Use of a biodegradable lubricant base, and method for the preparation thereof

Description

Technical field of the invention

[0001] The present invention relates to the technical field of biodegradable lubricants, preferably bio-based.

[0002] In particular, the present invention relates to a process for preparing a biodegradable lubricating base composed of vegetable oil esters for lubricating applications, notably for lubricating gears (e.g., in wind turbines), ground-mounted turbines, stern tubes and other equipment used in the marine sector, or chainsaw chains used in forestry operations. The present invention also relates to a lubricating base obtained according to the aforementioned process. The present invention further relates to the use of a lubricating base obtained by the aforementioned process or as defined above for lubricating devices and / or machines. State of the art

[0003] Lubrication is a process designed to reduce friction between two moving parts. Introducing a lubricant between two parts therefore reduces friction and the resulting negative effects, such as wear, fatigue, corrosion, breakage, etc.

[0004] Thus, a lubricating composition must, on the one hand, meet specific technical performance requirements, particularly in terms of viscosity, viscosity index, rheology (both cold and hot), and flash point. Viscosity is chosen according to the application and the system to be lubricated. For example, industrial gears require relatively viscous grades around ISO VG 220 and ISO VG 320, while stern oils require ISO VG 100 and ISO VG 150.

[0005] On the other hand, environmental considerations and protection have become major issues today. Indeed, some of the lubricants used in wind farms, forestry operations, or in marine environments (boats, wind turbines and offshore structures, etc.) are likely to be dispersed into the environment and can pollute seas / oceans, soil, runoff water, and groundwater. For example, in the case of oils that provide continuous lubrication for chainsaw chains, drops of oil constantly fall to the ground: this is a form of wasted lubrication, and the quantities of oil released into the environment are significant.The same pollution problems arise with hydraulic fluids used on machines: in this case it is no longer a question of lost lubrication but of dispersion of lubricants in the ambient environment following leaks due to lack of sealing or accidental ruptures of hoses and seals which are inherent to the operation of these machines.

[0006] Solutions have been proposed in prior art.

[0007] As an example, lubricating compositions based on alkyl isostearate or neopolyol have been developed and may correspond to the commercial products Nycobase SNG, NB 8318S, Nycobase STM, and Nycobase SMP. These esters are formed primarily from isostearic acid (iso-C18) produced during the industrial manufacturing of the dimer acid. These esters exhibit viscous grades ranging from ISO VG 46 to ISO VG 150, according to standard NF ISO 3448, which are suitable for lubrication process requirements. However, their synthesis remains relatively confidential and limited for the following reasons: The limited production of this isostearic acid, which is a minor co-product of the manufacture of the dimeric fatty acid and is therefore dependent on the latter and remains industrially difficult to access for more widespread use; the complex nature of the industrial mixture of isostearic acid, whose purity varies between 60 and 80%; the variable quality from one manufacturer to another leading to different compositions (variable content of unsaponifiables, cyclic structures, etc.), hence the difficulty in securing quality supplies; and the variable quality from one batch to another which can lead to variable application properties and thus, for example, to variable and problematic interfacial properties.

[0008] US patent 2,049,072, published in 1936, describes a process for manufacturing materials intended to form lubricants. Specifically, the purpose of this patent is to provide a lubricating composition for mixing with mineral oil and is therefore not intended to provide a biodegradable lubricating base.

[0009] The process described in this document includes: at least the partial esterification of an aliphatic organic material containing hydroxyl groups, such as castor oil, with an organic acid such as acetyl chloride, with or without a catalyst; optionally, a stabilization step, for example by hydrogenation, so as to obtain, for example, esterified and hydrogenated castor oil.

[0010] However, as will be demonstrated below in the experimental section, the present Applicant has carried out comparative tests and has demonstrated that the process described in this document and in particular those exemplified, do not allow obtaining a high-performance lubricating base with a good acid number, good resistance to oxidation and aging and good resistance to hydrolysis according to current standards, respectively ISO 6618 standard TOST and ASTM E222B.

[0011] The Applicant further points out that the authors of this document indicate that partial esterification leads to sufficient performance to improve the quality of mineral oil after blending. However, the Applicant reproduced partial esterification in the laboratory (equimolar ratio of castor oil and acetyl chloride) and found that the partially acetylated product was not liquid, but solid. Partial esterification therefore does not provide a usable (i.e., in liquid form) lubricating base for devices such as wind turbines.

[0012] Finally, the Plaintiff points out that this document dates from 1936 and yet, to her knowledge, no professional in the lubricants sector has offered such a castor oil-based lubricant on the market, either in the past or currently. This information has therefore not been heeded by professionals in the sector. This appears to be due to the fact that the lubricant bases described, even if they exhibit satisfactory results in terms of viscosity, are unsatisfactory in terms of other essential characteristics for a lubricant, such as acid number, aging resistance, and resistance to hydrolysis.

[0013] There is therefore a need for new lubricating compositions that are biodegradable and thus more environmentally friendly than traditional petroleum-derived lubricants, while maintaining at least similar technical performance, namely fluid compositions with fairly high viscosity grades ranging from ISO VG 46 to ISO VG 150, or even higher.

[0014] There is also a need in the state of the art for new biodegradable and preferably bio-based lubricating compositions, having adequate technical performance, with improved interfacial properties, while being easy to implement, i.e., while being easily feasible at the level of its preparation process, the process being capable of or configured to provide liquid compositions stable to water, to air, having identical or at least similar technical characteristics from one batch to another.

[0015] There is also a need in the state of the art for new lubricating compositions that exhibit good resistance to hydrolysis (i.e., water resistance), an adequate acid number, and would thus be particularly suitable for marine applications.

[0016] The aim of the present invention is therefore to propose a new lubricating base which meets at least partially the aforementioned needs. Presentation of the invention

[0017] To this end, the present invention relates to a method for preparing a lubricating base as defined in the set of claims.

