AQUEOUS COMPOSITION FOR THE TREATMENT OF EXHAUST GASES WITH IMPROVED DEFOAMING PROPERTIES

Description

[0001] The present invention relates to a composition for treating exhaust gases at the outlet of on-board or stationary thermal engines, whether the engines are engines for heavy vehicles such as heavy goods vehicles, transport vehicles, non-road vehicles known as "Off Road" such as agricultural machinery, boats, or engines for light and / or utility vehicles or even engines for stationary industrial applications. It also relates to the use of such a composition in any exhaust gas treatment device, as well as a method for treating exhaust gases using this composition. STATE OF THE PRIOR ART

[0002] European standards on pollution emitted by internal combustion engines, particularly those powered by diesel fuels, and particularly the standards applicable to heavy-duty vehicles, have led engine manufacturers to implement exhaust gas aftertreatment systems. These systems include SCR (Selective Catalytic Reduction), EGR (Exhaust Gas Recirculation), DOC (Diesel Oxidation Catalyst), DPF (Particulate Filters) and SCRF ®< (an SCR combined with a DPF). These different aftertreatment systems can be installed alone or in combination, as they do not always act on the same pollutants present in the exhaust gases.

[0003] To meet standards, particularly European standards (Euro IV and following standards for heavy goods vehicles and Euro 6 for light vehicles), most European car manufacturers have opted for SCR post-treatment of their engine exhausts. This post-treatment acts exclusively on reducing nitrogen oxides present in the gases. Another advantage of this technique is that it allows, through optimized engine settings, a significant reduction in fuel consumption, particularly compared to other post-treatment systems such as NOx traps.

[0004] SCR post-treatment consists of reducing nitrogen oxides NO and NO 2 (commonly called NOx) on a catalytic device which allows them to be brought into contact with a reducing agent. This device contains a catalyst comprising a support generally based on zeolites exchanged with iron or copper. This catalyst promotes the reduction of NOx to nitrogen, by reaction with the reducing agent. A classic reducing agent is for example ammonia (NH 3 ). To introduce gaseous ammonia into the exhaust gas treatment system, it is known to produce it directly in the pipe carrying these gases to the SCR system by vaporizing an aqueous solution of a precursor of this reducing agent such as for example urea. The urea solution, injected at an average exhaust temperature generally of 150 to 400°C, releases ammonia thanks to successive thermolysis and hydrolysis reactions.Other ammonia precursor compounds can be used under similar conditions. An injector is usually used to introduce the aqueous urea solution into the pipe carrying the exhaust gases to the SCR catalyst, upstream of it. A mixer, installed between this injector and the SCR catalyst, can be used to improve the vaporization of the aqueous urea solution spray into the exhaust gas stream. An example of a mixer is described in SAE 2015-01-1020 (“Advanced Close Coupled SCR Compact Mixer Architecture”, Michelin J. et al.).

[0005] Two classic, but non-limiting, examples of SCR post-treatment line configuration are described below. The first, called the "underfloor" configuration, consists of placing the SCR post-treatment device downstream of the engine, under the floor of the vehicle (generally more than 50 cm to 1 m from the combustion chamber outlet). It has the advantage of being able to install the post-treatment device in an area where a lot of space is available and thus place it in geometric conditions more favorable to vaporization of the aqueous urea solution. Another configuration, called the "close-coupled" configuration, consists of placing the SCR post-treatment device in the immediate vicinity of the engine (generally less than 50 cm from the combustion chamber outlet).Compared to the so-called "underfloor" configuration, this configuration has the advantage of benefiting from higher temperatures in the SCR catalyst, improving its initiation and efficiency. On the other hand, its disadvantage is that the available space is smaller than in the "underfloor" configuration, which implies that the injector of aqueous urea solution is placed closer to the mixer and the SCR catalyst. This configuration can lead to poorer vaporization of the aqueous urea solution. Documents SAE 2014-01-1522 ("Control of a Combined SCR on Filter and Under-Floor SCR System for Low Emission Passenger Cars", Balland J. et al.) and SAE 2015-01-0994 ("Next Generation All in One Close-Coupled Urea-SCR System", Kojima H. ​​et al.), or WO2014060987A1 describe these two types of configuration.

[0006] In certain installation configurations of the SCR device and the injection of ammonia precursor, particularly in the case of urea injection, manufacturers have observed the appearance of deposits in the exhaust pipes located between the injector and the SCR device. These deposits can be significant enough to cause partial or even total obstruction of the exhaust pipe linked to the exhaust back pressure and thus create engine power losses. At constant injection configuration, the quantity of deposits formed is greater at low temperatures than at high temperatures. These deposits, according to the analyses carried out in SAE technical publication 2016-01-2327, are of variable nature depending on the temperature at which they were formed. Thus, at temperatures below 250-300°C, they consist mainly of crystallized urea, and are mainly made up of cyanuric acid above 300°C.Cyanuric acid can sublimate and produce ammonia gas again. However, this reaction can only occur at very high temperatures, above 450°C. Such a temperature is rarely reached at this point in exhaust pipes.

[0007] These deposits were found to be present in pipes with bends due to lack of space in the vehicle, and when the distance between the urea injection and the first bend is too short, as in the "close-coupled" configurations described above. The hypothesis formulated is that in this type of configuration, some of the urea drops do not have time to vaporize and completely decompose into gaseous ammonia. The urea drops are deposited on the pipe wall, which is at a temperature too low to allow complete decomposition into gaseous ammonia, and they only partially decompose, forming cyanuric acid deposits stuck to the wall.Furthermore, it was also found that depending on the SCR line configuration and temperature, urea was likely to crystallize in the line, resulting in line obstruction (see document SAE 2017-26-0132 (“A Study on the Factors Affecting the Formation of Urea Crystals and Its Mitigation for SCR After-Treatment Systems”, Jain A. et al.).

