JP5482133B2 - Activated carbon fiber - Google Patents

Description

  The present invention relates to activated carbon fibers having particularly excellent adsorption performance for organic compounds having a boiling point in the range of -30 to 70 ° C.

  Activated carbon fiber has a large outer surface area compared to granular activated carbon, and has excellent adsorption performance due to the presence of pores on the surface. In addition, it can be processed into various forms such as paper and woven cloth because of its fibrous form. It is used in various fields.

As a conventional activated carbon fiber, for example, Japanese Patent Application Laid-Open No. 2005-138038 (Patent Document 1) discloses a specific surface area of 700 to 1500 m ² / g, a total pore volume of 0.3 to 0.7 cc / g, and a surface acidic group. An organic compound-adsorbing fibrous activated carbon having an amount of 0.5 meq / g or less is disclosed. According to such a fibrous activated carbon disclosed in Patent Document 1, an effect is exerted on an adsorption treatment of a low molecular weight, low boiling point compound having low adsorptivity to activated carbon such as methylene chloride and vinyl chloride monomer. When applied to exhaust gas treatment equipment, it is compact and low-cost, and can reduce the concentration of low molecular weight and low-boiling compounds emitted from industrial processes such as chemical factories and pharmaceutical factories, contributing to environmental purification and recycling. It can be done.

Further, for example, in JP-A-7-145516 (Patent Document 2), an equilibrium moisture content at 25 ° C. and a relative humidity of 37% is 0.05 to 1.0%, a BET specific surface area is 300 to 3000 m ² / g, fine. The pore volume with a pore volume of 0.25 to 2.00 cc / g and a pore radius measured by the water vapor method in the range of 7 to 14 mm or 9 to 20 mm, the pore radius is 100 mm or less An activated carbon fiber that is 80% or more of the volume occupied by the pores is disclosed. Such activated carbon fibers disclosed in Patent Document 2 are suitably used for adsorption of hydrophobic organic compounds having low solubility in water such as halogenated hydrocarbons that are dissolved in water.

Also, for example, in JP-A-6-99065 (Patent Document 3), the cumulative pore volume occupied by pores having a specific surface area of 800 m ² / g or more and a pore radius of 9 mm or less measured by the water vapor adsorption method is disclosed. The cumulative pore volume occupied by pores having a pore radius of 9 mm or less as measured by the water vapor adsorption method is 0.20 cc / g or more and 50% or more of the cumulative pore volume occupied by pores having a pore radius of 100 mm or less. A filler for water purifiers made of a certain fibrous activated carbon is disclosed. Such a water purifier filler (fibrous activated carbon) disclosed in Patent Document 3 has an extremely high ability to remove trihalomethane contained in water, and can effectively remove chloroform, which occupies most of the trihalomethane in tap water. It can be effectively used for water purifiers used in various places such as factories, stores, and companies.

Furthermore, in Japanese Patent Application Laid-Open No. 2005-903 (Patent Document 4) and Japanese Patent Application Laid-Open No. 2005-21851 (Patent Document 5), the equilibrium adsorption moisture content at 25 ° C. and a relative humidity of 37% is 1.0 to 15.0. %, BET specific surface area of 300~2500m ² / g or 500~2000m ² / g, pore volume of at 0.25~2.0cc / g or 0.25~1.5cc / g, and measured by a water vapor method The volume of the pores in the range of the pore radius of 6 to 16 mm is 80% or more of the volume occupied by pores having a pore radius of 100 mm or less, and in the diffraction peak on the (002) plane of the X-ray diffraction intensity curve An organic chlorine solvent recovery method using a fibrous activated carbon having a graphitic crystalline structure parameter Ip / Io of 0.35 or less is disclosed. According to the methods described in Patent Documents 4 and 5, the corrosion of the apparatus is reduced, and the organic chlorine solvent or the mixed solvent can be efficiently recovered.

JP 2005-138038 A JP-A-7-145516 JP-A-6-99065 JP-A-2005-903 JP 2005-21851 A

  An organic compound such as methylene chloride having a boiling point in the range of −30 to 70 ° C. has a property that the adsorbed molecule has a small volume and does not adsorb to large pores. When trying to make it adsorb | suck with a fiber, there exists a problem that the pore of an activated carbon fiber cannot be utilized effectively. Therefore, development of activated carbon fibers having particularly excellent adsorption performance for such organic compounds is desired.

