Fibrous activated carbon and method for recovering organic chlorine-based solvent using same

Abstract

One aspect of the present invention relates to fibrous activated carbon having a BET specific surface area of 800-2000 m2 / g, an oxygen concentration of 4.0 mass% or less as derived using an inert gas melting-non-dispersive infrared absorption (NDIR) method, and an oxygen content of 1.5 mass% or greater as derived using the NDIR method occurring at 800-1500°C.

Description

Fibrous activated carbon and method for recovering organochlorine solvents using the same

[0001] The present invention relates to a fibrous activated carbon and a method for recovering an organic chlorine-based solvent using the same.

[0002] Gases containing various organic chlorine solvents are generated in manufacturing processes in various industries, including the printing, electrical, and mechanical industries. For example, gases containing organic chlorine solvents at concentrations of approximately 0.1 to 1,000 ppm are generated in paint booths and magnetic tape coating processes. Since organic chlorine solvents cause acute and chronic toxicity, as well as strong carcinogenic and other toxicities, and have low biodegradability, the external release of such gases has been strictly restricted in recent years.

[0003] On the other hand, when the quality of solvents used in the manufacturing processes of various industries as mentioned above deteriorates, the deteriorated solvents are either discarded or regenerated and reused. However, even if they are discarded, if they are burned, the generation of dioxins and other substances becomes a problem, and if they are regenerated, the disposal of poor-quality solvents generated during the regeneration process becomes a problem. Under these circumstances, it is essential to efficiently separate and recover organic chlorine-based solvents from exhaust gases.

[0004] Conventionally, activated carbon has been used to recover organochlorine solvent gases such as methylene chloride. Specifically, a method has been reported in which a gas to be treated is supplied to a packed tower filled with activated carbon or activated carbon fiber, the contained organochlorine solvents are adsorbed and separated, and then the organochlorine solvents adsorbed on the adsorbent are desorbed and recovered (e.g., Non-Patent Document 1). The organochlorine solvent adsorbed on the activated carbon is desorbed from the activated carbon as a mixed gas of the organochlorine solvent gas and steam by blowing steam at 110°C to 160°C into the activated carbon.

[0005] In addition, Patent Document 1 reports on activated carbon and an apparatus that are preferable for recovering organic chlorine solvent gases. Furthermore, Patent Document 2 describes that it is preferable to use fibrous activated carbon having specific physical properties.

[0006] In the technology described in Non-Patent Document 1, the mixed gas is cooled and condensed, and the water and the organic chlorine solvent are separated in liquid form, thereby recovering the organic chlorine solvent and reusing it. Then, a gas containing the organic chlorine solvent is again passed through the activated carbon regenerated by steam heating to adsorb the organic chlorine solvent. It has been reported that by repeating this procedure, the organic chlorine solvent can be recovered and reused without discharging the harmful organic chlorine solvent to the outside.

[0007] When activated carbon is broadly classified into granular activated carbon and fibrous activated carbon from the viewpoint of materials for solvent recovery, it is said that when fibrous activated carbon is used to adsorb and desorb organochlorine solvents, the quality of the recovered solvent is better than that of granular activated carbon. The reason for this is that fibrous activated carbon has a faster adsorption and desorption rate than granular activated carbon, and therefore solvent adsorption and desorption can be performed more frequently, so the time that the solvent is adsorbed by the activated carbon is shorter and the solvent is less likely to deteriorate.

[0008] However, the most important problem with the above-mentioned conventional solvent recovery methods is the quality of the recovered organic chlorine solvent. That is, when an organic chlorine solvent is adsorbed on activated carbon, it decomposes and generates hydrochloric acid. This is also true for fibrous activated carbon, and it is inevitable that hydrochloric acid will be mixed into the organic chlorine solvent, gradually increasing the acidity of the solvent. As a result, the solvent recovery equipment will rapidly corrode, and there is currently a need for a method of recovering organic chlorine solvents that generates less hydrochloric acid.