[0008] Application WO2008 / 125745 describes an aqueous solution comprising a compound capable of releasing gaseous ammonia above 200°C and at least one polyfunctional additive whose HLB varies from 7 to 17 to limit the formation of cyanuric acid-based deposits in an exhaust gas post-treatment device, in particular of the SCR type. The polyfunctional additives used are in particular polyalkoxylated fatty alcohol ethers and polyalkoxylated fatty alcohol esters.

[0009] Application EP2337625 describes a mixture of surfactants for reducing the diameter of droplets in an aqueous urea solution, thereby promoting its vaporization and the transformation of urea into gaseous ammonia in an SCR system. The proposed solution consists of a mixture of polyalkoxylated fatty alcohols, with controlled degrees of alkoxylation.

[0010] Application EP2488283 describes additives for urea solution, of the particular polyalkoxylated fatty alcohol type. These additives are also intended to promote a reduction in the formation of deposits resulting from the decomposition of urea in SCR systems.

[0011] US Patent 5,453,257 teaches the reduction of the nitrogen oxide content in the combustion effluents of a carbonaceous fuel by introducing into said effluents an emulsion of a nitrogen oxide reducing compound and a hydrocarbon compound having a boiling point lower than that of the nitrogen oxide reducing agent.

[0012] However, it has been found that aqueous solutions of ammonia precursor containing surfactants tend to foam. This foaming occurs in particular during the transport and handling of the solution, for example when it is unloaded into storage tanks, then when the composition is introduced from a storage tank into the tank of a vehicle, which complicates the operation of filling the tank and can cause it to overflow. The common use of guns when dispensing the composition also promotes its foaming. In addition, the foaming of the composition when it occurs at the time of its injection into the vehicle's exhaust gas treatment system can lead to the introduction of a greater or lesser amount of air into said system. This phenomenon disrupts the control of the quantity of solution injected and affects the efficiency of the treatment system.

[0013] One solution to this problem is to add one or more anti-foaming agents to the aqueous solution. However, such additives often have a reduced effectiveness over the storage time of the composition prior to use, especially when the composition is stored at relatively high temperatures, above 30°C or even 35 or 40°C. Under such storage conditions, the composition generally cannot be stored for more than a few months (on average 5 months), which is very restrictive.

[0014] WO 2018 / 178592 A1 describes an aqueous composition which contains a NOx reducing agent as well as an additive which has surfactant properties. Advantageously the composition also comprises an anti-foaming agent which may be an aqueous siloxane-based solution.

[0015] There remains a need to be able to formulate compositions for the treatment of exhaust gases in the form of aqueous solutions based on a NOx reducing agent, for example ammonia, or a precursor of such a reducing agent, such as urea, which have optimized properties. This composition is expected to be able to avoid or reduce deposits when used on an SCR line, while avoiding foaming problems. This composition is also expected to be stable over time, i.e. to retain its properties over long periods of storage, including at high temperatures.

[0016] The Applicant found that this objective was achieved by adding to the aqueous composition at least one particular additive consisting of one or more copolymers consisting of grafted polydimethylsiloxanes as defined below.

[0017] The present invention thus relates to an aqueous composition comprising: at least one nitrogen oxide NOx reducing agent and / or at least one precursor of such an agent, at least one surfactant, and at least one anti-foam additive chosen from copolymers comprising a polydimethylsiloxane backbone with an average number of dimethylsiloxane units in the range of 150 to 300, grafted with polyoxyalkylene chains.

[0018] The present invention also relates to the use of such a composition for the treatment of exhaust gases at the outlet of on-board or stationary internal combustion engines, more particularly for the treatment of exhaust gases in a device for the selective catalytic reduction of nitrogen oxides.

[0019] The engine may in particular be chosen from Diesel engines, spark-ignition engines (including gasoline engines and CNG or natural gas engines for vehicles), and mixed fuel engines, in particular diesel-gas. Preferably, the engine is a Diesel engine.

[0020] The present invention applies to any type of engine capable of emitting nitrogen oxides, including on-board engines and stationary engines. The invention applies, among others, to marine engines, heavy goods vehicle engines, transport vehicle engines, construction machinery engines or agricultural machinery such as tractors, as well as to light and utility vehicle engines, as well as to engines used in stationary industrial applications.

[0021] A device for selective catalytic reduction of nitrogen oxides is a device known per se under the name SCR device for "Selective Catalytic Reduction" in English. Such a device comprises a Selective Catalytic Reduction catalyst (also called SCR catalyst).

[0022] The invention also relates to a method for treating exhaust gases from an internal combustion engine, preferably a diesel engine, equipped with a device for selective catalytic reduction of nitrogen oxides, this method being characterized in that it comprises at least one step of introducing a composition as defined above into the pipe which conveys the exhaust gases from the engine outlet to said selective catalytic reduction device.

[0023] In the following, the term SCR exhaust line or SCR line, in a manner known per se, also refers to the pipe which carries the exhaust gases from the outlet of an engine to a selective catalytic reduction device (SCR device).

[0024] The composition according to the invention has numerous advantages: it can be used in the same way and in the same equipment as the solutions of the prior art. It is at least as effective, or even more effective, than the solutions of the prior art, in particular urea-based solutions in reducing or preventing the formation of deposits in SCR systems, in particular in so-called "close-coupled" configurations. It causes little or no foaming during its handling, use, transfer and / or transport, for example during operations of transferring or filling containers such as drums, vehicle tanks, storage tanks or transport tanks. In particular, it makes it possible to avoid overflows when filling the storage tank of a vehicle.It also allows storage tanks and vehicle reservoirs to be filled more quickly, and in the latter case by limiting the jolts of the filling guns.

[0025] This composition also allows precise control of the quantity of composition injected, and in particular helps to avoid errors linked to the sensors being faulty by the foam.

