A lubricant additive comprising or consisting of a metal complex from the lanthanide group and their application as lubricants and a lubricant mixture

Abstract

An additive to lubricant, comprising or consisting of a metal complex with the formular (I): (I) wherein R is either PR1R2 or C-NR1R2 wherein in at least one of R1 or R2 comprises of optionally substituted alkanes with nine or more carbon atoms or R1 and R2 are inter-connected by optionally substituted hydrocarbon chains with at least nine carbon atoms, wherein L can be selected from a group consisting of one bidentate ligand, one monodentate ligand / or two separate monodentate ligands, where coordinating atoms are S, N, P and / or O and M is any lanthanide or a mixture of those, except Pm; a use of such compound and a lubricant mixture comprising such a compound.

Description

[0001] A LUBRICANT ADDITIVE COMPRISING OR CONSISTING OF A METAL COMPLEX FROM THE LANTHANIDE GROUP AND THEIR APPLICATION AS LUBRICANTS AND A LUBRICANT MIXTURE

[0002] Technical Field

[0003] The present invention relates a lubricant additive comprising or consisting of a metal complex, wherein the metal is selected from the lanthanide group, except Pm or as a part of a lubricant additive as well as their use as lubricant and in lubricant mixtures comprising said compounds functioning as lubricating additives. Said lubricants and lubricating additives are complexes of ligands with lanthanides.

[0004] Background Art

[0005] Compounds of this type with dithiocarbamate ligands were reported as lubricating additives for oils, which need to operate at high pressures. [R. B. Rastogi, J. L. Maurya, V. Jaiswal and D. Tiwary, Int. J. Ind. Chem., 2012, 3, 1-10.]

[0006] However, this document describes in this context the use of short hydrocarbon chains or cyclic (aromatic or non-aromatic) groups on nitrogen, which contained six carbon atoms or less. Thus, due to the need for high pressure conditions the lanthanide-compounds in the prescribed cases are not usable in numerous application such as engine oil.

[0007] The publication “Tribochemical characteristics of cerium dioctyl dithiocarbamate as an antiwear additive” Chen Ligong, Mocaxue Xuebao, Tribology vol. 16 no. 3, pages 247-256, 07.01.1996, ISSN: 1004-0595 discloses a cerium complex with three DTC-molecules.

[0008] The solubility of lanthanoid complexes in different media further depends on the number of complexation atoms around central metal ion. Lanthanoids have different ion diameter and charge. The number of complexation molecules, and thus the solubility in different media, may vary with the different lanthanoid ions and with their charge.

[0009] The publication “Thermal Studies on some Lanthanide (III) complexes of hexa- methylendithiocarbamate” by Kumar Dahiya Krishan et al., 31.12.1989 XP093223358 discloses the study of an LaDTC complex without any relevance for tribological behaviour. Thus a use of either a lubricant or a lubricant mixture cannot be derived from this study.

[0010] The publication “A series of bis (2-phenetyl)dithiophosphinate-based Ln (III) complexes: synthesis, magnetic and photoluminescent properties” inorganica chimica acta, Elsevier BV. ML, vol. 516, 22.10.2020, XP086427989; ISSN: 0020-1693 disclose a Lantanoid-complex without any reference to tribological properties or use as a lubricant - rather as a analytic agent due to photoluminescent properties.

[0011] The publication “synthesis, characterization and molecular modelling of bis(aquo)tris(dibutyldithiophosphato) gadolinium (III)” by Pratomo U et al., Proce- dia chemistry vol. 17, 31.12.2015, XP029376227 discloses the formation and the studies of properties of Gadolinium-complexes. Tribological properties were not of any relevance during the studies for a better characterization of these compounds.

[0012] The publication “Syntheses, characterization and biocidal aspects of O,O’-di- tolyl / dibenhyldithiophosphates of lanthanum (III) and their adducts with nitrogen and phosohorus donor b” by Syed A. et al., Monatshefte fur Chemie, Chemical Monthly, Springer Vienna, 03.04.2013, vol. 144, No. 8, XP035303899, ISSN: 0026-9247 disclose a specific lanthanium complex with different ligands having N and P complexation atoms. Tribological studies and references to lubrication functions of these compounds are not disclosed in this document.

