EP2207868A1 - Tractor hydraulic fluid compositions and preparation thereof - Google Patents

Abstract

A tractor hydraulic fluid composition is prepared from an isomerized base oil which: a) the product itself, its fraction, or feed originates from or is produced at some stage by isomerization of a waxy feed from a Fischer-Tropsch process ('Fischer-Tropsch derived base oils'); or b) made from a substantially paraffinic wax feed ('waxy feed'). In one embodiment, the tractor hydraulic fluid composition is characterized as having a reduced level of viscosity modifier in an amount of 0 to 10 wt. %, and a Brookfield viscosity at -35oC of less than 70,000 mPa.s.

Description

Tractor Hydraulic Fluid Compositions and Preparation Thereof

[001] This application claims benefit under 35 USC 119 of Provisional Application 60/975,720 filed September 27, 2007, the disclosure of which is incorporated herein by reference. FIELD OF THE INVENTION

[002] The invention relates generally to tractor hydraulic fluid compositions, and more specifically to tractor hydraulic fluid compositions having reduced levels of viscosity modifiers.

BACKGROUND [003] Tractor hydraulic fluids are multi-application lubricants that are used to lubricate the moving parts of off-highway mobile equipment, such as tractors, off- highway equipment, construction equipment, etc. In some embodiments, such fluids are designed to lubricate all of transmissions, differentials, final-drive planetary gears, wet-brakes, and hydraulic systems of such equipment, meeting specific manufacturer requirements. Equipment manufacturers want lower viscosities at lower temperature (i.e., -4O⁰C) while maintaining high temperature (i.e., 100⁰C) thickening.

[004] Tractor hydraulic fluid compositions in the prior art typically employ a Group I, II, III, IV (that is, a synthetic PAO (for poly α-olefin)), or mixtures thereof as a base oil stock. The groups are broad categories of base stocks developed by the American Petroleum Institute (API) for the purpose of creating guidelines for base oils. Recent reforming processes have formed a new class of oil, e.g., Fischer- Tropsch base oil (FTBO), wherein the oil, fraction, or feed originates from or is produced at some stage by a Fischer-Tropsch process.

[005] The Fischer-Tropsch synthesis products can be obtained by well-known processes such as, for example, the commercial SASOL® Slurry Phase Fischer- Tropsch technology, the commercial SHELL® Middle Distillate Synthesis (SMDS) Process, or by the non-commercial EXXON® Advanced Gas Conversion (AGC-21) process. Details of these processes and others are described in, for example, EP-A- 776959, EP-A-668342; U.S. Patent Nos. 4,943,672, 5,059,299, 5,733,839, and RE39073 ; and US Published Application No. 2005/0227866, WO-A-9934917, WO- A-9920720 and WO-A-05107935. The Fischer-Tropsch synthesis product usually comprises hydrocarbons having 1 to 100, or even more than 100 carbon atoms, and typically includes paraffins, olefins and oxygenated products. Fischer Tropsch is a viable process to generate clean alternative hydrocarbon products. In the process of making Fischer-Tropsch base oil, an intermediate feed or product may be fractionated by atmospheric or vacuum distillation, hi cases where a broad-boiling hydroisomerized base oil is fractionated, the bottoms material collected from the vacuum distillation column comprises a mixture of high-boiling hydrocarbons.

[006] U.S. Patent No. 7189682 discloses a tractor hydraulic fluid using a mixture of viscosity modifier types of: 2 to 30 wt. % of a first viscosity modifier having a weight average molecular weight of 10,000 to 60,000; and 1 to 6 wt. % of a second viscosity modifier having a weight average molecular weight greater than that of the first viscosity modifier, and in the range of 50,000 to 200,000. Suitable oils to be used in the tractor hydraulic fluid include those prepared by Fischer-Tropsch syntheses. [007] The use of viscosity modifiers may reduce the shear stability of tractor hydraulic fluid in certain applications. There is a need for an improved tractor hydraulic fluid composition having reduced levels of viscosity index modifiers, while still meeting the target kinematic viscosity and low temperature Brookfield viscosity specifications for tractor equipment. SUMMARY OF THE INVENTION

[008] In one embodiment, there is provided a tractor hydraulic fluid composition comprising (i) a lubricating base oil; (ii) from 0 to 10 wt % of a viscosity modifier; and (iii) 0-10 wt % of at least an additive package. The lubricating base oil has consecutive numbers of carbon atoms and less than 7.5 wt% naphthenic carbon by n-d-M. The tractor hydraulic fluid composition has a Brookfield viscosity of less than 70,000 mPa.s at -35⁰C. and a kinematic viscosity of at least 7.0 mm²/s at 100⁰C.

[009] In another embodiment, there is provided a method for producing a tractor hydraulic fluid composition having a Brookfield viscosity of less than 70,000 mPa.s at -35⁰C, a kinematic viscosity of at least 7.0 mm²/s at 100⁰C. The method comprising blending (i) a lubricating base oil having consecutive numbers of carbon atoms and less than 7.5 wt% naphthenic carbon by n-d-M; with (ii) from 0 to 10 wt % of a viscosity modifier; and (iii) 0-10 wt % of at least an additive package.

[010] In yet another embodiment, there is provided a process for lubricating equipment, comprising: supplying to a fluid reservoir of an off-highway mobile equipment a tractor hydraulic fluid composition comprising (i) a lubricating base oil ; (ii) from 0 to 10 wt % of a viscosity modifier; and (iii) 0-10 wt % of at least an additive package; wherein the lubricating base oil consists essentially of at least an isomerized base oil having consecutive numbers of carbon atoms and less than 7.5 wt% naphthenic carbon by n-d-M; and the tractor hydraulic fluid composition has a Brookfield viscosity of less than 70,000 mPa.s at -35⁰C, and a kinematic viscosity of at least 7.0 mm²/s. at 100⁰C.

DESCRIPTION OF THE DRAWINGS

[011] Figure 1 is a graph illustrating the effect of base oil viscosity on the Brookfield viscosity at -35⁰C, comparing blends employing isomerized base oils with prior art blends containing API Group I and API Group II base oils.

DETAILED DESCRIPTION

[012] The following terms will be used throughout the specification and will have the following meanings unless otherwise indicated.

[013] "Fischer-Tropsch derived" means that the product, fraction, or feed originates from or is produced at some stage by a Fischer-Tropsch process. As used herein, "Fischer-Tropsch base oil" may be used interchangeably with "FT base oil," "FTBO," "GTL base oil" (GTL: gas-to-liquid), or "Fischer-Tropsch derived base oil."

[014] As used herein, "isomerized base oil" refers to a base oil made by isomerization of a waxy feed. [015] As used herein, a "waxy feed" comprises at least 40 wt% n-paraffins. In one embodiment, the waxy feed comprises greater than 50 wt% n-paraffins. In another embodiment, greater than 75 wt% n-paraffins. In one embodiment, the waxy feed also has very low levels of nitrogen and sulphur, e.g., less than 25 ppm total combined nitrogen and sulfur, or in other embodiments less than 20 ppm. Examples of waxy feeds include slack waxes, deoiled slack waxes, refined foots oils, waxy lubricant raffinates, n-paraffin waxes, NAO waxes, waxes produced in chemical plant processes, deoiled petroleum derived waxes, macrocrystalline waxes, Fischer-Tropsch waxes, and mixtures thereof. In one embodiment, the waxy feeds have a pour point of greater than 5O⁰C. In another embodiment, greater than 60°C.

