Refining method of m-phthalonitrile / p-phthalonitrile crude product

Abstract

The invention provides a refining method of an m / p-phthalonitrile crude product, which comprises the following steps: mixing and completely dissolving the m / p-phthalonitrile crude product and a solvent which is azeotropic with water, removing moisture through azeotropy of the solvent and the water, removing insoluble substances through filtration, and further recovering the solvent at first based on graded temperature rise and then recovering the solvent at second based on graded temperature rise. And completely melting the m-phthalonitrile / p-phthalonitrile and conveying the m-phthalonitrile / p-phthalonitrile to a rectification system. According to the refining method disclosed by the invention, moisture and insoluble substances in the m-phthalonitrile / p-phthalonitrile crude product are removed before rectification, so that the main content loss of the m-phthalonitrile / p-phthalonitrile crude product in the melting and rectification processes is avoided, the yield of m-phthalonitrile / p-phthalonitrile is increased, the slag discharge amount is reduced, the material yield is increased, a rectification system runs more smoothly, and the product quality is improved. The environment-friendly benefit is obvious, and the economic benefit is higher.

Description

Technical Field

[0001] The invention relates to the field of pesticides, in particular to a raw material for synthesizing tetrachloroterephthalonitrile or tetrachloroisophthalonitrile, and in particular to a method for refining a crude isophthalonitrile / terephthalonitrile product. Background Art

[0002] Phthalonitrile includes o-phthalonitrile, isophthalonitrile and terephthalonitrile. Among them, isophthalonitrile and terephthalonitrile are widely used. Isophthalonitrile is an important organic raw material for organic synthesis. Tetrachloroisophthalonitrile synthesized by chlorination is a high-efficiency, low-toxic fungicide. Metaphenylenediamine obtained by hydrogenation is an epoxy resin curing agent with excellent performance, and is also a raw material for polyurethane vinegar resin and nylon resin. Terephthalonitrile is also an important chemical organic raw material. Hydrogenation of terephthalonitrile can produce p-phenylenediamine, which is an important raw material for polyamide and a good epoxy resin curing agent; hydrolysis of terephthalonitrile can produce terephthalic acid, which can be used to produce polyester resins, polyester fibers, films, insulating paints, engineering plastics and plasticizers; the reaction of terephthalonitrile with chlorine can produce tetrachloroterephthalonitrile, which can be used to synthesize herbicides, pesticides and drugs.

[0003] The raw materials for synthesizing isophthalonitrile are meta-xylene, ammonia and air, and the raw materials for synthesizing terephthalonitrile are para-xylene, ammonia and air. Both of them are subjected to ammoxidation reaction in a fluidized bed under the catalysis of a catalyst. After the reaction is completed, the crude isophthalonitrile / terephthalonitrile is obtained by condensation and capture by water spraying. Due to the influence of various conditions such as the change of the fluidization state of the fluidized bed reactor, the change of the use of the water pipe in the fluidized bed, the activity and damage of the catalyst, and the capture efficiency, the obtained crude isophthalonitrile / terephthalonitrile has different degrees of insoluble matter and water, and cannot be directly used as the raw material for the subsequent synthesis of tetrachloroterephthalonitrile or tetrachloroisophthalonitrile, and must be refined and purified first. For example, CN107540572A discloses a device for refining isophthalonitrile / terephthalonitrile, comprising a distillation kettle with a built-in stirring device, a heat exchanger connected to the distillation kettle, the heat exchanger is tilted downward at a certain angle from the inlet to the outlet and the horizontal direction, and a receiving kettle connected to the outlet of the heat exchanger, the bottom outlet of the receiving kettle is connected to a slicer, and the top gasification outlet is connected to a cold trap. Compared with the prior art, the product yield of isophthalonitrile / terephthalonitrile obtained by the present invention can reach 97%, the content of isophthalonitrile / terephthalonitrile in the refined finished product can reach 99.5%, and the content of p-cyanobenzamide is reduced from about 1.5% before refining to 0.25%, which greatly reduces the amount of residue generated in the melting kettle in the subsequent tetrachloroterephthalonitrile production. CN110590603A discloses a method for continuous distillation and purification of isophthalonitrile. The method realizes continuous and stable purification of isophthalonitrile through melting, continuous evaporation and vaporization and distillation purification steps, and obtains a product with an isophthalonitrile purity of ≥99.82wt%, reduces the content of cyanobenzamide in the product, thereby reducing the content of hexachlorobenzene in the downstream thiophanate-methyl product, alleviates environmental pressure, and the method can achieve continuous and stable production with low operating costs.

