Process for the preparation of long chain fatty acid polyol esters and use thereof

Abstract

The present application relates to a kind of long chain fatty acid polyol ester preparation method and its application, which comprises: long chain fatty acid and polyol are passed into continuous operation reactor in the mode of continuous feeding, contact with solid catalyst, esterification is carried out;The solid catalyst includes acidic molecular sieve and inert binder, and optional metal additive.The present application packs solid catalyst in continuous operation reactor, and long chain fatty acid and polyol are passed in the mode of continuous feeding, and the preparation of long chain fatty acid polyol ester is carried out, the above-mentioned method can realize on-line water separation under the condition of not using water-carrying agent, and can improve the conversion rate of raw material, there is no catalyst residue in product, no catalyst separation is needed after reaction, operation step is simple, the proportion of long chain fatty acid monoester in the product prepared is high, and it is suitable for ester base anti-wear agent.

Description

Technical Field

[0001] This invention relates to the field of esterification reactions, specifically to a method for preparing long-chain fatty acid polyol esters and their applications. Background Technology

[0002] With increasing emphasis on environmental issues both domestically and internationally, the requirements for impurity content in diesel fuel are becoming increasingly stringent. Sulfur, a harmful air pollutant, requires refining and removal. Furthermore, high sulfur content in diesel fuel can easily cause engine wear. Diesel refining generally employs hydrogenation, but while removing sulfur-containing components, it also reduces the proportion of nitrogenous and oxygen-containing compounds. The lubricity of diesel fuel depends on the proportion of anti-wear compounds, such as nitrides, oxides, and polycyclic aromatic hydrocarbons. Therefore, low-sulfur and ultra-low-sulfur diesel fuels have poor lubricity. The conventional method is to add oxygen-containing compounds with lubricating properties to improve diesel fuel performance.

[0003] Existing low-sulfur diesel anti-wear agents mainly include two types: acid-based and ester-based. Acidic anti-wear agents primarily consist of bio-based long-chain fatty acids, such as linoleic acid, linolenic acid, oleic acid, and palmitic acid. Ester-based anti-wear agents are products of the esterification reaction between these long-chain fatty acids and polyols; products obtained from incomplete esterification of the polyol's hydroxyl groups are more effective. Acidic anti-wear agents are low-cost and effective, but free fatty acids in diesel fuel easily undergo saponification reactions with alkaline dispersants in the fuel, generating calcium and magnesium salts of long-chain fatty acids, causing filter clogging. Ester-based anti-wear agents have low acid values ​​and good lubrication effects, thus showing better application prospects. In 2007, Sinopec began implementing access standards for diesel anti-wear agents, imposing strict requirements on fatty acid content, metal content, acid value, and viscosity in ester-based anti-wear agents. This standard has been recognized and adopted by other domestic diesel producers.

[0004] The synthesis of ester-based anti-wear agents typically employs a batch stirring apparatus, using homogeneous acid-base catalysts and solid acid-base catalysts to catalyze the esterification reaction of bio-based fatty acids with polyols such as glycerol and propylene glycol, with online water separation. This method can efficiently synthesize partially esterified fatty acid polyol esters. However, the resulting product requires neutralization and water washing steps to remove the acid-base catalysts, resulting in the discharge of waste residue and wastewater. Furthermore, the product composition varies from batch to batch.

[0005] CN 109957435A discloses a composite ester-based anti-wear agent and its preparation method. The main components of this anti-wear agent are a mixture of unsaturated fatty acid monoglycerides and diesters, with the unsaturated fatty acids primarily being C18 oleic acid, linoleic acid, and linolenic acid. The synthesis method employs a stirred tank apparatus for intermittent operation, adding 0.5%-1.0% of a solid superacid or homogeneous base as a catalyst. The reaction temperature is 160-200℃. The resulting product contains approximately 40-50% unsaturated fatty acid monoglycerides, approximately 45-48% fatty acid diglycerides, and approximately 5% triglycerides. The product requires further water washing and distillation to improve purity. After compounding, it was found that the ester-based anti-wear agent containing a small amount of fatty acids exhibits superior performance compared to commonly used ester and acid-based anti-wear agents.