[016] As used herein, "Pour Point Reducing Blend Component" refers to an isomerized waxy product with relatively high molecular weights and a specified degree of alkyl branching in the molecule, such that it reduces the pour point of lubricating base oil blends containing it. Examples of a Pour Point Reducing Blend Component are disclosed in U.S. Patent Nos. 6,150,577 and 7,053,254, and Patent Publication No. US 2005-0247600 Al . A Pour Point Reducing Blend Component can be: 1) an isomerized Fischer-Tropsch derived bottoms product; 2) a bottoms product prepared from an isomerized highly waxy mineral oil; or 3) an isomerized oil having a kinematic viscosity at 100°C of at least about 8 mm²/s made from polyethylene plastic.

[017] "Kinematic viscosity" is a measurement in mm²/s of the resistance to flow of a fluid under gravity, determined by ASTM D445-06.

[018] "Viscosity index" (VI) is an empirical, unit-less number indicating the effect of temperature change on the kinematic viscosity of the oil. The higher the VI of an oil, the lower its tendency to change viscosity with temperature. Viscosity index is measured according to ASTM D 2270-04. [019] The boiling range distribution (SIMDIST TBP) of base oil, by wt%, is determined by simulated distillation according to ASTM D 6352-04, "Boiling Range Distribution of Petroleum Distillates in Boiling Range from 174 to 700°C by Gas Chromatography."

[020] "Noack volatility" is defined as the mass of oil, expressed in weight %, which is lost when the oil is heated at 25O⁰C. with a constant flow of air drawn through it for 60 min., measured according to ASTM D5800-05, Procedure B. An alternative method to use is TGA Noack, by ASTM D6375-05. Where the TGA Noack is used, it is indicated.

[021] "Brookfield viscosity" is used to determine the internal fluid-friction of a lubricant during cold temperature operation, which can be measured by ASTM D 2983-04. [022] "Pour point" is a measurement of the temperature at which a sample of base oil will begin to flow under certain carefully controlled conditions, which can be determined as described in ASTM D 5950-02.

[023] "Ln" refers to natural logarithm with base "e." [024] "Traction coefficient" is an indicator of intrinsic lubricant properties, expressed as the dimensionless ratio of the friction force F and the normal force N, where friction is the mechanical force which resists movement or hinders movement between sliding or rolling surfaces. Traction coefficient can be measured with an MTM Traction Measurement System from PCS Instruments, Ltd. , configured with a polished 19 mm diameter ball (SAE AISI 52100 steel) angled at 220 to a flat 46 mm diameter polished disk (SAE AISI 52100 steel). The steel ball and disk are independently measured at an average rolling speed of 3 meters per second, a slide to roll ratio of 40 percent, and a load of 20 Newtons. The slide to roll ratio is defined as the difference in sliding speed between the ball and disk divided by the mean speed of the ball and disk, i.e. slide to roll ratio = (Speedl-Speed2)/((Speedl+Speed2)/2).

[025] As used herein, "consecutive numbers of carbon atoms" means that the base oil has a distribution of hydrocarbon molecules over a range of carbon numbers, with every number of carbon numbers in-between. For example, the base oil may have hydrocarbon molecules ranging from C22 to C36 or from C30 to C60 with every carbon number in-between. The hydrocarbon molecules of the base oil differ from each other by consecutive numbers of carbon atoms, as a consequence of the waxy feed also having consecutive numbers of carbon atoms. For example, in the Fischer- Tropsch hydrocarbon synthesis reaction, the source of carbon atoms is CO and the hydrocarbon molecules are built up one carbon atom at a time. Petroleum-derived waxy feeds have consecutive numbers of carbon atoms. In contrast to an oil based on poly-alpha-olefin ("PAO"), the molecules of an isomerized base oil have a more linear structure, comprising a relatively long backbone with short branches. The classic textbook description of a PAO is a star-shaped molecule, and in particular tridecane, which is illustrated as three decane molecules attached at a central point. While a star-shaped molecule is theoretical, nevertheless PAO molecules have fewer and longer branches than the hydrocarbon molecules that make up the isomerized base oil disclosed herein.

[026] "Molecules with cycloparaffinic functionality" mean any molecule that is, or contains as one or more substituents, a monocyclic or a fused multicyclic saturated hydrocarbon group.

[027] "Molecules with monocycloparaffϊnic functionality" mean any molecule that is a monocyclic saturated hydrocarbon group of three to seven ring carbons or any molecule that is substituted with a single monocyclic saturated hydrocarbon group of three to seven ring carbons. [028] "Molecules with multicycloparaffinic functionality" mean any molecule that is a fused multicyclic saturated hydrocarbon ring group of two or more fused rings, any molecule that is substituted with one or more fused multicyclic saturated hydrocarbon ring groups of two or more fused rings, or any molecule that is substituted with more than one monocyclic saturated hydrocarbon group of three to seven ring carbons.

[029] Molecules with cycloparaffinic functionality, molecules with monocycloparaffinic functionality, and molecules with multicycloparaffinic functionality are reported as weight percent and are determined by a combination of Field Ionization Mass Spectroscopy (FIMS), HPLC-UV for aromatics, and Proton NMR for olefins, further fully described herein.

[030] "Oxidator BN" measures the response of a lubricating oil in a simulated application. High values, or long times to adsorb one liter of oxygen, indicate good stability. Oxidator BN can be measured via a Dornte-type oxygen absorption apparatus (R. W. Dornte "Oxidation of White Oils," Industrial and Engineering Chemistry, Vol. 28, page 26, 1936). Using this apparatus, under 1 atmosphere of pure oxygen at 34O⁰F, the time to absorb 1000 ml of O₂ by 100 g of oil is reported. In the Oxidator BN test, 0.8 ml of catalyst is used per 100 grams of oil. The catalyst is a mixture of soluble metal-naphthenates simulating the average metal analysis of used crankcase oil. The additive package is 80 millimoles of zinc bispolypropylenephenyl- dithiophosphate per 100 grams of oil. [031] Molecular characterizations can be performed by methods known in the art, including Field Ionization Mass Spectroscopy (FIMS) and n-d-M analysis (ASTM D 3238-95 (Re-approved 2005) with normalization). In FIMS, the base oil is characterized as alkanes and molecules with different numbers of unsaturations. The molecules with different numbers of unsaturations may be comprised of cycloparaffins, olefins, and aromatics. If aromatics are present in significant amount, they would be identified as 4-unsaturations. When olefins are present in significant amounts, they would be identified as 1 -unsaturations. The total of the 1 -unsaturations, 2-unsaturations, 3 -unsaturations, 4-unsaturations, 5-unsaturations, and 6-unsaturations from the FIMS analysis, minus the wt % olefins by proton NMR, and minus the wt % aromatics by HPLC-UV is the total weight percent of molecules with cycloparaffmic functionality. If the aromatics content was not measured, it was assumed to be less than 0.1 wt % and not included in the calculation for total weight percent of molecules with cycloparaffmic functionality. The total weight percent of molecules with cycloparaffinic functionality is the sum of the weight percent of molecules with monocyclopraffinic functionality and the weight percent of molecules with multicycloparaffinic functionality.

[032] Molecular weights are determined by ASTM D2503-92 (Reapproved 2002). The method uses thermoelectric measurement of vapour pressure (VPO). In circumstances where there is insufficient sample volume, an alternative method of ASTM D2502-04 may be used; and where this has been used it is indicated.