  The present invention has been made in order to solve the above-mentioned problems, and an object of the present invention is to activate carbon fibers having particularly excellent adsorption performance for organic compounds having a boiling point in the range of -30 to 70 ° C. Is to provide.

The activated carbon fiber of the present invention has a BET specific surface area of 700 to 1500 m ² / g, a total pore volume of 0.3 to 0.7 cc / g, and a micropore pore volume of 1 nm or less in pore diameter of all micropores. It is characterized by being 95% or more of the pore volume and having a moisture adsorption rate of 15% or less at a temperature of 25 ° C. and a relative humidity of 52%.

  In the activated carbon fiber of the present invention, the amount of carboxyl groups is preferably 0.04 meq / g or less.

  The activated carbon fiber of the present invention is preferably used for adsorbing an organic compound having a boiling point in the range of −30 to 70 ° C.

  ADVANTAGE OF THE INVENTION According to this invention, the activated carbon fiber which has the especially outstanding adsorption | suction performance with respect to the organic compound in the range whose boiling point is -30-70 degreeC is provided.

One feature of the activated carbon fiber of the present invention is that the BET specific surface area is in the range of 700 to 1500 m ² / g. When the activated carbon fiber of the present invention has a BET specific surface area of less than 700 m ² / g, the adsorption area is too small and an organic compound such as methylene chloride having a boiling point in the range of −30 to 70 ° C. is sufficiently adsorbed. In addition, there is a problem that the organic compound such as methylene chloride having a boiling point in the range of −30 to 70 ° C. is not sufficiently adsorbed because the pores become large even when exceeding 1500 m ² / g. There is. In order to sufficiently adsorb an organic compound such as methylene chloride having a boiling point in the range of −30 to 70 ° C., the BET specific surface area of the activated carbon fiber is preferably in the range of 900 to 1200 m ² / g. The BET specific surface area means a specific surface area determined by a BET method using a nitrogen gas adsorption isotherm at a liquid nitrogen temperature, and is measured using, for example, a specific surface area / pore distribution measuring device Gemini 2375 (manufactured by Micromeritics). be able to.

  The activated carbon fiber of the present invention is also characterized in that the total pore volume is in the range of 0.3 to 0.7 cc / g. When the total pore volume of the activated carbon fiber of the present invention is less than 0.3 cc / g, the adsorption volume is too small and an organic compound such as methylene chloride having a boiling point in the range of −30 to 70 ° C. is sufficient. In addition, since the pores become large even when it exceeds 0.7 cc / g, organic compounds such as methylene chloride having a boiling point in the range of −30 to 70 ° C. are sufficiently adsorbed. There is a bug that is not done. The total pore volume of the activated carbon fiber is in the range of 0.4 to 0.5 cc / g so that an organic compound such as methylene chloride having a boiling point in the range of −30 to 70 ° C. can be sufficiently adsorbed. It is preferable. The total pore volume can be measured using, for example, a specific surface area / pore distribution measuring device Gemini 2375 (manufactured by Micromeritics).

  One feature of the activated carbon fiber of the present invention is that the micropore pore volume having a pore diameter of 1 nm or less is 95% or more of the total micropore pore volume. When the micropore pore volume having a pore diameter of 1 nm or less is less than 95% of the total micropore pore volume, the pores become too large, for example, methylene chloride having a boiling point in the range of −30 to 70 ° C. There is a problem that organic compounds such as are not sufficiently adsorbed. The ratio of the micropore pore volume having a pore diameter of 1 nm or less can be measured using, for example, a specific surface area / pore distribution measuring device Gemini 2375 (manufactured by Micromeritics).

  The activated carbon fiber of the present invention is also characterized in that the moisture adsorption rate at a temperature of 25 ° C. and a relative humidity of 52% is 15% or less. When the moisture adsorption rate at a temperature of 25 ° C. and a relative humidity of 52% exceeds 15%, water molecules are first adsorbed around the pores, so that the adsorption amount of the organic compound is not adsorbed in the pores. There is a problem that it is lowered accordingly. In order to make it less susceptible to the adsorption of water molecules, the moisture adsorption rate at a temperature of 25 ° C. and a relative humidity of 52% is preferably 13% or less. The moisture adsorption rate at a temperature of 25 ° C. and a relative humidity of 52% can be measured using, for example, a constant temperature and humidity chamber SH-661 (manufactured by Espec Corp.).

