Use of epoxides as stabilizers in phosphate ester electrohydraulic control fluids

Abstract

A method for stabilizing phosphate ester-based electrohydraulic control (EHC) fluids. The method comprises incorporating one or more epoxide compounds to the phosphate ester based EHC fluid, wherein the one or more epoxide compounds comprises phenylglycidyl ether type epoxy compounds, alkylglycidyl ether type epoxy compounds, glycidyl ester type epoxy compounds, aryl oxirane compounds, alkyl oxirane compounds, alicyclic epoxy compounds, epoxidized fatty monoesters, or epoxidized vegetable oils. The phosphate ester based EHC fluid is a tert-butylphenylphosphate (TBPP) based EHC fluid comprising a blend of p-t-butylphenyldiphenyl phosphate, bis(p-t-butylphenyl) phenyl phosphate, tris-tert-butylphenylphospate and triphenyl phosphate.

Description

[0001] Docket No.: P00300090-US-PSP

[0002] TITLE

[0003] Use of Epoxides as Stabilizers in Phosphate Ester Electrohydraulic Control Fluids

[0004] FIELD OF INVENTION

[0005] The present invention relates generally to epoxides as stabilizers in phosphate ester Electrohydraulic Control Fluids (EHC fluids) and applications thereof in turbines, such as turbines used in electrical power stations, power plants, turbine control systems, and the like.

[0006] BACKGROUND OF THE INVENTION

[0007] EHC fluids are specialized hydraulic fluids commonly found in industrial machinery, power plants, and aerospace applications. For example, EHC fluids may be used to operate the valves controlling the steam flow to the turbines in electrical power stations. Due to the high fire risk associated with very hot surfaces and the severe consequences of fire in power plants, it. is desirable to use fire resistant fluids in the EHC application. Aryl phosphate ester fluids are the most fire resistant of the possible fluid technologies used for EH C fluids and are therefore desirable for power plant operators who wish to minimize the risk of fire as much as possible.

[0008] In addition to being fire resistant, EHC fluids must maintain low total acid number (TAN) and high volume resistivity (high electrical resistance) to ensure effective operation. Low TAN is required to resist chemical corrosion and high volume resistivity is required to resist galvanic corrosion. Low TAN is also required to maintain fluid lifetime since high TAN is known to accelerate hydrolysis of the phosphate ester fluid, leading to fluid degradation and system performance issues.

[0009] For many years, EHC fluids based on trixylylphosphate (TXP) have been the industry standard. However, these TXP based EHC fluids are under increased scrutiny from regulatory agencies and environmental working groups. As a result of TXP based EHC fluids’ recent regulatory issues surrounding its reprotoxicity, TXP based EHC fluids are being phased out in many parts of the world and are being replaced with EHC fluids based on tert-butylphenylphosphate (TBPP). However, as is illustrated in Fig. 1, compared to TXP based EHC fluids, EHC fluidsDocket No.: P00300090-US-PSP

[0010] based on TBPP are more prone to hydrolysis. That is, TXP based EHC fluids are inherently more resistant to hydrolysis than TBPP based EHC fluids making TXP based EHC fluids easier to maintain in service.

[0011] Carbodiimide additives are known to stabilize various types of fluids to prevent fluid hydr olysis. Many of these carbodiimide additives also have suitable toxicity profiles. Nevertheless, as is illustrated in Fig. 2, when added to TBPP based EHC fluids, the carbodiimide additives adversely affect volume resistivity, making them unsuitable additive candidates for TBPP based EHC fluids.

[0012] EHC fluids may also include epoxide additives. Some epoxide additives are known to stabilize fluids and polymers, as exemplified by US 3,723,320 which discloses the use of 3,4-epoxycyclohexylmethyl-3,4- epoxycyclohexane carboxylate for the stabilization of alkyl phosphate ester aircraft hydraulic fluids; however, it is unknown whether such epoxide additives adversely affect volume resistivity since US 3,723,320 provides no fluid volume resistivity data, nor does it provide any examples of the epoxide additives’ use in arylphosphate esters.

[0013] Traditionally, to measure resistance to hydrolysis of a fluid, the DIN EN 14833 test is used as a test parameter in EHC fluid specifications. However, the severity of the DIN EN 14833 is insufficient to differentiate between the long-term resistance to hydrolysis of different formulations of phosphate ester fluids.

[0014] As such, there is an increased demand for EHC fluids that are environmentally friendly yet maintain their performance criteria. That is, there is a need for EHC fluids that have an increased resistance to TAN growth and fluid hydrolysis to match or exceed the TAN growth and fluid hydrolysis of TXP based fluids. In addition, there is an increased need for a test that accurately tests the long term hydrolytic stability of EHC fluids. These needs are met by the presently disclosed invention. In particular, it was surprisingly found in accordance with the present disclosure that a new additive technology for phosphate ester based EHC fluids comprising 3,3-epoxycyclohexylmethyl 3,3-epoxycyclohexanecarboxylate is capable of stabilizing the EHC fluids while suppressing TAN and hydrolysis and extending fluid lifetime while maintainingDocket No.: P00300090-US-PSP

[0015] important fluid parameters such as volume resistance, foam and air entrainment, and having a suitable toxicity profile. Further, in accordance with the present disclosure, an alternative test has been developed which is able to test long term hydrolytic stability of EHC fluids.

