Method for recycling lubricating grease

Abstract

The invention relates to a method for recycling used lubricating grease containing polymeric hydrocarbons or polymeric esters as a thickener. In said method, the base oil is recovered along with the thickener as a component of a recycled lubricating grease obtainable in this way.

Description

[0001] The present invention relates to a method for recycling used lubricating greases containing polymeric hydrocarbons or polymeric esters as thickeners, with recovery of the base oil together with the thickener as a component of a recycled lubricating grease thus obtained. State of the art

[0002] For many technical applications, the use of lubricants is essential to reduce friction and wear on the contact surfaces of moving parts. Depending on the application, lubricants of varying consistencies can be used. Lubricating oils have a liquid and free-flowing consistency, while lubricating greases have a semi-solid to solid – often gel-like – consistency.

[0003] A defining characteristic of a lubricating grease is that a liquid oil component is absorbed and held by a thickener component. The consistency of a lubricating grease, its spreadability, and its plastic deformability, combined with its adhesive properties, ensure that the grease wets the lubrication point and provides lubrication to tribologically stressed surfaces. They are used particularly for lubricating less well-sealed machine elements, such as rolling or sliding bearings, open gears, and guides.

[0004] Lubricating greases contain a thickener that is homogeneously dispersed in a base oil, as well as solid or liquid additives. Additional auxiliary substances, such as emulsifiers, are often used to ensure the thickener is stably dispersed in the base oil. A wide variety of liquids are known to serve as base oils. Both organic and inorganic compounds are used as thickeners.

[0005] In Germany, over 34,000 tons of used lubricating grease are generated annually, primarily in the lubrication of tribological systems such as rolling bearings, where lubricating grease accounts for approximately 80%. In many cases, these greases are used in so-called total-loss lubrication systems, resulting in large quantities of contaminated grease waste that must be disposed of in an environmentally sound manner.

[0006] Corresponding applications can be found, for example, in rolling and sliding bearings in energy plants (e.g., wind and hydropower), agriculture, the steel and cement industries, mining, and the food processing industry. In contrast to lifetime-lubricated machine elements or tribosystems, the greases used in loss-lubricated applications often age only slightly due to thermo-oxidative or mechanical processes, but are frequently contaminated with wear particles, dust, and moisture. This is because the lubrication points in these applications are insufficiently encapsulated against environmental influences, or the intention is even to flush out these contaminants by relubricating them with grease.

[0007] Even though lubricating greases have a comparatively small market share compared to lubricating oils, their recycling is worthwhile because lubricating greases are manufactured with a high expenditure of thermal and mechanical energy.

[0008] Several processes exist for thermally reprocessing used lubricating grease that is no longer suitable for its original purpose, with the aim of utilizing its energy content. However, such processes do not allow for material recycling, i.e., the reuse of the product as a lubricant.

[0009] In the rolling bearing industry, initial technical solutions now exist for collecting used grease generated by total-loss lubrication systems by type. EP2447485 B1, for example, describes a reusable used grease cartridge that allows for the removal of used grease from a rolling bearing by type and subsequent emptying into a waste collection container. Used grease is thus defined as used lubricating grease as it is found at or near the lubrication point, or in a reservoir associated with one or more lubrication points, without having already been collected and combined. Through collection and combination, the used grease becomes recycled grease, which is then subjected to a recycling process.

[0010] Up to now, the reuse of lubricating greases has generally involved purifying them by separating the thickener from the base oil, resulting in the loss of the thickener structure. With approximately 4 to 20% thickener and 75 to 95% base oil by mass, thickener and base oil are the main components of most lubricating greases. If both can be purified in a single recycling process, losses and the energy and time required for grease recycling can be minimized.

[0011] According to a recent survey by the National Lubricating Grease Institute (NLGI), the group of metal normal and complex soap greases represents the largest contingent of lubricating greases at approximately 90% (NLGI Grease Production Survey Report 2020).

[0012] According to DE19739659 A1, the oil-containing components are first removed from the preferably sorted used grease, along with impurities such as dirt and metal abrasion, in a multi-stage oil recovery process. The base oil is extracted from the used grease in an extractor by adding an extraction solvent. The resulting oil-extraction solvent mixture (extract) is then separated from the raffinate containing the thickener and impurities in a downstream separator. The raffinate with the thickener is in a semi-solid to solid state and is further dried to evaporate residual solvent. The multi-stage thickener recovery consists of an extraction stage and crystallization. The thickener is separated from the drying residue using a suitable solvent, such as methanol or a methanol-chloroform mixture.In the extraction stage, the thickening agents are dissolved by the added extraction solvent, while the impurities remain undissolved. Object of the invention

[0013] If total loss lubrication takes place in rolling or sliding bearings or gearboxes that are operated at low speeds or sliding velocities, a large proportion of the grease volume introduced into these applications for total loss lubrication often does not directly enter the shear engagement, but serves as a reservoir for sealing the tribological contact pairs.

[0014] In these cases, a comparatively large volume fraction of the lubricating grease is often subjected to little mechanical and / or oxidative stress, and the grease's thickener structure remains largely intact. Therefore, it is advisable to choose a recycling process that does not damage the grease's thickener structure, or only damages it to a comparatively small extent.

[0015] It is desirable not to separate the thickener and base oil during the reprocessing of lubricating greases and to purify them in separate steps. Furthermore, the reprocessing process should not cause any irreversible changes to the thickener structure and thus a loss of thickening effect. The object of the invention is therefore to avoid the disadvantages of the prior art described above and to offer a process by which lubricating greases can be recycled as cost-effectively and energy-efficiently as possible, requiring as few steps as possible. The process should also be applicable to lubricating greases whose components, particularly the thickener, are produced from renewable raw materials. This would allow materials produced using CO₂ to be reintroduced into a recurring product life cycle, thereby avoiding climate-damaging emissions. Summary of the invention

[0016] The invention is defined by the independent claims. Preferred embodiments are the subject of the dependent claims or described below.

