Activated carbon and activated carbon filter bodies

Abstract

To provide activated carbon and activated carbon filter bodies that exhibit superior chloroform removal performance. [Solution] The BET specific surface area calculated from nitrogen adsorption isotherms using the BET method is 900-1200 m². 2 The value is / g, and the pore volume of pores in the range of 0.25-0.65 nm, calculated by GCMC method from carbon dioxide adsorption isotherms, is 0.28 cm³. 3 The pore volume of pores larger than 2 nm, calculated by NLDFT method from nitrogen adsorption isotherms, is 0.0135 cm³ or more. 3 The pore volume of pores in the range of 0.37-0.65 nm, calculated by NLDFT method from nitrogen adsorption isotherms, is 0.09 cm³. 3 Activated carbon having a surface oxide content of 0.160 meq / g or less, and a surface oxide content of 0.160 meq / g or less.

Description

[Technical Field]

[0001] The present invention relates to activated carbon and activated carbon filters, and more particularly to activated carbon and activated carbon filters that are excellent at removing chloroform. [Background technology]

[0002] Water purifiers used to remove residual components and foreign matter from drinking water such as tap water have a structure that includes adsorption members made of inorganic materials such as activated carbon and ceramics, and, if necessary, organic polymer membranes for filtration.

[0003] Tap water is required to be disinfected with chlorine or other disinfectants for hygienic reasons. However, chlorine added for disinfection purposes oxidizes and decomposes humic substances, a type of natural organic matter, generating organochlorine compounds such as trihalomethanes, which are considered carcinogenic. Therefore, water purifiers using activated carbon, which have excellent trihalomethane removal capabilities, and especially chloroform removal capabilities, which are more difficult to remove, have been proposed (see, for example, Patent Document 1).

[0004] While this type of activated carbon does adsorb some chloroform, it cannot be said to have sufficient removal capabilities. Furthermore, under conditions requiring a fast adsorption rate, such as in water purifiers, it is difficult to achieve good chloroform removal performance unless the activated carbon is even more suitable for chloroform adsorption. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2022 / 004594 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] In view of the above, the present invention provides activated carbon and activated carbon filter bodies that can exhibit superior chloroform removal performance. [Means for solving the problem]

[0007] In other words, the first invention is a BET specific surface area of ​​900-1200 m² calculated by the BET method from nitrogen adsorption isotherms. 2 The value is / g, and the pore volume of pores in the range of 0.25-0.65 nm, calculated by GCMC method from carbon dioxide adsorption isotherms, is 0.28 cm³. 3 The pore volume of pores larger than 2 nm, calculated by NLDFT method from nitrogen adsorption isotherms, is 0.0135 cm³ or more. 3 The pore volume of pores in the range of 0.37-0.65 nm, calculated by NLDFT method from nitrogen adsorption isotherms, is 0.09 cm³. 3 The present invention relates to activated carbon characterized by having a surface oxide content of 0.160 meq / g or less and a surface oxide content of 0.160 meq / g or less.

[0008] The second invention relates to activated carbon in which the activated carbon raw material is coconut shell, as in the first invention.

[0009] The third invention relates to activated carbon, which, in the first invention, has a chloroform filtration performance of 250 L or more when water with a chloroform concentration adjusted to 0.060 ± 0.012 mg / L is passed through a column packed with 50 cc of activated carbon with a particle size of 0.25 to 0.50 mm at a flow rate of 1.0 L / min, according to the volatile organic compound removal performance test of the household water purifier test method specified in JIS S 3201 (2019).

[0010] The fourth invention relates to an activated carbon filter body obtained by adding a binder to any of the first to third activated carbons and molding it into a predetermined shape. [Effects of the Invention]

[0011] According to the activated carbon of the first invention, the BET specific surface area calculated by the BET method from nitrogen adsorption isotherms is 900 to 1200 m². 2 / g, and the pore volume of pores in the range of 0.25 to 0.65 nm calculated by the GCMC method from the carbon dioxide adsorption isotherm is 0.28 cm 3 / g or more, the pore volume of pores of 2 nm or more calculated by the NLDFT method from the nitrogen adsorption isotherm is 0.0135 cm 3 / g or less, the pore volume of pores in the range of 0.37 to 0.65 nm calculated by the NLDFT method from the nitrogen adsorption isotherm is 0.09 cm 3 / g or more, and the amount of surface oxide is 0.160 meq / g or less, so it can be used as activated carbon suitable for the adsorption of chloroform and has excellent chloroform removal performance.

