Methyl tetrahydrophthalic anhydride isomerization method

Abstract

The invention discloses an isomerization method of methyl tetrahydrophthalic anhydride. The isomerization method of methyl tetrahydrophthalic anhydride comprises the following steps: providing a liquid reactant; under the condition that nitrogen is introduced, an alkaline catalyst is added into the liquid reactant for an isomerization reaction, and an isomerization product is obtained. Wherein the liquid reactant is prepared from 3-methyl tetrahydrophthalic anhydride and 4-methyl tetrahydrophthalic anhydride. The content of the methyl tetrahydrophthalic anhydride dimer is less than 1.6 weight percent by taking the total weight of the isomerization product as 100 weight percent. The isomerization method provided by the invention can reduce the generation probability of the methyl tetrahydrophthalic anhydride dimer, thereby improving the yield of isomerized methyl tetrahydrophthalic anhydride.

Description

Technical Field

[0001] The present application relates to a method for isomerizing methyltetrahydrophthalic anhydride, and in particular to a method for isomerizing methyltetrahydrophthalic anhydride in which dimers are not easily generated during the process. Background Art

[0002] Methyltetrahydrophthalic anhydride is a hardener commonly used in organic anhydride epoxy resins. It has good heat resistance and stability, and can maintain good physical and electrical properties even in high temperature environments.

[0003] Generally speaking, the reactants for synthesizing methyltetrahydrophthalic anhydride include isoprene, isoprene and anhydride. In the prior art, the method for producing methyltetrahydrophthalic anhydride is to add the measured reactants into a reactor at once, and make the reactants undergo a Diels-Alder reaction (also known as a conjugated diene addition reaction) to produce methyltetrahydrophthalic anhydride. Then, the methyltetrahydrophthalic anhydride is subjected to an isomerization reaction with an acidic catalyst (e.g., sulfuric acid, p-toluenesulfonic acid) to improve the properties of methyltetrahydrophthalic anhydride.

[0004] However, the high temperature during the isomerization reaction of methyltetrahydrophthalic anhydride easily leads to dimerization of methyltetrahydrophthalic anhydride, which reduces the yield of the final product. Therefore, how to reduce the occurrence of dimerization through the improvement of the process and thus increase the yield of methyltetrahydrophthalic anhydride has become one of the important issues to be solved in this business. Summary of the invention

[0005] The technical problem to be solved by the present application is to provide a method for isomerizing methyltetrahydrophthalic anhydride in view of the deficiencies of the prior art.

[0006] In order to solve the above technical problems, one of the technical solutions adopted by the present invention is to provide a method for isomerizing methyltetrahydrophthalic anhydride. The method for isomerizing methyltetrahydrophthalic anhydride comprises: providing a liquid reactant; adding an alkaline catalyst to the liquid reactant under the condition of introducing nitrogen to carry out an isomerization reaction to obtain an isomerized product. The liquid reactant contains 3-methyltetrahydrophthalic anhydride and 4-methyltetrahydrophthalic anhydride. With the total weight of the isomerized product as 100 weight percent, the content of methyltetrahydrophthalic anhydride dimer is less than 1.6 weight percent.

[0007] Furthermore, the liquid reactants are subjected to an isomerization reaction at a temperature of 140°C to 160°C.

[0008] Furthermore, nitrogen is continuously introduced during the isomerization reaction, and the amount of nitrogen introduced is 0.4 L / hour to 0.8 L / hour.

[0009] Furthermore, nitrogen is introduced into the liquid reactant to remove oxygen and water vapor in the liquid reactant, and then an alkaline catalyst is added to the liquid reactant to perform an isomerization reaction.

[0010] Furthermore, nitrogen is introduced into the liquid reactant in the form of bubbles to remove oxygen and water vapor in the liquid reactant.

[0011] Furthermore, the liquid reactant undergoes an isomerization reaction in the reaction tank, and nitrogen is introduced into the reaction tank to remove oxygen and water vapor in the reaction tank.

[0012] Furthermore, the weight ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerization product is 4:1 to 5:1.

[0013] Furthermore, based on 100 parts by weight of the total weight of the liquid reactants, the amount of the alkaline catalyst added is 0.5 parts by weight to 1.5 parts by weight.

