Method for preparing p-chlorobenzonitrile through static melt crystallization

Abstract

The invention is applicable to the technical field of chemical purification, and provides a method for preparing p-chlorobenzonitrile by static melt crystallization, which comprises the following steps: melting a p-chlorobenzonitrile crude product from a rectification system into a liquid, and adding the liquid into a layered melt crystallizer for cooling crystallization treatment; carrying out heating sweating treatment on crystals obtained by cooling crystallization treatment, returning obtained sweating liquid and non-crystallized mother liquor to a rectification system for purification, and then adding the obtained sweating liquid and non-crystallized mother liquor into the melt crystallizer again for purification treatment; according to the cooling crystallization treatment procedure, the cooling rate is 1-3 DEG C / h, the cooling end point is 83-86 DEG C, and heat preservation is conducted for 1-1.5 h; the heating sweating treatment procedure is as follows: the heating rate is 0.5-3 DEG C / h, the temperature is increased to 91-93 DEG C, and the constant temperature is kept for 0.5-1 h. The method has the advantages of no need of additional addition of a solvent, no treatment of three wastes, high recovery rate and high product purity, is a green separation and purification process, and has the advantages of simple process, mild operation temperature, simple purification operation, low risk and high production safety coefficient.

Description

Technical Field

[0001] This application belongs to the technical field of chemical purification, and particularly relates to a method for preparing p-chlorobenzonitrile by static melting crystallization. Background Art

[0002] p-Chlorobenzonitrile, with the molecular formula C7H4ClN, is a white crystal at room temperature. p-Chlorobenzonitrile is an important organic intermediate and can be used to prepare various chemicals and pesticides. Due to the cyano group and chlorine atom in its chemical structure, it has high reactivity in chemical reactions. The chlorine atom in its structure is easily substituted under specific conditions. p-Chlorobenzonitrile can react with fluorine-containing reagents through nucleophilic substitution reactions to form fluorine-containing benzonitrile compounds. These fluorine-containing compounds have wide applications in medicine, pesticides, and materials science. Fluorine-containing 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, fluorine-containing compounds are often used to prepare high-performance polymers and other functional materials. Therefore, as a key intermediate in the synthesis of fluorine-containing compounds, the preparation and purification process of p-chlorobenzonitrile is particularly important for the efficient synthesis of downstream products and impurity control.

[0003] The most widely used synthetic method of p-chlorobenzonitrile in industry is to use p-chlorotoluene as the raw material and adopt the ammoxidation method to efficiently convert the methyl group into a cyano group. Specifically, p-chlorotoluene reacts under the action of ammonia and oxygen in the presence of high temperature, high pressure, and a suitable catalyst (such as molybdenum or iron-based catalysts) to produce p-chlorobenzonitrile.

[0004] Currently, there are few literatures or materials reporting on the purification method of p-chlorobenzonitrile. Generally, after the reaction, p-chlorobenzonitrile is purified by distillation. The main impurities after the direct ammoxidation reaction of p-chlorotoluene are residual raw material p-chlorotoluene, by-products p-chlorobenzamide, o-chlorobenzonitrile, m-chlorobenzonitrile, etc. The existing technology mainly uses distillation methods or solution crystallization methods for purification; among them, when using the distillation method for purification, there are problems such as too high a distillation reflux ratio or the need for multi-stage distillation, resulting in too high energy consumption; while when using the solution crystallization method for purification, there are problems such as a significant increase in process complexity and large equipment investment during the crystallization, filtration, and drying processes, and high energy consumption for solvent recovery. Summary of the Invention

[0005] The purpose of the embodiments of this application is to provide a method for preparing p-chlorobenzonitrile by static melting crystallization, aiming to solve the problems of high energy consumption and complex process existing in the existing p-chlorobenzonitrile purification methods.

[0006] The embodiments of this application are implemented as follows. A method for preparing p-chlorobenzonitrile by static melting crystallization includes: The crude 4-chlorobenzonitrile from the rectification system is melted into a liquid and then added to a layer-type melting crystallizer for cooling crystallization treatment; The crystals obtained from the cooling crystallization treatment are subjected to heating sweating treatment, and at the same time, the obtained sweating liquid and the uncrystallized mother liquor are returned to the rectification system for purification and then re-added to the melting crystallizer for purification treatment; Among them, the cooling crystallization treatment procedure is: the cooling rate is 1 - 3 °C / h, the cooling end point is 83 - 86 °C, and keep warm for 1 - 1.5 h; The heating sweating treatment procedure is: the heating rate is 0.5 - 3 °C / h, heat up to 91 - 93 °C, and keep constant temperature for 0.5 - 1 h.

