KR20070112934A - Amonia oxidation catalyst and removal method of ammonia using the same - Google Patents

Abstract

An ammonia oxidation catalyst and a removal method of ammonia in exhaust gas or wastewater using the same are provided to have a high ammonia removal ratio and a low production ratio of nitrogen oxides as byproducts even in a low temperature range, and have excellent durability even in the presence of sulfur compounds. In a catalyst used when oxidizing ammonia contained in exhaust gas or wastewater by a catalytic oxidation process, an ammonia oxidation catalyst is characterized in that Al2O3 is used as a carrier, and platinum(Pt) and niobium(Nb) are doped on the carrier. The ammonia oxidation catalyst comprises 0.5 to 3.0 wt.% of the platinum and 0.5 to 10.0 wt.% of the niobium based on the weight of the Al2O3. In a method for oxidizing ammonia contained in exhaust gas or wastewater by a catalytic oxidation process, a removal method of ammonia comprises supplying ammonia at a space velocity of 2,000 to 50,000 hr^-1 in the presence of the ammonia oxidation catalyst, thereby oxidizing ammonia at a temperature of 180 to 300 deg.C.

Description

Amonia oxidation catalyst and removal method of ammonia using the same}

1 is a schematic diagram of an experimental apparatus used in the present invention.

Figure 2 is a diagram showing the ammonia conversion rate by reaction temperature which is the experimental result of Example 1 and Comparative Example 1.

Figure 3 is a diagram showing the amount of nitrogen oxide generated by the reaction temperature of the experimental results of Example 1 and Comparative Example 1.

Figure 4 is a diagram showing the ammonia conversion rate by operating time which is the experimental result of Example 2 and Comparative Example 2.

<Description of the symbols for the main parts of the drawings>

12: ammonia flow regulator 14: nitrogen flow regulator

16: oxygen flow regulator 18: flow regulator regulator

22: mixing chamber 24: solvent transport pump

26: heating system 28: thermostat

32: inlet 34: outlet

42: mixer 44: thermocouple

46: heating regulator 52: gas analyzer

54 vent 60 reactor

The present invention relates to an ammonia oxidation catalyst, and more particularly, in a low temperature portion (180 ~ 300 ℃), by oxidizing ammonia contained in the exhaust gas or waste water to minimize the generation of nitrogen oxides to harmless nitrogen, sulfur oxides The present invention relates to an ammonia oxidation catalyst and ammonia removal method capable of minimizing durability reduction of the catalyst.

Ammonia, in the form of ammonium nitrate, urea and ammonium phosphate, is widely used for various purposes in petroleum refineries and chemical processes for coke production. In addition, denitrification facilities are installed to remove nitrogen oxides emitted from coal-fired power plants and incinerators. Unreacted ammonia is emitted when more ammonia is injected than necessary stoichiometry.

On the other hand, wastewater containing ammonia is one of the serious pollutants that cause eutrophication, and environmental regulations are getting stricter. Methods for removing wastewater contaminated with ammonia include biological treatment, adsorption, thermal incineration, and the use of catalysts. However, the biological treatment method has difficulty in managing the treatment capacity and microorganisms, and the adsorbent treatment method using the adsorbent has problems in regenerative exchange of the adsorbent and disposal of the waste adsorbent. In addition, the thermal incineration method using incineration has a problem in that the operation cost is high because the reaction temperature must be maintained at a high temperature.

The ammonia oxidation method using a catalyst can remove ammonia at a low temperature, has a low operating cost and can maintain the system for a long time, and has an advantage in terms of the environment in comparison with the conventional biological treatment or chemical treatment. Has

As a method of removing ammonia using a catalyst, (1) ammonia is decomposed into hydrogen and oxygen on a nickel (Ni) catalyst at 600 to 900 ° C, (2) ammonia is vaporized by stripping ammonia-containing wastewater and A method of oxidizing ammonia to nitrogen in the phase, and (3) a method of partially oxidizing ammonia to nitrogen oxide and converting ammonia and nitrogen oxide on a denitrification catalyst to nitrogen.

