Preparation method of castor oil-based biomass lubricant base oil

Abstract

The invention discloses a preparation method of castor oil-based biomass lubricant base oil, and belongs to the technical field of base oil. The preparation method comprises the following steps: ester exchange reaction, esterification reaction, epoxidation reaction, ring-opening reaction and bridging esterification reaction. The prepared base oil constructs a macromolecular structure through bridging esterification, so that the base oil is endowed with high viscosity; unstable carbon-carbon double bonds in the raw materials are eliminated through the epoxidation step, the flash point of the base oil is increased, and the service life of the oil product is prolonged; the introduced long-chain alkyl side chain effectively prevents molecules from crystallizing at low temperature, and the pour point is reduced; castor oil is used as an initial raw material, and the source is renewable; the final ester structure is easily decomposed by microorganisms and is environment-friendly; in a word, the biomass raw material is successfully converted into the base oil with'high viscosity index, low pour point, high flash point and good biodegradability 'through an innovative synthesis route, and the base oil has important application value in the technical field of base oil.

Description

Technical Field

[0001] This invention belongs to the field of base oil technology, specifically, it relates to a method for preparing a castor oil-based biomass lubricating oil base oil. Background Technology

[0002] Lubricating oil is an oily liquid primarily used to reduce labor load, improve work efficiency, and reduce equipment wear. Besides lubrication, it also provides cooling, rust prevention, corrosion prevention, cleaning, sealing, buffering, power transmission, and electrical insulation, thus finding wide application in industry, agriculture, military, medicine, aerospace, and daily life. In recent years, with rapid economic development and the continuous growth of automobile ownership, lubricating oil has long been in short supply. At the same time, the increasing demand for high-performance lubricating oil has prompted the lubricating oil industry to shift from a quantity-driven growth model to a quality-driven development model, demonstrating the broad application prospects of high-performance lubricating oil.

[0003] Lubricating oils are blended from base oils and additives, and the quality of the base oil determines the performance of the lubricating oil. Based on the source of raw materials, base oils are divided into three categories: Mineral base oils: made from crude oil fractions or residue oils, they have the largest market share, but their overall performance is generally poor, their biodegradability is low, and they are not renewable, so they are gradually being replaced. Bio-based oils: derived from animal / vegetable oils, they have advantages such as good lubricity, high viscosity index, and renewability, but components such as double bonds and β-hydrogen atoms in the raw materials reduce oxidation stability, thermal stability, and low-temperature fluidity, and large-scale production is difficult. Synthetic base oils: produced through chemical reactions, they have uniform components, easily controllable performance, and overall performance superior to the former two. Driven by both environmental regulations and performance requirements, the demand for synthetic base oils continues to grow. However, Europe and the United States monopolize the production technology of high-performance synthetic lubricating oils; therefore, developing independent technologies is of great significance.

[0004] Synthetic base oils mainly include synthetic hydrocarbons, ester oils, and polyalkylene glycols, but each has certain drawbacks: synthetic hydrocarbons have poor miscibility with polar additives and are difficult to degrade; the raw materials and pyrolysis products of polyalkylene glycols are toxic; phosphate esters have poor hydrolytic stability, and some varieties are highly toxic; silicone oils and fluorinated oils have poor miscibility and biodegradability, and fluorinated oils are only used in special fields due to their high price; ionic liquids usually contain phosphorus, boron, or halogens, which can easily cause equipment corrosion and environmental pollution. Among various synthetic base oils, ester base oils have the fewest defects. Except for slightly poor hydrolytic stability, they also have excellent lubricity, viscosity-temperature properties, low-temperature fluidity, biodegradability, and high thermal stability. Moreover, their viscosity is easy to control and can cover all viscosity grades, making them an ideal choice for high-performance, high-viscosity lubricants. However, traditional ester oil production often uses strong Brønsted acids as catalysts (such as concentrated sulfuric acid), which can easily trigger side reactions leading to excessive sulfur content and darkening of the product color. At the same time, the use of organic water-carrying agents also poses a threat to human health and the environment. Furthermore, the synthesis of high-viscosity ester oils faces challenges such as high reaction temperature, long reaction time, large amount of water generated, high system viscosity, and complex product structure. Therefore, it is urgent to develop efficient and environmentally friendly catalysts and synthesis processes.

