Lubricating oil composition containing graphene oxide and used for heavy-load methanol fuel engine and preparation method of lubricating oil composition

Abstract

The invention discloses a graphene oxide-containing lubricating oil composition for a heavy-load methanol fuel engine. The graphene oxide-containing lubricating oil composition is prepared from the following raw materials: a dispersing viscosity index agent, an antioxidant, an anti-wear agent, a clearing agent, a dispersing agent and base oil. The dispersing type viscosity index improver P (BMA + LMA + TMA + NVP) copolymer contains a strong N polar group, so that graphene oxide does not need to be continuously modified, surface functional groups do not need to be removed, the cost is greatly reduced, industrial application is facilitated, meanwhile, the dispersing type viscosity index improver is applied to a methanol fuel engine, can be absorbed with combustion products such as methanol and formic acid and is more beneficial to dispersion of graphene, and therefore, the dispersing type viscosity index improver has a good application prospect. The graphene additive is very suitable for being applied to methanol fuel engine lubricating oil and can be applied to a large scale in a new field.

Description

Technical Field

[0001] The present invention relates to the technical field of lubricating oils, and particularly to a lubricating oil composition for a heavy-duty methanol fuel engine containing graphene oxide and a preparation method thereof. Background Art

[0002] The research on methanol as an automotive fuel has been carried out for many years, but it has not yet been commercially applied on a large scale. The poor lubricity of methanol fuel still causes problems of engine wear and corrosion during use. Compared with diesel and gasoline engines, it has the following disadvantages: (1) Corrosiveness: Methanol and combustion products such as formaldehyde, formic acid, and water generated after combustion will react with the lubricating oil. The most important additive in the lubricating oil, the antioxidant and anti-wear agent ZDDP, reacts with methanol to form ZnO and weak acids, which will cause corrosion of the metal surface and decomposition of the anti-wear agent in the engine lubricating oil, significantly reducing the anti-wear effect of the engine. Substances such as formaldehyde and formic acid will corrode engine parts. Unburned methanol reacts with the metal in the engine, causing corrosion and cracking of the material surface. The main reason for the corrosion is that methanol has a large latent heat of vaporization, and it is easy to have poor vaporization and flow into the crankcase along the cylinder wall. On the one hand, methanol fuel has strong polarity, so the combustion products will dissolve in the methanol fuel. Once the methanol is evaporated, the corrosive combustion products will remain on the exposed metal surface and cause corrosion. On the other hand, the lubricating oil film on the cylinder wall is washed or diluted, resulting in direct contact between metal and metal without lubrication, causing excessive wear, thus accelerating the frictional wear of the piston and the cylinder wall, and damaging the lubricating oil film at the gap between the intake and exhaust valves and the valve guides. Methanol, as a strongly polar molecule, has good water absorption. When the engine is running, a large amount of water is easily carried into the oil sump by the methanol fuel and mixed with the engine lubricating oil. As the water-containing methanol fuel increases, the oil-water separation ability of the lubricating oil gradually decreases, and finally forms an emulsion of methanol + water + lubricating oil, resulting in the failure of functions such as lubrication and cooling. It will cause the inability to form an effective oil film between engine components such as crankshaft bearings, camshafts, connecting rod bearings, pistons, and cylinder liners. Due to poor lubrication of each component, the engine wears out rapidly and its service life is shortened. As the water content in the emulsified engine oil increases, harmful substances are continuously precipitated, and the corrosion of engine components becomes gradually serious. (2) Difficult cold start: The latent heat of vaporization of methanol is 3 to 4 times that of gasoline and diesel. The lower boiling point and higher latent heat of vaporization reduce the intake air temperature in the cylinder, making it difficult for the fuel to vaporize, and the mixture concentration cannot reach the flammable limit, resulting in difficult cold start. When the methanol engine is cold started, the working temperature is low, and it is easy to form a water-methanol-lubricating oil mixture. (3) Swelling property: Methanol is a polar organic solvent, and some components in the engine fuel supply system are made of plastic composite materials. Methanol will cause these materials to swell, resulting in an increase in volume and the material becoming brittle or soft.

[0003] At present, there is no special lubricating oil technology suitable for methanol fuel engines that can protect engine parts from corrosion. How to improve the anti-corrosion performance of engine oil is the key to the development of methanol engine lubricating oil technology. There is also no general technical standard for methanol engine oil at home and abroad.

[0004] In the existing technology, the invention patent with the application number CN201911032689.5 named "Lubricating Oil Composition for Methanol Engine and Preparation Method" discloses a lubricating oil composition for methanol engines, which consists of a viscosity index modifier, an antioxidant and anti-corrosion agent, a friction improver, a detergent, a demulsifier and a base oil composition, and no key component that can reduce corrosion is seen.

[0005] The invention patent with the application number 201310146696.4 named "Engine Oil Composition for Methanol Fuel and Its Manufacturing Method" discloses an engine oil composition for methanol fuel and its manufacturing method. This composition contains Mannich base, antioxidant, metal detergent, zinc dialkyldithiophosphate (ZDDP), organic molybdenum, metal corrosion inhibitor and lubricating oil base oil.

[0006] The zinc dialkyldithiophosphate (ZDDP), an essential antioxidant and anti-wear agent in traditional lubricating oils, is prone to react with methanol and lose its antioxidant and anti-wear effects. Through preliminary simulation tests, it was found that when methanol was added to new engine oil containing ZDDP, the four-ball machine anti-wear test was carried out on the mixed engine oil. The friction plate diameter increased sharply, and the anti-deposit test on the coking plate was carried out. The deposits increased sharply; after standing for a period of time, the methanol and engine oil were stratified. Elemental analysis was carried out on the upper layer of methanol, and it was found that the upper layer solution contained a large amount of zinc and phosphorus elements, while the zinc and phosphorus elements in the lower layer engine oil solution became less, indicating that the zinc dialkyldithiophosphate (ZDDP) in the lubricating oil has lost its function in the presence of methanol. Finding a suitable antioxidant and anti-wear agent has become one of the keys to the development of methanol engine lubricating oil technology.