[033] Density is determined by ASTM D4052-96 (Reapproved 2002). The sample is introduced into an oscillating sample tube and the change in oscillating frequency caused by the change in the mass of the tube is used in conjunction with calibration data to determine the density of the sample.

[034] Weight percent olefins can be determined by proton-NMR according to the steps specified herein. In most tests, the olefins are conventional olefins, i.e. a distributed mixture of those olefin types having hydrogens attached to the double bond carbons such as: alpha, vinylidene, cis, trans, and tri-substituted, with a detectable allylic to olefin integral ratio between 1 and 2.5. When this ratio exceeds 3, it indicates a higher percentage of tri or tetra substituted olefins being present, thus other assumptions known in the analytical art can be made to calculate the number of double bonds in the sample. The steps are as follows: A) Prepare a solution of 5- 10% of the test hydrocarbon in deuterochloroform. B) Acquire a normal proton spectrum of at least 12 ppm spectral width and accurately reference the chemical shift (pp^m) ^aχis₅ with the instrument having sufficient gain range to acquire a signal without overloading the receiver/ ADC, e.g., when a 30 degree pulse is applied, the instrument having a minimum signal digitization dynamic range of 65,000. In one embodiment, the instrument has a dynamic range of at least 260,000. C) Measure the integral intensities between: 6.0-4.5 ppm (olefin); 2.2-1.9 ppm (allylic); and 1.9-0.5 ppm (saturate). D) Using the molecular weight of the test substance determined by ASTM D 2503-92 (Reapproved 2002), calculate: 1. The average molecular formula of the saturated hydrocarbons; 2. The average molecular formula of the olefins; 3. The total integral intensity (=sum of all integral intensities); 4. The integral intensity per sample hydrogen (=total integral/number of hydrogens in formula); 5. The number of olefin hydrogens (=olefin integral/integral per hydrogen); 6. The number of double bonds (=olefin hydrogen times hydrogens in olefin formula/2); and 7. The wt% olefins by proton NMR = 100 times the number of double bonds times the number of hydrogens in a typical olefin molecule divided by the number of hydrogens in a typical test substance molecule. In this test, the wt% olefins by proton NMR calculation procedure, D, works particularly well when the percent olefins result is low, less than 15 wt%.

[035] Weight percent aromatics in one embodiment can be measured by HPLC-UV. In one embodiment, the test is conducted using a Hewlett Packard 1050 Series Quaternary Gradient High Performance Liquid Chromatography (HPLC) system, coupled with a HP 1050 Diode- Array UV-Vis detector interfaced to an HP

Chem-station. Identification of the individual aromatic classes in the highly saturated base oil can be made on the basis of the UV spectral pattern and the elution time. The amino column used for this analysis differentiates aromatic molecules largely on the basis of their ring- number (or double-bond number). Thus, the single ring aromatic containing molecules elute first, followed by the polycyclic aromatics in order of increasing double bond number per molecule. For aromatics with similar double bond character, those with only alkyl substitution on the ring elute sooner than those with naphthenic substitution. Unequivocal identification of the various base oil aromatic hydrocarbons from their UV absorbance spectra can be accomplished recognizing that their peak electronic transitions are all red-shifted relative to the pure model compound analogs to a degree dependent on the amount of alkyl and naphthenic substitution on the ring system. Quantification of the eluting aromatic compounds can be made by integrating chromatograms made from wavelengths optimized for each general class of compounds over the appropriate retention time window for that aromatic. Retention time window limits for each aromatic class can be determined by manually evaluating the individual absorbance spectra of eluting compounds at different times and assigning them to the appropriate aromatic class based on their qualitative similarity to model compound absorption spectra.

[036] Weight percent aromatic carbon ("Ca"), weight percent naphthenic carbon ("Cn") and weight percent paraffinic carbon ("Cp") in one embodiment can be measured by ASTM D3238-95 (Reapproved 2005) with normalization. ASTM

D3238-95 (Reapproved 2005) is the Standard Test Method for Calculation of Carbon Distribution and Structural Group Analysis of Petroleum Oils by the n-d-M Method. This method is for "olefin free" feedstocks which are assumed in this application to mean that that olefin content is 2 wt% or less. The normalization process consists of the following: A) If the Ca value is less than zero, Ca is set to zero, and Cn and Cp are increased proportionally so that the sum is 100%. B) If the Cn value is less than zero, Cn is set to zero, and Ca and Cp are increased proportionally so that the sum is 100%; and C) If both Cn and Ca are less than zero, Cn and Ca are set to zero, and Cp is set to 100%. [037] Extent of branching refers to the number of alkyl branches in hydrocarbons. Branching and branching position can be determined using carbon- 13 (¹³C) NMR according to the following nine-step process: 1) Identify the CH branch centers and the CH₃ branch termination points using the DEPT Pulse sequence (Doddrell, D.T.; D. T. Pegg; M.R. Bendall, Journal of Magnetic Resonance 1982, 48, 323ff). 2) Verify the absence of carbons initiating multiple branches (quaternary carbons) using the APT pulse sequence (Part, S. L.; J. N. Shoolery, Journal of Magnetic Resonance 1982, 46, 535ff.). 3) Assign the various branch carbon resonances to specific branch positions and lengths using tabulated and calculated values known in the art (Lindeman, L. P., Journal of Qualitative Analytical Chemistry 43, 1971 1245ff; Netzel, D.A., et.al., Fuel, 60, 1981, 307ff). 4) Estimate relative branching density at different carbon positions by comparing the integrated intensity of the specific carbon of the methyl/alkyl group to the intensity of a single carbon (which is equal to total integral/number of carbons per molecule in the mixture). For the 2-methyl branch, where both the terminal and the branch methyl occur at the same resonance position, the intensity is divided by two before estimating the branching density. If the 4-methyl branch fraction is calculated and tabulated, its contribution to the 4+methyls is subtracted to avoid double counting. 5) Calculate the average carbon number. The average carbon number is determined by dividing the molecular weight of the sample by 14 (the formula weight of CH₂). 6) The number of branches per molecule is the sum of the branches found in step 4. 7) The number of alkyl branches per 100 carbon atoms is calculated from the number of branches per molecule (step 6) times 100 / average carbon number. The measurements can be performed using any Fourier Transform NMR spectrometer, e.g., one having a magnet of 7.0 T or greater. After verification by Mass Spectrometry, UV or an NMR survey that aromatic carbons are absent, the spectral width for the ¹³C NMR studies can be limited to the saturated carbon region, 0-80 ppm vs. TMS (tetramethylsilane). Solutions of 25-50 wt. % in chloroform-dl are excited by 30 degrees pulses followed by a 1.3 seconds (sec.) acquisition time. In order to minimize non-uniform intensity data, the broadband proton inverse-gated decoupling is used during a 6 sec. delay prior to the excitation pulse and on during acquisition. Samples are doped with 0.03 to 0.05 M Cr (acac) ₃ (tris (acetylacetonato)-chromium (III)) as a relaxation agent to ensure full intensities are observed. The DEPT and APT sequences can be carried out according to literature descriptions with minor deviations described in the Varian or Bruker operating manuals. DEPT is Distortionless Enhancement by Polarization Transfer. The DEPT 45 sequence gives a signal all carbons bonded to protons. DEPT 90 shows CH carbons only. DEPT 135 shows CH and CH₃ up and CH₂ 180 degrees out of phase (down). APT is attached proton test, known in the art. It allows all carbons to be seen, but if CH and CH₃ are up, then quaternaries and CH₂ are down. The branching properties of the sample can be determined by ¹³C NMR using the assumption in the calculations that the entire sample was iso-paraffϊnic. The unsaturates content may be measured using Field Ionization Mass Spectroscopy (FIMS). [038] In one embodiment, the tractor hydraulic fluid composition comprises a number of components, including optional additives, in a matrix of base oil.

