A process for the preparation of an antioxidant

Abstract

The application discloses a method for preparing an antioxidant, comprising the following steps: 1) adding pentaerythritol and dipentaerythritol into a reaction kettle, then adding a catalyst, and finally performing nitrogen replacement; 2) increasing the temperature of the reaction kettle to a first temperature and reacting at the first temperature; 3) increasing the temperature of the reaction kettle to a second temperature which is 10-30 DEG C higher than the first temperature for refluxing, and then evaporating 35-methyl ester; 4) crystallizing at 45-65 DEG C; and 5) cooling, filtering, rinsing with methyl alcohol and drying to obtain the antioxidant 1010. The method adopts a specific catalyst combination, significantly reduces the amount of tin-containing catalyst and tin residue in the finished antioxidant under the condition of ensuring product quality and conversion rate, and has a good application prospect.

Description

Technical Field

[0001] This invention relates to a method for preparing antioxidants, belonging to the field of petrochemicals. Background Technology

[0002] Antioxidant 1010 (CAS No.: 6683-19-8) is a sterically hindered phenolic antioxidant, its Chinese name being pentaerythritol tetrakis(3,5-di-tert-butyl-4-hydroxyphenyl)propionate. It is widely used in the heat treatment of polypropylene, polyethylene, polyoxymethylene, ABS resins, etc., and can extend the service life of plastic products. It can also be used in various synthetic rubbers and petroleum products to improve their heat resistance, and is one of the superior antioxidants currently available.

[0003] Antioxidant 1010 is often prepared using alkaline catalysts. For example, methyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (referred to as "35-methyl ester") can be obtained by transesterification with alcohols such as pentaerythritol and dipentaerythritol in the presence of alkaline catalysts such as sodium tert-butoxide, potassium tert-butoxide, and potassium hydroxide.

[0004] To improve conversion rates, transesterification reactions typically require higher temperatures. However, excessively strong alkaline catalysts can lead to discoloration, negatively impacting product quality. Achieving high conversion rates at higher temperatures and obtaining high-quality antioxidant 1010 in a shorter time is a research trend. Current research focuses on catalyst selection. Among numerous candidate catalysts, lithium acetate, aluminum triisopropoxide, and magnesium acetate are considered unsuitable for reactions with polyols due to their poor reactivity. Lithium amide catalysts exhibit low reaction rates and poor reaction solution color at low temperatures; increasing catalyst dosage and reaction temperature exacerbates the discoloration, further affecting product quality. To date, these problems remain largely unresolved. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this invention provides a method for preparing antioxidants that features reduced tin content and tin residue in the finished antioxidant 1010 while ensuring product quality and conversion rate.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] This invention discloses a method for preparing antioxidants, the method comprising the following steps:

[0008] Step 1): Add pentaerythritol and dipentaerythritol to the reactor, then add the catalyst, then add 35-methyl ester, and finally purge with nitrogen.

[0009] Step 2): the reactor is heated to a first temperature ranging from 140°C to 180°C, and is reacted at this temperature for 2 to 3 hours;

[0010] Step 3): the temperature of the reactor is further heated to a second temperature which is 10°C to 30°C higher than the first temperature, and is not higher than 190°C, the vacuum pump is started, and the reaction is refluxed at the second temperature and under vacuum for 2 to 6 hours, and then the 35-methyl ester is distilled off;

[0011] Step 4): the vacuum pump is stopped, the temperature of the system is lowered to 95 to 105°C under nitrogen protection, an aqueous methanol solution and formic acid are added into the reactor and stirred uniformly, the system is slowly stirred so that the temperature is controlled at 80 to 90°C, and after melting, the temperature is lowered to 45 to 65°C, antioxidant 1010 seed crystals are added, and crystallization is carried out for 1 to 3 hours;

[0012] Step 5): the material in the reactor is cooled in water at 10 to 15°C, filtered, washed with methanol and dried, to obtain the antioxidant 1010.

[0013] Preferably, the catalyst is composed of a first catalyst and a second catalyst, the first catalyst is a tin-containing catalyst, and the second catalyst is lithium acetate and / or lithium amide.

