JP2005126292A - Manufacturing method of active carbon - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing active carbon containing a metal oxide by more simply controlling the decrease in the number of pores. <P>SOLUTION: This manufacturing method of the active carbon comprises a sugar preparation process 10 where a gel-like sugar material is prepared using carbonization treatment 16 of a sugar-containing material with an acid, a metal mixing process 20 where a metal compound is mixed with the gel-like sugar material obtained in the sugar preparation process 10, and an activation process 30 where the metal mixed material obtained in the metal mixing process 20 is activated. Since the metal compound is mixed in the gel-like sugar material, a desired quantity of the metal compound can be uniformly mixed in the sugar material having fluidity by stirring, etc., therefore, there is no fear of clogging of the pores of the active carbon by the addition of the metal or the metal compound, and its pore diameter, pore shape, pore number, etc., are controlled by the metal or the metal compound, and its performance such as gas adsorption, etc., can be improved by the metal or the metal oxide. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing activated carbon, and more particularly to a method for producing activated carbon suitable for gas adsorption.

  In recent years, as a technique for using natural gas as an alternative to petroleum resources such as gasoline is researched and developed, a lightweight and small-sized gas holding device capable of holding a larger amount of gas is required. In general, by increasing the pressure of gas, the amount of gas per unit volume can be increased to reduce the volume. It is not preferable for devices that have an adverse effect. For this reason, a technique has been considered in which a high pressure is suppressed by using a material capable of adsorbing and releasing gas, such as silica, activated alumina, zeolite, activated carbon, and the like, and more gas is retained.

  Among these materials, activated carbon is relatively inexpensive and easily available, and therefore various developments have been made aiming at materials capable of adsorbing a larger amount of gas at a lower pressure. Here, the activated carbon holds gas in fine pores existing on the surface. Therefore, it is possible to selectively adsorb a predetermined gas or a gas having a predetermined condition by controlling the pore diameter and the pore shape. In addition, the amount of gas adsorption per unit in these materials increases as the number of pores per unit increases, specifically, as the specific surface area or pore volume per unit increases. Therefore, a method for producing activated carbon by controlling these physical properties has been developed. For example, in order to produce activated carbon having a larger average pore diameter and specific surface area, a method of adding an Group 8 metal compound to activated carbon and performing an activation treatment is disclosed (for example, see Patent Document 1). In addition, a method is disclosed in which a metal capable of chemisorbing methane, which is one of the main components in natural gas, is added to activated carbon (see, for example, Patent Document 2).

Japanese Patent Laid-Open No. 7-155589 JP-A-6-55067

  However, in the method of adding a metal compound to the activated carbon once created, the metal compound adheres to the surface of the activated carbon, so the metal compound itself enters the hole or adheres to the entrance of the hole to block the pores. There is a possibility that it may be crushed or crushed, and in view of obtaining more pores, the efficiency may be poor. In addition, since activated carbon is hydrophobic and solid, even if a metal compound prepared in an aqueous solution is used, the amount of the metal compound that can be added may be limited or may be unevenly attached. Furthermore, in order to stabilize the metal compound to the activated carbon by chemical bonding, it is necessary to perform the heat treatment again, which is troublesome.

  Accordingly, an object of the present invention is to provide a method for producing activated carbon containing a metal oxide by suppressing the decrease in the number of pores more simply.

As means for solving the above-mentioned problems, the first invention of the present invention includes a saccharide preparation step of preparing a gel-like saccharide material using an acid carbonization treatment of a saccharide-containing material, and a saccharide preparation step. It is a manufacturing method of activated carbon provided with the metal mixing process which adds and mixes a metal compound to the gel-like saccharide material obtained, and the activation process which activates the metal mixing material obtained at a metal mixing process.
The second invention of the present invention is a method for producing activated carbon using a saccharide-containing material obtained by further removing lignin from vegetation.
3rd invention of this invention is a manufacturing method of one of the said activated carbon in which an activation process uses an alkali.
4th invention of this invention is a manufacturing method of any one of the said activated carbon which adds 1%-50% of metal compounds with respect to the dry weight of carbohydrate material at a metal mixing process.

