Polyol ester composition for fire-resistant hydraulic fluids

Abstract

The invention provides polyol ester compositions with a flash point of at least 290 °C, wherein the polyol ester composition is the reaction product of at least one polyol compound; at least one saturated dicarboxylic medium-chain fatty acid; and (c) at least one saturated monocarboxylic medium-chain or long-chain fatty acid. The invention also provides methods of preparing the polyol ester compositions and fire-resistant hydraulic fluid formulations comprising the polyol ester compositions.

Description

[0001] POLYOL ESTER COMPOSITION FOR FIRE-RESISTANT HYDRAULIC FLUIDS

[0002] FIELD OF INVENTION

[0003] The present invention provides polyol ester compositions. The present invention also provides fire-resistant hydraulic fluid formulations comprising the polyol ester compositions, and methods of preparing the polyol ester compositions.

[0004] BACKGROUND

[0005] The listing or discussion of a prior-published document in this specification should not necessarily be taken as an acknowledgement that the document is part of the state of the art or is common general knowledge.

[0006] Fire-resistant hydraulic fluids (FRHFs) are one of the largest industrial lubricant segments. They have seen rapid growth due to increased emphasis on operator safety (stringent implementation of safety standards at the workplace) and environment concerns (demand for bio-degradability and eco-friendly products). The main applications of FRHFs are in metal processing, aviation and marine industries, mining and others.

[0007] Polyol esters (POE) are a class of anhydrous-based FRHF and are considered alternatives to phosphate esters due to its superior corrosion inhibition, better wear protection, lower seal problems and compatibilities with paint. Trimethylolpropane trioleate (TMPTO) is widely accepted as the industrial standard for polyol ester for use in FRHF. However, the unsaturated nature of the fatty acid moiety originating from oleic acid residue results in TMPTO being susceptible to oxidative and faster thermal degradation.

[0008] Therefore, there is a need for improved and / or alternative polyol ester for use in fire-resistant hydraulic fluids.

[0009] SUMMARY

[0010] Aspects and embodiments of the current invention will now be described by reference to the following numbered clauses.

[0011] 1 . A polyol ester composition with a flash point of at least 290 °C, wherein the polyol ester composition is the reaction product of:

[0012] (a) at least one polyol compound;

[0013] (b) at least one saturated dicarboxylic medium-chain fatty acid; and

[0014] (c) at least one saturated monocarboxylic medium-chain or long-chain fatty acid. 2. The polyol ester composition according to clause 1 , wherein the polyol ester composition has a kinematic viscosity of from about 41 mm2s-1to about 1 10 mm2s-1at 40 °C.

[0015] 3. The polyol ester composition according to clause 1 or 2, wherein the polyol ester composition has a kinematic viscosity of from about 41 mm2s-1to about 51 mm2s-1at 40 °C.

[0016] 4. The polyol ester composition according to clause 1 or 2, wherein the polyol ester composition has a kinematic viscosity of from about 61 mm2s-1to about 75 mm2s-1at 40 °C.

[0017] 5. The polyol ester composition according to clause 1 or 2, wherein the polyol ester composition has a kinematic viscosity of from about 90 mm2s-1to about 1 10 mm2s-1at 40 °C.

[0018] 6. The polyol ester composition according to any one of the preceding clauses, wherein the at least one polyol compound is a primary alcohol with three or more hydroxyl groups, optionally wherein the at least one polyol compound is a primary alcohol with four hydroxyl groups.

[0019] 7. The polyol ester composition according to any one of the preceding clauses, wherein the at least one polyol compound is selected from a group consisting of glycerol, trimethylolpropane, and penta erythritol, optionally wherein the at least one polyol compound is pentaerythritol.

[0020] 8. The polyol ester composition according to any one of the preceding clauses, wherein the at least one saturated dicarboxylic medium-chain fatty acid is a linear or branched C6 to C12 saturated dicarboxylic acid, for example, a linear or branched C8 to C10 saturated dicarboxylic acid.

[0021] 9. The polyol ester composition according to any one of the preceding clauses, wherein the at least one saturated dicarboxylic medium-chain fatty acid is a linear or branched C9 saturated dicarboxylic acid, for example, azelaic acid.

[0022] 10. The polyol ester composition according to any one of the preceding clauses, wherein the at least one saturated monocarboxylic medium-chain or long-chain fatty acid is a linear or branched C6 to C18 saturated monocarboxylic acid, for example, a linear or branched C8 to C16 saturated monocarboxylic acid. 11 . The polyol ester composition according to any one of the preceding clauses, wherein the at least one saturated monocarboxylic medium-chain or long-chain fatty acid is a linear or branched C8 to C10 saturated monocarboxylic acid, for example decanoic acid, pelargonic acid or octanoic acid.

