Patent Application
20210347642
The present invention relates to a porous carbon material, and a method for producing the porous carbon material, and a filter, a sheet, and a catalyst carrier.
Porous carbon materials represented by activated carbon are obtained by activating charred products, which are made from plant materials (e.g., wood pulp, coconut shell, and chaff), mineral materials (e.g., coal, tar, and petroleum pitch), and synthetic resins, through treatment with gases or chemicals under a high temperature to thereby form fine pores. The fine pores form a network structure within carbon and result in a large surface area. Therefore, the porous carbon material is excellent in an adsorption ability. As a result, the porous carbon material has been widely used in a variety of applications such as odor removal, impurity removal in liquid, and solvent vapor recovery or removal. Additionally, the porous carbon material has also been used for a catalyst carrier tarring a catalyst.
There has been disclosed, as a plant-derived porous carbon material, for example, a porous carbon material which is obtained by charring a plant-derived material, followed by treating with an acid or an alkali, and which has a specific surface area of 10 m2/g or more as measured by the nitrogen BET method, a silicon content of 1% by mass or less, and a pore volume of 0.1 cm3/g or more (see, PTL 1).
Among porous carbon materials, a carbon material in which mesopores are developed is excellent in adsorption of large molecules and in a high-speed adsorption ability. However, such a porous carbon material has many cavities and a small bulk specific gravity. Therefore, when performance per volume is considered important in, for example, a filter cartridge, the porous carbon material is filled only one fifth to one fourth by weight as heavy as a commonly used coconut shell-derived activated carbon.
Therefore, the carbon material in which mesopores are developed is excellent in an adsorption property per weight, but its superiorities are not exhibited in terms of per volume in many times. Thus, there is a problem that the carbon material has difficulty in exhibiting a higher performance as, for example, a filter cartridge than conventional products.
The present invention aims to solve the above existing problems and achieve the following objects.
That is, an object of the present invention is to provide a porous carbon material in which mesopores are developed and which has a high bulk specific gravity, and a method for producing the porous carbon material, and a filter, a filter cartridge, a sheet, and a catalyst carrier using the porous carbon material.
Means for solving the above problems are as follows.
<1> A porous carbon material
wherein a particle diameter is 10 μm or more but 1 cm or less;
wherein a bulk specific gravity is 0.20 g/cm3 or more; and
wherein a mesopore volume is 0.10 cm3/g or more.
<2> The porous carbon material according to <1>, wherein the porous carbon material includes a plant-derived material.
<3> The porous carbon material according to <2>, wherein the plant-derived material is chaff.
<4> A filter including
the porous carbon material according to any one of <1> to <3>.
<5> The filter according to <4>, wherein the filter is for water purification.
<6> The filter according to <4>, wherein the filter is for air cleaning.
<7> A filter cartridge including
the filter according to any one of <4> to <6>.
<8> A sheet including
the porous carbon material according to any one of <1> to <3>.
<9> A catalyst carrier including
the porous carbon material according to any one of <1> to <3>.
<10> A method for producing the porous carbon material according to any one of <1> to <3>, the method including:
pressure-molding a plant-derived material to thereby obtain a molded product,
carbonizing the molded product to thereby obtain a carbonized product, and
activating the carbonized product.
<11> The method for producing the porous carbon material according to <10>, wherein the plant-derived material is chaff.
<12> The method for producing the porous carbon material according to <10> or <11>, wherein the molded product is obtained by pressure-molding the plant-derived material having a water content of 3% by mass or more but 30% by mass or less.
According to the present invention, it is possible to solve the above existing problems and achieve the above object. It is possible to provide a porous carbon material in which mesopores are developed and which has a high bulk specific gravity, and a method for producing the porous carbon material, and a filter, a filter cartridge, a sheet, and a catalyst carrier using the porous carbon material.
A porous carbon material of the present invention meets the following (1) to (3):
(1) a particle diameter is 10 μm or more but 1 cm or less;
(2) a bulk specific gravity is 0.20 g/cm3 or more; and
(3) a mesopore volume is 0.1 cm3/g or more.
A porous carbon material having the particle diameter of less than 10 μm has difficulty in having a high bulk specific gravity (e.g., 0.2 g/cm3 or more). A porous carbon material having the particle diameter of more than 1 cm tends to take a longer time to demineralize through an acid- or alkali-treatment, leading to a deteriorated manufacture efficiency.