According to the present invention, by providing a method for producing activated carbon containing a metal oxide by suppressing the decrease in the number of pores more easily, the property resulting from the number of pores can be better maintained. In addition, it is possible to easily obtain activated carbon to which desired properties are imparted by a metal oxide.
According to the first invention, the saccharide material is prepared in a gel form in the saccharide preparation step, and in the metal mixing step, the metal compound is added to the gel saccharide material. A desired amount of the metal compound can be more uniformly mixed with the carbohydrate material. In particular, when the metal compound is water-soluble, it can be dissolved in the water held by the saccharide material, so that it can be mixed into the saccharide material better. And by activating the mixed metal material, the pore size, pore shape, number of pores, etc. are controlled by the metal or metal compound, or the performance such as gas adsorption is improved by the metal or metal oxide. Thus, activated carbon can be produced. Therefore, this manufacturing method has no risk of clogging or filling the pores of the activated carbon due to the addition of a metal or metal compound, and the number of heating (firing) steps is reduced as compared with the case where the metal is added after the activated carbon is formed. it can.

According to the second invention, the use of petroleum resources can be reduced because vegetation is used as a raw material for activated carbon. In addition, when these vegetative materials are used after lignin removal treatment, when the carbohydrate material is activated, the formed pores are blocked by the lignin, or the formation of the pores themselves. Inhibition can be suppressed. Therefore, activated carbon having more pores can be efficiently produced.
According to the third invention, activated carbon having a higher specific surface area can be obtained at a higher yield by performing so-called alkali activation using an alkali in the activation step.
According to the 4th invention, while the effect | action by the metal and / or metal compound in an activation process, and the effect | action by the metal and / or metal oxide in the activated carbon obtained become significant, activated carbon which has predetermined intensity | strength can be obtained. .

The best mode for carrying out the present invention will be described below.
In the method for producing activated carbon according to the present invention, activated carbon imparted with a desired property by a metal or metal oxide, or activated carbon imparted with a desired physical property by a metal or metal compound during the production process can be produced. . The use of activated carbon is typically an adsorbent capable of adsorbing and releasing fuel gas such as methane and butane, but is not limited thereto, and includes known uses such as deodorization, deodorization, sterilization, and catalyst. be able to.
Hereinafter, a method for producing activated carbon assumed to be suitable for a gas adsorbent, particularly an adsorbent such as methane, will be described as an example with reference to FIG. The present invention includes a carbohydrate preparation step 10, a metal mixing step 20, and an activation step 30. The method of this embodiment further includes a pulverization process 12, a lignin removal process 14, and an acid carbonization process 16 in the carbohydrate preparation step 10.

(Sugar preparation process)
In the saccharide preparation step 10, a saccharide-containing material, that is, a saccharide-containing material can be activated into activated carbon and prepared in a state where a metal or a metal compound can be easily added.
The saccharide-containing material is a material containing saccharides, that is, monosaccharides, disaccharides, oligosaccharides, polysaccharides, and derivatives thereof. A synthetic sugar may be used, but a material derived from a plant can be suitably selected. The material derived from plant wood contains a large amount of sugar in the form of fibers such as cellulose and hemicellulose. The material derived from the vegetation may be a material derived from so-called woods such as conifers, hardwoods, tropical trees, but materials derived from herbs such as rice, Asa, jute, sisal, cotton, sugarcane, especially cultivation Materials derived from possible herbs are preferred. Specifically, for example, bast plants such as kenaf, sisal, and jute are preferred, and kenaf is particularly preferred because it is easy to grow on annual grasses and is easily available. The sugar-containing material may be anywhere as long as it contains vegetative sugar, but even if it is a part that is not suitable for collecting fibers or pulp, such as a core in the case of herbs. Can be used well. In the form shown in FIG. 1, a kenaf core was used as the carbohydrate-containing material.
In addition, the saccharide-containing material may be collected and appropriately dried, fractionated, or the like, or a saccharide-containing material obtained after treating vegetation such as pulp or sugarcane bagasse may be used.

  The carbohydrate-containing material is preferably made small in the carbohydrate preparation step 10 so that it can be prepared more uniformly in a short time. Specifically, the size is such that the whole is easily infiltrated when immersed in a liquid. Therefore, for example, it is preferable that chips, flakes, and materials having a larger shape are cut into small pieces in advance by a known method such as grinding or cutting. The means for fragmentation is not particularly limited, and a pulverizer such as a mill or a refiner can be used. In the form shown in FIG. 1, in the pulverization process 12, it is preferable that the kenaf core is pulverized to a size of about 1 mm or less by a pulverizer such as a known mill.

