JP4955952B2 - Production method of activated carbon - Google Patents

Description

  The present invention relates to a novel method for producing activated carbon, and more particularly to a novel method for producing activated carbon having a large specific surface area and excellent performance as a deodorizing material, adsorbing material, catalyst carrier and the like.

  Activated charcoal can be made from cellulose such as wood pulp, sawdust, coconut husk, cottonseed husk and rice husk, starchy materials such as straw, straw and corn, and vegetable raw materials such as lignin; coal, tar, petroleum Mineral raw materials such as pitch; furthermore, a method of carbonizing by using a synthetic resin such as phenol resin or polyacrylonitrile as a raw material and heating it in a non-oxidizing atmosphere is well known, and these carbonized products A method of activating by activating with a drug is also well known.

  Representative agents used for the activation of the agent include zinc chloride, phosphoric acid, calcium chloride, potassium sulfide, potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate and the like. It has also been confirmed that activated carbon having a large specific surface area can be obtained by mixing with a non-oxidizing atmosphere gas such as nitrogen or argon at 500 to 700 ° C. (Patent Document 1, etc.).

In recent years, activated carbon with a high specific surface area as high as 3000 m ² / g can be obtained by using potassium hydroxide as an effective drug, mixing it with an organic resin and heating it in a non-oxidizing atmosphere. Has been confirmed and attracting attention (Patent Document 2).

  However, this method requires an activator more than 4 times the amount of the organic resin. Therefore, although recovery and reuse of potassium have been attempted, the recovery rate is low and the cost is high. In the heating process, the alkali metal volatilizes and damages or damages the heating furnace, and also causes erosion when used as various industrial materials. Furthermore, activated carbon treated with an alkali metal compound is flammable. Many problems remain in practical use on an industrial scale, such as being highly flammable.

In addition, in the method using a chloride such as zinc chloride or calcium chloride as an activator, harmful gases such as chlorine and hydrochloric acid generated during firing may be a problem.
JP-A-9-118510 JP-A-9-86914

  The present invention has been made paying attention to the circumstances as described above, and the purpose thereof is to use an organic resin as a raw material and to use a specific drug as an activator together with the excellent productivity and An object of the present invention is to provide a method capable of producing a high-performance activated carbon having a large specific surface area under safety and operational stability.

  The production method of the present invention that has been able to solve the above-described problem is that the organic resin is at least an alkaline earth metal compound selected from the group consisting of oxides, hydroxides, carbonates, and organic acid salts of alkaline earth metals. A gist exists in a place including a step of mixing with one kind and heating and firing in a non-oxidizing atmosphere.

  In practicing the present invention, 40 to 700 parts by mass of at least one alkaline earth metal compound is mixed with 100 parts by mass of the organic resin, followed by heating and baking in a non-oxidizing atmosphere. A preferred temperature for heating and baking is 500 ° C. or higher.

  When heated and calcined by the above method, porous activated carbon can be obtained in a mixed state with an alkaline earth metal oxide, and when the mixture is treated with an acidic aqueous solution, the alkaline earth metal oxide is converted into a soluble salt. Since it dissolves in water, it can be filtered, washed with water and dried to obtain activated carbon.

  Further, according to the present invention, the pore size of the obtained activated carbon is determined according to the crystallite size of the alkaline earth metal oxide formed after mixing the alkaline earth metal compound to be used with the organic resin, firing and carbonizing. The pore distribution of the obtained activated carbon can be adjusted depending on the type of organic resin used.

  According to the present invention, an organic resin is used as a raw material, and at least one alkaline earth metal compound selected from the group consisting of an alkaline earth metal oxide, hydroxide, carbonate, and organic acid salt as an activator. By using seeds, high-performance activated carbon having a large specific surface area can be efficiently produced under excellent productivity, operational stability, and safety.

  Under the prior art as described above, the present inventors use organic resins including various polymers, thermoplastic resins, thermosetting resins, etc. as raw materials and heat them in a non-oxidizing atmosphere. By planning the improvement of the method for producing activated carbon by carbonization, especially by selecting the inorganic compound to be used as the activator, high-performance activated carbon with a large specific surface area without causing the problems as pointed out in the above prior art We have made extensive research to develop technologies that can manufacture As a result, it has been found that if an organic resin is mixed with a specific magnesium compound and heated and baked in a non-oxidizing atmosphere, porous activated carbon having an extremely large specific surface area can be obtained efficiently.

