Lubricant composition comprising re-refined base oil

Abstract

The present invention relates to an hydraulic oil composition comprising a Refined Base Oil and having a reduced Global Warming Potential.

Description

DescriptionTitle: Lubricant composition comprising Re-refined Base Oil.Technical Field

[0001] This disclosure pertains to the field of hydraulic oil compositions used to lubricate moving parts of a hydraulic system such as an air compressor. In particular, the present disclosure pertains to the use of re-refined base oil (RBO) for the formulation of hydraulic oil compositions.Background Art

[0002] Lubricant compositions, also called “lubricant”, are commonly used in the various components of mechanical systems such as, for example, hydraulic systems, industrial machinery or motor vehicles. Lubricant compositions mainly reduce friction forces between the various moving parts, in particular metal moving parts, of the components of mechanical systems. They are also effective in preventing premature wear or even damage to these moving parts, particularly their surfaces.

[0003] Hydraulic oil compositions are lubricant compositions intended to be used in hydraulic systems, in particular in hydrostatic hydraulic fluid power systems. Air compressor is an example of such hydraulic systems.

[0004] The technical properties of the hydraulic oil compositions have to meet a number of requirements, particularly with regard to the strict specifications imposed by the hydraulic systems manufacturers. For example, the hydraulic oil compositions must have satisfactory properties in terms of viscosity. These technical properties of the hydraulic oil composition are specified by ISO 11158:2023 HV.

[0005] Hydraulic oil compositions are typically composed of a base oil associated with one or more additives designed to boost the lubricating performance of the base oil but also to ensure that the technical properties of the compositions meet the requirements specified by ISO 11158:2023 HV.

[0006] Currently, the base oil of the hydraulic oil compositions is a conventional base oil (CBO) obtained from the refining of crude oils. A large quantity of crude oil is generally required to obtain conventional base oil. Typically, to extract 1 liter of conventional base oil, 37 liters of crude oil are required. In addition, oil refining processes are very energy-intensive and generate the emission of large quantities of carbon dioxide. The carbon footprint of the currently used hydraulic oil compositions therefore does not match the current environmental concerns and resource conservation issues.

[0007] Therefore, there is a need for a hydraulic oil composition having technical properties that meet the requirements specified by ISO 11158:2023 HV while having a reduced carbon footprint.Summary

[0008] The present invention therefore covers a hydraulic oil composition comprising:- a base oil comprising more than or equal to 5% by weight, based on the total weight of said hydraulic oil composition, of a re-refined Base Oil and 95% or less by weight of a ConventionalBase Oil,- a viscosity modifier, characterized in that the content of viscosity modifier in the hydraulic oil composition is reduced by at least 5% compared to the content of viscosity modifier needed to be added in a comparative hydraulic oil composition in which all the re-refined Base Oil is replaced by a Conventional Base Oil, to maintain the technical properties of the hydraulic oil composition as requested by ISO specification 1 1158:2023 HV.

[0009] The use of a re-refined Base Oil to formulate a hydraulic oil composition was never suggested in the prior art. The inventors demonstrated that the replacement, partial or total, of the Conventional Base Oil by a re-refined Base Oil in a hydraulic oil composition comprising a viscosity modifier proved to be surprisingly advantageous from an ecological and technical point of view.

[0010] Indeed, the hydraulic oil composition of the invention, while meeting the technical requirement of ISO specification 1 1 158:2023 HV, have a carbon footprint which is significantly lower than the carbon footprint of a conventional hydraulic oil composition comprising a base oil consisting of a Conventional Base Oil, thanks to the replacement, partial or total, by the re-refined Base Oil of the Conventional Base Oil obtained from the refining of crude oil.

[0011] The lower carbon footprint of the hydraulic oil composition of the invention can also be explained by the reduction of the content of viscosity modifier, which is conventionally synthesized from fossil fuel.

[0012] This reduction of the carbon footprint of the hydraulic oil composition of the invention can be quantified by a reduction of the Global-Warming Potential of the hydraulic oil composition in comparison to the Global Warming Potential of the comparative hydraulic oil composition in which all the RBO is replaced by a CBO, while maintaining the technical properties of the hydraulic oil composition as requested by ISO specification 1 1 158:2023 HV.Indeed, the Global-Warming Potential is a used to describe the relative potency, molecule for molecule, of all the substances contributing to the greenhouse effect. The lower the Global Warming Potential, the lower the carbon footprint. The Global Warming Potential can be determined by the IPCC 2021 regulation.

[0013] In comparison to the Global Warming Potential of the comparative hydraulic oil composition in which all the RBO is replaced by a CBO, while maintaining the technical properties of the hydraulic oil composition as requested by ISO specification 1 1 158:2023 HV, the Global Warming Potential of the hydraulic oil composition of the invention may be reduced by at least 10%, in particular by at least 25%, more particularly reduced by 40% to 50%.

[0014] Moreover, the replacement, partial or total, of the Conventional Base Oil by the re-refined Base Oil combined with the reduced content of viscosity modifier surprisingly improves the shear stability, the demulsibility and the wet filterability of the hydraulic oil composition.

[0015] These technical improvements may result in additional ecological improvements.

[0016] For example, the lifetime of the hydraulic oil composition of the present invention is increased thanks to its improved shear stability and wet filterability. Accordingly, the duration between two maintenance operations of the hydraulic system using the hydraulic oil composition of the present invention can be longer than the duration between two maintenance operations of the hydraulic system using the conventional hydraulic oil composition.

[0017] Moreover, the lifetime of the moving parts of the hydraulic system lubricated by the hydraulic oil composition of the present invention is increased thanks to the improved demulsibility of the hydraulic oil composition of the present invention. The hydraulic oil composition of the present invention thus allows to extend the period of time between the replacement of the moving parts.

[0018] Furthermore, thanks to these technical improvements, the hydraulic system using the hydraulic oil composition of the present invention can be operated in its optimum performance range for longer period without the need for maintenance operation, i.e. the performance of said hydraulic system are optimized.Therefore, during its lifetime, the hydraulic system using the hydraulic oil composition of the present invention has, advantageously,- an increased lifetime since the lifetime of its moving parts is increased, and- a reduced carbon footprint since it needs:- less hydraulic oil composition and less moving parts to be operated, and- less energy to be operated thanks to its optimized performance.

[0019] In another aspect, it is proposed an hydraulic oil composition comprising:- a base oil comprising more than or equal to 5% by weight, based on the total weight of said hydraulic oil composition, of a re-refined Base Oil and 95% or less by weight of a Conventional Base Oil- a viscosity modifier, characterized in that the content of viscosity modifier in the hydraulic oil composition is less than 8.5 % by weight based on the total weight of said hydraulic oil composition, in particular 4% to 8%, more particularly from 5% to 8%, even more particularly from 7.5% to 7.7%.

