Phenylacetonitrile melt crystallization purification method

Abstract

The invention discloses a phenylacetonitrile melt crystallization purification method, and belongs to the technical field of phenylacetonitrile purification methods. The acetonitrile crude product comprises the following raw materials: 75-79% of benzyl cyanide, 15-17% of benzyl alcohol, 3-5% of benzylamine and 2-4% of benzaldehyde; starting a program temperature control system and putting the filtered clear liquid into a melt crystallizer; the final benzyl cyanide crystal is obtained through initial cooling and crystal growing, heating and sweating, cooling and crystal growing and heating and sweating, and cooling and crystal growing and heating and sweating for the third time, and the purity of the final benzyl cyanide crystal is 99.90%-99.94%. The method is based on the fact that impurities have different partition coefficients between benzyl cyanide crystals and molten liquid. Under slow cooling, phenylacetonitrile with higher purity is preferentially crystallized, and impurities are discharged into mother liquor. The sweating operation further utilizes the characteristic that the melting point of the defect part in the crystal is lower, and the defect part is removed through precise temperature control, so that the ultra-high-purity crystal is obtained. A new scheme is provided for resource recovery, and the method is particularly suitable for recovering high-purity benzyl cyanide from production waste liquid or by-products with complex components.

Description

Technical Field

[0001] This invention relates to a method for purifying phenylacetonitrile by melt crystallization, belonging to the technical field of phenylacetonitrile purification methods. Background Technology

[0002] Phenylacetonitrile is mainly synthesized from benzyl chloride and sodium cyanide via a nucleophilic substitution reaction. The crude product contains impurities such as water, sodium chloride, unreacted benzyl chloride, byproducts benzyl alcohol, benzaldehyde, and homologues. Currently, the main methods for deep purification of phenylacetonitrile are as follows:

[0003] (1) Vacuum distillation (see textbooks such as "Organic Chemical Separation Engineering"): This is the most commonly used method. The crude product, after simple water and alkali washing, enters a vacuum distillation column. By controlling the top temperature, pressure, and reflux ratio, separation is achieved based on the differences in volatility of the components. The phenylacetonitrile product is collected from the middle or top of the column. Disadvantages of this method:

[0004] a) Huge energy consumption: Phenylacetonitrile has a high boiling point, and the distillation process requires a large amount of heat energy for vaporization. At the same time, it requires a supporting condensation and vacuum system, and energy consumption costs account for a large proportion of the total cost.

[0005] b) Product thermal decomposition: Under prolonged high temperature (>150℃) conditions, phenylacetonitrile and impurities will undergo polymerization, oxidation and other reactions, resulting in a decrease in product yield and yellowing (APHA color >30), affecting product quality and grade.

[0006] c) Bottleneck in separation capacity: For impurities with boiling points very close to phenylacetonitrile (such as certain methyl phenylacetonitrile isomers), the separation efficiency of distillation is very low, and it is difficult to remove them effectively by simply increasing the number of trays. The product purity is usually limited to below 99.5%.

[0007] (2) Solvent crystallization method (refer to published patent CN107417560B): This method involves adding solvents such as methanol and ethanol to crude phenylacetonitrile to reduce its solubility, then crystallizing at low temperature, filtering to obtain crystals, and melting the crystals to obtain the product. Disadvantages of this method:

[0008] a) Introduction of new impurities: The addition of solvent brings the risk of solvent residue, which may contaminate the product and require additional complex solvent recovery and purification steps.

[0009] b) Complex process and low yield: Multiple steps such as crystallization, filtration, and solvent recovery result in a long process flow and high equipment investment. Furthermore, crystals easily trap mother liquor, requiring multiple recrystallizations to improve purity, leading to a significant decrease in product yield.

[0010] c) Cost and safety: The use of large amounts of organic solvents increases material costs and potential safety risks in production. Summary of the Invention

[0011] The purpose of this invention is to solve the problems existing in the prior art and to provide a method for purifying phenylacetonitrile by melt crystallization.

[0012] The objective of this invention is achieved through the following technical solution:

[0013] A method for purifying phenylacetonitrile by melt crystallization includes the following steps:

