A biodegradable hydraulic fluid composition and a method of making the same

Abstract

The present application relates to a kind of biodegradable hydraulic oil composition and its preparation method, it includes the following weight parts of component: biodegradable base oil 96.0-98.5 parts and composite detergent 1.5-2.5 parts;The base oil is the mixture of pentaerythritol tetraester and trimethylolpropane triester, fatty acid chain is C8-C10 saturated fatty acid, saturation ≥90%, 28 days biodegradability meets the determination of OECD 301B;The composite detergent includes: octylated diphenylamine 0.45-0.90 parts, 2,6-di-tert-butyl-4-methylphenol 0.10-0.25 parts, 2-ethylhexyl acidic phosphate and its ethanolamine salt 0.60-1.20 parts, dodecenyl succinic acid di (2-ethylhexyl ester) 0.15-0.35 parts, and the mass ratio of octylated diphenylamine and 2,6-di-tert-butyl-4-methylphenol is 1.5:1~4:1.

Description

Technical Field

[0001] This invention relates to the field of hydraulic oil technology, and in particular to a biodegradable hydraulic oil composition and its preparation method. Background Technology

[0002] Hydraulic oil, as the working medium in hydraulic systems, plays multiple roles, including energy transmission, lubrication, cooling, and rust prevention. With the development of hydraulic technology towards higher pressure, higher speed, and greater precision, the performance requirements for hydraulic oil are constantly increasing, especially in applications with leakage risks such as engineering machinery, ships, and field construction equipment, where environmental impact is a growing concern. While existing mineral oil-based hydraulic oils possess high extreme pressure carrying capacity and excellent anti-deposition properties, their biodegradability is poor. Once leaked into soil or water, they can cause long-term environmental pollution, making it difficult to meet the requirements of environmental standards such as EU Ecolabel and OECD 301B.

[0003] To improve the environmental friendliness of hydraulic oils, existing technologies have proposed using synthetic esters as base oils for biodegradable hydraulic oils, especially saturated synthetic esters such as pentaerythritol esters and trimethylolpropane esters, which exhibit excellent performance in terms of biodegradability and hydrolysis resistance. However, highly saturated esters have lower molecular polarity, and their extreme pressure carrying capacity and boundary lubrication performance are generally lower than those of traditional mineral oil systems. Furthermore, they have limited ability to dissolve and disperse oxidation products and varnish precursors, making them prone to varnish and sludge deposition under high-temperature and high-pressure operating conditions. This can lead to valve sticking, increased filter differential pressure, and shortened cleaning cycles of the hydraulic system.

[0004] To balance biodegradability and core hydraulic oil performance, some technologies incorporate additives such as antioxidants, anti-wear and rust inhibitors, and dispersants into base oils. However, existing solutions often fail to optimize the base oil type, additive types, and proportions for the characteristics of highly saturated synthetic esters. This results in limited improvements in extreme pressure load-bearing capacity, high-cleanliness properties, and anti-deposit properties while enhancing environmental performance, making it difficult to meet the demands of long-life, high-reliability hydraulic systems. Therefore, there is an urgent need to develop a biodegradable hydraulic oil composition that can significantly improve anti-wear and high-cleanliness properties while maintaining high biodegradability. Summary of the Invention

[0005] This invention covers the following technical solutions:

[0006] One aspect of the present invention relates to a biodegradable hydraulic oil composition comprising the following components in parts by weight:

[0007] 96.0-98.5 parts of biodegradable base oil and 1.5-2.5 parts of compound detergent;

[0008] The base oil is a mixture of pentaerythritol tetraester and trimethylolpropane triester, with a fatty acid chain of C8-C10 saturated fatty acids, a saturation of ≥90%, and a 28-day biodegradability that meets the OECD 301B criteria.

[0009] The composite detergent comprises: 0.45-0.90 parts of octyl diphenylamine, 0.10-0.25 parts of 2,6-di-tert-butyl-4-methylphenol, 0.60-1.20 parts of 2-ethylhexyl acid phosphate and its ethanolamine salt, and 0.15-0.35 parts of dodecenyl succinate di(2-ethylhexyl ester), wherein the mass ratio of octyl diphenylamine to 2,6-di-tert-butyl-4-methylphenol is 1.5:1 to 4:1.