[0007] The present invention utilizes the advantages of graphene as a composition of lubricating oil to replace the key component of traditional lubricating oil, zinc dialkyldithiophosphate (ZDDP); graphene will shine in the new energy field; graphene is a new type of carbon nanomaterial with good anti-corrosion performance, closer to the components of lubricating oil, and very chemically stable, not easily reacting with other additives. Graphene can also improve the heat dissipation of the lubricating medium and provide antioxidant and anti-corrosion protection to the surface of the friction pair; graphene has an ultra-thin layered structure and low shear strength between the layers, with good lubricity. When the two friction surfaces come into contact and rub, the layered graphene enters between the two friction surfaces to form a graphene protective film, converting the friction and wear between the two friction surfaces into internal friction between the graphene layers, effectively hindering the contact between the two friction surfaces and reducing the friction and wear between the friction surfaces. As a derivative of graphene, graphene oxide has been widely used as an additive in lubricating materials due to its extremely small size and unique layered structure. Compared with graphene, graphene oxide contains a large number of hydrophilic oxygen-containing active groups such as hydroxyl, epoxy, carboxyl, and carbonyl groups on its surface, and there is a strong π-π interaction between the layers of graphene oxide, which is extremely prone to agglomeration in lubricating oil. This not only limits the lubricating effect of the lubricating oil but also causes precipitation, resulting in its agglomeration and sedimentation in the lubricating oil and being difficult to stably disperse in the lubricating oil. Therefore, solving the dispersion stability of graphene oxide in lubricating oil has become a key issue. Currently, researchers at home and abroad mainly use two methods to solve these problems. The first is to disperse graphene oxide into lubricating oil using a dispersant, which has become a research hotspot in the lubrication field, and screening or preparing a suitable dispersant has become the key. Existing research has shown that a dispersant can wrap a nanoparticle to repel another nanoparticle, thereby forming a uniform and stable suspension. The second method is to modify graphene oxide using an appropriate surface modifier to achieve surface grafting modification; the modification process of the second method will damage the structure of graphene itself to varying degrees, and its original mechanical properties will be affected to varying degrees; the present invention adopts the first method and uses a copolymer of (butyl methacrylate + dodecyl methacrylate + tetradecyl methacrylate + N-vinylpyrrolidone), abbreviated as: dispersant viscosity index improver P(BMA+LMA+TMA+NVP) copolymer. The advantages of this polymer: the molecular chain of this structure contains a five-membered ring with an N atom and belongs to an inner amide compound, having both hydrophilic and lipophilic groups, making it highly soluble in water and capable of dissolving many solvents such as alcohols and carboxylic acids, including methanol, formic acid, acetic acid, etc. Especially, graphene oxide contains a large number of hydrophilic oxygen-containing active groups such as hydroxyl, epoxy, carboxyl, and carbonyl groups on its surface. Therefore, the dispersant viscosity index improver P(BMA+LMA+TMA+NVP) copolymer has the best dispersibility for graphene oxide. At the same time, the polymer contains a lipophilic long-chain group and can also dissolve in base oil and can be used as a viscosity improver for lubricating oil to increase viscosity.

[0008] The dispersant is adsorbed on the surface of graphene for surface modification. It has poly(dodecyl methacrylate) with a larger molecular weight and higher activity (average molecular weight is 50,000). The poly(dodecyl methacrylate) chains with large molecular weight and high activity can effectively wrap on the surface of graphene, thus forming a steric barrier and generating a steric hindrance effect to avoid the agglomeration between graphene sheets, so as to make graphene evenly and stably dispersed in graphene lubricating oil.

[0009] When graphene is used as a lubricating oil additive, it usually forms a nano-scale superlubricating protective film on the friction surface. The lubricating film formed by graphene particles has the characteristics of high strength, high chemical stability, and weak intermolecular van der Waals forces. Therefore, complex friction phenomena will occur between the graphene sheets and the friction surface. When graphene is used as a lubricating oil additive, graphene can improve friction.

[0010] This polymer has the following characteristics:

[0011] 1. Surface activity: From the structure, the long molecular chain of the polymer contains both the lactam group which is hydrophilic, affinity and character group, and the lipophilic non-polar carbon chain; this molecular structure makes it have a low surface activity, the adsorption effect on the solid surface and the three-dimensional shielding ability formed by hydrophilicity, making the solid particles have excellent dispersion stability, and its hydrogen bond complexing ability with other organic and inorganic compounds also gives it a coagulation effect and solubilization ability, which can make the liquid clear and stable.

[0012] 2. Complexing property: The polymer has the "dissolving" ability, which is because its molecular structure contains highly polar characteristics and amide groups that can accept hydrogen bonds. At the same time, it has non-polar groups, which enables the polymer to form complexes with compounds containing hydroxyl groups, carboxyl groups and other active hydrogen atoms.

[0013] 3. Strong adsorption property: It can adsorb on the metal surface to form a thick viscous oil film. These oil films enhance the formation of the lubricating film under low-speed and high-temperature conditions, effectively reduce friction and wear, and can also play an isolation role to prevent acid corrosion.

[0014] 4. Thickening property: This structure contains poly(dodecyl methacrylate), which is a viscosity index improver, a kind of polymer with excellent shear resistance and can increase the viscosity of engine oil.

[0015] 5. Pour point depressant effect: This structure contains butyl methacrylate + dodecyl methacrylate + tetradecyl methacrylate + N-vinylpyrrolidone; Short chains with less than 7 carbon atoms mainly affect the viscosity index of the polymer solution and the molecular scale at low temperatures; Side chains with 8 - 13 carbon atoms can enhance the solubility of the polymer in hydrocarbon solutions; Long chains with more than 14 carbon atoms can interact with wax crystals to lower the pour point. In the present invention, a combination of butyl methacrylate with 4 carbon atoms, dodecyl methacrylate with 12 carbon atoms, and tetradecyl methacrylate with 14 carbon atoms is used to ensure good thickening ability and improve the viscosity-temperature performance of the oil product. At the same time, by introducing N-vinylpyrrolidone as a polar group, the solubility is further increased, the dispersibility is improved, and the low-temperature fluidity of the sample is increased. Summary of the Invention

[0016] The object of the present invention is to solve the deficiencies existing in the above-mentioned background technology and provide a lubricating composition for heavy-duty methanol fuel engines containing graphene oxide and a preparation method thereof.

[0017] To achieve the above object, the technical solution adopted by the present invention is:

[0018] A lubricating composition for heavy-duty methanol fuel engines containing graphene oxide, by mass fraction, includes the following raw materials:

[0019]

[0020] The dispersant viscosity index improver is a P(BMA + LMA + TMA + NVP) copolymer.

[0021] Preferably, the compound antioxidant is a mixture of a phenolic ester antioxidant and an amine antioxidant, and the mass ratio of the two is 1:1 - 2.

[0022] Preferably, the phenolic ester antioxidant is methyl 3,5-di-tert-butyl-4-hydroxyphenyl acrylate; the amine antioxidant is alkyl diphenylamine.

[0023] Preferably, the anti-wear agent is graphene oxide;

[0024] Preferably, the detergent is a mixture of alkyl salicylate and sulfonate.

[0025] Preferably, the dispersant is a borated polyisobutylene succinimide dispersant.

[0026] Preferably, the base oil is a coal-to-hydrocarbon synthetic base oil.

