JP2007111620A - Sulfur absorbing material, and exhaust emission control device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device in which nitrogen oxide purifying catalyst is not subjected to sulfur poisoning in an exhaust emission control system of a diesel engine or the like. <P>SOLUTION: A carrier capable of absorbing sulfur content and a material with sulfur absorbing content immersed therein are used for a sulfur absorbing material. The sulfur absorbing material is installed on the upstream side of the exhaust emission with respect to the nitrogen oxide purifying catalyst. Sulfur poisoning of the nitrogen oxide purifying catalyst is prevented by eliminating the substantial desorption of the once-absorbed sulfur in the situation of a regular internal combustion engine. By combining the oxidation catalyst, the performance of the sulfur content absorbing material can be further enhanced. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a material that absorbs sulfur contained in exhaust gas from an internal combustion engine, and to an apparatus that purifies exhaust gas from the internal combustion engine using the material.

  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 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 No. 2745985 (Patent Document 2) is provided with a means for estimating the amount of sulfur absorbed in the nitrogen oxide purification catalyst, and when a sulfur content exceeding the 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 on the upstream side 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.

Japanese Patent No. 2605586 Japanese Patent No. 2745985 Japanese Patent No. 2727914

  However, in these methods of removing the sulfur content once absorbed by the catalyst, the air-fuel ratio is controlled to be close to the theoretical air-fuel ratio when removing the sulfur content, so that a large amount of fuel is consumed, resulting in deterioration of fuel consumption. . In addition, since such a desorption treatment requires a high temperature of 650 ° C. or higher, there is a possibility that sintering may occur in the noble metal in the nitrogen oxide catalyst, and there is a concern that the catalyst characteristics may be deteriorated.

  These methods also require control over sulfur removal, which contributes to the complexity of exhaust treatment related systems.

  The above-mentioned problem is that a material that absorbs sulfur is installed upstream of the exhaust for the nitrogen oxide catalyst that is subject to sulfur poisoning, and the sulfur contained in the fuel is absorbed in this material. This can be solved by not substantially desorbing.

  As a specific sulfur content-absorbing material, a carrier composed of a material that does not substantially release a sulfur content-absorbing component mainly composed of an alkali metal and / or an alkaline earth metal, all or part of which absorbs the sulfur content. It is achievable by making it contain. This material is supported using a honeycomb structure and can be installed in an exhaust system of an internal combustion engine.

  As a specific example of the material that does not substantially release the sulfur component used for the carrier, a composite oxide containing an alkali metal and / or an alkaline earth metal can be used. Further, a mixture of an alkali metal and / or alkaline earth metal carbonate and an oxide of one or more other elements can be used. Alternatively, it is possible to use a mixture of a composite oxide containing an alkali metal and / or alkaline earth metal, an alkali metal and / or alkaline earth metal carbonate, and an oxide of one or more other elements. is there. Furthermore, alkaline earth metal carbonates can be used.

  Specific examples of the alkali metal in the composite oxide used as all or part of the support material include lithium, sodium, potassium, rubidium, and cesium. Specific examples of the alkaline earth metal in the composite oxide or carbonate include magnesium, calcium, strontium, and barium.

  In addition, it is possible to use these sulfur absorbing materials more effectively by installing an oxidation catalyst that oxidizes sulfur dioxide to sulfur trioxide on the upstream side of the exhaust with respect to the installation positions of these sulfur absorbing materials. It is. Alternatively, the oxidation catalyst can be used in a form integrated with the sulfur absorbing material.

  As described above, by installing such a sulfur content absorbing material, or a sulfur content absorbing material provided with an oxidation catalyst or integrated with the oxidation catalyst, in the exhaust system of the internal combustion engine, a nitrogen oxide purification catalyst In this case, it is necessary to dispose these sulfur-absorbing materials upstream of the exhaust with respect to the nitrogen oxide purification catalyst.

  As an internal combustion engine using this sulfur content absorbing material, application to various types of engines using a fuel containing sulfur content is conceivable, but it is particularly effective in a diesel engine.

  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.

  These sulfur content-absorbing materials can be installed in the exhaust passage with a reduced pressure loss by being supported by the honeycomb structure.