[0017] The invention relates to a method for reprocessing used lubricating greases (waste lubricating grease) that become waste lubricating grease through use and collection, comprising the following steps: a) Collecting used, homogeneous lubricating greases from lubrication points to obtain a used lubricating grease, wherein the used lubricating grease comprises at least a thickener, additives, a base oil and, if applicable, solid impurities, and the thickener comprises polymeric hydrocarbons or polymeric esters; b) Providing a solvent with a boiling point or, in the case of a boiling range, an upper boiling point of 40 to 140°C at standard pressure; c) Suspending the used lubricating grease in the solvent to obtain a suspension comprising a liquid phase comprising at least the base oil and the solvent and a solid phase in the liquid phase comprising at least the thickener in suspended form, wherein at least the base oil and the solvent are mixed in the form of a homogeneous liquid phase; d) Separating any solid impurities from the suspension, e.g., by sedimentation; e) Removing the solvent (e.g.,more than 75 wt.% or more than 90 wt.% of the solvent used) from the suspension by distillation or by extraction with supercritical CO2, to obtain a recycled lubricating grease comprising recovered base oil comprising base oil from the used lubricating grease and recovered thickener from the used lubricating grease and recovered additives comprising additives from the used lubricating grease, . wherein the used grease, the suspension and the recycled grease are not exposed at any point in the process to a temperature higher than the dropping point of the used grease minus 52°C, preferably minus 60°C or minus 75°C, particularly preferably minus 90°C, wherein the thickener is or comprises either a polymeric hydrocarbon or a polymeric ester, wherein the solvent in the case of polymeric hydrocarbons as thickener is a hydrocarbon (as a hydrocarbon solvent) and in the case of polymeric esters as thickener is a hydrocarbon, a C3 to C5 ketone, in particular a C3 and / or C4 ketone, or mixtures thereof, wherein if only hydrocarbons are used as solvents, these shall hereinafter also be referred to as hydrocarbon solvents.

[0018] The used lubricating grease comprises, in addition to the base oil, polymeric hydrocarbons or polymeric esters as thickeners, wherein the thickener is suspendable in the mixture of solvent and base oil as solid particles or in the form of solid particles.

[0019] Uniform lubricating greases are those that contain at least the same types of thickener and the same types of base oil (cumulatively), meaning that each grease contains a polymeric hydrocarbon or a polymeric ester as a thickener and the same type of base oil, in particular at least the same base oil. The fact that a suspension is obtained does not preclude the presence of other substances, also in emulsified form.

[0020] Base oil types of a uniform lubricating grease are those of a uniform compound type, e.g., the same or different hydrocarbons or the same or different esters as the base oil. If, for example, a used lubricating grease contains esters and hydrocarbons as the base oil, then the second lubricating grease combined with it also contains a mixture of the same or different esters and the same or different hydrocarbons; in particular, the base oils are identical.

[0021] In the case of thickeners based on polymeric hydrocarbons, various nonpolar base oils soluble in the described solvents can be used. These base oils are liquid at room temperature and, in particular, have a kinematic viscosity of 20 to 2500 mm² / s, especially 40 to 500 mm² / s, at 40°C. Suitable base oils include, in particular, hydrocarbons such as polyalphaolefins (PAO), mineral oils, and / or esters.

[0022] In the case of thickeners based on polymeric esters, in addition to non-polar base oils, more polar base oils such as esters or polyglycols can also be used.

[0023] The hydrocarbon solvent can be an aliphatic and / or cycloaliphatic hydrocarbon, preferably n-alkanes or branched alkanes, especially mixtures thereof.

[0024] The boiling point or boiling range of the solvent is in the range of 40 to 140°C at normal pressure (1023 mbar). If necessary, distillation is carried out under vacuum so that a boiling temperature is reached during distillation of the solvent that is no higher than a temperature of at least 52°C, preferably 60°C or 75°C and even better 90°C, in each case below the dropping point of the used lubricant.

[0025] In the case of a polymeric ester as a thickener, C3 to C5 ketones or a mixture of the previously described hydrocarbons and the C3 to C5 ketones can also be used, along with mixtures among the ketones.

[0026] According to one embodiment, the separation of any solid impurities from the suspension is carried out by filtration, whereby particles larger than 200 µm or larger than 30 µm, and in particular larger than 15 µm, remain in the filter residue. The filter cake can be washed with the solvent, and the eluate can be added to the suspension before or during step e). The suspension can be treated with a filter drying agent. Detailed description of the invention

[0027] Suitable greases for reconditioning are polyolefin-thickened greases, such as those known from US3850828, US2917458, US3290244, US3392119, US5874391, EP0942063A or EP0795597B1.

[0028] Used grease contains polymeric hydrocarbons as a thickener. Suitable examples include: Polyethylene, possibly in a mixture with atactic polypropylene, polypropylene, possibly in a mixture with atactic polypropylene or polyethylene, ethylene and polypropylene copolymer, possibly in a mixture with polypropylene and / or polyethylene, a polyolefin with a rubber component or mixtures of different rubber components, methylenepentene polymer, possibly in a mixture with polypropylene, with polyethylene and / or with ethylene and polypropylene copolymer.

[0029] Suitable thickeners are polyethylenes with a molecular weight of 20,000–500,000 g / mol, more preferably 50,000–250,000 g / mol (Mw) and preferably a density above 0.94 g / cm³, particularly in a mixture with an atactic polypropylene having a molecular weight preferably below 100,000 g / mol (Mw) and preferably a melt flow index above 20, particularly above 50. The ratio of the atactic polypropylene to the polyethylene is preferably 1:1 to 1:10, more preferably 2:1 to 5:1.

[0030] Thickeners based on oil-soluble amorphous polypropylenes with a molecular weight in the range of 300 to 10,000 g / mol and an intrinsic viscosity of up to 0.4 are particularly suitable, containing, in particular, 2 to 5 wt% of an isotactic polypropylene with a molecular weight in the range of 100,000 to 1,000,000 g / mol (Mw) and a melting point in the range of 121°C to 210°C. Preferably, copolymers or homopolymers of propylene with a weight-average molecular weight greater than or equal to 200,000 g / mol and a low-molecular-weight (co- or homo-)polymer of propylene with a weight-average molecular weight less than or equal to 100,000 g / mol.

[0031] Thickener compositions based on polymethylpentene (4-methylpentene-1-based polymer) with a melting point above 200°C, especially above 225°C, are particularly suitable in combination with the low molecular weight (average weight of 50,000 to 100,000 g / mol) propylene copolymers or homopolymers described in the previous section. For example, TPX DX 820 from Mitsui Chemicals Europe GmbH is a suitable commercial product. This is a 4-methylpentene-1 polyolefin.

[0032] The polymeric esters are in particular polyhydroxyalkanoates (PHAs), e.g., polyhydroxy(C4- to C12-)alkanoates, preferably poly-3-hydroxyalkanoates, most preferably poly-3-hydroxybutyric acid. The thickening power of the above polyhydroxyalkanoates can be further enhanced by chemical modifications with one or more crosslinking agents.

[0033] The thickener may contain other thickener components such as metal and metal complex soaps or polyureas.

[0034] The hydrocarbon or hydrocarbon solvent can be an aliphatic and / or cycloaliphatic hydrocarbon; n-alkanes or branched alkanes, especially mixtures thereof, are preferred. Typical examples are boiling-limit gasolines according to DIN 51632-1 and -2 with types 80 / 120, 100 / 125, (DIN Type I) 60 / 95, (DIN Type II) 80 / 110, (DIN Type III) 100 / 140, especially dearomatized grades, and particularly preferably boiling-limit gasoline 60 / 95. When the term "hydrocarbon" is used herein, it naturally includes several hydrocarbons or hydrocarbon mixtures.

