Method for recycling lubricating grease using a heating process

Abstract

The invention relates to a method for recycling used lubricating grease, said method involving the process of liquefying a base oil- and thickener-containing used lubricant, thereby heating same, and obtaining a recycled lubricating grease which at least proportionally comprises the base oil together with the thickener.

Description

[0001] Process for recycling lubricating greases by heating

[0002] The present invention relates to a process for recycling used lubricating greases comprising liquefying by heating a used lubricant comprising base oil and thickener containing polymeric hydrocarbons or polymeric esters as thickener and obtaining a recycled lubricating grease comprising at least a portion of the base oil together with the thickener.

[0003] State of the art

[0004] For many technical applications, it is important to use lubricants to reduce friction and wear on the contact surfaces of moving parts. Depending on the application, lubricants of different consistencies can be used. Lubricating oils have a liquid and flowable consistency, while lubricating greases have a semi-solid to solid—often gel-like—consistency.

[0005] The hallmark of a lubricating grease is that a liquid oil component is absorbed and held in place by a thickener component. The nature of a lubricating grease, its spreadable and easily deformable properties, combined with its adhesive properties, ensure that the grease wets the lubrication point and exerts its lubricating effect on the tribologically stressed surfaces. They are used in particular for the lubrication of less well-sealed machine components, such as rolling or plain bearings, open gears, and guides.

[0006] Lubricating greases contain a thickener that is homogeneously distributed in a base oil, as well as solid or liquid additives. Additional additives, such as emulsifiers, are often used to ensure the thickener is stably dispersed in the base oil. A wide variety of substances are known as base oils. Organic and inorganic compounds are used as thickeners. In the Federal Republic of Germany, over 34,000 tons of used lubricating grease are generated annually, particularly in the lubrication of tribological systems such as rolling bearings, where lubricating greases account for a share of approximately 80%. In many cases, lubricating greases are used in so-called loss lubrication, where large amounts of contaminated grease are generated and must be disposed of in an environmentally friendly manner. Examples of such applications include rolling and plain bearings in energy systems (e.g.,This is especially true in the following industries (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 undergo minimal thermo-oxidative or mechanical aging, but are frequently contaminated with wear particles, dust, and moisture. This is due to the fact that the corresponding lubrication points are inadequately protected against environmental influences, or even that the aforementioned contaminants are supposed to be flushed out by relubricated 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] Various processes are known for thermally recycling used lubricating grease that is no longer suitable for its original purpose, with the goal 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, the first technical solutions now exist for the separate collection of used or old lubricating grease resulting from loss lubrication. For example, EP2447485 B1 describes a reusable used lubricating grease cartridge that allows the separate removal of old lubricating grease from a rolling bearing and subsequent emptying into a waste collection container. By collecting and combining the old lubricating grease, or used lubricating grease, becomes used lubricating grease, which is then recycled. Until now, reuse has generally involved purifying the lubricating greases to separate the thickener and base oil, resulting in the loss of the thickener structure. With approximately 4 to 20% by mass of thickener and approximately 75 to 95% by mass of base oil, thickener and base oil are the main components of most lubricating greases.If both can be purified in one and the same recycling process, the amount of waste and the energy and time required for recycling lubricating greases can be minimized.

[0010] According to a recent survey by the National Lubricating Grease Institute (NLGI), the group of metal standard and complex soap greases represents the largest contingent of lubricating greases at approximately 90% (NLGI Grease Production Survey Report 2020).

[0011] According to DE19739659 A1, the oil-containing components, along with impurities such as dirt and metal debris, are first removed from the used lubricating grease, which is preferably collected separately, in a multi-stage oil recovery process. The base oil is extracted from the used lubricating grease in an extractor in a multi-stage extraction process by adding an extraction agent. The resulting oil-extraction agent mixture (extract) is then separated from the raffinate with thickener and impurities in a downstream separator. The raffinate with thickener is in a semi-solid to solid state and is further dried to evaporate solvent residues. The multi-stage thickener recovery process 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 thickeners are dissolved by the added extractant, while the impurities remain undissolved.

