Preparation method of high-purity 2, 4-dichlorobenzonitrile

Abstract

The invention is suitable for the technical field of chemical purification, and provides a high-purity 2, 4-dichlorobenzonitrile preparation method, which comprises: carrying out cooling crystallization treatment on a 2, 4-dichlorobenzonitrile liquid crude product at a cooling rate of 0.5-5 DEG C / h and a cooling end point of 50-53 DEG C, and carrying out heat preservation for 1-1.5 h; and performing heating sweating treatment on the crystal obtained by the cooling crystallization treatment at a heating rate of 0.5-3 DEG C / h, heating to 57-61 DEG C, and keeping the temperature for 0.5-1 h. According to the method, the high-purity 2, 4-dichlorobenzonitrile product with the purity being greater than or equal to 99.5% can be obtained, no additional solvent is needed, no other three-waste treatment is needed, the product purity is high, and the method is a green separation and purification process; in addition, the preparation process is simple and efficient, the investment of melt crystallization equipment is low, the operation condition is mild, the risk is low, the production safety coefficient is high, the total yield of purification is high after coupling with an upstream rectification process, and the method is suitable for industrial production.

Description

Technical Field

[0001] The present application belongs to the technical field of chemical purification, and in particular relates to a method for preparing high-purity 2,4-dichlorobenzonitrile. Background Art

[0002] 2,4-Dichlorobenzonitrile (2,4-DCBN), molecular formula C7H3Cl2N, melting point 59-62℃, white crystals at room temperature. As one of the dichlorobenzonitrile series (2,4-, 2,6-, 2,5-, 3,4-DCBN), 2,4-DCBN is an important organic intermediate that can be used to prepare a variety of chemicals and pesticides. Due to the cyano and chlorine atoms in its chemical structure, it has high reactivity in chemical reactions. The chlorine atoms in its structure are easily replaced under certain conditions, and 2,4-DCBN can react with fluorine-containing reagents through nucleophilic substitution reactions to generate fluorinated benzonitrile compounds. These fluorinated compounds are widely used in medicine, pesticides and materials science. Fluorinated compounds are of great significance in drug design due to their unique physical and chemical properties, such as improving the metabolic stability and biological activity of drugs. In addition, in materials science, fluorinated compounds are often used to prepare high-performance polymers and other functional materials. Therefore, as a key intermediate in the synthesis of fluorinated compounds, the preparation and purification process of 2,4-DCBN is particularly important for the efficient synthesis and impurity control of downstream products.

[0003] The most widely used synthesis method of 2,4-DCBN in industry is to use 2,4-dichlorotoluene as raw material and adopt ammoxidation method to efficiently convert methyl into cyano group. Specifically, 2,4-dichlorotoluene reacts under the action of ammonia and oxygen at high temperature and high pressure and in the presence of a suitable catalyst (such as molybdenum or iron-based catalyst) to generate 2,4-dichlorobenzonitrile. This method is relatively direct and efficient, and can obtain the target product with a high yield, so it is widely used in industrial synthesis. The prior art discloses a method for preparing 2,4-DCBN using an ammoxidation method with a special catalyst. In a fixed bed reactor, the conversion rate of 2,4-dichlorotoluene can be higher than 98%, the molar yield of 2,4-DCBN can be as high as 89.5%, and the product purity is higher than 98%.

[0004]

[0005] In addition, Yunzhao Dong et al. prepared 2,4-DCBN by direct ammoxidation of 2,4-dichlorobenzyl chloride, which had higher yield and lower reaction temperature compared with the ammoxidation of 2,4-dichlorotoluene.

[0006]

[0007] At present, there are few literature or data reports on the purification method of 2,4-DCBN. Generally speaking, 2,4-DCBN is purified by distillation after the reaction. The main impurities after the direct ammoxidation reaction of 2,4-dichlorotoluene are residual raw material 2,4-dichlorotoluene, by-product 2,4-dichlorobenzamide, o-chlorobenzonitrile and p-chlorobenzonitrile, etc. Since the boiling points of the product and the impurities are close, if the distillation method is used to obtain high-purity 2,4-DCBN, the distillation reflux ratio is too high or multi-stage distillation is required, resulting in excessive energy consumption. If the solution crystallization method is adopted, the crystallization filtration and drying process will greatly increase the process complexity and equipment investment, and the energy consumption of solvent recovery is high.

