Re-refined oil-based screw compressor lubricating composition

Abstract

The present invention relates to the use of a lubricating composition for the lubrication of moving parts in a screw compressor, this lubricating composition comprising an oil that is at least partly re-refined and has a reduced environmental impact.

Description

Title of the invention: Lubricating composition for screw compressor based on re-refined oil Technical field

[0001] The present disclosure relates to the field of lubricating compositions for screw compressors. More specifically, the present invention relates to the use of re-refined oils for the formulation of lubricating compositions for screw compressors. Prior art

[0002] A lubricating composition, also called "a lubricant", is commonly used in the various components of mechanical systems such as, for example, hydraulic systems, industrial machines or motor vehicles. The lubricating composition is mainly used to reduce the friction forces between the various moving metal parts in these mechanical systems. It is also effective in preventing premature wear or even damage to these parts, and in particular damage to their surface. A lubricating composition is conventionally composed of a base oil with which one or more dedicated additives are generally associated to adapt the lubricating performance of the base oil depending on the use of the lubricating composition.

[0003] A screw compressor is an industrial machine used in particular in fields such as automotive, brewing, food packaging, aerospace or construction, the proper functioning of which requires the use of a lubricating composition. Indeed, the screw compressor compresses air, thanks to two rotors present in a chamber. The two rotors being continuously in close contact, the lubricating composition reduces the mechanical wear of the two rotors.

[0004] During operation of the screw compressor, the lubricating composition used may oxidize in the presence of oxygen and degrade. This oxidation may be explained by various factors such as, for example, the high temperature and / or pressure conditions present in the screw compressor, the contact of the lubricating composition with impurities and the dissolution of metal particles capable of catalyzing the degradation by oxidation of the lubricating composition.

[0005] A lubricating composition can also be polluted during its use by contact with impurities.

[0006] The degradation and pollution of the lubricating composition are characterized by the formation of deposits and / or varnish, a blackening of the lubricating composition or even an increase in the viscosity of the lubricating composition.

[0007] These various phenomena of degradation and pollution thus lead to a reduction in the cleanliness of the lubricating composition and of the mechanical parts in contact with the lubricating composition, result in a loss of the initial performance of the lubricating composition and are therefore likely to impact the proper operation of the screw compressor. Early replacement of the lubricating composition is therefore necessary before the interval of 2000 hours of operation required by screw compressor manufacturers.

[0008] In addition, the base oil of screw compressor lubricating compositions is currently a conventional base oil obtained by refining crude oil. A large amount of crude oil is generally required to obtain the conventional base oil. Typically, to extract 1 liter of conventional base oil, 37 liters of crude oil are required. In addition, petroleum refining processes are very energy intensive and generate large amounts of carbon dioxide.

[0009] The carbon footprint of currently used screw compressor lubricating compositions therefore does not correspond to current environmental concerns and resource conservation issues.

[0010] There is therefore a need to provide a lubricating composition for a screw compressor allowing the proper operation of a screw compressor for at least 2000 hours and a reduced carbon footprint compared to a lubricating composition comprising a conventional base oil obtained by refining crude oil. Abstract

[0011] There is proposed a use of a lubricating composition for the lubrication of moving parts in a screw compressor, said lubricating composition comprising: a base oil comprising: - more than 5% by weight, relative to the total weight of the lubricating composition, of at least one at least partly re-refined oil, and - less than 95% by weight, relative to the total weight of the lubricating composition, of at least one conventional base oil, and at least one additive selected from an anti-corrosion agent, a metal passivation agent, a demulsifying agent, an antioxidant agent, an anti-wear agent, a calcium-based agent, an anti-foaming agent, a pour point depressant (PPD), an extreme pressure resistance agent, a detergent agent, a cleaning agent, a solvent, an anti-rust agent and mixtures thereof.

[0012] The use of an at least partly re-refined oil to formulate a lubricating composition for the lubrication of moving parts in a screw compressor has never been suggested in the prior art. And yet, the replacement of a conventional base oil by an oil at least partly re-refined in the lubricating composition used according to the invention proves to be surprisingly advantageous from an ecological and technical point of view.

[0013] Indeed, thanks to this replacement, the lubricating composition used according to the invention has a carbon footprint significantly lower than the carbon footprint of a lubricating composition comprising a base oil consisting of a conventional base oil obtained from the refining of crude oil.

