KR20200022931A - Diesel engine exhaust nitrogen oxide storage catalyst system and nitrogen oxide reduction method using the same - Google Patents

Abstract

The present invention provides a diesel engine emission nitrogen oxide absorbing catalyst system and a nitrogen oxide reduction method using the same which can efficiently reduce nitrogen oxide emitted by a diesel engine. According to the present invention, the absorbing catalyst system comprises: an atmospheric-pressure low-temperature plasma reactor to supply ozone produced by an oxidizing reaction of oxygen or air; and an absorbing catalyst reactor which is filled with an absorbing catalyst containing one or more elements among alkali earth metals, and uses ozone supplied to the atmospheric-pressure low-temperature plasma reactor to absorb nitrogen oxide contained in emission gas of a diesel engine. The ozone is supplied one or more times than the nitrogen oxide.

Description

Diesel engine exhaust nitrogen oxide storage catalyst system and nitrogen oxide reduction method using the same}

The present invention relates to a diesel engine exhaust nitrogen oxide storage catalyst system and a nitrogen oxide removal method using the same.

Nitrogen oxide (NO _x ) abatement technology from diesel engines is the most common with Urea-SCR (Urea-Selective Catalytic Reduction), which uses ammonia decomposed from Urea as a reducing agent for nitrogen oxides. Is being applied.

This method is the most widely applied because it shows effective NO _x removal performance even in the low temperature range of 200 ℃, but the most essential problem is that the continuous supply of urea from the outside.

Hydrocarbon-SCR technology, which has been competing since the introduction of Urea-SCR technology, is based on Selective Catalytic Reduction, which uses hydrocarbon as a reducing agent instead of Urea. Hydrocarbon-SCR has been in the spotlight in that it contains a large amount of hydrocarbon components and thus does not need to supply a separate reducing agent such as Urea-SCR.

However, due to the different reducing agent, the catalyst design must be different and stable NO _x removal performance is expressed only when the temperature is above 500 ° C. Therefore, the operating temperature range is limited to the high temperature compared to Urea-SCR.

The NO _x reduction technology completed by supplementing the limitations of the hydrocarbon-SCR is the NO _x Storage Catalyst technology. (Also called Lean NO _x Trap or NO _x Adsorber.) To summarize this technique:

Specific temperature (Ex: 300 ℃) in the low temperature region of below using the materials of the alkaline earth metal oxide based block the NO _x emissions by adsorbing or storing NO _x. This low temperature section is called a lean operation section because it is created when a diesel vehicle is supplied with a relatively small amount of fuel. When the exhaust gas temperature reaches a certain temperature (Ex: 300 ℃) according to the driving condition of the vehicle, artificially supplying a large amount of fuel to the engine to raise the exhaust gas temperature to around 500 ℃, the amount of unburned hydrocarbons Increasing the value of, creates conditions for the hydrocarbon-SCR catalyst to operate normally. This driving section is called 'rich operation' section. When the exhaust gas temperature is increased by the rich operation, NO _x adsorbed in the Lean Operation section is desorbed at once, but NO _x reduction is effective because the temperature and composition conditions for the hydrocarbon-SCR catalyst are formed. Proceeds to reduce NO _x emissions. The engine operating technology for NO _x Storage Catalyst operation is called 'Lean-Rich Operation'.

It is no exaggeration to say that the NO _x Storage Catalyst technology, along with Urea-SCR, divides the automotive NOx emission reduction technology market.

The technical factors that determine the performance of the NO _x Storage Catalyst include the NO _x reduction performance of the hydrocarbon-SCR catalyst and the performance of the adsorbent or adsorption system capable of adsorbing NO _x as much as possible in the Lean Operation section. Can be.

Currently commercially available NO _x Storage Catalyst systems employ catalysts of various compositions and structures, but are generally composed of noble and alkaline earth oxides.

Here, the noble metal represented by platinum catalyst (Pt) serves to oxidize NO to NO ₂ as follows.

