A method for purifying ethyl maltol

Abstract

The application discloses a method for purifying ethyl maltol, and particularly relates to the technical field of ethyl maltol production. The method comprises the following steps: firstly, adding ethyl maltol crude product and a small amount of deionized water into a distillation kettle, and performing water vapor distillation under reduced pressure to remove a small amount of low-boiling impurities with irritating odor, so as to obtain ethyl maltol crude product with low-boiling impurities removed; secondly, performing reduced pressure rectification or distillation on the ethyl maltol crude product with low-boiling impurities removed under nitrogen protection until normal pressure, collecting part of the front fraction, and then distilling the ethyl maltol out of the kettle to obtain ethyl maltol crystalline crude product; finally, dissolving the ethyl maltol crystalline crude product in a mixed solution by heating, and obtaining ethyl maltol product through crystallization by cooling, filtration and drying. The front fraction collected after the reduced pressure rectification or distillation can be continuously used as ethyl maltol crude product. The method provided by the application can purify ethyl maltol through water vapor distillation under reduced pressure, reduced pressure rectification / distillation and crystallization, and ethyl maltol product with a content of greater than 99.9% can be obtained.

Description

Technical Field

[0001] This invention relates to the field of fragrance and flavor production technology, specifically to the field of ethyl maltol production technology, and more specifically to a method for purifying ethyl maltol. Background Technology

[0002] Ethyl maltol is an ideal food additive and flavor enhancer, with a flavor-enhancing effect six times that of maltol and twenty-four times that of coumarin. It is widely used in cosmetics, beverages, food, cigarettes, and pharmaceuticals. Currently, most domestic production of ethyl maltol uses the furfural method (total synthesis method). This method uses furfural as raw material, prepares ethyl furfuryl alcohol via Grignard reaction, and then prepares crude ethyl maltol through chlorination and hydrolysis. Ethyl maltol has a melting point of 89-93℃ and a boiling point of 290℃. Due to its high melting and boiling points, current ethyl maltol production employs sublimation purification, vaporizing ethyl maltol and directly absorbing it into an ethanol solvent, followed by crystallization and drying to finally obtain the ethyl maltol product. Thermosensitivity studies have revealed that ethyl maltol exhibits certain thermosensitivity; the rate of thermosensitive deterioration accelerates significantly above 160℃, and thermosensitive deterioration is also pronounced upon contact with oxygen in the air at higher temperatures. Therefore, lowering the operating temperature and using nitrogen protection to reduce contact between high-temperature materials and oxygen in the air can effectively improve the heat loss of ethyl maltol. Currently, the sublimation process temperature reaches above 180℃, which causes some ethyl maltol to decompose during sublimation, reducing the yield. At the same time, the sublimation process is simply evaporation, which cannot avoid the inclusion of a small amount of dark droplets in the evaporated gas phase, resulting in a darker color and affecting the color of the crystallized product. Many ethyl maltol products on the market currently have low whiteness and an off-odor caused by impurities, affecting the quality of ethyl maltol products.

[0003] Chinese patent document CN101993428A discloses a method for purifying ethyl maltol through sublimation, comprising the following steps: (1) sublimating crude ethyl maltol; (2) dissolving; (3) cooling; (4) solid-liquid separation; and (5) drying to obtain the finished product. This patent sublimates crude ethyl maltol at 180-240℃, followed by dissolution, cooling, solid-liquid separation, and drying to obtain the finished product. Although this method achieves the purpose of separation and purification, the sublimation process is at a high temperature. Due to the heat sensitivity of ethyl maltol, it partially decomposes, resulting in a crude product yield of only 77.96%. To address the heat sensitivity issue of the sublimation method, patent document CN103113339A discloses a method for separating and purifying maltol through molecular distillation. Its characteristic is that a molecular distillation apparatus is used to complete the conventional sublimation operation steps, and the distillation process temperature is controlled at 110℃-120℃. However, this method fails to remove low-boiling impurities from the crude maltol, resulting in poor maltol aroma. Furthermore, this method requires expensive molecular distillation equipment and is performed under high vacuum, leading to high operating costs. Additionally, the evaporation temperature differs from the melting point of maltol by approximately 20°C. When cooling the gaseous maltol into a liquid, overcooling can easily cause maltol crystallization and blockage of the pipes; conversely, insufficient cooling can allow some maltol to enter the vacuum pipes and clog them. Summary of the Invention

