JP2020186690A - System control method - Google Patents

Abstract

To solve a problem that NOx elimination is deteriorated due to partial oxidation of ammonia in a range of 350°C to 500°C of an exhaust gas high temperature region regardless of NOx selective reduction in an SCR exhaust gas aftertreatment system.SOLUTION: Provided is a system control method in which a catalyst is zeolite containing copper and a consumption amount by partial oxidation of ammonia is supplied by controlling an ammonia amount that is an equimolar amount of NOx in exhaust gas, in an NOx selective catalytic reduction system using urea and/or ammonia.SELECTED DRAWING: Figure 3

Description

The present invention relates to NOx purification system control of an exhaust gas aftertreatment device corresponding to automobile load traveling.

One embodiment of the present invention relates to a copper zeolite catalyst and its control in an exhaust gas system designed to reduce nitrogen oxides (NOx). In addition, certain embodiments relate to controlling the supply of urea and ammonia as NOx selective reducing agents.

The NOx purification catalyst for diesel vehicles uses ammonia obtained by spraying urea water with an exhaust gas aftertreatment device and hydrolyzing the urea water as a reducing agent (selective catalytic reduction, generally referred to as an SCR catalyst). As a catalyst carrier, synthetic zeolite is known because it has a high ability to adsorb ammonia at the solid acid point.

In the exhaust gas aftertreatment device, several chemical reactions occur, all of which reduce NOx to nitrogen. The dominant reaction is represented by the reaction formula (1) in which NO and NH ₃ proceed in equal amounts.

[Chemical 1]
4NO ＋ 4NH ₃ ＋ O ₂ → 4N ₂ ＋ 6H ₂ O ・ ・ ・ (1)

As an SCR catalyst, copper ion exchange has a CHA-type crystal structure containing silica and alumina as main components, and the molar ratio of silica to alumina is about 15 or more, and the atomic ratio of copper to aluminum is about 0.25 or more. The use of zeolite is disclosed. (Patent Document 1)
The CuCHA catalyst represented by Patent Document 1 is SSZ-13 in which copper is ion-exchanged.

As an SCR catalyst other than the above, it is disclosed that an iron and / or copper ion-exchange zeolite of SAPO-34 having a CHA-type crystal structure containing phosphor oxide, alumina and silica as main components is used (Patent Document). 2). The catalyst represented by Patent Document 2 is SAPO-34 in which copper is ion-exchanged.

International Publication No. 2008/106519 International Publication No. 2008/118434

The CuCHA catalyst is excellent in low temperature activity from an exhaust gas temperature of 200 ° C. to 350 ° C. and durability activity after aging in hot water. However, there is a problem that the NOx purification rate decreases as the exhaust gas temperature rises from 350 ° C. to 500 ° C.

In the competing non-selective reaction with oxygen, as the exhaust gas temperature at the inlet of the SCR catalyst rises from 350 ° C to 500 ° C, the partial oxidation reaction of ammonia proceeds and N ₂ or N ₂ O (global warming). Chemical gas) production increases. Thus, the non-selective reaction consumes ammonia without using it for the reduction of NOx. It is shown in the reaction formula (2) and the reaction formula (3).

[Chemical 2]
4NH ₃ ＋ 3O ₂ → 2N ₂ ＋ 6H ₂ O ・ ・ ・ (2)

2NH ₃ ＋ 2O ₂ → N ₂ O ＋ 6H ₂ O ・ ・ ・ (3)

On the other hand, when the exhaust gas temperature at the inlet of the SCR catalyst exceeds 500 ° C., the complete oxidation reaction of ammonia proceeds. Ammonia is not used to reduce NOx and produces NOx directly from ammonia. When performing highly active NOx purification using a Cu zeolite catalyst in order to satisfy high exhaust gas regulations, the temperature of the exhaust gas cooling system such as EGR of the internal combustion engine is adjusted so that the exhaust gas temperature at the inlet of the SCR catalyst is 500 ° C or less. Need to control. However, when PM combustion is performed, the exhaust gas becomes 500 ° C or higher, but since the oxygen concentration is low and the atmosphere is reduced, NOx is reduced without spraying urea, so the SCR system is controlled at 500 ° C or lower. , Not limited to this.

