Complex lithium-based lubricating grease and preparation method thereof

Abstract

The invention provides composite lithium-based lubricating grease and a preparation method thereof. The composite lithium-based lubricating grease disclosed by the invention comprises the following components in percentage by weight based on the total mass of the lubricating grease: 0.1%-10% of an antioxidant, 0.1%-10% of an anti-rust agent, 0.1%-10% of an extreme pressure agent, 0.1%-10% of a multi-effect additive, 5%-25% of a composite lithium-based thickening agent and 70%-95% of pentaerythritol ester, the pentaerythritol ester comprises the following components in percentage by mass: 5 to 50 percent of pentaerythritol ester as shown in a formula (I) and 50 to 95 percent of pentaerythritol ester as shown in a formula (II), wherein an R group is C1-C14 straight chain or branched chain alkylene; the composite lithium-based lubricating grease provided by the invention has excellent high-temperature oxidation resistance and low-temperature performance, also has relatively good water spray resistance, corrosion and rust resistance and colloid stability, and can meet lubrication under low-temperature and high-speed working conditions.

Description

Technical Field

[0001] The present invention relates to lubricating grease, in particular to a composite lithium-based lubricating grease and a preparation method thereof. Background Art

[0002] Complex lithium-based grease has a high dropping point, is more suitable for use at high temperatures, and has good colloid stability and shear stability. It has a strong thickening ability for various types of mineral oils and synthetic oils. Therefore, it has developed rapidly since the 1960s.

[0003] However, with the rapid development of the machinery industry, higher and higher requirements have been placed on lubricating materials. Mechanical equipment that operates continuously under high loads, high speeds, and high (low) temperatures requires greases with a wider operating temperature range and better oxidation stability. Mineral oil greases are no longer able to meet such lubrication requirements. Therefore, synthetic oil-based lithium-complex greases have seen significant development in recent years.

[0004] CN 107828483A uses mPAO and PAO to prepare a composite lithium-based grease. The wear surface of the test steel ball is relatively smooth and the grooves are very shallow, indicating good anti-wear and wear-reducing properties. CN 103409208A uses a mixed oil of dipentaerythritol ester, polyα-olefin, and alkyl naphthalene to prepare a composite lithium-based grease with a wide operating temperature range, good waterproof and corrosion resistance, good low-temperature starting performance, and a long service life. It is also biodegradable, non-toxic, and harmless, and is a bearing grease that can be used for fan main shafts. CN 113980722A uses a mixed oil of polyα-olefin and polyol ester to prepare a composite lithium-based grease with excellent high-temperature resistance, low-temperature resistance, and durability, and is particularly suitable for lubricating mechanical parts and components under low-temperature working conditions and heavy-duty, high-load equipment. However, none of the above inventions simultaneously involve the anti-oxidation properties and -60°C low-temperature performance of the grease.

[0005] Developing complex lithium-based grease with a wider operating temperature range and better oxidation stability remains one of the research and development directions of technicians in this field. Summary of the Invention

[0006] The invention provides a composite lithium-based grease and a preparation method thereof.

[0007] The composite lithium-based grease of the present invention comprises, based on the total mass of the grease, 0.1% to 10% of an antioxidant, 0.1% to 10% of a rust inhibitor, 0.1% to 10% of an extreme pressure agent, 0.1% to 10% of a multi-effect additive, 5% to 25% of a composite lithium-based thickener, and 70% to 95% of a pentaerythritol ester; the pentaerythritol ester comprises, by mass, 5% to 50% of a pentaerythritol ester represented by formula (I) and 50% to 95% of a pentaerythritol ester represented by formula (II):

[0008]

[0009] The R group is C1~C 14 Each R' group is independently selected from a C3 to C9 straight chain or branched chain alkyl group.

[0010] According to the present invention, the R group is preferably a C2 to C8 straight chain or branched alkylene group; each R' group is preferably selected from two or more (for example, three or four) of a C3 straight chain or branched alkyl group, a C4 straight chain or branched alkyl group, a C5 straight chain or branched alkyl group, a C6 straight chain or branched alkyl group, a C7 straight chain or branched alkyl group, a C8 straight chain or branched alkyl group, and a C9 straight chain or branched alkyl group, more preferably selected from a C3 straight chain alkyl group, a C4 straight chain alkyl group, a C5 straight chain alkyl group, a C6 straight chain alkyl group, a C7 straight chain alkyl group, a C8 straight chain alkyl group. % of C5 linear alkyl, 5.0 mol% to 45.0 mol% of C6 linear alkyl, 0 to 30.0 mol% of C7 linear alkyl, 0 to 15.0 mol% of C8 linear alkyl, and 0 to 10.0 mol% of C9 linear alkyl.

