Biodegradable hydraulic fluid based on linear and branched carboxylic acid complex ester

Abstract

The present invention relates to a by a method for operating a hydraulic system comprising pressurizing a hydraulic fluid in the hydraulic system where the hydraulic fluid comprises a complex ester obtainable by reacting - a polyol selected from ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butylene glycol, 1,3- butylene glycol, 2,3-butylene glycol, neopentyl glycol, trimethylol propane, trimethylol ethane, pentaerythritol, and dipentaerythritol; - a diacid selected from aliphatic C3-C12 dicarboxylic acids; - a linear monoacid selected from linear aliphatic C6-C22 monocarboxylic acids; and - a branched monoacid selected from branched aliphatic C6-C12 monocarboxylic acids. The invention also relates the a hydraulic fluid.

Description

[0001] Biodegradable hydraulic fluid based on linear and branched carboxylic acid complex ester

[0002] The present invention relates to a by a method for operating a hydraulic system comprising pressurizing a hydraulic fluid in the hydraulic system where the hydraulic fluid comprises a complex ester obtainable by reacting

[0003] - a polyol selected from ethylene glycol, 1 ,2-propylene glycol, 1 ,3-propylene glycol, 1 ,2-butylene glycol, 1,3- butylene glycol, 2,3-butylene glycol, neopentyl glycol, trimethylol propane, trimethylol ethane, pentaerythritol, and dipentaerythritol;

[0004] - a diacid selected from aliphatic C3-C12 dicarboxylic acids;

[0005] - a linear monoacid selected from linear aliphatic C6-C22 monocarboxylic acids; and

[0006] - a branched monoacid selected from branched aliphatic C6-C12 monocarboxylic acids.

[0007] The invention also relates the a hydraulic fluid. Combinations of preferred embodiments with other preferred embodiments are within the scope of the present invention.

[0008] There are many known hydraulic fluids for use in hydraulic systems which usually have mechanical components driven by pressurized hydraulic fluids. The specific requirements upon these hydraulic fluids vary depending on the application but typically include a need for adequate fluid stability, low viscosity at low temperatures, high viscosity index, and low friction.

[0009] It is also becoming increasingly important that the hydraulic fluids have minimal environmental impact on disposal or release from a hydraulic system. This applies in particular to offshore oil and gas drilling, hydraulic applications on ships, and other production activities where released hydraulic fluids has the potential to enter the environment.

[0010] A number of disadvantages, particularly environmental disadvantages, associated with many known hydraulic fluids are attributable to their use of oil, especially mineral oil or synthetic hydrocarbon oil. It would be advantageous to provide hydraulic fluids, which include environmentally friendly components, which not rely on mineral or synthetic hydrocarbon oil formulations in order to work effectively.

[0011] Object was to overcome these disadvantages, especially to find environmentally friendly, biodegradable hydraulic fluids with excellent cold temperature properties and high viscosity index.

[0012] The object was solved by a method for operating a hydraulic system comprising pressurizing a hydraulic fluid in the hydraulic system where the hydraulic fluid comprises a complex ester obtainable by reacting

[0013] - a polyol selected from ethylene glycol, 1 ,2-propylene glycol, 1 ,3-propylene glycol, 1 ,2-butylene glycol, 1,3- butylene glycol, 2,3-butylene glycol, neopentyl glycol, trimethylol propane, trimethylol ethane, pentaerythritol, and dipentaerythritol; - a diacid selected from aliphatic C3-C12 dicarboxylic acids;

[0014] - a linear monoacid selected from linear aliphatic C6-C22 monocarboxylic acids; and

[0015] - a branched monoacid selected from branched aliphatic C6-C12 monocarboxylic acids.

[0016] The objects were also solved by a hydraulic fluid as defined in any of the preceeding claims, where the hydraulic fluid comprises a complex ester obtainable by reacting

[0017] - the polyol selected from ethylene glycol, 1 ,2-propylene glycol, 1 ,3-propylene glycol, 1 ,2-butylene glycol, 1,3- butylene glycol, 2,3-butylene glycol, neopentyl glycol, trimethylol propane, trimethylol ethane, pentaerythritol, and dipentaerythritol;

[0018] - the diacid selected from aliphatic C3-C12 dicarboxylic acids;

[0019] - the linear monoacid selected from linear aliphatic C6-C22 monocarboxylic acids; and

[0020] - the branched monoacid selected from branched aliphatic C6-C12 monocarboxylic acids.

[0021] Typically, the hydraulic system comprises

[0022] - a pump for pressurizing the hydraulic fluid,

[0023] - a control unit for controlling an oil pressure, a flow direction, or a flow rate of a pumped hydraulic fluid; and

[0024] - a conversion unit for converting a controlled hydraulic pressure of the hydraulic fluid into mechanical power.

[0025] The pump is driven, for example, by an electric motor to generate a hydraulic pressure by pumping the hydraulic fluid from a first oil tank. The pump may be a hydraulic pump, such as a hydraulic gear pump, a hydraulic screw pump, a hydraulic vane pump, a hydraulic plunger pump. The hydraulic fluid pressure generated by the pump is, for example, 5 to 50 MPa.

[0026] The control unit includes, for example, a pressure control valve for controlling the hydraulic pressure, a directional control valve for controlling the flow direction, or a flow control valve for controlling the flow rate. The pressure control valve, for example, adjusts the hydraulic fluid pressure generated by the pump, and allows a part of the hydraulic fluid to escape to a second oil tank when the pressure measured by a pressure gauge reaches a certain value or more. The pressure control valve may be a relief valve, a pressure reducing valve, an unloader valve, a sequence valve, a counterbalance valve. The direction control valve is composed of, for example, an electromagnetic switching valve and a check valve. The flow control valve may be, for example, a throttle valve or a flow regulating valve. In these valves, a deceleration valve may be incorporated.

