JPS5814817B2 - Method for manufacturing nitrogen oxide purification catalyst - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a nitrogen oxide reduction and purification catalyst (hereinafter referred to as a nitrogen oxide purification catalyst) comprising vanadium pentoxide and titanium dioxide.

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More specifically, this invention relates to vanadium pentoxide and carbon dioxide used in a method for purifying nitrogen oxides in exhaust gas by catalytically reducing them with a reducing substance such as ammonia in the presence of a catalyst and converting them into nitrogen and water. The present invention relates to a method for producing a catalyst for purifying nitrogen oxides made of titanium.

Conventionally, nitrogen monoxide NO and nitrogen dioxide N are emitted from fixed combustion equipment in power plants, steel mills, chemical plants, etc.
A method of purifying NOx in exhaust gas containing nitrogen oxides such as O2 by catalytically reducing it with a reducing substance such as ammonia in the presence of a catalyst and converting it into nitrogen and water.
Many catalysts and catalysts used in this process are already known.

Regarding nitrogen oxide purification catalysts made of vanadium pentoxide and titanium dioxide and methods for producing the same, see, for example, JP-A-49-122473 and JP-A-50-51966.
Publication No. 59287-1987, Japanese Patent Application Laid-Open No. 1983-59287
No. 65466, Japanese Patent Application Laid-open No. 128680/1983,
It is described in JP-A-51-87165, JP-A-52-147589, etc.

The nitrogen oxide purification catalyst, which is made of vanadium pentoxide and titanium dioxide, is highly active even at relatively low temperatures and is resistant to sulfur oxides and SOx, so it prevents SOx such as SO2 and SO3 from being included in the exhaust gas as well as NOx. Although the catalyst is rarely permanently poisoned by SOx,
The oxidation activity of SO2 is large and it oxidizes SO2 in the exhaust gas and converts it into SO3. Therefore, in the catalytic reduction reaction of NOx, the amount of SO3 increases, and this SO3 reacts with ammonia used in the catalytic reduction reaction to become acidic. Sulfur compounds such as ammonium sulfate NH4HSO4 are generated, and the sulfur compounds accumulate on the catalyst surface or adhere to the flue or heat exchanger, causing various problems such as temporary deterioration of the catalyst and corrosion of equipment. There was a problem.

Furthermore, according to the research of these inventors, a nitrogen oxide purification catalyst consisting of vanadium pentoxide and titanium dioxide is highly active at relatively low temperatures as mentioned above, but it is 250℃ discharged from the device
When applied to exhaust gas containing NOx at a low temperature, it does not show a sufficiently satisfactory NOx purification rate.
In addition, the activity decreases drastically over time,
When used as a low-temperature active industrial catalyst, problems remained in terms of activity and durability.

The inventors discovered that even if exhaust gas contains SO2 as well as NOx, its ability to oxidize SO2 to SO3 (SO2 oxidation activity) is small. As a result of intensive research aimed at developing a catalyst for purifying nitrogen oxides made of vanadium pentoxide and titanium dioxide, which can maintain stable and high activity for a long period of time, we have developed a method for producing the catalyst. This invention was realized by realizing that the objective could be achieved through improvement.

This invention relates to a method for producing a nitrogen oxide purification catalyst for reducing and purifying nitrogen oxides using ammonia consisting of vanadium pentoxide and titanium dioxide, in which the valence of vanadium is lower than pentavalence. After mixing a vanadium compound solution, ammonium sulfate and/or acidic ammonium sulfate and titanium dioxide, or impregnating titanium dioxide with a mixed solution of the vanadium compound solution and ammonium sulfate and/or acidic ammonium sulfate, drying; The present invention relates to a method for producing a catalyst for purifying nitrogen oxides, which is characterized in that the catalyst is then calcined at 400 to 650° C. in an oxygen-containing gas atmosphere to obtain a catalyst consisting of vanadium pentoxide and titanium dioxide.

The nitrogen oxide purification catalyst made of vanadium pentoxide and titanium dioxide produced by the method of the present invention has the following major features.

(1) Compared to a catalyst made of vanadium pentoxide and titanium dioxide produced by a conventionally known method that does not use ammonium sulfate and/or acidic ammonium sulfate during catalyst production, the NOx purification rate at a low temperature of about 250'C is improved. High << low-temperature activity is superior to conventional products.

