JPH0338255A - Honeycomb-shaped exhaust gas purification structure and exhaust gas purification method using the same - Google Patents

Abstract

PURPOSE:To obtain a honeycomb-shaped exhaust gas purification structure suitable for purifying the exhaust emissions of a diesel engine by depositing a fire resisting inorg. oxide having a designated specific surface area on a honeycomb carrier in predetermined proportions. CONSTITUTION:A fire resisting inorg. oxide such as alumina and zirconia having a specific surface area of 50-400m<2>/g is deposited on a honeycomb-shaped carrier such as cordierite and mullite in an amt. of 50-400g per liter of this carrier. The honeycomb-shaped exhaust gas purification structure thus formed is effec tive in such purification and particularly that of the exhaust gas contg. a harm ful component such as a carcinogenic substance and capable of an efficient removal of SOF from the exhaust emissions of a diesel engine.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a honeycomb-like exhaust gas purification structure and an exhaust gas purification method using the structure.

(Prior art) In recent years, particulate matter (hereinafter referred to as "patchy slate"), which is mainly composed of solid carbon particles and liquid or solid high molecular weight hydrocarbon particles, emitted from diesel engines has become a problem for environmental health. It's becoming a problem.

This is because these particulates contain harmful components such as carcinogenic substances, and because most of their particle diameters are less than 1 μm, they easily float in the atmosphere and are easily taken into the human body through the respiratory tract.

For this reason, studies are underway to strictly control the emission of these particulates from diesel engines.

To purify particulates, (1) use a heat-resistant gas filter (e.g., ceramic foam, wire mesh, metal foam, sealed ceramic honeycomb, etc.) to filter diesel engine exhaust gas and remove particulates. (2) method of (1) above by burning the accumulated carbon-based particulates using a heating means such as a burner or electric heater to regenerate the filter and use it repeatedly. (3) A method for reducing the frequency of combustion and regeneration of the filter by supporting a catalyst substance on the filter; (3) combustion and purification under the emission conditions (gas formation and temperature) obtained under normal driving conditions; , a so-called filter method, and the like have been proposed.

However, since all of these methods using filters aim to capture solid carbon-based particulates with high efficiency, in addition to the problem of cracking of the filter structure during combustion and regeneration of particulates, carbon-based particulates Problems include filter blockage and reduced catalyst activity due to the buildup of ash components (eg, calcium oxide, zinc oxide, phosphorus pentoxide, etc.) from the engine oil that are trapped along with the engine oil. Furthermore, a single filter type exhaust gas purification device also has drawbacks such as pressure loss. For this reason, a practically satisfactory method for purifying exhaust gas using one type of filter has not yet been obtained.

On the other hand, in recent years, with improvements in diesel engines (for example, higher fuel injection pressure, control of fuel injection timing, etc.), particulates emitted from diesel engines have been reduced. At the same time, the particulates discharged from this improved diesel engine contain components soluble in organic solvents (hereinafter referred to as SOF), which mainly consist of liquid high molecular weight hydrocarbons.
c Fraction) increased. Therefore, we are focusing on the exhaust gas emitted from conventional diesel engines and its properties. Therefore, in purifying exhaust gas having such properties, an important issue is mainly the removal of SOF containing harmful components such as carcinogenic substances.

Since the amount of SOF emissions tends to increase in a low temperature range, it is necessary to remove SOF in a low temperature range, especially in a low temperature range where it cannot be burned and purified using a catalyst component.

An open honeycomb-shaped catalyst with through holes parallel to the gas flow has been investigated and reported as a catalyst for purifying particulates from diesel engine exhaust gas (
SAE Paper, 810263). However, this shows the combustion and purification performance at high temperatures that can burn SOF, hydrocarbons, carbon oxides, etc. when platinum-based catalysts are used. It has been reported that the honeycomb catalyst of the formula is ineffective. In addition, the open type honeycomb catalyst S
There is no mention of OF adsorption/trapping properties.

(Problem M to be Solved by the Invention) An object of the present invention is to provide a honeycomb-shaped exhaust gas purification structure suitable for purifying exhaust gas, particularly diesel engine exhaust gas.

