Additive for cleaning SCR systems

Abstract

The present disclosure relates to the use of a polar solvent as an additive to a solution containing a component that releases ammonia at above 200 C. for the removal of deposits or impurities in a selective catalytic reduction system, wherein the polar solvent has a boiling point at 101.3 kPa of at least 140 C. The present disclosure further relates to a method of removing deposits or impurities in a selective catalytic reduction system and a method of operating a selective catalytic reduction system.

Claims

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

2. The method according to claim 1, wherein the polar solvent has an electric dipole moment of at least 510.sup.30 Cm.

3. The method according to claim 1, wherein the polar solvent is miscible with water in a concentration range from 10 ppm to 50% by weight without forming phases, turbidity or an emulsion.

4. The method according to claim 1, wherein the polar solvent is configured such that a surface tension of a solution of 32.5% by weight of urea and 100 ppm of the polar solvent in water at 20 C. is at least 55 mN/m.

5. The method according to claim 1, wherein the polar solvent is selected from the group consisting of amine oxides, organic carbonates, condensation products of carboxylic acids with sarcosine, glucosides, polyalkylene glycols, glycol ethers, alcohols, aminoalcohols and mixtures thereof.

6. The method according to claim 1, wherein 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.

7. The method according to claim 1, wherein the polar solvent has a boiling point at 101.3 kPa of at least 160 C.

8. The method according to claim 1, wherein the solution containing a component that releases ammonia at above 200 C. contains the polar solvent in an amount of 10 to 5000 ppm.

9. The method according to claim 1, wherein the component that releases ammonia at above 200 C. comprises urea or a derivative thereof.

10. The method according to claim 1, wherein the solution containing a component that releases ammonia at above 200 C. is an aqueous urea solution.

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

12. The method according to claim 11, wherein the polar solvent has an electric dipole moment of at least 510.sup.30 Cm.

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

14. The method according to claim 4, wherein the polar solvent is configured such that a surface tension of a solution of 32.5% by weight of urea and 100 ppm of the polar solvent in water at 20 C. is at least 65 mN/m.

15. The method according to claim 7, wherein the polar solvent has a boiling point at 101.3 kPa of at least 180 C.

16. The method according to claim 10, wherein the solution containing a component that releases ammonia at above 200 C. is an aqueous urea solution with a concentration of 31 to 34% by weight of urea.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows photographs of an SCR system before (FIG. 1A) and after (FIG. 1B) the addition of an additive according to the disclosure to a urea solution.

(2) FIG. 2 shows test results on the dependence of the surface tension of an AdBlue urea solution on the amount of an additive according to the disclosure added.

DETAILED DESCRIPTION OF THE DISCLOSURE

(3) Further details of the present disclosure and further embodiments thereof are described below. However, the present disclosure is not limited to the following detailed description, but merely serves to illustrate the teachings according to the disclosure.

(4) It should be noted that features described in connection with an exemplary embodiment may be combined with any other exemplary embodiment. In particular, features described in connection with an exemplary embodiment of a use according to the disclosure may be combined with any other exemplary embodiment of a use according to the disclosure and with any exemplary embodiment of a method according to the disclosure, and vice versa, unless expressly stated otherwise.

(5) When a term is denoted by an indefinite or definite article, such as a, an and the, in the singular, this also includes the term in the plural and vice versa, unless the context clearly specifies otherwise. The terms have or comprise as used herein not only include the meaning of contain or include, but may also mean consist of and consist essentially of.

(6) In a first aspect, the present disclosure relates to the use of a polar solvent as a (clean-up) additive to a solution containing a component that releases ammonia at above 200 C. for removing deposits or impurities in a selective catalytic reduction (SCR) system.

(7) The term clean up as used herein means, in particular, a removal of existing or pre-existing deposits or impurities, in contrast to keep clean, i.e. the prevention of the formation of new deposits or impurities.

(8) The term polar as used herein means in particular that the solvent so designated has a certain polarity, for example a (permanent) electric dipole moment of at least 510.sup.30 Cm, in contrast to an apolar or hydrophobic solvent, such as a hydrocarbon. The polar solvent can be protic or aprotic.

(9) In the context of the present application, a solvent is understood in particular to be a chemical compound which is capable of dissolving or at least partly dissolving or etching other components, in particular by-products or decomposition products of urea or isocyanic acid or other deposits or impurities which may be generated in an SCR system.

