JP2002530575A - Liquid urea additive for exhaust gas treatment - Google Patents

Abstract

  (57) [Summary] A method for treating a combustion effluent containing nitrogen oxides is provided. According to these methods, the combustion effluent is treated with a treatment additive composition comprising urea, water, and oxygenated organic compounds in the presence of a catalyst. The processing additive composition of the present invention has a lower freezing point than the water / urea solution, which allows the use of the processing additive at temperatures below 10 ° F (-12 ° C) if necessary. And storage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] This application is related to US Provisional Patent Application 60/109428, filed on November 23, 1998.
Claim priority in relation to the issue.

[0002] Co-pending US Patent Application Serial No. 09 / (Mobile Case No. 10088-1) relates to an additive dispenser system for a vehicle engine. The present invention relates to a method of treating combustion emissions for the removal of nitrogen oxides using a liquid composition of urea. Additives are present in the composition that impart properties to the composition that are particularly useful at low temperatures and in the treatment of motorized vehicle emissions.

[0003] The combustion of hydrocarbon fuels in internal combustion engines results in the production and emission of a mixture of combustion products. The main combustion products are carbon dioxide and water, both of a small amount of carbon monoxide (CO), usually accompanied by nitrogen oxides (NO ₂₎ and sulfur oxides (SO _2). Oxides of nitrogen and sulfur are involved in the formation of smog, acid rain, and other atmospheric problems, and should therefore be considered undesirable pollutants. Various measures have been taken in recent years to control the amount of these contaminants emitted from motorized vehicles. A decrease in the amount of sulfur in the fuel leads to reduced SO ₂ emission, the reduction of nitrogen oxide content in the vehicle emissions can not be treated in the same manner. Modification of progress as well as the composition of the fuel in the engine design may weaken the formation of nitrogen oxides, but the combustion of the air / fuel mixture will always have undesirable side effect of the release of NO _2.

Due to the sustainability issue of NO ₂ emissions from the combustion process, the most effective strategies for reducing the amount of polluting nitrogen oxides include treating post-combustion emissions. To date, this strategy has been applied primarily to static industrial processes, including furnaces, boilers, and static diesel engine applications. One method used for the removal of NO ₂ contaminants, including treatment with ammonia combustion emissions. In this method, ammonia is NO ₂ and selectively react with diatomic nitrogen (N ₂₎ and water, giving a harmless reduction products. When the reaction occurs by free radical formation and recombination at elevated temperatures, it is called selective non-catalytic reduction (SNCR). When the reaction takes place in the presence of a catalyst, it is called selective catalytic reduction (SCR). SCR-type methods for reducing NO ₂ emissions are preferred over SNCR methods because of higher NO ₂ removal efficiency, lower ammonia consumption, and less by-product formation. However, SCR process is sensitive to the ratio of ammonia to NO _2. Thus, SCR mainly has relatively the amount of NO ₂ which is constant, has been applied for the treatment of NO ₂ containing emissions emissions larger scale static industrial process. However, recent advances in accurate dosing of liquid reagents have
SCR for the treatment of emissions with various compositions from equipment such as motorized vehicles
Enabled application.

[0005] Ammonia used in the SCR process can be generated in situ by thermal decomposition and hydrolysis of urea at high temperatures. Unlike ammonia, urea is a safe, manageable starting material, and can be used either as a solid or in solution. Several methods have been disclosed that utilize urea for reduction of NO ₂ emissions. U.S. Pat. Nos. 4,208,386 and 4,325,924 describe a 1300.degree.
5 describes the use of a hydroxylic solution of urea in the treatment of combustion emissions in a non-catalytic treatment system at a temperature maintained above 5 ° C.). US Patent 471909
Nos. 2,4780289, 4978514, 5057293, 5286457, and 5298230 show methods for treating industrial combustion effluents using aqueous urea compositions containing chemically enhanced additives. Despite numerous industrial applications for urea composition in the process of the NO ₂ emissions, urea compositions described above, liquefiable at low temperature so continue useful in climatic conditions thereof wide range Not specifically designed to maintain. Further, known compositions include:
It is not considered for use in smaller mobile applications, for example, for the treatment of emissions from motorized vehicles.