[0020] In another aspect, it is proposed the use of one of the hydraulic oil compositions of the present invention for lubricating moving parts of an hydraulic system, in particular of a hydrostatic hydraulic fluid power system, more particularly of an air compressor.

[0021] In another aspect, it is proposed the use of a re-refined Base Oil to formulate or manufacture an hydraulic oil composition.

[0022] In another aspect, it is proposed the method for manufacturing an hydraulic oil composition comprising at least a step of obtaining a re-refined Base Oil from a used lubricant composition.

[0023] In another aspect, it is proposed a method of lubricating an hydraulic system comprising the following step: a) contacting moving parts of the hydraulic system needing an hydraulic oil composition to be lubricated with the hydraulic oil composition of the present invention.Figures

[0024] [Figure 1 ]

[0025] Figure 1 shows a two-dimensional chromatogram based on the retention times of columns A and B obtained using the GC-2D method described in the patent application filed under number FR 24 0623, illustrating the presence of PAO in the re-refined base oil RBO1 used in the examples. [Figure 2]

[0026] Figure 2 shows a two-dimensional chromatogram based on the retention times of columns A and B obtained using the GC-2D method described in the patent application filed under number FR 24 0623, illustrating the presence of PAO in the re-refined base oil RBO2 used in the examples.Description of Embodiments

[0027] The expressions "between ... and ..." and " from ... to ..." are to be understood inclusive, unless otherwise stated

[0028] In the description and examples, unless otherwise indicated, percentages are percentages by weight. Percentages are therefore expressed by mass in relation to the total mass of the composition.

[0029] In a first aspect, it is proposed an hydraulic oil composition comprising:- a base oil comprising more than or equal to 5% by weight, based on the total weight of said hydraulic oil composition, of a Re-refined Base Oil (RBO) and 95% or less by weight of a Conventional Base Oil (CBO),- a viscosity modifier, characterized in that the content of viscosity modifier in the hydraulic oil composition is reduced by at least 5% compared to the content of viscosity modifier needed to be added in a comparative hydraulic oil composition in which all the Re-refined Base Oil is replaced by a Conventional Base Oil, to maintain the technical properties of the hydraulic oil composition as requested by ISO specification 1 1 158:2023 HV.

[0030] For the purposes of the present application, the expression “hydraulic oil composition” refers to a composition used to lubricate the moving parts of an hydraulic system and having technical properties meeting the requirements of ISO specification 1 1 158:2023 HV.

[0031] For the purposes of the present application, the expression “Conventional Base OH” (also referred as CBO in the present application) refers to an oil which, as opposed to the RBO, is conventionally used in the lubricant field, is obtained directly from the refining of crude oil and has not yet been used. In particular, the CBO does not comprise any RBO admixed thereto. The CBO may be of the group I, II, III, IV and / or V of the classification API

[0032] Thes CBO can be, in particular, mineral or synthetic oils belonging to groups I to V as defined in the API classification (or their equivalents according to the ATIEL classification) and presented in the following table, or their mixtures.

[0033] [Table 1 ]

[0034] In particular, the CBO may be of groups I, II and / or III, more particularly of groups I and / or II and even more particularly group II.

[0035] In particular, the content of Conventional Base Oil (CBO) in the hydraulic oil composition of the present invention can be less than 94%, preferably less than 90%, preferably less than 80%, preferably less than 70%, preferably less than 60%, preferably less than 50%, preferably less than 40%, preferably less than 30%, preferably less than 20% and even more preferably less than 10% by weight,

[0036] For the purposes of the present application, the expression “Re-refined Base Oil” (also referred as RBO in the present application) refers to an oil derived at least in part from a used lubricant composition that has been subjected to one or more treatment steps known as re-refining treatment.

[0037] The characteristics of the RBO according to the invention may fulfil the criteria defined by the classification API for the base oil of groups I, II, III, IV and / or V, in particular of groups I, II and / or III, more particularly of groups I and / or II and even more particularly group II. It is said of a RBO fulfilling the criteria defined by the classification API for the base oil of groups I, II, III, IV and / or V that the RBO is assimilated to said base oil of groups I, II, III, IV and / or V.

[0038] In particular, the content of RBO in the hydraulic oil composition of the present invention can be greater than 10%, preferably greater than 20%, preferably greater than 30%, preferably greater than 40%, preferably greater than 50%, preferably greater than 60%, preferably greater than 70%, preferably greater than 80%, preferably greater than 90%.

[0039] In a particular embodiment the content of CBO in the hydraulic oil composition of the present invention is less than 20% and the content of RBO is greater than 80%, more particularly the content of CBO in the hydraulic oil composition of the present invention is less than 10% and the content of RBO is greater than 90%.

[0040] In a particular embodiment, the base oil of the hydraulic may comprise more than 50% by weight of RBO and less than 50% by weight of CBO, in particular more than 75% by weight of RBO and less than 25% by weight of CBO, more particularly more than 85% by weight of RBO and less than 15% by weight of CBO.

[0041] According to another embodiment, the base oil consists of RBO. This embodiment is advantageous in terms of reduction of carbon footprint since the hydraulic oil composition according to this embodiment does not comprise CBO obtained from the refining of crude oil.

[0042] For the purposes of the present application, the expression “viscosity modifier” refers to a chemical component that reduces the influence of temperature on the viscosity of the hydraulic oil composition.

[0043] In particular, the viscosity modifier can be selected from polyvinyl n-butyl ether and / or ethylene-propylene copolymer and / or polymethacrylate and / or polyisooctyl polyacrylate, preferably a polymethacrylate.

[0044] The content of viscosity modifier of the hydraulic oil composition may be less than 8.5 % by weight based on the total weight of said hydraulic oil composition, in particular from 4% to 8%, more particularly 5% to 8%, even more particularly from 7.5% to 7.7%.

[0045] Advantageously, such content of viscosity modifier is low. The Inventors are even of the opinion that this content is lower than the content of viscosity modifier in the known hydraulic oil composition.