(10) The polar solvent is characterized in particular in that it has a boiling point (or a boiling temperature) at 101.3 kPa (normal pressure) of at least 140 C. According to an exemplary embodiment, the polar solvent has a boiling point at 101.3 kPa of at least 150 C., in particular of at least 160 C., in particular of at least 180 C., in particular of at least 200 C. Advantageously, the polar solvent is in liquid form at the operating temperature of the SCR system. As a result, deposits or impurities in the SCR system can be removed particularly effectively by the polar solvent. The maximum boiling point of the polar solvent at 101.3 kPa is not particularly restricted and is preferably less than 500 C., in particular less than 400 C.

(11) According to an exemplary embodiment, the polar solvent has a (permanent) electric dipole moment of at least 510.sup.30 Cm. The electric dipole moment, and in particular the permanent electric dipole moment, is a measure of the polarity of a molecule, which is usually caused by polar atomic bonds (e.g. due to different electronegativities of the atoms involved) or also by charges (e.g. in the case of zwitterionic compounds). In particular, the polar solvent may have a (permanent) electric dipole moment of at least 5.510.sup.30 Cm, in particular of at least 610.sup.30 Cm, in particular of at least 6.510.sup.30 Cm, in particular of at least 710.sup.30 Cm.

(12) According to an exemplary embodiment, the polar solvent is miscible with water (at 20 C. and/or 101.3 kPa) in a concentration range from 10 ppm to 50% by weight (50% (m/m)), in particular without forming (two or more) phases, turbidity or an emulsion.

(13) According to an exemplary embodiment, the polar solvent is configured such that a surface tension of a solution of 32.5% by weight of urea and 100 ppm of the polar solvent in water at a temperature of 20 C. (and a pressure of 101.3 kPa) is at least 55 mN/m, in particular at least 60 mN/m, in particular at least 65 mN/m. In other words, the polar solvent may be configured such that when 100 ppm thereof is added to a solution of 32.5% by weight of urea in water, the surface tension of the solution is not reduced to below 55 mN/m, in particular not to below 60 mN/m, in particular not to below 65 mN/m, which is advantageous in terms of (substantial) compliance with ISO standard 22241.

(14) According to an exemplary embodiment, the polar solvent is characterized by a low foaming potential when used in an aqueous urea solution such as AdBlue or another ammonia-releasing solution.

(15) According to an exemplary embodiment, the polar solvent is selected from the group consisting of amine oxides, organic carbonates, condensation products of carboxylic acids with sarcosine, glucosides, polyalkylene glycols, glycol ethers, alcohols, aminoalcohols and mixtures thereof. Suitable amine oxides include in particular oxides of tertiary aliphatic amines, in particular C2-C22 alkyl amine oxides, such as N,N-dimethyl-C6-C14 alkylamine N-oxides. Suitable organic carbonates include, in particular, propylene carbonate. Suitable condensation products of carboxylic acids with sarcosine include in particular condensation products of fatty acids (in particular C2-C22 fatty acids) with sarcosine, optionally neutralized with amines or aminoalcohols. Suitable polyalkylene glycols include in particular polyalkylene glycols with a ratio of ethoxyl to propoxyl groups of at least 2:1 and polyethylene glycols (for example with an average molecular mass 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) -phenyl--hydroxy, diethylene glycol ethyl ether, diethylene glycol n-butyl ether and ethylene glycol n-butyl ether. Suitable alcohols include in particular 3-methoxy-3-methyl-1-butanol. Suitable amino alcohols include in particular triethanolamine. Mixtures of two or more of the polar solvents mentioned are also suitable.

(16) According to an exemplary embodiment, 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 has proven to be particularly suitable for the effective removal of existing deposits or impurities in an SCR system.

(17) According to an exemplary embodiment, the solution containing a component that releases ammonia at above 200 C. contains the polar solvent in an amount (concentration) of from 10 to 5000 ppm, in particular from 20 to 1000 ppm, in particular from 50 to 500 ppm, in particular from 75 to 400 ppm, in particular from 100 to 200 ppm. Amounts above 5000 ppm are also well suited, but generally do not bring about any further improvement in the removal of deposits or impurities.

(18) According to an exemplary embodiment, the component that releases ammonia at above 200 C. comprises urea or a derivative thereof.

(19) According to an exemplary embodiment, the solution containing a component that releases ammonia at above 200 C. is an aqueous urea solution, in particular with a concentration of 31 to 34% by weight of urea, in particular of about 32.5% by weight of urea, or alsofor example in maritime applicationswith a concentration of 38 to 42% by weight of urea, in particular of about 40% by weight of urea.