[0009] Patent Document 1 describes the properties of activated carbon suitable for recovering organic solvents, but while it presents an excellent match with chlorinated solvents due to its large pore volume and adsorption capacity, the pore radius is large and sufficient selectivity cannot be expected. Furthermore, the affinity with water during desorption using water vapor is not taken into consideration, and it is difficult to say that sufficient consideration has been given to the impact on the reduction of adsorption capacity due to regeneration.

[0010] Patent Document 2 discloses that the use of specific activated carbon makes it difficult for the quality of organic chlorine solvents to deteriorate even after repeated adsorption and desorption. However, it does not disclose the adsorption properties of organic chlorine solvents when they are repeatedly adsorbed and desorbed in the case of steam regeneration.

[0011] Therefore, in view of the above-mentioned current situation, a main object of the present invention is to provide a fibrous activated carbon that has high adsorption capacity for organic chlorine-based solvents and can maintain said adsorption capacity even after repeated adsorption and desorption of organic chlorine-based solvents.

[0012] "Advances and Practice of Deodorizing and Eliminating Technology", 1991, published by the General Technology Center, Chapter 5: Characteristics and Applications of Activated Carbon and Activated Carbon Fiber, pp. 389-391

[0013] JP 2018-34109 A Patent No. 4509523 A

[0014] As a result of intensive research to solve the above problems, the present inventors have found that the above problems can be solved by a fibrous activated carbon having the following composition. Based on this finding, further research has led to the completion of the present invention.

[0015] That is, the fibrous activated carbon according to the first aspect of the present invention has a BET specific surface area of ​​800 to 2000 m ２ / g, the oxygen concentration determined by an inert gas fusion-non-dispersive infrared (NDIR) method is 4.0% by mass or less, and the amount of oxygen generated at a temperature of 800°C or higher and 1500°C or lower determined by the NDIR method is 1.5% by mass or more.

[0016] Hereinafter, embodiments of the present invention will be specifically described, but the present invention is not limited to these.

[0017] (Fiber-like activated carbon) The fibrous activated carbon of this embodiment has a BET specific surface area of ​​800 to 2000 m ２ / g. Furthermore, in the fibrous activated carbon of this embodiment, the oxygen concentration determined by inert gas fusion-non-dispersive infrared absorption (NDIR) method is 4.0 mass% or less, and the amount of oxygen generated at a temperature of 800°C or higher and 1500°C or lower determined by the NDIR method is 1.5 mass% or more. By having such a configuration, the fibrous activated carbon has the excellent advantage of having high adsorption ability for organic chlorine-based solvents and being able to maintain this adsorption ability even after repeated adsorption and desorption of organic chlorine-based solvents.

[0018] That is, the present invention can provide a fibrous activated carbon that has high adsorption capacity for organic chlorine-containing solvents and can maintain the adsorption capacity even after repeated adsorption and desorption of organic chlorine-containing solvents, and a method for recovering organic chlorine-containing solvents using the same.

[0019] In this embodiment, the specific surface area is derived from the formation of pores in the fibrous activated carbon for adsorbing substances. ２ / g or more, the carbon black has high adsorption ability and adsorption speed for organic chlorine solvents. ２ / g or less, the fibrous activated carbon has sufficient mechanical strength and durability to withstand long-term use. ２ / g, and 860 to 1500m ２ More preferably, it is 900 m / g. ２ / g, 1000m ２ / g, 1100m ２ / g, 1200m ２ / g, 1300m ２ / g, 1500m ２ / g, 1750m ２ / g, etc.

[0020] In this embodiment, the BET specific surface area refers to the specific surface area calculated by the nitrogen adsorption method, and is a value measured by the method described in the examples below.

[0021] Furthermore, the fibrous activated carbon of this embodiment has an oxygen concentration of 4.0 mass% or less, as determined by an inert gas fusion-non-dispersive infrared (NDIR) method, and the amount of oxygen generated at 800°C or higher and 1500°C or lower is 1.5 mass% or more.

[0022] The inert gas fusion-non-dispersive infrared (NDIR) method used in this embodiment is a method for analyzing the species of combusted gases, similar to the general organic elemental analysis (CHN) method. ２ Since the oxygen content is directly observed by infrared light, it is not a value obtained by subtracting the amounts of other elements as in organic elemental analysis, but is a direct observation. Therefore, it has the advantage of high numerical accuracy and the existence state in the sample can be inferred from the observation temperature. Note that a specific method for measuring the oxygen content of the fibrous activated carbon of this embodiment and the amount of oxygen generated at temperatures between 800°C and 1500°C using NDIR will be described in the Examples below.