[0014] ① Weigh 500.0g of crude phenylacetonitrile raw material. The composition of the crude phenylacetonitrile raw material is: 75-79% phenylacetonitrile, 15-17% benzyl alcohol, 3-5% benzylamine, and 2-4% benzaldehyde; ② Filter the crude phenylacetonitrile raw material through filter paper to remove most of the visible polymer particles. Turn on the programmed temperature control system and place the filtered clear liquid into a melt crystallizer; ③ First, cool the liquid from -5℃ to -10℃ to -25℃ to -26℃ at a rate of 0.04℃ to 0.1℃ / min, and allow it to crystallize for 60 minutes; ④ Then, raise the temperature to -12℃ to -22℃ at a programmed rate of 0.05℃ to 0.15℃ / min, and allow it to sweat for 50 minutes. After removing the sweat, filter the liquid to obtain primary crystals with a purity of 97.8% to 98.5%; ⑤ Melt the primary crystals and proceed with the second... First-stage purification: The temperature is lowered to -30℃ to -32℃ at a rate of 0.08℃ to 0.15℃ / min, and crystallization is carried out for 90 min; ⑥ Subsequently, the temperature is raised to -25℃ to -27℃ at a rate of 0.04℃ to 0.06℃ / min, and then allowed to evaporate for 60 min. After filtration, secondary crystals are obtained with a purity of 99.60% to 99.69%; ⑦ The secondary crystals are melted and then subjected to third-stage purification: the temperature is lowered to -30℃ to -35℃ at a rate of 0.01℃ to 0.1℃ / min, and crystallization is carried out for 120 min; ⑧ Finally, the temperature is raised to -25℃ to -28℃ at a rate of 0.02℃ to 0.04℃ / min, and then allowed to evaporate for 60 min. After filtration again, final phenylacetonitrile crystals are obtained with a purity of 99.90% to 99.94%.

[0015] In step ①, the composition of the crude phenylacetonitrile raw material is: 77% phenylacetonitrile, 16% benzyl alcohol, 4% benzylamine and 3% benzaldehyde.

[0016] In step ③, the temperature is reduced from -8℃ to -26℃ at a rate of 0.1℃ / min.

[0017] In step ④, the temperature is programmed to rise to -12℃ at a rate of 0.15℃ / min.

[0018] In step ⑤, the temperature is reduced to -31℃ at a rate of 0.08℃ / min.

[0019] In step ⑥, the temperature is increased to -25℃ at a rate of 0.05℃ / min.

[0020] In step ⑦, the temperature is reduced to -35℃ at a rate of 0.1℃ / min.

[0021] In step ⑧, the temperature is increased to -28℃ at a rate of 0.03℃ / min.

[0022] The working principle of this invention is as follows: The method of this invention is based on the fact that impurities have different partition coefficients between styrene crystals and the molten liquid. Under slow cooling, higher purity styrene crystallizes preferentially, and impurities are discharged into the mother liquor. The sweating process further utilizes the characteristic that the melting point is lower at the internal defects of the crystals, and removes them through precise temperature control, thereby obtaining ultra-high purity crystals.

[0023] Key technical points: The successful implementation of the technical solution of this invention depends on a deep understanding of the melting points of each component of the mixture and precise control of the crystallization / sweating temperature to avoid the occurrence of eutectic phenomenon.

[0024] Melt crystallization: The process by which a substance cools from its molten liquid state and crystals precipitate out.

[0025] Sweatating: After crystallization, the process of slowly heating the crystal to preferentially melt and remove the impurities and lower melting point parts of the crystal is a key refining method in melt crystallization.

[0026] Compared with the closest prior art (distillation method), the beneficial effects of the present invention are as follows:

[0027] 1. Fundamentally solves the thermal decomposition problem: The entire process is carried out under low temperature conditions, completely eliminating all side reactions that inevitably occur at high distillation temperatures, such as the decarboxylation of phenylacetic acid, benzaldehyde polymerization, and benzylamine condensation, ensuring the feasibility and stability of the process flow. This is the biggest advantage.

[0028] 2. High product purity and yield: Utilizing the high selectivity of melt crystallization, phenylacetonitrile can be extracted directly from complex mixtures. The product purity can reach over 97% in one step, and 99.9% or higher can be achieved through two-stage purification. It also effectively avoids material loss during extraction and other processes, resulting in a high yield.

[0029] 3. Significantly reduced energy consumption and costs: Although refrigeration is required, its energy consumption is far lower than that required to maintain the long-term operation of a high-vacuum distillation column, and the equipment is simple, with a total cost significantly lower than that of the distillation method.

[0030] 4. Providing new solutions for resource recycling: This method is particularly suitable for recovering high-purity phenylacetonitrile from complex production waste liquids or by-products, turning waste into treasure and having a high added economic effect. Detailed Implementation

[0031] The present invention will be further described in detail below: This embodiment is implemented based on the technical solution of the present invention, and detailed implementation methods are given, but the protection scope of the present invention is not limited to the following embodiment.