[0012] According to the activated carbon according to the second invention, in the first invention, since the activated carbon raw material is coconut shell, stable procurement is possible.

[0013] According to the activated carbon according to the third invention, in the first invention, by the volatile organic compound removal performance test of the household water purifier test method specified in JIS S 3201 (2019), when water adjusted to a chloroform concentration of 0.060 ± 0.012 mg / L is passed through a column filled with 50 cc of activated carbon with a particle size of 0.25 to 0.50 mm at a flow rate of 1.0 L / min, the chloroform filtration performance obtained is 250 L or more. Therefore, it has particularly good chloroform removal performance compared with the prior art.

[0014] According to the activated carbon filter body according to the fourth invention, since a binder is added to any one of the first to third activated carbons and formed into a predetermined shape, an activated carbon filter body capable of exhibiting excellent chloroform removal performance can be provided.

Embodiments for Carrying out the Invention

[0015] The activated carbon of the present invention is an adsorbent for household and industrial use that mainly removes harmful substances contained in tap water and the like to purify water. The activated carbon is suitable for water purification applications because it is inexpensive, has excellent filtering ability, and its quality is stable. It can be installed in a water purifier as it is or as a water purification filter molded into a predetermined shape with an appropriate binder or the like.

[0016] The activated carbon is in an appropriate form such as granular activated carbon or fibrous activated carbon, and is obtained by carbonizing and activating an activated carbon raw material. Examples of the raw material of activated carbon include, for example, in the case of granular activated carbon, wood (waste wood, thinned wood, sawdust), coffee grounds, rice husks, coconut shells, tree bark, fruit cores, etc. These naturally derived raw materials are likely to develop pores by carbonization and activation. Also, since it is a secondary use of waste, it can be procured at a low cost. In addition, calcined products derived from synthetic resins such as tires, petroleum pitch, urethane resins, and phenolic resins, and furthermore, coal, etc. can also be used as raw materials. On the other hand, in the case of fibrous activated carbon, some are obtained by carbonizing and activating appropriate fibers, such as phenolic resin-based, acrylic resin-based, cellulose-based, coal pitch-based, etc. The fiber length, cross-sectional diameter, etc. of the fibrous activated carbon are appropriate. Among these activated carbon raw materials, coconut shells are preferred because stable procurement is possible.

[0017] The activated carbon raw material is heated and carbonized in a temperature range of 200°C to 600°C as needed to form micropores. Subsequently, the activated carbon raw material is exposed to water vapor and carbon dioxide gas in a temperature range of 600°C to 1200°C for activation treatment. As a result, activated carbon with various pores developed is produced. In addition, during activation, there is also zinc chloride activation, etc. Also, sequential washing is performed.

[0018] The adsorption performance of the target adsorbed substance is defined by the physical properties of the activated carbon thus produced. In the present invention, as activated carbon having good adsorption performance for chloroform, which is the target adsorbed substance, particularly for chloroform with a small molecular weight, the BET specific surface area calculated by the BET method from the nitrogen adsorption isotherm, the pore volume calculated by the GCMC method from the carbon dioxide adsorption isotherm, and the ratio of the pore volume of pores of 2 nm or more calculated by the NLDFT method to the total pore volume calculated by the NLDFT method from the nitrogen adsorption isotherm are used as indices to define it.

[0019] The BET specific surface area (m 2 / g) calculated by the BET method from the nitrogen adsorption isotherm is obtained by measuring the nitrogen adsorption isotherm at 77K and performing analysis by the multipoint method based on the BET equation, and is calculated from the straight line in the region where the relative pressure of the obtained curve is 0.35 or less. This BET specific surface area (m 2 / g) is used as an index indicating the amount of pores formed in the activated carbon and can define the adsorption performance of the activated carbon. A preferable BET specific surface area as the adsorption performance of the activated carbon is 900 to 1200 m 2 / g. If the BET specific surface area is too small, the adsorption performance of the whole activated carbon is considered insufficient. If the BET specific surface area is too large, in addition to the decrease in the strength of the activated carbon, it is considered that large pores unsuitable for the adsorption of chloroform will develop.