[0026] The composition according to the invention is stable during storage. It also exhibits antifoaming performance maintained over time, particularly over periods of up to one year, over a wide range of storage temperatures, from 5°C to 40°C.

[0027] Other objects, characteristics, aspects and advantages of the invention will appear even more clearly on reading the description and examples which follow.

[0028] In what follows, and unless otherwise indicated, the limits of a range of values ​​are included in this range, in particular in the expressions "between" and "ranging from ... to ...". Furthermore, the expressions "at least one" and "at least" used in the present description are respectively equivalent to the expressions "one or more" and "greater than or equal to". Finally, in a manner known per se, the term "CN compound or group" denotes a compound or group containing N carbon atoms in its chemical structure. DETAILED DESCRIPTION The reducing agent and / or the precursor of such an agent

[0029] The composition used in the invention comprises at least one nitrogen oxide reducing agent and / or at least one precursor of a nitrogen oxide reducing agent.

[0030] The term "nitrogen oxide reducing agent" means a compound capable of reducing at least partially, if not completely, nitrogen oxides (also called NOx to designate the compounds NO and NO 2 ) to nitrogen, under the conventional operating conditions of an SCR line, i.e. in the presence of an SCR catalyst and at a temperature ranging from 150 to 400°C. Among the NOx reducing agents, ammonia (NH 3 ) may be mentioned in particular.

[0031] “Precursor of a NOx reducing agent” means a compound capable of releasing a NOx reducing agent under the effect of temperature and / or by catalytic reaction.

[0032] Among the ammonia precursors, urea may be mentioned which, through successive thermolysis and hydrolysis reactions, produces ammonia according to a well-known process. The SCR exhaust line may comprise, upstream of the SCR catalytic system, a catalyst whose function is to transform a precursor of a NOx reducing agent into a NOx reducing agent, in particular into gaseous ammonia.

[0033] Preferably, the reducing agent or the precursor of the reducing agent is chosen from the list consisting of urea, ammonia, formamide, ammonium salts, in particular ammonium formate, ammonium carbamate, and guanidine salts, in particular guanidinium formate; and preferably from the list consisting of urea and ammonia.

[0034] In a preferred embodiment, urea is used, which is a precursor of a reducing agent. Indeed, urea has the advantage of being stable, non-volatile, non-explosive and non-flammable. It can be safely transported, stored and handled by an operator without specific training.

[0035] In this embodiment, the composition has a urea content preferably ranging from 25% to 42% by mass, more preferably from 30% to 40% by mass, even more preferably from 31 to 35% by mass and even better from 32% to 33% by mass, relative to the total mass of the composition. In a particularly preferred manner, the composition contains urea at a content of 32.5 ± 0.7% by mass, in accordance with the specifications of standard ISO 22241-1.

[0036] According to a particularly preferred variant of this embodiment, the aqueous solution according to the invention is prepared from the commercial product AdBlue ®< , which is an aqueous solution of urea at 32.5 ± 0.7% by mass. The term AdBlue ®< is used in the present description to designate indifferently the commercial products well known under the following names: AdBlue ®< , DEF, AUS32, ARLA32. By extension, this name is understood to mean all the products in the AdBlue ®< range, including the product marketed under the name AUS40 which corresponds to an aqueous solution of urea at approximately 40% by mass and is essentially intended for marine engines.

[0037] However, it also falls within the scope of the present invention to use aqueous compositions containing urea with a concentration greater than 32.5%, which can then be diluted just before use. This variant makes it possible to save money when transporting these urea-based compositions. Surfactants

[0038] The composition used in the invention comprises one or more surfactants, which may in particular be chosen from ionic, non-ionic or amphoteric surfactants, soluble in water.

[0039] The ionic surfactants may be chosen from cationic surfactants and anionic surfactants, and preferably from cationic surfactants. The latter generally comprise a cationic or ionizable nitrogen group in cationic form. They may in particular be chosen from linear alkylamines and alkylammoniums, linear diamines, aromatic or saturated heterocycles containing one or more nitrogen atoms, cyclic compounds of the imidazole type, etheramines and etheramides, oxyamines and ethoxyamines, taken alone or as a mixture.

[0040] Amphoteric surfactants can be chosen in particular from amino acids and their imide or amide derivatives, taken alone or in a mixture.

[0041] The non-ionic surfactants are preferably chosen from the following compounds: (a) mono- or polyalkylene glycol hydrocarbyl ethers, (b) polyol hydrocarbyl ethers, (c) mono- or polyalkylene glycol fatty acid esters, (d) mono- or polyglycerol fatty acid esters, (e) and mixtures of these compounds.

[0042] By “hydrocarbyl” is meant a group chosen from alkyl, alkenyl, alkynyl, aryl, aryl-alkyl or “aralkyl”; advantageously the hydrocarbyl is a C 1 -C 50 group.

[0043] By "C i -C j alkyl" is meant a saturated, linear, branched or cyclic hydrocarbon chain, comprising from i to j carbon atoms.

[0044] By “C x -C y alkenyl” is meant a linear, branched or cyclic hydrocarbon chain comprising at least one carbon-carbon double bond, and comprising from x to y carbon atoms.

[0045] By “C x -C y alkynyl” is meant a linear, branched or cyclic hydrocarbon chain comprising at least one carbon-carbon triple bond, and comprising from x to y carbon atoms.

[0046] By "C x -C y aryl" is meant a functional group that is derived from an aromatic hydrocarbon compound comprising from x to y carbon atoms. This functional group may be monocyclic or polycyclic. For illustration, a C 6 -C 18 aryl may be phenyl, naphthalene, anthracene, phenanthrene and tetracene.