[0012] Patent application DE 102023121428, unpublished at the time of filing, describes a recycling process for used polymer-thickened lubricating greases. In this process, the used lubricating grease is first suspended in an organic and non-polar solvent, e.g., special-boiling point spirit according to DIN 51632-1 and -2, to remove mechanical impurities. Subsequently, mechanical impurities such as metal abrasion and dirt particles can be removed by filtration or other suitable processes. The thickener and lubricating grease are then reconstituted by distillation, thus enabling the recovery of the used solvent, and further processing steps. This process uses flammable hydrocarbon solvents; however, it may be desirable to largely avoid solvents.

[0013] Object of the invention

[0014] If loss lubrication occurs in applications, particularly those operated at high rotational or sliding speeds, a large proportion of the lubricating grease volume introduced into these applications for loss lubrication can enter the shearing engagement directly and does not serve solely as a reservoir for sealing the tribological contact pairs. In these cases, a comparatively large volume proportion of the lubricating grease is often subjected to severe mechanical stress, and the thickener structure of the grease is largely destroyed by shearing during use. The present invention is also suitable for lubricating greases in which the thickener structure is mechanically destroyed or severely impaired during use of the grease. In contrast, the method according to DE 102023121428 aims to largely retain the thickener structure of the used lubricating grease during reprocessing.

[0015] When reprocessing lubricating greases, it is desirable not to separate the thickener and base oil and purify them in separate steps. During reprocessing, the mechanically destroyed thickener structure should be reconstructed together with the base oil in such a way that it thickens just as well, or at least almost as well, as when new in unused lubricating greases. Therefore, there should be no or only a minimal loss of thickening effect. The object of the invention is therefore to avoid the disadvantages of the prior art described above and to provide a process by which lubricating greases can be recycled as cost-effectively as possible, avoiding the addition of solvents, in an energy-efficient manner, and in as few steps as possible. Summary of the Invention

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

[0017] The invention relates to a method for reprocessing used lubricating greases, which become a used lubricating grease through use and collection, to obtain a recycled lubricating grease, comprising at least the following steps: a) collecting used lubricating greases, preferably uniform lubricating greases, from lubrication points to obtain a used lubricating grease, wherein the used lubricating grease contains at least one thickener, additives, a base oil and optionallycomprises solid impurities and the thickener comprises polymeric hydrocarbons or polymeric esters, b) heating at least the used lubricating grease to a temperature of 100 to 300 °C, preferably 160 to 260 °C, to liquefy the used lubricating grease to obtain a liquefied lubricating grease, wherein the heating is preferably carried out in a protective gas atmosphere and / or under reduced pressure, c) separating solid components from the liquefied lubricating grease, d) recreating a lubricating grease with a thickener structure by allowing the liquefied lubricating grease to solidify to form a thickener structure of the polymeric hydrocarbons by cooling by at least 40 °C, preferably by at least 60 °C, preferably on a cooled plate or a cooled conveyor belt or a rotating cooled drum, in particular without mechanical shearing, e) if necessary, homogenising the lubricating grease by mixing, if necessary.with the addition of additional additives and / or additional base oil to achieve the desired consistency; f) if necessary, further homogenization in a 3-roll mill, a toothed colloid mill, a high-pressure homogenizer, a rotor-stator or rotor-rotor disperser; g) if necessary, further filtering of the grease; h) if necessary, deaerating the grease. The used grease liquefies in the heat due to the melting of the thickener and / or the dissolution of the thickener, among other things, in the base oil.

[0018] The separation in step c) can be carried out by sedimentation, by centrifugation, by means of a magnetic separator for magnetic particles and / or by means of an electrostatic precipitator for ionizable particles and in particular by filtration, preferably with a filter with a pore size or mesh size of 15 pm and smaller.

[0019] The liquefied grease can be treated with a desiccant to remove water, particularly in the form of a filter desiccant. Furthermore, any water can be evaporated during heating, if necessary under reduced pressure. The recycled grease can also be dried, e.g., by freeze-drying.

[0020] In addition to the base oil, the used lubricating grease contains polymeric hydrocarbons as thickeners or polymeric esters.

[0021] The polymeric hydrocarbons preferably have a melting point of less than 260°C, in particular less than 240°C. Irrespective of this, the melting point is preferably above 100°C. The melting point or the onset of melting in relation to the melting range each relate to the raw material used.