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

[0015] Furthermore, the weight ratio of 3-methyltetrahydrophthalic anhydride to 4-methyltetrahydrophthalic anhydride in the liquid reactant is 7:3 to 3:7.

[0016] One of the beneficial effects of the present invention is that the isomerization method of methyltetrahydrophthalic anhydride provided by the present invention can reduce the probability of generating methyltetrahydrophthalic anhydride dimers and thereby improve the yield of isomerized methyltetrahydrophthalic anhydride through the technical scheme of "adding an alkaline catalyst to a liquid reactant to carry out an isomerization reaction to obtain an isomerized product under the condition of introducing nitrogen gas".

[0017] To further understand the features and technical contents of the present application, please refer to the following detailed description and drawings of the present application. However, the drawings provided are only for reference and illustration and are not intended to limit the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The schematic diagram of the isomerization process of methyltetrahydrophthalic anhydride of the present application is shown in FIG.

[0019] Figure 2 This is a schematic diagram of the equipment used for isomerization of methyltetrahydrophthalic anhydride in this application. DETAILED DESCRIPTION

[0020] The following is an explanation of the implementation method of the "isomerization method of methyltetrahydrophthalic anhydride" disclosed in the present invention through specific examples. Those skilled in the art can understand the advantages and effects of the present invention from the contents disclosed in this specification. The present invention can be implemented or applied through other different specific embodiments, and the details in this specification can also be modified and changed in various ways based on different viewpoints and applications without departing from the concept of the present invention. In addition, the drawings of the present invention are only simple schematic illustrations and are not depicted according to actual dimensions. It is stated in advance. The following implementation methods will further explain the relevant technical contents of the present invention in detail, but the disclosed contents are not intended to limit the scope of protection of the present invention. In addition, the term "or" used in this article may include any one or more combinations of the associated listed items depending on the actual situation.

[0021] In order to solve the problem that methyltetrahydrophthalic anhydride is prone to dimerization reaction in the past, resulting in low yield of methyltetrahydrophthalic anhydride, the present invention introduces nitrogen into the isomerization process of methyltetrahydrophthalic anhydride to avoid dimerization of methyltetrahydrophthalic anhydride, thereby achieving the effect of improving the yield of methyltetrahydrophthalic anhydride.

[0022] Furthermore, the present invention is to pass nitrogen into the liquid reactant containing 3-methyltetrahydrophthalic anhydride and 4-methyltetrahydrophthalic anhydride to remove oxygen and water vapor in the liquid reactant. The introduction and discharge of nitrogen can take away the oxygen and water vapor in the system. Moreover, compared with passing nitrogen from the system, directly passing nitrogen into the liquid reactant can further remove oxygen and water vapor in the system, thereby achieving the effect of reducing the probability of dimerization of methyltetrahydrophthalic anhydride.

[0023] Please refer to the combined Figure 1 and Figure 2 As shown, Figure 1 The present invention is a flow chart of the steps of the isomerization method of methyltetrahydrophthalic anhydride. Figure 2 This is a schematic diagram of the equipment used for isomerizing methyltetrahydrophthalic anhydride of the present invention. Figure 2 The devices shown in the figure can be used to implement the present invention, but will not limit the steps of the present invention.

[0024] In step S1 , a liquid reactant is provided, wherein the liquid reactant comprises 3-methyltetrahydrophthalic anhydride and 4-methyltetrahydrophthalic anhydride.

[0025] Due to the difference in stereostructure, 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 greater than the content of cis-3-methyltetrahydrophthalic anhydride. For example, the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride can be 1:4, 1:4.5, 1:5, 1:5.5, 1:6, 1:6.5 or 1:7. However, the present invention is not limited thereto.

[0026] Furthermore, 3-methyltetrahydrophthalic anhydride in the liquid reactant can be prepared by the addition reaction of maleic anhydride and isoprene. 4-methyltetrahydrophthalic anhydride in the liquid reactant can be prepared by the addition reaction of maleic anhydride and isoprene.

[0027] In an exemplary embodiment, maleic anhydride and isoprene may be added to a reaction tank first, and a first addition reaction may be performed at a temperature of 80° C. to 120° C. In the first addition reaction, maleic anhydride and isoprene react to generate 3-methyltetrahydrophthalic anhydride. Then, isoprene may be added to the reaction tank, and a second addition reaction may be performed at a temperature of 80° C. to 120° C. In the second addition reaction, maleic anhydride and isoprene react to generate 4-methyltetrahydrophthalic anhydride.

