Method for purifying tetrachloroterephthalonitrile

Abstract

The invention provides a method for purifying tetrachloro-terephthalonitrile, which comprises the following steps: mixing a tetrachloro-terephthalonitrile crude product with an organic solvent, heating and dissolving at the heating temperature of 100-140 DEG C, and then cooling and crystallizing, carrying out solid-liquid separation and drying in sequence to obtain the tetrachloro-terephthalonitrile product. According to the method disclosed by the invention, an organic solvent is adopted to remove impurities in a tetrachloro-terephthalonitrile crude product according to the types of impurities in the tetrachloro-terephthalonitrile crude product, and the tetrachloro-terephthalonitrile is recrystallized and purified by selecting the types of the organic solvent, so that the problems of low purity and high impurity content of the tetrachloro-terephthalonitrile crude product are solved, and the purity of the tetrachloro-terephthalonitrile crude product is improved. The purity and the yield of the tetrachloro-terephthalonitrile are effectively improved; the method is simple to operate, mild in condition, low in raw material cost, recyclable, low in energy consumption, 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 refinement, and relates to a method for purifying tetrachloroterephthalonitrile. Background Art

[0002] Phthalonitrile, as an important class of chemical products and also as an intermediate, can be further used to prepare complex chemical products according to the reactive groups and activation sites contained in its molecule. For example, tetrachlorophthalonitrile prepared by a halogenation reaction. According to the configuration of phthalonitrile, the corresponding tetrachlorophthalonitrile can also include three configurations: tetrachloroisophthalonitrile, tetrachloroterephthalonitrile, and tetrachloroorthophthalonitrile, and different configurations have different applications. Tetrachloroterephthalonitrile can be synthesized into tetrafluoroterephthalonitrile through a fluorination reaction. As an important fluorine-containing aromatic chemical intermediate, it is widely used in the synthesis of pharmaceuticals, pesticides, dyes, and fluorine-containing polymers; tetrachloroterephthalonitrile can be used to produce tetrachloroterephthalic acid through a solvent dissolution method, which can be used as a pharmaceutical intermediate to prepare herbicides. Therefore, the application fields of tetrachloroterephthalonitrile as an intermediate for many substances are also constantly expanding.

[0003] The synthesis of tetrachloroterephthalonitrile is to first obtain terephthalonitrile by ammoxidation of p-xylene with ammonia and an oxygen-containing gas, and then obtain tetrachloroterephthalonitrile by chlorination of terephthalonitrile; side reactions occur during this reaction, and the crude tetrachloroterephthalonitrile obtained contains various impurities, resulting in a low product purity. Therefore, it is necessary to purify the crude tetrachloroterephthalonitrile to obtain a high-purity tetrachloroterephthalonitrile product.

[0004] CN 118615732A discloses a rectification and purification device and method for tetrachloroterephthalonitrile. The device includes a feeding unit, a distillation unit, and a product collection unit. The feeding unit includes a melting device, the distillation unit includes a flash evaporation device and a rectification device, and the product collection unit includes a condensation device and a product receiving device; this method rectifies and purifies the crude tetrachloroterephthalonitrile through the setting of devices such as melting, flash evaporation, and rectification and related process operations. However, the boiling point of tetrachloroterephthalonitrile is relatively high, and the boiling points of some impurities in the crude product are not much different from that of tetrachloroterephthalonitrile, resulting in defects such as high energy consumption and incomplete separation of impurities in this method. Moreover, negative pressure rectification has high requirements for the process and is prone to problems such as equipment blockage.

[0005] CN 101962344 A discloses a method for purifying tetrachloroisophthalonitrile by crystallization. The method includes: placing the raw material tetrachloroisophthalonitrile containing harmful substances into a dissolution kettle filled with an organic solvent, starting the stirring device to stir and mix, raising the temperature in the dissolution kettle to 85 - 90 °C, maintaining the temperature for reaction for 1 - 1.5 h, then cooling the dissolution kettle to 20 - 30 °C with cooling water, and centrifuging to obtain the wet material, which is dried to obtain the finished product tetrachloroisophthalonitrile. This method is for purifying the crude tetrachloroisophthalonitrile, that is, the crude chlorothalonil, and is different from tetrachloroterephthalonitrile. The types of impurities to be removed in the two are also different, so different purification processes are required.