[039] Base Oil Matrix Component: In one embodiment, the base oil (or blends thereof) comprises at least an isomerized base oil which the product itself, its fraction, or feed originates from or is produced at some stage by isomerization of a waxy feed from a Fischer-Tropsch process ("Fischer-Tropsch derived base oils"). In another embodiment, the base oil comprises at least an isomerized base oil made from a substantially paraffinic wax feed ("waxy feed").

[040] Fischer-Tropsch derived base oils are disclosed in a number of patent publications, including for example U.S. Pat. Nos. 6080301, 6090989, and 6165949, and US Patent Publication No. US2004/0079678A1, US20050133409,

US20060289337. The Fischer-Tropsch process is a catalyzed chemical reaction in which carbon monoxide and hydrogen are converted into liquid hydrocarbons of various forms including a light reaction product and a waxy reaction product, with both being substantially paraffinic. [041] In one embodiment the isomerized base oil has consecutive numbers of carbon atoms and has less than 7.5 wt% naphthenic carbon by n-d-M with normalization. In another embodiment the isomerized base oil has consecutive numbers of carbon atoms and has less than 5 wt% naphthenic carbon by n-d-M with normalization. In one embodiment, the isomerized base oil made from a waxy feed has a kinematic viscosity at 100⁰C between 1.5 and 3.5 mm²/s.

[042] In one embodiment, the isomerized base oil is made by a process in which the hydroisomerization dewaxing is performed at conditions sufficient for the base oil to have: a) a weight percent of all molecules with at least one aromatic functionality less than 0.30; b) a weight percent of all molecules with at least one cycloparaffinic functionality greater than 10; c) a ratio of weight percent molecules with monocycloparaffmic functionality to weight percent molecules with multicycloparaffinic functionality greater than 20 and d) a viscosity index greater than 28 x Ln (Kinematic viscosity at 100⁰C.) + 80.

[043] In another embodiment, the isomerized base oil is made from a process in which the highly paraffinic wax is hydroisomerized using a shape selective intermediate pore size molecular sieve comprising a noble metal hydrogenation component, and under conditions of 600 - 75O⁰F. (315 - 399⁰C.) In the process, the conditions for hydroisomerization are controlled such that the conversion of the compounds boiling above 700⁰F (371⁰C.) in the wax feed to compounds boiling below 700⁰F (371⁰C.) is maintained between 10 wt % and 50 wt%. A resulting isomerized base oil has a kinematic viscosity of between 1.0 and 15 mm²/s at 100⁰C. and a Noack volatility of less than 50 weight %.

[044] In one embodiment the isomerized base oil has a Noack volatility less than an amount calculated by the following equation: 1000 x (Kinematic Viscosity at 100°C)^" . In another embodiment, the isomerized base oil has a Noack volatility less than an amount calculated by the following equation: 900 x (Kinematic Viscosity at lOO°C.) ^{"2 8}.

[045] In one embodiment, the isomerized base oil is made from a process in which the highly paraffinic waxy feed is hydroisomerized under conditions for the base oil to have a viscosity index of greater than 130. [046] In one embodiment, the isomerized base oil has a relatively low traction coefficient, specifically, its traction coefficient is less than an amount calculated by the equation: traction coefficient=0.009 x Ln (kinematic viscosity in mm²/s) -0.001, wherein the kinematic viscosity in the equation is the kinematic viscosity during the traction coefficient measurement and is between 2 and 50 mnϊVs. In one embodiment, the isomerized base oil has a traction coefficient of less than 0.023 (or less than 0.021) when measured at a kinematic viscosity of 15 mm /s and at a slide to roll ratio of 40%.

[047] In one embodiment, the base oil comprises greater than 10 wt. % and less than 70 wt. % total molecules with cycloparaffinic functionality, and a ratio of weight percent molecules with monocycloparaffinic functionality to weight percent molecules with multicycloparaffinic functionality greater than 15. [048] In one embodiment, the isomerized base oil is obtained from a process in which the highly paraffϊnic wax is hydroisomerized at a hydrogen to feed ratio from 712.4 to 3562 liter H₂/liter oil, for the base oil to have a total weight percent of molecules with cycloparaffinic functionality of greater than 10, and a ratio of weight percent molecules with monocycloparaffinic functionality to weight percent molecules with multicycloparaffinic functionality of greater than 15. In another embodiment, the base oil has a viscosity index greater than an amount defined by the equation: 28 x Ln (Kinematic viscosity at 100°C.) + 95.

[049] In one embodiment, the isomerized base oil contains between 2 and 7.5 wt% naphthenic carbon as measured by n-d-M. In one embodiment, the base oil has a kinematic viscosity of 1.5 - 3.0 mm²/s at 100°C. and 2-3 wt% naphthenic carbon. In another embodiment, a kinematic viscosity of 1.8 - 3.5 mm²/s at 100°C. and 2.5- 4 wt% naphthenic carbon. In a third embodiment, a kinematic viscosity of 3 - 6 mm²/s at 100°C. and 2.7 - 5 wt% naphthenic carbon. In a fourth embodiment, a kinematic viscosity of 10 - 15 mm²/s at 100°C. and between greater than 5.2 % and less than 7.5 wt% naphthenic carbon.

[050] In one embodiment, the tractor hydraulic fluid composition employs a base oil that consists of at least one of the isomerized base oils described above. In another embodiment, the composition consists essentially of at least a Fischer-Tropsch base oil. In yet another embodiment, the composition employs at least a Fischer- Tropsch base oil and optionally 5 to 95 wt. % of at least another type of oil, e.g., lubricant base oils selected from Group I, II, III, IV, and V lubricant base oils as defined in the API Interchange Guidelines, and mixtures thereof. Examples include conventionally used mineral oils, synthetic hydrocarbon oils or synthetic ester oils, or mixtures thereof depending on the application. Mineral lubricating oil base stocks can be any conventionally refined base stocks derived from paraffϊnic, naphthenic and mixed base crudes. Synthetic lubricating oils that can be used include esters of glycols and complex esters. Other synthetic oils that can be used include synthetic hydrocarbons such as polyalphaolefins; alkyl benzenes, e.g., alkylate bottoms from the alkylation of benzene with tetrapropylene, or the copolymers of ethylene and propylene; silicone oils, e.g., ethyl phenyl polysiloxanes, methyl polysiloxanes, etc., polyglycol oils, e.g., those obtained by condensing butyl alcohol with propylene oxide; etc. Other suitable synthetic oils include the polyphenyl ethers, e.g., those having from 3 to 7 ether linkages and 4 to 8 phenyl groups. Other suitable synthetic oils include polyisobutenes, and alkylated aromatics such as alkylated naphthalenes. [051] Viscosity Modifier Component: In one embodiment, the tractor hydraulic fluid composition comprises a reduced level of viscosity modifiers, while still meeting the target kinematic viscosity and low temperature Brookfϊeld viscosity specifications for mobile equipment. In one embodiment, this reduced level is in the range of 0 to 10 wt. %. In another embodiment, this reduced level ranges from 0.5 to 5 wt. %. In a third embodiment, the reduced level ranges from 1 - 3 wt. %. In a fourth embodiment, the reduced level is between 0.5 to 2 wt. %.

