JP5961881B2 - Nitrogen oxide purification material - Google Patents

Description

  The present invention relates to a pellet-shaped nitrogen oxide purifying material suitable for efficiently adsorbing and removing nitrogen oxides in diesel exhaust gas.

  In recent years, there are concerns about the negative impacts on natural ecosystems caused by global warming, and international environmental improvement efforts are urgently needed. Under these circumstances, diesel vehicles, which are more energy efficient than gasoline vehicles, are expected to be highly effective in combating global warming. However, emissions of nitrogen oxides and diesel particulates are large due to the combustion mode unique to diesel engines. Air pollution and adverse effects on the human body have been pointed out. However, since the nitrogen oxides and diesel particulates are in a trade-off relationship, it is difficult to remove them at the same time. Especially, effective and efficient measures have not yet been taken for nitrogen oxides. Currently.

  The nitrogen oxide remover is selected from at least one selected from hydroxides, carbonates, and bicarbonates of alkali metal elements and alkaline earth metal elements, Pt, Rh, Pd, and the like. Nitrogen Oxide Remover (Patent Document 1) that supports a single element of a transition element, at least one of its oxides or halides supported on zeolite, or an alkaline earth metal oxide and platinum supported on a porous carrier An exhaust gas purifying catalyst (Patent Document 2) and the like have been proposed.

  However, the removal agent and catalyst described in Patent Documents 1 and 2 work effectively when the diesel exhaust gas temperature is higher than 250 ° C, but the lower temperature of 250 ° C or less, which is the main temperature range in the diesel exhaust gas path. The above-mentioned conventional catalysts such as platinum group do not work effectively in the temperature range, and the platinum group catalyst is poisoned by the sulfur component contained in the exhaust gas, and the function must be lowered, and further securing of future and expensive materials There are many problems such as being worried about.

  Recently, as a method for reducing and removing nitrogen oxides in the presence of a reducing agent such as urea or ammonia, a catalyst in which silver and cobalt are supported on an alumina carrier (Patent Document 3), and an oxidation containing titanium and / or zirconium are used. A catalyst for removing nitrogen oxide (Patent Document 4) comprising a catalyst A component which is a product and a catalyst B component which is an oxide of vanadium, tungsten, manganese or the like has also been proposed.

  However, even in these methods, there are problems in infrastructure development for supplying reducing agents such as urea and ammonia, economic problems that require a large amount of cost for reducing agents, and some of the reducing agents diffuse into the atmosphere. As a result, it has fatal problems as countermeasures for nitrogen oxides in mobile sources such as diesel vehicles.

  JP-A-4-197447   JP-A-5-317652   JP 7-289905 A   Japanese Patent Publication No. 8-11194

  The present invention exhibits an excellent effect in removing nitrogen oxides in a relatively low temperature range of 250 ° C. or lower, which is difficult to remove with a conventional catalyst among diesel exhaust gases, and is also capable of sulfur poisoning and securing materials. The purpose of the present invention is to provide a nitrogen oxide purifying material that is extremely economical and highly practical.

In view of the above problems, the present inventors have examined in detail the relationship between the temperature in the exhaust gas path and the amount of nitrogen oxide produced in an actual running test. The production of nitrogen oxide is slow when the engine rotation is stable. However, it is relatively low regardless of the high speed, but when the engine speed changes due to accelerator operation, etc., even if the exhaust gas temperature is as low as about 50 ° C, the production of nitrogen oxides near 200 ppm can be seen. We came to the conclusion that measures against nitrogen oxides in the temperature range were important, and as a result of further studies from this point of view, potassium permanganate was decomposed and removed in a relatively low temperature range of about 100 to 300 ° C. Pay attention to the fact that there is an excellent effect and that siliceous shale with a specific specific surface area has a high adsorption capacity of nitrogen oxides in the temperature range of 100 ° C or less. It found that in the diesel exhaust, especially effective for purification of nitrogen oxides at low temperature region by, and have reached to complete the present invention.

That is, the present invention is a purifying material that absorbs and removes nitrogen oxides in diesel exhaust gas, and the purifying material contains inorganic pellets containing potassium permanganate upstream of the exhaust gas path, compared to the downstream side. Nitrogen comprising a porous pellet mainly composed of siliceous shale having a surface area of 100 m ² / g or more, wherein the weight ratio of the inorganic pellet to the porous pellet is 2: 8 to 8: 2. It is an oxide purification material.

