JPH0442328B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for manufacturing a fired titanium oxide product, and more specifically, it contains titanium oxide as the main component, has a large surface area, has excellent heat resistance, and has excellent mechanical strength after molding. , relates to a method for producing a fired titanium oxide product that can be suitably used as a catalyst carrier or as a catalyst as it is. Conventional technology It is already known that fired titanium oxide products are used as catalyst supports or catalysts, but the surface area, crystal shape, heat resistance, mechanical strength after molding, etc., which have important effects on the support or catalyst functions, are limited. Various manufacturing methods have been proposed in the past because they differ depending on the manufacturing method and the presence/absence, type, amount, etc. of additives. For example, if additives such as silica are added to titanium oxide and fired, the resulting fired product will generally have a larger surface area and improved heat resistance. According to the method, titanium oxide is formed by adding additives to titanium or titanium salts such as titanium sulfate, neutralizing and hydrolyzing the titanium salts, and calcining the titanium hydroxide thus formed. There is a problem in that titanium hydroxide tends to become orthotitanic acid, and therefore, when it is calcined, it tends to become rutile-type titanium oxide, which is unsuitable as a carrier or catalyst. On the other hand, it is already known that if metatitanic acid is calcined, anatase-type titanium oxide, which is a crystal form that is generally preferred as a carrier or catalyst, can be obtained, although there are other factors as well. However, according to the method of adding additives such as silica to metatitanic acid and baking it, it is difficult to obtain a mixture with a uniform composition. Because it is gel-like, additives cannot be uniformly dispersed in metatitanic acid.
Therefore, it is not possible to obtain a high-performance support or catalyst. Problems to be Solved by the Invention The present invention has been made to solve the various problems described above, and uses a tungsten compound and/or a molybdenum compound as well as fine particle silicic acid as an additive. By causing titanium oxide to exist in solized metatitanic acid and firing it, it suppresses the crystal growth of titanium oxide during firing of metatitanic acid and causes it to remain in ungrown anatase-type crystals.
In this way, it is possible to obtain a fired titanium oxide product that has a large surface area, excellent heat resistance, and excellent mechanical strength after molding, and can therefore be suitably used as a catalyst carrier or as a catalyst as it is. This discovery led to the present invention. Means for Solving the Problems The method for producing a fired titanium oxide product according to the present invention includes:
To the sol-formed metatitanic acid, (a) fine particle silicic acid,
(b) At least one compound selected from tungsten oxide, a tungsten compound that forms tungsten oxide when fired, molybdenum oxide, and a molybdenum compound that forms molybdenum oxide when fired is added, mixed, and fired. It is characterized by The fine particle silicic acid used in the present invention is known by another name of white carbon, and one of its characteristics is that it has a very large specific surface area. These fine particles of silicic acid may be produced by either a wet method or a dry method, and in the present invention, ordinary commercially available products can be used. Commercial products of fine particle silicic acid that can be suitably used in the present invention include, for example, "Fine Seal" (registered trademark, manufactured by Tokuyama Soda Co., Ltd.), "Aerosil" (registered trademark,
(manufactured by Nippon Aerosil Co., Ltd.), but among these, especially those with an average particle size of 10 to 50 mμ,
Those having a specific surface area of 200 to 300 m ² /g are preferably used. Further, the tungsten compound used in the present invention is tungsten oxide and a precursor that forms tungsten oxide by firing, and examples of this precursor include ammonium metatungstate. Similarly, the molybdenum compound used in the present invention is molybdenum oxide and a precursor that gives molybdenum oxide through calcination, and examples of the precursor include ammonium molybdate. In the present invention, the total amount of fine particle silicic acid, tungsten compound, and molybdenum compound added is 5 to 50% by weight based on titanium oxide. The effect of suppressing the crystal growth is poor, and the effect of improving the carrier or catalyst performance by adding these additives in the fired product is small.