[0014] In addition, the replacement of the conventional base oil with the at least partly re-refined oil combined with the additive surprisingly improves the resistance to degradation of the lubricating composition used according to the invention. This improvement in resistance to degradation is characterized by an improvement in the cleaning properties of the lubricating composition used according to the invention and a reduction in the variation in the viscosity of the lubricating composition used according to the invention.

[0015] These technical improvements may also lead to additional environmental improvements.

[0016] For example, improving the resistance to degradation of the lubricating composition used according to the invention allows: - to better protect the moving parts of the screw compressor, - to increase the service life of said lubricating composition to exceed 2000 hours, in particular 4000 hours, more particularly 8000 hours of operation in a screw compressor, while maintaining the lubrication performance targeted for this type of compressor. This advantageously makes it possible to increase the time between two consecutive oil changes of a screw compressor, and therefore - to operate the screw compressor in its optimum performance range for a longer period without the need for maintenance operations, i.e. to optimize the performance of said screw compressor.

[0017] Thus, a screw compressor using the lubricating composition implemented according to the invention advantageously has: - an improved lifespan because its moving parts are better protected, - a reduced carbon footprint because: - the quantities of lubricating composition and moving parts required for its proper functioning are reduced, and - its energy needs are reduced because its performance is optimized.

[0018] According to another aspect, there is provided a lubricating composition for a screw compressor comprising: a base oil comprising: - more than 5% by weight, relative to the total weight of the lubricating composition, of at least one at least partly re-refined oil, and - less than 95% by weight, relative to the total weight of the lubricating composition, of at least one conventional base oil, and at least one additive selected from an anti-corrosion agent, a metal passivation agent, a demulsifying agent, an antioxidant agent, an anti-wear agent, a calcium-based agent, an anti-foaming agent, a pour point depressant (PPD), and mixtures thereof.

[0019] According to another aspect, there is provided a method of lubricating a screw compressor comprising the following step: (a) bringing into contact the moving parts in the screw compressor requiring lubrication with a lubricating composition, said lubricating composition comprising: a base oil comprising: - more than 5% by weight, relative to the total weight of the lubricating composition, of at least one at least partly re-refined oil (RBO), and - less than 95% by weight, relative to the total weight of the lubricating composition, of at least one conventional base oil (CBO), and at least one additive selected from an anti-corrosion agent, a metal passivation agent, a demulsifying agent, an antioxidant agent, an anti-wear agent, a calcium-based agent, an anti-foaming agent, a pour point depressant (PPD), and mixtures thereof. Description of the embodiments

[0020] According to a first aspect, there is proposed a use of a lubricating composition for the lubrication of moving parts in a screw compressor, said lubricating composition comprising: a base oil comprising: - more than 5% by weight, relative to the total weight of the lubricating composition, of at least one oil which is at least partly re-refined and - less than 95% by weight, relative to the total weight of the lubricating composition, of at least one conventional base oil, and at least one additive selected from an anti-corrosion agent, a metal passivation agent, a demulsifying agent, an antioxidant agent, an anti-wear agent, a calcium-based agent, an anti-foaming agent, a pour point depressant (PPD), an extreme pressure resistance agent, a detergent agent, a cleaning agent, a solvent, an anti-rust agent and mixtures thereof.

[0021] For the purposes of the present application, the expression "at least partly re-refined oil" ("Refined Base OU" or "RBO" according to English terminology), also referred to more simply in the rest of the text as "re-refined oil", means an oil derived from a used lubricating composition which has been subjected to one or more re-refining treatment stages.

[0022] For the purposes of the present application, the expression "conventional base oil" ("Conventional Base OU" or "CBO" according to English terminology) designates an oil which, as opposed to a re-refined oil, is conventionally used in the field of lubricating compositions, is directly obtained by refining a crude oil and which has not yet been used.

[0023] For the purposes of the present application, the expression “used lubricating composition” designates any lubricating composition that has been used for the lubrication of moving parts, in particular metal parts, of a mechanical system, such as, but not limited to, bearings, gears or motors.

[0024] The lubricating composition used in the invention may have a kinematic viscosity at 40°C, measured according to the ISO 3014-2020 standard, greater than or equal to 40 mm2 / s, in particular from 40 mm2 / s to 49 mm2 / s, more particularly from 42 mm2 / s to 47 mm2 / s.