[0023] 12. The polyol ester composition according to any one of clauses 1 to 10, wherein the at least one saturated monocarboxylic medium-chain or long-chain fatty acid comprises two saturated monocarboxylic medium-chain fatty acids, wherein the two saturated monocarboxylic medium-chain fatty acids are:

[0024] (a) decanoic acid and pelargonic acid; or

[0025] (b) decanoic acid and octanoic acid.

[0026] 13. The polyol ester composition according to any one of clauses 1 to 10, wherein the at least one saturated monocarboxylic medium-chain or long-chain fatty acid comprises: one saturated monocarboxylic medium-chain fatty acid, wherein the saturated monocarboxylic medium-chain fatty acid is a C6 to C8 saturated monocarboxylic acid; and one saturated monocarboxylic long-chain fatty acid, wherein the saturated monocarboxylic long-chain fatty acid is isostearic acid.

[0027] 14. A method of preparing a polyol ester composition, the method comprising subjecting:

[0028] (a) at least one polyol compound;

[0029] (b) at least one saturated dicarboxylic medium-chain fatty acid; and

[0030] (c) at least one saturated monocarboxylic medium-chain or long-chain fatty acid, to an esterification reaction to provide the polyol ester composition, wherein the polyol ester composition has a flash point of at least 290 °C.

[0031] 15. The method according to clause 14, wherein the polyol ester composition has a kinematic viscosity of from about 41 mm2s-1to about 110 mm2s-1at 40 °C.

[0032] 16. The method according to clause 14 or 15, wherein the polyol ester composition has a kinematic viscosity of from about 41 mm2s-1to about 51 mm2s-1at 40 °C.

[0033] 17. The method according to clause 14 or 15, wherein the polyol ester composition has a kinematic viscosity of from about 61 mm2s-1to about 75 mm2s-1at 40 °C.

[0034] 18. The method according to clause 14 or 15, wherein the polyol ester composition has a kinematic viscosity of from about 90 mm2s-1to about 110 mm2s-1at 40 °C. 19. The method according to any one of clauses 14 to 18, wherein the at least one polyol compound is a primary alcohol with three or more hydroxyl groups, optionally wherein the at least one polyol compound is a primary alcohol with four hydroxyl groups.

[0035] 20. The method according to any one of clauses 14 to 19, wherein the at least one polyol compound is selected from a group consisting of glycerol, trimethylolpropane, and pentaerythritol, optionally wherein the at least one polyol compound is pentaerythritol.

[0036] 21. The method according to any one of clauses 14 to 20, wherein the at least one saturated dicarboxylic medium-chain fatty acid is a linear or branched C6 to C12 saturated dicarboxylic acid, for example, a linear or branched C8 to C10 saturated dicarboxylic acid.

[0037] 22. The method according to any one of clauses 14 to 21 , wherein the at least one saturated dicarboxylic medium-chain fatty acid is a linear or branched C9 saturated dicarboxylic acid, for example, azelaic acid.

[0038] 23. The method according to any one of clauses 14 to 22, wherein the at least one saturated monocarboxylic medium-chain or long-chain fatty acid is a linear or branched C6 to C18 saturated monocarboxylic acid, for example, a linear or branched C8 to C16 saturated monocarboxylic acid.

[0039] 24. The method according to any one of clauses 14 to 23, wherein the at least one saturated monocarboxylic medium-chain or long-chain fatty acid is a linear or branched C8 to C10 saturated monocarboxylic acid, for example decanoic acid, pelargonic acid or octanoic acid.

[0040] 25. The method according to any one of clauses 14 to 23, wherein the at least one saturated monocarboxylic medium-chain or long-chain fatty acid comprises two saturated monocarboxylic medium-chain fatty acids, the two saturated monocarboxylic medium-chain fatty acids are:

[0041] (a) decanoic acid and pelargonic acid; or

[0042] (b) decanoic acid and octanoic acid.

[0043] 26. The method according to any one of clauses 14 to 23, wherein the at least one saturated monocarboxylic medium-chain or long-chain fatty acid comprises: one saturated monocarboxylic medium-chain fatty acid, wherein the saturated monocarboxylic medium-chain fatty acid is a C6 to C8 saturated monocarboxylic acid; and one saturated monocarboxylic long-chain fatty acid, wherein the saturated monocarboxylic long-chain fatty acid is isostearic acid.

[0044] 27. The method according to any one of clauses 14 to 26, wherein the method comprises preparing a reaction mixture comprising (a), (b) and (c), wherein the reaction mixture has a hydroxyl group to carboxyl group molar ratio (HCR) of 0.94 or less than 1 .

[0045] 28. A polyol ester composition obtained by the method according to any one of clauses 14 to 27.