[Chemical 3]
4NH ₃ ＋ 5O ₂ → 4NO ＋ 6H ₂ O ・ ・ ・ (4)

The present invention relates to an SCR system control method capable of uniformly maintaining NOx reduction purification of urea water at 93% or more from a low temperature of 200 ° C. to a high temperature of 500 ° C. at the exhaust gas temperature under a vehicle running load.

In the present invention, urea and / or ammonia are used to select NOx. In a catalytic reduction system, the catalyst is a zeolite containing copper, and the consumption of ammonia due to partial oxidation is equal to that of NOx in the exhaust gas. It is a system control method characterized in that the amount of ammonia is controlled and supplied.

The present invention is to control the amount of ammonia supplied by taking into account the amount of ammonia consumed by the reaction formulas (2) and (3) regardless of NOx purification. Shown in (Equation 1).

The catalyst carrier used in the present invention is not particularly limited, but a zeolite having a CHA type and / or AEI type and AFX type crystal structure is preferable because of the material-specific properties of high durability to hot water.

Further, the catalyst metal is preferably copper from the viewpoint of low temperature activity, and the copper is preferably contained in an amount of 2.0% by mass to 5.0% by mass in terms of CuO.

It is a graph which compared Example 1, Example 2, Comparative Example 1 and Comparative Example 2 about the NOx purification rate at the exhaust gas temperature of this invention. It is a graph which compared Example 3, Example 4, Comparative Example 3 and Comparative Example 4 about the NOx purification rate at the exhaust gas temperature of this invention. This is an example of a system diagram of the exhaust gas aftertreatment device of the present invention.

The present invention is a known exhaust gas aftertreatment system used in a general vehicle as shown in FIG. 3, wherein the exhaust gas temperature of (Equation 1) uses the measured value of the temperature sensor (9) of the SCR catalyst inlet. , (Equation 1) catalyst upstream NOx volume concentration uses the measured value of (2) upstream NOx sensor at the engine outlet to control the system.

The constant C (Equation 1) of the present invention is an eigenvalue that differs depending on the acidity of various zeolites in the Cu zeolite catalyst. The constant C in the exhaust gas temperature is determined by the model gas performance test shown in the embodiment of the present invention, the exhaust gas temperature is measured by the (9) temperature sensor at the inlet of the SCR catalyst, and the system of the present invention is controlled.

In the model gas evaluation test of the present invention, as shown in Comparative Examples 1 and 2, the constant C is the catalyst inlet concentration of NO, NH ₃ , NO ₂ , N ₂ O and NO, NH ₃ , NO, NH ₃ , at each exhaust gas temperature. Obtain the concentrations of the catalyst outlets of NO ₂ and N ₂ O from the measured values.

First, at each exhaust gas temperature, the NOx purification rate is obtained according to (Equation 2).
(Number 2)
NOx purification rate = {1-([NO] outlet + [NO ₂ ] outlet / [NO] inlet + [NO ₂ ] inlet)} x 100

Next, at each exhaust gas temperature, the constant C is obtained according to (Equation 3).
(Number 3)
Constant C = {[NH ₃ ] Exit + ([NO _x ] entrance x [NO _x purification rate] x 2) + [NO _x ] Exit + 2 * [N ₂ O] Exit} / ([NOx] entrance + 2 * [N ₂ O])
However, it is expressed as [NOx] = [NO] + [NO ₂ ].

According to the present invention, the constant C obtained from (Equation 3) is applied to (Equation 1) to control the NOx purification system of the exhaust gas aftertreatment device corresponding to the actual vehicle load driving, the engine shown in FIG. The measured value of the (2) upstream NOx sensor at the outlet and the measured value of the (9) temperature sensor at the inlet of the SCR catalyst are calculated, and the system is controlled by the ANR (NH ₃ / NO _x ) shown in Table 1.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples of the present invention, but the present invention is not limited to these Examples.

