Synthesis of trimethylolpropane ester and its application in refrigeration oil

Abstract

The invention provides a method for synthesizing trimethylolpropane ester, comprising the following steps: S1: adding trimethylolpropane, solvent and aliphatic dibasic acid to a reactor, heating to 90-100°C, stirring reaction for 50-70min, and obtaining mixed solution A; S2: adding a catalyst and a polymerization inhibitor to step S1, heating to 120-140°C, stirring reaction for 1-2h, and obtaining mixed solution B; S3: cooling mixed solution B in step S2 to 105-115°C, adding an antioxidant and a water absorbent thereto, and continuing stirring reaction for 2-3h to obtain mixed solution C; S4: filtering mixed solution C in step S3, distilling the upper mother liquor, and reorganizing into trimethylolpropane ester. Applying it to the preparation of refrigeration oil can significantly improve the low temperature resistance and oxidation stability of refrigeration oil.

Description

Technical Field

[0001] The invention belongs to the technical field of ester preparation, and specifically relates to the synthesis of trimethylolpropane ester and the application of the trimethylolpropane ester in refrigeration oil. Background Art

[0002] Refrigeration oil is a special lubricant used in refrigeration systems. Its main functions are to provide lubrication, cooling, sealing and corrosion prevention in compressors. Choosing the right refrigeration oil is essential to ensure the efficient operation of the refrigeration system and extend the life of the equipment. According to the type of refrigerant and the application environment, refrigeration oil can be divided into the following categories: mineral oil, suitable for use with CFC (chlorofluorocarbon) and HCFC (hydrochlorofluorocarbon) refrigerants; has good chemical stability and thermal stability, but poor compatibility with new environmentally friendly refrigerants such as HFC (hydrofluorocarbon) and CO2; synthetic hydrocarbon oil and polyalkyl glycol are one of the most common synthetic hydrocarbon oils; have good compatibility with HFC refrigerants and are widely used in screw, centrifugal and scroll compressors; have excellent lubrication performance and low-temperature fluidity, but may have a swelling effect on some rubber sealing materials; polyester oil, suitable for use with HFC refrigerants, especially in small refrigeration equipment such as household air conditioners and refrigerators, has good solubility and anti-wear properties, and can effectively remove wax deposits in the system. Compared with mineral oil, POE oil is more expensive, but its performance is superior and suitable for applications with high performance requirements. Polyalphaolefin, a high-performance synthetic oil, has excellent thermal and oxidative stability. It is suitable for refrigeration systems under extreme temperature conditions, such as low-temperature cold storage and industrial refrigeration equipment under high temperature environment. Silicone oil is mainly used in special applications, such as vacuum pumps and refrigeration systems of high-precision instruments; it has extremely low volatility and excellent chemical inertness, but it is expensive and not common in conventional refrigeration systems.

[0003] Trimethylolpropane Ester (TMP Ester) is a type of ester compound formed by the reaction of trimethylolpropane (TMP) with an acid. Trimethylolpropane is an organic compound containing three hydroxyl groups (-OH) and its chemical formula is C6H14O3. Since it has three hydroxyl groups, it can react with monobasic acids (such as acetic acid, fatty acids, etc.) to form monoesters, diesters, or triesters.

[0004] Trimethylolpropane esters have the following common characteristics: High thermal and chemical stability: They can remain stable under high temperature conditions, are not easy to decompose or deteriorate, and are suitable for harsh working environments. Excellent lubrication performance: They can form a stable lubricating film on the metal surface, reduce friction and wear, and are particularly suitable for high temperature, high pressure and high speed conditions. Good low temperature fluidity: They can maintain good fluidity even under low temperature conditions, will not solidify or have too high viscosity, and are suitable for applications in cold environments. Low volatility: Compared with other types of ester compounds, trimethylolpropane esters have lower volatility, which reduces evaporation losses, energy consumption and the risk of environmental pollution. Good biodegradability: Some types of trimethylolpropane esters have a high biodegradability rate, are environmentally friendly, and meet modern environmental protection requirements. Non-toxic or low toxicity: Most trimethylolpropane esters are harmless to the human body and the environment or have extremely low toxicity, and meet food safety standards and environmental regulations. Good solubility and compatibility: They can dissolve a variety of additives well, and have good compatibility with a variety of plastics, rubbers and sealing materials without causing adverse reactions. Anti-corrosion performance: It can provide effective anti-corrosion protection in humid or corrosive environments and extend the service life of the equipment.