[0016] SUMMARY OF INVENTION

[0017] According on one aspect of the present invention, a method of stabilizing a phosphate ester based electrohydraulic control fluid may be provided. The method may comprise adding one or more epoxide compounds to the phosphate ester based electrohydraulic control fluid. The one or more epoxide compounds may comprise phenylglycidyl ether type epoxy compounds, alkylglycidyl ether type epoxy compounds, glycidyl ester type epoxy compounds, ary l oxirane compounds, alkyl oxirane compounds, alicyclic epoxy compounds, epoxidized fatty monoesters, or epoxidized vegetable oils. The one or more epoxide compounds may be 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexane carboxylate. The one or more epoxide compounds may be added at a treat rate of 0.095 wt% based on the total weight of the phosphate ester based electrohydraulic control fluid. The phosphate ester based electrohydraulic control fluid may be a tert-butylphenylphosphate based electrohydraulic control fluid. The tertbutylphenylphosphate based electrohydr aulic control fluid may comprise a blend of p-t-butylphenyldiphenyl phosphate, bis(p-t-butylphenyl) phenyl phosphate, tris-tert-butylphenylphospate and triphenyl phosphate. The p-t-butylphenyldiphenyl phosphate may be from about 30 to about 40 wt%, the bis(p-t-butylphenyl) phenyl phosphate is from about 25 wt% to about 30 wt%, the tri-tert-butylphenylphosphate is from about 5 wt% to about 7 wt%, and the triphenyl phosphate is from about 0 wt% to about 25 wt%, based on the total weight of the tert-butylphenylphosphate based electrohydraulic control fluid. The tert-butylphenylphosphate based electrohydraulic control fluid may comprise a blend of mono t-butyl phenyl phosphate, bis t- butyl phenyl phosphate, tris-t-butyl phenyl phosphate, and triphenyl phosphate, where the mono t-butyl phenyl phosphate may be from about 70 wt% to up to about 100 wt%, the bis t-buty phenyl phosphate may be up to about 25 wt%, tris-t-butyl phenyl phosphate may be up to about 1 wt% and triphenyl phosphate may be less than 0.1 wt%, preferably 0 wt%, based on the total weight of the tert-butylphenylphosphate based electrohydraulic control fluid. The phosphate ester based electrohydraulic control fluid may further comprise adding one or more performance additives selected from the group consisting of antioxidants, metal deactivators, flow additives.Docket No.: P00300090-US-PSP

[0018] corrosion inhibitors, foam inhibitors, demulsifiers, pour point depressants, and any combination thereof. The one or more performance additives may be present in an amount ranging from 0.0001 wt% to 3 wt%, based on the total weight of the phosphate ester based electrohydraulic control fluid.

[0019] According to another aspect of the present invention, a phosphate ester based electrohydraulic control fluid composition may be provided. The composition may comprise a phosphate ester base fluid and one or more epoxide compounds. The one or more epoxide compounds may comprise phenylglycidyl ether type epoxy compounds, alkylglycidyl ether type epoxy compounds, glycidyl ester type epoxy compounds, aryl oxirane compounds, alkyl oxirane compounds, alicyclic epoxy compounds, epoxidized fatty monoesters, or epoxidized vegetable oils. The one or more epoxide compounds may be 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexane carboxylate. The one or more epoxide compounds may be present in an amount of 0.095 wt% based on the total weight of the phosphate ester based electrohydraulic control fluid composition. The phosphate ester base fluid may be a tert-butylphenylphosphate based fluid, wherein the tert-butylphenylphosphate based fluid comprises a blend of p-t-butylphenyldiphenyl phosphate, bis(p-t-butylphenyl) phenyl phosphate, tris-tert-butylphenylphospate and triphenyl phosphate. The p-t-butylphenyldiphenyl phosphate may be from about 30 to about 40 wt%, the bis(p-t-butylphenyl) phenyl phosphate is from about 25 wt% to about 30 wt%, the tri-tert-butylphenylphosphate is from about 5 wt% to about 7 wt%, and the triphenyl phosphate is from about 0 wt% to about 25 wt%, based on the total weight of the tert-butylphenylphosphate based fluid.

[0020] The preceding summary is not intended to restrict in any way the scope of the claimed invention. In addition, it is to be understood that both the foregoing general description and the following detailed description are exemplary' and explanatory only and are not restrictive of the invention, as claimed.