[0005] Castor oil, as a renewable vegetable oil, is widely regarded as an ideal candidate raw material for environmentally friendly lubricating oil base oils due to its high hydroxyl value (approximately 140 mg KOH / g), excellent lubricity, and biodegradability (degradation rate > 90%). In existing technologies, its performance is typically improved through chemical modification methods such as esterification-epoxidation, hydrogenation, or a three-step process (ester exchange-epoxidation-ring opening). For example, epoxidation treatment after esterification to prepare methyl ester can significantly improve oxidation stability; hydrogenation treatment using a copper-titanium-based catalyst at 160-170℃ can improve oxidation stability by 40%, but low-temperature fluidity decreases; using octanol instead of butanol for ring opening can increase the viscosity index by more than 30% (> 180), but the process is complex and requires strict nitrogen protection.

[0006] Therefore, in response to the problems existing in the above-mentioned synthetic lubricants, there is an urgent need to develop a new method for preparing ester base oils with high viscosity, high viscosity index, low pour point, excellent thermal stability and biodegradability through a green and efficient synthetic route using castor oil as raw material, in order to meet current market demands. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing castor oil-based biomass lubricating oil base oil.

[0008] The objective of this invention can be achieved through the following technical solutions: A method for preparing a castor oil-based biomass lubricating oil base oil includes the following steps: transesterification reaction, esterification reaction, epoxidation reaction, ring-opening reaction, and bridging esterification reaction; the specific reaction steps are as follows: A1. Transesterification reaction: Castor oil, short-chain fatty alcohol and catalyst are added to a three-necked flask with a condenser. Under nitrogen protection, the mixture is heated to 80-120℃ and stirred for 3-10 hours. After the reaction is completed, the reaction solution is washed until neutral. The remaining short-chain fatty alcohol is removed by vacuum distillation to obtain castor oil acid short-chain fatty alcohol ester. In step A1, castor oil and short-chain fatty alcohols undergo transesterification under the action of a catalyst, as shown in the following reaction equation: A2. Esterification reaction: Castor oil short-chain fatty alcohol ester, short-chain fatty acid and catalyst are added to a three-necked flask with a water separator, followed by the addition of toluene as a water-carrying agent. The mixture is heated to 100-200℃ and reacted for 5-15 hours until no more excess water is generated in the water separator. The reaction is then complete. The mixture is washed until neutral and the remaining short-chain fatty acid and toluene are removed by vacuum distillation to obtain the esterified castor oil product. In step A2, the short-chain fatty alcohol ester of castor oil and the short-chain fatty acid undergo an esterification reaction under the action of a catalyst, as shown in the following reaction formula: A3. Epoxidation reaction: Esterified castor oil product and formic acid were added to a three-necked flask and stirred. The apparatus was placed in an ice-water bath at 0-10°C. Hydrogen peroxide solution (30% by mass) was then slowly added dropwise. After the addition was complete, the water bath was removed and the reaction was allowed to proceed at room temperature for 24 hours. After the reaction was completed, dichloromethane was added to extract the organic phase. The mixture was washed 2-3 times with distilled water and then distilled under reduced pressure to obtain the epoxidized product. In step A3, formic acid reacts with hydrogen peroxide to generate a more reactive peroxy acid. This peroxy acid acts as an epoxidizing agent, selectively oxidizing the carbon-carbon double bonds in the esterified castor oil product molecule to epoxy groups. The reaction formula is as follows: A4. Ring-opening reaction: The epoxidation product and catalyst are added to a reactor equipped with a mechanical stirrer and a reflux condenser, and then a methanol-water solution is added to dilute the system, controlling the H₂ content of the system. + The concentration was 0.2-0.8 mol / L. Then, it was heated to 40-80℃ and stirred for 2-8 hours at this temperature. After the reaction was completed, it was washed until neutral and the solvent was removed by vacuum distillation to obtain the dihydroxy compound. In step A4, the epoxy group in the epoxidation product undergoes ring-opening under acidic conditions, transforming into a more stable dihydroxy compound, as shown in the following reaction formula: A5. Epoxidation reaction: First, add the dihydroxy compound, short-chain dicarboxylic acid, short-chain fatty acid and catalyst to a reactor equipped with a mechanical stirrer and a reflux condenser. Stir and react at room temperature for 2-3 hours. Second, add the short-chain fatty acid, purge with nitrogen, and heat to 140-200℃. Stir and react at this temperature for 5-10 hours. After the reaction is complete, add ethyl acetate to dilute, filter to recover the catalyst, wash the organic phase until neutral, and distill under reduced pressure to obtain castor oil-based biomass lubricating oil base oil.

