Use of an aqueous lubricant composition in a hydrogen engine operating in a closed circuit

Abstract

The present invention relates to the use, in order to lubricate a stationary power generation system comprising an internal combustion engine powered by hydrogen and in which an inert gas circulates in a closed circuit, of a composition comprising: - water; - at least 10% by weight, relative to the total weight of the composition, of one or more polyalkylene glycols having a weight-average molar mass, Mw, of at least 1,500 g.mol-1. The present invention also relates to a method for operating a stationary power generation system using this composition, and to a power generation system comprising this composition.

Description

[0001] DESCRIPTION

[0002] TITLE: Use of an aqueous lubricating composition in a hydrogen engine operating in a closed circuit

[0003] The present invention relates to the use of a particular aqueous lubricating composition for lubricating an energy production system comprising an internal combustion engine powered by hydrogen and in which the air is replaced by an inert gas which circulates in a closed circuit.

[0004] The present invention also relates to a method of lubricating an internal combustion engine powered by hydrogen in an energy production system in which an inert gas circulates in a closed circuit, comprising a step of bringing at least one internal part of the engine into contact with a composition as described below.

[0005] STATE OF THE PRIOR ART

[0006] With the aim of developing new solutions for energy production from renewable sources, stationary systems based on the combustion of hydrogen (H2) have recently been developed.

[0007] The present invention relates to such stationary power generation systems, which comprise an internal combustion engine powered by hydrogen as fuel and by an oxygenated oxidant.

[0008] The significant energy generated by combustion is presented on the one hand in the form of mechanical energy transmitted by the engine, and on the other hand in the form of thermal energy carried by the combustion gases. When the oxidant is oxygen (O2), the combustion gases consist of water vapor.

[0009] In these closed-circuit systems, the water vapor escaping from the engine is conveyed by means of an inert gas that circulates between the engine and a heat exchanger in which the water vapor is condensed, allowing it to be removed from the system in liquid form. Also known per se, the hydrogen and oxygen powering the engine can be produced by electrolysis of water.

[0010] Such a system thus makes it possible to produce energy, particularly electricity, which is completely carbon-free and renewable.

[0011] Due to its closed-circuit operation, such a system does not release any emissions into the environment.

[0012] However, conventional mineral oil-based lubricating compositions used in these systems, particularly for lubricating the internal parts of the hydrogen engine, are, on the one hand, likely to escape into the circulation loop, and on the other hand, have been found to generate residues during their partial combustion in the engine, which are released, with the combustion gases, into the circulation loop. These hydrocarbon lubricant fractions and combustion residues, even when released in very small quantities, accumulate in the inert gas as the system operates, due to the closed-loop circuit. They thus pollute the inert gas loop, degrade the properties of the inert gas(es) and foul the circuit components such as the heat exchanger, the engine cylinders and valves, etc. They are also likely to pollute the water eliminated at the exchanger.

[0013] SUBJECT OF THE INVENTION

[0014] The present invention aims to overcome the particular problems described above, which arise in energy production systems using an engine powered by hydrogen and an inert gas in a closed circuit.

[0015] The Applicant has now discovered that a particular lubricant composition, comprising water and a polyalkylene glycol, overcomes these difficulties.

[0016] The present invention thus relates to the use, for lubricating a stationary energy production system comprising an internal combustion engine powered by hydrogen and in which an inert gas circulates in a closed circuit, of a composition comprising: - water; - at least 10% by mass, relative to the total mass of said composition, of one or more polyalkylene glycol(s) with a weight-average molar mass, Mw, of at least 1500 g. mol -1 .

[0017] In the remainder of the text, the term “aqueous lubricating composition” will refer to a composition used according to the invention as defined above.

[0018] The said composition makes it possible to very effectively lubricate the various moving parts in the closed-circuit energy production system, and in particular the internal parts of the engine, without releasing hydrocarbon compounds or combustion residues likely to pollute the circuit and in particular the circulating inert gas as well as the extracted water.

[0019] The use of such a composition thus makes it possible to increase the service life of the inert gas charge circulating in the system, but also to prevent fouling of the components of the entire circuit.

[0020] The present invention is therefore not intended to reduce emissions, particularly CO2 and hydrocarbons, since the closed-circuit energy production system does not generate emissions. However, it does make it possible to control the specific problems of circuit pollution that arise in this type of system.

[0021] The present invention also relates to a method of operating a stationary energy production system comprising an internal combustion engine powered by hydrogen and in which an inert gas circulates in a closed circuit, consisting of lubricating at least one part of said engine with a composition as described in the present application.

[0022] The present invention also relates to a stationary energy production system comprising an internal combustion engine powered by hydrogen and in which an inert gas circulates in a closed circuit, characterized in that it contains in at least one of the parts of the engine, a composition as described in the present application.

[0023] Other objects, characteristics, aspects and advantages of the invention will appear even more clearly on reading the description and examples which follow.

