Efficient purification method of ethyl maltol

Abstract

The invention discloses an efficient purification method of ethyl maltol, and particularly relates to the technical field of ethyl maltol production. The method comprises the following steps: firstly, adding an ethyl maltol crude product and a small amount of deionized water into a distillation kettle, carrying out reduced-pressure steam distillation, and removing a small amount of low-boiling-point impurities with irritant peculiar smell, so as to obtain an ethyl maltol crude product without the low-boiling-point impurities; introducing nitrogen into the ethyl maltol crude product from which the low-boiling-point impurities are removed to protect the ethyl maltol crude product to normal pressure, carrying out reduced-pressure rectification or distillation, collecting part of front fractions, and then evaporating all the ethyl maltol to obtain an ethyl maltol crystal crude product; and finally, heating and dissolving the ethyl maltol crystal crude product in the mixed solution, cooling, crystallizing, filtering and drying to obtain an ethyl maltol product. The front fraction of vacuum rectification or distillation is collected and then is continuously used as an ethyl maltol crude product. The invention provides a method for purifying ethyl maltol through reduced pressure steam distillation-reduced pressure rectification / distillation-crystallization. An ethyl maltol product with the content larger than 99.9% can be obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of spice and essence production, specifically to the technical field of ethyl maltol production, and more specifically to a method for highly efficient purification of ethyl maltol. Background Art

[0002] Ethyl maltol is an ideal food additive and flavor enhancer. Its flavor enhancing effect is six times that of maltol and twenty-four times that of coumarin. It is widely used in the fields of cosmetics, beverages, foods, cigarettes, and pharmaceuticals. Currently in China, the furfural method (total synthesis method) is mostly used to produce ethyl maltol. This method uses furfural as the raw material, prepares ethyl furfuryl alcohol through a Grignard reaction, and then prepares the crude ethyl maltol through a chlorination reaction and a hydrolysis reaction. The melting point of ethyl maltol is 89 - 93 °C and the boiling point is 290 °C. Due to its relatively high melting and boiling points, sublimation is currently used for purification during the production of ethyl maltol, achieving the vaporization of ethyl maltol and directly absorbing it into an ethanol solvent, and finally obtaining the ethyl maltol product through steps such as crystallization and drying. Through thermal sensitivity research, it is found that ethyl maltol has a certain thermal sensitivity. When the temperature is higher than 160 °C, the thermal degradation rate significantly accelerates, and when it contacts oxygen in the air at a higher temperature, thermal degradation is also more obvious. Therefore, reducing the operating temperature and using nitrogen protection to reduce the contact between high-temperature materials and oxygen in the air can effectively improve the heat loss of ethyl maltol. Currently, the temperature during the sublimation operation process reaches above 180 °C, which will cause partial decomposition of ethyl maltol during sublimation and reduce the yield; at the same time, the sublimation process is just simple evaporation, and it is impossible to avoid entraining a small amount of dark liquid droplets in the evaporated gas phase, resulting in a relatively dark color and affecting the chromaticity of the product after crystallization. Currently, many ethyl maltol products on the market have low whiteness and an off-flavor caused by impurities, which affects the quality of ethyl maltol products.

[0003] Chinese Patent Document CN101993428A discloses a method for purifying ethyl maltol by sublimation, which comprises the following steps: (1) sublimating the crude ethyl maltol; (2) dissolving; (3) cooling; (4) solid-liquid separation; and (5) drying to obtain the finished product. In this patent, the crude ethyl maltol is sublimated at 180-240°C and then obtained the finished product after dissolution, cooling, solid-liquid separation and drying. Although this method can achieve the purpose of separation and purification, the sublimation process has a relatively high temperature. Due to the thermal sensitivity of ethyl maltol, part of ethyl maltol is decomposed, and the yield of the crude product is only 77.96%. To solve the problem of thermal sensitivity in the sublimation method, Patent Document CN103113339A discloses a method for separating and purifying maltol by molecular distillation. Its characteristic is to complete the conventional sublimation operation steps by using a molecular distillation apparatus, and the temperature during the distillation process is controlled at 110°C - 120°C. However, this scheme does not remove the low-boiling impurities in the crude maltol, which will lead to poor aroma of maltol. At the same time, this scheme requires the use of expensive molecular distillation equipment, and the operation is completed under high vacuum, resulting in a relatively high operation cost. Meanwhile, the evaporation temperature is about 20°C different from the melting point of maltol. When cooling the gaseous maltol into a liquid, it is easy to overcool and cause maltol to crystallize and block the pipeline; but if not cooled sufficiently, part of the maltol will enter the vacuum pipeline and block the vacuum tube. Summary of the Invention