A particular factor in mobile combustion engines is believed to be in the design of possible emission treatment systems. First, the system must be composed of materials and components that are compact and lightweight to maintain vehicle efficiency and performance. Also, the system
Even for inexperienced users, it should be relatively easy to use. Thus, the materials of the system should have properties that are satisfactory and can be safely operated with minimal trouble and cost to the user. In addition, the material must be able to handle easily like a liquid, be easily stored in a vehicle, be pumpable, and be pumpable. In addition, the materials exceed typical vehicle storage and operating temperatures. Should retain desirable properties.

Of particular interest for liquid emission treatments is the liquid phase change at low temperatures typically encountered by vehicle users in cold climatic regions. Freezing is a particular problem with aqueous solutions and creates a need for liquid effluent treatments that remain liquid even when reduced to a storage temperature of -20 ° F (-30 ° C). In view of the potential application of the SCR method for reducing nitrogen oxide emissions in motorized vehicle emissions, certain urea compositions that resist solidification at low temperatures will have a future reduction in air pollution Can be an important contribution to.

[0008] The present invention is directed to a method for treating a combustion effluent containing nitrogen oxides. These methods include treating the combustion effluent with a treatment additive in the presence of a catalyst. A preferred application of this method relates to the treatment of emissions from motorized vehicles, especially those with diesel engines. Processing additives include water and urea. Preferred processing additives further include at least one oxygenated organic compound (or oxygen-containing organic compound) that is miscible with the aqueous urea solution. Preferred oxygenated organic compounds are alcohols. It has been discovered that the novel compositions of the present invention permit the use and storage of processing additives in normally encountered climatic conditions. Suitable alcohols include, but are not limited to, monohydric or polyhydric alcohols.

As used herein, the terms “fuel additive”, “treating agent” and “treating additive” are used interchangeably and collectively are effluents from fuel combustion A substance that is added to or used in a fuel to process the material. Preferred "processing additives" are aqueous solutions of urea, and optionally oxygenated organic compounds (or oxygen-containing organic compounds). The oxygenated organic compound includes an organic compound containing at least one oxygen atom. According to the present invention, oxygenated organic compounds include, but are not limited to, alcohols, ethers, esters, aldehydes, ketones and carboxylic acids. In addition, oxygenated organic compounds are substances that have useful uses in treating gasoline and combustion processes.

[0010] As used herein, the term "combustion effluent" refers collectively to the products of the combustion of hydrocarbons in the presence of air, including carbon dioxide, water, Includes hydrocarbons, carbon monoxide, sulfur oxides, and nitrogen oxides. The term "emissions" is used to describe the combustion emissions emitted by motorized vehicles. In addition, the term "
"Reaction zone" refers to the device, means or location where the combustion effluent and urea compound combine, and the reaction zone is usually one or more catalysts suitable for performing urea hydrolysis and SCR in motorized vehicles. including. A preferred reaction zone is the exhaust pipe of a motorized vehicle. The exhaust pipe of a motorized vehicle is used for selective catalytic reduction (S
(CR) A tube or pipe that connects the vehicle's engine to the device.

The terms “nitrogen oxide” or “NO ₂ ” collectively refer to both nitrogen oxides (NO) and nitrogen dioxide (NO ₂ ). Here, the term “NO ₂ emissions” or “nitrogen oxide emissions” refers to NO ₂ found in combustion effluents.

[0012] Alcohols are the preferred oxygenated organic compounds. As used herein, the term "alcohol" means a chemical compound having at least one hydroxyl group and having the desired properties for the present invention. “Alcohols” or “alcohols” are defined as polyhydric alcohols (ie, compounds having more than one hydroxyl group, eg, ethylene glycol, propylene glycol, glycerol, polyethylene glycol, and polyoxyalcohol amine glycols) and monohydric alcohols (ie, Compounds having only one hydroxyl group, such as, but not limited to, methanol, ethanol, propanol, and isopropanol).

The present invention provides a method for treating a combustion effluent containing nitrogen oxides (NO ₂ ). In particular, the present invention is urea, using a treatment liquid additive comprising water and oxygenated organic compounds, to a method for reducing NO ₂ emissions from the combustion device. Preferred oxygenated organic compounds include alcohols. Combustion effluents that can be treated include, but are not limited to, combustion engines that include both spark ignition and diesel. In particular, the method of the invention is particularly suitable for the treatment of emissions from combustion engines in motorized vehicles, including but not limited to cars, trucks, tractors, farm equipment, construction equipment, etc. I have. The method of the present invention preferably processes the effluent from motorized vehicle operating in a diesel engine comprising a higher NO ₂ emissions generally.

