JP3556085B2 - Activated carbon material and flue gas desulfurization method using this activated carbon material - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a water-repellent activated carbon material, and more particularly to an activated carbon material useful as an oxidation catalyst for use in a flue gas desulfurization process.
[0002]
[Prior art]
Activated carbon is widely used for catalysts and adsorbents. Catalysts using activated carbon include those utilizing the catalytic activity of activated carbon itself and those using activated carbon as a carrier such as a transition metal having catalytic activity. On the other hand, examples of using activated carbon as an adsorbent are well-known examples of removal of heavy metals and condensable gases in the gas phase, decolorization of sugar solution, removal of trace organic substances in water, and various wastewater treatments in the liquid phase. Have been.
[0003]
One of the reasons why activated carbon is useful as a catalyst (support) or adsorbent is that its specific surface area is large. Activated carbon particles have a large number of pores of various sizes ranging from sub-nanometers to sub-microns therein, which form a complex and intricate structure like a mesh. It is said that the total surface area including the inner surface of such pores reaches 1000 m ² per 1 g of activated carbon, and it is considered that a large number of catalytic active sites and adsorption active sites are distributed over such a large surface area.
[0004]
In some types of flue gas desulfurization processes (hereinafter referred to as "catalyzed sulfation processes"), activated carbon is used as an oxidation catalyst, and sulfur oxides such as sulfur dioxide contained in exhaust gas are ultimately reduced by coexisting oxygen. Is oxidized to sulfuric acid. This is recovered as sulfuric acid (dilute sulfuric acid) as it is depending on conditions such as the partial pressure of water vapor, or is recovered in the form of gypsum by reacting with a calcium compound. Activated carbon catalysts, unlike ceramic-based catalysts such as zeolites, themselves have a certain degree of activity as the above-mentioned oxidation catalysts, so there is no need to carry catalyst species such as transition metals, and the generated sulfuric acid catalyzes such metals. Advantageously, there is no problem of seed infestation.
[0005]
However, from a practical point of view, the performance of the activated carbon catalyst in the above-mentioned catalytic sulfation process is not always sufficient, and a higher activity is obtained while taking advantage of the above-mentioned advantage of not having to carry a catalyst species. Activated carbon catalysts are needed. Examining this point, it is said that the reason why the performance of the activated carbon catalyst is not sufficient is not that the amount and activity of the catalytic active site is small but that the intramolecular diffusion of the reactive molecule is limited. I understand that. Further investigation reveals that in the catalytic sulfation reaction, sulfuric anhydride generated at the catalytically active site reacts with water vapor in the atmosphere and immediately turns into a sulfuric acid aqueous solution and stays in the pores, where the reactive molecules enter the particles. It has also been found that internal catalytic active sites are not effectively utilized to block diffusion. In other words, if the generated sulfuric acid aqueous solution can be prevented from remaining in the catalyst, the catalytic activity can be expected to be greatly improved. For that purpose, it is important to improve the water repellency of the activated carbon catalyst surface. It turned out that it was.
[0006]
For example, Chem. Eng. Comm. vol. 60 (1987) p. 253, a dispersion of micron-sized polytetrafluoroethylene (PTFE) particles is sprayed on granular activated carbon having an average particle diameter of 0.78 mm, thereby performing the adsorption oxidation reaction of sulfurous acid gas in the region of 8 to 20% of PTFE addition. An example is shown in which the rate constant has increased threefold. Japanese Patent Application Laid-Open No. S59-36531 discloses that in order to oxidize sulfite ions accumulated in an absorbing solution that has absorbed sulfur dioxide gas, when granular activated carbon is added to the absorbing solution, the activated carbon is made water-repellent. It is shown that the treatment increases the sulfite ion adsorption oxidation activity. Specifically, it is shown that, by impregnating granular activated carbon having a particle size of 5 to 10 mm with a PTFE dispersion and heating at 200 ° C. for 2 hours, the activated carbon exhibits a much higher activity than that of the activated carbon alone. ing. In the above case, the activated carbon water-repellent has a PTFE particle size of a commercially available PTFE dispersion having a diameter of about 0.2 to 0.4 μm, and this particle size permeates the inside of the activated carbon particles. Is considered to be too large, it is considered that the outer surface of the activated carbon and only a very small portion of the macropores were activated carbon with water repellency.