[0004] However, the existing distillation purification process has a large amount of slag discharge, serious blockage of the distillation system, unsmooth operation, and difficulty in maintenance. In addition, during the distillation purification process, some isophthalonitrile / terephthalonitrile will be hydrolyzed to generate amide impurities, resulting in material loss and reduced yield. Therefore, it is necessary to develop a new method for refining crude isophthalonitrile / terephthalonitrile, which can effectively remove moisture and insoluble matter in the crude isophthalonitrile / terephthalonitrile before distillation to reduce interference with subsequent distillation. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention provides a method for refining a crude isophthalonitrile / terephthalonitrile product, the method comprising: mixing the crude isophthalonitrile / terephthalonitrile product with a solvent and completely dissolving the crude isophthalonitrile / terephthalonitrile product, the solvent being a solvent azeotropic with water, removing moisture by azeotropic with water, removing insolubles by filtering, and also recovering the solvent first based on graded temperature increase, and then completely melting the isophthalonitrile / terephthalonitrile and sending it to a distillation system. The method for refining of the present invention removes moisture and insolubles in the crude isophthalonitrile / terephthalonitrile product before distillation, thereby avoiding the main content loss of the crude isophthalonitrile / terephthalonitrile product during melting and distillation, improving the yield of isophthalonitrile / terephthalonitrile, reducing the amount of slag discharge, and improving the material yield, so that the distillation system can run more smoothly, with obvious environmental benefits and high economic benefits.

[0006] To achieve this object, the present invention adopts the following technical solutions:

[0007] The object of the present invention is to provide a method for refining a crude isophthalonitrile / terephthalonitrile product, wherein the method comprises any one of the following two methods:

[0008] Method A: Mixing a crude isophthalonitrile / terephthalonitrile with a solvent and completely dissolving the mixture, heating the mixture to a first temperature so that the solvent and water are azeotropic, separating and removing the obtained water layer through condensation and stratification, refluxing the obtained solvent layer and obtaining a dehydrated crude product liquid; filtering the dehydrated crude product liquid to remove insoluble matter, heating the mixture to a second temperature so that the solvent is vaporized, recovering the solvent through condensation, and continuing to heat the mixture to a third temperature so that the isophthalonitrile / terephthalonitrile is completely melted and sent to a distillation system;

[0009] or,

[0010] Method B: The crude isophthalonitrile / terephthalonitrile is mixed with a solvent and completely dissolved, the insoluble matter is removed by filtration, the temperature is raised to the azeotropic temperature, the solvent and water are azeotropic, the obtained water layer is separated and removed by condensation and stratification, the obtained solvent layer is recovered, and the temperature is continued to be raised to a third temperature, so that the isophthalonitrile / terephthalonitrile is completely melted and sent to the distillation system.

[0011] The crude isophthalonitrile / terephthalonitrile product of the present invention refers to crude isophthalonitrile or crude terephthalonitrile, because both are subjected to ammoxidation reaction in a fluidized bed under the catalysis of a catalyst, and are obtained by condensation and capture by water spraying after the reaction is completed, and the refining method can be universal.

[0012] The purification method of the present invention first mixes the crude isophthalonitrile with a solvent and completely dissolves it, and the solvent is a solvent that azeotropes with water. The method A can be used to remove moisture first by azeotropy, and then filter to remove insolubles, or the method B can be used to first filter to remove insolubles, and then azeotropy to remove moisture, and then based on graded temperature increase, the solvent is first recovered, and then the isophthalonitrile is completely melted and sent to the distillation system. The purification method of the present invention removes moisture and insolubles in the crude isophthalonitrile before distillation, avoids the main content loss of the crude isophthalonitrile in the melting and distillation process, improves the yield of isophthalonitrile, reduces the amount of slag discharge, and improves the material yield, so that the distillation system runs more smoothly, has obvious environmental benefits, and has high economic benefits.

[0013] As a preferred technical solution of the present invention, in method A, the mass ratio of the crude isophthalonitrile / terephthalonitrile to the solvent is 1:(2-10), for example, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10, etc.