[052] In one embodiment, the reduced amount of viscosity modifiers used is a mixture of modifiers selected from polyacrylate or polymefhacrylate and polymers comprising vinyl aromatic units and esterified carboxyl-containing units. In one embodiment, the first viscosity modifier is a polyacrylate or polymethacrylate having an average molecular weight of 10,000 to 60,000. In another embodiment, the second viscosity modifier comprises vinyl aromatic units and esterified carboxyl-containing units, having an average molecular weight of 100,000 to 200,000.

[053] In yet another embodiment, the reduced amount of viscosity modifiers comprises a blend of a polymethacrylate viscosity modifier having a weight average molecular weight of 25,000 to 150,000 and a shear stability index less than 5 and a polymethacryate viscosity modifier having a weight average molecular weight of 500,000 to 1,000,000 and a shear stability index of 25 to 60.

[054] In yet another embodiment the viscosity modifier is selected from the group consisting of ethylene propylene copolymers; styrene-isoprene copolymers; hydrated styrene isoprene copolymers; poly alkyl (meth) acrylates; functionalized poly alkyl (meth) acrylates; and mixtures thereof.

[055] Additive Package Component: The tractor hydraulic fluid comprises at least an additive package. An "additive package" is a mixture of chemical substances designed to impart specific performance properties to the tractor hydraulic fluid. [056] In one embodiment, the additive package comprises at least a surfactant, or also known as a dispersant, which can be generally classified as anionic, cationic, zwitterionic, or non-ionic. In some embodiments a dispersant may be used alone or in combination of one or more species or types of dispersants. Examples include an oil-soluble dispersant selected from the group consisting of succinimide dispersants, succinic ester dispersants, succinic ester-amide dispersant, Mannich base dispersant, phosphorylated forms thereof, and boronated forms thereof. The dispersants may be capped with acidic molecules capable of reacting with secondary amino groups. The molecular weight of the hydrocarbyl groups may range from 600 to 3000, for example from 750 to 2500, and as a further example from 900 to 1500. In one embodiment, the dispersant is selected from the group of alkenyl succinimides, alkenyl succinimides modified with other organic compounds, alkenyl succinimides modified by post-treatment with ethylene carbonate or boric acid, pentaerythritols, phenate-salicylates and their post-treated analogs, polyamide ashless dispersants, and mixtures thereof.

[057] In some embodiments, the ashless dispersant may include the products of the reaction of a polyethylene polyamine, e.g., Methylene tetramine or tetraethylene pentamine, with a hydrocarbon substituted carboxylic acid or anhydride made by reaction of a polyolefin, such as polyisobutene, of suitable molecular weight, with an unsaturated polycarboxylic acid or anhydride, e.g., maleic anhydride, maleic acid, fumaric acid, or the like, including mixtures of two or more such substances. In another embodiment, the ashless dispersant is a borated dispersant. Borated dispersants may be formed by boronating (borating) an ashless dispersant having basic nitrogen and/or at least one hydroxyl group in the molecule, such as a succinimide dispersant, succinamide dispersant, succinic ester dispersant, succinic ester-amide dispersant, Mannich base dispersant, or hydrocarbyl amine or polyamine dispersant.

[058] In one embodiment, the additive package further comprises one or more metallic detergents, which are the metal salts of organic acids. The acids, or mixtures thereof, are reacted with inorganic bases such as metal oxides, metal hydroxides, and/or metal carbonates. Examples of metallic detergent include an oil- soluble neutral or overbased salt of alkali or alkaline earth metal with one or more of the following acidic substances (or mixtures thereof): (1) a sulfonic acid, (2) a carboxylic acid, (3) a salicylic acid, (4) an alkyl phenol, (5) a sulfurized alkyl phenol, and (6) an organic phosphorus acid characterized by at least one direct carbon-to- phosphorus linkage, such as a phosphonate. Such an organic phosphorus acid may include those prepared by the treatment of an olefin polymer (e.g., polyisobutylene having a molecular weight of 1,000) with a phosphorizing agent such as phosphorus trichloride, phosphorus heptasulfide, phosphorus pentasulfide, phosphorus trichloride and sulfur, white phosphorus and a sulfur halide, or phosphorothioic chloride. In yet another embodiment, the metallic detergent is selected from the group of sulfurized or unsulfurized alkyl or alkenyl phenates, alkyl or alkenyl aromatic sulfonates, borated sulfonates, sulfurized or unsulfurized metal salts of multi-hydroxy alkyl or alkenyl aromatic compounds, alkyl or alkenyl hydroxy aromatic sulfonates, sulfurized or unsulfurized alkyl or alkenyl naphthenates, metal salts of alkanoic acids, metal salts of an alkyl or alkenyl multiacid, and chemical and physical mixtures thereof. [059] In one embodiment, the additive package further comprises at least a corrosion inhibitor selected from thiazoles, triazoles, and thiadiazoles. Examples of such compounds include benzotriazole, tolyltriazole, octyltriazole, decyltriazole, dodecyltriazole, 2-mercapto benzothiazole, 2,5-dimercapto-l,3,4-thiadiazole, 2- mercapto- 5 -hydrocarbylthio- 1 ,3 ,4-thiadiazoles, 2-mercapto- 5 -hydrocarbyldithio- 1 ,3 ,4- thiadiazoles, 2,5-bis(hydrocarbylthio)- 1 ,3 ,4-thiadiazoles, and 2,5- bis(hydrocarbyldithio)-l,3,4-thiadiazoles. Suitable compounds include the 1,3 ,4- thiadiazoles, a number of which are available as articles of commerce, and also combinations of triazoles such as tolyltriazole with a 1,3,5-thiadiazole such as a 2,5- bis(alkyldithio)-l,3,4-thiadiazole. The 1,3 ,4-thiadiazoles are generally synthesized from hydrazine and carbon disulfide by known procedures. See, for example, U.S. Pat. Nos. 2,765,289; 2,749,311; 2,760,933; 2,850,453; 2,910,439; 3,663,561; 3,862,798; and 3,840,549.

[060] In another example, the additive package further includes rust or corrosion inhibitors selected from the group of monocarboxylic acids and polycarboxylic acids. Examples of suitable monocarboxylic acids are octanoic acid, decanoic acid and dodecanoic acid. Suitable polycarboxylic acids include dimer and trimer acids such as are produced from such acids as tall oil fatty acids, oleic acid, linoleic acid, or the like. Another useful type of rust inhibitor may comprise alkenyl succinic acid and alkenyl succinic anhydride corrosion inhibitors such as, for example, tetrapropenylsuccinic acid, tetrapropenylsuccinic anhydride, tetradecenylsuccinic acid, tetradecenylsuccinic anhydride, hexadecenylsuccinic acid, hexadecenylsuccinic anhydride, and the like. Also useful are the half esters of alkenyl succinic acids having 8 to 24 carbon atoms in the alkenyl group with alcohols such as the poly glycols. Other suitable rust or corrosion inhibitors include ether amines; acid phosphates; amines; polyethoxylated compounds such as ethoxylated amines, ethoxylated phenols, and ethoxylated alcohols; imidazolines; aminosuccinic acids or derivatives thereof, and the like. Mixtures of such rust or corrosion inhibitors can be used. Other examples of rust inhibitors include a polyethoxylated phenol, neutral calcium sulfonate and basic calcium sulfonate.