[0008]

[0009] It can be seen that the existing purification methods of 2,4-DCBN have the problems of low product purity, complex process, large equipment investment, and high energy consumption for solvent recovery. Summary of the invention

[0010] The purpose of the embodiments of the present application is to provide a method for preparing high-purity 2,4-dichlorobenzonitrile, aiming to solve the problems of low product purity, complex process, large equipment investment, and high energy consumption for solvent recovery in the existing 2,4-DCBN purification method.

[0011] The embodiment of the present application is achieved by a method for preparing high-purity 2,4-dichlorobenzonitrile, comprising:

[0012] The crude liquid product of 2,4-dichlorobenzonitrile is subjected to cooling crystallization treatment; wherein the cooling crystallization treatment procedure is: cooling rate of 0.5-5°C / h, cooling end point of 50-53°C, and heat preservation of 1-1.5h;

[0013] The crystals obtained by the cooling crystallization treatment are subjected to a heating sweating treatment to obtain high-purity 2,4-dichlorobenzonitrile; wherein the heating sweating treatment procedure is: the heating rate is 0.5-3°C / h, the temperature is raised to 57-61°C, and the temperature is kept constant for 0.5-1h.

[0014] The preparation method of high-purity 2,4-dichlorobenzonitrile provided in the embodiment of the present application adopts melt crystallization to perform crystallization purification, and the crude liquid product of 2,4-dichlorobenzonitrile is crystallized according to a specific cooling program, and the obtained crystals are sweated according to a specific heating program to obtain a high-purity 2,4-dichlorobenzonitrile product with a purity of ≥99.5%. No additional solvent is required, no other three wastes are treated, and the product purity is high. It is a green separation and purification process. In addition, the preparation process of the present application is simple and efficient, with low investment in melt crystallization equipment, mild operating conditions, low risks, high production safety factor, and a high total purification yield after coupling with an upstream distillation process, which is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a flow chart of the preparation process of high-purity 2,4-dichlorobenzonitrile provided in the examples of the present application. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the embodiments and drawings. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0017] In order to solve the problems of low product purity, complex process, large equipment investment and high energy consumption for solvent recovery in the existing purification method of 2,4-DCBN, the embodiment of the present application provides a green separation and purification process for crystallization purification by melt crystallization. The process is simple and efficient, the investment in melt crystallization equipment is small, and the operating conditions are mild. The crude 2,4-dichlorobenzonitrile liquid product is crystallized according to a specific cooling program, and the obtained crystals are sweated according to a specific heating program to obtain a high-purity 2,4-dichlorobenzonitrile product with a purity of ≥99.5%. There is no need to add additional solvents, no other three wastes to be treated (the crystallization mother liquor and the sweating liquid can be returned to the distillation system for coupling), the recovery rate is high, and the product purity is high.

[0018] Specifically, the present invention provides a method for preparing high-purity 2,4-dichlorobenzonitrile, comprising:

[0019] The crude liquid product of 2,4-dichlorobenzonitrile is subjected to a cooling and crystallization treatment;

[0020] The crystals obtained by the cooling crystallization treatment are subjected to a heating sweating treatment to obtain high-purity 2,4-dichlorobenzonitrile;

[0021] Among them, the cooling crystallization treatment procedure is: cooling rate is 0.5-5℃ / h, cooling end point is 50-53℃, and heat preservation is 1-1.5h; heating sweating treatment procedure is: heating rate is 0.5-3℃ / h, heating to 57-61℃, and constant temperature is 0.5-1h. It is worth noting that the key to determining the product purity and yield corresponding to the preparation process of this application lies in the control of the cooling crystallization treatment parameters and the heating sweating treatment parameters. By strictly controlling the cooling crystallization treatment procedure and the heating sweating treatment procedure, a 2,4-dichlorobenzonitrile product with higher purity (purity ≥99.5%) and higher single-pass yield (≥78%) can be obtained.