[0011] According to the present invention, the pentaerythritol ester preferably comprises, by mass, 5% to 25% of the pentaerythritol ester represented by formula (I) and 75% to 95% of the pentaerythritol ester represented by formula (II).

[0012] The preparation method of pentaerythritol ester of the present invention comprises the following steps:

[0013] (1) Excessive monopentaerythritol and C 3～16 The dibasic fatty acid undergoes esterification reaction to obtain esterification product A1;

[0014] (2) Esterification product A1 and excess C 4～10 The monobasic fatty acids undergo esterification reaction and the products are collected.

[0015] According to the present invention, in step (1), the monopentaerythritol and C 3～16 The molar ratio of the dibasic fatty acid can be (2.05-100):1, preferably (3-60):1, and more preferably (3-30):1; in step (2), the hydroxyl group and C in the esterification product A1 4～10The molar ratio of the carboxyl groups in the monobasic fatty acid may be 1:(1.05-1.30), preferably 1:(1.10-1.20).

[0016] According to the present invention, the reaction temperature of step (1) is 50-180°C, preferably 80-150°C, and the reaction time is 1-20h, preferably 2-10h; the reaction temperature of step (2) is 50-250°C, preferably 100-220°C, and the reaction time is until water is no longer produced, which can generally be 1-20h, or 5-10h.

[0017] According to the present invention, the dibasic fatty acid can be one or more of malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, tetradecanedioic acid, and hexadecanedioic acid.

[0018] According to the present invention, the monobasic fatty acid is preferably selected from two or more (for example, three or four) of n-butyric acid, isobutyric acid, n-pentanoic acid, isovaleric acid, n-hexanoic acid, isohexanoic acid, n-heptanoic acid, isoheptanoic acid, n-octanoic acid, isooctanoic acid, n-nonanoic acid, isononanoic acid, n-decanoic acid, and isodecanoic acid, and is more preferably selected from two or more (for example, three or four) of n-butyric acid, n-pentanoic acid, n-hexanoic acid, n-heptanoic acid, n-octanoic acid, n-nonanoic acid, and n-decanoic acid. Further preferably, the monobasic fatty acid may include 0-10.0 mol% of n-butyric acid, 0-35.0 mol% of n-pentanoic acid, 30.0 mol%-75.0 mol% of n-hexanoic acid, 5.0 mol%-45.0 mol% of n-heptanoic acid, 0-30.0 mol% of n-octanoic acid, 0-15.0 mol% of n-nonanoic acid, and 0-10.0 mol% of n-decanoic acid.

[0019] According to the present invention, a catalyst may be added to the esterification reaction in step (1) and / or step (2), and the catalyst includes one or more of concentrated sulfuric acid, sodium bisulfate, p-toluenesulfonic acid, zinc oxide, a cation exchange resin, an ionic liquid, stannous oxide, a titanate, and activated carbon. The amount of the catalyst added may be in accordance with the amount used in the esterification reaction in the prior art and is not particularly limited. The catalyst may be removed after the esterification reaction by methods well known in the art, such as alkali washing, water washing, and filtration, and is not particularly limited.

[0020] According to the present invention, a solvent may be added during the esterification reaction in step (1) and / or step (2). The solvent may be one or more of xylene, toluene, and cyclohexane. The amount of the solvent added may be in accordance with the amount used in the esterification reaction in the prior art and is not particularly limited. The solvent may be removed after the esterification reaction by methods well known in the art, such as distillation, and is not particularly limited.

[0021] According to the present invention, the esterification reaction in step (1) and / or step (2) can be carried out under nitrogen protection.

[0022] According to the present invention, preferably, in step (2), the esterification product A1 is reacted with an excess of C 4～10 The product of the esterification reaction of the monobasic fatty acid is purified by one or more of the following methods: reduced pressure distillation, alkaline washing, dehydration, decolorization, and filtration. After the purification, a mixture of the pentaerythritol ester represented by formula (I) and the pentaerythritol ester represented by formula (II) with higher purity can be obtained.

[0023] The pentaerythritol ester of the present invention has a high viscosity index (>130), a low pour point (<-60°C), a relatively low kinematic viscosity at -40°C (<10000mm 2 / s) and good high temperature oxidation stability.