[0023] If the oxygen concentration in the fibrous activated carbon is too high, not only will the affinity with water decrease the adsorption performance when adsorbing organic chlorine-based solvents, but it may also cause pore blockage due to water during desorption using steam. Therefore, it is important that the oxygen concentration be 4.0% by mass or less. A more preferred oxygen concentration is 3.8% by mass or less. While there is no particular limit to the lower limit of the oxygen concentration, from the viewpoint that excessively high hydrophobicity reduces the adsorption capacity of polar molecules such as halogenated hydrocarbons such as methylene chloride, the oxygen concentration is preferably 1.5% by mass or more, more preferably 1.7% by mass or more, and even more preferably 2.0% by mass or more. The oxygen concentration is preferably 1.5 to 4.0% by mass, more preferably 1.7 to 4.0% by mass, and even more preferably 2.0 to 3.8% by mass.

[0024] On the other hand, in order to obtain a fibrous activated carbon that can maintain its adsorption ability even after repeated adsorption and desorption of organic chlorine-based solvents, it is important that the amount of oxygen generated in the temperature range of 800°C to 1500°C is 1.5% by mass or more relative to the fibrous activated carbon. Since the oxygen is contained in the carbon structure skeleton, it has the effect of imparting moderate hydrophilicity to the activated carbon. Furthermore, when adsorbed organic chlorine-based solvents are desorbed from the fibrous activated carbon under normal desorption conditions, the presence of a certain amount of oxygen is thought to prevent the properties of the activated carbon from changing even after repeated adsorption and desorption of organic chlorine-based solvents. Therefore, the oxygen amount is preferably 1.6% by mass or more. On the other hand, if the oxygen amount is too high, the carbon exhibits high adsorption ability for water, which may gradually accumulate in the pores, resulting in a decrease in the amount of organic chlorine-based solvent adsorbed (recovered). From the above viewpoints, the amount of oxygen generated at temperatures between 800° C. and 1500° C. is preferably 1.5 to 3.0 mass %, more preferably 1.6 to 2.8 mass %, and particularly preferably 1.6 to 2.5 mass %.

[0025] The fibrous activated carbon of this embodiment may have any of the above-described characteristics. Preferably, the equilibrium adsorption moisture regain at 25°C and 37% relative humidity is 1.0 to 15.0%, as calculated using the formula described in the Examples below. If the equilibrium adsorption moisture regain is 1.0% or more, the pore radius falls within an appropriate range, resulting in excellent adsorption performance for chlorinated organic solvents. If the equilibrium adsorption moisture regain is 15.0% or less, the hydrophilicity falls within an appropriate range, ensuring the adsorption performance for chlorinated organic solvents. Furthermore, when chlorinated organic solvents are desorbed from the fibrous activated carbon using steam, the moisture adsorbed by the fibrous activated carbon is easily released, facilitating the regeneration of the adsorption performance for chlorinated organic solvents when used for the next adsorption. It is more preferable that the equilibrium adsorption moisture regain at 25°C and 37% relative humidity is 1.5 to 10.0%.

[0026] In this embodiment, the equilibrium adsorption moisture content is determined by the following method.

[0027] After measuring the mass after drying using the method described in the Examples below, the sample was stored at 25°C and 37% relative humidity, and the sample mass was measured every 20 hours. Measurements were continued until the mass change between two consecutive measurements was within 2% by mass. The sample mass when the mass change was within 2% by mass was defined as the sample mass at equilibrium adsorption. The difference between the sample mass at equilibrium adsorption and the dry mass of the sample was defined as the equilibrium adsorption moisture content, and the equilibrium adsorption moisture content was calculated by dividing the equilibrium adsorption moisture content by the dry mass of the sample.