[0009] In step A5, the catalyst first activates the carboxyl group, and then undergoes esterification with the hydroxyl group in the dihydroxy compound. Since the diacid has two carboxyl groups and the dihydroxy compound has two hydroxyl groups, this reaction can extend bidirectionally in three-dimensional space, thereby "bridging" multiple molecules together. The added short-chain fatty acid acts as a capping agent, ultimately producing castor oil-based biomass lubricating oil base oil. The reaction formula is as follows: Preferably, the molar ratio of castor oil to short-chain fatty alcohol in step A1 is 1:2-5.

[0010] Preferably, the short-chain fatty alcohols in step A1 include all isomers of alcohols with a total carbon number of 5-18.

[0011] Preferably, in step A2, the molar ratio of short-chain fatty alcohol ester of castor oil to short-chain fatty acid is 1:2-5.

[0012] Preferably, the short-chain fatty acids in step A2 include all isomers of monocarboxylic acids with a total carbon number of 1-4.

[0013] Preferably, the catalyst in steps A1 and A2 is a Lewis acid catalyst, such as aluminum chloride, zinc chloride, boron trifluoride, or acidic ion exchange resin; or an organic base catalyst, such as triethylamine, cyclohexylamine, tetrabutylammonium bromide, or pyridine; the catalyst includes, but is not limited to, the above-mentioned catalysts.

[0014] Preferably, the molar ratio of esterified castor oil product to formic acid in step A3 is 1:2-5.

[0015] Preferably, the volume ratio of methanol to water in the methanol-water solution in step A4 is 1:1-3.

[0016] Preferably, the catalyst in step A4 is an aqueous solution of a Bronstein acid catalyst, such as sulfuric acid, hydrochloric acid, or trifluoroacetic acid solution; the catalyst includes, but is not limited to, the above-mentioned catalysts.

[0017] Preferably, the molar ratio of the dihydroxy compound, the short-chain dicarboxylic acid, and the short-chain fatty acid in step A5 is 2:2:3.

[0018] Preferably, the nitrogen flow rate in step A5 is 1.5-2.0 mL / min. -1 ·g -1 .

[0019] Preferably, the catalyst in step A5 is a solid superacid, such as SO4. 2- / M x O y Solid superacids; composite metal oxides, such as SiO2 / Al2O3, SiO2 / TiO2, SiO2 / ZrO2; or solid Lewis acid catalysts; the catalysts include, but are not limited to, the above-mentioned catalysts.

[0020] Preferably, the short-chain difatty acids in step A5 include all isomers of dicarboxylic acids with a total carbon number of 2-6.

[0021] Preferably, the short-chain fatty acids in step A5 include all isomers of monocarboxylic acids with a total carbon number of 1-8.

[0022] As can be seen from the structure in the above reaction formula, the base oil prepared by this invention has a "bridging" structure, which not only significantly increases the molecular weight but also "locks" the molecules together more firmly, greatly enhancing the intermolecular forces and making the fluid less prone to deformation under shear, thereby increasing viscosity. The long-chain alkyl side chains introduced through transesterification act as "anti-gelling agents" in the structure, effectively preventing the ordered arrangement and crystallization of macromolecules at low temperatures, thus ensuring that the oil can still flow at low temperatures and lowering the pour point. The epoxidation and ring-opening reactions eliminate the easily attacked carbon-carbon double bonds in castor oil raw materials, greatly improving the antioxidant capacity. Furthermore, the rigid skeleton and bridging structure of castor oil itself result in higher molecular bond energies, making it less prone to breakage under heat, thus increasing the flash point. Finally, using vegetable oils such as castor oil as raw materials endows the base oil with good biodegradability.