[0027] The conversion unit usually converts the hydraulic pressure to the power, for example, according to the flow rate controlled by the flow control valve. The conversion unit may be a hydraulic cylinder, a hydraulic motor or the like. Through control of the flow rate of the hydraulic fluid by the flow control valve, the movement speed of a hydraulic cylinder, a hydraulic motor or the like can be adjustable. The hydraulic cylinder may be of a single acting type, a double acting type, a special type or the like. The hydraulic motor may be a gear motor, a vane motor, a plunger motor, or the like.

[0028] The hydraulic fluid can be pressurized for example from 5 to 50 Mpa.

[0029] The complex ester is obtainable by reacting the polyol, the diacid, the linear monoacid and the branched monoacid, for example by an esterification reaction which may be catalyzed by esterification catalyst.

[0030] The esterification is typically carried out at a temperature range from 50 to 250°C. Water formed in the esterification can be removed by common methods, e.g. by distillation.

[0031] The esterification catalysts can be mineral acids (like sulfuric acid or phosphoric acid), organic sulfonic acids (like methanesulfonic acid and p-toluenesulfonic acid) and amphoteric catalysts (like titanium-, tin(ll), tin(IV) or zirconium compounds like tetraalkoxytitanium compounds, e.g. tetrabutoxytitanium, tin(ll) oxalate, and tin(IV)oxide). When the esterification catalyst is selected from organic acids or mineral acids, the esterification is preferably carried out at a temperature range from 50 to 160°C. If the esterification catalyst is selected from amphoteric catalysts, the esterification is preferably carried out at a temperature range from 100 to 250°C, more preferably from 120°C to 200°C.

[0032] The esterification catalyst can be used in an effective amount, typically in the range of from 0.05 to 10 wt%, more preferably 0.1 to 5.0 wt% based on the combined amount of acid component and the alcohol components.

[0033] The polyol is selected from ethylene glycol, 1 ,2-propylene glycol, 1 ,3-propylene glycol, 1 ,2-butylene glycol, 1,3- butylene glycol, 2,3-butylene glycol, neopentyl glycol, trimethylol propane, trimethylol ethane, pentaerythritol, and dipentaerythritol;. Mixtures of polyols are possible.

[0034] The polyol is preferably selected from neopentyl glycol, trimethylol propane, pentaerythritol, and dipentaerythritol. The polyol is in particular selected from neopentyl glycol and trimethylol propane. In a preferred form the polyol is neopentyl glycol. In another preferred form the polyol is trimethylol propane.

[0035] The diacid is selected from aliphatic C3-C12 dicarboxylic acids, such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, or dodenaedioic acid. Mixtures of diacids are possible.

[0036] The diacid is preferably selected from adipic acid. The linear monoacid is selected from linear aliphatic C6-C22 monocarboxylic acids. The linear monoacid is preferably selected from linear aliphatic Cs-C monocarboxylic acids. In another preferred form the linear monoacid is selected from linear aliphatic C10-C16 monocarboxylic acids.

[0037] Examples of the linear monoacid are pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, palmitic acid, heptadecanoic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, nonadecanoic acid, eicosanoic acid.

[0038] The linear monoacid is in particular lauric acid.

[0039] The branched monoacid selected from branched aliphatic C6-C12 monocarboxylic acids. Mixtures of branched monoacids are also possible. Examples of the branched monoacid are isohexanoic acid, isoheptanoic acid, isooctanoic acid, 2-ethylhexanoic acid, isononanoic acid, 3,5,5-trimethylhexanoic acid, and isodecanoic acid.

[0040] The branched monoacid is preferably selected from branched aliphatic Cs-Cg monocarboxylic acids, such as isooctanoic acid, 2-ethylhexanoic acid, isononanoic acid, and 3,5,5-trimethylhexanoic acid. The branched monoacid is in particular selected from 3,5,5-trimethylhexanoic acid.

[0041] The 3,5,5-trimethylhexanoic acid is often a main component of isononanoic acid. As used herein, isononanoic acid refers to one or more branched-chain aliphatic carboxylic acids with 9 carbon atoms. Embodiments of isononanoic acid may include 7-methyloctanoic acid, 6,6-dimethylheptanoic acid, 3,5,5-trimethylhexanoic acid,

[0042] 3.4.5-trimethylhexanoic acid, 2,5,5-trimethylhexanoic acid, 2,2,4,4-tetramethylpentanoic acid, and combinations thereof. In a preferred embodiment, isononanoic acid has as its main component greater than 90% of one of 7- methyloctanoic acid, 6,6-dimethylheptanoic acid, 3,5,5-trimethylhexanoic acid, 3,4,5-trimethylhexanoic acid,

[0043] 2.5.5-trimethylhexanoic acid, and 2,2,4,4-tetramethylpentanoic acid. The balance of the isononanoic acid may include other nine carbon carboxylic acid isomers and minor amounts of one or more contaminants. In another preferred embodiment, the isononanoic acid has as its main component greater than 90% of 3,5,5- trimethylhexanoic acid and even more preferably, the main component is greater than 95% 3,5,5- trimethylhexanoic acid.

[0044] The molar ratio of the branched monoacid to the linear monoacid can be from 3.5 : 1 to 1 : 1 .5, preferably from 2.7 : 1 to 1.3 : 1, and in particular from 2.2 : 1 to 1.6 : 1.

[0045] The complex ester may comprise at least 10 mol% preferably at least 15 mol%, and in particular at least 20 mol% of the polyol, such as neopentyl glycol or trimethylol propane. The complex ester may comprise up to 60 mol% preferably up to 55 mol%, and in particular up to 50 mol% of the polyol, such as neopentyl glycol or trimethylol propane.