Method (2) of the above method is operated at a relatively low temperature and in a simple manner, and has an advantage of relatively low installation and operating costs.

However, there is a problem in that nitrogen oxides such as NO, NO ₂ and N ₂ O are generated as by-products in the process of oxidizing ammonia to nitrogen using a catalyst. The nitrogen oxides are regulated as air pollutants that are released into the atmosphere and cause acid rain as well as photochemical smog. Therefore, it is necessary to develop a catalyst in which less by-products such as nitrogen oxides are produced in the ammonia oxidation catalyst.

Meanwhile, in the process of burning fossil fuels, the exhaust gas may include sulfur compounds in addition to nitrogen oxides. In the case where ammonia-containing wastewater is stripped to vaporize ammonia, sulfur compounds other than ammonia may be included in the stripped gas depending on the properties of the wastewater itself. The sulfur compound may generate salts such as sulfates in the presence of water and remain undecomposed at the surface of the catalyst, thereby causing catalyst poisoning. When the sulfur compound is converted to sulfuric acid, it may cause corrosion of the catalyst layer and the equipment of the rear stage.

In addition, Japanese Patent Publication No. 1997-001165 discloses an invention using a manganese (Mn) catalyst in treating ammonia-containing wastewater, but has a low ammonia decomposition activity at low temperatures, and N ₂ O, a nitrogen oxide, is generated as a by-product. When hydrogen sulfide (H ₂ S) or a sulfur compound contained in the catalyst had a problem of poor durability.

In addition, Japanese Patent Application Laid-Open No. 1996-89758 discloses an invention for decomposing ammonia in various exhaust gases by using a platinum (Pt) catalyst, but has a problem in that the maintenance cost is high because the operating temperature is 300 to 400 ° C.

Therefore, the first technical problem to be achieved by the present invention is a catalyst used for oxidizing ammonia in exhaust gas or waste water by catalytic oxidation method, which has a high ammonia removal rate at low temperature and low generation rate of byproduct nitrogen oxide, and sulfur compounds. It is to provide an ammonia oxidation catalyst with excellent durability even in the presence of.

The second technical problem to be achieved by the present invention is to provide a method for removing ammonia in the exhaust gas or waste water at a low temperature by using the ammonia oxidation catalyst.

The present invention, in order to achieve the first technical problem, in the catalyst used for the oxidation treatment of ammonia contained in the exhaust gas or waste water by the catalytic oxidation method, using Al ₂ O ₃ as a carrier, the platinum ( It provides an ammonia oxidation catalyst, characterized in that Pt) and niobium (Nb) are supported.

According to an embodiment of the present invention, the platinum may be 0.5 to 3.0% by weight, and the niobium may be 0.5 to 10.0% by weight based on the weight of the Al ₂ O ₃ .

According to another embodiment of the present invention, the catalyst may be prepared by coating on a support selected from the group consisting of metal plates, ceramic filters, foams and honeycombs.

According to another embodiment of the present invention, in the case of preparing the catalyst by coating on the support, the content of Al ₂ O ₃ may be characterized in that 0.5 to 3.0g / in ³ based on the support.

According to another embodiment of the present invention, the catalyst may be prepared by extrusion processing into a particle or monolith.

The present invention provides a method for oxidizing ammonia contained in exhaust gas or waste water by catalytic oxidation in order to achieve the second technical problem, in which ammonia is supplied at a space velocity of 2,000 to 50,000 hr ^{−1 in} the presence of the catalyst. By providing an ammonia removal method of oxidizing ammonia at a temperature of 180 ~ 300 ℃.

According to another embodiment of the present invention, the catalyst layer further comprises one or more elements selected from the group consisting of titanium (Ti), vanadium (V), molybdenum (Mo), and tungsten (W). It may be characterized by removing ammonia and nitrogen oxides.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings and examples, but the present invention is not limited thereto.