[0024] In what follows, and unless otherwise indicated, the limits of a domain of values ​​are included in this domain, notably in the expressions "between" and "ranging from ... to ..."

[0025] Furthermore, the expressions “at least one” and “at least” used in this description are respectively equivalent to the expressions “one or more” and “greater than or equal”.

[0026] Finally, in a manner known per se, the term CN compound or group refers to a compound or group containing N carbon atoms in its chemical structure.

[0027] DETAILED DESCRIPTION

[0028] The aqueous lubricating composition

[0029] The aqueous lubricating composition according to the present invention comprises water. In particular, water is present as the majority solvent, in other words in greater quantity than any other solvent possibly present in the composition.

[0030] The lubricating composition used in the present invention advantageously comprises at least 15% by mass of water, in particular from 15 to 85% by mass of water, relative to the total mass of the composition.

[0031] Preferably, the water content ranges from 20 to 80% by mass, more preferably from 30 to 70% by mass, and better still from 40 to 60% by mass, relative to the total mass of the composition.

[0032] According to a particular embodiment, the water used in said composition is osmosis or demineralized water, more preferably deionized water.

[0033] The term "osmosed water" means water that has undergone purification, in particular by a reverse osmosis process, which makes it possible to reduce the content of organic and / or mineral compounds, for example to a content of less than 5.0% by weight, preferably less than 1.0% by weight. In the present description, the expressions "demineralized water" or "ultrapure water" are considered equivalent or synonymous with the expression "osmosed water". In particular, the osmosed water may be "deionized water", in other words water that has undergone purification in order to reduce the content of ions, such as Ca ions 2+ and HCOs" generally present in water. Preferably deionized water does not contain ions.

[0034] According to a preferred embodiment, the composition used in the invention is single-phase, that is to say it consists of a single aqueous phase. In particular in this embodiment, the composition is not an emulsion such as an oil-in-water emulsion or a water-in-oil emulsion.

[0035] In this embodiment, the composition does not comprise water-insoluble compounds, and in particular no water-insoluble hydrocarbons including non-water-soluble base oils.

[0036] "Water-insoluble oil" means, in particular, an oil which does not dissolve substantially in water at room temperature (25°C). In particular, a water-insoluble oil has a solubility in water of less than 0.2 g / L at 25°C.

[0037] Advantageously, in this embodiment the composition does not comprise a lubricating base oil belonging to groups I to IV according to the classes defined in the API classification (or their equivalents according to the ATIEL classification).

[0038] The presence of water-insoluble hydrocarbons, even if it is not desired, is nevertheless tolerated within the framework of the invention insofar as it may come from a migration of residual compounds onto the engine parts coming for example from a previous hydrocarbon lubricant used in the engine.

[0039] Preferably, the composition used in the present invention comprises less than 2% by mass of water-insoluble hydrocarbons, more preferably less than 1% by mass, relative to the total mass of the composition.

[0040] More preferably, the composition comprises less than 2% by mass of water-insoluble lubricating base oil and even better less than 1% by mass, relative to the total mass of the composition. Advantageously, said composition is completely free of water-insoluble oil.

[0041] The composition used in the present invention advantageously has a kinematic viscosity, measured at 40°C according to standard ASTM D445, of between 20 mm 2 / s and 1000 mm 2 / s, preferably between 25 mm 2 / s and 100 mm 2 / s.

[0042] Advantageously, said composition has a viscosity index in the range from 100 to 350, preferably from 150 to 300.

[0043] Polyalkylene glycols

[0044] The aqueous lubricating composition according to the present invention contains one or more polyalkylene glycols.

[0045] Polyalkylene glycols (denoted “PAG”) are more particularly chosen from water-soluble or water-soluble polyalkylene glycols.

[0046] By "water soluble" is meant a polyalkylene glycol having a water solubility of at least 10 g / L, preferably at least 500 g / L, in water at room temperature (about 25°C).

[0047] Preferably, said polyalkylene glycol(s) used according to the invention are chosen from polyalkylene glycols having a cloud point (called “Cloud point” in English), in other words having the property of inverse demixing (or “inverse solubility” in English).

[0048] The reverse demixing property characterizes the property of certain polyalkylene glycols to be soluble in water up to a temperature beyond which they become insoluble. This turbidity or "cloudiness" indicates phase separation with water, which results in a deposition of said polyalkylene glycol on the surfaces in contact with the lubricant.

[0049] The temperature at which turbidity and insolubility occur is called the cloud point of the polyalkylene glycol. The cloud point can be determined, for example, according to ASTM D 2024 or DIN EN 1890, generally for a mixture of 1% by mass of polyalkylene glycol in water. Preferably, the polyalkylene glycol(s) have a cloud point of 70°C or higher.

[0050] The water solubility and reverse demixing properties of the said polyalkylene glycol(s) used according to the invention advantageously make it possible to increase the lubrication properties.

