JP2006272116A - Exhaust gas purifying apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive exhaust gas purifying apparatus capable of removing nitrogen oxides in the exhaust gas efficiently in e.g. an internal engine or combustion equipment operated practically under excess-air conditions. <P>SOLUTION: A nitrogen oxide adsorbent 4 is arranged in the exhaust duct. The adsorbent 4 comprises a lithium compound oxide of formula LiAxOy or LiAxPO<SB>4</SB>(wherein A is at least one selected from manganese(Mn), nickel(Ni), cobalt(Co), vanadium(V), chromium(Cr), iron(Fe), titanium(Ti), scandium(Sc) and yttrium(Y)), typically lithium manganate(LiMn<SB>2</SB>O<SB>4</SB>), lithium titanate(Li<SB>2</SB>TiO<SB>3</SB>) and lithium manganese phosphate(LiMnPO<SB>4</SB>). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an internal combustion engine such as a diesel engine, a gas engine, a gasoline engine, or a gas turbine engine, or an apparatus for purifying exhaust gas of combustion equipment such as an incinerator or a boiler, and more particularly to an internal combustion engine that performs normal operation in an excess air state. The present invention relates to an exhaust gas purification device suitable for removing nitrogen oxides.

  Substances that are subject to exhaust gas purification are particulate substances such as nitrogen oxides, carbon monoxide, unburned hydrocarbons, and soot. Various devices for purifying these substances have been developed in the past.

  As a device for reducing nitrogen oxide (NOx), a denitration device that selectively reduces nitrogen oxide by installing a reduction catalyst using ammonia or urea as a reducing agent in the exhaust passage has been put into practical use. Yes. In addition, relatively small gas engines and gasoline engines for automobiles have developed three-way catalysts capable of simultaneously decomposing nitrogen oxides, carbon monoxide (CO), and unburned hydrocarbons (HC). Contributes to effective gas purification.

  However, the three-way catalyst exhibits a purification action effectively when operated within the stoichiometric air-fuel ratio or a range close thereto, but is effective under other conditions, particularly in exhaust gas with excessive air (oxygen). It has been found that it does not work.

  In order to cope with this, in a gas or gasoline engine operated in an excess air condition, nitrogen oxide is temporarily occluded in the occlusion material during operation in an excess air (oxygen) condition, and then an excess fuel condition. A nitrogen oxide storage catalyst system that releases and reduces the stored nitrogen oxides by operating at a low pressure has been put into practical use.

As the nitrogen oxide storage catalyst type catalyst, various combinations of noble metals and alkali metal oxides or alkaline earth metal oxides have been conventionally developed (see Patent Document 1). In the case of excess air combustion in normal operation (lean combustion), these catalysts oxidize NO in exhaust gas on a noble metal catalyst to NO ₂ , and the NO ₂ is basic of alkali metal or alkaline earth metal. It reacts with oxides and occludes NOx as nitrates. Then, NO ₂ desorbed from the oxide during regeneration operation under rich fuel conditions (during rich operation) is reduced to N ₂ on the noble metal catalyst by a reducing substance such as hydrocarbon or CO and released in a detoxified state. ing.
JP 2001-000863 A

  A denitration device that selectively reduces nitrogen oxides using ammonia, urea, etc. is applied to relatively large industrial internal combustion engines and combustion equipment, but the device itself is large and very expensive. In addition, maintenance costs for the reducing agents ammonia and urea are also increased. Furthermore, there is a high possibility that ammonia that is not consumed is released into the atmosphere.

  As described above, the three-way catalyst does not exhibit a catalytic function in an internal combustion engine or a combustion device that is operated under an excess air condition.

  In the nitrogen oxide storage catalyst system that is put into practical use in the small gas engine and the gasoline engine for automobiles, since the precious metal is always included as a component of the catalyst, the purification device becomes expensive and can be completely reduced. The operating range (temperature, SV value, etc.) to be obtained is limited to a narrow range, and complicated lean / rich control (control of the supply amount of air and fuel) is required on the engine side.

(Object of invention)
It is an object of the present invention to provide an exhaust gas purification device that can efficiently remove nitrogen oxides in exhaust gas and render it harmless and discharged at an inexpensive cost in an internal combustion engine or combustion equipment that operates mainly in an excess air condition. It is to be. Another object of the present invention is to reduce the deterioration of the nitrogen oxide adsorbent due to sulfur poisoning so that the performance can be sufficiently exhibited even with a fuel containing a large amount of sulfur components.