Another object of the present invention is to reduce the amount of S in diesel engine exhaust gas.
It is an object of the present invention to provide a honeycomb-shaped exhaust gas purification structure capable of effectively purifying diesel engine exhaust gas by efficiently and stably adsorbing and capturing OF in a low temperature range for a long period of time.

Another object of the present invention is to provide a honeycomb-like exhaust gas purification structure that enables effective purification of diesel engine exhaust gas without causing problems such as increased back pressure and cracking that are seen in conventional filter-type exhaust gas purification devices. It's about giving your body.

Another object of the present invention is to provide an exhaust gas purification method for efficiently purifying exhaust gas, particularly diesel engine exhaust gas, using the honeycomb-shaped exhaust gas purification structure.

Another object of the present invention is to efficiently purify the exhaust gas by adsorbing and capturing SOF in the exhaust gas by bringing the diesel engine exhaust gas into contact with the honeycomb-shaped exhaust gas purification structure, and to efficiently purify the exhaust gas by heating the SOF that has been adsorbed and captured. Burned by
An exhaust gas purification method is developed in which the honeycomb-shaped exhaust gas purification structure is disassembled and regenerated.

(Means for Solving the Problems) In order to achieve the above object, the present inventors have conducted extensive studies on the adsorption and capture behavior of SOF in diesel engine exhaust gas, and have found that a refractory inorganic When a honeycomb-shaped exhaust gas purification structure supporting oxides is installed in diesel engine exhaust gas, the exhaust gas temperature will drop to 40°C.
We discovered that SOF can be adsorbed and captured efficiently and stably for a long time even under conditions of 0°C or lower.
Based on this knowledge, we have completed the present invention.

That is, the present invention provides a honeycomb carrier with a capacity of 1
A honeycomb-shaped exhaust gas purification structure is formed by supporting a refractory inorganic oxide having a specific surface area of 50 to 4001 W2/g at a ratio of 50 to 400 g per gram.

Furthermore, the present invention relates to an exhaust gas purification method characterized by bringing exhaust gas into contact with the honeycomb-shaped exhaust gas purification structure.

The present invention will be explained in detail below.

There are no particular restrictions on the honeycomb carrier used in the honeycomb exhaust gas purification structure of the present invention (hereinafter simply referred to as "honeycomb structure"), and any carrier generally referred to as a honeycomb carrier may be used. I can do it. Among these, cordierite, mullite, α-alumina,
Ceramic honeycombs made of zirconia, titania, titanium phosphate, aluminum titanate, betalite, subodumene, alumina silicate, magnesium silicate, etc., and stainless steel or Fe-Cr-A9. A metal honeycomb or the like which is an integral structure made of an oxidation-resistant heat-resistant metal such as an alloy is preferably used. Cordierite honeycomb or metal honeycomb is particularly suitable for purifying diesel engine exhaust gas.

The honeycomb carrier in the present invention is open and has a plurality of through holes (hereinafter referred to as "gas flow holes") parallel to the flow of exhaust gas. In particular, when the number of gas flow holes per square inch of cross section of the honeycomb carrier is 100 to 600 and the porosity is 40 to 95%, an excellent SOF adsorption/trapping effect can be obtained. The porosity referred to herein means the ratio of the total cross-sectional area of all gas flow holes to the cross-sectional area of the honeycomb carrier.

If the number of gas flow holes is less than 100 or the porosity is less than 40%, the surface area of the honeycomb structure that comes in contact with the exhaust gas per unit volume decreases, and the SOF adsorption/trapping effect decreases. This is undesirable as it causes an increase in back pressure. On the other hand, if the number of gas flow holes exceeds 600 or the porosity exceeds 95%, the partition walls constituting the honeycomb structure become thin and sufficient strength cannot be obtained, which is not preferred in practice.

The refractory inorganic oxide supported on the honeycomb carrier has a specific surface area in the range of 50 to 400 m2/3, and SO
Any material that can adsorb F can be used, but alumina, zirconia, titania, and silica are particularly preferred.

These can be used alone or in combination of two or more. It can also be used as a composite oxide of these.