[0004] Therefore, the present invention provides a method for purifying ethyl maltol to solve the existing problems.

[0005] This invention utilizes a coupled process of vacuum steam distillation-vacuum rectification / distillation-crystallization to obtain crude ethyl maltol, resulting in a high-purity product with excellent aroma. Vacuum steam distillation efficiently removes small amounts of impurities with irritating odors, ensuring a superior aroma. Vacuum rectification and distillation are performed at appropriate temperatures, reducing the evaporation temperature. Nitrogen protection during the process minimizes contact between the high-temperature material and oxygen in the air, effectively reducing heat loss of the ethyl maltol. Evaporation with a packed bed prevents liquid droplets from being entrained in the vapor phase, resulting in a colorless and transparent liquid ethyl maltol, ensuring good color after subsequent crystallization. The multiple recycling of the ethanol-water crystallization mother liquor effectively reduces solvent recovery, achieving energy savings and minimizing solvent loss. Gradual cooling during crystallization effectively prevents explosive nucleation, promoting uniform crystal growth and resulting in a product with large particle size and high uniformity. Compared to existing processes (CN101993428A), the purification yield of ethyl maltol is increased by approximately 20%.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for purifying ethyl maltol according to the present invention includes the following steps:

[0008] Step 1: Add crude ethyl maltol and a small amount of deionized water to a distillation kettle and perform vacuum steam distillation to remove a small amount of low-boiling impurities with an irritating odor, thereby obtaining crude ethyl maltol with the low-boiling impurities removed.

[0009] Step 2: After the crude ethyl maltol product from Step 1, which has had low-boiling impurities removed, is protected with nitrogen to atmospheric pressure, it is subjected to vacuum distillation, and a portion of the fore-distillate is collected; then all the ethyl maltol is distilled off under reduced pressure to obtain crude ethyl maltol crystals.

[0010] Step 3: The crude ethyl maltol crystals obtained in Step 2 are heated and dissolved in the mixed solution. After cooling and crystallization, filtration and drying, the ethyl maltol product is obtained.

[0011] In this invention, the crude ethyl maltol contains ≥98.5% ethyl maltol.

[0012] Furthermore, in step one, the proportion of deionized water added is 5% to 15% of the crude ethyl maltol mass. The crude ethyl maltol has a low content of low-boiling impurities, and adding 5% to 15% water can ensure relatively complete removal of low-boiling impurities, while avoiding excessive water distillation and high energy consumption.

[0013] Furthermore, in step one, the conditions for vacuum steam distillation are: temperature of 80~100℃ and pressure of 15~30mmHg.

[0014] Furthermore, in step two, the theoretical number of plates in the distillation column for vacuum distillation or vacuum evaporation is 5 to 10, thereby improving separation efficiency.

[0015] Furthermore, in step two, the temperature of vacuum distillation or vacuum distillation is 130~150℃, the pressure of vacuum distillation or vacuum distillation is 0.5~5mmHg, the reflux ratio of the first fraction is 1~5, and the remaining fractions are not refluxed.

[0016] Furthermore, in step two, the mass of the pre-distillate collected under reduced pressure is 5% to 10% of the crude ethyl maltol mass.

[0017] Furthermore, step two also includes returning the collected pre-distillation fraction to step one, where it is used together as crude ethyl maltol.