[0023] The beneficial effects of this invention are: 1. The base oil obtained by this invention has a high viscosity by constructing a macromolecular structure through "bridging esterification". 2. The epoxidation process eliminates unstable carbon-carbon double bonds in the raw materials, increases the flash point of the base oil, and extends the service life of the oil. 3. The introduced long-chain alkyl side chains effectively prevent the molecules from crystallizing at low temperatures, thus lowering the pour point; 4. Using castor oil as the initial raw material, the source is renewable; the final ester structure is easily decomposed by microorganisms, with a degradation rate much higher than that of mineral oil, making it environmentally friendly; In summary, this invention successfully transforms biomass raw materials into a lubricating oil base oil with "high viscosity index, low pour point, high flash point and good biodegradability" through an innovative synthetic route, which has important application value in the field of base oil technology. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0025] Example 1 A method for preparing a castor oil-based biomass lubricating oil base oil includes the following steps: A1. Transesterification reaction: 1000g castor oil, 1300g 2-ethylhexanol and sodium hydroxide catalyst (0.1% of the total mass of the reactants) were added to a three-necked flask equipped with a condenser. Under nitrogen protection, the mixture was heated to 70°C and stirred for 3 hours. After the reaction was completed, the reaction solution was washed until neutral. The remaining short-chain fatty alcohol was removed by vacuum distillation to obtain castor oil acid short-chain fatty alcohol ester. A2. Esterification reaction: 600g of short-chain fatty alcohol ester of castor oil, 300g of propionic acid and acidic ion exchange resin (model Amberlyst15, mass ratio of 1% of total reactants) were added to a three-necked flask equipped with a water separator. Toluene was then added as a water-carrying agent. The mixture was heated to 100℃ and reacted for 5 hours until no more excess water was generated in the water separator. The reaction was then completed. The mixture was washed until neutral and the remaining short-chain fatty acids and toluene were removed by vacuum distillation to obtain the esterified castor oil product. A3. Epoxidation reaction: 500g of esterified castor oil product and 100g of formic acid were added to a three-necked flask and stirred. The apparatus was placed in an ice-water bath at 0°C. Then, 500g of hydrogen peroxide solution (30% by mass) was slowly added dropwise. After the addition was complete, the water bath was removed and the reaction was allowed to proceed at room temperature for 24 hours. After the reaction was completed, dichloromethane was added to extract the organic phase. The mixture was washed three times with distilled water and then distilled under reduced pressure to obtain the epoxidized product. A4. Ring-opening reaction: 300g of epoxidized product and 100mL of dilute hydrochloric acid catalyst (2mol / L) were added to a reaction vessel equipped with a mechanical stirrer and a reflux condenser. Then, 500mL of methanol-water solution (methanol to water volume ratio of 1:2) was added. The mixture was then heated to 60℃ and stirred for 3h at this temperature. After the reaction was completed, the mixture was washed until neutral and the solvent was removed by vacuum distillation to obtain the dihydroxy compound. A5. Epoxidation Reaction: Step 1: Add 200g of dihydroxy compound, 55g of glutaric acid, 30g of 2-ethylhexanoic acid, and zirconium oxide sulfate-type solid superacid (1% of the total reactant mass) to a reactor equipped with a mechanical stirrer and a reflux condenser. Stir and react at room temperature for 2-3 hours. Step 2: Add 60g of 2-ethylhexanoic acid and purge with nitrogen gas (flow rate 2.0 mL / min). -1 ·g -1 The mixture was heated to 140°C and stirred for 5 hours. After the reaction was completed, ethyl acetate was added to dilute the mixture. The catalyst was recovered by filtration. The organic phase was washed