EP3344734B1 - Lubricating mixture having glycerides - Google Patents

Description

Technical field of application

The invention relates to a lubricating mixture which contains at least a proportion by mass of ≧50% of glycerides of natural origin and a proportion of fatty acid alkyl esters and is particularly suitable for use in gears, electric motors or internal combustion engines.

State of the art

Known from industrial use are lubricating liquids made from mineral oils, synthetic oils, vegetable oils or water, to which additives are usually added to improve the lubricating properties. The task of the liquids is to generate a liquid film on the surface of components, thereby reducing friction losses between components that move against one another and minimizing wear. In addition to established raw materials such as crude oil, natural raw materials are increasingly being used, which are often modified before being used as a lubricant (e.g. cellulose in the DE202009018507U1 ) and/or additives can be added. Very high demands are placed on gear or engine oils in the lubricant sector in particular, since they should be chemically stable over a long period of time and are often exposed to high temperature fluctuations, which can affect the lubricating properties. Those high In many cases, requirements cannot be met by either synthetic or natural fats and oils.

To evaluate the temperature dependency of lubricants, the so-called viscosity index was defined, which describes the temperature dependency of the kinematic viscosity of a lubricating oil. Oils with a low viscosity index show a greater change in viscosity with temperature than those with a high viscosity index. The latter are particularly desirable in lubricating applications.

The disadvantages of increased viscosity at low temperatures are discussed, for example, in DE 102010009030A1 received in more detail. According to this, transmission oils often have a significantly higher viscosity at low ambient temperatures compared to the operating temperature, which only slowly decreases after the vehicle has been put into operation solely due to the frictional heat generated in the transmission, which results in power losses. To avoid this disadvantage describes DE 102010009030A1 a process in which the transmission of a motor vehicle is preheated in order to keep the viscosity of the lubricant largely constant during use. However, this approach is associated with high costs.

In technical applications in gears or engines, petroleum-based hydrocarbons are usually used as the base medium, which can damage the environment and the use of which entails health risks. Vegetable oils are an environmentally friendly alternative to products based on Petroleum based and based on renewable natural resources. However, the use of vegetable oils as lubricants is limited by the property of some oils to solidify at low temperatures, due to a low viscosity index and because of the often lacking oxidative stability.

In the EP2350240A1 describes the use of vegetable oil with a high proportion of unsaturated fatty acids as gear oil or hydraulic fluid to improve the viscosity properties, the oil having a natural viscosity index (VI) of greater than or equal to 200 and a proportion of monounsaturated fatty acids of greater than 80%, a proportion twice unsaturated fatty acids of a maximum of 1-10% and a proportion of triunsaturated fatty acids of less than 1%. A part of the vegetable oil can be used in the form of an unsaturated ester of the vegetable oil. The description refers to the fact that gear oils or hydraulic oils should be thin at low temperatures (<40°C) in order to be easier to pump, which is achieved by using vegetable oil such as rapeseed or sunflower oil with a high proportion of unsaturated fatty acids. The occurrence of a solid phase in the lubricating medium should be avoided according to the description.

Industrial oils should also exhibit high oxidative stability, which is generally related to the unsaturated fatty acids present in vegetable fatty acid alkyl chains. The reaction of a vegetable oil with oxygen can lead to polymerization and crosslinking of the fatty acid alkyl chains and reduced oxidative stability. Oils based on saturated hydrocarbons contain little or no unsaturated fatty acids and therefore have high oxidative stability. In the DE60031505T2 describes a method for increasing the oxidative stability and improving the lubricating properties of a vegetable oil. The vegetable oil is transesterified with a short-chain fatty acid ester and volatile components are separated after transesterification. The vegetable oil can have a monounsaturated fatty acid content of at least 50% and can be selected, for example, from the group consisting of corn oil, rapeseed oil, soybean oil and sunflower oil. The short chain fatty acid ester can be saturated and is four to 10 carbon atoms in length. This type of transesterification with different synthetic components is an expensive process and therefore has economic disadvantages.