If it exceeds 50% by weight, the mixture with sol-formed metatitanic acid will gel, making it difficult to mix uniformly, and the resulting fired product will have a relatively low titanium oxide content. When this is used as a carrier or as a catalyst as it is, it is not preferable because the performance of the carrier and catalyst based on titanium oxide deteriorates. In the present invention, preferably, metatitanic acid is made into a sol, and particulate silicic acid and at least one compound selected from the above-mentioned tungsten compound and molybdenum are added thereto, mixed, and then fired. Alternatively, after adding fine particles of silicic acid and at least one compound selected from the above-mentioned tungsten compound and molybdenum to metatitanic acid, the metatitanic acid may be sol-formed and mixed. In any case, it is necessary to make the fine particles of silicic acid and the above-mentioned compounds exist in the metatitanic acid which has been partially or completely solified, so that these additives can be uniformly mixed with the metatitanic acid. I can do it. The method of solization is not particularly limited, and for example, metatitanic acid is washed with water to remove most of the sulfuric acid groups, and then hydrochloric acid or nitric acid is added to partially or completely solize it. Alternatively, if sulfate roots are not removed by washing with water, add alkaline earth metal chlorides such as barium chloride, strontium chloride, and calcium chloride to metatitanic acid, or alkaline earth metal chlorides such as barium nitrate, strontium nitrate, and calcium nitrate. Nitrate is added to fix the sulfate radicals as water-insoluble barium salts while the reaction mixture is partially or completely solified. The amount of these gelling agents added is appropriately selected depending on the degree to which the reaction mixture is to be turned into a sol. Note that metatitanic acid sol gels at a pH of 1 to 2 or higher, so it may be gelled if necessary, as long as the tungsten and/or molybdenum compound is sufficiently uniformly mixed therein. The thus obtained mixture of metatitanic acid, particulate silicic acid, and the tungsten and/or molybdenum compound is dried, and then
℃ or less, preferably at a temperature of 700-200℃,
When crushed, a powdered baked product is obtained. In this case, according to the present invention, metatitanic acid is used, resulting in anatase-type titanium oxide, which is preferable as a carrier or catalyst in calcination. In addition, when the fired product is used as a carrier or catalyst in a predetermined shape such as a honeycomb shape, the dried product obtained by drying the above mixture can be processed by any conventionally known method, such as extrusion molding or rolling granulation. It may be molded and fired by a method such as the above.
Further, the powdered fired product described above can be molded into a desired shape and then fired again. In this case, after forming into the desired shape, it may be fired again at a temperature of 800°C or lower, preferably 700 to 200°C. In this manner, according to the present invention, a fired titanium oxide product as a molded product can also be obtained. In addition, in the present invention, in any of the above cases, if a metatitanic acid sol or gel is newly added to the powdered dried product or fired product, the product is molded into the desired shape, and then fired, the mechanical strength and porosity,
Various physical properties such as specific surface area and pore distribution can be improved, and the shrinkage rate during firing can be suppressed. In such cases, the amount of metatitanic acid sol or gel added is 5 to 50% of the weight of the molded product in terms of titanium oxide.
Weight % is appropriate. Furthermore, it is of course possible to use conventionally known general molding aids such as methyl cellulose during molding. In the present invention, the firing atmosphere is not limited at all, and may be air, combustion gas, inert gas, or the like. As described above, the fired titanium oxide product obtained according to the present invention is not limited in any way by theory, but due to the presence of fine particles of silicic acid, a tungsten compound, and/or a molybdenum compound, metatitanic acid is oxidized during firing. Because the crystal growth of titanium is suppressed and remains as ungrown anatase crystals, the resulting fired product has a large surface area, excellent heat resistance, and excellent mechanical strength after molding, making it suitable as a catalyst carrier. Moreover, it can be suitably used as a catalyst as it is. The fact that the calcined product obtained according to the present invention contains ungrown anatase is confirmed by the fact that its X-ray spectrum shows a low and broad peak, as shown in Figure 1; In the case of anatase-type titanium oxide for pigments, its X-ray spectrum is shown in Figure 2, as the crystals have grown extremely well, so the peak is high, and
sharp. The fired titanium oxide product according to the present invention is suitable for use as a carrier, and depending on the type of reaction, it can be used as it is as a catalyst. For example, the above-mentioned fired product has a catalytic reduction activity of nitrogen oxides using ammonia as a reducing agent even as it is,
It can be put into practical use. However, if the titanium oxide fired product obtained as described above is used as a carrier and an oxide known to have a catalytic activity for removing nitrogen oxides is supported on this carrier, the fired product can be formed. Due to an unexpected synergistic effect with oxides that
A catalyst for removing nitrogen oxides having excellent selective catalytic reduction activity for nitrogen oxides using ammonia as a reducing agent can be obtained. Such a catalyst for removing nitrogen oxides contains vanadium, tungsten,