[0007]
As described above, it has been found that the water repellency of the activated carbon surface is an important requirement for use as a catalytic sulfation catalyst, but the same requirement is applicable to other uses such as an adsorbent. It is fully expected that the difficulty of intragranular diffusion of the condensed gas will greatly affect the substantial adsorption capacity, especially in the case of gas-phase adsorption containing a condensable gas. . Therefore, improving the water repellency of the activated carbon material surface is being demanded for various uses in which intragranular diffusion of the activated carbon material is considered.
[0008]
[Problems to be solved by the invention]
For the purpose of improving the water repellency of the surface of activated carbon, the present inventors have already carried out impregnation of activated carbon particles with a water-repellent substance, mixing of activated carbon powder and a water-repellent substance, and molding in advance. A product formed by mixing hydrated activated carbon powder with a water-repellent substance was developed. Here, impregnating and supporting the activated carbon particles with a water-repellent substance means impregnating a dispersion (sol) containing fine particles of a water-repellent organic substance such as a fluororesin or a part of a hydrocarbon resin, so that the fine particles are surfaced on the activated carbon particles. Mixing a water-repellent substance with activated carbon powder and molding it means mixing fine particles of such a water-repellent substance with activated carbon powder, compressing, granulating, etc. and molding into a predetermined shape. Things. The water-repellent treatment is a treatment of the activated carbon powder with a fine particle dispersion of the water-repellent substance or a solution of the water-repellent substance. However, it was found that the activated carbon material thus obtained had the following problems.
[0009]
First, in the case where the activated carbon particles are impregnated with a water-repellent substance, there is a problem that the catalytic activity and the adsorptive activity are not so high. This is because, in order to improve their activity, it is effective to make the macropores (pores having a diameter of 0.05 μm or more) of activated carbon (including shaped activated carbon) uniformly water-repellent from the outer surface to the inside of the particles. If the water-repellent substance is impregnated and supported on the activated carbon particles, it is considered that the macropores inside the activated carbon particles are not sufficiently water-repellent and the liquid inside the catalyst is not sufficiently discharged. In addition, when activated carbon powder and water-repellent substance fine particles are mixed and molded into a predetermined shape, the activity is higher than that of activated carbon particles impregnated with a water-repellent substance, but still has sufficient catalytic activity and adsorption activity. There is a problem that it does not become high. This is because simply mixing activated carbon powder and a water-repellent substance makes the entire macropore exhibiting a wide pore size distribution uniform water repellency and prevents the macropore inlet from being clogged with liquid. This is probably because uniform water repellency was not sufficient. Further, in the case where the activated carbon powder previously subjected to the water repellent treatment and the water repellent substance are mixed and formed into granules, there is a problem that it is difficult to stably obtain a catalyst having excellent performance. This is because it is difficult to uniformly attach the water-repellent substance to the surface of the activated carbon powder, and when the water-repellent treatment is performed by increasing the amount of the water-repellent substance, the active points are covered with the water-repellent substance, and the available active points are used. This is because it is difficult to make the outer surface of the activated carbon powder uniform and sufficiently water-repellent, because the number itself decreases. The present invention is intended to overcome these problems and realize the optimum water repellency of activated carbon particles.
[0010]
[Means for Solving the Problems]
The present invention mixes activated carbon powder and a water-repellent substance, forms the mixture into a predetermined shape, and then performs a water-repellent treatment, thereby uniformly and highly repelling the macropore surface inside the activated carbon material and the outer surface portion. It is intended to provide an activated carbon material useful for various uses in which intra-granular diffusion is taken into account, and particularly for use as an oxidation catalyst for flue gas desulfurization, thereby solving the above-mentioned problems. .
