Anti-wear additives and their use

Abstract

Use of dialkylphosphonocarboxylic acid esters as anti-wear additives.The use of dialkylphosphonocarboxylic acid esters of formula (1), wherein R1 is hydrogen or a C1-C4 alkyl group, R2 and R3 are C1-C4 alkyl groups, n represents a number from 6 to 9 as a wear protection additive in polyalkylene glycols. The use as an anti-wear additive can be, for example, in industrial applications such as polyglycol-based automatic transmission oils, refrigeration machine oil for hydrocarbon, NH3, and CO2 refrigerant applications for vehicle air conditioning systems and for heat pump applications, compressed air lubricants, and chain lubricants.

Description

[0001] Clariant International Ltd

[0002] Anti-wear additives and their use

[0003] Abstract

[0004] The present invention describes dialkylphosphonocarboxylic acid esters which can be used as neutral anti-wear additives in polyalkylene glycol-based engine and transmission oils. Advantages include the very low dosage rate and the replacement of conventional metal-containing sulfur compounds or branched-chain amine salts of phosphoric acid esters.

[0005] Background

[0006] The development of modem industry has led to increasingly demanding conditions for mechanical components. Working parts require improved friction reduction and wear resistance in harsh environments, especially at high temperatures and extreme pressures, to ensure operational reliability and safety. This requires the development of base oils and lubricant additives with superior tribological properties that can withstand these challenging conditions.

[0007] For decades, zinc dihydrocarbyl dithiophosphates (ZDDP) have been an integral part of mineral oil-based lubricant compositions and are valued for their wear-reducing properties. However, the production of zinc dithiophosphates is very complex and energy-intensive. ZDDP also reacts with air humidity to form zinc oxide and zinc sulfide, and these insoluble deposits can impair the oxidation stability and filterability of the oil used. Since zinc is very difficult to remove from the waste streams of the production plants, efforts are being made to limit the use of zinc compounds in lubricants.

[0008] Dialkyldithiophosphates can also be used ash-free, either in their neutral form or neutralized with a suitable amine. Even though these compounds do not contain zinc or molybdenum, the weight percentage of sulfur in these compounds is very high at approximately 10%.

[0009] These metal-containing and metal-free dithiophosphonates are mainly used in Group I-V base oils in combustion engines of automobiles, ships, or trains. The ash formation naturally contributes to fine dust pollution in the environment.Phosphoric acid esters can be used as wear protection additives in acidic form or neutralized with a long-chain amine. The advantages lie in their simple synthesis and handling. The best results are achieved by neutralization with secondary, branched amines. Since these compounds are organotoxic, their future use in some regions, such as Europe, is ruled out. In any case, these compounds contribute to the total acid number of the finished oils, which must be minimal in sensitive applications such as electromobility. Synthetic polyalphaolefins are primarily used as base oils for this class of substances. These are not rapidly biodegradable and can therefore only be used to a limited extent as "environmentally acceptable lubricants" (EAL) in special areas of application, such as shipping.

[0010] Tricresyl phosphate (TCP) is an excellent wear protection additive in hydrocarbons and ester oils, but the ortho-methyl groups are neurotoxic and must therefore be separated from the para- and meta-cresol compounds in a complex refining process. Triphenyl phosphate (TPP) and triphenyl phosphorothionate (TPPT) were used as substitute products on the market, but are now classified as endocrine disruptors and "substances of very high concern" (SVHC) and are being removed from commercial formulations by end users.

[0011] Dimercaptothiazoles and sulfur-bridged polymers are used as EP additives, but have the disadvantage of containing up to 30% sulfur by weight, which results in particularly high follow-up costs for disposal.

[0012] Methylene bis-dialkyldithiocarbamates also have a very high sulfur content of approx.

[0013] 30% and are mainly used as additives for gear oils, engine oils, and greases.

[0014] All of the above compounds have in common that they were developed primarily for mineral oils of groups I to V, for synthetic base oils such as polyalphaolefins (PAO) or for polar ester oils.