[0013] The publication “Tribological properties and tribochemical mechanism of lanthanum and boron compounds in oil” by Jiang S. et al., Lubrication science vol. 17 No. 1 , 01.11.2004, p. 63-73, XP 093223400 disclose a lanthanium compound being used as lubricant compound in oil. The complex is a DDP-complex with phosphate as a complexation agent. Most La-complexes are not fully soluble in oil. Thus the La-complex in oil represents rather a dispersion than a soluble compound.

[0014] The publication “The tribological behaviors of some rare earth complexes as lubricating additives part 2 - the antiwear and extreme pressure properties in lithium grease” by Yu L. et al., 01.02.1998, wear, Elsevier sequota, Lausanne, vol. 214, No. 2, p. 151.155, XP027546634 disclose different rare earth complexes. One of these complexes is a cerium complex with three complexations molecules and no further ligands. Although a lubrication property was mentioned in the disclosure the solubility in oil is not disclosed in detail. Thus dispersed complexation products are very likely.

[0015] Disclosure of the invention

[0016] An additive to a lubricant comprise or consist of a metal complex with the formula: wherein R is either

[0017] PR1 R2 or

[0018] C-NR1 R2. at least one of R1 or R2 comprises of optionally substituted alkanes with nine or more carbon atoms or R1 and R2 are interconnected by optionally substituted hydrocarbon chains with at least nine carbon atoms.

[0019] Alternatively, R1 and R2 are interconnected, where the interconnecting group contains at least six carbon atoms.

[0020] The transition metal complexes of lanthanides, shown in the formula above, is suitable for the use as anti-wear agent as primary function but could also be used as antioxidant and / or friction modifier as secondary function agent in engine oils. Said compound can also be used alone as a lubricant itself.

[0021] The surprising discovery here is that when both chains are short with groups containing less than 6 carbon atoms on nitrogen or below 6 carbon atoms on nitrogen did not serve the purpose for the engine oils. However, when at least one substituent has longer chain groups on nitrogen or phosphorus with at least 9 carbon atoms, the complex possesses excellent performance especially as a lubricant or as a compound within a lubricant mixture. According to the invention L can preferably be selected from a group consisting of one bidentate ligand, one monodentate ligand / or two separate monodentate ligands. This enhances the solubility of the complex, especially in oil.

[0022] The coordinating atoms are S, N, P and / or 0 - in other words sulfur, nitrogen, phosphor and / or oxygen.

[0023] M is any lanthanide species or mixture of those, except Pm. Said lanthanides mentioned before are thus a group of metal species consisting of lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and / or lutetium.

[0024] Further advantageous embodiments are subject matter of the dependent claims.

[0025] In a preferred embodiment M is lanthanum or a mixture of metal species comprising lanthanum.

[0026] It is of advantage when R = PR1 R2, wherein R1 and / or R2 comprises 1 -50 carbon atoms.

[0027] It is further of advantage when R = C-NR1R2and / or R = PR1R2with R1comprises at least 9 to 50 carbon atoms, and R2contains 1 to 50 carbon atoms.

[0028] Each R1 and R2 can preferably consist of a linear molecule structure.

[0029] Additionally, or alternatively R1 and / or R2 may comprise at least one cyclic molecule structure, preferably at least one aromatic molecule structure.

[0030] The molecule structure of the compound may further be provided with R1 and / or R2, preferably both R1 and R2, consist of a branched or linear molecular structure.

[0031] R1 and R2 groups are preferably interconnected, more preferably by forming a cyclic molecule structure, wherein still more preferably R1 and R2 are interconnected by at least 9 to 72 carbon atoms.

[0032] In a further preferred embodiment R1 and / or R2, preferably both R1 and R2, are linear or branched hydrocarbon chains containing 10-36 carbon atoms. It is further preferred if the binding atom(s) in L is or are nitrogen, sulfur, oxygen and / or phosphorus.