The particle diameter can be determined using, for example, a laser diffraction/scattering particle size distribution measurement device LA-950 (available from HORIBA, Ltd.). The LA-950 is used to measure a particle diameter distribution in a particle diameter range of 0.01 μm to 3,000 μm using a wet method. The particle diameter means a particle diameter (median diameter) corresponding to a median in a particle diameter distribution in which particle diameters and number frequencies are plotted on the horizontal axis and the vertical axis, respectively.
The bulk specific gravity of the porous carbon material is 0.20 g/cm3 or more, preferably 0.20 g/cm3 or more but 0.40 g/cm3 or less, more preferably 0.20 g/cm3 or more but 0.35 g/cm3 or less.
A porous carbon material in which mesopores are developed (i.e., the mesopore volume is 0.1 cm3/g or more) has generally the bulk specific gravity of about 0.10 g/cm3. Therefore, in terms of per volume, this porous carbon material cannot exhibit its superiorities such as excellent adsorption of large molecules and an excellent high-speed adsorption ability. Meanwhile, when the bulk specific gravity is 0.20 g/cm3 or more, the porous carbon material can exhibit its superiorities such as excellent adsorption of large molecules and an excellent high-speed adsorption ability in terms of per volume and also per weight.
The bulk specific gravity means a specific gravity (mass per unit volume) calculated by dividing a mass of powder, which has been formed into a predetermined shape by, for example, filling the powder into a container having a certain volume through free drop, by a volume of the powder at that time. The smaller the bulk specific gravity is, the more bulky the powder is.
The mesopore volume of the porous carbon material is 0.1 cm3/g or more, preferably 0.1 cm3/g or more but 0.3 cm3/g or less, more preferably 0.1 cm3/g or more but 0.2 cm3/g or less. When the mesopore volume is less than 0.1 cm3/g, the mesopores are far from developed and the superiorities such as excellent adsorption of large molecules and an excellent high-speed adsorption ability cannot be attained. Meanwhile, when the mesopore volume is too large, the bulk specific gravity has difficulty in being high.
The porous carbon material has many pores. The pores are classified into mesopores, micropores, and macropores. As used herein, the mesopores refer to pores having a pore diameter of 2 nm to 50 nm, the micropores refer to pores having a pore diameter of less than 2 nm, and the macropores refer to pores having a pore diameter of more than 50 nm.
The mesopore volume can be measured using, for example, the device described below.
The mesopore volume can be determined by measuring a nitrogen adsorption isotherm using 3FLEX (available from Micromeritics Instrument Corporation) and calculating the mesopore volume using the BJH method.
The BJH method is a widely used method as a pore distribution analysis method. When a pore distribution is analyzed based on the BJH method, nitrogen serving as adsorbing molecules is adsorbed on and desorbed from an adsorbent (porous carbon material) to determine a desorption isotherm. Then, based on the desorption isotherm, a thickness of an adsorption layer while the adsorbing molecules (e.g., nitrogen) are desorbed stepwise from a state in which pores are filled with the adsorbing molecules and an inner diameter of pores generated thereupon (twice as long as a core radius). A pore radius rp is calculated based on the expression (1) and a pore volume is calculated based on the expression (2). Then, based on the pore radius and the pore volume, rates of change in pore volume are plotted against pore diameters (2rp) (dVp/drp) to thereby generate a pore distribution curve (see, a manual of BELSORP-mini and BELSORP analysis software (available from MicrotracBEL Corp.), pages 85 to 88).
r
p
=t+r
k (1)
Vpn=Rn·dVn−Rn·dtn·c·ΣApj (2)
wherein Rn=rpn2/(rkn−1+dtn)2 (3)
In the above expressions,
rp: pore radius;
rk: core radius (inner diameter/2) when an adsorption layer having a thickness t is adsorbed on an inner wall of a pore having the pore radius rp at the pressure;
Vpn: pore volume when nitrogen is desorbed at the n th time;
dVn: amount of change at that time;
dtn: amount of change in thickness tn of the adsorption layer when nitrogen is desorbed at the n th time;
rkn: core radius at that time;
c: constant value; and
rpn: pore radius when nitrogen is desorbed at the n th time.
Also, ΣApj represents an integrated value of a wall surface area of the pore in a range of from j=1 to j=n−1.
Thirty milligrams of the porous carbon material is prepared. The 3FLEX which is set to the condition to measure in a relative pressure (P/P0) of 0.0000001 to 0.995 can be used to measure the mesopore volume.
A raw material of the porous carbon material is preferably a plant-derived material. When the raw material is plant-derived, a value of the mesopore volume is easily adjusted to the desired value described above. The plant-derived material is also advantageous in terms of a low environmental loading.
