Preparation process of natural menthol

Abstract

The invention discloses a preparation process of natural menthol. The preparation process comprises the following steps: performing reduced-pressure segmented rectification on crude mint oil or / and dementholized peppermint oil to obtain an olefin fraction, a menthone fraction and a menthol fraction; mixing and dissolving the obtained menthone fraction and the menthol fraction in proportion to form a material to be crystallized; cooling and crystallizing the material to be crystallized, and filtering to obtain menthol crystals; and drying the menthol crystal to obtain a finished product. The menthone fraction is obtained by adopting a rectification method and then is blended with the fraction with high content of L-menthol, so that the variety of impurities of the product is reduced, the crystallization process is convenient and controllable, and the problems that the variety of impurities is large, the crystallization time of the product is long, the yield is low and the like when natural peppermint oil is adopted for blending are avoided; the method has the advantages of rapid crystallization process, good crystal morphology and high crystallization yield.

Description

Technical Field

[0001] The invention relates to the technical field of chemical purification, and in particular to a preparation process of natural menthol. Background Art

[0002] There are relatively mature existing processes for the crystallization of natural menthol, such as: the menthol preparation method disclosed in patent CN202010816451.8: secondary freeze-thaw of crude peppermint oil to obtain crude menthol, the crude menthol products are combined, melted, dehydrated, and filtered to obtain primary brain oil, and baking oil and melted oil are added for cooling and crystallization, and wet brain and ice oil are obtained after separation; the wet brain is dried and sorted to obtain high-purity menthol.

[0003] The paper "Research on Separation of Peppermint Oil by Distillation-Cooling Crystallization" also proposed the process conditions for separating menthol from natural peppermint crude oil using distillation-freezing crystallization technology: the natural peppermint crude oil is distilled to obtain distillate and kettle components, the kettle components are blended with peppermint oil to have an L-menthol content of more than 80%, and then crystallized to obtain a menthol product with a content of >99.8%.

[0004] The existing preparation process is only different in the front-end processing method, and the ingredients are similar: all are prepared by diluting the content of L-menthol, an oil component in peppermint, to a suitable range and then cooling and crystallizing. The disadvantages of the existing preparation process are that there are many types of mixtures in the crystallization material, the crystal separation is difficult, the production cycle is long, the crystal morphology is not good, the product has many impurity types, and the yield is low.

[0005] In view of the above-mentioned defects, the inventors of the present invention finally obtained the present invention after a long period of research and practice. Summary of the invention

[0006] In order to solve the above technical defects, the technical solution adopted by the present invention is to provide a preparation process of natural menthol, comprising the steps of:

[0007] S1, subjecting peppermint crude oil and / or peppermint oil to vacuum fractional distillation to obtain an olefin fraction, a menthone fraction and an L-menthol fraction;

[0008] S2, mixing and dissolving the menthone fraction obtained in step S1 with the L-menthol fraction in proportion to form a material to be crystallized;

[0009] S3, cooling the material to be crystallized in step S2, crystallizing it, and filtering it to obtain menthol crystals;

[0010] S4, drying the menthol crystals to obtain a finished product.

[0011] Preferably, the peppermint crude oil and the peppermint oil are both obtained from steam distillation.

[0012] Preferably, in step S1, the vacuum fractionation distillation adopts a vacuum condition of -0.1Mpa to

[0013] -0.095Mpa, the temperature range of the olefin fraction is 40°C to 54°C, the reflux ratio is (0-5):1, the temperature range of the menthone fraction is 55°C to 70°C, the reflux ratio is (1-50):1.

[0014] Preferably, the weight ratio of the crystallized material is: menthone fraction: L-menthol fraction = (0.1-0.9):1.

[0015] Preferably, the weight ratio of the crystallized material is: menthone fraction: L-menthol fraction = (0.3-0.8):1.

[0016] Preferably, the menthone fraction includes menthone and isomenthone, and the weight ratio of the menthone to the isomenthone is: menthone:isomenthone=1:(0.05-1).

[0017] Preferably, the weight ratio of the menthone to the isomenthone is: menthone:isomenthone=1:(0.1-1).

