JP6375005B2 - Activated carbon fiber and production method thereof - Google Patents

Description

  The present invention relates to an activated carbon fiber having high hydrophilicity and excellent adsorption characteristics for polar substances such as water vapor and a method for producing the same.

  In recent years, porous materials such as activated carbon have been widely used as adsorbents, filter media, catalyst carriers, and the like. Such a porous body has a high specific surface area with many pores distributed, and the adsorption performance is obtained by taking the object into the pores and holding the object physically or chemically. Etc. Therefore, various porous bodies have been proposed, such as those having a higher specific surface area and those whose pore diameter is controlled within a specific range, depending on the application and required characteristics.

For example, Patent Document 1 discloses a porous body made of a nitrogen-containing carbon-based material, having a specific surface area of 600 m ² / g or more, an average pore diameter of 1 to 5 nm, and an atomic ratio of nitrogen atoms to carbon atoms of 0. Nitrogen-containing carbon-based porous bodies that are 08 to 0.3 are described.

Patent Document 2 describes alkali activated carbon having a specific surface area of 2000 to 3500 m ² / g and a total pore volume of 1.0 to 3.0 cm ³ / g.

  By the way, in general, activated carbon is hydrophobic and has poor adsorption performance for polar substances such as water vapor. For this reason, in applications that adsorb moisture (water vapor) in the air, such as adsorbents for adsorption heat pumps that use water vapor as a working medium, not only simply control the specific surface area, average pore diameter, etc. Giving hydrophilicity to the surface is an important issue.

  On the other hand, in Patent Document 3, for example, a carbonaceous porous material is obtained by using, as a carbon raw material, a mixture of a nitrogen-containing compound having a functional group attached to a triazine ring and an aromatic ring-containing thermosetting resin. A carbonaceous porous body with an increased amount of water vapor adsorption has been proposed by increasing the abundance ratio of heteroatoms (nitrogen, sulfur, silicon, phosphorus, etc.) on the surface of the substrate.

Japanese Patent Application Laid-Open No. 2004-165857 JP 2009-26964 A JP 2002-255331 A

  However, as in Patent Document 3, it is not easy to control the composition and reaction conditions of the carbon raw material in advance so that the abundance ratio of the heteroatoms in the carbonaceous porous material is in a specific range. There is a problem that a great deal of labor is required. For this reason, establishment of a method for imparting hydrophilicity to the activated carbon surface more easily is strongly demanded.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an activated carbon fiber having improved hydrophilicity utilizing the characteristics of the carbon raw material itself and a method for producing the same.

In order to achieve the above object, the present invention provides a polyacrylonitrile-based activated carbon fiber having a nitrogen content of 5% by weight or more, an average pore diameter of 2.4 nm or less , an acidic surface functional group amount and a basic surface functional group. The activated carbon fiber whose total amount of the base amount is 1 to 5 meq / g is defined as the first gist.

The present invention, among them, in particular, the pore volume of the second aspect of the activated carbon fiber is 0.2~2mL / g.

Furthermore, the present invention, among them, in particular, in the water vapor adsorption isotherm of the activated carbon fiber, the activated carbon fiber having an adsorption start relative pressure of 0.4 or less is the third gist, and among them, In particular, in the water vapor adsorption isotherm of the activated carbon fiber, a fourth gist is an activated carbon fiber having a water vapor adsorption amount (Q _0.3 ) of 0.08 g / g or more in liquid conversion at a relative water vapor pressure of 0.3. .

And this invention is a manufacturing method of the activated carbon fiber provided with the carbonization process process and the activation process process, Comprising: The said carbonization process process is a process of carbonizing the polyacrylonitrile-type fiber raw material at 500-900 degreeC. The activation treatment step is a step of bringing the carbonized product obtained by the carbonization treatment into contact with an alkali activator at 600 to 900 ° C. to perform the alkali activation treatment, and the alkali activated product obtained by the alkali activation treatment is The method for producing activated carbon fibers, which are activated carbon fibers having a nitrogen content of 5% by weight or more, an average pore diameter of 2.4 nm or less , and a total amount of acidic surface functional groups and basic surface functional groups of 1 to 5 meq / g It is set as the summary of 5 .