[0006] CN108018092A discloses an ester-based anti-wear agent and a method for synthesizing it via esterification. The patent mentions that esterification reactions typically employ acidic or basic catalysts or metal catalysts. Acidic catalysts include sulfuric acid, phosphoric acid, p-toluenesulfonic acid, acidic ion exchange resins, heteropoly acids, solid superacids, acidic clay, and acidic molecular sieves. Basic catalysts include NaOH, KOH, Ca(OH)₂, Mg(OH)₂, sodium methoxide, potassium methoxide, solid superbases, or organic amines. Metal oxide catalysts are mainly tin-containing substances, such as dibutyltin oxide and monobutyltin oxide. The amount used is 0-2% of the substrate. All of the above catalysts are used in a batch autoclave operation. During the esterification reaction, solvent reflux for water removal, inert gas for water removal, or vacuum dehydration can be used. The product requires secondary molecular distillation to eliminate residual acidic or basic catalysts.

[0007] Zhao Yingqiu et al. [Zhao Yingqiu, Huang Zhankai, Zhao Hong, Dong Guangqian, Zhang Xiaoxing, Wang Hui. Synthesis of ester-type anti-wear agents and their effects on diesel quality, Lubrication and Sealing, 2020, 45(8): 143-148] synthesized an ester-type anti-wear agent by esterification reaction of oleic acid and glycerol. The molar ratio of oleic acid to glycerol was 1:1.1. A solid acid catalyst was used, and the amount added was 16% of the total mass of oleic acid and glycerol. Then, 1.5 times the volume of toluene was added as a dehydrating agent. The reaction was carried out at 132℃ for more than 8 hours. Infrared spectroscopy showed that the ester-type anti-wear agent product was synthesized, but the proportions of oleic acid monoglyceride, diglyceride and triglyceride were not mentioned. Ma Zhiyuan et al. [Ma Zhiyuan, Yu Qun, Liu Meijing, Meng Xiangliang. Study on the synthesis process of oleic acid glyceride ester-type anti-wear agent.] [Tianjin Chemical Industry, 2020, 34(2): 17-19] Similarly, oleic acid and glycerol were used as raw materials, and toluene was used as a dehydrating agent to synthesize ester-based anti-wear agents through esterification reaction. The catalyst was homogeneous p-toluenesulfonic acid, and the amount used was 0.8% of the total mass of oleic acid and glycerol. The reaction was carried out at 130-150℃ for 6 hours. Zhang Xiaoliu et al. [Zhang Xiaoliu, Lei Kelin, Xia Minggui, Luan Lijun. Preparation and performance study of monooleic glycerol ester compound diesel anti-wear agent, Refining Technology and Engineering, 2014, 44(1): 61-64] also used unsaturated fatty acids and glycerol esterification reaction, using xylene as a dehydrating agent and p-toluenesulfonic acid as a catalyst. After the reaction, it was necessary to wash with water and separate the liquid, and then distill under reduced pressure and extract to obtain the product.

[0008] In summary, the typical synthesis method for ester-based anti-wear agents involves the esterification reaction of bio-based fatty acids with polyols, using homogeneous acid, basic, or oil-soluble metal catalysts. The stirring device operates intermittently. To promote the forward esterification reaction, a dehydrating agent is added online to remove the generated water. The catalyst remaining in the product after the reaction requires neutralization and water washing, resulting in wastewater discharge. Some technologies use solid acid catalysts with intermittent stirring devices, also with online water separation, and the product is separated by filtration. However, the catalyst is prone to pulverization during use, has limited reusability, and the operation is cumbersome. Since the operation process for each batch is affected by factors such as temperature, humidity, and operator, batch-to-batch variations exist. Furthermore, the product in the stirring device is in a completely backmixed state, and the reaction of fatty acids with polyols sequentially generates fatty acid monoglycerides, diglycerides, and triglycerides, making it difficult to obtain a mixture with a high proportion of fatty acid monoglycerides and a stable composition. Summary of the Invention

[0009] The purpose of this invention is to provide a method for preparing long-chain fatty acid polyol esters and their applications. This method can improve the conversion rate of raw materials, and the product has no catalyst residue. The operation steps are simple, and the prepared product has a high proportion of long-chain fatty acid monoesters, making it suitable for ester-based anti-wear agents.