[0011]
The activated carbon material provided by the present invention has a non-uniform water repellency within the particles. That is, in the activated carbon material of the present invention, the outer surface of the particles is more strongly water-repellent, and the inside of the particles is relatively weak and relatively uniformly water-repellent. This prevents the formation of a water film on the surface of the particles, prevents the macropore inlet from being clogged by the liquid, and strongly inhibits the invasion of water vapor and aqueous solution from the outside to the inside. Thus, the active sites inside the particles are effectively used, and high catalytic performance is obtained.
[0012]
The above-mentioned non-uniform water repellency is achieved by performing a water repellent treatment after mixing and molding the activated carbon powder and the water repellent substance. Since the activated carbon powder before the mixing and molding is not preliminarily subjected to the water-repellent treatment with the water-repellent substance, the active points inside the particles are not covered more than necessary with the water-repellent substance. The activated carbon powder is substantially uniformly water-repellent as a whole by mixing with a water-repellent substance, preferably by kneading, and further subjected to a water-repellent treatment after molding, whereby the particle surface is strongly water-repelled.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
In order to produce the activated carbon material of the present invention, first, activated carbon powder and a water-repellent substance are mixed intimately and molded. The activated carbon powder used preferably has an average particle diameter of 10 to 1000 μm. If the average particle size is smaller than this range, the molded particles tend to be too dense, and the gap formed between the powder particles constituting the molded particles tends to be too fine. Conversely, if the average particle size is larger than this range, the inside of the pores will not be sufficiently water-repellent, and the gap between the powder particles will be too large and the outer surface area of the molded particles will tend to be small. A more preferred range of the average particle size is 15 to 400 μm, most preferably 20 to 300 μm. Activated carbon powder is classified into coal type, coconut shell type, petroleum pitch type, etc. according to its raw material. Although the catalytic activity is generally high in a coal system, it can be used in the present invention irrespective of the type of coal. Further, as the activated carbon powder, a powder carrying a metal or firing may be used.
[0014]
On the other hand, examples of the water repellent substance include hydrocarbon resins such as polystyrene (PS) and polyethylene (PE), or polytetrafluoroethylene (PTFE), perfluoroalkoxy resin (PFA), and ethylene tetrafluoride hexafluoropropylene copolymer. Fluororesins such as coalesced (FEP) and ethylene trifluorochloride resins (PCTEF) can be suitably used. These water-repellent substances are commercially available as fine particle dispersions adjusted to various particle sizes, and after kneading such fine particle dispersion and activated carbon powder together, extruding, rolling, punching, etc. What is necessary is just to shape | mold into predetermined shapes, such as a cylinder shape, a plate shape, and a honeycomb shape. Fluororesin has high water repellency and strong adhesion to activated carbon powder, so it can maintain stable water repellency. Is particularly preferred in that is obtained. Good results can be obtained if the water-repellent substance is added in an amount of 1 to 30% by weight, preferably 2 to 20% by weight.
[0015]
If necessary, the obtained shaped particles are pulverized to adjust to an appropriate particle size, and then subjected to a water-repellent treatment. As a method of the water-repellent treatment, a dispersion of fine particles of the water-repellent substance or a solution in which the water-repellent substance is dissolved in an organic solvent such as toluene may be impregnated into the molded particles by a spray method or an immersion method. . In this case, as the water repellent substance, a fluororesin is preferable in that it exhibits high adhesion and high water repellency. On the other hand, when an organic solvent solution is used, it is preferable to dissolve a polymer water-repellent substance having a molecular weight of 10,000 or more before use. If the molecular weight is smaller than this, the active sites are unnecessarily covered with the water-repellent substance, and the number of effective active sites decreases. It is preferable that the water-repellent substance is impregnated with 0.1 to 3.5% by weight, preferably 0.2 to 3% by weight.
[0016]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples.