  In the activated carbon fiber of the present invention, the BET specific surface area, the total pore volume, the micropore pore volume ratio, and the moisture adsorption rate are within the above-described ranges, respectively, so that the boiling point is in the range of −30 to 70 ° C. Particularly high adsorption performance is exhibited for the inside (more preferably within the range of 20 to 60 ° C.) and the organic compound having a relatively low boiling point (low boiling point organic compound). It has pores suitable for adsorbing low-boiling organic compounds, which are activated carbon fibers with the BET specific surface area, total pore volume, micropore pore volume ratio and moisture adsorption rate described above. This is probably because of the reason.

  Here, examples of low-boiling organic compounds suitable for adsorption by the activated carbon fiber of the present invention include methylene chloride (dichloromethane) (boiling point: 39.8 ° C.), diethyl ether (boiling point: 34.4 ° C.), chloroform. (Boiling point: 61.2 ° C), pentane (boiling point: 36.1 ° C), hexane (boiling point: 68.7 ° C), acetone (boiling point: 56.1 ° C), tetrahydrofuran (boiling point: 66.0 ° C), methanol (Boiling point: 64.5 ° C.). Among these, methylene chloride is particularly suitable as an object to be adsorbed by the activated carbon fiber of the present invention because it is insoluble in water.

  In the activated carbon fiber of the present invention, the amount of carboxyl groups is preferably 0.04 meq / g or less, and more preferably 0.02 meq / g or less, for the reason that moisture hardly adsorbs. The amount of carboxyl groups of the activated carbon fiber can be measured by neutralization titration with a base.

  The amount of phenolic hydroxyl groups, the total amount of acidic groups, and the amount of total basic groups in the activated carbon fiber of the present invention are not particularly limited, but the amount of phenolic hydroxyl groups is usually 0.05 to 0.15 meq / The amount of g and total acidic groups is usually 0.05 to 0.25 meq / g, and the amount of total basic groups is usually 0.30 to 0.60 meq / g. In addition, the amount of phenolic hydroxyl groups and the total amount of acidic groups of the activated carbon fiber can be measured by neutralization titration with a base, and the amount of total basic groups can be measured by neutralization titration with an acid.

  The activated carbon fiber of the present invention is not particularly limited as a raw material (precursor), for example, phenol, cellulose, polyacrylonitrile, pitch, aramid, polyimide, polyamide, polyamideimide, polyphenylenebenzobisoxazole, Fibers commonly used as raw materials in the art such as polyvinyl alcohol, polysulfone ether, polysulfone, polyphenylene oxide, and the like can be used. Among these, the cellulose type has a high oxygen content in the raw material, and the amount of surface acidic groups is relatively large among activated carbons. The phenol type has a lower oxygen content than the cellulose type, has a small polar portion derived from ash, has a lower degree of polarity than the cellulose type, and is less susceptible to moisture adsorption. Among them, it is preferable to use phenol fiber as a raw material because it is highly hydrophobic and has both workability and practical strength.

  In producing the activated carbon fiber of the present invention, first, when phenol fiber is used as a raw material, the temperature is raised to a temperature of about 800 to 950 ° C. while moving in a tubular furnace under a nitrogen flow. In the state of holding for 5 to 2.0 hours, an activation process is performed in which pure water is continuously supplied. Here, by adjusting the retention time (activation time) described above, the BET specific surface area, the total pore volume, the ratio of the micropore pore volume, and the moisture adsorption rate in the obtained activated carbon fiber can be controlled.

  After the activation treatment, cooling is performed in a state where the oxygen concentration is 0.5% or less (preferably 0.1% or less). By setting the oxygen concentration during this cooling to 0.5% or less, the activated carbon fiber of the present invention having a moisture adsorption rate of 15% or less at a temperature of 25 ° C. and a relative humidity of 52% can be obtained. This is considered to be because the generation of surface functional groups of activated carbon fibers is suppressed in the cooling step. In order to reduce the oxygen concentration to 0.5% or less as described above, specifically, an operation may be performed in which the flow rate of nitrogen in the cooling process is increased and the furnace pressure at the inlet / outlet can be maintained at 2 Pa or higher. In this regard, conventionally, there is no focus on the oxygen concentration in the cooling step, and cooling is performed without performing the above-described operation, and the oxygen concentration is usually about 1%.

