Method for isomerizing methyltetrahydrophthalic anhydride

Abstract

To provide a method for isomerizing methyltetrahydrophthalic anhydride.SOLUTION: A method for isomerizing methyltetrahydrophthalic anhydride includes the following steps. A liquid reactant is provided. Under a condition of injecting nitrogen gas, an alkaline catalyst is added into the liquid reactant for an isomerization reaction, so as to obtain an isomerization product. Herein, the liquid reactant includes 3-methyltetrahydrophthalic anhydride and 4-methyltetrahydrophthalic anhydride. Based on a total weight of the isomerization product being 100 wt.%, an amount of a methyltetrahydrophthalic anhydride dimer is less than 1.6 wt.%.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for isomerizing methyltetrahydrophthalic anhydride, and more particularly to a method for isomerizing methyltetrahydrophthalic anhydride which is less likely to produce methyltetrahydrophthalic anhydride dimers during the production process. [Background technology]

[0002] Methyltetrahydrophthalic anhydride has good heat resistance and stability, and can maintain good physical and electrical properties even in high temperature environments, so it is widely used as a curing agent for organic acid anhydride-cured epoxy resins.

[0003] Generally, the reactants for synthesizing methyltetrahydrophthalic anhydride include piperylene, isoprene and acid anhydride. In the prior art, the method for producing methyltetrahydrophthalic anhydride is to add the measured reactants to a reactor at one time, and then carry out Diels-Alder reaction (also called addition reaction to conjugated dienes) to produce methyltetrahydrophthalic anhydride. Then, the properties of methyltetrahydrophthalic anhydride can be improved by isomerizing methyltetrahydrophthalic anhydride with an acid catalyst (e.g., sulfuric acid, p-toluenesulfonic acid).

[0004] However, the temperature required for the isomerization of methyltetrahydrophthalic anhydride is relatively high, which leads to dimerization of methyltetrahydrophthalic anhydride and a decrease in the yield of the final product. Therefore, it is an important task for this project to improve the yield of methyltetrahydrophthalic anhydride by improving the process to avoid the dimerization reaction. Summary of the Invention [Problem to be solved by the invention]

[0005] The technical problem to be solved by the present invention is to provide a method for isomerizing methyltetrahydrophthalic anhydride in response to the shortcomings of the prior art. [Means for solving the problem]

[0006] In order to solve the above technical problems, one technical means adopted by the present invention provides a method for isomerizing methyltetrahydrophthalic anhydride. The method for isomerizing methyltetrahydrophthalic anhydride includes providing a liquid reactant, and adding an alkali catalyst to the liquid reactant under nitrogen gas flow to carry out an isomerization reaction to obtain an isomerization product. The liquid reactant includes 3-methyltetrahydrophthalic anhydride and 4-methyltetrahydrophthalic anhydride. The content of methyltetrahydrophthalic anhydride dimer is less than 1.6% by weight, based on the total weight of the isomerization product being 100% by weight.

[0007] In one embodiment, the liquid reactants undergo the isomerization reaction at a temperature between 140°C and 160°C.

[0008] In one embodiment, nitrogen gas is continuously introduced during the isomerization reaction, and the amount of nitrogen gas introduced is 0.4 L / h to 0.8 L / h.

[0009] In one embodiment, oxygen gas and water in the liquid reactant are removed by introducing nitrogen gas into the liquid reactant, and then an alkali catalyst is added to the liquid reactant to carry out the isomerization reaction.

[0010] In one embodiment, nitrogen gas is bubbled into the liquid reactants to remove oxygen gas and moisture in the liquid reactants.

[0011] In one embodiment, the liquid reactants undergo an isomerization reaction in a reaction tank, and oxygen gas and water are removed from the reaction tank by introducing nitrogen gas into the reaction tank.

[0012] In one embodiment, the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride (trans-3-methyltetrahydrophthalic anhydride:cis-3-methyltetrahydrophthalic anhydride) in the isomerization product is 4:1 to 5:1.

[0013] In one embodiment, the amount of the alkali catalyst added is 0.5 parts by weight to 1.5 parts by weight, based on 100 parts by weight of the total weight of the liquid reactants.

[0014] In one embodiment, the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride (trans-3-methyltetrahydrophthalic anhydride:cis-3-methyltetrahydrophthalic anhydride) in the liquid reactant is 1:4 to 1:7.