[0021] BRIEF DESCRIPTION OF THE FIGURES FIG. 1. shows the hydrolytic stability of commercially available EFIC fluid technologies.Docket No.: P00300090-US-PSP

[0022] FIG. 2 shows the hydrolytic stability of TBPP based EHC fluid with carbodiimide additives. FIG. 3 shows the hydrolytic stability of TBPP based EHC fluid with epoxide additives.

[0023] DETAILED DESCRIPTION

[0024] Embodiments of the present invention relate generally to a method of stabilizing a phosphate ester based electrohydraulic control (EHC) fluid and its composition. More particularly, the present invention relates to a method of stabilizing a phosphate ester based electrohydraulic control (EHC) fluid comprising adding one or more epoxide compounds to the phosphate ester based EHC fluid.

[0025] The one or more epoxide compounds may be phenylglycidyl ether type epoxy compounds, alkylglycidyl ether type epoxy compounds, glycidyl ester type epoxy compounds, aryl oxirane compounds, alky l oxirane compounds, alicyclic epoxy compounds, epoxidized fatty monoesters or epoxidized vegetable oils.

[0026] The phenylglycidyl ether type epoxy compounds may include phenylglycidyl ether and alkylphenylglycidyl ether. The alkylphenylglycidyl ether used herein may be one having 1 to 3 alkyl groups each containing 1 to 13 carbon atoms, preferably one having one alkyl group containing to 10 carbon atoms. The preferable alkylphenylglycidyl ethers include n-butylphenylglycidyl ether, i-butylphenylglycidyl ether, sec-butylphenylglycidyl ether, tert-butylphenylglycidyl ether, pentylphenylglycidyl ether, hexylphenylglycidyl ether, heptylphenylglycidyl ether, octylphenylglycidyl ether, nonylphenylglycidyl ether and decylphenylglycidyl ether.

[0027] In many embodiments, the alkylglycidyl ether type epoxy compounds may include decylglycidyl ether, undecylglycidyl ether, dodecylglycidyl ether, tridecylglycidyl ether, tetradecylglycidyl ether, 2-ethylhexylglycidyl ether, neopentylglycoldiglycidyl ether, trimethylolpropane triglycidyl ether, pentaerythritol tetraglycidyl ether, 1,6-hexadiol diglycidyl ether, sorbitol polyglycidyl ether, polyalkyleneglycol monoglycidyl ether and polyalkyleneglycol diglycidyl ether.Docket No.: P00300090-US-PSP

[0028] The glycidyl ester type epoxy compounds may include phenylglycidyl ester, alkylglycidyl ester and alkenylglycidyl ester. The preferable glycidyl ester type epoxy compounds include glycidyl 2,2-dimethyloctanoate, glycidyl benzoate, glycidyl acrylate and glycidyl methacrylate.

[0029] The aryl oxirane compounds may include 1,2-epoxystyrene and alkyl- 1,2-epoxystyrene.

[0030] The alkyl oxirane compounds may include 1,2-epoxybutane, 1,2-epoxypentane, 1,2- epoxyhexane, 1,2-epoxyheptane, 1,2-epoxyoctane, 1,2-epoxynonane, 1,2-epoxydecane, 1,2-epoxyundecane, 1,2-epoxydodecane, 1,2-epoxytridecane, 1,2-epoxytetradecane, 1,2-epoxypentadecane, 1,2-epoxyhexadecane, 1,2-epoxyheptadecane, 1,2-epoxyoctadecane, 1,2-epoxynonadecane and 1,2-epoxyeicosane.

[0031] The alicyclic epoxy compounds may include 1,2-epoxycyclohexane, 1,2-epoxycyclopentane, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate, bis(3,4-epoxycyclohexylmethyl) adipate, exo-2,3-epoxynorbornane, bis(3,4-epoxy-6-methylcyclohexyImethyl) adipate, 2-(7-oxabicyclo 4.1. Q?hept-3-yl)-spiro(l,3-dioxane-5,3’- 7!oxabicyclo 4.1.0!) heptane, 4-(T-methylepoxy ethyl)- 1,2-epoxy-2-methylcyclohexane and 4-epoxyethyl- 1, 2-epoxycycIo hexane. In many embodiments the preferrable alicyclic epoxy compound is 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate.

[0032] In many embodiments, the epoxidized fatty monoesters may include an ester formed through a reaction between an epoxidized fatty' acid having 12 to 20 carbon atoms and an alcohol having 1 to 8 carbon atoms, phenol or an alkylphenol. In particular, epoxystearates such as butyl, hexyl, benzyl, cyclohexyl, methoxyethyl, phenyl and butylphenyl esters of epoxystearic acid are preferred.

[0033] In many embodiments, the epoxidized vegetable oils may include epoxy compounds of a vegetable oil such as soybean oil, linseed oil or cottonseed oil.Docket No.: P00300090-US-PSP

[0034] Examples of suitable epoxy compounds include fluids commercially available under the name Cardura E10P, Celloxide* 2021 P ERL-4221, Heloxy® Modifier 116 Denacol EX-121, or Heloxy® Modifier 68.