[0022] The dropping points of used lubricating greases with the thickener based on polymeric hydrocarbons are preferably 100 at 240°C.

[0023] In the case of polymeric esters, these preferably have a melting range of 100 to approximately 170°C. The melting point or the onset of melting in relation to the melting range depends on the raw material used.

[0024] The dropping points of used greases with the polymeric ester-based thickener are preferably 100 at 150°C. The recycled grease preferably has a cone penetration value (worked penetration) of 200 to 430 mm / 10 (at 25°C), preferably 220 to 385 mm / 10, determined according to ISO 2137.

[0025] Uniform lubricating greases are those that contain at least the same thickeners, i.e., compounds of the "polymeric hydrocarbon" or "polymeric ester" type, and the same type of base oil, e.g., the same compound class, in particular the same polymeric hydrocarbon as thickener or polymeric ester and the same base oil. At a minimum, the additional base oil must be uniformly miscible with the (first) base oil.

[0026] Different base oils can be used which are liquid at room temperature and in particular have a kinematic viscosity of 12 to 2500 mm 2 / s, preferably 20 to 2500 mm 2 / s, particularly preferably from 40 to 500 mm 2 / s, each at 40 °C. Particularly suitable base oils are hydrocarbons such as polyalphaolefins (PAO), mineral oils, and / or esters. The base oils preferably have boiling points above 260 °C, especially above 300 °C.

[0027] In the case of thickeners based on polymeric esters, in addition to non-polar base oils, more polar base oils such as esters can also be used.

[0028] According to one embodiment, any solid contaminants are removed from the melted lubricating grease by filtration, in which particles larger than 15 pm, preferably larger than 5 pm, and particularly preferably larger than 2 pm remain in the filter residue. The filtration device can be heated for this purpose and can furthermore have pore sizes or filter mesh sizes of less than 15 pm, preferably less than 5 pm, and particularly preferably less than 2 pm. It is also possible to perform several filtrations in succession with decreasing filter mesh / pore sizes.

[0029] Detailed description of the invention Lubricating greases suitable for reprocessing or used lubricating greases are polyolefin-thickened lubricating greases, as known for example from US3850828 A, US2917458 A, US3290244 A, US3392119 A, US5874391 A, EP0942063 A1 or EP0795597 B1.

[0030] The used grease contains polymeric hydrocarbons as thickeners. Suitable greases include:

[0031] - Polyethylene, possibly mixed with atactic polypropylene,

[0032] - Polypropylene, possibly mixed with atactic polypropylene or polyethylene,

[0033] - Ethylene and polypropylene copolymer, possibly in a mixture with polypropylene and / or polyethylene,

[0034] - a polyolefin with a rubber component or mixtures of different rubber components,

[0035] - Methylenepentene polymer, optionally in a mixture with polypropylene, with polyethylene and / or with ethylene and polypropylene copolymer.

[0036] Polymeric hydrocarbons are long-chain compounds in which more than 99%, in particular 99.9%, of all atoms consist of carbon and hydrogen.

[0037] Suitable thickeners are polyethylenes with a molecular weight of 20,000-500,000 g / mol, more preferably 50,000 to 250,000 g / mol (each Mw) and preferably a density above 0.94 g / cm 3 , in particular in a mixture with an atactic polypropylene having a molecular weight preferably below 100,000 g / mol (Mw) and preferably a melt index above 20, in particular 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.

[0038] Particularly suitable thickeners are those based on oil-soluble amorphous polypropylenes with a molecular weight in the range of 300 to 10,000 g / mol (Mw) and an intrinsic viscosity of up to 0.4, in particular 2 to 5 wt.%, as well as 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 (copolymer or homopolymer) of propylene with a weight-average molecular weight of less than or equal to 100,000 g / mol.Particularly suitable are thickener compositions based on polymethylpentene (4-methylpentene-1-based polymer) with a melting point of more than 200 °C, or more than 225 °C in combination with the low molecular weight (weight average of 50,000 to 100,000 g / mol) propylene copolymers or homopolymers described in the previous section. A commercially available product, for example, is TPX DX 820 from Mitsui Chemicals Europe GmbH. This is a 4-methylpentene-1-polyolefin. All polymers that can be completely liquefied and / or dissolved at elevated temperatures in the process are suitable.