[0017]
Example 1
Six types (A to F) of commercially available granular activated carbons such as coal-based, coconut-shell-based, beet-based, and the like, which were fired at 800 ° C. for 1 hour in a nitrogen stream and not fired, were prepared. After each granular activated carbon was crushed by a pulverizer, a classification operation was performed for 2 hours with a sieve shaker using a stainless steel sieve, and about 200 g of each fine activated carbon having a particle diameter of 106 to 212 μm was collected. The average value of the mesh of each sieve obtained by combining the representative diameters of the fine activated carbon particles thus obtained is referred to as “average particle diameter”. That is, the average particle diameter of each of the fine powdered activated carbons obtained above is 159 μm.
[0018]
Next, a commercially available aqueous PTFE (particle size: 0.2 to 0.4 μm) aqueous dispersion (10% by weight) was added to 50 g of each of the fine powder activated carbons in an amount of 56 g each and kneaded, followed by molding with a compression molding machine. A pressure of 500 kgf / cm ² ) was obtained. After drying each molded body thus obtained in a dryer at 45 to 50 ° C. for 12 hours, it is crushed and classified to obtain molded granules (mixed molding catalyst) having a particle size of 2.8 to 4.0 mm. Was. The PTFE content of the shaped granules is about 10% by weight.
[0019]
Next, an aqueous dispersion (10% by weight) of a commercially available spherical PTFE (particle size: 0.2 to 0.4 μm) aqueous solution was diluted 50-fold with deionized water. Each 20 g was immersed. This was vacuum impregnated and dried with a rotary evaporator, and then dried in a dryer at 45 to 50 ° C. for 12 hours to obtain spherical PTFE-supported granules (PTFE-supported mixed-molded catalyst) . The amount of PTFE carried on each of the spherical PTFE-supported molded particles thus obtained was determined from the difference between the dry weight of the molded particles before and after the support, and the amount of PTFE carried was about 1% by weight.
[0020]
Each of the spherical PTFE-supported molded granules prepared above and the six types of granular activated carbon used for the production were used as catalysts in a catalytic sulfation reaction test apparatus, and each was tested for catalytic activity. Each catalyst was charged into a jacketed glass reactor having an inner diameter of 16 mm by 40 ml, and a gas having the following composition was flowed at 50 ° C. and 600 dm ³ / hr (SV = 15000 hr ⁻¹ ),
SO ₂ 1000 ppm by volume
O ₂ 4% by volume
CO ₂ 10% by volume
N ₂ balance 100% relative humidity
The evaluation was performed by measuring the outlet SO ₂ concentration with a SO ₂ meter (ultraviolet, infrared). FIG. 1 shows the desulfurization performance of each catalyst (250 hours after the start of the test). From FIG. 1, all of the six types were obtained by mixing crushed materials with spherical PTFE, molding and then impregnating and supporting spherical PTFE (PTFE-supported mixed molding catalyst) , and those not impregnating and supporting spherical PTFE (mixing molding). It can be seen that the desulfurization performance was greatly improved as compared with the catalyst) .
[0021]
Example 2
Activated carbon A of Example 1 was ground and classified in the same manner as in Example 1. At this time, by using a combination of sieves having different meshes (0 to 20 μm, 20 to 53 μm, 53 to 106 μm, 106 to 212 μm, 212 to 300 μm, 2800 to 4000 μm), six types (10 μm, 36 μm) having different average particle diameters are used. 0.5 μm, 79.5 μm, 159 μm, 256 μm, 3400 μm). Hereinafter, in the same manner as in Example 1, a spherical PTFE-supported molded granule containing about 10% by weight of spherical PTFE and about 1% by weight of spherical PTFE was obtained.
[0022]
Using the reaction test apparatus described in Example 1, the catalytic activity of each of the spherical PTFE-supported molded granules prepared above was evaluated under the same conditions. FIG. 2 shows the desulfurization performance of each catalyst 250 hours after the start of the test. As shown in FIG. 2, a desulfurization rate of 60% or more is obtained when fine powdered activated carbon having an average particle diameter of 10 to 1000 μm is used, and is obtained when fine powdered activated carbon having an average particle diameter of 15 to 400 μm (more preferably, 20 to 300 μm) is used. It can be seen that the desired desulfurization performance is the highest.
