Process for preparing high-purity p-fluorobenzoyl chloride by continuous falling film melt crystallization method

Abstract

The invention provides a process for preparing high-purity p-fluorobenzoyl chloride by a continuous falling film melt crystallization method, and belongs to the field of fine chemical purification, the process comprises the following steps: carrying out reduced pressure distillation on a reaction solution obtained by hydrolysis reaction of p-fluorobenzyl trichloride to obtain a p-fluorobenzoyl chloride crude product; the method comprises the following steps: carrying out dehydration treatment, carrying out falling film crystallization treatment, carrying out multi-stage programmed heating sweating treatment on precipitated crystals, removing an impurity enrichment liquid, collecting a high-purity p-fluorobenzoyl chloride melt, and finally obtaining an electronic-grade or pharmaceutical-grade product with chromatographic purity of more than or equal to 99.9%, and carrying out the whole process under inert gas protection. The continuous falling film melt crystallization method provided by the invention effectively solves the technical problem that p-fluorobenzoyl chloride is easy to hydrolyze and eutectic in the purification process, has the advantages of low energy consumption, environment-friendly process and high product purity, can remarkably improve the production efficiency and quality of p-fluorobenzoyl chloride, and is suitable for industrial production. The harsh requirements of electronics and medicine industries on high-purity raw materials are met.

Description

Technical Field

[0001] This invention relates to the field of fine chemical purification technology, specifically to a process for preparing high-purity p-fluorobenzoyl chloride using a continuous falling film melt crystallization method. Background Technology

[0002] The fluorine atom in the p-fluorobenzoyl chloride structure enhances the drug's lipophilicity, metabolic stability, and targeting. The acyl chloride group reacts under mild conditions and is suitable for various functional group transformations. Therefore, p-fluorobenzoyl chloride is an important organic intermediate widely used in pharmaceuticals, pesticides, and materials. However, p-fluorobenzoyl chloride used in pharmaceuticals and materials requires high purity.

[0003] Patent CN119751251A discloses a "method and process for the photochlorination synthesis of high-purity p-fluorobenzoyl chloride." While this method focuses on inhibiting fluoride loss during the synthesis stage, the purification process still relies on vacuum distillation at a temperature of 110°C, resulting in high energy consumption and a purity of only 99.5%, which is insufficient for electronic-grade applications. Patent CN102989193A discloses a magnetic field-assisted static crystallization method, the core of which is a magnetic carrier-enhanced solid-liquid separation. This method is primarily suitable for stable organic compounds. However, no continuous purification process has been reported for the easily hydrolyzed and eutectic compounds mentioned in this invention.

[0004] p-Fluorobenzoyl chloride is extremely reactive, readily absorbing moisture and hydrolyzing to form impurities such as p-fluorobenzoic acid and p-fluorobenzoic anhydride. This characteristic significantly increases the challenges of its purification. Traditional distillation requires high temperatures, which can easily lead to prolonged thermal decomposition, polymerization, or hydrolysis of the product within the vessel, resulting in high energy consumption and difficulty in guaranteeing product yield and quality. Conventional melt crystallization methods are also susceptible to severe hydrolysis upon contact with even trace amounts of moisture or air, leading to crystallization failure and a decrease in product purity. Furthermore, p-fluorobenzoyl chloride and its hydrolyzed impurities easily form eutectics, which cannot be effectively separated by simple cooling-sweating processes, making it difficult to obtain electronic-grade ultra-high purity products. Intermittent crystallization processes suffer from long production cycles, low efficiency, high energy consumption per unit product, high labor intensity, and potential batch-to-batch product quality fluctuations, failing to meet the demands of continuous, stable, and large-scale modern chemical production.

[0005] In summary, existing purification technologies for p-fluorobenzoyl chloride suffer from three major drawbacks: high energy consumption in distillation, low efficiency in batch crystallization, and susceptibility to hydrolysis in conventional crystallization. Therefore, developing a purification process that can simultaneously address the hydrolysis sensitivity and eutectic challenges of p-fluorobenzoyl chloride while achieving continuous and automated production is of great significance for promoting the industrialization of this high-end intermediate. Summary of the Invention

[0006] In view of the technical problems existing in the background art, the present invention provides a process for preparing high-purity p-fluorobenzoyl chloride by continuous falling film melt crystallization, aiming to solve the technical problems of high energy consumption, low efficiency, easy hydrolysis, and difficulty in achieving electronic grade purity in existing p-fluorobenzoyl chloride purification technologies.