[0014] Preferably, the first catalyst used in combination with the second catalyst is reduced by 80% to 90% relative to the amount used when the first catalyst is used alone.

[0015] Preferably, a step of replacing the reactor with nitrogen is included before step 1).

[0016] Preferably, in step 1), the 35-methyl ester is respectively excessive by 10% to 50%.

[0017] Preferably, the total amount of catalyst is 0.25% to 1.25% relative to the amount of pentaerythritol.

[0018] Preferably, in step 2), the reactor is heated to 145°C, reacted for one hour, then heated to 155°C, reacted for 45 minutes, and then heated to 165°C, reacted for 45 minutes.

[0019] Preferably, the second temperature is 185°C to 190°C; and / or the vacuum degree of the vacuum gauge during the operation of the vacuum pump is -0.09 MPa.

[0020] Preferably, the distillation of the 35-methyl ester is carried out at 190 to 197°C.

[0021] Preferably, the aqueous methanol solution is an aqueous methanol solution with a methanol concentration of 2% to 5% by volume.

[0022] Beneficial effects: can be realized in the case of ensuring product quality (425 nm transmittance reaches more than 98%) and conversion rate (up to 96% based on pentaerythritol), significantly reducing the amount of tin-containing catalyst and tin residue in the finished antioxidant (which can be as low as 0.5 ppm). DETAILED DESCRIPTION

[0023] The application is further described below in conjunction with the embodiments of the specification, but the application is not limited to the following embodiments.

[0024] The application is further described below in conjunction with the embodiments of the specification, but the application is not limited to the following embodiments.

[0025] Step 1): pentaerythritol and dipentaerythritol are added to the reaction kettle, then the catalyst is added, then 35-methyl ester is added, and finally nitrogen replacement is performed;

[0026] Step 2): the reaction kettle is heated to a first temperature in the range of 140°C to 180°C, and reacted at this temperature for 2 to 3 hours;

[0027] Step 3): the temperature of the reaction kettle is further increased to a second temperature which is 10°C to 30°C higher than the first temperature and not higher than 190°C, the vacuum pump is started, and the reflux reaction is performed at the second temperature and under vacuum for 2 to 6 hours, and then the 35-methyl ester is distilled off;

[0028] Step 4): stop the vacuum pump, reduce the system temperature to 95 to 105°C under nitrogen protection, add methanol aqueous solution and formic acid into the reaction kettle and stir uniformly, slowly stir to control the system temperature at 80 to 90°C, after melting through, reduce the temperature to 45 to 65°C, add antioxidant 1010 seed crystals, and crystallize for 1 to 3 hours;

[0029] Step 5): cool the material in the reaction kettle in water at 10 to 15°C, filter, rinse with methanol and dry to obtain the antioxidant 1010.

[0030] The specific embodiments of the application include taking the left endpoint value of the range value to form an embodiment, taking the right endpoint value of the range value to form an embodiment, taking the middle value of the range value to form an embodiment, and taking any value within the range value to form an embodiment.

[0031] For example: a method for preparing an antioxidant, the method comprising the following steps:

[0032] (1) pentaerythritol and dipentaerythritol are added to the reaction kettle, then the catalyst is added, then 35-methyl ester is added, and finally nitrogen replacement is performed;

[0033] (2) the reaction kettle is heated to a first temperature in the range of 140°C to 180°C, and reacted at this temperature for 2 to 3 hours;

[0034] (3) The temperature of the reactor is then raised to a second temperature which is 10 to 30°C higher than the first temperature and not higher than 190°C, the vacuum pump is turned on, and a reflux reaction is carried out at the second temperature under vacuum for 2 to 6 hours, and then the 35-methyl ester is distilled off;

[0035] (4) The vacuum pump is stopped, the temperature of the system is lowered to 95 to 105°C under nitrogen protection, an aqueous methanol solution and formic acid are added into the reactor and stirred uniformly, the system is slowly stirred so that the temperature is controlled at 80 to 90°C, and after melting, the temperature is lowered to 45 to 65°C (for example, 45°C, 55°C or 65°C), a crystal seed of antioxidant 1010 is added, and crystallization is carried out for 1 to 3 hours (for example, 2 hours);

[0036] (5) The material in the reactor is cooled in water at 10 to 15°C, filtered, washed with methanol and dried to obtain the antioxidant 1010.