  Alkali metal compounds and / or alkaline earth compounds which are sulfur absorbing components in the sulfur absorbing material shown in the present invention, or a mixture containing them as a main component, easily react with the sulfur content in the exhaust gas and easily react with sulfuric acid. Form a salt. 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.

  Further, by using a material that does not substantially absorb and release sulfur in all or part of the carrier, it becomes possible to absorb sulfur in the carrier together with the sulfur component-absorbing component. The amount of sulfur that can be absorbed by the entire component-absorbing material can be greatly increased compared to the case of using only the absorbing component.

  It is essential that such a carrier does not deteriorate due to water vapor in the exhaust gas at the exhaust gas temperature discharged from the internal combustion engine. Further, it is necessary that the sulfur content is not substantially released from the compound formed by reacting with the sulfur content at the operating temperature and atmosphere. Examples of such a material include a composite oxide containing an alkali metal and / or alkaline earth metal, or a mixture of an alkali metal and / or alkaline earth metal carbonate and an oxide of one or more other elements. Or a mixture of a composite oxide containing an alkali metal and / or alkaline earth metal, an alkali metal and / or alkaline earth metal carbonate, and an oxide of one or more other elements, or an alkaline earth Metal carbonates can be used.

  Examples of the alkali metal element used as the above complex oxide or carbonate include lithium, sodium, potassium, rubidium, and cesium. Similarly, examples of the alkaline earth metal element include magnesium, calcium, strontium, and barium. In the sulfur content-absorbing material using the carrier using these elements, as described above, the compound formed by the reaction with the sulfur content in the exhaust gas from the internal combustion engine does not substantially release the sulfur content under the operating conditions of the internal combustion engine.

  By installing an oxidation catalyst that oxidizes sulfur on the upstream side of the exhaust with respect to the installation position of such a sulfur absorbing material, the absorption capacity of the sulfur absorbing material can be further increased. 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.

  In addition, as described later, the oxidation catalyst can improve the characteristics of the sulfur absorbing material as long as it has a function of converting the sulfur content into sulfur trioxide even if it is integrated with the sulfur absorbing material.

  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.

  FIG. 1 shows an example of an exhaust purification device using a sulfur content absorbing material 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. Sulfur trioxide is absorbed by the subsequent sulfur content absorbing material 4. Since the exhaust gas from which the sulfur content has been removed still contains nitrogen oxides, it is further purified by the downstream nitrogen oxide purification catalyst 5.

  The sulfur component once absorbed by the sulfur component absorbing material 4 is not substantially desorbed from any exhaust composition and temperature, and flows out to the subsequent nitrogen oxide purification catalyst. There is nothing to do. For this reason, the nitrogen oxide purification catalyst is not poisoned by the sulfur content derived from the fuel and exhibits a stable purification performance for a long period of time.

  In this figure, the nitrogen oxide catalyst is drawn away from the preceding oxidation catalyst and sulfur absorbing material, but if the positional relationship is the same as in FIG. 1, the nitrogen oxide purification catalyst is adjacent to the sulfur absorbing material. May be installed.

  For the sulfur content-absorbing material, for example, it is possible to use a material having a structure in which a carrier is coated on an inorganic material honeycomb substrate such as cordierite by some method and a component that absorbs sulfur content is dispersed therein. It is. In addition, it is also possible to use a material having a structure in which a material that absorbs sulfur is dispersed in a granular or fibrous substrate or carrier.

  FIG. 2 shows an example of an exhaust purification device in the case where the oxidation catalyst and the sulfur content absorbing material are integrated. Although similar to FIG. 1, the oxidation catalyst-integrated sulfur absorbing material 8 oxidizes and absorbs the sulfur content discharged from the internal combustion engine. In the oxidation catalyst-integrated sulfur absorbing material, as with the sulfur absorbing material of FIG. 1, the sulfur content once absorbed does not substantially desorb under any conditions thereafter. A nitrogen oxide purification catalyst 5 is installed at the subsequent stage, and, as in FIG. 1, since sulfur does not flow, stable nitrogen oxide purification is possible over a long period of time.

  As for the structure of the oxidation catalyst integrated sulfur absorbing material, for example, as shown in FIG. 3, the oxidation catalyst and the sulfur content absorbing material can be alternately arranged. Further, it is effective to further subdivide and arrange them in a mosaic manner or to arrange them randomly, as long as the oxidation catalyst has a function of oxidizing the sulfur content.