[0046] 29. The polyol ester composition of any one of clauses 1 to 13 or 28, or the method according to any one of clauses 14 to 27, wherein the polyol ester composition comprises a polyol ester of Formula I:

[0047] Formula I wherein,

[0048] Ri, R2, R3, R4, Rs and R6are each independently: a linear or branched saturated C6-18 alkyl ; or a linear or branched saturated CB-12 alkyl with a terminal carboxylic acid group which is optionally esterified with a polyol compound of formula R7-OH; wherein R7is a linear or branched primary polyol having from 3 to 8 carbon atoms and each alcohol functional group in R7is optionally esterified with a linear or branched saturated monocarboxylic acid having from 6 to 18 carbon atoms, or a linear or branched saturated dicarboxylic acid having from 6 to 12 carbon atoms. 30. The polyol ester composition, or the method according to clause 29, wherein, Ri, R2, R3, R4, Rs and R6are each independently: a linear Cs-w alkyl; or a linear Cg alkyl with a terminal carboxylic acid group which is optionally esterified with a polyol compound of formula R7-OH; wherein R7is a branched primary polyol having 5 carbon atoms and each alcohol functional group in R7is optionally esterified with a linear saturated monocarboxylic acid having from 8 to 10 carbon atoms, or a linear saturated dicarboxylic acid having 9 carbon atoms.

[0049] 31 . A fire-resistant hydraulic fluid formulation comprising:

[0050] (a) the polyol ester composition according to any one of claims 1 to 13 and 28 to 30; and

[0051] (b) a pour point depressant.

[0052] 32. The fire-resistant hydraulic fluid formulation according to clause 31 , wherein the pour point depressant is a polymeric aliphatic ester or an aromatic ester, for example, the pour point depressant may be selected from the group consisting of a polyadipate, a modified polyolefin (e.g. a polyalkylmethacrylate (PAMA)), a phthalate ester (e.g. diisononyl phthalate), and a combination of two or more thereof.

[0053] DESCRIPTION

[0054] The present inventors have developed fully-saturated polyol esters with a high flash point (> 290°C) aimed to meet the ISO VG 46 viscosity requirements intended for the use in fire- resistant hydraulic fluids. Furthermore, the fully-saturated polyol esters potentially improve the intrinsic oxidative stability of the fire-resistant hydraulic fluid. In addition, the method to prepare the saturated polyol ester does not involve the use of oleic acid, which is one of the most used in the food industry, as a raw material.

[0055] Thus, in a first aspect of the invention, there is provided a polyol ester composition with a flash point of at least 290 °C, wherein the polyol ester composition is the reaction product of:

[0056] (a) at least one polyol compound;

[0057] (b) at least one saturated dicarboxylic medium-chain fatty acid; and

[0058] (c) at least one saturated monocarboxylic medium-chain or long-chain fatty acid.

[0059] In embodiments herein, the word “comprising” may be interpreted as requiring the features mentioned, but not limiting the presence of other features. Alternatively, the word “comprising” may also relate to the situation where only the components / features listed are intended to be present (e.g. the word “comprising” may be replaced by the phrases “consists of’ or “consists essentially of’). It is explicitly contemplated that both the broader and narrower interpretations can be applied to all aspects and embodiments of the present invention. In other words, the word “comprising” and synonyms thereof may be replaced by the phrase “consisting of’ or the phrase “consists essentially of’ or synonyms thereof and vice versa.

[0060] The phrase, “consists essentially of’ and its pseudonyms may be interpreted herein to refer to a material where minor impurities may be present. For example, the material may be greater than or equal to 90% pure, such as greater than 95% pure, such as greater than 97% pure, such as greaterthan 99% pure, such as greaterthan 99.9% pure, such as greaterthan 99.99% pure, such as greater than 99.999% pure, such as 100% pure.

[0061] As disclosed herein, the term “polyol ester composition” refers to a composition comprising a polyol ester. The polyol esters according to the present invention are formed from (a) at least one polyol compound, (b) at least one saturated dicarboxylic medium-chain fatty acid, and (c) at least one saturated monocarboxylic medium-chain or long-chain fatty acid. As used herein, the term “medium-chain fatty acid” is used to refer to fatty acids that are 6 to 12 carbon atoms in carbon chain length (for example, decanoic acid, pelargonic acid and octanoic acid) the term “long-chain fatty acid” is used to refer to fatty acids that are 13 to 21 carbon atoms in carbon chain length (for example, isostearic acid, stearic acid, palmitic acid and myristic acid).

[0062] Advantageously, saturated fatty acids are used to improve the oxidative stability of the polyol ester compositions and the fire-resistant hydraulic fluids that they are used in.