[0027] Preferably, the structure of the alkyl salicylate is preferably as shown in Formula I:

[0028]

[0029] Among them, R is an alkyl group containing 10 to 20 carbon atoms, M is Ca or Mg, and m and n are positive integers not equal to zero;

[0030] The structure of the sulfonate is preferably shown as formula II:

[0031]

[0032] Among them, R1 is an alkyl group containing 14 to 28 carbon atoms, M is Ca or Mg, and m1 and n1 are positive integers not equal to zero;

[0033] The structure of the borated polyisobutylene succinimide dispersant is shown as formula III:

[0034]

[0035] Among them, PIB is polyisobutylene, the molecular weight is 900 to 1300, and r is a positive integer not equal to zero;

[0036] In the first aspect, in the above technical solution, the present invention provides a copolymer of butyl methacrylate (BMA), dodecyl methacrylate (LMA), tetradecyl methacrylate (TMA) and N-vinylpyrrolidone (NVP), including: mixing (BMA + LMA + TMA + NVP) with a solvent and an initiator; polymerizing at 40 °C to 70 °C for 4 to 8 hours, subjecting the toluene solution of the obtained polymerization product to vacuum distillation, and performing operations such as vacuum filtration and alcohol washing, and then drying in vacuum to obtain a white or light yellow (BMA + LMA + TMA + NVP) copolymer. The reaction formula is as follows:

[0037]

[0038] Preferably, the weight ratio of butyl methacrylate, dodecyl methacrylate, tetradecyl methacrylate and N-vinylpyrrolidone can be: (1 to 3):(2 to 5):(1 to 3):(1 to 3), and the present invention preferably 1:3:1:1.

[0039] Preferably, nitrogen is introduced into the device as a protective gas and pulsed stirring is performed. The polymerization reaction is heated in stages: reacting at 40 °C to 55 °C for 2 to 3 hours, reacting at 55 °C to 65 °C for 3 hours, and reacting at 65 °C to 70 °C for 2 to 3 hours to avoid the phenomenon of "explosive polymerization".

[0040] The initiator can be: azodicyanovaleric acid (ACVA), azobisisobutyronitrile (AIBN), benzoyl peroxide (BPO), azodiisobutyronitrile (ABVN), etc., or any combination thereof. The present invention preferably uses benzoyl peroxide (BPO). The dosage of the initiator can be 0.05% to 2.0% of the weight of the monomer, and the present invention preferably 1.5% as the best requirement.

[0041] Preferably, the amount of toluene used as the solvent is 15 - 35 mL / mol, and 20 mL / mol is preferred in the present invention.

[0042] Second aspect: The present invention also provides a preparation method of a lubricating oil composition for a heavy-duty methanol fuel engine containing graphene oxide, which includes the following steps:

[0043] Sol preparation: First, cut the dispersant viscosity index improver P(BMA + LMA + TMA + NVP) according to the formula ratio and mix it with an appropriate amount of base oil, heat it to 120 - 130 °C, stir and dissolve it, and let it stand for 4 - 6 hours to obtain product a;

[0044] Blending: Put product a and the remaining base oil into a blending kettle, sequentially add a dispersant, a pour point depressant, an antioxidant, an anti-wear agent, and a detergent according to the formula ratio, start stirring and heating to 50 - 60 °C and keep it warm, and continuously stir for 4 h - 6 h to obtain a lubricating oil composition for a heavy-duty methanol fuel engine containing graphene oxide.

[0045] Technical principle of the present invention:

[0046] I. Synthesis technical principle of the dispersant viscosity index improver P(BMA + LMA + TMA + NVP)

[0047] (I) Analysis of the roles of raw materials

[0048] 1. Synergistic effect of monomer selection

[0049] Butyl methacrylate (BMA)

[0050] Function: Provide short-chain alkyl (C4), adjust the flexibility and initial solubility of the copolymer, reduce the intermolecular force, and avoid excessive cross-linking of the polymer.

[0051] Key function: As a "spacer segment", balance the rigidity of long-chain alkyls (LMA, TMA), and ensure the appropriate fluidity of the copolymer in the oil phase.

[0052] Dodecyl methacrylate (LMA) and tetradecyl methacrylate (TMA)

[0053] Function: Introduce long-chain alkyls (C12, C14), form a strong lipophilic skeleton, and endow the copolymer with excellent oil solubility and dispersion ability for non-polar substances.

[0054] Synergistic effect: The mixing ratio of C12 and C14 (preferably 3:1) can optimize the intermolecular van der Waals force and avoid excessive crystallinity or insufficient solubility caused by a single long chain.

[0055] N-vinylpyrrolidone (NVP)

[0056] Function: Provide N-polar groups (pyrrole rings), which strongly interact with polar substances (such as water, formic acid, graphene oxide, etc.) through hydrogen bonds to form an amphiphilic structure.

[0057] Core function: The polar pyrrole ring is the key group to achieve "dispersion of polar substances", "oil-water emulsification" and "adsorption on metal surfaces".

[0058] 2. Role of initiator and solvent

[0059] Initiator (preferably BPO)

[0060] Function: Decompose to generate free radicals to initiate polymerization. The decomposition temperature of BPO (60 - 80 °C) matches the stepwise heating process to avoid explosive polymerization.

[0061] Dosage optimization: When the amount is 1.5% (by monomer weight), the free radical concentration is moderate, which not only ensures the polymerization rate but also avoids too fast chain termination resulting in too low molecular weight.

[0062] Solvent toluene

[0063] Function: Dissolve monomers and initiators, reduce the viscosity of the system, promote heat transfer, and inhibit explosive polymerization.

[0064] Dosage optimization: When the amount is 20 mL / mol, the solvation effect is balanced with the monomer concentration to ensure a polymerization conversion rate (>95%) and a controllable molecular weight distribution (PDI < 1.5).

[0065] (II) Necessity and technical effects of process parameter optimization

[0066] 1. Stepwise heating polymerization

[0067] Process design:

[0068] First stage: 40 - 55 °C (2 - 3 h), the initiator decomposes slowly to form initial free radicals, and the low conversion rate (20 - 30%) avoids a sudden increase in viscosity;

[0069] Second stage: 55 - 65 °C (3 h), accelerate polymerization, the conversion rate reaches 70 - 80%, and control the reaction heat release;

[0070] Third stage: 65 - 70 °C (2 - 3 h), complete polymerization, the conversion rate > 95%.

[0071] Technical effects:

[0072] Avoid explosive polymerization: Control the free radical concentration by gradient heating to prevent the "gel effect";

[0073] Controllable molecular weight: Prolong the polymerization time to make the chain growth uniform and the number average molecular weight (Mn) stable.

[0074] 2. Nitrogen protection and pulsed stirring

[0075] Nitrogen protection: Exclude oxygen (radical inhibitor) to ensure polymerization efficiency;

[0076] Pulsed stirring: Periodically strengthen mixing to avoid local enrichment of monomers / initiators and ensure the uniformity of copolymer composition.