[0006] CN 116199601 A discloses a refining and purification process for high-content chlorothalonil. The purification process includes: placing the crude chlorothalonil into a solvent, heating for dissolution, adding an acid to adjust the pH value of the system to not more than 1, 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 is also for purifying the crude chlorothalonil, which belongs to a different substance type from tetrachloroterephthalonitrile. The types of impurities to be removed and the types of solvents used are also 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 tetrachloroterephthalonitrile, 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, in order to achieve a better purification effect, obtain a high-quality tetrachloroterephthalonitrile 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 tetrachloroterephthalonitrile. The method uses an organic solvent to remove impurities from the crude tetrachloroterephthalonitrile. Through the recrystallization purification of tetrachloroterephthalonitrile, the purity and yield of tetrachloroterephthalonitrile 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 tetrachloroterephthalonitrile, and the method includes the following steps:

[0011] Mix the crude tetrachloroterephthalonitrile with an organic solvent and heat to dissolve it. The heating temperature is 100 - 140 °C, such as 100 °C, 105 °C, 110 °C, 115 °C, 120 °C, 125 °C, 130 °C, 135 °C or 140 °C, etc., but not limited to the listed values. Other unlisted values within this range are equally applicable. Then, perform cooling crystallization, solid-liquid separation, and drying in sequence to obtain the tetrachloroterephthalonitrile product.

[0012] In the present invention, for the crude tetrachloroterephthalonitrile obtained from the production process of tetrachloroterephthalonitrile, due to side reactions, it contains impurities and needs to be purified and refined. According to the composition and physical and chemical properties of the crude tetrachloroterephthalonitrile, the boiling points of some of the impurities are close to that of tetrachloroterephthalonitrile. Therefore, it is not suitable to use distillation for purification. The present invention uses an organic solvent for dissolution and adopts recrystallization for purification by selecting the type of organic solvent, thereby solving the problems of low purity and high impurity content of the crude tetrachloroterephthalonitrile, obtaining a high-purity tetrachloroterephthalonitrile product with a high product yield. The method has simple operation, mild conditions, low raw material cost, can be recycled, low energy consumption, and simple post-treatment process, which is convenient for industrial production.

[0013] 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 objectives and beneficial effects of the present invention can be better achieved and realized.

[0014] As a preferred technical solution of the present invention, the source of the crude tetrachloroterephthalonitrile includes that p-xylene is first subjected to gas-phase ammoxidation reaction to generate terephthalonitrile, and then terephthalonitrile is subjected to chlorination reaction to generate the crude tetrachloroterephthalonitrile.

[0015] Preferably, the content of tetrachloroterephthalonitrile in the crude tetrachloroterephthalonitrile is 98 - 99 wt%, such as 98 wt%, 98.2 wt%, 98.4 wt%, 98.5 wt%, 98.6 wt%, 98.8 wt% or 99 wt%, etc., but not limited to the listed values. Other unlisted values within this range are equally applicable.

[0016] Preferably, the impurities in the crude tetrachloroterephthalonitrile include pentachlorobenzonitrile, low-chlorine impurities, and tetrachloroisophthalonitrile.

[0017] Preferably, the low-chlorine impurities include any one or at least two combinations of monochloroterephthalonitrile, dichloroterephthalonitrile, or trichloroterephthalonitrile. Typical but non-limiting examples of the combinations are: the combination of monochloroterephthalonitrile and dichloroterephthalonitrile, the combination of dichloroterephthalonitrile and trichloroterephthalonitrile, the combination of monochloroterephthalonitrile, dichloroterephthalonitrile, and trichloroterephthalonitrile, etc.

[0018] In the present invention, the crude tetrachloroterephthalonitrile is obtained by reacting p-xylene through two steps. The terephthalonitrile obtained first needs to be refined. Therefore, the impurity by-products generated in the ammoxidation reaction will basically not be introduced into the crude tetrachloroterephthalonitrile, or further generate other by-products. That is, the crude tetrachloroterephthalonitrile basically does not contain inorganic impurities and has a low content of hexachlorobenzene, which can meet the quality requirements.

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

[0020] In the present invention, the dissolving solvent for the crude tetrachloroterephthalonitrile mainly selects benzene solvents, preferably xylene, especially m-xylene. This is mainly because m-xylene has better solubility for the impurity tetrachloroisophthalonitrile, and its crystallization difficulty is higher than that of tetrachloroterephthalonitrile. The purity of the recrystallized tetrachloroterephthalonitrile will be higher.

