JP4493813B2 - Highly water-repellent activated carbon structure for flue gas desulfurization and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an activated carbon structure for flue gas desulfurization having high water repellency and high air permeability and a method for producing the same. More specifically, the present invention is used effectively to remove sulfur oxides from the exhaust gas by adsorption oxidation by contacting the exhaust gas containing sulfur oxides such as sulfurous acid gas with an activated carbon catalyst. The present invention relates to a highly water-repellent and highly ventilated activated carbon structure for flue gas desulfurization containing an activated carbon catalyst and a method for producing the same.
[0002]
[Prior art]
In certain types of flue gas desulfurization processes (hereinafter referred to as “catalytic flue gas desulfurization processes”), sulfur oxides, typically sulfurous acid gas, contained in the exhaust gas are combined with oxygen and moisture in the presence of a catalyst. It reacts and is finally oxidized to sulfuric acid. This is recovered as sulfuric acid (dilute sulfuric acid) as it is, or reacted with a calcium compound and recovered in the form of gypsum (calcium sulfate). Activated carbon is generally said to be useful as a catalyst for this purpose. One of the reasons is that activated carbon has a large specific surface area and many active sites are distributed over such a large surface area.
[0003]
In order for the activated carbon to exhibit high catalytic activity in the above-mentioned contact method flue gas desulfurization process, it is important that the activated carbon has a high water repellency. This is because, unless the moisture in the exhaust gas condensed on the outer surface of the activated carbon and the pores and sulfuric acid produced by the reaction are not removed quickly, the active sites in the surface and pores are covered with moisture and sulfuric acid and blocked. Because it ends up. In order to improve the water repellency of activated carbon, the present inventors have already impregnated and supported activated carbon with a water-repellent substance, formed by mixing and kneading activated carbon powder and a water-repellent substance, and activated carbon powder. We have developed products that have been mixed and kneaded with water-repellent substances and then impregnated and supported with water-repellent substances.
[0004]
On the other hand, when exhaust gas is circulated through a column packed with activated carbon in order to bring the exhaust gas into contact with activated carbon, the packed bed of granular activated carbon has a pressure loss to treat a large volume of gas like a flue gas desulfurizer. Big and not economical. If the tower diameter is increased in order to reduce the pressure loss, it becomes difficult to make the gas distribution in the tower uniform, and at the same time, the site area of the apparatus increases, which is also not economical. As a means of reducing the pressure loss of activated carbon equipment, activated carbon or carbon material is added with a resin such as petroleum-based pitch or polypropylene as a binder, and this is molded into a honeycomb structure and fired, or metal with a honeycomb structure A product obtained by adding activated carbon to a product processed into a product has been studied or is commercially available.
[0005]
However, when activated carbon or a carbon material is added to a binder and formed into a honeycomb structure and fired, it is difficult and expensive to produce a large honeycomb structure due to distortion during firing, and a metal honeycomb structure base material. In the case where activated carbon is impregnated with aluminum, aluminum or the like is used as the base material, so that it has poor durability in exhaust gas containing corrosive sulfurous acid gas. Therefore, the present inventors knead a mixture containing activated carbon and a water-repellent resin, form this into a plate shape or a column shape, and form a primary processed product, and form a honeycomb structure from the primary processed product. In addition, a honeycomb-structured activated carbon catalyst having excellent strength and durability and being simple and inexpensive has been developed (Japanese Patent Application No. 26127).
[0006]
[Problems to be solved by the invention]
However, the diffusion flow path formed in the primary processed product has high water repellency but is small in size and has high resistance to gas diffusion and liquid discharge. For this reason, it was found that in the honeycomb structure formed from such a primary processed product, only activated carbon in the vicinity of the outer surface is subjected to the reaction, and activated carbon in the structure is not sufficiently utilized as a catalyst. This means that the effective filling amount of activated carbon is smaller than the actual amount of activated carbon used to form the structure, and the utilization efficiency as a catalyst is reduced. As a result, this particularly appears as a decrease in adsorption activity and reaction activity after a long period of time. That is, it is desired to increase the utilization efficiency as a catalyst by effectively utilizing the internal region of the activated carbon structure, and to improve the adsorption activity and reaction activity. For this purpose, resistance to gas diffusion and liquid discharge is required. There is a need to provide an activated carbon structure with fewer diffusion channels.
