JP2007309152A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an emission control device having an installation space equal to ever before in an exhaust emission control system of an diesel engine or the like and causing a nitrogen oxide removing catalyst not to be subject to sulfur poisoning because a special control system is necessary for regeneration when the nitrogen oxide-removing catalyst has sulfur poisoning and fuel consumption is lowered in regeneration. <P>SOLUTION: An exhaust particulate filter is united with sulfur content adsorbing material which does not substantially release sulfur content once adsorbed under ordinary conditions of an internal combustion engine and the filter is installed on an upstream side of the nitrogen oxide removing catalyst with respect to exhaust gas to prevent poisoning of the nitrogen oxide-removing catalyst. Performance of the sulfur content-absorbing material can be further improved by combination with an oxidation catalyst. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust particulate removal device using a material that absorbs sulfur contained in the exhaust gas of an internal combustion engine, and to an exhaust gas purification device for an internal combustion engine using the same.

  In order to purify nitrogen oxides generated from an internal combustion engine, a technique is often used in which nitrogen oxides are reduced to nitrogen by using a catalyst. Ordinary gasoline engines use a three-way catalyst that uses multiple precious metals, and the technology is almost complete.

  Also, lean burn gasoline engines and diesel engines cannot use a three-way catalyst because the air-fuel ratio is larger than that of ordinary gasoline engines. There is a technique such as selective catalytic reduction (SCR) using urea instead of a three-way catalyst, but in recent years, a nitrogen oxide storage type purification catalyst has been developed and used. When the air-fuel ratio is larger than the stoichiometric air-fuel ratio, nitrogen oxide is taken into the catalyst, and when the air-fuel ratio approaches the stoichiometric air-fuel ratio as in acceleration, the taken-in nitrogen oxide is reduced and released as nitrogen. It is.

  The nitrogen oxide purification catalyst for an internal combustion engine used in a region where these air-fuel ratios are large has a problem that it is poisoned by sulfur contained in the fuel and causes a decrease in performance. This is because sulfur oxides derived from fuel or engine oil behave in a similar manner to nitrogen oxides, and are taken into the purification catalyst to reduce the active sites of the catalyst that nitrogen oxides should react with. .

  The heavier fuel contains a larger amount of sulfur in the fuel. For this reason, in a diesel engine using light oil as a fuel, the activity of the above-described nitrogen oxide purification catalyst is likely to decrease compared to an internal combustion engine using gasoline as a fuel.

  A sulfur-poisoned nitrogen oxide purification catalyst uses a technique in which the sulfur content is reduced by high-temperature treatment in a region where the air-fuel ratio is close to the stoichiometric air-fuel ratio, and the catalytic activity is restored by releasing it in the form of hydrogen sulfide. .

  For example, in Japanese Patent Publication No. 2605586 (Patent Document 1), when the air-fuel ratio is larger than the stoichiometric air-fuel ratio and the exhaust gas is hot or the nitrogen oxide purification catalyst is hot, the air-fuel ratio is intermittently or continuously set. Thus, a method is described in which the catalyst is regenerated by desorbing the sulfur component poisoning the nitrogen oxide purification catalyst in the vicinity of the stoichiometric air-fuel ratio or smaller than the stoichiometric air-fuel ratio.

  Japanese Patent Publication No. 2745985 (Patent Document 2) is provided with means for estimating the amount of sulfur absorbed in the nitrogen oxide purification catalyst, and when a sulfur content exceeding a set amount is absorbed, exhaust gas is exhausted. A method is described in which the sulfur content absorbed is desorbed from the catalyst and regenerated by controlling the air-fuel ratio in the vicinity of the stoichiometric air-fuel ratio while heating the heater.

  In Japanese Patent No. 2727914 (Patent Document 3), a sulfur-absorbing material is installed upstream of the exhaust with respect to the nitrogen oxide purification catalyst, and means for adjusting the oxygen concentration flowing into each is provided. As a result, the oxygen concentration of the exhaust gas flowing into the nitrogen oxide purification catalyst is lowered in advance to create a state in which the sulfur content is difficult to be absorbed by the catalyst, and then the oxygen concentration flowing into the sulfur content absorbing material is lowered to reduce the sulfur content. It is possible to release the sulfur content absorbed by the absorbent material.

  WO 2005/090760 (Patent Document 4) describes that the sulfur content absorbed by the sulfur content-absorbing material is not released and the nitrogen oxide purification performance and fuel consumption performance are maintained. Further, in this case, control for removing the sulfur content is unnecessary, and it is possible to prevent complication of the exhaust treatment-related system.