[0063] As mentioned above, the polyol ester composition according to the present invention are suitable as industrial lubricants, more particularly, fire-resistant hydraulic fluids due to their high flash points of at least 290 °C while meeting various International Standards Organization (ISO) standards for hydraulic fluids, which may include ISO VG-46, ISO VG-68 and ISO VG- 100 (VG refers to viscosity grade and the number that follows refers to the kinematic viscosity of the hydraulic fluid at 40 °C). Flash point is the minimum temperature at which a liquid gives off vapor within a test vessel in sufficient concentration to form an ignitable mixture with the air near the surface of the liquid. Kinematic viscosity is a measure of a fluid's internal resistance to flow under gravitational forces. The polyol esters also have multiple ester groups, improving the polyol ester composition’s bio-degradability, which is desirable due to environmental concerns and the industrial demand for more eco-friendly products. In this regard, the polyol ester composition may have a kinematic viscosity of from about 41 mm2-s'1to about 110 mm2s-1at 40 °C. In some embodiments, the polyol ester composition may have a kinematic viscosity of from about 41 mm2s-1to about 51 mm2s-1at 40 °C. In other embodiments, the polyol ester composition may have a kinematic viscosity of from about 61 mm2-s'1to about 75 mm2s-1at 40 °C. In further embodiments, the polyol ester composition may have a kinematic viscosity of from about 90 mm2s-1to about 1 10 mm2s-1at 40 °C.

[0064] In certain embodiments, the at least one polyol compound may be a primary alcohol with three or more hydroxyl groups. In more preferred embodiments, the at least one polyol compound may be a primary alcohol with four hydroxyl groups. For example, the at least one polyol compound may be selected from a group consisting of glycerol, trimethylolpropane, and pentaerythritol. In certain exemplary embodiments, the at least one polyol compound may be pentaerythritol.

[0065] In certain embodiments, the at least one saturated dicarboxylic medium-chain fatty acid may be a linear or branched C6 to C12 saturated dicarboxylic acid, for example, a linear or branched C8 to C10 saturated dicarboxylic acid. In other embodiments, the at least one saturated dicarboxylic medium-chain fatty acid may be a linear or branched C9 saturated dicarboxylic acid. In certain exemplary embodiments, the at least one saturated dicarboxylic medium-chain fatty acid may be azelaic acid.

[0066] In certain embodiments, the at least one saturated monocarboxylic medium-chain or long- chain fatty acid may be a linear or branched C6 to C18 saturated monocarboxylic acid, for example, a linear or branched C8 to C16 saturated monocarboxylic acid. In other embodiments, the at least one saturated monocarboxylic medium-chain or long-chain fatty acid may be a linear or branched C8 to C10 saturated monocarboxylic acid. In further embodiments, the at least one saturated monocarboxylic medium-chain or long-chain fatty acid may be decanoic acid, pelargonic acid or octanoic acid.

[0067] In certain embodiments, the at least one monocarboxylic medium-chain or long-chain fatty acid may comprise more than one saturated monocarboxylic medium-chain or long-chain fatty acid or combination thereof. For example, there may be two saturated monocarboxylic medium-chain fatty acids or one saturated monocarboxylic medium-chain fatty acid and one saturated monocarboxylic long-chain fatty acid. In certain exemplary embodiments, the at least one monocarboxylic medium-chain or long-chain fatty acid may comprise two saturated medium-chain fatty acids, the two saturated medium-chain fatty acids may be decanoic acid and pelargonic acid or decanoic acid and octanoic acid. In other exemplary embodiments, the at least one saturated monocarboxylic medium-chain or long-chain fatty acid may comprise one saturated monocarboxylic medium-chain fatty acid, wherein the saturated monocarboxylic medium-chain fatty acid is a C6 to C8 saturated monocarboxylic acid and one saturated monocarboxylic long-chain fatty acid, wherein the saturated monocarboxylic long-chain fatty acid is isostearic acid.

[0068] A second aspect of the invention relates to a method of preparing a polyol ester composition, the method comprising subjecting:

[0069] (a) at least one polyol compound;

[0070] (b) at least one saturated dicarboxylic medium-chain fatty acid; and

[0071] (c) at least one saturated monocarboxylic medium-chain or long-chain fatty acid, to an esterification reaction to provide the polyol ester composition, wherein the polyol ester composition has a flash point of at least 290 °C.

[0072] As the method provides the polyol ester composition as disclosed hereinbefore, a discussion of the same materials mentioned hereinbefore will be omitted for the purposes of brevity.