[0028] Furthermore, the fibrous activated carbon of this embodiment preferably has a pore volume of 0.25 to 0.50 cc / g, more preferably 0.28 to 0.48 cc / g, and even more preferably 0.30 to 0.48 cc / g. A pore volume of 0.25 cc / g or more is preferable because the amount of organic chlorine-based solvent adsorbed increases, and a pore volume of 0.28 cc / g or more is more preferable, and a pore volume of 0.30 cc / g or more is even more preferable. A pore volume of 0.50 cc / g or less is preferable because it has the advantages of increasing the desorption rate of organic chlorine-based solvents, shortening the desorption time, improving the adsorption power for organic chlorine-based solvents, and improving adsorption performance at low concentrations, and a pore volume of 0.48 cc / g or less is more preferable.

[0029] In this embodiment, the pore volume of the activated carbon is a value measured by a gas adsorption method using nitrogen gas at a relative pressure of 0.93. The specific method will be described in the examples below.

[0030] The fibrous activated carbon preferably used in this embodiment may be any activated carbon obtained from any carbonaceous material, as long as the raw material fibers can be carbonized and activated to become fibrous activated carbon.

[0031] For example, the raw material for the fibrous activated carbon used in this embodiment may be a synthetic polymer compound, a semi-synthetic polymer compound, a natural polymer compound, natural or synthetic pitch, or the like.

[0032] Examples of synthetic polymer compounds include polyamide fibers such as nylon, polyvinyl alcohol (PVA) fibers such as vinylon, polyester fibers such as polyester, polyacrylonitrile fibers such as acrylic, polyolefin fibers such as polyethylene and polypropylene, polyurethane fibers such as polyurethane, and phenolic fibers such as phenolic resins.

[0033] Examples of semi-synthetic polymer compounds include cellulose fibers such as acetate and triacetate, and protein fibers such as Promix, etc. Examples of natural polymer compounds include cellulose fibers such as rayon, protein fibers such as casein fiber, and chitin fiber.

[0034] Among the above, from the viewpoints of the strength of the fiber, the diameter of the pores formed, and the stability of the pore volume, it is preferable that the fibrous activated carbon of this embodiment is a fibrous activated carbon made from phenolic fibers (phenolic fibrous activated carbon).

[0035] The raw material fibers used for the fibrous activated carbon of this embodiment are preferably 1 denier to 10 denier. 2 denier to 8 denier are particularly preferred. A smaller fiber diameter for the fibrous activated carbon of this embodiment improves adsorption / desorption performance, but if it is too small, there is a risk of increased pressure loss. A larger fiber diameter reduces pressure loss, but if it is too large, there is a risk of reduced adsorption / desorption performance, so the fiber diameter is preferably in the range of 5 μm to 30 μm. 8 μm to 20 μm is particularly preferred.

[0036] (Method for Producing Fibrous Activated Carbon) The fibrous activated carbon of this embodiment can be obtained by carbonizing and activating the raw materials described above.

[0037] Conventional carbonization methods can be used, typically by heating while blocking oxygen or air. However, since oxygen atoms are believed to be introduced into the activated carbon structure via ether bonds, it is important in this embodiment to appropriately control the carbonization of the fibers. In particular, when phenolic fibers are used as the raw material, oxygen atoms are introduced via a condensation reaction between phenolic hydroxyl groups and methylol groups. Therefore, excessively high carbonization temperatures are undesirable because oxygen functional groups are not incorporated into the structure, while excessively low temperatures are undesirable because they lead to activation under conditions where the structure is not fully constructed. Therefore, when phenolic fibers are used as the raw material, the carbonization temperature is preferably in the range of 250°C to 600°C, more preferably 300°C to 500°C. Furthermore, if the heating rate is too fast, various structures will be generated all at once, which may result in variations in pore size during activation (described below). Furthermore, if the heating rate is too slow, the functional groups will be removed, which is undesirable. Therefore, the time required to reach the carbonization temperature (rate of temperature rise) is preferably in the range of 25°C to 90°C / min, and more preferably 30°C to 80°C / min.

[0038] The carbonization time of the raw material is not particularly limited, but is usually in the range of 10 to 120 minutes, and in consideration of economic efficiency and the stability of the carbonization progress, a range of 20 to 100 minutes is more preferable.