(Reference example 1)
In Reference Example 1, CHA-type SSZ-13 zeolite was synthesized to prepare a CuCHA catalyst in which copper was ion-exchanged.

(Adjustment of zeolite raw material)
First, ion-exchanged water and pseudo-boehmite (Pural SB) are added to a glass container while stirring, and the mixture is stirred at room temperature for 20 minutes. Then, adamantyltrimethylammonium hydroxide (TMadaOH) is slowly added with stirring, and the mixture is kept at room temperature for 1 hour. Then, colloidal silica (Ludox AS40) was added, and stirring was continued for 5 minutes, and the suspension had a pH of 8.4, and the following composition was prepared.

0.033 (Al ₂ O ₃ ): 1.0 (SiO ₂ ): 0.19 (TMadaOH): 46 (H ₂ O)

(Hydrothermal synthesis)
The obtained suspension was transferred to an autoclave with stirring (pressure sterilizer), sealed, heated at 150 ° C. for 72 hours while stirring at a speed of 50 rpm, and then slowly cooled to room temperature. The gel composition obtained from the autoclave was taken out and the supernatant was set aside, and the pH of the supernatant was 10.6. An equal volume of ion-exchanged water was added to the gel composition from which the supernatant had been removed, the mixture was shaken, and washing and solid-liquid separation were repeated with a centrifuge.

(CHA type synthetic zeolite)
The obtained gel composition was transferred to a heat-resistant container, dried at 120 ° C. for 12 hours, and then the particle size was adjusted through a 20-mesh sieve net.
Based on the results of X-ray diffraction analysis of the obtained synthetic zeolite, the relative intensities (I) and lattice plane spacing (d) of the main diffraction peaks were determined by the X-ray diffraction pattern of the International Society for Synthetic Zeolite. In light of the database and the PDF of the ICDD, it was identified as a zeolite consisting of CHA-type SSZ-13 having a maximum oxygen ring number of 8 and a three-dimensional structure.

The resulting composition of the CHA type SSZ-13 synthetic zeolite, as a result of ICP analysis, SiO ₂ is 94.65wt%, Al ₂ O ₃ is at 5.35wt%, mol ratio of _{SiO 2 / Al 2 O 3 (} SAR ) Was 30.00.

Next, a CuCHA powder catalyst was produced by mixing 100 g of the CHA-type SSZ-13 synthetic zeolite with NH ₄ ⁺ -like CHA in 400 mL of a 1.0 M copper (II) nitrate solution. The pH was adjusted to 3.5 with acetic acid. Slurry was stirred for 1 hour at 80 ° C., it was subjected to ion exchange reaction between the NH ₄ ⁺ form CHA and the copper ions. The resulting mixture was then filtered and washed with 800 mL of deionized water until the filtrate was clear and colorless. The washed sample was then dried to 90 ° C.

The resulting CuCHA product was then baked at 700 ° C. for 2 hours. The obtained CuCHA catalyst contained 2.8% by mass of CuO as measured by ICP analysis.

(Reference example 2)
In Reference Example 2, a CuCHA catalyst in which copper was ion-exchanged was prepared in the same manner as in Reference Example 1 except that the synthetic zeolite of the catalyst carrier was replaced with CHA-type SAPO-34 synthetic zeolite.

(Adjustment of zeolite raw material)
First, ion-exchanged water and 85% by mass orthophosphoric acid are mixed in a glass container with stirring. Pseudo-boehmite (Pural SB) is added thereto, and the mixture is stirred at room temperature for 20 minutes. Then, tetraethylammonium hydroxide (TEAOH) is slowly added with stirring, and the mixture is kept at room temperature for 1 hour. Then, colloidal silica (Ludox AS40) was added, and stirring was continued for 5 minutes, and the suspension had a pH of 8.1 to prepare the following composition.

