Lubricating grease compositions containing pentacyclic triterpenes as co-thickeners, their use and methods for their production

Abstract

The invention relates to lubricating grease compositions containing a base oil, a soap or polyurea thickener and at least one pentacyclic triterpene with at least one OH group, their production and their use for lubricating lubrication points on machines in contact with food and feed.

Description

[0001] The invention relates to lubricating grease compositions comprising a base oil, a soap thickener, and at least one pentacyclic triterpene with at least one OH group, and their use for lubricating lubrication points on machinery in contact with food and feed. The soap thickener is a calcium soap, a calcium complex soap, an aluminum complex soap, or a mixture thereof. A process for producing the lubricating grease composition is also disclosed. Technical context of the invention

[0002] Lubricants serve to reduce friction and wear on the contact surfaces of moving parts, thereby increasing the service life of components and machines and minimizing power and energy losses due to friction. While lubrication with oils is possible in many applications, some require the use of a consistent lubricant, i.e., a grease. Consistency allows a grease, unlike oils, to remain in place. This consistency is achieved by the thickener, which absorbs and retains the liquid oil component. High-quality greases are characterized by consistent consistency over a long period, good mechanical stability, and a defined oil release behavior. A grease consists of a base oil, at least one thickener, and possibly additives that are added to increase the lubricant's service life and performance.

[0003] Common soap thickeners include calcium soaps, calcium complex soaps, calcium sulfonate complex soaps, lithium soaps, lithium complex soaps, and aluminum complex soaps. Polyurethanes, polyureas, bentonite, and pyrogenic SiO2 are also used as thickeners. However, conventional thickeners and the raw materials used to produce them are often not based on renewable resources, or only partially so.

[0004] Betulin (CAS 473-98-3) is a pentacyclic triterpene that can be obtained by extraction from birch bark (compare US 7482383 B2).

[0005] It is therefore a biogenic and renewable raw material. Betulin is a diol derived from the structure of lupane (CAS 464-99-3). Birch bark extracts contain, in addition to betulin as the main component (e.g., approx. 80% w / w), betulinic acid (CAS 472-15-1, e.g., approx. 4%), oleanolic acid (CAS 508-02-1, e.g., approx. 2% w / w), lupeol (CAS 545-47-1, e.g., approx. 4% w / w), erythrodiol (CAS 545-48-2, e.g., approx. 2% w / w), and a number of other compounds (e.g., approx. 8% other).

[0006] Oleanolic acid and erythrodiol are derived from the oleana backbone, which differs from the lupane backbone in that the fifth ring is a six-membered ring instead of a five-membered ring.

[0007] In addition to extraction from birch bark, betulin and betulinic acid are also accessible by biosynthetic production according to WO 2015 / 121168 A1.

[0008] Betulin is attributed with pharmacological properties; for example, it is used as an anti-inflammatory agent in skin or wound healing ointments (trade names Episalvan and Filsuvez). This utilizes another property of betulin, namely its ability to form oleogels (compare US 8536380 B1 / EP 1758555 B2). Vegetable oils and mineral oils, for example, have been suggested as carrier fluids for the oleogels.

[0009] In patent literature, birch bark extracts, betulin and / or betulinic acid are occasionally suggested as thickeners, but not in lubricating greases and especially not as co-thickeners together with a soap thickener.

[0010] US patent 2023 / 0174888 A1 discloses a water-based grease composition containing water, a salt-based thickener, a polymer thickener, and optionally an inorganic solid thickener, as well as a process for producing these grease compositions. The polymer thickener may contain polymers of natural or synthetic origin. Purpose of the invention:

[0011] The object of the invention is to provide lubricating greases with an advantageous thickening effect. The thickening systems thus obtained should exhibit a synergistic interaction between thickener and co-thickener and, according to at least one embodiment, be suitable for use in the food or feed processing industry according to the "NSF H1" standard as "food grade" or be approved for use there.