[0015] In one embodiment, the weight ratio of 3-methyltetrahydrophthalic anhydride to 4-methyltetrahydrophthalic anhydride in the liquid reactant is from 7:3 to 3:7. Effect of the Invention

[0016] The advantageous effect of the present invention is that the method for isomerizing methyltetrahydrophthalic anhydride according to the present invention has a technical feature of "obtaining an isomerized product by adding an alkali catalyst to a liquid reactant in a nitrogen gas flow state and carrying out an isomerization reaction", which reduces the possibility of producing methyltetrahydrophthalic anhydride dimer and improves the yield of isomerized methyltetrahydrophthalic anhydride. [Brief description of the drawings]

[0017] [Figure 1] 1 is a flow chart of the methyltetrahydrophthalic anhydride isomerization process of the present invention. [Diagram 2] FIG. 1 is a schematic diagram of an apparatus for isomerizing methyltetrahydrophthalic anhydride of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] In order to better understand the features and technical contents of the present invention, please refer to the following detailed description of the present invention and the accompanying drawings, which are provided for reference and explanation only and are not intended to limit the scope of the present invention.

[0019] The "method for isomerizing methyltetrahydrophthalic anhydride" according to the embodiment of the present invention will be described below by way of certain specific embodiments, and those skilled in the art will be able to understand the advantages and effects of the present invention based on the contents disclosed herein. The present invention can be implemented or applied by other different specific embodiments, and various modifications and changes can be made to each detail in the present specification based on different perspectives and applications without departing from the concept of the present invention. In addition, as described in advance, the accompanying drawings of the present invention are simple schematic illustrations and are not drawn to actual size. The technical contents of the present invention will be described in more detail based on the following embodiments, but the disclosure does not limit the scope of protection of the present invention. In addition, the term "or" used in the present specification may include any one or more combinations of the relevant items listed according to the actual situation.

[0020] In order to solve the problem of low yield of methyltetrahydrophthalic anhydride due to easy dimerization of methyltetrahydrophthalic anhydride, the present invention introduces nitrogen gas during the isomerization process of methyltetrahydrophthalic anhydride, thereby avoiding the dimerization of methyltetrahydrophthalic anhydride and improving the yield of methyltetrahydrophthalic anhydride.

[0021] In addition, in the present invention, oxygen gas and moisture in the liquid reactant containing 3-methyltetrahydrophthalic anhydride and 4-methyltetrahydrophthalic anhydride are removed by introducing nitrogen gas into the liquid reactant. The oxygen gas and moisture in the system can be discharged together by introducing and discharging nitrogen gas. In addition, compared with introducing nitrogen gas into the system, directly introducing nitrogen gas into the liquid reactant has a higher efficiency of removing oxygen gas and moisture in the system, and can reduce the possibility of the dimerization reaction of methyltetrahydrophthalic anhydride occurring.

[0022] The present invention will be described with reference to Figures 1 and 2. Figure 1 is a flow chart of the method for isomerizing methyltetrahydrophthalic anhydride of the present invention. Figure 2 is a schematic diagram of an apparatus for isomerizing methyltetrahydrophthalic anhydride of the present invention. The apparatus shown in Figure 2 can be used to carry out the present invention, but the process of the present invention is not limited thereto.

[0023] In step S1, a liquid reactant comprising 3-methyltetrahydrophthalic anhydride and 4-methyltetrahydrophthalic anhydride is provided.

[0024] Due to the difference in three-dimensional structure, 3-methyltetrahydrophthalic anhydride has optical isomers. Specifically, 3-methyltetrahydrophthalic anhydride includes trans-3-methyltetrahydrophthalic anhydride and cis-3-methyltetrahydrophthalic anhydride. In the liquid reactant, the content of trans-3-methyltetrahydrophthalic anhydride is less than that of cis-3-methyltetrahydrophthalic anhydride. For example, the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride (trans-3-methyltetrahydrophthalic anhydride:cis-3-methyltetrahydrophthalic anhydride) may be 1:4, 1:4.5, 1:5, 1:5.5, 1:6, 1:6.5 or 1:7, but the present invention is not limited thereto.

[0025] More specifically, the 3-methyltetrahydrophthalic anhydride in the liquid reactant may be produced by the addition reaction of maleic anhydride with piperylene, and the 4-methyltetrahydrophthalic anhydride in the liquid reactant may be produced by the addition reaction of maleic anhydride with isoprene.

[0026] In one exemplary embodiment, maleic anhydride and piperylene are first added to a reaction tank, and a first addition reaction is carried out at a temperature of 80°C to 120°C. In the first addition reaction, 3-methyltetrahydrophthalic anhydride is produced by the reaction of maleic anhydride with piperylene. Next, isoprene is added to the reaction tank, and a second addition reaction is carried out at a temperature of 80°C to 120°C. In the second addition reaction, 4-methyltetrahydrophthalic anhydride is produced by the reaction of maleic anhydride with isoprene.

[0027] In order to adjust the contents of 3-methyltetrahydrophthalic anhydride and 4-methyltetrahydrophthalic anhydride, the first addition reaction may be terminated when the conversion rate of maleic anhydride reaches 25% or more. That is, the content of 3-methyltetrahydrophthalic anhydride contained in the methyltetrahydrophthalic anhydride produced according to the present invention is at least 25%. Specifically, the first addition reaction may be terminated when the conversion rate of maleic anhydride reaches 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75% or 80%, but the present invention is not limited thereto.