[0022] In an optional embodiment of the present application, the crude 2,4-dichlorobenzonitrile liquid product is obtained by heating the crude 2,4-dichlorobenzonitrile from a distillation system to 70° C. to completely melt it into a liquid.

[0023] In an optional embodiment of the present application, the cooling and crystallization treatment of the crude liquid 2,4-dichlorobenzonitrile comprises:

[0024] The crude liquid product of 2,4-dichlorobenzonitrile was added into a layered melt crystallizer, the material temperature in the layered melt crystallizer was maintained at 70°C and in a completely liquid state, and a programmed cooling crystallization treatment was performed to obtain crystals and uncrystallized mother liquor.

[0025] In an optional embodiment of the present application, after the step of subjecting the crystals obtained by the cooling crystallization treatment to a sweating treatment at a higher temperature, the method further comprises: returning the sweating liquid obtained by the sweating treatment at a higher temperature and the uncrystallized mother liquor to a distillation system for purification, and then re-adding them to a layered melt crystallizer for purification. The mother liquor and the sweating liquid are returned to the distillation system for purification, and then enter the melt crystallization system for purification. There is no impurity outlet and no yield loss in the melt crystallization process.

[0026] In an optional embodiment of the present application, the method for preparing high-purity 2,4-dichlorobenzonitrile further includes: heating the material obtained by the temperature-raising sweating treatment until it is completely melted.

[0027] In an optional embodiment of the present application, the step of heating the material obtained by the temperature-raising sweating treatment until it is completely melted comprises: heating the material obtained by the temperature-raising sweating treatment to 70° C. to completely melt it.

[0028] In an optional embodiment of the present application, the crude 2,4-dichlorobenzonitrile is obtained by using 2,4-dichlorotoluene as a raw material through an ammoxidation method, and those skilled in the art can prepare it based on existing technologies.

[0029] In an optional embodiment of the present application, the crude 2,4-dichlorobenzonitrile has a mass percentage of ≥85%, and is preferably applicable to 2,4-DCBN from a distillation system with a mass percentage of ≥95%.

[0030] In an optional embodiment of the present application, Figure 1 The preparation process flow chart of high-purity 2,4-dichlorobenzonitrile shown in FIG. 1 is a process for preparing high-purity 2,4-DCBN, and the preparation method comprises the following steps:

[0031] Step 1) Melting feed: The solid 2,4-DCBN with a crude mass fraction of ≥95% from the distillation system is heated to 70°C and completely melted into liquid, and then added into the layer melt crystallizer, and the material temperature in the layer melt crystallizer is maintained at 70°C, which is completely liquid.

[0032] Step 2) Cooling crystallization: The liquid crude 2,4-DCBN with a content of ≥95% is subjected to programmed cooling at a cooling rate of 0.5-5°C / h, a cooling end point of 50-53°C, and the temperature is kept for 1-1.5h.

[0033] Step 3) Heating and sweating: After discharging the uncrystallized mother liquor, the temperature is raised to sweat the crystals at a heating rate of 0.5-3°C / h, and the temperature is raised to 57-61°C, and the temperature is kept constant for 0.5-1h. The sweating liquid is discharged, and the sweating liquid and the crystallization mother liquor can be returned to the distillation system for purification and then returned to the melt crystallizer for purification.

[0034] Step 4) Heating and melting the material: After the sweating liquid is discharged, the material is heated to 70°C to melt it completely and discharge it to obtain 2,4-DCBN with a purity of ≥99.5%, which is high-purity 2,4-DCBN.

[0035] The following is a detailed description of the preparation method of high-purity 2,4-dichlorobenzonitrile with specific examples, as shown below. The experimental methods used in the following examples are conventional methods unless otherwise specified; the materials, reagents, etc. used are all commercially available unless otherwise specified.