[0024] According to the present invention, the antioxidant can be selected from phenolic antioxidants, for example, one or more of 2,6-di-tert-butyl-p-cresol, 2-naphthol, 2,6-di-tert-butyl-α-dimethylamino-p-cresol, 4,4'-methylenebis(2,6-di-tert-butylphenol) and 2,6-di-tert-butyl-4-alkoxyphenol; the rust inhibitor can be selected from sulfonate-type rust inhibitors, for example, one or more of barium petroleum sulfonate, sodium petroleum sulfonate, barium dinonylnaphthalenesulfonate and zinc dinonylnaphthalenesulfonate; the extreme pressure agent can be selected from An organic sulfide can be used, for example, one or more of sulfided isobutylene, dibenzyl disulfide and sulfided cottonseed oil can be selected; the multi-effect additive can be selected from thiophosphates, for example, one or more of n-butyl isooctyl dithiophosphate zinc, dioctyl basic zinc thiophosphate, di-n-propyl antimony dithiophosphate and di(2-ethylhexyl) dithiophosphate oxymolybdenum sulfide can be selected; the composite lithium-based thickener is prepared by saponification reaction of acid with lithium hydroxide, and the acid is a mixed acid of fatty acid and auxiliary acid; the fatty acid can be C 12 ~C 20 Fatty acids and / or C 12 ~C 20 The hydroxy fatty acid can be selected from one or more of lauric acid, palmitic acid, stearic acid and 12-hydroxystearic acid, preferably 12-hydroxystearic acid and / or stearic acid; the auxiliary acid can be selected from one or more of acetic acid, propionic acid, oxalic acid, adipic acid, azelaic acid, sebacic acid, phosphoric acid and terephthalic acid, preferably sebacic acid and / or azelaic acid, wherein the molar ratio between the fatty acid and the auxiliary acid can be 1:0.1-5, preferably 1:0.5-2.

[0025] The preparation method of the composite lithium-based grease described in the present invention comprises: adding 50% to 80% of pentaerythritol ester, all fatty acids and auxiliary acids into a grease-making kettle, stirring evenly, heating to 80 to 90° C., adding a mixture of lithium hydroxide and water to carry out a saponification reaction for 60 to 240 minutes, heating to 190 to 220° C. and carrying out high-temperature refining for 5 to 20 minutes; adding the remaining pentaerythritol ester, cooling to 100 to 120° C., adding an antioxidant, a rust inhibitor, an extreme pressure agent, and a multi-effect additive, stirring evenly, and grinding into grease after cooling.

[0026] The composite lithium-based grease of the present invention has excellent high-temperature oxidation resistance and low-temperature performance, and also has good water spray resistance, corrosion and rust resistance, and colloid stability, and can meet the lubrication requirements under low-temperature and high-speed working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the infrared spectrum of monopentaerythritol raw material.

[0028] Figure 2 The infrared spectrum of the pentaerythritol ester product prepared in Example 1 is shown in FIG.

[0029] Figure 3 This is the Fourier transform ion cyclotron resonance spectrum of the pentaerythritol ester product prepared in Example 1. DETAILED DESCRIPTION

[0030] The present invention is further described in detail below by way of examples, but the present invention is not limited thereto.

[0031] The present invention is concerned with the monopentaerythritol, C 4～10 Monobasic fatty acids, C 3～16 The source of the dibasic fatty acid is not particularly limited, and any commercially available product or homemade product of the above raw materials well known to those skilled in the art can be used.

[0032] Example 1

[0033] In a 1 L four-necked flask equipped with a stirring rod, a thermometer, a condenser, and a water separator, 50.0 g of monopentaerythritol (0.367 mol), 4.3 g of adipic acid (0.027 mol), 80 ml of xylene, and 1.5 g of tetrabutyl titanate catalyst were added, and the mixture was reacted at 150° C. for 4 h under nitrogen protection to obtain an esterification product A1, which was then cooled to room temperature. Then, 36.0 g of n-pentanoic acid, 110.0 g of n-hexanoic acid, 58.0 g of n-heptanoic acid, and 2.0 g of tetrabutyl titanate catalyst were added, and under nitrogen protection, the reaction temperature was heated to 150° C., then raised to 220° C. using a temperature program of 10° C. / h, and reacted until no water was produced to obtain a crude esterification product B1. The mixture was cooled to room temperature, subjected to reduced pressure distillation, alkali washing, water washing, dehydration, decolorization, and filtration to obtain the pentaerythritol ester of the present invention, which was labeled J1.