[0035] In many embodiments, the phosphate ester based EHC fluid comprises no more than about 0.95 wt % 3,4-epoxycycIohexyImethyl 3,4-epoxycycIohexanecarboxylate epoxide, such as no more than about 0.5 wt% or such as no more than about 0.1

[0036]

[0037] or such as no more than 0.095 wt%, based on the total weight of the phosphate ester based EHC fluid.

[0038] In many embodiments, the phosphate ester based EHC fluid is a tert-butylphenylphosphate (TBPP) based EHC fluid. In many embodiments, TBPP may be a blend of p-t-butylphenyldiphenyl phosphate, bis(p-t-butylphenyl) phenyl phosphate, tris-tert-butylphenylphospate and triphenyl phosphate, where p-t-butyl phenyldiphenyl phosphate may be from about 30 to about 40 wt%, bis(p-t-butylphenyl) phenyl phosphate is from about 25 wt% to about 30 wt%, tri-tert-butyl phenyl phosphate is from about 5 vrt% to about 7 wt%, and triphenyl phosphate may be from about 0 wt% to about 25 wt%, such as from about 0.5 wt% or from about 1 wt% or from about 2.5 wt% or from about 3 wt% or from about 5 wt% to about 20 wt% or to about 15 wt%, based on the total weight of TBPP in the EHC fluid. In such embodiments, for example, the triphenyl phosphate may be present from about 0.5, from about 2, from about 5 or from about 10% by weight to about 40, to about 30, or to about 25% by weight, based on the total weight of TBPP in the EHC fluid. Often, the amount of triphenyl phosphate ranges from about 0 or from about 2% to about 25%, such as from about 0 or from about 2% to about 10 or to about 5% or from about 5 or from about 10% to about 25 or to about 20%, based on the total weight of all phosphate esters in the heat transfer fluid.

[0039] In many embodiments, TBPP may be a blend of mono t-butyl phenyl phosphate, bis t-butyl phenyl phosphate, tris-t-butyl phenyl phosphate, and triphenyl phosphate, where mono t-butyl phenyl phosphate is from about 70 wt% to up to about 100 wt%, bis t-buty phenyl phosphate is up to about 25 wt%, tris-t-butyl phenyl phosphate is up to about 1 wt% and triphenyl phosphate is less than 0.1 wt%, based on the total weight of TBPP in the EHC fluid. For example, in an embodiment, TBPP may be a blend of mono t-butyl phenyl phosphate, bis t-butyl phenylDocket No.: P00300090-US-PSP

[0040] phosphate, tris-t-butyl phenyl phosphate, and triphenyl phosphate, where mono t-butyl phenyl phosphate is about 79 wt%, bis t-buty phenyl phosphate is about 20 wt%, tris-t-butyl phenyl phosphate is about 0.4 wt% and triphenyl phosphate is less than 0.1 wt%, based on the total weight of TBPP in the EHC fluid.

[0041] Examples of suitable TBPP based fluid may include fluids commercially available under the name Reolube® Turbofluid 46B or Reolube® HYD 46B.

[0042] In many embodiments of the present invention, the method of stabilizing a phosphate ester based EHC fluid may further comprise adding one or more performance additives. Examples of such additives include, but are not limited to, antioxidants, metal deactivators, flow additives, corrosion inhibitors, foam inhibitors, demulsifiers, pour point depressants, and any combination or mixture thereof. Fully-formulated phosphate ester based EHC fluids typically contain one or more of these performance additives, and often a package of multiple performance additives. Often, one or more performance additives are present at 0.0001 wt% up to 3 wt%, or 0.05 wt% up to 1.5 wt%, or 0.1 wt% up to 1.0 wt%, based on the weight of the phosphate ester based EHC fluid.

[0043] Also disclosed is a phosphate ester based EHC fluid composition comprising a phosphate ester base fluid and one or more epoxide compounds. The one or more epoxide compounds may be phenylglycidyl ether type epoxy compounds, alkylglycidyl ether type epoxy compounds, glycidyl ester type epoxy compounds, aryl oxirane compounds, alkyl oxirane compounds, alicyclic epoxy compounds, epoxidized fatty monoesters or epoxidized vegetable oils.

[0044] The phenylglycidyl ether type epoxy compounds may include phenylglycidyl ether and alkylphenylglycidyl ether. The alkylphenylglycidyl ether used herein may be one having 1 to 3 allcyl groups each containing I to 13 carbon atoms, preferably one having one alkyl group containing to 10 carbon atoms. The preferable alkylphenylglycidyl ethers include n-butylphenylglycidyl ether, i-butylphenylglycidyl ether, sec-butylphenylglycidyl ether, tertbutylphenyl glycidyl ether, pentylphenylglycidyl ether, hexylphenylglycidyl ether,Docket No.: P00300090-US-PSP

[0045] heptylphenylglycidyl ether, octylphenylglycidyl ether, nonylphenylglycidyl ether and decylphenylglycidyl ether.