[0046] For the purposes of the present application, the expression "used lubricant composition" means any lubricant composition that has been used to lubricate moving parts, in particular metal parts, of a mechanical system, such as bearings, gears or motors. The mechanical system can be an hydraulic system, an industrial machinery or a motor vehicle. For the purposes of the present application, the technical properties of the hydraulic oil composition of the invention are « compared to a comparative hydraulic oil composition in which all the RBO is replaced by a CBO”. Since the RBO is assimilated to base oil of groups I, II, III, IV and / or V, the CBO used to replace the RBO should preferably belong to the same group and fulfil the same criteria defined by the classification API as the RBO it replaces For example, if the RBO used in the hydraulic oil composition of the invention is assimilated to a base oil of group II, then the comparative hydraulic oil composition will replace said RBO by a CBO of group II.

[0047] The CBO used to replace the RBO of the hydraulic oil of the invention can preferably be the same CBO used in said hydraulic oil, if applicable. For example, if RBO and CBO are used in the hydraulic oil composition of the present invention, then the comparative hydraulic oil composition will replace said RBO by the same CBO used in the hydraulic oil composition.

[0048] For the purposes of the present application, the expression "maintain the technical properties" means that:- the technical properties of the hydraulic oil composition of the present invention and the technical properties of the comparative hydraulic oil meet the requirements of ISO specification1 1158:2023 HV, and the absolute difference between the technical properties of the hydraulic oil composition of the present invention and the technical properties of the comparative hydraulic oil is less than 10%, in particular less than 5%, more particularly less than 1 %. This means that the absolute difference of each technical property of the hydraulic oil composition according to the present invention as defined by ISO specification 1 1 158:2023 HV and the corresponding technical property of the comparative hydraulic oil is less than 10%, in particular less than 5%, more particularly less than 1 %.

[0049] The technical property of the hydraulic oil composition according to the present invention requested by ISO specification 1 1 158:2023 HV may be a kinematic viscosity at 40°C higher than 46 mm2 / s, in particular higher than 46 mm2 / s and lower than or equal to 50 mm2 / s, more particularly from 47 mm2 / s to 49 mm2 / s.

[0050] So for example, for the purposes of the present application, if the comparative hydraulic oil has a kinematic viscosity at 40°C of 55 mm2 / s, the hydraulic oil composition of the present invention should have a kinematic viscosity at 40°C of 50 mm2 / s + / - 10% i.e. between 45 and 55 mm2 / s.

[0051] The technical property of the hydraulic oil composition according to the present invention requested by ISO specification 1 1 158:2023 HV may be a viscosity index higher than 160, in particular from 161 to 170, more particularly from 164 to 166.

[0052] An hydraulic oil composition having a kinematic viscosity at 40°C and / or a viscosity index within these ranges fulfils the requirements of ISO specification 1 1 158:2023 HV and may be used in a hydraulic system, in particular in a hydrostatic hydraulic fluid power system, more particularly in an air compressor.

[0053] The kinematic viscosity at 100°C of the hydraulic oil composition according to the present invention may be higher than 8.0 mm2 / s, in particular higher than 8.0 mm2 / s and lower than or equal to 9.0 mm2 / s, more particularly from 8.7 mm2 / s to 8.9 mm2 / s.

[0054] The kinematic viscosity at 100°C of the RBO 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.

[0055] The kinematic viscosity at 40°C of the RBO may be from 4.0 to 40 mm2 / s, particularly from 25 mm2 / s to 40 mm2 / s, more particularly from 30 mm2 / s to 35 mm2 / s, more particularly from 31 .5 mm2 / s to 33.0 mm2 / s.

[0056] According to one embodiment, the kinematic viscosity of the re-refined base oil measured at 100°C can be greater than or equal to 3.0 mm2 / s, particularly greater than or equal to 4.0 mm2 / s, specifically between 4.0 and 12 mm2 / s, particularly greater than or equal to 4.3 mm2 / s, and more particularly between 4.4 and 10 mm2 / s, specifically between 4.5 and 6 mm2 / s.

[0057] The viscosity index of the RBO may be from 1 10 to 150, in particular from 1 15 to 130, more particularly from 120 to 125.

[0058] Alternatively, the viscosity index of the re-refined base oil can be greater than or equal to 1 10, particularly between 1 10 and 130, preferably between 1 12 and 125, and more particularly between 1 18 and 124.

[0059] The molar mass of the RBO 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. According to an embodiment, the molar mass of the RBO may be from 425 g / mol to 440 g / mol.

[0060] The pour point of the RBO may be from -40°C to 0°C, in particular from -35°C to -10°C, more particularly from -30°C to -15°C.

[0061] The pour point of the RBO may be from -35°C a -5°C, particularly from -20°C a -9°C, for instance -9°C, -12°C, or -15°C.

[0062] Preferably, the re-refined base oil used according to the invention exhibit reduced volatility compared to conventional base oils of an equivalent group according to the API classification.

[0063] The volatility properties can be more particularly evaluated by determining the Noack volatility according to the CEC L-40-93 standard.

[0064] Advantageously, a re-refined base oil used according to the invention has a Noack volatility of less than or equal to 15%, particularly less than or equal to 14%.

[0065] More preferably, a re-refined base oil used according to the invention can have a Noack volatility strictly less than 12%, particularly between 6% and 1 1 %, more particularly from 7% to 1 1 %.

[0066] Methods for re-refining or reconditioning used lubricant compositions have been developed, in order to regenerate these compositions and enable their subsequent reuse as RBO. A RBO is thus an oil obtained after one or more treatment steps of a used lubricant composition, aimed at eliminating, at least in part, a certain number of contaminating elements present therein, such as dust, water, fuel, metallic elements, polycyclic aromatic hydrocarbons and other residues resulting from the degradation of the used lubricant composition and that are not wanted to formulate hydraulic oil composition.

[0067] Therefore, a RBO differs from a used lubricant composition, in particular due to the reduced content of certain undesirable contaminants, such as water, fuel, metallic elements or certain heteroatoms.

[0068] The sulfur content of the RBO may be from 5°ppm to 1500°ppm, in particular from 10°ppm to 1 100°pmm, more particularly from 1000 ppm to 1050 ppm or from 20 ppm to 40 ppm.

[0069] The nitrogen content of the RBO may less than or equal to 100°ppm, in particular from 0°ppm to 75°ppm, more particularly from 1 ppm to 60 ppm.

[0070] The silicon content of the RBO may be less than or equal to 300 ppm, in particular from 1 ppm to 200 ppm.

[0071] The phosphorus content of the RBO may be less than or equal to 100 ppm, in particular from 0 ppm and 50 ppm, for example 0 ppm.

[0072] The chlorine content of the RBO may be less than or equal to 50 ppm, in particular from 0 ppm and 25 ppm, for example 0 ppm.