In addition, among the above, the activated carbon in which the ratio of the alkali activator to the polyacrylonitrile-based fiber raw material is set to 1/1 to 4/1 on the basis of weight in the alkali activation treatment step is particularly preferable. The manufacturing method of the fiber is a sixth gist.

  That is, the activated carbon fiber of the present invention is a polyacrylonitrile-based (hereinafter abbreviated as “PAN-based”) activated carbon fiber, which is obtained by carbonizing and activating a PAN-based fiber raw material. In the conventional PAN-based activated carbon fiber, in the process of carbonization treatment and activation treatment, nitrogen atoms derived from the PAN-based fiber raw material are removed as much as possible to form a regular carbon skeleton. The PAN-based fiber raw material is carbonized and activated under relatively mild conditions so that the final nitrogen content is 5% by weight or more.

  Therefore, the activated carbon fiber of the present invention has a high hydrophilicity because many carbon-nitrogen bonds exist on the surface of the activated carbon fiber. Moreover, since the overall shape is fibrous, and fine pores with an average pore diameter of 2.4 nm or less are distributed on the surface of the elongated fiber, for polar substances such as moisture (water vapor) in the air, Processing performance such as excellent adsorption performance can be exhibited.

The active carbon fiber of the present invention, in particular, total amount of acidic surface functional group amount and the basic amount of surface functional groups is, since it is 1~5meq / g, since the hydrophilicity becomes higher, a polar material On the other hand, more excellent processing performance can be exhibited.

  Furthermore, among the activated carbon fibers of the present invention, those having a pore volume of 0.2 to 2 mL / g are considered to have many fine pores suitable for water vapor adsorption. In particular, it is possible to exhibit excellent processing performance against water vapor.

  Among the activated carbon fibers of the present invention, in particular, in the water vapor adsorption isotherm of the activated carbon fiber, the one having an adsorption start relative pressure of 0.4 or less starts water vapor adsorption even at low humidity. For this reason, it is difficult to be influenced by the atmospheric humidity, and in particular, it is possible to exhibit processing performance with excellent responsiveness.

Among the activated carbon fibers of the present invention, in particular, in the water vapor adsorption isotherm of the activated carbon fiber, the water vapor adsorption amount (Q _0.3 ) at a relative water vapor pressure of 0.3 is 0.08 g / g or more in liquid conversion. It exhibits a certain degree of adsorption performance under low humidity, and as the humidity increases, the adsorption performance does not level out and exhibits further adsorption characteristics, so it can exhibit better processing performance. it can.

  And, as described above, the method for producing the activated carbon fiber of the present invention includes carbonizing the PAN-based fiber raw material under relatively mild conditions, and subjecting the activated carbon of the present invention to alkali activation treatment under relatively mild conditions. The fiber is obtained. According to this method, since many nitrogen atoms derived from the PAN-based fiber raw material are present on the fiber surface of the activated carbon fiber in a carbon-nitrogen bonded form, an activated carbon fiber having high hydrophilicity is obtained. be able to.

  Among the production methods of the present invention, in particular, in the alkali activation treatment step, the ratio of the alkali activator to the PAN-based fiber raw material is set to 1/1 to 4/1 on a weight basis. More nitrogen atoms can be left, which is preferable.

(A) is the partial external view which shows typically one Embodiment of the activated carbon fiber of this invention, (b) is the partial expanded sectional view. It is a typical partial expanded sectional view of granular activated carbon. It is explanatory drawing of the water vapor | steam adsorption isotherm for showing the characteristic of the activated carbon fiber of this invention.

  Next, a mode for carrying out the present invention will be described in detail.

The activated carbon fiber of the present invention is a PAN-based activated carbon fiber having a nitrogen content of 5% by weight or more, an average pore diameter of 2.4 nm or less , and the total amount of acidic surface functional groups and basic surface functional groups. Is 1 to 5 meq / g .

  The said characteristic can be achieved by selecting suitably the kind of PAN type fiber raw material used for this invention, carbonization conditions, activation conditions, etc. Details will be described below.

  The activated carbon fiber used in the present invention can be obtained by carbonizing a PAN-based fiber raw material into carbon fiber and then activating it.