[0007] In a first aspect, the present invention provides a process for preparing high-purity p-fluorobenzoyl chloride by continuous falling film melt crystallization, comprising the following steps: S1. The reaction solution obtained by hydrolysis of p-fluorotrichlorobenzyl is subjected to vacuum distillation to obtain crude p-fluorobenzoyl chloride; then the crude p-fluorobenzoyl chloride is subjected to dehydration treatment. S2. The dehydrated crude product is continuously fed into the top of the falling film crystallizer for falling film crystallization treatment, and the uncrystallized mother liquor is returned to the vacuum distillation section. S3. The crystalline material undergoes a multi-stage programmed heating and sweating process. First, the temperature is raised to 10-15℃ and held for 1-3 hours to allow the material to soften. The first sweating liquid is collected and returned to the falling film crystallization section. Then, the sweated crystals are heated to 18-23℃ and sweated for another 1-3 hours. The second sweating liquid is collected to obtain the high-purity p-fluorobenzoyl chloride product. The remaining crystals are completely melted and returned to the distillation section. Steps S1 to S3 are all performed under inert gas protection.

[0008] Preferably, in step S1, the conditions for vacuum distillation are: pressure ≤ -0.09MPa and temperature 90~100℃.

[0009] Preferably, in step S1, the moisture content of the crude product after dehydration treatment does not exceed 50 ppm.

[0010] Preferably, the dewatering material used in the dewatering process includes molecular sieves; the amount of molecular sieves used is 10-30w of the crude product.

[0011] Preferably, the molecular sieve includes activated 3A molecular sieve or 4A molecular sieve.

[0012] Preferably, the activation temperature is 300~450℃.

[0013] Preferably, in step S2, the feed temperature of the falling film crystallizer is controlled at 30~40℃, and the crystallization temperature of the falling film crystallization treatment is controlled at 5~10℃.

[0014] Preferably, in step S3, the heating rate of the multi-stage programmed heating and sweating treatment is 0.5~5℃ / h.

[0015] Preferably, the falling film crystallizer is equipped with a material distributor at the top, which enables the material to form a uniform liquid film on the inner wall of the crystallization tube; the material distributor is a spiral liquid distributor with a distribution uniformity of ≥90% and a liquid film thickness deviation of ≤0.5mm.

[0016] Preferably, the inert gas protection is nitrogen protection, with nitrogen purity ≥99.999%, oxygen content ≤0.05%, and pressure maintained at 0.005~0.015 MPa.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a continuous falling film melt crystallization process for preparing high-purity p-fluorobenzoyl chloride. This process integrates vacuum distillation, dehydration, continuous falling film crystallization, and multi-gradient sweating, with high-purity nitrogen protection and strict dehydration control throughout. The combination of continuous falling film crystallization and multi-gradient sweating effectively solves the technical challenges of easy hydrolysis and eutectic formation of p-fluorobenzoyl chloride during purification, achieving efficient purification and precise separation of impurities. This process features continuous material feeding and discharging, a high degree of automation, and significantly improved production efficiency, making it ideal for large-scale industrial production. The continuous steady-state production process avoids quality fluctuations caused by batch operations, resulting in extremely high product consistency. Furthermore, the falling film heat transfer efficiency is high, and the continuous process has a high degree of thermal integration, further reducing unit product energy consumption by 20%~30% compared to intermittent processes. The continuous falling film and sweating processes ensure more complete solid-liquid mass transfer, better separation, stable product purity ≥99.9%, and higher yield. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the process flow for preparing high-purity p-fluorobenzoyl chloride using the continuous falling film melt crystallization method in an embodiment of the present invention. Detailed Implementation

[0019] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solution of the present invention and are therefore intended to limit the scope of protection of the present invention.

[0020] To address the technical problems of high energy consumption, low efficiency, easy hydrolysis, and difficulty in achieving electronic-grade purity in existing p-fluorobenzoyl chloride purification technologies, this invention provides a process for preparing high-purity p-fluorobenzoyl chloride using a continuous falling film melt crystallization method. This process integrates "reduced pressure distillation + dehydration + continuous falling film crystallization + multi-gradient sweating" to achieve highly efficient purification of p-fluorobenzoyl chloride.