In order to solve the above-mentioned problem, the basic invention described in claim 1 of the present application is an exhaust gas purification device installed in an exhaust passage of an internal combustion engine or a combustion device, wherein a nitrogen oxide adsorbent is disposed in the exhaust passage, Nitrogen oxide adsorbents include manganese (Mn), nickel (Ni), cobalt (Co), vanadium (V), chromium (Cr), iron (Fe), titanium (Ti), scandium (Sc) and yttrium (Y ), A lithium composite oxide represented by the general formula LiAxOy or LiAxPO4 having at least one element A and lithium (Li) as constituent elements. For example, it is formed of a lithium composite oxide such as lithium manganate (LiMn ₂ O ₄ ), lithium titanate (Li ₂ TiO ₃ ), or lithium manganese phosphate (LiMnPO ₄ ).

Complex oxides of alkali metal lithium (Li) and transition metals such as manganese (Mn) are currently manufactured in large quantities as positive electrode materials for lithium ion batteries and are now on the market. Can be obtained. As a result, a reduction in the device cost can be achieved, and the inclusion of a transition metal such as manganese (Mn) makes it easier to react with lattice oxygen, so that NO can be rapidly oxidized to NO _2. The amount of saturated NOx adsorption can be increased, and the NOx adsorption capacity is improved.

  According to a second aspect of the present invention, in the exhaust gas purifying apparatus according to the first aspect, a noble metal is added to the nitrogen oxide adsorbing material.

  When the noble metal is added as in the above configuration, the cost of the apparatus is higher than when no noble metal is included, but the entire nitrogen oxide adsorbent is inexpensive and the positive electrode of a lithium ion battery that is distributed in large quantities on the market. By using the material, it is possible to improve the NOx absorption capacity while suppressing the cost increase.

According to a third aspect of the present invention, in the exhaust gas purifying apparatus according to the second aspect, the noble metal is platinum (Pt), and the lithium composite oxide is lithium titanate (Li ₂ TiO ₃ ).

By using lithium titanate to which platinum is added as a noble metal (Pt—Li ₂ TiO ₃ ) as in the above configuration, SOx resistance is improved, nitrogen oxide adsorbent is prevented from being poisoned, and life is increased. Can be extended.

The invention according to claim 4 is the exhaust gas purifying apparatus according to any one of claims 1 to 3, wherein the nitrogen oxide adsorbent is aluminum oxide (Al ₂ O ₃ ) and / or anatase type titanium oxide (TiO _2). ).

When the nitrogen oxide adsorbent is supported on a porous carrier having a large specific surface area as in the above configuration, the NOx absorption capacity is further improved. Anatase-type titanium oxide (TiO ₂ ) is stable at low temperatures and has a large comparative surface area compared to rutile-type titanium oxide that is stable at high temperatures.

The invention according to claim 5 is the exhaust gas purification device according to any one of claims 1 to 4, wherein the nitrogen oxide adsorbent is added in an amount of 10 to 20% by weight as lithium oxide (Li ₂ O). It is.

When lithium oxide (Li ₂ O) is added at a weight ratio as in the above configuration, the NOx absorption capacity is further improved.

  According to a sixth aspect of the present invention, in the exhaust gas purifying apparatus according to any of the first to fifth aspects, the nitrogen oxide adsorbent is fired within a range of 400 ° C to 500 ° C.

  By firing within the temperature range as described above, a large specific surface area can be secured, the amount of saturated NOx adsorption can be increased, and the NOx absorption capacity can be further improved. Most preferably, baking is performed at approximately 450 ° C.

  The invention according to claim 7 is the exhaust gas purifying apparatus according to any one of claims 2 to 6, wherein an adsorbent desorbing means is disposed upstream of the exhaust of the nitrogen oxide adsorbent, and the nitrogen oxide adsorbent A combustion device is disposed downstream of the exhaust.

According to the above arrangement, when that normal operation of the internal combustion engine, particularly but when tends nitrogen oxide ₂ such NO and NO are generated which are usually operated with excess air conditions, the NO and NO ₂ and the like of occurrence Nitrogen oxide is temporarily adsorbed by the nitrogen oxide adsorbent. Then, when the NOx adsorption amount reaches a predetermined value, the nitrogen oxide desorbing means and the combustion device are operated to perform a regeneration operation. In this regeneration operation, first, nitrogen oxides are desorbed by the adsorbed substance desorbing means while the nitrogen oxide adsorbing material is heated or reduced. When no precious metal is contained in the nitrogen oxide adsorbent, most of the nitrogen oxide is desorbed in the form of nitrogen oxides such as NO and NO ₂ , and these desorbed NOx is fuel rich combustion in the downstream combustion device. It is reduced to N ₂ in the area, detoxified and discharged.