[0047] By "C x -C y aralkyl" is meant an aromatic hydrocarbon compound, preferably monocyclic, substituted by at least one linear or branched alkyl chain and whose total number of carbon atoms of the aromatic ring and its substituents ranges from x to y carbon atoms. By way of illustration, a C 7 -C 18 aralkyl may be chosen from the group formed by benzyl, tolyl and xylyl.

[0048] For the purposes of the present invention, the term “polyol” means an oxygenated hydrocarbon compound comprising at least two alcohol functions. The polyols may optionally contain one or more other oxygenated functions, such as, for example, an acetal function, an ether bridge, an ester group.

[0049] By fatty acid is meant, in a manner known per se, a carboxylic acid comprising a linear or branched C 4 -C 30 alkyl or alkenyl chain, preferably C 8 -C 30 . (a) Hydrocarbyl ethers of mono or polyalkylene glycol

[0050] Hydrocarbyl ethers of mono or polyalkylene glycol may be mono ethers or diethers, depending on whether the polyalkylene glycol chain is substituted on one or both ends by a hydrocarbyl group.

[0051] The hydrocarbyl and mono or polyalkylene glycol ethers are advantageously chosen from those comprising a C 1 -C 50 hydrocarbyl group and from 1 to 60 alkylene glycol units.

[0052] The hydrocarbyl and mono or polyalkylene glycol ethers are more preferably chosen from the following compounds: mono- or poly-alkoxylated hydrocarbyl monoethers of formula (I): R-(Y) n -OH; mono- or poly-alkoxylated hydrocarbyl di-ethers of formula (II): R-(Y) m -OR'; mono- or poly-alkoxylated hydrocarbyl di-ethers of formula (III): HO-(Y) n -R"-(Y') m -OH; and mixtures of these compounds.

[0053] In formulas (I) to (III) above, R and R' independently represent C 3 -C 40 alkyl or alkenyl or alkynyl or aryl or aralkyl groups; R" represents an alkane diyl or alkene diyl or alkyne diyl group or an aryl diradical or a C 3 -C 40 aralkyl diradical.

[0054] To facilitate the description, the same designation of alkyl or alkenyl or alkynyl or aryl or aralkyl radical will be used in the following for a mono radical (R, R') and for a di-radical (R").

[0055] In formulas (I) to (III) above, Y and Y' are groups chosen independently of one another from the following groups: -(O-CH 2 -CH 2 )-, -(O-CH(CH 3 )-CH 2 )- and -(O-CH 2 -CH 2 -CH 2 )-.

[0056] In the same compound of formula (I), (II) or (III), the groups Y, respectively Y', may all be identical or may be different. For example, -(Y) n - may represent a copolymer with ethylene oxide and propylene oxide units, such as for example a block copolymer.

[0057] Preferably, in formulas (I) to (III), the groups Y, respectively Y', are all identical.

[0058] More preferably, in formulas (I) to (III), the groups Y, respectively Y', are all ethylene oxide of formula -(O-CH 2 -CH 2 )-.

[0059] In formulas (I) to (III) above, n, m represent the degree of alkoxylation of the molecule, and independently of each other denote an integer ranging from 1 to 60, advantageously from 1 to 30, even better from 1 to 20. More preferably, n and m vary from 3 to 15, even better from 5 to 12.

[0060] Advantageously, in formula (III) the groups Y and Y' represent -(O-CH 2 -CH 2 )- and n=m.

[0061] According to a first embodiment, in formulas (I), (II) and (III), advantageously R, R' and R" are chosen from alkyl and alkenyl groups, linear or branched, preferably linear.

[0062] Even more advantageously, R, R' and R" are chosen from C 5 -C 32 alkyl groups, more preferably C 8 -C 30 alkyl groups.

[0063] The compounds of formula (I) may be particularly chosen from linear or branched polyalkoxylated fatty alcohols comprising from 4 to 30 carbon atoms, preferably 8 to 30 carbon atoms, better still 10 to 24 carbon atoms; and from 5 to 12 ethylene oxide and / or propylene oxide units, preferably ethylene oxide.

[0064] Among the commercially available compounds of formula (I) we can cite the products of the Marlipal ®< range and those of the Surfaline ®< range.

[0065] According to a second embodiment, in formulas (I), (II) and (III), R, R' and R" are chosen from C 4 -C 50 alkynyls.

[0066] Advantageously, this embodiment relates to formula (III), in which R" is a C 4 -C 50 alkynyl.

[0067] For example, according to this embodiment, the compound of formula (III) may be represented by formula (IV) below: in which R1, R2, R3, R4 independently of each other represent H or a C1-C20 alkyl group and x and y independently of each other represent an integer ranging from 1 to 60, preferably from 1 to 30.

[0068] An example of a commercial product meeting this formula is Surfynol 104 ®< marketed by the company Air Products.

[0069] According to a third embodiment, in formulas (I), (II) and (III), R, R' and R" are chosen from aralkyl groups comprising from 9 to 30 carbon atoms.

[0070] Preferably, this embodiment relates to formula (I), in which R represents a group chosen from aralkyls comprising from 9 to 30 carbon atoms.

[0071] More preferably, R is chosen from para-alkylphenyls comprising a C 1 -C 24 alkyl group, more preferably a C 3 -C 20 alkyl group, and better still a C 5 -C 18 alkyl group.

[0072] According to this embodiment, the compound of formula (I) can be represented by the formula (V) below: in which R5 represents a C 1 -C 24 alkyl group, preferably C 3 -C 20 , better still C 5 -C 18 , and x represents an integer ranging from 1 to 50, preferably from 1 to 30.

[0073] An example of such a compound is the product Dynol 800 ®< marketed by the company Air Products, which has the following formula:

[0074] The compounds of formula (I) may advantageously be mixtures obtained by reaction of alcohols R-OH with n units of ethylene oxide and / or propylene oxide. n represents the number of moles of alkylene oxide which have been reacted with one mole of alcohol R-OH.