[0046] The complex ester may comprise 10 - 60 mol%, preferably 15 - 50 mol%, and in particular 20 - 45 mol% of the polyol, such as neopentyl glycol or trimethylol propane.

[0047] The amounts of the building blocks of the complex ester (e.g. the polyol, the diacid, the linear monoacid, and the branched monoacid) usually refer to the amount which is reacted to obtain the complex ester, e.g. in the esterification reaction which may be catalyzed by the esterification catalyst.

[0048] The complex ester may comprise at least 0.2 mol% preferably at least 0.5 mol%, and in particular at least 1 .0 mol% of the diacid, such as the adipic acid.

[0049] The complex ester may comprise up to 27 mol% preferably up to 35 mol%, and in particular up to 40 mol% of the diacid, such as the adipic acid.

[0050] The complex ester may comprise 0.2 - 40 mol%, preferably 0.5 - 35 mol%, and in particular 1 .0 - 28 mol% of the diacid, such as the adipic acid.

[0051] The complex ester may comprise at least 3 mol% preferably at least 6 mol%, and in particular at least 9 mol% of the linear monoacid, such as linear aliphatic Cs-C monocarboxylic acids.

[0052] The complex ester may comprise up to 45 mol% preferably up to 35 mol%, and in particular up to 30 mol% of the linear monoacid, such as linear aliphatic Cs-C monocarboxylic acids.

[0053] The complex ester may comprise 3 - 45 mol%, preferably 6 - 35 mol%, and in particular 9 - 30 mol% of the linear monoacid, such as lauric acid.

[0054] The complex ester may comprise at least 10 mol% preferably at least 15 mol%, and in particular at least 20 mol% of the branched monoacid, such as branched aliphatic Cs-Cg monocarboxylic acids.

[0055] The complex ester may comprise up to 65 mol% preferably up to 60 mol%, and in particular up to 55 mol% of the branched monoacid, such as branched aliphatic Cs-Cg monocarboxylic acids.

[0056] The complex ester may comprise 10 - 65 mol%, preferably 15 - 60 mol%, and in particular 20 - 55 mol% of the branched monoacid, such as 3,5,5-trimethylhexanoic acid.

[0057] The complex ester may comprise - 10 - 60 mol% of the polyol, such as neopentyl glycol, trimethylol propane, pentaerythritol, or dipentaerythritol;

[0058] - 0.2 - 40 mol% of the diacid, such as the adipic acid;

[0059] - 3 - 45 mol% of the linear monoacid, such as linear aliphatic C8-C18 monocarboxylic acids; and

[0060] - 10 - 65 mol% of the branched monoacid, such as branched aliphatic Cs-Cg monocarboxylic acids; and where the components sum up to 100 wt%.

[0061] The complex ester may comprise

[0062] - 15 - 50 mol% of the polyol, such as neopentyl glycol, trimethylol propane, pentaerythritol, or dipentaerythritol;

[0063] - 0.5 - 35 mol% of the diacid, such as the adipic acid;

[0064] - 6 - 35 mol% of the linear monoacid, such as linear aliphatic C8-C18 monocarboxylic acids; and

[0065] - 15 - 60 mol% of the branched monoacid, such as branched aliphatic Cs-Cg monocarboxylic acids; and where the components sum up to 100 wt%.

[0066] The complex ester may comprise

[0067] - 20 - 45 mol% of the polyol, such as neopentyl glycol or trimethylol propane;

[0068] - 1 .0 - 28 mol% of the diacid, such as the adipic acid;

[0069] - 9 - 30 mol% of the linear monoacid, such as lauric acid; and

[0070] - 20 - 55 mol% of the branched monoacid, such as 3, 5,5-trimethyl hexanoic acid; and where the components sum up to 100 wt%.

[0071] The hydraulic fluid may comprise at least 5, 10, 20, 25, 30, 40, 50, 70, 80, 90, 95, 98 or 99 wt% of the complex ester. The hydraulic fluid comprises preferably at least 20 wt% of the complex ester. In another preferred form the hydraulic fluid comprises at least 95 wt% of the complex ester. The hydraulic fluid may comprise up to 100, 99, 95, or 90 wt% of the complex ester.

[0072] The hydraulic fluid usually comprises additives in addition to the complex ester. Suitable additives may be selected from viscosity index improvers, polymeric thickeners, corrosion inhibitors, detergents, dispersants, antifoam agents, dyes, wear protection additives, extreme pressure additives, anti-wear additives, friction modifiers, metal deactivators, pour point depressants.

[0073] The additives preferably used in hydraulic fluids include pour-point depressants, viscosity index improvers, defoamers, oxidation inhibitors, rust and corrosion inhibitors, and antiwear compounds

[0074] The total combined amount of the additive in the hydraulic fluid may include ranges of 0-25 wt%, or 0.01-20 wt%, or 0.1-15 wt% or 0.5-10 wt%, or 1-5 wt% of the hydraulic fluid. The viscosity index improvers include high molecular weight polymers that increase the relative viscosity of an oil at high temperatures more than they do at low temperatures. Viscosity index improvers include poly acrylates, polymethacrylates, alkylmethacrylates, vinylpyrrolidone / meth-acrylate copolymers, poly vinylpyrrolidones, polybutenes, olefin copolymers such as an ethylene-propylene copolymer or a styrene-butadiene copolymer or polyalkene such as RIB, styrene / acrylate copolymers and polyethers, and combinations thereof. The most common VI improvers are methacrylate polymers and copolymers, acrylate polymers, olefin polymers and copolymers, and styrenebutadiene copolymers. Other examples of the viscosity index improver include polymethacrylate, polyisobutylene, alpha-olefin polymers, alpha-olefin copolymers (e.g., an ethylenepropylene copolymer), polyalkylstyrene, phenol condensates, naphthalene condensates, a styrenebutadiene copolymer and the like. Of these, polymethacrylate having a number average molecular weight of 10000 to 300000, and alphaolefin polymers or alpha-olefin copolymers having a number average molecular weight of 1000 to 30000, particularly ethylene- alpha-olefin copolymers having a number average molecular weight of 1000 to 10000 are preferred. The viscosity index increasing agents can be added and used individually or in the form of mixtures, conveniently in an amount within the range of from > 0.05 to < 20.0 % by weight, in relation to the weight of the base stock.