[0035] In the case of polymeric esters as thickeners, polar solvents such as C3 to C5 ketones, especially a C3 and / or C4 ketone, can also be used, either in pure form, as a mixture of the ketones themselves, or in a mixture of one or more of the ketones with the hydrocarbons described above. Examples of ketones that can be used are acetone, methylethyl ketone (butan-2-one), pentan-2-one, pentan-3-one, or mixtures thereof.

[0036] Various nonpolar base oils soluble in the described solvents can be used, wherein the base oils are liquid at room temperature with a kinematic viscosity of 20 to 2500 mm² / s, in particular of 40 to 500 mm² / s, each at 40°C.

[0037] Such a base oil can be classified as a mineral oil or a synthetic oil. Mineral oils include, for example, naphthenic and paraffinic mineral oils, as classified according to API Group I. Chemically modified aromatic and low-sulfur mineral oils with a low saturated content and improved viscosity / temperature behavior compared to API Group I oils, classified according to API Groups II and III, are also suitable. Synthetic oils include, in particular, polyalphaolefins, alkyl aromatics, alkylnaphthalenes, and mixtures thereof.Esters can also be used, particularly those soluble in the aforementioned solvents, such as esters of aromatic di-, tri-, or tetracarboxylic acids with one or a mixture of C2 to C22 alcohols; esters of adipic acid, sebacic acid, trimethylolopropane, neopentyl glycol, pentaerythritol, or dipentaerythritol with aliphatic branched or unbranched, saturated or unsaturated C2 to C22 carboxylic acids; C18 dimer esters with C2 to C22 alcohols; and complex esters, either as single components or in mixtures. Esters based on rapeseed oil, sunflower oil, and other oilseeds are also suitable, possibly in mixtures with the aforementioned base oils, provided the base oil is soluble in the solvent or miscible with it without phase separation.

[0038] The polyglycols are suitable as base oils for the polymeric ester thickeners. The polyglycols used as base oils can contain free hydroxyl groups, but can also be fully etherified or end-group esterified and / or produced from a starting compound with one or more hydroxy and / or carboxyl groups (-COO(̵H)̵).

[0039] According to a particular embodiment, the polyglycols contain (-O-(CH₂)₄-)n units having the following structural unit with respect to the linkage -O-(CH₂)₄-O-, and optionally also other alkylene oxide units, such as ethylene oxide (-O-(CH₂CH₂)-) and / or propylene oxide (-O-(CH₂CH(CH₃)-) units, either in blocks or statistically distributed. These polyglycols are less suitable as base oils for hydrocarbon thickeners.

[0040] Diphenyl ethers or polyphenyl ethers, possibly alkylated, are also possible as sole components or as mixed components.

[0041] Suitable base oils can also be or contain polyalphaolefins, e.g. those obtainable from the polymerization, possibly using metallocene catalysts, of C4 and C14 LAO (LAO = linear alpha olefin), C6 and C16 LAO; C8, C10 and C12 LAO; C8 and C14 LAO; C6, C10 and C14 LAO; C4 and C12 LAO as copolymers or as mixtures of the respective homopolymers.

[0042] Suitable additives include antioxidants, anti-wear agents, corrosion inhibitors, detergents, dyes, lubricity improvers, adhesion promoters, viscosity modifiers, friction modifiers, high-pressure additives, metal deactivators, and solid lubricants, preferably in concentrations < 5%. Suitable additives are polyisobutenosuccinic acid and / or polyisobutenosuccinic acid-polyacrylamide. Additives remaining in the filter residue can be subsequently added back to the recycled grease.

[0043] In one embodiment, the suspension is filtered using suitable filtration methods in which particles larger than 200 µm or larger than 30 µm, and particularly larger than 15 µm, remain in the filter residue. The filter can have a pore size or mesh size of 200 µm and smaller, preferably 30 µm and smaller, and particularly preferably 15 µm and smaller. The filter material can be paper, textile fabric, metal, or a packed bed. Suitable filtration methods include suction filtration or pressure filtration, edge gap filters, filter presses (preferably chamber filter presses), and hot filtration processes, in which the maximum filtration temperature is preferably at least 52°C, at least 60°C, or at least 75°C, and preferably at least 90°C below the dropping point temperature of the used grease. Depth filtration methods using glass fiber or synthetic fiber fabrics are also suitable.

[0044] During or after filtration, the suspension can be washed with the same solvent used to suspend the thickener. The filterability of the suspension can be improved by ultrasonic treatment or treatment in a dispersant.

[0045] Particles smaller than 15 µm, such as wear particles, can be removed from the suspension. Magnetic separators are used to remove magnetic iron and steel particles, which can occur during the wear of lubricated machine elements. Electrostatic precipitators can be used to separate ionizable wear particles, and fractional centrifugation or hydrocyclones can be used to separate abrasion and dirt particles that have a higher density than the grease thickening particles, such as sand or metal particles.

[0046] Furthermore, methods for removing polar degradation products from the suspension can be carried out, such as fractional solid / liquid and liquid / liquid extraction with solvents of different polarity (e.g. water / alcohol mixtures), chromatographic methods or electrophoretic methods.

[0047] The filterability of the suspension can be improved by ultrasonic treatment or treatment in a disperser.

[0048] A simple method for incorporating additives is to add them to the suspension, particularly after filtration and independently before solvent removal. This allows the additives to disperse more homogeneously in the lubricating grease because the improved solubility of the solvent-base oil mixture, or rather its lower viscosity, can be utilized before the solvent is removed. Examples of such additives include amine and phenolic antioxidants, alkylated or aromatic phosphate esters, zinc dithiophosphates, and sulfur-containing esters. These are soluble or suspendable additives.

[0049] The removal of solvent from the suspension can be achieved by distillation, supercritical carbon dioxide extraction, or drying. Solvent removal is preferably carried out under reduced pressure, e.g., at < 850 mbar to 2 mbar, where the pressure is adjusted so that the boiling point, or in the case of a boiling range of the solvent, the upper boiling point, does not exceed a temperature calculated from the dropping point of the used grease of -52°C, preferably -60°C, and particularly preferably -90°C. Solvent removal does not necessarily mean that it must be completely removed. The solvent can be recovered and recycled by condensation. During recovery, it can be subjected to fractional distillation for purification.Water can be separated by phase separation, drying agents, hygroscopic filter absorbers, or as part of vacuum distillation.

[0050] The inventive method may further include, among other things, the following optional steps: Liquid or solid additives, further base oil and / or further thickener, each as described above, may be added to the recycled lubricating grease, in particular to achieve the desired consistency.

[0051] The recycled grease can be homogenized, for example, using a rotor / stator homogenizer, a high-pressure homogenizer, and / or a toothed colloid mill, especially after the addition of further additives, base oil, and / or thickener. Furthermore, the recycled grease can be deaerated using a perforated disc or vacuum deaerator.

[0052] The process may also include drying the recycled lubricating grease, in particular freeze-drying.