1.0 (Al ₂ O ₃ ): 1.0 (P ₂ O ₅ ): 0.3 (SiO ₂ ): 1.0 (TEAOH): 64 (H ₂ O)

(Hydrothermal synthesis)
The obtained suspension was transferred to an autoclave with stirring (pressure sterilizer), sealed, heated at 170 ° C. for 72 hours while stirring at a speed of 50 rpm, and then slowly cooled to room temperature. The gel composition obtained from the autoclave was taken out and the supernatant was set aside, and the pH of the supernatant was 10.2. An equal volume of ion-exchanged water was added to the gel composition from which the supernatant had been removed, the mixture was shaken, and washing and solid-liquid separation were repeated with a centrifuge.

(CHA type synthetic zeolite)
The obtained gel composition was transferred to a heat-resistant container, dried at 120 ° C. for 12 hours, and then the particle size was adjusted through a 20-mesh sieve net.
From the results of X-ray diffraction analysis of the obtained synthetic zeolite, the relative intensity (I) and lattice plane spacing (d) of the main diffraction peaks were determined by the X-ray diffraction pattern of the International Society of Synthetic Zeolite. In light of the database and the PDF of the ICDD, it was identified as a zeolite consisting of CHA-type SAPO-34 having a maximum oxygen ring number of 8 and a three-dimensional structure.

As a result of ICP analysis, the composition of the obtained CHA-type synthetic SAPO-34 zeolite was 44.50 wt% for P ₂ O ₅ , 9.60 wt% for SiO ₂ , 45.90 wt% for Al ₂ O ₃ , and SiO ₂ The mol ratio (SAR) of / Al ₂ O ₃ was 0.355.

Next, in the same manner as in Reference Example 1, a CuCHA powder catalyst was produced by mixing 100 g of the CHA-type SAPO-34 synthetic zeolite with NH ₄ ⁺ -like CHA with 400 mL of a 1.0 M copper (II) nitrate solution. .. The pH was adjusted to 3.5 with acetic acid. Slurry was stirred for 1 hour at 80 ° C., it was subjected to ion exchange reaction between the NH ₄ ⁺ form CHA and the copper ions. The resulting mixture was then filtered and washed with 800 mL of deionized water until the filtrate was clear and colorless. The washed sample was then dried to 90 ° C.

The resulting CuCHA product was then baked at 700 ° C. for 2 hours. The obtained CuCHA catalyst contained 2.8% by mass of CuO as measured by ICP analysis.

(Reference example 3)
In Reference Example 3, a CuAEI catalyst in which copper was ion-exchanged was prepared in the same manner as in Reference Example 1 except that the synthetic zeolite of the catalyst carrier was replaced with AEI type SSZ-39 synthetic zeolite.

(Adjustment of zeolite raw material)
First, ion-exchanged water is placed in a glass container, and a predetermined amount of 1N NaOH and N, N-diethyl-cis-2,6-dimethylpiperazinium cation hydroxide (DEDMPOH) are added to the glass container while stirring. Stir at room temperature for 20 minutes. Then, NH ₄ ⁺ form Y-type zeolite and colloidal silica (Ludox AS40) with a predetermined amount was added, stirring was continued for 5 minutes, the suspension is at a pH of 9.2, were prepared following composition.

0.06 (Al ₂ O ₃ ): 1.0 (SiO ₂ ): 0.35 (DEDMPOH): 43 (H ₂ O)

(Hydrothermal synthesis)
The obtained suspension was transferred to an autoclave with stirring (pressure sterilizer), sealed, heated at 140 ° C. for 7 days while stirring at a speed of 50 rpm, and then slowly cooled to room temperature. The gel composition obtained from the autoclave was taken out and the supernatant was set aside, and the pH of the supernatant was 11.3. An equal volume of ion-exchanged water was added to the gel composition from which the supernatant had been removed, the mixture was shaken, and washing and solid-liquid separation were repeated with a centrifuge.