[0075] Suitable polymeric thickeners include, but are not limited to, polyisobutenes (RIB), oligomeric co-polymers (OCPs), polymethacrylates (PMAs), copolymers of styrene and butadiene, or high viscosity esters (complex esters).

[0076] Corrosion inhibitors may include various oxygen-, nitrogen-, sulfur-, and phosphorus-containing materials, and may include metal-containing compounds (salts, organometallics, etc.) and nonmetal-containing or ashless materials. Corrosion inhibitors may include, but are not limited to, additive types such as, for example, hydrocarby I-, aryl-, alkyl-, arylalkyl-, and alkylaryl versions of detergents (neutral, overbased), sulfonates, phenates, salicylates, alcoholates, carboxylates, salixarates, phosphites, phosphates, thiophosphates, amines, amine salts, amine phosphoric acid salts, amine sulfonic acid salts, alkoxylated amines, etheramines, polyetheramines, amides, imides, azoles, diazoles, triazoles, benzotriazoles, benzothiadoles, mercaptobenzothiazoles, tolyltriazoles (TTZ-type), heterocyclic amines, heterocyclic sulfides, thiazoles, thiadiazoles, mercaptothiadiazoles, dimercaptothiadiazoles (DMTD-type), imidazoles, benzimidazoles, dithiobenzimidazoles, imidazolines, oxazolines, Mannich reactions products, glycidyl ethers, anhydrides, carbamates, thiocarbamates, dithiocarbamates, polyglycols, etc., or mixtures thereof.

[0077] Detergents include cleaning agents that adhere to dirt particles, preventing them from attaching to critical surfaces. Detergents may also adhere to the metal surface itself to keep it clean and prevent corrosion from occurring. Detergents include calcium alkylsalicylates, calcium alkylphenates and calcium alkarylsulfonates with alternate metal ions used such as magnesium, barium, or sodium. Examples of the cleaning and dispersing agents which can be used include metal-based detergents such as the neutral and basic alkaline earth metal sulphonates, alkaline earth metal phenates and alkaline earth metal salicylates alkenylsuccinimide and alkenylsuccinimide esters and their borohydrides, phenates, salienius complex detergents and ashless dispersing agents which have been modified with sulphur compounds. These agents can be added and used individually or in the form of mixtures, conveniently in an amount within the range of from > 0.01 to < 1.0 % by weight in relation to the weight of the base stock; these can also be high total base number (TBN), low TBN, or mixtures of high / low TBN.

[0078] Dispersants are additives that help to prevent sludge, varnish and other deposits from forming on critical surfaces. The dispersant may be a succinimide dispersant (for example N-substituted long chain alkenyl succinimides), a Mannich dispersant, an ester-containing dispersant, a condensation product of a fatty hydrocarbyl monocarboxylic acylating agent with an amine or ammonia, an alkyl amino phenol dispersant, a hydrocarbyl-amine dispersant, a polyether dispersant or a polyetheramine dispersant. In one embodiment, the succinimide dispersant includes a polyisobutylene-substituted succinimide, wherein the polyisobutylene from which the dispersant is derived may have a number average molecular weight of about 400 to about 5000, or of about 950 to about 1600. In one embodiment, the dispersant includes a borated dispersant. Typically, the borated dispersant includes a succinimide dispersant including a polyisobutylene succinimide, wherein the polyisobutylene from which the dispersant is derived may have a number average molecular weight of about 400 to about 5000. Borated dispersants are described in more detail above within the extreme pressure agent description.

[0079] Anti-foam agents may be selected from silicones, polyacrylates, and the like. The amount of anti-foam agent in the compositions described herein may range from > 0.001 wt.-% to< 0.1 wt.-% based on the total weight of the formulation. As a further example, an anti-foam agent may be present in an amount from about 0.004 wt.-% to about 0.008 wt.-%.

[0080] Suitable extreme pressure agent is a sulfurcontaining compound. In one embodiment, the sulfur-containing compound may be a sulfurised olefin, a polysulfide, or mixtures thereof. Examples of the sulfurised olefin include a sulfurised olefin derived from propylene, isobutylene, pentene; an organic sulfide and / or polysulfide including benzyldisulfide; bis-(chlorobenzyl) disulfide; dibutyl tetrasulfide; di-tertiary butyl polysulfide; and sulfurised methyl ester of oleic acid, a sulfurised alkylphenol, a sulfurised dipentene, a sulfurised terpene, a sulfurised Diels-Alder adduct, an alkyl sulphenyl N'N dialkyl dithiocarbamates; or mixtures thereof. In one embodiment, the sulfurised olefin includes a sulfurised olefin derived from propylene, isobutylene, pentene or mixtures thereof. In one embodiment the extreme pressure additive sulfur-containing compound includes a dimercaptothiadiazole or derivative, or mixtures thereof. Examples of the dimercaptothiadiazole include compounds such as 2,5- dimercapto-1 ,3,4-thiadiazole or a hydrocarbyl-substituted 2,5-dimercapto-1 ,3,4-thiadiazole, or oligomers thereof. The oligomers of hydrocarbyl-substituted 2,5-dimercapto-1 ,3,4-thiadiazole typically form by forming a sulfur-sulfur bond between 2,5-dimercapto-1 ,3,4-thiadiazole units to form derivatives or oligomers of two or more of said thiadiazole units. Suitable 2,5-dimercapto-1 ,3,4-thiadiazole derived compounds include for example 2,5-bis(tert- nonyldithio)-1 ,3,4-thiadiazole or 2-tert-nonyldithio-5-mercapto-1 ,3,4-thiadiazole. The number of carbon atoms on the hydrocarbyl substituents of the hydrocarbyl-substituted 2, 5-dimercapto-1, 3, 4-thiadiazole typically include 1 to 30, or 2 to 20, or 3 to 16. Extreme pressure additives include compounds containing boron and / or sulfur and / or phosphorus. The extreme pressure agent may be present in the compositions at 0 wt.-% to about 20 wt.-%, or at about 0.05 wt.-% to about 10.0 wt.-%, or at about 0.1 wt.-% to about 8 wt.-% of the composition.