[0018] The process for preparing a lubricant base according to the invention comprises a step (i) of preparing at least one compound of formula (I) corresponding to the following formula: in which R1, R2 and R3 are independently saturated hydrocarbon groups, linear or branched, comprising at least 16 carbon atoms, at least one group among R1, R2 and R3 is branched on its hydrocarbon chain by at least one ester group O-CO-R4 in which R4 is a linear or branched alkyl radical comprising from 1 to 10 carbon atoms, preferably from 1 to 6 carbon atoms,

[0019] said step (i) comprising the following successive steps and preferably comprising only the following three steps: (a) the supply of at least one previously hydrogenated vegetable oil or the hydrogenation of a vegetable oil, said vegetable oil being composed of at least one triglyceride comprising at least 50% (relative % determined by GC) of fatty acids having at least one hydrocarbon chain, saturated or unsaturated, linear or branched, comprising at least 16 carbon atoms, preferably at least 18 carbon atoms, one of said fatty acids being branched by at least one hydroxyl group -OH; (b) the selective esterification at said at least hydroxyl group -OH of said hydrogenated vegetable oil obtained at the end of step (a) with at least one organic acid anhydride comprising monitoring the esterification reaction until a hydroxyl number (IOH) of less than or equal to 2 mg KOH / g measured according to ISO 6618 is obtained; (b1) a topping step; (b3) a neutralization step;(c) the recovery of at least one vegetable oil ester corresponding to formula (I); so as to obtain a lubricating base comprising an acid value, in mg KOH / g, measured according to ISO 6618, ranging from 0 to 0.5.

[0020] Other non-limiting and advantageous features of the process according to the invention, taken individually or in all technically possible combinations, are as follows: The vegetable oil in step (a) comprises at least one triglyceride of the following formula: in which the hydrocarbon groups R1, R2 or R3 are independently of saturated hydrocarbon groups, linear or branched, comprising at least 16 carbon atoms, at least one group among R1, R2 and R3 is branched on its hydrocarbon chain by at least one hydroxyl group -OH; at least two and typically all three groups among R1, R2 or R3 are branched on their hydrocarbon chains by at least one hydroxyl group -OH; between said selective esterification step (b) and before proceeding to step (c) of recovering said at least one vegetable oil ester, the process may include the following intermediate steps: (b1) the topping step; (b2) a cooling step; (b3) the neutralization step; (b4) optionally a fine filtration step;the lubricating base comprises, by mass, relative to its total mass, at least 50%, preferably at least 80%, in particular at least 90% and typically 100% of said at least compound of formula (I); the process may include a step (ii) which comprises mixing said at least vegetable oil ester corresponding to formula (I) obtained at the end of step (i) with at least one other biodegradable lubricating compound; the vegetable oil is selected from one or more of the following oils: castor oil, lesquerella oil or any other oil comprising at least 50% fatty acids (relative % determined by GC) selected from: ricinoleic acid (C18:1-OH), densipoleic acid (C18:2-OH), lesquerolic acid (C20:1-OH), or auricolic acid (C20:2-OH); The organic acid anhydride corresponds to the formula (II) below: ; where R and R' are independently chosen from a linear or branched alkyl chain comprising from 1 to 12, in particular from 1 to 6 and typically from 1 to 4 carbon atoms; the organic acid anhydride is chosen in particular from the group consisting of acetic anhydride, propionic anhydride, butyric anhydride or isobutyric anhydride and a mixture thereof.

[0021] The present invention also relates to a lubricating base obtained by the preparation process as defined above, characterized in that it has an acid number, in mg KOH / g, measured according to ISO 6618, ranging from 0 to 0.5.

[0022] Preferably, the lubricating base exhibits resistance to hydrolysis, measured according to DEF STAN 05-50 (part 61), method 6, which varies from 300 to 2000 hours.

[0023] Finally, the present invention relates to the use of a lubricating base obtained by the preparation process as described above or of a lubricating base as described above, comprising said at least one bio-based and biodegradable compound of formula (I) for lubricating devices and / or machines, such as wind turbines and stern tubes.

[0024] Other non-limiting and advantageous features of the use according to the invention, taken individually or in all technically possible combinations, are as follows: the hydrocarbon groups R 1 , R 2 and R 3 comprise from 18 to 24 carbon atoms, preferably from 18 to 20 carbon atoms; the group R 4 of the ester group -O-CO-R 4 is chosen from a radical: methyl, ethyl, propyl or isopropyl; on said at least one hydrocarbon chain from R 1 , R 2 and R 3 branched by the ester group -O-CO-R 4, the latter is positioned at position 9, 10 or 12 or at position 14; at least two hydrocarbon groups from R 1 , R 2 and R 3 and preferably all the hydrocarbon groups R 1 , R 2 and R 3 are branched by the ester group -O-CO-R 4; the lubricating base also includes at least one other biodegradable, or partially biodegradable, lubricating compound, different from the compound of formula (I), such as an alkyl or neopolyol isostearate, a polyalphaolefin (PAO), a mineral oil or a mixture thereof;the lubricating base exhibits a tendency to foam, measured according to ASTM D 892, ranging from 0 to 200 mL, preferably ranging from 0 to 100 mL and typically ranging from 0 to 50 mL; the lubricating base exhibits a demulsification time, measured according to ASTM D 1401, ranging from 0 to 30 minutes, preferably ranging from 0 to 15 minutes and typically ranging from 0 to 10 minutes; the lubricating base exhibits an oil deaeration time, measured according to standard NF ISO 9120, December 1999, ranging from 1 to 10 minutes, preferably ranging from 1 to 5 minutes and typically ranging from 1 to 3 minutes, the lubricating base exhibits a resistance to hydrolysis, measured according to standard DEF STAN 05-50 (part 61) method 6 (“Ministry of Defence, Defence Standard 05-50 (Part 61), Method 6”), which varies from 300 to 2000 hours, preferably from 600 to 1500 hours and typically ranges from 750 to 900 hours;the lubricating base comprises, by mass, in relation to its total mass, at least 50%, preferably at least 80%, in particular at least 90% and typically 100% of said at least compound of formula (I).

[0025] Of course, the different features, variants and embodiments of the invention can be combined with each other in various ways as long as they are not incompatible or mutually exclusive.

[0026] In addition, various other features of the invention emerge from the attached description which illustrate non-limiting forms of embodiment of the invention. Detailed description of the invention

[0027] The Applicant has focused on developing new fluid, branched, saturated fatty long-chain ester lubricating compositions intended for use in both hot and cold conditions for lubrication needs, such as for the lubrication of machines and / or devices like wind turbines (onshore or offshore).

[0028] The Applicant has also focused on developing new bio-based and biodegradable fluid lubricating compositions that also meet the European Ecolabel for lubricants (NF511).

[0029] For this purpose, the present invention relates to the use of a lubricating base obtained by the preparation process as described below or of a lubricating base as defined below comprising at least one bio-based and biodegradable ester compound of formula (I) for lubricating devices and / or machines, such as wind turbines and stern tubes, in which said at least one compound of formula (I) corresponds to the following formula: in which R1, R2 and R3 are independently saturated hydrocarbon groups, linear or branched, comprising at least 16 carbon atoms, at least one group among R1, R2 and R3 is branched on its hydrocarbon chain by at least one ester group O-CO-R4 in which R4 is a linear or branched alkyl radical comprising from 1 to 10 carbon atoms, preferably from 1 to 6 carbon atoms, and in which said lubricating base has an acid number, in mg KOH / g, measured according to ISO 6618, which ranges from 0 to 0.5.