[0010] In some embodiments, the mass ratio of pentaerythritol tetraester to trimethylolpropane triester is 80:20 to 90:10.

[0011] In some embodiments, the ethanolamine salting ratio in the 2-ethylhexyl acid phosphate is 40%-60%, and the acid value of the acid phosphate is 50-70 mgKOH / g.

[0012] In some embodiments, the biodegradable hydraulic oil composition further comprises at least one of a biodegradable antifoaming agent, a demulsifier, and a pour point depressant.

[0013] In some embodiments, the antifoaming agent is 0.001-0.006 parts of a polyalkyl methacrylate type defoamer.

[0014] In some embodiments, the demulsifier is 0.0005-0.0015 parts of an EO / PO block copolymer.

[0015] In some embodiments, the pour point depressant is 0.03-0.12 parts of a polymethacrylate pour point depressant.

[0016] In some embodiments, the composition has an ash content of ≤0.02 wt% and a sulfur content of ≤0.3 wt%.

[0017] In some embodiments, the composition exhibits a biodegradability of ≥80% after 28 days using the OECD 301B method and complete oil-water separation within 10 minutes in the ASTM D1401 (54°C) water separation test.

[0018] According to another aspect of the present invention, a method for preparing the biodegradable hydraulic oil composition as described above is also provided, characterized by comprising the following steps:

[0019] (1) Add the mixture of the pentaerythritol tetraester and the trimethylolpropane triester into a stirring container and heat it to 40°C-60°C;

[0020] (2) Under stirring conditions, add octyl diphenylamine and 2,6-di-tert-butyl-4-methylphenol in sequence until they are fully dissolved. Then add 2-ethylhexyl acid phosphate and partially neutralize it with ethanolamine until the salting ratio is 40%-60% and the acid value of the system is 50-70 mgKOH / g. Continue stirring for 10-20 minutes. Then add the remaining components and stir for 10-20 minutes until homogeneous.

[0021] (3) Cool to room temperature.

[0022] This invention has at least one of the following technical effects:

[0023] 1. Significantly improved biodegradability and environmental performance.

[0024] By using a specific C8–C10 saturated pentaerythritol tetraester / trimethylolpropane triester combination with a saturation of ≥90%, and a biodegradability of ≥80% within 28 days under the OECD 301B method, leakage pollution can be reduced.

[0025] It has a low acid value and high hydrolysis stability, but its extreme pressure bearing capacity and sediment control capacity are lower than those of traditional mineral oil systems.

[0026] 2. Utilizing specific compound detergents to compensate for the shortcomings of base oils and achieve synergistic performance.

[0027] 2-Ethylhexyl acid phosphate and its ethanolamine salt form a chemical protective film on the metal surface, improving extreme pressure and anti-wear properties;

[0028] Di(2-ethylhexyl) dodecenyl succinate disperses and inhibits deposit formation;

[0029] Octyl diphenylamine and BHT work synergistically to resist oxidation, delay base oil oxidation, and reduce sludge and varnish film.

[0030] Ultimately, the composition achieves a high level in terms of environmental friendliness, wear resistance, and high-cleanliness. Detailed Implementation

[0031] Reference will now be made to detailed embodiments of the present invention, one or more of which are described below. Each example is provided for explanation and not for limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made to the invention without departing from its scope or spirit. For example, features described or illustrated as part of one embodiment may be used in another embodiment to produce further embodiments.

[0032] Unless otherwise stated, all terms used to disclose this invention (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Further guidance is provided below for a better understanding of the teachings of this invention. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0033] In this invention, unless otherwise stated, scientific and technical terms used herein have the meanings commonly understood by those skilled in the art.

[0034] The terms “containing,” “comprising,” and “including” as used in this invention are synonyms and are inclusive or open-ended, not excluding additional, uncited members, elements, or method steps.

[0035] In this invention, the numerical range represented by endpoints includes all numerical values ​​and fractions contained within that range, as well as the endpoints mentioned.

[0036] As used in this invention, the term "about" or "approximately" means within 20%, preferably within 10%, and more preferably within 5%, of a given value or range. It also includes specific numbers, such as about 20 including 20.