[0053] A particular aspect of the invention is the recycling of lubricating greases used in total-loss lubricated rolling bearings, plain bearings, or gears, for example, in wind turbines, hydroelectric power plants, rolling mills, machine tools, paper machines, ore processing plants, cement mills, and plants in food production and agriculture, where either large amounts of grease waste are generated or the exposure of used lubricating grease to the environment is to be avoided. Another particular aspect of the invention is the recycling of lubricating greases used in lifetime lubricated applications where they have only undergone slight oxidative aging and can be reprocessed using the inventive method. Such applications include, for example, the lubrication of wheel bearings in vehicles, rolling and plain bearings in stationary machines and assemblies, as well as encapsulated constant velocity joints and dual-mass flywheels.

[0054] The following results are typically obtained after recycling using the grease recycling process according to the invention, in each case in comparison of used grease to recycled grease and in particular (unused) grease (equivalent to fresh grease) to recycled grease: Consistency drop determined by cone penetration according to DIN ISO 2137 (walk penetration) by a maximum of plus 40 units (0.1 mm), preferably a maximum of plus 30 units (0.1 mm), dropping point drop according to DIN ISO 22285 by a maximum of 15°C, preferably by a maximum of 10°C, and particularly preferably a maximum of 5°C, recycling yield >60 wt.% based on the amount of grease used, particularly > 80 wt.% based on the amount of grease used (used grease).

[0055] The invention is explained through the characters: Fig. 1 illustrates the general procedure with possible implementation variants Fig. 2shows a SEM image of the used grease 1 Fig. 3 shows a SEM image of the recycled lubricating grease according to Example 1 (invention) for comparison with Fig. 2 Fig. 4 shows an SEM image of a recycled lubricating grease according to example 2 (reference with no longer fibril-like thickener structure). Experimental section

[0056] To illustrate the invention and reference examples for the recycling process, used fats with simulated, i.e., recreated, mechanical impurities were produced. Used greases 1 and 4

[0057] The service greases were manufactured according to US 5874391 Example 1 with the following compositions, which differed in the base oil and additives as well as the subsequent stirring in of added mechanical impurities: Table 1 Used grease 1 Lubricating grease: component type Weight % low molecular weight polypropylene Polypropylene homopolymer Mw approx. 90,000 g / mol 12,3 High molecular weight polypropylene Polypropylene co-polymer Mw approx. 230,000 g / mol 0,7 base oil PAO 8 84,4 Additive - Antioxidant commercial grease additives 2 Contamination stirred in type Weight % Metallic impurities 100Cr6 metal abrasion 0,2 Inorganic impurities Quartz sand 0,4 Properties of the lubricating grease before the addition of impurities Test method Unit Measurement Walk penetration DIN ISO 2337 0.1mm 289 NLGI class DIN 51818 2 Dropping point DIN ISO 22286 °C 152 Properties of used grease 1 after the addition of impurities Test method Unit Measurement Dropping point DIN ISO 22286 °C 151

[0058] The SEM image of the lubricating grease to used lubricating grease 1, before its contamination, is in Fig. 2 depicted and shows a net-like thickening structure. Table 2 Used grease 4 lubricating grease component type Weight % low molecular weight polypropylene Polypropylene homopolymer Mw approx. 90,000 g / mol 9,9 High molecular weight polypropylene Polypropylene co-polymer Mw approx. 230,000 g / mol 0,6 base oil Paraffinic and naphthenic mineral oil in a 1:1 ratio 82,88 Additives (antioxidant, corrosion protection, wear protection) commercial grease additives 6% Table 2 (continued) Contamination stirred in type Weight % Metallic impurities 100Cr6 metal abrasion 0,17 Inorganic impurities Quartz sand 0,45 Properties of lubricating grease before the addition of impurities Test method Unit Measurement Walk penetration DIN ISO 2337 0.1mm 320 NLGI class DIN 51818 1 Dropping point DIN ISO 22286 °C 150 Properties of used grease 4 after the addition of impurities Test method Unit Measurement Dropping point DIN ISO 22286 °C 148 Used greases 2 and 3

[0059] Production according to EP0795597B1 and its embodiment using the polymer thickener with the following compositions, which differ in the base oil and in the additives, an additional polypropylene polymer and the subsequent stirring in of simulated mechanical impurities: Table 3 Used grease 2 lubricating grease component type Weight % Low molecular weight polypropylene, melting point <200°C Polypropylene homopolymer Mw approx. 90,000 g / mol 4,8 High molecular weight polypropylene with a melting point of <200°C Polypropylene co-polymer Mw approx. 230,000 g / mol 0,5 Methylpentene polymers with a melting point of 235°C Mitsui TPX DX 820 9,1 base oil Mineral oil, PAO and alkyl aromatic in a ratio of 2:1:1 76,1 Additives (antioxidant, corrosion protection, wear protection) Commercial grease additives 7,9 Solid lubricants PTFE 1 Table 3 (continued) Contamination stirred in type Weight % Metallic impurities 100Cr6 metal abrasion 0,15 Inorganic impurities Quartz sand 0,45 Properties of lubricating grease before the addition of impurities Test method Unit Measurement Walk penetration DIN ISO 2337 0.1mm 295 NLGI class DIN 51818 2 Dropping point DIN ISO 22286 °C 202 Properties of used grease 1 after the addition of impurities Test method Unit Measurement Dropping point DIN ISO 22286 °C 191 Table 4 Used grease 3 lubricating grease component type Weight % Polypropylene with low molecular weight and melting point <200°C Polypropylene homopolymer Mw approx. 90,000 g / mol 5,6 High molecular weight polypropylene with a melting point of <200°C Polypropylene co-polymer Mw approx. 230,000 g / mol 0,6 Methylpentene polymer with a melting point of 235°C Mitsui TPX DX 820 10,4 base oil PAO and ester in a ratio of 3:1 78,2 Additives (antioxidant, corrosion protection, wear protection) commercial grease additives 4,6 Solid lubricants PTFE 1 Contamination stirred in type Weight % Metallic impurities 100Cr6 metal abrasion 0,15 Inorganic impurities Quartz sand 0,45 Properties of lubricating grease before the addition of impurities Test method Unit Measurement Walk penetration DIN ISO 2337 0.1mm 295 NLGI class DIN 51818 2 Dropping point DIN ISO 22286 °C 222 Properties of used grease 1 after the addition of impurities Test method Unit Measurement Dropping point DIN ISO 22286 °C 211 Used grease 5

[0060] To simulate mechanical impurities, 0.15 wt.% metallic impurities (100Cr6 metal shavings) and 0.45 wt.% inorganic impurities (quartz sand) were introduced into 99.4 wt.% of a commercially available lithium soap-thickened mineral oil grease (RENOLIT UNIRAIL 2 from Fuchs Lubricants Germany) to simulate mechanical impurities. Before and after the addition of the mechanical impurities, the grease, both as fresh and used grease, had a dropping point of 194°C. Used grease 6