Japanese Patent Publication No. 2605586 Japanese Patent No. 2745985 Japanese Patent Publication No. 2727914 International Publication WO2005 / 090760

  In the case of using a scavenger that does not easily release sulfur, it is necessary to increase the amount of the trapping material in order to increase the amount of trapped sulfur. On the other hand, when the amount of the capturing material is increased, there is a problem that the pressure loss due to the thickness of the capturing material layer increases.

  The present application solves the above problems.

  A feature of the present invention that solves the above-mentioned problems is that particulates contained in the exhaust gas from the internal combustion engine are removed by an exhaust particulate filter, and nitrogen oxides in the exhaust gas are removed from the exhaust particulate filter on the gas downstream side. In an exhaust purification device that purifies with a purification catalyst, a material that absorbs sulfur upstream of the exhaust with respect to the nitrogen oxide catalyst that is subject to sulfur poisoning and does not substantially desorb the once absorbed sulfur content. The absorbent material is to be integrated with the exhaust particulate filter.

  However, when the sulfur content absorbing material is integrated with the exhaust particulate filter, it is necessary that the pressure loss in the filter does not increase significantly as compared with the case without the sulfur content absorbing material.

  By integrating the sulfur content-absorbing material with the filter, the installation space for the exhaust gas purification device can be reduced to the same level as a conventional exhaust gas purification system that does not use the sulfur content-absorbing material. For this purpose, it is necessary to install the sulfur-absorbing material without blocking the through holes in the exhaust particulate filter wall. When the filling rate is high, the portion that was previously a gap is closed, and the pressure loss in the filter becomes large. Therefore, it is necessary to provide an appropriate gap in the filling portion.

  Therefore, when integrating, the pores (voids) of the honeycomb constituting the exhaust particulate filter are filled with particulate or fibrous sulfur-absorbing material, and an appropriate gap is provided in the filling part to increase the pressure loss. It is possible to incorporate the required amount of sulfur-absorbing material.

  In order to provide voids, the sulfur-absorbing material filled in the honeycomb voids is made granular or fibrous. As a result, it is possible to ensure an appropriate gap.

  As a specific sulfur content-absorbing material, it can be achieved by containing a sulfur content-absorbing component mainly composed of alkali metal and / or alkaline earth metal in the carrier. Alkali metal compounds and / or alkaline earth compounds, or a mixture mainly composed of them and containing other compounds react with the sulfur content in the exhaust gas to easily form sulfates. Since these sulfates are in a region where the decomposition temperature is higher than the exhaust temperature of a normal internal combustion engine, once they are formed, they are extremely stable and virtually no sulfur desorption occurs.

  In addition, by installing an oxidation catalyst that oxidizes sulfur dioxide to sulfur trioxide on the upstream side of the exhaust with respect to the installation position of these sulfur content absorption materials, use these sulfur content absorption materials more effectively. Is possible. This is because the oxidation catalyst causes the sulfur content to be in the form of sulfur trioxide, which makes it easier to react with the alkali metal-containing compound and alkaline earth metal-containing compound that are sulfur-absorbing components.

  As described above, the oxidation catalyst is not limited as long as it has the ability to oxidize sulfur dioxide to sulfur trioxide under internal combustion engine operating conditions. For example, the active component is a noble metal and the carrier is a group 3-6 element compound. Alternatively, it can be configured as an aluminum compound, a silicon compound, a mixture based on them, or a zeolite.

  In the exhaust gas purification system for an internal combustion engine according to the present invention, once absorbed sulfur is not forcibly desorbed by external air-fuel ratio control, such control is unnecessary and the control system is complicated. Without.

  In the present invention, by installing the sulfur content absorbing material upstream of the exhaust of the nitrogen oxide purification catalyst, the generated sulfur content resulting from the fuel is absorbed by the sulfur content absorbing material, and this is not substantially desorbed. Sulfur is not contained in the exhaust gas flowing into the nitrogen oxide purification catalyst. This prevents the nitrogen oxide purification catalyst from being poisoned, and makes it possible to maintain a stable nitrogen oxide purification function over a long period of time.

  Nitrogen oxide purification installed at the subsequent stage of the sulfur-absorbing material in the exhaust temperature and the exhaust composition atmosphere during operation of the internal combustion engine means that the sulfur component is not substantially desorbed from the sulfur-absorbing material. This means that the catalyst is so small that it does not deteriorate for a long time due to sulfur poisoning.

  By installing an oxidation catalyst that oxidizes sulfur dioxide to sulfur trioxide upstream of the sulfur content absorbing material, it is possible to effectively use the sulfur content absorbing material.