(AEI type synthetic zeolite)
The obtained gel composition was transferred to a heat-resistant container, dried at 120 ° C. for 12 hours, and then the particle size was adjusted through a 20-mesh sieve net.
From the results of X-ray diffraction analysis of the obtained synthetic zeolite, the relative intensity (I) and lattice plane spacing (d) of the main diffraction peaks were determined by the X-ray diffraction pattern of the International Society of Synthetic Zeolite. In light of the database and the PDF of the ICDD, it was identified as a zeolite consisting of AEI type SSZ-39 having a maximum oxygen ring number of 8 and a three-dimensional structure.

The composition of the obtained AEI type SSZ-39 zeolites, as a result of ICP analysis, SiO ₂ is 89.65wt%, Al ₂ O ₃ is at 10.35wt%, mol ratio of _{SiO 2 / Al 2 O 3 (} SAR) Was 14.7.

Then, in the same manner as in Example 1, the NH ₄ ⁺ form AEI of said AEI type SSZ-39 synthesized zeolite 100g by mixing copper (II) nitrate solution of 1.0M of 400 mL, to prepare a CuAEI powder catalyst .. The pH was adjusted to 3.5 with acetic acid. Slurry was stirred for 1 hour at 80 ° C., it was subjected to ion exchange reaction between the NH ₄ ⁺ form AEI and copper ions. The resulting mixture was then filtered and washed with 800 mL of deionized water until the filtrate was clear and colorless. The washed sample was then dried to 90 ° C.

The resulting CuAEI product was then baked at 700 ° C. for 2 hours. The obtained CuAEI catalyst contained 2.8% by mass of CuO as measured by ICP analysis.

(Reference example 4)
In Reference Example 4, a CuAEI catalyst in which copper was ion-exchanged was prepared in the same manner as in Reference Example 1 except that the synthetic zeolite of the catalyst carrier was replaced with the AEI type SAPO-18 synthetic zeolite.

(Adjustment of zeolite raw material)
First, ion-exchanged water and 85% by mass orthophosphoric acid are mixed in a glass container with stirring. Pseudo-boehmite (Pural SB) is added thereto, and the mixture is stirred at room temperature for 20 minutes. Then, tetraethylammonium hydroxide (TEAOH) is slowly added with stirring, and the mixture is kept at room temperature for 1 hour. Then, colloidal silica (Ludox AS40) was added, and stirring was continued for 5 minutes, and the suspension had a pH of 7.8, and the following composition was prepared.

1.0 (Al ₂ O ₃ ): 0.98 (P ₂ O ₅ ): 0.075 (SiO ₂ ): 1.0 (TEAOH): 64 (H ₂ O)

(Hydrothermal synthesis)
The obtained suspension was transferred to an autoclave with stirring (pressure sterilizer), sealed, heated at 215 ° C. for 120 hours while stirring at a speed of 50 rpm, and then slowly cooled to room temperature. The gel composition obtained from the autoclave was taken out and the supernatant was set aside, and the pH of the supernatant was 9.2. An equal volume of ion-exchanged water was added to the gel composition from which the supernatant had been removed, the mixture was shaken, and washing and solid-liquid separation were repeated with a centrifuge.

(AEI type synthetic zeolite)
The obtained gel composition was transferred to a heat-resistant container, dried at 120 ° C. for 12 hours, and then the particle size was adjusted through a 20-mesh sieve net.
From the results of X-ray diffraction analysis of the obtained synthetic zeolite, the relative intensity (I) and lattice plane spacing (d) of the main diffraction peaks were determined by the X-ray diffraction pattern of the International Society of Synthetic Zeolite. In light of the database and the PDF of the ICDD, it was identified as a zeolite consisting of AEI-type SAPO-18 having a maximum oxygen ring number of 8 and a three-dimensional structure.

As a result of ICP analysis, the composition of the obtained AEI type SAPO-18 zeolite was 61.00 wt% for P ₂ O ₅ , 1.80 wt% for SiO ₂ , and 37.20 wt% for Al ₂ O ₃ , and SiO ₂ /. The mol ratio (SAR) of Al ₂ O ₃ was 0.082.