In addition, in the regeneration operation, when CO and hydrocarbons are generated in the fuel rich combustion region of the adsorbent desorption means or the combustion device, these CO and hydrocarbons are oxidized in the fuel lean combustion region of the combustion device. To CO ₂ and H ₂ O, detoxified and discharged. Since the combustion temperature is low in the fuel lean combustion region of the combustion apparatus, N2 desorbed by the adsorbed material desorbing means will not be oxidized again and will not return to nitrogen oxides.

  In this way, by arranging the combustion device downstream of the nitrogen oxide adsorbent, even an inexpensive nitrogen oxide adsorbent that does not contain a noble metal can be used in the exhaust gas in the same manner as when a catalyst containing a noble metal is used. The nitrogen oxides can be detoxified and discharged, which is economical. Moreover, normal operation and regeneration operation can be performed without performing complicated lean / rich control on the engine side.

  The invention according to claim 8 is the exhaust gas purifying apparatus according to claim 2, wherein the combustion apparatus is a fuel lean combustion system.

According to the above configuration, when the nitrogen oxide adsorbent contains a noble metal, most of the substance desorbed from the nitrogen oxide adsorbent is reduced to the N ₂ state by the catalytic action of the noble metal, and therefore The combustion device disposed on the downstream side may be a combustion device that performs only lean fuel combustion that renders only CO and hydrocarbons harmless, thereby saving fuel consumption.

  According to a ninth aspect of the present invention, in the exhaust gas purifying apparatus according to any one of the third to seventh aspects, the temperature of the adsorbed substance desorbing means is set near or below the firing temperature. For example, when the firing temperature is 450 ° C., control is performed so as to burn near 450 ° C. or lower.

  As in the above configuration, by suppressing the temperature at the time of desorption of nitrogen oxides to near or below the firing temperature, sintering and loss of lithium (Li) are prevented, thereby suppressing performance deterioration and nitrogen oxidation. The life of the material adsorbent can be extended.

  According to a tenth aspect of the present invention, in the exhaust gas purifying apparatus according to the first aspect, a sulfur oxide adsorbing material is disposed on the exhaust upstream side of the nitrogen oxide adsorbing material.

With the above configuration, during normal operation of the internal combustion engine, sulfur oxide in the exhaust gas is adsorbed by the sulfur oxide adsorbent before reaching the nitrogen oxide adsorbent, so the nitrogen oxide adsorbent is sulfur poisoned. It is possible to prevent a decrease in the adsorption amount of nitrogen oxides due to sulfur poisoning. In addition, durability is improved. In particular, lithium composite oxides composed of transition metal elements other than titanium (Ti) (for example, LiMn ₂ O ₄ ) have lower SOx absorbability than those containing titanium (Ti). By arranging the sulfur oxide adsorbent, poisoning of the nitrogen oxide adsorbent can be prevented.

  An eleventh aspect of the present invention is the exhaust gas purifying apparatus according to the tenth aspect, wherein the sulfur oxide adsorbing material includes copper oxide and zirconium oxide.

  According to the above configuration, since the copper oxide and the zirconium oxide have an excellent ability to absorb sulfur oxide (SOx), the amount of sulfur oxide adsorbed can be increased.

  According to a twelfth aspect of the present invention, in the exhaust gas purifying apparatus according to the eleventh aspect, the sulfur oxide adsorbing material has a metal ratio of copper to zirconium of 1: 1.

  With the above configuration, the amount of sulfur oxide adsorbed can be increased.

  The invention according to claim 13 is the exhaust gas purifying apparatus according to claim 11 or 12, wherein an adsorbent detachment means is disposed upstream of the sulfur oxide adsorbent, and the exhaust gas downstream of the nitrogen oxide adsorbent. A combustion device is arranged in

  Because copper oxide and zirconium oxide can reversibly absorb and desorb sulfur oxides, exhaust gas purification with nitrogen oxide desorption means upstream of the nitrogen oxide adsorbent and combustion device downstream In the equipment, by switching between normal operation and regeneration operation, nitrogen oxide is adsorbed by the nitrogen oxide adsorbent at the same time as excessive air combustion in normal operation, and at the same time, sulfur oxide is adsorbed by the sulfur oxide adsorbent, At the time of excessive fuel combustion in the regeneration operation, nitrogen oxides and sulfur oxides adsorbed on the respective adsorbents are desorbed, and the nitrogen oxides can be rendered harmless by the downstream combustion device and discharged.