[0012] It has been found that betulin-thickened oleogels, without further thickener, exhibit strong shear thinning under mechanical stress and strong post-hardening at rest, which is disadvantageous for use as a lubricant. Therefore, the object of the present invention was to improve the mechanical stability and storage stability. Summary of the invention

[0013] The problem is solved by the subject matter of the independent claims. Preferred embodiments are the subject matter of the dependent claims or described below.

[0014] The lubricating grease composition according to the invention comprises: a) a base oil (possibly comprising a base oil mixture) in an amount of 55 to 95 wt.% and preferably 70 to 90 wt.%; b) at least one soap thickener in an amount of 1 to 20 wt.%, preferably 1.5 to 15 wt.%, wherein the soap thickener is a calcium soap, a calcium complex soap, an aluminum complex soap or mixtures thereof; c) at least one pentacyclic triterpene with at least one hydroxy group, preferably from the lupane group, particularly preferably (3beta)-Lup-20(29)-ene-3,28-diol, in an amount of 0.5 to 10 wt. %, preferably 1 to 5 wt. %, as a co-thickener.

[0015] The lubricating grease composition according to the invention exhibits a synergistic interaction between betulin and the soap thickener. The co-thickener can substitute for the soap thickener to a certain extent, so that, as a result, less soap thickener is required. The lubricating grease compositions are also characterized by improved mechanical stability. Furthermore, unlike greases thickened solely with betulin, they exhibit no or negligible post-hardening and no or negligible shear-thinning behavior. Detailed description of the invention

[0016] The derivatives of baueran, friedelan, gammaceran, glutinan, hopan, lupan, multifloran, oleanan, taraxeran, and ursan, containing at least one OH group, can be used as pentacyclic triterpenes. Rings A to D of these pentacyclic triterpenes have six members. Ring E can have five or six members. The derivatives of lupan and oleanan are preferred. Mixtures of such pentacyclic triterpenes are available in the form of birch bark extracts. The basic structure of the pentacyclic triterpenes always has at least one hydroxyl group, e.g., at the 3-position, and can—even independently of this—have one or more methyl groups, e.g., at positions 4, 4, 5, 8, 10, 13, 14, 17, 20, 20, 22, and / or 22. The pentacyclic triterpene can, for example, also have two hydroxy groups.

[0017] Lupanes are a class of triterpenes with a pentacyclic structure. Like all triterpenes, lupanes are composed of six isoprene units and therefore typically have 30 carbon atoms. Lupanes have a structure consisting of four six-membered rings and one five-membered ring. Lupane C30H52 (CAS number 464-99-3) has methyl groups at positions 4, 4, 8, 10, 14, and 17, as well as an isopropyl group at position 19. The diol derived from the monounsaturated compound (20(29)-lupane), with OH groups at positions 3 and 28, is betulin (3(beta)-lupan-20(29)-ene-3,28-diol), which is the main component of birch bark extracts. In addition, such extracts also contain other lupan derivatives such as the monool lupeol (Lup-20(29)-en-3(beta)-ol), as well as the various oxidation products of the diol, such as betulinaldehyde (3(beta)-hydroxy-20(29)-lupen-28-aldehyde), betulinic acid (3(beta)-hydroxy-20(29)-lupen-28-ic acid) and betulonic acid (3-oxo-20(29)-lupen-28-ic acid).

[0018] Oleanans have a pentacyclic structure, with all five rings containing six members. Leanan C30H52 (CAS number 471-67-0) has methyl groups at positions 4, 4, 8, 10, 14, 17, 20, and 20. The diol erythrodiol (3(beta)-olean-12-ene-3,28-diol, CAS number 545-48-2), derived from the monounsaturated compound (12-oleanes), and its oxidation product oleanolic acid (3(beta)-hydroxy-12-oleanene-28-acid) are also found in birch bark extracts.

[0019] The base oils are liquid at room temperature (20 °C). The base oil preferably has a kinematic viscosity of 18 to 2500 mmol / L. 2 / s, especially from 25 to 1500 mm 2 / s, especially preferred 40 to 500 mm 2 / s, each at 40 °C (measured according to DIN EN ISO 3104). The term base oil in this context also includes a mixture of different base oils. Suitable base oils for food-grade (NSF H1) greases include, for example, highly refined white oils, gas-to-liquid (GTL) oils, polyalphaolefins as oligomers of C8 to C12 alpha olefins with a degree of oligomerization of 2 to 25, in particular 3 to 18, polyisobutylenes, poly(C2 to C4)alkylene glycols, C4 to C18 alkylated naphthalenes, native and synthetic esters, polyethers, polydimethylsiloxanes, as well as alcohols and polyols. Preferably, the base oil is an oil made from polyalphaolefins and / or synthetic esters.