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

[0005] The crude ethyl maltol of the present invention undergoes a process coupling of vacuum steam distillation - vacuum rectification / distillation - crystallization. The finally obtained ethyl maltol product has high purity and good aroma; a small amount of impurities with pungent odor are efficiently removed through vacuum steam distillation to ensure good aroma of the product; the temperature of the evaporation operation is reduced by realizing vacuum rectification and distillation operations at appropriate temperatures; meanwhile, nitrogen protection is adopted during the process to reduce the contact between the high-temperature material and oxygen in the air, which can effectively reduce the heat loss of ethyl maltol; at the same time, evaporation under the condition of a packing layer can block the entrainment of liquid droplets in the gas phase during the evaporation process, obtaining colorless and transparent liquid ethyl maltol, ensuring good color of the product after subsequent crystallization. The multiple recycling and reuse of the ethanol-water crystallization mother liquor adopted in the operation effectively reduce the solvent recovery amount, achieving energy conservation and reducing solvent loss. The gradient cooling method is adopted during the crystallization process, effectively avoiding burst nucleation and promoting the uniform growth of crystal nuclei. The obtained product has large particle size and high particle size uniformity. Compared with the existing process (CN101993428A), the purification yield of ethyl maltol is increased by about 20%.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] According to an efficient purification method for ethyl maltol provided by the present invention, it comprises the following steps:

[0008] Step 1: Add crude ethyl maltol and a small amount of deionized water into a distillation kettle, conduct vacuum steam distillation to remove a small amount of low-boiling impurities with pungent and peculiar smells, and obtain crude ethyl maltol with low-boiling impurities removed.

[0009] Step 2: After the crude ethyl maltol with low-boiling impurities removed in Step 1 is protected by nitrogen and returned to normal pressure, conduct vacuum rectification, and collect a part of the fore-fractions; then distill all the ethyl maltol under vacuum to obtain crude ethyl maltol crystals.

[0010] Step 3: Heat and dissolve the crude ethyl maltol crystals obtained in Step 2 in a mixed solution, and obtain ethyl maltol products through cooling crystallization, filtration, and drying.

[0011] In the crude ethyl maltol of the present invention, the content of ethyl maltol ≥ 98.5%.

[0012] Furthermore, in Step 1, the proportion of deionized water added is 5% - 15% of the mass of the crude ethyl maltol. The content of low-boiling impurities in the crude ethyl maltol is relatively low. Adding 5% - 15% of water can ensure relatively complete removal of low-boiling impurities, and at the same time can avoid high energy consumption due to excessive water evaporation.

[0013] Furthermore, in Step 1, the conditions of vacuum steam distillation are: temperature is 80 - 100 °C, and pressure is 15 - 30 mmHg.

[0014] Furthermore, in Step 2, the number of theoretical plates of the rectification column for vacuum rectification or vacuum distillation is 5 - 10; the separation efficiency is improved.

[0015] Furthermore, in Step 2, the temperature of vacuum rectification or vacuum distillation is 130 - 150 °C, the pressure of vacuum rectification or vacuum distillation is 0.5 - 5 mmHg, the reflux ratio of the fore-fractions is 1 - 5, and there is no reflux for the remaining fractions.

[0016] Furthermore, in Step 2, the mass of the fore-fractions collected by vacuum rectification is 5% - 10% of the mass of the crude ethyl maltol.

[0017] Furthermore, Step 2 also includes returning the fore-fractions collected by vacuum rectification to Step 1 and continuing to use them together as the crude ethyl maltol.