When using vegetation as the saccharide-containing material, it is preferable to perform the lignin removal treatment 14 before the activation step 30. In addition to saccharide components such as cellulose, vegetation contains a large amount of lignin, and in general, lignin inhibits the formation of pores of activated carbon in the activation step 30. The lignin removal process 14 is a process for separating lignin from saccharides such as cellulose, and a method similar to a known pulping method can be used. Specifically, for example, a method of adding sulfuric acid to a saccharide-containing material derived from vegetation and dissolving the acid, a method of treating the saccharide-containing material with a nitric acid and an alkali (so-called nitric acid method), and a saccharide-containing material with a hydrotrope. A method of treating with a salt solution (so-called hydrotropic method) can be used.
When the lignin removal treatment 14 is performed before the carbonization treatment 16 with an acid, it is easy to separate the lignin from the carbohydrate, which is preferable. Further, the method using sulfuric acid suitably used in the carbonization treatment 16 with an acid described later is preferable because the number of chemicals used can be reduced and the treatment can be efficiently performed.

  In the embodiment shown in FIG. 1, treatment with sulfuric acid was performed as the lignin removal treatment 14. By introducing plant material into sulfuric acid with a concentration of 70% and stirring at room temperature for 1 hour, saccharides and lignin are separated by hydrolysis, and the saccharide dissolves in the aqueous solution, while lignin precipitates as a solid. To do. Then, for example, by separating the solid and the liquid by centrifugation or the like and collecting only the liquid, the precipitated lignin can be easily removed to obtain a saccharide solution (sulfuric acid solution).

  In the carbonization treatment 16 using an acid, the hydrophobicity is improved and the ratio of carbon is improved. That is, in the carbonization treatment 16 with an acid, a portion having a low molecular weight and containing more carbon (a saccharide material) is precipitated in a state where there are fewer other components. In the carbonization treatment 16 with an acid, heating is performed in the presence of a strong acid. As a result, a dehydration reaction and a similar reaction can be mainly caused, and polar groups (hydroxyl groups, thiol groups, etc.) are removed from carbohydrates, or polar parts are decomposed. Thereby, the nitrogen atom and sulfur atom in carbohydrate material can also be reduced, and it can suppress that a harmful substance generate | occur | produces to a human body or an environment at the time of baking. In the carbonization treatment 16 with an acid, a saccharide material that can be gelled in a short time can be precipitated by treatment at a higher temperature. For example, a 1-hour gel-like saccharide material can be obtained by treating at 180 ° C. for 1 hour. On the other hand, as shown in FIG. 1, a gel-like saccharide material having a more uniform particle size can be obtained by treating it under a relatively mild heating condition such as 90 ° C. for a longer time, for example, 5 hours. . If the strong acid used in the carbonization treatment 16 with an acid is evaporated by heating, the working environment is deteriorated or the acid concentration of the treatment liquid is lowered. Therefore, nonvolatile sulfuric acid is suitable.

  After the carbonization treatment with acid 16, the acid is removed to prepare a gel having a desired water content. For example, in this embodiment, as shown in FIG. 1, after adding water to the solution after the carbonization treatment 16 with acid and diluting it three times, the saccharide was collected by filtration and further washed with water. The water content of the gel-like saccharide material thus obtained was 90% in the embodiment shown in FIG. 1, for example.

(Metal mixing process)
In the metal mixing step 20, a metal compound, preferably a water-soluble metal compound, is added to the gel-like saccharide material and mixed. The metal compound can be directly added to the gel-like saccharide material. When a water-soluble metal compound is used, it dissolves in water in the gel-like saccharide material, so that it can be dispersed well. Also, in the case of a metal compound insoluble in water, since the gel-like saccharide material has fluidity, it can be held in a well dispersed state by stirring. In addition, the metal compound can be stabilized in a state of adhering to the saccharide material by the viscosity of the gel saccharide material or the surface tension by water.