[0037] In the present application, the 35-methyl ester is 3-(3,5-di-tert-butyl-4- hydroxyphenyl)propionic acid methyl ester (CAS No.: 6386-38-5), which reacts with pentaerythritol under the presence of a catalyst to generate the antioxidant 1010 and release methanol, and the reaction equation is shown as follows:

[0038]

[0039] In the present application, the purity of the 35-methyl ester as the reaction raw material is preferably above 99.5%.

[0040] In some preferred embodiments, the catalyst is composed of a first catalyst and a second catalyst, the first catalyst is a tin-containing catalyst, and the second catalyst is lithium acetate and / or lithium amide.

[0041] In the present application, the tin-containing catalyst can be an alkyl tin compound, for example, an alkyl tin oxide, such as a monoalkyl tin oxide or a dialkyl tin oxide, wherein the alkyl group is, for example, a linear alkyl group or a branched alkyl group containing 1 to 12 carbon atoms, such as methyl, ethyl, propyl, butyl, octyl. More preferably, the alkyl group is butyl. For example, the tin-containing catalyst is monobutyl tin oxide or dibutyl tin oxide. Further more preferably, the tin-containing catalyst is dibutyl tin oxide.

[0042] In the case of being used alone, the amount of the tin-containing catalyst is usually 0.01 to 1% molar %, preferably 0.1 to 0.5 molar % based on the amount of the 35-methyl ester. However, when used in combination with the second catalyst, the amount of the tin-containing catalyst can be reduced to 0.001 to 0.2% molar %, preferably 0.01 to 0.1 molar % based on the amount of the 35-methyl ester.

[0043] Thus, the first catalyst used in conjunction with the second catalyst can be reduced by 80% to 90% relative to the amount used when the first catalyst is used alone.

[0044] In the present application, dipentaerythritol is added to reduce the production of by-products (triple substitution of the hydroxyl group on the 35-methyl ester) in the transesterification reaction.

[0045] It is additionally preferred that a step of replacing the reactor with nitrogen be included prior to step 1). For example, 2 to 4 nitrogen replacements are performed first.

[0046] It is additionally preferred that in step 1), the 35-methyl ester be present in an excess of 10% to 50%, for example 10%, 20%, 30%, 40%, 50%, respectively, to increase the conversion rate of the pentaerythritol.

[0047] It is additionally preferred that the total amount of catalyst be 0.25% to 1.25%, for example 0.25%, 0.50%, 0.75%, 1.0%, 1.25%, relative to the amount of pentaerythritol.

[0048] It is additionally preferred that in step 2), the reactor be heated to 145°C for one hour, then heated to 155°C for 45 minutes, and then heated to 165°C for 45 minutes.

[0049] In some preferred embodiments, the second temperature is 185°C to 190°C, for example 186, 187, 188, 189, or 190°C.

[0050] In some preferred embodiments, the vacuum gauge of the vacuum pump is -0.09 MPa during operation.

[0051] In some preferred embodiments, the evaporation of the 35-methyl ester is performed at 190 to 197°C. For example, after the transesterification reaction is complete, the vacuum pump is stopped, the system temperature is lowered to about 100°C (the cooling process is protected by nitrogen), an aqueous methanol solution (for example, mass ratio 96.5 / 3.5) and formic acid are added to the reactor, the system temperature is controlled at about 85°C while stirring, and after melting (about 10 to 15 minutes), the temperature is lowered to 55°C (the melting process is shortened as much as possible to prevent alcoholysis), seed crystals (for example, 3% to 4% of the pentaerythritol by mass with a bulk density of 0.6 or more) are added, and crystallization is performed for 2 hours while stirring.

[0052] In some preferred embodiments, the aqueous methanol solution is an aqueous methanol solution with a methanol concentration of 2% to 5% by volume, for example, water:methanol = 95:5, 96:4, 96.5:3.5, 97:3, 98:2, to control the bulk density of the antioxidant 1010 obtained.