[0007] The method for preparing 4-chlorobenzonitrile by static melting crystallization provided by the embodiment of the present application melts the crude 4-chlorobenzonitrile from the rectification system into a liquid and then adds it to a layer-type melting crystallizer for cooling crystallization treatment. Then, the crystals obtained from the cooling crystallization treatment are subjected to heating sweating treatment. At the same time, the obtained sweating liquid and the uncrystallized mother liquor are returned to the rectification system for purification and then re-added to the melting crystallizer for purification treatment, so that a high-purity 4-chlorobenzonitrile product can be obtained. Moreover, there is no need to add solvents additionally, there is no other three-waste treatment (the mother liquor and sweating liquid are returned to the rectification system for coupling), the recovery rate is high, and the product purity is high. It is a green separation and purification process; in addition, the process of the present application is simple, the operating temperature is mild, the purification operation is simple, the risk is low, and the production safety factor is high. Description of the Drawings

[0008] Figure 1 It is a process flow chart of the method for preparing 4-chlorobenzonitrile by static melting crystallization provided by the embodiment of the present application. Detailed Embodiments

[0009] In order to make the purpose, technical solution and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and embodiments. 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.

[0010] In order to solve the problems of high energy consumption and complex process existing in the existing purification method of p-chlorobenzonitrile, the embodiment of the present application provides a method for preparing p-chlorobenzonitrile by static melting crystallization. After melting the crude p-chlorobenzonitrile from the rectification system into a liquid, it is added to a layer-type melting crystallizer for cooling crystallization treatment. Then, the crystals obtained from the cooling crystallization treatment are subjected to heating sweating treatment. At the same time, the obtained sweating liquid and the uncrystallized mother liquor are returned to the rectification system for purification and then re-added to the melting crystallizer for purification treatment, so as to obtain a high-purity p-chlorobenzonitrile product. Moreover, no additional solvent needs to be added, there is no other three-waste treatment (the mother liquor and sweating liquid are returned to the rectification system for coupling), the recovery rate is high, and the product purity is high, which is a green separation and purification process. In addition, the process of the present application is simple, the operating temperature is mild, the purification operation is simple, the risk is low, and the production safety factor is high.

[0011] Specifically, the embodiment of the present application provides a method for preparing p-chlorobenzonitrile by static melting crystallization, including: Melting the crude p-chlorobenzonitrile from the rectification system into a liquid and then adding it to a layer-type melting crystallizer for cooling crystallization treatment; Performing heating sweating treatment on the crystals obtained from the cooling crystallization treatment. At the same time, returning the obtained sweating liquid and the uncrystallized mother liquor to the rectification system for purification and then re-adding them to the melting crystallizer for purification treatment; Among them, the cooling crystallization treatment procedure is: the cooling rate is 1-3 °C / h, the cooling end point is 83-86 °C, and the heat preservation is 1-1.5 h; the heating sweating treatment procedure is: the heating rate is 0.5-3 °C / h, heating to 91-93 °C, and maintaining a constant temperature for 0.5-1 h. It should be noted that the key to determining the product purity and yield corresponding to the preparation process of the present 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 p-chlorobenzonitrile product with higher purity and higher single-pass yield can be obtained.

[0012] In an alternative embodiment of the present application, the step of melting the crude p-chlorobenzonitrile from the rectification system into a liquid and then adding it to a layer-type melting crystallizer for cooling crystallization treatment includes: Adding the crude p-chlorobenzonitrile from the rectification system to the layer-type melting crystallizer, maintaining the temperature of the material in the layer-type melting crystallizer at 100 °C and in a liquid state, and performing programmed cooling crystallization treatment to obtain crystals and uncrystallized mother liquor.

[0013] In an alternative embodiment of the present application, the crude p-chlorobenzonitrile from the rectification system is obtained by ammoxidation of p-chlorotoluene. Those skilled in the art can prepare it based on the existing technology.

