JPS5935027A - Preparation of calcined titanium oxide and catalyst - Google Patents

Abstract

PURPOSE:To prepare the titled calcined material, having a large surface area and improved strength and heat resistance, and suitable for a catalyst or catalytic carrier, by calcining metatitanic acid in the form of a sol containing a fine particulate silicic acid. CONSTITUTION:Metatitanic acid in the form of a sol containing fine particulate silicic acid, preferably having 10-50mmu average particle diameter and 200- 300m<2>/g specific surface area, is calcined to give the aimed calcined titanium oxide. The fine particulate silicic acid is present in the metatitanic acid in the form of the sol, and the resultant mixture is calcined to disperse the fine particulate silicic acid uniformly in the resultant calcined material. The titanium oxide remains as the ungrown anatase type crystal by the action of the fine particulate silicic acid, and the surface area is large with the remarkably improved mechanical strength and heat resistance. The resultant calcined titanium oxide is used as a carrier for supporting the metallic oxide having the catalytic activity of removing the nitrogen oxide to give the improved catalyst having the activity of removing the nitrogen oxide for a long term by the synergistic action of the anatase type titanium oxide and the fine particulate silicic acid and a low oxidation ratio of SO2 into SO3.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a fired titanium oxide product and a catalyst.
In detail, the main component is titanium oxide, which has a large surface area.
A method for producing a fired titanium oxide product that has excellent strength and heat resistance and can therefore be suitably used as a catalyst carrier or as a catalyst as it is, and a catalyst for removing nitrogen oxides using the fired titanium oxide product as a carrier. Regarding the method.

It is already known that fired titanium oxide products are used as carriers or catalysts, but surface area, crystal form, mechanical strength, heat resistance, etc., which have important effects on carrier or catalyst functions, depend on the manufacturing method and the presence or absence of additives. , differs depending on the type, amount, etc., and various manufacturing methods have been proposed in the past.

For example, if silica is 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 of adding silica to titanium salts, neutralizing and hydrolyzing them, and calcining the titanium hydroxide thus produced to form titanium oxide, the titanium hydroxide produced by the hydrolysis is orthotitanic acid. Therefore, if this is fired, there is a problem that it tends to become Rudil-type titanium oxide, which is unsuitable as a carrier or a catalyst.

On the other hand, if titanium salt is thermally hydrolyzed, it will easily become metatitanic acid, and if this is calcined, it will give anatase titanium oxide, which is a crystalline form (generally preferred as a carrier or catalyst, although there are other factors involved). is already known. However, according to the method of adding silica to the titanium hydroxide or titanium oxide obtained in this way and firing it, it is difficult to prepare a mixture with a uniform composition. When added, since titanium hydroxide is in a gel state, silica cannot be uniformly dispersed in titanium hydroxide, and therefore a high-performance support or catalyst cannot be obtained.

The present invention has been developed in order to solve the various problems described above, and it has a structure in which fine particles of silicic acid are uniformly dispersed in titanium oxide.
A calcined titanium oxide product that has excellent thermal properties and can therefore be suitably used as a catalyst as a catalyst carrier or as a catalyst, and a nitrogen oxide removal product with unprecedented performance improved by using such a calcined product as a carrier. An object of the present invention is to provide a method for producing a catalyst.

The method for producing a fired product according to the present invention is characterized by firing a sol-formed metatitanic acid containing fine particles of silicic acid.

The fine particle silicic acid used in the present invention is also known as 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. Commercially available fine particle silicic acid products that can be suitably used in the present invention include, for example, Fine Seal, Hi-Sil, Valka Sil, Carplex, Nip Seal, Toxil, Vita Seal, Siloid, Aerosil, etc. Especially those with an average particle size of 10~
50 mμ, specific surface area 200~b The amount of fine particle silicic acid added is 5~5 based on titanium oxide.
When the amount is 0% by weight and less than 5% by weight, the effect of improving the carrier or catalyst performance by adding fine particles of silicic acid in the fired product is small; on the other hand, when it exceeds 50% by weight, the oxidation is relatively When the content of titanium is reduced and it is used as a carrier or as a catalyst as it is, the performance of the carrier and catalyst based on titanium oxide deteriorates, which is not preferable.゛In the method of the present invention, preferably, the above-mentioned fine particles of silicic acid are added to the metatitanic acid sol and fired after stirring and mixing, but if necessary, after adding the fine particles of silicic acid to metatitanic acid, , metatitanic acid may be made into a sol. Since metatitanic acid is in the form of a gel, by making it into a sol, fine particles of silicic acid can be more uniformly dispersed in metatitanic acid.