[0036] Example 1: Preparation of high-purity 2,4-dichlorobenzonitrile

[0037] In a 200mL layer melt crystallizer, 150g of crude 2,4-DCBN with a content of 98.72% was put into the crystallizer. After the temperature was raised to 70°C and kept for 0.5h, it was completely melted into liquid. The temperature was then lowered to 59°C at 5°C / h, and then lowered to a final temperature of 53°C at 0.5°C / h. After keeping the temperature for 1h, the mother liquor was discharged. The temperature was then raised to 61°C at 0.5°C / h and kept for 1h to sweat. After the sweating liquid was discharged, the melted material was heated to obtain a product with a purity of 99.90% and a single-pass yield of 80.35%.

[0038] Example 2: Preparation of high-purity 2,4-dichlorobenzonitrile

[0039] In a 200mL layer melt crystallizer, 150g of crude 2,4-DCBN with a content of 98.72% was put into the crystallizer. After the temperature was raised to 70°C and kept for 0.5h, it was completely melted into liquid. The temperature was then lowered to 59°C at 5°C / h, and then lowered to a final temperature of 50°C at 0.5°C / h. After keeping the temperature for 1h, the mother liquor was discharged. The temperature was then raised to 61°C at 0.5°C / h and kept for 1h to sweat. After the sweating liquid was discharged, the melted material was heated to obtain a product with a purity of 99.70% and a single-pass yield of 82.10%.

[0040] Example 3: Preparation of high-purity 2,4-dichlorobenzonitrile

[0041] In a 200mL layer melt crystallizer, 150g of crude 2,4-DCBN with a content of 98.72% was put into the crystallizer. After the temperature was raised to 70°C and kept for 0.5h, it was completely melted into liquid. The temperature was then lowered to 59°C at 5°C / h, and then lowered to a final temperature of 53°C at 0.5°C / h. After keeping warm for 1h, the mother liquor was discharged. The temperature was then raised to 57°C at 0.5°C / h, and kept warm for 1h to sweat. After the sweating liquid was discharged, the melted material was heated to obtain a product with a purity of 99.51% and a single-pass yield of 85.23%.

[0042] Example 4: Preparation of high-purity 2,4-dichlorobenzonitrile

[0043] In a 200mL layer melt crystallizer, 150g of crude 2,4-DCBN with a content of 98.72% was put into the crystallizer. After the temperature was raised to 70°C and kept for 0.5h, it was completely melted into liquid. The temperature was then lowered to 59°C at 5°C / h, and then lowered to a final temperature of 53°C at 5°C / h. After keeping the temperature for 1h, the mother liquor was discharged. The temperature was then raised to 61°C at 0.5°C / h and kept for 1h to sweat. After the sweating liquid was discharged, the melted material was heated to obtain a product with a purity of 99.63% and a single-pass yield of 80.69%.

[0044] Example 5: Preparation of high-purity 2,4-dichlorobenzonitrile

[0045] In a 200mL layer melt crystallizer, 150g of crude 2,4-DCBN with a content of 98.72% was put into the crystallizer. After the temperature was raised to 70°C and kept for 0.5h, it was completely melted into liquid. The temperature was then lowered to 59°C at 5°C / h, and then lowered to a final temperature of 53°C at 0.5°C / h. After keeping warm for 1h, the mother liquor was discharged. The temperature was then raised to 61°C at 3°C / h and kept warm for 1h to sweat. After the sweating liquid was discharged, the melted material was heated to obtain a product with a purity of 99.74% and a single-pass yield of 79.88%.

[0046] Example 6: Preparation of high-purity 2,4-dichlorobenzonitrile

[0047] In a 200mL layer melt crystallizer, 150g of crude 2,4-DCBN with a content of 97.50% was put into the crystallizer. After the temperature was raised to 70°C and kept for 0.5h, it was completely melted into liquid. The temperature was then lowered to 59°C at 5°C / h, and then lowered to a final temperature of 53°C at 0.5°C / h. After keeping warm for 1h, the mother liquor was discharged. The temperature was then raised to 61°C at 0.5°C / h and kept warm for 1h to sweat. After the sweating liquid was discharged, the melted material was heated to obtain a product with a purity of 99.56% and a single-pass yield of 78.33%.