[0018] Furthermore, in Step 3, 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.

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

[0020] Further, in Step 3, gradient cooling is adopted for cooling crystallization. After the crude ethyl maltol crystals are heated and dissolved in the mixed solution, the temperature is first decreased at a rate of 1-2 °C / h to 30-35 °C; then the temperature is decreased at a rate of 3-5 °C / h to 20-25 °C; then the temperature is decreased at a rate of 5-10 °C / h to 5-10 °C, and then through filtration and drying, the ethyl maltol product is obtained.

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

[0022] Further, Step 3 also includes recycling the obtained ethyl maltol crystallization mother liquor multiple times until the content of ethyl maltol in the mother liquor is lower than 99.5%, and then the mother liquor can be recovered and used continuously.

[0023] In the present invention, too high drying temperature will cause partial melting and caking of the product. Therefore, the drying conditions are selected as: vacuum drying (35-45 °C, -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 rectification / distillation - crystallization, and an ethyl maltol product with a content greater than 99.9% can be obtained.

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

[0027] (3) By using vacuum steam distillation - vacuum rectification / distillation to replace the conventional sublimation method for purifying ethyl maltol, the present invention reduces the operating temperature, can effectively reduce the loss of ethyl maltol due to thermal degradation. At the same time, the purity of the crude ethyl maltol crystals is relatively high, 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%. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only exemplary, and for those of ordinary skill in the art, without creative efforts, other implementation drawings can also be obtained according to the provided drawings.

[0029] The structures, ratios, sizes, etc. shown in this specification are only used to cooperate with the content disclosed in the specification for those familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention. Therefore, they do not have substantial technical significance. Any modification of the structure, change in the proportional relationship, or adjustment of the size, without affecting the efficacy that the present invention can produce and the purpose that can be achieved, should still fall within the scope that can be covered by the technical content disclosed in the present invention.

[0030] Figure 1 It is a flow chart of a method for highly efficient purification of ethyl maltol provided by the present invention;

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

[0032] Figure 3 It is a flow chart of the sublimation method for purifying ethyl maltol in Comparative Example 1 of the present invention;

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

[0034] Figure 5 It is a particle size distribution diagram of the ethyl maltol product measured by a focused beam reflectance measurement (FBRM) in the present invention. Specific Embodiments

[0035] The following specific embodiments illustrate the implementation manners of the present invention. Those familiar with this technology can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present invention.

[0036] According to the flow chart as Figure 1 A method for highly efficient purification of ethyl maltol is provided:

[0037] Step 1: Add the crude ethyl maltol and a small amount of deionized water into a distillation kettle, perform reduced-pressure steam distillation to remove a small amount of low-boiling impurities with a pungent odor, and obtain the crude ethyl maltol with low-boiling impurities removed;

[0038] Step 2: After purging the crude ethyl maltol with low-boiling impurities removed in Step 1 with nitrogen to normal pressure, perform reduced-pressure rectification, collect a part of the fore-fraction; then distill all the ethyl maltol under reduced pressure to obtain the crude ethyl maltol crystals;

[0039] Step 3: Heat and dissolve the crude ethyl maltol crystals obtained in Step 2 in a mixed solution, and obtain ethyl maltol products through cooling crystallization, filtration, and drying.

[0040] Step 4: The mass of the pre-fraction collected before vacuum rectification in Step 2 is about 5% - 10% of the mass of the crude ethyl maltol. Combine this pre-fraction with the raw materials in Step 1 and continue to use them together as the crude ethyl maltol.

[0041] Step 5: The cooling crystallization adopts a gradient cooling method. After the crude ethyl maltol crystals are heated and dissolved in the mixed solution, first cool at a rate of 1 - 2 °C / h to 30 - 35 °C; then cool at a rate of 3 - 5 °C / h to 20 - 25 °C; then cool at a rate of 5 - 10 °C / h to 5 - 10 °C, and then through filtration and drying, obtain ethyl maltol products.

[0042] Step 6: The mother liquor of ethyl maltol crystals obtained in Step 3 can be recycled multiple times until the content of ethyl maltol in the mother liquor is lower than 99.5%. The mother liquor can be recovered and reused.