  The PAN-based fiber raw material may be a PAN-based resin spun into a fiber shape, a fiber already in a fiber shape, or a recycled product. And even if it consists only of PAN, the blend goods which contain another resin in one part may be sufficient. Moreover, you may mix the fiber which consists of another resin in the one part. Furthermore, the copolymer which has an acrylonitrile monomer as a main component and used the other monomer as a subcomponent may be sufficient. Alternatively, polyacrylonitrile may be modified by introducing a functional group. And these PAN type fiber raw materials may be used independently or may be used in combination of 2 or more type.

  In the PAN-based fiber raw material, the method of spinning from a resin into a fiber is not particularly limited. For example, an appropriate method can be adopted from various spinning methods such as an electrostatic spinning method and a blend spinning method. .

  Incidentally, the above-mentioned electrostatic spinning method is a method in which a raw material resin solution dissolved in a solvent is discharged into an electrostatic field formed between electrodes, and the formed fibrous material is accumulated on a collection substrate, whereby the raw material resin Is a method for obtaining a fiber comprising: The blend spinning method is a method of obtaining a fiber made of a raw material resin by spinning the mixture of the raw material resin and the thermoplastic resin, stabilizing the raw material resin, and removing the thermoplastic resin.

  The form of the PAN-based fiber raw material used in the present invention may be a long fiber as spun or a short fiber obtained by cutting it into an appropriate length. Moreover, according to the use, forms, such as a nonwoven fabric, a woven fabric, a knitted fabric, a twisted thread, a string, may be sufficient.

  Next, as a method for carbonizing the PAN-based fiber raw material into carbon fiber, a method of heat treatment under an inert gas atmosphere such as nitrogen is generally used. Processing temperature is 400 degreeC or more normally, Preferably it is 500-900 degreeC, More preferably, it is 550-750 degreeC, More preferably, it is 600-700 degreeC.

  In addition, as a method of activating the PAN-based carbon fiber obtained by the carbonization treatment to obtain a PAN-based activated carbon fiber, generally, a steam activation method or an alkali activation method, or a combination of a steam activation method and an alkali activation method is used. Although a method is known, in the present invention, it is preferable to use an alkali activation method.

  The alkali activation method is to impregnate the target carbon fiber with an alkaline activator and raise the temperature to a predetermined temperature range so that the carbon structure of the carbon fiber is eroded, and the activator is further incorporated into the carbon structure. In this method, many pores are formed by intrusion. According to this method, as compared with the steam activation method, erosion of the active surface can be suppressed, so that a large number of nitrogen atoms can be left on the surface, which is preferable.

Examples of the activator used in the alkali activation method include alkali metal hydroxides such as LiOH, KOH and NaOH, alkaline earth metal hydroxides such as Ba (OH) ₂ , Li ₂ CO ₃ and Na ₂ CO. ₃ , alkaline metal carbonates such as K ₂ CO ₃ , alkaline earth metal carbonates such as CaCO _{3 and the} like. Among these, KOH and NaOH are particularly preferable. The treatment temperature during alkali activation is usually 400 to 1000 ° C., although it varies depending on the activator used. In the present invention, mild conditions such as 500 to 950 ° C. are preferable, and 600 to 900 ° C. are more preferable. And the ratio of the activator with respect to a carbon raw material is 1 / 2-6 / 1 normally on a weight basis, Preferably it is 1 / 1-4 / 1, More preferably, it is 1 / 1-3 / 1.

  In addition, since the alkali of an activator remains on the surface of the PAN-based activated carbon fiber obtained by the alkali activation method, it is usually preferable to perform alkali removal by water washing or acid washing after the alkali activation treatment.

  The activated carbon fiber of the present invention thus obtained typically has an appearance as shown in FIG. 1 (a), for example, and an enlarged cross section of the surface portion thereof is as shown in FIG. 1 (b). It has become. That is, it can be seen that a large number of pores (so-called micropores) 1 are distributed on the surface of the elongated fiber, and the number of pores 1 per unit surface area is large.

  On the other hand, as shown in FIG. 2, which is a schematic partial sectional view, granular activated carbon that has been widely used conventionally has a relatively large opening 2 (so-called macropore) on the surface, and pores inside the opening 2. 1 is formed. For this reason, even if the activated carbon is given hydrophilicity, water vapor or the like to be adsorbed hardly enters the inside of the pores 1 and cannot sufficiently exhibit the adsorption performance for water vapor or the like. In addition, when the column is packed, the periphery of the opening 2 may collapse and the pores 1 may be crushed. Therefore, the performance as in the present invention cannot be obtained.