Hydraulic oils based on mineral oil are known. These usually have a viscosity index of around 100. Additives are added to the mineral oil to ensure protection against corrosion and increase its resistance to aging. In addition, viscosity index improvers are added. These are long-chain synthetic hydrocarbon compounds that are homogeneously distributed in cold oils and only slightly increase viscosity, but unfold at higher operating temperatures and increase in volume when dissolved in the oil. This thickens the oil and increases the viscosity index. Such viscosity index improvers have the disadvantage, however, that the long-chain hydrocarbon compounds are broken down into smaller fragments under stress, as a result of which their original thickening effect is sometimes significantly altered. This effect is also known as permanent shear loss.

In the US4783274A describes a hydraulic medium which is based on triglycerides from fatty acids. The triglycerides used in this lubricating medium must have an iodine number between 50 and 100. This includes non-drying and semi-drying triglycerides such as peanut, olive, sunflower, corn, and canola oils. Such oils have a cloud point of around 5°C, in the case of olive oil even -5°C. That in the US4783274A The vegetable oil-based lubricating medium described thus has no solid content at temperatures above 10°C.

In the DE20305164U1 a lubricant based on fatty acid esters is described. For this purpose, vegetable or animal fats are transesterified with monohydric alcohols, which have a chain length of between three and six carbon atoms. In this transesterification process, glycerol is a by-product and is separated because it is insoluble in the fatty acid alkyl esters. The Indian DE20305164U1 The lubricant described therefore contains no glycerides.

In the US2003040444A1 a biodegradable penetrating oil with anti-corrosive properties is described. The lubricant consists of natural or synthetic triglycerides, one organic solvent and an antioxidant. Lactic acid ethyl ester (ethyl lactate), mineral oils and mixtures of both are suggested as solvents. In order to improve the penetration behavior of the lubricant, fatty acid methyl esters from soybean oil can optionally be added. The use of partial glycerides is not described. Since this lubricant is explicitly a penetrating oil, i.e. a medium with low viscosity and good penetration properties, a solids content is undesirable.

In the US2005112267A1 describes a lubricant consisting of palm oil and palm oil by-products. Base fluid for this lubricating medium is palm olein, a liquid fraction of palm oil. According to this document, the iodine value of the palm olein used must be at least 56 in order to avoid the formation of fat crystals. Other lubricant components are tocopherols from palm oil and fatty acid alkyl esters. The latter are synthesized from free fatty acids and hindered polyhydric alcohols. Neopentyl glycol, trimethylolpropane, pentaerythritol and dipentylerythritol are used as hindered alcohols. Thus, the resulting esters are not mono- and diglycerides. Due to the use of palm olein, the lubricant has no solid fraction.

In the US2011039742A1 a lubricant additive obtained from vegetable oil is described. For the production, unsaturated vegetable oils are cross-linked by the action of heat. Subsequent transesterification of the unpolymerized oils allows them Separation. Thus, the additive described consists of poly-triglycerides linked via covalent bonds.

In the WO 2010/118891 A1 describes a lubricating fluid and a method for its production. This is a mixture of mono-, di- and triacylglycerides, free fatty acids and fatty acid alkyl esters. This lubricant is explicitly a liquid. A solid content is not described.

The object of the present invention is to provide a lubricating medium with a high viscosity index, which can be used advantageously in gears, engines or other units to be lubricated, which can be produced inexpensively and can also consist entirely of renewable raw materials and thus does not present a high hazard potential if released into the environment.

Presentation of the invention

The object is achieved by the lubricating mixture according to patent claim 1. Advantageous configurations of the mixture are the subject matter of the dependent patent claims or can be found in the following description and the exemplary embodiments.

