Proanthocyanidin-based lubricating oil antioxidant and preparation method and application thereof

Abstract

The application provides a procyanidine-based lubricating oil antioxidant and a preparation method and application thereof, and belongs to the technical field of lubricating oil additives. The antioxidant comprises 0.8-1.5 wt% of procyanidine derivatives, 0.1-0.5 wt% of amine antioxidants, 0.05-0.1 wt% of metal deactivators and a residual amount of base oil. The procyanidine derivatives are oligomeric procyanidine skeletons formed by condensation of 2-10 flavan-3-ol units through C4-C8 bonds and / or C4-C6 bonds, and the molecules are simultaneously connected with C16-C18 fatty acid ester groups and C8-C12 linear alkyl groups, and free phenolic hydroxyl groups are retained. The oil solubility and thermal stability of the procyanidine are significantly improved through esterification and alkylation modification.

Description

Technical Field

[0001] This invention belongs to the field of lubricating oil technology, specifically relating to a proanthocyanidin-based lubricating oil antioxidant, its preparation method, and its application. Background Technology

[0002] During the operation of mechanical equipment, lubricating oil inevitably comes into contact with oxygen in the air. Under conditions such as high temperature and metal catalysis, it undergoes an oxidation reaction, generating harmful byproducts such as acidic substances, gums, and varnishes. This leads to increased viscosity, higher acid value, and decreased lubrication performance of the lubricating oil, and in severe cases, accelerated equipment wear or even equipment failure. Adding antioxidants is the most effective way to delay lubricating oil oxidation and extend its service life.

[0003] Currently, the antioxidants widely used in the lubricating oil industry mainly fall into two categories: amine antioxidants (such as alkylated diphenylamine) and phenolic antioxidants (such as 2,6-di-tert-butyl-p-cresol). However, traditional synthetic antioxidants have many limitations: insufficient high-temperature resistance; phenolic antioxidants are prone to decomposition and failure at temperatures exceeding 200°C; some amine antioxidants exhibit poor dispersibility at low temperatures; and the raw materials for synthetic antioxidants are mostly derived from petrochemical routes, resulting in high energy consumption and significant pollution during production, which does not align with the principles of green chemistry and sustainable development. As industrial equipment evolves towards high-temperature, high-pressure, and long-cycle operation, higher requirements are placed on the oxidation stability of lubricating oils. Developing efficient, environmentally friendly, and low-cost novel lubricating oil antioxidants has become an urgent technical challenge in this field.

[0004] In recent years, natural polyphenols have attracted much attention for their antioxidant applications in food, cosmetics, and other fields due to their excellent free radical scavenging ability and good biocompatibility. Proanthocyanidins (OPCs) are a class of oligomeric or polymeric polyphenols formed by the condensation of flavan-3-ol units through C4-C8 or C4-C6 bonds, and their antioxidant capacity is significantly better than that of traditional synthetic antioxidants. However, the direct application of proanthocyanidins to lubricating oil systems faces a fundamental obstacle: proanthocyanidin molecules contain a large number of phenolic hydroxyl groups, exhibiting strong hydrophilicity and weak lipophilicity, making them difficult to dissolve or uniformly disperse in non-polar lubricating oil base oils. To address this issue, some studies have attempted to modify proanthocyanidins through esterification, such as using stearoyl chloride to esterify lotus proanthocyanidin oligomers in the food industry to improve their lipophilicity. However, the existing technology still has the following shortcomings: First, the improvement of oil solubility by single esterification modification is limited, and the fat solubility of the modified product is difficult to meet the dispersion requirements of the lubricating oil system; Second, the existing modification research mainly focuses on food oil systems and does not involve the high temperature and long cycle conditions of lubricating oils, and the thermal stability and high temperature oxidation resistance of the modified products have not been verified.

