Patent Application
20060154815
1. Field of the Invention
The present invention relates to pelletized activated carbon and a production method for the same. The pelletized activated carbon of the invention is excellent in adsorptivity and hardness, so that it is preferably used for deodorization, solvent recovery, prevention of motor fuel transpiration, and catalyst in a vapor phase or liquid phase.
2. Description of the Prior Art
Recently, in order to effectively perform adsorbing operations, formed activated carbon in a form of pelletized activated carbon, a block, or a honeycomb has been used, and particularly, among these, in terms of cost, performance, and handling ease, pelletized activated carbon has been mainly used. Most of pelletized activated carbon is produced by so-called activation after pelletizing, wherein a carbonaceous material as a main material is added with a binder such as coal tar pitch, pulp spent liquor, blackstrap molasses or the like and pelletized, and then carbonized at several hundreds degrees C., and further activated in the atmosphere of an oxidized gas such as steam or carbon dioxide at high temperature 600 to 1100° C.
On the other hand, pelletized activated carbon pelletized by adding a binder to activated carbon, that is, pelletized activated carbon obtained by pelletization after activating is also generally known. For example, Japanese Published Examined Patent Application No. S48-7194 discloses a method for forming a block compact in which granular activated carbon with 4 to 40 meshes (4.75 to 0.420 mm) is mixed with oil-resistant staple fibers and filled into a container for adsorption, and these are bound integrally in a form of a millet cake by using a butadien-acrylonitrile-based, urethane-based, or styrene-butadien-based oil resistant emulsion type latex, and then dried to form a block compact.
Furthermore, Japanese Published Examined Patent Application No. H05-26747 discloses a production method in which powdery activated carbon obtained in advance by being activated is added with an inorganic binder such as bentonite white clay or water glass, pelletized, and fired at several hundreds degrees C., and Japanese Published Unexamined Patent Application No. H02-80315 discloses a pelletization method in which activated carbon activated by using meso-carbon microbeads that are optically anisotropic is pelletized by using at least one kind of a cellulose-based resin, a phenol resin, polyimide, bentonite, coal tar pitch, etc.
Furthermore, Japanese Published Unexamined Patent Application No. S52-108388 discloses a method for producing granulated activated carbon which is excellent in water resistance and has a high strength by pelletizing powdery activated carbon by using a water-soluble organic binder such as alginic acid or sodium salt of carboxymethylcellulose, etc., drying and curing it, and then substituting sodium with a bivalent or trivalent metal such as calcium, barium, copper, iron, or chromium.
However, the above-mentioned prior arts have the following problems. That is, pelletized activated carbon obtained by activation after pelletizing in which a carbonaceous material is carbonized and activated after being added with a binder and formed is easily cracked or powdered due to thermal distortion and activating contraction in the process of heating to a high temperature, and in particular, when it is attempted to obtain a highly activated high-performance product, these phenomena become conspicuous, so that it is difficult to realize both high adsorptivity and high hardness. Furthermore, adsorptivity and pore distribution are normally controlled by selection of the material and activating conditions, however, arbitrary adjustment of these is difficult.
The method disclosed in Japanese Published Examined Patent Application No. S48-7194 is effective for restraining vibration abrasion, however, it is difficult to apply this method to forming of normal pelletized activated carbon with a diameter of 2 to 6 mm like that of the invention, and use in bulk is difficult since the carbon is put in a container. Furthermore, the method does not increase the strength of each grain of pelletized activated carbon. Furthermore, it is mentioned that the oil resistant emulsion can be mixed with carboxymethylcellulose (CMC), however, necessity of mixing with CMC is not mentioned at all, and the strength improvement effect is not clearly mentioned.
Japanese Published Examined Patent Application No. H05-26747 discloses a method using an inorganic binder such as bentonite as a method for forming after activating, and this is advantageous in that activated carbon to be used as a base can be comparatively freely selected, however, not only inorganic impurities as an ash content increase but also the bulk density becomes higher than necessary, and further high-temperature treatment at approximately 600° C. or higher becomes necessary.
In the method disclosed in Japanese Published Unexamined Patent Application No. H02-80315, the cost is originally high since meso-carbon microbeads are formed into pelletized activated carbon by refining pitch, and addition of a reaction accelerator or activation by using alkali such as KOH is required since the reaction rate with an oxidized gas is low, and these increase the cost higher than normal oxidized gas activation. Furthermore, in the method disclosed in Japanese Published Unexamined Patent Application No. S52-108388, a sodium salt such as alginic acid is used as a binder and is substituted with a bivalent or trivalent metal in a post-process, so that the procedures are complicated and inevitably increase the cost. Therefore, an object of the invention is to provide general-purpose pelletized activated carbon excellent in adsorptivity and hardness and an industrially advantageous production method for pelletized activated carbon.