[0028] Since the melting point of 3-methyltetrahydrophthalic anhydride is lower than that of 4-methyltetrahydrophthalic anhydride, when the content of 3-methyltetrahydrophthalic anhydride in the liquid reactant is low, the liquid reactant has a relatively high viscosity. When the content of 3-methyltetrahydrophthalic anhydride in the liquid reactant is high, the liquid reactant has a relatively low viscosity. Therefore, the present invention adjusts the viscosity of the curing agent by controlling the weight ratio of 3-methyltetrahydrophthalic anhydride and 4-methyltetrahydrophthalic anhydride, which is favorable for the progress of the subsequent reaction (for example, by introducing nitrogen gas). For example, the viscosity of the liquid reactant may be 50 cps to 100 cps, but the present invention is not limited thereto.

[0029] In step S2, an isomerization reaction is carried out by adding an alkali catalyst to the liquid reactant while passing nitrogen gas through the liquid reactant, thereby obtaining an isomerization product.

[0030] In one exemplary embodiment, the isomerization reaction is carried out at a temperature of 140° C. to 160° C. Before the isomerization reaction, the content of trans-3-methyltetrahydrophthalic anhydride in the liquid reactant is less than the content of cis-3-methyltetrahydrophthalic anhydride. After the isomerization reaction, the content of trans-3-methyltetrahydrophthalic anhydride in the liquid reactant is greater than the content of cis-3-methyltetrahydrophthalic anhydride.

[0031] However, in an environment where oxygen and moisture are present, oxygen and moisture promote the opening of the double bond of methyltetrahydrophthalic anhydride. At high temperatures or in the presence of an initiator, the opened double bond of methyltetrahydrophthalic anhydride may undergo polymerization reaction to produce methyltetrahydrophthalic anhydride dimer.

[0032] In the present invention, no initiator is added, but the high temperature (140°C to 160°C) during the isomerization reaction may cause polymerization of methyltetrahydrophthalic anhydride into methyltetrahydrophthalic anhydride dimer. That is, dimerization of methyltetrahydrophthalic anhydride may occur simultaneously with the isomerization reaction at high temperature.

[0033] In order to avoid the formation of methyltetrahydrophthalic anhydride dimer, in the present invention, oxygen gas and moisture are removed from the system by introducing nitrogen gas into the system. The oxygen gas and moisture contained in the system come from the addition of raw materials or are originally present in the pipes of the device, and therefore cannot be intentionally avoided.

[0034] As shown in Fig. 2, liquid reactant L is placed in a reaction tank R, and nitrogen gas is introduced through an air supply pipe 1 at the bottom of the reaction tank R, and the nitrogen gas is introduced in the form of bubbles into the liquid reactant L, thereby replacing the oxygen gas and moisture in the liquid reactant. Then, the nitrogen gas is discharged through an exhaust pipe 2 at the top of the reaction tank R so that the oxygen gas and moisture in the reaction tank R are discharged together.

[0035] In another embodiment, the oxygen gas and moisture in the reaction tank R may be replaced by introducing nitrogen gas through another air supply pipe 3 at the top of the reaction tank R and discharging it from the exhaust pipe 2 at the top of the reaction tank R. In addition, the introduction of nitrogen gas creates a pressure difference between both sides of the reaction tank R, so that the oxygen gas and moisture in the liquid reactant L are simultaneously discharged when the nitrogen gas is discharged.

[0036] Both of the above-mentioned two methods of introducing nitrogen gas can achieve the effect of removing oxygen gas and moisture in the system, but the present invention is not limited thereto.

[0037] In this way, oxygen gas and moisture that promote the opening of the double bond of methyltetrahydrophthalic anhydride are not contained in the reaction tank R. Even if the reaction tank R is heated to 140°C to 160°C to carry out the isomerization reaction, it is not easy to produce an excessive amount of methyltetrahydrophthalic anhydride dimer.

[0038] Therefore, in order to effectively reduce the production of methyltetrahydrophthalic anhydride dimer, nitrogen gas is introduced into the reaction tank R before heating, and the introduction of nitrogen gas is stopped after the isomerization reaction is completed and the reaction tank is cooled.

[0039] In the isomerization reaction, the amount of nitrogen gas introduced may be 0.4 L / h to 0.8 L / h, preferably 0.5 L / h, 0.6 L / h or 0.7 L / h. If the amount of nitrogen gas introduced is too low, the effect of suppressing the production of methyltetrahydrophthalic anhydride dimer is poor, and if the amount of nitrogen gas introduced is too high, it is not economical for the production process.

