Method for purifying isophthalonitrile by solvent method

Abstract

The invention provides a method for purifying isophthalonitrile by a solvent method, which comprises the following steps: mixing an isophthalonitrile crude product with an organic solvent and water, heating, preserving heat, standing, layering the solution, and separating a water layer at the lower part from insoluble substances; and after layering the solution, sequentially carrying out cooling crystallization, solid-liquid separation and drying on an organic layer at the upper part to obtain an isophthalonitrile product. According to the method disclosed by the invention, a solvent method is adopted, water and an organic solvent are adopted to carry out impurity removal on the isophthalonitrile crude product according to impurity types in the isophthalonitrile crude product, inorganic impurities and organic impurities in the isophthalonitrile crude product are respectively removed, and particularly, the isophthalonitrile is recrystallized and purified by selecting the types of the organic solvents, so that the purity of the isophthalonitrile is improved. The purity and the yield of isophthalonitrile can be effectively improved; the method is simple to operate, mild in condition, low in raw material cost, capable of being recycled, simple in post-treatment process and convenient for industrial production.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic purification and refining, and relates to a method for purifying isophthalonitrile by a solvent method. Background Art

[0002] Phthalonitrile, as an important class of chemical products, mainly includes isophthalonitrile, terephthalonitrile, and phthalonitrile. Different configurations have different applications. Among them, isophthalonitrile is a white needle-like crystal and an important intermediate in organic synthesis. Due to the highly reactive cyano group and other easily activated sites in its molecule, it can be used to prepare chemical products for the fields of pesticides, pharmaceuticals, building materials, dyes, etc. through reactions such as hydrogenation, hydrolysis, halogenation, and polymerization. For example, isophthalonitrile can be synthesized into tetrachloroisophthalonitrile through a chlorination reaction, which is chlorothalonil, a highly efficient and low-toxic fungicide and one of the most important applications of isophthalonitrile at present.

[0003] The main preparation method of isophthalonitrile is to directly prepare isophthalonitrile by a gas-phase ammoxidation catalytic method using m-xylene, ammonia, and air as raw materials. This method has the advantages of low raw material cost, no pollution discharge, normal pressure operation, and medium reaction temperature. However, the crude isophthalonitrile obtained by trapping the steam flowing out of the ammoxidation fluidized bed reactor contains various impurities. The inorganic impurities include water, catalyst powder, rust, etc., and the organic impurities include cyanobenzamide, phthalimide, methylbenzonitrile, etc. Using isophthalonitrile containing the above impurities in the production of chlorothalonil will seriously affect the quality of chlorothalonil. Therefore, it is necessary to purify and refine the crude isophthalonitrile to make the subsequent produced chlorothalonil products meet the quality requirements.

[0004] CN 109593051A discloses a method for refining isophthalonitrile as a raw material for chlorothalonil. The method includes: adding isophthalonitrile and a solvent into a refining kettle equipped with a reflux condenser and a tail gas absorption tower, adding a dehydrating agent, heating to carry out a dehydration reaction; cooling, dripping water to quench the reaction, stirring and then separating the liquid, adding washing water to the organic phase, stirring and separating the liquid, adding water to the organic phase, heating for azeotropic distillation, separating the suspension of isophthalonitrile and water by solid-liquid separation, and drying the isophthalonitrile. This method uses a dehydrating agent to dehydrate the amide bond on the amide impurities in isophthalonitrile to generate a cyano group to achieve the purpose of purification. However, this method can only remove the cyanobenzamide impurities and cannot remove inorganic impurities and other organic impurities.

[0005] CN 110963942 A discloses a method for refining phthalonitrile, which includes: dissolving the phthalonitrile to be refined in liquid ammonia to obtain solution A, and through solid-liquid separation, obtaining solution B after impurity removal; subsequently, performing deammoniation treatment on solution B, and the way of the deammoniation treatment is ammonia volatilization or crystallization treatment to obtain refined phthalonitrile. This method selectively dissolves phthalonitrile with liquid ammonia to separate it from impurities, but the types of impurities are not clearly defined, so it is impossible to ensure that the impurities are insoluble in liquid ammonia. At the same time, when liquid ammonia is used as a solvent, it has high requirements for parameters such as temperature and pressure, and the process is not easy to control.