The plant-derived material is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include chaff or straw of rice, barley, wheat, rye, Japanese millet, and millet. Alternatively, reed or wakame stem may be used. Additional examples thereof include vascular plants living on the ground, pteridophyte, bryophyte, algae, and seaweeds. Note that, these materials may be used as the raw material alone or in a mixture of a plurality of them. A shape or form of the plant-derived material is also not particularly limited. For example, the chaff or straw may be used as it is or subjected to drying treatment. Moreover, those which have been subjected to various treatments such as fermentation treatment, roast treatment, and extraction treatment in food and drink processing such as beer, wines, and spirits may be used. In particular, in terms of attempting to recycle industrial wastes, straw and chaff which have been processed, e.g., thrashed are preferably used. These straw and chaff which have been processed can be abundantly and easily available from, for example, agricultural cooperatives, brewing manufactures, and food companies.
A method for producing the porous carbon material is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably the below-described method for producing a porous carbon material.
A method for producing a porous carbon material of the present invention includes a molded product producing step, a carbonized product producing step, and an activation step, and preferably a demineralizing step; and, if necessary, further includes other steps.
The method for producing a porous carbon material is a method for producing the porous carbon material of the present invention.
The molded product producing step is not particularly limited and may be appropriately selected depending on the intended purpose, as long as it is a step of pressure-molding a plant-derived material to thereby obtain a molded product.
The plant-derived material is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include the plant-derived materials exemplified in the section “Porous carbon material.” Among them, the chaff is preferable because a desired porous carbon material is easily produced.
A shape of the molded product is not particularly limited and may be appropriately selected depending on the intended purpose.
In the pressure molding, for example, a pelletizer commonly used in molding of biomass is used. The chaff is ground, added with water so as to have a water content of 3% by mass or more but 30% by mass or less, preferably 5% by mass or more 20% by mass or less, and then molded. A pressure at this time is determined by friction resistance between a mold and the chaff when the chaff passes through a molding machine. Therefore, it is desirable to adjust an amount of water depending on a size of a molded product.
Heat may be generated through friction in the pressure molding, but additional heat may be applied by a heating device.
The molded product is believed to be produced as follows. A water-soluble component included in the plant-derived material is extracted by appropriately adjusting water, pressure, and heat. Powder is adhered together by the action of the water-soluble component to thereby form the molded product.
By pressure-molding the plant-derived material, a porous carbon material in which mesopores are developed and which has a higher bulk specific gravity than that when the plant-derived material is not pressure-molded is obtained.
The carbonized product producing step is not particularly limited and may be appropriately selected depending on the intended purpose, as long as it is a step of carbonizing (charring) the molded product to thereby obtain a carbonized product (carbonaceous material).
The carbonization (charring) generally means that an organic material (plant-derived material herein) is converted into a carbonaceous material through a heat treatment (e.g., see JIS M0104-1984). Note that, examples of an atmosphere under which the charring takes place include an oxygen-blocked atmosphere, in particular, a vacuum atmosphere, an inert gas atmosphere such as a nitrogen gas and an argon gas, and an atmosphere under which the molded product is in a kind of steam-roasted state. A heating rate to reach a charring temperature may be 1° C./min or more, preferably 3° C./min or more, more preferably 5° C./min or more under such an atmosphere. The upper limit of a charring time may include but not limited to 10 hours, preferably 7 hours, more preferably 5 hours. The lower limit of the charring time may be a time during which the molded product is surely charred.
Examples of a temperature at which the heat treatment is performed include 300° C. to 1,000° C.
The activation step is not particularly limited and may be appropriately selected depending on the intended purpose, as long as it is a step of activating the carbonized product. Examples thereof include a gas activation method and a chemical activation method.
The activation as used herein means developing a pore structure in a carbonaceous material and adding pores to the carbonaceous material.
The gas activation method is a method in which the carbonized product is heated under a gas atmosphere using, as an activator, oxygen, water vapor, carbon dioxide, air etc. at, for example, 700° C. to 1,000° C. for from several ten minutes to several hours to thereby develop a fine structure by a volatile component or a carbon molecules in the carbonized product. Note that, a heating temperature may be appropriately selected depending on a kind of the plant-derived material, and a kind and a concentration of the gas, but is preferably 800° C. to 950° C.