[0051] Advantageously, the polyalkylene glycol(s) comprise at least 50% by mass, in particular at least 80% by mass, more preferably at least 90% by mass, or even at least 95% by mass of propylene oxide and / or ethylene oxide units. In particular, the polyalkylene glycols used according to the invention consist of propylene oxide and / or ethylene oxide units.

[0052] The polyalkylene glycol(s) may be a copolymer, in particular a random copolymer, of ethylene oxide (EO) and propylene oxide (PO). In particular, the ethylene oxide (EO) and propylene oxide (PO) units are present in the copolymer in an EO / PO mass ratio of between 50 / 50 and 90 / 10, in particular between 60 / 40 and 85 / 15, and more particularly between 70 / 30 and 80 / 20.

[0053] Preferably, the polyalkylene glycol(s) are obtained by polymerization from one or more alkylene oxide monomers, in particular ethylene oxide and / or propylene oxide, initiated by a compound of alcohol type, in particular of polyol type, preferably by a diol compound.

[0054] In particular, the polyalkylene glycol(s) comprise terminal hydroxyl functions. For the purposes of the invention, the term "terminal functions" means the functions located at the ends of the polymer chains.

[0055] As indicated previously, the polyalkylene glycol(s) used according to the invention have a weight-average molar mass (Mw) greater than or equal to 1500 g / mol.

[0056] In particular, a polyalkylene glycol is distinguished from alkylene glycol oligomers having a number of monomeric units less than or equal to ten.

[0057] Preferably, the polyalkylene glycol(s) have a weight-average molar mass (Mw) of at least 2000 g. mol - 1 , in particular of at least 2500 g. mol 1 , in particular of at least 3000 g. mol' 1 , and more particularly between 3000 and 50,000 g. mol 1 , especially between 5000 and 25,000 g. mol 1 , preferably between 5,000 and 15,000 g. mol 1 .

[0058] Weight-average molar mass can be measured by gel permeation chromatography (GPC).

[0059] Preferably, the polyalkylene glycol(s) have a kinematic viscosity measured at 100°C (KV100), according to standard ASTM D445, of between 100 and 25,000 mm 2 / s, especially between 150 and 15,000 mm 2 / s.

[0060] Preferably, the polyalkylene glycol(s) have a kinematic viscosity measured at 40°C (KV40), according to standard ASTM D445, of between 500 and 100,000 mm 2 / s, more particularly between 1,000 and 70,000 mm 2 / s.

[0061] The flash point of the polyalkylene glycol(s) used according to the invention is preferably greater than or equal to 160°C, in particular greater than or equal to 220°C. The flash point can be measured by the ISO 2592 or ASTM D92 standard.

[0062] Preferably, the polyalkylene glycol(s) have a viscosity index measured according to standard ASTM D2270, between 100 and 800, preferably between 250 and 550.

[0063] It is understood that a single polyalkylene glycol or a mixture of several different polyalkylene glycols, in particular as described above, can be used according to the invention.

[0064] In particular, an aqueous lubricating composition according to the invention may comprise a mixture of at least two distinct polyalkylene glycols, more particularly at least one polyalkylene glycol of low weight average molar mass and at least one polyalkylene glycol of high weight average molar mass.

[0065] It is within the general skills of a person skilled in the art to adjust the nature and content of low and high weight-average molar mass polyalkylene glycols in the polyalkylene glycol mixture, particularly with regard to the viscosity targeted for the final lubricating composition. According to a particularly advantageous embodiment, said polyalkylene glycol(s) used according to the invention are biosourced.

[0066] For the purposes of the invention, a “bio-sourced” compound means a compound derived, partially or totally, from biomass, or obtained from renewable raw materials derived from biomass, in particular from plants.

[0067] Advantageously, the implementation according to the invention of one or more bio-sourced PAGs thus makes it possible to further reduce the carbon footprint of the aqueous lubricating composition.

[0068] According to a preferred embodiment, the assembly consisting of water and said polyalkylene glycol(s) represents at least 80% by mass, preferably at least 90% by mass and better still at least 95% by mass, relative to the total mass of the aqueous lubricating composition.

[0069] Antifreeze additives

[0070] According to a preferred embodiment, the aqueous lubricating composition used in the present invention comprises a very low content of antifreeze additive(s), also called antifreeze compound(s), chosen from glycols, in particular alkylene glycols having from 2 to 6 carbon atoms such as monoethylene glycol and / or monopropylene glycol and oxyalkylene glycols having from 4 to 14 carbon atoms such as diethylene glycol; aliphatic monoethers of said glycols and polyhydric aliphatic alcohols such as glycerol. This content is, as a reference, less than 1% by mass, relative to the total mass of said composition.