[0033] According to a further aspect of the invention the inventive compound can be used for the lubrication of a movable machine part as a standalone lubricant.

[0034] Therefore, the use of a compound being a metal complex with the formular: wherein R is either

[0035] PR1 R2 or

[0036] C-NR1 R2 wherein in at least one of R1 or R2 comprises of optionally substituted alkanes with nine or more carbon atoms or

[0037] R1 and R2 are interconnected by optionally substituted hydrocarbon chains with at least nine carbon atoms, wherein L can be selected from a group consisting of one bidentate ligand, one monodentate ligand / or two separate monodentate ligands, where coordinating atoms are S, N, P and / or 0 and wherein M is any lanthanide or a mixture of those, except Pm; as engine oil is a further part of the invention.

[0038] A preferred use is for the lubrication of a movable machine part as a standalone lubricant, if the metal complex is not a solid.

[0039] Further part of the invention is a lubricant mixture with the inventive compound as a lubricating additive, preferably a lubricant mixture serving as an engine oil or a gear oil. The additive is dissolved in a base oil, preferably a petroleum base oil, more preferably a group III base oil, according to API (American Petroleum Institute) definition.

[0040] Said inventive Lubricant mixture further comprises the compound being a metal complex with the formular: wherein R is either

[0041] PR1 R2 or

[0042] C-NR1 R2 wherein in at least one of R1 or R2 comprises of optionally substituted alkanes with nine or more carbon atoms or R1 and R2 are inter-connected by optionally substituted hydrocarbon chains with at least nine carbon atoms, wherein L can be selected from a group consisting of one bidentate ligand, one monodentate ligand / or two separate monodentate ligands, where coordinating atoms are S, N, P or 0 and M is any lanthanide and / or a mixture of those, except Pm,

[0043] In a preferred embodiment the concentration of the lubricant in said mixture is at least less than 5.0% by weight and preferably more than 0.05 % by weight.

[0044] Brief Description of the Drawings

[0045] The compound according to the invention is described in more detail herein below by way of exemplary embodiments and with reference to the attached drawings, in which:

[0046] Fig. 1 shows a schematic view of the test conditions for the VKA-Test;

[0047] Fig. 2 shows two results of a wear analysis of the surface taken with means of optical microscopy a) with base oil and b) with 0.7 % by weight of the novel lanthanum complex in the base oil; and

[0048] Fig. 3 shows a graph representing a Weibull analysis of base oil and of different lubricant mixtures of a base oil with different concentrations of the novel lubricating complex. Description of Embodiments

[0049] In the following description certain terms are used for reasons of convenience and are not to be interpreted as limiting. The terms Tight”, “left”, “up”, “down”, “under" and “above" refer to directions in the figures. The terminology comprises the explicitly mentioned terms as well as their derivations and terms with a similar meaning.

[0050] Two embodiments of the invention are described below:

[0051] A Preparation of the complex

[0052] Ditridecylamine (39.72 g, 104.0 mmol) was put under vacuo to remove trace volatile low molecular weight amines. Ethanol (100 mL) was added, and all was cooled to 0°C and the mixture was degassed. Carbon disulfide (8.40 g, 110 mmol) was added by syringe under argon. Separately, NaOH pellets (4.20 g, 105 mmol) were dissolved in ethanol (100 mL), and the solution was degassed. This solution was added dropwise to the amine-CS2 solution. Stirring of the yellow solution was continued for 1 h at r.t.

[0053] Lanthanum chloride (LaCh .7H2O, 12.82 g, 34.5 mmol) was dissolved in ethanol (80 mL) and this was added dropwise to the NaC DTC solution. A fine precipitate of NaCI formed and the product oiled out as well. After stirring for 2 h, a solution of 2,2’-bipyridine (5.38 g, 34.4 mmol) in ethanol (30 mL) was added dropwise to the ethanolic emulsion / suspension. The mixture turned yellowish. The volatiles were evaporated under vacuo and toluene (100 mL) was added. The reaction mixture was transferred to a separatory funnel and vigorously shaken with water (30 mL). After standing for 30 minutes, the bottom layer was drained, as well as a small part of the organic layer which contains insoluble organic-inorganic byproducts. The organic layer was vacuum-dried (2 mbar / 120°C) to afford 56.0 g (97 % from theory) of LaC DTC-bipy - further referred to as LaDTC. This complex can be used as standalone lubricant.