[0021] Please refer to Figure 1 In a first aspect, embodiments of the present invention provide a process for preparing high-purity p-fluorobenzoyl chloride by continuous falling film melt crystallization, comprising the following steps: S1. The reaction solution obtained by hydrolysis of p-fluorotrichlorobenzyl is subjected to vacuum distillation to obtain crude p-fluorobenzoyl chloride; then the crude p-fluorobenzoyl chloride is subjected to dehydration treatment. S2. The dehydrated crude product is continuously fed into the top of the falling film crystallizer for falling film crystallization treatment, and the uncrystallized mother liquor is returned to the vacuum distillation section. S3. The crystalline material undergoes a multi-stage programmed heating and sweating process. First, the temperature is raised to 10-15℃ and held for 1-3 hours to allow the material to soften. The first sweating liquid is collected and returned to the falling film crystallization section. Then, the sweated crystals are heated to 18-23℃ and sweated for another 1-3 hours. The second sweating liquid is collected to obtain the high-purity p-fluorobenzoyl chloride product. The remaining crystals are completely melted and returned to the distillation section. Steps S1 to S3 are all performed under inert gas protection.

[0022] In the technical solution of this invention embodiment, the purification mechanism of p-fluorobenzoyl chloride is as follows: During the crystallization stage, the temperature of the falling film crystallizer is controlled at 5~10℃. This temperature works in conjunction with the water content ≤50ppm after dehydration by molecular sieves to eliminate free water molecules in the system, thereby reducing the chance of p-fluorobenzoyl chloride and p-fluorobenzoic acid forming hydrogen bonds through water to co-crystallize. At the same time, combined with the solubility difference at this temperature, an optimal solubility difference window is created, thereby avoiding the formation of co-crystallization between p-fluorobenzoyl chloride and p-fluorobenzoic acid, which facilitates selective separation. The multi-stage programmed temperature rise and sweating treatment stage includes two temperature gradients: the first gradient temperature is 10~15℃, used to remove the low-melting-point impurity p-fluorotrichlorobenzyl; the second gradient temperature is 18~23℃, used to collect high-purity p-fluorobenzoyl chloride product. The temperature difference between the two gradients ≥5℃ can achieve efficient separation of impurities. The crystals remaining after sweating are mainly the high-melting-point by-product impurity p-fluorobenzoic acid.

[0023] Furthermore, in some embodiments, in step S1, the conditions for vacuum distillation are: pressure ≤ -0.09 MPa and temperature 90~100℃.

[0024] In the technical solution of this invention embodiment, p-fluorobenzoyl chloride is initially purified by vacuum distillation, with the temperature controlled at 90~100℃, which can ensure the smooth distillation of p-fluorobenzoyl chloride and minimize the co-distillation of impurities.

[0025] Furthermore, in some embodiments, in step S1, the moisture content of the crude product after dehydration treatment does not exceed 50 ppm.

[0026] In the technical solution of this invention embodiment, by strictly controlling the moisture content of the crude product after dehydration treatment, the risk of hydrolysis of p-fluorobenzoyl chloride due to the presence of moisture during subsequent crystallization can be effectively reduced, while inhibiting the formation of eutectic between p-fluorobenzoyl chloride and p-fluorobenzoic acid, thus significantly improving product purity.

[0027] Furthermore, in some embodiments, the dehydration material used in the dehydration process includes molecular sieves; the amount of molecular sieves used is 10-30w of the crude product.

[0028] Furthermore, in some embodiments, the molecular sieve includes an activated 3A molecular sieve or a 4A molecular sieve.

[0029] In the technical solution of this invention embodiment, the activated 3A molecular sieve or 4A molecular sieve has excellent adsorption performance and can effectively adsorb trace amounts of moisture in the crude product, ensuring that the moisture content of the crude product after dehydration meets the requirements of the subsequent crystallization process, thereby ensuring the stability of the entire purification process and the high purity of the product.

[0030] Furthermore, in some embodiments, the activation temperature is 300~450°C.

[0031] In the technical solution of this invention embodiment, the molecular sieve is activated at a temperature of 300~450℃, which can fully stimulate the adsorption activity of the molecular sieve, make its internal pore structure more unobstructed, and enhance its adsorption capacity for water.

[0032] Furthermore, in some embodiments, in step S2, the feed temperature of the falling film crystallizer is controlled at 30~40°C, and the crystallization temperature of the falling film crystallization process is controlled at 5~10°C.