  Since the activated carbon fiber of the present invention exhibits particularly excellent adsorption performance for low boiling point organic compounds having a boiling point in the range of -30 to 70 ° C, such low boiling point organic compounds are mainly adsorbed. It can apply suitably to the filter which does. The filter to which the activated carbon fiber of the present invention is applied can alternately switch between adsorption and desorption with water vapor, and exhaust gas for removing and recovering low-boiling organic compounds discharged from industrial processes such as chemical factories and pharmaceutical factories. It is suitably used for a processing apparatus.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

<Example 1>
Using a tubular furnace having an inner diameter of 70 mm and an effective length of 30 cm, a phenol fiber having a fiber diameter of 24 μm was heated to 900 ° C. at a temperature increase rate of 5 ° C./min under a nitrogen flow at 5 L / min for 1 hour (activation time ) Purified water was continuously supplied at a rate of 0.6 mL / min while being held, and an activation treatment was performed. Thereafter, the furnace pressure at the entrance / exit was maintained at 2 Pa or higher and cooled to room temperature. In order to maintain the furnace pressure at the inlet / outlet at 2 Pa or higher, the flow rate of nitrogen is gradually increased as the temperature in the furnace decreases, and finally, by flowing 30 L / min of nitrogen, the oxygen concentration during cooling is reduced. 0.05% (measured with a zirconia oxygen concentration meter LC-750L manufactured by Toray Engineering Co., Ltd.). Thus, the activated carbon fiber of Example 1 was obtained.

<Example 2>
An activated carbon fiber of Example 2 was obtained in the same manner as in Example 1 except that the activation time was 1.5 hours.

<Comparative Example 1>
An activated carbon fiber of Comparative Example 1 was obtained in the same manner as in Example 1 except that the cooling step was performed without controlling the oxygen concentration (oxygen concentration: 1.0%).

<Comparative example 2>
An activated carbon fiber of Comparative Example 2 was obtained in the same manner as Comparative Example 1 except that the activation time was 1.5 hours.

  The following evaluation tests were performed on the activated carbon fibers obtained in Examples 1 and 2 and Comparative Examples 1 and 2.

(1) BET specific surface area (m ² / g)
About 30 mg of a sample was collected, vacuum-dried at 120 ° C. for 12 hours, weighed, and measured using a specific surface area / pore distribution measuring device Gemini 2375 (manufactured by Micromeritics). The adsorption amount of nitrogen gas at the boiling point of liquid nitrogen (-195.8 ° C.) was measured in the range of relative pressure of 0.02 to 0.95, and the adsorption isotherm of the sample was created. Based on the results in the relative pressure range of 0.02 to 0.15, the BET specific surface area (unit: m ² / g) per weight was determined by the BET method.

(2) Total pore volume (cc / g)
About 30 mg of a sample was collected, vacuum-dried at 120 ° C. for 12 hours, weighed, and measured using a specific surface area / pore distribution measuring device Gemini 2375 (manufactured by Micromeritics). The adsorption amount of nitrogen gas at the boiling point of liquid nitrogen (-195.8 ° C.) was measured in the range of relative pressure of 0.02 to 0.95, and the adsorption isotherm of the sample was created. The total pore volume (unit: cc / g) was calculated from the result at a relative pressure of 0.95.

(3) Total micropore pore volume (A) (cc / g)
About 30 mg of a sample was collected, vacuum-dried at 120 ° C. for 12 hours, weighed, and measured using a specific surface area / pore distribution measuring device Gemini 2375 (manufactured by Micromeritics). The adsorption amount of nitrogen gas at the boiling point of liquid nitrogen (-195.8 ° C.) was measured in the range of relative pressure of 0.02 to 0.95, and the adsorption isotherm of the sample was created. This result was analyzed by the MP method with an analysis range of 0 to 20 cm and a t-determining formula H.264. Analysis was performed under the conditions of J, and the total micropore pore volume (A) (unit: cc / g) was calculated from the results of the micropore pore diameter distribution number table at the time of adsorption.