[0021] Preferably, the mass ratio of the crude tetrachloroterephthalonitrile to the organic solvent is 1:(5-15), such as 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14 or 1:15, etc., but not limited to the listed values. Other unlisted values within this numerical range are equally applicable, and preferably 1:(8-12).

[0022] In the present invention, using xylene as the organic solvent can dissolve tetrachloroterephthalonitrile and its organic impurities. If the amount of the organic solvent used is too low, incomplete dissolution of tetrachloroterephthalonitrile will occur, and the undissolved part will be mixed with the crystallization product, resulting in a low purity of the recrystallized product. If the amount of the organic solvent used is too high, the crystallization precipitation amount of tetrachloroterephthalonitrile and impurities will decrease, resulting in a reduced yield. In addition, it will cause waste of the solvent.

[0023] As a preferred technical solution of the present invention, the heating temperature is 120-135 °C, such as 120 °C, 122 °C, 125 °C, 128 °C, 130 °C, 132 °C or 135 °C, etc., but not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0024] Preferably, stirring is carried out during the heating process, and the heating method includes oil bath heating.

[0025] Preferably, the time for heating to complete dissolution is 50 to 80 min, such as 50 min, 55 min, 60 min, 65 min, 70 min, 75 min or 80 min, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0026] As a preferred technical solution of the present invention, the way of cooling crystallization includes natural cooling or water cooling, preferably water cooling.

[0027] Preferably, the cooling rate of the cooling crystallization is 1.5 to 3 °C / min, such as 1.5 °C / min, 1.8 °C / min, 2 °C / min, 2.2 °C / min, 2.5 °C / min, 2.7 °C / min or 3 °C / min, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0028] As a preferred technical solution of the present invention, the cooling crystallization is cooled to 0 to 50 °C, such as 0 °C, 5 °C, 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, 40 °C, 45 °C or 50 °C, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable, preferably 15 to 30 °C.

[0029] Preferably, the time for the cooling crystallization is 1.5 to 2.5 h, such as 1.5 h, 1.75 h, 2 h, 2.25 h or 2.5 h, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0030] In the present invention, the time for the cooling crystallization refers to the total time from the start of temperature reduction plus the maintenance of crystallization.

[0031] As a preferred technical solution of the present invention, the solid-liquid separation includes filtration separation.

[0032] Preferably, the liquid phase obtained by the solid-liquid separation is recycled and reused as an organic solvent to dissolve the crude product of tetrachloroterephthalonitrile again.

[0033] Preferably, the solid phase obtained by the solid-liquid separation is dried.

[0034] As a preferred technical solution of the present invention, the temperature for drying is 60 to 100 °C, such as 60 °C, 65 °C, 70 °C, 75 °C, 80 °C, 85 °C, 90 °C, 95 °C or 100 °C, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable, preferably 75 to 85 °C.

[0035] Preferably, the drying time is 0.5 to 3 h, such as 0.5 h, 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, preferably 1 to 1.5 h.

[0036] As a preferred technical solution of the present invention, the purity of the tetrachloroterephthalonitrile product 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.

[0037] As a preferred technical solution of the present invention, the method comprises the following steps:

[0038] Mix the crude tetrachloroterephthalonitrile with an organic solvent. The content of tetrachloroterephthalonitrile in the crude tetrachloroterephthalonitrile is 98 - 99 wt%. The impurities include pentachlorobenzonitrile, low-chlorine impurities and tetrachloroisophthalonitrile. The low-chlorine impurities include any one or at least two combinations of monochloroterephthalonitrile, dichloroterephthalonitrile or trichloroterephthalonitrile. The organic solvent includes any one or at least two combinations of m-xylene, p-xylene, o-xylene or toluene. The mass ratio of the crude tetrachloroterephthalonitrile to the organic solvent is 1:(5 - 15). Stir and heat in an oil bath until the crude tetrachloroterephthalonitrile is completely dissolved. The heating temperature is 100 - 140 °C, and the time required to heat to complete dissolution is 50 - 80 min. Then, carry out cooling crystallization, solid-liquid separation and drying in sequence. The cooling crystallization method includes natural cooling or water cooling. The cooling rate of the cooling crystallization is 1.5 - 3 °C / min. The cooling crystallization is cooled to 0 - 50 °C, and the time of the cooling crystallization is 1.5 - 2.5 h. The solid-liquid separation includes filtration separation. The liquid phase obtained from the solid-liquid separation is recycled, and the obtained solid phase is dried. The drying temperature is 60 - 100 °C, and the time is 0.5 - 3 h to obtain the tetrachloroterephthalonitrile product, and the purity of the tetrachloroterephthalonitrile product is above 99.5 wt%.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] (1) According to the types of impurities in the crude tetrachloroterephthalonitrile, the method of the present invention uses an organic solvent to remove impurities from the crude tetrachloroterephthalonitrile, and recrystallizes and purifies the tetrachloroterephthalonitrile by selecting the type of organic solvent, thereby solving the problems of low purity and high impurity content of the crude tetrachloroterephthalonitrile, effectively improving the purity and yield of tetrachloroterephthalonitrile. The purity can reach more than 99.5 wt%, and the yield can reach more than 80%.