[0039] The polymeric esters are in particular polyhydroxyalkanoates (PHA), e.g. polyhydroxy(C4- to C12-)alkanoates, preferably poly-3-hydroxyalkanoates, very preferably poly-3-hydroxybutyric acid. -The thickening performance of the above polyhydroxyalkanoates can be further enhanced by further chemical modifications with one or more crosslinkers,

[0040] The thickener may contain other thickeners such as metal and metal complex soaps or polyureas, provided that these can be completely liquefied at elevated temperatures and / or dissolved in the base oil.

[0041] Various polar and non-polar base oils can be used in the used lubricating grease, which are liquid at room temperature with a kinematic viscosity of 12 to 2500 mm 2 / s, especially from 40 to 500 mm 2 / s, each at 40 °C. The base oil can be classified as mineral oil or synthetic oil. Examples of mineral oils include naphthenic mineral oils and paraffin-based mineral oils, as classified according to API Group I. Chemically modified mineral oils with low aromatic and sulfur content, low in saturated compounds, and improved viscosity-temperature behavior compared to API Group I oils, classified according to API Group II and III, are also suitable. Base oils include, in particular, polyalphaolefins, alkyl aromatics, alkyl diphenyl ethers, alkyl naphthalenes, and mixtures thereof.Esters 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, trimethylolpropane, neopentyl glycol, pentaerythritol, or dipentaerythritol with aliphatic branched or unbranched, saturated or unsaturated C2 to C22 carboxylic acids, C18 dimer acid esters with C2 to C22 alcohols, and complex esters can also be used as individual components or in mixtures. Esters of unsaturated fatty acids, such as esters of oleic acid with polyols, are also suitable.

[0042] As base oils for the polymeric hydrocarbons, in particular polyalphaolefins (PAO), e.g. C8-C14, especially C10 oligomers of alpha-olefins, alkyl aromatics, alkyl diphenyl ethers, alkyl naphthalenes and their mixtures and hydrocarbon oils, such as mineral oils, can be used.

[0043] Esters such as esters of aromatic di-, tri-, or tetracarboxylic acids with one or more C2 to C22 alcohols present in the polymeric esters, or in mixtures thereof, esters of adipic acid, sebacic acid, trimethylolpropane, neopentyl glycol, pentaerythritol, or dipentaerythritol with aliphatic branched or unbranched, saturated or unsaturated C2 to C22 carboxylic acids, C18 dimer acid esters with C2 to C22 alcohols, and complex esters, as individual components or in mixtures, can be used as base oils for the polymeric esters. Esters of unsaturated fatty acids, such as oleic acid esters with polyols, are also suitable.

[0044] Suitable additives include antioxidants, wear inhibitors, corrosion inhibitors, detergents, dyes, lubricity improvers, adhesion improvers, viscosity additives, friction reducers, and extreme pressure additives, metal deactivators, as well as solid lubricants, preferably in concentrations of less than 5%. Suitable additives include polyisobutenesuccinic acid and / or polyisobutenesuccinic acid polyacrylamide. Additives remaining in the filter residue can be subsequently added back to the recycled grease.

[0045] Hot filtration is performed using a filtration process in which particles larger than 15 pm or larger than 5 pm, and particularly larger than 2 pm, remain in the filter residue. The filter can be made of paper, textile fabric, or metal as the filter material, or it can be a loose-fill filter mass. To prevent oxidation of the grease or filter material, filtration can also be performed under a protective gas atmosphere. Depth filtration processes using glass fiber or synthetic fiber fabrics are also suitable. If, in addition to foreign contaminants or metal abrasion, solid, undissolved or melted grease additives remain in the filtration residue, such as oil-insoluble solid lubricants, these can be re-added with new substances during the further processing process.

[0046] Solids can be removed from the liquefied used grease, for example, using magnetic separators to separate magnetic iron and steel particles, which can occur during wear of lubricated machine components. Electrostatic precipitators can be used to separate ionizable wear particles.

[0047] The process according to the invention may further comprise the following optional steps: Liquid or solid additives, further base oil and / or further thickeners, each as described above, may be added to the liquefied lubricating grease, preferably during or after heating, in particular to achieve the desired consistency.