[0023]
Example 3
Using activated carbon A of Example 1, a molded granular material containing about 10% by weight of PTFE was obtained in the same manner as in Example 1. Then, a commercially available spherical PTFE aqueous dispersion (10% by weight) is diluted with deionized water to adjust various concentrations (0 to 5% by weight), and 20 g of each of the molded particles is added to each 100 cc of the diluted dispersion. Each was immersed. This was impregnated and dried by a rotary evaporator under reduced pressure, and then dried in a dryer at 45 to 50 ° C. for 12 hours to obtain various supported molded granules (PTFE-supported mixed-molded catalyst) having different amounts of spherical PTFE carried.
[0024]
Separately, the aqueous dispersion of the spherical PS was adjusted to various concentrations (0 to 5% by weight), and 20 g of each of the molded particles was immersed in 100 cc of each of the diluted dispersions. This was impregnated and dried by a rotary evaporator under reduced pressure, and then dried in a dryer at 45 to 50 ° C. for 12 hours to obtain various supported molded granules (PS-supported mixed-formed catalyst) having different amounts of spherical PS supported.
[0025]
Using the reaction test apparatus described in Example 1, the catalyst activity was evaluated for the supported or unsupported shaped granules prepared above under the same conditions. FIG. 3 shows the desulfurization performance of each catalyst 250 hours after the start of the test. From FIG. 3, it is found that the optimum amount of the spherical PS or spherical PTFE-supported molded granules with respect to the desulfurization performance is 0.2 to 3% by weight. In addition, it can be seen that those carrying PTFE have higher desulfurization performance than those carrying PS.
[0026]
Comparative Example 1
Using the activated carbon A of Example 1, fine activated carbon having an average particle diameter of 159 μm was obtained in accordance with the procedure of Example 1. Next, a commercially available aqueous dispersion of spherical PTFE (particle size: 0.2 to 0.4 μm) (10% by weight) is diluted 50-fold with deionized water, and 20 g of the fine powder activated carbon is immersed in each 100 cc of the diluted dispersion. did. This was impregnated and dried by a rotary evaporator under reduced pressure, and then dried in a dryer at 45 to 50 ° C. for 12 hours to obtain PTFE-supported fine powder activated carbon having a spherical PTFE support amount of about 1% by weight.
[0027]
Next, 56 g of an aqueous dispersion (10% by weight) of a commercially available spherical PTFE (particle size: 0.2 to 0.4 μm) aqueous dispersion (50% by weight) was added to 50 g of the above-mentioned PTFE-supported fine powdered activated carbon and kneaded, followed by molding with a compression molding machine (molding pressure). 500 kgf / cm ² ) to obtain a molded body. The molded body thus obtained was dried in a dryer at 45 to 50 ° C. for 12 hours, and then crushed and classified to obtain molded granules having a particle diameter of 2.8 to 4.0 mm. This is referred to as spherical PTFE pre-supported shaped granules (PTFE pre-supported mixed and formed catalyst) , which contains about 1% by weight of supported PTFE and about 10% by weight of kneaded PTFE.
[0028]
Using the reaction test apparatus described in Example 1, the above-mentioned spherical PTFE pre-supported molded granules were evaluated for catalytic activity as a catalytic sulfation catalyst under the same conditions as in Example 1. 250 hours after the start of the test, the desulfurization performance was compared with the spherical PTFE-supported molded granules (PTFE-supported mixed-molded catalyst) and the unsupported molded granules (mixed-molded catalyst) of Example 1 (both using activated carbon A). FIG. FIG. 4 shows that the spherical PTFE-supported molded granules exhibit higher desulfurization performance than the spherical PTFE pre-supported molded granules. That is, it is better to perform the water-repellent treatment after mixing and molding with the water-repellent substance first than the procedure of mixing and molding with the water-repellent substance after performing the water-repellent treatment first. It is shown.
