KR20220133443A - Method and Apparatus for Reducing NOX with First and Second Catalysis - Google Patents

Abstract

The present invention relates to a device and a method for catalytic treatment of a passing gas stream to reduce NOx present in the gas stream. The device includes: a first catalyst which is applied to the catalytic treatment of a gas stream in a first temperature zone and is composed of silver-containing alumina; and a second catalyst which is positioned on the downstream side of the first catalyst, is composed of copper-containing zeolite, and is applied to catalytic treatment of a gas stream in a second temperature zone lower than the first temperature zone.

Description

Apparatus and method for reducing NX by primary and secondary catalysis {Method and Apparatus for Reducing NOX with First and Second Catalysis}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and method for removing noxious gases from an exhaust gas stream formed during combustion during operation of internal combustion engines, furnaces, power plants, and the like. In particular, it relates to catalysts used to remove nitrogen oxides (NOX) from exhaust gases produced during combustion.

There has been an ongoing effort for many years to develop methods and systems for removing harmful gases from exhaust gases produced by combustion devices. In recent years, environmental regulations have been enacted in countries around the world as part of an effort to reduce harmful exhaust gases emitted into the atmosphere from combustion devices.

The most problematic is the production of nitrogen oxides (NOX) by vehicles running on internal combustion engines such as gasoline engines, especially diesel engines. Combustion devices such as factory-installed furnaces, industrial or domestic heating appliances, and power plant units are of course also a problem.

During the combustion process in such an apparatus, nitrogen oxides are produced when nitrogen in the air reacts with oxygen in the combustion chamber under the high temperature and pressure normally present inside the combustion chamber (eg, the cylinder of an internal combustion engine). These nitrogen oxides are referred to as NOx emissions and include nitrogen monoxide, nitrogen dioxide, or mixtures thereof. NOX exhaust is a typical air pollutant that causes smog and acid rain. Leading developed countries around the world have enacted regulations on NOX emission reduction.

As a result, many long-term efforts are underway to develop methods and systems for substantially eliminating the emissions of nitrogen oxides or NOx to the atmosphere by exhaust gases from combustion devices. Realizing that automobile exhaust is a major cause of air pollution, the state of California passed a law requiring the use of an exhaust control system on vehicles for 1966 models sold in California. Similar legislation was enacted in the United States for 1968 cars onwards.

The #8220#complete mixing of fuel and air #8221# in the combustion process is thermodynamically called #8220#stoichiometric#8221#. The point is that the amount of air is just the right amount to burn all of the fuel, leaving no excess oxygen. For many reasons, internal combustion engines do not operate stoichiometrically, but run on lean combustion in which the amount of oxygen to fuel exceeds the stoichiometric conditions. Both gasoline and diesel internal combustion engines operate in lean burn, but mainly diesel engines are operated in lean burn, and unwanted amounts of NOx emissions are produced from the exhaust gases of these engines. Occasionally the engine runs on rich combustion and becomes fuel rich relative to oxygen. For gasoline the stoichiometric mixing is 14.6:1. Even under these conditions, some nitrogen in the atmosphere reacts with oxygen to form NOx.

Because exhaust gas streams from lean burn engines contain significant amounts of oxygen, the efficient removal of NOx from the gas stream using traditional exhaust catalysts such as #8220#3-way catalyst #8221# is not recommended. interfere As a result, NOx traps or NOx storage/reduction systems have been developed to help remove NOx from current lean burn engines. However, these systems must rely on close engine control to alternate between overburning and lean burn conditions of the exhaust gas stream. Catalysts employed in lean burn conditions store NOx. In excess combustion conditions, the catalyst reduces NOX to N2. HC-SCR systems have also been improved for use in reducing NOx from exhaust gases of internal combustion engines, but these systems have been found to be limited in use.