[0041] (2) The method of the present invention is simple in operation, mild in conditions, low in raw material cost, can be recycled, low in energy consumption, and simple in post-treatment process, which is convenient for industrial production. Specific Embodiments

[0042] To better illustrate the present invention and facilitate 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 patent protection of the present invention. The scope of protection of the present invention is subject to the claims.

[0043] The specific embodiments of the present invention provide a method for purifying tetrachloroterephthalonitrile, and the method includes the following steps:

[0044] Mix the crude tetrachloroterephthalonitrile with an organic solvent, heat and dissolve it, the heating temperature is 100-140 °C, and then carry out cooling crystallization, solid-liquid separation and drying in sequence to obtain the tetrachloroterephthalonitrile product.

[0045] The following are typical but non-limiting embodiments of the present invention:

[0046] Example 1:

[0047] This example provides a method for purifying tetrachloroterephthalonitrile, and the method includes the following steps:

[0048] Mix the crude tetrachloroterephthalonitrile with an organic solvent. The content of tetrachloroterephthalonitrile in the crude tetrachloroterephthalonitrile is 98.5 wt%, and the impurities include pentachlorobenzonitrile, low-chlorine impurities, and tetrachloroisophthalonitrile. The low-chlorine impurities include monochloroterephthalonitrile, dichloroterephthalonitrile, and trichloroterephthalonitrile. The organic solvent is m-xylene. The mass ratio of the crude tetrachloroterephthalonitrile to the organic solvent is 1:9. Stir and heat in an oil bath until the crude tetrachloroterephthalonitrile is completely dissolved. The heating temperature is 130 °C, and the time required to heat until complete dissolution is 60 min. Then, perform cooling crystallization, solid-liquid separation, and drying in sequence. The cooling crystallization method is water cooling. The cooling rate of cooling crystallization is 2.5 °C / min. Cool down to 20 °C during cooling crystallization, and the time for cooling crystallization is 2 h. The solid-liquid separation is filtration separation. The filtrate obtained from the solid-liquid separation is recycled, and the obtained filter cake is dried. The drying temperature is 80 °C, and the time is 1 h to obtain the tetrachloroterephthalonitrile product.

[0049] Example 2:

[0050] This example provides a method for purifying tetrachloroterephthalonitrile. The method includes the following steps:

[0051] Mix the crude tetrachloroterephthalonitrile with an organic solvent. The content of tetrachloroterephthalonitrile in the crude tetrachloroterephthalonitrile is 98.2 wt%, and the impurities include pentachlorobenzonitrile, low-chlorine impurities, and tetrachloroisophthalonitrile. The low-chlorine impurities include monochloroterephthalonitrile, dichloroterephthalonitrile, and trichloroterephthalonitrile. The organic solvent is m-xylene. The mass ratio of the crude tetrachloroterephthalonitrile to the organic solvent is 1:7. Stir and heat in an oil bath until the crude tetrachloroterephthalonitrile is completely dissolved. The heating temperature is 120 °C, and the time required to heat until complete dissolution is 70 min. Then, perform cooling crystallization, solid-liquid separation, and drying in sequence. The cooling crystallization method is natural cooling. The cooling rate of cooling crystallization is 2 °C / min. Cool down to 30 °C during cooling crystallization, and the time for cooling crystallization is 1.75 h. The solid-liquid separation is filtration separation. The filtrate obtained from the solid-liquid separation is recycled, and the obtained filter cake is dried. The drying temperature is 60 °C, and the time is 3 h to obtain the tetrachloroterephthalonitrile product.