[0043] Among them, in the crude ethyl maltol, the content of ethyl maltol ≥ 98.5%. The proportion of deionized water added in Step 1 is 5% - 15% of the mass of the crude ethyl maltol. The temperature of vacuum steam distillation is 80 - 100 °C, and the pressure is 15 - 30 mmHg. The number of theoretical plates of the rectification column in Step 2 is 5 - 10. The temperature of vacuum rectification / distillation is 130 - 150 °C, and the pressure is 0.5 - 5 mmHg. The reflux ratio of the pre-fraction is 1 - 5, and there is no reflux for the remaining fractions. In Step 3, the mass ratio of the ethanol and water mixed solution is 1:0.5 - 1:1.5, and the mass ratio of ethyl maltol to the mixed solution is 1:1.5 - 1:3.

[0044] In Examples 1 - 7, the recovery rate of ethyl maltol is calculated using the following formula:

[0045] Recovery rate = product mass * product purity / (raw material mass * raw material purity - pre-fraction mass before vacuum rectification * pre-fraction purity before vacuum rectification).

[0046] Example 1

[0047] This example provides a method for highly efficient purification of ethyl maltol:

[0048] Add 600 g of crude ethyl maltol with an ethyl maltol content of 98.5% in a 1000 mL three-necked flask, and then add 90 g of deionized water. Place it in an oil bath heater. Basically dissolve the materials by oil bath heating, turn on the vacuum steam distillation, control the temperature of the vacuum steam distillation at 100 °C and the pressure at 30 mmHg. After all the water is distilled off, stop the vacuum to terminate the vacuum steam distillation, and introduce nitrogen to protect until the normal pressure is reached. Change the vacuum steam distillation device to a vacuum rectification device and turn on the vacuum rectification. The number of theoretical plates in the rectification column is 5, control the temperature of the vacuum rectification at 130 °C, the pressure at 0.5 mmHg, and the reflux ratio at 1. Collect 30 g of the fore fraction with an ethyl maltol content of 98.8% in the fore fraction. After collecting the fore fraction, stop the reflux and fully collect the distilled product, and a total of 560 g of distillate is collected.

[0049] Place 560 g of the ethyl maltol distillate in a 2000 mL three-necked flask, and add 840 g of a fresh ethanol-water mixed solution, where the mass ratio of ethanol to water in the ethanol-water mixed solution is 1:0.5. Heat to 40 °C to completely dissolve the ethyl maltol. After complete dissolution, perform gradient cooling on the system: Gradient cooling one: 2 °C / h, cool for 5 h to reach 30 °C; Gradient cooling two: 3 °C / h, cool for 3.3 h to reach 20 °C; Gradient cooling three: 5 °C / h, cool for 3 h to reach 5 °C; Then, after filtration and drying, a total of 535 g of ethyl maltol product is obtained. The gas chromatogram of the product is as Figure 2 shown; the product purity is 99.98%, and the recovery rate is 95.3%. The D50 of the ethyl maltol product is 94, and the results are shown in Figure 5 shown.

[0050] Example 2

[0051] This example provides a method for highly efficient purification of ethyl maltol:

[0052] Add 570 g of crude ethyl maltol and 30 g of the fore fraction of the ethyl maltol vacuum rectification recovered in Example 1 in a 1000 mL three-necked flask. After mixing, use them together as the crude ethyl maltol with an ethyl maltol content of 98.5%. Then add 30 g of deionized water and place it in an oil bath heater. Basically dissolve the materials by oil bath heating, turn on the vacuum steam distillation, control the temperature of the vacuum steam distillation at 80 °C and the pressure at 15 mmHg. After all the water is distilled off, stop the vacuum to terminate the vacuum steam distillation, and introduce nitrogen to protect until the normal pressure is reached. Change the vacuum steam distillation device to a vacuum rectification device and turn on the vacuum rectification. The number of theoretical plates in the rectification column is 5, control the temperature of the vacuum rectification at 150 °C, the pressure at 5 mmHg, and the reflux ratio at 5. Collect 60 g of the fore fraction with an ethyl maltol content of 98.9% in the fore fraction. After collecting the fore fraction, stop the reflux and fully collect the distilled product, and a total of 530 g of distillate is collected.