[0034] Infrared spectra of the monopentaerythritol raw material and the pentaerythritol ester product prepared in Example 1 were respectively tested. The infrared spectra of the monopentaerythritol raw material were shown in FIG. Figure 1 The infrared spectrum of the pentaerythritol ester product obtained in Example 1 is shown in FIG. Figure 2 By comparison, in the infrared spectrum of monopentaerythritol, 3200~3400cm -1 is the absorption peak of the alcoholic hydroxyl group in monopentaerythritol; the 3200-3400 cm-1 peak does not exist in the infrared spectrum of the pentaerythritol ester product prepared in Example 1. -1 Absorption peak, including 1744cm -1 It is the stretching vibration peak of the C=O bond in the pentaerythritol ester product prepared in Example 1, indicating that the excess monobasic fatty acid in step (2) causes the excess monopentaerythritol in step (1) to react completely, and there is no alcoholic hydroxyl group in the product.

[0035] Example 2

[0036] In a 1 L four-necked flask equipped with a stirring rod, a thermometer, a condenser, and a water separator, 50.0 g of monopentaerythritol (0.367 mol), 8.6 g of adipic acid (0.06 mol), 100 ml of xylene, and 2.0 g of p-toluenesulfonic acid catalyst were added, and the mixture was reacted at 150° C. for 7 h under nitrogen protection to obtain an esterification product A1, which was then cooled to room temperature. Then, 56.0 g of n-pentanoic acid, 92.0 g of n-hexanoic acid, 23.0 g of n-heptanoic acid, 25.5 g of n-octanoic acid, and 2.0 g of p-toluenesulfonic acid catalyst were added, and under nitrogen protection, the reaction temperature was heated to 150° C., then raised to 220° C. using a temperature program of 10° C. / h, and reacted until no water was produced to obtain a crude esterification product B1. The mixture was cooled to room temperature, subjected to reduced pressure distillation, alkali washing, water washing, dehydration, decolorization, and filtration to obtain the pentaerythritol ester of the present invention, which is labeled J2.

[0037] Example 3

[0038] In a 1 L four-necked flask equipped with a stirring rod, a thermometer, a condenser, and a water separator, 50.0 g of monopentaerythritol (0.367 mol), 7.6 g of malonic acid (0.073 mol), 4.0 g of suberic acid (0.023 mol), 100 ml of xylene, and 1.5 g of tetrabutyl titanate catalyst were added, and the mixture was reacted at 150° C. for 7 h under nitrogen protection to obtain an esterification product A1, which was then cooled to room temperature. Then, 36.0 g of n-pentanoic acid, 98.5 g of n-hexanoic acid, 46.0 g of n-heptanoic acid, 12.7 g of n-octanoic acid, and 2.0 g of tetrabutyl titanate catalyst were added. Under nitrogen protection, the reaction temperature was heated to 150° C., then increased to 220° C. using a temperature program of 10° C. / h, and reacted until no water was produced to obtain a crude esterification product B1. The mixture was cooled to room temperature, subjected to reduced pressure distillation, alkali washing, water washing, dehydration, decolorization, and filtration to obtain the pentaerythritol ester of the present invention, which was labeled J3.

[0039] The pentaerythritol ester prepared in Example 1 was subjected to Fourier transform ion cyclotron resonance (FTIR) analysis using an electrospray ionization source (ESI+) in positive ion mode. The test conditions were: ion transport capillary temperature of 350°C, spray voltage of 2.8 kV, m / z scanning range of 100-1500, and mass resolution of 70,000. The measured spectrum is shown in FIG. Figure 3 .from Figure 3 It can be seen that C 26 H 46 O8~C 36 H 36 O8 represents the ester formed by monopentaerythritol and monobasic fatty acid (hereinafter referred to as monobasic acid ester), C 51 H 88 O 16 ~C 59 H 104 O 16 with C 73 H 124 O 24 ~C 79 H 136 O 24 It represents the ester formed by the esterification product of adipic acid and monopentaerythritol and then reacting with a monobasic fatty acid (hereinafter abbreviated as dibasic acid ester).