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 the metatitanic acid.

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. A nitrate is added to fix the sulfate radical as a water-insoluble barium salt, and a part or all of it is made into a sol. The amount of these gelling agents added is appropriately selected depending on the degree to which metatitanic acid is to be sol-formed.

In addition, since metatitanic acid gels at a pH of 1 to 2 or higher, it may be gelled as long as the fine particles of silicic acid are uniformly dispersed, if necessary.

The mixture of metatitanic acid and particulate silicic acid thus obtained is washed with water, then calcined at a temperature of 800°C or less, preferably 700 to 200°C, and pulverized.
Obtain a powdered baked product. 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 a catalyst in a predetermined shape such as a honeycomb shape, the dried product obtained by drying the above mixture may be processed by any conventionally known method such as extrusion molding, transfer granulation, etc. It may be baked after being molded by the method described 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 way, according to the present invention, a fired titanium oxide product can be obtained in the form of a powder or a molded product.

In addition, in the present invention, in any of the above cases,
By adding metatitanic acid sol or gel to a powdered dried or fired product, molding it into the desired shape, and firing it, various physical properties such as mechanical strength, porosity, specific surface area, and pore distribution can be improved. The shrinkage rate during firing can be suppressed. In such cases, the amount of metatitanic acid sol or gel added is 5 to 5% of the weight of the molded product in terms of titanium oxide.
0% by weight is suitable. In addition, it goes without saying that conventionally known molding aids, such as Avicel and methyl cellulose, may also be used 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 titanium oxide fired product made by the present invention is not limited in any way by theory, but
Due to the presence of fine particles of silicic acid, the crystal growth of titanium oxide is suppressed during firing of metatitanic acid, and the crystals remain as ungrown anatase-type crystals, so the fired product obtained has a large surface area, and has high mechanical strength and heat resistance. It is also excellent in
It can be suitably used as a catalyst carrier or as a catalyst as it is.

It is confirmed that the fired product obtained by the present invention contains ungrown anatase, as shown in the figure, as its X-ray spectrum shows a low and broad peak. As shown in Figure 2, the X-ray spectrum of anatase-type titanium oxide has a high peak due to extremely well-grown crystals.
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 a catalyst as it is. If this carrier is loaded with an oxide known to have catalytic activity for removing nitrogen oxides, an unexpected synergistic effect with the oxides constituting the fired product will cause ammonia to become a reducing agent. A nitrogen oxide removal catalyst having excellent selective catalytic reduction activity for nitrogen oxides can be obtained.

That is, the nitrogen oxide removal catalyst according to the present invention is produced by calcining solized metatitanic acid containing fine particles of silicic acid, and adding a mixture of vanadium, tungsten, molybdenum, copper, iron, chromium, manganese, and cerium to the thus obtained calcined product. It is characterized by supporting an oxide of at least one element. In this method, the fired product is manufactured as described above.

The method for making the titanium oxide fired product according to the present invention contain the above oxide can be any method conventionally used for making catalysts. For example, the above-mentioned oxide or After impregnating or coating with a solution or dispersion containing the precursor, it may be fired to a predetermined temperature as necessary. Of course, it is also possible to obtain the nitrogen oxide removal catalyst of the present invention by kneading the powdered calcined product with the solution or the above solution, molding it into a desired shape, and then calcining it to a predetermined temperature as necessary. I can do it.

In order to remove nitrogen oxides from a mixed gas containing nitrogen oxides using the catalyst of the present invention, ammonia is added in an amount of 0.5 to 5 times the mole of nitrogen oxides contained in the mixed gas, preferably 1 to 2 times the mole of nitrogen oxides contained in the mixed gas. is added and 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.

Since the catalyst of the present invention contains particulate silicic acid and has excellent heat resistance, the reaction temperature may range from 200 to 600'C, but preferably from 300 to 500'C. Also, the space velocity of gas is 1ooo~100000hr
, preferably in the range of 3,000 to 300,000 hr.