[0007]
[Means for Solving the Problems]
The present invention relates to a highly water-repellent activated carbon structure for flue gas desulfurization composed of a secondary assembly in which primary assembly particles made of activated carbon and a resin are assembled, and the primary diffusion channel formed in the primary assembly particles And a secondary diffusion channel formed between the primary aggregate particles constituting the secondary assembly, and the gas or liquid passes through these primary and secondary diffusion channels and flows inside the structure. The above problem is solved by providing an activated carbon structure characterized in that it can be diffused.
[0008]
The activated carbon structure of the present invention is produced by crushing a mixture of activated carbon and resin to form primary aggregate particles, which are then molded into a predetermined shape to form secondary aggregates. That is, the activated carbon structure of the present invention does not directly form a mixture and kneaded of activated carbon and a resin, but finely crushes the mixed kneaded material into primary aggregate particles, which are molded by pressure molding or the like. Thus, there is a feature in that a relatively large diffusion channel is formed between the primary aggregate particles that are manufactured by forming the secondary aggregate and constitute the secondary aggregate.
[0009]
[Action]
Each activated carbon particle has an extremely large surface area and has many catalytic active sites on its surface, so it is effective as a catalyst, but when this is used for catalytic flue gas desulfurization, The generated sulfuric acid covers the catalytic activity point. Therefore, in order to quickly release water and sulfuric acid, the surface of the activated carbon is hydrophobized by mixing and kneading such a resin having a low affinity with the polar compound with the activated carbon. By the way, activated carbon has a very large surface area because it has fine pores inside, and such pores have extremely high resistance to gas diffusion and liquid discharge. In addition, when the activated carbon and the resin are mixed and kneaded, the gap between the activated carbon particles is not completely filled with the resin. Therefore, the diffusion channel (primary diffusion channel) having a size larger than the pores in the particles is used. However, the size of the diffusion channel is inevitably limited due to the demand for effective hydrophobization of the activated carbon surface, which is not necessarily sufficient in terms of gas and liquid diffusion rates. Therefore, the movement of gas and liquid between the activated carbon in the inner part of the structure and the outside is not easy, and the activated carbon in the inner part of the structure is hardly used as a catalyst as it is.
[0010]
Therefore, in the present invention, in order to allow gas and liquid to move quickly between the activated carbon in the inner part of the structure and the surface of the structure, in the present invention, a diffusion channel (primary diffusion channel) consisting of voids between the activated carbon particles in the structure is used. A large diffusion channel (secondary diffusion channel) is formed. The secondary diffusion channel is formed between the primary aggregate particles by configuring the structure (secondary aggregate) as an aggregate of primary aggregate particles made of activated carbon and resin. The primary aggregate particles are obtained by mixing and kneading activated carbon and a resin and crushing them. Thus, the activated carbon structure of the present invention has two types of diffusion channels of different sizes, a primary diffusion channel and a secondary diffusion channel, thereby sufficiently hydrophobizing the activated carbon surface having catalytic active sites. It satisfies the two requirements of rapid gas and liquid movement at the same time.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
In order to produce the activated carbon structure of the present invention, first, activated carbon and resin are mixed and kneaded. As the activated carbon, powdered activated carbon is generally used, and the average particle size is preferably 20 to 200 μm. If the average particle size is smaller than this range, the size of the primary diffusion channel formed in the primary aggregate particles is reduced, and the resistance to diffusion of gas and liquid in the primary aggregate particles is increased. On the contrary, if the average particle diameter is larger than this range, the pores are not sufficiently water-repellent, and the gap between the activated carbon particles tends to be too large and the specific surface area of the activated carbon structure tends to be small. Here, the “average particle size” of activated carbon refers to a 50% particle size, that is, a particle size of 50% on a weight-based integrated sieve.