[0029]
Comparative Example 2
The commercially available activated carbon A used in Example 1 was calcined, crushed and classified to obtain calcined granular activated carbon having a particle size of 2.8 to 4.0 mm. Next, an aqueous dispersion (10% by weight) of an aqueous dispersion of spherical PTFE (average particle size: 0.05 μm) was diluted 50 times with deionized water, and 20 g of the calcined activated carbon was immersed in each 100 cc of the diluted dispersion. This was impregnated and dried by a rotary evaporator under reduced pressure, and then dried in a dryer at 45 to 50 ° C. for 12 hours to obtain activated carbon (PTFE-supported granular activated carbon catalyst) having a PTFE support amount of about 1% by weight.
[0030]
The PTFE-supported granular activated carbon catalyst prepared above was evaluated for desulfurization performance when used as a catalytic sulfation catalyst in the same manner as in Example 1. The result is shown in FIG. From FIG. 4, it can be seen that the activated carbon only supporting spherical PTFE shows much lower desulfurization performance.
[Brief description of the drawings]
FIG. 1 shows a comparison of desulfurization performance of various activated carbon powders obtained by mixing a water-repellent substance with a water-repellent substance and then subjected to a water-repellent treatment.
FIG. 2 shows a change in desulfurization performance when the average particle size (crushed particle size) of the activated carbon powder used is changed.
FIG. 3 shows a change in desulfurization performance when water-repellent substance fine particles having various particle sizes are used in the water-repellent treatment and the amount of impregnation carried is changed.
[4] The difference in the desulfurization performance when changing a mixed molding for powdered activated carbon the order of impregnation-supporting, having been subjected only mixed molding powdered activated carbon (mixed molded catalyst) and only impregnation was performed granular activated carbon This is shown in comparison with the time (PTFE-supported granular activated carbon catalyst) .

Claims (14)

After mixing the activated carbon powder and water repellent material was formed into a predetermined shape, the facilities Succoth water-repellent, activated carbon material, wherein the outer surface is more strongly water-repellent. The activated carbon material according to claim 1, wherein said activated carbon powder has an average particle size of 10 to 1000 µm. The activated carbon material according to claim 2, wherein the average particle diameter of the activated carbon powder is 15 to 400 µm. The activated carbon material according to claim 3, wherein the average particle size of the activated carbon powder is 20 to 300 µm. The activated carbon material according to any one of claims 1 to 4, wherein the water-repellent substance is fine particles of a fluororesin. The activated carbon material according to claim 5, wherein the activated carbon powder and the fine particles of the fluororesin are mixed and kneaded. 7. The activated carbon material according to claim 5, wherein the fluororesin is selected from polytetrafluoroethylene, perfluoroalkoxy resin, ethylene tetrafluoride hexafluoropropylene copolymer, and ethylene trifluoride chloride resin. The activated carbon material according to any one of claims 1 to 4, wherein the water-repellent substance is contained in an amount of 1 to 30% by weight. The activated carbon material according to claim 6, wherein the water-repellent substance is contained in an amount of 2 to 20% by weight. The activated carbon material according to any one of claims 1 to 9, wherein the water repellent treatment impregnates and supports a fine particle of a fluororesin or polystyrene. The activated carbon material according to claim 10, wherein the fine particles of the fluororesin or polystyrene are impregnated and supported by 0.1 to 3.5% by weight. The activated carbon material according to claim 11, wherein the fluororesin or polystyrene fine particles are impregnated and supported by 0.2 to 3% by weight. An oxidation catalyst for flue gas desulfurization, comprising the activated carbon material according to claim 1. 13. A flue gas desulfurization system comprising: contacting an activated carbon material according to any one of claims 1 to 12 with an exhaust gas containing sulfur oxides, oxygen and water vapor to adsorb and remove sulfur oxides in the exhaust gas. Method.

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