Accordingly, there is a need for techniques that will advance apparatus and methods for removing NOx from exhaust gases of combustion devices such as internal combustion engines.

detailed description

The present invention relates to a method and apparatus for catalytic treatment to remove or at least substantially reduce NOx compounds present in a gas stream.

The device according to the invention provides an efficient means for reducing or eliminating NOx compounds in exhaust gases generated by internal combustion engines. In particular, the device according to the invention works efficiently on exhaust gases from, for example, lean-burn engines, such as diesel engines which exhibit a relatively large oxygen potion. In order to obtain a synergistic effect, the present invention uses a combination of a primary catalyst exhibiting NOx conversion activity at a relatively high temperature and a secondary catalyst exhibiting at least similar activity at a lower temperature. The present invention is characterized by a wide operating temperature range and enhanced gas stream processing capacity. In particular, the present invention uses catalyst mixtures that can produce a suitable combination of intermediate nitrogen compounds with a primary catalyst and reduce them with a secondary catalyst, resulting in a synergistic effect better than the sum of the parts of each catalyst.

The device according to the invention generally consists of a primary catalyst adapted to operate at an optimal primary temperature and a secondary catalyst adapted to operate at an optimal secondary temperature lower than the primary temperature. The primary catalyst is located upstream of the secondary catalyst so that exhaust gas in the form of a gas stream flows from the primary catalyst to the secondary catalyst. The primary catalyst and the secondary catalyst may be arranged consecutively or may be arranged at intervals.

According to one embodiment of the present invention, a reducing agent in the form of a hydrocarbon compound is introduced into the gas stream to enhance the NOx removal activity through selective hydrocarbon catalytic reduction (HC-SCR).

According to a preferred embodiment of the present invention, the primary catalyst consists of a metal containing alumina material and the secondary catalyst consists of a metal containing zeolitic material. During operation, the exhaust gases pass through the device and act sequentially on the primary and secondary catalysts. The primary and secondary catalysts are mixed with each other and act to remove or at least substantially reduce NOx compounds and convert them into environmentally friendly by-products in a simple and cost-effective manner.

According to one aspect of the present invention, there is provided an apparatus for catalytic treatment through which a gas stream is passed to reduce the presence of NOx present in the gas stream. The apparatus comprises a first catalyst having a first optimum treatment temperature zone for gas stream catalytic treatment, and a first temperature zone for gas stream catalytic treatment accompanying the first catalyst, located downstream of the first catalyst. It is composed of a secondary catalyst having a lower secondary optimum processing temperature range compared to .

According to a particular aspect of the present invention, there is provided an apparatus for catalytic treatment through which a gas stream is passed to reduce the presence of NOx present in the gas stream. The apparatus comprises: a primary catalyst composed of metal-containing alumina and having a first optimum processing temperature zone for catalytic treatment of a gas stream; and a metal-containing zeolite located downstream of the primary catalyst; It is composed of a secondary catalyst having a second optimum processing temperature zone lower than the primary temperature zone for the gas stream catalytic treatment accompanying the

According to another aspect of the present invention, a method for catalytic treatment for reducing NOx present in a gas stream is provided. The method comprises the steps of directing a gas stream to a first catalyst having a first optimal treatment temperature zone for catalytic treatment of the gas stream, and directing the gas stream from the first catalyst to a gas stream catalyst entraining the first catalyst. and transferring to a second catalyst having a second optimum treatment temperature zone lower than the first temperature zone for treatment.

The present invention relates to a method and apparatus for catalytic treatment for the removal or at least substantial reduction of NOx compounds present in a gas stream. The apparatus and method according to the present invention provide an effective means for removing or reducing NOx compounds in exhaust gases produced from internal combustion engines. The apparatus and method according to the present invention are intended to promote the catalytic conversion of NOx compounds present in exhaust gases into environmentally friendly substances. It was observed that the device according to the present invention exhibits a synergistic effect by using a mixture of the primary catalyst and the secondary catalyst, using a minimum packing space, under the condition that a reducing agent in the form of a hydrocarbon is generally present. The apparatus disclosed herein is believed to be suitable for use in lean NOx exhaust aftertreatment systems.