[0012]
Activated carbon is classified into coal types such as coal-based, coconut shell-based, and petroleum pitch-based depending on the raw material. The catalytic activity is generally high in coal-based, but in the present invention, it can be used regardless of the type of coal. In addition, although it is preferable to use the activated carbon having a particle size of 20 to 200 μm that is commercially available as powdered activated carbon, granular activated carbon having a particle size larger than this may be pulverized to a desired particle size.
[0013]
On the other hand, the resin is preferably a fluororesin from the viewpoint of imparting water repellency, but is not necessarily limited to the fluororesin. As the fluororesin, polytetrafluoroethylene (PTFE) resin, perfluoroalkoxy (PFA) resin, tetrafluoroethylene hexafluoropropylene (FEP) copolymer, ethylene trifluoride chloride (PCTEF) resin, etc. are suitable. Can be used. These fluororesins are commercially available as fine particle dispersions adjusted to various particle sizes. It is preferable that 1-30 weight% of resin is contained with respect to activated carbon.
[0014]
In order to mix and knead the fine particle dispersion and activated carbon closely, typically a pressure kneader or a Banbury mixer is used. However, the present invention is not necessarily limited to this, and a kneading action such as shearing or compression is effective for the material. Anything that can be given to can be used in general. When a pressure kneader or a Banbury mixer is used, a desired close kneaded product can be obtained by continuing the mixing and kneading operation for about 0.2 to 1.0 hour. This kneading operation is performed in order to bring the activated carbon and the resin into close contact with each other and to impart sufficient water repellency to the activated carbon surface.
[0015]
Next, in order to obtain primary aggregate particles, the kneaded product (lumps) is typically finely crushed using a pin mill or a cutter mill. The kneaded product of activated carbon and resin forms a structure in which the resin is intertwined and has a high pressure breakdown / impact resistance strength. For example, a ball mill or a roll type pulverizer usually used for pulverization is sufficiently pulverized. Absent. For pulverization of a material having a high pressure breakdown resistance / impact resistance strength such as the kneaded product, it is necessary to select a pulverizer having a function of cutting as a pulverization principle. Examples of the pulverizer having such a cutting function include a rotary disk type pulverizer (pin mill, impact mill, etc.), a cutting type pulverizer (cutter mill, knife mill, etc.), a hammer mill, and the like. In this specification, it will be referred to as “pulverization” in order to distinguish from a normal pulverization operation.
[0016]
Once the kneaded product of activated carbon and resin is crushed into primary aggregate particles, the purpose of forming the secondary aggregate again is a secondary diffusion flow with a size that facilitates diffusion of gas and liquid. The path is to be formed inside the secondary assembly. Accordingly, the particle size of the primary aggregate particles needs to be adapted to such purpose, and is larger than the average particle size of the powdered activated carbon, and preferably the 50% particle size is 0.05 to 10 mm, more preferably 0. The range is 1 to 5 mm. When the 50% particle size is smaller than this range, the size of the secondary diffusion flow path becomes small, and it becomes difficult to obtain the effect of facilitating diffusion of gas and liquid. On the other hand, if the 50% particle size is larger than the above range, the number of secondary diffusion channels formed is reduced, and the activated carbon surface in contact with the channels decreases, so the effect of forming the secondary diffusion channels is sufficient. It becomes difficult to obtain. Here, the “50% particle size” is the particle size of 50% on the weight-based integrated sieve obtained by dry sieving.
[0017]
The secondary aggregate is obtained by forming the primary aggregate particles thus obtained into a desired shape. For forming, extrusion molding or pressure molding is suitable. For forming into a plate shape, pressure molding is suitable, and there are a method in which the primary aggregate particles are passed through a roll machine as it is, and a method in which the primary aggregate particles are uniformly spread on a mold and pressed with a press machine. It is also possible to make the thickness of the molded product uniform by passing it through a roll machine after being molded by a press machine. On the other hand, for forming into a columnar shape, primary aggregate particles may be spread on a columnar mold and press-molded, but it can be extruded from a hole having a desired shape such as a circle or a rectangle using an extrusion molding machine. Further, if the corrugated plate is filled with the primary aggregate particles and pressed by a press, a corrugated plate for forming a honeycomb structure can be produced.