[0033] In the technical solution of this invention embodiment, the feed temperature of the falling film crystallizer is controlled at 30~40℃, which ensures that the crude product is in a suitable flow state when entering the crystallizer. This prevents premature crystallization and pipe blockage due to excessively low temperature, and also avoids increased energy consumption due to excessively high temperature. Simultaneously, controlling the crystallization temperature at 5~10℃ synergizes with the condition that the moisture content after molecular sieve dehydration does not exceed 50ppm, effectively reducing the possibility of p-fluorobenzoyl chloride and p-fluorobenzoic acid forming hydrogen bonds through moisture for co-crystallization, thus providing favorable conditions for selective separation.

[0034] Furthermore, in some embodiments, in step S3, the heating rate of the multi-stage programmed heating and sweating treatment is 0.5~5℃ / h.

[0035] Furthermore, in some embodiments, a material distributor is provided at the top of the falling film crystallizer, which enables the material to form a uniform liquid film on the inner wall of the crystallization tube; the material distributor is a spiral liquid distributor with a distribution uniformity of ≥90% and a liquid film thickness deviation of ≤0.5mm.

[0036] In the technical solution of this invention embodiment, a spiral liquid distributor is provided at the top of the falling film crystallizer, which enables the material to form a uniform liquid film with small thickness deviation on the inner wall of the crystallization tube. This not only enhances the heat transfer efficiency, but also facilitates the uniform distribution of temperature during the crystallization process, thereby further improving the purity and quality of the crystallized product.

[0037] Furthermore, in some embodiments, the inert gas protection is nitrogen protection, with nitrogen purity ≥99.999%, oxygen content ≤0.05%, and pressure maintained at 0.005~0.015 MPa.

[0038] In the technical solution of this invention embodiment, the entire process is protected by high-purity nitrogen, which can effectively isolate moisture and oxygen in the air and prevent hydrolysis and oxidation reactions of p-fluorobenzoyl chloride during the purification process, thereby ensuring the purity and quality stability of the product.

[0039] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0040] Example 1 A process for preparing high-purity p-fluorobenzoyl chloride by continuous falling film melt crystallization includes the following steps: (1) Preparation and dehydration of crude product: 1000 kg of the reaction solution obtained by hydrolysis of p-fluorotrichlorobenzyl was distilled for 3 h under a vacuum of -0.095 MPa and a temperature of 95 °C to obtain 950 kg of crude p-fluorobenzoyl chloride with a purity of 95.20%. The above material was dehydrated for 16 h in a dehydration tower. The packing material of the dehydration tower was 95 kg of 3A molecular sieve activated at 300 °C, and the nitrogen pressure in the tower was 0.01 MPa. 945 kg of dehydrated crude product with a moisture content of 26 ppm was obtained.

[0041] (2) Continuous falling film crystallization purification: The dehydrated crude product is melted at 30℃ and fed into the top of the falling film crystallizer at a flow rate of 130kg / h under nitrogen protection (pressure 0.01MPa, oxygen content ≤0.05%). The material forms a uniform liquid film on the inner wall of the crystallization tube through the distributor. The temperature outside the tube is controlled by circulating heat transfer oil. The temperature of the crystallization section is controlled at 8℃. The fluorobenzoyl chloride crystals precipitate on the inner wall surface of the crystallization tube. The uncrystallized mother liquor is returned to the vacuum distillation section for recycling.

[0042] (3) Sweating is controlled by programmed temperature rise in the falling film crystallizer: First, the crystal layer is heated to 12°C and kept at a constant temperature for 1 hour. The sweating liquid discharged in this stage (purity 92.6%) is returned to the crystallization feed end. Then, the crystal layer is heated to 19°C and kept at a constant temperature for 1 hour. The high-purity melt liquid (purity 99.92%) in this stage is collected, which is the high-purity p-fluorobenzoyl chloride product. The remaining crystals after sweating are mainly by-product p-fluorobenzoic acid. The remaining crystals are completely melted and returned to the distillation section for recycling.

[0043] Online moisture detectors are installed throughout the process, located at the outlet of the dehydration unit, the inlet of the crystallizer, and the product collection tank, to ensure that moisture content is controllable throughout the entire process.

[0044] The system ran stably for 7.3 hours, collecting a total of 835 kg of product, with a yield of 92.3%. The entire process was continuous and stable, and the product quality was highly uniform.