[0040] In one exemplary embodiment, the content of methyl tetrahydrophthalic anhydride dimer is monitored by gel permeation chromatography (GPC) (Shimadzu, model number: NEXERA LC40D GPC).

[0041] The content of methyltetrahydrophthalic anhydride dimer is less than 1.6 wt%, based on the total weight of the isomerization product being 100. Specifically, the content of methyltetrahydrophthalic anhydride dimer may be 1.5 wt%, 1.4 wt%, 1.3 wt%, 1.2 wt%, 1.0 wt%, 0.8 wt%, 0.7 wt%, or 0.6 wt%, based on the total weight of the isomerization product being 100.

[0042] In addition, in the present invention, an isomerization reaction is carried out by adding an alkali catalyst. The addition of an alkali catalyst can reduce the viscosity of the curing agent. Thus, the low-viscosity curing agent according to the present invention has good processability and wider applications. To be more specific, the viscosity of the isomerization product is 30 cps to 40 cps.

[0043] For example, the alkaline catalyst may be an organic base or an inorganic base. The organic base may be an alkanolamine, in particular selected from the group consisting of ethanolamine, diethanolamine and triethanolamine. The inorganic base may be selected from the group consisting of potassium carbonate, sodium carbonate, sodium hydroxide and potassium hydroxide.

[0044] After removing oxygen gas and water, there is no need to worry about the double bond opening during the isomerization reaction of methyltetrahydrophthalic anhydride to produce methyltetrahydrophthalic anhydride dimer, so a relatively large amount of alkali catalyst can be added to accelerate the isomerization reaction. In one exemplary embodiment, the total weight of the liquid reactants is 100 parts by weight, and the amount of alkali catalyst added can be 0.5 parts by weight to 1.5 parts by weight.

[0045] After the isomerization reaction, the content of trans-3-methyltetrahydrophthalic anhydride in the isomerization product is higher than the content of cis-3-methyltetrahydrophthalic anhydride. Specifically, the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerization product can be monitored by gas chromatography (GC) (brand: Agilent, product number: 8860 GC).

[0046] In one exemplary embodiment, the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerization product (trans-3-methyltetrahydrophthalic anhydride:cis-3-methyltetrahydrophthalic anhydride) may be 3:1 to 6:1. Preferably, the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerization product (trans-3-methyltetrahydrophthalic anhydride:cis-3-methyltetrahydrophthalic anhydride) is 4:1 to 5:1. Specifically, the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerization product (trans-3-methyltetrahydrophthalic anhydride:cis-3-methyltetrahydrophthalic anhydride) may be 3.5:1, 4.2:1, 4.5:1, 4.7:1, 5.0:1, or 5.5:1.

[0047] In step S3, the isomerization product is subjected to reduced pressure distillation to remove methyltetrahydrophthalic anhydride dimers and obtain methyltetrahydrophthalic anhydride.

[0048] The content of methyltetrahydrophthalic anhydride dimer in the isomerization product is not high, so that an ideal purity can be achieved by a relatively short treatment time.In addition, when a fixed amount of raw material is used, the isomerization method of methyltetrahydrophthalic anhydride of the present invention can achieve a higher yield.

[0049] In order to explain the method for isomerizing methyltetrahydrophthalic anhydride of the present invention, the following Examples 1 to 7 and Comparative Examples 1 and 2 will be used. The reaction parameters and characteristic measurements of Examples 1 to 5 are as shown in Table 1. The reaction parameters and characteristic measurements of Examples 6 to 7 and Comparative Examples 1 and 2 are as shown in Table 2.

[0050] [Example 1] A liquid reactant having a total weight of 10,000 kg was charged into the reaction tank. The liquid reactant contained 7,500 kg of 3-methyltetrahydrophthalic anhydride and 2,500 kg of 4-methyltetrahydrophthalic anhydride. Here, the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in 3-methyltetrahydrophthalic anhydride (trans-3-methyltetrahydrophthalic anhydride:cis-3-methyltetrahydrophthalic anhydride) was 1:6. For ease of explanation, in Tables 1 and 2, the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in 3-methyltetrahydrophthalic anhydride is referred to as the trans / cis ratio of MTHPA.

[0051] Nitrogen gas was introduced into the bottom of the reaction tank, and the nitrogen gas was introduced directly into the liquid reactant in the form of bubbles, thereby removing oxygen gas and water from the liquid reactant. Under the condition of continuing to introduce nitrogen gas, the reaction tank was heated to 140°C and 150 kg of sodium hydroxide (alkali catalyst) was added to carry out an isomerization reaction. That is, the amount of the alkali catalyst added was 1.5 parts by weight per 100 parts by weight of the liquid reactant. For the sake of simplicity, the amount of the alkali catalyst added (relative to the liquid reactant) in the following was 1.5 / 100.