[0040] The physical and chemical properties of the pentaerythritol ester of the present invention are illustrated by taking commercial pentaerythritol ester as comparative example 1. The commercial pentaerythritol ester is mixed pentaerythritol ester MIXPE1 produced by Zhejiang Quzhou Chemical Co., Ltd., and its kinematic viscosity at 100°C is 5.02 mm 2 / s.

[0041] The physical and chemical properties of the pentaerythritol esters of Examples 1-3 and the pentaerythritol ester of Comparative Example 1 were evaluated. The results are shown in Table 1.

[0042] The content distribution of the pentaerythritol esters prepared in Examples 1-3 and the pentaerythritol ester of Comparative Example 1 was determined according to the method for determining the boiling range distribution of petroleum fractions (NB / SH / T 0829), i.e., the content of the monobasic and dibasic esters in Examples 1-3 or the content of the monopentaerythritol ester and dipentaerythritol ester in Comparative Example 1 was determined. The results of the determinations are shown in Table 1. For example, the results of the determination of the product of Example 1 showed that the content of the ester formed by monopentaerythritol and a monobasic fatty acid (i.e., the monobasic ester) was 88.2% (with a boiling range of 350-500°C), and the content of the ester formed by the esterification product of adipic acid and monopentaerythritol and then reacting with a monobasic fatty acid (i.e., the dibasic ester) was 11.8% (with a boiling range of >500°C).

[0043] As can be seen from Table 1, compared with the comparative pentaerythritol ester MIXPE1, the pentaerythritol ester of the present invention has a lower pour point (≤-66°C) and a higher viscosity index (≥135), indicating that the pentaerythritol ester base oil of the present invention has better low-temperature fluidity and viscosity-temperature properties.

[0044] Table 1 Physical and chemical indicators of pentaerythritol esters

[0045]

[0046] The sources of the main raw materials used in the grease prepared below are as follows: lithium hydroxide monohydrate, dodecanedioic acid from Zhengzhou Bangnuo Chemical Products Co., Ltd., stearic acid from Zhengzhou Jinbang Chemical Co., Ltd., sebacic acid from Suzhou Yuantairun Chemical Co., Ltd., azelaic acid from Henan Shenghua Chemical Products Co., Ltd., 2,6-di-tert-butyl-p-cresol from Henan Shenghua Chemical Products Co., Ltd., and Guangzhou Qitai Chemical Co., Ltd.

[0047] 2-Naphthol, Shanghai Zhanyun Chemical Co., Ltd.

[0048] Barium petroleum sulfonate, Suixin Chemical Co., Ltd.

[0049] Sodium petroleum sulfonate, Suixin Chemical Co., Ltd.

[0050] Sulfurized isobutylene, Shenyang Feida Chemical Co., Ltd.

[0051] Dibenzyl disulfide, Inokite Technology Co., Ltd.

[0052] Zinc n-butyl isooctyl dithiophosphate, Wuxi Southern Petroleum Additives Co., Ltd.

[0053] Dioctyl thiophosphate basic zinc salt, Liaoning Jiazhi Chemical Products Manufacturing Co., Ltd.

[0054] Example I-1 of preparing grease

[0055] Raw material components: 85 g of pentaerythritol ester product J1 of Example 1; 3.1 g of lithium hydroxide monohydrate; 10.9 g of 12-hydroxystearic acid; 3.7 g of sebacic acid; 0.5 g of 2,6-di-tert-butyl-p-cresol; 2 g of barium petroleum sulfonate; 2 g of isobutylene sulfide; and 2 g of zinc n-butylisooctyl dithiophosphate.

[0056] Preparation method: 60g of pentaerythritol ester J1, 10.9g of 12-hydroxystearic acid and 3.7g of sebacic acid are added to a fat-making kettle, stirred evenly, heated to 90°C, and a lithium hydroxide aqueous solution (containing 3.1g of lithium hydroxide monohydrate and 15g of water) is added to carry out saponification reaction for 60 minutes, and then heated to 190°C for high-temperature refining for 5 minutes; the remaining pentaerythritol ester J1 is added, the temperature is cooled to 100°C, 0.5g of 2,6-di-tert-butyl-p-cresol, 2g of barium petroleum sulfonate, 2g of sulfided isobutylene, and 2g of n-butyl isooctyl zinc dithiophosphate are added, and stirred evenly; after cooling, the mixture is ground into fat using a three-roll mill.