The present invention aims to promote synergy from the mixing of different catalysts by tailoring intermediate reactive species to produce ammonia, mine, nitriles and other organic nitrogen species. According to the present invention, it is possible to obtain a high NOx reduction result while maintaining the same packing area and space velocity.

1 , there is shown a schematic view of a device 10 according to the invention coupled to a lean burn engine 12 in a diesel engine. Here, #8220#lean-burn engine#8221# refers to an engine that produces oxygen-rich exhaust. The oxygen-rich exhaust means exhaust having oxygen in a molar ratio higher than the total molar ratio of reducing compounds such as CO, hydrogen and hydrocarbons. Sugar exhaust has an oxidative environment. Examples of such engine systems include diesel engine systems, spark-ignited natural gas or alternative fuel engine systems, liquefied or gas-fueled turbine engines, and various lean-burn gasoline engine systems. A diesel engine system as shown in FIG. 1 produces exhaust typically having an oxygen content of 4% to 16%, depending on the loading conditions and the running mode of the diesel engine.

An oxygen rich exhaust 13 is present in the engine 12 and is directed to the device 10 . Preferably, this exhaust is further supplemented with atomized hydrocarbons or mixtures of hydrocarbons 18 . In the example shown, as one source of these hydrocarbons, diesel fuel 15 in tank 2 is possible, which is used as the main fuel source for diesel engine 12 . As a hydrocarbon reducing agent, residual hydrocarbons left in the exhaust after the combustion process during the engine cycle are possible. Alternatively, the auxiliary hydrocarbon may be introduced as post injection, preferably during the power stroke or exhaust stroke of a four-cycle diesel engine. Alternatively, as shown, an auxiliary hydrocarbon of the exhaust system located downstream of the engine cylinder is introduced using the auxiliary injector 17 controlled by the engine control module (ECM) 19 . It is also widely known to use hydrocarbons other than diesel main fuel.

The engine exhaust is directed to a device 10 consisting of a catalyst unit 14 . Deposited in catalyst unit 14 are metal containing catalyst mixtures having the tuned physical and chemical properties disclosed herein, which yield high NOX removal performance, as well as other advantageous lean NOX catalyst performance properties. The details of the mixing composition ratio of the metal-containing catalyst together with the catalytic reaction are shown below.

As shown in FIG. 2 , the device 10 includes a catalyst unit 14 located downstream of the lean burn engine 12 along an exhaust pipe 16 . Exhaust 13 (indicated by arrows) from engine 12 in the form of a gas stream travels along exhaust pipe 16 in the direction indicated by the arrow in FIG. 2 . In one embodiment of the present invention, the device 10 comprises a hermetic housing 24 defining a packing area 30 occupied by the catalyst unit 14 and an inlet port 26 located at one end. ), and an outlet port (28) located at the other end. Packing area 30 is in fluid communication between inlet port 26 and outlet port 28, respectively. An inlet port 26 supplies exhaust 13 from the combustion engine, and an outlet port 28 draws out the purified exhaust gas stream 21 .

The catalyst unit 14 of the apparatus 10 comprises a primary catalyst 20 having a first optimum treatment temperature range for catalytic treatment of an exhaust 13 gas stream, and downstream of the primary catalyst 20 . a secondary catalyst 22 located therein. The secondary catalyst 22 exhibits a lower secondary optimum processing temperature range compared to the primary temperature range for treating the gas stream catalyst accompanying the primary catalyst 20 . In particular, the primary catalyst 20 promotes the reaction of NOx with hydrocarbons to produce nitrogen-containing intermediate products such as amines, ammonia, organic nitrogen species, and oxygenates. These intermediate species desorb into the gas phase together with the active NOX species. The secondary catalyst 22 promotes the reduction of these intermediates to N2. The inventors have found that the primary catalyst not only converts some of the NOx directly to N2, but also produces an intermediate species from the remainder of the NOx that later reacts with the secondary catalyst to form N2.