The ammonia oxidation catalyst according to the present invention is a catalyst which can be used for oxidizing ammonia contained in exhaust gas or waste water by catalytic oxidation method, using Al ₂ O ₃ as a carrier, and platinum (Pt) and age on the carrier. It may be characterized in that the Obium (Nb) is supported.

By using Al ₂ O ₃ as a carrier, ammonia can be removed even at a low temperature portion (temperature below 250 ° C.). Pt / Al ₂ O ₃ catalyst may exhibit ammonia removal rate of 80% or more at 180 ℃.

In the high temperature part (above 300 ° C), the ammonia removal rate may show a constant value without being greatly influenced by the type of carrier. However, when Al ₂ O ₃ is used as the carrier, the low temperature part (temperature below 250 ° C) is compared with other types of carriers. The removal rate of ammonia can be high. The reason is that the specific surface area of Al ₂ O ₃ used as the carrier is 300 m ² / g and can be judged to be larger than other types of carriers. This is because the adsorption reaction according to the specific surface area of the catalyst affects the activity of the catalyst in the temperature range where the activity of the catalyst is insufficient.

The platinum (Pt) can be used in the present invention because it is excellent in ammonia oxidation performance among noble metals (Ag, Ir, Pd, Pt, Rh, etc.). When ammonia is converted in a reaction temperature range of 200 to 400 ° C. using 1.3 wt% Pt / Al ₂ O ₃ catalyst, more than 99% of ammonia may be converted in the entire temperature range.

In the preparation of the platinum (Pt) catalyst, precursors are H ₂ PtCl ₆ , Pt (NO ₃ ) ₂ , Pt (NH ₃ ) ₂ (NO ₂ ) ₂ , Pt (NH ₃ ) ₄ (NO ₃ ) ₂ , and Pt (SO ₃ ) _x may be used.

In addition, the preparation of Al ₂ O ₃ The platinum (Pt) may be 0.5 to 3.0% by weight based on weight. This is because there is a concern that the performance of the catalyst is significantly reduced when less than 0.5% by weight, the catalyst performance does not increase any more than 3.0% by weight, but there is a risk of economic disadvantages.

The niobium (Nb) may have characteristics such as high heat resistance to steam and sulfur compounds contained in exhaust gas, and low sintering when generating high reaction heat. Since the metal component supported on the support reacts with the sulfur compound contained in the exhaust gas to become a sulfate and the like, thereby reducing ammonia decomposition performance, niobium (Nb) can be used to overcome this problem. In addition, in the present invention, by forming a composite metal compound of niobium (Nb) and platinum (Pt) it can also minimize the sulfate of platinum (Pt). Precious metals such as platinum may have low endothelial toxicity, so making a composite metal with niobium (Nb), which is highly endothelial, will protect platinum (Pt).

In addition, the preparation of Al ₂ O ₃ The niobium (Nb) may be 0.5 to 10.0% by weight based on weight. This is because there is a concern that the performance of the catalyst is significantly reduced when less than 0.5% by weight, the catalyst performance does not increase any more than 10.0% by weight, but there is a risk of economic disadvantages.

The composite metal compound of platinum (Pt) and niobium (Nb) was added to the Al ₂ O ₃ Supporting the carrier can increase the ammonia oxidation rate and increase the endothelial toxicity to the sulfur compound of the catalyst.

When the catalyst is prepared by a method of coating on a support, the support may be prepared by coating Al ₂ O ₃ on the support by selecting from a group consisting of a metal plate, a ceramic filter, a foam, and a honeycomb. In this case, the coating process may be performed according to a method well known in the art.

When the Al ₂ O ₃ carrier is coated on the support, the content of Al ₂ O ₃ may be 0.5 to 3.0 g / in ³ . It is because there is a fear that the performance of the catalyst is significantly reduced when less than 0.5g / in ³ , and if the content exceeds 3.0g / in ³ there is a fear that the catalytic performance no longer increases.