[0037] Furthermore, in describing representative embodiments of the invention, this specification may present the methods and / or processes of the invention as a specific sequence of steps. However, the method or process should not be limited to the specific order of the steps described herein, to the extent that the method or process does not depend on the specific order of the steps presented herein. As will be understood by those skilled in the art, other sequences of steps are also possible. Therefore, the specific order of steps presented in the specification should not be construed as a limitation of the claims. Additionally, the claims relating to the methods and / or processes of the invention should not be limited to the execution of their steps in the order they are written, and those skilled in the art will readily recognize that the sequence can be changed while still remaining within the spirit and scope of the invention.

[0038] This invention relates to concentration values, which include fluctuations within a certain range. For example, fluctuations are allowed within a corresponding precision range. For instance, 2% can fluctuate within ±0.1%. For larger values ​​or values ​​that do not require overly precise control, even greater fluctuations are permitted. For example, 100mM can fluctuate within ranges of ±1%, ±2%, ±5%, etc. Regarding molecular weight, fluctuations of ±10% are allowed.

[0039] As used in this invention, unless otherwise stated, the singular forms of the articles “a,” “an,” and “the” include plural referents.

[0040] In this invention, the terms "multiple" or "various" are used unless otherwise specified, referring to a quantity of 2 or more.

[0041] In this invention, the technical features described in an open-ended manner include both closed-ended technical solutions composed of the listed features and open-ended technical solutions that include the listed features.

[0042] In this invention, terms such as "preferred," "better," "more suitable," and "ideal" merely describe implementation methods or embodiments with better effects and should be understood not to limit the scope of protection of this invention. In this invention, terms such as "optionally," "optionally," and "optional" mean that something is optional, that is, selected from either "with" or "without" a parallel solution. If multiple "optional" statements appear in a technical solution, unless otherwise specified and without contradiction or mutual constraint, each "optional" statement is independent.

[0043] The embodiments of the present invention will be described in detail below with reference to examples. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. For experimental methods in the following embodiments where specific conditions are not specified, please refer to the guidelines given in this invention, or follow experimental manuals or conventional conditions in the art, or other experimental methods known in the art, or follow the conditions recommended by the manufacturer.

[0044] In the specific embodiments described below, the measurement parameters involving raw material components may have slight deviations within the weighing accuracy range unless otherwise specified. Temperature and time parameters are subject to acceptable deviations due to instrument testing accuracy or operational precision.

[0045] The raw material ratios for Examples 1-3 are shown in the table below.

[0046] Raw material name Example 1 Example 2 Example 3 Pentaerythritol tetraester (C8 / C10 saturated fatty acid ester) 84.00 83.50 83.80 Trimethylolpropane triester (C8 / C10 saturated fatty acid ester) 14.50 14.80 14.40 Octyl diphenylamine 0.60 0.65 0.55 2,6-Di-tert-butyl-4-methylphenol 0.15 0.18 0.15 2-Ethylhexyl acid phosphate 0.60 0.80 0.65 Ethanolamine (used for salification) Appropriate amount of a Appropriate amount of a Appropriate amount of a Di(2-ethylhexyl) dodecenyl succinate 0.20 0.22 0.20 Polyalkyl methacrylate type defoamer 0.003 0.002 0.003 EO / PO block copolymer demulsifier 0.001 0.001 — Polymethyl methacrylate pour point depressants — — 0.06

[0047] The amount of α-ethanolamine used is such that the salting ratio of 2-ethylhexyl acid phosphate is 40%–60%, and the acid value of the system is controlled at 50–70 mgKOH / g.

[0048] Example 1 (Standard Biodegradable Hydraulic Oil Composition)

[0049] Add the two base oils to the mixing container, heat to 50°C and stir until homogeneous;

[0050] Add octyl diphenylamine and 2,6-di-tert-butyl-4-methylphenol sequentially, and stir until completely dissolved;

[0051] Add 2-ethylhexyl acid phosphate, and add ethanolamine dropwise to adjust the salting ratio to 45%, with an acid value of about 60 mgKOH / g. Stir for 15 minutes.

[0052] Add dodecenyl succinate di(2-ethylhexyl ester), antifoaming agent, and demulsifier, and continue stirring for 15 minutes;

[0053] Cool to room temperature, filter to remove impurities, and obtain a transparent and homogeneous liquid.