[0073] In certain embodiments, the reaction mixture has a hydroxyl group to carboxyl group molar ratio (HCR) of 0.94 or less than 1. The HCR ratios may influence the properties of the polyol ester composition and subsequently, the fire-resistant, hydraulic fluid. For example, a reduced HCR may result in an increased molecular weight causing an increase in kinetic viscosity and decrease in volatility / higher flash point. An increased ratio of HCR results in decreased molecular weight causing a decrease in kinetic viscosity and increase in volatility / lower flash point. This is because a reduction in HCR leads to increased incorporation of the primary polyol hydroxyl groups leading to increased molecular weights if the primary polyol has two hydroxyl groups and increased crosslinking if the primary polyol has three or more hydroxyl groups. Thus, control of the HCR as well as choice of primary polyols, dicarboxylic acids and monocarboxylic acid can be used to produce a wide range of polyol ester compositions having varying structures, kinetic viscosities, and volatilities.

[0074] In this regard, another aspect of the invention relates to a polyol ester composition comprising a polyol ester of Formula I:

[0075] Formula I wherein,

[0076] R1, R2, R3, R4, Rs and R6are each independently: a linear or branched saturated Ce-isalkyl ; or a linear or branched saturated Ce-^alkyl with a terminal carboxylic acid group which is optionally esterified with a polyol compound of formula R7-OH; wherein R7is a linear or branched primary polyol having from 3 to 8 carbon atoms and each alcohol functional group in R7is optionally esterified with a linear or branched saturated monocarboxylic acid having from 6 to 18 carbon atoms, or a linear or branched saturated dicarboxylic acid having from 6 to 12 carbon atoms.

[0077] As used herein, “alkyl” refers to an unbranched or branched, cyclic, saturated hydrocarbyl radical, which may be substituted or unsubstituted.

[0078] In certain embodiments, R1, R2, R3, R4, Rs and R6may be each independently: a linear Cs alkyl ; or a linear C9alkyl with a terminal carboxylic acid group which is optionally esterified with a polyol compound of formula R7-OH; wherein R7may be a branched primary polyol having 5 carbon atoms and each alcohol functional group in R7may be optionally esterified with a linear saturated monocarboxylic acid having from 8 to 10 carbon atoms, or a linear saturated dicarboxylic acid having 9 carbon atoms.

[0079] As mentioned above, the fully-saturated polyol esters with high flash point (>290 °C) according to the present invention are useful in fire-resistant hydraulic fluids. Therefore, another aspect of the invention relates to a fire-resistant hydraulic fluid formulation comprising: the polyol ester composition and an additive, such as a pour point depressant. As used herein, the term “pour point depressant” refers to an additive that is used to reduce the pour point of a fluid, allowing the fluid to flow at low temperatures.

[0080] In certain embodiments, the pour point depressant may be a polymeric aliphatic ester or an aromatic ester. For example, the pour point depressant may be selected from the group consisting of a polyadipate, a modified polyolefin (e.g. a polyalkylmethacrylate (PAMA)), and a phthalate ester (e.g. diisononyl phthalate), and a combination of two or more thereof. Typically, the pour point depressant is present in the fire-resistant hydraulic fluid formulation of the present invention at a concentration for less than about 0.5 wt%.

[0081] Further aspects and embodiments of the invention will now be discussed by reference to the following non-limiting examples.

[0082] EXAMPLES

[0083] Example 1 : Preparation of Polyol Ester Compositions

[0084] Example 1 .1 : HFP-07-23

[0085] Azelaic acid technical grade, 80% purity (0.07 mol, 12.13 g), decanoic acid (1 .64 mol, 281 .63 g), and pentaerythritol (0.41 mol, 56.24 g) and 0.11 g tin (II) oxide were mixed in a round bottom flask fitted with heating mantle and thermocouple, a gas inlet tube for nitrogen gas blanketing, with magnetic bar on a magnetic stirrer, a distillation column fitted with a cooled condenser and collection flask to collect distilled water by-product. The mixture was initially homogenized at 150 °C using mechanical stirring, followed by gradual temperature increase to 180 °C and subsequently to 215 °C over 18 h of reaction time. To drive the esterification to near completion, inert gas was sparged into the reaction mixture at a rate of 0.5 L min-1during the final 5 h of reaction time. The crude ester was then neutralised with KOH solution to remove excess fatty acids from the reaction, to achieve acid value of <0.1 mgKOH / g. The final properties of the ester including kinematic viscosities at 40 °C and 100 °C, density at 25 °C (in accordance with ASTM D7042) viscosity index (calculated according to ASTM D2270), pour point (ASTM D6749), and flash point (Cleveland Open Cup method, ASTM D92) were measured. Example 1 .2: HFP-08-23