  In the activated carbon fiber of the present invention, the average fiber diameter [the fiber diameter is indicated by X in FIG. 1 (a)] is not particularly limited, but is usually 0.1 to 100 μm, particularly 1 to 50 μm. It is preferable that it is 5-30 micrometers. That is, if the average fiber diameter is too small, the activated carbon fiber becomes brittle, and in the process of handling, the activated carbon fiber may break and become dusty. Conversely, if the average fiber diameter is too large, the activation treatment is uniform. This is because it may be difficult to proceed.

  In the present invention, the aspect ratio [fiber length Y / fiber diameter X, see FIG. 1 (a)] of the activated carbon fiber is usually 100000/1 to 3/1, preferably 10000/1 to 5 /. 1, more preferably 1000/1 to 10/1. This is because if the aspect ratio is too large, inconvenience may occur in terms of handleability, and conversely if the aspect ratio is too small, the superiority of the fiber shape may not be maintained.

  Furthermore, the activated carbon fiber of the present invention is characterized by a nitrogen content of 5% by weight or more. Especially, it is preferable that nitrogen content is 5 to 30 weight%, and it is more preferable that it is 10 to 20 weight%. That is, as the nitrogen content increases, as described above, more carbon-nitrogen bonds are formed on the surface (edge surface) and a part of nitrogen is an amino group. As a result, it has high hydrophilicity as a whole. However, if the nitrogen content is too high, the alkali activation reaction based on the carbon structure may be difficult to proceed, which is not preferable.

  Another important feature of the activated carbon fiber of the present invention is that the average pore diameter is 2.4 nm or less. Especially, it is preferable that an average pore diameter is 1-2 nm. That is, the smaller the average pore diameter, the better the ability to adsorb polar substances such as water vapor. However, if the average pore diameter is too small, the desorption characteristics may be lowered, which is not preferable.

  In the activated carbon fiber of the present invention, the more the amount of acidic surface functional groups and the amount of basic surface functional groups present on the surface, the better the wettability of the activated carbon fiber surface. Examples of such acidic surface functional groups include a carboxyl group, a carbonyl group, a phenolic hydroxyl group, and a lactone group. Examples of basic surface functional groups include amino groups, acridine groups, groups having a chromene structure, groups having a pyrone structure, and the like.

In the present invention, the sum of these acidic surface functional group amount and the basic amount of surface functional groups is, Ru 1~5meq / g der. Among them, it is good Masui is 2~5meq / g. In order to increase the total amount from the above range, the production cost may increase due to the necessity of increasing the number of post-treatment steps (oxidation treatment or the like), which is not preferable.

  Furthermore, in the present invention, the pore volume formed in the activated carbon fiber (the meaning of the total pore volume, hereinafter the same) is usually 0.1 to 5 mL / g, and 0.2 to 2 mL / g. It is preferable that it is 0.3 to 1 mL / g. If the pore volume is too small, the adsorption performance may be insufficient. On the other hand, if the pore volume is too large, the start of adsorption under low humidity may be delayed, which is not preferable.

Then, in the present invention, the specific surface area of the activated carbon fibers is usually 400 meters ² / g or more, preferably 600 meters ² / g or more, more preferably 800~3500m ² / g. That is, the larger the specific surface area, the larger the contact area with the object to be treated, so that the treatment performance is improved, but if it is too large, the structure of the activated carbon fiber may become brittle.

  The activated carbon fiber of the present invention preferably has an adsorption start relative pressure of 0.4 or less, more preferably 0.3 or less, in the water vapor adsorption isotherm of the activated carbon fiber. That is, the low adsorption start relative pressure means that the water vapor adsorption starts even at low humidity, and is an indicator that the adsorption performance with excellent responsiveness is exhibited regardless of the atmospheric humidity. become.

In the activated carbon fiber of the present invention, similarly, in this water vapor adsorption isotherm, the water vapor adsorption amount (Q _0.3 ) at a relative water vapor pressure of 0.3 is preferably 0.08 g / g or more in terms of liquid. More preferably, it is at least 13 g / g. That is, those having a large water vapor adsorption amount (Q _0.3 ) at a relative water vapor pressure of 0.3 exhibit a certain level of adsorption performance under low humidity, and the adsorption performance does not level off as the humidity increases. This is because a further superior processing performance can be exhibited in order to exhibit further adsorption characteristics.