[0039] The phenolic fiber used in this embodiment may contain a catalyst component to facilitate the condensation reaction. Examples of catalyst components include mineral acids such as hydrochloric acid, sulfuric acid, and phosphoric acid; metal salts such as aluminum chloride, calcium chloride, magnesium chloride, iron chloride, zinc chloride, copper chloride, aluminum bromide, calcium bromide, magnesium bromide, iron bromide, zinc bromide, and copper bromide; and ammonium salts such as ammonium chloride and ammonium bromide. From the perspective of volatility, the use of mineral acids is undesirable. While metal salts do not pose a volatilization problem, they are undesirable because residual metals tend to increase pore size during activation. Therefore, the use of ammonium chloride and ammonium bromide is preferred, and from an economical perspective, ammonium chloride is preferred.

[0040] Next, the carbonized material obtained above is activated. Either a gas activation method or a chemical activation method can be used to activate the carbonized material, and the gas activation method and the chemical activation method may be combined.

[0041] When gas activation is performed, the carbonized material can be exposed to water vapor, carbon dioxide gas, or a mixed gas thereof in a predetermined temperature range using a fluidized bed, a multi-stage furnace, a rotary furnace, or the like, which are common activated carbon production equipment, to perform the activation treatment.

[0042] In this case, activation is preferably carried out at a temperature of 950°C or less so as not to develop the crystalline structure of the fibrous activated carbon. At activation temperatures exceeding 950°C, the crystalline structure develops, which may prevent the formation of an appropriate pore structure. A more preferred activation temperature is 900°C or less, but if the activation temperature is too low, the activation reaction rate decreases, and activation to the same activation level tends to result in an increased pore size, so activation is preferably carried out at 700°C or more.

[0043] The gas used for activation is not particularly limited, but it is preferable to use a mixed gas of water vapor and carbon dioxide gas. In order to obtain the fibrous activated carbon of this embodiment, it is preferable to activate at a low temperature to create an amorphous carbon structure. In order to proceed with activation at a relatively low temperature, it is preferable to use water vapor, which has a fast activation reaction rate. On the other hand, in order to proceed with activation in a state where the pores are small, it is preferable to use carbon dioxide, which has a slow reaction rate.

[0044] From the above viewpoint, in order to obtain the fibrous activated carbon of this embodiment having the above-mentioned properties while maintaining an amorphous structure, it is desirable to use a mixed gas of water vapor and carbon dioxide gas, preferably at a mixing ratio of water vapor / carbon dioxide gas of 1 / 0.5 to 0.5 / 1.

[0045] After the activation treatment, the obtained fibrous activated carbon may be washed with a washing solution containing an acid to remove impurities such as metal components contained in the activated carbon. Acid washing can be performed, for example, by immersing the activated carbon in a washing solution containing an acid. In the acid washing step, the raw activated carbon may be washed with hydrochloric acid and then washed with water, or an appropriate combination of water washing and acid washing may be used, such as by repeating acid washing and water washing. The acid washing solution preferably includes inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid, and organic acids such as saturated carboxylic acids such as formic acid, acetic acid, propionic acid, oxalic acid, tartaric acid, and citric acid, and aromatic carboxylic acids such as benzoic acid and terephthalic acid. Among these, washing with hydrochloric acid is more preferred. When hydrochloric acid is used as the acid washing solution, it is preferable to use dilute hydrochloric acid.

[0046] (Method for recovering organic chlorine-based solvent) This embodiment also includes a method for recovering organic chlorine-based solvent using the above-mentioned fibrous activated carbon.

[0047] Specifically, the recovery method of this embodiment includes adsorbing the organic chlorine-based solvent onto the above-mentioned fibrous activated carbon, and then desorbing the organic chlorine-based solvent from the fibrous activated carbon with steam.

[0048] In this embodiment, examples of organic chlorine-based solvents to be adsorbed include methyl chloride, methylene chloride (dichloromethane), chloroform (trichloromethane), carbon tetrachloride (tetrachloromethane), ethyl chloride (chloroethane), 1,1-dichloroethane, 1,2-dichloroethane, etc. Among these, methylene chloride is the least toxic of the chlorinated methanes, and is suitable as a solvent from the standpoint of safety, is widely used, and exhibits a high degree of effectiveness, making it an ideal organic chlorine-based solvent to be recovered.