[0020] The pore volume (cm 3The pore volume ( / g) is calculated by measuring the carbon dioxide adsorption isotherm at 298K and performing analysis using the GCMC method. The pores measured by the GCMC method are ultramicropores (pores with a diameter of 0.25 to 0.65 nm). Therefore, the pore volume calculated by the GCMC method corresponds to the pore volume of ultramicropores, and a larger value indicates that many ultramicropores capable of adsorbing chloroform, which has a small molecular weight, are formed. Accordingly, the pore volume calculated by the GCMC method is used as one of the indicators of chloroform adsorption performance. The pore volume calculated by the GCMC method for activated carbon with good chloroform adsorption performance is 0.28 cm³. 3 The value is 1 / g or more. The pore volume calculated by the GCMC method is 0.28 cm³. 3 If the amount is less than / g, the development of ultramicropores formed on the activated carbon is insufficient, making it difficult to properly adsorb chloroform and thus difficult to ensure the desired chloroform removal performance.

[0021] Total pore volume (cm³) calculated from nitrogen adsorption isotherms using the NLDFT method 3 The pore volume (cm³ / g) is calculated by measuring the nitrogen adsorption isotherm at 77K and performing analysis using the NLDFT method. 3 The value of ( / g) represents the pore volume calculated by performing NLDFT analysis on the above nitrogen adsorption isotherm, targeting mesopores to macropores (pores with a diameter of 2 nm or more). A larger pore volume value for pores with a diameter of 2 nm or more indicates the formation of many mesopores and macropores that are not suitable for chloroform adsorption.

[0022] Here, in order to simulate the distribution of pore sizes in activated carbon, particularly the degree of development of mesopores and macropores within the total pores of activated carbon, the ratio (%) of the pore volume of pores larger than 2 nm to the total pore volume, calculated by the NLDFT method, was used as an indicator. The ratio of the pore volume of pores larger than 2 nm to the total pore volume represents the proportion of mesopores and macropores, which are pores that do not adsorb chloroform, to the total pores of the activated carbon as a whole. Therefore, paradoxically, it can be used as an indicator of the chloroform removal performance of the activated carbon as a whole. The lower the ratio of the pore volume of pores larger than 2 nm, the more suitable the activated carbon is for chloroform removal. The preferable ratio of the pore volume of pores larger than 2 nm for activated carbon with good chloroform adsorption performance is 4.0% or less. If the ratio of the pore volume of pores larger than 2 nm exceeds 4.0%, it is thought that the proportion of mesopores and macropores in the activated carbon as a whole becomes too high, leading to a decrease in chloroform adsorption performance.

[0023] The activated carbon of the present invention satisfies all of the above conditions, as shown in the examples below, in relation to the BET specific surface area which defines the adsorption performance of the activated carbon, the pore volume calculated by the GCMC method which is an indicator of the chloroform adsorption performance, and the ratio of the pore volume of pores of 2 nm or larger to the total pore volume calculated by the NLDFT method which is an indicator of the chloroform removal performance of the activated carbon as a whole, thereby making it possible to produce activated carbon with suitable performance for adsorbing chloroform with a small molecular weight.

[0024] Furthermore, in the activated carbon of the present invention, the pore volume of pores in the range of 0.37 to 0.65 nm, calculated from nitrogen adsorption isotherms using the NLDFT method, is 0.09 cm³. 3It is preferable that the value is 1 / g or higher. Pores with a diameter in the range of 0.37 to 0.65 nm are ultramicropores, and the pore volume calculated by the NLDFT method also corresponds to the pore volume of ultramicropores. Therefore, similar to the pore volume calculated by the GCMC method that shows the pore volume of ultramicropores as described above, it is considered that the larger the value of the pore volume of pores in the range of 0.37 to 0.65 nm calculated by the NLDFT method, the more favorably the activated carbon can adsorb chloroform, which has a smaller molecular weight. In other words, the pore volume of pores in the range of 0.37 to 0.65 nm calculated by the NLDFT method can be added as one of the indicators of chloroform adsorption performance.