[0046] In many embodiments, the alkylglycidyl ether type epoxy compounds may include decylglycidyl ether, undecylglycidyl ether, dodecylglycidyl ether, tridecylglycidyl ether, tetradecylglycidyl ether, 2-ethylhexylglycidyI ether, neopentylglycoldiglycidyl ether, trimethylolpropane triglycidyl ether, pentaerythritol tetraglycidyl ether, 1,6-hexadiol diglycidyl ether, sorbitol polygiycidyl ether, polyalkyleneglycol monoglycidyl ether and polyalkyleneglycol diglycidyl ether.

[0047] The glycidyl ester type epoxy compounds may include phenylglycidyl ester, alkylglycidyl ester and alkenylglycidyl ester. The preferable glycidyl ester type epoxy compounds include glycidyl 2,2-dimethyloctanoate, glycidyl benzoate, glycidyl acrylate and glycidyl methacrylate.

[0048] The aryl oxirane compounds may include 1,2-epoxystyrene and alkyl- 1,2-epoxystvrene.

[0049] The alkyl oxirane compounds may include 1,2-epoxybutane, 1,2-epoxypentane, 1,2-epoxyhexane, 1,2-epoxyheptane, 1,2-epoxyoctane, 1,2-epoxynonane, 1,2-epoxydecane, 1,2-epoxyundecane, 1,2-epoxydodecane, 1,2-epoxytridecane, 1,2-epoxytetradecane, 1,2-epoxypentadecane, 1,2-epoxyhexadecane, 1,2-epoxyheptadecane, 1,2-epoxyoctadecane, 1,2- epoxynonadecane and 1,2-epoxyeicosane.

[0050] The alicyclic epoxy compounds may include 1,2-epoxycyclohexane, 1,2-epoxycyclopentane, 3.4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate, bis(3,4-epoxycyc lohexy Imethyl) adipate, exo-2,3-epoxynorbornane, bis(3,4-epoxy-6-methylcyclohexylmethyl) adipate, 2-(7-oxabicyclo[4.1,0]hept-3-yl)-spiro( 1,3-dioxane-5,3'-[7]oxabicyclo[4.1.0] ) heptane, 4-(l '-methylepoxyethyl)- 1,2-epoxy-2-methylcyclohexane and 4-epoxyethyl- 1,2-epoxycyclohexane. In many embodiments the preferrable alicyclic epoxy compound is 3,4-epoxycyclohexylmethyl- 3.4-epoxycyclohexane carboxylate.

[0051] In many embodiments, the epoxidized fatty monoesters may include esters formed through a reaction between an epoxidized fatty acid having 12 to 20 carbon atoms and an alcohol having 1Docket No.: P00300090-US-PSP

[0052] to 8 carbon atoms, phenol or an alkylpheno]. In particular, epoxystearates such as butyl, hexyl, benzyl, cyclohexyl, methoxyethyl, phenyl and butylphenyl esters of epoxystearic acid are preferred.

[0053] In many embodiments, the epoxidized vegetable oils may include epoxy compounds of a vegetable oil such as soybean oil, linseed oil or cottonseed oil.

[0054] Examples of suitable epoxy compounds include fluids commercially available under the name Cardura E10P, Celloxide® 2021 P ERL-4221, Heloxy* Modifier 116 Denacol EX-121, or Heloxy® Modifier 68.

[0055] In many embodiments, the phosphate ester based EHC fluid is a tert-butylphenylphosphate (TBPP) based EHC fluid. In many embodiments, TBPP may be a blend of p-t-butylphenyldiphenyl phosphate, bis(p-t-butylphenyl) phenyl phosphate, tris-tert-butylphenylphospate and triphenyl phosphate, where p-t-butyl phenyldiphenyl phosphate may be from about 30 to about 40 wt%, bis(p-t-butylphenyl) phenyl phosphate is from about 25 wt% to about 30 wt%, tri-tert-butyl phenyl phosphate is from about 5 w't% to about 7 wt%, and triphenyl phosphate may be from about 0 wt% to about 25 wt%, such as from about 0.5 wt% or from about 1 wt% or from about 2.5 wt% or from about 3 wt% or from about 5 wt% to about 20 wt% or to about 15 wt%, based on the total weight of TBPP in the EHC fluid. In such embodiments, for example, the triphenyl phosphate may be present from about 0.5, from about 2, from about 5 or from about 10% by weight to about 40, to about 30, or to about 25% by weight, based on the total weight of TBPP in the EHC fluid. Often, the amount of triphenyl phosphate ranges from about 0 or from about 2% to about 25%, such as from about 0 or from about 2% to about 10 or to about 5% or from about 5 or from about 10% to about 25 or to about 20%, based on the total weight of all phosphate esters in the heat transfer fluid.