[0049] The process of adsorbing the organic chlorine-based solvent onto the fibrous activated carbon is not particularly limited, and may involve, for example, introducing a gas to be treated containing the organic chlorine-based solvent to be recovered into a treatment tank filled with the fibrous activated carbon of this embodiment, and adsorbing the organic chlorine-based solvent in the gas to be treated onto the fibrous activated carbon. The treated gas can be discharged from the treatment tank as a purified gas.

[0050] The step of desorbing organic chlorine solvents from the fibrous activated carbon is not particularly limited, and can be carried out by introducing steam (water vapor) as a desorption gas into the treatment tank after the adsorption step. The fibrous activated carbon from which organic chlorine solvents have been desorbed by steam has its adsorption performance restored, so it can be used again in the above-mentioned adsorption step. The fibrous activated carbon of this embodiment has high adsorption ability for organic chlorine solvents and can maintain this adsorption ability even after repeated adsorption and desorption of organic chlorine solvents, making it very useful for recovering organic chlorine solvents.

[0051] The steam containing the organic chlorine solvent used in the desorption step is discharged from the treatment tank. The steam is then cooled to liquefy it, and can be separated into a recovered liquid containing the organic chlorine solvent and water using a separator or the like. The separated recovered liquid (waste liquid) can be discarded, or it can be reused as steam for desorbing the organic chlorine solvent from the fibrous activated carbon.

[0052] According to the recovery method of this embodiment, the organic chlorine-based solvent can be recovered and used semi-permanently, which is practical.

[0053] This specification discloses various aspects of the technology as described above, but the main technologies among them are summarized below.

[0054] That is, the fibrous activated carbon according to the first aspect of the present invention has a BET specific surface area of ​​800 to 2000 m ２ / g, the oxygen concentration determined by an inert gas fusion-non-dispersive infrared (NDIR) method is 4.0% by mass or less, and the amount of oxygen generated at a temperature of 800°C or higher and 1500°C or lower determined by the NDIR method is 1.5% by mass or more.

[0055] The activated carbon fiber according to a second aspect of the present invention is the activated carbon fiber according to the first aspect, which has an equilibrium adsorption moisture regain of 1.0 to 15.0% at 25° C. and a relative humidity of 37%.

[0056] The fibrous activated carbon according to the third aspect of the present invention is the fibrous activated carbon according to the first or second aspect, which has a pore volume of 0.25 to 0.50 cc / g.

[0057] A fourth aspect of the present invention provides the activated carbon fiber of any one of the first to third aspects, wherein the activated carbon fiber is a phenol-based activated carbon fiber.

[0058] A method for recovering an organic chlorine-containing solvent according to a fifth aspect of the present invention comprises adsorbing the organic chlorine-containing solvent onto the fibrous activated carbon according to any one of the first to fourth aspects, and then desorbing the organic chlorine-containing solvent from the fibrous activated carbon with steam.

[0059] A method for recovering an organic chlorine solvent according to a sixth aspect of the present invention is the method for recovering an organic chlorine solvent according to the fifth aspect, in which the organic chlorine solvent is methylene chloride.

[0060] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0061] First, the test methods for evaluating the properties in the present example will be described.

[0062] [Measurement of Nitrogen Adsorption Isotherm] Using a BELSORP-MAX II manufactured by Microtrac-Bell Corporation, the fibrous activated carbon was heated at 300°C for 3 hours under reduced pressure (vacuum degree: 0.1 kPa or less), and then the nitrogen adsorption isotherm of each fibrous activated carbon at 77K was measured.

[0063] [Measurement of BET Specific Surface Area] The nitrogen adsorption isotherm obtained by the above method was analyzed by the multipoint method using the BET equation, and the specific surface area was calculated from the straight line in the region of the relative pressure P / P0 = 0.01 to 0.1 of the obtained curve.