  According to the nitrogen oxide purifying material of the present invention, it is effective for purifying nitrogen oxides in exhaust gas at a relatively low temperature range in a moving source such as a diesel vehicle, and also combines a catalytic function and an adsorption function. In addition to high practicality, such as an efficient purification effect, the use of rare noble metals also has an immeasurable effect in terms of countermeasures against depletion of noble metals.

Is a schematic diagram showing an example of a state of mounting the purification material of the present invention in a diesel engine exhaust gas path, Shows an example of the cross-sectional shape of each pellet.

  Hereinafter, the nitrogen oxide purification material of the present invention will be described in detail.

In the present invention, the inorganic pellets arranged on the upstream side are dispersed or impregnated with potassium permanganate in pellets mainly composed of at least one of alumina, zeolite, silica, cordierite, zirconia, silicon carbide and the like. Therefore, the effect of removing nitrogen oxides mainly in the temperature range of 100 to 300 ° C. is achieved. The content of potassium permanganate in the inorganic pellets may be appropriately determined according to the required performance in the range of 3 to 20% by weight, preferably 5 to 15% by weight from the viewpoint of performance and pellet strength. In addition, as said pellet, an alumina is preferable at points, such as performance, heat resistance, and a price .

The shape of the inorganic pellet may be any shape. However, as illustrated in FIGS. 2A to 2D, the shape of the pellet may be a spherical shape, a cylindrical shape, a rod shape, a honeycomb shape, a gear shape, or the like. A pellet having a large external surface area or the like can be used alone or mixed, and the pellet has a length and a diameter of 1 to 50 mm, preferably 2 from the viewpoint of exhaust gas pressure loss, nitrogen oxide removal efficiency, and the like. ˜30 mm and a volume of about 5 to 5000 mm ³ are preferable.

On the other hand, the porous pellet arranged on the downstream side of the inorganic pellet is mainly composed of siliceous shale having a specific surface area of 100 m ² / g or more, and the temperature of 100 ° C. or less is mainly obtained by using such a pellet. To remove nitrogen oxides in the area. The siliceous shale used in the present invention is a sediment based on diatomaceous mud, but it is a hard and fragile shale that has been hardened by crystallization. Although it belongs, it is often treated separately from its unique properties. Among them, Wakkanai siliceous shale produced in the Tenpoku region of Hokkaido has a sharp pore size distribution with a pore diameter of 7 to 15 nm, a total pore volume of 0.1 to 1.0 ml / g, and a specific surface area. 80 to 180 m ² / g, and has a unique property of having a large number of extremely fine pores having an average pore diameter of about 9 nm. The Wakkanai siliceous shale has a specific surface area 6 to 9 times that of ordinary diatomaceous earth as exemplified in Table 1 below, and the pore volume at a pore diameter of 7 to 15 nm is extremely large. In recent years, it has been proposed to be used mainly in the building material field as a humidity control material, and its moisture absorption and release characteristics are independently controlled to a relative humidity of 70 to 90% in addition to a high water absorption capacity of approximately 18%. It has a unique property of adjusting, and these characteristics are equivalent to 3 to 5 times that of zeolite or general diatomaceous earth commonly used as this kind of material.

  In Table 1 above, the specific surface area and total pore volume were measured with a gas adsorption method surface area and pore distribution measuring device (Belsorb II manufactured by Nippon Bell Co., Ltd.), and the specific surface area was set to BET method. The moisture absorption rate of the moisture absorption / release rate was determined by placing the specimen in a constant temperature and humidity chamber at 25 ° C. and 50% RH and measuring the weight of the specimen measured after 48 hours, and then at 25 ° C. and 90% RH. The weight increase rate was calculated | required from the weight of the said test body measured 24 hours after putting in a thermo-hygrostat, and the value was made into the moisture absorption rate. On the other hand, the moisture release rate is the above test when the specimen is cured for 48 hours in a constant temperature and humidity chamber at 25 ° C. and 50% RH and then kept in a constant temperature and humidity chamber at 25 ° C. and 90% RH for 24 hours. The weight reduction rate was determined from the weight of the body and the weight of the test body after being kept in a constant temperature and humidity chamber at 25 ° C. and 50% RH for 24 hours, and the value was taken as the moisture release rate.