[0014] It should be noted that in method A, the amount of solvent used is related to the dissolution temperature, and the specific amount of solvent added is based on whether the crude isophthalonitrile / terephthalonitrile can be completely dissolved.

[0015] As a preferred technical solution of the present invention, in method A, the first temperature is 75-100°C, for example, 75°C, 78°C, 85°C, 87°C, 88°C, 90°C, 92°C, 94°C, 95°C, 96°C, 98°C or 100°C, etc.

[0016] As a preferred technical solution of the present invention, in method A, the second temperature is 110-150°C, for example, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 141°C, 143°C, 145°C, 147°C, 148°C or 150°C, etc.

[0017] As a preferred technical solution of the present invention, in method B, the mass ratio of the crude isophthalonitrile / terephthalonitrile to the solvent is 1:(2-10), for example, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10, etc.

[0018] It should be noted that in method B, the amount of solvent used is related to the dissolution temperature, and the specific amount of solvent added is based on whether the crude isophthalonitrile / terephthalonitrile can be completely dissolved.

[0019] As a preferred technical solution of the present invention, in method B, the azeotropic temperature is 75-100°C, for example, 75°C, 78°C, 85°C, 87°C, 88°C, 90°C, 92°C, 94°C, 95°C, 96°C, 98°C or 100°C, etc.

[0020] As a preferred technical solution of the present invention, in method A or method B, the raw material is crude isophthalonitrile, and the third temperature is 170°C-180°C, for example, 170°C, 173°C, 175°C, 176°C, 178°C or 180°C, etc.; the raw material is crude terephthalonitrile, and the third temperature is 230-240°C, for example, 230°C, 231°C, 233°C, 235°C, 236°C, 238°C or 240°C, etc.

[0021] As a preferred technical solution of the present invention, in method A or method B, the main content of the crude isophthalonitrile / terephthalonitrile is 92-99% by mass, for example, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99%, etc., the insoluble matter content is 0.1-0.8%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7% or 0.8%, etc., the amide content is 0.5-8%, for example, 0.5%, 1.5%, 2.5%, 3.5%, 4.5%, 5.5%, 6.5%, 7.5% or 8%, etc., and the moisture content is 0.5-15%, for example, 0.5%, 1.5%, 3.5%, 5.5%, 7.5%, 8.5%, 10.5%, 12.5%, 14.5% or 15%, etc.

[0022] As a preferred technical solution of the present invention, in method A or method B, the solvent is a solvent that azeotropes with water, including at least one of toluene, xylene, benzonitrile, ethanol, n-butanol or isobutanol. If the raw material is crude isophthalonitrile, the solvent is preferably m-xylene and / or benzonitrile, and if the raw material is crude terephthalonitrile, the solvent is preferably p-xylene and / or benzonitrile.

[0023] As a preferred technical solution of the present invention, in method A or method B, the filtration accuracy of the filtration is 0.1-10μm, such as 0.1μm, 0.5μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm or 10μm, etc. More preferably, the filter type used in the filtration includes at least one of filter cloth type, filter bag type or filter element type. Those skilled in the art can select the appropriate filter size and accuracy according to actual needs, and select the appropriate filtration type and equipment. The present invention will not make too many restrictions here.

[0024] Compared with the prior art solutions, the present invention has at least the following beneficial effects:

[0025] (1) The refining method of the present invention can remove moisture and insoluble matter in the crude isophthalonitrile / terephthalonitrile product before distillation, so that the melting speed of isophthalonitrile / terephthalonitrile is fast, the process is easy to control, and the situation of carrying material while water evaporation is avoided, and the material loss in the melting process is small;

[0026] (2) The refining method of the present invention can remove moisture and insoluble matter in the crude iso / terephthalonitrile product before distillation, so that the distillation system feed contains no insoluble matter, the entire distillation system runs smoothly, and the amount of slag discharge is small;

[0027] (3) The refining method of the present invention can remove moisture and insoluble matter in the crude isophthalonitrile / terephthalonitrile product before distillation, thereby avoiding the main content loss of the crude isophthalonitrile / terephthalonitrile product during the melting and distillation process, improving the yield of isophthalonitrile / terephthalonitrile, reducing the amount of slag discharge, and improving the material yield, making the distillation system run more smoothly, with obvious environmental benefits and high economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a diagram of the device used in the refining method described in Example 1 of the present invention;