[0025] Advantageously, a lubricating composition having such a kinematic viscosity at 40°C is particularly suitable for use in a screw compressor. In addition, the inventors have noted that the viscosity of a lubricating composition having a viscosity at 40°C in these ranges, in particular from 42 mm2 / s to 47 mm2 / s, is particularly stable.

[0026] The base oil of the lubricating composition used according to the invention may comprise from 50% by weight to 75% by weight, relative to the total weight of the lubricating composition, of re-refined oil, in particular from 60% to 71% by weight.

[0027] The base oil of the lubricating composition used according to the invention may comprise from 20% by weight to 40% by weight, relative to the total weight of the lubricating composition, of the conventional base oil, in particular from 27% to 35% by weight.

[0028] The inventors have noted that the lubricating composition used according to the invention comprising a base oil whose contents of re-refined oil and / or conventional base oil are in the ranges described is suitable for use in a screw compressor. In particular, such a lubricating composition can exhibit cleanliness performances making it possible to reduce, or even prevent, the formation of deposits and varnish on the moving parts of the screw compressor, which is characteristic of improved resistance to degradation.

[0029] The kinematic viscosity at 40°C of the re-refined oil may be from 3.0 mm2 / s to 10.0 mm2 / s, in particular from 4.0 mm2 / s to 7.5 mm2 / s, more particularly from 5.5 mm2 / s to 6.0 mm2 / s.

[0030] The kinematic viscosity at 100°C of the re-refined oil may be from 25 mm2 / s to 40 mm2 / s, in particular from 30 mm2 / s to 35 mm2 / s, more particularly from 31.5 mm2 / s to 33.0 mm2 / s.

[0031] The viscosity index of the re-refined oil may be from 110 to 150, in particular from 115 to 130, more particularly from 120 to 125.

[0032] The molar mass of the re-refined oil may be from 350 g / mol to 600 g / mol, in particular from 400 g / mol to 500 g / mol, more particularly from 430 g / mol to 450 g / mol.

[0033] The pour point of the re-refined oil may be from -40°C to 0°C, in particular from -35°C to -10°C, more particularly from -30°C to -15°C.

[0034] The inventors have noted that a lubricating composition comprising a re-refined oil having at least one of the five characteristics presented above, in particular at least two, more particularly at least three, most particularly at least four, most particularly the five characteristics presented above is suitable for use in a screw compressor.

[0035] Re-refining treatments for used lubricating compositions have therefore been developed in order to regenerate these compositions and allow their subsequent reuse as re-refined oil. A re-refined oil is thus an oil obtained at the end of one or more re-refining treatment stages of a used lubricating composition, aimed at eliminating, at least in part, a certain number of contaminating elements present therein, such as dust, water, fuel fractions, metallic elements, polycyclic aromatic hydrocarbons and other residues resulting from the degradation of the additives present in the used lubricating compositions.

[0036] Thus, the composition of a re-refined oil differs from the composition of a used lubricating composition at least by a reduced content of contaminating elements present therein.

[0037] The sulfur content of the re-refined oil may be from 5 ppm to 1500 ppm, in particular from 10 ppm to 1100 ppm, more particularly from 1000 ppm to 1050 ppm or from 20 ppm to 40 ppm.

[0038] The nitrogen content of the re-refined oil may be less than or equal to 100 ppm, in particular from 0 ppm to 75 ppm, more particularly from 1 ppm to 60 ppm.

[0039] The silicon content of the re-refined oil may be less than or equal to 300 ppm, in particular from 1 ppm to 200 ppm.

[0040] The phosphorus content of the re-refined oil may be less than or equal to 100 ppm, in particular from 0 ppm to 50 ppm, for example 0 ppm.

[0041] The chlorine content of the re-refined oil may be less than or equal to 50 ppm, in particular from 0 ppm to 25 ppm, for example 0 ppm.

[0042] The contents of sulfur, nitrogen, silicon, phosphorus and chlorine can be determined by any techniques known to those skilled in the art, for example by X-ray fluorescence (XRF), by infrared spectroscopy or by UV spectroscopy.

[0043] The inventors have noted that a lubricating composition comprising a re-refined oil having at least one of the five contents presented above, in particular at least two, more particularly at least three, most particularly at least four, most particularly the five contents presented above is suitable for use in a screw compressor.