[0010] To achieve the above objectives, the first aspect of this disclosure provides a method for preparing long-chain fatty acid polyol esters, the method comprising: feeding long-chain fatty acids and polyols into a continuously operated reactor in a continuous feeding manner, contacting them with a solid catalyst, and carrying out an esterification reaction;

[0011] The solid catalyst comprises an acidic molecular sieve and an inert binder, as well as an optional metal additive.

[0012] Optionally, in the solid catalyst, the content of the acidic molecular sieve is 60-95% by weight, the content of the inert binder is 5-35% by weight, and the content of the metal additive is 0-5% by weight.

[0013] Preferably, the content of the acidic molecular sieve is 65-85% by weight, the content of the inert binder is 10-30% by weight, and the content of the metal additive is 0.5-5% by weight.

[0014] Preferably, the acidic molecular sieve content is 73-85% by weight, the inert binder content is 14-25% by weight, and the metal additive content is 0.5-2% by weight.

[0015] Optionally, the acidic molecular sieve includes one or more of NaY molecular sieve, X-type molecular sieve with a silica-alumina ratio of more than 1, all-silica ZSM-5 molecular sieve, and all-silica ZSM-48 molecular sieve.

[0016] The inert binder includes one or more of silica sol, amorphous titanium dioxide, anatase titanium dioxide, zirconium dioxide, and viscous graphite;

[0017] The metal additive is a metal oxide additive, preferably including one or more of tin dioxide, zinc dioxide, magnesium dioxide, manganese dioxide and germanium dioxide.

[0018] Optionally, the solid catalyst is spherical with a diameter of 0.5-5 mm and a strength of 15 N / particle or higher; or,

[0019] The solid catalyst is strip-shaped, with a length of 3-8 mm and a strength of 10 N / mm or more.

[0020] Optionally, the polyol includes one or more saturated polyols having 2-5 carbon atoms, preferably one or more of ethylene glycol, 1,2-propanediol, 1,3-propanediol and glycerol.

[0021] Optionally, the long-chain fatty acid includes saturated fatty acids with 8-24 carbon atoms and / or unsaturated fatty acids with 8-24 carbon atoms;

[0022] Preferably, the saturated fatty acid includes one or more of lauric acid, palmitic acid and stearic acid, and the unsaturated fatty acid includes one or more of oleic acid, linoleic acid and linolenic acid.

[0023] Optionally, the esterification reaction conditions include: a temperature of 160-300℃, a pressure of 0.1-5.0 MPa, and a feed mass hourly space velocity of 0.05-1.5 h⁻¹ based on the total mass of the long-chain fatty acid and the polyol. -1 The molar ratio of the carboxyl group in the long-chain fatty acid to the hydroxyl group in the polyol is 1:(2-27).

[0024] Optionally, the method further includes: preheating the long-chain fatty acid and the polyol before introducing them into the continuous operation reactor, wherein the preheating temperature is 160-200°C.

[0025] Optionally, the esterification reaction is carried out in multiple continuously operated reactors connected in series, with a flash tank provided between two adjacent continuously operated reactors to remove at least a portion of the water generated by the esterification reaction.

[0026] Optionally, the continuously operating reactor is a fixed-bed reactor or a continuous stirred tank reactor.

[0027] The second aspect of this disclosure provides long-chain fatty acid polyol esters prepared using the preparation method described in the first aspect of this disclosure.

[0028] This disclosure provides a third aspect regarding the use of the long-chain fatty acid polyol esters described in the second aspect of this disclosure in ester-based anti-wear agents.