[0025] Furthermore, the activated carbon of the present invention exhibits superior chloroform removal performance due to its surface oxide content being 0.160 meq / g or less. The chloroform removal performance of activated carbon is also determined by the acidic functional groups present on its surface. The acidic functional groups that increase due to surface oxidation of activated carbon are mainly hydrophilic groups such as carboxyl groups and phenolic hydroxyl groups. The acidic functional groups on the surface of activated carbon affect its collection capacity. The amount of these acidic functional groups can be determined as the amount of surface oxide.

[0026] In water, it is hypothesized that when the amount of surface oxides on activated carbon increases, the pores become clogged with water molecules strongly adsorbed to the surface functional groups by hydrogen bonding, and the resulting clusters of water molecules, thereby hindering the physical access of the target adsorbed substance to the adsorption site (micropores). Therefore, it is thought that a lower amount of surface oxides on activated carbon increases the hydrophobicity of the activated carbon surface, and thus improves the adsorption performance of hydrophobic substances such as chloroform.

[0027] Known methods such as heat treatment under an inert gas atmosphere can be used to reduce surface oxides in activated carbon, thereby reducing acidic functional groups such as phenolic hydroxyl groups and carboxyl groups on the activated carbon surface.

[0028] In the activated carbon of the present invention, it is preferable that the chloroform filtration performance obtained when water with a chloroform concentration adjusted to 0.060 ± 0.012 mg / L is passed through a column packed with 50 cc of activated carbon with a particle size of 0.25 to 0.50 mm at a flow rate of 1.0 L / min is 250 L or more, according to the volatile organic compound removal performance test of the household water purifier test method specified in JIS S 3201 (2019). Chloroform filtration performance corresponds to the chloroform removal performance. Specifically, 50 cc of the prototype activated carbon is packed into a cylindrical column with an inner diameter of 40 mm and a height of 100 mm, and water with a chloroform concentration adjusted to 0.060 ± 0.012 mg / L is used as test water, at a flow rate of 1.0 L / min and a space velocity (SV) of 1200 hr. -1 Under these conditions, water was passed through the column, and the amount of water that passed through when the removal rate fell below 80% was defined as the breakthrough point. If the chloroform filtration performance is less than 250 L, the chloroform removal performance is insufficient.

[0029] The activated carbon of the present invention can be used as activated carbon filter bodies, such as dry filters formed by being held and molded by molten thermoplastic resin, or wet filters formed by mixing with an appropriate binder, such as a fibrous binder, to form an aqueous slurry into a predetermined shape. In particular, wet filters are suitable for water purification applications because they have superior water permeability compared to dry filters, due to the use of fibrous components as a binder. Therefore, the activated carbon of the present invention can be utilized more effectively for water purification applications.

[0030] Furthermore, the activated carbon of the present invention can be suitably used as an adsorption material for water purifiers. The form of the adsorption material for water purifiers can be as appropriate, such as being used as is or being molded into an activated carbon filter body for water purification. [Examples]

[0031] [Production of activated carbon] In the production of the activated carbon prototypes 1-6, coconut shells were used as raw materials, while coal was used for prototypes 7 and 8. The carbonized material, heated to 400-600°C, was then heated to approximately 800-900°C and maintained there, and activation was promoted by introducing steam. After activation, it was allowed to cool naturally to near room temperature. After cooling, it was sieved using a 30-60 mesh sieve to obtain the activated carbon prototypes 1-7 with a particle size of approximately 0.25-0.50 mm.

[0032] [Measurement of activated carbon] For the activated carbon prototypes 1-8, the BET specific surface area, pore volume by GCMC method, and pore volume by NLDFT method (total pore volume, pore volume of pores larger than 2 nm, and pore volume of pores between 0.37 and 0.65 nm), surface oxide content, and chloroform filtration performance were measured. Based on these measurements, the ratio of the pore volume of pores larger than 2 nm in the NLDFT method to the total pore volume was determined. The results are shown in Table 1 below.