[0044] The re-refined oil may have characteristics satisfying the criteria defined by the API classification for Group I, Group II, Group III oils or their combinations, in particular Group I, Group II or their combinations, more particularly Group I or Group II. These characteristics of the re-refined oil may be the content of saturated compounds, the sulfur content and / or the viscosity index.

[0045] The used lubricating composition may be a mixture of several used lubricating compositions, originating from the same source or from several different sources.

[0046] The used lubricating compositions comprise, in the majority quantity, one or more base oils conventionally used in the field of lubricants, such as mineral oils, synthetic oils, natural oils or their mixtures. Natural oils are naturally occurring oils, such as those derived from plants or animals, such as vegetable, animal, and fish oils, and their mixtures. Examples of such oils are rapeseed oil, canola oil, tall oil, sunflower oil, soybean oil, hemp oil, olive oil, linseed oil, mustard oil, palm oil, peanut oil, castor oil, coconut oil, animal fats, and their mixtures. Mineral or synthetic oils that can be used as base oils conventionally used in the lubricant field can belong to Group I, Group II, Group III, Group IV and / or Group V according to the classes defined in the API classification.

[0047] For example, the re-refined oil may be derived at least in part from a used lubricating composition having been subjected to one or more re-refining treatment steps, said used lubricating composition comprising a base oil belonging to group I, group II, group III, group IV, group V or their combinations according to the APL classification.

[0048] The used lubricating composition may comprise at least 50% by weight of base oil(s) relative to its total weight, in particular at least 60% by weight of base oil(s), and more particularly between 60 and 99% by weight of base oil(s).

[0049] The used lubricating composition may comprise various conventional additives in the lubricant field, such as friction modifier additives, extreme pressure additives, anti-wear additives, detergents, antioxidants, viscosity index (VI) improvers, pour point depressant (PPD) additives, dispersing agents, anti-foaming agents, thickeners, and mixtures thereof.

[0050] Due to their origin, the used lubricating composition may comprise a number of degradation products derived from the composition itself or from the additives it contains and resulting from the use of the lubricating composition for a more or less long period. The used lubricating composition may also comprise metal particles, metal oxides and other elements, for example from a mechanical system. In particular, a used lubricating composition may contain a high content of undesirable elements, for example calcium (Ca), iron (Fe), magnesium (Mg), sodium (Na), nickel (Ni), phosphorus (P), silicon (Si), chlorine (Cl), zinc (Zn) etc.

[0051] The re-refined oil may more particularly come from a used lubricating composition having been subjected to one or more prior pre-treatment steps chosen from a dehydration step, a distillation step, a filtration step, a hydrogenation step, a liquid / liquid extraction step, a decantation step, a step of passing said used lubricating composition over an adsorbent material or combinations thereof, in particular a step of passing said used lubricating composition over an adsorbent material.

[0052] The dehydration step makes it possible to eliminate any water present in the used lubricating composition. The dehydration step can be carried out by any method known to those skilled in the art, for example by distillation, evaporation, decantation, heating or passing a stream of hot air through the used lubricating composition. The dehydration step can be carried out at a temperature of between 50°C and 250°C, preferably between 100°C and 200°C. In particular, it can be carried out at a pressure of between 50,000 and 150,000 Pa, preferably at atmospheric pressure.

[0053] Advantageously, the re-refined oil may comprise a water content of less than or equal to 10% by mass, in particular less than or equal to 5% by mass, in particular less than or equal to 2% by mass and more particularly less than or equal to 1% by mass, relative to the total mass of said re-refined oil.

[0054] The distillation step can be carried out after the dehydration step. The distillation step can be carried out by any technique known to man. of the trade such as atmospheric distillation or distillation under reduced pressure. The distillation step may for example be carried out at a temperature between 100°C and 500°C, preferably between 200°C and 400°C, more preferably between 300°C and 380°C. In particular, it may be carried out at a pressure between 25 and 2,000 Pa, preferably between 50 and 1,000 Pa, more particularly between 50 and 250 Pa.

[0055] The filtration step can be implemented after the dehydration step. The filtration step can be implemented by any method known to those skilled in the art. This filtration step can be a particulate or non-particulate filtration step. It can for example be implemented by diatomaceous earth type systems.

