Additive for cleaning SCR systems

Abstract

The present invention provides an additive for removing deposits or impurities in a selective catalytic reduction system for exhaust gases of a diesel fuel internal combustion engine. [Solution] The present invention relates to the use of a polar solvent as an additive to a solution containing a component that releases ammonia at temperatures above 200°C in order to remove deposits or impurities in a selective catalytic reduction system, wherein the polar solvent has a boiling point of at least 140°C at 101.3 kPa. The present invention further relates to a method for removing deposits or impurities in a selective catalytic reduction system and a method for operating a selective catalytic reduction system. The present invention further relates to a method for removing deposits or impurities in a selective catalytic reduction system, wherein the system is operated using a solution containing a component that releases ammonia at temperatures above 200°C, and the solution further contains a polar solvent having a boiling point of at least 140°C at 101.3 kPa.

Description

[Technical Field]

[0001] The present invention relates to the use of a polar solvent as an additive to an ammonia-releasing solution to remove deposits or impurities in a selective catalytic reduction system, a method for removing deposits or impurities in a selective catalytic reduction system, and a method for operating a selective catalytic reduction system. [Background technology]

[0002] One of the major problems caused by internal combustion engines is nitrogen oxides (NOx). x ) emissions. At the EU level, NO x The NEC Directive (EU2016 / 2284) stipulates minimum obligations to reduce total emissions. This directive sets targets of a 39% reduction by 2020 compared to 2005 levels, and a 65% reduction by 2030. To achieve these targets, NO x This necessitates significant contributions from all sectors that emit ethanol. For internal combustion engines, this means the need to use selective catalytic reduction (SCR) systems. Here, ammonia is separated or otherwise released from a compound (usually urea) at operating temperatures, and this ammonia is then released into the medium material. x It reacts with nitrogen (N2) and water. The medium material is usually a vanadium-based or zero-light-based material, depending on the operating temperature.

[0003] The main application areas of SCR systems in internal combustion engines are diesel engines in automobiles, commercial vehicles, railway vehicles, and ships. Urea solutions are typically used. In the marine sector, the urea concentration is 40% (ISO 18611), while in other sectors, it is 32.5% urea (DIN 70070 or ISO 22241). These standards specify not only the urea content but also the permissible amounts of impurities (for example, ISO 22241 requires a minimum of 65 mN / m), various other physicochemical parameters such as surface tension at 20°C, and descriptions related to transportation and manufacturing. In the automotive sector, AdBlue (registered trademark), a product name or trademark of the German Association of the Automotive Industry (VDA), is particularly well-established. Standardization has the advantage of making the standard solution available to consumers at a low cost, and on the other hand, because each parameter and each contained substance is well-described, catalyst poisoning and malfunctions cannot occur in various SCR structures.

[0004] In SCR systems, urea is first decomposed in the catalyst into ammonia (NH3) and isocyanic acid (HNCO). This isocyanic acid further reacts with water to produce ammonia and CO2. The resulting ammonia then reacts with nitrogen oxides removed from the exhaust gas to produce nitrogen and water, which are harmless substances. Depending on the shape, droplet distribution, residence time, and temperature at various points in the SCR system, isocyanic acid side reactions can occur, leading to undesirable deposits. Common by-products or decomposition products of urea or isocyanic acid include biuret, cyanuric acid, ammerido, ammerine, and melamine. Deposit formation due to urea decomposition side reactions is relatively uncommon and depends on individual operating conditions (ambient temperature, operating / load / motion profile). Typically, the system is configured to be maintenance-free under normal operation.

[0005] However, once deposit formation begins, this leads to a chain reaction of surface changes in the SCR medium at various points, and consequently reduces the efficiency of the medium and the entire SCR system. In the worst case, a malfunction occurs, exhaust gas levels fall below standards, and the vehicle / machine must be taken out of service. This may even necessitate complex cleaning or parts replacement. This results in significant costs and resource waste due to cleaning or parts replacement and the need for alternative vehicles or machines.