[0018] Furthermore, in step three, the mixed solution is a mixture of ethanol and water, wherein the mass ratio of ethanol to water is 1:0.5 to 1:1.5.

[0019] Furthermore, in step three, the mass ratio of ethyl maltol to the mixed solution is 1:1.5 to 1:3.

[0020] Furthermore, in step three, the cooling crystallization adopts a gradient cooling method. After the crude ethyl maltol crystals are heated and dissolved in the mixed solution, they are first cooled to 30-35°C at a rate of 1-2°C / h; then cooled to 20-25°C at a rate of 3-5°C / h; then cooled to 5-10°C at a rate of 5-10°C / h, and then filtered and dried to obtain the ethyl maltol product.

[0021] The cooling crystallization process adopts a three-gradient cooling method. The initial cooling rate is relatively slow, which is conducive to the primary nucleation and crystal growth of ethyl maltol. The subsequent cooling rate is faster, which can effectively reduce the material residence time. At the same time, gradient cooling can effectively avoid explosive nucleation, resulting in better batch-to-batch stability of the product.

[0022] Furthermore, step three also includes repeatedly recycling the obtained ethyl maltol crystallization mother liquor until the ethyl maltol content in the mother liquor is less than 99.5%, at which point the mother liquor can be recovered and reused.

[0023] In this invention, excessively high drying temperatures can cause some products to melt and clump together. Therefore, the following drying conditions are selected: vacuum drying (35-45℃, -0.07 to -0.09 MPa) for 10-12 hours to avoid thermal degradation.

[0024] The present invention has the following advantages:

[0025] (1) The present invention provides a method for purifying ethyl maltol by vacuum steam distillation-vacuum distillation / distillation-crystallization, which can obtain ethyl maltol products with a content greater than 99.9%.

[0026] (2) By controlling the distillation by vacuum steam distillation and vacuum rectification, low-boiling impurities with irritating odors can be efficiently removed. At the same time, vacuum rectification / distillation can effectively reduce droplet entrainment, and the resulting ethyl maltol product has a pure aroma and excellent whiteness.

[0027] (3) By replacing the conventional sublimation method with vacuum steam distillation-vacuum distillation / distillation, this invention reduces the operating temperature, which can effectively reduce the loss of ethyl maltol due to heat-sensitive deterioration; at the same time, the purity of the crude ethyl maltol crystals is higher, the difficulty of crystallization separation is reduced, and the yield of the crystallization process is improved. Compared with the existing process, the purification yield of ethyl maltol is increased by about 20%. Attached Figure Description

[0028] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0029] The structures, proportions, sizes, etc. illustrated in this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed herein, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0030] Figure 1 A flowchart of an ethyl maltol purification method provided by the present invention;

[0031] Figure 2 This is a gas chromatogram of the ethyl maltol product provided in Example 1 of the present invention;

[0032] Figure 3 This is a flowchart of the sublimation method for purifying ethyl maltol in Comparative Example 1 of the present invention.

[0033] Figure 4 This is a gas chromatogram of the ethyl maltol product purified by sublimation in Comparative Example 1 of the present invention.

[0034] Figure 5 This is a particle size distribution diagram of ethyl maltol product measured using a focused beam reflectance meter (FBRM) in this invention. Detailed Implementation

[0035] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] According to such Figure 1 The flowchart provides a method for purifying ethyl maltol:

[0037] Step 1: Add crude ethyl maltol and a small amount of deionized water to a distillation kettle and perform vacuum steam distillation to remove a small amount of low-boiling impurities with an irritating odor, thereby obtaining crude ethyl maltol with the low-boiling impurities removed.

[0038] Step 2: After removing the low-boiling impurities in Step 1, the crude ethyl maltol product is protected with nitrogen to atmospheric pressure and then subjected to vacuum distillation to collect a portion of the fore-distillate; then all the ethyl maltol is distilled off under reduced pressure to obtain crude ethyl maltol crystals.