[0056] The step of passing the used lubricating composition over an adsorbent material can be implemented by flowing the used lubricating composition over an adsorbent material. The adsorbent material advantageously makes it possible to selectively adsorb aromatic compounds, in particular polycyclic aromatic hydrocarbons. In particular, passing over an adsorbent material, preferably over activated carbon, advantageously makes it possible to reduce the content of polycyclic aromatic hydrocarbons, in particular chosen from chrysene, benzo[b]fluoranthene, benzo[j]fluoranthene, benzo[k]fluoranthene, benzo[e]pyrene, benzo[a]pyrene, dibenz[a,h]anthracene and / or benz[a]anthracene, of the used lubricating composition.

[0057] The flow rate of the used lubricating composition may be between 1 m3 / h and 15 m3 / h, for example between 5 and 10 m3 / h.

[0058] The adsorbent materials may be, for example, activated carbon, zeolites, clays or functionalized porous compounds. Preferably, it is activated carbon.

[0059] In the case of passing the used lubricating composition over activated carbon, the quantity of activated carbon used is preferably between 0.5 and 60 g of activated carbon per liter of used lubricating composition, preferably between 0.5 and 50 g / L, preferably from 1 to 50 g / L, preferably between 1 and 30 g / L, for example between 5 and 60 g / L, preferably between 5 and 50 g / L.

[0060] Preferably, the activated carbon is characterized by a density of between 200 and 500 kg / m3, for example measured according to the ASTDM D2854 standard.

[0061] Preferably, the activated carbon is a coal, preferably comprising from 70 to 95%, advantageously from 80 to 90% by weight of carbon.

[0062] The step of passing the used lubricating composition over an adsorbent material, preferably over activated carbon, is advantageously preceded by the following steps: - one or more distillation stages; and - a filtration step, in particular as defined previously.

[0063] For example, re-refined oil may be obtained from the treatment of a used lubricating composition according to the method described in WO 2018 / 109208.

[0064] The hydrogenation step can be carried out by any technique known to those skilled in the art and generally consists of treating the lubricating oil with hydrogen, generally in the presence of a hydrogenation catalyst. Such a catalyst can contain, for example, at least one oxide or a sulfide of at least one group VI metal and / or at least one group VIII metal, such as molybdenum, tungsten, nickel or cobalt, and a support, for example alumina, silica-alumina or a zeolite. The hydrogenation step may preferably follow a dehydration and / or distillation step.

[0065] The liquid / liquid extraction step using a solvent advantageously makes it possible to lighten a dark-colored used oil, to eliminate at least in part the bad odor or the aromatic compounds, in particular the PAHs. The liquid / liquid extraction step can be implemented by any technique known to those skilled in the art. The liquid / liquid extraction step is generally carried out in a mixer-decanter or in an extraction column, using a suitable extraction solvent. The liquid / liquid extraction step by a solvent may preferably follow a dehydration and / or distillation step.

[0066] The decantation step can be implemented by any technique known to those skilled in the art.

[0067] The conventional base oil of the lubricating composition used according to the invention may be an oil of mineral or synthetic origin belonging, according to the API classification, to group I, group II, group III or their combinations, in particular to group I, group II or their combinations, more particularly to group I or group II.

[0068] The lubricating composition used according to the invention comprises at least one additive chosen from an anti-corrosion agent, a metal passivation agent, a demulsifying agent, an antioxidant agent, an anti-wear agent, a calcium-based agent, an anti-foaming agent, a pour point depressant (PPD), an extreme pressure resistance agent, a detergent agent, a cleaning agent, a solvent, an anti-rust agent and mixtures thereof.

[0069] These additives are known to those skilled in the art and are therefore not described more precisely.

[0070] The lubricating composition used according to the invention may comprise from 0.5% by weight to 6% by weight, relative to the total weight of the lubricating composition, of said at least one additive, in particular from 0.9% to 1.10% by weight.

[0071] The implementation according to the invention may comprise at least two, at least three, at least four, at least five, at least six, at least seven, at least eight, at least nine, at least ten, at least eleven, at least twelve or the thirteen additives described above.

[0072] For example, the additive may be a mixture of metal passivating agent, antioxidant agent, anti-wear agent, calcium-based agent, pour point depressant (PPD) and anti-foaming agent.

[0073] Alternatively, the additive may be a mixture of metal passivating agent, antioxidant, solvent, extreme pressure resistance agent, anti-wear agent, anti-corrosion agent, pour point depressant (PPD), anti-foaming agent, detergent agent, cleaning agent and demulsifying agent.