[0073] The content of sulfur, nitrogen, silicon, phosphorous and chlorine can be assessed by any method known to the person skilled in the art, for example by X-ray fluorescence (XRF), or by infrared or ultraviolet spectroscopy.

[0074] According to one embodiment, the re-refined base oil(s) may have an aromatic compound content greater than or equal to 0.5% by weight, particularly greater than or equal to 1 % by weight, specifically between 1 % and 25% by weight, more particularly between 2.5% and 20% by weight, relative to the total weight of said re-refined base oil(s).

[0075] Preferably, in the hydraulic oil composition of the invention, the re-refined base oil(s) have an aromatic compound content between 4% and 15% by weight, specifically between 5% and 10% by weight, relative to the total weight of said re-refined base oil(s).

[0076] The content of these different elements can be determined by any method known to those skilled in the art, for example by X-ray fluorescence (XRF) or by infrared or ultraviolet spectroscopy.

[0077] A re-refined base oil according to the present invention may comprise one or more alkylphenols. By "alkylphenol," it is meant a phenolic compound with an alkyl group R1 in the para position, and thus of the formula R1 -C6H4-OH.

[0078] The presence of alkylphenol is characteristic of re-refined base oils, given that conventional base oils (unused) do not contain alkylphenol. Preferably, the content of alkylphenol(s) in the rerefined base oil according to the present invention is between 5 and 3200 ppm, preferably between 10 and 2000 ppm, more preferably between 15 and 1500 ppm of alkylphenol(s).

[0079] According to one embodiment, a re-refined base oil according to the present invention comprises between 10 and 300 ppm, preferably between 15 and 250 ppm, of alkylphenol(s).

[0080] According to one embodiment, a re-refined base oil according to the present invention comprises between 150 and 2000 ppm, preferably between 200 and 1500 ppm, of alkylphenol(s), preferably 1 160(+ / -1 16) ppm, i.e., from 1044 ppm to 1276 ppm.

[0081] According to one embodiment, a re-refined base oil according to the present invention comprises between 100 and 300 ppm, preferably between 145 and 180 ppm, of alkylphenol(s), preferably 165(+ / -16) ppm, i.e., from 149 to 181 ppm.

[0082] The content of alkylphenol(s) in the re-refined base oil is measured according to the method described in the patent application filed under number FR 23 15133.

[0083] This method is based on the implementation of liquid chromatography and mass spectrometry steps, using a standard compound which is 4-hexadecylphenol.

[0084] For the liquid chromatography steps, a column filled with C8-bonded silica particles is used. Measurements are carried out at 40°C with a flow rate of 0.4 mL / min. Here, a reverse-phase columnis used to separate the different components of the sample (here, the re-refined base oil to be analyzed) based on their polarity.

[0085] The composition of the mobile phase is adjusted over time to modify these interactions and thus elute the different molecules of the analyzed sample (here, the re-refined base oil) gradually.

[0086] The mobile phase is used in the form of a gradient as indicated in the table below, starting from a solution A comprising 50% water and 50% acetonitrile and a solution B comprising 100% methanol.

[0087] [Table 2]

[0088] Using mass spectrometry detection, it is possible to obtain the signal produced only by the molecules of interest, identified by both their mass and retention time. The ionization source used is preferably electrospray ionization (ESI), which selectively ionizes polar compounds. In the method used here, the chosen detection mode is negative detection, as it selectively ionizes polar compounds with acidic characteristics. The mass range (m / z) varies from 100 to 1200.

[0089] In particular, the method for measuring the alkylphenol content in the re-refined base oil used according to the invention includes a first step of preparing the standard solution (4-hexadecylphenol) and the solution to be analyzed (re-refined base oil):Preparation of a standard solution at different concentrations to obtain a calibration curve as explained below, by dilution in THF with the addition of 2% ammonium hydroxide; andPreparation of a solution of the re-refined base oil by dilution in THF with the addition of 3% ammonium hydroxide.

[0090] To establish the calibration curve, the intensity of the chromatographic peak associated with the 4-hexadecylphenol ion of the standard is obtained by plotting an "extracted ion chromatogram" (EIC). This allows for a chromatogram extracted only for a given m / z, here 317.28 for the standard molecule, the deprotonated form corresponding to the ion [C22H37O]-. The EIC intensities are then obtained for each analysis at the different tested concentrations.

[0091] The obtained data allows for the construction of the calibration curve. This calibration curve is obtained by injecting several standard solutions at different concentrations: the curve is constructed by linear regression, and the calculation of the correlation coefficient (R2) verifies the linearity of the detector and the correct preparation of the standard solutions. The associated equation then allows predicting the concentration of an unknown sample by entering the experimentally obtained y value. Here, the equation is as follows: y=1001 .9x-15309

[0092] To quantify the alkylphenols in the re-refined base oil according to the invention, the analysis method includes a step of identifying the m / z of the alkylphenol residues on the average mass spectrum by integrating the entire chromatogram. This average spectrum corresponds to an average of all the mass spectra obtained over the complete chromatographic run. This allows for the identification of all the compounds ionized during the analysis. From this average mass spectrum, a mass list is extracted, grouping all the m / z ratios of the ions with their associated intensities.

[0093] The next step is to construct a Kendrick diagram with this mass list. This is a molecular mapping that identifies series of compounds of the same type but with different degrees of alkylation, eliminating the mass defect of the hydrogen atoms in the CH2 group. The Kendrick diagram can be created by calculating the following values:KM=mass (IUPAC or EXPER)x14.0000014.01565 where KM corresponds to the Kendrick mass, mass IUPAC corresponds to the theoretical mass calculated from the sum of each element constituting the molecule of interest, here for the standard molecule hexadecylphenol with the formula C22H37O-, the IUPAC mass = 317.284440 g / mol, and mass EXPER corresponds to an experimental mass measurement, measured during an experiment.

[0094] The Kendrick mass KM is calculated for each peak in the average mass spectrum, determined as explained above. Then, the Kendrick mass defect KMD is typically calculated according to the following equation:KMD=NKM-KM where KMD corresponds to the Kendrick mass defect,KM corresponds to the Kendrick mass, andNKM is the nearest integer to the Kendrick mass KM.

[0095] The Kendrick mass defect KMD is calculated for each peak (each peak corresponding, for example, to a compound present in the re-refined base oil). The Kendrick diagrams correspond to a 2D molecular mapping representing the KMD as a function of the NKM. Homologous compounds varying by their degree of alkylation appear as horizontal lines. The set of m / z of the alkylphenols is obtained by applying a filter on the y-axis (KMD): it is the value KMD = 0.069. Once all the m / z at KMD = 0.069 are identified, they are used to construct "extracted ion chromatograms (EIC)" as described for the standard molecule. This allows for a chromatogram dependent only on the requested m / z. The EIC intensities of each m / z corresponding to the alkylphenols are then summed to obtain the total intensity (several alkylphenol-type molecules are obtained on the spectra of the re-refined base oil according to the invention, these molecules varying by the length of their alkyl chain).