[0006] The literature describes various solutions, but all are based on reducing or suppressing sediment formation during continuous use (the so-called keep-clean approach).

[0007] International application No. 94 / 08893 describes a method for reducing the particle size of an injected urea solution by adding a surfactant. This is intended to reduce deposit formation. Although numerous anionic, cationic, and nonionic surfactants are described, the focus is on alcohol ethoxylates.

[0008] International application 2008 / 125745A2 describes the addition of a “multifunctional” substance with an HLB value of 7 to 17 to an ammonia-releasing solution, particularly to reduce the formation of cyanuric acid-based deposits.

[0009] European Patent Application No. 2337625B1 describes a method for reducing the particle size of a urea solution to which a mixture of alcohols ethoxylated at two different intensities can be injected, while simultaneously preventing turbidity (solubility issues) at low temperatures.

[0010] European Patent Application No. 2488283B1 describes the addition of an additive consisting of a hydrocarbon chain and an ethoxylated moiety. This additive is also intended to reduce the formation of undetailed deposits, consisting of a 32.5% urea solution, in the SCR medium.

[0011] However, since all of these proposals are based on a keep-clean approach, i.e., avoiding the formation of new deposits, it is necessary to add each of the aforementioned additives to the urea solution as permanently as possible during operation, and therefore the use of inexpensive, standardized urea aqueous solutions such as AdBlue® is not feasible.

[0012] Each of the problem-solving solutions described in the literature is based on the use of surfactants that further significantly reduce surface tension. This leads to immediate foam formation on the one hand, and on the other hand, to a surface tension that falls significantly below the 65 mN / m at 20°C specified in ISO standard 22241. In either case, depending on the detailed structure, the reliable function of the SCR medium is jeopardized. Foam formation can lead to significant problems, especially in compressed air-based injection systems.

[0013] Therefore, there is a need to overcome the aforementioned problems and shortcomings of the prior art. In particular, there is a need for additives to ammonia emission solutions (such as AdBlue®) that can remove existing deposits or impurities in selective catalytic reduction systems for diesel fuel internal combustion engine exhaust gases, and that are not permanent but only needed when necessary, especially when contamination already exists. [Overview of the project] [Problems that the invention aims to solve]

[0014] Therefore, the object of the present invention is to provide an additive to an ammonia emission solution (such as AdBlue®) for removing (existing) deposits or impurities in a selective catalytic reduction system for exhaust gas of a diesel fuel internal combustion engine.

[0015] This so-called cleanup approach, i.e., the removal of existing deposits or impurities, allows for the cleaning of already contaminated SCR systems without the need to shut down the vehicle or machinery, nor the need to replace the SCR system or any part thereof. Furthermore, it eliminates the need to permanently add such additives to the ammonia-releasing solution, allowing the SCR system to be operated for most of the time using inexpensive, standardized urea aqueous solutions such as AdBlue®. The cleanup additives should only be used when impurities are generated or formed in the SCR system, for example, by adding them to the urea solution. Simultaneously, the surface tension and foaming behavior of the reformed solution should be as close as possible to the behavior of the original urea solution and meet the respective standards. In addition, the additives should have good solubility in commercially available urea solutions such as AdBlue® at both low and high concentrations and should have long-term stability in the solution.

[0016] The inventors of this invention conducted extensive research to solve the problem. Surprisingly, it became clear that the reduction in surface tension plays no or only a secondary role in the removal of existing deposits or impurities. Therefore, the addition of substances with surfactant properties in the cleanup process is not necessary, and is even detrimental due to the associated foaming behavior.

[0017] Rather, special polar solvents with relatively high boiling points have proven to be suitable additives for solving the aforementioned objectives and problems, and furthermore, to ensure the effective removal of existing deposits or impurities in the SCR system, only relatively small amounts of each of these polar solvents need to be added to the ammonia-releasing solution (such as AdBlue®). [Means for solving the problem]

[0018] Therefore, the present invention relates to the use of a polar solvent as an additive to a solution containing a component that releases ammonia above 200 °C for removing existing deposits or impurities in a selective catalytic reduction system (of a diesel fuel internal combustion engine), the polar solvent having a boiling point (boiling temperature) at 101.3 kPa of at least 140 °C.