[0005] Due to its unique properties, trimethylolpropane ester is widely used in lubricants and lubricant additives, coatings and inks, plastic plasticizers, cosmetics and personal care products, emulsifiers or moisturizers, synthetic resins and other industries. Currently, refrigeration oil has problems such as poor low temperature performance, poor oil-water separation performance, poor oxidation stability, and easy carbon deposition. Therefore, a trimethylolpropane ester used in refrigeration oil is developed to improve the refrigeration oil problem. Summary of the invention

[0006] The purpose of the present invention is to provide a method for synthesizing trimethylolpropane ester, which uses trimethylolpropane and an aliphatic dibasic acid as reactants to obtain trimethylolpropane ester in the presence of a catalyst or the like; and the method is applied to the preparation of refrigeration oil to significantly improve the low temperature resistance and oxidation stability of the refrigeration oil.

[0007] In order to achieve the above object, the present invention provides the following technical solutions: A method for synthesizing trimethylolpropane ester comprises the following steps: S1: Add trimethylolpropane, solvent and aliphatic dibasic acid into a reaction kettle, heat to 90-100°C, stir and react for 50-70 minutes to obtain a mixed solution A; S2: Add the catalyst and the polymerization inhibitor to step S1, raise the temperature to 120-140°C, and stir the reaction for 1-2h to obtain a mixed solution B; S3: Cooling the mixed solution B in step S2 to 105-115°C, adding an antioxidant and a water absorbent thereto, and continuing to stir and react for 2-3 hours to obtain a mixed solution C; S4: filtering the mixed solution C in step S3, distilling the upper mother solution, and recombining it into trimethylolpropane ester; The amount of the catalyst in step S2 is 3-5% of the mass of the mixed solution A; the catalyst is an activated carbon or molecular sieve-loaded p-toluenesulfonic acid solution; the preparation process of activated carbon-loaded p-toluenesulfonic acid is as follows: according to the solid-liquid ratio of 1g:15-25mL, 200-300 mesh activated carbon is added to a 35% mass fraction p-toluenesulfonic acid aqueous solution, the temperature is increased to 130-150°C, and the reaction is stirred for 2-4h; after filtering, it is placed in a muffle furnace and roasted at a temperature of 500-600°C for 10-15min.

[0008] Preferably, in step S1, the molar ratio of trimethylolpropane to aliphatic dibasic acid is 1:5-7; and the amount of the solvent is 2-3 times that of trimethylolpropane and aliphatic dibasic acid.

[0009] Preferably, the solvent in step S1 is cyclohexane; the aliphatic dibasic acid is one or a mixture of glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid and sebacic acid.

[0010] Preferably, the preparation process of the molecular sieve loaded with p-toluenesulfonic acid is as follows: according to the solid-liquid ratio of 1g:10-20mL, take 200-300 mesh activated carbon and add it to a 55% mass fraction of p-toluenesulfonic acid aqueous solution, increase the temperature to 100-110°C, stir and react for 3-5h; after filtering, put it into a muffle furnace and roast it at a temperature of 400-500°C for 15-25min.

[0011] Preferably, the amount of the polymerization inhibitor in step S2 is 0.5-1.5% of the mass of the mixed solution A; the polymerization inhibitor is hydroquinone or p-hydroxyanisole.

[0012] Preferably, in step S3, the amount of the antioxidant used is 0.3-0.8% of the mass of the mixed solution B; the antioxidant is tributyl phosphate or thioglycolic acid; the amount of the water absorbent used is 2-4% of the mass of the mixed solution B; the water absorbent is polyacrylate.

[0013] Preferably, the parameters of the distillation process in step S4 are: the vacuum degree in the evaporator is less than 10 KPa, and the removal temperature is 80-90°C.

[0014] The trimethylolpropane ester synthesized above is applied to refrigeration oil.

[0015] Aliphatic dicarboxylic acids are a class of organic compounds containing two carboxyl groups (-COOH), which are usually located at the ends of the carbon chain. They are aliphatic compounds, which means that their carbon skeleton is mainly composed of saturated or unsaturated carbon-carbon single bonds, and does not contain aromatic ring structures. Aliphatic dicarboxylic acids are widely used in industry and chemistry. Due to the presence of two carboxyl groups, aliphatic dicarboxylic acids can participate in a variety of chemical reactions, such as esterification, amidation, condensation, etc., and can form a variety of derivatives such as esters, amides, polyesters, etc. with other compounds. Adjustable molecular structure: By selecting dicarboxylic acids with different carbon chain lengths, the properties of the final product, such as melting point, solubility, flexibility, etc., can be adjusted. Good biodegradability: Many aliphatic dicarboxylic acids and their derivatives are biodegradable, environmentally friendly, and meet modern environmental protection requirements. For example, long-chain dicarboxylic acids such as adipic acid and sebacic acid are often used in the production of degradable plastics. Low toxicity: Most aliphatic dibasic acids are harmless or have very low toxicity to humans and the environment, and are suitable for use in food contact materials, cosmetics, and personal care products.