  As an internal combustion engine using such an exhaust purification device, application to various types of engines using a fuel containing sulfur is conceivable, but it is particularly effective in a diesel engine.

  According to the present invention, it is possible to provide a compact exhaust gas purification device with little pressure loss and a large amount of sulfur trapped.

  FIG. 1 shows an example of an exhaust emission control device according to the present invention. Exhaust gas discharged from the internal combustion engine 1 enters the oxidation catalyst 3 through the exhaust passage 2. Here, the sulfur content in the exhaust is oxidized to sulfur trioxide. The particulates and sulfur content in the exhaust are captured by the exhaust particulate filter 4 integrated with the sulfur absorbing material. Since the exhaust gas from which the particulates and sulfur content in the exhaust gas are removed still contains nitrogen oxides, it is further purified by the downstream nitrogen oxide purification catalyst 5.

  The oxidation catalyst 3 can be installed adjacent to the exhaust particulate filter 4 in which the sulfur content absorbing material is integrated as shown in FIG. 1, or can be installed separately as shown in FIG.

  1 and 2, the nitrogen oxide purification catalyst 5 is drawn away from the exhaust particulate filter 4 in which the upstream oxidation catalyst 3 and the sulfur content absorbing material are integrated with respect to the exhaust flow. 1 and 2, the nitrogen oxide purification catalyst 5 may be installed adjacent to the exhaust particulate filter 4 in which the sulfur content absorbing material is integrated.

FIG. 3 shows a schematic diagram of an exhaust particulate filter integrated with a sulfur content absorbing material. This figure shows the concept of the present invention, and the actual dimensional ratio of each component is different from this figure. The exhaust particulate filter usually uses a honeycomb made of a ceramic such as cordierite or silicon carbide. The honeycomb wall 11 is porous and does not allow exhaust particulates to pass therethrough, but gas can permeate without undergoing a large pressure loss. In the honeycomb, adjacent honeycomb holes 15 and 16 are alternately plugged 12 at both ends, and the exhaust flow enters from one end and always passes through the honeycomb wall 11.

  The honeycomb holes 16 on the outlet side with respect to the exhaust flow are filled with a sulfur content absorbing material 13. In FIG. 3, the particulate sulfur content-absorbing material is filled, and the sulfur content in the exhaust is absorbed therein. The sulfur content-absorbing material 13 is filled so as to leave an appropriate gap in the honeycomb hole, so that a large pressure loss does not occur when the exhaust gas passes through the layer of the sulfur content-absorbing material.

  The amount of voids needs to be 30% or more (filling rate is 70% or less). This is because if it is filled more than this, the pressure loss is high, and the sulfur-absorbing material is not fully utilized. The sulfur content-absorbing material may be mixed with particles having different sizes and shapes, but the porosity is reduced particularly when large and small particles are mixed.

  When the porosity is 80% or less, the effect of the sulfur content absorbing material can be obtained. In particular, if it is 70% or less, the activity can be obtained for most of the sulfur-absorbing materials in practical use.

  Further, a mesh 14 having an interval at which the exhaust gas flows out but the sulfur component absorbing material does not pass is provided at the exhaust flow outlet of the outlet side honeycomb hole 16 so that the sulfur component absorbing material does not spill out.

  The sulfur content once absorbed by the sulfur content-absorbing material 13 is not substantially desorbed from any exhaust composition and temperature, and therefore nitrogen on the downstream side of the exhaust flow. It does not flow out to the oxide purification catalyst. For this reason, the nitrogen oxide purification catalyst is not poisoned by sulfur contained in the exhaust gas, and exhibits a stable purification performance for a long period of time.

  FIG. 4 is a schematic view showing another example of the exhaust particle filter in which the sulfur content absorbing material according to the present invention is integrated. FIG. 4 also shows the function of the present invention as in FIG.

As in the case of FIG. 3, the exhaust enters from the inlet side honeycomb hole, and the particulates in the exhaust are captured when passing through the honeycomb wall 11. A fibrous sulfur content-absorbing material 17 is installed in the honeycomb hole on the outlet side with respect to the exhaust flow, and the sulfur content in the exhaust is captured by this. The fibrous sulfur content-absorbing material 17 has an appropriate gap, and no large pressure loss occurs even if the exhaust gas passes through this layer.

  The shape of the sulfur-absorbing material may be spherical, cylindrical, or uniform in size or irregular in particle size.

  However, in any case, it is important to provide a void in the packed bed so that the pressure loss does not increase.