[0005] Therefore, there is an urgent need in this field to develop a proanthocyanidin-based lubricating oil antioxidant, its preparation method, and its application, in order to alleviate or solve the above problems. Summary of the Invention

[0006] To address the technical problems of proanthocyanidins being unable to be directly applied to lubricating oil systems due to their strong hydrophilicity, and the limited improvement in oil solubility and insufficient high-temperature thermal stability of existing single esterification modification products, this invention provides a proanthocyanidin-based lubricating oil antioxidant, comprising: 0.8~1.5 wt% proanthocyanidin derivatives, 0.1~0.5 wt% amine antioxidants, 0.05~0.1 wt% metal passivators, with the balance being base oil; The proanthocyanidin derivative is an oligomeric proanthocyanidin skeleton formed by the condensation of 2 to 10 flavan-3-ol units through C4-C8 bonds and / or C4-C6 bonds. Its molecular structure contains ester-modifying groups and alkyl-modifying groups, and retains free phenolic hydroxyl groups. The ester modification group is a C16~C18 fatty acid ester group, which is attached to the phenolic hydroxyl group of the oligomeric proanthocyanidin skeleton; the alkyl modification group is a C8~C12 straight-chain alkyl group, which is attached to the phenolic hydroxyl group of the oligomeric proanthocyanidin skeleton.

[0007] Furthermore, the preparation of the proanthocyanidin derivative includes: Oligomeric proanthocyanidins were esterified with an esterifying agent under the action of a first catalyst to obtain the esterified product. The esterified product is subjected to an alkylating agent under the action of a second catalyst to undergo an alkylation reaction, thereby obtaining a dual-modified product; The dual-modified product was separated and dried to obtain the proanthocyanidin derivative.

[0008] Furthermore, the esterifying agent comprises oleic acid or oleic anhydride, and the first catalyst comprises toluenesulfonic acid; the amount of the first catalyst added is 0.5~1 wt% of the mass of the oligomeric proanthocyanidins. The esterification reaction is carried out at a temperature of 60-80°C for 4-6 hours.

[0009] Furthermore, the alkylating agent comprises dodecane bromide or octane bromide, the second catalyst comprises potassium carbonate, and the amount of the second catalyst added is 5-10 wt% of the weight of the oligomeric proanthocyanidins. The alkylation reaction is carried out at a temperature of 80-100°C for 6-8 hours.

[0010] Furthermore, the amine antioxidant includes diphenylamine compounds; the diphenylamine compounds are selected from at least one of p,p'-dioctyl-diphenylamine and monotert-butyldiphenylamine.

[0011] Furthermore, the metal passivating agent includes benzotriazole compounds, which are selected from at least one of methyl benzotriazole and benzotriazole derivatives.

[0012] This invention provides a method for preparing the proanthocyanidin-based lubricating oil antioxidant as described above, comprising the following steps: Obtain crude oligomeric proanthocyanidins; The crude oligomeric proanthocyanidins were subjected to esterification and alkylation reactions in sequence to obtain a double-modified product. The dual-modified product was subjected to impurity removal and drying treatments in sequence to obtain the proanthocyanidin derivative. The proanthocyanidin derivative is mixed with amine antioxidants, metal passivators, and base oil in a certain proportion to obtain the proanthocyanidin-based lubricating oil antioxidant.

[0013] Furthermore, the acquisition of the oligomeric proanthocyanidins includes the following steps: The bark of Pinus massoniana was extracted with a solvent at a solid-liquid ratio of 1:8-12, and the liquid phase was collected to obtain the pine bark proanthocyanidin extract. The pine bark proanthocyanidin extract was successively purified and concentrated and dried to obtain the crude oligomeric proanthocyanidin product. Based on dry bark, the extraction rate of the oligomeric proanthocyanidins is 8-12%; the content of proanthocyanidins in the crude oligomeric proanthocyanidins is ≥60%.

[0014] Furthermore, the purification process includes: The pine bark proanthocyanidin extract was loaded onto a macroporous adsorption resin column, washed with water to remove impurities, and then eluted with a 40-60 vol% ethanol aqueous solution. The eluent was collected. The concentration and drying process includes: The eluent was concentrated under reduced pressure at a vacuum of 0.05-0.6 MPa and a temperature of 50-70°C to a Baume degree of 8-15°, and then spray-dried to obtain the crude oligomeric proanthocyanidins.

[0015] This invention provides an antioxidant application of the proanthocyanidin-based lubricating oil antioxidant prepared by the method described above in the high-temperature lubrication system of petrochemical equipment and / or metallurgical equipment.