[0039] Step 3: The crude ethyl maltol crystals obtained in Step 2 are heated and dissolved in the mixed solution. After cooling and crystallization, the product is filtered and dried to obtain the ethyl maltol product.

[0040] Step 4: The mass of the pre-distillate collected in Step 2 is approximately 5% to 10% of the crude ethyl maltol mass. This pre-distillate is combined with the raw material from Step 1 and used together as crude ethyl maltol for further processing.

[0041] Step 5: Cooling and crystallization. A gradient cooling method is used. After the crude ethyl maltol crystals are heated and dissolved in the mixed solution, the temperature is first lowered to 30-35℃ at a rate of 1-2℃ / h; then lowered to 20-25℃ at a rate of 3-5℃ / h; and then lowered to 5-10℃ at a rate of 5-10℃ / h. After filtration and drying, the ethyl maltol product is obtained.

[0042] Step 6: The ethyl maltol crystallization mother liquor obtained in Step 3 can be recycled multiple times until the ethyl maltol content in the mother liquor is less than 99.5%, at which point the mother liquor can be recovered and reused.

[0043] The crude ethyl maltol contains ≥98.5% ethyl maltol. In step one, the proportion of deionized water added is 5%–15% of the crude ethyl maltol mass. The temperature of vacuum steam distillation is 80–100℃, and the pressure is 15–30 mmHg. In step two, the theoretical plate number of the distillation column is 5–10. The temperature of vacuum distillation / distillation is 130–150℃, and the pressure is 0.5–5 mmHg. The reflux ratio of the first fraction is 1–5, and there is no reflux of the remaining fractions. In step three, the mass ratio of the ethanol and water mixture is 1:0.5–1:1.5, and the mass ratio of ethyl maltol to the mixture is 1:1.5–1:3.

[0044] The recovery rates of ethyl maltol in Examples 1-7 were calculated using the following formula:

[0045] Recovery rate = Product quality * Product purity / (Raw material quality * Raw material purity - Mass of fraction before vacuum distillation * Purity of fraction before vacuum distillation).

[0046] Example 1

[0047] This embodiment provides a method for purifying ethyl maltol:

[0048] Add 600g of crude ethyl maltol (98.5% ethyl maltol content) to a 1000mL three-necked flask, then add 90g of deionized water and place the flask in an oil bath heater. Heate the material in the oil bath until it is essentially dissolved, then begin vacuum steam distillation at 100℃ and 30mmHg. After all the water has evaporated, stop the vacuum steam distillation and purge with nitrogen to maintain atmospheric pressure. Then, convert the vacuum steam distillation apparatus to a vacuum rectification apparatus and begin vacuum rectification. The rectification column has 5 theoretical plates, and the vacuum rectification temperature is controlled at 130℃, the pressure at 0.5mmHg, and the reflux ratio at 1. Collect the first 30g of the distillate, which contains 98.8% ethyl maltol. After collecting the first fraction, stop the reflux and collect all the distillate, for a total of 560g of distillate.

[0049] 560g of ethyl maltol distillate was placed in a 2000mL three-necked flask, and 840g of fresh ethanol-water mixture was added, wherein the mass ratio of ethanol to water in the ethanol-water mixture was 1:0.5. The mixture was heated to 40℃ to completely dissolve the ethyl maltol. After complete dissolution, the system was subjected to gradient cooling: Gradient cooling 1: 2℃ / h, cooling for 5h to reach 30℃; Gradient cooling 2: 3℃ / h, cooling for 3.3h to reach 20℃; Gradient cooling 3: 5℃ / h, cooling for 3h to reach 5℃. After filtration and drying, a total of 535g of ethyl maltol product was obtained. The gas chromatogram of the product is shown below. Figure 2 As shown; the product purity is 99.98%, and the recovery rate is 95.3%. The D50 of the ethyl maltol product is 94, as shown in the results below. Figure 5 As shown.