[0096] To obtain a quantification, the sum of the obtained EIC intensities is used as the y value for the calibration curve equation. For example, if the obtained value is 2.45E6, the quantification of alkylphenol residues in the re-refined base oil used according to the invention is: y=1001 .9x-15309 x=(y+15309) / 1001 .9 and thus x equals 2460.6 ppm.

[0097] According to one embodiment, a re-refined base oil according to the present invention comprises one or more polyalphaolefins (PAO). The presence of polyalphaolefins is characteristic of re-refined lubricating oils, given that conventional base oils (unused) do not contain polyalphaolefins (PAO).

[0098] Reference is now made to Figures 1 and 2, each showing a two-dimensional chromatogram based on the retention times of columns A and B obtained using the GC-2D method described in the patent application filed under number FR 24 0623, illustrating the presence of PAO in the re-refined base oils RBO1 and RBO2 used in the examples. The arrow on each figure indicates the characteristic peak of polyalphaolefins PAO (in C30), a marker of re-refined base oils.

[0099] According to one embodiment, a re-refined base oil according to the present invention comprises one or more polyalphaolefins (PAO) with fewer than 40 carbon atoms, and preferably with 30 carbon atoms.

[0100] The presence of PAO in the re-refined base oil is determined according to the method described in the patent application filed under number FR 24 0623.

[0101] This method is based on the implementation of comprehensive two-dimensional gas chromatography (GCxGC) and classification steps.

[0102] In particular, it is implemented via a chromatography device, the chromatography device comprising a comprehensive two-dimensional gas chromatography module including a first column A and a second column B, and capable of separating different compounds of the product based on their volatility and polarity, the chromatography device further comprising a flame ionization detector capable of measuring an ionization current intensity generated for each compound contained in the product, the chromatography device being calibrated with at least one calibration product, allowing for the correction of the retention time of the different compounds present in the product.

[0103] The method is further implemented by an electronic classification device, comprising the following steps:Determining a table describing the ionization current intensity generated for each compound contained in the product based on the corrected retention times in columns A and B, from a measurement performed by the chromatography device on the product;Assigning a class to the product, among a plurality of classes, by applying a multivariate statistical algorithm to the table, the algorithm being trained on tables obtained from reference products.

[0104] The chromatography device comprises a comprehensive two-dimensional gas chromatography module including a first column A and a second column B. The comprehensive two- dimensional gas chromatography modules (2DGC or GCxGC) that can be used in the context of the present disclosure are those described in the literature.

[0105] These modules generally include an injection module, a vaporization module, a first column A, a modulator, and a second column B. They allow for two-dimensional separation of complex mixtures, as the product is subjected to two separations, resulting in a two-dimensional chromatogram based on the retention times of columns A and B and a table describing the ionization current intensity generated for each compound contained in the product based on the corrected retention times in columns A and B.

[0106] According to one embodiment, the first column A and the second column B are columns based on polydimethylsiloxane partially functionalized with phenyl groups. The percentage of phenyl group functionalization can be between 2% and 50%. According to a particular embodiment, the percentage of phenyl group functionalization of column A is higher than the percentage of phenyl group functionalization of column B. Advantageously, the length of column A is greater than that of column B. The diameters of the two columns A and B can be equivalent. The two columns can have a film thickness of 0.1 pm suitable for separating low-volatility samples. According to one embodiment, the temperature gradient applied to the oven is 2°C / min up to 400°C.

[0107] A quantity of product is injected into the first column A to obtain a first separation, then via the modulator, into the second column B to obtain a second separation. The product can be injected directly without pretreatment, particularly in the case of lubricating oil analysis. The GCxGC device is coupled to a flame ionization detector (FID). This detector is capable of measuring an ionization current intensity generated for each compound contained in the product. The flame ionization detector is located at the exit of the second column.

[0108] Following the analysis by the flame ionization detector, a table describing the ionization current intensity generated for each compound contained in the product, based on the corrected retention times in columns A and B, is determined. The table is thus derived from a two-dimensional chromatogram obtained from a measurement performed by the chromatography device on the product.

[0109] Additionally, during this initial step, an external calibration allowing for the correction of the retention time of the different compounds present in the product is performed. This is done by injecting at least one calibration product. In the case where the product to be classified is a lubricating oil, the calibration product can be a lubricating oil, preferably recycled. According to one embodiment, the calibration product includes at least one marker, preferably at least two markers. The marker canbe selected from n-paraffins, polyalphaolefins, and their mixtures. The correction of the retention times can be performed by software.

[0110] At the end of this initial step, the classification device proceeds to the next step, during which it assigns, via its assignment module, a respective class to the product among the plurality of classes, by applying a multivariate statistical algorithm to the table, the algorithm being trained on tables obtained from reference products.

[0111] The multivariate statistical algorithm used during the assignment step can be a partial least squares regression (PLS) algorithm; the multivariate statistical algorithm is preferably chosen from the group consisting of: a partial least squares regression algorithm, and a partial least squares regression algorithm with discriminant analysis. The algorithm is typically a partial least squares regression algorithm, such as the PLS algorithm or the PLS-DA algorithm.

[0112] The multivariate statistical algorithm used during the assignment step is trained on tables obtained from reference products. In partial least squares discriminant analysis (PLS-DA), the prediction coefficient on a scale of 0 to 1 represents the probability or confidence of an sample belonging to a particular class. Here is how this coefficient is calculated and used:

[0113] Creation of latent variables:

[0114] PLS-DA creates latent variables (components) that capture the maximum variance of the X data (predictors) while maximizing the covariance with the Y classes (categorical responses).

[0115] Calculation of scores:

[0116] Samples are projected onto these latent variables, producing scores that are used to discriminate the classes.

[0117] Modeling:

[0118] A linear model is fitted to these scores to predict the Y values. In the case of PLS-DA, Y is often coded in a binary manner to represent the classes (e.g., 0 for group A and 1 for group B).

[0119] Prediction:

[0120] During prediction for new samples, the scores of these samples are calculated and passed through the linear model to obtain a continuous prediction. This continuous prediction is then transformed into a probability on a scale of 0 to 1 .