[0018]
The secondary aggregate formed by extruding or pressure-molding the primary aggregate particles preferably has a primary diffusion channel and a secondary diffusion channel at an appropriate ratio. Such a preferable secondary aggregate generally has a bulk density of 0.10 to 0.60 g / cm 3, preferably about 0.20 to 0.40 g / cm 3, and a porosity of 20 to 65%, preferably It was about 30-55%. The porosity was measured as follows. After contacting the activated carbon structure with a known volume with simulated exhaust gas containing sulfurous acid gas for more than 100 hours in order to eliminate the effect of the space not used for the diffusion of activated carbon pores, etc., this activated carbon structure is connected to a measuring cylinder with a stopper. The sample was filled with pure water, suctioned with a vacuum pump, the space volume was determined from the reduced liquid volume (volume of liquid entering the activated carbon structure), and the porosity was calculated. The amount of water evaporation was corrected by performing a blank test.
[0019]
The primary aggregate particles can be molded as they are, but in order to increase the mechanical strength of the molded secondary aggregate, it is preferable to mix a binder and, if necessary, mold while heating. According to this method, pressure molding can be performed at a low pressure. As the binder, a water-soluble polymer or a thermoplastic resin is preferably used. As the water-soluble polymer, water-soluble starches, gum arabic, gelatin, carboxymethyl cellulose, methyl cellulose, polyvinyl alcohol and the like are used. As the thermoplastic resin, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyvinylidene chloride, fluororesin, polymethyl methacrylate, polyamide, polyester, polycarbonate, polyphenylene oxide, thermoplastic polyurethane, polyacetal, and the like are used.
[0020]
The water-soluble polymer is typically suitably used for spraying and mixing the primary aggregate particles, and forming the sheet into a sheet by passing it through a roll machine. It is preferable to prepare two sheets thus obtained and sandwich a reinforcing material sheet between them to form a sandwich-structured panel because the mechanical strength is further increased. As such a reinforcing material sheet, a net of polyethylene or polypropylene is preferably used. On the other hand, a thermoplastic resin is typically mixed with primary aggregate particles in a powder form, filled into a flat plate or columnar mold, and heated with a press while heating to near the melting point of the thermoplastic resin. It is suitably used for pressure forming.
[0021]
As a suitable activated carbon structure, for example, in order to form a honeycomb structure, a secondary aggregate such as a flat plate shape, a corrugated plate shape, and a column shape obtained as described above may be combined. For example, a honeycomb structure can be formed by alternately laminating flat plate shaped products and corrugated plate shaped products as a secondary assembly, or arranging staggered tubular shaped products in a staggered manner. . Alternatively, the honeycomb structure can be formed by directly filling the primary aggregate particles into a honeycomb-shaped mold and performing pressure molding.
[0022]
【Example】
Example 1
Obtained by mixing and kneading activated carbon powder (coal-based powder activated carbon with an average particle size of 30 μm) and fluororesin powder (PTFE particle dispersion with an average particle size of 200 nm, 60% by weight) using a pressure kneader at a ratio of 9: 1. The lump was pulverized with a cutter mill to obtain primary aggregate particles having an average particle diameter of 0.6 mm. Methyl cellulose as a binder was sprayed and mixed with the primary aggregate particles at 10% by weight with respect to the primary aggregate particles, and formed into a sheet having a thickness of 0.5 mm by a roll machine. This is crimped to both sides of a polyethylene net with a thickness of 0.3 mm to form a flat panel, and after some of the panels are processed into a corrugated sheet, the flat panel and the corrugated panel are alternately formed. By laminating, the honeycomb structure shown in FIG. 1 was formed. The honeycomb structure thus obtained was filled in a rectangular reactor having a cross section of 35 mm × 40 mm to a height of 0.8 m, and a gas having the following composition (45 ° C.) was flowed at a gas superficial velocity of 4 m / s. did.