[0016] Compared with the prior art, the present invention has at least the following advantages: This invention employs a dual modification strategy, simultaneously introducing C16-C18 fatty acid ester groups and C8-C12 straight-chain alkyl groups onto the phenolic hydroxyl groups of the proanthocyanidin oligomeric backbone. The ester groups provide initial lipophilicity, while the alkyl groups further increase the hydrophobic volume. The synergistic effect of both enables the derivative to achieve a solubility of over 5 wt% in mineral base oils, fundamentally solving the technical problem that proanthocyanidins cannot be directly applied to lubricating oil systems due to their strong hydrophilicity.

[0017] The introduction of long-chain alkyl groups in this invention not only enhances oil solubility, but also provides high bond energy for the saturated alkane structure under high-temperature conditions, effectively inhibiting the oxidative degradation and intermolecular aggregation of the proanthocyanidin skeleton at high temperatures. Simultaneously, the introduction of ester groups reduces the density of intermolecular hydrogen bonds, minimizing heat-induced condensation side reactions. This results in an evaporation loss of less than 2.5% for the modified product at 200°C, with a pour point as low as -48°C, making it suitable for applications requiring a wide temperature range.

[0018] After modification via a dual pathway of esterification and alkylation, a sufficient amount of free phenolic hydroxyl groups remain unsubstituted in the proanthocyanidin backbone. These free phenolic hydroxyl groups serve as free radical scavenging sites, enabling proanthocyanidins to continuously exert their excellent antioxidant function (20-30 times that of vitamin E), ensuring that the modified product possesses both good oil solubility and highly efficient free radical scavenging activity.

[0019] Proanthocyanidin derivatives act as the primary antioxidants to scavenge free radicals and terminate the oxidation chain reaction. Amine antioxidants act as auxiliary antioxidants to capture peroxide free radicals and form a regeneration cycle with phenolic hydroxyl groups. Metal passivators inhibit the catalytic effect of metal ions on the oxidation reaction by chelating metal ions. The three form a gradient protection of phenol-amine synergy + metal passivation. Experimental results show that the lubricating oil containing 1.0 wt% of formulation 1 has an oxidation induction period of 32.27 min at 240℃, which is 126% higher than the traditional amine / phenol compound system (14.2 min) and 280% higher than the blank base oil (8.5 min). Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the preparation process of proanthocyanidin derivatives in one embodiment of the present invention. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0024] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention, as well as the prior art known to those skilled in the art and the description of the invention, may be implemented using any prior art methods, devices, and materials similar to or equivalent to the methods, devices, and materials in the embodiments of the present invention.

[0025] This invention provides a proanthocyanidin-based lubricating oil antioxidant, comprising: 0.8-1.5 wt% proanthocyanidin derivatives, 0.1-0.5 wt% amine antioxidants, 0.05-0.1 wt% metal passivators, with the balance being base oil; The proanthocyanidin derivative is an oligomeric proanthocyanidin skeleton formed by the condensation of 2 to 10 flavan-3-ol units through C4-C8 bonds and / or C4-C6 bonds. Its molecular structure contains ester-modifying groups and alkyl-modifying groups, and retains free phenolic hydroxyl groups. The ester modification group is a C16~C18 fatty acid ester group, which is attached to the phenolic hydroxyl group of the oligomeric proanthocyanidin skeleton; the alkyl modification group is a C8~C12 straight-chain alkyl group, which is attached to the phenolic hydroxyl group of the oligomeric proanthocyanidin skeleton.

[0026] In this invention, the functions of each component include: Proanthocyanidin derivatives are the main antioxidants, which scavenge free radicals and terminate the oxidation chain reaction, while also having excellent lipophilicity and thermal stability.

[0027] Amine antioxidants act as auxiliary antioxidants, scavenging free radicals and synergistically enhancing their effects with proanthocyanidin derivatives. Specifically, proanthocyanidin derivatives and amine antioxidants form a phenol-amine synergistic system. Phenols primarily decompose hydroperoxides, while amines primarily scavenge free radicals. The synergistic effect of both significantly prolongs the oxidation induction period.