[0121] Interpretation of probabilities:

[0122] These probabilities are then interpreted to assign the samples to different classes. For example:If the probability is less than 0.4, the sample is classified in group A (here the group of rerefined base oils); andIf the probability is greater than or equal to 0.4, the sample is classified in group B (group of conventional base oils).

[0123] The used lubricant composition may be a mixture of several used lubricant compositions, from the same source or from several different sources.

[0124] Used lubricant compositions comprise, as a main component, one or more base oils conventionally used in the lubricant field, such as mineral oil, synthetic oil, natural oil or mixtures thereof.

[0125] The natural oils are of natural origin, for example from plants or animals, such as vegetable oil, animal oil, fish oil or mixtures thereof. Examples of natural oil 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 mixtures thereof.The oils of mineral or synthetic origin that can be used as base oils conventionally used in the lubricant field may belong to the group I, the group II, the group III, the group IV and / or the group V of the classification API.

[0126] For example, the used lubricant composition may comprise at least one base oil of the group I, the group II, the group III, the group IV and / or the group V of the classification API conventionally used in the lubricant field.

[0127] In particular, the used lubricant composition from which the RBO of the hydraulic oil composition according to the invention is obtained may comprise at least 50% by weight of the base oil(s) conventionally used in the lubricant field relative to its total weight, in particular at least 60% by weight of base oil(s) conventionally used in the lubricant field, and more particularly from 60% to 99% by weight of base oil(s) conventionally used in the lubricant field.

[0128] Used lubricant compositions may contain one or more additives conventional in the field of lubricants, such as a passivation additive, a demusilfier additive, an antioxidant additive, an anti-wear additive, a defoamer additive, a calcium-based additive, an anti-corrosion additive, a frictionmodifying additive, an extreme-pressure additive, a detergent, a pour point depressant (PPD) additive, a dispersant, or mixtures thereof.

[0129] Due to their origin, used lubricant composition may also include a number of degradation products derived from the oil itself or the additives and produced during the use of said used lubricant composition over a longer or shorter period of time. Used lubricant composition may also contain metal particles, metal oxides and other elements from the mechanical system. In particular, used lubricant compositions may contain a high level of undesirable elements, such as calcium (Ca), iron (Fe), magnesium (Mg), sodium (Na), nickel (Ni), phosphorus (P), silicon (Si), chlorine (Cl), zinc (Zn) etc.

[0130] The RBO of the present invention may be obtained by subjecting a used lubricant composition to one or more treatment steps among a dehydration step, a distillation step, a filtration step, an hydrogenation step, a liquid / liquid extraction step, a decantation step and / or a passage of the used lubricant composition over an adsorbent material, in particular a passage of the used lubricant composition over an adsorbent material.

[0131] The dehydration step removes any water present in the used lubricant composition. The dehydration step can be carried out by any method known to the skilled person, for example by distillation, evaporation, decantation, heating or passing a stream of hot air over the used lubricant composition. For example, 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 operated at a pressure of between 50,000 and 150,000 Pa, preferably at atmospheric pressure.Advantageously, the RBO obtained by subjecting a used lubricant composition to a dehydration step comprises 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 RBO.

[0132] The distillation step can be carried out, preferably, after the dehydration step. The distillation step can be carried out by any technique known to the skilled person, such as atmospheric distillation or distillation under reduced pressure. The distillation step can be carried out, for example, at a temperature of between 100°C and 500°C, preferably between 200°C and 400°C, more preferably between 300°C and 380°C and at a pressure of between 25 and 2,000 Pa, preferably between 50 and 1 ,000 Pa, more particularly between 50 and 250 Pa.

[0133] The filtration step can be carried out before the dehydration step. The filtration step can be carried out by any method known to the skilled person. The filtration step may or may not be a particulate filtration step. It may, for example, be carried out by diatomaceous earth-type systems.

[0134] The passage of the used lubricant composition over an adsorbent material can be carried out by flowing the used lubricant composition over an adsorbent support. Advantageously, the adsorbent material enables aromatic compounds, in particular polycyclic aromatic hydrocarbons (PAHs), to be selectively adsorbed. In particular, passage over an adsorbent material, preferably activated carbon, advantageously makes it possible to reduce the content of PAHs, notably 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, in the used lubricant composition.

[0135] The flow rate of the used lubricant composition can be between 1 m3 / h and 15 m3 / h, for example between 5 m3 / h and 10 m3 / h.

[0136] Adsorbent materials can include activated carbon, zeolites, clays or functionalized porous compounds. Activated carbon is preferred.

[0137] A content from 0.5 to 60 g of adsorbent material per liter of used lubricant composition, preferably between 0.5 g / L and 50 g / L, more preferably between 1 g / L and 50 g / L, more preferably between 1 g / L and 30 g / L, for example between 5 g / L and 60 g / L, more preferably between 5 g / L and 50 g / L is particularly adapted to activated carbon used as adsorbent material.

[0138] Preferably, the activated carbon is characterized by a density of between 200 and 500 kg / m3, for example measured in accordance with ASTDM D2854.

[0139] Preferably, the activated carbon is a hard coal, preferably comprising from 70 to 95%, advantageously from 80 to 90%, by weight of carbon.

[0140] The passage of the used lubricant composition over an adsorbent material, preferably activated carbon, is advantageously preceded by the following preliminary steps:- one or more distillation steps; and- a filtration step, in particular a filtration step as defined above.

[0141] For example, the RBO according to the invention can be obtained from the treatment of a used lubricant composition according to the process described in document WO 2018 / 109208.

[0142] The hydrogenation step can be carried out by any technique known to the skilled person and generally consist of treating the lubricant oil with hydrogen generally in the presence of a hydrogenation catalyst. Such a catalyst may contain, for example, at least one oxide or 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 a distillation step.

[0143] Liquid / liquid solvent extraction is advantageous for lightening dark-colored used oil, at least partially removing bad odor or aromatic compounds, in particular PAHs. The liquid / liquid extraction step can be carried out by any technique known to the skilled person. The liquid / liquid extraction step is generally performed in a mixer-settler or in an extraction column, using a suitable extraction solvent. Advantageously, the liquid / liquid solvent extraction step may, preferably, follow a dehydration and / or distillation step.

[0144] The decantation step can be carried out by any technique known to the skilled person.

[0145] The kinematic viscosity at 100°C of the CBO 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.

[0146] The kinematic viscosity at 40°C of the CBO 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.

[0147] The viscosity index of the CBO may be from 80 to 150, in particular from 1 15 to 130, more particularly from 120 to 125.

[0148] The hydraulic oil composition of the present invention may also comprise one or more additives (different from the viscosity modifier discussed previously).

