Method for purifying by-product new menthol in menthol production line

Abstract

The invention relates to a method for purifying a by-product of neomenthol in a menthol production line, which is characterized in that a reaction product obtained by hydrogenating thymol to produce menthol is used as a raw material, and the extraction of high-purity neomenthol is realized through a process of combining rectification and crystallization. The method specifically comprises the following steps: rectifying by using a rectifying tower with a specific specification under the conditions that the temperature is 115-125 DEG C, the vacuum degree is 15-20mmHg and the reflux ratio is (20: 2)-(50: 2), and enriching neomenthol to 75-77%; and carrying out plate-type crystallization treatment twice, carrying out crystallization under the conditions that the temperature is reduced to 25-27 DEG C through primary crystallization and the temperature is reduced to 35 DEG C through secondary programmed cooling, and carrying out further purification through heating and sweating to finally obtain a neomenthol product with the purity of 99.5%. The method is simple in process and low in energy consumption, does not need a solvent, can be directly connected with an existing production line, and is suitable for large-scale production of medicine and spice-grade high-purity neomenthol.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for purifying the byproduct menthol in a menthol production line. BACKGROUND

[0002] The current industrial production of L-menthol is mainly through the hydrogenation of thymol, and the specific process is disclosed in Chinese patent CN201510809332.9. During the process, stereoisomer byproducts such as neomenthol and isomenthol are produced. Neomenthol has important application value in the fields of perfumes, medicines, and cosmetics, but its boiling point is similar to that of menthol (the difference is only 4-5℃), and it is difficult to achieve efficient separation by traditional rectification. The existing technology has the following problems:

[0003] 1. The traditional crystallization method needs to be repeated 3-4 times to reach 90% purity, which is high in energy consumption and low in efficiency.

[0004] 2. The separation efficiency of rectification is low, and the close boiling points of isomers make separation difficult, so it is difficult to reach high-purity standards.

[0005] 3. The purity of neomenthol after rectification is usually less than 90%, and some methods involve complex derivatization steps, which increase the process cost and may introduce impurities. SUMMARY

[0006] The technical problem to be solved by the present application is to provide a method for purifying the byproduct neomenthol in a menthol production line. The method realizes efficient separation and purification through rectification and crystallization operation units, and can be directly connected to the existing menthol production line, which is low in modification and production cost.

[0007] To solve the above technical problems, the present application provides a method for purifying the byproduct neomenthol in a menthol production line, comprising the following steps:

[0008] (1) Prepare a rectification column with a column height of 140 cm, an inner diameter of 30 mm, and a filler of 3mm*3mm Westinghouse ring filler. The vacuum pump has a pumping capacity of 2L / min;

[0009] (2) The reaction product of thymol hydrogenation to produce menthol is fed into the rectification column kettle, and the kettle temperature is controlled at 115-125℃, the vacuum degree is 15-20mmHg, and the reflux ratio is 20:2-50:2. Neomenthol and menthone are enriched at the same time, and the enriched mixture is collected. The content of neomenthol in the mixture is 75%-77%;

[0010] (3) In the plate crystallizer, add the mixture containing 75-77% neomenthol. After all the mixture is dissolved at 60℃, the temperature of the material is reduced to 25-27℃, and the mother liquor is discharged. After the mother liquor is discharged, the temperature is raised to melt the material to obtain neomenthol with a content of 93-95%;

[0011] (4) In a plate crystallizer, add 93-95% new menthol obtained from the first crystallization in step (3). After it is completely melted at 60°C, the material temperature drops to 42-43°C. After adding a small amount of seed crystals, start the programmed cooling to 35°C. The cooling time is 6-8 hours. After the cooling is completed, drain the mother liquor. By heating at 1°C / h to induce sweating, a product with a content of 99.5% new menthol can be obtained.

[0012] Advantages of this invention: This invention uses the reaction product of thymol hydrogenation to produce menthol as raw material, and achieves efficient separation and purification of new menthol through distillation and crystallization operation units. The purity of the produced new menthol reaches 99.5%, meeting pharmaceutical grade standards; the process can be directly connected to existing menthol production lines with low modification costs; solvent-free crystallization eliminates the need for solvent recovery, resulting in low energy consumption and high efficiency; production costs are low; and the product is more competitive in the market. Detailed Implementation

[0013] Example 1:

[0014] A method for purifying a new menthol byproduct from a menthol production line includes the following steps:

[0015] (1) Prepare a distillation column with a column height of 140cm, an inner diameter of 30mm, and packing material of 3mm*3mm West Tower ring packing. The vacuum pump has a pumping capacity of 2L / min.

[0016] (2) The reaction product of hydrogenation of thymol to produce menthol is fed into the bottom of a distillation column. The bottom temperature is controlled at 115℃, the vacuum degree is 15mmHg, and the reflux ratio is 20:2. Neomenthol and menthone are enriched simultaneously. The enriched mixture is collected. The neomenthol content in the mixture is 75%~77%.