[0014] In an alternative embodiment of the present application, the p-chlorobenzonitrile purified by melt crystallization according to the method of the present application is applicable to p-chlorobenzonitrile from the rectification system with a percentage content of ≥85%, preferably ≥95%. The process of the present application obtains a high-purity p-chlorobenzonitrile crystalline product. The mother liquor and the sweating liquor enter the secondary melt crystallization system for purification, and then enter the primary melt crystallization system for purification. The secondary melt crystallization mother liquor and the sweating liquor are the impurity outlets.

[0015] In an alternative embodiment of the present application, as Figure 1 shown in the process flow chart of the method for preparing p-chlorobenzonitrile by static melt crystallization, the method for preparing p-chlorobenzonitrile by static melt crystallization includes the following steps: Step 1) Melting and feeding: The solid p-chlorobenzonitrile with a crude product mass fraction of ≥95% from the rectification system is heated to 100 °C and completely melted into a liquid, and then added to the layer melt crystallizer, maintaining the material temperature in the layer melt crystallizer at 100 °C, in a completely liquid state.

[0016] Step 2) Cooling and crystallization: The liquid crude p-chlorobenzonitrile with a percentage content of ≥95% is cooled at a programmed rate, the cooling rate is 1 - 3 °C / h, the cooling end point is 83 - 86 °C, and it is kept warm for 1 - 1.5 h.

[0017] Step 3) Heating and sweating: After discharging the uncrystallized mother liquor, the crystal is heated for sweating, the heating rate is 0.5 - 3 °C / h, heated to 91 - 93 °C, kept at a constant temperature for 0.5 - 1 h, and the sweating liquor is discharged. The sweating liquor and the crystallization mother liquor can be returned to the rectification system for purification and then back to the melt crystallizer for purification.

[0018] Step 4) Heating and melting: After discharging the sweating liquor, the material is heated to 100 °C to completely melt and discharge to obtain high-purity p-chlorobenzonitrile.

[0019] The following describes in detail the method for preparing p-chlorobenzonitrile by static melt crystallization with specific examples, as shown below. The experimental methods used in the following examples are all conventional methods unless otherwise specified; the materials, reagents, etc. used are all commercially available unless otherwise specified.

[0020] Example 1: Method for preparing p-chlorobenzonitrile by static melt crystallization In a 200 ml layer melt crystallizer, 150 g of p-chlorobenzonitrile crude product with a content of 97.32% was put in, heated to 100 °C and kept warm for 0.5 h to completely melt into a liquid state. It was cooled to 90 °C at a rate of 3 °C / h, and then cooled to the final temperature of 83 °C at a rate of 0.5 °C / h. After keeping warm for 1 h, the mother liquor was discharged; then it was heated to 91 °C at a rate of 0.5 °C / h, kept warm for 1 h for sweating; after discharging the sweating liquor, the material was heated and melted to obtain a product with a purity of 99.85% and a single-pass yield of 85.32%.

[0021] Example 2: Method for Preparing p-Chlorobenzonitrile by Static Melting Crystallization In a 200 ml layer-type melting crystallizer, 150 g of crude p-chlorobenzonitrile with a content of 97.32% was charged. After heating to 100 °C and holding for 0.5 h to completely melt into a liquid state, it was cooled to 90 °C at a rate of 1 °C / h, and then cooled to the final temperature of 83 °C at a rate of 0.5 °C / h. After holding for 1 h, the mother liquor was discharged; then it was heated to 91 °C at a rate of 0.5 °C / h and held for 1 h for sweating; after discharging the sweating liquid, the material was heated and melted to obtain a product with a purity of 99.91% and a single-pass yield of 96.21%.

[0022] Example 3: Method for Preparing p-Chlorobenzonitrile by Static Melting Crystallization In a 200 ml layer-type melting crystallizer, 150 g of crude p-chlorobenzonitrile with a content of 97.32% was charged. After heating to 100 °C and holding for 0.5 h to completely melt into a liquid state, it was cooled to 90 °C at a rate of 3 °C / h, and then cooled to the final temperature of 86 °C at a rate of 0.5 °C / h. After holding for 1 h, the mother liquor was discharged; then it was heated to 91 °C at a rate of 0.5 °C / h and held for 1 h for sweating; after discharging the sweating liquid, the material was heated and melted to obtain a product with a purity of 99.82% and a single-pass yield of 84.23%.