[0028] Metal passivators can inhibit the catalytic oxidation of metals and form a passivation film to protect the metal surface.

[0029] For example, the content of the proanthocyanidin derivative in the antioxidant can be 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, and each of the above minimum and maximum values, or a range of any two values.

[0030] For example, the content of the amine antioxidant in the antioxidant can be 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, and each of the above minimum and maximum values, or a range of any two values.

[0031] For example, the content of the metal passivating agent in the antioxidant can be 0.05 wt%, 0.06 wt%, 0.07 wt%, 0.08 wt%, 0.09 wt%, 0.1 wt%, and each of the above minimum and maximum values, or a range of any two values.

[0032] In this invention, the preparation of proanthocyanidin derivatives may include: S21. The oligomeric proanthocyanidins are esterified with an esterifying agent under the action of a first catalyst to obtain the esterified product; S22. The esterified product is subjected to an alkylating agent under the action of a second catalyst to undergo an alkylation reaction to obtain a dual-modified product; S23. The double-modified product is separated and dried to obtain the proanthocyanidin derivative.

[0033] It should be noted that during the esterification process, oleic acid or oleic anhydride is used as the esterifying agent to react with the hydroxyl groups in the proanthocyanidin molecules, introducing C16-C18 fatty acid chains. The introduction of fatty acid chains significantly improves the lipophilicity of the molecules, allowing them to be uniformly dispersed in the lubricating oil base oil.

[0034] In the alkylation reaction, dodecane bromide or octane bromide is used as the alkylating agent to react with the remaining hydroxyl groups in the proanthocyanidin molecule, introducing C8-C12 long-chain alkyl groups. The introduction of long-chain alkyl groups further enhances oil solubility and improves the thermal stability of the molecule.

[0035] The synergistic effects of the esterification and alkylation reactions significantly optimize the fat solubility and thermal stability of proanthocyanidin-based lubricating oil antioxidants.

[0036] In some embodiments, the esterifying agent comprises oleic acid or oleic anhydride, and the first catalyst comprises toluenesulfonic acid; the amount of the first catalyst added is 0.5-1 wt% of the mass of the oligomeric proanthocyanidins. The esterification reaction is carried out at a temperature of 60-80°C for 4-6 hours.

[0037] For example, the amount of the first catalyst added can be 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1.0 wt% of the oligomeric proanthocyanidin mass, as well as each of the minimum and maximum values ​​mentioned above, or a range of any two values.

[0038] For example, the temperature of the esterification reaction can be 60°C, 65°C, 70°C, 75°C, 80°C, and any value between the minimum and maximum values ​​mentioned above, or a range of any two values.

[0039] For example, the esterification reaction time can be 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, and any value between the minimum and maximum values ​​mentioned above, or a range of any two values.

[0040] In some embodiments, the alkylating agent comprises dodecane bromide or octane bromide, the second catalyst comprises potassium carbonate, and the amount of the second catalyst added is 5-10 wt% of the weight of the oligomeric proanthocyanidins. The alkylation reaction is carried out at a temperature of 80-100°C for 6-8 hours.

[0041] For example, the amount of the second catalyst added can be 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt% of the oligomeric proanthocyanidin mass, as well as each of the minimum and maximum values ​​mentioned above, or a range of any two values.

[0042] For example, the temperature of the alkylation reaction can be 80°C, 85°C, 90°C, 95°C, 100°C, and any value between the minimum and maximum values ​​mentioned above, or a range of any two values.

[0043] For example, the alkylation reaction time can be 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, and any value between the minimum and maximum values ​​mentioned above, or a range of any two values.

[0044] like Figure 1As shown, in some more specific embodiments, steps S21 to S23 are performed in conjunction with the reaction apparatus. The entire process relies on a product separation device consisting of an esterification reactor, an alkylation reactor, and a distillation column, and a spray dryer connected in series to complete material transfer and reaction purification. The supporting equipment and operation procedures for each step are detailed as follows: For step S21, an esterification reactor is used as the esterification reaction vessel. Oligomeric proanthocyanidins, esterifying agents, and the first catalyst are added into the reactor through the oleic acid inlet on the side. At the same time, nitrogen is continuously introduced into the reactor through the nitrogen inlet to isolate oxygen. A condenser is installed on the top of the reactor to achieve solvent reflux. The stirring mechanism inside the reactor continuously stirs to ensure homogeneous reaction of the materials. After the esterification reaction is complete, the esterification product is discharged through the bottom discharge pipe and directly sent to the downstream alkylation reactor through the conveying pipe, thus completing the continuous feeding from step S21 to step S22.

