A process for the synthesis of liquid methyltetrahydrophthalic anhydride

Abstract

The application belongs to the technical field of anhydride synthesis, and discloses a synthesis method of liquid methyltetrahydrophthalic anhydride. The synthesis method comprises the following steps: adding an isomerization catalyst into crude methyltetrahydrophthalic anhydride, and then performing isomerization rectification for 1-2 hours to obtain liquid methyltetrahydrophthalic anhydride; the temperature of isomerization rectification is 140-200 DEG C, and the vacuum degree of isomerization rectification is -0.09-0.1 MPa. The synthesis method of liquid methyltetrahydrophthalic anhydride can simplify the traditional isomerization and rectification process, complete the high-temperature isomerization and reduced-pressure rectification two-step process in one step, effectively reduce the high-temperature reaction duration by more than 30%, shorten the overall reaction process, and reduce the energy consumption by more than 10%, and the synthesis method can reduce the carbonization and other side reactions, so that the prepared liquid methyltetrahydrophthalic anhydride has good quality.

Description

Technical Field

[0001] This invention belongs to the field of acid anhydride synthesis technology, specifically relating to a method for synthesizing liquid methyltetrahydrophthalic anhydride. Background Technology

[0002] Liquid methyltetrahydrophthalic anhydride is a cyclic carboxylic anhydride with characteristics such as low melting point, low toxicity, low volatility, non-aromatic structure, and ease of use.

[0003] Liquid methyltetrahydrophthalic anhydride exhibits high reactivity and good miscibility with epoxy resins, making it an excellent curing agent for epoxy resins. Using liquid methyltetrahydrophthalic anhydride as a curing agent results in epoxy resins with excellent electrical insulation and mechanical properties, indicating promising market prospects. Currently, the preparation process of liquid methyltetrahydrophthalic anhydride mainly involves a three-stage process: synthesis, isomerization, and vacuum distillation. The isomerization and vacuum distillation stages require high temperatures (generally 200-235℃) and long durations (generally more than 2 hours), resulting in high energy consumption. Furthermore, high temperatures can increase side reactions and even lead to product carbonization and darkening of color, severely affecting the product's appearance.

[0004] Therefore, there is an urgent need to provide a method for synthesizing liquid methyltetrahydrophthalic anhydride that can reduce the time or temperature of isomerization and distillation, thereby reducing energy consumption. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a method for synthesizing liquid methyltetrahydrophthalic anhydride. The synthesis method provided by the present invention can prepare liquid methyltetrahydrophthalic anhydride, and can reduce the time for isomerization and distillation, lower the reaction temperature, and thus significantly reduce energy consumption.

[0006] This invention provides a method for synthesizing liquid methyltetrahydrophthalic anhydride.

[0007] Specifically, a method for synthesizing liquid methyltetrahydrophthalic anhydride includes the following steps:

[0008] An isomerization catalyst is added to crude methyltetrahydrophthalic anhydride, followed by isomerization distillation for 1-2 hours to obtain liquid methyltetrahydrophthalic anhydride. The isomerization distillation temperature is 140℃-200℃, and the vacuum degree of the isomerization distillation is -0.09MPa to -0.1MPa.

[0009] The structural formula of the crude methyltetrahydrophthalic anhydride is shown in formulas (1)-(2), and the liquid methyltetrahydrophthalic anhydride is isomerized methyltetrahydrophthalic anhydride, with structural formulas shown in formulas (3)-(12).

[0010]

[0011] In formulas (1)-(12), the methyl group contains either an a bond or an e bond.

[0012] In the synthesis of liquid methyltetrahydrophthalic anhydride, the inventors discovered that by combining the two-step process of high-temperature isomerization and vacuum distillation into a single-step isomerization distillation method, and by controlling the temperature and vacuum level of the isomerization distillation, not only is the isomerization reaction not affected, but the reaction time is also significantly shortened, and the degree of side reactions is reduced. Compared with the conventional process of high-temperature isomerization followed by vacuum distillation, the synthesis method provided by this invention can produce products with similar or even better performance than traditional products; moreover, it can reduce the reaction temperature, shorten the reaction time, accelerate the reaction process, improve production efficiency, effectively reduce energy consumption, and has high energy efficiency.

[0013] Preferably, the crude methyltetrahydrophthalic anhydride is maleic anhydride methyltetrahydrophthalic anhydride.

[0014] Preferably, the isomerization catalyst comprises anhydrous potassium acetate and / or phosphorus pentoxide.

[0015] Preferably, the amount of the isomerization catalyst added is 0.2%-2% of the mass of the crude methyltetrahydrophthalic anhydride; more preferably, the amount of the isomerization catalyst added is 0.2%-1% of the mass of the crude methyltetrahydrophthalic anhydride.