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

Sodium carbonate and anatase titania were weighed to a molar ratio of 2: 1, mixed using a ball mill, and treated in an electric furnace at 650 ° C. for 2 hours. As a result of analysis by powder X-ray diffraction, almost all of the processed powder was sodium titanate (Na ₂ TiO ₃ ).

  This powder was mixed with silica sol and water to prepare a slurry, which was then coated by using a cordierite honeycomb of 400 cells / in 2 to give an amount of 200 g / L. This was impregnated with a mixed solution of sodium nitrate and barium acetate to 11.5 g / L and 68.7 g / L in terms of sodium weight and barium weight, respectively, and then calcined at 650 ° C. for 1 hour in air. A sulfur-absorbing material was used.

  The same 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 quartz glass reaction tube in the order of the oxidation catalyst honeycomb and the sulfur absorbing material honeycomb with respect to the gas flow direction, the temperature was raised 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 40,000 h- ¹ .

  A water trap was provided at the outlet, and a sulfur dioxide analyzer was placed at the subsequent stage to measure the sulfur dioxide concentration.

  The total amount of sulfur in the water trap was measured by the oxygen bomb combustion method, and the total amount of sulfur dioxide measured with a sulfur dioxide analyzer was added to this to determine the amount of sulfur that could not be absorbed by the sulfur-absorbing material. It was 0.5 wt% with respect to the amount.

After the gas flow test, the temperature was raised from normal temperature to 700 ° C. in an electric furnace while flowing a gas simulating a region where the air-fuel ratio was close to the theoretical air-fuel ratio, and the concentrations of sulfur dioxide and hydrogen sulfide were measured. The flow 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 might 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 40,000 h- ¹ .

  The total sulfur amount in the water trap at the outlet, the analysis value of the sulfur dioxide analyzer, and the analysis value of hydrogen sulfide were 0.01 wt% with respect to the above-mentioned added sulfur content. .

  After these tests, the sulfur absorbing material was ground 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.

  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.

Lithium nitrate, calcium nitrate tetrahydrate and zirconia powder were weighed to a molar ratio of 2: 1: 2 and mixed by a ball mill. This is 700 ° C in an electric furnace. Time processed. As a result of analysis by powder X-ray diffraction, a mixture of lithium zirconate (Li ₂ ZrO ₃ ), lithium carbonate, calcium zirconate (CaZrO ₃ ), calcium carbonate and zirconia was obtained.

  In the same manner as in Example 1, this powder was wash coated on a cordierite honeycomb at an amount of 180 g / L, and further impregnated with potassium nitrate and barium acetate to prepare a sulfur absorbing material.

  Cordierite honeycombs were wash coated with mordenite having a Si / Al ratio of 200 in an amount of 160 g / L. This was impregnated with a chloroplatinic acid solution so that platinum would be 2.6 g / L. This was calcined at 600 ° C. for 1 hour in a hydrogen stream 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 by the sulfur content absorbing material was 99.5% or more of the initial charge.

  As can be seen from this example, it is possible to use a mixture composed of a complex oxide of an alkali metal, a carbonate of an alkali metal and an alkaline earth metal, and an oxide of another element as the carrier of the sulfur absorbing material. .

Barium acetate and niobium pentoxide were weighed to a molar ratio of 1: 1, mixed by a ball mill, and then treated at 750 ° C. for 1 hour in an electric furnace. As a result of analysis by powder X-ray diffraction, the treated powder was a mixture of barium niobate (BaNb ₂ O ₆ ), barium carbonate, and niobium pentoxide.

  This powder was wash coated on the honeycomb in the same amount as in Example 1, but in an amount of 150 g / L, and further impregnated in the same manner as in Example 1 to obtain a sulfur content absorbing material.

  An oxidation catalyst was prepared as in Example 2, except that mesoporous silica (MCM-41) was used as the support.

  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 99.2% or more of the initial charge.

  Basic magnesium carbonate was heat-treated at 600 ° C. for 2 hours in a carbon dioxide stream. As a result of analysis by powder X-ray diffraction, the composition of the powder after the treatment was magnesium carbonate.

  This powder was wash-coated on the honeycomb in the same amount as in Example 1, but in an amount of 150 g / L, and a sulfur-absorbing component was impregnated in the same manner as in Example 1 to prepare a sulfur-absorbing material.