The “water vapor adsorption isotherm” means, for example, as shown in FIG. 3, the water vapor pressure is changed, the water vapor adsorption amount at that time is measured, and the relative pressure (adsorption) is plotted on the horizontal axis (X axis). FIG. 5 is a diagram in which water vapor adsorption amount is plotted on the vertical axis (Y axis) of equilibrium pressure P / saturated water vapor pressure P ₀ ). In the figure, the isotherm from the start of the adsorption of water vapor to the saturated state is indicated by a thick solid line, and the isothermal line from the saturated state until all the water vapor is desorbed is indicated by a thick broken line.

The “adsorption start relative pressure” is indicated by an intersection R between the tangent line at the time of adsorption and the X axis. Further, the water vapor adsorption amount (Q _0.3 ) at a relative water vapor pressure of 0.3 is a position shown in the diagram, and is about 0.20 g / g in the diagram.

Incidentally, in the above diagram, the following can be referred to as other indexes indicating the adsorption characteristics.
Desorption end relative pressure: intersection S of tangent line and X axis during desorption
Saturated adsorption amount: Adsorption amount T indicated by the intersection of the tangent line during adsorption and the tangent line during saturated adsorption
Saturated adsorption relative pressure: Relative pressure U indicated by the intersection of the tangent at adsorption and the tangent at saturation adsorption

  Thus, the activated carbon fiber of the present invention is a PAN-based activated carbon fiber, has a nitrogen content of 5% by weight or more, has many carbon-nitrogen bonds, and has high hydrophilicity. Moreover, since fine pores with an average pore diameter of 2.4 nm or less are distributed on the surface of the elongated fibers, it has excellent adsorption performance for polar substances such as moisture (water vapor) in the air. Performance can be demonstrated.

  Moreover, the activated carbon fiber of the present invention can be suitably used in applications that require higher functions by combining with materials specialized for other functions such as treatment of substances having no hydrophilicity.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to the following examples unless it exceeds the gist.

[Examples 1-8, Comparative Examples 1-4]
<Preparation of activated carbon fiber>
By performing carbonization treatment and activation treatment on the carbon materials shown in Tables 1 and 2 described later under the conditions shown in Tables 1 and 2, 8 types of example products and 4 types of comparative example products were prepared. Details of the carbon raw material, carbonization treatment, and activation treatment are shown below.

<Carbon raw material>
PAN-based (fibrous): PAN-based fiber cut to an average fiber diameter of 10 μm and a length of 30 mm.
Pitch-based (fibrous): pitch-based fibers cut to an average fiber diameter of 15 μm and a length of 30 mm.

<Carbonization treatment>
The carbon raw material was put into an atmosphere box furnace (manufactured by Koyo Thermo Systems Co., Ltd.), heated to a predetermined temperature under a nitrogen flow at a heating rate of 10 ° C./min, and then carbonized by holding for a predetermined time. .

<Activation processing>
10 g of carbon raw material and a predetermined amount of KOH are put into a container and mixed in a small furnace, heated in a nitrogen stream (1 L / min) at a heating rate of 10 ° C./min, and then at a predetermined activation temperature. The alkali activation treatment was performed while maintaining the time. The treated sample was boiled in 2 L of a 5.25 wt% aqueous hydrochloric acid (HCl) solution for 1 hour and then filtered. The filtered sample was washed with 60 ° C. warm water and vacuum filtered, and repeatedly washed until the pH of the filtrate reached 6.5 or higher. The washed sample was boiled in 2 L of warm water for 1.5 hours, then washed with 4 L of hot water at 60 ° C., and vacuum filtered. The dehydrated product after filtration was dried at 115 ° C. for a whole day and night.

[Comparative Examples 5 to 7]
The product of Comparative Example 5 is an alkali activated carbon (MSP-20X, manufactured by MC Evatech Co., Ltd.) having an average particle size of 9 μm derived from a non-PAN resin material, and the product of Comparative Example 6 is an average particle size derived from a petroleum material. This is 88 μm alkali activated carbon (MC Evatech, MSC-30). The product of Comparative Example 7 is a commercially available steam activated charcoal having an average particle diameter of 5 μm derived from the coconut shell raw material.