[0020] Suitable soap thickeners include calcium soap, calcium complex soap, aluminum complex soap, or mixtures thereof.

[0021] Aluminum complex soaps are obtained by reacting a suitable aluminum source, e.g., aluminum oxyisopropoxylate (= oxo(propan-2-olato)aluminum), with at least one fatty acid and at least one aromatic carboxylic acid as a complexing agent. Suitable fatty acids are saturated or unsaturated monocarboxylic acids with 10 to 24 carbon atoms, such as lauric acid, myristic acid, palmitic acid, oleic acid, or stearic acid. Suitable aromatic carboxylic acids are monocarboxylic acids derived from a substituted or unsubstituted aromatic parent compound. Examples include benzoic acid, salicylic acid, p-toluic acid, phenylacetic acid, or 3-phenylpropionic acid.

[0022] Instead of the aluminum source, an aluminum fatty acid carboxylate (e.g., aluminum oxystearate) can also be used as the aluminum source, which is reacted with at least one aromatic carboxylic acid as a complexing agent. An idealized aluminum complex thickener containing equal amounts of stearate (as a fatty acid) and benzoate (as a complexing aromatic carboxylic acid) can be described as aluminum stearoyl benzoyl hydroxide (CAS 977098-49-9).

[0023] Calcium soaps are obtained by reacting calcium hydroxide with suitable carboxylic acids and, if necessary, additional inorganic acids such as phosphoric acid, whereby for calcium complex soaps a complexing agent is also reacted during the reaction.

[0024] Calcium soaps are salts of calcium with one or more saturated or unsaturated monocarboxylic acids with 10 to 24 carbon atoms, optionally with corresponding substituted monocarboxylic acids, such as preferably corresponding hydroxycarboxylic acids, e.g., 12-hydroxystearic acid. Suitable carboxylic acids include, for example, lauric acid, myristic acid, or behenic acid. In addition to the aforementioned straight-chain fatty acids, saturated or unsaturated branched-chain fatty acids can also be used. Naphthenic acids, neodecanoic acids, or comparable neoacids can also be employed.

[0025] Complexing agents within the meaning of the present invention are: (a) the alkali and / or alkaline earth salt, in particular calcium salts, of a saturated or unsaturated monocarboxylic acid or also hydroxycarboxylic acids with 2 to 8, in particular 2 to 4 carbon atoms, or alkali and / or alkaline earth salts of a dicarboxylic acid with 2 to 16, in particular 2 to 12 carbon atoms, each optionally substituted, and / or (b) the alkali or alkaline earth salt of boric acid and / or phosphoric acid, in particular as reaction products with NaOH and / or Ca(OH)2, wherein the boric acid and / or phosphoric acid may also be in the form of an ester of boric acid or phosphoric acid with unbranched or branched alkyl groups having 2 to 32 carbon atoms, preferably 8 to 32 carbon atoms.

[0026] The preferred complexing agent is (a). Particularly suitable monocarboxylic acids for the complexing agent are acetic acid and propionic acid. Also suitable are hydroxybenzoic acids such as parahydroxybenzoic acid, salicylic acid, 2-hydroxy-4-hexylbenzoic acid, metahydroxybenzoic acid, 2,5-dihydroxybenzoic acid (gentisic acid), 2,6-dihydroxybenzoic acid (gammaresorcylic acid), or 4-hydroxy-4-methoxybenzoic acid. Adipic acid (C6H6) is particularly suitable as a dicarboxylic acid. 10 O4), Sebatic acid (C 10 H 18 O4), azelaic acid (C9H 16 O4) and / or 3-tert-butyladipic acid (C 10 H 18 O4).