[0006] CN 116199601 A discloses a refining and purification process for high-content chlorothalonil. The purification process includes: placing the crude chlorothalonil in a solvent, heating to dissolve it, then adding an acid to adjust the pH value of the system to be no greater than 1, and then cooling for recrystallization, centrifuging, and drying to obtain a chlorothalonil product with a chlorothalonil content ≥ 99 wt%; the solvent is a mixed solution of water and an organic solvent. This method purifies the crude chlorothalonil, which belongs to a different substance type from m-xylene. The types of impurities to be removed and the types of solvents used will also be different, and the auxiliary process operations required during the impurity removal process are also different.

[0007] In summary, for the purification and refining of crude isophthalonitrile, it is necessary to select a suitable process for impurity removal according to the types of impurities therein, especially to select a suitable type of solvent, so as to achieve a better purification effect, obtain a high-quality phthalonitrile product, and improve the yield and reduce the cost. Summary of the Invention

[0008] Aiming at the problems existing in the prior art, the purpose of the present invention is to provide a method for purifying isophthalonitrile by the solvent method. The method respectively uses water and an organic solvent to remove impurities from the crude isophthalonitrile, removing its inorganic impurities and organic impurities respectively. Especially through the recrystallization purification of isophthalonitrile, the purity and yield of isophthalonitrile can be effectively improved, and the solvent used can be recycled, which helps to reduce the production cost.

[0009] To achieve this purpose, the present invention adopts the following technical solutions:

[0010] The present invention provides a method for purifying isophthalonitrile by the solvent method, and the method includes the following steps:

[0011] (1) Mix the crude isophthalonitrile with an organic solvent and water, heat and then keep it warm and stand still. After the solution is layered, separate the lower water layer and insoluble substances;

[0012] (2) Perform cooling crystallization, solid-liquid separation and drying on the upper organic layer after the solution is layered in step (1) in sequence to obtain the isophthalonitrile product.

[0013] In the present invention, for the crude isophthalonitrile obtained from the process of producing isophthalonitrile from m-xylene, purification and refinement are required. The present invention adopts the solvent method. According to the types of impurities in the crude isophthalonitrile, water and an organic solvent are mixed with it, so that after the solution is layered, the inorganic impurities are deposited in the water layer, and the organic impurities are dissolved in the organic layer and the water layer. By selecting the type of organic solvent and using the method of recrystallization for purification, a high-purity isophthalonitrile product is obtained, and the product yield is high; the method has simple operation, mild conditions, low raw material cost, can be recycled, and the post-treatment process is simple, which is convenient for industrial production.

[0014] The following are the preferred technical solutions of the present invention, but not the limitations of the technical solutions provided by the present invention. Through the following technical solutions, the technical purposes and beneficial effects of the present invention can be better achieved and realized.

[0015] As a preferred technical solution of the present invention, the source of the crude isophthalonitrile in step (1) includes the reaction product obtained by the gas-phase ammoxidation of m-xylene.

[0016] Preferably, the content of isophthalonitrile in the crude isophthalonitrile in step (1) is 87-96 wt%, such as 87 wt%, 88 wt%, 89 wt%, 90 wt%, 91 wt%, 92 wt%, 93 wt%, 94 wt%, 95 wt% or 96 wt% etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0017] Preferably, the impurities in the crude isophthalonitrile in step (1) include inorganic impurities and organic impurities.

[0018] In the present invention, according to the reaction source of the crude isophthalonitrile, the inorganic impurities contained therein mainly include water, catalyst powder and rust, and the organic impurities mainly include isocyano-benzamide, phthalimide, methylbenzonitrile, etc., and organic solvents and water are required for dissolution.

[0019] As a preferred technical solution of the present invention, the organic solvent in step (1) includes any one or at least two combinations of m-xylene, p-xylene or o-xylene. Typical but non-limiting examples of the combination are: the combination of m-xylene and p-xylene, the combination of p-xylene and o-xylene, the combination of m-xylene, p-xylene and o-xylene, etc.

[0020] Preferably, the mass ratio of the crude isophthalonitrile to the organic solvent in step (1) is 1:(5-10), such as 1:5, 1:6, 1:6.5, 1:7, 1:7.5, 1:8, 1:9 or 1:10 etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable, and preferably 1:(6-8).