[0032] Example 1

[0033] The phenylacetonitrile melt crystallization purification method in this embodiment is as follows:

[0034] ① Weigh 500.0g of crude phenylacetonitrile raw material (GC analysis composition: phenylacetonitrile 75-79%, benzyl alcohol 15-17%, benzylamine 3-5%, and benzaldehyde 2-4%). ​​② Filter the crude raw material through ordinary filter paper to remove most of the visible polymer particles. Place the filtrate in a melt crystallizer, and turn on the programmed temperature control system to place the filtered clear liquid into the crystallizer. ③ First, cool the material at a rate of 0.04℃-0.1℃ / min from -5℃ to -10℃ to -25℃ to -26℃, and allow it to crystallize for 60 minutes. ④ Then, raise the temperature at a rate of 0.05℃-0.15℃ / min to -12℃ to -22℃, and allow it to sweat for 50 minutes. After removing the sweat, quickly filter the material to obtain primary crystals (GC purity 97.8%-98.5%). ⑤ After melting the primary crystals, a second purification stage is performed: the temperature is lowered to -30℃ to -32℃ at a rate of 0.08℃ to 0.15℃ / min, and crystallization is carried out for 90 min. ⑥ Subsequently, the temperature is raised to -25℃ to -27℃ at a rate of 0.04℃ to 0.06℃ / min, and then allowed to evaporate for 60 min. After filtration, secondary crystals are obtained (GC purity 99.60% to 99.69%). ⑦ After melting the secondary crystals, a third purification stage is performed: the temperature is lowered to -30℃ to -35℃ at a rate of 0.01℃ to 0.1℃ / min, and crystallization is carried out for 120 min. ⑧ Finally, the temperature is raised to -25℃ to -28℃ at an extremely slow rate of 0.02℃ to 0.04℃ / min, and then allowed to evaporate for 60 min. After rapid filtration again, the final phenylacetonitrile crystals are obtained. GC analysis shows that the purity of the final product is as high as 99.90% to 99.94%.

[0035] Example 2

[0036] The phenylacetonitrile melt crystallization purification method in this embodiment is as follows:

[0037] ① Weigh 500.0g of crude phenylacetonitrile raw material (GC analysis composition: phenylacetonitrile 77%, benzyl alcohol 16%, benzylamine 4%, and benzaldehyde 3%). ② Filter the crude product through ordinary filter paper to remove most visible polymer particles. Place the filtrate in a melt crystallizer, and turn on the programmed temperature control system to place the clarified filtrate into the crystallizer. ③ First, cool from -8℃ to -26℃ at a rate of 0.1℃ / min and allow crystals to grow for 60min. ④ Then, increase the temperature to -20℃ at a programmed rate of 0.05℃ / min to induce sweating for 50min. After removing the sweat, quickly filter to obtain primary crystals (GC purity 97.9%). ⑤ After melting the primary crystals, perform a second-stage purification: cool to -32℃ at a rate of 0.08℃ / min and allow crystals to grow for 90min. ⑥ The temperature was then increased to -25℃ at a rate of 0.05℃ / min for 60 min, followed by filtration to obtain secondary crystals (GC purity 99.6%). ⑦ The secondary crystals were melted and subjected to a third stage of purification: the temperature was decreased to -30℃ at a rate of 0.01℃ / min for 120 min. ⑧ Finally, the temperature was increased to -28℃ at an extremely slow rate of 0.03℃ / min for 60 min, followed by rapid filtration again to obtain the final phenylacetonitrile crystals. GC analysis showed that the final product had a purity of up to 99.90%.

[0038] Example 3

[0039] The phenylacetonitrile melt crystallization purification method in this embodiment is as follows:

[0040] ① Weigh 500.0g of crude phenylacetonitrile raw material (GC analysis composition: phenylacetonitrile 77%, benzyl alcohol 16%, benzylamine 4%, and benzaldehyde 3%). ② Filter the crude product through ordinary filter paper to remove most visible polymer particles. Place the filtrate in a melt crystallizer, and turn on the programmed temperature control system to place the clarified filtrate into the crystallizer. ③ First, cool from -5℃ to -25℃ at a rate of 0.08℃ / min and allow crystals to grow for 60min. ④ Then, increase the temperature to -12℃ at a rate of 0.15℃ / min to induce sweating for 50min. After removing the sweat, quickly filter to obtain primary crystals (GC purity 98.3%). ⑤ After melting the primary crystals, perform a second-stage purification: cool to -30℃ at a rate of 0.15℃ / min and allow crystals to grow for 90min. ⑥ The temperature was then increased to -27℃ at a rate of 0.05℃ / min for 60 min, followed by filtration to obtain secondary crystals (GC purity 99.65%). ⑦ The secondary crystals were melted and subjected to a third stage of purification: the temperature was decreased to -35℃ at a rate of 0.1℃ / min for 120 min. ⑧ Finally, the temperature was increased to -25℃ at an extremely slow rate of 0.03℃ / min for 60 min, followed by rapid filtration again to obtain the final phenylacetonitrile crystals. GC analysis showed that the final product had a purity of up to 99.92%.