  Using a cordierite honeycomb of 400 cells / in 2, zirconia powder was washcoated in an amount of 180 g / L. A dinitrodiammine platinum solution was used for this and impregnated so as to be 2.5 g / L of platinum. This was calcined in air at 600 ° C. for 1 hour to obtain an oxidation catalyst.

  In the same manner as in 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. However, the absorption temperature was 350 ° C. and the absorption time was 1 hour. As a result, the sulfur absorbed and retained in the sulfur content absorbing material was 99.8% or more of the initial charge.

  As can be seen in this example, an alkaline earth metal carbonate can be used as a support for the sulfur-absorbing material.

Strontium carbonate and 20% titania sol were weighed so that the molar ratio of strontium and titanium was 1: 1 and mixed by a ball mill. This was treated in an electric furnace at 650 ° C. for 1 hour. As a result of analysis by powder X-ray diffraction after the treatment, the composition of the powder was all strontium titanate (SrTiO ₃ ).

  This powder was wash-coated in the same manner as in Example 1, but in an amount of 175 g / L, and a sulfur-absorbing component was impregnated as in Example 2 to obtain a sulfur-absorbing material.

  As in Example 2, except that silica coated with 160 g / L on the support was used as 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 by the sulfur content absorbing material was 99.4% or more of the initial charge.

Rubidium nitrate, cesium nitrate and rutile type titania were weighed so as to have a molar ratio of 1: 1: 1, mixed by a ball mill, and then treated at 700 ° C. for 1 hour in an electric furnace. As a result of analysis by powder X-ray diffraction, the composition of the powder was a mixture of rubidium titanate (Rb ₂ TiO ₃ ), cesium titanate (Cs ₂ TiO ₃ ), rubidium carbonate and titania.

  This powder was used to wash coat the honeycomb in an amount of 150 g / L in the same manner as in Example 1, and impregnated with a sulfur content-absorbing component as in Example 1 to obtain a sulfur content-absorbing material.

  As in Example 2, except that silica coated with 200 g / L on the support was used as 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 99.2% or more of the initial charge.

Calcium carbonate and 20% silica sol were weighed so that the molar ratio of calcium to silicon was 1: 1, mixed with a ball mill, and then treated in an electric furnace at 750 ° C. for 1 h. As a result of performing powder X-ray diffraction on the obtained powder, the composition was a mixture of calcium silicate (CaSiO ₃ ), calcium carbonate and silica.

Potassium acetate and zirconia powder were weighed to a molar ratio of 2: 1, mixed with a ball mill, and then treated in an electric furnace at 700 ° C. for 1 hour. As a result of analyzing the composition of the obtained powder by powder X-ray diffraction, all were potassium zirconate (K ₂ ZrO ₃ ).

  These two kinds of heat-treated powders were mixed and slurried, and washed on a cordierite honeycomb of 400 cells / square inch at an amount of 180 g / L. This was impregnated with a sulfur-absorbing component in the same manner as in Example 1 to obtain a sulfur-absorbing material.

  Further, an oxidation catalyst was prepared in the same manner as in Example 3.

  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 by the sulfur content absorbing material was 99.5% or more of the initial charge.

Barium hydroxide octahydrate and anatase-type titania were weighed so as to have a molar ratio of 2: 1, mixed with a ball mill, and then treated in an electric furnace at 950 ° C. for 1 hour. As a result of analyzing the composition of the treated powder by powder X-ray diffraction, it was a mixture of barium titanate (BaTiO ₃ ), barium orthotitanate (Ba ₂ TiO ₄ ), and barium carbonate.

  This powder was slurried and washed on the honeycomb in the same manner as in Example 1 and then impregnated with a sulfur-absorbing component to obtain a sulfur-absorbing material.

  An oxidation catalyst was prepared in the same manner as in Example 2.

  Using these, 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 99.3% or more of the initial charge.

  Using a sulfur component absorbing material and an oxidation catalyst having the same composition as in Example 1, a total of six layers of the oxidation catalyst and the sulfur component absorbing material were alternately arranged as shown in FIG.

  As a result of the same sulfur content absorption and desorption treatment as in Example 1, the sulfur absorbed and retained by the sulfur content absorbing material was 99.6% or more of the initial charge.