The proposed mixture contains at least a mass fraction of ≥ 50% natural glycerides Origin and a proportion of fatty acid alkyl esters with 1 to 4 carbon atoms in the alkyl group. The glycerides are at least partly mono- and/or diglycerides, which form a mass fraction of ≥ 10% in the mixture, and the mixture has a temperature range of > 10°C to at least 15°C, preferably to at least 20°C, a liquid phase with a solids content of ≥ 1% by volume, which is formed from a proportion of the glycerides and/or the fatty acid alkyl esters.

The occurrence of the solid phase (solids content) is characterized by the fact that the light transmission of the mixture is 10% to 90% lower than that of a completely liquid reference of the same composition at a correspondingly higher temperature. The proportion of solids is preferably selected in such a way that the light transmission is 10% to 50%, ideally 10% to 20%, lower than that of the reference. Methods for determining the light transmission are, for example, photometers or measuring devices that work according to the TURBISCAN ^® principle.

The lubricating mixture according to the invention, also referred to below as lubricant, thus fulfills the lubricating effect of two systems at once by combining the properties of lubricating oils (liquid phase) and lubricating greases (solid phase). The mixture has a predominantly liquid consistency, so the volume fraction of liquid in the mixture is >40%, advantageously >80%, especially advantageously >90%. The mixture can also be formed or produced entirely from renewable raw materials, in particular vegetable oils and fats.

Surprisingly, the proportion of solids does not impair the properties of the lubricant, or only insignificantly, but leads to better chemical resistance of the lubricant than when using pure vegetable oils. The lubricant can therefore be used in technical lubrication applications without any problems.

The size of the solid particles that form the solids content of the proposed mixture have an edge length in the range between 4 μm and 5 mm. They show a good lubricating effect, since they get into the space between the gear wheels in transmissions, for example, and can develop an advantageous lubricating effect there. This significantly reduces the wear between the metal surfaces compared to other non-lubricating solid particles in the lubricant and prevents abrasive components from penetrating between the gears or into gaps and developing their abrasive effect there.

The lubricant according to the invention consists predominantly of triglycerides and partial glycerides natural oils and fats and fatty acid alkyl esters with 1 to 4 carbon atoms in the alkyl group. Particularly advantageous properties result when the mass fraction of the triglycerides in the lubricant is >30%, preferably >40%, ideally >50%. In a particularly advantageous embodiment of the invention, the mass fraction of fatty acid alkyl esters is >10%, ideally >15%. Particularly advantageous properties result when the proportion of diglycerides is >10%, ideally >15%, and that of monoglycerides is >5%.

In one embodiment of the invention, the lubricant contains a proportion of unbound monohydric or polyhydric alcohol. This proportion is preferably between 0.1 and 4%, ideally between 0.1 and 2%.

The solids content will advantageously consist of components that are contained in the natural raw material (fat, oil) from which the glycerides for the mixture are obtained or that are obtained from this raw material. In a particularly advantageous embodiment of the invention, the lubricant contains, in addition to the above-mentioned solids based on fats and oils and/or fatty acid alkyl esters, other organic or inorganic components which do not come from the natural raw material and which remain active even at high temperatures of at least 90°C are always fixed. These particles preferably have a diameter of 0.1 to 1.5 μm, ideally 0.2 to 1 μm, and surprisingly improve the running-in properties of gears. The proportion of this solid fraction in the lubricant is preferably between 0.1 and 3%, ideally between 0.15 and 2%. Examples of such foreign particles are non-oxidative metals and metal compounds such as iron or aluminum oxides, inert silicon-based compounds such as silicon oxide, and synthetic and natural polymers such as polystyrene, polyethylene, polyethylene terephthalate, polypropylene, polycarbonate, polyhydroxyalkanoates, polylactic acid, proteins, starches, Celluloses and their derivatives.

In an advantageous embodiment of the invention, the composition of the solid particles from the glycerides differs from the composition of the liquid phase. Thus, the monoglyceride content in the solid phase is ideally higher by a factor of >1.5, advantageously by a factor of >2, particularly advantageously by a factor of >5, than in the liquid phase.