[0056] In many embodiments, TBPP may be a blend of mono t-butyl phenyl phosphate, bis t-butyl phenyl phosphate, tris-t-butyl phenyl phosphate, and triphenyl phosphate, where mono t-butyl phenyl phosphate is from about 70 wt% to up to about 100 wt%, bis t-buty phenyl phosphate is up to about 25 wt%, tris-t-butyl phenyl phosphate is up to about 1 wt% and triphenyl phosphateDocket No.: P00300090-US-PSP

[0057] is less than 0.1 wt%, based on the total weight of TBPP in the EHC fluid. For example, in an embodiment, TBPP may be a blend of mono t-butyl phenyl phosphate, bis t-butyl phenyl phosphate, tris-t-butyl phenyl phosphate, and triphenyl phosphate, where mono t-butyl phenyl phosphate is about 79 wt%, bis t-buty phenyl phosphate is about 20 wt%, tris-t-butyl phenyl phosphate is about 0.4 wt% and triphenyl phosphate is less than 0.1 wt%, such as for example 0 wt%, based on the total weight of TBPP in the EHC fluid.

[0058] Examples of suitable TBPP based fluid may include fluids commercially available under the name Reolube® Turbofluid 46B or Reolube® HYD 46B.

[0059] In many embodiments of the present invention, the phosphate ester based EHC fluid may further comprise one or more performance additives. Examples of such additives include, but are not limited to, antioxidants, metal deactivators, flow additives, corrosion inhibitors, foam inhibitors, demulsifiers, pour point depressants, and any combination or mixture thereof. Fully- formulated phosphate ester based EHC fluids typically contain one or more of these performance additives, and often a package of multiple performance additives. Often, one or more performance additives are present at 0.0001 wt% up to 3 wt%, or 0.05 wt% up to 1.5 wt%, or 0.1 wt% up to 1.0 wt%, based on the weight of the phosphate ester based EHC fluid.

[0060] Also disclosed is a method of testing long term hydrolytic stability of the inventive TBPP based EHC fluid. Typically, the test according to DIN EN 14833 is used to measure the resistance to hydrolysis for an EHC fluid. However, the severity of the DIN EN 14833 is insufficient to differentiate between the long-term and short-term resistance to hydrolysis of different formulations of EHC fluids. The inventive method of testing long term hydrolytic stability of the inventive TBPP based EHC fluid comprises adding 100 ml of water to 300 ml of phosphate ester fluid, placing the mixture in an oven at 90°C for a period of up to 19 days and testing the TAN at various time intervals. Preferably, the pass limit in inventive method is set to <1 mgKOH / g TAN.

[0061] Unless otherwise specified, the following terms are defined as follows:Docket No.: P00300090-US-PSP

[0062] As used herein, the articles “a”, “an”, and “the” preceding an element or component of the invention are intended to be nonrestrictive regarding the number of instances (i.e., occurrences) of the element or component. Therefore “a”, “an”, and “the” should be read to include one or at least one, and the singular word form of the element or component also includes the plural unless the number is obviously meant to be singular.

[0063] As used herein, the term “comprising” means the presence of the stated features, integers, steps, or components as referred to in the claims, but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof. The term “comprising” is intended to include embodiments encompassed by the terms “consisting essentially of” and “consisting of,” unless the context dictates otherwise.

[0064] As used herein, the term “about” modifying the quantity of an ingredient or reactant employed refers to variation in the numerical quantity that can occur, for example, through typical measuring and liquid handling procedures used for making concentrates or use solutions in the real world; through inadvertent error in these procedures; through differences in the manufacture, source, or purity of the ingredients employed to make the compositions or carry out the methods; and the like.

[0065] Where present, all ranges are inclusive and combinable. For example, when a range of “1 to 5” is recited, the recited range should be construed as including ranges “1 to 4”, “1 to 3”, “1-2”, “1-2 & 4-5”, “1-3 & 5”, and the like.

[0066] When a parameter is given either as a range, preferred range, or a list of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. Where a range of numerical values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range. The scope of the invention is not intended to be limited to the specific values and examples as recited in the specification.

[0067] EXAMPLESDocket No.: P00300090-US-PSP

[0068] The following examples demonstrate that the epoxide of the present disclosure, when incorporated into the TBPP based EHC fluid, stabilized the TBPP based EHC fluid. The TBPP based EHC fluid with the epoxide also maintained the TBPP based EHC fluid’s low total acid number, high volume resistivity, low foaming, low air entrainment, while maintaining a suitable toxicity profile.

[0069] Typically, the TBPP based EHC fluid comprising the epoxide of the present disclosure has a volume resistivity according to ICE 60247 of > 150 MOhm-m; low foaming according to ISO 6247 of <100-0 ml-ml; and low air entrainment according to ASTM D 3427 of < 6 min.

[0070] Blends representative of the presently disclosed invention and used in the following experimental examples are shown in Table 1.

[0071] Table 1.