Scheme 1

In addition, alkaline earth metal oxides represented by BaO are stored in the form of nitrate (Nitrate) by reacting with NO ₂ as shown below to store NO _x .

Scheme 2

However, since the air pollution problem caused by diesel vehicles has recently reached a serious level, there is a demand for a method to further increase the amount of NO _x occluded in the storage catalyst system using the noble metal and alkaline earth metal oxide.

Korea Patent Registration 10-1863940

In order to solve the above problems of the prior art, it is intended to propose a storage catalyst system and a method for reducing nitrogen oxide using the same, which can efficiently reduce nitrogen oxide discharged from a diesel engine.

In order to achieve the above object, according to an embodiment of the present invention, the atmospheric pressure low-temperature plasma reactor for supplying ozone generated through the oxidation reaction of oxygen or air; And an adsorption catalyst reactor filled with an occlusion catalyst including one or more elements of alkaline earth metals, and occluding nitrogen oxides contained in a diesel engine exhaust gas using ozone supplied to the atmospheric low temperature plasma reactor. Is provided an occlusion catalyst system that is supplied more than 1 times compared to the nitrogen oxide.

The stoichiometric ratio of the nitrogen oxide and the ozone may range from 1: 1.5 to 1: 3.5.

The occluding catalyst may be γ-Al ₂ O ₃ powder carrying BaO.

According to the excess supply of the ozone, the following reaction may occur in the storage catalyst reactor.

The NO ₂ , NO ₃ and N ₂ O ₅ may react with an active point distributed on the occlusion catalyst surface. end

Further comprising an ozone removal unit for removing excess ozone in the storage catalyst reactor, the ozone removal unit may be filled with Mn-based catalyst.

According to another aspect of the present invention, there is provided a diesel engine exhaust nitrogen oxide removal method using a storage catalyst system, comprising: providing a storage catalyst including at least one element of alkaline earth metals to the storage catalyst reactor; Supplying ozone generated through an oxidation reaction of oxygen or air into the storage catalyst reactor in an amount of at least one-time greater than that of the nitrogen oxides; Occluding the nitrogen oxide contained in the diesel engine exhaust gas on the occlusion material surface by using the ozone supplied in excess in the occlusion catalyst reactor; And it provides a diesel engine exhaust nitrogen oxide removal method comprising the step of removing the ozone removed after the reaction.

According to the present invention, by supplying an excessive amount of ozone there is an advantage that can increase the diesel engine emission nitrogen oxide reduction efficiency.

1 is a view showing a NO _x occlusion experiment procedure according to an embodiment of the present invention.
Figure 2 is a diagram showing the results of the NO occlusion experiment at 1000 ppm NO + 10% oxygen + nitrogen atmosphere, 200 mL / min.
3 is a view showing the results of the NO occlusion experiment at 1000 ppm NO + 1000 ppm ozone + 10% oxygen + nitrogen atmosphere, 200 mL / min, NO: ozone = 1: 1.
4 is a view showing the results of the NO occlusion experiment at 1000 ppm NO + 1500 ppm ozone + 10% oxygen + nitrogen atmosphere, 200 mL / min, NO: ozone = 1: 1.5.
5 is a view showing the results of the NO occlusion experiment at 1000 ppm NO + 3500 ppm ozone + 10% oxygen + nitrogen atmosphere, 200 mL / min, NO: ozone = 1: 3.5.
6 is 1000 ppm NO + 3500 ppm ozone + 10% oxygen + nitrogen atmosphere, 200 mL / min, NO: ozone = 1: 3.5, 10wt.% BaO / Al ₂ O ₃ catalyst for decomposing ozone discharged after occlusion A diagram showing a reaction experiment.
7 is a view showing the configuration of the storage catalyst system according to an embodiment of the present invention.

As the present invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description.

However, this is not intended to limit the present invention to specific embodiments, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

The present invention is to increase the NOx reduction efficiency by adding ozone in the NO _x Storage System using a noble metal and alkaline earth metal oxide as a catalyst for the reduction of diesel engine emissions NOx.