[0071] Glycols are diols in which the two hydroxyl groups are carried by different carbon atoms, preferably by vicinal carbon atoms. Glycol antifreeze additives are more particularly alkylene glycols having from 2 to 6, preferably from 2 to 4, carbon atoms, such as monoethylene glycol, monopropylene glycol and monobutylene glycol, and oxyalkylene glycols, preferably oxyethylene and oxypropylene glycols, having from 4 to 14 carbon atoms, preferably from 4 to 10 carbon atoms, such as diethylene glycol, dipropylene glycol, triethylene glycol, tetraethylene glycol and tripropylene glycol.

[0072] Preferably, the content of glycol-type antifreeze compound(s), for example monoethylene glycol, diethylene glycol, and / or monopropylene glycol, if present in an aqueous lubricating composition according to the invention, is less than 1.0% by mass, preferably less than or equal to 0.5% by mass, in particular less than or equal to 0.1% by mass, relative to the total mass of the composition.

[0073] Advantageously, an aqueous lubricating composition according to the invention is completely free of glycol-type antifreeze compound, and thus makes it possible to avoid the toxicity effects associated with these compounds. An aqueous lubricating composition according to the invention thus advantageously has reduced toxicity.

[0074] Advantageously, by comprising a reduced quantity, or even being free of glycol-type antifreeze additives, the aqueous lubricating composition used according to the invention has reduced toxicity and environmental footprint.

[0075] The environmental footprint associated with the production of a lubricant can be assessed according to different indicators defined by the European Union, including in particular the "climate change" indicator which is a measure of the global warming potential associated with the emission of greenhouse gases, expressed in kilograms of carbon dioxide equivalent (kg CO2 eq).

[0076] Known antifreeze additives for aqueous lubricants may still be aliphatic monoethers of glycols as mentioned above, for example monomethyl, monoethyl, monopropyl and monobutyl ethers.

[0077] These may also be polyhydric aliphatic alcohols, particularly glycerol, diglycerol, triglycerol, erythritol and pentaerythritol.

[0078] In particular, the aqueous lubricating composition according to the invention comprises a content of antifreeze additives chosen from glycols, aliphatic monoethers of said glycols and polyhydric aliphatic alcohols, strictly less than 1% by mass, in particular less than or equal to 0.5% by mass and more particularly less than or equal to 0.1% by mass, relative to the total mass of the composition.

[0079] According to a preferred embodiment, an aqueous lubricating composition according to the invention is free of such antifreeze additives.

[0080] In a particularly preferred embodiment, an aqueous lubricating composition according to the invention comprises:

[0081] - at least 15%, in particular at least 30% and more particularly from 30% to 85% of water, preferably deionized water;

[0082] - at least 15%, in particular from 15% to 50%, more particularly from 15% to 30%, of one or more polyalkylene glycol(s) (PAG(s)) with an average molar mass, Mw, of at least 1500 g. mol - 1; the mass ratio of the total quantity of polyalkylene glycol(s) to the quantity of water being less than or equal to 0.30, in particular between 0.10 and 0.30, more particularly between 0.15 and 0.25, and in particular between 0.15 and 0.20; said composition comprising a content of antifreeze additive(s) chosen from glycols, aliphatic monoethers of said glycols and polyhydric aliphatic alcohols, less than 1%, preferably less than or equal to 0.5%, more preferably less than or equal to 0.1%; and better still the composition not comprising such antifreeze additive(s); the contents being indicated by mass, relative to the total mass of said composition.

[0083] Additional additives

[0084] The aqueous lubricating composition may further contain one or more additional additives, other than the polyalkylene glycols as described above and the antifreeze additives defined above.

[0085] It is understood that the said additional additive(s) are compatible with their implementation in an aqueous medium. Advantageously, the additives are implemented in a form that is soluble or emulsifiable in water, for example in the form of salts or ionic liquids.

[0086] Such additives may be more particularly chosen from anti-foam agents, biocides, pH regulators, corrosion inhibitors, anti-wear and / or extreme pressure additives, sequestering agents, metal passivating agents, colorants, dispersants, and mixtures thereof.

[0087] Advantageously, the composition used in the invention may comprise one or more additives chosen from antifoam agents, extreme pressure agents, corrosion inhibitors, pH regulators, metal passivating agents, colorants, and mixtures thereof.

[0088] The composition may more particularly comprise from 0.1 to 20% by mass of additives, in particular from 2.0 to 15% by mass of additives, in particular from 5.0 to 13% by mass, relative to the total mass of the composition.

[0089] pH regulators

[0090] The aqueous lubricating composition may comprise at least one pH regulating additive, in particular an alkaline buffer. The pH regulator advantageously makes it possible to maintain the desired pH of the lubricating composition, in particular in order to preserve an alkaline pH, advantageously between 8 and 15.

[0091] The said pH regulator(s), by ensuring that the pH of the aqueous lubricating composition is maintained between 8 and 15, makes it possible in particular to prevent corrosion of metal surfaces, but also to promote the solubilization of the various compounds in the lubricating composition, in particular the polyalkylene glycol(s).