[0149] The one or more additives may be a passivation additive, a demusilfier additive, an antioxidant additive, an anti-wear additive, a defoamer additive, a calcium-based additive, an anticorrosion additive, a friction-modifying additive, an extreme-pressure additive, a detergent, a pour point depressant (PPD) additive, a dispersant, or mixtures thereof, in particular an anti-corrosion additive, a passivation additive, a demusilfier additive, an antioxidant additive, an anti-wear additive, a pour point depressant (PPD) additive, a defoamer additive, a calcium based additive or mixtures thereof, more particularly a mixture of an anti-corrosion additive, a passivation additive, a demusilfier additive, an antioxidant additive, an anti-wear additive, a calcium based additive, a pour point depressant (PPD) additive and a defoamer additive.

[0150] The content of the one or more additives may be less than 1 .5% by weight based on the total weight of the hydraulic oil composition of the present invention, in particular from 0.95% to 1 %, more particularly from 0.98% to 0.99%. Indeed, the inventors have discovered that the hydraulic oil compositions could meet the technical requirement of ISO specification 1 1 158:2023 HV with a very limited amount of additives.

[0151] For example, the hydraulic oil composition of the present invention may comprise: from 0.9 % to 1 % by weight, based on the total weight of the hydraulic oil composition of the present invention, of a mixture of an anti-corrosion additive, a passivation additive, a demusilfier additive, an antioxidant additive, an anti-wear additive, a calcium based additive, and from 0.01 to 0.05% be weight, based on the total weight of the hydraulic oil composition of the present invention, of a defoamer additive.

[0152] This limited content of additives (different from the viscosity modifier) contributes to the reduction of the carbon footprint of the hydraulic oil composition of the invention. The content of the one or more additives (including the viscosity modifiers) may be less than 9% by weight based on the total weight of the hydraulic oil composition of the present invention, in particular from 8.0% to 8.8%, more particularly from 8.5% to 8.7%. The overall limitation of additives + viscosity modifier reduced the carbon footprint of the hydraulic oil composition of the invention.

[0153] Within the meaning of the invention, an eco-material index is defined as the ratio, in percentage, between the weight of the RBO of the hydraulic oil composition and the weight of the hydraulic oil composition.

[0154] The hydraulic oil composition of the present invention has an eco-material index of at least 5%, in particular of at least 50%, more particularly of at least 75%, even more particularly of at least 85%, even more particularly of at least 95%.

[0155] In a second aspect, it is proposed an hydraulic oil composition comprising:- a base oil comprising more than or equal to 5% by weight, based on the total weight of said hydraulic oil composition, of a re-refined Base Oil and less than or equal to 95% by weight of a Conventional Base Oil,- a viscosity modifier,- optionally additives, characterized in that the content of viscosity modifier in the hydraulic oil composition is less than 8.5 % by weight based on the total weight of said hydraulic oil composition, in particular from 4% to 8%, more particularly from 5% to 8%, even more particularly from 7.5% to 7.7% and / or the content of additives is less than 1 .5% by weight based on the total weight of the hydraulic oil composition of the present invention, in particular from 0.95% to 1 %, more particularly from 0.98% to 0.99% and / or the content of additives + viscosity modifier less than 9.0 % by weight based on the total weight of the hydraulic oil composition, in particular from 5% to 8.9%, more particularly from 7% to 8.8%.

[0156] The base oil, the re-refined Base Oil, the Conventional Base Oil, the viscosity modifier and the additives are as defined above in relation to the hydraulic oil composition of the first aspect of the present invention.

[0157] For example, the hydraulic oil composition of the present invention may comprise: less than 8.5 % by weight, based on the total weight of said hydraulic oil composition, in particular from 4% to 8%, more particularly 5% to 8%, even more particularly from 7.5% to 7.7% of the viscosity modifier, from 0.8 % to 1 % by weight, based on the total weight of the hydraulic oil composition of the present invention, of a mixture of an anti-corrosion additive, a passivation additive, a demusifier additive, an antioxidant additive, an anti-wear additive, a calcium based additive, and from 0.01 to 0.05% be weight, based on the total weight of the hydraulic oil composition of the present invention, of a defoamer additive.

[0158] The viscosity modifier may be a pour point depressant (PPD) additive.

[0159] In this case, the hydraulic oil composition of the invention may comprise: less than 8.5 % by weight, based on the total weight of said hydraulic oil composition, in particular from 4% to 8%, more particularly 5% to 8%, even more particularly from 7.5% to 7.7% of a pour point depressant (PPD), from 0.8 % to 1 % by weight, based on the total weight of the hydraulic oil composition of the present invention, of a mixture of an anti-corrosion additive, a passivation additive, a demusifier additive, an antioxidant additive, an anti-wear additive, a calcium based additive, and from 0.01 to 0.05% be weight, based on the total weight of the hydraulic oil composition of the present invention, of a defoamer additive.

[0160] In another aspect, it is proposed the use of one of the hydraulic oil compositions of the present invention for lubricating moving parts of an hydraulic system, in particular of a hydrostatic hydraulic fluid power system, more particularly of an air compressor.

[0161] In another aspect, the present invention is also directed to the use of a RBO in a hydraulic oil composition comprising a base oil consisting of a CBO, and a viscosity modifier, to decrease the amount of viscosity modifier and / or to decrease the amount of additives different from viscosity modifier and / or to decrease the total amount of additives (including the viscosity modifier and other additives).

[0162] In this aspect of the invention, wherein the amount of viscosity modifier is decreased by at least 5% compared to the amount need to be added in a comparative hydraulic oil composition in which all the RBO is replaced by a CBO.

[0163] In another aspect, it is proposed a use of a re-refined Base Oil to formulate or manufacture the hydraulic oil composition of the present invention.

[0164] The re-refined Base Oil is as defined above in relation to the hydraulic oil composition of the first aspect of the present invention.

[0165] In another aspect, it is proposed a method for manufacturing the hydraulic oil composition of the present invention comprising at least a step of obtaining a Re-refined Base Oil from a used lubricant composition.

[0166] The re-refined Base Oil and the used lubricant composition are as defined above in relation to the first aspect of the present invention.

[0167] In another aspect, it is proposed a method of lubricating an hydraulic system comprising the following step: a) contacting moving parts of the hydraulic system needing an hydraulic oil composition to be lubricated with the hydraulic oil composition of the present invention.Examples

[0168] Example 1 : Composition and lubricant properties

[0169] The composition and lubricant properties of three hydraulic oil compositions have been evaluated. Hydraulic oil compositions 1 and 2 are according to the invention. Comparative hydraulic oil composition is not according to the invention.