[0081] Examples of anti-wear additives include organo borates, organo phosphites such as didodecyl phosphite, organic sulfur-containing compounds such as sulfurized sperm oil or sulfurized terpenes, zinc dialkyl dithiophosphates, zinc diaryl dithiophosphates, phosphosulfurized hydrocarbons and any combinations thereof.

[0082] Friction modifiers may include metal-containing compounds or materials as well as ashless compounds or materials, or mixtures thereof. Metal-containing friction modifiers include metal salts or metalligand complexes where the metals may include alkali, alkaline earth, or transition group metals. Such metal-containing friction modifiers may also have lowash characteristics. Transition metals may include Mo, Sb, Sn, Fe, Cu, Zn, and others. Ligands may include hydrocarbyl derivative of alcohols, polyols, glycerols, partial ester glycerols, thiols, carboxylates, carbamates, thiocarbamates, dithiocarbamates, phosphates, thiophosphates, dithiophosphates, amides, imides, amines, thiazoles, thiadiazoles, dithiazoles, diazoles, triazoles, and other polar molecular functional groups containing effective amounts of O, N, S, or P, individually or in combination. In particular, Mo- containing compounds can be particularly effective such as for example Mo-dithiocarbamates, Mo(DTC), Mo- dithiophosphates, Mo(DTP), Mo-amines, Mo (Am), Mo-alcoholates, Mo alcohol-amides, and the like.

[0083] Ashless friction modifiers may also include materials that contain effective amounts of polar groups, for example, hydroxyl-containing hydrocarbyl base oils, glycerides, partial glycerides, glyceride derivatives, and the like. Polar groups in friction modifiers may include hydrocarbyl groups containing effective amounts of O, N, S, or P, individually or in combination. Other friction modifiers that may be particularly effective include, for example, salts (both ash-containing and ashless derivatives) of fatty acids, fatty alcohols, fatty amides, fatty esters, hydroxyl- containing carboxylates, and comparable synthetic long-chain hydrocarbyl acids, alcohols, amides, esters, hydroxy carboxylates, and the like. In some instances, fatty organic acids, fatty amines, and sulfurized fatty acids may be used as suitable friction modifiers. Examples of friction modifiers include fatty acid esters and amides, organo molybdenum compounds, molybdenum dialkylthiocarbamates and molybdenum dialkyl dithiophosphates.

[0084] Suitable metal deactivators include benzotriazoles and derivatives thereof, for example 4- or 5- alkylbenzotriazoles (e.g. triazole) and derivatives thereof, 4,5,6,7-tetrahydrobenzotriazole and 5,5'- methylenebisbenzotriazole; Mannich bases of benzotriazole or triazole, e.g. 1-[bis(2-ethyl-hexyl) aminomethyl) triazole and 1-[bis(2- ethylhexyl) aminomethyl)benzotriazole; and alkoxy-alkylbenzotriazoles such as 1- (nonyloxymethyl)benzotriazole, 1-(1 -butoxyethyl) benzotriazole and 1-(1-cyclohexyloxybutyl) triazole, and combinations thereof. Additional non-limiting examples of the one or more metal deactivators include 1,2,4- triazoles and derivatives thereof, for example 3-alkyl(or aryl)-1, 2,4-triazoles, and Mannich bases of 1,2,4- triazoles, such as 1-[bis(2-ethylhexyl) aminomethyl -1, 2,4-triazole; alkoxyalkyl -1, 2,4-triazoles such as 1-(1-bu- toxyethyl)-1, 2,4-triazole; and acylated 3-amino-1, 2,4-triazoles, imidazole derivatives, for example 4,4'- methylenebis(2-undecyl-5-methylimidazole) and bis[(N-methyl)imidazol-2-yl]-carbinol octyl ether, and combinations thereof. Further non-limiting examples of the one or more metal deactivators include sulfur- containing heterocyclic compounds, for example 2-mercapto-benzothiazole, 2,5-dimercapto-1 , 3,4-thia-diazole and derivatives thereof; and 3,5-bis[di(2- ethylhexyl) aminomethyl]-1, 3,4-thiadiazolin-2-one, and combinations thereof. Even further non-limiting examples of the one or more metal deactivators include amino compounds, for example salicylidenepropylenediamine, salicylami-noguanidine and salts thereof, and combinations thereof. The one or more metal deactivators are not particularly limited in amount in the composition but are typically present in an amount of from about 0.01 to about 0.1, from about 0.05 to about 0.01, or from about 0.07 to about 0.1, wt- % based on the weight of the composition. Alternatively, the one or more metal deactivators may be present in amounts of less than about 0.1, of less than about 0.7, or less than about 0.5, wt.-% based on the weight of the composition.