[0029] Through the above technical solution, this disclosure loads a solid catalyst including acidic molecular sieves into a continuous operation reactor, and introduces long-chain fatty acids and polyols in a continuous feeding manner to prepare long-chain fatty acid polyol esters. The above method can achieve online water separation without the use of dehydrating agents, and can improve the conversion rate of raw materials. There is no catalyst residue in the product, and no catalyst separation is required after the reaction. The operation steps are simple, and the prepared product has a high proportion of long-chain fatty acid monoesters, which is suitable for ester-based anti-wear agents.

[0030] Other features and advantages of the present invention will be described in detail in the following detailed description section. Detailed Implementation

[0031] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0032] The present invention will be further illustrated by the following examples, but the present invention is not limited thereto.

[0033] The first aspect of this disclosure provides a method for preparing long-chain fatty acid polyol esters, the method comprising: feeding long-chain fatty acids and polyols into a continuously operated reactor in a continuous feeding manner, contacting them with a solid catalyst, and carrying out an esterification reaction;

[0034] The solid catalyst comprises an acidic molecular sieve and an inert binder, as well as an optional metal additive.

[0035] In this disclosure, the surface of the solid catalyst is hydrophobic, so the water generated during the esterification reaction will not be adsorbed onto the catalyst surface and reduce its activity, but will enter the mobile phase of the material. The phase state adjustment achieves a microscopic online water separation effect, resulting in a high conversion rate of the esterification reaction.

[0036] In one embodiment of this disclosure, the solid catalyst contains, by weight percentage, 60-95% acidic molecular sieve, 5-35% inert binder, and 0-5% metal additive; preferably, by weight percentage, 65-85% acidic molecular sieve, 10-30% inert binder, and 0.5-5% metal additive; more preferably, by weight percentage, 73-85% acidic molecular sieve, 14-25% inert binder, and 0.5-2% metal additive. The addition of the metal additive can inhibit the polymerization of olefins and further improve the conversion rate.

[0037] In one embodiment of this disclosure, the acidic molecular sieve includes one or more of NaY molecular sieve, X-type molecular sieve with a silica-to-alumina ratio of 1 or higher, all-silica ZSM-5 molecular sieve, and all-silica ZSM-48 molecular sieve; the inert binder includes one or more of silica sol, amorphous titanium dioxide, anatase titanium dioxide, zirconium dioxide, and viscous graphite; the metal additive is a metal oxide additive, preferably including one or more of tin dioxide, zinc dioxide, magnesium dioxide, manganese dioxide, and germanium dioxide.

[0038] In one embodiment of this disclosure, the solid catalyst can be of any shape. Preferably, the solid catalyst is spherical with a diameter of 0.5-5 mm and a strength of 15 N / particle or more; or, the solid catalyst is strip-shaped with a length of 3-8 mm and a strength of 10 N / mm or more. The cross-section of the strip-shaped catalyst can be of any shape, such as circular, rectangular, or irregular. The strip-shaped catalyst can also be cylindrical with a length of 3-8 mm and a diameter of 0.5-5 mm. The aforementioned strength is lateral compressive strength, tested using the single-particle strength method. The set values ​​ensure that during long-term use of the catalyst, significant catalyst breakage does not occur, preventing excessive pressure drop in the catalyst bed.

[0039] In this disclosure, the preparation steps and molding methods of the solid catalyst are conventional in the art, including but not limited to tableting, extrusion molding, and spheroidizing, and will not be described in detail here.

[0040] In this disclosure, the long-chain fatty acid is a bio-based long-chain fatty acid, which may include long-chain fatty acids obtained by hydrolysis or rancidity of vegetable oils and animal oils, and has 8 or more carbon atoms, preferably long-chain fatty acids with 8-24 carbon atoms.