[0018] Compared with the prior art, the invention has the following beneficial effects: the invention adopts a rectification method to obtain a menthone fraction, and then mixes it with a fraction containing a high L-menthol component, so that the types of impurities in the product are reduced, and the crystallization process is convenient and controllable, thereby avoiding the problems of many types of impurities, long product crystallization time, low yield, etc. when natural peppermint oil is used for preparation, and has the advantages of fast crystallization process, good crystal morphology, and high crystallization yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The figure is a schematic diagram of the process for preparing the natural menthol. DETAILED DESCRIPTION

[0020] The above and other technical features and advantages of the present invention are described in more detail below in conjunction with the accompanying drawings.

[0021] The preparation process of the natural menthol of the present invention comprises the steps of:

[0022] S1, subjecting peppermint crude oil and / or peppermint oil to vacuum fractional distillation to obtain an olefin fraction, a menthone fraction and an L-menthol fraction;

[0023] S2, mixing and dissolving the menthone fraction obtained in step S1 with the L-menthol fraction in proportion to form a material to be crystallized;

[0024] S3, cooling the material to be crystallized in step S2, crystallizing it, and filtering it to obtain menthol crystals;

[0025] S4, drying the menthol crystals to obtain a finished product.

[0026] Preferably, the peppermint crude oil and the peppermint oil are both obtained from steam distillation.

[0027] Preferably, in step S1, the vacuum fractionation distillation adopts a vacuum condition of -0.1Mpa to

[0028] -0.095Mpa, the temperature range of the olefin fraction is 40°C to 54°C, the reflux ratio is (0-5):1, the temperature range of the menthone fraction is 55°C to 70°C, the reflux ratio is (1-50):1.

[0029] Preferably, the weight ratio of the crystallized material is m (menthone fraction): m (L-menthol fraction).

[0030] =(0.1~0.9):1.

[0031] Preferably, the weight ratio of the crystallized material is m(menthone fraction):m(L-menthol fraction)=(0.3-0.8):1.

[0032] Preferably, the menthone fraction includes menthone and isomenthone in a weight ratio of m(menthone):m(isomenthone)=1:(0.05-1).

[0033] Preferably, the weight ratio is m(menthone):m(isomenthone)=1:(0.1-1).

[0034] The invention uses peppermint crude oil / peppermint oil as a raw material, adopts a purification process of distillation, blending, freezing crystallization and drying, firstly obtains olefin components, menthone components and L-menthol components by vacuum distillation, then blends the obtained menthone components with L-menthol components to make the L-menthol ratio reach an appropriate concentration, and then cools down and crystallizes to obtain L-menthol with a content of more than 99.0%, thereby optimizing the natural menthol crystallization process.

[0035] The invention adopts a rectification method to obtain menthone components, and then mixes them with a fraction containing a high L-menthol component, so that the types of product impurities are reduced, the crystallization process is convenient and controllable, and the problems of many types of impurities, long product crystallization time, low yield, etc. in the preparation of natural peppermint oil are avoided. The invention has the advantages of fast crystallization process, good crystal morphology and high crystallization yield.

[0036] The present invention is easy to operate, simplifies traditional processes, and improves production efficiency. At the same time, the menthone components used in the proportioning of step S2 are obtained by distillation in step S1 and come from the mint crude oil / mint oil itself. The entire process maintains natural properties and no artificial synthetic substances are added as solvents.

[0037] Compared with the traditional process, the new process of the present invention does not contain α-pinene, β-pinene, limonene and other components in the material system to be crystallized, which reduces the types of impurities and facilitates the rapid crystallization of mint. At the same time, the material system to be crystallized does not contain α-pinene, β-pinene, limonene and other components, the product is not easy to be oxidized, and the material color is not easy to darken, which further ensures the appearance and quality of the product.

[0038] Embodiment 1

[0039] Take 300.00g of mint crude oil, place it in a 1L round-bottom distillation bottle, connect it to a distillation tower, a production device, and a condenser, and there is bulk filler in the tower column. Heat it under vacuum -0.096Mpa, receive the fraction at 40-54℃, and the reflux ratio is 0:1, and 33.05g of olefin fraction is obtained. After that, receive the fraction at 55-60℃, and the reflux ratio is 3:1, and 35.14g of menthol fraction is obtained. Stop the operation, release the vacuum, and obtain 231.81g of the contents in the kettle, that is, the L-menthol fraction.

[0040] Take 40.00g of the contents in the kettle, add 35.00g of the menthone fraction, stir to dissolve, cool to crystallize, obtain menthol crystals, filter to obtain 26.50g of wet weight, dry to obtain 26.30g. The detected content is 99.50% of L-menthol.