[0030] Due to its characteristics, the lubricating base according to the invention presents both adequate lubrication properties, while being environmentally friendly.

[0031] In particular, it exhibits a high level of biodegradability, a high renewable carbon content, and a non-palm origin, thus limiting its environmental and societal impact. Indeed, the long-chain saturated fatty esters according to the invention are bio-based and are derived, for example, from one or more vegetable oils, such as castor oil or Lesquerella oil. These esters are also biodegradable and comply with the European Ecolabel for lubricants (NF511). Furthermore, they exhibit low, or even zero, aquatic toxicity. This low ecotoxicity is illustrated by the test on daphne (EL50-48h (g / 1000g) >0.11 / 1000 according to OECD 202) and biodegradability (80.3% according to OECD 301B).

[0032] On the other hand, as will be demonstrated in the experimental part below, the lubricating base according to the invention exhibits high resistance to hydrolysis and improved interfacial properties, in particular compared to the viscous esters obtained from isostearic acid mentioned above in the description of the prior art.

[0033] In addition, it has an excellent acidity index which makes it compatible with the components of devices and / or machines to be lubricated, such as elastomer-based seals, namely it has little or no impact on the service life of the materials in contact with it (particularly from a mechanical point of view).

[0034] It also has a viscosity grade generally between 135 and 165 cSt, which is a grade comparable to the most viscous (simple) isostearate available on the market (ISO VG 150 grade).

[0035] Hereafter "fluid" means that the lubricating base is able to flow at room temperature and is in liquid form under normal temperature (i.e.: room temperature) and pressure (i.e.: atmospheric pressure) conditions.

[0036] According to the invention, "bio-based" means a lubricating base entirely or at least partially made from materials of biological origin (for example, plant or animal) derived from renewable resources, such as a vegetable oil.

[0037] Also, according to the invention, a "biodegradable lubricating base" is defined as one whose ability to be degraded by microorganisms present in the natural environment. The action of bacteria on the lubricant in the presence of water and oxygen transforms it, under ideal thermal and temporal conditions, into carbon dioxide, mineral salts, and water.

[0038] There are several ways to measure biodegradability. a) CEC L33 A 93 Test

[0039] Primary biodegradability measures the disappearance of the starting compound over a given period. The CEC L33 A 93 approved test, performed in a liquid medium, is the most commonly used. A substance exhibits high biodegradability when its degradation rate exceeds 90%. A vegetable-based oil shows a 90% degradation rate after 120 days of testing. In contrast, a mineral-based lubricant degrades by only 70% over the same period. b) OECD Test 301B

[0040] Ultimate biodegradability is based on the amount of carbon dioxide emitted over a given period (OECD 301B approved test). This measure is more stringent, and biodegradable products achieve lower rates than those measured by primary biodegradability. This criterion better reflects the actual biodegradability of products since it takes into account the complete assimilation of the product by living organisms. Ultimate biodegradability, determined in a reactor using a soil medium, shows a degradation rate of over 70% for biolubricants compared to only 30% for mineral-based lubricants.

[0041] The lubricating base according to the invention here exhibits a degradation rate greater than or equal to 90% during the CEC L 33 A93 test and a degradation rate equal to or greater than 70%, preferably equal to or greater than 75% and generally equal to or greater than 80% determined according to the OECD 301B test.

[0042] The structure of the compounds of formula (I) (esters) according to the invention will be described below.

[0043] As mentioned above, the hydrocarbon groups R1, R2 and R3 of the compounds of formula (I) are independently of the saturated hydrocarbon groups, linear or branched comprising at least 16 carbon atoms, at least one of these groups is branched by the ester group O-CO-R4 (i.e. the ester function is not located at the termination of the hydrocarbon groups R1, R2 or R3).

[0044] By "at least 16 carbon atoms" is meant a hydrocarbon chain comprising the following number of carbon atoms or any interval between these values: 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; etc.

[0045] Generally, hydrocarbon groups R1, R2 and R3 comprise 18 to 24 carbon atoms, preferably 18 to 22 carbon atoms and typically 18 to 20 carbon atoms.

[0046] The term "alkyl group" refers to a linear or branched saturated hydrocarbon group comprising from 1 to 10 carbon atoms (C1 to C10), preferably from 1 to 6 carbon atoms (C1 to C6). According to the invention, "1 to 10 carbon atoms" includes the following values ​​and any interval between these values: 1; 2; 3; 4; 5; 6; 7; 8; 9; 10.

[0047] In general, the R 4 group of the ester group -O-CO-R 4 is chosen from a radical: methyl, ethyl, propyl or isopropyl.

[0048] In particular, at least two hydrocarbon groups among R1, R2 and R3, and typically all hydrocarbon groups among R1, R2 and R3, are branched by the ester group -O-CO-R4

[0049] As will be described below, compounds of formula (I) can be formed by esterification from a hydrogenated vegetable oil which includes at least one fatty acid branched by a hydroxyl group (not hydroxyl-terminated), such as castor oil (C18:1-OH) or lesquerella oil (C20:2-OH).

[0050] The esterification reaction occurs at the hydroxyl group (-OH) of these oils. Thus, the hydrocarbon groups R1, R2, and R3 can correspond to the hydrocarbon chains of the fatty acids contained in these oils. When the esterification reaction is carried out using castor oil, all hydrocarbon groups R1, R2, and R3 are branched by an ester group -O-CO-R4, and when the esterification reaction is carried out using Lesquerella oil, two hydrocarbon groups among R1, R2, and R3 include an ester group -O-CO-R4.

[0051] Advantageously, on said at least one hydrocarbon chain R 1 , R 2 and R 3 of the compound(s) of formula (I) branched by the ester group -O-CO-R 4, the latter is positioned at position 9, 10, 12 or at position 14 and is typically at position 12 or at position 14.

[0052] In general, the lubricating base comprises, by mass, in relation to its total mass, at least 50%, preferably at least 80%, in particular at least 90% and typically 100% of said at least compound of formula (I).

[0053] According to the invention, "the lubricating base comprises, by mass, in relation to its total mass, at least 50% of said at least compound of formula (I)" comprises the following values ​​and any interval between these values: 50; 55; 60; 65; 70; 75; 80; 85; 86; 87; 88; 89; 90; 91; 92; 93; 94; 95; 96; 97; 98; 99; 100.