[0052] During the isomerization process, when the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerization product measured by gas chromatography exceeds 4:1, the isomerization reaction is terminated to obtain the isomerization product, and the total time of the isomerization reaction in Example 1 is 24 hours.

[0053] When the isomerized product was measured by gel permeation chromatography, the content of methyltetrahydrophthalic anhydride dimer was 1.1% by weight, with the total weight of the isomerized product being 100% by weight.When the isomerized product was measured by gas chromatography, the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerized product was 4.21:1.

[0054] [Example 2] A liquid reactant having a total weight of 10,000 kg was charged into the reaction tank. The liquid reactant contained 7,500 kg of 3-methyltetrahydrophthalic anhydride and 2,500 kg of 4-methyltetrahydrophthalic anhydride. The content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in 3-methyltetrahydrophthalic anhydride (trans-3-methyltetrahydrophthalic anhydride:cis-3-methyltetrahydrophthalic anhydride) was 1:6.

[0055] Nitrogen gas was introduced into the bottom of the reaction tank, and the nitrogen gas was introduced directly into the liquid reactant in the form of bubbles, thereby removing oxygen gas and water from the liquid reactant. Under the condition of continuing to introduce nitrogen gas, the reaction tank was heated to 150°C and 150 kg of sodium hydroxide (alkali catalyst) was added to carry out the isomerization reaction.

[0056] During the isomerization process, when the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerization product measured by gas chromatography exceeds 4:1, the isomerization reaction is terminated to obtain the isomerization product, and the total time of the isomerization reaction in Example 2 is 6 hours.

[0057] When the isomerized product was measured by gel permeation chromatography, the content of methyltetrahydrophthalic anhydride dimer was 0.53% by weight, with the total weight of the isomerized product being 100% by weight.When the isomerized product was measured by gas chromatography, the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerized product was 4.17:1.

[0058] [Example 3] A liquid reactant having a total weight of 10,000 kg was charged into the reaction tank. The liquid reactant contained 7,500 kg of 3-methyltetrahydrophthalic anhydride and 2,500 kg of 4-methyltetrahydrophthalic anhydride. The content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in 3-methyltetrahydrophthalic anhydride (trans-3-methyltetrahydrophthalic anhydride:cis-3-methyltetrahydrophthalic anhydride) was 1:6.

[0059] Nitrogen gas was introduced into the bottom of the reaction tank, and the nitrogen gas was introduced directly into the liquid reactant in the form of bubbles, thereby removing oxygen gas and water from the liquid reactant. Under the condition of continuing to introduce nitrogen gas, the reaction tank was heated to 150°C and 50 kg of sodium hydroxide (alkali catalyst) was added to carry out the isomerization reaction.

[0060] During the isomerization process, when the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerization product measured by gas chromatography exceeds 4:1, the isomerization reaction is terminated to obtain the isomerization product, and the total time of the isomerization reaction in Example 3 is 36.5 hours.

[0061] When the isomerization product was measured by gel permeation chromatography, the content of methyltetrahydrophthalic anhydride dimer was 0.79% by weight, with the total weight of the isomerization product being 100% by weight.When the isomerization product was measured by gas chromatography, the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerization product was 4.23:1.

[0062] [Example 4] A liquid reactant having a total weight of 10,000 kg was charged into the reaction tank. The liquid reactant contained 7,500 kg of 3-methyltetrahydrophthalic anhydride and 2,500 kg of 4-methyltetrahydrophthalic anhydride. The content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in 3-methyltetrahydrophthalic anhydride (trans-3-methyltetrahydrophthalic anhydride:cis-3-methyltetrahydrophthalic anhydride) was 1:6.

[0063] Nitrogen gas was introduced into the bottom of the reaction tank, and the nitrogen gas was introduced directly into the liquid reactant in the form of bubbles, thereby removing oxygen gas and water from the liquid reactant. Under the condition of continuing to introduce nitrogen gas, the reaction tank was heated to 140°C and 100 kg of sodium hydroxide (alkali catalyst) was added to carry out the isomerization reaction.

[0064] During the isomerization process, when the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerization product measured by gas chromatography exceeds 4:1, the isomerization reaction is terminated to obtain the isomerization product, and the total time of the isomerization reaction in Example 4 is 26 hours.

[0065] When the isomerized product was measured by gel permeation chromatography, the content of methyltetrahydrophthalic anhydride dimer was 1.24% by weight, with the total weight of the isomerized product being 100% by weight.When the isomerized product was measured by gas chromatography, the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerized product was 4.19:1.

[0066] [Example 5] A liquid reactant having a total weight of 10,000 kg was charged into the reaction tank. The liquid reactant contained 7,500 kg of 3-methyltetrahydrophthalic anhydride and 2,500 kg of 4-methyltetrahydrophthalic anhydride. The content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in 3-methyltetrahydrophthalic anhydride (trans-3-methyltetrahydrophthalic anhydride:cis-3-methyltetrahydrophthalic anhydride) was 1:6.