Next, in the same manner as in Example 1, a CuAEI powder catalyst was produced by mixing 100 g of the AEI-type SAPO-18 synthetic zeolite with NH ₄ ⁺ -like AEI with 400 mL of a 1.0 M copper (II) nitrate solution. .. The pH was adjusted to 3.5 with acetic acid. Slurry was stirred for 1 hour at 80 ° C., it was subjected to ion exchange reaction between the NH ₄ ⁺ form AEI and copper ions. The resulting mixture was then filtered and washed with 800 mL of deionized water until the filtrate was clear and colorless. The washed sample was then dried to 90 ° C.

The resulting CuAEI product was then baked at 700 ° C. for 2 hours. The obtained CuAEI catalyst contained 2.8% by mass of CuO as measured by ICP analysis.

The SCR catalyst powder containing copper of Reference Examples 1 to 4 was prepared with a colloidal silica binder (solid content: 20% by mass) and a slurry liquid, and deposited on a known cordierite honeycomb flow-through type substrate.

(Slurry combination)
Ion-exchanged water: 30 g
SCR catalyst powder: 30 g
Colloidal silica binder: 15g

The slurry liquid was dispersed by a ball mill and deposited at 200 g / L per volume of the honeycomb base material. Then, it was dried at 80 ° C. and calcinated at 500 ° C., and an exhaust gas purification performance test using the system control of the present invention was performed.

(Exhaust gas purification performance test)
Catalyst inlet temperature: 200 ° C, 250 ° C, 300 ° C, 350 ° C, 400 ° C, 450 ° C, 500 ° C
Space velocity (SV): 50,000 / h
NO: 500ppm
NH ₃ : Examples 1 to 4 are supplied by the index of the present invention Comparative Examples 1 to 4 are constant CO ₂ : 10% at 500 ppm.
O ₂ : 10%
H ₂ O: 10%
N ₂ : BALANCE
Exhaust gas concentration detector: FT-IR
Detected concentration gas components at catalyst inlet and outlet: NO, NH ₃ , NO ₂ , N ₂ O, CO ₂ , H ₂ O
However, O ₂ is a calculated concentration adjustment.

Table 1 shows the relationship between the NOx exhaust gas concentration and the NH ₃ supply control concentration in Examples 1 to 4 and Comparative Examples 1 to 4 as ANR (NH ₃ / NOx).

Table 2 shows the results of NOx purification performance in Examples 1 to 4 and Comparative Examples 1 to 4.

Table 3 shows the results of the NH ₃ slip (SCR catalyst downstream leakage) concentration in Examples 1 to 4 and Comparative Examples 1 to 4.

Based on the above results, the NOx purification rate of Examples 1 to 4 was clearly improved in the range of 350 ° C. to 500 ° C. as compared with Comparative Examples 1 to 4.

On the other hand, in the NH ₃ slip (leakage), in Examples 1 to 4, a small amount of leakage is observed in the exhaust gas high temperature range of 350 ° C. to 500 ° C. as compared with Comparative Examples 1 to 4. The AMOX catalyst (ammonia oxidation catalyst) provided below the target SCR catalyst of the present invention is in a sufficient range for purification. Further, in the low and high temperature region of the exhaust gas, since it depends on the low temperature activity of the SCR catalyst, Examples 1 to 4 have the same amount of NH ₃ slip (leakage) as those of Comparative Examples 1 to 4. It was.

Claims (4)

NOx with urea and / or ammonia in a selective catalytic reduction system
The catalyst is a copper-containing zeolite,
A system control method characterized in that the amount of ammonia consumed by partial oxidation is supplied by controlling the amount of ammonia that is equivalent to the amount of NOx in the exhaust gas. The system control method according to claim 1, wherein the relational expression between the inlet exhaust gas temperature of the catalyst and the supply amount of ammonia gas and / or ammonia gas composed of hydrolysis of urea satisfies the following.
The system control method according to claim 1 or 2, wherein the zeolite has a CHA-type, AEI-type, and AFX-type crystal structure. The system control method according to any one of claims 1 to 3, wherein the zeolite contains 2.0% by mass to 5.0% by mass of CuO.