[0028] In order to adjust the content of 3-methyltetrahydrophthalic anhydride and 4-methyltetrahydrophthalic anhydride, the first addition reaction can be terminated when the conversion rate of maleic anhydride reaches more than 25%. That is to say, the content of 3-methyltetrahydrophthalic anhydride in the methyltetrahydrophthalic anhydride generated by the present invention is at least 25wt%. Specifically, the first addition reaction can be selected to stop when the conversion rate of maleic anhydride is 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75% or 80%. However, the present invention is not limited to this.

[0029] The fusing point of 3-methyltetrahydrophthalic anhydride is lower than that of 4-methyltetrahydrophthalic anhydride. When the content of 3-methyltetrahydrophthalic anhydride is lower in the liquid reactant, the liquid reactant can have a higher viscosity. When the content of 3-methyltetrahydrophthalic anhydride is higher in the liquid reactant, the liquid reactant can have a lower viscosity. Therefore, the present invention can adjust the viscosity of the liquid reactant by controlling the weight ratio of 3-methyltetrahydrophthalic anhydride and 4-methyltetrahydrophthalic anhydride, so as to facilitate the carrying out of subsequent reactions (for example: passing into nitrogen). For example, the viscosity of the liquid reactant can be 50cps to 100cps. However, the present invention is not limited thereto.

[0030] In step S2, an alkaline catalyst is added to the liquid reactant under nitrogen flow to perform an isomerization reaction to obtain an isomerization product.

[0031] In an 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 lower than that of cis-3-methyltetrahydrophthalic anhydride. After the isomerization reaction, the content of trans-3-methyltetrahydrophthalic anhydride in the liquid reactant is higher than that of cis-3-methyltetrahydrophthalic anhydride.

[0032] However, in the presence of oxygen and water, oxygen and water will induce methyltetrahydrophthalic anhydride to open its double bonds. At high temperatures or in the presence of initiators, methyltetrahydrophthalic anhydride with its double bonds opened will have a chance to undergo polymerization to form methyltetrahydrophthalic anhydride dimers.

[0033] In the present invention, no initiator is added, but unfortunately, the high temperature (140°C to 160°C) of the isomerization reaction is sufficient to polymerize methyltetrahydrophthalic anhydride to form methyltetrahydrophthalic anhydride dimer. In other words, while the isomerization reaction is carried out at high temperature, the dimerization reaction of methyltetrahydrophthalic anhydride may also occur.

[0034] In order to avoid the formation of methyltetrahydrophthalic anhydride dimer, the present invention introduces nitrogen into the system to remove oxygen and water in the system. The oxygen and water in the system may come from the addition of raw materials or originally exist in the equipment pipeline, so they cannot be deliberately avoided.

[0035] See also Figure 2 As shown, the liquid reactant L is placed in a reaction tank R, and nitrogen is introduced from an air inlet pipe 1 at the bottom of the reaction tank R. The nitrogen can be injected into the liquid reactant L in the form of bubbles, and replace the oxygen and water vapor originally present in the liquid reactant L. Then, the nitrogen is discharged from the exhaust pipe 2 at the top of the reaction tank R, and takes away the oxygen and water vapor in the reaction tank R.

[0036] In another embodiment, nitrogen may be introduced from another inlet pipe 3 at the top of the reaction tank R and discharged from the exhaust pipe 2 at the top of the reaction tank R, thereby taking away the oxygen and water vapor in the reaction tank R. In addition, the introduction of nitrogen will form a pressure difference on both sides of the reaction tank R, so that when the nitrogen is discharged, the oxygen and water vapor in the liquid reactant L will also be taken away.

[0037] The above two methods of introducing nitrogen can both achieve the effect of removing oxygen and water vapor from the system. However, the present invention is not limited thereto.

[0038] Thus, there is no oxygen and water vapor in the reaction tank R that may induce the double bond of methyltetrahydrophthalic anhydride to open. Even if the temperature of the reaction tank R is raised to 140° C. to 160° C. for the isomerization reaction, it is not easy to generate too much methyltetrahydrophthalic anhydride dimer.