[0077] (III) Importance of optimizing raw material ratio

[0078] 1. Monomer weight ratio (1:3:1:1, BMA:LMA:TMA:NVP)

[0079] Polarity - hydrophilic - lipophilic balance (HLB value):

[0080] The ratio of NVP (polar) to LMA + TMA (lipophilic) is 1:4, and the HLB value is approximately 8 - 10, with both oil solubility and the dispersibility of polar substances;

[0081] BMA acts as a "neutral segment" to adjust the HLB value and avoid excessive hydrophilicity or lipophilicity.

[0082] Verification of technical effects:

[0083] When the proportion of NVP < 1, the polar groups are insufficient and cannot effectively disperse water and formic acid;

[0084] When the proportion of LMA + TMA > 4, the copolymer has too strong oil solubility and the polar dispersion ability decreases.

[0085] (IV) Unexpected technical effects

[0086] 1. Multi - effect combined functional synergy

[0087] Limitations of traditional viscosity index improvers: Polyisobutylene succinimide (PIBSI) only focuses on dispersibility and cannot solve the polar corrosion and emulsification problems of methanol engines.

[0088] Breakthrough of the present invention:

[0089] Polar dispersion + emulsion stabilization: The pyrrole ring of NVP adsorbs water and formic acid simultaneously through hydrogen bonds, and the long - chain alkyl forms a water - in - oil interfacial film, with the emulsion stability reaching 96 h (tested by standard method);

[0090] High - temperature anti - deposition + anti - wear: Polar groups form an adsorption film on the metal surface (thickness ≈ 50 - 80 nm), and at the same time disperse high - temperature deposits (such as the deposit amount at the piston ring is reduced by 70%).

[0091] 2. Efficient dispersion of graphene oxide

[0092] Unexpected discovery: The pyrrole ring of the copolymer forms a dual interaction of TT-TT conjugation + hydrogen bond with the hydroxyl and carboxyl groups of graphene oxide (GO), combined with the steric hindrance of the long-chain alkyl group, reducing the sedimentation rate of GO in lubricating oil by 90% (compared with the system without dispersant).

[0093] Mechanism of action:

[0094] The polar end adsorbs on the surface of GO, and the lipophilic end anchors in the oil phase, forming a "core-shell" structure;

[0095] The long chains entangle to form a network scaffold to counteract the gravitational sedimentation of GO.

[0096] (V) Summary

[0097] Through the design of the polar-lipophilic monomer ratio, the optimization of the staged polymerization process, and the regulation of multi-scale interfacial interactions, the present invention has achieved a leapfrog upgrade of the viscosity index improver from "single viscosity increasing" to "viscosity increasing + dispersing + anti-corrosion + anti-wear + nanomaterial stabilization". Especially in the harsh environment of methanol engines, the three major problems of polar corrosion, oil-water separation, and high-temperature deposition that have long existed in the industry have been solved, and its effect far exceeds that of traditional single-component viscosity index improvers, demonstrating the synergistic innovation value of molecular structure design and process optimization.

[0098] II. Preparation technical principle of the lubricating oil composition for heavy-duty methanol fuel engines containing graphene oxide

[0099] (I) Analysis of the functions of raw materials

[0100] 1. Graphene oxide (GO)

[0101] Anti-wear and friction reduction: The lamellar structure adsorbs on the friction surface to form a physical isolation film, reducing direct metal contact; filling corrosion pits and enhancing the bearing capacity of the oil film.

[0102] Anti-corrosion: The surface oxygen-containing groups (-OH, -COOH) chelate with the combustion products of methanol (formic acid) to inhibit acidic corrosion. No modification is required: The N polar group of the viscosity index improver P has a strong interaction with the oxygen-containing groups of GO, and it can be directly dispersed without removing functional groups, reducing costs.

[0103] 2. Antioxidant system (phenolic ester type + amine type)

[0104] Phenolic ester antioxidant (methyl 3,5-di-tert-butyl-4-hydroxyphenyl acrylate): It has good high-temperature stability, inhibits high-temperature sludge and deposits, and makes up for the defect of easy volatilization of traditional phenols.

[0105] Amine antioxidant (alkyl diphenylamine): It has strong high-temperature durability, extends the oxidation induction period, and controls viscosity growth.

[0106] Synergistic effect: Phenolic type inhibits initial oxidation, amine type inhibits later oxidation. The combined use is superior to single components and avoids the invalidation of the reaction between ZDDP and methanol.

[0107] 3. Detergent (compound of salicylate + sulfonate)

[0108] Salicylate: High base number, quickly neutralizes formic acid, but the base number decays rapidly when used alone.

[0109] Sulfonate: Stable micelle structure, slow-release neutralization, maintains the base number under high-concentration formic acid, and protects sensitive metals such as copper and lead. Advantages of compounding: Taking into account both rapid neutralization and long-term anti-corrosion, reducing the corrosion of acidic products to the engine.

[0110] (2) Necessity for optimizing raw material dosage and process parameters

[0111] 1. Optimization of the ratio of viscosity index improver P

[0112] Carbon chain length synergy: 4C (BMA), 12C (LMA), and 14C (TMA) are compounded in a specific ratio to balance the thickening ability, hydrocarbon solubility, and pour point depressing effect.

[0113] Content of NVP: Excessive polar groups will cause a sharp increase in the viscosity of the system, and the ratio needs to be controlled to ensure low-temperature fluidity.

[0114] 2. Addition amount of graphene oxide

[0115] 0.1% - 0.5% (mass fraction): Excessive amount will cause agglomeration and reduce dispersibility; too little amount will result in insufficient anti-wear effect. Experiments show that the oil film thickness is maximized and the extreme pressure performance is optimal at 0.3%.

[0116] 3. Sol process parameters

[0117] Temperature (120 - 130 °C): Ensure that viscosity index improver P is completely dissolved and avoid caking at low temperatures; exceeding 130 °C will cause the decomposition of NVP.

[0118] Standing time (4 - 6 hours): Promote the stretching of polymer molecular chains to form a stable sol. Shortening the time will result in uneven dispersion.

[0119] 4. Blending process parameters

[0120] Temperature (50 - 60 °C): Avoid the high-temperature oxidation of graphene oxide and ensure the dissolution of additives at the same time; the dispersion efficiency of antioxidants decreases when the temperature is lower than 50 °C.

[0121] Stirring time (4 - 6 hours): Ensure the full infiltration of graphene oxide and base oil. Excessive stirring time may damage the lamellar structure.

[0122] (3) Technical effects

[0123] 1. Replace ZDDP to solve the methanol compatibility problem

[0124] Traditional ZDDP reacts with methanol to form methyl phosphate, which becomes ineffective. Through the GO + phenolic ester / amine antioxidant system in the present invention, the oxidation induction period is extended by 2 times, and the viscosity growth rate is reduced by 60% in the high-temperature oxidation test at 150 °C.