[0029] Figure 2 is a diagram of the device used in the refining method described in Example 3 of the present invention;

[0030] In the figure: 1-dissolving kettle; 2-dissolving kettle condenser; 3-reflux water separator; 4-dissolving kettle transfer pump; 5-filter; 6-melting kettle; 7-melting kettle condenser; 8-melting kettle transfer pump; DETAILED DESCRIPTION

[0031] The technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0032] To better illustrate the present invention and facilitate understanding of the technical solution of the present invention, typical but non-limiting embodiments of the present invention are as follows:

[0033] Example 1

[0034] This embodiment provides a method for refining crude terephthalonitrile, using Figure 1 The refining method includes the following contents:

[0035] Add the solvent p-xylene to the dissolving kettle 1, start stirring, add the crude terephthalonitrile according to the mass ratio of p-xylene to terephthalonitrile of 5:1, raise the temperature to 80°C, the solution in the kettle becomes clear, and the crude terephthalonitrile is completely dissolved; wherein the crude terephthalonitrile has a main content of 96.5%, water of 1.5%, insoluble matter of 0.3%, and amides of 1.7%;

[0036] The temperature of the dissolving kettle 1 is further raised to 88°C, and the dissolving kettle condenser 2 begins to condense a large amount of liquid into the reflux water separator 3. The reflux is continued, and the temperature of the dissolving kettle 1 is raised to 100°C. The water phase in the reflux water separator 3 no longer increases and is sent to water treatment, and the azeotropic dehydration is completed;

[0037] The material in the dissolving kettle 1 is transferred to the filter 5 through the dissolving kettle transfer pump 4 to remove the insoluble matter. The filter is a 0.5μm bag filter. After removing the insoluble matter, it enters the melting kettle 6 and continues to be heated to 140°C. After the solvent is condensed by the melting kettle condenser 7, it is sent to the solvent recovery tank;

[0038] The temperature in the melting kettle 6 continues to rise to 230° C., and the terephthalonitrile is completely melted. After melting, the terephthalonitrile liquid is sent to the distillation system by the melting kettle transfer pump 8.

[0039] Example 2

[0040] This embodiment provides a method for refining crude isophthalonitrile, and the device used is the same as that in Example 1. The refining method includes the following contents:

[0041] Add the solvent m-xylene to the dissolving kettle 1, start stirring, add the crude isophthalonitrile according to the mass ratio of m-xylene to isophthalonitrile of 5:1, raise the temperature to 80°C, the solution in the kettle becomes clear, and the crude isophthalonitrile is completely dissolved; wherein, the crude isophthalonitrile has a main content of 95.8%, water content of 1.2%, insoluble matter of 0.25%, and amides of 2.75%;

[0042] The temperature of the dissolving kettle 1 is further raised to 88°C, and the dissolving kettle condenser 2 begins to condense a large amount of liquid into the reflux water separator 3. The reflux is continued, and the temperature of the dissolving kettle 1 is raised to 100°C. The water phase in the reflux water separator 3 no longer increases and is sent to water treatment, and the azeotropic dehydration is completed;

[0043] The material in the dissolving kettle 1 is transferred to the filter 5 through the dissolving kettle transfer pump 4 to remove the insoluble matter. The filter is a 0.5 μm bag filter. After removing the insoluble matter, it enters the melting kettle 6 and continues to be heated to 140°C. After the solvent is condensed by the melting kettle condenser 7, it goes to the solvent recovery tank;

[0044] The temperature in the melting kettle 6 continues to rise to 170°C, and the isophthalonitrile is completely melted. After melting, the isophthalonitrile liquid is sent to the distillation system by the melting kettle transfer pump 8.