  In short, according to the present invention, by using a lithium composite oxide containing lithium (Li) used as a positive electrode material of a lithium ion battery and a transition metal such as manganese (Mn) as a nitrogen oxide adsorbent, An inexpensive nitrogen oxide adsorbing material having a good NOx absorption capacity can be provided, whereby an exhaust gas purifying apparatus having a low amount of saturated NOx adsorption can be provided. In particular, by using lithium titanate to which platinum is added as a lithium titanium composite oxide, or by arranging a sulfur oxide adsorbent on the exhaust upstream side of the nitrogen oxide adsorbent, the nitrogen oxide adsorbent It can also prevent poisoning.

[First Embodiment of the Invention]
FIG. 1 shows an embodiment of an exhaust gas purifying apparatus according to the present invention. An exhaust passage 2 of an internal combustion engine 1 or combustion equipment is branched into first and second branched exhaust passages 2a and 2b. A switching valve 20 is provided in the branch portion on the exhaust upstream side, and both branch exhaust passages 2a and 2b merge at the end portion on the exhaust downstream side and are connected to the downstream exhaust passage 2c. By switching the switching valve 20, the exhaust gas from the internal combustion engine 1 is selectively discharged to one of the branch exhaust passages 2a and 2b, and the remaining branch exhaust passage can be regenerated. Examples of the internal combustion engine 1 include a diesel engine, a gas engine, a gasoline engine, and a gas turbine engine, and examples of the combustion equipment include an industrial boiler. These are operated mainly under an excess air condition.

  In each of the branch exhaust passages 2a and 2b, the adsorbed substance desorbing means 3, the particulate adsorption filter 40, the nitrogen oxide adsorbing material (hereinafter referred to as “NOx adsorbing material”) 4 and the combustion device 5 are sequentially arranged from the exhaust upstream side. Are arranged at intervals in the exhaust flow direction.

The NOx adsorbent 4 is a transition metal, particularly manganese (Mn), nickel (Ni), cobalt (Co), vanadium (V), chromium (Cr), iron (Fe), titanium (Ti), scandium (Sc). And lithium complex oxide represented by the general formula LiAxOy or LiAxPO ₄ having at least one element A and lithium (Li) as constituent elements in the element group of yttrium (Y). Specific examples of the general formula LiAxOy include, for example, lithium manganate (LiMn ₂ O ₄ ) and lithium titanate (Li ₂ TiO ₃ ). Specific examples of the general formula LiAxPO ₄ include phosphorus There are lithium manganese oxide (LiMnPO ₄ ) and the like.

In the present embodiment, a material obtained by adding platinum (Pt), a noble metal, to the lithium composite oxide is used. Further, in order to maintain high NOx absorption capacity and SOx resistance, a lithium composite oxide is used. Lithium titanate (Li ₂ TiO ₃ ) containing titanium (Ti) as a constituent element is used.

The nitrogen oxide adsorbent 4 has an addition amount of 10 to 20% by weight as lithium oxide Li ₂ O, and is fired within a range of 400 ° C. to 500 ° C. Preferably, baking is performed at approximately 450 ° C.

In this embodiment, the platinum and lithium titanate (Li ₂ TiO ₃ ) are supported on a carrier made of aluminum oxide (Al ₂ O ₃ ) and / or anatase-type titanium oxide (TiO ₂ ).

  The adsorbed substance desorbing means 3 arranged on the most upstream side of the exhaust gas is composed of a fuel nozzle 31, an ignition device 32 and an air supply means 33. The fuel nozzle 31 is connected to the fuel tank 11 via the fuel metering device 10. The fuel supply amount and supply timing are controlled by an electronic control unit (hereinafter referred to as “ECU”) 12. The air supply means 33 is connected to the air supply source 17 via the air metering device 16, and the air metering device 16 is controlled by the ECU 12 in the amount and timing of air supply. By controlling the fuel supply amount and the supply timing and the air supply amount and the supply timing as described above, for example, fuel rich combustion is performed, and the temperature in the corresponding branch exhaust passage 2a or 2b is raised and simultaneously reduced atmosphere. can do.