[0061] To simulate mechanical impurities, 0.15 wt.% metallic impurities (100Cr6 metal shavings) and 0.45 wt.% inorganic impurities (quartz sand) were introduced into 99.4 wt.% of a commercially available polyurea-thickened PAO grease (RENOLIT PU PEM 2 from Fuchs Lubricants Germany) to simulate mechanical impurities. Before the addition of the mechanical impurities, the grease produced in this way has a dropping point of 268°C as a lubricating grease and a dropping point of 256°C as a used grease. Used grease 7

[0062] According to Table 5, 83.97% of a commercially available sunflower oil with an oleic acid content of over 90 wt.% ("High Oleic Sunflower Ester Oil Dakolub MB 9300 from DAKO AG") was heated to 150°C in a stirred tank with 15 wt.% of cross-linked poly-3-hydroxybutyric acid until the poly-3-hydroxybutyric acid was completely melted in the base oil. The mixture was then cooled to 60°C, 1.03 wt.% of additives were added, and the mixture was homogenized using a three-roll mill. The resulting grease was modified into used grease by adding 0.7 wt.% iron abrasion and 0.63 wt.% quartz sand as technical impurities. Before the addition of these mechanical impurities, the grease produced in this way had a dropping point of 120°C, and the used grease also had a dropping point of 120°C. Table 5 Used grease 7 Lubricating grease: component type Weight % polymeric ester based on polyhydroxyalkanoates (PHA) Cross-linked poly-3-hydroxybutyric acid, 15 base oil High Oleic Sunflower Oil 83.97 Additive - Antioxidant commercial grease additives 1,03 Contamination stirred in type Weight % Metallic impurities 100Cr6 metal abrasion 0,7 Inorganic impurities Quartz sand 0,63 Properties of the lubricating grease before the addition of impurities Test method Unit Measurement Walk penetration DIN ISO 2337 0.1mm 301 NLGI class DIN 51818 1 to 2 Dropping point DIN ISO 22286 °C 120 Properties of used grease 1 after the addition of impurities Test method Unit Measurement Dropping point DIN ISO 22286 °C 120 Example 1 (Invention)

[0063] The used grease 1 was recycled as follows: 50g used grease 1, determination of the dropping point of the used grease: 151°C, addition of 100g boiling point gasoline 60 / 95, suspension of the used grease in a stirred tank at room temperature, separation of the metal particles in the suspension by a permanent magnet, filtration of the suspension through a paper filter with a pore size of 12 to 15µm, washing of the filter residue with another 50g boiling point gasoline 60 / 95, filling of a rotary evaporator with the filtrate, heating of the filtrate to 60°C (=89°C below the determined dropping point), stepwise application of vacuum down to 14mbar, distillation and condensation of the boiling point gasoline 60 / 95 and drying for 45h at room temperature to obtain the recycled grease.

[0064] The recycled grease has the following characteristics compared to the original grease: lubricating grease recycled grease delta Walk penetration [0.1mm] 289 310 +21 NLGI class 2 1 -1 Dropping point [°C] 152 151 - 1

[0065] The following quantity balance was achieved in the recycling process: 50,3g weighed used grease 1 150g Petrol (for suspending and rinsing) 4,5g Filter residue for disposal 42g recycled grease

[0066] The SEM image of the recycled lubricating grease is in Fig. 3 depicted and shows a net-like thickening structure, which is largely that of the lubricating grease (see Fig. 2 ) is similar. Example 2 (reference)

[0067] The recycling of used grease 1 was carried out as follows: 51g used grease 1, determination of the dropping point of the used grease: 151°C, addition of 110g boiling point gasoline 60 / 95, suspension of the used grease in a stirred tank at room temperature, separation of the metal particles in the suspension by a permanent magnet, filtration of the suspension through a paper filter with a pore size of 12 to 15 µm, washing of the filter residue with a further 56g boiling point gasoline, filling of a rotary evaporator with the filtrate, heating of the filtrate to 60°C (=89°C below the determined dropping point), stepwise application of vacuum to 16mbar, distillation and condensation of the boiling point gasoline 60 / 95 and drying of the reformed grease for 4h at 100°C in a drying oven. The drying temperature is therefore only 51°C below the dropping point and was already too high because the recycled grease showed signs of softening.

[0068] The recycled grease has the following characteristics compared to the original grease: lubricating grease recycled grease delta Walk penetration [0.1mm] 289 340 +53 NLGI class 2 1 -1 Dropping point [°C] 152 150 -2

[0069] The following quantity balance was achieved in the recycling process: 51g weighed used grease 1 166g Petrol (for suspending and rinsing) 3,2g Filter residue for disposal 41g recycled grease

[0070] The following scanning electron microscope images show that at excessively high process temperatures, the recycled grease has a thickener that, compared to the original grease, is destroyed in its fibril-like structure and therefore no longer thickens well.

[0071] The SEM image of the recycled lubricating grease is in Fig. 4 depicted and shows a thickener structure that is no longer fibril-like. Example 3 (Invention)

[0072] Recycling of used grease 2 a) 25g used grease 2, b) Determination of the dropping point of the used grease: 191°C, c) Addition of 75g boiling point gasoline 60 / 95, d) Suspension of the grease in a stirred tank at room temperature, e) Separation of the metal particles in the suspension using a permanent magnet, f) Filtration of the suspension through a paper filter with a pore size of 12 to 15 µm, g) Washing of the filter residue with a further 53g boiling point gasoline, h) Filling of a rotary evaporator with the filtrate, i) Heating of the filtrate to 60°C, j) Gradual application of vacuum down to 14mbar, k) Distillation and condensation of the boiling point gasoline 60 / 95, and l) Drying of the recovered grease for 18h at room temperature in a vacuum chamber at 200mbar to obtain the recycled grease.

[0073] The recycled grease has the following characteristics compared to the original grease: lubricating grease recycled grease delta Walk penetration [0.1mm] 295 324 +29 NLGI class 2 1 -1 Dropping point [°C] 202 196 -6

[0074] The following quantity balance was achieved in the recycling process: 25g weighed used grease 2 128g Boiling limit gasoline 60 / 95 (for suspension and rinsing) 0,94g Filter residue for disposal 22,1g recycled lubricating grease. Example 4 (Invention)

[0075] Recycling of used grease 3 a) 25.3 g used grease 3, b) Determination of the dropping point of the used grease: 211°C, c) Addition of 75 g of boiling point gasoline 60 / 95, d) Suspension of the used grease in a stirred tank at room temperature, e) Separation of the metal particles in the suspension using a permanent magnet, f) Filtration of the suspension through a paper filter with a pore size of 12 to 15 µm, g) Washing of the filter residue with a further 25 g of boiling point gasoline 60 / 95, h) Filling of a rotary evaporator with the filtrate, i) Heating of the filtrate to 60°C, j) Gradual application of vacuum down to 16 mbar, k) Distillation and condensation of the boiling point gasoline 60 / 95, l) Drying of the reformed grease for 18 h at room temperature in a vacuum chamber at 200 mbar to obtain the recycled lubricating grease.