[0016] Preferably, the temperature of the isomeric distillation is 140℃-190℃, and the vacuum degree of the isomeric distillation is -0.09MPa to -0.098MPa; more preferably, the temperature of the isomeric distillation is 140℃-190℃, and the vacuum degree of the isomeric distillation is -0.095MPa to -0.098MPa.

[0017] Preferably, the time for the isomeric distillation is 1.5-2 hours.

[0018] Preferably, the crude methyltetrahydrophthalic anhydride is prepared as follows: pentadiene, maleic anhydride, and a polymerization inhibitor are mixed and then subjected to an addition reaction. After the reaction is complete, unreacted pentadiene is removed under reduced pressure to obtain crude methyltetrahydrophthalic anhydride.

[0019] Preferably, the addition reaction is carried out at a temperature of 50-70°C for 2-4 hours.

[0020] Preferably, the polymerization inhibitor is an aromatic phenolic compound, such as p-tert-butylcatechol.

[0021] Preferably, the pentadiene is isoprene or / and isoprene.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] The method for synthesizing liquid methyltetrahydrophthalic anhydride provided by this invention simplifies the traditional isomerization and distillation process, completing the two-step process of high-temperature isomerization and vacuum distillation in one step. This not only effectively reduces the duration of high-temperature reaction by more than 30%, shortens the overall reaction process, and reduces energy consumption by more than 10%, but also reduces the generation of side reactions such as carbonization, resulting in liquid methyltetrahydrophthalic anhydride with good quality. Detailed Implementation

[0024] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention.

[0025] Unless otherwise specified, the raw materials, reagents or devices used in the following examples are available from conventional commercial sources or can be obtained by existing known methods.

[0026] Example 1

[0027] A method for synthesizing liquid methyltetrahydrophthalic anhydride includes the following steps:

[0028] Add 400g of maleic anhydride to a 2000mL flask, heat to melt, then add 0.8g of p-tert-butylcatechol, stir well, and then add 536g of mixed pentadiene (the mass ratio of isoprene to pentadiene is 1:1, the same below). The reaction temperature is 60℃, and after reacting for 2 hours, remove the unreacted mixed pentadiene under reduced pressure to obtain the crude product.

[0029] Add 2.5g of anhydrous potassium acetate to the crude product, then heat to 140℃ and perform isomerization distillation under a vacuum of -0.095MPa. Collect the fraction with a stable intermediate boiling point. The isomerization distillation is completed after 2 hours. The collected fraction is liquid methyltetrahydrophthalic anhydride.

[0030] The calculated overall product yield is 60%.

[0031] Comparative Example 1

[0032] A method for synthesizing liquid methyltetrahydrophthalic anhydride includes the following steps:

[0033] Add 400g of maleic anhydride to a 2000mL flask, heat to melt, then add 0.8g of p-tert-butylcatechol, stir well, and then add 536g of mixed pentadiene dropwise. The reaction temperature is 60℃. After reacting for 2 hours, remove the unreacted mixed pentadiene under reduced pressure to obtain the crude product.

[0034] Add 2.5g of anhydrous potassium acetate to the crude product, then heat to 140℃ and isomerize for 3 hours. Then distill under a vacuum of -0.095MPa to collect the fraction with a stable intermediate boiling point. Stop the distillation after 2 hours and collect the fraction as liquid methyltetrahydrophthalic anhydride.

[0035] The calculated overall product yield is 58%.

[0036] Comparative Example 2

[0037] A method for synthesizing methyltetrahydrophthalic anhydride includes the following steps:

[0038] Add 400g of maleic anhydride to a 2000mL flask, heat to melt, then add 0.8g of p-tert-butylcatechol, stir well, and then add 536g of mixed pentadiene dropwise. The reaction temperature is 60℃. After reacting for 2 hours, remove the unreacted mixed pentadiene under reduced pressure to obtain the crude product.

[0039] Add 2.5g of anhydrous potassium acetate to the crude product, then heat to 130℃ and perform isomerization distillation under a vacuum of -0.095MPa. No obvious fractions were distilled off. After cooling to room temperature, the product in the reactor was solid and liquid methyltetrahydrophthalic anhydride could not be obtained.

[0040] Example 2

[0041] A method for synthesizing liquid methyltetrahydrophthalic anhydride includes the following steps:

[0042] Add 800g of crude methyltetrahydrophthalic anhydride (purity >99%, maleic anhydride) to a 2000mL flask, heat to melt, then add 2g of phosphorus pentoxide, raise the temperature to 200℃, and perform isomerization distillation under a vacuum of -0.095MPa. Collect the fraction with a stable intermediate boiling point. Stop the isomerization distillation after 2 hours, and collect the fraction as liquid methyltetrahydrophthalic anhydride.