In addition, the catalyst of the present invention may be used in the form of extrusion or granular (monolith) in the form of extrusion processing may be carried out according to methods well known in the art.

The process of catalytic oxidation of ammonia contained in exhaust gas or wastewater using the catalyst of the present invention is carried out at a temperature range of 180 to 300 ° C. by supplying ammonia at a space velocity of 2,000 to 50,000 hr ^{−1 in} the presence of the catalyst. This can be done by.

When the reaction temperature is less than 180 ℃ there is a fear that the reaction hardly occurs, and when it exceeds 300 ℃ high ammonia conversion, but there is a possibility that a considerable amount of nitrogen oxides are generated because it is not preferable. When the reaction temperature exceeds 300 ° C. and reaches 500 ° C., there is a concern that nitrogen oxide in an amount corresponding to the stoichiometry of the injected ammonia is generated.

If the space velocity is less than 2,000hr ^{- 1,} there is a concern that the catalytic performance will not increase any more, and if it exceeds 50,000hr ^-1 , there is a fear that the performance of the catalyst is significantly reduced.

If water is contained in the gas, the ammonia conversion may decrease little by little as the amount of water increases. At this time, the reduction in ammonia conversion may be a disadvantage, but the production concentration of by-product nitrogen oxide may also decrease little by little. However, stripping is essential if you want to remove ammonia in the wastewater. The reason is that the ammonia conversion rate does not decrease significantly even if it contains water, but if it contains water, there is a problem that the gas must be heated to react on the catalyst. Therefore, to keep the water content below 30% by volume to reduce the burden of raising the temperature. can do.

The stripping refers to ammonia stripping, and the ammonia stripping is to increase the pH to 11 by adding alkali to convert ammonium ions into ammonia dissolved in water, and then to lower the partial pressure to degas into the atmosphere. In other words, the contact of air and liquid in a high pH water bath changes the ammonia from the liquid phase to the gas phase.

In addition, a catalyst that can be used to remove nitrogen oxides and ammonia may be additionally used to remove nitrogen oxides and residual ammonia generated after the ammonia contained in exhaust gas or waste water is treated by catalytic oxidation using the above catalyst.

The catalyst used for the further treatment may be characterized in that it comprises at least one element selected from the group consisting of titanium (Ti), vanadium (V), molybdenum (Mo), tungsten (W).

Preparation Example 1

Pt-Nb / Al ₂ O ₃ Preparation of the catalyst

Alumina (Al ₂ O ₃ ) [Spheralite 557, Axens, France] was slowly added to the deionized water with vigorous stirring to form a uniform slurry. The prepared slurry was coated on a cordierite honeycomb molded body (Ceracomm, Korea) having a size of 15 × 15 × 10 cm and a cell density of 200 cells / in ² (84 × 84 cells), and then dried naturally for one day. After drying at 120 ° C. for 2 hours, the temperature was raised to 2.8 ° C. per minute and calcined at 450 ° C. for 3 hours.

Aqueous solution of dynatrodiammoniumplatinum (Pt (NH ₃ ) ₂ (NO ₂ ) ₂ ) [Gold Gold, South Korea] and niobium chloride (NbCl ₅ ) [Sigma-Aldrich, USA] Impregnated in and then allowed to dry for one day.

After drying for 2 hours at 120 ℃, the temperature was raised to 2.8 ℃ per minute and calcined at 450 ℃ for 3 hours, flowing H ₂ 1% by volume / Air [Daedeok Gas, South Korea] and heated up to 650 ℃ 2 at this temperature Keeping time, Pt-Nb / Al ₂ O ₃ catalyst was prepared.

The composition of the catalyst prepared by the above method was 1.2 g / in ³ of alumina / honeycomb, and platinum (Pt) and niobium (Nb) were 1.3 wt% and 3.0 wt%, respectively, based on alumina.