[0021] In the present invention, m-xylene is used as an organic solvent to dissolve isophthalonitrile and its organic impurities. If the amount of the organic solvent m-xylene is too low, isophthalonitrile will not be completely dissolved. If the amount of the organic solvent m-xylene is too high, the crystallization precipitation amount of isophthalonitrile and impurities will decrease, resulting in a reduction in the yield, but an increase in purity. In addition, it will also cause waste of the solvent.

[0022] Preferably, the mass ratio of the crude isophthalonitrile to water in step (1) is 1:(0.1-1.2), such as 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:1 or 1:1.2, etc., but not limited to the listed values. Other unlisted values within this numerical range are equally applicable, and preferably 1:(0.4-0.8).

[0023] In the present invention, water is used as an auxiliary solvent, which can not only deposit and separate inorganic impurities in the crude isophthalonitrile, but also dissolve the main impurity, isophthaloyl cyanide, in isophthalonitrile. If only m-xylene is used as the solvent, isophthaloyl cyanide can only be dissolved in this solvent. When m-xylene and water are used together, it is more soluble in water, and isophthaloyl cyanide can be separated in advance during layering. This is because isophthaloyl cyanide is more likely to precipitate in the single solvent m-xylene and cannot be crystallized and separated from m-xylene. If the amount of water is too low, isophthaloyl cyanide cannot be completely dissolved in water and remains in the organic layer, resulting in a reduction in the purity of isophthalonitrile. If the amount of water is too high, since isophthalonitrile has a certain solubility in water, the yield of isophthalonitrile will decrease.

[0024] As a preferred technical solution of the present invention, the heating temperature in step (1) is 50-95°C, such as 50°C, 60°C, 70°C, 75°C, 80°C, 85°C, 90°C or 95°C, etc., but not limited to the listed values. Other unlisted values within this numerical range are equally applicable, and preferably 70-90°C.

[0025] Preferably, stirring is carried out during the heating process in step (1).

[0026] Preferably, the heat preservation and static settlement time in step (1) is 5-20 min, such as 5 min, 6 min, 8 min, 10 min, 12 min, 14 min, 15 min, 16 min, 18 min or 20 min, etc., but not limited to the listed values. Other unlisted values within this numerical range are equally applicable, and preferably 8-15 min.

[0027] As a preferred technical solution of the present invention, after the heat preservation and static settlement in step (1), it is divided into an aqueous layer and an organic layer. The inorganic impurities in the crude isophthalonitrile form insoluble substances and deposit in the aqueous layer, and part of the organic impurities dissolve in the water.

[0028] Preferably, after the aqueous layer and the inorganic insoluble substances are separated, they are first cooled to room temperature, the organic impurities precipitate out, and then the water is solid-liquid separated from the insoluble substances and the precipitates, and the obtained water is returned to step (1) for use.

[0029] As a preferred technical solution of the present invention, the cooling crystallization method in step (2) is natural cooling or water cooling, preferably water cooling.

[0030] Preferably, the cooling rate of the cooling crystallization in step (2) is 1.2 - 2.5 °C / min, such as 1.2 °C / min, 1.4 °C / min, 1.5 °C / min, 1.6 °C / min, 1.8 °C / min, 2.0 °C / min, 2.2 °C / min, 2.4 °C / min or 2.5 °C / min, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0031] Preferably, the cooling crystallization in step (2) is cooled to 10 - 25 °C, such as 10 °C, 12 °C, 15 °C, 18 °C, 20 °C, 22 °C, 24 °C or 25 °C, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0032] Preferably, the time of the cooling crystallization in step (2) is 0.5 - 3 h, such as 0.5 h, 1 h, 1.25 h, 1.5 h, 1.75 h, 2 h, 2.5 h or 3 h, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable, preferably 1 - 2 h.

[0033] In the present invention, the time of the cooling crystallization refers to the total time from the start of cooling plus the maintenance of crystallization.

[0034] As a preferred technical solution of the present invention, the solid-liquid separation in step (2) includes filtration separation.

[0035] Preferably, the liquid phase obtained by the solid-liquid separation is used as a raw material for the production of phthalonitrile.

[0036] Preferably, the solid phase obtained by the solid-liquid separation is dried.

[0037] As a preferred technical solution of the present invention, the temperature of the drying in step (2) is 40 to 80 °C, such as 40 °C, 45 °C, 50 °C, 55 °C, 60 °C, 65 °C, 70 °C, 75 °C or 80 °C, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable, preferably 50 to 70 °C.