[0045] For step S22, an alkylation reactor is used as the alkylation reaction vessel. After the esterification product is fed into the alkylation reactor, the alkylating agent and the second catalyst are added into the reactor through the alkylation reagent inlet on the side of the reactor. At the same time, nitrogen is introduced from the nitrogen inlet of the alkylation reactor to maintain an inert protective atmosphere. The reaction solvent is circulated back through the condenser at the top of the reactor, and the internal stirring mechanism continuously stirs the reactor to carry out the alkylation modification reaction. After the alkylation reaction is completed, the alkylation product (i.e., the double-modified crude product) is discharged from the bottom pipeline of the reactor. The material is directly transported to the product separation device distillation column on the right side of the attached diagram and enters the separation process in S23.

[0046] Step S23 is divided into two continuous unit operations: separation and drying. First, the double-modified crude product is sent to a distillation column for distillation separation. The distillation column is equipped with a condenser and a circulating pump to remove solvent and impurities, thereby purifying the product. The purified product after distillation separation is sent to the terminal spray dryer by a transfer pump. Spray drying is used to dehydrate and dry the material. Finally, the purified and dried proanthocyanidin derivative is collected from the bottom of the spray dryer.

[0047] In this invention, the amine antioxidant includes diphenylamine compounds; the diphenylamine compounds are selected from at least one of p,p'-dioctyl-diphenylamine and monotert-butyldiphenylamine.

[0048] In this invention, the metal passivating agent includes benzotriazole compounds, which are selected from at least one of methyl benzotriazole and benzotriazole derivatives.

[0049] This invention provides a method for preparing a proanthocyanidin-based lubricating oil antioxidant, comprising the following steps: S1. Obtain crude oligomeric proanthocyanidins; S2. The crude oligomeric proanthocyanidins are subjected to esterification and alkylation reactions in sequence to obtain a double-modified product; the double-modified product is subjected to impurity removal and drying treatment in sequence to obtain the proanthocyanidin derivative. S3. The proanthocyanidin derivative is mixed with amine antioxidants, metal passivators and base oil in a certain proportion to obtain the proanthocyanidin-based lubricating oil antioxidant.

[0050] In this invention, obtaining the oligomeric proanthocyanidins includes the following steps: S11. Extract the bark of Pinus massoniana using a solvent at a solid-liquid ratio of 1:8-12, collect the liquid phase, and obtain the pine bark proanthocyanidin extract.

[0051] In some embodiments, the solvent in step S11 may be an aqueous ethanol solution, wherein the volume concentration of ethanol in the aqueous ethanol solution is 50-80%.

[0052] In some embodiments, in step S11, the extraction is reflux extraction, the extraction temperature is 50~60℃, and the extraction time is 2~3 hours.

[0053] In some more specific embodiments, the extraction is performed in two steps: first, 8-12 times (w / v) of an aqueous ethanol solution is added and extracted for 2-3 hours, and the extract is filtered to obtain the first extract; second, 4-6 times (w / v) of an aqueous ethanol solution is added and extracted for 1-2 hours, and the extract is filtered to obtain the second extract; the two extracts are combined.

[0054] S12. The pine bark proanthocyanidin extract is successively purified and concentrated and dried to obtain the crude oligomeric proanthocyanidin product. Based on dry bark, the extraction rate of the oligomeric proanthocyanidins is 8-12%; the content of proanthocyanidins in the crude oligomeric proanthocyanidins is ≥60%.