[0041] In one embodiment of this disclosure, the long-chain fatty acids include saturated fatty acids with 8-24 carbon atoms and / or unsaturated fatty acids with 8-24 carbon atoms; preferably, the saturated fatty acids include one or more of lauric acid, palmitic acid and stearic acid, and the unsaturated fatty acids include one or more of oleic acid, linoleic acid and linolenic acid.

[0042] In one embodiment of this disclosure, the polyol includes one or more saturated polyols having 2-5 carbon atoms. The saturated polyol may have 2 or 3 hydroxyl groups. The polyol preferably includes one or more of ethylene glycol, 1,2-propanediol, 1,3-propanediol and glycerol.

[0043] In one embodiment of this disclosure, the esterification reaction conditions include: a temperature of 160-300°C, a pressure of 0.1-5.0 MPa, and a feed space velocity of 0.05-1.5 h⁻¹ based on the total mass of long-chain fatty acids and polyols. -1 The molar ratio of the carboxyl group in the long-chain fatty acid to the hydroxyl group in the polyol is 1:(2-27). The esterification reaction temperature can be any temperature between 160-300℃, for example, 200℃, 210℃, 220℃, 240℃, etc.; the esterification reaction pressure can be any pressure between 0.1-1.5MPa, for example, 0.3MPa, 0.8MPa, 1.0MPa, 1.5MPa, etc.; the feed mass hourly space velocity can be 0.05-1.5h. -1 Any mass space velocity between these values, for example, could be 0.3h.-1 0.4h -1 0.5h -1 1.0h -1 wait.

[0044] In one embodiment of this disclosure, the continuous operation reactor is a fixed-bed reactor or a continuous stirred tank reactor, preferably a fixed-bed reactor.

[0045] In this disclosure, "feeding long-chain fatty acids and polyols into a continuous operation reactor in a continuous feeding manner" can mean feeding long-chain fatty acids and polyols into the continuous operation reactor separately in a continuous feeding manner, or feeding long-chain fatty acids and polyols together into the continuous operation reactor in a continuous feeding manner.

[0046] In one embodiment of this disclosure, the method further includes: preheating the long-chain fatty acids and polyols before introducing them into a continuous operation reactor, wherein the preheating temperature is 160-200°C; specifically, the long-chain fatty acids and polyols can be preheated separately in a heat exchanger, then mixed in a mixer, and then introduced into the continuous operation reactor.

[0047] In one embodiment of this disclosure, the method further includes: passing the first mixture obtained from the esterification reaction into a buffer tank and introducing nitrogen gas into the buffer tank to maintain a stable reaction pressure, ensure smooth material flow, and achieve low-pressure separation.

[0048] In one embodiment of this disclosure, the esterification reaction is carried out in multiple continuously operated reactors connected in series. A flash tank is provided between two adjacent continuously operated reactors. The temperature of the flash tank can be maintained at around 160-180°C, and the pressure can be atmospheric pressure, to remove at least some of the water generated in the esterification reaction. The above operation can further improve the conversion efficiency, and the reaction conditions of the multiple continuously operated reactors connected in series can be the same.

[0049] The long-chain fatty acid polyol ester product obtained by the above preparation method has a monoester content of 55% by weight or more, preferably 60% by weight or more, for example 60-75% by weight, or 60-70% by weight, and can be used as an ester-based anti-wear agent.

[0050] The second aspect of this disclosure provides long-chain fatty acid polyol esters prepared using the preparation method described in the first aspect of this disclosure.

[0051] This disclosure provides a third aspect regarding the use of the long-chain fatty acid polyol esters described in the second aspect of this disclosure in ester-based anti-wear agents.

[0052] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way.

[0053] All raw materials used in the examples and comparative examples were obtained commercially and, unless otherwise specified, were of analytical grade.

[0054] Lateral compressive strength testing method: single-particle strength method;

[0055] Chromatographic test conditions and instrument model: Chromatography model Agilent 7890B, chromatographic column HT-01, 0.32mm×0.2μm×30m, temperature program 60℃, 5℃ / min to 240℃, hold for 30min, then continue to 5℃ / min to 290℃, hold for 30min.