[0048] Furthermore, in the preliminary experiments, the present application studied the process parameters of the cooling crystallization treatment procedure and the heating sweating treatment procedure respectively, and found that by strictly controlling the cooling crystallization treatment procedure and the heating sweating treatment procedure, a 2,4-dichlorobenzonitrile product with higher purity and higher single-pass yield can be obtained. Some comparative experiments are shown in the following comparative examples.

[0049] Comparative Example 1: In a 200mL layer melt crystallizer, 150g of crude 2,4-DCBN with a content of 98.72% was put into the crystallizer. After the temperature was raised to 70°C and kept for 0.5h, it was completely melted into liquid. The temperature was lowered to 59°C at 5°C / h, and then lowered to a final temperature of 48°C at 0.5°C / h. After keeping warm for 1h, the mother liquor was discharged. The temperature was then raised to 55°C at 0.5°C / h, kept warm for 1h, and sweated. After the sweating liquid was discharged, the melted material was heated to obtain a product with a purity of 99.01% and a single-pass yield of 89.24%.

[0050] Comparative Example 2: In a 200mL layer melt crystallizer, 150g of crude 2,4-DCBN with a content of 98.72% was put into the crystallizer. The temperature was raised to 70°C and kept for 0.5h to completely melt into liquid. The temperature was then lowered to a final temperature of 53°C at a rate of 10°C / h, and the mother liquor was discharged after being kept for 1h. The temperature was then raised to 61°C at a rate of 0.5°C / h, and kept for 1h to sweat. After the sweating liquid was discharged, the melted material was heated to obtain a product with a purity of 99.01% and a single-pass yield of 67.25%.

[0051] Comparative Example 3: In a 200mL layer melt crystallizer, 150g of crude 2,4-DCBN with a content of 98.72% was put into the crystallizer. The temperature was raised to 70°C and kept for 0.5h to completely melt into liquid. The temperature was then lowered to a final temperature of 53°C at a rate of 0.1°C / h, and the mother liquor was discharged after being kept for 1h. The temperature was then raised to 61°C at a rate of 0.5°C / h, and kept for 1h to sweat. After the sweating liquid was discharged, the melted material was heated to obtain a product with a purity of 99.92% and a single-pass yield of 70.21%.

[0052] Comparative Example 4: In a 200mL layer melt crystallizer, 150g of crude 2,4-DCBN with a content of 98.72% was put into the crystallizer. After the temperature was raised to 70°C and kept for 0.5h, it was completely melted into liquid. The temperature was then lowered to 59°C at 5°C / h, and then lowered to a final temperature of 54°C at 0.5°C / h. After keeping the temperature for 1h, the mother liquor was discharged. The temperature was then raised to 61°C at 0.5°C / h, and kept for 1h to sweat. After the sweating liquid was discharged, the melted material was heated to obtain a product with a purity of 99.91% and a single-pass yield of 65.25%.

[0053] Comparative Example 5: In a 200mL layer melt crystallizer, 150g of crude 2,4-DCBN with a content of 98.72% was put into the crystallizer. After the temperature was raised to 70°C and kept for 0.5h, it was completely melted into liquid. The temperature was lowered to 59°C at 5°C / h, and then lowered to a final temperature of 49°C at 0.5°C / h. After keeping warm for 1h, the mother liquor was discharged. The temperature was then raised to 61°C at 0.5°C / h, kept warm for 1h, and sweating was carried out. After the sweating liquid was discharged, the melted material was heated to obtain a product with a purity of 98.92% and a single-pass yield of 73.55%.

[0054] Comparative Example 6: In a 200mL layer melt crystallizer, 150g of crude 2,4-DCBN with a content of 98.72% was put into the crystallizer. After the temperature was raised to 70°C and kept for 0.5h, it was completely melted into liquid. The temperature was lowered to 59°C at 5°C / h, and then lowered to a final temperature of 53°C at 0.5°C / h. After keeping the temperature for 0.5h, the mother liquor was discharged. The temperature was then raised to 61°C at 0.5°C / h, kept for 1h, and sweated. After the sweating liquid was discharged, the melted material was heated to obtain a product with a purity of 99.85% and a single-pass yield of 68.25%.