According to the present invention, a processing liquid additive comprising urea is combined with the combustion effluent in the reaction zone before the effluent is released to the atmosphere. Processing additives are stored in storage containers and are added to the effluent by injection or spraying. Preferably, the amount of processing additives to be added may be the maximum amount of NO ₂ is reacted to form N ₂ and water, and those only minimal amounts of by-products (for example, an excess of ammonia) as to produce It is. Preferably, the molar ratio NO ₂ urea is 0.1: 1 to 1: 1 or more, preferably in the range of from 1: theoretical amount of 2. For both decomposition and NO ₂ and ammonia in the reaction of the urea, high temperature is also required in the reaction zone. The effluent entering the reaction zone can be in a temperature range from ambient to 1000 ° F (540 ° C). The reaction zone also contains a catalyst, such as a transition metal or metal oxide, which may be any known substance or combination of substances used in urea hydrolysis or SCR reactions. Specific catalysts (or SCR catalysts) include metal oxides, transition metal oxides, transition metals, noble metals, vanadium oxides, tungsten oxides, titanium oxides, iron oxides, manganese oxides, chromium oxides, copper Including but not limited to oxides, zeolites, platinum, palladium, rhodium and iridium. The catalytic material is preferably supported on a support comprising ceramic or zeolite.

[0015] In a preferred embodiment of the present invention, a processing additive comprising urea is added to the motorized vehicle in the reaction zone prior to discharge of the effluent to the atmosphere. Effluent requiring treatment typically includes a NO ₂ in the range of 100～1100Ppm. Processing additives are added to the effluent in the amounts and molar ratios described above. Typical temperatures in motorized vehicle emissions are in the presence of any of the catalysts or combinations of catalysts described above.
It is sufficiently high to facilitate both the reaction of the ammonia and NO ₂ decomposition and resulting into ammonia urea. The discharge temperature in the reaction zone is from ambient temperature to 1000 °
F (540 ° C.). The treated effluent subtracting NO ₂ content, which 30 to 99%, preferably is reduced from 50 to 99%.

Preferred processing additives according to the method of the present invention include liquid compositions comprising water and urea. In a preferred embodiment, the processing additive further comprises at least one oxygenated organic compound. In one embodiment, the processing additive comprises at least two oxygenated organic compounds. In another embodiment, the processing additive comprises three or more oxygenated compounds. Preferred oxygenated compounds are alcohols. Alcohols according to the present invention include, but are not limited to, monohydric and polyhydric alcohols that have a lower solidification temperature than water and mix with water to form solutions. Polyhydric alcohols are preferred. Examples of preferred polyhydric alcohols include, but are not limited to, ylene glycol, propylene glycol, glycerol, polyethylene glycol and polyoxyalcoholamine. A suitable polyhydric alcohol is ethylene glycol. Monohydric alcohols can also be used in the method of the present invention. Monohydric alcohols that may be suitable according to the method of the present invention include, but are not limited to, methanol, ethanol, propanol and isopropanol.

[0017] Processing additives further include other agents, including, but not limited to, demineralizing agents and dyes. A demineralizing agent may be added to prevent scaling, which reduces the efficiency of the method of the invention. Dyes can also be added to the processing additive or to components that may be toxic, such as alcohol, in the processing additive to ensure safe handling.

[0018] The amount of each component in the processing additive is determined by the intended use of the present invention. However, it is generally preferred that the relative amount of urea in the composition be maximized so that a minimum volume of processing additive can be used to efficiently process the nitrogen oxide containing effluent. Similarly, it is preferable to include an oxygenated organic compound in an amount sufficient to achieve the target solidification point. The target solidification point of the liquid composition is preferably less than the solidification point of the urea / water solution (eg, 10 ° F. or −13 ° C. for a 30 wt% urea solution), and less than −15 ° F. (−26 ° C.). Is more preferred, and -20 ° F (
(−29 ° C.) or lower. Further, it is desirable to include water in the composition in an amount sufficient to maintain the urea as a solution. In a preferred embodiment, the processing additive composition comprises 30-70% by weight water, 20-40% by weight urea, and 1-40% by weight oxygenated organic compound. More preferably, the processing additive composition comprises 35-45% water, 25-35% urea, and 25-35% by weight.
Oxygenated organic compounds. In another embodiment, the treatment additive composition comprises 40% by weight water, 30% by weight urea, and 30% by weight oxygenated organic compound.