[0067] Nitrogen gas was introduced into the bottom of the reaction tank, and the nitrogen gas was introduced directly into the liquid reactant in the form of bubbles, thereby removing oxygen gas and water from the liquid reactant. Under the condition of continuing to introduce nitrogen gas, the reaction tank was heated to 140°C and 50 kg of sodium hydroxide (alkali catalyst) was added to carry out the isomerization reaction.

[0068] During the isomerization process, when the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerization product measured by gas chromatography exceeds 4:1, the isomerization reaction is terminated to obtain the isomerization product, and the total time of the isomerization reaction in Example 5 is 72 hours.

[0069] When the isomerized product was measured by gel permeation chromatography, the content of methyltetrahydrophthalic anhydride dimer was 1.31% by weight, with the total weight of the isomerized product being 100% by weight.When the isomerized product was measured by gas chromatography, the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerized product was 4.11:1.

[0070] [Example 6] A liquid reactant having a total weight of 10,000 kg was charged into the reaction tank. The liquid reactant contained 7,500 kg of 3-methyltetrahydrophthalic anhydride and 2,500 kg of 4-methyltetrahydrophthalic anhydride. The content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in 3-methyltetrahydrophthalic anhydride (trans-3-methyltetrahydrophthalic anhydride:cis-3-methyltetrahydrophthalic anhydride) was 1:6.

[0071] Nitrogen gas was introduced into the bottom of the reaction tank, and the nitrogen gas was introduced directly into the liquid reactant in the form of bubbles, thereby removing oxygen gas and water from the liquid reactant. Under the condition of continuing to introduce nitrogen gas, the reaction tank was heated to 160°C and 150 kg of sodium hydroxide (alkali catalyst) was added to carry out the isomerization reaction.

[0072] During the isomerization process, when the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerization product measured by gas chromatography exceeds 4:1, the isomerization reaction is terminated to obtain the isomerization product, and the total time of the isomerization reaction in Example 6 is 3.5 hours.

[0073] When the isomerized product was measured by gel permeation chromatography, the content of methyltetrahydrophthalic anhydride dimer was 1.55% by weight, with the total weight of the isomerized product being 100% by weight.When the isomerized product was measured by gas chromatography, the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerized product was 4.22:1.

[0074] [Example 7] A liquid reactant having a total weight of 10,000 kg was charged into the reaction tank. The liquid reactant contained 7,500 kg of 3-methyltetrahydrophthalic anhydride and 2,500 kg of 4-methyltetrahydrophthalic anhydride. The content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in 3-methyltetrahydrophthalic anhydride (trans-3-methyltetrahydrophthalic anhydride:cis-3-methyltetrahydrophthalic anhydride) was 1:6.

[0075] Nitrogen gas was introduced into the top of the reaction tank and discharged out the other end of the top of the reaction tank to remove oxygen gas and water in the reaction tank. Under the condition of continuing to introduce nitrogen gas, the reaction tank was heated to 140°C and 150 kg of sodium hydroxide (alkali catalyst) was added to carry out the isomerization reaction.

[0076] During the isomerization process, when the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerization product measured by gas chromatography exceeds 4:1, the isomerization reaction is terminated to obtain the isomerization product, and the total time of the isomerization reaction in Example 7 is 24 hours.

[0077] When the isomerized product was measured by gel permeation chromatography, the content of methyltetrahydrophthalic anhydride dimer was 1.52% by weight, with the total weight of the isomerized product being 100% by weight.When the isomerized product was measured by gas chromatography, the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerized product was 4.21:1.

[0078] [Comparative Example 1] A liquid reactant having a total weight of 10,000 kg was charged into the reaction tank. The liquid reactant contained 7,500 kg of 3-methyltetrahydrophthalic anhydride and 2,500 kg of 4-methyltetrahydrophthalic anhydride. The content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in 3-methyltetrahydrophthalic anhydride (trans-3-methyltetrahydrophthalic anhydride:cis-3-methyltetrahydrophthalic anhydride) was 1:6.

[0079] Under conditions where no nitrogen gas was introduced, the reaction tank was heated to 140°C and 150 kg of sodium hydroxide (alkali catalyst) was added to carry out an isomerization reaction.

[0080] During the isomerization process, when the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerization product measured by gas chromatography exceeds 4:1, the isomerization reaction is terminated to obtain the isomerization product, and the total time of the isomerization reaction in Comparative Example 1 was 24 hours.

[0081] When the isomerized product was measured by gel permeation chromatography, the content of methyltetrahydrophthalic anhydride dimer was 4 wt%, with the total weight of the isomerized product being 100 wt%.When the isomerized product was measured by gas chromatography, the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerized product was 4.24:1.