  The present invention will be specifically described below with reference to examples.

  Barium carbonate and anatase type titania were weighed so as to have a molar ratio of barium to titanium of 2: 1, mixed using a ball mill, and treated in an electric furnace at 650 ° C. for 2 hours. This powder was mixed with polyvinyl alcohol and warm water to prepare a slurry, and granulated by spray drying. The granulated powder is degreased by heating at 650 ° C. for 2 hours, and the mixed solution of sodium nitrate and barium acetate is converted to sodium weight and barium weight to 11.5 g / L and 68.7 g / L, respectively. After impregnation, the sulfur content-absorbing material was baked in air at 650 ° C. for 1 hour. The sulfur component absorbing material was spherical and the average particle size was 150 μm.

  A sulfur-absorbing material was filled in a hole on the outlet side of a cordierite exhaust particulate filter honeycomb (length: 20 mm), and the outlet was closed with a 200-mesh net. The porosity of the outlet-side honeycomb holes determined from the relationship between the weight and the average particle diameter was 65%.

  A cordierite honeycomb was wash-coated with a silica slurry in an amount of 170 g / L. A dinitrodiammine platinum solution was used for this and impregnated so as to be 3 g / L in terms of platinum weight. This was calcined at 600 ° C. for 1 hour to obtain an oxidation catalyst.

Arranged in the order of the oxidation catalyst honeycomb and the exhaust particulate filter in the gas flow direction, the quartz glass reaction tube was heated to 300 ° C. in an electric furnace, and a gas containing sulfur was circulated for 5 hours. As gas components, oxygen 10vol%, carbon monoxide 0.2vol%, nitric oxide 200 in dry conversion
volppm, sulfur dioxide 150ppm, balance nitrogen. Water was added to this so that it would be 3 vol% in terms of gas standard state volume with respect to the total amount of gas. The space velocity of gas distribution was 30000 h ⁻¹ . The differential pressure before and after the glass reaction tube was measured with a differential pressure gauge. As a result of measuring the pressure loss of only the oxidation catalyst, it was found that the pressure loss was almost negligible, and most of the pressure loss was caused by the exhaust particulate filter.

After the gas flow test, the temperature was raised in an electric furnace from room temperature to 700 ° C. while flowing a gas simulating a region where the air-fuel ratio was close to the theoretical air-fuel ratio. The distribution gas composition was converted to the oxygen content of 0.5 vol%, carbon monoxide 0.5 vol%, nitrogen monoxide 800 volppm, and the balance nitrogen. Water was added to this so that it would be 3 vol% in terms of gas standard state volume with respect to the total amount of gas. The space velocity of gas distribution was 30000 h ⁻¹ .

  After these tests, the sulfur-absorbing material was pulverized and the sulfur content in the powder was quantified using a sulfur analyzer. As a result, 99.4% of the amount initially added with sulfur dioxide was detected.

  The pressure loss before and after the glass reaction tube during the test was about 1.3 kPa.

  From these results, it can be seen that almost all the sulfur content is absorbed by the sulfur content-absorbing material and does not desorb at 700 ° C. or lower. Further, the pressure loss during the flow of these gases is 0.65 kPa / cm per filter length, which is a sufficiently practical pressure loss region.

  A 30% acidic titania sol was mixed with strontium acetate dissolved in an acetic acid aqueous solution to prepare a dip solution. Silica fibers were immersed in this solution and pulled up at a speed of 10 mm / min. This was dried at 120 ° C. for 24 hours and then calcined at 600 ° C. for 1 hour. This was immersed in a potassium acetate solution, dried and fired at 650 ° C. to obtain a fibrous sulfur content-absorbing material. After the fibers were aligned, the exhaust particulate filter integrated with the sulfur content-absorbing material was prepared by inserting it into the hole on the outlet side of the exhaust particulate filter.

  A cordierite honeycomb was wash-coated with a mordenite slurry in an amount of 200 g / L. A hexaammine platinum solution was used for this and impregnated so as to be 2.5 g / L in terms of platinum weight. This was calcined at 600 ° C. for 1 hour to obtain an oxidation catalyst.

  Similarly to Example 1, sulfur content absorption processing in a region where the air-fuel ratio containing sulfur dioxide is large and sulfur content desorption processing in a region where the air-fuel ratio is close to the theoretical air-fuel ratio were performed. As a result, the sulfur absorbed and retained in the sulfur content absorbing material was 99.1% or more of the initial charge. In this case, the pressure loss in the exhaust particulate filter was 0.55 kPa / cm.