[0027] The borate (b) can be, for example, metaborate, diborate, tetraborate, or orthoborate, or an alkali or alkaline earth metal such as monosodium orthoborate. Suitable phosphates include alkali (preferably lithium) and alkaline earth (preferably calcium) dihydrogen phosphate, hydrogen phosphate, or pyrophosphate, or calcium or lithium hydroxyapatite. Esters of boric acid and phosphoric acid with unbranched or branched alkyl groups of 2 to 32, preferably 8 to 32, carbon atoms can be used.

[0028] The compositions according to the invention preferably further contain additives. Additives can be antioxidants, high-pressure additives, corrosion inhibitors, metal deactivators, viscosity index improvers, friction reducers or anti-wear additives, solid lubricants and / or dyes.

[0029] Examples of antioxidants include amine compounds such as alkylamines or 1-phenylaminonaphthalene, aromatic amines such as phenylnaphtylamines or diphenylamines, polymeric hydroxyquinolines such as 2,2,4-trimethyl-1,2-dihydroquinoline polymer (TMQ), phenolic compounds such as 2,6-di-tert-butyl-4-methylphenol, zinc dithiocarbamate or zinc dithiophosphate; phosphites such as tris(2,4-ditert-butylphenyl phosphite or bis(2,4-ditert-butylphenyl)-pentaerythritol diphosphite; and thioethers such as cresol thioethers.

[0030] Examples of high-pressure additives and / or anti-wear additives include organic sulfur compounds such as polysulfides or sulfurized olefins, thiophosphates such as triphenyl thiophosphate and dithiophosphates, phosphites and phosphonates such as di-n-octylphosphonate, phosphates such as substituted triphenyl phosphates or amine-neutralized alkyl phosphates, inorganic or organic boron compounds, thiocarbamates and / or dithiocarbamates such as methylene bis(dibutyldithiocarbamate).

[0031] Examples of corrosion inhibitors include sulfonates such as petroleum sulfonate, dinonylnaphthalene sulfonate; neutral or hyperbasic calcium sulfonates, magnesium sulfonates, sodium sulfonates, calcium and sodium naphthalene sulfonates, sulfonic acid esters, amine phosphates and / or N-methyl-N-(1-oxo-9-octadecenyl)glycine.

[0032] Examples of metal deactivators include benzotriazoles such as methylbenzotriazole dialkylamine, sterically hindered phenols and / or sodium nitrite.

[0033] Examples of viscosity index improvers include polymethacrylate, polyisobutylene and / or polystyrene.

[0034] Examples of friction modifiers include organic acids, such as isostearic acid, fatty acid esters, possibly ethoxylated polyols like glycerol or sorbitan, partial glycerides, animal or vegetable oils, molybdenum dialkyl dithiophosphates, molybdenum dialkyl dithiocarbamates, zinc dithiocarbamate, zinc dithiophosphate, functional polymers such as oleylamides, organic compounds based on polyethers and amides, such as alkyl polyethylene glycol tetradecylene glycol ethers, PIBSI (polyisobutylene succinic imide) or PIBSA (polyisobutylene succinic anhydride), dialkyl hydrogen phosphonates, and alkyl succinates. These friction modifiers can also act as anti-wear additives.

[0035] Solid lubricants that can be used include: polymer powders such as polyamides, polyimides, polyphenylene sulfide (PPS) or polytetrafluoroethene (PTFE), melamine cyanurate, melamine polyphosphate, graphite, metal oxides, boron nitride, silicates, e.g. magnesium silicate hydrate (talc), sodium tetraborate, potassium tetraborate, metal sulfides such as molybdenum disulfide, tungsten disulfide or mixed sulfides based on tungsten, molybdenum, bismuth, tin and zinc, inorganic salts of alkali and alkaline earth metals, such as calcium carbonate, sodium and calcium phosphates, as well as carbon black or other carbon-based solid lubricants such as nanotubes. Manufacturing process

[0036] The process for manufacturing the lubricating grease composition comprises the following steps: - Base oil and aluminum complex precursor are heated to obtain a mixture; - Fatty acid and complexing agent are added to the mixture at at least 60°C and the mixture is heated further to at least 80°C, preferably at least 90°C; - the pentacyclic triterpene, optionally as an oleogel in part of the base oil, is added to the mixture at at least 80°C, in particular 80-110°C, preferably at least 90°C, in particular 90-100°C, and is further heated to at least 180°C; - the mixture is cooled to below 80°C, preferably below 60°C; - the grease obtained in this way is homogenized and, if necessary, ground to obtain the lubricating grease composition.