[0015] Ester oils have proven to be a popular choice for high-temperature applications and are widely used in aircraft engine oils, chain / steel belt oils, and greases. Their popularity is based on a combination of desirable properties: high thermal stability, low volatility, favorable viscosity-temperature behavior, excellent biodegradability, and reliable lubricity.However, the high polarity of ester oils poses a significant challenge. This property leads to competitive adsorption on metal surfaces, which may impair the tribological functions of conventional additives in polar ester oils. In addition, the industry faces a shortage of effective anti-wear additives, especially those suitable for high-temperature applications in ester oils.

[0016] Polyalkylene glycols have the advantage of occupying a polarity between the highly polar ester oils and non-polar polyalphaolefins. They are shear-stable, thermally resilient, and generally have a good viscosity index. Further advantages include a high flash point, low self-ignition, and low flammability. Many polyalkylene glycols also have a very favorable ecotoxicity profile, which makes them ideal for applications in ecologically sensitive areas.

[0017] Polyalkylene glycols also have other advantageous physical properties. For example, the heat capacity [kJ K’1L’1] and thermal conductivity [W rrr1K’1] of polyalkylene glycols are generally higher than those of polyalphaolefins with comparable viscosity. Both properties are highly significant for the development of innovative cooling and lubricant concepts with improved energy efficiency and heat transfer, as required in the field of electromobility, for example.

[0018] In view of these challenges, there is an urgent need to provide novel additives that ensure excellent friction and wear protection and can be used in alternative base oils, such as polyalkylene glycols. These additives should also be as ash-free as possible, i.e., free of zinc, molybdenum, or other metallic elements, and have a reduced nitrogen and sulfur content to prevent the emission of their climate-damaging oxides after the end of their useful life. New types of additives should also be chemically neutral in order to meet the increased property requirements of new machine, industrial, and gear oils, such as dielectricity. Additional tasks include compliance with Ell labeling regulations and the provision of wear protection additives from renewable sources.

[0019] These new formulations must exhibit excellent tribological properties, especially at elevated temperatures, in order to meet the evolving requirements of modern industrial applications. The development of such additives represents a significant opportunity for progress in the field of lubricant technology.Short-chain dialkylphosphonocarboxylic acid esters as wear protection additives are known from the literature.

[0020] EP 3492563 describes formulations of refrigeration oils containing short-chain dialkylphosphonic acid esters as wear protection additives. The wear values listed in the document are exceeded by other additives from the same test series. Such short-chain variants can convert into eye-irritating compounds during use and must therefore be replaced for occupational health reasons.

[0021] EP 0510633 describes a lubricant composition for refrigeration machines that use 1,1,1,2-tetrafluoroethane (HFC-134a) as a refrigerant. The organic dialkylphosphonocarboxylic acid esters listed there, which have a maximum carbon chain length of propionates, can be used as a pure substance or as an additive to base oils, such as polyalkylene glycols. Tests were carried out at a dosage of 1.0%. The dialkylphosphonocarboxylic acid esters described in EP 0510633 are soluble in oilsoluble polyalkylene glycols with an excess of propylene oxide to ethylene oxide.

[0022] DE 69332096 describes additives from the phosphonate product class. For example, ethyl 3-diethylphosphonopropionate is used in a concentration of 2% by weight in a polyester of aliphatic polyhydric alcohol with linear or branched fatty acids with 3 to 12 carbon atoms.

[0023] The dialkylphosphonocarboxylic acid esters described in the literature have in common that the carbon chain between phosphonate phosphorus and carbonyl carbon comprises a maximum of two methylene groups.

[0024] Surprisingly, it has now been found that dialkylphosphonocarboxylic acid esters of formula (1) with a medium-sized carbon backbone exhibit significantly higher lubricating performance in polyalkylene glycols than the prior art.

[0025] The subject of the invention is therefore the use of dialkylphosphonic acid esters of formula (1)

[0026]

[0027] where

[0028] R1 is hydrogen or a C1 -C4 alkyl group,

[0029] R2 and R3 independently represent a C1-C4 alkyl group, and

[0030] n for a number from 6 to 9

[0031] as a wear protection additive in polyalkylene glycols.