[0041] Example 4

[0042] The phenylacetonitrile melt crystallization purification method in this embodiment is as follows:

[0043] ① Weigh 500.0g of crude phenylacetonitrile raw material (GC analysis composition: phenylacetonitrile 77%, benzyl alcohol 16%, benzylamine 4%, and benzaldehyde 3%). ② Filter the crude product through ordinary filter paper to remove most visible polymer particles. Place the filtrate in a melt crystallizer, and turn on the programmed temperature control system to place the clarified filtrate into the crystallizer. ③ First, cool from -10℃ to -26℃ at a rate of 0.04℃ / min and allow crystals to grow for 60min. ④ Then, increase the temperature to -22℃ at a rate of 0.05℃ / min to induce sweating for 50min. After removing the sweat, quickly filter to obtain primary crystals (GC purity 98.5%). ⑤ After melting the primary crystals, perform a second-stage purification: cool to -31℃ at a rate of 0.08℃ / min and allow crystals to grow for 90min. ⑥ The temperature was then increased to -26℃ at a rate of 0.05℃ / min for 60 min, followed by filtration to obtain secondary crystals (GC purity 99.69%). ⑦ The secondary crystals were melted and subjected to a third stage of purification: the temperature was decreased to -33℃ at a rate of 0.05℃ / min for 120 min. ⑧ Finally, the temperature was increased to -28℃ at an extremely slow rate of 0.03℃ / min for 60 min, followed by rapid filtration again to obtain the final phenylacetonitrile crystals. GC analysis showed that the final product had a purity of up to 99.94%.

[0044] The above description is merely a preferred embodiment of the present invention. These specific embodiments are different implementations based on the overall concept of the present invention, and the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for purifying phenylacetonitrile by melt crystallization, characterized in that, The purification method of phenylacetonitrile by melt crystallization is as follows: ① 500.0 g of crude phenylacetonitrile raw material is weighed, and the composition of the crude phenylacetonitrile raw material is: 75-79% of phenylacetonitrile, 15-17% of benzyl alcohol, 3-5% of benzylamine and 2-4% of benzaldehyde; ② the crude phenylacetonitrile raw material is filtered through filter paper to remove most of the visible polymer particles, and the filtered clear liquid is placed in a melt crystallizer by opening the program control system; ③ first, the temperature is lowered from -5°C to -10°C at a rate of 0.04°C-0.1°C / min to -25°C to -26°C, and the crystal is incubated for 60 min; ④ then, the temperature is programmed to rise to -12°C to -22°C at a rate of 0.05°C-0.15°C / min, and then sweating for 50 min, and the first grade crystal is obtained by filtration after the sweat is discharged, and the purity of the first grade crystal is 97.8%-98.5%; ⑤ after the first grade crystal is melted, the second purification is carried out: the temperature is lowered to -30°C to -32°C at a rate of 0.08°C-0.15°C / min, and the crystal is incubated for 90 min; ⑥ then, the temperature is raised to -25°C to -27°C at a rate of 0.04°C-0.06°C / min, and then sweating for 60 min, and the second grade crystal is obtained by filtration, and the purity of the second grade crystal is 99.60%-99.69%; ⑦ after the second grade crystal is melted, the third grade refining is carried out: the temperature is lowered to -30°C to -35°C at a rate of 0.01°C-0.1°C / min, and the crystal is incubated for 120 min; ⑧ finally, the temperature is raised to -25°C to -28°C at a rate of 0.02°C-0.04°C / min, and then sweating for 60 min, and the final phenylacetonitrile crystal is obtained by filtration again, and the purity of the final phenylacetonitrile crystal is 99.90%-99.94%.

2. The phenylacetonitrile purification by melt crystallization process according to claim 1, characterized in that, In step ①, the composition of the crude phenylacetonitrile raw material is: 77% of phenylacetonitrile, 16% of benzyl alcohol, 4% of benzylamine and 3% of benzaldehyde.

3. The phenylacetonitrile purification by melt crystallization process of claim 1, wherein, In step ③, the temperature is lowered from -8°C to -26°C at a rate of 0.1°C / min.

4. The phenylacetonitrile purification by melt crystallization process of claim 1, wherein, In step ④, the temperature is programmed to rise to -12°C at a rate of 0.15°C / min.

5. The phenylacetonitrile purification by melt crystallization process of claim 1, wherein, In step ⑤, the temperature is lowered to -31°C at a rate of 0.08°C / min.

6. The phenylacetonitrile purification by melt crystallization process of claim 1, wherein, In step ⑥, the temperature is raised to -25°C at a rate of 0.05°C / min.

7. The phenylacetonitrile purification by melt crystallization process of claim 1, wherein, In step ⑦, the temperature is lowered to -35°C at a rate of 0.1°C / min.

8. The phenylacetonitrile purification by melt crystallization process of claim 1, wherein, In step ⑧, the temperature is raised to -28°C at a rate of 0.03°C / min.