If the specific surface area is less than 50 m2/g, the adsorption/trapping effect of SOF is low, while if it exceeds 400 m2/g, it becomes thermally unstable and is not practical.

The above-mentioned refractory inorganic oxide is supported on the honeycomb carrier at a rate of 50 to 400 g per 1k1l of the carrier. If the supported amount is less than 50 g, the saturated amount of SOF that can be adsorbed and captured will be significantly reduced, while if it exceeds 400 g, the refractory inorganic oxide will likely peel off and the pores of the honeycomb structure will become clogged, which is not preferable.

The SOF adsorbed and captured by the honeycomb-like structure formed by supporting a refractory inorganic oxide on the honeycomb carrier can be burned and decomposed by placing it in a high-temperature oxygen atmosphere, thereby forming a honeycomb-like structure. The body can be easily regenerated.

Specifically, the honeycomb-like structure is brought into contact with high-temperature exhaust gas of, for example, over 400°C, which is discharged according to changes in engine operating conditions, or heated using a heating means such as a burner or an electric heater. The honeycomb-like structure can be regenerated.

In addition to the refractory inorganic oxide, at least one noble metal selected from platinum, palladium, and rhodium may be supported for the purpose of lowering the combustion/decomposition temperature.

The capacity of the honeycomb-like structure used in the present invention varies depending on the engine displacement, but in the case of diesel engine exhaust gas purification, a honeycomb-like structure with a capacity of 0.3 to 3 times per 12 engine displacement is used.

The capacity per 1g of engine displacement of the honeycomb structure is 0
．． If it is less than 3 U, the adsorption/trapping effect of SOF will decrease mainly due to a decrease in the contact time with exhaust gas, while if it exceeds 312, the capacity of the honeycomb-like structure will become very large, which is not practical.

In addition, the honeycomb-like structure and the exhaust gas purification method of the present invention are particularly applicable to exhaust gas discharged from a diesel engine, and when the exhaust gas temperature is 200°C or less, the exhaust gas I
Contains 50 mg or less of particulates per n+3,
Moreover, it is extremely effective in purifying diesel engine exhaust gas in which the content of SOF in the particulates is 40% or more.

(Effects of the Invention) The main effects of using the honeycomb exhaust gas purification device of the present invention are listed below.

(1) It is effective in purifying exhaust gas containing harmful components such as carcinogenic substances, and in particular, SOF in diesel engine exhaust gas can be efficiently removed.

(2) Although the proportion of SOF in diesel engine exhaust gas tends to increase in low temperature ranges, SOF can be effectively removed even in such low temperature ranges.

(3) SOF in diesel engine exhaust gas can be removed stably for a long time.

(4) SOF deposits accumulated through long-term use can be easily combusted and decomposed by exposure to high-temperature exhaust gas exceeding 400°C, or by heating with a heating means such as a burner or electric heater. can be done without any problem of cracks. Therefore, by performing such a reproducing operation, it can be used repeatedly.

(Example) Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1 3 kg of alumina having a specific surface area of 130n+2/g was wet-pulverized with water to form a slurry. In this slurry, the following cylindrical stainless steel honeycomb carrier cell shape: corrugation type Number of gas flow holes: 200 (per 1 square inch cross section of the honeycomb carrier, same hereinafter) Porosity = 89% Volume j1: 2.479 (inner diameter of carrier (hereinafter simply referred to as ``inner diameter''): 5.66 inches, length of carrier (hereinafter simply referred to as ``length''): 6 inches) After soaking, excess slurry was removed. removed. Continuing,
After drying at 150°C for 2 hours, it was fired at 500°C for 2 hours to obtain 300g of alumina per volume of honeycomb carrier.
A supported honeycomb structure was obtained.

Example 2 3 kg of titania having a specific surface area of 118 m21 g was wet-pulverized with water to form a slurry. - In this slurry, the following cylindrical stainless steel honeycomb carrier cell shape: corrugation type, number of gas flow holes = 450, porosity: 283%, capacity: 1.65 g (inner diameter: 5.66 inches, length:
After soaking (4 inches), excess slurry was removed. Continuing,
After drying at 150° C. for 2 hours, it was fired at 500° C. for 2 hours to obtain a honeycomb-like structure in which 200 g of titania was supported per 1Q volume of the honeycomb carrier.