[0017] (3) In a plate crystallizer, add the above mixture containing 75-77% new menthol. After it is completely melted at 60°C, the mother liquor is discharged after the material temperature drops to 25°C. After the mother liquor is discharged, the material is heated to obtain new menthol with a content of 93-95%.

[0018] (4) In a plate crystallizer, add 93-95% new menthol obtained from the first crystallization in step (3). After it is completely melted at 60°C, the material temperature drops to 42°C. After adding a small amount of seed crystals, start the program to cool down to 35°C. The cooling time is 6 hours. After the cooling is completed, drain the mother liquor. By heating up at 1°C / h to sweat, a product with a content of 99.5% new menthol can be obtained.

[0019] Example 2:

[0020] A method for purifying a new menthol byproduct from a menthol production line includes the following steps:

[0021] (1) Prepare a distillation column with a column height of 140cm, an inner diameter of 30mm, and packing material of 3mm*3mm West Tower ring packing. The vacuum pump has a pumping capacity of 2L / min.

[0022] (2) The reaction product of hydrogenation of thymol to produce menthol was fed into the bottom of a distillation column. The bottom temperature was controlled at 120°C, the vacuum degree was 17.5 mmHg, and the reflux ratio was 35:2. Neomenthol and menthone were enriched simultaneously. The enriched mixture was collected. The neomenthol content in the mixture was 75%~77%.

[0023] (3) In a plate crystallizer, add the above mixture containing 75-77% new menthol. After it is completely melted at 60°C, the mother liquor is discharged after the material temperature drops to 26°C. After the mother liquor is discharged, the material is heated to obtain new menthol with a content of 93-95%.

[0024] (4) In a plate crystallizer, add 93-95% new menthol obtained from the first crystallization in step (3). After it is completely melted at 60°C, the material temperature drops to 42.5°C. After adding a small amount of seed crystals, start the program to cool down to 35°C. The cooling time is 7 hours. After the cooling is completed, drain the mother liquor. By heating up at 1°C / h to sweat, a product with a content of 99.5% new menthol can be obtained.

[0025] Example 3:

[0026] A method for purifying a new menthol byproduct from a menthol production line includes the following steps:

[0027] (1) Prepare a distillation column with a column height of 140cm, an inner diameter of 30mm, and packing material of 3mm*3mm West Tower ring packing. The vacuum pump has a pumping capacity of 2L / min.

[0028] (2) The reaction product of hydrogenation of thymol to produce menthol is fed into the bottom of a distillation column. The bottom temperature is controlled at 125℃, the vacuum degree is 20mmHg, and the reflux ratio is 50:2. Neomenthol and menthone are enriched simultaneously. The enriched mixture is collected. The neomenthol content in the mixture is 75%~77%.

[0029] (3) In a plate crystallizer, add the above mixture containing 75-77% new menthol. After it is completely melted at 60°C, the mother liquor is discharged after the material temperature drops to 27°C. After the mother liquor is discharged, the material is heated to obtain new menthol with a content of 93-95%.

[0030] (4) In a plate crystallizer, add 93-95% new menthol obtained from the first crystallization in step (3). After it is completely melted at 60°C, the material temperature drops to 43°C. After adding a small amount of seed crystals, start the program to cool down to 35°C. The cooling time is 8 hours. After the cooling is completed, drain the mother liquor. By heating up at 1°C / h to sweat, a product with a content of 99.5% new menthol can be obtained.

[0031] The Sita ring packing used in the above embodiments is an existing product that can be purchased externally.

Claims

1. A method for purifying menthol, a byproduct of a menthol production line, characterized in that, Includes the following steps: (1) Prepare a distillation column with a column height of 140cm, an inner diameter of 30mm, and packing material of 3mm*3mm West Tower ring packing. The vacuum pump has a pumping capacity of 2L / min. (2) The reaction product of hydrogenation of thymol to produce menthol is fed into the bottom of a distillation column. The bottom temperature is controlled at 115~125℃, the vacuum degree is 15~20mmHg, and the reflux ratio is 20:2~50:

2. Neomenthol and menthone are enriched simultaneously. The enriched mixture is collected. The neomenthol content in the mixture is 75%~77%. (3) In a plate crystallizer, add the above mixture containing 75-77% new menthol. After it is completely melted at 60°C, the mother liquor is discharged after the material temperature drops to 25-27°C. After the mother liquor is discharged, the material is heated to obtain new menthol with a content of 93-95%. (4) In a plate crystallizer, add 93-95% new menthol obtained from the first crystallization in step (3). After it is completely melted at 60°C, the material temperature drops to 42-43°C. After adding a small amount of seed crystals, start the programmed cooling to 35°C. The cooling time is 6-8 hours. After the cooling is completed, drain the mother liquor. By heating at 1°C / h to induce sweating, a product with a content of 99.5% new menthol can be obtained.