  That is, in the present invention, as described above, an organic resin is used as a raw material, which is mixed with a specific alkaline earth metal compound and then heated in a non-oxidizing atmosphere to be thermally decomposed.

  As the organic resin used as a raw material, various organic polymers, thermoplastic resins, and thermosetting resins can be used. Specifically, polyvinyl alcohol, aliphatic or aromatic polyester resins, polyolefin resins Resins, acrylic resins, styrene resins, polyamide resins, polyacrylonitrile resins, various synthetic resins such as elastomers mainly composed of polybutadiene and polyisoprene, and thermoplastic resins such as natural rubber and petroleum resin Polymers or thermosetting resins such as phenol resins, furan resins, epoxy resins and alkyd resins are used. Among these, polyvinyl alcohol, a polyester resin, a styrene resin, a petroleum resin, or the like in which the polymer or resin is substantially composed only of carbon, hydrogen, and oxygen is particularly preferable.

  These organic resins can be used in any shape such as powder, pellets, and lumps, and in some cases, can be used as a solution or dispersion dissolved or dispersed in an organic solvent.

  In contrast to these organic resins, alkaline earth metal compounds used as activators do not degrade the heat treatment furnace or generate pollutant gases in the heating and baking process, and promote the porous formation of carbides. As an obtained, an oxide of an alkaline earth metal is selected. In addition, alkaline earth metal hydroxides and carbonates that become oxides by thermal decomposition, and organic acid salts such as acetates, oxalates, citrates, acrylates and methacrylates are used in the same way. If necessary, two or more of these may be used in any combination.

  However, alkaline earth metal salts such as sulfate, nitrate and chloride are excluded. The reason for this is that sulfate, nitrate, chloride, etc. not only cause sulfite gas, nitric acid gas, hydrogen chloride gas, etc. generated during heating and firing to deteriorate the heat treatment furnace and related equipment, but also the reason. This is because an alkaline earth metal metal such as magnesium is generated during pyrolysis, and the activated carbon cannot be made porous to the level intended by the present invention.

  Examples of the alkaline earth metal include magnesium, calcium, strontium, barium, and the like. Among these, magnesium and calcium are preferable, and magnesium is particularly preferable.

  The form of the alkaline earth metal oxide, hydroxide, carbonate, organic acid salt is not particularly limited, and can be used in any form such as powder, pellet, granule, paste, etc. Is a powder or granule which is easy to mix uniformly with the organic resin and is most effective for making the carbide porous.

  The blending ratio of the alkaline earth metal compound with respect to the organic resin is not particularly limited, but is particularly preferably in the range of 40 to 700 parts by mass of the latter with respect to 100 parts by mass of the former in order to enhance the porosity of the obtained activated carbon. is there. Incidentally, if the blending ratio of the alkaline earth metal compound is less than 40 parts by mass, the effect of enhancing the porosity with respect to the activated carbon tends to be insufficient, and it becomes difficult to obtain activated carbon having the specific surface area intended by the present invention. On the other hand, from the viewpoint of the porous action of activated carbon, there is no upper limit to the blending ratio of the alkaline earth metal compound, but the action is almost saturated at 700 parts by mass, and even if blended more, the specific surface area is more This is not preferable because not only the amount of the alkaline earth metal compound used is increased unnecessarily, but also the workability of removing the alkaline earth metal compound after carbonization is lowered. The more preferable lower limit of the blending amount of the alkaline earth metal compound is 100 parts by mass, and the more preferable upper limit is 300 parts by mass.

  There is no particular limitation on the blending form of the organic resin and the alkaline earth metal compound. In addition to uniform mixing of solids such as the most common powders and granules, for example, the organic resin is heated and melted to A material in which an alkaline earth metal compound is uniformly dispersed and then secondary molded into a spherical shape, a pellet shape, a lump shape or the like, or a mixed solution of an organic resin and an alkaline earth metal compound dissolved in an organic solvent or water, It can be used in any form such as a slurry or a dried product thereof.