  Here, the metal to be added is not particularly limited, and a metal compound suitable for imparting desired properties can be used. For example, magnesium, nickel, calcium, iron, titanium and the like can be mentioned. In particular, magnesium, nickel, and calcium are expected to improve the adsorption performance of methane. The metal compound is not particularly limited, and includes inorganic salts such as chlorides, sulfates, nitrates, carbonates and phosphates, and organic salts such as acetates, formates and citrates. When alkali activation is performed in the activation step 30 to be described later, these salts may be changed to hydroxides by addition of alkali. The metal compound is preferably a metal salt, such as a hydroxide, which does not easily generate a harmful substance upon firing and is easily converted into an oxide. Oxides are also preferred. Accordingly, for example, water-soluble magnesium hydroxide, calcium hydroxide, nickel hydroxide and the like that do not contain phosphorus, nitrogen, sulfur, and the like are preferable. Titanium and iron can be present in a dispersed state in the saccharide material, for example, as titanium oxide or iron hydroxide powder added to the gel-like saccharide material and stirring.

  The amount of the metal compound to be added is not particularly limited, but when it exceeds 50%, there is a high possibility that the pores of the activated carbon are blocked, and the amount is significantly reduced. In addition, when the amount of the metal compound is less than 1% with respect to the weight of the saccharide material in the dry state, the effect of adding the metal is hardly exhibited. Therefore, the addition amount of the metal compound is preferably 1% or more and 50% or less, more preferably 10% or more and 20% or less, with respect to the weight of the saccharide material in the dry state, and the obtained activated carbon has a predetermined strength. That is, it can retain its shape.

(Activation process)
The gel-like saccharide material is preferably dried before the activation step 30. Thereby, while being able to reduce the thermal energy required in the activation process 30, the explosion (rupture of saccharide material) accompanying water evaporation can be prevented. Drying is a temperature at which evaporation of water is accelerated, such as 105 ° C. The gel-like saccharide material can be appropriately shaped by extrusion or the like. In this case, it is dried after being molded by extrusion molding or the like or filled in a mold.
In addition, when using alkali activation in the activation process 30 mentioned later, it is preferable to add powder, such as potassium hydroxide, and to mix by stirring etc. before drying a gelatinous saccharide | sugar material. Thereby, the addition process of an alkali can be simplified.

The activation step 30 may be a known activation method in the case of producing activated carbon, chemical activation such as alkali activation, zinc chloride activation, phosphoric acid activation, or gas activation using water vapor, carbon dioxide, nitrogen dioxide, or the like. . Preferably, when activated by alkali, activated carbon having a large specific surface area can be obtained in a high yield. The treatment conditions for activation are not particularly limited, and can be the same conditions as known activation conditions.
The fired body after heating can be converted into activated carbon by pulverization, washing with an acid such as dilute hydrochloric acid and water, and removing moisture by drying.
Note that the saccharide may be further carbonized by baking treatment once before the activation step 30. In this case, the alkali for alkali activation can be added after a baking process.

According to this production method, since the metal compound is added to the gel-like saccharide material, the metal compound can be easily mixed in the saccharide material in a dispersed state by stirring or the like. In addition, since the metal compound is added to the gel-like saccharide material, the desired amount of the metal compound is added to the saccharide material more reliably than when activated carbon is immersed in an aqueous solution of the metal compound and dried. Can be attached. Then, by drying in this state and performing the activation step 30, pores can be formed in a state where the metal is added, and the pores once formed by the metal are blocked or gas to the pores is formed. Protruding so as to inhibit the approach of molecules can be suppressed. In addition, it is expected that the metal can be disposed, for example, on the inside or the back of the pore. Therefore, in the present invention, activated carbon to which a metal (metal oxide) is added in a good dispersion state can be obtained with less firing treatment. Furthermore, it is possible to arrange the metal at a position different from the case where the metal is added after the activated carbon is formed, and it is expected that the action and effect of the metal (metal oxide) can be increased or obtained in a different form.
Further, in the method according to this embodiment, since the metal compound is added to the gel-like saccharide material subjected to the lignin removal treatment 14 and the acid carbonization treatment 16 in particular, there are few impurities in the material before becoming activated carbon. Unexpected or undesirable reaction with the metal compound can be satisfactorily suppressed. In addition, when alkali activation is performed, by adding alkali (potassium hydroxide or the like) to the gel-like saccharide material, as in the case of the metal compound, the activated carbon or the like is immersed in an aqueous alkaline solution and dried more. The amount of alkali can be reliably controlled.