[0074] Some agents can combine several functions. For example, an agent can be detergent and cleaning. This is also the case, for example, of spiroboronate, which is known as a detergent agent and which, unexpectedly, also acts as an antioxidant agent in the composition of the present invention.

[0075] Indeed, the inventors have found that the PAI of the lubricating composition used according to the invention comprising spiroboronate is low, which proves the unexpected antioxidant effect of spiroboronate.

[0076] Thus, spiroboronate can be at least one of the additives of the lubricating composition used according to the invention.

[0077] For example, the lubricating composition used according to the invention may comprise from 0.1% by weight to 1% by weight, relative to the total weight of the lubricating composition, of spiroboronate, in particular from 0.4% to 0.6% by weight.

[0078] The lubricating composition used according to the invention may comprise, relative to the total weight of the lubricating composition: from 0.50% to 1.5% by weight of a mixture of metal passivation agent, antioxidant agent, anti-wear agent, calcium-based agent, in particular from 0.80% to 1% by weight, from 0.05% to 0.25% by weight of pour point depressant (PPD), in particular from 0.10% to 0.20% by weight, and from 0.01% to 0.15% by weight of antifoaming agent, in particular from 0.04% to 0.1% by weight.

[0079] Alternatively, the lubricating composition used according to the invention may comprise, relative to the total weight of the lubricating composition: from 0.01% to 0.15% by weight of metal passivation agent, in particular from 0.04% to 0.06% by weight, from 0.10% to 1% by weight of antioxidant agent, in particular from 0.4% to 0.5% by weight, from 0.50% to 1.5% by weight of solvent, in particular from 0.9% to 1% by weight, from 0.05% to 0.5% by weight of a mixture of extreme pressure resistance agent and anti-wear agent, in particular from 0.20% to 0.25%, from 0.01% to 0.10% by weight of anti-corrosion agent, in particular from 0.04% to 0.06%, from 0.05% to 0.5% by weight of pour point depressant (PPD), in particular from 0.1 to 0.3% by weight, from 1% to 3% by weight of a mixture of detergent agent and cleaning agent, in particular from 1.8% to 2.2% by weight, and from 0.05% to 1% by weight and demulsifying agent, in particular from 0.4% to 0.6% by weight.

[0080] For the purposes of the present application, the expression "eco-material content" designates the ratio, in percentage, between the weight of the re-refined oil of the lubricating composition used according to the invention on the total weight of said lubricating composition.

[0081] Thus, the lubricating composition used according to the invention may have an eco-material content of at least 5%, in particular from 50% to 75%, more particularly from 65% to 71%.

[0082] According to another aspect, there is provided a use of a re-refined oil to increase the eco-material content of a lubricating composition for a screw compressor.

[0083] According to another aspect, there is provided a lubricating composition for a screw compressor comprising: a base oil comprising: - more than 5% by weight, relative to the total weight of the lubricating composition, of at least one at least partly re-refined oil, and - less than 95% by weight, relative to the total weight of the lubricating composition, of at least one conventional base oil, and at least one additive selected from an anti-corrosion agent, a metal passivation agent, a demulsifying agent, an antioxidant agent, an anti-wear agent, a calcium-based agent, an anti-foaming agent, a pour point depressant (PPD), and mixtures thereof.

[0084] The base oil, the at least partly re-refined oil, the conventional base oil and the additive are as defined above in connection with the use of a lubricating composition for the lubrication of moving parts in a screw compressor.

[0085] According to another aspect, there is proposed a use of the lubricating composition for improving the eco-performance of a screw compressor.

[0086] The lubricating composition used in this use is as defined above in connection with the use of a lubricating composition for the lubrication of moving parts in a screw compressor.

[0087] For example, eco-performance is the increase in the life of the screw compressor, the decrease in the environmental impact of the screw compressor or both.

[0088] Indeed, as explained above, the lubricating composition used according to the invention has improved resistance to degradation which allows: - to better protect the moving parts of the screw compressor, and therefore to increase the service life of said screw compressor, and - to reduce the quantities of lubricating composition, moving parts and energy required for the proper operation of the screw compressor, and therefore to reduce the environmental impact of said screw compressor.