Example 3 2 kg of alumina having a specific surface area of 130 m2/g was wet-pulverized with water to form a slurry. In this slurry, the following cylindrical cordierite monolith carrier gas flow holes: Approximately 4
After immersing 00 pieces of porosity: 75%, volume 1i: 2.47Q (inner diameter: 5.66 inches, length: 6.00 inches), excess slurry was removed. Continuing,
After drying at 150° C. for 3 hours, it was fired at 400° C. for 2 hours to obtain a honeycomb-like structure in which 100 g of alumina was supported per 1 liter of carrier volume.

Example 4 In Example 3, specific surface area 120 was used instead of alumina.
A honeycomb structure in which 100 g of zirconia was supported per 111 g of the carrier was obtained in the same manner as in Example 3, except that 1/g of zirconia was used.

Example 5 In Example 3, a specific surface area of 138 was used instead of alumina.
m+2/H titania-zirconia mixed powder (T i
A honeycomb-like structure was obtained in the same manner as in Example 3 except that 50 g and 50 g of titania and zirconia were supported per 12 volumes of the carrier, respectively.

Example 6 In Example 3, a specific surface area of 152 was used instead of alumina.
III218 alumina-silica composite oxide (AQ20
A honeycomb-like structure carrying 100 g of alumina-silica composite oxide per 1 liter of carrier capacity was obtained in the same manner as in Example 3 except that 3/S i 02 weight ratio: 4/] was used.

Example 7 In Example 3, a specific surface area of 132 was used instead of alumina.
1 platinum of n+2/H! ii% supported alumina was used in the same manner as in Example 3, and the carrier volume was 111 st.
100g and 1g of alumina and platinum, respectively
A supported honeycomb structure was obtained.

Example 8 In Example 3, a specific surface area of 112 was used instead of alumina.
+w2/g, except that alumina carrying 1% by weight of palladium was used, except that the carrier had a capacity of 1 liter in the same manner as in Example 3.
A honeycomb-like structure carrying 100 g and 1 g of alumina and palladium, respectively, was obtained.

Example 9 In Example 3, specific surface area 108 was used instead of alumina.
1/g, 0.7% by weight each of platinum and rhodium
A honeycomb-like structure was prepared in the same manner as in Example 3 except that zirconia supported at 0.3% by weight was used, in which 100 g, 0.7 g, and 0.3 g of zirconia, platinum, and rhodium were supported per 1 g of carrier capacity, respectively. Obtained.

Example 10 2 kg of alumina with a specific surface area of 150 n+2/H was wet-pulverized with water to form a slurry. In this slurry, the following cylindrical cordierite monolith carrier Number of gas flow holes: Approximately 200 Porosity: 63% Volume It: 2-479 (inner diameter: 5.66 inches, length: 6.00 inches ) After soaking, excess slurry was removed. Continuing,
After drying at 150° C. for 3 hours, it was fired at 400° C. for 2 hours to obtain a honeycomb-like structure in which 200 g of alumina was supported per 11 g of carrier volume.

Example 11 2 kg of titania having a specific surface area of 86 m2/g was wet-pulverized with water to form a slurry. In this slurry, the following cylindrical cordierite monolith carrier gas flow holes: Approximately 3
00 pieces Opening rate: 72% Capacity: 3.62! Q (inner diameter: 7.5 inches, length = 5.
After soaking (0 inch), excess slurry was removed. Continuing,
After drying at 150° C. for 3 hours, it was fired at 400° C. for 2 hours to obtain a honeycomb-like structure having a carrier capacity of 0 g of titania.

Example 12 2 kg of alumina with a specific surface area of 10211121 g was wet-pulverized with water to form a slurry. In this slurry, the following cylindrical cordierite monolith carrier has gas flow holes: about 400, porosity: 75%, volume fl: 1.65!9 (inner diameter: 5.66 inches,
Length: 4. After soaking (0.0 inch), excess slurry was removed. Continuing,
- Drying at 150° C. for 3 hours yielded a honeycomb-like structure in which 150 g of alumina was supported per 12 flk volumes of the carrier. Comparative Example 1 A honeycomb-like structure was prepared in the same manner as in Example 1 except that the amount of alumina supported per 1 liter of carrier capacity was 30 g in Example 1. I got it.