<Measurement and calculation of physical properties>
For each of the obtained Example products and Comparative product, values were obtained for the following items according to the following method, and the results are shown in Tables 1 and 2 below.

<How to Find Average Fiber Diameter: Examples 1-8, Comparative Examples 1-4>
The average fiber diameter was randomly sampled from activated carbon fiber so as to have an area of 5 mm × 10 mm, fixed to the SEM sample stage, and then vacuumed by ion sputtering (manufactured by Hitachi High-Technologies Corporation, E-1030). Gold deposition was performed at 15 mA for 300 seconds. This sample was set in a scanning electron microscope (S-3000N, manufactured by Hitachi High-Technologies Corporation), and a visual field of 5 fields per sample was randomly photographed so as not to overlap with an applied voltage of 15 kV and a magnification of 3000 times. Next, five fibers were selected in each field of view, and the fiber diameter was measured by converting to fiber diameter using the scale on the image. The average fiber diameter was calculated by the arithmetic average of each measured value.

<How to Obtain Average Particle Size: Comparative Examples 5-7>
Activated carbon is measured using a laser diffraction particle size distribution analyzer (SALD (registered trademark) -2200, manufactured by Shimadzu Corporation), and a volume-based cumulative frequency curve is obtained from the particle size distribution measurement results. The diameter was defined as the average particle diameter.

<How to find the nitrogen (N) content>
The weight ratio of carbon (C), hydrogen (H), and nitrogen (N) contained in the sample was measured with an elemental analyzer (JM-1000HCN, manufactured by Jay Science Co., Ltd.). From the measurement result, the nitrogen content (% by weight) was calculated.

<Determination of specific surface area and pore volume>
After 0.2 g of a sample (activated carbon) was heated at 250 ° C. under vacuum, a nitrogen adsorption isotherm was obtained using a nitrogen adsorption device (ASAP-2405, manufactured by Micromeritic), and a specific surface area (m ² / m g) was determined. The pore volume (= total pore volume, mL / g) was calculated from the nitrogen adsorption amount up to a pore diameter of 30 nm at a relative pressure (P / P ₀ ) of 0.93 from the nitrogen adsorption isotherm.

<How to find the average pore size>
The average pore diameter was calculated based on the following formula (1) assuming that the pores of the activated carbon were cylindrical.
[formula]
Average pore size (nm)
= [4 × total pore volume (mL / g)] / [specific surface area (m ² / g) × 1000] (1)

<How to determine the amount of acidic surface functional groups>
The amount of the acidic surface functional group was determined according to the Boehm method (details thereof are described in the document “HP Boehm, Adzan. Catal, 16, 179 (1966)”). Specifically, first, 50 mL of an aqueous sodium ethoxide solution (0.1 mol / L) was added to 1 g of a sample (activated carbon), and the mixture was stirred for 2 hours at 500 rpm, and then allowed to stand for 24 hours. Thereafter, the mixture was further stirred for 30 minutes and separated by filtration. 0.1 mol / L hydrochloric acid was dripped with respect to 25 mL of obtained filtrates, and hydrochloric acid titration when pH 4.0 was measured was measured. As a blank test, 0.1 mol / L hydrochloric acid was added dropwise to 25 mL of the aqueous sodium ethoxide solution (0.1 mol / L), and the hydrochloric acid titration amount was measured when the pH reached 4.0. And the amount of acidic functional groups (meq / g) was computed by following formula (2).
[formula]
Acid surface functional group amount (meq / g)
= (A−b) × 0.1 / (S × 25/50) (2)
a: Hydrochloric acid titration in blank test (mL)
b: Hydrochloric acid titration (mL) when the sample was reacted
S: Sample mass (g)