[0041] As shown in the following Table 1, Table 1 is a table of components of various materials in the vacuum staged distillation process of this embodiment.

[0042] Table 1

[0043]

[0044] Embodiment 2

[0045] Take 300.00g of peppermint oil and place it in a 1L round-bottom distillation bottle, connect it to a distillation tower, a extraction device, and a condenser. There is bulk filler in the tower column. Heat it under vacuum -0.095Mpa, receive the fraction at 40-54℃, and the reflux ratio is 5:1 to obtain 62.97g of olefin fraction. After that, receive the fraction at 55-65℃, and the reflux ratio is 50:1 to obtain 106.91g of menthone fraction. Stop the operation, release the vacuum, and obtain 130.12g of the contents in the kettle, which is the L-menthol fraction.

[0046] Take 130.00g of the contents in the kettle, add 39.00g of the menthone fraction, stir to dissolve, cool and crystallize to obtain menthol crystals, filter to obtain 64.00g of wet weight, dry to obtain 63.80g. The detected content is 99.30% of L-menthol.

[0047] As shown in the following Table 2, Table 2 is a table of components of various materials in the vacuum staged distillation process of this embodiment.

[0048] Table 2

[0049]

[0050] Embodiment 3

[0051] Take 300.00g of peppermint oil and place it in a 1L round-bottom distillation bottle, connect it to a distillation tower, a extraction device, and a condenser. There is bulk filler in the tower column. Heat it under vacuum -0.098Mpa, receive the fraction at 40-54℃, and the reflux ratio is 1:1 to obtain 60.00g of olefin fraction. After that, receive the fraction at 55-65℃, and the reflux ratio is 40:1 to obtain 105.38g of menthone fraction. Stop the operation, release the vacuum, and obtain 134.62g of the contents in the kettle, i.e., the L-menthol fraction.

[0052] Take 100g of the contents in the kettle, add 80g of the menthone fraction, stir to dissolve, cool to crystallize, obtain menthol crystals, filter to obtain 37.70g of wet weight, and dry to obtain 37.50g. The detected content is 99.73% of L-menthol.

[0053] As shown in Table 3 below, Table 3 is a table of components of various materials in the vacuum staged distillation process of this embodiment.

[0054] Table 3

[0055]

[0056] The above description is only a preferred embodiment of the present invention, which is only illustrative and not restrictive of the present invention. Those skilled in the art understand that many changes, modifications, and even equivalences may be made to the present invention within the spirit and scope defined by the claims of the present invention, but all of them will fall within the scope of protection of the present invention.

Claims

1. A process for preparing natural menthol, characterized in that: Includes steps: S1, subjecting mint crude oil and / or mint oil to vacuum fractional distillation to obtain an olefin fraction, a menthone fraction and a menthol fraction; S2, mixing and dissolving the menthone fraction obtained in step S1 with the menthol fraction in proportion to form a material to be crystallized; S3, cooling the material to be crystallized in step S2, crystallizing it, and filtering it to obtain menthol crystals; S4, drying the menthol crystals to obtain a finished product.

2. The process for preparing natural menthol as claimed in claim 1, characterized in that: The peppermint crude oil and the peppermint essential oil are both obtained from steam distillation.

3. The process for preparing natural menthol as claimed in claim 1, characterized in that: In the step S1, the reduced pressure fractional distillation adopts a reduced pressure vacuum condition of -0.1Mpa to -0.095Mpa, the temperature range of the olefin fraction is 40°C to 54°C, the reflux ratio is (0 to 5):1, the temperature range of the menthone fraction is 55°C to 70°C, and the reflux ratio is (1 to 50):

1.

4. The process for preparing natural menthol as claimed in claim 1, characterized in that: The weight ratio of the crystallized material is: menthone fraction: menthol fraction = (0.1-0.9):

1.

5. The process for preparing natural menthol as claimed in claim 4, characterized in that: The weight ratio of the crystallized material is: menthone fraction: menthol fraction = (0.3-0.8):

1.

6. The process for preparing natural menthol according to claim 1, characterized in that: The menthone fraction includes menthone and isomenthone, and the weight ratio of the menthone to the isomenthone is: menthone:isomenthone=1:(0.05-1).

7. The process for preparing natural menthol as claimed in claim 6, characterized in that: The weight ratio of the menthone to the isomenthone is: menthone:isomenthone=1:(0.1-1).

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