SO2: 800 volume ppm
O2: 4% by volume
CO2: 10% by volume
N2: Remaining relative humidity: 100%
When the catalyst activity was evaluated by measuring the SO2 concentration in the outlet gas with an SO2 meter (infrared type), a desulfurization rate of 22% was obtained 100 hours after the start of the test.
[0023]
Example 2
The primary aggregate particles obtained in the same manner as in Example 1 were mixed with 15% by weight of polyethylene powder as a binder with respect to the primary aggregate particles, filled in a honeycomb-shaped mold and heated to 150 ° C. The honeycomb structure shown in FIG. 1 was formed by pressure forming with a press. Using the honeycomb structure thus obtained, an activity test was conducted in the same manner as in Example 1. As a result, a desulfurization rate of 25% was obtained 100 hours after the start of the test.
[0024]
Comparative Example 1
The same activated carbon powder and fluororesin powder as used in Example 1 were mixed and kneaded at a ratio of 9: 1 using a pressure kneader in the same manner as in Example 1, and the kneaded product was directly treated with a roll machine to a thickness of 0. Molded into a 5 mm sheet. This was crimped to both sides of a 0.3 mm thick polyethylene net to form a flat panel. Further, some of the panels were processed into a corrugated plate, and the honeycomb structure shown in FIG. 1 was formed by alternately laminating flat plate-like panels and corrugated plate-like panels. Using the honeycomb structure thus obtained, an activity test was performed in the same manner as in Example 1. As a result, the desulfurization rate after 15 hours from the start of the test was 15%.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a honeycomb structure according to a preferred embodiment of the present invention.

Claims (11)

For flue gas desulfurization consisting of secondary aggregates of primary aggregate particles obtained by pulverizing a mixture of kneaded activated carbon having an average particle size of 20 to 200 μm and a resin having a low affinity for polar compounds A highly water-repellent activated carbon structure, wherein the primary aggregate particles have a 50% particle size of 0.05 to 10 mm, a primary diffusion channel formed in the primary aggregate particles, and the secondary aggregate A secondary diffusion channel formed between the primary aggregate particles constituting the gas, so that gas and liquid can diffuse inside the structure through the primary and secondary diffusion channels. An activated carbon structure characterized by comprising.   The activated carbon structure according to claim 1, wherein the primary aggregate particles have a 50% particle size of 0.1 to 5 mm. The activated carbon structure according to claim 1 or 2, wherein the resin is contained in an amount of 1 to 30% by weight based on the activated carbon. The activated carbon structure according to any one of claims 1 to 3 , wherein the resin is a fluororesin. The activated carbon structure according to any one of claims 1 to 4 , which is formed into a honeycomb shape. The activated carbon structure according to any one of claims 1 to 5 , comprising the secondary assembly and a reinforcing material. Crushing a kneaded mixture of activated carbon having an average particle size of 20 to 200 μm and a resin having a low affinity with a polar compound to form primary aggregate particles; The method for producing an activated carbon structure according to any one of claims 1 to 6 , further comprising a step of forming a next aggregate. The method according to claim 7 , wherein the primary aggregate particles are pressed to form secondary aggregates. The method according to claim 8 , wherein an additive for improving the strength is added for pressure molding. The method according to claim 9, wherein the additive is a water-soluble polymer or a thermoplastic resin. The activated carbon structure according to any one of claims 1 to 6 or the activated carbon structure produced by the method according to any one of claims 7 to 10 is contacted with an exhaust gas containing sulfur oxides in the presence of oxygen and moisture. And removing sulfur oxide from the exhaust gas by separating and separating the sulfur oxide from the activated carbon structure by adsorption and oxidation of the sulfur oxide, thereby removing the sulfur oxide from the exhaust gas.

Images