The catalyst according to the invention can be used in the treatment of any gas containing nitrogen/encrushes, but in particular boiler exhaust gas,
That is, in addition to 100 to 1000 ppm of nitrogen oxides, mainly nitrogen monoxide, 200 to 2000 ppm of sulfur oxides, mainly sulfur dioxide, 1 to 10% by volume of oxygen, and 5 to 20% by volume of carbon dioxide. It can be suitably used to remove nitrogen oxides from exhaust gas containing water vapor of 5 to 2% by volume.

As described above, in the method of the present invention, fine particles of silicic acid are made to exist in metatitanic acid partially or completely solified, and this is fired, so that the fine particles of silicic acid are uniformly dispersed in the resulting fired product. Moreover, since the titanium oxide remains in the ungrown anatase type crystal due to the action of the fine silicic acid particles, the surface area is large and the mechanical strength and heat resistance are significantly improved. Therefore, in the nitrogen oxide removal catalyst of the present invention obtained by using a calcined product as a carrier and supporting metal oxides having catalytic activity for removing nitrogen oxides, it is necessary to suppress the growth of these metal oxides. The synergistic effect with anatase-type titanium oxide and fine-grained silicic acid not only maintains high nitrogen oxide removal activity over a long period of time even under severe usage conditions, but also improves the conversion of sulfur dioxide to sulfur trioxide. Since the oxidation rate is extremely low, it is excellent as a practical and industrial catalyst for removing nitrogen oxides.

The present invention will be explained below with reference to Examples, but the present invention is not limited in any way by these Examples.

Example 1 Titanium sulfate obtained from the titanium oxide production process using the sulfuric acid method was thermally hydrolyzed to obtain metatitanic acid, and 1 kg of this was taken out as titanium oxide, and barium chloride (dihydrate) was extracted.
80 g was added and stirred to form a sol. Next, 200 g of fine particle silicic acid Fine Seal (manufactured by Tokuyama Soda ■) was added, thoroughly stirred and mixed, dried at 100° C. for 12 hours, and then baked at a temperature of 500° C. for 3 hours. This calcined product was pulverized using a sample mill, the particle size was adjusted, and the product was used as a support for the following catalyst for removing nitrogen oxides.

The X-ray spectrum of the carrier thus obtained is shown in FIG. Since the peak is low and broad, it is clear that the anatase crystal remains ungrown.

In addition, the X-ray spectra were obtained using Rigaku-a X-ray diffraction system fiR.
The measurement was performed using AD-1rA, and the measurement conditions were as follows.

Scanning speed 1°/4 minutes full scale 1000 cps time constant
1 second chart speed 10 m/min Target Steel tube voltage 30 KV Tube current 10 mA For comparison, the X-ray spectrum of commercially available pigment anatase titanium oxide is shown in FIG. The measurement conditions were the same as in Section 2 above, except that the full scale was 4000 cps.

Next, 250 ml of a lO% medimethimine solution containing 110 g of ammonium paratungstate and 10 g of ammonium metavanadate was added to the carrier obtained above, kneaded, and then extruded into a lattice-shaped molded product using an extruder. ”C to dry, then 500℃
The mixture was fired for 3 hours to obtain a catalyst for removing nitrogen oxides on which tungsten oxide and vanadium oxide were supported.

Example 2 As in Example 1, 200 g of fine silicic acid fine seal was added to 1 kg of metatitanic acid in terms of titanium oxide,
After kneading, 80 g of barium chloride (dihydrate) was added to form a sol and stirred. This was dried and calcined, and tungsten oxide and vanadium oxide were supported on this calcined product in the same manner as in Example 1 to obtain a catalyst for removing nitrogen oxides.

Example 3 A carrier was produced in exactly the same manner as in Example 1, except that Aerosil (manufactured by Nippon Aerosil ■), which is obtained by vapor phase hydrolysis of silicon tetrachloride, was used as the fine particle silicic acid. This was loaded with tungsten oxide and vanadium oxide in the same manner as in Example INI to obtain a catalyst for removing nitrogen oxides.

Comparative Example 1 A fired titanium oxide product containing fine silicic acid particles was obtained in exactly the same manner as in Example 1 except that metatitanic acid was not solized, and this was treated in the same manner as in Example 1. A catalyst for removing nitrogen oxides on which tungsten oxide and vanadium oxide were supported was obtained.