The chemical activation method is a method in which the carbonized product is activated using, for example, zinc chloride, iron chloride, calcium phosphate, calcium hydroxide, magnesium carbonate, potassium carbonate, and sulfuric acid instead of oxygen or water vapor used in the gas activation method, washed with hydrochloric acid, pH-adjusted with an alkaline aqueous solution, and dried.
The demineralizing step is not particularly limited and may be appropriately selected depending on the intended purpose, as long as it is a step of removing a mineral in the carbonized product. Examples thereof include a method in which the carbonized product is immersed in an acid aqueous solution or an alkaline aqueous solution.
Prior to the demineralizing step, the carbonized product is preferably pulverized to a size at which the acid aqueous solution or the alkaline aqueous easily penetrates thereinto.
One example of the method for producing the porous carbon material will now be described below.
A carbonized product is obtained by heating pressure-molded chaff in a nitrogen gas stream at 500° C. for 5 hours to thereby carbonize. Thereafter, 10 g of the carbonized product is placed into an alumina melting pot, heated in a nitrogen gas stream (10 L/min) to 1,000° C. at a heating rate of 5° C./min, and charred at 1,000° C. for 5 hours to thereby convert into a carbonaceous material (porous carbon material precursor). Then, the resultant carbonaceous material is cooled to room temperature. Note that, during charring and cooling, the nitrogen gas is continuously allowed to flow through. Next, the carbonaceous material is coarsely pulverized to a size of 1 cm or less, which is such a size as to easily undergo an alkali treatment, and a mineral in the material is removed with 1 mol % aqueous sodium hydroxide solution. Thereafter, the material is washed to thereby remove an alkali on a surface of the material and further washed. Then, the material is heat-treated at 950° C. under a water vapor atmosphere. Thus, a plant-derived porous carbon material having a high bulk specific gravity is obtained.
A sheet of the present invention includes the porous carbon material of the present invention; and, if necessary, other members.
The sheet is obtained by, for example, subjecting a powder which contains the porous carbon material to wet papermaking. For example, the sheet may be produced using a known technique as follows. The powder which contains the porous carbon material is mixed, sheared, and uniformly dispersed using devices such as a pulper, a beater, and a refiner to thereby produce a slurry. The resultant slurry may be adjusted to any basis weight by allowing to flow over a wire at a predetermined flow rate to dehydrate. Then, the resultant sheet is passed through a press part, dried in a drier part, smoothed in a calender part, and wound on a reel. A thickness of the sheet may be adjusted to any thickness by, for example, a heat press roller.
A filter of the present invention includes the porous carbon material of the present invention; and, if necessary, further includes other members.
The filter is used as a filter for water purification or a filter for air cleaning.
The filter is obtained, for example, by molding the sheet.
Examples of a molding method for obtaining the filter include but not limited to a method in which the sheet of the present invention is wound up and heat-treated to thereby form a columnar or cylindrical filter or a method in which the sheets are laminated together and punched into any shape to thereby form a filter.
A filter cartridge of the present invention includes at least the filter of the present invention; and, if necessary, further includes other members such as a housing.
The filter is contained in, for example, the housing.
The housing includes, for example, a housing body, a fluid inlet portion, and a fluid outlet portion.
The fluid inlet portion is disposed in the housing body and configured to allow a fluid to be filtered to flow therein.
The fluid outlet portion is disposed in the housing body and configured to allow a fluid having being filtered to flow therefrom.
A catalyst carrier of the present invention includes the porous carbon material of the present invention; and, if necessary, further includes other members.
For example, the catalyst carrier is the porous carbon material itself.
The catalyst carrier can abundantly hold a catalyst such as a noble metal. Therefore, a catalyst-carried body in which a catalyst is carried on the catalyst carrier can promote a variety of chemical reactions and improve a yield.
In addition to the above applications, the porous carbon material of the present invention can also be used for, for example, electrode materials for capacitors, and a variety of adsorbents, masks, and adsorption sheets.
Examples of the present invention will now be described, but the present invention is not limited to thereto.
In Examples, a particle diameter, a bulk specific gravity, and a mesopore volume were measured by the methods described above.
A residual chlorine removing performance was measured by the flow test described below.
In both of Examples and Comparative Examples, the flow test was performed as follows. A sample which had passed through a 10 mesh sieve but had not passed through a 32 mesh sieve was filled into a column. A liquid having a residual chlorine concentration of 0.5±0.1 mg/L at an inlet was fed and a space velocity was SV=2,000/h.
Color development at 435 nm was measured with a spectrophotometer using an o-tolidine method. Thus, free residual chlorine in the liquid which had passed through the column was quantified.