[0054] Thus, the lubricating base may also include at least one other biodegradable lubricating compound, different from the compound of formula (I), such as an alkyl isostearate, for example in C1-C10 or neopolyol, a polyalphaolefin (PAO), a mineral oil or a mixture thereof.

[0055] Typically, the lubricating base is composed of / is made up of only said at least compound of formula (I).

[0056] The lubricating base or said at least compound of formula (I) according to the invention advantageously has the following characteristics: a Gardner color, measured according to ASTM 1544, which ranges from 1 to 8, preferably from 1 to 5 and typically ranges from 1 to 2; a density, measured according to ASTM D4052, which ranges from 0.930 to 0.970, preferably from 0.940 to 0.960 and typically ranges from 0.950 to 0.960; a viscosity at 100°C, measured according to ISO 3104 with a laboratory viscometer of the cannon fenske type, which ranges from 16 to 22 mm² / s, preferably from 18 to 20 mm² / s and typically ranges from 18.5 to 19.5 mm² / s; a viscosity at 40°C, measured according to ISO 3104 with a laboratory viscometer of the cannon fenske type, which varies from 100 mm 2 < / s to 200 mm 2 < / s, preferably from 130 mm 2 < / s to 170 mm 2 < / s and typically ranges from 160 mm 2 < / s to 165 mm 2 < / s; a viscosity index, measured according to ISO 2909, which varies from 110 to 170, preferably from 125 to 155 and typically ranges from 130 to 135;an acid value, in mg KOH / g, measured according to ISO 6618, ranging from 0 to 0.5, preferably from 0 to 0.20 and typically from 0 to 0.05; a hydroxyl value, measured according to ASTM E 222B, ranging from 0 to 10, preferably from 0 to 5 and typically from 0 to 3; an iodine value, in g / 100 of oil, measured according to ISO 3961, ranging from 0 to 10, preferably from 0 to 5 and typically from 0 to 3; a COC flash point, measured according to ASTM D92, ranging from 250 to 320, preferably from 265 to 310 and typically from 295 to 305; resistance to hydrolysis, measured according to DEF STAN 05-50 (part 61) method 6, which varies from 300 to 2000 hours, preferably from 600 to 1500 hours and typically ranges from 750 to 900 hours; the lubricating base and / or said at least compound of formula (I) according to the invention also exhibits enhanced interfacial properties in contact with air and water;a tendency to foam, which corresponds to the volume of foam measured in a graduated cylinder after five minutes of blowing air through said lubricating base, measured according to ASTM D 892 carried out at three temperature sequences: sequence 1 at 24°C, sequence 2 at 93.5°C, then cooling to sequence 3 at 24°C, ranging from 0 to 200 mL, preferably ranging from 0 to 100 mL and typically ranging from 0 to 50 mL, and ideally does not foam; a demulsification time, measured according to ASTM D 1401, ranging from 0 to 30 minutes, preferably ranging from 0 to 15 minutes and typically ranging from 0 to 10 minutes (according to the ASTM D 1401 method, a known volume of oil (40 ml) is mixed with water (40 ml); the time required for the two fluids to separate is measured in minutes; the faster the separation, the better the demulsification);an oil deaeration time, measured according to standard NF ISO 9120, December 1999, ranging from 1 to 10 minutes, preferably ranging from 1 to 5 minutes and typically ranging from 1 to 3 minutes (in particular, deaeration is the time, in minutes, during which the air dispersed in the lubricating base is reduced to 0.2% of the total volume, at a prescribed temperature; in other words, deaeration is the time required during which the lubricating base manages, by itself, to reduce the air it contains); a variation in oil acid number (mg KOH / g) ranging from 0.0 to 5.0, preferably ranging from 0.0 to 2.0 and typically ranging from 0.0 to 1.0 according to the ASTM D664 method as described in Example C below; a volatile acidity (mg KOH / g) ranging from 0.0 to 5.0, preferably ranging from 0.0 to 2.0 and typically ranging from 0.0 to 1.0 according to ASTM D974 method as described in comparative test C below;a viscosity variation (%) ranging from -20 to +30, preferably from -10 to +10 and typically from 0.0 to 5.0 according to the ASTM D445 method as described in comparative test C below; a deposit (mg / 100ml) ranging from 0 to 100, preferably from 0 to 50 and typically from 0 to 20 by gravimetry as described in comparative test C below; a mass variation of the metals in g (steel-copper spiral) ranging from 0.00 to 1.00, preferably from 0.00 to 0.50 and typically from 0.00 to 0.10 as described in comparative test C below (obtained by weighing).

[0057] As will be demonstrated in the tests below, the resistance to hydrolysis is increased for the oil esters according to the invention, particularly compared to a reference product (the isostearate mentioned above, which corresponds to the NYCOBASE SMP product marketed by NYCO). The hydrolysis stability according to DEF STAN 05-50 (Part 61) Method 6 increases from 400 hours for the NYCOBASE SMP product to between 790 and 850 hours for the compounds of formula (I) according to the invention.

[0058] The lubricating base and / or said at least compound of formula (I) possesses enhanced hydrolysis resistance properties in marine, aqueous, or humid environments. In particular, the lubricating base / said at least compound of formula (I) according to the invention exhibits hydrolysis stability, measured according to DEF STAN 05-50 (Part 61) Method 6, greater than or equal to 300 hours and typically greater than or equal to 600 hours. By way of example, the lubricating base / said at least compound of formula (I) according to the invention exhibits hydrolysis stability, measured according to DEF STAN 05-50 (Part 61) Method 6, preferably ranging from 650 hours to 2000 hours, in particular from 750 hours to 900 hours and typically from 780 hours to 900 hours. The hydrolysis resistance of the lubricating base according to the invention is thus 25% to 100% greater than that of an iso-stearate of identical viscosity grade as defined above.

[0059] According to the invention, "a range greater than or equal to 300 hours" includes the following values ​​or any interval between these values: 300; 350; 400; 450; 500; 550; 560; 570; 580; 590; 600; 610; 620; 630; 640; 650; 660; 670; 680; 690; 700; 710; 720; 730; 740; 750; 760; 770; 780; 790; 800; 810; 820; 830; 840; 850; 860; 870; 880; 890; 900; 910; 920; 930; 940; 950; 1000; 1100; 1200; 1300; 1400; 1500; 1600; 1700; 1800; 1900; 2000; 2100; 2200; 2300; 2400; 2500; 2600; 2700; 2800; 2900; 3000; 3100; 3200; 3300; 3400; 3500; etc.

[0060] The present invention relates to a method for preparing a lubricating base as defined in the set of claims.