[0053] Place 530 g of ethyl maltol distillate in a 2000 mL three-necked flask, and add 1060 g of fresh ethanol-water mixed solution, where the mass ratio of ethanol to water in the ethanol-water mixed solution is 1:1. Heat to 40 °C to completely dissolve the ethyl maltol. After complete dissolution, perform gradient cooling on the system: Gradient cooling one: 1 °C / h, cool for 5 h to reach 35 °C; Gradient cooling two: 3 °C / h, cool for 3.3 h to reach 25 °C; Gradient cooling three: 10 °C / h, cool for 2 h to reach 5 °C; Then, after filtration and drying, a total of 511 g of ethyl maltol product is obtained, with a product purity of 99.97% and a recovery rate of 96.1%. The D50 of the ethyl maltol product is 92.

[0054] Example 3

[0055] This example provides a method for the efficient purification of ethyl maltol:

[0056] Add 540 g of crude ethyl maltol and 60 g of the pre-fraction of the recovered ethyl maltol before vacuum distillation in Example 2 to a 1000 mL three-necked flask. After mixing, they are used together as the crude ethyl maltol, with an ethyl maltol content of 98.6%. Then add 30 g of deionized water and place it in an oil bath heater. The material is basically dissolved by oil bath heating, and vacuum steam distillation is started. The temperature of the vacuum steam distillation is controlled at 100 °C and the pressure is controlled at 30 mmHg. After all the water is distilled off, stop the vacuum to stop the vacuum steam distillation, and pass nitrogen to protect it to atmospheric pressure. Change the vacuum steam distillation device to a vacuum distillation device and start vacuum distillation. The number of theoretical plates in the distillation column is 10, control the vacuum distillation temperature at 140 °C, the pressure at 3 mmHg, and the reflux ratio at 3. Collect 45 g of the pre-fraction, and the ethyl maltol content in the pre-fraction is 99.0%. After collecting the pre-fraction, stop the reflux and collect all the distilled products, and a total of 545 g of distillate is collected.

[0057] Place 545 g of ethyl maltol distillate in a 5000 mL three-necked flask, and add 1635 g of fresh ethanol-water mixed solution, where the mass ratio of ethanol to water in the ethanol-water mixed solution is 1:1.5. Heat to 45 °C to completely dissolve the ethyl maltol. After complete dissolution, perform gradient cooling on the system: Gradient cooling one: 2 °C / h, cool for 5 h to reach 35 °C; Gradient cooling two: 3 °C / h, cool for 3.3 h to reach 25 °C; Gradient cooling three: 5 °C / h, cool for 3 h to reach 10 °C; Then, after filtration and drying, a total of 528 g of ethyl maltol product is obtained, with a product purity of 99.97% and a recovery rate of 96.5%. The D50 of the ethyl maltol product is 90.

[0058] Example 4

[0059] This example provides a method for the efficient purification of ethyl maltol:

[0060] Add 555 g of crude ethyl maltol and 45 g of the pre-fraction of the ethyl maltol recovered in Example 3 before vacuum rectification into a 1000 mL three-necked flask. After mixing, they are taken together as the crude ethyl maltol, with an ethyl maltol content of 98.6%. Then add 60 g of deionized water and place it in an oil bath heater. The material is basically dissolved by heating in the oil bath, and vacuum steam distillation is started. The temperature of the vacuum steam distillation is controlled at 80 °C and the pressure is controlled at 15 mmHg. After all the water is distilled off, stop the vacuum to terminate the vacuum steam distillation, and pass nitrogen to protect it to normal pressure. Change the vacuum steam distillation device to a vacuum rectification device and start vacuum rectification. Among them, the number of theoretical plates of the rectification column is 8, the temperature of the vacuum rectification is controlled at 130 °C, the pressure is 0.5 mmHg, and the reflux ratio is 2. Collect 30 g of the pre-fraction, and the ethyl maltol content in the pre-fraction is 98.9%. After collecting the pre-fraction, stop the reflux and fully collect the distilled product, and a total of 560 g of distillate is collected.