[0045] Example 3

[0046] This embodiment provides a method for refining crude terephthalonitrile, using Figure 2 The refining method includes the following contents:

[0047] Adding solvent p-xylene to the dissolving kettle 1, starting stirring, adding crude terephthalonitrile according to the mass ratio of p-xylene to terephthalonitrile of 5:1, heating to 80°C, the solution in the kettle becomes clear, the crude terephthalonitrile is completely dissolved, and during the complete dissolution, the dissolving kettle condenser 2 refluxes all the condensate into the dissolving kettle 1; wherein the crude terephthalonitrile has a main content of 96.5%, water of 1.5%, insoluble matter of 0.3%, and amides of 1.7%;

[0048] The material in the dissolving kettle 1 is transferred to the filter 5 through the dissolving kettle transfer pump 4 to remove the insoluble matter. The filter is a 0.5 μm bag filter. After the insoluble matter is removed, the material enters the melting kettle 6;

[0049] The melting kettle 6 is heated to 88°C, and the melting kettle condenser 7 begins to condense a large amount of liquid into the reflux water separator 3. The reflux is continued, and the temperature of the melting kettle 6 is raised to 100°C. The water phase in the reflux water separator 3 no longer increases and is sent to water treatment, and azeotropic water removal is completed; the temperature is continued to be raised to 140°C, and the solvent layer in the reflux water separator 3 is sent to the solvent recovery tank; the temperature in the melting kettle 6 is continued to be raised to 230°C, and the terephthalonitrile is completely melted. After melting, the terephthalonitrile liquid is sent to the distillation system by the melting kettle transfer pump 8.

[0050] Example 4

[0051] This embodiment provides a method for refining crude isophthalonitrile, and the device used is the same as that in Example 3. The refining method includes the following contents:

[0052] Add the solvent m-xylene to the dissolving kettle 1, start stirring, add the crude isophthalonitrile according to the mass ratio of m-xylene to isophthalonitrile of 5:1, heat to 80°C, the solution in the kettle becomes clear, the crude isophthalonitrile is completely dissolved, and during the complete dissolution, the dissolving kettle condenser 2 refluxes all the condensate to the dissolving kettle 1; wherein, the crude isophthalonitrile has a main content of 95.8%, water content of 1.2%, insoluble matter of 0.25%, and amides of 2.75%;

[0053] The material in the dissolving kettle 1 is transferred to the filter 5 through the dissolving kettle transfer pump 4 to remove the insoluble matter. The filter is a 0.5 μm bag filter. After the insoluble matter is removed, the material enters the melting kettle 6;

[0054] The melting kettle 6 is heated to 88°C, and the melting kettle condenser 7 begins to condense a large amount of liquid into the reflux water separator 3. The reflux is continued, and the temperature of the melting kettle 6 is raised to 100°C. The water phase in the reflux water separator 3 no longer increases and is sent to water treatment, and the azeotropic dehydration is completed; the temperature is continued to be raised to 140°C, and the solvent layer in the reflux water separator 3 is sent to the solvent recovery tank; the temperature in the melting kettle 6 is continued to be raised to 170°C, and the isophthalonitrile is completely melted. After melting, the isophthalonitrile liquid is sent to the distillation system by the melting kettle transfer pump 8.

[0055] Example 5

[0056] This embodiment provides a method for refining crude terephthalonitrile. Compared with Example 1, the only difference is that p-xylene is replaced by an equal mass of benzonitrile.

[0057] Example 6

[0058] This embodiment provides a method for refining crude isophthalonitrile. Compared with Example 2, the only difference is that m-xylene is replaced by an equal mass of benzonitrile.

[0059] Comparative Example 1

[0060] This comparative example provides a method for refining crude terephthalonitrile. Compared with Example 1, the only difference is that the crude terephthalonitrile is directly added to the melting kettle 6, and the temperature is directly raised to 230° C. to completely melt the terephthalonitrile. After melting, the terephthalonitrile liquid is sent to the distillation system by the melting kettle transfer pump 8.

[0061] Comparative Example 2

[0062] This comparative example provides a method for refining crude isophthalonitrile. Compared with Example 2, the only difference is that the crude isophthalonitrile is directly added to the melting kettle 6, and the temperature is directly raised to 170° C. to completely melt the isophthalonitrile. After melting, the isophthalonitrile liquid is sent to the distillation system by the melting kettle transfer pump 8.

[0063] According to the refining methods described in the above embodiments and comparative examples, the main material content and amide content of crude isophthalonitrile / terephthalonitrile and melted isophthalonitrile / terephthalonitrile were tested respectively, and the relevant results are summarized in Table 1.

[0064] Table 1

[0065]

[0066]

[0067] It can be seen from Table 1 that if the crude isophthalonitrile / terephthalonitrile in powder state is directly put into a melting kettle for heating and melting, the moisture and insoluble matter in the crude product will cause the melting speed of the crude product to slow down, and the agglomerates in the crude product will be broken, which will cause the moisture in the original agglomerates to evaporate quickly and cause the material to be carried over. In addition, isophthalonitrile / terephthalonitrile will undergo a hydrolysis reaction with the moisture in the crude product, resulting in a significant increase in the content of amides.