Various methods are available for producing the proposed mixture, with fats containing a high proportion of saturated fatty acids being used at least in part as the raw material. These can be vegetable fats such as palm oil, palm kernel oil or coconut fat or other fats that contain a high proportion of saturated fatty acids >30% by mass, particularly advantageously >80% by mass and are still solid at a temperature of 20°C. By converting some of the triglycerides of these fats into mono- and/or diglycerides, a very oxidation-stable lubricant is obtained, which is largely liquid at a temperature of 20°C, so that pumping is possible and a surprisingly high lubricating effect is achieved . This is not the case with untreated vegetable fat.

The use of unrefined or only partially refined vegetable oils and fats as raw material is particularly advantageous. The lubricant obtained from this has particularly good oxidation stability.

Furthermore, the lubricant has particularly advantageous properties if only the hydratable phospholipids are removed in the refining process or if fat components, which are usually separated off in vegetable oil refining, are not removed or added back. Examples of such compounds are carotenoids, non-hydratable lecithins, phenols and phenolic acids, tocopherols, phorbol esters, etc.

Surprisingly, the mixture of triglycerides and partial glycerides and fatty acid esters according to the invention has a higher viscosity index of >200 compared to the untreated oils and fats.

Mixtures in which some of the glycerides are present as a solid phase at temperatures of at least 20° C. are particularly advantageous.

To further improve the viscosity index of the mixtures, it is advantageous to use components of vegetable oils that are liquid at this temperature and contain long-chain unsaturated fatty acids in addition to the fat components that are still solid at a temperature of 20°. This can be achieved by adding oils that a contain a high content of unsaturated fatty acids, such as rapeseed or sunflower oil, with the proportion of these oils being selected to be less than 50% by mass, advantageously less than 10% by mass, in order to maintain oxidation stability. It is possible to add the low-viscosity oil before the conversion of the triglycerides or after the conversion.

In a particularly simple embodiment of the invention, it may be sufficient to obtain the advantageous properties to produce a mixture of fats and oils that can be pumped at room temperature. A surprisingly good lubricating effect in gears or engines is also achieved with such mixtures.

Such mixtures can also be fractions of vegetable oils in the form of pumpable residues which are separated off as minor components during the winterization of oils. At a temperature of 20°C, these contain both liquid and solid components, which have a surprisingly good lubricating effect. Further configurations can be mixtures of these winterization residues with fats or oils, which are optionally also subjected to a partial transesterification.

Even if the mixture according to the invention has good resistance and stability even without further components or additives due to a high proportion of saturated fatty acids, it is still advantageous to add antioxidant substances to further increase the oxidation stability. For this plant ingredients are used to advantage, which are also contained in natural fats and are also soluble there. These can be carotenes, tocopherols, tocotrienols and other oil-soluble substances with an antioxidant effect. Depending on the proportion of unsaturated fatty acids, between 0.1 and 10% by mass of antioxidant plant substances should be used for technical applications.

Surprisingly, it turns out that the lubricant has particularly advantageous properties if it has a low proportion of inorganic particles (<1.5 μm). These serve as nuclei for fat crystallization and accelerate the formation of the solid phase.

example

The composition and application of the proposed lubricant are shown below using an example.

example

57% by mass of unrefined palm oil, 22% by mass of fatty acid ethyl esters from palm oil, 16% by mass of palm diglycerides and 5% by mass of palm monoglycerides are mixed at a temperature of 50°C. After cooling to a temperature of 20° C., the resulting mixture has a solids content of >40% by volume.

In a short gear test according to DIN ISO 14635-1, damage load level 7 is achieved with the additive-free lubricant. The lubricating properties of the palm-based medium are thus comparable with lightly additive-based lubricants based on mineral oil.