[0052] Example 3:

[0053] This example provides a method for purifying tetrachloroterephthalonitrile. The method includes the following steps:

[0054] Mix the crude tetrachloroterephthalonitrile with an organic solvent. The content of tetrachloroterephthalonitrile in the crude tetrachloroterephthalonitrile is 98.8 wt%, and the impurities include pentachlorobenzonitrile, low-chlorine impurities, and tetrachloroisophthalonitrile. The low-chlorine impurities include monochloroterephthalonitrile, dichloroterephthalonitrile, and trichloroterephthalonitrile. The organic solvent is p-xylene. The mass ratio of the crude tetrachloroterephthalonitrile to the organic solvent is 1:12. Stir and heat in an oil bath until the crude tetrachloroterephthalonitrile is completely dissolved. The heating temperature is 110 °C, and the time required to heat until complete dissolution is 75 min. Then, successively perform cooling crystallization, solid-liquid separation, and drying. The cooling crystallization method is water cooling. The cooling rate of cooling crystallization is 3 °C / min. The temperature is cooled to 10 °C during cooling crystallization, and the time of cooling crystallization is 1.5 h. The solid-liquid separation is filtration separation. The filtrate obtained from the solid-liquid separation is recycled, and the obtained filter cake is dried. The drying temperature is 100 °C, and the time is 0.5 h to obtain the tetrachloroterephthalonitrile product.

[0055] Example 4:

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

[0057] Mix the crude tetrachloroterephthalonitrile with an organic solvent. The content of tetrachloroterephthalonitrile in the crude tetrachloroterephthalonitrile is 98 wt%, and the impurities include pentachlorobenzonitrile, low-chlorine impurities, and tetrachloroisophthalonitrile. The low-chlorine impurities include monochloroterephthalonitrile and dichloroterephthalonitrile. The organic solvent is m-xylene. The mass ratio of the crude tetrachloroterephthalonitrile to the organic solvent is 1:6. Stir and heat in an oil bath until the crude tetrachloroterephthalonitrile is completely dissolved. The heating temperature is 135 °C, and the time required to heat until complete dissolution is 50 min. Then, successively perform cooling crystallization, solid-liquid separation, and drying. The cooling crystallization method is natural cooling. The cooling rate of cooling crystallization is 1.5 °C / min. The temperature is cooled to 40 °C during cooling crystallization, and the time of cooling crystallization is 2.5 h. The solid-liquid separation is filtration separation. The filtrate obtained from the solid-liquid separation is recycled, and the obtained filter cake is dried. The drying temperature is 75 °C, and the time is 2 h to obtain the tetrachloroterephthalonitrile product.

[0058] Example 5:

[0059] This example provides a method for purifying tetrachloroterephthalonitrile. The method includes the following steps:

[0060] Mix the crude tetrachloroterephthalonitrile with an organic solvent. The content of tetrachloroterephthalonitrile in the crude tetrachloroterephthalonitrile is 99 wt%, and the impurities include pentachlorobenzonitrile, low-chlorine impurities, and tetrachloroisophthalonitrile. The low-chlorine impurities include dichloroterephthalonitrile and trichloroterephthalonitrile. The organic solvent is xylene, and the mass ratio of m-xylene, p-xylene, and o-xylene in the xylene is 3:1:1. The mass ratio of the crude tetrachloroterephthalonitrile to the organic solvent is 1:10. Stir and heat in an oil bath until the crude tetrachloroterephthalonitrile is completely dissolved. The heating temperature is 100 °C, and the time required to heat to complete dissolution is 80 min. Then, perform cooling crystallization, solid-liquid separation, and drying in sequence. The cooling crystallization method is water cooling, the cooling rate of cooling crystallization is 2.2 °C / min, the cooling crystallization is cooled to 0 °C, and the time of cooling crystallization is 2.25 h. The solid-liquid separation is filtration separation. The filtrate obtained from the solid-liquid separation is recycled, and the obtained filter cake is dried. The drying temperature is 85 °C, and the time is 1.5 h to obtain the tetrachloroterephthalonitrile product.

[0061] Example 6:

[0062] This example provides a method for purifying tetrachloroterephthalonitrile. The method refers to the method in Example 1, with the only difference being that the recycled m-xylene filtrate is directly used as the organic solvent.

[0063] Comparative Example 1:

[0064] This example provides a method for purifying tetrachloroterephthalonitrile. The method refers to the method in Example 1, with the only difference being that the mass ratio of the crude tetrachloroterephthalonitrile to the organic solvent is 1:4.