[0064] [Measurement of Oxygen Concentration by NDIR] Elemental analysis was performed using an oxygen, nitrogen, and hydrogen analyzer (Horiba, Ltd., "EMGA-930") based on the inert gas fusion method. The detection method for this device was oxygen: inert gas fusion-nondispersive infrared absorption (NDIR), and calibration was performed using Sn capsules with SS-3 and SS-10 (O standard samples). As a pretreatment, 5 mg of each sample (fibrous activated carbon) dried at 250°C for approximately 10 minutes was placed in a Sn capsule and inserted into the elemental analyzer. After degassing for 30 seconds under nitrogen flow, the sample holder was measured. After degassing was completed, the temperature was first raised, and the total amount from 250°C to 1500°C was taken as the oxygen content of the sample. The oxygen concentration was calculated by dividing this oxygen content by the sample mass after drying during pretreatment.

[0065] The test was carried out on three samples, and the average value was used as the analytical value of the oxygen content. When measuring the oxygen content, the amount of oxygen desorption during temperature rise was simultaneously measured.

[0066] [Measurement of the amount of oxygen generated at 800° C. or higher and 1500° C. or lower] For each sample (fibrous activated carbon), the amount of oxygen desorption detected from 800° C. to 1500° C. in the above-mentioned oxygen concentration measurement by NDIR was measured. Based on this amount of oxygen desorption, the mass percentage (mass%) per fibrous activated carbon was calculated, and this was defined as the amount of oxygen (mass%) generated at 800° C. or higher and 1500° C. or lower.

[0067] [Measurement of equilibrium adsorption moisture content] Approximately 2 g of each sample (fibrous activated carbon) was placed in a crucible and dried at 120°C for 6 hours using a hot air dryer. The mass after drying was accurately measured, and this mass was taken as the dry mass of the sample. The sample was then left in a constant temperature and humidity chamber at a temperature of 25°C and a humidity of 37%. The sample mass was measured every 20 hours, and measurements were continued until the mass change between two consecutive measurements was within 2% by mass. The sample mass when the mass change was within 2% by mass was taken as the sample mass at equilibrium adsorption, and the equilibrium adsorption moisture content was calculated according to the following formula: Equilibrium adsorption moisture content [%] = (sample mass at equilibrium adsorption - sample dry mass) / (sample dry mass) × 100

[0068] [Measurement of Pore Volume (BET Method)] Using a BELSORP-mini manufactured by Microtrac-Bell Co., Ltd., each sample (fibrous activated carbon) was heated at 300°C for 3 hours under a nitrogen stream (nitrogen flow rate: 50 mL / min), and then the nitrogen adsorption isotherm of the sample was measured at 77.4 K. The total pore volume was calculated from the amount of nitrogen adsorbed at a relative pressure P / P0 = 0.93 in the obtained adsorption isotherm.

[0069] [Fiber-like activated carbon] (Example 1) Production of fibrous activated carbon using phenolic resin fiber as a starting material: Phenolic resin fiber (phenolic resin fiber manufactured by Gun-ei Chemical Industry Co., Ltd., trade name: Kynol fiber) was used, and the fiber was processed in a carding machine and further needle-punched to produce a nonwoven fabric.

[0070] The resulting nonwoven fabric was heated to 500°C at a rate of 50°C / min, and the fibers were carbonized with a residence time of 20 minutes at 500°C. The carbonized fibers were activated at 850°C for 1 hour in the presence of a mixed gas of water vapor and carbon dioxide (mixing ratio of water vapor / carbon dioxide = 1 / 1), yielding a fibrous activated carbon. The BET specific surface area, pore volume, oxygen concentration, amount of oxygen generated at 800 to 1500°C, and equilibrium adsorption moisture regain of the resulting phenolic fibrous activated carbon are shown in Table 1 below.

[0071] Examples 2 to 4 Fibrous activated carbons were obtained in the same manner as in Example 1, except that the carbonization temperature, carbonization temperature rise rate, residence time, activation temperature and activation time were changed as shown in Table 1.

[0072] Comparative Examples 1 to 3 Fibrous activated carbons were obtained in the same manner as in Example 1, except that the carbonization temperature, carbonization temperature rise rate, residence time, activation temperature and activation time were changed as shown in Table 1.