[0092] The pH regulator can be chosen from the amine family, in particular alkanolamines and amino alcohols.

[0093] This may include a pH regulating additive selected from alkanolamines, such as dimethylethanolamine (DMEA), ethanolamines, such as monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), isopropanolamines, such as monoisopropanolamine (MIPA), diisopropanolamine (DIPA) and triisopropanolamine (TIPA); diglycolamine (DGA); ethylene amines, such as ethylene diamine (EDA), diethylene triamine (DETA), triethylene tetramine (TETA) and tetraethylene pentamine (TEPA); cyclamines, such as cyclohexylamine; 2-amino-2-ethyl-1,3-propanediol; 2-amino-2-methyl-1-propanol; and mixtures thereof.

[0094] The composition may in particular comprise from 0.1% to 10% by mass of pH regulating additive(s), preferably from 0.5% to 5% by mass, relative to the total mass of the composition.

[0095] Advantageously, the composition used in the invention comprises at least one pH regulating additive making it possible to maintain the pH of said lubricating composition between 8 and 15, in particular between 8.5 and 14, more particularly between 9 and 13, said pH regulating additive being chosen in particular from alkanolamines, preferably ethanolamines, and more particularly from dimethylethanolamine (DMEA), triethanolamine (TEA), diglycolamine (DGA) and mixtures thereof.

[0096] Corrosion inhibitors

[0097] The aqueous lubricating composition may comprise at least one corrosion inhibiting agent. Corrosion inhibitors advantageously make it possible to reduce or even prevent corrosion of metal parts. The nature of the corrosion inhibitor(s) may be chosen with regard to the metal to be protected against corrosion, such as aluminum, steel, galvanized steel, yellow metals, for example copper or brass.

[0098] Inorganic corrosion inhibitors include nitrites, sulfites, silicates, borates, sodium, potassium, calcium or magnesium phosphates, alkali metal phosphates, hydroxides, molybdates, zinc, magnesium or nickel sulfates.

[0099] Among the organic corrosion inhibitors that may be mentioned are alkanolamines, such as triethanolamine, aliphatic monocarboxylic acids, in particular having from 4 to 15 carbon atoms, for example octanoic acid, aliphatic dicarboxylic acids having from 4 to 15 carbon atoms, for example decanedioic acid, undecanedioic acid, dodecanedioic acid or mixtures thereof, polycarboxylic acids optionally neutralized by triethanolamine, such as 1,3,5-triazine-2,4,6-tri-(6-aminocaproic acid), alkanoylamidocarboxylic acids, in particular isononanoylamidocaproic acid, and mixtures thereof. Borated amides, products of the reaction of amines or amino alcohols with boric acid, may also be used.

[0100] Preferably, the corrosion inhibitor(s) are distinct from the pH regulating additive(s), in particular making it possible to maintain the pH of the composition between 8 and 15 defined previously.

[0101] The composition may in particular comprise from 0.1% to 5% by mass of corrosion inhibitor(s), in particular as defined above, preferably from 0.5% to 4% by mass, more preferably from 1% to 2.5% by mass, relative to the total mass of the composition.

[0102] Anti-wear / extreme pressure additive

[0103] The aqueous lubricating composition may comprise at least one anti-wear and / or extreme pressure additive. Their function is to reduce wear and the coefficient of friction, or to prevent metal-metal contact by forming a protective film adsorbed on these surfaces.

[0104] There is a wide variety of anti-wear additives, among which can be mentioned those chosen from phosphosulfur additives such as metal alkylthiophosphates or their salts.

[0105] Additives that do not contain phosphorus may also be suitable, such as, for example, polysulfides, particularly sulfur-containing olefins.

[0106] According to a particular embodiment, an aqueous lubricating composition according to the invention may comprise at least one extreme pressure additive chosen from sulfur-containing fatty acids and dimercaptothiadiazoles, preferably used in their neutralized form, in particular by inorganic alkalizing agents or alkanolamines, emulsifiable or soluble in water.

[0107] The composition may comprise less than 0.1% by mass of extreme pressure additive of the sulfur-containing fatty acid type, in particular in a neutralized form, preferably less than 0.01% by mass, more particularly less than 0.001% by mass, relative to the total mass of the composition, or even is completely free of extreme pressure additive of the sulfur-containing fatty acid type.

[0108] Sulfur-containing fatty acids can contain from 8 to 22 carbon atoms, particularly from 12 to 18 carbon atoms.

[0109] The quantity of sulfur according to standard ASTM D2622 provided by said sulfur-containing fatty acid(s) may be between 5% and 30% by mass, in particular between 10% and 20% by mass, relative to the total mass of the composition.

[0110] Preferably, the quantity of active sulfur at 150°C according to standard ASTM D 1662 provided by said sulfur-containing fatty acid(s) in the aqueous lubricating composition according to the invention is less than or equal to 2% by mass, in particular less than or equal to 1% by mass, more particularly less than 0.1% by mass, relative to the total mass of the lubricating composition.