until neutral and then distilled under reduced pressure to obtain castor oil-based biomass lubricating oil base oil. Performance tests were conducted on Example 1, and the results are shown in Table 1: Table 1 Testing items Test Results Test methods Acid value / mgKOH / g 0.1654 DL / T 264 <![CDATA[40℃ kinematic viscosity / mm 2 / s]]> 238.7 GB / T 265 <![CDATA[100℃ kinematic viscosity / mm 2 / s]]> 34.09 Viscosity Index 178 GB / T 1995 Pour point / ℃ -45 GB / T 3535 Flash point (open cup) / °C 273 GB / T 3536 Example 2 A method for preparing a castor oil-based biomass lubricating oil base oil includes the following steps: A1. Transesterification reaction: 1000g castor oil, 1000g hexanol and sodium hydroxide catalyst (0.1% of the total mass of reactants) were added to a three-necked flask equipped with a condenser. Under nitrogen protection, the mixture was heated to 90°C and stirred for 3 hours. After the reaction was completed, the reaction solution was washed until neutral. The remaining short-chain fatty alcohol was removed by vacuum distillation to obtain castor oil acid short-chain fatty alcohol ester. A2. Esterification reaction: 600g of short-chain fatty alcohol ester of castor oil, 250g of acetic acid and acidic ion exchange resin (model Amberlyst15, mass ratio of 1% of total reactants) were added to a three-necked flask equipped with a water separator. Toluene was then added as a water-carrying agent. The mixture was heated to 110℃ and reacted for 5 hours until no more excess water was generated in the water separator. The reaction was then completed. The mixture was washed until neutral and the remaining short-chain fatty acids and toluene were removed by vacuum distillation to obtain the esterified castor oil product. A3. Epoxidation reaction: 500g of esterified castor oil product and 200g of formic acid were added to a three-necked flask and stirred. The apparatus was placed in an ice-water bath at 0°C. Then, 600g of hydrogen peroxide solution (30% by mass) was slowly added dropwise. After the addition was complete, the water bath was removed and the reaction was allowed to proceed at room temperature for 24 hours. After the reaction was completed, dichloromethane was added to extract the organic phase. The mixture was washed three times with distilled water and then distilled under reduced pressure to obtain the epoxidized product. A4. Ring-opening reaction: 300g of epoxidized product and 150mL of dilute hydrochloric acid catalyst (2mol / L) were added to a reaction vessel equipped with a mechanical stirrer and a reflux condenser. Then, 500mL of methanol-water solution (methanol to water volume ratio of 1:2) was added. The mixture was then heated to 60℃ and stirred for 3h at this temperature. After the reaction was completed, the mixture was washed until neutral and the solvent was removed by vacuum distillation to obtain the dihydroxy compound. A5. Epoxidation Reaction: Step 1: Add 200g of dihydroxy compound, 50g of succinic acid, 25g of hexanoic acid, and zirconia sulfate-type solid superacid (1% of the total reactant mass) to a reactor equipped with a mechanical stirrer and a reflux condenser. Stir and react at room temperature for 2-3 hours. Step 2: Add another 50g of hexanoic acid and purge with nitrogen gas (flow rate 2.0 mL / min). -1 ·g -1 The mixture was heated to 200°C and stirred for 5 hours. After the reaction was completed, ethyl acetate was added to dilute the mixture. The catalyst was recovered by filtration. The organic phase was washed until neutral and then distilled under reduced pressure to obtain castor oil-based biomass lubricating oil base oil. Performance tests were conducted on Example 2, and the results are shown in Table 2: Table 2 Testing items Test Results Test methods Acid value / mgKOH / g 0.1231 DL / T 264 <![CDATA[40℃ kinematic viscosity / mm 2 / s]]> 210.3 GB / T 265 <![CDATA[100℃ kinematic viscosity / mm 2 / s]]> 28.19 Viscosity Index 165 GB / T 1995 Pour point / ℃ -42 GB / T 3535 Flash point (open cup) / °C 268 GB / T 3536 Comparative Example It uses commercially available high-performance synthetic ester base oil, model: NYCOBASE 1040X.