[0045] Example 2 This example examines the effect of different moisture contents on product purity.

[0046] Referring to the process steps of Example 1, in step (1) crude product preparation and dehydration: 1000 kg of the reaction solution obtained by hydrolysis of p-fluorotrichlorobenzyl was distilled for 3 h under a vacuum of -0.095 MPa and a temperature of 95 °C to obtain 950 kg of crude p-fluorobenzoyl chloride with a purity of 95.20%. The above materials were dehydrated in a dehydration tower for 2 h, 8 h, and 16 h respectively. The packing material of the dehydration tower was 95 kg of 3A molecular sieve activated at 300 °C, and the nitrogen pressure in the tower was 0.01 MPa. Finally, the moisture content of the dehydrated crude products was 80 ppm, 50 ppm, and 30 ppm respectively. Steps (2) and (3) are the same as in Example 1. The final product purity results are shown in Table 1 below.

[0047] Table 1

[0048] The results in Table 1 show that by strictly controlling the moisture content of the crude product after dehydration, the risk of hydrolysis of p-fluorobenzoyl chloride due to the presence of moisture during subsequent crystallization can be effectively reduced, while reducing the formation of eutectic and significantly improving product purity.

[0049] Comparative Example 1 The process for preparing p-fluorobenzoyl chloride by batch melt crystallization includes the following steps: (1) The vacuum distillation and dehydration were the same as in Example 1, and 945 kg of dehydrated product with a moisture content of 26 ppm was obtained.

[0050] (2) Low temperature crystallization: The above materials are cooled to 10°C at room temperature at a rate of 1.5°C / h; after reaching 8°C, crystallization is carried out for 3 hours. The uncrystallized mother liquor is returned to the vacuum distillation section to obtain 895 kg of crystallized material.

[0051] (3) Sweating and melting: The above-mentioned crystallized material is heated to 15°C and melted for 3 hours. The purity of the sweating liquid is 90.9%, and it is returned to the crystallization section. The crystals are heated to 20°C and sweated for 2 hours. 820 kg of sweating liquid is collected, and the purity of p-fluorobenzoyl chloride is 99.95%. The first-time yield is 90.6%. The remaining crystals are completely melted and returned to the distillation section.

[0052] The nitrogen pressure inside the crystallization reactor is maintained within the range of 0.01~0.015MPa, and the nitrogen purity is ≥99.999%, while the oxygen content of the system is ≤0.05%.

[0053] The energy consumption of this comparative embodiment is compared with that of Example 1. Detailed data are shown in Table 2 below.

[0054] Table 2 Comparison of Energy Consumption of the Two Processes

[0055] The table above shows that the continuous falling film crystallization process saves 55 kWh of energy compared to the intermittent melt crystallization process, representing a saving of 17.2%. Comparative Example 2 The traditional distillation process for preparing p-fluorobenzoyl chloride includes the following steps: Vacuum distillation: 1000 kg of the reaction solution obtained by hydrolysis of p-fluorotrichlorobenzyl was distilled at -0.095 MPa and 95 °C for 3 h to obtain 950 kg of crude p-fluorobenzoyl chloride with a purity of 95.2%.

[0056] Distillation: Vacuum degree -0.095MPa, reflux ratio 3:1, top temperature 110℃, bottom temperature 120℃, after 4 hours, 850kg of p-fluorobenzoyl chloride product with a purity of 99.5% was obtained.

[0057] The energy consumption of this comparative embodiment is compared with that of Example 1. Detailed data are shown in Table 3 below.

[0058] Table 3 Comparison of energy consumption between the two processes

[0059] The table above shows that the continuous falling film crystallization process saves 285 kWh of energy compared to the intermittent melt crystallization process, representing a 52% reduction.

[0060] Comparative Example 3 The difference between this comparative example and Example 1 is that in step (3), the temperature is directly raised to 19°C and sweating is performed for 3 hours to obtain 850 kg of sweat liquid with a purity of 98.5% and a yield of 92.5%.

[0061] Comparative Example 3 data verified the key role of the multi-gradient sweating process in impurity separation. If the first-gradient sweating step is omitted and the temperature is directly raised to a higher temperature for sweating, low-melting-point impurities (such as trichlorofluorobenzyl) will not be fully discharged and will remain in the crystal, ultimately affecting the purity of the product.