[0111] For the purposes of the present invention, the term "active sulfur" means the sulfur that a chemical compound is capable of yielding or releasing when this compound is placed under the conditions of the ASTM D 1662 standard. The ASTM D-1662 standard defines an active sulfur level of a compound at a given temperature as a difference expressed as a weight percentage of sulfur content before and after reaction of a sample of this sulfur compound with a given quantity of copper for a fixed time.

[0112] As indicated above, said sulfur-containing fatty acid(s) are generally used in an aqueous lubricating composition in their form neutralized by an alkalizing agent, such as sodium hydroxide, potassium hydroxide, or an alkanolamine, such as monoethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine and triisopropanolamine.

[0113] The composition may in particular comprise between 0.01% and 10% by mass of anti-wear and / or extreme pressure additive(s), preferably between 0.2% and 5% by mass, relative to the total mass of the composition. Anti-foam

[0114] The aqueous lubricating composition may comprise at least one anti-foam additive. These additives make it possible to prevent foaming of the lubricating fluid.

[0115] It may be, for example, an anti-foaming agent based on polysiloxanes or acrylate polymers. Preferably, the anti-foaming agent is chosen from three-dimensional siloxanes.

[0116] Antifoam additives can also be polar polymers such as polymethylsiloxanes or polyacrylates.

[0117] The composition may comprise from 0.001% to 3.0% by mass of anti-foam additive(s), preferably from 0.005% to 1.5% by mass, more preferably from 0.01% to 1.0% by mass, relative to the total mass of the lubricating composition.

[0118] Metal passivating agents

[0119] The aqueous lubricating composition may include at least one metal passivating agent. Metal passivating agents protect metal parts by promoting the formation of metal oxide on their surface.

[0120] The metal passivating agents may be chosen, for example, from triazole derivatives, such as tetrahydrobenzotriazole (THBTZ), tolyltriazole (TTZ), benzotriazole (BTZ), amines substituted with a triazole group, such as N,N-bis(2-ethylhexyl)-

[0121] 1,2,4-triazol- l -yl methanamine, N'-bis(2 ethylhexyl)-4-methyl- 1H benzotriazol- 1 -methyl- amine, N,N-bis(heptyl)-ar-methyl- lH- b enzotriazole- 1 -methanamine, N,N-bis(nonyl)-ar-methyl- lH- benzotriazole- 1 -methanamine, N,N-bis(decyl)-ar-methyl- lH- benzotriazole- 1 -methanamine, N,N-bis(undecyl)-ar-methyl- lH- benzotriazole- 1 -methanamine, N,N-bis(dodecyl)-ar-methyl- 1H benzotriazole- 1 -methanamine, N,N-bis(2-ethylhexyl)-ar-methyl- l H- benzotriazole- l -methanamine, the 1 ,2,4-triazoles, benzimidazoles, 2-alkyldithiobenzimidazoles, 2-alkyldithiobenzothiazoles, 2-(N,N-dialkyldithiocarbamoyl)benzothiazoles, 2,5-bis(alkyldithio)-1,3,4-thiadiazoles, such as 2,5-bis(tert-octyldithio)- l ,3,4-thiadiazole, 2,5-bis(tert-nonyldithio)-l,3,4-thiadiazole, 2,5-bis (tert-decyl dithio)-1,3,4-thiadiazole, 2,5-bis(tert-undecyldithio)-

[0122] 1,3,4-thiadiazole, 2,5-bis(tert-dodecyldithio)- l,3,4-thiadiazole,

[0123] 2.5-bis(tert-tridecyldithio)-1,3,4-thiadiazole, 2,5-bis(tert-tetradecyldithio)-1,3,4-thiadiazole, 2,5-bis(tert-pentadecyldithio)-

[0124] 1,3,4-thiadiazole, 2,5-bis(tert-hexadecyldithio)-1,3,4-thiadiazole,

[0125] 2.5-bis(tert-heptadecyldithio)-1,3,4-thiadiazole, 2,5-bis(tert-octadecyldithio)-1,3,4-thiadiazole, 2,5-bis(tert-nonadecyldithio)-

[0126] 1,3,4-thiadiazole, 2,5-bis(tert-eicosyldithio)-l,3,4-thiadiazole,

[0127] 2,5-bis(N,N-dialkyldithiocarbamoyl)-1,3,4-thiadiazoles, 2-alkyldithio-5-mercaptothiadiazoles, and mixtures thereof.

[0128] Preferably, the metal passivating agents are chosen from tetrahydrobenzotriazole (THBTZ), tolyltriazole (TTZ), benzotriazole (BTZ), and their salts, taken alone or in mixtures.