(4) Micropore pore volume with pore diameter of 1 nm or less (B) (cc / g)
About 30 mg of a sample was collected, vacuum-dried at 120 ° C. for 12 hours, weighed, and measured using a specific surface area / pore distribution measuring device Gemini 2375 (manufactured by Micromeritics). The adsorption amount of nitrogen gas at the boiling point of liquid nitrogen (-195.8 ° C.) was measured in the range of relative pressure of 0.02 to 0.95, and the adsorption isotherm of the sample was created. This result was analyzed by the MP method with an analysis range of 0 to 2 nm and a t-determining formula H.264. Analyzing under the conditions of J, subtracting the micropore pore volume with a pore diameter of 1.003 nm or more from the total micropore pore volume (A) from the results of the micropore pore diameter distribution number table at the time of adsorption, The micropore pore volume B (unit: cc / g) of 1 nm or less was calculated.

(5) Moisture adsorption rate (%) at a temperature of 25 ° C. and a relative humidity of 52%
About 0.2 mg of a sample was collected, vacuum-dried at 120 ° C. for 12 hours, weighed, and placed in a thermo-hygrostat SH-661 (manufactured by Espec) for 2 hours at a temperature of 25 ° C. and a relative humidity of 52%. The moisture adsorption rate (%) was determined from the change in weight.

(6) Total acidic group content (meq / g)
After washing and drying the sample, about 1 g was collected, vacuum-dried at 120 ° C. for 12 hours, weighed, immersed in 50 ml of 1/10 M NaOH aqueous solution, and shaken at 25 ° C. for 2 hours. This solution was filtered with a glass filter, and 20 ml of the filtrate was accurately collected and back-titration was performed with a 1/10 M aqueous HCl solution. In the titration, a 0.1 w / v% methyl orange solution (manufactured by Wakken Pharmaceutical Co., Ltd.) was used as an indicator. The blank test was performed in the same manner, and the total amount of acidic groups (unit: meq / g) was determined from the value obtained by subtracting the titration value in the blank test.

(7) Carboxyl group amount (meq / g)
After the sample was washed with water and dried, about 1 g was collected, vacuum dried at 120 ° C. for 12 hours, weighed, immersed in 50 ml of 1/20 M Na ₂ CO ₃ aqueous solution, and shaken at 25 ° C. for 2 hours. This solution was filtered with a glass filter, and 20 ml of the filtrate was accurately collected and back-titration was performed with a 1/10 M aqueous HCl solution. In the titration, a 0.1 w / v% methyl orange solution (manufactured by Wakken Pharmaceutical Co., Ltd.) was used as an indicator. The blank test was performed in the same manner, and the carboxyl group amount (unit: meq / g) was determined from the value obtained by subtracting the titration value in the blank test.

(8) Amount of phenolic hydroxyl group (meq / g)
The amount of phenolic hydroxyl groups (unit: meq / l) was determined by subtracting the amount of carboxyl groups from the total amount of acidic groups.

(9) Total basic group amount (meq / g)
After the sample was washed with water and dried, about 1 g was collected, vacuum dried at 120 ° C. for 12 hours, weighed, immersed in 50 ml of 1/10 M HCl aqueous solution, and shaken at 25 ° C. for 2 hours. This liquid was filtered with a glass filter, and 20 ml of the filtrate was accurately collected and back titrated with a 1/10 M NaOH aqueous solution. In the titration, a 0.1 w / v% methyl orange solution (manufactured by Wakken Pharmaceutical Co., Ltd.) was used as an indicator. The blank test was performed in the same manner, and the total basic group amount (unit: meq / g) was determined from the value obtained by subtracting the titration value in the blank test.

(10) Adsorption performance evaluation for methylene chloride Methylene chloride gas having a concentration of 500 ppm, a temperature of 30 ° C., a humidity of 50%, and an air volume of 10 m ³ / min was passed through an adsorption device equipped with two adsorption tanks filled with about 3 kg of a sample. An average adsorption breakthrough time (minutes) was determined by repeating the cycle of adsorption for a certain period of time and desorption by ejecting water vapor into the adsorption tank at the end of adsorption.

  The results obtained for the activated carbon fibers of Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Tables 1 and 2, respectively.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

Claims (3)

BET specific surface area is 700-1500 m ² / g, total pore volume is 0.3-0.7 cc / g, and micropore pore volume with pore diameter of 1 nm or less is 95% or more of total micropore pore volume. An activated carbon fiber having a water adsorption rate of 15% or less at a temperature of 25 ° C. and a relative humidity of 52%.   The activated carbon fiber according to claim 1, wherein the amount of carboxyl groups is 0.04 meq / g or less.   The activated carbon fiber according to claim 1 or 2, which is used for adsorbing an organic compound having a boiling point in the range of -30 to 70 ° C.