[0050] Example 2

[0051] This embodiment provides a method for purifying ethyl maltol:

[0052] Add 570g of crude ethyl maltol and 30g of the pre-distillation fraction of ethyl maltol recovered in Example 1 to a 1000mL three-necked flask. Mix them together to obtain the crude ethyl maltol, which has an ethyl maltol content of 98.5%. Add 30g of deionized water and place the flask in an oil bath heater. The materials are essentially dissolved by heating in the oil bath. Start vacuum steam distillation, controlling the temperature at 80℃ and the pressure at 15mmHg. After all the water has evaporated, stop the vacuum steam distillation and purge with nitrogen to maintain atmospheric pressure. Then, convert the vacuum steam distillation apparatus to a vacuum distillation apparatus and start vacuum distillation. The distillation column has 5 theoretical plates, and the vacuum distillation temperature is controlled at 150℃, the pressure at 5mmHg, and the reflux ratio at 5. Collect 60g of the pre-distillation fraction, which has an ethyl maltol content of 98.9%. After collecting the pre-distillation fraction, stop reflux and collect all the distillate, collecting a total of 530g of distillate.

[0053] 530g of ethyl maltol distillate was placed in a 2000mL three-necked flask, and 1060g of fresh ethanol-water mixture was added, wherein the mass ratio of ethanol to water in the ethanol-water mixture was 1:1. The mixture was heated to 40℃ to completely dissolve the ethyl maltol. After complete dissolution, the system was subjected to gradient cooling: Gradient cooling 1: 1℃ / h, cooling for 5h to reach 35℃; Gradient cooling 2: 3℃ / h, cooling for 3.3h to reach 25℃; Gradient cooling 3: 10℃ / h, cooling for 2h to reach 5℃. After filtration and drying, a total of 511g of ethyl maltol product was obtained, with a purity of 99.97% and a recovery rate of 96.1%. The D50 of the ethyl maltol product was 92.

[0054] Example 3

[0055] This embodiment provides a method for purifying ethyl maltol:

[0056] Add 540g of crude ethyl maltol and 60g of the pre-distillation fraction of ethyl maltol recovered in Example 2 to a 1000mL three-necked flask. Mix them together as the crude ethyl maltol, with an ethyl maltol content of 98.6%. Add 30g of deionized water and place the flask in an oil bath heater. The materials are essentially dissolved by heating in the oil bath. Start vacuum steam distillation, controlling the temperature at 100℃ and the pressure at 30mmHg. After all the water has evaporated, stop the vacuum steam distillation and purge with nitrogen to maintain atmospheric pressure. Then, convert the vacuum steam distillation apparatus to a vacuum distillation apparatus and start vacuum distillation. The distillation column has 10 theoretical plates, and the vacuum distillation temperature is controlled at 140℃, the pressure at 3mmHg, and the reflux ratio at 3. Collect 45g of the pre-distillation fraction, which contains 99.0% ethyl maltol. After collecting the pre-distillation fraction, stop reflux and collect all the distillate, collecting a total of 545g of distillate.

[0057] 545g of ethyl maltol distillate was placed in a 5000mL three-necked flask, and 1635g of fresh ethanol-water mixture was added, wherein the mass ratio of ethanol to water in the ethanol-water mixture was 1:1.5. The mixture was heated to 45℃ to completely dissolve the ethyl maltol. After complete dissolution, the system was subjected to gradient cooling: Gradient cooling 1: 2℃ / h, cooling for 5h to reach 35℃; Gradient cooling 2: 3℃ / h, cooling for 3.3h to reach 25℃; Gradient cooling 3: 5℃ / h, cooling for 3h to reach 10℃. After filtration and drying, a total of 528g of ethyl maltol product was obtained, with a purity of 99.97% and a recovery rate of 96.5%. The D50 of the ethyl maltol product was 90.