In a preferred embodiment of the present invention, the primary catalyst 20 is comprised of a catalytically active metal-containing alumina (AL2O3) material, preferably a metal-containing gamma-phase alumina material, and the secondary catalyst 22 is a catalytically active metal-containing alumina (AL2O3) material. a zeolitic material containing an active metal, preferably a ZSM-5 material containing a metal. The primary catalyst 20 and the secondary catalyst 22 are structurally arranged in the catalyst layer as monoliths shaped bodies such as powders, pellets, particles, washer coatings or honeycombs.

The metal of the primary catalyst 20 is preferably selected from the group consisting of silver, indium, gallium, tin, cobalt, and mixtures thereof, and more preferably silver (Ag). The metal loading of the primary catalyst 20 is preferably about 1 to 15 wt%, more preferably about 2 to 5 wt%, based on the total weight of the primary catalyst. A metal loading of at least 2% is preferred if the use of a reducing agent in the exhaust 13 is involved. In a preferred embodiment of the present invention, as the primary catalyst 20, silver-containing alumina catalyst (Ag/alumina) was used.

It has been confirmed that alumina formed by the sol-gel method produces a material with unique properties used in the treatment of lean NOX catalysts in oxygen-rich exhaust. Various methods of forming alumina compounds have been studied. In one example, gamma-phase alumina was obtained by a complexing agent-assisted sol-gel method. In another example, a gamma-phase alumina material (support) was obtained by a sol-gel method without using a complexing agent.

The alumina compound of the primary catalyst 20 is preferably synthesized through a sol-gel method using a complexing agent together with a washing step employing an alcohol such as 2-propanol. The sol-gel method is superior in that the result is characterized by basic pH and excellent hydrothermal stability, and in that it optimizes the metal dispersion on the alumina compound to maximize loading capacity and uniformity. For this reason, the sol-gel method enhances the reduction of NOx compared to the conventional production method. Details of the sol-gel process will be described later in Example 2. For further details of the synthesis of alumina via a sol-gel process, to the extent not in conflict with this specification, reference may be made to US Patent Nos. 6,703,343 and 6,706,660.

Metal doping or loading of the alumina material is preferably done in one of two ways. In one method, the metal dopant is dissolved in water used to stop gelation during the sol-gel process described above.

In the second method, calcined sol-gel gamma-phase alumina is doped with metal by an incipient wetness impregnation method. In a preferred incipient wet impregnation method, the calcined powder sol-gel gamma-phase alumina is contacted with a solution of a suitable metal. The solution of the metal is present in an amount equal to or greater than the total pore volume of the gamma-phase alumina sample. The total pore volume of the prepared gamma alumina is preferably between about 1.5 and about 2.0 cc/g of alumina.

To form gamma-phase alumina doped with indium or indium oxide by incipient wet impregnation, an appropriate amount of In(NO3)3 (or InCl3) is dissolved in an aqueous solution and brought into contact with sol-gel gamma-phase alumina. The gamma-phase alumina catalyst doped with indium or indium oxide is then calcined at 600° C. for 5 hours.

Gamma-phase alumina doped with tin or tin oxide is obtained in the same manner using SnCl3 in an ethanol solution instead of water. The gamma-phase alumina catalyst doped with tin or tin oxide was calcined at 600° C. for 5 hours and then at 800° C. for 2 hours.

The third possible metal accelerator is gallium or gallium oxide. Gamma-phase alumina doped with gallium or gallium oxide is obtained by exposing gamma-phase alumina to an aqueous solution of Ga(NO3)3-H20 to which aluminum oxide gel is added during preparation of gamma-phase alumina by a sol-gel method. Gamma-phase alumina catalyst doped with gallium or gallium oxide is calcined at 600° C. for 5 hours to form an oxide of gallium-containing alumina.