[0056] Example 1

[0057] Take 100.0g of all-silicon ZSM-48 molecular sieve, mix it with 6.0g of viscous graphite, stir evenly, grind it to 160-200 mesh, and dry it at 120℃ for 8h. Then use a hydraulic tablet press to press the powder into cylinders with a diameter of 4mm and a height of 4-6mm to obtain catalyst 1#, with a lateral compressive strength of 15N / mm;

[0058] In the catalyst, the content of molecular sieve is 94.3% by weight, and the content of inert binder is 5.7% by weight;

[0059] Catalyst #1 was crushed into 10-20 mesh particles, and 15.0 g was weighed. It was then loaded into a fixed-bed reactor. The fixed-bed reactor had an inner diameter of 12 mm and a top-in, bottom-out feed method. The reaction temperature was 220℃, and the reaction pressure was 1.0 MPa. Oleic acid and glycerol were pumped separately to a heat exchanger, preheated to 200℃, then mixed and continuously fed into the reactor. A buffer tank was installed after the reactor, and nitrogen gas was introduced into it to maintain the reaction pressure. The molar ratio of carboxyl to hydroxyl groups was 1:6, and the feed mass hourly space velocity (WHSV) was 0.40 h⁻¹ based on the total mass of oleic acid and glycerol. -1 The product undergoes a single-pass esterification reaction. After collection, it separates into two phases. After thorough mixing, 2 mL of the product is dissolved in 5 mL of methanol to form a homogeneous solution, which is then subjected to chromatographic analysis. The analytical results and conversion rate calculations are shown in Table 1.

[0060] Example 2

[0061] Take 100.0g of NaY molecular sieve, grind it to 160-200 mesh, and mix it with 65g of silica gel solution with a solid content of 35%. The mixing method is to rapidly stir the molecular sieve powder, add the silica gel solution dropwise to the powder, knead the mixture evenly, and then extrude the mixture into strips with a diameter of 2mm using a twin-screw extruder. Dry at 120℃ for 8 hours and calcine at 550℃ for 4 hours to obtain catalyst #2. Then break it into cylindrical segments with a length of 2-3mm and a lateral compressive strength of 10N / mm.

[0062] In the catalyst, the content of molecular sieve is 82.0% by weight, and the content of inert binder is 18.0% by weight;

[0063] 15.0 g of catalyst #2 was weighed and loaded into a fixed-bed reactor. The fixed-bed reactor has an inner diameter of 12 mm and a top-in, bottom-out feed method. The reaction temperature was 240℃, and the reaction pressure was 1.0 MPa. Oleic acid and glycerol were pumped separately to a heat exchanger, preheated to 200℃, then mixed and continuously fed into the reactor. A buffer tank was installed after the reactor, and nitrogen gas was introduced into it to maintain the reaction pressure. The molar ratio of carboxyl to hydroxyl groups was 1:4.5, and the feed mass hourly space velocity (WHSV) was 0.30 h⁻¹ based on the total mass of oleic acid and glycerol. -1 The product undergoes a single-pass esterification reaction. After collection, it separates into two phases. After thorough mixing, 2 mL of the product is dissolved in 5 mL of methanol to form a homogeneous solution, which is then subjected to chromatographic analysis. The analytical results and conversion rate calculations are shown in Table 1.

[0064] Example 3

[0065] Take 80.0g of all-silica ZSM-5 molecular sieve, weigh 3.72g of SnCl4·5H2O solid, and dissolve them in 23mL of deionized water to obtain an aqueous solution containing Sn. Stir the molecular sieve powder, then add the Sn-containing aqueous solution dropwise and stir until homogeneous. Let it stand at room temperature for 4h, then dry at 120℃ for 8h and calcine at 600℃ for 5h. Grind the dried powder to 160-200 mesh and mix it with 45g of silica gel solution with a solid content of 35%. The mixing method is to rapidly stir the powder and add the silica gel solution dropwise to the powder. After kneading the mixture until homogeneous, extrude the mixture into strips with a diameter of 2mm using a twin-screw extruder. Dry at 120℃ for 8h and calcine at 550℃ for 4h to obtain catalyst #3. Then break it into cylindrical segments with a length of 2-3mm and a lateral compressive strength of 10N / mm.