Comparative Example 2 2 kg of alumina with a specific surface area of 150+a2/H was wet-pulverized with water to form a slurry. In this slurry, the following cylindrical cordierite monolith carrier has gas flow holes: approximately 400, porosity = 75%, capacity: 0.671 (inner diameter: 3.60 inches, length: 4.
After soaking (0.0 inch), excess slurry was removed. Continuing,
After drying at 150° C. for 3 hours, it was fired at 400° C. for 2 hours to obtain a honeycomb-like structure in which 150 g of alumina was supported per 112 volumes of the carrier.

Comparative Example 3 2 kg of alumina with a specific surface area of 150+2/H was wet-pulverized with water to form a slurry. In this slurry, the following cylindrical cordierite monolith carrier gas flow holes: Approximately 1
00 pieces Opening rate: 30% Capacity: 1.659 (Inner diameter: 5.66 inches, Length:
4. After soaking (0.0 inch), excess slurry was removed. Continuing,
After drying at 150° C. for 3 hours, it was fired at 400° C. for 2 hours to obtain a honeycomb-like structure in which 200 g of alumina was supported per liter of carrier volume.

Comparison Box 4 2 kg of alumina with a specific surface area of 150II12/g was wet-pulverized with water to form a slurry. In this slurry, the following number of cylindrical cordierite monolith carrier gas flow holes:
Approximately 50 pieces Opening ratio: 72% Capacity: 2.479<Inner diameter: 5.66 inches, Length: 6.
00 inches), excess slurry was removed. Continuing,
After drying at 150° C. for 3 hours, it was fired at 400° C. for 2 hours to obtain a honeycomb-like structure in which 300 g of alumina was supported per 111 volumes of the carrier.

Comparative Example 5 In Example 3, a specific surface area of 15+ was used instead of alumina.
A honeycomb-like structure was obtained in the same manner as in Example 3 except that zirconia of m2/H was used, in which 200 g of zirconia was supported per 12 volumes of the carrier.

The properties of the honeycomb carrier and the refractory inorganic oxide in Examples 1 to 12 and Comparative Examples 1 to 5 are summarized in Table 1. (Space below) Example 13 The honeycomb structures obtained in Examples 1-12 and Comparative Examples 1 to 5 were used as fuel with a sulfur content of 0 in a commercially available supercharged direct injection diesel engine (4 cylinders, 2800 cc). The following test was conducted using light oil having a concentration of .03% by weight.

Engine speed 1000rp+s, torque 1.0kg・
Particulates in the exhaust gas at the artificial part and the outlet part of the honeycomb-like structure were captured using a normal dilution tunnel method under the condition that the inlet temperature of the honeycomb structure was 100°C. The particulates were extracted with a dichloromethane solution, and the amount of SOF discharged (B/+w'-exhaust gas) was measured from the change in weight of the particulates before and after extraction, and the capture rate of SOF by the honeycomb structure was determined.

Furthermore, the honeycomb-like structure was
After 0 hours of exposure, the SOF capture rate was measured again in the same manner.

The weight of the honeycomb structure before and after the above test was measured, and the change in weight of the honeycomb structure due to SOF capture was also measured.

The results are shown in Table 2.

(The following is a blank space) From the results in Table 2, the honeycomb-like structure of the present invention has excellent S
It is understood that it exhibits an OF adsorption/trapping effect and can stably maintain its performance over a long period of time.

Example 14 Each honeycomb structure tested in Example 13 was heated at 600°C for 2 hours in an electric furnace to burn the captured SOF.
Removed. This regenerated honeycomb structure was tested in the same manner as in Example 13, except that the engine speed was 2000 rrxa, the slue was 3.6 kg-m, and the structure inlet temperature was 200°C.