[0125] 2. Multiple anti-wear and anti-corrosion mechanisms

[0126] GO physical film: The friction coefficient is reduced from 0.12 to 0.06, and the wear volume is reduced by 75%.

[0127] Detergent compounding: The copper strip corrosion grade is reduced from grade 3 to grade 1 in the formic acid environment, and the lead corrosion weight loss is reduced by 80%.

[0128] 3. Simplify the formula and reduce costs

[0129] The viscosity index improver P has three functions simultaneously: thickening, pour point depressing, and dispersing. It eliminates the traditional pour point depressant and part of the dispersant, and the formula cost is reduced by 20%.

[0130] (IV) Unexpected technical effects

[0131] 1. "Reverse dispersion" of graphene oxide in a methanol environment

[0132] Traditional graphene needs to be chemically modified to be dispersed in hydrocarbon base oils, but in the present invention, the oxygen-containing groups of GO form hydrogen bonds with the N polar groups of the viscosity index improver P, and the combustion products of methanol (polar substances) instead enhance the dispersion stability of GO, forming a unique effect of "polar environment promoting dispersion".

[0133] 2. "Intelligent response" characteristics of the viscosity index improver P

[0134] At low temperatures, the long chain of TMA combines with wax crystals to inhibit crystal growth; at high temperatures, the short chain of BMA maintains molecular flexibility, and the viscosity index (VII) reaches 180, which is better than that of traditional single-component viscosity index improvers (VI = 150).

[0135] 3. "Acid-base buffer pool" effect of detergent compounding

[0136] Salicylate quickly neutralizes low-concentration formic acid (pH > 3), and sulfonate releases alkalinity at high-concentration formic acid (pH < 3), forming two-stage neutralization, which reduces the total base number (TBN) decay rate of the oil product by 50%.

[0137] (V) Conclusion

[0138] The present invention solves the three major problems of oxidation failure, acidic corrosion, and low-temperature fluidity of methanol engine lubricating oil through functionalized viscosity index improver design, antioxidant synergistic compounding, graphene oxide interface optimization, and detergent acid-base complementarity, achieving ZDDP-free, low-cost, and high-performance characteristics, and providing a breakthrough solution for lubricating oils for new fuel engines.

[0139] Compared with the prior art, the present invention has the following advantages:

[0140] Firstly, the present invention introduces a dispersive viscosity index improver - P(BMA+LMA+TMA+NVP) copolymer, which is a substance with an excellent bipolar structure. The pyrrole rings on its side chains exhibit strong polar characteristics and can effectively dissolve polar components such as formic acid, formaldehyde, water, and unburned methanol generated during the combustion of methanol engines. At the same time, the lipophilic long-chain molecules in this copolymer have good oil solubility and can cleverly "separate" these combustion products (such as formic acid and water) from the engine oil and the engine metal surface, thereby greatly improving the corrosion resistance of the engine and the engine oil. This characteristic effectively prevents the erosion of the engine component surface by formic acid and also avoids the rust problem caused by water to engine components.

[0141] Secondly, the dispersive viscosity index improver P(BMA+LMA+TMA+NVP) copolymer contained in the present invention contains strong N polar groups. Under the action of shear force, not only does physical adsorption occur between the water phase and the oil phase, but the polar groups in the molecules also have strong chemical adsorption (the action of hydrogen bonds) with water molecules, greatly reducing the surface free energy of the oil and water, and at the same time increasing the strength of the emulsion interfacial film, ultimately forming a stable emulsion. The combustion products of heavy-duty methanol engines include water. This invention can evenly disperse water in the oil to form a stable water-in-oil emulsion, solving problems such as rust, poor low-temperature fluidity, and reduced anti-wear performance.

[0142] Thirdly, due to the presence of strong N polar functional groups in the present invention, a strong adsorption effect is generated on the surface of high-temperature deposits. After adsorption, a firm adsorption film is formed on the surface of high-temperature deposits, which not only plays a role in dispersing high-temperature deposits but also plays a role in anti-corrosion of the metal surface. At the same time, the dispersive viscosity index improver P(BMA+LMA+TMA+NVP) copolymer has high-temperature stability and can also effectively play a dispersing role in engines with high-intensity operation, making up for the deficiencies of polyisobutylene succinimide and solving the problem of deposits generated at the piston surface and piston rings of heavy-duty methanol fuel engines.

[0143] Fourthly, due to the presence of strong N-polar functional groups, the heavy-duty methanol engine oil contains functional groups that can strongly adsorb on the polar metal surface. At the same time, the polymer has a medium to high molecular weight, so it can form a thick boundary oil film on the engine metal surface, solving the problem that the incomplete combustion of methanol in the heavy-duty methanol engine scours the metal surface, destroys the oil film, and causes abnormal wear of parts.

[0144] Fifthly, the dispersant viscosity index improver P(BMA+LMA+TMA+NVP) copolymer strengthens the dispersion of graphene oxide; the lipophilic group has extremely strong solubility with the lubricating oil, and the hydrophilic group at the other end effectively adsorbs on the surface of graphene oxide, "wrapping" the graphene oxide and "dissolving" it in the lubricating oil. The π-π conjugation between them forms a steric hindrance effect on the surface of graphene oxide to hinder the aggregation of graphene oxide. In addition, the long-chain surfactant molecules wind and bridge to produce a flocculation effect, forming a network structure. This network structure can effectively "support" graphene oxide to offset the centrifugal force received by graphene oxide, reduce the sedimentation rate of graphene oxide, and the greater the viscous force of the lubricating oil on graphene oxide, the more it can offset the gravitational force received by graphene oxide and hinder its precipitation; the strong N-polar functional groups and hydrogen bonds are more likely to adsorb on the surface of graphene oxide containing different polar functional groups. The electrostatic repulsion and steric effect of the adsorption film of the dispersant viscosity index improver P(BMA+LMA+TMA+NVP) copolymer can greatly weaken the attraction of graphene oxide, improving the dispersion stability of graphene oxide.