[0033] [BET specific surface area] For the activated carbon prototypes 1-8, nitrogen adsorption isotherms at 77K were measured using a specific surface area / pore distribution analyzer (Microtrac-Bell Co., Ltd., "ELSORP-miniII"). The obtained nitrogen adsorption isotherms were then analyzed using a multipoint method based on the BET method. The specific surface area (m²) was calculated from the straight line in the region of the obtained curve where the relative pressure is 0.35 or less. 2 The values ​​(per g) were calculated for each.

[0034] [Pore volume of the GCMC method] For the activated carbon prototypes 1-8, the specific surface area / pore distribution isotherm at 298K was measured using a specific surface area / pore distribution analyzer (Microtrac-Bel Co., Ltd. "BELSORP-miniII"). The obtained carbon dioxide adsorption isotherms were then analyzed using the GCMC method with graphite carbon as the adsorbent and the pore shape set to a slit model, and the pore volume (cm³) of pores between 0.25 and 0.65 nm was determined. 3 We calculated / g) for each.

[0035] [Pore volume in the NLDFT method] For the activated carbon prototypes 1-8, the nitrogen adsorption isotherms obtained during the measurement of the BET specific surface area were analyzed using the NLDFT method with the adsorbent set to graphite carbon and the pore shape to a slit model, and the total pore volume (cm³) was determined. 3 ( / g), pore volume of pores larger than 2 nm (cm³) 3 ( / g), pore volume (cm³) of pores with a size of 0.37-0.65 nm 3 We calculated / g) for each.

[0036] [Surface oxide amount] For the activated carbons of prototypes 1 to 8, Boehm's method was applied. Each activated carbon was shaken in a 0.05 N sodium hydroxide aqueous solution for 24 hours, then filtered. The amount of sodium hydroxide obtained when the filtrate was neutralized and titrated with a 0.05 N hydrochloric acid aqueous solution was defined as the amount of surface oxide (meq / g).

[0037] [Chloroform filtration performance] For the activated carbon prototypes 1-8, the chloroform removal performance was measured in accordance with the volatile organic compound removal performance test of the household water purifier test method specified in JIS S 3201 (2019). First, 50cc of the prototype activated carbon was packed into a cylindrical column with an inner diameter of 40mm and a height of 100mm. Water adjusted to a chloroform concentration of 0.060±0.012mg / L was used as the test water, and the flow rate was 1.0L / min, with a space velocity (SV) of 1200hr. -1 Under these conditions, water was passed through the column, and the amount of water that passed through when the removal rate fell below 80% was defined as the breakthrough point was measured as the filtration performance.

[0038] [Table 1]

[0039] [Results and Discussion] As can be seen from Table 1, the activated carbons of prototypes 1-3 showed good chloroform filtration performance, while the activated carbons of prototypes 4-8 showed poor chloroform filtration performance. In particular, the activated carbons of prototypes 7 and 8 showed remarkably low chloroform filtration performance.

[0040] This study compares prototypes 1-3, which exhibit good chloroform removal performance, with prototypes 4-8, which exhibit poor chloroform removal performance. Compared to prototypes 1-3, prototypes 5-8 have a larger ratio of pore volume of pores larger than 2 nm to the total pore volume, as calculated by the NLDFT method, which indicates the degree of mesopore and macropore development. Furthermore, prototypes 7 and 8 have smaller pore volumes, as calculated by the GCMC method, which indicates the degree of ultramicropore development. In addition, prototype 4 does not show significant differences in pore distribution, such as the ratio of pore volume of pores larger than 2 nm to the total pore volume, as calculated by the NLDFT method, compared to prototypes 1-3, but it has a larger surface oxide content.