  Moreover, this Wakkanai layer siliceous shale has high adsorption ability with respect to water-soluble gases, such as nitrogen oxide and ammonia. The high gas adsorption capacity of this siliceous shale is not only due to the gas adsorption effect on the normal pore surface, but also due to gas dissolution in the condensed water in the pores stored by the high water absorption capacity of the siliceous shale. In particular, the high adsorption capacity for water-soluble gases such as nitrogen oxides and ammonia is unique to the siliceous shale of the present invention having a large number of extremely fine pores and high water absorption capacity. It is.

The siliceous shale used in the present invention is mainly composed of the Wakkanai layer siliceous shale having a specific surface area of 100 m ² / g or more, preferably 120 m ² / g or more. When the specific surface area is out of the range of the present invention, the pore volume becomes relatively small, the adsorption capacity becomes insufficient, and the adsorption ability of moisture, nitrogen oxides and the like becomes insufficient.

  In the present invention, at least a portion of the pores of the siliceous shale are alkali metal such as potassium and sodium or alkaline earth metal such as calcium, magnesium and barium, chloride, carbonate and silicate. It is possible to improve the nitrogen oxide removal efficiency by supporting at least one alkali compound selected from the above.

  The porous pellet of the present invention is mainly composed of a siliceous shale having an average particle size of 1 to 200 μm obtained by pulverizing the above-described siliceous shale ore and firing at a temperature of 500 to 900 ° C., if necessary. Add binders such as Kibushi clay, Sasame clay, gypsum, slaked lime, alumina cement in less than 50% by weight of the pellet, and also silica, alumina, zeolite, sepiolite, silica, activated clay, cordierite, Otani stone, It is made by adding a filler such as coal ash, talc, kaolin, hydrite, etc., adding a molding aid or water, kneading, extruding, drying, firing and the like. As the molding aid used at that time, general binders and lubricants used in this type of inorganic extrusion molding can be used. For example, examples of the binder include water-soluble cellulose derivatives such as methyl cellulose, hydroxyethyl cellulose, hydroxymethyl cellulose, hydroxypropyl cellulose, and carboxymethyl cellulose, and examples of the lubricant include polyalkylene derivatives. Furthermore, molding aids such as polyvinyl alcohol, alkali metal stearate, starch paste and glycerin can be used, and one or more of these are used in combination.

Such porous pellets have a cross-sectional shape such as a spherical shape, a cylindrical shape, a rod shape, a honeycomb shape, a gear shape, a macaroni shape, etc., as illustrated in FIGS. A large pellet or the like can be used alone or in combination, but from the viewpoint of exhaust gas pressure loss, nitrogen oxide removal efficiency, etc., the length and diameter are 1 to 50 mm, preferably 2 to 30 mm, and the volume is 5 to 5000 mm ^3. Therefore, a pellet having a cross-sectional shape such as a honeycomb shape, a gear shape, or a macaroni shape having an external surface area of 10 cm ² / g or more is preferable.

  In the purification material of the present invention, the inorganic pellet and the porous pellet are used in a weight ratio of 2: 8 to 8: 2, preferably 3: 7 to 7: 3. When the ratio of both pellets is outside this range, a stable nitrogen oxide removal effect in a wide temperature range up to 50 to 300 ° C. cannot be obtained. The amount of inorganic pellets and porous pellets used depends on the amount of nitrogen oxides to be absorbed and removed, but in diesel vehicles with a displacement of about 500 to 5000 cc, if inorganic pellets and porous pellets are used in amounts of 100 g to 3 kg, respectively. Good.

In the present invention, the inorganic pellets and the porous pellets are arranged in the exhaust gas path. At that time, as shown in FIG. 1, it is necessary to arrange the inorganic pellets on the upstream engine side and the porous pellets downstream thereof. is there. The reason for this is that, as mentioned above, the activation temperature range of potassium permanganate is higher than the nitrogen oxide adsorption temperature range of siliceous shale, and inorganic pellets are placed on the engine side where the gas temperature is relatively high in the exhaust gas path. The porous pellets are arranged in a region where the gas temperature is relatively low downstream.

  These pellets are arranged in the exhaust gas path as they are, but it is preferable from the viewpoint of handling property to arrange them in a heat-resistant box unit. In this case, other conventional platinum and palladium are disposed in the exhaust gas path. Needless to say, genuine catalysts such as copper oxide and DPF may be used in combination.

  EXAMPLES Hereinafter, although this invention is demonstrated based on an Example, this invention is not limited to these Examples.