[0129] The composition may in particular comprise from 0.01% to 2.0% by mass of metal passivating agent(s), preferably from 0.1% to 1.0% by mass, more preferably from 0.2% to 0.8% by mass, relative to the total mass of the composition.

[0130] Dyes

[0131] The aqueous lubricating composition may include one or more colorants. The colorants may be natural or synthetic, generally organic.

[0132] The colorants that can be used in an aqueous lubricant composition can be more particularly chosen from natural or synthetic water-soluble colorants, for example the colorants FDC Red 4, DC Red 6, DC Red 22, DC Red 28, DC Red 30, DC Red 33, DC Orange 4, DC Yellow 5, DC Yellow 6, DC Yellow 8, FDC Green 3, DC Green 5, FDC Blue 1, betanin (beetroot), carmine, a chlorophyllin, methylene blue, anthocyanins (enocyanin, black carrot and hibiscus), caramel and riboflavin.

[0133] An aqueous lubricating composition used according to the invention may comprise between 0.01% and 2.0% by mass of colorant(s), preferably between 0.01% and 1.5% by mass, more preferably between 0.02% and 1.0% by mass, relative to the total mass of the composition.

[0134] Sequestering agents

[0135] The aqueous lubricating composition may comprise at least one sequestering agent. Sequestering agents, also called chelating agents, make it possible to limit the encrustation of metal ions in the composition.

[0136] Examples of sequestering agents include those derived from phosphonic acids and phosphonates, such as diethylenetriaminepentamethylphosphonic acid (DTPMPA), aminotri(methylenephosphonic acid) (ATMP), hydroxyethanediphosphonic acid (HEDP), 1,1-hydroxyethylidene diphosphonate, 2-hydroxyethylamine di(methylenephosphonic acid) (HEAMBP), diethylenetriaminopenta(methylenephosphonic acid) (DTMP), multifunctional organic acids and hydroxy acids, such as ethylenediaminetetraacetic acid (EDTA), pteroyl-L-glutamic acid (PGLU), organic polyacids, such as maleic acid and polyaspartic acid, polysaccharides and carbohydrates, such as inulin, carboxymethylinulin and carboxymethylchitosan.

[0137] The composition may comprise from 0.001% to 2.0% by mass of sequestering agent(s), preferably from 0.01% to 1.0% by mass, relative to the total mass of the composition.

[0138] Biocides and fungicides

[0139] The aqueous lubricating composition may comprise at least one biocidal and / or fungicidal agent. Biocides and fungicides may be used to improve the biological stability of the composition by limiting the proliferation of bacteria, fungi and yeasts in the lubricating fluid.

[0140] Such biocides may be selected from parabens, aldehydes, reactive acetylacetone compounds, isothiazolinones, phenolic compounds, acid salts, halogenated compounds, quaternary ammoniums, certain alcohols and mixtures thereof. Preferably, the biocides may be selected from optionally substituted benzisothiazolinones (BIT), such as N-butyl-1,2-benzisothiazolin-3-one, methylisothiazolinones (MIT), mixtures of methylisothiazolinone and chloromethylisothiazolinone (MIT / CMIT), orthophenyl-phenol (OPP) or its sodium salt, 3-iodo-2-propynylbutylcarbamate (IPBC), chloro-cresol and N,N-methylene-bis-morpholine (MBM); sorbic acid; preferably from orthophenyl-phenol (OPP) or its sodium salt, 3-iodo-2-propynylbutylcarbamate, chloro-cresol, benzisothiazolinones and N,N-methylene-isomorpholine.

[0141] The composition may in particular comprise between 0.01% and 10% by mass of biocide(s) and / or fungicide(s), preferably between 0.5% and 5.0% by mass, relative to the total mass of the composition.

[0142] Phosphorus compounds

[0143] According to a preferred embodiment, the aqueous lubricating composition used in the present invention does not comprise phosphorus compounds.

[0144] In this embodiment, said composition is therefore free of phosphorus compounds.

[0145] A phosphorus compound is any compound containing at least one phosphorus atom. Phosphorus compounds include both water-soluble and water-emulsifiable forms, particularly in the form of ionic salts.

[0146] Compounds excluded from the composition in this embodiment include, but are not limited to, amine phosphates; phosphates such as phosphate esters, particularly alkyl, alkenyl or aryl phosphates; polyphosphates; phosphonates such as phosphonate esters, particularly alkyl, alkenyl or aryl phosphonates; polyphosphonates; carbamyl phosphates; and phosphinates.

[0147] In particular, an aqueous lubricating composition implemented in this embodiment does not comprise salts of phosphate esters, in particular alkali metal salts of phosphate esters, in particular alkyl or dialkyl phosphate esters, for example of the potassium butylphosphate and potassium dibutylphosphate type.

[0148] The use

[0149] According to the present invention, the aqueous lubricating composition is used as a lubricant in a stationary power generation system comprising an internal combustion engine powered by hydrogen and in which an inert gas circulates in a closed circuit.

