the activation step, where the carbon content is increased and at the same time activated to obtain spherical activated carbon.

In the carbonization activating step, generally, a gas such as water vapor or carbon dioxide, an oxygen-containing gas is used as an activating agent in an amount of 400
Used under heating at ℃ to 1100 ℃. Of these, steam is the most common. In this carbonization activation step, carbon is partially gasified by the reaction between the activator and carbon, mainly using this point as an active point, uniform pore opening and generation occur, and the resulting spherical activated carbon is used as an adsorbent. Express excellent function.

Further, in the carbonization activation step, the volatile content in the infusibilized fiber and the thermally unstable portion in the pitch molecule are decomposed and volatilized to develop a six-membered ring structure, and a structure having a large carbon content is formed. And produces activated carbon having strength. In this step, an electric furnace or a heating furnace using various heating elements can be used for heating. Even if any furnace is used, the furnace is at a high temperature, and when steam is used as an activator, a particularly large endothermic reaction consumes a large amount of energy, so it is necessary to carry out the activation efficiently. is there.

[0019]

As described above, in the present invention, the thermoplastic fiber as the raw material is processed into short fibers to expand the surface area, and since the short fibers are in direct contact with the oxidizing gas, infusibilization requires a long time. Moreover, since the fiber diameter is small, uniform infusibilization is performed. Moreover, since the short fibers have a higher packing density than the tow-shaped fibers, the production efficiency of the infusibilization using the fluidized bed apparatus is one digit or more higher in the method of the present invention using the short fibers than in the conventional method using the tow-shaped fibers. Further, in the fluidized bed, since the temperature distribution is more uniform than in the conventional rotary furnace, the product is more uniform. It is difficult to fluidize short fibers because they have a large angle of repose, but in the present invention, the short fibers can be easily fluidized by causing the short fibers to flow while applying vibration.

[0020]

EXAMPLES Next, the present invention will be described with reference to Examples and Comparative Examples. In the examples, the all-optical isotropic pitch was used as the heat-meltable pitch, but the present invention is not limited to this. The softening point (° C) of the pitch was measured by the temperature gradient method. The infusibilizing treatment was carried out by circulating air through a batch type vibrating fluidized bed apparatus equipped with a vibrating frame, a fluidized bed body, a gas dispersion plate, a filter, a heater and the like.

Further, in these examples, the weight average fiber length was calculated from the following formula by obtaining a fiber length distribution by image analysis:

[Equation 1] The production efficiency was indicated by the unit volume of the vibrating fluidized bed and the amount of infusible fiber produced per hour.

Example 1 A coal pitch containing 16% by weight of benzene insoluble matter and a trace amount of quinoline insoluble matter was vacuumed in a nitrogen gas atmosphere at a vacuum degree of 5 mmHg.
Under the above conditions, heat treatment was performed at a temperature of 400 ° C. to obtain a fully optically isotropic pitch having a softening point of 215 ° C. containing 56% by weight of benzene insoluble matter. The obtained pitch was melt-spun at a winding speed of 200 m / min with an extrusion spinning machine having a spinning diameter of 0.3 mm. Pitch fibers with a fiber diameter of 13 μm obtained were weight average fiber length 200 μm
Cut into short pitch fibers.

Short pitch fibers were filled in a batch type vibrating fluidized bed apparatus, and air was circulated at a superficial velocity of 10 cm / sec, and an amplitude of 2 was applied.
mm, frequency 30 Hz, heating rate 1 ° C / min, 30
The temperature was raised to 0 ° C. for infusibilization treatment. Production efficiency is 10 kg / m ³ h
Met. The oxygen content of the obtained infusibilized short fiber was 9.1% by weight, and the oxygen concentration distribution in the radial direction was measured by an electron probe X-ray microanalyzer (EPMA). As a result, oxygen was uniformly distributed in the fiber. No fusion due to mutual fusion of fibers was observed in the infusibilizing treatment. Further, the weight average fiber length after the infusibilization treatment was 170 μm, which shows that the prevention of fiber breakage was achieved.

The infusibilized short fibers obtained were mixed in a plate-type rolling granulator with 10% by weight of coal-based pitch having a softening point of 110 ° C. containing a trace amount of quinoline-insoluble matter and granulated to obtain an average particle size. Spherical infusible particles having a diameter of 6 mm were obtained. The obtained spherical infusible particles were heated at 950 ° C using a continuous kiln furnace while flowing steam.
It was retained for 6 hours for activation. The yield of the obtained spherical activated carbon was 25% by weight based on the weight of short pitch fibers, the average particle size was 4.3 mm, and the specific surface area by the BET method was 1610 m ² / g.

The spherical activated carbon was packed in an adsorption column,
The butane effective adsorption amount measured after repeating butane adsorption and desorption with air was 10 for 100cc of spherical activated carbon.
It was g of butane.

Example 2 Short pitch fibers obtained in the same manner as in Example 1 were infusibilized in the same manner as in Example 1 while imparting 10 Hz pulsation to air by a rotary valve in a batch type fluidized bed apparatus. ..
After the infusibilization treatment, no fusion due to melting of the fibers was observed.