(2) Compared to a catalyst made of vanadium pentoxide and titanium dioxide using a conventionally known method, there is almost no SO2 oxidation activity under the conditions of the catalytic reduction reaction of NOx, so SO2 is contained in the exhaust gas. Also, the formation of sulfur compounds such as acidic ammonium sulfate can be suppressed, and various troubles that occur when sulfur compounds are formed can be prevented.

(3) Stable catalyst activity can be maintained for a long time even in exhaust gas containing high concentrations of SOx, and frequent regeneration is not required and maintenance costs are low.

(4) Of course, it also has SOx resistance, and is also a clean gas that does not contain SOx, such as N discharged from a nitric acid factory.
It shows a high NOx purification rate even for exhaust gas containing Ox.

In the method for producing a catalyst for nitrogen oxide purification comprising vanadium pentoxide and titanium dioxide according to the present invention, ammonium sulfate and/or acidic ammonium sulfate are used, and in particular, the valence of vanadium is reduced by firing in an oxygen-containing gas atmosphere. It is important to add ammonium sulfate and/or acidic ammonium sulfate before converting to pentavalent vanadium, ie vanadium pentoxide.

When ammonium sulfate and/or acidic ammonium sulfate is not used, or after acid treatment of titanium dioxide as described in JP-A-51-87165, for example,
It is difficult to achieve the object of the present invention using a method for producing a catalyst made of vanadium pentoxide and titanium dioxide.

Although ammonium sulfate or acidic ammonium sulfate may be used in the method of the present invention, ammonium sulfate is preferred because it is economical, has good reproducibility of catalyst activity, and provides the best results.

The amount of ammonium sulfate and/or acidic ammonium sulfate used is 1 to 2 sulfur S per 1 atom of vanadium.
It is preferable to use an amount such that the ratio is 2 atoms, and even if an amount that is more than 2 atoms is used, the addition effect will not improve as the amount used increases, so the above range is preferable. .

Ammonium sulfate and/or acidic ammonium sulfate must be added before firing, and may be added at any time before firing.

In this invention, a solution of a vanadium compound in which the valence of vanadium is lower than pentavalent, generally tetravalent, is used, and the vanadium is finally converted into pentavalent vanadium pentoxide by calcination. .

A solution of a vanadium compound in which the valence of vanadium is lower than pentavalence may be prepared by any conventionally known method, and generally includes ammonium metavanadate, metavanadate, vanadium pentoxide, vanadyl oxalate, A compound prepared by dissolving a vanadium compound such as vanadyl dichloride or vanadyl trichloride in water, an organic acid, etc. can be used.

In the method of this invention, it is possible to use a solution of a vanadium compound prepared using various vanadium compounds as a starting material as described above, in which the valence of vanadium is lower than pentavalence. From this point of view, ammonium metavanadate or vanadium pentoxide is used as a starting material, and these are dissolved together with water using an organic carboxylic acid that can reduce the valence of vanadium to a low valence; Vanadyl oxalate dissolved in water is suitable.

Examples of organic carboxylic acids capable of reducing the valence of vanadium to a low valence include oxalic acid, citric acid, and tartaric acid, of which oxalic acid is preferred.

A solution of a vanadium compound in which the valence of vanadium is less than pentavalent, which gives the most favorable results in the method of this invention, is obtained by suspending ammonium metavanadate in water, adding oxalic acid to reduce vanadium, and It is a solution of ammonium metavanadate.

In this solution, vanadium is thought to exist as a tetravalent vanadium compound, that is, vanadyl oxalate produced by the reaction of ammonium metavanadate and oxalic acid.

2NH4VO3+3(C00H)2→2■0(COO)
2+2NH40H+2H20+2CO2The amount of oxalic acid used is 1.5 to 3 per mole of ammonium metavanadate.
．． 5 mol, preferably 1.6 to 3.0 mol is suitable.

The titanium dioxide used in the method of the present invention may be either anatase type or rutile type, but when using the anatase type, a catalyst exhibiting better catalytic activity can be obtained than when using the rutile type. The anatase type is more suitable.

The shape of titanium dioxide may be powdered, spherical, pelleted, etc., and the shape is not particularly limited.

