A kind of L-menthol purification process

Abstract

The invention belongs to the field of spice purification, and specifically relates to an L-menthol purification process, comprising the following steps: S1, heating a crystallizer to which a L-menthol raw material to be purified has been added to 48-52°C at a heating rate of 5-10°C / h, and after all the raw material is dissolved, cooling to 37-39°C at a cooling rate of 3-5°C / h, and adding crystal seeds; S2, further cooling to 33°C at a cooling rate of 0.01-0.03°C / h, and crystals begin to appear. Precipitation, cooling to 30°C, cooling rate of 0.1-0.3°C / h, then cooling to 26°C, cooling rate of 1°C / h, extracting the uncrystallized mother liquor in the crystallizer; S3, heating to 35°C, heating rate of 1°C / h, then heating to 42°C, heating rate of 0.1-0.5°C / h, extracting the dissolved mother liquor in the crystallizer; S4, taking out the terpene-like L-menthol crystals in the crystallizer, and obtaining the purified L-menthol. Beneficial effect: The purification process provided by the present invention greatly reduces energy consumption compared with the distillation process, and can also improve the purity of L-menthol.

Description

Technical Field

[0001] The invention belongs to the field of spice purification, and specifically relates to an L-menthol purification process. Background Art

[0002] Menthol is a naturally occurring active ingredient widely used in pharmaceuticals, the food industry and cosmetics. In natural sources such as peppermint oil, menthol exists in the form of four diastereoisomer pairs, of which only the major component, (-)-menthol or L-menthol, has the desired taste and other organoleptic properties. L-menthol is used as a flavoring agent in toothpaste, perfume, beverages and candies. In medicine, it is used as a stimulant, acting on the skin or mucous membranes, with a cooling and antipruritic effect; it can be taken internally as a carminative for headaches and inflammation of the nose, pharynx and throat.

[0003] The L-menthol raw material to be purified comes from the liquid collected by steam distillation of natural mint and then melting and crystallizing. Its purity is 96%-98%. The main impurity is menthone, and its impurity content is generally around 1%-1.5%. The boiling point of menthol is 216.4°C and the freezing point is 42°C. The boiling point of menthone is 207-210°C and the freezing point is -6°C. Because the boiling points are very different, the energy consumption of the reaction will be greatly increased by the distillation method. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a L-menthol purification process, comprising the following steps:

[0005] S1. Heat the crystallizer to which the L-menthol raw material to be purified has been added to 48-52°C at a heating rate of 5-10°C / h. After all the raw materials are dissolved, cool the crystallizer to 37-39°C at a cooling rate of 3-5°C / h, and add seed crystals.

[0006] S2, continue to cool to 33 ° C, the cooling rate is 0.01-0.03 ° C / h, crystals begin to precipitate, cool to 30 ° C, the cooling rate is 0.1-0.3 ° C / h, then cool to 26 ° C, the cooling rate is 1 ° C / h, the uncrystallized mother liquor in the crystallizer is extracted;

[0007] S3, heating to 35°C at a heating rate of 1°C / h, then heating to 42°C at a heating rate of 0.1-0.5°C / h, and extracting the mother liquor dissolved in the crystallizer;

[0008] S4, taking out the terpene-like L-menthol crystals in the crystallizer to obtain purified L-menthol.

[0009] Preferably, the L-menthol raw material to be purified comes from the liquid collected by steam distillation of natural mint and then melt crystallization, and its purity is 96%-98%, and the main impurity is menthone.

[0010] Preferably, the method further comprises the following steps: analyzing the purity of L-menthol in the mother liquor extracted in step S2 and step S3, and if the purity is greater than 90%, combining the mother liquor with the L-menthol raw material to be purified for purification.

[0011] Preferably, the purity of L-menthol in the mother liquor extracted in step S2 and step S3 is analyzed. If the purity is less than 90%, it is first distilled through a distillation tower, and an L-menthol fraction with a purity of 96%-98% is collected from the top of the distillation tower, and then combined with the L-menthol raw material to be purified for purification.