[0061] In particular, the process according to the invention makes it possible to obtain compounds of formula (I) composing the lubricating base described above, namely branched long-chain fatty esters from at least one vegetable oil, in a single step, and can be summarized as follows: Huile végétale + anhydride organique → ester d ′ huile végétale + acide organique .

[0062] As an example, the reaction scheme could be as follows:

[0063] For this purpose, the process according to the invention for preparing the lubricating base comprises at least one step (i) of preparing said at least one compound of formula (I) as above, said step (i) comprising the following successive steps and in general comprising only the following three steps: (a) the supply of at least one previously hydrogenated vegetable oil or the hydrogenation of a vegetable oil, said vegetable oil (hydrogenated or not) being composed of at least one triglyceride comprising at least 50% (relative % determined by GC) of fatty acids having at least one hydrocarbon chain, saturated or unsaturated, linear or branched, comprising at least 16 carbon atoms, preferably at least 18 carbon atoms, one of said fatty acids being branched by at least one hydroxyl group -OH; (b) the selective esterification at said at least hydroxyl group -OH of said at least fatty acid of said hydrogenated vegetable oil obtained at the end of step (a) with at least one organic acid anhydride comprising monitoring the esterification reaction until a hydroxyl number (IOH) of less than or equal to 2 mg KOH / g measured according to ISO 6618 is obtained; (b1) a topping step; (b3) a neutralization step;(c) the recovery of at least one vegetable oil ester corresponding to formula (I) and of a possible organic acid, ; so as to obtain a lubricating base comprising an acid value, in mg KOH / g, measured according to ISO 6618, ranging from 0 to 0.5.

[0064] Preferably, the vegetable oil in step (a) comprises at least one triglyceride of the following formula: in which the hydrocarbon groups R 1 , R 2 or R 3 are as defined above except that at least one group among R 1 , R 2 and R 3 is branched on its hydrocarbon chain by at least one hydroxyl group -OH.

[0065] Generally, at least two groups and typically all three groups among R1, R2 and R3 are branched on their hydrocarbon chains by at least one hydroxyl group -OH.

[0066] In particular, the esterification step (b) is carried out on said at least one hydrocarbon chain R 1 , R 2 and R 3 in position 9, 10, 12 or in position 14.

[0067] In general, the vegetable oil is chosen from one or more of the following oils: castor oil, lesquerella oil or any other oil comprising at least 50% fatty acids (relative % determined by GC) chosen from: ricinoleic acid (C18:1-OH), densipoleic acid (C18:2-OH), lesquerolic acid (C20:1-OH), or auricolic acid (C20:2-OH).

[0068] Typically, vegetable oil is chosen: castor oil, lesquerella oil or a mixture thereof.

[0069] Step (a) of hydrogenating a vegetable oil is known to those skilled in the art and will not be described in further detail below. Alternatively, it is possible to obtain a vegetable oil as defined above that has been previously hydrogenated.

[0070] The esterification step (b) is thus carried out between the hydrogenated vegetable oil and an organic acid anhydride.

[0071] Preferably, the organic acid anhydride corresponds to formula (II) below: where R and R' are independently chosen from a linear or branched alkyl chain comprising from 1 to 12, in particular from 1 to 6 and typically from 1 to 4 carbon atoms.

[0072] In particular, the organic acid anhydride is chosen from the group consisting of an acetic (ethanoic) anhydride, a propanoic anhydride, a butyric anhydride or an isobutyric anhydride, an ethanoic propanoic anhydride, a pentanoic anhydride, an isopentanoic anhydride, a hexanoic anhydride, a heptanoic anhydride, an octanoic anhydride, a nonanoic anhydride, a decanoic anhydride, an undecanoic anhydride, a dodecanoic anhydride.

[0073] This is introduced into the hydrogenated vegetable oil preferably continuously at a flow rate ranging from 0.05L / h / kg to 0.2 L / h / kg of hydrogenated vegetable oil, preferably from 0.06L / h / kg to 0.15L / h / kg of hydrogenated vegetable oil and typically from 0.08L / h / kg to 0.12L / h / kg of hydrogenated vegetable oil.

[0074] According to the invention, "a flow rate ranging from 0.05L / h / kg to 0.2 L / h / kg of hydrogenated vegetable oil" includes the following values ​​or any range between these values: 0.05; 0.06; 0.07; 0.08; 0.09; 0.10; 0.11; 0.12; 0.13; 0.14; 0.15; 0.16; 0.17; 0.18; 0.19; 0.20.

[0075] In general, the organic acid anhydride is added continuously (to the hydrogenated vegetable oil mixture) at a rate of 0.001 to 1 L / h / kg, preferably 0.005 to 0.05 L / h / kg and typically 0.01 L / h / kg of hydrogenated vegetable oil or in a single addition.

[0076] The esterification step (b) is generally carried out at a temperature below 200°C, in particular from 90°C to 150°C, preferably from 100°C to 140°C and typically from 110°C to 130°C.

[0077] This step (b) generally lasts from 3 to 7 hours, in particular from 4 to 6 hours and typically around 5 hours. This duration can be much shorter with a continuous flow reaction, for example through a static reactor.

[0078] It is ideal to monitor the acid value measured according to ISO 6618 and the hydroxyl value by Fourier transform infrared (FTIR) spectroscopy. According to the invention, at the end of step (b), we obtain a hydroxyl value (IOH) less than or equal to 2 mg KOH / g, preferably less than or equal to 1 mg KOH / g.

[0079] The esterification step (b) can be carried out with or without a catalyst.

[0080] For example, a basic or acidic catalyst such as strong acids and sulfonic resins like AMBERLYST or NAFION may be suitable. In general, the use of a catalyst makes it possible to reduce the temperature used during this esterification step (b) and / or increase the reaction rate.

[0081] Between this esterification step (b) and before proceeding to the recovery of the compound of formula (I) according to the invention (c), the following intermediate steps can be carried out: (b1) the topping step; (b2) a cooling step; (b3) a neutralization step; (b4) optionally a fine filtration step

[0082] During the topping step (b1), the organic acid formed is removed by heating the product obtained at the end of step (b) to a temperature above the boiling point of the organic acid anhydride. The boiling point of acetic anhydride, for example, is 139°C at atmospheric pressure. This step can therefore be carried out at a temperature ranging from 140°C to 200°C, preferably from 150°C to 190°C, and generally from 160°C to 170°C. To reduce the temperature, a vacuum can be applied during this step. Depending on the temperature and vacuum chosen, this step (b1) can last from 1 to 5 hours, preferably from 2 to 4 hours, and generally lasts 3 hours.According to the invention, it is necessary to monitor the reaction, for example by Fourier transform infrared (FTIR) spectroscopy, until the hydroxyl number IOH is less than or equal to 2 mg KOH / g and preferably, until the acid number is less than or equal to 1 mg KOH / g, preferably less than or equal to 0.5 mg KOH / g (ISO 6618).