Comparative Example 1 Pitch fibers obtained in the same manner as in Example 1 were cut into weight-average fiber lengths of 20 μm and 700 μm, and the average fiber diameters were respectively cut.
20 μm pitch short fibers A and pitch short fibers B were obtained.
This was infusibilized under the same conditions as in Example 1. With the pitch short fiber A, the infusibilized short fiber could not be obtained due to fusion of the fibers in the fluidized bed due to melting. In pitch short fiber B, temperature runaway occurs near the fluidized bed temperature of 190 ℃,
Further, due to the fusion of the fibers in the fluidized bed due to melting, the infusibilized short fibers could not be obtained.

Comparative Example 2 The entire surface optical isotropic pitch obtained in the same manner as in Example 1 was
It was crushed and sieved to obtain pitch C having an average particle size of 1.2 mm. The batch type fluidized bed apparatus was filled with pitch C and air was supplied to 18
The mixture was circulated at a superficial velocity of cm / sec, and heated to 300 ° C. under the condition of a heating rate of 1 ° C./min to infusibilize. The oxygen content of the obtained infusible particles was 5.1% by weight, and the oxygen concentration distribution in the radial direction was measured by EPMA. As a result, the oxygen concentration near the particle surface was high, and oxygen was unevenly distributed in the particles. .. No fusion due to mutual melting of particles was observed in the infusibilizing treatment.

The infusible particles thus obtained were activated by being retained for 15 hours at 950 ° C. in a continuous kiln while flowing steam. In the obtained particles, foaming and fusion of particles were observed, and uniform activation was not achieved.

Comparative Example 3 The entire surface optical isotropic pitch obtained in the same manner as in Example 1 was
It was crushed and sieved to obtain a pitch D having an average particle size of 20 μm. This was infusibilized in the same manner as in Example 1. Due to the fusion of the pitches D in the fluidized bed due to melting, a temperature runaway occurred around the fluidized bed temperature of 210 ° C., and the fusion of the particles in the fluidized bed due to the fusion of the particles caused the pitch D to be a votive shape.

Comparative Example 4 An optically isotropic pitch over the entire surface was obtained in the same manner as in Example 1.
The obtained pitch was melt-spun with an extrusion spinning machine having a spinneret diameter of 0.3 mm, and the obtained pitch fiber having a fiber diameter of 32 μm was cut into a weight average fiber length of 200 μm to obtain a pitch short fiber E. This was infusibilized in the same manner as in Example 1. The oxygen content of the obtained infusibilized short fiber was 7.2% by weight, and the oxygen concentration distribution in the radial direction was measured by EPMA. As a result, the oxygen concentration in the vicinity of the fiber surface was high, and oxygen was unevenly distributed in the fiber. It was The fusion due to the mutual fusion of the fibers in the fluidized bed was observed in a part of the fibers.

The infusibilized short fibers thus obtained were mixed in a plate-type rolling granulator with 10% by weight of coal-based pitch having a softening point of 110 ° C. and containing a trace amount of quinoline-insoluble matter, and granulated. Spherical infusible particles having a diameter of 6 mm were obtained. The obtained spherical infusible particles were heated at 950 ° C using a continuous kiln furnace while flowing steam.
It was retained for 6 hours for activation. The yield of the obtained spherical activated carbon was 32% by weight based on the weight of short pitch fibers, the average particle diameter was 4.0 mm, and the specific surface area by the BET method was 1310 m ² / g.

The spherical activated carbon was packed in an adsorption column,
The butane effective adsorption capacity measured after repeating butane adsorption and desorption with air was 100cc of spherical activated carbon.
It was 4.8 g of butane.

[0034]

According to the present invention, short fibers having a large packing density, a large surface area, and an appropriately thin fiber diameter are directly contacted with an oxidizing gas in a fluidized bed under good fluidizing conditions, so that they are infusibilized. The reaction heat at this time is efficiently removed by the oxidizing gas, fusion and breakage of the fibers can be prevented, and uniform infusibilization can be performed quickly and efficiently in a simplified production process. Further, by granulating and activating the infusibilized short fibers obtained by the present invention by a conventional technique, the particle size of the spherical activated carbon can be easily increased arbitrarily, and therefore the pressure loss in using the activated carbon is reduced. And is no longer limited to a particular form of use and application. The activated carbon thus obtained is
It is industrially possible to increase the adsorption capacity per unit volume.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Fumihiro Miyoshi 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Technical Research Division (72) Seiji Hanatani 1 Kawasaki-cho, Chiba-shi Kawasaki Steel Co., Ltd. Research Headquarters (72) Inventor Yukihiro Osugi 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Corporation Technical Research Headquarters

Claims (1)

[Claims] 1. To rapidly and uniformly infusibilize a thermoplastic fiber by an oxidation treatment, the thermoplastic short fiber having a weight-average fiber length of 30 to 500 μm is vibrated under flowing conditions to form the short fiber. A method for infusibilizing a thermoplastic fiber, which comprises contacting with an oxidizing gas to perform an oxidation treatment.