[0065] Comparative Example 2:

[0066] This example provides a method for purifying tetrachloroterephthalonitrile. The method refers to the method in Example 1, with the only difference being that the mass ratio of the crude tetrachloroterephthalonitrile to the organic solvent is 1:16.

[0067] Comparative Example 3:

[0068] This comparative example provides a method for purifying tetrachloroterephthalonitrile. The method refers to the method in Example 1, with the only difference being that the heating temperature is 90 °C.

[0069] Comparative Example 4:

[0070] This comparative example provides a method for purifying tetrachloroterephthalonitrile. The method refers to the method in Example 1, with the only difference being that the heating temperature is 145 °C.

[0071] Comparative Example 5:

[0072] This comparative example provides a method for purifying tetrachloroterephthalonitrile. The method refers to the method in Example 1, with the only difference being that the cooling crystallization temperature is lowered to -5°C.

[0073] Comparative Example 6:

[0074] This comparative example provides a method for purifying tetrachloroterephthalonitrile. The method refers to the method in Example 1, with the only difference being that the cooling crystallization temperature is raised to 55°C.

[0075] The yields and purities of the tetrachloroterephthalonitrile products obtained in Examples 1 - 6 and Comparative Examples 1 - 6 were calculated, and the results are shown in Table 1.

[0076] Table 1

[0077] Yield / % Purity / wt% Example 1 83.6 99.57 Example 2 84.2 99.59 Example 3 82.8 99.55 Example 4 83.1 99.51 Example 5 83.9 99.52 Example 6 97.8 99.43 Comparative Example 1 84.3 99.05 Comparative Example 2 71.6 99.58 Comparative Example 3 84.5 99.13 Comparative Example 4 - - Comparative Example 5 84.0 99.25 Comparative Example 6 77.8 99.58

[0078] As can be seen from Table 1, when purifying isophthalonitrile using the above method, in Examples 1 - 5, by selecting appropriate solvent types, ratios, and temperatures, etc., the yields of the purified isophthalonitrile can all reach over 82.8%, and the purities can all reach over 99.5 wt%.

[0079] In Example 6, when directly using the recycled m - xylene filtrate as the organic solvent, the yield of tetrachloroterephthalonitrile increased significantly, but the purity decreased slightly, indicating that the solvent recycled after purifying tetrachloroterephthalonitrile can be reused a limited number of times, effectively saving costs.

[0080] In Comparative Example 1, due to the too - low dosage of the organic solvent m - xylene, incomplete dissolution of tetrachloroterephthalonitrile occurred, and the undissolved tetrachloroterephthalonitrile was mixed with the crystallization product, resulting in a decrease in the purity of the tetrachloroterephthalonitrile product, which was only 99.05%. In Comparative Example 2, due to the too - high dosage of the organic solvent m - xylene, the amount of tetrachloroterephthalonitrile crystallized out decreased, causing a decrease in the yield of the tetrachloroterephthalonitrile product, which was only 71.6%. Additionally, the increased solvent dosage also caused solvent waste.

[0081] In Comparative Example 3, due to the too - low temperature for heating and dissolution, incomplete dissolution of the crude tetrachloroterephthalonitrile occurred, which also caused a decrease in the product purity. In Comparative Example 4, due to the too - high temperature for heating and dissolution, exceeding the boiling point of the m - xylene solvent, the dissolution and crystallization processes could not proceed.

[0082] In Comparative Example 5, since the cooling crystallization temperature was too low, some impurities might precipitate at this temperature, resulting in a slight increase in the yield of the product and a decrease in purity; in Comparative Example 6, since the cooling crystallization temperature was too high, incomplete precipitation of the tetrachloroterephthalonitrile product might occur, resulting in a significant decrease in the yield, which was only 77.8%.

[0083] From the above-mentioned examples and comparative examples, it can be seen that the method of the present invention removes impurities from the crude tetrachloroterephthalonitrile by using an organic solvent according to the types of impurities in the crude tetrachloroterephthalonitrile, and recrystallizes and purifies the tetrachloroterephthalonitrile by selecting the type of organic solvent, thereby solving the problems of low purity and high impurity content of the crude tetrachloroterephthalonitrile, effectively improving the purity and yield of tetrachloroterephthalonitrile. The purity can reach more than 99.5 wt%, and the yield can reach more than 80%; the method has simple operation, mild conditions, low raw material cost, can be recycled, low energy consumption, simple post-treatment process, and is convenient for industrial production.