[0039] Therefore, in order to effectively reduce the formation of methyltetrahydrophthalic anhydride dimer, nitrogen can be continuously introduced into the reaction tank R before the temperature is raised, and the introduction of nitrogen is stopped only after the isomerization reaction is completed and the temperature is lowered.

[0040] During the entire isomerization reaction, the amount of nitrogen introduced can be 0.4 liters / hour to 0.8 liters / hour, preferably 0.5 liters / hour, 0.6 liters / hour or 0.7 liters / hour. If the amount of nitrogen introduced is too low, the effect of inhibiting the formation of methyltetrahydrophthalic anhydride dimer is poor, and if the amount of nitrogen introduced is too large, it is not economically effective for the overall manufacturing process.

[0041] In an exemplary embodiment, the content of methyltetrahydrophthalic anhydride dimer can be monitored by gel permeation chromatography (GPC) (brand: Shimadzu, model: NEXERA LC40D GPC).

[0042] Taking the total weight of the isomerized product as 100 weight percent, the content of methyltetrahydrophthalic anhydride dimer in the isomerized product is less than 1.6 weight percent. Specifically, the content of methyltetrahydrophthalic anhydride dimer can be 1.5 weight percent, 1.4 weight percent, 1.3 weight percent, 1.2 weight percent, 1.0 weight percent, 0.8 weight percent, 0.7 weight percent or 0.6 weight percent.

[0043] In addition, the present invention selects to add an alkaline catalyst to perform an isomerization reaction. Adding an alkaline catalyst to perform an isomerization reaction can achieve the effect of reducing the viscosity of the hardener. In this way, the low-viscosity hardener of the present invention can have good processability and a wider range of uses. Specifically, the viscosity of the isomerization product can be 30cps to 40cps.

[0044] For example, the alkaline catalyst can be an organic base or an inorganic base. The organic base can be an alcohol amine, especially selected from the group consisting of ethanolamine, diethanolamine and triethanolamine. The inorganic base can be selected from the group consisting of potassium carbonate, sodium carbonate, sodium hydroxide and potassium hydroxide.

[0045] After removing oxygen and moisture, there is no need to worry about the methyltetrahydrophthalic anhydride opening double bonds to form methyltetrahydrophthalic anhydride dimers during the isomerization reaction, so a large amount of alkaline catalyst can be added to accelerate the isomerization reaction. In an exemplary embodiment, based on the total weight of the liquid reactants being 100 parts by weight, the amount of alkaline catalyst added can be 0.5 parts by weight to 1.5 parts by weight.

[0046] After the isomerization reaction, the content of trans-3-methyltetrahydrophthalic anhydride in the isomerization product is higher than that 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 tracked by gas chromatograph (GC) (brand: Agilent, model: 8860GC).

[0047] In an exemplary embodiment, the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerized product may be 3:1 to 6:1. Preferably, the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerized product may be 4:1 to 5:1. Specifically, the content ratio of trans-3-methyltetrahydrophthalic anhydride to 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.

[0048] In step S3, the isomerization product is subjected to a reduced pressure distillation treatment to remove methyltetrahydrophthalic anhydride dimer to obtain a methyltetrahydrophthalic anhydride product.

[0049] Since the content of methyltetrahydrophthalic anhydride dimer in the isomerized product is not high, a relatively short processing time is required to achieve an ideal purity. In addition, since the content of methyltetrahydrophthalic anhydride dimer is not high, the isomerization method of methyltetrahydrophthalic anhydride of the present invention can achieve a relatively high yield when certain raw materials are used.

[0050] In order to conveniently illustrate the isomerization method of methyltetrahydrophthalic anhydride of the present invention, the following Examples 1 to 7 and Comparative Examples 1 to 2 are used for illustration. The reaction parameters and characteristic measurements in Examples 1 to 5 are shown in Table 1, and the reaction parameters and characteristic measurements in Examples 6 to 7 and Comparative Examples 1 to 2 are shown in Table 2.

[0051] [Example 1]

[0052] A total weight of 10,000 kg of liquid reactants was put into a reaction tank. The liquid reactants included 7,500 kg of 3-methyltetrahydrophthalic anhydride and 2,500 kg of 4-methyltetrahydrophthalic anhydride. Among them, the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in 3-methyltetrahydrophthalic anhydride was 1:6. For the convenience 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.