[0038] Preferably, the drying time in step (2) is 1 to 3 h, such as 1 h, 1.5 h, 2 h, 2.5 h or 3 h, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0039] As a preferred technical solution of the present invention, the purity of the isophthalonitrile product in step (2) is above 99.5 wt%, such as 99.5 wt%, 99.52 wt%, 99.54 wt%, 99.55 wt%, 99.56 wt%, 99.58 wt%, 99.6 wt%, 99.65 wt%, 99.7 wt% or 99.8 wt%, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0040] As a preferred technical solution of the present invention, the method comprises the following steps:

[0041] (1) Mix the crude isophthalonitrile with an organic solvent and water. The content of isophthalonitrile in the crude isophthalonitrile is 87 to 96 wt%. The impurities include inorganic impurities and organic impurities. The organic solvent includes any one or a combination of at least two of m-xylene, p-xylene or o-xylene. The mass ratio of the crude isophthalonitrile to the organic solvent is 1:(5 - 10), and the mass ratio of the crude isophthalonitrile to water is 1:(0.1 - 1.2). After stirring and heating, keep warm and stand still. The heating temperature is 50 to 95 °C, and the time for keeping warm and standing still is 5 to 20 min. The solution is divided into an aqueous layer and an organic layer. The inorganic impurities in the crude isophthalonitrile form insoluble substances and deposit in the lower aqueous layer. Part of the organic impurities dissolve in water. Separate the lower aqueous layer and the inorganic insoluble substances, cool them to room temperature, and organic impurities precipitate. Then, through solid-liquid separation, the obtained water is returned to step (1) for use;

[0042] (2) After the solution in step (1) is layered, the upper organic layer is successively subjected to cooling crystallization, solid-liquid separation and drying. The cooling crystallization method is natural cooling or water cooling. The cooling rate of the cooling crystallization is 1.2 - 2.5 °C / min. The cooling crystallization is cooled to 10 - 25 °C. The time of the cooling crystallization is 0.5 - 3 h. The solid-liquid separation includes filtration separation. The liquid phase obtained from the solid-liquid separation is used as a raw material for the production of phthalonitrile, and the obtained solid phase is dried. The drying temperature is 40 - 80 °C and the time is 1 - 3 h to obtain isophthalonitrile product. The purity of the isophthalonitrile product is above 99.5 wt%.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] (1) The method of the present invention adopts the solvent method. According to the types of impurities in the crude isophthalonitrile, water and organic solvents are used to remove impurities from the crude isophthalonitrile, and inorganic impurities and organic impurities are removed respectively. Especially through the selection of the type of organic solvent, the isophthalonitrile is recrystallized and purified, which can effectively improve the purity and yield of isophthalonitrile. The purity can reach above 99.5 wt%, and the yield can reach above 85%;

[0045] (2) The method of the present invention is simple in operation, mild in conditions, low in raw material cost, and can be recycled. The post-treatment process is simple and convenient for industrial production. Detailed implementation manners

[0046] To better illustrate the present invention and facilitate the understanding of the technical solution of the present invention, the present invention will be further described in detail below. However, the following embodiments are only simple examples of the present invention and do not represent or limit the scope of the protection of the present invention. The scope of protection of the present invention is subject to the claims.

[0047] The detailed implementation manners part of the present invention provides a method for purifying isophthalonitrile by the solvent method. The method includes the following steps:

[0048] (1) Mix the crude isophthalonitrile with an organic solvent and water, heat and then keep warm and stand still. After the solution is layered, separate the lower water layer and insoluble substances;

[0049] (2) After the solution in step (1) is layered, the upper organic layer is successively subjected to cooling crystallization, solid-liquid separation and drying to obtain isophthalonitrile product.