  As can be seen from this example, even if a fibrous sulfur content absorbing material is used, an exhaust particulate filter capable of absorbing sulfur content effectively with a sufficiently small pressure loss can be configured.

  An oxidation catalyst having the same composition as that of Example 1 and an exhaust particulate filter integrated with a sulfur content absorbing material were used. However, both were 0.9L and 2.1L as the honeycomb for actual vehicles, respectively. A nitrogen oxide purification catalyst was arranged on the downstream side of these, and the time dependence of the nitrogen oxide purification performance of diesel engine exhaust was investigated.

  The test was conducted with 400 ppm thiophene added to the fuel for acceleration. The total sulfur content in the fuel after addition of thiophene is about 150 wtppm in terms of sulfur.

  The engine was operated for 1 minute at an air-fuel ratio of 14, and then a cycle of operating at an air-fuel ratio of 6 for 10 seconds was repeated. The operation was continued for a certain time, gas was sampled from before and after the nitrogen oxide purification catalyst, and the amount of nitrogen oxide was analyzed to determine the nitrogen oxide purification rate at the catalyst.

  FIG. 5 shows the change in the nitrogen oxide purification rate when the above operation pattern is carried out for a long time. For comparison, the change in the nitrogen oxide purification rate when the same test was conducted with the configuration of the oxidation catalyst, exhaust purification catalyst, and nitrogen oxide purification catalyst without inserting the sulfur content absorbing material into the exhaust particulate filter was also combined. Show. As can be seen from the figure, when the exhaust particulate filter filled with the sulfur content-absorbing material is not inserted, the purification rate decreases as the operating time elapses, while the sulfur content-absorbing material and the oxidation catalyst are combined with the nitrogen oxide purification catalyst. When installed upstream, the purification rate hardly decreases.

  INDUSTRIAL APPLICABILITY The present invention can be used for an exhaust gas purification apparatus for an internal combustion engine. In particular, when a nitrogen oxide purification catalyst is poisoned by a sulfur content, such as a diesel engine, exhaust gas that has been regenerated by a special method in the past. It can be used in a purification device.

1 is an example of an exhaust emission control device according to the present invention. It is another example of the exhaust gas purification apparatus by this invention. It is an example (schematic diagram) of the exhaust particulate filter which integrated the sulfur content absorption material. It is another example (schematic diagram) of the exhaust particulate filter which integrated the sulfur content absorption material. Time change of purification rate of nitrogen oxide purification catalyst when using an exhaust purification filter integrated with a sulfur content absorbing material according to the present invention, and time of purification rate when a conventional sulfur content absorbing material is not used as a comparison It is the figure which showed the change.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine, 2 ... Exhaust passage, 3 ... Oxidation catalyst, 4 ... Exhaust particulate filter which integrated sulfur content absorption material, 5 ... Nitrogen oxide purification catalyst, 11 ... Honeycomb wall of exhaust particulate filter, 12 ... Exhaust particulate Filter sealing, 13 ... Sulfur content absorbing material (granular), 14 ... Mesh, 15 ... Inlet side honeycomb hole of exhaust particulate filter, 16 ... Exit side honeycomb hole of exhaust particulate filter, 17 ... Sulfur content absorbing material (fibrous) ).

Claims (6)

An exhaust particulate filter that removes particulates contained in the exhaust from the internal combustion engine;
In the exhaust gas purification apparatus having a nitrogen oxide purification catalyst disposed on the gas downstream side of the exhaust particulate filter and purifying nitrogen oxide in the exhaust gas,
The exhaust particulate filter is composed of a honeycomb, and the exhaust purification device is characterized in that a void content of the honeycomb is filled with a sulfur-absorbing material that absorbs sulfur but does not substantially release it. The exhaust emission control device according to claim 1,
An exhaust emission control device, wherein the sulfur content absorbing material is filled in a honeycomb at a filling rate of 30 to 80%. The exhaust emission control device according to claim 1,
2. The exhaust gas purification apparatus according to claim 1, wherein the sulfur content absorbing material is fibrous or granular. The exhaust emission control device according to any one of claims 1 to 3,
An exhaust emission control device comprising an oxidation catalyst for oxidizing sulfur dioxide to sulfur trioxide. The exhaust emission control device according to claim 4,
The exhaust purification apparatus according to claim 1, wherein the oxidation catalyst is installed upstream of the exhaust of the sulfur-absorbing material. The exhaust emission control device according to any one of claims 1 to 5,
The exhaust gas purification apparatus, wherein the internal combustion engine is a diesel engine.

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