[0053] Nitrogen is introduced into the bottom of the reaction tank, and the nitrogen is directly introduced into the liquid reactant in the form of bubbles to remove oxygen and water vapor in the liquid reactant. Under the condition of continuous nitrogen introduction, the reaction tank is heated to 140°C, and 150 kg of sodium hydroxide (alkaline catalyst) is added to carry out isomerization reaction. In other words, the amount of alkaline catalyst added is 1.5 parts by weight relative to 100 parts by weight of the liquid reactant. For the sake of convenience, the relative amount of alkaline catalyst added (to the liquid reactant) is 1.5 / 100.

[0054] During the isomerization process, the isomerization reaction was stopped when the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerization product was greater than 4:1 by gas chromatograph detection, and the isomerization product was obtained. The total time of the isomerization reaction in Example 1 was 24 hours.

[0055] After the isomerization product was detected by gel chromatography, the content of methyltetrahydrophthalic anhydride dimer was 1.1 weight percent, with the total weight of the isomerization product being 100 weight percent. After the isomerization product was detected by gas chromatography, the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerization product was 4.21:1.

[0056] [Example 2]

[0057] A total weight of 10,000 kg of liquid reactants is put into a reaction tank. The liquid reactants include 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 is 1:6.

[0058] Nitrogen is introduced into the bottom of the reaction tank, and the nitrogen is directly introduced into the liquid reactant in the form of bubbles to remove oxygen and water vapor in the liquid reactant. Under the condition of continuous introduction of nitrogen, the reaction tank is heated to 150°C, and 150 kg of sodium hydroxide (alkaline catalyst) is added to carry out isomerization reaction.

[0059] During the isomerization process, the isomerization reaction was stopped when the ratio of the content of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerization product was greater than 4:1 as detected by gas chromatograph, and the isomerization product was obtained. The total time of the isomerization reaction in Example 2 was 6 hours.

[0060] After the isomerization product was detected by gel chromatography, the content of methyltetrahydrophthalic anhydride dimer was 0.53 weight percent, with the total weight of the isomerization product being 100 weight percent. After the isomerization product was detected by gas chromatography, the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerization product was 4.17:1.

[0061] [Example 3]

[0062] A total weight of 10,000 kg of liquid reactants is put into a reaction tank. The liquid reactants include 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 is 1:6.

[0063] Nitrogen is introduced into the bottom of the reaction tank, and the nitrogen is directly introduced into the liquid reactant in the form of bubbles to remove oxygen and water vapor in the liquid reactant. Under the condition of continuous introduction of nitrogen, the reaction tank is heated to 150°C, and 50 kg of sodium hydroxide (alkaline catalyst) is added to carry out isomerization reaction.

[0064] During the isomerization process, the isomerization reaction was stopped when the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerization product was greater than 4:1 as detected by gas chromatograph, and the isomerization product was obtained. The total time of the isomerization reaction in Example 3 was 36.5 hours.

[0065] After the isomerization product was detected by gel chromatography, the content of methyltetrahydrophthalic anhydride dimer was 0.79 weight percent, with the total weight of the isomerization product being 100 weight percent. After the isomerization product was detected by gas chromatography, the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerization product was 4.23:1.

[0066] [Example 4]

[0067] A total weight of 10,000 kg of liquid reactants is put into a reaction tank. The liquid reactants include 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 is 1:6.

[0068] Nitrogen is introduced into the bottom of the reaction tank, and the nitrogen is directly introduced into the liquid reactant in the form of bubbles to remove oxygen and water vapor in the liquid reactant. Under the condition of continuous introduction of nitrogen, the reaction tank is heated to 140°C, and 100 kg of sodium hydroxide (alkaline catalyst) is added to carry out isomerization reaction.

[0069] During the isomerization process, the isomerization reaction was stopped when the ratio of the content of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerization product was greater than 4:1 as detected by gas chromatograph, and the isomerization product was obtained. The total time of the isomerization reaction in Example 4 was 26 hours.

[0070] After the isomerization product was detected by gel chromatography, the content of methyltetrahydrophthalic anhydride dimer was 1.24 weight percent, with the total weight of the isomerization product being 100 weight percent. After the isomerization product was detected by gas chromatography, the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerization product was 4.19:1.

[0071] [Example 5]

[0072] A total weight of 10,000 kg of liquid reactants is put into a reaction tank. The liquid reactants include 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 is 1:6.