[0054] Example 2 (High-load biodegradable hydraulic fluid composition)

[0055] The preparation method is the same as in Example 1, but the amount of acidic phosphate added and the ratio of ethanolamine are adjusted to improve the extreme pressure bearing capacity.

[0056] Example 3 (Low-Temperature Biodegradable Hydraulic Oil Composition)

[0057] The preparation method is the same as in Example 1, but a pour point depressant is added to improve fluidity and start-up performance under low-temperature operating conditions.

[0058] Comparative Example

[0059] Using 98.50 parts of Group II mineral base oil 150N as the base oil, 1.425 parts of common composite additive (containing 40% zinc dialkyl dithiosulfate, 20% butylphenol, 5% calcium sulfonate, and the remainder being mineral oil) were added, along with 0.0050 parts of polyalkyl methacrylate type defoamer, 0.0011 parts of EO / PO block copolymer demulsifier, and 0.0689 parts of polymethacrylate type pour point depressant. The base oil was added to a stirring container, heated to 50°C, and the common composite additive, defoamer, demulsifier, and pour point depressant were added sequentially under stirring. The mixture was stirred for 15 minutes until the system was uniform and transparent. After cooling to room temperature, the comparative hydraulic oil composition was obtained.

[0060] Performance tests were conducted on Examples 1-3, i.e., the comparative examples, and the results are shown in the table below:

[0061] Test Project Test methods Example 1 Example 2 Example 3 Comparative Example Biodegradation rate (28 days) / % OECD 301B 82 81 82 18 Four-ball mill grinding scar diameter (392 N, 75℃) / mm ASTM D4172 0.35 0.30 0.36 0.52 FZG gear test failure level DIN 51354 12 12 11 9 Water separation performance (54℃, separation time) / min ASTM D1401 6 7 6 >30 Copper strip corrosion (100℃, 3 h) level ASTM D130 1a 1a 1a 1b MPC chromaticity value (ΔE) ASTM D7843 10 8 9 28 Pour point / ℃ ASTM D97 –36 –34 –42 –21 Viscosity Index ASTM D2270 182 181 185 95

[0062] As can be seen from the table above, the biodegradable hydraulic oil compositions of Examples 1-3 of the present invention all exhibited a biodegradation rate of 81% to 82% after 28 days under the OECD 301B method, which is significantly higher than the 18% of the comparative example. This indicates that using a mixture of C8-C10 saturated fatty acids, namely pentaerythritol tetraester and trimethylolpropane triester, as the base oil can significantly improve the biodegradability of hydraulic oil and meet environmental regulations.

[0063] Regarding wear resistance, the wear scar diameters of Examples 1-3 in the ASTM D4172 four-ball wear test were 0.35 mm, 0.30 mm, and 0.36 mm, respectively, all significantly lower than the 0.52 mm of the comparative example. Example 2, due to its higher content of 2-ethylhexyl acid phosphate and its ethanolamine salt, exhibited the smallest wear scar diameter, indicating that the composite detergent in this invention has a significant effect on improving extreme pressure bearing capacity. The FZG gear test results also show that the failure levels of Examples 1-3 were all 11 or higher, higher than the 9 level of the comparative example, further demonstrating the improved wear resistance.

[0064] Regarding high-definition cleanliness, the MPC color values ​​of Examples 1-3 all did not exceed 10, while the comparative example reached 28, indicating that the composite detergent of the present invention can effectively disperse and inhibit the deposition of oxidation products, maintaining the cleanliness of the hydraulic system. Water separation performance (ASTM D1401) test results show that the oil-water separation time of Examples 1-3 at 54°C did not exceed 7 minutes, significantly better than the comparative example's greater than 30 minutes, indicating that the composition of the present invention can quickly restore oil purity and reduce the risk of emulsification under water-containing conditions.

[0065] Regarding low-temperature performance, Example 3 added a polymethacrylate pour point depressant, which lowered the pour point to -42°C, significantly lower than the levels of Examples 1, 2 and the comparative examples, making it suitable for use in hydraulic systems in cold regions.

[0066] Furthermore, the viscosity indices of Examples 1-3 were all above 180, significantly higher than the 95 of the comparative example, indicating that the use of saturated synthetic ester base oil can impart excellent viscosity-temperature characteristics to the composition, ensuring stable operation of the hydraulic system over a wide temperature range.