[0066] In the catalyst, the content of molecular sieve is 82.9% by weight, the content of inert binder is 15.5% by weight, and the content of metal additive is 1.6% by weight.

[0067] 15.0 g of catalyst #3 was weighed and loaded into a fixed-bed reactor. The fixed-bed reactor has an inner diameter of 12 mm and a top-in, bottom-out feed method. The reaction temperature was 210 °C, and the reaction pressure was 1.0 MPa. Oleic acid and glycerol were pumped separately to heat exchangers, preheated to 180 °C, and then mixed before entering the reactor. A buffer tank was installed after the reactor, and nitrogen gas was introduced into it to maintain the reaction pressure. The molar ratio of carboxyl to hydroxyl groups was 1:9, and the feed mass hourly space velocity (WHSV) was 0.50 h⁻¹ based on the total mass of oleic acid and glycerol. -1 The product undergoes a single-pass esterification reaction. After collection, it separates into two phases. After thorough mixing, 2 mL of the product is dissolved in 5 mL of methanol to form a homogeneous solution, which is then subjected to chromatographic analysis. The analytical results and conversion rate calculations are shown in Table 1.

[0068] Example 4

[0069] The esterification reaction was carried out using catalyst #2 and reaction conditions from Example 2, the difference being that oleic acid was replaced with palmitic acid, glycerol was replaced with ethylene glycol, the molar ratio of carboxyl to hydroxyl groups was 1:6, and the feed space velocity (HSV) was 0.40 h⁻¹ based on the total mass of palmitic acid and ethylene glycol. -1 The product undergoes a single-pass esterification reaction. After collection, it separates into two phases. After thorough mixing, 2 mL of the product is dissolved in 5 mL of methanol to form a homogeneous solution, which is then subjected to chromatographic analysis. The analytical results and conversion rate calculations are shown in Table 1.

[0070] Example 5

[0071] The esterification reaction was carried out using catalyst #2 and reaction conditions from Example 2. The difference was that the reactor consisted of two reactors connected in series. The fixed-bed reactor type, size, and catalyst state were identical. The reaction conditions for the first and second reactors were the same as in Example 2. The connection sequence was: first reactor, buffer tank, flash tank, second reactor, and buffer tank again. Nitrogen gas was introduced into the first and second reactors through the buffer tank to maintain the reaction pressure. The fixed-bed reactor had an inner diameter of 12 mm and a top-in, bottom-out feed method. The reaction temperature was 210°C, and the reaction pressure was 1.0 MPa. Oleic acid and glycerol were pumped to heat exchangers, preheated to 180°C, and then mixed before entering the first reactor. The reaction products entered the flash tank. The temperature in the flash tank was controlled at 160-180°C, and the pressure was atmospheric pressure. The liquid level in the flash tank was maintained at 40-65%. Then, the liquid in the flash tank was continuously pumped into the second reactor for further reaction. The product collected after the second reactor still exists as a two-phase mixture. After thorough stirring, 2 mL of the product was dissolved in 5 mL of methanol to form a homogeneous solution, which was then subjected to chromatographic analysis. The analytical results and conversion rate calculations are shown in Table 1.

[0072] Comparative Example 1

[0073] Weigh 5.0 g of catalyst #3 and place it in a 500 mL reactor. Mix oleic acid and glycerol, with a carboxyl to hydroxyl molar ratio of 1:9, totaling 200 g of oleic acid and glycerol. At this point, oleic acid and glycerol are immiscible. After stirring thoroughly, add the mixture to a stirred tank. Seal the reactor and purge the air inside three times with nitrogen at 2.0 MPa at room temperature. Then pressurize with nitrogen to 1.0 MPa. Heat the reactor to 240 °C and stir for 6 hours. The product separates into two phases. After stirring thoroughly, take 2 mL of the product and dissolve it in 5 mL of methanol to form a homogeneous solution. Then perform chromatographic analysis. The analytical results and conversion calculation are shown in Table 1.