[0083] During the cooling step (b2), the temperature of the product from step (b1) is lowered to a temperature of 60°C or less, preferably 50°C or less, and typically 40°C or less. This step (b2) can last from 0.5 hours to 3 hours, preferably from 0.75 hours to 2.5 hours, and generally lasts from 1 to 2 hours.

[0084] During the neutralization step (b3), the cooled product from step (b2) is neutralized. For this, less than 5%, in particular less than 3%, and typically 0.5 to 1% of neutralizing additive is used, by mass, relative to the total mass of the product from step (b2); the product is then placed in a vacuum reactor to remove water; it is heated to a maximum temperature of 100°C, preferably 90°C and typically 80°C until the medium is dehydrated and the product is generally placed on a filter of the filter press type, for example on a bed of Dicalite®.

[0085] During the fine filtration step (b4), the product from step (b3) is optionally placed on a filter allowing fine filtration, such as a Gauthier ®< filter for example at a maximum temperature of 70°C.

[0086] Following this step (b4), an ester of formula (I) is recovered (step (c) of the process) and, if applicable, an organic acid if it has not been eliminated during the esterification reaction.

[0087] The preparation process according to the invention offers numerous advantages. First, it incorporates an esterification step (b) which is generally carried out at a lower temperature than conventional esterification reactions and is therefore less energy-intensive (the temperature is around 120-160°C compared to 220-260°C for a conventional esterification reaction). Second, the heating and cooling ramps used in the preparation process (esterification step (b) / topping step (b1) / cooling step (b2)) are shorter. Furthermore, the times for each step, and especially the number of steps from the initial extracted and refined oil, are reduced, particularly compared to the production of isostearate mentioned in the prior art description. Indeed, the production of isostearate requires at least four synthesis steps from refined oil (i.e.: hydrolysis of rapeseed oil into fatty acids / dimerization and production of isostearic acid / hydrogenation and distillation / esterification to isostearic acid) versus two for the process according to the invention. Of course, the various embodiments described above for the use of the compounds of formula (I) also apply to the preparation process and will not be repeated below (and conversely, the various embodiments described above for the preparation process according to the invention also apply to the use according to the invention).

[0088] By way of example, the lubricating base comprises, by mass, in relation to its total mass, at least 50%, preferably at least 80%, in particular at least 90% and typically 100% of said at least compound of formula (I).

[0089] Thus, the process may include a step (ii) which comprises mixing said at least vegetable oil ester corresponding to formula (I) obtained at the end of step (i) with at least one other biodegradable lubricating compound.

[0090] Said other biodegradable lubricating compound, different from compound of formula (I) may be an alkyl isostearate, for example in C1-C10 or neopolyol, a polyalphaolefin (PAO), a mineral oil or a mixture thereof.

[0091] The present invention also relates to a lubricating base obtained by the preparation process as defined above, characterized in that it has an acid number, in mg KOH / g, measured according to ISO 6618, ranging from 0 to 0.5.

[0092] Preferably, the lubricating base exhibits resistance to hydrolysis, measured according to DEF STAN 05-50 (part 61) method 6, which varies from 300 to 2000 hours.

[0093] In general, the lubricating base comprises, by mass, in relation to its total mass, at least 50%, preferably at least 80%, in particular at least 90% and typically 100% of said at least compound of formula (I).

[0094] Of course, the different embodiments described above for the use of the compounds of formula (I) or the preparation process described above also apply to the lubricating composition (and vice versa) and will not be repeated below. Examples A°) Examples of preparation of compounds (I) according to the invention Example 1 : Process for preparing a compound of formula (I) (branched long-chain fatty ester) obtained by esterification of castor oil with acetic anhydride.

[0095] The process is carried out using the following raw materials in the proportions indicated in Table 1 below: [Table 1] Raw materials Supplier Quantity in L Castor oil Jayant Agro Organics or Berg Schmidt (Sternoil HCO) comprising, by mass, relative to the total mass, 80-85% ricinoleic acid 20L Acetic anhydride Carlo Erba 0.1 L / h / kg of castor oil

[0096] In general, the preparation process takes place under very mild conditions (with or without a catalyst) at a temperature of 120°C, by removing the acetic acid formed during the esterification reaction: The process begins with the hydrogenation of castor oil, resulting in castor oil with all its hydrocarbon fatty chains saturated. The hydrogenated castor oil is heated to 120°C until it melts completely (the theoretical melting point is 90°C). Acetic anhydride is continuously introduced at a rate of 0.1 L / h / kg of hydrogenated castor oil. Simultaneously, the hydroxyl value is monitored by Fourier transform infrared (FTIR) spectroscopy until the hydroxyl value (IOH) is less than 1 mg KOH / g. These steps generally take 5 hours, resulting in a clear product. The acetic acid formed is then eliminated by increasing the temperature from 120°C to 160°C (the boiling point of acetic acid is 118°C and that of acetic anhydride is 139°C at atmospheric pressure) for a period of 3 hours at a pressure of 20 mbar; the product obtained is then cooled from 160°C to 40°C;The product obtained is neutralized by adding 0.5 to 1% of neutralizing agent and black (by mass relative to the total mass of product); the product is placed in a vacuum reactor to remove water; it is heated to a maximum temperature of 80°C until the medium is dehydrated and filtered through Dicalite®; filtration is then carried out through a Gauthier® filter at a maximum temperature of 70°C to obtain a clear, brilliant product. Example 2 : Process for preparing a compound of formula (I) (branched long-chain fatty ester) obtained by esterification of castor oil with butyric anhydride

[0097] For this example, the procedure is the same as for example 1, except that acetic anhydride is replaced by butyric anhydride under the conditions shown in Table 2 below: [Table 2] Raw materials Supplier % by mass Castor oil Jayant Agro Organics or Berg Schmidt (Sternoil HCO) comprising, by mass, relative to the total mass, 85% ricinoleic acid 20L Butyric anhydride Aldrich 0.1 L / h / kg of castor oil Example 3 : Process for preparing a compound of formula (I) (branched long-chain fatty ester) obtained by esterification of castor oil with isobutyric anhydride