[0058] Example 4

[0059] This embodiment provides a method for purifying ethyl maltol:

[0060] Add 555g of crude ethyl maltol and 45g of the ethyl maltol pre-distillate recovered in Example 3 to a 1000mL three-necked flask. Mix them together as crude ethyl maltol with a content of 98.6%. Add 60g of deionized water and place the flask in an oil bath heater. The materials are essentially dissolved by oil bath heating. Start vacuum steam distillation, controlling the temperature at 80℃ and the pressure at 15mmHg. After all the water has evaporated, stop the vacuum steam distillation and purge with nitrogen to maintain atmospheric pressure. Then, convert the vacuum steam distillation apparatus to a vacuum distillation apparatus and start vacuum distillation. The distillation column has 8 theoretical plates, and the vacuum distillation temperature is controlled at 130℃, the pressure at 0.5mmHg, and the reflux ratio at 2. Collect 30g of the pre-distillate, which contains 98.9% ethyl maltol. After collecting the pre-distillate, stop reflux and collect all the distillate, collecting a total of 560g of distillate.

[0061] 560g of ethyl maltol distillate was placed in a 2000mL three-necked flask, and 1120g of an ethanol-water mixture was added. This mixture was the mother liquor from five cycles of crystallization, with an ethanol-water mass ratio of 1:1. The mixture was heated to 40℃ to completely dissolve the ethyl maltol. After complete dissolution, the system was subjected to gradient cooling: Gradient cooling 1: 1℃ / h, cooling for 10h to reach 30℃; Gradient cooling 2: 5℃ / h, cooling for 2h to reach 20℃; Gradient cooling 3: 5℃ / h, cooling for 3h to reach 5℃. After filtration and drying, 540g of ethyl maltol product was obtained, with a purity of 99.97% and a recovery rate of 96.1%. The D50 of the ethyl maltol product was 89.

[0062] Example 5

[0063] This embodiment provides a method for purifying ethyl maltol:

[0064] Add 570g of crude ethyl maltol and 30g of the pre-distillation fraction of ethyl maltol recovered in Example 4 to a 1000mL three-necked flask. Mix them together as the crude ethyl maltol, with an ethyl maltol content of 98.6%. Add 45g of deionized water and place the flask in an oil bath heater. The materials are essentially dissolved by oil bath heating. Start vacuum steam distillation, controlling the temperature at 90℃ and the pressure at 20mmHg. After all the water has evaporated, stop the vacuum steam distillation and purge with nitrogen to maintain atmospheric pressure. Then, convert the vacuum steam distillation apparatus to a vacuum distillation apparatus and start vacuum distillation. The distillation column has 10 theoretical plates, and the vacuum distillation temperature is controlled at 150℃, the pressure at 5mmHg, and the reflux ratio at 1. Collect 60g of the pre-distillation fraction, which contains 99.0% ethyl maltol. After collecting the pre-distillation fraction, stop reflux and collect all the distillate, collecting a total of 530g of distillate.

[0065] 530g of ethyl maltol distillate was placed in a 2000mL three-necked flask, and 795g of an ethanol-water mixture was added. This mixture was the mother liquor from seven cycles of crystallization, with an ethanol-water mass ratio of 1:0.5. The ethyl maltol was heated to 45℃ to dissolve completely. After complete dissolution, the system was subjected to gradient cooling: Gradient cooling 1: 2℃ / h, cooling for 5h to reach 35℃; Gradient cooling 2: 5℃ / h, cooling for 3h to reach 20℃; Gradient cooling 3: 5℃ / h, cooling for 3h to reach 5℃. After filtration and drying, a total of 512g of ethyl maltol product was obtained, with a purity of 99.96% and a recovery rate of 96.2%. The D50 of the ethyl maltol product was 95.