Preparation Example 2

Pt / Al ₂ O ₃ Preparation of the catalyst

It prepared by the same method as the catalyst of Preparation Example 1. No niobium chloride was added.

The composition of the catalyst prepared by the above method was 1.2 g / in ³ of alumina / honeycomb, and platinum (Pt) was 1.3 wt% based on alumina.

Example 1

Ammonia catalytic oxidation experiment was conducted using the catalyst prepared in Preparation Example 1.

The experimental apparatus shown in FIG. 1 was used for the ammonia catalytic oxidation experiment.

As shown in FIG. 1, the experimental apparatus includes an ammonia flow controller 12, a nitrogen flow controller 14, an oxygen flow controller 16, a flow controller controller 18, a mixing chamber 22, and a solvent transport pump ( 24, heating system 26, thermostat 28, mixer 42, thermocouple 44, heating regulator 46, vent 54, gas analyzer 52, inlet 32, It consists of the outlet part 34 and the reactor 60.

The reactor 60 [Samson Hi-Tech, South Korea] is a rectangular shape of 4cm in diameter, 100cm in length made of SUS304, it is composed of a square so that the honeycomb type catalyst can enter. In addition, a furnace consisting of three heating sections [Lindburg, USA] was used to heat the reactor, and the temperature was controlled by using a heat controller 46. In addition, the temperature inside the reactor was measured using the thermocouple 44.

In addition, the solvent supply pump 24 [SP930D, Yeonglin equipment, Korea] to supply the water, and the supplied line (line) was heated using the heating system 26 to maintain the vaporized state of water. . In addition, the temperature of the mixed gas injected into the reactor 60 by the temperature control device 28 was adjusted. In order to inject a gas such as nitrogen, oxygen, and ammonia into the reactor 60 by a predetermined amount, the ammonia flow regulator 12, the nitrogen flow regulator 14, the oxygen flow regulator 16, and the flow regulator regulator 18 are used. It was. The flow regulator was controlled using F-201C-FAC-22-V [Bronkhorst, Netherlands] to control the flow rate of the gas and to maintain the gas phase at a constant concentration by using the mixing chamber 22 to obtain nitrogen, oxygen and ammonia. Mixed.

Inside the reactor 60, a fan-shaped mixer 42 was installed in the reactor so that the mixed gas and the moisture could be sufficiently mixed to increase the reactivity with the catalyst in the reactor.

In order to measure the gas concentration before and after the reaction in the reactor (60), it was possible to take a sample from the inlet 32 and the outlet 34, the sample was analyzed by the gas analyzer (52). The gas analyzer 52 used detection tubes (3L, 3La, 3M) [Gastec, Japan] to measure the concentration of ammonia, and gas such as oxygen, nitrogen monoxide, and nitrogen dioxide was a portable gas analyzer, MK-. It was measured using II [Eurotron, Italy]. The remaining gas from which the sample was taken was discharged using the vent 54. In addition, ammonia conversion was calculated by the following equation (1).

NH ₃ conversion ratio (%) = [(NH ₃ concentration before reaction After reaction NH ₃ concentration) / NH ₃ concentration before reaction] × 100 (%)

Using the experimental apparatus was carried out experiments on the catalyst prepared in Preparation Example 1.

The volume of the catalyst used in the experiment was 45 cm ³ , the reaction conditions were space velocity 10,000h ^-1 .

Table 1 shows the composition of the inlet gas used in the experiment.

 Constellation NH ₃ H ₂ O O ₂ N ₂  density  500ppmv  3.28% by volume  18.00% by volume  78.67% by volume

The ammonia conversion rate and the concentration of the produced nitrogen oxide obtained as a result of the above experiment are shown in FIGS. 2 and 3.

Comparative Example 1

Experiments were carried out in the same manner as in Example 1, using the catalyst prepared in Preparation Example 2, and the resulting ammonia conversion and concentration of the resulting nitrogen oxides are shown in FIGS. 2 and 3.