  Carbonization of the raw material mixture is performed by heating in a non-oxidizing atmosphere. Specifically, the raw material mixture is charged into an arbitrary heating apparatus such as an electric furnace, the inside is replaced with a non-oxidizing gas, and then heated while blowing the non-oxidizing gas into the apparatus. Then, the organic resin in the raw material mixture is pyrolyzed by heating in a non-oxidizing atmosphere, and carbonized while releasing the pyrolysis gas. The pyrolysis gas is sequentially discharged out of the heating furnace together with the blowing gas, and the alkaline earth metal oxide remains with the carbide in the heating furnace.

  The heating conditions for carbonization are not particularly limited, but the temperature is usually raised at a rate of about 0.1 to 0.5 ° C / second, and heated at 500 ° C or higher, more preferably 700 ° C or higher for about 1 to 2 hours. By doing. The upper limit of the heating temperature is not particularly present, but is generally about 1500 ° C. or lower, and more generally about 1200 ° C. or lower. In this heating process, non-oxidizing gas is continuously introduced into the heating device, and carbonization proceeds by sequentially releasing the generated pyrolysis gas out of the system. The reason for this pyrolysis-carbonization process is not clarified, but the porosity of the carbide produced by the action of the coexisting alkaline earth metal compound is significantly increased, and the specific surface area is significantly higher than that of ordinary activated carbon. Large activated carbon is obtained.

  The type of non-oxidizing gas suppresses the combustion (oxidation) of the organic resin and proceeds carbonization in the dry distillation state, so there is no particular restriction unless it contains oxidizing gas, but generally inert gases such as argon and helium Or nitrogen gas. In some cases, a reducing gas such as hydrogen gas can be contained in an appropriate amount. If necessary, a small amount of an oxidizing gas such as water vapor may be contained for activation. However, the oxidizing gas causes the carbide to burn and lowers the yield, so even if it is used, it should be stopped at a temperature of about 200 to 300 ° C. for a very short time.

  During this time, oxides of alkaline earth metal compounds are thermally extremely stable, and hydroxides, carbonates and organic acid salts are thermally decomposed into stable oxides at the initial stage of heat treatment. Then, the carbonization reaction can proceed safely without deteriorating the refractory lining the heating furnace or generating harmful gases that cause environmental pollution in the subsequent heat treatment step.

  After the carbonization is completed, the carbide is taken out after the heating device is cooled to room temperature, but the product contains an oxide of an alkaline earth metal together with the carbide. It was confirmed that the surface of the product particles was generated in a state where carbon having a large specific surface area was coated. Inferring from these existence forms, in the carbonization step, carbonization of the organic resin proceeds on the surface of the oxide powder, and in the carbonization step, the oxide has some effect to increase the porosity of the generated coal. It seems that there is.

  The activated carbon thus obtained is produced in the coexistence state with the alkaline earth metal oxide as described above, and the product is obtained with an aqueous solution of a mineral acid such as sulfuric acid or hydrochloric acid, or an organic acid such as acetic acid or oxalic acid. When treated, alkaline earth metal oxides, such as sulfates, hydrochlorides, acetates, and oxalates, dissolve into the aqueous solution, and are filtered, washed with water, and dried to give a purity of 100%. Of activated carbon can be obtained (direct recovery).

  Moreover, when implementing this invention, the pore diameter and pore distribution of the activated carbon obtained can be adjusted with the kind, mixing method, mixing ratio, etc. of the alkaline earth metal compound and organic resin to be used.

  That is, as will be clarified in the examples described later, for example, when an Mg compound is used, the pore size of the activated carbon is almost determined by the crystallite size of magnesium oxide formed after being mixed with an organic resin, calcined and carbonized. The reason is that the generated magnesium oxide crystallites are eluted by an acid, so that pores corresponding to the size of the magnesium oxide crystallites are generated.

  That is, if an alkaline earth metal compound is present when the organic resin is carbonized, an alkaline earth metal oxide is produced in the resulting carbonized product, but the produced alkaline earth metal oxide is then eluted with an acid. Therefore, pores corresponding to the size of the generated alkaline earth metal oxide (crystallite size) are generated in the carbonized product. In addition, what is necessary is just to adjust the magnitude | size of an alkaline-earth metal oxide with the kind of alkaline-earth metal compound, a mixing method, a mixing ratio with an organic resin, etc.