[0074] Table 1

[0075]

[0076] According to the data in Table 1, the esterification reaction of long-chain fatty acids and polyols using the method disclosed herein can achieve a high acid conversion rate and a high proportion of monoesters in the product, making it suitable for ester-based anti-wear agents.

[0077] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0078] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0079] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for preparing a long-chain fatty acid polyol ester, characterized in that, The method includes: feeding long-chain fatty acids and polyols into a continuously operated reactor in a continuous feed manner, contacting them with a solid catalyst, and carrying out an esterification reaction; The solid catalyst comprises an acidic molecular sieve, an inert binder, and a metal additive; In the solid catalyst, by weight percentage, the content of the acidic molecular sieve is 60-95% by weight, the content of the inert binder is 5-35% by weight, the content of the metal additive is 0.5-5% by weight, and the total content of all components in the solid catalyst is 100% by weight. The acidic molecular sieves include all-silica ZSM-5 molecular sieves and / or all-silica ZSM-48 molecular sieves; The surface of the solid catalyst has hydrophobic properties; The inert binder includes one or more of silica sol, amorphous titanium dioxide, anatase titanium dioxide, zirconium dioxide, and viscous graphite; The metal additives include one or more of tin dioxide, zinc oxide, magnesium oxide, manganese dioxide, and germanium dioxide; The esterification reaction conditions include: a temperature of 160-300℃, a pressure of 0.1-5.0 MPa, and a feed space velocity of 0.05-1.5 h⁻¹ based on the total mass of the long-chain fatty acid and the polyol. -1 The molar ratio of the carboxyl group in the long-chain fatty acid to the hydroxyl group in the polyol is 1:(2-27).

2. The preparation method according to claim 1, wherein, In the solid catalyst, the content of the acidic molecular sieve is 65-85% by weight, the content of the inert binder is 10-30% by weight, and the content of the metal additive is 0.5-5% by weight.

3. The preparation method according to claim 1, wherein, In the solid catalyst, the content of the acidic molecular sieve is 73-85% by weight, the content of the inert binder is 14-25% by weight, and the content of the metal additive is 0.5-2% by weight.

4. The preparation method according to claim 1, wherein, The solid catalyst is spherical with a diameter of 0.5-5 mm and a strength of 15 N / particle or higher; or, The solid catalyst is strip-shaped, with a length of 3-8 mm and a strength of 10 N / mm or more.

5. The preparation method according to claim 1, wherein, The polyols include one or more of the saturated polyols having 2-5 carbon atoms.

6. The preparation method according to claim 5, wherein, The saturated polyols having 2-5 carbon atoms include one or more of ethylene glycol, 1,2-propanediol, 1,3-propanediol, and glycerol.

7. The preparation method according to claim 1, wherein, The long-chain fatty acids include saturated fatty acids with 8-24 carbon atoms and / or unsaturated fatty acids with 8-24 carbon atoms.

8. The preparation method according to claim 7, wherein, The saturated fatty acids with 8-24 carbon atoms include one or more of lauric acid, palmitic acid, and stearic acid, and the unsaturated fatty acids with 8-24 carbon atoms include one or more of oleic acid, linoleic acid, and linolenic acid.

9. The preparation method according to claim 1, wherein, The method further includes: preheating the long-chain fatty acid and the polyol before introducing them into the continuous operation reactor, wherein the preheating temperature is 160-200℃.

10. The preparation method according to claim 1, wherein, The esterification reaction is carried out in a plurality of continuously operated reactors connected in series, with a flash tank provided between two adjacent continuously operated reactors to remove at least a portion of the water generated by the esterification reaction.

11. The preparation method according to any one of claims 1-10, wherein, The continuous operation reactor is either a fixed-bed reactor or a continuous stirred tank reactor.

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