[0089] According to another aspect, there is provided a method of lubricating a screw compressor comprising the following step: (a) bringing moving parts in the screw compressor requiring lubrication into contact with a lubricating composition

[0090] The lubricating composition used in this method is as defined above in connection with the use of a lubricating composition for the lubrication of moving parts in a screw compressor. Examples

[0091] Measurement of the properties of lubricating compositions

[0092] The cleanliness performance of various lubricating compositions was evaluated by a test according to ASTM 7873-2022 modified ("TOST", acronym for "Thermal Oxidation Stability Test"), this test being modified as follows. The lubricating composition is heated to 140°C in the presence of copper and steel catalysts in a glass container placed in an oil bath. Oxygen is bubbled through the lubricating composition maintained at 140°C for a certain period of time. At the end of the test, the visual appearance of the container is observed. It is noted whether deposits and / or varnishes have formed on the surface of the glass, as well as their appearance. The appearance of the catalysts is also observed. A sample of the composition obtained at the end of the test is filtered through a filter capable of filtering out particles larger than 1 μm. The color of the filtered particles is noted.

[0093] The visual appearance of the glass container and the filtered particles created makes it possible to classify the performance in terms of maintaining the cleanliness of the lubricating composition evaluated: 0 The glass container is covered with a non-transparent black deposit and / or varnish and the filtered particles are very dark black / brown; + The glass container is covered with a rather transparent black / dark brown deposit and / or varnish and the filtered particles are black / dark brown; ++ The glass container is coated with a transparent black deposit and / or varnish and the filtered particles are black / dark brown; +++ The glass container is covered with a light deposit and / or clear varnish and the filtered particles are black / dark brown; ++++ No deposit is visible on the surface of the glass container and the filtered particles are yellow / light beige.

[0094] The duration of the thermal oxidation stability test is: 216 hours for compositions II and Cl presented below, 168 hours for compositions 12 and C2 presented below, and 336 hours for compositions 13 and the comparative commercial lubricant composition ROT AIR presented below.

[0095] The kinematic viscosity at 40°C of the lubricating composition is measured according to the ISO 3104-2020 standard. At the end of the thermal oxidation stability test described above, the lubricating composition is recovered and its kinematic viscosity at 40°C is measured according to ISO 3104-2020 to calculate the viscosity variation at 40°C.

[0096] The PAI of the lubricating composition is measured according to DIN 51453-2004

[0097] Example 1: Preparation of lubricating compositions.

[0098] Lubricating compositions according to the invention (II to 13) and comparative lubricating compositions (C1 and C2) were formulated.

[0099] Table 1 shows the properties of the two re-refined oils, denoted RBO 1 or RBO 2 in Table 1, included in the lubricating compositions according to the invention (II to 13)

[0100] [Tables] Properties Measurement method RBO 1 RBO 2 Kinematic viscosity at 40°C ASTM D445 31.92 mm2 / s 32.91 mm2 / s Kinematic viscosity at 100°C ASTM D445 5.717 mm2 / s 5.869 mm2 / s Viscosity index NF ISO 2909 121 123 Molar mass ASTM D2502 436 g / mol 443 g / mol Pour point ASTM D5950 -30°C -15°C Sulphur content ASTM D2226 33 ppm 1009 ppm Nitrogen content ASTM 4629 4 ppm 58 ppm

[0101] Tables 2, 3 and 4 present the compositions and properties of the lubricating compositions according to the invention (II to 13), of the comparative lubricating compositions (C1 and C2) and of a commercial comparative lubricating composition (ROTAIR) free of re-refined oil. The percentages are percentages by weight relative to the total weight of the lubricating composition.

[0102] Conventional base oil (denoted CBO in Tables 2 to 4) is group IL

[0103] Additive mixture 1 comprises a metal passivation agent, an antioxidant agent, an anti-wear agent and a calcium-based agent.

[0104] Additive mixture 2 comprises a metal passivating agent, an antioxidant agent, a solvent, an extreme pressure resistance agent, an anti-wear agent, an anti-corrosion agent, a pour point depressant (PPD), an anti-foaming agent, a detergent agent, a cleaning agent and a demulsifying agent.

[0105] Table 2 highlights that the substitution of the conventional base oil with the re-refined RBO 1 oil strongly stabilizes the kinematic viscosity at 40°C and improves the cleanliness performance of the lubricating composition.