[0085] Pour point depressants (PPD) include polymethacrylates, alkylated naphthalene derivatives, and combinations thereof. Commonly used additives such as alkylaromatic polymers and polymethacrylates are also useful for this purpose. Typically, the treat rates range from > 0.001 wt.-% to < 1 .0 wt.-%, in relation to the weight of the base stock.

[0086] Demulsifiers include trialkyl phosphates, and various polymers and copolymers of ethylene glycol, ethylene oxide, propylene oxide, or mixtures thereof.

[0087] The hydraulic fluid can be prepared by contacting the complex ester and the additives, e.g. by mixing.

[0088] The hydraulic fluid may have a kinematic viscosity at 40 °C of 1 to 2000 mm2 / s. The viscosity classification for hydraulic fluids is usually defined by ASTM D2422 (ISO STD 3448), which establishes 18 viscosity grades (ISO VG) in the range of 2 - 1500 mm2 / s.

[0089] The hydraulic fluid usually comprises less than 5, 3, 1 , or 0.5 wt% of water. Preferably, the hydraulic fluid usually comprises less than 1 wt% water. In another form the hydraulic fluid can be free of water.

[0090] The hydraulic fluid may comprises in addition to the complex ester a mineral oil, such as naphthenic, paraffinic or aromatic mineral oils. The hydraulic fluid may comprises at least 1, 5, or 10 wt% of the mineral oil, and up to 70, 50, or 30 wt% of the mineral oil. In a preferred form, the hydraulic fluid is free of the mineral oil. The hydraulic fluid may comprises in addition to the complex ester a carboxylic acid ester which is different from the complex ester. A suitable carboxylic acid ester is a monoester, diester, polyester, second complex ester, or mixture thereof. The carboxylic acid ester is more preferred a diester, polyester, or second complex ester. The second complex ester is different from the complex ester. The carboxylic acid ester may comprise a mixture of different carboxylic acid esters.

[0091] The carboxylic acid esters may comprise aliphatic, aromatic, or a mixture of aliphatic and aromatic alcohols and / or acids. In one form the carboxylic acid esters consists of aliphatic alcohols and aliphatic acids. In another form the carboxylic acid esters consists of aliphatic alcohols and aliphatic and / or aromatic acids.

[0092] The carboxylic acid esters may comprise saturated, unsaturated or a mixture of saturated and unsaturated alcohols and / or acids. In one form the carboxylic acid esters may comprise saturated alcohols and saturated acids. In one form the carboxylic acid esters may comprise saturated alphatic alcohols and saturated aliphatic acids.

[0093] Suitable carboxylic acid ester are obtainable by reacting

[0094] (I) at least one linear or branched C2-C24 monocarboxylic acid with at least one linear or branched C1-C20 monoalcohol (also called "monoester”) or;

[0095] (II) at least one linear or branched C2-C20 dicarboxylic acid with at least one linear or branched C1-C20 monoalcohol (also called "diester”)or;

[0096] (ill) at least one linear or branched C2-C24 monocarboxylic acid with at least one C2-C20 polyol having 2-10 hydroxyl group (also called "polyester”)or;

[0097] (iv) a mixture comprising at least one linear or branched C2-C24 monocarboxylic acid and at least one linear or branched C2-C20 dicarboxylic acid and at least one C2-C20 polyol having 2-10 hydroxyl group (also called "second complex ester”) or;

[0098] (v) at least one linear or branched C2-C20 dicarboxylic acid with at least one C2-C20 polyol having 2-10 hydroxyl group or;

[0099] (vi) a mixture comprising at least one linear or branched C2-C24 monocarboxylic acid and at least one linear or branched C2-C20 dicarboxylic acid and at least one linear or branched C1-C20 monoalcohol or;

[0100] (vii) a mixture comprising at least one linear or branched C2-C24 monocarboxylic acid and at least one linear or branched C2-C20 dicarboxylic acid and at least one C2-C20 polyol having 2-10 hydroxyl group and at least one C1-C20 monoalcohol.

[0101] In one form the carboxylic acid ester is a monoester obtainable by reacting at least one linear or branched C5-C20 monocarboxylic acid selected from the group consisting of pentanoic acid, iso-pentanoic acid, hexanoic acid, iso-hexanoic acid, heptanoic acid, iso-heptanoic acid, octanoic acid, iso-octanoic acid, nonanoic acid, iso-nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, palmitic acid, heptadecanoic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, nonadecanoic acid, eicosanoic acid with at least one linear or branched C1-C18 monoalcohol selected from the group consisting of methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, 1-octanol, 3-methyl-1 -butanol, nonanol, decanol, undecanol, dodecanol, tridecanol, tetradecanol, pentadecanol, hexadecanol, heptadecanol, octadecanol, iso-propanol, iso-butanol, 2-octanol, 3-octanol, iso-nonanol, iso-decanol, iso-undecanol, iso-dodecanol iso-tride-canol, iso-tetradecanol, iso-pentadecanol, iso-hexadecanol, iso-heptadecanol, iso-octadecanol, neo-pentanol , t- butanol, 2-methyl-2-butanol, 2,3-dimethyl-2-butanol, 2-methyl-2-pentanol, 3-methyl-3-pentanol, 3-ethyl-3-pentanol, 2,3-dimethyl-2-pentanol, 2,3-dimethyl-2- pentanol, 2,3-dimehtyl-2-pentanol, 2,3-dimethyl-3-pentaol, 2,3,4-tri-methyl-3-pentanol, 2-methyl-2-hexanol and 3-methyl-3-hexanol.