[0150] The composition is useful for lubricating any moving part or element of the power generation system, and in particular for lubricating all or part of the moving parts in said internal combustion engine.

[0151] In other words, the composition is advantageously used to reduce friction between moving parts inside the engine. It is also used to reduce wear of said parts. The part(s) of the internal combustion engine lubricated by means of the aqueous lubricating composition are advantageously chosen from: pistons, rings, cylinders, connecting rods, piston pins, bearings, crankshafts, oil pumps, turbochargers, camshafts, distribution systems (including in particular cams, tappets, levers, rocker arms, oil pump).

[0152] The method

[0153] According to the invention, a method of operating a stationary energy production system comprising an internal combustion engine powered by hydrogen and in which an inert gas circulates in a closed circuit, consists of lubricating at least one part of said engine with an aqueous lubricating composition as described above.

[0154] The part(s) of the internal combustion engine lubricated by means of the aqueous lubricating composition are advantageously chosen from: pistons, segments, cylinders, connecting rods, piston pins, bearings, crankshafts, oil pumps, turbochargers, camshafts, distribution systems (including in particular cams, tappets, levers, rocker arms, oil pump).

[0155] Advantageously, the internal combustion engine is powered by oxygen (O2) as the oxidant. The system

[0156] The present invention also relates to a stationary energy production system comprising an internal combustion engine powered by hydrogen and in which an inert gas circulates in a closed circuit, characterized in that it contains in at least one of the parts of the engine, an aqueous lubricating composition as described above.

[0157] The internal combustion engine is typically a spark-ignition engine.

[0158] The inert gas circulating in said system may be any known inert gas such as, for example, nitrogen, argon and noble gases such as helium, neon, krypton, xenon and radon. According to a preferred embodiment, the noble gas is argon.

Claims

CLAIMS 1. Use, for lubricating a stationary energy production system comprising an internal combustion engine powered by hydrogen and in which an inert gas circulates in a closed circuit, of a composition comprising: - water; - at least 10% by mass, relative to the total mass of said composition, of one or more polyalkylene glycol(s) with a weight-average molar mass, Mw, of at least 1500 g. mol -1 .

2. Use according to the preceding claim, characterized in that the polyalkylene glycol(s) comprise at least 50% by mass, in particular at least 80% by mass, more preferably at least 90% by mass, or even at least 95% by mass of propylene oxide and / or ethylene oxide units.

3. Use according to any one of the preceding claims, characterized in that the polyalkylene glycol(s) have a weight-average molar mass (Mw) of at least 2000 g. mol - 1 , in particular of at least 2500 g. mol - 1 , in particular of at least 3000 g. mol 1 , and more particularly between 3000 and 50,000 g. mol - 1 , especially between 5000 and 25,000 g. mol 1 , preferably between 5,000 and 15,000 g. mol 1 .

4. Use according to any one of the preceding claims, characterized in that the composition contains at least 15% by mass of said polyalkylene glycol(s), preferably from 15 to 50% by mass, more preferably from 15 to 30% by mass and even more preferably from 16 to 20% by mass, relative to the total mass of the composition.

5. Use according to any one of the preceding claims, characterized in that in the composition the mass ratio of the total quantity of polyalkylene glycol(s) to the quantity of water is less than or equal to 0.30, in particular between 0.10 and 0.30, more particularly between 0.15 and 0.25, and in particular between 0.15 and 0.

20.

6. Use according to any one of the preceding claims, characterized in that the composition comprises a content of antifreeze additives chosen from glycols, aliphatic monoethers of said glycols and polyhydric aliphatic alcohols, strictly less than 1% by mass, preferably less than or equal to 0.5% by mass and more preferably less than or equal to 0.1% by mass, relative to the total mass of the composition.

7. Use according to the preceding claim, characterized in that the composition is free from such antifreeze additives.

8. Use according to any one of the preceding claims, characterized in that the composition is free from phosphorus compounds.

9. Use according to any one of the preceding claims, for lubricating all or part of the moving parts in said internal combustion engine, preferably chosen from: pistons, segments, cylinders, connecting rods, piston pins, bearings, crankshafts, oil pumps, turbochargers, camshafts, distribution systems (including in particular cams, tappets, levers, rocker arms, oil pump).

10. Method of operating a stationary energy production system comprising an internal combustion engine powered by hydrogen and in which an inert gas circulates in a closed circuit, consisting of lubricating at least one part of said engine with a composition as described in any one of claims 1 to 8. 1 1. Stationary energy production system comprising an internal combustion engine powered by hydrogen and in which an inert gas circulates in a closed circuit, characterized in that it contains in at least one of the parts of the engine, a composition as described in any one of claims 1 to 8.

12. System according to the preceding claim, characterized in that the inert gas is chosen from nitrogen, argon and noble gases such as helium, neon, krypton, xenon and radon and preferably the inert gas is argon.