[0053] The application will be further described by examples below, but the scope of protection of the application is not limited to the examples.

[0054] Example

[0055] The main reagents used in the examples include:

[0056] 35-methyl ester (molecular weight 292.41, purity more than 99.5%);

[0057] Catalyst (monobutyl tin oxide (CAS number: 51590-67-1, molecular weight 191.82), dibutyl tin oxide (CAS number: 818-08-6, molecular weight 248.94), lithium amide (CAS number: 7782-89-0), lithium acetate (CAS number: 546-89-4), all of which are analytical pure);

[0058] Pentaerythritol (molecular weight: 136.15, analytical pure);

[0059] Dipentaerythritol (molecular weight: 254.28, analytical pure);

[0060] Formic acid (purity more than 90%, density: 1.2141, melting point 8.2℃, boiling point 100.5℃);

[0061] Methanol (analytical pure).

[0062] The instruments used include: 1L double-layer glass reaction kettle, constant temperature oil bath circulating tank (heat-conducting silicone oil 100cs, room temperature ~ 200℃), liquid chromatograph (UV detector, chromatographic column specifications: C18, ) and other auxiliary accessories, serpentine condenser, thermometer, glass rod, electronic balance, circulating water vacuum pump, glass thermometer (range 200℃), other commonly used glassware.

[0063] Example 1

[0064] In this example, 35-methyl ester and pentaerythritol are used as raw materials to prepare antioxidant 1010, and the preparation method includes the following steps:

[0065] 1. Replace the 1L glass reaction kettle with nitrogen once and check the airtightness;

[0066] 2. Put 30 g (about 0.220 mole) of pentaerythritol and 0.22 g (0.0009 mole) of dipentaerythritol into a reaction kettle, then add 0.03 g of dibutyl tin oxide, 0.05 g of lithium amide (0.17 mass %) and 0.15 g of anhydrous lithium acetate (0.5 mass %), and finally add 360 g of 35-methyl ester (about 1.225 mole) and perform three nitrogen replacements;

[0067] 3. Raise the temperature of the reaction kettle to 145°C, react for 1 hour, then raise the temperature to 155°C, react for 45 minutes, then raise the temperature to 165°C, react for 45 minutes, and the temperature raising speed is as uniform as possible;

[0068] 4. Then uniformly raise the temperature to 185-190°C, start the vacuum pump, and perform high-temperature reflux reaction, the vacuum gauge is -0.09 MPa, and the 35-methyl ester is obviously refluxed, and the reaction is performed for 3 hours;

[0069] 5. Maintain the temperature of the reaction kettle at about 190°C, perform the operation of evaporating the 35-methyl ester, and collect the unreacted 35-methyl ester, when the outflow is less, raise the temperature to 195-197°C, continue to evaporate for 15 min, and remove the 35-methyl ester completely;

[0070] 6. Stop the vacuum pump, and lower the temperature of the system to about 100°C (the lowering process is protected by nitrogen), add 700 g of methanol aqueous solution (mass ratio 96.5 / 3.5) and 0.3 g of formic acid into the reaction kettle, slowly stir, and control the temperature of the system at about 85°C, slowly lower the temperature to 55°C after melting (10-15 min), add 1 g of crystal seed (the bulk density is above 0.6 of antioxidant 1010), slowly stir, and crystallize for 2 h.

[0071] 7. Put the materials in the kettle into a beaker, and completely cool in water at 10-15°C, and the crystallization is completed;

[0072] 8. Use a Buchner funnel to filter, wash once with methanol, and dry to obtain the finished antioxidant 1010.

[0073] Example 2

[0074] The same as example 1 is basically adopted, except that 0.023 g of monobutyl tin oxide is used instead of the dibutyl tin oxide.

[0075] Example 3

[0076] The same as example 1 is basically adopted, except that the amount of 35-methyl ester is 308 g.

[0077] Example 4

[0078] The same way as example 1 basically, the difference is that the use of 35-methyl ester is 335g.

[0079] Example 5

[0080] The same way as example 3, the difference is that 0.023g of monobutyl tin oxide is used instead of the dibutyl tin oxide.