In the method of the present invention, the order of mixing the vanadium compound solution, ammonium sulfate and/or acidic ammonium sulfate, and titanium dioxide is not particularly limited and may be mixed in any order.

As long as the mixture is sufficiently mixed, the activity of the resulting catalyst will not vary greatly due to a difference in the mixing order.

In the method of the present invention, after mixing the vanadium compound solution, ammonium sulfate and/or acidic ammonium sulfate, and titanium dioxide, or a mixed solution of the vanadium compound solution and ammonium sulfate and/or acidic ammonium sulfate, the solution is mixed with titanium dioxide. After impregnating, it is dried and then calcined at 400 to 650°C, preferably 410 to 600°C, in an oxygen-containing gas atmosphere, generally air, to change the valence of vanadium to pentavalent, resulting in the desired pentoxide. A catalyst consisting of vanadium and titanium dioxide is produced.

The drying temperature is generally 80 to 2000C, preferably 90C.
-150 DEG C. and a drying time of generally 8 to 24 hours, preferably 10 to 20 hours.

Further, the firing temperature is suitably within the above temperature range, and the firing time is generally from 1 to 24 hours, preferably from 5 to 20 hours.

If the calcination temperature is too low, vanadium will not be sufficiently converted to vanadium pentoxide, and if it is too high, the effect of using the ammonium salt of sulfuric acid will be lost and it will be difficult to obtain a catalyst that exhibits high activity at low temperatures. Therefore, it is not appropriate.

In this invention, the composition of the catalyst consisting of vanadium pentoxide and titanium dioxide is a solution of the vanadium compound,
When producing by mixing ammonium sulfate and/or acidic ammonium sulfate and titanium dioxide, and when producing by mixing the above vanadium compound solution with ammonium sulfate and/or titanium dioxide.
It is slightly different from the case where titanium dioxide is impregnated with a mixed solution containing acidic ammonium sulfate, and the amount of vanadium pentoxide may be smaller in the latter case, but generally the amount of vanadium pentoxide is 0. 1-40% by weight
, preferably 1 to 30% by weight of titanium dioxide.
It is appropriate that the amount be 60% by weight, preferably 99% to 70% by weight.

There are no particular restrictions on the shape of the catalyst, such as pellets,
It is preferable to take a shape such as a sphere, a cylinder, a plate, a rod, or a honeycomb depending on the conditions of use.

Next, examples and comparative examples will be shown.

(1) In each example, the activity test was carried out by filling a U-shaped stainless steel reaction tube with an inner diameter of 17 nm with 36 mg of the catalyst, and maintaining the tube at a temperature of 250°C and 300°C in a salt bath.
300ppm NO, 30ppm NH3 in the reaction tube
m, SO2700ppm, H2010%,
02 A model gas consisting of 3% and the remaining N2 was flowed at a flow rate of 5000 hr-1 space velocity, and after 30 minutes,
The NOx content in the gas at the inlet and outlet of the reaction tube was measured using a chemiluminescent NOx analyzer, and the NOx purification rate (%) was determined according to the following formula.

(2) In addition, in Example 1 and Comparative Example 1, in order to examine the long-term activity of the catalyst, an activity test was conducted continuously for a long time at 250°C under the same conditions as the above activity test.
Purification rate (%) was determined.

(3) In addition, in Example 1, Example 2, and Comparative Example 1, in order to check the oxidation activity against S02,
A stainless steel U-shaped reaction tube with an inner diameter of 17 mm was filled with rIll, maintained at the specified temperature listed in Table 3, and a model gas consisting of 0.1% SO2, 1025% SO2, and the remaining N2 was charged into the reaction tube at a space velocity of Flow at a flow rate of 5000hr',
The SO2 concentration in the gas at the inlet and outlet of the reaction tube is
It was measured with an O2 analyzer, and the SO2 oxidation activity of koji was determined using the following formula.

Example 1 100 ml of water was heated to 80°C, 38.0 g of ammonium metavanadate [NH4VO3] was added thereto, and 57 g of oxalic acid [(COOH)2] was gradually added while stirring to dissolve the ammonium metavanadate. Vanadium is reduced and ammonium sulfate ((NH4)2SO4) is added to it.
Add 64.3g of titanium dioxide powder, then add 300g of titanium dioxide powder (anatase type), mix thoroughly, heat and knead to remove moisture until it becomes hard enough to extrude with an extruder, then use an extruder to 5mmt;! After extrusion molding into the rod shape of 5,
Dry at 110°C for 16 hours and cut the dried rods into lengths of 5
It was cut into mm pieces and made into pellets.