  The fuel supply amount and the air supply amount are set so that the combustion temperature of the adsorbed substance desorbing means 3 is close to or lower than the firing temperature (400 ° C. to 500 ° C.) of the nitrogen oxide adsorbent 4. It is. For example, if the firing temperature is 450 ° C., it is set to around 450 ° C. or lower.

  The combustion device 5 arranged on the most downstream side includes a fuel nozzle 6, an ignition device 7, and an air supply means 15, and when the combustion device 5 is in an operating state, there is excess fuel on the exhaust upstream side and downstream side of the air supply means 15. A rich combustion region X1 and a fuel lean combustion region X2 can be formed. The fuel nozzle 6 is connected to a fuel tank 11 via a fuel metering device 10, and a fuel supply amount and a supply timing are controlled by an electronic control unit 12. The air supply means 15 is connected to an air supply source 17 via an air metering device 16, and the air metering device 16 is controlled by the ECU 12 for the air supply amount and the supply timing.

  When the NOx adsorbent 4 does not contain a noble metal such as platinum, the combustion device 5 has the fuel rich combustion region X1 and the fuel lean combustion on the exhaust upstream side and downstream side of the air supply means 15 as described above. The fuel supply amount and the air supply amount are controlled so as to form the region X2, but when the NOx adsorbent 4 contains a noble metal such as platinum as in the present embodiment, the fuel supply amount is reduced. It is also possible to control so that only the lean fuel combustion region X2 is formed by increasing the air supply amount.

(Operation of the embodiment)
When the internal combustion engine 1 is operated, the switching valve 20 switches the connection destination of the exhaust passage 2 so that one of the branch exhaust passages 2a and 2b is used as the exhaust gas exhaust passage of the internal combustion engine 1, while the other Will regenerate as needed. The state shown in FIG. 1 is a state where the second branch exhaust passage 2b is used as an exhaust gas discharge passage of the internal combustion engine 1 and the first branch exhaust passage 2a is used for a regeneration operation.

  During the operation of the internal combustion engine 1, the combustion device 5 and the adsorbed substance desorbing means 3 are stopped in the second branch exhaust passage 2b used as the exhaust gas exhaust passage in FIG. The internal combustion engine 1 is operated under an excess air condition, and therefore, there is a high possibility that a large amount of NOx is contained, although there is little CO or the like in the exhaust gas. The exhaust gas flows into the second branch exhaust passage 2b from the exhaust passage 2, and first, particulate matter is removed by the particulate filter 40, and NOx is adsorbed by the NOx adsorbent 4, and is downstream in a detoxified state. Is discharged through the exhaust passage 2c.

  On the other hand, in the first branch exhaust passage 2a to be regenerated, the combustion device 5 and the adsorbed substance desorbing means 3 are operated. In the adsorbed substance desorbing means 3, the fuel from the fuel nozzle 31 is supplied to the air supply means 33. By burning with air from the high temperature, high temperature air is supplied to the NOx adsorbent 4, and NOx is desorbed from the NOx adsorbent 4. That is, the NOx adsorbent 4 is regenerated. In this case, since the combustion temperature of the adsorbed material desorbing means 3 is near or below the firing temperature of the NOx adsorbent 4, sintering does not occur and lithium (Li) does not disappear.

  When platinum (Pt) is added to the NOx adsorbent 4 as in the present embodiment, during the regeneration operation, NOx is reduced to N2 by the catalytic action of platinum and desorbed in a detoxified state. And discharged.

When no noble metal is added to the NOx adsorbent 4, the combustion device 5 forms the fuel rich combustion region X1 and the fuel lean combustion region X2 as described above. NOx desorbed from the fuel is reduced to N ₂ in the fuel rich combustion region X1.

In the fuel lean combustion region X2 of the combustion apparatus 5, CO and hydrocarbons are harmless is oxidized to CO ₂ and H ₂ O, etc., it is discharged. In the lean combustion zone X2, the combustion temperature is low, so that N2 is not oxidized. Further, in the case where no noble metal is added to the NOx adsorbent 4, CO and hydrocarbons may be generated in the fuel rich combustion region X1, and these CO and hydrocarbons are present in the fuel lean combustion region on the downstream side. In X2, it is oxidized and detoxified.