[0098] For this example, the procedure is the same as for example 1, except that acetic anhydride is replaced by isobutyric anhydride under the conditions shown in Table 3 below. [Table 3] Raw materials Supplier % by mass Castor oil Jayant Agro Organics or Berg Schmidt (Sternoil HCO) comprising, by mass, relative to the total mass, 85% ricinoleic acid 20L Isobutyric anhydride Aldrich 0.1 L / h / kg of castor oil Examples 4 to 7 : Method for preparing a lubricating base according to the invention

[0099] Lubricating bases according to the invention were prepared by mixing the compound of formula (I) of example 1 with an isostearate (NYCOBASE SMP marketed by NYCO) according to the following mass contents (by mass, relative to the total mass of the lubricating base composition thus formed): [Table 4] Examples (invention) 4 5 6 7 Vegetable oil ester according to Ex.1 60 75 50 25 Isostearate 40 25 50 75 B°) Characterization of esters according to examples 1 to 7 described above and a comparative example (isostearate)

[0100] The lubricant bases according to the invention and prepared according to Examples 1 to 4 have the following characteristics (Table 5). For comparison, the comparative example, hereinafter referred to as " Comp. 1 » illustrates a lubricating base composed of 100% of the isostearate mentioned above (NYCOBASE SMP product marketed by NYCO): [Table 5] Features Units Lubricating base (invention) Comp.1 (previous article) Methods Ex.1 Ex.2 Ex.3 Ex.4 Appearance -- Crystal clear Crystal clear crystal clear Crystal clear Crystal clear Visual Gardner Color 1 2 1.5 - 3 ASTM D 1544 Alpha Color 200 - - - - ASTM 1209 Density -- 0,956 0,946 0,944 - 0,922 ASTM D4052 Viscosity at 100°C mm 2< / s 19,1 18,5 18,0 18,2 18,2 ISO 3104 Viscosity at 40°C mm 2< / s 163 136 135 149,5 147,4 ISO 3104 Viscosity index -- 134 153 149 136 138 ISO 2909 Acid value mg KOH / g 0,02 0,01 0,01 - 0,02 ISO 6618 Hydroxyl index 1,51 0 0 - 6 ASTM E 222B COC Flashpoint 302 294 272 - 318 ASTM D92 Foaming at 24°C ml / ml 0 / 0 - - - 580 / 480 ASTM D 892 Foaming at 94°C ml / ml 0 / 0 - - - 30 / 0 ASTM D 892 Foaming at 24°C / 94°C ml / ml 0 / 0 - - - 580 / 420 ASTM D 892 Demulsification at 82°C min 5 - - - 15 ASTM D 1401 Deaeration at 75°C min 2.5 - - - 3 NF ISO 9120 Copper corrosion Copper plate appearance 1b 3b unchanged ASTM D130 Hydrolysis stability h 797 837 850 - 400 ASTM D2619

[0101] As shown in Table 5 above, the lubricating bases according to the invention exhibit adequate technical lubrication performance close to the comparative example Comp.1 (isostearate), particularly in terms of viscosity grade, viscosity index and flash point.

[0102] However, Table 5 also shows that the lubricating bases according to the invention exhibit improved interfacial properties compared to those of Comp. 1: no foaming issues, and rapid demulsification and deaeration times. They also exhibit better hydrolysis stability (resistance to hydrolysis) than Comp. 1. The lubricating compositions according to the invention thus exhibit enhanced stability in marine, aqueous, or humid environments and are therefore ideal for lubricating gears located, for example, in offshore or onshore wind farms.

[0103] Table 6 below shows the technical performance of the lubricating compositions of examples 1, 4 to 7 according to the invention and of example Comp.1: [Table 6] Features Units Ex.1 Ex.4 Ex. 5 Ex. 6 Ex.7 Comp.1 Method Viscosity at 100°C mm 2< / s 19,1 18,2 18,7 18,4 18,2 18,5 ISO 3104 Viscosity at 40°C mm 2< / s 163 149,5 154 151 149 151 ISO 3104 Viscosity index -- 134 136 137 137 136 138 ISO 2909

[0104] As mentioned above, and although this is not necessary insofar as the compounds of formula (I) exhibit adequate technical lubrication performance. C) Comparative test between the process according to the invention and the process described in the document US 2,049,072

[0105] A comparative test was carried out by the Applicant in order to compare the performance of vegetable oil esters obtained according to the process according to the invention and those obtained according to the process described in document US 2,049,072 (hereinafter referred to as US'072).

[0106] In particular, Examples 1 and 2 of this document have been reproduced following the parameters / standards described in this US'072 document. These examples are named below Comp.2 And Comp. 3, respectively.

[0107] The results of this comparative test are summarized in Table 7 below. The first column corresponds to the characteristics of pure castor oil, the second and fourth columns correspond respectively to the characteristics of Ex.1 and Ex.2 described in document US'072, the third and fifth columns correspond to the characteristics of Ex.1 and Ex.2 measured by the Applicant and the sixth column corresponds to the castor oil ester according to Ex.1 of the invention. [Table 7] Comp.2 (Ex.1 of US'072) Comp.2 Ex.1 of US'072 reproduced by NYCO) Comp.3 (Ex.2 of US'072) Comp.3 (Ex.2 of US'072 reproduced by NYCO) Ex.1 (invention) Gardner Color - 4 - 4 4 Viscosity at 100°F (SSU) 569 533 815 788 751 Viscosity at 40°C (mm² / s) 111 115 158 170 162 Viscosity at 210°F (SSU) 81 80.3 96.5 98.1 93.8 Viscosity at 100°C (mm² / s) 15.4 15.6 19.0 19.9 18.9 VI (viscosity index) US'072 129 - 125 - - VI (viscosity index) measured by NYCO 146 143 137 135 133 Acid value (mg KOH / g) - 0.5 - 6.5 0.07 Hydrolysis stability - 74 - < 24 400-700

[0108] This comparative example shows that the characteristic measurements of these examples are similar between those described in document US'072 and those measured by the Applicant (except for the viscosity measurements at 100°C (SSU) and the viscosity index VI measurement, where there is a significant difference). The difference in the viscosity index measurement can likely be explained by the use of a different calculation method.

[0109] This test shows that the castor oil ester obtained according to the process described in this US document 072 has an excessively high acid content. Without being bound by any theory, it would appear that the process in this document (acetylation, followed by hydrogenation combined with the use of acetyl chloride) would not allow for a selective reaction of a castor oil ester, but that, on the contrary, numerous acidic by-products would also be formed.

[0110] Given the acidity of the product obtained (Ex.2 of US'072), this product would be incompatible and would degrade, for example, elastomer-based seals of devices to be lubricated, such as housings.