  In addition, the pore distribution of the obtained activated carbon is greatly influenced by the type of organic resin to be used. For example, when polyvinyl alcohol is used as the organic resin, activated carbon with many micropores around 0.8 nm is obtained, On the other hand, when polyethylene terephthalate or hydroxypropylene glycol is used as the organic resin, a relatively large mesopore-rich activated carbon of about 20 to 30 nm is obtained.

  The activated carbon obtained by the present invention is used as an adsorbent, deodorant, catalyst carrier, electrode of lithium battery, fuel cell and capacitor material as in the case of conventional activated carbon as described later. Since the coexisting oxide exists only as an inert substance, it can be used in a mixed state without being eluted and removed depending on the application. That is, the specific surface area itself as activated carbon hardly changes depending on whether or not the oxide is eluted and removed, and the oxide is merely mixed as an inert component. Can be used. However, the amount of adsorption per unit mass decreases due to the coexistence of oxides, and naturally decreases as compared with 100% activated carbon. Therefore, it is naturally desirable to use the oxides after separating and removing them.

  Alkaline earth metal compounds separated from activated carbon, such as water-soluble sulfates and chlorides, are recovered as insoluble hydroxides and carbonates of alkaline earth metals by neutralizing the aqueous solution with alkali, Since it can be utilized, the alkaline earth metal compound is not wasted. Moreover, when an organic acid is used, it can be recovered as an organic acid salt of an alkaline earth metal, which can be reused as a carbon activator.

The activated carbon thus obtained is a highly active one having a high specific surface area of about 400 to 2000 m ² / g, although it depends on the blending ratio of the alkaline earth metal compound at the time of heating and firing. Therefore, the activated carbon is used for adsorbents, deodorizers, catalyst carriers, etc., as well as conventional activated carbons, specifically, adsorbents for wastewater treatment and air purification, catalyst carriers for organic synthesis, It can be used widely and effectively as electrode materials for various batteries including lithium batteries and fuel cells, and electrode materials for capacitors.

  Moreover, compared to conventional activated carbon obtained using chlorides or alkali metals as activators, for example, there is no risk of harmful chlorides or alkali metals being mixed, so there is no concern about their volatilization. Can be used for

  In addition, in the conventional production method using chloride or alkali metal salt, as mentioned above, there is a risk of deterioration of the heat treatment furnace or incidental equipment due to volatilization of chlorine-based gas or alkali metal. Since a stable alkaline earth metal oxide is used, such a problem does not occur.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. It is also possible to implement, and they are all included in the technical scope of the present invention.

Example 1
PVA powder (reagent manufactured by Tokyo Chemical Industry Co., Ltd., polyvinyl alcohol, average polymerization degree 2000) is used as the organic resin, and MgO powder (reagent manufactured by Kanto Chemical Co., Inc.) is used as the activator. These are uniformly in the ratios shown in Table 1 below. Then, the mixture is placed in an alumina firing boat and charged into an electric furnace. Next, the inside of the furnace is replaced with argon gas, and the temperature is raised to 900 ° C. at a rate of 10 ° C./min while blowing argon gas at a rate of 50 to 100 mL ³ / min, and heating is continued at the same temperature for 1 hour. By this heat treatment, the PVC powder is pyrolyzed and carbonized to obtain a powdered mixed powder of magnesium oxide and carbide.

  After the thermal decomposition, the mixed powder was taken out after the temperature was lowered and observed with a microscope. It was confirmed that the surface of the magnesium oxide powder was adhered in a state covered with porous carbon.

  This mixed powder is poured into a 1 to 100-fold amount of 1 molar sulfuric acid aqueous solution in a mass ratio with respect to the powder and stirred at room temperature, and magnesium oxide is eluted as magnesium sulfate, followed by filtration and further washing with water. After drying, activated carbon powder is obtained. From the mass of the activated carbon powder obtained by this method and the mass of the mixed powder obtained by the thermal decomposition treatment, the content of activated carbon in the mixed powder was calculated, and the results are shown in Table 1.

  Further, the BET specific surface area of the obtained activated carbon powder was measured using a specific surface area measuring device manufactured by Yuasa Ionics Co., Ltd., trade name “AUTOSORB”, and the results are also shown in Table 1.