[0061] Place 560 g of the ethyl maltol distillate in a 2000 mL three-necked flask, and add 1120 g of an ethanol-water mixed solution, which is the crystallization mother liquor after five cycles of crystallization. The mass ratio of ethanol to water in the ethanol-water mixed solution is 1:1. Heat to 40 °C to completely dissolve the ethyl maltol. After complete dissolution, perform gradient cooling on the system: Gradient cooling one: 1 °C / h, cool for 10 h to reach 30 °C; Gradient cooling two: 5 °C / h, cool for 2 h to reach 20 °C; Gradient cooling three: 5 °C / h, cool for 3 h to reach 5 °C; Then, after filtration and drying, a total of 540 g of ethyl maltol product is obtained, with a product purity of 99.97% and a recovery rate of 96.1%. The D50 of the ethyl maltol product is 89.

[0062] Example 5

[0063] This example provides a method for highly efficient purification of ethyl maltol:

[0064] Add 570 g of crude ethyl maltol and 30 g of the pre-fraction of the ethyl maltol recovered in Example 4 before vacuum rectification into a 1000 mL three-necked flask. After mixing, they are taken together as the crude ethyl maltol, with an ethyl maltol content of 98.6%. Then add 45 g of deionized water and place it in an oil bath heater. The material is basically dissolved by heating in the oil bath, and vacuum steam distillation is started. The temperature of the vacuum steam distillation is controlled at 90 °C and the pressure is controlled at 20 mmHg. After all the water is distilled off, stop the vacuum to terminate the vacuum steam distillation, and pass nitrogen to protect it to normal pressure. Change the vacuum steam distillation device to a vacuum rectification device and start vacuum rectification. Among them, the number of theoretical plates of the rectification column is 10, the temperature of the vacuum rectification is controlled at 150 °C, the pressure is 5 mmHg, and the reflux ratio is 1. Collect 60 g of the pre-fraction, and the ethyl maltol content in the pre-fraction is 99.0%. After collecting the pre-fraction, stop the reflux and fully collect the distilled product, and a total of 530 g of distillate is collected.

[0065] Place 530 g of ethyl maltol distillate in a 2000 mL three-necked flask, and add 795 g of ethanol-water mixed solution. This mixed solution is the crystallization mother liquor after seven cycles of crystallization. The mass ratio of ethanol to water in the ethanol-water mixed solution is 1:0.5. Heat to 45 °C to completely dissolve ethyl maltol. After complete dissolution, perform gradient cooling on the system: Gradient cooling one: 2 °C / h, cool for 5 h to reach 35 °C; Gradient cooling two: 5 °C / h, cool for 3 h to reach 20 °C; Gradient cooling three: 5 °C / h, cool for 3 h to reach 5 °C; Then, after filtration and drying, a total of 512 g of ethyl maltol product is obtained. The product purity is 99.96%, and the recovery rate is 96.2%. The D50 of the ethyl maltol product is 95.

[0066] Example 6

[0067] This example provides a method for efficient purification of ethyl maltol:

[0068] Add 540 g of crude ethyl maltol and 60 g of the pre-fraction of ethyl maltol recovered in Example 5 before vacuum distillation into a 1000 mL three-necked flask. After mixing, they are used together as the crude ethyl maltol, and its ethyl maltol content is 98.7%. Then add 90 g of deionized water and place it in an oil bath heater. The material is basically dissolved by oil bath heating, and vacuum steam distillation is started. The temperature of vacuum steam distillation is controlled at 100 °C, and the pressure is controlled at 30 mmHg. After all the water is distilled off, stop the vacuum to stop the vacuum steam distillation, and pass nitrogen to protect until normal pressure. Convert the vacuum steam distillation device to a vacuum distillation device and start vacuum distillation. The theoretical number of plates in the distillation column is 6. Control the vacuum distillation temperature at 140 °C, the pressure at 3 mmHg, and the reflux ratio at 4. Collect 50 g of the pre-fraction, and the ethyl maltol content in the pre-fraction is 99.0%. After collecting the pre-fraction, stop the reflux and collect all the distillation products. A total of 540 g of distillate is collected.