The pellets were calcined at 450° C. for 16 hours in an air atmosphere to produce a catalyst containing 8.96% by weight of vanadium pentoxide and 91.04% by weight of titanium dioxide.

The results of the activity test of the catalyst thus produced are shown in Table 1, the results of the long-term activity test are shown in Table 2, and the results of the SO2 oxidation activity test are shown in Table 3.

Example 2 220 ml of water was heated to 80°C, 119.7.9 ammonium metavanadate was added thereto, and 23 ml of oxalic acid was added with stirring.
Gradually add 9.3 g of ammonium metavanadate to dissolve vanadium and reduce vanadium, add 202.6 g of ammonium sulfate, then add 500 g of titanium dioxide powder (anatase type), mix thoroughly, and extrude with an extruder. Heat and knead to remove moisture until it becomes as hard as possible, then extrude it into a 5 mm 9! rod shape using an extruder, dry it at 110°C for 16 hours, and cut the dried rod shape into 5 mm long rods. It was cut into pellets.

The pellets were calcined at 410° C. for 16 hours in an air atmosphere to produce a catalyst containing 15.7% by weight of vanadium pentoxide and 84.3% by weight of titanium dioxide.

The results of the activity test of the catalyst thus produced are shown in Table 1, and the results of the SO2 oxidation activity test are shown in Table 3.

Comparative Example 1 160ml of water was heated to 80°C, 96.5g of ammonium metavanadate was added thereto, and 121ml of oxalic acid was added with stirring.
Gradually add 5g of ammonium metavanadate to dissolve the ammonium metavanadate and reduce the vanadium, add 225g of titanium dioxide powder (anatase type), mix well, and dry at 110°C for 16 hours. 5
It was molded into a pellet of mmpX5mm+H and calcined at 400° C. for 5 hours in an air atmosphere to produce a catalyst consisting of 25% by weight of vanadium pentoxide and 75% by weight of titanium dioxide.

The results of the activity test of the catalyst thus produced are shown in Table 1, the results of the long-term activity test are shown in Table 2, and the results of the SO2 oxidation activity test are shown in Table 3.

Examples 3 and 4 The catalyst was heated under the same conditions as in Example 1, except that the calcination temperature and time were changed to 500°C for 10 hours (Example 3) and 550°C for 6 hours (Example 4). Manufactured.

Table 4 shows the results of the activity test of the catalyst thus produced.

Example 5 A catalyst was produced under the same conditions as in Example 1, except that the amount of ammonium sulfate used was changed to 85.7 g.

Table 4 shows the results of the activity test of the catalyst thus produced.

Example 6 15077 Il of water was heated to 80°C, 18.9 g of ammonium metavanadate was added thereto, and 3 oxalic acid was added with stirring.
Gradually add 7.8 g of ammonium metavanadate to dissolve vanadium and reduce vanadium, add 32.0 g of ammonium sulfate, then add titanium dioxide powder (anatase type) 501, mix thoroughly, and extrude with an extruder. The mixture was heated and kneaded to remove moisture until it became hard enough to be rolled out, then extruded into a 5 mm rod shape using an extruder, dried at 110°C for 16 hours, and cut the dried rod shape into 5 mm lengths. Made into pellets.

The pellets were calcined at 410° C. for 16 hours in an air atmosphere to produce a catalyst containing 2.86% by weight of vanadium pentoxide and 97.14% by weight of titanium dioxide.

Table 4 shows the results of the activity test of the catalyst thus produced.

Example 7 150 ml of water was heated to 80°C, 30 g of ammonium metavanadate was added thereto, and 45 g of oxalic acid was gradually added while stirring to dissolve the ammonium metavanadate and reduce the vanadium.
0.8g was added and dissolved.

To the solution obtained in this way, 300 g of spherical titanium dioxide (anatase type) with a spherical diameter of 4 to 6 mm was added.
After soaking for a minute and impregnating titanium dioxide with the solution,
Titanium dioxide was dried at 110° C. for 16 hours and then calcined at 450° C. for 16 hours in an air atmosphere to produce a catalyst containing 2.51% by weight of vanadium pentoxide and 97.49% by weight of titanium dioxide.