[0073] Nitrogen is introduced into the bottom of the reaction tank, and the nitrogen is directly introduced into the liquid reactant in the form of bubbles to remove oxygen and water vapor in the liquid reactant. Under the condition of continuous introduction of nitrogen, the reaction tank is heated to 140°C, and 50 kg of sodium hydroxide (alkaline catalyst) is added to carry out isomerization reaction.

[0074] During the isomerization process, the isomerization reaction was stopped when the ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerization product was greater than 4:1 as detected by gas chromatograph, and the isomerization product was obtained. The total time of the isomerization reaction in Example 5 was 72 hours.

[0075] After the isomerization product was detected by gel chromatography, the content of methyltetrahydrophthalic anhydride dimer was 1.31 weight percent, with the total weight of the isomerization product being 100 weight percent. After the isomerization product was detected by gas chromatography, the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerization product was 4.11:1.

[0076] [Example 6]

[0077] A total weight of 10,000 kg of liquid reactants is put into a reaction tank. The liquid reactants include 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 is 1:6.

[0078] Nitrogen is introduced into the bottom of the reaction tank, and the nitrogen is directly introduced into the liquid reactant in the form of bubbles to remove oxygen and water vapor in the liquid reactant. Under the condition of continuous introduction of nitrogen, the reaction tank is heated to 160°C, and 150 kg of sodium hydroxide (alkaline catalyst) is added to carry out isomerization reaction.

[0079] During the isomerization process, the isomerization reaction was stopped when the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerization product was greater than 4:1 as detected by gas chromatograph, and the isomerization product was obtained. The total time of the isomerization reaction in Example 6 was 3.5 hours.

[0080] After the isomerization product was detected by gel chromatography, the content of methyltetrahydrophthalic anhydride dimer was 1.55 weight percent, with the total weight of the isomerization product being 100 weight percent. After the isomerization product was detected by gas chromatography, the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerization product was 4.22:1.

[0081] [Example 7]

[0082] A total weight of 10,000 kg of liquid reactants is put into a reaction tank. The liquid reactants include 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 is 1:6.

[0083] Nitrogen was introduced into the top of the reaction tank and discharged from the other end of the top of the reaction tank to remove oxygen and water vapor in the reaction tank. While nitrogen was continuously introduced, the reaction tank was heated to 140°C and 150 kg of sodium hydroxide (alkaline catalyst) was added to carry out isomerization reaction.

[0084] During the isomerization process, the isomerization reaction was stopped when the ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerization product was greater than 4:1 as detected by gas chromatograph, and the isomerization product was obtained. The total time of the isomerization reaction in Example 7 was 24 hours.

[0085] After the isomerization product was detected by gel chromatography, the content of methyltetrahydrophthalic anhydride dimer was 1.52 weight percent, with the total weight of the isomerization product being 100 weight percent. After the isomerization product was detected by gas chromatography, the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerization product was 4.21:1.

[0086] [Comparative Example 1]

[0087] A total weight of 10,000 kg of liquid reactants is put into a reaction tank. The liquid reactants include 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 is 1:6.

[0088] Without introducing nitrogen, the reaction tank was heated to 140° C., and 150 kg of sodium hydroxide (alkaline catalyst) was added to carry out an isomerization reaction.

[0089] During the isomerization process, the isomerization reaction was stopped when the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerization product was greater than 4:1 as detected by gas chromatograph, and the isomerization product was obtained. The total time of the isomerization reaction in Comparative Example 1 was 24 hours.

[0090] After the isomerization product was detected by gel chromatography, the content of methyltetrahydrophthalic anhydride dimer was 4 weight percent, with the total weight of the isomerization product being 100 weight percent. After the isomerization product was detected by gas chromatography, the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerization product was 4.24:1.

[0091] [Comparative Example 2]

[0092] A total weight of 10,000 kg of liquid reactants is put into a reaction tank. The liquid reactants include 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 is 1:6.

[0093] Without introducing nitrogen, the reaction tank was heated to 140° C., and 100 kg of sodium hydroxide (alkaline catalyst) was added to carry out an isomerization reaction.

[0094] During the isomerization process, the isomerization reaction was stopped when the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerization product was greater than 4:1 as detected by gas chromatograph, and the isomerization product was obtained. The total time of the isomerization reaction in Comparative Example 2 was 26 hours.