[0019] The present invention further relates to a method for removing deposits or impurities in a selective catalytic reduction system (of exhaust gas of a diesel fuel internal combustion engine), the system being operated using a solution containing a component that releases ammonia above 200 °C, the solution further containing a polar solvent having a boiling point at 101.3 kPa of at least 140 °C.

[0020] The present invention further relates to a method for operating a selective catalytic reduction system (of exhaust gas of a diesel fuel internal combustion engine), the method comprising injecting into the system a solution containing a component that releases ammonia above 200 °C and further containing a polar solvent having a boiling point at 101.3 kPa of at least 140 °C, and heating the solution in the system to a temperature above 200 °C.

[0021] Further problems and advantages of each embodiment of the present invention will become apparent from the detailed description and the accompanying drawings.

Brief Description of the Drawings

[0022] [Figure 1A] Each photograph of the SCR system before adding the additive according to the present invention to the urea solution. [Figure 1B] Each photograph of the SCR system after adding the additive according to the present invention to the urea solution. [Figure 2] Test results regarding the dependence of the surface tension of AdBlue® urea solution on the addition amount of the additive according to the present invention.

Modes for Carrying Out the Invention

[0023] Further details of the present invention and examples of further embodiments are described below. However, the present invention is not limited to the following detailed description, which is merely illustrative of the teachings of the present invention.

[0024] Furthermore, each feature described in relation to one exemplary embodiment can be combined with any other exemplary embodiment. Unless otherwise explicitly stated, each feature described in relation to an exemplary embodiment relating to the use of the present invention can be combined with any other exemplary embodiment relating to the use of the present invention and any exemplary embodiment relating to the method of the present invention, and vice versa.

[0025] When a term is described in the singular form with an indefinite or definite article, such as "masculine indefinite article," "feminine indefinite article," "neuter indefinite article," "masculine definite article," "feminine definite article," or "neuter definite article," it also includes the plural form of the term unless explicitly stated otherwise, and vice versa. In this specification, expressions such as "contain" or "include" may mean not only "to include" or "to encompass," but also "to consist of" and "essentially consist of."

[0026] In a first aspect, the present invention relates to the use of a polar solvent as a (cleanup) additive to a solution containing a component that releases ammonia at temperatures above 200°C for the removal of deposits or impurities in a selective catalytic reduction system (SCR system).

[0027] As used herein, the term "clean up" specifically refers to the removal of existing or already occurring deposits or impurities, as opposed to "keep clean," which means preventing the formation of new deposits or impurities.

[0028] As used herein, the term "polar" refers to a solvent that, in contrast to nonpolar or hydrophobic solvents such as hydrocarbons, is particularly polar in nature, such as at least 5 × 10⁻¹⁰. -30It means having a (permanent) electric dipole moment of Cm. The polar solvent can be protic or aprotic.

[0029] In the scope of the present application, "solvent" is understood to be a chemical compound that can dissolve or at least loosen other components, especially by-products or decomposition products of urea or isocyanic acid or other deposits or impurities that can occur in the SCR system.

[0030] The polar solvent is characterized in particular by having a boiling point (or boiling temperature) of at least 140 °C at 101.3 kPa (normal pressure). According to an exemplary embodiment, the polar solvent has a boiling point at 101.3 kPa of at least 150 °C, particularly at least 160 °C, particularly at least 180 °C, particularly at least 200 °C. It is advantageous for the polar solvent to be in liquid form at the operating temperature of the SCR system. Thereby, deposits or impurities in the SCR can be removed particularly effectively by the polar solvent. The maximum boiling point of the polar solvent at 101.3 kPa is not particularly limited and is preferably less than 500 °C, particularly less than 400 °C.