[0050] The following are typical but non-limiting embodiments of the present invention:

[0051] Example 1:

[0052] This example provides a method for purifying isophthalonitrile by the solvent method. The method includes the following steps:

[0053] (1) Mix the crude isophthalonitrile with an organic solvent and water. The content of isophthalonitrile in the crude isophthalonitrile is 90.2 wt%. The impurities include inorganic impurities and organic impurities. The organic solvent is m-xylene. The mass ratio of the crude isophthalonitrile to the organic solvent is 1:8, and the mass ratio of the crude isophthalonitrile to water is 1:0.5. After stirring and heating, keep it warm and stand still. The heating temperature is 75 °C, and the time for keeping warm and standing still is 15 min. The solution is divided into an aqueous layer and an organic layer. The inorganic impurities in the crude isophthalonitrile form insoluble substances and deposit in the lower aqueous layer. The organic impurity, isocyano benzamide, dissolves in water. Separate the lower aqueous layer and the inorganic insoluble substances, cool them to room temperature, and the organic impurities precipitate. Then, through solid-liquid separation, the obtained water is returned to step (1) for use;

[0054] (2) Cool, crystallize, conduct solid-liquid separation, and dry the upper organic layer after the solution is layered in step (1). The cooling and crystallization method is water cooling. The cooling rate of the cooling and crystallization is 2.0 °C / min. Cool and crystallize to 20 °C, and the time for cooling and crystallization is 1.5 h. White crystal particles precipitate. The solid-liquid separation is filtration separation. The filtrate obtained from the solid-liquid separation is used as a raw material for the production of isophthalonitrile. The obtained filter cake is dried. The drying temperature is 60 °C, and the time is 2 h to obtain the isophthalonitrile product.

[0055] Example 2:

[0056] This example provides a method for purifying isophthalonitrile by the solvent method. The method includes the following steps:

[0057] (1) Mix the crude isophthalonitrile with an organic solvent and water. The content of isophthalonitrile in the crude isophthalonitrile is 89.7 wt%. The impurities include inorganic impurities and organic impurities. The organic solvent is m-xylene. The mass ratio of the crude isophthalonitrile to the organic solvent is 1:6, and the mass ratio of the crude isophthalonitrile to water is 1:0.25. After stirring and heating, keep it warm and stand still. The heating temperature is 90 °C, and the time for keeping warm and standing still is 10 min. The solution is divided into an aqueous layer and an organic layer. The inorganic impurities in the crude isophthalonitrile form insoluble substances and deposit in the lower aqueous layer. The organic impurity, isocyano benzamide, dissolves in water. Separate the lower aqueous layer and the inorganic insoluble substances, cool them to room temperature, and the organic impurities precipitate. Then, through solid-liquid separation, the obtained water is returned to step (1) for use;

[0058] (2) After the solution in step (1) is layered, the upper organic layer is successively subjected to cooling crystallization, solid-liquid separation, and drying. The cooling crystallization is carried out by water cooling. The cooling rate of the cooling crystallization is 2.5 °C / min. The cooling crystallization is cooled to 25 °C. The time of the cooling crystallization is 2 h, and white crystal particles are precipitated. The solid-liquid separation is filtration separation. The filtrate obtained from the solid-liquid separation is used as a raw material for the production of isophthalonitrile. The obtained filter cake is dried. The drying temperature is 50 °C, and the time is 2.5 h to obtain the isophthalonitrile product.

[0059] Example 3:

[0060] This example provides a method for purifying isophthalonitrile by the solvent method. The method includes the following steps:

[0061] (1) The crude isophthalonitrile is mixed with an organic solvent and water. The content of isophthalonitrile in the crude isophthalonitrile is 91.5 wt%. The impurities include inorganic impurities and organic impurities. The organic solvent is m-xylene. The mass ratio of the crude isophthalonitrile to the organic solvent is 1:7. The mass ratio of the crude isophthalonitrile to water is 1:0.6. After stirring and heating, it is kept warm and static. The heating temperature is 78 °C, and the time of keeping warm and static is 8 min. The solution is divided into an aqueous layer and an organic layer. The inorganic impurities in the crude isophthalonitrile form insoluble substances and deposit in the lower aqueous layer. The organic impurity, isocyano benzamide, dissolves in water. The lower aqueous layer and the inorganic insoluble substances are separated and cooled to room temperature. The organic impurities precipitate, and then through solid-liquid separation, the obtained water is returned to step (1) for use;

[0062] (2) After the solution in step (1) is layered, the upper organic layer is successively subjected to cooling crystallization, solid-liquid separation, and drying. The cooling crystallization is carried out by natural cooling. The cooling rate of the cooling crystallization is 1.5 °C / min. The cooling crystallization is cooled to 15 °C. The time of the cooling crystallization is 2.5 h, and white crystal particles are precipitated. The solid-liquid separation is filtration separation. The filtrate obtained from the solid-liquid separation is used as a raw material for the production of isophthalonitrile. The obtained filter cake is dried. The drying temperature is 70 °C, and the time is 1.5 h to obtain the isophthalonitrile product.