[0111] This test also shows that the castor oil ester obtained according to the process described in this US'072 document exhibits very poor resistance to hydrolysis and cannot be intended for use in an aqueous, marine or humid environment.

[0112] The Applicant also carried out comparative oxidation and aging tests (Table 8 below).

[0113] This test was carried out according to the modified NF 61125 method C standard on the following parameters: a. Immersed steel / copper spiral metals used according to ISO 4263 b. Use of the oxygen flow rate of 4263: 3l / h c. Duration 168h and temperature 120°C (NF 61125). [Table 8] Comp.2 (Ex.1 of US'072 reproduced by NYCO) Comp.3 (Ex.2 of US'072 reproduced by NYCO) Ex.1 (invention) Comp.1 (previous article) Variation in oil acid number (mgKOH / g) Unusable, completely polymerized Unusable, completely polymerized and degraded 0,5 0,6 Volatile acidity (mgKOH / g) 50 70 0,5 0,1 Variation in the viscosity index KV (%) 2,4 2,1 Deposits important important 12 6 Mass variation of metals (g) (steel-copper spiral) 0,02 0,02

[0114] This test shows very clear differences in oxidation behavior, which implies drastically different lubricant service lives, shortened in the case of the examples reproduced from the state of the art US'072.

Claims

1. A process for preparing a lubricating base comprising a step (i) of preparing said at least one compound of the formula (I) having the following formula: wherein R1, R2 and R3 are independently linear or branched saturated hydrocarbon groups comprising at least 16 carbon atoms, at least one group of R1, R2 and R3 is branched on its hydrocarbon chain with at least one ester group O- CO-R4 wherein R4 is a linear or branched alkyl radical comprising from 1 to 10 carbon atoms, preferably from 1 to 6 carbon atoms, said step (i) including the following successive steps: (a) providing at least one previously hydrogenated vegetable oil or hydrogenating a vegetable oil, said vegetable oil being comprised of at least one triglyceride comprising at least 50% (relative % determined by GPC) of fatty acids having at least one saturated or unsaturated, linear or branched hydrocarbon chain comprising at least 16 carbon atoms, preferably at least 18 carbon atoms, one of said fatty acids being branched with at least one hydroxyl group -OH; (b) selectively esterifying, at said at least one hydroxyl group - OH of said at least one fatty acid of said hydrogenated vegetable oil obtained at the end of step (a) with at least one organic acid anhydride comprising monitoring the esterification reaction until a hydroxyl value IOH lower than or equal to 2 mg KOH / g is obtained, measured in accordance with ISO 6618; (b1) a topping step; (b3) a neutralisation step; (c) the recovery of at least one vegetable oil ester corresponding to formula (I), so as to obtain a lubricating base comprising an acid number, in mg KOH / g, measured in accordance with ISO 6618, ranging from 0 to 0.5.

2. Process for preparing according to claim 1, wherein the vegetable oil of step (a) comprises at least one triglyceride having the following formula: in which the hydrocarbon groups R1, R2 or R3 are independently saturated, linear or branched hydrocarbon groups comprising at least 16 carbon atoms, and at least one of R1, R2 and R3 is branched on its hydrocarbon chain by at least one hydroxyl group -OH.

3. Process for preparing according to claim 1 or 2, wherein the vegetable oil is selected from one or more of the following oils: castor oil, lesquerella oil or any other oil comprising at least 50% fatty acids (relative % determined by GPC) selected from: ricinoleic acid (C18:1-OH), densipolic acid (C18:2-OH), lesquerolic acid (C20:1-OH), or auricolic acid (C20:2-OH).

4. Process for preparing according to any one of claims 1 to 3, wherein the lubricating base has a resistance to hydrolysis, measured according to standard DEF STAN 05-50 (part 61), method 6, which ranges from 300 to 3500 hours, preferably ranges from 600 to 3000 hours, and typically ranges from 750 to 900 hours.

5. Process for preparing according to any one of claims 1 to 4, wherein the organic acid anhydride has the formula (II) below: where R and R' are independently selected from a linear or branched alkyl chain comprising from 1 to 12, in particular from 1 to 6 and typically from 1 to 4 carbon atoms and is preferably selected from the group consisting of acetic anhydride, butyric anhydride or isobutyric anhydride and a mixture thereof.

6. Lubricating base obtained by the process for preparing according to any one of claims 1 to 5, characterised in that it has an acid number, in mg KOH / g, measured in accordance with ISO 6618, ranging from 0 to 0.5.

7. Lubricating base according to claim 6, characterised in that it exhibits a hydrolysis resistance, measured in accordance with DEF STAN 05-50 (Part 61), method 6, ranging from 300 to 3500 hours.

8. Use of a lubricating base obtained by the process for preparing according to any one of claims 1 to 5 or of a lubricating base as defined in claim 6 or 7, comprising said at least one biosourced and biodegradable compound of formula (I) for lubricating devices and / or machines, such as gears, stern tubes and hydraulic systems.

9. Use according to claim 8, wherein the hydrocarbon groups R1, R2 and R3 comprise from 18 to 24 carbon atoms, preferably from 18 to 20 carbon atoms.

10. Use according to claim 8 or 9, wherein the group R4 of the ester group -O-CO-R4 is selected from: a methyl, ethyl, propyl or isopropyl radical.

11. Use according to any one of the preceding claims 8 to 10, wherein, on said at least one hydrocarbon chain R1, R2 and R3 branched by the ester group -O-CO-R4, the latter is positioned at position 9, 10, 12 or at position 14.

12. Use according to any one of the preceding claims 8 to 11, wherein at least two hydrocarbon groups among R1, R2 and R3, and preferably each hydrocarbon group R1, R2 and R3, are branched by the ester group -O-CO-R4.

13. Use according to any one of the preceding claims 8 to 12, wherein the lubricating base also comprises at least one other biodegradable lubricating compound, different from the compound of formula (I), such as an alkyl or neopolyol isostearate, a polyalphaolefin (PAO), a mineral oil or a mixture thereof.

14. Use according to any one of the preceding claims 8 to 13, wherein the lubricating base has a demulsification time, measured according to ASTM D 1401, ranging from 0 to 30 minutes, preferably ranging from 0 to 15 minutes and typically ranging from 0 to 10 minutes.

15. Use according to any of the preceding claims 8 to 14, wherein the lubricating base exhibits a hydrolysis resistance, measured in accordance with DEF STAN 05-50 (Part 61) Method 6, which ranges from 300 to 3500 hours, preferably from 600 to 3000 hours and typically ranges from 750 to 900 hours.

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