It can be obtained by supporting an oxide of at least one element selected from molybdenum, copper, iron, chromium, manganese, and cerium. The method for supporting the above-mentioned oxide on the titanium oxide fired product can be any method conventionally used for preparing catalysts. For example, the above-mentioned oxide or its precursor is supported on the fired product formed into a predetermined shape. After impregnating or coating with the solution or dispersion contained therein, it may be fired to a predetermined temperature as necessary. Of course, the catalyst for removing nitrogen oxides can also be obtained by kneading the powdered calcined product with the solution or dispersion, molding it into a desired shape, and then calcining it to a predetermined temperature as necessary. can. In order to remove nitrogen oxides from a mixed gas containing nitrogen oxides using such a catalyst, 0.5 to 5 times the mole of nitrogen oxides contained in the mixed gas,
Preferably, 1 to 2 times the mole of ammonia is added, and this is passed through a reaction bed filled with a catalyst. Any of a moving bed, a fluidized bed, a fixed bed, etc. can be used as the reaction bed. The catalyst using the calcined titanium oxide product as a carrier according to the present invention contains fine particles of silicic acid and has excellent heat resistance, so the reaction temperature may range from 200 to 600°C, but preferably from 300 to 500°C. range. Further, the space velocity of the gas is in the range of 1000 to 100000 hr ^-1 , preferably 3000 to 300000 hr ^-1 . The above catalyst can be used to treat any gas containing nitrogen oxides, but in particular boiler exhaust gas, i.e. 100-1000 ppm nitrogen oxides, mainly nitrogen monoxide, as well as 200-2000 ppm sulfur oxides. It can be suitably used to remove nitrogen oxides from exhaust gas containing mainly sulfur dioxide, 1 to 10% by volume of oxygen, 5 to 20% by volume of carbon dioxide, and 5 to 20% by volume of water vapor. I can do it. Effects of the Invention According to the method of the present invention, as described above, since fine particles of silicic acid and at least one selected from a tungsten compound and a molybdenum compound are present in the sol-formed metatitanic acid, these compounds are present in the resulting mixture. It is uniformly dispersed, and when it is fired, the titanium oxide remains in the ungrown anatase crystals due to the action of the above compounds, so the fired product has a large surface area and has remarkable heat resistance. In addition to being improved, it also has excellent mechanical strength after molding. Therefore, the fired titanium oxide product according to the present invention is suitable for use as a support for a catalyst for removing nitrogen oxides, for example. The catalyst for removing nitrogen oxides obtained by using the fired titanium oxide product of the present invention as a carrier has a severe It not only maintains high nitrogen oxide removal activity over a long period of time under the conditions of use, but also has an extremely low oxidation rate of sulfur dioxide to sulfur trioxide, making it a practical and industrial nitrogen oxide removal catalyst. It is excellent as such. EXAMPLES The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples in any way. The properties of the fired titanium oxide product according to the present invention were evaluated based on the performance of a catalyst for removing nitrogen oxides using the fired product as a carrier. Example 1 A titanium sulfate solution obtained from the titanium oxide manufacturing process using the sulfuric acid method was thermally hydrolyzed to obtain metatitanic acid, and 1 kg of this was taken out as titanium oxide. 80 g of barium chloride (dihydrate) was added to this. The mixture was made into a sol and thoroughly stirred and mixed. Next, fine particle silicic acid "Fine Seal" (registered trademark, Tokuyama Soda Co., Ltd.)
) 200g and ammonium paratungstate
After adding 250 ml of a 10% methylamine solution containing 110 g and thoroughly stirring and mixing, the mixture was dried at 100°C for 12 hours and further calcined at 500°C for 3 hours. This fired product was pulverized using a sample mill to adjust the particle size. Add an appropriate amount of water to this, knead it, and then extrude it into a lattice-shaped molded product using an extruder.
It was dried by heating to 100°C, and then fired at 500°C for 3 hours to obtain a fired product. This calcined product was used as it was as a catalyst for removing nitrogen oxides. The X-ray spectrum of the fired product thus obtained is shown in FIG. Since the peak is low and broad, it is clear that the anatase crystal remains ungrown. The X-ray spectrum was measured using an X-ray diffractometer RAD-A manufactured by Rigaku Denki Co., Ltd., and the measurement conditions were as follows. Scanning speed 1°/4 minutes full scale 1000cps Time constant 1 second Chart speed 10mm/min Target Copper tube voltage 30KV Tube current 10mA For comparison, the X-ray spectrum of commercially available pigment anatase titanium oxide is shown in Figure 2. . The measurement conditions are the same as above except that the full scale is 4000 cps. Example 2 In Example 1, ammonium molybdate 120 was used instead of ammonium paratungstate.
A baked product was obtained in exactly the same manner as in Example 1, except that 300 ml of a methylamine solution containing g was used. This was used as it was as a catalyst for removing nitrogen oxides. Example 3 A 10% methylamine solution containing 110 g of ammonium paratungstate and 10 g of ammonium metavanadate was added to the powdered calcined product obtained in Example 1.