The metal of the secondary catalyst 22 is preferably selected from the group consisting of copper, iron, cobalt, or a mixture thereof, and more preferably copper (Cu). The metal loading of the secondary catalyst 22 is preferably about 2 to 15 wt%, more preferably about 3 to 11.5 wt%, based on the total weight of the secondary catalyst. In a preferred embodiment of the present invention, the secondary catalyst 22 used a copper-containing zeolite catalyst (Cu/zeolite). The zeolite component may be selected from suitable zeolites such as ZSM-5, ZSM-11, ZSM-35, MCM-22, MCM-49, Beta, MCM-56, ITQ-13, and MCM-68. not. A preferred zeolite is ZSM-5. Details regarding doping or loading of the metal into the ZSM-5 component are described later in Example 1.

The primary catalyst 20 and the secondary catalyst 22 of the catalyst unit 14 are arranged in a packing region 30 of the housing 24 with the primary catalyst 20 positioned upstream of the secondary catalyst 22 . ) is placed in The amount of the primary catalyst and the secondary catalyst is present in a ratio of about 1:2 to 2:1, with a ratio of 1:1 being preferred. In this embodiment, the primary catalyst 20 and the secondary catalyst 22 are arranged in parallel. Alternatively, the primary catalyst 20 and the secondary catalyst 22 are spaced apart from each other by some distance L. In general, performance increases as dwell time decreases. The primary catalyst 20 combined with the secondary catalyst 22 receives the exhaust 13 gas stream via the inlet port 26 of the apparatus 10 and sends it out in purified form to the outlet port 28 . and serves to convert and reduce NOx present in the exhaust 13 gas stream.

As described above, a reducing agent may be injected into the exhaust 13 in front of the catalyst unit 14 in order to enhance the catalytic reaction that converts NOx into NO2. The reducing agent may be withdrawn from the fuel tank 15 associated with the combustion engine 12 and injected into the exhaust 13 by a fuel injector or other suitable means. Examples of suitable reducing agents for diesel engines include dodecane, ethanol, propane, diesel engines, kerosene, diesel-range paraffin, diesel range non-aromatic streams, and the like. Examples of reducing agents suitable for gasoline engines include gasoline, propane, ethanol, octane and the like.

The apparatus and method according to the present invention make it possible to remove or at least substantially reduce NOx compounds present in a gas stream.

An apparatus and method for catalytic treatment through which a gas stream is passed to reduce NOx present in the gas stream, the apparatus comprising: a primary catalyst composed of silver-containing alumina that is applied to the catalytic treatment of a gas stream in a primary temperature zone and a secondary catalyst located downstream of the primary catalyst and composed of a copper-containing zeolite, wherein the secondary catalyst is applied to the catalytic treatment of the gas stream in a secondary temperature zone lower than the primary temperature zone.

exhaust gas stream, NOx, reduction, catalyst, alumina, zeolite

The apparatus and method according to the present invention make it possible to remove or at least substantially reduce NOx compounds present in a gas stream.

An apparatus and method for catalytic treatment through which a gas stream is passed to reduce NOx present in the gas stream, the apparatus comprising: a primary catalyst composed of silver-containing alumina that is applied to the catalytic treatment of a gas stream in a primary temperature zone and a secondary catalyst located downstream of the primary catalyst and composed of a copper-containing zeolite, wherein the secondary catalyst is applied to the catalytic treatment of the gas stream in a secondary temperature zone lower than the primary temperature zone.

exhaust gas stream, NOx, reduction, catalyst, alumina, zeolite

Claims (1)

An apparatus for catalytically treating a gas stream passing therethrough to reduce NOx present in the gas stream, the apparatus comprising: a primary catalyst having a first optimum processing temperature zone for catalyzing the gas stream; and a secondary catalyst having a second optimum processing temperature zone lower than the primary temperature zone for gas stream catalytic processing accompanying the primary catalyst.