[0055] In some embodiments, the purification process includes: The pine bark proanthocyanidin extract was loaded onto a macroporous adsorption resin column, washed with water to remove impurities, and then eluted with a 40-60 vol% ethanol aqueous solution. The eluent was collected. In some embodiments, the concentration and drying process includes: The eluent was concentrated under reduced pressure at a vacuum of 0.05-0.6 MPa and a temperature of 50-70°C to a Baume degree of 8-15°, and then spray-dried to obtain the crude oligomeric proanthocyanidins.

[0056] More specifically, the inlet air temperature of the spray dryer is 200~230℃, and the outlet air temperature is 100~120℃.

[0057] In some embodiments, step S3 includes the following steps: S31. Add the proanthocyanidin derivative to the base oil and stir under heating conditions to make the proanthocyanidin derivative uniformly dispersed in the base oil; S32. Add an amine antioxidant to the mixture obtained in step S31 and continue stirring under heating conditions; S33. Add a metal passivating agent to the mixture obtained in step S32, continue stirring under heating conditions, and obtain the proanthocyanidin-based lubricating oil antioxidant after cooling.

[0058] In some more specific embodiments, in step S31, the amount of the proanthocyanidin derivative added is 0.8 to 1.5 wt% of the base oil, the heating temperature is 50 to 70°C, and the stirring time is 20 to 40 minutes.

[0059] In some more specific embodiments, in step S32, the amount of amine antioxidant added is 0.1 to 0.5 wt% of the base oil weight, the heating temperature is 50 to 70°C, and the stirring time is 15 to 30 minutes.

[0060] In some more specific embodiments, in step S33, the amount of metal passivator added is 0.05~0.1 wt% of the base oil weight, the heating temperature is 50~70℃, and the stirring time is 5~15 minutes.

[0061] In some more specific embodiments, step S3 further includes step S34: after cooling the mixture obtained in step S33 to room temperature, filter to remove insoluble matter to obtain the proanthocyanidin-based lubricating oil antioxidant.

[0062] This invention provides an antioxidant application of the proanthocyanidin-based lubricating oil antioxidant as described above or prepared by the method described above in the high-temperature lubrication system of petrochemical equipment and / or metallurgical equipment.

[0063] To facilitate a further understanding of the present invention by those skilled in the art, the following examples are provided: Example 1 Obtain crude oligomeric proanthocyanidins.

[0064] S11. Take the bark of Masson pine (waste from a timber processing plant), remove the outer old bark, take the inner bark, dry it, and crush it to a particle size ≤0.5mm for later use.

[0065] Extraction: Add 10 times the weight of the raw material of 70% ethanol solution to the bark of Masson pine, reflux extract at 55℃ for 2.5 hours, filter through a 300-mesh pipe filter to obtain the first extract; add 5 times the weight of ethanol solution, reflux extract at 55℃ for 1 hour, filter to obtain the second extract; combine the two extracts to obtain the pine bark proanthocyanidin extract.

[0066] S12. Concentration: The extract is concentrated under reduced pressure at a vacuum of 0.6 MPa and a temperature of 50°C, and the ethanol is recovered to obtain a concentrated solution with a Baume degree of 10°.

[0067] Purification: The concentrate was slowly fed onto an AB8 macroporous resin column, where proanthocyanidins were selectively adsorbed by the resin; the resin column was rinsed with purified water to remove impurities; the eluent was slowly eluted with 50% ethanol and collected.

[0068] Drying: The eluent is concentrated to 15° Baumé under vacuum of 0.6 MPa and temperature of 70°C, and then pumped into a spray drying tower with an inlet air temperature of 215°C and an outlet air temperature of 106°C to obtain a brownish-red powdered proanthocyanidin product, namely crude oligomeric proanthocyanidins.

[0069] Results of crude oligomeric proanthocyanidins: Extraction rate: 10.5% (based on dry bark); Proanthocyanidin content: 65%; Oligomer (dimer to decamer) percentage: 78%.

[0070] Example 2 Obtain proanthocyanidin derivatives.

[0071] Raw material: Crude oligomeric proanthocyanidins obtained in Example 1.

[0072] S21. Esterification modification: Dissolve 100g of crude oligomeric proanthocyanidins in 500ml of acetone, and add 150g of oleic acid and 1g of p-toluenesulfonic acid catalyst.