<Measurement method of nitrogen oxide purification rate of pellet>
Using a gas flow type fixed bed reactor, about 25 g of pellets were loaded into a quartz reaction tube having a diameter of 26 mm, and the outer periphery thereof was heated to the reaction temperature in an electric furnace. After the reaction temperature reaches the set value, a gas in which 10% oxygen (O ₂ ) and 500 ppm nitric oxide (NO) are mixed in a nitrogen (N ₂ ) gas base as a carrier gas is reacted at a rate of 2 L / min. The NO concentration (ppm) after passing through the tube and passing through the pellets was measured by a gas chromatograph. The NO removal rate was determined from the following formula (1) from the NO concentration after passing through the pellets 1 hour after the start of measurement.
[(NO concentration after passing through pellets after 500-1 hours (ppm)) / 500] × 100 (1)

(Adjustment of inorganic pellets)
To 920 g of α-alumina having an average particle size of about 3 μm, 1000 g of an 8% by weight potassium permanganate aqueous solution was added, stirred and dried, granulated into a spherical shape having a diameter of about 7 mm, and then dried at 110 ° C. An alumina inorganic pellet (a) containing 8% by weight of potassium acid was prepared.

(Adjustment of porous pellets)
A specific surface area of ^{144m 2 / g, 108m 2 /} g, the ^82m 2 / g and 80 wt% three different siliceous shale, 20 wt% kibushi clay respectively molding aids 15 parts by weight of such cellulose, water 35 After adding parts by weight and kneading, a gear-shaped pellet having the cross-sectional shape of FIG. 1 (C) is formed by an extruder, and further microwave drying and baking at 800 ° C. are performed, and the outer diameter is about 7 mm and the length is about 7 mm. 10 mm porous pellets (b), (c) and (d) were produced. In this case, the breakdown of each porous pellet is as follows: pellet (b) using siliceous shale with a specific surface area of 144 m ² / g, pellet (c) using siliceous shale with 108 m ² / g ), 82 m ² / g of siliceous shale was used as pellet (d).

(Tests 1 to 4)
Nitrogen oxide purification of the pellets (a), (b), (c), and (d) at a reaction temperature of 50, 100, 150, 200, 250, and 300 ° C. using a gas flow type fixed bed reactor. The results of measuring the rate are shown in Table 2.

From the results in Table 2, the nitrogen pellet removal rate in the low temperature range of 100 ° C. or lower is obtained in the inorganic pellet (a) of Test 1, whereas the porous pellets (b) and (c) of Test 2 and Test 3 are 100 ° C. The removal rate of nitrogen oxides in the higher temperature range is low, and in the porous pellet (d) having a specific surface area of less than 100 m ² / g in Test 4, the nitrogen oxide removal rate is low even in the low temperature range of 100 ° C. or lower. I understand that.

(Examples 1-3, Comparative Examples 1-2)
Using the gas flow type fixed bed reactor, the reaction is made of quartz by changing the ratio of the inorganic pellet (a) and the porous pellet (b) in the order of the inorganic pellet (a) and the porous pellet (b) so that the total of both is about 25 g. The nitrogen oxide purification rate was measured by the same method as in the above test except that it was loaded into the tube.

  From the results of Table 3 above, the pellets (a) and (b) having a loading ratio in the range of the present invention (Examples 1 to 3) are relatively high in nitrogen oxidation over a wide temperature range of 50 to 300 ° C. It was confirmed to have an effect of removing objects. On the other hand, when the loading ratio of the pellets (a) and (b) is outside the range of the present invention (Comparative Examples 1 and 2), the nitrogen oxide removal rate is low in either the high temperature range or the low temperature range and is practical. You can see that it ’s not right.

  Since the nitrogen oxide purification material of the present invention is excellent in nitrogen oxide purification performance in a relatively low temperature range, nitrogen oxide emission materials from various diesel engines such as automobiles, steamers, boilers, generators, etc. It is extremely useful as a purification material.

DESCRIPTION OF SYMBOLS 1 ... Inorganic pellet filling unit 2 ... Porous pellet filling unit 3 ... Pipe of exhaust gas path 4 ... Flow direction of exhaust gas (upstream side)
5 ... Flow direction of exhaust gas (downstream side)

Claims (1)

A purification material that absorbs and removes nitrogen oxides in diesel exhaust gas, the purification material containing inorganic pellets containing potassium permanganate on the upstream side of the exhaust gas path, and a specific surface area of 100 m ² / g or more on the downstream side A nitrogen oxide purifying material comprising porous pellets mainly composed of siliceous shale, wherein the weight ratio of the inorganic pellets to the porous pellets is 2: 8 to 8: 2.

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