Activated carbon according to the present invention (Example 1) and comparative activated carbon (Comparative Examples 1 and 2) were produced by the following method.
Example 1:
(1) The kenaf core material is pulverized to a particle size of about 1 mm or less, dissolved in 70% sulfuric acid at room temperature for about 1 hour, and the reaction mixture is centrifuged at 1300 G for 10 minutes to obtain solids (eg, lignin sulfate). Removed.
(2) The liquid phase obtained in (1) is heated at 90 ° C. for 5 hours, this liquid phase is diluted 3 times with water, filtered through a glass filter, and the filtrate is washed with water until pH 4 is reached. Thus, a gel-like solid was obtained.
(3) 10 g of magnesium hydroxide was added to 100 g of the gel-like solid content (water content 90%) of (2) and stirred at room temperature.
(4) Further, 10 g of potassium hydroxide was added to the solid content of (3), stirred at room temperature for 2 hours, and dried at 105 ° C. to remove moisture.
(5) The dried product obtained in (4) was calcined at 750 ° C. for about 5 hours in an N ₂ atmosphere to obtain a calcined product. After the calcined product was crushed and washed with dilute hydrochloric acid and water, the alkali was removed. The filtrate was dried at 105 ° C. for 48 hours to obtain activated carbon. This was designated Example 1.

Comparative Example 1:
(6) 10 g of potassium hydroxide was added to 100 g of the gel-like solid content (water content 90%) obtained in (2) of Example 1, stirred at room temperature for 2 hours, and dried at 105 ° C. to remove moisture. did.
(7) The dried product obtained in (6) was calcined at 750 ° C. for about 5 hours in an N ₂ atmosphere to obtain a calcined product, which was pulverized and washed with dilute hydrochloric acid and water to remove the alkali. The filtrate was dried at 105 ° C. for 48 hours to obtain activated carbon. This was designated as Comparative Example 1.
Comparative Example 2:
(8) 3 g of the activated carbon obtained in (7) of Comparative Example 1 was impregnated in 20 mL of a 10 wt% magnesium nitrate aqueous solution and stirred for 24 hours.
(9) 1N potassium hydroxide is added to the solution of (8) to adjust the aqueous solution to pH 10, stirred for 12 hours, dispersed in 5 L of water, filtered through a glass filter, washed with water, Firing was performed at 300 ° C. for 1 hour under reduced pressure to obtain activated carbon. This was designated as Comparative Example 2.

About these activated carbons, the specific surface area was calculated | required by the BET method using nitrogen gas, respectively, and the pore volume was calculated | required by T-plot based on this. The results are shown in Table 1.

  This revealed that the activated carbon of Example 1 had a larger specific surface area and an increased number of pores compared to the activated carbon of Comparative Example 1 in which no metal was added. Moreover, in the comparative example 2 which added the metal later to the activated carbon of the comparative example 1, the specific surface area is smaller than that of the comparative example 1, and the pores are blocked or buried by adding the metal. It became clear. From this, it was found that the pores of the activated carbon can be favorably increased by the method of the present invention in which a metal is added to the carbonaceous material before activation, that is, before activation. In Example 1, the pore volume was increased by 0.2 mL / g compared to Comparative Example 1, and it is expected that pores having a larger pore diameter were formed by the addition of the metal compound. . On the other hand, in Comparative Example 2 in which a metal is added to activated carbon, the pore volume is smaller than in Comparative Example 1, and it is considered that the metal compound is clogged in the pores or the pores are blocked. It is done.

It is a figure which shows the flow of the manufacturing method of the activated carbon which concerns on one Embodiment of this invention.

Explanation of symbols

10 Carbohydrate Preparation Process 12 Grinding Process 14 Lignin Removal Process 16 Acid Carbonization Process 20 Metal Mixing Process 30 Activation Process

Claims (4)

A saccharide preparation step of preparing a gel-like saccharide material using carbonization treatment of the saccharide-containing material with an acid;
A metal mixing step of adding and mixing a metal compound to the gel-like saccharide material obtained in the saccharide preparation step;
A method for producing activated carbon, comprising: an activation step of activating the metal mixed material obtained in the metal mixing step.   The method for producing activated carbon according to claim 1, wherein a saccharide-containing material obtained by removing lignin from vegetation is used.   The method for producing activated carbon according to claim 1, wherein the activation step uses an alkali. The method for producing activated carbon according to any one of claims 1 to 3, wherein in the metal mixing step, 1% to 50% of a metal compound is added to the dry weight of the saccharide material.

Images