[0054] B Preparation of a liquid lubricant mixture

[0055] The complex LaC DTC-bipy was dissolved at different dosages in a high-quality petroleum base oil (API group III base oil; CAS 64742-54-7) with a kinematic viscosity at 100°C of 6 cSt. The base oil is a mixture of saturated Hydrocarbons (C20-C50) without impurities of metals or hetero-elements like phosphorus or sulphur. The dosages of the Lanthanum complex of Example 1 were as following: 0.4%, 0.7%, 2.0% by weight.

[0056] C Tribological tests

[0057] For the tribological tests the Four-Ball-Tester (DIN 51350) - also called VKATest - was chosen. The concept of this test is shown in Fig. 1 . A defined load is applied to an arrangement of steel balls. The balls are standardized (DIN 5401 ) and made of 100Cr6 1.3505 bearing steel. The tests were performed at steady-state temperature. This was by design, to ensure only the energy, which is predominant in the tribological contact, is available for the activation of the additive, if such energy is needed at all.

[0058] The load of 400 N is distributed evenly over the three ball-to-bal I contacts. The resulting maximum Hertzian pressure is 3468.7 MPa at the beginning of the test. With such a high pressure these ball-to-ball contacts are very demanding. Due to the wear the contact area increases which results in a decreased pressure during the test. The speed of 1450 rpm results in a contact speed of 0.56 m / s. The tests were conducted for a duration of 1 hour each. After the tests, the balls were extracted, and the surfaces measured with laser scanning microscope.

[0059] Exemplary results are shown in Fig. 2. In this figure one can see an indentation of the ball surface either with the pure base oil herein referred to as sample 2 or with addition of the LaDTC -complex with a concentration of 0.7% by weight in the base oil herein referred to as sample 1 . The mean diameter of the deformation of the ball with a lubrication of sample 2 is 515 pm, wherein the mean diameter of the ball with a lubrication of sample 1 is 909 pm. Thus, the deformation by using sample 2 is significantly lower than the deformation with sample 1 . The wear volume of sample 1 is 0.956 x 106pm3wherein the wear volume of sample 2 is 10 x 106pm3, thus about 10 times higher than in sample 1. The nominal surface pressure EOT in sample 1 is 251 .4 MPa wherein the nominal surface pressure EOT in sample 2 is 782,5 MPa.

[0060] D Results

[0061] As can be determined by the aforementioned tribological test, the wear when using a liquid lubricant mixture said LaDTC-complex with 0.7% by weight in said base oil is significantly lower than in comparison with the pure base oil. Due to the constant load of 400 N with a smaller contact surface, a higher load-bearing capacity can also be observed. A statistical evaluation was conducted analogous to DIN 51819-3 using Weibull analysis.

[0062] Fig. 3 shows the Weibull evaluations for four test series, base oil, and base oil with 0.4%, 0.7% and 2.0% LaDTC. Each test series consists of three trials, with three tribological-relevant contacts between the stationary balls and the rotating ball. The wear volume was measured for each stationary ball and added to the Weibull analysis. According to the Weibull analysis, each measurement is assigned a probability of failure. For the regression lines the maximum likelihood estimation method was used, which generates meaningful results and is the industrial standard. The 90 % confidence boundaries were added for each series of tests. The distribution of the Weibull analysis is shown in Fig. 3. With a 90% probability the results of future trials are likely to be in the marked ranges. The typical Weibull Parameters [3 (Slope) and n (characteristic lifetime -63.2%) for all tests are listed in the following Table 1 .