2 shows that the ammonia conversion of Example 1 is higher than that of Comparative Example 1 in the temperature range of 180 ℃ to 250 ℃. On the other hand, as shown in Figure 3 it can be seen that the nitrogen oxide is not produced in the temperature range of 180 ℃ to 240 ℃ is rapidly increased as the temperature increases. In the case of Example 1 it can be seen that the amount of nitrogen oxides produced in comparison with Comparative Example 1 in the temperature range of 240 ℃ to 350 ℃. In addition, since the generation amount of nitrogen oxide does not increase rapidly at the temperature below 300 ℃, it is advantageous in terms of suppressing the generation of nitrogen oxide when operating below 300 ℃. As a result, the ammonia removal method of the present invention can be carried out while achieving a goal of producing a small amount of nitrogen oxides but a high ammonia conversion rate may be 180 ℃ to 300 ℃.

Example 2

Experiment was carried out as in Example 1 using the catalyst prepared in Preparation Example 1. However, in order to further inject sulfur dioxide into the reactor, the composition of the inlet gas was as shown in Table 2 below, and the reaction temperature was fixed at 250 ° C. The resulting ammonia conversion is shown in FIG. 4.

 Constellation NH ₃ SO ₂ H ₂ O O ₂ N ₂  density  500ppmv  50ppmv  3.28% by volume  18.00% by volume  78.67% by volume

Comparative Example 2

Experiment was carried out as in Example 2 using the catalyst prepared in Preparation Example 2. The resulting ammonia conversion is shown in FIG. 4.

As a result of Figure 4 it can be seen that the effect of sulfur dioxide on the durability of the catalyst in Example 2 and Comparative Example 2.

In the case of Comparative Example 2 it can be seen that the conversion rate decreases with time as the initial ammonia conversion rate is 92.6% and then maintains about 85% after 30 hours. On the other hand, in Example 2, the initial ammonia conversion was maintained at 94%.

These results indicate that the catalyst of the present invention maintains the oxidizing power despite the presence of sulfur dioxide in the exhaust gas, and shows that the endothelial toxicity to sulfur dioxide is excellent.

As described above, according to the present invention, the ammonia removal rate is high, the production rate of nitrogen oxide as a by-product is low, and the ammonia in the exhaust gas or the waste water at low temperature is catalyzed by using an ammonia oxidation catalyst having excellent durability even in the presence of sulfur compounds. It can be oxidized by. In addition, the use of the ammonia oxidation catalyst has the advantage that it is possible to remove ammonia in the exhaust gas or waste water even in a low temperature portion.

Claims (7)

A catalyst used for oxidizing ammonia contained in exhaust gas or waste water by a catalytic oxidation method, wherein Al ₂ O ₃ is used as a support, and platinum (Pt) and niobium (Nb) are supported on the support. Ammonia oxidation catalyst. The ammonia oxidation catalyst according to claim 1, wherein the platinum is 0.5 to 3.0% by weight and the niobium is 0.5 to 10.0% by weight based on the weight of Al ₂ O ₃ . An ammonia oxidation catalyst prepared by coating the catalyst of claim 1 or 2 on a support selected from the group consisting of a metal plate, a ceramic filter, a foam and a honeycomb. The ammonia oxidation catalyst according to claim 3, wherein the content of Al ₂ O ₃ is 0.5 to 3.0 g / in ³ based on the support. An ammonia oxidation catalyst prepared by extruding the catalyst of claim 1 or 2 into a particle or a monolith. In the method of oxidizing ammonia contained in exhaust gas or waste water by catalytic oxidation method, ammonia is oxidized at a temperature of 180 to 300 ° C. by supplying ammonia at a space velocity of 2,000 to 50,000 hr ^{−1 in} the presence of the catalyst of claim 1. To remove ammonia. The catalyst layer of claim 6, further comprising at least one element selected from the group consisting of titanium (Ti), vanadium (V), molybdenum (Mo), and tungsten (W). Ammonia removal method characterized in that the oxide is removed.

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