[0082] [Comparative Example 2] A liquid reactant having a total weight of 10,000 kg was charged into the reaction tank. The liquid reactant contained 7,500 kg of 3-methyltetrahydrophthalic anhydride and 2,500 kg of 4-methyltetrahydrophthalic anhydride. The content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in 3-methyltetrahydrophthalic anhydride (trans-3-methyltetrahydrophthalic anhydride:cis-3-methyltetrahydrophthalic anhydride) was 1:6.

[0083] Under conditions where no nitrogen gas was introduced, the reaction tank was heated to 140°C and 100 kg of sodium hydroxide (alkali catalyst) was added to carry out an isomerization reaction.

[0084] During the isomerization process, when the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerization product measured by gas chromatography exceeded 4:1, the isomerization reaction was terminated to obtain the isomerization product, and the total time of the isomerization reaction in Comparative Example 2 was 26 hours.

[0085] When the isomerized product was measured by gel permeation chromatography, the content of methyltetrahydrophthalic anhydride dimer was 3.72% by weight, with the total weight of the isomerized product being 100% by weight.When the isomerized product was measured by gas chromatography, the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerized product was 4.19:1.

[0086] [Table 1]

[0087] [Table 2]

[0088] According to the above experimental results, the method for isomerizing methyltetrahydrophthalic anhydride of the present invention can reduce the generation of methyltetrahydrophthalic anhydride dimer. Taking the total weight of the isomerization product as 100 weight%, the content of methyltetrahydrophthalic anhydride dimer in the isomerization product is less than 3.5 weight%, and most preferably less than 1.6 weight%.

[0089] According to Comparative Examples 1 and 2, when the isomerization reaction was carried out under the condition that nitrogen gas was not introduced, the time required for the isomerization reaction was shorter as the amount of the alkali catalyst added was higher, but oxygen gas and water promoted the opening of the double bond of methyltetrahydrophthalic anhydride to form methyltetrahydrophthalic anhydride dimer. Therefore, the faster the isomerization reaction, the higher the possibility of producing methyltetrahydrophthalic anhydride dimer.

[0090] That is, when the isomerization reaction is carried out under conditions in which nitrogen gas is not introduced, the time required for the isomerization reaction is inversely proportional to the amount of methyltetrahydrophthalic anhydride dimer produced.

[0091] In the present invention, the problem of the excessively high content of methyltetrahydrophthalic anhydride dimer in Comparative Examples 1 and 2 can be solved by introducing nitrogen gas during the isomerization reaction. According to Examples 1, 4 and 5, oxygen gas and water in the liquid reactant are almost completely eliminated, and the double bond of methyltetrahydrophthalic anhydride is prevented from being opened by oxygen gas and water to form methyltetrahydrophthalic anhydride dimer during the isomerization reaction. Therefore, the higher the amount of alkali catalyst added, the shorter the time required for the isomerization reaction and the smaller the amount of methyltetrahydrophthalic anhydride dimer produced.

[0092] That is, when the isomerization reaction is carried out under the condition of introducing nitrogen gas, the time required for the isomerization reaction is directly proportional to the amount of methyltetrahydrophthalic anhydride dimer produced. Thus, the method for isomerizing methyltetrahydrophthalic anhydride according to the present invention achieves both a short reaction time and a low impurity amount, and eliminates the phenomenon that the time required for the isomerization reaction is inversely proportional to the amount of methyltetrahydrophthalic anhydride dimer produced.

[0093] According to Examples 1, 2 and 6, the temperature of the isomerization reaction affects the time required for the isomerization reaction and the amount of methyltetrahydrophthalic anhydride dimer produced. The higher the temperature of the isomerization reaction, the shorter the time required for the low isomerization reaction. However, in a relatively high temperature environment, the possibility of forming methyltetrahydrophthalic anhydride dimer increases.

[0094] Therefore, in order to achieve both a short reaction time and low impurity levels, it is preferable to carry out the isomerization reaction at a temperature of 145°C to 155°C, thereby making the content of methyltetrahydrophthalic anhydride dimer less than 1% by weight, preferably less than 0.8% by weight, and more preferably less than 0.6% by weight.

[0095] According to Examples 1 and 7, the difference in the nitrogen gas introduction method also affects the effect of eliminating oxygen and moisture. Introducing nitrogen gas from the liquid reactant can eliminate oxygen and moisture in the liquid reactant. Compared with introducing nitrogen from the top of the reaction tank, introducing nitrogen gas from the liquid reactant can efficiently eliminate oxygen gas and moisture gas in the system and reduce the possibility of generating methyltetrahydrophthalic anhydride dimer.