[0081] Example 6

[0082] The same way as example 4, the difference is that 0.023g of monobutyl tin oxide is used instead of the dibutyl tin oxide.

[0083] Example 7

[0084] The same way as example 1 basically, the difference is that no tin-containing catalyst is added. The antioxidant product prepared in each example is detected by liquid chromatography (see HG / T 3713-2019 for details), and the results are shown in Table 1.

[0085] Table 1. Conversion rate, purity, light transmittance (425nm) and tin content (spectrophotometry) of antioxidant 1010 product prepared in each example.

[0086] Example Conversion (%) Transmittance (%) Tin content (ppm) Example Conversion (%) Transmittance (%) Tin content (ppm) Example Conversion (%) Transmittance (%) Tin 1 96.2 98.6 0.5 2 89.3 98.2 2 3 92.4 98.5 0.8 4 94.5 98.8 0.7 5 87.6 98.5 1.7 6 88.9 98.6 2.1 7 85.4 98.5 -

[0087] Note: "-" means not detected.

[0088] The present application uses a specific catalyst combination, which significantly reduces the amount of tin-containing catalyst and the tin residue (as low as 0.5ppm) of the finished antioxidant product while ensuring product quality and conversion rate (based on pentaerythritol).

[0089] Finally, it should be noted that the present application is not limited to the above examples, but can have many variations. All variations that can be directly derived or inferred from the disclosure of the present application by those of ordinary skill in the art should be considered within the scope of the present application.

Claims

1. A process for the preparation of an antioxidant characterized in that The preparation method comprises the following steps: Step 1): pentae-rythritol and di-pentae-rythritol are added into a reaction kettle, then a catalyst is added, then 35-methyl ester is added, and finally nitrogen replacement is performed; Step 2): the reaction kettle is warmed to a first temperature in the range of 140 DEG C to 180 DEG C, and is reacted at the temperature for 2 to 3 hours; Step 3): the temperature of the reaction kettle is further warmed to a second temperature which is 10 DEG C to 30 DEG C higher than the first temperature and not higher than 190 DEG C, a vacuum pump is started, and a reflux reaction is performed at the second temperature and under vacuum for 2 to 6 hours, and then 35-methyl ester is distilled off; Step 4): the vacuum pump is stopped, the temperature of the system is lowered to 95 to 105 DEG C under nitrogen protection, methanol aqueous solution and formic acid are added into the reaction kettle and stirred uniformly, slow stirring is performed, the temperature of the system is controlled at 80 to 90 DEG C, after melting through, the temperature is lowered to 45 to 65 DEG C, antioxidant 1010 crystal seeds are added, and crystallization is performed for 1 to 3 hours; Step 5): the material in the reaction kettle is cooled in water at 10 to 15 DEG C, is filtered, is washed with methanol and is dried, and the antioxidant 1010 is obtained; The catalyst is composed of a first catalyst and a second catalyst, the first catalyst is a tin-containing catalyst, and the second catalyst is lithium acetate and / or lithium amide; The first catalyst used in cooperation with the second catalyst is reduced by 80% to 90% relative to the amount used when the first catalyst is used alone; A step of replacing the reaction kettle with nitrogen is included before step 1); In step 1), the 35-methyl ester is respectively excessive by 10% to 50%; The total amount of the catalyst is 0.25% to 1.25% relative to the amount of pentae-rythritol.

2. A process for the preparation of an antioxidant as claimed in claim 1, wherein, In step 2), the reaction kettle is warmed to 145 DEG C, is reacted for one hour, is then warmed to 155 DEG C, is reacted for 45 minutes, and is then warmed to 165 DEG C, is reacted for 45 minutes.

3. The process for the preparation of an antioxidant as claimed in claim 1, wherein: The second temperature is 185 DEG C to 190 DEG C; and / or the vacuum degree of the vacuum gauge during the working of the vacuum pump is -0.09 MPa.

4. The method of claim 1, wherein the antioxidant is prepared by the steps of: The distillation of 35-methyl ester is performed at 190 to 197 DEG C.

5. The method of claim 1, wherein the antioxidant is prepared by the steps of: The methanol aqueous solution is a methanol aqueous solution with a methanol concentration of 2% to 5% by volume.

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