[0067] In summary, the embodiments of the present invention maintain high biodegradability while also possessing excellent anti-wear properties, high cleanliness, water separation properties, and low-temperature fluidity, and their performance is comprehensively superior to traditional mineral oil-based hydraulic oil formulations.

[0068] Experimental Example: Verifying the synergistic improvement of the shortcomings of composite detergents on highly saturated synthetic ester base oils

[0069] 1. Experimental Objective

[0070] This study aims to verify whether a specific composite detergent (octyl diphenylamine, 2,6-di-tert-butyl-4-methylphenol, 2-ethylhexyl acid phosphate and its ethanolamine salt, and dodecenyl succinate di(2-ethylhexyl ester)) can achieve synergistic performance in anti-wear / extreme pressure, high-definition cleaning / deposition inhibition and antioxidant life in a system using pentaerythritol tetraester / trimethylolpropane triester (C8–C10, saturation ≥90%) as a biodegradable base oil, thereby compensating for the shortcomings of the base oil in extreme pressure load carrying capacity and deposition control.

[0071] 2. Experimental Materials

[0072] Base oil: Pentaerythritol tetraester and trimethylolpropane triester (C8–C10 saturated fatty acid mixed ester).

[0073] Additives: Octyl diphenylamine (ODPA), 2,6-di-tert-butyl-4-methylphenol (BHT), 2-ethylhexyl acid phosphate (partially neutralized with ethanolamine to form an amine salt), and dodecenyl succinate di(2-ethylhexyl ester); if necessary, use trace amounts of polyalkyl methacrylate type defoamer and EO / PO block copolymer demulsifier to ensure test feasibility (maintain consistency across groups and exclude from composite detergent statistics).

[0074] 3. Sample formulation and grouping (unit: parts by weight)

[0075] Group Purpose base oil Octyl diphenylamine 2,6-Di-tert-butyl-4-methylphenol 2-Ethylhexyl acid phosphate a Dodecenyl succinate di(2EH) ester Remark G1 Baseline (base oil only) 100.00 — — — — Verify the shortcomings of base oil G2 Antioxidant only 99.25 0.60 0.15 — — Stable oxygen supply, no EP / dispersion provided. G3 EP / Abrasion-resistant only 99.40 — — 0.60 — Membrane construction only, lacking stable oxygen / dispersion G4 Dispersible / anti-coating only 99.80 — — — 0.20 Dispersible only, not antioxidant / EP G5 Antioxidant + EP 98.65 0.60 0.15 0.60 — No dispersion G6 Antioxidant + Dispersant 99.05 0.60 0.15 — 0.20 No EP G7 EP + Dispersed 99.20 — — 0.60 0.20 No antioxidants G8 Complete compound detergent 98.45 0.60 0.15 0.60 0.20 Example 1 G9 Comparative Example 98.50 (Mineral oil 150N) — 0.15 ZDDP is included in common compound additives — Traditional mineral oil system

[0076] α-2-ethylhexyl acid phosphate is partially neutralized with ethanolamine, the salting ratio is controlled at 40%–60%, and the acid value of the system is 50–70 mgKOH / g (determined by on-site titration).

[0077] 4. Sample preparation steps

[0078] (1) Add the base oil to the mixing container, heat to 50°C and stir until homogeneous; (2) Add octyl diphenylamine and 2,6-di-tert-butyl-4-methylphenol (if any) according to Table 1, and stir until completely dissolved; (3) Add 2-ethylhexyl acidic phosphate, add ethanolamine dropwise for partial neutralization, and control the salting ratio at 40%–60% and the system acid value at 50–70 mgKOH / g by acid value titration in real time, and stir at a constant speed for 10–20 min; (4) Add dodecenyl succinate di(2-ethylhexyl) (if any), and continue stirring for 10–20 min until homogeneous; (5) Cool to room temperature, filter through a 5–10 μm filter to remove impurities, and seal to protect from light for later use. If each group needs to add trace amounts of defoamer / demulsifier, keep them at the same level (e.g., 0.003 parts of defoamer and 0.001 parts of demulsifier), and do not include them in the composite detergent statistics.