[061] In one embodiment, the additive package further comprises at least a friction modifier selected from the group of succinimide, a bis-succinimide, an alkylated fatty amine, an ethoxylated fatty amine, an amide, a glycerol ester, an imidazoline, fatty alcohol, fatty acid, amine, borated ester, other esters, phosphates, phosphites, phosphonates, and mixtures thereof.

[062] In one embodiment, the additive package further comprises at least an antiwear additive. Examples of such agents include, but are not limited to, phosphates, carbamates, esters, alkali metal or mixed alkali metal borates, alkaline earth metal borates, dispersions of hydrated alkali metal borates, dispersions of alkaline-earth metal borates, molybdenum complexes, and mixtures thereof. In one embodiment, the antiwear additive is selected from the group of a zinc dialkyl dithio phosphate (ZDDP), an alkyl phosphite, a trialkyl phosphite, and amine salts of dialkyl and mono-alkyl phosphoric acid.

[063] In one embodiment, the additive package may further comprise at least an antioxidant selected from the group of phenolic antioxidants, aromatic amine antioxidants, sulfurized phenolic antioxidants, and organic phosphites, among others. Examples of phenolic antioxidants include 2,6-di-tert-butylphenol, liquid mixtures of tertiary butylated phenols, 2,6-di-tert-butyl-4-methylphenol, 4,4'-methylenebis(2,6-di- tert-butylphenol), 2,2'-methylenebis(4-methyl6-tert-butylphenol), mixed methylene- bridged polyalkyl phenols, 4,4'-thiobis(2-methyl-6-tert-butylphenol), 4,4'-butylidene-bis(3-methyl-6-tert-butylphenol), 4,4'-isopropylidene-bis(2,6-di-tert-butylphenol), 2,2'-methylene-bis(4- methyl-6-nonylphenol), 2,2'-isobutylidene-bis(4,6-dimethylphenol), 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-ethylphenol, 2,4-dimethyl-6-tert-butyl-phenol, 2,6-di-tert-l-diniethylamino-p-cresol, 2,6-di-tert-4-(N,N'-dimethylaminomethylphenol), 4,4'-thiobis(2-methyl-6-tert-butylphenol), 2,2'-thiobis(4-methyl-6-tert-butylphenol), bis(3 -methyM-hydroxy-S-tert- 1 O-butylbenzyl)-sulfide, bis(3,5-di-tert-butyl-4-hydroxybenzyl),

2,2'-5-methylene-bis(4-methyl-6-cyclohexylphenol), N,N'-di-sec-butyl- phenylenediamine, 4-isopropylaminodiphenylamine, phenyl-.alpha.-naphthyl amine, and ring-alkylated diphenylamines. Examples include the sterically hindered tertiary butylated phenols, bisphenols and cinnamic acid derivatives and combinations thereof. In yet another embodiment, the antioxidant is an organic phosphonate having at least one direct carbon-to-phosphorus linkage. Diphenylamine-type oxidation inhibitors include, but are not limited to, alkylated diphenylamine, phenyl-alpha-naphthylamine, and alkylated-alpha-naphthylamine. Other types of oxidation inhibitors include metal dithiocarbamate (e.g., zinc dithiocarbamate), and 15-methylenebis(dibutyldithiocarbamate).

[064] In one embodiment, the additive package comprises at least an extreme pressure anti-wear agent (EP/ AW Agent). Examples include zinc dialky-1-dithiophosphate (primary alkyl, secondary alkyl, and aryl type), diphenyl sulfide, methyl trichlorostearate, chlorinated naphthalene, fluoroalkylpolysiloxane, lead naphthenate, neutralized phosphates, dithiophosphates, and sulfur-free phosphates.

[065] The additive package may also include conventional additives in addition to those described above. Examples include but are not limited to seal swell agents, colorants, antifoam and defoamer additives such as alkyl methacrylate polymers and dimethyl silicone polymers, and / or air expulsion additives. Such additives may be added to provide, for example, multiple functionality.

[066] In one embodiment, the additional components are added as a fully formulated additive package, fully formulated to meet an original equipment manufacturer's requirements for a tractor hydraulic fluid, e.g., giving the fluid the capacity to meet bench and dynamometer tests. The package to be used depends in part on the requirements of the specific equipment to receive the lubricant composition. Examples of additives and additive packages that have been used in tractor hydraulic fluids are disclosed in U.S. Pat. Nos. 5,635,459 and 5,843,873. Other examples of additive packages for use in tractor hydraulic fluid include but are not limited to those commercially available from the Lubrizol Corporation such as the Lubrizol 9990 series, Universal Tractor Transmission Oil (UTTO) package and Super Tractor Oil Universal (STOU) package. The key difference between Super Tractor Oil Universal (STOU) and Universal Tractor Transmission Oil (UTTO), is that, STOU can be used as a tractor engine oil as well as a transmission, final drive, wet brake and hydraulic fluid. Other than that, the two fluids are used in the same types of vehicles and equipment. In one embodiment, the additive comprises a material having the following characteristics: viscosity of 208 mm²/s at 25⁰C; 107 at 4O⁰C; 17.8 at 100⁰C; a pour point of -4O⁰C, and a flash point of 18O⁰C. In another embodiment, the additive package comprises among other materials, metal-containing detergents, such as 1 - 2% (e.g. 1.41%) of a calcium-overbased sulfonate detergent; antioxidants or anti-wear agents, such as 1 - 2% (e.g., 1.69%) of a zinc dialkyldithiophosphate; 0.5 to 2% (e.g. 1.03%) of friction modifiers; and 0.1 to 2 % (e.g., 0.25%) of a nitrogen- containing dispersant such as succinimide dispersants. Other conventional components may also be present, if desired.

[067] Pour Point Depressant: In one embodiment, the tractor hydraulic fluid comprises a sufficient amount of pour point depressant so that the pour point of the tractor hydraulic fluid blend is at least 3⁰C. below the pour point of a blend that does not have the pour point depressant. Pour point depressants are known in the art and include, but are not limited to, esters of maleic anhydride-styrene copolymers, polymethacrylates, polyacrylates, polyacrylamides, condensation products of haloparaffin waxes and aromatic compounds, vinyl carboxylate polymers, and terpolymers of dialkylfumarates, vinyl esters of fatty acids, ethylene-vinyl acetate copolymers, alkyl phenol formaldehyde condensation resins, alkyl vinyl ethers, olefin copolymers, and mixtures thereof. [068] Pour Point Reducing Blend Component: In one embodiment, the lubricating base oil contains a Pour Point Reducing Blend Component. In one embodiment, the Pour Point Reducing Blend Component is an isomerized Fischer- Tropsch derived vacuum distillation bottoms product, which is a high boiling syncrude fraction which has been isomerized under controlled conditions to give a specified degree of alkyl branching in the molecule. Syncrude prepared from the Fischer-Tropsch process comprises a mixture of various solid, liquid, and gaseous hydrocarbons. When the Fischer-Tropsch waxes are converted into Fischer-Tropsch base oils by various processes, such as by hydroprocessing and distillation, the base oils produced fall into different narrow-cut viscosity ranges. The bottoms that remains after recovering the lubricating base oil cuts from the vacuum column is generally unsuitable for use as a lubricating base oil itself and is usually recycled to a hydrocracking unit for conversion to lower molecular weight products.