  Using an oxidation catalyst and a sulfur content-absorbing material having the same composition as in Example 1, a nitrogen oxide purification catalyst was disposed on the downstream side thereof, and the time dependence of the nitrogen oxide purification performance of diesel engine exhaust was examined.

  The test was performed 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. 4 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 of the nitrogen oxide purification rate when the same test is carried out with the nitrogen oxide purification catalyst alone without inserting an oxidation catalyst and a sulfur content absorbing material is also shown. As can be seen from the figure, the purification rate of the nitrogen oxide purification catalyst alone decreases with the passage of operating time, whereas the purification rate when the sulfur absorbing material and the oxidation catalyst are installed upstream of the nitrogen oxide purification catalyst. Is hardly reduced.

  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.

An example of the exhaust gas purification apparatus using the sulfur content absorption material by this invention. An example of an exhaust purification device in which a sulfur content absorbing material and an oxidation catalyst are integrated. An example of the structure of the sulfur content absorption material integrated with the oxidation catalyst. The figure which showed the time change of the purification rate of a nitrogen oxide purification catalyst at the time of using the oxidation catalyst by this invention, and a sulfur content absorption material, and the time change of the purification rate by the conventional nitrogen oxide purification catalyst alone as a comparison It is.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine, 2 ... Exhaust passage, 3 ... Oxidation catalyst, 4 ... Sulfur content absorption material, 5 ... Nitrogen oxide purification catalyst, 6 ... Oxidation catalyst integrated sulfur content absorption material.

Claims (14)

  A material for absorbing sulfur contained in exhaust gas from an internal combustion engine, wherein the sulfur content absorbing material uses a sulfur content-absorbing component mainly composed of an alkali metal compound and / or an alkaline earth metal compound. A sulfur content-absorbing material characterized in that a material that does not substantially absorb and release is used for all or part of the carrier.   2. The sulfur content absorbing material according to claim 1, wherein the sulfur content absorbing material is supported by a honeycomb structure.   3. The sulfur-absorbing material according to claim 1 or 2, wherein the material that does not substantially release by absorbing the sulfur used as the carrier is a composite oxide containing an alkali metal and / or an alkaline earth metal. .   3. The material according to claim 1 or 2, wherein the material that does not substantially absorb and release sulfur used as the carrier is an alkali metal and / or alkaline earth metal carbonate and an oxide of one or more other elements. A sulfur content-absorbing material characterized by being a mixture.   3. The composite oxide containing an alkali metal and / or an alkaline earth metal, and an alkali metal and / or an alkaline earth metal according to claim 1 or 2, wherein the material that absorbs sulfur and does not substantially release the carrier is used. A sulfur content-absorbing material, characterized in that it is a mixture of a carbonate of the above and an oxide of one or more other elements.   The sulfur content-absorbing material according to claim 1 or 2, wherein the material that absorbs and does not substantially release the sulfur component used as the carrier is an alkaline earth metal carbonate.   6. The sulfur content-absorbing material according to claim 1, wherein the alkali metal is at least one of lithium, sodium, potassium, rubidium, and cesium.   7. The sulfur content-absorbing material according to claim 1, wherein the alkaline earth metal is at least one of magnesium, calcium, strontium, and barium.   It is a sulfur content absorption material of Claim 1-8, Comprising: The oxidation catalyst which oxidizes sulfur dioxide to sulfur trioxide with the said material is attached, The sulfur content absorption material characterized by the above-mentioned.   The sulfur content-absorbing material according to claim 9, wherein the oxidation catalyst is installed on the upstream side of the exhaust gas from the installation position of the sulfur content-absorbing material.   In Claim 9, The said oxidation catalyst is united with the said sulfur content absorption material, The sulfur content absorption material characterized by the above-mentioned.   An exhaust emission control device, wherein the sulfur content absorbing material according to claim 1 is installed in an exhaust gas purification system of an internal combustion engine to absorb sulfur content contained in exhaust gas from the internal combustion engine.   13. The exhaust emission control device according to claim 12, wherein the installation position of the sulfur content absorbing material is installed upstream of the exhaust gas from the nitrogen oxide purification catalyst installed in the same internal combustion engine. .   The exhaust emission control device according to claim 12 or 13, wherein the internal combustion engine is a diesel engine.

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