[0026] The performance of the comparative examples is shown in Table 3: Table 3 project result <![CDATA[Kinematic viscosity at 40 °C / mm 2 / s]]> 94.0 Pour point / ℃ -27 Flash point (open cup) / °C 264 As can be seen from the table above, the base oil prepared by the embodiments of the present invention can rival high-end foreign products in key indicators. Therefore, the present invention has important application value in the field of base oil technology.

[0027] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for preparing a castor oil-based biomass lubricating oil base, characterized in that, Includes the following steps: A1. Castor oil, short-chain fatty alcohol and catalyst are added to a flask, heated to 80-120℃ under nitrogen protection, and stirred for 3-10 hours. When the reaction is completed, castor oil short-chain fatty alcohol ester is obtained. A2. Add the short-chain fatty alcohol ester of castor oil, short-chain fatty acid and catalyst to a flask, then add toluene, heat to 100-200℃, react for 5-15 hours until no more excess water is generated, the reaction is completed, and the esterified castor oil product is obtained. A3. Add the esterified castor oil product and formic acid to a flask, stir and mix, place in an ice-water bath at 0-10℃, then add hydrogen peroxide solution dropwise. After the addition is complete, remove the water bath and react at room temperature for 24 hours. The reaction is then complete, and the epoxidized product is obtained. A4. Add the epoxidation product and catalyst to the reactor, then add an aqueous methanol solution, controlling the H2O of the system. + The concentration was 0.2-0.8 mol / L. Then, the mixture was heated to 40-80℃ and stirred for 2-8 hours. After the reaction was completed, a dihydroxy compound was obtained. A5. First, add the dihydroxy compound, short-chain dicarboxylic acid, short-chain fatty acid and catalyst to the reaction vessel and stir for 2-3 hours at room temperature. Second, add the short-chain fatty acid, introduce nitrogen gas and heat to 140-200℃. Stir for 5-10 hours at this temperature. After the reaction is completed, castor oil-based biomass lubricating oil base oil is obtained.

2. The method for preparing a castor oil-based biomass lubricating oil base oil according to claim 1, characterized in that, In step A1, the molar ratio of castor oil to short-chain fatty alcohol is 1:2-5.

3. The method for preparing a castor oil-based biomass lubricating oil base oil according to claim 1, characterized in that, In step A1, short-chain fatty alcohols include all isomers of alcohols with a total carbon number of 5-18.

4. The method for preparing a castor oil-based biomass lubricating oil base oil according to claim 1, characterized in that, The short-chain fatty acids in step A2 include all isomers of monocarboxylic acids with a total carbon number of 1-4.

5. The method for preparing a castor oil-based biomass lubricating oil base oil according to claim 1, characterized in that, The catalysts mentioned in steps A1 and A2 are Lewis acid catalysts or organic base catalysts.

6. The method for preparing a castor oil-based biomass lubricating oil base oil according to claim 1, characterized in that, In step A3, the molar ratio of esterified castor oil product to formic acid is 1:2-5.

7. The method for preparing a castor oil-based biomass lubricating oil base oil according to claim 1, characterized in that, In step A4, the catalyst is an aqueous solution of Bronstein acid catalyst.

8. The method for preparing a castor oil-based biomass lubricating oil base oil according to claim 1, characterized in that, In step A5, the molar ratio of the dihydroxy compound, the short-chain dicarboxylic acid, and the short-chain fatty acid is 2:2:

3.

9. The method for preparing a castor oil-based biomass lubricating oil base oil according to claim 1, characterized in that, In step A5, the catalyst is a solid superacid, a composite metal oxide, or a solid Lewis acid catalyst.

10. The method for preparing a castor oil-based biomass lubricating oil base oil according to claim 1, characterized in that, The short-chain dicarboxylic acids in step A5 include all isomers of dicarboxylic acids with a total carbon number of 2-6; the short-chain fatty acids in step A5 include all isomers of monocarboxylic acids with a total carbon number of 1-8.

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