[0055] Comparative Example 7: In a 200mL layer melt crystallizer, 150g of crude 2,4-DCBN with a content of 98.72% was put into the crystallizer. After the temperature was raised to 70°C and kept for 0.5h, it was completely melted into liquid. The temperature was lowered to 59°C at 5°C / h, and then lowered to a final temperature of 53°C at 0.5°C / h. After keeping the temperature for 2h, the mother liquor was discharged. The temperature was then raised to 61°C at 0.5°C / h, kept for 1h, and sweated. After the sweating liquid was discharged, the melted material was heated to obtain a product with a purity of 99.91% and a single-pass yield of 70.36%.

[0056] Comparative Example 8: In a 200mL layer melt crystallizer, 150g of crude 2,4-DCBN with a content of 98.72% was put into the crystallizer. After the temperature was raised to 70°C and kept for 0.5h, it was completely melted into liquid. The temperature was lowered to 59°C at 5°C / h, and then lowered to a final temperature of 53°C at 0.5°C / h. After keeping warm for 1h, the mother liquor was discharged. The temperature was then raised to 61°C at 0.1°C / h, kept warm for 1h, and sweating was carried out. After the sweating liquid was discharged, the melted material was heated to obtain a product with a purity of 99.91% and a single-pass yield of 70.46%.

[0057] Comparative Example 9: In a 200mL layer melt crystallizer, 150g of crude 2,4-DCBN with a content of 98.72% was put into the crystallizer. After the temperature was raised to 70°C and kept for 0.5h, it was completely melted into liquid. The temperature was lowered to 59°C at 5°C / h, and then lowered to a final temperature of 53°C at 0.5°C / h. After keeping warm for 1h, the mother liquor was discharged. The temperature was then raised to 61°C at 3.5°C / h, kept warm for 1h, and sweated. After the sweating liquid was discharged, the melted material was heated to obtain a product with a purity of 99.25% and a single-pass yield of 69.45%.

[0058] Comparative Example 10: In a 200mL layer melt crystallizer, 150g of crude 2,4-DCBN with a content of 98.72% was put into the crystallizer. The temperature was raised to 70°C and kept for 0.5h to completely melt into liquid. The temperature was then lowered to 59°C at 5°C / h, and then lowered to a final temperature of 53°C at 0.5°C / h. The mother liquor was discharged after being kept for 1h. The temperature was then raised to 56°C at 0.5°C / h, and kept for 1h to sweat. After the sweating liquid was discharged, the melted material was heated to obtain a product with a purity of 98.95% and a single-pass yield of 73.35%.

[0059] Comparative Example 11: In a 200mL layer melt crystallizer, 150g of crude 2,4-DCBN with a content of 98.72% was put into the crystallizer. The temperature was raised to 70°C and kept for 0.5h to completely melt into liquid. The temperature was then lowered to 59°C at 5°C / h, and then lowered to a final temperature of 53°C at 0.5°C / h. The mother liquor was discharged after being kept for 1h. The temperature was then raised to 62°C at 0.5°C / h, and kept for 1h to sweat. After the sweating liquid was discharged, the melted material was heated to obtain a product with a purity of 99.92% and a single-pass yield of 65.25%.

[0060] Comparative Example 12: In a 200mL layer melt crystallizer, 150g of crude 2,4-DCBN with a content of 98.72% was put into the crystallizer. After the temperature was raised to 70°C and kept for 0.5h, it was completely melted into liquid. The temperature was then lowered to 59°C at 5°C / h, and then lowered to a final temperature of 53°C at 0.5°C / h. After keeping the temperature for 1h, the mother liquor was discharged. The temperature was then raised to 61°C at 0.5°C / h, and kept for 1.5h to sweat. After the sweating liquid was discharged, the melted material was heated to obtain a product with a purity of 99.89% and a single-pass yield of 70.41%.