[0072] Blend Components of Blend

[0073] Example 1 TBPP based EHC fluid + 0.095 wt% Epoxide 1

[0074] Example 2 TBPP based EHC fluid + 0.95 wt% Epoxide 1

[0075] Comparative Example 1 TBPP based EHC fluid

[0076] Comparative Example 2 TXP based EHC fluid

[0077] Comparative Example 3 TBPP based EHC fluid + 0.5 wt% Carbodiimide 1 Comparative Example 4 TBPP based EHC fluid + 1.0 wt% Carbodiimide 2 Comparative Example 5 TBPP based EHC fluid + 1.0 wt% Epoxide 2

[0078] Comparative Example 6 TBPP based EHC fluid + 0.05% Epoxide 3

[0079]

[0080] Epoxide 1 = 3, 4-epoxycyclo hexylmethyl 3,4-epoxycyclohexanecarboxylate

[0081] Epoxide 2 = 2-ethylhexyl glycidyl ether

[0082] Epoxide 3 = 2,3 -epoxypropyl neodecanoate

[0083] Carbodiimide 1 = polymeric carbodiiamide 1

[0084] Carbodiimide 2 = polymeric carbodiiamide 2

[0085] BlendingDocket No.: P00300090-US-PSP

[0086] Components of Example 1 were weighed in a beaker and stirred with an Ultra Turrax (dispersing equipment) at 9500 rpm at room temperature for 30 minutes. Afterwards the blend was heated to 70°C and stirred for 30 minutes to finalize the homogenization process. This blending procedure was followed to prepare the blends of Example 2 and the Comparative Examples of Table 1. For purposes of the present disclosure, “room temperature” means a temperature ranging from 20 to 25°C.

[0087] Hydrolytic stability - Inventive Oven test

[0088] In an Erlenmeyer flask, 300 g of a blend of Table 1 and 100 g water were weighed and mixed according to the standard DIN EN 14833. The Erlenmeyer flask was then loosely closed with a stopper and stored at 90°C in a drying oven for a period of up to 19 days. At specified time intervals, the TAN (total acid number, according to ASTM D 664) of the blend was measured. The pass limit for this oven test was set to <1 mgKOH / g TAN.

[0089] Foam behavior

[0090] The foam behaviors of each blend of Table 1 was measured according to ISO 6247.

[0091] Air release

[0092] The air release properties of each blend of Table 1 was measured according to ASTM D 3427.

[0093] Volume resistivity

[0094] The volume resistivity of each blend of Table 1 was measured according to IEC 60247.

[0095] Demulsibility

[0096] The demulsibility (water separation property ) of each blend of Table 1 was measured according to DIN ISO 6614.

[0097] Table 2

[0098] Test

[0099] Foaming behavior

[0100] Parameter Air release Volume resistivity Demulsibility’

[0101] ASTM

[0102] Test Method ISO 6247 D3427 IEC 60247 ISO 6614 Sequence I Sequence II Sequence II phases Tendency- Tendency- Tendency- (water-oil- separation Stability Stability Stability emulsion) time Units [ml-ml] [ml-ml] [ml-ml] time [min] Rho+ [Mohm*m] [mL] [min]time Limit <100-0 <100-0 <100-0 < 6 > 150 <15

[0103]

[0104] FormulationDocket No.: P00300090-US-PSP

[0105] Comparative

[0106] Example 1 0-0 20-0 10-0 3.3 425 40-40-0 2 x 5 min Comparative

[0107] Example 2 208

[0108] Comparative

[0109] Example 3 30-0 10-0 20-0 5 65 40-40-0 2 x 15 min Comparative

[0110] Example 4 20-0 20-0 20-0 4.1 44 40-40-0 2 x 5 min Comparative

[0111] Example 5 10-0 0-0 20-0 4.3 87 40-40-0 2 x 5 min Example 1 20-0 30-0 30-0 4.3 542 40-40-0 2 x 10 min Example 2 120-0 20-0 80-0 3.2 613 40-40-0 2 x 10 min Comparative

[0112]

[0113] Example 6 0-0 10-0 0-0 4.5 61 40-40-40 2 x 5 min

[0114] As shown in Table 2 above, each of Examples 1 and 2, both of which include the epoxide compound of the present invention at different wt%, had a volume resistivity > 150 MOhm-m, foaming <100-0 ml-ml, often <30-0, air entrainment < 6 min, often < 4.3 min. That is, the epoxide compound of the present invention sufficiently stabilized the TBPP based EHC fluid from hydrolyzing, maintained low TAN while maintaining a suitable toxicity profile and not adversely affecting other EHC fluid parameters.

[0115] This is further illustrated in Fig. 3, which depicts the hydrolytic stabi lity of the inventive Example 2 and Comparative Examples 1-2 and 5. In accordance with the present invention, TBPP based EHC fluids with the inventive epoxide compound (Examples 1 and 2 above) had greater hydrolytic stability when compared to the TBPP based EHC fluid, either alone (Comparative Example 1), in combination with carbodiimides (Comparative Examples 3 and 4), or in combination with epoxides not of the invention ( Comparative Examples 5 and 6). Further, Comparative Examples 3 and 4, both of which are blends of TBPP based EHC fluid and a carbodiimide, had volume resistivity of less than 150 MOhm-m, falling outside of the preferred range.