[0016] Activated carbon is a specially treated carbon material with a highly developed pore structure and a large specific surface area, which can effectively adsorb impurities in gases, liquids or colloids. Activated carbon is widely used in air purification, water treatment, solvent recovery, food processing, medicine and other fields. Activated carbon has the following characteristics: High specific surface area: The internal pore structure of activated carbon is very developed, providing a huge surface area, usually up to 500-1500 square meters per gram of activated carbon. This makes it have a very strong adsorption capacity. Porous structure: The pore size distribution of activated carbon is wide, including micropores (< 2nm), mesopores (2-50 nm) and macropores (> 50 nm). Pores of different pore sizes can adsorb molecules of different sizes to meet a variety of application requirements. Chemical stability: Activated carbon shows good chemical stability in acids, alkalis and organic solvents, and is not easily corroded or decomposed. Physical stability: Activated carbon has high mechanical strength and wear resistance, and can be used for a long time in various environments without being easily broken or pulverized. Non-toxic and low-toxicity: Most activated carbons are harmless or have very low toxicity to humans and the environment, and comply with food safety standards and environmental regulations.

[0017] Molecular sieves are a class of crystalline materials with highly ordered microporous structures that can selectively adsorb and separate molecules in gases or liquids. The pore size of molecular sieves is very uniform, usually between a few angstroms (Å) and a few nanometers (nm), which allows them to selectively adsorb molecules based on their size, shape and polarity. Molecular sieves are widely used in petrochemicals, air separation, gas purification, drying, catalysis and other fields. Molecular sieves have the following characteristics: Highly ordered microporous structure: The crystal structure of molecular sieves contains a large number of regularly arranged micropores with very uniform pore sizes, usually 3-10 Å. This highly ordered structure enables molecular sieves to selectively adsorb molecules of specific sizes and shapes while excluding other molecules. High specific surface area: Molecular sieves have a very large specific surface area, usually up to 500-1000 square meters per gram of molecular sieve. This gives it a very strong adsorption capacity. Good thermal and chemical stability: Molecular sieves show good stability in high temperature and acid-base environments and are not easy to decompose or deteriorate. This makes them suitable for harsh working conditions such as high temperature, high pressure and corrosive environments.

[0018] Inhibitors are chemicals used to prevent or slow down the spontaneous polymerization of monomers. They are useful in a variety of situations, such as when storing and transporting easily polymerizable monomers, or when controlling the rate of polymerization to obtain a desired polymer structure. Inhibitors stop the polymerization reaction by reacting with free radicals or other reactive intermediates, thereby terminating the chain growth process.

[0019] Compared with the prior art, the advantages and beneficial effects of the present invention are: The invention synthesizes trimethylolpropane ester by reacting trimethylolpropane and aliphatic dibasic acid in the presence of a catalyst, etc.; the esterification rate and conversion rate are improved by optimizing the amount of catalyst, the molar ratio of trimethylolpropane and aliphatic dibasic acid, the reaction temperature, the amount of inhibitor, etc.; the prepared trimethylolpropane ester has good low temperature resistance, oxidation resistance and stability, etc. The trimethylolpropane ester prepared by the invention has a long carbon chain and a flexible structure, can maintain good fluidity at low temperature, and is not easy to solidify or become too viscous; this molecular flexibility helps to reduce the solidification point and glass transition temperature (Tg) of the material, so that it can still maintain good fluidity and mechanical properties under low temperature environment. By adding an antioxidant, free radicals are captured, the chain propagation of the oxidation reaction is prevented, and the oxidation process is delayed. The trimethylolpropane ester of the invention has high thermal stability and is not easy to decompose or deteriorate at high temperature, which enables them to remain stable for a long time under high temperature environment and reduce oxidation and degradation caused by high temperature. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] Example 1