[0032] Another subject of the invention is a process for reducing wear by using a lubricant containing polyalkylene glycols, in which a dialkylphosphonocarboxylic acid ester of formula (1)

[0033]

[0034] where

[0035] R1 is hydrogen or a C1 -C4 alkyl group,

[0036] R2 and R3 independently represent a C1-C4 alkyl group, and

[0037] n represents a number from 6 to 9

[0038] is added.

[0039] Another subject of the invention is a lubricant which, in addition to polyalkylene glycols, contains at least one dialkylphosphonocarboxylic acid ester of formula (1)

[0040]

[0041] where

[0042] R1 is hydrogen or a C1 -C4 alkyl group,

[0043] R2 and R3 independently represent a C1-C4 alkyl group, and

[0044] n represent a number from 6 to 9.

[0045] The invention thus relates to a lubricant containing polyalkylene glycols as a base. Base means that the lubricant consists predominantly of polyalkylene glycols, generally more than 90% by weight. The described use or process is carried out in a lubricant of this type.

[0046] In formula (1), R1 preferably represents hydrogen or ethyl, in particular hydrogen.

[0047] In formula (1), R2 and R3 independently represent preferably methyl or ethyl. In a particularly preferred embodiment, R2 represents methyl. In a further particularly preferred embodiment, R3 represents ethyl.

[0048] In formula (1), n preferably represents 8 or 9, particularly preferably 8.

[0049] Preferably, in compound (1), R1 represents hydrogen and ethyl, R2 and R3 represent methyl and ethyl, and n represents 8 and 9.

[0050] In the compound (1), R1 is preferably hydrogen and ethyl, R2 is methyl, R3 is ethyl, and n is 8 and 9.

[0051] In particular, in compound (1), R1 preferably represents hydrogen, R2 represents methyl, R3 represents ethyl, and n represents 8.In contrast to short-chain dialkylphosphonocarboxylic acid esters, medium-chain derivatives with a total chain length of 8-12 carbon atoms are also non-irritating to the skin and eyes and are therefore classified as non-hazardous to health.

[0052] The dialkylphosphonocarboxylic acid esters according to the invention can be produced by the radical phosphonylation of dialkyl phosphite on unsaturated compounds (e.g., according to US3101325, column 2, line 55 ff), such as diethyl phosphite on 9-decenoic acid methyl ester, 10-undecenoic acid methyl ester, or 10-dodecenoic acid methyl ester. Polyalkylene glycols are obtained by the basic or multimetallic cyanide compound-catalyzed addition of alkylene oxides to monohydric or polyhydric alcohols or amines. The addition can be blockwise or random. The extent of the addition, i.e., the molecular weight of the final product, determines the kinematic viscosity of the compounds obtained. Monohydric alcohols such as methanol or butanol, but also polyhydric alcohols such as ethylene glycol, propylene glycol, glycerin, or trimethylolpropane can act as alcohols. Ethylene oxide (C2H2O), propylene oxide (C3H6O) or butylene oxide (C4H8O) can be used as alkylene oxides; higher homologous alkylene oxides are possible but less commonly used.

[0053] The base oils to which the compound of formula (1) is added are preferably polyalkylene glycols produced by the addition of ethylene oxide, propylene oxide, or both to methanol, butanol, ethylene glycol, propylene glycol, glycerin, or trimethylolpropane.

[0054] One or more terminal hydroxy functions of the polyalkylene glycols produced in this way can be converted into an ether function by subsequent alkylation with alkyl halide or dimethyl sulfate.

[0055] Examples

[0056] Polyalkylene glycols are used as base oils in the examples.

[0057] The ISO VG system, which comprises a total of 18 viscosity classes, is authoritative for the classification of industrial oils. This classification applies to all lubricating oils, except for engine and transmission oils for combustion motor vehicles. The classification isbased on the kinematic viscosity at 40°C, with deviations of up to 10% from the center viscosity permitted. The scale ranges from very thin oils (ISO VG 2) to highly viscous oils (ISO VG 1500). Most machine oils have a viscosity range of 20 to 320 mm2 / s at 40°C.