Claims

Docket No.: P00300090-US-PSPWhat is claimed is:

1. A method of stabilizing a phosphate ester based electrohydraulic control fluid, the method comprising:adding one or more epoxide compounds to the phosphate ester based electrohydraulic control fluid, wherein the one or more epoxide compounds comprises phenylglycidyl ether type epoxy compounds, alkylglycidyl ether type epoxy compounds, glycidyl ester type epoxy compounds, aryl oxirane compounds, alkyl oxirane compounds, alicyclic epoxy compounds, epoxidized fatty monoesters, or epoxidized vegetable oils.

2. The method of claim 1, wherein the one or more epoxide compounds is 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexane carboxylate.

3. The method of claim 1, wherein the one or more epoxide compounds is added at a treat rate of 0.095 wt% based on the total weight of the phosphate ester based electrohydraulic control fluid.

4. The method of claim 1, wherein the phosphate ester based electrohydraulic control fluid is a tert-butylphenyl phosphate based electrohydraulic control fluid.

5. The method of claim 4, wherein the tert-butylphenylphosphate based electrohydraulic control fluid comprises a blend of p-t-butylphenyldiphenyl phosphate, bis(p-t-butylphenyl) phenyl phosphate, tris-tert-butylphenylphospate and triphenyl phosphate.

6. The method of claim 5, wherein the p-t-butylphenyldiphenyl phosphate is from about 30 to about 40 wt%, the bis(p-t-butylphenyl) phenyl phosphate is from about 25 wt% to about 30 wt%, the tri-tert-butylphenylphosphate is from about 5 wt % to about 7 wt%, and the triphenyl phosphate is from about 0 wt% to about 25 wt%, based on the total weight of the tert-butylphenylphosphate based electrohydraulic control fluid.Docket No.: P00300090-US-PSP7. The method of claim 4, wherein the tert-butylphenylphosphate based electrohydraulic control fluid comprises a blend of mono t-butyl phenyl phosphate, bis t-butyl phenyl phosphate, tris-t-butyl phenyl phosphate, and triphenyl phosphate.

8. The method of claim 7, wherein the mono t-butyl phenyl phosphate is from about 70 wt% to up to about 100 wt%, the bis t-buty phenyl phosphate is up to about 25 wt%, tris-t-butyl phenyl phosphate is up to about 1 wt% and triphenyl phosphate is less than 0.1 wt%, preferably 0 wt%, based on the total weight of the tert-butylphenylphosphate based electrohydraulic control fluid.

9. The method of claim 1, wherein the phosphate ester based electrohydraulic control fluid further comprises adding one or more performance additives selected from the group consisting of antioxidants, metal deactivators, flow additives, corrosion inhibitors, foam inhibitors, demulsifiers, pour point depressants, and any combination thereof.

10. The method of claim 9, wherein the one or more performance additives are present in an amount ranging from 0.0001 wl% to 3 wt%, based on the total weight of the phosphate ester based electrohydraulic control fluid.

11. A phosphate ester based electrohydraulic control fluid composition comprising:a phosphate ester base fluid; andone or more epoxide compounds, w’herein the one or more epoxide compounds comprises phenylglycidyl ether type epoxy compounds, alkylglycidyl ether type epoxy compounds, glycidyl ester type epoxy compounds, aryl oxirane compounds, alkyl oxirane compounds, alicyclic epoxy compounds, epoxidized fatty monoesters, or epoxidized vegetable oils.

12. The phosphate ester based electrohydraulic control fluid composition of claim 11, w'herein the one or more epoxide compounds is 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexane carboxylate.Docket No.: P00300090-US-PSP13. The phosphate ester based electrohydraulic control fluid composition of claim 11, wherein the one or more epoxide compounds is present in an amount of 0.095 wt% based on the total weight of the phosphate ester based electrohydraulic control fluid composition.

14. The phosphate ester based electrohydraulic control fluid composition of claim 11, wherein the phosphate ester base fluid is a tert-butylphenylphosphate based fluid, wherein the tertbutylphenylphosphate based fluid comprises a blend of p-t-butylphenyldiphenyl phosphate, bis(p-t-butylphenyl) phenyl phosphate, tris-tert-butylphenylphospate and triphenyl phosphate.

15. The phosphate ester based electrohydraulic control fluid composition of claim 14, wherein the p-t-butylphenyldiphenyl phosphate is from about 30 to about 40 wt%, the bis(p-t-butylphenyl) phenyl phosphate is from about 25 wt% to about 30 wt%, the tri-tert-butylphenylphosphate is from about 5 wt% to about 7 wt%, and the triphenyl phosphate is from about 0 wt% to about 25 wt%, based on the total weight of the tert-butylphenylphosphate based fluid.

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