[069] In one embodiment, the Pour Point Reducing Blend Component is an isomerized Fischer-Tropsch derived vacuum distillation bottoms product having an average molecular weight between 600 and 1100 and an average degree of branching in the molecules between 6.5 and 10 alkyl branches per 100 carbon atoms. Generally, the higher molecular weight hydrocarbons are more effective as Pour Point Reducing Blend Components than the lower molecular weight hydrocarbons. In one embodiment, a higher cut point in a vacuum distillation unit which results in a higher boiling bottoms material is used to prepare the Pour Point Reducing Blend

Component. The higher cut point also has the advantage of resulting in a higher yield of the distillate base oil fractions. In one embodiment, the Pour Point Reducing Blend Component is an isomerized Fischer-Tropsch derived vacuum distillation bottoms product having a pour point that is at least 3⁰C. higher than the pour point of the distillate base oil it is blended with. [070] In another embodiment, the Pour Point Reducing Blend Component is an isomerized petroleum derived base oil containing material having a boiling range above about 1050⁰F. In one embodiment, the isomerized bottoms material is solvent dewaxed prior to being used as a pour point reducing blend component. The waxy product further separated during solvent dewaxing from the pour point reducing blend component was found to display excellent improved pour point depressing properties compared to the oily product recovered after the solvent dewaxing.

[071] In one embodiment, the Pour Point Reducing Blend Component has an average degree of branching in the molecules within the range of from 6.5 to 10 alkyl branches per 100 carbon atoms. In another embodiment, the Pour Point Reducing Blend Component has an average molecular weight between 600 - 1100. In a third embodiment, between 700 - 1000.

[072] In another embodiment, the Pour Point Reducing Blend Component is an isomerized oil having a kinematic viscosity at 100⁰C of at least about 8 mm²/s made from polyethylene plastic. In another embodiment, the Pour Point Reducing Blend Component is made from waste plastic. In yet another embodiment the Pour Point Reducing Blend Component is made from a process comprising: pyrolysis of polyethylene plastic, separating out a heavy fraction, hydrotreating the heavy fraction, catalytic isomerizing the hydrotreated heavy fraction, and collecting the Pour Point Reducing Blend Component having a kinematic viscosity at 100°C of at least about 8 mm²/s. In one embodiment, the Pour Point Reducing Blend Component derived from polyethylene plastic has a boiling range above 1050°F. (565°C), or even a boiling range above 1200⁰F (649°C).

[073] Method for Making: Additives used in formulating the compositions can be blended into the base oil matrix individually or in various sub-combinations. In one embodiment, all of the components are blended concurrently using an additive concentrate (i.e., additives plus a diluent, such as a hydrocarbon solvent). The use of an additive concentrate takes advantage of the mutual compatibility afforded by the combination of ingredients when in the form of an additive concentrate. [074] In another embodiment, the tractor hydraulic fluid composition is prepared by mixing the base oil matrix with the separate additives or additive package(s) at an appropriate temperature, such as approximately 6O⁰C, until homogeneous.

[075] Properties: The tractor hydraulic fluid composition in one embodiment is characterized as having an excellent shear stability, with an unsheared kinematic viscosity at 100⁰C. of at least 9.1 mm²/s, a sheared kinematic viscosity at 100⁰C. of at least 7.1 mm²/s, and a Brookfield viscosity at -40⁰C. of less than 20,000 mPa.s. Shear stability can be expressed by a shear stability index (SSI), which is a measure of the tendency of tractor hydraulic fluid compositions to degrade and lose their ability to thicken and maintain viscosity, when subjected to shearing. Shearing can occur in pumps, gears, engines, etc. SSI can be measured by the Sonic Shear Method as set forth in ASTM Test D5621-01, per equation below: SSI = (μ; - μ_f) * 100 / (μ; - μ_o), wherein μ; is the initial viscosity of the fresh, unsheared fluid in mm²/s at 100⁰C, μ_f is the final viscosity of the tractor hydraulic fluid after test in mm²/s at 100⁰C, and μ₀ is the viscosity in mm²/s at 100⁰C. of the tractor hydraulic fluid with all additives except the viscosity modifiers.

[076] In one embodiment, the tractor hydraulic fluid exhibits a Brookfield viscosity at -35⁰C. of less than 70,000 mPa.s. In a second embodiment, the Brookfield viscosity at -35⁰C. is less than 50,000 mPa.s. In a third embodiment, less than 40,000 mPa.s. In a fourth embodiment, the Brookfield viscosity at -35⁰C. is less than 22,000 mPa.s. In a fifth embodiment, the Brookfield viscosity at -35 °C. is less than 18,000 mPa.s.

[077] Applications: In one embodiment, the tractor hydraulic fluid composition is supplied to the fluid reservoir of the equipment to be lubricated, and thence to the moving parts of the equipment itself including but not limited to tractors and / or off-highway mobile equipment. Moving parts include a transmission, a hydrostatic transmission, a gear box, a final drive, a hydraulic system, etc.

[078] The following Examples are given as non-limitative illustration of aspects of the present invention.

[079] EXAMPLES. Unless specified otherwise, the Examples are prepared by mixing the components in the amounts indicated in the tables. Mixing is accomplished in a beaker or a reactor vessel with mechanical stirring. Unless specified otherwise, the components in the examples are as follows:

[080] FT base oils are from Chevron Corporation of San Ramon, CA, indicated as FTBO-XL, FTBO-L, FTBO-M, and FTBO-H. The properties of the FTBO base oils used in the examples are shown in Tables 2 and 5.

[081] Chevron UCBO 4R and UCBO 7R are API Group III base oils from Chevron Corporation.

[082] Viscoplex™ 1-604 and Viscoplex™ 1-3006 are pour point depressants from Degussa of Germany. [083] Viscoplex™ 8-220 and Viscoplex™ 8-944 are viscosity modifiers from Degussa.

[084] 218-3 is a foam inhibitor.

[085] OLOA™ A, OLO A™ B, and OLO A™ C are additive packages from Chevron Oronite Company LLC of San Ramon, CA. [086] Examples 1-6: Table 1 lists the components and results of formulated blends employing different FT base oils (with the properties as shown in Table 2) as examples 1- 6. The samples were tested against John Deere J20C specification. The John Deere J20C specification for tractor hydraulic fluid requires a Brookfield viscosity of less than 70,000 cP at -35⁰C and a kinematic viscosity of at least 9.1 mm²/s at 100⁰C. In example 1 , the J20C requirements are easily achieved with the addition of 3 wt% viscosity modifier. In example 2, the base oil viscosity can be increased thereby requiring less viscosity modifier (1.5 wt%), while still meeting the J20C requirements. Example 3 shows that a blend without viscosity modifier did not meet the Brookfield viscosity requirements. Examples 4-6 are duplicates of Examples 1-3, except that the blends in Examples 4-6 are made with a combination of FTBO-L and FTBO-H, whereas the blends in Examples 1-3 are made with a combination of FTBO-M and FTBO-H. Table 1

Table 2

[087] Figure 1 is a graph comparing the Brookfield viscosity at -35⁰C versus the base oil viscosity at 100⁰C used in the blend. The graph compares typical data for API Group I and API Group II base oils with results from Examples 1-6, formulated tractor hydraulic fluid blends containing embodiments of isomerized base oils ("FTBO"). As shown, for a given value of base oil viscosity, the low temperature viscosities of the blends made with FTBO are much better than the blends made with either API Group I or II base oils. This allows the use of higher base oil viscosity for fluids made with FTBO, and the resultant use of less viscosity modifier in order to achieve the final product blend viscosity at 100⁰C. Besides the economic factor of using less viscosity modifier and thus less formula cost, the use of less viscosity modifier will also improve the shear stability of the final product.