Chaff was used as a raw material. The chaff was pulverized and formed into molded products having a diameter of 6 mm and a length of several millimeters to several ten meters by the S-5 type flat-die pelletizer (available from Shinkou Kouki Corporation). Water contents upon molding, bulk specific gravities of the molded products, and states of the molded products are presented in Table 1.
Note that, the water contents upon molding were adjusted by spraying water to the raw material using a sprayer and depending on sprayed amounts.
The water content (% by mass) means an amount of water contained in the raw materials and was measured using a heat-drying moisture meter. Specifically, 1 g of a sample was dried at 150° C. for 20 min and measured for the water content based on a change in weight between before and after drying using ML-50 (available from A&D Company, Limited). For example, when 1.0 g of a sample is changed to 0.9 g after drying, the water content is 10% by mass.
Next, the produced molded product having the water content of 16% by mass was heated under a nitrogen gas stream at 600° C. for 3 hours to thereby obtain a carbonized product.
Then, the carbonized product was coarsely pulverized to a size of about 2 mm, immersed in 1 mol % aqueous sodium hydroxide solution to thereby demineralize, and then washed.
Then, the resultant was activated by heating under a water vapor atmosphere at 950° C. for 3.5 hours to thereby obtain a porous carbon material.
The resultant porous carbon material was pulverized with a Raikai mixer and classified with a sieve.
A relationship between a particle diameter and a bulk specific gravity of the thus-classified porous carbon material was determined and illustrated in
A specific surface area and a mesopore volume of the classified porous carbon material are presented in Table 2.
Note that, all samples having particle diameters plotted in
Chaff was used as a raw material.
Next, the chaff was heated under a nitrogen gas stream at 600° C. for 3 hours to thereby obtain a carbonized product.
Then, the carbonized product was immersed in 1 mol % aqueous sodium hydroxide solution to thereby demineralize, and then washed.
Then, the resultant was activated by heating under a water vapor atmosphere at 950° C. for 3 hours to thereby obtain a porous carbon material.
The resultant porous carbon material was pulverized with a Raikai mixer and classified with a sieve.
A relationship between a particle diameter and a bulk specific gravity of the thus-classified porous carbon material was determined and illustrated in
A specific surface area and a mesopore volume of the classified porous carbon material are presented in Table 3.
Note that, all samples having particle diameters plotted in
As can be seen from
Especially in a region in which the particle diameter is 100 μm or more, the bulk specific gravity was about 3 times as high as that of the Comparative Example. Because the bulk specific gravity was about 3 times, a weight to be filled in the same container is also increased. For example, when the porous carbon material is used in a filter for water purification, a water purification performance is significantly improved.
Moreover, a residual chlorine removal performance for the same volume was examined using the method described above. The results are illustrated in
An adsorption capacity is increased by improving the bulk specific gravity. Therefore, for example, a flow volume per material volume at which a removal rate is decreased to 80% or less is 27 L/mL for the Comparative Example 1. Whereas, in the Example 1, the removal rate is still more than 80% even when the flow volume per material volume is more than 100 L/mL. This indicates that a product life as a residual chlorine removal filter is increased about 4 times.
A porous carbon material was produced in the same manner as in Example 1, except that the activation time was changed from 3.5 hours to 3 hours. A specific surface area and a mesopore volume of the resultant porous carbon material are presented in Table 4.
Note that, values of the particle diameter and the bulk specific gravity for Example 2 were comparable to those for Example 1 (
A porous carbon material was produced in the same manner as in Comparative Example 1, except that the activation time was changed from 3.5 hours to 2.5 hours. A specific surface area and a mesopore volume of the resultant porous carbon material are presented in Table 4.
Note that, values of the particle diameter and the bulk specific gravity for Comparative Example 2 were comparable to those for Comparative Example 1 (
Moreover, a residual chlorine removal performance for the same volume was also examined for the porous carbon materials obtained in Example 2 and Comparative Example 2 using the method described above. The results are illustrated in
The results comparable to those for Example 1 and Comparative Example 1 were obtained for Example 2 and Comparative Example 2 which had different specific surface area and mesopore volume.
The porous carbon material of the present invention has developed mesopores and a high bulk specific gravity and thus can be used for, for example, filters, electrode materials for capacitors, and a variety of adsorbents, masks, adsorption sheets, and catalyst carriers.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-007915 | Jan 2016 | JP | national |
| 2016-256447 | Dec 2016 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 16070303 | Jul 2018 | US |
| Child | 17380665 | US |