[0022] This embodiment provides a method for synthesizing trimethylolpropane ester, comprising the following steps: S1: Trimethylolpropane and glutaric acid were added to a reactor in a molar ratio of 1:5, and then cyclohexane solvent with a volume twice that of the trimethylolpropane and glutaric acid was added, the temperature was raised to 90°C, and the mixture was stirred at a rate of 500 r / min for 50 min to obtain a mixed solution A; S2: According to the solid-liquid ratio of 1g:15mL, add 200-300 mesh activated carbon into a 35% mass fraction p-toluenesulfonic acid aqueous solution, raise the temperature to 130°C, and stir at a rate of 500r / min for 2h; after filtering, put it into a muffle furnace and calcine it at a temperature of 500°C for 10min to obtain an activated carbon-supported p-toluenesulfonic acid catalyst; Then, 3% of the catalyst by weight of the mixed solution A and 0.5% of the polymerization inhibitor hydroquinone by weight of the mixed solution A were added to step S1, the temperature was raised to 120° C., and the mixture was stirred at a rate of 600 r / min for 1 hour to obtain a mixed solution B; S3: Cooling the mixed solution B in step S2 to 105° C., adding 0.3% of the weight of the mixed solution B in the amount of an antioxidant and 2% of the weight of the mixed solution B in the amount of a water absorbent sodium polyacrylate, and continuing to stir and react at a rate of 500 r / min for 2 h to obtain a mixed solution C; S4: Filter the mixed solution C in step S3, distill the upper mother liquor, the vacuum degree in the evaporator is 8 KPa, the removal temperature is 80° C., and the recombinant fraction is trimethylolpropane ester.

[0023] Example 2

[0024] This embodiment provides a method for synthesizing trimethylolpropane ester, comprising the following steps: S1: Trimethylolpropane and aliphatic dibasic acid (pimelic acid: suberic acid = 3:1) were added into a reactor in a molar ratio of 1:7, and then cyclohexane solvent with a volume of 3 times that of trimethylolpropane and aliphatic dibasic acid was added, the temperature was raised to 100°C, and the mixture was stirred at a rate of 500 r / min for 70 min to obtain a mixed solution A; S2: According to the solid-liquid ratio of 1g:20mL, add 200-300 mesh molecular sieves into a 55% mass fraction p-toluenesulfonic acid aqueous solution, raise the temperature to 110°C, and stir at a rate of 500r / min for 5h; after filtering, put it into a muffle furnace and calcine it at a temperature of 500°C for 25min to obtain a molecular sieve-loaded p-toluenesulfonic acid catalyst; Then, 5% of the catalyst by weight of the mixed solution A and 1.5% of the polymerization inhibitor hydroquinone by weight of the mixed solution A were added to step S1, the temperature was raised to 140° C., and the mixture was stirred at a rate of 600 r / min for 2 h to obtain a mixed solution B; S3: Cooling the mixed solution B in step S2 to 115° C., adding an antioxidant accounting for 0.8% of the weight of the mixed solution B and a water-absorbing agent sodium polyacrylate accounting for 4% of the weight of the mixed solution B, and continuing to stir and react at a rate of 500 r / min for 3 hours to obtain a mixed solution C; S4: Filter the mixed solution C in step S3, distill the upper mother liquor, the vacuum degree in the evaporator is 6 KPa, the removal temperature is 90° C., and the recombinant fraction is trimethylolpropane ester.

[0025] Example 3

[0026] This embodiment provides a method for synthesizing trimethylolpropane ester, comprising the following steps: S1: Trimethylolpropane and aliphatic dibasic acid (zelaic acid: sebacic acid = 1:1.5) were added into a reactor in a molar ratio of 1:6, and then cyclohexane solvent with a volume of 3 times that of trimethylolpropane and aliphatic dibasic acid was added, the temperature was raised to 100°C, and the mixture was stirred at a rate of 500 r / min for 70 min to obtain a mixed solution A; S2: According to the solid-liquid ratio of 1g:25mL, add 200-300 mesh activated carbon to a 35% mass fraction p-toluenesulfonic acid aqueous solution, raise the temperature to 150°C, and stir at a rate of 600r / min for 4h; after filtering, put it into a muffle furnace and calcine it at a temperature of 600°C for 15min to obtain an activated carbon-supported p-toluenesulfonic acid catalyst; Then, 5% of the catalyst by weight of the mixed solution A and 1.5% of the polymerization inhibitor hydroquinone by weight of the mixed solution A were added to step S1, the temperature was raised to 140° C., and the mixture was stirred at a rate of 600 r / min for 2 h to obtain a mixed solution B; S3: Cooling the mixed solution B in step S2 to 115° C., adding an antioxidant accounting for 0.8% of the weight of the mixed solution B and a water-absorbing agent sodium polyacrylate accounting for 4% of the weight of the mixed solution B, and continuing to stir and react at a rate of 500 r / min for 3 hours to obtain a mixed solution C; S4: Filter the mixed solution C in step S3, distill the upper mother liquor, the vacuum degree in the evaporator is 6.5 KPa, the removal temperature is 90° C., and the recombinant fraction is trimethylolpropane ester.

[0027] Comparative Example 1 The difference from Example 1 is that p-toluenesulfonic acid is directly used as a catalyst in step S2, and the other steps remain unchanged.