[0170] Table 3 presents the properties of the RBO present in Hydraulic oil compositions 1 and 2 and the method used to determine each of said properties.

[0171] Table 4 presents the composition of each of the three hydraulic oil compositions. The percentages are expressed by weight, relative to the total weight of the composition.

[0172] Each of the three different CBO is of group II, and each of the RBO fulfils the criteria defined by the classification API for the base oil of groups II.

[0173] The mixture of additives comprises an anti-corrosion additive, a passivation additive, a demusilfier additive, an antioxidant additive, an anti-wear additive, a calcium based additive and a pour point depressant (PPD) additive.

[0174] Table 5 presents the properties of each of the three hydraulic oil compositions and the method used to determine each of said properties.

[0175] [Table 3]

[0176] [Table 4]

[0177] As evidenced by Table 5, the three hydraulic oil compositions meet the technical requirements of the ISO specification 1 1 158:2023 HV, i.e. : - a kinematic viscosity at 40°C between 41 .4 Cst and 50.6 Cst, and- a viscosity index higher than 140.

[0178] As further evidenced by Table 5, in comparison to the comparative hydraulic oil composition, the hydraulic oil compositions 1 and 2 of the present invention have:- improved shear stability. Indeed, the kinematic viscosity loss after 20 hours of KRL Shear of the composition 1 and 2 is at least 34% less than the kinematic viscosity loss after 20 hours ofKRL Shear of the comparative composition,- improved wet filterability. Indeed, the comparative hydraulic oil composition cannot be filtered during the stage II filterability while the composition 1 and 2 can be filtered, and- improved demulsibility. Indeed, the time necessary to the composition 1 and 2 to release water is at least 37% less than the time necessary to the comparative composition to release water.

[0179] [Table 5]

[0180] Example 2: Global Warming Potential

[0181] The Global Warming Potential of each of the three composition of Example 1 is measured applying the IPCC 2021 requirements.

[0182] In comparison to the Global Warming Potential of the Comparative Hydraulic oil composition:- the Global Warming Potential of the Hydraulic oil composition 1 comprising a base oil consisting of RBO is reduced by 50%, and- the Global Warming Potential of the Hydraulic oil composition 2 comprising a base oil comprising RBO and 5% of CBO is reduced by 40%.

Claims

Claims

1. Hydraulic oil composition comprising:- a base oil comprising more than or equal to 5% by weight, based on the total weight of said hydraulic oil composition, of a re-refined Base Oil (RBO) and 95% or less by weight of a Conventional Base Oil (CBO),- a viscosity modifier, characterized in that the content of viscosity modifier in the hydraulic oil composition is reduced by at least 5% compared to the content of viscosity modifier needed to be added in a comparative hydraulic oil composition in which all the RBO is replaced by a CBO, to maintain the technical properties of the hydraulic oil composition as requested by ISO specification 1 1 158:2023 HV.

2. Hydraulic oil composition according to claim 1 , wherein the technical property requested by ISO specification 1 1 158:2023 HV is a kinematic viscosity at 40°C higher than 46 mm2 / s.

3. Hydraulic oil composition according to any one of claims 1 or 2, wherein the technical property requested by ISO specification 1 1 158:2023 HV is a viscosity index higher than 160.

4. Hydraulic oil composition according to any one of claims 1 to 3, wherein the kinematic viscosity at 40°C of the Refined Base Oil is from 3.0 mm2 / s to 10.0 mm2 / s.

5. Hydraulic oil composition according to any one of claims 1 to 4, wherein the viscosity index of the Refined Base Oil is from 1 10 to 150.

6. Hydraulic oil composition according to any one of claims 1 to 5, wherein the pour point of the Refined Base Oil is from -40°C to 0°C.

7. Hydraulic oil composition according to any one of claims 1 to 6, wherein the characteristics of Refined Base Oil fulfil the criteria defined by the classification API for the base oil of groups I, II, III, IV and / or V, in particular of groups I, II and / or III, more particularly of groups I and / or II.

8. Hydraulic oil composition according to any one of claims 1 to 7, wherein the CBO is of the group I, II, III, IV and / or V of the classification API.

9. Hydraulic oil composition according to any one of claims 1 to 7, wherein the base oil consists of Refined Base Oil.

10. Hydraulic oil composition according to any one of claims 1 to 9, wherein the content of viscosity modifier is less than 8.5 % by weight based on the total weight of said hydraulic oil composition.

11. Hydraulic oil composition according to any one of claims 1 to 10 further comprising one or more additives being a passivation additive, an antioxidant additive, an anti-wear additive, a defoamer additive, a calcium-based additive, an anti-corrosion additive, a friction-modifying additive, an extreme-pressure additive, a detergent, a pour point depressant (PPD) additive, a dispersant, or mixtures thereof.

12. Hydraulic oil composition according to any one of claims 1 to 1 1 having an eco-material index of at least 5%, the eco-material index being defined as the ratio, in percentage, between the weight of the Refined Base Oil (RBO) of the hydraulic oil composition and the weight of the hydraulic oil composition.

13. Hydraulic oil composition according to any one of claims 1 to 12 having a Global Warming Potential reduced by at least 10% compared to the Global Warming Potential of the comparative hydraulic oil composition.

14. In a second aspect, it is proposed an hydraulic oil composition comprising:- a base oil comprising more than or equal to 5% by weight, based on the total weight of said hydraulic oil composition, of a Re-refined Base Oil and less than or equal to 95% by weight of a Conventional Base Oil,- a viscosity modifier,- optionally additives, characterized in that the content of viscosity modifier in the hydraulic oil composition is less than 8.5 % by weight based on the total weight of said hydraulic oil composition, and / or the content of additives is less than 1 .5% by weight based on the total weight of the hydraulic oil composition of the present invention, and / or the content of additives + viscosity modifier less than 9.0 % by weight based on the total weight of the hydraulic oil composition.

15. Use of the hydraulic oil composition as defined in any one of claims 1 to 14 for lubricating moving parts of an hydraulic system.

16. Use of a RBO in a hydraulic oil composition comprising a base oil consisting of a CBO and a viscosity modifier, to decrease the amount of viscosity modifier and / or to decrease the amount of additives different from viscosity modifier and / or to decrease the total amount of additives including the viscosity modifier and other additives.

17. A method of lubricating an hydraulic system comprising the following step: a) contacting moving parts of the hydraulic system needing an hydraulic oil composition to be lubricated with an hydraulic oil composition as defined in any one claims 1 to 14.

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