<How to determine the amount of basic surface functional groups>
The amount of basic surface functional groups was determined by back titration when measuring the amount of acidic surface functional groups. Specifically, 50 mL of hydrochloric acid (0.1 mol / L) was added to 1 g of a sample (activated carbon), and the mixture was stirred for 2 hours at 500 rpm and then allowed to stand for 24 hours. Thereafter, the mixture was further stirred for 30 minutes and separated by filtration. 0.1 mol / L sodium hydroxide was added dropwise to 25 ml of the obtained filtrate, and the sodium hydroxide titration when pH was 8.0 was measured. As a blank test, 0.1 mol / L sodium hydroxide was added dropwise to 25 ml of the hydrochloric acid (0.1 mol / L), and the sodium hydroxide titration was measured when the pH reached 8.0. And the basic surface functional group amount (meq / g) was computed by following formula (3).
[formula]
Basic surface functional group amount (meq / g)
= (Cd) × 0.1 / (S × 25/50) (3)
c: Sodium hydroxide titration in blank test (mL)
d: Sodium hydroxide titration (mL) when the sample is reacted
S: Sample mass (g)

<How to find the total amount of acidic surface functional groups and basic surface functional groups>
The total amount (meq / g) was determined by adding the amount of the acidic surface functional group and the amount of the base surface functional group.

<Evaluation of water vapor adsorption characteristics>
A vapor adsorption amount measuring device (manufactured by Micro Trap Bell, BELSORP-max) was prepared. Then, about 40 mg of the sample was put into the cell, pretreated by vacuum heating at 250 ° C. for 5 hours, and then a replacement gas was introduced and weighed. The water vapor adsorption measurement was performed in a water bath maintained at 25 ° C. by a circulating thermostat in a relative pressure (P / P ₀ ) range of 0.0 to 0.85. From the obtained water vapor isotherm, The value of each item shown in Table 3 was calculated | required (refer FIG. 3).

  From the above results, in each of Examples 1 to 8, the adsorption start relative pressure is 0.4 or less, and the rise is quick. In addition, at an early stage where the relative pressure is in the range of 0.0 to 0.3, the water vapor adsorption amount exhibits excellent adsorption performance of 0.08 g / g or more in terms of liquid. And in the range whose relative pressure is 0.3-0.8, the amount of adsorption | suction does not become flat and adsorption | suction performance is maintained. Accordingly, it is possible to exhibit an excellent water vapor adsorption performance that has not been achieved conventionally. On the other hand, all of Comparative Examples 1 to 7 have an adsorption start relative pressure exceeding 0.4, and it is understood that water vapor cannot be adsorbed unless the humidity is increased to some extent, and the rise is slow.

  Since the activated carbon fiber of the present invention has a high nitrogen content and hydrophilicity, it can be widely used as a treatment material for various polar substances such as adsorption of water vapor. Moreover, the manufacturing method of the activated carbon fiber of this invention can be widely utilized as a method of manufacturing the activated carbon fiber to which hydrophilicity was provided efficiently.

Claims (6)

A polyacrylonitrile-based activated carbon fiber having a nitrogen content of 5% by weight or more, an average pore diameter of 2.4 nm or less , and a total amount of acidic surface functional groups and basic surface functional groups of 1 to 5 meq / g . An activated carbon fiber characterized by being. Claim 1 Symbol placing active carbon fiber pore volume is 0.2~2mL / g. The activated carbon fiber according to claim 1 or 2 , wherein an adsorption start relative pressure is 0.4 or less in the water vapor adsorption isotherm of the activated carbon fiber. In water vapor adsorption isotherm of the activated carbon fiber, the amount of adsorbed water vapor at a relative vapor pressure 0.3 (Q _0.3) is, according to any one of claims 1 to 3 in a liquid in terms of 0.08 g / g or more Activated carbon fiber. A method for producing activated carbon fiber comprising a carbonization treatment step and an activation treatment step, wherein the carbonization treatment step is a step of carbonizing a polyacrylonitrile fiber raw material at 500 to 900 ° C., and the activation treatment step is The carbonized product obtained by the above carbonization treatment is a step of bringing the carbonized product into contact with an alkali activator at 600 to 900 ° C. to perform an alkali activation treatment, and the alkali activated product obtained by the alkali activation treatment has a nitrogen content of 5% by weight. A method for producing activated carbon fibers, characterized in that the activated carbon fibers have an average pore diameter of 2.4 nm or less and a total amount of 1 to 5 meq / g of an acidic surface functional group amount and a basic surface functional group amount . 6. The process for producing activated carbon fibers according to claim 5 , wherein in the alkali activation treatment step, the ratio of the alkali activator to the polyacrylonitrile fiber raw material is set to 1/1 to 4/1 on a weight basis.

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