As is clear from Table 1, the specific surface area of the activated carbon obtained varies depending on the blending ratio of PVA and MgO, but in any case, activated carbon having a specific surface area of 800 m ² / g level or more is obtained. In addition, since magnesium oxide used as a raw material powder in the above experiment is thermally stable, no corrosive gas or the like is generated in the thermal decomposition process, and the gas generated in the thermal decomposition is substantially water vapor and carbon dioxide or one gas. Since it was only carbon oxide, there was almost no deterioration of the refractory and the crucible of the electric furnace.

Example 2
Activated carbon powder was obtained in the same manner as in Example 1 except that magnesium hydroxide (a reagent manufactured by Kanto Chemical Co., Inc.) was used as an activator at a mass ratio of 1/1 to PVA. The specific surface area of the obtained activated carbon powder was 650 m ² / g.

Example 3
Except that magnesium acetate tetrahydrate (reagent manufactured by Kishida Chemical Co., Ltd.) was used as an activator at a mass ratio of 1/4, 1/1 and 7/3 in terms of anhydride relative to PVA. In the same manner as in No. 1, activated carbon powder was obtained. The specific surface area of the resulting activated carbon powder was ^{495m 2 / g, 1085m 2 /} g and 1749m ² / g.

Example 4
Activated carbon powder was obtained in the same manner as in Example 1 except that basic magnesium carbonate (a reagent manufactured by Wako Pure Chemical Industries, Ltd.) was used as an activator at a mass ratio of 1/1 to PVA. The specific surface area of the obtained activated carbon powder was 1300 m ² / g.

Example 5
Magnesium acetate tetrahydrate (reagent manufactured by Kishida Chemical Co., Ltd.) is used as an activator, and hydroxypropylcellulose (HPC) powder (manufactured by Tokyo Chemical Industry Co., Ltd.) is used as a carbon source in water at a mass ratio of 3/1, 5 /. Activated carbon powder was obtained in the same manner as in Example 1 except that a mixed powder obtained by dissolving and drying at 1 or 7/1 was used. The specific surface area of the obtained activated carbon powder, respectively 1470m ² / g, was 1330m ² / g or 1160m ² / g.

Example 6
PET powder (product name “SA2106”, manufactured by Unitika Ltd.) is used as the organic resin, and MgO powder manufactured by Kanto Chemical Co. is used as the activator. These are used at a mass ratio of 1/1, and the heating conditions are Activated carbon powder was obtained in the same manner as in Example 1 except that the heating rate was 10 ° C./min, 900 ° C., and 1 hour. The specific surface area of the obtained activated carbon powder was 750 m ² / g.

Example 7
PVA powder (same as above) is used as an organic resin, CaO powder manufactured by Wako Pure Chemical Industries, Ltd. is used as an activator, and these are used at a mass ratio of 1/1. Activated carbon powder was obtained in the same manner as in Example 1 except that min, 900 ° C. and 1 hour were used. The specific surface area of the obtained activated carbon powder was 475 m ² / g.

Comparative Examples 1-3
In Example 1 above, no magnesium compound was used, or sodium chloride was used instead of magnesium oxide, the mixing ratio with PVA was 1: 1, the heating rate and heating conditions were 5 ° C./min, 700 ° C. (Or 900 ° C.) Carbonization was carried out under the same conditions as in Example 1 except that the time was 1 hour. After carbonization, sodium chloride was washed away and dried to obtain powdered activated carbon. Table 2 shows the specific surface area of the obtained activated carbon together with the experimental conditions.

As is clear from Table 2, when no activator was used by using PVA alone, only activated carbon having a level of less than 100 m ² / g was obtained, and when sodium chloride was used, The specific surface area is even lower and only a value of less than 20 m ² / g is obtained.

Example 8
MgO powder (reagent manufactured by Kanto Chemical Co., Inc.), magnesium hydroxide (reagent manufactured by Kanto Chemical Co., Inc.), magnesium acetate tetrahydrate (reagent manufactured by Kishida Chemical Co., Ltd.), alkaline resin, PVA powder as organic resin (Reagent manufactured by Tokyo Chemical Industry Co., Ltd., average polymerization degree 2000) was used to produce activated carbon by the following method, and the crystallite size of the obtained carbon coat MgO and the average pore diameter of the activated carbon were examined. The crystallite size of MgO is calculated from the half-value width of the diffraction line using a powder XRD diffractometer (trade name “RINT2500” manufactured by Rigaku Corporation; CuKα 40 kV-100 mA) according to Scherrer's formula. The average pore diameter was calculated by the BJH method (Barrett-Joyner-Halenda method) from the adsorption isotherm at 77K with nitrogen gas.