[088] Example 7: Table 3 lists the components and results of a low viscosity blend prepared to meet the John Deere J20D specification, namely a Brookfield viscosity of less than 20,000 cP at -4O⁰C and a kinematic viscosity of at least 7.0 mm²/s at 100⁰C. Table 3

[089] Examples 8-10: Table 4 lists the components and results of formulated blends comparing blends made with prior art base oils with blends containing FT base oils (with the properties as shown in Table 5) as examples 8 - 10. As shown, the blends containing FT base oils meet the requirements of both John Deere J20C and J20D specifications, thus allowing the blends to be used in a very wide range of ambient temperatures because of their exceptional viscosities at both low (-4O⁰C) and high (100°C) temperatures. These types of tractor hydraulic fluids are referred to as "all season" or "all weather" fluids. Example 8 shows an "all weather" fluid made with commercial Group III base oil. Examples 9 and 10 show that the use of FT base oils has allowed a higher base oil viscosity for the blend, 5.2 mm²/s versus 5.0 mm²/s for Example 8 (prior art base oils). The higher base oil viscosity results in the use of less viscosity modifier because less thickening is needed to achieve the final product blend viscosity of about 9.4 mm²/s at 100°C. Less viscosity modifier will result in a more shear stable product because the viscosity modifier is the component in the blend which exhibits poor stability against sheardown. Table 4

Table 5

[090] For the purposes of this specification and appended claims, unless otherwise indicated, all numbers expressing quantities, percentages or proportions, and other numerical values used in the specification and claims, are to be understood as being modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained and / or the precision of an instrument for measuring the value. Furthermore, all ranges disclosed herein are inclusive of the endpoints and are independently combinable. In general, unless otherwise indicated, singular elements may be in the plural and vice versa with no loss of generality. As used herein, the term "include" and its grammatical variants are intended to be non- limiting, such that recitation of items in a list is not to the exclusion of other like items that can be substituted or added to the listed items.

Claims

WHAT IS CLAIMED IS:

1. A tractor hydraulic fluid composition comprising (i) a lubricating base oil ; (ii) from 0 to 10 wt % of a viscosity modifier; and (iii) 0-10 wt % of at least an additive package; wherein • the lubricating base oil consists essentially of at least an isomerized base oil having consecutive numbers of carbon atoms and less than 7.5 wt% naphthenic carbon by n-d-M; and

• the tractor hydraulic fluid composition has a Brookfield viscosity of less than 70,000 mPa.s at -35⁰C, and a kinematic viscosity of at least 7.0 mm²/s. at 100⁰C.

2. The tractor hydraulic fluid composition of claim 1 , having a viscosity index of greater than 130 and a Brookfield viscosity of less than 50,000 mPa.s at - 35⁰C.

3. The tractor hydraulic fluid composition of any of claims 1 - 2, having a viscosity index of greater than 150 and a Brookfield viscosity of less than 40,000 mPa.s at -35⁰C.

4. The tractor hydraulic fluid composition of any of claims 1 - 3, having a

Brookfield viscosity of less than 20,000 mPa.s at -4O⁰C.

5. The tractor hydraulic fluid composition of any of claims 1 - 4, having a traction coefficient less than 0.023, measured at a viscosity of 15 mni²/s and a slide to roll ratio of 40%.

6. The tractor hydraulic fluid composition of any of claims 1 - 5, comprising from 0.5 to 5 wt. %. of a viscosity modifier.

7. The tractor hydraulic fluid composition of any of claims 1 - 6, comprising from 1 to 3 wt. %. of a viscosity modifier.

8. The tractor hydraulic fluid composition of any of claims 1 - 7, wherein the lubricating base oil has a kinematic viscosity at 100°C in the range of 1 and 15 mm²/s and a Noack volatility less than an amount defined by the equation: 900 x (kinematic viscosity at 100⁰C) ^{"2 8} .

9. The tractor hydraulic fluid composition of any of claims 1 - 8, wherein the lubricating base oil comprises a Pour Point Reducing Blend Component with an average molecular weight between 600 and 1100, and an average degree of branching in the molecules between 6.5 and 10 alkyl branches per 100 carbon atoms.

10. The tractor hydraulic fluid composition of any of claims 1 - 9, wherein the tractor hydraulic fluid composition comprises at least a pour point depressant selected from the group of polymethacrylates; polyacrylates; polyacrylamides; condensation products of haloparaffϊn waxes and aromatic compounds; vinyl carboxylate polymers; terpolymers of dialkylfumarates, vinyl esters of fatty acids, and alkyl vinyl ethers; and mixtures thereof; wherein the additive package comprises at least an antioxidant selected from the group consisting of phenolics, aromatic amines, compounds containing sulfur and phosphorus, organosulfur compounds, organophosphor^ous compounds, and mixtures thereof; and wherein the viscosity modifier is selected from the group of: ethylene-propylene copolymers; styrene-isoprene copolymers; hydrated styrene-isoprene copolymers; poly alkyl (meth) acrylates; functionalized poly alkyl (meth) acrylates; a polyisobutylene having a weight average molecular weight ranging from 700 to 2,500; a graft copolymer comprising a polymer backbone which has been grafted by reacting the polymer backbone with a reactant comprising N-p- diphenylamine,l,2,3,6-tetrahydrophthalimide; 4-anilinophenyl methacrylamide; 4- anilinophenyl maleimide; 4-anilinophenyl itaconamide; an acrylate or methacrylate ester of 4-hydroxydiphenylamine; a reaction product of p-aminodiphenylamine or p- alkylaminodiphenylamine with glycidyl methacrylate; a reaction product of p- aminodiphenylamine with isobutyraldehyde, a derivative of p-hydroxydiphenylamine; a derivative of phenothiazine; a vinylogous derivative of diphenylamine; and mixtures thereof.

11. The tractor hydraulic fluid composition of any of claims 1 - 9, wherein the additive package comprises at least a metal detergent selected from an oil-soluble neutral or overbased salt of alkali or alkaline earth metal made from one or more of: (1) a sulfonic acid, (2) a carboxylic acid, (3) a salicylic acid, (4) an alkyl phenol, (5) a sulfurized alkyl phenol, (6) an organic phosphorus acid characterized by at least one direct carbon-to-phosphorus linkage; and (7) mixtures thereof.

12. The tractor hydraulic fluid composition of any of claims 1 - 11, wherein the isomerized base oil is a Fischer-Tropsch derived base oil.

13. The tractor hydraulic fluid composition of any of claims 1 - 12, wherein the isomerized base oil is made from a substantially paraffinic wax feed.

14. The tractor hydraulic fluid composition of claim I₅ wherein the additive package comprises at least one of: a Universal Tractor Transmission Oil (UTTO) additive package; and a Super Tractor Oil Universal (STOU) additive package.

15. A method for producing a tractor hydraulic fluid composition having a Brookfield viscosity of less than 70,000 cP at -35⁰C. and a kinematic viscosity of at least 7.0 mm²/s at 100⁰C, the method comprising blending (i) a lubricating base oil having consecutive numbers of carbon atoms and less than 7.5 wt% naphthenic carbon by n-d-M; with (ii) from 0 to 10 wt % of a viscosity modifier; and (iii) 0-10 wt % of at least an additive package, wherein the lubricating base oil is Fischer-Tropsch derived with less than 5 wt% naphthenic carbon and having a viscosity index greater than 130.