[0058] Table 1 provides an overview of the composition and kinematic viscosity of the base oils used. The viscosity at 40°C was determined using the STABINGER method in accordance with ASTM D 7042.

[0059] Table 1: Composition and classification of polyalkylene glycol-based base oils

[0060]

[0061] EO = ethylene oxide; PO = propylene oxide

[0062] Table 2 provides information about the wear protection additives of the dialkylphosphonocarboxylic acid ester type used. Examples 1, 2, and 3 reflect the state of the art, while examples 4, 5, and 6 are products with medium chain length.

[0063] Table 2: State-of-the-art anti-wear additives and dialkyl phosphonocarboxylic acid esters according to the invention

[0064]

[0065] Examples 4-6 and the examples from the prior art were each dissolved in the base oils at 0.2% by weight and then subjected to an application test using the four-ball apparatus test (DIN 51350-3) (see Table 3).

[0066] Table 3: Testing of dialkylphosphonocarboxylic acid esters in various base oils

[0067]

[0068] Four-ball test according to DIN 51350-3 (load 300 N, time 1 h, rotation 1450 rpm); data in mm Abrasion;

[0069] As can be seen from Table 3, medium-chain dialkylphosphonic acid esters provide better wear protection in various polyalkylene glycols than the short-chain variants known from the literature. This effect occurs in a wide viscosity range of various polyalkylene glycols based on different starting alcohols and ratios of ethylene oxide topropylene oxide. ISO VG classes 15-1000 are suitable, ISO VG classes 46-1000 are preferably suitable, and ISO VG classes 68-1000 are particularly preferably suitable.

Claims

Claims1. Use of dialkylphosphonic acid esters of formula 1 ,whereR1 is hydrogen or a C1 -C4 alkyl group,R2 and R3 independently represent a C1-C4 alkyl group, andn represents a number from 6 to 9as a wear protection additive in polyalkylene glycols.

2. Use according to claim 1 , wherein R1 represents hydrogen or ethyl, in particular hydrogen.

3. Use according to claim 1 and / or 2, wherein R2 and R3 independently represent methyl or ethyl.

4. Use according to one or more of claims 1 to 3, wherein R2 is methyl.

5. Use according to one or more of claims 1 to 4, wherein R3 is ethyl.

6. Use according to one or more of claims 1 to 5, wherein n is 8 or 9, particularly preferably 8.

7. Use according to claim 1 , whereinR1 represents hydrogen, R2 represents methyl, R3 represents ethyl, and n represents 8, orR1 is hydrogen, R2 is methyl, R3 is ethyl, and n is 9, orR1 is ethyl, R2 is methyl, R3 is ethyl, and n is 8.

8. Use according to one or more of claims 1 to 7, wherein the polyalkylene glycols were produced by the addition of ethylene oxide, propylene oxide, or both to methanol, butanol, ethylene glycol, propylene glycol, glycerin, or trimethylolpropane.

9. Use according to one or more of claims 1 to 8 as a wear protection additive in industrial applications.

10. Use according to one or more of claims 1 to 8 as wear protection additives in automatic transmission fluids.

11. Use according to one or more of claims 1 to 8 as wear protection additives in refrigeration machine oil for hydrocarbon, NH3 and CO2 refrigerant applications for vehicle air conditioning systems and for heat pump applications.

12. Use according to one or more of claims 1 to 8 as wear protection additives in polyglycol-based compressed air lubricants.

13. Use according to one or more of claims 1 to 8 as wear protection additives in polyglycol-based chain lubricants.

14. Method for reducing wear by using a lubricant containing polyalkylene glycols, wherein a dialkylphosphonocarboxylic acid ester of formula (1)whereR1 is hydrogen or a C1 -C4 alkyl group,R2 and R3 independently represent a C1-C4 alkyl group, andrepresents a number from 6 to 9is added.

15. Lubricant which, in addition to polyalkylene glycols, contains at least one dialkylphosphonocarboxylic acid ester of formula (1 )whereR1 is hydrogen or a C1 -C4 alkyl group,R2 and R3 independently of one another represent a C1-C4 alkyl group, and n is a number from 6 to 9.

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