[0084] The applicant declares that the present invention illustrates the detailed method of the present invention through the above-mentioned examples, 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 tetrachloroterephthalonitrile, characterized in that: The method comprises the following steps: The crude tetrachloroterephthalonitrile is mixed with an organic solvent, heated to dissolve, the heating temperature is 100-140° C., and then cooled for crystallization, solid-liquid separation and drying are performed in sequence to obtain a tetrachloroterephthalonitrile product.

2. The method according to claim 1, characterized in that The source of the crude tetrachloroterephthalonitrile comprises: firstly subjecting p-xylene to a gas phase ammoxidation reaction to generate terephthalonitrile, and then subjecting terephthalonitrile to a chlorination reaction to generate the crude tetrachloroterephthalonitrile; Preferably, the content of tetrachloroterephthalonitrile in the crude tetrachloroterephthalonitrile is 98-99 wt %; Preferably, the impurities in the crude tetrachloroterephthalonitrile include pentachlorobenzonitrile, low-chlorine impurities and tetrachloroisophthalonitrile; Preferably, the low-chlorine impurities include any one of monochloroterephthalonitrile, dichloroterephthalonitrile or trichloroterephthalonitrile, or a combination of at least two thereof.

3. The method according to claim 1 or 2, characterized in that: The organic solvent includes any one of m-xylene, p-xylene, o-xylene or toluene or a combination of at least two thereof, preferably m-xylene; Preferably, the mass ratio of the crude tetrachloroterephthalonitrile to the organic solvent is 1:(5-15), preferably 1:(8-12).

4. The method according to any one of claims 1 to 3, characterized in that: The heating temperature is 120-135°C; Preferably, stirring is performed during the heating process, and the heating method includes oil bath heating; Preferably, the time for heating until complete dissolution is 50 to 80 minutes.

5. The method according to any one of claims 1 to 4, characterized in that: The cooling crystallization method includes natural cooling or water cooling, preferably water cooling; Preferably, the cooling rate of the cooling crystallization is 1.5-3°C / min.

6. The method according to any one of claims 1 to 5, characterized in that: The cooling crystallization is cooled to 0-50°C, preferably 15-30°C; Preferably, the cooling crystallization time is 1.5 to 2.5 hours.

7. The method according to any one of claims 1 to 6, characterized in that: The solid-liquid separation includes filtration separation; Preferably, the liquid phase obtained by the solid-liquid separation is recovered and reused as an organic solvent to dissolve the crude tetrachloroterephthalonitrile; 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 is 60-100°C, preferably 75-85°C; Preferably, the drying time is 0.5 to 3 hours, preferably 1 to 1.5 hours.

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

10. The method according to any one of claims 1 to 9, characterized in that: The method comprises the following steps: A crude tetrachloroterephthalonitrile product is mixed with an organic solvent, wherein the content of tetrachloroterephthalonitrile in the crude tetrachloroterephthalonitrile is 98-99wt%, impurities include pentachlorobenzonitrile, low-chlorine impurities and tetrachloroisophthalonitrile, the low-chlorine impurities include any one of monochloroterephthalonitrile, dichloroterephthalonitrile or trichloroterephthalonitrile or a combination of at least two thereof, the organic solvent includes any one of meta-xylene, para-xylene, o-xylene or toluene or a combination of at least two thereof, the mass ratio of the crude tetrachloroterephthalonitrile product to the organic solvent is 1:(5-15), stirring and heating in an oil bath until the crude tetrachloroterephthalonitrile product is completely dissolved, the heating temperature is 100-1 40°C, heating to completely dissolve for 50 to 80 minutes; then sequentially performing cooling crystallization, solid-liquid separation and drying, wherein the cooling crystallization method includes natural cooling or water cooling, the cooling crystallization cooling rate is 1.5 to 3°C / min, the cooling crystallization is cooled to 0 to 50°C, the cooling crystallization time is 1.5 to 2.5 hours, the solid-liquid separation includes filtration separation, the liquid phase obtained by the solid-liquid separation is recycled, the obtained solid phase is dried, the drying temperature is 60 to 100°C, the time is 0.5 to 3 hours, and a tetrachloroterephthalonitrile product is obtained, and the purity of the tetrachloroterephthalonitrile product is above 99.5wt%.