[0076] The recycled grease has the following characteristics compared to the original grease: lubricating grease recycled grease delta Walk penetration [0.1mm] 238 275 +37 NLGI class 3 2 -1 Dropping point [°C] 222 218 -4

[0077] The following quantity balance was achieved in the recycling process: 25,3g weighed used grease 3 101g Boiling limit gasoline 60 / 95 (for suspension and rinsing) 1,6g Filter residue for disposal 20,0g recycled grease Example 5 (Invention)

[0078] Recycling of used grease 1 with, for example, 1 alternative solvent. a) 25.5 g used grease 1, b) Determination of the dropping point of the used grease: 151°C, c) Addition of 80 g cyclohexane, d) Suspension of the grease in a stirred tank at room temperature, e) Separation of the metal particles in the suspension using a permanent magnet, f) Filtration of the suspension through a paper filter with a pore size of 12 to 15 µm, g) Washing of the filter residue with a further 25 g cyclohexane, h) Filling of a rotary evaporator with the filtrate, i) Heating of the filtrate to 60°C, j) Gradual application of vacuum down to 30 mbar, k) Distillation and condensation of the cyclohexane, l) Drying of the recovered grease for 18 h at room temperature in a vacuum chamber at 200 mbar to obtain the recycled grease.

[0079] The recycled grease has the following characteristics compared to the original grease: lubricating grease recycled grease delta Walk penetration [0.1mm] 289 328 +39 NLGI class 2 1 1 Dropping point [°C] 152 150 -2

[0080] The following quantity balance was achieved in the recycling process: 25,5g weighed used grease 1 105g Cyclohexane (for suspension and rinsing) 1,1g Filter residue for disposal 19,9 recycled grease Example 6 (Invention)

[0081] Recycling of used grease 1 with, for example, 1 alternative solvent. a) 25.7 g used grease 1, b) Determination of the dropping point of the used grease: 151°C, c) Addition of 50.2 g of boiling point gasoline 40 / 60, d) Suspension of the grease in a stirred tank at room temperature, e) Separation of the metal particles in the suspension using a permanent magnet, f) Filtration of the suspension through a paper filter with a pore size of 12 to 15 µm, g) Washing of the filter residue with a further 41 g of boiling point gasoline 40 / 60, h) Filling of a rotary evaporator with the filtrate, i) Heating of the filtrate to 60°C, j) Gradual application of vacuum down to 27 mbar, k) Distillation and condensation of the boiling point gasoline 40 / 60, l) Drying of the reformed grease for 18 h at room temperature in a vacuum chamber at 200 mbar to maintain the recycled lubricating grease.

[0082] The recycled grease has the following characteristics compared to the original grease: lubricating grease recycled grease delta Walk penetration [0.1mm] 289 302 +13 NLGI class 2 1,5 -0,5 Dropping point [°C] 152 150 -2

[0083] The following quantity balance was achieved in the recycling process: 25,7g weighed used grease 1 91,2g Boiling limit gasoline 40 / 60 (for suspension and rinsing) 1,3g Filter residue for disposal 20,1g recycled grease Example 7 (Invention)

[0084] The recycling of the used grease 4 was carried out as follows: 25.8g used grease 4, determination of the dropping point of the used grease: 148°C, addition of 50.2g boiling point gasoline 60 / 95, suspension of the grease in a stirred tank at room temperature, separation of the metal particles in the suspension by a permanent magnet, filtration of the suspension through a paper filter with a pore size of 12 to 15 µm, washing of the filter residue with a further 32.7g boiling point gasoline 60 / 95, filling of a rotary evaporator with the filtrate, heating of the filtrate to 60°C, stepwise application of vacuum to 44 mbar, distillation and condensation of the boiling point gasoline 60 / 95, drying of the recovered grease for 18h at room temperature in the vacuum chamber at 200mbar to obtain the recycled grease.

[0085] The recycled grease has the following characteristics compared to the original grease: lubricating grease recycled grease delta Walk penetration [0.1mm] 320 342 +22 NLGI class 1 1 0 Dropping point [°C] 150 149 -1

[0086] The following quantity balance was achieved in the recycling process: 25,8g weighed used grease 4 82,9g Boiling limit gasoline 60 / 95 (for suspension and rinsing) 0,5g Filter residue for disposal 21,1g recycled grease Example 8 (Invention)

[0087] Recycling of used grease 2 with, for example, 3, an alternative solvent a) 25.7 g used grease 2, b) Determination of the dropping point of the used grease: 191°C, c) Addition of 56.4 g of 40 / 60 benzine (boiling point gasoline), d) Suspension of the grease in a stirred tank at room temperature, e) Separation of the metal particles in the suspension using a permanent magnet, f) Filtration of the suspension through a paper filter with a pore size of 12 to 15 µm, g) Washing of the filter residue with a further 100.5 g of 40 / 60 benzine (boiling point gasoline), h) Filling of a rotary evaporator with the filtrate, i) Heating of the filtrate to 59°C, j) Gradual application of vacuum down to 45 mbar, k) Distillation and condensation of the 40 / 60 benzine (boiling point gasoline), l) Drying of the reformed grease for 18 h at room temperature in the vacuum chamber at 200mbar to preserve the recycled lubricating grease.

[0088] The recycled grease has the following characteristics compared to the original grease: lubricating grease recycled grease delta Walk penetration [0.1mm] 299 317 +18 NLGI class 1,5 1 -0,5 Dropping point [°C] 202 194 -8

[0089] The following quantity balance was achieved in the recycling process: 25,7g weighed used grease 2 156,9g Boiling limit gasoline 40 / 60 (for suspension and rinsing) 3,2g Filter residue for disposal 16,8g recycled grease Example 9 (Invention)

[0090] Recycling of used grease 3 with, for example, 4, an alternative solvent a) 26.0 g used grease 3, b) Determination of the dropping point of the used grease 3: 211°C, c) Addition of 84 g of boiling point gasoline 40 / 60, d) Suspension of the grease in a stirred tank at room temperature, e) Separation of the metal particles in the suspension using a permanent magnet, f) Filtration of the suspension through a paper filter with a pore size of 12 to 15 µm, g) Washing of the filter residue with a further 122 g of boiling point gasoline 40 / 60, h) Filling of a rotary evaporator with the filtrate, i) Heating of the filtrate to 60°C, j) Stepwise application of vacuum to 51 mbar, k) Distillation and condensation of the boiling point gasoline 40 / 60, l) Drying of the reformed grease for 18 h at room temperature in the vacuum chamber at 200 mbar to obtain the recycled lubricating grease.