After adding 250ml and kneading, it was extruded into a lattice-shaped molded product using an extruder, heated from room temperature to 100°C to dry, and then fired at 500°C for 3 hours to support tungsten oxide and vanadium oxide. A catalyst for removing nitrogen oxides was obtained. Example 4 The powdered calcined product obtained in Example 2 was treated in the same manner as in Example 3 to obtain a catalyst for removing nitrogen oxides on which tungsten oxide and vanadium oxide were supported. Comparative Example 1 A fired product was obtained in exactly the same manner as in Example 1, except that metatitanic acid was not sol-formed using barium chloride. This was used as it was as a catalyst for removing nitrogen oxides. Comparative Example 2 In Example 1, metatitanic acid was not sol-formed with barium chloride, and ammonium paratungstate was replaced with ammonium paratungstate in Example 1.
A baked product was obtained in exactly the same manner as in Example 1, except that 300 ml of a methylamine solution containing 120 g of ammonium molybdate was used. This was used as it was as a catalyst for removing nitrogen oxides. Comparative Example 3 An aqueous solution containing 10 g of ammonium metavanadate and 25 g of oxalic acid was added to the fired product obtained in Comparative Example 1, and after thorough kneading, extrusion molding was performed.
After drying at ℃ for 2 hours, baking at 500℃ for 3 hours,
A catalyst for removing nitrogen oxides was obtained. Comparative Example 4 An aqueous solution containing 10 g of ammonium metavanadate and 25 g of oxalic acid was added to the baked product obtained in Comparative Example 2, and after thorough kneading, extrusion molding was performed.
After drying at ℃ for 2 hours, baking at 500℃ for 3 hours,
A nitrogen oxide removal catalyst was obtained. Comparative Example 5 1 kg of the same metatitanic acid as in Example 1 was taken out as titanium oxide, and 80 g of barium chloride (dihydrate) was taken out.
After adding, solizing, stirring and mixing thoroughly,
It was dried at 100°C for 12 hours and then fired at 500°C for 3 hours. This was crushed and the particle size was adjusted. This includes fine particle silicic acid "Fine Seal" (registered trademark, Tokuyama Soda Co., Ltd.)
) 200g and ammonium paratungstate
Add 250ml of a 10% methylamine solution containing 110g, stir and mix thoroughly, then add an appropriate amount of water, knead, extrude into a lattice-shaped product using an extruder, and heat from room temperature to 100℃. and dry, then
The mixture was calcined at 500°C for 3 hours to obtain a catalyst for removing nitrogen oxides. Comparative Example 6 Except for using the fired product obtained in Comparative Example 5,
A nitrogen oxide removal catalyst was obtained in exactly the same manner as in Comparative Example 3. Each of the nitrogen oxide removal catalysts obtained in the above Examples and Comparative Examples contained 200 ppm of nitrogen oxides and ammonia.
200ppm, 10% water vapor, 12% carbon dioxide, 800ppm sulfur dioxide, and the balance nitrogen are brought into contact at a temperature of 380℃ and a space velocity of 5000hr ^-1 .
The nitrogen oxide (NOx) removal rate and sulfur dioxide (SO ₂ ) oxidation rate were measured. The results are shown in Table 1.
Note that the nitrogen oxide removal rate (%) and the sulfur dioxide oxidation rate (%) were determined by the following formulas. Nitrogen oxide removal rate (%) = (catalyst layer inlet NOx concentration - catalyst layer outlet NOx concentration) / (catalyst layer inlet NOx
concentration) x 100 Sulfur dioxide oxidation rate (%) = (catalyst layer inlet SO ₂ concentration - catalyst layer outlet SO ₂ concentration) / (catalyst layer inlet (SO ₂
+SO ₃ ) concentration) x 100

[Table] As is clear from the above results, the catalyst using the calcined titanium oxide product of the present invention as a carrier has a high nitrogen oxide removal rate, but a low sulfur dioxide oxidation rate. Disadvantages due to the formation of sulfur trioxide when removing substances can be eliminated.

[Brief explanation of drawings]

Figure 1 shows the X-ray spectrum of the fired titanium oxide product obtained by the method of the present invention, and Figure 2 shows the
The X-ray spectrum of pigment titanium oxide is shown for comparison.

Claims (1)

[Claims] 1 To the sol-formed metatitanic acid, (a) fine particle silicic acid, (b) tungsten oxide, a tungsten compound that forms tungsten oxide upon firing, molybdenum oxide, and a molybdenum compound that forms molybdenum oxide upon firing. at least 1
A method for producing a fired titanium oxide product, which comprises adding a seed compound, mixing it, and firing it.