[0063] Example 4:

[0064] This example provides a method for purifying isophthalonitrile by the solvent method. The method includes the following steps:

[0065] (1) Mix the crude isophthalonitrile with an organic solvent and water. The content of isophthalonitrile in the crude isophthalonitrile is 94.6 wt%. The impurities include inorganic impurities and organic impurities. The organic solvent is p-xylene. The mass ratio of the crude isophthalonitrile to the organic solvent is 1:5, and the mass ratio of the crude isophthalonitrile to water is 1:0.2. After stirring and heating, keep it warm and stand still. The heating temperature is 85 °C, and the time for keeping warm and standing still is 20 min. The solution is divided into an aqueous layer and an organic layer. The inorganic impurities in the crude isophthalonitrile form insoluble substances and deposit in the lower aqueous layer. The organic impurity, isocyano benzamide, dissolves in water. Separate the lower aqueous layer and the inorganic insoluble substances, cool them to room temperature, and the organic impurities precipitate. Then, through solid-liquid separation, the obtained water is returned to step (1) for use;

[0066] (2) Cool, crystallize, conduct solid-liquid separation, and dry the upper organic layer after the solution is layered in step (1). The way of cooling crystallization is natural cooling. The cooling rate of cooling crystallization is 1.8 °C / min. Cool the crystallization to 18 °C, and the time for cooling crystallization is 1 h. White crystal particles precipitate. The solid-liquid separation is filtration separation. The filtrate obtained from the solid-liquid separation is used as a raw material for the production of terephthalonitrile. The obtained filter cake is dried. The drying temperature is 40 °C, and the time is 3 h to obtain the isophthalonitrile product.

[0067] Example 5:

[0068] This example provides a method for purifying isophthalonitrile by a solvent method. The method includes the following steps:

[0069] (1) Mix the crude isophthalonitrile with an organic solvent and water. The content of isophthalonitrile in the crude isophthalonitrile is 87.5 wt%. The impurities include inorganic impurities and organic impurities. The organic solvent is o-xylene. The mass ratio of the crude isophthalonitrile to the organic solvent is 1:10, and the mass ratio of the crude isophthalonitrile to water is 1:1. After stirring and heating, keep it warm and stand still. The heating temperature is 65 °C, and the time for keeping warm and standing still is 5 min. The solution is divided into an aqueous layer and an organic layer. The inorganic impurities in the crude isophthalonitrile form insoluble substances and deposit in the lower aqueous layer. The organic impurity, isocyano benzamide, dissolves in water. Separate the lower aqueous layer and the inorganic insoluble substances, cool them to room temperature, and the organic impurities precipitate. Then, through solid-liquid separation, the obtained water is returned to step (1) for use;

[0070] (2) After the solution in step (1) is layered, the upper organic layer is successively subjected to cooling crystallization, solid-liquid separation, and drying. The cooling crystallization is carried out by water cooling, the cooling rate of the cooling crystallization is 1.2 °C / min, the cooling crystallization is cooled down to 10 °C, the time of the cooling crystallization is 3 h, and white crystal particles are precipitated. The solid-liquid separation is filtration separation. The filtrate obtained from the solid-liquid separation is used as a raw material for the production of phthalonitrile, and the obtained filter cake is dried. The drying temperature is 80 °C and the time is 1 h to obtain isophthalonitrile product.

[0071] Example 6:

[0072] This example provides a method for purifying isophthalonitrile by solvent method. The method refers to the method in Example 1, with the only difference being that in step (1), the mass ratio of the crude isophthalonitrile to the organic solvent is 1:4.

[0073] Example 7:

[0074] This example provides a method for purifying isophthalonitrile by solvent method. The method refers to the method in Example 1, with the only difference being that in step (1), the mass ratio of the crude isophthalonitrile to the organic solvent is 1:12.

[0075] Example 8:

[0076] This example provides a method for purifying isophthalonitrile by solvent method. The method refers to the method in Example 1, with the only difference being that in step (2), the filtrate obtained from the solid-liquid separation is directly returned to step (1) and used as the organic solvent.