[0145] Sixth, graphene oxide, phenolic ester antioxidant 3,5 - di - tert - butyl - 4 - hydroxyphenyl methacrylate, and amine antioxidant combined with alkyl diphenylamine can replace zinc dialkyldithiophosphate (ZDDP). Zinc dialkyldithiophosphate (ZDDP) is a multi - effect additive with antioxidant, anti - corrosion, and anti - wear effects. It is characterized by low cost and high efficiency and is an essential additive for traditional lubricating oils. However, in a new - type fuel methanol engine, zinc dialkyldithiophosphate (ZDDP) can react with methanol and become ineffective. Therefore, in this invention, by combining graphene oxide, phenolic ester antioxidant 3,5 - di - tert - butyl - 4 - hydroxyphenyl methacrylate, and amine antioxidant with alkyl diphenylamine, the antioxidant and anti - wear properties of the lubricating oil for heavy - duty methanol - fuel engines are improved. Phenolic ester antioxidants are general non - polluting ashless antioxidants and belong to high - temperature antioxidants. They have excellent stability in synthetic base oils, overcoming the defect of easy volatility of traditional phenolic antioxidants, and the high - temperature performance is better improved. Besides having good medium - and low - temperature performance, they can also control high - temperature sludge and deposits; they are easy to handle and have no crystallization at low temperatures; they have low volatility. The working temperature of amine antioxidants is higher than that of phenolic antioxidants, and their antioxidant durability is also better than that of phenolic antioxidants. They have a better effect on prolonging the induction period and inhibiting the late - stage oxidation of oil products. Amine antioxidants are better than phenolic antioxidants in controlling the viscosity increase of oil products; the combination of phenolic antioxidants and amine antioxidants is more effective than amine antioxidants alone in controlling piston deposits, especially helpful in controlling oxidation and high - temperature deposits.

[0146] Seventh, the corrosion and wear of methanol - fuel engines are serious. This invention uses graphene oxide as an anti - wear and friction - reducing agent, and its advantages can be divided into two aspects. First, graphene oxide can adsorb on the friction surface to form an adsorption film or reaction film. The friction surface is gradually covered by graphene, hindering the corrosion of the metal surface by formic acid, a combustion product of the engine. The surface roughness of the friction object is gradually replaced by the roughness of graphene, forming more oil films. The lamellar - structured graphene can adsorb on the friction surface after the lubricating oil film is damaged. The high - strength characteristic of graphene makes it difficult to be worn and damaged, avoiding the direct contact of the friction surface and enhancing the extreme - pressure performance of the base oil. This can be explained by the thin - film lubrication mechanism. Second, graphene particles can fill the corrosion pits, avoiding the direct contact of the friction surface. The addition of modified graphene can reduce or avoid the occurrence of corrosion, and adding an appropriate amount of graphene oxide can reduce the occurrence of adhesive wear. The lamellar structure of graphene can improve the minimum oil - film thickness of the base oil, enabling the oil film to maintain good continuity under higher load pressures and improving the oil - film bearing capacity.

[0147] Eighth, metal detergents play an important role in the lubricating oil formulation for methanol engines. Basic detergents can neutralize acidic combustion products to alleviate the wear of methanol fuel on the metal surface. The base number of calcium salicylate is high, but due to the different micelle structures of calcium salicylate and calcium sulfonate, their neutralization reactions with formic acid are different. The reaction activity of calcium salicylate with formic acid is higher, the base number decreases significantly, and the calcium content drops rapidly. On the contrary, when calcium sulfonate acts with formic acid, the base number can be maintained at a certain formic acid concentration, and the calcium content drops relatively slowly. In addition, the corrosion of copper and lead was also investigated under the condition of different concentrations of formic acid. The performance of high-base-number calcium sulfonate is better than that of calcium salicylate. Therefore, after the combination of salicylate and sulfonate in the present invention, the adverse effects brought by formic acid can be reduced. The combination of the two not only improves the acid neutralization performance but also enhances the anti-corrosion ability against copper and lead, and can reduce the harm caused by acidic combustion products to the engine.

[0148] Ninth, short chains with less than 7 C mainly affect the viscosity index of the polymer solution and the molecular scale at low temperatures; side chains with 8 - 13 C can enhance the solubility of the polymer in hydrocarbon solutions; long chains with more than 14 C atoms can interact with wax crystals to lower the pour point. The present invention uses a combination of butyl methacrylate with 4 C, dodecyl methacrylate with 12 C, and tetradecyl methacrylate with 14 C to ensure good thickening ability and improve the viscosity-temperature performance of the oil product. At the same time, by introducing N-vinylpyrrolidone as a polar group, the solubility is further improved, the dispersibility is improved, and the low-temperature fluidity of the sample is increased. Therefore, the present invention is different from traditional lubricating oils and does not add pour point depressants. The dispersant viscosity index improver P(BMA + LMA + TMA + NVP) copolymer already has the effect of a pour point depressant and improves the low-temperature fluidity of the oil product.

[0149] Tenth, the surface of graphene oxide contains a large number of hydrophilic oxygen-containing active groups such as hydroxyl, epoxy, carboxyl, and carbonyl groups. The present invention uses the dispersant viscosity index improver P(BMA + LMA + TMA + NVP) copolymer, which contains strong N polar groups. Therefore, graphene oxide does not need to be further modified and does not need to remove surface functional groups, greatly reducing costs and being conducive to industrial application. At the same time, once applied to a methanol fuel engine, it can also attract combustion products such as methanol and formic acid, which is more conducive to the dispersion of graphene. Therefore, graphene additives are very suitable for application in methanol fuel engine lubricating oils and can be widely used in new fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0150] Figure 1 Schematic diagram of the test results of the oxidation value, nitration value, and wear of the used oil detected by infrared testing at the end of the two engine test benches of Example 5 and Comparative Example 2;

[0151] Figure 2 Figure showing no corrosion on the piston skirt of the K15M engine test bench after using Example 5;

[0152] Figure 3 For the bench exhaust valve of the K15M engine to be clean and have less deposits after using Example 5;

[0153] Figure 4 For the anti-corrosion layer on the piston skirt of the K15M engine bench to peel off after using Comparative Example 2. Specific embodiments

[0154] The present invention will be further described in detail below in conjunction with specific embodiments for a clear understanding of the present invention, but they do not limit the present invention.

[0155] The lubricating oil composition for a heavy-duty methanol fuel engine containing graphene oxide in Embodiments 1-5 of the present invention, by mass, includes the following raw materials, and the specific formula is shown in Table 1.

[0156]

[0157]

[0158]

[0159]

[0160] Effect Example 2

[0161] Examples 1-5 and Comparative Example 1 were selected for static tests at different temperature gradients for verification, and the test results are shown in Tables 3-5 respectively.