[0057] Example I-2 of preparing grease

[0058] Raw material components: 80 g of pentaerythritol ester product J2 of Example 2; 6.3 g of lithium hydroxide monohydrate; 8.2 g of stearic acid; 10.9 g of azelaic acid; 1 g of 2-naphthol; 1 g of sodium petroleum sulfonate; 3 g of dibenzyl disulfide; and 4 g of basic zinc bis(octyl)thiophosphate.

[0059] Preparation method: add 60g of pentaerythritol ester J2, 8.2g of stearic acid and 10.9g of azelaic acid into a fat-making kettle, stir evenly, heat to 80°C, add lithium hydroxide aqueous solution (containing 6.3g of lithium hydroxide monohydrate and 25g of water) to carry out saponification reaction for 120 minutes, heat to 200°C and carry out high-temperature refining for 10 minutes; add the remaining pentaerythritol ester J2, cool to 100°C, add 1g of 2-naphthol, 1g of sodium petroleum sulfonate, 3g of dibenzyl disulfide, and 4g of dioctyl alkaline zinc salt of thiophosphate, and stir evenly; after cooling, grind into fat through a three-roll mill.

[0060] Example I-3 of preparing grease

[0061] Raw material components: 88 g of pentaerythritol ester product J3 of Example 3; 2.3 g of lithium hydroxide monohydrate; 7.8 g of 12-hydroxystearic acid; 4.9 g of azelaic acid; 1.5 g of 2,6-di-tert-butyl-p-cresol; 1 g of barium petroleum sulfonate; 3 g of dibenzyl disulfide; and 5 g of zinc n-butylisooctyl dithiophosphate.

[0062] Preparation method: 60g of pentaerythritol ester J3, 7.8g of 12-hydroxystearic acid and 4.9g of azelaic acid are added to a fat-making kettle, stirred evenly, heated to 85°C, and a lithium hydroxide aqueous solution (containing 2.3g of lithium hydroxide monohydrate and 10g of water) is added to carry out saponification reaction for 150min, and then heated to 210°C for high-temperature refining for 20min; the remaining pentaerythritol ester J3 is added, cooled to 100°C, 1.5g of 2,6-di-tert-butyl-p-cresol, 1g of barium petroleum sulfonate, 3g of dibenzyl disulfide, and 5g of n-butyl isooctyl zinc dithiophosphate are added, and stirred evenly; after cooling, the mixture is ground into fat using a three-roll mill.

[0063] Comparative Example D-1 for preparing grease

[0064] A lubricating grease was prepared according to the method of Example I-1, except that the pentaerythritol ester J1 was replaced with the mixed pentaerythritol ester MIXPE1.

[0065] The performance of the above-mentioned grease examples and comparative examples was evaluated using the following method:

[0066] The dropping point was determined using the GB / T 3498 method;

[0067] The cone penetration was determined using the GB / T 269 method;

[0068] The oxidation stability was determined using the SH / T 0325 method;

[0069] The oil separation of steel mesh is determined using the NB / SH / T 0324 method;

[0070] The water resistance was determined using the SH / T 0109 method;

[0071] The anti-corrosion performance was determined using the GB / T 5018 method;

[0072] GB / T 7326 method was used to determine copper corrosion;

[0073] The low temperature performance is determined using the SH / T 0338 method;

[0074] The evaluation results are shown in Table 2.

[0075] Table 2 Performance evaluation of grease

[0076]

Claims

1. A composite lithium-based grease comprising, based on the total mass of the grease, 0.1% to 10% of an antioxidant, 0.1% to 10% of a rust inhibitor, 0.1% to 10% of an extreme pressure agent, 0.1% to 10% of a multi-effect additive, 5% to 25% of a composite lithium-based thickener, and 70% to 95% of a pentaerythritol ester; the pentaerythritol ester comprising, by mass, 5% to 50% of a pentaerythritol ester of formula (I) and 50% to 95% of a pentaerythritol ester of formula (II): The R group is C1~C 14 Each R' group is independently selected from a C3 to C9 straight chain or branched chain alkyl group.

2. The lithium complex grease according to claim 1, characterized in that: The R group is a straight chain or branched chain alkylene group of C2 to C8; each R' group is selected from two or more of a straight chain or branched chain alkyl group of C3, a straight chain or branched chain alkyl group of C4, a straight chain or branched chain alkyl group of C5, a straight chain or branched chain alkyl group of C6, a straight chain or branched chain alkyl group of C7, a straight chain or branched chain alkyl group of C8, and a straight chain or branched chain alkyl group of C9.