The inventors focused on the fact that selection of properties of activated carbon and a binder were important for achieving the above-mentioned object, and arrived at the invention through earnest examination. Namely, the invention provides pelletized activated carbon pelletized by adding a binder to powdery or granular activated carbon, where at least one kind of binder selected from a group (A group) consisting of acrylic emulsions and acryl-styrene-based emulsions and at least one kind of binder selected from a group (B group) consisting of cellulose ether and polyvinyl alcohol-based polymers are used as the binder.
Furthermore, another aspect of the invention provides a production method for pelletized activated carbon wherein at least one kind of binder selected from a group (A group) consisting of acrylic emulsions and acryl-styrene-based emulsions and at least one kind of binder selected from a group (B group) consisting of cellulose ether and polyvinyl alcohol-based polymers are added to powdery or granular activated carbon, kneaded, and pelletized, and the obtained pelletized activated carbon is dried at 200° C. or lower and cured, and then cooled to room temperature.
The invention provides pelletized activated carbon that can be widely used for various purposes and an industrially advantageous production method for pelletized activated carbon. The pelletized activated carbon of the invention has high strength as well as excellent adsorptivity, so that fine powder is hardly produced during transportation or use, and the pelletized activated carbon of the invention can be used for a purpose which involves vibration and impact applied and cannot use conventional pelletized activated carbon, and therefore, it can be preferably used in a vapor phase or liquid phase. Furthermore, by blending a plurality of kinds of activated carbons, the pore distribution and the adsorptivity can be arbitrarily controlled, so that pelletized activated carbon can be produced which is applicable to a variety of uses not only for adsorbing removal of mono chemical compositions such as nitrogen, methane, butane, toluene, etc., but also for deodorization, solvent recovery, prevention of motor fuel transpiration, catalyst and so on.
A carbonaceous material as a raw material of the activated carbon used in the invention is not especially limited as long as it is formed into activated carbon by being activated, and can be selected from various isotropic carbonaceous materials of plant-based materials, mineral-based materials, natural materials, and synthetic materials. Concretely, as plant-based carbonaceous materials, wood, sawdust, charcoal, nut shells such as coconut shells and walnut shells, and fruit seeds, etc., are available, as mineral-based carbonaceous materials, coals such as peat, lignite, brown coal, bituminous coal, and anthracite, etc., petroleum-based and/or coal-based pitch, coke, tars such as coal tar and petroleum tar, petroleum distillation residue, etc., are available, and as natural materials, natural fibers such as cotton and hemp, regenerated fibers such as rayon and viscose rayon, semisynthetic fibers such as acetate and triacetate are available, and as synthetic materials, polyamide-based materials such as nylon, polyvinyl alcohol-based materials such as vinylon, polyacrylonitril-based materials such as acryl, polyolefin-based materials such as polyethylene and polypropylene, polyurethane, phenol-based resins, polyvinyl alcohol (abbreviated to PVA), polyvinyl chloride-based resins, vinylidene chloride, ion-exchange resins or carbides thereof are available.
In the invention, use of activated carbon obtained by blending at least two kinds with different pore distributions as the powdery or granular activated carbon is preferable since production of pelletized activated carbon with an arbitrary pore diameter distribution becomes easy and the adsorptivity can be controlled.
Furthermore, in the invention, as the powdery or granular activated carbon, use of activated carbon obtained by blending at least one kind selected among coal, petroleum-based coke, coal ash, and clay with the powdery or granular activated carbon is preferable for controlling the bulk density and adsorptivity.
The form of the carbonaceous material is not limited, and various forms such as powder, grains, fibers, and sheets can be used, however the grain size of 0.3 mm or less of the powdery or granular activated carbon is suitable for pelletization and preferable.
It is desirable that pelletized activated carbon is excellent not only in mechanical strength against abrasion and pressures in filling into and removal from an adsorbing tower and adsorbing operations but also in water resistance and oil resistance, and the greatest characteristic of the invention is in that pelletized activated carbon is produced by selecting a binder to be added for achieving this object. As the binder, at least one kind selected from a group (A group) consisting of acrylic emulsions and acryl-styrene-based emulsions and at least one kind selected from a group (B group) consisting of cellulose ether and PVA-based polymers are used.
Among the A-group binders, as acrylic-based emulsions, for example, trade names RX-866A and RX-878A, etc., made by Nippon Carbide Industries Co., Inc. can be used, and as acryl-styrene-based emulsions, for example, trade names RX-383B and RX-832A, etc., made by Nippon Carbide Industries Co., Inc. can be used. Among the acrylic emulsions, acryl copolymer-based emulsions are preferable, and as such emulsions, for example, trade names FX-619 and FX-6074 made by Nippon Carbide Industries Co., Inc., can be used.