[0106] Table 3 shows that the substitution of the conventional base oil with the re-refined RBO 2 oil does not alter the stability of the kinematic viscosity at 40°C. Indeed, the variations in kinematic viscosity at 40°C of compositions 12 and C2 are of the same order of magnitude. Table 3 also highlights that the substitution of conventional base oil with re-refined RBO 2 oil does not change the cleanliness performance of the lubricating composition.

[0107] Table 4 shows that the substitution of the conventional base oil with the re-refined RBO 1 oil and the use of spiroboronate as an additive makes it possible: to increase the resistance to oxidation of the lubricating composition, because the PAI decreases significantly, and to improve the cleanliness performance of the lubricating composition.

[0108] [Tables2] Compounds II Cl Base oil RBO 1 70% RBO 2 CBO: Group II 28.9% 98% Additives Additive blend 1 0.9% 0.85% PPD agent 0.15% 0.15% Antifoam agent 0.05% 1% Kinematic viscosity at 40°C (mm2 / s) 44.0 46.35 A Kinematic viscosity at 40°C (%) 0.6 12.0 Cleanliness performance + + + + 0

[0109] [Tables3] Compounds 12 C2 Base oil RBO 1 62% CBO: Group II 32.5% 94.5% Additives Additive blend 2 2% 2% Antifoam agent 1% 1% Detergent and washing agent 2% 2% Demulsifying agent 0.5% 0.5% Thermal oxidation stability test duration 168 hours Kinematic viscosity at 40°C (mm2 / s) 41.9 45.9 A Kinematic viscosity at 40°C (%) 3.7 2.9 Cleanliness performance + + + + + + + +

[0110] [T ables 4] Compounds 13 ROTAIR Base oil RBO 1 70% / CBO: Group II 28.35% Additives Additive blend 1 0.9% PPD agent 0.15% Antifoam agent 0.1% Spiroboronate 0.5% PAI 22.5 335.3 Cleanliness performance + + + 0

Claims

Claims

1. Use of a lubricating composition for lubricating moving parts in a screw compressor, said lubricating composition comprising: a base oil comprising: - more than 5% by weight, relative to the total weight of the lubricating composition, of at least one at least partly re-refined oil, and - less than 95% by weight, relative to the total weight of the lubricating composition, of at least one conventional base oil, and at least one additive selected from an anti-corrosion agent, a metal passivating agent, a demulsifying agent, an antioxidant, an anti-wear agent, a calcium-based agent, an anti-foaming agent, a pour point depressant (PPD), an extreme pressure resistance agent, a detergent agent, a cleaning agent, a solvent, an anti-rust agent and mixtures thereof.

2. Use according to claim 1, wherein the base oil comprises from 50% by weight to 75% by weight, relative to the total weight of the lubricating composition, of said at least one at least partly re-refined oil.

3. Use according to claim 1 or claim 2, wherein the base oil comprises from 20% by weight to 40% by weight, relative to the total weight of the lubricating composition, of said at least one conventional base oil.

4. Use according to any one of claims 1 to 3, in which the lubricating composition has a kinematic viscosity at 40°C greater than or equal to 40 mm2 / s.

5. Use according to any one of claims 1 to 4 wherein said at least one at least partly re-refined oil has characteristics satisfying the criteria defined by the API classification for oils of group I, group II, group III or their combinations.

6. Use according to any one of claims 1 to 5 wherein said at least one conventional base oil is an oil of mineral or synthetic origin belonging, according to the API classification, to group I, group II, group III or their combinations.

7. Use according to any one of claims 1 to 6 in which spiroboronate is at least one of the additives of the lu- composition brifying.

8. Use according to claim 7 in which the lubricating composition comprises from 0.1% by weight to 1% by weight, relative to the total weight of the lubricating composition, of spiroboronate.

9. Use according to any one of claims 1 to 8, wherein the lubricating composition has an eco-material content of at least 5%, the eco-material content being defined as the ratio, in percentage, between the weight of said at least one at least partly re-refined oil of said lubricating composition and the total weight of said lubricating composition.

10. Use of a lubricating composition for improving the eco-performance of a screw compressor, said lubricating composition being as defined in any one of claims 1 to 9.

11. Use according to claim 10, wherein the eco-performance is increasing the life of the screw compressor, decreasing the environmental impact of the screw compressor or both.

12. A method of lubricating a screw compressor comprising the following step: a) contacting the moving parts in the screw compressor requiring lubrication with a lubricating composition, said lubricating composition being as defined in any one of claims 1 to 9.