[0048] The recycled grease can be homogenized, for example, using a toothed colloid mill, a high-pressure homogenizer, or a roller mill, especially after adding additional additives, additional base oil, and / or additional thickener. Furthermore, the recycled grease can be deaerated using a perforated disc or vacuum deaerator.

[0049] A particular aspect of the invention is the recycling of lubricating greases used in loss-lubricated rolling bearings, plain bearings, or gears, for example in wind turbines, hydropower 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 in which they have undergone only minimal oxidative aging and can be reprocessed using the process according to the invention. 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.

[0050] With the lubricating grease recycling process according to the invention, the following results can typically be obtained after recycling, each comparing used lubricating grease with recycled lubricating grease and in particular (unused) lubricating grease (equal to fresh lubricating grease) with recycled lubricating grease:

[0051] - Change in consistency determined with the cone penetration (worked penetration) according to DIN ISO 2137 from a maximum of minus 50 to a maximum of plus 40 units (0.1 mm), preferably from a maximum of minus 30 to a maximum of plus 30 units (0.1 mm),

[0052] - Dropping point change according to DIN ISO 22285 from maximum -15 °C to maximum +30 °C, preferably from maximum -10 °C to maximum +25 °C,

[0053] - Recycling yield greater than 70 wt.% based on the amount of grease used, particularly greater than 90 wt.% based on the amount of lubricating grease used (used lubricating grease).

[0054] The general procedure with possible implementation variants is illustrated in Fig. 1.

[0055] Experimental part

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

[0057] Used grease 1

[0058] Used grease 1 was produced according to EP0795597B1 and its embodiment using the polymer thickener with the following composition, which differs in the base oil and additives, an additional polypropylene polymer, and the subsequent stirring in of simulated mechanical impurities: Table 1

[0059] Used grease 2

[0060] According to Table 2, 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 until it 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 then homogenized using a 3-roll mill. The resulting lubricating grease was modified by adding 0.7 wt.% iron abrasion and 0.63 wt.% quartz sand as technical impurities to the used lubricating grease. Before the addition of the mechanical impurities, the lubricating grease produced in this way had a dropping point of 120°C, and as used grease, it also had a dropping point of 120°C. Table 2

[0061] Example 1 (Invention)

[0062] Used grease 1 was recycled as follows:

[0063] - 500 g used lubricating grease 1 ,

[0064] - Determination of the dropping point of the used lubricating grease: 221 °C,

[0065] - Filling the used lubricating grease into a heatable, pressure-tight stirred reactor,

[0066] - Creating a protective gas atmosphere (nitrogen),

[0067] - Heating the grease to 190 °C so that it is completely liquefied,

[0068] - Separation of the metal particles by a permanent magnet,

[0069] - Multi-stage filtration of the hot and liquid lubricating grease in the following arrangement

[0070] 1 ) via a coarse dirt metal filter 220 pm mesh size

[0071] 2) then through a metal filter with 40 pm mesh size

[0072] 3) Then pass through a paper filter with 5 pm pore size

[0073] - Cooling of the liquefied lubricating grease by applying it to a metal plate pre-cooled to 15 °C from 190 °C to 120 °C in 4 minutes without mechanical shearing, - Scraping the cooled lubricating grease from the cooling plate and filling it into another stirred tank,

[0074] - Stirring to homogenize the grease,

[0075] - Stir in 3.75 g of the additives (as previously used, in 4 g of the base oil on Table 1 ),

[0076] - Homogenization of the grease on a 3-roller mill and venting under vacuum.

[0077] The recycled grease has the following characteristics compared to the lubricating grease:

[0078] Grease recycled grease Delta

[0079] Worked penetration [0.1 mm] 287 245 -42 NLGI class 2 3 +1 Dropping point [°C] 221 245 +24

[0080] Example 2 (Invention)

[0081] Used grease 2 was recycled as follows:

[0082] - 500 g used lubricating grease 2,

[0083] - Determination of the dropping point of the used lubricating grease: 221 °C,

[0084] - Filling the used lubricating grease into a heatable, pressure-tight stirred reactor,