[0095] After the isomerization product was detected by gel chromatography, the content of methyltetrahydrophthalic anhydride dimer was 3.72 weight percent, with the total weight of the isomerization product being 100 weight percent. After the isomerization product was detected by gas chromatography, the content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerization product was 4.19:1.

[0096] Table 1

[0097]

[0098]

[0099] Table 2

[0100]

[0101] According to the above experimental results, the isomerization method of methyltetrahydrophthalic anhydride of the present invention can reduce the generation of methyltetrahydrophthalic anhydride dimer. Taking the total weight of the isomerized product as 100 weight percent, the content of methyltetrahydrophthalic anhydride dimer in the isomerized product is less than 3.5 weight percent, and the best can reach less than 1.6 weight percent.

[0102] It can be seen from Comparative Examples 1 and 2 that when the isomerization reaction is carried out without nitrogen, the higher the amount of alkaline catalyst added, the shorter the time required for the isomerization reaction. However, oxygen and water vapor will induce methyltetrahydrophthalic anhydride to open the double bond and form methyltetrahydrophthalic anhydride dimer. Therefore, when the isomerization reaction is faster, the probability of forming methyltetrahydrophthalic anhydride dimer is also increased.

[0103] That is, when the isomerization reaction is carried out without introducing nitrogen, the time required for the isomerization reaction is inversely proportional to the amount of methyltetrahydrophthalic anhydride dimer produced.

[0104] The present invention introduces nitrogen during the isomerization reaction, which can overcome the problem of too high content of methyltetrahydrophthalic anhydride dimer in Comparative Examples 1 and 2. As can be seen from Examples 1, 4 and 5, most of the oxygen and water vapor in the liquid reactant have been removed, so when the isomerization reaction is carried out, it can be avoided that oxygen and water vapor induce methyltetrahydrophthalic anhydride to open double bonds and form methyltetrahydrophthalic anhydride dimer. Therefore, when the amount of alkaline catalyst added is higher, the time required for the isomerization reaction is shorter, and the amount of methyltetrahydrophthalic anhydride dimer generated is also less.

[0105] That is to say, when nitrogen is introduced, the isomerization reaction is carried out, and the time required for the isomerization reaction is proportional to the amount of methyltetrahydrophthalic anhydride dimer produced. Accordingly, the isomerization method of methyltetrahydrophthalic anhydride of the present invention can have the effects of low reaction, low time consumption and low impurities, and changes the phenomenon that the time required for the isomerization reaction is inversely proportional to the amount of methyltetrahydrophthalic anhydride dimer produced.

[0106] It can be seen from Examples 1, 2 and 6 that the isomerization reaction temperature affects the time required for the isomerization reaction and the amount of methyltetrahydrophthalic anhydride dimer generated. The higher the isomerization reaction temperature, the shorter the time required for the isomerization reaction, but a higher temperature environment increases the probability of methyltetrahydrophthalic anhydride forming dimers.

[0107] Therefore, in order to achieve both low reaction time and low impurity effects, it is preferred to conduct the isomerization reaction at a temperature of 145° C. to 155° C., so that the content of methyltetrahydrophthalic anhydride dimer can be reduced to less than 1 weight percent, preferably less than 0.8 weight percent, and more preferably less than 0.6 weight percent.

[0108] It can be seen from Examples 1 and 7 that different nitrogen introduction methods will also affect the removal effect of oxygen and water vapor. Introducing nitrogen from the liquid reactant can directly remove oxygen and water vapor in the liquid reactant. Compared with introducing nitrogen from the top of the reaction tank, it can more efficiently remove oxygen and water vapor in the system to reduce the probability of generating methyltetrahydrophthalic anhydride dimer.

[0109] [Beneficial Effects of Embodiments]

[0110] One of the beneficial effects of the present invention is that the isomerization method of methyltetrahydrophthalic anhydride provided by the present invention can reduce the probability of generating methyltetrahydrophthalic anhydride dimers and thereby improve the yield of isomerized methyltetrahydrophthalic anhydride through the technical scheme of "adding an alkaline catalyst to a liquid reactant to carry out an isomerization reaction to obtain an isomerized product under the condition of introducing nitrogen gas".