[0073] The reaction was stirred at 70°C for 5 hours, with nitrogen gas introduced for protection during the reaction.

[0074] After the reaction was completed, acetone was removed by vacuum distillation, and the catalyst and unreacted oleic acid were removed by washing with water to obtain the esterified product.

[0075] S22. Alkylation modification: Dissolve the esterification product in 300 ml of ethyl acetate, and add 80 g of bromododecane and 8 g of potassium carbonate catalyst.

[0076] The reaction was stirred at 90°C for 7 hours, with nitrogen gas introduced for protection during the reaction.

[0077] After the reaction was completed, ethyl acetate was removed by vacuum distillation, and the catalyst and unreacted alkylating agent were removed by washing with water to obtain the double-modified product.

[0078] S23. Drying and shaping: The double-modified product is dried under a vacuum of 0.6 MPa and a temperature of 80°C to obtain a brown powdery pine bark proanthocyanidin derivative, i.e., proanthocyanidin derivative.

[0079] Test results of proanthocyanidin derivatives: oil solubility: solubility in mineral oil ≥5 wt%; high temperature evaporation loss (200℃, 2h): 2.1%; pour point: -48℃.

[0080] Example 3 Preparation of proanthocyanidin-based lubricating oil antioxidants.

[0081] Formula: Pine bark proanthocyanidin derivative: 1.0 wt%; p,p'-dioctyl-diphenylamine: 0.3 wt%; methyltriazole: 0.08 wt%; balance is mineral base oil (500SN).

[0082] Preparation method: S31. Pine bark proanthocyanidin derivatives are added to mineral base oil and stirred at 60°C for 30 minutes to ensure uniform dispersion.

[0083] S32. Add p,p'-dioctyl-diphenylamine and continue stirring for 20 minutes.

[0084] S33. Add methyltriazole and stir for 10 minutes. Cool to room temperature, filter to remove insoluble matter, and obtain the proanthocyanidin-based lubricating oil antioxidant product.

[0085] Example 4 The performance of the proanthocyanidin-based lubricating oil antioxidant prepared in Example 3 was tested; the mass ratio of T501 to T511 in the traditional amine / phenol compound system was 1.5:1, which served as a reference.

[0086] Test method: GB / T 12581-2023 Rotating oxygen bomb method.

[0087] Test conditions: Temperature: 240℃; Oxygen pressure: 0.5 MPa; Sample amount: 50g.

[0088] Test results: Conclusion: The oxidation induction period of the proanthocyanidin-based lubricating oil antioxidant of this invention is increased by 126% compared with the traditional amine / phenol compound system, and its antioxidant performance is significantly better than that of the prior art.

[0089] Example 5 Application of proanthocyanidin-based antioxidants in lubricating oils.

[0090] Application scenario: Lubrication system of centrifugal compressor unit in a refining and chemical enterprise.

[0091] Operating conditions: Speed: 8500 rpm; Outlet temperature: 110℃; Continuous operation cycle requirement: ≥12 months.

[0092] The original antioxidant formula was replaced with the proanthocyanidin-based lubricating oil antioxidant of this invention, and the total base number (TBN) was adjusted to 7.2 mg KOH / g.

[0093] Application effects: Oil change interval: extended from 6 months to 9 months (50% increase); Acid value growth rate: reduced by 45%; Bearing wear particle count: reduced by 42% (ISO 4406 standard); Acid value after 18 months of operation: 0.8 mg KOH / g; Viscosity change rate at 40℃: <10%.

[0094] The above technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made under the technical concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A proanthocyanidin-based lubricating oil antioxidant, characterized in that, include: Proanthocyanidin derivatives 0.8~1.5 wt%, amine antioxidants 0.1~0.5 wt%, metal passivators 0.05~0.1 wt%, balance base oil; The proanthocyanidin derivative is an oligomeric proanthocyanidin skeleton formed by the condensation of 2 to 10 flavan-3-ol units through C4-C8 bonds and / or C4-C6 bonds. Its molecular structure contains ester-modifying groups and alkyl-modifying groups, and retains free phenolic hydroxyl groups. The ester modification group is a C16~C18 fatty acid ester group, which is attached to the phenolic hydroxyl group of the oligomeric proanthocyanidin skeleton; the alkyl modification group is a C8~C12 straight-chain alkyl group, which is attached to the phenolic hydroxyl group of the oligomeric proanthocyanidin skeleton.