  When the NOx adsorption amount of the NOx adsorbent 4 in the second branch exhaust passage 2b reaches a predetermined amount (saturation amount or a prescribed amount less than that) by performing normal operation several times, the switching valve 20 is switched to the first branch. Switching to the exhaust passage 2a side, the combustion device 5 and the adsorbed material desorbing means 3 in the first branch exhaust passage 2a are stopped, while the combustion device 5 and the adsorbed material desorbing means 3 in the second branch exhaust passage 2b are stopped. To the operating state. That is, the normal operation is performed in the first branch exhaust passage 2a, and the regeneration operation is performed in the second branch exhaust passage 2b at the same time.

(Effect of embodiment)
(1) As shown in FIG. 1, the exhaust passage 2 of the exhaust gas purifying apparatus is branched into two branch exhaust passages 2a and 2b, one of which is used as an exhaust gas exhaust passage during normal operation and the other is exhausted from the engine. Since the regeneration operation is performed by shutting off from the passage 2 and operating the nitrogen oxide desorbing means 3 and the combustion device 5, the air for desorbing the adsorbed material and the air for the combustion device regardless of the amount of exhaust gas from the internal combustion engine 1. The amount can be set, and the fuel supply amount of the adsorbent detachment means 3 and the fuel supply amount in the combustion device 5 can be saved. Of course, the regeneration operation can be performed without performing complicated lean / rich control on the engine side.

(2) Since the particulate filter 40 is disposed upstream of the NOx adsorbent 4, exhaust gas from which particulate matter has been removed by the particulate filter 40 during normal operation (when used as an exhaust gas exhaust passage) Can be caused to flow into the NOx adsorbent 4, and a decrease in the adsorption rate of NOx by the NOx adsorbent 4 can be prevented.

(3) When the noble metal platinum (Pt) is added to the NOx adsorbent 4, the amount of saturated NOx adsorption can be greatly increased. That is, FIG. 3 shows a lithium composite oxide comprising lithium manganate (LiMnO ₃ ) with no precious metal added, lithium manganese phosphate (LiMnPO ₄ ) with no precious metal added, and noble metal platinum (Pt). It is a graph comparing the amount of saturated NOx adsorbed by added lithium titanate (Pt-Li ₂ TiO ₃ ), and is necessary and sufficient for lithium manganate (LiMnO ₃ ) and lithium manganese phosphate (LiMnPO ₄ ) to which no noble metal is added Saturated NOx adsorption amount can be secured, but in the case of lithium titanate (Pt—Li ₂ TiO ₃ ) added with platinum, it is twice that of the lithium manganate (LiMnO ₃ ) and lithium manganese phosphate (LiMnPO ₄ ). 3 times the amount of saturated NOx adsorption can be secured, and the NOx adsorption performance is excellent. Hunt.

(4) When lithium titanate (Li ₂ TiO ₃ ) is used as the NOx adsorbent 4, the NOx adsorbent 4 having excellent SOx resistance can be provided. It can prevent poisoning and extend the life. FIG. 4 is a graph showing the SOx resistance of the NOx adsorbent 4, and the two graphs on the left side described as the present invention are NOx formed of lithium titanate (Pt—Li ₂ TiO ₃ ) added with platinum. The two graphs on the right side, which are adsorbents 4 and described as comparative examples, are NOx adsorbents 4 formed of barium oxide (Pt—BaO system) to which platinum is added, and each hatched graph represents NOx adsorption. When the exhaust gas flowing through the material 4 does not contain SOx, the cross line graph shows the respective saturated NOx adsorption amounts when the exhaust gas flowing through the NOx adsorbent 4 contains 300 ppm of SOx. Yes. As can be understood from the graph of FIG. 4, the NOx adsorbent 4 formed of lithium titanate (Pt—Li ₂ TiO ₃ ) to which platinum is added includes the case where SOx is contained in the exhaust gas, but the SOx is not contained. The same amount of saturated NOx adsorption is secured. On the other hand, in the case of barium oxide (Pt—BaO system) to which platinum is added, when the exhaust gas contains SOx, the saturated NOx adsorption amount is greatly reduced.

(5) FIG. 5 shows a NOx adsorbent 4 formed of lithium titanate (Pt—Li ₂ TiO ₃ ) to which platinum is added, and aluminum oxide (Al ₂ O ₃ ) and / or titanium oxide as a carrier for supporting this. is a graph showing changes in saturation NOx adsorption amount in the case of changing the weight ratio of the (TiO _2), up to 0-80% proportion by weight of carrier, the saturated NOx adsorbed amount in proportion to the increase of the carrier is increasing. Therefore, it is preferable to set the weight ratio of aluminum oxide (Al ₂ O ₃ ) between about 80% or more and about 95%.