[0077] Comparative Example 1:

[0078] This comparative example provides a method for purifying isophthalonitrile by solvent method. The method refers to the method in Example 1, with the only difference being that in step (1), the solvent mixed with the crude isophthalonitrile does not include water, only m-xylene.

[0079] Comparative Example 2:

[0080] This comparative example provides a method for purifying isophthalonitrile by solvent method. The method refers to the method in Example 1, with the only difference being that after the solution in step (1) is layered, only the inorganic impurities deposited in the water layer are separated, and the organic layer and the remaining water layer are jointly subjected to the operation of step (2).

[0081] The yields and purities of the isophthalonitrile products obtained in Examples 1-8 and Comparative Examples 1-2 are calculated, and the results are shown in Table 1.

[0082] Table 1

[0083] Yield / % Purity / wt% Example 1 85.5 99.60 Example 2 85.7 99.53 Example 3 85.8 99.62 Example 4 85.1 99.51 Example 5 85.4 99.58 Example 6 45.3 99.57 Example 7 83.3 99.68 Example 8 89.5 99.42 Comparative Example 1 86.5 99.09 Comparative Example 2 85.8 99.40

[0084] As can be seen from Table 1, when purifying isophthalonitrile by the above method, in Examples 1-5, by selecting appropriate parameters such as solvent type, ratio and temperature, the yield of the purified isophthalonitrile can reach over 85%, and the purity can reach over 99.5 wt%;

[0085] In Example 6, due to the too low dosage of the organic solvent m-xylene, incomplete dissolution of isophthalonitrile will occur. The undissolved isophthalonitrile will be separated out together with water and insoluble substances after standing, resulting in a reduction in the yield of the isophthalonitrile product, which is only 45.3%; in Example 7, due to the too high dosage of the organic solvent m-xylene, the amount of crystallized isophthalonitrile will decrease, resulting in a reduction in the yield of the isophthalonitrile product. At the same time, the amount of precipitated impurities also decreases, and the content of isophthalonitrile increases. In addition, the increase in solvent dosage will also cause solvent waste; in Comparative Example 1, since water is not used as an auxiliary solvent, but m-xylene is used alone, the impurity isocyano benzamide is more likely to precipitate in pure m-xylene, resulting in a reduction in the purity of isophthalonitrile in the precipitated crystalline product, which is only 99.09 wt%;

[0086] In Example 8, the recovered m-xylene filtrate is directly used as the m-xylene solvent. Since a small amount of isophthalonitrile and impurities are dissolved in the filtrate, the yield of isophthalonitrile increases, but the purity decreases to 99.42 wt%; in Comparative Example 2, after standing and separating the layers, the water layer is not separated, but is cooled and crystallized together with the organic layer. Since some organic impurities are dissolved in the water, the purity of isophthalonitrile decreases to 99.40 wt%.

[0087] Based on the above examples and comparative examples, it can be seen that the method of the present invention uses the solvent method. According to the types of impurities in the crude isophthalonitrile, water and organic solvents are used to remove impurities from the crude isophthalonitrile, removing its inorganic and organic impurities respectively. Especially through the selection of the type of organic solvent, the isophthalonitrile is recrystallized and purified, which can effectively improve the purity and yield of isophthalonitrile. The purity can reach over 99.5 wt%, and the yield can reach over 85%; the method has simple operation, mild conditions, low raw material cost, can be recycled, and the post-treatment process is simple, facilitating industrial production.

[0088] The applicant declares that the present invention uses the above examples to illustrate the detailed method of the present invention, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the method of the present invention, addition of auxiliary steps, selection of specific methods, etc. all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for purifying isophthalonitrile by solvent method, characterized in that: The method comprises the following steps: (1) mixing a crude isophthalonitrile with an organic solvent and water, heating the mixture, and then keeping the mixture warm and standing the mixture, and separating the lower water layer and insoluble matter after the solution is layered; (2) After the solution in step (1) is layered, the upper organic layer is cooled and crystallized, solid-liquid separated and dried in sequence to obtain an isophthalonitrile product.

2. The method according to claim 1, characterized in that: The source of the crude isophthalonitrile in step (1) includes a reaction product obtained by a gas phase ammoxidation of meta-xylene; Preferably, the isophthalonitrile content in the crude isophthalonitrile product of step (1) is 87-96 wt %; Preferably, the impurities in the crude isophthalonitrile in step (1) include inorganic impurities and organic impurities.