As B-group binders, cellulose ether and PVA-based polymers are available. As detailed examples of cellulose ether, for example, methylcellulose, ethylcellulose, substitutions and derivatives of these, carboxyalkylcellulose such as carboxymethylcellulose, carboxyethylcellulose, and carboxymethylethylcellulose, sodium salts and ammonium salts of these are available. Furthermore, as PVA-based polymers, for example, PVA, denatured PVA, etc., are available. It is preferable that the B-group binders are used in the form of solutions, and therefore, water-soluble materials are desirable.
Particularly, as a binder, a binder made of an acryl copolymer-based emulsion and carboxymethylcellulose is preferably used. This combination provides a hardness higher than in the case where the same blending amount of another binder is used.
The form of pelletized activated carbon is not especially limited, however, in terms of production ease and handling ease, a columnar shape is preferable. The diameter of the column is preferably 0.6 to 12 mm, and the ratio of the height to diameter is preferably 1 through 10. More preferably, diameter of the column is 1 to 5 mm, and the ratio of the height to diameter is 2 through 3.
The hardness of the pelletized activated carbon is preferably 10% or more, more preferably, 15% or more, and still more preferably, 30% or more. The hardness of the pelletized activated carbon of the invention is micro strength hardness (MS hardness) obtained by a coke strength test method. The MS hardness is obtained by applying a one coke strength test method to pelletized activated carbon, and describing simply, a 5 g sample and 10 steel balls with a diameter of 8 mm are placed into an iron-made container with a diameter of 1 inch and a length of 12 inches and rotated 1000 turns at 25 rpm, and then a weight staying on a standard sieve with 0.3 mm meshes is expressed in percent. Next, a production method for the pelletized activated carbon of the invention is described.
At least one kind of binder selected from a group (A group) consisting of acrylic emulsions and acryl-styrene-based emulsions and a binder made of at least one kind of solution selected from a group (B group) consisting of cellulose ether such as methylcellulose, ethylcellulose, carboxymethylcellulose, etc., and PVA-based polymers such as PVA as mentioned above, are added to powdery or granular activated carbon, kneaded, pelletized, and then dried at 200° C. or lower, cured, and cooled to room temperature, whereby the pelletized activated carbon of the invention is produced.
As the amounts of the binders to be added, to 100 parts by weight of activated carbon, as solid contents, 2 to 40 parts by weight of the A group and 0.5 to 10 parts by weight of the B group are preferably added, and 10 to 20 parts by weight of the A group and 2 to 4 parts by weight of the B group are more preferably added. To produce the pelletized activated carbon, first, the binders are added to powdery or granular activated carbon, and then kneaded by a kneader, etc. The mixture is then pelletized by a pelletizing machine such as a pelleter, dried at a temperature of 200° C. or lower, cured, and cooled to the room temperature, whereby the pelletized activated carbon is produced.
The pelletized activated carbon of the invention can be used for various purposes of deodorization, solvent recovery, prevention of motor fuel transpiration, and catalyst, and in particular, it is preferably used for prevention of motor fuel transpiration.
In
The adsorptivity of the pelletized activated carbon of the invention can be confirmed by measuring the benzene adsorptivity. The benzene adsorptivity can be measured according to the measurement of solvent vapor adsorptivity of JIS K1474, and is expressed in equilibrium adsorption at a concentration 1/10 of the saturated concentration. The central pore radius of the pelletized activated carbon was calculated from a pore distribution curve obtained by a vapor adsorption method. In the pelletized activated carbon of the invention, lowering in benzene adsorptivity due to pelletization is slight, and adsorptivity of 70 through 90% can be obtained with respect to the activated carbon raw material. Hereinafter, the invention is described in detail on the basis of examples, however, the invention is not limited to these. The mixing ratios in the examples and comparative examples are all expressed in parts by weight.