[0023] Example 4: Method for Preparing p-Chlorobenzonitrile by Static Melting Crystallization In a 200 ml layer-type melting crystallizer, 150 g of crude p-chlorobenzonitrile with a content of 97.32% was charged. After heating to 100 °C and holding for 0.5 h to completely melt into a liquid state, it was cooled to 90 °C at a rate of 3 °C / h, and then cooled to the final temperature of 86 °C at a rate of 0.5 °C / h. After holding for 1 h, the mother liquor was discharged; then it was heated to 93 °C at a rate of 0.5 °C / h and held for 1 h for sweating; after discharging the sweating liquid, the material was heated and melted to obtain a product with a purity of 99.63% and a single-pass yield of 83.21%.

[0024] In the early stage of process research and development of this application, a series of studies were carried out on the cooling crystallization treatment parameters and the heating and sweating treatment parameters. It was found that by strictly controlling the cooling crystallization treatment procedure and the heating and sweating treatment procedure, p-chlorobenzonitrile products with higher purity and higher single-pass yield can be obtained. See the following comparative examples for details.

[0025] (1) On the basis of Example 2, by changing some of the cooling crystallization program parameters and keeping the same heating and sweating program (heating to 91 °C at a rate of 0.5 °C / h and holding for 1 h), Comparative Examples 1-7 were set up, and the corresponding product purities and single-pass yields are shown in Table 1 below.

[0026] Table 1 (2)On the basis of Example 2, with the same cooling crystallization procedure (cooling to 90°C at 1°C / h and then to the final temperature of 83°C at 0.5°C / h), some of the parameters of the heating and sweating procedure were changed, and Comparative Examples 8-13 were set up. The corresponding product purity and single-pass yield are shown in Table 2 below.

[0027] Table 2 The above-described embodiments merely represent several implementation manners of the present application. The description is relatively specific and detailed, but it should not be construed as a limitation on the patent scope of the present application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several deformations and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the appended claims.

[0028] The above is only the preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing p-chlorobenzonitrile by static melt crystallization, characterized in that: include: The crude p-chlorobenzonitrile from the distillation system is melted into liquid and then added into a layered melt crystallizer for cooling and crystallization treatment; The crystals obtained by the cooling crystallization treatment are subjected to a heating sweating treatment, and the sweating liquid and the uncrystallized mother liquor are returned to the distillation system for purification and then re-added to the melt crystallizer for purification; The cooling crystallization treatment procedure is as follows: cooling rate is 1-3°C / h, cooling end point is 83-86°C, and heat preservation is 1-1.5h; The heating and sweating treatment procedure is: heating rate is 0.5-3℃ / h, heating to 91-93℃, and constant temperature is 0.5-1h.

2. The method for preparing p-chlorobenzonitrile by static melt crystallization according to claim 1, characterized in that: The method comprises: melting the crude p-chlorobenzonitrile from the distillation system into a liquid and then adding the liquid into a layered melt crystallizer for cooling and crystallization treatment, comprising: The crude p-chlorobenzonitrile from the distillation system is added into a layered melt crystallizer, the material temperature in the layered melt crystallizer is maintained at 100° C. and in a liquid state, and a programmed cooling crystallization treatment is performed to obtain crystals and uncrystallized mother liquor.

3. The method for preparing p-chlorobenzonitrile by static melt crystallization according to claim 1, characterized in that: The crude p-chlorobenzonitrile from the distillation system is obtained by ammoxidation of p-chlorotoluene.

4. The method for preparing p-chlorobenzonitrile by static melt crystallization according to claim 1, characterized in that: The mass percentage of the crude p-chlorobenzonitrile from the distillation system is ≥85%.

5. The method for preparing p-chlorobenzonitrile by static melt crystallization according to claim 1, characterized in that: The mass percentage of the crude p-chlorobenzonitrile from the distillation system is ≥95%.

6. The method for preparing p-chlorobenzonitrile by static melt crystallization according to claim 1, characterized in that: The method for preparing p-chlorobenzonitrile by static melt crystallization also includes: The material obtained by the temperature-raising sweating treatment is heated until it is completely melted and then discharged.

7. The method for preparing p-chlorobenzonitrile by static melt crystallization according to claim 6, characterized in that: The method of heating the material obtained by the sweating treatment until it is completely melted and then discharged comprises: The material obtained by the sweating treatment is heated to 70°C to completely melt it and then discharged.

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