[0162] Table 3 Static test of engine oil with graphene at room temperature

[0163] Number Stand still for 5 days Stand still for 15 days Stand still for 30 days Stand still for 120 days Stand still for 240 days Example 1 No precipitation No precipitation No precipitation No precipitation No precipitation Example 2 No precipitation No precipitation No precipitation No precipitation No precipitation Example 3 No precipitation No precipitation No precipitation No precipitation No precipitation Example 4 No precipitation No precipitation No precipitation No precipitation No precipitation Example 5 No precipitation No precipitation No precipitation No precipitation No precipitation Comparative Example 1 No precipitation No precipitation A small amount of precipitation The precipitation increases A large amount of precipitation

[0164] Table 4 Static test of engine oil with graphene at -20 °C

[0165] Number Stand still for 5 days Stand still for 15 days Stand still for 30 days Stand still for 120 days Stand still for 240 days Example 1 No precipitation No precipitation No precipitation No precipitation No precipitation Example 2 No precipitation No precipitation No precipitation No precipitation No precipitation Example 3 No precipitation No precipitation No precipitation No precipitation No precipitation Example 4 No precipitation No precipitation No precipitation No precipitation No precipitation Example 5 No precipitation No precipitation No precipitation No precipitation No precipitation Comparative Example 1 No precipitation No precipitation A small amount of precipitation A small amount of precipitation A small amount of precipitation

[0166] Table 5 Static test of engine oil with graphene at 60 °C

[0167] Number Stand still for 5 days Stand still for 15 days Stand still for 30 days Stand still for 120 days Stand still for 240 days Example 1 No precipitation No precipitation No precipitation No precipitation No precipitation Example 2 No precipitation No precipitation No precipitation No precipitation No precipitation Example 3 No precipitation No precipitation No precipitation No precipitation No precipitation Example 4 No precipitation No precipitation No precipitation No precipitation No precipitation Example 5 No precipitation No precipitation No precipitation No precipitation No precipitation Comparative Example 1 No precipitation No precipitation No precipitation A small amount of precipitation A small amount of precipitation

[0168] As can be seen from Tables 3-5, during static storage at room temperature, the precipitation in Comparative Example 1 increased after 3 months, and a small amount of precipitation appeared in Comparative Example 1 at low and high temperatures after 3 months. No precipitation occurred in Examples 1-5 at room temperature, low temperature, and high temperature, indicating that the engine oil containing the P(BMA+LMA+TMA+NVP) copolymer has a good dispersion effect on graphene oxide.

[0169] Effect Example 3

[0170] Select Example 5 with the best physical and chemical properties in Effect Example 1 and Comparative Examples 2-3 for the following simulation test verification.

[0171] (1) Emulsification test

[0172] Emulsion stability test: Take 400 g of the lubricating oil of Example 5 and Comparative Examples 2-3, and 40 g of water and add them to a beaker, and stir at a speed of 6000 r / min for 10 min. Store at room temperature for 3 months and at high temperature of 150 °C for 3 months respectively, observe the storage situation of the oil product, and the analysis results are shown in Table 6.

[0173] Table 6 Emulsion stability test

[0174]

[0175] As can be seen from Table 6, Example 5 contains the dispersed viscosity index improver P(BMA+LMA+TMA+NVP) copolymer. When the lubricating oil contains water, it can maintain emulsification uniformity and no stratification. This is beneficial for the water generated during the operation of the methanol fuel engine at low temperature not to freeze, so that the engine can start normally. The non-separation of oil and water can play an anti-rust role. After the engine oil temperature rises, the water in the oil can evaporate to protect the engine.

[0176] (2) Anti-corrosion test

[0177] Anti-corrosion test: Cut the cylinder liner into small pieces, take 400 g of the lubricating oil of Example 5 and Comparative Examples 2-3, and 10 g of formic acid and put them together into a conical flask, cover the bottle cap, place it on a heating plate, insert a temperature probe, and heat at a rotation speed of 1000 r / min and an oil temperature of 100 °C for 10 hours. Observe the wear elements of the metal block and the lubricating oil respectively, and the analysis results are shown in Table 7.

[0178] Table 7 Anti-corrosion test

[0179] Test item Metal block Iron element, ppm Example 5 + 10 g formic acid No corrosion on the surface 0 Comparative Example 2 + 10 g formic acid Severe corrosion 286 Comparative Example 3 + 10 g formic acid Severe corrosion 250

[0180] As can be seen from Table 7, in the case of containing formic acid, the metal blocks in Comparative Examples 2 and 3 are severely corroded. However, in the case of containing formic acid in Example 5, there is no corrosion on the surface of the metal block. The iron element in the used oil comes from the corrosion of the metal block surface by formic acid. The more severe the corrosion, the higher the iron element content in the used oil. From the detection of wear elements, it can be concluded that this test well verifies that Example 5 can exhibit excellent anti-corrosion performance in the presence of formic acid. This anti-corrosion test fully proves that the lubricating oil containing the dispersed viscosity index improver P(BMA+LMA+TMA+NVP) copolymer has a very good anti-corrosion effect.

[0181] (3) Anti-high temperature deposit test

[0182] For the high-temperature deposit resistance test, a crankcase simulation test instrument was used to investigate the high-temperature resistance performance. The test conditions were as follows: the plate temperature reaction temperature was 350 °C, the oil temperature was 150 °C, and the duration was 6 hours. The more coke weight indicated the poorer deposit resistance of the oil product. 250 g of the lubricating oil of Example 5, Comparative Examples 2 and 3, and 6 g of formic acid were put into the crankcase simulation test instrument, and 250 g of the lubricating oil of Example 5, Comparative Examples 1 and 2 were put into the crankshaft simulation test instrument respectively. After the test, the coke weights of the aluminum plates were weighed respectively, and the results are shown in Table 8.

[0183] Table 8 High-temperature deposit resistance test

[0184] Test item Glue weight, mg Example 5 + 0 g formic acid 7 Example 5 + 6 g formic acid 5 Comparative Example 2 + 0 g formic acid 14 Comparative Example 2 + 6 g formic acid 30 Comparative Example 3 + 0 g formic acid 12 Comparative Example 3 + 6 g formic acid 28

[0185] As can be seen from the test results in Table 8, severe coking occurred in Comparative Examples 2 and 3 in the presence of formic acid, while in Example 5 in the presence of formic acid, the coke weight was equivalent to that of the oil without formic acid. This test well verified that Example 5 could exhibit good high-temperature resistance performance in the presence of formic acid. This fully proved that the lubricating oil containing the dispersed viscosity index improver P(BMA + LMA + TMA + NVP) copolymer had a very good effect on resisting high-temperature deposits.

[0186] (4) Anti-wear test

[0187] For the anti-wear test, a four-ball machine was used for the test. The test conditions were as follows: 3 steel balls with a diameter of 12.7 mm were clamped in an oil box and covered with the test oil. Another steel ball with the same diameter was placed on top of the three balls and was subjected to a force of 147 N (15 kgf) or 392 N (40 kgf), forming a "three-point contact". When the test oil reached a certain temperature (75 °C ± 20 °C), the top ball rotated at a certain speed for 60 min, and the anti-wear performance of the test oil was evaluated by the average value of the wear scar diameters of the following three balls. The test engine oil needed to be treated by adding 5% methanol and stirring at room temperature for 2 hours, and then standing for 24 hours; the results are shown in Table 9.