[0111] Furthermore, the present invention introduces nitrogen before the temperature is raised for the isomerization reaction to remove most of the oxygen and water vapor in the system. During the isomerization reaction, oxygen and water vapor can be prevented from inducing methyltetrahydrophthalic anhydride to open double bonds to form methyltetrahydrophthalic anhydride dimers. Since it is impossible to completely remove oxygen and water vapor in the system, nitrogen can be continuously introduced during the entire isomerization reaction to maintain a good reaction environment.

[0112] The nitrogen can be introduced in the form of bubbles from the liquid reactants to directly remove oxygen and water vapor in the liquid reactants, or it can be introduced from the top of the reactor to indirectly remove oxygen and water vapor in the system through the flow of nitrogen. It can be seen from the experimental data of the present invention that both methods can reduce the amount of methyltetrahydrophthalic anhydride dimer generated.

[0113] In addition, due to the introduction of nitrogen, the present invention changes the phenomenon that the time required for the isomerization reaction is inversely proportional to the amount of methyltetrahydrophthalic anhydride dimer produced. After the introduction of nitrogen, the isomerization method of methyltetrahydrophthalic anhydride of the present invention can make the time required for the isomerization reaction be proportional to the amount of methyltetrahydrophthalic anhydride dimer produced, and can have the effects of low reaction, low time consumption and low impurities.

[0114] The contents disclosed above are only preferred feasible embodiments of the present application, and are not intended to limit the protection scope of the claims of the present application. Therefore, all equivalent technical changes made using the contents of the present application specification and drawings are included in the protection scope of the claims of the present application.

Claims

1. A method for isomerizing methyltetrahydrophthalic anhydride, characterized in that: The isomerization method of methyltetrahydrophthalic anhydride comprises: Providing a liquid reactant, wherein the liquid reactant comprises 3-methyltetrahydrophthalic anhydride and 4-methyltetrahydrophthalic anhydride; and Under the condition of nitrogen gas being introduced, adding an alkaline catalyst to the liquid reactant to carry out an isomerization reaction to obtain an isomerization product; Wherein, based on the total weight of the isomerization product being 100 weight percent, the content of methyltetrahydrophthalic anhydride dimer is less than 1.6 weight percent.

2. The isomerization method of methyltetrahydrophthalic anhydride according to claim 1, characterized in that: The liquid reactant is subjected to the isomerization reaction at a temperature of 140°C to 160°C.

3. The isomerization method of methyltetrahydrophthalic anhydride according to claim 1, characterized in that: During the isomerization reaction, nitrogen is continuously introduced at an amount of 0.4 to 0.8 L / hour.

4. The isomerization method of methyltetrahydrophthalic anhydride according to claim 1, characterized in that: Nitrogen is introduced into the liquid reactant to remove oxygen and water vapor in the liquid reactant, and then the alkaline catalyst is added to the liquid reactant to perform the isomerization reaction.

5. The isomerization method of methyltetrahydrophthalic anhydride according to claim 4, characterized in that: Nitrogen is introduced into the liquid reactant in the form of bubbles to remove oxygen and water vapor in the liquid reactant.

6. The isomerization method of methyltetrahydrophthalic anhydride according to claim 1, characterized in that: The liquid reactant undergoes the isomerization reaction in the reaction tank, and nitrogen is introduced into the reaction tank to remove oxygen and water vapor in the reaction tank.

7. The isomerization method of methyltetrahydrophthalic anhydride according to claim 1, characterized in that: The weight ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the isomerization product is 4:1 to 5:

1.

8. The isomerization method of methyltetrahydrophthalic anhydride according to claim 1, characterized in that: Based on 100 parts by weight of the total weight of the liquid reactant, the amount of the alkaline catalyst added is 0.5 parts by weight to 1.5 parts by weight.

9. The isomerization method of methyltetrahydrophthalic anhydride according to claim 1, characterized in that: The content ratio of trans-3-methyltetrahydrophthalic anhydride to cis-3-methyltetrahydrophthalic anhydride in the liquid reactant is 1:4 to 1:

7.

10. The isomerization method of methyltetrahydrophthalic anhydride according to claim 1, characterized in that: The weight ratio of the 3-methyltetrahydrophthalic anhydride to the 4-methyltetrahydrophthalic anhydride in the liquid reactant is 7:3 to 3:7.

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