[0075] The compounds of formula (II) may advantageously be mixtures obtained by reaction of alcohol compounds R-OH with m units of ethylene oxide and / or propylene oxide followed by an etherification reaction with an alcohol compound R'-OH. m represents the number of moles of alkylene oxide which have been reacted with one mole of alcohol R-OH.

[0076] The compounds of formula (III) can advantageously be obtained by reaction of a diol HO- R"-OH with (n+m) units of ethylene oxide and / or propylene oxide. Advantageously in formula (III): n=m. (m+n) represents the number of moles of alkylene oxide which have been reacted with one mole of diol HO-R"-OH.

[0077] Compounds of formula (I), (II) and (III) are generally in the form of mixtures of compounds having varying degrees of alkoxylation. b) Hydrocarbyl ethers and polyols

[0078] The hydrocarbyl ethers and polyols are advantageously chosen from ethers derived from an alcohol comprising a C 1 -C 50 alkyl or alkenyl group, preferably C 3 -C 40 , more advantageously C 5 -C 32 , even better C 8 -C 30 , and from a polyol.

[0079] The polyols referred to here are different from mono and polyalkylene glycols.

[0080] Advantageously, according to a first variant, the polyol is chosen from compounds belonging to the carbohydrate family and their oligomers. In particular, the polyol is chosen from cyclic carbohydrate compounds, such as, for example, glucopyranose oligomers. The invention relates in particular to hydrocarbyl and cyclic polyglucoside ethers.

[0081] Among the hydrocarbyl and cyclic polyglucoside ethers, we can cite alkyl polyglucosides such as the product marketed under the name Triton CG650 ®< by the Dow Chemical company.

[0082] Advantageously, according to a second variant, the polyol is glycerol or a glycerol oligomer, for example an oligomer comprising 2 to 30 glycerol units, preferably 3 to 20 glycerol units. (c) Fatty acid esters of mono or polyalkylene glycol

[0083] Fatty acid esters of mono or polyalkylene glycol are molecules resulting from the condensation of at least one fatty acid with 1 to 60 alkylene glycol units, preferably 1 to 50 alkylene glycol units. Advantageously, they are derived from the reaction of a fatty acid with 1 to 50 ethylene glycol units.

[0084] Fatty acids are generally molecules comprising an alkyl or alkenyl chain, carrying a carboxylic acid function at its end, and comprising 4 to 30 carbon atoms, preferably 8 to 30 carbon atoms, more advantageously 8 to 24 carbon atoms.

[0085] The fatty acid group can be a single molecule or a mixture corresponding to the fatty acid distribution of an animal or vegetable oil.

[0086] Among the fatty acids, mention may be made, without limitation, of a saturated fatty acid such as n-caproic acid, caprylic acid, n-capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, arachidic acid or an unsaturated fatty acid such as palmitoleic acid, oleic acid, linoleic acid, linolenic acid, arachidonic acid or docosahexaenoic acid.

[0087] The esters of fatty acids and mono or polyalkylene glycol advantageously comprise from 3 to 50, even better from 5 to 40 alkylene oxide units. Even better, the esters of fatty acids and mono or polyalkylene glycol comprise from 3 to 50, even better from 5 to 40 ethylene oxide units.

[0088] Examples of fatty acid esters and polyalkylene glycols include the product DUB S PEG 30S (PEG-30 stearate) marketed by the company Stéarinerie Dubois. d) Fatty acid esters of mono or polyglycerol

[0089] Fatty acid esters of mono or polyglycerol are molecules resulting from the condensation of at least one fatty acid with 1 to 60 alkylene glycol units, preferably 1 to 50 glycerol units.

[0090] The fatty acids are the same as those described in point c) above.

[0091] The esters of fatty acids and mono or polyglycerol advantageously comprise from 3 to 50, even better from 5 to 40 glycerol units.

[0092] Examples of fatty acid esters of polyglycerol include the product Polyaldo 10-1-0 KFG ®< (polyglycerol laurate) marketed by the company LONZA.

[0093] According to a preferred embodiment, the surfactant(s) are chosen from non-ionic surfactants. It is particularly preferred to use one or more surfactants chosen from hydrocarbyl and mono or polyalkylene glycol ethers, and more preferably from mono- or poly-alkoxylated hydrocarbyl monoethers of formula (I): R-(Y) n -OH, in which: R represents a C 3 -C 40 alkyl, alkenyl or alkynyl group, preferably C 8 -C 30 , even more preferably C 10 -C 24 ; Y is chosen from: -(O-CH 2 -CH 2 )-, -(O-CH(CH 3 )-CH 2 )- and -(O-CH 2 -CH 2 -CH 2 )-; and preferably Y denotes -(O-CH 2 -CH 2 )-; n is an integer ranging from 1 to 60, preferably from 1 to 30, more preferably from 1 to 20, better still from 3 to 15, even better still from 5 to 12.

[0094] The surfactant(s) are advantageously present at a total content ranging from 5 to 10,000 ppm by mass, preferably from 50 to 5,000 ppm by mass, more preferably from 100 to 2,500 ppm by mass, and better still from 200 to 1,000 ppm by mass, relative to the total mass of the composition. Anti-foam additives

[0095] The composition used in the invention comprises one or more anti-foam additive(s) chosen from copolymers comprising a polydimethylsiloxane backbone with an average number of dimethylsiloxane units in the range of 150 to 300, grafted with polyoxyalkylene chains.

[0096] These copolymers are therefore grafted polymers, with a polydimethylsiloxane backbone and polyoxyalkylene side chains (or grafts) grafted onto the backbone.

[0097] The backbone of these polymers consists of a polydimethylsiloxane chain (also commonly referred to as PDMS), i.e. a chain of formula -[Si(CH 3 ) 2 -O] n -, with n a number in the range from 150 to 300.