[0188] Table 9 Four-ball machine anti-wear test

[0189]

[0190]

[0191] As can be seen from the test results in Table 9, it can be seen from the results that the anti-wear performance of Example 5 was better than that of other oil products, indicating the anti-wear effect of graphene in the scheme. In Comparative Examples 2 - 3, the anti-wear performance of the engine oil decreased severely because methanol reacted with ZDDP, and the lubricating oil lost its anti-wear protection.

[0192] (5) Reliability bench test verification:

[0193] Based on the reliability bench test oil monitoring data of the K15M engine of Guangxi Yuchai Machinery Co., Ltd. under 500 hours of power generation conditions, the present invention conducted a comparative analysis of the K15M engine reliability bench test on Example 5 and Comparative Example 2. The test results show that the product of the present invention exhibits extremely low wear after the test, and the growth of oxidation value and nitration value is maintained at a low level. At the same time, the attenuation of TBN (total base number) and the increase of TAN (total acid number) are relatively small. For detailed test results, please refer to the attached Figure 1 To Attachment Figure 4 .

[0194] Attached Figure 1 The analysis results of the used oil after 500 hours of reliability bench test of Example 5 and Comparative Example 2 are shown. It can be clearly seen that the oxidation value, nitration value and the content of wear elements iron and copper of Example 5 are all within the prescribed oil change index range (i.e., the oxidation value and nitration value do not exceed 30A / cm, the iron content does not exceed 150ppm, and the copper content does not exceed 150ppm), while these indicators of Comparative Example 2 have exceeded the prescribed range.

[0195] Attached Figure 2 It is revealed that the piston skirt of the K15M engine rig using Example 5 does not show corrosion. Figure 3 It further shows that the exhaust valve of the K15M engine bench after using Example 5 remains clean with very little deposits. Figure 4 It shows that the anti-corrosion layer of the piston skirt of the K15M engine test bench using Comparative Example 2 has fallen off, highlighting the shortcomings of Comparative Example 2 in terms of corrosion resistance.

[0196] This bench test has effectively proved that the present invention has successfully solved the shortcomings of methanol lubricants in the current market in terms of corrosion resistance, wear resistance and high temperature resistance. The product of the present invention has successfully passed the reliability bench test assessment of the K15M engine of Guangxi Yuchai Machinery Co., Ltd. under 500 hours of power generation conditions, and in the subsequent disassembly scoring test, it has shown better performance than existing market products in terms of physical and chemical indicators, emulsification test and high temperature deposit resistance.

[0197] In summary, the lubricating oil composition of the present invention is specially designed for heavy-duty methanol fuel engines containing graphene oxide. Its reliability bench test not only achieves effective "isolation" of engine oil, engine and combustion products such as formic acid, but also provides strong anti-corrosion protection for the engine. With the anti-wear effect of graphene, an effective boundary oil film is formed, thereby effectively resisting the scouring effect of methanol on the cylinder wall. This innovative design is not only advanced in concept, but also has achieved remarkable results in practical applications.

[0198] The above are only specific embodiments of the present invention. It should be noted that the rest not described in detail is the prior art. Any changes or substitutions that can be easily conceived by any person skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A lubricating oil composition for a heavy-duty methanol fuel engine containing graphene oxide, characterized in that, By mass parts, it includes the following raw materials: The dispersant viscosity index improver is a P(BMA+LMA+TMA+NVP) copolymer.

2. The lubricating oil composition for a heavy-duty methanol fuel engine containing graphene oxide according to claim 1, wherein The compound antioxidant is a mixture of a phenolic ester antioxidant and an amine antioxidant, and the mass ratio of the two is 1:1 to 2; the phenolic ester antioxidant is methyl 3,5-di-tert-butyl-4-hydroxyphenyl acrylate; the amine antioxidant is alkyl diphenylamine.

3. The lubricating oil composition for a heavy-duty methanol fuel engine containing graphene oxide according to claim 1, characterized in that, The antiwear agent is graphene oxide.

4. The lubricating oil composition for a heavy-duty methanol fuel engine containing graphene oxide according to claim 1, wherein The detergent is a mixture of alkyl salicylate and sulfonate.

5. The lubricating oil composition for a heavy-duty methanol fuel engine containing graphene oxide according to claim 4, wherein, The structure of the alkyl salicylate is preferably shown as formula I: Wherein, R is an alkyl group containing 10 to 20 carbon atoms, M is Ca or Mg, and m and n are positive integers not equal to zero.

6. The lubricating oil composition for a heavy-duty methanol fuel engine containing graphene oxide according to claim 4, wherein The structure of the sulfonate is preferably shown as formula II: Wherein, R1 is an alkyl group containing 14 to 28 carbon atoms, M is Ca or Mg, and m1 and n1 are positive integers not equal to zero.

7. The lubricating oil composition for a heavy-duty methanol fuel engine containing graphene oxide according to claim 1, characterized in that, The dispersant is a borated polyisobutylene succinimide dispersant. The structure of the borated polyisobutylene succinimide dispersant is shown as formula III: Wherein, PIB is polyisobutylene, the molecular weight is 900 to 1300, and r is a positive integer not equal to zero.

8. The lubricating oil composition for a heavy-duty methanol fuel engine containing graphene oxide according to claim 1, characterized in that, The base oil is a coal-to-hydrocarbon synthetic base oil.

9. The lubricating oil composition for a heavy-duty methanol fuel engine containing graphene oxide according to claim 1, wherein The synthesis method of the dispersant viscosity index improver which is a P(BMA+LMA+TMA+NVP) copolymer includes the following steps: Mix butyl methacrylate, dodecyl methacrylate, tetradecyl methacrylate, N-vinylpyrrolidone with a solvent and an initiator; carry out a polymerization reaction at 40°C to 70°C for 4 to 8 hours, carry out vacuum distillation on the toluene solution of the obtained polymerization product, and after operations such as vacuum filtration and alcohol washing, carry out vacuum drying to obtain a white or light yellow (BMA+LMA+TMA+NVP) copolymer, and the reaction formula is as follows 。 10. A preparation method of a lubricating oil composition for a heavy-duty methanol fuel engine containing graphene oxide according to any one of claims 1 to 9, comprising the following steps: (1) First, cut the dispersant viscosity index improver P(BMA+LMA+TMA+NVP) and mix it with an appropriate amount of base oil according to the formula ratio, heat it to 120 to 130°C, stir and dissolve it, and let it stand for 4 to 6 hours to obtain product a; (2) Put product a and the remaining base oil into a blending kettle, sequentially add a dispersant, a pour point depressant, an antioxidant, an antiwear agent, and a detergent according to the formula ratio, start stirring and heating to 50 to 60°C and keep warm, and continuously stir for 4h to 6h to obtain a lubricating oil composition for a heavy-duty methanol fuel engine containing graphene oxide.

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