(6) FIG. 6 is a graph showing the relationship between the addition amount as lithium oxide (Li ₂ O) and the saturated NOx adsorption amount for the NOx adsorbent 4, and as can be understood from this graph, lithium oxide (Li It can be understood that when the addition amount as ₂ O) is 10 to 20% by weight, the saturated NOx adsorption amount is maintained at a substantially maximum value. Therefore, by adding lithium oxide (Li ₂ O) at 10 to 20% by weight of the entire nitrogen oxide adsorbent, the amount of saturated NOx adsorbed can be increased and the NOx absorption capacity can be improved.

(7) FIG. 7 is a graph showing the relationship between the temperature at which the NOx adsorbent 4 is fired, the specific surface area, and the saturated NOx adsorption amount. The cases where the firing temperature is 450 ° C. and 600 ° C. Comparing. As can be understood from FIG. 7, a larger specific surface area and a larger saturated NOx adsorption / absorption amount are obtained when the firing temperature is 450 ° C. than the case where the firing temperature is 600 ° C., and the NOx absorption capacity is excellent. I understand that.

(8) FIG. 8 is a graph showing the relationship between the temperature of the adsorbed substance desorbing means 3 and the saturated NOx adsorption amount when the firing temperature of the NOx adsorbent 4 is 450 ° C., and near the firing temperature of 450 ° C. It can be seen that the maximum saturated NOx adsorption amount can be obtained, and the saturated NOx adsorption amount rapidly decreases even when the temperature is higher than 450 ° C or lower. However, if the temperature of the adsorbing substance desorbing means 3 is higher than the firing temperature, the possibility of sintering and loss of lithium (Li) increases, so the temperature of the desorbing means 3 during the regeneration operation is the firing temperature. It can be seen that the vicinity of 450 ° C. is optimal.

[Second Embodiment of the Invention]
FIG. 2 shows a second embodiment of the exhaust gas purifying apparatus according to the present invention. Compared with the embodiment of FIG. 1, a sulfur oxide adsorbent (hereinafter referred to as “sulfur oxide adsorbent”) is disposed between the particulate filter 40 and the NOx adsorbent 4. , Referred to as “SOx adsorbent”) 42. Other configurations are the same as those in FIG. 1, and the same components are denoted by the same reference numerals.

  In the present embodiment, the SOx adsorbent 42 is an oxide of copper and zirconium, and the metal ratio of copper and zirconium is 1: 1.

(Operation of the embodiment)
Except for the action of the SOx adsorbent 42, it is basically the same as that of the embodiment of FIG.

During normal operation of the internal combustion engine 1, SOx in the exhaust gas is adsorbed by the SOx adsorbent 42. Thereby, SOx does not flow to the NOx adsorbent 4, and sulfur poisoning of the NOx adsorbent 4 can be prevented. In particular, when a lithium oxide other than lithium titanate (Pt—Li ₂ TiO ₃ ) to which a noble metal is added is used as the NOx adsorbent 4, the SOx resistance is low, so that the upstream of the NOx adsorbent 4 as described above. By arranging the SOx adsorbent 42 on the side, the NOx adsorbent 4 can be prevented from being poisoned.

  During the regeneration operation, high-temperature air is also supplied to the SOx adsorbent 42 from the adsorbent desorption means 3, and the SOx adsorbed on the SOx adsorbent 42 is desorbed. That is, the SOx adsorbent 42 is regenerated. The detached SOx is discharged as it is. In the regeneration operation, the NOx adsorbent 4 is also desorbing as described above, so that the SOx desorbed from the SOx adsorbent 42 is not likely to be readsorbed by the NOx adsorbent 4.

  The sulfur oxide adsorbing material 42 includes copper oxide and zirconium oxide as described above, and when the metal ratio of copper and zirconium is 1: 1, the amount of sulfur oxide adsorbed is increased. Can do.

  In addition, since copper oxide and zirconium oxide can reversibly absorb and desorb sulfur oxides, exhaust with nitrogen oxide desorbing means upstream of the nitrogen oxide adsorbent and combustion device downstream. By switching between normal operation and regeneration operation in the gas purification device, nitrogen oxide is adsorbed by the nitrogen oxide adsorbent and at the same time sulfur oxide is adsorbed by the sulfur oxide adsorbent at the time of excessive air combustion in normal operation. Then, during the fuel overcombustion in the regeneration operation, the nitrogen oxides and sulfur oxides adsorbed on the respective adsorbents are desorbed, and the nitrogen oxides can be made harmless by the downstream combustion device and discharged. .