Ozone is applied in the occlusion catalyst system according to the present embodiment, and NO and ozone may react to convert NO into NO ₂ as follows.

Scheme 3

This means that ozone may partially replace the function in Scheme 1 by the precious metal catalyst component in the existing occlusion catalyst system.

The advantage of ozone applications is that in addition to replacing some of the functions of expensive precious metals, they can also occlude NO _x even at very low temperatures near room temperature (eg engine starting section).

Oxidation of NO to NO ₂ by noble metals usually begins to show a conversion rate of around 50% from 250 ° C., but oxidation of NO to NO ₂ by ozone shows 100% conversion at room temperature.

Therefore, as the ozone injection device is applied in the occlusion catalyst system according to the present embodiment, the oxidation of NO to NO ₂ may proceed regardless of the temperature condition.

According to an exemplary embodiment of the present invention, even when supplying NO and ozone in a ratio of 1: 1 stoichiometric ratio in Scheme 3, it is possible to achieve a certain level of NO _x occlusion, but when supplying in excess of ozone, NO _x occlusion It was confirmed that the amount could increase significantly.

When ozone participates in the reaction at an excessive concentration, the following reaction may proceed in addition to the chemical reaction of Scheme 3 above.

Scheme 4

The NO ₃ thus generated may react with NO ₂ again to generate N ₂ O ₅ .

Scheme 5

Preferably, in consideration of the production efficiency of ozone, ozone may be supplied in the range of 1.5 to 3.5 times the NO _x concentration.

Since NO ₃ and N ₂ O ₅ produced by this ozone excess application are more unstable and more reactive than NO ₂ , they react with various active sites distributed on the surface of the occlusion material of alkaline earth metal oxides (eg, BaO ₂ ). Can be stored.

Example  One: Occlusion catalyst  Produce

The occlusion catalyst was used γ-Al ₂ O ₃ powder (10wt.% BaO / Al ₂ O ₃ ) loaded with 10% by weight of BaO and was prepared by the following method.

(1) 25 mL of 0.325 g / mL Ba (CH ₃ CO ₂ ) ₂ aqueous solution is prepared. The concentration of the aqueous solution is set forth Ba (CH ₃ CO _{2) 2,} when all is assumed to be converted to BaO, the aqueous solution is exactly fill a Pore volume of Al ₂ O ₃ BaO is Al ₂ O ₃ It was calculated taking into account 10 wt.% Loading by weight.

(2) Add 2 ~ 3 drops of Ba (CH ₃ CO ₂ ) ₂ solution to 3g Al ₂ O ₃ (PoreVolume: mL / g = 1.56 mL), and stir the wet powder to absorb the solution completely.

(3) After the completion of the loading, air conditions are dried at 120 ° C. for 6 hours.

(4) After drying, firing was carried out for 3 hours at 600 ° C under air conditions.

Example  2: Occlusion experiment

As shown in Figure 1, the occlusion experiment according to this embodiment was carried out through the following procedure.

(1) 50 mg of the occlusion catalyst is charged into a flow-type fixed bed reactor made of quartz.

(2) The temperature of the fixed bed is raised to 150 ° C while flowing 200 mL / min of nitrogen.

(3) When the temperature is stable at 150 ° C, adsorb NO _x while flowing a gas mixture in a nitrogen atmosphere containing 1000 ppm NO and 0, 1000, 2500 or 3500 ppm ozone and 10% oxygen at a flow rate of 200 mL / min.

(4) When NO _x adsorption is found to be saturated and reached equilibrium, remove excess NO _x adsorbed on the adsorbent surface by flowing 200 mL / min of nitrogen at the same temperature.

(5) While adsorbing 200 mL / min of nitrogen, desorb the chemisorbed NO _x while increasing the temperature from 150 to 800 ° C at 5 ° C / min.