3. The lithium complex grease according to claim 1, characterized in that: The pentaerythritol ester comprises, by mass, 5.0% to 25% of the pentaerythritol ester represented by formula (I) and 75% to 95% of the pentaerythritol ester represented by formula (II).

4. The lithium complex grease according to claim 1, characterized in that: The preparation method of the pentaerythritol ester comprises the following steps: (1) Excessive monopentaerythritol and C 3～16 The dibasic fatty acid undergoes esterification reaction to obtain esterification product A1; (2) Esterification product A1 and excess C 4～10 The monobasic fatty acids undergo esterification reaction and the products are collected.

5. The lithium complex grease according to claim 4, characterized in that: In step (1), the monopentaerythritol and C 3～16 The molar ratio of the dibasic fatty acid is (2.05-100):1; in step (2), the hydroxyl group and C 4～10 The molar ratio of the carboxyl group in the monobasic fatty acid is 1:(1.05~1.30).

6. The lithium complex grease according to claim 4, characterized in that: The reaction temperature of step (1) is 50-180° C., and the reaction time is 1-20 h; the reaction temperature of step (2) is 50-250° C., and the reaction time is until water is no longer produced.

7. The lithium complex grease according to claim 4, characterized in that: The dibasic fatty acid is one or more of malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, tetradecanedioic acid, and hexadecanedioic acid; the monobasic fatty acid is selected from two or more of n-butyric acid, isobutyric acid, n-valeric acid, isovaleric acid, n-hexanoic acid, isohexanoic acid, n-heptanoic acid, isoheptanoic acid, n-octanoic acid, isooctanoic acid, n-nonanoic acid, isononanoic acid, n-decanoic acid, and isodecanoic acid.

8. The lithium complex grease according to claim 4, characterized in that: Adding a catalyst to the esterification reaction of step (1) and / or step (2), wherein the catalyst is selected from one or more of concentrated sulfuric acid, sodium bisulfate, p-toluenesulfonic acid, zinc oxide, cation exchange resin, ionic liquid, stannous oxide, titanate and activated carbon; and / or, The esterification reaction in step (1) and / or step (2) is carried out under nitrogen protection.

9. The lithium complex grease according to any one of claims 1 to 8, characterized in that: The antioxidant is selected from phenolic antioxidants; the rust inhibitor is selected from sulfonate rust inhibitors; the extreme pressure agent is selected from organic sulfides; the multi-effect additive is selected from thiophosphates; and the composite lithium-based thickener is formed by saponification reaction between acid and lithium hydroxide.

10. The lithium complex grease according to claim 9, characterized in that: The antioxidant is selected from one or more of 2,6-di-tert-butyl-p-cresol, 2-naphthol, 2,6-di-tert-butyl-α-dimethylamino-p-cresol, 4,4'-methylenebis(2,6-di-tert-butylphenol) and 2,6-di-tert-butyl-4-alkoxyphenol; the rust inhibitor is selected from one or more of barium petroleum sulfonate, sodium petroleum sulfonate, barium dinonylnaphthalenesulfonate and zinc dinonylnaphthalenesulfonate; the extreme pressure agent is selected from one or more of sulfided isobutylene, dibenzyl disulfide and sulfided cottonseed oil; the multi-effect additive is selected from one or more of n-butyl isooctyl dithiophosphate zinc, dioctyl basic zinc sulfate, di-n-propyl antimony dithiophosphate and di(2-ethylhexyl) dithiophosphate oxymolybdenum sulfide; the acid is a mixed acid of a fatty acid and an auxiliary acid; the fatty acid is selected from C 12 ~C 20 Fatty acids and / or C 12 ~C 20 the auxiliary acid is selected from one or more of acetic acid, propionic acid, oxalic acid, adipic acid, azelaic acid, sebacic acid, phosphoric acid and terephthalic acid.

11. A method for preparing the complex lithium-based grease according to any one of claims 1 to 10, comprising: Add 50% to 80% of pentaerythritol ester, all fatty acids and auxiliary acids into a fat-making kettle, stir evenly, heat to 80-90°C, add a mixture of lithium hydroxide and water to carry out saponification reaction for 60-240 minutes, heat to 190-220°C to carry out high-temperature refining for 5-20 minutes; add the remaining pentaerythritol ester, cool to 100-120°C, add antioxidant, rust inhibitor, extreme pressure agent and multi-effect additives, stir evenly, cool and grind into fat.

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