[0028] Comparative Example 2 The difference from Example 1 is that no polymerization inhibitor is added in step S2, and the other steps remain unchanged.

[0029] Comparative Example 3 The difference from Example 1 is that step S3 is missing, and the other steps remain unchanged.

[0030] Comparative Example 4 The difference from Example 1 is that antioxidant is missing in step S3, and other steps remain unchanged.

[0031] Comparative Example 5 The difference from Example 1 is that the water absorbing agent is missing in step S3, and the other steps remain unchanged.

[0032] Performance Testing: The esterification rate and acid value in the above-mentioned embodiments and comparative examples were applied to the preparation of refrigeration oil. Synthetic oil, mineral oil, and trimethylolpropane ester obtained in the embodiments and comparative examples were mixed, stirred at a temperature of 180°C for 40 minutes, and filtered to obtain water-resistant refrigeration oil. The results are shown in the following table.

[0033] Table 1

[0034] It can be seen from the above performance test results that the trimethylolpropane esters prepared in Examples 1-3 have good performance. In particular, Example 3 has better comprehensive performance. However, since Comparative Examples 1-5 do not adopt the necessary technical solutions, their corresponding performance tests are significantly worse than those of the Examples. The above experimental results further prove the importance of the technical solutions defined in the present invention for its technical effects.

[0035] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for synthesizing trimethylolpropane ester, characterized in that: The steps include: S1: Add trimethylolpropane, solvent and aliphatic dibasic acid into a reaction kettle, heat to 90-100°C, stir and react for 50-70 minutes to obtain a mixed solution A; S2: Add the catalyst and the polymerization inhibitor to step S1, raise the temperature to 120-140°C, and stir the reaction for 1-2h to obtain a mixed solution B; S3: Cooling the mixed solution B in step S2 to 105-115°C, adding an antioxidant and a water absorbent thereto, and continuing to stir and react for 2-3 hours to obtain a mixed solution C; S4: filtering the mixed solution C in step S3, distilling the upper mother solution, and recombining it into trimethylolpropane ester; The amount of catalyst used is 3-5% of the mass of the mixed solution A; the catalyst is activated carbon or molecular sieve loaded p-toluenesulfonic acid solution; The preparation process of activated carbon loaded with p-toluenesulfonic acid is as follows: according to the solid-liquid ratio of 1g:15-25mL, take 200-300 mesh activated carbon and add it to a 35% mass fraction of p-toluenesulfonic acid aqueous solution, increase the temperature to 130-150°C, stir and react for 2-4h; after filtering, put it into a muffle furnace and roast it at a temperature of 500-600°C for 10-15min.

2. The method for synthesizing trimethylolpropane ester according to claim 1, characterized in that: In step S1, the molar ratio of trimethylolpropane to aliphatic dibasic acid is 1:5-7; and the amount of the solvent is 2-3 times the amount of trimethylolpropane and aliphatic dibasic acid.

3. The method for synthesizing trimethylolpropane ester according to claim 1, characterized in that: The solvent in step S1 is cyclohexane; the aliphatic dibasic acid is one or a mixture of glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid.

4. The method for synthesizing trimethylolpropane ester according to claim 1, characterized in that: The preparation process of the molecular sieve loaded with p-toluenesulfonic acid is as follows: according to the solid-liquid ratio of 1g:10-20mL, 200-300 mesh activated carbon is added to a 55% mass fraction p-toluenesulfonic acid aqueous solution, the temperature is increased to 100-110°C, and the reaction is stirred for 3-5h; after filtering, the mixture is placed in a muffle furnace and roasted at a temperature of 400-500°C for 15-25min.

5. The method for synthesizing trimethylolpropane ester according to claim 1, characterized in that: The amount of the polymerization inhibitor in step S2 is 0.5-1.5% of the mass of the mixed solution A; the polymerization inhibitor is hydroquinone or p-hydroxyanisole.

6. The method for synthesizing trimethylolpropane ester according to claim 1, characterized in that: In step S3, the amount of the antioxidant is 0.3-0.8% of the mass of the mixed solution B; the antioxidant is tributyl phosphate or mercaptoacetic acid; the amount of the water absorbent is 2-4% of the mass of the mixed solution B; the water absorbent is polyacrylate.

7. The method for synthesizing trimethylolpropane ester according to claim 1, characterized in that: The parameters of the distillation process in step S4 are: the vacuum degree in the evaporator is less than 10 KPa, and the removal temperature is 80-90°C.

8. Use the trimethylolpropane ester synthesized according to any one of claims 1 to 7 in refrigeration oil.

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