1 is a schematic view of a first embodiment of an exhaust gas purification apparatus to which the present invention is applied. It is the schematic of 2nd Embodiment of the exhaust-gas purification apparatus to which this invention is applied. And LiMn ₂ O _3, a diagram and LiMnPO _4, was compared to a saturated NOx adsorbed amount of Pt-Li ₂ TiO _3. A NOx adsorbent which is formed by Pt-Li ₂ TiO ₃ of the present invention, the NOx adsorbent which is formed by Pt-BaO ₂ system of the comparative example, and shows different saturated NOx adsorbed amount, in the exhaust gas The case where SOx is included and the case where it does not include are shown, respectively. And Pt-Li ₂ TiO ₃ NOx adsorbent formed by a graph showing changes in saturation NOx adsorption amount in the case of changing the weight ratio of the carrier. In the NOx adsorbent is a diagram showing the relationship between the mixing amount of the saturated NOx adsorbed amount of the lithium oxide (Li ₂ O). It is a figure which shows the relationship between the calcination temperature at the time of making NOx adsorption material, and a specific surface area. It is a figure which shows the relationship between the temperature of an adsorbent desorption means, and saturated NOx adsorption amount when the baking temperature of NOx adsorbent is 450 degreeC.

Explanation of symbols

1 Internal combustion engine 2 Exhaust passages 2a, 2b Branch exhaust passage 2c Downstream exhaust passage 3 Adsorbed substance desorbing means 4 NOx adsorbent 5 Combustion device 40 Fine particle filter 42 SOx adsorbent X1 Fuel rich combustion region X2 Fuel lean combustion region

Claims (13)

In an exhaust gas purification device installed in an exhaust passage of an internal combustion engine or combustion equipment,
A nitrogen oxide adsorbent is disposed in the exhaust passage, and the nitrogen oxide adsorbent is
Among the element groups of manganese (Mn), nickel (Ni), cobalt (Co), vanadium (V), chromium (Cr), iron (Fe), titanium (Ti), scandium (Sc) and yttrium (Y), An exhaust gas purification apparatus formed of a lithium composite oxide represented by a general formula LiAxOy or LiAxPO ₄ having at least one element A and lithium (Li) as constituent elements.   The exhaust gas purifier according to claim 1, wherein a noble metal is added to the nitrogen oxide adsorbent. The exhaust gas purifying apparatus according to claim 2, wherein the noble metal is platinum (Pt) and the lithium composite oxide is lithium titanate (Li ₂ TiO ₃ ). The exhaust according to any one of claims 1 to 3, wherein the nitrogen oxide adsorbent is supported on a carrier made of aluminum oxide (Al ₂ O ₃ ) and / or anatase titanium oxide (TiO ₂ ). Gas purification device. The nitrogen oxide adsorbent, the exhaust gas purifying apparatus according to claim 1 amount of the lithium oxide (Li ₂ O) is characterized in that 10 to 20% by weight.   The exhaust gas purification apparatus according to any one of claims 1 to 5, wherein the nitrogen oxide adsorbent is fired within a range of 400 ° C to 500 ° C.   The adsorbed substance desorbing means is disposed upstream of the nitrogen oxide adsorbent on the exhaust side, and a combustion device is disposed on the exhaust downstream side of the nitrogen oxide adsorbent. Exhaust gas purification device.   The exhaust gas purification device according to any one of claims 2 to 7, wherein the combustion device is a lean fuel combustion system.   8. The exhaust gas purifying apparatus according to claim 7, wherein the temperature of the adsorbing substance desorbing means is set near or below the firing temperature.   The exhaust gas purification device according to claim 1, wherein a sulfur oxide adsorbing material is disposed upstream of the nitrogen oxide adsorbing material.   The exhaust gas purifying device according to claim 10, wherein the sulfur oxide adsorbing material contains copper oxide and zirconium oxide.   The exhaust gas purification device according to claim 11, wherein the sulfur oxide adsorbent has a metal ratio of copper to zirconium of 1: 1.   The adsorbed substance removing means is arranged on the exhaust upstream side of the sulfur oxide adsorbent, and the combustion device is arranged on the exhaust downstream side of the nitrogen oxide adsorbent. Exhaust gas purification device.

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