[0069] Place 540 g of ethyl maltol distillate in a 2000 mL three-necked flask, and add 1620 g of ethanol-water mixed solution. This mixed solution is the crystallization mother liquor after ten cycles of crystallization. The mass ratio of ethanol to water in the ethanol-water mixed solution is 1:1.5. Heat to 45 °C to completely dissolve ethyl maltol. After complete dissolution, perform gradient cooling on the system: Gradient cooling one: 2 °C / h, cool for 7.5 h to reach 30 °C; Gradient cooling two: 5 °C / h, cool for 2 h to reach 20 °C; Gradient cooling three: 10 °C / h, cool for 1.5 h to reach 5 °C; Then, after filtration and drying, a total of 522 g of ethyl maltol product is obtained. The purity of the crystalline product is 99.90%, and the recovery rate is 96.0%. The D50 of the ethyl maltol product is 90. The purity of ethyl maltol in the crystallization mother liquor is 99.49%. After recovering the crystallization mother liquor, it is reconfigured into an ethanol-water mixed solution with a certain ratio and reused for crystallization.

[0070] Example 7

[0071] This example provides a method for highly efficient purification of ethyl maltol:

[0072] Add 550 g of crude ethyl maltol and 50 g of the pre-fraction of the recovered ethyl maltol before vacuum distillation in Example 6 to a 1000 mL three-necked flask. After mixing, they are taken together as the crude ethyl maltol, with an ethyl maltol content of 98.6%. Then add 80 g of deionized water and place it in an oil bath heater. The material is basically dissolved by oil bath heating, and vacuum steam distillation is started. The temperature of the vacuum steam distillation is controlled at 90 °C and the pressure is controlled at 20 mmHg. After all the water is distilled off, stop the vacuum and the vacuum steam distillation, and pass nitrogen to protect until normal pressure is reached. Convert the vacuum steam distillation device to a vacuum distillation device and start vacuum distillation. Among them, the number of theoretical plates of the distillation column is 7, the temperature of the vacuum distillation is controlled at 150 °C, the pressure is 5 mmHg, and the reflux ratio is 5. Collect 45 g of the pre-fraction, and the ethyl maltol content in the pre-fraction is 98.9%. After collecting the pre-fraction, stop the reflux and fully collect the distilled product, and a total of 545 g of distillate is collected.

[0073] Place 545 g of the ethyl maltol distillate in a 2000 mL three-necked flask, and add 818 g of an ethanol-water mixed solution, which is the crystallization mother liquor after circulating crystallization for ten times. The mass ratio of ethanol to water in the ethanol-water mixed solution is 1:0.5. Heat to 40 °C to completely dissolve the ethyl maltol. After complete dissolution, perform gradient cooling on the system: Gradient cooling one: 1 °C / h, cool for 5 h to reach 35 °C; Gradient cooling two: 3 °C / h, cool for 5 h to reach 20 °C; Gradient cooling three: 10 °C / h, cool for 1.5 h to reach 5 °C; Then, after filtration and drying, a total of 526 g of ethyl maltol product is obtained. The purity of the crystalline product is 99.90% and the recovery rate is 96.0%. The D50 of the ethyl maltol product is 94. The purity of ethyl maltol in the crystallization mother liquor is 99.48%. After recycling the crystallization mother liquor, it is reconfigured into an ethanol-water mixed solution with a certain ratio and reused for crystallization.

[0074] Comparative Example 1

[0075] This comparative example provides a method for highly efficient purification of ethyl maltol:

[0076] This comparative example provides a method for highly efficient purification of ethyl maltol. The process is as Figure 3 shown, prepared by the method of Example 1 of Chinese Patent CN101993428A. The gas chromatogram of the product is as Figure 4 shown. The recovery rate of the crude product is 78.0% and the purity is 99.78%.