Comparative Example 2 In Example I, after turning metatitanic acid into a sol, it was filtered and washed with water without adding fine particle silicic acid, and 1 (1
After drying at 0'C for 12 hours, it was calcined at a temperature of 500C for 3 hours and pulverized to obtain a carrier.

Using this carrier, in exactly the same manner as in Example 1, a catalyst for removing nitrogen oxides having -U supported on tungsten oxide and vanadium oxide was obtained.

Comparative Example 3 250 g of a 10% methylamine solution containing 110 g of ammonium paratungstate and 10 g of ammonium metavanadate was added to the titanium oxide fired product carrier obtained in Comparative Example 2.
Add m1 and 200g of fine silicic acid fine seal,
Kneaded. Next, this was extruded into a grid shape and heated to 100°C.
The catalyst was dried for 12 hours at 500° C. and further calcined for 3 hours at 500° C. to obtain a catalyst for removing nitrogen oxides on which tungsten oxide and vanadium oxide were supported.

Each of the nitrogen oxide removal catalysts obtained in the above examples and comparative examples contained 200 ppm of nitrogen oxides and 200 ppm of ammonia.
, water vapor 10%, carbon dioxide 12%, sulfur dioxide 80%
A mixed gas with a composition of 0 ppm and the balance nitrogen was heated to a temperature of 38
Nitrogen oxide (NOx) removal rate and sulfur dioxide (So□) were contacted at 0°C and a space velocity of 5000 hr-'.
The oxidation rate was measured. The results are shown in Table 2. 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 -
NOx concentration at catalyst layer outlet)/(NOx concentration at catalyst layer inlet>
xio.

Sulfur dioxide oxidation rate (%) - (catalyst preparation SO□ concentration -
SO concentration at catalyst layer outlet)/(catalyst layer inlet (So□+5O3
) Concentration) The catalyst of the invention has a high nitrogen oxide removal rate while a low sulfur dioxide oxidation rate, and can eliminate the disadvantages due to the formation of sulfur dioxide when removing nitrogen oxides in a gas mixture.

[Brief explanation of drawings]

FIG. 1 shows an X-ray spectrum of a fired titanium oxide product obtained by the method of the present invention, and FIG. 2 shows an X-ray spectrum of a comparative rounded pigment titanium oxide. Patent Applicant: Mitsubishi Heavy Industries, Ltd. $1 Figure 2 and 3 24 Do5”
z6 z7 4-6-22 Juuki Kannon Shinmachi, Hiroshima City, Mitsubishi Heavy Industries, Ltd. Hiroshima Research Center 0 authors Takafuru Kobayashi Nagasaki Heavy Artillery No. 1-1 Uramachi, Mitsubishi Heavy Industries, Ltd. Nagasaki Shipyard & Machinery Works 0 authors Toru Seto Mitsubishi Heavy Industries, Ltd. Hiroshima Research Center, 4-6-22 Kannon Shinmachi, Kuruma-ku, Hiroshima Author Junsuke Miyake 2-5-1 Marunouchi, Chiyoda-ku, Tokyo 0 accidents Mitsubishi Heavy Industries, Ltd. Power Systems Business Headquarters Author: Abe- 0 in the Sakai Chemical Industry Co., Ltd. Central Research Laboratory, 5-1 Ebisujima-cho, Sakai City Author: Tadao Nakatsuji 0 in the Sakai Chemical Industry Co., Ltd. Central Research Laboratory, 5-1 Ebisujima-cho, Sakai City Author: Toshikatsu Baba Ebisujima-cho, Sakai City 5-1, Sakai Chemical Industries, Ltd. Central Research Laboratory Inventor: Toshiaki Matsuda, 5-1 Ebisujima-cho, Sakai City, Sakai Chemical Industries, Ltd. Central Research Laboratory, 5-1 Application entered: Sakai Chemical Industries, Ltd. 5-1 Ebisujima-cho, Sakai City street address

Claims (1)

[Claims] (11@ A method for producing a fired titanium oxide product characterized by firing a sol-formed metatitanic acid containing particulate silicic acid. The fired product thus obtained contains vanadium,
A method for producing a catalyst for removing nitrogen oxides, which comprises supporting an oxide of at least one element selected from tungsten, molybdenum, copper, iron, chromium, manganese, and cerium.