The NO _x concentration was measured continuously using the Chemilunescence NO _x Analyzer (Thermo Fisher 42i-HL), and the NO _x adsorption amount was calculated by dividing the total amount of desorbed NO _x by the adsorbent weight.

Example  3: 1000 ppm NO  + Oxygen 10% Occlusion experiment  (When ozone is not supplied)

Figure 2 shows the results of the occlusion test when only 1000 ppm NO and 10% oxygen is supplied. That is, ozone was not supplied in this experiment.

As shown in FIG. 2, the NO occlusion was completed in 10 minutes (the adsorption reached equilibrium in 10 minutes at NO 1000 ppm), and the occlusion process was completed after 50 minutes.

Desorption curve (second graph below the Figure 2) can be seen that the size is very small compared to other experiments, the calculated NO _x occlusion was 6.5 mmol / mg (catalyst).

Example  4: 1000 ppm NO  + 1000 ppm  Ozone + oxygen 10% Occlusion experiment (1: 1 stoichiometric ozone supply)

Figure 3 shows the results of the occlusion experiment when 1000 ppm NO and 1000 ppm ozone and 10% oxygen is supplied.

Unlike the previous example 3, the time required for NO occlusion lasts for 80 minutes, and it can be predicted that a larger amount of nitrogen oxide is occluded.

As a result, the observed desorption curve size was much larger than that of Example 3, and the calculated NO _x occlusion amount was 32.7 mmol / mg (catalyst), which was five times higher than that of Example 3.

Example  5: 1000 ppm NO  + 1500 ppm  Ozone + oxygen 10% Occlusion experiment (1: 1.5 Concession  Ozone supply)

4 shows the results of the occlusion experiment when 1000 ppm NO, 1500 ppm ozone, and 10% oxygen were supplied. In this experiment, the ozone concentration ratio to NO is 1: 1.5, and the ozone is excessively supplied.

The time required for NO occlusion was about 90 minutes, similar to Example 4, and the desorption curve shows that NO was desorbed even at a high temperature of 500 ° C. or higher, which was not observed in Example 4. This is determined to be an advantage in the way, which NO _x reduction efficiency side view of that it is advantageous for means and, NO _x reduction the more the higher temperature Hydrocarbon SCR catalyst performance to be matched to the NO _x Storage component that the NO _x storing and much more do.

The calculated NO _x occlusion amount was 49.2 mmol / mg (catalyst), which was about 33% higher than the one supplied with ozone (Example 4).

Example  6: 1000 ppm NO  + 3500 ppm  Ozone + oxygen 10% Occlusion experiment (1: 3.5 Concession  Ozone supply)

5 shows the results of the occlusion experiment when 1000 ppm NO, 3500 ppm ozone, and 10% oxygen were supplied. This experiment is a case where the ozone concentration ratio to NO is 1: 3.5 and 40% more ozone is supplied than (Example 5).

The time required for NO occlusion was 130 minutes, which is the longest of all embodiments, and the size of the desorption curve was the largest and the amount of NO desorbed even at a high temperature of 500 ° C. or higher was also the largest.

The NO _x occlusion amount was the highest at 53.4 mmol / mg (catalyst), which was 63.3% higher than that of 1: 1 supplied ozone (Example 4).

Therefore, as shown in (Examples 2 to 6), the supply amount of ozone is higher than the stoichiometric ratio, so that the occlusion amount of NO _x is increased. .

Example  7: 1000 ppm NO  + 3500 ppm  Ozone + oxygen 10% Occlusion experiment  Experiment of removing ozone emitted after

Figure 6 shows the result of decomposition of the ozone emitted by the catalyst after attempting to occlude on the 10wt.% BaO / Al ₂ O ₃ catalyst under 1000 ppm NO + 3500 ppm ozone + oxygen 10% conditions.

The ozone discharged after occlusion is up to 2500 ppm, and Mn series catalyst, which is well known as ozone decomposition catalyst under gas flow rate of 200 mL / min, shows that 100% of ozone is decomposed using a small amount of 10 mg of catalyst. have.