[0073] The BET specific surface area, pore volume, oxygen concentration, amount of oxygen generated at 800 to 1500°C, and equilibrium adsorption moisture content of the phenolic fibrous activated carbons obtained in Examples 2 to 4 and Comparative Examples 1 to 3 are shown in Table 1 below.

[0074] <Evaluation Method> [Organic Chlorine Solvent (Methylene Chloride) Removal Rate] 500 g of each fibrous activated carbon obtained in the Examples and Comparative Examples was packed into a 40φ×1000 mm column, and 25 g of methylene chloride at a concentration of 1000 ppm was passed through it at a relative humidity of 30 to 40%. The methylene chloride concentrations at the inlet and outlet of the column were measured, and the methylene chloride removal rate was calculated. The results are shown in Table 1.

[0075] [Adsorption Performance Retention Rate] After methylene chloride was adsorbed onto the fibrous activated carbon, steam at 120°C was passed through the column to desorb the methylene chloride. The desorbed methylene chloride was cooled to liquefy it and separated into a water layer (separated waste liquid) and a methylene chloride layer using a separator. The separated methylene chloride was reused for ventilation, and the separated waste liquid was used as steam for regenerating the fibrous activated carbon. Because the separated waste liquid dissolves methylene chloride, even in small amounts, it should not be discarded as is; it is preferable to reuse it. Therefore, in the methylene chloride recovery experiment, taking this into consideration, a closed system for methylene chloride was configured.

[0076] The regenerated fibrous activated carbon was repeatedly subjected to re-adsorption and re-desorption of methylene chloride, and the removal rate after the tenth adsorption was compared with the removal rate after the first adsorption (both of which were determined by the above-described method), and the adsorption performance maintenance rate was calculated using the following formula: Adsorption performance maintenance rate = methylene chloride removal rate after the tenth adsorption / methylene chloride removal rate after the first adsorption × 100

[0077] The results are shown in Table 1.

[0078]

[0079] (Discussion) As is clear from the results in Table 1, the fibrous activated carbons of the Examples all had excellent adsorption performance for organic chlorine-containing solvents, and also had high adsorption performance and a high adsorption performance retention rate after repeated adsorption and desorption. However, the fibrous activated carbons of the Comparative Examples, which did not satisfy either the oxygen concentration or the amount of oxygen generated at 800 to 1500°C, were inferior in adsorption performance for organic chlorine-containing solvents, and in adsorption performance and adsorption performance retention rate after repeated adsorption and desorption.

[0080] This application is based on Japanese Patent Application No. 2024-032690 filed on March 5, 2024, the contents of which are incorporated herein by reference.

[0081] In order to express the present invention, the present invention has been properly and sufficiently described above through embodiments with reference to specific examples, etc. However, it should be recognized that those skilled in the art can easily change and / or improve the above-described embodiments. Therefore, unless changes or improvements made by those skilled in the art deviate from the scope of the claims set forth in the claims, such changes or improvements are construed as being encompassed within the scope of the claims.

[0082] The present invention has wide industrial applicability in technical fields relating to activated carbon, a method for regenerating the same, and the removal of organic compounds using the same.

Claims

1. BET specific surface area is 800 to 2000 m ２ / g, wherein the oxygen concentration determined by an inert gas fusion-non-dispersive infrared (NDIR) method is 4.0% by mass or less, and the amount of oxygen generated at a temperature of 800°C or higher and 1500°C or lower determined by the NDIR method is 1.5% by mass or more relative to the fibrous activated carbon.

2. The fibrous activated carbon according to claim 1, which has an equilibrium adsorption moisture content of 1.0 to 15.0% at 25°C and a relative humidity of 37%.

3. The fibrous activated carbon according to claim 1, having a pore volume of 0.25 to 0.50 cc / g.

4. The fibrous activated carbon of claim 1, wherein the fibrous activated carbon is a phenolic fibrous activated carbon.

5. A method for recovering an organic chlorine solvent, comprising: adsorbing the organic chlorine solvent onto the fibrous activated carbon according to any one of claims 1 to 4; and then desorbing the organic chlorine solvent from the fibrous activated carbon using steam.

6. The recovery method according to claim 5, wherein the organic chlorine solvent is methylene chloride.