[0086] Azelaic acid technical grade, 80% purity (0.07 mol, 12.53 g), decanoic acid (0.85 mol, 145.53 g), pelargonic acid (0.85 mol, 133.68 g) and pentaerythritol (0.43 mol, 58.26 g) 0.1 1 g tin (II) oxide were mixed in a round bottom flask fitted with a heating mantle and thermocouple, a gas inlet tube for nitrogen gas blanketing, with magnetic bar on a magnetic stirrer, a distillation column fitted with a cooled condenser and collection flask to collect distilled water by-product. The mixture was initially homogenized at 150 °C using mechanical stirring, followed by gradual temperature increase to 180 °C and subsequently to 215 °C over 18 h of reaction time. To drive the esterification to near completion, inert gas was sparged into the reaction mixture at a rate of 0.5 L min-1 during the final 5 h of reaction time. The crude ester was then neutralised with KOH solution to remove excess fatty acids from the reaction, to achieve acid value of <0.1 mgKOH / g. The final properties of the ester including kinematic viscosities at 40 °C and 100 °C, density at 25 °C (in accordance with ASTM D7042) viscosity index (calculated according to ASTM D2270), pour point (ASTM D6749), and flash point (Cleveland Open Cup method, ASTM D92) were measured.

[0087] Example 1 .3: HFP-08-020124

[0088] Azelaic acid technical grade, 80% purity (0.067 mol, 12.62 g), decanoic acid (0.68 mol, 117.26 g), pentaerythritol (0.43 mol, 58.67 g), pelargonic acid (1.02 mol, 161.51 g) and 0.1 1 g tin (II) oxide were esterified using similar apparatus and procedure as earlier described. The crude ester was then neutralised with KOH solution to remove excess fatty acids from the reaction, to achieve acid value of <0.1 mgKOH / g. The final properties of the ester including kinematic viscosities at 40 °C and 100 °C, density at 25 °C (in accordance with ASTM D7042) viscosity index (calculated according to ASTM D2270), pour point (ASTM D6749), and flash point (Cleveland Open Cup method, ASTM D92) were measured.

[0089] Example 1 .4: HFP- 5608-1

[0090] Azelaic acid technical grade, 80% purity (0.07 mol, 12.74 g), decanoic acid (0.35 mol, 103.58 g), pentaerythritol (0.44 mol, 59.29 g), fatty acid mixtures comprising octanoic-decanoic acids (1 .12 mol, 174.38 g) into the flask and 0.1 1 g tin (II) oxide were esterified using similar apparatus and procedure as earlier described. The crude ester was then neutralised with KOH solution to remove excess fatty acids from the reaction, to achieve acid value of <0.1 mgKOH / g. The final properties of the ester including kinematic viscosities at 40 °C and 100 °C, density at 25 °C (in accordance with ASTM D7042) viscosity index (calculated according to ASTM D2270), pour point (ASTM D6749), and flash point (Cleveland Open Cup method, ASTM D92) were measured.

[0091] Example 1 .5: HFP-68-03

[0092] Azelaic acid technical grade, 80% purity (0.13 mol, 23.51 g), decanoic acid (0.65 mol, 112.03 g), pentaerythritol (0.44 mol, 60.11 g), pelargonic acid (0.98 mol, 154.35 g) into the flask and 0.11 g tin (II) oxide were esterified using similar apparatus and procedure as earlier described. The crude ester was then neutralised with KOH solution to remove excess fatty acids from the reaction, to achieve acid value of <0.1 mgKOH / g. The final properties of the ester including kinematic viscosities at 40 °C and 100 °C, density at 25 °C (in accordance with ASTM D7042) viscosity index (calculated according to ASTM D2270), pour point (ASTM D6749), and flash point (Cleveland Open Cup method, ASTM D92) were measured.

[0093] Example 1 .6: HFP-100-01

[0094] Azelaic acid technical grade, 80% purity (0.17 mol, 31 .97 g), decanoic acid (0.63 mol, 108 g), pentaerythritol (0.45 mol, 61 .23 g), pelargonic acid (0.94 mol, 148.81 g) into the flask and 0.1 1 g tin (II) oxide were esterified using similar apparatus and procedure as earlier described. The crude ester was then neutralised with KOH solution to remove excess fatty acids from the reaction, to achieve acid value of <0.1 mgKOH / g. The final properties of the ester including kinematic viscosities at 40 °C and 100 °C, density at 25 °C (in accordance with ASTM D7042) viscosity index (calculated according to ASTM D2270), pour point (ASTM D6749), and flash point (Cleveland Open Cup method, ASTM D92) were measured.

[0095] Table 1 : Reactant mixtures of high flash point ester candidates Example 2: Characterisation of Polyol Ester Compositions

[0096] The properties of the polyol ester compositions were measured, including kinematic viscosities at 40 °C and 100 °C, density at 25 °C (in accordance with ASTM D7042), viscosity index (calculated according to ASTM D2270), pour point (ASTM D6749), and flash point (Cleveland Open Cup method, ASTM D92).