[0031] According to an exemplary embodiment, the polar solvent has a (permanent) electric dipole moment of at least 5×10 -30 Cm. The electric dipole moment, especially the permanent electric dipole moment, is a measure of the polarity of a molecule, and the polarity is usually caused by polar atomic bonds (e.g., due to different electronegativities of the atoms involved) or (e.g., in the case of zwitterionic compounds) charges. In particular, the polar solvent can have a (permanent) electric dipole moment of at least 5.5×10 -30 Cm, particularly at least 6×(10) -30 Cm, particularly at least 6.5×(10) -30 Cm, particularly at least 7×(10) -30 Cm.

[0032] According to exemplary embodiments, polar solvents are miscible with water (at 20°C and / or 101.3 kPa) in a concentration range of 10 ppm to 50% by weight (50% (m / m)) without the formation of (two or more) phases, turbidity, or emulsions.

[0033] According to exemplary embodiments, the polar solvent is configured such that the surface tension of a solution consisting of water, 32.5% by weight urea, and 100 ppm of the polar solvent is at least 55 mN / m, particularly at least 60 mN / m, and particularly at least 65 mN / m, at a temperature of 20°C (and a pressure of 101.3 kPa). In other words, the polar solvent may be configured such that when 100 ppm of the polar solvent is added to a solution of water and 32.5% by weight urea, the surface tension of the solution does not fall below 55 mN / m, particularly below 60 mN / m, and particularly below 65 mN / m, which is advantageous with respect to (substantial) compliance with ISO standard 22241.

[0034] According to exemplary embodiments, the polar solvent is characterized by having low effervescence when used in an aqueous urea solution such as AdBlue® or other ammonia-releasing solutions.

[0035] According to exemplary embodiments, the polar solvent is selected from the group consisting of amine oxides, organic carbonates, condensation products of carboxylic acids and sarcosine, glucosides, polyalkylene glycols, glycol ethers, alcohols, amino alcohols, and mixtures thereof. Preferred amine oxides include oxides of tertiary aliphatic amines, particularly C2-C22 alkylamine oxides such as N,N-dimethyl-C6-C14 alkylamine N-oxide. Preferred organic carbonates include propylene carbonates. Preferred condensation products of carboxylic acids and sarcosine include condensation products of fatty acids (particularly C2-C22 fatty acids) and sarcosine, which are optionally neutralized with an amine or amino alcohol. Suitable polyalkylene glycols include polyalkylene glycols having an ethoxyl group to propoxyl group ratio of at least 2:1, and polyethylene glycols (e.g., with an average molecular weight of 200 to 800 g / mol). Suitable glycol ethers include, in particular, dipropylene glycol n-propyl ether, dipropylene glycol n-butyl ether, propylene glycol n-butyl ether, propylene glycol n-propyl ether, tripropylene glycol n-butyl ether, propylene glycol phenyl ether, dipropylene glycol phenyl ether, dipropylene glycol dimethyl ether, propylene glycol methyl ether, propylene glycol methyl ether acetate, dipropylene glycol methyl ether, dipropylene glycol methyl ether acetate, tripropylene glycol methyl ether, ethylene glycol hexyl ether, diethylene glycol hexyl ether, ethylene glycol propyl ether, diethylene glycol phenyl ether, ethylene glycol phenyl ether, poly(oxy-1,2-ethanediyl) α-phenyl-ω-hydroxy, diethylene glycol ethyl ether, diethylene glycol n-butyl ether, and ethylene glycol n-butyl ether. Preferred alcohols include, in particular, 3-methoxy-3-methyl-1-butanol.A particularly suitable amino alcohol is triethanolamine. A mixture of two or more of the listed polar solvents is also suitable.