[0066] Example 6

[0067] This embodiment provides a method for purifying ethyl maltol:

[0068] Add 540g of crude ethyl maltol and 60g of the pre-distillate of ethyl maltol recovered in Example 5 to a 1000mL three-necked flask. Mix them together as crude ethyl maltol with a content of 98.7%. Add 90g of deionized water and place the flask in an oil bath heater. The materials are essentially dissolved by heating in the oil bath. Start vacuum steam distillation, controlling the temperature at 100℃ and the pressure at 30mmHg. After all the water has evaporated, stop the vacuum steam distillation and purge with nitrogen to maintain atmospheric pressure. Replace the vacuum steam distillation apparatus with a vacuum distillation apparatus and start vacuum distillation. The distillation column has 6 theoretical plates, and the vacuum distillation temperature is controlled at 140℃, the pressure at 3mmHg, and the reflux ratio at 4. Collect 50g of the pre-distillate, which contains 99.0% ethyl maltol. After collecting the pre-distillate, stop reflux and collect all the distillate, collecting a total of 540g of distillate.

[0069] 540g of ethyl maltol distillate was placed in a 2000mL three-necked flask, and 1620g of an ethanol-water mixture was added. This mixture was the mother liquor from ten cycles of crystallization, with an ethanol-water mass ratio of 1:1.5. The mixture was heated to 45℃ to completely dissolve the ethyl maltol. After complete dissolution, the system was subjected to gradient cooling: Gradient cooling 1: 2℃ / h, cooling for 7.5h to reach 30℃; Gradient cooling 2: 5℃ / h, cooling for 2h to reach 20℃; Gradient cooling 3: 10℃ / h, cooling for 1.5h to reach 5℃. After filtration and drying, a total of 522g of ethyl maltol product was obtained. The purity of the crystallized product was 99.90%, and the recovery rate was 96.0%. The D50 of the ethyl maltol product was 90. The purity of ethyl maltol in the crystallization mother liquor was 99.49%. After recovering the crystallization mother liquor, it was reconstituted into a certain proportion of ethanol-water mixed solution for reuse in crystallization.

[0070] Example 7

[0071] This embodiment provides a method for purifying ethyl maltol:

[0072] Add 550g of crude ethyl maltol and 50g of the ethyl maltol pre-distillate recovered in Example 6 to a 1000mL three-necked flask. Mix them together to obtain the crude ethyl maltol, which has an ethyl maltol content of 98.6%. Add 80g of deionized water and place the flask in an oil bath heater. The materials are essentially dissolved by heating in the oil bath. Start vacuum steam distillation, controlling the temperature at 90℃ and the pressure at 20mmHg. After all the water has evaporated, stop the vacuum steam distillation and purge with nitrogen to maintain atmospheric pressure. Then, convert the vacuum steam distillation apparatus to a vacuum distillation apparatus and start vacuum distillation. The distillation column has 7 theoretical plates, and the vacuum distillation temperature is controlled at 150℃, the pressure at 5mmHg, and the reflux ratio at 5. Collect 45g of the pre-distillate, which has an ethyl maltol content of 98.9%. After collecting the pre-distillate, stop reflux and collect all the distillate, collecting a total of 545g of distillate.

[0073] 545g of ethyl maltol distillate was placed in a 2000mL three-necked flask, and 818g of an ethanol-water mixture was added. This mixture was the mother liquor from ten cycles of crystallization, with an ethanol-water mass ratio of 1:0.5. The mixture was heated to 40℃ to completely dissolve the ethyl maltol. After complete dissolution, the system was subjected to gradient cooling: gradient cooling 1: 1℃ / h, cooling for 5h to reach 35℃; gradient cooling 2: 3℃ / h, cooling for 5h to reach 20℃; gradient cooling 3: 10℃ / h, cooling for 1.5h to reach 5℃. After filtration and drying, a total of 526g of ethyl maltol product was obtained. The purity of the crystallized product was 99.90%, and the recovery rate was 96.0%. The D50 of the ethyl maltol product was 94. The purity of ethyl maltol in the crystallization mother liquor was 99.48%. This mother liquor was recovered and reconstituted into an ethanol-water mixture for reuse in crystallization.