[0097] Table 2 provides a summary of the measured properties. Based on the results, the polyol ester compositions according to the above Examples 1.1 , 1.3 and 1 .4 demonstrate high flash point of > 295 °C and while matching ISO VG 46 viscosity grade (KV @ 40 °C = 46 cSt ± 10%), which are desirable properties for use in fire-resistant hydraulic fluids. The polyol ester compositions also have high viscosity indexes (Vis), which indicate stability in viscosity changes when temperature changes (VI is calculated based on the KVs at 40 °C and 100 °C). Additionally, examples 1 .5 and 1 .6 demonstrate that higher viscosity values can be achieved from the same starting materials with Examples 1 .2 and 1 .3, while maintaining high flash point characteristics, by simply increasing the dicarboxylic: mono-carboxylic ratio (DMR).

[0098] Table 2: Summary of measured properties

Claims

CLAIMS1 . A polyol ester composition with a flash point of at least 290 °C, wherein the polyol ester composition is the reaction product of:(a) at least one polyol compound;(b) at least one saturated dicarboxylic medium-chain fatty acid; and(c) at least one saturated monocarboxylic medium-chain or long chain fatty acid.

2. The polyol ester composition according to Claim 1 , wherein the polyol ester composition has a kinematic viscosity of from about 41 mm2s-1to about 1 10 mm2s-1at 40 °C.

3. The polyol ester composition according to Claim 1 , wherein the polyol ester composition has a kinematic viscosity of from about 41 mm2s-1to about 51 mm2s-1at 40 °C.

4. The polyol ester composition according to Claim 1 , wherein the polyol ester composition has a kinematic viscosity of from about 61 mm2s-1to about 75 mm2s-1at 40 °C.

5. The polyol ester composition according to Claim 1 , wherein the polyol ester composition has a kinematic viscosity of from about 90 mm2s-1to about 1 10 mm2s-1at 40 °C.

6. The polyol ester composition according to Claim 1 , wherein the at least one polyol compound is a primary alcohol with three or more hydroxyl groups, optionally wherein the at least one polyol compound is a primary alcohol with four hydroxyl groups.

7. The polyol ester composition according to Claim 1 , wherein the at least one polyol compound is selected from a group consisting of glycerol, trimethylolpropane, and pentaerythritol, optionally wherein the at least one polyol compound is pentaerythritol.

8. The polyol ester composition according to Claim 1 , wherein the at least one saturated dicarboxylic medium-chain fatty acid is a linear or branched C6 to C12 saturated dicarboxylic acid, for example, a linear or branched C8 to C10 saturated dicarboxylic acid.

9. The polyol ester composition according to Claim 1 , wherein the at least one saturated dicarboxylic medium-chain fatty acid is a linear or branched C9 saturated dicarboxylic acid, for example, azelaic acid.

10. The polyol ester composition according to Claim 1 , wherein the at least one saturated monocarboxylic medium-chain or long-chain fatty acid is a linear or branched C6 to C18 saturated monocarboxylic acid, for example, a linear or branched C8 to C16 saturated monocarboxylic acid.11 . The polyol ester composition according to Claim 1 , wherein the at least one saturated monocarboxylic medium-chain or long-chain fatty acid is a linear or branched C8 to C10 saturated monocarboxylic acid, for example decanoic acid, pelargonic acid or octanoic acid.

12. The polyol ester composition according to Claim 1 , wherein the at least one saturated monocarboxylic medium-chain or long-chain fatty acid comprises two saturated monocarboxylic medium-chain fatty acids, wherein the two saturated monocarboxylic medium-chain fatty acids are:(a) decanoic acid and pelargonic acid; or(b) decanoic acid and octanoic acid.

13. The polyol ester composition according to Claim 1 , wherein the at least one saturated monocarboxylic medium-chain or long-chain fatty acid comprises: one saturated monocarboxylic medium-chain fatty acid, wherein the saturated monocarboxylic medium-chain fatty acid is a C6 to C8 saturated monocarboxylic acid; and one saturated monocarboxylic long-chain fatty acid, wherein the saturated monocarboxylic long-chain fatty acid is isostearic acid.

14. A method of preparing a polyol ester composition, the method comprising subjecting:(a) at least one polyol compound;(b) at least one saturated dicarboxylic medium-chain fatty acid; and(c) at least one saturated monocarboxylic medium-chain or long-chain fatty acid, to an esterification reaction to provide the polyol ester composition, wherein the polyol ester composition has a flash point of at least 290 °C.

15. The method according to Claim 14, wherein the polyol ester composition has a kinematic viscosity of from about 41 mm2s-1to about 110 mm2s-1at 40 °C.