[0037] To produce the lubricating grease composition according to the invention, in a preferred embodiment the pentacyclic triterpene is added as a co-thickener after the formation of the primary thickener, particularly when the formation of the primary thickener is largely complete. The reaction to form the primary thickener takes place in at least a portion of the base oil, at temperatures between 60 and 100°C, preferably at temperatures between 70 and 90°C. In this process, at least one carboxylic acid is added to a solution or suspension of a reactive precursor compound (e.g., aluminum oxystearate) and reacted by thorough mixing, or a reactive precursor compound (e.g., calcium hydroxide) is added to a solution or suspension of at least one carboxylic acid and reacted by thorough mixing. Any water that may be formed is removed by heating the mixture to temperatures above 100°C.

[0038] The pentacyclic triterpene is added at a temperature between 80 and 110°C, preferably between 90 and 100°C. The pentacyclic triterpene can be added in powder form or as an oleogel in a portion of the base oil. The pentacyclic triterpene and the primary thickener are heated together with stirring to a final upper temperature. Depending on the type of primary thickener, this upper temperature is between 120 and 220°C, preferably between 150 and 210°C.

[0039] Once the upper final temperature is reached, the mixture is cooled to a temperature below 80°C, preferably below 60°C. Optionally, at least one additive can be added at this temperature.

[0040] The resulting lubricating grease is homogenized using a colloid mill or a three-roll mill. use

[0041] The lubricating grease composition according to the invention is particularly suitable for use in gears, plain and rolling bearings, sliding guides, spindle drives, linear drives and ball screws, especially those used in the food (including the beverage industry) or animal feed industry. The lubricating grease composition according to the invention can be used for lubricating lubrication points on machines or devices in contact with food and animal feed.

[0042] The grease composition is intended for applications where the lubricant may come into contact with food during the production process, regardless of whether this contact is unavoidable or only occasional. For this purpose, the grease composition must be approved according to international regulations as per "NSF H1," as granted by "NSF International." Another standard is DIN ISO 21469. Experimental examples

[0043] In the following examples, the characteristic data of the lubricating greases according to the invention, co-thickened by betulin, are compared with those based on a pure soap thickener.

[0044] Aluminum complex grease 1 (AX1): In a heated reaction vessel with a stirrer, 1055.7 g of the polyalphaolefin Synfluid PAO 8 cSt (Chevron Phillips Chemical, PAO 8, kinetic viscosity at 40°C approx. 46 mm) were mixed. 2 / s) and 120.0 g of the aluminum complex precursor Komad 8418 VO (MOL, aluminum oxystearate in white oil) were placed in the mixture and heated to 80–85 °C with stirring. 6.2 g of stearic acid and 18.1 g of benzoic acid were added together. With continuous stirring and the activation of a rotor-stator homogenizer (4000 rpm), the mixture was maintained at 85 °C for one hour (reaction phase). Subsequently, the mixture was heated at a rate of 1 K / min to a final temperature of 205 °C (heating phase). Upon reaching the final temperature, the rotor-stator homogenizer was switched off and the mixture was cooled to below 60 °C (cooling phase). The resulting fat was homogenized by milling in a colloid mill.

[0045] The other aluminum complex greases AX2, AX3, and AX4 were produced analogously, i.e., using the same process but with correspondingly larger proportions of the thickening agents. In the case of AX4, the ester Linplast 810 TM (Sasol, trimellitic acid ester of linear C8 / C10 alcohols, kinetic viscosity at 40°C approx. 50 mm) was used instead of the base oil PAO 8. 2 / s).