[0096] [Advantageous Effects of the Embodiments] The advantageous effect of the present invention is that the method for isomerizing methyltetrahydrophthalic anhydride according to the present invention has a technical feature of "obtaining an isomerized product by adding an alkali catalyst to a liquid reactant in a nitrogen gas flow state and carrying out an isomerization reaction", which reduces the possibility of producing methyltetrahydrophthalic anhydride dimer and improves the yield of isomerized methyltetrahydrophthalic anhydride.

[0097] To further explain, the present invention introduces nitrogen gas before heating and carrying out the isomerization reaction, thereby almost eliminating oxygen gas and moisture in the system. During the isomerization reaction, oxygen gas and moisture can be prevented from opening the double bond of methyltetrahydrophthalic anhydride to form methyltetrahydrophthalic anhydride dimer. In addition, since oxygen gas and moisture in the system cannot be completely removed, nitrogen gas can be continuously introduced throughout the entire isomerization reaction process to maintain a good reaction environment.

[0098] As for the method of introducing nitrogen gas, nitrogen gas can be directly introduced into the liquid reactant in the form of bubbles to remove oxygen gas and moisture in the liquid reactant. Alternatively, nitrogen gas can be introduced from the top of the reaction tank, and the flow of nitrogen gas can indirectly remove oxygen gas and moisture in the system. According to the experimental data of the present invention, both of the two methods can reduce the amount of methyltetrahydrophthalic anhydride produced.

[0099] In addition, in the present invention, the introduction of nitrogen gas changes the time required for the isomerization reaction from being inversely proportional to the amount of methyltetrahydrophthalic anhydride dimer produced. In the method for isomerizing methyltetrahydrophthalic anhydride according to the present invention, the time required for the isomerization reaction is directly proportional to the amount of methyltetrahydrophthalic anhydride dimer produced, and both the effects of a short reaction time and low impurities are achieved.

[0100] The above disclosure is merely a preferred embodiment of the present invention, and the scope of the claims of the present invention is not limited thereto. Therefore, all equivalent technical modifications made by utilizing the specification and drawings of the present invention are included in the scope of the claims of the present invention. [Explanation of symbols]

[0101] R...Reaction tank L...liquid phase reactant 1...Air supply pipe 2...Exhaust pipe 3...Air supply pipe

Claims

1. providing a liquid reactant comprising 3-methyltetrahydrophthalic anhydride and 4-methyltetrahydrophthalic anhydride; and adding an alkali catalyst to the liquid reactant under nitrogen gas flow to carry out an isomerization reaction to obtain an isomerization product.

2. A method for isomerizing methyltetrahydrophthalic anhydride, wherein the content of methyltetrahydrophthalic anhydride dimer is less than 1.6% by weight, based on 100% by weight of the total weight of the isomerization product.

2. 2. The method for isomerizing methyltetrahydrophthalic anhydride according to claim 1, wherein the liquid reactant is subjected to the isomerization reaction at a temperature of 140°C to 160°C.

3. 2. The method for isomerizing methyltetrahydrophthalic anhydride according to claim 1, wherein nitrogen gas is continuously introduced during the isomerization reaction, and the amount of the nitrogen gas introduced is 0.4 L / h to 0.8 L / h.

4. 2. The method for isomerizing methyltetrahydrophthalic anhydride according to claim 1, wherein oxygen gas and water are removed from the liquid reactant by introducing nitrogen gas into the liquid reactant, and then the alkali catalyst is added to the liquid reactant to carry out the isomerization reaction.

5. 5. The process for isomerizing methyltetrahydrophthalic anhydride according to claim 4, wherein nitrogen gas is bubbled into the liquid reactant to remove oxygen gas and water from the liquid reactant.

6. 2. The method for isomerizing methyltetrahydrophthalic anhydride according to claim 1, wherein the liquid reactant is subjected to the isomerization reaction in a reaction tank, and oxygen gas and water are removed from the reaction tank by introducing nitrogen gas into the reaction tank.

7. The method for isomerizing methyltetrahydrophthalic anhydride according to claim 1, wherein the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride (trans-3-methyltetrahydrophthalic anhydride:cis-3-methyltetrahydrophthalic anhydride) in the isomerization product is 4:1 to 5:

1.

8. 2. The method for isomerizing methyltetrahydrophthalic anhydride according to claim 1, wherein the amount of the alkali catalyst added is 0.5 to 1.5 parts by weight, based on 100 parts by weight of the total weight of the liquid reactants.

9. 2. The method for isomerizing methyltetrahydrophthalic anhydride according to claim 1, wherein the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride (trans-3-methyltetrahydrophthalic anhydride:cis-3-methyltetrahydrophthalic anhydride) in the liquid reactant is 1:4 to 1:

7.

10. 2. The method for isomerizing methyltetrahydrophthalic anhydride according to claim 1, wherein in the liquid reactant, the weight ratio of 3-methyltetrahydrophthalic anhydride to 4-methyltetrahydrophthalic anhydride is 7:3 to 3:7.

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