[0036] According to exemplary embodiments, the polar solvent is selected from the group consisting of N,N-dimethyldecylamine-N-oxide, propylene carbonate, polyethylene glycol, 3-methoxy-3-methyl-1-butanol, triethanolamine, and mixtures thereof. In particular, N,N-dimethyldecylamine-N-oxide proved to be especially suitable for the effective removal of existing deposits or impurities in SCR systems.

[0037] According to exemplary embodiments, the solution containing a component that releases ammonia above 200°C includes a polar solvent in amounts (concentrations) of 10 to 5000 ppm, particularly 20 to 1000 ppm, particularly 50 to 500 ppm, particularly 75 to 400 ppm, and particularly 100 to 200 ppm. Amounts exceeding 5000 ppm are also preferred, but generally do not result in further improvement in the removal of deposits or impurities.

[0038] According to an exemplary embodiment, the component that releases ammonia at temperatures above 200°C comprises urea or a derivative thereof.

[0039] According to exemplary embodiments, the solution containing a component that releases ammonia above 200°C is an aqueous urea solution, particularly having a concentration of 31 to 34% by weight of urea, especially about 32.5% by weight of urea, or, for example in applications in the marine sector, 38 to 42% by weight of urea, especially about 40% by weight of urea.

[0040] In another embodiment, the present invention relates to a method for removing deposits or impurities in a selective catalytic reduction system (particularly of exhaust gases from a diesel fuel internal combustion engine), wherein the system is operated using a solution containing a component that releases ammonia at over 200°C, the solution further comprising a polar solvent having a boiling point of at least 140°C at 101.3 kPa.

[0041] According to exemplary embodiments, the polar solvents detailed above can be used.

[0042] According to exemplary embodiments, a solution containing a component that releases ammonia above 200°C includes a polar solvent in an amount (concentration) of 10 to 5000 ppm, particularly 20 to 1000 ppm, particularly 50 to 500 ppm, particularly 75 to 400 ppm, and particularly 100 to 200 ppm.

[0043] In a further embodiment, the present invention relates to a method for operating a selective catalytic reduction system (particularly for exhaust gases of a diesel fuel internal combustion engine), the method comprising the steps of: injecting a solution into the system containing a component that releases ammonia at over 200°C and further containing a polar solvent having a boiling point (boiling temperature) of at least 140°C at 101.3 kPa; and heating the solution in the system to a temperature of over 200°C. This makes it possible to achieve the removal of deposits or impurities, particularly in an SCR system.

[0044] According to exemplary embodiments, the polar solvents detailed above can be used.

[0045] According to exemplary embodiments, a solution containing a component that releases ammonia above 200°C includes a polar solvent in an amount (concentration) of 10 to 5000 ppm, particularly 20 to 1000 ppm, particularly 50 to 500 ppm, particularly 75 to 400 ppm, and particularly 100 to 200 ppm.

[0046] The present invention will be further described below with reference to the following embodiments, but these embodiments are merely for illustrating the teachings of the present invention and are not intended to limit the scope of the invention. [Examples]

[0047] Investigation of the cleanup behavior of various additives in SCR systems The additives investigated -N,N-dimethyldecylamine-N-oxide (Example 1) - Polyethylene glycol 400 (Example 2) - C9-C11 fatty alcohol ethoxylate having 8 ethoxyl units (Comparative Example 1)

[0048] Each mixture was prepared by adding 100 ppm of each investigated additive to AdBlue®, and the surface tension of each mixture was measured at 20°C. Pure AdBlue® (i.e., no additives) had a surface tension of 73.0 mN / m at 20°C. The cleanup behavior of each mixture in an SCR system heavily loaded with sediment was further investigated, and the presence of sediment was visually evaluated on a scale from 0 (clean) to 4 (heavily contaminated).

[0049] The survey results are shown in Table 1. [Table 1]

[0050] When 100 ppm of N,N-dimethyldecylamine-N-oxide (Example 1) was used, the resulting solution showed only a slight decrease in surface tension, falling just below the baseline of 65 mN / m, and extremely low foaming behavior. However, considerable cleanup behavior was observed in actual SCR systems heavily loaded with sediment. Figure 1 shows photographs of the SCR system before (Figure 1A) and after (Figure 1B) use of the mixture from Example 1.