(20) In a further aspect, the present disclosure relates to a method of removing deposits or impurities in a selective catalytic reduction system (in particular of exhaust gases from internal combustion engines fueled by diesel), wherein the system is operated with a solution containing a component that releases ammonia at above 200 C., wherein the solution further contains a polar solvent having a boiling point at 101.3 kPa of at least 140 C.

(21) According to an exemplary embodiment, a polar solvent as described in more detail above can be used.

(22) According to an exemplary embodiment, the solution comprising a component that releases ammonia at above 200 C. comprises the polar solvent in an amount (concentration) of from 10 to 5000 ppm, in particular from 20 to 1000 ppm, in particular from 50 to 500 ppm, in particular from 75 to 400 ppm, in particular from 100 to 200 ppm.

(23) In still a further aspect, the present disclosure relates to a method of operating a selective catalytic reduction system (in particular of exhaust gases from diesel-fueled internal combustion engines), the method comprising injecting a solution containing a component that releases ammonia at above 200 C. into the system, the solution further containing a polar solvent having a boiling point at 101.3 kPa of at least 140 C., and heating the solution to a temperature above 200 C. in the system. By doing so, a removal of deposits or impurities in the SCR system may in particular be achieved.

(24) According to an exemplary embodiment, a polar solvent as described in more detail above can be used.

(25) According to an exemplary embodiment, the solution comprising a component that releases ammonia at above 200 C. comprises the polar solvent in an amount (concentration) of from 10 to 5000 ppm, in particular from 20 to 1000 ppm, in particular from 50 to 500 ppm, in particular from 75 to 400 ppm, in particular from 100 to 200 ppm.

(26) The present disclosure is further described with reference to the following examples, which, however, serve only to illustrate the teachings according to the disclosure and are in no way intended to limit the scope of the present disclosure.

EXAMPLES

(27) Tests about the Clean-Up Behavior of Various Additives in an SCR System

(28) Additives Tested:

(29) N,N-Dimethyldecylamine-N-oxide (example 1) Polyethylene glycol 400 (example 2) C9-C11 fatty alcohol ethoxylate with 8 ethoxyl units (comparative example 1)

(30) Mixtures of AdBlue with 100 ppm of each of the tested additives were prepared and the surface tension of the resulting mixtures was determined at 20 C. A surface tension at 20 C. of 73.0 mN/m was determined for pure AdBlue (i.e. without additives). In addition, the clean-up behavior of the mixtures was investigated in an SCR system heavily contaminated with deposits, whereby the presence of deposits was evaluated by visual assessment on a scale from 0 (clean) to 4 (heavily contaminated).

(31) The results of the test are shown in Table 1:

(32) TABLE-US-00001 TABLE 1 Comparative Example 1 Example 2 example 1 Surface tension of 57.1 73.0 28.2 the mixture at 20 C. [mN/m] Visual assessment 3 4 4 of the deposits before using the mixture Visual assessment 0 1 2 of the deposits after using the mixture

(33) When using 100 ppm N,N-dimethyldecylamine-N-oxide (example 1), only a slight reduction in surface tension below the standard value of 65 mN/m and very low foaming behavior of the resulting solution was observed in the real application. However, considerable clean-up behavior was observed in a real SCR system that was very contaminated with deposits. FIG. 1 shows photographs of the SCR system before (FIG. 1A) and after (FIG. 1B) the use of the mixture according to example 1.

(34) PEG 400 (example 2) has also proven to be an efficient additive for removing deposits in an SCR system, which further does not lead to a reduction in the surface tension of AdBlue, so that the standard value of 65 mN/m can be maintained.

(35) The tests have also shown that a surfactant character of the additive, as in comparative example 1, even leads to a deterioration of the clean-up behavior and is also disadvantageous due to a strong foam development and a strong lowering of the surface tension.

(36) In addition, the dependence of the surface tension of an AdBlue urea solution on the added amount of the additive N,N-dimethyldecylamine-N-oxide according to the disclosure was investigated. The test results are shown in FIG. 2. As can be seen from this, even higher concentrations of this additive only lead to a slight further reduction in surface tension.

(37) The present disclosure has been described with reference to specific embodiments and examples. However, the disclosure is not limited thereto and various modifications thereof are possible without departing from the scope of the present disclosure.