[0062] Comparative Example 4 The difference between this comparative example and Example 1 is that molecular sieve dehydration is not performed in step (1), nitrogen protection is not provided, the product purity is only 96.7%, and the p-fluorobenzoic acid content is 2.57%.

[0063] Comparative Example 4 data shows that if the molecular sieve dehydration step is omitted and nitrogen protection is not used, the residual moisture and oxygen in the system will trigger the hydrolysis reaction of p-fluorobenzoyl chloride, and at the same time promote its formation of eutectic with p-fluorobenzoic acid through hydrogen bonding, resulting in a significant decrease in product purity and a substantial increase in impurity content.

[0064] It should be noted that the present invention is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments that have the same structure and perform the same effects as the technical concept within the scope of the present invention are included within the scope of the present invention. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of the present invention, are also included within the scope of the present invention.

Claims

1. A process for the preparation of high purity p-fluorobenzoyl chloride by continuous falling film melt crystallization, characterized in that, The method comprises the following steps: S1, subjecting the reaction liquid obtained by hydrolysis reaction of p-fluorotri-chlorobenzyl to reduced pressure distillation to obtain p-fluorobenzoyl chloride crude product; and then subjecting the p-fluorobenzoyl chloride crude product to dehydration treatment; S2, continuously feeding the dehydrated crude product into the top of a falling film crystallizer for falling film crystallization treatment, and returning the uncrystallized mother liquor to the reduced pressure distillation section; S3, subjecting the crystal material to multi-stage programmed temperature sweating treatment, first heating to 10-15℃ and keeping constant for 1-3h for material melting, collecting the first sweating liquid and returning it to the falling film crystallization section, and then heating the sweated crystal to 18-23℃ for further sweating for 1-3h, collecting the second sweating liquid to obtain high-purity p-fluorobenzoyl chloride product; and returning the remaining crystal to be completely melted to the distillation section; The steps S1-S3 are all carried out under inert gas protection.

2. A process for the preparation of high purity p-fluorobenzoyl chloride by continuous falling film melt crystallization according to claim 1, characterized in that, In the step S1, the reduced pressure distillation is carried out at a pressure of ≤-0.09MPa and a temperature of 90-100℃.

3. A process for the preparation of high purity p-fluorobenzoyl chloride by continuous falling film melt crystallization according to claim 1, characterized in that, In the step S1, the moisture content of the crude product after dehydration treatment is not more than 50ppm.

4. A process for the preparation of high purity p-fluorobenzoyl chloride by continuous falling film melt crystallization according to claim 3, characterized in that, The dehydration material used in the dehydration treatment comprises molecular sieves; and the amount of the molecular sieves is 10-30w% of the crude product.

5. A process for the preparation of high purity p-fluorobenzoyl chloride by continuous falling film melt crystallization according to claim 4, characterized in that, The molecular sieves comprise activated 3A molecular sieves or 4A molecular sieves.

6. A process for the preparation of high purity p-fluorobenzoyl chloride by continuous falling film melt crystallization according to claim 5, characterized in that, The activation temperature is 300-450℃.

7. A process for the preparation of high purity p-fluorobenzoyl chloride by continuous falling film melt crystallization according to claim 1, characterized in that, In the step S2, the feeding temperature of the falling film crystallizer is controlled to be 30-40℃; and the crystallization temperature of the falling film crystallization treatment is controlled to be 5-10℃.

8. A process for the preparation of high purity p-fluorobenzoyl chloride by continuous falling film melt crystallization according to claim 1, characterized in that, In the step S3, the heating rate of the multi-stage programmed temperature sweating treatment is 0.5-5℃ / h.

9. A process for the preparation of high purity p-fluorobenzoyl chloride by continuous falling film melt crystallization according to claim 1, characterized in that, The top of the falling film crystallizer is provided with a material distributor, which makes the material form uniform liquid film on the inner wall of the crystallization tube; the material distributor is a spiral liquid distributor, and the uniformity of distribution is ≥90%, and the deviation of liquid film thickness is controlled to be ≤0.5mm.

10. A process for the preparation of high purity p-fluorobenzoyl chloride by continuous falling film melt crystallization according to claim 1, characterized in that, The inert gas protection is nitrogen protection, and the purity of nitrogen is ≥99.999%, the oxygen content is ≤0.05%, and the pressure is kept at 0.005-0.015MPa.

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