[0061] Comparative Example 13: In a 200mL layer melt crystallizer, 150g of crude 2,4-DCBN with a content of 98.72% was put into the crystallizer. After the temperature was raised to 70°C and kept for 0.5h, it was completely melted into liquid. The temperature was then lowered to 59°C at 5°C / h, and then lowered to a final temperature of 53°C at 0.5°C / h. After keeping the temperature for 1h, the mother liquor was discharged. The temperature was then raised to 61°C at 0.5°C / h, and kept for 2h to sweat. After the sweating liquid was discharged, the melted material was heated to obtain a product with a purity of 99.85% and a single-pass yield of 70.52%.

[0062] In summary, the method for preparing high-purity 2,4-dichlorobenzonitrile provided in the embodiment of the present application is to crystallize the crude 2,4-dichlorobenzonitrile liquid product according to a specific cooling program, and then sweat the obtained crystals according to a specific heating program, so as to obtain a high-purity 2,4-dichlorobenzonitrile product with a purity of ≥99.5%, a single-pass yield of ≥78%, and no additional solvent is required, no other three wastes are treated, the process is simple and efficient, the melt crystallization equipment has a small investment, the operating conditions are mild, and the production safety factor is high, which is suitable for industrial production.

[0063] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

[0064] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing high-purity 2,4-dichlorobenzonitrile, characterized in that: include: The crude liquid product of 2,4-dichlorobenzonitrile is subjected to cooling crystallization treatment; wherein the cooling crystallization treatment procedure is: cooling rate of 0.5-5°C / h, cooling end point of 50-53°C, and heat preservation of 1-1.5h; The crystals obtained by the cooling crystallization treatment are subjected to a heating sweating treatment to obtain high-purity 2,4-dichlorobenzonitrile; wherein the heating sweating treatment procedure is: the heating rate is 0.5-3°C / h, the temperature is raised to 57-61°C, and the temperature is kept constant for 0.5-1h.

2. The method for preparing high-purity 2,4-dichlorobenzonitrile according to claim 1, characterized in that: The crude 2,4-dichlorobenzonitrile liquid product is obtained by heating the crude 2,4-dichlorobenzonitrile from the distillation system to 70° C. to completely melt it into liquid.

3. The method for preparing high-purity 2,4-dichlorobenzonitrile according to claim 2, characterized in that: The step of subjecting the crude 2,4-dichlorobenzonitrile liquid product to a cooling and crystallizing treatment comprises: The crude liquid product of 2,4-dichlorobenzonitrile was added into a layered melt crystallizer, the material temperature in the layered melt crystallizer was maintained at 70°C and in a completely liquid state, and a programmed cooling crystallization treatment was performed to obtain crystals and uncrystallized mother liquor.

4. The method for preparing high-purity 2,4-dichlorobenzonitrile according to claim 3, characterized in that: After the step of subjecting the crystals obtained by the cooling crystallization treatment to a heating sweating treatment, the method further comprises: The sweating liquid obtained by the temperature-raising sweating treatment and the uncrystallized mother liquor are returned to the distillation system for purification, and then added back into the layered melt crystallizer for purification.

5. The method for preparing high-purity 2,4-dichlorobenzonitrile according to claim 1, characterized in that: Also includes: The material obtained by the temperature-raising sweating treatment is heated until it is completely melted.

6. The method for preparing high-purity 2,4-dichlorobenzonitrile according to claim 5, characterized in that: The step of heating the material obtained by the sweating treatment until it is completely melted comprises: The material obtained by the sweating treatment was heated to 70°C to completely melt it.

7. The method for preparing high-purity 2,4-dichlorobenzonitrile according to claim 2, characterized in that: The crude 2,4-dichlorobenzonitrile is obtained by using 2,4-dichlorotoluene as a raw material through an ammoxidation method.

8. The method for preparing high-purity 2,4-dichlorobenzonitrile according to claim 2 or 7, characterized in that: The mass percentage of the crude 2,4-dichlorobenzonitrile is ≥85%.

9. The method for preparing high-purity 2,4-dichlorobenzonitrile according to claim 2 or 7, characterized in that: The mass percentage of the crude 2,4-dichlorobenzonitrile is ≥95%.

10. The method for preparing high-purity 2,4-dichlorobenzonitrile according to claim 1, characterized in that: The purity of the high-purity 2,4-dichlorobenzonitrile is ≥99.5%.

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