[0051] PEG400 (Example 2) also proved to be an effective additive for removing deposits in SCR systems, and in addition, it does not reduce the surface tension of AdBlue®, thus maintaining the standard value of 65 mN / m.

[0052] Further investigation revealed that, as shown in Comparative Example 1, the surfactant properties of the additive can even lead to a deterioration of the cleanup behavior, and that the significant foam generation and substantial decrease in surface tension are also disadvantages.

[0053] The dependence of the surface tension of AdBlue® urea solution on the amount of the additive N,N-dimethyldecylamine-N-oxide according to the present invention was further investigated. The test results are illustrated in Figure 2. As can be seen from this, even at higher concentrations of the additive, the decrease in surface tension is only slight.

[0054] The present invention has been described using specific embodiments and examples. However, the present invention is not limited thereto, and various modifications can be made without departing from the scope of the invention.

Claims

1. Use of a polar solvent as an additive to a solution containing a component that releases ammonia at temperatures above 200°C for the removal of deposits or impurities in a selective catalytic reduction system, wherein the polar solvent has a boiling point of at least 140°C at 101.3 kPa.

2. The polar solvent is at least 5 × 10 －３０ The use according to claim 1, having an electric dipole moment of Cm.

3. The use according to claim 1 or 2, wherein the polar solvent is miscible with water in a concentration range of 10 ppm to 50% by weight without the formation of phases, turbidity, or emulsions.

4. The use according to any one of the preceding paragraphs, wherein the surface force of a solution consisting of water, 32.5% by weight of urea, and 100 ppm of the polar solvent is configured to be at least 55 mN / m, and more particularly at least 65 mN / m, at a temperature of 20°C.

5. The polar solvent is selected from the group consisting of amine oxides, organic carbonates, condensation products of carboxylic acids and sarcosine, glucosides, polyalkylene glycols, glycol ethers, alcohols, amino alcohols, and mixtures thereof, as described in any one of the preceding paragraphs.

6. The polar solvent is selected from the group consisting of N,N-dimethyldecylamine-N-oxide, propylene carbonate, polyethylene glycol, 3-methoxy-3-methyl-1-butanol, triethanolamine, and mixtures thereof, as described in any one of the preceding paragraphs.

7. The polar solvent has a boiling point at 101.3 kPa of at least 160°C, and more particularly at least 180°C, as described in any one of the preceding paragraphs.

8. The use described in any one of the preceding paragraphs, wherein the solution containing a component that releases ammonia at temperatures above 200°C contains the polar solvent in an amount of 10 to 5000 ppm.

9. The use described in any one of the preceding paragraphs, wherein the component that releases ammonia at temperatures above 200°C comprises urea or a derivative thereof.

10. The use described in any one of the preceding paragraphs, wherein the solution containing a component that releases ammonia at temperatures above 200°C is an aqueous urea solution, and more particularly having a urea concentration of 31 to 34% by weight.

11. A method for removing deposits or impurities in a selective catalytic reduction system, comprising operating the system with a solution containing a component that releases ammonia at temperatures above 200°C, wherein the solution further contains a polar solvent having a boiling point of at least 140°C at 101.3 kPa.

12. A method for operating a selective catalytic reduction system, wherein the method is as follows: The steps include: injecting the system with a solution containing a component that releases ammonia at temperatures above 200°C, and further containing a polar solvent having a boiling point of at least 140°C at 101.3 kPa; The step of heating the aforementioned solution to a temperature exceeding 200°C in the aforementioned system. A driving method that includes the following.

13. The method according to claim 11 or 12, wherein the polar solvent is defined as any one of claims 2 to 7.

14. The method according to any one of claims 11 to 13, wherein the solution containing a component that releases ammonia at temperatures above 200°C contains the polar solvent in an amount of 10 to 5000 ppm.

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