[0012] Preferably, the number of plates of the distillation tower is 5-20, the reflux ratio of the distillation process is 1-3, and the vacuum degree is controlled at 10-30 mmHg.

[0013] Preferably, the terpene-like L-menthol crystals have a length of 1-3 cm and a thickness of 1-3 mm.

[0014] The beneficial effects of the present invention are:

[0015] 1. The present invention provides a L-menthol purification process. The melt crystallization refining technology is a method for separating and purifying substances based on the different solidification points between the separated substances. It is mainly used for the separation of organic compounds and has the characteristics of high product purity, low energy consumption, no need to add other solvents, and little environmental pollution. It greatly reduces energy consumption compared with the distillation process and can also improve the purity of L-menthol.

[0016] 2. The purity of L-menthol separated by the present invention can reach 99.9%, which meets the production requirements of L-menthol. The crystal length is 1-3 cm and the thickness is 1-3 mm. After multiple separation and purification, L-menthol with a total yield of more than 90% can be finally obtained. DETAILED DESCRIPTION

[0017] The present invention is described in detail below with reference to specific embodiments.

[0018] Example 1

[0019] A L-menthol purification process comprises the following steps:

[0020] S1. Raise the temperature of the crystallizer to which the L-menthol raw material to be purified has been added to 48°C at a rate of 5°C / h. When all the raw materials are dissolved, lower the temperature to 37°C at a rate of 3°C / h, and add seed crystals.

[0021] S2, continue to cool down to 33 ° C, the cooling rate is 0.01 ° C / h, crystals begin to precipitate, cool down to 30 ° C, the cooling rate is 0.1 ° C / h, a large number of crystals begin to precipitate, then cool down to 26 ° C, the cooling rate is 1 ° C / h, the uncrystallized mother liquor in the crystallizer is extracted;

[0022] S3, heating to 35°C at a heating rate of 1°C / h, then heating to 42°C at a heating rate of 0.1°C / h, and extracting the mother liquor dissolved in the crystallizer;

[0023] S4. Taking out the terpene-like L-menthol crystals with a length of 1-3 cm and a thickness of 1-3 mm from the crystallizer, the purified L-menthol was obtained. The purity was 99.54% and the yield was 71%.

[0024] The L-menthol raw material to be purified comes from the liquid collected by steam distillation of natural mint and then melting and crystallization, with a purity of 96%-98%, and the main impurity is menthone.

[0025] Example 2

[0026] A L-menthol purification process comprises the following steps:

[0027] S1. Raise the temperature of the crystallizer to which the L-menthol raw material to be purified has been added to 50°C at a rate of 7.5°C / h. After all the raw materials are dissolved, lower the temperature to 38°C at a rate of 4°C / h, and add seed crystals.

[0028] S2, continue to cool to 33 ° C, cooling rate is 0.02 ° C / h, crystals begin to precipitate, cool to 30 ° C, cooling rate is 0.2 ° C / h, a large number of crystals begin to precipitate, then cool to 26 ° C, cooling rate is 1 ° C / h, the mother liquor that has not been crystallized in the crystallizer is extracted;

[0029] S3, heating to 35°C at a heating rate of 1°C / h, then heating to 42°C at a heating rate of 0.3°C / h, and extracting the mother liquor dissolved in the crystallizer;

[0030] S4. Taking out the terpene-like L-menthol crystals with a length of 1-3 cm and a thickness of 1-3 mm from the crystallizer, the purified L-menthol was obtained. The purity was 99.97% and the yield was 75%.

[0031] The L-menthol raw material to be purified comes from the liquid collected by steam distillation of natural mint and then melting and crystallization, with a purity of 96%-98%, and the main impurity is menthone.

[0032] Example 3

[0033] A L-menthol purification process comprises the following steps:

[0034] S1. Raise the temperature of the crystallizer to which the L-menthol raw material to be purified has been added to 52°C at a rate of 10°C / h. After all the raw materials are dissolved, lower the temperature to 39°C at a rate of 5°C / h, and add seed crystals.