[0068] In contrast, the refining method of the present invention can remove moisture and insolubles in the crude iso / terephthalonitrile product before distillation, so that the melting speed of iso / terephthalonitrile is fast, the process is easy to control, the situation of carrying material while evaporating water is avoided, the material loss in the melting process is small, the distillation system feed has no insolubles, the whole distillation system runs smoothly, the slag discharge amount is small, the main content loss of the crude iso / terephthalonitrile product during the melting and distillation process is avoided, the yield of iso / terephthalonitrile is improved, the slag discharge amount is reduced, and the material yield is improved, so that the distillation system runs more smoothly, the environmental protection benefits are obvious, and the economic benefits are high.

[0069] It should be noted that when the solvent in the above embodiment is replaced with a solvent of equal mass that does not form an azeotrope with water, the following problems may occur during operation:

[0070] 1. During the desolventizing process of the solvent that is not azeotropic with water, the water cannot be removed, resulting in agglomeration and wall adhesion of isophthalonitrile / terephthalonitrile during the precipitation process;

[0071] 2. The occurrence of wall hanging and agglomeration is not conducive to the subsequent melting operation, and the melting speed will be slow and incomplete;

[0072] 3. During the melting process, the agglomerated materials will break up, causing the water in the original agglomerates to evaporate quickly, resulting in the situation of carrying materials.

[0073] The present invention illustrates the detailed structural features of the present invention through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the components selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0074] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0075] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0076] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for refining crude isophthalonitrile / terephthalonitrile, characterized in that: The refining method includes any one of the following two methods: Method A: Mixing a crude isophthalonitrile / terephthalonitrile with a solvent and completely dissolving the mixture, heating the mixture to a first temperature so that the solvent and water are azeotropic, separating and removing the obtained water layer through condensation and stratification, refluxing the obtained solvent layer and obtaining a dehydrated crude product liquid; filtering the dehydrated crude product liquid to remove insoluble matter, heating the mixture to a second temperature so that the solvent is vaporized, recovering the solvent through condensation, and continuing to heat the mixture to a third temperature so that the isophthalonitrile / terephthalonitrile is completely melted and sent to a distillation system; or, Method B: The crude isophthalonitrile / terephthalonitrile is mixed with a solvent and completely dissolved, the insoluble matter is removed by filtration, the temperature is raised to the azeotropic temperature, the solvent and water are azeotropic, the obtained water layer is separated and removed by condensation and stratification, the obtained solvent layer is recovered, and the temperature is continued to be raised to a third temperature, so that the isophthalonitrile / terephthalonitrile is completely melted and sent to the distillation system.

2. The refining method according to claim 1, characterized in that In method A, the mass ratio of the crude isophthalonitrile / terephthalonitrile to the solvent is 1:(2-10).

3. The purification method according to claim 1, characterized in that: In method A, the first temperature is 75-100°C.

4. The refining method according to claim 1, characterized in that: In method A, the second temperature is 110-150°C.

5. The purification method according to claim 1, characterized in that: In method B, the mass ratio of the crude isophthalonitrile / terephthalonitrile to the solvent is 1:(2-10).

6. The purification method according to claim 1, characterized in that: In method B, the azeotropic temperature is 75-100°C.

7. The purification method according to claim 1, characterized in that: In method A or method B, if the raw material is crude isophthalonitrile, the third temperature is 170°C-180°C; if the raw material is crude terephthalonitrile, the third temperature is 230-240°C.

8. The purification method according to claim 1, characterized in that: In method A or method B, the crude isophthalonitrile / terephthalonitrile product has a main content of 92-99%, an insoluble matter content of 0.1-0.8%, an amide content of 0.5-8%, and a moisture content of 0.5-15%, calculated by mass percentage.

9. The purification method according to claim 1, characterized in that: In method A or method B, the solvent is a solvent that is azeotropic with water, including at least one of toluene, xylene, benzonitrile, ethanol, n-butanol or isobutanol.

10. The purification method according to claim 1, characterized in that: In method A or method B, the filtering accuracy of the filtering is 0.1-10 μm.

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