[0046] The production of the model greases M1, M2 and M3 according to the invention was carried out analogously to the production of the pure aluminum complex greases, i.e. using the same process but with correspondingly lower proportions of the raw materials, and with the difference that a corresponding amount of birch bark extract with a betulin content of approximately 80%, hereinafter referred to as betulin, was added after the reaction phase. Table 1 Part 1: Reference and model greases. Key figure Unit / Method AX1 M1 AX2 M2 base oil PAO 8 PAO 8 PAO 8 PAO 8 Thickener type Al complex Al-complex / Betulin Al complex Al-complex / Betulin Al complex soap content [Weight %] 7 7 8 7 Betulin content [Weight %] - 1 - 3 PW 60 [0, 1mm] / DIN ISO2137 340 330 324 297 PW 100,000 398 383 388 332 Δ PW 58 53 64 35 Part 2: Reference and model greases Key figure Unit / Method AX3 AX4 M3 AX5 base oil PAO 8 Ester Ester Ester Thickener type Al complex Al complex Al-complex / Betulin Al complex Al complex soap content [Weight %] 10 7 7 10 Betulin content [Weight %] - - 3 - PW 60 [0.1mm] / 260 363 358 291 PW 100,000 DIN ISO 346 414 368 352 Δ PW 2137 86 51 10 61

[0047] Due to the thickening effect of betulin, the model greases M1, M2 and M3 have an improved consistency compared to the reference greases AX1 and AX4, which is more or less pronounced depending on the amount used and the type of base oil.

[0048] In comparison with the reference greases AX1 and AX4 (same content of Al complex soap) and also compared to AX2, AX3 and AX5 (same total thickener content), the model greases M1, M2 and M3 according to the invention exhibit improved mechanical stability (lower Δ PW), measured as the difference in walking penetration PW 100,000 with 100,000 strokes minus PW 60 with 60 strokes.

Claims

[1] Grease composition comprising a) a base oil in a quantity of 55 to 95 wt.%; b) at least one soap thickener in an amount of 1 to 20% by weight, wherein the soap thickener is a calcium soap, a calcium complex soap, an aluminum complex soap or a mixture thereof; and c) at least one pentacyclic triterpene with at least one OH group in an amount of 0.5 to 10 wt.%. [2] Lubricating grease composition according to claim 1 comprising a) the base oil in a quantity of 70 to 90 wt.%; b) the soap thickener in an amount of 1.5 to 15 wt.%; c) the pentacyclic triterpene with at least one OH group in an amount of 1 to 5 wt.% as a co-thickener. [3] Grease composition according to at least one of the preceding claims, wherein the pentacyclic triterpene is from the lupane group of substances and is preferably betulin and / or lupeol. [4] Grease composition according to at least one of the preceding claims, wherein the base oil has a kinematic viscosity of 18 to 2500 mm². 2 / s, especially from 25 to 1500 mm 2 / s, especially preferred 40 to 500 mm 2 / s, each at 40 °C. [5] Grease composition according to at least one of the preceding claims, wherein the base oil is a hydrocarbon oil and / or an ester oil. [6] Grease composition according to at least one of the preceding claims, wherein the soap thickener is an aluminum complex soap. [7] Grease composition according to at least one of the preceding claims, wherein the grease composition further comprises additives selected from antioxidants, high-pressure additives, corrosion inhibitors, metal deactivators, viscosity index improvers, friction reducers or anti-wear additives, solid lubricants, dyes and mixtures thereof. [8] A method for producing the lubricating grease composition according to at least one of the preceding claims, wherein the soap thickener is an aluminum complex soap, comprising the following steps, - Base oil and aluminum complex precursor are heated to obtain a mixture; - Fatty acid and complexing agent are added to the mixture at at least 60°C and it is heated further to at least 80°C; - the pentacyclic triterpene is added to the mixture at at least 80°C and it is further heated to at least 180°C; - the mixture is cooled to below 80°C, preferably below 60°C; - The grease obtained in this way is homogenized to maintain the composition of the lubricating grease. [9] Use of the lubricating grease composition according to at least one of the preceding claims 1 to 7, for lubricating lubrication points on machines or devices that are in contact with food and feed.