[0085] - Creating a protective gas atmosphere (nitrogen),

[0086] - Heating the grease to 190 °C so that it is completely liquefied,

[0087] - Separation of the metal particles by a permanent magnet,

[0088] - Multi-stage filtration of the hot and liquid lubricating grease in the following arrangement

[0089] 1 ) via a coarse dirt metal filter 220 pm mesh size

[0090] 2) then through a metal filter with 40 pm mesh size

[0091] 3) Then pass through a paper filter with 5 pm pore size

[0092] - Cooling of the liquefied lubricating grease by applying it to a metal plate pre-cooled to 15 °C from 190 °C to 120 °C in 4 minutes without mechanical shearing,

[0093] - Scraping the cooled lubricating grease from the cooling plate and filling it into another stirred tank,

[0094] - Stir to homogenize the grease, - Stir in 3.75 g of the additives (as previously used, in 4 g of the base oil in Table 1 ),

[0095] - Homogenization of the grease on a 3-roller mill and venting under vacuum.

[0096] The recycled grease has the following characteristics compared to the lubricating grease:

[0097] Grease recycled grease Delta

[0098] Worked penetration [0.1 mm] 301 275 -26 NLGI class 1 to 2 2

[0099] Dropping point [°C] 120 120 +0

Claims

Patent claims 1. A method for reprocessing used lubricating greases which, through use and collection, become a used lubricating grease to obtain a recycled lubricating grease, comprising at least the following steps: a) collecting used lubricating greases from lubrication points to obtain a used lubricating grease, wherein the used lubricating grease contains at least one thickener, additives, a base oil and, if appropriate,comprises solid impurities and the thickener comprises polymeric hydrocarbons or polymeric esters, b) heating at least the used lubricating grease to a temperature of 100 to 300 °C, preferably 120 to 260 °C, to liquefy the used lubricating grease to obtain a liquefied lubricating grease, c) separating solid components from the liquefied lubricating grease, d) recreating a lubricating grease with a thickener structure by allowing the liquefied lubricating grease to solidify to form a thickener structure of the polymeric hydrocarbons or the polymeric esters by cooling by at least 40 °C.

2. The method according to claim 1, wherein the reconstitution of a lubricating grease with a thickener structure is carried out by allowing the liquefied lubricating grease to solidify to form a thickener structure of the polymeric hydrocarbons or the polymeric esters by cooling by at least 60 °C.

3. A process according to claim 1 or 2, wherein the base oil - is liquid at 25 °C and / or - the base oil has a kinematic viscosity of 12 to 2500 mm 2 / s, preferably 20 to 2500 mm 2 / s, particularly preferably from 40 to 500 mm 2 / s, each at 40 °C.

4. 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 polymethylenepentene having a melting point above 200 °C, in particular above 225 °C.

5. The process according to at least one of the preceding claims, wherein the polymeric hydrocarbon has an average molecular weight of greater than 20,000 g / mol (Mw).

6. The 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, and also independently thereof less than 300 °C and in particular less than 260 °C.

7. The method according to any one of claims 1, 2 and / or 3, wherein the thickener comprises a polymeric ester based on polyhydroxyalkanoates, preferably poly-3-hydroxybutyric acid, wherein preferably in each case a further chemical modification is carried out with one or more crosslinkers.

8. The method according to at least one of the preceding claims, wherein the method further comprises adding lubricant additives and / or further base oil and / or further thickener to the liquefied lubricating grease.

9. The method according to at least one of the preceding claims, wherein the method comprises treating the liquefied lubricating grease with a drying agent, in particular in the form of a filter drying agent to separate water and / or any water is evaporated during heating.

10. The method according to at least one of the preceding claims, wherein the separation in step c) is carried out by filtration, in particular with a filter having a pore size or mesh size of 15 pm and smaller.

11. The method according to at least one of the preceding claims, wherein the separation in step c) - by sedimentation - by centrifugation, - by means of a magnetic separator for magnetic particles and / or - by means of an electrostatic precipitator for ionizable particles.

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

13. The method according to at least one of the preceding claims, wherein the method comprises drying the recycled lubricating grease, in particular freeze-drying.

14. The process according to at least one of the preceding claims, wherein the cooling takes place within up to 5 minutes, preferably without shearing, to form a thickener structure of the polymeric hydrocarbons.

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