[0074] Comparative Example 1

[0075] This comparative example provides a method for purifying ethyl maltol:

[0076] This comparative example provides a method for purifying ethyl maltol, the process is as follows: Figure 3 As shown, the product was prepared using the method described in Example 1 of Chinese Patent CN101993428A. The gas chromatogram of the product is shown below. Figure 4 As shown, the crude product recovery rate was 78.0%, and the purity was 99.78%.

[0077] Comparative Example 2

[0078] This comparative example follows the preparation method of Example 1, except that the ethyl maltol crystallization process did not use gradient cooling, but instead cooled from 45°C to 5°C at a rate of 3°C / h. Other operating conditions and parameters remained unchanged. A total of 532g of ethyl maltol product was obtained, with a purity of 99.98%, a recovery rate of 94.9%, and a D50 of 44. The results are shown in [Figure Number]. Figure 5 As shown.

[0079] Comparative Example 1 used a conventional sublimation method at a high temperature, resulting in significant heat loss of ethyl maltol. The mother liquor was not recovered and reused, leaving some ethyl maltol still present. Furthermore, the sublimation method failed to effectively remove low-boiling impurities. Ultimately, this resulted in a low yield of ethyl maltol, and although the purity met national standards, it still had a noticeable off-odor.

[0080] Comparative Example 2 did not use a gradient cooling method, but instead cooled from 45℃ to 5℃ at a rate of 3℃ / h. The rapid cooling in the early stage resulted in a large supersaturation, which easily led to explosive nucleation, resulting in smaller particle size and poor particle size uniformity of the ethyl maltol product.

[0081] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for purifying ethyl maltol, characterized by, The method comprises the following steps: Step one, adding ethyl maltol crude product and a small amount of deionized water into a distillation kettle, the ratio of deionized water to ethyl maltol crude product is 5% to 15% of the mass of ethyl maltol crude product, and then performing reduced pressure steam distillation to remove a small amount of low boiling impurities with irritating odor, thereby obtaining ethyl maltol crude product with low boiling impurities removed; the reduced pressure steam distillation is performed at a temperature of 80-100°C and a pressure of 15-30mmHg; Step two, after the ethyl maltol crude product with low boiling impurities removed in step one is protected by nitrogen to normal pressure, performing reduced pressure rectification to collect part of the front fraction, and then distilling out the ethyl maltol to obtain ethyl maltol crystalline crude product; the reduced pressure rectification is performed at a temperature of 130-150°C and a pressure of 0.5-5mmHg, the front fraction has a reflux ratio of 1-5, and the remaining fraction has no reflux; Step three, heating and dissolving the ethyl maltol crystalline crude product obtained in step two in a mixed solution, first cooling at a rate of 1-2°C / h to 30-35°C, then cooling at a rate of 3-5°C / h to 20-25°C, and then cooling at a rate of 5-10°C / h to 5-10°C, and then filtering and drying to obtain ethyl maltol product; the mixed solution is a mixed solution of ethanol and water, and the mass ratio of ethanol to water is 1:0.5-1:1.

5.

2. The method of purifying ethyl maltol according to claim 1, wherein, In step two, the number of theoretical plates of the rectification column for the reduced pressure rectification is 5-10.

3. The method of purifying ethyl maltol according to claim 1, wherein, In step two, the mass of the collected front fraction of the reduced pressure rectification is 5%-10% of the mass of the ethyl maltol crude product.

4. The method of purifying ethyl maltol according to claim 1, wherein, Step two further comprises returning the collected front fraction of the reduced pressure rectification to step one for use together as ethyl maltol crude product.

5. The method of purifying ethyl maltol according to claim 1, wherein In step three, the mass ratio of ethyl maltol to the mixed solution is 1:1.5-1:3.

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