Therefore, considering such ozone post-treatment (ie, suppression of excess ozone emission), it is judged that the optimum ozone injection rate is 3.5 times higher than NO injection.

7 is a view showing the configuration of the storage catalyst system according to an embodiment of the present invention.

As shown in FIG. 7, the storage catalyst system according to the present embodiment may include a plasma reactor 700, a storage catalyst reactor 702, and a redundant ozone remover 704 installed in the exhaust system.

The plasma reactor 700 according to the present embodiment may be an atmospheric low temperature plasma reactor operating under atmospheric pressure, such as Dielectric Barrier Discharge (DBD) or Corona Discharge (Corona Discharge).

The oxygen supply necessary for ozone generation may be used without branching the air flow from the vehicle compressor and purifying it with high purity oxygen.

The occlusion catalyst reactor 702 is filled with an occlusion catalyst including one or more elements of alkaline earth metals, and occludes nitrogen oxide contained in exhaust gas using ozone supplied to the plasma reactor.

Here, the ozone may be supplied more than one times compared to the nitrogen oxide, preferably, the stoichiometric ratio of the nitrogen oxide and ozone may range from 1: 1.5 to 1: 3.5.

As described above, the ozone according to the present embodiment is preferably supplied in an excessive amount compared to the nitrogen oxide, ozone may be supplied 1.5 times or more than the nitrogen oxide so as to increase the storage efficiency of the nitrogen oxide even at high temperatures.

The excess ozone remover 704 is filled with a Mn-based catalyst and removes excess ozone without reacting in the storage catalyst reactor 702.

The above-described embodiments of the present invention are disclosed for the purpose of illustration, and those skilled in the art having ordinary knowledge of the present invention may make various modifications, changes, and additions within the spirit and scope of the present invention. Should be considered to be within the scope of the following claims.

Claims (8)

An atmospheric low temperature plasma reactor for supplying ozone generated through oxidation of oxygen or air; And
A storage catalyst including one or more elements of alkaline earth metals is filled, and the absorption catalyst reactor is configured to absorb nitrogen oxides contained in diesel exhaust gas by using ozone supplied to the atmospheric low temperature plasma reactor.
The ozone is occluded catalyst system is supplied more than 1 times than the nitrogen oxide. The method of claim 1,
The stoichiometric ratio of said nitrogen oxide and said ozone is in the range of 1: 1.5 to 1: 3.5. The method of claim 1,
The occlusion catalyst is a occlusion catalyst system of BaO-supported γ-Al ₂ O ₃ powder. The method of claim 1,
According to the excess supply of the ozone, the occlusion catalyst system in which the following reaction occurs in the occlusion catalyst reactor.

The method of claim 4, wherein
And a storage catalyst system in which the NO ₂ , NO ₃ and N ₂ O ₅ react with an active point distributed on the surface of the storage catalyst. The method of claim 1,
Further comprising an ozone removal unit for removing excess ozone in the storage catalyst reactor,
The ozone removal unit is a storage catalyst system is filled with Mn-based catalyst. A method of removing nitrogen oxide exhausted nitrogen oxides using a storage catalyst system,
Providing a storage catalyst comprising at least one element of alkaline earth metals to the storage catalyst reactor;
Supplying ozone generated through an oxidation reaction of oxygen or air into the storage catalyst reactor in an amount of at least one-time greater than the nitrogen oxides;
Occluding the nitrogen oxide contained in the diesel engine exhaust gas on the occlusion material surface by using the ozone supplied in excess in the occlusion catalyst reactor; And
Diesel engine exhaust nitrogen oxide removal method comprising the step of removing the ozone removed after the reaction. The method of claim 7, wherein
The stoichiometric ratio of the nitrogen oxide and the ozone has a range of 1: 1.5 to 1: 3.5 diesel engine exhaust nitrogen oxide removal method.

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