The treatment additive composition of the present invention can be stored and used at a wide range of temperatures. These compositions are particularly well-stored at low temperatures, since they have a lower solidification temperature than water / urea solutions, and the temperature is regularly or optionally below the solidification point of the urea / water solution. It is to be kept in a liquid state when it can be lowered (eg 10 ° F. or -13 ° C. for a 30% by weight urea solution). By this nature,
The processing additives of the present invention are particularly useful in applications where the combustion device is operated at a temperature below 10 ° F (-13 ° C).

EXAMPLES Example 1 Urea Blend Suitable for Use in Vehicle Emissions Treatment An aqueous solution comprising 40% by weight of water, 30% by weight of urea, and 30% by weight of ethylene glycol was formulated. The freezing point of a solution is the point at which the liquid becomes half melted ice
It was determined to be 20 ° F (-29 ° C).

Example 2 Urea Blend Suitable for Use in Vehicle Emissions Treatment An aqueous solution comprising 50% by weight water, 30% by weight urea, and 20% by weight ethylene glycol was formulated. The blend remained clear and fluid at -15 ° F (-26 ° C).

Example 3 Treatment of Emissions from a Diesel Vehicle with a Liquid Urea Composition Emissions emitted from a motorized vehicle diesel engine contain an average amount of NO ₂ of 4 g / mile and an average temperature of 400 ° F. Having. A solution comprising 40% by weight of water, 30% by weight of urea and 30% by weight of ethylene glycol in an amount of 13 g / mile is added to the effluent by means of spraying. The mixture of effluent and spray material, is reacted with NO ₂ through the upper Zeioraito catalyst. Treated effluent exits the vehicle with NO ₂ content of 0.4 g / mile (0.25 g / miles), in the effluent showed a total reduction of 3.6 g / mile (2.2 g / miles), which Is similar to an effluent treated with an aqueous urea solution lacking oxygenated organic compounds.

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Claims (16)

[Claims] 1. A method for treating emissions from a motorized vehicle comprising nitrogen oxides, the method comprising adding a processing additive comprising water and urea to the emission. 2. The method of claim 1, wherein the processing additive further comprises at least one oxygenated organic compound. 3. The method of claim 1, wherein the motorized vehicle is operated with a diesel engine. 4. The method of claim 1, further comprising adding a processing additive to the effluent in the presence of the SCR catalyst. 5. The method according to claim 2, wherein the oxygenated organic compound is an alcohol. 6. The method according to claim 1, wherein the alcohol is ethylene glycol, propylene glycol,
The method according to claim 5, which is polyethylene glycol, glycerol or polyoxyalcoholamine glycol. 7. The method according to claim 5, wherein the alcohol is methanol, ethanol, propanol or isopropanol. 8. The method of claim 2, wherein the processing additive comprises 30-70% by weight water, 20-40% by weight urea, and 1-40% by weight oxygenated organic compound. 9. The method of claim 8, wherein the processing additive comprises 35-45% by weight water, 25-35% by weight urea, and 25-35% by weight ethylene glycol. 10. The method of claim 15, wherein the processing additive comprises 40% by weight of water, 30% by weight of urea, and 30% by weight of ethylene glycol. 11. 30 to 70% by weight of water, 20 to 40% by weight of urea, and 1
A diesel engine emissions treatment additive comprising -40% by weight of oxygenated organic compounds. 12. 35 to 45% by weight of water, 25 to 35% by weight of urea, and 2
The processing additive of claim 11, comprising 5-35% by weight of the oxygenated organic compound. 13. The processing additive according to claim 12, comprising 40% by weight of water, 30% by weight of urea, and 30% by weight of oxygenated organic compounds. 14. The treatment additive according to claim 23, wherein the oxygenated organic compound is ethylene glycol. 15. The processing additive according to claim 11, wherein the alcohol is ethylene glycol, propylene glycol, polyethylene glycol, glycerol or polyoxyalcoholamine glycol. 16. The processing additive according to claim 11, wherein the alcohol is methanol, ethanol, propanol or isopropanol.