[0079] 5. Test items and methods (n=5 per group)

[0080] category index Methods and conditions End point / judgment Anti-wear / Extreme Pressure Four-ball wear scar diameter ASTM D4172, 392 N, 75℃ The smaller the value, the better. Transmission load FZG Failure Level DIN 51354 The higher the level, the better. High-definition clean / deposition MPC chromaticity ΔE Samples were taken after 100 hours of circulation using a ASTM D7843, 35VQ25 pump. The smaller the value, the better. Oxidation stability RPVOT lifespan ASTM D2272 The higher the value, the better. Emulsification and separation Water separation time ASTM D1401, 54℃ The shorter the time, the better. corrosion Copper sheet corrosion level ASTM D130, 100℃, 3 h 1a is qualified Viscosity stability viscosity growth rate ASTM D445, before and after comparison of pump station The lower the better

[0081] 6. Statistical Methods

[0082] One-way ANOVA was used to compare the differences between each group and G1 / G8. Two-way / three-way ANOVA was used to assess the main effects and interaction effects of the antioxidant system (A=ODPA+BHT), the EP system (B=2-ethylhexyl acid phosphate / amine salt), and the dispersion system (C=dodecenyl succinate). Tukey's method was used for post-hoc tests. P<0.05 was considered significant.

[0083] 7. Experimental Results

[0084] Group Four-ball wear scar diameter / mm FZG Failure Level MPC ΔE RPVOT / min Water separation / min Copper corrosion grade Viscosity growth rate / % G1 0.50±0.01 9 28±0.6 150±5 32±1.5 1b 15.2±0.5 G2 0.48±0.01 9 22±0.5 230±6 30±1.2 1a 9.3±0.4 G3 0.38±0.01 11 26±0.5 160±4 20±0.8 1a 13.1±0.5 G4 0.49±0.01 9 18±0.4 155±5 14±0.7 1a 12.4±0.5 G5 0.34±0.01 12 20±0.5 240±6 22±0.9 1a 8.1±0.3 G6 0.44±0.01 10 14±0.4 235±5 16±0.7 1a 8.4±0.3 G7 0.36±0.01 12 15±0.4 170±5 18±0.8 1a 10.2±0.4 G8 0.30±0.01 12 8±0.3 260±7 8±0.4 1a 6.0±0.3 G9 0.52±0.02 9 28±0.6 140±5 ≥30 1b 16.0±0.6

[0085] Collaborative statistical determination (ANOVA interaction term significance summary, p < 0.05 is marked as "yes")

[0086] index A×B A×C B×C A×B×C Synergistic conclusions Four-ball wear scar diameter yes yes yes yes Complete compound formulations are significantly superior to any pairwise combinations. MPC ΔE yes yes yes yes Deposition inhibition exhibits positive synergy RPVOT lifespan yes no yes no Antioxidant and EP interact significantly Water separation time no no yes no The dosage of dispersant and EP needs to be balanced.

[0087] In the above table:

[0088] A (Antioxidant system): Composed of octyl diphenylamine (ODPA) + 2,6-di-tert-butyl-4-methylphenol (BHT).

[0089] B (Extreme Pressure / Anti-wear system): Composed of 2-ethylhexyl acid phosphate and its ethanolamine salt.

[0090] C (Dispersant / Cleanliness system): Composed of dodecenyl succinate di(2-ethylhexyl ester).

[0091] 8. Discussion of Results

[0092] (1) Wear resistance / extreme pressure: The diameter of the four ball wear scars of G8 is 0.30±0.01 mm, which is about 40% lower than that of G1, and ≥10% lower than any pair combination (G5 / G6 / G7). This indicates that there is a super-additive boundary film stabilization and frictional heat reduction effect under the combined action of three factors: anti-oxidation (A), EP (B), and dispersion (C).

[0093] (2) High-definition clean / deposition: The MPC ΔE of G8 is 8±0.3, which is ≥70% lower than that of G1 and ≥15% lower than that of G5 / G6 / G7. This indicates that the solvation-carrying effect of the dispersion system on the oxidation / polymerization precursor and the chain termination of the antioxidant system promote each other, inhibiting the coating film and sludge from the source and process through two pathways.