[0098] Preferably, the polydimethylsiloxane backbone comprises an average number of dimethylsiloxane units in the range of 180 to 250. This corresponds to a value of the number n in the range of 180 to 250.

[0099] The polyoxyalkylene chains advantageously correspond to the formula -(RO) m - with R designating one or more C1 to C4 alkylene groups, branched or linear, preferably C2 or C3, and m a number in the range from 10 to 55.

[0100] Preferably, the average number m of oxyalkylene units is in the range from 20 to 50, more preferably from 30 to 50.

[0101] Also preferably, R denotes one or more C2 and / or C3 alkylene groups, and more preferably the polyoxyalkylene chains are chosen from polyoxyethylene (EO) of formula -(CH 2 -CH 2 -O) m -, polyoxypropopylenes (PO) of formula -(CH 2 -CH(CH 2 )-O) m -, and chains formed from oxyethylene units and oxypropylene units (EO / PO).

[0102] According to a particularly preferred embodiment, the polyoxyalkylene chains are formed from oxyethylene (EO) units and oxypropylene (PO) units. Preferably, the ratio of the average number of EO units to the average number of PO units is in the range from 0.2 to 2, preferably from 0.3 to 1.3. Preferably, these chains are formed from polyoxyethylene blocks and polyoxypropylene blocks.

[0103] The grafting rate of the copolymers (i.e. the average proportion in number of dimethylsiloxane units carrying a polyoxyalkylene side chain) is advantageously in the range from 0.5% to 5%, preferably from 1% to 2%.

[0104] Unless expressly stated otherwise, all averages mentioned in this description are number averages.

[0105] According to a preferred embodiment, the copolymers constituting the anti-foam additive are crosslinked. Such crosslinking gives them a three-dimensional structure.

[0106] The anti-foam additive(s) are advantageously present at a total content ranging from 1 to 200 ppm by mass, preferably from 2 to 100 ppm by mass, more preferably from 3 to 50 ppm by mass, better still from 4 to 25 ppm by mass and better still from 5 to 15 ppm by mass, relative to the total mass of the composition.

[0107] The copolymers described above are known per se and commercially available.

[0108] In commercial products, these copolymers can in particular be presented in diluted form, in a mixture containing them.

[0109] In this case, the content of copolymer(s) in such mixtures is generally in the range from 10 to 80% by mass, preferably from 20 to 60% by mass, more preferably from 30 to 50% by mass and better still from 35 to 45% by mass.

[0110] Thus, according to one embodiment, the anti-foam additive(s) are used in a mixture with an inorganic oxide, such as, for example, solid hydrophobic silica.

[0111] According to another embodiment, the anti-foam additive(s) are used in a mixture with one or more emulsifying agents, which may in particular be chosen from polyoxyalkylene polymers as described above, and more preferably EO / PO copolymers. These polymers generally come from the synthesis of the copolymer and correspond to a proportion of polyoxyalkylene chains not grafted onto the polydimethylsiloxane backbone.

[0112] According to a particularly preferred embodiment, the anti-foam additive(s) are used in a mixture with an inorganic oxide and an emulsifying agent, such as in particular with hydrophobic silica and one or more polyoxyalkylene polymer(s) as described above.

[0113] Products containing the anti-foam additive(s) may be in the form of a solid product, in particular anhydrous (i.e. free of water), or in the form of a solution in a solvent which may be water or an organic solvent. Other constituents

[0114] The aqueous composition may optionally contain one or more other compounds, other than the nitrogen oxide reducing agents and their precursors, surfactants and anti-foam additives described above.

[0115] The composition may thus comprise, in a non-limiting manner, one or more organic fluids miscible or immiscible with water such as for example alcohols, polyols, paraffinic fluids, and / or one or more metallic compounds. The composition and its methods of realization

[0116] The composition used in the present invention is an aqueous composition, that is, its main component is water. The water content of the composition is preferably in the range of 50 to 90 by mass, preferably 60 to 80 by mass, and more preferably 65 to 70% by mass, relative to the total mass of the composition.

[0117] The composition may be prepared in the usual manner by mixing its constituents, preferably at room temperature, typically in a temperature range generally from 10 to 60°C.

[0118] According to a preferred embodiment, the aqueous composition is prepared from a preformulated aqueous solution of urea, such as for example a commercial composition known as AdBlue ®< comprising 32.5% by mass of urea.

[0119] A first embodiment consists of adding the surfactant(s) and the anti-foam additive(s) to this preformulated aqueous urea solution, in the quantity required to reach the contents defined above.

[0120] A second embodiment consists in adding to this preformulated aqueous urea solution a concentrated aqueous composition of additive urea. According to this embodiment, the concentrated aqueous composition of additive urea comprises the surfactant(s) and the anti-foam additive(s) at contents much higher than that of the final aqueous composition introduced into the SCR line, in an aqueous urea solution, preferably at a content of 32.5% by mass of urea. The mixing of the two compositions in an appropriate ratio to obtain the desired final contents is carried out just before injection into the SCR line.

[0121] The same embodiments can be implemented from a preformulated aqueous solution of a precursor other than urea. The use

[0122] The aqueous composition according to the invention is used to treat the exhaust gases leaving an internal combustion engine in a device for selective catalytic reduction of nitrogen oxides or SCR device.

[0123] For this purpose, it is introduced into the SCR exhaust line, downstream of the engine and upstream of the SCR device. This introduction is typically achieved by pumping the composition from one or more reservoirs and injecting it by means of one or more injectors, which allow the composition to be sprayed into the exhaust gas flow. These devices are known per se.

[0124] The use according to the invention also makes it possible to prevent or reduce deposits in the pipe which carries the exhaust gases from the outlet of an internal combustion engine to said selective catalytic reduction device.