Table 4 shows the results of the activity test of the catalyst thus produced.

Comparative example 2 Vanadyl sulfate [■OSO4・3H20) 2 6.6
After thoroughly mixing G and titanium dioxide powder (anatase type) 181 with a small amount of water, they were dried at 110°C for 16 hours, then formed into pellets of 5 mm $ x 5 mm H, and then heated in air at 450°C for 16 hours. Calcination in atmosphere yields 583% by weight of vanadium pentoxide and 94.1% by weight of titanium dioxide.
A catalyst consisting of 7% by weight was produced.

Table 4 shows the results of the activity test of the catalyst thus produced.

Comparative Example 3 Titanium dioxide powder (anatase type) 5mm x 5mm
100 g of titanium dioxide obtained by molding into H and baking at 600°C for 3 hours in an air atmosphere was mixed with 10 g of concentrated sulfuric acid.
After soaking in 0ml for 1 hour, rinse with water 3 times and heat to 110°C.
The product was dried for 16 hours and calcined at 500° C. for 3 hours in an air atmosphere to obtain acid (sulfuric acid) treated titanium dioxide.

Next, 50 ml of water was heated to 80°C, 10 g of ammonium metavanadate was added thereto, and 15 g of g acid was added under stirring.
was gradually added to dissolve ammonium metavanadate and reduce vanadium, and the acid-treated titanium dioxide was added to this solution and immersed for 3 hours to impregnate titanium dioxide with the vanadium-reduced solution.
Dry at 0°C for 16 hours, then dry at 500°C under air atmosphere.
C. for 3 hours to produce a catalyst containing 31% by weight of vanadium pentoxide and 969% by weight of titanium dioxide.

Table 4 shows the results of the activity test of the catalyst thus produced.

Comparative example 4 25.73 ammonium metavanadate in 100 ml of water
After dissolving and suspending 180 g of titanium dioxide powder (anatase type) and mixing, the mixture was heated at 110°C for 16
The catalyst was dried for an hour, then molded into a 5 mm x 5 mm H shape, and calcined in an air atmosphere at 400°C for 5 hours to produce a catalyst containing 10% by weight of vanadium pentoxide and 90% by weight of titanium dioxide.

Table 4 shows the results of the activity test of the catalyst thus produced.

Example 8 A catalyst was produced in the same manner as in Example 1, except that 58 g of acidic ammonium sulfate ((NH4)HSO4) was used in place of 64.3 g of ammonium sulfate in Example 1.

As a result of an activity test on this catalyst, NO
The x purification rate was 92.9%, and the NOx purification rate at 300°C was 97.8%.

Comparative Example 5 A catalyst obtained in the same manner as in Comparative Example 1 (a catalyst produced without using ammonium sulfate) was immersed in a 10% by weight ammonium sulfate aqueous solution for 10 minutes, and then immersed in an air atmosphere.
Catalyst A was prepared by drying at 100°C for 4 hours.

As a result of an activity test for this catalyst A, the NOx purification rate at 250°C was 83.8%, and the NOx purification rate at 300°C was 90.3%.

Comparative Example 6 Catalyst A obtained in the same manner as Comparative Example 5 was calcined at 400° C. for 3 hours in an air atmosphere to produce Catalyst B.

As a result of the activity test for this catalyst B, the N
The Ox purification rate was 81.0%, and the NOx purification rate at 300°C was 89.2%.

Claims (1)

[Claims] 1. In a method for producing a nitrogen oxide purification catalyst for reducing and purifying nitrogen oxides using ammonia consisting of vanadium pentoxide and titanium dioxide, a vanadium compound in which the valence of vanadium is lower than pentavalence is used. After mixing the solution, ammonium sulfate and/or acidic ammonium sulfate, and titanium dioxide, or after impregnating titanium dioxide with a mixed solution of the solution of the vanadium compound and ammonium sulfate and/or acidic ammonium sulfate, it is dried, and then oxygen 1. A method for producing a catalyst for purifying nitrogen oxides, which comprises firing at 400 to 650[deg.] C. in a containing gas atmosphere to obtain a catalyst consisting of vanadium pentoxide and titanium dioxide.