3. The method according to claim 1 or 2, characterized in that: The organic solvent in step (1) includes any one of m-xylene, p-xylene or o-xylene, or a combination of at least two thereof; Preferably, the mass ratio of the crude isophthalonitrile to the organic solvent in step (1) is 1:(5-10), preferably 1:(6-8); Preferably, the mass ratio of the crude isophthalonitrile to water in step (1) is 1:(0.1-1.2), preferably 1:(0.4-0.8).

4. The method according to any one of claims 1 to 3, characterized in that: The heating temperature in step (1) is 50 to 95° C., preferably 70 to 90° C.; Preferably, stirring is performed during the heating process in step (1); Preferably, the heat preservation and standing time in step (1) is 5 to 20 minutes, preferably 8 to 15 minutes.

5. The method according to any one of claims 1 to 4, characterized in that: After the step (1) is allowed to stand for 3 hours at room temperature, the mixture is separated into a water layer and an organic layer, wherein the inorganic impurities in the crude isophthalonitrile product form insoluble substances and are deposited in the water layer, and part of the organic impurities are dissolved in the water; Preferably, after the water layer and the inorganic insoluble matter are separated, they are first cooled to room temperature to allow the organic impurities to precipitate, and then the water is separated from the insoluble matter and the precipitate by solid-liquid separation, and the obtained water is returned to step (1) for use.

6. The method according to any one of claims 1 to 5, characterized in that: The cooling crystallization in step (2) is carried out by natural cooling or water cooling, preferably water cooling; Preferably, the cooling rate of the cooling crystallization in step (2) is 1.2 to 2.5°C / min; Preferably, the cooling crystallization in step (2) is cooled to 10-25°C; Preferably, the cooling crystallization time in step (2) is 0.5 to 3 hours, preferably 1 to 2 hours.

7. The method according to any one of claims 1 to 6, characterized in that: The solid-liquid separation in step (2) comprises filtration separation; Preferably, the liquid phase obtained by the solid-liquid separation is used as a raw material for the production of phthalonitrile; Preferably, the solid phase obtained by the solid-liquid separation is dried.

8. The method according to any one of claims 1 to 7, characterized in that: The drying temperature in step (2) is 40 to 80° C., preferably 50 to 70° C.; Preferably, the drying time in step (2) is 1 to 3 hours.

9. The method according to any one of claims 1 to 8, characterized in that: The purity of the isophthalonitrile product in step (2) is above 99.5wt%.

10. The method according to any one of claims 1 to 9, characterized in that: The method comprises the following steps: (1) mixing crude isophthalonitrile with an organic solvent and water, wherein the crude isophthalonitrile contains 87-96 wt % isophthalonitrile, and impurities include inorganic impurities and organic impurities. The organic solvent includes any one of meta-xylene, para-xylene or o-xylene or a combination of at least two thereof. The mass ratio of the crude isophthalonitrile to the organic solvent is 1:(5-10), and the mass ratio of the crude isophthalonitrile to water is 1:(0.1-1.2). After stirring and heating, the mixture is kept warm and allowed to stand. The heating temperature is 50-95° C., and the keeping warm and standing time is 5-20 min. The solution is separated into an aqueous layer and an organic layer. The inorganic impurities in the crude isophthalonitrile form insolubles and are deposited in the lower aqueous layer. Part of the organic impurities are dissolved in water. The lower aqueous layer and the inorganic insolubles are separated and cooled to room temperature. The organic impurities are precipitated, and then subjected to solid-liquid separation. The obtained water is returned to step (1) for use. (2) the upper organic layer after the solution of step (1) is layered is subjected to cooling crystallization, solid-liquid separation and drying in sequence, wherein the cooling crystallization is carried out by natural cooling or water cooling, the cooling rate of the cooling crystallization is 1.2-2.5°C / min, the cooling crystallization is cooled to 10-25°C, the cooling crystallization time is 0.5-3h, the solid-liquid separation includes filtration separation, the liquid phase obtained by the solid-liquid separation is used as a raw material for the production of isophthalonitrile, the obtained solid phase is dried, the drying temperature is 40-80°C, the time is 1-3h, and an isophthalonitrile product is obtained, and the purity of the isophthalonitrile product is 99.5wt% or more.