[0125] These deposits are typically deposits of nitrogen compounds, containing the reducing agent(s) of nitrogen oxides and / or their precursor(s), and / or decomposition products of said precursors. The invention makes it possible in particular to prevent and / or reduce deposits of urea and / or cyanuric acid, and more particularly deposits of cyanuric acid in the SCR exhaust pipe.

[0126] As indicated above, the invention makes it possible to reduce or avoid these deposits regardless of the configuration of the SCR line. The invention is particularly, but not limited to, suitable for so-called "close-coupled" and "underfloor" SCR exhaust lines as described above.

[0127] In particular, the invention makes it possible to reduce such deposits, while avoiding foaming phenomena of the composition.

[0128] As explained above, the composition injected into the SCR line is pumped from one or more conventional storage tanks, known per se.

[0129] According to a first variant, all the components of the composition according to the invention, in particular the nitrogen oxide reducing agent(s) and / or their precursor(s), the surfactant(s) and the anti-foam additive(s) are formulated in the same aqueous composition at the desired contents, and this composition is introduced into a single reservoir.

[0130] According to a second variant, a first intermediate aqueous composition is formulated comprising the nitrogen oxide reducing agent(s) and / or their precursor(s), at the desired contents in the final composition resulting from the mixing of the two intermediate compositions. This first intermediate composition is introduced into a first tank. A second concentrated intermediate aqueous composition with additives is also formulated, comprising the nitrogen oxide reducing agent(s) and / or their precursor(s) at the desired contents in the final composition resulting from the mixing of the two intermediate compositions, as well as the surfactant(s) and the anti-foam additive(s) in a more concentrated content than the desired content in said final composition.

[0131] This second composition is introduced into a second tank, separate from the first tank. The two tanks feed the same injection system, allowing the mixing of the two intermediate compositions. A vehicle comprising two tanks for the implementation of such a variant is described in particular in EP2541012. The process

[0132] The process (or method) according to the invention makes it possible to treat the exhaust gases from an internal combustion engine, preferably a Diesel engine, equipped with an SCR system.

[0133] This method comprises a step of introducing an aqueous composition as described above into the pipe conveying the exhaust gases leaving an engine to a device for selective catalytic reduction of nitrogen oxides. This introduction is typically carried out by pumping the composition from one or more reservoirs and injecting it into said pipe by means of one or more injectors, as described above.

[0134] The following examples are given as illustrations of the invention, and should not be interpreted in such a way as to limit its scope. EXAMPLES Compositions tested:

[0135] As a base composition, a commercial aqueous solution of 32.5% by mass of AdBlue ®< urea, complying with ISO 22241, was used, to which 500 ppm by mass of a surfactant consisting of a mixture of polyethoxylated fatty alcohols, commercially available from Arkema under the name Surfaline ®< 1308L at 85% by mass of active material, was added. These polyethoxylated fatty alcohols are polyoxyethylenated hydrocarbyl monoethers corresponding to formula (I) defined above, and comprising between 1 and 20 units derived from ethylene glycol and in which the hydrocarbyl group is a C 8 -C 30 alkyl group. 500 ppm of the commercial product Surfaline ®< 1308L was used for each composition, which corresponds to a surfactant content of 425 ppm by mass.

[0136] This basic composition comprising urea and surfactant is called C0.

[0137] The various anti-foam additives A1 to A4 defined below were added to the basic composition C0, to obtain the respective compositions C1 to C4: A1 (comparative): anti-foam additive in the form of a crosslinked siloxane emulsion in water, marketed under the name Foam Ban ®< MS-525 by the company Münzing; A2: crosslinked copolymer comprising a PDMS backbone with an average number of dimethylsiloxane units of 195, grafted by chains formed from polyoxyethylene blocks and polyoxypropylene blocks having an average number of EO units = 9 and an average number of OP units = 23; grafting rate of 1.76%; this copolymer is in the form of a mixture also containing hydrophobic silica and EO / OP copolymers, the mixture containing 40% by mass of said copolymer; A3: crosslinked copolymer comprising a PDMS backbone with an average number of dimethylsiloxane units of 230, grafted by chains formed from polyoxyethylene blocks and polyoxypropylene blocks having an average number of EO units = 21 and an average number of OP units = 18; grafting rate of 1.41%;this copolymer is in the form of a mixture further containing hydrophobic silica and EO / OP copolymers, the mixture containing 40% by mass of said copolymer; A4: crosslinked copolymer comprising a PDMS backbone with an average number of dimethylsiloxane units of 200, grafted by chains formed from polyoxyethylene blocks and polyoxypropylene blocks having an average number of EO units = 16 and an average number of OP units = 30; grafting rate of 1.57%; this copolymer is in the form of a mixture further containing hydrophobic silica and EO / OP copolymers, the mixture containing 40% by mass of said copolymer. ;

[0138] The contents of each anti-foam additive in the tested compositions are listed in Table 1 below, with MP meaning raw material and MA active material: [Table 1] Composition Anti-foam additive Content C0 (comparative) - - C1 (comparative) A1 25 ppm MP (1)< C2 (invention) A2 5 ppm MA C3 (invention) A3 5 ppm MA C4 (invention) A4 5 ppm MA (1)< Composition C1 contains 25 ppm by mass of the commercial product Foam Ban ®< MS-525. Test method

[0139] The foaming level of these different compositions was determined using a DFA100 foaming bench marketed by the company Krüss.

[0140] In this system, foaming is generated by the supply of ascending air, introduced through a sintered glass located at the bottom of a column containing the composition to be tested. The device allows direct reading of the volume of foam formed as a function of time.

[0141] The measurements were carried out each time after an air injection time of 30 s, at a flow rate of 0.3 L / min. The composition volume introduced into the column for each test was 40 ml. The foam volumes were measured 600 s after the start of the test.