16. The method according to Claim 14, wherein the polyol ester composition has a kinematic viscosity of from about 41 mm2s-1to about 51 mm2s-1at 40 °C.

17. The method according to Claim 14, wherein the polyol ester composition has a kinematic viscosity of from about 61 mm2s-1to about 75 mm2s-1at 40 °C.

18. The method according to Claim 14, wherein the polyol ester composition has a kinematic viscosity of from about 90 mm2s-1to about 110 mm2s-1at 40 °C.

19. The method according to Claim 14, wherein the at least one polyol compound is a primary alcohol with three or more hydroxyl groups, optionally wherein the at least one polyol compound is a primary alcohol with four hydroxyl groups.

20. The method according to Claim 14, wherein the at least one polyol compound is selected from a group consisting of glycerol, trimethylolpropane, and pentaerythritol, optionally wherein the at least one polyol compound is pentaerythritol.21 . The method according to Claim 14, wherein the at least one saturated dicarboxylic medium-chain fatty acid is a linear or branched C6 to C12 saturated dicarboxylic acid, for example, a linear or branched C8 to C10 saturated dicarboxylic acid.

22. The method according to Claim 14, wherein the at least one saturated dicarboxylic medium-chain fatty acid is a linear or branched C9 saturated dicarboxylic acid, for example, azelaic acid.

23. The method according to Claim 14, wherein the at least one saturated monocarboxylic medium-chain or long-chain fatty acid is a linear or branched C6 to C18 saturated monocarboxylic acid, for example, a linear or branched C8 to C16 saturated monocarboxylic acid.

24. The method according to Claim 14, wherein the at least one saturated monocarboxylic medium-chain or long-chain fatty acid is a linear or branched C8 to C10 saturated monocarboxylic acid, for example decanoic acid, pelargonic acid or octanoic acid.

25. The method according to Claim 14, wherein the at least one saturated monocarboxylic medium-chain or long-chain fatty acid comprises two saturated monocarboxylic medium-chain fatty acids, the two saturated monocarboxylic medium-chain fatty acids are:(a) decanoic acid and pelargonic acid; or(b) decanoic acid and octanoic acid.

26. The method according to Claim 14, wherein the at least one saturated monocarboxylic medium-chain or long-chain fatty acid comprises: one saturated monocarboxylic medium-chain fatty acid, wherein the saturated monocarboxylic medium-chain fatty acid is a C6 to C8 saturated monocarboxylic acid; and one saturated monocarboxylic long-chain fatty acid, wherein the saturated monocarboxylic long-chain fatty acid is isostearic acid.

27. The method according to Claim 14, wherein the method comprises preparing a reaction mixture comprising (a), (b) and (c), wherein the reaction mixture has a hydroxyl group to carboxyl group molar ratio (HCR) of 0.94 or less than 1 .

28. A polyol ester composition obtained by the method according to Claim 14.

29. The polyol ester composition of Claim 1 , or the method according to Claim 14, wherein the polyol ester composition comprises a polyol ester of Formula I:Formula I wherein,Ri, R2, R3, R4, Rs and R6are each independently: a linear or branched saturated C6-18 alkyl ; or a linear or branched saturated CB-12 alkyl with a terminal carboxylic acid group which is optionally esterified with a polyol compound of formula R7-OH; wherein R7is a linear or branched primary polyol having from 3 to 8 carbon atoms and each alcohol functional group in R7is optionally esterified with a linear or branched saturated monocarboxylic acid having from 6 to 18 carbon atoms, or a linear or branched saturated dicarboxylic acid having from 6 to 12 carbon atoms.

30. The polyol ester composition, or the method according to Claim 29, wherein, Ri, R2, R3, R4, Rs and R6are each independently: a linear Cs-w alkyl; or a linear Cg alkyl with a terminal carboxylic acid group which is optionally esterified with a polyol compound of formula R7-OH; wherein R7is a branched primary polyol having 5 carbon atoms and each alcohol functional group in R7is optionally esterified with a linear saturated monocarboxylic acid having from 8 to 10 carbon atoms, or a linear saturated dicarboxylic acid having 9 carbon atoms.31 . A fire-resistant hydraulic fluid formulation comprising:(a) the polyol ester composition according to Claim 1 ; and(b) a pour point depressant.

32. The fire-resistant hydraulic fluid formulation according to Claim 31 , wherein the pour point depressant is a polymeric aliphatic ester or an aromatic ester, for example, the pour point depressant may be selected from the group consisting of a polyadipate, a modified polyolefin (e.g. a polyalkylmethacrylate (PAMA)), a phthalate ester (e.g. diisononyl phthalate), and a combination of two or more thereof.