[0063] Table 1: Weibull factors

[0064] All graphs in Fig. 3 show a slope bigger than one, which indicates a wear-based system, whereas a slope of one would signal a fatigue-based problem. A slope of less than one would occur when early failures are present.

[0065] Compared to the base oil - LaDTC enriched base oil shows a significant reduction in wear which represented by the characteristic lifetime n and the position of the graphs, in fact under these conditions it is almost impossible, that LaDTC generate wear level as the base oil. The biggest reduction in wear is achieved when 0.7% LaDTC is added to the base oil. The large slope value for LaDTC 2.0% is not unusual for wear determent tribological systems and results from a small spread in the results. This shows a change in action when different amounts of LaDTC are added to base oil and underlines the effectiveness of LaDTC to control the tribological system under these conditions.

Claims

Claims1 . A lubricant additive comprising or consisting of a metal complex with the for- mular:wherein R is eitherPR1 R2 orC-NR1 R2 wherein in at least one of R1 or R2 comprises of optionally substituted alkanes with nine or more carbon atoms or R1 and R2 are interconnected by optionally substituted hydrocarbon chains with at least nine carbon atoms, wherein L can be selected from a group consisting of one bidentate ligand, one monodentate ligand / or two separate monodentate ligands, where coordinating atoms are S, N, P and / or 0 and M is any lanthanide or a mixture of those, except Pm.

2. Additive according to claim 1 , wherein more preferably M is lanthanum or a mixture of metal species comprising lanthanum.

3. Additive according to one of the preceding claims, characterized in that R = PR1R2, wherein R1 and / or R2 comprises 1 -50 carbon atoms.

4. Additive according to one of the preceding claims, characterized in thatR = C-NR1R2and / or R = PR1R2with R1comprises at least 9 to 50 carbon atoms, and R2contains 1 to 50 carbon atoms.

5. Additive according to one of the preceding claims, characterized in that each R1 and R2 consist of a linear molecule structure.

6. Additive according to one of the preceding claims, characterized in that R1 and / or R2 comprise at least one cyclic molecule structure, preferably at least one aromatic molecule structure.

7. Additive according to one of the preceding claims, characterized in that R1 and / or R2, preferably both R1 and R2, consist of a branched molecule structure.

8. Additive according to one of the preceding claims, characterized in that, said R1and R2groups are interconnected, preferably by forming a cyclic molecule structure, wherein more preferably R1and R2are interconnected by at least 9 to 72 carbon atoms.

9. Additive according to one of the preceding claims, characterized in that, R1 and / or R2, preferably both R1 and R2, are linear or branched hydrocarbon chains containing 10-36 carbon atoms.

10. Use of a compound being a metal complex with the formular:wherein R is eitherPR1 R2 orC-NR1 R2 wherein in at least one of R1 or R2 comprises of optionally substituted alkanes with nine or more carbon atoms or R1 and R2 are interconnected by optionally substituted hydrocarbon chains with at least nine carbon atoms, wherein L can be selected from a group consisting of one bidentate ligand, one monodentate ligand / or two separate monodentate ligands, where coordinating atoms are S, N, P and / or 0. M is any lanthanide or a mixture of those, except Pm;as engine oil, preferably for the lubrication of a movable machine part as a standalone lubricant, if the metal complex is not a solid.11 . Lubricant mixture with a compound being a metal complex with the formular:wherein R is eitherPR1 R2 orC-NR1 R2 wherein in at least one of R1 or R2 comprises of optionally substituted alkanes with nine or more carbon atoms or R1 and R2 are interconnected by optionally substituted hydrocarbon chains with at least nine carbon atoms, wherein L can be selected from a group consisting of one bidentate ligand, one monodentate ligand / or two separate monodentate ligands, where coordinating atoms are S, N, P and / or 0 and M is any lanthanide or a mixture of those, except Pm, as a lubricating compound dissolved in a base oil, preferably a petroleum base oil, more preferably a group III base oil, according to API (American Petroleum Institute) definition.

12. Lubricant mixture according to claim 11 , wherein the concentration of the compound in said mixture is less than 5.0 % by weight.

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