2. The proanthocyanidin-based lubricating oil antioxidant according to claim 1, characterized in that, The preparation of the proanthocyanidin derivative includes: Oligomeric proanthocyanidins were esterified with an esterifying agent under the action of a first catalyst to obtain the esterified product. The esterified product is subjected to an alkylating agent under the action of a second catalyst to undergo an alkylation reaction, thereby obtaining a dual-modified product; The dual-modified product was separated and dried to obtain the proanthocyanidin derivative.

3. The proanthocyanidin-based lubricating oil antioxidant according to claim 2, characterized in that, The esterifying agent includes oleic acid or oleic anhydride, and the first catalyst includes toluenesulfonic acid; the amount of the first catalyst added is 0.5~1 wt% of the mass of the oligomeric proanthocyanidins. The esterification reaction is carried out at a temperature of 60-80°C for 4-6 hours.

4. The proanthocyanidin-based lubricating oil antioxidant according to claim 2, characterized in that, The alkylating agent includes dodecane bromide or octane bromide, the second catalyst includes potassium carbonate, and the amount of the second catalyst added is 5-10 wt% of the weight of the oligomeric proanthocyanidins. The alkylation reaction is carried out at a temperature of 80-100°C for 6-8 hours.

5. The proanthocyanidin-based lubricating oil antioxidant according to claim 1, characterized in that, The amine antioxidants include diphenylamine compounds; the diphenylamine compounds are selected from at least one of p,p'-dioctyl-diphenylamine and monotert-butyl-diphenylamine.

6. The proanthocyanidin-based lubricating oil antioxidant according to claim 1, characterized in that, The metal passivating agent includes benzotriazole compounds, which are selected from at least one of methyl benzotriazole and benzotriazole derivatives.

7. A method for preparing the proanthocyanidin-based lubricating oil antioxidant according to any one of claims 1-6, characterized in that, Including the following steps: Obtain crude oligomeric proanthocyanidins; The crude oligomeric proanthocyanidins were subjected to esterification and alkylation reactions in sequence to obtain a double-modified product. The dual-modified product was subjected to impurity removal and drying treatments in sequence to obtain the proanthocyanidin derivative. The proanthocyanidin derivative is mixed with amine antioxidants, metal passivators, and base oil in a certain proportion to obtain the proanthocyanidin-based lubricating oil antioxidant.

8. The method for preparing the proanthocyanidin-based lubricating oil antioxidant according to claim 7, characterized in that, The acquisition of the oligomeric proanthocyanidins includes the following steps: The bark of Pinus massoniana was extracted with a solvent at a solid-liquid ratio of 1:8-12, and the liquid phase was collected to obtain the pine bark proanthocyanidin extract. The pine bark proanthocyanidin extract was successively purified and concentrated and dried to obtain the crude oligomeric proanthocyanidin product. Based on dry bark, the extraction rate of the oligomeric proanthocyanidins is 8-12%; the content of proanthocyanidins in the crude oligomeric proanthocyanidins is ≥60%.

9. The method for preparing the proanthocyanidin-based lubricating oil antioxidant according to claim 8, characterized in that, The purification process includes: The pine bark proanthocyanidin extract was loaded onto a macroporous adsorption resin column, washed with water to remove impurities, and then eluted with a 40-60 vol% ethanol aqueous solution. The eluent was collected. The concentration and drying process includes: The eluent was concentrated under reduced pressure at a vacuum of 0.05-0.6 MPa and a temperature of 50-70°C to a Baume degree of 8-15°, and then spray-dried to obtain the crude oligomeric proanthocyanidins.

10. The application of a proanthocyanidin-based lubricating oil antioxidant according to any one of claims 1-6 or a proanthocyanidin-based lubricating oil antioxidant prepared by any one of claims 7-9 in the anti-oxidation protection of high-temperature lubrication systems in petrochemical equipment and / or metallurgical equipment.

Images