  1) The above MgO powder and PVA powder were mixed at a ratio of 70/30 (mass ratio), fired at 900 ° C. for 1 hour in an argon gas atmosphere, and the powder coated XRD pattern of the obtained carbon-coated MgO was measured to obtain MgO. The average mesopore of the activated carbon was determined by the BJH method from the adsorption isotherm of nitrogen gas at 77K using activated carbon obtained by eluting MgO with 1 mol sulfuric acid aqueous solution, washing with water and drying. The size was determined.

2) The crystallite size of MgO and the average mesopore size of activated carbon were determined in the same manner except that Mg (OH) ₂ powder was used instead of MgO powder in 1) above.

  3) The crystallite size of MgO and the average mesopore size of activated carbon were determined in the same manner except that magnesium acetate powder was used instead of MgO powder in 1) above and the mixing ratio with PVA powder was 50/50. .

  4) Magnesium acetate and PVA are dissolved in purified water at a ratio of 50/50 (mass ratio), evaporated to dryness, and then pulverized. Using this powder, the following experiment was conducted in the same manner as in 1) above.

  The results are shown in Table 3.

  As is apparent from Table 3, it can be seen that the average mesopore size of the activated carbon obtained in this experiment substantially corresponds to the average diameter of the MgO crystal size derived from the used Mg compound.

Example 9
PVA powder (same as above, average molecular weight 2000), HPC powder (same as above) or PET powder (same as above) is used as the organic resin, and each is mixed with MgO powder (same as above) at a mass ratio (50/50). After calcination at 900 ° C. for 1 hour in an argon gas atmosphere, the resultant was washed with 1 molar sulfuric acid to elute MgO, sufficiently washed with water and dried to obtain activated carbon powder. The BET specific surface area of each obtained activated carbon was measured by the same method as above, and the distribution of micropores and mesopores was examined by the BJH method (Barrett-Joyner-Halenda method) from the adsorption isotherm at 77K using nitrogen gas. As a result, the results shown in Table 4 and FIGS.

  As is clear from Table 4 and FIGS. 1 and 2, when PVA powder is used as the organic resin, there are many 0.8 nm micropores and the number of mesopores is small. On the other hand, when HPC powder is used as the organic resin, although a small amount of micropores of 0.55 nm and 1.1 nm are present, the main component is mesopores of 10 to 50 nm (maximum is 20 nm). When PET powder is used as the resin, although a small amount of 0.8 nm and 1.1 nm micropores are present, it is understood that the main components are 10 to 50 nm (maximum 20 nm) mesopores. It was confirmed that the fractions of micropores and mesopores were not greatly affected by the type of alkaline earth metal compound powder and were almost determined by the type of organic resin.

It is a figure which shows the micropore distribution of the activated carbon obtained in Example 9. It is a figure which shows the mesopore distribution of the activated carbon obtained in Example 9.

Claims (4)

The organic resin is mixed with at least one alkaline earth metal compound selected from the group consisting of alkaline earth metal oxides, hydroxides, carbonates, and organic acid salts, and heated and fired in a non-oxidizing atmosphere. A process for producing activated carbon including a process,
A method for producing activated carbon, wherein the pore size of the activated carbon is adjusted according to the crystallite size of the alkaline earth metal oxide formed after mixing an alkaline earth metal compound with an organic resin, calcining and carbonizing .   The manufacturing method of Claim 1 which mixes 40-700 mass parts of at least 1 sort (s) of the said alkaline-earth metal compound with respect to 100 mass parts of organic resin, and heat-fires in non-oxidizing atmosphere.   The manufacturing method of Claim 1 or 2 which performs the said heat baking at the temperature of 500 degreeC or more.   The method according to any one of claims 1 to 3, wherein the alkaline earth metal oxide is removed by acid treatment after the heating and baking.

Images