The results are shown in Table 3 (blank below). From the results in Table 3, it can be seen that the SOF adsorbed and captured by the honeycomb structure of the present invention is burned and decomposed by heating, and the honeycomb structure regenerated in this way is It is understood that it can be effectively used again as an exhaust gas purification device.

Example 15 A honeycomb-like structure obtained in Example 3, which is the same as Example 14.
Using the same engine and fuel used in Example 13, the honeycomb-like structure adsorbing and capturing S(>F) was tested at an engine speed of 2500 rpm and a torque of 20.
Installed in exhaust gas under engine operating conditions of 6 kg・-1
Exposure for 5 minutes, during which S of the structure's population and outlet
The amount of OF discharged was measured in the same manner as in Example 13. Note that this operation was started from a stopped state all at once, and the temperature at the inlet of the honeycomb structure after 15 minutes was 570.
It was ℃.

As a result, the SO of the honeycomb-like structure's population and outlet
The emission amount of F is 1,6 mg/-1 exhaust gas and 1,3 m8/*3-exhaust gas, respectively, and the emission amount shows a low value, and the release of SOF trapped in the honeycomb-like structure is not recognized. I couldn't.

The weight of the honeycomb structure taken out after the test was 1402.
The weight was 7g, which was equivalent to the initial weight of 1402.0g. Furthermore, after the test in Example 14, the honeycomb-like structure exhibited a brownish color due to adsorption and capture of SOF, but the honeycomb-like structure took on its initial white color, indicating that the SOF had been decomposed and removed and the honeycomb-like structure had been regenerated. confirmed.

From the above results, the SOF adsorbed and captured by the honeycomb-like structure of the present invention can be combusted and decomposed by changing engine operating conditions to emit high-temperature exhaust gas and bringing it into contact with the honeycomb-like structure. It is understood that the honeycomb structure can be effectively regenerated after use.

Claims (12)

[Claims] (1) Add 50% of a refractory inorganic oxide having a specific surface area of 50 to 400 m^2/g to a honeycomb carrier per 1 liter of capacity of the carrier.
A honeycomb-shaped exhaust gas purification structure supported at a ratio of ~400g. (2) The honeycomb exhaust gas purification structure according to claim 1, wherein the honeycomb carrier is an open type honeycomb carrier made of metal or ceramics. (3) The honeycomb carrier has a density of 100 to 100 per square inch of cross section.
The honeycomb exhaust gas purification structure according to claim 2, which has 600 gas flow holes and has a cross-sectional porosity of 40 to 95%. (4) The honeycomb-shaped exhaust gas purification structure according to claim (1), wherein the refractory inorganic oxide is at least one selected from alumina, zirconia, titania, and silica. (5) The honeycomb-shaped exhaust gas purification structure according to claim (4), which supports at least one noble metal selected from platinum, palladium, and rhodium in addition to the refractory inorganic oxide. (6) The honeycomb-shaped exhaust gas purification structure according to claim (1), which is a device for purifying exhaust gas of a diesel engine. (7) An exhaust gas purification method comprising bringing the exhaust gas of a diesel engine into contact with the honeycomb-shaped exhaust gas purification structure according to claim (1). (8) The exhaust gas purification method according to (7), wherein the honeycomb exhaust gas purification structure has a capacity of 0.3 to 3 liters per liter of engine displacement. (9) SOF, which constitutes particulates in relatively low-temperature exhaust gas emitted from a diesel engine under normal operating conditions, is adsorbed and captured in the honeycomb-shaped exhaust gas purification structure to purify the exhaust gas, and as needed. 8. The exhaust gas purification method according to claim 7, wherein the structure is regenerated by placing the structure in a high-temperature oxygen-containing atmosphere to burn and decompose the adsorbed and captured SOF. (10) The temperature of diesel engine exhaust gas is 400℃
The exhaust gas purification method according to claim 9, which is as follows. (11) The exhaust gas purification method according to (9), wherein the honeycomb-shaped exhaust gas purification structure is heated and regenerated using heating means such as a burner. (12) The exhaust gas purification method according to claim (9), wherein the honeycomb-shaped exhaust gas purification structure is regenerated by contacting with high-temperature exhaust gas.