Coal-based powdery activated carbon (KG-DH made by Kuraray Chemical Co., Ltd.) having a benzene adsorptivity of 50%, a specific surface area of 1400 m2/g, and in a pore distribution obtained by a vapor adsorption method, a central pore diameter of 30 Å, and a grain size of 0.1 mm or less was mixed with carboxymethylcellulose (abbreviated to CMC) WSC made by Dai-Ichi Kogyo Seiyaku Co., Ltd. as a B-group binder by a mixing ratio fixed to 3 parts by weight and an acryl-styrene-based emulsion RX-383B (abbreviated to ASE) made by Nippon Carbide Industries Co., Inc. as an A-group binder by mixing ratios changed among 3 through 30, kneaded, and pelletized, and pelletized activated carbons thus obtained were dried at 130° C. and cured, and then cooled to room temperature, and the benzene adsorptivity and MS hardness of the produced pelletized activated carbons were measured (Examples 1 through 5). Furthermore, the benzene adsorptivity and MS hardness when A-group binder was fixed to 10 parts by weight of ASE and the CMC amount as a B-group binder was changed among 1 through 5 parts by weight were measured (Examples 6 and 7). The sizes of the pelletized activated carbons were adjusted by changing the dies pore diameter. The effects of the pelletized activated carbon sizes are shown in Examples 8 and 9.
By using the A-group binder and the B-group binder separately from each other, pelletized activated carbons were produced, and the benzene adsorption and MS hardness were measured in the same manner (Comparative examples 1 and 2). Furthermore, the measurement was made in the case where the CMC amount was fixed to 3 parts by weight and the ASE amount was reduced, and the results of the measurement are shown in Example 10.
Pelletized activated carbon was produced in the same manner as in Example 5 except that hydroxyethylcellulose HEC-SP900 made by Daicel Chemical Industries, Ltd. was used as the B-group binder. The benzene adsorption amount of the pelletized activated carbon was 33.6%, the ratio to the raw material was 67.2%, and the MS hardness was 86.0%.
Pelletized activated carbons were produced by fixing the B-group binder to 3 parts by weight of CMC and changing the A-group binder to an acrylic emulsion RX-878A (abbreviated to AE) made by Nippon Carbide Industries Co., Inc., and the benzene adsorptivity and MS hardness were measured. The results of measurement are shown in Table 2.
Pelletized activated carbons were produced by fixing the B-group binder to 3 parts by weight of CMC and changing the A-group binder to an acrylic copolymer-based emulsion FX-6074 (abbreviated to AC) made by Nippon Carbide Industries Co., Inc., and the benzene adsorptivity and MS hardness were measured. The results of measurement are shown in Table 3.
Pelletized activated carbons were produced by fixing the A-group binder to 10 parts by weight of ASE and changing the B-group binder to PVA 217 made by Kuraray Co., Ltd., and the benzene adsorptivity and MS hardness were measured. The results of measurement are shown in Table 4.
Pelletized activated carbons were produced by fixing the B-group binder to 3 parts by weight of CMC and adding 8 through 42 parts by weight of a phenol resin emulsion PR-51464 made by Sumitomo Durez Co., Ltd. as an A-group binder, and the benzene adsorptivity and MS hardness were measured. The results of measurement are shown in Table 5.
Pelletized activated carbons were produced by using bentonite as a binder, and the benzene adsorptivity and MS hardness were measured. The results of measurement are shown in Table 6.
Furthermore, in place of the coconut shell activated carbon, a blend of coal coke and coal-based activated carbon by a weight ratio of 4 to 6 and a blend of coal ash and coal-based activated carbon by a weight ratio of 6 to 4 were used to produce pelletized activated carbons (Examples 25 and 26). Comparative examples 8 and 9 are obtained by changing the blending ratios of the binders. The results are shown in Table 7.
Pore distribution curves of these pelletized activated carbons are shown in
Pelletized activated carbon was produced in the same manner as in Example 26 except that Kaolin clay made by Hujilight Industrial Co., Ltd. was used in place of coal ash. The benzene adsorption amount of the pelletized activated carbon was 16.2%, the MS hardness was 83.4%. The pore distribution curve was almost the same as in the case of coal ash (illustration omitted).
Coal-based granular activated carbon having a butane working capacity (abbreviated to BWC) of 12 g/dL (deciliters) measured by ASTM D5228 as a typical performance evaluation method for motor fuel transpiration preventive activated carbon and a bulk density of 0.40 g/mL (milliliters) was pulverized into a grain size of 0.1 mm or less to produce pelletized activated carbons under conditions of Examples 3 and 13, and then BWC was measured (Examples 28 and 29). For comparison, the BWC of the original coal-based activated carbon was measured and the results of measurement are also shown as Comparative example 10. The results of measurement are shown in Table 8.
2200 mL of activated carbon 3GX made by Kuraray Chemical Co., Ltd. (bulk density: 0.34 g/mL, BWC 15.1 g/dL (ASTM, D5228-92)) was used as the activated carbon of the reference number 7 in
The DBL test method was carried out on the basis of “Impact and Control of Canister Bleed Emissions,” R. S. Williams and C. R. Clontz, Technical Paper 2001-01-0733. The results of this test are shown in Table 8.