Claims (18)

1. Lubricating mixture, particularly for use in transmissions and engines, containing at least

   - a mass fraction of ≥ 50% glycerides of natural origin, wherein at least a part of the glycerides is obtained from vegetable fats which contain a mass fraction of at least 30% saturated fatty acids and are solid at a temperature of 20 °C, and

   - a proportion of fatty acid alkyl esters having 1 to 4 C atoms in the alkyl group,

   wherein

   - at least a part of the glycerides are mono- and/or diglycerides which form a mass fraction of ≥ 10% in the mixture, and

   - the mixture has a liquid phase with a solids content of ≥ 1% by volume in a temperature range from > 10 °C to at least 15 °C,

   - which is formed from a proportion of the glycerides and/or the fatty acid alkyl esters, and is formed by solid particles having an expansion in the range between 4 µm and 5 mm, and

   - wherein a proportion of liquid in the mixture amounts to > 40% by volume in the temperature range from > 10 °C to at least 15 °C.
2. Lubricating mixture according to Claim 1,
   characterized in that
   the mixture contains the liquid phase with the solids content of ≥ 1% by volume in the temperature range from > 10 °C to at least 20 °C.
3. Lubricating mixture according to Claim 1 or 2, characterized in that
   in the temperature range from > 10 °C to at least 15 °C or to at least 20 °C the mixture contains a liquid phase having a solids content of ≥ 50% by volume.
4. Lubricating mixture according to Claim 1 or 2, characterized in that
   in the temperature range from > 10 °C to at least 15 °C or to at least 20 °C the liquid phase has a proportion of ≥ 80% by volume of the mixture.
5. Lubricating mixture according to any one of Claims 1 to 4,
   characterized in that
   the mixture contains a mass fraction of ≥ 30% triglycerides.
6. Lubricating mixture according to any one of Claims 1 to 5,
   characterized in that
   the mixture contains a mass fraction of > 10% diglycerides and a mass fraction of > 5% monoglycerides.
7. Lubricating mixture according to Claim 5 or 6, characterized in that
   the mass fraction of triglycerides amounts to > 40%, preferably > 50%.
8. Lubricating mixture according to Claim 6 or 7, characterized in that
   the mass fraction of diglycerides amounts to > 15%.
9. Lubricating mixture according to any one of Claims 1 to 8,
   characterized in that
   the mixture contains a mass fraction of > 10%, preferably > 15% of the fatty acid alkyl esters.
10. Lubricating mixture according to any one of Claims 1 to 9,
    characterized in that
    the mixture contains a mass fraction between 0.1% and 4% of unbound monohydric or polyhydric alcohol.
11. Lubricating mixture according to any one of Claims 1 to 10,
    characterized in that
    in addition to the solids content of the glycerides and/or fatty acid alkyl esters the mixture also contains solid particles of other organic and/or inorganic substances, which are still solid even at a temperature of at least 90 °C.
12. Lubricating mixture according to Claim 11, characterized in that
    the solid particles from the other organic and/or inorganic substances are contained in the mixture with a mass fraction between 0.1% and 3%.
13. Lubricating mixture according to Claim 11 or 12, characterized in that
    the solid particles from the other organic and/or inorganic substances have an expansion in the range between 0.1 µm and 1.5 µm.
14. Lubricating mixture according to any one of Claims 1 to 13,
    characterized in that
    the glycerides in the solids content have a proportion of monoglycerides which is at least 1.5 greater than that of the glycerides in the liquid phase.
15. Lubricating mixture according to any one of Claims 1 to 14,
    characterized in that
    at least a part of the glycerides is derived from palm butter and/or coconut oil.
16. Lubricating mixture according to any one of Claims 1 to 15, characterized in that
    a part of the glycerides is derived from vegetable oils which are liquid at a temperature of 20 °C.
17. Use of the lubricating mixture according to one or more of the preceding claims as a lubricant.
18. Use according to Claim 17 as a lubricant for transmissions or engines.