[0094] (3) Oxidation stability: The RPVOT lifetime of G8 is 260±7 min, which is about 73% higher than that of G1 and 8%–15% higher than that of G5 / G6 / G7, reflecting the dual effect of “reducing metal contact and frictional heat (B) + inhibiting free radical chain oxidation (A)”.

[0095] (4) Water separation and corrosion: The water separation time of D1401 in G8 was 8±0.4 min, which was significantly shorter than that in G4 / G7; the corrosion grade of copper sheet was 1a. This indicates that under the conditions of controlling the amount of dispersant and the salinity of EP (40%–60%), both emulsification risk and protective effect were taken into account.

[0096] In summary, the complete composite detergent showed a statistically significant synergistic improvement in the anti-wear, high-cleanliness, and antioxidant stability of highly saturated synthetic ester base oils, proving that it can effectively compensate for the shortcomings of base oils and achieve unified performance. Furthermore, it should be noted that not all indicators in the A×B×C table are significant, but the insignificant interaction effect of the three factors does not affect the optimal overall performance of this combination.

[0097] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims, and the specification can be used to interpret the content of the claims.

Claims

1. A biodegradable hydraulic oil composition, characterized in that, The components include the following parts by weight: 96.0-98.5 parts of biodegradable base oil and 1.5-2.5 parts of compound detergent; The base oil is a mixture of pentaerythritol tetraester and trimethylolpropane triester, with a fatty acid chain of C8-C10 saturated fatty acids, a saturation of ≥90%, and a 28-day biodegradability that meets the OECD 301B criteria. The composite detergent comprises: 0.45-0.90 parts of octyl diphenylamine, 0.10-0.25 parts of 2,6-di-tert-butyl-4-methylphenol, 0.60-1.20 parts of 2-ethylhexyl acid phosphate and its ethanolamine salt, and 0.15-0.35 parts of dodecenyl succinate di(2-ethylhexyl ester), wherein the mass ratio of octyl diphenylamine to 2,6-di-tert-butyl-4-methylphenol is 1.5:1 to 4:1; The mass ratio of pentaerythritol tetraester to trimethylolpropane triester is 80:20 to 90:

10.

2. The biodegradable hydraulic oil composition according to claim 1, characterized in that, The 2-ethylhexyl acid phosphate has an ethanolamine salting ratio of 40%-60%, and the acid value of the acid phosphate is 50-70 mgKOH / g.

3. The biodegradable hydraulic oil composition according to claim 1 or 2, characterized in that, It also includes at least one of biodegradable antifoaming agents, demulsifiers, and pour point depressants.

4. The biodegradable hydraulic oil composition according to claim 3, characterized in that, The antifoaming agent is a polyalkyl methacrylate type defoamer, consisting of 0.001-0.006 parts.

5. The biodegradable hydraulic oil composition according to claim 3, characterized in that, The demulsifier is 0.0005-0.0015 parts of EO / PO block copolymer.

6. The biodegradable hydraulic oil composition according to claim 3, characterized in that, The pour point depressant is 0.03-0.12 parts of a polymethacrylate-based pour point depressant.

7. The biodegradable hydraulic oil composition according to any one of claims 1, 2, 4-6, characterized in that, The composition has an ash content of ≤0.02 wt% and a sulfur content of ≤0.3 wt%.

8. The biodegradable hydraulic oil composition according to claim 1, characterized in that, The composition exhibits a biodegradability of ≥80% after 28 days using the OECD301B method and complete oil-water separation within 10 minutes in the ASTM D1401, 54°C water separation test.

9. A method for preparing a biodegradable hydraulic oil composition according to any one of claims 1-8, characterized in that, Includes the following steps: (1) Add the mixture of the pentaerythritol tetraester and the trimethylolpropane triester into a stirring container and heat it to 40°C-60°C; (2) Under stirring conditions, add octyl diphenylamine and 2,6-di-tert-butyl-4-methylphenol in sequence until they are fully dissolved. Then add 2-ethylhexyl acid phosphate and partially neutralize it with ethanolamine until the salting ratio is 40%-60% and the acid value of the system is 50-70 mgKOH / g. Continue stirring for 10-20 minutes. Then add the remaining components and stir for 10-20 minutes until homogeneous. (3) Cool to room temperature.