[0091] The recycled grease has the following characteristics compared to the original grease: lubricating grease recycled grease delta Walk penetration [0.1mm] 238 249 +11 NLGI class 3 3 0 Dropping point [°C] 222 220 -2

[0092] The following quantity balance was achieved in the recycling process: 26,0g weighed used grease 3 206g Boiling limit gasoline 40 / 60 (for suspension and rinsing) 1,2g Filter residue for disposal 23,2g recycled grease Example 10 (reference)

[0093] Recycling of used grease 1 with fluorinated and chlorinated solvents a) 25.5 g used grease 1, b) Determination of the dropping point of the used grease 1: 151°C, c) Addition of 89.3 g 1,2,2-trifluoro-1,2,2-trichloroethane, d) Suspension of the grease in a stirred tank at room temperature, e) Separation of the metal particles in the suspension using a permanent magnet, f) Filtration of the suspension through a paper filter with a pore size of 12 to 15 µm, g) Washing of the filter residue with a further 72.3 g 1,2,2-trifluoro-1,2,2-trichloroethane, h) Filling of a rotary evaporator with the filtrate, i) Heating of the filtrate to 63°C, j) Stepwise application of vacuum to 53 mbar, k) Distillation and condensation of the 1,2,2-trifluoro-1,2,2-trichloroethane. l) Drying of the regenerated lubricating grease for 36h at room temperature in the vacuum chamber at 200mbar to obtain the recycled lubricating grease.

[0094] The recycled grease has the following characteristics compared to the original grease: lubricating grease recycled grease delta Walk penetration [0.1mm] 289 377 +88 NLGI class 2 0 -2 Dropping point [°C] 152 134 -18

[0095] The following quantity balance was achieved in the recycling process: 25,5g weighed used grease 1 161,6g Trifluorotrichloroethane (for suspension and rinsing) 1,7g Filter residue for disposal 24,6g recycled grease

[0096] The recycled grease is significantly softened by more than one NLGI grade (-2) compared to the examples of the invention. It is assumed that some of the polymeric thickener dissolved and then failed to recrystallize in its original, highly thickening form. Example 11 (Reference)

[0097] Recycling of used grease 1 with chlorinated solvent a) 25.7 g used grease 1, b) Determination of the dropping point of the used grease: 151°C, c) Addition of 92 g dichloromethane, d) Suspension of the used grease in a stirred tank at room temperature, e) Separation of the metal particles in the suspension using a permanent magnet, f) Filtration of the suspension through a paper filter with a pore size of 12 to 15 µm, g) Washing of the filter residue with a further 60.3 g dichloromethane, h) Filling of a rotary evaporator with the filtrate, i) Heating of the filtrate to 61°C, j) Stepwise application of vacuum to 63 mbar, k) Distillation and condensation of the dichloromethane, l) Drying of the regenerated grease for 36 h at room temperature in the vacuum chamber at 200 mbar to obtain the recycled grease.

[0098] The recycled grease has the following characteristics compared to the original grease: lubricating grease recycled grease delta Walk penetration [0.1mm] 289 410 +121 NLGI class 2 00 -3 Dropping point [°C] 152 101 - 51

[0099] The following quantity balance was achieved in the recycling process: 25,7g weighed used grease 1 152,3 g Dichloromethane (for suspension and rinsing) 6,8 g Filter residue for disposal 16,7g recycled grease

[0100] The recycled grease, compared to the examples of the invention, was significantly softened by more than three NLGI grades (-3) and exhibited a considerably greater dropping point depression. It was observed that the thickener did not suspend uniformly into fine particles, resulting in a large amount of residue remaining in the filter and primarily filtering out only base oil. Example 12 (reference)

[0101] Recycling of used grease 5, as an example of a lithium soap-thickened lubricating grease, and solvents according to examples 6, 8 and 9 a) 25.3 g used grease 5, b) Determination of the dropping point of the used grease 5: 194°C, c) Addition of 151.3 g of boiling point gasoline 40 / 60, d) Suspension of the used grease in a stirred tank at room temperature, e) Separation of the metal particles in the suspension using a permanent magnet, f) Filtration of the suspension through a paper filter with a pore size of 12 to 15 µm, g) Washing of the filter residue with a further 99.3 g of boiling point gasoline 40 / 60, h) Filling of a rotary evaporator with the filtrate, i) Heating of the filtrate to 62°C, j) Stepwise application of vacuum to 66 mbar, k) Distillation and condensation of the boiling point gasoline 40 / 60, l) Drying of the reformed lubricating grease for 36 h at room temperature in a vacuum chamber at 200 mbar to preserve the recycled lubricating grease.

[0102] The recycled grease has the following characteristics compared to the original grease: lubricating grease recycled lubricating grease Walk penetration [0.1mm] 276 no lubricating grease NLGI class 2 Dropping point [°C] 194

[0103] The following quantity balance was achieved in the recycling process: 25,3g weighed used grease 5 250,6g Boiling limit gasoline 40 / 60 (for suspension and rinsing) 16,1g Filter residue for disposal 7,8g Recovered oily substance, which is not a lubricating grease.

[0104] This experiment demonstrates that soap-thickened lubricating greases cannot be sufficiently suspended to filter effectively using a low-temperature process with aliphatic or cycloaliphatic solvents, even with a comparatively high amount of solvent. This is evidenced by the relatively high filter residue, in which a large portion of the thickener remained. Example 13 (reference)

[0105] Recycling of used grease 6, as an example of a polyurea-thickened lubricating grease, and solvents according to Examples 6, 8 and 9 a) 25.5 g used grease 6, b) Determination of the dropping point of the used grease: 256°C, c) Addition of 105.9 g of boiling point gasoline 40 / 60, d) Suspension of the used grease in a stirred tank at room temperature, e) Separation of the metal particles in the suspension using a permanent magnet, f) Filtration of the suspension through a paper filter with a pore size of 12 to 15 µm, g) Washing of the filter residue with a further 109.5 g of boiling point gasoline 40 / 60, h) Filling of a rotary evaporator with the filtrate, i) Heating of the filtrate to 61°C, j) Stepwise application of vacuum to 70 mbar, k) Distillation and condensation of the boiling point gasoline 40 / 60, l) Drying of the reformed lubricating grease for 36 h at room temperature in a vacuum chamber at 200 mbar to preserve the recycled lubricating grease.

[0106] The recycled grease has the following characteristics compared to the original grease: lubricating grease recycled grease Walk penetration [0.1mm] 255 no lubricating grease NLGI class 2 to 3 Dropping point [°C] 268

[0107] The following quantity balance was achieved in the recycling process: 25,5g weighed used grease 6 215,4g Boiling limit gasoline 40 / 60 (for suspension and rinsing) 16,3g Filter residue for disposal 10,6g Recovered oily substance, which is not a lubricating grease.