[0077] Comparative Example 2

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

[0079] In Comparative Example 1, the conventional sublimation method was used, and the temperature was relatively high, resulting in more heat loss of ethyl maltol; the crystallization mother liquor was not recovered and reused, and some ethyl maltol still remained in the crystallization mother liquor; at the same time, the sublimation method failed to effectively remove low-boiling impurities. Eventually, the yield of the ethyl maltol product was relatively low. Although the purity met the national standard requirements, there was still a certain peculiar smell.

[0080] In Comparative Example 2, the gradient cooling method was not adopted, but it was cooled from 45°C to 5°C at a rate of 3°C / h. The cooling rate was relatively fast in the early stage, and the supersaturation was relatively large, which was prone to explosive nucleation, resulting in a relatively small particle size of the ethyl maltol product and poor particle size uniformity.

[0081] Although the present invention has been described in detail with general descriptions and specific examples above, based on the present invention, some modifications or improvements can be made, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection required by the present invention.

Claims

1. A method for highly efficient purification of ethyl maltol, characterized in that, It includes the following steps: Step 1: Add ethyl maltol crude product and a small amount of deionized water into a distillation kettle, and perform reduced-pressure steam distillation to remove a small amount of low-boiling impurities with pungent odors, obtaining ethyl maltol crude product with low-boiling impurities removed. Step 2: After purging the ethyl maltol crude product with low-boiling impurities removed in Step 1 with nitrogen to normal pressure, perform reduced-pressure rectification, and collect a part of the fore-fraction; then distill all of the ethyl maltol under reduced pressure to obtain crude ethyl maltol crystals. Step 3: Heat and dissolve the crude ethyl maltol crystals obtained in Step 2 in a mixed solution, and obtain ethyl maltol product through cooling crystallization, filtration, and drying.

2. The high-efficiency purification method of ethyl maltol according to claim 1, wherein In Step 1, the proportion of deionized water added is 5% - 15% of the mass of the ethyl maltol crude product.

3. The high-efficiency purification method of ethyl maltol according to claim 1, characterized in that In Step 1, the conditions for reduced-pressure steam distillation are: temperature is 80 - 100 °C, and pressure is 15 - 30 mmHg.

4. A method for highly efficient purification of ethyl maltol according to claim 1, characterized in that, In Step 2, the number of theoretical plates of the rectification column for reduced-pressure rectification or reduced-pressure distillation is 5 - 10.

5. A method for highly efficient purification of ethyl maltol according to claim 1, characterized in that, In Step 2, the temperature for reduced-pressure rectification or reduced-pressure distillation is 130 - 150 °C, the pressure for reduced-pressure rectification or reduced-pressure distillation is 0.5 - 5 mmHg, the reflux ratio of the fore-fraction is 1 - 5, and there is no reflux for the remaining fractions.

6. The highly efficient purification method of ethyl maltol according to claim 5, characterized in that, In Step 2, the mass of the fore-fraction collected by reduced-pressure rectification is 5% - 10% of the mass of the ethyl maltol crude product.

7. A method for highly efficient purification of ethyl maltol according to claim 1, characterized in that, Step 2 further includes returning the fore-fraction collected by reduced-pressure rectification to Step 1 and using it together as the ethyl maltol crude product.

8. A method for highly efficient purification of ethyl maltol according to claim 1, characterized in that, In Step 3, the mixed solution is a mixed solution of ethanol and water, where the mass ratio of ethanol to water is 1:0.5 - 1:1.

5.

9. A method for highly efficient purification of ethyl maltol according to claim 1, characterized in that, In Step 3, the mass ratio of ethyl maltol to the mixed solution is 1:1.5 - 1:

3.

10. A method for highly efficient purification of ethyl maltol according to claim 1, characterized in that, In Step 3, gradient cooling is used for cooling crystallization. After the crude ethyl maltol crystals are heated and dissolved in the mixed solution, first cool at a rate of 1 - 2 °C / h to 30 - 35 °C; then cool at a rate of 3 - 5 °C / h to 20 - 25 °C; then cool at a rate of 5 - 10 °C / h to 5 - 10 °C, and then obtain the ethyl maltol product through filtration and drying.

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