[0142] Each composition was tested immediately after its preparation (results at T 0 ), then after storage for a period of 12 months (results at T 12 ) at different temperatures: room temperature TA (25°C), 8°C and 40°C. Results

[0143] The results obtained are detailed in Tables 2 and 3 below. [Table 2] Composition Foam volume at T 0 Foam volume at T 12 storage at TA C0 (comparative) 70 ml 100 ml C1 (comparative) 18 ml 95 ml C2 (invention) 13 ml 20 ml C3 (invention) 12 ml 20 ml C4 (invention) 10 ml 27 ml [Table 3] Composition Foam volume at T 12 - storage at 8°C Foam volume at T 12 - storage at 40°C C0 (comparative) 113 ml 134 ml C1 (comparative) 66 ml 121 ml C2 (invention) 30 ml 80 ml C3 (invention) 28 ml 50 ml C4 (invention) 34 ml Not realized

[0144] The above results show that compositions C2 to C4 according to the invention have a foaming level much lower than that of composition C0 not comprising an anti-foam additive, and than composition C1 comprising a comparative anti-foam additive at a higher treatment rate.

[0145] The performances of the three compositions according to the invention remain superior to those of the comparative compositions after one year of storage, both at room temperature and at low (8°C) or high (40°C) temperatures.

Claims

1. An aqueous composition comprising: - at least one agent reducing nitrogen oxides and / or at least one precursor of such an agent, - at least one surfactant, and - at least one defoaming additive selected from copolymers comprising a polydimethylsiloxane backbone with an average number of dimethylsiloxane units in the range of 150 to 300, grafted with polyoxyalkylene chains.

2. The composition according to the preceding claim, characterised in that< / b> the reducing agent or the precursor of the reducing agent is selected from the list consisting of urea, ammonia, formamide, ammonium salts, and guanidine salts; and preferably from the list consisting of urea and ammonia; and more preferably the precursor of the reducing agent is urea.

3. The composition according to any of the preceding claims, characterised in that the composition contains urea in a content ranging from 25% to 42% by mass, preferably from 30% to 40% by mass, more preferably from 31 to 35% by mass and even more preferably from 32% to 33% by mass, relative to the total mass of the composition; and even more preferably 32.5 ± 0.7% by mass, relative to the total mass of the composition.

4. The composition according to any of the preceding claims, characterised in that the surfactant(s) are selected from water-soluble ionic, non-ionic, or amphoteric surfactants; and preferably from non-ionic surfactants chosen from the following compounds: a) hydrocarbyl and mono- or poly-alkylene glycol ethers, b) hydrocarbyl and polyol ethers, c) mono- or poly-alkylene glycol fatty acid esters, d) mono- or poly-glycerol fatty acid esters, and e) mixtures of these compounds.

5. The composition according to the preceding claim, characterised in that the surfactant(s) are selected from mono- or poly-alkoxylated hydrocarbyl monoethers of the formula (I) :         R-(Y)n-OH, in which: R represents a C3-C40 preferably C8-C30; even more preferably C10-C24 alkyl, alkenyl or alkynyl group; Y is selected from: -(O-CH2-CH2)-, -(O-CH(CH3)-CH2)- and - (O-CH2-CH2-CH2)-; and preferably -(O-CH2-CH2)-; n is an integer ranging from 1 to 60, preferably from 1 to 30, more preferably from 1 to 20, even better from 3 to 15, still better from 5 to 12.

6. The composition according to any of the preceding claims, characterised in that the surfactant(s) are present in a total content ranging from 5 to 10,000 ppm by mass, preferably from 50 to 5,000 ppm by mass, more preferably from 100 to 2,500 ppm by mass, and still better from 200 to 1000 ppm by mass, relative to the total mass of the composition.

7. The composition according to any of the preceding claims, characterised in that the polydimethylsiloxane backbone of said copolymers comprises an average number of dimethylsiloxane units in the range from 180 to 250.

8. The composition according to any of the preceding claims, characterised in that the polyoxyalkylene chains of said copolymers have the formula -(RO)m- with R denoting one or more C1 to C4 alkylene groups and m a number in the range from 10 to 55, preferably polyoxyalkylene chains are selected from polyoxyethylene (EO), polyoxypropopylene (PO), and chains formed from oxyethylene and oxypropylene units (EO / PO), and even more preferably from the chains formed by oxyethylene (EO) and oxypropylene (PO) units with a ratio of the average number of EO units to the average number of PO units, preferably in the range from 0.2 to 2, more preferably from 0.3 to 1.3.

9. The composition according to any of the preceding claims, characterised in that the grafting rate of said copolymers is within the range from 0.5% to 5%, preferably from 1% to 2%.

10. The composition according to any of the preceding claims, characterised in that said copolymer is crosslinked.

11. The composition according to any of the preceding claims, characterised in that the defoaming additive(s) are present in a total content ranging from 1 to 200 ppm by mass, preferably from 2 to 100 ppm by mass, more preferably from 3 to 50 ppm by mass, better from 4 to 25 ppm by mass and still better from 5 to 15 ppm by mass, relative to the total mass of the composition.

12. The composition according to any of the preceding claims, characterised in that its water content is in the range from 50 to 90 by mass, preferably from 60 to 80 by mass, and still better from 65 to 70% by mass, relative to the total mass of the composition.

13. Use of a composition as defined in any of the preceding claims for treating exhaust gases at the outlet of onboard or stationary internal combustion engines.

14. Use of a composition as defined in any one of claims 1 to 12 for preventing or reducing deposits in the pipe that conveys the exhaust gases from the outlet of an internal combustion engine towards a device for the selective catalytic reduction of nitrogen oxides.

15. A method for treating exhaust gases from an internal combustion engine, preferably a diesel engine, equipped with a device for selective catalytic reduction of nitrogen oxides, characterised in that it includes at least one step of introducing a composition as defined in any of claims 1 to 12 into the pipe which conveys the exhaust gases from the outlet of the engine to said selective catalytic reduction device.