[0108] This experiment demonstrates that even polyurea-thickened lubricating greases cannot be sufficiently suspended for filtering using a low-temperature process with aliphatic or cycloaliphatic solvents, even with high solvent concentrations. This is indicated by the comparatively high filter residue, in which a large portion of the thickener remained. Example 14 (Invention with cross-linked 3-PHA derivative and biodegradable ester)

[0109] The used grease 7 was recycled as follows: 12g used grease 7, determination of the dropping point of the used grease: 120°C, addition of 31g boiling point gasoline 60 / 95, suspension of the used grease in a stirred tank at room temperature, separation of the metal particles in the suspension by a permanent magnet, filtration of the suspension through a paper filter with a pore size of 12 to 15µm, washing of the filter residue with a further 10g boiling point gasoline 60 / 95, filling of a rotary evaporator with the filtrate, heating of the filtrate to 60°C (=60°C below the determined dropping point), stepwise application of vacuum down to 14mbar, distillation and condensation of the boiling point gasoline 60 / 95 and drying for 36h at room temperature to obtain the recycled grease.

[0110] The recycled grease has the following characteristics compared to the original grease: lubricating grease recycled grease delta Walk penetration [0.1mm] 301 279 -22 NLGI class 1 to 2 2 -1,5 Dropping point [°C] 120 120 0

[0111] The following quantity balance was achieved in the recycling process: 12g weighed used grease 1 41g Petrol (for suspending and rinsing) 1,4g Filter residue for disposal 9,8g recycled grease

Claims

1. A process for reconditioning used lubricating greases which become a residual lubricating grease by use and collection of a lubricating grease, comprising the following steps: a) collecting used uniform lubricating greases from lubrication points to obtain a residual lubricating grease, the residual lubricating grease comprising at least one thickener, additives, a base oil and where applicable solid impurities, and the thickener comprising polymeric hydrocarbons or polymeric esters, b) providing a solvent with a boiling point or an upper boiling point in the case of a boiling range of 40 to 140°C at standard pressure, c) suspending the residual lubricating grease in the solvent to obtain a suspension comprising a liquid phase comprising at least the base oil and the solvent, and a solid phase in the liquid phase, comprising at least the thickener in suspended form, wherein at least the base oil and the solvent are mixed in the form of a uniform liquid phase, d) separating any solid impurities from the suspension, e) removing the solvent from the suspension by distillation or by extraction with supercritical CO2, to obtain a recycled lubricating grease comprising - recovered base oil comprising base oil from the residual lubricating grease and - recovered thickeners from the residual lubricating grease and - recovered additives comprising additives from the residual lubricating grease, wherein the residual lubricating grease, the suspension and the recycled lubricating grease are at no time during the process exposed to a temperature higher than the dropping point of the residual lubricating grease minus 52°C, preferably minus 60°C, particularly preferably minus 90°C; wherein the thickener is or comprises either a polymeric hydrocarbon or a polymeric ester, wherein the solvent - in the case of the polymeric hydrocarbons as thickener is a hydrocarbon as hydrocarbon solvent and - in the case of the polymeric esters, the thickener is a hydrocarbon, a C3, C4 or C5 ketone or mixtures thereof.

2. Process according to claim 1, wherein the recycled lubricating grease has an increase in the worked penetration by at most plus 40 0.1 mm, preferably by at most plus 30 0.1 mm, compared with the residual lubricating grease, in particular compared with the lubricating grease.

3. Process according to claim 1 or 2, wherein the recycled lubricating grease has a reduction in the dropping point by at most 15°C, preferably by a at most 10°C, and particularly preferably by at most 5°C compared to the residual lubricating grease, in particular compared to the lubricating grease.

4. Process according to at least one of the preceding claims, wherein the process further comprises homogenizing the recycled lubricating grease in a three-roll mill, a rotor / stator homogenizer, a high-pressure homogenizer and / or a tooth colloid mill, optionally with the addition of lubricant additives, further base oil and / or thickener to the recycled lubricating grease before or during homogenization.

5. Process according to at least one of the preceding claims, wherein the separation in step d) is carried out by filtration to obtain a filter cake, in particular with a filter having a pore size or mesh size of 200 µm or less , preferably 30 µm or less , and particularly preferably 15 µm or less .

6. Process according to claim 5, wherein the filter cake is washed with the solvent and the eluate is added to the suspension before or during step e).

7. Process according to at least one of the preceding claims, wherein the separation in step d) is carried out by sedimentation.

8. Process according to at least one of the preceding claims, wherein the separation in step d) is carried out by centrifugation or hydrocyclones.

9. Process according to at least one of the preceding claims, wherein magnetic particles are removed from the suspension by means of a magnetic separator and / or ionizable particles are removed from the suspension by means of an electrostatic separator.

10. Process according to at least one of the preceding claims, wherein the removal of the solvent is carried out by distillation, preferably under negative pressure, wherein the negative pressure is set such that the boiling point or the upper boiling point in the case of a boiling range of the solvent does not exceed a temperature calculated from the dropping point of the residual lubricating grease minus 90°C.

11. Process according to at least one of the preceding claims, wherein the process further comprises treating the suspension with a liquid extractant which forms a decantable 2-phase system with the liquid phase.

12. Process according to at least one of the preceding claims, wherein the process further comprises adding lubricant additives and / or further base oil to the suspension before step e).

13. Process according to at least one of the preceding claims, wherein the process comprises treating the suspension with a drying agent, in particular in the form of a filter drying agent.

14. Process according to at least one of the preceding claims, wherein the thickener in the form of a polymeric hydrocarbon is a polyolefin, in particular - a mixture of a polyethylene and an atactic polypropylene, - an ethylene / propylene copolymer, - a mixture of a polyolefin and a rubber polymer, in particular based on natural rubber, polyisobutadiene, styrene-butadiene rubber, ethylene-propylene-diene rubber, ethylene-propylene rubber and / or polyisobutylene; or - a polymethylene pentene with a melting point of more than 200°C, in particular more than 225°C15. Process according to at least one of the preceding claims, wherein the polymeric hydrocarbon has an average molecular weight of greater than 20000 g / mol (Mw).

16. Process according to at least one of the preceding claims, wherein the polymeric hydrocarbon has a melting point of greater than 100°C, in particular greater than 120°C.

17. Process according to at least one of the preceding claims, wherein the hydrocarbon, in particular the hydrocarbon solvent, comprises aliphatic and / or cycloaliphatic hydrocarbons and preferably alkanes, and particularly preferably is boiling point gasoline 40 / 60 or 60 / 95.

18. Process according to at least one of the preceding claims, wherein the process comprises drying the recycled lubricating grease, in particular freeze-drying.

19. Process according to at least one of the preceding claims, wherein the base oil is liquid at 25°C, is soluble in the solvent, in particular the hydrocarbon solvent, and the base oil has a kinematic viscosity of from 20 to 2500 mm2 / s, in particular from 40 to 500 mm2 / s, in each case at 40°C.

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