[0102] In another form the monoester is obtainable by reacting at least one linear or branched C12-C20 monocarboxylic acid with at least one linear or branched C6-C16 monoalcohol. In another form the monoester is obtainable by reacting at least one linear or branched C14-C18 monocarboxylic acid with at least one linear or branched C6-C12 monoalcohol. Examples for monosters are 2-ethylhexyl oleate, 2-ethylhexyl cocoate, 2-ethylhexyl palmitate, 2- ethylhexylstearate, and 2-ethylhexyl tallowate.

[0103] In another form the carboxylic acid ester is a diester obtainable by reacting

[0104] - at least one linear or branched C3-C12 dicarboxylic acid selected from the group consisting of malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, azelaic acid, sebacic acid, brassilic acid, docdecanedioic acid, diglycolic acid, 1,4-cyclohexanedicarboxylic acid, 1 ,3-cyclohexanedicarboxylic acid and 2,6-decahydro-naphthalenedicarboxylic acid with

[0105] - at least one branched C5-C14 monoalcohol selected from the group consisting of pentanol, hexanol, heptanol, iso-pentanol, iso-hexanol, iso-heptanol, 2-ethylhexanol,

[0106] 2-propylheptanol, 2-propyl-4-methyl-hexanol, 2-propyl-5-methyl-hexanol, 2-isopropyl-4-methyl-hexanol, 2- isopropyl-5-methyl-hexanol, 2-propyl-4,4-dimethylpentanol, 2-ethyl-2,4-dimethylhexanol, 2-ethyl-2-methyl- heptanol, 2-ethyl-2,5-dimethylhexanol, 2-iso-propyl-heptanol, 2-butyl-1 -octanol and 2-pentyl-1-nonanol.

[0107] In one form the diesters are obtainable by reacting at least one linear or branched C4-C8 di-carboxylic acid with at least one branched Ce-C monoalcohol. In one form the diesters are obtainable by reacting at least one linear or branched Ce-Cs dicarboxylic acid with at least one branched Ce-Cu monoalcohol. Examples for diesters are diisodecyl adipate, diisotridecyl adipate, di-(isopropylheptyl)-adipate (DPHA) and diisononyladipate (DNA).

[0108] In another form the carboxylic acid ester is the second complex ester obtainable by reacting a mixture comprising at least one linear or branched C5-C18 monocarboxylic acid selected from the group consisting of pentanoic acid, caproic acid, heptanoic acid, caprylic acid, nonanoic acid capric acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, oleic acid, palmitoleic acid and at least one linear or branched C3-C10 dicarboxylic acid selected from the group consisting of malonic acid, succinic acid, glutaric acid, adipic acid, heptanedioic acid, octananedioic acid, nonanedioic acid, decanedioic acid and at least one C2-C20 polyol having 2-10 hydroxyl group selected from the group consisting of ethylene glycol, 1 ,2-propylene glycol, 1 ,3-propylene glycol, 1,2-butylene glycol, 1,3-butylene glycol, 2, 3-butylene glycol neopentyl glycol, trimethylol propane, trimethylol ethane, pentaerythritol, sorbitol, and dipentaerythritol.

[0109] The hydraulic fluid may comprises at least 1, 5, or 10 wt% of the the carboxylic acid ester, and up to 70, 50, or 30 wt% of the the carboxylic acid ester.

[0110] Examples

[0111] TMP: 1,1,1 -trimethylol propane

[0112] NPG: neopentyl glycol

[0113] ADA: adipic acid

[0114] INA: 3,5,5-trimethylhexanoic acid (commercially available from BASF SE)

[0115] C12: lauric acid ( 99%)

[0116] Example 1 - Preparation of complex esters

[0117] The complex ester A was prepared by the general method as follows with the amounts of starting materials given in Table 1 :

[0118] A one-liter three necked flask was filled with adipic acid (6,95 g), trimethylolpropane (105,6 g), 3,5,5-trimethylhexanoic acid (238,2 g) and lauric acid (149,25 g). Stannous oxalate (Reaxis® C160, 0.28 % by weight) was added to this reaction mixture.

[0119] Nitrogen was bubbled through the mixture and the mixture was heated to 140 °C for a period of 3 hours while stirring. Then the mixture was heated to 200 °C for a period of 5 hours. A vacuum was gradually applied. When an acid value measured according to ISO 660 of below 0,5 mgKOH / g was reached, the remaining acids were distilled of by applying a vacuum at 230 °C. The mixture was cooled to 90 °C and water was added. The liquid reaction mixture was dried by applying a vacuum at 130 °C and filtered.

[0120] The other Esters B to K were prepared accordingly with the amounts listed in Table 1. Example 2 - Application properties of complex esters

[0121] The application properties of the complex esters were analyzed and are summarized in Table 1 .

[0122] The kinematic viscosity at 40 °C (KV40) or at 100 °C (KV100) was determined according to ASTM D 445. The viscosity index (VI) was calculated based on the KV40 and KV100, e.g. according to ASTM D2270. The pour point (PP) was determined according to ASTM D97.

[0123] Table 1. Composition and properties of complex esters a) Comparative example

[0124] The data demonstrated that the complex esters in Examples A to G have excellent low temperature propierties for hydraulic fluids as show by their low pour points. At the same time their viscosity index remained at a high level.

[0125] For comparison, when the linear monoacid lauric acid was omitted, then the pour point increased and the viscosity index decreased (Examples H, I and K).