[0041] In prototypes 4-8, where chloroform removal performance was insufficient, prototypes 7 and 8 likely exhibited poor chloroform removal performance because the pore volume of the GCMC method was small, and the ultra-micropores that adsorb chloroform were not sufficiently developed. Furthermore, even if the pore volume of the GCMC method was above a certain level, as in prototypes 5 and 6, a large ratio of mesopores to macropores would result in a large number of mesopores and macropores in the activated carbon that do not adsorb chloroform, thus reducing chloroform removal performance. In particular, prototypes 7 and 8 not only had a small pore volume of the GCMC method, but also an extremely large ratio of mesopores to macropores compared to the other prototypes, which is likely why their chloroform removal performance was extremely poor. On the other hand, in prototype example 4, the BET specific surface area was within a certain range, the pore volume of the GCMC method was large and the ultramicropores were well developed, and the ratio of mesopores to macropores was small, resulting in a pore distribution with few mesopores and macropores that prevented chloroform adsorption into the activated carbon. However, it is thought that the chloroform removal performance was reduced due to the large amount of surface oxides.

[0042] Prototypes 1-3, which exhibited good chloroform removal performance, showed excellent chloroform filtration performance because their BET specific surface area was within a certain range, their pore volume was large due to the GCMC method, and their ratio of mesopores to macropores was small. Furthermore, because their surface oxide content was low and their pore volume in the 0.37-0.65 nm range was also large, their chloroform filtration performance was significantly better than that of prototypes 4-8. Therefore, it is considered that, in addition to BET specific surface area, GCMC method pore volume, and the ratio of mesopores to macropores, the pore volume in the 0.37-0.65 nm range and the surface oxide content also contribute to improving chloroform removal performance.

[0043] These results suggest that activated carbon capable of suitably adsorbing chloroform with a small molecular weight should have a specific surface area of ​​900-1200 m² to ensure a certain level of adsorption performance as activated carbon. 2 The pore volume of pores in the 0.25-0.65 nm range, calculated using the GCMC method (an indicator of activated carbon with sufficiently developed ultramicropores), is 0.28 cm³ / g. 3 It was found that the requirements were met: the amount was greater than or equal to / g, and the ratio of the pore volume of pores larger than 2 nm to the total pore volume, which represents the proportion of mesopores and macropores that do not adsorb chloroform, was 4.0% or less.

[0044] At this time, the pore volume of pores in the range of 0.37 to 0.65 nm, calculated by the NLDFT method which indicates the degree of development of ultramicropores, is 0.09 cm³. 3 It was found that activated carbon satisfying the requirements of having a surface oxide content of 0.160 meq / g or less and a concentration of 0.160 meq / g or less can be given even better chloroform removal performance. [Industrial applicability]

[0045] The activated carbon of the present invention can suitably adsorb chloroform, which has a low molecular weight. Therefore, it is promising as a replacement for conventional activated carbon used in water purification. Furthermore, this activated carbon can be suitably used as an activated carbon filter body for water purification.

Claims

1. The BET specific surface area calculated using the BET method from nitrogen adsorption isotherms is 900 to 1200 m². ２ / g, The pore volume of pores in the 0.25–0.65 nm range, calculated by the GCMC method from carbon dioxide adsorption isotherms, was 0.28 cm³. ３ / g or more, The pore volume of pores larger than 2 nm, calculated by the NLDFT method from nitrogen adsorption isotherms, was 0.0135 cm³. ３ / g or less, The pore volume of pores in the range of 0.37–0.65 nm, calculated from nitrogen adsorption isotherms using the NLDFT method, was 0.09 cm³. ３ / g or more, The surface oxide content is 0.160 meq / g or less. Activated carbon characterized by the following features.

2. The activated carbon according to claim 1, wherein the activated carbon raw material is coconut shell.

3. The activated carbon according to claim 1, wherein, according to the volatile organic compound removal performance test of the household water purifier test method specified in JIS S 3201 (2019), when water with a chloroform concentration adjusted to 0.060 ± 0.012 mg / L is passed through a column packed with 50 cc of activated carbon with a particle size of 0.25 to 0.50 mm at a flow rate of 1.0 L / min, the chloroform filtration performance obtained is 250 L or more.

4. An activated carbon filter body obtained by adding a binder to the activated carbon described in any one of claims 1 to 3 and molding it into a predetermined shape.

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