[0043] The product yield was calculated to be 90%.

[0044] The difference between Example 1 and Example 2 is that Example 1 starts with maleic anhydride, synthesizes crude methyltetrahydrophthalic anhydride, and then obtains liquid methyltetrahydrophthalic anhydride through isomerization distillation; while Example 2 directly obtains liquid methyltetrahydrophthalic anhydride from crude methyltetrahydrophthalic anhydride through isomerization distillation. The product yield in Example 1 also includes the yield of the synthesized crude product. Because a portion of the mixed pentadiene (>30%) cannot react during the synthesis, a significant loss in yield occurs, hence the huge difference between the yields of Example 1 and Example 2.

[0045] Comparative Example 3

[0046] A method for synthesizing liquid methyltetrahydrophthalic anhydride includes the following steps:

[0047] Add 800g of crude methyltetrahydrophthalic anhydride (purity >99%, maleic anhydride) to a 2000mL flask, heat to melt, add 2g of phosphorus pentoxide, heat to 200℃, isomerize for 2 hours, then distill under a vacuum of -0.095MPa, collect the fraction with a stable intermediate boiling point, stop distillation after 1 hour, and collect the fraction as liquid methyltetrahydrophthalic anhydride.

[0048] The calculated product yield is 89%.

[0049] Product effectiveness test

[0050] The properties of methyltetrahydrophthalic anhydride or liquid methyltetrahydrophthalic anhydride prepared in Examples 1-2 and Comparative Examples 1-3 were tested, specifically including color, crystallization point, viscosity, acid value, and anhydride content. Color: tested according to GB / T 9281; a higher value indicates a darker color and more severe side reactions such as carbonization. Crystallization point: tested after refrigeration for 24 hours. Viscosity: tested using an Anton Paar viscometer at 25°C. Acid value: tested according to chemical acid-base titration methods. Anhydride content: tested according to the acetone-methanol esterification followed by acid-base titration method. The test results are shown in Table 1.

[0051] Table 1

[0052]

[0053]

[0054] As shown in Table 1, the liquid methyltetrahydrophthalic anhydride prepared in the embodiments of the present invention exhibits excellent performance, similar to or even superior to commercially available products. However, the synthesis method provided in the embodiments of the present invention has a significantly shorter high-temperature reaction time than the comparative example, with isomerization distillation time not exceeding 2 hours. This reduces the high-temperature reaction duration by more than 30%, lowers energy consumption by more than 10%, shortens the overall reaction process, improves production efficiency, and is more conducive to industrial production.

[0055] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for synthesizing liquid methyltetrahydrophthalic anhydride, characterized in that, Includes the following steps: An isomerization catalyst was added to crude methyltetrahydrophthalic anhydride, followed by isomerization distillation for 1-2 hours to obtain liquid methyltetrahydrophthalic anhydride; the isomerization distillation temperature was 140℃-190℃, and the vacuum degree of the isomerization distillation was -0.09MPa to -0.098MPa. The isomerization catalyst comprises anhydrous potassium acetate and / or phosphorus pentoxide; the amount of the isomerization catalyst added is 0.2%-2% of the mass of the crude methyltetrahydrophthalic anhydride.

2. The synthesis method according to claim 1, characterized in that, The crude methyltetrahydrophthalic anhydride is maleic anhydride in the form of methyltetrahydrophthalic anhydride.

3. The synthesis method according to claim 1, characterized in that, The amount of the isomerization catalyst added is 0.2%-1% of the mass of the crude methyltetrahydrophthalic anhydride.

4. The synthesis method according to claim 3, characterized in that, The temperature of the isomerization distillation is 140℃-190℃, and the vacuum degree of the isomerization distillation is -0.095MPa to -0.098MPa.

5. The synthesis method according to claim 1 or 4, characterized in that, The time for the heterodistillation is 1.5-2 hours.

6. The synthesis method according to claim 1, characterized in that, The preparation method of the crude methyltetrahydrophthalic anhydride is as follows: pentadiene, maleic anhydride, and polymerization inhibitor are mixed and then subjected to an addition reaction. After the reaction is completed, unreacted pentadiene is removed under reduced pressure to obtain crude methyltetrahydrophthalic anhydride.

7. The synthesis method according to claim 6, characterized in that, The polymerization inhibitor is an aromatic phenolic compound.

8. The synthesis method according to claim 6, characterized in that, The pentadiene is isoprene or / and isoprene.

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