[0035] S2, continue to cool to 33 ° C, cooling rate is 0.03 ° C / h, crystals begin to precipitate, cool to 30 ° C, cooling rate is 0.3 ° C / h, a large number of crystals begin to precipitate, then cool to 26 ° C, cooling rate is 1 ° C / h, the mother liquor that has not been crystallized in the crystallizer is extracted;

[0036] S3, heating to 35°C at a heating rate of 1°C / h, then heating to 42°C at a heating rate of 0.5°C / h, and extracting the mother liquor dissolved in the crystallizer;

[0037] S4. Taking out the terpene-like L-menthol crystals with a length of 1-3 cm and a thickness of 1-3 mm from the crystallizer, thus obtaining purified L-menthol, which has a purity of 99.49% and a yield of 65%.

[0038] The L-menthol raw material to be purified comes from the liquid collected by steam distillation of natural mint and then melting and crystallization, with a purity of 96%-98%, and the main impurity is menthone.

[0039] Example 4

[0040] A L-menthol purification process comprises the following steps:

[0041] S1. Raise the temperature of the crystallizer to which the L-menthol raw material to be purified has been added to 49°C at a rate of 5°C / h. When all the raw materials are dissolved, lower the temperature to 39°C at a rate of 5°C / h, and add seed crystals.

[0042] S2, continue to cool down to 33 ° C, the cooling rate is 0.02 ° C / h, crystals begin to precipitate, cool down to 30 ° C, the cooling rate is 0.1 ° C / h, a large number of crystals begin to precipitate, then cool down to 26 ° C, the cooling rate is 1 ° C / h, the uncrystallized mother liquor in the crystallizer is extracted;

[0043] S3, heating to 35°C at a heating rate of 1°C / h, then heating to 42°C at a heating rate of 0.3°C / h, and extracting the mother liquor dissolved in the crystallizer;

[0044] S4. Taking out the terpene-like L-menthol crystals with a length of 1-3 cm and a thickness of 1-3 mm from the crystallizer, the purified L-menthol was obtained. The purity was 99.38% and the yield was 68%.

[0045] The L-menthol raw material to be purified comes from the liquid collected by steam distillation of natural mint and then melting and crystallization, with a purity of 96%-98%, and the main impurity is menthone.

[0046] Example 5

[0047] The L-menthol in the mother liquor extracted in step S2 and step S3 of Example 1-4 was collected, and the purity thereof was detected to be less than 90%, specifically, 73.7% L-menthol, 13.8% menthone, and 12.5% ​​other impurities. The mother liquor was first rectified by a distillation tower with 5 plates, a vacuum degree of 30 mmHg, and a reflux ratio of 3:1. The menthol crude product (menthol content 96.8%, menthone content 1.7%, and other impurities 1.5%) was obtained, and the crude product was combined with the L-menthol raw material to be purified for purification.

[0048] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A process for purifying L-menthol, characterized in that: The steps include: S1. Raise the temperature of the crystallizer to which the L-menthol raw material to be purified has been added to 50°C at a rate of 7.5°C / h. After all the raw materials are dissolved, lower the temperature to 38°C at a rate of 4°C / h, and add seed crystals. S2, continue to cool to 33 ° C, cooling rate is 0.02 ° C / h, crystals begin to precipitate, cool to 30 ° C, cooling rate is 0.2 ° C / h, a large number of crystals begin to precipitate, then cool to 26 ° C, cooling rate is 1 ° C / h, the mother liquor that has not been crystallized in the crystallizer is extracted; S3, heating to 35°C at a heating rate of 1°C / h, then heating to 42°C at a heating rate of 0.3°C / h, and extracting the mother liquor dissolved in the crystallizer; S4, taking out the terpene-like L-menthol crystals with a length of 1-3 cm and a thickness of 1-3 mm from the crystallizer, to obtain purified L-menthol, the purity of which is 99.97% and the yield is 75%; The L-menthol raw material to be purified comes from the liquid collected by steam distillation of natural mint and then melting and crystallization, with a purity of 96%-98%, and the main impurity is menthone.