[0126] Example 3 - Reduced Friction

[0127] The complex esters B and F from Example and and the comparative ester K were tested in the MTM (MiniTraction Machine) instrument using the so-called traction test mode. In this mode, the friction coefficient is measured at a constant mean speed of over a range of slide roll ratios (SRR) to give the traction curve. The disc is held in a bath contain-ing a test lubricant so that the contact between the ball and flat is fully immersed. The ball shaft is aligned with respect to the disk so as to prevent spin in the contact and the slide-roll ratio is controlled independently by driving both the ball and the disk with separate motors. The disc and ball used for the experiments were made of steel (AISI 52100), with a hardness of 750 HV and Ra < 0,02 pm. The diameter was 45,0 mm and 19,0 mm for the disc and the ball respectively. The tractions curves were run 38 Newton, 2000 mm / s speed and 70 °C temperature. The slide-roll ratio (“SRR") was varied from 0 to 50 percent and the traction coefficient (“T.C.”) measured.

[0128] The resulting diagram is shown in Figure 1.

[0129] The continuous line represents the data for the inventive Ester B, the doted line represents the data for the inventive Ester E, and the dashed line the data for the comparative Ester K. This demonstrated the improved friction properties of the inventive complex ester.

[0130] Example 4 - Hydraulic fluid formulations with complex esters

[0131] The complex esters A and C from Table 1 were be used to prepare the hydraulic fluid formulations listed in Table 2 and their properties analyzed. The thermal oxidative stability "RPVOT” was tested according to ASTM D2272. The Esters B to G can be formulated the same manner as hydraulic oil formulation.

[0132] Table 2. Hydraulic oil formulations rganox® L06: octylated phenyl-alpha-naphthylamine antioxidant, BASF SE.

[0133] Irganox® L135: liquid, high molecular weight phenolic antioxidant, BASF SE. Irgacor® L12: an alkenyl succinic acid half ester, corrosion inhibitor, BASF SE.

[0134] Irgamet® TTZ: a tolutriazole a metal deactivator, BASF SE.

[0135] I rgalube® 353: a dialkyl dithiophosphate derivative, an ashless EP / antiwear additive, BASF SE.

[0136] Example 5 - Biodegradability

[0137] The biodegradability was determined according to OECD standard 301 B for Ester B and Ester F which had the composition as shown in Table 1. For both compounds a biodegradability of >60% were found.

Claims

Claims1 . A method for operating a hydraulic system comprising pressurizing a hydraulic fluid in the hydraulic system where the hydraulic fluid comprises a complex ester obtainable by reacting- a polyol selected from ethylene glycol, 1 ,2-propylene glycol, 1 ,3-propylene glycol, 1 ,2-butylene glycol, 1 ,3-butylene glycol, 2,3-butylene glycol, neopentyl glycol, trimethylol propane, trimethylol ethane, pentaerythritol, and dipentaerythritol;- a diacid selected from aliphatic C3-C12 dicarboxylic acids;- a linear monoacid selected from linear aliphatic C6-C22 monocarboxylic acids; and- a branched monoacid selected from branched aliphatic C6-C12 monocarboxylic acids.

2. The method according to claim 1 where the molar ratio of the branched monoacid to the linear monoacid is from 3.5 : 1 to 1 : 1.5, preferably from 2.7 : 1 to 1.3 : 1 , and in particular from 2.2 : 1 to 1 .6 : 1 .

3. The method according to claim 1 or 2 where the branched monoacid is selected from branched aliphatic Cs- C9 monocarboxylic acids.

4. The method according to any of claims 1 to 3 where the branched monoacid is selected from 3,5,5- trimethylhexanoic acid.

5. The method according to any of claims 1 to 4 where the polyol is selected from neopentyl glycol, trimethylol propane, pentaerythritol, and dipentaerythritol.

6. The method according to any of claims 1 to 5 where the polyol is selected from neopentyl glycol or trimethylol propane.

7. The method according to any of claims 1 to 6 where the diacid is selected from adipic acid.

8. The method according to any of claims 1 to 7 where the monoacid is selected from linear aliphatic Cs-C monocarboxylic acids.

9. The method according to any of claims 1 to 8 where the monoacid is selected from lauric acid.

10. The method according to any of claims 1 to 9 where the complex ester comprises 10 - 65 mol%, preferably15 - 60 mol%, and in particular 20 - 55 mol% of the branched monoacid.11 . The method according to any of claims 1 to 10 where the complex ester comprises 10 - 60 mol% of the polyol;0.2 - 40 mol% of the diacid;3 - 45 mol% of the linear monoacid; and10 - 65 mol% of the branched monoacid; and where the components sum up to 100 wt%.

12. The method according to any of claims 1 to 10 where the complex ester comprises 15 - 50 mol% of the polyol;0.5 - 35 mol% of the diacid;6 - 35 mol% of the linear monoacid; and15 - 60 mol% of the branched monoacid; and where the components sum up to 100 wt%.

13. The method according to any of claims 1 to 12 where the hydraulic fluid comprises at least 20 wt% of the complex ester.

14. The method according to any of claims 1 to 13 where the hydraulic system comprises- a pump for pressurizing the hydraulic fluid,- a control unit for controlling an oil pressure, a flow direction, or a flow rate of a pumped hydraulic fluid; and- a conversion unit for converting a controlled hydraulic pressure of the hydraulic fluid into mechanical power.

15. A hydraulic fluid as defined in any of the preceeding claims, where the hydraulic fluid comprises a complex ester obtainable by reacting- the polyol selected from ethylene glycol, 1 ,2-propylene glycol, 1 ,3-propylene glycol, 1 ,2-butylene glycol, 1 ,3-butylene glycol, 2,3-butylene glycol, neopentyl glycol, trimethylol propane, trimethylol ethane, pentaerythritol, and dipentaerythritol;- the diacid selected from aliphatic C3-C12 dicarboxylic acids;- the linear monoacid selected from linear aliphatic C6-C22 monocarboxylic acids; and- the branched monoacid selected from branched aliphatic C6-C12 monocarboxylic acids.

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